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   Full-text available via subscription Subscription journal
   ISSN (Online) 2161-4296
   Published by John Wiley and Sons Homepage  [1589 journals]
  • An Implementation of Variable IF Tracking Loop (VITAL) and Initial Test
    • Authors: Chun Yang; Thomas Pany, Andrey Soloviev
      Abstract: Correlation at an intermediate frequency (IF) produces a composite correlation function of an envelope being that of the underlying code and an internal structure being that of the IF carrier. By varying the IF, one can introduce zero-crossings to the envelope so as to shape and sharpen the main peak. Such a variable peak is desired for accurate timing of the direct signal while isolating close-in multipath and spoofing signals. The functionality of variable IF correlation in acquisition and its multipath performance are analyzed in a recent paper published in this journal. In this paper, the details of an implementation of variable IF tracking loop are presented with a theoretical background analysis. A publically available open-source software GPS receiver (SoftGNSS V3.0) is modified into variable IF tracking loop and tested on real-world GPS C/A-code signals. The preliminary test results demonstrate increased code tracking accuracy as well as increased positioning performance. Copyright © 2017 Institute of Navigation
      PubDate: 2017-12-03T20:25:48.430951-05:
      DOI: 10.1002/navi.212
  • Performance Analysis of Optimal Combinations for Triple-Frequency BDS
    • Authors: Leizheng Shu; Wenbin Wang, Ran Ding, Huabo Wei
      Abstract: A theoretical and experimental investigation on the BeiDou Navigation Satellite System triple-frequency combination theory is presented. The optimal combination strategies under different application circumstances are given in consideration of the combination wavelength, noise, and ionosphere amplification factor as the main criteria. On this basis, the performance of BeiDou Navigation Satellite System triple-frequency optimal combinations, in regard to ambiguity resolution and relative positioning accuracy, is verified by four static tests with baseline lengths of 4.8, 12.4, 20, and 36.8 km, respectively. Finally, a few suggestions about the optimal phase combinations used in relative navigation applications are given. Copyright © 2017 Institute of Navigation
      PubDate: 2017-11-16T19:40:47.819324-05:
      DOI: 10.1002/navi.211
  • Improving DCB Estimation Using Uncombined PPP
    • Authors: Yan Xiang; Yang Gao
      Abstract: Differential Code Biases (DCBs) are much more relevant when GNSS data processing with code measurements is involved, such as in ionospheric sensing, positioning, and timing. The current approach to estimate DCBs is based on carrier-phase smoothed code observations together with ionospheric modeling. A limiting factor of the method is the effect of the leveling errors from the smoothing process on the DCB estimate. To reduce the leveling errors, a new DCB estimation method based on an Uncombined Precise Point Positioning (UPPP) model is proposed. A month's data from a global network in a high solar activity year from May 1 to 31, 2014 are processed to validate the method. The results show that most satellite DCB estimates are found to be more stable than when using the smoothed code method. The improvement can be up to about 0.22 ns. The stability and accuracy of the receiver DCB estimates is also enhanced. Copyright © 2017 Institute of Navigation
      PubDate: 2017-10-26T18:10:40.176741-05:
      DOI: 10.1002/navi.207
  • Observability Analysis and Concept of Usage of Air Data Attitude and
           Heading Reference Systems (AD-AHRS)
    • Authors: Fedor Baklanov; Johann Dambeck
      Abstract: This paper addresses the problem of proper integration of an inertial navigation system with an air data system. First, we present a mathematical formalism of the system's mechanization, i.e., navigation equations for spheroidal Earth, air data observation equations, and error propagation equations for optimal Kalman filtering. Next, an analytical observability analysis is conducted and demonstrated by means of a simulation. Finally, we draw conclusions about expected benefits and the most suitable applications. Copyright © 2017 Institute of Navigation
      PubDate: 2017-10-23T21:12:28.909066-05:
      DOI: 10.1002/navi.206
  • The Next Generation GPS Time
    • Authors: Ken L. Senior; Michael J. Coleman
      Abstract: The next generation Global Positioning System (GPS) ground control segment will entail a number of GPS ground system upgrades from the existing ground control segment. One of these upgrades is the inclusion of a new modernized timescale algorithm used to generate GPS Time. The timescale is currently being designed as a separate modular unit (given the acronym ETF, or Ensemble Timescale Filter) within the ground system navigation package and is based upon a U-D Kalman Filter implementation that utilizes measurements of all clocks in the ground network and satellite constellation.The new ETF module will include a number of features that improve the stability of the GPS Time timescale and provide more user/operator autonomy to include: multi-weight clock weighting for better handling of mixed clock types in the same filter; automated clock break detection and handling; robust outlier and anomalous clock behavior mitigation; admission of multiple external timescale solutions, including alternate ETF realizations; and adaptive clock parameter estimation. The preliminary results presented in this paper demonstrate some of the performance capabilities and robustness characteristics of the ETF. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.
      PubDate: 2017-10-09T01:06:05.351705-05:
      DOI: 10.1002/navi.208
  • Characterization of Tropospheric Gradients for the Ground-Based
           Augmentation System Through the Use of Numerical Weather Models
    • Authors: Alizé Guilbert; Carl Milner, Christophe Macabiau
      Abstract: In the scope of the Single European Sky Air Traffic Management Research (SESAR) Work Package 15.3.7, a number of research threads are being undertaken to improve the performance of multi-constellation multi-frequency ground-based augmentation system to support CAT II/III precision approaches. Several challenges and key issues must be solved including those related to atmospheric modeling.However, there are a number of arguments for revisiting this topic and specifically addressing the tropospheric threat. First, recent observations, reported at the last International Civil Aviation Organization Navigation System Panel meeting, showed unexpected atmospheric behavior. The source could be related to a non-modeled behavior of the troposphere. Second, in the advent of dual-frequency ground-based augmentation system, the main contributor to the atmospheric error will come from the tropospheric delay.That is why this paper explains a methodology to reassess the tropospheric threat within two main steps: an analysis of European meteorological data and an analysis of a new bounding methodology for dealing with the troposphere threat and its impact on vertical protection levels. Copyright © 2017 Institute of Navigation
      PubDate: 2017-10-03T01:56:30.891463-05:
      DOI: 10.1002/navi.205
  • Issue Information
    • Pages: 307 - 307
      Abstract: No abstract is available for this article.
      PubDate: 2017-10-02T04:33:06.508112-05:
      DOI: 10.1002/navi.153
  • Equatorial Plasma Bubble Threat Parameterization to Support GBAS
           Operations in the Brazilian Region
    • Authors: Moonseok Yoon; Jiyun Lee, Sam Pullen, Joseph Gillespie, Navin Mathur, Rich Cole, Jonas Rodrigues Souza, Patricia Doherty, Rezy Pradipta
      Pages: 309 - 321
      Abstract: The Brazil ionospheric study project aims to develop a new ground-based augmentation system (GBAS) ionospheric threat model to better reflect Brazil's low-latitude conditions. Data processing from the global navigation satellite system for 123 active ionospheric days identified 1017 anomalous ionospheric gradients caused by nighttime equatorial plasma bubbles (EPBs). A significant number of gradients, including the largest verified gradient of 850.7 mm/km, exceed the upper bound (375–425 mm/km) of the conterminous United States (CONUS) threat model. This paper defines a series of parameters to model the geometry of EPBs. A maximum ionospheric delay drop of 35 m and a transition zone between 20 and 450 km are estimated for EPBs that move roughly eastward and parallel to the geomagnetic equator with speeds between 40 and 250 m/s. These parameters are key to the development of a GBAS ionospheric mitigation and safety case for operational approval in Brazil and other low-latitude locations. Copyright © 2017 Institute of Navigation
      PubDate: 2017-09-17T19:50:40.381408-05:
      DOI: 10.1002/navi.203
  • Orbital Filter Aiding of a High Sensitivity GPS Receiver for Lunar
    • Authors: Vincenzo Capuano; Paul Blunt, Cyril Botteron, Pierre-André Farine
      Pages: 323 - 338
      Abstract: Recent studies have shown that weak global navigation satellite system (GNSS) signals could potentially be used to navigate from Earth to the Moon. This would increase autonomy, robustness, and flexibility of the navigation architectures for future lunar missions. However, the utilization of GNSS signals at very high altitudes close to the Moon can be significantly limited by the very low power levels seen at the receiver's antenna. This can result in a strongly reduced visibility of the GNSS satellites, which can worsen the already poor relative geometry of the GNSS receiver to the GNSS satellites. Furthermore, during most of a Moon transfer orbit (MTO), the very weak GNSS signals are also affected by Doppler shifts and Doppler rates larger than the ones generally experienced on Earth, due to the much higher relative dynamics between the receiver and the transmitters. As a consequence, commercial GNSS receivers for terrestrial use cannot successfully acquire and track such signals. More advanced architectures and specific implementations are thus required to use GNSS for lunar missions. In this paper, we propose the use of an adaptive orbital filter to aid the GNSS acquisition and tracking modules and to strongly increase the achievable navigation accuracy. The paper describes the orbital filter architecture and tests results carried out by processing realistic radio frequency (RF) signals generated by our Spirent GSS 8000 full constellation simulator for a highly elliptical MTO. Copyright © 2017 Institute of Navigation
      PubDate: 2017-06-05T18:45:41.464145-05:
      DOI: 10.1002/navi.185
  • Providing a Resilient Timing and UTC Service Using eLoran in the United
    • Authors: Gerard Offermans; Stephen Bartlett, Charles Schue
      Pages: 339 - 349
      Abstract: More and more systems are becoming solely dependent on GPS or other Global Navigation Satellite Systems (GNSS) for their precise position, timing, and frequency information. Along with this explosive growth comes an increasing awareness of GNSS vulnerabilities such as interference, jamming, and spoofing.eLoran is a high-power, low-frequency, ground-wave radio broadcast system, capable of providing 10-meter positioning accuracy, Stratum-1 frequency distribution, and UTC timing well within 1 μs across very large areas (1,000 mi). Application of differential corrections for timing further improves the accuracy to better than 100 ns. eLoran is a proven technology, well established for providing services very similar to those delivered by GNSS, with characteristics and failure modes that are complementary to GNSS.This paper discusses the general concept of eLoran timing and UTC distribution, and the current prototype service. It highlights plans for an initial four-station CONUS-wide timing service, which can be expanded to provide increased coverage and redundancy and deeper penetration into buildings. Additional stations enable positioning and navigation services. Copyright © 2017 Institute of Navigation
      PubDate: 2017-06-20T21:11:29.190424-05:
      DOI: 10.1002/navi.197
  • A Comparison of Opportunistic Signals for Wireless Syntonization Using the
           Modified Cramér–Rao Lower Bound
    • Authors: Hans-Martin Tröger; Joerg Robert, Lucila Patino-Studencki, Albert Heuberger
      Pages: 351 - 363
      Abstract: The exact adjustment of the oscillators within a wireless sensor network is one basic requirement for precise time difference of arrival localization methods. Typically, GPS is used for the required syntonization of the oscillators, but its performance is not sufficient for high-precision network timing. In contrast, a wired clock distribution is very cumbersome and expensive. In this article, we describe a new method of adjusting the oscillators of distributed receiver nodes with the help of so-called Signals of Opportunity (SoO). We derive the required signal properties of optimal SoO, and we show that Orthogonal Frequency Division Multiplexing (OFDM)-based waveforms offer ideal properties. After a discussion of the OFDM signal structure, we compare different OFDM signals with the help of the Modified Cramér–Rao Lower Bound (MCRLB) regarding their syntonization performance. We also show how signal decision can be used to further improve the accuracy. Finally, we prove our theoretical bounds by means of simulation results. Copyright © 2017 Institute of Navigation
      PubDate: 2017-09-11T23:36:29.25053-05:0
      DOI: 10.1002/navi.204
  • Analysis of Cross-Rate Interference Cancelation by Use of a Novel Phase
           Code Interval in Loran Navigation System
    • Authors: Meysam Bayat; Mohammad Hossein Madani
      Pages: 365 - 376
      Abstract: This work concentrates on improving performance of the Loran system with rejection of cross-rate interference (CRI) by the use of a new phase code interval, the so-called Bayat Phase Code Interval (BPCI), and on the signal in the frequency domain. Indeed, interference will be canceled by removing the common spectral lines between main and interference chains in all integer coefficients of the greatest common divisor frequency of two code intervals. In addition, all interference originating from sky waves that have delay greater than 700 μs is removed by employing both the presented phase code and averaging algorithm. The results demonstrate that if the design is desirable, in the sense that the inverse of the greatest common divisor of BPCI of the considered chain with adjacent interfering chains is equal to an integer multiple of 0.5 kHz, then the proposed BPCI rejects all of the spectral lines of the undesired chain. Copyright © 2017 Institute of Navigation
      PubDate: 2017-08-28T20:31:36.538179-05:
      DOI: 10.1002/navi.202
  • Robust Chi-square Monitor Performance with Noise Covariance of Unknown
           Aspect Ratio
    • Authors: Jason H. Rife
      Pages: 377 - 389
      Abstract: This paper identifies a bound for the worst-case (largest) missed-detection and false-alarm probabilities for a chi-square monitor in which the input signal vector cannot be perfectly decorrelated. A new method for bounding monitor missed-detection performance is introduced that leverages the aspect ratio (aka, condition number) for the covariance matrix of the imperfectly decorrelated signal. An application to signal deformation monitoring for the global positioning system indicates that the new bound is both tight and relatively inexpensive to compute. Copyright © 2017 Institute of Navigation
      PubDate: 2017-06-06T23:15:53.248366-05:
      DOI: 10.1002/navi.192
  • Performance Evaluation of an Automatic GPS Ionospheric Phase Scintillation
           Detector Using a Machine-Learning Algorithm
    • Authors: Yu Jiao; John J. Hall, Yu T. Morton
      Pages: 391 - 402
      Abstract: Ionospheric phase scintillation can cause errors or outage in GNSS navigation solutions. Timely detection of phase scintillation will enable adaptive processing to mitigate its effects on navigation solutions. This paper presents a machine-learning algorithm to autonomously detect phase scintillation based on frequency domain features. Validation using data from Gakona shows phase scintillation detection accuracy around 92 percent. Test results using data from Poker Flat, Jicamarca, Singapore, and Hong Kong demonstrate the capability of the trained detector to be applied more generally. Performance evaluation reveals that the values of phase scintillation index σϕ may be poor indications of scintillation activities. Concurrent phase and amplitude scintillation detection using similar machine-learning algorithms is further investigated with low-latitude data. Results suggest that at low latitudes an amplitude detector alone is sufficient to capture scintillation in general, while at high latitudes, a phase scintillation detector is necessary to capture the dominating phase scintillation events. Copyright © 2017 Institute of Navigation
      PubDate: 2017-06-06T00:25:41.555026-05:
      DOI: 10.1002/navi.188
  • Issue Information
    • Pages: 403 - 407
      Abstract: No abstract is available for this article.
      PubDate: 2017-10-02T04:33:08.586043-05:
      DOI: 10.1002/navi.154
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