无辅助GNSS信号捕获技术研究

发布时间：2018-04-13 11:49

本文选题：高动态 + 弱信号　；参考：《西安电子科技大学》2016年博士论文

【摘要】：随着全球导航卫星系统(Global Navigation Satellite System,GNSS)定位技术的广泛应用,对恶劣环境下利用GNSS信号定位提出了更高的要求。如接收机在室内、城市峡谷或是茂密丛林的定位,在这种环境下通常接收的信号非常微弱,再比如飞行器的定位、卫星的定位和导弹的定位。它们接收的信号具有一定的动态性而且信号通常较弱,而且对接收机的功耗有一定的要求,在这种情况下提出了无辅助接收技术。其中,GNSS信号捕获是GNSS定位的重要步骤,利用信号捕获来完成信号参数的初步估计,本文对这种高动态、弱信号环境下GNSS信号的捕获问题展开深入研究。对GNSS接收信号进行了系统地建模,针对不同环境下的接收信号展开具体分析并提出相应的解决方法,其主要创新性工作及研究成果如下：1.为了克服在高动态弱信号环境下信号的积分峰值会受到比特符号翻转和频率误差的影响,本文提出了一种基于离散Chirp傅里叶变换(Discrete Chirp Fourier Transform,DCFT)块补零方法。与传统闭环捕获和跟踪的接收机结构相比,该方法适用于开环捕获。为了避免像块积累半相干积分(Block Accumulating Semi-coherent Integration of Correlations,BASIC)方法一样计算块间共轭积降低原始信号的信噪比,该方法结合了DCFT和块补零思想,能够使后相关信号在剥离比特符号后进行相干积累并且同时进行高动态参数精准预测。同时,对提出方法的检测性能进行分析推导了本文方法的捕获概率和虚警概率表达式,最后仿真实验表明本文方法较传统的BASIC方法能在更低的信噪比下捕获信号并精准地估计信号参数。2.为了提高卫星信号在低信噪比、小频偏时的捕获概率,提出了两种基于变换域滤波的捕获方法。一种称为基于快速傅里叶变换(Fast Fourier Transform,FFT)滤波的捕获方法。由于小波变换较离散余弦变换(Discrete Cosine Transform,DCT)或傅里叶变换(Fourier Transform,FT)可以自由选择小波基函数,提出了一种基于小波域滤波的捕获方法,该方法通过对信号在小波域内进行频带划分,接着进行选择性重构信号,极大地滤除了噪声且保留了有用信号能量,使检测概率提高。此外该方法给出利用滤波前后有用信号能量来计算能量比的小波函数选取准则。仿真分别在恒虚警条件下给出高斯信道和衰落信道的检测概率,表明本文方法较一般方法能极大地提高信号的检测概率。3.为了解决在乘性和加性噪声条件下捕获问题,提出了一种联合均值函数和自相关函数捕获方法,证明了接收信号的循环平稳特性,利用信号循环平稳特性来捕获信号,通过选择适当循环频率点检测峰值完成信号参数估计的目的。该方法利用信号能量比阈值的方式决定是利用均值函数还是自相关函数去预测接收信号的频率。克服了传统方法仅仅利用均值函数或自相关函数的缺陷。仿真实验证明本文方法较传统方法在不同乘性噪声下具有更好的鲁棒性。4.为了实现在信噪比较高的高动态环境下的GNSS信号快速捕获,提出一种基于近邻差分积累的压缩感知捕获方法,对后相关信号进行近邻差分积累,而后利用沃尔什哈达玛变换分成两步对积累后信号进行压缩检测,推导了该方法的检测概率。由于近邻差分积累可以减少比特反转和频率误差对积累峰值的影响,两步压缩检测可以极大降低检测时间,所以本文方法可以实现在高动态下GNSS信号的快速捕获。最后仿真实验表明实际检测概率和理论推导的一致性和在恒虚警条件下较对比方法有更高的检测概率和更少的捕获时间。通过本文的研究工作,为完成在特殊环境下GNSS信号捕获提出了基于DCFT块补零参数估计方法、基于变换域滤波的码捕获方法、联合均值函数和自相关函数信号捕获方法和利用相邻差分改善的压缩信号捕获方法,并通过理论推导和实验仿真说明了本文方法能有效地提高了无辅助条件下的GNSS信号捕获性能。本文的研究理论不仅为提升GNSS信号的检测性能提供了依据,而且可以结合辅助捕获手段为提高我国北斗导航精准定位提供理论依据。
[Abstract]:With the development of global navigation satellite system (Global Navigation Satellite System, GNSS) widely used in positioning technology, put forward higher requirements on the use of GNSS positioning signals under harsh environment. Such as the receiver in the room, city or location of a jungle Canyon, usually receiving signal in this environment is very weak, such as vehicle positioning positioning, satellite positioning and missiles. They received signals with dynamic signal and some are often weak, and power consumption of the receiver has certain requirements, in this case the auxiliary receiving technology. Among them, GNSS signal acquisition is an important step in the localization of GNSS, preliminary estimates using signal acquisition to complete signal the parameters, the high dynamic, in-depth research on acquisition of GNSS signal in weak signal environment. The GNSS signal was studied systematically for modeling. The received signal under different environment to analyze and put forward the corresponding solution, the main innovative work and research results are as follows: 1. in order to overcome the weak points in the high dynamic environment for the signal peak signal will be affected by bit symbol flipping and frequency error, this paper proposes a Fourier transform based on discrete Chirp transform (Discrete Chirp Fourier Transform, DCFT) block zero method. Compared with the traditional closed-loop receiver structure acquisition and tracking, this method is suitable for open-loop capture. In order to avoid accumulation as a semi coherent integration (Block Accumulating Semi-coherent Integration of Correlations, BASIC) method calculation block conjugate product to reduce the original signal to noise ratio, the method of combining DCFT and block zero thought, can make signal after coherent integration and at the same time in high dynamic parameters in peel bit symbol Accurate prediction. At the same time, analyzed the detection probability and false alarm probability of this method to detect the performance of the proposed method. Finally, the simulation results show that the BASIC method in this paper compared with the traditional method in lower SNR signal acquisition and accurate estimation of signal parameters in order to improve the.2. satellite signal in low SNR. Low frequency offset acquisition probability of the proposed two acquisition methods based on transform domain filtering. A method called based on fast Fourier transform (Fast Fourier Transform, FFT) to capture the filtering method. Because wavelet transform with the discrete cosine transform (Discrete Cosine Transform, DCT) or Fourier transform (Fourier Transform FT) can the freedom to choose the wavelet basis function, proposes an acquisition method of wavelet filtering based on the signal frequency division in the wavelet domain, and then choose the reconstruction of the letter In addition, filter noise greatly and retain the useful signal energy, to improve the detection probability. In addition the method given by the before and after filtering useful signal energy to calculate the energy ratio of wavelet function selection criterion. The simulation in CFAR under the condition of given Gauss channel and fading channel detection probability, shows that this method can greatly improve the.3. signal detection probability in order to solve the problem in the condition of capture by additive noise and compared with the general method, proposes a combined mean function and autocorrelation function of capture method, prove the cyclostationarity of the received signal, using the cyclostationarity of signals to capture the signal, by selecting the appropriate cyclic frequency peak signal detection parameter estimation. By using the method of signal energy than the decision threshold way or autocorrelation function to predict the received signal by the mean value function Frequency. To overcome the traditional method using only the mean function or defect of the autocorrelation function. The simulation experiments prove that this method is superior to the traditional methods in robustness.4. multiplicative noise is better in order to realize the fast acquisition of GNSS signal in high dynamic environment under high SNR, proposes a compressed sensing method of capture neighbor difference the accumulation based on the difference of neighbor accumulation after correlation signal, and then divided into two steps of accumulation after signal compression detection using Walsh Hadamard transform, deduces the probability of detection of the method. The nearest neighbor difference accumulation can reduce the bit reversal frequency error and the influence on the accumulation of the peak, the two step detection can be greatly compressed reduce the detection time, so this method can be achieved in high dynamic and fast acquisition of GNSS signals. Finally, simulation results show that the detection probability of the actual and theoretical derivation Consistency and in constant false alarm conditions compared with the control method has higher detection probability of capture time and less. Through this research, to complete in the special environment of GNSS signal acquisition is proposed DCFT block zero parameter estimation method based on transform domain filter code acquisition method based on joint function and mean the autocorrelation function of signal acquisition method and differential compression using adjacent signal acquisition method improved, and through theoretical analysis and experimental simulation shows that this method can effectively improve the performance of GNSS signal acquisition without auxiliary conditions. This paper studies the theory not only provides a basis for the detection performance of GNSS signals, and can be combined with auxiliary capture means to provide a theoretical basis for improving China's Beidou navigation and precise positioning.

【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN967.1

【参考文献】