System framework for mobile device location

• US 7,994,981 B1
• Filed: 09/07/2010
• Issued: 08/09/2011
• Est. Priority Date: 09/07/2010
• Status: Active Grant

• Current Assignee: Etherwhere Corporation
• Original Assignee: Etherwhere Corporation
• Inventors: Lee, Edmund Gregory, Farrokhi, Farrokh, Wong, Dickson T., Collmeyer, Arthur J.
• Primary Examiner(s): Tarcza; Thomas
• Assistant Examiner(s): MCGUE, FRANK J
• Application Number:
  US12/807,463
• Time in Patent Office: 336 Days
• Field of Search: 342/386
• US Class Current: 342/386
• CPC Class Codes: G01S 19/10 providing dedicated supplementary positioning signals
• CPC Class Codes: G01S 5/0249 Determining position using measurements made by a non-stationary device other than the device whose position is being determined

Abstract

A method for estimating the location of a beacon from an ensemble of measurements associated with said beacon, where, contained in each measurement, are GPS data from which surfaces of location may be extracted, together with the ID'"'"'s of beacons detectable at the point of measurement, is disclosed. The method comprises extracting the canonical set of surfaces of location implicit in each of the associated measurements, and determining the estimate of the location of the beacon as the point for which the sum of the squares of the distances to each of the surfaces so extracted is minimized. A system for the compilation of a database of beacon locations from measurements containing a time-stamped recording of the composite GPS signal (which recording is referred to as a datagram), together with the ID'"'"'s and associated signal strengths of beacons detectable at the point of measurement, is also disclosed. The system comprises GPS signal processing means for extracting, from each time-stamped datagram, the canonic set of surfaces of location, and beacon location estimation means for estimating the location of a beacon from an ensemble of surfaces of location associated with said beacon.

Claims

1. A method for building a database of beacon locations within a geographical area of interest, said method comprising:

deploying one or more mobile beacon database-building devices throughout said geographical area of interest, each having a GPS receiver and a beacon signal receiver;

each mobile beacon database-building device periodically measuring and recording a time-stamped composite GPS signal together with the beacon IDs detectable at the point of measurement;

deriving, from each time stamped composite GPS signal, the start-of-transmission and the time-of-arrival (TOA) from an identified GPS satellite;

constructing, for each of said identified GPS satellites, a spherical surface of location;

centered on said GPS satellite'"'"'s position at the start-of-transmission, with a radius corresponding to the difference between the time-of-arrival (TOA) and the start-of transmission;

storing said spherical surfaces of location, each with the beacon IDs detectable at the point of measurement, in a beacon survey database;

estimating beacon locations by determining the points for which the sum of the squares of the distances to each of three or more spherical surfaces of location sharing one of the beacon IDs detectable at the point of measurement is minimized; and

storing each estimated beacon location, together with the corresponding shared one of the beacon IDs detectable at the point of measurement, in a beacon location database.

2. A method for building a database of beacon locations within a geographical area of interest, said method comprising:

deploying one or more mobile beacon database-building devices throughout said geographical area of interest, each having a GPS receiver and a beacon signal receiver;

each mobile beacon database-building device periodically measuring and recording a composite GPS signal together with the beacon IDs detectable at the point of measurement;

deriving, from each composite GPS signal, the start-of-transmission from each of two identified GPS satellites and the difference in the times of arrival (TDOA);

constructing, for each pair of identified GPS satellites, a hyperplane of location comprised of points for which the difference between the distances from each point to the positions of each of said pair of identified satellites at the start-of-transmission is fixed by the difference in the times of arrival (TDOA);

storing said hyperplanes of location, each with the beacon IDs detectable at the point of measurement, in a beacon survey database;

estimating beacon locations by determining the points for which the sum of the squares of the distances to each of three or more hyperplanes of location sharing one of the beacon IDs detectable at the point of measurement is minimized; and

storing each estimated beacon location, together with the corresponding shared one of the beacon IDs detectable at the point of measurement, in a beacon location database.

3. A method for building a database of beacon locations within a geographical area of interest, said method comprising:

deploying one or more mobile beacon database-building devices throughout said geographical area of interest, each mobile beacon database-building device having a GPS receiver and a beacon signal receiver;

each mobile beacon database-building device periodically measuring and recording a time-stamped composite GPS signal together with the beacon IDs detectable at the point of measurement;

extracting the canonical set of surfaces of location from each of the time stamped composite GPS signals;

storing said surfaces of location, each with the beacon IDs detectable at the point of measurement, in a beacon survey database;

estimating, from surfaces of location sharing one of the beacon IDs detectable at the point of measurement, the location of the beacon corresponding to said shared one of the beacon IDs detectable at the point of measurement; and

storing each estimated beacon location, together with the corresponding shared one of the beacon IDs detectable at the point of measurement, in a beacon location database.

4. The method of claim 3, wherein the estimated location of the beacon corresponding to said shared one of the beacon IDs detectable at the point of measurement is the estimated location of the one or more mobile beacon database-building devices at such times as said shared one of the beacon IDs detectable at the point of measurement was detected, determined as the point for which the sum of the squares of the distances to each of three or more surfaces of location sharing the one of the beacon IDs detectable at the point of measurement is minimized.

5. The method of claim 3, wherein each measurement contains the strengths of the signals from the beacons corresponding to the beacon IDs detectable at the point of measurement.

6. The method of claim 5, wherein the strength of a signal is recorded as received signal strength indicator (RSSI).

7. The method of claim 6, where the RSSI recorded with a given measurement is used to weight the influence of said measurement, in estimating, from surfaces of location sharing one of the beacon IDs detectable at the point of measurement, the location of said beacon.

8. A system for building a database of beacon locations within a geographical area of interest, said system comprising:

one or more mobile beacon database-building devices, each having a GPS receiver and a beacon signal receiver;

a survey process, whereby each of said one or more mobile beacon database-building devices, operating within said geographical area of interest, periodically measures and records a time-stamped composite GPS signal together with beacon signature pairs comprising the IDs and associated signal strengths of beacons detected at the point of measurement;

GPS signal processing means for extracting the canonical set of surfaces of location from the time stamped composite GPS signals;

surface of location database means for storing surfaces of location, each with its associated beacon signature pairs;

beacon location estimation means for estimating, from surfaces of location sharing one of the beacon IDs detectable at the point of measurement, the location of the beacon corresponding to the shared one of the beacon IDs; and

beacon location database means for storing the estimated beacon locations, each with its corresponding shared one of the beacon IDs.

9. The system of claim 8, wherein the estimation of beacon location is accomplished by estimating the location of the one or more mobile beacon database-building devices at such times as said beacon was detected, determined as the point for which the sum of the squares of the distances to each of three or more surfaces of location sharing said one of the beacon IDs detectable at the point of measurement is minimized.

10. The system of claim 8, wherein the GPS signal processing means utilizes a perfect reference.

11. The system of claim 8, wherein the time stamped composite GPS signals span multiple cycles of GPS'"'"' 50 Hz data overlay.