Maximizing sum rate of OFDM transmission with decode-and-forward relaying

In this paper, we aim to maximize the sum rate of an Orthogonal Frequency Division Multiplexing (OFDM) system with a relay. The relay is half-duplex, and capable of decoding the message on a particular subcarrier in one time slot, and re-encoding and forwarding it on a different subcarrier in the next time slot. When the relay is active, the destination combines the signals from the source and the relay pertaining to the same message in the two time slots. For the situations where the relay does not transmit on some subcarriers because doing so does not improve the sum rate, we allow the source to transmit new messages on these idle subcarriers. Joint optimization of subcarrier assignment and power allocation for a two-slot period is performed. Based on the optimization result, an algorithm to achieve feasible solutions is also proposed. Simulation results show that the proposed algorithm almost achieves the optimal sum rate, and outperforms the existing methods.