Showing papers on "Assisted GPS published in 1987"

Aircraft Positioning Using Global Positioning System Carrier Phase Data

Abstract: Results from a flight test of a GPS carrier phase tracking receiver operated on a NASA Orion P-3 aircraft are presented. The trajectory of the aircraft relative to a second, fixed receiver has been determined. The test was made over water, and the GPS vertical trajectory is compared to airborne lidar measured altitude data from the NASA Airborne Oceanographic Lidar. The two data sets compare with a relative accuracy of 12 centimeters rms, under poor GPS satellite geometry for vertical positioning. Analysis indicates that 1 to 2 centimeters relative vertical positioning is achievable with carrier phase tracking receivers and good GPS geometry.

Method and apparatus for processing data in a GPS receiving device in a road vehicle

Abstract: A method for processing data received by a receiving device which outputs present location data for a movable vehicle based on the Global Positioning System and is positioned in the vehicle, including the steps of calculating an average of a predetermined number of data output from the receiving device while the vehicle stops, determining the average to be an effective data if the standard deviation of the data is within a predetermined range, and processing the averaged data as the present location data for the vehicle.

Integration of GPS and Strapdown Inertial Subsystems into a Single Unit

Abstract: Most GPS receivers are designed for stand-alone operation. Single-channel, slow-sequencing receivers are recognized to be lowest cost, but lack dynamic capability, while multiplexed and multichannel designs allow operation during acceleration, but add cost, weight and power. It is also well recognized that a marriage of GPS data with strapdown inertial data enhances the quality of both, and many people are looking at integration of available GPS receivers with various available inertial systems. However, direct design at the outset of a tightly integrated GPS and strapdown INS allows optimization of both for performance and cost. Using this approach, a properly designed slow-sequencing, single-channel receiver, married to a low-cost strapdown inertial unit, provides satellite tracking during 10-g acceleration, very high jamming suppression, improved strapdown inertial outputs, and improved GPS navigation accuracy. Packaging this “GPS/I” in a single unit reduces software and hardware redundancies, and results in a very low-cost design.

Vehicle navigation apparatus

Abstract: PURPOSE:To obtain highly accurate position information, by combining position information from GPS (global positioning system) and a direction sensor. CONSTITUTION:A running position of a vehicle is calculated in a CPU3, basing upon vehicle running direction detected by a direction sensor 1 and vehicle running distance detected by a speed sensor 2 and the position data are displayed continuously on a screen for display of a displaying apparatus 10. At the same time, position signals sent from three artificial satellites 9 of a GPS system are received by a GPS receiver 7 and magnetization correction of the sensor 1 is performed basing upon this for preventing deviation of a road on the display screen from a running locus. This magnetization correction is performed properly at the time of the deviation, eliminating necessity of a circular detecting operation by rotating the vehicle through an angle of 360 deg..

Vehicle on-board type navigator device

Abstract: PURPOSE: To prevent the generation of a traffic accident based on a jump phenomenon, by neglecting a GPS data which has been obtained at some time point, when the GPS data at some time point exceeds a GPS data at the time point immediately before it. CONSTITUTION: A difference is taken between a whole world position measuring system GPS data at some time point, and GPS data immediately before, which is obtained immediately before said data and has been stored temporarily in a GPS data storage device 63, and whether its result enters into a prescribed range or not is decided by a compatator 62. When a result of its decision is YES, its own present position is displayed, based on the GPS data being a satellite data. On the other hand, when a result of its decision is NO, its own present position is displayed, based on a self-standing type data. In such a way, the generation of the jump phenomenon is prevented surely, and it does not occur that the present position is misconceived. COPYRIGHT: (C)1988,JPO&Japio

Satellite navigation system

Abstract: PURPOSE:To find an accurate position by comparing the output level of a clockwise circular polarization antenna with the output level of a counterclockwise circular polarization antenna and detecting a multipath wave. CONSTITUTION:A controller 8 operates an antenna switch 3 to send the outputs of antennas 1 and 2 installed on a moving body to a GPS (global positioning system) receiver 4. The output of the GPS receiver 4 is distributed to outputs of the antennas to an antenna level detector 7, and the levels of the antennas 1 and 2 are compared with each other. Then, when the output of the antenna 2 becomes a predetermined value larger than the output level of the antenna 1, information on that is sent to a multipath detector 9 and the system is so controlled to acquire another satellite because the acquired satellite sends the multipath wave. This operation is repeated to acquire four satellites which send no multipath waves, and data on them are sent to a position measuring computer 5 to find the three-dimensional position of a GPS user, which is displayed 6.

Independent Ground Monitor Coverage of GPS Satellites

Abstract: The Federal Aviation Administration plans to independently monitor signals in space from the Global Positioning System (GPS) for the purpose of providing immediate awareness to civil aviation users of the operational status of GPS when it is used in the National Airspace System. The operational status will be disseminated to Air Traffic Control and will possibly be broadcast from ground monitoring stations to GPS aviation users via a dedicated integrity channel. An algorithm is described that measures the coverage of a configuration of ground monitoring station locations, and is applied to several different configurations of ground monitoring stations to compare the coverage provided. Also included are the resulting ground monitoring station configurations that give the best coverage of GPS signals for several specific geographical areas, the conterminous United States (CONUS), Canada, and Alaska.

Tidal current measuring instrument

Abstract: PURPOSE:To simplify the constitution of a device by comparing speed data on a ship with water speed data and computing the velocity and direction of a tidal current. CONSTITUTION:A GPS receiver 1 sends out position data, speed data, etc., with a GPS signal from each satellite. The position data and speed data on this ship obtained by arithmetic 102 and offset data on a reference oscillator 103 are inputted to a processor PU 3. Bow-directional and literal transmitters 6 and 7 send ultrasonic waves through transmitter and receivers 8 and 9 and reflected waves are inputted to the PU 3 through receivers 10 and 11 and counters 12 and 13. Then the PU 3 stores respective data in a RAM 4 to calculate the speed and direction of the tidal current. In this case, the offset data from the receiver 1 is used to correct error components of the respective frequency data.

Helicopter Terminal Approach Using Differential GPS with Vertical-Axis Enhancement

Abstract: The NAVSTAR Global Positioning System (GPS) in differential mode (DGPS) has been shown to be least accurate in the vertical axis. The vertical axis also has the most stringent accuracy requirements for aircraft precision approach and landing. A series of flight tests were conducted to evaluate a concept for improving the DGPS vertical axis navigation performance. These tests incorporated augmentation sensors to aid the DGPS navigation solution during terminal approach operations. A GPS receiver was installed on board a NASA helicopter and interfaced with a real-time digital computer system. A reconfigurable navigation filter programmed in the digital computer provided an augmented DGPS solution, with selectable inputs from a low-cost vertical accelerometer, a barometric altimeter, and the aircraft attitude gyros. The reference aircraft position was determined by a laser tracker. Extensive post-test analysis was done to optimize the filter performance during the terminal approach operation. Test results show that baro-altimeter aiding can significantly improve vertical axis performance. Follow-on tests are planned for the optimized configurations.

Global Positioning System and Time and Frequency Measurements

Abstract: : The Global Positioning System (GPS) has been used for time synchronization among major national timekeeping facilities for nearly ten years. Its reliability and accuracy are well documented. While older GPS equipment has operated well in a laboratory environment, more advanced receivers now on the market provide enhanced performance at a lower cost while expanding GPS time accuracies to new applications. The Collins Air Transport Division of Rockwell International has developed a commercial GPS sensor known as the NAVCORE I which derives position, velocity, and time data from GPS satellite signals. Digital data outputs are updated at the rate of one complete solution per second, making the sensor function applicable to a wide range of dynamic and static time and navigation applications. This paper describes time performance of the NAVCORE receiver and the design of a time and frequency system based on NAVCORE.

Proper Treatment of the Delta-Range Measurement in an Integrated GPS/Inertial System

Abstract: Pseudorange and delta-range are the basic measurements that a GPS receiver provides in an integrated GPS/inertial system Usually the delta-range measurement is treated as an instantaneous velocity measurement in the Kalman filter integration of the two systems This is an approximation since the actual measurement is proportional to the integral of the Doppler shift over the delta-range integration interval The Kalman filter model can be modified to accommodate the true measurement situation, and the results of the true model can be compared with those obtained with the approximate instantaneous velocity model Error covariance analysis was performed to compare the relative accuracy between the two measurement models for an eight-state Kalman filter and an integration interval of one second The main difference between the two models occurs in the velocity estimates (in contrast to the position estimates), where the approximate model predicts RMS velocity errors which are much less than those determined with the true measurement model This is to say that the approximate velocity model often used in error analysis yields overly optimistic results for the velocity estimates

Evaluation of a Large Ship GPS System: Direct Computation and Dynamic Differential

Abstract: A GPS system utilizing a TI 4100 and a microprocessor has been installed and tested on two Air Force radar tracking ships. The system has been evaluated using an Autotape radio position system (accuracy at lm level) as a reference. The system provides both a real time solution via an eight state Kalman filter and records data for post processing. The accuracy of the position and velocity solutions from the real time Kalman filter and from post processing using a shore based reference site are presented.

Deciding method for position measurement accuracy of gps navigation

Abstract: PURPOSE:To preclude a wrong judgment due to low-accuracy position measurement data by stopping the display of a position measured value when deciding that the difference between the reference oscillation frequency of a receiver and the frequency of a received signal from a satellite is abnormal. CONSTITUTION:A position measurement arithmetic part 15 calculates position measurement data by using data from a track data gathering part 13 and a pseudo distance measurement part 14. this data contains an error in the GPS system time of the timepiece of a GPS navigation aid, so the frequency error DELTAf of the reference oscillator of a GPS receiver is calculated and outputted to a DELTAf abnormality decision part 17. The error DELTAf has a peak if a radio wave from the satellite is cut off or reflected by a building or mountain, etc. The decision part 14 decides whether or not the error DELTAf is abnormal and stops the display of the position measurement data on a display part 16 on deciding that the error is abnormal, thereby precluding a wrong judgement due to a decrease in accuracy.

GPS Program Status

Abstract: The Navstar Global Positioning System (GPS) Program is composed of three segments ? Space, Control, and User Equipment. The Space segment is responsible for the development and launch of the GPS satellite constellation. The Control segment is responsible for monitoring the satellite telemetry and providing updated navigation information to the satellites. The User Equipment (UE) segment is responsible for the development and procurement of the GPS receivers for a variety of host vehicle platforms. Recently, approval was given to the User segment to enter Low Rate Initial Production (LRIP). This approval marks the beginning of Phase III (production and deployment) of the GPS program. This paper will discuss the overall status of all three segments with an emphasis on the User Equipment segment as it enters the production phase of the program.

Ship position recognizing instrument

Abstract: PURPOSE:To increase the accuracy and reliability of a ship position recognition in the whole and in the whole seasons by estimating optimum acceleration and speed on the basis of the data from a GPS receiver, an inertial navigation instrument and a pattern matching instrument CONSTITUTION:The data from a GPS receiver 10 for outputting the speed and the position of a navigating ship on the basis of the received signals from an artificial satellite, an inertial navigation instrument 20 for outputting the data of an acceleration, the speed and the position on the basis of the acceleration and the angular velocity of the ship and a pattern matching instrument 30 of a radar video and an electronic chart are inputted to a navigation processor 40 Optimum acceleration and speed are estimated on the basis of the effective data in accordance with the effectiveness of the data Further, an abnormality in sensors is detected on the basis of an estimated present position and the speed and an optimum speed, an optimum position and the estimated position are computed by a Kalman filter to be displayed on a display 50

GPS Receiver Technology

Abstract: The NAVSTAR/GPS system is already widely used for geodetic positioning, although the full capability is not yet available. Various types of receivers, using the C/A and/or P codes or codeless, are available as prototypes or commercially. This paper reviews these receivers.