MGF Methods for Fixed and Gain Saturated Optically Preamplified FSO Links Impaired by Misalignments and Atmospheric Turbulence

Abstract

The Gaussian approximation is commonly used to evaluate the performance of free space optical communication systems. However, other performance evaluation methods such as the saddle point approximation, Chernoff bound and the modified Chernoff bound have also been used. This paper investigates the performance of fixed and gain saturated optically preamplified communication systems limited by factors such as strong atmospheric turbulence and pointing errors using various evaluation methods. Average bit error rate results are obtained over a range of average transmitted powers for free space optical communication systems without pointing error and those with pointing error using different saturation regimes, normalised beam widths and pointing error standard deviations. Results obtained in this paper show over a propagation distance of 1500 m, a receiver diameter of 0.15 m performed better than a receiver diameter of 0.03 m when the pointing error standard deviation is 0.1. Also, a receiver diameter of 0.03 m performed better than a receiver diameter of 0.15 m when the pointing error standard deviation is 4.These results show that while larger receiving lenses performed better when pointing error effects are minimal or absent, smaller receiving lenses are better when pointing error effects are dominant. Additionally, it is shown in this paper that while fixed and gain saturated optical preamplifiers produced similar performances when the decision threshold at the receiver is adaptive, the saddle point approximation is not useful for gain saturated optically preamplified receivers. Also, results in this paper showed optimal and near-optimal adaptive decision thresholds for the modified Chernoff bound and Gaussian approximation, respectively.

Multiple Transmitters for Gain Saturated Pre-Amplified FSO Communication Systems Limited by Strong Atmospheric Turbulence and Pointing Error

“…2(a), minimum average BER results for FSO communication systems using a non-adaptive decision threshold show that in gain saturated and fixed gain preamplified FSO communication systems using single or multiple transmitters, the best average BER performances were observed with 𝐷 𝑟𝑒𝑙 values of about 0. values of about 0.5. These results for FSO communication systems with increased number of transmitters align with earlier works [20], [30] with a single transmitter, where it was shown that to obtain optimal average BER performances, 𝐷 𝑟𝑒𝑙 should have values of about 0.2 and 0.5 when a non-adaptive decision threshold and an adaptive decision threshold is used at the receiver respectively. Note that based on these results, the 𝐷 𝑟𝑒𝑙 used for the adaptive and non-adaptive decision thresholds in Figs.…”

“…The advantage of using a preamplifier was also shown in [3] as systems with a preamplifier performed better than systems without a preamplifier by about 6dB at the same target BER. In [20], the author used evaluation methods such as the gaussian approximation (GA), saddle point approximation (SPA) and modified Chernoff bound (MCB) to analyse the performance of FSO communication system consisting of a single receiver and a single transmitter. In [20], BER results were obtained while considering AT, GS, PE and ASE noise effects.…”

“…In [20], the author used evaluation methods such as the gaussian approximation (GA), saddle point approximation (SPA) and modified Chernoff bound (MCB) to analyse the performance of FSO communication system consisting of a single receiver and a single transmitter. In [20], BER results were obtained while considering AT, GS, PE and ASE noise effects. Also, [20] dealt with various OA operating modes and decision thresholding schemes.…”

“…In [20], BER results were obtained while considering AT, GS, PE and ASE noise effects. Also, [20] dealt with various OA operating modes and decision thresholding schemes. However, since only a single transmitter was considered in [20], the advantage of using multiple transmitters in an atmosphere limited by AT and PE was not considered.…”