Showing papers on "GNSS augmentation published in 2020"

Automatic Generation of Sentinel-1 Continental Scale DInSAR Deformation Time Series through an Extended P-SBAS Processing Pipeline in a Cloud Computing Environment

Abstract: We present in this work an advanced processing pipeline for continental scale differential synthetic aperture radar (DInSAR) deformation time series generation, which is based on the parallel small baseline subset (P-SBAS) approach and on the joint exploitation of Sentinel-1 (S-1) interferometric wide swath (IWS) SAR data, continuous global navigation satellite system (GNSS) position time-series, and cloud computing (CC) resources. We first briefly describe the basic rationale of the adopted P-SBAS processing approach, tailored to deal with S-1 IWS SAR data and to be implemented in a CC environment, highlighting the innovative solutions that have been introduced in the processing chain we present. They mainly consist in a series of procedures that properly exploit the available GNSS time series with the aim of identifying and filtering out possible residual atmospheric artifacts that may affect the DInSAR measurements. Moreover, significant efforts have been carried out to improve the P-SBAS processing pipeline automation and robustness, which represent crucial issues for interferometric continental scale analysis. Then, a massive experimental analysis is presented. In this case, we exploit: (i) the whole archive of S-1 IWS SAR images acquired over a large portion of Europe, from descending orbits, (ii) the continuous GNSS position time series provided by the Nevada Geodetic Laboratory at the University of Nevada, Reno, USA (UNR-NGL) available for the investigated area, and (iii) the ONDA platform, one of the Copernicus Data and Information Access Services (DIAS). The achieved results demonstrate the capability of the proposed solution to successfully retrieve the DInSAR time series relevant to such a huge area, opening new scenarios for the analysis and interpretation of these ground deformation measurements.

An Online SBAS Service to Improve Drone Navigation Performance in High-Elevation Masked Areas

Abstract: Owing to the high demand for drone operation in high-elevation masked areas, it is necessary to develop a more effective method of transmitting and applying Satellite-Based Augmentation System (SBAS) messages for drones. This study proposes an onboard module including correction conversion, integrity information calculation, and fast initialization requests, which can enable the application of an online SBAS to drone operation. The proposed system not only improves the position accuracy with timely and proper protection levels in an open sky, but also reduces the initialization time from 70-100 s to 1 s, enabling a drone of short endurance to perform its mission successfully. In SBAS signal-denied cases, the position accuracy was improved by 40% and the uncorrected 13.4 m vertical error was reduced to 5.6 m by applying an SBAS message delivered online. The protection levels calculated with the accurate position regardless of the current location could denote the thrust level and availability of the navigation solution. The proposed system can practically solve the drawbacks of the current SBAS, considering the characteristics of the low-cost receivers on the market. Our proposed system is expected to be a useful and practical solution to integrate drones into the airspace in the near future.

Validating InSAR-SBAS results by means of different GNSS analysis techniques in medium- and high-grade deformation areas

Abstract: This study aimed to validate the interferometric synthetic aperture radar (InSAR) method by using relative and absolute Global Navigation Satellite System (GNSS) techniques. In this context, two land subsidence areas, one high (Mexico City) and one medium (Aguascalientes), were monitored between 2014 and 2018 by using Sentinel 1A satellite data. The monitoring was carried out with the Small Baseline Subset (SBAS) technique using 46 images for Mexico City and 18 images for Aguascalientes. Concordantly, the GNSS Continuously Operating Reference Station (CORS) data in the regions were analyzed with relative and Precise Point Positioning (PPP) GNSS analysis techniques. The time series obtained from three different analyses were compared and the results were evaluated in light of statistical criteria. According to the results, it is determined that the InSAR-SBAS technique can vary up to ± 20 mm from the displacement values obtained from GNSS due to various noise sources. Such deviations were limited to a few samples, and in general the differentiations were reasonable in the range of 7–8 mm. The difference between the deformation velocity estimation results obtained from the three different methods varied between 3 and 10 mm/year. In this context, these findings suggest that the InSAR-SBAS technique is an effective method for monitoring land deformation with the accuracy of sub-centimeter decided. In addition, PPP which has become an increasingly popular technique showed fast and reliable results in the range of 5–10 mm for InSAR verification. Moreover, with this study, most current results for Mexico City, which is the world’s fastest subsiding metropole, were achieved. In the central region of the city, the detected 300 mm/year of subsidence rate was updated as 370 mm/year. In addition, Aguascalientes was monitored by using the Sentinel 1A satellite mission for the first time in this study. The 60 mm/year subsidence rate obtained for Aguascalientes in previous studies was updated and it was estimated that there are zones where this rate reaches up to − 115 mm/year levels. In this regard, it was concluded that the deformation rate has increased for both regions since the previous monitoring studies.

Examination of Multi-Receiver GPS/EGNOS Positioning with Kalman Filtering and Validation Based on CORS Stations.

Abstract: This paper presents the concept of precise navigation based on SBAS technology and CORS stations. In a kinematic test, three rover Global Positioning System (GPS) receivers, properly spaced relatively to each other, were used in order to estimate reliable and redundant GPS/EGNOS positions. Next, the Kalman filter was employed to give the final solution. It was proven that EGNOS positioning allows to obtain an accuracy in the range of about 0.5-1.5 m. The proposed solution involving the use of three mobile receivers and Kalman filtering allowed to reduce the 3D error to a level below 0.3 m. Such an accuracy was achieved using only GPS L1 code observations and EGNOS corrections. Additionally, a reliable monitoring of quality of GPS/EGNOS positioning in the test area based on CORS stations was presented.

An SVM Based Weight Scheme for Improving Kinematic GNSS Positioning Accuracy with Low-Cost GNSS Receiver in Urban Environments

Abstract: High-precision positioning with low-cost global navigation satellite systems (GNSS) in urban environments remains a significant challenge due to the significant multipath effects, non-line-of-sight (NLOS) errors, as well as poor satellite visibility and geometry. A GNSS system is typically implemented with a least-square (LS) or a Kalman-filter (KF) estimator, and a proper weight scheme is vital for achieving reliable navigation solutions. The traditional weight schemes are based on the signal-in-space ranging errors (SISRE), elevation and C/N0 values, which would be less effective in urban environments since the observation quality cannot be fully manifested by those values. In this paper, we propose a new multi-feature support vector machine (SVM) signal classifier-based weight scheme for GNSS measurements to improve the kinematic GNSS positioning accuracy in urban environments. The proposed new weight scheme is based on the identification of important features in GNSS data in urban environments and intelligent classification of line-of-sight (LOS) and NLOS signals. To validate the performance of the newly proposed weight scheme, we have implemented it into a real-time single-frequency precise point positioning (SFPPP) system. The dynamic vehicle-based tests with a low-cost single-frequency u-blox M8T GNSS receiver demonstrate that the positioning accuracy using the new weight scheme outperforms the traditional C/N0 based weight model by 65.4% and 85.0% in the horizontal and up direction, and most position error spikes at overcrossing and short tunnels can be eliminated by the new weight scheme compared to the traditional method. It also surpasses the built-in satellite-based augmentation systems (SBAS) solutions of the u-blox M8T and is even better than the built-in real-time-kinematic (RTK) solutions of multi-frequency receivers like the u-blox F9P and Trimble BD982.

BDS Satellite-Based Augmentation Service Correction Parameters and Performance Assessment

Abstract: BDS (Beidou Navigation Satellite System) integrates the legacy PNT (Positioning, Navigation, Timing) service and the authorized SBAS (Satellite-Based Augmentation Services) service. To support the requirement of decimeter-level positioning, four types of differential corrections are developed in the BDS SBAS, including the State Space Representation (SSR)-based satellite orbit/clock corrections, the Observation Space Representation (OSR)-based ionospheric grid corrections, and the partition comprehensive corrections. In this study, we summarize the features of these differential corrections, including their definition and usages. The function model of precise point positioning (PPP) for dual- and single-frequency users using the four types of BDS SBAS corrections are proposed. Datasets are collected from 34 stations over one month in 2019, and PPP is performed for all the datasets. Results show that the root mean square (RMS) of the positioning errors for static/kinematic dual-frequency (DF) PPP are of 12 cm/16 cm in horizontal and 18 cm/20 cm in vertical component, while for single-frequency (SF) PPP are of 14 cm/32 cm and 22 cm/40 cm, respectively. With regard to the convergence performance, the horizontal and vertical positioning errors of kinematic DF-PPP can converge to 0.5 m in less than 15 min and 20 min, respectively. As for the kinematic SF-PPP, it could converge to 0.8 m in horizontal and 1.0 m in vertical within 30 min, where the ionosphere-constrained PPP performs better than the UofC PPP approach, owing to the contribution of the ionospheric grid corrections.

Monitoring Aircraft Position Using EGNOS Data for the SBAS APV Approach to the Landing Procedure.

Abstract: The aim of this paper is to present the problem of the implementation of the EGNOS (European Geostationary Navigation Overlay Service) data for the processing of aircraft position determination. The main aim of the research is to develop a new computational strategy which might improve the performance of the EGNOS system in aviation, based on navigation solutions of an aircraft position, using several GNSS (Global Navigation Satellite System) onboard receivers. The results of an experimental test conducted by the Cessna 172 at EPDE (European Poland Deblin) (ICAO (International Civil Aviation Organization) code, N51°33.07'/E21°53.52') aerodrome in Deblin are presented and discussed in this paper. Two GNSS navigation receivers with the EGNOS positioning function for monitoring changes in the parameters of the aircraft position in real time during the landing phase were installed onboard a Cessna 172. Based on obtained research findings, it was discovered that the positioning accuracy was not higher than 2.1 m, and the integrity of positioning did not exceed 19 m. Moreover, the availability parameter was found to equal 1 (or 100%); also, no intervals in the continuity of the operation of the EGNOS system were recorded. In the paper, the results of the air test from Deblin were compared with the parameters of positioning quality from the air test conducted in Chelm (ICAO code: EPCD, N51°04'57.8" E23°26'15"). In the air test in Chelm, the obtained parameters of EGNOS quality positioning were: better than 4.9 m for accuracy, less than 35.5 m for integrity, 100% for availability, and no breaks in continuity. Based on the results of the air tests in Deblin and Chelm, it was concluded that the parameters of the EGNOS positioning quality in aviation for the SBAS (Satellite Based Augmentation System) APV (Approach to Vertical guidance) procedure were satisfied in accordance with the ICAO (International Civil Aviation Organization) requirements. The presented research method can be utilized in the SBAS APV landing procedure in Polish aviation. In this paper, the results of PDOP (Position Dilution of Precision) are presented and compared to the two air tests in Deblin and Chelm. The maximum results of PDOP amounted to 1.4 in the air test in Deblin, whereas they equaled 4.0 in the air test in Chelm. The paper also shows how the EGNOS system improved the aircraft position in relation to the only GPS solution. In this context, the EGNOS system improved the aircraft position from about 78% to 95% for each ellipsoidal coordinate axis.

Performance benefit from dual-frequency GNSS-based aviation applications under Ionospheric Scintillation: A new approach to fading process modeling

Abstract: Deep signal fading due to ionospheric scintillation may cause loss-of-lock on one or more satellites in GNSS receiver tracking loops, which can degrade the navigation availability of GNSS-based aviation applications. Scintillation impact can be mitigated via the frequency diversity, which decreases the chance of satellite loss in the presence of deep and frequent signal fades. This study presents an improved fading process model that generates correlated fading processes of dual-frequency signals and simulates the resulting scintillation impact to evaluate the availability benefit of utilizing dual-frequency GNSS in aviation applications under scintillation. The correlated fading process was described by combining single-frequency only and dual-frequency concurrent fading processes under the assumption that each fading process can be modeled as a Poisson process. Times between deep fading onsets and fading durations observed from GPS L1/L5 dual-frequency measurements collected at Hong Kong in March 2nd, 2014 were used to model the GPS L1 only, L5 only, and L1/L5 concurrent fading processes. Availability simulations for SBAS service supporting the LPV200 phase of flight were conducted by considering the effects of satellite geometry degradation and shortened carrier smoothing time, which are caused by signal losses from deep fades generated by the newly proposed fading process model. A parametric analysis of availability resulting from variations in both the probability of loss-of-lock (under deep fading) and the receiver reacquisition time (following loss-of-lock) was conducted to provide receiver requirement standards for SBAS-based aviation under severe scintillation. The results show noticeable availability improvement from dual-frequency SBAS-based aviation applications over existing single-frequency SBAS.

Detecting Hazardous Spatial Gradients at Satellite Acquisition in GBAS

Abstract: In this article, we develop a ground monitor capable of detecting anomalous signal-in-space spatial gradients for rising, newly acquired, and reacquired satellites in the ground-based augmentation system using either single or dual frequency. These gradients can be caused by satellite orbit ephemeris faults and ionospheric fronts. The monitor utilizes differential code and carrier phase measurements across multiple reference receiver antennas as the basis for detection. We show that the new monitor significantly improves performance over existing detection algorithms and is capable of meeting Category III precision approach and landing requirements.

Estimation method of SBAS dual-frequency range error integrity parameter

Abstract: The development of a dual-frequency multi-constellation satellite-based augmentation system (DFMC SBAS) is in progress worldwide. The broadcasted dual-frequency range error (DFRE) integrity parameter reflects the effects of satellite ephemeris and clock corrections. A user uses the DFRE to calculate the protection level and then determines whether the DFMC SBAS service satisfies the requirements of the current flight phase. However, the calculation of the DFRE has not been reported. Herein, a DFRE estimation method is proposed based on the projection method. Using the ephemeris–clock covariance matrix of each satellite, the maximal projection direction was solved, and the projection of the covariance matrix on this direction was used as the DFRE to form an envelope for the maximal corrected error. Results show that the DFRE can form an envelope of the maximal corrected error with a set probability, and the integrity performance in the user segment satisfies the Category I precision approach requirement.

Evaluation of GBAS flight trials based on BDS and GPS

Abstract: Ground-based augmentation systems (GBASs) are widely used augmentation systems using satellite navigation. GBAS can improve the performance of BeiDou navigation satellite system (BDS) in civil aviation application. Evaluation is necessary before using a GBAS. On the basis of the flight trials conducted at the Dongying airport, evaluation results show that based on both the global positioning system (GPS) L1 signal and BDS B1I signal, ground accuracy designators (GADs) of four reference receivers are consistent with GAD-C levels. The improvement in accuracy obtained with GBAS differential process is ∼60%, and the differential position error based on the BDS B1I signal is 40% greater than that of the GPS L1 signal, because currently incomplete BDS satellites distribution is worse than that of GPS. Airborne protection levels assessments show that the approach trials based on the BDS B1I signal exhibit several false alarm events. Further analysis indicates that BDS vertical protection levels were larger because of larger pseudoinverse S result from low elevation angle and unsatisfactory geometric distribution of BDS satellites. Besides, monitors show that BDS B1I signal is more affected by ionospheric delay than GPS L1 signal, which can also contribute to false alarm events.

Characterizing Background Signals and Noise in Spaceborne GNSS Reflection Ocean Observations

Abstract: This letter analyzes the background signals and thermal noise received over ocean scenes in spaceborne global navigation satellite system (GNSS)-reflectometry (GNSS-R) remote sensing using observations from the cyclone GNSS (CYGNSS) constellation. The measured noise floor contains a stable and predictable radiometric thermal noise component and a more variable background signal component from unintended specular reflections within the CYGNSS receive antenna pattern from all GNSS satellite constellations (GPS, Galileo, GLONASS, Beidou, and all SBAS). The presence of SBAS reflections, in particular, is evident in the noise floor measurements, especially the U.S. wide area augmentation system (WAAS) satellites. The results show that the impact is negligible, since background signal contributions by other GNSS transmitters affect both the “signal” and “noise” portions of CYGNSS’s delay Doppler map measurements, and therefore cancel when the measured noise floor is subtracted from the desired signal. The potential increase in measurement uncertainty introduced by any residual background signal to the CYGNSS calibration is analyzed.

First results of using the second generation SBAS in Australian urban and suburban road environments

Abstract: In this study, the first results of the next-generation dual-frequency multi-constellation SBAS-based kinematic positioning in Australian urban environments are presented and analysed. As the stand...

Present and Future of Air Navigation: PBN Operations and Supporting Technologies

Abstract: The present work reviews the new concept of operation that will be soon implemented in SESAR and NextGen (January 2020) using new state-of-the-art technology mainly based on onboard avionics: data link equipment, broadcast and surveillance systems, and Global Navigation Satellite System (GNSS) area augmentation. One of the main improvements of Performance-Based Navigation (PBN) is the use of satellites and more precise and accurate onboard instruments than current standard avionics related to ground-based navigation aids (VOR, NDB, DME, etc.). Air navigation systems have been without mayor updates for nearly 40 years, when most Very High Frequency Omnidirectional Range (VOR) and Tactical Air Navigation (TACAN) systems were implemented worldwide in the civil and military fields, respectively. These standard navigation systems lack new required performance navigation and required big deal of maintenance, especially in redundant systems. Recently, the development of new and precise GNSS and communication systems has allowed their use on different scenarios: Instrumental Flight Rules (IFR) departures, initial and final approaches, etc. Additionally, in several international airports, Ground Based Augmentation System (GBAS) approaches have been already successfully tested and implemented. Related to GBAS, the Automatic Dependent Surveillance Broadcast (ADS-B) is a cooperative technology that enhances pilots and controllers’ situation awareness, since ADS-B broadcasts own and other aircraft position. Controller Pilot Data Link Communications (CPDLC) may be another key element of the PBN concept of operations (CONOPS), since it provides air–ground data communications for the air traffic control (ATC) service and the aircrew, reducing risks associated to human factor: poor speaking, radio congestion, message confusion, standardization, etc. The main goal of this review is to present the PBN concept and the potentially supporting Communication, Navigation and Surveillance (CNS) systems, in the context of the NextGen and SESAR Air Traffic Management (ATM) modernization programmes.

Comparison Between PS and SBAS InSAR Techniques in Monitoring Shallow Landslides

Abstract: The main aim of this study is to compare the two commonly used multi-temporal interferometric synthetic aperture radar (InSAR) techniques, i.e. permanent scatterers (PS) and small baseline subset (SBAS), in monitoring shallow landslides. PS and SBAS techniques have been applied to ascending and descending Sentinel-1 SAR data to measure the rate of surface deformation and the displacement time series in the Rovegliana area (NE Italian pre-Alps) from 2014 to 2019. As expected, PS results cover only urban areas, while those obtained by SBAS cover up to the 85% of the investigated area. Velocity maps obtained by the two techniques show that some sectors of the investigated slope are affected by active shallow landslides which threaten the stability of buildings, walls and road network. The comparison between ascending and descending velocity maps along the satellite line of sight reveals the presence of a horizontal component in the east–west direction which is consistent with the landslide kinematic. The analysis of the displacement time series shows that, in the case of linear deformation trends, PS and SBAS results are similar, whereas, in the case of high oscillations and non-linear behavior, SBAS technique can provide a better estimation of the displacements. Besides, SBAS provides smoother and less noisy displacement time series. However, both the techniques showed their high capability in monitoring the evolution of the landslides, which is crucial for the implementation of effective risk prevention and mitigation strategies. To deep investigate the differences between the two techniques, other geomatic methodologies, based on global navigation satellite system and terrestrial laser scanning, should be used.

Integrity Concept for Maritime Autonomous Surface Ships' Position Sensors.

Abstract: The primary means for electronic position fixing currently in use in majority of contemporary merchant ships are shipborne GPS (Global Positioning System) receivers or DGPS (Differential GPS) and IALA (International Association of Lighthouse Authorities) radio beacon receivers. More advanced GNSS (Global Navigation Satellite System) receivers able to process signals from GPS, Russian GLONASS, Chinese Beidou, European Galileo, Indian IRNSS, Japan QZSS, and satellite-based augmentation systems (SBAS), are still relatively rare in maritime domain. However, it is expected that such combined or multi-system receivers will soon become more common in maritime transport and integrated with gyro, inertial, radar, laser, and optical sensors, and they will become indispensable onboard maritime autonomous surface ships (MASS). To be prepared for a malfunction of any position sensors, their state-of-the-art integrity monitoring should be developed and standardized, taking into account the specificity of MASS and e-navigation safety. The issues of existing requirements, performance standards, and future concepts of integrity monitoring for maritime position sensors are discussed and presented in this paper.

Efficient Methods of Utilizing Multi-SBAS Corrections in Multi-GNSS Positioning.

Abstract: Various combining methods have been proposed to utilize multi-satellite-based augmentation system (SBAS) correction to provide accurate position in the global navigation satellite system (GNSS) receiver. However, the proposed methods have not been objectively compared and analyzed, making it difficult to know which ones are effective for multi-GNSS positioning. This paper presents efficient methods of combining multi-SBAS corrections in multi-GNSS positioning by comparing three methods: correction domain integration, measurement domain integration, and position domain integration. The performance of the three methods were analyzed through a covariance analysis that was expanded to multi-GNSS and multi-SBAS. Then, the results were verified by experiments using real measurements and corrections. Furthermore, implementation issues, such as computational complexity, availability, and flexibility, are analyzed. As a result, three methods had the same precision, but different complexity, availability, and flexibility. These results will be important guidelines to design, implement, and analyze navigation systems based on multi-GNSS with multi-SBAS corrections.

Extending access to localizer performance with vertical guidance approaches by means of an SBAS to GBAS converter

Abstract: Currently, many commercial airline aircraft cannot perform three-dimensionally guided approaches based on satellite-based augmentation systems. We propose a system to rebroadcast the correction and integrity data via a data link as provided by the ground-based augmentation system such that aircraft equipped with a GPS landing system (GLS) can use the wide-area corrections and perform localizer performance with vertical guidance (LPV) approaches while maintaining the same level of integrity. In consequence, the system loses some availability and the time to alert is slightly increased. We build a prototype system and present data collected for one week, confirming technical feasibility. There is a loss of 5.3 percent of availability during a 1-week data collection cycle in which we compared our system to standalone LPV service. We tested our prototype with two commercially available GLS receivers with positive results and successfully demonstrated the functionality with a conventional Airbus 319 equipped with a standard GLS receiver.

Klobuchar, NeQuick G, and EGNOS Ionospheric Models for GPS/EGNOS Single-Frequency Positioning under 6–12 September 2017 Space Weather Events

Abstract: The ionosphere is one of the main factors affecting the accuracy of global navigation satellite systems (GNSS). It is a dispersive medium for radio signals, and for multi-frequency receivers, most of its effect can be removed. The problem is for the single-frequency devices, which must rely on a correction model. The motivation of this paper is the adoption of different ionospheric models in GPS/EGNOS (Global Positioning System/European Geostationary Navigation Overlay Service) positioning to mitigate the impact of geomagnetic storms. The aim of this article is to examine the accuracy of GPS/EGNOS single-frequency positioning. In all the examined solutions, GPS L1 data augmented with the EGNOS clock and ephemeris corrections were used in position calculation. The changes were only made to the ionospheric model. The examined scenarios are as follows: without any model (off), Klobuchar, NeQuick G, and EGNOS model. The analysed period is 6–12 September 2017, during which the last strong geomagnetic storm took place. In order to perform a reliable analysis, the study was conducted at three International GNSS Service (IGS) stations in different geographical latitudes, within the EGNOS APV-1 (Approach with Vertical Guidance) availability border. The obtained results prove that the EGNOS ionospheric model meets the aviation positioning accuracy criteria for the APV-1 approach during the studied geomagnetic storm. The EGNOS average horizontal positioning error of 0.75 m was on average almost two times lower than the other solutions. For vertical positioning, the EGNOS error of 0.93 m proved to be two times lower than those of the Klobuchar and NeQuick G models, while it was more than three times lower for the off solution.

NaviSoC: High-Accuracy Low-Power GNSS SoC with an Integrated Application Processor

Abstract: A dual-frequency all-in-one Global Navigation Satellite System (GNSS) receiver with a multi-core 32-bit RISC (reduced instruction set computing) application processor was integrated and manufactured as a System-on-Chip (SoC) in a 110 nm CMOS (complementary metal-oxide semiconductor) process. The GNSS RF (radio frequency) front-end with baseband navigation engine is able to receive, simultaneously, Galileo (European Global Satellite Navigation System) E1/E5ab, GPS (US Global Positioning System) L1/L1C/L5, BeiDou (Chinese Navigation Satellite System) B1/B2, GLONASS (GLObal NAvigation Satellite System of Russian Government) L1/L3/L5, QZSS (Quasi-Zenith Satellite System development by the Japanese government) L1/L5 and IRNSS (Indian Regional Navigation Satellite System) L5, as well as all SBAS (Satellite Based Augmentation System) signals. The ability of the GNSS to detect such a broad range of signals allows for high-accuracy positioning. The whole SoC (system-on-chip), which is connected to a small passive antenna, provides precise position, velocity and time or raw GNSS data for hybridization with the IMU (inertial measurement unit) without the need for an external application processor. Additionally, user application can be executed directly in the SoC. It works in the -40 to +105 °C temperature range with a 1.5 V supply. The assembled test-chip takes 100 pins in a QFN (quad-flat no-leads) package and needs only a quartz crystal for the on-chip reference clock driver and optional SAW (surface acoustic wave) filters. The radio performance for both wideband (52 MHz) channels centered at L1/E1 and L5/E5 is NF = 2.3 dB, G = 131 dB, with 121 dBc/Hz of phase noise @ 1 MHz offset from the carrier, consumes 35 mW and occupies a 4.5 mm2 silicon area. The SoC reported in the paper is the first ever dual-frequency single-chip GNSS receiver equipped with a multi-core application microcontroller integrated with embedded flash memory for the user application program.

Performance Evaluation of Adjusted Spherical Harmonics Ionospheric Model Over Indian Region

Abstract: The ionosphere is perceived to be a predominant source of ranging error of Global Navigation Satellite System (GNSS) signals to degrade the positional accuracy. The suitable ionospheric model is necessary to improve the positional accuracy of GNSS and Satellite-Based Augmentation System (SBAS) users. In this paper, the regional ionospheric model (RIM) over the Indian region is implemented based on the adjusted spherical harmonics function (ASHF) model from dense GPS TEC stations over the Indian region. Also, the evaluation of the different ASHF order models conducted to identify the proper order of the ASHF model for Indian low latitude ionospheric calm and adverse space weather conditions. The results confirm that the 4th order ASHF ionospheric model can identify the northern Equatorial Ionization Anomaly (EIA) TEC crest patterns over the Indian region. The comparison of the 4th order ASHF ionospheric model carried out with dual and single frequency ionospheric models like as Klobuchar model, Centre for Orbit Determination in Europe (CODE) Klobuchar model, NeQuick G model, BeiDou System (BDS2) model and CODE Global Ionospheric Maps (GIM) models. The outcome of the results indicates that the 4th Order ASHF ionospheric model would be potential for single and dual-frequency ionospheric models for GNSS and SBAS systems.

NIGCOMSAT-1R Satellite-Based Augmentation System(SBAS) test bed trial

Abstract: In October, 2016 China Great Wall Industry Corporation and Spacestar Technology Company Ltd of China entered into cooperative agreement with Nigerian Communications Satellite Ltd on a Satellite-Based Augmentation System (SBAS) performance test and assessment of the Nigerian Communications Satellite (NIGCOMSAT-1R) augmentation System exploiting NIGCOMSAT-1R L Band. This paper examines test bed experimentation conducted in conjunction with partners to validate functional requirements, performance validation of units, sub-systems and systems of both the SBAS payload and ground infrastructure before a pilot project demonstration of capabilities and proof-of-concept nationwide and extension to parts and regions of Africa.

Aircraft positioning using DGNSS technique for GPS and GLONASS data

Abstract: The purpose of this paper is to present the problem of implementation of the differential global navigation satellite system (DGNSS) differential technique for aircraft accuracy positioning. The paper particularly focuses on identification and an analysis of the accuracy of aircraft positioning for the DGNSS measuring technique.,The investigation uses the DGNSS method of positioning, which is based on using the model of single code differences for global navigation satellite system (GNSS) observations. In the research experiment, the authors used single-frequency code observations in the global positioning system (GPS)/global navigation satellite system (GLONASS) system from the on-board receiver Topcon HiperPro and the reference station REF1 (reference station for the airport military EPDE in Deblin in south-eastern Poland). The geodetic Topcon HiperPro receiver was installed in Cessna 172 plane in the aviation test. The paper presents the new methodology in the DGNSS solution in air navigation. The aircraft position was estimated using a “weighted mean” scheme for differential global positioning system and differential global navigation satellite system solution, respectively. The final resultant position of aircraft was compared with precise real-time kinematic – on the fly solution.,In the investigations it was specified that the average accuracy of positioning the aircraft Cessna 172 in the geocentric coordinates XYZ equals approximately: +0.03 ÷ +0.33 m along the x-axis, −0.02 ÷ +0.14 m along the y-axis and approximately +0.02 ÷ −0.15 m along the z-axis. Moreover, the root mean square errors determining the measure of the accuracy of positioning of the Cessna 172 for the DGNSS differential technique in the geocentric coordinates XYZ, are below 1.2 m.,In research, the data from GNSS onboard receiver and also GNSS reference receiver are needed. In addition, the pseudo-range corrections from the base stations were applied in the observation model of the DGNSS solution.,The presented research method can be used in a ground based augmentation system (GBAS) augmentation system, whereas the GBAS system is still not applied in Polish aviation.,The paper is destined for people who work in the area of aviation and air transport.,The study presents the DGNSS differential technique as a precise method for recovery of aircraft position in civil aviation and this method can be also used in the positioning of aircraft based on GPS and GLONASS code observations.

Satellite-Based Augmentation Systems (SBASs)

Abstract: The concept of Satellite‐Based Augmentation System (SBAS) has its roots in the 1980s. An SBAS is a system designed to improve global navigation satellite system (GNSS) service such that the augmented service meets the strict requirements of air navigation. This chapter uses the existing Wide Area Augmentation System L1 design to describe the different SBAS monitors. The SBAS protection level equations are based upon the observation that the error sources are approximately Gaussian and that an inflated Gaussian model can be used to conservatively describe the positioning errors. The SBAS integrity parameters sent to the users are the user differential range errors to bound the ranging errors to a specific satellite and the grid ionospheric vertical errors to bound the estimated errors in the SBAS ionospheric delay model. The chapter is intended to provide an overview to assist the reader in understanding how the different message types connect together to form a differential GPS correction.

SBAS/EGNOS for Maritime

Abstract: The Global Navigation Satellite System (GNSS) has become the primary means of obtaining Position, Navigation, and Timing (PNT) information at sea. The current capabilities of the Global Positioning System (GPS) constellation, although adequate for ocean navigation, have some shortfalls for coastal navigation: some user communities have a need for enhanced performance and they can benefit from the available “augmentation” techniques, resulting in improved GPS performance. Nowadays, the users can take advantage of Satellite-Based Augmentation Systems (SBASs). The maritime domain has been used SBAS for several years and it is supported by GNSS receivers used in the recreational and professional sectors. The SBAS/European Geostationary Navigation Overlay Service (EGNOS) can be used to complement the differential GNSS (DGNSS) for the provision of enhanced accuracy and integrity information with additional benefits. There are different possible solutions for the transmission of SBAS/EGNOS information to maritime users, considering that the corrections can be available from different transmission means. The different options for the use of SBAS for maritime navigation, the benefits brought to mariners, as well as the associated regulations, standardization and service provision aspects, are presented in this article.

An SBAS Integrity Model to Overbound Residuals of Higher-Order Ionospheric Effects in the Ionosphere-Free Linear Combination

Abstract: The next generation of satellite-based augmentation systems (SBAS) will support aviation receivers that take advantage of the ionosphere-free dual-frequency combination. By combining signals of the L1 and L5 bands, about 99% of the ionospheric refraction effects on the GNSS (Global Navigation Satellite Systems) signals can be removed in the user receivers without additional SBAS corrections. Nevertheless, even if most of the negative impacts on GNSS signals are removed by the ionospheric-free combination, some residuals remain and have to be taken into account by overbounding models in the integrity computation conducted by safety-of-live (SoL) receivers in airplanes. Such models have to overbound residuals as well, which result from the most rare extreme ionospheric events, e.g., such as the famous “Halloween Storm”, and should thus include the tails of the error distribution. Their application shall lead to safe error bounds on the user position and allow the computation of protection levels for the horizontal and vertical position errors. Here, we propose and justify such an overbounding model for residual ionospheric delays that remain after the application of the ionospheric-free linear combination. The model takes into account second- and third-order ionospheric refraction effects, excess path due to ray bending, and increased ionospheric total electron content (TEC) along the signal path due to ray bending.

Single-Frequency Time-Step Ionospheric Delay Gradient Estimation at Low-Latitude Stations

Abstract: The irregularity of the local-area ionospheric delay is a primary impediment for Ground-Based Augmentation System (GBAS) services. Excessive ionospheric delay gradients may degrade aircraft positioning for high precision landing systems. Therefore, the spatial gradients of the nominal background ionosphere must be studied as their statistics will be sent to the approaching aircraft. For the well-known station-pair method, ionospheric delay gradient estimation requires at least 2 Global Navigation Satellite System (GNSS) reference stations. This method can be applied to both single or dual-frequency GNSS receivers. However, when the GNSS stations are far apart, it is not suitable for estimating the ionospheric delay gradients at short baselines, and the time-step method is an attractive alternative. In this work, we propose a single-frequency time-step method for ionospheric delay gradient estimation. Careful baseline length selection is needed, due to ionospheric piercing point movements. We applied our method to GNSS data in 2014, at the peak of the 24th solar cycle, and showed that the standard deviations of the vertical ionospheric delay gradients were comparable to those derived from the dual-frequency time-step method. The standard deviations of vertical ionospheric gradients, $\sigma _{\mathrm {VIG}}$ , ranged between 4 and 6 mm/km. The $\sigma _{\mathrm {VIG}}$ values around the equinoxes were ~1.5 mm/km greater than at other times.