Research On The Channel Spatial Correlation Of Receive Diversity Laser Communication System In Horizontal Non-kolmogorov Turbulence

Laser communication has attracted considerable attention owing to its unique advantages,such as far transmission distance,high data transfer rate,strong anti-interference ability,and high confidentiality.The receive spatial diversity technology can effectively mitigate the influence of atmospheric turbulence,which has great potential and competitiveness in the construction of future high-speed laser communication networks.In the receive diversity laser communication link,atmospheric turbulence results in rapid fluctuations at the received signal(scintillation)and other optical turbulence effects,degrading the performance of the receive spatial diversity laser communication system.At the same time,under the influence of atmospheric turbulence,the channels of receive spatial diversity system may be correlated,which will reduce the atmospheric mitigation effect of receive spatial diversity technology.In practice,laser communication terminals operate with pointing errors,which is caused by platform vibration,mechanical noise of the turntable,machining process adjustment and so on.Pointing errors can aggravate the random fluctuation of signal light,resulting in additional performance degradation of the receive diversity laser communication system.Moreover,many recent theoretical and experimental studies have shown that the Non-Kolmogorov turbulence model can describe actual atmospheric turbulence more accurately.Some key problems need to be re-researched for the actual situation of receive spatial diversity laser communication system.In this paper,the channel spatial correlation of the receive diversity system in horizontal Non-Kolmogorov turbulence is theoretical studied and experimentally verified.The average bit error rate(BER)performance of the receive diversity system over correlated horizontal Non-Kolmogorov turbulence fading is also investigated.In addition,the average BER performance of the receive diversity system under the combined effect of correlated horizontal non-Kolmogorov fading and pointing errors is analyzed.The details are as follows:(1)The channel spatial correlation of the receive diversity system in horizontal Non-Kolmogorov turbulence is studied.The analytical expressions of the channel correlation coefficient and the large-and small-scale channel correlation coefficient of the receive diversity system in horizontal Non-Kolmogorov turbulence are derived.Based on the derived analytical expressions,the restrictive relation between the power spectrum power law ?,the atmospheric turbulence inner scale 0l and the outter scale 0L with the channel correlation coefficient are given.The dependence of channel correlation distance on the spectrum power law ? is obtained,which provide an important reference for the design of the receive diversity system.(2)The average BER performance of the receive diversity system over correlated horizontal Non-Kolmogorov turbulence fading is studied.The analytical expressions of the average BER of coherent detection and direct detection maximum ratio combining(MRC),equal gain combining(EGC)and selection combining(SC)receive diversity systems over correlated horizontal Non-Kolmogorov turbulence fading are derived.Based on the derived analytical expressions,the effect of power spectrum power law ? and channel separation distance on the BER of coherent detection and direct detection MRC,EGC and SC receive diversity systems are obtained.(3)The average BER performance of the receive diversity system under the combined effect of correlated horizontal non-Kolmogorov fading and pointing errors is studied.The analytical expressions of the average BER of coherent detection and direct detection MRC,EGC and SC receive diversity systems under the combined effect are derived.Based on the derived analytical expressions,the influence of the spectrum power law ?,pointing error parameters and channel separation distance on the BER of different systems under the combined effect are analyzed.These systems include coherent detection and direct detection MRC,EGC and SC receive diversity systems.In addition,the optimal channel separation distances of coherent detection and direct detection MRC,EGC and SC receive diversity system are obtained.(4)The theoretical verification experiment of the receive diversity system in 11.16 km urban horizontal link was conducted.The spectrum power law ? and the channel correlation coefficient of the receive diversity system are measured.The average BER of the coherent detection and direct detection MRC and EGC receive diversity systems are analyzed according to the experimental light intensity samples.The experimental results show that the atmospheric turbulence of the urban horizontal link is Non-Kolmogorov turbulence,and the measured values of the channel correlation coefficient agree well with the theoretical values.The average BER results of the experimental samples of the coherent detection and direct detection MRC and EGC receive diversity systems are consistent with the theoretical analysis results.In this thesis,our work is a basic research based on the actual situation of receive spatial diversity laser communication system.The work of this thesis can provide theoretical and experimental basis for the analysis,design and optimization of receive spatial diversity laser communication system in horizontal Non-Kolmogorov turbulence.