A switched-gain nonlinear observer for LED optical communication

Alignment for maintaining Line-of-Sight (LoS) between the receiver and the transmitter in a LED optical communication system is a challenging problem due to the constant movement of the underlying optical platform that is caused by vibration effects and atmospheric turbulence. In this paper, we propose a robust switched-gain nonlinear observer to estimate the angular position and velocity of the receiver orientation, which is used subsequently to follow the receiver orientation. The optical communication system model involves highly nonlinear and non-monotonic output measurement equations. Furthermore, tracking the receiver with perfect alignment results in loss of local observability. Hence, a two-receiver system is utilized to provide a robust tracking system that retains observability over the entire range of operation of the system. Lyapunov function-based analysis that ensures global stability is used to design the observer; then, a static feedback controller drives the receiver orientation based on the state estimate. Finally, numerical simulations are presented on the performance of the observer-based static feedback control in accurately estimating and tracking the angular position and velocity of the receiver orientation.