Joint subcarrier pairing and power allocation for two-way energy-efficient relay networks

In this paper, energy-efficient resource allocation algorithms are investigated to improve the energy efficiency (EE) in two-way multi- carrier amplify-and-forward (AF) relay networks by ensuring the quality-of-service (QoS) and balancing the EE of the user links. We formulate an EE-balancing optimization problem that maximizes the ratio of the spectral efficiency (SE) and the total network power consumption by jointly designing the subcarrier pairing at the relay node and power allocation at all nodes under the total transmit power and QoS constraints, thereby leading to a mixed integer programming problem which turns out to be non-convex. Further, we resolve the problem by a series of convex transformations and propose an iterative EE algorithm to determine the solution through Lagrangian dual decomposition. Moreover, a suboptimal EE algorithm is also investigated with reduced complexity at the cost of acceptable performance degradation. Simulation results validate the performance gain of the proposed algorithms and show the performance tradeoff between EE and SE.