Research On Key Techniques Of Mobile-Phone Camera Based Visible Light Communication

With the rapid development of mobile Internet and Internet of Things(IoT)technologies,the number of mobile terminals and IoT devices will explode growth,which will bring huge challenges to existing wireless communication technologies in terms of spectrum resources,power consumption and cost.With the development and popularization of light-emitting diode(LED)lighting,LED-based visible light communication(VLC)technology has attracted extensive research and attention.VLC has the advantages of rich spectrum resources,no need for authorization and certification,low cost,no radio frequency interference,strong confidentiality and harmless to the human body.Therefore,it can solve the challenges of spectrum resources,power consumption and cost faced by existing wireless communication technologies.Using the mobile phone camera as the receiver of the VLC system can significantly reduce the cost and complexity,and have good mobility.In the future,indoor positioning and navigation,key authorization and other fields,mobile phone camera based VLC has a good application prospect.Since the research of VLC technology started late,there are still some key problems to be solved before the actual application.To this end,this paper establishes the research topic and conducts in-depth research on key technologies of the mobile phone camera based VLC.In this paper,the key problems in the traditional signal demodulation scheme of the mobile phone camera based VLC system are studied in depth,including large grayscale value random noise,large column grayscale value fluctuation and low robustness.In addition,the performance of the line of sight-optical camera communication(LOS-OCC)and non-line of sight-optical camera communication(NLOS-OCC)systems is analyzed and compared in detail.It is worth noting that LOS-OCC and NLOS-OC.C refer to the mobile phone camera based VLC using line of sight and non-line of sight link optical signals,respectively.The main research contents and innovations of this paper are as follows:(1)Column grayscale value selection scheme with low random noise is proposed.The column grayscale value selected for signal demodulation has severe random noise interference,which affects the performance of the system.In response to the problem,this paper proposes a column grayscale value selection scheme with low random noise.The experimental results show that the column grayscale value selected by the proposed column grayscale value selection scheme in this paper has extremely low random noise interference.(2)Algorithms for reducing the fluctuation of grayscale value are proposed.The selected column grayscale value for signal demodulation fluctuates severely,so that the grayscale value points cannot be uniformly distributed on both sides of the threshold curve,which affects the correct rate of the grayscale value converted into a logical value,thereby affecting the system performance of.In response to this problem,this paper proposes the moving exponential average(MEA)algorithm and the exponential transform(ET)algorithm to reduce the grayscale value fluctuation.The experimental results show that both MEA and ET algorithms can effectively reduce the grayscale value fluctuation and significantly improve the transmission rate and distance of the system.(3)Thresholding schemes against grayscale value fluctuation are proposed.The traditional polynomial fitting based thresholding scheme can not resist the grayscale value fluctuation,and the computational complexity is high,which seriously affects the performance of the system.Aiming at this problem,this paper proposes a piecewise polynomial fitting based thresholding scheme,a weighted moving average based thresholding scheme and a stripe boundary pixels based thresholding scheme.The experimental results show that compared with the traditional polynomial fitting based thresholding scheme,the three thresholding schemes against grayscale value fluctuation proposed in this paper can significantly improve the system performance.(4)Image processing based signal demodulation scheme is proposed.The traditional signal demodulation scheme only selects a column of grayscale value data from the grayscale image to demodulate the signal,resulting in low robustness of system performance.In response to this problem,this paper proposes a robust signal demodulation scheme based on image processing.The scheme utilizes all grayscale values of the grayscale image for signal demodulation,and has high system performance robustness.The experimental results show that the signal demodulation scheme based on image processing is feasible and can achieve better system performance.(5)Performance of the LOS-OCC and NLOS-OCC systems is analyzed and compared.Now,the mobile phone camera based VLC research is mainly focused on LOS-OCC.However,in practical applications,LOS-OCC and NLOS-OCC exist simultaneously.In response to this problem,this paper analyzes and compares the performance of LOS-OCC and NLOS-OCC systems.The experimental results show that the NLOS-OCC system can obtain better system performance than the LOS-OCC system.In summary,this paper proposes a number of key technologies to improve the performance of mobile phone camera based VLC system,including low random noise column grayscale value selection scheme,algorithms to reduce grayscale value fluctuation and thr-esholding schemes against grayscale value fluctuation,and the highly robust image processing-based signal demodulation scheme.In addition,the system comprehensively analyzes and compares the performance of the LOS-OC C and NLOS-OCC systems.The research results of this paper lay a solid foundation for the research and application of mobile phone camera based VLC.