Joint Optimization for Proportional Fairness in OFDMA Relay-Enhanced Cellular Networks

The deployment of relay stations in OFDMA cellular networks is a promising solution to provide ubiquitous high-data-rate coverage. However, it makes the resource allocation a more crucial and challenging task. In OFDMA relay-enhanced cellular networks, we formulate the optimal instantaneous resource allocation problem including path selection, power allocation and subchannel scheduling to achieve the proportional fairness in the long term. We first propose a low-complex resource allocation algorithm named ´VF w PF´ under the constant uniform power allocation, and then use a void filling method to make full use of the wasted resources caused by the unbalanced data rates of the two hops in a relaying path. We further use a dual decomposition approach to solve the original optimization problem efficiently in its Lagrangian dual domain, and propose a modified iterative water-filling algorithm named ´PA w PF´. Simulation results show that our resource allocation algorithms improve the throughput for cell-edge users, and achieve a tradeoff between system throughput maximization and fairness among users. Moreover, compared with the constant power allocation, the optimal power allocation can not gain much in system throughput but can significantly improve the throughput for cell-edge users and also the fairness.