Low complexity power allocation scheme for regenerative multi-user relay networks

In relay assisted wireless communications, the multi-source, single relay and single destination system (an M-1-1 system) has garnered significant interest, due to the increased demand for higher network throughput and connectivity. Previously, power allocation at the relay in M-1-1 systems have assumed availability of instantaneous channel state information (CSI), which is rather idealistic. In this paper we consider an M-1-1 Decode-and-Forward (DF), Full-Duplex, orthogonal frequency division multiple access (OFDMA) based relay system with statistical-CSI and analyze the achievable rate R of such a system. We show how R can only be maximized by numerical power allocation schemes which have high-complexity of order O(M³). By introducing a rational approximation in the achievable rate analysis, we develop a low-complexity power allocation scheme at the relay that can obtain a system achievable rate very close to the maximum R. Most importantly, we show that the complexity of our power allocation scheme is of the order O(M log M). Our power allocation scheme is suitable for a multiuser relay system, where the priority is to maximize the system throughput. The work we present in this paper will be of value to the design and implementation of real-time multi-user relay systems operating under realistic channel conditions.