Packet combining for turbo-diversity in HARQ systems with integrated turbo-equalization

In this paper, we present a simple and effective packet combining method for a turbo-diversity transmit scheme in hybrid automatic repeat request (HARQ) systems over frequency-selective channels. We first show by using a distance spectrum-based analysis that the turbo-diversity scheme outperforms the identical interleaving transmit scheme in terms of frame error rate (FER) performance under a maximum-likelihood receiver, especially for high order modulations. Then, we propose a low complexity combining method with integrated turbo-equalization based on a separate linear equalization for each HARQ transmission followed by a joint decoding instead of an iterative combining strategy. The proposed method has the advantage to be operational for both HARQ modes: namely, Chase combining (CC) and the incremental redundancy (IR). Numerical simulations show that the proposed method can efficiently exploit the potential of the turbo-diversity scheme.