Latest GNSS Signal in Space Developments GPS, QZSS and the new Beidou 3 under examination

Nowadays one can use four global navigation satellite systems (GNSS). Two of them are complete constellations (GPS, Glonass) and two (Beidou, Galileo) are already usable and will be finish in the near future. Additionally satellite based augmentation systems (SBAS) like WAAS, EGNOS, GAGAN or QZSS complement the GNSS service. However, within all systems one can observe changes, modifications, and updates every year. This can be related to satellite renewables leading to signal property changes. Especially, for safety critical applications using GNSS, like advanced receiver autonomous integrity monitoring (ARAIM) or ground-based augmentation systems (GBAS) the new or changed Signal properties are of high interest. With the help of detailed information about the signal deformation and the received signal power it is possible to calculate realistic error bounds and consequently realistic protection level for these kinds of safety critical applications. This paper presents an overview of the findings according new signals or signal configurations of GPS, Beidou and QZSS of the last two years. After a brief introduction of the measurement facility the paper will introduce basic analysis about the quality of the signal shape in spectral and modulation domain. Using our precise calibrated measurement facility, we will also present an analysis of the transmitted satellite signal power including estimates about the power sharing among individual signal components within each band. Considering the measured power in relation to the boresight angle of the satellite one can derive a cut through the antenna pattern of the satellite and can assess the antenna symmetry properties. Examples for different satellites will be presented. Finally, we will end with a conclusion regarding the considered signal developments and its impact on GNSS users

Latest GNSS signal in space developments – GPS, QZSS & the new Beidou 3 under examination

Nowadays one can use four global navigation satellite systems (GNSS). Two of them are complete constellations (GPS, Glonass) and two (Beidou, Galileo) are already usable and will be finish in the near future. Additionally satellite based augmentation systems (SBAS) like WAAS, EGNOS, GAGAN or QZSS complement the GNSS service. However, within all systems one can observe changes, modifications, and updates every year. This can be related to satellite renewables leading to signal property changes. Especially, for safety critical applications using GNSS, like advanced receiver autonomous integrity monitoring (ARAIM) or ground-based augmentation systems (GBAS) the new or changed signal properties are of high interest. With the help of detailed information about the signal deformation and the received signal power it is possible to calculate realistic error bounds and consequently realistic protection level for these kinds of safety critical applications. This paper presents an overview of the findings according new signals or signal configurations of GPS, Beidou and QZSS of the last two years. After a brief introduction of the measurement facility the paper will introduce basic analysis about the quality of the signal shape in spectral and modulation domain. Using our precise calibrated measurement facility, we will also present an analysis of the transmitted satellite signal power including estimates about the power sharing among individual signal components within each band. Considering the measured power in relation to the boresight angle of the satellite one can derive a cut through the antenna pattern of the satellite and can assess the antenna symmetry properties. Examples for different satellites will be presented. Finally, we will end with a conclusion regarding the considered signal developments and its impact on GNSS users

Impact of Satellite Biases on the Position in Differential MFMC Applications

Global navigation satellite systems (GNSS) are used in many applications and have been part of our daily life since years. In this work error contributions based on the satellite hardware have been investigated and their impact on safety critical applications has been assessed. The paper starts with an introduction of the measurement facility and analysis of the satellite payload imperfections as well as the impact of signal deformations on the pseudo-range for different GPS (Block IIF) and Galileo satellites. The analysis is based on in-phase (I) and quadrature-phase (Q) data captured with a high gain antenna, which offers almost interference and multipath-free signal reception. Using these measurements, the biases for different receiver parameters in terms of correlator spacing and bandwidth are derived. The differential code biases are estimated using a fixed configuration for the ground station, e.g. 0.1 chips for L1 and 1 chip for L5 as specified in the current DFMC MOPS (EUROCAE WG62) and 24 MHz (double-sided) bandwidth. For the user receiver, we extend the receiver parameters to the following design space: 0.01 - 1 chips correlator spacing and 2 – 50 MHz bandwidth for L1, 0.01 – 0.5 chips correlator spacing and 4 – 50 MHz bandwidth for E1, and 0.01 - 1 chips correlator spacing and 10 – 50 MHz bandwidth for and L5/E5a signals. In addition, an analysis of the magnitude of the differential satellite code biases and position errors within the design space defined for GPS L1 (RTCA DO-229E), and within the DFMC design space proposed in the DFMC SBAS MOPS (EUROCAE WG62) is shown. Based on the derived satellite differential code biases, the impact on the position solution for one location and different geometries is presented

GNSS Visibility and Performance Implications for the GENESIS Mission

The GENESIS mission prepared for launch in 2027 integrates the four space-geodetic techniques on a single spaceborne platform in medium Earth orbit. With its unique observations and alternative tie concepts, the mission aims to contribute to an improved accuracy and homogeneity of future terrestrial reference system realizations. To assess the expected contribution of Global Navigation Satellite System (GNSS) tracking, a comprehensive GNSS coverage analysis is performed based on detailed link-budget simulations, taking into account the best available gain patterns and signal-specific transmit power estimates derived for this work from measurements of a high-gain dish antenna. The benefit of different receiver antenna concepts for the GENESIS spacecraft is assessed and it is demonstrated that a single-antenna system with either a nadir-looking or side-looking boresight is a viable alternative to the dual-antenna configuration considered in initial mission studies. Compared to terrestrial users and missions in low Earth orbit, GENESIS will collect GNSS signals transmitted at up to two times larger off-boresight angles. Only limited information on the actual transmit antenna phase patterns is presently available in this region, which hampers a quantitative assessment of the expected measurement and orbit determination accuracy. As such, a comprehensive release of manufacturer calibrations is encouraged for all blocks of GPS and Galileo satellites. In parallel, a need for in-flight characterization and calibration of the GNSS transmit antennas for off-boresight angles of up to 30 deg using observations of the GENESIS mission itself is expected. The impact of such calibrations on the overall quality of terrestrial reference frame parameters will need to be assessed in comprehensive simulations of global GNSS network solutions with joint processing of terrestrial and GENESIS GNSS observations

Evaluation of GPS L5 and Galileo E1 and E5a Performance for Future Multi Frequency and Multi Constellation GBAS

In this paper, we show a performance analysis of different signals from the new Galileo satellites in the E1 and E5a frequency bands as well as GPS L5 signals in DLR’s experimental Ground Based Augmentation System (GBAS). We show results of noise and multipath evaluations of the available Galileo satellites and compare their performance to the currently used GPS L1 and the new GPS L5 signals which were presented in a recent paper. The results show that the raw noise and multipath level of Galileo signals is smaller than of GPS. Even after smoothing, Galileo signals perform somewhat better than GPS and are less sensitive to the smoothing time constant. Another issue to be considered in a future multi frequency system is inter-frequency bias. These biases differ between satellites and depend on satellite and receiver hardware, but they can be determined a priori. With known receiver and antenna configurations, it is possible to correct for these biases and avoid errors introduced by different hardware in the airborne receiver and GBAS ground system. A residual uncertainty associated with the bias correction has to be taken into account. This can be modelled as part of σ_(pr\_gnd)

Absolute Calibration of Dual Frequency Timing Receivers for Galileo

The timing service of Global Navigation Satellite Systems (GNSS) is being steadily improved. Generally, this fact traces back to increasing accuracy of the provided ephemeris data, improvements in Precise Point Positioning, continuous refinement of time transfer techniques, the utilization of modern signals, the use of wider bandwidth, and a growing number of available satellites—the latter particularly due to the coexistence of an increasing number of independent GNSSs available. The accuracy achievable by the GNSS common view time transfer method is within range of nanoseconds. In particular the upcoming Galileo in combination with the Global Positioning System is expected to improve that accuracy even further. In this paper, we present results for an approach for absolute calibration of Galileo timing receivers operating in the L1BC and E5 signal bands. The internal receiver delays for Galileo E1 and GPS L1 signals of the institute’s Septentrio PolaRx4 TR PRO are assessed. The approach utilizes a hardware simulator, which is an expanded version of a GSS7790 GNSS simulator from Spirent Communications. The simulator, the receiver under test, as well as the utilized measurement equipment use the 10 MHz signal from the same cesium clock as reference

GPS III Vespucci: Results of half a year in orbit

The spacecraft nicknamed Vespucci is the first GPS III satellite launched in December 2018. Numerous receivers of the global International GNSS Service network tracked the signals of this new generation of GPS spacecraft from January to July 2019. This data set serves as the basis for analysis of broadcast ephemeris performance and clock stability, as well as solar radiation pressure and satellite antenna phase center models. Different empirical orbit models are tested, and box-wing models are developed based on approximate dimensions, mass, and assumed optical properties. The box-wing models show in general a better performance than the empirical models. Compared to Block IIF satellites, the stability of the GPS III rubidium clock is higher for integration times up to 10 s. At longer integration times, the stability of both clocks is similar but the GPS III clock does not suffer from frequency-specific line bias variations that affect the apparent IIF clock. Estimated antenna phase center offsets agree on the centimeter level with the calibrations published by the manufacturer. Measurements with a 30-m high-gain antenna revealed that the satellite did not stop signal transmission in July 2019 but switched to non-standard codes and codes beyond the tracking capabilities of commercial GNSS receivers. Prior to this hibernation mode, a 70 days test without broadcast ephemeris update was conducted during which the user range error increased to roughly 1 km

Reconstructing antenna gain patterns of Galileo satellites for signal power monitoring

Monitoring the quality of global navigation satellite system (GNSS) signals is of primary importance for a variety of applications requiring high levels of robustness, reliability and integrity. A key element in the signal quality verification is the evaluation of the available power at the user location, including its spatial characteristics. As such, the expected performance of the GNSS satellite antenna is, for most applications, assumed as nominal. However, due to a variety of reasons such as degradation due to heavy strains during launch as well as space environment factors, it is possible that the GNSS satellite antennas exhibit non-nominal performance in the transmitted power. An analysis and evaluation of the navigation signal quality require the investigation of such cases. To this end, this study describes a methodology for the estimation and reconstruction of non-absolute GNSS satellite antenna gain patterns, focusing on satellites of the Galileo navigation system. A key feature of the presented strategy is the employed setup of reduced complexity, which includes a low-gain antenna that allows monitoring signals from several navigation satellites at the same time. The results obtained pave the way for future multi-satellite, multi-constellation analyses of transmitted signal power, which may significantly support safety-critical applications. Additionally, the presented methodology may serve as the basis for the reconstruction of absolute antenna gain patterns, which are of particular interest for GNSS reflectometry applications

Proposal of GNSS satellite antenna performance evaluation based on reconstructed gain patterns

The evaluation of available power at user location is an important task as part of a navigation signal quality verification. This is particularly important for safety critical applications using signals from the Global Navigation Satellite Systems (GNSS). Due to a variety of factors, the performance of GNSS satellite antennas may exhibit a non-nominal performance. Efforts to characterize gain patterns of such antennas have been conducted in the past using complex observation setups. In this contribution, GNSS antenna gain patterns are reconstructed using observations from a simple measurement setup. Reconstructed patterns have been used for a characterization of performance of GNSS satellites antennas. The results may prove to be useful for safety critical and domain-specific applications, such as GNSS reflectometry