GSM Traffic Channel Processing through physical layer
Introduction
This article on traffic channel processing through physical layer covers Speech channel at Full rate(TCH/FS),Speech channel at Half rate(TCH/HS), Speech channel at Half rate(TCH/EFR),Adaptive Multi rate speech channel at full rate(TCH/AFS), Adaptive Multi rate speech channel at full rate(TCH/AHS),Wideband Adaptive Multi Rate Speech Channel at full rate (TCH/WFS),Data Channel at full rate 12.0 Kbits/s radio interface rate (TCH/F9.6) as per 3GPP TS 45.003 standard. The idea of this article is to provide block schematic view of traffic channel processing(speech/data).
Speech channel at Full rate(TCH/FS)
Speech channel at Half rate(TCH/HS)
Speech channel at Half rate(TCH/EFR)
Adaptive Multi rate speech channel at full rate(TCH/AFS)
This section of the page describes the coding for the different frame formats used for TCH/AFS.
SID_UPDATE Used to convey comfort noise parameters during DTX
SID_FIRST Marker to define end of speech, start of DTX
ONSET Used to signal the Codec mode for the first speech frame after DTX
SPEECH Speech frames
RATSCCH Frames used to convey RATSCCH messages
| Codec Mode | Rate | No. of input bits to Conv.Encoder | No. of output bits from Conv.Encoder | No. of punctured bits |
|---|---|---|---|---|
| TCH/AFS12.2 | 1/2 | 250 | 508 | 60 |
| TCH/AFS10.2 | 1/3 | 210 | 642 | 194 |
| TCH/AFS7.95 | 1/3 | 165 | 513 | 65 |
| TCH/AFS7.4 | 1/3 | 154 | 474 | 26 |
| TCH/AFS6.7 | 1/4 | 140 | 576 | 128 |
| TCH/AFS5.9 | 1/4 | 124 | 520 | 72 |
| TCH/AFS5.15 | 1/5 | 109 | 565 | 117 |
| TCH/AFS4.75 | 1/5 | 101 | 535 | 87 |
Adaptive Multi rate speech channel at full rate(TCH/AHS)
This section of the page describes the coding for the different
frame formats used for TCH/AHS.
SID_UPDATE Used to convey comfort noise parameters during DTX
SID_UPDATE_INH Used to inhibit the second part of a SID_UPDATE frame if there is a speech onset
SID_FIRST_P1 First part of marker to define end of speech, start of DTX
SID_FIRST_P2 Second part of marker to define end of speech, start of DTX
SID_FIRST_INH Used to inhibit the second part of a SID_FIRST_P1 frame if there is a speech onset
ONSET Used to signal the Codec mode for the first speech frame after DTX
SPEECH Speech frames
RATSCCH_MARKER Marker to identify RATSCCH frames
RATSCCH_DATA Frame that conveys the actual RATSCCH message
| Codec Mode | No. of input bits to Conv.Encoder | Rate | No. of output bits from Conv.Encoder | No. of punctured bits |
|---|---|---|---|---|
| TCH/AHS7.4 | 129 | 1/2 | 266 | 78 |
| TCH/AHS7.4 | 126 | 1/2 | 260 | 64 |
| TCH/AHS6.7 | 116 | 1/2 | 240 | 40 |
| TCH/AHS5.9 | 108 | 1/2 | 224 | 16 |
| TCH/AHS5.15 | 97 | 1/3 | 303 | 91 |
| TCH/AHS4.75 | 89 | 1/3 | 285 | 73 |
Wideband Adaptive Multi Rate Speech Channel at full rate (TCH/WFS)
This section of the page describes the
coding for the different frame formats used for TCH/WFS.
SID_UPDATE Used to convey comfort noise parameters during DTX
SID_FIRST Marker to define end of speech, start of DTX
ONSET Used to signal the Codec mode for the first speech frame after DTX
SPEECH Speech frames
RATSCCH Frames used to convey RATSCCH messages
| Codec Mode | Rate | No. of input bits to Conv.Encoder | No. of output bits from Conv.Encoder | No. of punctured bits |
|---|---|---|---|---|
| TCH/WFS12.65 | 1/2 | 259 | 526 | 78 |
| TCH/WFS8.85 | 1/3 | 183 | 561 | 113 |
| TCH/WFS6.60 | 1/4 | 140 | 576 | 128 |
Data Channel at full rate 12.0 Kbits/s radio interface rate (TCH/F9.6)
Useful Links
GSM tutorial covering GSM basics,network architecture,network elements,system specifications,applications,GSM burst types,GSM frame structure or frame hierarchy, logical channels,physical channels, GSM physical layer or speech processing and GSM mobile network entry or call setup procedure,
Read more.
GSM Protocol stack , covers layer 1,2 and 3 of GSM network elements MS,BTS,BSC and MSC.READ MORE.
GSM Standard References
3GPP TS 45.002 describes burst building and burst multiplexing
3GPP TS 45.003 describes coding and interleaving
3GPP TS 45.004 describes differential encoding and modulation
3GPP TS 45.005 describes transmitter,receiver and antenna part
3GPP TS 43.020 & 23.221 describes encryption/ciphering part
RELATED LINKS
GSM RF planning
GSM mobile originated call flow
GSM Mobile Terminated Call flow
GSM Tutorial
GSM protocol stack
GSM physical layer
GPRS protocol stack
GPRS tutorial