Dithered largest spread cubic permutation polynomial interleavers for Turbo codes

Permutation polynomial (PP) based interleavers have proven to give the Turbo codes their prominent performance in the recent years. Quadratic permutation polynomial (QPP) interleavers have already been used for many applications. The cubic permutation polynomial (CPP) interleaver has been investigated in recent few papers. Largest spread cubic permutation polynomial (LSCPP) interleavers were introduced to reduce the time of searching for the appropriate polynomial coefficients. In this paper, a modified CPP interleaver is proposed. The modification involves dithering read and write vectors used to locally permute bits before and after CPP interleaving step, respectively. The new interleaver gives better performance for some frame lengths. Simulations and error measures show improved bit error rate (BER) and frame error rate (FER) performances.