The Technology Research Of An Ultraviolet Laser Communication System Based On Low Bit Rate Speech Coding Algorithm

Ultraviolet speech communication system has gradually became the focus of research in the field of military communication because of its strong anti-interference ability to noise performance, good secrecy, non line of sight(NLOS), and all weather communication. However the optical communication meets the difficults of the limited channel resource and the high bit error rate. Two aspects are emphased by researchers: the method of modulation and the source coding which is the most effective way to solve those problems. So it is important to the speech coding way which is the high speech quality and the low coding rate. The aim of the subject is to achieve the coding speech signal which is based on the theory of predictive coding and extracte and code the characteristic parameter in a FPGA development board. The PMT receives the ultraviolet which is sent by the UV laser. The UV laser is drivered by the coding speech signal. The PMT turns the optical signal into electrical signal. The electrical signal is decoded and restored the speech signal in the FPGA development board. So the ultraviolet speech communication system is realized.This paper deals with the atmosphere absorption effect and the scattering effect, analyzes the Realeigh and Mie scattering, and build the single scattering and the ellipsoid model of the UV communication. In addition, the encoding algorithm of LPC-10 is presented. The algorithm can sample audio at 8 kHz frequency to 180 samples as one-frame, in order to achieve the speech coding rate is 2.4 kb/s. While linear predictive analysis of the speech is adapted, the filter parameters are given. It is the foundation to encode the speech. This paper also provides the theory of A-law.The emission source and the photodetector for communication system are briefly introduced. Finally the UV laser and PMT are choosed after their performance were compared and analysed. FPGA development board is used to process the data stream. According to the principles of FPGA design process and programming, the deserializer, the RAM, the model of parameter calculation, and other models are designed and processed timing simulation to ensure the correctness.Two communication systems which are based on the red laser drived by A-law and the UV laser drivered by LPC-10 are builded. And a number of test in laboratory are done. The results show that the encoding rate of A-law speech coding is 64 kb/s and MOS?3.0, and the encoding rate of LPC-10 is 2.4 kb/s, which indicates the realization of law-rate coding.