Investigation Of High-speed Visible Light Communication Technology For Intelligent Transportation System

In recent years,the development of the semiconductor industry has led to the widespread use of LEDs in transportation facilities and vehicles.The intelligent transport system(ITS)based on high-speed VLC communication has broad application prospects and research value,and therefore has attracted attention from national and international scholars.The challenges faced by the intelligent transportation-oriented VLC system include improving the system’s transmission rate under the LED bandwidth-constrained condition,and improving VLC light-of-sight transmission performance in dynamic environment.To achieve a high data rate in a bandlimited VLC system for ITS,in this thesis,low-complexity carrier-free amplitude-phase(CAP)combined with hybrid digital domain equalization is proposed.The VLC channel model is supplemented and improved by introducing the baseline wander characteristic for the practical VLC channel,which is used for investigation of its impact on the transmission performance.A linear equalizer cascaded adapitive DFE equalizer structure is proposed to eliminate the inter-symbol interference resulted from the bandwidth-constrained VLC channel and can greatly improve the system performance.Compared with the traditional equalization structures,the receiver complexity can be reduced for the same transmission performance.A CAP high-speed VLC experimental platform with vehicle and traffic lights was established.Based on the single-carrier CAP modulation technology and the proposed digital domain equalization technology,single-carrier 312.5Mb/s transmission over a 10m VLC link was achieved.In addition,based on the FPGA platform,a single-carrier 200Mb/s high-speed real-time CAP VLC system was designed and implemented.The performance of the relevant equalization algorithm was explored.With the red traffic light,200Mb/s transmission overl5m was achieved.Considering the baseline wander caused by the low frequency cut-off of analog-to-digital converters(ADCs)in the real-time CAP system,theoretical and experimental analysis is made of the impacts of the roll-off factor and signal bandwidth on the suppression performance of baseline wander.On the other hand,for the study of transmission performance in vehicle-based mobile environments,considering fluctuation of road surface,mechanical vibration,moving speed of vehicles and the LED lighting model,investigation is given to the relation between signal-to-noise ratio and moving speed/distance.Based on the mobile platform and real-time tracking system,experimental results show that at a given moving speed,the BER distribution for 5m is more converged than that for 3m.For a given distance,the BER distribution for a moving speed of 2m/s is more converged than that for 0.25m/s.