Research On Channel Impairments And System Design Of Visible Light Communication In Multiple Scenarios

With the rapid development of mobile communication and the advent of artificial intelligence era,various large-capacity communication services continue to grow explosively,people's demand for high-speed wireless communication systems is increasing.Compared with traditional radio frequency communication,visible light communication technology has attracted widespread attention from both academia and industry in recent years due to its ultra-wide spectrum frequency band,high speed,high security and immunity from jamming.It is also considered to be one of the potential key technologies to break through the bottleneck of high-speed data transmission and spectrum resources,and has broad application prospects in the Internet of Things,underwater wireless communications,intelligent transportation,and future 6G networks.Despite all these advantages,channel impairments such as multipath scattering,turbulence fading,and ambient light noises pose key challenges to this emerging technology.These problems can seriously degrade the performance of visible light communication systems,limit the viable communication range,data rate and large-scale commercial development.To address these issues,this thesis focuses on the research of channel impairments and visible light communication system design in multiple scenarios including the underwater,outdoor and indoor environment.We accomplished theoretical analysis,simulation platform design,compensation algorithm implementation and prototype testing.The main contributions are as follows:(1)Focusing on the problem of shallow underwater multipath dispersion and ambient light noises,a scalable PTA-based simulation platform is designed and verified through experimental prototype test.This platform integrates channel modeling and performance estimation functions,combined with the real-measured sea-level solar irradiance data,and provides a quantification method of ambient light intensity at different working depths.A comprehensive investigation of underwater channel characteristics is carried out in terms of temporal dispersion,spatial illumination distribution,statistical attenuation and BER performance.Based on the simulation results,the overall design of an underwater optical wireless communication prototype is accomplished,the accuracy of the simulation algorithm is verified through the experimental results,and the viable communication range is derived.This research is of guiding significance in real-time prototype design and link performance evaluation under different water quality.(2)Focusing on the problem of ambient light noises in outdoor long-range VLC system,an adaptive filtering algorithm is implemented based on FPGA for noise mitigation.We establish a flexible transceiver prototype to collect real-measured noise data.The performance of different adaptive filtering algorithms is analyzed via MATLAB and the optimal parameters are determined.Experimental results reveal that this method can effectively suppress the impact of ambient light noises,and 7.84dB performance improvement is achieved when the input signal-to-noise ratio(SNR)is 2dB.(3)Focusing on the automatic recognition system design in maritime optical morse-based communication,we propose a modified clustering algorithm and implement it in embedded system.Aiming at the deficiency of traditional method,a k-means algorithm of machine learning is designed to optimize the decision threshold for binarization and identify elements in optical morse signals.To tackle with the decreasing accuracy due to strong noise channels,a novel correction scheme is presented and experimentally demonstrated to eliminate errors caused by emerging spikes.Simulation and experimental results indicate that over 99%of real-time recognition accuracy is realized with a SNR greater than 5 dB,and the system can achieve good robustness under conditions with low SNR.(4)Focusing on the problem of indoor multipath interference and energy consumption of IoT nodes,we make the first attempt to propose an analytical framework of a large-scale visible light backscatter communication network(VLBackCom)and investigate its performance.The network topology is modeled using the analytical tractable generalized Gauss-Poisson process.The expressions of the success VLBackCom probability and network capacity are clearly derived to characterize the VLBackCom link's reliability as well as the spatial success transmission density,respectively.Compared with numerical simulation analysis,this method can greatly reduce the calculation time and determine the optimal backscatter parameters,yielding a lower bound for practical VLBackCom network.This work provides a new approach for the design of extremely low-power communication in the Internet of Things.