Showing papers in "Annual of Navigation in 2012"
TL;DR: A monitor in the Radio Frequency (RF) front end using the automatic gain control (AGC) mechanism is outlined, making spoofing no more of a threat than the much less sophisticated radio frequency interference/jamming.
Abstract: The idea of Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) “spoofing,” or the ability to mislead a satellite navigation receiver into establishing a position or time fix which is incorrect, has been gaining attention as spoofing has become more sophisticated. Various techniques have been proposed to enable detection if a receiver is being spoofed – with varying degrees of success and computational complexity. In this paper, a monitor in the Radio Frequency (RF) front end using the automatic gain control (AGC) mechanism is outlined. It has low computational complexity and is an extremely powerful means to detect spoofing, making spoofing no more of a threat than the much less sophisticated radio frequency interference/jamming. The technique is validated using live testing. Copyright © 2012 Institute of Navigation.
208 citations
TL;DR: A practical technique is proposed to authenticate civil GPS signals that combines cryptographic authentication of the GPS navigation message with signal timing authentication based on statistical hypothesis tests to secure civil GPS receivers against spoofing attacks.
Abstract: A practical technique is proposed to authenticate civil GPS signals. The technique combines cryptographic authentication of the GPS navigation message with signal timing authentication based on statistical hypothesis tests to secure civil GPS receivers against spoofing attacks. The notion of GNSS signal authentication is defined in probabilistic terms. Candidate GPS signal authentication schemes are evaluated in terms of effectiveness and practicality leading to a proposal for incorporating digital signatures into the extensible GPS civil navigation (CNAV) message. The proposal is sufficiently detailed to facilitate near-term implementation of security-hardened civil GPS. Copyright © 2012 Institute of Navigation.
189 citations
TL;DR: In this paper, a Ground Based Augmentation System (GBAS) ground-based monitor capable of detecting anomalous ionospheric gradients at the time of satellite acquisition is described.
Abstract: This paper describes a Ground Based Augmentation System (GBAS) ground-based monitor capable of instantly detecting anomalous ionospheric gradients at the time of satellite acquisition. The monitor utilizes differential carrier phase measurements across multiple reference station baselines as the basis for detection. Performance analysis shows that the monitor is highly sensitive to the quality of the carrier phase measurements. Therefore, data collected from a GBAS prototype ground facility is used to quantify the measurement quality and validate the concept monitor.
48 citations
TL;DR: In this paper, a group of multi-frequency linear combinations that include both code and carrier phase measurements were proposed to improve the reliability of integer ambiguity resolution. But the accuracy of the float solution was not improved.
Abstract: This paper provides two methods to improve the reliability of carrier phase integer ambiguity resolution: The first one is a group of multi-frequency linear combinations that include both code and carrier phase measurements, and allow an arbitrary scaling of the geometry, an arbitrary scaling of the ionospheric delay, and any preferred wavelength. The maximization of the ambiguity discrimination results in combinations with a wavelength of several meters and a noise level of a few centimeters. These combinations could be beneficial for both Real-Time Kinematics (RTK) and Precise Point Positioning (PPP).
The second method incorporates some statistical a priori knowledge of attitude into the actual fixing. The a priori knowledge includes the length and direction of the baseline between two receivers and is given either as a uniform or Gaussian distribution. It enables a substantial reduction of the search space volume but also ensures a large robustness over errors in the a priori information.
Both methods improve the accuracy of the float solution, which motivates a simple rounding for ambiguity fixing. A method is described, which enables an efficient computation of its success rate with a few integral transformations. Copyright © 2012 Institute of Navigation.
44 citations
TL;DR: A method to predict satellite orbits in a stand-alone consumer-grade GNSS navigation device to reduce the startup time of a navigation device without the use of network assistance is presented.
Abstract: A method to predict satellite orbits in a stand-alone consumer-grade GNSS navigation device is presented. The motivation for this work was to reduce the startup time of a navigation device without the use of network assistance. The presented orbit prediction method works for both GPS and GLONASS, achieving median accuracies of 58 and 23 m in satellite position, respectively, for prediction up to four days ahead. A simple method for prediction of the satellite's clock offsets is also discussed. A basic analysis indicates that the method gives a line of sight range error of 15 m, for both GPS and GLONASS, with most of the error due to the clock offset prediction. Copyright © 2012 Institute of Navigation.
39 citations
TL;DR: A direct comparison of the apparent clock performance for GIOVE-B and the first Block IIF satellite (SVN62) is provided and an empirical clock correction model is discussed, which offers a notable reduction of the Allan variance at orbital time scales.
Abstract: The passive hydrogen maser of GIOVE-B and the new GPS Block IIF Rubidium clock have demonstrated a superior stability in ground tests. In practice, however, the apparent clock performance for GNSS users is limited by measurement errors and imperfections of the signal chain that affect the clock variance at different time scales. Within this paper, we provide a direct comparison of the apparent clock performance for GIOVE-B and the first Block IIF satellite (SVN62). Periodic errors in the apparent clocks of both satellites are analyzed and an effort is made to separate the impact of orbit determination errors from physical clock or line bias variations. For SVN62 an empirical clock correction model is discussed, which offers a notable reduction of the Allan variance at orbital time scales. Furthermore, triple-frequency observations are used to demonstrate the presence of thermally induced line bias variations and to quantify the resulting inter-frequency clock biases.
33 citations
TL;DR: Results indicate that increasing DME station reply rate reduces availability for avionics at the current minimum operational performance standards (MOPS), however, with reasonable MOPS changes, DME could support anticipated air traffic levels.
Abstract: Alternative position, navigation, and timing (APNT) systems are needed by aviation to maintain operations for prolonged periods during an absence of Global Positioning System (GPS) service. This is especially important in the future as the Federal Aviation Administration (FAA) Next Generation Air Transportation System (NextGen) utilizes GPS to efficiently handle the anticipated twofold increase in air traffic over the next 15 years. Thus, an APNT system must be able to support the full capacity of future airspace. One candidate APNT system is distance measuring equipment (DME). Since DME has capacity limits, it is important to understand these limits and how they may be increased. This paper models DME capacity and uses the model to examine potential means of improving capacity. Results indicate that increasing DME station reply rate reduces availability for avionics at the current minimum operational performance standards (MOPS). However, with reasonable MOPS changes, DME could support anticipated air traffic levels. Copyright © 2012 Institute of Navigation.
32 citations
TL;DR: In this paper, an orientation state estimator is proposed for smart weapons applications using feedback from wide field-of-view thermal sensors and magnetometers, leveraging preflight predictions of the projectile flight path.
Abstract: An orientation state estimator is proposed for smart weapons applications using feedback from wide field-of-view thermal sensors and magnetometers. The state estimation system possesses several key advantages over current designs in that it maintains low cost, lacks moving parts, and is free from reliance on GPS or other state feedback. In order to enhance robustness against disturbances that reduce thermopile performance, the filter incorporates heuristics feedback, leveraging preflight predictions of the projectile flight path. Realistic simulations demonstrate estimation performance during conditions in which terrain and weather phenomena distort or obscure the horizon. The article begins with a discussion of sensor modeling techniques and descriptions of how weather and terrain effects are captured. Then, an Extended Kalman filter is developed to estimate Euler angles and projectile spin rate. Example results, incorporating realistic sensor errors and environmental disturbances, demonstrate estimator performance. Monte Carlo results verify filter robustness and effective use of heuristics feedback. Copyright © 2012 Institute of Navigation.
29 citations
TL;DR: A compact, light and relatively inexpensive system capable of providing the Required Navigation Performance (RNP) in all phases of flight of a small UAV, with a special focus on precision approach and landing, where Vision Based Navigation (VBN) techniques can be fully exploited in a multisensor integrated architecture.
Abstract: In this paper we present a new low-cost navigation system designed for small size Unmanned Aerial Vehicles (UAVs) based on Vision-Based Navigation (VBN) and other avionics sensors. The main objective of our research was to design a compact, light and relatively inexpensive system capable of providing the Required Navigation Performance (RNP) in all phases of flight of a small UAV, with a special focus on precision approach and landing, where Vision Based Navigation (VBN) techniques can be fully exploited in a multisensor integrated architecture. Various existing techniques for VBN were compared and the Appearance-Based Approach (ABA) was selected for implementation. Feature extraction and optical flow techniques were employed to estimate flight parameters such as roll angle, pitch angle, deviation from the runway and body rates. Additionally, we addressed the possible synergies between VBN, Global Navigation Satellite System (GNSS) and MEMS-IMU (Micro-Electromechanical System Inertial Measurement Unit) sensors, as well as the aiding from Aircraft Dynamics Models (ADMs).
23 citations
TL;DR: This paper describes changes that should then be made to WAAS to support the new protection level equations and provide dual-frequency service.
Abstract: GPS has launched its first L5 capable satellites and plans to achieve L5 Full Operational Capability (FOC) in the 2019 time frame. L5 is of great interest to the Wide Area Augmentation System (WAAS) and the aviation community, as it will allow aircraft to measure and remove the ionospheric delay affecting each ranging observation. Currently, this error source is the most significant cause of unavailability for WAAS users. Its elimination will result in greater performance and a larger service area under WAAS. However, in order to take advantage of L5, both the aircraft and WAAS will need to be updated. We have previously recommended changes to the airborne protection level calculations to exploit these new signals. In this paper we describe changes that should then be made to WAAS to support the new protection level equations and provide dual-frequency service. Copyright © 2012 Institute of Navigation
19 citations
TL;DR: A projection methodology using GNSS signals is proposed for the calibration of antenna arrays, using the Gram Schmidt process along with the properties of the signal steering vectors to determine linear relationships between the recovered signals and the calibration parameters.
Abstract: Antenna array processing techniques require calibration algorithms that often rely on the availability of signal sources at known locations, a good knowledge of the array manifold, or a reference antenna. An alternative is provided by GNSS signals that provide the location of their sources as part of their navigation data. In this paper, a projection methodology using GNSS signals is proposed for the calibration of antenna arrays. The Gram Schmidt process is used along with the properties of the signal steering vectors to determine linear relationships between the recovered signals and the calibration parameters. The obtained system of equations is then solved in the Minimum Mean Square Error (MMSE) sense leading to the estimated calibration parameters. The proposed algorithm accounts for signal gain/phase mismatches and mutual coupling between array elements. Finally, the effectiveness of the proposed technique and its suitability for beamforming and Direction-of-Arrival (DoA) applications is supported by several experiments performed using live GPS signals and a GNSS software receiver. Copyright © 2012 Institute of Navigation.
TL;DR: A novel method for detecting GPS satellite clock excessive acceleration faults is presented, which allows users of GBAS to detect clock faults even during extended outages of the Differentially Corrected Positioning Service (DCPS).
Abstract: A novel method for detecting GPS satellite clock excessive acceleration faults is presented, which allows users of GBAS to detect clock faults even during extended outages of the Differentially Corrected Positioning Service (DCPS). The method is based on monitoring residuals of the acceleration solution computed from carrier-phase measurements. To demonstrate its function, the algorithm is verified using data collected from a hardware receiver. Because the algorithm is designed to react to rare events, a simulation is used to study algorithm performance in the presence of a fault. The proposed method represents a significant reduction in ranging error, by two orders of magnitude for the same probability of missed detection, as compared to conventional Receiver Autonomous Integrity Monitoring (RAIM). Copyright © 2012 Institute of Navigation
TL;DR: In this paper, a continuous satellite surveying of railway track by the use of the relative phase method based on the Polish Active Geodetic Network ASG-EUPOS and RTK (GPRS) real time service was carried out at the Gdansk University of Technology and Polish Naval Academy.
Abstract: Abstract In 2009, at the Gdansk University of Technology and Polish Naval Academy there has been carried out, for the first time, continuous satellite surveying of railway track by the use of the relative phase method based on the Polish Active Geodetic Network ASG-EUPOS and RTK (GPRS) real time service - NAVGEO. The analysis indicated strong connection between location of GNSS receiver and accuracy of position determination, the horizon obstruction deteriorated accuracy and impacts terrain obstructions, the precise GPS planning process on the position solution. It can be stated that implemented measuring technique opens a whole new perspective on applied research. As proved, it enables very precise determination of basic data definition for railway line modernization design. On-going research works focuses on the GNSS multi-receivers platform evaluation for projecting and stocktaking. Analyses also focused on the values of deviations of transverse position XTE (Cross Track Error). In order to eliminate the influence of random measurement errors and to obtain the coordinates representing the actual shape of the track, the XTE variable was performed by different statistical and regression methods (least square method - LSM, weighted least squares - WLS, Linear Chebyshev low-pass filtering and fast Fourier transform). The paper presents the result of trial analyses realized on the newly constructed (rectilinear) and old-used up railway lines. The authors were searching the methods for filtering random measurement GNSS errors different from instantaneous shape deformations of the straight rail track.
TL;DR: Which parameters of the AIS position report and to what extent, are affected are clarified and the detailed data analysis gives answers on how reliable the A IS data in different traffic areas is.
Abstract: Since its introduction the Automatic Identification System (AIS) has played an important part in improving safety at sea, making bridge watchkeeping duties more comfortable and enhancing vessel traffic management ashore. However the analysis of a AIS data set describing the vessel traffic of the Baltic Sea came to conclusion, that specific parameters with relevance to navigation seemed to be defective or implausible. Essentially, it concerned the true heading (THDG) and the rate of turn (ROT) parameters. With the paper we are trying to clarify, which parameters of the AIS position report and to what extent, are affected. The detailed data analysis gives answers on how reliable the AIS data in different traffic areas is.
TL;DR: This paper discusses how the proposed requirements can be interpreted in order to develop a fault model that describes the magnitude and dynamics of malfunction induced navigation systems errors for malfunctions that are undetected, or prior to their detection.
Abstract: A new type of service has been proposed for Ground Based Augmentation Systems (GBAS) that is intended to support approach and landing operations down to the lowest minimums (i.e., CAT IIIb). Proposed standards for this new service type have been drafted and are currently being validated. This so called GBAS Approach Service Type D (GAST D) includes new low level requirements for monitoring as well as a requirement for additional geometry screening in order to protect the user from failures of several types. This paper discusses how the proposed requirements can be interpreted in order to develop a fault model that describes the magnitude and dynamics of malfunction induced navigation systems errors for malfunctions that are undetected, or prior to their detection. Such a fault model can be used to demonstrate acceptable airplane system level responses to malfunctions as part of airworthiness approvals. The paper includes a review of the types of malfunctions that are anticipated and the monitoring requirements that limit the impact of those malfunctions. Then a dynamic error model is proposed and the parameters of that model are presented for each type of failure. The relationship between the largest undetected errors and the user defined geometry screening is explored for each type of malfunction. Some discussion of how this model is anticipated to be used in the context of airworthiness demonstrations is included. This work represents an important step towards development of airworthiness requirements needed in order for GBAS to support CAT III operations in the future. Copyright © 2012 Institute of Navigation.
TL;DR: The algorithm for baseline vector and yaw attitude estimation is introduced and results based on real measurements collected with five QZSS-capable receivers of the CONGO network are presented.
Abstract: The first satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has been launched in September 2010, and its signal transmission has been activated at the end of the same year. The satellite transmits five signals from its L-band main antenna, including C/A code and L1C on L1, and the SAIF signal from a dedicated antenna mounted with an offset to the main antenna. Using differential pseudorange and carrier-phase measurements, it is possible to compute the phase center offset vector, or baseline vector,
between these two antennas, if the satellite’s attitude is known. Using this vector as a priori information, it is furthermore possible to compute the yaw attitude of the spacecraft. This is a unique feature of the QZSS satellites and particularly interesting since their attitude mode is switched between yaw-steering and orbit-normal orientation during certain periods. Precise knowledge and consistent modeling of the satellite’s attitude is essential when processing carrier-phase measurements or satellite
laser ranging measurements. This paper introduces the algorithm for baseline vector and yaw attitude estimation and presents results based on
real measurements collected with five QZSS-capable receivers of the CONGO network. The observability of the baseline vector and the accuracy of the yaw angle estimates are discussed. The analysis for the yaw attitude estimation includes a switch from yaw-steering to orbit-normal orientation as well as changes of the attitude mode during an
orbit maintenance maneuver.
TL;DR: In this paper, a GPS/INS integration algorithm based on the direction cosine matrix (DCM) attitude representation model and its performance was derived and compared with an Euler angles-based unscented Kalman filter (UKF).
Abstract: In this paper, we derive a GPS/INS integration algorithm based on the direction cosine matrix (DCM) attitude representation model and analyze its performance. The motivation for this work is to find an algorithm that is capable of tracking the variation of the gyro bias vector during operations and that benefits from the established DCM based attitude estimation algorithms. Filter performance is evaluated using a simulation based on an air vehicle trajectory profile and is compared with an Euler angles-based unscented Kalman filter (UKF). We investigate the effects of improper initialization of the state vector on the filter performance. These results are supplemented using experimental data collected along a car route with two different grades of inertial measurement units (IMUs). The DCM based model has some advantages over other attitude representations due to its relatively moderate computational load and applicability with different categories of inertial sensors. Copyright © 2012 Institute of Navigation
TL;DR: A novel robust probabilistic Bayesian-based approach using received-signal-strength (RSS) measurements with varying path-loss exponent in wireless networks with heterogeneous medium for relative positioning of nodes in a wireless network with a heterogeneousmedium is proposed.
Abstract: Precise positioning and tracking information in networks with a heterogeneous transmission medium presents a novel networking paradigm. Most of the localization algorithms are vulnerable to the variations of signal propagation speed, dielectric constant, and path-loss coefficient resulting in unreliable location estimation. In this paper, we propose a novel robust probabilistic Bayesian-based approach using received-signal-strength (RSS) measurements with varying path-loss exponent in wireless networks with heterogeneous medium. An application of such a localization method is relative positioning of nodes in a wireless network with a heterogeneous medium such as gastrointestinal tract monitoring using wireless video capsule endoscopy. The results of this study showed that the localization root mean square error (RMSE) of our Bayesian-based method when a sensor node was covered by four anchors was 1.0 mm which is smaller than that of other existing localization approaches under the same conditions such as classical MDS (43.1 mm), dwMDS (24.7 mm), MLE (21.8 mm) and POCS (1.7 mm). Copyright © 2012 Institute of Navigation
TL;DR: An algorithm of trajectory choice has been developed, taking into account the parameters of the area, own ship, target ship and other vessels sailing in vicinity, and the ship domain has been adopted as a safety criterion.
Abstract: This article focuses on the problem of determining a sa fe trajectory of a ship proceeding in a restricted area. An algorithm of trajectory choice has been developed, taking into account the parameters of the area, own ship, target ship and other vessels sailing in vicinity. The ship domain has been adopted as a safety criterion. The research results for selected test trials are presented and analyzed. The applicability of the proposed method of trajectory choice in real conditions is considered.
TL;DR: The issues of determination of spatial database model appropriate for an indoor system, improvement of accuracy of positioning algorithms utilizing spatial data and methodology of generating graphical and voice directions for indoor navigation are presented.
Abstract: The development of indoor navigation systems should utilize advanced teleinformation, geoinforma tion and cartographical knowledge. The authors analyzed available specifications of prototypes of indoor navigation systems and drew conclusions about how to enhance the use of cartographical methods in the whole process of designing a new system. The analysis proves that cartographical methodology is still very limited in the process of designing indoor navigation systems. Researchers focus mainly on improving the positioning accuracy, and they often neglect the issue of developing spatial databases and the rules of their effective visualization. The process of designing indoor navigation systems, just like in the case of outdoor navigation systems, consists of a number of tasks that can be supported by the theory and practice of cartography. This article presents the issues of determination of spatial database model appropriate for an indoor system, improvement of accuracy of positioning algorithms utilizing spatial data and methodology of generating graphical and voice directions for indoor navigation. In the authors’ opinion, the discussed cartographical methods and techniques may considerably enhance indoor navigation systems and accelerate their development. The fundamental knowledge of cartographical methods should be within the interest of designers of these systems. At present the first attempts in this field may be observed, although they are still not mature and complex.
TL;DR: Technical aspects of different GPS devices are compared and results of their dynamic accuracy evaluation are presented.
Abstract: Producers of GPS receivers nowadays offer many easy-to-use , mobile units for amateur and professional athletes. Similar functionality parameters and a relatively low price make it difficult for the average user to make a choice. This article compares technical aspects of different GPS devices and presents results of their dynamic accuracy evaluation. Selected GNSS units were divided into two groups: specialized dedicated to sports and GPS data loggers. The tests were carried out on the sports stadium of the Gdansk University of Physical Education and Sport, where the lanes were measured with the use of the GPS Total Station phase receivers Leica GS-15 VIVA, supported by Polish Active Geodetic Network ASG-EUPOS. The ellipsoidal coordinates logged in the GNSS sports receivers were transformed in Gauss-Kruger projection to conformal x, y coordinates and statistical distributions of the predictable accuracy were calculated. The article also discusses other (important from a functional point of view) characteristics of GPS receivers used by athletes.
TL;DR: The EGNOS performance before and after applying a novel methodology called Error Extraction is tested using real data, confirming that the designed new algorithms allow reduction of the error standard deviation and significant availability improvement without breaches of the integrity.
Abstract: Abstract In this work the EGNOS performance before and after applying a novel methodology called Error Extraction is tested using real data. These data are collected at the EGNOS Monitoring Station placed in Sofia by Eurocontrol. The tests concern aircraft navigation, namely Approach with Vertical Guidance services. All results confirm that the designed new algorithms are very promising. They allow reduction of the error standard deviation and significant availability improvement without breaches of the integrity. The probability of system discontinuity decreases substantially.
TL;DR: The used measurement facility and strategies for obtaining a sufficient amount of measurement data based on the used simplified satellite attitude and yaw steering model are introduced and it is shown that transmitter power variations of the navigation satellite over time can be characterized and separated from the pure influence of the satellite antenna.
Abstract: The payload of a typical navigation satellite encounters heavy strains during launch. This indicates the need to characterize and assess the antenna and consequently the total signal performance of a satellite in orbit. Using ground measurements with a high gain antenna seems to be a powerful basis for this analysis. This paper introduces the used measurement facility and strategies for obtaining a sufficient amount of measurement data based on the used simplified satellite attitude and yaw steering model. The analysis algorithms will be described in detail and as a side product itwill be shown that transmitter power variations of the navigation satellite over time can be characterized and separated from the pure influence of the satellite antenna. The last section presents the exemplary antenna pattern characterization for the second Galileo test satellite GIOVE-B (Galileo In-Orbit Validation Element) based on calibrated flux density measurements taken with DLR’s 30 m high gain antenna for the E1 frequency band.
TL;DR: This paper models MLAT capacity for the two ADS-B protocols and uses the model to examine means of improving capacity, indicating methods of implementing MLAT that can increase capacity and make it a more viable APNT.
Abstract: United States air traffic is anticipated to increase twofold over the next 15 years. To support those levels, the Federal Aviation Administration is implementing the NextGen. NextGen relies heavily on GPS. However, alternative position navigation and timing (APNT) systems will be necessary to allow users to navigate when GPS is unavailable. One alternative is to use multilateration (MLAT) using automatic dependent surveillance broadcast (ADS-B) signals (currently being implemented for surveillance).
The APNT must be capable of supporting the full capacity of future airspace. ADS-B frequencies are shared amongst all aircraft and so MLAT has a finite capacity. Additionally, using MLAT for navigation involves changes from the surveillance MLAT that further stresses capacity. This paper models MLAT capacity for the two ADS-B protocols and uses the model to examine means of improving capacity. Results indicate methods of implementing MLAT that can increase capacity and make it a more viable APNT. Copyright © 2012 Institute of Navigation.
TL;DR: Taking into consideration the recordings of the studies and technical specification of AIS, the results of inconsistent data has been analysed in the context of collision avoidance.
Abstract: Commonly used AIS devices on the ships covered by SOLAS Convention creates ideas of the use of AIS data in the situation of the risk of collision. AIS position report is a source of supplementary information derived from error leveraged radar measurement. However, many of users has opinions with regard to inconsistent AIS dynamic data in the process of decision-making by the officer of the watch. Taking into consideration the recordings of the studies and technical specification of AIS, the results of inconsistent data has been analysed in the context of collision avoidance.
TL;DR: In this paper, an assessment of the IOV signals on the E5 band is presented, investigating the signal features compared with the expected characteristics as described in the Galileo Interface Control Document (ICD).
Abstract: An assessment of the Galileo In-Orbit Validation (IOV) signals on the E5 band is presented in this paper, investigating the signal features compared with the expected characteristics as described in the Galileo Interface Control Document (ICD) specifications. In detail, the re-sults in terms of signal acquisition and tracking during multiple satellite passes are discussed, providing also a description of the experimental setup used in order to separately receive and process E5a and E5b signals. The analysis covers the received signal strength versus the satellite elevation, the modulation format, and the presence of navigation data and secondary code chips. Since at time of writing both the two Galileo IOV satellites (PFM and FM2) are broadcasting E5 signals, the results obtained processing their E5a and E5b signals are dis-cussed. In addition, these signals are also compared with those currently transmitted by the two experimental Galileo satellites, GIOVE-A and GIOVE-B
TL;DR: In this article, a detailed methodology for characterizing the temporal/spatial behavior of indoor GNSS signal amplitude is presented, and the proposed methodology is then used to extract the signal amplitude and its empirical Probability Density Function is compared against several standard distributions.
Abstract: In this paper, the problem of characterizing and simulating indoor Global Navigation Satellite Systems (GNSS) signals is addressed. A detailed methodology for characterizing the temporal/spatial behavior of indoor GNSS signal amplitude is first presented. The proposed methodology is then used to extract the signal amplitude and its empirical Probability Density Function is compared against several standard distributions. From the analysis, it emerges that the slow and fast fading components affecting received GNSS signals need to be modeled separately. In this respect, a composite Rice/Log-Normal model able to effectively capture the behavior of the indoor signal amplitude is considered. Several experiments have been conducted and the validity of the composite model has been validated against measurements. It is shown that the spectra of the slow and fast fading components can be effectively modeled using a 4 th order low-pass Butterworth filter. A simulation scheme is finally suggested for the generation of indoor GNSS signals.
TL;DR: This paper presents an alternate two-threshold monitor implementation, which features both a subcritical threshold and a critical threshold, only the latter of which triggers a loss of continuity.
Abstract: Integrity monitors are an essential component of ensuring the quality of navigation measurements for safety-critical GNSS augmentation systems. The sensitivity of these monitors is closely related to requirements limiting monitor false alarms. This paper shows that the risk of false alarms interrupting safety critical operations (loss of continuity) is closely tied to monitor-noise correlation. Analysis shows that specific continuity risk may be as high as 50% for conventional monitor implementations, when time correlation is considered. This paper presents an alternate two-threshold monitor implementation, which features both a subcritical threshold and a critical threshold, only the latter of which triggers a loss of continuity. Using this two-threshold implementation, we introduce methods to compute specific continuity risk in the presence of time-correlated noise. Subsequently, through simulation, we quantify how specific continuity risk is influenced by varying levels of time-correlation, which may be present in the raw monitor data or introduced by smoothing. Copyright © 2012 Institute of Navigation.
TL;DR: In this paper, the authors proposed a phase prediction approach to reduce the carrier phase reacquisition time by integrating the estimated Doppler computed from the navigation solution in the standard and advanced receiver architectures.
Abstract: The objective of this work is to reduce the carrier phase reacquisition time using a phase prediction method in the standard and advanced receiver architectures. In the phase prediction approach, carrier phase measurements are predicted for satellites that have lost lock by integrating the estimated Doppler computed from the navigation solution. In so doing, the predicted phase error is typically accurate enough to yield significant improvements in phase reacquisition times. Predicted phase quality is evaluated and all algorithms are tested using real data collected under mild to moderate operational conditions. Standard, vector-based, and ultra-tight architectures are considered. Copyright © 2012 Institute of Navigation.
TL;DR: The authors attempt to present the computational problem related to the navigational algorithm (meridian arc formula) implemented in the software applied in marine navigation electronic devices and systems, such as GNSS, Galileo, AIS, ECDIS/ECS, and other marine GIS.
Abstract: In the paper the authors attempt to present the computational problem related to the navigation al algorithm (meridian arc formula) implemented in the software applied in marine navigation electronic devices and systems, such as GNSS (GPS, GLONASS, Galileo), AIS, ECDIS/ECS, and other marine GIS. From the early days of the development of the basic navigational software built into satellite navigational receivers, it has been noted that for the sake of simplicity and a number of other reasons, this navigational software is often based on the simple methods of limited accuracy. It is surprising that even nowadays the use of navigational software is still used in a loose manner, sometimes ignoring basic computational principles and adopting oversimplified assumptions and errors such as the wrong combination of spherical and ellipsoidal calculations in different steps of the solution of a particular sailing problem. The lack of official standardization on both the ‘accuracy required’ and the equivalent ‘methods employed’, in conjunction to the ‘black box solutions’ provided by GNSS navigational receivers and navigational systems (ECDIS and ECS) suggest the necessity of a thorough examination of the issue of sailing calculations for navigational systems and GNSS receivers.