| The development of science and technology has brought changes to people's lives.The advanced communication brings convenience to everyone.At the same time,the demand for communication bandwidth and speed is also rising.The problem of wireless communication frequency band resource exhaustion and network interference is increasingly serious,so a new wireless communication mode is urgently needed.In recent years,visible light communication has attracted the attention of scholars all over the world because of its advantages such as no electromagnetic interference,unlimited spectrum and security.The display screen and camera can provide a convenient and easy to realize interface of visible light communication system.On the one hand,the display and camera are widely used in daily life,and the communication function is added to the display and video recording function,which has high commercial value;on the other hand,the two-dimensional bar code is rising in recent years,but it can only transmit static data with limited capacity,while the screen camera communication can realize the dynamic data transmission of array signal points,this new communication mode has great potential in transmission capacity.In this thesis,a Screen-Camera visible light communication system is proposed,which uses the luminous pixels on the display screen as the light transmitter and the image sensor in the camera as the light receiver.In order to make the system communicate reliably and efficiently,the communication technology of system signal point positioning method,sampling method,grayscale modulation and demodulation method are studied in depth.The main research work in this paper is as follows:1.The composition and principle of Screen-Camera communication system are introduced and analyzed,including optical transmitter display,optical receiver camera and spatial optical transmission channel.According to the system composition,the experimental platform of Screen-Camera communication system is built.On this experimental platform,firstly,the single point communication is studied,the positioning method of signal point is designed and analyzed,and the feasibility of double sampling is verified.2.Through the performance test of the system,the factors that affect the performance of the Screen-Camera communication system are studied,including the influence of noise and the influence of the communication distance between the screen and the camera.Through the analysis,it is found that the reliability of the screen camera communication system can be guaranteed when the system works in the dark environment direct link and the communication distance is 40 cm.3.In order to improve the capacity of screen camera communication system,an array signal point communication scheme using multi-level gray modulation is designed.Aiming at the location problem of array signal points,a method of correcting the received image with barrel distortion and perspective distortion by using the coordinate transformation equation of pixel points is proposed;aiming at the sampling offset caused by progressive scanning of screen,a method of adding up and down check code in each frame of image at the sending end is designed,which is of innovative significance to the research of screen camera communication at present;aiming at the communication system For the non-linear response problem of receiving and sending gray value,the modulation and demodulation technology of multi-level gray value is designed by using the method of predistortion,which simplifies the receiving decision of data.Finally,by comparing the error rate of communication experiment under different parameter settings,the text transmission with 274.6kbps of screen camera communication system in this paper is successfully realized. |
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