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GSM Packet Switched Channel Processing through physical layer

Introduction

This article on packet switched channel processing through physical layer covers GPRS Channel Coding(CS1,CS2,CS3,CS4) and EGPRS Channel Coding (MCS1,MCS2,MCS3,MCS4,MCS5,MCS6,MCS7,MCS8,MCS9) processing.

Coding parameters for GPRS Modulation and Coding Schemes-CS1,CS2,CS3,CS4

In GPRS various coding schemes are available to take care of noise,interference and fading of the air interface. These coding schemes have inverse relation ship between data rates and robustness. These schemes CS1,CS2,CS3,CS4 are outlined below in the table.



Scheme Code rate USF Pre-
coded
USF
Radio
block
(exclude
USF/BCS)
BCS Tail Coded
Bits
Punc-
tured
bits
Data rate
(kbps)
CS1 1/2 3 3 181 40 4 456 0 9.05
CS2 2/3 3 6 268 16 4 588 132 13.4
CS3 3/4 3 6 312 16 4 676 220 15.6
CS4 1 3 12 428 16 - 456 - 21.4

EDGE/EGPRS Modulation and Coding Schemes

In the EGPRS radio interface is the same as that in GPRS. Concept of 52-frame multiframe, physical channels(PDCH), logical channels (PBCCH/PCCCH/PRACH/PDTCH/PTCCH and PACCH) and logical channel to physical channel mapping is the same as that in GPRS. The difference is only in modulation and coding schemes as outlined below in the table.

Modulation-
coding
scheme
Modulation Code rate Max.
throughput
(kbps)
Raw data
within
radio block
RLC Blocks/
Radio Block
Family
MCS1 GMSK 0.37 8.8 178 1 C
MCS2 GMSK 0.49 11.2 226 1 B
MCS3 GMSK 0.53 14.8 298 1 A
MCS4 GMSK 0.66 17.6 354 1 C
MCS5 8-PSK 0.76 22.4 450 1 B
MCS6 8-PSK 0.85 29.6 594 1 A
MCS7 8-PSK 0.92 44.8 2 x 450 2 B
MCS8 8-PSK 1.0 54.4 2 x 546 2 A
MCS9 8-PSK 1.0 59.2 2 x 594 2 A

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

GPRS useful Links

GPRS protocol stack
GPRS Modem vendors
GSM versus GPRS
EDGE/EGPRS Basics
What is GPRS
GPRS/EGPRS Modulation-Coding Schemes

RF and Wireless Terminologies


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