System and Method for Using CDMA PN Offset to Maintain Instrument Timing Reference

• US 20090073951A1
• Filed: 03/17/2008
• Published: 03/19/2009
• Est. Priority Date: 03/27/2007
• Status: Active Grant

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Matos, Soraya J., Young, Jerry A., Elliot, Thomas A., Kuntz, Thomas L.
• Granted Patent: US 8,184,608 B2
• Time in Patent Office: Days
• US Class Current: 370/342
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/31 Acquisition or tracking of other signals for positioning
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04W 56/006 using known positions of transmitter and receiver

Abstract

A system and method is provided enabling identification of different PN offsets values for CDMA signals without access to a GPS signal, such as when making measurements within indoor environments. When a timing reference, such as that provided by a GPS signal, is lost, the frame boundary timestamp of the CDMA signal itself is used. The parameters of the strongest available PN offset are used. The timing error is determined and the new timing reference timestamp is estimated. The strongest PN is used as the time reference and tau is corrected for. In further embodiments, a user may be able to provide identifying information allowing the estimated timing reference timestamp to be determined even when a GPS signal was never established for providing an initial timing reference.

Claims

1. A method of maintaining a timing reference for a mobile communications signal comprising;

extracting an Even Second Clock (ESC) from a global positioning system (GPS) signal;

measuring a PN offset for a first Base Transceiver Station (BTS);

deriving a time reference from the first BTS when the GPS signal is lost; and

identifying a second PN offset for a second BTS based upon the derived time reference.

2. The method of claim 1, wherein the first BTS has the strongest signal.

3. The method of claim 1, wherein a frame boundary of a CDMA signal is used when deriving the time reference.

4. The method of claim 1, wherein tau is adjusted form when deriving the time reference.

5. The method of claim 1, further comprising deriving a time reference from a different BTS other than the first BTS when the first BTS signal is lost.

6. The method of claim 5, wherein the different BTS has the strongest signal at the time when the first BTS signal is lost.

7. A method of maintaining a timing reference in the absence of a global positioning system (GPS) Even Second Clock (ESC) timing reference comprising:

obtaining a value for a PN offset for a first Base Transceiver Station (BTS);

deriving a time reference from the first BTS; and

identifying a second PN offset for a second BTS based upon the derived time reference.

8. The method of claim 7, wherein the first BTS has the strongest signal.

9. The method of claim 7, wherein a frame boundary of a CDMA signal is used when deriving the time reference.

10. The method of claim 7, wherein tau is adjusted form when deriving the time reference.

11. The method of claim 7, further comprising deriving a time reference from a different BTS other than the first BTS when the first BTS signal is lost.

12. The method of claim 11, wherein the different BTS has the strongest signal at the time when the first BTS signal is lost.