Backflash Mitigation via Scheduling in FSO Systems With Quantum Key Distribution

Quantum key distribution (QKD) is a potential technology suitable for fulfiling the stringent requirements of upcoming 6G wireless networks in terms of privacy and security. Nevertheless, QKD systems have several practical limitations in terms of hardware design and implementation, making them vulnerable to malicious attacks. Specifically, we adopt a detection scheme using a single-photon avalanche diode and due to the avalanche effect, a secondary photon is emitted, called backflash, which can be captured by an eavesdropper. To mitigate this security loophole and enhance the secrecy performance, we consider a selection mechanism which schedules a single user for secret key exchange purposes. In particular, we propose an intelligent two-stage selection scheme in a multiuser free-space optical QKD deployment. We derive closed-form expressions for the secrecy success probability by considering a generalized pointing error model. Our results confirm that the proposed scheme yields significant secrecy gains over conventional methods.