Emitter identification from radio signals using keyclick algorithm
First Claim
1. A system for emitter identification of a transmitting platform using microphone keyclick analysis, comprising:
- means to detect transmission activity on a radio channel in the audio frequency range;
means to detect the boundaries of transmitter keyclicks at the beginning and end of said transmission;
means to extract keying envelopes from said detected keyclick boundaries;
means to analyze said keying envelopes to extract features characteristic of said keyclicks;
means to execute a decision function based on said extracted characteristic features to identify the platform of said transmitter based on the features of said keyclick.
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Abstract
An algorithm for emitter identification of a transmitting platform using microphone keyclick analysis, and a system utilizing said algorithm, wherein said algorithm processes audio signals to detect transmission activity on a radio channel in the audio frequency range, detects the boundaries of transmitter keyclicks at the beginning and end of said transmission; extracts keying envelopes from said detected keyclick boundaries; and analyzes said keying envelopes to extract features characteristic of said keyclicks. The algorithm and system then proceed to execute a decision function based on said extracted characteristic features to identify the platform of said transmitter based on the features of said keyclick. A second algorithm, which may be executed in parallel with the first by said system, processes said transmission data using a fast fourier transform, detecting gaps in said processed transmission data. It then extracts spectral features consisting of normalized energy per unit frequency from said gaps; and correlates identification of said emitter platforms based on said extracted spectral features with identification of said emitter platforms based on said extracted keyclick features.
40 Citations
18 Claims
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1. A system for emitter identification of a transmitting platform using microphone keyclick analysis, comprising:
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means to detect transmission activity on a radio channel in the audio frequency range;
means to detect the boundaries of transmitter keyclicks at the beginning and end of said transmission;
means to extract keying envelopes from said detected keyclick boundaries;
means to analyze said keying envelopes to extract features characteristic of said keyclicks;
means to execute a decision function based on said extracted characteristic features to identify the platform of said transmitter based on the features of said keyclick. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
means to select an adaptive noise floor;
means to update said noise floor periodically;
means to determine an energy threshold of a transmission relative to said adaptive noise floor;
means to determine the transitions from transmit on to transmit off relative to said adaptive noise floor, thereby determining end of transmission boundaries; and
means to store said end of transmission boundaries.
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3. The system of claim 2, wherein said means to detect the boundaries of a transmitter keyclick further comprises:
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means to analyze said approximate end of transmission boundary to determine energy peaks;
means to cross-correlate said peaks with a template of known emitters, thereby detecting the precise boundaries of a keyclick.
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4. The system of claim 3, wherein said means to extract a keying envelope further comprises:
means to develop an envelope around each peak using a leaky integration of the form;
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5. The system of claim 4, wherein said means to extract features characteristic of keyclicks, comprises:
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means to determine the number of peaks in each of said envelopes;
means to calculate the average ratio of each peak to the first peak in each of said envelopes;
means to calculate the average ratio of each peak to its following valley in each of said envelopes;
thereby extracting statistical data constituting said features.
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6. The system of claim 5, wherein said means to execute a decision function further comprises:
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means to establish a decision tree based on scatter plots of past known identities;
means to establish a set of rules based on past analyses, and to determine thresholds for said rules; and
means to apply currently extracted features to a data base constructed with said rules and thresholds.
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7. The system of claim 5, wherein said means to identify an emitting platform further comprises:
means to utilize a vector quantization algorithm to determine minimum distortion of a current vector compared to past vectors.
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8. The system of claim 7, wherein said vector quantization algorithm comprises:
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at least one codebook having at least one cluster developed on the basis of training data;
means to score said extracted features with each codebook;
means to calculate the minimum distortion of said extracted features; and
means to identify a platform based on said scores.
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9. The system of claim 1, further comprising:
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means to process said transmission data using a fast fourier transform;
means to detect gaps in said processed transmission data;
means to extract spectral features of each transmission from said gaps, consisting of normalized energy per unit frequency; and
means to correlate identification of said emitter platforms based on said extracted spectral features with identification of said emitter platforms based on said extracted keyclick features.
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10. A method of emitter identification of a transmitting platform using microphone keyclick analysis, comprising the steps of:
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detecting transmission activity on a radio channel in the audio frequency range;
detecting the boundaries of transmitter keyclicks at the beginning and end of said transmission;
extracting keying envelopes from said detected keyclick boundaries;
analyzing said keying envelopes to extract features characteristic of said keyclicks;
executing a decision function based on said extracted characteristic features to identify the platform of said transmitter based on the features of said keyclick. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
selecting an adaptive noise floor;
updating said noise floor periodically;
determining an energy threshold of a transmission relative to said adaptive noise floor;
determining the transitions from transmit on to transmit off relative to said adaptive noise floor, thereby determining end of transmission boundaries; and
storing said end of transmission boundaries.
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12. The method of claim 11, wherein said step of detecting the boundaries of a transmitter keyclick further comprises the steps of:
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analyzing said approximate end of transmission boundary to determine energy peaks; and
cross-correlating said peaks with a template of known emitters, thereby detecting the precise boundaries of a keyclick.
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13. The method of claim 12, wherein said step of extracting a keying envelope further comprises the step of:
developing an envelope around each peak using a leaky integration of the form;
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14. The method of claim 13, wherein said step of extracting features characteristic of keyclicks, further comprises the steps of:
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determining the number of peaks in each of said envelopes;
calculating the average ratio of each peak to the first peak in each of said envelopes; and
calculating the average ratio of each peak to its following valley in each of said envelopes;
thereby extracting statistical data constituting said features.
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15. The method of claim 14, wherein said step of executing a decision function further comprises the steps of:
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establishing a decision tree based on scatter plots of past known identities;
establishing a set of rules based on past analyses, and determining thresholds for said rules; and
applying currently extracted features to a data base constructed with said rules and thresholds.
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16. The method of claim 15, wherein said step of identifying an emitting platform further comprises the step of:
utilizing a vector quantization algorithm to determine minimum distortion of a current vector compared to past vectors.
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17. The method of claim 16, wherein said step of utilizing a vector quantization algorithm further comprises the steps of:
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utilizing at least one codebook having at least one cluster developed on the basis of training data;
scoring said extracted features with each codebook;
calculating the minimum distortion of said extracted features; and
identifying an emitting platform based on said scores.
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18. The method of claim 10, further comprising the steps of:
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processing said transmission data using a fast fourier transform;
detecting gaps in said processed transmission data;
extracting spectral features of each transmission from said gaps, consisting of normalized energy per unit frequency; and
correlating identification of said emitter platforms based on said extracted spectral features with identification of said emitter platforms based on said extracted keyclick features.
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Specification