Gprs Edge Channel Coding (Hss-spg)

GPRS GP RS/E /EDG DGE E Channel Chann el Cod Codii ng

GSM/EDGE lecture Nov 2004

© 2002 Hughes Software Systems Ltd.

Ag A g en end da

2

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RLC/MAC Bl Block St Structure

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GPRS GP RS/E /EGP GPRS RS Ch Chan anne nell Co Codi ding ng Ov Over ervi view ew

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GPRS Ch Channel Co Coding

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EGPRS Channel Coding

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GPRS GP RS/E /EGP GPRS RS Con Contr trol ol Cha Chann nnel el Cod Codin ing g


3

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RLC/MAC Bl Block St Structure

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GPRS GP RS/E /EGP GPRS RS Ch Chan anne nell Co Codi ding ng Ov Over ervi view ew

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GPRS Ch Channel Co Coding

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GPRS GP RS/E /EGP GPRS RS Con Contr trol ol Cha Chann nnel el Cod Codin ing g


Pack cke et Segm gme ent nta ati tion on • Se Segm gmen enta tati tion on an and d Fra Frami ming ng

Layer

Segment

Segment

FH

Segment

4


114 bits

RLC/MAC

Physical

456 bits Burst

LLC/RLC

Block

BCS Tail

SNDCP

LLC

½ rate convolution codeing Segment Segment

BH

114 bits

Segment

Frame

FCS

Segment

Burst

Network (e.gTCP/IP)

N-PDU

PH

Burst

Burst

114 bits

114 bits

PH FH FCS BCS BH

Packet Header Frame Header Frame Check Sequence Block Check Sequence Block Header

RLC/MAC Block Structure

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Different RLC/MAC block structures are defined for data transfers and for control message transfers.

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The RLC/MAC block structures for data transfers are different for GPRS and EGPRS. The RLC data units contains octets from one or more LLC PDUs.

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The same RLC/MAC control message block structure is used for control message transfers for GPRS and EGPRS.

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The RLC/MAC Blocks undergo channel coding


RLC/MAC Blocks •

The RLC/MAC block for GPRS data transfer RLC/MAC block RLC data block

MAC header RLC header

•

RLC data unit

Spare bits

The RLC/MAC block for EGPRS data transfer. MCS-1,2,3,4,5 and 6 have one RLC data block, whereas MCS-7,8 and 9 have two RLC data blocks RLC/MAC block RLC/MAC header

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RLC data block 1

RLC data block 2 (conditional)

The RLC/MAC block for GPRS/EGPRS control message RLC/MAC block

MAC header

6


RLC/MAC control block


7

8

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Different RLC/MAC block structures are defined for data transfers and for control message transfers.

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The RLC/MAC block structures for data transfers are different for GPRS and EGPRS. The RLC data units contains octets from one or more LLC PDUs.

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The same RLC/MAC control message block structure is used for control message transfers for GPRS and EGPRS.

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The RLC/MAC Blocks undergo channel coding


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GPRS/EGPRS Channel Coding Overview

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GPRS Channel Coding

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GPRS/EGPRS Control Channel Coding


Packet Data Channel coding •

Packet channel characteristics/requirements’ – Retransmissions/delay possible – Link adaptability required – RLC Header information needs better protection – Capability to handle high payload – if possible re-use existing channel coding functions

9


GPRS/EGPRS Channel Coding •

Thirteen coding schemes are specified for the packet data traffic channels. CS1-4 and MCS1-9

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GPRS – Four coding schemes, CS-1 to CS-4, are defined for the GPRS packet data traffic channels – For all other GPRS packet control channels except PRACH and PTCCH/U, coding scheme CS-1 is always used

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EGPRS – Nine modulation and coding schemes, MCS-1 to MCS-9, are defined for the EGPRS packet data traffic channels – The RLC/MAC header part is independently coded from the data part to provide stronger header protection

10


GPRS/EGPRS Coding Schemes • GMSK Modulation is used for GPRS CS1-4 coding schemes and MCS schemes MCS1-4 • For higher payload schemes MCS5-9, 8PSK modulation is used Coding Scheme

11

Modulatio n

Payload Bytes per Radio Block

Gros rate on RLC/MAC (including protocol overhead) [kbit/sec]

CS – 1

GMSK

22

8.8

CS – 2

GMSK

32

12.8

CS – 3

GMSK

38

15.2

CS – 4

GMSK

52

20.8

MCS-1

GMSK

22

8.8

MCS-2

GMSK

28

11.2

MCS-3

GMSK

37

14.8

MCS-4

GMSK

44

17.6

MCS-5

8-PSK

56

22.4

MCS-6

8-PSK

74

29.6

MCS-7

8-PSK

2x56

44.8

MCS-8

8-PSK

2x68

54.4

MCS-9

8-PSK

2x74

59.2

GSM – GPRS

GSM – EGPRS


USF coding • The USF has 8 states, which are represented by a binary 3 bit field in the MAC Header • For CS-1, the whole Radio Block is convolutionally coded and USF needs to be decoded as part of the data • Coding schemes CS-2 to CS-4 and MCS-1 to MCS-4 – generate the same 12 bit code for USF. The USF can be decoded either as a block code or as part of the data – the first three bits (USF-bits) of the data block are encoded such that the first twelve coded bits are representing the same bit pattern, irrespective of the coding scheme, depending only on the USF-bits – the USF-bits can therefore always be decoded from these twelve bits in the same way 12


13

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GPRS Channel Coding

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GPRS CC parameters

• CS-1 is the same coding scheme as specified for SACCH. It consists of a half rate convolution code for FEC and a 40 bit FIRE code for BCS (and optionally FEC) • CS-2 and CS-3 are punctured versions of the same half rate convolution code as CS-1/SACCH/TCH-FS for FEC • CS-4 has no FEC

14


GPRS CC parameters

• CS-2 to CS-4 use the same 16 bit CRC for BCS. The CRC is calculated over the whole uncoded RLC Data Block including MAC Header • For CS-1, the whole Radio Block is convolutionally coded and USF needs to be decoded as part of the data • In order to simplify the decoding, the stealing bits of the block are used to indicate the actual coding scheme

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GPRS CC parameters • CS1 coding schemes adds more protection to the payload than CS-4, and hence processes less payload -Tradeoff • Link adaptation CS

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CS1

PCU Spare Bits USF Block USFD CRC Tail Conv Rate Conv Punc Total Ident Total Burst In Out 1 (8) 2 184 184 0 184 0 40 4 228 2 456 0 456 0xFF 464 116

CS2

264

+7=271

3

268

6

CS3

312

+3=315

3

312

6

CS4

424

+7=431

3

428

12

16 16 16

4

294

2

588

-132

456

0xC8

464

116

4

338

2

676

-220

456

0x21

464

116

0

456

1

456

0

456

0x16

464

116

CS

Payload

Punc.Conv.Code rate

Kbit/s

CS1

184

-1/2

9.05

CS2

264

-2/3

13.4

CS3

312

-3/4

15.6

CS4

424

1

21.4


CS1 Channel Coding CS1 Same channel coding as for SACCH

USF + RLC/MAC Header + RLC Data = 23 octets = 184 bits

FIRE + Tail = 44 bits

Rate 1/2 convolutional coding 456 bits

456 bits

SB = 8

116 bits

116 bits

116 bits

116 bits

464 bits 17


CS2 Channel Coding CS2 USF PrcdUSF

RLC/MAC Header + RLC Data = 268 bits

Parity + Tail = 20 bits



Rate 1/2 convolutional coding (294 bits to 2*294 bits) 588 encoded bits Puncturing 456 punctured bits

SB = 8

116 bits

18


116 bits

116 bits

116 bits

CS3 Channel Coding USF PrcdUSF





Rate 1/2 convolutional coding (338 bits to 2*338 bits) 676 encoded bits Puncturing 456 punctured bits

SB = 8

116 bits

19

116 bits

116 bits

116 bits


Channel Coding CS4 USF Percoded_USF





No convolutional coding (456 bits) 456 "encoded" bits No puncturing 456 "punctured" bits

SB = 8

116 bits

20


116 bits

116 bits

116 bits

Interleaving CS1-CS4 Rectangular Interleaving(CS1-CS4) 0,8

1,9

2,10 3,11

4,12 5,13 6,14 7,15

Diagonal Interleaving (FR speech) 0,8

1,9

2,10 3,11 4,12 5,13 6,14 7,15

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Interleaving Table CS1-CS4

22

kmod8=

0

1

2

3

j=0

k=0

57

114

171

2

64

121

178

4

128

185

6

192

8

100

4

5

6

7

j=1

228

285

342

399

235

3

292

349

406

7

242

299

5

356

413

14

71

249

306

363

7

420

21

78

135

256

313

370

427

9

28

85

142

199

8

65

122

179

101

236

293

350

407

72

129

186

243

300

357

414

15

136

193

250

307

364

421

22

79

200

257

314

371

428

29

86

143

264

321

378

435

36

93

150

207

110

328

385

442

43

111

100

157

214

271

112

392

449

50

107

113

164

221

278

335


k mod 8=

23

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GPRS Channel Coding

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EGPRS RLC data coding

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The RLC/MAC block holds one RLC data block for MCS1-6 and two RLC data block exist for MCS7,8,9. Each RLC data block is coded separately

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Always uses 12 parity bits, rate 1/3 convolution code is used.Data coding is same in UL as in DL

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For each MCS more than one puncturing options existsMCS3,4,7,8,9 have 3 puncturing schemes (PS) specified while the rest have two.For a MCS schemes the punctured bits of each PS are mutually exclusive

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Each of the MCS8 and 9 data block is interleaved over two bursts only. For MCS-7, these blocks are interleaved over four bursts. All the other MCSs carry one RLC block which is interleaved over four bursts


EGPRS RLC header •

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In each transfer direction, uplink and downlink, three different RLC/MAC header types are defined. In decoding, they are identified by the SF sequence Header type 1

is used with MCS-7,8,9

Header type 2

is used with MCS-5,6

Header type 3

is used with MCS-1,2,3,4.

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Header part is robustly coded (8bit parity, 1/3 rate convolution mother code,Puncturing) so that the receiver is able to determine the block identities for all transmissions, even if the payload cannot be decoded

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The coding of the header for all MCS schemes of a particular Header type are similar.But coding for header of Uplink is different from that for downlink, as the header of of different sizes

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The header is coded and interleaved over four bursts


EGPRS : MCS Families • The MCSs are divided into different families A, B and C. Each family has a different basic unit of payload: 37 (and 34), 28 and 22 octets respectively

MCS-3 Family A

37 octets

37 octets 37 octets

37 octets

MCS-6 MCS-9

MCS-2

• Different code rates within a family are achieved by transmitting a different number of payload units(1,2 or 4) within one RLC/MAC Block

Family B

28 octets

28 octets 28 octets

MCS-5 MCS-7 MCS-1 Family C

22 octets

22 octets

MCS-4

26


28 octets

MCS Families Family C

Family A

MCS-1

MCS-3

22

37

MCS-4

MCS-6

44

74 MCS-9

Family B 74

MCS-2

74

28

MCS-6 68

MCS-5 56

MCS-8 68

MCS-7 56

27

68

56


EGPRS CC parameters Scheme Code rate

Header Modulation RLC blocks Code rate per Radio Block (20ms)

MCS-9

1.0

0.36

MCS-8

0.92

0.36

MCS-7

0.76

0.36

MCS-6

0.49

1/3

8PSK

2x12

2x6

Data rate kb/s

2

2x592

A

2

2x544

A

54.4

2

2x448

B

44.8

1

592 544+48

A

29.6 27.2

59.2

8

MCS-5

0.37

1/3

1

448

B

MCS-4

1.0

0.53

1

352

C

17.6

MCS-3

0.80

0.53

1

296 272+24

A

14.8 13.6

GMSK

12

6

22.4

MCS-2

0.66

0.53

1

224

B

11.2

MCS-1

0.53

0.53

1

176

C

8.8

NOTE:

28

HCS Raw Data Fam il y B CS Tail payload within one Radio Block


the italic captions indicate the padding.

MCS1 Channel Coding MCS-1: rate 0.53 GMSK, one RLC block per Radioblock 3 bits USF

36 bits RLC/MAC HCS Hdr.

196 bits FBI

E

Data = 22 octets = 176 bits

BCS

TB


108 bits

588 bits puncturing

puncturing SB = 12

12 bits

372 bits

68 bits

372 bits

P1

P2

464 bits 29



36 bits RLC/MAC HCS Hdr.

244 bits FBI

E


BCS

TB


108 bits

672 bits puncturing

puncturing SB = 12

12 bits

68 bits

372 bits P1

464 bits 30


372 bits P2


36 bits RLC/MAC HCS FBI Hdr.

316 bits E


BCS

TB


108 bits

948 bits puncturing

puncturing SB = 12

12 bits

372 bits

68 bits

372 bits

P1

372 bits

P2

P3

464 bits 31


MCS4 Channel Coding MCS-4: uncoded GMSK, one RLC block per Radioblock 3 bits USF


372 bits E


BCS

TB


108 bits

1116 bits puncturing

puncturing SB = 12

12 bits

68 bits

372 bits P1

464 bits 32


372 bits P2

372 bits P3

MCS5 Channel Coding MCS-5: rate 0.37 8PSK, one RLC block per Radioblock 3 bits USF


468 bits E


BCS

TB


99 bits

1404 bits puncturing

+1 bit SB = 8

36 bits

P1

P2

1248 bits

100 bits

1248 bits

1392 bits 33


MCS6 Channel Coding MCS-6: rate 0.49 8PSK, one RLC block per Radioblock 3 bits USF


612 bits E


BCS

TB


99 bits +1 bit

SB = 8

36 bits

100 bits

1836 bits puncturing P1 1248 bits

1392 bits 34


P2 1248 bits

MCS7 Channel Coding MCS-7: rate 0.76 8PSK, two RLC blocks per Radioblock 3 bits USF

45 bits

468 bits

468 bits

RLC/MAC HCS FBI E Data = 448 bits BCS Hdr.

TB


135 bits

36 bits

124 bits

TB

Rate 1/3 convolutional coding

1404 bits

1404 bits

puncturing

puncturing SB = 8

FBI E Data = 448 bits BCS

puncturing

612 bits

612 bits

612 bits

612 bits

612 bits

612 bits

P1

P2

P3

P1

P2

P3

1392 bits 35


MCS8 Channel Coding MCS-8: rate 0.92 8PSK, two RLC blocks per Radioblock 3 bits USF

45 bits

564 bits


564 bits TB


135 bits

36 bits

124 bits


1692 bits

puncturing

puncturing

612 bits

612 bits

612 bits

612 bits

612 bits

612 bits

P1

P2

P3

P1

P2

P3

1392 bits 36

TB


1692 bits

puncturing SB = 8


MCS9 Channel Coding MCS-9: uncoded 8PSK, two RLC blocks per Radioblock 3 bits USF

45 bits

612 bits


612 bits TB


135 bits

36 bits

124 bits

TB


1836 bits

1836 bits

puncturing

puncturing SB = 8


puncturing

612 bits

612 bits

612 bits

612 bits

612 bits

612 bits

P1

P2

P3

P1

P2

P3

1392 bits 37


Combining Retransmissions •

The different puncturing schemes used for a MCS scheme puncture different bits

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If a data block sent is PS1 fails decoding, the block is stored

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The retransmission happens with P2. This new block is combined with the stored

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This EGPRS feature known as “Incremental redundancy” original data

1/3 coded data

1st xmission

r = 1/1

r = 1/1 1st decoding attempt

2nd xmission

r = 1/2

r = 1/1 2nd decoding attempt

3rd xmission

r = 1/3

r = 1/1 3rd decoding attempt

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GPRS Channel Coding

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Channel Coding of Control Channels

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The channel coding for the PACCH, PBCCH, PAGCH, PPCH,PNCH and downlink PTCCH is the same as the coding scheme CS-1

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The coding scheme used for uplink PTCCH is the same as for PRACH

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Two types of packet access burst may be transmitted on PRACH: an 8 information bits access burst or an 11 information bits access burst called the extended packet access burst

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The channel coding used for the PRACH burst carrying the 8 data bit packet access uplink message is identical to the coding of the access burst as defined for RACH

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The channel coding for 11 bit access burst is the punctured version of the same coding as used for 8 bit access burst


Summary

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GPRS Channel Coding

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Any questions ?

42


Gprs Edge Channel Coding (Hss-spg)

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