Comparison between Ω'-QPP and random interleavers for space-time turbo codes using doubly iterative decoding algorithm

The performances of a low complexity doubly iterative decoder are analyzed for space-time turbo codes on a quasi-static fading channel. In order to improve them, here is used a quadratic permutation polynomial interleaver with the best Ω' metric (Ω'-QPP) and the obtained frame error rate (FER) and bit error rate (BER) performances are compared to those of random interleavers. To reduce the spatial interference of the received signal, the decoder uses preliminary soft values of the coded symbols, obtained after a limited number of turbo iterations. To improve the quality of the soft values, new turbo iterations are performed. From simulation results it can be seen that in BER domain the obtained coding gain decreases when the number of doubly iterations increases and in FER domain the obtained coding gain is more significant as the number of double iterations increases. When the number of doubly iterations increases, the number of erroneous frames decreases more than the number of errors per frame.