The Core Technology Research Of An Ultraviolet Laser Communication System Utilizing Inner Pulse Modulation

Ultraviolet communication has become a hot spot of domestic and beendeveloped by many foreign research institutions because of its good secrecy andanti-jamming. Compared with the visible light communication, UV light can achievenon line-of-sight communications, and has the characteristic of strong anti-jammingcapability and all-weather work of military communication system.This paper dealt with the absorption of ultraviolet light propagation in theatmosphere effect and scattering effect, analyzed the molecular and aerosol scatteringwhich both can make the physical principle of UV light is not spread along a straightline. The overall architecture of the simplex communication system, the core device ofchoice, improvement and selection of the algorithm were introduced. Finally acommunication system experiment platform was set up, and the impulse response,signal-to-noise ratio and bit error rate was tested.In order to improve the communication distance, a UV laser was used, which canincrease the communication to3hundred meters. FPGA development board was usedas a signal processing module. The modulation algorithm is based on the traditionalFSK modulation for a certain improvement, which can enhance the robustness of thesystem, and effectively reduce the bit error rate. High order modulation (4FSK) wasapplied to improve the communication rate. In order to further reduce the system BER,BCH channel coding method was used to improve error correction capability of thesystem.The communication system of signal transmission and processing procedure for:binary signal generated by the PC, and then sent to the modulation coding module. Thecoding module encodes the signal and output it to the source driver, and the source sentUV with signal carried to the wireless channel. The receiving module receives a signalcarrier in wireless channel and converses the electromagnetic signal to electrical signal,and then filtered and enlarged by a shaping circuit so that it can be easily demodulated.The demodulation decodes the signal and output to another PC to displaye the signal.So a simplex communication process is realized.A communication system experiment platform was set up for the outdoor test.First, the atmospheric scattering after absorption and the impulse response were testedand got the conclusion that the resulting in LOS mode communication rate up to1.6 Mbit/s, NLOS mode of the upper limit of14.3Mbit/s. After testing the signal to noiseratio of UV signal of laser Angle dependency, found that launch Angle must be lessthan0.02rad during the day, night launch Angle should be less than0.27rad, so as toachieve11dB SNR; Finally, the bit error rate under different conditions was tested andgot the maximum to be10-6. It is concluded that the coding gain of BCH is about2.5dB.