GSM Traffic Channel Processing in the Physical Layer

gsm
physical layer
speech channel
data channel
3gpp

This article covers traffic channel processing through the physical layer for various GSM channels as per the 3GPP TS 45.003 standard. Specifically, we’ll look at:

  • Speech channel at Full rate (TCH/FS)
  • Speech channel at Half rate (TCH/HS)
  • Speech channel at Enhanced Full Rate (TCH/EFR)
  • Adaptive Multi rate speech channel at full rate (TCH/AFS)
  • Adaptive Multi rate speech channel at half 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)

The goal of this article is to provide a block schematic view of traffic channel processing (speech/data).

Speech channel at Full rate (TCH/FS)

speech channel full rate TCH/FS

Speech channel at Half rate (TCH/HS)

speech channel half rate TCH/HS

Speech channel at Half rate (TCH/EFR)

speech channel half rate TCH/EFR

Adaptive Multi rate speech channel at full rate (TCH/AFS)

This section describes the coding for the different frame formats used for TCH/AFS.

  • SID_UPDATE: Used to convey comfort noise parameters during DTX (Discontinuous Transmission).
  • SID_FIRST: Marker to define the end of speech and the 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 (Radio Access Technology Selection Cell Change Handover) messages
Codec ModeRateNo. of input bits to Conv.EncoderNo. of output bits from Conv.EncoderNo. of punctured bits
TCH/AFS12.21/225050860
TCH/AFS10.21/3210642194
TCH/AFS7.951/316551365
TCH/AFS7.41/315447426
TCH/AFS6.71/4140576128
TCH/AFS5.91/412452072
TCH/AFS5.151/5109565117
TCH/AFS4.751/510153587

Adaptive Multi rate speech channel full rate AMR/TCH-AFS/SID UPDATE

Adaptive Multi rate speech channel full rate AMR/TCH-AFS/SID FIRST

Adaptive Multi rate speech channel full rate AMR/TCH-AFS/ONSET

gsm physical layer transmitter

gsm physical layer transmitter

Adaptive Multi rate speech channel at half rate (TCH/AHS)

This section 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 the marker to define end of speech, start of DTX
  • SID_FIRST_P2: Second part of the 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 ModeNo. of input bits to Conv.EncoderRateNo. of output bits from Conv.EncoderNo. of punctured bits
TCH/AHS7.41291/226678
TCH/AHS7.41261/226064
TCH/AHS6.71161/224040
TCH/AHS5.91081/222416
TCH/AHS5.15971/330391
TCH/AHS4.75891/328573

Wideband Adaptive Multi Rate Speech Channel at full rate (TCH/WFS)

This section 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 ModeRateNo. of input bits to Conv.EncoderNo. of output bits from Conv.EncoderNo. of punctured bits
TCH/WFS12.651/225952678
TCH/WFS8.851/3183561113
TCH/WFS6.601/4140576128

Data Channel at full rate 12.0 Kbits/s radio interface rate (TCH/F9.6)

data channel full rate TCH/F9.6

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
GSM Physical Layer (Layer-1) Explained

GSM Physical Layer (Layer-1) Explained

Explore the GSM physical layer (layer-1) functions, including baseband processing, FEC, ciphering, burst formation, and modulation for mobile station transmission.

gsm
physical layer
modulation