Wireless networks - Lecture 20: EDGE

Wireless networks - Lecture 20: EDGE. The main topics covered in this chapter include: walsh codes; IS-95 reverse link; EDGE introduction; modulation and coding schemes; link adaptation and incremental redundancy; capacity planning; dynamic abis pool;...

Wireless Networks

Lecture 20EDGE

Dr Ghalib A Shah

 Link Adaptation and Incremental Redundancy

 Capacity Planning

► Self-jamming, near-far problem, soft handoff

Forward Link Channel ParametersChannel Sync Paging Traffic rate Set 1 Traffic Rate Set 2

IS-95 Reverse Link

 Consists of upto 94 logical channels each

occupying same bandwidth of 1228 KHz

 It supports 32 access channels and 62 traffic

channels

 Access channel is used to initiate a call, to

respond to paging channel and for location

update

 In reverse, convolutional encoder has a rate of

1/3, thus trippling the effective rate to a max of 28.8 kbps

IS-95 CDMA Reverse Channel

 Uses OQPSK for power efficiency and QPSK

demodulation is easy

 No spreading of the data using orthogonal

codes

► Data coming out of the block interleaver are grouped

in units of 6 bits that serves as an index to select a row of the 64x64 Walsh matrix and that row is

substituted for the input

► Thus data rate is expanded by a factor of 64/6 to

307.2 kbps

Enhanced Data rates for GSM Evolution

 GPRS data rates still fall short compared to

that promised by 3G

 The delay in deployment of 3G technology led

to the emergence of EDGE

 Phase 1 (Release’99 & 2002 deployment)

supports best effort packet data at speeds up

to about 384 kbps

 Phase 2 (Release’2000 & 2003 deployment)

will add Voice over IP capability

GPRS Architecture

BTS

BTS MS

EDGE Functionality

Similar to GPRS but

some changes for higher

data rates Important

change is modulation

scheme

 GMSK is used in GPRS, only one bit per

symbol is used

 In EDGE, Octogonal PSK (8-PSK) is used

which enables a threefold higher data rate of 59.2 kbps per radio time slot

► Achieved by transmitting 3 bits per symbol.

 GMSK has constant amplitude modulation

while 8-PSK has variations in amplitude

 This changes the radio frequency

characteristics requiring changes in BS

 minor changes in hardware and software in

existing systems, leads to major changes in

network performance

► Coding Scheme: nine modulation and coding

schemes (MCS) that provide different throughput as shown in table

Payload Format

37 octets 37 octets 37 octets

37 octets MCS­3

MCS­6 Family A

MCS­9

28 octets 28 octets 28 octets

28 octets MCS­2

MCS­5

MCS­7 Family B

22 octets MCS­1

34+3 octets 34+3 octets

► Based on this coding, a data rate of 8 x 59.2 =

473kbps can be achieved

throughput

decreased sensitivity of the system This has impact

on coverage and in turn network planning

between different coding schemes takes place easily

i.e data block can be sent with better protection on failure

► not possible in GPRS to switch to different coding

scheme on reception failure , retransmission uses the

Link Adaptation and Incremental

Redundancy

 Link Adaptation (LA)

► As propagation condition changes, quality of signal

changes  MCS changes all the time

► LA is used for maximizing the throughput per

channel by changing the coding scheme

► LA algorithms are based on bit error probability

(BEP) measurements

► Improves the throughput and is done by

automatically adapting the transmitted redundancy

to the channel conditions

► Achieved through ARQ and FEC

Incremental Redundancy (IR)

 Send redundancy only if necessary

 Generalized Type-II ARQ

► Finer granularity of code rate

Rate 1 1st attempt

Rate 1/2 2nd attempt

Rate 1/3 3rd attempt

Transmitter Receiver

State Diagram for IR

Data

Block DetectionError

ARQ

Error Detection

Accept data block

No error

Deliver to upper layer

Capacity Planning in EDGE

some aspects of planning

different frequencies.

three sites/cluster, wherein each site is three sectored

each other

 The actual reuse employed - for traffic or control - is operator

controlled and limited only by the available spectrum

 Typically, 4/12 is used for control and 1/3 for traffic However,

other combinations are also possible subject to performance

requirements, environment and spectrum availability.

1/3 Frequency Re-use (EDGE Compact)

• 3 x 200 kHz carrier, reused in every site 

• <1MHz x 2 initial deployment

• 3 sectors per site

 EDGE-capable and non-EDGE-capable TRX in a one

sector can be configured to have only one BCCH

GPRS and EDGE radio network to be multiplexed

dynamically on one time slot

suffers in both the uplink and downlink

► In UL, GPRS suffers due to large amount of 8-PSK

retransmissions.

► In DL, it is due to GMSK modulation where 8-PSK can carry

higher data rate for EDGE

Dynamic Abis in EDGE

channels and static for GSM/GPRS

which is insufficient for data beyond MCS2

concept is used in EDGE

(DAP) for data calls from EGPRS when needed

 For Operators

 IS-95 Reverse Link

 Link Adaptation and Incremental Redundancy

 Capacity Planning

► WCDMA