Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1999-06-28
2001-06-12
Pihulic, Daniel T. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
Reexamination Certificate
active
06246361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method and apparatus for determining a geographical location of a mobile unit and more specifically to a method and apparatus for determining a geographical location of a mobile unit using an apparatus traveling above the surface of the Earth.
2. Description of the Related Art Communication systems and techniques for determining the location of a mobile unit are known. Many techniques utilize Global Positioning Systems (GPS) which allow a mobile unit to determine its position based on signals from at least three satellites. GPS systems work well when the mobile unit is in an open area such on an ocean or in the air. However, GPS systems are limited in that the mobile unit must have unobstructed paths to at least three GPS satellites. Some GPS systems require a minimum of four satellites to determine the location of a mobile unit. If substantially clear signals cannot be received from the required satellites by the mobile unit, the mobile unit cannot determine its position.
Techniques have been proposed that utilize Low Earth Orbit (LEO) satellite systems. Satellites in LEO systems orbit at a lower altitude than GPS satellites and are not geostationary but rather orbit the Earth at a high speed relative to GPS satellites. LEO satellite communication systems contain many more satellites than GPS systems in order to attain global coverage at a lower altitude.
At least one proposed technique for determining the position of a mobile unit, such as described in U.S. Pat. No. 5,610,615, attempts to take advantage of the LEO satellite's lower orbit and higher speed. This technique allows a mobile unit to determine its position by obtaining a signal from one satellite and determining an instantaneous elevation angle, angles related to the orbit track of the satellite and other parameters. However, this technique is disadvantaged in that calculations are complex requiring higher production and maintenance costs of the system. Further, the technique requires that the mobile unit process information and perform calculations, adding complexity, size and cost to mobile units. In addition to the disadvantages discussed above, the positioning method described in the references patent does not allow for an accuracy suitable for locating a mobile unit in emergency situations.
Systems requiring the mobile unit to determine its location are further disadvantaged in emergency situations. In emergency situations, a user may not be able to forward location information to emergency services. For example, a user may be losing consciousness or have limited communication abilities due to physical trauma experienced in an accident.
Therefore, there exists a need for a method and apparatus for simply and efficiently locating a mobile user and communicating the location to emergency service providers in times of emergency.
SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for locating a mobile unit using an apparatus traveling above the surface of the Earth by observing the travel times for signals transmitted between the mobile unit and the apparatus.
In several embodiments of the invention, travel times of signals transmitted between the mobile unit and a single satellite orbiting the Earth are used to determine instantaneous distances between the satellite and the mobile unit. Each of the instantaneous distances can be represented with a circle having the satellite as the center at a specific time. The intersection of any two circles results in two possible locations of the mobile unit. One of the two possible locations is identified as the location of the mobile unit by observing a movement of the mobile unit due to the rotation of the Earth.
In one embodiment of the invention, several signal pulses are transmitted from the satellite to the mobile unit. The mobile unit retransmits the signal pulses to the satellite after a predetermined retransmission delay. The satellite measures the elapsed time between the transmission of the signals from the satellite and the reception of the signals at the satellite. The instantaneous distance is calculated by subtracting the known retransmission delay from the elapsed time and dividing the result by twice the speed of the signal.
In another embodiment, the signals originate from a terrestrial station, are relayed by the satellite to the mobile unit and are re-transmitted to the terrestrial station through the satellite. The signal travel times between the satellite and the mobile unit are determined by subtracting the retransmission delays in the satellite and the mobile unit and subtracting signal travel times between the terrestrial station and the satellite.
In another embodiment of the invention, a terrestrial station determines the location of a mobile unit based on information forwarded by a single satellite orbiting the Earth including times of reception of signals transmitted from the mobile unit. The terrestrial station calculates the location of the mobile unit using the velocity (speed and direction) of the satellite, the location of the satellite, the difference between times of reception of the signal transmitted by the mobile, and the Earth's rotation.
In another embodiment of the invention, signals are transmitted from the mobile unit at times separated by predetermined time intervals. The instantaneous distances are determined by observing the reception times of the signals at the satellite.
REFERENCES:
patent: 5610615 (1997-03-01), Chiodini
patent: 5623269 (1997-04-01), Hirshfield et al.
patent: 5634190 (1997-05-01), Wiedeman
patent: 5678175 (1997-10-01), Stuart et al.
patent: 5729205 (1998-03-01), Kwon
patent: 5758261 (1998-05-01), Wiedeman
patent: 6072430 (2000-06-01), Wyrwas et al.
patent: 0 298 571 A1 (1989-01-01), None
patent: 0 462 648 A2 (1991-12-01), None
patent: 2 321 812 (1998-08-01), None
patent: WO 98/01768 A1 (1998-01-01), None
Sutton Gary
Weill Lawrence R.
Brown Martin Haller & McClain
Pihulic Daniel T.
Sutton Gary
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