Kinematic Absolute Positioning with Quad-Constellation GNSS

The absolute positioning technique is based on a point positioning mode with a single Global Navigation Satellite System (GNSS) receiver, which has been widely used in many fields such as vehicle navigation and kinematic surveying. For a long period, this positioning technique mainly relies on a single GPS system. With the revitalization of Global Navigation Satellite System (GLONASS) constellation and two newly emerging constellations of BeiDou Navigation Satellite System (BDS) and Galileo, it is now feasible to carry out the absolute positioning with quad-constellation of GPS, GLONASS, BDS, and Galileo. A combination of multi-constellation observations can offer improved reliability, availability, and accuracy for position solutions. In this chapter, combined GPS/GLONASS/BDS/Galileo point positioning models for both traditional single point positioning (SPP) and precise point positioning (PPP) are presented, including their functional and stochastic components. The traditional SPP technique has a positioning accuracy at a meter level, whereas the PPP technique can reach an accuracy of a centimeter level. However, the later relies on the availability of precise ephemeris and needs a long convergence time. Experiments were carried out to assess the kinematic positioning performance in the two different modes. The positioning results are compared among different constellation combinations to demonstrate the advantages of quad-constellation GNSS

Evaluating the differences and accuracies between GNSS applications using PPP

Global Navigation Satellite Systems (GNSS) are satellite systems with global coverage. There are currently several GNSS systems in operation today including the United States NAVSTAR Global Positioning System, Russian GLONASS, Chinese Beidou and the European Union’s Galileo system. The Galileo and Beidou systems are currently undergoing upgrading in order to achieve more sustainable and comprehensive worldwide exposure, ultimately providing users with a broader option of systems and wider more reliable coverage. In recent years, in addition to the GPS constellation, the ability to utilise extra satellites made available through the GLONASS and Beidou systems has enhanced the capabilities and possible applications of the precise point positioning (PPP) method. Precise Point Positioning has been used for the last decade as a cost-effective alternative to conventional DGPS-Differential GPS with an estimated precision adequate for many applications. PPP requires handling different types of errors using proper models. PPP precision varies with the use of observations from different satellite systems (GPS, GLONASS and mixed GPS/GLONASS/Beidou) and the duration of observations. However, the fundamental differences between GPS, GLONASS, Beidou and Galileo and the lack of a fully tested global tracking network of multi-Global Navigation Satellite Systems necessitate the evaluation of their combined use. More studies are required in order to confirm the reliability and accuracy of the results obtained by the various methods of PPP. This is outside the scope of this paper. This research paper will evaluate and analyse the accuracy and reliability between different GNSS systems using the Precise Point Positioning technique with emphasis on the function and performance of single systems compared with combined GNSS systems. A methodology was designed to ensure accurate and reliable results have been achieved. Solutions generated from identical data will be compared for bias, accuracy and reliability between single standalone GPS and combined GNSS systems. This study focused on the performance of these systems over a twenty four hour observation period, decimated into 1, 2, 6, 12 and 24 hours. The study found that the reliability and performance of GNSS systems over standalone GPS was insignificant over a twenty four hour period. In fact, where satellite availability and constellation are at a premium, standalone GPS systems can produce equivalent quality results compared with combined GNSS. Having said this, the combined GNSS systems achieved quicker convergence times than standalone systems. With limited access and availability to resources, in particular GNSS receivers, the results can be seen as preliminary testing enhancing the knowledge of GNSS users. Nonetheless, this dissertation covers a wide range of topics and field testing providing relevant reliable data on the accuracy, precision and performance of both standalone and combined Global Navigation Satellite Systems

A Decentralized Processing Schema for Efficient and Robust Real-time Multi-GNSS Satellite Clock Estimation

Real-time multi-GNSS precise point positioning (PPP) requires the support of high-rate satellite clock corrections. Due to the large number of ambiguity parameters, it is difficult to update clocks at high frequency in real-time for a large reference network. With the increasing number of satellites of multi-GNSS constellations and the number of stations, real-time high-rate clock estimation becomes a big challenge. In this contribution, we propose a decentralized clock estimation (DECE) strategy, in which both undifferenced (UD) and epoch-differenced (ED) mode are implemented but run separately in different computers, and their output clocks are combined in another process to generate a unique product. While redundant UD and/or ED processing lines can be run in offsite computers to improve the robustness, processing lines for different networks can also be included to improve the clock quality. The new strategy is realized based on the Position and Navigation Data Analyst (PANDA) software package and is experimentally validated with about 110 real-time stations for clock estimation by comparison of the estimated clocks and the PPP performance applying estimated clocks. The results of the real-time PPP experiment using 12 global stations show that with the greatly improved computational efficiency, 3.14 cm in horizontal and 5.51 cm in vertical can be achieved using the estimated DECE clock

Helmert Variance Component Estimation for Multi-GNSS Relative Positioning

The Multi-constellation Global Navigation Satellite System (Multi-GNSS) has become the standard implementation of high accuracy positioning and navigation applications. It is well known that the noise of code and phase measurements depend on GNSS constellation. Then, Helmert variance component estimation (HVCE) is usually used to adjust the contributions of di¿erent GNSS constellations by determining their individual variances of unit weight. However, HVCE requires a heavy computation load. In this study, the HVCE posterior weighting was employed to carry out a kinematic relative Multi-GNSS positioning experiment with six short-baselines from day of year (DoY) 171 to 200 in 2019. As a result, the HVCE posterior weighting strategy improved Multi-GNSS positioning accuracy by 20.5%, 15.7% and 13.2% ineast-north-up(ENU) components, compared to an elevation-dependent (ED) priori weighting strategy. We observed that the weight proportion of both code and phase observations for each GNSS constellation were consistent during the entire 30 days, which indicates that the weight proportions of both code and phase observations are stable over a long period of time. It was also found that the quality of a phase observation is almost equivalent in each baseline and GNSS constellation, whereas that of a code observation is different. In order to reduce the time consumption off the HVCE method without sacrificing positioning accuracy, the stable variances of unit weights of both phase and code observations obtained over 30 days were averaged and then frozen as a priori information in the positioning experiment. The result demonstrated similar ENU improvements of 20.0%, 14.1% and 11.1% with respect to the ED method but saving 88% of the computation time of the HCVE strategy. Our study concludes with the observations that the frozen variances of unit weight (FVUW) could be applied to the positioning experiment for the next 30 days, that is, from DoY 201 to 230 in 2019, improving the positioning ENU accuracy of the ED method by 18.1%, 13.2% and 10.6%, indicating the effectiveness of the FVUW.Peer ReviewedPostprint (published version

Characterizing Power Consumption of Dual-Frequency GNSS of a Smartphone

Location service is one of the most widely used features on a smartphone. More and more apps are built based on location services. As such, demand for accurate positioning is ever higher. Mobile brand Xiaomi has introduced Mi 8, the world's first smartphone equipped with a dual-frequency GNSS chipset which is claimed to provide up to decimeter-level positioning accuracy. Such unprecedentedly high location accuracy brought excitement to industry and academia for navigation research and development of emerging apps. On the other hand, there is a significant knowledge gap on the energy efficiency of smartphones equipped with a dual-frequency GNSS chipset. In this paper, we bridge this knowledge gap by performing an empirical study on power consumption of a dual-frequency GNSS phone. To the best our knowledge, this is the first experimental study that characterizes the power consumption of a smartphone equipped with a dual-frequency GNSS chipset and compares the energy efficiency with a single-frequency GNSS phone. We demonstrate that a smartphone with a dual-frequency GNSS chipset consumes 37% more power on average outdoors, and 28% more power indoors, in comparison with a singe-frequency GNSS phone.Comment: Published in IEEE Global Communications Conference (GLOBECOM

BeiDou-3 orbit and clock quality of the IGS Multi-GNSS Pilot Project

Within the Multi-GNSS Pilot Project (MGEX) of the International GNSS Service (IGS), precise orbit and clock products for the BeiDou-3 global navigation satellite system (BDS-3) are routinely generated by a total of five analysis centers. The processing standards and specific properties of the individual products are reviewed and the BDS-3 orbit and clock product performance is assessed through direct inter-comparison, satellite laser ranging (SLR) residuals, clock stability analysis, and precise point positioning solutions. The orbit consistency evaluated by the signal-in-space range error is on the level of 4-8 cm for the medium Earth orbit satellites whereas SLR residuals have RMS values between 3 and 9 cm. The clock analysis reveals sytematic effects related to the elevation of the Sun above the orbital plane for all ACs pointing to deficiencies in solar radiation pressure modeling. Nevertheless, precise point positioning with the BDS-3 MGEX orbit and clock products results in 3D RMS values between 7 and 8 mm.Comment: 13 pages, 5 figure

gLAB upgrade with BeiDou navigation system signals

The gLAB tool suit is an educational and professional multipurpose GNSS data processing software. It has been developed by gAGE/UPC under a contract of the European Space Agency (ESA). The current version of gLAB allows full GPS data processing with High Accuracy Positioning capability (at the centimetre level), but only a very limited data handling of Galileo and GLONASS. The Chinese Global Satellite Navigation System Beidou was not included in the initial requirements of ESA. The target of this project is to upgrade gLAB with the necessary functions to allow this software to compute user solutions with the Beidou signals

Multi-GNSS integer ambiguity resolution enabled precise positioning

In this PhD thesis multi-Global Navigation Satellite System (GNSS) positioning results when combining the American Global Positioning System (GPS), Chinese BeiDou Navigation Satellite System (BDS), European Galileo and Japanese Quasi-Zenith Satellite System (QZSS) will be presented. The combined systems will be evaluated in comparison to the single-systems, for short (atmosphere-fixed) to long (atmosphere-present) baselines. It will be shown that the combined systems can provide for improved integer ambiguity resolution and positioning performance over the single-systems

Improving the Performance of Multi-GNSS (Global Navigation Satellite System) Ambiguity Fixing for Airborne Kinematic Positioning over Antarctica

Conventional relative kinematic positioning is difficult to be applied in the polar region of Earth since there is a very sparse distribution of reference stations, while precise point positioning (PPP), using data of a stand-alone receiver, is recognized as a promising tool for obtaining reliable and accurate trajectories of moving platforms. However, PPP and its integer ambiguity fixing performance could be much degraded by satellite orbits and clocks of poor quality, such as those of the geostationary Earth orbit (GEO) satellites of the BeiDou navigation satellite system (BDS), because temporal variation of orbit errors cannot be fully absorbed by ambiguities. To overcome such problems, a network-based processing, referred to as precise orbit positioning (POP), in which the satellite clock offsets are estimated with fixed precise orbits, is implemented in this study. The POP approach is validated in comparison with PPP in terms of integer ambiguity fixing and trajectory accuracy. In a simulation test, multi-GNSS (global navigation satellite system) observations over 14 days from 136 globally distributed MGEX (the multi-GNSS Experiment) receivers are used and four of them on the coast of Antarctica are processed in kinematic mode as moving stations. The results show that POP can improve the ambiguity fixing of all system combinations and significant improvement is found in the solution with BDS, since its large orbit errors are reduced in an integrated adjustment with satellite clock offsets. The four-system GPS+GLONASS+Galileo+BDS (GREC) fixed solution enables the highest 3D position accuracy of about 3.0 cm compared to 4.3 cm of the GPS-only solution. Through a real flight experiment over Antarctica, it is also confirmed that POP ambiguity fixing performs better and thus can considerably speed up (re-)convergence and reduce most of the fluctuations in PPP solutions, since the continuous tracking time is short compared to that in other regions