Adaptive energy-efficient configuration of power resource for OFDMA with opportunistic DF relaying

In this paper, adaptive power allocation (PA) on the source and relay is investigated to maximize energy efficiency (EE) for OFDMA opportunistic DF links (O2RL). We derive EE function from O2RL model by appropriate definition of variables to represent source/relay PA, subcarrier transmission mode selection (STMS) elegantly. Theoretical analysis demonstrates that EE function for O2RL is strictly quasi-concave with respect to the overall transmit power. Exploiting the quasi-concavity property of the EE function, an EE-oriented optimal PA iterative method for O2RL is proposed which used the bisection method to speed up the search of the optimum. Simulation results demonstrate that the O2RL is more energyefficient than traditional cooperative relaying strategies (TCRS), and the proposed method as compared to the sum throughput maximization PA method (STMPA) is able to significantly improve performance in terms of system EE.