Convolutional coding and decoding in hybrid type-II ARQ schemes on wireless channels

We studied the performance of the hybrid type-II automatic repeat request (ARQ) system on Rayleigh fading channels. This system is based on high rate optimized rate compatible punctured convolutional (HRO-RCPC) codes combined with simple repetition coder. The performance is investigated for different packet sizes and constraint lengths of the convolutional encoder. Additionally the effect of packet size on the performance in different fading environments is studied in more detail. We have also studied the performance of the HRO-RCPC codes combined with optimized rate compatible repetition convolutional (RCRC) codes as another alternative for channel coding in hybrid type-II ARQ schemes. The simulation results show that HRO-RCPC codes combined with optimized RCRC codes with high parent code rate perform almost as good as the HRO-RCPC codes with simple repetition codes at lower parent code rate. Also a tailbiting decoder using the circular Viterbi algorithm (CVA) is examined for different hybrid type-II ARQ schemes and packet sizes. It is shown that the improvement of the performance due to tailbiting is noticeable only for short packets. For long packets, the sub-optimality of CVA decoding compared to the general Viterbi algorithm (GVA) degrades the performance considerably