Stochastic modelling considering ionospheric scintillation effects on GNSS relative and point positioning

Global Navigation Satellite Systems (GNSS), in particular the Global Positioning System (GPS), have been widely used for high accuracy geodetic positioning. The Least Squares functional models related to the GNSS observables have been more extensively studied than the corresponding stochastic models, given that the development of the latter is significantly more complex. As a result, a simplified stochastic model is often used in GNSS positioning, which assumes that all the GNSS observables are statistically independent and of the same quality, i.e. a similar variance is assigned indiscriminately to all of the measurements. However, the definition of the stochastic model may be approached from a more detailed perspective, considering specific effects affecting each observable individually, as for example the effects of ionospheric scintillation. These effects relate to phase and amplitude fluctuations in the satellites signals that occur due to diffraction on electron density irregularities in the ionosphere and are particularly relevant at equatorial and high latitude regions, especially during periods of high solar activity. As a consequence, degraded measurement quality and poorer positioning accuracy may result.     

一种GPS定位信息可用性的实时判定方法

基于GPS接收机输出数据,采用3级AR模型来预测下一时刻的GPS输出值,并与实际的输出值相比较,以一定的检测门限,判断当前时刻定位信息的可用性。通过仿真证明该方法的有效性,为GPS的可用性判定提供了一种方法。     

基于北斗接收机的车载卫星导航系统的设计

基于北斗卫星导航系统、北斗地基增强系统、移动通信网络,设计开发了 一款小体积、高精度车载导航系统。主要在接收基站差分信息以及实现高精度定位方面 进行探索。通过单点定位和差分定位的野外跑车对比试验得出,该系统性能稳定、可靠 性高,其差分定位精度能够满足车辆导航的要求。     

基于火箭橇的北斗动态定位精度鉴定方法

介绍了几种现有的以GPS/北斗为主要代表的卫星导航系统的动态定位精度 鉴定方法,分析了这几种方法在模拟实际使用环境、鉴定精度等方面的优缺点,提出了 一种基于火箭橇试验平台的北斗导航定位系统动态定位精度鉴定方法。该方法能够很好 地模拟北斗导航定位系统实际工作环境（速度、加速度、振动和天线角度等）,解决高 动态、高精度北斗导航定位系统动态定位精度鉴定问题,并对该方法的原理和实施方法 作了详细的论述,最后分析了该方法的不确定度及误差,并提出了改进措施。     

角度棱镜方位对干涉仪测角范围的影响

在激光测角干涉仪中,由于角度棱镜安置的方位不同,将导致该仪器角度测量范围的变化。分析了角度棱镜的方向和位置对角度测量范围的影响,比较了不同方案的优劣,并给出了结论。     

基于GPS/IMU/太阳敏感器的空间飞行器组合姿态确定

GPS定姿是GPS在空间飞行器上应用的一个重要方向 ,本文在建立GPS 惯性组件 太阳敏感器组合定姿系统的非线性模型的基础上 ,采用扩展卡尔曼滤波实现了该组合定姿方案。通过理论分析和仿真结果均验证了方案的可行性。为GPS定姿在空间飞行器的实际应用提供一定的参考。     

45°(N)纬度带的Klobuchar like电离层延迟季节修正模型与评估

电离层延迟是全球卫星导航系统（GNSS）的主要误差源之一。对于装配GNSS单频接收机的航空器,选择简单有效的Klobuchar广播电离层模型来改正电离层延迟误差,其修正率为50%～60%。针对45°（N）纬度带,提出了更高电离层修正需求。考虑到季节因素对中高纬度地区电离层的显著影响,利用GIMs（Global Ionospheric Maps）分析了昼夜中TEC（Total Electron Content）的峰值和谷值随季节（年积日）的变化,建立了一种适用于45°（N）纬度带的Klobuchar like电离层模型。该模型不增加广播模型系数,新模型的夜间和VTEC高峰时电离层修正率分别达到了82%和80%,表明在穿刺点集中的45°(N)纬度地区使用该模型可以更精确地描述该地区的电离层,帮助航空器实现更高精度的定位。     

Real-time clock comparison and monitoring with multi-GNSS precise point positioning: GPS,GLONASS and Galileo

The precise point positioning (PPP) technique is widely used in time and frequency applications. Because of the real-time service (RTS) project of the International GNSS Service, we can use the PPP technique for real-time clock comparison and monitoring. As a participant in the RTS, the Centre National d’Etudes Spatiales (CNES) implements the PPPWIZARD (Precise Point Positioning with Integer and Zero-difference Ambiguity Resolution Demonstrator) project to validate carrier phase ambiguity resolution. Unlike the Integer-PPP (IPPP) of the CNES, fixing ambiguities in the post-processing mode, the PPPWIZARD operates in the real-time mode, which is also called real-time IPPP (RT-IPPP). This paper focuses on applying the RT-IPPP for real-time clock comparison and monitoring. We review the principle of real-time clock comparison and monitoring, and introduce the methodology of the RT-IPPP technique. The observations of GPS, GLONASS and Galileo were processed for the experiments. Five processing modes were provided in the experiment to analyze the benefits of ambiguity resolution and multi-GNSS. In the clock comparison experiment, the average reduction ratios of standard deviations with respect to the G PPP mode range from 9.7% to 35.0%. In the clock monitoring experiment, G PPP mode can detect clock jumps whose magnitudes are larger than 0.9 ns. The RT-IPPP technique with GRE PPP AR (G) mode allows for the detection of any clock jumps larger than 0.6 ns. For frequency monitoring, G PPP mode allows detection of frequency changes larger than 1.1 × 10⁻¹⁴. When the RT-IPPP technique is applied, monitoring with GRE PPP AR (G) mode can detect frequency changes larger than 6.1 × 10⁻¹⁵.     

Carrier phase prediction method for GNSS precise positioning in challenging environment

Since the signals of global navigation satellite system (GNSS) are blocked frequently in challenging environments, the discontinuous carrier phases seriously affect the application of GNSS precise positioning. To improve the carrier phase continuity, this paper proposes a carrier phase prediction method based on carrier open-loop tracking. In the open-loop tracking mode, the carrier numerically controlled oscillator (NCO) is controlled by the predicted Doppler, but not by the loop filter output. To improve the phase prediction effective time, accurate receiver clock drift estimation is studied in the prediction method. The phase prediction performance is tested on GNSS software receiver. In the phase prediction effective time tests, open-loop processes were set for the tested channel. The test results show that, when some satellite signals are blocked in 15?s, the probability of carrier phase error less than quarter cycles is more than 94%. In the real time kinematic (RTK) positioning tests, some satellite signals are blocked in 10–15?s repeatedly. The test results show that, the carrier phase continuity is basically not affected by the signal interruption, and the RTK can almost keep continuous centimeter-level positioning accuracy without re-fixing the integer ambiguity.     

通信导航融合定位技术发展综述

详细分析了蓝牙、Wi-Fi、超宽带、移动通信网络等多种无线网络通信导航融合定位技术的发展现状,并阐述了其面临的挑战,提出了多网融合方法可以提升室内无缝高精度位置服务的可靠性。利用5G移动通信网络,与北斗/GNSS卫星导航系统结合,可以实现相互增强。最后,从天地一体定位导航与授时体系和仿生通信定位导航两方面介绍了通信导航融合定位技术的未来发展趋势。