Research On Atmospheric Optical Communicatio Optimization Based On Adaptive Threshold

Wireless optical communication uses atmospheric channels as the transmission medium,when the light beam is transmitted in the atmosphere,the complex atmospheric environment will have a great impact on the system performance of optical wireless communications.Especially when it is affected by atmospheric turbulence,wave front random fluctuations occur in transmission beams,which could cause atmospheric turbulence effects such as flicker of light intensity,affects the stability and reliability of the system.In order to reduce the impact of atmospheric turbulence on the optical communication link,necessary measures of atmospheric turbulence suppression should be taken.When processing a received signal,it is a very important step in signal detection to implement demodulation of the transmitted signal by comparing the received signal with a threshold value.However,in the existing atmospheric laser communication system,generally the threshold is fixed when demodulating the signal,and the atmospheric channel noise is not a single additive noise but a complex superimposed noise.Because of the influence of noise,the amplitude of the signal fluctuates greatly.So it is very disadvantageous and insufficient to use a fixed threshold to judge and demodulate the signal.Therefore,we need a threshold that can be dynamically adjusted following atmospheric noise changes to demodulate the signal.In this paper,we study the signal detection and demodulation techniques based on adaptive threshold in atmospheric laser systems.First of all,the paper introduces and analyzes the formation of turbulence effects and its influence on atmospheric laser communication systems,and establishes the transmission model of the atmospheric laser system.Secondly,compared and analyzed several commonly used threshold technologies on the aspect of basic principles and performances.Based on these theory,we use the maximum likelihood signal detection method to determine the optimal threshold,and import the technology of adaptive threshold detection based on fading Kalman filtering to update the threshold,which could let the decision threshold of the signal can be adjusted dynamically in accordance with the changing trend of the atmospheric noise,so that the effect of better signal detection and demodulation can be obtained.Finally,the performance of the adaptive threshold detection technology based on the fading Kalman filter in the atmospheric optical communication system is simulated and performed.Experiments show that the adaptive threshold detection technology based on the fading Kalman filter can effectively reduce the influence of noise:When SNR = 10,the BER of the signal detection algorithm based on the adaptive threshold Kalman filter has been improved by 3 orders of magnitude compared with the fixed threshold,which is improved by 1 order of magnitude compared with the traditional Kalman filtering algorithm;When BER = 10,the signal detection algorithm based on the adaptive threshold of the evanescent-memory Kalman filter has a 4 dB improvement over the fixed threshold algorithm,which have about 0.5 dB improvement compared to the traditional Kalman filter algorithm.Therefore,this algorithm has a high practical value.