In this paper, we study two adaptive beam control techniques, where the beam divergence angle is adjusted at the transmitter to (i) maximize link availability or (ii) minimize transmitter power while maintaining target link availability. For this purpose, we provide closed-form expressions about the link availability and optimum beam divergence angle under the effect of generalized two-dimensional Gaussian distribution of the alignment error between the transmitter and receiver. These simple and closed-form expressions reduce the computational complexity for performance optimization. Thus, they can be used to (i) reduce the power consumption required for adaptive beam control and (ii) facilitate the fast operation of the control techniques. The results show that the adaptive beam control techniques can improve system performance under various scenarios. (C) 2018 Optical Society of America
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