Study On Modulation And Demodulation Technique Of Ultraviolet Semiduplex Communication System

Ultraviolet communication is a new communication technology using ultravioletlight as a carrier to transmit information of voices, data and images in space. It providessimultaneous transmission and reception in both directions. The low tapping rate, highinterference resistance, all-weather of the ultraviolet communication make it anattractive technology for wireless communication in a certain military application. Andit made up for the blank about military communication in close range communication.This technology can be an important complement to wireless military communications.Modulation and demodulation technology directly affects the data transmission rate andBER performance, so it particularly important to find a suitable modulation method forultraviolet communication.A series of experiment amid to military application have been completed in ourlaboratory. This work is supported by the National Natural Science Fund and thePostgraduate Innovation Fund.In this paper, the main work includes four aspects：①It has analyzed the transmission principle of ultraviolet communication system.And it has also studied on the characteristics about UV transmission and scattering inatmospher based on Rayleigh scattering and Mie scattering theory. Then we haveinterpreted the elaborated vision communication model, single scatteringcommunication model and multiple scattering communication models. Furthermore, wefocus on the single scattering model based on the ellipsoidal coordinates.②Based on the comparison of different light sources and the detectors, we choosethe most suitable device as the experimental communications equipment. Using thedeep UV LED array to as the light source, and the PMT as photoelectric detectiondevice, the basic experimental framework is primary assured.③The modulation and demodulation methods have been analyzed by comparisonof five different methods which include OOK, FSK, LPPM, DPPM and MPPM.According to the analysis of these methods, the LPPM is chosen.④We have designed LPPM modulation and demodulation based on FPGA. Theframe synchronization is realized through an addition of frame head mode, and thismethod strictly limits the relative position of each pulse. Combined with the CRC checkcoding technology, the system has a certain error correction capability which reduces the data transmission error rate, and improves the stability of the system. At last, thehalf duplex communication is completed.The experimental results show that the system improves the data communicationPotter speed from the traditional2.4K to115.2K. The transmission distance increases,and the bit error rate and lower power consumption targets are both reduced. Andcompared with OOK mode, the experimental results and the analysis show thesuperiority of the LPPM applied in UV communication system.