Internal calibration method for receiver system of a wireless location system

• US 6,492,944 B1
• Filed: 08/10/2000
• Issued: 12/10/2002
• Est. Priority Date: 01/08/1999
• Status: Expired due to Term

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Stilp, Louis A.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/635,703
• Time in Patent Office: 852 Days
• Field of Search: 342/165, 342/174, 342/385, 342/387, 342/450, 342/457
• US Class Current: 342/387
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 2205/006 for emergency situations
• CPC Class Codes: G01S 2205/008 using a mobile telephone network
• CPC Class Codes: G01S 2205/06 Emergency
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0215 Interference
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/02216 Timing or synchronisation of the receivers
• CPC Class Codes: G01S 5/0244 Accuracy or reliability of position solution or of measurements contributing thereto
• CPC Class Codes: G01S 5/0246 involving frequency difference of arrival or Doppler measurements G01S5/02685 takes precedence
• CPC Class Codes: G01S 5/02521 using a radio-map
• CPC Class Codes: G01S 5/0268 by deriving positions from different combinations of signals or of estimated positions in a single positioning system
• CPC Class Codes: G01S 5/0284 Relative positioning
• 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 4/90 Services for handling of emergency or hazardous situations, e.g. earthquake and tsunami warning systems [ETWS]
• 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 76/50 for emergency connections
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Methods and apparatus for calibrating a Wireless Location System to enable the system to make highly accurate TDOA and FDOA measurements are disclosed. An external calibration method in accordance with the present invention comprises the steps of transmitting a first reference signal from a reference transmitter; receiving the first reference signal at first and second receiver systems; determining a first error value by comparing a measured TDOA (or FDOA) value with a theoretical TDOA (or FDOA) value associated with the known locations of the receiver systems and the known location of the reference transmitter; and utilizing the first error value to correct subsequent TDOA measurements associated with a mobile transmitter to be located. An internal calibration method in accordance with the present invention comprises the steps of injecting a comb signal into the first receiver system; utilizing the comb signal to obtain an estimate of the manner in which the transfer function varies across the bandwidth of the first receiver system; and utilizing the estimate to mitigate the effects of the variation of the first transfer function on the time measurements made by the first receiver system.

Claims

1. An internal calibration method for calibrating a first receiver system, wherein said first receiver system is characterized by a time- and frequency-varying transfer function, said transfer function defining how the amplitude and phase of a received signal will be altered by said first receiver system, and wherein the first receiver system is utilized in a location system that is operative to determine the location of a mobile transmitter by, in part, determining a difference in time of arrival of a signal transmitted by a mobile transmitter and received by said first receiver system and another receiver system, and wherein the accuracy of the location determination is dependent, in part, upon the accuracy of time measurements made by said receiver systems, the method comprising the steps of:

(A) injecting an internally generated stable, known signal into said first receiver system;

(B) utilizing the internally generated stable, known signal to obtain an estimate of the manner in which said transfer function varies across the bandwidth of said first receiver system; and

(C) utilizing said estimate to mitigate the effects of said variation of the first transfer function on the time measurements made by the first receiver system.

2. A method as recited in claim 1, wherein the internally generated stable, known signal is a comb signal having multiple discrete frequency elements of consistent amplitude and spacing.

3. A method as recited in claim 1, wherein the estimate of the manner in which the transfer function varies across the bandwidth of the first receiver system is weighted by a quality factor prior to being used to mitigate the effects of the transfer function.

4. A method as recited in claim 3, wherein the estimate of the transfer function is used by the location system to mitigate the effect of the transfer function only if the quality factor exceeds a prescribed threshold value.

5. A method as recited in claim 3, wherein the quality factor is based upon the output of a cross-correlation function of the internally generated stable, known signal and the same signal after it has passed through the transfer function.

6. A method as recited in claim 1, wherein an antenna is first isolated from the receiver system prior to the injection of the internally generated stable, known signal.

7. A method as recited in claim 6, wherein an electronically controlled RF relay is used to automatically isolate the antenna from the receiver system.

8. A method as recited in claim 1, wherein the internally generated stable, known signal is routed to the receiver system using an electronically controlled RF relay.