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The precise point positioning (PPP) technique, which is still being developed, provides position accuracy at the centimetre (cm) level and is widely employed in scientific research. In the PPP technique, cm-level accuracy can be achieved by evaluating raw data obtained from a single Global Navigation Satellite Systems (GNSS) receiver using precise satellite orbit and clock correction data and other parameters. The majority of studies in the literature are based on 24-hour data obtained from the International GNSS Service (IGS) and similar stations. However, there are fewer articles in which analyzes based on short-term measurements are taken. In this study; the effect of GLONASS on the static PPP technique was investigated with independent short measurement times. For this purpose, measurements were made at 7 different test points on consecutive days using a single GNSS receiver. A 4-hour static measurement was made at each test point. The data obtained were processed in two different scenarios, only GPS and GPS + GLONASS using the Canadian Spatial Reference System – PPP (CSRS-PPP) and Trimble RTX online process software. The processes were completed at 4, 2, 1, and 0.5 h. As a result of the analysis, it has been observed that GLONASS improves the results by 76%, but negatively affects some solutions (24%). It was also observed that GLONASS drastically reduced the outlier values. With this study, it is aimed to show the accuracy that users who make short-term measurements with a single GNSS receiver can be achieved in the static PPP technique by using GPS + GLONASS systems, with repeated measurements. [ABSTRACT FROM AUTHOR]

To improve the efficiency of estimation of deriving OTLD parameters with higher accuracy and take full advantage of multi-GNSS data, we investigate the potential of using global ocean tide model predictions as prior constraint for GLONASS and combined GPS+GLONASS kinematic precise point positioning (PPP), analyzing one year of GPS and GLONASS data from 20 Crustal Movement Observation Network China (CMONC) sites distributed along China coast. Seven global ocean tide models predictions are employed as prior constraint in kinematic PPP. Compared with the results of GPS-only kinematic PPP with priori information constraint, the result shows that GPS+GLONASS and GLONASS can improve the accuracy of OTLD estimates more than 40% in three components over GPS. The comparison of the effect of OTLD estimates on long-period signals in position time series shows that the correction effect of the kinematic PPP with seven different priori information constraint estimates is all as same as the reference model in three components. [ABSTRACT FROM AUTHOR]

In this study, the latest contribution of the BeiDou-3 FOC satellites to GPS/GLONASS/Galileo/BDS-2 combined static and kinematic precise point positioning (PPP) is investigated over a one-month period in 2021 considering the three different cut-off angles (7°, 15°, and 30°). The results show that the contribution of BDS-3 to GPS/GLONASS/Galileo PPP is generally marginal for 7° and 15° cut-off angles. The largest BeiDou-3 contributions to static and kinematic positioning accuracy are found to be 9%, 6%, and 19% (for 3-h sessions with the 15° cut-off angle) and 9%, 15%, and 8% (with the 30° cut-off angle) for the north, east, and up components, respectively. The largest reductions in static and kinematic convergence time by adding BDS-3 to GPS/GLONASS/Galileo are found to be 13%, 10%, and 6% (for the 30° cut-off angle) and 17%, 7%, and 6% (for the 30° cut-off angle) for the north, east, and up components, respectively. [ABSTRACT FROM AUTHOR]

In the middle of 2011, Trimble introduced the RTX correction service to support RT-PPP applications. In this study, the performance of Trimble RTX correction service is investigated over a one-month period using five different GNSS constellations – namely, GPS-only, GPS + GLONASS, GPS + Galileo, GPS + GLONASS + Galileo, and GPS + GLONASS + Galileo + BeiDou. The results show that positioning accuracy and convergence time are significantly improved with the use of the multi-GNSS constellation compared with the GPS-only solution. The result of the converged positioning accuracy indicates that the GPS + GLONASS + Galileo + BeiDou combination improves the accuracy by 63%, 54%, and 60% for north, east, and up components, respectively, compared with the GPS-only solution. The mean convergence time is reduced by the GPS + GLONASS+ Galileo + BeiDou combination by 70%, 71%, and 38.6% compared with the GPS-only solution in the north, east, and up components, respectively. 1.2 (north), 1.5 (east), and 2.3 cm (up) root mean square errors (RMSEs) of converged positioning from the GPS + GLONASS + Galileo + BeiDou combination are computed. [ABSTRACT FROM AUTHOR]

Ocean Tide Loading Displacement (OTLD) parameters, derived by Global Positioning System (GPS) approach, need more time to converge to a stable state and show poor precision of K1 and K2 constituents. Combining multi-system Global Navigation Satellite System (GNSS) data can greatly improve the positioning accuracy and significantly reduce the convergence time compared to single GPS PPP, combined GPS+GLONASS with ambiguity resolved in kinematic Precise Point Positioning (PPP) is improved on the basis of the algorithm of GPS kinematic PPP. We collected eight years of continuous observations of 11 worldwide sites from International GNSS Service to generate three dimensional OTLD parameters of eight constituents using GPS with ambiguity fixed, GLONASS with ambiguity free and combined GPS+GLONASS with ambiguity fixed kinematic PPP approach. The results show the eight constituents derived by GPS_FX and GPS+GLONASS_FX solution need four years and three years to converge to stable values, respectively. GLONASS can significantly improve the convergence rate of K1 and K2 constituents which needs only two years to converge to stable values, and S2 and P1 constituents which need three years to stable values. The results also show the GPS+GLONASS/reference misfits are the smallest for the most constituents in three components (less than 2mm) except for K2 and K1 in vertical and north directions. GLONASS can improve more than 40% in vertical and north components over GPS and GPS+GLONASS for K2 and K1 constituents and show very close agreement with GPS_FX solution in vertical and north component for S2 and P1 constituents. Ambiguity resolved in OTLD estimation can significantly accelerate the convergence and improve the accuracy for eight constituents, especially for combined GPS+GLONASS kinematic PPP mode, but no single constellation mode solution for all eight major constituents exists. [ABSTRACT FROM AUTHOR]

The performance of precise point positioning (PPP) mainly depends on satellite orbit and clock accuracy. Ultra-rapid and rapid orbit/clock products have been creating by analysis centres (ACs) for time-critical applications. In this paper, GPS-, GLONASS-, Galileo-, and BeiDou (BDS-2)-only PPP with ultra-rapid and rapid products from seven ACs (i.e. CODE, ESA, IGS, GFZ, JPL, NRCan, and WUHAN) are investigated for PPP performance. A two-month period in 2020 was chosen for conducting static and kinematic PPP using data from 32 Multi-GNSS Experiment (MGEX) stations. For GPS-only PPP with different ACs, GFZ/NRCan and CODE/NRCan rank first for ultra-rapid and rapid PPP processes, respectively. For GLONASS-only PPP, positioning performances using ultra-rapid products are comparable with each other except for CODE and ESA products. CODE rapid product ranks last for GLONASS-only PPP. For Galileo and BeiDou-only PPP, GFZ AC performs the best for ultra-rapid processes. For Galileo-only PPP using rapid products, CODE ranks first. [ABSTRACT FROM AUTHOR]

Development of navigation satellites systems as GPS, GLONASS, Galileo and Beidou has increased the accuracy and reliability. On the other hand, by employing more satellites, the receivers' computational load increases, and their power consumption rises. Therefore, the selection of optimum satellites from the visible satellites can provide good accuracy. At the same time, the computational burden does not increase significantly. A new algorithm for optimal satellite selection is proposed in this paper. This algorithm is based on a down-top recursive that initial combination of satellites is obtained in a simple method, and then a satellite from the remaining satellites with a special GDOP-based metric is added to this subset. In the next step, a satellite is removed from this new combination with another specific criterion. The process of increasing and decreasing the number of satellites will continue for a certain number of repetitions, and eventually the optimal combination of satellites is achieved. The computational load of this method has been decreased by two factors. One is the reduction of the number of repetitive loops to achieve an optimal subset, and the other is the selection of initial combination with fewer satellites. This method in some cases improves accuracy compared to previous methods. This new approach is evaluated via collected data from four stations. The results indicate that this new algorithm can reduce the number of multiplication and addition operations more than Top-Down recursive method by 20% and 56%, respectively. [ABSTRACT FROM AUTHOR]

Urban-canyon positioning encounters many problems such as successive attenuation and even blocking of the signals. Vectorised receiver is a solution in which stronger signals aid weak and blocked ones to be tracked and reacquired. On the other hand, limited accessibility to the sky makes trouble in the performance of navigation filter. As the result, integration of satellite-based positioning systems is suggested to increase the number of visible satellites in the receiver view. In this paper, the architecture of an implemented GPS-combined-GLONASS Vectorised Receiver (GGVR) in a software platform is explored and its advantages rather than a GPS-only Vectorised Receiver (GVR) are demonstrated analytically. Experimental tests in different static and dynamic scenarios are also included. The results show that in the urban-canyon trajectory where the GVR has only 80% availability, the GGVR positioning solution is 100% available in the whole movement duration. [ABSTRACT FROM AUTHOR]

We develop new single-frequency PPP models, which combine the observations of the current GNSS constellations, including GPS, GLONASS, Galileo and BeiDou. Four single-frequency GNSS PPP models are developed, namely, the undifferenced single-frequency GNSS PPP model, the undifferenced ionosphere-free (IF) code and phase model known as quasi-phase model, the between-satellite-single-difference model (BSSD) and the between-satellite-single-difference ionosphere-free (BSSDIF) model. The IGS final precise products are used to account for the orbital and clock errors. For both undifferenced and BSSD models, the IGS final global ionospheric maps (GIM) model is used to correct the ionospheric delay. The GNSS inter-system biases are treated as additional unknowns in the estimation process for the undifferenced models, while a loosely coupled technique is used for the BSSD models. Various GNSS combinations are considered in the assessment for each PPP model, including GPS/GLONASS, GPS/Galileo, GPS/BeiDou and quad-constellation GNSS observations. It is shown that the multi-GNSS observations enhance the PPP solution accuracy in comparison with the GPS-only solution. Furthermore, the use of IF-PPP technique enhances the positioning accuracy by 25, 20, 24, 20 and 19% compared with the GIM-based PPP model for the GPS-only, GPS/GLONASS, GPS/Galileo, GPS/BeiDou and quad-GNSS combinations, respectively, for 1 h of GNSS data processing. In addition, an average of 15% positioning accuracy improvement can be obtained when the BSSD techniques are used compared with the undifferenced techniques. However, for 6 h of processing, comparable positioning accuracy can be obtained from all four single-frequency models. [ABSTRACT FROM AUTHOR]

The single point positioning (SPP) mode has been widely used in many fields such as vehicle navigation, Geographic Information System and land surveying. For a long period, the SPP technology mainly relies on GPS system. With the recent revitalisation of the GLONASS constellation and two newly emerging constellations of BeiDou and Galileo, it is now feasible to investigate the performance of quad-constellation integrated SPP (QISPP) with GPS, GLONASS, BeiDou and Galileo measurements. As a satellite-based positioning technology, the QISPP is expected to improve the accuracy and availability of positioning solutions due to the increased number of visible satellites and the improved satellite sky distribution. In this study, a QISPP model is presented to simultaneously process observations from all four Global Navigation Satellite System (GNSS) constellations. Datasets collected at 47 globally distributed Multi-GNSS Experiment (MGEX) stations on two consecutive days and a kinematic experimental dataset are employed to fully assess the QISPP performance in terms of positioning accuracy and availability. Given that most navigation users are using single-frequency receivers, only the observations on a single frequency are utilised. The results indicate that the QISPP improves the positioning accuracy by an average of 16, 13 and 12% using the MGEX datasets, and 43, 31 and 51% using the kinematic experimental dataset over the GPS-only case in the east, north and up components, respectively. The availability of the QISPP solutions remains 100% even for a mask elevation angle of 40°, whereas it is only 37% for the GPS-only case. All these results are achieved using geodetic-type receivers and they are possibly optimistic for users who use navigation-type receivers. [ABSTRACT FROM PUBLISHER]

Multi-Global Navigation Satellite System (GNSS) integration can effectively improve the satellite geometry strength, and certain effect on the precise point positioning (PPP) accuracy and convergence speed. Taking the system difference into account, this paper deduces the unified GNSS observation model, which is extended to the multi-GNSS PPP functional model. Meanwhile, the stochastic model used in Kalman filter parameter estimation is presented in the paper. Furthermore, to evaluate the performance of the multi-GNSS PPP in Asia-Pacific region, observed data from the International GNSS Service reference stations are analysed using the self-developed software. In detail, the results from Global Positioning System (GPS)-, GLObal NAvigation Satellite System (GLONASS)- and BeiDou Navigation Satellite System (BDS)-only PPP, double combined PPP and GPS/GLONASS/BDS combined PPP under the different observation duration and cut-off elevation angles are analysed. Results demonstrate: (1) compared with the single system PPP, the convergence speed of the multi-GNSS PPP is improved while the accuracy is not significantly improved after processing the 24-h data set; (2) when the observation duration is short, such as 0.5 h, the mean convergence percentage of the BDS combined with GPS and GLONASS PPP increases by an average of 49.6% compared with the single individual systems except for BDS, respectively, under the cut-off angle of 5° and (3) when PPP positioning with high cut-off elevation angles, and at the point of centimetre-level positioning, the GPS/GLONASS/BDS combined PPP has a better performance on the convergence percentage and convergence speed. For example, the percentages of the position biases within 0–5 cm for GPS/GLONASS/BDS are increased by 7.2 and 4.5% in North and East direction compared with GPS/GLONASS under the cut-off angle of 35°, more than any other. And the mean convergence time is only 14.5 min. [ABSTRACT FROM PUBLISHER]

We developed a new GNSS PPP model, which combines the observations of GPS, GLONASS, Galileo and BeiDou satellite navigation systems for precise applications. Both undifferenced and between-satellite single-difference (BSSD) ionosphere-free GNSS PPP models are developed. The contribution of the new GNSS observations is assessed compared with the existing GPS and GPS/GLONASS PPP using three-hours GNSS static data positioning results for several GNSS stations and four consecutive days. Inter-system biases between GPS and other GNSS systems are obtained as additional unknowns in the developed PPP filter. The results indicate that both GPS and GPS/Galileo PPP present comparable positioning accuracy level, which is attributed to the limited number of Galileo satellites. The additional BeiDou observations enhances the positioning accuracy after 15 minutes by 5 cm, 4 cm and 9 cm in latitude, longitude and altitude, respectively compared with GPS only positioning accuracy. However, the BeiDou only PPP results present less accurate positioning accuracy compared with the GPS only PPP. The multi-constellation GNSS PPP enhances the positioning accuracy by 8 cm, 6 cm and 11 cm in latitude, longitude and altitude, respectively Compared with the GPS PPP results. Compared with the undifferenced PPP results, the BSSD model enhances the positioning accuracy after 15 minutes for the different GNSS constellations based PPP. The GPS/Galileo PPP positioning accuracy improves by 30%, 27% and 10% in latitude, longitude and altitude, respectively and the GPS/BeiDou PPP positioning accuracy, enhances by 17%, 22% and 15% in latitude, longitude and altitude, respectively while the multi-constellation GNSS PPP positioning accuracy improves by 22% and 15% in latitude and altitude, respectively over the undifferenced PPP technique. Additionally, the BSSD model is found to be superior with respect to the convergence times for the different GNSS combinations based PPP over the traditional undifferenced PPP model. [ABSTRACT FROM PUBLISHER]

With the rapid development of BeiDou system (BDS) and steady progress of Galileo system, the current GNSS (Global Navigation Satellite System) constellations consist of GPS, GLONASS, BeiDou and Galileo. The real signals from the four constellations have been available, which allows us to analyse and compare their measurement noises and multipath effects. In this study, a zero-baseline test is conducted using two ‘Trimble NetR9’ receivers to assess and compare the noises and multipath of measurements on multiple frequencies from the four satellite systems. The zero-baseline double difference approach is utilised to analyse the receiver noises. The code multipath combination and triple-frequency carrier phase combination approaches are exploited to analyse a comprehensive effect of the multipath and noises on the code and carrier phase measurements, respectively. Based on the analysis of the zero-baseline dataset, the results indicate that the code measurement noise levels range from 5 to 25 cm while the carrier phase noise levels vary within 0.9–1.5 mm for different frequencies and constellations. The code multipath and noise (CMN) level for GLONASS is the largest with a root mean square (RMS) value of 39 cm on both G1 and G2 frequencies whereas the Galileo code measurements exhibit a smallest level on the E5 frequency with a RMS value of only 10 cm. The RMS of the carrier phase multipath and noises (PMN) ranges from 1.3 to 2.6 mm for BeiDou and Galileo satellites. By contrast, the triple-frequency carrier phase combinations from the GPS Block IIF satellites demonstrate a much larger RMS value of 5.6 mm owing to an effect of inter-frequency clock biases. [ABSTRACT FROM PUBLISHER]