Kyle O'Keefe

Tightly-coupled GPS/UWB Integration

Ultra-wideband (UWB) ranging radios, an emerging technology that offers precise, short distance range measurements are investigated as a method to augment carrier-phase GPS positioning. A commercially available UWB ranging system is used in a tightly-coupled GPS and UWB real-time kinematic (RTK) system. The performance of the tightly-coupled system is evaluated in static and kinematic testing. This work demonstrates that UWB errors can be successfully estimated in a real-time filter. The results of static testing show that the integrated solution provides better accuracy, better ability to resolve integer ambiguities and enhanced fixed ambiguity solution availability compared with GPS alone. In kinematic testing in a degraded GPS environment, sub-decimetre accuracy was maintained.

Measuring Aircraft Carrier Flexure in Support of Autonomous Aircraft Landings

This paper quantifies the experimental measurements of aircraft carrier flexure (deformation) at sea in support of the United States Department of Defense sea-based Joint Precision Approach and Landing System (JPALS) that aims to deliver automatic landing capabilities to inbound aircraft aboard aircraft carriers. The methodology for measuring ship flexure using the Global Positioning System (GPS) and inertial sensors is described. Results indicate that flexure on the aircraft carrier used for testing has a standard deviation of approximately 1-2 cm. For the ship tested, the most significant flexure effects are in the port/starboard direction and correlate best with roll or lateral acceleration.

Ultra-wideband ranging precision and accuracy

This paper provides an overview of ultra-wideband (UWB) in the context of ranging applications and assesses the precision and accuracy of UWB ranging from both a theoretical perspective and a practical perspective using real data. The paper begins with a brief history of UWB technology and the most current definition of what constitutes an UWB signal. The potential precision of UWB ranging is assessed using Cramer?Rao lower bound analysis. UWB ranging methods are described and potential error sources are discussed. Two types of commercially available UWB ranging radios are introduced which are used in testing. Actual ranging accuracy is assessed from line-of-sight testing under benign signal conditions by comparison to high-accuracy electronic distance measurements and to ranges derived from GPS real-time kinematic positioning. Range measurements obtained in outdoor testing with line-of-sight obstructions and strong reflection sources are compared to ranges derived from classically surveyed positions. The paper concludes with a discussion of the potential applications for UWB ranging.

Assessing Three New GPS Combined L1/L2C Acquisition Methods

This paper presents three new global positioning system acquisition methods that make use of both L1 C/A and L2C signals in a combined way. The methods perform joint estimation of the Doppler frequencies and code delays on L1 and L2 without increasing the coherent integration time. Each method is assessed in terms of theoretical probabilities of false alarm and detection as well as through testing with real intermediate frequency data. The first method is a noncoherent summation of L1 and L2 correlator outputs. The second method implements an independent differential summation of L1/L2 correlator outputs, and the third method uses a noncoherent plus dependent differential summation. While each method provides increased detection performance compared with the standard noncoherent acquisition applied on L1 C/A, the noncoherent plus dependent differential summation method outperforms all of the others in the scenarios investigated.

A piecewise matched-field tracking algorithm

Matched-field tracking (MFT) algorithms have been successfully applied to both simulated and measured data to determine the most likely positions of a sound source that is localized ambiguously by a matched-field processing (MFP) system. They have been used to track sources moving linearly or on a circular path at constant speed and heading. The input to the trackers is a set of ambiguity surfaces, contiguous in time, generated by MFP. These algorithms assume that the track start and end times are known a priori; this restriction is removed in the piecewise MFT algorithm (PTA). The PTA was applied to narrow-band measured data collected during the PACIFIC SHELF 93 trial to successfully identify the significant source track segments.

Comparing Multicarrier Ambiguity Resolution Methods for Geometry-Based GPS and Galileo Relative Positioning and Their Application to Low Earth Orbiting Satellite Attitude Determination

This 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.

Tightly-coupled GPS/UWB positioning

A tightly-coupled filter integrating GPS and ultra-wideband observations is implemented and tested in an urban canyon environment. Bias and scale factor errors in the UWB measurements are estimated in-run and used with GPS pseudorange and phase measurements to survey several corner points of an eight story building. Sub-meter level position solutions are maintained using tight-coupling in conditions where using GPS or UWB alone is unreliable or provides no solution at all.

An Investigation of tightly-coupled UWB/low-cost GPS for vehicle-to-infrastructure relative positioning

A method for tightly-coupling carrier-phase differential GPS with ultra-wideband (UWB) ranging for vehicle-to-infrastructure relative navigation is proposed. Relative position, velocity, clock errors, GPS phase ambiguities and UWB systematic errors are estimated using an extended Kalman filter. The method is tested with real data and evaluated in terms of position accuracy, GPS float ambiguity convergence, time to fix ambiguities, and correctness of the ambiguity solution. Performance with geodetic and consumer grade GPS receivers is compared. The effect of UWB operational range and the number of available UWB ranging sources is also evaluated.

Benefit of partial L2C availability to estimate ionospheric delay for dual-frequency GPS ambiguity resolution

This paper evaluates the benefit of the partial availability of GPS satellites with L2C signal capability in estimating the ionospheric delay using the dual-frequency L1/L2 code and phase measurements using real data. Compared to the strategy of estimating one slant ionospheric delay (SID) for each satellite, a simplified single differential zenith ionospheric delay (ZID) method is proposed to account for the ionospheric effect using the limited number of L2C measurements. The algorithms and models are implemented in a Kalman filter (KF) based code and phase observations processor using between receiver single difference (SD) GPS L1/L2 observations. Using data sets from three International GNSS Service (IGS) stations with both L2C and L2P code measurements, the performance of using L1 observations only, L1/L2 dual-frequency observations without estimating ionospheric delay, and L1/L2 dual-frequency observations with estimating either SID or differential ZID is compared in terms of ambiguity resolution (AR) and positioning accuracy in conjunction with ionospheric delay estimation. The results show L1/L2 AR outperforms L1 only in several scenarios, and the proposed method improves vertical accuracy of the fixed position approximately 10 cm with estimating the single differential ZID.

Monocular-based pose estimation using vanishing points for indoor image correction

This paper assesses the estimation of the orientation of a camera rigidly attached to a vehicle body using vanishing points and then uses the estimated rotation to rectify images for navigation in indoor environments. The approach is facilitated by the fact that many indoor environments are rich in vertical and horizontal lines that are used for detecting vanishing points. The performance of the monocular-based navigation is evaluated as well as the image rotation rectification. Results of the proposed methods show that using a single image, we are able to obtain the camera, and thus the platform, 3D orientation as well as accurately correct the image for camera inclination.