Interleaving and Termination in Unpunctured Symmetric Turbo Codes

The turbo code interleaver design problem is considered for large block sizes, where the effect of trellis termination is less marked. The performance is compared for various interleavers with a similar block size, including an implementation of the uniform interleaver. An optimised interleaver design technique based on simulated annealing is proposed. The results obtained show that the error performance may be significantly improved without increasing the delay. Finally, interleaver design for small turbo codes is considered. In this case it is shown that while correct termination improves the performance for an average interleaver, its effect on turbo codes with optimised interleavers is negligible. Using the proposed simulated annealing design technique it is easier to include restrictions which make the interleaver correctly-terminating or odd-even. While the S-random algorithm serves well for specifying interleaver spread, the authors believe that their algorithm is better suited for more sophisticated design criteri