导航信息对抗技术研究

卫星导航手段的成功应用深刻地影响着现代信息化条件下的作战模式,针对卫星导航的信息对抗对未来战争影响巨大。研究了GNSS框架下导航信息对抗方案和需要解决的关键技术问题,并利用卫星导航信号模拟器、GNSS接收机、组合导航设备等进行了相关技术试验,得到了有意义的结论,为导航战提供了参考。      

地面伪卫星测试环境中关于精度因子的仿真研究

诸如接收机、信号模拟器之类的卫星导航产品在投入正式运行之前需要在地面上对其进行测试和校准,因此需要在地面建立模拟天上GPS卫星星座的测试环境,并通过修建伪卫星发射塔来发射类GPS卫星信号。通过对地面伪卫星测试环境中精度因子进行仿真研究,进而指导伪卫星发射塔的选址修建,兼顾建造成本的考虑,给出相应的最优化的配置方案。最后通过实例分析和验证,得出相应的结论。     

GPS接收机工作原理及发展现状

根据GPS接收机的工作原理,分为连续接收机、序贯接收机和多元接收机。讨论了接收机的应用分类,分别为高精度测量型接收机,导航接收机及授时型接收机。根据GPS卫星信号的情况,介绍了GPS接收机的性能指标。根据GNSS的发展现状和卫星信号的实施论述了新一代多模双频接收机指标,根据测试结果证明：这种接收机将是未来GPS接收机的发展方向。     

基于卡尔曼滤波算法的卫星导航高精度定位方法

为保证卫星导航的定位精准性,降低定位误差,提出基于卡尔曼滤波算法的卫星导航高精度定位方法。该方法采用支持向量机分类卫星导航信号,获取信号中不含伪距的直达信号,依据该信号获取终端接收机的三维空间坐标;将该坐标和接收机的时钟偏差以及频率漂移作为核心,采用改进的卡尔曼滤波算法获取终端接收机的位置坐标,即卫星导航的定位结果;并采用粒子群算法优化卡尔曼滤波算法获取的定位结果,以此提升卫星导航定位精准性。测试结果显示：该方法具有较好的应用性能,在X、Y、Z三个方向上的定位误差结果均在5 m以内;高程定位误差均在3.5 m以内,可精准完成导航载体所在位置的定位,掌握导航载体的运动轨迹。     

集成电离层闪烁仿真的数字中频GPS信号模拟器设计验证

电离层闪烁造成GPS接收机测距误差增大、以致强闪烁条件下的频繁周跳和卫星信号失锁,集成闪烁仿真功能的GPS信号模拟器能够为接收机抗闪烁算法研究和性能测试提供必要的信号源。首先设计了基于AJ-Stanford模型和Cornell模型的电离层闪烁仿真软件,可以灵活配置闪烁时间、数据更新周期以及各模型参数,从而得到闪烁影响下的GPS信号幅度衰落及相位波动序列;然后开发了集成电离层闪烁仿真功能的数字中频GPS信号模拟器,该模拟器作为抗闪烁研究平台工具,可以灵活调整闪烁卫星号、模型及相关参数、开始时间和持续时间;其设计正确性通过实验室自研的软件GPS接收机得到了验证。     

卫星导航信号高精度模拟产生与控制技术

卫星导航信号模拟器是卫星导航用户机检测和开展系统应用研究的关键设备.这里主要研究了信号模拟中的高精度时廷控制和多普勒处理技术,设计并提出了采用高精度数字时廷滤波器实现码相位时延精确控制的方案.通过多普勒调制和数字基带合成技术实现对卫星导航信号多普勒频移的模拟.仿真结果表明,该方法模拟仿真精度高,合理可行.     

卫星信号发射时刻的无偏恢复

卫星信号发射时刻在导航定位中是一个重要的参数,但是在城市峡谷等弱信号条件下,接收机可能完成不了所有卫星信号发射时刻的组装。在伪距定位中卫星信号发射时刻的组装和粗时段导航中卫星信号发射时刻的恢复(有偏)技术基础上,提出一种无偏的卫星信号发射时刻恢复方法,前提是卫星至少能完成一颗星的伪距测量,并且具有150km误差范围内的先验位置和辅助星历。利用BDS B1和GPS L1中频数据在软件接收机平台进行了BDS,GPS信号发射时刻无偏恢复验证实验证明了方法的有效性。     

基于GPS软件接收机的SINS／GPS紧组合系统仿真

为了系统验证SINS／GPS紧组合系统的性能,基于GPS软件接收机,进行了仿真系统构建。仿真系统由轨迹发生器、GPS中频信号模拟器、IMU信号模拟器、GPS软件接收机、SINS导航解算模块、组合滤波算法和导航性能分析模块等部分构成,其中详细设计了GPS软件接收机中的捕获和跟踪算法、SINS解算以及基于伪距和伪距率的组合滤波算法。仿真结果表明：紧组合导航系统收敛性较好,能够一定程度上抑制惯导系统误差的积累,有较好的导航性能。设计的该系统满足紧组合导航系统性能验证的需要,也为后续的超紧组合研究奠定了良好的基础。     

一种SINS/GPS深组合导航系统技术问题分析

为了满足高动态用户及强干扰条件下的应用需求,提出了一种基于卫星信号矢量跟踪的SINS/GPS深组合导航方法,设计了基于FPGA硬件平台的实施方案。利用组合卡尔曼滤波器反馈回路取代了传统接收机中独立、并行的跟踪环路,能够同时完成所有可视卫星信号的跟踪和导航信息处理;通过矢量跟踪算法对所有可视卫星信号进行集中处理,能够增强跟踪通道对信号载噪比变化的适应能力,从而提高接收机在强干扰或信号中断条件下的跟踪性能;根据SINS导航参数和星历信息推测GPS伪码相位和多普勒频移等参数,用以辅助卫星信号的捕获和跟踪,能够大大缩短接收机的搜索捕获时间,并增强接收机在高动态条件下的跟踪性能。基于矢量跟踪的深组合方法不仅在GPS信号短暂中断期间,能够保证系统的导航精度和可靠性,而且在强干扰环境中能够维持较好的伪码相位和载波频率跟踪性能。     

电磁干扰对卫星定位ZJCORS台站的影响分析

电磁干扰对ZJCORS站接收机运行影响很大。讨论了导航卫星信号到地强度,站点电磁干扰及测试分析方法,并指出了接收机性能改进的途径。     

A study on the dependency of GNSS pseudorange biases on correlator spacing

We provide a comprehensive overview of pseudorange biases and their dependency on receiver front-end bandwidth and correlator design. Differences in the chip shape distortions among GNSS satellites are the cause of individual pseudorange biases. The different biases must be corrected for in a number of applications, such as positioning with mixed signals or PPP with ambiguity resolution. Current state-of-the-art is to split the pseudorange bias into a receiver- and a satellite-dependent part. As soon as different receivers with different front-end bandwidths or correlator designs are involved, the satellite biases differ between the receivers and this separation is no longer practicable. A test with a special receiver firmware, which allows tracking a satellite with a range of different correlator spacings, has been conducted with live signals as well as a signal simulator. In addition, the variability of satellite biases is assessed through zero-baseline tests with different GNSS receivers using live satellite signals. The receivers are operated with different settings for multipath mitigation, and the changes in the satellite-dependent biases depending on the receivers’ configuration are observed.     

基于多接收机模糊度关联的动态PPP快速重新收敛方法

针对由于遮挡等原因造成卫星信号中断后精密单点定位（precise point positioning,PPP）需要重新收敛的问题,提出了一种基于多接收机模糊度关联的动态PPP快速重新收敛方法。以远海地区精密定位为背景,充分利用了远海地区实践应用中经常在测量船的不同位置上架设多台接收机的基本特点,建立不同接收机的模糊度之间的关系,获取发生数据中断的接收机的先验模糊度,进而完成动态PPP的快速重新收敛。实验结果表明,附加基线长度约束的两个接收机单历元固定双差模糊度的成功率在99%以上;在单历元固定双差模糊度的情况下,无论数据中断多长时间,所提算法都可以单历元完成动态PPP的重新收敛,并且收敛后的定位精度同数据中断前的定位精度相同。     

Performance comparison of semicodeless GPS receivers for LEO satellites

This report provides a detailed performance analysis of three semicodeless dual-frequency GPS receivers for use in low Earth orbit (LEO). The test set comprises the IGOR receiver, which represents a follow-on of the flight-proven BlackJack receiver, as well as two geodetic receivers (NovAtel OEM4-G2 and Septentrio PolaRx2), which are entirely based on commercial-off-the-shelf technology (COTS). All three receivers are considered for upcoming flight projects or experiments and have undergone at least a preliminary environmental qualification program. Using extensive signal simulator tests, the cold start signal acquisition, tracking sensitivity, differential code biases, raw measurement accuracy, and navigation accuracy of each receiver have been assessed. All tests are based on a common scenario that is representative of an actual space mission and provides a realistic simulation of the signal dynamics and quality on a scientific LEO satellite. Compared to the other receivers, the IGOR instrument exhibits a superior tracking sensitivity and is thus best suited for occultation measurements with low tangent point altitudes. The OEM4-G2 and PolaRx2 receivers are likewise shown to properly track dual-frequency GPS signals and normal signal levels and to provide accurate code and carrier phase measurements. Given their limited resource requirements, these receivers appear well suited for precise orbit determination applications and ionospheric sounding onboard of microsatellites with tight mission budgets.     

北斗导航信号源发展现状分析

北斗导航信号源是检测北斗用户机性能的重要测试设备,它通过仿真卫星星座、卫星星钟、电离层等环境效应、用户轨迹等来模拟再现北斗导航卫星信号。分析了国内外导航信号源的发展现状以及信号源的功能特点,指出未来导航信号源的发展趋势。     

卫星导航欺骗干扰信号检测技术综述

卫星导航欺骗干扰信号检测是卫星导航接收机实施欺骗干扰抑制、防止产生错误定位和测速、定时信息的必要步骤.在介绍了导航战背景下卫星导航欺骗干扰技术的基础上,分析比较了当前主要卫星导航欺骗干扰信号检测技术的实现难度、效果和场景适应性,指出了现阶段卫星导航接收机端最具研究价值的欺骗干扰信号检测技术.最后对欺骗干扰检测技术研究的趋势和发展方向进行了总结展望.      

Using the Global Positioning System (GPS) for geodetic positioning

The development of relatively inexpensive satellite receivers in the early 1970's has resulted in cost-effective applications of satellites for a variety of geodetic surveying needs. Currently achievable accuracies range from 10 to 20 centimeters. The NAVSTAR Global Positioning System, now under development by the Department of Defense, incorporates advanced technology which has the potential capability of revolutionizing satellite geodesy. Several concepts for utilizing GPS signals are briefly reviewed, and another concept, called the reconstructed carrier phase method, is described in some detail. This concept is being pursued by the Defense Mapping Agency, National Oceanic and Atmospheric Administration, and the U.S. Geological Survey. These agencies have numerous requirements for accurate positioning. Several prototype receivers are planned to be available for testing in mid-1982. These receivers should be highly portable, consume little power, and obtain base line accuracies of several centimeters in several hours of observation time. However, water vapor radiometers will be needed in order to achieve the full accuracy. Initial simulation results utilizing the reconstructed carrier phase method are included.     

GPS软件接收机跟踪通道信号统计分析

传统的基于硬件的接收机由于芯片的封装性很难用来进行通道信号的分析研究,而基于软件无线电技术的软件接收机则很容易做到。软件接收机的跟踪通道信号统计分析可用于接收机算法的测试与比对以及卫星信号性能的分析与评估。这里搭建了GPS软件接收机L1中频数字信号处理平台,对跟踪通道输出的I、Q支路信号进行了均值、标准方差以及均方根(RMS)统计。分析了各统计值与通道对应卫星的高度角、信号强度以及噪声之间的关系。基于统计结果提出了一种估计信道信噪比的方法。最后比较了不同信号采样频率对相关三角形和导航定位解算精度的影响。     

北斗B1C、B2a信号非理想性分析及接收约束建议

卫星导航信号的非理想性会导致不同接收机之间出现测距偏差,是影响卫星导航系统服务精度和完好性的重要因素。首先,针对北斗系统B1C、B2a新体制信号的非理想性进行分析,利用大口径天线采集了全部北斗三号在轨卫星播发的B1C、B2a信号（共27颗卫星）,评估了不同接收带宽、码鉴相间距下测距偏差的大小与变化特点;然后,以双频多星座星基增强服务应用为例,分析了两个信号在相应接收机中的设计约束条件。研究结果发现,在接收机常用的参数范围内,B1C、B2a信号非理想性引入的测距偏差分别不超过0.68 m、0.44 m;在测距偏差小于0.1 m的性能约束下,B1C、B2a信号可用的约束条件参数范围优于国际民航标准草案中的相关要求。     

Investigation on the effect of strong out-of-band signals on global navigation satellite systems receivers

The mitigation of radio frequency interference (RFI) has a fundamental role in global navigation satellite system (GNSS) applications, especially when a high level of availability is required. Several electromagnetic sources, in fact, might degrade the performance of the global positioning system (GPS) and Galileo receivers, and their effects can be either in-band (i.e., secondary harmonics generated by transmitters of other communication systems due to non-linearity distortions) or out-of-band (i.e., strong signals that occupy frequency bandwidths very close to GNSS bands). We investigated the effects of real out-of-band signals on GNSS receivers and analyzed the impact on the overall receiver chain in order to evaluate the impact of the interference source. In particular, the analysis focuses on the spectrum at the front-end output, on the automatic gain control (AGC) behavior, as well as on the digital processing stages (signal acquisition and tracking) at the analog digital converter (ADC) output. This study refers to several experiments and data collections performed in interfered areas of downtown Torino (Italy). The obtained results underline how digital/analog TV transmissions represent a potential interference source for GNSS applications and might be critical for the safety of life services.     

A new evil waveforms evaluating method for new BDS navigation signals

With the advent of new global navigation satellite systems (GNSSs) and new signals, GNSS users will rely more on them to obtain higher-accuracy positioning. Evil waveform monitoring and assessment are of great importance for GNSS to achieve its positioning, velocity, and timing service with high accuracy. However, the advent of new navigation signals introduces the necessity to extend the traditional analyzing techniques already accepted for binary phase-shift keying modulation to new techniques. First, the well-known second-order step thread model adopted by the International Civil Aviation Organization is introduced. Then the extended new general thread models are developed for the new binary offset carrier modulated signals. However, no research has been done on navigation signal waveform symmetry yet. Simulation results showed that, waveform asymmetry may also cause tracking errors, range biases, and position errors in GNSS receivers. It is thus imperative that the asymmetry be quantified to enable the design of appropriate error budgets and mitigation strategies for various application fields. A novel evil waveform analysis method, called waveform rising and falling edge symmetry (WRaFES) method, is proposed. Based on this WRaFES method, the correlation metrics are provided to detect asymmetric correlation peaks distorted by received signal asymmetry. Then the statistical properties of the proposed methods are analyzed, and a proper deformation detection threshold is calculated. Finally, both simulation results and experimentally measured results of Beidou navigation satellite system (BDS) M1-S B1Cd signal are given, which show the effectiveness and robustness of the proposed thread models.