Research On Demodulating And Decoding Of Solar Blind Ultraviolet Speech Communication

Solar-blind Ultraviolet Communication is a new type communication in free space optical communication field. Atmospheric gases, particularly ozone and oxygen, are strong absorbers of light in the spectral region between 200nm to 280nm, so that the amount of solar radiation reaching the ground in this waveband is negligible. The ultraviolet in this waveband is so-called solar-blind urtraviolet. A new generation of communications using Solar-blind UV as medium will not be affected by daytime and nighttime environment, thus the communication ability of anti-jamming can be greatly improved. This device also has some unique advantages, such as flexible, all-dimentional, and non-line-of-sight communication, which can meet the needs of warships, aircraft squadron confidentiality communications.Firstly, some characteristics are discussed, such as atmospheric absorption, atmospheric scattering and atmospheric turbulence, which affect the performance of Ultraviolet Optical transmission characteristics. According to the single scattering model developed by Luegtten used in research on atmospheric channel model for NLOS ultraviolet communication, the power loss in Ultraviolet Communication can be analyzed quantitatively. The results of simulations indicate: (1) the value of transmission loss can be minimum, while both the transmitter apex angle and the receiver apex angle are less than 90o in NLOS ultraviolet communication; (2) the value of transmission loss will decrease, while the transmitter beam divergence and the receiver half-field view increase.Secondly, the design of ultraviolet receiver is described in details according to the modulation of ultraviolet transmitter and the ultraviolet characteristics. First, applying FM technology to UV gas discharge lamp, the electric signals will be converted into optical signals. Next, optical signal is received by photomultiplier tube in receiver, which is converted into electrical signals. Then, electrical signal is filtered, amplified and converted into TTL pulse signal. Finally, the original signal can be extracted by FPGA based on the principle of zero-crossing detection from the modulated signal. Besides, it is difficult to improve the data rate of UV communication system. The maximum data rate is only 9600bit/s, which can not directly meet speech transmission. Consequently, the real-time speech compression technology has become the key point of the system. In order to meet the real-time voice transmission demand of UV communication system, the speech encoding and decoding chip AMBE-1000 is selected.Base on the above research, the prototype of ultraviolet communication has been designed and realized. Experimental results indicate that this device is flexible and stable, Within the distance of 200m, the real-time speech communication and character transmission can be performed in the the transmission rate of 9600bit/s. In ordor to improve transmission distance and full-duplex communication, some good suggestions will be proposed in the end of this paper.