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Published April 18, 2005 | Published
Book Section - Chapter Open

Coherent optical receiver for PPM signals under atmospheric turbulence

Abstract

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.

Additional Information

© 2005 Society of Photo-Optical Instrumentation Engineers (SPIE). The research described in this publication was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The authors would like to acknowledge Carlos Esproles for his help in the laboratory.

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