Research On Channel Estimation Technology Of Visible Light Communication

In recent years,with the rapid development of mobile communication technologies,the 4th generation mobile communication technology has been widely applied in most cities.However,it has also come up with some problems,such as the shortage of frequency spectrum resources,the high cost of rate improvement and the harm of electromagnetic radiation.Visible light communication meets an unprecedented development opportunity due to its advantages of free spectrum and no electromagnetic radiation.This paper focuses on the preamble design,nonlinearity estimation and channel estimation of VLC system.Simulation results are given under the measured channel,and the performance of algorithms is verified.The paper also provides implementation schemes of the transmitters on FPGA hardware platform.Firstly,the paper gives an overview of the VLC systems.The basic principle of circuits is discussed,including the characteristics of photoelectric devices and the basic circuits structures.The paper also intro-duces the channel model of VLC systems,and according to its characteristics,the channel can be modeled as linear channel.Analysis for the noise is presented,and gaussian white noise model is applied.Additionally,the preamble design and nonlinearity estimation of VLC system is studied.The perfor-mance of different synchronization sequences such as PN,ZC are compared at first.Then the paper analyzes the baseband model and frame structure,and proposes a novel preamble design method for the nonlinearity estimation in VLC system.Applied the designed preamble in the nonlinearity estimation,the amplitude lim-iting error model,amplitude limiting percentage model and judging schemes are proposed.Simulation results confirm that the designed preamble performs well in nonlinearity estimation.Furthermore,the paper investigates channel estimation methods of VLC systems.The traditional channel estimation algorithms for OFDM system are introduced,such as LS,LMMSE,and SVD algorithms for block type pilot and interpolation algorithms for the comb type pilot.Then we compares the performance of these estimation algorithms using preamble designed in chapter 3,and discuss the effect of nonlinear amplitude limiting to the estimation results.The paper also analyses the characteristics of the channel of multi-color VLC systems,and two novel schemes of pilot design and channel estimation are proposed.Simulations under multiple channel scenarios show that these two novel schemes have better performance than other methods.Finally,the hardware implementation of VLC transmitters on FPGA platform is discussed.The paper presents the overall structure of VLC system and the parameters of a variety of devices in the hardware system.Then the implementation of several key modules,such as CRC coding,scrambling,LDPC coding,constellation labeling and IFFT,are described in detail.A presentation of our VLC demo system is given out at last.