Research And Implementation Of Outdoor Bidirectional Visible Light Communication System

Visible light communication has the advantages of broadening spectrum resources,green energy saving,no electromagnetic interference,and strong confidentiality.It is a supplementary method of traditional radio frequency communication.LED visible light communication refers to the use of LEDs as the light source in the system and the use of drive circuits to switch the light and dark states of LEDs at high speed to achieve lighting and communication.At present,LED has been applied in the fields of intelligent transportation,smart cities,smart homes,etc.Its application places and methods are also diverse.Applications and methods are also diverse.According to the application scenario and range,it can be divided into outdoor visible light communication with complex environment,many types of noise,and large environmental influence factors.And indoor visible light communication with small communication range,weak environmental light interference and low complexity.The research on outdoor medium and long-distance visible light communication systems can provide a means for communication in special outdoor environments,and also make a step towards the practical application of outdoor visible light communication results.This paper is aimed at the research of outdoor visible light communication system.By researching and analyzing the characteristics of outdoor channels,a white light visible light communication system suitable for medium and long distances is designed and implemented.The system uses LEDs as signal emission sources,and near-ground air as the channel environment.Optical and electrical means are used to suppress noise,making outdoor visible light communication systems reliable and practical.The main contents and innovations of this article are as follows:1. This paper models the outdoor visible light communication system,actually measures the outdoor noise characteristics,and analyzes the channels in outdoor complex environments.Through the comparative analysis with the LED's emission curve and light emission spectrum,theoretically analyze the factors affecting system performance and the difficulties and difficulties of the system.2. Aiming at the non-co-frequency noise in the system,the spectral shape of the band-pass filter is determined by analyzing the characteristic curves of the background light and the LED.A kind of bandpass filter is simulated,and the simulation results can effectively filter the noise.For a specific outdoor environment,a noise filtering and limiting amplifier circuit is designed to suppress noise from a circuit perspective.3. In outdoor VLC systems,RSis used to suppress the interference of co-frequency noise and improve the reliability of the system.And the system adopts DC equalization to improve the practicability and optimize the performance of the system.4. This paper completes the overall software flow design of the system on the ARM-based Linux embedded development platform,and optimizes the device parameters through outdoor actual testing.The system can achieve reliable real-time white-light VLC communication at 75 m outdoor in the middle and long distance,and the bit error rate is lower than 10^-5.Finally,we analyze the main factors affecting system performance.