【作者】 夏芸；

【导师】 金韬；

【作者基本信息】 浙江大学 ， 电磁场与微波技术， 2007， 硕士

【摘要】 目前，大气湍流是自由空间光通信所面临的一个重要难题。当激光通过大气层传输时，就必须要考虑其引起的附加效应，尤其是大气层产生的附加空间损耗和可能的光束畸变，这些都会严重影响系统信标光的定位和信号光的接收，从而对瞄准捕获与追踪(APT)系统以及信号接收系统产生难以预测的影响，直接关系到整个卫星通信系统的通信质量。大气对光通信的影响包括大气衰减和湍流效应，而湍流效应又包括光束扩展、光强闪烁、光束漂移以及到达角起伏等等。基于Rytov方法及Markov近似理论，本文以星地光通信为研究背景，从高斯光在湍流大气中传播的基本理论出发，建立了考虑湍流内、外尺度因素的高斯光闪烁模型和光束漂移模型，并通过数值分析及仿真，研究了各种参量对光束闪烁指数和光束漂移量的影响。本文还在各种模型分析研究的基础之上，分别给出了上下行链路接收端光斑的光强分布模型，并通过计算仿真，得到不同湍流强度下由CCD重心算法计算出的光斑定位位置与光斑实际位置的误差，从而进一步讨论了在强湍流区域内CCD重心模型是否仍适用于光斑定位的问题。鉴于大气湍流效应对光通信具有不可忽视的影响，本文从激光参数、调制方式这两个角度出发，分析了两种提高系统性能的方案，直接建立了光束发射功率与系统误码率的关系模型，并通过详细的理论研究和仿真比较，肯定了这两种方案在改善系统性能方面的可行性。更多还原

【Abstract】 At present, atmospheric turbulence is an important concern in free-space optical communication. Addictive effects must be taken into account when the laser is transmitted through the aerosphere, especially the append space ullage and possible beam aberration caused, which will affect beacon orientation and signal detection severely. All of above will produce unpredictable effects on the APT and signal detection system, which in turn has a direct connection with the communication quality of the whole system.The optical communication is not only influenced by atmospheric attenuation, but also turbulence domino. However, the turbulence dominos include beam spreading, scintillation, spot dancing and variance of the angle-of-arrival. Based on the Rytov Method, Markov Theory as well as the Gaussian diffusion equation in atmospheric turbulence, this paper has studied different Gaussian turbulence domino models with consideration of the inner-scale and outer-scale of turbulence. With the background of space-to-ground optical communication, the effects upon the models of different parameters are studied by numerical analysis and computer simulation. Further more, beam intensify distributing models of both up-link and down-link are built in the latter section including all the turbulence dominos above. So, we can work out the error between facular position calculated by CCD barycenter arithmetic and the actual one. And according to the error, we further discussed the problem of whether the CCD barycenter model can still be used in facular positioning in the area of strong turbulence. All the research above can be used as reference in optical communication system design.Due to the unneglectable turbulence effects, this paper will also propose several schemes to improve the system performance from the views of modulation methods and beam parameters. Meanwhile, the relationship model between beam launching power and system BER is also set up. The feasibility and effect are confirmed and demonstrated by detailed theory research and numerical analysis.更多还原