Forward computation of backward path metrics for MAP decoder

In the implementation of the MAP algorithm for turbo decoding, the memory management is an important issue. When the sliding window is not used, either the forward or the backward path metrics need to be stored for the whole frame. An alternative method is proposed to reduce the storage of the path metrics. Most path metrics are calculated as needed with only a small portion of those metrics drawn from memory. A simulation study is performed to justify the choice of the block size for this method. This technique can reduce the memory requirement by at least 50% without compromising the performance while incurring a small penalty in computation complexity