A memory-efficient optimal APP symbol-decoding algorithm for linear block codes

We propose a simple modification of the famous Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm for linear block codes. The modified algorithm requires one forward and two backward recursions in the code trellis, but eliminates the need to store the whole trellis. Compared with the BCJR algorithm, the computational complexity is slightly increased, but the storage requirement is reduced.