Method for reducing multipath propagation effects during the processing of replies in mode “S”

• US 7,936,300 B2
• Filed: 12/05/2007
• Issued: 05/03/2011
• Est. Priority Date: 12/12/2006
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Billaud, Philippe Jean
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US12/518,770
• Publication Number:
  US 20100026553A1
• Time in Patent Office: 1,245 Days
• Field of Search: 342 29- 40, 342/43, 342/46
• US Class Current: 342/37
• CPC Class Codes: G01S 13/782 using multimoding or selective addressing

Abstract

The processing method according to the invention is a method of processing replies from targets interrogated by a surveillance radar according to a mode S interrogation of all the targets present in the receiving lobe of the radar, whereby the different targets present in the receiving lobe of the radar are interrogated at least once, the set of the mode S reply signals received for this lobe are collected after each interrogation, a reply detection processing operation is performed for each target and errors are detected and, if necessary, corrected then the corresponding blips are extracted, and this method is characterized in that said signal quality detection and determination processing operation consists in forming a synthetic message with the set of replies to each interrogation for each target, establishing, for each bit of the message, the value and the quality of this bit and performing the error detection and correction using this synthetic message, and the three variables Σ, Δ and monopulse of all the failed replies from the same target are exploited to construct the synthetic message.

This processing operation is useful in highly polluted electromagnetic environments where the existing methods are inadequate: the same target may be asked the question again for reasons other than a reply failure.

Claims

1. A method of processing replies from targets interrogated by a surveillance radar for interrogations in mode S, independently for each target present in the reception lobe of the radar, whereby the different targets present in the reception lobe of the radar SSR are interrogated at least once, all the reply signals received for this lobe for each target are collected after each interrogation, a reply detection processing operation is performed in a signal processing module and errors are detected and corrected and the corresponding blips are extracted,

wherein said signal quality detection and determination processing operation is implemented, in the event of decoding failure by the signal processing operation, by a data processing module which forms a synthetic message with the stored set of replies to each interrogation for one and the same target, establishing, for each bit of each message, the value and the quality of this bit and performing the detection and correction of errors using this synthetic message.

2. The method as claimed in claim 1, wherein the synthetic message comprises the value and the quality of each bit of the mode S message.

3. The method as claimed in claim 1, wherein, for each mode S reply that is not decoded following a correction attempt performed unsuccessfully by the signal processing operation, or that could not be decoded because of an excessive number of bad quality bits in an incorrect message to attempt the correction, the signal processing module transmits:

the value of the reply for the three output variables of the radar receiver (SUM, DIFFERENCE and MONOPULSE) and the maximum number of samples consistent with this value for the three variables,

for each pulse that is potentially in the position of each bit of the reply message, the value for said three variables and the number of associated samples, thus giving a pulse value quality indicator,

information indicating the reply detection conditions.

4. The method as claimed in claim 1 wherein, as soon as at least two received replies are considered to be not decoded or not decodable by the signal processing module, the data processing module reconstructs a reply by carrying out the following steps:

it establishes, for each bit of the mode S message, an estimator based on the analysis of the information from the potential pulses of the bit for all the received replies, such information being for each output variable from the radar receiver;

the number of consistent samples in the reply, the reply quality flags, the value and the number of samples of each pulse, it decodes for each bit of the message the position of the pulse having the greatest value of the estimator and assigns a quality to each bit, always according to the value of the estimator and the presence of several pulses per bit,

it detects the errors by exploiting the new decoding of the message.

5. The method as claimed in claim 1, wherein, when it is possible and necessary to correct a message, the data processing module tries to correct the bits of the message by exploiting the new qualities of each bit.

6. The method as claimed in claim 3, wherein, to increase the possibilities of success, the attempt to decode the message is performed independently:

on the two variables SUM and MONOPULSE,

on the two variables DIFFERENCE and MONOPULSE,

on all three variables SUM, DIFFERENCE and MONOPULSE

to best exploit the characteristics of the pollution (amplitude, misalignment, absence of time stability, etc.) since it is sufficient for one success out of the three attempts for the mode S message to be considered to be correctly decoded.

7. The method as claimed in claim 1, wherein, when there is sufficient real time computation power available, the number of selective interrogations is reduced by exploiting those already received in real time in each lobe.

8. The method as claimed in claim 1, wherein, at the end of a lobe, the received replies are exploited, not in real time, to be able to decode the message if this was not done for one of the replies from the lobe.

9. The method as claimed in claim 1, wherein, for a radar operating at rotation speeds greater than approximately 4 s for a revolution, the All Call and Roll Call periods are eliminated in order to best distribute the radar time according to the nature of the targets present in the lobe of the radar.

10. The method as claimed in claim 9, wherein the interrogations in mode S are placed by taking into account the set of the SSR/SIF blips present in the lobe.