Power allocation for energy harvesting-based D2D communication underlaying cellular network

Cellular network with energy harvesting (EH) powered Device-to-Device (D2D) communication can increase cellular network capacity and meanwhile keep a high efficiency of spectrum and energy. In this paper, we consider a single cellular network, where one pair of D2D user (DU) reuses the uplink channel of a cellular user (CU), and the D2D transmitter has EH capability. In order to investigate the optimal power allocation scheme for both CU and DU, we formulate a short-term weighted system rate maximization problem, which has a non-concave nature. Meanwhile, the constraints of minimum transmission rate and maximum available power of both CU and DU are also considered in the optimization problem. Subsequently, we convert the non-concave problem to a concave one by introducing a tight lower bound for the original weighted system rate and a transformation equation. By solving the concave problem, the closed-form expression of optimal power allocation scheme for both CU and DU can be obtained. In the simulation, we evaluate the optimal power allocation scheme, and show the maximal achievable system rate under different EH power and rate. Besides, we expose the results on the relationship between system rate and channel distance of CU and DU link, as well as the relationship between system rate and battery size of the D2D transmitter.