Research And Implementation On The Key Technology Of Visible Light Implicit Imaging Communication

Visible light communication（VLC）is a research hotspot in the field of wireless communication in recent years,and optical camera communication（OCC）is an important research direction in VLC.With the popularization of smartphones equipped with high definition cameras and liquid crystal displays（LCDs）with high resolution,the communication between display and camera link develops rapidly,providing a new application scenario for OCC.The most common application of display-camera link is using a mobile phone to scan a quick response code（QR-Code）for achieving information.Moreover,unobtrusive communication between display and camera imperceptible to human eyes attracts more and more researchers'attention.However,the research of visible light implicit imaging communication technology is still in the primary stage,and many problems need to be solved urgently.This paper launches a preliminary research on visible light implicit imaging communication,focusing on the research of visible light implicit imaging communication mixing characteristics modeling,mixing detecting and estimating and system designing.The main work and innovation is as follows:1.Aiming at the secondary imaging mixing problem in visible light implicit imaging communication,the mixing problem of implicit imaging communication is modeled based on the imaging integral sampling characteristics,then the mixing factor is introduced as main parameter to describe imaging mixing.The above model is deeply analyzed,and corresponding experimental verification is carried out.The conclusions are drawn on the imaging mixing areas and the variation rule of mixing factor under different imaging conditions.Based on the imaging integral sampling characteristics,a mathematical model of the imaging mixing problem is proposed and the mixing factor is introduced as the main parameter to describe the imaging mixing.Combining the row-by-row refresh characteristics of the display and the rolling shutter characteristics of the camera,the model is analyzed under different combinations of refresh rates and imaging direction.Further experiments are carried out under the corresponding imaging conditions,and the experimental phenomena accord with the model analysis,which verifies the rationality of the model.On the basis of the model,the time variation rule of mixing factors is analyzed,and the theoretical calculation method of mixing factor and its variation period is derived.This work provides a basic theoretical model for the following research.2.On the basis of the model,a frame mixing detecting algorithm and a frame losing detecting algorithm based on the statistical characteristics of the difference frame,a maximum likelihood based mixing factor estimating algorithm are proposed.Considering the imaging mixing between display and camera leading to poor bit error rate（BER）performance of complementary frame scheme,the implicit imaging mixing detecting and estimating is studied on the premise that the camera frame rate is equal to the display refresh rate.The imaging mixing problem of the display-camera link is studied by leveraging the statistical characteristics of the difference frame,a frame mixing detecting algorithm based on the statistical characteristics of the difference frame is proposed.Taking mixing factor time-varying due to unsynchronized transceiver refresh rate into account,the variation of the mixing factor is studied and a maximum likelihood based mixing factor estimating algorithm is proposed.Considering the frame losing phenomenon in the imaging process,a unified model is given by combining the frame loss with the frame mixture.And a frame losing detecting algorithm based on the statistical characteristics of the difference frame is proposed.The algorithms test shows that the frame mixing detecting algorithm and the frame losing detecting algorithm can effectively detect the mixing areas and frame losing locations,and the mixing factor estimating algorithm can effectively estimate the mixing factor and its variation trend which is consistent with the theoretical analysis results.3.Aiming at low reliability of information transmission caused by secondary imaging mixing in complementary frame implicit imaging communication system,a difference frame mixing detecting based design scheme of visible light implicit imaging communication is proposed.A visible light implicit imaging communication demonstration system is set up to conduct related tests.In this chapter,on the premise of retaining the outstanding advantages of simple detecting process in the complementary frame design,through reasonable design of the sender frame format,and using the frame mixing detecting algorithm proposed in the paper,the best difference frame with the lowest degree of image mixing is selected before information detecting process.The simulation result shows that the syetem design scheme can effectively improve system BER performance.Furthermore,an implicit imaging communication offline demonstration system based on difference frame mixing detecting is built,and its implicit effect,transmission rate and system BER performance are tested.Test results show that when the transceiver refresh rate is 60Hz,the carrier video is a static video,the embedding intensity is 8,the spatial diversity multiplexing is 36×64,the capturing distance is 60cm,and the capturing angle is 0 degree,the system can achieve a transmission rate of 46.08 Kbps under the premise of guaranteeing the implicit effect,and the average BER is 3.4×10^-4 without using any channel coding technology.