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| Subscriber terminal temperature regulation |
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| Personal data collection and reporting system |
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| High volume uplink in a broadband satellite communications system |
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| Error monitoring algorithm for broadband signaling |
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| Procedure and system for ensuring emergency communication in a wireless local loop environment |
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Automatic cellular phone tracking
| Details |
Inventors: Schipper, John F.;
Assignee: Trimble Navigation Limited (Sunnyvale, CA)
Primary Examiner: Tsang; Fan
Assistant Examiner: Sobutka; Philip J.
Attorney, Agent or Firm: Schipper; John F.
A system for tracking the location of, and for providing cellular telephone handoff for, a mobile cellphone user as the cellphone user moves from one cellzone to another. A boundary curve B12 between a first cellzone and an adjacent second cellzone is defined in an electronic map by an equation h.sub.B12 (x,y,z)-K12=0 for points with spatial location coordinates (x,y,z) lying on the curve B12, where K12 is a selected constant. First and second quasi-boundary curves QB1 and QB2, lying within the first and second cellzones, respectively, are defined, where each point on the curve QBi (i=1,2) lies at a selected distance di from the boundary curve B12. A region CR12 of points lying between the quasi-boundary curves QB1 and QB2 and including the boundary curve B12 is defined. The present location of the cellphone user is determined using a Satellite Positioning System (SATPS) such as GPS or GLONASS. Cellular telephone service for the cellphone user is provided (1) by a first cellular service provider or (2) by a second cellular service provider, when the cellphone user is located (1) within the first cellzone, not including the overlap region CR12, or (2) within the second cellzone, not including the overlap region CR12. When the cellphone user enters the region CR12 from within the first cellzone and proceeds toward the boundary curve B12, the system carried by the cellphone user notifies at least one of the first and second cellular service providers that the cellphone user is about to leave the first cellzone and about to enter the second cellzone. The system may be extended (1) to determine the approximate location of a missing vehicle and (2) to dynamically change the boundary curves of at least one cellzone to relieve cellular service overloading that occurs within that cellzone. |
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DETAILED DESCRIPTION These needs are met by the invention, which provides a system that may be local or global for automatically tracking the movements of a plurality of cellphone subscribers from one cellzone to another.
The invention might be characterized as "Where Am I?".
A cellphone system carried by a subscriber (or by the subscriber's vehicle) includes a Satellite Positioning System (SATPS) antenna and receiver/processor and carries a transmitter that uses a preselected frequency not within the cellular transmission bands.
The SATPS receiver/processor includes an electronic map with the coordinates of the boundary curves of each cellular exchange or cellzone within a selected region R, which region can be a portion or all of a town, city, county, state, country or continent.
Each time the subscriber crosses such a boundary curve, from a first cellzone to a second cellzone, a cellular telephone service provider in one or both of these cellzones is advised of the subscriber's new cellzone location.
When a telephone caller seeks to reach a cellular phone subscriber, the initial inquiry is directed to a central cellular station, such as a mobile cellular telephone switching office (MCTSO) that communicates with all cellular phone exchanges within the region R.
The central MCTSO transmits or broadcasts an inquiry and is informed of the cellzone in which the subscriber is presently located.
The central MCTSO need not separately inquire about the present location of a given subscriber or estimate the subscriber's present location from recent cellphone calls, if any, made or received by the subscriber.
Because each of two cellzone service providers is aware of the subscriber's present cellzone, loss or compromise of this information by one of these cellzone service providers does not preclude response to the central MCTSO's inquiry by the other cellzone service provider.
The central MCTSO receives a response, identifying the cellzone where the subscriber is presently located, and patches the call through from the telephone caller to the subscriber in this cellzone
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Cell Phones 
