Showing papers on "GPS/INS published in 1988"

Control theoretic approach to inertial navigation systems

Abstract: In this work, the analysis of inertial navigation systems (INS) is approached from a control theory point of view. Linear error models are presented and discussed and their eigenvalues are computed in several special cases. It is shown that the exact expressions derived for the eigenvalues differ slightly from the commonly used expressions. The observability of INS during initial alignment and calibration at rest is analyzed. A transformation that is based on physical insight is introduced that enables us to determine the unobservable subspace and states rather easily by inspection of the new dynamics matrix. Finally, the relationship between system observability and quality of estima- tion is presented. ever, as will be shown in the sequel, the inclusion of the vertical channel does alter the eigenvalues slightly. In the examination of system observability, we use a straightforward transforma- tion into observable and unobservable subsystems that, in turn, expose the states that hamper the estimation of INS errors during the initial alignment and calibration phase of operation. This approach was adopted successfully in the past by Kor- tum3 who considered the problem of INS platform alignment in which the measurements were the horizontal accelerometer outputs, whereas in the present case the measurements are the INS horizontal velocity components. In addition, the compari- son of this approach to the classical one that is presented in the present paper, as well as the discussion of uniqueness and the relationship between observability and quality of estimation, provide additional insight into the observability issue. It is hoped that the examination of INS as a unified system from a control theory point of view will shed more light on the system and contribute additional insight into the analysis of INS. In the next section, we describe the INS linear error model that will be the investigated plant. In Sec. Ill, we investigate the eigenvalues of INS in various phases of operation, and in Sec. IV, the issues of controllability and observability of the system are discussed. The relation between system observability and the ability to estimate its states during initial alignment is discussed in Sec. V. Finally, in Sec. VI, the conclusions are presented.

GPS/self-contained combination type navigation system

Abstract: In a global positioning system (GPS)/self-contained combination type navigation system for a vehicle, the GPS navigation data are received by the GPS antenna of the navigation system which are simultaneously transmitted from more than 3 pieces of satellites inclusively. From the GPS navigation data, GPS type velocity data is calculated, whereas self-contained type velocity data is calculated from self-contained type navigation data such as azimuth data and drive-distance data of the vehicle. Only when a difference between the self-contained type velocity data and the GPS type velocity data exceeds a threshold velocity, the GPS type velocity data is voided so as to determine the present position of the vehicle.

A Kalman filter for integrating dead reckoning, map matching and GPS positioning

Abstract: A Kalman filter has been developed to integrate the three positioning systems (differential odometer dead reckoning, map matching, and Global Positioning System or GPS) used in the Automatic Vehicle Location System (AVL 2000) being designed and developed in the Department of Surveying Engineering at the University of Calgary The system is being targeted for on road applications and incorporates a digital map The filter has been designed to take into account uncertainties via covariance matrices In wide-open spaces GPS positioning will dominate, while in zones where the GPS signal is obstructed, dead reckoning will be used as interpolation between GPS position fixes Simulation studies and covariance analyses have been performed on a test route located in a sector of the city of Calgary >

High-Accuracy Kinematic Positioning by GPS-INS

Abstract: Recent results achieved with relative GPS positioning techniques indicate that accuracies at the meter level are possible in land vehicle mode if the cycle slip problem can be minimized. One of the possible solutions to the problem is the integration of GPS and inertial data. Results from inertial surveys show that, with regular, accurate coordinate or range updates, an INS will give velocity estimates at the cm/s level [1]. By integrating differential GPS measurements with an INS, the effect of cycle slips over short intervals may be eliminated from the positioning results. A Kalman filter-smoother to handle this problem has been developed. It integrates differential range and phase measurements with data from an inertial navigation system. The optimal backward smoother improves the filter estimates for periods of poor geometry and multiple cycle slips. The package has been tested with GPS and INS data from a baseline survey near Calgary, Canada. Results of the test show that sub-meter kinematic positioning accuracies and cm/s velocity accuracies are achievable with an integrated GPS-INS.

Sensor array dynamic position and orientation determination system

Abstract: A system, which uses inertial measurement units, is shown for determining the position and orientation of a towed array of sensors used for target detection. The system uses an onboard master inertial navigation system and a relative position determination mechanism to generate a first estimated position for each inertial measurement unit within the array. Each inertial measurement unit measures force and angular change information used by an onboard computer to create a second estimated position by known methods for each inertial sensor. An error signal represented by the difference between the two estimated positions for each inertial unit is processed over time by a Kalman filter to reduce the error in the heading and attitude determined for each inertial unit to establish an accurate location for each inertial unit and, thus, the towed array of such units.

Gps navigation system

Abstract: PURPOSE:To prevent a serious accident due to the jump phenomenon of GPS position measurement from occurring by employing both the GPS position measurement using an artificial satellite and self-contained position measurement based upon azimuth data and moving distance data. CONSTITUTION:An antenna 11 for GPS which receives radio waves from plural artificial satellites is connected to a reception part 12 and its output is inputted to a position measurement arithmetic part 13 which finds the two-dimensional position and three-dimensional position of a moving body. An azimuth sensor 14A which detects a moving azimuth and a distance sensor 14B which detects the moving distance are provided and connected to a self-contained position detecting means 14. The result of the arithmetic part 13 is sent to a position detecting means 14 through a calibrating means 19 to make necessary correction. The position determining means 15 has a selecting function and employs it when the GPS position measurement is possible or self-contained position detection when not to supply data to a drawing function part 17, thereby displaying the position on a map by a display device 18.

Use of an external cascade Kalman filter to improve the performance of a Global Positioning System (GPS) inertial navigator

Abstract: The accuracy of in-air inertial navigation system (INS) alignment has been analyzed for several methods of GPS/INS integration. It is found that an external filter which operates on the outputs of the GPS receiver achieves a faster alignment than the GPS receiver alone. Steady-state accuracy is not significantly improved by the use of the external filter. The data rate of this external filter should be one update per second, which is the same as the GPS receiver's update rate and is the fastest that the external filter could be updated. In-air alignment of a second INS can be performed as a transfer alignment. In this procedure, the INS, which is integrated with the GPS, transfers its alignment to the second INS using an external filter. The performance of this external filter is analyzed and it is found that for a medium-accuracy INS, and also for a low-accuracy attitude heading reference system (AHRS), the fastest update rate provides the best alignment response. >

An integrated gps/irs design approach

Abstract: Development and testing of a prototype GPS receiver housed in a commercial inertial reference system has recently been completed. A flight test program in 1986 demonstrated dynamic performance in maneuvering flight, operation in low signal/noise environments, and operation at zero degree satellite elevation angles with 20–30 m typical accuracies using the Block I GPS satellites. The effects of altitude and clock aiding were also demonstrated. Many of the recognized limitations of an inertial system (including unbounded position error and pilot initialization as well as stand-alone GPS limitations such as poor satellite geometry, dynamic noise and satellite masking) are overcome with this integrated design approach. This paper describes the advantages of GPS/IRS integration as well as a design approach that utilizes them. The paper also summarizes some test results of the prototype GPS receiver.

Sole means navigation through hybrid Loran-C and GPS

Abstract: A minimum of four GPS range measurements or two Loran-C time differences are normally required for a position solution for en route navigation, area navigation, and nonprecision approaches. This paper describes a new technique that hybridizes GPS and Loran-C used in the pseudorange mode to process efficiently all available navigation information. Emphasis is placed on combined GPS and Loran-C timing, both for the ground/space facilities and the user. The hybrid system has the potential to solve the GPS and Loran-C integrity problems; more range measurements are available than are required for the navigation solution.

A Kalman filter for an integrated Doppler/GPS navigation system

Abstract: A Kalman filter has been designed to integrate a Doppler radar navigation system with a GPS (global positioning system) system The filter uses eight states for flights over land, and ten over water Simulation data shows navigation errors of 1 m or less on each axis under good operating conditions The performance is equivalent in position error to the standard standalone GPS filter in straight and level flight, and superior in maneuvering flight under dynamic conditions The filter implementation was also designed to provide additional improvement in the performance of a Doppler navigation system The results demonstrate that this capability was achieved >

Aiding gps with calibrated loran-c

Abstract: GPS is currently being installed; when it is operational, five satellites will be in view virtually 100 percent of the time. However, the full constellation will not be in place for several years, and even then satellite failures may introduce coverage holes. Additionally, even with the full constellation, a GPS receiver will not always be able to monitor signal integrity unless some external aid is used. Loran-C can be used effectively to aid GPS. A hybrid receiver can combine Loran lines of position with GPS lines of position to provide a system with great integrity, reliability, and time availability. Indeed, Loran is independent of GPS and can be used to detect GPS system or receiver failures. However, the hybrid receivers must include sophisticated Loran propagation models, which account for both the spatial and temporal anomalies of the propagation paths. Fortunately, GPS can be used to efficiently gather the data for these models. Additionally, GPS observations could be used to calibrate (or tune) these models in real time. This paper reviews the theory of Loran propagation and gives a basic Loran pseudorange model. It also presents some basic approaches for combining Loran and GPS pseudoranges in a position-fixing receiver. Finally, it estimates the accuracy of the hybrid system.

An Option for Mechanizing Integrated GPS/INS Solutions

Abstract: The GPS Joint Program Office has directed the delivery of GPS user equipment incorporating standard hardware and software. The resulting package, RCVR-3A, is designed to provide specified navigation performance under a wide range of alternative avionics interface requirements and aircraft mission scenarios. However, various integration studies have demonstrated that some of the RCVR-3A's potential performance is not realized because of the software design compromises made to accommodate standardization requirements. This is particularly the case when GPS measurements are integrated with INS outputs in RCVR-3A INS-mode operation. Therefore, some integrators have chosen to mechanize an independent navigation filter in a host vehicle mission computer when their system requirements exceed the GPS specifications. An alternative approach is to provide custom tuning for the RCVR-3A navigation filter to improve the receiver's own estimates of velocity and platform alignment. This paper summarizes the results of studies indicating that filter tuning is a cost-effective approach for certain combinations of INS and aircraft mission requirements. The paper concludes with a discussion of alternative means of mechanizing the RCVR-3A retuning.

Analysis of a cascaded INS calibration filter

Abstract: The authors address some critical issues associated with improving the system performance of integrated GPS (global positioning system) sand inertial systems Emphasis is placed on the correlated data coming from a primary filter into a cascaded or secondary filter A sophisticated Monte Carlo simulator was used to simulate the primary GPS system and a cascaded INS (inertial navigation system) calibration filter The primary system is either an 11-state unaided or a 12-state inertially aided system The cascaded filter is coupled with a gimbaled inertial system and is simulated in a 15-state configuration (position, velocity, tilts, gyro drifts, and accelerometer biases) >

Reference Trajectories From GPS Measurements

Abstract: A closed-form solution of the GPS pseudorange equations, an unaided Kalman filter, and an inertially-aided Kalman filter are used with differential GPS postprocessing to produce reference trajectories for evaluation of GPS user-equipment, for evaluation of integrated host vehicle navigation, and for accurate Time Space Position Information over large operating areas. The closed-form solution was developed in a derivation of existence conditions for solutions to GPS pseudorange equations. The derivation is included here as an Appendix. Positions calculated from the closed-form solution are used for starting and monitoring the Kalman filters, and for responding to uploads and constellation changes. Custom interface modules adapt common core modules of the aided Kalman filter to various inertial navigators.

Dynamic Interaction of Separate INS/GPS Kalman Filters (Filter- Driving - Filter Dynamics)

Abstract: This paper examines the basic behavior of the inertial navigation system (INS) errors under high-dynamic conditions, such as combat maneuvering of a fighter aircraft. While the nominal vertical channel INS instability is understood, the instabilities induced by high dynamic maneuvering have not been characterized. Examination of the INS linearized error dynamics eigenvalue migrations, during various dynamic maneuvers, reveals significantly stronger instability· than the classical vertical channel instability. The Global Positioning System (GPS) offers high accuracy navigation performance benefits with global coverage. However the GPS has limitations during the dynamic maneuvering of fighter aircraft. The optimal integration of the GPS with an INS promises synergistic system performance benefits not realizable with either system individually. The accuracy and stability limitations of a suboptimally integrated INS/GPS in a dynamically maneuvering vehicle are not understood. A candidate maneuver is selected (from among several dynamically stressful) for which a covariance analysis is performed to demonstrate the performance characteristics of an optimally integrated INS/GPS system. Although the full system dynamic interaction analysis has not yet been completed, significant insight into the potential instability of a particular INSJGPS integration scheme is presented. The characteristic and unstable behavior of the INS error dynamics eigenfunctions (time-varying eigenvalues) provides the basis for the "filter-driving-filter" performance analysis. In this study, several phenomena were observed which should aid future efforts attempting to characterize the performance of various INS/GPS integration methods.

Precision trajectory reconstruction

Abstract: A precision trajectory reconstruction technique based on photoscoring has been developed to evaluate the airborne accuracy performance of guidance and navigation systems The sensors include a reference inertial navigation system (INS) and a motion picture camera The camera is mounted in the aircraft at a known position and attitude with respect to the inertial system and is used to photograph marker panels placed at precisely surveyed locations on the ground The camera includes a time display device which is driven by a clock associated with the inertial data The image data from the camera are processed with a modern Kalman filter/smoother to estimate the inertial system errors The trajectory is then reconstructed by correcting the inertial system data with the estimated errors It is shown using covariance analysis that the precision photoscoring technique can be used to reconstruct the flight trajectory with a position error of 04 m under baseline conditions In addition, flight tests were used to evaluate the accuracy of the photoscoring process >

Low-cost GPS/INS guided stand-off weapon study

Abstract: The results are summarized of a six-month study of three candidate low-cost Global Positioning System/Inertial Navigation System (GPS/INS) guided stand-off weapons. Among the technical issues of interest were an assessment of the performance of several GPS translator configurations and the potential benefits of differential GPS. The principal focus was placed on the weapon accuracy which would be achieved by each of these three configurations. Costs of the various concepts were not evaluated. The scope of this study consisted of a top-level design and evaluation of the candidate configurations. Error models and a closed-loop covariance simulation (which includes a navigation filter and a controller) were developed. An accuracy comparison of the three configurations was performed,. >