Moving Relays in Downlink Multiuser Networks - a Physical-Layer Security Perspective

Moving relay (MR) has been proved to be an effective technique to eliminate vehicle penetration loss (VPL) in vehicular communications. In this paper, the function of MR in a downlink multiuser network is investigated from the perspective of physical-layer security. Secure probability (SP), defined as the probability that the user inside a vehicle can receive downlink messages without any information leakage to the eavesdroppers outside of the vehicle, is considered as the performance metric. By comparing SP performance, MR aided dual-hop transmission is shown to outperform direct and fixed relay (FR) aided transmissions, particularly in high VPL region. Then, we propose two user scheduling schemes for the considered downlink multiuser network, which select the user with minimum eavesdropper information and maximum MR information respectively. Closed-form expressions of SPs for the proposed two scheduling schemes are derived. Experiment results show that the proposed scheduling schemes enhance SP performance compared with random scheduling. The scheduling scheme selecting the user with minimum eavesdropper information achieves higher SP than the one selecting the user with maximum MR information.