Design and Optimization for Energy-Efficient Full-Duplex Transmission With Direct Links

Full-duplex (FD) technique has been extensively studied recently, due to its effective improvement in spectral efficiency (SE) and significant advance on self-interference cancellation (SIC). Relay technique can expand network coverage, reduce power consumption and improve energy efficiency (EE) under bad direct links situation. Combining the FD technique with the relay technique can further improve the system's SE and EE. In this paper, both bidirectional direct and relay FD transmission strategies for transmitting the signal as much as possible with fewer antennas and less self-interference are designed first. At the same time, the SE analysis of the designed transmission strategies under the existence of residual self-interference (RSI) is given. In addition, minimum total energy consumption (TEC) problems and their solutions of the designed transmission strategies with joint optimization of transmit power (TP) and transmit time (TT) are given. The minimum TEC problems consider non-ideal power amplifiers (PAs) efficiency and non-negligible circuit powers (CPs) consumption. Furthermore, a simple EE analysis of the designed transmission strategies with symmetric and asymmetric transmission tasks in two directions is given. Simulations reveal that when RSI coefficients are below 0.2, our two-way FD relay transmission (TWFDT) strategy can improve the system's SE and EE.