Browsing by Author "Lachapelle, Gérard"
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- ItemOpen Access3D Building Model-Assisted Snapshot GNSS Positioning Method(2017) Kumar, Rakesh; Petovello, Mark; Petovello, Mark; Lachapelle, Gérard; O'Keefe, Kyle; Fapojuwo, AbrahamGlobal Navigation Satellite Systems (GNSS) have proven to be a viable and reliable solution in interference-free environments and in presence of Line-of-Sight (LOS) signals only. However, in urban canyons, multipath signals directly affect the pseudorange measurements resulting in degraded positioning performance of traditional GNSS receivers. Moreover, traditional GNSS receivers cannot distinguish between non-LOS (NLOS) and LOS signals, resulting in even worse performance if the receiver tracks NLOS-only signal. Hence, NLOS and multipath signals remains a dominant source of error in satellite-based navigation. Most of the existing research has focused on identifying and rejecting NLOS measurements. However, little research has used NLOS signals constructively. In this regard, this research uses snapshots of GNSS data in order to estimate position, utilizing all NLOS signals constructively with the help of a 3D Building Model (3DBM). Using a 3DBM and a ray-tracing algorithm, the number of reception paths and the corresponding path delays of reflected signals is predicted across a grid of candidate positions. These predictions are then used to compute least-squares fit to the GNSS receiver’s correlator outputs and the position with smallest residuals is selected as the position estimate. This approach is termed Signal Delay Matching (SDM) and yields a solution that is nearly unaffected by traditional GNSS error sources, and has capability of providing a position solution using a single satellite only. The use of snapshots of data mean the receiver need not perform tracking operations, thus making it easier to implement and power efficient. The feasibility and performance of the algorithm was tested using data collected in downtown Calgary, Canada, where buildings reach heights of over 200 m. Contrary to traditional approaches, results for the proposed method show that positioning error decreases as sky-visibility decreases. For sky-visibility below 20%, the median error was found to be just over 3 m. Compared to two pseudorange-based receivers, the proposed method yields RMS errors improvements of 22% to 48% in the horizontal plane.
- ItemOpen AccessA Ray-Tracing Technique to Characterize GPS Multipath in the Frequency Domain(2015-09-28) Gowdayyanadoddi, Naveen S.; Curran, James T.; Broumandan, Ali; Lachapelle, GérardMultipath propagation is one of the major sources of error in GPS measurements. In this research, a ray-tracing technique is proposed to study the frequency domain characteristics of multipath propagation. The Doppler frequency difference, also known as multipath phase rate and fading frequency, between direct (line-of-sight, LOS) and reflected (non-line-of-sight, NLOS) signals is studied as a function of satellite elevation and azimuth, as well as distance between the reflector and the static receiver. The accuracy of the method is verified with measured Doppler differences from real data collected in a downtown environment. The use of ray-tracing derived predicted Doppler differences in a receiver, as a means of alleviating the multipath induced errors in the measurement, is presented and discussed.
- ItemOpen AccessA superresolution based cellular positioning system using GPS time synchronization(1997) Klukas, Richard Walter; Lachapelle, Gérard
- ItemOpen AccessAccuracy and reliability of various DGPS approaches(1996) Tang, Chuanya; Lachapelle, Gérard
- ItemOpen AccessAn analysis of some critical error sources in static GPS surveying(1994) Qiu, Weigen; Lachapelle, GérardSome critical error sources in static GPS surveying and methods to reduce these errors on baseline determinations are investigated. Ambiguity search strategies in rapid static surveying are discussed and some modifications are explored. Based on the assumption that the impact of the periodic multipath error on code and carrier phase measurements can be minimized by averaging the observations, an attempt is made to estimate the site occupation time in order to correctly resolve the integer ambiguities using spectral analysis in postprocessing mode. The relationship between code and carrier phase multipath is investigated. For single frequency users, an ionospheric model is developed by using code and carrier phase measurements. The accuracy of this model and results of baselines by applying this model are analysed.
- ItemOpen AccessAnalysis of NGS CORS network for GPS RTK performance using external NOAA tropospheric corrections integrated with a multiple reference station approach(2005) Ahn, Yong Won; Lachapelle, Gérard; Skone, Susan
- ItemOpen AccessApproaches for the combined tracking of gps l1/l5 signals(2010) Salem, Dina Reda; Lachapelle, Gérard
- ItemOpen AccessAssessment of Measurement Distortions in GNSS Antenna Array Space-Time Processing(2016-02-17) Marathe, Thyagaraja; Daneshmand, Saeed; Lachapelle, GérardAntenna array processing techniques are studied in GNSS as effective tools to mitigate interference in spatial and spatiotemporal domains. However, without specific considerations, the array processing results in biases and distortions in the cross-ambiguity function (CAF) of the ranging codes. In space-time processing (STP) the CAF misshaping can happen due to the combined effect of space-time processing and the unintentional signal attenuation by filtering. This paper focuses on characterizing these degradations for different controlled signal scenarios and for live data from an antenna array. The antenna array simulation method introduced in this paper enables one to perform accurate analyses in the field of STP. The effects of relative placement of the interference source with respect to the desired signal direction are shown using overall measurement errors and profile of the signal strength. Analyses of contributions from each source of distortion are conducted individually and collectively. Effects of distortions on GNSS pseudorange errors and position errors are compared for blind, semi-distortionless, and distortionless beamforming methods. The results from characterization can be useful for designing low distortion filters that are especially important for high accuracy GNSS applications in challenging environments.
- ItemOpen AccessAugmentation of GPS with a barometer and a heading rate gyroscope for urban vehicular navigation(1996) Hayashi, Nobuyuki; Lachapelle, Gérard
- ItemOpen AccessAugmentation of GPS with pseudolites in a marine environment(1997) Morley, Thomas G.; Lachapelle, Gérard
- ItemOpen AccessAutomated traffic incident detection using GPS-based transit probe vehicles(2004) Basnayake, Chaminda; Lachapelle, Gérard; MacIver, AndrewThe recent advancements in electronics, communication and information processing and the application of such technologies to transportation through Intelligent Transportation Systems (ITS) have resulted in safer, faster and more efficient surface transportation systems. ITS have contributed significantly to the current state of technology in automated traffic monitoring, and probe vehicle-based traffic monitoring is one of these techniques. Although the potential of probe vehicle-based traffic monitoring was well understood, its wider application was severely restricted by the state of vehicle positioning system capabilities and associated cost considerations. This thesis presents the devolvement and performance analysis of a probe vehicle-based automated traffic incident detection system that uses transit vehicles equipped with GPS as a passive probe vehicle fleet. Since these vehicles serve primary purposes other than providing vehicle-tracking data, such vehicles are more likely to be equipped with systems such as GPS, thus providing multiple benefits. However, passive probe vehiclebased traffic incident detection has its own challenges over dedicated probe vehicles. These challenges are addressed and solutions are developed in two stages in this thesis. Firstly, the need for a GPS positioning technique that provides better performance in urban environments is addressed with an outline of advantages of High Sensitivity GPS (HSGPS). HSGPS error mitigation techniques are discussed with the emphasis on mapmatching augmentations; a major advantage being their independence from vehicle sensors. A discussion of HSGPS map-matching issues, pros and cons of using internally filtered HSGPS positions, and alternative filtering techniques are also presented. Secondly, probe-based incident detection algorithms and their performances are analyzed. Instead of conducting a complex field data collection for probe and traffic incident data collection, a traffic microsimulation model was developed to simulate transit probe vehicles with and without simulated incidents. The simulation model is calibrated using actual transit vehicle and non-transit vehicle data collected over several days. Incidents detection performance was analyzed with respect to three indicators: Detection Rate (DR), Time to Detect (TTD) and False Alarm Rate (FAR). Performance under varying incident characteristics and GPS performance levels were investigated and the results show over a 90 % DR and a TTD of under 5 minutes for all simulated scenarios.
- ItemOpen AccessBenefits of combined gps/glonass processing for high sensitivity receivers(2011) Tamazin, Mohamed Essam Hassan Roshdy; Lachapelle, Gérard
- ItemOpen AccessCalibration and analysis of LORAN-C using a mobile GPS system(1994) Townsend, Bryan R.; Lachapelle, Gérard
- ItemOpen AccessCharacterization of Signal Quality Monitoring Techniques for Multipath Detection in GNSS Applications(2017-07-05) Pirsiavash, Ali; Broumandan, Ali; Lachapelle, GérardThe performance of Signal Quality Monitoring (SQM) techniques under different multipath scenarios is analyzed. First, SQM variation profiles are investigated as critical requirements in evaluating the theoretical performance of SQM metrics. The sensitivity and effectiveness of SQM approaches for multipath detection and mitigation are then defined and analyzed by comparing SQM profiles and multipath error envelopes for different discriminators. Analytical discussions includes two discriminator strategies, namely narrow and high resolution correlator techniques for BPSK(1), and BOC(1,1) signaling schemes. Data analysis is also carried out for static and kinematic scenarios to validate the SQM profiles and examine SQM performance in actual multipath environments. Results show that although SQM is sensitive to medium and long-delay multipath, its effectiveness in mitigating these ranges of multipath errors varies based on tracking strategy and signaling scheme. For short-delay multipath scenarios, the multipath effect on pseudorange measurements remains mostly undetected due to the low sensitivity of SQM metrics.
- ItemOpen AccessCo-processor aiding for real-time software gnss receivers(2010) Knezevic, Aleksandar; Lachapelle, Gérard; O'Driscoll, Cillian
- ItemOpen AccessCombined Acquisition and Tracking Methods for GPS L1 C/A and L1C Signals(Hindawi Publishing Corporation, 2010-09-18) Macchi-Gernot, Florence; Petovello, Mark; Lachapelle, Gérard
- ItemOpen AccessCombined Acquisition and Tracking Methods for GPS L1 C/A and L1C Signals(2010-12-01) Macchi-Gernot, Florence; Petovello, Mark G.; Lachapelle, GérardAs part of the GPS modernization, the GPS L1 C/A signal will be augmented by the L1C signal. With this improvement, for the first time, several signals from the same constellation will be available at the same frequency. In this paper, an acquisition method is implemented to combine the GPS L1 C/A and L1C signals before correlation. The combined acquisition succeeds to acquire the signal at low C/N0, whereas the acquisition of the L1C data channel alone fails. Concerning the tracking, a method to combine the GPS L1 C/A and L1C signals before the discriminator is developed. This method shows better performance than the traditional tracking using only one signal. Finally, a Kalman filter to combine the signals in the tracking is developed. It shows better performance than the traditional tracking in all conditions. Since the L1C signal will not be broadcast before 2013, these methods are tested using a software signal simulator.
- ItemOpen AccessComparing Multicarrier Ambiguity Resolution Methods for Geometry-Based GPS and Galileo Relative Positioning and Their Application to Low Earth Orbiting Satellite Attitude Determination(Hindawi Publishing Corporation, 2009-03-08) O'Keefe, Kyle; Petovello, Mark; Cao, Wei; Lachapelle, Gérard; Guyader, EricThis paper presents an evaluation of several GNSS multicarrier ambiguity (MCAR) resolution techniques for the purpose of attitude determination of low earth orbiting satellites (LEOs). It is based on the outcomes of the study performed by the University of Calgary and financed by the European 6th Framework Programme for Research and Development as part of the research project PROGENY. The existing MCAR literature is reviewed and eight possible variations of the general MCAR processing scheme are identified based on two possible options for the mathematical model of the float solution, two options for the estimation technique used for the float solution, and finally two possible options for the ambiguity resolution process. The two most promising methods, geometry-based filtered cascading and geometry-based filtered LAMBDA, are analysed in detail for two simulated users modelled after polar orbiting LEOs through an extensive covariance simulation. Both the proposed Galileo constellation and Galileo used in conjunction with the GPS constellation are tested and results are presented in terms of probabilities of correct ambiguity resolution and float and fixed solution baseline accuracies. The LAMBDA algorithm is shown to outperform the cascading method, particularly in the single-frequency dual-GNSS system case. Secondly, more frequencies and multiple GNSS always offer improvement, but the single-frequency dual-system case is found to have similar performance to the dual-frequency single-system case.
- ItemOpen AccessComplete Triaxis Magnetometer Calibration in the Magnetic Domain(Hindawi Publishing Corporation, 2010-10-26) Renaudin, Valérie; Afzal, Muhammad Haris; Lachapelle, Gérard