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The new Global Positioning System (GPS) Civil Navigation Message (CNAV) has been transmitted by Block IIR-M and Block IIF satellites since April 2014, both on the L2C and L5 signals. Compared to the Legacy Navigation Message (LNAV), the CNAV message provides six additional parameters (two orbit parameters and four Inter-Signal Correction (ISC) parameters) for prospective civil users. Using the precise products of the International Global Navigation Satellite System Service (IGS), we evaluate the precision of satellite orbit, clock and ISCs of the CNAV. Additionally, the contribution of the six new parameters to GPS Single Point Positioning (SPP) is analysed using data from 22 selected Multi-Global Navigation Satellite System Experiment (MGEX) stations from a 30-day period. The results indicate that the CNAV/LNAV Signal-In-Space Range Error (SISRE) and orbit-only SISRE from January 2016 to March 2018 is of 0·5 m and 0·3 m respectively, which is improved in comparison with the results from an earlier period. The ISC precision of L1 Coarse/Acquisition (C/A) is better than 0·1 ns, and those of L2C and L5Q5 are about 0·4 ns. Remarkably, ISC correction has little effect on the single-frequency SPP for GPS users using civil signals (for example, L1C, L2C), whereas dual-frequency SPP with the consideration of ISCs results have an accuracy improvement of 18·6%, which is comparable with positioning accuracy based on an ionosphere-free combination of the L1P (Y) and L2P (Y) signals.

The distribution of clock correction and ephemeris (CCE) parameters in navigation messages broadcast by operational satellite vehicles (SVs) of the Global Navigation Satellite System (GNSS) is studied. For this purpose, two evaluation metrics are proposed, namely atypical navigation message structures and time to complete CCE sets (TTCS). The evaluation metrics are used to analyze three and a half years of operational Galileo F/NAV and GPS LNAV messages. The study considers arbitrary and healthy-only signal-in-space (SIS) health statuses. The frequently used receiver independent exchange format (RINEX) navigation files are shown to not provide sufficient information to determine the CCE parameters transmitted at every time instance. Due to the identified limitations, binary navigation data collected by a worldwide network of monitoring stations are used for the analysis. During operations, the maximum of the TTCS metric is shown to be impacted by the issue of data (IOD) update periods and structures with mismatched IOD parameters, potentially introducing an additional delay to the time to first fix (TTFF). The message timing requirements of dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) are shown to be in line with the minimum times needed to obtain multiple complete Galileo F/NAV and GPS LNAV CCE sets.

This paper proposes new sets of suitable broadcast ephemeris parameters for geosynchronous (GEO) and inclined geosynchronous (IGSO) navigation satellites (NSs). Despite the increasing number of GEO and IGSO NSs, global positioning system (GPS)-type ephemeris parameters are still widely used for them. In an effort to provide higher fit accuracy, we analyze a variety of broadcast ephemeris parameters for GEO and IGSO satellites along with their orbital characteristics and propose optimal sets of parameters. Nonsingular elements and orbital plane rotation are adopted for alleviating/avoiding the singularity issues of GEO satellites. On the basis of 16 parameters of GPS LNAV, we add one to four parameters out of 28 correction ones to determine optimal sets of ephemeris parameters providing higher accuracy. All possible parameter sets are tested with the least-square curve fit for four BeiDou GEOs and six BeiDou IGSOs. Their fit accuracies are compared to determine the optimal broadcast ephemeris parameters that provide minimum fit errors. The set of optimal ephemeris parameters depends on the type of orbit. User range error (URE) accuracies of the proposed optimal ephemeris parameters ensure results within 2.4 cm for IGSO and 3.8 cm for GEO NSs. Moreover, the experimental results present common parameter sets for both IGSO and GEO for compatibility and uniformity. Compared with four conventional/well-known sets of ephemeris parameters for BeiDou, our proposed parameters can enhance accuracies of up to 34.5% in terms of URE. We also apply the proposed optimal parameter sets to one GEO and three IGSO satellites of QZSS. The effects of fitting intervals, number of parameters, total bits, and orbit types on the fit accuracy are addressed in detail.

We designed and built a system intended to combine the advantages of both the ground based and the satellite based augmentation systems (GBAS, SBAS) by using a converter between them. We installed a prototype system at Salzburg Airport and flight tested it on 12th of February 2020 using DLR's A320 test aircraft equipped with flight test instrumentation. Using our system, 3D GLS type approaches are possible at any airport within the coverage of the SBAS. The system includes an SBAS-capable global navigation satellite systems receiver with a database and a GBAS-compatible data link. The correction and integrity data received from the SBAS satellite are automatically translated into GBAS compatible structures and sent to the airborne GBAS receiver using the final approach segment data block Without SBAS the system can revert to differential GPS. In both GBAS and SBAS, instant integrity information is provided by estimating protection levels, a high probability bound for the computed position. This is then compared to the alert limit of the respective system. Since both systems are quite similar, and the SBAS signal can nowadays be decoded even by low cost receivers, one can receive the augmentation data from the SBAS, slightly modify it to fit into the GBAS data structure and broadcast this data to a GBAS equipped aircraft. Said aircraft could execute a RNP approach with the Localizer Performance and Vertical guidance (LPV) final approach segment which would otherwise not be available. This may come especially handy in places where no non-precision minima are published, such as the RNP-E approach into Innsbruck and Salzburg. Since there are slight differences between the two systems, we made sure that integrity for the safety-of-life approach service is ensured. We named the system GLASS (GLS Approaches using SbaS), built a prototype and tested it with real GBAS avionics hardware. We performed 4 approaches to Salzburg Airport in Austria (LOWS). Salzburg is now equipped with a RNP approach using LPV only to runway 15 with significantly a lower minimum than the RNP approach with LNAV minimum called the RNP E 15. This is due to the location of the new missed approach point. Using the GLASS system, all GLS equipped aircraft would be able to take advantage of this new minimum line. We followed the approach track using FMS guidance and recorded the ARINC 429 output from the Collins GLU925 Multimode Receiver (MMR). The GLASS guidance was provided to the pilot on the electronic flight bag display for reference. We show a complete analysis of integrity data, MMR status information and MMR output guidance. We compare the GLS data from the MMR with standard SBAS data from an onboard Septentrio PolaRx3 receiver. The GLASS system provides the LPV final approach segment to GLS-only equipped aircraft such as the Boeing 737-800. This can enable increased access to airports that are currently not equipped with an xLS type approach such as Innsbruck (LOWI). Especially approaches in France could be of interest, since the government has officially declared to decommission all category I ILS installations in favor of RNP approaches with LPV. The system could also be carried on the airborne side rather than be a fixed installation on the ground. With a pilot selectable FAS block, it could enable LPV approaches without modifications to existing airborne hardware. Thus, any GLS capable aircraft could fly LPV approaches without requiring ground infrastructure modifications. In this case, the protection level scaling from GBAS is not an issue, since it can be compensated for by the GLASS system.

PBN Vertical Navigation (VNAV) flight procedure refers to 3D RNP approach with vertical guidance, while Lateral Navigation (LNAV) refers to 2D RNP approach without vertical guidance. According to the relevant requirements of RNAV (GPS) approach procedures in ICAO PANS-OPS and USA FAA TERPS criteria for PBN instrumentation procedure design (8260.58A chg1 and 2), the impact of the two specifications on the key design parameters and vertical path angle of VNAV procedures, especially the horizontal protection area and vertical obstacle clearance margin in OAS surface(ICAO) and OCS surface(FAA) is discussed in this paper. Taking runway 06 of an airport as a case analysis, this paper designs VNAV procedures of two specifications when RNP values are 1 and 0.3(only the final segment), evaluates and determines key obstacles, and gives suggestions for PBN in Barometric Vertical Navigation specification.

In this paper, we propose a new approach to generate the Integrity Support Message (ISM) for Advanced Receiver Autonomous Integrity Monitoring (ARAIM). In our approach, we analyze the satellite ephemeris parameters that directly contribute to the satellite position error and thus, result in the ranging error for an ARAIM user. First, we develop an ephemeris parameter error model for the broadcast GPS legacy navigation message (LNAV) under nominal conditions. Then, we describe the procedure to produce Signal-In-Space Ranging Error (SISRE) using the ephemeris parameter error model. The nominal SISRE bias and standard deviation are generated for the ISM to capture GPS constellation performance.

The Global Navigation Satellites Systems (GNSS) are used every day in a huge panel of applications. Currently, the European’s GNSS has about 1 billion of estimated number of Galileo-enabled smartphones. Users expect from GNSS a reliable, robust, continuous and accurate service. CNES, the French Space Agency, is involved in independent Galileo performance assessment activities since the first GIOVE and Galileo Launches. CNES also performs a continuous monitoring of GPS and SBAS systems for years. Based on that experience, navigation performances are analyzed and compared in this paper, with figures and midterm trends for Galileo and GPS systems. While Galileo is on-track toward the Full Operational Capability (FOC), this paper synthetize the navigation performances achieved since the Initial Services Declaration and provide an instructive comparison with GPS, the first GNSS system to have ever been operational. The usual system driven performance metrics are computed both for GPS LNAV (L1 C/A) and Galileo (Open Services) for the longest period of time since the Galileo initial Services declaration in December 2016. This paper demonstrates that both Galileo and GPS performances are good with respect to the Minimum Performance Levels (MPL) defined in GPS SPS PS and in the Galileo OS SDD documents.

Current aviation primarily utilizes the GPS constellation for aircraft navigation; however, the aviation community plans to utilize additional GNSS constellations as more constellations become available with guaranteed performance standards. As a result, multi-constellation airborne navigation requires changes to Receiver Autonomous Integrity Monitoring (RAIM), first approved for aviation in 1992 [1], based on Minimum Operational Performance Standards (MOPS) developed by RTCA, Inc. [2]. RAIM utilizes redundant signals to detect a single-satellite fault, and it may exclude the malfunctioning satellite from the navigation solution using Fault Detection and Exclusion (FDE) methods. The probabilities, detection thresholds and performance of RAIM are designed to support en route, terminal and lateral navigation (LNAV) phases of flight with GPS. Recently, RTCA, Inc. published MOPS for the use of two satellite constellations, GPS and GLONASS, for en route, terminal, and LNAV phases of flight [3]. Though airborne navigation may benefit in terms of accuracy, continuity, integrity, and availability from multi-constellation navigation, it comes at the cost of an increased number of fault modes and resulting algorithm complexity. This paper proposes a fault detection and exclusion algorithm for a combined GPS and GLONASS position solution. GPS and GLONASS signals collected during flight testing are used to demonstrate the performance of the algorithm for en route, terminal, and LNAV phases of flight. The algorithm implements the integrity requirements outlined in the GPS/GLONASS MOPS [3] using the principles of the solution separation method [4]. The algorithm is tested against multiple simulated faults associated with multi-constellation navigation. New developments in this paper include a logic diagram to process the seven fault modes for the GPS/GLONASS solution, as well as an implementation of the solution separation method to handle multiple fault modes.

A standard receiver autonomous integrity monitoring (RAIM) technique for the global positioning system (GPS) has been dedicated to provide an integrity monitoring capability for safety-critical GPS applications, such as in civil aviation for the en-route (ER) through non-precision approach (NPA) or lateral navigation (LNAV). The performance of the existing RAIM method, however, may not meet more stringent aviation requirements for availability and integrity during the precision approach and landing phases of flight due to insufficient observables and/or untimely warning to the user beyond a specified time-to-alert in the event of a significant GPS failure. This has led to an enhanced RAIM architecture ensuring stricter integrity requirement by greatly decreasing the detection time when a satellite failure or a measurement error has occurred. We thus attempted to devise a user integrity monitor which is capable of identifying the GPS failure more rapidly than a standard RAIM scheme by incorporating the RAIM with the relative entropy, which is a likelihood ratio approach to assess the inconsistence between two data streams, quite different from a Euclidean distance. In addition, the delay-coordinate embedding technique needs to be considered and preprocessed to associate the discriminant measure obtained from the RAIM with the relative entropy in the new RAIM design. In simulation results, we demonstrate that the proposed user integrity monitor outperforms the standard RAIM with a higher level of detection rate of anomalies which could be hazardous to the users in the approach or landing phase and is a very promising alternative for the detection of deviations in GPS signal. The comparison also shows that it enables to catch even small anomalous gradients more rapidly than a typical user integrity monitor.

Precise satellite orbit and clock corrections are essential to precise point positioning (PPP). The standard GPS legacy navigation (LNAV) message disseminated by the satellite is one of the most widely used sources for deriving orbit and clock corrections in real-time using efficient analytical user algorithms. However, the quality of the satellite orbit and clock corrections computed with the standard LNAV is not adequate for real-time PPP mainly due to the low update rate. In this study, we proposed an improved LNAV which is estimated based on the IGS ultra-rapid (IGU) orbit and real-time service (RTS) clock products. Two advantages characterize this improved LNAV message. The first one is that scalable update rates can be used for disseminating satellite orbit and clock corrections. Users can decide to receive and decode the improved LNAV message at the desired update rate considering the availability of correction streams, communication bandwidth, and targeted accuracy. With sufficiently high update rates, the improved LNAV can be applied for high-precision applications such as real-time PPP. The second advantage is that the legacy user algorithms can be maintained for computing real-time satellite orbit and clock corrections. Since the improved LNAV has the same parameter representation as the standard LNAV, no changes are required at the user algorithms. To validate the proposed method, the quality of real-time orbit and clock corrections computed with the improved LNAV, IGU products, Centro Nacional de Estudios Espaciales (CNES) real-time products, and the standard LNAV is compared, while the IGS final products are used as the reference. The numerical results indicate that the improved LNAV can achieve comparable orbit accuracy as CNES real-time products, while the clock accuracy highly depends on the update rate. A globally distributed network of 40 IGS stations is used to assess the kinematic PPP performance. Using the improved LNAV with update intervals of 5 min, an average positioning accuracy of 0.122, 0.100, and 0.242 m at 95% confidence level can be obtained in the east, north, and up directions, respectively. Even when the update intervals extend to 2 h, the positioning accuracy is still about 1.2 times better than that of using IGU products. The proposed method provides a scalable and flexible way to improve the standard LNAV for real-time PPP users.

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.

GPS broadcast ephemeris error is an important factor affecting the real-time positioning accuracy. Since April 2014, the IGS provided two new broadcast ephemeris products, namely LNAV (Legacy Navigation Message) and CNAV (Civil Navigation Message). Compared with LNAV, CNAV was broadcasted only on Block IIR-M and IIF satellites. This paper introduces the parameters of satellite orbit calculation in CNAV, and algorithm of satellite orbits calculation is introduced by using CNAV broadcast ephemeris. CNAV satellite orbits and clocks of one year are calculated and evaluated by using the IGS precise products as reference. Results show that mean and RMS of CNAV orbits error is less than 0.4 and 2 m for all three components, respectively; RMS of 3D orbits error is about 3 m. RMS of CNAV satellite clock error is about 1.5 ns. CNAV SISRE is around 0.6 m. User pseudo-range positioning using CNAV shows similar performance as the LNAV.

Airports Authority of India (AAI) in collaboration with Indian Space Research Organization (ISRO) has planned to demonstrate Wide Area Differential GPS (WADGPS), over the Indian Flight Information Region for civil aviation application purpose. In GAGAN-TDS (GPS Aided Geo Augmented Navigation-Technology Demonstration System), with a configuration of eight Reference Stations, one Indian Master Control Station, one Indian Land Uplink station with one GEO stationary satellite, accuracy and availability of GAGAN was demonstrated. GAGAN-TDS is leading to a Fully Operational Phase (FOP) Indian SBAS (Space Based Augmentation System). GAGAN will operationally provide Accuracy, Integrity, Continuity, Availability and level of Service.