Filter-and-Forward Strategy for Multiple Access Relay Channel with a Multi-antenna Relay

In this paper, the filter-and-forward (FF) relay design for a multiple access relay channel (MARC) with a multiantenna relay is considered. The relay uses the FF strategy, in which it is equipped with finite impulse response (FIR) filter to suppress the effect of inter-symbol interference (ISI) caused by the frequency selectivity of the channel. We consider two design criteria for optimizing the relay filter. The first criterion is the minimization of the multi-antenna relay transmit power subject to signal-to-interference-plus-noise ratio (SINR) constraints, and we solve this non-convex problem based on a convex relaxation. For the second criterion we formulate the problem of joint power allocationandrelayfilterdesignforthemaximizationoftheworst received SINR subject to constraints on total transmit power of sources and the relay transmit power, and we solve it with an alternating optimization algorithm. Simulation results show that in the frequency selective fading case, the proposed FF approach can significantly improve the performance as compared to the commonly used amplify-and-forward (AF) relaying strategy. Also, providing simulation results, we investigate the effect of the number of relay antennas and relay filter length on the performance