Joint beamforming and resource allocation for wireless-powered device-to-device communications in cellular networks

In this paper, we develop wireless-powered device-to-device (D2D) communications underlaying a time-division duplex cellular network, where D2D users (DUs) coexist with cellular users (CUs) and harvest energy from a base station during the downlink time for sustaining communications during the uplink time. Two spectrum access modes, coexistence and hybrid, are considered for the DUs. Our goal is to maximize the sum rate of the DUs by jointly designing beamforming and time allocation as well as DU transmit power, while maintaining the quality-of-service for the CUs. In a single DU scenario, the joint design problems in the downlink and uplink are decoupled and solved in sequence. By doing so, the optimal downlink beamforming is found via a semi-definite relaxation (SDR) approach. From a DU power control perspective, a scheme is proposed for obtaining the optimal solution of the remaining uplink design in the coexistence and hybrid modes. For a scenario with multiple DUs, a converted SDR problem is considered to attain the optimal solution of the original problem when the uplink receive beamforming is appropriately predetermined to null out the DU interference. We present simulation results to quantify the impact of various network parameters on the performance of the proposed schemes.