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Characterization of GNSS observations from a Nexus 9 Android tablet
KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
2019 (English)In: GPS Solutions, ISSN 1080-5370, E-ISSN 1521-1886, Vol. 23, no 1, article id UNSP 21Article in journal (Refereed) Published
Abstract [en]

Global navigation satellite system (GNSS) raw data were made available in the application programming interface (API) starting from version 7.0 of the Android operating system. This opens possibilities for precise positioning with Android devices, as externally generated GNSS corrections can now be included in the positioning estimation in a convenient way. The Nexus 9 tablet is a good candidate for an early assessment of the raw GNSS observables and the corresponding derived precise positions, as it also supports many of the optional features and observation types presented by the API, including carrier phase observations which play an important role in many precise positioning techniques. It is known from the previous studies that poor handling of multipath in smartphones and tablets is a big challenge when it comes to precise GNSS positioning with these kinds of devices. Hence, this study assesses the raw GNSS observations and the calculated precise positions of the Nexus 9 tablet in two experimental setups with different multipath impacts. In addition, various biases of the observations are determined, some of which is not present on high-grade geodetic receivers. The analysis is done for GPS and GLONASS, which are supported by the Nexus 9 tablet. The study shows that multipath plays an important role for the expected accuracy of the calculated precise positions, both due to the induced error on the measurements, and due to loss of lock of the GNSS signals, which significantly affects precise positioning from carrier-phase measurements. Position accuracy ranges from just below 1m to a few decimeters between the experimental setups with moderate and low levels of multipath respectively, for positioning based on carrier-phase observations. It is, furthermore, demonstrated that consideration of code inter-system biases and code inter-frequency biases of the Nexus 9 tablet are crucial for differential GNSS with multiple GNSS systems and when GLONASS observations are used in the positioning solutions. Besides these expected biases, also other less expected behaviors were discovered in the Nexus 9 GNSS observations, including various drifts for the code and phase observations. This study also proposes some strategies to handle these.

Place, publisher, year, edition, pages
SPRINGER HEIDELBERG , 2019. Vol. 23, no 1, article id UNSP 21
Keywords [en]
GNSS positioning, Characterization, Biases, Android, Mass market, GPS, GLONASS
National Category
Human Geography
Identifiers
URN: urn:nbn:se:kth:diva-241187DOI: 10.1007/s10291-018-0818-7ISI: 000454562800001Scopus ID: 2-s2.0-85059346560OAI: oai:DiVA.org:kth-241187DiVA, id: diva2:1281082
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2020-01-31Bibliographically approved
In thesis
1. GNSS hardware biases in code and carrier phase observables
Open this publication in new window or tab >>GNSS hardware biases in code and carrier phase observables
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

GNSS hardware biases appear in code and phase observations, and originates both from the receiver and satellite hardware. The presence of biases in GNSS observations might affect the accuracy in precise GNSS positioning applications, and might also be of relevance in other GNSS applications. They may also be a cause of incompatibility between different receiver types or GNSS constellations.

In this thesis, which is based on four papers, the biases in GNSS code and carrier phase observables are investigated. This is done by: characterizing and analyzing some selected biases; revealing some previously unknown biases; developing new methods to estimate some of the biases; and compiling and presenting information about biases in a new and comprehensive way.

Paper 1 gives a full review of how various kinds of biases affect various applications of precise GNSS positioning, including multi-GNSS positioning and ambiguity resolved PPP.

In Paper 2, two cases of relative phase biases, that potentially could degrade the positioning accuracy in precise positioning applications, are investigated. Fortunately, these biases turns out to be small in size with negligible effect on the positioning accuracy in both cases, which involves relative between-receivers biases for receivers of different type and between-signals biases for carrier phase observations of different signals associated with the same carrier frequency.

Paper 3 characterizes GNSS observations from a Nexus 9 Android tablet. By doing this, it reveals a number of earlier unknown biases. A drift between the code and phase observable of -3 and 2 mm/s is revealed for GPS and GLONASS, respectively. Additionally, an unexpected variation in the GLONASS phase observable, which seems to be dependent on the topocentric range rate of the satellite, is discovered.

In Paper 4, the existence of nadir dependent code biases is confirmed for GNSS observations from BeiDou-2 satellites of the BeiDou constellation by analyzing the residuals of 2-D and 3-D ionosphere modeling. This a new method to derive this kind of bias, independent of the earlier employed approach based on the multipath linear combination. The estimated effect is, however, too small to infer a similar nadir dependence for GPS and Galileo as well.

Abstract [sv]

Hårdvaru-relaterade GNSS biases uppträder i kod- och bärvågsobservationer som små avvikelser eller fel. Dessa är karaktäristiska för en viss typ av hårdvara och har sitt ursprung både i satellit och mottagare. Förekomsten av biases i GNSS-observationer har en potentiell negative påverkan för mätosäkerheten för tillämpningar av noggrann GNSS-positionering. Även i andra GNSS-tillämpningar kan biases i vissa fall vara relevanta. Förekomsten av biases kan också vara en orsak till kompatibilitetsproblem när GNSS-observationer från olika mottagartyper eller GNSS-konstellationer kombineras.

Denna avhandling, som är baserad på fyra artiklar, tittar närmare på biases som förekommer i kod- och bärvågsobservationer. Mer specifikt så involverar detta: karaktärisering och analys av några utvalda biases; avlöjande av vissa tidigare okända biases; utvecklande av nya metoder för estimering av biases; och sammanställning och presentation av biases på ett nytt och övergripande sätt.

Artikel 1 är en litteraturstudie som behandlar hur olika typer av biases påverkar tillämpningar för noggrann GNSS-positionering. Dessa tillämpingar innefattar bland annat GNSS-positionering som involverar flera GNSS-konstellationer och PPP med heltalslösning av periodobekanta.

Artikel 2 undersöker två typer av relativa biases för bärvågsobservationer. Dessa skulle potentiellt sett kunna ha en negativ inverkan på mätosäkerheten för noggranna GNSS-tillämpningar. De två typerna innefattar biases relativa mellan två mottagare, och biases relativa mellan två signaler. Lyckligtvis så visade det sig att dessa är så små att de endast har en försumbar effekt i de flesta GNSS-tillämpningar.

I artikel 3 karaktäriseras GNSS-observationerna från en surfplatta av modell Nexus 9 och med Android som operativsystem. Här avslöjas två tidigare okända biases: drift mellan kod- och bärvågsobservablerna motsvarande -3 och 2 mm/s för GPS och Glonass; samt en variation i Glonass bärvågsobservabel som verkar bero på den topocentriska hastigheten.

Artikel 4 bekräftar förekomsten av ett nadir-beroende för kod-biases för BeiDou-observationer gällande de satelliter som betecknas BeiDou-2. Detta resultat är härlett från jonosfärsmodellering i två och tre dimensioner genom analys av motsvarande residualer. Den presenterade metoden för denna härledning är ny, då metoden utnyttjad i tidigare studier istället använder sig av flervägsfelslinjärkombinationen av kod- och bärvågsobservationer.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 56
Series
TRITA-ABE-DLT ; 203
Keywords
GNSS, GNSS positioning, hardware biases, phase biases, multi-GNSS, GPS, GLONASS, Galileo, BeiDou, satellite dependency, characterization, android, mass market, Group delay variations, nadir dependence, ionosphere modeling, ionospheric tomography
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Engineering and Technologies Geotechnical Engineering
Research subject
Geodesy and Geoinformatics; Geodesy and Geoinformatics, Geodesy
Identifiers
urn:nbn:se:kth:diva-267044 (URN)978-91-7873-454-2 (ISBN)
Public defence
2020-02-28, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20200104

Available from: 2020-02-04 Created: 2020-01-31 Last updated: 2020-02-04Bibliographically approved

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