Showing papers on "GPS/INS published in 1999"

Adaptive Kalman Filtering for INS/GPS

Abstract: After reviewing the two main approaches of adaptive Kalman filtering, namely, innovation-based adaptive estimation (IAE) and multiple-model-based adaptive estimation (MMAE), the detailed development of an innovation-based adaptive Kalman filter for an integrated inertial navigation system/global positioning system (INS/GPS) is given. The developed adaptive Kalman filter is based on the maximum likelihood criterion for the proper choice of the filter weight and hence the filter gain factors. Results from two kinematic field tests in which the INS/GPS was compared to highly precise reference data are presented. Results show that the adaptive Kalman filter outperforms the conventional Kalman filter by tuning either the system noise variance–covariance (V–C) matrix `Q' or the update measurement noise V–C matrix `R' or both of them.

Robust localization using relative and absolute position estimates

Abstract: A low cost strategy based on well calibrated odometry is presented for localizing mobile robots The paper describes a two-step process for correction of 'systematic errors' in encoder measurements followed by fusion of the calibrated odometry with a gyroscope and GPS resulting in a robust localization scheme A Kalman filter operating on data from the sensors is used for estimating position and orientation of the robot Experimental results are presented that show an improvement of at least one order of magnitude in accuracy compared to the un-calibrated, un-filtered case Our method is systematic, simple and yields very good results We show that this strategy proves useful when the robot is using GPS to localize itself as well as when GPS becomes unavailable for some time As a result robot can move in and out of enclosed spaces, such as buildings, while keeping track of its position on the fly

GPS signal diffraction modelling: the stochastic SIGMA-δ model

Abstract: The SIGMA-Δ model has been developed for stochastic modelling of global positioning system (GPS) signal diffraction errors in high precision GPS surveys. The basic information used in the SIGMA-Δ model is the measured carrier-to-noise power-density ratio (C/N0). Using the C/N0 data and a template technique, the proper variances are derived for all phase observations. Thus the quality of the measured phase is automatically assessed and if phase observations are suspected to be contaminated by diffraction effects they are weighted down in the least-squares adjustment. The ability of the SIGMA-Δ model to reduce signal diffraction effects is demonstrated on two static GPS surveys as well as on a kinematic high-precision GPS railway survey. In cases of severe signal diffraction the accuracy of the GPS positions is improved by more than 50% compared to standard GPS processing techniques.

Method and apparatus for increasing the sensitivity of a global positioning satellite receiver

Abstract: Method and apparatus providing enhanced sensitivity for GPS receivers (400, 500, 600, 700) by allowing coherent integration of a correlation over several code periods of a GPS signal in one embodiment, and by performing a time to frequency domain conversion to the output from a correlation processor (507) in a second embodiment. In the case in which coherent integration is performed over several code periods, advantage is taken of the fact that CDMA cellular telephone base stations transmit information that allows the receiver to determine GPS time before beginning a GPS signal acquisition process. The integration can be expanded to include code periods from more than one bit period, if the GPS receiver (400, 500, 600, 700) takes advantage of the fact that known bit patterns are transmitted at particular times within the transmission from a GPS satellite. If no base station is within range, then the output from a correlator (507) that integrates a correlation over one code period is used to generate values that are input to a discrete time domain to frequency domain transform processor (511). The output from the transform processor (511) will indicate the presence of a signal from a particular satellite and the offset between locally generated signal and the received GPS signal.

Inertial navigation system aided by aircraft dynamics

Abstract: In this work the possibility of using the model of aircraft dynamics as a means for aiding an inertial navigation system is studied. The method is of particular interest for low-grade inertial navigating system (INS). The aiding formulation is introduced, its corresponding mathematical model is derived and used in the design of an appropriate extended Kalman filter. Sensitivity analysis of the errors caused by perturbations in the parameters of the aircraft dynamics demonstrates the robustness of the scheme. The importance of maneuvers for observability is also presented. Simulations show that the use of aircraft dynamics for aiding a low-grade inertial navigation system yields a navigation system whose performance is considerably better than that of the pure INS. This improvement is made possible by the fact that the errors in the aircraft dynamics model are observable when performing appropriate calibration maneuvers.

Stand alone global positioning system (gps) and method with high sensitivity

Abstract: A method is provided for determining the position of a user terminal utilizing global positioning system (GPS) satellites, each of the GPS satellites transmitting a signal containing information indicative of the orbital parameters of the respective GPS satellite, timing and synchronization data and clock correction parameters. The method includes the steps of approximating an expected range of Doppler frequencies within which at least one GPS satellite should be located, within this range, searching for and acquiring a first GPS signal from a first GPS satellite at the user terminal strong enough to demodulate, the first GPS signal containing information indicative of the orbital parameters of the first GPS satellite, timing and synchronization data and clock correction parameters, demodulating the first GPS signal to obtain time of week information, measuring code phase synchronization for the first GPS signal utilizing the time of week information, searching for and acquiring second, third and fourth GPS signals at the user terminal from second, third and fourth GPS satellites, respectively, measuring code phase synchronizations for the second, third and fourth GPS signals utilizing the time of week information, and calculating the position of the user terminal utilizing the code phase synchronizations of the first through fourth GPS signals.

Sensor fusion based on fuzzy Kalman filtering for autonomous robot vehicle

Abstract: Presents a method of sensor fusion based on adaptive fuzzy Kalman filtering. This method has been applied to fuse position signals from the Global Positioning System (GPS) and inertial navigation system (INS) for autonomous mobile vehicles. The presented method has been validated in a 3-D environment and is of particular importance for guidance, navigation, and control of flying vehicles. The extended Kalman filter (EKF) and the noise characteristic have been modified using a fuzzy logic adaptive system and compared with the performance of the regular EKF. It has been demonstrated that the fuzzy adaptive Kalman filter gives better results (more accurate) than the EKF.

Testing and evaluation of an integrated GPS/INS system for small AUV navigation

Abstract: A Small Autonomous Underwater Vehicle Navigation System (SANS) is being developed at the Naval Postgraduate School. The SANS is an integrated Global Positioning System/Inertial Navigation System (GPS/INS) navigation system composed of low-cost and small-size components. It is designed to demonstrate the feasibility of using a low-cost strap-down inertial measurement unit (IMU) to navigate between intermittent GPS fixes. The present hardware consists of a GPS/DGPS receiver, IMU, compass, water speed sensor, water depth sensor, and a data processing computer. The software is based on a 12-state complementary filter that combines measurement data from all sensors to derive a vehicle position/orientation estimate. This paper describes hardware and software design and testing results of the SANS. It is shown that results from tilt table testing and bench testing provide an effective means for tuning filter gains. Ground vehicle testing verifies the overall functioning of the SANS and exhibits an encouraging degree of accuracy.

Development of a nonlinear psi-angle model for large misalignment errors and its application in INS alignment and calibration

Abstract: This work presents a general nonlinear psi-angle approach that does not require coarse alignment. In this psi-angle model, the three misalignment angles are assumed all large. Three states are used to describe three psi-angles rather than the four used in previous works. The approach is identical to the standard small error methods when the process errors diminish to small angles. The position and velocity error models are also presented. Standard extended Kalman filter techniques are used to solve the nonlinear data fusion problem. Experimental results of in-flight inertial navigation systems (INS) alignment and calibration are presented considering total uncertainty in azimuth orientation using a low cost inertial measurement unit aided with a differential global positioning system.

Carrier-phase time transfer

Abstract: We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10/sup -15/ for an average time of 1 day.

Integrated Navigation and Guidance Systems

Abstract: Principles of Navigation and the Concept of an Integrated Navigation System Newton's Laws Applied to Navigation (Geodesics, Basic Reference Frames, Simplified Aerospace Vehicle Equation) Inertial Navigation Systems (INS) and Global Positioning System (GPS) Uncertainty in Navigation, INS Error Propagation, Probabilities, Autocorrelation and the Method of Least Squares Kalman Filters and Their Key Role in the Integration of Aircraft Avionics Systems GPS Theory and its Application to Navigation (Including System Accuracy) GPS Application to Precision Approach and Landing, Attitude Control and Air Traffic Control Flight Testing of Navigation Systems Computer Exercises.

Direct exterior orientation of airborne imagery with gps/ins system: performance analysis.

Abstract: Integrating the Global Positioning System (GPS) with an Inertial Navigation System (INS) allows for direct image georeferencing, offering a possibility of relaxing the demand for aerial triangulation (AT) in airborne surveying/mapping. The performance of the prototype of the Airborne Integrated Mapping System (AIMS™), based on GPS/INS/CCD (charge-coupled device) integration, developed by The Ohio State University Center for Mapping, is investigated in this paper. A brief description of the essential features of the integrated system and its practical implementation is presented. The performance of AIMS™ is primarily assessed based on the photogrammetric processing of 1:6,000 large-scale aerial imagery considered as a truth reference. An accuracy analysis and discussion of the impact of direct orientation and the multi-sensor system calibration on the photogrammetric data extraction process are also addressed.

Method of enhancing receiver autonomous GPS navigation integrity monitoring and GPS receiver implementing the same

Abstract: A global positioning system (GPS) receiver or navigation apparatus for use on an aircraft is disclosed. The receiver implements improved methods of performing both navigation and fault detection and exclusion (FDE) functions. The GPS receiver includes an antenna adapted to receive GPS satellite signals from each of a multiple GPS satellites. Navigation solution determining circuitry coupled to the antenna receives the GPS satellite signals and performs navigation and FDE functions. The navigation solution determining circuitry is adapted to determine both a horizontal position of a least squares navigation solution for the receiver and a horizontal position of a first navigation solution for the receiver as functions of the received GPS satellite signals. The horizontal position of the first navigation solution for the receiver is offset from the horizontal position of the least squares navigation solution for the receiver. The first navigation solution can be either of a maximal accuracy or a maximal integrity navigation solution.

GPS receiver having a fast time to first fix

Abstract: A global positioning system (GPS) receiver having a fast time to first fix using the velocity of a GPS satellite and an approximate time The GPS receiver includes a GPS antenna for receiving a GPS signal, radio frequency circuitry for downconverting and sampling the GPS signal, a reference timer for providing a reference clocking signal, a digital signal processor for receiving the sampled GPS signal, and a microprocessor for executing program codes in a memory The digital signal processor cooperates with the microprocessor for correlating the sampled GPS signal to an internal GPS replica signal based upon the reference clocking signal The memory includes program codes for a pseudorange detector for measuring code phase offsets, a directional cosine calculator for calculating unit vectors, a satellite velocity calculator for calculating vector velocities, a pseudorange linearizer for determining linearized pseudoranges, and a velocity-enhanced location calculator The velocity-enhanced location calculator uses an approximate absolute time with the linearized pseudoranges, unit vectors, and velocities of five or more GPS satellites for determining a GPS-based location for the GPS receiver before receiving a Z-count in a GPS signal The error in the approximate time may be up to at least 100 seconds

System and method for improved accuracy in locating and maintaining positions using GPS

Abstract: A system and method are provided for using multiple GPS antennas and corresponding processors on a single vehicle in order to both maintain position information when fewer than four GPS satellites are visible and to reduce position errors by minimizing multipath induced errors using information combined from the multiple systems. The system and method calculates differential path lengths between the received position information signals and at least two antenna/processor pairs to determine cone angles therebetween. The position information of the mobile vehicle is maintained based on the initial position information and the determined cone angles.

GPS receiver having improved signal acquisition at a low signal to noise ratio

Abstract: A GPS receiver having a fast acquisition of a GPS signal having a low signal-to-noise ratio. The GPS receiver adjusts a local frequency for iteratively downconverting raw GPS signal samples to baseband GPS signal code data, combining a plurality of code epochs of the GPS signal code data in chunks and super chunks for providing representative code epochs, and correlates the representative code epochs to a replica code epoch for providing correlation times. A microcontroller processes the correlation times for providing the frequency corrections and computes a GPS pseudorange when the error in the corrected local frequency is less than a threshold. The GPS pseudoranges for several GPS satellites are transmitted back to the base for computing the GPS-based location of the GPS receiver.

Global positioning system satellite selection method

Abstract: The satellite selection method as utilized by the spaceborne Global Positioning System receiver provides navigational solutions and is designed for use in low Earth orbit. The satellite selection method is a robust algorithm that can be used a GPS receiver to select appropriate GPS satellites for use in calculating point solutions or attitude solutions. The method is takes into account the difficulty of finding a particular GPS satellite phase code, especially when the search range in greatly increased due to Doppler shifts introduced into the carrier frequency. The method starts with an update of the antenna pointing and spacecraft vectors to determine the antenna backplane direction. Next, the GPS satellites that will potentially be in view of the antenna are ranked on a list, whereby the list is generated based on the estimated attitude and position of each GPS satellite. Satellites blocked by the Earth are not entered on this list. A second list is created, whereby the GPS satellites are ranked according to their desirability for use in attitude determination. GPS satellites are ranked according to their orthogonality to the antenna backplane, and according to geometric dilution of precision considerations. After the lists are created, the channels of the spaceborne GPS receiver are assigned to various GPS satellites for acquisition and lock. Preliminary Doppler frequencies for searching are assigned to the various channels.

Time transfer using multi-channel GPS receivers

Abstract: This report is on time transfer experiments using a Global Positioning System (GPS) receiver constructed using a commercial GPS "engine" and a standard PC. The receiver measures the time difference between the local clock and a 1 pps signal synchronized to GPS time using data from up to 8 satellites. The receiver also reports the difference between GPS time as estimated using each of the satellites being tracked and the composite output pulses that have a rate of 1 Hz (1 pps signal). These data can be used to construct the standard 13-minute tracks as defined in the BIPM standard; the same data also can be averaged in other ways that make better use of the multi-channel capabilities of the hardware. The 13-minute averages can be directly compared with standard time-transfer receivers using common-view analysis. The results of the tests suggest that the methods currently used for national and international time and frequency coordination should be re-examined, and an alternative approach based on multi-channel receivers is suggested that should be more flexible, simpler, and easier to operate than the current system.

Method and system for incorporating two-way ranging navigation as a calibration reference for GPS

Abstract: A method and system for using two-way ranging navigation to accurately determine the range along the path from source to destination by measuring the time delay during round-trip communication via satellite. The two-way ranging navigation measurements are used as calibration references, thereby improving the positioning accuracy of GPS. The system includes GPS and a two-way ranging navigation system for taking position measurements of a target. A correction factor is determined as a function of the measurements and the GPS position is adjusted by the correction factor. The method for calibrating GPS using two-way ranging navigation involves taking a two-way ranging navigation measurement and a GPS measurement of a target, determining a correction factor as a function of the measurements, and correcting the GPS position by taking a second GPS measurement and adjusting it by the correction factor.

Q-factor map matching method using adaptive fuzzy network

Abstract: Many hybrid algorithms which estimate car's position and velocity from GPS signals and INS signals suffer from the unknown GPS noise characteristics such as S/A noise. The unknown characteristics make it impossible to remove the noise completely. As a result, the estimated position information from the hybrid algorithms will be contaminated with undesirable position errors. It is very desirable and effective to use a digital road map to correct the position error, which is known as a map matching method. In this paper, a novel map matching method is proposed. The effectiveness of this algorithm is verified by the real road experiments. For experimental testing, a car navigation system is built with a DSP chip. It uses one GPS receiver, one vehicle speed sensor and one vertical gyroscope.

Unmanned running controller

Abstract: PROBLEM TO BE SOLVED: To provide an unmanned running controller to reduce an error in a dead-reckoning navigation even when positioning is not performed for a long time by a GPS(global positioning system). SOLUTION: This controller is provided with a dead-reckoning navigation controller 15 to detect a relative position of a vehicle 1 from a specified absolute position by a running sensor mounted on the vehicle 1, a GPS controller 14 to detect an absolute position of the vehicle by GPS communication from a GPS satellite 5, a running controller 13 to control speed and steering of the vehicle 1 and a vehicle controller 16 to correct the relative position by every specified time by the GPS and to make the vehicle 1 run on a specified route for a specified time by the dead-reckoning navigation, precision of GPS positioning information is decided, based on the GPS communication from the GPS controller 14, a running condition to indicate a running state of the vehicle 1 is decided, based on decision of the precision and an instruction is outputted to the running controller 13, based on this decision. COPYRIGHT: (C)2000,JPO

Determining aircraft position and attitude using GPS position data

Abstract: The present invention is a method and apparatus to determine flight parameters of an aircraft. Data received from a global positioning system (GPS) receiver are converted to position data. The position data are filtered based on a least-squares fitting to generate smoothed position data which provide the flight parameters.

The Applanix Approach to GPS/INS Integration

Abstract: The Position and Orientation System for Direct Georeferencing (POS/DG) is an off-the-shelf integrated GPS/inertial system designed specifically for airborne applications. POS/DG measures the position and orientation of the sensor with accuracies sufficient to produce Digital Terrain Models (DTM), Orthophotos and Maps that are suitable for a wide range of applications. Over the past four years POS/DG has been installed on various airborne sensors requiring high-accuracy position and attitude measurements: aerial cameras, digital line scanners and digital cameras, laser scanners, and Synthetic Aperture Radar (SAR). For aerial and digital frame cameras, POS/DG enables the direct georeferencing of aerial photos without the need for aerial triangulation or tie points and only minimal ground control. For line and laser scanners POS/DG performs line-to-line geometric correction and direct georeferencing of the data. For SAR systems POS/DG is used for the motion compensation over the aperture length and he data geocoding of the derived DTM. The common element in all these application is a substantial reduction in the post-processing effort and rapid turnaround of data. In the case of the line and laser scanners in particular, the incorporation of POS/DG has actually enabled their use as a mapping tool an application that was previously not possible with scanning-type sensors.

Robust autonomous GPS time reference for space application

Abstract: A receiver clock bias signal for a spacecraft in motion is is used to obtain a real-time navigation Kalman filter solution of the clock bias and provide a robust autonomous GPS time reference, even when there are less than 4 GPS satellites within the view of the receiver in the spacecraft. The Kalman filter of the spacecraft provides an accurate solution of the clock bias, with less than 4 GPS satellite signals, by means of a system which uses the knowledge of the dynamic motion of the satellite in conjunction with GPS signals for a robust estimation of time. The system provides an accurate GPS time reference by transferring timing information from an atomic reference standard (GPS) to a spacecraft in motion by directly measuring the GPS signal and without depending upon the tracking of multiple GPS satellites or a static receiver. Implementation in current aerospace qualified GPS receivers, e.g., the “GPS TENSOR™”, and known orbital dynamics are used to predict receiver position which aids in the transfer of the GPS time.

Portable position detector for pedestrian navigation has positioning system based on pedometer, terrestrial magnetic field detector and accelerometer

Abstract: The distance covered is calculated from the number of steps times the length of a step. The length of a step is corrected using the accelerometer (23). The direction of movement is determined using the terrestrial magnetic field detector (13). Thus the position of a pedestrian can be estimated based on the distance and direction. The position detector may include a GPS unit for measuring the current position and correcting the estimated position when GPS information is available. An Independent claim is given for a position management system.

A PIM-aided Kalman Filter for GPS Tomography of the Ionospheric Electron Content

Abstract: We develop the formalism to perform PIM-based stochastic tomography of the ionospheric electron content with a Kalman filter, in which the inversion problem associated with four-dimensional ionospheric stochastic tomography is regularized. For consistency, GPS data is used to select dynamically the best PIM parameters, in a 3DVAR fashion. We demonstrate the ingestion of (10S and GPS/MEI) GPS data into a parameterized ionospheric model, in order to select the set of parameters that minimize a suitable cost functional. The resulting PIM-fitted model is compared to direct 3D voxel tomography. We demonstrate the value of this method analyzing IGS and GPS/M ET GPS data, and present our results in terms of a 4D model of the ionospheric electronic density.

Carrier phase differential GPS/INS positioning for formation flight

Abstract: A method for implementing and testing algorithms for combining differential carrier phase GPS and an INS system for formation flight of two NASA F-18 aircraft is presented. A computer architecture based on the PC-104 AT bus and commercial, off-the-shelf components is used for implementing the algorithms. Processing the carrier phase measurements using an INS with online calibration by a tightly coupled extended Kalman filter should provide relative position measurements to within 10 cm without the use of a stationary base station. Two methods are suggested for solving the integer ambiguity problem. The method of Farrell et al. uses hypothesis testing combined with least squares processing to determine the initial integer values. A second method uses the multiple model adaptive Kalman filter with improved convergence properties to estimate the integers. In order to test these algorithms and hardware, a hardware in the loop simulation using an IEC GPS Constellation Simulator will be constructed to validate accuracy claims.

An innovative estimation method with own-ship estimator for an allaccelerometer-type inertial navigation system

Abstract: An innovation estimation scheme is conceived to solve the initial and divergent problems for an all-accelerometer inertial navigation system (INS) The system uses six accelerometers mounted diagonally on each surface of a cube The method exploits the presence of the gravity effect which gives additional information that helps to determine the sense of the angular velocity It also provides an upper bound value for the initiation of the platform attitude A simulation case is investigated, which verifies the effectiveness of using this information-infusing concept in obtaining a convergent INS state estimation, through using the own-ship trajectory estimator to provide the pseudo-measurements for the position and velocity of the vehicle