| Laser Communication (LaserCom) offers some profound advantages over RF-based systems, such as higher-bandwidth, lower power consumption, and lower probability of intercept. However, the effect of turbulence on laser propagation is a significant challenge to current electro-optical systems. While atmospheric compensation techniques in space object imaging and high-energy laser weapons have been thoroughly investigated, optimizing these techniques for LaserCom has not been examined to the same degree. This research investigates performance-metric driven atmospheric compensation techniques to improve reliability of free-space LaserCom systems.; Several receiver-based techniques were developed and analyzed while considering constraints relevant to tactical airborne platforms. First, wavefront control techniques were considered. In a moderate range air-to-air scenario, focal plane image breakup is identified as the dominant failure mechanism causing deep fades. This led to investigation of peak intensity tracking, which reduces fade probability by greater than 50% over conventional centroid trackers and Adaptive Optics (AO) systems for scenarios studied. Second, atmospheric compensation requirements were examined based on deep fade phenomenology. Fades are classified based on complexity of the required compensation technique. For compensation techniques studied, regions of superior performance, in terms of fade probability, are identified. Peak tracking is shown to outperform AO for thresholds below approximately 4% of the unaberrated intensity. Furthermore, the boundary between superior performance regions is nearly invariant to turbulence strength. This boundary invariance simplifies operation of a composite system which is able to adaptively select compensation methodology in near real-time. An adaptive binary decision threshold is the third major focus of this research. Analytic results show that an adaptive threshold provides a bit-error rate improvement of up to 1.60 orders of magnitude (33-fold decrease) for a 10 Gbps link, and up to 0.56 orders of magnitude (3.6-fold decrease) for a 10 Mbps link. Adaptive thresholding yields improved performance without the additional cost, weight, and/or complexity of increasing source power, incorporating wavefront control at receiver, or incorporating AO at the transmitter. |
