Clock system and corresponding method for providing a clock time accounting for systematic error

• US 6,573,799 B1
• Filed: 12/12/2001
• Issued: 06/03/2003
• Est. Priority Date: 12/12/2001
• Status: Expired due to Fees

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Akopian, David
• Primary Examiner(s): Mis, David C.
• Application Number:
  US10/016,655
• Time in Patent Office: 538 Days
• Field of Search: 331/44, 331/64, 331/74, 331/78, 331/158, 331/175, 342/350, 342/352, 342/357-1-3, 701/200, 701/207, 701/213, 701/214
• US Class Current: 331/64
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude

Abstract

Method for accounting for factors (such as temperature) causing systematic errors (time-varying or constant) in a clock, such as a clock used in a ranging receiver (for use with a positioning system such as the Global Positioning System), and a corresponding clock system (including a clock and a filter such as a Kalman filter) for providing clock time and error, used for example in a ranging receiver. The invention adds new state vector components to account for systematic error. The process update equation used in the navigation solution is accordingly extended to include the additional components of the state vector.

Claims

1. A method of providing an estimate of a current state of a clock having a clock phase indicating a value for time, the method comprising:

a) a step (41) of providing a clock measurement (z) indicating information about the clock; and

b) a step (42), responsive to the clock measurement (z), for determining the estimate of a current state of the clock using a state filter adapted to use a four-component state (x′

) including as components a clock phase component and a clock fractional frequency component, and also including a clock error component and a clock error rate component, and further adapted to use a measure of four-state process noise covariance (Q′

).

2. A method as in claim 1, wherein the clock measurement (z) indicates information about the clock phase and clock fractional frequency.

3. A method as in claim 2, wherein the measure of process noise covariance (Q′

) is a process noise covariance matrix (Q′

), and wherein the process noise covariance matrix (Q′

) includes as diagonal terms respective variances in the values for each of the four components of the four-component state (x′

).

4. A method as in claim 3, wherein the four-state process noise covariance matrix (Q′

) is based on a definition of a process noise covariance matrix Q given by,

5. A method as in claim 3, wherein the four-state process noise covariance matrix (Q′

) is derived from a two-state process noise covariance (Q) for a two-state clock model in a way that preserves the components of the process noise covariance (Q) for the two-state clock model, regardless of the manner in which the components of the process noise covariance (Q) for the two-state clock model are defined.

6. A method as in claim 2, wherein the state (x′

) of the ranging receiver includes as components the clock phase component, the clock fractional frequency component, the clock error component, and the clock error rate component, and also includes either a position component or a velocity component indicating either the position or velocity of the ranging receiver, respectively.

7. A method as in claim 1, wherein the step (42) for determining the estimate of a current state of the clock is performed as part of a step of providing an estimate of a current state (x′

) of a ranging receiver used in conjunction with beacons of a positioning system, and wherein the method further comprises a step of providing pseudoranges from the beacons of the positioning system.

8. A clock system (30) for providing an estimate of a current state of a clock (22);

the clock system comprising;

a) the clock (22), for providing clock measurements (z) indicating information about the clock; and

b) a state filter (31), responsive to the clock measurements (z), for providing the estimate of the current state of the clock using a four-state clock model based on a two-state clock model providing a two-component state (x), with clock phase and clock fractional frequency as components, and a two-state measure of process noise covariance (Q), the four-state clock model including a four-component state (x′

) combining the two-component state (x) with a clock error component and a clock error rate component, and including a measure of four-state process noise covariance (Q′

).

9. A clock system (30) as in claim 8, wherein the clock measurement (z) indicates information about the clock phase and clock fractional frequency.

10. A clock system (30) as in claim 9, wherein the measure of process noise covariance (Q′

) is a process noise covariance matrix (Q′

), and wherein the process noise covariance matrix (Q′

) includes as diagonal terms respective variances in the values for each of the four components of the four-component state (x′

).

11. A ranging receiver (20) including a clock system (30) as in claim 8, the ranging receiver for use in conjunction with beacons of a positioning system, wherein the state filter (31) is adapted for use in the ranging receiver (20), and wherein the state filter (31) is further responsive to pseudoranges determined from signals provided by the beacons of the positioning system, and wherein the state (x′

) estimated by the state filter (31) includes the state of the clock (22) as well as the state of the ranging receiver (20) in respect to an aspect of the position of the ranging receiver as a function of time.

12. A ranging receiver (20) as in claim 11, wherein the clock measurement (z) indicates information about the clock phase and clock fractional frequency.

13. A ranging receiver (20) as in claim 12, wherein the measure of process noise covariance (Q′

) is a process noise covariance matrix (Q′

), and wherein the process noise covariance matrix (Q′

) includes as diagonal terms respective variances in the values for each of the four components of the four-component state (x′

).

14. A ranging receiver (20) as in claim 13, wherein the state (x′

) of the ranging receiver includes as components the clock phase component, the clock fractional frequency component, a clock error component, and a clock error rate component, and also includes either a position component or a velocity component indicating either the position or velocity of the ranging receiver, respectively.

15. A ranging receiver (20) as in claim 13, wherein the four-state process noise covariance matrix (Q′

) is based on a definition of a process noise covariance matrix Q given by,

16. A ranging receiver (20) as in claim 13, wherein the four-state process noise covariance matrix (Q′

) is derived from a two-state process noise covariance (Q) for a two-state clock model in a way that preserves the components of the process noise covariance (Q) for the two-state clock model, regardless of the manner in which the components of the process noise covariance (Q) for the two-state clock model are defined.

17. A ranging receiver (20) as in claim 13, wherein the ranging receiver includes means (25) for communicating with an external computing facility via wireless communication, and wherein the external computing facility performs at least some of the computation required to provide a navigation solution and so an estimate of the current state (x′

) of the ranging receiver based on information the external computing facility receives from the ranging receiver via wireless communication.

18. A system, comprising a ranging receiver (20) as in claim 11, and further comprising the beacons of the positioning system.