Research On Theory And Technology Of Hybrid Asymmetric Limited Optical OFDM Transmission In Visible Light Communication

Visible Light Communication has been gaining wide attention in academic and industrial fields due to its advantages of wide bandwidth,high reliability and low cost.Visible Light Communication which uses light-emitting Diode to provide wireless network connection has rich spectrum resources.Recently,with the development of LED market,Visible Light Communication has been developing rapidly.Visible Light Communication transmits information by high-frequency switching LED lights.The receiver receives optical signals through the sensor to realize information transmission and adjusting the amplitude of the signal achieves dimming control.Researchers are dedicated to improve the performance of system and propose many Visible Light Communication transmission schemes.In this paper,we mainly focus on the dimming control of hybrid ACO-OFDM and the communication transmission system and dimming control system of Preprocessed hybrid ACO-OFDM.The main research of the paper is as follows:(1)This paper proposes a dimming control system based on Hybrid ACO-OFDM.This excellent transmission system has high carrier utilization rate.Therefore,it is proposed to integrate this scheme with VOOK for dimming control.The dimming control of HACO-OFDM is implemented by integrating Variable On Off Keying,and it is realized by adjusting the duty cycle of VOOK.In the process of VOOK fusion,the property of Fourier transform is used to make VOOK interfere-free with the transmission of HACO-OFDM signals.In addition,due to the integration of VOOK,the transmitted signal does not meet the linear requirements.Based on this problem,a kind of time selective bias is proposed to achieve the dimming control and communication functions of the system?The simulation results show that the dimming control scheme can achieve a wide range of dimming without affecting the signal transmission.(2)Although the HACO-OFDM system improves the subcarrier utilization rate of the system,the receiving end will generate noise on the even subcarriers after ACO-OFDM clipping.The noise will affect the signal detection of PAM-DMT.Hence,noise reconstruction must be introduced before receiving,resulting in increasing complexity of the receiving end.So,in this part,we propose a hybrid ACO-OFDM system based on preprocessing.The noise is first deleted at the transmitter,so that the noise generated at the receiving end can be offset.Finally,there is no interference between the two signals at the receiving end,the receiving end can detect the two signals at the same time and reduce the complexity of the receiving end system.The simulation results confirm that the BER performance of the system is consistent with that of HACO-OFDM under the premise of low complexity of the receiver.(3)The hybrid Visible Light Communication system based on preprocessing proposed in(2)has the advantage of low complexity at the receiver end.Therefore,in this part we propose a dimming control scheme to achieve low complexity at the receiver end.Similar to the dimming control of Hybrid ACO-OFDM,this dimming control scheme also uses the VOOK with higher security for dimming control.Adding appropriate time selective bias to make the final dimming signal meet the linear requirements and finally it realizes the communication and dimming control functions of the system in different scenes.Through simulation comparison between this scheme and the dimming control scheme of the Hybrid ACO-OFDM,it can be seen that the BER performance of this scheme is as good as that of the Hybrid ACO-OFDM.Compared with the dimmable hybrid ACO-OFDM,the complexity of the receiver end of this scheme is lower and the battery life of the receiving device is stronger.