一种GPS信号转发欺骗干扰检测技术

针对 GPS 信号的码相关特性,本文提出一种基于 FFT 的卫星信号转发欺骗干扰检测方法,该方法可以一次性同时输出多个码相位对应的相关值。利用转发信号延迟于真实信号的特点,超过检测门限的滞后相关峰对应信号即为欺骗信号。经仿真验证,上述方法可以有效识别转发延迟不小于 1.5 个码片的欺骗干扰信号。     

基于NELDER-MEAD的GNSS欺骗干扰参数估计方法

欺骗干扰对关键领域的导航服务带来了重大挑战,因此有必要发展欺骗干扰监测系统,欺骗信号参数估计是欺骗干扰监测的重要组成部分。当欺骗信号的码相位与真实信号重叠时,无法采用多通道技术对真实信号和欺骗信号分别进行跟踪估计。本文通过分析小时延场景下的信号参数空间,引入导航信号相关峰形状、宽度等先验信息,提出了一种基于NELDER-MEAD的欺骗信号参数估计方法,利用NELDER-MEAD算法直接搜索信号的码相位,在此基础上采用最小二乘法对功率和载波相位进行估计,能够在减小计算量的同时准确估计出欺骗信号与真实信号的参数。仿真结果表明,本文方法的相关域搜索次数比传统MLE方法降低了90%以上。最后通过无线测试,验证了该方法在实际场景中的有效性。      

利用信号重构的全球导航卫星系统欺骗干扰抑制方法

欺骗式干扰通过发射与真实卫星信号相似的信号误导接收机产生错误的定位结果，具有极大的危害。该文针对转发式欺骗干扰，提出一种基于信号重构的单天线欺骗干扰抑制方法。该方法首先通过参数估计方法估计出欺骗信号载波频率和码相位，然后构建欺骗信号子空间正交投影矩阵以抑制干扰。仿真实验结果表明该方法对欺骗干扰具有良好的抑制效果，能够保障接收机在干扰环境中实现有效定位，并具有较低的运算复杂度。     

GPS接收机Z跟踪技术抗干扰性能分析

Z跟踪技术是民用GPS接收机为消除或减弱AS（Anti—Spoofing）政策影响,实施精密测距和高精度导航定位的一种有效方法。通过分析Z跟踪技术载波相位测量的基本原理,研究了GPS接收机Z跟踪技术的抗压制干扰、抗欺骗干扰性能。结果表明：采用Z跟踪技术的GPS接收机与C／A码接收机的抗压制干扰基本相同;其在信号捕获状态下的抗欺骗干扰能力取决于欺骗干扰信号与GPS信号的相关程度,而在信号跟踪状态下抗欺骗干扰能力则等同于抗伪随机噪声码干扰能力。     

直序扩频系统中扩频码同步技术的研究

针对扩频通信中伪随机序列的快速捕获问题,文中提出了扩频信号快速捕获方法,来解决低信噪比条件下伪码序列的捕获问题.首先对直接扩频通信系统的基础理论做了探讨,而后重点研究了两种基带扩频信号同步捕获方案--序列相位搜索捕获法和不连续相位滑动相关法,序列相位搜索捕获法主要适用于m序列码周期较短的情况,而不连续滑动相关法则克服了...     

多载频MIMO-SAR对消处理抗欺骗干扰

 根据多发多收合成孔径雷达(MIMO-SAR)的特点,提出在重叠等效相位中心(EPC)处采用对消处理抑制欺骗干扰的方法.MIMO-SAR采用收发同置天线配置可形成多组位置相同的等效相位中心;发射多载频线性调频(LFM)信号将使每组位置重叠等效相位中心处的回波相位有所差异.利用此特点,可以在子回波相位补偿后采用对消处理对欺骗干扰进行抑制.文中给出了收发同置MIMO-SAR的系统模型,分析了欺骗干扰下的回波特点,指出在位置重叠等效相位中心处的欺骗干扰信号对间仅存在相位差异,给出了对消处理完成欺骗干扰抑制的信号流程,实验结果证明了本文方法的有效性.     

直序扩频信号PN码相位的自适应测量算法

提出了基于FFT的直序扩频信号PN码相位的自适应测量算法.算法首先利用FFT确定信号的可测性及可有效检测到目标信号的最低采样频率,并计算最低采样频率下信号的PN码相位,然后逐级提高采样频率,用循环卷积法求取各级采样频率下的PN码相位,直至达到测量精度要求.与其他基于FFT的方法相比,该算法可在同等测量精度要求下明显减少计算量,或在计算量相当情况下有效提高测量精度.该算法的主要应用领域为卫星定位信号和直序扩频测距信号PN码相位的精确测量.     

基于分段相关-视频积累方法的伪码串行捕获优化设计

本文主要针对载波多普勒下的伪码捕获问题,研究了基于分段相关-视频积累方法的伪码串行捕获系统的优化设计.通常的优化设计为假设峰值点的伪码相位偏差为0.但对于实际的捕获系统,由于接收到的伪码相位与本地伪码相位关系随机,在串行搜索过程中过门限值的伪码相位残差可能不为0,从而对捕获性能产生影响.本文主要分析伪码相位偏移残差对峰值点的信噪比和检测概率的影响,并给出了最大伪码相位偏移残差下的平均捕获时间表达式.同时基于平均捕获时间最小准则,给出了搜索步进推荐值.对虚警概率指定和未指定两种情况分别进行了优化设计,得到了最优的中频积累和视频积累设计值,该设计值与载噪比、多普勒容限等因素相关.研究成果可用于指导扩频接收机伪码捕获模块的设计.     

多激光制导目标时激光角度欺骗干扰问题研究

针对多机编队空对地激光制导精确打击时激光角度欺骗干扰问题,对多目标时指示激光信号的方位和编码特征进行了理论研究。结果表明:当指示激光信号时间差小于任一信号的重复周期且信号的重复周期为整数倍关系,或者指示激光信号时间差大于激光欺骗干扰设备解码时间时,激光欺骗干扰设备可以对组合信号进行解码,并分析了相应干扰方法。上述两种情况之外则会组合为伪随机序列码信号,激光欺骗干扰设备不能正确解码及实施干扰。     

基于GNSS-R的车辆探测定位实验研究

针对目前导航卫星应用领域中一个新的热点研究内容,利用GNSS卫星反射信号作为无源雷达进行目标探测和定位,基于GNSS-R技术进行车辆探测定位实验研究,并给出反射信号相对于直射信号的延迟时间求解方法。实验对接收到的直射信号进行处理,提取直射信号信息作为先验条件,进行反射信号的细捕获,缩小反射信号捕获的搜索范围,采用基于FFT的并行码相位捕获算法将码相位延迟时间精确到1/16码片。将实验数据与理论值进行对比分析,验证了该方法的正确性。     

利用周期重复CLEAN的GNSS欺骗式干扰抑制算法

欺骗式干扰能够引导接收机出现定位错误甚至是控制接收机,对全球卫星导航系统在民用以及军事领域的安全应用构成极大的威胁。本文针对转发式欺骗干扰的问题,提出了一种基于周期重复CLEAN的卫星导航欺骗式干扰抑制算法。首先,利用欺骗式干扰空间和功率特征以及C/A码的周期重复特性,采用CLEAN方法估计多个欺骗式干扰源来向以及欺骗式干扰源个数。其次,结合线性约束最小方差（LCMV）算法和一阶微分约束算法,计算天线自适应权值。高保真数据实验表明本文方法能抑制多个欺骗干扰,且无需接收机反馈信息,可以作为一个独立的抗欺骗式干扰模块嵌入普通接收机。      

Improving GPS Receivers Positioning in Weak Signal Environments Based on Fuzzy SSMF-FFT and Fuzzy Kalman Filter

With the advent of global positioning system (GPS) and the increasing expansion of technology, improving GPS receivers positioning has attracted great attention. When the signal received by these receivers is weak, receiver functioning becomes impaired. Due to the existing noise and the presence of Doppler shift in weak signal conditions, the signal acquisition section becomes problematic and in weak signal conditions or phase lock loop (PLL), the tracking section design of noise conditions gets difficult. In case of a lock loss on the signal, the user will not be able to calculate the Doppler frequency and the system will diverge. Therefore, a robust algorithm for the GPS receiver PLL is very vital. In this paper, the squared segmented matched filter-fast Fourier transform algorithm is used to improve the acquisition of weak GPS signals with an average SNR of 15 dB. By using the matched filter, the SNR is maximized and the code phase estimation will be more accurately. Also, the use of a segmented filter before the FFT reduces the number of FFT points and therefore, the computational complexity is reduced. To calculate the number of batches and obtain the best acquisition output, in the proposed algorithm, the system becomes fuzzy. In tracking section, fractional Fourier transform (FRFT) with the PLL based on fuzzy Kalman filter (FKF) is used to reinforce it against weak signal environments. The FRFT is used for estimating frequency and acceleration, and a third-order FKF is used for designing the PLL. As a result of these changes, the RMSE of positioning is improved more than 35%.

     

Performance Analysis of GPS Receivers in Non-Gaussian Noise Incorporating Precorrelation Filter and Sampling Rate

Global positioning system (GPS) receivers find growing applications in indoor and outdoor communication environments, including urban and rural areas. Interference and noise sources for GPS receivers may assume Gaussian or non-Gaussian distributions. The GPS receiver performance under Gaussian additive noise has been studied. Non-Gaussian noise may equally contaminate the GPS satellite signals and disturb the receiver delay lock loops (DLL), producing significant tracking errors. These sources include impulsive noise, ultra-wideband (UWB) signals, and impulse and noise radar signals for target tracking and indoor imaging applications. This paper considers non-Gaussian noise of finite variance and examines its effect on the discriminator outputs for the commercial GPS receiver that uses the coarse acquisition (C/A) code. The correlator noise output components are produced from the correlation between the noise sequence and the early, late, and punctual reference C/A code. Due to the long time averaging, which is characteristic of the GPS correlation loops, these components assume Gaussian distributions. The discriminator tracking error variance is derived, incorporating the effect of noise, the front-end precorrelation filter, and the sampling rate.     

转发欺骗干扰对卫星导航接收机载波环的影响研究

本文研究了转发欺骗干扰对卫星导航接收机载波跟踪环的影响。推导出在存在转发欺骗条件下卫星导航接收机载波跟踪环输出的相位误差公式，分析了不同强度的转发欺骗干扰对卫星导航接收机跟踪环路的作用，得出了使卫星导航接收机跟踪环路失锁转发欺骗干扰所需的最小功率强度。通过试验验证了本文分析结论的正确性。     

GPS接收机的迭代处理技术研究

导航接收机系统作为一种卫星导航系统的终端接收,在军事和民用方面都得到重大应用。高精确定位性能是导航接收机应用追求的目标。针对导航接收机工作环境各种复杂干扰,及为进一步提高导航接收机系统的抗干扰性能,提出了一种迭代处理技术的应用方案,并对方案可行性进行分析研究。通过应用迭代处理,在接收混合信号中消除了干扰信号影响,使得捕获跟踪精度提高以此提高GPS接收机的性能。理论分析和仿真结果表明,在GPS接收机中引入迭代处理技术能很好的提高系统抗干扰能力,干扰抑制效果更好。     

GNSS CODE AND CARRIER TRACKING IN THE PRESENCE OF MULTIPATH

It is well known that multipath represents a major error source in differential GNSS positioning. Errors produced are unique to each antenna position and so are uncorrelated between the reference station and the mobile receiver. Reduction techniques, such as narrow correlator spacing¹ and the multipath estimating delay lock loop (MEDLL)² have improved the situation. However, reflected signals emanating close to the antenna are not reduced by either technique. Carrier multipath is a particular problem because short delay multipath signals cause maximum carrier errors. This study describes the analysis that has been carried out into code and carrier tracking in the presence of multipath. Code tracking in this situation produces a non-zero mean error,³ and the source of this bias has been investigated. Code and carrier multipath errors of the global orbiting navigation satellite system (GLONASS) have been compared with those of the global positioning system (GPS). The effects of pre-correlation filtering on code and carrier multipath errors have been determined using data from a measured correlation function. The multipath fading bandwidth is also discussed, and fast and slow fading effects are presented. A comparison has been made of the performance of typical coherent and non-coherent code discriminators in the presence of multipath. The performance of the GPS and GLONASS P code signals have been determined with respect to code and carrier multipath errors. © 1997 by John Wiley & Sons, Ltd.     

基于FPGA的GPS接收机实现

利用可编程片上系统(SOPC)技术,设计了一种基于FPGA的GPS接收机。提出了基于多普勒频域移位的捕获策略,并分析了捕获时间。基于延迟锁定环与Costas环跟踪方法,给出接收机的SOPC实现。实验结果表明,该接收机的信号捕获、跟踪方法正确可行,且在静态条件下水平定位精度优于4.5m(标准差),具有良好的实时性、灵活性和可扩展性。     

一种利用C/A码GPS接收机实现电离层延时双频改正的方法

电离层传播延迟是C/A码GPS导航定位的主要误差源之一。本文提出了一种利用C/A码GPS接收机实现电离层延迟实时双频改正的方法,并对实现这一方法的电路框图的原理进行了分析,从理论上说明了其可行性。     

一种改进的窄带GPS接收机的抗多径干扰技术

GPS(Global Positioning System)在全球范围内得到了越来越广泛的应用,车载和手持市场的普及使GPS接收机的应用环境变得很复杂.多径干扰成为GPS定位精度的误差主要来源.窄带GPS接收机有着良好的抗干扰能力,但是其抗多径性能却不太理想.传统的窄带抗多径技术收敛时间过长,不能满足工程应用.本文提出了一种改进的窄带GPS接收机的抗多径干扰技术,大大提高了收敛速度,并且在抗多径性能上又略有改善.     

A method for dual-frequency ionospheric time-delay correcting using a C/A code GPS receiver

The ionospheric time delay is one of the main error sources in C/A code GPS navigation and positioning applications. In this paper, a method is proposed for real-time dual-frequency ionospheric time-delay correcting using a C/A code GPS receiver, and the principle of the circuit block diagram for this method is analyzed with its feasibility theoretically demonstrated.