Method and apparatus for mitigating multipath effects at a satellite signal receiver using a sequential estimation filter

• US 7,095,370 B1
• Filed: 10/27/2005
• Issued: 08/22/2006
• Est. Priority Date: 10/27/2005
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Podshivalov, Sergei, Abraham, Charles, van Diggelen, Frank
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US11/259,767
• Time in Patent Office: 299 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.12, 342/357.15, 701/207, 701/213, 701/215
• US Class Current: 342/357.61
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/42 Determining position

Abstract

A method and apparatus for mitigating multipath effects in a satellite signal receiver is described. In one example, measured pseudoranges are obtained from the satellite signal receiver to a plurality of satellites. For each measured pseudorange: an expected pseudorange is derived from a sequential estimation filter in the satellite signal receiver. The measured pseudorange and the expected pseudorange are differenced to compute a pseudorange residual. The measured pseudorange is applied to the sequential estimation filter only if the pseudorange residual is within a window.

Claims

1. A method of mitigating multipath effects in a satellite signal receiver, comprising:

obtaining measured pseudoranges from the satellite signal receiver to a plurality of satellites; and

for each measured pseudorange of the measured pseudoranges;

deriving an expected pseudorange from a sequential estimation filter in the satellite signal receiver;

differencing the measured pseudorange and the expected pseudorange associated therewith to compute a pseudorange residual; and

applying the measured pseudorange to the sequential estimation filter only if the pseudorange residual is within a window.

2. The method of claim 1, wherein the measured pseudoranges comprise sub-millisecond pseudoranges.

3. The method of claim 1, wherein the sequential estimation filter comprises a Kalman filter.

4. The method of claim 1, wherein the step of applying comprises:

if the pseudorange residual is within a window, updating a state vector of the sequential estimation filter using the measured pseudorange.

5. The method of claim 4, wherein the step of applying further comprises:

if the pseudorange residual is within a window, updating a state covariance matrix of the sequential estimation filter using the state vector as updated.

6. The method of claim 1, wherein the step of deriving comprises:

computing a predicted state from a previous state vector of the sequential estimation filter and a dynamic model for the satellite signal receiver;

computing the expected pseudorange from the predicted state.

7. The method of claim 1, wherein the window is symmetric or asymmetric about an expected delay.

8. The method of claim 1 wherein the window varies in response to at least one of:

sequential estimation filter state covariance, number of satellites in view, satellite dilution of precision, or signal-to-noise-ratio.

9. A mobile device, comprising:

a satellite signal receiver for processing signals from a plurality of satellites to obtain measured pseudoranges; and

a sequential estimation filter configured to sequentially process each measured pseudorange of the measured pseudoranges by deriving an expected pseudorange, differencing the measured pseudorange and the expected pseudorange to compute a pseudorange residual, and updating a state vector only if the pseudorange residual is within a window.

10. The mobile device of claim 9, wherein the measured pseudoranges comprise sub-millisecond pseudoranges.

11. The mobile device of claim 9, wherein the sequential estimation filter comprises a Kalman filter.

12. The mobile device of claim 9, wherein the sequential estimation filter comprises a processor configured to execute program code for sequentially processing the measured pseudoranges.

13. The mobile device of claim 9, wherein the sequential estimation filter is further configured to:

if the pseudorange residual is within a window, update a state covariance matrix using the state vector as updated.

14. The mobile device of claim 9, wherein the sequential estimation filter is further configured to:

compute a predicted state from a previous state vector and a dynamic model for the satellite signal receiver;

compute the expected pseudorange from the predicted state and a sample processing model for the satellite signal receiver.

15. The method of claim 9 wherein the window is symmetric or asymmetric about an expected delay.

16. The method of claim 9 wherein the window varies in response to at least one of:

sequential estimation filter state covariance, number of satellites in view, satellite dilution of precision, or signal-to-noise-ratio.