Statistical approach to ML decoding of linear block codes on symmetric channels

Maximum-likelihood (ML) decoding of linear block codes on a symmetric channel is studied. Exact ML decoding is known to be computationally difficult. We propose an algorithm that finds the exact solution to the ML decoding problem by performing a depth-first search on a tree. The tree is designed from the code generator matrix and pruned based on the statistics of the channel noise. The complexity of the algorithm is a random variable. We characterize the complexity by means of its first moment, which for binary symmetric channels we find in closed-form. The obtained results indicate that the expected complexity of the algorithm is low over a wide range of system parameters.