On the probability of symbol error in Viterbi decoders

An upper bound is derived on the probability that at least one of a sequence of B consecutive bits at the output of a Viterbi decoder is in error. Such a bound is useful for the analysis of concatenated coding schemes employing an outer block code over GF(2(B)) (typically a Reed-Solomon (RS) code), an inner convolutional code, and a symbol (GF(2(B))) interleaver separating the two codes. The bound demonstrates that in such coding schemes a symbol interleaver is preferable to a bit interleaver, It also suggests a nem criterion for good inner convolutional codes.