Papr And LED Nonlinearity Distortion Suppression For Visible Light Communication Multicarrier Systems

In modern society,people have higher requirements for high speed transmission of mobile data.At the same time,spectrum resources in radio frequency communication are facing serious shortages.Under the background of the limited spectrum resources,visible light communications(VLC)has been proposed and attracted wide attention.VLC can realize high speed data transmission by using light emitting diodes(LEDs)without occupying the radio frequency spectrum band.However,VLC systems still face many challenges due to the limited bandwidth and nonlinear distortion characteristics of LEDs.Based on the traditional unipolar asymmetrically clipped optical orthogonal frequency division multiplexing(UACO-OFDM)modulation,an enhanced UACOOFDM modulation is proposed in this dissertation.The signal structure of UACOOFDM is analyzed in detail.Based on the structural characteristics of UACO-OFDM signals,the receiving decision operation is added to improve the recovery performance of the system.Then,the power allocation scheme for each layer of UACO-OFDM is improved,which reduces the overall bit error rate(BER)of the system effectively.The simulation results show that the enhanced UACO-OFDM modulation has better BER performance than the traditional UACO-OFDM.Aiming at the problem of LED nonlinear distortion and high peak-to-average power ratio(PAPR)of VLC multi-carrier systems,a spatial superposition based multiLED transmission system is proposed.In order to avoid the effect of the nonlinearity of LED,the signals are compressed linearly at the transmitter.The traditional ?-law companding is used to compand the transmitted signals to reduce PAPR.For intensity modulation/direct detection(IM/DD)VLC systems,the visible light unipolar realvalued signals can be superimposed in free space.The signals from multiple LEDs are superimposed spatially to allow effective compensation for signal distortion caused by linear compression and nonlinear ?-law companding.Moreover,the problem of channel difference between multiple LEDs is analyzed.An LED selecting scheme is proposed to eliminate the influence caused by channel difference.Simulation results show that the proposed method provides PAPR suppression and LED nonlinear distortion mitigation performance significantly better than existing methods.The proposed method makes a good compromise in terms of system computational complexity,BER performance,spectral efficiency as well as energy efficiency.