GLONASS FDMA data for RTK positioning: a five-system analysis

The use of the GLONASS legacy signals for real-time kinematic positioning is considered. Due to the FDMA multiplexing scheme, the conventional CDMA observation model has to be modified to restore the integer estimability of the ambiguities. This modification has a strong impact on positioning capabilities. In particular, the ambiguity resolution performance of this model is clearly weaker than for CDMA systems, so that fast and reliable full ambiguity resolution is usually not feasible for standalone GLONASS, and adding GLONASS data in a multi-GNSS approach can reduce the ambiguity resolution performance of the combined model. Partial ambiguity resolution was demonstrated to be a suitable tool to overcome this weakness (Teunissen in GPS Solut 23(4):100, 2019). We provide an exhaustive formal analysis of the positioning precision and ambiguity resolution capabilities for short, medium, and long baselines in a multi-GNSS environment with GPS, Galileo, BeiDou, QZSS, and GLONASS. Simulations are used to show that with a difference test-based partial ambiguity resolution method, adding GLONASS data improves the positioning performance in all considered cases. Real data from different baselines are used to verify these findings. When using all five available systems, instantaneous centimeter-level positioning is possible on an 88.5 km baseline with the ionosphere weighted model, and on average, only 3.27 epochs are required for a long baseline with the ionosphere float model, thereby enabling near instantaneous solutions

From Past to Present: Investigating Retrofitted GPS Antennas for Multi-GNSS Functionality

This paper investigates the re-use of highly precise equipment through the retrofitting of historical GPS choke ring antennas to accommodate Multi-GNSS systems. Specifically, it focuses on the former "reference" antenna of the International GNSS Service (IGS), the AOAD/M_T NONE antenna in a JPL 2d choke ring design, supported by the the GeoForschungsZentrum Potsdam (GFZ). The Institut für Erdmessung (IfE), a calibration institution certified by the International GNSS Service (IGS), had two different types of such antennas available: one delivered with the original Low Noise Amplifier (LNA) and retrofitted with the updated LNA, and another already equipped with the updated LNA. The IfE performed calibrations with both the original and retrofitted LNAs, providing legacy GPS L1/L2 calibrations and Multi-GNSS calibrations for broader variety of signals and frequencies. These calibrations are based on the robot calibration approach with a robot arm on a short baseline with common clock to reduce all external error sources. In this study, we present the different performance of the antenna with the retrofitted LNA based on Signal-to-Noise decrease functions, signal and frequency comparisons, variations in carrier phase, and analysis of code phase (group delays). Furthermore, we have performed an analysis on the basis of the pattern domain of PCC (Phase Center Corrections) and GDV (Group Delay Variations), as well as on the parameter domain, including positioning and other parameters such as clock corrections. Comprehensive performance analysis has been carried out to evaluate the effectiveness of such retrofitted antennas to also support Multi-GNSS systems. Additionally, we apply newly developed scalar measures for comparisons and performance analysis, providing a robust framework for assessing the suitability of retrofitted antennas for modern navigation needs. The findings shed light on the practical implications and technical considerations involved in adapting historical GPS choke ring antennas, emphasising responsible equipment re-use and performance optimisation in today's technological landscape

Stability analysis of the Iraqi GNSS stations

The Iraqi GNSS network was installed in 2005 with help from the USA and UK. The network consists of seven GNSS stations distributed across Iraq. The network GNSS data have been comprehensively analyzed in this study; this, in turn, allowed us to assess the impact of various geophysical phenomena (e. g., tectonic plate motion and Earthquakes) on its positional accuracy, stability, and validity over time. We processed daily GPS data, spanning over more than five years. The Earth Parameter and Orbit System software (EPOS.P8), developed by the German Geoscience Research Center (GFZ), was used for data processing by adopting the Precise Point Positioning (PPP) strategy. The stacked time series of stations coordinates was analyzed after estimating all modeled parameters of deterministic and stochastic parts using the least-squares technique. The study confirmed a slight impact of the recent M 7.3 Earthquake on the Iraqi GNSS stations and concluded that the stations are stable over the study period (2013 up to 2018) and that the GNSS stations represent the movement of the Arabian plate

Two methods to determine scale-independent GPS PCOs and GNSS-based terrestrial scale: comparison and cross-check

The GPS satellite transmitter antenna phase center offsets (PCOs) can be estimated in a global adjustment by constraining the ground station coordinates to the current International Terrestrial Reference Frame (ITRF). Therefore, the derived PCO values rest on the terrestrial scale parameter of the frame. Consequently, the PCO values transfer this scale to any subsequent GNSS solution. A method to derive scale-independent PCOs without introducing the terrestrial scale of the frame is the prerequisite to derive an independent GNSS scale factor that can contribute to the datum definition of the next ITRF realization. By fixing the Galileo satellite transmitter antenna PCOs to the ground calibrated values from the released metadata, the GPS satellite PCOs in the z-direction (z-PCO) and a GNSS-based terrestrial scale parameter can be determined in GPS + Galileo processing. An alternative method is based on the gravitational constraint on low earth orbiters (LEOs) in the integrated processing of GPS and LEOs. We determine the GPS z-PCO and the GNSS-based scale using both methods by including the current constellation of Galileo and the three LEOs of the Swarm mission. For the first time, direct comparison and cross-check of the two methods are performed. They provide mean GPS z-PCO corrections of −186±25 mm and −221±37 mm with respect to the IGS values and +1.55±0.22 ppb (parts per billion) and +1.72±0.31 in the terrestrial scale with respect to the IGS14 reference frame. The results of both methods agree with each other with only small differences. Due to the larger number of Galileo observations, the Galileo-PCO-fixed method leads to more precise and stable results. In the joint processing of GPS + Galileo + Swarm in which both methods are applied, the constraint on Galileo dominates the results. We discuss and analyze how fixing either the Galileo transmitter antenna z-PCO or the Swarm receiver antenna z-PCO in the combined GPS + Galileo + Swarm processing propagates to the respective freely estimated z-PCO of Swarm and Galileo

CubETH: low cost GNSS space experiment for precise orbit determination

CubETH is a project to evaluate and demonstrate possibilities of low-cost GNSS receivers on a nano-satellite by following the Cubesat standard. The development of this new Swiss cubesat mission is underway at the Swiss Polytechnical Schools, launch is planned for 2016. Scientific goal are: precise orbit determination and estimate of satellite attitude based on a very short baseline together with a number of other experimental measurements. Programmatic goal is to implement this project in cooperation between federal (ETH/EPF domain) and cantonal (FH/HES domain) engineering schools and industrial partners. The educational objective is to involve engineering students from various schools across Switzerland to promote innovative teaching of engineering of complex systems. In this paper, we will discuss performance requirements for the CubETH spacecraft and its payload. We also show how lessons learned from the Swisscube satellite were used for the design and implementation of this project

GENESIS: Co-location of Geodetic Techniques in Space

Improving and homogenizing time and space reference systems on Earth and, more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation for predicting natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities which has enunciated geodesy requirements for Earth sciences. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, proposed as a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this white paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS

Geocenter Coordinates from a Combined Processing of LEO and Ground-based GPS Observations

ISSN:1029-7006ISSN:1607-796

GLONASS FDMA data for RTK positioning: a five-system analysis

The use of the GLONASS legacy signals for real-time kinematic positioning is considered. Due to the FDMA multiplexing scheme, the conventional CDMA observation model has to be modified to restore the integer estimability of the ambiguities. This modification has a strong impact on positioning capabilities. In particular, the ambiguity resolution performance of this model is clearly weaker than for CDMA systems, so that fast and reliable full ambiguity resolution is usually not feasible for standalone GLONASS, and adding GLONASS data in a multi-GNSS approach can reduce the ambiguity resolution performance of the combined model. Partial ambiguity resolution was demonstrated to be a suitable tool to overcome this weakness (Teunissen in GPS Solut 23(4):100, 2019). We provide an exhaustive formal analysis of the positioning precision and ambiguity resolution capabilities for short, medium, and long baselines in a multi-GNSS environment with GPS, Galileo, BeiDou, QZSS, and GLONASS. Simulations are used to show that with a difference test-based partial ambiguity resolution method, adding GLONASS data improves the positioning performance in all considered cases. Real data from different baselines are used to verify these findings. When using all five available systems, instantaneous centimeter-level positioning is possible on an 88.5 km baseline with the ionosphere weighted model, and on average, only 3.27 epochs are required for a long baseline with the ionosphere float model, thereby enabling near instantaneous solutions.Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)https://saegnss2.curtin.edu/ldc/ftp://cddis.gsfc.nasa.gov/gnss/data/ftp://ftp.gfz-potsdam.de/GNSS/products/mgex

Geocenter variations derived from a combined processing of LEO and ground-based GPS observations

ISSN:0949-7714ISSN:1432-139