Energy Efficiency of Full- and Half-Duplex Decode-and-Forward Relay Channels

This article studies the energy efficiency (EE) of a three-node decode-and-forward (DF) relay channel, where the relay operates in full-duplex (FD) or half-duplex (HD) mode. In particular, for the FD mode, both the residual self-interference (RSI) and the extra circuit power consumption introduced by the self-interference cancellation (SIC) at the relay node are considered and modeled as linear functions over the relay transmission power. Under this setup, the EE maximization problems for the considered FD and HD modes subject to the total transmission power and spectral efficiency (SE) constraints are formulated as max-min problems, whose optimal power allocation is computed by fractional programming. Next, the EEs for the FD, HD, and direct transmission (DT) modes are compared under different channel conditions, and a hybrid mode selection scheme, i.e., selecting the one with the maximum EE among the above three modes, is proposed. Besides, we also prove that both the EE and the SE monotonically increase with the total transmission power under a given condition. Finally, numerical results show that the maximum EE of the FD relaying exceeds those of the HD and DT ones when the required SE is relatively high. Furthermore, the proposed hybrid mode selection scheme can provide up to 192.4% higher EE compared with the DT mode.