Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reissue Patent
2000-09-15
2001-10-16
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
Reissue Patent
active
RE037408
ABSTRACT:
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
When a Satellite Positioning System (SATPS) receiver/processor powers up, or when the receiver/processor experiences SATPS signal interruption, if the receiver/processor has no almanac that indicates the present location of the visible SATPS satellites, the receiver/processor and associated SATPS antenna will perform a blind satellite search to find a sufficient number of SATPS satellites, usually three or more, to begin establishing the antenna's SATPS-determined location and/or proper time. The SATPS antenna and receiver/processor will usually select SATPS satellite numbers at random for the search. This procedure will often consume several tens of seconds before “lock” on an adequate number of SATPS satellite signals is achieved. For an SATPS receiver/processor with five or more channels, this time to first fix (“TTFF”) is of the order of 60-100 seconds, or longer. An SATPS signal receiver/processor with fewer channels will often have a longer TTFF, as much as 120-180 seconds. Workers in electrical communications have disclosed methods and/or apparati for reducing the time or difficulty of acquiring signals communicated from satellites.
U.S. Pat. No. 4,384,293, issued to Deem et al, discloses apparatus for providing pointing information, using one or more GPS satellites and two antennas spaced apart about ten carrier signal wavelengths. The difference in phase of GPS signals received by the two antennas determines the pointing direction determined by the line of sight between the two antennas. Phase differences of GPS signals received by arrays of three or more collinear or non-collinear antennas are used to determine the attitude of an object on which the antennas are mounted in U.S. Pat, No. 5,021,792, issued to Hwang, and in U.S. Pat. No. 5,101,356, issued to Timothy et al.
Use of faster-than-real-time signal correlators, together with GPS code signals that are stored in memory at a GPS station, to provide a plurality of virtual channels for initially acquiring and tracking GPS satellites is disclosed by Gorski-Popiel in U.S. Pat. No. 4,426,712.
Taylor et al, in U.S. Pat. No. 4,445,118. disclose generation and transmission of an initial signal from a first ground-based station to a second ground-based station, to aid in acquisition of signals from GPS satellites by the second station. This initial signal provides coordinates of in-view GPS satellites with the best geometry and elevation and estimates Doppler shifts for these satellites, to simplify equipment at the second station.
A system for audibly verifying initial acquisition of signals from a selected GPS satellite is disclosed in U.S. Pat. No. 4,910,525, issued to Stulken. A Doppler-shifted GPS signal is mixed with a local oscillator signal having an adjustable frequency and is filtered to produce an audio beat frequency signal, whose presence indicates presence of a GPS signal from the selected satellite.
U.S. Pat. No. 4,968,981, issued to Sekine, discloses GPS receiver apparatus that quickly maximizes correlation between a received GPS pseudo-random noise (PRN) code and an internally stored GPS code. This approach uses a separate channel for each of N PRN codes and shifts the phase of the internally stored code n/2 bits at a time (n=1, 2, . . . N), in a search for a position of increased code correlation value.
Fast Fourier Transform analysis of a received composite of GPS satellite signals is used to acquire and track signals from in-view GPS satellites in U.S. Pat. No. 4,998,1111, issued to Ma et al. The FFT analysis identifies which signals are present with suitable strength, based on expected Doppler shifts of the incoming signals.
In U.S. Pat. No. 5,036,329, Ando discloses a satellite reacquisition or initial acquisition method applicable to GPS satellites. Using an estimate of the average Doppler shifted frequency f
avg
manifested by the GPS signals received from a visible GPS satellite, a narrow band search is first performed in the frequency range f
avg
−8600 Hz<f<f
avg
+8600 Hz. If no GPS satellite signals are found in this range within 3.75 minutes, the search range is widened until at least one GPS satellite signal is found.
A simultaneous multi-channel search for reacquisition of GPS satellite signals after signal interruption occurs is disclosed by Sakaguchi and Ando in U.S. Pat. No. 5,059,969. This method first searches for the GPS satellite with the highest elevation angle relative to the GPS antenna and receiver/processor. Two or more sequences of signal frequency ranges are swept over in parallel until at least one GPS signal is reacquired.
U.S. Pat. No. 5,061,936, issued to Suzuki discloses attitude control for a rotationally mobile antenna. If the strength of the initial signal received by the antenna from a spacecraft (whose position is yet unknown) is below a first selected threshold and above a second selected threshold, the antenna attitude is scanned over a relatively small range, to increase the signal strength toward or above the first threshold value. If the signal strength is initially below the second threshold, the antenna attitude is scanned over a larger range, to increase the signal strength above the second threshold value so that a smaller range antenna scan can be implemented.
Durboraw, in U.S. Pat. No. 5,119,504, discloses a satellite-aided cellular communications system in which a subscriber unit self-determines its own (changing) location and transmits this information to the satellites for use in subsequent communications. This requires that each subscriber unit transmit and receive signals, and one subscriber unit does not communicate directly with, or provide satellite location information for, another subscriber unit.
An electronic direction finder that avoids reliance on sensing of terrestrial magnetic fields for establishing a preferred direction for satellite signal acquisition is disclosed by Ghaem et al in U.S. Pat. No. 5,146,231. The apparatus uses a receiver/processor for GPS or similar navigation signals received from a satellite, and requires (stored) knowledge of the present location of at least one reference satellite from which signals are received. The orientation of the finder or its housing relative to a line of sight vector from the finder to this reference satellite is determined. This orientation is visually displayed as a projection on a horizontal plane. Any other direction in this horizontal plane can then be determined with reference to this projection from a knowledge of the reference satellite location.
Ando, in U.S. Pat. No. 5,155,491, discloses a method for tracking radio signals from GPS satellites that follow a single orbit around the Earth. At most four GPS satellites follow one of the six GPS orbits, as the constellation is presently configured. The CIA-code and/or P-code is known for each of the at-most-four GPS satellites in a single orbit so that searching along a single orbit requires acquisition of only one of the four known codes associated with these satellites, and at least one of these four GPS satellites is not visible at a particular observation time. After acquisition of whatever GPS satellites on a particular GPS orbit can be tracked, the system moves sequentially from one GPS orbit to another orbit until all trackable GPS satellites are found. The system then selects the three or four GPS satellites that are most suitable for global positioning computations.
In U.S. Pat. No. 5,177,490, Ando et al disclose a GPS signal tracking system that rapidly recaptures a lost signal by repeatedly performing a narrow band search for a selected incoming signal, over a specified search time interval, centered along a Doppler shift curve for the selected signal, and performing a wider band search at the same time.
Parallel searches by different GPS receiver channels over a divided frequency range for a given satellite, to reduce the time required for satellite signal acquisition, is disclosed by Kawasaki in U.S. Pat. No. 5,185,761.
Kennedy discloses use of time
Braisted Paul
Eschenbach Ralph
Lau Chung
Loomis Peter V. W.
Cooper & Dunham LLP
Dowden Donald S.
Issing Gregory C.
Pelton William E.
Trimble Navigation Ltd.
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