Abstract
Recently, alternate-relaying cooperative (ARC) systems have appeared as an efficient technique to overcome the bandwidth loss problem of traditional cooperative transmissions. However, to the best of the authors' knowledge, the previously reported investigations for ARC systems are limited to single-carrier and single-user transmissions. In addition, they follow the assumption of having perfect knowledge about channel impulse responses (CIRs) between nodes; however, practical systems typically employ a channel estimation algorithm. In this paper, we propose the use of ARC with orthogonal frequency division multiple access (OFDMA) to improve the performance of wireless broadcasting systems. We address the problem of joint data detection and CIRs estimation for uplink OFDMA-ARC systems. The problem is investigated in the context of bit-interleaved coded modulation iterative decoding (BICM-ID) and decode-and-forward relaying scheme. The structure of ARC and BICM-ID transmission is beneficially exploited to develop an optimal detector and an optimal CIRs estimator. It is shown that the optimal detector can be implemented by a bank of maximum a posteriori algorithms and the CIRs estimation can be computed using the space alternating generalized expectation-maximization algorithm, in which the soft information provided by the detector is utilized as a priori information to refine the estimates. The performance of the proposed estimator and the detector is evaluated via Monte Carlo simulations, and the results demonstrate their effectiveness.