The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) - Achievements, prospects and challenges

Precise point positioning with quad-constellations: GPS, BeiDou, GLONASS and Galileo

A joint-processing model for multi-GNSS (GPS, GLONASS, BDS and GALILEO) precise point positioning (PPP) is proposed, in which raw code and phase observations are used. In the proposed model, inter-system biases (ISBs) and GLONASS code inter-frequency biases (IFBs) are carefully considered, among which GLONASS code IFBs are modeled as a linear function of frequency numbers. To get the full rank function model, the unknowns are re-parameterized and the estimable slant ionospheric delays and ISBs/IFBs are derived and estimated simultaneously. One month of data in April, 2015 from 32 stations of the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) tracking network have been used to validate the proposed model. Preliminary results show that RMS values of the positioning errors (with respect to external double-difference solutions) for static/kinematic solutions (four systems) are 6.2 mm/2.1 cm (north), 6.0 mm/2.2 cm (east) and 9.3 mm/4.9 cm (up). One-day stabilities of the estimated ISBs described by STD values are 0.36 and 0.38 ns, for GLONASS and BDS, respectively. Significant ISB jumps are identified between adjacent days for all stations, which are caused by the different satellite clock datums in different days and for different systems. Unlike ISBs, the estimated GLONASS code IFBs are quite stable for all stations, with an average STD of 0.04 ns over a month. Single-difference experiment of short baseline shows that PPP ionospheric delays are more precise than traditional leveling ionospheric delays.

Multi-GNSS precise point positioning (MGPPP) using raw observations

At present, the BeiDou system (BDS) enables the practical application of triple-frequency observable in the Asia-Pacific region, of many possible benefits from the additional signal; this study focuses on exploiting the contribution of zero difference (ZD) ambiguity resolution (AR) to the precise point positioning (PPP). A general modeling strategy for multi-frequency PPP AR is presented, in which, the least squares ambiguity decorrelation adjustment (LAMBDA) method is employed in ambiguity fixing based on the full variance-covariance ambiguity matrix generated from the raw data processing model. Because of the reliable fixing of BDS L1 ambiguity faces more difficulty, the LAMBDA method with partial ambiguity fixing is proposed to enable the independent and instantaneous resolution of extra wide-lane (EWL) and wide-lane (WL). This mechanism of sequential ambiguity fixing is demonstrated for resolving ZD satellite phase bias and performing triple-frequency PPP AR with two reference station networks with a typical baseline of up to 400  and 800 km, respectively. Tests show that about $$90\,\%$$
 of the EWL and WL phase bias of BDS has a consistency of better than 0.1 cycle, and this value decreases to $$<$$
 80 % for L1 phase bias for Experiment I, while all the solutions of Experiment II have a similar RMS of about 0.12 cycles. In addition, the repeatability of the daily mean phase bias agree to 0.093 cycles and 0.095 cycles for EWL and WL on average, which is much smaller than 0.20 cycles of L1. To assess the improvement of fixed PPP brought by applying the third frequency signal as well as the above phase bias, various ambiguity fixing strategy are considered in the numerical demonstration. It is shown that the impact of the additional signal is almost negligible when only float solution involved. It is also shown that by fixing EWL and WL together, as opposed to the single ambiguity fixing, will leads to an improvement in PPP accuracy by about $$20.6\,\%$$
 on average. Attributed to the efficient resolution of EWL 
 $$+$$
  WL within about 2 min in Experiment I, the 0.5 m level positioning can be achieved in 10 min for both horizontal and vertical, compared to 50 min for horizontal and 30 min for vertical by the NONE/EWL/WL fixed solution. While, for Experiment II, the improvement in the convergence can only be seen for the horizontal as the TTFF takes about 40 min for EWL and WL to be resolved.

BeiDou phase bias estimation and its application in precise point positioning with triple-frequency observable

A review of the research conducted until present on the subject of Global Navigation Satellite System (GNSS) hardware-induced phase and code biases is here provided. Biases in GNSS positioning occu ...

/pdf/review-of-code-and-phase-biases-in-multi-gnss-positioning-3sp4kaa5qr.pdf

Review of code and phase biases in multi-GNSS positioning

State of the art Precise Point Positioning (PPP) is currently based on dual-frequency processing of GPS and Glonass navigation systems. The International GNSS Service (IGS) is routinely providing the most accurate or- bit and clock products for these constellations, allowing pointpositioningatcentimeter-levelaccuracy.Atthesame time, the GNSS landscape is evolving rapidly, with the deployment of new constellations, such as Galileo and BeiDou. The BeiDou constellation currently consists of 14 operational satellites, and the 4 Galileo In-Orbit Vali- dation (IOV) satellites are transmitting initial Galileo sig- nals. This paper focuses on the integration of Galileo and BeiDou in PPP, together with GPS and Glonass. Satellite orbits and clocks for all constellations are generated us- ing a network adjustment with observation data collected by the IGS Multi-GNSS Experiment (MGEX), as well as from Fugro proprietary reference station network. The or- bit processing strategy is described, and orbit accuracy for Galileo and BeiDou is assessed via orbit overlaps, for dif- ferent arc lengths. Kinematic post-processed multi-GNSS positioning results are presented. The benets of multi- constellation PPP are discussed in terms of enhanced availability and positioning accuracy.

https://www.degruyter.com/downloadpdf/j/jogs.2014.4.issue-1/jogs-2014-0008/jogs-2014-0008.xml

Precise orbit determination and point positioning using GPS, Glonass, Galileo and BeiDou

Ambiguity fixing in Precise Point Positioning (PPP) has been extensively studied in recent years. The provision of uncalibrated hardware delays (UHDs) to the PPP algorithm, on top of precise orbits and clocks, allows the recovery of the integer values of the carrier-phase ambiguities. Experimental results show that integer ambiguity resolution increases the accuracy in the position domain. Most of the research so far has been done on GPS, where the wide- and narrow-lane approach for ambiguity resolution has proven successful. In the context of multi-GNSS PPP, the aim of this study is to extend the method to Galileo. Initial results for UHD estimation for Galileo satellites are presented. The contribution of ambiguity-fixing to GPS+Galileo PPP is assessed.

Estimation of Galileo Uncalibrated Hardware Delays for Ambiguity-Fixed Precise Point Positioning

Satellite positioning is evolving rapidly, with the deployment of Galileo and BeiDou systems, in addition to the modernisation programmes for GPS and GLONASS. At the time of writing, the BeiDou constellation consists of 5 Geostationary Orbit (GEO), 5 Geosynchronous Orbit (IGSO) and 4 Medium-Earth Orbit (MEO) satellites. The constellation design is particularly interesting as it allows visibility of a sufficient number of BeiDou satellites over Asia for autonomous positioning. In this paper, possibilities for real-time precise point positioning (PPP) using BeiDou are explored. For real-time generation of orbit and clock products, observation data from Fugro’s proprietary station network are used, together with data from the IGS Multi-GNSS Experiment (MGEX). In order to perform orbit estimation, the NAPEOS (Navigation Package for Earth Orbiting Satellites) software has been extended for processing BeiDou data. Satellite orbits are generated every hour and include a predicted part which can be used for real-time positioning. In order to estimate the accuracy of the real-time orbit, a validation with post-processed products is presented. A Kalman filter has been extended to process BeiDou observation data, in order to estimate satellite clock biases in real-time. For precise point positioning, Fugro’s kinematic PPP engine is used. The engine is fed with real-time orbits and clocks, as well as observation data from test receivers. Kinematic PPP results are presented, in real-time and post-processing, including BeiDou standalone and in combination with GPS.

Real-Time Precise Point Positioning Using BeiDou

Estimation of Galileo Uncalibrated Hardware Delays for Ambiguity-fixed Precise Point Positioning

Abstract In order to achieve high-accuracy positioning, either Real-Time Kinematic (RTK) or Precise Point Positioning (PPP) techniques can be used. While RTK normally delivers higher accuracy with shorter convergence times, PPP has been an attractive technology for maritime applications, as it delivers uniform positioning performance without the direct need of a nearby reference station. Traditional PPP has been based on ambiguity-float solutions using GPS and Glonass constellations. However, the addition of new satellite systems, such as Galileo and BeiDou, and the possibility of fixing integer carrier-phase ambiguities (PPP-AR) allow to increase PPP accuracy. In this article, a performance assessment has been done between RTK, PPP and PPP-AR, using GNSS data collected from two antennas installed on a ferry navigating in Oslo (Norway). RTK solutions have been generated using short, medium and long baselines (up to 290 km). For the generation of PPP-AR solutions, Uncalibrated Hardware Delays (UHDs) for GPS, Galileo and BeiDou have been estimated using reference stations in Oslo and Onsala. The performance of RTK and multi-constellation PPP and PPP-AR are presented.

Javier Tegedor

Papers

Precise orbit determination and point positioning using GPS, Glonass, Galileo and BeiDou

Estimation of Galileo Uncalibrated Hardware Delays for Ambiguity-Fixed Precise Point Positioning

Real-Time Precise Point Positioning Using BeiDou

Estimation of Galileo Uncalibrated Hardware Delays for Ambiguity-fixed Precise Point Positioning

Comparison between multi-constellation ambiguity-fixed PPP and RTK for maritime precise navigation