System and method for high-integrity detection and correction of cycle slip in a carrier phase-related system

• US 6,166,683 A
• Filed: 02/19/1998
• Issued: 12/26/2000
• Est. Priority Date: 02/19/1998
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Hwang, Patrick Y.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/026,545
• Time in Patent Office: 1,041 Days
• Field of Search: 342/357.06, 342/357.04, 342/357.11, 342/357.03, 342/357.12, 701/213
• US Class Current: 342/357.37
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/55 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A system and method of detecting and correcting for cycle slip in a GPS attitude determination system is presented. The method employs several techniques for detecting and correcting for faults in high integrity carrier phase-related applications. A delta single difference is used as a primary measurement residual in detecting cycle slip. The delta single difference represents the difference in phase of a carrier signal of a GPS satellite at two receiving antennas over two points in time. This delta single difference is compared to a detection failure threshold computed based on certain high integrity needs. Satellites showing a failure are excluded. In addition, satellites that fail a detectability test, indicating the inability to detect a fault, are pre-excluded from attitude solution computation. When re-resolving integer ambiguities associated with fault detection and correction, the method ensures that the integer ambiguity is resolvable via a resolvability algorithm before implementing a solution-based integer ambiguity resolution.

Claims

1. In an attitude determination system having a plurality of satellites and having first and second antennas, a method of detecting and correcting cycle slip in said system comprising:

at a first processing epoch,

measuring a first phase of a first carrier signal at said first antenna from a first satellite,

measuring a second phase of said first carrier signal at said second antenna from said first satellite, and

establishing a first single difference from said first and second phases;

at a second processing epoch,

measuring a third phase of said first carrier signal at said first antenna from said first satellite,

measuring a fourth phase of said first carrier signal at said second antenna from said first satellite, and

establishing a second single difference from said third and fourth phases;

establishing a delta single difference from said first and second single differences;

establishing a detection test statistic from said delta single differences;

establishing a failure detection threshold using a geometry of said plurality of satellites and a false alert rate;

comparing the detection test statistic to the failure detection threshold; and

declaring existence of a cycle slip based on said comparing further comprising;

at said first processing epoch,

measuring a first phase of a second carrier signal at said first antenna from a second satellite,

measuring a second phase of said second carrier signal at said second antenna from said second satellite; and

at said second processing epoch,

measuring a third phase of said second carrier signal at said first antenna from said second satellite,

measuring a fourth phase of said second carrier signal at said second antenna from said second satellite,

wherein said establishing a first single difference is established from said first and second phases of said first carrier signal and said first and second phases of said second carrier signal, and

wherein said establishing a second single difference is established from said third and fourth phases of said first carrier signal and said third and fourth phases of said second carrier signal.

2. The method of claim 1, further comprising determining which of said first or second satellites is associated with the cycle slip.

3. The method of claim 2, further comprising:

if said first or second satellite associated with the cycle slip is found, tagging the satellite associated with the cycle slip for post-exclusion; and

if said first or second satellite associated with the cycle slip is not found, tagging both said first and second satellites for post-exclusion.

4. The method of claim 3, further comprising reporting all satellites tagged for post-exclusion.

5. In an attitude determination system having first and second antennas, each antenna receiving a plurality of carrier signals from a plurality of respective satellites, a method for detecting and correcting cycle slip in said system comprising:

testing the detectability of said plurality of satellites wherein said testing comprises;

establishing a detectability threshold using a geometry of said plurality of satellites,

establishing a detectability test statistic,

comparing said detectability test statistic to said detectability threshold to determine which of said plurality of satellites are detectable and which are non-detectable, and

tagging each of said non-detectable satellites for pre-exclusion based on said comparing wherein said at least one of said plurality of satellites has an unresolved integer ambiguity and wherein at least three of said satellites have resolved integer ambiguities, further comprising the step of testing the resolvability of said at least one of said plurality of satellites and,

wherein said testing the resolvability comprises;

calculating a resolvability test statistic for said at least one of said plurality of satellites;

establishing a minimum integrity requirement;

establishing a resolvability threshold based on said minimum integrity requirement;

comparing the resolvability test statistic with the resolvability threshold;

declaring the unresolved integer ambiguity of said at least one of said plurality of satellites resolvable based on said comparing.

6. The method of claim 5, further comprising resolving the unresolved integer ambiguity only if the integer ambiguity is resolvable.

7. In a carrier phase-related system having first and second antennas for receiving a plurality of carrier signals, one from each of a plurality of satellites, wherein at least one of said plurality of satellites has an unresolved integer ambiguity and wherein at least three of said satellites have resolved integer ambiguities, a method for detecting and correcting cycle slip in said system comprising:

testing the resolvability of said at least one of said plurality of satellites, comprising;

calculating a resolvability test statistic for said at least one of said plurality of satellites;

establishing a minimum integrity requirement;

establishing a resolvability threshold based on said minimum integrity requirement;

comparing the resolvability test statistic with the resolvability threshold;

declaring the unresolved integer ambiguity of said at least one of said plurality of satellites resolvable based on said comparing.

8. The method of claim 7, further comprising resolving the unresolved integer ambiguity only if the integer ambiguity is resolvable.

9. An apparatus for detecting and correcting cycle slip in a GPS attitude determination system having a plurality of satellites, comprising:

means for establishing detectability criteria;

means for testing the detectability of said plurality of satellites using said detectability criteria to establish non-detectable satellites;

means for tagging non-detectable satellites for pre-exclusion;

means for establishing resolvability criteria;

means for testing resolvability of ambiguities associated with satellites tagged for pre-exclusion and post-exclusion to establish resolvable satellites;

means for resolving ambiguities associated with satellites tagged for pre-exclusion and post-exclusion only if they are resolvable based on said testing.