Research On Laser's Transmission Channels And Properties Improvement Of Optical Communication In The Atmosphere

The Space Optical Communication is a corresponding method of taking Laser as the carrying wave and the atmosphere as the transmission channel,a major means of the future inter-satellite and satellite-earth communications,which is also the optimal solution of the digital satellite correspondence with high speed and broadband network and the only means of the heaven-earth integrative correspondence network in the future quantum communication as well. As the atmosphere channel is changeable, Laser may produce the phenomena like flickering, flexing, drifting, expanding, mutating and losing light energy when it is transmitted in the atmosphere channel, which can influence the quality of correspondence and decrease communication reliabilities in the process of the Space Optical Communication. Therefore, a study on the channel model of atmosphere and properties improvement of the Space Optical Communication is an important research project in this field.The main contents of this dissertation are presented in the followings:The first step is to prove a channel model of Laser's gamma distribution in the atmosphere with strong turbulent based on Feynman's Path Integral Theory. The two light beams with the independent exponential distribution of separate statistics are added to obey the negative exponential distribution. Multiple beams with the negative exponential distribution of separate statistics are put together to satisfy gamma distribution while those with the gamma distribution of separate statistics are added to satisfy gamma distribution. The explanation of the gamma distribution principle is given in theory and the experiment data are confirmed.The second step is to analyze theoretically how the space-time diversity technology improves the properties of Space Optical Communication, based on the channel model of laser's gamma distribution, through which the conclusion of equivalence of the space-time diversity technology and the guidance of how to apply appropriately the space-time diversity technology are obtained. The third step is to offer the SD-LMS adaptive signal processing algorithm of Space Optical Communication, through combining selection diversity technology with adaptive signal processing algorithm. Based on LMS adaptive signal processing algorithm,"the expected signal"can be gained through space selection diversity technology so that the outputting signal-to-noise rate can be raised with the increase of the numbers of the diversity signal inputting brunches while the distortion of the outputting signals is similar to that of the single-way inputting ones. The outputting signal-to-noise rate can be raised while the outputting signal distortion can be improved so that the LMS adaptiive signal processing algorithm properties can also be heightened.The fourth step is to offer the strategies of developing China's Space Optical Communication according to China's climate situations through specific analysis of the usability of Space Optical communication in cities. The weather data within three years of 194 cities in China are taken as samples to compute the usability of Space Optical Communication in the 194 cities based on its transmitting models of the Space Optical Communication System. According to the statistical data, China's cities may be divided into three sorts: the advocated,the usable and the forbidden Space Optical Communication System. It is suggested that China should develop the Space Optical Communication technology to build up heaven-earth integrative communication networks and recommend some appropriate cities as the basic earth-station of the Space Optical Communication.In this dissertation, the channel models and the technology and methods of improving the Space Optical Communication properties are proved to be effective in both theory and experiments as well, which might be able to have some important and instructional significance for the designing and realizing of the Space Optical Communication Systems.