Non-Orthogonal Amplify-and-Forward Relaying with Partial Channel State Information

Wireless amplify-and-forward relay networks in which the source communicates with the relays and destination in the first phase and the relays simultaneously forward signals to the destination in the second phase over uncorrelated Rayleigh fading channels are considered. We examine the scenario in which each relay only knows the perfect information of its source-relay channel while the destination knows the exact information of the relay-destination channels and the statistics of the source-relay channels. Based on a combiner developed at the destination, we propose an efficient beamforming scheme at the relays and develop its quantized version using Lloyd's algorithm to work with a limited-rate feedback channel. Simulation results show that the non-orthogonal relaying with the proposed beamforming scheme outperforms the orthogonal relaying with power allocation in terms of the ergodic capacity. In terms of the signal-to-noise ratio, the non-orthogonal scheme also becomes superior to the orthogonal scheme when the number of quantization regions increases.