Research On Baseband Key Techniques In Visible Light Communication System

In recent years,with the serious shortage of wireless spectrum resources,visible light communication?VLC?has emerged.VLC is a wireless communication technology that uses visible light to replace electro-magnetic waves for information transmission.It has the advantages of energy efficiency,without bandwidth limitation,low electromagnetic radiation and anti-eavesdropping.Therefore,VLC technology has received extensive attention from researchers in various countries.The transmission speed has been continuously im-proved,and the practicality has become stronger,which shows the great potential and value of VLC.This paper mainly focuses on precoding and pre-equalization techniques.The specific research contents of this paper is as follows.Firstly,this paper introduces the basic principle of visible light communication system and detailes the key components including LED,optical filter and etc.The system model and system channel of single input single output VLC system are briefly introduced.In order to maximize the spectral efficiency,a typical Orthogonal Frequency Division Multiplexing?OFDM?scheme in visible light communication,namely Direct Current Biased OFDM?DCO-OFDM?,is discussed.In order to fully exploit the transmission resources of the VLC system,this paper also introduces the multi-color transmission system.Secondly,this paper studies the pre-equalization in the single input single output OFDM VLC system to expand the transmission bandwidth of commercial LEDs.Starting from the traditional equalizer methods,three pre-equalization schemes are proposed based on the channel characteristics of visible light communica-tion channel,including analog filter pre-equalization,digital zero-forcing frequency-domain pre-equalization,analog and digital joint pre-equalization.Then,combined with the actual system,the analog filter pre-equalization and digital zero-forcing pre-equalization scheme are designed respectively,and the performance difference between the above two schemes is verified by simulation and hardware.Finally,considering sev-eral aspects of the two schemes in terms of cost,difficulty and performance,digital pre-equalization is deter-mined as the transmission pre-equalization scheme.Thirdly,considering the channel capacity limitation of monochromatic visible light communication sys-tem,a multi-color VLC technology is further introduced.At the same time,due to the non-ideal characteristics of the optical filter,the multi-color VLC system has crosstalk at the receiver.This issue can be effectively solved by the transmitter precoding technique.In this paper,the objective function of precoding optimiza-tion problem is established by minimizing the mean square error.Then,through mathematical derivation,a precoding matrix row decomposition algorithm is proposed and works better compared with the iterative op-timization method and subgradient optimization method in the existing literature.Moreover,the performance of the proposed method is verified by the experimental platform.Finally,two FPGA design schemes for off-line test platform for VLC are implemented.Moreover,the design of the demonstration platform for DCO-OFDM multi-color visible light communication system is discussed.The hardware platform is presented and key performances of the platform are given.Red Green Blue?RGB?DCO-OFDM VLC system can achieve a 938.7Mbps transmission rate when the distance is 3m and the air interface rate reaches at 1.25Gbps.The total frame error rate is less than 10^-4.