18 April 2005 Coherent optical receiver for PPM signals under atmospheric turbulence
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In free-space optical communications, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal. We propose to use focal-plane arrays to collect optical signals from different spatial modes simultaneously, and then recombine them optimally. Experimental setup for proof-of-concept coherent adaptive array detection experiment using 32-Pulse Position Modulated (PPM) signals under atmospheric turbulence has been completed. Adaptive combining of experimentally obtained heterodyned PPM signals with pulse-to-pulse coherence, in the presence of simulated atmospheric turbulence is demonstrated. The adaptively combined PPM signals are phased up via a Least-Mean-Square (LMS) algorithm suitably optimized to operate with PPM in the presence of additive shot-noise, and detected via a maximum likelihood software receiver. Convergence study of the algorithm is presented and results with simulated PPM signals and real PPM signals experimentally obtained at the laboratory are presented.
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Michela Munyoz Fernandez, Victor A. Vilnrotter, "Coherent optical receiver for PPM signals under atmospheric turbulence", Proc. SPIE 5712, Free-Space Laser Communication Technologies XVII, (18 April 2005); doi: 10.1117/12.591269; https://doi.org/10.1117/12.591269

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