Research On Key Technologies Of Visible Light Communication Links Based On LED

Visible light communication(VLC)system based on LED transfers information through the visible light signal radiated by LED with high frequency response,which can realize high speed wireless data transmission and the requirement of illumination,simultaneously.Compared with RF wireless communication,visible light communication using(VLC Mentioned in this thesis following all means VLC based on LED)the wavelength from 380 nm to 780 nm visible light signal,has the advantages of high anti-interference,wide spectrum band,high level communication rate,no electromagnetic interference,high safety and security,and no spectrum license.Compared with infrared and ultraviolet communication,VLC has the benefits of high signal power and no healthy threat,so that it has become one of the most popular researches.This thesis studies the one of the VLC key problems,the channel link.VLC channel link includes the visible light source,signal propagation,and wireless access,which is the whole process of the light signal from the source terminal to the destination terminal.The work of this thesis mainly includes the following points.1.Through the propagation process,interference and noise are the two main issues.Solar light noise suppression method based on Hilbert-Huang theory,with consideration of Poisson random network theory,visible light channel model and the characters of background light noise is proposed in this thesis.Also transmission method with variable data rate is proposed,based on the relationship betw een the VLC system’s achievable data rate and propagation distance.The approximation signal to noise power ratio of VLC channel is proposed based on the Poisson random network theory,as well as the estimation probability distribution of received light signal,light signal source power,interference light power,multipath light power.The experimental platform was designed,according to the visible light channel model,and constructed to measure the spectral distribution and time variation characters of background light noise in the wireless channel,as well as the power probability distribution character of received visible light signal.And the related noise suppression techniques based on Hilbert-Huang theory were proposed with respect to the experimental data,and could eliminate the solar noise,effectively.Also,the variation characteristics for data rate and communication distance in VLC system was studied based on the pass loss characterization.The data rate will be adjust according to the communication distance for the purpose of the stability of the system in real time.2.Through the visible light link source process,the design of LED light source array is researched,and also the optimization method of communication performance based on the direction angle and beam angle of LED array is researched.Distribution pattern of LED array with one,two or more LED light is carefully designed according to the measurement between communication and illuminance,and combined with experimental data,the indoor LED communication performance of the beam angle of LED array was analyzed and the related optimization technique was proposed based on the direction angle and beam angle of LED array.The technique can adjust the data transmission rate of a certain are a through changing the direction angle of LED array.The data transmission rate and SNR performance of indoor VLC system for a certain area on the receiving plane is optimized and the requirement of omni-bearing and all standing illumination is satisfied,too.3.Through the wireless access process,a wireless access method for multi-user is proposed for the RGB LED array.Since visible light signal cannot penetrate walls and the coverage area of LED signal is small,a multiple access method for multi-user combined with the space-wavelength division multiplexing technology is proposed in this thesis,based on the spectral character of RGB white LED illumination device.It can achieve multi-user access and high data transmission under the requirement of indoor lighting criteria.This technique has no interference with the existing RF communication network,and there is no interference among multiple users within one area.Also,due to the small coverage area of LED signal,there is only a little interference between different areas.