Development Of Platform And Research Of Synchronization Technology For Visible Light Communications Based On DCO-OFDM

Visible Light Communication(VLC)is a new type of optical wireless communication technology that uses Light Emitting Diode(LED)as a light source to achieve high-speed data communications while illuminating.Compared with traditional wireless radio frequency(RF)communications,VLC has the advantages of rich spectrum resources,high data transmission rate,strong confidentiality,no electromagnetic pollution,low cost,etc.It has broad application prospects in many fields,like the IoT(Internet of Things),smart city,smart home,subway,high-speed railway,indoor positioning navigation,underground operations,etc.It is currently the potential of wireless communication technology.The research work of this thesis is supported by Huawei Innovation Research Project(HIRP)(No.20150101).Due to the limited modulation bandwidth of LEDs,it is difficult to meet the requirements of high-rate communications.Therefore,Orthogonal Frequency Division Multiplexing(OFDM)modulation technology in traditional wireless RF communications is introduced into the VLC system.One of the most classic ones is DCO-OFDM(Direct Current Biased Optical-OFDM)modulation technology.Due to its high spectral efficiency and low system complexity,it has been thoroughly researched and widely used.This paper studies the VLC system based on DCO-OFDM.The main research contents of this thesis are as follows:1.For the demand of low-cost,high-stability experimental platform in the research of VLC,VLC platform based on DCO-OFDM is designed and implemented.It uses software defined radio(SDR),and is based on USRP(Universal Software Radio Peripheral)hardware platform and the open source GNU Radio software platform.This platform consists of a hardware subsystem and a software subsystem.The hardware selection and circuit implementation are completed.The DCO-OFDM modulation method is realized by building flow diagrams.VLC Demo Java program is developed for file transfer and testing,and VLC media player is used for visual video real-time transmission.The measured results show that the VLC platform based on DCO-OFDM achieves the real-time transmission of files and videos visually,and it can communicate stably within a distance of 160cm while the packet loss rate is less than 10-2.It provides a good experimental verification platform for subsequent theoretical research.2.For the problem of the low timing synchronization accuracy in VLC system based on DCO-OFDM,the synchronization technology of VLC system based on DCO-OFDM is studied.The Park-PN timing synchronization algorithm is proposed.A new method of calculating the decision metric function is designed by using the weighting method of PN sequence in time domain.The Park-Bias timing synchronization algorithm is proposed.The Park-Bias joint decision metric function is designed by adding DC offset additionally on the training sequence and using the normalized mean function to determine the timing decision range.The simulation results and the measured results of the platform show that the Park-PN algorithm has the best synchronization performance when the signal-to-noise ratio(SNR)is high.The Park-Bias algorithm has the best synchronization performance when the SNR is low.Both algorithms can effectively improve the accuracy of timing synchronization and improve the overall communication performance of the system.