Internal calibration method for receiver system of a wireless location system

• US 6,317,081 B1
• Filed: 01/31/2000
• Issued: 11/13/2001
• 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:
  US09/495,421
• Time in Patent Office: 652 Days
• Field of Search: 342/165, 342/174, 342/385, 342/450, 342/457, 342/387
• 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

An internal calibration method, used to calibrate a receiver system used in a wireless location system, comprises injecting a signal into the receiver system and utilizing the signal to obtain an estimate of the manner in which the transfer function of the receiver system varies across the bandwidth of the receiver system. This estimate is used to mitigate the effects of the variation of the transfer function on time measurements made by the receiver system. Such time measurements are used to locate mobile transmitters.

Claims

1. An internal calibration method for a receiver system characterized by a time- and frequency-varying transfer function, wherein the receiver system is used in a wireless location system, comprising the steps of:

injecting a stable, known wideband signal into the receiver system;

using the wideband signal to estimate the transfer function across a prescribed bandwidth of the receiver system; and

using the estimate to mitigate the variation of the transfer function on subsequent time measurements.

2. A method as recited in claim 1, wherein the internally generated wideband signal is a comb signal.

3. A method as recited in claim 2, wherein the comb signal is characterized by multiple discrete frequencies and consistent amplitude and spacing between the discrete frequencies.

4. A method as recited in claim 1, wherein the estimate of the transfer function is weighted by a quality factor prior to mitigation of the effects of the transfer function.

5. A method as recited in claim 4, wherein the estimate of the transfer function is used only if the quality factor exceeds a predetermined threshold value.

6. A method as recited in claim 5, wherein the quality factor is based on a cross correlation function before and after the transfer function.

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

8. A method as recited in claim 7, wherein an electronically controlled RF relay is used for isolation.

9. A method as recited in claim 8, wherein the known wideband signal is routed to the receiver system using the electronic RF relay.