Full-Duplex Relay for Ultraviolet Communications Using Photomultiplier Tube Receivers

Ultraviolet (UV) communication is a promising technology for future vehicle communication systems due to its inherent advantages including the non-line-of-sight ability, low background noise, and high local security. Full-duplex relay-assisted UV communications can achieve longer communication distances and higher efficiency of time-frequency utilization compared with direct UV communications. However, the full-duplex relay suffers from serious self-interferences due to the strong scattering or reflection of UV signals. To explore the influence of the self-interference, we first derive the bit-error rate (BER) for the full-duplex relay-assisted UV communication using photomultiplier tube receivers. Then we use the Gaussian approximation to derive an analytical threshold, which can be used as the initial point for searching the optimal threshold for minimizing the BER. Besides, we investigate the optimal relay placement for the full-duplex relay-assisted UV communication for minimizing the BER. The numerical results show that the derived analytical threshold is close to the optimal threshold. Besides, we find that the optimal relay placement under small self-interference is equidistant between the source node and the destination node; and the optimal relay placement will gradually approach the source node as the self-interference increases.