本文關(guān)鍵詞： 異步擴頻 低信噪比 高動態(tài) 捕獲跟蹤 符號同步　出處：《南京理工大學》2017年碩士論文　論文類型：學位論文

【摘要】：異步擴頻測控體制在我國的衛(wèi)星導航測距領(lǐng)域應(yīng)用廣泛,該體制的研究重點就是如何實現(xiàn)對異步擴頻信號的解擴解調(diào)。異步擴頻信號的解擴解調(diào)過程中,又大致分為以下幾個部分:偽碼相位與多普勒頻偏的粗捕、偽碼相位的跟蹤、載波頻率的捕獲與同步、符號同步等。在星地通信中,對擴頻信號捕獲和跟蹤的難度遠大于地面通信,其原因主要有兩個方面:首先是信道環(huán)境較為復雜,接收到的信號信噪比難以保障;另一方面,通信設(shè)備所在載體往往具有較高的移動速度和加速度,這就帶來了較高的多普勒頻移和頻移變化率,大大增加了的難度。本文針對課題要求,在對現(xiàn)有常用捕獲、跟蹤方法進行研究的基礎(chǔ)上,設(shè)計了針對低信噪比、高動態(tài)的異步直接擴頻信號進行捕獲和跟蹤的算法,并對其進行了仿真和FPGA實現(xiàn)。主要內(nèi)容包括:闡述了擴頻通信領(lǐng)域目前常用的幾種偽碼捕獲方法,分析了它們各自的實現(xiàn)原理與性能情況,指出其優(yōu)缺點,并使用Matlab加以仿真;提出了改進的"基于頻域并行捕獲技術(shù)"方案,不但可以適應(yīng)較大的輸入信噪比范圍和多普勒范圍,而且大大縮小了運算量,將捕獲時間縮短至1.4秒以內(nèi),仿真表明,它可以在載噪比55dBHz下實現(xiàn)捕獲概率100%,誤捕概率為0;設(shè)計了跟蹤精度較高的載波輔助的DLL碼跟蹤環(huán)路架構(gòu);設(shè)計了能在較大的動態(tài)下完成相位的精確跟蹤的雙環(huán)路載波跟蹤環(huán);設(shè)計了基于早遲門的符號同步方案。最后,針對某航天工程應(yīng)用,本文對異步直接擴頻信號的捕獲和載波同步算法進行了硬件實現(xiàn)。
[Abstract]:Asynchronous spread spectrum measurement and control system is widely used in the field of satellite navigation and ranging in China. The research focus of this system is how to realize despreading demodulation of asynchronous spread spectrum signal and despreading demodulation process of asynchronous spread spectrum signal. It can be divided into the following parts: coarse capture of pseudo-code phase and Doppler frequency offset, tracking of pseudo-code phase, acquisition and synchronization of carrier frequency, symbol synchronization and so on. The difficulty of acquisition and tracking of spread spectrum signal is much more difficult than that of ground communication. There are two main reasons: firstly, the channel environment is more complex and the signal to noise ratio is difficult to guarantee; On the other hand, the carrier of communication equipment often has higher moving speed and acceleration, which brings higher Doppler frequency shift and frequency shift change rate, which greatly increases the difficulty. Based on the research of the existing acquisition and tracking methods, an algorithm for acquisition and tracking of asynchronous direct spread spectrum signals with low signal-to-noise ratio and high dynamic performance is designed. The main contents are as follows: the common methods of PN code acquisition in the field of spread spectrum communication are described, and their implementation principle and performance are analyzed. Its advantages and disadvantages are pointed out and simulated by Matlab. An improved "parallel acquisition technique based on frequency domain" is proposed, which can not only adapt to the larger range of input SNR and Doppler, but also greatly reduce the computational cost and shorten the acquisition time to less than 1.4 seconds. The simulation results show that the acquisition probability is 100 and the false capture probability is 0 under the carrier noise ratio of 55 dBHz. A carrier assisted DLL code tracking loop architecture with high tracking accuracy is designed. A double loop carrier tracking loop is designed, which can accurately track the phase in a large dynamic state. The symbol synchronization scheme based on the early and late gate is designed. Finally, the acquisition of asynchronous direct spread spectrum signals and the carrier synchronization algorithm are implemented in hardware for a space engineering application.
【學位授予單位】：南京理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN914.42

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