Adaptive Minimization of Direct Sunlight Noise on V2V-VLC Receivers

Shot noise due to direct sunlight is the major cause of SNR degradation in vehicle to vehicle visible light communications (V2V-VLC) outdoors. This shot noise can be simply reduced by the receiver ‘looking away’ from the sun rays. However, this has to be done without reducing the received optical signal power, which is a 3-D tracking problem, where both transmitter and receiver are moving. This paper analyzes the resulting optimization problem and finds the optimal angle at which the instantaneous SNR is maximized. This depends on the incident angle of the optical signal as well as the incident angle of the sunlight. Note, the mobility adds random additive noise in addition to rapid angle variations. The paper uses an extended- Kalman filter to minimize the error and possible drift in the optimal angle in the presence of noisy measurements. This results in an adaptive SNR optimization system for real-time vehicle to vehicle visible light communications. We have also presented the analytical solution to the SNR optimization problem. Simulation results, on a curved freeway on a bright sunny day, demonstrate close matching between the actual optimal SNR and that achieved by the extended-Kalman filter.