【作者】 安建梅；

【导师】 王胜坤；

【作者基本信息】 太原理工大学 ， 通信与信息系统， 2007， 硕士

【摘要】 大气激光通信是自由空间光通信在地面上的特定实现，在近距离通信时能以灵活的方式，用比现有系统低得多的成本，获得光纤传送的容量。由于具有设计简单、接入方便、速率高、成本低等优点，是目前所见到的解决接入网“最后一公里”问题的最有效的解决方案，广泛应用于智能建筑、军事等方面。在大气激光通信系统中，由于大气散射、折射、湍流等诸多因素的影响，会造成激光信号在传输过程中能量衰减，光强闪烁，光束随机偏转。能否克服这些影响是大气激光通信推广应用的关键，因此对大气激光通信信道的研究格外重要。本论文研究的主要内容：(1)介绍了无线激光通信的特性、国内外的研究动态、无线激光通信系统的原理和关键技术以及未来在无线激光领域内需要研究的课题等。(2)基于大气信道的特点，分析了大气吸收、大气散射、大气湍流对激光传输的影响。大气吸收和大气散射引起了光能量的衰减，即大气衰减。大气湍流引起了光强的起伏，其表现形式为光强闪烁、光束漂移、到达角起伏等。(3)探讨了大气吸收和大气散射引起的大气衰减。由于大气吸收和大气分子的散射时很小，通常用气溶胶的散射引起衰减来表示大气衰减，大气衰减的强弱通常用透射率来表示。通过分析透射率随传输距离和波长的关系，发现仿真结果和理论偏差较大，并且偏差随着波长的增加而变大，经分析，发现出现的偏差与大气衰减方程中的q值有关。本文针对上述现象对q值进行拟合、修正，进一步采用修正后的q值模拟透射率，找出了在不同的波长的情况下，趋于一致的q值。(4)基于大气湍流的的麦克斯韦方程和大气湍流的特性，推导了光传输过程中光强起伏的麦克斯韦方程和接收面上光强分布的方程；通过分析接收面上光强起伏的累计概率和统计规律，探索了增加接收面上的相关面元可减小光接收面上光强起伏方差的原因，进一步研究了多孔径发射和湍流的相干性对光强起伏的影响，结果显示多孔径发射可以增加接收面上的相干面元，从而减小光强起伏方差。最后对单孔径发射和多孔径发射以及在多孔径发射下相关系数对系统误码率的影响进行了分析，阐述了长波长、多孔径发射能够有效降低系统误码率的机理。更多还原

【Abstract】 The atmospheric laser communication is free-space optical communication’ specific implementation on earth. It is primarily feathered by flexible access method and low cost in short distance and can acquire the same capacity as fiber transmission. It is easy to be designed, is convenient to be switched-on, has high-speed and low-cost, so it is one of the most effective schemes to settle the problem of "The Last One Kilometer" and has been widely applied in such fields as intelligence building and military.In systems of atmospheric laser communication, because effects of atmospheric scattering, interception, turbulence and other factors, during the course of transmission, laser signals’ energy attenuation, light intensity flashing, light beam’ random inflection. Whether we can overcome these effects is the key of atmospheric laser communication’ population, so it is extremely important to research atmospheric laser communication channel. The main contents of this paper are:Firstly, this paper introduces characters of atmospheric laser communication and existing condition at home and abroad. Analyses its principle and key technologies and the subject studied future. Secondly, Based on the analysis of atmosphere channel, we analysis the atmospheric absorbing, scattering and turbulent. Atmospheric absorbing and scattering cause the attenuation of light energy. Atmospheric turbulent cause the flashing of the light intensity and so on.Thirdly, we explore the atmospheric attenuation, because the atmospheric attenuation that atmospheric absorbing and atmospheric molecule scattering cause can be ignored. We study the effects of atmospheric decay, scattering and turbulence on laser communication. Emulates atmospheric decay, finds the results is different greatly with theoretical value, and the deviation becomes greater with wavelength’ increase, after analyzing gets the conclusion the results has relation with q. Fits and amendments q, analogues atmospheric decay with the new q, finds the correct q.In the end, Based on atmospheric turbulence’ Maxwell equation and characters, get Maxwell equation of light intensity fluctuation in atmospheric turbulence and distribution of light intensity on receiving area. Through analysis cumulative probability and statistical regularity of the light intensity fluctuation. Finds increase the receiving surface elements can decrease the variance of the light intensity fluctuation. Further we study the quantity of apertures sending can reduce the variance of the light intensity fluctuation. In the end, we analysis the BER that be caused by single aperture and quantity of apertures. The conclusion shows that n apertures and long wavelength can reduce the BER.更多还原