Soft decision maximum likelihood encoder and decoder

摘要

A soft decision maximum likelihood detection method and apparatus. Both encoding and decoding schemes are provided for a forward error correcting code. The decoding technique utilizes soft decision maximum likelihood decoding especially suited for codes that operate on symbols rather than bits. The decoding technique utilizes a maximum likelihood function in combination with an erasure correcting coding scheme to correct b+1 errors in a block wherein the erasure correcting code itself can correct up to b erasures. The decoding method uses likelihood values for all possible symbol values for each received symbol in addition to hard decisions. First, the (b+1)error is corrected by assuming a single error in each symbol location. Then, for each symbol in a codeword all valid symbol possibilities are tested. For each symbol possibility, the metric of the resulting codeword is calculated using the likelihoods provided by the receiver. The remaining b errors are corrected by assuming erasures in all possible combinations of b symbols. The codeword yielding the maximum metric is selected and subsequently decoded and output.