Research On FSO Link Power Control Method Under The Background Of Pointing Errors

Free Space Optical Communication(FSO)technology is a technology that utilizes wireless broadband access.The effectiveness and reliability of FSO links are severely affected by atmospheric attenuation,turbulence,and pointing errors(PE)in practical applications,leading to a decrease in system effectiveness and reliability.In severe cases,it can cause communication interruption of FSO links.In addition,energy constrained systems pose another pressing challenge,which is the need to address the issue of efficient energy consumption.The adoption of adaptive transmission optimization algorithms based on power control in the transmission process of FSO links and the establishment of variable wavelength optimization models for power control using emerging quantum cascade lasers are of great significance for improving the performance of atmospheric laser communication systems and promoting the development of FSO communication link reliability.The research content of this article mainly includes:1.This article elaborates on the effects of atmospheric attenuation,turbulence,and pointing errors on FSO communication systems,and provides a detailed introduction to the Gamma-Gamma atmospheric turbulence distribution,zero and nonzero boresight pointing errors,as well as the composite channel of Gamma-Gamma atmospheric turbulence distribution and pointing errors,The expression of negative exponential function of Gamma-Gamma distribution and the expression of hypergeometric function of composite channel of Gamma-Gamma atmospheric turbulence distribution and pointing error are derived.2.A power control based adaptive subcarrier phase shift keying(MPSK)algorithm was proposed,and the joint adaptation of modulation format and average transmission power was studied.The optimization problem of maximizing system throughput under the constraint of average transmission power was solved using the KKT(Karush Kuhn Tucker)theory.The asymptotic expressions for system throughput and interrupt probability were derived based on the Meijer G function.The effects of different turbulence intensities,beam waist radius,jitter standard deviation,weather conditions,and maximum modulation order on the throughput and interruption probability of the adaptive MPSK modulation system were evaluated under the target error rate requirements.And evaluated the system throughput and outage probability under two channel scenarios:Gamma-Gamma turbulence channel,Gamma-Gamma turbulence and pointing errors composite channel,with wavelengths of 1550nm,1350nm,850nm,and different visibility.3.Considering the application of Quantum Cascade Laser(QCL)technology to FSO links,a power controlled variable wavelength MPSK modulation optimization algorithm was proposed.Based on this,normalized emission power,normalized energy gain,normalized wavelength,etc.were defined.In addition,the optimization algorithm was used to investigate the nonzero boresight pointing error,The system selects the optimal wavelength based on the state information of the channel to alleviate the impact of building jitter and atmospheric interference on the communication system.In addition,the optimization issues of transmitter power,transmitter wavelength,and transmitter telescope gain were studied,and how to choose the optimal wavelength under different atmospheric turbulence conditions was analyzed.