本文關鍵詞： GNSS 弱信號捕獲 PMF-FFT 加窗　出處：《廣東工業(yè)大學》2014年碩士論文　論文類型：學位論文

【摘要】：全球導航衛(wèi)星系統(tǒng)GNSS(Global Navigation Satellite System)發(fā)展至今,美國的GPS導航系統(tǒng)已經深入而廣泛的應用到各個領域,俄羅斯的GLONASS、歐盟的GALILEO系統(tǒng)以及我國正在發(fā)展的北斗導航系統(tǒng)等也逐漸普及。目前導航定位技術在諸多領域都擔任著重要的角色,人們對于導航定位技術的要求給導航定位技術帶來極大挑戰(zhàn)。 多數(shù)應用中需要有GNSS系統(tǒng)的精確定位。信號同步過程是GNSS系統(tǒng)能精確定位的前提,要實現(xiàn)信號的同步,首先要完成捕獲過程,然后才能進入跟蹤階段。但低軌道處的GNSS系統(tǒng)由于其傳播信道的復雜性,在傳播過程中容易受到大幅度衰減以及噪聲的影響,到達地面的信號可能經歷反射、折射等環(huán)境因素的干擾,加上接收機的快速移動問題,從而產生各種衰落,導致存在著較大的多普勒頻偏及碼延遲。這樣,接收碼和本地偽碼同步過程中的相關峰值將會急劇下降,GNSS接收機對偽碼捕獲的難度加大,捕獲時間延長。且由于無線設備接收到的信號功率非常低,通常載噪比C/N。小于25dB-Hz,傳統(tǒng)的GNSS信號接收機甚至無法正常工作。因此,在弱信號環(huán)境下,實現(xiàn)偽碼和多普勒頻偏的快速捕獲,無論在民用領域或是軍事領域都具有重要的研究意義。 目前,GNSS弱信號捕獲主要可分為輔助型和無輔助兩種,而無輔助的GNSS弱信號捕獲技術主要以提高信號處理增益和合理選擇捕獲策略為主。針對以上問題,本文就基于PMF-FFT的弱信號捕獲算法進行優(yōu)化,再將基于PMF-FFT的碼捕獲算法與幾種頻偏估計算法進行結合,對聯(lián)合捕獲算法進行加窗減少扇貝損失,改善頻偏對捕獲概率的影響。并在不同的移動速度下,通過MATLAB仿真結果找出該速度和環(huán)境下最合適的捕獲方法。本文的主要工作可以概括為以下四點： 1.深入研究GNSS信號結構及捕獲定位技術,并建立數(shù)學模型； 2.分析部分匹配濾波PMF的原理以及用于捕獲算法中的優(yōu)勢； 3.總結分析現(xiàn)有的GNSS系統(tǒng)弱信號環(huán)境下基于部分匹配濾波的碼捕獲算法； 4.對弱信號條件下基于PMF-FFT的碼和多普勒聯(lián)合捕獲算法進行加窗處理,減小扇 貝損失,提高檢測概率,并在不同移動速度下對比仿真結果選擇最優(yōu)捕獲算法。
[Abstract]:Global navigation satellite system (GNSS(Global Navigation Satellite system) has been developed so far. The GPS navigation system of the United States has been deeply and widely used in various fields, Russia's GLONASS. The GALILEO system of the European Union and the Beidou navigation system which is developing in our country are also gradually popularized. At present, the navigation and positioning technology plays an important role in many fields. The requirement of navigation and positioning technology brings great challenge to navigation and positioning technology. In most applications there is a need for accurate positioning of GNSS system. Signal synchronization is the premise of accurate positioning in GNSS system. In order to achieve signal synchronization the first step is to complete the acquisition process. But the GNSS system in low orbit is vulnerable to large attenuation and noise due to the complexity of its propagation channel. The signal arriving at the ground may experience the interference of environmental factors such as reflection refraction and so on plus the problem of the fast moving of the receiver which results in a variety of fading which leads to the existence of large Doppler frequency offset and code delay. The correlation peak value in the synchronization process between the received code and the local PN code will dramatically reduce the difficulty of GNSS receiver acquisition of PN code, and the acquisition time will be prolonged. Moreover, the signal power received by wireless equipment is very low. Usually the carrier noise ratio C / N. Is less than 25dB-Hz. the traditional GNSS signal receiver can not even work normally. Therefore, in the weak signal environment, the fast acquisition of pseudo-code and Doppler frequency offset is realized. It is of great significance in both civil and military fields. At present, the weak signal acquisition of GNSS can be divided into two types: auxiliary and non-auxiliary. But the unaided GNSS weak signal acquisition technology is mainly to improve the signal processing gain and reasonably select the acquisition strategy. In this paper, the weak signal acquisition algorithm based on PMF-FFT is optimized, and then the code acquisition algorithm based on PMF-FFT is combined with several frequency offset estimation algorithms. The joint acquisition algorithm is windowed to reduce scallop loss, and the influence of frequency offset on acquisition probability is improved. Through the MATLAB simulation results to find out the most suitable capture method under this speed and environment. The main work of this paper can be summarized as follows: 1. Deeply study the structure of GNSS signal and capture and position technology, and establish mathematical model; 2. Analyze the principle of partial matched filter (PMF) and its advantages in acquisition algorithm; 3. The code acquisition algorithm based on partial matched filter in weak signal environment of GNSS system is summarized and analyzed. 4. The joint acquisition algorithm of code and Doppler based on PMF-FFT under weak signal condition is windowed to reduce fan. The detection probability is improved and the optimal acquisition algorithm is selected by comparing the simulation results with different moving speeds.
【學位授予單位】：廣東工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN96.1

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