How Secure are AAV-Based FSO Links With Modulating Retroreflectors?

Free-space optical (FSO) links based on Modulating Retroreflectors (MRRs) present an attractive solution for autonomous aerial vehicle (AAV) communications due to their weight and power consumption benefits. However, they face a significant security challenge since any unauthorized user within the MRR's Field-of-View (FoV) can access the channel information. This letter addresses this security concern by developing an accurate channel model for MRR-based FSO links, which includes the effects of angular fluctuations of the AAV, the relative position of the eavesdropper, and the MRR's FoV size. We then model the eavesdropping probability as a function of these parameters and demonstrate that reducing the MRR's FoV, while improving link security, increases the outage probability for the legitimate user. Our analysis shows that optimizing the MRR's FoV is crucial for balancing the trade-off between security and link performance. Comprehensive simulations validate the accuracy of the analytical results and illustrate the impact of channel parameters on the system's security and performance.