System and method for using CDMA PN offset to maintain instrument timing reference

• US 8,184,608 B2
• Filed: 03/17/2008
• Issued: 05/22/2012
• Est. Priority Date: 03/27/2007
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Matos, Soraya J., Kuntz, Thomas L., Elliot, Thomas A., Young, Jerry L.
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): MEW, KEVIN D
• Application Number:
  US12/050,103
• Publication Number:
  US 20090073951A1
• Time in Patent Office: 1,527 Days
• Field of Search: 370328-329, 370331-332, 370/335, 370/338, 370341-342, 342/357.71, 34235762-35763
• 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 signal for a portable test instrument comprising the steps of:

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

measuring a PN offset for a first Base Transceiver Station (BTS) signal based on the timing reference signal;

when the portable test instrument is moved to an indoor environment and the GPS signal is lost, deriving a timing reference signal from the first BTS signal based on the PN offset of the first BTS signal as the timing reference signal; and

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

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

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

4. The method of claim 1, wherein a timing error between an ideal and a measured PN offset starting time is adjusted when deriving the timing reference signal.

5. The method of claim 1, further comprising the step of deriving a timing reference signal from the second BTS signal based on the PN offset of the second BTS signal as the timing reference signal when the first BTS signal is lost.

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

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

obtaining a user-specified reference PN offset for a first Base Transceiver Station (BTS) signal;

deriving a timing reference signal for the portable test instrument from the first BTS signal based on the user-specified reference PN offset of the first BTS signal;

identifying a PN offset for a second BTS signal based upon the derived timing reference signal from the first BTS signal; and

deriving a timing reference signal for the portable test instrument from the second BTS signal based on the PN offset of the second BTS signal when the first BTS signal is lost.

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

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

10. The method of claim 7, wherein a timing error between an ideal and a measured PN offset starting time is adjusted when deriving the timing reference signal from the first BTS signal.

11. The method of claim 7, wherein the second BTS signal is the strongest signal at the time when the first BTS signal is lost.