Search

Broadcast ephemeris plays an important role in positioning, navigation, and timing (PNT) services. With the rise of new constellations of Galileo and BDS3, satellite services are moving towards multi-GNSS fusion. Therefore, systematic evaluation of the multi-GNSS broadcast ephemeris and determination of the impact of ranging errors of different constellations in the multi-GNSS standard single point positioning (SPP) are necessary. In the contribution, the 120-day broadcast ephemeris from 1 January 2022 to 30 April 2022 and precise ephemeris provided by three analysis centers (German Research Center for Geosciences (GFZ), European Centre for Orbital Determination (CODE), and Wuhan University (WHU)) are used to analyze the orbits, clock offsets, and signal-in-space ranging error (SISRE) for GPS, GLONASS, Galileo, BDS2, BDS3, and QZSS (G, R, E, C2, C3, and J). The ephemeris analysis shows that the assessments using the precise ephemeris from the three analysis centers are consistent. The average daily SISREs for different constellations evaluated by GFZ products are 0.16 ± 0.07 m (E), 0.38 ± 0.19 m (J), 0.46 ± 0.19 m (C3), 0.50 ± 0.17 m (G), 1.30 ± 0.27 m (C2), and 2.40 ± 0.73 m (R), respectively. In addition, we propose a weight determination method using joint weighting of SISREs and satellite elevation angle (Ele + SIS) based on the analysis. One consecutive week of observations tracked by 23 permanent reference stations is selected, and a comparison experiment is conducted using the classical elevation angle weighting scheme (Ele) and the Ele + SIS scheme in dynamic SPP to verify the feasibility. Compared to the classic Ele scheme, the positioning accuracy of GREC2C3J combined SPP using the Ele + SIS scheme is improved by 34.2 % in the 3D direction, and the 95th percentile of the positioning errors is reduced by 31.5 %. The same dynamic SPP test using data after one year of modeling the Ele + SIS weighting scheme shows that the enhancement of the positioning accuracy of the Ele + SIS scheme decreases by only 3.7 %, which demonstrates that the Ele + SIS scheme can be used in real-time application. [ABSTRACT FROM AUTHOR]

The Galileo High Accuracy Service (HAS) has undergone substantial development in recent years, offering users free access to GPS and Galileo satellite orbit, clock, and code bias corrections for Precise Point Positioning (PPP) on a global scale. This paper explores the use of the currently available HAS corrections for smartphone positioning. Due to hardware disparities and limited tracking capabilities, smartphone processing with only two GNSS constellations struggles to ensure satisfactory satellite geometry and sufficient observations in realistic user environments. To fully harness all observed measurements and the orbit and clock information directly disseminated from satellites, this study introduces a new PPP algorithm combing HAS corrections and broadcast ephemerides (HAS and BRDC PPP) for smartphone processing. Through four vehicle experiments in urban environments, the proposed HASandBRDC PPP solutions demonstrated a notable reduction in positioning errors. Specifically, the horizontal rms and 95th percentile error decreased from 2.0 and 3.3 m to 1.6 and 2.4 m, respectively, when compared to the HAS PPP solutions. These results are highly comparable to four-constellation PPP solutions utilizing Centre National d'Etudes Spatiales (CNES) ultra-rapid products, which can achieve a horizontal rms of 1.4 m. Additionally, the inclusion of smartphone inertial measurement unit (IMU) measurements results in a notable 59% average reduction in PPP gross errors. This study provides an original comparison of the 2022 and 2023 HAS corrections, demonstrating the feasibility of real-time lane-level navigation with smart devices even in remote areas without Internet connectivity, which has not been previously explored. [ABSTRACT FROM AUTHOR]

The task of improving the GLONASS characteristics in the context of the modern competitive development of global satellite navigation systems is considered. The authors consider research and development related, firstly, to improving the signal-in-space ratio indicator in the operational mode by creating new technological cycles onboard a spacecraft (SC) and involving onboard hardware in these processes; and, secondly, with the formation of a reserve with the subsequent implementation of the functionality of orbital groupings (OGs) without downloading the ephemeris-temporal information and time-frequency corrections from the ground control complex. This article considers the main factors hindering the implementation of the currently set goals and also suggests ways to eliminate or compensate the influence of these factors by developing and implementing special information technologies using modern and promising onboard hardware placed onboard a GLONASS SC and its potential additions. [ABSTRACT FROM AUTHOR]

This study comprehensively evaluated the signal-in-space range errors (SISREs) and investigated the systematic error characteristics for GPS and BDS broadcast ephemeris. The analysis reveals that on March 28, 2021, the satellite antenna model used by GPS ground operation centre to generate GPS II series navigation ephemeris changed from the manufacturer model to the International GNSS Service (IGS) model. This transition is carefully considered in our GPS SISRE evaluation. Experimental statistics indicate that the SISRE for GPS IIR, IIF, and III satellites is approximately 0.50, 0.46, and 0.34 m, respectively, with a value of 0.44 m for the overall constellation. With enhancements in inter-satellite links, BDS-3 GEO, IGSO, and MEO satellites exhibit SISRE of 1.20, 0.62, and 0.46 m, respectively, representing improvements of 14.3, 27.5 and 48.8 % over their BDS-2 counterparts. The ephemeris performance of BDS-3 MEOs is comparable to GPS. However, the BDS orbit quality significantly degrades over a 3-day period following manoeuvre operations and during eclipse seasons. Furthermore, the systematic error characteristics of broadcast ephemeris are analysed based on satellite laser ranging (SLR) checks and Helmert transformation. The SLR residuals of nearly all of the BDS-2/3 satellites tracked by the International Laser Ranging Service vary linearly with the Sun elongation angle. Moreover, the Z -geocentre component of the GPS/BDS orbit-realises frame exhibits obvious annual periodicity. These indicate that the GPS/BDS broadcast orbit models need further improvement. Compared with GPS, the BDS broadcast orbit-realised frame can better maintain the X - and Y -geocentric components but presents significant systematic scale bias and rotation errors. These errors for BDS are attributable to the inconsistency in the radial disturbance models between broadcast and Multi-GNSS Experiment precise orbits as well as prediction errors of the Earth rotation parameter used. The overall SLR residual mean for BDS-3 CAST and SECM MEOs are approximately 7.8 and −4.7 cm, respectively, with a standard deviation of approximately 9.9 cm, 3–4 times better than that of the BDS-2 satellites. The SLR residual dispersion of BDS-3 MEO C43 and C44 satellites is significantly larger than that of other BDS-3 MEOs, likely because of the inaccurate official coordinates of laser retroreflector arrays. [ABSTRACT FROM AUTHOR]

The signal-in-space range error (SISRE) has a direct impact on the performance of global navigation satellite systems (GNSSs). It is an important indicator of navigation satellite space server performance. The new B-CNAV navigation messages (B-CNAV1 and B-CNAV2) are broadcast on the satellites of the Beidou Global Navigation Satellite System (BDS-3), and they are different from D1 navigation messages in satellite orbit parameters. The orbit accuracy of B-CNAV navigation messages lacks analyses and comparisons with D1. The accuracy and stability of the new hydrogen and rubidium clocks on BDS-3 satellites need annual analyses of long time series, which will affect the service quality of this system. Based on precise ephemeris products from the Center for Orbit Determination in Europe (COD), the orbit error, clock error, and SISRE of 24 medium Earth orbit (MEO) satellite D1 and B-CNAV navigation messages of BDS-3 were computed, analyzed, and compared. Their annual evolution processes for the entire year of 2022 were studied. Thanks to the use of inter-satellite links (ISLs) adopted by BDS-3 MEO satellites, the ages of the ephemeris are accurate and the percent of ages of data, ephemerides (AODEs), and ages of data and clocks (AODCs) shorter than 12 h were 99.95% and 99.96%, respectively. In addition, the broadcast orbit performance was also improved by ISLs. The root mean square (RMS) values of the BDS-3 MEO broadcast ephemeris orbit error were 0.067 m, 0.273 m, and 0.297 m in the radial, cross, and along directions, respectively. Moreover, the 3D RMS value was 0.450 m. Thanks to the use of new orbit parameters in the B-CNAV navigation messages of BDS-3 MEO, its satellite orbit accuracy was obviously better than that of D1 in the radial direction. Its improved accuracy can reach up to about 1.2 cm, and the percentage of its accuracy improvement was about 19.06%. With respect to clock errors, the timescale differences between the two clock products were eliminated to assess the accuracy of broadcasting ephemeris clock errors. A standard deviation value of 0.256 m shows good performances as a result of the use of the two new types of atomic clocks, although the RMS value was 0.541 m due to a nonzero mean bias. Overall, the accuracy of atomic clocks was good. For the new hydrogen and rubidium atomic clocks, their RMS and standard deviation were 0.563 m and 0.231 m and 0.519 m and 0.281 m, respectively. The stability of the former was better than that of the latter. However, due to the nonzero mean bias the latter was better than the former in accuracy. The RMS value of the SISRE of BDS-3 MEO's broadcast ephemeris was 0.556 m, and the value was 0.920 m when it had a 95% confidence level. In contrast, after deducting the influence of the clock error, the value of SISRE_ORB was 0.092 m. Since the satellite clock error was substantially larger than the orbit radial error, the SISRE was mainly affected by the clock error, and their annual evolutions were consistent. Because of the improvement to the B-CNAV's navigation message with respect to orbit radial accuracy, SISRE_ORB has improved in accuracy. Compared to D1, it had a significant effect on improving the accuracy of SISRE_ORB, and the percentage of the accuracy improvement was 8.40%. [ABSTRACT FROM AUTHOR]

Since 2020, the BeiDou Navigation Satellite System (BDS) has launched new precise point positioning service which provides precise correction of GPS and BDS-3 satellites to help users realize real-time precise point positioning, known as PPP-B2b service. After being fully operational for more than one year, this contribution comprehensively analyzes the performance of PPP-B2b in terms of correction availability, clock and orbit quality and positioning accuracy with PPP-B2b messages of nearly 48 weeks from 2021 to 2022. The results show that in the PPP-B2b service, the orbit radial differences of BDS-3 MEO, GPS, and BDS-3 IGSO satellites are 0.056 m, 0.069 m, and 0.172 m, respectively, compared to the GFZ final orbit, while the difference of along-track and cross-track is more than three times the radial. For BDS-3 MEO satellites from different manufacturers, the RMS of Satellite Laser Ranging (SLR) residuals is different, with a maximum of 0.11 m. Restricted by the regional tracking network, the correction series of PPP-B2b service are discontinuous, and there are constant satellite-specific clock biases in different arcs of the satellite. Thus, the STD and RMS of satellite clock offset and signal-in-space ranging error (SISRE) are calculated using the method of weighting by arcs. The STD of SISRE for BDS-3 MEO, GPS and BDS-3 IGSO are 0.059 m, 0.092 m and 0.174 m, respectively. A total of 108 days of observation data from 12 MGEX stations of the East Asia region are selected to analyze the positioning performance of PPP-B2b. The results of day-by-day static PPP are stable at the centimeter level, while the average convergence time of GPS-only (61.65 min) is longer than BDS-3-only (45.12 min), which the constant bias in clock offset may cause. To analyze the effect of this bias, the bias is calculated and used as a correction to the PPP-B2b clocks. The convergence time of BDS-3 and GPS positioning is reduced by 48.7% and 65.9%, respectively, after correcting this bias, which confirms the influence of clock constant bias on positioning convergence. [ABSTRACT FROM AUTHOR]

The signal-in-space range error (SISRE) has a direct impact on the performance of global navigation satellite systems (GNSSs). It is an important indicator of navigation satellite space server performance. The new B-CNAV navigation messages (B-CNAV1 and B-CNAV2) are broadcast on the satellites of the Beidou Global Navigation Satellite System (BDS-3), and they are different from D1 navigation messages in satellite orbit parameters. The orbit accuracy of B-CNAV navigation messages lacks analyses and comparisons with D1. The accuracy and stability of the new hydrogen and rubidium clocks on BDS-3 satellites need annual analyses of long time series, which will affect the service quality of this system. Based on precise ephemeris products from the Center for Orbit Determination in Europe (COD), the orbit error, clock error, and SISRE of 24 medium Earth orbit (MEO) satellite D1 and B-CNAV navigation messages of BDS-3 were computed, analyzed, and compared. Their annual evolution processes for the entire year of 2022 were studied. Thanks to the use of inter-satellite links (ISLs) adopted by BDS-3 MEO satellites, the ages of the ephemeris are accurate and the percent of ages of data, ephemerides (AODEs), and ages of data and clocks (AODCs) shorter than 12 h were 99.95% and 99.96%, respectively. In addition, the broadcast orbit performance was also improved by ISLs. The root mean square (RMS) values of the BDS-3 MEO broadcast ephemeris orbit error were 0.067 m, 0.273 m, and 0.297 m in the radial, cross, and along directions, respectively. Moreover, the 3D RMS value was 0.450 m. Thanks to the use of new orbit parameters in the B-CNAV navigation messages of BDS-3 MEO, its satellite orbit accuracy was obviously better than that of D1 in the radial direction. Its improved accuracy can reach up to about 1.2 cm, and the percentage of its accuracy improvement was about 19.06%. With respect to clock errors, the timescale differences between the two clock products were eliminated to assess the accuracy of broadcasting ephemeris clock errors. A standard deviation value of 0.256 m shows good performances as a result of the use of the two new types of atomic clocks, although the RMS value was 0.541 m due to a nonzero mean bias. Overall, the accuracy of atomic clocks was good. For the new hydrogen and rubidium atomic clocks, their RMS and standard deviation were 0.563 m and 0.231 m and 0.519 m and 0.281 m, respectively. The stability of the former was better than that of the latter. However, due to the nonzero mean bias the latter was better than the former in accuracy. The RMS value of the SISRE of BDS-3 MEO’s broadcast ephemeris was 0.556 m, and the value was 0.920 m when it had a 95% confidence level. In contrast, after deducting the influence of the clock error, the value of SISRE_ORB was 0.092 m. Since the satellite clock error was substantially larger than the orbit radial error, the SISRE was mainly affected by the clock error, and their annual evolutions were consistent. Because of the improvement to the B-CNAV’s navigation message with respect to orbit radial accuracy, SISRE_ORB has improved in accuracy. Compared to D1, it had a significant effect on improving the accuracy of SISRE_ORB, and the percentage of the accuracy improvement was 8.40%.

Based on one year of data, a comprehensive assessment of broadcast group delays and differential code biases (DCBs) from network solutions is presented for all open BeiDou signals. Daily DCB estimates exhibit a precision of 0.1 ns, which also places a limit on long-term variations of the satellite group delays. On the other hand, the estimated DCBs show a notable dependence on the employed receivers, which causes inconsistencies at the few-nanosecond level between BeiDou-2 and BeiDou-3 satellites. Systematic satellite-specific offsets can likewise be identified in broadcast group delay values and clock offsets. These constitute the dominant contribution of the signal-in-space range error (SISRE) budget and are a limiting factor for single point positioning and timing. Use of the modernized B1C/B2a signals is therefore recommended instead of B1I/B3I. This offers a SISRE reduction from about 0.6 m to 0.45 m and also improves the consistency of precise clock and bias products derived from heterogeneous receiver networks. [ABSTRACT FROM AUTHOR]

Since BeiDou Navigation Satellite System (BDS) and Japan's Quasi-Zenith Satellite System (QZSS) have more visible satellites in the Asia-Pacific region, and navigation satellites of Global Positioning System (GPS), Galileo satellite navigation system (Galileo), and GLONASS satellite navigation system (GLONASS) are uniformly distributed globally, the service level of multi-mode Global Navigation Satellite System (GNSS) in the Asia-Pacific region should represent the best service capability. Based on the observation data of 10 Multi-GNSS Experiment (MGEX) stations, broadcast ephemeris and precision ephemeris from 13 to 19 October 2021, this paper comprehensively evaluated the service capability of multi-GNSS in the Asia-Pacific region from three aspects of observation data quality, broadcast ephemeris performance, and precision positioning level. The results show that: (1) the carrier-to-noise-density ratio (C/N0) quality of the GPS and Galileo is the best, followed by BDS and GLONASS, and QZSS is the worst. GPS, BDS-2, GLONASS, and QZSS pseudorange multipath values range from 0 to 0.6 m, while Galileo system and BDS-3 pseudorange multipath values range from 0 to 0.8 m. (2) In terms of broadcast ephemeris accuracy, BDS-3 broadcast ephemeris has the best orbit, and the three-dimensional (3D) Root Mean Square (RMS) is 0.21 m; BDS-2 was the worst, with a 3D RMS of 1.99 m. The broadcast ephemeris orbits of GPS, Galileo, QZSS, and GLONASS have 3D RMS of 0.60 m, 0.62 m, 0.83 m, and 1.27 m, respectively. For broadcast ephemeris clock offset: Galileo has the best performance, 0.61 ns, GLONASS is the worst, standard deviation (STD) is 3.10 ns, GPS, QZSS, BDS-3 and BDS-2 are 0.65 ns, 0.75 ns, and 1.72 ns, respectively. For signal-in-space ranging errors (SISRE), the SISRE results of GPS and Galileo systems are the best, fluctuating in the range of 0 m–2 m, followed by QZSS, BDS-3, Galileo, and BDS-2. (3) GPS, BDS, GLONASS, Galileo, GPS/QZSS, and BDS/QZSS were used for positioning experiments. In static PPP, the convergence time and positioning accuracy of GPS show the best performance. The positioning accuracy of GPS/QZSS and BDS/QZSS is improved compared with that of GPS and BDS. In terms of kinematic PPP, the convergence time and positioning accuracy of GPS/QZSS and BDS/QZSS are improved compared with that of GPS and BDS. In addition to GLONASS and Galileo systems, the other combinations outperformed 3 cm, 3 cm, and 5 cm in the east, north, and up directions. [ABSTRACT FROM AUTHOR]

The China BeiDou global navigation satellite system (BDS-3) has started to provide free and open precise positioning services to users in China and surrounding areas since Jul 2020 on the GEO B2b signal. The initial assessment of BDS-3 PPP-B2b products and the PPP performance over a period of near five months from Jul 26, 2020 to Dec 19, 2020 was carried out in this work. Taking the GBM products as a reference, the average signal-in-space ranging error (SISRE) of the disseminated orbit and clock products is approximately 82.3 cm (RMS) and 3.9 cm (STD) for BDS-3 satellites, and about 135.8 cm (RMS) and 7.5 cm (STD) for GPS. The average positioning error RMS at six permanent stations in China is about 2.1 (1.8) and 2.6 (2.1) cm in the horizontal and vertical components respectively for BDS-only (BDS + GPS) static PPP. In the kinematic PPP mode, the average positioning error (95%) at the same six stations is about 21.5 (15.2) and 33.4 (30.3) cm in the horizontal and vertical component respectively for BDS-only (BDS + GPS), with an average convergence time of 17.4 (16.2) min. In addition, two vehicle-based kinematic PPP tests show average position error (95%) of about 23.5 (18.6) and 48.8 (37.1) cm in horizontal and vertical respectively, and an average convergence time of 10.4 (14.2) min for BDS-only (BDS + GPS) PPP. The assessment results are overall in accordance with the official claim of centimeter-level in static mode and decimeter-level in kinematic mode from BDS-3 PPP service. [ABSTRACT FROM AUTHOR]

The number and scope of space applications of global navigation satellite systems have grown significantly. However, the availability and the navigation performance for a spacecraft operating within and beyond the space services volume are different from those of terrestrial service volume users. To effectively evaluate the space service performance of navigation satellite systems, we present the calculation method of signal-in-space ranging error for space users. Considering the geometric visibility and the constraints of the lowest carrier-to-noise ratio, we analyze the feasibility of receiving the signal transmitted from the different off-nadir angles and obtain the coverage area of navigation satellite. Then, the relationship between the weighting factors of ephemeris errors and the orbital height of the user spacecraft is analyzed. Finally, the statistics characteristic of signal-in-space ranging error of typical navigation satellites is presented. The results show that the signal-in-space ranging error increases first and then decreases as the orbital height of the user increases. Generally, when the user's orbital height is slightly higher than the orbital height of the navigation satellite, the signal-in-space ranging error reaches a maximum. In particular, due to the significant horizontal orbit error, global signal-in-space ranging error of the Beidou geostationary orbits satellites increase significantly compared with the user located on the ground. Therefore, the impact of user height changes on the statistical properties of signal-in-space ranging error cannot be ignored when evaluating the navigation performance of the space user.

Since BeiDou Navigation Satellite System (BDS) and Japan’s Quasi-Zenith Satellite System (QZSS) have more visible satellites in the Asia-Pacific region, and navigation satellites of Global Positioning System (GPS), Galileo satellite navigation system (Galileo), and GLONASS satellite navigation system (GLONASS) are uniformly distributed globally, the service level of multi-mode Global Navigation Satellite System (GNSS) in the Asia-Pacific region should represent the best service capability. Based on the observation data of 10 Multi-GNSS Experiment (MGEX) stations, broadcast ephemeris and precision ephemeris from 13 to 19 October 2021, this paper comprehensively evaluated the service capability of multi-GNSS in the Asia-Pacific region from three aspects of observation data quality, broadcast ephemeris performance, and precision positioning level. The results show that: (1) the carrier-to-noise-density ratio (C/N0) quality of the GPS and Galileo is the best, followed by BDS and GLONASS, and QZSS is the worst. GPS, BDS-2, GLONASS, and QZSS pseudorange multipath values range from 0 to 0.6 m, while Galileo system and BDS-3 pseudorange multipath values range from 0 to 0.8 m. (2) In terms of broadcast ephemeris accuracy, BDS-3 broadcast ephemeris has the best orbit, and the three-dimensional (3D) Root Mean Square (RMS) is 0.21 m; BDS-2 was the worst, with a 3D RMS of 1.99 m. The broadcast ephemeris orbits of GPS, Galileo, QZSS, and GLONASS have 3D RMS of 0.60 m, 0.62 m, 0.83 m, and 1.27 m, respectively. For broadcast ephemeris clock offset: Galileo has the best performance, 0.61 ns, GLONASS is the worst, standard deviation (STD) is 3.10 ns, GPS, QZSS, BDS-3 and BDS-2 are 0.65 ns, 0.75 ns, and 1.72 ns, respectively. For signal-in-space ranging errors (SISRE), the SISRE results of GPS and Galileo systems are the best, fluctuating in the range of 0 m–2 m, followed by QZSS, BDS-3, Galileo, and BDS-2. (3) GPS, BDS, GLONASS, Galileo, GPS/QZSS, and BDS/QZSS were used for positioning experiments. In static PPP, the convergence time and positioning accuracy of GPS show the best performance. The positioning accuracy of GPS/QZSS and BDS/QZSS is improved compared with that of GPS and BDS. In terms of kinematic PPP, the convergence time and positioning accuracy of GPS/QZSS and BDS/QZSS are improved compared with that of GPS and BDS. In addition to GLONASS and Galileo systems, the other combinations outperformed 3 cm, 3 cm, and 5 cm in the east, north, and up directions.

GNSS positioning relies on orbit and clock information, which is predicted on the ground and transmitted by the individual satellites as part of their broadcast navigation message. For an increased autonomy of either the space or user segment, the capability to predict a GNSS satellite orbit over extended periods of up to two weeks is studied. A tailored force model for numerical orbit propagation is proposed that offers high accuracy but can still be used in real‐time environments. Using the Galileo constellation with its high‐grade hydrogen maser clocks as an example, global average signal‐in‐space range errors of less than 25 m RMS and 3D position errors of less than about 50 m are demonstrated after two‐week predictions in 95% of all test cases over a half‐year period. The autonomous orbit prediction model thus enables adequate quality for a rapid first fix or contingency navigation in case of lacking ground segment updates. [ABSTRACT FROM AUTHOR]

Focusing on the global integrity monitoring performance of the BDS-3, the integrity failure model and effect analysis (IFMEA) of the system space segment and the ground control segment were carried out, and the system integrity risk tree model was established according to the IFMEA results. To evaluate the system’s integrity risk probability more reasonably, this paper establishes an abnormal event prediction model with a Bayesian method, based on actual operation data, under a situation in which the BDS-3 just opened service. With statistical analysis results of system anomalies since 27 December 2018—which is the date the BDS-3 began providing basic service—according to the anomaly prediction model, the system’s integrity risk probability under the 95% confidence limit was calculated to be approximately 0.9e-7/h, meeting the design index requirements of 1e-7/h. The analysis results also show that the main risk factors affecting the integrity of BDS-3 are ‘pseudorange measurement anomaly’ and ‘miss-detection of satellite autonomous integrity monitoring’. The results are important references with practical engineering significance for improving the integrity performance of BDS-3.

The new Global Positioning System (GPS) Civil Navigation Message (CNAV) has been transmitted by Block IIR-M and Block IIF satellites since April 2014, both on the L2C and L5 signals. Compared to the Legacy Navigation Message (LNAV), the CNAV message provides six additional parameters (two orbit parameters and four Inter-Signal Correction (ISC) parameters) for prospective civil users. Using the precise products of the International Global Navigation Satellite System Service (IGS), we evaluate the precision of satellite orbit, clock and ISCs of the CNAV. Additionally, the contribution of the six new parameters to GPS Single Point Positioning (SPP) is analysed using data from 22 selected Multi-Global Navigation Satellite System Experiment (MGEX) stations from a 30-day period. The results indicate that the CNAV/LNAV Signal-In-Space Range Error (SISRE) and orbit-only SISRE from January 2016 to March 2018 is of 0·5 m and 0·3 m respectively, which is improved in comparison with the results from an earlier period. The ISC precision of L1 Coarse/Acquisition (C/A) is better than 0·1 ns, and those of L2C and L5Q5 are about 0·4 ns. Remarkably, ISC correction has little effect on the single-frequency SPP for GPS users using civil signals (for example, L1C, L2C), whereas dual-frequency SPP with the consideration of ISCs results have an accuracy improvement of 18·6%, which is comparable with positioning accuracy based on an ionosphere-free combination of the L1P (Y) and L2P (Y) signals. [ABSTRACT FROM AUTHOR]

The Korean government has a plan to build a new regional satellite navigation system called the Korean Positioning System (KPS). The initial KPS constellation is designed to consist of seven satellites, which include three geostationary Earth orbit (GEO) satellites and four inclined geosynchronous orbit (IGSO) satellites. KPS will provide an independent positioning, navigation, and timing (PNT) service in the Asia-Oceania region and can also be compatible with GPS. In the simulation for KPS, we employ 24 GPS as designed initially and 7 KPS satellites. Compared to the true orbit that we simulated, the averaged root mean square (RMS) values of orbit-only signal-in-space ranging errors (SISRE) are approximately 4.3 and 3.9 cm for KPS GEO and IGSO. Two different positioning solutions are analyzed to demonstrate the KPS performance. KPS standard point positioning (SPP) errors in the service area are about 4.7, 3.9, and 7.1 m for east (E), north (N), and up (U) components, respectively. The combined KPS+GPS SPP accuracy can be improved by 25.0%, 31.8%, and 35.0% compared to GPS in E, N, and U components. The averaged position errors for KPS kinematic precise point positioning (KPPP) are less than 10 cm. In the fringe of the KPS service area, however, the position RMS errors can reach about 40 cm. Unlike KPS, GPS solutions show high positioning accuracy in the KPS service area. The combined KPS+GPS can be improved by 28.7%, 27.1%, and 30.5% compared to GPS in E, N, and U components, respectively. It is noted that KPS can provide better performance with GPS in the Asia-Oceania region.

The positioning accuracy of global and regional navigation satellite systems (GNSS/RNSS) depends on a variety of influence factors. For constellation-specific performance analyses it has become common practice to separate a geometry-related quality factor (the dilution of precision, DOP) from the measurement and modeling errors of the individual ranging measurements (known as user equivalent range error, UERE). The latter is further divided into user equipment errors and contributions related to the space and control segment. The present study reviews the fundamental concepts and underlying assumptions of signal-in-space range error (SISRE) analyses and presents a harmonized framework for multi-GNSS performance monitoring based on the comparison of broadcast and precise ephemerides. The implications of inconsistent geometric reference points, non-common time systems, and signal-specific range biases are analyzed, and strategies for coping with these issues in the definition and computation of SIS range errors are developed. The presented concepts are, furthermore, applied to current navigation satellite systems, and representative results are presented along with a discussion of constellation-specific problems in their determination. Based on data for the January to December 2017 time frame, representative global average root-mean-square (RMS) SISRE values of 0.2 m, 0.6 m, 1 m, and 2 m are obtained for Galileo, GPS, BeiDou-2, and GLONASS, respectively. Roughly two times larger values apply for the corresponding 95th-percentile values. Overall, the study contributes to a better understanding and harmonization of multi-GNSS SISRE analyses and their use as key performance indicators for the various constellations. [ABSTRACT FROM AUTHOR]

The GPS Directorate initiated a pre-operational routine generation and transmission of the Civil Navigation Message (CNAV) starting on 28 April 2014. CNAV data of the Block IIR-M and IIF satellites have been collected with a small set of globally distributed receivers. Starting in 2015, CNAV uploads are performed on a daily basis. Since then, the Signal-in-Space Range Error (SISRE) amounts to roughly 0.6 m, which is essentially identical to the LNAV SISRE for the same satellites. The new broadcast Inter-Signal Corrections (ISCs) agree with differential code biases derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1-2 ns level depending on the ISC type. Use of these ISCs enables, for the first time, a consistent point positioning based on the exclusive use of civil L1C/A and L2C observations. Copyright © 2015 Institute of Navigation [ABSTRACT FROM AUTHOR]

A consistent analysis of signal-in-space ranging errors (SISREs) is presented for all current satellite navigation systems, considering both global average values and worst-user-location statistics. The analysis is based on 1 year of broadcast ephemeris messages of the Global Positioning System (GPS), GLONASS, Galileo, BeiDou and QZSS collected with a near-global receiver network. Position and clock values derived from the navigation data are compared against precise orbit and clock products provided by the International GNSS Service and its multi-GNSS experiment. Satellite laser ranging measurements are used for a complementary and independent assessment of the orbit-only SISRE contribution. The need for proper consideration of antenna offsets is highlighted and block-/constellation-specific radial antenna offset values for the center-of-mass correction of broadcast orbits are derived. Likewise, the need for application of differential code biases in the comparison of broadcast and precise clock products is emphasized. For GPS, the analysis of the legacy navigation message is complemented by a discussion of the CNAV message performance based on the first CNAV test campaign in June 2013. Global average SISRE values for the individual constellations amount to 0.7 ± 0.02 m (GPS), 1.5 ± 0.1 m (BeiDou), 1.6 ± 0.3 m (Galileo), 1.9 ± 0.1 m (GLONASS), and 0.6 ± 0.2 m (QZSS) over a 12-month period in 2013/2014. [ABSTRACT FROM AUTHOR]

The computation of a navigation satellite position and clockis a general task in GPS positioning, and the data needed for this task can be obtained from navigation messagesand IGS precise ephemerides.This study analyzesbroadcast orbit and clock error variations by comparing them with IGS precise ephemerides. Orbit and clock errorsfrom 2001 to 2013 are computed for all GPS satellites as well as for the group of satellites visible inKorea. Orbit and clock errors versus GPS satellite typesare also analyzed. Correlationswith shadow conditions, solar activity, and geomagnetic activityare analyzed.Clock errors and signal-in-spacerange errorsare reduced with the new generation of GPS satellites. The correlations show thatorbit errors increase by 3.2% in shadows.Solar activity and orbit errorhave a high correlation until 2008,but have a low correlation after 2009. [ABSTRACT FROM AUTHOR]

Focusing on the global integrity monitoring performance of the BDS-3, the integrity failure model and effect analysis (IFMEA) of the system space segment and the ground control segment were carried out, and the system integrity risk tree model was established according to the IFMEA results. To evaluate the system's integrity risk probability more reasonably, this paper establishes an abnormal event prediction model with a Bayesian method, based on actual operation data, under a situation in which the BDS-3 just opened service. With statistical analysis results of system anomalies since 27 December 2018—which is the date the BDS-3 began providing basic service—according to the anomaly prediction model, the system's integrity risk probability under the 95% confidence limit was calculated to be approximately 0.9e-7/h, meeting the design index requirements of 1e-7/h. The analysis results also show that the main risk factors affecting the integrity of BDS-3 are 'pseudorange measurement anomaly' and 'miss-detection of satellite autonomous integrity monitoring'. The results are important references with practical engineering significance for improving the integrity performance of BDS-3. [ABSTRACT FROM AUTHOR]

The Korean government has a plan to build a new regional satellite navigation system called the Korean Positioning System (KPS). The initial KPS constellation is designed to consist of seven satellites, which include three geostationary Earth orbit (GEO) satellites and four inclined geosynchronous orbit (IGSO) satellites. KPS will provide an independent positioning, navigation, and timing (PNT) service in the Asia-Oceania region and can also be compatible with GPS. In the simulation for KPS, we employ 24 GPS as designed initially and 7 KPS satellites. Compared to the true orbit that we simulated, the averaged root mean square (RMS) values of orbit-only signal-in-space ranging errors (SISRE) are approximately 4.3 and 3.9 cm for KPS GEO and IGSO. Two different positioning solutions are analyzed to demonstrate the KPS performance. KPS standard point positioning (SPP) errors in the service area are about 4.7, 3.9, and 7.1 m for east (E), north (N), and up (U) components, respectively. The combined KPS+GPS SPP accuracy can be improved by 25.0%, 31.8%, and 35.0% compared to GPS in E, N, and U components. The averaged position errors for KPS kinematic precise point positioning (KPPP) are less than 10 cm. In the fringe of the KPS service area, however, the position RMS errors can reach about 40 cm. Unlike KPS, GPS solutions show high positioning accuracy in the KPS service area. The combined KPS+GPS can be improved by 28.7%, 27.1%, and 30.5% compared to GPS in E, N, and U components, respectively. It is noted that KPS can provide better performance with GPS in the Asia-Oceania region. [ABSTRACT FROM AUTHOR]