An algorithm for detecting unreliable code sequence segments and its applications

Let the Viterbi algorithm be applied for maximum-likelihood decoding of a terminated convolutional code using a trellis. We propose an additional procedure that permits a receiver to locate unreliable segments within an estimated code sequence. This reliability output may be used, for example, to request retransmissions, in systems with error concealment, or in channel-coding systems with unequal error protection.