Adaptive turbo-coded hybrid-ARQ in OFDM systems over fading channels

The performance of an adaptively-modulated and adaptive-rate hybrid automatic-repeat-request (hybrid-ARQ) scheme is proposed for wideband communications based on orthogonal frequency division multiplexing (OFDM). The adaptation scheme presents the optimal code rate and signal constellation in order to maximize the spectral efficiency per sub-carrier. By employing type-III turbo hybrid-ARQ with OFDM, utilization of a complete set of sub-carriers is achieved. The adaptation scheme is presented for both Gaussian and fading channels. It is found that the proposed adaptive approach achieves near capacity rates for wideband transmission.