Soft information in concatenated codes

A new soft decision criterion is derived. This is useful in communication systems where the combination of modulation, interleaving, and error correction is used. The new algorithm is attractive to implement since traceback techniques can be used and only a little extra memory is required to obtain the soft information associated with every symbol. Furthermore, the operations involved are not recursive and the execution is time independent of the received signal quality. The performance of the new algorithm is typically within 0.25-0.1 dB (bit error rate (BER)=10/sup -1/) of that of a significantly more complex algorithm reported previously.