Trellis code design for periodic interleavers

A standard technique for correlated fading combines trellis codes designed for independent fading with interleaving that makes correlated fading appear to be independent for symbols within the Viterbi traceback depth. When the fading correlation is persistent and delay constraints preclude deep interleaving, some correlation remains among symbols within the traceback depth. Incorporating this post-interleaver correlation improves the trellis code design. This article presents such a trellis code design technique for periodic interleavers. Bit error rate simulations demonstrate that the new design technique can provide a dramatic performance improvement when fading or interference is severe and persistent.