Performance Research On Flat-topped Beam Wireless Optical Communication

Optical wireless communication(OWC)possesses the advantages of high data-rate,immunity of electromagnetic interference,small volume,light weight,and low power consumption,which is treated as one of next-generation communication technologies,especially for the payload constrained small satellite and unmanned aerial vehicles(UAV).Most of OWC researches are based on Gaussian beam.However,flat-topped beam's central irradiance of is more uniform,and beam radius is less broadened under atmospheric turbulence,which has the potential to improve the performance of OWC and attacks more and more attention.However,the previous researches on the performance of flat-topped beam OWC are generally based on the classical optical transmission theory with stationary optical axis,and the research conclusions are only valid in stationary application.In mobile application,the OWC link must be established and maintained by acquisition,tracking and pointing(ATP)mechanism.The pointing error from ATP mechanism will lead to the random jitter of optical axis.In this case,the scientific problem for the performance research of flattopped beam OWC is to integrate the pointing error theory and the classical optical transmission theory.In this paper,the application scenes with pointing errors are fouced on the small satellites and UAVs.The performance models for flat-topped beam wireless optical communication in free space and atmospheric turbulence are presented.The simulation environments are established.And the contrast analyses are also carried out.The research contents are detailed described as following:1.Performance researches on flat-topped beam based OWC in free space.Base on the free space diffraction theory of flat-topped beam,the flat-topped beam far-field irradiance distribution is obtained.Combined with the pointing error probability density function(PDF),the performance statistical models including received power,signal-to-noise ratio,power fluctuation PDF,fade probability and average bit error rate are presented.The analytic formulas of the performance statistical models for the flat-topped beam OWC in free space are deduced for the first time by approximating the far-field irradiance distribution to the cylindrical distribution and the circular receiving aperture to an arc aperture.Then the Monte Carlo simulation environment is established,the accuracy of theorical results is validated and the contrast analyses on the performances of flat-topped beam and Gaussian beam based OWC are carried out.The results show that the flat-topped beam is insensitive to pointing errors in free space.If the attitude control accuracy of small satellite can reach tens of ?rad,adopting flat-topped beam can simplify the system complexity by removing the MEMS mirror.2.Performance researches on flat-topped beam based OWC under atmospheric turbulence.Base on the atmospheric propagation theory of flat-topped beam,the flat-topped beam long-term average irradiance is obtained.Combined with the pointing error PDF and turbulence induced power fluctuation PDF,the performance statistical models including average received power,average signal-to-noise ratio,joint PDF,fade probability and average bit error rate are presented.The analytic formulas of the performance statistical models for the flat-topped beam OWC under atmospheric turbulence are deduced for the first time by approximating the long-term average irradiance distribution to the Gaussian distribution and the circular receiving aperture to the square aperture.Then the phase screen simulation environment with pointing errors is established,the accuracy of theorical results is validated and the contrast analyses on the performances of flat-topped beam and Gaussian beam based OWC are carried out.The results show that although flat-topped beam is more sensitive to pointing errors under atmospheric turbulence,adopting flat-topped beam can greatly improve the UAVs OWC performance at pointing errors of dozen ?rad.In conclusion,this paper solved the problems of performance analysis and design for flat-topped beam OWC in free space and atmospheric turbulence.And the application modes and effects of flat-topped beam in small satellites and UAVs OWC have been discussed comprehensively.This work provides a solid theoretical foundation and a specific design guidance for the development of the OWC terminal.