Research On Spectrum Utilization Improvement And Signal Processing Algorithm Of Wireless Optical Communication System

With the increasing popularity of smart mobile devices, the wireless data traffic is growing exponentially [1]. This has resulted in shortage of the radio frequency (RF) spectrum and made the RF spectrum become a precious commodity. Since the RF spectrum is limited and expensive due to the license fees, the optical wireless communications (OWC) has evolved to become a high-capacity complementary technology to the RF communications, which can alleviate the spectrum shortage. Meanwhile,OWC has many other advantages such as license-free operation,environmental friendly, high-security and flexible deployment. As a result,it has important research value and broad application prospects.Depending on the environment of application, OWC can be divided into indoor and outdoor communication, indoor communication including visible light communication (VLC), outdoor communication including ultraviolet detection.In the indoor VLC system, the light emitting diode (LED) chip as a signal transmitter, which is only several MHz due to the slow time constant of the yellow phosphor cannot meet the high-speed communication requirements.Focusing on the requirements and difficulties of wireless optical communication, this paper focuses on exploring and researching the spectrum utilization improvement and intelligent decision algorithm of visible light communication and the denoising algorithm of ultraviolet detection image. The main contents are as follows:Firstly, summarizes the research status and basic principles of visible light communication and ultraviolet detection technology.Secondly, in order to solve the problem of limited bandwidth of the LED in visible light communication, the system of superposed pulse amplitude modulation (SPAM) in visible light communication was designed to improve the spectral efficiency by utilizing the spatial resources of the LED array. We presented an experimental VLC system using 8-SPAM modulation to realize data transmission for an indoor environment. The experimental results indicated the 8-SPAM system can increase the transfer rate of 3 times.Thirdly, in order to achieve higher date rate, the off-line experiment system of WDM-DCO-OFDM based on Wavelength Division Multiplexing (WDM) and orthogonal frequency division multiplexing is designed and experimentally demonstrated. In order to improve the system performance, digital filtering technology and channel equalization Technology are used. The experiment result shows that the system bit error rate less than 10-4 in the transmission distance of 25 cm and the system data rate is 1.2Gbps.Fourthly, in view of the lack of intelligent learning in the direct decision algorithm, the machine learning technology is introduced into the visible light communication. A support vector machine (SVM)-based data detection for 8-SPAM and DCO-OFDM in visible light communication is proposed and experimentally demonstrated. The results show that the performance of SVM is superior to the traditional direct decision demodulation algorithm.Fifthly, a denoising algorithm based on thresholding and filtering fusion is studied for the characteristics of ultraviolet detection image. The expriment results show that this method can effectively eliminate the background noise of the ultraviolet detection image.