本文選題：動態(tài)等離子體 + 寄生調(diào)制　； 參考：《西安電子科技大學》2015年碩士論文

【摘要】：飛行器再入過程中受到空氣強大的擠壓,與空氣發(fā)生劇烈的摩擦,從而在其表面形成很強的激波壓縮,導致表面的流場內(nèi)部產(chǎn)生湍流及震蕩。覆蓋在飛行器表面的等離子鞘套會呈現(xiàn)出復雜的動態(tài)特性,導致穿過等離子鞘套的通信信號出現(xiàn)幅度以及相位上的雙重調(diào)制現(xiàn)象,這種現(xiàn)象稱為等離子鞘套的寄生調(diào)制效應。寄生調(diào)制效應的存在會降低信號傳輸質(zhì)量,嚴重時甚至會致使信息傳輸中斷。削弱由等離子引起的寄生調(diào)制效應存在兩點困難:一是目前對等離子鞘套動態(tài)特性的研究尚不深入,難以準確預測等離子鞘套傳輸環(huán)境;二是寄生調(diào)制效應為通信信號引入了一個乘性噪聲,不能采用技術(shù)成熟的線性濾波方法濾除噪聲。針對這兩點困難,本文提出兩點應對思路:一是研究等離子透射信號與反射信號幅相起伏之間的相關(guān)性,通過反射信號對等離子鞘套傳輸環(huán)境進行實時測量;二是通過同態(tài)變換方法將頻域上相依賴的噪聲和信號分離。具體的工作包括:(1)、首先分析了動態(tài)等離子寄生調(diào)制效應的產(chǎn)生機理和對通信信號造成的影響,并通過實驗驗證了寄生調(diào)制對BPSK、QPSK、FSK以及MFSK四種典型通信信號的影響;(2)、利用基于相關(guān)性系數(shù)的滑動窗法分析了等離子反射信號與透射信號幅相起伏之間的相關(guān)性,為通過反射信號對等離子鞘套傳輸環(huán)境進行實時測量提供理論基礎(chǔ)。(3)、論述了反射測量以及同態(tài)變換的基本理論,提出了一種動態(tài)等離子寄生調(diào)制效應的削弱方法,并針對實際應用場景利用Matlab搭建通信系統(tǒng)來驗證這種方法的有效性。經(jīng)過仿真驗證表明,本文中提出的動態(tài)等離子寄生調(diào)制效應削弱方法能有有效減弱寄生調(diào)制效應對通信信號的影響。這種方法通過反射信號來推算等離子鞘套信道透射信號的變化,為等離子鞘套下信息可靠傳輸提供了新的思路。
[Abstract]:In the process of reentry, the aircraft is squeezed by the air, and the friction with the air is intense, which forms a strong shock compression on the surface, resulting in turbulence and oscillation in the surface flow field. The plasma sheath covering the surface of the aircraft presents complex dynamic characteristics, which leads to the amplitude and phase double modulation of the communication signal passing through the plasma sheath, which is called the parasitic modulation effect of the plasma sheath. The existence of parasitic modulation effect will reduce the quality of signal transmission and even lead to the interruption of information transmission. There are two difficulties in weakening the parasitic modulation effect caused by plasma. One is that the research on the dynamic characteristics of plasma sheath is not deep, so it is difficult to accurately predict the transmission environment of plasma sheath; The second is that parasitic modulation introduces a multiplicative noise to the communication signal, so it is not possible to filter the noise by using the mature linear filtering method. In view of these two difficulties, this paper puts forward two countermeasures: first, to study the correlation between the amplitude and phase fluctuation of the plasma transmission signal and the reflected signal, and to measure the transmission environment of the plasma sheath in real time through the reflected signal; Second, the frequency dependent noise and signal are separated by homomorphic transformation. The specific work includes 1: 1. Firstly, the mechanism of dynamic plasma parasitic modulation and its influence on communication signal are analyzed. The effects of parasitic modulation on the four typical communication signals of BPSK, QPSK, FSK and MFSK are verified by experiments. The correlation between the amplitude-phase fluctuations of plasma reflected signals and transmitted signals is analyzed by the sliding window method based on correlation coefficient. In order to provide a theoretical basis for real-time measurement of plasma sheath transmission environment by reflected signal, the basic theory of reflection measurement and homomorphism transformation is discussed, and a method to weaken the dynamic plasma parasitic modulation effect is proposed. Matlab is used to build communication system to verify the effectiveness of this method. The simulation results show that the method proposed in this paper can effectively attenuate the effect of parasitic modulation on the communication signal. This method calculates the change of the transmission signal of the plasma sheath channel by reflecting signal, and provides a new idea for the reliable transmission of the information under the plasma sheath.
【學位授予單位】：西安電子科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：V243.1

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