The Research And Design Of Ultraviolet Communication System Based On FPGA Bed

Ultraviolet (UV) communications utilize light waves in the solar blind region (wavelength 200nm-280nm) to transmit data. Since ultraviolet lights can be scattered by atmospheric particles, non-line-of-sight (NLOS) communications can be realized. In the process of atmospheric scattering and absorption, the optical energy decays relatively fast, and the transmission distance is relatively short. Thus, UV communications can provide good security of data. At present, all reported experimental UV systems only provide point to point communication links.The first chapter of this thesis investigates the present research and developments of UV communications at home and abroad, and proposes the main contents of this thesis.The second chapter analyzes the single scattering ellipsoid model of atmospheric transmission channel proposed by the Luegtten etc. Through this model, we simulate the relationship between received optical power, distance, field of view (FOV) and elevation angle of the receiver, as well as the relationship between delay and beam angle of the transmitter. Numerical results provide a theoretical basis for hardware experiments.Chapter 3 of this thesis presents the design of the transmitter and receiver of a UV communication system. In order to improve the synchronization in signal demodulation, we modify the traditional modem scheme by adding a ’1’ bit as synchronization pulse to the beginning of each byte. The modified modem scheme avoids bit errors caused by desynchronizing. Then, we set up a test system based FPGA, and analyze and compare the performances of four modem methods (OOK, PPM, DPPM, DPIM), including power utilization, bandwidth utilization, channel capacity and error of slot. Experimental results shows that the choice of a modem method should be based on the performance requirements of data communications.After realizing the physical interfaces, the forth chapter presents a basic design of data link layer. Based on the existing HDLC protocol, we design a frame structure, implement the data frame process in FPGA and finally realize data transmission in frames.The last chapter concludes our research work already finished, and gives some topics for future study.