Research On Receiving Systems Of Wireless Optical Communication

In today's world, warfare forms of military conflicts and local wars have changed from traditional weapons to"Information Warfare". To overcome all of above insufficient, States military is looking for a new medium of communication. 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. 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. In order to solve the above problems, the paper majors on the following tasks:①FM technology have been selected via analysis of the modulation and demodulation theory;②Researching on UV transmission characteristics, we selected a photomultiplier tube as detection of UV signal detection and receiving device, In addition, the installation of UV filter improve the UV-band accuracy;③The receiver will converted optical signals to electrical signals. Then the signals will be preprocessed and F/V conversion. The original digital signal will be demodulated.④Selection MELP speech compression codec technology, application DSP with high-speed processing capability, Digital Voice signals have been effective filtered and compressed, to meet the real-time voice transmission speed of the 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.