Research On Precoding O-OFDM System Of Visible Light Communication

With the rapid development of the Internet and the Internet of Things,users have put forward higher requirements for the data transmission rate and information security of communication,but radio frequency(RF)communication is facing problems such as extremely tight available spectrum resources and serious electromagnetic interference(EMI).Visible light communication(VLC)uses light emitted by light emitting diode(LED)as a carrier to achieve communication,and the available spectrum resources exceed 400 terahertz(THz),which has the advantages of good confidentiality and no EMI.Optical orthogonal frequency division multiplexing(O-OFDM)systems applied to VLC have the advantages of high communication rate and high spectrum utilization,but due to the nonlinear characteristics of LED,the deterioration of system performance is more obvious due to excessive O-OFDM system peak-to-average power ratio(PAPR).Compared with other PAPR suppression techniques,precoding techniques have lower computational complexity and better compatibility,and do not require the transmission of sideband information when the precoding scheme used is known at the receiver and transmitter,so this paper conducts a theoretical study of the PAPR and bit error rate(BER)performance of precoding O-OFDM systems as follows:1.Theoretical analysis of the PAPR of precoding direct current-biased optical orthogonal frequency division multiplexing(DCO-OFDM)and precoding asymmetrically clipped optical orthogonal frequency division multiplexing(ACO-OFDM)systems,demonstrating that precoding suppresses the PAPR by reducing the autocorrelation of the frequency domain signal.Because the time domain signals of precoding ACO-OFDM and precoding DCO-OFDM systems do not obey the standard mathematical distribution,it is difficult to obtain the theoretical distribution of PAPR.Based on the subcarrier mapping structure and the randomness of the modulation sequence of the precoding ACO-OFDM and precoding DCO-OFDM systems,the maximum power of each time domain sampling signal in the system is derived,and the theoretical upper bound of PAPR approximated with PAPR is finally obtained.Finally,the PAPR of the discrete Fourier transform(DFT),discrete cosine transform(DCT)and discrete Hartley transform(DHT)precoding O-OFDM system is analyzed using Monte Carlo method,and the conclusion that the PAPR suppression effect of the precoding scheme with lower frequency domain signal autocorrelation is more obvious is verified,and the simulation results show that the upper bound of the derived PAPR has good compactness with PAPR.2.The precoding ACO-OFDM system and the precoding DCO-OFDM system are introduced,and the receiver signal-to-noise ratio(SNR)expressions are derived under line-of-sight propagation(LOS)channel and multipath channel,respectively,based on the calculated receiver decoded signal expressions.It is demonstrated that precoding has no effect on the system BER under LOS channel,and under multipath channel,precoding can equalize optical wireless channel frequency selective fading to homogenize the receiver subcarrier SNR of the O-OFDM system,thus improving the system BER performance.Moreover,it is demonstrated that the improvement of system BER by precoding is independent of the used precoding scheme when the clipping noise is neglected.Futhermore,a Monte Carlo method is used to simulate the system performance to verify the correctness of the theoretical analysis.Finally,the conclusion that the system BER performance of the precoding scheme with more significant PAPR suppression is better when the clipping distortion is larger is verified by considering the LED bilateral clipping.The theoretical analysis of the PAPR and BER performance of the precoding O-OFDM system provides a theoretical basis for the study of precoding to improve the PAPR and BER performance of O-OFDM system and provides reference value for the application of O-OFDM system in VLC.