Research On Channel Model And Dimming Method In Visible Light Communication System

In the background of limited energy,light emitting diode(LED)will replace the traditional light sources gradually and being the next generation light source due to the advantages of its low energy consumption,good reliability,small size,fast response,and high brightness ability.Visible light communication(VLC)combined illumination LED with wireless communication technology,using a quickly and dark flashing ways that LED lights to transmit signals.It provided a new method on short-range wireless communication.There are many factors affect the characteristics of the communication channel in indoors VLC,such as communication link pattern,path loss and delay multipath dispersion produced.These characteristics determine many aspects on the design of communication system,so it is essential to analysis the characteristics on VLC channel.It is obviously that the modulation characteristics of VLC is different from the other wireless communication systems,so the method which we selected about data transmission modulation scheme will affect the brightness and stability of light.For the highest possible data transmission communication,at the same time to ensure that the LED does not flash and meet the sufficient brightness,it is essential to adjust the lights.So,the main work in this paper are as follows:1.Channel modeling on considered the multipath reflections.The paper introduced two link modes of indoor visible light communication radio channel,then we analyzed the channel characteristics and the influence of its multipath.On the basis of the establishment of indoor simulation model,calculated the channel impulse response by tracking site iterative algorithm based on ray tracing model considering zero(LOS direct link),first and secondary reflection.Based on the results of simulation experiments by using MATLAB,this paper analyzed the receiving illumination on the working-face,optical power,SNR and BER.Through the simulation and theoretical analysis,this channel can reflect the influence of indoor channel more truly on visible light communication,and it can be used for the design of indoor visible light communication link.2.A dimming study based on the SC-LPPM modulation method.Dimming is the brightness control.In this paper,the principle of pulse width modulation(PWM)is presented.In consideration of the communication control,the principle of sub-carrier pulse position modulation(SC-LPPM)is analyzed.When L=4,under the premise of meeting the requirements of lighting and communication,we proposed a method to reduce the total power consumption of the system.The formula deduction of the relevant formula is carried out,and the corresponding objective function and constraint conditions are given.On the basis of considering the two reflection,considering the characteristics of the visible light communication wireless channel,thorough the simulation analysis,we achieved the goal of optimize the energy efficiency significantly that the total optical power consumption of the system.