| The advantages of free space optical communication such as high transmission rate,good confidentiality,strong anti-interference ability and large capacity attract more and more researchers to develop their potential in different application fields.The refractive index fluctuations caused by different atmospheric turbulence conditions,which leads to the destruction of the optical field coherence.Therefore,the light intensity scintillation model is very important for studying the communication quality of space optical communication.We study the signal-to-noise ratio,bit error rate,and interruption probability of the entire system communication process through the light intensity after the light wave passes through different atmospheric turbulence.Etc.communication performance.Even in clear weather,the intensity and phase of light waves fluctuate when the wireless optical link propagates through a turbulent medium.In recent years,a new statistical model of Malaga light intensity distribution has been proposed to simulate the boundaryless optical wavefront(plane wave and spherical wave)propagating through turbulent media under all irradiance fluctuations in uniform isotropic turbulence Irradiance fluctuates.Multi-aperture receiving technology is very effective in suppressing atmospheric turbulence in space optical communication transmission.Simultaneous transmission of multiple signals is independent of each other,which reduces the probability of the receiver identifying false information.The combination of modes reduces the impact of overall fading.The diversity technology and the combination technology have strong resistance to atmospheric channel attenuation,ensuring the quality of transmission.Among them,the two most commonly used combining methods are maximum ratio combining(MRC)and equal gain combining(EGC).The weighting coefficient of each branch is proportional to the signal-to-noise ratio of the branch.The greater the signal-to-noise ratio,the greater the weighting coefficient and the greater the contribution to the combined signal.This paper will analyze the probability density function of light irradiance under the atmospheric turbulence model based on the Malaga distribution in the horizontal launch system as the light intensity scintillation model caused by atmospheric turbulence.The comprehensive effects of light intensity flicker and fiber coupling efficiency caused by atmospheric turbulence are studied.The main research work is as follows:(1)The theoretical numerical solution based on the Malaga distribution model and the matching degree of the field experimental transmission data are fitted to verify the correctness of the theoretical model,and the widely used atmospheric turbulence models such as Gamma-gamma distribution and K distribution are used for theoretical simulation The matching of the curve and the experimental data fit curve to verify that the Malaga distribution is a unified model of light intensity flicker.(2)Based on the probability density function of light irradiance under the Malaga distribution model,the system communication performance is studied.Using the probability density function of the coupling efficiency of space light to single-mode fiber under the influence of Malaga distributed atmospheric turbulence,the signal-to-noise ratio and bit error rate of the fiber coupled MRC and EGC multi-aperture receiving system under direct detection are calculated,and finally the error of the receiving system The relationship between the bit rate and the signal-to-noise ratio.(3)Based on the probability density function of light irradiance under the Malaga distribution model,under different turbulent conditions,the direct detection mode MRC and EGC combination mode results in the relationship between the interruption probability and the signal-to-noise ratio.(4)The subject conducts ground simulation experiments on horizontal links.We can conduct a long-distance link experiment between Jiangbei and the Science Park.Although horizontal link experiments are very common,reports of urban horizontal links are rarely heard..In this paper,a long-distance urban link experiment is designed,and a 11.16 km ground simulation experiment is designed in the city.The optical signal of the optical terminal Jiangbei District transmitter is modulated with OOK.After passing through the atmospheric turbulence,we compensate and restore the wavefront distortion phase Then received by the receiving end of Harbin Institute of Technology,using APD and bit error meter,so that the bit error rate within the time can be tested.The research in this paper lays the foundation for the subsequent application of the direct detection multi-aperture receiving system in the horizontal link,provides a theoretical basis for the development of the Malaga light intensity distribution model,and provides experimental verification for the performance analysis of the space optical communication system. |
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