Method and apparatus for advising cellphone users of possible actions to avoid dropped calls

• US 6,038,444 A
• Filed: 09/15/1997
• Issued: 03/14/2000
• Est. Priority Date: 08/19/1994
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Najafi, Hamid, Janky, James M., Schipper, John F.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US08/929,597
• Time in Patent Office: 911 Days
• Field of Search: 455/421, 455/440, 455/441, 455/456, 455/457, 455/422, 455/517, 455/550, 455/575, 455/566
• US Class Current: 455/421
• CPC Class Codes: G01S 2205/007 for management of a communication system
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: H04B 7/18541 for handover of resources
• CPC Class Codes: H04B 7/18552 using a telephonic control signal and a second ranging satellite determining absolute distances from a plurality of spaced points of known location G01S5/14
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 36/322 by location data
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Method and apparatus for tracking the location of, and for providing cellular telephone handoff for, a mobile cellphone user as the user moves from one cell to another. A boundary curve B12 between a first cell and an adjacent second cell is defined in an electronic map. First and second quasi-boundary curves QB1 and QB2, lying within the first and second cell, respectively, are defined, where each point on the curve QBi (i=1,2) lies at a selected distance from the boundary curve B12. A common region CR12 of points lying between the quasi-boundary curves QB1 and QB2 and including the boundary curve B12 is defined. The present cellphone location of the cellphone user is determined using a location determination system, such as GPS or GLONASS or a ground-based system. Cellular telephone service for the cellphone user is provided by a first cell site or by a second cell site, when the cellphone user is located within the first cell or the second cell, not including the overlap region CR12. When the cellphone user enters the region CR12 from within the first cell and proceeds toward the boundary curve B12, the user cellphone notifies at least one of the first and second cell sites that the cellphone user is about to leave the first cell and about to enter the second cell. The system advises the user if the cellphone is about to pass to another cell in which a cellular connection is likely to be dropped because no handoff cellular frequencies are available, or because the cellphone is about to enter a hole region where signal strength is less than an acceptable threshold value.

Claims

1. A method for providing information on an imminent cellular phone handoff between cells for a mobile cellphone user, the method comprising the steps of:

determining a present location vector and a present velocity vector of a cellphone used by a cellphone user;

identifying a first cell on a cell map in which the cellphone is presently located;

identifying a second cell that is adjacent to the first cell, where the first and second cell are separated by a cell boundary, and the cellphone will pass into the second cell if the cellphone velocity vector is unchanged;

when the cellphone location vector is within the first cell and the cellphone is engaged in a cellular communication, estimating a remaining time Δ

t1 before the cellphone will pass into the second cell, if the cellphone velocity vector is unchanged;

advising the cellphone user of the remaining time when the remaining time lies in a selected range of times, determining whether an unused cellular frequency pair is available within said second cell to provide servicing of said cellular communication in which said cellphone user is engaged;

advising said cellphone user if an unused cellular frequency pair is not available within said second cell to provide servicing of said cellular communication in which said cellphone user is engaged; and

advising said cellphone user of at least one alternative action that may be taken to avoid passing into said second cell, when an unused cellular frequency pair is not available within said second cell.

2. The method of claim 1, further comprising the step of choosing said selected range of times to include the range 3-30 sec.

3. The method of claim 1, further comprising the steps of:

selecting at least one alternative velocity vector, having substantially the same magnitude as, but having a different direction than, the present velocity vector;

identifying a candidate cell, which is adjacent to said first cell and which can but need not coincide with said second cell, where said first cell and the candidate cell are separated by a second boundary, and said cellphone will pass into the candidate cell if said present velocity vector is replaced by the alternative velocity vector and said cellphone moves in the direction of the alternative velocity vector;

when said cellphone location vector is within said first cell and said cellphone is engaged in a cellular communication, estimating a second remaining time Dt2 before said cellphone will pass into the candidate cell, if said present velocity vector is replaced by the alternative velocity vector and said cellphone moves in the direction of the alternative velocity vector; and

advising said cellphone user of the second remaining time.

4. The method of claim 1, wherein said step of determining said present location vector and said present velocity vector of said cellphone used by said cellphone user comprises the step of providing indicia for at least a portion of a route that said cell phone user will follow in said first cell and said second cell.

5. A method for minimizing loss of a cellular connection within a cellzone, the method comprising the steps of:

determining a present location vector and a present velocity vector of a cellphone used by a cellphone user;

identifying a cell on a cell map in which the cellphone is presently located;

identifying a signal strength hole region within the cell within which signal strength of a cellular connection is below a selected signal strength threshold;

using information on the present location vector and present velocity vector of the cellphone to determine whether the cellphone is likely to pass into the signal strength hole region, if the cellphone velocity vector is unchanged;

when the cellphone is determined to be likely to pass into the signal strength hole region, determining the time remaining before this likelihood occurs and advising the cellphone user of this likelihood and of the estimated time remaining before this likelihood occurs; and

advising said cellphone user of at least one alternative action that may be taken to avoid passing into said signal strength hole region, when said cellphone is determined to be likely to pass into said signal strength hole region.

6. The method of claim 5, further comprising the step of advising said cellphone user of said likelihood and of said estimated remaining time before said likelihood occurs, when said remaining time is no greater than a selected remaining time threshold.

7. The method of claim 5, further comprising the step of choosing said remaining time threshold to be in the range 3-30 sec.

8. The method of claim 5, wherein said step of identifying said signal strength hole region comprises the steps of:

identifying at least three locations at which said signal strength of said cellular connection is below said selected signal strength threshold; and

estimating said signal strength hole region to be the convex hull of the at least three locations.

9. The method of claim 5, wherein said step of determining said present location vector and said present velocity vector of said cellphone used by said cellphone user comprises the step of providing indicia for at least a portion of a route that said cell phone user will follow in said cell.

10. Apparatus for providing information on an imminent cellular phone handoff between cells for a mobile cellphone user, the apparatus comprising:

a location determination (LD) system that receives LD signals and determines a present location vector and a present velocity vector of a cellphone used by a cellphone user; and

a computer that communicates with the LD system and that is programmed;

to identify a first cell on a cell map in which the cellphone is presently located;

to identify a second cell that is adjacent to the first cell, where the first and second cell are separated by a cell boundary, and the cellphone will pass into the second cell if the cellphone velocity vector is unchanged;

when the cellphone location vector is within the first cell and the cellphone is engaged in a cellular communication, to estimate a remaining time Dtl before the cellphone will pass into the second cell, if the cellphone velocity vector is unchanged;

to advise the cellphone user of the remaining time when the remaining time lies in a selected range of times;

to determine whether an unused cellular frequency pair is available within said second cell to provide servicing of said cellular communication in which said cellphone user is engaged;

to advise said cellphone user if an unused cellular frequency pair is not available within said second cell to provide servicing of said cellular communication in which said cellphone user is engaged; and

to advise said cellphone user of at least one alternative action that may be taken to avoid passing into said second cell, when an unused cellular frequency pair is not available within said second cell.

11. The apparatus of claim 10, wherein said selected range of times is chosen to include the range 3-30 sec.

12. The apparatus of claim 10, wherein said computer is further programmed:

to select at least one alternative velocity vector, having substantially the same magnitude as, but having a different direction than, the present velocity vector;

to identify a candidate cell, which is adjacent to said first cell and which can but need not coincide with said second cell, where said first cell and the candidate cell are separated by a second boundary, and said cellphone will pass into the candidate cell id said present velocity vector is replaced by the alternative velocity vector and said cellphone moves in the direction of the alternative velocity vector;

when said cellphone location vector is within said first cell and said cellphone is engaged in a cellular communication, to estimate a second remaining time Dt2 before said cellphone will pass into the candidate cell, if said present velocity vector is replaced by the alternative velocity vector and said cellphone moves in the direction of the alternative velocity vector; and

to advise said cellphone user of the second remaining time.

13. The apparatus of claim 10, wherein said computer determines said present location vector and said present velocity vector of said cellphone used by said cellphone user by providing indicia for at least a portion of a route that said cell phone user will follow in said first cell and said second cell and by estimating if and where said cellphone will cross a boundary from said first cell into said second cell.

14. Apparatus for minimizing loss of a cellular connection within a cellzone, the apparatus comprising:

a location determination (LD) system that receives LD signals and determines a present location vector and a present velocity vector of a cellphone used by a cellphone user; and

a computer that communicates with the LD system and that is programmed;

to identify a cell on a cell map in which the cellphone is presently located;

to identify a signal strength hole region within the cell within which signal strength of a cellular connection is below a selected signal strength threshold;

to use information on the present location vector and present velocity vector of the cellphone to determine whether the cellphone is likely to pass into the signal strength hole region, if the cellphone velocity vector is unchanged;

when the cellphone is determined to be likely to pass into the signal strength hole region, to determine the time remaining before this likelihood occurs and advising the cellphone user of this likelihood and of the estimated time remaining before this likelihood occurs; and

to advise said cellphone user of at least one alternative action that may be taken to avoid passing into said signal strength hole region, when said cellphone is determined to be likely to pass into said signal strength hole region.

15. The apparatus of claim 14, wherein said computer is further programmed to advise said cellphone user of said likelihood and of said estimated remaining time before said likelihood occurs, when said remaining time threshold.

16. The apparatus of claim 14, wherein said remaining time threshold is chosen to be in the range 3-30 sec.

17. The apparatus of claim 14, wherein said computer identifies said signal strength hole region by:

identifying at least three locations at which said signal strength of said cellular connection is below said selected signal strength threshold; and

estimating said signal strength hole region to be the convex hull of the at least three locations.

18. The apparatus of claim 14, wherein said computer determines said present location vector and said present velocity vector of said cellphone used by said cellphone user by providing indicia for at least a portion of a route that said cellphone user will follow in said cell and estimating if and where said cellphone user will pass into said signal strength hole region.