【摘要】：GPS (Global Positioning System)系統(tǒng)是使用最為廣泛的導(dǎo)航定位系統(tǒng),為軍民領(lǐng)域的諸多方面提供服務(wù)。隨著GPS技術(shù)的不斷發(fā)展,高動態(tài)環(huán)境下GPS定位系統(tǒng)的應(yīng)用也越來越重要,但由于在高動態(tài)環(huán)境中,GPS載波上會產(chǎn)生較大的多普勒頻率,容易造成GPS信號跟蹤失鎖,無法穩(wěn)定跟蹤。為克服多普勒頻率的影響,本文對高動態(tài)下GPS信號跟蹤環(huán)路算法進(jìn)行了研究,主要從以下幾個方面進(jìn)行研究:(1)分析載噪比對傳統(tǒng)載波跟蹤環(huán)路GPS信號跟蹤結(jié)果的影響。通過調(diào)整載噪比的大小,找到鎖相環(huán)和鎖頻環(huán)的最佳工作狀態(tài),載噪比越高,鎖相環(huán)和鎖頻環(huán)的性能越好,但由于噪聲帶寬過高,噪聲功率會增大,當(dāng)超過載波跟蹤環(huán)的承受能力時,會導(dǎo)致環(huán)路失鎖。(2)將擴展卡爾曼濾波應(yīng)用到載波跟蹤環(huán)路中,將傳統(tǒng)載波跟蹤環(huán)路的濾波器和鑒別器替換為擴展卡爾曼濾波器,通過對高動態(tài)中的非線性函數(shù)進(jìn)行泰勒展開式,并進(jìn)行一階線性化截斷,將其余高階項去除,從而將非線性問題轉(zhuǎn)換成為線性問題,實現(xiàn)載波跟蹤。(3)將無跡卡爾曼濾波應(yīng)用到載波跟蹤環(huán)路中,將傳統(tǒng)載波跟蹤環(huán)路的濾波器和鑒別器替換為無跡卡爾曼濾波器,以UT變換為基礎(chǔ),對高動態(tài)中非線性函數(shù)的概率密度分布進(jìn)行近似,采用一系列的采樣點來逼近狀態(tài)的后驗概率密度,最終實現(xiàn)載波跟蹤。通過仿真結(jié)果可以得出,當(dāng)載噪比比較低時,傳統(tǒng)載波跟蹤環(huán)路對多普勒頻率的估計誤差比較大,導(dǎo)致跟蹤失鎖,提高載噪比,傳統(tǒng)載波跟蹤環(huán)路對多普勒頻率的估計誤差有所改善,但是對多普勒頻率的一階導(dǎo)數(shù)和二階導(dǎo)數(shù)估計誤差比較大。在低載噪比的情況下,擴展卡爾曼跟蹤環(huán)路和無跡卡爾曼跟蹤環(huán)路在跟蹤精度和動態(tài)應(yīng)力方面都比傳統(tǒng)跟蹤環(huán)路的性能好,對多普勒頻率及其一階導(dǎo)數(shù)、二階導(dǎo)數(shù)的估計誤差減小,提高載噪比,擴展卡爾曼跟蹤環(huán)路和無跡卡爾曼跟蹤環(huán)路的跟蹤精度有所提高,而且,在跟蹤精度和收斂速度方面,UKF載波跟蹤算法要比EKF載波跟蹤算法的性能更好一些。
[Abstract]:GPS (Global Positioning System) system is the most widely used navigation and positioning system, which provides services for many aspects of military and civilian fields. With the development of GPS technology, the application of GPS positioning system in high dynamic environment is becoming more and more important. However, in the high dynamic environment, the large Doppler frequency will occur on the GPS carrier, which will easily lead to the GPS signal tracking lose lock and can not be tracked stably. In order to overcome the influence of Doppler frequency, this paper studies the algorithm of GPS signal tracking loop in high dynamic state, mainly from the following aspects: (1) the influence of carrier noise ratio on the GPS signal tracking results of traditional carrier tracking loop is analyzed. By adjusting the ratio of carrier to noise, the optimum working state of PLL and FLL is found. The higher the ratio of carrier to noise, the better the performance of PLL and FLOL, but the higher the noise bandwidth is, the greater the noise power will be. When the capacity of carrier tracking loop is exceeded, the loop will lose lock. (2) the extended Kalman filter is applied to the carrier tracking loop, and the filter and discriminator of the traditional carrier tracking loop are replaced by the extended Kalman filter. The nonlinear function in high dynamics is transformed into a linear problem by Taylor expansion and first order linearization truncation to remove the other higher order terms. (3) the unscented Kalman filter is applied to the carrier tracking loop, and the filter and discriminator of the traditional carrier tracking loop are replaced by the unscented Kalman filter, which is based on the UT transform. The probability density distribution of nonlinear function in high dynamic state is approximated, and a series of sampling points are used to approximate the posteriori probability density of the state. Finally, carrier tracking is realized. The simulation results show that when the carrier / noise ratio is low, the estimation error of Doppler frequency in the traditional carrier tracking loop is relatively large, which leads to the tracking loss and increases the carrier noise ratio. The traditional carrier tracking loop improves the Doppler frequency estimation error, but the first and second derivative estimation errors of the Doppler frequency are relatively large. In the case of low load to noise ratio, the performance of the extended Kalman tracking loop and the unscented Kalman tracking loop is better than that of the traditional tracking loop in terms of tracking accuracy and dynamic stress, and the Doppler frequency and its first derivative are obtained. The estimation error of the second derivative is reduced, the carrier noise ratio is increased, the tracking accuracy of the extended Kalman tracking loop and the unscented Kalman tracking loop is improved, and the tracking accuracy of the extended Kalman tracking loop and the unscented Kalman tracking loop are improved. In terms of tracking accuracy and convergence speed, the performance of UKF carrier tracking algorithm is better than that of EKF carrier tracking algorithm.
【學(xué)位授予單位】：西安理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P228.4

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