Hop capacity balancing in OFDMA relay networks

A novel scheduling scheme for the orthogonal frequency division multiple access (OFDMA) relay systems is proposed. In the relay systems, downlink frame is divided into two slots for two-hop transmission, corresponding to the base station (BS)–relay station (RS) and the RS–mobile station (MS) transmissions, respectively. If the capacities of two hops are not equal, cell throughput can be degraded by the bottleneck hop and radio resource can be underutilized on the non-bottleneck hop. The proposed scheme aims at increasing cell throughput while guaranteeing the minimum rate requirements of MSs, by balancing the capacities of two hops. We formulate a throughput maximization problem which satisfies the minimum rate requirements of MSs, by adjusting the lengths of both slots and allocating the subchannels appropriately. To alleviate the high computational complexity of the problem, we suggest a practical scheduling scheme that uses linear programming relaxation and postprocessing algorithm. The simulation results show that the proposed scheme guarantees the minimum rate requirements of real-time MSs more properly and provides higher cell throughput compared to the existing hop capacity balancing schemes for OFDMA relay systems.