【作者】 王妮；

【导师】 柯熙政；

【作者基本信息】 西安理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 大气激光通信是指利用激光束作为载体在大气中进行语音、数据、图像信息双向传送的一种技术,它在解决“最后一公里”问题、应急通信等方面有着良好的应用前景。尽管大气激光通信身兼无线和宽带这两个特点,但同时这种以大气为媒介,激光为载波的点对点式通信技术,有其自身不可避免的缺点,激光在大气中传输会受到大气信道中各种因素的影响,引起信号衰减和符号间干扰,导致误码率增加。为了保证激光通信链路的正常、可靠运行,研究克服大气信道传输因素对激光传输影响的技术具有非常重要的意义。本文采用盲均衡技术来解决大气激光通信中的符号间干扰问题。首先简要介绍了大气激光通信系统及其特点,分析了国内外研究机构在大气激光通信方面的研究现状,然后根据大气激光通信的特点,提出了大气激光通信系统中的盲均衡方案,对隐含和直接使用高阶统计量的盲均衡算法的性能进行了研究。研究内容主要包括以下几个方面:1.研究了Bussgang类盲均衡算法的数学模型及其相关算法,包括Sato算法、Godard算法和判决引导算法;提出了判决引导法与基于累积量的自适应滤波算法相结合的盲均衡算法,并对该算法进行仿真。仿真结果表明,该算法可获得较小于判决引导法的剩余均方误差,但由于此算法计算量较大,不利于实时均衡。2.研究了几种直接使用高阶累积量的算法,包括基于三阶累积量的奇数阶(三、二阶)归一化法和直接法,分析了这几种算法的性能,通过仿真比较可知,直接法收敛速度较快,该算法使用较长数据对信道特性初始值估计时,可获得更好的均衡效果;而基于奇数阶(三、二阶)归一化算法实现较为简单,算法稳定性较好。3.针对在不同天气状况下的大气激光通信信道对信号传输的影响不同,利用实际测量功率值模拟大气激光信道对几种算法进行仿真,并对算法性能进行了比较和评估。更多还原

【Abstract】 Atmosphere Laser Communication (ALC) refers to the technology of transmitting voice, data and graphics using laser bean. Because of its advantage of narrow transmission bean, small antenna size, broad information capability and high performance to price, it impressed many people in communication area. So it has good application foreground in resolve of "The Last Kilometer Problem" and emergence communication.Although the Atmosphere Laser Communication has the two characteristics of board-band and wireless, this point to-point communication based atmosphere channel and medium of laser have inevitable defect itself. The transmission of laser in atmosphere was affected by kinds of factors in atmosphere channel. It brought signal attenuation and inter-symbol interferences. It leaded the addition of bit error rate. Approach the technique of being against the effect of atmosphere channel transmission factor to ladder transmission for ensure the normal of laser communication link have a very important meaning.This paper solved the problem about signal attenuation and ISI in the ALC system through blind equalization technique. Firstly, the dissertation introduced the Atmosphere Laser Communication system and its characteristic simply, and then the scheme about research of blind equalization in atmosphere laser communication system was advanced. The dissertation focuses on the performance of blind equalization using higher-order statistics implicitly and explicitly in accordance according the characteristic of Atmosphere Laser Communication channel. The research consists of several aspects as follows:1.The mathematics’ model of Bussgang BE and its relevant algorithm including Sato alg--orithm, Godard algorithm and DD(Decision-Directed) algorithm is discussed in our research, and the adaptive CDLMS filter base third-order cumulant algorithm, combining the conventional blind equalization algorithm with the decision direction, is presented. Furthermore, the result from the simulation about that algorithm which is presented in this paper is that the smaller steady-state error results from these algorithms than the DD (Decision-Directed) algorithm.2.The explicitly cumulant algorithms and the even-order normalized cumulant algorithm’s is studied. The result of simulation about performance of these algorithm is that the rapidity of convergence of the explicitly cumulant algorithms is faster than the even-order normalized cumulant algorithms; the stability of the even-order normalized cumulant algorithms is very good.3.According to the problem of the different effect on the signal transmission by different the weather regime, The ALC channel is analog, using the data measuring from the ALC system. We demonstrate the efficiency of several blind equalization algorithms based the analogic ALC channel, including comparison study and evaluation of their performance.更多还原