GNSS satellite-based augmentation systems for Australia

For real-time precise orbit determination (POD) of low earth orbit (LEO) satellites, high-accuracy global navigation satellite system (GNSS) orbit and clock products are necessary in real time. Recently, the Japanese multi-GNSS advanced demonstration of orbit and clock analysis precise point positioning (PPP) service and the new generation of the Australian/New Zealand satellite-based augmentation system (SBAS)-aided PPP service provide free and precise GNSS products that are directly broadcast through the navigation and geostationary earth orbit satellites, respectively. With the high quality of both products shown in this study, a 3D accuracy of centimeters can be achieved in the post-processing mode for the reduced-dynamic orbits of small LEO satellites having a duty cycle down to 40% and at sub-dm to dm level for the kinematic orbits. The results show a promising future for high-accuracy real-time POD onboard LEO satellites benefiting from the precise free-of-charge PPP corrections broadcast by navigation systems or SBAS.

This paper presents an investigation into the performance of real-time Global Navigation Satellite Systems (GNSS) Precise Point Positioning (PPP) in New Zealand. The motivation of the research is to evaluate the feasibility of using PPP technique and a satellite based augmentation system such as the Japanese Quasi-Zenith Satellite System (QZSS) to deliver a real-time precise positioning solution in support of a nation-wide high accuracy GNSS positioning coverage in New Zealand. Two IGS real-time correction streams are evaluated alongside with the PPP correction messages transmitted by the QZSS satellite known as MDC1. MDC1 corrections stream is generated by Japan Aerospace Exploration Agency (JAXA) using the Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis (MADOCA) software and are currently transmitted in test mode by the QZSS satellite. The IGS real-time streams are the CLK9B real-time corrections stream generated by the French Centre National D’études Spatiales (CNES) using the PPP-Wizard software, and the CLK81 real-time corrections stream produced by GMV using their MagicGNSS software. GNSS data is collected from six New Zealand CORS stations operated by Land Information New Zealand (LINZ) over a one-week period in 2015. GPS and GLONASS measurements are processed in a real-time PPP mode using the satellite orbit and clock corrections from the real-time streams. The results show that positioning accuracies of 6 cm in horizontal component and 15 cm in vertical component can be achieved in real-time PPP. The real-time GPS+GLONASS PPP solution required 30 minutes to converge to within 10 cm horizontal positioning accuracy.

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.

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.

The Satellite Based Augmentation System (SBAS) can transmit a variety of correction information through satellite, such as ephemeris error, satellite clock error, ionospheric delay and integrity information, which will provide better navigation information for civil aviation aircrafts. Compared with the Instrument Landing System (ILS) commonly used in civil commercial aviation, the SBAS has the advantages of low environmental requirements and lower equipment cost. And the SBAS can provide lower-cost navigation services for civil aviation (including general aviation), so that the significant economic and social benefits will be produced. Based on SBAS satellite broadcast signals, using the navigation receiver with SBAS functions to get the broadcast correction information and integrity information from the Multi-Functional Satellite Augmentation System (MSAS) of Japan. The raspberry pi will receive the information through the USB interface and select them. Finally, the data will be Displayed on the external display. The user uses the display to input fixed instructions to select and compare whether to use SBAS positioning accuracy, which provides a visual demonstration platform for civil aviation teaching.

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.

Tropospheric delay acts as a systematic error source in the Global Navigation Satellite Systems (GNSS) positioning. Empirical models UNB3, UNB3m, UNB4 and EGNOS have been developed for use in Satellite-Based Augmentation Systems (SBAS). Model performance, however, is limited due to the low spatial resolution of the look-up tables for meteorological parameters. A new design has been established in this study for improving performance of the tropospheric delay model by more effectively eliminating the error produced by tropospheric delay. The spatiotemporal characteristics of the Zenith Tropospheric Delay (ZTD) were analyzed with findings that ZTD exhibits different annual variations at different locations and decreases exponentially with height increasing. Spherical harmonics are utilized based on the findings to fit the annual mean and amplitude of the ZTD on a global scale and the exponential function is utilized for height corrections, yielding the ZTrop model. On a global scale, the ZTrop features an average deviation of -1.0 cm and Root Mean Square (RMS) of 4.7 cm compared with the International GNSS Service (IGS) ZTD products, an average deviation of 0.0 cm and RMS of 4.5 cm compared with the Global Geodetic Observing System (GGOS) ZTD data, and an average deviation of -1.3 cm and RMS of 5.2 cm compared with the ZTD data from the Constellation Observing System of Meteorology, Ionosphere, and Climate (COSMIC). The RMS of the ZTrop model is 14.5% smaller than that of UNB3, 6.0% smaller than that of UNB3m, 16% smaller than that of UNB4, 14.5% smaller than that of EGNOS and equivalent to the sophisticated GPT2+Saas model in comparison with the IGS ZTD products. The ZTrop, UNB3m and GPT2+Saas models are finally evaluated in GPS-based Precise Point Positioning (PPP), as the models act to aid in obtaining PPP position error less than 1.5 cm in north and east components and relative large error (>5 cm) in up component with respect to the random walk approach.

: The various satellite-based augmentation systems currently under development utilize geostationary earth orbit (GEO) satellites to provide the user with ranging signals that also contain integrity data on GPS, GLONASS, and Galileo satellites. These signals are generated on the ground and provided via C-band (or K-band) uplink to the GEO. The GEO's navigation transponder frequency translates the signals to L1 and C-band (or K-band) downlink frequencies, and then broadcasts the signals throughout the GEO's coverage footprint. An important aspect of the navigation transponder is its frequency stability. To maintain code-carrier coherency, the code phase, carrier phase, and carrier frequency are controlled via the uplink signal. This is accomplished using closed-loop algorithms that are capable of maintaining the code chipping rate and carrier frequency of the received signal in a constant ratio of 1:1540, as well as maintaining the correct Doppler and ionospheric divergence as observed by the user. This paper describes and presents the field results for code-carrier coherency and clock stability obtained at Wide Area Augmentation System (WAAS) GEO uplink subsystems (GUSs) for the AOR-W and POR satellites. In these tests, the GUS is integrated with the remainder of WAAS in a closed system via the Type 9 navigation message from the correction and verification function of the wide-area master station (WMS), as compared with earlier prototype stand-alone tests. The results meet the specifications for short- and long-term code-carrier coherency and for clock stability over 1–10 s, just as with GPS signals [1, 2].

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.

During the past few decades, the presence of global navigation satellite systems (GNSSs) such as GPS, GLONASS, Beidou and Galileo has facilitated positioning, navigation and timing (PNT) for various outdoor applications. With the rapid increase in the number of orbiting satellites per GNSS, enhancements in the satellite-based augmentation systems (SBASs) such as EGNOS and WAAS, as well as commissioning new GNSS constellations, the PNT capabilities are maximized to reach new frontiers. Additionally, the recent developments in precise point positioning (PPP) and real time kinematic (RTK) algorithms have provided more feasibility to carrier-phase precision positioning solutions up to the third-dimensional localization. With the rapid growth of internet of things (IoT) applications, seamless navigation becomes very crucial for numerous PNT dependent applications especially in sensitive fields such as safety and industrial applications. Throughout the years, GNSSs have maintained sufficiently acceptable performance in PNT, in RTK and PPP applications however GNSS experienced major challenges in some complicated signal environments. In many scenarios, GNSS signal suffers deterioration due to multipath fading and attenuation in densely obscured environments that comprise stout obstructions. Recently, there has been a growing demand e.g. in the autonomous-things domain in adopting reliable systems that accurately estimate position, velocity and time (PVT) observables. Such demand in many applications also facilitates the retrieval of information about the six degrees of freedom (6-DOF - x, y, z, roll, pitch, and heading) movements of the target anchors. Numerous modern applications are regarded as beneficiaries of precise PNT solutions such as the unmanned aerial vehicles (UAV), the automatic guided vehicles (AGV) and the intelligent transportation system (ITS). Hence, multi-sensor fusion technology has become very vital in seamless navigation systems owing to its complementary capabilities to GNSSs. Fusion-based positioning in multi-sensor technology comprises the use of multiple sensors measurements for further refinement in addition to the primary GNSS, which results in high precision and less erroneous localization. Inertial navigation systems (INSs) and their inertial measurement units (IMUs) are the most commonly used technologies for augmenting GNSS in multi-sensor integrated systems. In this article, we survey the most recent literature on multi-sensor GNSS technology for seamless navigation. We provide an overall perspective for the advantages, the challenges and the recent developments of the fusion-based GNSS navigation realm as well as analyze the gap between scientific advances and commercial offerings. INS/GNSS and IMU/GNSS systems have proven to be very reliable in GNSS-denied environments where satellite signal degradation is at its peak, that is why both integrated systems are very abundant in the relevant literature. In addition, the light detection and ranging (LiDAR) systems are widely adopted in the literature for its capability to provide 6-DOF to mobile vehicles and autonomous robots. LiDARs are very accurate systems however they are not suitable for low-cost positioning due to the expensive initial costs. Moreover, several other techniques from the radio frequency (RF) spectrum are utilized as multi-sensor systems such as cellular networks, WiFi, ultra-wideband (UWB) and Bluetooth. The cellular-based systems are very suitable for outdoor navigation applications while WiFi-based, UWB-based and Bluetooth-based systems are efficient in indoor positioning systems (IPS). However, to achieve reliable PVT estimations in multi-sensor GNSS navigation, optimal algorithms should be developed to mitigate the estimation errors resulting from non-line-of-sight (NLOS) GNSS situations. Examples of the most commonly used algorithms for trilateration-based positioning are Kalman filters, weighted least square (WLS), particle filters (PF) and many other hybrid algorithms by mixing one or more algorithms together. In this paper, the reviewed articles under study and comparison are presented by highlighting their motivation, the methodology of implementation, the modelling utilized and the performed experiments. Then they are assessed with respect to the published results focusing on achieved accuracy, robustness and overall implementation cost-benefits as performance metrics. Our summarizing survey assesses the most promising, highly ranked and recent articles that comprise insights into the future of GNSS technology with multi-sensor fusion technique.

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.

Between May 2017 and August 2020, a second-generation satellite-based augmentation system has been demonstrating SBAS and PPP services in Australia and New Zealand. This prototype system (Testbed) has provided Satellite Based Augmentation (SBAS) and real-time Precise Point Positioning (PPP) capabilities through the SBAS L1 and L5 signals broadcast from the Inmarsat 4F1 geostationary satellite. The Australia and New Zealand SBAS and PPP Testbed was promoted by Geoscience Australia (GA), and Land Information New Zealand (LINZ). The Testbed was developed in collaboration with industry partners, including Lockheed Martin, Inmarsat and GMV. The primary objective of the Testbed wasto assess the benefits of satellite navigation technologies in different transport and industrial sectors. This second-generation SBAS Testbed brings together two of the most demanding augmentation needs for GNSS users: integrity and high accuracy. These SBAS technologies have been designed and implemented to support regional aviation procedures, which have the integrity of the navigation solution as one of its primary requirements. Additionally, multimodal users of the SBAS signal in sectors such as agriculture, maritime, transportation or general industry can benefit from a GNSS signal improving the GPS accuracy performance. PPP services designed to support high accuracy needs with a typical RMS user error in the 10 cm range make for an excellent complement to the safety of life service. The objective of this paper is to provide, from the perspective of industrial system developers, an update on the Testbed service definition, infrastructure status and performance achieved during the more than three years of operation.

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.

High-rate multi-constellation global navigation satellite system (GNSS) precise point positioning (PPP) has been recognized as an efficient and reliable technique for large earthquake monitoring. However, the displacements derived from PPP are often overwhelmed by the centimeter-level noise, therefore they are usually unable to detect slight deformations which could provide new findings for geophysics. In this paper, Global Positioning System (GPS), GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and BeiDou navigation satellite system (BDS) data collected during the 2017 Mw 6.5 Jiuzhaigou earthquake were used to further exploit the capability of BDS-only and multi-GNSS PPP in deformation monitoring by applying sidereal filtering (SF) in the observation domain. The equation that unifies the residuals for the uncombined and undifferenced (UCUD) PPP solution on different frequencies was derived, which could greatly reduce the complexity of data processing. An unanticipated long-term periodic error term of up to ± 3 cm was found in the phase residuals associated with BDS satellites in geostationary Earth orbit (GEO), which is not due to multipath originated from the ground but is in fact satellite dependent. The period of this error is mainly longer than 2000 s and cannot be alleviated by using multi-GNSS. Compared with solutions without sidereal filtering, the application of the SF approach dramatically improves the positioning precision with respect to the weekly averaged positioning solution, by 75.2%, 42.8%, and 56.7% to 2.00, 2.23, and 5.58 cm in the case of BDS-only PPP in the east, north, and up components, respectively, and 71.2%, 27.7%, and 37.9% to 1.25, 0.81, and 3.79 cm in the case of GPS/GLONASS/BDS combined PPP, respectively. The GPS/GLONASS/BDS combined solutions augmented by the SF successfully suppress the GNSS noise, which contributes to the detection of the true seismic signal and is beneficial to the pre- and post-seismic signal analysis.

On 14th and 15th March 2011 for the first time approach with vertical guidance (APV-I) was conducted on Polish territory in Katowice, Kraków and Mielec. This was the milestone for GNSS (Global Navigation Satellite System) and Area Navigation (RNAV) use as a new instrument approach chance for NPA (Non-Precision Approach) and PA (Precision Approach) in Poland. The paper presents the experiment study of EGNOS SIS (Signal in Space) due to APV (Approach with Vertical Guidance) procedures development possibilities in the south-eastern part of Poland. Researches were conducted from January 2014 till June 2014 in three Polish cities: Warszawa, Kraków and Rzeszów. EGNOS as SBAS (Satellite Based Augmentation System) in according with ICAO's Annex 10 has to meet restrictive requirements for three dimensional accuracy, system integrity, availability and continuity of SIS. Because of ECAC (European Civil Aviation Conference) states to EGNOS coverage in the eastern part of Europe, location of mention above stations, shows real usefulness for SIS tests and evaluation of the results [EUROCONTROL, 2008].