Resource allocation for downlink two-user OFDMA systems with wireless network coding

We first address a sum-rate maximization problem under a sum-power constraint. By introducing the concept of virtual user, we solve the problem by using the Lagrange dual method. We then look into a sum-power minimization problem under sum-rate constraints. The Lagrange dual method and an exhaustive search method are proposed, which achieve similar performance, but the former has a lower complexity. Our simulation shows about 3-dB power saving of our scheme over an OFDMA system without network coding.