Telecom Tutorials by Samir Amberkar

Convolutional coding [Under GSM > Full rate speech coding illustration]

Convolutional coding is applied to reordered 189(=50+132+3+4) bits, 1/2 rate coding with following formulas (Ref 45.003:3.1.2.2):

G0 = 1 + D³ + D⁴
G1 = 1 + D + D³ + D⁴

D^y is cyclically shifted (by y bits) version of original bit sequence.

G0 and G1 (189 bits each) are put together (G0 at even bits and G1 at odd bits) as below.

G0 =	u(k) +	u(k - 3) +	u(k - 4)

G1 =	u(k) +	u(k - 1) +	u(k - 3) +	u(k - 4)

This with not-coded 78 bits, totaling 456 bits, forms coded speech frame.

References: GSM book by Mouly and Pautet.

© Copyright Samir Amberkar 2013

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