Single-frequency RTK GNSS positioning
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Date
2017
Publication Type
Doctoral Thesis
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yes
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Abstract
Real Time Kinematic (RTK) GNSS positioning is a carrier-phase differential positioning
technique depending upon the fixing of the carrier phase integer ambiguities to ensure cm-
level positioning accuracy. It is up to now the most viable technique to achieve cm-level
accuracy for kinematic positioning in post-processing mode and particularly in real time mode.
(Odijk 2014) discussed RTK and Precise Point Positioning (PPP) techniques for single-frequency
case. It is suggested that instantaneous ambiguity fixing is achievable for single-frequency
multi-constellation RTK, but single-frequency PPP integer ambiguity fixing is more challenging
due to the need of additional information like satellite hardware phase biases and ionospheric
corrections. Thus, single-frequency RTK GNSS positioning is the most feasible technique to
achieve centimeter-level high precision positioning in real time using low-cost single-
frequency GNSS antennas and receivers. It is a promising technique, which answers the
growing high-precision navigation demand from industrial drones, self-driving cars and
automated farming in which low-cost is crucial to democratize its application.
Compared to the expensive geodetic GNSS receivers and antennas, low-cost single-frequency
GNSS antennas and receivers do have some limitations in their performances like larger
measurement variance and less suppression off multipath errors. In this thesis, the variances
of code and carrier phase measurements of the single-frequency antenna and u-blox receiver
are analyzed through computing the empirical standard deviation of code and carrier phase
residuals in zero baseline tests and short-baseline tests. Multiplying the obtained variances
with a proper weighting function of the measurements, a realistic stochastic model is
constructed. The author proposes a mixed weighting function, where both C/N0 and satellite
elevation angle are taken into account to better dilute the multipath error’s effect. The
antenna C/N0 pattern is modeled using measurements of geostationary satellites and this
pattern is used as the input to the proposed mixed weighting function. The results show that
the proposed weighting function can well detect and down-weight the multipath
contaminated carrier phase measurements and leads to better RTK positioning accuracy. The
author has also estimated the phase center variations of the Trimble Bullet III antenna by
processing the GNSS measurements collected from 4 sessions with the antenna pointing to 0°,
90°, 180° and 270°. Applying the estimated antenna phase center variations to RTK processing
indeed reduces the systematic trend and biases/offsets in the carrier-phase residuals. Finally,
by comparing the GPS-only RTK solution with GPS + BeiDou and GPS + GLONASS solution, the
results indicate that using more satellites from additional constellations can significantly
increase the ratio of ambiguity-fixed to ambiguity-float solutions in single-frequency RTK GNSS
positioning.
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published
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Editor
Contributors
Examiner : Geiger, Alain
Examiner : Schwieger, Volker
Examiner : Rothacher, Markus
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Pages / Article No.
Publisher
ETH Zurich
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Subject
GNSS; Real Time Kinematic GNSS; cm accurate positioning; GPS data processing; Navigation System
Organisational unit
03824 - Rothacher, Markus (emeritus) / Rothacher, Markus (emeritus)