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GPS接收机抗干扰技术研究
中文摘要

随着全球定位系统(GPS)使用范围的增加和使用环境的日益恶化,对卫星信号的可用性和完整性提出了更高的要求。在有环境干扰和人为阻塞的情况下,接收机的定位精度会下降,严重时载波环路和伪码跟踪环路无法锁定卫星信号。如何在存在干扰情况下提高接收机的性能成为近年来的研究热点。 本文以GPS接收机为对象,对数字接收通道中信号处理的抗干扰算法进行了研究。 比较有代表性的干扰类型为窄带干扰、线性调频干扰和部分频带噪声干扰三种。不同的技术对不同干扰的效果也是不同的。GPS接收机处理卫星信号是以扩频信号的相关操作为基础进行的。因此,使用相关裕量来衡量各种抗干扰算法的性能,能更本质地反映伪码相关函数的性质,计算上更为方便。 论文分析了GPS信号的频域谱线的统计分布特性,据以提出了一种迭代式频域自适应干扰消除算法。根据信号的统计值,动态调整频域处理门限,通过迭代渐次消除接收信号中的干扰成分。仿真表明频域处理的方法对窄带干扰十分有效。 小波变换具有良好的时频分析特性,能够更准确的定位和消除信号中的干扰成分。根据信号在小波域各个尺度上的性质计算信号噪声方差,利用通用阈值的方法在小波域上处理信号,从而达到抑制干扰的目的。研究结果表明,该方法对窄带干扰和时变的线性调频干扰有良好的效果,对带宽较小的部分频带噪声干扰也有一定的抑制效果。 最后,在空域处理方法中,改进了对角加载法,提出了一种针对小采样支持数据的稳健的自适应波束形成算法,这种算法根据协方差矩阵的估计误差来确定加载值,从而减小了因采样支持数不足而带来的阵列波束畸变。本文从线性约束最小方差准则出发建立空间滤波器的状态空间方程,将Kalman滤波算法纳入空间阵列实现。 论文研究对比了各种技术在不同干扰类型和强度下的性能,为设计高性能接收机提供了依据。 关键词:GPS抗干扰;频域变换;小波包变换;阵列天线;Kalman滤波

英文摘要

With the increasing adoption of the global position system and the degradation of the electromagnetic environment, higher and higher requirement to the and availability integrity of signals is demanded. The primary motivation of this dissertation is to study how to improve the performance of GPS receivers at the existence of various interferences. Due to the miscellaneity of interference, it is hard to counter them all by a single method. Therefore, various algorithms are studied in frequency domain, wavelet domain and space domain, respectively, to deal with different types of interferences. The dissertation starts from summarizing the type of interferences, which helps to makes the narrowband interferences, linear frequency modulated interferences and partial-band noise as the main object of the following research. The term covariance margin is then put forward as a criterion to performance evaluation of various anti-jamming algorithm. Compared to the BER or SNR of the anti-jammer system, covariance margin is more intuitional in formation and more convenient in calculation. The first interference canceling algorithm is considered based on signal processing in frequency-domain. After a review of the basic principle of frequent signal processing together with the frequency leakage effect, signal windowing and overlap processing method are introduced as the primary solutions of signal analyzing and reconstruction, respectively. Then we analyze the characteristics of stochastic distribution of the spectrum of GPS signals. This work leads to our FFT-based iterative adaptive interference canceling algorithm. By dynamically adjusting the threshold in frequency-domain according to the statistics of signal, the algorithm gradually eliminates the interferential part from the contaminated signal in an iterative manner. Simulation results show that this algorithm is very efficient to deal with the narrow-band interference. In view of the disadvantage of the FFT-based algorithm in coping with the broad-band interferences, the transform field needs to be enlarged. We adopt wavelet transform as a novel tool for our work. After a brief review of some preparatory theory including the destruction method by wavelet package, a wavelet package based algorithm is proposed. According to the variances in every scale of the wavelet domain, the noise energy can be precisely calculated. Then by using a universal threshold in wavelet domain, interferences can be restrained to a certain degree. Results show that this algorithm is efficient in countering both the narrow-band and time-variant linear modulated interferences. In space-domain data processing area, we firstly propose a robust adaptive beamforming algorithm based on the traditional diag loading, and achieve better performance after doing some important modifications. The proposed algorithm is specially suit for small shotnap data processing. By taking the estimation error of the covariance matrix of signal into account to determine the value, the distortion of array beam caused by the shortage of snapshot is diminished. Secondly, we derive a status space equation of the space filter by minimizing the variance of some linear constrains in space array processing. Hence the traditional time-domain Kalman filtering algorithm is introduced to the space domain. Simulation results show that our spatial Kalman filter is able to take significant effect to a variety of interferences. Keywords: GPS anti-jamming; FFT transform; wavelet transform; antenna array; Kalman filter

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