Pulse repetition interval autocorrelator system

• US 4,209,835 A
• Filed: 07/21/1978
• Issued: 06/24/1980
• Est. Priority Date: 07/21/1978
• Status: Expired due to Term

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Guadagnolo, Robert N.
• Primary Examiner(s): Malzahn, David H.
• Application Number:
  US05/926,971
• Time in Patent Office: 704 Days
• Field of Search: 364/715, 364/728, 343/5 DP, 343/17.1 PF, 343/100 CL
• US Class Current: 708/426
• CPC Class Codes: G01R 29/033 giving an indication of the number of times this occurs , i.e. multi-channel analysers (the characteristic being frequency)
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals
• CPC Class Codes: G01S 7/38 Jamming means, e.g. producing false echoes
• CPC Class Codes: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00

Abstract

A PRI (pulse repetition interval) autocorrelator that functions as a data analyzer for recognition of PRIs in a data set composed of time ordered TOA (time of arrival)) words representing the time of reception of a plurality of pulses from a plurality of emitters. The processing of a data set is performed at each of a plurality of cells of a plurality of coarse map intervals or octaves by adding an incremental assumed periodicity τ to the time of arrival and performing an autocorrelation comparison of the data set for each cell to provide correlation counts. An amplitude ordered list is then formed of the cell correlation counts which are greater than a threshold and subcells of each cell on the list are subject to a fine level autocorrelation for determining the PRI.

Claims

1. An autocorrelation system for determining the PRI of a plurality of emitters emitting pulses of energy comprising:

first means for storing a plurality of TOA words each representing the time of arrival of a pulse;

a source of a plurality of assumed periodicity values having coarse level and fine level periodicity values;

second means coupled to said first means and to to said source for autocorrelating said TOA words at said plurality of assumed periodicity values and providing correlation counts related to an assumed periodicity value, said second means being controllable to provide said correlation counts at coarse levels or at fine levels;

third means coupled to control said source of periodicity values and to control said second means to selectively correlate said TOA words at a pluralty of said coarse level periodicity values and said fine level periodicity values, and respectively provide coarse level and fine level correlation counts; and

fourth means included in said third means for selecting correlation counts as a function of value and reporting a PRI corresponding to the assumed periodicity value of said selected correlation count.

2. The combination of claim 1 further comprising fifth means included in said second means and coupled to said first means and responding to said fourth means selecting a correlation count to delete corresponding TOA words in said first means.

3. A system for determining PRI values from emitters comprising:

memory means for providing a data set of time ordered TOA words;

first calculator means coupled to said memory means responsive to said TOA words to autocorrelate said TOA words and provide time correlation counts;

a source of periodicity values τ

coupled to said calculator means for applying different τ

values thereto representing increasing periodicity, to be combined with said TOA words for developing said time correlation counts; and

second calculator means coupled to said source of periodicity values and to said first calculator means and responsive to said τ

values and said time correlation counts for determining PRI values of emitters.

4. The combination of claim 3 in which said second calculator means further includes means coupled to said memory means for deleting, from further correlation, TOA words corresponding to the τ

related to a determined PRI value.

5. The combination of claim 4 in which said source of periodicity values includes means to provide τ

values over a selected number of octaves and over a selected number of time cells, each octave having a predetermined number of time cells.

6. The combination of claim 5 in which said second calculator means further includes control means coupled to said source and to said first calculator means so that the correlations and deletions of TOA words for each octave are sequentially completed.

7. The combination of claim 6 in which said second calculator means further includes means to control said source and said first calculator means to first provide a coarse level map of correlation counts of the cells of an octave and then provide a fine level map of correlation counts of selected cells of said octave, said second calculator means selecting from said fine level map of correlation counts, the τ

value corresponding to an emitter for the PRI value.

8. The combination of claim 7 in which said second calculator means further includes threshold determining means for forming a list of cells from said coarse level map having correlation counts above a coarse level threshold and forming said fine level map from said list.

9. The combination of claim 8 in which said fine level threshold determining means forms a list of cells from said fine level map having correlation counts above threshold and said second calculator means further includes means for selecting the τ

value corresponding to an emitter as that value associated with the maximum fine level correlation count above said threshold.

10. The combination of claim 9 in which said second calculator means further includes means to form a new coarse level map after said means for deleting has completed the operation.

11. The combination of claim 10 in which said second calculator means further includes means coupled to said source for providing a τ

for the next octave when a coarse level map is formed without any correlation count values that exceeds said coarse level threshold value.

12. A system for forming a correlation count from a plurality of TOA words comprising:

memory means for storing said TOA words in time order for access;

a source of τ

values and limit values;

comparator means;

first means coupled to said memory means, to said comparator means and to said source for combining a first TOA word with τ and

said limit values to apply a first comparison TOA word to said comparator means,

second means coupled to said memory means, to said comparator means and to said source for appying at least a second TOA word thereto for correlation with said first TOA word;

correlation counts means; and

third means coupled to said comparator means, to said correlation count means and to said memory means to control said comparator means for applying a correlation count to said correlation count means, and for controlling said memory means to apply a new first TOA word to said first means.

13. The combination of claim 12 further including means coupled to said source of τ

values and to said first means for providing double the values of τ and

the limits of said first and second TOA words upon detection of a correlation of said first and second TOA words and for applying a correlation count to sad correlation count means upon a second correlation between the first and second TOA words having double values of τ and

the limits.

14. The combination of claim 13 further including P-counter means coupled to said memory means for addressing said first TOA words, C-counter means coupled to said memory means for addressing said second TOA word, and control means coupled to said third means, to said P-counter means and to said C-counter means for incrementing said C-counter means for each second TOA word and for incrementing said P-counter means in response to at least the detection of a second correlation.

15. A system for determining PRI from a plurality of TOA words representing the time of arrival of pulses from a plurality of emitters comprising:

a source of assumed periodicity τ

values for defining a plurality of map periods each having a plurality of time cells;

cell calculator means responsive to said TOA words and said source of assumed periodicity values to detect correlation matches and provide a coarse level data map of correlation counts for the time cells of a map period;

first means coupled to said cell calculator means and to said source of assumed periodicity values for responding to each coarse level data map to form an additional subcell data map of correlation counts and for selecting a subcell as a correlation count representative of an emitter PRI and having a PRI value related to the corresponding τ

value.

16. A system for determining PRI from a plurality of TOA words representing repetitive pulse trains comprising:

memory means for storing said TOA words for time ordered access;

a source of assumed periodicity values defining a plurality of octave periods and a plurality of periods of each octave period;

calculator means coupled to said memory means and to said source of assumed periodicity values, for autocorrelating said TOA words at said assumed periodicity values during each of said plurality of octave periods to provide correlation counts; and

control means coupled to said calculator means to select as a function of value, correlation counts that represent repetitive pulse trains, said control means sequentially controlling said calculator means for autocorrelating each octave until none of the correlation counts are selected.

17. The combination of claim 16 in which said calculator means includes means for autocorrelate said TOA words at a coarse level, and at least one fine level in which selected ones of said plurality of periods of an octave period are expanded in time.

18. The combination of claim 16 in which said control means further includes means to delete TOA words which autocorrelate with the corresponding periodicity value.

19. A system for determining PRI from a plurality of emitters transmitting pulses of energy comprising:

receiving means responsive to said pulses of energy to develop TOA words,

memory means coupled to said receiving means for storing said TOA words for time ordered access;

a source of assumed periodicity values defining a plurality of octave periods and a plurality of periods during each octave period;

calculator means coupled to said memory means and to said source of assumed periodicity values, for autocorrelating said TOA words at said assumed periodicity values during each period of said plurality of octave periods to provide correlation counts; and

control means coupled to said calculator means to select as a function of value, correlation counts that represent repetitive pulse trains, said control means controlling said calculator means to sequentially autocorrelate each octave until none of the correlation counts are selected.

20. The combination of claim 19 in which said control means further includes means to delete TOA words which autocorrelate with the corresponding periodicity vale.

21. A system for determining the group PRI of a plurality of TOA words each representing the time of arrival of a pulse of energy from an emitter comprising:

first means for storing said plurality of TOA words

a source of a plurality of assumed group periodicity values;

having coarse level and fine level periodicity values;

second means coupled to said first means and to said source for autocorrelating said TOA words at said plurality of assumed periodicity values and providing correlation counts related to an assumed periodicity value, said second means being controllable to provide said correlation counts at coarse levels or at fine levels;

third means coupled to control said source of periodicity values and to control said second means to selectively correlate said TOA words at a plurality of said coarse level periodicity values and said fine level periodicity values, and respectively provide course level and fine level correlation counts; and

fourth means included in said third means for selecting correlation counts as a function of value and reporting a group PRI corresponding to the assumed periodicity value of said selected correlation count.