Method and system for synchronizing receiver systems of a wireless location system

• US 6,351,235 B1
• Filed: 01/31/2000
• Issued: 02/26/2002
• 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
• Application Number:
  US09/495,417
• Time in Patent Office: 757 Days
• Field of Search: 342/352, 342/356, 342/357.06, 342/457, 701/213, 331/3, 331/44, 331/47
• US Class Current: 342/357.62
• 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

In a wireless location system (WLS) including a plurality of geographically separated receiver systems, a system for synchronizing the respective receiver systems includes the use of an enhanced GPS receiver including a mechanism for receiving GPS signals and removing at least a portion of the timing instability of the GPS signals. An output of the enhanced GPS receiver is provided to a low phase noise phase-locked loop circuit that is used to produce reference signals with less than 0.01 degrees RMF of phase noise.

Claims

1. A receiver system including an external synchronization capability, the receiver system being employed in a wireless location system (WLS) and comprising:

(a) an enhanced GPS receiver including means for receiving GPS signals and a mechanism for removing at least a portion of any timing instability of the GPS signals, and (b) a low phase noise phase-locked loop circuit;

wherein the output of the enhanced GPS receiver is input to the phase-locked loop circuit, and wherein the phase-locked loop circuit produces reference signals with less than 0.01 degrees RMS of phase noise.

2. A receiver system as recited in claim 1, wherein the WLS comprises a plurality of signal collection systems (SCSs) and is overlaid on a wireless communications system such that a plurality of said SCSs share an antenna with a base station of the wireless communications system, and wherein the receiver system is part of one of said SCSs.

3. A receiver system as recited in claim 1, wherein the phase-locked loop circuit is driven by an oven controlled crystal oscillator.

4. A receiver system as recited in claim 1, wherein the phase-locked loop circuit generates a plurality of signals employed within the receiver system, each signal being synchronized in time and frequency to a signal output by the enhanced GPS receiver, and each generated signal having a low phase noise.

5. A receiver system as recited in claim 1, wherein the enhanced GPS receiver further includes a mechanism for outputting (1) a 10 MHz reference signal and (2) a one pulse per second (1 PPS) reference signal.

6. A receiver system as recited in claim 1, wherein the enhanced GPS receiver comprises a receiver capable of receiving time signals from GPS satellites and additional circuitry and processing capability that removes the time varying effect of a selective availability function in the GPS satellites.

7. A wireless location system (WLS) comprising a plurality of signal collection systems (SCSs), wherein each SCS comprises a receiver system including an external synchronization capability, the receiver system comprising an enhanced GPS receiver including means for receiving GPS signals and a mechanism for removing at least a portion of any timing instability of the GPS signals, and wherein the enhanced GPS receiver further includes a mechanism for outputting a periodic reference pulse that is within ten nanoseconds of the reference pulse produced by the receiver system(s) in other SCS(s) of the WLS.

8. A WLS as recited in claim 7, wherein the receiver system of each SCS further comprises a low phase noise phase-locked loop circuit;

wherein the output of the enhanced GPS receiver is input to the phase-locked loop circuit, and wherein the phase-locked loop circuit produces reference signals with less than 0.01 degrees RMS of phase noise.

9. A WLS as recited in claim 7, wherein the WLS is overlaid on a wireless communications system such that a plurality of said SCSs share an antenna with a base station of the wireless communications system, and wherein the receiver system is part of one of said SCSs.

10. A WLS as recited in claim 8, wherein the phase-locked loop circuit is driven by an oven controlled crystal oscillator.

11. A WLS as recited in claim 8, wherein the phase-locked loop circuit generates a plurality of signals employed within the receiver system, each signal being synchronized in time and frequency to a signal output by the enhanced GPS receiver, and each generated signal having a low phase noise.

12. A WLS as recited in claim 7, wherein the enhanced GPS receiver includes a mechanism for outputting (1) a 10 MHz reference signal and (2) a one pulse per second (1 PPS) reference signal.

13. A WLS as recited in claim 7, wherein the enhanced GPS receiver comprises a receiver capable of receiving time signals from GPS satellites and additional circuitry and processing capability that removes the time varying effect of a selective availability function in the GPS satellites.

14. A method for synchronizing multiple, geographically separated receiver systems in a wireless location system (WLS), comprising:

in each receiver system, employing an enhanced GPS receiver to generate a reference signal with less than 0.01 degrees RMS of phase noise, and employing said reference signal in each receiver system to generate a clock signal that is substantially synchronized with the clock signals generated in other receiver systems of the WLS.

15. A method as recited in claim 14, wherein the enhanced GPS receiver in each receiver system is employed to receive GPS signals and remove at least a portion of any timing instability of the GPS signals, and wherein the method includes providing an output of the enhanced GPS receiver to a phase-locked loop circuit and employing the phase-locked loop circuit to produce said reference signals with less than 0.01 degrees RMS of phase noise.

16. A method as recited in claim 14, wherein the WLS comprises a plurality of signal collection systems (SCSs) and is overlaid on a wireless communications system such that a plurality of said SCSs share an antenna with a base station of the wireless communications system, and wherein each receiver system is part of one of said SCSs.

17. A method as recited in claim 15, wherein the phase-locked loop circuit is driven by an oven controlled crystal oscillator.

18. A method as recited in claim 15, wherein the phase-locked loop circuit of each receiver system generates a plurality of signals employed within the receiver system, each signal being synchronized in time and frequency to a signal output by the enhanced GPS receiver, and each generated signal having a low phase noise.

19. A method as recited in claim 14, wherein the enhanced GPS receiver outputs a 10 MHz reference signal and a one pulse per second (1 PPS) reference signal.

20. A method as recited in claim 14, wherein the enhanced GPS receiver is employed to receive time signals from GPS satellites and remove the time varying effect of a selective availability function in the GPS satellites.