本文關鍵詞：基于自適應光學的自由空間光通信指向性誤差校正　出處：《吉林大學》2017年碩士論文　論文類型：學位論文

  更多相關文章： 自由空間光通信 自適應光學 波前畸變 指向性誤差 快速反射鏡 PI控制

【摘要】：隨著社會的不斷發(fā)展以及信息時代的到來,傳統(tǒng)通信方式已經逐漸無法滿足人們的需求�；ヂ摼W、大數據技術的應用使信息量呈爆炸性增長,這就需要通信網和通信業(yè)務的質量和水平也隨之相應提高,以適應時代的發(fā)展。自由空間光通信(Free Space Optical,FSO)以其頻帶寬、信息容量大、保密性高、無需頻譜認證等優(yōu)點成為當下新型通信技術的研究熱點之一。但是由于大氣效應的存在,FSO通信并未在人們的日常生活中普遍使用。其主要問題是,光在空間傳輸過程中受大氣折射率的隨機變化影響會產生波前畸變,從而影響FSO通信系統(tǒng)的通信質量。此外,由此產生的指向性誤差使得系統(tǒng)的誤碼率(Bit Error Rate,BER)上升,耦合效率下降。因此,解決大氣效應引起的光束波前畸變問題對于FSO通信技術的應用意義重大。將自適應光學(Adaptive Optics,AO)技術應用到FSO通信系統(tǒng)中是解決波前畸變問題的有效方法。在閱讀了大量文獻的基礎上,在實驗室內搭建了自適應光學實驗平臺,針對大氣湍流造成的指向性誤差進行了研究工作。我們搭建的自適應光學系統(tǒng)由三個部分組成,分別為波前探測單元、波前控制單元和波前校正單元。實驗中采用高速相機作為波前探測器,用來檢測系統(tǒng)回路的誤差;采用計算機作為波前處理單元,它相當于整個系統(tǒng)的大腦,通過計算為校正器提供實時的控制信號;采用快速反射鏡(Fast Steering Mirror,FSM)作為波前校正單元,它相當于一個執(zhí)行機構,對大氣湍流造成的指向性誤差進行補償。在介紹了經典的比例積分微分(Proportion Integration Differentiation,PID)算法和模糊比例積分算法后,實驗中選用工業(yè)上有效、常用的PI控制算法來實時地控制FSM,并用實驗法整定了比例系數。實驗結果表明閉環(huán)后系統(tǒng)的指向性誤差標準差有了明顯下降。通過分析多組實驗數據發(fā)現,在大氣波動強烈的條件下,PI算法的校正效果有待進一步提高。因此對PI算法進行必要的改進,提出了P-PI控制方法。該方法在大氣波動強烈的時候,以較大的比例系數去逼近目標位置,當誤差下降到一定范圍內的時候,再采用PI控制策略。實驗結果表明,P-PI算法的上升時間大約是PI算法上升時間的一半。在正弦函數和偽隨機函數作用下,采用P-PI算法控制時,系統(tǒng)的指向性誤差標準差更小。本文分析了焦平面上系統(tǒng)的BER和指向性誤差之間的關系,表明系統(tǒng)的指向性誤差越小,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.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN929.1

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