July 2009 - DSP LOG

Viterbi with finite survivor state memory

In the post on Viterbi decoder and soft input Viterbi decoder, we discussed a convolutional encoding scheme with rate 1/2, constraint length $K=3$ and having generator polynomial $K=3$ and having generator polynomial $\left[ 7, 5\right]_8$ . If the number of uncoded bits is $N$ , then the number of coded bits at the output of the convolutional encoder is $2(N+K-1)$ . Decoding the convolutionaly encoded bits by Viterbi algorithm consisted of the following steps.

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Softbit for 16QAM

In the post on Soft Input Viterbi decoder, we had discussed BPSK modulation with convolutional coding and soft input Viterbi decoding in AWGN channel. Let us know discuss the derivation of soft bits for 16QAM modulation scheme with Gray coded bit mapping. The channel is assumed to be AWGN alone.

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