Filter-and-Forward Relay Design for OFDM-based Multiple Access Relay Channel

In this paper, we study the filter-and-forward (FF) relaying strategy for a multiple access relay channel (MARC) based on orthogonal frequency division multiplexing (OFDM) transmission. To reduce OFDM demodulation and redemodulation complexity at the relay, the FF-relay directly filters the incoming signal with a finite impulse response (FIR) filter and forwards it to the destination. We intend to design the relay filter subject to ensuring quality of service (QoS) at the destination. We propose an optimization criterion that is the joint sources power allocation and relay filter design, to maximize the worst subcarrier channel signal-to-noise ratio (SNR) subject to the sources and the relay transmit power constraints. We employ an alternating optimization algorithm to find the relay filter and the allocated power to sources, for our problem that is nonconvex. Simulation results show that the proposed FF approach has a better performance for OFDM based MARC in frequency selective channels in comparison to the amplify and forward (AF) strategy. Also, we investigate the effect of the relay filter length on the system performance.