Telecom Tutorials by Samir Amberkar

Coding steps [Under GSM > Full rate speech coding illustration]

In this article, we will take a top look at GSM coding as applied to full rate speech (TCH/F). As shown in example DL configuration in article on Radio Physical Layer, TCH operate in 26 frame cycle. A time slot denote one TCH carrying (full rate) speech at 13 kbps.

A speech frame (block of 260 bits) pass through following stages (Ref 45.001:Annex A):

Coding & Interleaving

Encryption

Burst formation

Modulation

Transmission

Coding has further following steps (Ref 45.003:2.1):

speech frame 260 bits = 50+132+78

interface 1

parity + tail 267 bits = (182+3+4)+78

interface 2

convolutional coding 456 bits = (189+189)+78

interface 3

reordering/partitioning/interleaving 456 bits in 8 bursts (57 each)

interface 4

(towards encryption unit)

At interface 2, input is a speech frame of 260 bits. 3 parity bits are generated for first 50 bits and 4 tail bits (value 0) are added and re-ordered as below (Ref 45.003:3.1.2.1):

References: GSM book by Mouly and Pautet.

© Copyright Samir Amberkar 2013

.

GSM Index

» Convolutional coding