Research On Receiving Systems Of Ultraviolet Ray Voice Communication

In today's world, warfare forms of military conflicts and local wars have changed from traditional weapons to"Information Warfare". In battlefield environment, establishing and maintaining anti-capture and anti-jamming secure wireless local area network has been focused by foreign force and our force. At present, common communication systems can be roughly divided into three categories: Cable Communication, relying on radio frequency (RF) wireless communication systems and relying on infrared and visible light communications. Radio communication has the mature technology advantages, but it is also susceptible to radio signals intercepted, and to the measured interference. The confidentiality of information is relative shortage. Cable communication with stable performance, higher quality and better confidentiality is an important military communication means, but there are some disadvantages, such as: long time to be built, great investment, difficult maintenance, poor mobility and vulnerable to be damaged. Compared with Radio communication, Free Space Optical Communications (FSO) technology has flexible and anti-intercepted advantages. However, the traditional FSO technologies use infrared light as a transmission medium. In specific environment, it is susceptible to interference to normal work.To overcome all of above insufficient, States military is looking for a new medium of communication. It is noteworthy that the United States GTE Corporation (telephone and electronic equipment company) has developed a new concealed - UV communication system for the U.S. military in recent years, thus, our communication capabilities of the development have been toughly challenged. By reason of the atmosphere, there is not below the 290 nm wavelength UV on the ground. A new generation of communication system 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. The system also has some unique advantages, such as flexible, all-round, and non-line-of-sight communication, and can meet warships, aircraft squadron confidentiality communications needs. Moreover, the UV has diffuse reflectance characteristics in the air. Ultraviolet communication system also has the ability to bypass the barrier.Modulation-demodulation of the UV is still a difficulty. Applying FM technology to UV gas discharge lamp load modulation frequency, the electric signals will be converted into optical signals. Then the receiver will receive optical signals, which are converted to electrical signals and carried on frequency-to-voltage conversion. Finally, the original digital signal can be gained. The demodulation system has some advantages: stable signal, easy to realize its benefits. Meanwhile, it is difficult to improve the speed of transmission for UV communication system, the fastest speed is only 4800bit/s in the world by far and not directly matches voice transmission speed. Consequently, the real-time voice compression technology has become the key point of the system. Making use of MELP speech compression codec technology, digital audio signal can be effective real-time filtered and compressed by means of real-time and high-speed processing capability of DSP, in order to meet the real-time voice transmission demand of UV communication system.The demodulation system is flexible and stable. Within the one-kilometer area, the transmission rate is up to 1.2kbps, and can be carried on reliable transmission of the characters through outdoor tests. Through a separate test, speech decoding system can achieve the rate of 2.4kbps real-time processing. Nevertheless, on the whole system's tests for voice communications, as the error rate of demodulation system is high at 2.4kbps transmission rate, the speech quality is poor, and even some of the sound is difficult to differentiate. Thus, the demodulation devices and voice compression scheme need to be further refined and improved, while some of the key control parameters of circuit need to be further optimized, in order to achieve full-duplex, high-quality and real-time voice communication.