Energy-efficient mode selection and power control for device-to-device communications

Device-to-device (D2D) communications have been a promising technique for future long term evolution (LTE) systems. In this paper, we aim to maximize the system energy efficiency (EE) of a communication system including both conventional cellular users and D2D users. We consider two different D2D access cases depending on whether all D2D users can be accessed or not. In both cases, the EE maximization problem is formulated as a combinatorial fractional programming problem. We then use the fractional programming and the branch-and-bound (BnB) method to find the optimal solution. Furthermore, low complexity algorithms are proposed according to the network load. Simulation results demonstrate the effectiveness of the proposed algorithms.