Efficient Implementation of Continuous MAP Decoders and a Synchronisation Technique for Turbo Decoders

A method of efficiently implementing a continuous MAP decoding algorithm is presented. A sliding window technique is used to reduce the block size at the expense of extra computations. The smaller block size results in a large reduction in memory storage requirements, reduced delay, and the ability to implement a continuous MAP decoder. A technique for reducing the synchronisation time for a turbo decoder without the use of synchronisation words is also presented. This technique artificially forces the low delay inner decoder to synchronise to a large number of states so that the large delay outer decoder (due to the interleaver between the inner and outer decoder) has fewer states to synchronise to. The overall synchronisation time is thus reduced. Index Terms MAP decoding, continuous decoding, turbo codes, synchronisation