An assessment of smartphone and low-cost multi-GNSS single-frequency RTK positioning for low, medium and high ionospheric disturbance periods

The emerging GNSSs make single-frequency (SF) RTK positioning possible. In this contribution two different types of low-cost (few hundred USDs) RTK receivers are analyzed, which can track L1 GPS, B1 BDS, E1 Galileo and L1 QZSS, or any combinations thereof, for a location in Dunedin, New Zealand. These SF RTK receivers can potentially give competitive ambiguity resolution and positioning performance to that of more expensive (thousands USDs) dual-frequency (DF) GPS receivers. A smartphone implementation of one of these SF receiver types is also evaluated. The least-squares variance component estimation (LS-VCE) procedure is first used to formulate a realistic stochastic model, which assures that our receivers at hand can achieve the best possible ambiguity resolution and RTK positioning performance. The best performing low-cost SF RTK receiver types are then assessed against DF GPS receivers and survey-grade antennas. Real data with ionospheric disturbances at low, medium and high levels are analyzed, while making use of the ionosphere-weighted model. It will be demonstrated that when the presence of the residual ionospheric delays increases, instantaneous RTK positioning is not possible for any of the receivers, and a multi-epoch model is necessary to use. It is finally shown that the low-cost SF RTK performance can remain competitive to that of more expensive DF GPS receivers even when the ionospheric disturbance level reaches a Kp-index of 7-, i.e. for a strong geomagnetic storm, for the baseline at hand

Low-cost, high-precision, single-frequency GPS–BDS RTK positioning

The integration of the Chinese BDS with other systems, such as the American GPS, makes precise RTK positioning possible with low-cost receivers. We investigate the performance of low-cost ublox receivers, which cost a few hundred USDs, while making use of L1 GPS + B1 BDS data in Dunedin, New Zealand. Comparisons will be made to L1 + L2 GPS and survey-grade receivers which cost several thousand USDs. The least-squares variance component estimation procedure is used to determine the code and phase variances and covariances of the receivers and thus formulate a realistic stochastic model. Otherwise, the ambiguity resolution and hence positioning performance would deteriorate. For the same reasons, the existence of receiver-induced time correlation is also investigated. The low-cost RTK performance is then evaluated by formal and empirical ambiguity success rates and positioning precisions. It will be shown that the code and phase precision of the low-cost receivers can be significantly improved by using survey-grade antennas, since they have better signal reception and multipath suppression abilities in comparison with low-cost patch antennas. It will also be demonstrated that the low-cost receivers can achieve competitive ambiguity resolution and positioning performance to survey-grade dual-frequency GPS receivers

PPP-RTK and inter-system biases: the ISB look-up table as a means to support multi-system PPP-RTK

PPP-RTK has the potential of benefiting enormously from the integration of multiple GNSS/RNSS systems. However, since unaccounted inter-system biases (ISBs) have a direct impact on the integer ambiguity resolution performance, the PPP-RTK network and user models need to be flexible enough to accommodate the occurrence of system-specific receiver biases. In this contribution we present such undifferenced, multi-system PPP-RTK full-rank models for both network and users. By an application of (Formula presented.)-system theory, the multi-system estimable parameters are presented, thereby identifying how each of the three PPP-RTK components are affected by the presence of the system-specific biases. As a result different scenarios are described of how these biases can be taken into account. To have users benefit the most, we propose the construction of an ISB look-up table. It allows users to search the table for a network receiver of their own type and select the corresponding ISBs, thus effectively realizing their own ISB-corrected user model. By applying such corrections, the user model is strengthened and the number of integer-estimable user ambiguities is maximized

IRNSS/NavIC and GPS: a single- and dual-system L5 analysis

The Indian Regional Navigation Satellite System (IRNSS) has recently (May 2016) become fully operational. In this contribution, for the fully operational IRNSS as a stand-alone system and also in combination with GPS, we provide a first assessment of L5 integer ambiguity resolution and positioning performance. While our empirical analyses are based on the data collected by two JAVAD receivers at Curtin University, Perth, Australia, our formal analyses are carried out for various onshore locations within the IRNSS service area. We study the noise characteristics (carrier-to-noise density, measurement precision, time correlation), the integer ambiguity resolution performance (success rates and ambiguity dilution of precision), and the positioning performance (ambiguity float and ambiguity fixed). The results show that our empirical outcomes are consistent with their formal counterparts and that the GPS L5-data have a lower noise level than that of IRNSS L5-data, particularly in case of the code data. The underlying model in our assessments varies from stand-alone IRNSS (L5) to IRNSS (Formula presented.) GPS (L5), from unconstrained to height-constrained and from kinematic to static. Significant improvements in ambiguity resolution and positioning performance are achievable upon integrating L5-data of IRNSS with GPS

On the performance of a low-cost single-frequency GPS+BDS RTK positioning model

© 2017, Institute of Navigation. All rights reserved.When the GPS was the only satellite constellation in orbit, instantaneous single-frequency precise (millimeter-level) positioning was not possible and more expensive survey-grade multiple-frequency receivers had to be used. With the advent of the GNSSs, such as the Chinese BDS, low-cost receiver precise positioning will potentially become feasible. In this contribution we investigate the performance of such a low-cost single-frequency GPS+BDS model, making use of ublox EVK-M8T receivers, and compare its performance to a survey-grade dual-frequency GPS receiver solution, in Dunedin New Zealand. The least-squares variance-component estimation (LS-VCE) procedure is used to investigate the precision of the receiver code and phase observables of the low-cost receivers. The estimated (co)variances are needed so as to formulate a realistic stochastic model for precise RTK positioning. The performance of ambiguity resolution would otherwise deteriorate and hence the achievable positioning precisions as well. The low-cost RTK performance is then evaluated by formal and empirical ambiguity success-rates and positioning precisions. Our results indicate that the quality of the antennas used plays an important role, especially in suppressing multipath. We will demonstrate that the low-cost solution, which costs a few hundred USDs, can give a competitive ambiguity resolution and positioning performance to the survey-grade receivers, which cost several thousand USDs

Single-frequency, dual-GNSS versus dual-frequency, single-GNSS: a low-cost and high-grade receivers GPS-BDS RTK analysis

The concept of single-frequency, dual-system (SF-DS) real-time kinematic (RTK) positioning has become feasible since, for instance, the Chinese BeiDou Navigation Satellite System (BDS) has become operational in the Asia-Pacific region. The goal of the present contribution is to investigate the single-epoch RTK performance of such a dual-system and compare it to a dual-frequency, single-system (DF-SS). As the SF-DS we investigate the L1 GPS + B1 BDS model, and for DF-SS we take L1, L2 GPS and B1, B2 BDS, respectively. Two different locations in the Asia-Pacific region are analysed with varying visibility of the BDS constellation, namely Perth in Australia and Dunedin in New Zealand. To emphasize the benefits of such a model we also look into using low-cost ublox single-frequency receivers and compare such SF-DS RTK performance to that of a DF-SS, based on much more expensive survey-grade receivers. In this contribution a formal and empirical analysis is given. It will be shown that with the SF-DS higher elevation cut-off angles than the conventional 10∘ or 15∘ can be used. The experiment with low-cost receivers for the SF-DS reveals (for the first time) that it has the potential to achieve comparable ambiguity resolution performance to that of a DF-SS (L1, L2 GPS), based on the survey-grade receivers

Combined GPS+BDS+Galileo+QZSS for long baseline RTK positioning

In this contribution we will focus on long single-baseline real-time kinematic (RTK) positioning when combining the American GPS, Chinese BDS, European Galileo and Japanese QZSS. The main objective is to demonstrate the potential benefits for RTK when combining the next generation GNSSs, as compared to using the systems separately. With long baseline we refer to the necessity to model the slant ionospheric delays by the ionosphere- float strategy. The (wet) Zenith Tropospheric Delay (ZTD) will be estimated as well. The ionosphere-float model implies that the slant ionospheric delays are assumed completely unknown. We will focus on overlapping frequencies between the systems. The advantage with overlapping frequencies is that the redundancy of the model can be maximized if the inter-system biases (ISBs) can be calibrated. This also allows for a common pivot satellite between the systems when parameterizing the double-differenced integer ambiguities. It will be shown that with the ionosphere-float model at least two overlapping frequencies between the systems are required to benefit from calibration of ISBs. The GNSS real data is collected in Perth Australia, a country where the multi-system satellite visibility is almost at a global maximum. The single-baseline RTK performance is evaluated by a formal and empirical analysis, consisting of ambiguity dilution of precision (ADOP), bootstrapped success rates and positioning precisions. It will be shown that the combination of the four systems provides for shorter ambiguity/positioning convergence times, improved integer ambiguity resolution and positioning performance over the single-, dual- and triple-systems

Improving GNSS PPP‑RTK through global forecast system zenith wet delay augmentation

202401 bckwVersion of RecordRGCOthersNational Natural Science Foundation of ChinaPublishedCUP (2024)T

An analysis of combined COMPASS/BeiDou-2 and GPS single- and multiple-frequency RTK positioning

The COMPASS/BeiDou-2 Navigation Satellite System from China has attained regional operational status and is expected to reach the same level of popularity as GPS one it has reached its full constellation. Already now Australia is a beneficiary of the regional COMPASS configuration as enough satellites are available to perform Positioning, Navigation and Timing (PNT). This contribution considers combined COMPASS-GPS single point positioning (SPP), relative code positioning and single- and multiple-frequency single-baseline RTK, in Western Australia, Perth. A combined system increases the redundancy and thus allows for more precise position estimates, improved reliability and robustness against failure of any of the systems. We will compare its performance with that of COMPASS- and GPS-only. For single-baseline RTK, we focus our attention on single-epoch ambiguity resolution with the advantage that the system becomes independent of cycle slips. The performance is evaluated by ambiguity success-rates and by comparing the estimated positions to very precise benchmark coordinates. We make use of the LAMBDA method for integer ambiguity resolution, in combination with the Fixed Failure-rate Ratio Test to validate the resolved ambiguities. It will be shown that the increased strength of the combined model allows for improved ambiguity resolution performance and increased positioning robustness and accuracy over the COMPASS- and GPS-only solutions