Adaptive Hybrid ARQ in Gaussian and Turbo Coded Systems

We consider the design of adaptive hybrid automatic retransmission request (ARQ) with incremental redundancy (IR) in which the transmission rates of different blocks in one hybrid ARQ process can be different. The throughput of adaptive IR hybrid ARQ in block fading channels is formed based on the renewal-reward theorem. Two types of input signals are considered, namely, Gaussian inputs and practical turbo coded modulation. For Gaussian inputs, the error probability after each transmission is obtained from the outage rate. For turbo coded modulation, we obtain the error rate after each transmission block by applying union-Bhattacharyya (UB) bound for parallel channels. The throughput optimization is then formed to seek the optimal transmission rates. The results show that adaptive IR HARQ provides higher throughput than non-adaptive IR HARQ and chase combining in the moderate-to-high SNR region.