Method for use with analog FM cellular telephones

• US 6,239,748 B1
• Filed: 05/19/1999
• Issued: 05/29/2001
• Est. Priority Date: 03/25/1994
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gilhousen, Klein S.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/314,188
• Time in Patent Office: 741 Days
• Field of Search: 342/442, 342/457, 342/458, 455/456
• US Class Current: 342/442
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 76/20 Manipulation of established connections

Abstract

A method for determining the location of a mobile unit within a cellular system. A synchronized signal at a common phase is generated at each base station in a system. The mobile unit transmits a signal tone. Each base station compares the phase of the signal tone to the common phase of the synchronized signal to produce a phase offset. A system controller compares the difference between the phase offset of a first base station and the phase offset of a second base station and determines the difference in distance between the first base station and the mobile unit and the second base station and the mobile unit defining a hyperbolic curve of locations. The system controller determines the intersection of the first and second hyperbolic curves thus determining the location of the mobile unit. The mobile station transmits the signal tone on a second channel that is distinct from a first channel over which user information is transmitted. The mobile station switches to the second channel in response to a request by a base station to the mobile station.

Claims

1. A method for operating a cellular telephone system comprising the steps of:

a) establishing communication from a mobile unit to a first base station on a first reverse channel;

b) establishing communication from the first base station to the mobile unit via a first forward channel;

c) generating a location request within the first base station and transmitting the location request to the mobile unit over the first forward channel;

d) switching a transmitter in the mobile unit to a second reverse channel different from the first reverse channel, transmitting a ranging tone from the mobile unit to the plurality of base stations via the second reverse channel, and then switching the transmitter in the mobile unit back to the first reverse channel in order to continue any call that may be in progress;

e) receiving the ranging tone via the second reverse channel at the plurality of base stations, the base stations also receiving a comparison tone;

f) calculating a plurality of phase differences, corresponding to the plurality of base stations, between the ranging tone and the comparison tone;

g) calculating a plurality of distances between the plurality of base stations and the mobile unit and an associated plurality of location curves using the plurality of phase differences; and

h) resolving a location of the mobile unit using the plurality of location curves.

2. The method of claim 1, wherein the step of switching a transmitter in the mobile unit to a second reverse channel different from the first reverse channel is performed for a short interval.

3. The method of claim 2, wherein the short interval is in the range of about one millisecond to about 10 milliseconds.