Satellite Mobile System Architectures - CORDIS

ASMS-Task Force Technical Group

Page 1

Ref.: Doc ASMS_TG-Arch Version 2: Rev. July 02 Date: 17/07/02

Satellite Mobile System Architectures Report of The R&D Group of the Advanced Satellite Mobile System Task Force


Page 2


TABLE OF CONTENT TABLE OF CONTENT.................................................................................................................................................................... 2 INTRODUCTION..................................................................................................................................................................... 7

1 1.1

SUMMARY ................................................................................................................................................................................ 7

1.2

SCOPE OF REPORT ................................................................................................................................................................... 8

1.3

LIST OF ACRONYMS................................................................................................................................................................. 9

2

ASMS REQUIREMENTS.....................................................................................................................................................15

2.1

GENERAL USER REQUIREMENTS.......................................................................................................................................... 16

2.2

TERMINALS............................................................................................................................................................................. 17

2.2.1

Handheld terminals...................................................................................................................................................... 18

2.2.2

Transportable terminals (Palmtop and Laptop Terminals) .................................................................................. 19

2.2.3

Vehicular terminals...................................................................................................................................................... 20

2.2.4

Broadcast Receivers..................................................................................................................................................... 21 U SER INTERFACES................................................................................................................................................................. 22

2.3 2.3.1

Non-broadcasting......................................................................................................................................................... 23

2.3.2

Broadcasting ................................................................................................................................................................. 23 A PPLICATIONS ....................................................................................................................................................................... 24

2.4


2.4.1

Broadcasting ................................................................................................................................................................. 24

2.4.2

PRICING REQUIREMENTS...................................................................................................................................................... 25

2.5 2.5.1


2.5.2

Broadcasting ................................................................................................................................................................. 25 SERVICE REQUIREMENTS..................................................................................................................................................... 26

2.6

Non –broadcasting....................................................................................................................................................... 26

2.6.1 2.6.1.1

ASMS services as a complement to T-UMTS services ............................................................................................... 28

Broadcasting ................................................................................................................................................................. 28

2.6.2

OPERATORS REQUIREMENTS............................................................................................................................................... 28

2.7 2.7.1

Infrastructure operators.............................................................................................................................................. 28

2.7.2

Service operators.......................................................................................................................................................... 29

2.7.3

Application operators .................................................................................................................................................. 29

2.7.3.1


2.7.3.2

Broadcasting................................................................................................................................................................. 30

REPRESENTATIVE SATELLITE SYSTEMS WHICH MAY SUPPORT ASMS APPLICATIONS .......... 30

3

COMMUNICATION TYPE SATELLITE SYSTEMS................................................................................................................ 30

3.1 3.1.1

ACeS................................................................................................................................................................................ 30

3.1.1.1

Overview...................................................................................................................................................................... 31

3.1.1.2

Services ........................................................................................................................................................................ 31

3.1.1.3

Satellites....................................................................................................................................................................... 32


Page 3


3.1.1.4

Terminals ..................................................................................................................................................................... 32

3.1.1.5

Gateways ..................................................................................................................................................................... 32

3.1.1.6

Call routing.................................................................................................................................................................. 33

3.1.1.7

Air interface ................................................................................................................................................................. 33

Thuraya .......................................................................................................................................................................... 33

3.1.2 3.1.2.1

Overview...................................................................................................................................................................... 33

3.1.2.2

Services ........................................................................................................................................................................ 34

3.1.2.3

Satellites....................................................................................................................................................................... 34

3.1.2.4

Terminals ..................................................................................................................................................................... 35

3.1.2.5

Gateways ..................................................................................................................................................................... 35

3.1.2.6

Call routing.................................................................................................................................................................. 35

3.1.2.7

Air interface ................................................................................................................................................................. 35

ICO.................................................................................................................................................................................. 35

3.1.3 3.1.3.1

Overview...................................................................................................................................................................... 36

3.1.3.2

Services ........................................................................................................................................................................ 36

3.1.3.3

ICO System Architecture............................................................................................................................................. 37

3.1.3.4

ICO-Network Architecture.......................................................................................................................................... 38

3.1.3.5

ICO Space Segment ..................................................................................................................................................... 39

3.1.3.5.1

Satellites.............................................................................................................................................................. 39

3.1.3.5.2

Satellite Coverage ............................................................................................................................................... 39

3.1.3.5.3

ICO Satellite Payload.......................................................................................................................................... 41

3.1.3.6

ICO Ground Segment .................................................................................................................................................. 42

3.1.3.7

Terminals ..................................................................................................................................................................... 43

3.1.3.8

Call routing.................................................................................................................................................................. 43

3.1.3.9

Air interface ................................................................................................................................................................. 43

3.1.3.10

3.1.4

ICO Ancillary Terrestrial Component .................................................................................................................... 44

Globalstar...................................................................................................................................................................... 45

3.1.4.1

Overview...................................................................................................................................................................... 45

3.1.4.2

Services ........................................................................................................................................................................ 46

3.1.4.3

Satellites....................................................................................................................................................................... 47

3.1.4.4

Terminals ..................................................................................................................................................................... 47

3.1.4.5

Gateways ..................................................................................................................................................................... 47

3.1.4.6

Call routing.................................................................................................................................................................. 47

3.1.4.7

3.1.5

Air interface ................................................................................................................................................................. 47

The Iridium system........................................................................................................................................................ 48

3.1.5.1

Overview...................................................................................................................................................................... 48

3.1.5.2

Services ........................................................................................................................................................................ 50

3.1.5.3

Satellites....................................................................................................................................................................... 50

3.1.5.4

Terminals ..................................................................................................................................................................... 51

3.1.5.5

Gateways ..................................................................................................................................................................... 51

3.1.5.6

Call routing.................................................................................................................................................................. 51

3.1.5.7

Air interface ................................................................................................................................................................. 52


Page 4


INMARSAT..................................................................................................................................................................... 53

3.1.6 3.1.6.1

Overview...................................................................................................................................................................... 53

3.1.6.2

Services ........................................................................................................................................................................ 53

3.1.6.3

Satellites....................................................................................................................................................................... 58

3.1.6.4

Terminals ..................................................................................................................................................................... 59

3.1.6.5

Gateways ..................................................................................................................................................................... 61

3.1.6.6

Call routing.................................................................................................................................................................. 61

3.1.6.7

Air interface ................................................................................................................................................................. 62

BROADCAST TYPE SATELLITES............................................................................................................................................ 65

3.2

The WorldSpace system............................................................................................................................................... 66

3.2.1 3.2.1.1

Overview...................................................................................................................................................................... 66

3.2.1.2

Key parameters of the system...................................................................................................................................... 67

3.2.1.3

WorldSpace mobile applications................................................................................................................................. 68

3.2.1.4

The WorldSpace satellites ........................................................................................................................................... 68

The Sirius Satellite Radio System............................................................................................................................... 69

3.2.2 3.2.2.1

The system overview ................................................................................................................................................... 69

3.2.2.2

Sirius Satellite Radio.................................................................................................................................................... 70

3.2.2.3

Car and Receivers ........................................................................................................................................................ 70

XM™ Satellite Radio................................................................................................................................................... 72

3.2.3 3.2.3.1

Overview...................................................................................................................................................................... 72

3.2.3.2

Key parameters of the system...................................................................................................................................... 72

3.2.3.3

The XM TM Satellite...................................................................................................................................................... 72

3.2.4

Satellite Digital Radio Broadcasting in Europe ..................................................................................................... 73

3.2.5

Satellite Digital Radio Broadcasting Technology .................................................................................................. 74

3.2.5.1

Digital broadcasting..................................................................................................................................................... 74

3.2.5.2

Digital Radio Broadcasting.......................................................................................................................................... 74

3.2.5.3

Satellite Digital Radio Broadcasting............................................................................................................................ 75

ENABLING TECHNOLOGIES AND ARCHITECTURES ..................................................................................... 76

4

GSM/GPRS RELATED TECHNOLOGIES.......................................................................................................................... 76

4.1 4.1.1

INMARSAT Regional Broadband Global Area Network (R-BGAN)................................................................... 76

4.1.1.1

Abstract ....................................................................................................................................................................... 76

4.1.1.2

Project R-BGAN System Architecture........................................................................................................................ 76

4.1.1.3

Project R-BGAN Air Interface .................................................................................................................................... 77

4.1.1.4

Project R-BGAN Channelization ................................................................................................................................ 77

4.1.1.5

Satellite Access Station................................................................................................................................................ 77

4.1.1.6

SAS Radio Equipment ................................................................................................................................................. 78

4.1.1.7

SAS Protocol Processing............................................................................................................................................. 78

4.1.1.8

User Terminal .............................................................................................................................................................. 79

4.1.2

INMARSAT Broadband Global Area Network (BGAN) ........................................................................................ 79

4.1.2.1

Abstract ....................................................................................................................................................................... 79

4.1.2.2

The Technology ........................................................................................................................................................... 79


Page 5


4.1.2.3

New Powerful Satellites............................................................................................................................................... 80

4.1.2.4

Advanced Multimedia Network .................................................................................................................................. 80

4.1.2.5

User Terminal Product Portfolio ................................................................................................................................. 81

4.1.2.6

The Services................................................................................................................................................................. 82

4.1.2.7

Bearer Services ............................................................................................................................................................ 82

4.1.2.8

Communication Services ............................................................................................................................................. 83

4.1.2.9

Service Deployment and Phasing Strategy .................................................................................................................. 83

UMTS / IMT-2000 TECHNOLOGY................................................................................................................................ 83

4.2

Point to Point architecture.......................................................................................................................................... 83

4.2.1 4.2.1.1

3G Technologies .......................................................................................................................................................... 83

4.2.1.1.1 4.2.1.2

S-UMTS as in integral part of the UMTS network............................................................................................ 83

Satellite Network Architectures .................................................................................................................................. 84

4.2.1.2.1

S-UMTS architecture.......................................................................................................................................... 85

4.2.1.2.2

GSO systems ...................................................................................................................................................... 85

4.2.1.2.3

NGSO systems.................................................................................................................................................... 89

Point to Multipoint architecture ................................................................................................................................ 91

4.2.2 4.2.2.1

General approach......................................................................................................................................................... 91

4.2.2.1.1

Overall Vision..................................................................................................................................................... 91

4.2.2.1.2

Multicast / Broadcast Services Provision ........................................................................................................... 92

4.2.2.1.3

Transmission Standard........................................................................................................................................ 93

4.2.2.1.4

Preliminary System Concept.............................................................................................................................. 94

4.2.2.1.5

Broadcast Infrastructures Integration.................................................................................................................. 96

4.2.2.1.6

Conclusions......................................................................................................................................................... 96

4.2.2.2

Satellite based multicast layer architecture for mobile networks................................................................................ 97

4.2.2.2.1

S-DMB mission.................................................................................................................................................. 97

4.2.2.2.2

S-DMB Services ................................................................................................................................................. 97

4.2.2.2.3

System architecture............................................................................................................................................. 99

4.2.2.2.4

System characteristics....................................................................................................................................... 100

DVB-DERIVED TECHNOLOGIES FOR M OBILE ................................................................................................................. 102

4.3 4.3.1

Introduction................................................................................................................................................................. 102

4.3.2

DVB-RCS...................................................................................................................................................................... 103

4.3.3

Satellite Interactive Network and Terrestrial Interface....................................................................................... 103

4.3.4

Network Integration................................................................................................................................................... 105

4.3.5

DVB-RCS Air Interface.............................................................................................................................................. 105

4.3.5.1

DVB-S Forward Link................................................................................................................................................. 105

4.3.5.2

DVB-RCS Return Link.............................................................................................................................................. 106

4.3.6

Radio Resource Management................................................................................................................................... 106

4.3.7

Services......................................................................................................................................................................... 106

4.3.8

DVB-RCS for ASMS.................................................................................................................................................... 107

4.3.8.1

Air Interface............................................................................................................................................................... 107

4.3.8.2

Mobility Management................................................................................................................................................ 107

4.3.8.3

Handover.................................................................................................................................................................... 108


4.3.8.4

4.3.9 5

Page 6


Power conservation.................................................................................................................................................... 108

Hybrid Systems............................................................................................................................................................ 108

CONCLUDING REMARKS ...............................................................................................................................................108

References ............................................................................................................................................................................. 110 ANNEX I GSM based Satellite Systems ................................................................................................................ 110 A1 Commonalities between terrestrial and satellite systems ................................................................................ 110 A 2 GMR-1 general system description......................................................................................................................... 112 A 2.1 Overview and system elements........................................................................................................................................ 112 A 2.2 System architecture and external interfaces...................................................................................................................... 115 Functional description of system elements................................................................................................................................. 116 A 2.3 GSM-based services ........................................................................................................................................................ 117 A 2.4 Enhanced services and features ....................................................................................................................................... 118 A 2.5 Protocol modifications..................................................................................................................................................... 118

A 3 GMR-2 general system description................................................................................................................................ 120 A 3.1 Overview and system elements........................................................................................................................................ 120 A.3.2 Functional description of system elements...................................................................................................................... 122 A.3.3 Features of the GMR-2 System ....................................................................................................................................... 123


1 1.1

Page 7


INTRODUCTION SUMMARY

The report, which is built upon contributions from members of the Working Group 1 on R&D (formerly known as Technical Group) of the Advanced Satellite Mobile Systems Task Force (ASMS-TF), gives an overview of architectures and enabling technologies for the near future development of broadband mobile satellite systems. The report has a set of user group and service specifications worked out by the ASMS Commercial Group as one of its inputs. The second chapter of the report gives a translation of these more general requirements into associated technical requirements. Overall requirements are similar to those of the terrestrial equivalent (UMTS). The systems must be reliable, affordable, provide voice, data and video services, available everywhere (except in buildings). Terminals are grouped into four categories: handheld terminals, transportable terminals including briefcase, laptop and palmtop, vehicular terminals, and broadcast receivers with possibilities for multimode functionality. The capabilities and the functionality of the different terminal groups is defined in the document. Chapter 3 gives a summary on representative satellite systems which may support ASMS applications. For the short term this includes the satellite communication systems AceS, Thuraya, ICO, Globalstar,Inmarsat 3, and Iridium and the digital audio broadcast systems Sirius, XMT M, and WorldSpace.

Some near term enabling technologies presented in Chapter 4 are grouped in 4 classes: • GSM/GPRS related technologies represented by the Inmarsat Regional Broadband Global Area Network to be operated on Thuraya from late 2002 and the Inmarsat Broadband Global Area Network to be operated on Inmarsat 4 from late 2004. • S-UMTS related technologies ready for implementation in both geostationary satellite systems and non-geostationary systems. Dedicated satellites are not yet available, but implementations covered by the phrase representing an initial phase are possible using existing satellites like ACeS, Thuraya and Inmarsat 4. • Different satellite broadcast systems have the ability for different multicast/interactive type of services in addition to broadcast. • Combined or hybrid systems represented by a combination or an integration of communication and broadcast systems have the advantage that they can support a complete set of communication, multicast and broadcast services. This may be a more long term issue due to regulatory conditions.


Page 8


The main conclusion is that the mobile satellite is now steadily on the move into the multimedia age establishing the possibilities for support of a differentiated set of broadband services. In a few years there will be a number of regional and global systems in orbit. The main challenge is to develop attractive services, have user friendly and cost efficient equipment and efficient standards supporting global usage. Development has started but there are many remaining challenges.

1.2

SCOPE OF REPORT

The main objective of the report is to give an overview of architectures and technologies that can be used for implementation of a first generation of advanced mobile satellite systems for provision of broadband multimedia services. Focus is on the short term scenario of 1-4 years but with development into the more longer 4-10 year scenario as an important issue. The work is carried out by the Technical Group of the ASMS-TF with representatives from satellite industry, operators and research organisations. The ASMS-TF has a focus period of approximately 10 years consisting of a short term scenario of 1-4 years and a more long term scenario of 4 –10 years. For the short term scenario it has been concluded that possible implementations must be based on existing technologies/architectures with minor modifications. It has been anticipated that development will take place in several phases determined by factors like market demands, the terrestrial introduction and development from 2.5 G into 3.0 G, and the potential of available satellite technologies. The taken approach is based on evolution from the present situation for both satellite and terrestrial networks in the short term scenario. For the satellite segment this means that only existing systems or systems planned for operation in the near future are of interest for the short term. The long term scenario has possibilities for and must include a transition into the future of multimedia communications with more advanced and complex approaches depending on development in the first critical phase. The work is closely linked to work in the Commercial Group of the ASMS-TF where specifications of user groups and services to be provided has been worked out [1]. Basically it is required that the same services as those intended to be delivered by terrestrial UMTS should be supported, but there are additional requirements for multicast/broadcast. The requirements are addressed in chapter 2 and the commercial specifications [1] translated into technical requirement operational conditions, terminal types for the different user groups and services to be supported. An overview of representative existing satellite systems for communication and broadcast, that may support ASMS applications in the initial phase is given in Chapter 3. In the near term scenario we may well have a situation where they all independently approach different market segments with slightly different approaches. Chapter 4 on enabling technologies has a more long term focus starting with GSM/GPRS technologies which are already becoming operational, then an overview of the S-UMTS/IMT2000 technology. Satellite audio broadcast systems and video broadcast systems can


Page 9


contribute with broadcast/multicast and data communication if they are made interactive. A more advanced approach is to integrate satellite communication, satellite broadcast and terrestrial UMTS to some degree. An example of such an approach is also given in chapter 4. This belongs to a more long term scenario requiring work on standardization and perhaps even frequency allocations. A scenario with along the UMTS approach starting from GPRS is one possibility. The now planned or in early operation DAB systems may employ GPRS by satellite or in the terrestrial network for the return, DVB-S based systems are planned for delivery of data services to passenger airplanes. The return channel could be RCS or an Inmarsat based return. There are several possibilities. One possibility for a future architecture is an integration of the different systems taking advantage of synergies offered through such things as common access systems and management, efficient resource sharing and effective use of adaptive equipment technologies. These are considerations represented in the discussion of future scenarios. The basic question is to come up with complementing scenarios rather than competing. A long term development may bring us from today’s situation of separate systems into a situation of integrated systems. 1.3

LIST OF ACRONYMS

ACEA

Association des Constructions d`Automobil

AMN

Advanced Multimedia Network

AOC

Advanced Operations Center

ASM

Advanced Satellite Mobile

ASMS-TF

Advanced Satellite Mobile Systems-Task Force

BER

Bit Error Rate

BSC

Base Station Controller

BGAN

Broadband Global Area Network

BSP

Broadcast Service Provider

BSS

Business Support System

BSS

Base Station Subsystem

BTS

Base Transceiver Station

CCCS

Common Control Channel Subsystem

CDMA

Code Division Multiple Access


Page 10


CIR

Committed Information Rate

CMIS

Customer Management Information Center

CONUS

Continental United States

COTS

Commercial Off The Shelf

CU

Communication Unit

DA

Demand Assigned

DAB

Digital Audio Broadcasting

DARS

Digital Audio Radio Service

DCN

Data Communication Network

DMS

Direct Media Service

DVB

Digital Video Broadcasting

DVB-T

Terrestrial Digital Video Broadcasting

EMC

Electromagnetic Compability

EPIRB

Emergency Position Indicating Radio Beacons

EPIRD

Emergency Position Indicating Radio Devices

ERM

Electromagnetic Compatibility and Radio Spectrum Matters

ETSI

European Telecommunications Standardisation Institute

FDD

Frequency Division Duplex

FDMA

Frequency Division Multiple Access

GAN

Global Area Network

GBO

Globalstar Business Office

GCC

Globalstar Control Center

GCMIS

Gateway Customer Management Information System

GDN

Globalstar Data Network

GGSN

Gateway GPRS Support Node


Page 11

GMPRS

Geo-Mobile Packet Radio Service

GMR

Geo-Mobile Radio

GOCC

Ground Operation Control Center

GPRS

General Packet Radio Service

GPS

Global Positioning System

GSC

Gateway Station Controller

GSM

Global System for Mobile communication

GSS

Gateway Station Subsystem

GW

Gateway

HLR

Home Location Register

HSD

High Speed Data

HTTP

Hypertext Transfer Protocol

IDS

IF Distribution System

IETF

Internet Engineering Task Force

IOT

In-Orbit Tests

IPPSD

IP Packet Switched Data Bearer Service

ISL

Inter Satellite Link

LAI

Location Area Identification

LAN

Local Area Netwok

LCF

Launch Control Facility

LEO

Low Earth Orbit

LES

Land Earth Station

LOS

Line of Sight

MAC

Medium Access Control

MCM

Multi Carrier Modulation



ME

Mobile Equipment

MEO

Medium Earth Orbit

MES

Mobile Earth Station

Page 12


MF-TDMA Multi Frequency Time Division Multiple Access MIR

Maximum Information Rate

MPE

Multi Protocol Encapsulation

MRCC

Maritime Rescue Coordination Center

MSC

Mobile Switching Center

MSP

Multicast Service Provider

MSS

Mobile Satellite System

MT

Mobile Terminal

NCC

Network Control Center

NCS

Network Coordination Stations

NMC

Network Management Center

NOC

Network Operations Center

NSS

Network Switching System

OFDM

Orthogonal Frequency Division Multiplex

OSS

Operational Support System

PAC

Perceptive Radio Coding

PBSC

Packet Base Station Controller

PDA

Personal Digital Assistant

PLMN

Public Land Mobile Network

PMC

Packet Modem Controller

PN

Pseudorandom Noise

PoP

Point of Presence


Page 13

PRCU

Packet Radio Channel Unit

PRMS

Packet Resource Management System

PSTN

Public Switched Telephone Network

QoS

Quality of Service

RAN

Radio Access Network

RBGAN

Regional Broadband Global Area Network

RCS

Return Channel Satellite

RCST

Return Channel Satellite Terminal

RFS

Radio Frequency Subsystem

RLC

Radio Link Control

RNC

Radio Network Controller

RRM

Radio Resource Management

RSS

Radio Switching Subsystem

RTT

Radio Transmission Technologies

SA

Service Area

SAN

Satellite Access Node

SAS

Satellite Access Station

SCC

Satellite Control Center

SCF

Satellite Control Facility

SCPC

Single Channel Multiple Access

SFN

Single Frequency Network

SGF

Satellite Ground Facilities

SGSN

Serving GPRS Support Node

SI

Service Information

SIM

Subscriber Identity Module



Page 14


SNR

Signal to Noise Ratio

SOC

Satellite Operations Center

SOCC

Satellite Operations Control Center

SPCC

Service Provider Control Center

SPCC

Service Provider Control Center

SRWI

Short Range Wireless Interface

S-UMTS

SatelliteUniversal Mobile Telephone System

TCP

Transmission Control Protocol

TCR

Tracking Control and Ranging

TCS

Traffic Control System

TCU

Telemetry Control Unit

TDMA

Time Division Multiple Access

TtT

Terminal to Terminal

T-UMTS

Terrestrial Universal Mobile Telephone System

UDP

User Datagram Protocol

UE

User Equipment

UMTS

Universal Mobile Telephone System

UT

User Terminal

UtU

User to User

VLR

Visitor Location Register

VoIP

Voice over IP

VPN

Virtual Private Network


2

Page 15


ASMS REQUIREMENTS

ASM systems will differ significantly from today’s mobile satellite systems in terms of supported services and deployed technology. This implies moving from voice communication to an interactive multimedia-based personal and business environment. ASM systems will enable faster transmission speeds, providing mobile access to high-quality video, audio, graphics and multimedia. The ASMS user will have wide set of requirements ranging from service cost to application performance. These requirements are captured in terms of the user’s perspective in [1, 2]. This chapter translates these general requirements into the associated technical requirements. The headings used in [2] are used in this section to maintain continuity and enable cross reference.


Page 16


Integration of ASM systems with terrestrial networks will be possible at several levels, including: user terminal, service management, numbering and mobility management. This document highlights the impacts of this integration where appropriate. Where a service identified in [1, 2] indicates that new work is required to deliver that requirement, this chapter will identify the issues that need to be addressed. Where appropriate, this chapter will identify existing technical standards that support a specified service requirement, or point to relevant ongoing standards activity. The requirements provided in [1] are applicable in the short term. Assuming that the terrestrial component of UMTS will be operational by 2004, the ASM systems should be operational at the same date. Other requirements will be identified for the longer term perspective. 2.1

GENERAL USER REQUIREMENTS

This section addresses the technical impact of the general service requirements from the user, service provider and operator point of view and provides a backdrop for the subsequent sections covering specific issues. The overall requirements for ASM systems are very similar to their terrestrial equivalents with similar technology implications. In general ASM systems should exhibit the following characteristics. ASM systems should be reliable. This implies that ASM systems must be built with proven, stable technology. This in turn indicates a standards based approach in order to ensure equipment, network and service compatibility. However, reliability can also be interpreted in other ways, e.g. in terms of the probability of being able to originate and complete a call or receive a paging signal anywhere within the coverage area. ASM systems should be affordable. This implies that ASM systems must be based on open standards that enable multiple manufacturers and end service providers to enter a competitive market with compatible products. ASM systems should provide voice, data and video services. This requires a flexible multiservice architecture. This does not necessitate all services being delivered over the same satellite platform. ASM systems should have a suitable display and user interface to support the required services. This means that user terminals must support a range of ‘fit-for-application’ terminals such as handheld, PDAs and laptop computers. This requirement is the same as for terrestrial systems and it is not envisaged that ASMS specific user interfaces are provided, but rather that they will reuse those developed for terrestrial terminals. ASM systems should be available ‘everywhere’. This implies global coverage for quasistationary, handheld, car, ship, train and plane use. It does not imply that all ASMS services should be available in buildings.


Page 17


ASM systems should have a single service interface. This means a single interface in terms of billing and service management for the ASM system itself. There may be other interfaces for specific services provided independently of the ASMS, e.g. Internet access. 2.2

TERMINALS

This section identifies the technical implications of the user terminal requirements that are identified in [1, 2]. It also identifies the safety issues associated with European and global EMC and EPFD limits and their impact on the technical requirements of the antenna and supported services. ASMS users will use a range of communications devices to view high-quality video, work with graphics-rich document files, browse, buy and access a whole new world of information and entertainment services. Four main categories of terminals have been identified as follows: •

Handheld terminals.

•

Transportable terminals: briefcase, laptop, palmtop.

•

Vehicular terminals: business (truck, train, coach, maritime, aeronautical), consumer (car, maritime etc.).

•

Broadcast receivers.

Each of these categories has the potential to cover a range of terminals types with specific user segments and applications, as follows: •

ASMS only terminals.

•

Generic multi-mode terminal, capable of connecting to a arbitrary number of systems.

•

Dual-mode ASMS/T-UMTS terminals.

•

Dual-mode ASMS/GPRS terminals.

•

Tri-mode ASMS/T-UMTS/GPRS terminals.

The characteristics of each of these has an impact on the technology used to realise these terminals. It is assumed that all handheld terminals will be dual-mode ASMS/T-UMTS. The level of integration between terrestrial and satellite components also varies for the other terminal types. Single-mode terminals are pure ASMS terminals, while multi-mode terminals are capable of communicating with both ASMS systems and terrestrial systems. The technology impact of integration varies: •

Common user interfaces. This limits integration to elements such as menus, address lists, capacity to switch modes, etc.. The hardware and software of the terminals would otherwise be completely independent.


Page 18


•

Common control systems. This implies that the behaviour in one mode would depend on the operational state of the other modes (off, out of coverage, busy, etc.) requiring a deeper system and user terminal software integration.

•

Common modem functions. This covers reuse of functions such as multiple access, modulation and synchronisation schemes. Integration of the hardware should be possible at this point, but with the likely result of a sub-optimal ASMS air interface.

•

Common RF systems. This covers reuse of RF elements such as antennas and HPAs. This would reduce terminal cost, with the disadvantage of sub-optimisation of the ASMS air interface and terminal design.

•

The user terminals may also include other capabilities such as the integration of Galileo receivers for navigation purposes.

Note that in-building operation of handheld terminals has been assumed through the use of exciters and/or repeaters. The technical requirements of all of these terminal types is covered in more detail in the following sections. 2.2.1

Handheld terminals

Handheld ASMS terminals should be at least dual mode, thus permitting the terminal to connect to terrestrial networks (T-UMTS and beyond). They are viewed as being potential mass market devices, implying a low cost solution. The target ASMS service set is to be supported while the terminal is on the move. Services will comprise: •

Telephony

•

Messaging

•

Web/WAP browsing

•

Audio streaming

•

Low-rate data streaming (broadcast/multicast)

•

Non real time video streaming

•

Video storage capability of up to 30 minutes of material

•

E-commerce services

•

Location-based services

It is envisaged that handheld terminals will not support services requiring high data rates on the return path (maximum data rate assumed of the order of 16kbps). The terminals are envisaged to be similar to current handheld MSS terminals, or possibly more like a PDA. A


Page 19


display of an appropriate size would be required to show images and video (typically 5cm x 5cm). In addition to containing a user interface, the handheld terminal is likely to contain a cable interface or a short-range wireless interface (SRWI) enabling it to connect to other devices like PDA’s or laptop PCs. However, the main usage of the terminal will be via the user interface, not via the SRWI. It is assumed that the ASMS systems will generally not support use in buildings or while the user terminal does not have a line of sight (LOS) path to the satellite. Therefore, some user co-operation will be necessary. Exceptions will occur where the user is close to an appropriate window in a building, or where local repeaters are provided. The desirability (or need) for in-call handover between ASM systems and terrestrial systems has not been identified. These commercial requirements translate to the following general technical requirements: •

To achieve low cost, ASM handheld devices will require the maximum technology reuse from terrestrial mobile systems, i.e. T-UMTS and beyond. Non-handheld ASMS terminals will also take advantage of this commonality. This implies either a common air interface with one or more terrestrial systems, or the use by ASM systems of a cut-down version of a terrestrial standard in order to minimise chip count and software development.

•

It also implies use of the same, or an adjacent, frequency band for the satellite and terrestrial services in order to minimise the RF component count, mass and cost. The only frequency band that can meet this requirement is the 2GHz IMTS2000 band. However, if T-UMTS gains access to other frequency bands then could also open up opportunities for ASM systems.

2.2.2

Transportable terminals (Palmtop and Laptop Terminals)

Transportable (or nomadic) terminals will be fixed during communications. Three types are defined: briefcase-size, palmtop-size and laptop-size. Reference [2] assumes that palmtopsized terminals are about 10 x 17 cm; the laptop-sized terminal is about twice as large (20 x 20 cm). Both single-mode ASMS terminals and multi-mode transportable terminals are envisioned. No requirement has been identified in terms of depth, mass or power consumption. For transportable terminals it is assumed that the antenna is directional and must be pointed towards the satellite. The fixed azimuth and elevation angles of GSO satellites simplify the use of such a terminal compared with NGSO satellite systems. Because of this configuration, transportable terminals are likely to contain a cable interface or a short-range wireless interface (SRWI) enabling it to connect to other devices like PDA’s or laptop PCs. The supported service set is the same as for the handheld terminals, with the addition of realtime video streaming. The peak forward and return channel rates are provided in Table 2.1.


Page 20


Terminal Type

Peak Forward Data Rate

Peak Return Data Rate

Palmtop

200 kbps

64

Laptop

384 kbps

144

Briefcase

384 kbps

384

Table 2.1 Transportable Terminal Channel Rates 2.2.3

Vehicular terminals

Two classes of vehicle terminal are envisaged: the consumer terminal fitted to cars (and possibly small boats); and the business terminal fitted to commercial vehicles such as trucks, trains, coaches etc.. In contrast to handheld and transportable terminals, the vehicular terminals are expected to be modular, i.e. elements such as the antenna, front-end and user interfaces may be distributed within the vehicle. The actual implementation may vary with vehicle type and application. Table 2.2 shows the transmit and receive channel requirements for each vehicle type.

Terminal Type

Peak Forward Data Rate

Peak Return Data Rate

Consumer

200kbps

64kbps

Business

384kbps

384kbps

Maritime

384kbps

384kbps

Aeronautical 384kbps

384kbps

Table 2.2 Vehicle Terminal Channel Rates The key technical concern is the antenna. For low bandwidth services (similar to handheld terminals) and 2GHz operation, the antenna could be a small whip antenna located on a vehicle in the same way as an existing cellular antenna (possibly even combined). Higher data rates will require a distributed or directional antenna and this has different implications for the different terminal types. Similarly, different vehicles have different amounts of mounting space available in the dashboard and elsewhere and they also have different wiring loom requirements and capabilities.


Page 21


A car terminal needs to have low mass and power requirements, simple installation (preferably at the time of car manufacture) and have no impact on other car facilities such as roof racks, sun roofs, convertibles, spare wheel mounts, hatch backs etc.. For directional antennas this implies that the car manufacturer will need to have several mounting options across its model range. The concept of distributed antenna elements with a combined input/output is worthy of further investigation, but it is likely to result in a complex receiver implementation and installation requirements. The location of the DCE will also vary from vehicle to vehicle: dashboard, boot/trunk, or with the antenna. Trucks should present a simpler requirement: typically the cab roof will be the preferred location for the antenna. The use of detachable bodies and articulated trailers makes the use of distributed antenna elements unlikely. However, cab roofs also have clutter that has to be taken into account: air dams, overhanging refrigeration units, sleeping compartments etc.. This implies that the whip antenna (for low rate services) and steerable flatplate antennas (for higher rate services) will be the preferred solutions. Accommodation of the DCE and DTE equipment within the cab, or external storage compartments, should be a relatively simple issue. Maritime terminals could use the same antenna technologies as land based vehicles in order to take advantage of reduced costs. However, maritime vessels have a variety of installation issues that may preclude the use of distributed antenna technology, e.g. watertight bulkheads, ceilings etc.. Therefore, it is more likely that maritime terminals will use either electronically steerable flatplate arrays or gimballed directional antennas (e.g. parabolic reflector). Vehicle terminals may contain a Short Range Wireless Interface (e.g. DECT, Blue tooth) similar to that of transportable terminals. Hence, users inside and in the vicinity of the vehicle may use it to connect their portable PC, T-UMTS terminal or some other device to the ASMS system. Aeronautical terminals present the greatest challenge with respect to the user terminal. It has taken considerable time and effort to deliver today’s relatively low rate aeronautical terminals in a form acceptable to aircraft manufacturers and operators. Antenna and DCE accommodation are difficult technical challenges on any class of aircraft and this will require significant further study. Aeronautical terminals are unlikely to have an SRWI interface, but will tend to provide wired interfaces. With respect to electronic interference, the ETSI Technical Committee Electromagnetic compatibility and Radio spectrum Matters (ERM) is developing a harmonised European standard related to electromagnetic compatibility (EMC). This includes communications systems in road vehicles, and a joint work group (ETSI ERM TG4) has been created together with ACEA (Association des Constructeurs Européens d’Automobiles) to address this. Special requirements will apply to the aeronautical terminals. 2.2.4

Broadcast Receivers


Page 22


All four categories of ASMS terminal will be capable of receiving broadcast services, but this section addresses broadcast only receivers. This category covers vehicle, transportable and handheld (including wearable) devices equipped with short-range radio access interface or wired interface. The key difference between broadcast only receivers and the other categories of ASMS terminal is that there is no requirement for broadcast/multicast services to operate in the same frequency bands as the interactive services, i.e. the IMT-2000 bands. Integration with terrestrial networks and services may not be an issue (the future of digital terrestrial radio services is uncertain). This could release spectrum for interactive services. However, if the other categories of terminal are to receive the same broadcast/multicast services, it would be logical to support them through the same front-end if possible. This trade-off needs to be examined further.

Car

Handset

Transportabl e

Wearable

Terminal size

Typically 15 x 20 x DIN A5 max 8 cm

DIN A4

A few cm x 10cm

Antenna size

Various options

?

DIN A4

?

Weight

Typically a few kgs

Few hundred Less than 1kg Few hundred g. g.

Autonomy

Always on-battery

5h

10h

3h

Table 2.3 Target specifications for broadcast receiver terminals 2.3

USER INTERFACES


Page 23


This section identifies the technical impact of the required interfaces with the user (display, keyboard, separate CTE, interaction requirements, billing) on the design of user terminals and applications. It identifies gaps in current technical capabilities and standards, e.g. flat screen displays, video drivers, equipment physical interfaces etc.. 2.3.1

Non-broadcasting

In terms of user interfaces, ASMS systems face exactly the same challenges as their terrestrial counterparts: the reconciliation of friendly visual displays with miniaturised environments and the replacement of the traditional keyboard as an input device. It is therefore logical to assume that ASMS terminal manufacturers will use the same technology solutions as their terrestrial counterparts, particularly as there is a need to reuse as much technology as possible in order to drive down costs. Table 2.4 identifies the user interface requirements identified by the UMTS Forum, along with the expected timeline. It is appropriate to assume that the ASMS terminal manufacturers will utilise the same technologies as they become available.

Table 2.4 Description of 3G devices 2.3.2

Broadcasting

The user interface for broadcast applications will be a subset of those provided for nonbroadcast services depending on the type of information. For broadcast receive only terminals, facilities such as channel tuning and interface ports (such as an audio jack) will still need to be included, but these are still sub-sets of the non-broadcasting requirements.


2.4

Page 24


APPLICATIONS

An “application” corresponds to a set of characteristics integrating information processing and communication which allow an user to perform operations. An application means a set of activities which are aggregated to answer users needs, corresponding to a given situation: business, entertainment, education. This implies software modules and\or hardware which execute in a automatic way or not, locally or to distance via Telecommunications or Broadcast network services. This section identifies the technology implications of the application requirements identified in [1]. This includes identification of the relationship between applications and bearer services, impact on user terminals, network connectivity, service management and end-to-end service delivery. 2.4.1

Non-broadcasting

ASMS applications will be the same as for the equivalent terrestrial mobile services and each will have its own technical requirements. They can be categorised as follows: •

Internet Access: mobile access to Internet as well as file transfer, electronic mail and streaming audio and video.

•

Intranet/Extranet Access: secure mobile access to corporate Local Area Networks (LAN) and Virtual Private Networks (VPN) to offer business applications.

•

Customised Infotainment: access to personalised content via structured-access mechanisms (e.g. mobile portals).

•

Multimedia Messaging Application: real-time and non real-time multimedia (voice, text, video) messaging capability. This includes closed user groups facilities.

•

Location-based Applications: includes enhancements of other services (e.g. customised information and entertainments).

•

Rich Voice: includes videophone and delivery of multimedia communications.

The main technical implication of the target service set is the fact that all applications will be IP based, with a variety of layer 4 protocols sitting on top of it, e.g. TCP, UDP, HTTP etc.. These applications also have differing requirements in terms of QoS. Some of these QoS requirements have been identified by the IETF, ETSI etc., and some of them are still being developed, particularly with respect to delivery over satellite. These issues are addressed in the service requirements section. 2.4.2

Broadcasting


Page 25


There is a range of potential broadcasting and multicasting applications for ASMS. Some will have parallels with terrestrial mobile networks and some will be an extension of fixed network applications. Services will include: •

Real time and non real time video streams, e.g. entertainment.

•

Real time and non real time audio streams, e.g. traffic reports.

•

Real time and non real time data streams, e.g. mapping information.

•

Short messages, e.g. selected web site update notifications.

The key technology impacts on ASM systems of this service type are: •

The ability to identify and track groups of receivers for each application type.

•

Support of different QoS requirements, e.g. best efforts or guaranteed delivery.

2.5

PRICING REQUIREMENTS

This section identifies the relationship between application and service delivery and costs (i.e. system resource costs) and identifies the technology implications. 2.5.1

Non-broadcasting

ASMS service take-up will be determined by the price of the service and the terminal, and the attractiveness of the service bundle. Competition plays a key role in determining the service price points, but the underlying cost of provision is determined by the applied technology. User terminal costs are driven by component costs and these are determined by volumes. Significant volumes are unlikely to be generated by the ASMS-only market, thus driving system and user terminal designers towards maximum commonality with terrestrial systems. In terms of the network, the cost can only be reduced by the use of standardised transmission & network technologies and associated interfaces, rather than proprietary solutions. This implies that the network itself is unlikely to be a source of service differentiation. Many different models for pricing could be envisaged for a Service Provider depending on users’ profile and usage. Assuming that an individual user is choosing from a range of standard service offerings, then the key impact on the technical comes from whether those services are billed on usage or not. Billing on usage requires the network and service providers to measure service usage on a time or volume basis for each individual user. 2.5.2

Broadcasting


Page 26


In terms of technology the charging for broadcast (or multicast) services can be done either by real-time transactions initiated at the user terminal (i.e. pay-per-view type), or by an off-line process between the end user and the service provider (service subscription). The handheld, transportable and vehicle terminals will be able to support real-time service transactions through their return channel. The broadcast receive only terminal does not have this facility and therefore necessitates provision of an off-line process for service access. 2.6

SERVICE REQUIREMENTS

The term “service” means capacities bought or rented by a user from a supplier of services. Services can be classified in several ways, e.g. in terms of the use of network resources, symmetry/asymmetry, interactivity etc. (see [1] for discussion). However, in terms of the impact on ASMS technical requirements, the delivery of a service can be viewed predominantly in terms of the delivery of bearer services capable of supporting the target applications. A first set of services has been defined for the main classes of terminals in [2]. It is proposed that ASM systems follow the ITU-T B-ISDN service classification [3]: bearer services, teleservices, supplementary services (including AAC functions, call forwarding etc), Connected/Non-connected modes and Access to other infrastructures (Internet etc.). In addition to these services, there are a range of other service characteristics that must be supported: •

Positioning related services will be provided to all types of user terminal. Positioning information will not be provided by the ASM systems themselves, but will be provided by other means. An appropriate receiver will be incorporated in all ASMS terminals.

•

An ‘always on’ capability.

•

A level of service availability at least the equal of existing comparable Inmarsat services.

The following sections discuss specific service requirements. 2.6.1

Non –broadcasting

A variety of bearer services will be provided, which may differ in flexibility and offer different capabilities. Bearers are characterised by parameters such as “throughput”, “delay tolerance”, “maximum bit error rate” and “symmetry”. These bearers transfer the information necessary for the provision of teleservices and end user applications. The provision of ASMS QoS is also achieved at the bearer level, although the required performance will be defined at higher layers. Several bearers may be associated with a single call and bearers can be added to a call and/or to be released from a call in real time. The bearers should be independent of radio environments, radio interface technology and fixed wire transmission systems.


Page 27


Adaptation/Inter-working functions are required in order to take account of the differences between the bearers used for the provision of a teleservice/application in the fixed network and the bearers. Adaptation/Inter-working functions are required which take account of the discontinuous and/or asymmetrical nature of most teleservices/applications. The service platform shall provide interfaces (to serving networks and home environments) for the creation, support and control of supplementary services, teleservices and user applications. The service platform will also provide interfaces enabling subscribers to control supplementary services, tele-services and user applications. There are also requirements at the IP layer that will need to be addressed separately and in conjunction with the B-ISDN requirements. These requirements are not exclusive to ASMS, but ASMS has to be able to support and exploit the standardised solutions. These include: •

Requirements defined within ETSI TIPHON.

•

Requirements for IP multicast and secure IP multicast.

•

The emerging QoS architectures (DiffServe and IntServe) and their related signaling requirements. These QoS architectures do not consider mobile nodes. These area need to be reviewed by the ASMS TG in order to identify any additions or changes that may be needed.

QoS mechanisms enable and enforce the sharing of bandwidth among services and users. Thus, there must be mechanisms available to identify bearers with different QoS attributes. Thus, supporting roaming users is an essential feature of the end-to-end signaling and control system of IP network as well as the bearer services. IP v6 will support most of these functions in a native way - mobility, QoS and flow control are embedded in the new protocol version. However, there are some issues surrounding the security mechanisms within IP v6 that could cause problems relative to the existing IP v4 IPSec implementations. There is significant work taking place in this area within the Broadband Satellite Multimedia group within ETSI TCSES and this will need to be addressed in detail. A number of specific service and QoS characteristics have been identified in [1, 2]. These need to be evaluated by the Technical group in the light of the proposed ASMS solution and other potentially conflicting requirements and standards: •

The quality of service has been defined accordingly to the following parameters: 1. Voice services: MOS equal or better than 3.5 (as for GSM-EFR). 2. Video services: a Picture SNR of 35 dB or better is requested. 3. Data services: a BER of at least 10-6 is requested.

•

Delay and delay jitter : the 3 GPP are applicable also in the case of the ASMS.


Page 28


•

Real time (constant delay): Maximum transfer delay of 400 ms; Bit Error Rate in the range 10-3–10-7.

•

Non real time (variable delay): Maximum transfer delay (for 95% of the data) of 1200 ms, or more; Bit Error Rate in the range 10-5–10-8. 2.6.1.1 ASMS services as a complement to T-UMTS services

ASMS services could complement T-UMTS services in two ways and each has technical implications: •

Geographic extension of basic services. This will require a network level interface similar (preferably identical) to the interface between T-UMTS networks.

•

Functional extension services; where the ASMS is used to provide services that extend the functionality of UMTS services. This includes multicast and broadcast services which not be efficiently provided by T-UMTS.

2.6.2

Broadcasting

The majority of broadcasting applications identified in [1, 2] have little impact on the service requirements for broadcast services. They all use the same standard bearers (albeit of different rates). The ‘back office’ functions, such as timed delivery of specific content, repetition of content and carousel management, do not have a direct impact on ASMS implementation. EUREKA – 147 is a standard that provides compatibility at consumer level (in line with DAB-T). Mobile reception is the primary target, fixed reception is the secondary target. Automotive telematics compatibility is also provided. Interactive mobile services can be provided with IMT-2000 return channels. Return links may be required for some closed user group and/or secure multicast applications. High Speed content distribution on the forward link requires return channel for through selective acknowledgements or negative acknowledgements. 2.7

OPERATORS REQUIREMENTS

This section identifies the requirements from the different operators. Three types of operators are identified: infrastructure, service and application. 2.7.1

Infrastructure operators

These operators provide and maintain the space and ground infrastructure upon which the communication links are established. They will have different needs that may conflict with, or complement, the service requirements, e.g. they will want to maximise capacity and flexibility to deliver services, but with minimal cost, power consumption, accommodation etc..


Page 29


All the network solutions and the related protocols for ASMS are expected to follow what will be developed for terrestrial cases. The all-IP solutions are expected to follow the requirements identified by the Internet Engineering Task Force (IETF). The IETF is active in the definition of the requirements for the third generation of wireless IP. 2.7.2

Service operators

These operators provide users with terminals and with services (help desk, billing, roaming, etc.). This will impact on the technical interface between service operators and infrastructure providers, e.g. SML interface requirements for service creation, management, billing & cessation. This could also impact on terminal and infrastructure complexity. The convergence point for supply of information and entertainment will be the Mobile Multimedia Portal. As the end-user’s preferred point of entry into all IP-based services and content, the portal is where the customer interacts with the entity that provides the services. Three main categories of service might be distinguished: •

Mobile ISP.

•

Mobile Portal.

•

Mobile Specialised Services.

Figure 1.1 Service operator positioning (source UMTS Forum) 2.7.3

Application operators

These operators provide users with applications to be used with the user terminals. For instance this could be internet surfing, gaming, e-business applications etc.. This will necessitate interconnection with application server farms distributed within other networks. The applications supported will have an impact on the required bearer services, interfaces and billing strategies.


Page 30


2.7.3.1 Non-broadcasting

Providing the Portal does not imply creating the applications or the content. Content feeds are likely to come from existing content providers but with subscriber data being captured by the Service Operator. It naturally follows that the first applications should focus on building the subscriber base and increasing airtime. Next should come applications, which drive subscriber profile data capture, such as personalised subscription based content, push and wireless personal information synchronisation. Only after building the profile database can mobile ecommerce and advertising be successful. 2.7.3.2

Broadcasting

Choice will be key to development of the broadcast business. Broadcast consumers will demand a wide range of services and broadcasters will need to choose delivery methods that suit the circumstances, ranging from sending the same programme to millions, through to delivering personalised multimedia content to an individual mobile user. 3G could deliver the latter, but there are many scenarios in between that serve to illustrate a business driver, from the broadcasters’ perspective, for close co-operation between broadcast and cellular networks.

3

REPRESENTATIVE SATELLITE SUPPORT ASMS APPLICATIONS

SYSTEMS

WHICH

MAY

During the shot term period considered there are basicly two groups of satellite segments available : •

the communication type satellites, providing point to point communications, represented by ACeS, Thuraya and Inmarsat 4, and possibly also new ICO, and

•

the digital audio broadcast (DAB) satellites systems represented by The Sirius system, the XMT M Satellite Radio System and the WorldSpace System. These systems have developed technologies allowing to provide large content to mobile terminals through satellite.

The communication satellites operate in MSS band while the broadcast satellite systems operate in BSS bands.

3.1 3.1.1

COMMUNICATION TYPE SATELLITE SYSTEMS ACeS


Page 31


3.1.1.1 Overview

ACeS will use first one and later two geostationary satellites to provide coverage throughout Western and Central Asia, Eastern Europe and parts of Northern Africa. The second satellite will serve as a backup and can later increase system capacity and coverage to include Eastern Europe and parts of Northern Africa. The services that will be provided are voice, low speed data/ fax and messaging. The system is based on the GSM standard, however, both dual-mode ACeS/GSM and ACeS/AMPS terminals will be available. Global roaming agreements will give subscribers access to GSM networks worldwide when being outside ACeS satellite coverage. The satellite will use L-band frequencies for the mobile links and C-band frequencies for the gateway links. From its orbital slot at 123°E, the ACeS satellite will cover 11 million square miles of Asia and reach 60% of the world's population. ACeS only needs a fixed cellular beam pattern. An analogue low-level beam forming network, using simple passive components, and an on-board digital switch provide dynamic routing of individual frequency sub-bands to any beam and frequency slot. The L-Band coverage has 140 beams, which are formed by separate transmit and receive 12 m antenna subsystems. This multi-beam configuration can support a frequency reuse factor of 20 with a 7-cell frequency reuse pattern. The L-Band feed-arrays and reflectors are identical for both transmit and receive. Each beam is formed by the low-level beam forming network which provides the amplitude and phase weighting. Signals are then presented to the multi-port power amplifiers and the transmit antenna feed assembly. The role of the 88 L-Band cupdipole radiator feed array is to receive a pre-determined distribution of RF signals from the bmatrix power amplifiers and to illuminate the mesh reflectors to form 140 spot beams. The feed elements are shared between beams and the power is shared between multi-port power amplifiers. This enables a high degree of power distribution flexibility between beams to accommodate traffic variation among beams while minimising the number of feed elements and power amplifiers. The antennas' deployable reflectors, made of gold-plated molybdenum, provide the gain for communication links to handheld phones 40,000 km away. 3.1.1.2 Services

ACeS services are: •

Voice (3.6 kbps).

•

Group III facsimile, duplex data and DTMF signalling (2.4 kbps).

•

Standard GSM features for call transfer, call forwarding, call waiting, call holding, conference calls, three-party service, call barring, operator intervention, operator assistance and operator call trace.


Page 32


•

"High Penetration Alerting" informing the subscriber that the attempted call cannot be connected due to signal blockage thereby informing the subscriber to move to a better location (e.g. a window).

•

Optional features including Short Message Service, Voice Mail, Store and Forward Fax and High Power Paging (similar to High Penetration Alerting but also transmitting an alphanumeric message).

3.1.1.3 Satellites

Two satellites, Garuda-1 and Garuda-2, are produced. The second is initially serving as a back-up but can later be used to increase system capacity. These geostationary satellites are using state-of-the-art design and are built on the Lockheed Martin Corporation A2100 AXX spacecraft bus. When starting service the Garuda satellites will be the most powerful commercial communications satellites ever, providing at least 11,000 simultaneous telephone channels, capable of supporting up to 2 million subscribers. Service life is at least 12 years. The communications payload features two 12 meter antennas providing links to the handsets via 140 satellite spot beams. The payload has a digital signal processor for on-board routing and switching of calls to the correct beam. The Satellite Control Facility (SCF), located in Indonesia, houses the hardware, software and other facilities necessary to manage and monitor the Garuda satellites. The SCF includes a 15.5 meter tracking antenna for links with the satellites. 3.1.1.4 Terminals

ACeS user terminals have a standard GSM subscriber identity module (SIM) and a single network access code (telephone number). Subscribers can be reached on one number whether being in satellite or GSM mode. Subscribers to GSM networks worldwide can use ACeS while travelling in Asia using their normal GSM SIM and an (e.g. rented) ACeS terminal. There are both handheld terminals and terminals for fixed operation. 3.1.1.5 Gateways

The ACeS Network Control Center (NCC) is located with the SCF facilities in Indonesia. The NCC controls the ACeS network resources and assigns radio resources to the gateways. The NCC shares the 15.5 meter tracking antenna with the SCF. The NCC also has the ACeS Customer Management Information System (ACMIS). The ACMIS collects satellite-circuit usage data for the gateways and generates bills to the gateways based on this data. The ACMIS also maintains a central database of ACeS subscribers and user terminals. Each gateway is capable of providing full services to all ACeS subscribers over the entire service area. They also provide the same services to all PLMN subscribers who have signed roaming agreements with AceS. A roaming agreement between ACeS and a PLMN enables the PLMN's subscribers to use all ACeS gateways.


Page 33


Initially, the ACeS system will consist of at least three national gateways located at Jakarta (Indonesia), Manila (the Philippines) and Bangkok (Thailand). Several other gateways are planned. Each gateway has a 12 meter antenna for links with the satellites. Incorporated within each gateway is a Gateway Customer Management Information System (GCMIS). The GCMIS includes subscriber management, user terminal management, numbering management, call rating, customer service/inquires, traffic monitoring, SIM generation, billing, payments, settlements and fraud detection. 3.1.1.6 Call routing

The NCC performs the common signalling for the entire system so that call establishment and clearing are performed at the NCC. It means that paging of the terminals for call set-up is centralised at the NCC and the terminals will listen for pages on the common channel from the NCC. This is the same approach as used in the Inmarsat M and B systems. 3.1.1.7 Air interface

The air interface for ACeS has been developed by Lockheed Martin, Ericsson and ACeS and is proposed as a general air interface for geo-systems under the acronym GMSS (GMR-2 standard, se Annex). With some modifications the same air interface is planned used by EAST as well. The air interface is asymmetrical such that there is more FDMA and less TDMA in the reverse channel compared to the forward channel. The reason is that the power transmitted by the handheld terminal is minimized by this approach. 3.1.2

Thuraya

3.1.2.1 Overview

Thuraya will use a geostationary satellite. Coverage will span Europe, North and Central Africa, the Middle East, Central Asia and the Indian Subcontinent. Services will extend beyond boundaries of terrestrial networks and reach remote areas not accessible by conventional modes of mobile telecommunications. The satellite, to be positioned at 44°East, has an expected lifetime of 12 to 15 years. The satellite system will cover in excess of 40 per cent of the world and its most populated regions. •

The system will provide least cost routing and single-hop terminal to terminal calls. Terminals can be dual-mode GSM/ satellite.

The Thuraya system architecture is shown in the figure below.


Page 34


Figure 3.1 Thuraya system architecture

Thuraya launched the first satellite in October 2000, with commercial operation beginning in March 2001; it expects to launch the second satellite two to three years later, subject to demand. 3.1.2.2 Services

The following services will be supported: •

Telecommunications Services including voice, fax at 2.4, 4.8 and 9.6 Kbps and data at 2.4, 4.8 and 9.6 Kbps.

•

GSM Standard Supplementary Services: Call Forwarding, Call Barring, Calling Line Identification, Call Line Identification Restriction, Closed User Group, Multiparty, Call Waiting, Short Messages Service, SM Beam Broadcast.

•

Value Added Services/ Intelligent Network Services: Pre-paid SIM Card Services, Hot Billing Services, Free Phone Service, Premium Rate Service, IVR Services, Voice Mailbox Service, Location Determination: within 100m accuracy (Global Positioning System - GPS). 3.1.2.3 Satellites

The satellites are produced by Hughes Space and Communications International, Inc. A spare ground satellite is also manufactured and may be launched at a later date to expand system capacity. Each satellite has a capacity of about 13,750 telephone channels. The satellite has


Page 35


250-300 spot beams with digital beam forming (which provides for dynamic area coverage and optimises over change in traffic demand). Single hop connections can be made for mobile-to-mobile communications. 3.1.2.4 Terminals

The following terminal types will be provided: •

Hand-held. Similar to GSM terminals in appearance, size and weight. GSM and satellite mode.

•

Vehicular. Consists of handheld terminal and vehicular fixed kit. GSM and satellite mode.

•

Fixed terminal. Consists of handheld terminal and indoor fixed kit. Satellite mode only.

•

Payphones. 3.1.2.5 Gateways

The ground network consists of one primary gateway and several regional (national) gateways. The primary gateway (located in Sharjah, UAE) handles satellite control and common resource management functions in addition to normal communications also provided by the regional gateways. The primary gateway can handle calls to and from all the 99 countries being covered. The design of the regional gateways, which will be based upon that of the Primary Gateway, will provide the necessary interface with other Thuraya gateways (via satellite) and public terrestrial networks. Regional gateways will be set up to meet the specific requirements of the local markets. 3.1.2.6 Call routing

Thuraya provides “optimised routing” to provide most economic call routing. Single hop connections are supported for terminal to terminal calls anywhere in the coverage area. The network access and call tariff are based on caller terminal GPS position. 3.1.2.7 Air interface

The air interface is the GSM based GMR-1 standard (See Annex). 3.1.3

ICO

ICO represents one of the planned systems. The ICO system when initially planned was structured around the re-use of GSM technology for the ground infrastructure and therefore offered primarily GSM-like circuit switched services. However, the current program underway is to upgrade the system to provide both circuit and packet switched services.


Page 36


3.1.3.1 Overview

The ICO system will use 10 satellites (plus 2 in-orbit spares) in a Medium Earth Orbit (MEO) constellation using 2 inclined circular orbits to provide global coverage. ICO circuit switched services are basic voice at 4.8 kbps, enhanced voice at variable rates, and data and fax at 2.4 kbps in addition to a short message service. The addition of the packet core network will provide a portfolio of services with much higher rates than that possible with the circuit switched segment. ICO's system is unique in that it uses a constellation of MEO satellites that orbits the earth at a height of 10,390 km. The high elevation angle (averaging 40-50 degrees) reduces the probability of calls being blocked by ground based obstacles. The orbital constellation is designed for significant coverage overlap, ensuring that usually two and sometimes three or even four satellites will be in view at any time. Each satellite covers approximately 30% of the earth's surface, offering customers a greater chance of being in the field of view of more than one satellite, and thereby giving a high possibility of providing path diversity. The Satellite Access Nodes (SAN) provides the interface between the satellite and the terrestrial networks. The SANs are interconnected via a ground based network termed the ICONET. ICO will provide a range of terminals including personal accessories, fixed phones, maritime terminals etc. The personal accessory allows a customer to use a normal phone to connect to the satellite segment. Customers can also have an ICO SIM and roam into cellular network when being in such coverage. Such users will be reached by the same number whether being connected to a cellular or the ICO network. ICO will use GSM and IP technologies for the core network. The air interface is TDMA based. Handovers will be less frequent than for Low Earth Orbit (LEO) systems due to the higher altitude of the ICO satellites thereby reducing the probability of call drop-outs significantly. With MEO satellites, ICO users will have high elevation angles most of the time. The constellation allows for future growth by adding more satellite planes. Specialized (non-handheld) terminals will be provided for use e.g. aboard small craft, ships, medium or long-haul aircraft and land vehicles. Communities beyond the reach of terrestrial wired or wireless networks can use ICO fixed terminals. These will either take the form of stand-alone payphones or will act as local wireless hubs, offering access to national and international networks. The roll-out of the ICO system starting with integration, customer trials and commercial launch is scheduled to take place in 2004. 3.1.3.2 Services

The ICO system will support voice telephony service comparable to 3G cellular services. The ICO system also will provide an emergency call service that is functionally equivalent to 3G cellular emergency call services. The ICO system will provide an automatic facsimile service compatible with terminals operating in accordance with ITU-T Recommendation T.30.


Page 37


The ICO system will provide to users text message services that are equivalent to 3rd generation Short Message Service (SMS), Instant Messaging etc. The ICO system also supports a set of supplementary functions comparable with 3G cellular networks (line identification, call forwarding, call restriction services etc.). The ICO system will also support IP Packet Switched Data Bearer Service (IPPSD) that provides bi-directional IP packet transport between a user on the ICO system and points on the Internet or private IP based networks. Datarates in the range of 6 kbps to 28 kbps are supported on the return link and 20 kbps to 144 kbps are supported on the forward link. 3.1.3.3 ICO System Architecture

The ICO system consists of the space, network, and user segments. The current ground infrastructure consists of 11 globally distributed operational Satellite Access Nodes (SANs). The SANs are interconnected to form the ICONET. All calls are placed via the SANs, which comprise of 5 C-band tracking antennas, the Satellite Base Station equipment, the packet and circuit switching cores, and the associated databases for mobility management (VLR, HLR etc.). The SANs typically connect to service provider networks. The management of the ground infrastructure is under the global and local Network Management Systems. The Satellites are monitored and controlled via the Satellite Control Center (SCC). Figure 3.2 shows the current ICO system architecture based on the circuit switched core.


Page 38


ICO system - overall configuration Service Link 1.9/2.1 GHz

Feeder Link and TT&C 5/7 GHz

GW SAN SAN GW GW Handheld SAN SAN Vehicular

Aeronautical

GW GW

PSDN

GW GW

PSTN/ISDN

GW GW

PLMN PLMN

10 Satellites in in 22 Planes Planes ++ 22 Spares Spares SAN SAN

Maritime

SCC SCC

N NM MC C ADC ADC

Semi-Fixed User User Segment Segment

Space Space Segment

ICONET ICONET (12 Interconnected SANs)

Gateways Gateways

Public Public Fixed Fixed && Mobile Networks

Figure 3.2 ICO-System Architecture 3.1.3.4 ICO-Network Architecture

The SANs are all interconnected into a ring type architecture referred to as the ICONET. Figure 3.3 depicts the network architecture of the ICO system.


Page 39


ICONET Gateways: Switch between PSTN/PSDN /PLMN & ICO Network

G

G

12 Satellite Access Nodes (SAN): Satellite Connectivity to Gateways Global roaming facility

Gateway

G

V

G

V S

V

G

Antennas VLR V

S

V

S

V

S Switch

S

S

V

G

S

S

V

Shared HLR* V

S

V

Link between Gateway and SAN V

S

V

V

S

S

Inter-SAN Network (generic only)

S

The ICONET consists of the Satellite Access Nodes, the Links between them, and the mobility databases. * VLR, HLR:mobility databases (using GSM terminology)

Figure 3.3 ICONET Architecture

3.1.3.5 ICO Space Segment 3.1.3.5.1 Satellites

The satellites will be launched one per launch vehicle, with one satellite currently in orbit (ICO-F2). The satellites use a ‘bent-pipe’ architecture and using digital beam forming generates 163 beams each at S-band. With 10 operational satellites there are a total of 1630 beams for the whole system. Additional circuits can be configured for use in spot-beams in order to meet very high peaks of demand in a specific region, whether it be a city or a large country (“hot-spots”). The satellites can respond to traffic and interference requirements as they change through the orbit. However, there are mechnisms incorporated in the system that allow for pre-planned and semi-real time allocation of resources to the SANs and satellites. The satellites are designed for a 12 years minimum lifetime. 3.1.3.5.2 Satellite Coverage


Page 40


The constellation chosen by ICO is one from a set of optimized configurations. Figure 3.4 shows the ICO constellation, and the coverage from this constellation is depicted in Figure 3.5 for elevations down to 10 degrees. In most locations, multiple satellite visibility is possible and therefore the user has a choice of communicating via two or more satellites, i.e. diversity of path. With the system designed for a minimum margin of 9 dB, the diversity path effectively improves the performance, by avoiding shadowing and blocking effects. Since all mobile satellite systems work only with line of sight to satellite, diversity offers much improved performance.

Figure 3.4 The ICO constellation


Page 41


Orbit Selection: ICO Coverage 90.0

10 ICO Satellites, 10355 km, 10 deg elevation coverage

60.0 L A

30.0

T I

0.0

T U -30.0 D E -60.0

-90.0 -180.0

-120.0

-60.0

0.0

60.0

120.0

180.0

LONGITUDE

Figure 3.5 ICO-Satellite Coverage for 10 Degree Elevation 3.1.3.5.3 ICO Satellite Payload

The ICO satellite is designed around a fully digital payload with narrowband digital beamforming and channelization offering variable bandwidth to the 163 beams. The signals received from the SAN at C-band are down-converted to around 400 MHz before prior to being input to he digital processor. The processor does not demodulate and regenerate the signals and it is therefore transparent. The processor performs channelization and routing towards the 163 spot beams. Each satellite has a bank of 490 filter channels, each of bandwidth 170 kHz, that can be routed to any of the beams depending on traffic and interference conditions. The return transponder (terminal to SAN) essentially performs the reverse function of the forward transponder. This resource management for the satellites is accomplished via channelization plans formulated at the Network Management Center (NMC) and transmitted to the SANs, for onward routing to the satellite via the Payload Command Subsystem. The variability of bandwidth allocation to the beams also means that there is an inherent flexibility for the offering of current and future services which may need bandwidths which are undefined at satellite construction time. Figure 3.6 below shows the channelization and the corresponding frequency routing.


Page 42


The 163 spot beams have a 4-cell frequency reuse. The beams can be grouped into 19 different sets of beams where each set has the same range of path delay and Doppler. The frequency plan ensures that the trailing beams of one satellite will not interfere with the leading beams of the next satellite.

Figure 3.6 C-Band to S-Band Mapping 3.1.3.6 ICO Ground Segment

The gateway portion of the ground segment of the ICO system consists currently of eleven SANs which are interconnected to form the ICONET, the terrestrial backbone of the ICO system. The minimum number of SANs required to provide global services is seven, but it has been decided to install eleven stations to achieve better coverage and reliability. The system design is such that any number of SANs can easily be accommodated. The commercial element of the ICO system consists of the Business Support System (BSS) which has the responsibility of service provisioning, customer care, and billing. The ICO system avoids bypass of existing terrestrial networks: it does integrate them, connecting customers through the existing local cellular service providers and fixed network operators and offering the ICONET as a means of interconnection to/from the satellite segments anywhere, whenever local infrastructure are not available. The ICONET also includes a NMC, a Satellite Control Center (SCC), and their respective back-ups. The SANs, the NMC and the SCC are connected via terrestrial links for carrying network management, signaling and communications traffic.


Page 43


The six SANs which have co-located TT&C facilities guarantee seamless telemetry, tracking and commands of the satellite fleet on a real-time basis. The In-Orbit Tests for the satellites (IOT) are to be conducted from one of these TT&C SANs. Each SAN will consist of six main elements: 1. five ground-based antennas, each with associated equipment to communicate with the satellites; 2. both packet and circuit-switched nodes to route traffic on the ICONET and to interconnecting land-based fixed and mobile networks; 3. location registers to support mobility, call and service access management; 4. platforms to provide value-added services such as voice, facsimile and data messaging services; 5. packet data equipment which will support data services; 6. Gateways that link the ICO network with external networks. Communications and TT&C carriers at the TT&C sites share the RFTs equipment, with the TT&C having the capability to override the communications traffic in case of satellite emergencies. The satellites transmit telemetry and payload data on a continuous basis which is initially analyzed at the SANs. The overall control of the satellite resides at the SCC but the payload configuration is maintained by the NMC. 3.1.3.7 Terminals

The ICO system supports a variety of user terminals including handheld, vehicular, maritime, aeronautical and fixed installations. All these terminals can support different data rates with some of the terminals supporting up to a maximum of 144 kbps. All terminals also support either wired or a wireless connection to different types of terminal equipment for voice and data connectivity. 3.1.3.8 Call routing

Calls from a terminal are routed through a satellite to the SAN responsible for the service area. From the SAN the call is routed through the ICO network to the SAN being closest to the terrestrial user. Calls to a terminal is routed via the SAN closest to the calling party. The HLR where the terminal belongs is contacted to find information about the current location of the terminal. The call is then routed through the ICO network to the SAN where the terminal is currently registered (in the VLR). This SAN will connect to the terminal using a satellite currently covering the relevant area. 3.1.3.9 Air interface

The air interface is using FDMA/ TDMA/ FDD for multiple access. The RF channel spacing is 25 kHz and the bandwidth for a duplex channel is therefore 50 kHz (FDD). Each frame of


Page 44


40 ms has 6 timeslots. The bit rate of the channel in 36 kbps. Each timeslot can transfer 2.4 kbps data (before coding). The modulation is GMSK for the return link and QPSK/ BPSK for the forward link. The minimum frequency band required is 2 x 15 MHz. Space diversity is provided by allowing a terminal to have connections towards more than one satellite. This will reduce the effect of fading and shadowing. This feature also allows to have soft-handover with a make-before-break procedure. Handover is supported between beams of the same satellite, between beams of different satellites and between SANs. 3.1.3.10 ICO Ancillary Terrestrial Component

More recently ICO is considering the use of an innovative scheme to better utilize the limited MSS spectrum resources. This is particularly relevant to multi-spot beam satellites. One of the limitations of MSS systems to date has been the difficulty in the provision of services to subscribers not in the line-of-sight to the satellite. The implication of this is that in most urban areas (for example, in-building use) the MSS frequencies cannot be used due to penetration problems. The ICO ATC methodology allows for the spectrum to be used by a Terrestrial radio system, under control and coordinated by the satellite radio resource manager, in order to complement the satellite coverage. The general way in which ATCs might be integrated into an MSS network is depicted in Figure 3.7. The figure shows the MSS space segment of satellites with a Satellite Control facility on the ground. The ground segment consists of interconnected ground stations (Satellite Access Nodes or “SANs”), which interconnect to public fixed or mobile terrestrial networks. The ancillary terrestrial component would be built upon a standard, for example, third generation, terrestrial cellular infrastructure (e.g. cdma2000). The integrated network management center would dynamically configure the satellite part (frequency plans and satellite payload configuration) and the ATC cell plan to allow for efficient and coordinated frequency re-use. Subscribers would choose from a wide range of user terminal options, capable of operating in either satellite-only mode or combined satellite plus ATC mode, depending on coverage. Different frequency plans are possible within this general framework. ICO has developed at least four basic architectures that 2 GHz MSS operators could use in order to integrate ATCs into their networks without interfering with themselves or adjacent users. The use of ATC technique is only feasible when spectrum management in under full control of the satellite operator. These options will provide a consistent set of services and applications to various communities of users in fixed or mobile environments.


Page 45


Satellite Access Network

Space Segment

Gateways

Public Fixed & Mobile Networks

PSDN GW Handheld

SAN

PSTN/ ISDN PLMN

Personal Repeater

Transportatio n

TT&C SCC

Maritime

Aviation

User Segment Dual mode UE or Repeater products

NMC

Network BTS

T1/E1

Network BSC

IS-634

MSC

ATC component

Figure 3.7 General Architecture of Integrated MSS Network with ATC 3.1.4

Globalstar

3.1.4.1 Overview

GLOBALSTAR is a satellite-based cellular telephone system that allows users to talk from anyplace in the world between 70 north and south latitudes. It provides clear communication thanks to Code Division Multiple Access (CDMA) transmission and avoids outages caused by blockage of signals by using diversity signals from two satellites. The Globalstar system consists of a Walker 48-8-1 constellation; that is, 48 low-orbiting (1414-km altitude) satellites in eight orbits, inclined 52 with respect to the equator with six satellites in each orbital plane. They contact users on the 1.6- GHz -band and 2.5-GHz -band and communicate with the large Gateway ground antennas on the 5- and 7-GHz -bands. CDMA provides for extensive frequency reuse through the use of orthogonal codes in the 1.23-MHz channels. Each large ground station (Gateway) has the capacity to connect up to 1000 users to the Public Switched Telephone Network (PSTN). The constellation has the capacity to serve up to 30 million subscribers (not simultaneously). Gateways will be distributed around the world in order to connect users with their local PSTN. The Globalstar system consists of the following major elements. •

User Terminal (UT): User’s radio telephone.


Page 46


•

Gateway (GW) System: Fixed ground station that connects with the satellite and PSTN. Telemetry Control Unit (TCU) equipped Gateways include a TCU rack which allows communication with the telemetry and control system of the satellites.

•

Service Provider’s Control Center (SPCC): Staffed office for Gateway operations.

•

Satellites and Launch Services: Satellites are used for all UT–GW communication

•

Satellite Operations Control Center (SOCC)/Launch Control Facility (LCF): Manages all satellite telemetry and command functions, launch operations, orbit raising, and in-orbit tests.

•

Ground Operations Control Center (GOCC): Controls system planning and execution

•

Globalstar Data Network (GDN): Provides communication between the ground-based facilities of the Globalstar system.

•

Globalstar Business Office (GBO): Manages the financial and administrative aspects of Globalstar.

•

Globalstar Control Center (GCC): This facility manages and maintains the Globalstar system and houses the GOCC and SOCC. 3.1.4.2 Services

The Globalstar system provides voice telephone service with a quality at least as good as that provided by terrestrial cellular systems, and it also carries digital and FAX data. It also has provisions to operate as a paging system and to leave short messages with either one or a group of users. The Globalstar provides also data services. The data terminal can allow two data transmission modes: •

Asynchronous

•

Packet Data

The active antenna provided with the Globalstar data terminal is omni directional and it does not depend on the particular outdoor location where the data terminal is located. In asynchronous mode, the link is established from the Globalstar Modem to a Standard PSTN Modem or to a Remote Access Server located in the MCC; the gateway routes the call on the PSTN to reach the other end, using the switch installed in the gateway itself. This solution is based on the usage of a single satellite modem, ensuring a gross throughput of 9.6 kbit/s and a net throughput of ~7.2 kbit/s. The alternative to the Asynchronous Mode is to use the Globalstar Modem in Packet Data Mode. In Packet Data Mode the connection is established between the Globalstar Modem and the terrestrial Gateway using a particular connection code. The Gateway has an Interworking Function that is able to establish an IP session assigning an IP address to the modem (in a Static or Dynamic way depending on the application), which can send Traffic Data using


Page 47


protocols determined by the application (TCP or UDP or FTP, etc.). Packets generated at the application level are transmitted to the Gateway and routed on to the MCC via the data link set on PDN or dedicated line. The gross Data Rate is 9.6 kbit/s while the net Data Rate is around 7.5 kbit/s. In Packet Data Mode it is possible to use several Globalstar modems to reach the desired throughput for new generation of Digital Sensors able to transmit 19.2 kbit/s or higher bit rates up to 64 kbit/s. 3.1.4.3 Satellites

The satellite is three-axis stabilized with the earth facing panel always parallel to the orbit tangent. A global positioning system (GPS) receiver is used to accurately determine the orbit parameters and also to supply accurate time and frequency to the satellite systems. Solar panels and a large nickel-hydrogen battery provide power for all phases of the mission. Battery recharge takes place over the oceans, where there is less traffic. The attitude control system uses small (one Newton) thrusters for attitude control. Yaw steering is employed to provide sufficient solar array power during all phases of the mission. 3.1.4.4 Terminals

The UT will typically be a dual-mode unit, although a variety of one-, two-, and three-mode units will be available, operating on both the Globalstar system and one or more of several terrestrial cellular systems. In Globalstar operation it will transmit an average EIRP of about 10 dBW (maximum -4 dBW) and contains a three-channel rake receiver so that it can receive signals from more than one satellite simultaneously. The basic UT is a hand-held unit that looks like a cellular phone with a longer and thicker antenna. Automobiles will be supplied with a kit with a higher gain antenna and power amplifier that will adapt the hand-held unit for mobile use. Globalstar will also employ fixed user terminals, which will typically be a solar-powered phone booth in a village. 3.1.4.5 Gateways

The antennas are approximately 6 m in diameter. The Gateway contains all the electronics to perform the CDMA communication, including rake receivers, in addition to having a home location register (HLR) and visitor location register (VLR) for security, access, and roaming and billing for all those using the system. It also connects to the PSTN through a switch and also provides a global system for mobile (GSM) interface, the interface of the European cellular standard. 3.1.4.6 Call routing

Globalstar system allows interconnection between the user terminal and fixed networks through the gateways. The inteconnection between two Globalstar terminal is established through the satellite, processed by the gateway, forwarded to the PSTN and then through the satellite again. 3.1.4.7 Air interface


Page 48


The Globalstar air interface [(GAI)—the specification for the link operation] specifies a forward link CDMA waveform that uses a combination of frequency division, pseudorandom (Walsh) code division and orthogonal signal multiple access techniques. Frequency division is employed by dividing the available spectrum into nominal 1.23-MHz bandwidth channels. Normally, a mobile satellite service (MSS) Gateway would be implemented in a beam service area with the number of radio channels that demand requires. One Walsh circuit has a maximum usable data rate of 4.8 kbit/s. A Gateway with a single radio channel transmits on a single frequency. Pseudorandom noise (PN) binary codes are used to distinguish between the signals from different beams or satellites, with a different time offset to each beam of each satellite in its view. 3.1.5

The Iridium system

3.1.5.1 Overview

The Iridium system uses 66 satellites in 6 planes in a LEO (780 km) constellation to provide global coverage. Iridium services are voice at 2.4/4.8 kbps, data and fax at 2.4 kbps in addition to a paging/ messaging service. Iridiums plans for terminals includes solar powered phone booths, aeronautical and handheld phones. The handheld phones can be dual mode cellular/satellite. The Iridium World Page Service is available as a stand-alone service or as a complement to the Iridium World Satellite Service. The pagers can be belt-worn. Inter-satellite links (ISL) are used to route calls between the satellites thus minimizing the terrestrial cost of a connection to a PSTN subscriber. The use of ISLs greatly complicates the design of the system, but allows global service to be provided with a fairly small number of gateways (in principle down to a single gateway). The satellites use on-board processing. Gateways are used to interface the terrestrial network. Iridium terminal to terminal calls can be routed directly (not via a gateway) using one or more satellites. A satellite has links to its four neighbour satellites. Each satellite has 48 beams giving a total of 3168 beams for the whole system. All beams are not always active, as some beams will be switched off when passing the earth poles due to considerable overlap in these regions. The system concept is illustrated in the figure below.


Page 49


Figure 3.8 Iridium system overview Iridium call processing is based on the GSM architecture. The gateways include a GSM MSC in addition to the satellite system specific part handling GSM BSS functionality. The system is based on FDMA/ TDMA. A separate country code is assigned to the system for correct routing of calls from the PSTN to an Iridium gateway. The system calculates terminal position, and the location information is stored in the HLR and VLR (as in GSM). Call restrictions may be applied based on the position of a terminal (some countries may not allow terminals to be used). The Iridium system was conceived in 1987 and started operations late in 1998. The original configuration was planned for 77 satellites, and was named after the Iridium atom having 77 orbiting electrons. To reduce system costs after optimising satellite coverage the constellation was changed to 66 satellites in polar orbits. The satellite constellation is shown in the following figure.

Figure 3.9 Iridium constellation with 66 satellites in LEO orbit


Page 50


3.1.5.2 Services

Services provided by Iridium are: •

Voice

•

Data at 2.4 kbps

•

Paging. The paging service allows customers to receive alphanumeric messages of up to 200 characters in any one of 16 languages, and numeric messages of up to 200 digits

•

Supplementary services: voice mail, call forwarding, call waiting, emergency calling, and conference calling 3.1.5.3 Satellites

The 66 Iridium satellites orbit at 780 km above the earth in six planes in near circular orbit, with 11 satellites is each plane (plus one in-orbit spare per plane). The planes are inclined at 86.4 degrees. All planes rotates effectively in the same direction, but at the seam where plane 1 and 6 meets, the satellites appears to rotate in the opposite direction. It may therefore be said that four planes rotate in one direction and two planes (one and six) in the other direction. Corotating planes are spaced 31.6 degrees apart while the counter rotating ones are 22 degrees apart. The velocity of the satellites are around 27 000 km/h with an orbital period slightly above 100 minutes. Each satellite covers a circular area with a diameter of about 4400 km. The minimum practical elevation angle is 8.2 degrees. From a point on the earth a specific satellite is in view around 9 minutes. One spot-beam will be in view around 1 minute. The satellites perform on-board switching with up to four inter-satellite links (ISL) for routing of signalling and user data. ISL are used between satellites in the same plane (intra-plane) and between satellites in adjacent planes (inter-plane). The intra-plane ISLs are permanently maintained (links to the satellite in front and behind), while the inter-plane ISLs are dynamically established and released as the satellite orbits. The satellites in the four corotating planes have four ISLs each, while the satellites in the counter-rotating planes have three (two intra-plane). Due to the variation in horizontal azimuth between the satellites it is necessary to have steerable antennas for the inter-orbital ISL. The ISL operate at 25 Mbps in Ka-band. It is a routing table in each satellite showing how to reach a specific satellite that can deliver the call to a user. In the event that a link between satellites fails, new routing tables must be delivered to all the satellites in the vicinity of the failed link. Linking between satellites that are in ascending and descending planes is particularly difficult and may require that packets be routed around the globe in opposite direction. (Not implemented by Iridium). Each satellite has three phased array antennas with 16 spot beams each giving a total of 48 spot beams. The on-board processor is constructed using VLSI circuits specifically designed. It includes 512 demodulators, which, via the signalling channel, can centre the arriving bursts


Page 51


- from the terminals – in frequency and time. The observed Doppler shift of these arriving bursts is routed to the intended gateway to determine user’s location. (Service is then provided (or denied) based on country-by-country service agreements.) Starting with the first launch May 5, 1997 the entire constellation was deployed in around 12 months on launch vehicles from three continents: the US Delta II (five satellites per launch), The Russian Proton (seven satellites per launch), and the Chinese Long March (two satellites per launch). With a life-time of 5-8 years about a dozen satellites will have to be replaced each year. 3.1.5.4 Terminals

There are terminals for fixed, portable(handheld) and vehicle use. 3.1.5.5 Gateways

Iridium uses 12 gateways for interconnection with the terrestrial network. The gateways are run by 15 operating companies (some gateways supports more than one operating company). Each operating company has one or more business offices that distributes the Iridium services through cellular/PCS operators, PTTs, directly to the end user or another distribution channel. The ground switching equipment is the Siemens GSM-D900. The Iridium constellation with ISL does not require that a gateway is present in the foot-print of each satellite as signals can be routed via one or more satellites to reach a gateway. This creates a network in the sky and a few large gateways may be used instead of having a gateway in each satellite footprint. The minimum gateway elevation angle is 8.2 degrees. The System Control serves as the central management component for the system. It provides satellite control and network management in conjunction with the satellite and network operations center (located in Virginia, USA). In addition there are three TT&C centres located in Hawaii and Canada. 3.1.5.6 Call routing

Each user has a single subscriber number to be used whether being registered in Iridium or roaming into a cellular network. This is a 12 digit number consisting of the Iridium country code (8816 or 8817), a three digit geographical code plus a five digit subscriber number. The geographical code is used to identify a users home country in regions where one gateway services more than one country. When a user switches on the phone, it will access the satellite overhead (providing the best link), and the satellite will route the access request to a gateway. If the gateway is not in the footprint of the satellite serving the user, the ISL link will be used to forward the request to a satellite covering the gateway. If the accessed gateway is not the users home gateway the user will be registered in the VLR and the visited gateway will inform the home gateway about the location of the user and having the user profile transferred from the HLR. The actual call is routed through the ISL and drops down to the gateway closest to the destination. From there it


Page 52


is routed through the terrestrial network to the called terrestrial user. The call set-up procedures are very similar to those used by the AMPS cellular system. Mobile terminated calls (from the fixed network or another Iridium user) are routed via the home gateway that knows the location of the user. The home gateway then sends a ring signal through the necessary ISL to the satellite above the mobile. It is estimated that 95 % of calls will be between an Iridium terminal and a fixed location, while 5 % will be between Iridium terminals. If the user is in a visited gateway region the home gateway will send a signal to the visited gateway to ring the user. The visited gateway determines the user location (VLR) and sends a ring signal to the satellite over the user (via ISL if necessary). The actual user data (voice) do not have to be routed through a gateway. For mobile to mobile calls the gateway takes part in the call set-up, then the communication is directly between the two mobiles through the necessary ISL. The maximum acceptable end-to-end delay for voice is considered to be around 400 ms. Iridium has a delay of 100 – 210 ms depending on the number of ISL connections. The delay with twelve satellites in the path is a bit more than 200 ms. Adding some time for potential queuing delay it should still be well below the required 400 ms. 3.1.5.7 Air interface

Iridium uses FDMA/ TDMA/ TDD with a TDMA frame of 90 ms containing four full-duplex channels at a burst rate of 50 kbps. Each frame have four downlink and four uplink timeslots of 8.29 ms each. The voice channels operate at 2.4 or 4.8 kbps. Data is transmitted at 2.4 kbps. Forward error coding (FEC) is ¾ and the modulation is QPSK. The mobile link uses L-band operating in the range 1616 MHz to 1626.5 MHz. This gives a 10.5 MHz bandwidth. (See Note below.) This is divided up into 240 channels of 41.67 kHz each, plus a total of 500 kHz for guard bands. The frequency reuse factor is 12, i.e. it is 12 spot beams in each cluster. The 240 channels are therefore divided into 20 frequency channels per spot beam. It is four user channels per frequency giving a total of 80 user channels per spot beam. The 66 satellites with 48 spot beams each provides a total of 3168 spot beams. Some of the spots will overlap, especially near the poles where the orbits cross, and to save power only 2150 spots will be active. The total system capacity is therefore 2150 * 80 = 172 000 simultaneous users. For other air interface parameters refer also to the tables at the end of this document. A number of details regarding the Iridium air interface is proprietary information that have not been published.

.


3.1.6

Page 53


INMARSAT

3.1.6.1

Overview

Inmarsat offers a mature range of modern communications services to maritime, land-mobile, aeronautical and other users. Formed as a maritime-focused intergovernmental organization over 20 years ago, Inmarsat has been a limited company since 1999, serving a broad range of markets. Starting with a user base of 900 ships in the early 1980s, it now supports links for phone, fax and data communications at up to 64kbit/s to more than 210,000 ship, vehicle, aircraft and portable terminals. That number is growing at several thousands a month. Inmarsat Ltd is a subsidiary of the Inmarsat Ventures plc holding company. It operates a constellation of geostationary satellites designed to extend phone, fax and data communications all over the world. The constellation comprises five third-generation satellites backed up by four earlier spacecraft. Figure 3.11 shows Inmarsat’s coverage and figure 3.11 illustrates the main components of its system. The satellites are controlled from Inmarsat's headquarters in London, which is also home to Inmarsat Ventures as well as the small Inter Government Organisation (IGO) created to supervise the company's public-service duties to the maritime community (Global Maritime Distress and Safety System) and aviation (air traffic control communications). Inmarsat has regional offices in Dubai, Singapore and India. Inmarsat system is used by independent service providers to offer a range of voice and multimedia communications. Users include ship owners and managers, journalists and broadcasters, health and disaster-relief workers, land transport fleet operators, airlines, airline passengers and air traffic controllers, government workers, national emergency and civil defence agencies, and peacekeeping forces. Through its partnership of service providers, manufacturers, retailers, and system integrators, the Inmarsat system offers its customers a wide range of global services and facilities. The Inmarsat business strategy is to pursue a range of new opportunities at the convergence of information technology, telecom and mobility while continuing to serve traditional maritime, aeronautical, land-mobile and remote-area markets. Keystone of the strategy is the new Inmarsat I-4 satellite system, which from 2004 will support the Inmarsat Broadband Global Area Network (B-GAN) - mobile data communications at up to 432 kb/s for Internet access, mobile multimedia and many other advanced applications. 3.1.6.2 Services

Inmarsat provides a large variety of services each tailored for specific range of applications and matched to the applicable physical environment. Inmarsat-A is 20 years old. Yet it has stood up well and actually benefited from improved and newer technologies. This means that the infrastructure is capable of fulfilling modern needs well into the 21st century. The Inmarsat-A mobile Satellite communications system provides two-way direct-dial phone (high quality voice), fax, telex, electronic mail and data communications to and from anywhere in the world with the exception of the poles. It also provides distress communication capabilities. It is based upon analogue technology. It


Page 54


supports data rates of between 9,600 bps through up to 64,000 bps depending upon different elements of the end-to-end connection. Inmarsat-B is a global communication system which extends the advantages of modern digital technology to the field of mobile satellite communications. Inmarsat-B is seen as the eventual successor to the highly successful Inmarsat-A analogue system, although the two will continue to co-exist well into this decade. Compared with Inmarsat-A, Inmarsat-B makes improved use of satellite power and bandwidth, enabling service providers to offer users much lower charges while maintaining high quality and reliability. Inmarsat-B appeals particularly to existing high-volume users of Inmarsat-A. In the maritime environment these include the offshore exploration industry and cruise-ship operators. On land, customers include the media (compressed video and broadcast-quality audio transmission over highspeed data links), government agencies and peacekeeping forces (using the encryption capability), aid organizations and all those who require full office communications in areas lacking a fixed telecommunications infrastructure. Inmarsat-B, supports high-speed data services (HSD) offering 64 kb/s connections to the international ISDN network. Inmarsat-B HSD services are designed to accommodate the needs of a wide range of users with large amounts of data to transmit; these HSD services are suitable for applications such as highspeed file transfer, store-and-forward video, high-quality audio transmission, videoconferencing and multiplexed channels combining voice, fax and data. Inmarsat-B HSD services provide a go-anywhere, satellite-based extension of the terrestrial ISDN network to users who would otherwise be unable to access ISDN. Dial-up networking using ISDN enables any number of Local Area Networks (LANs) to be quickly and easily linked; the establishment of global video-conferencing standards for use over ISDN has led to the widespread availability of desk-top PC-based video conferencing systems; the development of audio coding (compression and digitisation) techniques and standards for the transmission of broadcast quality audio over ISDN has eliminated the need for dedicated audio transmission circuits for broadcasters –to mention but a few applications. The Inmarsat Global Area Network (GAN) taking advantage of Inmarsat-3 satellites spot beam technology, integrates, for the first time, the corporate IT network with a global, mobile communications network on a small mobile platform. So business critical information can now be provided at both the bandwidth and speed that enterprises demand. Solutions such as remote LAN access, e-mail, e-commerce, intranet access, image transfer, and store-andforward video can now be used wherever they are needed - as well as, of course, high-quality voice and fax. The Inmarsat Global Area Network offers two powerful and flexible services – mobile ISDN and Mobile Packet Data. These high-speed services are delivered at speeds of up to 64 kb/s, rapidly extending local and wide area networks (LANs and WANs) to where businesses need information. All the end-user needs to access the Inmarsat Global Area Network is a mobile satcoms unit (MSU). Mobile Packet data is a cost-effective communication of packets of data at high quality and up to 64 kb/s. The user is charged for volume of data transmitted as opposed to length of time connected (as with Mobile ISDN). The service is ideally suited to applications such as e-mail, intranet access, remote LAN access, Internet access and e-commerce. Mobile ISDN service enables communication of all forms of data and voice through a single interface, at high quality and at 64 kb/s. The service is ideally suited to data functions that require the highest bandwidth and are time critical in transmission - for example, video conferencing, data streaming and telephone.


Page 55


Inmarsat mini-M phone provides high-quality mobile office applications (voice fax and data) and 98 per cent land mass coverage, with the exception of the poles. Designed to exploit the spot-beam power of the Inmarsat-3 satellites, Mini-M usage has grown rapidly since the launch of the initial service in January 1997. Customers include journalists, diplomats, aid workers, business people, border patrols, emergency services and anyone operating in areas beyond the reach of cellular or fixed communications. The latest, most compact mini-Ms are aimed at international business and remote-site customers. Features include subscriber identity module (SIM) card capability. Cards can be easily installed and removed, making it possible to share a mini-M among a number of users without having to create complex billing arrangements. A SIM card also protects the user from fraud because the information stored on it — user identity and billing details — is encrypted, making it very difficult to copy. If a card is lost or stolen, it can be cancelled and replaced very quickly, without any need for complicated re-programming of the mini-M. The Inmarsat-C satellite system provides two-way low bit rate data communications globally with the exception of polar region. Inmarsat-C terminals are simple, low-cost units small enough to be hand-carried or fitted to any vessel, vehicle or aircraft. Communications via the Inmarsat-C system are data or message-based. Messages are transferred to and from an Inmarsat-C terminal at an information rate of 600 bits/sec. Messages can be directed to mobiles in or approaching specific regions such as the sea area around a rescue co-ordination center. Inmarsat-C can handle messages up to 32 Kbytes in length. Each message from a mobile earth station (MES) is transmitted in data packets via satellite to an land earth station, where it is reassembled and then sent to the ultimate addressee via the national and international telecommunications networks. In the reverse direction, callers may send messages to a single MES or to a group. Many Inmarsat-C users need to acquire information from vehicles or vessels, or to interrogate automatic data-gathering platforms at fixed or variable intervals. Data reporting allows for the transmission of information in packets of up to 32 bytes on request or at prearranged intervals. Polling allows the user base to interrogate an MES at any time, triggering automatic transmission of the required information. InmarsatC terminals can be integrated with a wide variety of navigation systems to provide a highly reliable position reporting system. There are two main types of enhanced group call (EGC) supported by Inmarsat-C system: SafetyNET provides an efficient and low-cost means of transmitting maritime safety information to vessels at sea. FleetNET allows commercial information to be sent to a virtually unlimited number of pre-designated mobile terminals simultaneously. It is suitable for use by services specialising in the distribution of news, stock exchange reports, sporting results, weather analyses, and road and port information. Inmarsat's D+ offers global two-way data communications, utilising equipment no bigger than a personal CD player. Complete with integrated GPS, Inmarsat-D+ systems are ideally suited for tracking, tracing, short data messaging and SCADA applications. Applications include point-to- multipoint broadcast of information, typically: financial data such as exchange rates and stock-exchange prices; credit-card listings; disaster alerts. road transport applications include introduction of simple, low-cost fleet management systems for road transport operators. D+ supports entry-level products capable of basic tracking and messaging. With its greatly reduced power consumption, D+ is a very effective way of remotely collecting basic environmental and industrial data. The service provides the capabilities to transmit from the base to the mobile subscriber: Tone Only – Up to four alert signals; Numeric – Up to 32 numeric or special characters (0..9, Space, (, ), +, X) together with one of four alerts signals


Page 56


may be transmitted as a single message. Messages longer than 32 characters may be sent as multiple messages provided the application used incorporates the facility to concatenate; Alpha-Numeric – Up to 128 characters may be transmitted as a single message together with one of four alert signals. Messages longer than 128 characters may be sent as multiple messages provided the application used incorporates the facility to concatenate; Transparent Data – Messages of up to 2000 bits together with one of four alert signals may be sent as a single message. Messages longer than 2000 bits may be sent as multiple messages provided the application used incorporates the facility to concatenate. Group Calls – The service provides the capability to send a message to a group of mobile subscribers. Inmarsat-E is a non-commercial service for global maritime distress and alerting. Distress alerts transmitted from Inmarsat-E Emergency Position Indicating Radio Beacons (EPIRBs) are relayed through Inmarsat satellites to dedicated receiving equipment located at four Coast Earth Stations (CESs): Raisting, Germany (T-Mobil), Niles Canyon, USA, Perth, Australia and BT Atlantic, UK. Following reception of the distress alert, it is immediately forwarded automatically to a Maritime Rescue Co-ordination Center (MRCC) via an X.25 connection so that appropriate action can be taken. The time taken from the transmission of a distress alert to reception at the MRCC is within five minutes and typically under two minutes. Carriage of a satellite EPIRB is required by the International Maritime Organisation’s (IMO) Global Maritime Distress and Safety System (GMDSS). The carriage requirement for satellite EPIRBs came into effect on August 1 1993. GMDSS regulations apply to all vessels of over 300 gross registered tonnes and all passenger vessels engaged on international voyages. Inmarsat’s aeronautical satellite communications system (Inmarsat Aero) offers phone, fax and data services for passenger, operational, administrative and air traffic control communications on board commercial, corporate and general-aviation aircraft worldwide. There are three main applications for aeronautical satcoms: passenger services; air traffic control; and airline operational and administrative communications. Inmarsat supports multichannel phone, packet-mode data messaging at up to 10.5kbit/sec, fax, and circuit-mode data at up to 4.8kbit/sec. In addition to being able to make phone calls and send faxes to virtually anywhere in the world while in flight, passengers are being offered a growing range of data services. They include duty-free shopping; airline, hotel and car-hire reservations; and realtime world and financial news. Inmarsat aeronautical satcoms are playing a major role in the implementation of ICAO’s CNS/ATM (Communications Navigation Surveillance/Air Traffic Management) concept for air traffic control in oceanic and remote airspace. The Inmarsat satellites will support direct pilot/controller voice and data communications and automatic dependent surveillance (ADS). ADS is the reporting via satcoms of position and intention information derived from the aircraft’s own navigation systems. Presented on radar-like displays at oceanic control centres, it will give controllers real-time knowledge of the traffic situation, permitting more fuel-efficient routing and reduced separation standards. Improved routing is expected to yield millions of dollars in fuel and other operational cost savings to airline operators, while reduced separations will increase the capacity of oceanic and remote airspace. The Inmarsat Aero data link is used for routine pilot/controller communications such as requests for clearances and advisories. Voice communications are used for non-routine and emergency communications. Use of satellite data link to integrate aircraft in flight into airline information systems can yield significant increases in operational and administrative efficiency for the airlines. Applications include support of extended-range twin engine


Page 57


operations; in-flight troubleshooting of technical problems; and improved handling of irregular operations resulting from weather and other delays. Inmarsat services for aircraft are supported by seven principal systems: Aero-L, low-speed (600 bit/sec) real-time data communications, mainly for airline ATC, operational and administrative purposes. Aero-I, uses an intermediate-gain terminal exploiting the higher power of the Inmarsat-3satellites. Aero-I allows aircraft flying within spot-beam coverage to receive multi-channel voice, fax and circuit mode data services through smaller, cheaper terminals. Packet data services are available virtually worldwide in the global beams. Aero-H, provides channel rates up to 10.5kb/sec supporting multichannel voice, fax and data communications anywhere in the global beam for passengers, operational, administrative and safety services applications. Aero-H+, an evolution of the Aero-H service that uses the higher power of the Inmarsat-3 satellites when operating within the spot-beam coverage area. When operating outside these areas, the terminal operates using the global beam as a standard AeroH system. Aero-H+ supports the same services as Aero-H. In addition, Aero-C, the aeronautical version of Inmarsat-C low-rate data system, allows store-and-forward text or data messages — flight safety communications excluded — to be sent and received by aircraft operating. The mini-M Aero system is designed to provide a single-channel voice, fax or data service for small corporate aircraft and general aviation users. Swift64 is circuit-mode and packet-mode aeronautical high speed data services being developed to support the full range of Integrated Digital Services Network (ISDN) compatible communications and TCP-IP Internet connectivity. Both services have been designed to meet the needs of aircraft passengers, corporate users and the flight deck and are based on technology developed by Inmarsat for land based services. They are designed to take advantage of existing Inmarsat Aero-H/H+ installations, making use of major components of these installations already to be found on a large number of airline and corporate jet aircraft. They are delivered through the spot beams of Inmarsat-3 satellites and are available in all areas covered by these beams. Uniquely, the combination of the circuit-mode (Swift64 Mobile ISDN) and packet-mode (Swift64 Mobile Packet Data) services gives access to both the high quality and speed of a full ISDN service and the cost-effective flexibility of a full IP service. For airline passengers and corporate users this combination offers unmatched access to modern communications through Inmarsat Global Area Network (GAN), offering immediate access to the Internet and to business-critical information virtually wherever it is needed. The Swift64 Mobile ISDN service offers: 64 kb/s ISDN two-way communications; Alternatively, a 64 kb/s UDI (Unrestricted Digital Information) channel; Multi-channel avionics; Cooperative operation with other Inmarsat aero services provided by Aero-H/H+ systems via the Aero-H/H+ aircraft antenna; Stand-alone installation is possible; Operation within the spot beam coverage of Inmarsat-3 satellites virtually world-wide; Affordable service charges based on per minute usage; SIM (Subscriber Identity Module) card capability. The Swift64 Mobile Packet Data service will offer: The same features and benefits as Swift64 Mobile ISDN; Service with a packet-mode IP connection instead of the circuit-mode connection; Full TCP-IP connectivity; Per-bit charging. Applications include: Cost-effective extension of modern 64 kb/s per channel data communications, both circuit-mode and packet-mode, to aircraft based on the well-established Aero-H/H+ technology allows access to a range of terrestrial communications facilities. The ISDN access of Swift64 provides direct and efficient errorfree connection to terrestrial ISDN-compatible circuits and systems, allowing the easy integration of corporate and airline airborne platforms into ground-based private networks.


Page 58


The Swift64 Mobile Packet Data service allows unlimited Internet connectivity and efficient, cost effective access to company intranet and global-e-mail solutions . 3.1.6.3

Satellites

Inmarsat's primary satellite constellation consists of four Inmarsat-3 satellites in geostationary orbit. Between them, the global beams of the satellites provide overlapping coverage of the whole surface of the Earth apart from the poles. The Inmarsat-3 satellites are backed up by a fifth Inmarsat-3 and four previous-generation Inmarsat-2s, also in geostationary orbit. A key advantage of the Inmarsat-3s over their predecessors is their ability to generate a number of spot-beams as well as single large global beams. Spot-beams concentrate extra power in areas of high demand as well as making it possible to supply standard services to smaller, simpler terminals. Launched in 1996-8, the Inmarsat-3s were built by Lockheed Martin Astro Space (now Lockheed Martin Missiles & Space) of the USA, responsible for the basic spacecraft, and the European Matra Marconi Space (now Astrium), which developed the communications payload. The Inmarsat-3 communications payload can generate a global beam and a maximum of seven spot-beams. The spot-beams are directed as required to make extra communications capacity available in areas where demand from users is high. Inmarsat-3 F1 was launched in 1996 to cover the Indian Ocean Region. Over the next two years F2 entered service over Atlantic Ocean Region-East, followed by F3 (Pacific Ocean Region), F4 (Atlantic Ocean Region-West) and F5 (back-up and leased capacity). Launched in the early 1990s, the four second-generation satellites were built to Inmarsat specification by an international group headed by British Aerospace (now BAE Systems). The three-axis-stabilized Inmarsat-2s were designed for a 10-year life. Inmarsat-2 F1 was launched in 1990 and is now located over the Pacific as a back-up for Inmarsat-3 F3. F2, launched in 1991, is over the western Atlantic, providing leased capacity and backing up Inmarsat-3 F4. Also orbited in 1991, F3 is stationed over the Indian Ocean, backing up Inmarsat-3 F1. The fourth Inmarsat-2 was launched in 1992 and is used to provide leased capacity over the western Atlantic. The satellites are controlled from the Satellite Control Center (SCC) at Inmarsat HQ in London. The control teams there are responsible for keeping the satellites in position above the Equator, and for ensuring that the onboard systems are fully functional at all times. Data on the status of the nine Inmarsat satellites is supplied to the SCC by four tracking, telemetry and control (TT&C) stations located at Fucino, Italy; Beijing in China; Lake Cowichan, western Canada; and Pennant Point, eastern Canada. There is also a back-up station at Eik in Norway. Responding to the growing demand from corporate mobile satellite users for high-speed Internet access and multimedia connectivity, Inmarsat is now building its fourth generation of satellites. The company has awarded European spacecraft manufacturer Astrium a US$700 million contract to build three Inmarsat I-4 satellites. Astrium is the European company that includes the former Matra Marconi Space, which built the Inmarsat-2 satellites and the payload for the Inmarsat-3s. The job of the satellites will be to support the new Broadband Global Area Network (B-GAN), to be introduced in 2004 to deliver Internet and intranet


Page 59


content and solutions, video on demand, videoconferencing, fax, e-mail, phone and LAN access at speeds up to 432kbit/s almost anywhere in the world. B-GAN will also be compatible with third-generation (3G) cellular systems. The satellites will be 100 times more powerful than the present generation and B-GAN will provide at least 10 times as much communications capacity as today's Inmarsat network. The spacecraft will be built largely in the United Kingdom. The bus will be assembled at Astrium's factory in Stevenage and the payload in Portsmouth. The two sections will then be united in Toulouse, France, together with the US-built antenna and German-built solar arrays. To deliver its services Inmarsat operates a worldwide network of ground stations in addition to the satellite constellatio 3.1.6.4 Terminals

Use of Inmarsat compatible satellite communications equipment is mandatory within the network. Inmarsat does not manufacture or sell terminals but specifies the main characteristics of each type of terminal while terminal manufacturers produce the user equipment in compliance to the Inmarsat’s specifications. The performance of each terminal type must be type approved by Inmarsat prior to mass production. There are a number of manufacturers and hence a range of units is available, each with generic features and applications. Each manufacturer gives the hardware its own product name, and adds some additional benefits of its own. Terminals are distributed and supported through their worldwide dealer networks. Prior to the start of operation, each user terminal has to be commissioned by Inmarsat. Characteristics of a few representative terminals are included here. A basic Inmarsat-B mobile terminal can provide all the communications of a well equipped office - direct-dial, high quality telephone, Group 3 facsimile, telex, and 64 kb/s and 56 kb/s high speed connections. A 9.6 kb/s data connection is also part of the service. Enhanced and modified terminals are available from some manufacturers for fixed, multiple-channels and other special applications such as compressed or delayed video transmission using high-speed data. Inmarsat-B maritime terminals use tracking antenna of about 80cms in diameter, stabilised to remain locked on to the satellite regardless of vessel movement. To protect it from the elements, the antenna is housed in a radome and should be mounted in a position where it cannot be masked by the superstructure of the vessel. Below-decks equipment is compact (only a little larger than the average video recorder) making Inmarsat-B suitable for installation where space is limited. The International Maritime Organisation has certified Inmarsat-B as satisfying requirements for its Global Maritime Distress and Safety System, giving safety coverage for virtually all of the world’s navigable ocean waters. Many of Inmarsat’s users are on land, and this proportion is growing rapidly as customers discover the potential of a high quality communications service that operates anywhere, without the need for any support infrastructure. Suitcase sized transportable terminals offering the latest in compact design are already in widespread use, and other terminals are available for specialized applications. The typical Inmarsat-C mobile earth station (MES) has a small omni-directional antenna which, because of its light weight and simplicity, can be easily mounted on a vehicle or vessel. Directional antennas are also available for use in semi-fixed installations. The main electronics unit is compact, weighing only 3-4 kg. Briefcase terminals are also


Page 60


available, bringing the advantages of the system to international business travelers and field operators. Some terminals have built-in message-preparation and display facilities, others come with a standard RS-232 port so that users can connect their own PCs or other data equipment. The power requirements of Inmarsat-C terminals are modest and can be easily met from mains, vehicular or battery sources. Over 100 different terminal models from nearly 40 manufacturers have now been approved to operate with Inmarsat-C. Inmarsat-C terminals can be programmed to receive multiple-address messages known as Enhanced Group Calls (EGC). A special header is added to the text to indicate the group of mobiles or the geographical area to which the message is to be sent. EGCs can be transmitted in most languages or alphabets. The Inmarsat-E system supports “Float Free” EPIRBs which incorporate the following features: •

Global Positioning System (GPS) position which is accurate to within 200 meters;

•

automatic activation when the EPIRB is released by “floating free”;

•

remote activation and information input from vessels bridge or other manned situation;

•

optional Search and Rescue Radar Transponder (SART);

•

optional 121.5MHz locator beacon;

•

high intensity, low duty cycle flashing light.

The size of the EPIRB is between 22cm and 70cm high and weighs about 1.2kg, (depending on manufacturer and model). The EPIRB may be activated from a remote control position on the bridge or the conning position of the vessel; manually by using a switch on the side of the equipment if the EPIRB has been carried into the survival craft; or automatically as soon as the EPIRB has been released by immersion in water (hydrostatic release). Inmarsat-E EPIRB models are also available for such small craft, enabling them to transmit distress alerts and obtain the services of rescue authorities much faster and more reliably than by conventional means. It is imperative that owners of all Inmarsat-E EPIRBs register them with Inmarsat, giving details of the vessel or craft on which they are installed, as soon as possible after installation. MRCCs hold details of all registered Inmarsat-E EPIRBs. A wide variety of aeronautical equipment is now available enabling operators to choose the right package to suit their particular aircraft and communications needs. The range of services available depends on the type of equipment chosen. Aero-H Inmarsat-compatible satellite communications equipment must be installed onboard an aircraft in order to access the Inmarsat Aero-H service. This equipment comprises a steerable high gain antenna and suitable avionics. Other peripheral equipment such as telephone sets, facsimile machines and personal computers complete the installation. Aero-L equipment consists of a low gain antenna, avionics and data terminal equipment. The aircraft Aero-C equipment comprises an antenna, a diplexer and a transceiver. The transceiver requires an interconnection to cockpit text based data terminal equipment and/or a laptop type personal computer. The option exists to also connect the system to a printer for hard copy printouts. At present, production of


Page 61


Swift64 airborne terminal equipment is under active consideration by all the leading manufacturers of Inmarsat aeronautical sitcoms equipment. Inmarsat-D+ terminals can store and display up to 40 messages of up to 128 characters each. Subscribers can receive tone, numeric and alphanumeric messages, as well as clear data. In addition, D+ terminals will be able to transmit position information – derived from integral GPS - and short messages. Mini-Ms are the small, light and cost effective mobile satcom units, weighing about 2kg and resembling a laptop computer in size. Power consumption is modest: internal batteries yield typical talk times of 1.5-2.5 hours and standby times of up to 50 hours. Batteries can be readily topped up with a car cigarette lighter adapter or an AC/DC adapter/charger. STU-III encrypted voice is also available. Call forwarding, calling line identity, voice and fax mail are all supported. Mini-Ms are also available in vehicular, coastal vessel and rural-phone versions, with the latter being fitted with an 80cm dish antenna. Featuring gyro-stabilised antenna platforms, maritime units are installed in coastal vessels and yachts. Similarly, the antennas of vehicular versions are readily roof-mounted on cars, trucks and trains. 3.1.6.5 Gateways

Essentially, each land earth station (LES), acts as a gateway into the terrestrial telecom networks. There are about 40 LESs, located in 30 countries. The flow of communications traffic through the Inmarsat network is monitored and managed by the Network Operations Center (NOC) at Inmarsat HQ. The NOC is supported by Network Coordination Stations (NCS). The primary role of NCS is to help set up each call by assigning a channel to the MES and the appropriate LES. There is one NCS for each ocean region and for each Inmarsat system (Inmarsat A, B, C, etc). Each NCS communicates with all the land earth station operators in its ocean region, the other NCS and the NOC, making it possible to distribute operational information throughout the system. At present the aeronautical system does not use network co-ordination stations. The LESs are owned and operated by LES operators in compliance to Inmarsat specifications. Each LES has to be approved by Inmarsat. However the next generation services (BGAN) will operate through Inmarsat owned and operated LES known as Satellite Access Station (SAS). Distress support is a mandatory non-commercial obligation of Inmarsat. Distress alerts transmitted from Inmarsat-E Emergency Position Indicating Radio Beacons (EPIRBs) are relayed through Inmarsat satellites to dedicated receiving equipment located at four Coast Earth Stations (CESs): Raisting, Germany; Niles Canyon, USA; Perth, Australia; and BT Atlantic, UK. 3.1.6.6 Call routing

Inmarsat services are available worldwide through several LESs in each ocean region. A call from an Inmarsat terminal is routed via the Inmarsat satellite system to a land earth station (LES) and thence into the national and international phone and data networks. We consider the mobile packet data service call routing as it is a recent introduction.


Page 62


The Mobile Packet Data service of GAN can be configured to route packets over any public network, such as the Internet and ISDN. Some packets could be routed for certain addresses over one type of network, and packets for all other addresses over another type of network. However, Public Network Access is not necessarily secure, due to the very nature of the Internet. Encryption is recommended for sensitive documents, and where highly confidential information is being transferred, Private Network Access would be more appropriate. Private networks can be accessed using Mobile Packet Data by setting up a Virtual Private Network (VPN). This allows the corporate network to be extended to the mobile user, with the global Mobile Packet Data infrastructure used for corporate network access, but, most importantly, keeping access control and address management within the corporate infrastructure. This means the corporation continues to control who can connect to their network, what they are allowed to do, and what network addresses are used - in exactly the same way as if the remote user was using a direct, leased line connection to the network. A virtual private network is a private data network that makes use of the public networks (typically the Internet), maintaining privacy through the use of a tunnelling protocol and security procedures. Using a VPN involves a technique called "secure tunneling", which involves encrypting data before sending it through the public network and decrypting it at the receiving end using the L2TP protocol. An additional level of security involves encrypting not only the data but also the originating and receiving network address. Mobile office applications typically use less than half the available bandwidth of the channel. A virtual private network can be contrasted with a system of owned or leased lines that can only be used by one company. The idea of the VPN is to give the company the same capabilities at a much lower cost by using the shared public infrastructure rather than a private one. Companies today are looking at using a VPN for both extranets and wide-area intranets. Inmarsat-E services are Inmarsat’s non commercial services and need therefore to be supported by a few selected LESs. The LESs are selected such that the distress alert transmitted by an Inmarsat-E terminal (EPIRB) will always be received by two LES in each ocean region, giving 100 percent duplication for each ocean region in case of failures or outages associated with any of the LESs. Following reception of the distress alert, the message is immediately forwarded automatically to a Maritime Rescue Coordination Center (MRCC) via an X.25 connection so that appropriate action can be taken. The time taken from the transmission of a distress alert to reception at the MRCC is within five minutes and typically under two minutes. 3.1.6.7 Air interface

Inmarsat uses C-band in its feeder link and L-band in the service link. L-band spectrum lies within 1525 – 1559 MHz downlink and 1626.5 – 1660.5 MHz (uplink) in compliance to the MSS operator agreement. In addition, a CXC link on Inmarsat-3 is used for passing operations related traffic between land earth stations. A wide variety of modulation, coding and accessing schemes are in use within the network. In general, bulletin board use Time division multiplexing (TDM) with a simple modulation scheme such as Binary Phase Shift keying (BPSK) and call requests are made on Aloha channels. Circuit mode traffic is generally supported over frequency division multiplexed (FDM), demand assigned (DA), single channel multiple access (SCPC) centrally controlled access scheme, except in the aeronautical system where a distributed DA architecture is used. For data transmissions


Page 63


DA/TDM in the forward in conjunction with DA/TDMA in the return is in general use. Consider some representative systems. Inmarsat-A system is an analogue system using frequency modulation for its circuit mode demand assigned services and B-PSK for data transmissions. Inmarsat-B and M family of services use O-QPSK for the demand assigned service. The more recent introduction of this family, GAN, uses 16QAM technology with turbo-coding. Inmarsat-C uses BPSK with powerful codes and store and forward technique to provide a highly robust performance. Inmarsat D+ uses 32 level FSK in the forward direction. Inmarsat aero system has a large variant of air interfaces depending on the type and class of service. In general A-BPSK and AQPSK modulation schemes are in common use with both FDM/DA/SCPC and DA/TDMA. Details of Inmarsat air interface design are generally propriety and are therefore provided to the industry under standard confidential agreement.


Page 64


Figure 3.10 Inmarsat coverage


Page 65


Figure 3.11 Inmarsat system components

3.2

BROADCAST TYPE SATELLITES

Satellite Digital Radio Broadcasting to mobile or portable terminal is currently in full expansion worldwide. WorldSpace, the first worldwide Digital Radio Broadcasting satellite system, has started satellite broadcasting in developing countries of Africa and Asia. XM™ Satellite Radio, one of the two Digital Audio Radio System (DARS) for the United States, has started service at fall 2001, and Sirius Satellite Radio will start its service in 2002. At least one satellite programs (MB SAT) is being started in Japan, with the procurement of a satellite. These systems offer at the same time wide service areas, high quality, and portable and mobile reception. In addition to sound and thanks to the digital format, complementary services such as broadcasting of multimedia and internet data are part of the delivery to enrich the content received. The expansion of these systems, demonstrates that satellite is now optimized for broadcasting to portable or mobile receivers, compared to terrestrial broadcasting that requires far more investment.


Page 66


There are currently two initiatives in Europe to promote radio broadcasting by satellite, which are Globalradio, a start up company, and S-DSB, involving WorldSpace and Alcatel.

3.2.1

The WorldSpace system

3.2.1.1 Overview

WorldSpace is the first satellite Digital Radio Broadcasting system providing portable reception. The WorldSpace system offers a worldwide coverage, over developing countries, using geostationnary satellites, and broadcasting in L-band. The service targets are mainly underserved radio markets, where low cost radio and radio portability are key. Alcatel Space was contracted in 1995 by WorldSpace for the turn-key delivery of the entire system. The WorldSpace system is composed of 3 medium size geostationary satellites: AfriStar™, launched in late 1998, covering Africa and Middle East, AsiaStar™, launched in early 2000, covering Asia, and AmeriStar™, to be launched in 2001, covering Latin America. Each satellite provides three beams of coverage (see figure 3.12). In addition to the satellites, the system comprises a comprehensive ground infrastructure deployed on the five continents comprising various control centers (satellite, mission and broadcast) and service providers feeder link stations. Obviously such service needed the development of a new generation of radio receivers, available today on the market. These receivers are based on chipsets developed by ST Microelectronics and Micronas. First generation receivers are manufactured by Hitachi, JVC, Panasonic, Sanyo. Low price second generation radio are now available.

Figure 3.12 WorldSpace Coverage Area There are currently about fifty radio programs per beam, a large part of them provided by well-known broadcasters, such as BBC, RFI, Europe 1, CNN, Bloomberg.


Page 67


In addition to audio content, WorldSpace is also providing multimedia contents, such as Direct Media Service (DMS). DMS provides huge amounts of the best web content, selected by the subscriber, directly to the hard drive of the user's PC, without the need for a telephone line. The early experience with the system has confirmed the sound technical choices and demonstrated excellent performance in the various reception conditions, portable and mobile, as well as in interference environments. 3.2.1.2 Key parameters of the system

The WorldSpace system is referenced as System D within ITU recommended systems for Broadcasting Satellite Service (Rec. ITU-R BO.1130) [2]. The uplink frequency band is the 7025 to 7075 MHz frequency band. The downlink frequency band is the 1467 to 1492 MHz frequency band, world-wide (except some areas, such as US, Japan) allocated to Satellite Sound Broadcasting. The signal audio sources are digitally coded using the ISO/Audio MPEG 2 layer III standard, worldwide known as MP3. The digitally coded source bit rates range from 16 kbps for monoral near AM quality to 64 kbps for stereo, FM quality. Each satellite has the capacity to transmit a capacity of 50 to 200 programs per beam. The WorldSpace system uses a TDM QPSK transmission on downlink, including high efficiency concatenated FEC (Convolutional and Reed Solomon codes), well suited for satellite broadcasting. Each downlink beam offers a link margin which helps combat typical signal losses in the path between the satellite and the receiver, providing full quality reception. Radio receivers in disadvantaged locations can be connected to high gain antennas, or to antennas located in a unobstructed positions. For example, reception in large buildings may need a common roof antenna for the entire building or an individual reception antenna near a window. To cope with the various broadcaster requirements, the WorldSpace system uses two communication missions: •

A processed communication mission offers the capability for all potential broadcasters to have a direct access from theirs own facilities to the satellite using a Frequency Division Multiplex Access (FDMA) mode.

•

A transparent communication mission deals with time division transmission of bouquets of programs and with broadcasters that have no direct access to the satellite, for which a hub station is preferred.


Page 68


Whatever the mission, the complete WorldSpace transmission path is transparent to the overall channel capacity allocated to a broadcaster, so that the broadcaster has full dynamic control, and may configure it at his discretion. 3.2.1.3 WorldSpace mobile applications

The WorldSpace system was primarily tailored for portable and fixed reception. But the selected waveform (TDM QPSK), together with the high satellite EIRP also allows for straightforward mobile reception. It is common use to listen to the WorldSpace programs in a car with the receive antenna behind the windscreen or on the roof! Achieved availability is very high in rural and sub urban areas, even in Southern Europe. To improve availability in dense urban areas suffering blockages, WorldSpace has extended its system to an hybrid satellite/terrestrial system, identified as System Dh within ITU [2]. A complementary terrestrial component retransmits the satellite TDM signal using Multi-Carrier Modulation (MCM) in L band. MCM is a Orthogonal Frequency Division Multiplex technique, especially designed for multipath environment, allowing for Single Frequency Network, and used in digital terrestrial broadcasting systems, such as EU 147 DAB (ITU system A) or DVB-T. WorldSpace MCM has been optimized for L band mobile reception in high multipath environment. MCM also benefits from the same high efficiency FEC as the satellite component, compatible with any audio compression scheme and data transmission. Dedicated radios receive signals from both satellite and terrestrial components, with seamless hand over between the two. To improve the availability in conditions where only a satellite signal is present, WorldSpace has also incorporated a time diversity technique, based on the broadcasting of the same content twice but with a time interval of several seconds. The time interval makes the two contents uncorrelated with respect to blockages for mobile reception. A dedicated receiver is able to combine the two contents for a seamless reception. This hybrid system has been implemented and successfully tested in Germany (Erlangen) and in South Africa (Pretoria), using the AfriStar satellite. 3.2.1.4 The WorldSpace satellites

To meet the system requirements, a specific payload design has been implemented by Alcatel Space on a standard Eurostar 2000+ platform from Matra Marconi Space (now Astrium) to form the WorldSpace satellites. The WorldSpace processed mission is based on the baseband processing concept of the satellite payload, already used on advanced technology satellites, but only recently emerging on commercial programs. The WorldSpace transparent mission is based on the bent pipe concept of the satellite payload, widely used on commercial programs, except that it specifically uses a small frequency band with narrow channel bandwidth leading to a unique payload design for filtering and demultiplexing.


3.2.2

Page 69


The Sirius Satellite Radio System

3.2.2.1 The system overview

The Sirius Radio System has been conceived to provide a Digital Audio Radio Service (DARS) directly from satellites to vehicles across the Continental United States (CONUS) region. Sirius Radio offers a wide selection of music formats and program types using Perceptive Audio Coding (PAC) technique to efficiently digitally encode the analogue audio signal. Sirius has alliances to install three-band (AM/FM/SAT) radios in Ford, Chrysler, BMW, Mercedes, Mazda, Jaguar and Volvo vehicles as well as Freightliner and Sterling heavy trucks. Numerous manufacturers furnish radios to auto-makers, and also provide adapters to electronics retailers that allow radios in existing vehicles to receive Sirius broadcasts. To guarantee coverage with good visibility (high elevation angle) the Sirius Radio System employs three satellites in elliptic orbits at an inclination of 63.4°, with two satellites in visibility in any moment. Terrestrial repeaters are present in major urban areas to permit continuous reception also in the presence of obstacles that might block the space-based signal. The satellites receive in X-band (7060-7072.5 MHz) and transmit in S-band (2320-2332.5 MHz). The 12.5 MHz S-band assigned to Sirius Radio is segmented into three sub-bands. The upper and lower sub-bands, each with a bandwidth of 4.2 MHz, are assigned to the two transmitting satellites that transmit the same broadcast material, time shifted of 4 s to increase diversity. The middle sub-band, 4.1 MHz wide, is used by terrestrial repeaters which get the signal from a separate satellite The access method used by satellites is TDM (Time Division Multiplex) while terrestrial repeaters use the OFDM multiplexing technique. The Sirius system is supported with satellites by Loral and digital technology by Lucent. Alenia Spazio provided satellite Tx/Rx antennas and payload receiver. The spacecrafts are designed to provide 15 years of uninterrupted service life. The system for the Sirius Satellite Radio is shown in figure 3.13. The satellite apogee altitude is 47102 km and the perigee altitude is 24469 km. This altitude combination results in an orbit of 24 hours. There are two satellites over CONUS at all times and, from any point in CONUS, there will be a satellite appearing at an elevation angle of at least 60°. The three satellites generate identical ground tracks, following one another at 8hour intervals.


Page 70


VSAT Satellite

SIRIUS Satellite

TDM Ground Repeaters TDM

OFDM

Remote Uplink Site

TDM

Mobile Receiver

OFDM TDM

12.5 MHz

National Broadcast Studio

Figure 3.13 The Sirius Radio System 3.2.2.2 Sirius Satellite Radio

The music channels are compressed by application of a Perceptual Audio Coding (PAC) algorithm developed by Lucent Technologies. The PAC encoder can work with a set of output data rates, corresponding to different audio quality: -

128 kb/s transparent CD quality for stereo signals

-

96 kb/s CD-like quality

-

64 kb/s near CD quality

-

48 kb/s FM grade quality

-

24 kb/s audio bandwidth 6 to 8 kHz (mono/stereo)

After encoding, the channels are digitally multiplexed together (TDM-time division multiplex) with interleaving in time, resulting in an approximately 4 Mb/s output signal. The data blocks of the output signal are Reed-Solomon coded, RS (128,120), then convolutionally encoded (R=3/2, K=9) with time interleaving and finally transmitted to the satellites using Offset Quadrature Phase Shift Keying (OQPSK) modulation. 3.2.2.3 Car and Receivers


Page 71


The satellite signals are received by the mobile platforms, particularly vehicle automobiles. Most DARS in-car radios consist of three parts. Firstly, there is the digital radio black box, which is stored in the boot of the car. Secondly, there is a compatible head-unit, fitted with either a CD or cassette option and thirdly there is a compact digital aerial. All in-car DARS receivers combine DARS, FM and AM. Many manufacturers offer the option of DARS receivers which are already compatible with head-units sold in the past few years. However, some manufacturer's also have receivers which do not require a black box. The antenna module picks up signals from the satellites or the ground repeaters, amplify the signal and filter out any interference. The signal is passed on to the receiver module. Inside the receiver module there is a chipset consisting of eight chips. The chipset converts the signals from 2.3 GHz to a lower intermediate frequency. Sirius also offer an adapter that allows continental car radios to receive satellite signals. The adapter costs about $199.

Figure 3.14 CD Radio Satellite Audio System (Source CD Radio Inc.) The mobile platform G/T at worst operational aspect angle is –19 dB/K. The antenna is designed to provide 3 dBi gain within a 20°- 60° elevation angle range at all azimuths. The antenna is physically 2.5 cm in radius and 0.4 cm thick, designed to be embedded in automobiles rooftops. After radio frequency reception, amplification and down conversion, the transmission from each satellite is individually demodulated. The signals are time phased together using a maximal ratio combiner and then demodulated. The user selects the specific music or voice channel desired which is then routed to the decompressor, the digital-toanalogue converter and the audio amplifier-loud speaker subsystem.


Page 72


The radio receivers have different demodulator channels, one for each satellite. Three different types of diversity reception are attributed to the Sirius system. The first two are spatial diversity and frequency diversity. The third is time diversity, which is achieved by inserting a 4-second delay buffer into one of the two active channels.

3.2.3

XM™ Satellite Radio

3.2.3.1 Overview

The XM™ Satellite Radio service is a Satellite Digital Audio Radio Service (DARS) licensed by the FCC for the United States. It is commercially operating since Fall 2001, and provides over the United States high-quality compressed audio, as well as text and other digital data to car, home, and portable personal receivers via a pair of geostationary satellites and a network of terrestrial repeaters. Distinctive features of this new radio service include: a coast-to-coast coverage, creating a truly national listening audience in the United States; a superior digital quality reception; and a superior choice of programming. 3.2.3.2 Key parameters of the system

The XM™ Satellite Radio system uses the 2332.5 to 2345 MHz frequency band. It has been optimized for this S band spectrum in order to ensure reliable performance in both urban and rural environments throughout CONUS. The system’s flexible time-division multiplexing (TDM) scheme allows broadcast of up to one hundred of channels of music and voice, each of which can be supplemented by service components (sub-channels) for carrying text and other data. Each satellite transmits the same content, using QPSK modulation, so that a receiver can construct the service signal from either satellite signal. The two satellites configuration provides space, time and frequency diversity, which improve the availability of the service. All content is up-linked to the satellites from the XM™ Satellite Radio programming center. To maximize the signal availability to mobile receivers everywhere within the Continental United States (CONUS), the system employs two high-powered geostationnary satellites and a network of urban repeaters for re-broadcasting. To cope with terrestrial transmission environment, broadcasting from repeaters uses COFDM modulation. Repeaters are fed by the signal broadcast by satellites in S band. The system provides seamless reception between the satellite and repeater components. 3.2.3.3 The XM TM Satellite

The XM™ Radio S-band satellites are constructed by Boeing Space Systems, with its payload being supplied by Alcatel Space. The satellites are located at 115° W and 85° W longitude on


Page 73


the geostationary orbit. Satellites have a 15 years lifetime, and are based on HS-702 platform, using high-efficiency solar arrays, and Xenon-Ion thrusters. These satellites, with a 4.45 tons launch mass, are launched by Sea Launch. Upon launch, these satellites are the most powerful commercial satellites in operation, producing over 15.5 kW of power at end of life. The XM™ Satellite Radio payload is composed of 2 bent pipe transponders. Each transponder includes an antenna composed of a shaped 5-meter aperture reflector with a single feed. The beam coverage is tailored to the shape of CONUS, with high EIRP biased towards the areas with lower elevation angles to the satellites and also to areas with higher population density. Each transponder also includes High Power Amplification composed of sixteen 216-Watt TWTA’ s operating in parallel at saturation. Combination of both antenna and High Power Amplification produces a peak EIRP in excess of 68 dBW.

3.2.4

Satellite Digital Radio Broadcasting in Europe

Satellite Digital Radio Broadcasting will surely become a large success in coming years, as experienced through the WorldSpace and XM™ Satellite Radio systems. This success is largely based on the involvement of European companies that have participated to these programs. But surprisingly, no satellite Digital Radio Broadcasting system for Europe has ever succeeded up to now, although Digital Radio Broadcasting studies started more than ten years ago in Europe. More than 10 years ago, Europe decided to promote satellite Digital Radio Broadcasting. Through the project EU 147, DAB (Digital Audio Broadcasting) was born. The system was based on the use of OFDM modulation, and MPEG 2 layer 2 (MUSICAM) audio coding. OFDM allows the use of the Single Frequency Network (SFN) concept (reuse of the same frequency on all transmitters), which was expected to be used for the satellites and the terrestrial repeaters of the system. In the frame of DAB, the Archimedes satellite project was envisioned, using the L band frequency resource allocated at WARC 92 only with OFDM. Unfortunately, satellite technology was not able to provide satisfactory performance at that time, and the thought in Europe that satellite could not be used for Digital Radio Broadcasting emerged. Yet, DAB activities continued, but only limited to terrestrial broadcasting (T-DAB). Today, even after 10 years, the EU 147 based T- DAB has enjoyed only limited development. Main reasons are: •

A limited number of attractive programs, compared to the current analog radio offerings, especially in FM

•

A limited coverage, due to the lack of a huge terrestrial infrastructure investment


Page 74


•

A limited capacity of programs, due to the use of rather old, inefficient audio coding scheme (older than MP3)

•

A limited FEC performance, only optimized for the specified audio coding scheme, but not to higher performance audio coding scheme, nor to data transmission which needs high error protection.

3.2.5

Satellite Digital Radio Broadcasting Technology

Significant improvements have been achieved in these last years, allowing for satellite based Digital Radio Broadcasting to become a reality. The reasons are described below. 3.2.5.1 Digital broadcasting

Digital audio signal compression has improved to a point where the digital audio signal occupies less bandwidth than an analog signal for the same quality, much lower bandwidth than the CD standard. Current ISO MPEG 2 Audio layer 3 (MP3) provides quasi-stereo CD quality at 64 kbps, that is reduced by more than 15 fold compared to CD. New ISO MPEG-2 AAC/AAC+ audio coding provides CD quality at 48 kbps. Digital signals are more robust with respect to external interference thanks to dedicated error correcting digital signal processing. Digital audio signals may be multiplexed with any other signal, such as image, test or files, and offers an enriched multimedia content. Also interfaces with other applications are eased. Digital signal processing is cheaper than analog processing thanks to silicon large scale integration. 3.2.5.2 Digital Radio Broadcasting

Analog radio is available from terrestrial transmission in well-established frequency bands (FM, MW, SW). But the analog signal susceptibility to digital signals and the lack of available frequency spectrum make it difficult to share these frequency bands. To avoid these compatibility problems, other frequencies have been allocated. WARC 92 allocated the 1452 -1492 MHz band (L band) for Digital Radio Broadcasting over the major part of the world, including the WorldSpace service area, and Europe. In the US, the FCC has allocated the 2320 to 2345 MHz band for Digital Radio Broadcasting. But use of these new frequency bands for terrestrial only broadcasting is expensive, because it requires the implementation of a huge terrestrial infrastructure, denser than FM as frequencies are higher, involving larger propagation attenuation. The best solution to limit the amount of ground infrastructure is to use satellites, which are able to offer large coverage from their vantage point in the sky. An analogy may be performed with digital TV broadcasting, where satellite reception is already largely used, while there is still no digital terrestrial reception available yet.


Page 75


3.2.5.3 Satellite Digital Radio Broadcasting

The largest possible availability in portable and/or mobile receive conditions for the end user is based on the following key parameters: •

The visibility of the satellite

•

The modulation scheme for satellite transmission

•

The satellite EIRP

•

The complementary terrestrial retransmission

Visibility of the satellite

Reception from satellite is sensitive to blockage, occurring not only when a satellite is seen with low elevation angle. Even with high elevation angle, trees and houses may shadow the satellite. So whatever the satellite configuration, HEO or GEO, high availability performance requires the use of specific techniques, such as space and time diversity. Space diversity is achieved with two satellites having the same earth coverage, providing the same content, but from different orbital locations. In that case, a location on earth is in visibility of the two satellites, and the probability of blockage occurrence is accordingly reduced. An HEO satellite configuration, providing high elevation angle on the coverage area, requires generally at least three satellites. A GEO satellite configuration, requires two satellites if space diversity is used. Modulation scheme for satellite transmission

Unlike terrestrial transmission, modulation used for satellites does not require provision for multipath environments. Thus power efficient modulation, such as TDM QPSK may be used for satellite broadcasting. MCM/COFDM, an efficient type of modulation adapted to multipath environment, is largely used in digital terrestrial broadcasting systems, such as the WorldSpace hybrid system, viz. ITU System Dh or ITU System A. Using the same satellite parameters, the same bit rates and the same propagation environment, an overall link budget difference of at least 7 dB in favor of the TDM QPSK modulation is obtained between COFDM and TDM QPSK link budgets, due to: The need for COFDM modulation to operate in linear mode as it uses multicarrier signals, leading to output back-off and non linearity losses (about 3 dB difference) The use of non coherent demodulation for COFDM (about 3 dB difference)


Page 76


The specific losses of the COFDM modulation, that is guard time and overhead allowance (about 1 dB difference) Satellite EIRP

Availability is function of the link budget margin, defined from the service to be provided. For mobile applications, high power satellites are necessary, with EIRP in excess of 60 dBW. Such levels of EIRP in L band have been possible only in the last few years. Complementary terrestrial retransmission

Even if high satellite link margins may be achieved now, there are still some receive areas where obstacles are numerous (dense urban areas). There, terrestrial repeaters may complement satellite reception. Concepts developed and tested by WorldSpace and DARS systems are applicable.

4

ENABLING TECHNOLOGIES AND ARCHITECTURES

4.1 4.1.1

GSM/GPRS RELATED TECHNOLOGIES INMARSAT Regional Broadband Global Area Network (R-BGAN)

4.1.1.1 Abstract

R-BGAN (Broadband Global Area Network-Regional) is the system Inmarsat plans to launch in Q4, 2002, offering a range of multimedia services to mobile/portable terminals with data rates up to 144 kbit/s. Hughes Network Systems is the prime contractor in the development of the project tasked to deliver a new ground system, business support system and terminals. Project R-BGAN represents an intermediate step towards the full set of services and virtual global coverage which will be achieved by BGAN (Broadband Global Area Network) 4.1.1.2 Project R-BGAN System Architecture

The R-BGAN system makes use of the geo-synchronous Thuraya satellite which currently offers service throughout the Middle East, Northern Africa, Europe, India and parts of Asia. While it uses certain parts of the Thuraya ground segment in the United Arab Emirates RBGAN is primarily a separate system. It comprises of a Satellite Access Station (SAS) in


Page 77


Fucino Italy, a Network Operations Center and Business Support System in London and a Data Communications Network. 4.1.1.3 Project R-BGAN Air Interface

The air interface used is the GeO-Mobile Packet Radio Service standard (GMPRS) built on the circuit-switched GeO Mobile Radio-1 (GMR-1) standard. Based on terrestrial GSM standards GMR-1 incorporates capabilities unique to satellite systems, such as integrated position-based services, single-hop terminal-to-terminal calling and modifications to deal with the inherent delay in GeO-Mobile Satellite systems. The R-BGAN system design supports data rates up to 144 kbps for early service and 432 kbps with planned future enhancements. GMPRS will accommodate such features as extended modulation, coding scheme code points and transition from packet idle mode to packet transfer mode in a single phase access. GMPRS also implements a slow release of the uplink temporary flow identity (TFI) in combination with periodic unsolicited uplink grants so that the terminal has an uplink resource if new packets arrive in the terminal’s uplink queue. 4.1.1.4 Project R-BGAN Channelization

The allocation of satellite resources to spot beams in the space segment is based on bandwidth allocations, with a nominal 156.25 kHz designated as sub-bands. The number of sub-bands allocated to a particular spot beam, and the frequency of the sub-bands is a system configuration issue. The factors involved in the allocation of sub-bands to spot beam are traffic demands in the particular spot beam, frequency reuse considerations, the effective available spectrum as a result of coordination with other systems, and the terms of the satellite leasing agreement. 4.1.1.5 Satellite Access Station

The Satellite Access Station (SAS) provides the data path interface between the service providers and the satellite. The architecture of the SAS, including some primary interfaces, is shown in the following figure.


Page 78


SAS (AMN Segment) Space Segment

PBSS

LSRF PGCS POAM

PRS PRCU PMC RFS TE

IDS

CDS

L A N S W I T C H

PBSC

NSS

E1 Gb

PRMS

SGSN/ VLR

OSS

GGSN

BGW

Enterp. GGSN

Internet

BSS

MT

UT Segment

T1

GTS

GSC TCS

SAS OMC

HLR/ AuC

BSS Segment SOG

CCCS LSRF AOC/GS

Figure 4.1 SAS Architecture in Fucino, Italy

The strong resemblance to GSM of the Air Interface allows the integration of standard GSM services and components in the terrestrial Network Switching System (NSS) which is provided by Ericsson. As with any GPRS system, the key elements are the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). In addition, the NSS includes the HLR and authentication center, a billing gateway and service order gateway to interface to the BSS and the Operational Support System (OSS) interfacing to the Network Operations Center based in London. 4.1.1.6 SAS Radio Equipment

On the radio side there is a 13-meter satellite antenna and associated radio frequency subsystem (RFS), furnished by SED of Canada. HNS provides the IF Distribution System (IDS) to interface between the RFS and the rest of the SAS radio equipment. There are two kinds of baseband channel unit equipment provided. For narrowband the Common Control Channel Subsystem (CCCS) and for wideband the Packet Radio Channel Unit (PRCU) hardware which consists of Commercial Off The Shelf (COTS) and custom designed modules fitted into a standard compact PCI chassis. 4.1.1.7 SAS Protocol Processing

The Packet Base Station Controller (PBSC) provides the interface between the radio system and the NSS. It includes the E1 interface as well as the BSSGP protocol. The Packet Modem Controller (PMC) is responsible for the Radio Link Control (RLC) and Medium Access Control (MAC) layers of the Air Interface as well as other ancillary functions. Note that the PMC is responsible for multiplexing the several data sessions onto a single carrier in both the forward (downlink) and return (uplink) directions.


Page 79


The remaining PBSS components are the Packet Resource Management System (PRMS) and the various network management computers. The PRMS is responsible for determining when and where sub-bands are to be located (including the dark beam activation), assigning channels to channel units and PMC and PBSC computers, and assigning users as they access the system. 4.1.1.8 User Terminal

The Inmarsat Project R-BGAN user terminal encompasses both the user furnished computer, assumed to be a laptop or portable, and an Inmarsat supplied Mobile Terminal (MT) which is 'laptop-sized', roughly 30 cm long, 24 cm wide and 4 cm deep. The HNS/Inmarsat Mobile Terminal acts as a satellite modem to the terminal equipment and as far as the various application software is concerned, the MT appears little different from any other standard modem. The MT includes a flat-panel directional antenna to interface to the satellite, along with tools to assist in antenna pointing. In addition, the MT provides a GPS antenna and system to provide accurate location information, an interface to the standard Subscriber Identity Module (SIM), and a power management system to conserve power when the integral battery is in use. 4.1.2

INMARSAT Broadband Global Area Network (BGAN)

4.1.2.1 Abstract

The BGAN system is positioned as the satellite component of IMT-2000 (specifically the UMTS standard). The system will provide a near-global coverage overlay for the terrestrial network scheduled to enter service in 2004. The network infrastructure will consist of a constellation of new geostationary satellites (I4 satellites) and an optimised ground network interconnecting with a variety of terrestrial networks at local ‘points of presence’. The system will employ bandwidth efficient modulation and coding techniques, capable of supporting variable bit-rate services and quality of service depending on the needs of the application. A range of terminals will be supported, from small personal devices linking up with handheld and notebook PCs, aeronautical and maritime vehicular installations linking up with on-board entertainment and communications systems, to remote base stations linking up with local area networks. Depending on the terminal type, user data rates up to 432 kbit/s will be supported. Inmarsat is now developing the BGAN system, aimed at delivering multi-media services to personal, mobile and portable terminal users. The BGAN system will be compatible with terrestrial 3rd Generation UMTS/IMT-2000 services, enabling users equipped with BGAN terminals to access these services over the near-global coverage provided by the BGAN system. 4.1.2.2 The Technology

The new technology being implemented is creating new more powerful Inmarsat-4 satellites enabling Inmarsat to develop smaller user terminals (UT’s) with higher data rates currently available. In addition, new ground infrastructure will provide the terrestrial network


Page 80


interconnect, enabling further enhancements to Inmarsat’s current range of services to be developed 4.1.2.3

New Powerful Satellites

The Inmarsat-4 satellites will use the geostationary orbit, which simplifies the network control and operations, enables the use of simpler user terminal technology for high speed data communications, and avoids the risk of data loss during satellite-to-satellite handovers that are necessary for non-geo constellations. The satellites will use the L-band spectrum for the mobile link services to ensure backward compatibility with currently operational Inmarsat systems. the Inmarsat-4 satellites also incorporate transponders for Mobile to Mobile links, C to C links and also a Navigation transponder providing positioning information compatible with the GPS Navigation satellite system. The satellite payload is also highly efficient in terms of spectrum utilisation, achieving more than 20 times frequency reuse at L-Band. A satellite’s coverage area will be serviced by two types of spot beams: •

Around 200 narrow spot beams providing coverage of continental land masses within the satellite field of view. The new BGAN UT’s utilise multimedia services at user data rates up to 432 kbps.

•

19 wide spot beams providing coverage over the entire satellite field of view for existing Inmarsat services, enabling higher data rates to be delivered to evolved version of the current range of UT’s. 4.1.2.4 Advanced Multimedia Network

Inmarsat’s strategy of network architecture is the alignment of BGAN with terrestrial 3G mobile networks. There are obvious benefits in such compatibility, such as lower development and production costs for user terminal and ground network infrastructure, as well as service commonality and roaming with 3G terrestrial networks. As a result, users would be able to roam between terrestrial and satellite networks using a common subscription and service provision relationship. Inmarsat’s existing voice and low speed data services will continue to be offered via the current network and service providers. The Network Operation Center (NOC) exercises the overall network control and management which is integrated with Satellite Control Center (SCC) which controls the satellites, dynamically reconfigure and allocate channel resources to the spot beams as a function of network traffic and geographic traffic distribution. Schematic of the AMN is given in Figure 2. The four new SAS’s are interconnected by a Data Communication Network (DCN). (Two per satellite region to provide redundancy backup in case of failure of either SAS.) The DCN will be procured as a managed bandwidth service from global network operators. The BGAN network interconnects with terrestrial networks at several Point of Presence (PoPs) used as switching and multiplexing node. The Business Support System (BSS) is a modular system comprising a wholesale billing system, along with customer activation and other functions. The SAS itself can logically be divided in two parts: The first is the Radio Switching Subsystem (RSS), which maps into the UMTS RAN (Radio Access Network), implementing air interface communication over the satellite, as well as the radio frequency components of


Page 81


the station. 16 QAM Modulation and Turbo coding FEC schemes are employed. The second part is Network Switching Subsystem is essentially off-the-shelf UMTS switching nodes integrated into the network.

INM-4 F1

INM-4 F2

Network Management

Satellite Region 1

Satellite Region 2

Inter-site VPN

SAS

SAS

SAS

SAS

Service Provider PoP PSTN

Internet

Access link

GPRS/ UMTS

Figure 4.2 Advanced Multimedia Network

4.1.2.5 User Terminal Product Portfolio

Inmarsat Maritime, Aero and Land mobile product portfolio can effectively be classified into two main classes: 1. Existing products and evolved products currently using I-3, I-4 global and wide spot beams. 2. New BGAN products, which would be capable of operation only over I-4 narrow spot beams covering land, major aero and coastal maritime routes. Figure 4.3 shows the two currently planned versions of the BGAN units: the notebook (A4 size) and the pocket (A5 size). These units will effectively represent plug and play satellite modems typically for PC laptops or PDA (Personal Digital Assistant) Table4.2 shows the main terminal characteristics.


Page 82


Figure 4.3 Pocket Terminal (left) and Notebook Terminal Concept

Characteristics

BGAN Notebook

BGAN Pocket

Size & Dimensions

~ A4 (21x30x3cm)

~ A5 (15x21x3 cm)

Mass (incl batteries)

~ 1.0 kg

~ 0.75 kg

Operating Time

1 hr transmit, 36 hr 1 hr transmit, 36 hr standby standby

Interfaces

USB, Ethernet

Location Determination

GPS receiver

Data Rate

Bluetooth, USB, Bluetooth

Transmission 144(U)/432(D) kbit/s

GPS receiver 64(U)/216(D) kbit/s

Table 4.2 BGAN User Terminals

4.1.2.6 The Services

In order to make use of the BGAN services the user is required to obtain a subscription, a smart (SIM) card, and a BGAN communications unit (CU) to allow a PC to send and receive data directly via satellite. 4.1.2.7 Bearer Services

Fundamentally, the BGAN system offers a variable bandwidth service on a per session basis to the BGAN CU. The variable bandwidth session has 2 basic attributes as described below:


•

Page 83


Committed Information Rate (CIR), guaranteed minimum data rate committed for the duration of the session;

• Maximum Information Rate (MIR), which is potential maximum data rate, which could be made available to the session, on the basis of available spare capacity. 4.1.2.8 Communication Services

The BGAN system is able to support a range of different networking protocols and serve numerous communication applications, with no additional development for the PC user. It is intended to provide some or all of the following communication services for use by PC applications: data modem, fax modem, voice modem, ISDN modem. 4.1.2.9 Service Deployment and Phasing Strategy

Global coverage would be provided by the combination of the I-4 and I-3 satellites. The I-4 satellites are expected to be launched by end 2003 and be in operation in 2004. The third I-4 satellite is a ground spare, which may be launched either to replace a previous launch failure or to extend the coverage area to global, based on business and operational considerations.

4.2 4.2.1

UMTS / IMT-2000 TECHNOLOGY Point to Point architecture

4.2.1.1 3G Technologies

The Universal Telecommunications System is a member of the IMT-2000 family of global systems. Satellite-UMTS is an integral part of UMTS and provides direct access to the UMTS core network via the Iu interface. Figure 4-1 shows the overall structure of the S-UMTS concept. The International Telecommunications Union (ITU) has approved five technical options for 3rd Generation (3G) terrestrial networks and six different options for the satellite component of IMT 2000 (RSPEC M.1457) [14]. These RTTs (Radio Transmission Technologies) are further described in Clause 8. The Universal Mobile Telecommunications System (UMTS), being developed by the 3rd Generation Partnership Project (3GPP), uses Wideband Code Division Multiple Access (W-CDMA) for Frequency Division Duplex (FDD) and TD-CDMA for Time Division Duplex (TDD). Although UMTS has been evolved from the highly successful GSM standard, it is expected that the UMTS core network will become Internet Protocol (IP) based when 3GPP Release 5 specifications are introduced. Some current 2G networks will employ GPRS and EDGE to deliver limited 3G services during and after the initial phase of UMTS deployment. 4.2.1.1.1 S-UMTS as in integral part of the UMTS network


Page 84


Satellite-UMTS systems may use one of the previously mentioned six radio air interfaces endorsed by the ITU. Future RTTs, subject to the ITU evaluation process, may also be used. Some of the benefits to be gained from a fully integrated S-UMTS/T-UMTS system are:

•

Seamless service provision;

•

Re-use of the terrestrial infrastructure;

•

Highly integrated multi-mode user terminals.

The satellite component of UMTS may provide services in areas covered by cellular systems, complementary services, e.g. broadcasting, multicasting, and in those areas not planned to be served by terrestrial systems. This is illustrated in the following figure reproduced from a UMTS Forum Report.

Global Satellite

Suburban

Urban In- Building

Micro-Cell Macro-Cell

Home-Cell Pico-Cell

Audio/visual Terminals

Inter-Network Roaming

Seamless end-to-end Service Figure 4.4 The role of S-UMTS as an integral part of the UMTS network (UMTS Forum) 4.2.1.2 Satellite Network Architectures

This section gives a description of various architecture aspects for •

regenerative/transparent satellites

•

ground network/interconnect


Page 85


It is based on the ETSI S-UMTS “General Aspects” document. Some illustrating examples are given. 4.2.1.2.1 S-UMTS architecture 4.2.1.2.1.1 Segments

A S-UMTS can be divided into three segments: a space segment, a user segment and a ground segment. The space segment is composed of one or several GSO satellites and/or by a constellation of non-GSO satellites, with or without Inter Satellite Links, its associated Tracking Control and Ranging (TCR) stations and Satellite Control Center (SCC). The user segment is made of the User Equipment (UE): these are also referred to as Mobile Earth Stations (MES). The ground segment comprises Network Control Center(s), gateway(s) and inter-sites communication facilities. The NCC provides the fault, anomaly, configuration, performance, and security functions for management of the network and the gateways interface with other telecommunication networks 4.2.1.2.1.2 Satellite systems classification

Satellite systems can be classified as follows: a) Satellite constellation: GSO or NGSO b) Single-hop or double-hop architecture c) Bent-pipe or regenerative satellite d) Inter-Satellite Links: ISL or non-ISL A number of systems can be designed by combining the above parameters. However, the major impact on the UMTS and UTRAN architectures is found in the first two parameters: the constellation and the single/double hop architecture. We illustrate this with some examples. 4.2.1.2.2 GSO systems 4.2.1.2.2.1 GSO double-hop system

A double-hop satellite system based on a GSO constellation is shown in figure 4.5.


Page 86


NCC RNC

Node B

Feeder links

Gateway

Satellite User links

RNC

Node B

Feeder links

Core Network

Iur

Gateway

User segment

Uu

Space segment

Ground segment

Iu

Double hop call path: UE1 to Core Network to UE2

Figure 4.5 Double-hop, GSO model for S-UMTS The following elements are used in this model: •

RNC (radio network controller)

•

Node B entities

•

NCC (network control center).

The RNC is responsible for the control of the mobile communication. It is located in the gateway. The Node B entities provide mainly RF functions and these are located in the gateway in the case of a transparent satellite payload. The Node B functions may be located in the satellite in the case of regenerative payload. The NCC provides resource management functions for the whole UMTS satellite network. A single NCC is assumed and this will typically be co-located at one of the gateways. The space segment may be composed of one or several GSO satellites depending on the assumed coverage (global or regional). In this double-hop case the satellite system is only performing radio access network (USRAN) functions, whereby the satellite system is only used to route traffic between the UE and the core network. The interfaces are based on interfaces defined in 3GPP/T-UMTS as follows: The Iu interface is the interface between the RNC and the core network. This interface should preferable use the same Iu interface as defined for T-UMTS in order to allow the USRAN to connect to a standard T-UMTS core network.


Page 87


The Uu interface is the interface between the Node B and the user equipment. This interface is based on the Uu interface as defined for T-UMTS with minimum adaptation for the satellite radio path. Minimum adaptation is desirable to optimise the terminal design for a dual mode (S-UMTS and T-UMTS) terminal. An optional Iur interface may also be added to provide a direct interface between the gateways for S-UMTS. This interface should be based on the Iur interface as defined for TUMTS. 4.2.1.2.2.2 GSO single-hop system

A single-hop satellite system based on a GSO constellation is shown in figure 4.6

NCC RNC

Node B

Feeder links

Gateway

Satellite

RNC

Feeder links

Node B

User links

Core Network

Iur

Gateway

User segment

Uu*

Space segment

Ground segment

Iu*

Single-hop call path: UE1 to UE3

Figure 4.6 Single-hop, GSO model for S-UMTS In this case the satellite segment is performing limited routing functions (in addition to the access functions) that are used to route traffic between two Ues in a single hop without going through the core network. This ability means that the satellite access network contains some of the functions that are normally provided by the core network and this additional functionality may require modifications to the both the Uu and Iu interfaces as follows: The Iu* interface is a modified version of the Iu interface between the RNC and the core network. This modified interface enables the USRAN to perform the single hop traffic routing in addition to the functions provided in the double-hop model. The Iu* interface should be closely based on the Iu interface defined for T-UMTS in order to allow the USRAN to connect to a standard T-UMTS core network with minimal changes to the core network. The Uu* is a modified version of the Uu interface between the Node B and the user equipment with the additional functions to support single hop traffic. As for the double-hop


Page 88


case, this interface is based on the Uu interface as defined for T-UMTS with minimum adaptation for the satellite radio path. Minimum additions and modifications to support the single-hop case is desirable to optimise the terminal design for a dual mode (S-UMTS and TUMTS) terminal. 4.2.1.2.2.3 GSO S-UMTS systems

Figure 4.7 illustrates an example of a GSO S-UMTS system. It consists of a geo-stationary transparent satellite payload, a number of gateways, network and satellite control centres, and the user terminals. GEO satellite Gateways User segment

Vehicular Terminal

SGF

Handheld Terminal

Core Network

Palmtop/Laptop Terminal

NCC

Figure 4.7 GSO system example for S-UMTS The space segment consists of the satellite (or satellites) and the SGF (Satellite Ground Facilities). The system has a large number (>100) of separate spot beams to provide the user links. These high-gain spot beams enable the system to operate with hand-held terminals. The system has a small number of separate feeder beams which provide the feeder links to one or more gateways. The ability to support single hop UE–UE connections is optional and this service may not be supported in some cases (eg a GSO bent pipe S-UMTS system).


Page 89


The satellite gateway provides similar functionality to the RNC+Node B in T-UMTS and this group of gateway functions interfaces to the core network through the standard Iu interface. 4.2.1.2.3 NGSO systems 4.2.1.2.3.1 NGSO single-hop system

A single-hop satellite system based on a LEO constellation with inter-satellite links is shown in figure 4.8. Gateway Satellite

NCC Satellite Gateway

Satellite

Uu

User Equipment Domain

[Yu]

Access + Serving + Home Network Domains

Transit Network Domain

Figure 4.8 Single-hop, regenerative, ISL, LEO model for S-UMTS In this model we can see that the satellite segment is performing both access and routing functions. Because of that, users can communicate directly without going through the gateway. In this model only the Uu interface can be standardised. There is no clear separation between the access and the serving network. Due to this, the overall system will act as an independent network that connects to other transit networks via the [Yu] interface. 4.2.1.2.3.2 NGSO double-hop system

The architecture that may be adopted for double-hop, bent-pipe, LEO system is shown in figure 4.9.


Page 90


Gateway

RNC

Node B

Satellite

NCC Satellite CN Gateway

RNC

Node B

Satellite

Uu

User Equipment Domain

Iu

Access Network Domain

Serving + Transit + Home Network Domains

Figure 4.9 Double-hop, bent-pipe, LEO model for S-UMTS The following elements taken from 3GPP specifications are used in this model: •

the Radio Network Controller (RNC). Controls the radio resources. It may be colocated with the gateway and is equivalent to the BSC-Base Station Controller of GSM;

•

the Node B. This is a base station or a set of base stations. It is usually co-located with the gateway but in the regenerative case it may be located elsewhere in the system. The 3GPP specification for the base station (Node B) may need to be adapted to cope with the movement of satellites and in particular for LEO satellites. The dynamic allocation of satellite spot beams make the interface between the Nodes B and the user terminal more complex than in the terrestrial case. This is also true for Geostationary satellites which are not truly stationary in relation to the earth’s surface due to the earth’s diurnal movement. Node B is equivalent to the BTS-Base Transceiver Station of GSM;

•

the RNS-Radio Network Subsystem. This is made up of one RNC and one Node B. It is equivalent to the BSS-Base station Subsystem of GSM and is co-located with the gateway.

In addition to the previous elements, a Network Control Center (NCC) has been introduced in order to co-ordinate the use of satellite resources among all gateways. Interfaces are described as follows:


Page 91


•

the Iu interface is the interface between the RNS and the core network. It is equivalent to the A interface of GSM. The Iu interface, which is already defined for the terrestrial component of UMTS, may be shared with the satellite component with a minimum of adaptations with respect to the current specifications;

•

the Uu interface is the air interface located between the user terminal and the satellite.

4.2.2

Point to Multipoint architecture

Broadcast/Multicast is a key application of satellites. On the other hand, mobile terrestrial networks are mainly optimised for point to point communications. With regard to multimedia 3G applications, multicast will be of prime importance, thus offering opportunities to satellite. A general approach is first described. Then a specific architecture, the Satellite Digital Multimedia Broadcasting (S-DMB) system, aimed at providing 3G Content delivery services through satellite multicasting within 3G networks, is described. 4.2.2.1 General approach 4.2.2.1.1 Overall Vision

The vision herein pursued is that of an integrated satellite / terrestrial system intended to provide the point-to-point mobile communication services as well as the multicast and the broadcast mobile services defined in the ASMS-TF Vision document. Within such a integrated system it is possible to distinguish a terrestrial component and a satellite component. The terrestrial component includes both a communication segment and a broadcast segment. More precisely: •

the communication segment coincides with the terrestrial UMTS, which is designed to support all the narrow- and wide-band services that are envisaged for the 3rd-generation mobile system. This segment should however mainly be used to support the point-to-point communication services (such as telephony, Web browsing, file transfer, etc.), as those services implying the transmission of the same content to multiple users (generally referred to as the point-to-multipoint services) should preferably be routed over the satellite component. Diverting the multicast services away from terrestrial UMTS will permit not to re-transmit the same content in each cell, thus allowing to spare precious bandwidth. The provision of an important category of UMTS services (i.e. the multicast ones) would so almost exclusively rely upon satellite systems, that should therefore be planned in time for the initial terrestrial UMTS deployment phase

•

the terrestrial broadcast segment coincides with the future terrestrial digital mobile broadcasting infrastructure, intended to provide e.g. audio, music and TV channels on a wide geographical scale, but which has not yet substantially developed. On purely


Page 92


technical ground, digital mobile broadcast services could be supported by the terrestrial UMTS, but such a solution has not been seriously considered so far as it does not well match the pico cell nature of UMTS; therefore a dedicated terrestrial broadcast infrastructure will most likely have to be deployed. Demanding the coverage of rural areas to the satellite component would largely reduce the cost of setting up a new broadcast infrastructure that achieves a very high coverage percentage of the service area. That said, the role of the satellite component is already quite clear: on the one hand it shall complement the terrestrial UMTS by supporting the so-called multicast UMTS services; on the other hand it shall co-operate with the future terrestrial digital mobile broadcast network in achieving a very high coverage area at minimum total cost. To summarise, the proposed integrated system will offer overall: •

the point-to-point UMTS services as already envisaged today, i.e. by means of 3G terrestrial cellular networks:

•

the point-to-multipoint UMTS services in a more efficient manner than initially expected, such services being now diverted to the satellite component;

•

the digital mobile broadcast services at a lower cost than today estimated, it being conceivable to only deploy the terrestrial broadcast infrastructure on limited geographical areas, the coverage of unserved zones being demanded to the satellite system.

Clearly, for maximum service fruition flexibility, users shall be equipped with multi-mode terminals able to support the various services. As a final remark, a return channel via cellular systems (e.g. GPRS, UMTS) may be provided (if service requires it) to support some form of interactivity for both the multicast and the broadcast services. This concept may change in future system generations, where a satellite return channel could be utilised. 4.2.2.1.2

Multicast / Broadcast Services Provision

Despite multicasting and broadcasting are both point-to-multipoint services, they have some different requirements and constraints. Multicast services typically address selected user communities or users groups. Moreover they are defined as non-real-time services that usually require data integrity. To achieve this goal two main strategies can be pursued: •

redundancy: file segments are cyclically repeated, so that a lost segment (e.g. due to temporary satellite shadowing) can be recovered at a subsequent re-transmission.

re-transmission: lost segments could conceivably be re-transmitted by the network upon user request (most likely via the terrestrial component)


Page 93


Passing to consider the mobile broadcast services, these are typically real-time 1 “streaming” services. Losing a data segment would just imply a brief service interruption, and requesting its retransmission would then make no sense. Considering that the average user has developed quite a high sensitivity to the quality of audio and TV services that exists since long, the reduction of shadowing/blockage events is a mandatory requirement and will imply both the dimensioning of the satellite link with appropriate margins and the usage of time/space diversity techniques. As already mentioned, the mobile satellite digital broadcasting will represent an effective complement to the terrestrial broadcasting infrastructure, which has not yet significantly grown up. The satellite system will offer the possibility to reduce the overall costs incurred in setting-up an infrastructure able to serve a great percentage of the service area. 4.2.2.1.3

Transmission Standard

Another level of synergy that is considered important to achieve regards the transmission standard. Having a common standard for the terrestrial point-to-point services, for the satellite multicast services and for the complementary satellite / terrestrial broadcast services, would permit to simplify the implementation of multi-service user terminals. With an expectedly large base of users possessing a (terrestrial) UMTS terminal that supports the W-CDMA standard, it would seem logical to explore the possibility of adopting this technique also for the provision of satellite point-to-multipoint services. Other reasons that support such a guideline are: •

for a heavily-coded system (like all mobile systems) the wide-band property of W-CDMA makes it robustness against multi-path. In addition W-CDMA can exploit the terrestrial multi-path diversity to reduce the required link SNIR and supports full frequency reuse. W-CDMA is therefore well suitable also for the terrestrial broadcast infrastructure;

•

moreover, still for a heavily-coded system, the degradation suffered by W-CDMA in presence of non-linearity should be quite limited;

•

W-CDMA could allow a more flexible frequency planning than TDM for a multi-beam satellite system, it not showing an abrupt threshold with regard to tolerable C/I (soft degradation);

•

the moderate rate per W-CDMA stream (384 Kbps) is well suited to be handled by portable equipment compared to other standards (as DVB-T) that were not devised initially for mobile applications;

1

the term real-time is here used just to indicate that broadcast services are, by their nature, time-continuous. An absolute delay of several seconds, or even minutes in some cases, may however be irrelevant.


Page 94


•

a terrestrial broadcast infrastructure can better co-operate with a broadcast satellite system, with regard to providing a seamless service, if they both adopt W-CDMA;

•

finally, UMTS terminals are more open to modern source coding (compression) btechniques than other standards as DAB.

The above reasons are considered sufficient to support the view that using W-CDMA across the various components of the integrated system should be a serious candidate for advanced mobile systems. 4.2.2.1.4

Preliminary System Concept

Figure 4.10 shows the layout of the overall network which includes, in addition to the satellite segment, also the user segment, the 2.5/3 G terrestrial infrastructure and the terrestrial broadcasting infrastructure permitting to reach a higher coverage percentage of the service area. Satellites

Broadcasting Satellite L/S Band or X / Ku / Ka Band X / Ku / Ka Band

Terrestrial Broadcast Infrastructure Feeder Stations Broadcasting Satellite L/S Band

B/M SP

User Segment B/M SP NCC Control Centre

Cellular Mobile L/S Band

NCC = Network Control Centre B/M SP = Broadcast/Multicast Service Provider

Figure 4.10 System Architecture Overview

2.5/3G Terrestrial Infrastructure


Page 95


The user segment includes the terminals capable to receive both terrestrial and satellite signals FSs will be used either by the Multicast Service Providers (MSPs) or by the Broadcast Service Providers (BSPs) to transmit to the satellite their contents. FSs will transmit W-CDMA codes either on the same carrier frequency, or on more frequencies if the system envisages the utilisation of several frequency-staggered W-CDMA carriers to meet the capacity demand. If only one FS is used, all data generated by MSPs / BSPs will have to be delivered to it via the terrestrial network. Therefore in a wide regional scenario, where different MSPs / BSPs could be located in different and far-away countries, utilising several FSs could result to be advantageous. In any case distributed uplink capability from small stations sharing the same band could be an advantage for the small service providers as it allows to avoid the use of dedicated terrestrial digital lines to the central up-linking facility. In a multi-feeder station environment, the W-CDMA multiplex is created “on-the air” and synchronisation among W-CDMA codes will be required to avoid loss of orthogonality (and hence loss of capacity). This could be implemented by means of either an open loop scheme based on GPS or a closed-loop scheme based on the reception, by each FS, of the codes it transmits to the satellite. This implies that FSs should also be equipped with an antenna receiving in the users frequency band. In case of a multi-beam system a FS may not be able to receive its own codes with sufficient quality, in this case a feedback closed-loop synchronisation scheme can be proposed, whereby the NCC undertakes the role of relay point of the synchronisation information for the various FSs. The space segment is assumed to be transparent and several configurations could be implemented. A first-generation system could achieve a regional coverage (for example Europe or USA) with a single spot. Therefore it should be composed by a constellation of either GEO or HEO “bent pipe” satellites with a medium-size antenna reflector (diameter 2~3 meters). This system could be realisable in very short term, the related technology being well consolidated in Europe. A second-generation system could utilise a large reflector antenna aiming to realise separate coverages within the overall service area. In this case two architectures can be envisaged: §

the first one is based on several satellites, each dedicated to one country or homogenous language area. The coverage is realised by a single-spot large antenna offering high gain and then high link margin, exploitable to serve also lower G/T terminals (e.g. handheld terminals), or to allow a higher indoor penetration, or to give better quality of service;

§

the second one foresees a single satellite with a multiple-spot (6~8) large antenna. Each spot again covers a given country or homogeneous language area. With respect to the previous configuration this one would offer lower link margin if the same total onboard RF power is used for all beams. This approach could result to be more economic, though it may not yield a comparable service quality due to total RF power limitations. However the handling multiple beams with very high RF power may not be trivial.

Potential frequency bands for the mobile Broadcasting Satellite Service (also including multicast services as defined by the ASMS-TF) are the L band at present allocated for S-DAB services (1467.5-1492 MHz) or the S band allocated to S-UMTS, the former allowing an


Page 96


higher link margin (about 3 dB) for the same coverage area, but requiring a larger antenna (about 70% greater than at S band). 4.2.2.1.5 Broadcast Infrastructures Integration

As already mentioned, a mobile satellite system cannot be viably designed for a link margin such as to provide, alone, a good-quality broadcast service even in urban canyons or indoor. Terrestrial transmitters, repeating the same content delivered over satellite, are therefore required to fill the gaps that can not be adequately covered by satellites. Under such assumption, mobile receivers shall obviously be designed such as to handle both satellite and terrestrial signal types. •

Differently from other system concepts (e.g. SIRIUS), with the proposed W-CDMAbased architecture both the satellite and the gap filler signals could operate over the same frequency channel, this being a clear advantage from the total bandwidth occupancy viewpoint. Use of Rake receivers will permit coherently combining signals coming over different paths, thus improving Eb /N o .

Whilst conventional terrestrial broadcast systems utilise high-power transmitters conveniently located (e.g. mountain-top sites), that illuminate wide areas, in an integrated terrestrial / satellite system it would alternatively be possible to adopt a different approach featuring a (great) number of terrestrial relatively low-power transmitters only aiming to jointly cover high-population agglomerates, and so demanding to satellites the coverage of the rural areas, or perhaps even the sub-urban ones. Adopting W-CDMA also for such terrestrial infrastructure, the low-power transmitters could just have the role of repeating the same signal transmitted by the satellite, with no format or access scheme conversion. Several alternative terrestrial gap-filler configurations are possible: a. transparent repeater operating in the same receiving and trasmitting frequency bands (L or S); b. frequency converting repeater receiving directly from satellite in a frequency band different from the transmitting one; c. frequency converting repeater receiving from a local feeder station in a frequency band different from the transmitting one. 4.2.2.1.6

Conclusions

The proposed integrated system concept should represent an efficient and cost-effective solution to support mobile wideband applications, by maximizing synergies among services, infrastructures and technologies. It offers an important role to satellites that are mainly utilized where the specific advantages of satellite systems can best be exploited. On the other hand, it requires a significant extent of coordination between terrestrial and satellite operators that can only be achieved if specific efforts are paid at this regard in a compatible time frame.


Page 97


4.2.2.2 Satellite based multicast layer architecture for mobile networks

This section provides an overview of a satellite based multicast system for 3G mobile networks relying on terrestrial UMTS standards and making use of the allocated IMT2000 bands to MSS systems. It is referred as Satellite Digital Multimedia Broadcasting system (SDMB) and is based on a combined satellite and terrestrial repeaters architecture over 3G cellular networks. The S-DMB architecture aims at providing an efficient and cost effective answer to solve the identified issues of multimedia services delivery on 3G networks, inducing exciting market opportunities for 3G mobile operators. By relieving unicast networks of the most cumbersome and less profitable traffic, the S-DMB delivery mechanisms will provide 3G mobile operators with more efficient and more profitable usage of radio frequency resources. 4.2.2.2.1 S-DMB mission

The S-DMB concept is derived from Content Delivery Network architectures developed for fixed IP networks. The main rationale of a content delivery systems is that rich media audience on internet is concentrating on a rather limited part of available content, that might be better served if it is brought as close as possible to the user. As price evolution of storage and transfer technologies is increasingly favouring storage, architectures which rely on oneto-many distribution mechanism of content to be locally cached (“push and store”) will increase in the coming year their business advantage toward remote & centralised client/server architecture. Therefore the basic mission of the S-DMB system is to provide traffic optimisation mechanisms that rely on multicast content delivery to the user and are exclusively intended to increase content transfer capacity over 3G networks. The concept also relies on the ability of any kind of UMTS handset to access this multicast layer. This is based on the use of the wide band CDMA UTRA FDD air interface. Relying on MSS frequency bands adjacent to IMT-2000 remove also expensive frequency range requirement on user terminal, thus allowing the provision of multi-mode terminals (unicast and multicast) at marginal extra-cost. 4.2.2.2.2 S-DMB Services

The main purpose of S-DMB system is to provide mobile network operators and content providers with the Content Delivery services.


Local Access

Page 98


Content Distribution (to the Terminal)

(End User Cache)

Remote access for undelivered content (Terminal to Server)

Missing content

Multicast Layer

Available prestored content

3GPP Core Network 3GPP RAN RNC Node B

retransmitted content

Content provider 1 Content Networking

CDN data Server

Content provider 2

Figure 4.11 A content delivery architecture for mobile networks 4.2.2.2.2.1 Content delivery service

The Satellite based multicast layer architecture enables mobile network operators to deliver rich multimedia content at lower cost towards mobile users with less restriction on the audience served. The S-DMB data server will push or forward multimedia content to the 3G mobile terminals with different capability. •

Data streaming capability: The multimedia content is played directly upon reception at the mobile terminal. It is used for audio, video multicasting as well as real time data update. A multicast layer will greatly help mobile operators to avoid traffic congestion on their network when real time retransmission of highly popular event drain large audience.

•

Push and store capability: on demand usage of infotainment, entertainment, software delivery, and rich media applications will be served by pushing the multimedia contents to a local cache for later usage. Through pre-stored content, users will experience on demand services with better quality and availability than if provided by point to point connections, because local content become available anywhere anytime. although users will rely on a real connection process through terrestrial network to have this content available.

•

User request download capability: Data download requested by mobile users will be forwarded to the terminal via the most suitable route between both multicast and unicast network according to the overall demand. Typically unicast traffic is routed on the terrestrial cellular network and multicast traffic is routed on the unidirectional network. But a better and more dynamic approach is possible where unicast & multicast traffic are routed dynamically on the most efficient path according for example to transmission cost, number of user request, delay, congestion status constraints.

•

Peer to peer traffic optimisation: SDMB provides a means to lower transmission cost for applications such as collaborative work, large scale games, videoconferences, telemedicine, remote surveillance involving many to many connectivity between a group of


Page 99


mobile terminals. The multicast traffic streams are forwarded over the space segment to the mobile terminal group. 4.2.2.2.2.2 Emergency service

With an outstanding coverage, the satellite provides messaging capabilities to inform or alert large audience of general emergency and national security announcements including public security, health, specific threats and concerns. In addition, a low data satellite return link is under investigation. It will use the paired up-link IMT-2000 band allocated to mobile satellite service and UTRA FDD W-CDMA air interface to allow T-UMTS handset to transmit low volume of data. It will provide assistance and data collection service outside GSM coverage. Coupled with Global Navigation Satellite System (GNSS) , the capability is extended to search & rescue as well as tracking features. It can also be used by government as well as public in case of natural or man made disaster. 4.2.2.2.3 System architecture

The satellite based multicast layer architecture is designed to avoid any modification to the 3GPP architecture with which it interacts. It uses terrestrial 3GPP, IETF standardised technology to access a large market. It consists in a space segment made of satellites and terrestrial repeaters. Mobile terminals receive appealing multimedia contents prepared or forwarded by the S-DMB server and conveyed in a point to multipoint connection provided by the space segment. The service is delivered with a point to point connection provided by a mobile network (2G or 3G). S-DMB satellite

FSS band W-CDMA MSS band

W-CDMA MSS band

UMTS/GPRS Multi mode terminal « S-DMB enabled »

S-DMB HUB

S-DMB Terrestrial repeater

Content provider

3GPP RAN

Node B

RNC

3GPP CORE NETWORK

CDN S-DMB server

Content provider

Figure 4.12 Satellite based multicast layer architecture for mobile networks


Page 100


The S-DMB server interacts with the mobile network via standard interfaces. It consists in a central part co-located with a hub in charge of content multicasting and secondary entities installed in different countries to handle the point to point connections. The S-DMB server is responsible for the content acquisition from external content providers via content distribution networks or from other sources. To adapt to the satellite channel characteristics, the server applies on the multimedia content some efficient transport techniques relevant to the targeted service requirements. It relies on preventive techniques such as Forward Error Correction coding, interleaving (defined in IETF standard Reliable MulTicast Protocol RMTP) as well as content retransmission. If still some blocks are lost during the transmission, selective block recovery mechanisms are provided by making use of the point to point connectivity via the terrestrial mobile network. The server implements routing features to allow interoperability between the S-DMB space segment and the mobile cellular network. This heterogeneous network interconnection allows to establish the point to point connectivity also referred as return link. Thanks to the increasing size in terms of available power of satellites, transmitted power are compatible to mobile handset applications, even at low elevation angles. Operation in the MSS S bands allows to provide either single beam or multi-beam coverage. To counter heavy shadowing and provide coverage continuity in urban and sub-urban areas, low cost terrestrial repeaters will be deployed in the Line Of Sight (LOS) of the satellite. The repeaters are designed to be smoothly co-sited with 3G/2G base stations. S-DMB signal reception requires standard 3GPP terminal parts. S-DMB requires terminal to accommodate local storage capability which is no issue considering the technology trends. The S-DMB software package is designed to run in any mobile terminal environment. It shall also allow operation on a 3GPP network (GPRS or T-UMTS) to establish a point to point session with the server for the interactive link. The S-DMB system is designed to ensure a combination of the S-DMB signals received from the satellite as well as the terrestrial repeaters with a standard rake receiver. The terminal establishes a S-DMB point to point connection with the server via a 2G or 3G mobile network to achieve retrieval of missing packets to reconstruct damaged files, data collection for audience and service usage measurement, user profiling management, exchange of MMI commands and m-commerce transaction on the received contents. 4.2.2.2.4 System characteristics

System implementation perspectives are primarily focused on Europe. Key actions are undertaken in regulatory and standardisation bodies to secure the development of the system.


Page 101


4.2.2.2.4.1 Key technological parameters

•

Coverage

European satellite coverage is achieved thanks to a global beam and several spot beams covering major linguistic group areas as depicted in the following figure.

Global Beam

Multibeam

Figure 4.13 S-DMB european coverage •

Capacity

The available throughput will mainly depend on the selected satellite architecture, i.e. global or/and multi-beam. Each spot beam is able to handle a data rate of around 1 Mb/s while the global beam solution provides an overall throughput of 3.84 Mb/s. A single spot beam delivers more than 10 Gbytes of data per day which is very significant considering the performance of current and emerging multimedia encoding techniques.

4.2.2.2.4.2 Technology trends justifying the system

•

Local cache

With the current technology, two types of storage may be envisaged. The first one is based on micro hard disk drive product dedicated to handheld devices such as laptop and the second one is related to Multimedia Memory card used in current generation cellular devices. It is both a market and technological evidence that storage devices will keep growing in capacity and decrease in price and volumes within 5 next years, with many new products and technologies permanently entering this market.


•

Page 102


Satellite

The GSO reference system is selected for the S-DMB system. The satellite segment of SDMB system requires high RF power, large platform and shall accommodate large deployable antenna (i.e. multi-beam architecture) to fulfil the expected mission. This platform shall be able to handle up to 5 KW RF and to accommodate 8 meters deployable antenna reflector. Such requirements are compatible with platform development plan in the 2006 timeframe and no critical technological key issues are expected to manufacture the S-DMB satellite segment whatever the selected architecture. •

UMTS chipset

One of the key issue for the success of the S-DMB system is to use of-the-shelf UMTS chipset without any modification at least at hardware level. Analysis of 3GPP UTRA FDD-mode standard has shown that only a subset of channels is actually needed for the multicast link provided by the S-DMB system. The Rake receiver architecture of the S-DMB terminal is the core issue of the base-band processing since it has to cope with S-DMB signals (i.e. gap-filler, satellite and associated multi-path) coming from different sources, levels and large delay spread figures. •

UMTS technology

The S-DMB will rely on the Multimedia Broadcast Multicast Service (MBMS) architecture which is being defined for 3GPP release 6. The S-DMB system is designed to allow smooth integration with the 3G mobile network implementing the Internet Protocol Multimedia Subsystem (IMS).

4.3 4.3.1

DVB-DERIVED TECHNOLOGIES FOR MOBILE Introduction

Digital Video Broadcast (DVB) is a European initiative to standardise digital broadcasting worldwide. The DVB Standards were developed under the DVB Project, which was founded in 1993. The standards are published by ETSI and are based on the ISO MPEG-2 standards for source coding and transmission of multiplexed data streams. The DVB standards apply to a range of bearer networks. One of the earliest was DVB-S for digital video broadcasting via satellite (ETS 300421, 1994). The standard was intended for Ku-band transponders and fixed use and covers a range of bandwidths or data rates. With a typical satellite channel of about 35 MHz and a maximum data rate of about 38 Mbps, a variety of TV, radio and data broadcast services may be provided. The DVB-S standard identifies the synergy between digital broadcasting and Web delivery and specifies an option for a return channel and interactive data services. The return link can be implemented using various media. The satellite return channel alternative was later standardised as DVB-RCS (Return Channel by Satellite).


Page 103


The DVB-S and DVB-RCS standards are defined for broadband fixed terminals operating in Ku-band. However, with reasonable modifications to the air interface, DVB-based systems may also be suitable for mobile/portable terminals operating in L/S-bands and offering data rates of 400-2000 kbps. No standard has been developed for this yet. 4.3.2

DVB-RCS

DVB-RCS (Return Channel by Satellite) is an ETSI standard for interactive multimedia services (EN 301790, 2000). DVB-RCS is based on using the DVB-S standard for the forward channel. The return channel is based on MF-TDMA access scheme and uses an efficient transport layer. DVB-RCS employs dynamic resource allocation and specifies several capacity request or QoS categories. The standard is not specific on frequency bands or data rate. DVB-RCS provides for a broad spectre of IP-based multimedia interactive applications and services. One of the major advantages of DVB-RCS is efficient and low-cost implementation of multicasting and broadcasting services. However, point-to-point services, such as Voice-overIP, can be supported as well. 4.3.3

Satellite Interactive Network and Terrestrial Interface

The generic physical architecture of the overall DVB-RCS Satellite Interactive Network is shown in figure 4.14. One implementation would be to combine the forward and return satellites into one. The Feeder station and Gateway station could also be integrated. Figure 4.15 depicts the functional view of a DVB gateway in which Feeder, DVB-RCS Gateway and NCC are integrated.


Page 104


Figure 4.14 DVB-RCS Satellite Interactive Network

Internet

Feeder GW (forward channel)

Other DVB GWs

PSTN/ISDN

Backbone network and terrestrial interface

NCC

Ref. & Sync

GPS

Traffic GW (return channel)

Network Management System

NOC Billing Centre

Figure 4.15 Functional Block Diagram for DVB Gateway

RCST (Return Channel Satellite Terminal) is the user terminal based on the DVB-RCS standard and IP-based communication. The Feeder Gateway transmits the forward link DVB-S signal, onto which are multiplexed the user data and/or the control and timing signals needed for the operation of the network. It also does the conversion from IP packets to the DVB format.


Page 105


The Traffic Gateway receives the User Terminal return signals and performs downconversion, demodulation, decoding, descrambling and demultiplexing of satellite network signalling and user traffic data. It does the conversion from the DVB format to IP packets, as well as conversion between VoIP and circuit switched connections. The NCC (Network Control Center) provides monitoring and control functions. It generates and updates the various Service Information (SI) tables and sends SI tables, formatted into MPEG-2 TS packets, to the Feeder Gateway. The NCC receives and acts upon MAC messages from the terminals and will grant or deny access to the system according to a set of rules. The NCC will also be in charge of radio resource management. The Network Management for the DVB Gateway handles fault management, configuration, message trace and subscriber authorisation, authentication and accounting management. On the terrestrial side, the gateway can interface with the Internet and private Intranets. The interface towards the public telephony network can be a set of 2 Mbps E1 trunks with SS7 or ISDN PRI signalling. 4.3.4

Network Integration

The DVB-RCS system can be considered to be a self-standing system that includes all functions needed to support internal mobility. In the minimum solution there is no location register interworking with terrestrial mobile communication systems. Such interworking is possible if this is an economically viable solution and if there is a demand for such interworking. The DVB-RCS system can be interconnected to both fixed and mobile terrestrial communications systems as well as other mobile satellite communication systems (e.g. Inmarsat M/B/Mini-M/M4/F). 4.3.5

DVB-RCS Air Interface

4.3.5.1 DVB-S Forward Link

The Feeder transmits one or more forward link channels, each with a continuous stream of DVB frames. The DVB frames carry the MPEG-2 packets, which form a Transport Stream – each packet 188 byte long. The MPEG-2 packets have an identifier called Program Identification (PID) that is used to form several streams of information, Elementary Streams (ES), that are interlaced. The basic types of ES are control data, video, audio and data (synchronous or asynchronous). The user data information consists mainly of IP datagrams. In the forward channel these are encapsulated in datagram sections in a particular “table” which is especially designed to handle multi-protocol encapsulation (MPE). A MAC address field inside the section is used to identify the RCST. The DVB system is controlled by a set of tables sent to the RCSTs by the DVB forward broadcast channels. The standard DVB forward link is described by the following sets:


Page 106


Program Specific Information Tables (PSI) and Additional Service Information Tables (DVBSI). 4.3.5.2 DVB-RCS Return Link

The RCST sends data and signalling back to the network on one or more loosely coupled Multi-Frequency Time Division Multiple Access channels (MF-TDMA). The RCST transmits in TDMA timeslots distributed in both time and frequency. The timeslots and burst transmissions are controlled by tables. Data and signalling are sent in four types of bursts: Traffic, synchronisation, acquisition and common signalling channel bursts. The traffic bursts may contain MPEG-2 packets or ATM cells. For a DVB-RCS system a set of tables is added for the return link: RCS Service Information Tables (RCS-SI). This set consists of tables describing the FD-TDMA channels (5) and tables for general information to the RCST (2). 4.3.6

Radio Resource Management

The Radio Resource Management (RRM) provides for allocation of bandwidth on the satellite carriers based on the types and amounts of traffic. It is possible to perform segmentation (in frequency and time) of the return link into superframes, frames and time slots. The SI tables for frame segmentation may be configured manually via a GUI implemented as a part of NMS. The NCC can perform automatic regeneration of these tables to provide optimal use of the return link capacity. Allocation of capacity to individual user terminals can be performed according to the subscriber profile of the user terminal for each capacity request category. A Burst Time Plan algorithm can optimise the use of radio resources and attempt to ensure QoS levels requested by the terminals. Capacity can be allocated by building and sending the Terminal Burst Time Plan (TBTP) based on capacity requests from the terminals and log on/off. The TBTP may be updated for each transmission due to changing capacity requests from the terminals. Information got from monitoring of time slot utilisation and how well the capacity requests are served can be used together with information about bit error rate, rain fading/power level, satellite power consumption, and total bandwidth in the capacity segmentation/reservation algorithm. 4.3.7

Services

DVB-RCS may support a broad spectre of IP-based mobile multimedia services via satellite: •

Distribution and streaming services: Real time and background multicast streaming and file transfer.

•

Interactive Internet access: Web browsing, file transfer, e-mail etc.

•

LAN extension / Intranet access.


•

Page 107


Conversational services: Voice-over-IP, video conferencing.

Any application that runs on top of IP will be supported given that the QoS required by the application can be granted. The DVB-RCS air interface is best suited for distribution and interactive services with less stringent real time requirements. For IP-based conversational services (VoIP) the minimum delay will be 0,5 seconds (including satellite connection). The present DVB-RCS standard only specifies QoS for the return link, although it can be controlled for both directions. 4.3.8

DVB-RCS for ASMS

4.3.8.1 Air Interface

If the DVB-RCS standard shall be applied to mobile/portable satellite systems operating in the L/S-band, the spectral efficiency must be increased to achieve acceptable capacity for smaller bandwidths. The MPEG-2 packets should be Turbo-encoded instead of Reed-Solomon. For the forward link higher order modulation (16QAM) should be employed. For the return link, however, the modulation format should be limited to QPSK to limit RCST and satellite power consumption and heat dissipation. DVB-RCS is a low-complexity air interface with low signalling overhead and is thus suited for low-capacity systems. The overhead for mobile use relates to several factors, the most important being how often signalling tables are transmitted, the complexity of the system configuration, and the number of simultaneous users. For IP-based services the overall efficiency depends strongly on the IP packet length. For short packets the MPEG-2 based encapsulation is not efficient and there is a need for substitution of MPEG-2 with a more flexible and adaptable segmentation for the forward channel to increase efficiency. A modified standard for mobile use should also include the possibility for individually adaptive modulation and coding schemes per user. At present a modified DVB-RCS standard for mobile use has not been developed. 4.3.8.2 Mobility Management

Terminals in a mobile DVB-RCS system are able to roam between spot beam footprints in a ”satellite coverage” region or from a spot beam footprint in one satellite coverage region to a spot beam footprint in another satellite coverage region. Each DVB-RCS mobile can be allocated a dynamic IP address by a DHCP server at registration/logon. This IP address could be stored in the location register of a roaming mobility management database together with the DVB-RCS Gateway identifier, satellite, spot beam, and carrier associated with the location where the satellite terminal/user is presently located. For circuit switched services (converted to VoIP/FoIP in the Gateway) calls can be routed directly to a DVB-RCS Gateway provided the switching exchanges are able to differentiate the calls based on the numbering plan for the DVB-RCS mobiles. The gateway will check the


Page 108


roaming mobility database to see if the call can be completed via this gateway. If not, the call is routed to the DVB-RCS gateway through which the DVB-RCS terminal/user is accessible. For packet switched services routed through IP based networks, the addressing for the DVBRCS mobile could be based on host name. The domain name can be associated with the dynamic IP address and stored in the location register of the roaming mobility management database. This makes it possible to establish connections between entities in IP based networks and DVB-RCS mobile terminals. 4.3.8.3 Handover

A spot beam handover that preserves the call session during the transition from the current beam to the next beam is envisaged. For geostationary satellites this spot beam handover is assumed to be necessary and practical only between spot beams of the same satellite and not between satellites, although this can also be implemented. This view is supported by the fact that except for omidirectional antennas, handover between satellites would also mean a repointing of the antenna of the terminal. Omidirectional antennas are only envisaged for handheld terminals and these terminals will not move so fast that handover between satellites during a call session is assumed to be necessary. 4.3.8.4 Power conservation

For battery-powered mobile terminals it is important to conserve power and employ a mechanism for lowest possible power consumption. This could be achieved in DVB-RCS the terminals, a sleep-mode where it will listen to the received stream only at various intervals, and a non-sleep mode where it listens all the time. The feeding system only sends information to a terminal at certain times when it is known that it will listen in. When any terminal receives specific information (other than common system tables) it will immediately exit sleep-mode. This scheme requires that common system information be clumped together in certain slots in time. The slotted scheme for information to terminals in sleep-mode also covers a method for the satellite to conserve power when there is little traffic in a particular spot. This is accomplished by simply turning off its carrier in the time-slots when there is no information to send. 4.3.9

Hybrid Systems

There is a trend towards convergence of broadcast and mobile satellite systems. For systems combining broadcast/multicast and point-to-point communications there will normally be a need for larger capacity for the broadcast component. For portable or semi-fixed use this can be achieved by assigning the forward link to Ku-band and the return link to L/S-band. Such hybrid systems could be efficiently implemented using a combined air interface with DVB-S for the broadcast channel and a point-to-point optimised air interface for the return link.

5

CONCLUDING REMARKS

The architectures presented in this report are refered to the short and medium term development within Mobile Satellite Systems. They do however represent different phases in


Page 109


this development, a group of systems that are operational represented by existing Inmarsat systems, Globalstar and Thuraya, a second group which is becoming operational represented by AceS, Thuraya and Inmarsat 4 and a third group which in under discussion represented by combinations of communication and broadcast systems in order to offer efficient multicast services. Experience to be gained through the use of Aces, Thuraya and Inmarsat 4 and new ICO during the next 2-4 years will be of great significance for further development. In Europe the communication based systems seems to be in the lead relative to the new broadcast systems that are more dependent on the use of terrestrial repeaters requiring some sort of standard/allocation to avoid lengthy discussions. Some reflections from development so far are the following. Satellite technology is now in an upgrading phase to the demands of the multimedia age. The reference for the development has been the terrestrial network/service development and the existing satellite systems. The lack of success with the first systems, intended for GSM type of services, may have many explanations, too much capacity, too complicated systems, and not least outdated business plans. Implementation of ten year old ideas has not been a success and strong growth in terrestrial GSM was not a criteria for success for GSM related satellite systems. The mobile satellite world is now ready for launch of broadband UMTS type of services and the near term period defined by ASMS will be relatively critical. There are many critical issues to watch like •

Availability of reliable and low cost equipment.

•

The development in the terrestrial UMTS market. It is for the time being characterised by delays and some skeptisism. Many operators may not offer bitrates above 64 kbit/s during the first phase. This may have an effect on service development which may also include the satellite segment. The more stepwise approach starting from GPRS may fit well with this situation.

•

Some of the requirements may be difficult to fulfil during the first phase. This includes central topics like Always on and multicast. Always on is a bottleneck with the limited availability in-door and in non-line of sight areas. This also affects the applicability of multicast. A lot of effort is required to establish good and reliable solutions to such problems.

•

Standardisation is more and more a critical issue as the number of users is growing. They will also require interoperability of their user terminals with the different regional systems around the world.

•

Interoperability/roaming with terrestrial netwoks seems to be important. It is observed that for instance ACeS has several roaming agreements with mobile operators in Asia.

Satellite capacity suited for the first phase of advanced satellite mobile systems is available.


Page 110


References [1]

ASMS Commercial Group document “Input document from the commercial group to the technical group”, Draft A, 25th April 2001

[2]

ASMS Commercial Group temporary Requirements”, Revision 3, April 2001

[3]

Recommendation I.610 (11/95) - B-ISDN operation and maintenance principles and functions. ITU-T

[4]

Recommendation Q.2931 (02/95) – Broadband Integrated Services Digital Network (B-ISDN) - Digital subscriber signalling system no. 2 (DSS2) – User-network interface (UNI) - Layer 3 specification for basic call/connection Control. ITU-T.

[5]

UNI Signalling 4.0 af-sig-0061.000. ATM Forum

[6]

O. Courseille, P. Fournié, J.F. Gambart, "On-air with the WorldSpace Satellite System", 48th IAF Congress, 1997

[7]

“Systems for digital sound broadcasting to vehicular, portable and fixed receivers for broadcasting satellite service (sound) bands in the frequency range 1400-2700 MHz” Rec. ITU-R BO.1130-3.

document

“Temporary

Commercial

ANNEX I GSM based Satellite Systems A1 Commonalities between terrestrial and satellite systems There are a number of similarities and differences between a terrestrial cellular system such as GSM (Global System for Mobile communications) and GMR (Geo-Mobile Radio interface). They are as follows: Similarities: 1)

Spotbeams in the GMR system play the role as cells in GSM.

2)

Both GMR and GSM exploit a frequency reuse concept.


3)

Page 111


Layers above the physical layer in both GMR and GSM are very similar to each other.

Differences: 1) Geosynchronous Satellite: The distance between the user terminals and the Gateways in a GMR system (user terminal to satellite + satellite to gateway) is much larger than the distance between user terminals and the Base Stations in GSM. This fact has several consequences: •

large attenuation of radio signals;

•

large propagation delays in GMR systems compared to GSM systems.

2) Propagation Delay: The large propagation delay in GMR systems has several consequences: •

impact on conversational dynamics in voice communications;

•

increased annoyance due to echoes in the system;

•

a need for a single hop connection for a mobile-to mobile-voice call;

•

impact on handshake protocols such as Fax protocol T.30;

•

impact on System Timing Synchronization.

3) Spotbeam Size: Spotbeams in a GMR system are much larger than cells in GSM. This leads to several consequences: •

reduced benefits from frequency reuse;

•

larger variation of propagation delay across a spotbeam compared to the variation across a cell, necessitating sophisticated timing synchronization schemes;

•

reduced need for inter-spotbeam handovers.

4) Satellite Power: In GMR systems, the satellite power is a system resource that is shared by all the spotbeams in the entire coverage region. In contrast, in GSM systems, the power of a BTS is not shared directly between various cells. Thus, system power control is needed in GMR systems. 5) Link Margins: Due to the fact that satellite power is shared, forward (from satellite-touser terminal) link margins are low in GMR systems compared to GSM systems. Due to the fact that the user terminal signals are highly attenuated, (because of the large distance between the user terminal and the satellite) the return (user terminal-to-satellite) link margins are low compared to GSM.


Page 112


6) Line-of-Sight operation: Due to the high attenuation of radio signals, it is necessary to require line-of-sight operation for GMR systems. In other words, radio communication is not possible using multipath signals alone, as it is possible in GSM systems. If the user is not in line-of-sight with the satellite, then the user is said to be in a disadvantaged situation or mode. 7) User co-operation: Due to the fact that line-of-sight is required in GMR systems, the user has to co-operate for Mobile Originated calls. If the user is in a disadvantaged mode, then Mobile Terminated calls cannot be established. This leads to special alerting procedures, that alert the user of an incoming call, following which the user has to co-operate by moving to an advantaged location. 8) Radio Channel characteristics: Due to the assumption of a line-of-sight with the satellite, the radio channel has a Ricean characteristic rather than a Rayleigh characteristic, as in GSM systems. 9) Interference: The interference from adjacent cells in a GSM system is primarily due to transmitted power and cell size. In GMR systems, the interference from adjacent spotbeams is due to power and sidelobe characteristics of the satellite antenna array producing the multiple spotbeams. 10) Network Architecture: In a GMR system, a user terminal located anywhere in the coverage area can access any of the Gateways (entry points into the fixed network), whereas in a terrestrial cellular system, a given cell can access only one particular MSC. 11) Optimal Call Routing: In GMR system, a Mobile Originated (MO) call can be routed to a gateway that is nearest to the called party, thereby minimizing the cost of the landline connection. In GSM systems, such optimization is not possible

ETSI has produced two sets of specifications for GEO-mobile radio-interface derived from GSM standards. These specifications are called GMR-1 (used by Thuraya) and GMR-2 (used by ACeS) specifying some adaptations of the GSM standards to cope with some specifities of geostationnary systems. There are also some works being done in ETSI to adapt in the same way the GPRS standards to the satellite. This adaptation is called GMPRS (Geo-Mobile Packet Radio Service) but actually the work is at a very early stage and no technical specifications were published. A 2 GMR-1 general system description A 2.1 Overview and system elements

The GMR-1 system extends terrestrial GSM cellular system coverage. The GMR-1 system provides GSM-like services and features such as voice, data, fax, point-to-point short message service, cell broadcast short message service and supplemental services between mobile and fixed users and provides world-wide connectivity through public and private switched telecommunications networks. Fixed network connectivity includes the Public Switched


Page 113


Telephone Network (PSTN); Public Land Mobile Networks (PLMNs); and private networks (PN).

Space segment

Gateway stations

PSTN

Spot-beam coverage at L-band

Feeder links

Gateway station GS

PSTN

SOC

PSTN Mobile Earth Stations

Figure A 1 : Example of GMR-1 system elements

PSTN


Page 114


The elements of a typical GMR-1 system are shown in figure A1. The system elements include one or more geostationary satellites, a Satellite Operations Center (SOC), a number of Gateway Stations (GS), and a large number of user terminals, referred to as Mobile Earth Stations (MES) in the GMR-1 specifications. The range of possible MESs include handportable terminals (handsets), vehicle terminals, and fixed terminals. The Gateway stations have external interfaces to existing fixed telecommunications infrastructure as well as to the GSM mobility management networks. A GS includes one or more gateway transceiver subsystems (GTS) which correspond to a GSM BTSs, one or more gateway station controllers (GSC), which correspond to a GSM BSCs, one or more mobile switching centers (MSC) which may be GSM MSCs, and one Traffic Control Subsystem (TCS) which has no corresponding functional element in the GSM base station. The GMR-1 TCS is required to support position based services, optimal routing and other satellite specific services and features, not found in GSM. Mobile services are provided in a large regional coverage area, defined by the orbital location of the geosynchronous satellite and the satellite payload performance. Subscribers located anywhere in the coverage area may have full use of the GMR-1 system services. An example of a regional coverage area showing a typical distribution of spot beams is shown in figure A2.

Figure A 2 : Example of regional coverage by multiple spot beams from a geosynchronous satellite Satellite spot beams differ from GSM cells in that they are large, regularly shaped and all originate from the same point source, i.e., the satellite, and thus are synchronized. Because of


Page 115


their large size, several hundred kilometres in diameter, they overlap national boundaries and service areas. GSM cells, on the other hand, are very small, irregularly shaped by terrain features and buildings and originate from different geographical locations. GSM cells are always assumed to be contained within a single country. These differences necessitate very different treatments. A 2.2 System architecture and external interfaces

User voice and data is transmitted in traffic channels between user terminals and Gateways, or directly between user terminals. Signalling to access the system, set-up calls, and manage link quality occurs on the broadcast, common, and dedicated signalling links. Each GS provides its own set of common control channels (CCCH) into the spot beams within its service area (SA). The protocol architecture is shown in figure 3. In the first case, the GMR-1 system provides two-way connectivity between a user terminal and a fixed network subscriber, using L-band and Feeder links to the satellite (shown with solid lines in figure A 3). Access to fixed telecommunication networks is provided by connections through the Gateway Station. Fixed network connectivity includes the Public Switched Telephone Network (PSTN); Public Land Mobile Networks (PLMNs); and private networks (PN). In the second case, the GMR-1 system provides two-way connectivity between two user terminals in the same or different spot beams by performing direct connection of the two Lband to L-band connections in the satellite. This special case of single-hopped terminal to terminal (TtT) calls is described in clause 6.1.


Page 116


Satellite MES

GSM SIM GPS rcvr

GSM MSC

GSC + GTS + TCS

GMR-1 Um-Interface CM

CM

MM

MM

RR

RR

BSSMAP

BSSMAP

DLL

DLL

SCCP

SCCP

PHYS

MTP

MTP

PHYS

PHYS PHYS

Spot beams L-band

Feeder link Ku or C-band

GSM/ A-Interface (CCS7)

Figure A 3 : GMR-1 Protocol architecture Functional description of system elements

The functional network elements shown in figure A 3 are listed below.

The Gateway Station Subsystem (GSS)

The Gateway Station Subsystem (GSS) is the system of gateway station equipments (transceivers, controllers, etc.) which is viewed by the MSC as being the entity responsible for communicating with Mobile Earth Stations in a certain coverage area. The radio equipment of a GSS may support one or more spot beams. The GSS consists of one Gateway Station Controller (GSC) and one or more Gateway Transceiver Stations (GTS). A Gateway Station Controller (GSC) is a network component in the Satellite Network that controls one or more GTS.

The Mobile Earth Station (MES)

The Mobile Earth Station (MES) consists of the physical equipment used by a GMR-1 subscriber; it comprises the Mobile Equipment (ME) and the Subscriber Identity Module (SIM).


Page 117


The GeoMobile Radio (GMR-1) Satellite

The GMR-1 satellite consists of the physical equipment that provides gateway-mobile, mobile-gateway, and mobile-mobile communication connectivity.

The Advanced Operations Center (AOC)

The Advanced Operations Center (AOC) performs the services of centralized functions. These include performing management of the system and monitoring and controlling resource allocation to the gateway stations. The AOC may be collocated with one of the gateway stations.

The Traffic Control Subsystem (TCS)

The Traffic Control Subsystem (TCS) manages the real-time resources that are allocated to the Gateway Station by the AOC. The TCS manages the GMR-1 specific enhanced services and features which are not normally associated with GSM such as single hopped terminal-toterminal calls, optimal routing, high penetration alerting, and position based services. A 2.3 GSM-based services Standard services

The GMR-1 system provides a standard set of services based on the GSM phase 2 services. Roaming The GMR-1 system supports GMR subscribers roaming to GSM networks with their SIM card assuming appropriate roaming agreements are in place, and the participating networks can support GSM MAP protocols. Single number routing

The system can support dual mode GMR-1/GSM stations with automatic routing to a single number. Numbers and addressing

The GMR-1 system uses the same numbering and addressing scheme as in GSM with the exception of the location area identification (LAI) which is modified to accommodate spot beam identification and gateway station identification. Authentication and privacy

GMR-1 preserves GSM authentication and privacy features including TMSI security.


Page 118


A 2.4 Enhanced services and features

Several new integrated services are introduced into the GMR-1 system which are not integrated into conventional Phase 2 GSM.

Single-hopped terminal-to-terminal calls

In order to avoid the large delay associated with a double satellite hopped mobile terminal to mobile terminal call, such calls can be routed directly through the satellite from any terminal in any spot beam to any other terminal in any other spot beam as a single hopped call.

Optimal routing

The GMR-1 system allows MES originated calls to be optimally routed to a preferred GS, different than the GS to which the MES is registered. Criteria for optimal routing can include the subscriber’s service provider, the called party number and/or the MES position. The network functionality to support this feature resides in the TCS.

High penetration alerting

The GMR-1 system allows subscribers to be paged even when the MES is normally out of coverage area due to additional propagation path losses.

Position based services

Position based services depend on the use of the GPS satellite system to provide the raw position information to the GMR-1 user terminals. A 2.5 Protocol modifications

L-band radio interface The GMR-1 protocol architecture, shown in figure 3, is similar to GSM. However, the lower layers of the GMR-1 protocol contain several differences due to the combination of the physical reality of a very different propagation path and the enhanced services and features of the GMR-1 system. GSM cells are on the order of a few kilometers or less in radius, the propagation delay is a fraction of a millisecond and the path loss is model is characterized by Rayleigh fading. GMR-1 spot beams are on the order of a few hundred kilometers in radius, the one-way propagation delay via a geostationary earth orbit satellite system is approximately 270 milliseconds and the path loss model is characterized by Ricean fading with a typical k-factor of between 7 and 9.


Page 119


Furthermore, spectrum resources are typically more constrained in a satellite system as compared with a cellular system because the frequency reuse distance is much greater. For a terrestrial cellular system the exponential loss factor is typically 4 or more so that signals rapidly deteriorate beyond the cell boundary. Thus, frequencies can be reused within a few kilometers or a few tens of kilometers at most. In a satellite system, all spot beam signals are transmitted by the same satellite, a point source, and propagate with a free space exponential loss factor of 2 and the segregation between neighbouring spot beams is determined by the satellite antenna sidelobe performance. Frequencies can only be reused within hundreds or thousands of kilometers. It is therefore important that spectral efficiencies of mobile satellite systems be greater than terrestrial cellular systems. Since all spot beam signals are transmitted via the same satellite, the schedules for the broadcast of control channels from multiple spot beams can be coordinated, which benefits spot beam selection. Physical layer

The GMR-1 physical layer offers similar services to the GSM physical layer, but this layer contains substantial differences to accommodate the different radio propagation environment as described above. Data link layer

The data link layer protocol is a modified version of the GSM data link layer protocol. The data link layer modifications include the use of a selective reject and repeat protocol called group reject. The modifications also include larger window size and new timer values. Because of the additional propagation delay the radio link protocol (RLP) for data and telemetric services includes some phase 2+ features of GSM.

Radio Resource management sublayer

The radio resource (RR) management sublayer is modified from GSM to accommodate the physical differences in the radio interface. Of special note is the random access channel (RACH) procedure which is modified to accommodate the large differential path delay within a spot beam as well as to accommodate the enhanced services and features such as position based services, optimal routing and terminal-to-terminal call establishment, which are not part of the GSM phase 2 services.

Mobility Management sublayer

The mobility management (MM) sublayer entity in the MSC is unchanged from GSM. However, the peer entity in the MES is modified to accommodate position based services and optimal routing. The modifications to the mobility management protocol on the network side are handled by the TCS functional network element so that the MSC and the A-interface remain unchanged from the GSM specification.


Page 120


A 3 GMR-2 general system description A 3.1 Overview and system elements

The GMR-2 system provides voice, data, fax, and supplemental communication services between mobile and fixed/mobile users and worldwide connectivity through public and private switched telecommunications networks. Mobile communication services are provided in a large regional coverage area, defined by the orbital location of the geosynchronous satellite and satellite payload performance. The connectivity is provided by the satellite and fixed ground equipment, whose main elements are gateways and network control center. Examples are now given for the typical mobile coverage area, the system elements, and subscriber connectivity. The mobile coverage area defines where mobile services are provided. Subscribers located anywhere in this area have full use of system services. Figure A 5 shows an example coverage area that includes a portion of the Middle East, India, China, and Southeast Asia. The area is covered by a single C-band feeder-link beam for communication between the satellite and the ground equipment. The same area is covered by a large (140 in this example) number of Lband user-link spotbeams for communication between the satellite and the user terminals of the subscribers. As shown in the figure, the feeder-link and user-links also carry signalling information in addition to traffic communication. The spotbeams are highly focussed beams, providing signal concentration and making possible communication with a small handheld user terminal. Additionally, the spotbeams play the role of cells in a GSM system, allowing frequency reuse, while limiting interference between spotbeams using the same frequencies.

Geo Satellite

C -Band Feeder Link

Traffic Signalling

L -B a n d User Link

Signalling

T r affic

Regional Coverage Beam

C -B a n d R e g i o n a l C o v e r a g e B e a m f o r S i g n a l l i n g & C o m m u n i c a t i o n s

L -B a n d S p o t b e a m s f o r M S S U s e r

Figure A 5: Mobile Coverage region of an example system


Page 121


Figure A 6 shows the various system elements, including a geostationary satellite, a Network Control Center (NCC), a Satellite Control Facility (SCF), a Customer Management Information Center (CMIS), a number of Gateways, and a large number of user terminals, referred to as Mobile Earth Stations (MES) in the GMR-2 specifications. The user terminals (MES) include handsets, vehicle-mounted terminals, and fixed terminals. The Gateways have external interfaces to existing fixed telecommunications infrastructure, namely PSTN, PN and PLMN. From a functional point of view, the Gateways implement the radio modem functions of the terrestrial BTS, the radio resource management functions of BSC and switching functions of MSC, along with databases for subscriber data. These are shown in figure A 7. An example of traffic and signalling channels connectivity is shown in figure A 8. Two-way connectivity (of traffic and associated signalling) between a user terminal and fixed network subscriber uses L-band and C-band links to the satellite. Access to fixed telecommunications networks takes place through the Gateway. Fixed network connectivity includes the Public Switched Telephone Network (PSTN), Public Land Mobile Networks (PLMNs), and private networks (PN). Broadcast and Common control signalling channels are provided by the NCC and are used during initial call set up. A single hop user-to-user traffic link through the satellite uses L-band links. Call control for user-to-user circuits are performed by the NCC, Gateways, and by switching on the satellite, to achieve single-hop connectivity. Traffic Signalling

GEO Satellite

C-Band L-Band C-Band C-Band

User Terminals

Gateway 1

C-Band -

Shared RF/IF

PSTN PN PLMN

Satellite Control Facility Gateway 2

-


(Collocated facilities)

Gateway 3

Customer Mgmt Information System

PSTN PN PLMN

PSTN PN PLMN

Figure A 6: System Elements


Page 122


GA

TCE

RF/IF

GA= TCE= GSC = MSC =

PSTN PN GSM AMPS

MSC

GSC

Data Bases HLR & VLR

Gateway Antenna Traffic Channel Equipment Gateway Station Controller Mobile Switching Center

Figure A 7: Gateway Internal structure Legend for RF Links: 1) Call Traffic 2) Broadcast signalling 3) Common control signalling 4) Dedicated control signalling 5) Interstation communications 6) SCF-to-satellite communications

GEO Satellite

L- Band

2 1 C- Band

1

4

5

2

User Terminals

3

L- Band

3 5

6

To NCC

Gateway

4

C- Band

2

3

1

To SCF

4

Shared RF/IF


Satellite Control Facility PSTN PN PLMN

User Terminals

(Collocated facilities) Customer Mgmt Information System

Figure A 8: Connectivity in a GMR-2 system

A.3.2 Functional description of system elements

Table A 1 shows the top-level functions performed by each of the system elements given in the previous figure. Beacon receive terminals, described at the bottom of the table, are part of


Page 123


beam congruency operations. The example GMR-2 system uses separate L-band transmit and receive antennas and the Beam congruency system ensures that the corresponding beams are aligned on the ground.

System Element NCC, Network Control Center

Functional Description Network Management: Develop call traffic profiles; Manage system resources and network synchronization; Provide Operations & Maintenance functions; Manage inter-station signalling links; Perform congestion control; Provide support in user terminal commissioning. Call Control: Perform common channel signalling functions; Manage Gateway selection for mobile origination; Define payload configurations;

GW, Gateway

Manages dedicated signalling and traffic channels; Provide connectivity to external fixed networks; Perform mobility management; provide interoperability with AMPS and GSM; Provide authentication and encryption services; Assign frequencies/slots & map traffic channel equipment to beams; Provide support in user terminal commissioning.

SCF, Satellite Control Facility

Satellite Control: Generate & distribute satellite ephemera; Generate and transmit commands for payload & bus & receive and process telemetry; Transmit beam pointing commands for congruency; Generate and transmit commands for inclined orbit operations; Perform range calibration and real-time ranging; Call Control: provide real-time switching for mobile-mobile calls.

Satellite

Receive & implement payload and bus commands; Collect, process, and transmit telemetry & payload configuration data; Implement real-time switching for mobile-to-mobile calls.

CMIS, Customer Maintain Gateway configuration data; Perform system billing and accounting; process call detail records; Management Information System User Terminal Receive broadcast, paging, and access grant data; Perform call request, authentication, and encryption functions; Provide SIM capability; Transmit & receive two-way voice communication; Transmit DTMF signalling messages from handheld and vehicle phones over an established voice link; Provide interface for data and fax; Support commissioning procedures. Beacon Receive Receive forward beacons; Perform beam congruency measurements; Terminals

Table A.1: System Elements and Functional Descriptions

A.3.3 Features of the GMR-2 System GSM Roaming

The GMR-2 system supports GMR subscribers roaming to GSM networks with their SIM card assuming appropriate roaming agreements are in place, and the participating networks can support MAP protocols. The GMR-2 system also supports non-GMR GSM subscribers roaming to GMR-2 with their SIM card, assuming that appropriate roaming agreements are in place, and the participating networks can support MAP protocols.


Page 124


Single number routing

The GMR-2 system provides the capability to support dual mode GMR-2/GSM stations with automatic routing to a single number. The GMR-2 system also provides the capability to support dual mode GMR-2/AMPS stations with automatic routing to a single number.

Optimal MO-Call Routing

The GMR-2 supports optimal routing of MO calls, such that the landline segment of the endto-end connection is minimized. During call set-up, the NCC determines the gateway which is closest to the called PSTN terminal and assigns the call to that gateway. This procedure minimizes the landline costs of 'long-haul' calls.

Single-Hop Mobile-to-Mobile Voice Calls

Due to the large propagation delay, voice calls from a GMR-2 user to another GMR-2 user are implemented using switching on the satellite. This makes the connection a single hop connection and minimizes the end-to-end propagation delay.

Handovers

Due to the large size of the spotbeams, handovers from one spotbeam to another spotbeam are not necessary and are not implemented. However, intra-spotbeam handovers to different frequency, time slot and/or error correction coding assignments are supported to improve circuit quality in cases of local interference or blockage.

Satellite Power Control

Due to the fact that satellite power is shared among all the spotbeams of the GMR-2 system, a global power optimization is performed.