Hasil untuk "Canals and inland navigation. Waterways"

Zhen Zhu, Sanjeev Gunawardena, Eric Vinande et al.

The time-differenced carrier phase can be computed from measurements recorded by a multi-global navigation satellite system software-defined radio receiver such as PyChips, from which the user displacement and receiver clock drift can be solved. PyChips is able to simultaneously track authentic and inauthentic signals in separate channels, which makes it possible to observe both types of measurements with corresponding navigation data. A random sample consensus algorithm has been introduced to assess the consistency between the measurements and data. This algorithm successfully separated authentic channels from inauthentic channels when they are broadcast simultaneously.

Sandeep Jada, Mathieu Joerger

In this paper, we develop and evaluate two new methods to derive high-integrity models of measurement error time correlation from experimental data. These models enable the determination of sequential estimation error variance bounds in safety-critical navigation applications such as aircraft localization based on global navigation satellite systems and inertial navigation systems. We achieve tight bounding models from empirical data based on lagged product distributions instead of autocorrelation functions in the time domain and based on scaled periodogram distributions instead of power spectra in the frequency domain. We bound these distributions using first-order Gauss–Markov process (FOGMP) models, which provide a means to account for error time correlation and can be easily incorporated in linear estimators. To determine bounding models, we identify theoretical probability density functions of lagged products and derive the cumulative distribution function of scaled periodograms for FOGMPs. We implement and evaluate these two methods using simulated samples and experimental Global Positioning System data collected in a mild multipath environment.

Jason Anderson, Sherman Lo, Todd Walter

Combinatorial watermarking can help establish trust in global navigation satellite system (GNSS) signals. In combinatorial watermarking, the GNSS provider elects to secretly invert a subset of ranging code chips and then later distributes those inversions to receivers. From these ranging code perturbations, receivers can use signal statistics to determine the authenticity of the signal. In previous work, we demonstrated how one can design combinatorial watermarking schemes and derive the distributions of receiver statistics to ensure low probabilities of missed detection and false alarm, assuming that an adversary does not attempt to estimate the watermarked chips and replay. In this work, we extend the analysis of combinatorial watermarking to adversaries capable of engaging in security code estimation and replay (SCER) attacks. We derive the distributions of our statistics for defense against SCER-capable adversaries. Provided a bound on the estimation capability of the SCER-capable adversary, one can use this work to design a combinatorial watermarking scheme that meets security requirements.

Richard B. Langley

Welcome to the Winter 2024 issue of NAVIGATION. In this issue, we again feature articles on a wide range of topics on positioning, navigation, and timing including navigation underground, in urban canyons, for Earth-orbiting satellites, and even on the Moon. All that and very much more.

Andreas Ettlinger, Andreas Wieser, Hans Neuner

We introduce an algorithm that provides robust three-dimensional orientation of a smartphone for pedestrian indoor localization. The algorithm focuses on integration of the magnetometer and a reformulated observation model such that the influence of magnetic anomalies is mitigated. The methodological novelty of this approach lies in the use of an extended Kalman filter (EKF), based on a state vector that contains only the slow-varying systematic deviation components of the magnetometer. We apply a statistical test to the EKF residuals to detect the presence of magnetic anomalies and update the absolute heading when beneficial conditions prevail. Otherwise, the heading is propagated based on gyroscope observations. We investigate the properties of the proposed algorithm by using simulated smartphone sensor observations with different scenarios of systematic deviations. In experiments with very accurate ground truth, the proposed algorithm achieves a root mean square error of 17.4° for the computed heading, outperforming state-of-the-art algorithms by at least 40%.

Kevin Gutsche, Thomas Hobiger, Stefan Winkler

Incorrect offsets between a satellite’s center of mass and its global navigation satellite system antenna phase center pose challenges to the precise orbit determination (POD) of many current Earth observation missions. Based on hardware-in-the-loop simulations, this paper demonstrates the more adverse effects on agile satellites, which perform frequent attitude maneuvers around all spacecraft axes. However, findings obtained from an observability analysis and Monte Carlo simulations indicate that rapid attitude changes enable the direct estimation of otherwise unobservable offsets. Application to the POD of agile satellites leads to a consistent and significant performance improvement in the presence of incorrect phase center offsets. Directly estimated corrections for the phase center offset of Sentinel-6A, which performs slews on several occasions, are consistent with values obtained from other studies via independent methods. These results underscore the possibility of estimating the lever arm for both agile and non-agile satellites in dedicated calibration maneuvers.

Leonardo Marini-Pereira, Alison de Oliveira Moraes, Sam Pullen

This paper proposes a strategy for improving ionospheric detection of threatening conditions, motivated by issues with ground-based augmentation systems (GBASs) at low latitudes. A methodology is developed for a real-time alerting system that monitors the ionosphere state using surrounding ground stations and sends alerts to differential global navigation satellite systems services when threatening conditions are detected. The method is based on time-step gradients and data gap analysis to detect ionospheric disturbances and to declare periods for affected satellite signals to be unavailable. Validation was performed with real data using the largest observed gradients from the Brazilian ionospheric threat model. The results demonstrate that the method is effective, detecting the vast majority of previously known threatening gradients. An availability assessment was also performed to assess for a loss of availability resulting from the implementation of this technique. Applications of the developed technique include the improvement of low-latitude nighttime GBAS availability.

Richard B. Langley

ION promotes the research of journal authors in a variety of ways including video abstracts hosted on the ION website. The latest video abstracts are documented below. You can find the video abstract for any recently published article under the article’s supplemental menu item on the journal’s website. ION also engages with the PNT community, through its webinar series, to highlight current topics of interest to the community. The most recent webinar is also documented below.

Daniele Borio, Melania Susi

Global navigation satellite system (GNSS) signals from different frequencies can be effectively treated as a single entity, characterized by common delays and carrier phases, leading to so-called GNSS meta-signals. A convenient approach for deriving meta-signal acquisition and tracking algorithms has been recently introduced based on bicomplex numbers, which are a bidimensional extension of complex numbers. Bicomplex numbers allow one to represent two signals from different frequencies as a single quantity, providing a compact notation for algorithm development. In this work, an error-state Kalman filter (KF) is developed, and two signals from different frequencies are tracked simultaneously using the bicomplex number paradigm. A triple-loop architecture, in which loop filters are replaced by a single KF, is developed, implemented, and tested using real Galileo alternative binary offset carrier and BeiDou B1I/B1C meta-signals. This analysis clearly shows the advantages of KF tracking for processing GNSS meta-signals with components from different frequencies.

Junwoo Park, Sungjoong Kim, Kyungwoo Hong et al.

This paper proposes a visual map-based position and heading estimation system that is invariant to image rotation and consistent over time, which is achieved by exploiting the radial and azimuthal distributions of semantic segments. To characterize the specific position and heading, a novel concept termed “visual semantic context” is applied, which collects semantics in a polar-coordinated fashion in collaboration with measures of discrepancy. The system then matches visual semantic contexts: one from a semantically segmented aerial image aided by deep learning technology and others from a semantics-labeled database. Two-stage minimization alleviates the expensive computation of an exhaustive search. The first stage marginalizes the heading and coarsely searches for positions. At the same time, the Kolmogorov–Smirnov test significantly reduces the search domain by rejecting unlikely candidates, and the second stage refines the estimates. Numerical experiments show that the proposed algorithm fixes the position and heading, is invariant to image rotation, and is also robust to imprecise scale information.

James E. Yoder, Todd E. Humphreys

A vehicular pose estimation technique is presented that tightly couples multi-antenna carrier-phase differential GNSS (CDGNSS) with a low-cost MEMS inertial sensor and vehicle dynamic constraints. This work is the first to explore the use of consumer-grade inertial sensors for tightly coupled urban CDGNSS, and first to explore the tightly coupled combination of multi-antenna CDGNSS and inertial sensing (of any quality) for urban navigation. An unscented linearization permits ambiguity resolution using traditional integer least-squares while both implicitly enforcing known-baseline-length constraints and exploiting the multi-baseline problem’s inter-baseline correlations. A novel false fix detection and recovery technique is developed to mitigate the effect of conditioning the filter state on incorrect integers. When evaluated on the publicly available TEX-CUP urban positioning data set, the proposed technique achieves, with consumer- and industrial-grade inertial sensors, respectively, a 96.6% and 97.5% integer fix availability, and a 12.0-cm and 10.1-cm overall (fix and float) 95th percentile horizontal positioning error.

Mike Horton, David Chen, Yudan Yi et al.

This paper explains some design and architecture decisions around the GEODNET network and the GeoDAO decentralized autonomous organization, which aims to create and operate a truly decentralized public GNSS reference sensing network. This paper covers the motivation of the network, the capabilities of current and future reference stations, the blockchain and GEOD token mechanics, and how the network powers applications ranging from climate change monitoring to real-time centimeter-accurate positioning.

Jiarui Cui, Wenqi Wu, Tiefeng Ma et al.

This paper focuses on a heterogeneous redundant inertial navigation system (INS) that consists of one three-axis rotation-modulation fiber optic gyroscope (FOG) INS and one strapdown ring laser gyroscope (RLG) INS. A novel co-calibration method is proposed to estimate the FOG scale factor instability and RLG bias instability error in real time, in which the geometric constraints of the FOG-INS rotating axis are deployed to establish the observation equation without external reference information. In addition, the proposed method has a global navigation capability, which is achieved by using the normal vector of the earth ellipsoid and the state transformation extended Kalman filter to predict positioning errors. An output position error compensation method is used without disturbing the original INSs. Simulation and physical experiment results show that the positioning error of the heterogeneous redundant marine INS is reduced by more than 30% over 300 h of navigation.

Julie Antic, Odile Maliet, Sébastien Trilles

According to aviation minimum operational performance standards (MOPS), protection levels for satellite-based augmentation systems (SBASs) are to be computed as the product of the estimated standard deviation of errors and a scaling, or K-factor. MOPS recognized that K-factors were originally chosen to be consistent with certain assumptions that may not hold under all conditions. Considering the limited applicability of aviation-based K-factors, it will be important to identify a more rigorous method for deriving new SBAS applications for road, rail, or maritime use. Here we describe an innovative method applicable to any integrity risk (e.g., at 10-7 for aviation or 10-5 for maritime applications) and time interval T (e.g., 150 seconds to 1 hour for aviation or 3 hours for maritime use). This new method relies on rigorous probability justification. No restrictive assumptions are needed for the time correlation pattern of the errors. The method is easy-to-implement and applicable to any type of integrity risk or time interval T.

Sihan Yang, Ding Yi, Sudha Vana et al.

With the ubiquitous use of global navigation satellite system (GNSS) receivers, navigation solutions from smartphones have become integrated in various applications throughout our lives. These ultra-low-cost GNSS receivers have the drawbacks of insufficient observations and poorer signal reception quality than higher-cost receivers. Since 2016, smartphones using the Android operating system have been able to output raw GNSS pseudorange and carrier-phase measurements, thereby enabling improved navigation capabilities. The realm of sensor fusion is also being explored by using smartphone sensors, including inertial measurement units (IMUs), cameras, and other fusion techniques. The research presented herein deployed only IMU and GNSS sensors native to existing smartphones and achieved a standalone solution using PPP/IMU integration that outperformed standard techniques. In open-sky vehicle experiments, the sensor integration algorithm achieved 1.6-m horizontal RMS, thus reducing 80% of horizontal errors in GNSS-challenging environments through a tightly coupled GNSS-PPP solution that is yet to appear in publications.

Thomas Vonier

Sriramya Bhamidipati, Shreyas Kousik, Grace Gao

Unlike many urban localization methods that return point-valued estimates, a set-valued representation enables robustness by ensuring that a continuum of possible positions obeys safety constraints. One strategy with the potential for set-valued estimation is GNSS-based shadow matching (SM) in which one uses a three-dimensional (3D) map to compute GNSS shadows (where line-of-sight is blocked). However, SM requires a point-valued grid for computational tractability, with accuracy limited by grid resolution. We propose zonotope shadow matching (ZSM) for set-valued 3D-map-aided GNSS localization. ZSM represents buildings and GNSS shadows using constrained zonotopes, a convex polytope representation that enables propagating set-valued estimates using fast vector concatenation operations. Starting from a coarse set-valued position, ZSM refines the estimate depending on the receiver being inside or outside each shadow as judged by received carrier-to-noise density. We demonstrate our algorithm’s performance using simulated experiments on a simple 3D example map and on a dense 3D map of San Francisco.

Mark L. Psiaki, Brian D. Slosman

Methods are developed to acquire and track orthogonal frequency division multiplexing (OFDM) digital FM radio signals. These methods are being developed with the goal of using FM signals’ pseudorange and accumulated delta-range observables to navigate. Delay lock loop and phase lock loop discriminator outputs are computed by solving an optimal fitting problem in the frequency domain for each OFDM symbol. Single-differencing of the signals’ observables between a roving user receiver and a reference station receiver can remove transmitter clock drift effects. Wideband data collected in Roanoke, Virginia, and in Charlotte, North Carolina, have been processed offline and used to study these signals’ suitability for navigation. Single-differenced pseudorange measurement and bias errors relative to a base station can be on the order of 100 m, but single-differenced accumulated delta-range precision can be better than 0.1 m. A system that uses accumulated delta range may be able to yield 5-m level positioning accuracy if multipath effects can be compensated for. The present study represents an initial effort toward the goal of achieving this level of accuracy. Only pseudorange-based navigation is tested here, however, and its observed errors are on the order of 500 m.

Peizhao Liu, Junping Chen

Real-time precise global navigation satellite system (GNSS) orbit and clock products play a key role for real-time GNSS-based applications, both in the scientific and industrial communities. Different from the typical two-step procedure to generate orbit and clock solutions separately, we estimate the real-time orbit and clock products simultaneously using a Kalman filter. For this purpose, we developed a GNSS data processing software that can run in pseudo-real-time mode with RINEX files and is ready to run in real-time mode once given the real-time observation stream. Meanwhile, a quasi-orbit-fixed solar radiation pressure (SRP) model is developed. In order to verify the performance of the software and the new SRP model, several experiments with a global network of 60 tracking stations over a time span of three months were conducted to generate real-time Global Positioning System (GPS) orbit and clock products. Then, the results were assessed in terms of accuracy and efficiency, both critical for real-time precise GNSS applications. Compared to the International GNSS Service (IGS) final orbits, the real-time GPS orbit accuracy was 2.82 cm, 5.45 cm, and 5.47 cm in the radial, along-track, and cross-track components, respectively. The precision of the clock product in terms of standard deviation (STD) value was about 0.1 ns. Moreover, the average execution time per epoch was usually less than 1.0 s, which ensures the high efficiency of the processing.

Jian Wen, Hong Li, Mingquan Lu

Global navigation satellite systems (GNSS) are vulnerable to spoofing attacks. To shut down a spoofer, it is necessary to locate the spoofer first. Many spoofer localization systems use long cables for the synchronization of multiple receivers. However, a flexible spoofer localization system free from cables is sometimes essential so the receivers can move freely and are flexible to deploy. This paper solves two major problems in developing such a system: spoofing discrimination without requiring synchronization and having an effective method using asynchronous raw measurements with no other assistance. First, this paper proposes to use the extended pseudorange double-difference method to discriminate spoofing signals. The performance is then analyzed and the effectiveness is verified. Then, a quasi-synchronization spoofer localization method (QSSL) is proposed, and it is verified that its localization performance can attain the Cramer-Rao lower bound. Above all, a field experiment demonstrates the effectiveness of the proposed methods and the feasibility of such system.