Spatial Multiplexing and Scheduling in Cellular Networks with Relay Stations

Relay stations (RSs) are usually used to enhance the signal strength of the mobile stations (MSs) close to the cell boundary. However, the introduction of RSs to the cellular networks increases the interference to the MS served by the base station (BS) under spatial multiplexing mode. In this paper, we propose a method which can cancel the interference through a novel use of dirty paper coding (DPC). Then, under a practical spatial multiplexing frame structure, we evaluate the cellular- relay system performance under three scheduling algorithms, Round Robin (RR) algorithm, Maximum Signal to Interference and Noise Ratio (MaxSINR) algorithm and Proportional Fair (PF) algorithm. Simulation and analytical results show that the spectral efficiency (SE) of cellular-relay system can be dramatically increased by 30% by the proposed interference cancellation method, and RR algorithm achieves the highest gain, while the gain of MaxSINR algorithm is limited gain in our scheme. Index Terms— Relay, spatial multiplexing, dirty paper coding (DPC), scheduling relaying gain, has come to engineers' mind as a result. To create a fair comparison with the traditional cellular systems, we consider a spatial multiplexing mode that all links use the same spectrum and no more spectrum is added. However, in this mode, the introduction of RSs to the cellular networks increases the interference to the MS served by the BS. To deal with this problem, in this paper we propose an interference cancellation method for the downlink transmission in the cellular-relay system. The proposed method exploits the dirty paper coding (DPC) technique at the BS to pre-subtract any foreseeable interference to the MS from the RS in the same