Abstract
We analyze the ergodic capacity and epsilon-outage capacity of coherent optical links through the turbulent atmosphere. 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 wavefront phase distortion. We study the effect of various parameters, including the ratio of receiver aperture diameter to wavefront coherence diameter, the strength of the scintillation index, and the number of modes compensated.
Highlights
In this study we study the maximal rate at which the information may be transferred through free-space optical communication links using coherent detection
We study the ε-outage capacity Cε Eq (10) for different outage probabilities ε as a function of the average turbulence free signal-to-noise ratio (SNR) γ0, the receiver aperture diameter D, the number of spatial modes J removed by the compensation system, and the strength of atmospheric turbulence
We have developed analytical expressions for the ergodic and outage capacities for free-space optical communication links using coherent detection and active modal compensation of wavefront phase distortion to overcome turbulence-induced fading
Summary
In this study we study the maximal rate at which the information may be transferred through free-space optical communication links using coherent detection. The applicability of this result is shown by noting that, in the regime of weak turbulence when the signal coherent term is very strong (r→∞), the density function (2) becomes highly peaked around the mean value γ0, and there is no fading to be considered In this case, as should be expected, Eq (10) tends towards the Shannon limit log2(1+γ0). We study the ε-outage capacity Cε Eq (10) for different outage probabilities ε as a function of the average turbulence free SNR γ0, the receiver aperture diameter D, the number of spatial modes J removed by the compensation system, and the strength of atmospheric turbulence. For the normalized aperture D/r0=10, compensation of J=20 modes eliminates almost completely the 50-dB fade margin penalty at ε=0.001
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