Research And Design Of PPM Modulation And Demodulation System For Wireless Optical Communication

Wireless optical communication,also known as free space optical communication,which transmits information through optical signals propagating in free space.It has the advantages of traditional radio communication and optical fiber communication,and has the advantages of transmission bandwidth,unregulated frequency band resources,strong anti-electromagnetic interference and high confidentiality.With the progress of optical device technology and the growth of the demand for mass data communication brought about by the rapid development of information technology such as 5G,wireless optical communication technology has a broad application prospect.In wireless optical communication system,intensity modulation with direct detection(IM/DD)is widely used,the commonly used modulation methods are OOK and pulse position modulation(PPM),while PPM modulation has a higher power efficiency and lower error rate,OOK is simpler,and bandwidth efficiency is higher,but anti-jamming is not as good as PPM.Considering the optical signal attenuation caused by the absorption and scattering of the atmospheric channel,and the influence of atmospheric turbulence on the optical signal,this paper chooses PPM modulation as the modulation method of the wireless optical communication system.This article focuses on the PPM modulation and demodulation method,analyzes the principles of each step in the PPM modulation and demodulation in detail,and puts forward a new method of symbol synchronization,which is simpler,more direct,stable and reliable than the traditional method of symbol synchronization.Based on FPGA,we also realizes the modulation,bit synchronization,symbol synchronization and demodulation of PPM signal.Finally,the PPM modulation and demodulation scheme designed in this paper is adopted in the wireless optical communication system,and zero error code communication can be realized,which was confirmed by the test of the error code tester.The main work of this article is as follows:1.Through theoretical analysis and calculation,the characteristics of PPM modulation and OOK modulation in power efficiency,bandwidth efficiency,transmission capacity and error probability are compared.2.Based on FPGA,the PPM modulation scheme is designed,the simulation experiment is carried out in the software simulation platform,and the code is downloaded to FPGA,and the correct modulation of PPM is realized.3.The advantages and disadvantages of the traditional symbol synchronization method are analyzed,and a brand new method of symbol synchronization is proposed,which is simple,direct and more reliable,and the simulation experiment is carried out in the software simulation platform,and the code is downloaded to FPGA,and the correct symbol synchronization of PPM is realized.4.Based on FPGA,the design of digital phase-locking ring is realized,and the bit synchronization of PPM signal is realized,and the correct bit synchronization of PPM is realized through simulation and experiment on FPGA.In the wireless optical communication system,the PPM modulation and demodulation scheme designed in this paper is adopted,and the actual experiment is carried out to realize the zero-error code communication process.