Secrecy capacity and pressure in multiple-lane vehicle-to-vehicle visible light communication channel: an empirical analysis

In vehicle-to-vehicle visible light communication (V2V-VLC), the irregular shape of the vehicle headlight radiation pattern, dynamic traffic conditions and ambient noise variation at different times of the day contribute to a built-in physical-layer security (PLS) for the system. In this paper, we investigate the secrecy capacity of the V2V-VLC system based on an empirical model of the multiple-lane V2V-VLC configuration. The study considers the variations in the received optical power at positions that emulate the trajectories of vehicles obtained from the Next Generation Simulation (NGSIM) initiative of the Federal Highway Administration in the USA. In addition, we investigate the secrecy pressure that forecasts the probability of the eavesdropper (Eve) presence at certain positions around the legitimate receiver (Bob). Closed-form expressions of the lower and upper bounds on the secrecy capacity and secrecy pressure are derived and evaluated based on the measurements. The results confirm the inherent security characteristics of dynamic V2V-VLC systems using headlights as transmitters because the channel conditions between the transmitter (Alice) and Bob which differs from the conditions between Alice and Eve. The position-dependent channel conditions result in varying secrecy capacities across different lanes and relative positions of Bob and Eve to Alice. The attained secrecy capacity can reach up to 1 nats/s/Hz, corresponding to the scenario when Bob is in the highest received power area on the middle lane at a distance of 9 m from Alice, and Eve is in the lowest received power area on the right-hand lane with a separation distance of 40 m from Alice. The secrecy pressure on the middle lane is lower than the right-hand and left-hand lanes.