LTE: An Overview - WordPress.com

Centre Tecnol` ogic de Telecomunicacions de Catalunya

Long Term Evolution An Overview

Charalampos Kalalas Early Stage Researcher [email protected]

ADVANTAGE project February 9, 2015 Charalampos Kalalas (CTTC)

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Cellular Wireless Systems Evolution 1G (Early 1980s) I I I

Analog speech communications Analog FDMA Example: AMPS

2G (Early 1990s) I

I I

I

Digital modulation of speech communications Advanced security and roaming TDMA and narrowband CDMA Examples: GSM, IS-95 (cdmaOne), and PDC

3G (Late 1990s) I

I I

Global harmonization and roaming Wideband CDMA Examples: UMTS, cdma2000, and TD-SCDMA

Charalampos Kalalas (CTTC)

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3GPP evolution Long Term Evolution (LTE) I

I

3GPP work on the Evolution of the 3G Mobile System started in November 2004 Standardized in the form of Rel-8


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Requirements of LTE

Peak data rate I

100 Mbps DL/ 50 Mbps UL within 20 MHz bandwidth

Up to 200 active users in a cell (5 MHz) Less than 5 ms user-plane latency Mobility I I I

Optimized for 0 - 15 km/h. 15 - 120 km/h supported with high performance. Supported up to 350 km/h or even up to 500 km/h.

Enhanced multimedia broadcast multicast service (E-MBMS) Spectrum flexibility: 1.25 - 20 MHz Enhanced support for end-to-end QoS


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LTE Enabling Technologies

OFDM (Orthogonal Frequency Division Multiplexing) Frequency domain equalization SC-FDMA (Single Carrier FDMA) MIMO (Multi-Input Multi-Output) Multicarrier channel-dependent resource scheduling Fractional frequency reuse


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LTE Enabling Technologies

Single Carrier FDMA (SC-FDMA) I

SC-FDMA is a new single carrier multiple access technique which has similar structure and performance to OFDMA • Utilizes single carrier modulation and orthogonal frequency multiplexing using DFT-spreading in the transmitter and frequency domain equalization in the receiver

I

A salient advantage of SC-FDMA over OFDM/OFDMA is low PAPR • Efficient transmitter and improved cell-edge performance


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Key features of LTE

Multiple access scheme I I

DL: OFDMA with CP UL: Single Carrier FDMA (SC-FDMA) with CP

Adaptive modulation and coding I I

DL/UL modulations: QPSK, 16QAM, and 64QAM Convolutional code and Rel-6 turbo code

Advanced MIMO spatial multiplexing techniques I I

(2 or 4)x(2 or 4) downlink and uplink supported Multi-user MIMO also supported

Support for both FDD and TDD H-ARQ, mobility support, rate control, security, and etc.


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Protocol Architecture


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LTE Network Architecture E-UTRAN (Evolved Universal Terrestrial Radio Access Network)


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LTE Network Architecture

eNB I

All radio interface-related functions

MME I

Manages mobility, UE identity, and security parameters

S-GW I

Node that terminates the interface towards E-UTRAN

P-GW I

Node that terminates the interface towards PDN.


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LTE Network Architecture Services External Networks: Operator Services (IMS) and Internet

SGi

P-GW

PCRF

HSS

S5/S8

S6a

Gxc

S11 S10

S-GW

MME

S1-U

S1-MME

E-UTRAN

X2

eNodeB

Services Connectivity Layer

EPC

SAE GW

Gx

IP Connectivity Layer, The EPS

Rx

LTE-Uu

User Equipment UE


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LTE Network Architecture eNodeB Inter Cell RRM

RB Control

Connection Mobility Cont. MME

Radio Admission Control

NAS Security

eNodeB Measurement Configuration & Provision

Idle State Mobility Handling

Dynamic Resource Allocation (Scheduler)

EPS Bearer Control RRC

PDCP S-GW

RLC

MAC

PHY

P-GW

Mobility Anchoring

UE IP Address Allocation

S1

Packet Filtering Internet

E-UTRAN


EPC

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LTE Network Architecture User-Plane Protocol Stack Application IP

IP Relay

PDCP

Relay

PDCP

GTP-U

GTP-U

GTP-U

GTP-U

RLC

RLC

UDP/IP

UDP/IP

UDP/IP

UDP/IP

MAC

MAC

L2

L2

L2

L2

L1

L1

L1

L1

L1

LTE-Uu

S1-U

UE

eNodeB

L1 S5/S8a

S-GW

SGi P-GW

Control-Plane Protocol Stack NAS

NAS Relay

RRC

S1-AP

PDCP

PDCP

SCTP

RLC

RLC

IP

IP

MAC

MAC

L2

L2

L1

L1

L1 LTE-Uu UE


S1-AP

RRC

SCTP

L1 S1-MME

eNodeB

SGi MME

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Frame Structure

Two radio frame structures defined I I

Frame structure type 1 (FS1): FDD Frame structure type 2 (FS2): TDD

A radio frame has duration of 10 ms A resource block (RB) spans 12 subcarriers over a slot duration of 0.5 ms. One subcarrier has bandwidth of 15 kHz, thus 180 kHz per RB


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Frame Structure Type 1 FDD frame structure One frame, 10 ms

#0

#1

#2

...

#3

#18

#19

One slot 0.5 ms One subframe, 1 ms

0

1

2

3

4

5

6

7 OFDM symbols (short CP)


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Frame Structure Type 2 TDD frame structure


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Resource grid

6≤N≤110 Resource Blocks

20 slots = 1 frame (10 ms) 

                   

... . . .

. . .

. . .

. . .

. . .

. . .

2 slots = 1 subframe = TTI (1 ms)

             

Number of subcarriers

frequency

time

  

Number of symbols


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Length of CP


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LTE Bandwidth/Resource Configuration


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Bandwidth Configuration


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LTE Physical Channels

DL I I I I I I

Physical Physical Physical Physical Physical Physical

Broadcast Channel (PBCH) Control Format Indicator Channel (PCFICH) Downlink Control Channel (PDCCH) Hybrid ARQ Indicator Channel (PHICH) Downlink Shared Channel (PDSCH) Multicast Channel (PMCH)

UL I I I

Physical Uplink Control Channel (PUCCH) Physical Uplink Shared Channel (PUSCH) Physical Random Access Channel (PRACH)


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LTE Transport Channels

Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers. DL I I I I

Broadcast Channel (BCH) Downlink Shared Channel (DL-SCH) Paging Channel (PCH) Multicast Channel (MCH)

UL I I

Uplink Shared Channel (UL-SCH) Random Access Channel (RACH)


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LTE Logical Channels

Logical channels are offered by the MAC layer Control Channels: Control-plane information I I I I I

Broadcast Control Channel (BCCH) Paging Control Channel (PCCH) Common Control Channel (CCCH) Multicast Control Channel (MCCH) Dedicated Control Channel (DCCH)

Traffic Channels: User-plane information I I

Dedicated Traffic Channel (DTCH) Multicast Traffic Channel (MTCH)


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Channel Mappings


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LTE layer 2 Layer 2 has three sublayers I I I

MAC (Medium Access Control) RLC (Radio Link Control) PDCP (Packet Data Convergence Protocol)


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RRC layer

Terminated in eNB on the network side Functions I I I I I I

Broadcast Paging RRC connection management RB (Radio Bearer) management Mobility functions UE measurement reporting and control

RRC states I I

RRC IDLE RRC CONNECTED


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UE states In LTE, a terminal can be in two different states, RRC CONNECTED and RRC IDLE.


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UE states In RRC IDLE, There is no RRC context in the radio-access network and the terminal does not belong to a specific cell. No data transfer may take place as the terminal sleeps most of the time in order to reduce battery consumption. Uplink synchronization is not maintained and hence the only uplink transmission activity that may take place is random access, to move to RRC CONNECTED. When moving to RRC CONNECTED The RRC context needs to be established in both the radio-access network and the terminal. Compared to leaving DRX this takes a somewhat longer time. In the downlink, terminals in RRC IDLE periodically wake up in order to receive paging messages, if any, from the network.


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Resource Scheduling of Shared Channels

Dynamic resource scheduler resides in eNB on MAC layer Radio resource assignment based on radio condition, traffic volume, and QoS requirements Radio resource assignment consists of: I I

Physical Resource Block (PRB) Modulation and Coding Scheme (MCS)


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Default schedulers

1. Round-robin (RR) scheduler, where channel conditions are not taken into account. 2. Proportional-fair (PF) scheduler, where short-term channel variations are exploited while maintaining the long-term average user data rate. 3. Max-C/I scheduler, where the user with the best instantaneous channel quality in absolute terms is scheduled.


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Radio Resource Management

Radio bearer control (RBC) Radio admission control (RAC) Connection mobility control (CMC) Dynamic resource allocation (DRA) or packet scheduling (PS) Inter-cell interference coordination (ICIC) Load balancing (LB)


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LTE Bearer Establishment

E-UTRAN

UE

EPC

eNodeB

S-GW

Internet

Peer Entity

P-GW

End-to-end service External bearer

EPS bearer E-RAB Radio bearer

Radio


S5/S8 bearer S1 bearer

S1

S5/S8

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SGi

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QoS Provisioning

Priority

Packet delay budget (ms)

Packet loss rate

1

2

100

10−2

Conversational Voice

2

4

150

10−3

Conversational Video (Live Streaming)

3

50

10−3

Real Time Gaming

4

5

300

10−6

Non-Conversational Video (Buffered Streaming)

5

1

100

10−6

IMS Signaling

6

6

300

10−6

QCI

3

Resource type

GBR

Example services

Video (Buffered Streaming), TCP-based (e.g. www, e-mail, ftp, p2p file sharing, etc.) 7

Non-GBR

7

8

8

9

9

100

10−3

Voice, Video (Live Streaming), Interactive Gaming

300

10−6

Video (Buffered Streaming) TCP-based (e.g. www, e-mail, ftp, p2p file sharing, etc.)

Table: Standardized QCI characteristics


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Other features

ARQ (RLC) and H-ARQ (MAC) Mobility Rate control DRX (Discontinuous Reception) MBMS QoS Security


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DL overview

DL physical channels I I I I I I

Physical Physical Physical Physical Physical Physical

Broadcast Channel (PBCH) Control Format Indicator Channel (PCFICH) Downlink Control Channel (PDCCH) Hybrid ARQ Indicator Channel (PHICH) Downlink Shared Channel (PDSCH) Multicast Channel (PMCH)

DL physical signals I I

Reference signal (RS) Synchronization signal

Available modulation for data channel I

QPSK, 16-QAM, and 64-QAM


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DL Physical Channel Processing


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DL Reference Signal


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DL MIMO

Supported up to 4x4 configuration. Support for both spatial multiplexing (SM) and Tx diversity (TxD) I SM • Unitary precoding based scheme with codebook based feedback from user. • Multiple codewords I

TxD: SFBC/STBC, switched TxD, CDD (Cyclic Delay Diversity) considered

MU-MIMO supported


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UL Overview

UL physical channels I I I

Physical Uplink Shared Channel (PUSCH) Physical Uplink Control Channel (PDCCH) Physical Random Access Channel (PMCH)

UL physical signals I

Reference signal (RS)

Available modulation for data channel I

QPSK, 16-QAM, and 64-QAM


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UL Rersource Block


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UL Physical Channel Processing


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SC-FDMA Modulation in LTE UL


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Random Access Non-synchronized random access Open loop power controlled with power ramping similar to WCDMA RACH signal bandwidth: 1.08 MHz (6 RBs) Preamble based on CAZAC sequence


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Other procedures

Synchronization procedures I I I

Radio link monitoring Inter-Cell synchronization for MBMS Transmission timing adjustments

Power control for DL and UL UE procedure for CQI (Channel Quality Indication) reporting UE procedure for MIMO feedback reporting UE sounding procedure


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Device-to-device communication No Network assistance

Network assistance

Licensed spectrum (D2D-dedicated or cellular, controlled interference)

Unlicensed spectrum (unpredictable interference)


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Network-assisted D2D communication

Cellular communication

Network control

Direct (D2D) communication

Direct device-to-device communications imply that wireless devices in the proximity of each other communicate in a peer-to-peer fashion without the user-plane involvement of a cellular infrastructure Charalampos Kalalas (CTTC)

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Release 12

Although LTE is capable of handling a wide range of machine-type communication scenarios already from the first release, several improvements are being discussed as part of the release-12 work, for example: Support low-cost and low-complexity device types to match low performance requirements (for example in peak data rates and delay) of certain MTC applications. Allow for very low energy consumptions for data transfers to ensure long battery life. Provide extended coverage options for MTC devices in challenging locations. Handle very large numbers of devices per cell.


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Relaying

In the context of LTE, relaying implies that the terminal communicates with the network via a relay node that is wirelessly connected to a donor cell using the LTE radio-interface technology. From a terminal point of view, the relay node will appear as an ordinary cell.


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Heterogeneous deployments

Heterogeneous deployments refer to deployments with a mixture of network nodes with different transmit power and overlapping geographical coverage. A typical example is a pico node placed within the coverage area of a macro cell


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Summary

Key technologies of LTE system I

Multicarrier-based radio air interface

I

I

IP-based flat network architecture Multi-input multi-output (MIMO) Active interference avoidance and coordination

I

Fast frequency-selective resource scheduling

• OFDMA and SC-FDMA I

• Fractional frequency re-use (FFR)


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Summary


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References

1. S. Sesia, I. Toufik, and M. Baker, LTE: The UMTS Long Term Evolution from theory to practice. John Wiley & Sons Ltd., 2009. 2. 3GPP, ”Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” March 2010. 3. A. Larmo, M. Lindstrom, M. Meyer, G. Pelletier, J. Torsner, and H. Wiemann, ”The LTE link-layer design,” Communications Magazine, IEEE, vol. 47, pp. 5259, Apr. 2009. 4. E. Dahlman, S. Parkvall, and J. Skld, ”Chapter 6 - Scheduling, Link Adaptation, and Hybrid ARQ,” in 4G LTE/LTE-Advanced for Mobile Broadband (E. Dahlman, S. Parkvall, and J. Skld, eds.), pp. 79 93, Oxford: Academic Press, 2011.


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Acknowledgement

Current research receives funding from the European Community’s Seventh Framework Programme (FP7-PEOPLE-2013-ITN) under grant agreement no 607774


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