本文選題：高靈敏度 + FFT鑒頻�。� 參考：《武漢大學》2017年碩士論文

【摘要】：隨著智能設備的普及,導航應用的需求逐漸被挖掘,基于用戶位置的服務也慢慢地成為了人們的生活的一部分。同時,應用場景多變、復雜的特性也對導航設備的性能提出了挑戰(zhàn),GNSS作為最重要的室外導航方式,其性能的提升對導航的發(fā)展起著至關(guān)重要的作用。城市樓群、峽谷、森林等環(huán)境下,信號的透射、折射、反射等都會導致能量衰減,嚴重影響著GNSS接收機的捕獲、跟蹤性能,導致接收機定位精度、連續(xù)性嚴重惡化,因此高靈敏度接收機應運而生。捕獲作為信號同步的第一步,直接影響著接收機的性能。針對捕獲參數(shù)配置與優(yōu)化問題,在分析各因素對弱捕獲性能影響后,設計了一種基于蒙特卡洛仿真的捕獲性能評估方法;針對弱信號環(huán)境下互相關(guān)干擾嚴重的問題,基于理論分析和測試驗證對其特性進行了定量分析,為互相關(guān)干擾的抑制提供了依據(jù);針對信號能量衰減導致常規(guī)比特同步方法不適用的問題,通過仿真對比分析了直方圖法和比特能量法的性能,同時分析了不同比特跳變概率下比特能量法的同步效果。跟蹤是對信號參數(shù)進行精細估計的過程,對弱信號的跟蹤水平很大程度上決定了接收機對復雜環(huán)境的適應能力。針對常規(guī)鑒頻器積分時長受比特跳變限制問題,設計了一種適用于弱信號的FFT鑒頻器;針對動態(tài)與靈敏度互相矛盾的問題,在環(huán)路中引入了慣性輔助,提高了動態(tài)環(huán)境下的跟蹤靈敏度;晶振誤差是影響跟蹤靈敏度的重要因素,為此提出了一種基于鎖相環(huán)分析晶振誤差的方法,并闡明了晶振誤差反饋至NCO的必要條件;針對弱信號環(huán)境下子幀無法同步、偽距(發(fā)射時間)無法提取的問題,本文提出了輔助信息下基于信號匹配的偽距提取的方法。最后,設計實現(xiàn)了一套完整的軟件接收機系統(tǒng)。仿真器定量測試表明:在多普勒和碼相位的輔助條件下,750ms積分對22dB-Hz信號具有90%的檢測率;當定位誤差達到100m(或60m)時,靜態(tài)的跟蹤靈敏度為11dB-Hz(或14dB-Hz),低于0.75g的動態(tài)跟蹤靈敏度為15dB-Hz(或16dB-Hz),慣性輔助的跟蹤靈敏度為12dB-Hz(或14dB-Hz)。車載實測表明:在開闊環(huán)境、復雜環(huán)境下,本文研制的軟件接收機均展現(xiàn)了魯棒性強的捕獲、跟蹤能力,接收機的整體定位效果與Ublox LEA-6T 的接近。
[Abstract]:With the popularity of intelligent devices, the needs of navigation applications have been gradually mined, and user-location-based services have gradually become a part of people's lives. At the same time, the application scene is changeable, the complex characteristic also proposed the challenge to the navigation equipment performance. GNSS is the most important outdoor navigation way, its performance enhancement plays the vital role to the navigation development. In urban buildings, canyons, forests and other environments, the transmission, refraction and reflection of signals will lead to energy attenuation, which will seriously affect the acquisition and tracking performance of the GNSS receiver, lead to the positioning accuracy of the receiver, and the continuity of the receiver will deteriorate seriously. Therefore, the high sensitivity receiver emerges as the times require. As the first step of signal synchronization, acquisition directly affects the performance of receiver. Aiming at the problem of configuration and optimization of acquisition parameters, after analyzing the influence of various factors on the performance of weak acquisition, a method of performance evaluation based on Monte Carlo simulation is designed, and the problem of serious cross-correlation interference in weak signal environment is discussed. Based on the theoretical analysis and test verification, the characteristics are quantitatively analyzed, which provides a basis for the suppression of cross-correlation interference, and aims at the problem that the conventional bit synchronization method is not applicable due to the attenuation of signal energy. The performance of the histogram method and the bit energy method are compared by simulation. The synchronization effect of the bit energy method with different bit hopping probability is also analyzed. Tracking is the process of fine estimation of signal parameters. The level of weak signal tracking determines the adaptability of the receiver to complex environment to a great extent. Aiming at the problem that the integration time of conventional frequency discriminator is limited by bit jump, a FFT frequency discriminator suitable for weak signals is designed, and an inertial assistant is introduced into the loop to solve the contradiction between dynamic and sensitivity. The tracking sensitivity in dynamic environment is improved, and the crystal oscillator error is an important factor affecting the tracking sensitivity. A method for analyzing the crystal oscillator error based on PLL is proposed, and the necessary condition for the crystal oscillator error to be fed back to NCO is expounded. In order to solve the problem that subframe can not be synchronized and pseudo-range (transmit time) can not be extracted in weak signal environment, a method of pseudo-range extraction based on signal matching under auxiliary information is proposed in this paper. Finally, a complete software receiver system is designed and implemented. The quantitative test of the simulator shows that under the auxiliary condition of Doppler and code phase, the integral of 750ms has 90% detection rate for 22dB-Hz signal, and when the positioning error reaches 100m (or 60m), The static tracking sensitivity is 11dB-Hz (or 14dB-HzN), the dynamic tracking sensitivity less than 0.75g is 15dB-Hzn (or 16dB-HzN), and the inertial assistant tracking sensitivity is 12dB-Hz( or 14dB-HzN). The in-vehicle measurement shows that in the open and complex environment, the software receivers developed in this paper show robust capture and tracking ability, and the overall positioning effect of the receiver is close to that of Ublox LEA-6T.
【學位授予單位】：武漢大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P228.4

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