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Reserch On Atmospheric Influence And Mitigation Technology In Near Sea Level Laser Communicaton

Posted on:2016-10-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:S J GaoFull Text:PDF
GTID:1108330464451480Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
Because the laser communication system has the advantage of high bandwidth, high speed, strong anti-interception ability, strong anti-interference ability and small light, it is very suitable for deep space, star to star, air to air and air to ground link communication. Therefor it has attracted much attention in recent years. With the continuous development of China’s marine forces, the application prospect of laser communication system on the ship to ship, ship to shore is more and more broad.Compared with the deep space, star to star, air to air and other different application environments, signal transmission mediumof ship borne laser communication device is the atmosphere located above the sea of tens of meters.The atmospheric attenuation and atmospheric turbulencein the area has serious interference to the keep of communication link and communication quality. Therefore, the theoretical analysis and experimental verification was carried out in this paper, the atmosphere influence of offshore laser communication was analyzed, the method of inhibiting atmosphere effect was studied.Firstly, on the basis of introducing the composition of offshore atmospheric laser communication systemand working principle, the link model of offshore atmospheric laser communication system and the key atmospheric parameters estimation model which influence the quality of communication were analyzed in this paper, focused on the analysis of the absorption effect, scattering effect and flickering and drifting effect caused by refractive index fluctuation.Secondly, in order to evaluate the influence of atmospheric attenuation and atmospheric turbulence to offshore laser communication, measurement scheme of several key atmospheric parameters was designed. Measuring principle and scheme were proposed using simultaneous measurement of two band laser,850nm and 1550nm.The measurementmainly includes:using optical power meterto measurethe extinction coefficient of atmospheric absorption effect; using near infrared camera to measure the scintillation index of laser spot andthe angle of arrival fluctuation variance. After obtaining the measurement data of all time, the scintillation index and the angle of arrival fluctuation variance of 1550nm wave band laser image can be calculated. Putting the calculation results in the classical calculation method of the atmospheric structure constant of refractive index, we can get the scintillation index and the angle of arrival fluctuation variance of the target in 850nm wave band laser image, and then get the comparison result between thecalculated result andthe measured synchronous 850nmimageof laser spot.Based on the results of above data analysis, and on the basis of the domestic and foreign scholars’study and improvement, the paper further modified plane wave scintillation model proposed by Tatarskii, and derived theformula in improved Hill spectrum and Von Karman spectrum, and also improved the drift model caused by the angle of arrival fluctuation used in the U.S. Naval Research Laboratory, to make it more suitable to describethe sea surface atmospheric environment in task area.Thirdly, suppression methods were proposed respectively aiming at the effect of the atmosphere on the stability of communication link and the quality of communication.Link stability of offshore atmospheric laser communication mainly rely on the acquisition, tracking and pointing(ATP) of the system to the beacon. The ATP positioning system for laser generally used the CCD optical imaging device.When the laser communication link passed through the atmosphere, due to the influence of the atmosphere, the laser spot image acquired by the ATP system was degraded image. It wouldcause the tracking and pointing precision drops, even make it unable to complete the acquisition. The morphological filtering method was commonly used in engineering, this method needed relatively smaller amount of calculation, and was easily implemented by hardware system, but the physical meaning of algorithm itself did not restore the original shape and positionof the spot. In recent years, the commonly used method of adaptive optics had been widely used in large aperture astronomical observation, but for high frequency laser communication, there was lack of adequate experimental validation, and the technology of adaptive optics system was complexand cost highly. So this paper researched on the problem of the laser communication system beacon image influenced by atmospheric turbulence, through improved constrained conjugate gradient iterative algorithm. It proposed a fast blind restoration method of degraded laser spot image. On the basisof rapid recovery in the spot image, the spot target was segmented, and the connected domain was calculated to extract recovery spot center location information in real time to improve extraction accuracy of ATP system on the spot center.In the inhibitory effect of the atmosphere on the quality of communication, this paper presented a diversity receiving scheme using real-time image processing technology.2 near infrared cameraswith 150mm aperture lens and infrared camera with large aperture lens were used to acquirespot image synchronously, and the datawas analyzed and compared by the previously mentionedquantitative method, to verify the inhibition effect ofdiversity reception on the atmospheric influence.Finally, through the laser communicationexperiment of 2.1 km in the city and 8.9 km near the sea surface, theoretical analysis combined with experimental data was used.According to the parameters, such ascommunication error rate, receiving light power, the communication link receiving light power between theory analysis and the measured data was up to 70% with high consistency. The accuracy ofthe proposed improvement of atmospheric parameters estimation model and the effectiveness of the blind deconvolution algorithm were verified to provide powerful support for the follow-up project practice.
Keywords/Search Tags:near sea level laser communication, refractive index structure constant, dual band measurement, MIMO, VPI simulation, power communication links, communication link bit error rate
PDF Full Text Request
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