Satellite Based Augmentation System Research Articles

Performance Evaluation and Application Field Analysis of Precise Point Positioning Based on Different Real-Time Augmentation Information

The most commonly used real-time augmentation services in China are the International GNSS Service’s (IGS) real-time service (RTS), PPP-B2b service, and Double-Frequency Multi-Constellation (DFMC) service of the BeiDou Satellite-Based Augmentation System (BDSBAS) service. However, research on the performance evaluation, comparison, and application scope of these three products is still incomplete. This article introduces methods for obtaining real-time augmentation information and real-time orbit and clock offset recovery. Based on real-time orbit and clock offset accuracy, positioning accuracy, and positioning availability, this article systematically evaluates the performance and analyzes the application fields of Centre National d’Études Spatiales (CNES), PPP-B2b, and BDSBAS augmentation information. The results of the evaluation revealed that the radial accuracy of the CNES and PPP-B2b real-time orbit product is consistent, and the Root Mean Square (RMS) is better than 5 cm. The CNES real-time orbit product can achieve centimeter-level accuracy in both along-track and cross-track components, surpassing PPP-B2b’s decimeter-level accuracy. Both services demonstrate consistent accuracy in the real-time clock offset, with PPP-B2b showing similar standard deviations (STDs) of 0.16 ns for different satellites. However, for CNES, the STD of the real-time clock offset varies, with values of 0.10 ns, 0.19 ns, and 0.60 ns, respectively, for GPS, BDS-3 Medium Earth Orbit (MEO), and BDS-3 Inclined Geosynchronous Satellite Orbit (IGSO) satellites. Centimeter-level accuracy is achieved after convergence and positioning availability exceeds 99% for CNES and PPP-B2b services. Therefore, the difference between the two services in application areas depends on the acquisition of augmentation information. However, BDSBAS, which concentrates on code observations, demonstrates inferior performance in real-time orbit, clock offset, positioning accuracy, and positioning availability when compared to the other two services. Its primary application is in the aviation and maritime domains, where there is a greater need for service integrity, continuity, and reliability.

Code-Carrier coherence monitoring for dual frequency SBAS

User differential range error (UDRE) is used to bound satellite clock and orbit errors in satellite-based augmentation system (SBAS). The code carrier incoherence (CCI) originated from satellite payload faults may degrade generated satellite corrections and corresponding UDRE/DFRE bounding. To ease the burden on UDRE caused by the CCI induced ranging error, a code carrier coherence (CCC) monitor is implemented. With SBAS evolving towards L1-L5 dual-frequency multi-constellation direction, ionosphere-free smoothing is preferred for both ground and airborne data processing, saving the great effort of bounding the ionosphere correction. Due to the more pronounced CCI fault in the L5 signal compared to the L1 signal, its impact on user positioning is magnified. It has been analyzed that the presence of satellite clock failure CCI fault does not undermine the accuracy of the generated satellite corrections. However, to enhance the system availability, the satellite clock failure should be considered and a dual-frequency CCC monitor is required to monitor the measurements from both frequencies, while excluding the effects of ionosphere delay. One solution is to add another L1-like monitor for monitoring the additional L5 signal. Since only ionosphere-free errors need to be bounded in the dual-frequency system, an ionosphere-free monitor is another choice. Furthermore, a chi-squared monitor is proposed combining of three ionosphere-free statistics to monitor both frequencies simultaneously. These options are compared on the protected fault space and the performance on the probability of missed detection. It is concluded that the chi-squared monitor is an optimal choice, which protects user against an arbitrary CCI fault space excluding the ones with the form of ionosphere anomalies, and at the same time, achieves lower probability of missed detection than other monitors with the same fault magnitude.

Local mitigation of higher-order ionospheric effects in DFMC SBAS and system performance evaluation

Dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) is a new SBAS standard for aeronautical navigation systems. It supports aircraft navigation from the enroute to approach phases via the L1 and L5 frequencies (1575.42 and 1176.45 MHz). Although the ionosphere-free (IF) combination in the DFMC SBAS operation removes the first-order ionospheric delays in the pseudorange measurement, remaining terms including the satellite-clock offset errors and higher-order ionospheric (HOI) delays are still unaccounted for. The DFMC SBAS accuracy and integrity can be affected by the HOI effects, especially during severe ionospheric disturbances. In this work, we present the local DFMC SBAS corrections with and without the mitigation of HOI delays. We first estimate the HOI delay terms using the received pseudorange followed by separate satellite and receiver bias estimations based on the minimum sum-variance technique. The integrity terms can then be obtained. The performances of DFMC SBAS using the global navigation satellite system (GNSS) data including GPS, Galileo, and QZSS are evaluated using obtained GNSS data at stations in Thailand on the ionospheric quiet and disturbed days. The results show that with the HOI mitigation, the vertical positioning errors (VPE) on the quiet and disturbed days can be improved by 12% and 9%, whereas the vertical protection levels (VPL) are improved by 16% and 21%, respectively. In addition, we perform a preliminary assessment of DFMC SBAS based on the International Civil Aviation Organization (ICAO) requirements of two categories: Localizer Performance with Vertical guidance (LPV-200) and Category I precision approach (CAT-I) showing promising results.

Implementation of GAGAN augmentation on smart mobile devices and development of a cooperative positioning architecture

Abstract This study presents an Android-based cooperative positioning (CP) architecture to improve the GNSS positioning performance on mobile devices. SBAS (Satellite Based Augmentation System) augmentation increases positioning accuracies significantly by sharing corrections between SBAS-enabled and non-capable devices via wireless connection or using a central server. The Indian GAGAN (GPS Aided GEO Augmented Navigation) is employed and assessed in the experiments. If GAGAN corrections are applied, all three chosen mobile devices showed a positioning accuracy improvement of around 95 %. The average 2D RSME was reduced from 75.23 to 1.35 m for the single-frequency GNSS smartphone Xiaomi Redmi Note 8 and from 33.25 to 1.62 m for the dual-frequency Google Pixel 4. As expected, the third GIS mapping device, Stonex S70 tablet, showed the highest performance, achieving sub-meter positioning accuracies. Thus, the experiment has proven the suitability of GAGAN augmentation for mobile devices, providing positive insight for further development of the CP architecture.

Enabling the Galileo high accuracy service with open-source software: integration of HASlib and RTKLIB

The Galileo high accuracy service (HAS) is a free-of-charge service designed to deliver decimeter-level accuracy in real-time precise point positioning (PPP) applications using global navigation satellite systems (GNSS). With the intention of facilitating the use of HAS corrections with open access tools, we present the open-source library named HASlib and its integration with another open-source library named RTKLIB. HASlib decodes the Reed–Solomon encoded Galileo E6 navigation data pages and outputs the corrections in commonly used formats. This enables the utilization of HAS with conventional GNSS receivers and PPP engines that lack native support for HAS formats. For instance, the outputs from HASlib enable the use of HAS corrections in RTKLIB. In order to validate this integration, we demonstrate that HAS can allow decimeter-level accuracy using only free-of-charge services and tools. We have obtained a 3D root mean square error below 20 cm (1 sigma) after a convergence time of 10–90 min in Finland. This accuracy has overcome classical real-time solutions with broadcast and satellite-based augmentation system (SBAS) data by one order of magnitude. Compared to post-processed multi-GNSS PPP, HAS corrections required longer convergence times, given the real-time nature. Furthermore, our assessment revealed that the longer convergence time, compared to prior literature, was attributed to RTKLIB filtering procedure and geometry deficiencies in high latitudes. Nevertheless, once convergence was attained, a sub-decimeter level of accuracy was observed in both horizontal and vertical components. These findings highlight the effectiveness of Galileo HAS, HASlib, and RTKLIB as powerful tools for providing open-access to real-time PPP solutions.

Satellite Navigation Message Authentication in GNSS: Research on Message Scheduler for SBAS L1.

SBAS is mainly used in civil aviation and navigation, and will be applied to autonomous driving in the future. Given the open signal format of the Satellite Based Augmentation System (SBAS), which exposes security threats such as spoofing attacks, the utilization of SBAS navigation message authentication technology can improve the SBAS anti-spoofing ability from the system side. SBAS message authentication technology has become the future direction of SBAS system development. However, during the initial design of SBAS on L1, message authentication technology was not considered, and the addition of authentication messages will lead to further strain on existing message bandwidth resources. Therefore, in response to the issue of insufficient bandwidth resources after adding authentication messages to SBAS L1, a study on message scheduler for SBAS L1 authentication was conducted. A fixed time sequence dynamic message scheduler for incorporating authentication messages was proposed. This scheduler reduces the frequency of broadcasting clock error parameters to mitigate the impact of adding authentication messages. Furthermore, an optimized fixed time sequence dynamic message scheduler based on SBAS clock error messages was introduced. The results show that the message scheduler can not only improve the flexibility of SBAS message broadcasting, but also shorten the update interval of various types of messages under the premise of meeting the maximum update interval requirement. With minimal impact on the maximum message update interval, it improves the integrity, authenticity, and availability of messages. This approach can increase the effective message ratio in SBAS to over 91%, and the optimal solution reduces the initial user positioning time to 26 s.

Developing an Algorithm to Improve Positioning Accuracy of Low-Cost Global Navigation Satellite System Modules

Global Navigation Satellite System (GNSS) technology is the most widely used technique for obtaining positioning and navigation information for various applications. However, GNSS is not an error free technology. Differential GNSS techniques are used to mitigate these errors and different commercial brands of GNSS receivers have been developed to avoid some errors where quality and performance depends heavily on the price tag of such advance GNSS receivers due to the fact that technological capabilities adopted and embedded in each single GNSS receiver. There are user cases where the few or more those capabilities has to keep leave behind thereby compromise the cost to benefit ratio. As an alternative to above problem, some low-cost GNSS modules are now available in the market which has quite low position accuracy but can be developed to address unique requirements of some user cases. In practical situations, Real-Time-Kinematic (RTK) positioning systems cannot be used everywhere due to its technical limitations and GNSS receivers use different levels of techniques such as moving baseline system or Satellite Based Augmentation System (SBAS). Further, heading information is also a very important parameter in marine industry for obtaining the vessel’s orientation. This research attempts to assess the capability of u-blox NEO M8N GNSS module for hydrographic surveys by developing a moving baseline GNSS configuration and simple Kalman filter based algorithm. The developed prototype was tested in both static and kinematic observations. The prototype achieved 0.5-2.5 meters of position accuracy at the 95% confidence level in static observations, while it archived around 3 meters of positioning accuracy in kinematic observations. This is a sufficient accuracy for Order 1a, Order 1b and Order 2 standards of hydrographic surveys according to the IHO S-44 guidelines.

GNSS positioning accuracy performance assessments on 1st and 2nd generation SBAS signals in Thailand

Abstract This research evaluates the performance of the first and second-generation satellite-based augmentation system (SBAS) GAGAN and BDSBAS services in Thailand. The study initially analyses GNSS observations from 40 local continuously operating reference stations (CORS) over the past 12 months in 2022, providing initial horizontal and vertical accuracies at 2.03 and 3.66 m respectively with the single point positioning (SPP) mode. The positioning accuracies are 2.27 m horizontally and 2.54 m vertically as of GAGAN, while 2.94 m horizontally and 3.90 m vertically as of BDSBAS with the first-generation system. Since the 1st generation SBAS performance is affected by the ionosphere, especially in the equatorial and auroral regions, the ionosphere-free combination is applied in the SPP algorithm as well as the 2nd generation SBAS with the Dual-Frequency Multi-Constellation (DFMC) capable receivers for BDSBAS only. The SPP accuracies are 1.51 m horizontally and 3.26 m vertically, where the BDSBAS results are 2.16 m horizontally and 4.28 m vertically. Demonstrated results show that the positioning accuracy cannot be improved significantly when applying the 1st generation GAGAN and BDSBAS systems and the 2nd generation BDSBAS system in Thailand due to the low number of common satellites available, especially when using the SBAS outside their ground tracking network; therefore, it is expected to apply the GNSS observation and computed satellite error correction from the regional ground tracking network to enhance the performance of the 2nd generation SBAS. The positioning accuracy result could be achieved at sub-metre level, which will greatly benefit high-accuracy applications such as air, land, and sea navigation in the region.

Potential of Satellite-Based Augmentation Systems (SBAS) in Test and Evaluation of Missiles in Indian Test Range Applications

Potential of Satellite-Based Augmentation Systems (SBAS) in Test and Evaluation of Missiles in Indian Test Range Applications

MLP-based user-applicable method for SBAS GIVD calibration: A comparative study based on CODE final GIM products

Satellite-Based Augmentation Systems (SBASs) are designed to enhance the performance of Global Navigation Satellite Systems (GNSSs) for civil aviation users. As SBAS Geostationary Earth Orbit (GEO) satellite signals are received in a wide area, far more non-aeronautical GNSS users utilize SBAS to improve navigation performance. Since ionospheric delay is the principal error source of GNSS and a leading correction aspect of SBAS, the GEO-broadcast ionospheric data quality of six SBASs over the past three years is assessed in this article. Results show that European Geostationary Navigation Overlay Service (EGNOS), System for Differential Correction and Monitoring (SDCM), and Wide-Area Augmentation System (WAAS) have the highest Grid Ionospheric Vertical Delay (GIVD) accuracy judged by the residual Standard Deviation (STD), then followed by BeiDou SBAS (BDSBAS) and Multi-functional Satellite Augmentation System (MSAS), while GPS-Aided GEO Augmented Navigation (GAGAN) is the worst. The 6 m Grid Ionospheric Vertical Error (GIVE) availability is over 90 percent of the time for most Ionospheric Grid Points (IGPs) of all tested SBASs. However, GAGAN and WAAS have a significant availability decline at 3 m GIVE. In addition, the integrity limits of MSAS and WAAS are fairly conservative. In contrast, the confidence bounds of BDSBAS and SDCM are excessively radical that fail to meet the integrity requirement. To improve the ionospheric data quality received from SBAS, a Multi-Layer Perceptron (MLP)-based user-applicable GIVD calibration method is proposed in the article. A well-trained MLP learned temporal and spatial correlations of the IGP delays and extracted transfer functions between broadcast and reference GIVDs to eliminate error. The SBAS processing errors in Differential Code Bias (DCB) compensation, GIVD estimation modeling, and GEO message quantization are rectified by the MLP trained by abundant historical data with Center for Orbit Determination in Europe (CODE) final Global Ionospheric Maps (GIMs) as reference. Test results on real-time data show that over 85 percent IGPs have STD decline after calibration. The STD declination rates of six SBASs except for SDCM are over 15 percent, and the Mean Absolute Error (MAE) and Root Mean Square Error (RMS) calibration effects are dramatic for all systems. Finally, the average GIVEs are reduced by more than 50 percent for EGNOS, GAGAN, MSAS, and WAAS with a 99.9 percent integrity level maintained. Despite no promotion on availability for BDSBAS and SDCM, the proposed method compensates for the integrity issues of the systems.

Ocean-Surface Wave Measurements Using Scintillation Theories on Seaborne Software-Defined GPS and SBAS Reflectometry Observations.

In this study, a low-cost, software-defined Global Positioning System (GPS) and Satellite-Based Augmentation System (SBAS) Reflectometry (GPS&SBAS-R) system has been built and proposed to measure ocean-surface wave parameters on board the research vessel New Ocean Researcher 1 (R/V NOR-1) of Taiwan. A power-law, ocean-wave spectrum model has been used and applied with the Small Perturbation Method approach to solve the electromagnetic wave scattering problem from rough ocean surface, and compared with experimental seaborne GPS&SBAS-R observations. Meanwhile, the intensity scintillations of high-sampling GPS&SBAS-R signal acquisition data are thought to be caused by the moving of rough surfaces of the targeted ocean. We found that each derived scintillation power spectrum is a Fresnel-filtering result on ocean-surface elevation fluctuations and depends on the First Fresnel Zone (FFZ) distance and the ocean-surface wave velocity. The determined ocean-surface wave speeds have been compared and validated against nearby buoy measurements.

SBAS-based navigation system for precision approach in CAT II LVC

Due to lack of advanced navigation systems, secondary airports are normally unable to support instrument approaches in low visibility conditions (LVC) more adverse than Category (CAT) I, making them inaccessible during such conditions. Incoming flights are then delayed, diverted to adjacent airports, or cancelled before take-off. This paper presents an onboard navigation solution, under development in scope of SESAR 2020 Solution PJ02-W2- 17.2, which focuses on technology development to mitigate these traffic disruptions by enabling instrument approaches in CAT II LVC with minimum airport and air navigation service provider investments. The concept builds upon global navigation satellite systems (Global Positioning System L1 frequency – GPS L1, satellite-based augmentation system), which currently enables Localizer Performance with Vertical guidance (LPV) operation down to LPV 200 minima. The designed system includes radio altimeter-based aiding and innovative integrity algorithm to improve navigation performance in support of operations below 200ft down to CAT II / LPV 100 minima. As no such requirements have yet been officially published, authors also defined sets of candidates based on Instrument Landing System Collision Risk Model and other sources. The team developed and verified a Monte-Carlo fast-time simulation toolset to enable representative and statistically significant evaluation of the concept feasibility via its availability throughout Europe, as well as sensitivity to proposed sets of alert limits. Also, flight data collection and a developed software prototype allow for further validations. Simulations demonstrated over 95% average availability with the best results achieving level of 99% depending on used set of requirements. The solution enabling operations in LVC allows unlocking various benefits to business/airline operators (e.g., avoided extra costs, increased predictability), passengers (avoided opportunity loss) and airports (retained profit from flights, less traffic at diversion airports). Technology development also marks an important step towards gate-to-gate autonomous operations.

Performance analysis of the BDSBAS-B1C message in trial operation stage

BeiDou Satellite-based Augmentation System (BDSBAS) has come into the trial operation stage since July, 2020. To evaluate the characteristic of the augmentation message in BDSBAS-B1C signal, the effectiveness of the message content was firstly analyzed, and then the validity of the broadcasting strategy was estimated. Finally, the accuracy of the user equivalent ranging error (UERE) and the single frequency positioning error with different correction parameters in BDSBAS-B1C message was evaluated. Based on the above analysis, the effectiveness of the augmentation message was preliminarily verified with the results showing that: (1) the BDSBAS-B1C message type, information content and update interval have basically met the international standard; (2) the accuracy of the UERE obtained with the augmentation message had an obvious improvement in contrast to that of the UERE obtained with the usual navigation message of the GPS satellites, and the ionospheric delay was one of the important factors which affected the accuracy of the UERE; (3) the positioning accuracy obtained with the augmentation message was also improved, and the improvement was more obvious in the service areas with high availability of the ionospheric parameters.

Recent Advancements in Controlled Flight into Terrain (CFIT) Prevention

A properly operating aircraft can experience a controlled flight into terrain (CFIT), which is a type of aviation mishap that causes the loss of life and property when it crashes into land or water. The aviation industry has been very concerned about CFIT accidents, and great efforts have been made to avoid them. The most current developments in CFIT prevention are summarised in this research paper. The study analyses existing CFIT prevention technologies, such as enhanced ground proximity warning systems (EGPWS), synthetic vision systems (SVS), and terrain awareness and warning systems (TAWS). It also looks at the possibility of cutting-edge technologies to improve CFIT prevention, such as automatic dependent surveillance-broadcast (ADS-B) and satellite-based augmentation systems (SBAS). The use of CFIT prevention technologies in different aircraft types is discussed in the paper, which also emphasises how effective these systems are at lowering CFIT accidents. It also examines the difficulties and constraints involved in putting CFIT prevention technologies into practice, such as the requirement for appropriate training and the expense of equipment. In order to further improve aviation safety, the paper emphasises the significance of ongoing study and development of CFIT prevention technologies. The use of these technologies can greatly lower the occurrence of CFIT accidents and increase the safety of air travel, especially when combined with pilot training and situational awareness.

Fast GPU based acquisition with minimum loss and downsampling techniques for weak BeiDou SBAS signals

AbstractFor a receiver of the BeiDou Satellite Based Augmentation System (BDSBAS), the acquisition aims to coarsely estimate the pseudo‐code delays and carrier Doppler shifts of the received signals. The use of downsampling techniques to accelerate this acquisition process for weak signals has been an emerging topic. However, the acquisition probabilities of conventional algorithms with downsampling are inadequate and need to be enhanced to prevent excessive false alarms due to degradation of the peak signal‐to‐noise ratios (PSNRs) during acquisition. To improve signal acquisition performance, we introduce an enhancer function before downsampling to achieve the minimum PSNR loss during acquisition. Then, we use graphic processing unit (GPU) functions to speed up the processing loop, matrix multiplication and fast Fourier transform operations. We thus present a fast GPU‐based acquisition method by using minimum loss and downsampling techniques. Our experimental results show the remarkable effectiveness of our method for receiving weak BDSBAS signals as compared to legacy downsampling algorithms. This work seeks not only to solve the current issue of achieving fast acquisition of weak BDSBAS signals but also to inspire creative new ideas that spur further advances in this promising field in the future.

Flight Testing GLS Approaches Enabled by Wide Area Corrections in Kerkyra, Greece

Many airports with a high value to commercial air traffic have spatial or budgetary constraints which prevent the installation of a precision approach system. We previously designed a low-cost precision approach system which combines the advantages of both ground-based and satellite-based augmentation systems by using a converter between them in order to allow GAST-A approach types. We installed, operated, and flight-tested such a system at Kerkyra Airport using an A320 aircraft. During these, we recorded data from a commercial multimode receiver as well as GPS raw data in order to prove the feasibility of the system. Data were analyzed using the Pegasus toolset as well as a highly precise reference trajectory computed from postprocessed carrier phase data. The data recorded show excellent performance for approach guidance that is no different from that of the more expensive GPS landing system GLS and provides guidance in accordance with the localizer performance with vertical guidance standards. Our low-cost precision approach system can provide precision approach-like guidance to appropriately equipped transport aircraft. Kerkyra Airport is extremely limited in availability of usable surface area, such that conventional precision landing aids cannot be placed on airport property. The system provides the ground-based augmentation system approach service type A, a category defined in Annex 10 to the convention of Chicago. This category has not seen any operational use until now but offers an opportunity to provide precision approaches based on GLS where guidance down to a certain altitude will be sufficient.

Designing the Signal Quality Monitoring Algorithm Based on Chip Domain Observables for BDS B1C/B2a Signals under the Requirements of DFMC SBAS

To guarantee the integrity of a global navigation satellite system (GNSS) for safety-critical users, a satellite-based augmentation system (SBAS) makes use of the integrity monitoring architecture, of which the signal quality monitor (SQM) is an important component to address the potential risks caused by satellite-induced signal anomalies. Due to the introduction of dual-frequency multi-constellation (DFMC) techniques in 2025, the ranging uncertainty will be reduced by the elimination of first-order ionospheric delay, but the biases measured in each individual signal will be inflated by the ionosphere-free combinations. Moreover, multiple modulations of DFMC signals might introduce applicability uncertainty of a traditional SQM method that has been protecting GPS L1C/A signal only. Thus, higher requirements are put forward for future SQM methods in detection sensitivity and modulation independence. This paper first proposes a design methodology for the SQM algorithm for BDS B1C/B2a signals, which could be easily extended to the DF combinations of other GNSS core constellations. Then, by comparing the performances of SQM baseline algorithms based on traditional multi-correlator and emerging chip domain observables (CDOs), respectively, the superiority of CDO-based SQM is declared. Detailed design iterations are further discussed, including the algorithm practicalization with optimizing code-phase bin length and lowering sampling frequency, as well as the metric simplification, to promote the overall performance while preserving a lower implementation complexity. Ultimately, a CDO-based SQM algorithm for BDS B1C/B2a signals is reached, which would be considered as an effective candidate in new generation DFMC SBASs.

An operational concept flying GLS approaches using satellite-based augmentation systems

A new converter technology allows suitably equipped aircraft to use data provided by the satellite-based augmentation system in receivers originally designed for the ground-based augmentation landing system. For these aircraft, that system enables a lower decision altitude and, hence, improved access to airports. To make this technology usable, air crews require an operational concept and the flight crew has to be presented with the appropriate information in the form of approach charts. Two different possibilities for an operational concept were developed and the corresponding approach charts created. One option is a modified area navigation approach chart, to which the specific information is added. The other chart is an entirely separate procedure for the approach. These two options were tested with airline pilots in an Airbus A320 full-flight training simulator. During the simulator flights, aircraft performance data was recorded and the participants filled in questionnaires regarding workload and quality of the operational concept. The results show different behavior during the intercept of the final course, but all approaches remained within the required limits. The questionnaires revealed that the workload is higher during the area navigation variant and that all participants prefer the separate ground-based augmentation landing system variant.

SBAS Protection Levels with Gauss-Markov K-Factors for Any Integrity Target

<h3>Abstract</h3> According to aviation minimum operational performance standards (MOPS), protection levels for satellite-based augmentation systems (SBASs) are to be computed as the product of the estimated standard deviation of errors and a scaling, or K-factor. MOPS recognized that K-factors were originally chosen to be consistent with certain assumptions that may not hold under all conditions. Considering the limited applicability of aviation-based K-factors, it will be important to identify a more rigorous method for deriving new SBAS applications for road, rail, or maritime use. Here we describe an innovative method applicable to any integrity risk (e.g., at 10⁻⁷ for aviation or 10⁻⁵ for maritime applications) and time interval <i>T</i> (e.g., 150 seconds to 1 hour for aviation or 3 hours for maritime use). This new method relies on rigorous probability justification. No restrictive assumptions are needed for the time correlation pattern of the errors. The method is easy-to-implement and applicable to any type of integrity risk or time interval <i>T</i>.

Smartphone-Based Positioning Augmented by BDSBAS Ionospheric Corrections

BeiDou Satellite Based Augmentation System (BDSBAS) can notably improve the GNSS L1 positioning performance by transmitting the orbit, clock and ionosphere corrections. Aside from terrestrial geodetic receivers, the mass-market smartphones also benefit from the augmentation service. In this paper, the smartphone-based GPS-L1 standard point positioning (SPP) augmented by BDSBAS corrections is analyzed using Huawei-P40 smartphone. The quality of BDSBAS-B1C ionospheric information is evaluated by ionospheric observables retrieved from the selected 20 stations. Compared to the BDS-3 global ionosphere model (BDGIM) and the Global Ionosphere Maps (GIM) of the International GNSS Service (IGS), the accuracy of BDSBAS ionospheric correction is about 28% better than BDGIM and 11% better than the IGS-GIM. Compared to the GPS-L1 SPP, the accuracy of BDSBAS augmented smartphone positioning increases by 27% in the horizontal component and 41% in vertical component in the open-sky environment, and 50% improvement in both directions in the second experiment where the smartphone connects with an external geodetic GNSS antenna to reduce the negative effects of multipath errors.