基于预报星历和基准站辅助的BDS实时精密单点定位

基于预报星历的常规实时精密单点定位存在相位模糊度难以收敛、定位精度低等问题.文中采用附加基准站改正信息的PPP算法,消除与卫星有关误差影响.依托香港卫星定位参考站网,采用WHU预报星历获取实时卫星轨道和钟差改正,开展基于预报星历和基准站辅助的中国北斗卫星导航系统实时PPP应用研究,并对其定位性能进行分析.试验结果表明,...     

低轨增强北斗PPP-RTK定位方法与实验分析

低轨星座具有卫星数目多、几何构型变化快等优势，有利于精密单点定位(PPP)中模糊度参数的快速收敛，从而提升其收敛速度与定位精度.但由于未能精确消除大气误差的影响，难以实现瞬时厘米级定位.提出一种低轨增强北斗PPP-实时动态(RTK)方法，结合高精度大气增强信息与模糊度固定方法(AR)，进一步改进北斗快速精密定位性能.首先设计了包含192颗低轨卫星的极轨星座，仿真了22个地面测站的观测数据，在估计相位小数偏差与精密大气延迟改正数后，分别测试了低轨增强北斗PPP、PPP-AR与PPP-RTK的定位性能.结果表明：在低轨星座增强下，可视卫星数目增加6～8颗，22个测站北斗PPP的平均初始化时间由552.1 s缩短至102 s,提升了81.52%.模糊度固定后，初始化时间进一步缩短至1 min以内.通过180 km地面参考网增强后，低轨增强北斗PPP-RTK可以实现瞬时厘米级定位，定位精度相较于PPP提升98.5%.将地面参考网扩大至500 km后，低轨增强北斗PPP-RTK仍可以实现约10 s的快速收敛.     

GNSS载波相位整数等变估计及其PPP性能提升算法

精密单点定位技术能够提供全球高精度定位结果,其主要技术瓶颈在于定位收敛时间长,载波相位模糊度固定技术是加快PPP收敛速度、改善定位精度的主要手段之一。模糊度固定的可靠性问题在PPP定位中尤为突出,因为模糊度浮点解质量取决于服务端产品质量、接收机噪声特性和观测环境等多种因素,所以高可靠PPP模糊度固定技术仍然充满巨大挑战。为了保障PPP定位的可靠性,本文将最优整数等变估计(best integer equivariant,BIE)引入PPP模糊度估计过程中。BIE法利用GNSS模糊度整数解加权融合以获得最优的浮点模糊度估计值,可有效降低模糊度错误固定风险,同时又利用了模糊度整数解信息来提升模糊度估值精度,从而提升PPP定位精度,缩短模糊度收敛时间。本文选取了105个全球分布的MGEX测站对BIE估计PPP模糊度的性能进行验证,试验结果表明,与模糊度固定解相比,采用BIE估计PPP模糊度能够进一步改善坐标三分量(东、北、垂向)定位性能,收敛时间分别减少了37%、28%与31%,收敛后定位精度分别提高了9%、8%和3%。此外,BIE估计PPP模糊度定位结果的毛刺和阶跃现象更少。     

GNSS RTK实时自适应换站方法

在中长基线的GNSS动态相对定位中,随着基线长度的增加,参考站与流动站之间误差的相关性会下降,导致模糊度无法快速固定,定位性能下降。在多GNSS参考站条件下,可以通过自适应选择距离更近的参考站,形成更加合理的基线,以保障RTK定位的精度。为解决换站后重新初始化模糊度所带来的定位结果重新收敛问题,本文提出了一种GNSS RTK实时自适应参考站换站算法,引入原参考站与新参考站之间的双差模糊度作为辅助,从而得到准确的新参考站与流动站之间的双差模糊度先验信息,避免了换站后模糊度的重新初始化,得到了连续的高精度定位结果。该方法可适用于实时定位,能够满足大范围RTK高精度连续定位的需求。利用香港CORS站数据进行验证,结果表明,本文换站算法能够克服换站导致的定位重收敛问题,且能够保障换站前后获得连续的高精度定位结果。     

整数相位钟法精密单点定位模糊度固定模型及效果分析

精密单点定位(PPP)模糊度固定方法有3种:星间单差法、整数相位钟法和钟差解耦法,但目前仅法国CNES公开发布用于整数相位钟法PPP模糊度固定的产品,因此研究基于整数相位钟法的用户端PPP模糊度固定模型很有必要.本文分析了整数相位钟法PPP模糊度固定模型,着重指出该模型与传统浮点解PPP模型的区别;提出一种顾及质量控制的逐级模糊度固定策略用于具体实施PPP模糊度固定.大量动态PPP解算试验表明:与浮点解PPP相比,固定解PPP具有更快的收敛速度且定位精度和稳定性更好.     

星间单差精密单点定位部分模糊度固定方法

针对传统的精密单点定位(PPP)技术由于收敛速度慢、获取高精度位置信息所需时间较长而无法满足用户对于快速高精度定位的需求的问题,该文采用了单差小数周偏差(FCB)产品固定模糊度的方法,以及部分模糊度固定的固定策略,来达到最优化使用固定解的PPP.通过对测站的数据的静态和仿动态实验分析验证,结果表明,进行部分模糊度固定的固定解定位精度要优于使用模糊度浮点解进行PPP得到的实数解的定位精度,收敛速度也有提升;而且相比于全模糊度固定策略,部分模糊度固定策略可以提升模糊度的历元固定率,使更多的固定模糊度的卫星可以参与定位,提升了定位的精度和收敛速度.     

多尺度区域增强PPP-RTK理论与应用

在PPP模糊度固定技术的应用中,使用未校准的相位延迟(UPD )产品进行 PPP模糊度固定可以显著缩短PPP收敛所需的时间并提高定位精度.如果用户位于一个稠密的参考站网中,利用参考站网生成的大气延迟改正数可以进一步缩短收敛时间,甚至实现瞬时的模糊度固定,该技术被称为区域增强 PPP.论文着眼于UPD产品估计、模糊度固定、改正数生成与使用、内插模型选取和改正数随机模型等几个主题研究区域增强PPP算法的相关问题.     

区域对流层约束的BDS-3 PPP性能分析

针对PPP定位解算过程中收敛时间较长的问题,提出一种附加区域对流层延迟模型值约束PPP的方法,利用电力北斗精准位置服务网湖南区域的16个基准站观测数据,构建区域对流层延迟模型,通过对流动站HNYZ和CZZX的PPP定位实验,分别从PPP定位精度、收敛时间、模糊度参数和观测模型几何强度等方面,对该算法的改进效果进行了对比分析。实验结果表明,该算法具有更好的PPP模型几何强度,可以显著地改善高程方向的定位性能,静态模式下,收敛时间分别提升18.23%和12.96%,定位精度分别提升8.79%和1.87%;动态模式下,收敛时间分别提升7.32%和6.78%,定位精度分别提升6.07%和20.53%。     

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。     

利用广播星历和区域参考网实现实时精密单点定位算法研究

提出并实现了一种基于广播星历和区域参考网的实时精密单点定位的新算法——NAPPP(network augmented precise point positioning)。采用可实时获取的广播星历,将用户站与附近的若干参考站一起联合处理,实时估计用户站位置参数以及导航卫星轨道和钟差改正数。实验结果表明,NAPPP算法静、动态实时定位精度分别为1～2cm和2～6cm,其定位精度和收敛速度明显优于基于IGS最终轨道和30s钟差的PPP定位结果,与基于CODE最终轨道和5s钟差的PPP定位结果相当。     

Regional reference network augmented precise point positioning for instantaneous ambiguity resolution

Integer ambiguity fixing can significantly shorten the initialization time and improve the accuracy of precise point positioning (PPP), but it still takes approximate 15 min of time to achieve reliable integer ambiguity solutions. In this contribution, we present a new strategy to augment PPP estimation with a regional reference network, so that instantaneous ambiguity fixing is achievable for users within the network coverage. In the proposed method, precise zero-differenced atmospheric delays are derived from the PPP fixed solution of the reference stations, which are disseminated to, and interpolated at user stations to correct for L1, L2 phase observations or their combinations. With the corrected observations, instantaneous ambiguity resolution can be carried out within the user PPP software, thus achieving the position solutions equivalent to the network real-time kinematic positioning (NRTK). The strategy is validated experimentally. The derived atmospheric delays and the interpolated corrections are investigated. The ambiguity fixing performance and the resulted position accuracy are assessed. The validation confirms that the new strategy can provide comparable service with NRTK. Therefore, with this new processing strategy, it is possible to integrate PPP and NRTK into a seamless positioning service, which can provide an accuracy of about 10 cm anywhere, and upgrade to a few centimeters within a regional network.     

基于部分整周模糊度固定的非差GPS精密单点定位方法

近年来,精密单点定位(PPP)模糊度固定技术不断发展,模糊度正确固定后可以提高短时间的定位精度。然而固定错误的模糊度,将引起严重的定位偏差,因此对PPP模糊度固定的成功率和可靠性进行研究很有必要。本文探讨了采用非差小数偏差(FCBs)改正的PPP模糊度固定方法;同时提出了一种分步质量控制的PPP部分模糊度固定(PAR)策略。通过欧洲CORS数据对该方法进行验证,结果表明:PPP模糊度固定可以提高小时解静态PPP定位精度。同时,采用部分模糊度固定策略,能够有效控制未收敛模糊度影响,提高用户端PPP模糊度固定成功率。     

Multifrequency algorithms for precise point positioning: MAP3

We present the new MAP3 algorithms to perform static precise point positioning (PPP) from multifrequency and multisystem GNSS observations. MAP3 represents a two-step strategy in which the least squares theory is applied twice to estimate smoothed pseudo-distances, initial phase ambiguities, and slant ionospheric delay first, and the absolute receiver position and its clock offset in a second adjustment. Unlike the classic PPP technique, in our new approach, the ionospheric-free linear combination is not used. The combination of signals from different satellite systems is accomplished by taking into account the receiver inter-system bias. MAP3 has been implemented in MATLAB and integrated within a complete PPP software developed on site and named PCube. We test the MAP3 performance numerically and contrast it with other external PPP programs. In general, MAP3 positioning accuracy with low-noise GPS dual-frequency observations is about 2.5 cm in 2-h observation periods, 1 cm in 10 h, and 7 mm after 1 day. This means an improvement in the accuracy in short observation periods of at least 7 mm with respect to the other PPP programs. The MAP3 convergence time is also analyzed and some results obtained from real triple-frequency GPS and GIOVE observations are presented.     

Three-frequency BDS precise point positioning ambiguity resolution based on raw observables

All BeiDou navigation satellite system (BDS) satellites are transmitting signals on three frequencies, which brings new opportunity and challenges for high-accuracy precise point positioning (PPP) with ambiguity resolution (AR). This paper proposes an effective uncalibrated phase delay (UPD) estimation and AR strategy which is based on a raw PPP model. First, triple-frequency raw PPP models are developed. The observation model and stochastic model are designed and extended to accommodate the third frequency. Then, the UPD is parameterized in raw frequency form while estimating with the high-precision and low-noise integer linear combination of float ambiguity which are derived by ambiguity decorrelation. Third, with UPD corrected, the LAMBDA method is used for resolving full or partial ambiguities which can be fixed. This method can be easily and flexibly extended for dual-, triple- or even more frequency. To verify the effectiveness and performance of triple-frequency PPP AR, tests with real BDS data from 90 stations lasting for 21 days were performed in static mode. Data were processed with three strategies: BDS triple-frequency ambiguity-float PPP, BDS triple-frequency PPP with dual-frequency (B1/B2) and three-frequency AR, respectively. Numerous experiment results showed that compared with the ambiguity-float solution, the performance in terms of convergence time and positioning biases can be significantly improved by AR. Among three groups of solutions, the triple-frequency PPP AR achieved the best performance. Compared with dual-frequency AR, additional the third frequency could apparently improve the position estimations during the initialization phase and under constraint environments when the dual-frequency PPP AR is limited by few satellite numbers.     

GLONASS phase bias estimation and its PPP ambiguity resolution using homogeneous receivers

Integer ambiguity resolution (IAR) appreciably improves the position accuracy and shortens the convergence time of precise point positioning (PPP). However, while many studies are limited to GPS, there is a need to investigate the performance of GLONASS PPP ambiguity resolution. Unfortunately, because of the frequency-division multiple-access strategy of GLONASS, GLONASS PPP IAR faces two obstacles. First, simultaneously observed satellites operate at different wavelengths. Second and most importantly, distinct inter-frequency bias (IFB) exists between different satellites. For the former, we adopt an undifferenced method for uncalibrated phase delay (UPD) estimation and proposed an undifferenced PPP IAR strategy. We select a set of homogeneous receivers with identical receiver IFB to perform UPD estimation and PPP IAR. The code and carrier phase IFBs can be absorbed by satellite wide-lane and narrow-lane UPDs, respectively, which is in turn consistent with PPP IAR using the same type of receivers. In order to verify the method, we used 50 stations to generate satellite UPDs and another 12 stations selected as users to perform PPP IAR. We found that the GLONASS satellite UPDs are stable in time and space and can be estimated with high accuracy and reliability. After applying UPD correction, 91 % of wide-lane ambiguities and 99 % of narrow-lane ambiguities are within (?0.15, +0.15) cycles of the nearest integer. After ambiguity resolution, the 2-hour static PPP accuracy improves from (0.66, 1.42, 1.55) cm to (0.38, 0.39, 1.39) cm for the north, east, and up components, respectively.     

基于GPS非差观测值进行精密单点定位研究

介绍了精密单点定位所用的数学模型及解算方案，着重分析了基于GPS非差双频观测值进行精密单点定位的误差模型、数据质量控制方法、卫星钟差的估算和内插、数据和解的一致性及精密单点定位能达到的精度等问题，并和双差结果作了比较。结果表明，利用精密星历及卫星钟改正参数的精密单点定位可达到cm级精度。     

The impact of errors in predicted GPS orbits on zenith troposphere delay estimation

The impact of precise GPS ephemeris errors on estimated zenith tropospheric delays (ZTD) is studied for applications in meteorology. First, the status of IGS ultra-rapid orbit prediction is presented and specific problems are outlined. Second, a simplified analytical solution of the impact of ephemeris errors on estimated ZTDs is presented. Two widely used methods are studied—the precise point positioning technique (PPP) and the double-difference network approach. A simulation experiment is additionally conducted for the network approach to assess the capability of ephemeris error compensation by the ambiguities. An example of marginal requirements for ephemeris accuracy is presented, assuming the compensation by ZTD only and admitting the error of 1 cm in ZTD. The requirement for the maximum orbit error 1 cm for radial and 8 cm for tangential position components using PPP approach, versus 217 cm (radial) and 19 cm (tangential) using network solution. Furthermore, an assessment of possible compensations of ephemeris errors by other estimated parameters was considered. In radial orbit position, an error of a few meters can be still absorbed by satellite clocks (96%) and phase ambiguities (96%) even for the PPP technique. A tangential orbit position error up to 16 cm for PPP and 38 cm for network solutions should not bias ZTD by more than 1 cm, but any bigger error could, in general. The error impact on ZTD in such cases depends on the compensation ability of ambiguities and clocks (PPP).     

Rapid initialization of real-time PPP by resolving undifferenced GPS and GLONASS ambiguities simultaneously

Rapid initialization of real-time precise point positioning (PPP) has constantly been a difficult problem. Recent efforts through multi-GNSS and multi-frequency data, though beneficial indeed, have not proved sufficiently effective in reducing the initialization periods to far less than 10 min. Though this goal can be easily reached by introducing ionosphere corrections as accurate as a few centimeters, a dense reference network is required which is impractical for wi de-area applications. Leveraging the latest development of GLONASS PPP ambiguity resolution (PPP-AR) technique, we propose a composite strategy, where simultaneous GPS and GLONASS dual-frequency PPP-AR is carried out, and herein, the reliability of partial AR improves dramatically. We used 14 days of data from a German network and divided them into hourly data to test this strategy. We found that the initialization periods were shortened drastically from over 25 min when only GPS data were processed to about 6 min when GPS and GLONASS PPP-AR were accomplished simultaneously. More encouragingly, over 50% of real-time PPP solutions could be initialized successfully within 5 min through our strategy, in contrast to only 4% when only GPS data were used. We expect that our strategy can provide a promising route to overcoming the difficulty of achieving PPP initializations within a few minutes.     

北斗/GPS实时精密卫星钟差融合解算模型及精度分析

实时GNSS精密单点定位(PPP)技术必须使用实时的高精度卫星精密轨道和钟差。本文研究了精密卫星钟差融合解算模型及策略,并利用滤波算法实现了北斗/GPS实时精密卫星钟差融合估计算法。仿真实时试验结果显示:获得的北斗/GPS实时钟差与GFZ事后多GNSS精密钟差(GBM)的标准差在0.15 ns左右;使用该钟差进行GPS动态PPP试验,收敛后水平精度优于5 cm,高程精度优于10 cm;使用仿真实时钟差进行的北斗动态PPP与使用GFZ事后多GNSS精密钟差开展的试验相比精度相当,可实现分米级定位。