利用时间差分载波相位的GNSS/INS紧组合导航

载波相位观测值精度远高于伪距,利用时间差分载波相位的组合导航可避免整周模糊度解算问题。本文以简化的时间差分载波观测模型为基础,分析其误差特性,说明了短期内时间差分载波观测更新的特点。时间差分载波在距离域本质上是相对观测值,存在误差积累,提出了利用伪距在另一个更长的组合周期上进行系统的观测更新方法。重点推导了双周期组合情况下时间差分载波观测值的实用随机模型确定公式,并结合多普勒观测值进一步保证姿态修正的精度。将采用时间差分载波的组合方案与传统伪距组合方案进行比较。结果表明,时间差分载波精度组合系统高,在观测随机模型可靠的情况下优于传统的伪距紧组合导航,误差最大的高程方向精度提高可达47%。     

BDS载波相位历元间差分测速方法研究

针对载波相位历元间差分测速前后历元选取不同广播星历计算时,卫星钟差跳变导致测速结果错误突变的问题,提出前后历元仍采用相同的广播星历来计算卫星位置和钟差的改进方法。用北斗实测数据验证了方法的正确性,并评估了北斗测速的精度。实验结果表明:静态条件下,北斗载波相位历元间差分测速精度可达mm/s级;动态条件下,采样率1Hz,测速结果与高精度组合导航测速结果符合精度为cm/s级;并且测速精度与物体的动态条件(如加速度)有一定的相关性。     

基于 EEMD 和 Husrt 指数的 GNSS 基准站的垂向速率估计

连续的全球卫星导航系统(GNSS)基准站的坐标时间序列中包含了复杂的噪声信号、非构造形变及其它因素的影响,尤其在垂直方向,对GNSS基准站在国际地球参考框架(ITRF)下的运动速率估计产生了较大的干扰。为进一步提高速率精度,文中采用整体模态分解(EEMD)方法对GNSS基准站的垂向观测时间序列进行分解,并根据各种信号的Hurst值进行分类及重构为噪声信号、季节性信号和长期趋势信号,采用最小二乘方法拟合长期趋势信号得到垂向速率。通过对中国大陆构造环境监测网络(CMONOC)的GNSS台站从2001—2013年近13a的垂向坐标时间序列的实例分析,采用基于EEMD和Husrt指数的最小二乘法能够准确地估计GNSS基准站的垂向速率。     

Higher order ionospheric effects in precise GNSS positioning

With the increasing number of precise navigation and positioning applications using Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS), higher order ionospheric effects and their correction become more and more important. Whereas the first-order error can be completely eliminated by a linear combination of dual- frequency measurements, the second- and third-order residual effects remain uncorrected in this approach. To quantify the second-order residual effect, a simple formula has been derived for GNSS users in Germany. Our proposed correction algorithm reduces the second-order effects to a residual error of fractions of 1 mm up to 2 mm at a vertical total electron content level of 10¹⁸ electrons/m² (100 TECU), depending on satellite azimuth and elevation angles. The correction formula can be implemented in real-time applications as it does not require the knowledge of the geomagnetic field or the electron density distribution in the ionosphere along the signal path. It is expected that the correction will enable more accurate positioning using the line-of-sight carrier-phase measurements.     

Analyzing GNSS data in precise point positioning software

This work demonstrates that precise point positioning (PPP) can be used not only for positioning, but for a variety of other tasks, such as signal analysis. The fact that the observation model used for accurate error modeling has to take into consideration the several effects present in GPS signals, and that observations are undifferenced, makes PPP a powerful data analysis tool sensitive to a variety of parameters. The PPP application developed at the University of New Brunswick, which is called GAPS (GPS Analysis and Positioning Software), has been designed and built in order to take advantage of available precise products, resulting in a data analysis tool for determining parameters in addition to position, receiver clock error, and neutral atmosphere delay. These other estimated parameters include ionospheric delays, code biases, satellite clock errors, and code multipath among others. In all cases, the procedures were developed in order to be suitable for real-time as well as post-processing applications. One of the main accomplishments in the development described here is the use of very precise satellite products, coupled with a very complete observation error modeling to make possible a variety of analyses based on GPS data. In this paper, several procedures are described, their innovative aspects are pointed out, and their results are analyzed and compared with other sources. The procedures and software are readily adaptable for using data from other global navigation satellite systems.     

不同精密星历对震时高频GNSS解算结果精度分析

进行震时高频全球卫星导航系统（GNSS）数据解算时,不同的精密星历对GNSS解算结果会有不同的影响．本文针对IGS数据中心提供的最终精密星历(IGF)和快速精密星历(IGR)在震时高频GNSS数据解算结果中的精度进行分析,从理论上探讨不同星历对震时高频GNSS数据精度的影响,选取2010年Baja地震的高频GNSS数据采用GAMIT／TARACK单历元动态定位方法进行解算分析,结果表明,两种星历对震时高频GNSS数据结果相差不大, 在E、N方向上差值最大不超过2.2 cm,在U方向上差值最大不超过4 cm,且两种星历E、N、U方向均方根偏差小于2,解算震时高频GNSS数据时不同精密星历对解算结果精度影响差别在厘米级,当进行震时高频GNSS数据处理工作时,可使用不同精密星历进行替代解算．      

GNSS测站速度估计模型重建

获取准确的GNSS测站速度对于研究全球板块运动、地壳形变、地震活动及其地球动力学过程至关重要。为此,以GNSS基线解算后的基线向量作为观测值,重建了最小二乘综合速度解算模型和卡尔曼滤波速度估计模型。模型中,考虑了测站坐标、运动速度、年、半年周期项一同作为参数,在基线解网平差的同时,一并求解获取速度估值。同时,利用坐标时序分析的方法,顾及白噪声和幂律噪声的影响,对单日解坐标时间序列重建了时序速度拟合估计模型,以获取长期趋势项作为速度值。基于3种模型,对川滇地区中国地壳运动观测网络2010—2014年21个GPS基准站的观测数据进行了速度估计与对比分析。结果表明:3种模型所估计测站速度非常接近,差异基本处于0~1mm/a范围之内;速度估值中误差均在亚毫米水平。由此得出,3种速度估计模型具有本质的一致性,均可正确估计测站运动速度,能够满足高精度地壳形变研究的需要。     

GNSS多频融合精密单点定位频率间卫星钟偏差研究

全球导航卫星系统(GNSS)提供多频信号,多频融合已经成为一种趋势。在精密钟差估计(PCE)的过程中,卫星钟差参数会吸收卫星端稳定的伪距偏差和时变的相位偏差,这些偏差均与频率相关。因而使用不同的观测值进行PCE时,得到的卫星钟差估值是不同的,它们之间的差值被定义为频率间卫星钟偏差(IFCB)。按组成成分,IFCB可以分成伪距相关的IFCB(CIFCB)和相位相关的IFCB(PIFCB)两部分。国际GNSS服务(IGS)提供的精密卫星钟差产品是基于双频消电离层(IF)组合观测值生成的。由于IFCB的存在,导致IGS卫星钟差产品不能直接应用于多频精密单点定位(PPP)。IFCB的精确考虑已经成为多频PPP的一个关键问题。本研究旨在对IFCB特性和估计方法开展系统深入的研究,并评估其对多频PPP解的影响。     

一种改进的加权整体最小二乘GNSS船姿估计方法

为提高GNSS船姿测量精度,该文构建了基于先验模糊度信息的乘性欧拉角GNSS载波观测方程,提出了一种基于部分变量误差模型(Partial-EIV)的加权整体最小二乘(WTLS)动态船姿估计方法。首先利用GNSS动对动加以基线长约束快速精确固定模糊度,然后将整周模糊度固定解作为已知值代入乘性姿态角载波观测误差方程,并将观测方程进行向量化;针对状态方程以及观测方程系数矩阵包含随机元素和固定元素的结构特征,引入Partial-EIV模型,采用一种改进目标函数的WTLS方法估计乘性欧拉角,该方法可以同时顾及状态方程以及观测方程误差,充分利用观测值以及姿态约束信息,减小误差累积。通过实测GNSS三天线匀速测姿算例对本文方法进行验证,结果表明,该文方法优于动态参考站差分(MBD)基线姿态直接解法,对于复杂海洋环境船姿测量具有一定的参考价值。     

Zero-correlation transformation and threshold for efficient GNSS carrier phase ambiguity resolution

The key point of accurate and precise applications of Global Navigation Satellite Systems lies in knowing how to efficiently obtain correct integer ambiguity. One of the methods in solving the ambiguity resolution problem is applying the ambiguity searching technique coupled with an ambiguity decorrelation technique. Traditionally, an integer-valued limitation of the transformation matrix ensures that the integer characteristic of candidates exists after the inverse transformation, but this also makes the decorrelation imperfect. In this research, the float transformation matrix will be considered. To ensure both the integer characteristic and perfect decorrelation can be reached, the float transformation is used indirectly. To solve the ambiguity resolution problem, the problem is transformed by integer and float transformation matrices. The objective of integer transformation is reducing the number of candidates. The target of float transformation is validating these reduced candidates. A zero correlation domain or a near complete diagonalization covariance matrix can be obtained via the float transformation. A space in this domain will be used as the threshold; hence the zero correlation domain is called the threshold domain. The number of ambiguity candidates based on integer transformation can be reduced once again through the proposed method. The experiments in this paper prove that the method can make the ambiguity resolution become more efficient without any drop in the accuracy.     

Generalized integer aperture estimation for partial GNSS ambiguity fixing

In satellite navigation, the key to high precision is to make use of the carrier-phase measurements. The periodicity of the carrier-phase, however, leads to integer ambiguities. Often, resolving the full set of ambiguities cannot be accomplished for a given reliability constraint. In that case, it can be useful to resolve a subset of ambiguities. The selection of the subset should be based not only on the stochastic system model but also on the actual measurements from the tracking loops. This paper presents a solution to the problem of joint subset selection and ambiguity resolution. The proposed method can be interpreted as a generalized version of the class of integer aperture estimators. Two specific realizations of this new class of estimators are presented, based on different acceptance tests. Their computation requires only a single tree search, and can be efficiently implemented, e.g., in the framework of the well-known LAMBDA method. Numerical simulations with double difference measurements based on Galileo E1 signals are used to evaluate the performance of the introduced estimation schemes under a given reliability constraint. The results show a clear gain of partial fixing in terms of the probability of correct ambiguity resolution, leading to improved baseline estimates.     

一种卫星导航抗干扰处理器低功耗设计方法

提出一种适用于全球卫星导航系统(GNSS)智能天线的低功耗抗干扰处理器设计方法. 通过改进GNSS抗干扰架构中混频器的设计,优化掉数字高中频混频器和滤波器. 为进一步降低功耗和硬件资源占用,引入输出双倍速率寄存器(ODDR)技术,实现高中频信号的直接合成. 实验测试结果表明,本设计功耗降低11％,硬件资源减少14％,可应用到GNSS智能天线系统中.      

GNSS/SINS/视觉多传感器融合的精密定位定姿方法与关键技术EI北大核心CSCD

全球导航卫星系统作为国家重要的空间信息基础设施,具备全球、全天候、高精度连续定位、导航和授时的功能,然而,到达地面的GNSS卫星信号非常微弱,存在遮挡、干扰和欺骗三大脆弱性问题,无法在电磁干扰、物理遮蔽等复杂环境下使用,为了保障国家PNT系统的坚韧性,提升导航与位置服务的能力,我国开始推进以北斗为核心的国家综合PNT体系建设,其中多传感器集成、多源异质信息融合是未来PNT技术的重要发展方向,也是从根本上解决单一导航系统局限性和脆弱性的有效途径,为了实现连续可用,精准可靠的PNT服务体系,迫切需要解决多传感器融合的精密定位定姿关键技术。论文主要工作如下。     

基于GNSS精密单点定位的高精度云平台授时

采用GNSS精密单点定位(PPP)技术和时钟驯服技术,构建了基于PPP的云平台高精度授时方案,研制了搭载多系统GNSS接收机板卡、恒温晶振(OCXO)和数字信号处理器(DSP)的授时原理样机。利用协同精密定位平台分析中心(武汉)提供的5 s间隔卫星轨道和钟差产品,采用PPP技术实时解算授时终端坐标和钟差,通过驯服恒温晶振输出亚纳秒精度的1 PPS,实现了长时间高精度的授时能力。本文通过短基线比较和与UTC绝对时间基准比较,验证了精密单点授时精度(RMS)优于1 ns。     

大型桥梁桥塔监测的GNSS相对对流层延迟估计

针对大型桥梁桥塔与基站高程差异较大,残余对流层延迟成为影响全球卫星导航系统(GNSS)监测成功率与精度的主要因素之一。该文基于随机过程理论,对桥梁监测GNSS残余对流层湿延迟进行参数估计,有效地提高了桥梁塔顶监测GNSS模糊度固定率。通过采用对流层经验模型改正对流层干延迟,将基准站和塔顶观测站对流层湿延迟组成相对对流层湿延迟,并联合位置参数和模糊度参数建立双差卡尔曼模型,最后利用最小二乘模糊度降低相关平差法(LAMBDA)对双差模糊度进行固定,并估计位置参数与相对对流层延迟参数。实验结果表明,该方法可以有效估计相对对流层延迟,有效提高GNSS模糊度固定率。     

Optimum stochastic modeling for GNSS tropospheric delay estimation in real-time

GPS Solutions - In GNSS data processing, the station height, receiver clock and tropospheric delay (ZTD) are highly correlated to each other. Although the zenith hydrostatic delay of the...     

On the probability distribution of GNSS carrier phase observations

When processing observational data from global navigation satellite systems (GNSS), the carrier phase measurements are generally assumed to follow a normal distribution. Although full knowledge of the probability distribution of the observables is not required for parameter estimation, for example when using the least-squares method, the distributional properties of GNSS observations play a key role in quality control procedures, such as outlier and cycle-slip detection, in ambiguity resolution, as well as in the reliability assessment of estimation results. In addition, when applying GNSS positioning under critical observation conditions with respect to multipath and atmospheric effects, the validity of the normal distribution assumption of GNSS observables certainly comes into doubt. This paper illustrates the discrepancies between the normal distribution assumption and reality, based on a large and representative data set of GPS phase measurements covering a range of factors, including multipath impact, baseline length, and atmospheric conditions. The statistical inferences are made using the first through fourth sample moments, hypothesis tests, and graphical tools such as histograms and quantile–quantile plots. The results show clearly that multipath effects, in particular the near-field component, produce the dominant influence on the distributional characteristics of GNSS observables. Additionally, using surface meteorological data, considerable correlations between distributional deviations from normality on the one hand and atmospheric relative humidity on the other are detected.     

Positioning Precision Analysis of GNSS Multi-frequency Carrier Phase Combinations

GPS positioning precision is affected by various error sources, and traditional combinations of GPS carrier phase observations have their own limitations such as the wide-lane, the narrow-lane and the ...     

Positioning precision analysis of GNSS multi-frequency carrier phase combinations

GPS positioning precision is affected by various error sources, and traditional combinations of GPS carrier phase observations have their own limitations such as the wide-lane, the narrow-lane and the ionospheric-free combinations. To obtain the optimal positioning precision, a new linear combination method is addressed through the variance-covariance (VCV) of the GPS multi-frequency carrier phase combination equations, and the impact of the positioning precision is analyzed with the changing of the observation errors deduced by the law of error propagation. For the high precision positioning with only one carrier phase combination, the optimal combination method is deduced and further validated by an example of a baseline resolution with 60 km length. The result indicates that this method is the simplest, and the positioning precision is the best. Therefore, it is useful for long baseline quick positioning for different precision requirements in various distances.