Research And Implementation Of Synchronization Method In Visible Light Image Transmission System

Indoor Visible Light Communication(VLC)based on Light Emitting Diode(LED)has attracted much attention in the concept of sustainable development with low carbon as the background due to its advantages such as UWB,anti-electromagnetic interference and green energy saving.Wireless LAN is the key development direction.Aiming at the characteristics of Orthogonal Frequency Division Multiplexing(OFDM)modulation and indoor visible light communication channel,In order to facilitate the fusion of WIFI(Wireless Fidelity)and LIFI(Light Fidelity),this paper improves the frame structure of IEEE 802.11 a,and researches,optimizes and verifies the synchronization method involved in visible light image transmission.The main work of this paper is as follows:Firstly,the characteristics of visible light image transmission and channel are analyzed.In order to improve the spectrum utilization and facilitate the fusion of WIFI and LIFI,this paper proposes an OFDM visible light image transmission scheme based on secondary modulation.Compared with the conventional visible light communication scheme based on DCO-OFDM(DC Biased Optical OFDM),the spectrum utilization rate of this transmission scheme could be increased by one time.Secondly,based on the secondary modulation OFDM scheme,the frequency synchronization,timing synchronization and sampling synchronization are analyzed.Combined with indoor visible light channel analysis,this paper optimized the leading part of WIFI frame structure.Specifically:For frequency synchronization,based on the classical frequency synchronization algorithm,two weighted frequency synchronization algorithms are verified and analyzed.The analysis results show that the joint frequency estimation based on pilot and leader sequence has better MSE(Mean Square Error)performance than the joint frequency estimation based on CP-leader sequence in indoor visible channel.For timing synchronization,the classical timing synchronization algorithm based on Pseudo-Noise Code(PN)sequence is analyzed.Since the Correlation peak of timing synchronization algorithm based on PN sequence is not sharp,this paper further analyzes the timing synchronization algorithm based on Constant Amplitude Zero Auto Correlation(CAZAC)sequence and cross correlation algorithm.The results show that both algorithms have sharp correlation peaks,but the timing synchronization estimation based on CAZAC sequence has less resource consumption.Therefore,a timing synchronization algorithm based on CAZAC sequence is proposed in this paper.Analysis and verification show that the algorithm has the best BER(Bit Error Rate)performance in visible channel.Finally,based on the AD9361 evaluation board and the self-developed visible light communication driver circuit,the synchronization algorithm based on the frame structure is implemented in hardware,and the visible light image transmission system is measured.With 1W LED transmitting power,the communication range is 2.3m,and the communication rate of the visible light transmission system is 10 Mbps.The system can play 1080 P and 30FPS(Frames Per Second)videos smoothly,which proves the high efficiency of the visible light transmission system.