Integration of Broadband Wireless Technologies ... - Semantic Scholar

Fourth International Conference on Networking and Services

Integration of Broadband Wireless Technologies and PMR Systems for Professional Communications Annalisa Durantini, Marco Petracca

Francesco Vatalaro

RadioLabs Consorzio Universit`a Industria Laboratori di Radiocomunicazioni Rome, Italy

University of Rome Tor Vergata Via del Politecnico 1 Rome, Italy

Fulvio Ananasso

access technologies are needed to achieve target performances for applications such as Emergency and Medical Services, Video Streaming, bulky file transfer, remote access to database and applications, location based services. With reference to the latter case, it should be noted that broadband access is required to handle data collected from a high density sensor network and to quickly refresh location information. Some critical issues are to be faced in order to allow data sharing among different networks, related to items such as Access Control and Command and Control. Intense research activity on this topic has been promoted in recent years [7], [8] and network level solutions have been suggested. In the paper we present a system architecture able to guarantee a wide variety of services under any type of emergency conditions and to acquire and disseminate information in a capillary fashion, by integrating heterogeneous communication standards, such as TETRA, Simulcast (analogical PMR network), WiFi, WiMAX and GSM/GPRS/UMTS. The integrated platform ensures network adaptability to resources availability, user profile and requested Quality of Service (QoS), as well as extreme resilience in all emergency conditions. Interoperability is achieved through the introduction of interworking gateways (GW), as well as mobility agents. To make continuous network coverage possible for mobile users regardless of their location, Mobile IP is employed. It is independent from the access technology and it allows IP-based applications to keep an active session during vertical handover (VHO). However, in order to achieve complete convergence among heterogeneous networks, it is also necessary to provide the user with a multimode terminal, which can automatically select and switch to the most proper access network, in line with an Always Best Connected (ABC) approach. In order to prove and to assess the performances of the integration platform, some applications are tested where audio and data services are shared among coexisting digital and analogue systems. The advantages of networks integration are also outlined for an infrastructure free environment which is a quite common scenario occurring in emergency or disaster situations. The paper is organized as follows. In Section II the issues related to regulatory framework are debated. In Section III we show the envisaged scenarios for operation of devised PSDR mobile integration solution. In Section IV we describe

Abstract— The paper contributes to the evolution of Public Safety and Disaster Relief (PSDR) communications by specifying a solution for interoperability and integration among Professional Mobile Radio systems (TETRA and Simulcast), public systems (GSM/GPRS/UMTS), and broadband wireless technologies, such as WiMAX. A policy for PSDR services scheduling and fundamental guidelines for mapping the quality of service over heterogeneous networks are presented. Hence, the paper outlines the key issues to be debated by a regulatory authority. Operation of the devised PSDR mobile integration solution is tested to ensure complete connectivity among users adopting different communication standards, as well as to enable distributed services provisioning guaranteeing always best connection to bandwidth demanding applications provided by an IP-based core network. Finally, the employment of the envisaged integration platform is detailed in Mobile Ad-Hoc and Wireless Sensor Networks.

I. I NTRODUCTION Ensuring reliable, continuous and high quality communications is a fundamental goal in emergency situations to the aim of guaranteeing efficient interventions and optimizing mission critical management. To meet the evolving needs of the Public Safety and Disaster Relief (PSDR) market, substantial benefits come from the realization of a platform that enables interoperability and integration between Private Mobile Radio (PMR) systems such as Terrestrial Trunked Radio (TETRA), public communication networks, and broadband systems. TETRA [1] is the telecommunication standard for PMR systems deployed by ETSI to provide network controlled services and direct mobile to mobile communications, with a range of functionalities such as group calls, instantaneous connections of calls, encryption, real time localization, high priority connections. TETRA interoperability and integration with other narrowband and/or broadband systems results to be useful in order to ensure complete connectivity in emergency scenarios, such as interconnection of relief squads using different communication standards, e.g. due to different existing infrastructures or user needs. An integrated network solution also enables distributed services provisioning. According to the Next Generation Network (NGN) paradigm, the mobile users seamlessly access heterogeneous networks (including ad hoc networks) for reaching a common IP-based core network and enjoying various services and multimedia sessions via an unique multi-mode personal device. In particular, broadband

0-7695-3094-X/08 $25.00 © 2008 IEEE DOI 10.1109/ICNS.2008.30

Alberto Civardi

Selex Communications AGCOM - Autorit`a per le Genoa, Italy Garanzie nelle Comunicazioni Naples, Italy

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the system architecture both for data communications and supervisory control and data acquisition in a heterogeneous network environment. In Section V we report results about some significant applications tested to assess the performances of the integrated platform. Hence, in Section VI we suggest a policy for PSDR services scheduling. In Section VII we define the fundamental guidelines for mapping the quality of service over heterogeneous networks. In Section VIII we detail the employment of integration platform in an infrastructureless environment. Finally conclusions are drawn in Section IX. II. R EGULATORY F RAMEWORK The goal of interoperability and integration among different public safety organizations should be also faced from a regulatory point of view. In fact, the integrated system architecture is not a single network, but a collection of networks operated either by the same or by different service providers. At each network boundary a network interconnection is required. Network interconnection agreements are put in place to cover not only items such as interconnection points, signaling, timing, billing and tariffs, bearer transport, but also the regulatory requirements needed to guarantee fair and non-discriminatory conditions. In order to optimize flexibility and resilience of the integrated system architecture, communications services should be provided both by full-service networks and by layered contributions of independent suppliers. The essence of access regulation is to delink the services provisioning layers, allowing multiple service providers to participate in the chain of production on terms subject to government control. The network and service convergence process which is taking place makes the differences among the various networks less accentuated. In particular, the use of the Internet Protocol (IP), as the common platform for all communications, reduces such differences considerably, especially at the level of the central architecture of the transmission infrastructure, that is the core network.

Fig. 1. Integrated network architecture for communications and data networking.

means of devices like a VoIP Gateway (GW) and a Softswitch located at the edges of two infrastructures. As an evolution of this case, an advanced softphone can be embedded in the portable terminal to reproduce some main TETRA features. 2) Other scenarios consider the opportunity for PSDR customers to obtain services from a core network or to communicate with each other through technology that offers best performances with regard to traffic and service type. Some representative cases are listed below: •

III. O PERATIONAL S CENARIOS As already mentioned, convergence between TETRA and other access technologies can be achieved by addressing both network level and terminal level functionalities. We report same typical examples, inherent to the most attractive applications of technology. With reference to overlapping scenarios, i.e. overlapping radio coverage of heterogenous networks, and non overlapping scenarios, it is possible to identify some fundamental cases of interest, showing an increasing integration level: 1) This scenario refers to the situation of people from different organizations that use their own access network to interact and to exchange voice or data, by accessing a common platform. In particular, we can refer to the case of a non TETRA customer equipped with a simple-mode device with standard Voice over IP (VoIP) softphone which gains access (by authority received) to services supplied by the TETRA core network or communicates to a TETRA customer. Interoperability is possible by

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User terminals are connected to a vehicular device, the multi-mode mobile router device. It is a wireless network entity, in charge of enabling convergence by selecting the most appropriate radio carrier based on traffic type and service requirements and in accordance with a policy of PSDR services scheduling. Realization of mobile multi-mode hand-held terminals, able to access TETRA as well as other available networks, discriminating the most suitable technology based on an opportune policy and eventually maintaining more than one active session at the same time, in order to preserve quality of service in mobility conditions. IV. S YSTEM A RCHITECTURE

Figure 1 shows the system architecture of the mobile integration solution envisaged for mission critical communications.

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wireless network, multihoming strategies are needed to the purpose of balancing the network load evenly among different networks and optimally associating traffic flows of different applications to different radio bearers. Smart data and voice routing, based on user profile, context information, service typology and traffic features, is supported by MN with multiple wireless interfaces, able to attach to various networks and obtain multiple IP addresses simultaneously.

A. User Equipment In order to access at the same time various technologies, the end-user can utilize two types of terminals: a simple-mode terminal able to connect to a vehicular device, the Mobile Node (MN), i.e. a multi-mode mobile router and, in a more evolute scenario, a multi-mode hand-held terminal able to access different networks according to coverage or communication resource availability. Both hand-held and vehicular terminals support localization services such as Automatic Vehicle/Person Localization (AVL/APL) via GPS and inertial correction localizer. The vehicular TETRA terminal is also able to monitor vehicle status (speed, engine status, trip data). As Figure 1 shows, the MN can participate a mesh network operating both in infrastructure and in ad-hoc network mode. In that case, MNs host a Mesh network client, as well as a Mobile IP client for mobility management. Instead, Mobile IP Foreign Agent is embedded in network elements denoted as Mesh Nodes. They implement automatic neighboring nodes search and they support dynamic routing. Both multi-mode MNs and Mesh Nodes are multi-radio devices able to guarantee multiple radio links to other mesh nodes by means of 802.11b/g/a [4]–[6]. MN guarantees ”always-on connectivity” by network interfaces toward different access technologies, such as TETRA, GSM, GPRS, WiFi and WiMAX, and it allows digital and analogue systems to coexist and to share voice and data services. In civil/public safety missions the MN supports voice switching, IP routing, data/voice applications between heterogeneous systems, both public and private. The main MN functionalities can be summarized as follows: • •

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B. Network Elements TETRA terminals connect to a TETRA radio Base Station (BS), which is controlled by the TETRA Switching Node. It is the network component where the main switching networking, gateway, database management and interfacing capabilities for the system are located. It has interfaces towards BSs, Dispatchers, other TETRA Switching Nodes, SoftSwitch and Network Management System. The TETRA Switching Node can be considered the core part of the TETRA network and it offers call management (individual calls, half duplex and fullduplex, group and emergency calls), resource management, mobility management and all the services specified by TETRA standard [1], such as short data service (SDS), circuit and packet data transmission. TETRA Switching Node uses a distributed switching capability with an Ethernet/IP interconnection bus and integrates a networking IP platform. Moreover, it is able to schedule packet traffic based on QoS and to provide node connectivity with an external IP network. System architecture also encompasses WiMAX technology [2], [3]. In particular, the Access Service Network (ASN) GW is compliant with profile C, in accordance with WiMAX Forum specifications. All available technologies in the area share a common IP network. TETRA and Simulcast can access the IP network through a VoIP gateway that converts the analogue and digital voice signal to VoIP protocol. The VoIP ”flows” are managed by the Softswitch equipment. The IP Network provides switching capabilities between different analogue and digital PMR technologies, as well as inter-systems mobility services. The Application Network is responsible for services sharing among the different network technologies. It includes Application servers, AVL servers and VoIP dispatchers, able to communicate with TETRA, Simulcast and VoIP terminals. The Management Network is constituted by the network management system and by the provisioning and accounting graphic user interface (GUI).

HW discovery, i.e detection of network interfaces; Management of Layer 2 triggers (according to an IEEE 802.21-like approach): MN detects the events at each network interface and notifies the measurements related to the handover; it offers a set of commands for checking the status of the links involved in the handover procedure and it provides an information model and a data collection useful to optimize the handover process, such as features relating to services and performances offered by networks in the operative environment (handover manager); Management of connection establishment, based on security, mobility and quality of service degree required for target application (policy decision function and connection manager); Interface to MIP for mobility management based on a defined policy; Network mobility (NEMO) management, to maintain the session continuity between the mobile network nodes and their correspondent nodes, as well as to guarantee the reachability of the mobile network, upon the MN’s change of point of attachment; Support of security, mobility and QoS policies to be employed during handover decision phase, connection establishment and traffic routing (policy based and context aware routing entity); Multihoming capabilities: in a heterogeneous overlay

V. S YSTEM P ERFORMANCE VALIDATION In order to verify the performances of the integration platform and to prove the efficiency of network elements, sharing of voice and data services across heterogeneous networks is demonstrated by deploying a test bed in scenarios of cooperation between different public safety organizations in emergency situations: • Voice services: – VoIP Call between a WiFi PDA (within WiFi coverage area) and a TETRA mobile terminal (within

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TETRA coverage area): the user equipped with WiFi PDA calls TETRA user; VoIP Gateway converts the digital voice signal into VoIP signaling; the Softswitch switches the voice call between these technologies to establish communication. – A VoIP Dispatcher communicates to all users belonging to TETRA, Simulcast and other networks and it dynamically creates heterogeneous groups enabling group communication across networks. Data services: TETRA users can enjoy advanced data services by using broadband access technologies (WiFi/WiMAX) as overlay networks to TETRA narrowband network infrastructure, as shown in the following scenarios: – First case concerns the simultaneous transfer of data flows toward an application server via multiple carriers. In particular, a video streaming H264 is transmitted from a camera located on a running car to a video server by TETRA/WiFi connection: before the car leaves, the UDP H264 video session is started by the multi-mode terminal and WiFi network; hence video transmission continues while the car moves within WiFi coverage area. An operator managing video server verifies the effective reception of H.264 frames. The video stream is sent at the same time through TETRA and WiFi networks in LOS condition, at the rate of 1 frame/s on the TETRA link and 30 frame/s on the WiFi link, respectively. The result seen on the display of a dispatcher station can be classified as Excellent for WiFi and Good for TETRA using the ACR scale (Absolute Category Rating). – Second scenario refers to a situation where vertical handover is required, while accessing an IP application server (e.g. FTP, Web) of the Intranet from a running car. A TCP session is activated from PC on board; once the effective reception of data from server is verified, an operator drives the car across WiFi/TETRA coverage area. Since TETRA coverage exceeds WiMAX service area, VHO between TETRA and WiMAX is performed across the two networks, obtaining about 1 sec of hand-off time, and the session is kept active.

Ratio), as regards the physical layer; throughput, available bandwidth, traffic congestion, Frame Loss Rate (before retransmission), jitter (for voice and video services), as for the MAC layer; link security level, as concerns the administrative issues. Once the presence of a wireless network is detected, the user can obtain services choosing one out of the accessible network connections, according to the following policies: 1) Service Level Agreement (SLA) established with the network service provider; 2) Availability of radio resources and load balancing; 3) QoS level required by the particular service type. For each link parameter a dynamic threshold is defined to perform VHO. 4) Class of Service as determined by the criticality of the actual communication. Each service is classified, e.g. mission-critical, critical, non-critical, and associated to a specific class. 5) Cost for the particular service in each network; 6) Security level provided by the network. Application

AUDIO Conversational voice (Real time) Voice messaging (Interactive) DATA Telemetry control (Real time) Biodynamic vital data sampling, including ECG (Data Transfer) or Real time) Web browsing (Interactive) E-mail with attachments (Interactive) Bulk data transfer/retrieval (Streaming) Image (Streaming) VIDEO STREAMING Broadcast Desktop video

VI. C ONTEXT- AWARE PSDR S ERVICES S CHEDULING The goal of seamless service can be achieved, provided that the user terminal implements functionalities such as automatic detection of available wireless networks, discovery of provided resources, support of policy-based and dynamic network selection, updating of information about current network. In order to enjoy services, the user seamlessly exploits different access technologies by means of a multi-mode mobile device able to rapidly detect all wireless networks in the area which it can connect to. Link status and quality are checked and compared with reference to some significant parameters: BER (Bit Error Rate), RSSI (Link signal strength) and SNR (Signal to Noise

Videophone/ video conference Internet terminal

Typical bit rate

Parameters and target values End-to-end one-way delay

Delay variation

4 − 25 kbit/s

< 150 ms preferred < 400 ms limit

< 1 ms

4 − 13 kbit/s

< 1 s for playback; < 2 s for record

< 1 ms

28.8 kbit/s

< 250 ms

NA

20 − 50 kbit/s

< 250 ms

NA NA

10s− 100s kbit/s

< 4 s/page

NA

100s kbit/s