On sufficient conditions for testing optimality of codewords in ISI channels

For the memoryless AWGN channel, there exists low complexity methods to test the optimality of any chosen candidate codeword (i.e., whether the codeword in question equals the most-likely codeword or not). Such optimality tests find application in practical decoders that perform heuristic searches for the most-likely codeword. If some located codeword passes the optimality test, then the search may be terminated and computations saved. In this paper, we generalize techniques for determining if a codeword is optimal, for intersymbol interference (ISI) channels.