Research On Receiving Technology Of High-Speed Multi-Color Visible Light Communication Systems

In recent years, there has been a fast development of mobile communication technologies. However, it has also encountered some problems, such as the shortage of frequency spectrum resources and the harm caused by electromagnetic radiation. Visible light communication (VLC) technology has become a promis-ing solution to indoor short-range wireless communication, due to its advantages of free spectrum, natural confidentiality, low energy consumption and no electromagnetic radiation. This paper focuses on the receiv-ing technologies, such as pilot design, channel estimation, signal detection and interference cancellation, of multi-color VLC DCO-OFDM systems. Multiple algorithms are studied and simulation results are given un-der different channel conditions. The paper also provides implementation schemes of the receivers on FPGA hardware platform.Firstly, the paper gives an overview of the VLC systems. The architecture of the circuits are described, and the characteristics of electro-optical/optical-electro conversion devices are discussed. DCO-OFDM tech-nology is used in the system because of its high spectrum efficiency. Its signal processing procedure is dis-cussed, with its advantages outlined and difference from traditional OFDM highlighted. The paper also in-troduces the channel model of the multi-color VLC systems.Secondly, the channel estimation issue of VLC systems is studied. Different methods such as LS, mod-ified LS, and LMMSE channel estimators are compared. Simulation results show that modified LS channel estimator with optimized parameters has good performance in the VLC systems. For multi-color VLC sys-tems, three novel schemes of pilot design and channel estimation based on Alamouti code are proposed. Simulations under multiple channel scenarios confirm that these novel schemes has better performance than common methods.Thirdly, the paper investigates the signal detection technologies in multi-color VLC systems to deal with interference. ZF and MMSE linear detectors are simulated under different channel scenarios to show their abil-ities to mitigate interference. Interference cancellation technologies such as OSIC, ZF-OSIC, MMSE-OSIC, PIC, ZF-PIC, MMSE-PIC are also investigated. Simulation results show that these interference cancellation methods have different performance under different channel scenarios.At last, the hardware implementation of multi-color VLC receivers on FPGA platform is discussed. The implementation of several key module, such as synchronization, channel estimation and equalization, soft demodulation, interference cancellation, are described. The paper also provides the parameters of the hardware. The RGBA WDM DCO-OFDM VLC system can achieve a transmission rate of 932Mbps with FER under 10-6.