An LMI-based discrete time nonlinear observer for Light-Emitting Diode optical communication

Light-Emitting Diode (LED) optical wireless communication is a potentially low-cost, sustainable approach for enabling high-speed free-space and underwater transmissions within a limited communication range. Establishing a tightly controlled line of sight (LOS) between transmitter and receiver is a significant challenge because the angle of the alignment is not directly measured and has to be estimated. To address this problem, we propose a novel switched-gain discrete-time nonlinear observer for an LED-based optical communication model in which the nonlinear output functions are composed of nonlinear vector functions of multi-scalar combinations of the states. Lyapunov function-based analysis that ensures global stability is used to design the proposed observer in each piecewise monotonic region of the LED output functions. Furthermore, we prove via a quadratic Lyapunov-based approach that a constant stabilizing observer gain design approach has no feasible solution when the entire LED optical communication range is considered. Therefore, a suitable switched-gain nonlinear observer is derived for non-monotonic output measurement equations. Simulation results are shown together with extensive comparisons with the Extended Kalman Filter (EKF) to illustrate the performance of the proposed switched-gain observer design.