Research Of Application Of OFDM For Dimming Control VLC System

Visible light communication(VLC)is a kind of optical wireless communication system which use LED(Light Emitting Diode)as the emission light source.Compared to the traditional incandescent and fluorescent,LED has a long service life,low power consumption,less heat,etc.As a powerful complement to traditional radio frequency communication technology,VLC has attracted wide attention of researchers around the world,and quickly become a hot research topic in the field of wireless optical communication.VLC use the intensity modulation of LED to transmit information,realize the communication.Compared with radio frequency communication,VLC is green environmental protection,harmless to human body,no band resources,confidentiality.Orthogonal Frequency Division Multiplexing(OFDM)is a multi?carrier modulation method.OFDM is applied to VLC system due to its high transfer rate and resistance to inter-symbol interference,which can improve the performance of visible light communication system.Different from RF system,only real and positive signal can be used to modulate the intensity of LED in IM/DD VLC system.Firstly,this paper investigate the performance of a proposed optical orthogonal frequency-division multiplexing(OFDM)in a short-range intensity-modulated,direct-detected(IM/DD)optical channel.Because of the high peak-to-average power ratio(PAPR)problem of the OFDM modulation scheme,the beneficial clipping method has been proposed to improve the performance of communication system,In the optical OFDM system,light emitting diode(LED)is the nonlinear product and cannot been neglected.Therefore.we derive the bit error ratio(BER)expression when the OFDM signal through the third-order polynomial model of LED in this paper.The experiment of beneficial clipping method for a DCO-OFDM based visible light communication system is conducted.With a best clipping ratio,the BER improvement of the system achieves 5.56dB.similar to the theory analysis result.Finally,considering the dimming function is an indispensable part of the VLC system in practical application.The Beneficial Clipping is applied to enhance BER performance.The performance of a Beneficial clipping asymmetrically clipped optical orthogonal frequency division multiplexing(ACO-OFDM)based dimming control visible light communication system is investigate.The expression signal-to-noise ratio and bit error rate are derived.The performance analysis are conducted by Monte-Carlo simulations.From the simulation result,the Beneficial clipping ACO-OFDM can improved BER performance about 10dB,the dimming range just decreases about 5%.