SYSTEM AND METHOD FOR AUTOMATIC RECOVERY AND COVARIANCE ADJUSTMENT IN LINEAR FILTERS

• US 20100027603A1
• Filed: 07/31/2007
• Published: 02/04/2010
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: North South Holdings Incorporated (Spherix Incorporated)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: DISHMAN, John F., BEADLE, Edward R.
• Granted Patent: US 7,894,512 B2
• Time in Patent Office: Days
• US Class Current: 375/226
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering

Abstract

A communications device includes a time/frequency error measurement circuit that receives a communications signal and measures its timing and frequency errors. A Kalman filter receives the communications signal from the time/frequency error measurement circuit and processes the signal using a multi-level state error covariance matrix P for controlling the Kalman gain in the Kalman filter. An on-line monitoring circuit is operative with the Kalman filter for monitoring the actual state errors in time and frequency and controlling the state error covariance matrix P based on a measured error threshold.

Claims

1. A communications device, comprising:

a time/frequency error measurement circuit that receives a communications signal and measures its timing and frequency errors within the communications signal;

a Kalman filter that receives the communications signal from the time/frequency error measurement circuit and processes the communications signal using a multi-level state error covariance matrix P for controlling the Kalman gain in the Kalman filter; and

an online error monitoring circuit operative with the Kalman filter for monitoring the actual state errors in time and frequency and controlling the state error covariance matrix P based on a measured error threshold.

2. The communications device according to claim 1, wherein levels within the multi-level state error covariance P are defined initially as true initial errors.

3. The communications device according to claim 1, wherein the state error covariance matrix P is reset from a theoretical P to an actual P to open up bandwidth to an actual state error covariance matrix P when one of at least excessive time and frequency errors occur.

4. The communications device according to claim 1, wherein said multi-level state error covariance matrix P comprises a value determined from a look-up table comprising a plurality of downlink tracking states having different synchronization pulse types.

5. The communications device according to claim 4, wherein said online error measuring circuit is operative for receiving and passing residuals at a maximum limit for each of a plurality of track states.

6. The communications device according to claim 4, wherein said look-up table comprises a plurality of steady state time tracking errors and steady state frequency tracking errors.

7. The communications device according to claim 6, wherein said multi-level state error covariance matrix P comprises a steady state time or frequency tracking error value determined from said look-up table.

8. The communications device according to claim 1, wherein said Kalman filter is operative for producing minimum mean square error (MMSE) estimates of timing and frequency errors.

9. The communications device according to claim 1, and further comprising a time/frequency tracker operative to acquire and track time and frequency variations in synchronization signals conveyed over communications links.

10. The communications device according to claim 9, and further comprising a receiver clock, wherein said time/frequency tracker is operative to synchronize the receiver clock with a clock signal embedded within the communications signal.

11. The communications device according to claim 10, and further comprising a front-end demodulator in which said receiver clock is incorporated.

12. A communications system, comprising:

a plurality of signal sources that transmit communications signals operating at respectively different data rates over respective ones of a plurality of communications links;

a receiver that receives the plurality of communications signals, and comprising a

a front end demodulator having a receiver clock that is used in the recovery of data from communications signals received from the signal sources;

a time/frequency error measurement circuit that receives the communications signal and measures the timing and frequency errors with the communications signals;

a Kalman filter that receives communications signals from the time/frequency error measurement circuit and processes the communications signals using a multi-level state error covariance matrix P for controlling the Kalman gain within the Kalman filter;

an online error monitoring circuit operative with the Kalman filter for monitoring the actual state errors in time and frequency and controlling the state error covariance matrix P based on a measured error threshold; and

a time/frequency tracker operative to acquire and track time and frequency variations in synchronization signals conveyed over the communications links and operative to synchronize the receiver clock with a clock signal embedded within the communications signal.

13. The communications system according to claim 12, wherein levels within the multi-level state error covariance P are defined initially as true initial errors.

14. The communications system according to claim 12, wherein the state error covariance matrix P is reset from a theoretical P to an actual P to open up bandwidth to an actual state error covariance matrix P when one of at least excessive time and frequency errors occur.

15. The communications system according to claim 12, wherein said multi-level state error covariance matrix P comprises a value determined from a look-up table comprising a plurality of downlink tracking states having different synchronization pulse types.

16. The communications system according to claim 15, wherein said online error measuring circuit is operative for receiving and passing residuals at a maximum limit for each of a plurality of track states.

17. The communications system according to claim 15, wherein said look-up table comprises a plurality of steady state time tracking errors and steady state frequency tracking errors.

18. The communications system according to claim 12, wherein said Kalman filter is operative for producing minimum mean square error (MMSE) estimates of timing and frequency errors.

19. A method of communicating, comprising:

receiving a communications signal and measuring the timing and frequency errors within a time/frequency error measurement circuit;

processing data from the time/frequency error measurement circuit using a multi-level state error covariance matrix P for controlling the Kalman gain in the Kalman filter; and

monitoring the actual state errors in time and frequency and controlling the state error covariance matrix P based on a measured error threshold.

20. The method according to claim 19, which further comprises resetting the state error covariance matrix P is reset from a theoretical P to an actual P to open up bandwidth to an actual state error covariance matrix P when one of at least excessive time and frequency errors occur.

21. The method according to claim 19, which further comprises receiving and passing residuals at a maximum limit for each of a plurality of track states.

22. The method according to claim 19, which further comprises generating a multi-level state error covariance matrix P from a value determined from a look-up table comprising a plurality of downlink tracking states having different synchronization pulse types.