Spectral-Energy Efficiency Tradeoff in Relay-Aided Cellular Networks

A relay cooperation scheme is proposed for the downlink of multicell multiple-input-multiple-output cellular networks. The relay stations (RSs) will cooperatively transmit the signal replicas of all the user equipments obtained during the broadcast phase. We consider different RS decoding strategies during the broadcast phase and joint relay transmission with different degrees of channel state information (CSI) sharing during the relay phase. We also propose the partial semi-orthogonal user selection (PSUS) method designed specifically for relay cooperation. The spectral and energy efficiencies are then evaluated for the relay cooperation scheme. Its cooperative costs for different cooperation levels are also investigated. Simulation results indicate that joint RS decoding outperforms independent RS decoding but a cooperative link with a bit rate of an order of magnitude greater than that achievable by the relay network is required. Compared to the competing user selection methods that require global CSI, the proposed PSUS method utilized for relay phase joint transmission operates at less than half of the cooperative cost while introduces only a slight degradation in system performance.