Showing papers on "Assisted GPS published in 1985"

Global positioning system course acquisition code receiver

Abstract: A GPS satellite receiver is disclosed in which the frequency of the received satellite signal is down converted in a single step by a balanced mixer driven by a half-frequency local oscillator and the down-converted satellite signal is converted from analog-to-digital form by a hard limiter.

GPS-Based Satellite Tracking System for Precise Positioning

Abstract: NASA is developing a Global Positioning System (GPS) based measurement system to provide precise determination of Earth satellite orbits, geodetic baselines, ionospheric electron content, and clock offsets between worldwide tracking sites. The system will employ variations on the differential GPS observing technique and will use a network of nine fixed ground terminals. Satellite applications will require either a GPS flight receiver or an on-board GPS beacon. Operation of the system for all but satellite tracking will begin by 1988. The first major satellite application will be a demonstration of decimeter accuracy in determining the altitude of TOPEX in the early 1990's. By then the system is expected to yield long-baseline accuracies of a few centimeters and instantaneous time synchronization to 1 ns.

Overview of differential gps methods

Abstract: A local GPS reference receiver (RR) can be used to eliminate common errors in the GPS navigation solution of other nearby receivers. A threefold improvement in remote GPS position accuracy can be achieved by this technique under optimum conditions. Several methods of accomplishing this process are presented.

Apparatus for and a method of determining compass headings

Abstract: A compass system and method incorporating a global positioning system (GP such as the NAVSTAR/GPS multi-satellite system, is configured to acquire accurate compass heading information without being affected by magnetic anomalies and without being dependent on the elapsed time since a previous position fix. The compass system comprises, inter alia, two antenna/preamplifiers located, for example, fore and aft a ship or aircraft separated by a predetermined distance d. A microprocessor/minicomputer portion of the system causes an electronic coaxial switch to switch a GPS receiver between the two antenna/preamplifiers automatically thereby measuring their absolute positions. The microprocessor/minicomputer computes and displays on a display unit a compass heading based on the knowledge of the absolute positions of the antenna/preamplifiers and the distance d therebetween.

GPS doppler processing for precise positioning in dynamic applications

Abstract: A doppler processing technique for smoothing the GPS code-phase measurements is presented. It is shown that this technique can enhance the resolution of C/A pseudo-range measurements to better than 1 centimeter. Data is presented to show that it is possible to obtain position fixes with an runs scatter of a few centimeters from the C/A code. Although the presented technique is applicable to both static and dynamic situations, it is particularly attractive in dynamic applications, where position averaging cannot be performed. This is shown to be a key factor in obtaining sub-meter differential accuracy in low dynamic applications. The interchannel biases in multichannel receivers are also discussed. It is shown how the advantages of multichannel design can be retained without suffering from this effect. The above techniques are implemented in the TRIMBLE 4000A LOCATORs and results are presented in this paper.

Application of GPS in a high precision engineering survey network

Abstract: A GPS satellite survey was carried out with the Macrometer to support construction at the Stanford Linear Accelerator Center (SLAC). The network consists of 16 stations of which 9 stations were part of the Macrometer network. The horizontal and vertical accuracy of the GPS survey is estimated to be 1 to 2 mm and 2 to 3 mm respectively. The horizontal accuracy of the terrestrial survey, consisting of angles and distances, equals that of the GPS survey only in the ''loop'' portion of the network. All stations are part of a precise level network. The ellipsoidal heights obtained from the GPS survey and the orthometric heights of the level network are used to compute geoid undulations. A geoid profile along the linac was computed by the National Geodetic Survey in 1963. This profile agreed with the observed geoid within the standard deviation of the GPS survey. Angles and distances were adjusted together (TERRA), and all terrestrial observations were combined with the GPS vector observations in a combination adjustment (COMB). A comparison of COMB and TERRA revealed systematic errors in the terrestrial solution. A scale factor of 1.5 ppM +- .8 ppM was estimated. This value is of the same magnitudemore » as the over-all horizontal accuracy of both networks. 10 refs., 3 figs., 5 tabs.« less

Gps integrity channel

Abstract: This paper documents a system description and operational concept for ensuring the integrity of the Global Positioning System (GPS) signals-in-space for use in the National Airspace System. The concept employs a ground monitoring network, L-band transponders placed onboard already planned geostationary communication satellites to broadcast integrity data, and an integrated receiver containing both the GPS and the GPS Integrity Channel (GIC). The three, aforementioned system segments are described. The feasibility of employing a network of only four ground monitors to cover CONUS is analyzed. A discussion concerning implementation of such a system is also presented.

A GPS measurement system for precise satellite tracking and geodesy

Abstract: NASA is pursuing two key applications of differential positioning with the Global Positioning System (GPS): sub-decimeter tracking of earth satellites and few-centimeter determination of ground-fixed baselines. Key requirements of the two applications include the use of dual-frequency carrier phase data, multiple ground receivers to serve as reference points, simultaneous solution for use position and GPS orbits, and calibration of atmospheric delays using water vapor radiometers. Sub-decimeter tracking will be first demonstrated on the TOPEX oceanographic satellite to be launched in 1991. A GPS flight receiver together with at least six ground receivers will acquire delta range data from the GPS carriers for non-real-time analysis. Altitude accuracies of 5 to 10 cm are expected. For baseline measurements, efforts will be made to obtain precise differential pseudorange by resolving the cycle ambiguity in differential carrier phase. This could lead to accuracies of 2 or 3 cm over a few thousand kilometers. To achieve this, a high-performance receiver is being developed, along with improved calibration and data processing techniques. Demonstrations may begin in 1986.

Autonomous navigation of gps satellites: a challenge for the future

Abstract: As the Global Positioning System (GPS) is maturing, potential enhancements and improvements to the system have been studied. One such potential enhancement is the ability of the GPS satellites to navigate in an autonomous mode, which would significantly reduce the Control Segment's (CS's) service requirements. Conceptual feasibility has been established recently and reported elsewhere. This paper addresses the implementation feasibility of autonomous navigation as applied to a Block II type of space vehicle. Operational issues affecting the CS and Space Segment (SS) are also addressed.

Global positioning system operational control system accuracies

Abstract: In early 1985, an improved ground Operational Control System (OCS) will maintain the navigation service. Primary among the OCS improvements over past GPS navigation systems is a global network of ground antennas (to upload satellite navigation data) and tracking/monitor stations. In addition, a refined Kalman filter will continuously estimate the Global Positioning System (GPS) satellite ephemerides and clock phases and frequencies. Although the user-GPS interface remains unaltered, the accuracy of the GPS navigation service is expected to improve by a factor of three. Using real and simulated GPS pseudo range radiometric tracking data, The Aerospace Corporation has completed a detailed error analysis which shows that the satellite clock noise contributes more than 90 percent of the total satellite-to-user pseudo range error. If the number of OCS uploads is increased to three per day (as planned), then the accuracy of the navigation service is also expected to improve by nearly a factor of three because the clock-noise contribution to the range error increases linearly with time. Also, this analysis shows the consequence of satellite ephermeris uncertainties in the GPS navigation application.

Receiver for global positioning system and method for determining position of a stationary station using same

Abstract: A GPS receiver (10, 20, 50) sets up an equation based on known position data and propagation delay time data transmitted from two satellites and received simultaneously, and independent of time epoch errors in the clocks of the satellites and the receiver. The receiver accumulates equations as data is received. The position of the receiver station can then be derived from the accumulated equations. In order to enable the foregoing process, the GPS receiver is provided with a timer which is reset at the timing of transmission of the epoch signals from satellites so as to measure the signal propagation interval by latching the timer value upon receipt of each satellite signal. In practice, the receiver uses the following equations: where x 1j , y 1j , z 1j are known coordinates of a first satellite; x 2j , y 2j , z 2i are known coordinates of the second satellite; T 1j and T 2j are respectively measured propagation delay times of the first and second satellite, t j is a constant indicative of timing errors; and c is the velocity of light.

Gps navigation system

Abstract: PURPOSE: To reduce a time from turning ON a power supply to performing the position measuring calculation on a satellite signal by restricting the range of a frequency for searching the satellite signal while referring to the temperature characteristics of a temperature compensating type quartz oscillator to a minimum requirement when the power supply is turned ON. CONSTITUTION: A temperature sensor 24 is arranged near the temperature compensating compensation type quartz oscillator 16 of a GPS receiver. The temperature characteristic information of the oscillation frequency of an oscillator 22 is stored in memory means in an oscillation frequency prediction arithmetic unit 22 in advance. After the power supply of the GPS receiver is turned ON, when a radio wave signal from a satellite is frequency-converted 14 and caught by a satellite signal catching and tracking unit 20, the signal of the sensor 24 is read out and, using the signal as an address signal, the temperature characteristic information stored in the arithmetic unit 22 is introduced to the tracking unit 20. By restricting the range of a frequency for searching the satellite signal based on the temperature characteristic information by the tracking unit 20 to a minimum requirement, a time from turning ON the power supply of the receiver until a GPS radio wave is caught and a position measuring calculation is performed can be reduced as small as possible. COPYRIGHT: (C)1988,JPO&Japio

Present position recognition apparatus for vehicle

Abstract: PURPOSE: To always enable the recognition of the present position with good accuracy, by mounting a present position recognizing means by an earth magnetic sensor and a present place confirming means by GPS. CONSTITUTION: A present position recognizing means (b) is constituted of an earth magnetic sensor 5 and a running distance measuring device 6 and the sensor 5 outputs a signal showing the azimuth of the present position and the measuring device 6 outputs a signal showing a running distance measured thereby to the control circuit 1. A present position recognizing means (d) is constituted of GPS7 to receive signals from a plurality of GPS satellites and directly calculates the coordinates of the present position to output the signal showing the coordinates to the circuit 1. A predetermined formulas for calculating distance correction and drift angle correction and others are stored in a memory circuit 3. By this method, the present position is recognized in a usual state by the means (b). At this time, a distance correction constant and a drift angle correction constant calculated according to the predetermined formula stored in the circuit 3 are used. Next, when a GPS receiving state is good, the circuit 1 changes over from the means (b) to the means (d) to perform the recognition of the present position. When the GPS receiving state becomes unsatisfactory, the means (d) is returned to the means (b) to recognize the present position. COPYRIGHT: (C)1987,JPO&Japio

Gps reception system

Abstract: PURPOSE: To determine the position of a satellite accurately and to perform high-precision position measurement by synchronizing a user clock with the clock of a GPS system CONSTITUTION: A spread spectrum signal of 15GHz transmitted by the satellite is synchronized with a C/A code determined according to the satellite, and then an epoch signal with a 1msec period is obtained Further, a synchronizing signal is detected and a demodulated signal of 1bit/20msec is obtained through a COSTAS circuit For the purpose, a user timer is synchronized with the variation timing of the demodulated signal shown by a downward arrow The user clock is reset at the variation timing of the demodulated signal and dummy distances R 1 WR 4 are measured at this resetting point of time or at intervals of 20msec (user timer) from the resetting point of time Consequently, satellite positions U 1 WW 1 are found accurately and high-precision position measurement is carried out COPYRIGHT: (C)1987,JPO&Japio

Development of a GPS Time-Transfer Receiver and Time Comparison Results

Abstract: The performances of the rece iver deve loped by PRL a r e ; t ime f l uc tua t ion o f 6 to 20 n s a t c a r r i e r t o n o i s e d e n s i t y r a t i o (C/NoL8 of +40 t o +55 dBHz and f r e q u e n c y s t a b i l i t y o f 2 x 1 0 / t a u . The ove r -a l l receiver de l ay was measured by us ing a CPS s i g n a l s i m a l a t o r with accuracy o f 15 ns. The r ece ive r does s o t use the ionosphere compensation data from the GPS s a t e l l i t e s . b u t u s e s i t s own model based on t o t a l e l e c t r o n c o n t e n t s da t a measu red a t RRL.

A survey of potential Australian users of the global positioning system

Abstract: Although originally conceived to cater for the future navigation needs of the United States military, the Global Positioning System (GPS) has also proved to be a revolutionary surveying tool Yet we sense a general apathy towards GPS within the profession Why this apathy? To find out, we formulated a questionnaire and sent this to about 180 surveyors in government, industry and academia The responses indicate that surveyors are dissatisfied with the TRANSIT system and that they want higher accuracies more rapidly and cheaply They realise that GPS will meet these demands but are reluctant to change until the present high cost of receivers drops and the system is more fully developed The majority supports the establishment of a GPS central facility whose functions would include disseminating satellite ephemerides and acting as a base station for relative positioning