Download - 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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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
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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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
Control Channel Encoding
456 bits
184
184 4
Fire Code TailBits
Convolutional Code
456
184 bits
40
ParityBits
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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
Interleaving
TRAU FrameType
Speech
Control
Data
Number ofGSM Bursts
Spread Over
8
4
22
Note:TRAU = Transcoder Rate Adaption Unit
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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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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FOR TRAINING PURPOSES ONLYRef: CP02 - Section 6
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