| Free space optical communication has the advantages of high transmission rate,large transceiver bandwidth,fast construction cycle,low system budget cost,compatibility with traditional telecommunication network and adapt to complex terrain environment.It is considered as the alternative of the next generation of high-speed wireless broadband transmission or access technology.In recent years,terminal users have increasingly higher requirements for the bandwidth and flexibility of high-speed signal access.In order to achieve broadband wired access,high-speed wireless access,and improve the signal stable transmission distance in tunnel and other complex terrain areas,the FSO system integrated with radio over fiber technology has attracted increasing attention.Although Ro F technology takes into account the application advantages of massive bandwidth of wired communication and ubiquitous of wireless communication.It often requires secondary modulation and demodulation of subcarrier and continuous optical carrier.In particular,when it is integrated with FSO system,application characteristics of different kinds of channels,parameters of photoelectric devices and interface configuration need to be further considered.Therefore,it is very important to select and study several advanced modulation and demodulation schemes with large bandwidth,high speed,low single-bit information transmission cost and adapt to the applications of transceiver and transmission link in Ro F-FSO system.In order to reduce the system cost as much as possible and improve the communication capacity as much as possible,the polarization multiplexing technology is used to modulate the FSO system and the Ro F-FSO system,and the transmission performance of the two systems is compared and analyzed,and some advanced modulation and demodulation schemes are used to carry out related research work.This paper analyzes the structure configuration and working principle of FSO system,and expounds the architecture mode and application characteristics of Ro F system.On this basis,the transceiver,transmission and access characteristics of high-speed signals in FSO system and Ro F-FSO system are studied.Aiming at the above two kinds of systems,the polarization multiplexing technology,alternate mark inversion technology,n-ary pulse amplitude modulation technology,and orthogonal frequency division multiplexing modulation technology are mainly introduced and introduced,and related simulation experiments are completed.The specific research results are described as follows,the FSO communication system and the Ro F-FSO communication system using the polarization multiplexing AMI technology are designed.The transmission of 10Gbit/s single polarization AMI signal and double polarization AMI signal in FSO communication system and Ro F-FSO communication system is realized.The FSO communication system and the Ro F-FSO communication system using polarization multiplexing pulse amplitude modulation are designed.The research results show that when the bit error rate is lower than 10-3.The transmission of 10Gbit/s single polarization PAM-N signal and double polarization PAM-N signal in FSO communication system and Ro F-FSO communication system is realized.AMI has stronger atmospheric turbulence resistance effect compared with PAM technology,and dual polarization can increase the transmission capacity of the system more than single polarization.The FSO communication system and the Ro F-FSO communication system using MQAM-OFDM are designed.The 60 Gbit/s 64QAM-OFDM signal,70 Gbit/s 128QAM-OFDM signal and 80 Gbit/s 256QAM-OFDM signal are transmitted through the FSO communication system and the Ro F-FSO communication system respectively.The transceiver and transmission of the signal are realized,and the reception quality of the 64QAM-OFDM signal under different laser line widths is compared.The results show that compared with 128QAM-OFDM and 64QAM-OFDM modulated signals,256QAM-OFDM modulated signals can improve the spectrum utilization rate and lead to the increase in bit error rate. |
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