Research On Enhancement And Evolution Of Visible Light Communication

With the increasing requirement of high quality,low delay and high rate of data communication in today’s society,the frequency spectrum resources of radio frequency signals are increasingly saturated.Visible optical communication has attracted extensive attention of researchers at home and abroad for its rich frequency domain resources.Since visible light communication uses light intensity for data transmission,in order to meet the requirements of positive real number of visible light signal,the conversion from complex signal to positive real signal can be realized through discrete Fourier transform,Hartley transform and LED index modulation.Based on two typical discrete Fourier transform modulation schemes,Asymmetrically Clipped Optical OFDM(ACO-OFDM)and DCO(DC-Biased Optical OFDM),The enhanced LACO(Layered-ACO)communication system is implemented in the downlink data channel.Compared with ACO,the spectrum utilization rate of LACO is improved.Compared with DCO,LACO system has improved power efficiency.However,in actual transmission,LACO adopts multi-layer data superposition transmission mode,so it is affected by Inter-Layer Interference(ILI).As a result,the performance deteriorates with more layers.It can be considered that LACO performance is closely related to ILI size.Therefore,this paper first analyzed and studied the performance differences between different LACO layers and the variation rule of the differences between layers with the signal-to-noise ratio.Simulation experiments found that in addition to the influence of the signal-to-noise ratio,the proportional relationship between the used bandwidth and the actual bandwidth and the power distribution mode of LACO layers would also affect the ILI between layers.After obtaining the variation trend of ILI between layers and the factors affecting its magnitude,this paper further carried out the research on the optimization scheme of LACO transmission.In order to reduce the impact of ILI on LACO performance,this paper firstly realized the preprocessing scheme of interference elimination at the sending end,then proposed the symbol constellation optimization scheme at the receiving end,and compared the transmission reliability of the two ILI optimization schemes.The simulation results showed that,In this paper,the symbollevel optimization scheme at the receiving end brings greater performance improvement and higher power efficiency.In addition,a data interleaving mapping scheme is proposed in the symbolic mapping to interleave the high level signal with the low level signal,so as to optimize the performance of LDPC channel coding and improve the transmission reliability of LACO.At the same time,this paper also optimizes the noise equalization used in data equalization at the receiving end to realize more accurate equalization and demodulation of multi-layer LACO data.Finally,this paper extends the single-code word LACO transmission system and realizes the multi-code word LACO transmission system.It not only optimizes the flexible configuration of MCS,but also compares the data transmission capability.The simulation results show that multi-TB has better transmission capability under most signal-to-noise ratios.