Improved Angle-of-Arrival Estimation of Narrow Gaussian Beams for Mobile FSO Platforms

Due to the narrow beamwidths of laser Gaussian beams, accurate tracking of laser beam's angle of arrival is an important problem in mobile free-space optical communications. In most optical receivers today, fine tracking of angle of arrival involves estimating the location of the focused beam spot projected onto a focal plane array. However, for very thin Gaussian beams, both the location, as well as the energy of the spot varies considerably with the variation of angle of arrival. In this study, we have analyzed the relationship between the angle of arrival and the energy of laser spot on the focal plane. We then exploited this relationship to enhance the angle-of-arrival estimation performance of our proposed receiver that takes into account both the location as well as the energy of the laser spot while estimating the angle of arrival. The derived Cramér-Rao bounds indicate that the system performance can be enhanced significantly for narrow Gaussian beams when both the spot location and energy are exploited for angle-of-arrival estimation.