GPS receiver for emergency location reporting during...

Telecommunications – Radiotelephone system – Emergency or alarm communication

Reexamination Certificate

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Details

C455S456500, C455S427000, C342S357490, C342S357490, C701S213000

Reexamination Certificate

active

06298229

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to mobile telephones and, more particularly, to a global positioning satellite (GPS) receiver incorporated into a mobile telephone for emergency location reporting during intermediate shadowing of the receiver.
2. Description of the Prior Art
The space-based global positioning system (GPS) implemented by the United States Department of Defense constitutes a convenient instrumentality for determining geographical position in real time. The GPS is a multiple satellite-based radio positioning system in which each satellite transmits data that allow precise measurement of the distance from selected ones of the GPS satellites to the antenna of a user's receiver so as to enable the user to compute position, velocity and time parameters through known triangulation techniques. The signals provided by the GPS can be received both globally and continuously.
The GPS is intended for use in a wide variety of applications, including space, air, sea and land vehicle navigation, precise positioning, time transfer, altitude referencing and surveying. A typical GPS receiver comprises a number of subsystems, including an antenna assembly, an RF (radio frequency) assembly, and a GPS processor assembly. The antenna assembly receives and amplifies the L-band GPS signal prior to insertion into the RF assembly. The RF assembly mixes the L-band GPS signal down to a convenient intermediate frequency (IF) signal. This signal is then fed to the GPS processor assembly where the PRN (pseudo random) code modulating the L-band signal is tracked through code-correlation at the receiver. This provides the processing gain needed to achieve a signal-to-noise (S/N) ratio sufficient for demodulating the navigation data and signal-transmission time stamp. The Doppler shift of the received L-band signal is also measured through a carrier tracking loop. The code correlation and carrier tracking functions can be performed using either analog or digital signal processing.
By differencing the signal transmission time with the time of reception, as determined by the clock of the receiver, the (pseudo) range between the receiver and the satellite being tracked may be determined. The pseudo-range includes both the true range to the satellite and the affected offset of the receiver clock from the GPS master time reference. The pseudo range and Doppler measurements (and navigation data) from four satellites are used to compute a three dimensional position and velocity fix, and to calibrate the receiver's clock offset and provide an indication of GPS time. Other approaches are possible, as described in co-pending patent application Ser. No. 08/924,478 filed Aug. 25, 1997, now U.S. Pat. No. 5,752,218, issued May 12, 1998, by Daniel D. Harrison for “Reduced Power GPS-Based System for Tracking Multiple Objects from a Central Location”. General information on GPS may be obtained from the book by Tom Logsdon entitled
The Navstar Global Positioning System,
published by Van Nostrand Reinhold (1992).
GPS receivers are now being placed in mobile telephones so that the telephone location can be reported to a central location during an emergency. U.S. legislation has mandated that by the year 2000 mobile telephone position be provided for all 911 calls. If a GPS receiver is used to obtain the telephone location, a position fix is not possible when the telephone is shadowed from the GPS satellites. Shadowing may occur when the telephone is indoors.
SUMMARY OF THE INVENTION
Accordingly, it would be desirable to provide periodic low-power GPS data in a mobile telephone, from which a GPS postion fix can be obtained, and to validate and store the data so that the most recent data are available whenever the telephone is shadowed.
According to a preferred embodiment of the invention, a controller in the mobile telephone periodically commands GPS circuitry, also in the mobile telephone, to power-on, capture and process the signals from the GPS satellites. The signals are then processed to the point that sufficient data are obtained to determine a GPS position fix. Such data may be pseudo-range data or propagation time-difference data, as described in co-pending patent application Ser. No. 08/924,478, now U.S. Pat. No. 5,752,218. After the signals are processed, the pseudo-range or propagation time-difference data, GPS time, and satellite numbers are stored in non-volatile random access memory (RAM) and the GPS circuitry is then powered off. When an emergency signal is present, the controller tries to capture and process signals from the GPS satellites. If no GPS signals are received, the controller reports the stored information in non-volatile RAM to a central location through the mobile telephone transmitter. The central location can then use the information to compute the last valid GPS location of the GPS receiver. The periodic sampling of the GPS signal reduces power consumption and obtains a valid GPS location before shadowing occurs.
The invention is applicable to a variety of mobile telephones, including cellular telephones and satellite telephones. According to one aspect of the invention, the amount of data that needs to be transmitted to a central location is minimized and, therefore, power is saved by using the general location or region of the mobile telephone at the central location to resolve ambiguity in time-difference measurements. For a cellular telephone, the general location or region is the cell in which the cellular telephone is broadcasting. For a satellite telephone, the general location or region is the satellite beam location.


REFERENCES:
patent: 5528247 (1996-06-01), Nonami
patent: 5736962 (1998-04-01), Tendler
patent: 5752218 (1998-05-01), Harrison et al.
patent: 5963861 (1999-10-01), Hanson
patent: 6104340 (2000-08-01), Krasner
patent: 6108558 (2000-08-01), Vanderspool, II

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