Variable coherence integration for the location of weak signals

• US 7,924,224 B2
• Filed: 08/15/2008
• Issued: 04/12/2011
• Est. Priority Date: 08/15/2008
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: LeFever, Ronald, Anderson, Robert J., Mia, Rashidus S.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): MCGUE, FRANK J
• Application Number:
  US12/192,842
• Publication Number:
  US 20100039326A1
• Time in Patent Office: 970 Days
• Field of Search: 342/387, 342/165, 342/173, 455/456, 455/456.1, 340/515
• US Class Current: 342/387
• CPC Class Codes: G01S 5/0221 Receivers
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• 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

Abstract

In a network-based Wireless Location System (WLS), geographically distributed Location Measurement Units (LMUs) must be able to detect and use reverse channel (mobile to network) signals across multiple BTS coverage areas. By using Matched Replica correlation processing with the local and reference signals subdivided into discrete segments prior to correlation, the effects of mobile clock drift and Doppler shifts can be mitigated allowing for increased processing gain.

Claims

1. A method for employing partial coherence processing paths to determine a precise time of arrival (TOA) of a transmission of a wireless device, comprising:

receiving a transmission of a wireless device;

generating a first digital sample set representing discrete samples of the transmission over a collection duration;

providing to first and second partial coherence processing paths copies of a reference and copies of the first digital sample set, wherein the copies are divided into m1 and m2 discrete subdivisions, wherein m1 and m2 are integers greater than 1 and m2 is greater than m1;

executing, in the first partial coherence processing path, a first correlation process in which a first set of sample segments is correlated with said reference, said first set of sample segments comprising a first plurality (m1) of segments, each of the m1 segments comprising a subset of said first digital sample set, wherein the execution of said first correlation process yields m1 outputs, wherein the m1 outputs comprise m1 complex numbers;

non-coherently summing the m1 outputs of the first correlation process to produce a number representing the sum of the magnitudes of the m1 complex numbers;

executing, in the second partial coherence processing path, a second correlation process in which a second set of sample segments is correlated with said reference, said second set of sample segments comprising a second plurality (m2) of segments, each of the m2 segments comprising a subset of said first digital sample set, wherein the execution of said second correlation process yields m2 outputs, wherein the m2 outputs comprise m2 complex numbers;

non-coherently summing the m2 outputs of the second correlation process to produce a number representing the sum of the magnitudes of the m2 complex numbers;

searching outputs of the correlation processes to identify a peak corresponding to an earliest arriving signal in each output set;

selecting one of said earliest arriving signals to determine a time of arrival (TOA) value for use in location processing, wherein the selecting is based on the peaks in the outputs of the correlation processes; and

using the TOA value in location processing to determine a precise geographic location of said wireless device.

2. A method as recited in claim 1, further comprising executing, in a full coherence path, a third correlation process in which said first digital sample set is correlated with said reference over the collection duration.

3. A method as recited in claim 2, wherein the full coherence path and the first and second partial coherence paths are executed in parallel.

4. A method as recited in claim 1, further comprising determining, based on the collection duration and before initiating the first and second correlation processes, that variable coherence processing is to be performed.

5. A wireless location system (WLS) including a plurality of location measuring units (LMUs), wherein at least one LMU comprises:

a receiver for receiving a transmission of a wireless device;

means for generating a first digital sample set representing discrete samples of the transmission over a collection duration;

means for providing copies of a reference and copies of the first digital sample set, wherein the copies are divided into m1 and m2 discrete subdivisions, wherein m1 and m2 are integers greater than 1 and m2 is greater than m1;

a first partial coherence path including means for executing a first correlation process in which a first set of sample segments is correlated with said reference, said first set of sample segments comprising a first plurality (m1) of segments, each of the m1 segments comprising a subset of said first digital sample set, wherein the execution of said first correlation process yields m1 outputs, wherein the m1 outputs comprise m1 complex numbers;

means for non-coherently summing the m1 outputs of the first correlation process to produce a number representing the sum of the magnitudes of the m1 complex numbers;

a second partial coherence path including means for executing a second correlation process in which a second set of sample segments is correlated with said reference, said second set of sample segments comprising a second plurality (m2) of segments, each of the m2 segments comprising a subset of said first digital sample set, wherein the execution of said second correlation process yields m2 outputs, wherein the m2 outputs comprise m2 complex numbers;

means for non-coherently summing the m2 outputs of the second correlation process to produce a number representing the sum of the magnitudes of the m2 complex numbers;

means for searching outputs of the correlation processes to identify an earliest arriving signal in each output set; and

means for comparing the identified earliest arriving signal in the outputs of the correlation processes and selecting one of said earliest arriving signals to determine a time of arrival (TOA) value for use in location processing.

6. A system as recited in claim 5, further comprising a full coherence path including means for executing a third correlation process in which said first digital sample set is correlated with said reference over the collection duration.

7. A system as recited in claim 6, wherein the full coherence path and the first and second partial coherence paths are configured as parallel paths.

8. A system as recited in claim 5, further comprising means for determining, based on the collection duration and before initiating the first and second correlation processes, that variable coherence processing is to be performed.