| In the past two decades,the unprecedented growth of wireless communication systems and the growing demand for wireless data services have limited and expensive RF spectrum availability,which has driven the demand for complementary wireless transmission technologies.Visible light communication?VLC?technology,as a new wireless communication scheme since the 21st century,which uses visible light band?380 nm to 760 nm?as information carrier to provide a large number of unregulated electromagnetic spectrum and extremely large bandwidth.It has the advantages of low-carbon,near-zero communication loss,frequency reuse,high signal-to-noise ratio and no electromagnetic interference.It is a very promising technical solution in future wireless communication.This thesis focuses on space applications and conducts in-depth research on key technologies related to high-speed VLC systems in confined spaces/free spaces.The main work and innovations of the thesis are as follows:1.The channel characteristics of visible light communication system are studied.Starting from the basic structure of point-to-point visible light communication system,the effects of bandwidth and non-linearity of commercial phosphor LED?P-LED?and multi-color LED?RGBA-LED?sources on the system link are discussed,and the digital predistortion compensation model of non-linearity effect is modeled.Finally,the single-carrier modulation and multi-carrier modulation in VLC are compared and analyzed.The DCO-OFDM-based VLC system platform and the key technologies in OFDM experiments are introduced.2.To solve the problem of bandwidth limitation,a?-type passive equalization network is proposed,which is composed of?-type attenuation circuit with the LC parallel resonance and the series resonance point.It is used for the post-equalization of the VLC system,so that the 3-dB bandwidth of a point-to-point VLC system built from common commercial phosphor LEDs and PIN photodiodes is extended from 2.4 MHz to 82.6MHz,and real-time data transmission of 164 Mbps is achieved with NRZ-OOK modulation.To achieve Gbps-level links,it is necessary to further expand the system's3-dB modulation bandwidth and reduce design complexity.In this paper,a post-equalization network based on two-stage transistors is designed,and its frequency response characteristics are studied through simulation.The 3-dB modulation bandwidth of the RGBA-LED-VLC system with post-EQC is effectively broadened by optimizing the parameters when RGBA-LED is used,and the 3-dB bandwidth of four channels of red,green,blue and amber are extended to 226 MHz,218 MHz,220 MHz and 205 MHz,respectively.The offline transmission experiment is built,and the 5.2Gbps offline data transmission is realized by using the above-mentioned equalized RGBA-LED.3.For the closed space VLC of 5 m×5 m×3 m,considering the illumination uniformity,power consumption and link performance,the contribution of NLOS primary reflection is considered and the performance of different LED layout schemes is studied under the requirements of international lighting standard indoor illumination.By adjusting the topological distribution,a square matrix combined with ring layout model is proposed and the dynamic range of illuminance and signal-to-noise ratio?SNR?on the receiving plane is compressed by power distribution.Aiming at the shortcomings of the proposed compensating model that the uniformity and fluctuation value on the receiving plane increasing with the increase of the number of central ring LEDs,a three-dimensional optimization scheme is proposed to optimize the layout height of the center ring LED on the basis of two-dimensional optimization.The simulation results show that compared with the traditional square matrix layout,the square matrix combined with ring layout increases the illumination uniformity and SNR uniformity of the receiving plane while the number of light sources is reduced by 48,and the bit error rate?BER?performance is doubled,which reduces system power consumption and inter-symbol interference?ISI?.4.For the free space application scenario,the effects of long-distance channel fading,atmospheric scattering absorption,atmospheric turbulence and background light interference are analyzed,and several types of IM/DD modulation schemes are compared from power efficiency and bandwidth efficiency.The channel gain of outdoor VLC links is modified and the power analysis model of long-distance visible light communication is proposed,and the power demand of the transmitter under different communication indicators is also proposed.The numerical simulations in daytime,night and deep space scenarios are completed.The simulation results show that under the same experiment conditions as the distance is 10 km and BER is 1×10-4,night scenario requires the transmitting optical power to be at least 238 W for a data rate of75 kbps while deep space scenario requires 1.02 W for a data rate of 112.5 Mbps.5.The feasibility and system design of VLC space application are studied.The feasibility of short or medium distanc inter-satellite communication using VLC in multi-satellite networks is studied.Based on STK platform,a double-star companion configuration with two-way VLC function is designed.The simulation shows the variation of the solar angle of the two satellites in orbit for one year and the VLC link of the satellite accompanying the orbit can be used normally when the field of view angle of the visible communication module is 5°.In order to improve the link capacity and reliability,the SIMO-VLC system based on inter-satellite link is further constructed,and the effects of different diversity merging algorithms on link performance are evaluated by numerical simulation.The simulation results show that SIMO-based diversity detection scheme can achieve better performance than SISO system.Aiming at the current situation of short life of conductive slip ring and electromagnetic interference in radio,the two-way communication function between stator and rotor in centrifuge is realized by VLC.The overall scheme and hardware and software development of the system are designed,including data transmission protocol,FPGA main control board,transmitter and receiver layout,centrifuge channel modeling,transceiver module circuit design,etc.,the current system works stably in electrical components. |
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