Theoretical Research And Experimental Analysis Of Dsss-based Optical Wireless Communication System And Channel

Wireless optical communication is a kind of communication technology,which takes the light as the carrier and the free space as the communication channel.In the mobile communication,the number of mobile communication users is increasing,the wireless spectrum bandwidth becomes more and more intense,and the wireless optical communication technology has been widely concerned because of its wide bandwidth.As one kind of wireless optical communication,UV communication has the characteristics of small interference and non line of sight communication.It can be used in special occasions to meet the needs of special communication,so it has important research value and extensive application scenarios.Ultraviolet wireless optical communication technology is still in its infancy and development stage,there are some key technical issues to be resolved.Ultraviolet communication channel is a free space in the atmosphere,with the complexity and diversity of the open,signal receiving sites,the transmission of ultraviolet light signal transmission brings a lot of uncertainty,so to combine many kinds of communication technology to improve the reliability and flexibility of the system.In depth understanding of the characteristics of the atmospheric UV channel,design different communication systems according to the actual application requirements,and continuously improve the performance of the communication system,which is the hot spot and difficult point of ultraviolet wireless optical communication.Supported by the National Natural Science Foundation of China,this paper studies the basic theory and experiment of ultraviolet non line of sight spread spectrum communication,and the main innovations are as follows:(1)based on Monte Carlo method,the multi scattering channel model is established,which can obtain the channel impulse response of different receiving and transmitting elevation angle,beam angle,field of view,communication distance and different weather conditions.The effects of different channel scene parameters on the impulse response of the channel are analyzed from two aspects of pulse broadening and channel loss.The accuracy of the model is verified by the channel loss experiment to a certain extent.Based on this,the upper bound of the ultraviolet communication distance is calculated by the simulation results.(2)in view of the problem of interference in the ultraviolet communication system,the paper presents the scheme of the ultraviolet spread spectrum communication technology,and carries out the system simulation and experiment of the communication rate of 8 Kbps.The simulation and experiment results show that the spread spectrum scheme can effectively reduce the error rate and improve the system performance.Due to the limitations of the device can not be carried out more high rate experiments,the paper uses simulation platform to compare the performance of different rate spread spectrum and OOK(Keying On-Off)system.(3)in view of the problem that the loss of the channel is very large and the receiving end is very weak,the paper proposes a scheme of RAKE receiver diversity.The scheme is based on the ultraviolet spread spectrum system,which uses the multipath propagation of the ultraviolet light signal,and carries out the weighted adjustment and compounding of the multipath signals to enhance the signal to noise ratio of the receiving end.Three ways of merging are simulated and compared.The results show that the RAKE scheme can improve the signal to noise ratio and reduce the bit error rate of the ultra violet communication system.