Free-space laser communication performance in the atmospheric channel

Abstract

In spite of the tremendous technical advancement of available components, the major limitation of free-space laser communication (lasercom) performance is due to the atmosphere, because a portion of the atmospheric path always includes turbulence and multiple scattering effects. Starting from a fundamental understanding of the laser communications system under diverse weather conditions, this chapter provides a comprehensive treatment of the evaluation of parameters needed for analyzing system performance. The significance of higher-order statistics of probability density functions of irradiance fluctuations due to turbulence to performance analysis is explained. Starting from link analysis, the necessary expressions relating link margin, bit-error-rate, signal-to-noise-ratio, and probability of fade statistics are presented. Results for laboratory-simulated atmospheric turbulence and multiple scattering are presented. Example numerical results for simulations of lasercom systems operating under various atmospheric conditions are presented for various scenarios such as uplink-downlink (e.g., between ground and satellite, aircraft or UAV) and horizontal (terrestrial) link. Both turbulence and multiple scattering effects have been included in the analysis with both on-off keying and pulse-position modulation schemes. Statistical estimation and computation of communication parameters presented in this chapter will be useful in designing and optimizing lasercom systems that are reliable under all weather conditions.

Effect of avalanche photodiode and thermal noises on the performance of binary phase‐shift keying‐subcarrier‐intensity modulation/free‐space optical systems over turbulence channels

“…So far, several atmospheric turbulence channel models have been proposed, of which log-normal and gamma-gamma models are the most commonly used for the cases of weak-to-moderate and moderate-to-strong turbulences, respectively. Previous works showed that they provided a good agreement between theoretical and experimental data [2,[4][5][6][7].…”

“…where s 2 s is the log intensity variance that depends on the channel's characteristics as given as [4,6] …”

“…When the turbulence is weak, it is generally accepted that the primary influence of turbulence X(t) is a random process with log-normal distribution. Assuming that the average of the random process X is normalised to unity, its probability density function (pdf) is given by Majumdar [6] …”

Bayesian and frequentist estimation of the performance of free space optical channels under weak turbulence conditions

“…For weak to moderate atmospheric turbulence conditions, the turbulence-induced fading can be assumed as a random process that follows the lognormal distribution model which has the following probability density function (pdf) with respect to I [3,17],…”

“…For an outdoor line-of-sight optical channel link, atmospheric turbulence represents an important capacity mitigation factor, in the sense that the received optical signal intensity fluctuates due to variation of the refractive index along the propagation path [3][4][5][6][7][8][9]. Hence, it is reasonable to expect that in a real FSO environment, optical channels will appear to have randomly time-varying characteristics.…”