Time Domain Hybrid Modulation Scheme For Visible Light Communication

With the in-depth study of VLC,people often use more complex modulation technologies such as orthogonal frequency division multiplexing technology so as to improve communication performance.Of course,the cost of modulation equipment also increases.Based on the existing modulation methods of visible light communication,this paper proposes a time-domain hybrid modulation scheme for OOK and PPM.The modulation scheme is composed of OOK and PPM.It combines the advantages of OOK and PPM,which simplifies the complexity of modulation equipment and ensures better communication performance.Firstly,this paper investigates the basic working principle of indoor visible light communication,analyzes the channel modeling of indoor visible light communication and introduces two simplest single carrier modulation technologies OOK and PPM in visible light communication,and points out that the effect of only using OOK or PPM in some scenarios is unsatisfactory,which paves the way for the future time-domain hybrid modulation scheme.Secondly,this paper proposes OOK/PPM time-domain hybrid modulation scheme in visible light communication system,describes the working principle of OOK/PPM time-domain hybrid modulation scheme,and analyzes the two application scenarios mentioned above for OOK/PPM modulation,so as to verify the feasibility of OOK/PPM modulation in the above two application scenarios.The simulation results show that if the bit error ratio is set to 10^-3,the received power required for OOK/PPM in the power-limited scenario is between OOK and PPM and is less than1dB compared to OOK.In scenarios with different transmission requirements,the bit error ratio of OOK/PPM is between OOK and PPM,and achieve 10^-33 or better bit error ratio performance ahead of OOK in the same received signal-to-noise ratio.Finally,in order to ensure that the LED lamp does not flicker and the brightness is enough to meet the lighting requirements,it is necessary to dim the light.Therefore,after the OOK/PPM hybrid modulation scheme is proposed,it is combined with the commonly used dimming scheme PWM in visible light communication.In addition,combination of OOK and PWM or PPM and PWM have many shortcomings,so the performance comparison of the three systems proves that OOK/PPM and PWM combination scheme can reach a compromise in receiver sensitivity and other performance.The simulation results show that the receiver sensitivity of PWM dimming scheme based on OOK/PPM is less than 1 dB compared to the PWM dimming scheme based on OOK so as to maintain the bit error ratio less than 10^-3.In order to maintain the constant speed and reliability of the dimming system,the symbol rate required by PWM dimming method based on OOK/PPM is lower than the PWM dimming method based on PPM by 2 Mb/s or more,so the former system is easier to implement.