Low complexity power allocation for two-way decode-and-forward OFDM relay networks

In a Gaussian two-way Decode-and-Forward (DF) Orthogonal Frequency Division Multiplexing (OFDM) relay network, the achievable rate region can be effectively improved by proper power allocation. However, when joint coding among all subcarriers is considered during the multiple-access (MAC) phase, the complicated multi-user detection (MUD) operation at the relay node has to be performed to approach the rate region. In this paper, the frequency-division multiple access (FDMA) constraint is involved to simplify the MUD operation, while the corresponding optimal power allocation for achievable rate region is not convex any more. Then a duality-based proximal optimization algorithm is proposed to solve this non-convex problem efficiently. Simulation results show that our simplified scheme with the FDMA constraint has only a little rate loss compared with the original optimal one, while obtaining even a minor sum rate improvement than the scheme in [6]. Therefore, by our FDMA-constraint low complexity power allocation scheme, a good tradeoff between the complexity and performance for the practical system implementation is achieved.