Vector light-field distribution in non-line-of-sight ultraviolet wireless communication.

Extensive studies on non-line-of-sight ultraviolet (NLOS UV) communications have primarily focused on path loss or channel impulse response. By leveraging Monte Carlo-based methods that can track photon trajectories and capture angular information of received photons, this paper further investigates the directional distribution characteristics of the arriving light at the receiver. To this end, we first establish a three-dimensional vector light-field distribution model for arbitrary sampling points in space based on Monte Carlo photon trajectory tracking. Then, by constructing the response distribution over discrete detection directions, we extract the dominant receiving direction and its corresponding angle, which characterize the principal arrival orientation of photon energy. Based on the proposed model, the effects of transmitter elevation angle, spatial position, and related parameters on the directional response distribution and the dominant receiving direction are analyzed. Experiments are conducted in representative scenarios under both coplanar and non-coplanar conditions. The experimental results agree well with the theoretical analysis, demonstrating that the proposed method can effectively characterize the directional properties of NLOS UV channels. The obtained results provide useful insights for future studies on receiver orientation optimization, direction selection, and spatial/angular diversity reception design.