channel coding on the air.ppt

8/10/2019 channel coding on the air.ppt

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FOR TRAINING PURPOSES ONLYVersion 0.1

Channel Coding on the Air Interface

Section 6


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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6

Objectives

On completion of this section the student will be able to:

Draw the structure of a GSM burst and identify the purpose of each

component.

Understand the different mechanisms used to protect the air interfacefrom errors on speech, data and control channels


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GSM Burst and TDMA Frame

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

FRAME 2FRAME 1

NORMAL BURSTTRAINING SEQUENCEINFO INFO

STEALINGFLAGS

TAIL BITS

GUARD

PERIOD

GUARD

PERIOD

TAIL BITS


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GSM Burst Types

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

FRAME 2FRAME 1

NORMAL BURST (NB)

FREQ CORRECTION BURST (FB)

SYNCHRONISATION BURST (SB)

DUMMY BURST

ACCESS BURST

3

57 57

31 1

26

3

Information Training Sequence InformationTB GPTB

TB GP

TB GP

3

TB

Fixed Bits

142

3

TB

8

TB

39

Encoded

39

Encoded

64

Synchronisation Sequence

3

57

31 1

26

Fixed Bits Training SequenceTBGPTB

57

Fixed Bits

TBGP

68.25

3

41

Synchronisation Sequence

36

Encrypted Bits

577 m sec

3

time


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Error Protection and Detection

EFR SpeechFrame 244 bits

EFR SpeechFrame 260 bits

BCCH, PCH, AGCH, SDCCH,FACCH, SACCH,CBCH 184 bits

Data Traffic9.6/4.8/2.4k

N0 bitsRACH + SCH

P0 bits

Cyclic Code + RepetitionIn: 244

Out: 260

Class 1a Cyclic Code + TailIn: 260

Out: 267

Firecode + TailIn: 184 bits

Out: 228 bits

Add in TailIn: N0 bits

Out: N1 bits

Cyclic Code + TailIn: P0 bits

Out: P1 bits

Convolutional CodeIn: 267 bits

Out: 456 bits

Convolutional CodeIn: 228 bits

Out: 456 bits

Convolutional Code+ PunctureIn: N1 bits

Out: 456 bits

Convolutional CodeIn: P1 bits

Out: 2 x P1 bits

Re-ordering & Partitioning+ Stealing Flag

In: 456 bitsOut: 8 subblocks

TCH/2.4

Diagonal Interleaving+ Stealing Flags

In: 456 bitsOut: 8 subblocks

Block Diagonal InterleavingIn: 8 blocks

Out: Pair of blocks

Block Rectangular InterleavingIn: 8 subblocks

Out: Pair of subblocks

8 x TCH FR (Bursts)8x TCH EFT (Bursts)8 x FACH/TCH (Bursts)8 x TCH 2-4kbps (Bursts)

4 x BCCH, PCH, AGCH4 x SDCCH, SACCH4 x CBCH (Bursts)

16 x TCH 9.6 kbps (Bursts) 1 x RACH1 x SCH (Burst)


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Speech Channel Coding

456 bits

Class 1a50 bits

260 bits

ParityCheck TailBits

Convolutional Code

Class 1b132 bits

Class 278 bits

50 3 132 4

78378


7/14FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6

Preliminary Coding for Enhanced Full Rate Speech

244 bits

Class 1a50 bits

Class 1b124 bits

Class 270 bits

Class 1a50 bits

Class 278 bits

Class 1b132 bits

8 bit CRCadded to Class 1b

8 repetitionbits added toClass 2 bits

260 bits


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Control Channel Encoding

456 bits

184

184 4

Fire Code TailBits

Convolutional Code

456

184 bits

40

ParityBits


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Interleaving

TRAU FrameType

Speech

Control

Data

Number ofGSM Bursts

Spread Over

8

4

22

Note:TRAU = Transcoder Rate Adaption Unit


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Diagonal Interleaving - Speech

5

654321

Full-rate speech blocks from one conversation arrive after encoding.They each contain 456 bits.

456bits

Speech Blocks

block 5 even bitsblock 4 odd bits

block 6 even bitsblock 5 odd bits

Shared by blocks 4 & 5 Shared by blocks 5 & 6

57bits

even odd

57bits

57bits

57bits

57bits

57bits

57bits

57bits

even odd even odd even odd


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Diagonal Interleaving - Speech

3

FRAME 1

54

654321

6

Full rate encoded speech blocks from 1 conversation arrive from the speech codec.

FRAME 2 FRAME 3

0 1 2 4 5 6 7

456bits

Bursts

TDMA frames

Speech Blocks

30 1 2 4 5 6 7 30 1 2 4 5 6 7


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Rectangular Interleaving - Control

3

FRAME 1

54

654321

6

FRAME 2 FRAME 3

0 1 2 4 5 6 7

456bits

Bursts

TDMA frames

Control Blocks

30 1 2 4 5 6 7 30 1 2 4 5 6 7

114bits

114bits

114bits

114bits

even odd even odd


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Diagonal Interleaving - Data

5

654321

456bits

Data Blocks

114 114 114 114

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

114bits

114bits

114bits

114bits

First 6bits

First 6bits

First 6bits

First 6bits

Last 6bits

Last 6bits

Last 6bits

Last 6bits

channel coding on the air.ppt

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