Optimal power allocation for coordinated wireless backhaul in OFDM based relay systems

Coordinated multi-point (CoMP) and wireless relaying are two transmissions technologies that are expected to be widely deployed in future LTE-Advanced (LTE-A), to improve high data rate coverages and cell-edge throughputs. Motivated by the common cooperative diversity feature, in this paper we propose a novel OFDM-based relay system with coordinated wireless backhaul (i.e., CoMP backhaul), in which two cooperative base stations (CBS) simultaneously transmit information to an infrastructure-based cell-edge relay node (RN). This proposal allows to enhance the rate of the backhaul link, and consequently enables an improvement in end-to-end (e2e) throughput that the mobile user perceives. In order to maximize the achievable e2e rate, a new co-phasing waterfilling power allocation scheme is developed for the multi-carrier CoMP backhaul. By the aid of first-order Taylor series expansion, a simplified iterative co-phasing waterfilling (ICPWF) algorithm is proposed to determine the optimal power allocation solution. Numerical results are presented to verify the optimality of the derived scheme, and to quantify the e2e throughput gains that our prosposed scheme provides when compared to traditional non-coordinated ones.