Tracking Algorithm for Multi-Beam Laser Communication Terminals

Abstract

The low beam divergence of free space optical communications offer increased data rates that are not restricted by interference. Both single and multi-Beam laser communication terminals (SBTs and MBTs) require efficient algorithms for tracking multiple beams with sub-millirad accuracy and between 100Hz - 1kHz control bandwidths. In addition, MBT tracking systems track the full frame in order to acquire and track multiple beams in multiple places on the detector at once. To our knowledge, no suitable algorithms exist that offer multi-beam tracking for MBTs which simultaneously allow beams to move and (dis)appear randomly. We propose a novel multi-beam tracking algorithm using computationally inexpensive temporal-based techniques inspired by multiple target tracking. This method leverages frame association based on directional beam behavior and statistical analysis for accurate beam classification and labeling. Experimental results using commercially available hardware show that our algorithm can track 1000 beams with over 99% precision at 1 ms per frame overhead, utilizing a 1.8 GHz processor. The tracked beam location is within 1 pixel of the true center. An analytical model of the algorithm was derived from mixed replacement urn problems and complete homogeneous symmetric polynomials. Combining these yielded in a, to our knowledge, new probability distribution we coined CombiTron. Our temporal-based tracking technique significantly enhances MBT performance with minimal computational overhead. This approach can be useful to applications outside of multi-beam tracking, including single beam tracking. The theory matches simulations and experiments, allowing for accurate estimation of tracking performance and requirements.