Detection and Relay Selection for Virtual Full-Duplex Amplify-Forward Relay Systems

This work proposes low-complexity detection and relay selection strategies for virtual full-duplex (VFD) amplify–forward (AF) relay systems with practical digital modulations. We first derive maximum likelihood detection and the corresponding optimal relay selection (RS) rule, which achieve the best error performance but incur prohibitive complexity. To address this problem, a suboptimal separate detection (SepD) method is developed, enabling symbol-by-symbol detection with minimal delay. Based on error probability analysis, a SepD-based RS (SepRS) is further introduced. Simulation results show that SepRS achieves near-optimal error performance with significantly lower computational complexity, making VFD-AF relaying more practical.