Proportional fair-based joint subcarrier and power allocation in relay-enhanced orthogonal frequency division multiplexing systems

There has emerged lots of interests in the resource allocation of the relay-enhanced orthogonal frequency division multiplexing (OFDM) system. Most of the existing research works are with the aim to maximise the transmit rate of the system. However, few of them have taken into account the fairness requirements. In order to achieve the trade-off between the system transmit rate and user fairness, this study originally studies the optimality of proportional fairness (PF) in a downlink relay-enhanced OFDM system, where one source communicates with multiple destinations by the aid of one or many relays. We investigate the joint subcarrier and power allocation problem with PF constraint. Firstly, the resource allocation problem is formulated. Then, the problem is studied in the framework of concave maximisation. By using mathematical decomposition techniques, the optimisation problem is decomposed into multiple-layer subproblems which can be resolved efficiently. With this method, a cross-layer algorithm is derived to achieve the near optimal solution. Finally, numerical results are illustrated. Compared to the existing schemes, our proposed algorithm can both maximise the sum of logarithmic per user average transmit rate and enhance the system transmit rate.