Research On Digital Signal Processing And Spread Spectrum Technology In Ultraviolet Communication

The optical wireless communications (OWC) is a new technologythat combines wireless communication and optical communication.Non-line of sight (NLOS) ultraviolet (UV) communication is a new typeof OWC, which has been considered as a valuable optical wirelesscommunication supplementing the traditional communication for itsunique characteristics. Compared with other wireless communications,ultraviolet communication has good secrecy and low backgroundinterference. Therefore, it has important research value and broadapplications. Currently, UV communication is still in its infancy stage with manykey technical problems need to be solved. The researches in China focuson channel simulation and methods to improve the performance of UVcommunication. In NLOS UV communication, it is difficult to receivecorrect signal from the unfavorable environment due to interferencesignals emitted by other nearby communication equipment and solarbackground noise. In order to improve the performance of UVcommunication systems, the analysis of noises in photoelectric detector,digital denoise methods and other researches to improve the systemperformance are very important. As core device of UV communication system, photoelectricconverter has a large impact on the whole system. The noises of threecommon photoelectric detectors are analyzed and tested. In order to reduce the noise in UV communication system, thedissertation analyzes the performance of median filter and mean filter in improving UV system. In addition, a self-adaptive filter is purposed and proved to be effective in improving SNR in UV communication. Experimental results show that the self-adaptive filter is able to improve the signal-to-noise ratio (SNR) in receiver by approximately8dB.In order to suppress the damage from the interference, direct sequence spread spectrum (DSSS) technique is introduced into NLOS UV communication. The feasibility of the scheme is analyzed and an experimental system is designed and implemented. Outdoor experiments are conducted and the results of field measurements with and without DSSS are evaluated. The results show that the spread spectrum technique is able to suppress noise in UV atmospheric channel and thus improve the performance of NLOS UV system evidently. However, the communication distance in laboratory is usually limited by devices. In order to determine the actual performance of UV communication system, communication distance is estimated based on Monte-Carlo model.