The structure of bidirectional syndrome decod- ing for binary rate(n — 1)/n convolutional codes is investigated. It is shown that forback ward decoding based on the trellis of a syndrome former H~T, htsyndrome sequence must be gener- ated in time-reversed order using anextra syndrome former H~*T, where H~*T is a generator matrix of thereciprocal dual code of the original code. It is also shown that ifthe syndrome bits are generated once and only once using H~T andH~*T, then the cor- responding two error sequences have theintersection of ν' × n error symbols, where ν' is the memorylength of H~T.
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