GSM Packet Switched Channel Processing Through Physical Layer

gsm
gprs
egprs
coding scheme
physical layer

Introduction

This article delves into the processing of packet-switched channels within the GSM (Global System for Mobile Communications) framework, focusing on the physical layer. We will explore GPRS (General Packet Radio Service) channel coding schemes (CS1, CS2, CS3, CS4) and EGPRS (Enhanced GPRS) channel coding schemes (MCS1, MCS2, MCS3, MCS4, MCS5, MCS6, MCS7, MCS8, MCS9).

Coding Parameters for GPRS Modulation and Coding Schemes (CS1, CS2, CS3, CS4)

GPRS employs various coding schemes to mitigate the effects of noise, interference, and fading in the air interface. These schemes offer a trade-off between data rates and robustness; higher data rates generally correspond to lower robustness and vice versa. The four primary coding schemes, CS1 through CS4, are detailed in the following table:

SchemeCode RateUSFPre-coded USFRadio Block (exclude USF/BCS)BCSTail Coded BitsPunctured BitsData Rate (kbps)
CS11/2331814044569.05
CS22/33626816458813.4
CS33/43631216467615.6
CS4131242816-45621.4

USF: Uplink State Flag, BCS: Block Check Sequence

EDGE/EGPRS Modulation and Coding Schemes

In EGPRS, the radio interface remains the same as in GPRS. The concepts of the 52-frame multiframe, physical channels (PDCH), logical channels (PBCCH/PCCCH/PRACH/PDTCH/PTCCH and PACCH), and logical channel to physical channel mapping are also consistent with GPRS.

The primary difference lies in the modulation and coding schemes used, as outlined in the table below:

Modulation-Coding SchemeModulationCode RateMax. Throughput (kbps)Raw Data within Radio BlockRLC Blocks/Radio BlockFamily
MCS1GMSK0.378.81781C
MCS2GMSK0.4911.22261B
MCS3GMSK0.5314.82981A
MCS4GMSK0.6617.63541C
MCS58-PSK0.7622.44501B
MCS68-PSK0.8529.65941A
MCS78-PSK0.9244.82 x 4502B
MCS88-PSK1.054.42 x 5462A
MCS98-PSK1.059.22 x 5942A

GMSK: Gaussian Minimum Shift Keying, 8-PSK: 8-Phase Shift Keying, RLC: Radio Link Control

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/GPRS/EGPRS Throughput Explained

Understand GSM/GPRS/EGPRS throughput, including coding schemes (CS1-CS4) and modulation (MCS1-MCS9), factors affecting data rates, and normalized throughput calculations.

gsm
gprs
egprs
GSM Uplink Packet Switched Data Call Flow

GSM Uplink Packet Switched Data Call Flow

Explore the packet switched (PS) data call flow in GSM uplink, detailing GPRS attach and PDP context activation between mobile devices and network elements.

gsm
packet switching
data communication