Preprocessor and adaptive beamformer for active signals of arbitrary waveform
First Claim
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1. A signal processor for processing an echo signal received by an array of receiving elements from a distant target ensonified or irradiated by a transmitted signal, comprising:
- a receiver operably coupled to said array of receiving elements for receiving element outputs;
a digitizer operably coupled to said receiver for generating a digitized time series from each of said element outputs;
a block generator operably coupled to said digitizer for forming a series of uncompressed time blocks from said digitized time series within a total receiving time of said element outputs, wherein said uncompressed time blocks contain sufficient data to correlate and synchronize time segments from said digitized time series with a replica of said transmitted signal;
a replica correlator operably coupled to said block generator for correlating each of said uncompressed time blocks with said replica of said transmitted signal to form a series of correlated time blocks;
a time shifter operably coupled to said replica correlator for forming a series of synchronized groups from said series of correlated time blocks, wherein said synchronized groups are synchronized to within one sample period for each of a plurality of steering directions; and
a time window generator operably coupled to said time shifter for forming a contiguous series of time windows from said series of synchronized groups, wherein each of said time windows extends from an initial time to a final time appropriate to an arrival time and a duration of said echo signal.
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Abstract
A pre-processor and adaptive beamformer processes an echo received by an array of receiving elements from a distant target from a transmitted signal having an arbitrary waveform capable of being represented as a complex modulation of a carrier frequency. Time blocks are formed from each element output represented by a series of time windows extending from an initial time appropriate to the arrival time of the echo to a final time appropriate to the time block. A correlation is performed of each time block with a replica of the transmitted signal. The correlation products are aligned with respect to time difference to within one sample period. The beamformer further aligns the correlation products with respect to time difference to substantially the same phase for each steering direction. Covariance estimates are formed using techniques of spatial averaging to generate adaptive weights optimized to suppress interfering signals without requiring the use of time averaging.
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Citations
27 Claims
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1. A signal processor for processing an echo signal received by an array of receiving elements from a distant target ensonified or irradiated by a transmitted signal, comprising:
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a receiver operably coupled to said array of receiving elements for receiving element outputs; a digitizer operably coupled to said receiver for generating a digitized time series from each of said element outputs; a block generator operably coupled to said digitizer for forming a series of uncompressed time blocks from said digitized time series within a total receiving time of said element outputs, wherein said uncompressed time blocks contain sufficient data to correlate and synchronize time segments from said digitized time series with a replica of said transmitted signal; a replica correlator operably coupled to said block generator for correlating each of said uncompressed time blocks with said replica of said transmitted signal to form a series of correlated time blocks; a time shifter operably coupled to said replica correlator for forming a series of synchronized groups from said series of correlated time blocks, wherein said synchronized groups are synchronized to within one sample period for each of a plurality of steering directions; and a time window generator operably coupled to said time shifter for forming a contiguous series of time windows from said series of synchronized groups, wherein each of said time windows extends from an initial time to a final time appropriate to an arrival time and a duration of said echo signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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12. The signal processor of claim 4, wherein said surface array is spherical.
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13. The signal processor of claim 4, wherein said surface array is cylindrical.
- 14. The signal processor of claim 5, wherein said rank-M element covariance estimate generator includes a second element covariance generator operably coupled to said estimator for generating a second covariance estimate C'"'"'pn for reducing sensitivity to errors and for matching said rank-M covariance estimate by rank to M stronger signals to mask interfering signals, wherein said second element covariance estimate includes noise augmentation of diagonal components of said rank-M element covariance estimate substantially according to
- space="preserve" listing-type="equation">C'"'"'.sub.pn =C.sub.p +f.sub.n NP.sub.e I,
where Cp represents said rank-M element covariance estimate prior to noise augmentation, Pe represents element power averaged over said vector of element outputs, N represents a dimension of said covariance matrix, fn represents a numeric parameter, and I represents an identity matrix having a dimension N, wherein said second element covariance estimate is incorporated by said weight adaptor to derive each of said adapted weight vectors substantially according to ##EQU18##
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- 15. The signal processor of claim 7, wherein said rank-M beam covariance estimate generator includes a second covariance generator operably coupled to said estimator for generating a second covariance estimate B'"'"' for reducing sensitivity to errors and for matching said rank-M beam covariance estimate by rank to M stronger signals to mask interfering signals, wherein said second covariance estimate includes noise augmentation of diagonal components of said rank-M element covariance estimate substantially according to
- space="preserve" listing-type="equation">B'"'"'=B+f.sub.n NP.sub.e I,
where B represents said rank-M beam covariance estimate prior to noise augmentation, Pe represents element power averaged over said vector of element outputs, N represents a dimension of said beam covariance matrix, fn represents a numeric parameter, and I represents an identity matrix having a dimension N, wherein said covariance estimate is incorporated by said weight adaptor to derive each of said adapted weight vectors substantially according to ##EQU19##
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18. A method for processing an echo of a transmitted signal received by an array of receiving elements from a target at a range R ensonified or irradiated by a transmitted signal, comprising the steps of:
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(a) receiving element outputs fn (tk) as a digitized time series for forming time block element outputs fn (tk) representing portions of said element outputs fn (tk) containing sufficient data to correlate and synchronize a time segment having a duration T of said digitized time series with a replica of said transmitted signal; (b) performing a replica correlation of said time block element outputs with a time series of digital samples of said replica of said transmitted signal to generate a series of correlated time blocks; (c) time shifting said correlated time blocks to generate a series of synchronized groups, wherein each of said synchronized groups includes corresponding said correlated time blocks from said plurality of element outputs, synchronized to within one sample period for each of a plurality of steering directions; and (d) time windowing said synchronized groups to form a series of time-windowed groups having an initial time T0 appropriate to an arrival time of said echo signal at said receiving array and a final time Tf =T0 +T. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27)
- 26. The method of claim 22, wherein said step of generating a rank-M covariance estimate includes a further step of generating a second covariance estimate for reducing sensitivity to errors and for matching said rank of said covariance estimate for masking interfering signals from M stronger signals, wherein said second covariance estimate includes augmentation of the diagonal components of said covariance estimate substantially according to
- space="preserve" listing-type="equation">C'"'"'.sub.p =C.sub.p +f.sub.n NP.sub.e I,
where Cp represents an average covariance prior to augmentation, Pe represents element power averaged over said vector of element outputs, N represents a dimension of said covariance matrix, fn represents a numeric parameter, and I represents an identity matrix of dimension N, wherein said second covariance estimate is incorporated in said step of generating a series of adapted weight vectors to derive said adapted weight vectors substantially according to ##EQU27##
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- 27. The method of claim 24, wherein said step of generating a rank-M covariance estimate includes a further step of generating a second covariance estimate for reducing sensitivity to errors and for matching said rank of said covariance estimate for masking interfering signals from M stronger signals, wherein said second covariance estimate includes augmentation of the diagonal components of said covariance estimate substantially according to
- space="preserve" listing-type="equation">B'"'"'=B+f.sub.n NP.sub.e I,
where B represents an average covariance prior to augmentation, represents element power averaged over said vector of element outputs, N represents a dimension of said covariance matrix, fn represents a numeric parameter, and I represents an identity matrix of dimension N, and wherein said second covariance estimate is incorporated in said step of generating a series of adapted weight vectors to derive said adapted weight vectors substantially according to ##EQU28##
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Current Assigneethe united states of america as represented by the secretary of the navy
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Original Assigneethe united states of america as represented by the secretary of the navy
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InventorsLockwood, James C.
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Primary Examiner(s)Issing, Gregory C.
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Application NumberUS08/405,487Time in Patent Office474 DaysField of Search342/375, 342/378, 342/379, 342/380, 342/382, 342/383, 367/103US Class Current342/378CPC Class CodesG01S 7/2813 Means providing a modificat...G01S 7/36 Means for anti-jamming , e....G01S 7/52003 Techniques for enhancing sp...G01S 7/527 Extracting wanted echo sign...G01S 7/537 Counter-measures or counter...G10K 11/341 Circuits thereforH01Q 3/2605 Array of radiating elements...
