Memory Management in a Viterbi Decoder

Management of the memory contents in a Viterbi decoder is a major design problem for both hardware and software realizations. In a naive implementation, every bit in the memory must be changed (read, modified, and rewritten) for each message bit decoded, and, in addition, some double buffering is required. An especially annoying feature is the need to read and rewrite long words, forty bits in a typical case. In this note we describe a memory organization which overcomes these problems. The techniques described here are not novel, but neither are they widely known.