Non-redundant Multi-layer Superimposition Based PAPR Reduction And Nonlinearity Mitigation For ACO-OFDM Visible Light Communication Systems

As the demand for high-speed transmission of mobile data continues to grow,spectrum resources are facing a serious shortage.Visible light communication(VLC)can provide abundant visible light spectrum resources to solve the problem of shortage of wireless spectrum resources.Asymmetrically clipped optical-orthogonal frequency division multiplexing(ACO-OFDM),as a multi-carrier modulation method in VLC,has high energy efficiency,but there is also a high peak-to-average power ratio(PAPR).Signals with high PAPR pass through non-linear devices such as light emitting diode(LED),which will cause signal distortion.Aiming at high PAPR and LED nonlinearity of ACO-OFDM systems,this paper proposes a PAPR reduction algorithm and a nonlinearity mitigation algorithm,based on the superposition of non-redundant multilayer information streams.The proposed two algorithms require no pilot and no side information,which improves the spectral efficiency of the VLC system.Aiming at the LED nonlinear problem,this paper proposes a nonlinearity mitigation algorithm based on the superposition of two data sub-stream layers.Based on the anti-symmetry property that a non-redundant signal and its symmetric signal share the same absolute value and their sum is equal to zero,a non-redundant signal is used to reduce the large amplitude of the ACO-OFDM signal and enhance its symmetric ACOOFDM signal that is zero due to negative signal clipping,allowing LED nonlinearity mitigation.However,the existing signal detection is not available on odd subcarriers for ACO-OFDM systems,as the designed non-redundant signals fall on odd subcarriers and interfere with source signals.Therefore,this paper propose a novel signal detection approach based on even subcarriers for ACO-OFDM VLC systems.This is the first work to investigate the distortion caused by negative signal clipping of source signals on even subcarriers,and utilize the distortion to recover source signals rather than being abandoned as traditional ACO-OFDM signals.Simulation results show that the proposed approach outperforms a number of existing methods in the literature,and provides performance better than ACO-OFDM with no LED nonlinearity mitigation,in terms of bit error rate(BER).Aiming at high PAPR of multi-carrier transmission signals,this paper proposes a PAPR reduction algorithm based on three-layer data sub-stream superposition.The useful data signals modulated by ACO-OFDM are the first-layer signals.A number of second-layer signals are designed to reduce large-amplitude first-layer signals,and a number of third-layer signals are designed to enhance small-amplitude first-layer signals,for PAPR reduction.The useful data signals are not interfered by two non-redundant signal streams in frequency domain,as odd subcarriers are occupied by useful data signals,while even subcarriers are occupied by the designed signals instead of being null as in traditional ACO-OFDM signals.The negative signals are reversed to positive to reduce the impact of large-amplitude signal reduction,rather than being clipped off as in traditional ACO-OFDM signals.A scaling factor is introduced in the reversed signals to allow trade-off between BER and PAPR reduction.Simulation results show that the proposed algorithm is better than other existing algorithms in terms of BER and PAPR.