Abstract
We model the impact of atmospheric turbulence-induced phase and amplitude fluctuations on free-space optical links using synchronous detection. We derive exact expressions for the probability density function of the signal-to-noise ratio in the presence of turbulence. We consider the effects of log-normal amplitude fluctuations and Gaussian phase fluctuations, in addition to local oscillator shot noise, for both passive receivers and those employing active modal compensation of wave-front phase distortion. We compute error probabilities for M-ary phase-shift keying, and evaluate the impact of various parameters, including the ratio of receiver aperture diameter to the wave-front coherence diameter, and the number of modes compensated.
Highlights
Evaluating the performance of a heterodyne or homodyne receiver in the presence of atmospheric turbulence is generally difficult because of the complex ways turbulence affects the coherence of the received signal that is to be mixed with the local oscillator
By noting that the down converted electrical signal current can be characterized as the sum of many contributions from different coherent regions within the aperture, we showed that the probability density function (PDF) of this signal can be described by a modified Rice distribution
The parameters describing the PDF depend on the turbulence conditions and the number of modes compensated at the receiver
Summary
Evaluating the performance of a heterodyne or homodyne receiver in the presence of atmospheric turbulence is generally difficult because of the complex ways turbulence affects the coherence of the received signal that is to be mixed with the local oscillator. Later analyses have attempted to overcome these limitations and fully characterize the statistics of heterodyne optical systems by assuming a highly simplified model of atmospheric effects [3,4]. An alternate approach, aimed at overcoming the limitations of previous work, is based on numerical simulation of heterodyne optical systems [5,6] None of these prior works have resulted in an accurate statistical description of the performance of phase-compensated homodyne or heterodyne systems. We provide analytical expressions for the error probability of synchronous communication systems, and use them to study the effect of various parameters on performance, including turbulence level, signal strength, receive aperture size, and the extent of wavefront compensation
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