In free-space optical links, relative motion of stations requires an active mechanism to maintain optical alignment between the stations. Cooperative optical beam tracking is a viable solution to this problem. In this alignment scheme, each station tracks the arrival direction of its impinging beam to employ it as a guide to precisely point its own beam toward the opposite station. In short range applications in which the light propagation delay is negligible, the transmitter points its optical beam along the arrival direction. However, in long distance applications with significant propagation delay, a point- ahead mechanism is necessary to compensate for displacement of the receiving station during propagation time. This requires the transmitter to predict future location of the receiver and point its optical beam toward the predicted location. This paper is devoted to a stochastic approach in designing a control law for the cooperative optical beam tracking systems with significant propagation delay. The main contribution of the paper is introducing the propagation delay in previously developed models and employing the modified model to develop an appropriate controller design approach.
['Arash Komaee', 'P. S. Krishnaprasad', 'Prakash Narayan']
Stochastic control for long range cooperative optical beam tracking