Earlier works have studied the energy efficiency (EE) of half-duplex Device-to-Device (D2D) communications. However, the EE of full-duplex D2D communications underlaying cellular networks which undergoes residual self-interference (SI) has not been investigated. In this paper, we focus on the EE of full-duplex D2D communications with uplink channel reuse and compare it with the half-duplex counterpart, aiming to show which mode is more energy-efficient. Our goal is to find the optimal transmission powers to maximize the system EE while guaranteeing required signal-to-interference-plus-noise ratios (SINRs) and transmission power constraints. The optimal power allocation problem is modeled as a noncooperative game, in which each user equipment (UE) is self-interested and wants to maximize its own EE. An optimal iterative bisection-alternate optimization method is proposed to solve the optimization problem from the noncooperative game-theoretic perspective. Simulation results show that the proposed method can achieve EE close to that obtained by an existing method but with lower complexity in half-duplex D2D communications underlaying cellular networks. Moreover, the full-duplex D2D communications underlaying cellular networks outperform the half-duplex D2D communications underlaying cellular networks in terms of EE when effective SI mitigation techniques are applied.
Spectrum-Efficient Transmission Mode Selection for Full-Duplex-Enabled Two-Way D2D Communications