基于自适应光学的自由空间光通信指向性误差校正

发布时间：2018-01-06 00:22

本文关键词：基于自适应光学的自由空间光通信指向性误差校正　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着社会的不断发展以及信息时代的到来,传统通信方式已经逐渐无法满足人们的需求。互联网、大数据技术的应用使信息量呈爆炸性增长,这就需要通信网和通信业务的质量和水平也随之相应提高,以适应时代的发展。自由空间光通信(Free Space Optical,FSO)以其频带宽、信息容量大、保密性高、无需频谱认证等优点成为当下新型通信技术的研究热点之一。但是由于大气效应的存在,FSO通信并未在人们的日常生活中普遍使用。其主要问题是,光在空间传输过程中受大气折射率的随机变化影响会产生波前畸变,从而影响FSO通信系统的通信质量。此外,由此产生的指向性误差使得系统的误码率(Bit Error Rate,BER)上升,耦合效率下降。因此,解决大气效应引起的光束波前畸变问题对于FSO通信技术的应用意义重大。将自适应光学(Adaptive Optics,AO)技术应用到FSO通信系统中是解决波前畸变问题的有效方法。在阅读了大量文献的基础上,在实验室内搭建了自适应光学实验平台,针对大气湍流造成的指向性误差进行了研究工作。我们搭建的自适应光学系统由三个部分组成,分别为波前探测单元、波前控制单元和波前校正单元。实验中采用高速相机作为波前探测器,用来检测系统回路的误差;采用计算机作为波前处理单元,它相当于整个系统的大脑,通过计算为校正器提供实时的控制信号;采用快速反射镜(Fast Steering Mirror,FSM)作为波前校正单元,它相当于一个执行机构,对大气湍流造成的指向性误差进行补偿。在介绍了经典的比例积分微分(Proportion Integration Differentiation,PID)算法和模糊比例积分算法后,实验中选用工业上有效、常用的PI控制算法来实时地控制FSM,并用实验法整定了比例系数。实验结果表明闭环后系统的指向性误差标准差有了明显下降。通过分析多组实验数据发现,在大气波动强烈的条件下,PI算法的校正效果有待进一步提高。因此对PI算法进行必要的改进,提出了P-PI控制方法。该方法在大气波动强烈的时候,以较大的比例系数去逼近目标位置,当误差下降到一定范围内的时候,再采用PI控制策略。实验结果表明,P-PI算法的上升时间大约是PI算法上升时间的一半。在正弦函数和伪随机函数作用下,采用P-PI算法控制时,系统的指向性误差标准差更小。本文分析了焦平面上系统的BER和指向性误差之间的关系,表明系统的指向性误差越小,BER越低。
[Abstract]:With the continuous development of society and the arrival of the information age, the traditional communication mode has been gradually unable to meet the needs of people. The application of Internet and big data technology makes the amount of information explosive growth. Therefore, the quality and level of communication network and communication services should be improved accordingly, in order to adapt to the development of the times. Free Space Optical for free space optical communication. FSO) has become one of the research hotspots of the new communication technology due to its advantages of frequency bandwidth, large information capacity, high confidentiality and no spectrum authentication. However, due to the existence of atmospheric effects. FSO communication is not widely used in people's daily life. The main problem is that the wavefront distortion will be caused by the random change of atmospheric refractive index in the process of space transmission. Thus, the communication quality of the FSO communication system is affected. In addition, the resulting directivity error causes the bit Error rate of the system to rise. Therefore, solving the problem of beam wavefront distortion caused by atmospheric effect is of great significance to the application of FSO communication technology. Adaptive Optics will be adopted by adaptive optics. AOO is an effective method to solve the problem of wavefront distortion in FSO communication system. Based on reading a lot of literature, an experimental platform of adaptive optics is built in the laboratory. In this paper, the directivity error caused by atmospheric turbulence is studied. The adaptive optical system is composed of three parts, which are wavefront detection units. In the experiment, the high speed camera is used as the wave front detector to detect the error of the system loop. The computer is used as the wavefront processing unit, which is equivalent to the whole system's brain, and provides real-time control signal for the corrector by calculation. Fast Steering mirror is used as the wavefront correction unit, which is equivalent to an actuator. In this paper, the classical proportional integro-differential (PDD) is introduced to compensate the directivity error caused by atmospheric turbulence. Proportion Integration Differentiation. After the FSM algorithm and fuzzy proportional integration algorithm, the industrial effective Pi control algorithm is used to control the FSM in real time. The experimental results show that the standard deviation of the directional error of the system has obviously decreased after the closed loop. Through the analysis of many groups of experimental data, it is found that under the condition of strong atmospheric fluctuation. The correction effect of Pi algorithm needs to be further improved. Therefore, a P-PI control method is proposed, which is necessary to improve Pi algorithm. When the error decreases to a certain range, Pi control strategy is adopted. The rising time of P-PI algorithm is about half of that of Pi algorithm. Under the action of sinusoidal function and pseudorandom function, P-PI algorithm is used to control. In this paper, the relationship between BER and directivity error of the system on focal plane is analyzed. It is shown that the smaller the directivity error of the system is, the lower the directivity error is.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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