Method For Pre-Detecting Responses in a Secondary Radar or Application to the Detection of Mode S Responses

• US 20080238758A1
• Filed: 09/29/2004
• Published: 10/02/2008
• Est. Priority Date: 10/10/2003
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Billaud, Philippe Jean, De Volder, Claude Rene
• Granted Patent: US 7,688,250 B2
• Time in Patent Office: Days
• US Class Current: 342/32
• CPC Class Codes: G01S 13/781 Secondary Surveillance Radar [SSR] in general
• CPC Class Codes: G01S 13/782 using multimoding or selective addressing
• CPC Class Codes: G01S 13/784 Coders or decoders therefor; Degarbling systems; Defruiting systems

Abstract

The invention relates to a method for pre-detecting responses in a secondary radar. It applies in particular to the detection of mode S responses. An aim of the invention is to process the signals received before decoding the responses so as to allow the detection of mixed responses, and avoid the detection of ghost responses. For this purpose, the invention has in particular as subject a method for pre-detecting responses in a secondary radar, the responses to be pre-detected comprising a message coded by a modulated signal, characterized in that the presence of a signal exhibiting modulation characteristics in accordance with those of a message of a response to be pre-detected is identified; the duration of the signal identified is measured; this duration is compared with a minimum duration, this minimum duration being determined on the basis of the duration of the messages of the responses to be pre-detected.

Claims

1-12. -12. (canceled)

13. A method for pre-detecting responses in a secondary radar, the responses to be pre-detected including a message coded by a modulated signal, the method comprising:

a step of identification, during which the presence of a signal exhibiting modulation characteristics in accordance with those of a message of a response to be pre-detected is detected;

a step of measurement during which the duration of the identified signal is measured; and

a step of comparison during which the said duration of the signal identified is compared to a minimum duration, the minimum duration being determined on the basis of an expected duration of the messages of the responses to be pre-detected.

14. The method as claimed in claim 13, wherein the messages are coded by a position-modulated signal, the presence of a signal is identified when a sequence of pulses is present in which each pulse of the sequence is separated from that which precedes by at the most a duration of the order of a modulation period.

15. The method as claimed in claim 14, wherein generating a slot whose duration is substantially equal to the duration separating the first from the last pulse of the sequence of pulses, to within a modulation period identifies the presence of a signal.

16. The method as claimed in claim 15, wherein the said slot is generated from, the detected pulses and from a stable signal generated on the basis of the detection for a duration equal to the maximum time until the next detection of a message pulse.

17. The method as claimed in claim 16, wherein the said pulses are detected by thresholding with respect to a level determined as a function of a peak level.

18. The method as claimed in claim 16, wherein the duration of the said stable signal generated on the basis of a falling edge is substantially equal to the duration of a modulation period plus 20%.

19. The method as claimed in claim 18, in which the said pulses are detected by thresholding with respect to a level determined as a function of a peak level.

20. The method as claimed in claim 15, in which the duration of the identified signal is measured by measuring the duration of the slot.

21. The method as claimed in claim 13, in which the responses to be pre-detected being mode S responses, the minimum duration of the messages is of the order of 56 microseconds for short responses or of the order of 112 microseconds for long responses.

25. A method for detecting responses in a secondary radar, the responses to be detected comprising a message coded by a modulated signal, said method comprising:

a step of detection during which method of pre-detection as claimed in claim 13, to pre-detect the responses to be detected, is implemented and a step of generation during which a clock signal is generated at a message-based binary tempo;

the position of the beginning of the response is precisely determined on the basis of the beginning or of the end of the message.