新体制卫星导航信号特性与跟踪环路设计

从新体制卫星信号的特性出发,论述新体制卫星导航信号跟踪环路的一种实现方式,即三环双估计器跟踪环路的设计方法,并以一个仿真系统为例给出各项参数推导的详细过程,最终的仿真结果证明所述方法合理可行。     

高精度导航计算机实现技术研究

惯性导航系统是一种自主式导航系统,其核心部件是导航计算机。介绍了导航计算机实现的技术原理;分析了导航计算机实现的关键技术,包括高精度浮点处理技术、导航传感器功能集成技术、高精度导航技术、智能接口技术和集成化的软件开发调试环境;针对惯性导航系统对精度和实时性的要求,提出了一种高精度导航计算机的设计方案,其实现技术先进,具有广泛的应用前景。     

Correlation of GPS signal fades due to ionospheric scintillation for aviation applications

Deep and frequent Global Positioning System (GPS) signal fading due to strong ionospheric scintillation is a major concern for GPS-guided aviation in equatorial areas during high solar activity. A GPS aviation receiver may lose carrier tracking lock under deep fading, and a lost channel cannot be used for position calculation until lock is reestablished. Hence, frequent loss of lock due to frequent fading can significantly reduce the availability of GPS aviation. However, the geometric diversity of the satellites can mitigate scintillation impact on GPS aviation depending on the correlation level of deep fades between satellites. This paper proposes a metric to measure the correlation level of two fading channels from the perspective of GPS aviation. Using this metric, the satellite-to-satellite correlation is studied based on real scintillation data. The low satellite-to-satellite correlation shown in this paper envisions notable availability benefit from the geometric diversity of satellites under strong scintillation. In addition, this paper proposes a way to generate correlated fading processes with arbitrary correlation coefficients. Using this correlated fading process model, the availability of Localizer Performance with Vertical guidance (LPV)-200 under severe scintillation scenarios is analyzed. The result emphasizes the importance of a fast reacquisition capability of an aviation receiver after a brief outage, which is not currently mandated by the aviation receiver performance standards.     

Ionospheric path delay models for spaceborne GPS receivers flying in formation with large baselines

GPS relative navigation filters could benefit notably from an accurate modeling of the ionospheric delays, especially over large baselines (>100 km) where double difference delays can be higher than several carrier wavelengths. This paper analyzes the capability of ionospheric path delay models proposed for spaceborne GPS receivers in predicting both zero-difference and double difference ionospheric delays. We specifically refer to relatively simple ionospheric models, which are suitable for real-time filtering schemes. Specifically, two ionospheric delay models are evaluated, one assuming an isotropic electron density and the other considering the effect on the electron density of the Sun aspect angle. The prediction capability of these models is investigated by comparing predicted ionospheric delays with measured ones on real flight data from the Gravity Recovery and Climate Experiment mission, in which two satellites fly separated of more than 200 km. Results demonstrate that both models exhibit a correlation in the excess of 80% between predicted and measured double-difference ionospheric delays. Despite its higher simplicity, the isotropic model performs better than the model including the Sun effect, being able to predict double differenced delays with accuracy smaller than the carrier wavelength in most cases. The model is thus fit for supporting integer ambiguity fixing in real-time filters for relative navigation over large baselines. Concerning zero-difference ionospheric delays, results demonstrate that delays predicted by the isotropic model are highly correlated (around 90%) with those estimated using GPS measurements. However, the difference between predicted and measured delays has a root mean square error in the excess of 30 cm. Thus, the zero-difference ionospheric delays model is not likely to be an alternative to methods exploiting carrier-phase observables for cancelling out the ionosphere contribution in single-frequency absolute navigation filters.     

How Navigational Aids Impair Spatial Memory: Evidence for Divided Attention

Abstract

Research has demonstrated navigational aids impair spatial memory, but has not considered important spatial cognitive concepts. For example, impairment may stem from spatial perspective switches between route-based aids and survey-based memory assessments. Further, the verbal format of aid instructions may selectively interfere with verbal working memory (VWM). To address these potential explanations, participants navigated desktop virtual environments in a goal-directed manner. In each within-participants condition, participants either navigated with a verbal or tonal aid that presented mixed spatial perspective instructions or without aid. Both aids yielded slight navigational advantages and steep spatial memory costs despite their mixed perspective instructions. The equivalent impairment between information formats suggests navigational aids impair spatial memory by dividing attention rather than selective interference of VWM.     

基于多模PPP-AR技术的大气水汽探测性能分析

精密单点定位（precise point positioning，PPP）反演大气可降水量（precipitable water vapor，PWV）具有精度高、实时性强等优点，能够在灾害监测、降雨预报及探测降水信息等方面发挥重要作用。为评估整周模糊度固定模式下PPP-AR（PPP ambiguity resolution）反演PWV的性能，选取全球范围16个MGEX站2022年4个时段的观测数据，采用最终精密星历解算，设置不同星座组合（GPS,BDS-3,GPS+BDS-3,GPS+GLO+GAL+BDS-3）获取对流层延迟（zenith total delay，ZTD）估值，并转换为PWV。从PPP-ZTD与IGS-ZTD的相关性、PPP-ZTD收敛时间、ZTD估值精度和PPP-PWV估值精度4个方面评价多模PPP-AR探测水汽的性能。结果表明，与单（G、C）、双系统（GC）固定解相比，多系统（GREC）固定解获取ZTD估值更加精确，相关系数更高。相较于单、双系统，多系统具有更快的收敛速度，收敛时间分别缩短了27%,25%和20%，多系统固定解与浮点解相比收敛时间缩短11%。此外，对GNSS PPP反演的PWV与探空站PWV（RS-PWV）进行对比，结果表明，WUH2站与HOB2站单、双、多系统固定解、多系统浮点解（float-GREC）的平均均方根误差分别为6.40 mm,6.48 mm,6.19 mm,6.17 mm,6.19 mm和5.82 mm,5.77 mm,5.72 mm,5.62 mm,5.70 mm。多模下得到的PWV估值精度最高，可为高精度的水汽反演提供支持。     

Qualitative Spatial Reasoning for Topological Map Learning

Abstract

In this paper we investigate the application of qualitative spatial reasoning methods for learning the topological map of an unknown environment. We develop a topological mapping framework that achieves robustness against ambiguity in the available information by tracking all possible graph hypotheses simultaneously. We then exploit spatial reasoning to reduce the space of possible hypotheses. The considered constraints are qualitative direction information and the assumption that the map is planar. We investigate the effects of absolute and relative direction information using two different spatial calculi and combine the approach with a real mapping system based on Voronoi graphs.     

捷联姿态解算宏汇编软件

编制捷联姿态解算软件是捷联惯性姿态参考系统研制中的重要一环。由于对计算的实时性和精度都有较高的要求，又在专用的弹上计算机上进行，所以增加了制作的难度。从变量取值范围、比例因子确定、字长选择、程序结构等几方面介绍了捷联姿态解算软件的编制情况。该软件是在导弹计算机上用ＴＭＳ３２０Ｃ２５宏汇编语言编制的。该软件经过地面实物试验，验证了其正确性。     

陀螺RRW在惯导系统中的误差传播特性

角速率随机游走是高精度光纤陀螺的一项主要随机误差源,对惯性导航系统的误差有着较大影响。分析了角速率随机游走的统计特性,推导了角速率随机游走引起的惯性导航系统姿态、位置误差的解析表达式,研究了静基座环境下的惯性导航系统在长时间导航环境下的随机误差传播规律,对角速率随机游走作用下的惯性导航系统误差进行了仿真与实验,验证了所推导公式的正确性,对惯性导航系统的设计与误差分析具有一定的参考意义。     

基于交互式多模型的飞机编队相对导航算法研究

在飞机编队飞行时,成员间的相对位置信息是实现系统协同作战的重要保证,为了提高机群编队飞行的相对导航定位精度,在无地面基准的机群编队飞行JTIDS/GPS/TACAN/IFDL组合的相对导航系统中,采用交互式多模型扩展卡尔曼滤波(IMM-EKF)算法,设计实现了多传感器相对导航系统,克服了飞机动态模型参数变化导致使用单一动态模型滤波精度下降的问题。仿真分析结果表明,交互式多模型算法可以提高相对导航系统的定位精度和可靠性,特别在GPS可见卫星很少的情况下,依然能够具有良好的定位性能。