title: Anisoplanatism in airborne laser communication.
abstract: Airborne laser-communication systems require special considerations in size, complexity, power, and weight. We reduce the variability of the received signal by implementing optimized multiple-transmitter systems to average out the deleterious effects of turbulence. We derive the angular laser-beam separation for various isoplanatic and uncorrelated (anisoplanatic) conditions for the phase and amplitude effects. In most cases and geometries, the angles ordered from largest to smallest are: phase uncorrelated angle (equivalent to the tilt uncorrelated angle), tilt isoplanatic angle, phase isoplanatic angle, scintillation uncorrelated angle, and scintillation correlation angle (Theta(psiind) > Theta(TA) > Theta(0) > Theta(chiind) > Theta(chic)). Multiple beams with angular separations beyond Theta(chic) tend to reduce scintillation variations. Larger separations such as Theta(TA) reduce higher-order phase and scintillation variations and still larger separations beyond Theta(psiind) tend to reduce the higher and lower-order (e.g. tilt) phase and scintillation effects. Simulations show two-transmitter systems reduce bit error rates for ground-to-air, air-to-air, and ground-to-ground scenarios.
authors.affiliation: Department of Electrical and Computer Engineering, Air Force Institute of Technology, 2950 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433-7765, USA. james.louthain@afit.edu
authors.forename: James A
authors.initials: JA
authors.lastname: Louthain
authors.forename: Jason D
authors.initials: JD
authors.lastname: Schmidt