Apparatus and method for determining receiver performance in a multilateration system

• US 7,928,908 B2
• Filed: 05/04/2006
• Issued: 04/19/2011
• Est. Priority Date: 07/01/2005
• Status: Expired due to Fees

• Current Assignee: ROKE Manor Research Limited (Chemring Group PLC)
• Original Assignee: ROKE Manor Research Limited (Chemring Group PLC)
• Inventors: Weedon, Robert John, Galloway, Philip Edward Roy, Fisher, James Joseph, Quilter, Timothy John
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Galt; Cassi
• Application Number:
  US11/994,462
• Publication Number:
  US 20090027270A1
• Time in Patent Office: 1,811 Days
• Field of Search: 342/387, 342/385, 342/386, 342/465, 342/451, 342/463
• US Class Current: 342/465
• CPC Class Codes: G01S 5/0221 Receivers

Abstract

In a multilateration system receivers are grouped into two groups. The first group is used to determine a position of a signal source, for example, an aircraft equipped with a SAR transponder. From the determined position, predicted time of arrival values are produced for the second group receivers. These are compared with the actual time of arrival values for the signals arriving at the second group receivers. A difference is determined and then the variation of that difference is determined as the aircraft travels in its track. The groupings are then varied and further variations determined. When the minimum variation is determined an alert is given that the second group has a receiver which is operating with a larger than desirable group time delay.

Claims

1. Apparatus for identifying which receiver in a plurality of receivers in known positions in a multilateration system is experiencing a significant group time delay comprising for in a first and subsequent pass:

a processor that

determines from a first group of receivers a detected position of an aircraft providing a signal source;

determines from the detected position of the aircraft and the known positions of a receiver or receivers of a second group a predicted difference in time of arrival of the signal from the aircraft for the second group, using a receiver from the first group as a reference;

compares the predicted difference in time of arrival with an actual difference time of arrival at the second group to derive a difference in time of arrival difference;

derives a variation in successive difference in time of arrival differences over a segment of a flight path of the aircraft; and

determines, in the absence of a significant variation in successive differences between predicted and actual time of arrival differences, and in the presence of a difference between predicted and actual time of arrival differences, that a receiver in the second group is experiencing significant time delay.

2. Apparatus as claimed in claim 1 wherein grouping of receivers varies between passes.

3. Apparatus as claimed in claim 2 wherein the second group is formed of one receiver of the plurality.

4. Apparatus as claimed in claim 3 wherein each of the plurality of receivers forms, for at least one pass, the second group.

5. Apparatus as claimed in claim 1 wherein the determination of when there is a difference in predicted and actual time of arrival differences involves a comparison of the differences with one of a threshold and/or a difference derived from at least one earlier pass.

6. Apparatus as claimed in claim 1 wherein the at least one filter is a Kalman filter.

7. A multilateration system comprising apparatus as claimed in claim 1.

8. A method of determining which receiver of a plurality of receivers of known locations in a multilateration system is experiencing a significant group delay comprising the steps of:

determining the position of an aircraft providing a signal source using a first group of the plurality of receivers;

determining from the determined position of the aircraft, and the known location of a receiver in a second group, a predicted difference time of arrival of the signal from the aircraft at that receiver, using a receiver from the first group as a reference;

determining a difference in the difference in time of arrival from the predicted and the actual difference in time of arrival;

deriving from a set of differences a variation in the differences over a segment of a flight path of the aircraft; and

in the absence of a significant variation in differences between predicted and actual time of arrival differences, and in the presence of a difference between predicted and actual time of arrival differences, concluding that the receiver in the second group is experiencing a significant group time delay.

9. A method as claimed in claim 8 comprising the steps of:

for subsequent passes re-allocating at least some of the receivers between the first and the second group.

10. A method of determining which receiver of a plurality of receivers of known locations in a multilateration system is experiencing a significant group delay comprising the steps of:

a) selecting some of the plurality of receivers as a first group of receivers;

b) selecting a remaining receiver as a second group of receivers;

c) determining the position of an aircraft providing a signal source using the first group of the plurality of receivers;

d) determining from the determined position of the aircraft, and the known location of the receiver in the second group, a predicted difference time of arrival of the signal from the aircraft at that receiver, using a receiver from the first group as a reference;

e) determining a difference in the difference in time of arrival from the predicted and the actual difference in time of arrival as a first difference in a set of differences;

f) changing receivers in the first and second groups of receivers over a segment of a flight path of the aircraft and repeating steps a)-e) until each of the plurality of receivers is selected as part of the second group of receivers to produce further sets of differences;

deriving from each set of differences a variation in the differences; and

in the absence of a significant variation in differences between predicted and actual time of arrival differences, and in the presence of a difference between predicted and actual time of arrival differences, concluding that a receiver in the second group is experiencing a significant group time delay.