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