Full-Duplex or Half-Duplex D2D Mode? Closed Form Expression of the Optimal Power Allocation

In this paper, we investigate and derive a closed-form expression for the power allocation scheme of full duplex (FD) device to device (D2D) communications underlaying wireless cellular network. In this scenario, we consider the FD-D2D pair sharing the uplink resources of cellular users. We first derive a closed-form expression for the ergodic rate of the D2D link. Then we formulate the optimization problem which aims to maximize the D2D link rate while fulfilling the minimum QoS requirement of the cellular user. We further derive a closed-form expression for the optimal power allocation strategy for both D2D and cellular users. The simulation results show the accuracy of the derived power allocation scheme and provide important insights on the separation distance between the D2D users and the interfering cellular user. In addition, the results provide important conditions to switch between FD and half duplex (HD) D2D modes.