Research On Technology Of Optimizing Communication Performance In Point-to-point Visible Light Transmission System

With the increasing demand of high-speed and low delay data interaction services,short-range wireless transmission system has become an important part in the communication professional research.Compared with WLAN,Bluetooth,RFID and other short-range wireless access technologies,visible light communication is emerging as an information transmission medium with many advantages,such as low cost,high bandwidth,no occupation of wireless spectrum and so on.As a useful help of 5G high-performance data interaction service,the close point-to-point high-speed VLC system is more suitable for supporting data interaction with secure private demands in some specific practical applications.In the research and development of VLC direct transmission system,on the one hand,it is necessary to set the transmission power of LED and the number of lamp beads.By designing a more reasonable light source layout,the target plane can obtain bright and balanced light intensity and effective receiving power,furthermore,the signal-to-noise ratio of received signal is improved.In addition,considering the combination VLC with adaptive modulation technology to take full advantage of the modulation bandwidth of OFDM subchannel,the adaptive bit power allocation methods are studied to speed up transmission rate in point-to-point visible light direct data communication system.This paper briefly introduces the development process and application prospect of visible light communication technology,and highlights the research status of light source layout and adaptive bit power allocation methods.In terms of the theoretical basis related to the research work,the fundamental concepts of point-to-point VLC system model,light source selection and layout,modulation technology,and channel estimation are described.The working characteristics of three commonly used multicarrier modulation technologies in VLC system are also compared and analyzed.In the research of VLC light source optimal layout,according to the formula of light intensity superposition,the maximum distance between LED light beads under the condition of uniform illumination is deduced.Based on the square,hexagon,ring and other traditional array light layout,a new ring-angle compensation array light layout suitable for point-to-point high-speed data transmission is proposed by adding compensation array at four corners based onthe traditional ring array light layout.The results of calculation and experiment show that the new light source layout can balance the illumination and improve the signal-to-noise ratio of the received signal,so as to meet the quality requirements of high-speed data transmission in the short distance VLC system.In the research of power allocation methods of short-range VLC system,firstly,the common fixed allocation schemes are analyzed;secondly,the allocation algorithms such as Greedy,Fischer and Chow in adaptive allocation are discussed,and the computational complexity,system bit error rate differences and algorithm operation time among them are compared;Then,the simple packet bit allocation algorithm based on different thresholds is studied in depth,and a new packet bit power allocation algorithm is proposed to simplify the feedback signaling transmission of carrier power.In addition,the modulation module,adaptive parameter generation module and demodulation module related to adaptive technology are designed in the point-to-point VLC hardware system.And complete the test of high-speed file transmission performance.The research results show that the improved allocation algorithm can effectively simplify the calculation amount of power allocation under the condition of guaranteeing the bit error rate performance.Meanwhile,it can improve the bandwidth efficiency of signal transmission in the process of data file communication and then improve the information exchange rate in the short distance communication system.