Communications: electrical – Continuously variable indicating – With meter reading
Reexamination Certificate
1998-10-26
2001-05-29
Zimmerman, Brian (Department: 2635)
Communications: electrical
Continuously variable indicating
With meter reading
C342S357490
Reexamination Certificate
active
06239721
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to determination of location of a moving signal receiver and of associated signal sources.
BACKGROUND OF THE INVENTION
Use of location satellite-based location determination (LD) systems, such as the Global Positioning System (GPS), the Global Orbiting Navigational Satellite System (GLONASS) or a Low Earth Orbit (LEO) system, such as Iridium or Globalstar, to determine the location of a mobile LD station may become (temporarily) unavailable when the LD station is adjacent to or within a signal canyon, such as an urban canyon, a natural canyon (steep canyon walls, a deep open mining pit, an underground mine, etc.), a forest, inside a large warehouse, or a similar signal-interfering structure (referred to collectively here as a “canyon”). One response to such occurrence is to resort to dead reckoning, using an inertial guidance system, using accelerometers, magnetic field sensors and the like, whenever sufficient LD signals are unavailable. This method is suitable for time intervals of modest length, where the inaccuracy and drift of the sensors used are within tolerable limits.
However, for tracking of the location of a mobile LD station over longer time intervals, the dead reckoning approach may be unsuitable. What is needed is a system that uses receipt of primary LD signals, when such signals are still available, to determine the locations of one or more secondary LD signal sources that can subsequently be used to determine the mobile LD station location when the primary LD signals become unavailable. Preferably, this system should be flexible enough to work with all types of primary and secondary LD signal sources, including mixtures thereof, and should, in principle, allow for location determination anywhere within or adjacent to the canyon. Preferably, the system should be able to determine, without further human input, when sufficient primary LD signals are available and when sufficient primary LD signals are unavailable for location determination.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides a system and associated method for (1) receiving and analyzing primary LD signals at a mobile LD station to determine (i) the present location of the LD station and (ii) the location (relative or absolute) of each of one or more secondary LD signal sources whose signals are also received at the LD station, and (2) receiving and analyzing secondary LD signals, after the secondary LD signal source locations have been determined, when primary LD signals in sufficient numbers are no longer available. The method includes the steps of: (1) receiving primary LD signals from two or more primary LD signal sources, whose locations are accurately known, at a mobile LD station and determining a present location of the LD station at two or more distinct LD station locations, (2) receiving secondary LD signals from one or more (preferably two or more) secondary LD signal sources at each of the two or more distinct LD station locations and determining the locations of the secondary LD signal source(s) from the secondary signals received, and (3) when primary LD signals in sufficient numbers are unavailable, receiving secondary LD signals and using these signals and their now-known locations to determine a present location of the LD station.
REFERENCES:
patent: 4983980 (1991-01-01), Ando
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patent: 5072227 (1991-12-01), Hatch
patent: 5177490 (1993-01-01), Ando et al.
patent: 5276972 (1994-01-01), Staney
patent: 5309162 (1994-05-01), Uematsu et al.
patent: 5712899 (1998-01-01), Pace, II
patent: 5757315 (1998-05-01), Aoki
Schipper John F.
Trimble Navigation Limited
Zimmerman Brian
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