Modulation System Research On Solar Blind Ultraviolet Communication In Free Space

Ultraviolet Speech Communication is a new type communication system in free space optics communication field. Some excellent performances such as safety,anti-interference, Non Line-of-Sight, make it different from other communication mode. Hence, ultraviolet optics communication may be applied in some special occasion to make up for the shortage of traditional communication modes.When the solar ultraviolet radiation pass through atmosphere, oxygen will filter out the vacuum ultraviolet, and furthermore, the ozonosphere over the troposphere absorbs the 200-300nm ultraviolet band so strongly that it can not reach ground surface. The ultraviolet is so-called solar-blind ultraviolet. In practice, the 254nm ultraviolet was selected as free space optics communication carrier. And ultraviolet is suitable for Non Line- of -Sight communication for its high level scattering performance. It is also another advantage compared with other models.Firstly, this paper analyses the factors, such as atmosphere, atmosphere media and atmospheric turbulent, that effect Ultraviolet Optics transmitting performance. Introduce the single - scattering model based the ellipse - spherical coordinate system. Employing it, the receiving optic power transmitted in NLOS style can be calculated. And according to the experimental conclusion of Zhengyuan Xu, the transmiting and receiving angle can be optimized.Secondly, according to the ultraviolet characteristics, some important devices are discussed and selected. For some superiorities such as high transforming efficiency, wide power range, excellent spectral line performance, the low voltage mercury lamp was used. And then, we discussed the ultraviolet receiver based PTM, and introduced speech process system which consist of AD73311L, AMBE2000 and 51 microcontroller.To make the right modulation scheme, the low voltage mercury lamp lighting characteristics is specified. And also considering the baseband signal is a binary style, the 2FSK model finally was selected.Thirdly, mercury lamp is driven by electronic ballast, so half-bridge resonance circuit,L6574 control chip circuit, APFC circuit based on L6561 and EMI filter are introduced both in working principle and design process. The purpose of the design is to utilize the current technology and resource to do some elementary research on ultraviolet optics speech communication. For three years hard works, we accumulated some experiences in modulating of ultraviolet optics and speech encoding. In present, the system can transmit character information in 9.6Kbps with a low bit error rate. It testifies that real-time ultraviolet speech communication can be realized.