Hybrid ARQ for turbo coded modulation with mixed combining

In this paper, we consider the hybrid automatic retransmission request (ARQ) for turbo coded systems with QAM modulations through block fading channels and the rates are different among (re)transmission blocks. Due to coexistence of incremental redundancy (IR) and repetition, both chase combining (CC) and IR code combining are employed at the receiver. Based on the bucket-filling analysis for the hybrid ARQ process with mixed IR and repetitions, we obtain the error rates by applying the union-Bhattacharyya (UB) bound for parallel channels. We then form the throughput optimization of hybrid ARQ with mixed combining and obtain the optimal assignment rates and modulation set. The results show that the mixed combining performs better than non-adaptive IR and Chase combining based hybrid ARQ schemes.