Research On The Modulation Technology Of ACO-OFDM In Visible Light Communication

Visible Light Communication(VLC)can not only achieve lighting and communication at the same time,but also because of its green environmental protection,easy maintenance,high security and privacy,visibility,and controllability.So,it is widely studied.Visible light has a large bandwidth,which makes up for the shortcomings of radio frequency communication band crowding and meets the communication of a large amount of data,and is used without application,reducing communication costs.However,when the optical signal is transmitted in the outdoor atmospheric channel,due to the complex atmospheric composition,it will absorb,scatter and put atmospheric turbulence effects on the optical signal passing through the atmosphere.Among them,atmospheric turbulence will cause the optical signal to flicker,drift and expand,affecting the quality and power of the received beam.In severe cases,it will cause the interruption of visible light communication,which is one of the main reasons that hinder the application of outdoor visible light communication.In order to suppress the impact of atmospheric turbulence on outdoor visible light communication systems,this article takes the communication between vehicles and LED traffic lights in the field of intelligent transportation as an application scenario and establishes a visible light communication system for vehicles and traffic lights based on Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing(ACO-OFDM).The suppression effect of ACO-OFDM on turbulence are studied.The main research contents of this article are as follows:First of all,Compare ACO-OFDM with on-off keying modulation(OOK),pulse position modulation(PPM)and other modulation technologies.Analyze and summarize the advantages of ACO-OFDM in visible light communication systems.Immediately after the modulation and demodulation process of ACO-OFDM is studied in detail.Simulate the bit error performance and normalized transmission bit rate of ACO-OFDM.Secondly,the illuminance of the traffic light emission surface is calculated,and the causes,formation processes and effects of atmospheric turbulence are analyzed.A model for simulating atmospheric turbulence was established,and the effect of turbulence of different intensities on the visible light signal of traffic lights was simulated.Finally,a visible light communication system for communication between vehicles and traffic lights under atmospheric turbulence is established,and PPM and ACO-OFDM are introduced into the system respectively.The bit error rates of the two modulation systems under atmospheric turbulence channels are compared through simulation.The suppression effect of two modulation techniques on turbulent flow is described.The results show that under weak turbulence,medium turbulence and strong turbulence,ACO-OFDM has a better suppression effect on turbulence than PPM,indicating that ACO-OFDM is feasible in outdoor visible light communication systems.