The wide-area difference demonstration terminal based on SBAS satellite broadcast signal

We provided an overview of various satellite-based augmentation systems (SBAS) options for augmented GNSS services in Australia, and potentially New Zealand, with the aim to tease out key similarities and differences in their augmentation capabilities. SBAS can technically be classified into two user categories, namely SBAS for aviation and "non-aviation" SBAS. Aviation SBAS is an International Civil Aviation Organization (ICAO) certified civil aviation safety-critical system providing wide-area GNSS augmentation by broadcasting augmentation information using geostationary satellites. The primary aim was to improve integrity, availability and accuracy of basic GNSS signals for aircraft navigation. On the other hand, "non-aviation" SBAS support numerous GNSS applications using positioning techniques such as wide-area differential-GNSS (DGNSS) and precise point positioning (PPP). These services mainly focus on delivering high-accuracy positioning solutions and guaranteed levels of availability, and integrity remains secondary considerations. Next-generation GNSS satellites capable of transmitting augmentation signals in the L1, L5 and L6 frequency bands will also be explored. These augmentation signals have the data capacity to deliver a range of augmentation services such as SBAS, wide-area DGNSS and PPP, to meet the demands of various industry sectors. In addition, there are well-developed plans to put in place next-generation dual-frequency multi-constellation SBAS for aviation. Multi-constellation GNSS increases robustness against potential degradation of core satellite constellations and extends the service coverage area. It is expected that next-generation SBAS and GNSS will improve accuracy, integrity, availability and continuity of GNSS performance.

The aim of the paper is to analyse the distribution of update periods of Issue of Data (IOD) parameters in Galileo F/NAV and Navstar Global Positioning System (GPS) LNAV messages. For this purpose, a new method aiming at the reconstruction of IOD update periods reported by a network of monitoring stations is proposed. Over one year of Galileo F/NAV and over three years of GPS LNAV data is processed and consolidated using the proposed method. A reconstruction rate of 99.66% is achieved for the Galileo F/NAV messages. To extract the information on the consecutive update periods of IOD parameters, two metrics are proposed. It was observed that Galileo F/NAV messages can experience fast single and fast double updates. Double updates happen at worst over two subsequent Galileo F/NAV sub-frames. The obtained results suggest a possible impact on Satellite-Based Augmentation System (SBAS). In order to assess the impact on a drafted Dual Frequency Multi Constellation (DFMC) SBAS Standards And Recommended Practices (SARPs), a Galileo F/NAV IOD selector, whose task is to select a specific IOD for augmentation in SBAS, is proposed and implemented. The design of the Galileo F/NAV IOD selector takes into account the observed IOD update periods as well as relevant requirement defined in the drafted DFMC SBAS Minimum Operational Performance Standards (MOPS). The selector aims at maximising the minimum time that the SBAS user has to decode the navigation message identified by the IOD before it is selected for augmentation. In addition, the maximum time that the SBAS would be using IOD, which is no longer transmitted by the Satellite Vehicle (Sv), is also over bounded by the design. According to the analysed data, it is identified that an optimal time to trigger the selection of new IOD of Galileo F/NAV message for augmentation is 350s when maximising the minimum decoding time. The trigger time guarantees that the SBAS user would always have at least 200s available to decode the Galileo F/NAV message.

A strategy to realize the tropospheric delay correction in satellite based augmentation systems is presented. The tropospheric delay is one of the major error sources of the GNSS signals. It is attempted to generate the correction information from the numerical weather prediction data to realize the tropospheric delay correction in real-time for mobile positioning. To introduce the correction information into the satellite based augmentation system, the amount of the correction data must be minimized without degrading the correction accuracy. In this paper, through several statistical evaluations using the long-term observation data, the appropriate contents and the data amount of the correction message are investigated. It is shown that the correction message should consist of the information of the tropospheric zenith delay and its average gradient in height. The amount of the correction data is also successfully minimized, and users in the region of Japan can receive the sufficient correction information by receiving only 3 messages. The results of the analyses clearly show the feasibility of the presented strategy.

The shipping industry is moving towards an e-Navigation concept where a range of electronic and radio navigation technologies will provide harmonized, safe and reliable support for maritime navigation. Augmented GNSS is one of the supporting technologies for e-Navigation. Satellite Based Augmentation Systems (SBAS) could be used to improve accuracy and provide integrity to users. Vessels bound by the International Maritime Organization’s (IMO) Safety of Life as Sea convention (SOLAS) are required to use type approved receivers. Currently, there are neither standards nor regulations to define how the shipborne receiver has to process the SBAS signal from a safety perspective. Non-SOLAS vessels are free to use non-certified receivers and many receivers apply SBAS information, albeit with no guarantees. Shipborne receivers on board SOLAS ships will be able to use SBAS messages through the use of the Multi-system shipborne radionavigation receiver (MSR) standard [1]. SEASOLAS (EGNOS Dual-Frequency Dual Constellation Maritime Safety Service) project analysed a potential safety service with an integrity concept tailored for maritime and inland waterways users. EGNOS V3 Dual Frequency Multi-Constellation service will be available as of 2025. SEASOLAS project was fully financed by the European Commission under the Horizon 2020 program for research and innovation and has been developed by a consortium led by GMV with the European Satellite Service Provider (ESSP), General Lighthouse Authorities (GLA) of the United Kingdom and Ireland, VVA Brussels and Kongsberg Seatex as partners. SEASOLAS project developed a number of advanced solutions based on a receiver that processes EGNOS V3 data and implements autonomous integrity techniques to deal with local error sources whose behaviour is difficult to model and predict. The proposed solutions aim at, on one hand, providing integrity at user level (by bounding the position error with a high confidence level, i.e. the integrity risk); and on the other hand, fulfilling the required performance, at user level, of the SEASOLAS worst-case scenarios. This paper summarises the main outcomes of the activities developed in the frame of the project.

Global navigation satellite systems (GNSSs) will broadcast two open signals for civil aviation within the next ten years. Satellite-based augmentation system (SBAS) providers are currently developing the dual-frequency multi-constellation (DFMC) SBAS interface control document (ICD) to take advantage of the four GNSSs and two signals. In order to ensure the interoperability, a SBAS provider is allowed to determine the correspondence between DFREI and σDFRE based on the performance of its service within the frame of the ICD. Considering that the search space of the correspondence determination is too larger, an algorithm is proposed, which reduces the search space by decorrelating DFREIs. The evaluation based on real data shows that the effect of quantitation error resulted from the correspondence determined by the algorithm to SBAS service performance is neglectable, indicating that the algorithm is efficient. The algorithm could be of value for SBAS providers to design the correspondence.

Design of BDS-3 integrity monitoring and preliminary analysis of its performance

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.

Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on quiet days and locally disturbed days in 2019. More reductions in the positioning errors are found in September and December than other months. In addition, we perform a preliminary availability assessment of two critical phases of flights. The GAGAN performances with the proposed method for the APV-I and LPV-200 categories are improved up to 57% and 53%, respectively, in comparison with the baseline method of the IGP correction.

With the increasingly high performance requirements of civil aviation for satellite navigation system, Satellite-Based Augmentation System (SBAS) is applied. SBAS can augment Global Navigation Satellite System (GNSS) by broadcasting correction and integrity parameters to users in service area through geostationary satellites (GEOs). Therefore, reasonable schedule and normal broadcast of SBAS messages are important guarantee for SBAS to provide efficient service. By analyzing the single frequency SBAS message scheduler at home and abroad, and combining with the current broadcast messages of the BeiDou Satellite-Based Augmentation System (BDSBAS), this paper proposes a fixed time sequence dynamic message scheduler for BDSBAS. Compared with the fixed sequence message scheduler adopted by BDSBAS at present, the message scheduler proposed in this paper can not only improve the flexibility of message broadcasting, but also achieve the effective message proportion of 100%. On the basis of meeting the message update cycle specified by the International Civil Aviation Organization Standards and Recommended Practices (ICAO SARPs), the update time of all kinds of messages is shortened, and the time required for users to receive all message types for the first time is reduced about 11.7%, which provides more time slot margin support for message alarm and upload failure, and greatly ensures the integrity and continuity of BDSBAS service.

The integrity analysis of systems like Satellite-Based Augmentation Systems (SBAS), Ground-based Augmentation Systems (SBAS), Receiver Autonomous Integrity Monitoring (RAIM), or Advanced RAIM (ARAIM) requires proving that the actual distribution of errors can be replaced by a simpler distribution, often a gaussian distribution. Two key results have been used to generate these overbounding distributions: cdf bounding and paired overbounding. Although these two results are very powerful, each of them has a weakness that limits their direct application. The goal of this paper is to overcome some of these weaknesses. We will first present a method to determine gaussian overbounding distributions that combines cdf bounding and paired overbounding. This method is based on the determination of an intermediate overbounding distribution that is symmetric and unimodal. Then, we present a modification of the paired overbounding theorem that relaxes the cdf paired overbounding requirement mentioned above. These techniques are the basis of a MATLAB toolset that computes rigorous gaussian overbounding distributions for any sample distribution.

GAGAN (GPS - Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits signals both in L1 and L5 frequency channels. We used the GAGAN signals for an experimental common-view time transfer between IPE Prague and PTB Braunschweig which is a distance of 370 km and we also tested the time transfer properties using a single clock common-view. The L1 and ionosphere-free code measurements have markedly lower accuracy compared to a GPS common-view because of rather narrow bandwidth of the SBAS signal in L1 frequency channel. L5 code measurement provides much better precision. It results from the single clock common-view that the observed fluctuations can be described as white noise with standard deviations of 6 ns, 1.3 ns and 14 ns for L1, L5 and ionosphere-free combination. The results obtained from the carrier phase measurements are promising. The single clock common-view precision was approximately 30 ps RMS even for the ionosphere-free combination. Interesting results followed from the comparison at the long distance where relatively fast fluctuations induced by ionosphere are obvious in the single frequency measurements. We believe that using GAGAN and other SBASs for permanent carrier phase frequency transfer could be an ideal solution for continuous comparisons of precise frequency sources.

Receivers able to track satellites belonging to different GNSSs (Global Navigation Satellite Systems) are available on the market. To compute coordinates and velocities it is necessary to identify all the elements that contribute to interoperability of the different GNSSs. For example the timescales kept by different GNSSs have to be aligned. Receiver-specific biases, or firmware-dependent biases, need to be calibrated. The reference frame used in the representation of the orbits must be unique. In this paper we address the interoperability issues from the standpoint of a Single Point Positioning (SPP) user, i.e., using pseudoranges and broadcast ephemeris. The biases between GNSSs timescales and receiver-dependent biases are analyzed for a set of 31 MGEX (Multi-GNSS Experiment) stations over a time span of more than three years. Time series of biases between timescales of GPS (Global Positioning System), GLONASS (Global Navigation Satellite System), Galileo, BeiDou, QZSS (Quasi-Zenith Satellite System), SBAS (Satellite Based Augmentation System) and NAVIC (Navigation with Indian Constellation) are investigated, in addition to the identification of events like discontinuity of receiver-dependent biases due to firmware updating. The GPS broadcast reference frame is shown to be aligned to the one (IGS14) realized by the precise ephemeris of CODE (Center for Orbit Determination in Europe) to within 0.1 m and 2 milliarcsec, with values dependent on whether IIR-A, IIR-B/M or IIF satellite blocks are considered. Larger offsets are observed for GLONASS, up to 1 m for GLONASS K satellites. For Galileo the alignment of the broadcast orbit to IGS14/CODE is again at the 0.1 m and several milliarcsec level, with the FOC (Full Operational Capability) satellites slightly better than IOV (In Orbit Validation). For BeiDou an alignment of the broadcast frame to IGS14/CODE comparable to GLONASS is observed, regardless of whether IGSO (Inclined Geosynchronous Orbit) or MEO (Medium Earth Orbit) satellites are considered. For all satellites, position differences according to the broadcast ephemeris relative to IGS14/CODE orbits are projected to the radial, along-track and crosstrack triad, with the largest periodic differences affecting mostly the along track component. Sudden discontinuities at the level of up to 1 m and 2–3 ns are observed for the along-track component and the satellite clock, respectively. The time scales of GLONASS, Galileo, QZSS, SBAS and NAVIC are very closely aligned to GPS, with constant offsets depending on receiver type. The offset of the BeiDou time scale to GPS has an oscillatory pattern with peak-to-peak values up to 100 ns. To characterize receiver-dependent biases the average of six Septentrio receivers is taken as reference, and relative offsets of the other receiver types are investigated. These receiver-dependent biases may depend on the individual station, or for the same station on the update of the firmware. A detailed calibration history is presented for each multiGNSS station studied.

본 논문에서는 국토해양부 해양교통시설과의 연구개발과제인 '광역보정시스템(WA-DGNSS) 구축기술개발' 과제에서 현재까지 개발된 지상국 부분에 대한 성능 검증에 대하여 설명한다. 본 연구개발과제에서는 전국토에 균일한 정확도, 가용성 및 무결성 성능을 보장할 수 있는 광역보정시스템의 핵심알고리듬을 개발하고 지상기반 데모시스템 구축을 완료하여 최종 년도에는 의사위성을 통한 실시간 데모를 실시할 예정이다. 또한 미래 다중 GNSS에 대비하여 GLONASS 및 Galileo를 포함하는 광역보정시스템의 성능을 시뮬레이션을 통해 예측하였다. 본 과제에서 개발된 연구 결과들은 알고리즘 설명서 및 핵심기술권고사항으로 문서화되어 2014년부터 진행될 위성기반 광역보정시스템(SBAS)의 개발에 직접적으로 활용될 예정이다. This paper describes the progress and results of 'Wide Area Differetial GNSS (WA-DGNSS) Development' project which is supported by Korea Ministry of Land, Transport and Maritime Affairs. This project develops the main algorithm of the WA-DGNSS which can guarantee the improved accuracy, availability and integrity all over the Korean peninsula. After the establishment of WA-DGNSS ground system, a real time demonstration using pseudolite will be conducted. Product of this project will be directly utilized in Korean Satellite Based Augmentation System(SBAS) development project which is planned to be started from 2014.

Although GAGAN satellite-based augmentation system (SBAS) provides ionospheric correction service to India and surrounding areas, the correction values do not cover the entire region of Thailand and even at provided grids, they may not be sufficiently accurate. Hence, this work, we propose a local ionospheric delay estimation method based on the geo-free ionospheric delay estimation. Then the estimated ionospheric delays are applied together with the fast and long-term corrections of GAGAN SBAS to improve the positioning errors. The results show that the estimated ionospheric delays can improve the user positioning errors in terms of horizontal and vertical errors up to 0.5 and 1 meter, respectively.

An experiment to measure equatorial amplitude scintillations on the geostationary Wide Area Augmentation System (WAAS) Satellite Based Augmentation System (SBAS) signal was conducted in Cachoeira Paulista (22.70°S, 45.01°W geographic coordinates; −17.74°N, 21.74°E geomagnetic coordinates), Brazil from December 2003 through February 2004. The purpose of this paper is to estimate the scattering height of the irregularities using the WAAS signal scintillations as compared to nearby Global Positioning System (GPS) signal scintillations. Estimating the scattering height is important because the calculated zonal drift velocity of the irregularities using the measured scintillation pattern velocity on the ground is height dependent. Accurate height estimation is also required if one wishes to develop phase screen scintillation models. The difference in the pattern velocities is due to the different signal puncture point velocities with respect to the ionospheric drift. Two east‐west receivers are used to measure the scintillation pattern drift velocity and to compare the results of the geostationary WAAS satellite signal to that of a GPS satellite signal, which has a nonzero ionospheric signal puncture point velocity. By varying the assumed scattering height for the measurements from the nearby GPS signal, the zonal velocity measurements from the GPS scintillations can be matched to those of the WAAS scintillations, and a scattering height estimate can be made. When the puncture points have minimal separation, the inferred ionospheric irregularity zonal velocities should be equal. On the two nights for which data are available, scattering height estimates of 669 ± 209 km for the first night and 388 ± 139 km for the second night were obtained. On the second night, the reported mean hmF2 as calculated using a collocated Digisonde was 385 ± 17 km over the same period as the GPS/WAAS scattering height estimate. The geometry of this experiment was not optimal, but analysis demonstrates that future experiments could be substantially more accurate.