GPS multipath detection method and system

• US 5,917,445 A
• Filed: 12/31/1996
• Issued: 06/29/1999
• Est. Priority Date: 12/31/1996
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Vallot, Lawrence C., Schipper, Brian W., Sheikh, Suneel I.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US08/775,501
• Time in Patent Office: 910 Days
• Field of Search: 342/357, 701/213, 701/214
• US Class Current: 342/357.61
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/54 using carrier phase measurements; using long or short baseline interferometry

Abstract

A multipath detection method for use in a GPS position determination system includes providing a code pseudorange measurement representative of a range of an antenna to a space vehicle and a carrier phase pseudorange measurement representative of the range of the antenna to the space vehicle. A code-carrier measurement difference is then generated between the code pseudorange measurement and the carrier phase pseudorange measurement. This code-carrier measurement difference is examined to determine if a multipath component is present. If, the difference indicates that multipath is likely to be present, use of such measurements in computing position solutions, such as attitude solutions, is avoided. A multipath detection system for carrying out the method is also described.

Claims

1. A multipath detection method for use in a GPS position determination system including a plurality of antennas for receiving signals from a plurality of space vehicles to compute position solutions, the method comprising the steps of:

providing a code pseudorange measurement representative of a range of an antenna of the plurality of antennas to a space vehicle of the plurality of space vehicles;

providing a carrier phase pseudorange measurement representative of the range of the antenna to the space vehicle;

generating a code-carrier measurement difference between the code pseudorange measurement and the carrier phase pseudorange measurement;

examining the code-carrier measurement difference to determine if a multipath component is present; and

avoiding, the use of measurements generated using the antenna and the space vehicle in computing a position solution if a multipath component of the code-carrier measurement difference is detected.

2. The method according to claim 1, wherein the examination step includes extracting a multipath component from the code-carrier measurement difference, if present.

3. The method according to claim 2, wherein the code-carrier difference includes components of at least one of ionospheric error, random noise and multipath, and further wherein the extraction step includes bandpass filtering the code-carrier difference to detect a multipath component, if present.

4. A multipath detection method for use in a GPS attitude determination system, the GPS attitude determination system for computing attitude solutions includes three or more antennas for receiving signals from at least two space vehicles, the method comprising the steps of:

providing a code pseudorange measurement representative of a range of one of the three or more antennas to a space vehicle;

providing a carrier phase pseudorange measurement representative of the range of the one antenna to the space vehicle;

generating a code-carrier measurement difference between the code pseudorange measurement and the carrier phase pseudorange measurement;

detecting the potential presence of multipath signal associated with the carrier phase pseudorange measurement using the code-carrier measurement difference; and

avoiding, the use of measurements generated using the one antenna and the space vehicle in computing an attitude solution if a multipath component of the code-carrier measurement difference is detected.

5. The method according to claim 4, wherein the detection step includes extracting a multipath component from the code-carrier measurement difference, if present, and comparing the multipath component to a threshold for determining if the one antenna and the space vehicle are to be avoided in computing an attitude solution.

6. The method according to claim 5, wherein the code-carrier difference includes components of at least one of ionospheric error, random noise and multipath, and further wherein the extraction step includes bandpass filtering the code-carrier difference to detect a multipath component, if present.

7. The method according to claim 4, further including the step of providing a post-update measurement residual corresponding to each set of two antennas and a space vehicle used for computation of an attitude solution, and further wherein a code-carrier measurement difference is generated only if the post-update measurement residual corresponding to a set of two antennas and the space vehicle exceeds a measurement residual threshold.

8. The method according to claim 7, wherein the code-carrier difference includes components of at least one of ionospheric error, random noise and multipath, and further wherein the detection step includes extracting a multipath component by bandpass filtering the code-carrier difference, if present, and comparing the multipath component to a threshold for determining if the one antenna and the space vehicle are to be avoided in computing an attitude solution.

9. A multipath detection method for use in a GPS attitude determination system, the GPS attitude determination system for computing attitude solutions using three or more antennas and signals from at least two space vehicles, the method comprising the steps of:

providing a post-update measurement residual corresponding to each set of two antennas and a space vehicle used for computation of an attitude solution;

comparing each post-update measurement residual to a measurement residual threshold and if the post-update measurement residual corresponding to one set of two antennas and a space vehicle exceeds the measurement residual threshold, then a code-carrier measurement difference for each antenna/space vehicle pair of the one set is generated, the code-carrier measurement difference is the difference between a code pseudorange measurement representative of a range between the antenna and space vehicle of the pair and a carrier phase pseudorange measurement representative of the range between the antenna and space vehicle of the pair;

examining any code-carrier measurement differences generated for antenna/space vehicle pairs to determine if multipath signals are present; and

avoiding, the use of measurements generated using an antenna/space vehicle pair in computation of an attitude solution using the GPS attitude determination system if multipath signals are determined to be present upon examination of the code-carrier measurement difference generated for the antenna/space vehicle pair.

10. The method according to claim 9, wherein the antenna/space vehicle pair can be avoided in the computation of the attitude solution only if the antenna/space vehicle pair is not necessary to enable the computation to be performed.

11. A multipath detection system for use in GPS attitude determination, the system comprising:

at least three antennas for receiving signals from at least two space vehicles;

means for generating a code-carrier measurement difference between a code pseudorange measurement representative of a range of an antenna to a space vehicle and a carrier phase pseudorange measurement representative of the range of the antenna to the space vehicle;

means for examining the code-carrier measurement difference to determine if a multipath component of the code-carrier measurement difference is present;

means for computing attitude solutions using the at least three antennas; and

means for avoiding the use of measurements generated using the antenna and the space vehicle in the computation of an attitude solution if the code-carrier difference indicates the presence of multipath signals.

12. The system according to claim 11, wherein the examination means includes means for extracting the multipath component from the code-carrier measurement difference, if present.

13. The system according to claim 12, wherein the code-carrier difference includes components of at least one of ionospheric error, random noise and multipath, and further wherein the extraction means includes a bandpass filter to generate the multipath component, if present.

14. The system according to claim 11, further including:

means for providing a post-update measurement residual corresponding to each set of two antennas and a space vehicle used for computation of attitude solutions computed using the at least three antennas and the signals from at least two space vehicles;

means for controlling the generation means by comparing each post-update measurement residual to a measurement residual threshold and if a post-update measurement residual corresponding to one set of two antennas and a space vehicle does not exceed the measurement residual threshold, then a code-carrier measurement difference for the two antennas and the space vehicle of the one set are not generated by the generation means.