High level testing to test and recover the damaged differential corrections

• US 6,018,818 A
• Filed: 10/14/1997
• Issued: 01/25/2000
• Est. Priority Date: 05/05/1995
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Sheynblat, Leonid
• Primary Examiner(s): Baker, Stephen M.
• Application Number:
  US08/943,307
• Time in Patent Office: 833 Days
• Field of Search: 714/811, 701/215
• US Class Current: 714/811
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]

Abstract

The method and apparatus for high level testing are disclosed. The high level testing is used to test and recover the damaged differential corrections. The high level test measures the Correction Quality Indicator (CQI) and is based on the information included in the current pseudorange correction (PRC), in the previous range rate correction (RRC), and in the previous PRC projected to a time tag of a current PRC. The method computes CQI and compares the computed CQI value with the threshold value T(FAR), wherein the T(FAR) is the threshold value based on a false alarm rate and confidence interval. If the CQI does not exceed the threshold value T(FAR) the corrections for the tested satellite or a combination of tested satellites are marked as valid for further use in the user receiver differential solution.

Claims

1. A method of high level testing of differential corrections, said differential corrections being used in a GPS receiver for determining a differential solution to a navigational problem, said method comprising the steps of:

computing a Correction Quality Indicator CQI=PRC_t2 -[PRC_t1 +RRC_t1 * (t2-t1)];

wherein a current pseudo range correction PRC_t2 is taken at a time t2; and

wherein said time t2 is the Modified Z-Count of the current correction received for that satellite; and

wherein the Modified Z-Count is defined as the time of the start of the frame as well as the reference time for the message parameters; and

wherein the Modified Z-Count provides the time into the hour (0 through 3599.4 seconds) and is sent in units of 0.6 seconds; and

wherein said previous pseudo range correction PRC_t1 taken at a time t1 is projected to a current time tag; and

wherein said time t1 is synchronized with the Modified Z-Count for a current pseudorange correction (PRC) which was generated at t1; and

comparing said computed CQI value with a threshold value T(FAR);

wherein said threshold value T(FAR) is based on a false alarm rate and on a confidence interval;

and wherein if said CQI exceeds said threshold value T(FAR) said differential corrections are marked as invalid for further use in said GPS receiver differential solution.

2. The method of claim 1, wherein said step of computing said Correction Quality Indicator (CQI) further comprises the step of:

computing a Trimble Correction Quality Indicator (TCQI)=PRC_t2 -RRC_t2 *(t2-t1)/2-[PRC_t1 +RRC_t1 *(t2-t1)/2];

wherein a current pseudo range correction RRC_t2 is interpolated to a time t3 within a time interval [t1, t2]; and

wherein t1 is synchronized with the Modified Z-Count for a PRC which was generated at t1; and

wherein t2 is the Modified Z-Count of the current correction received for that satellite.