Energy efficiency maximization of full-duplex two-way relay-assisted device-to-device communications underlaying cellular networks

With the substantial progress in self-interference (SI) cancelation, the full-duplex (FD) technique, which allows the communication user to transmit and receive signals over the same frequency band simultaneously, enables a significant enhancement of spectral efficiency (SE) in comparison with the traditional half-duplex (HD) technique. Recently, relay-assisted device-to-device (D2D) communications underlaying cellular networks have aroused a great deal of research interests due to its high SE. For the new meaningful paradigm of the combination of the FD and the amplify-and-forward (AF) relay-assisted D2D communications, analyzing the SE and energy efficiency (EE) is crucial, which have not been investigated in the existing works. In this paper, we focus on the EE of the FD two-way (FDTW) relay-assisted D2D communications with uplink channel reuse by considering the residual SI at the D2D users and compare it with the HD counterpart. Our goal is to find the optimal transmission powers and amplification gain to maximize the system EE while guaranteeing SE requirements and maximum transmission power constraints. A new two-tier alternative iteration optimization algorithm is proposed to solve the optimization problem. Simulation results show that (1) the results obtained by the proposed algorithm is very close to those obtained by the exclusive searching method, (2) smaller residual power of SI leads to better performance of EE and SE, (3) the SE obtained by FDTW relay-assisted D2D networks is higher than the SE obtained by the HD counterpart, and (4) the EE comparison of FDTW relay-assisted D2D networks and its HD counterpart depends on the residual power of SI. The EE obtained by FDTW relay-assisted D2D is higher than the EE obtained by HD counterpart only when the residual power of SI is sufficiently small.