US 6,665,332 B1Granted

CDMA geolocation system

AssigneeAllen Telecom Inc.

InventorsJohn P. Carlson, Thomas B. Gravely, Mark C. Sullivan

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Abstract

A geolocation system for geolocating a mobile transceiver operating in a CDMA communication system is disclosed having improved time of arrival extraction which allows the extracting of time of arrival information of weak CDMA emissions. The improved time of arrival extraction is accomplished by breaking the received CDMA emission into M identical processing stages. Each stage performs despreading/demodulating at over sampled chip offsets from the next processing stage. The P-point fast Fourier transform of the M stages is taken and in effect a two dimensional time versus frequency cross ambiguity function is created. The peak of the function may be interpolated to create an accurate estimate of the time of arrival of the emission from the mobile transceiver, thus improving the accuracy of time of arrival measurements and adjusting for doppler frequency shifts that may otherwise corrupt the measurements when integrating over a long period of time.

Claims32

Dependent claims

A geolocation system for providing geolocation of a mobile transceiver capable of spread spectrum coded radio frequency emissions and communication, said geolocation system comprising:

a plurality of base stations comprising a primary base station and one or more secondary base stations for receiving the spread spectrum coded radio frequency emissions, the primary base station being in communication with the mobile transceiver and the secondary base stations for conveying selected coded information bits from the mobile transceiver to the secondary base stations via the primary base station;
means for synchronizing the plurality of base stations to the mobile transceiver in time;
means for determining the geolocation of the mobile transceiver based on times of arrival of the spread spectrum coded radio frequency emissions at the plurality of base stations;
wherein each of the plurality of base stations comprises:
means for identifying a signal of interest in a spread spectrum coded radio frequency emission received at the base station, a portion of the signal of interest including the selected coded information bits conveyed from the mobile transceiver to the secondary base stations via the primary base station;
means for determining a time of arrival of the spread spectrum coded radio frequency emission received at the base station;
and wherein said means for determining the time of arrival of the spread spectrum coded radio frequency emission received at the one or more secondary base stations comprises:
means for dividing the spread spectrum coded radio frequency emission received at the one or more secondary base stations into a plurality of stages as a function of an estimated propagation distance;
despreader/demodulator means for despreading/demodulating each of the plurality of stages into the selected coded information bits;
and
calculating means for calculating the fast Fourier transform of each of the plurality of stages to produce a time-frequency cross ambiguity function to filter and isolate strongest peak.

8 more elements

A method of ascertaining the geolocation of a mobile transceiver capable of spread spectrum coded radio frequency emissions and which is in communication with a plurality of base stations, said method comprising the steps of:

designating a primary base station and one or more secondary base stations from the plurality of base stations;
receiving spread spectrum coded radio frequency emissions from the mobile transceiver at the of primary base stations;
establishing the primary base station in communication with the mobile transceiver and the secondary base stations;
conveying selected coded information bits from the mobile transceiver to the secondary base stations via the primary base station;
synchronizing the plurality of base stations to the mobile transceiver in time;
extracting a signal of interest from a spread spectrum coded radio frequency emission received at each of the base stations;
determining the primary base station based on the extracted signal of interest and identifying a portion of the signal of interest including the selected coded information bits conveyed from the mobile transceiver to the secondary base stations via the primary base station;
forwarding the selected coded information bits of interest from the primary base station to the secondary base stations, the secondary base stations comprising all of the plurality of base stations except the primary base station;
determining times of arrival of the spread spectrum coded radio frequency emission received at one or more of the secondary base stations;
determining a time of arrival of the spread spectrum coded radio frequency emission received at the primary base station;
determining the geolocation of the mobile transceiver utilizing the determined times of arrival.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/392,965Filed 9 Sep 1999 · us provisional application
Priority: 9 Sep 1998
Granted: 16 Dec 2003
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

G01S 5/02213
Receivers: receivers arranged in a network for determining the position of a transmitter
G01S 11/02
Systems for determining distance or velocity not using reflection or reradiation: using radio waves
G01S 5/06
Using radio waves: position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements
G01S 5/14
Using radio waves: determining absolute distances from a plurality of spaced points of known location