Research On Anti-fading Technology Of Optical Wireless Communication In Atmospheric Turbulence

With the widespread popularization and development of the fifth-generation mobile communication technology and the Internet of Things,high-speed communication is constantly facing new demands and challenges.No matter in the civil or military field,the demand for the validity and reliability of high-speed communication is increasingly urgent.Optical Wireless Communication(OWC)technology,as a kind of communication technology based on the information carrier of optical waves propagating in space,has the characteristics of high speed,safety,green,flexible layout and free from spectrum restrictions.It has important application prospect and research value in modern social development and military fields.However,atmospheric turbulence effect is an important factor that hinders the extensive deployment of OWC systems.How to improve the anti-fading performance of OWC systems under atmospheric turbulence and achieve more high-speed and reliable communication has become an important challenge faced by researchers.Based on the above requirements,this paper under the atmospheric turbulence owcs antifading technology of the system,and from the launch of the constellation design in the process of communication,the receiver array and signal detection problem study,this paper research content including multi-user antifading constellation design,receiving aperture array layout and antifading receiver design from three aspects,connect with each other and gradually in-depth.The main work and innovation points of this paper are summarized as follows:Part I: An anti-fading method for multi-user communication system under atmospheric turbulence is proposed from the point of view of constellation design.A multiplicative and unique decomposable anti-fading constellation design with intensity modulation is proposed for multi-user OWC systems under atmospheric turbulence.The constellation is designed based on the statistical characteristics of channel fading under spatially related atmospheric turbulence,which can effectively deal with the performance loss caused by signal fading.The designed constellation can combine the information of multiple users and uniquely decompose it at each user's receiving end to meet the communication needs of multiple users.In order to reduce the detection complexity,rapid demodulation and decoding of the received noisy signal are realized.The designed anti-fading constellation can be flexibly assigned to different sub-constellations to meet the needs of different users for priority and transmission rate.Simulation results show that the proposed design has a significant performance improvement compared with the TDMA scheme at the same transmission rate.Part ?: The performance loss of spatially dependent fading channel is dealt with from the perspective of receiver aperture array layout design.In order to reduce the performance loss of spatially dependent fading channels in atmospheric turbulence,an optimal layout design of aperture array at receiver terminals based on hexagonal lattice distribution was proposed.By analyzing the fading statistical model of multi-aperture receiver in atmospheric turbulence,according to the theoretical bit error rate of the system under the model,the quality factor measurement method of aperture array layout is proposed,and the aperture array layout is designed.On this basis,the performance gain of the designed array is analyzed,and the optimal range of the number of receiving apertures is obtained.The simulation results show that the evaluation results of the proposed metric method are consistent with the experimental results,and the designed layout can deal with the signal fading problem in the spatially dependent fading channel.Compared with the traditional square array layout,the proposed receiver array layout can reduce the bit error rate effectively and obtain greater performance gain in a limited area.Part ?: From the point of view of receiver design,an anti-fading method under atmospheric turbulence is proposed.Aiming at the performance loss caused by spatially dependent fading channel and background noise in atmospheric turbulence,an anti-fading receiver design based on neural network is proposed.In order to effectively improve the system error characteristics under the fading channel jointly affected by spatially related atmospheric turbulence effect and strong background noise,this paper applies convolutional neural network to optimize the receiver anti-fading performance.By setting an appropriate training set,neural network is used to deeply explore the fading characteristics of signals.The simulation results show that the proposed anti-fading receiver design can effectively deal with the signal fading,has a significant performance improvement under strong background noise,and is close to the theoretical bit error rate of the system under high signal-to-noise ratio.At the same time,the convolutional neural network edge information loss problem is experimentally analyzed,and the input layer is optimized according to the results.