Relay-Assisted Satellite QKD Systems using MMW Radio-over-FSO for Vehicular Networks

This paper aims at proposing a novel satellite quantum key distribution (QKD) system for vehicular networks. Quantum key from a satellite (i.e., a trusted node) is transmitted through a free-space optical (FSO) channel to a high-attitude platform (HAP) using radio-over-FSO (RoFSO) technique. HAP playing a role as a relaying node forwards the key to moving vehicles via millimeter-wave (MMW) channel. Key information generated is encoded on MMW subcarrier using binary phase shift keying (BPSK) signaling and then recovered at the receiver thanks to a dual-threshold detector. We derive the mathematical expressions for security analysis of the proposed QKD system in terms of quantum bit error rate and ergodic secret-key rate taking into account the channel loss and receiver noise. The numerical results confirm the feasibility of the proposed QKD system.