Communications: directive radio wave systems and devices (e.g. – With particular circuit – Spectrum analysis
Reexamination Certificate
1990-12-07
2001-04-10
Hellner, Mark (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
Spectrum analysis
C324S076120
Reexamination Certificate
active
06215439
ABSTRACT:
BACKGROUND OF THE INVENTION
This application pertains generally to digital signal processing, and in particular to the processing of detected radio signals emitted in the audio frequency bands. Specifically, this invention pertains to an algorithm which analyzes unintentional emissions from audio frequency emitting platforms using transmitters and identifies the emitting platforms by analysis of the gaps between speech transmissions.
Intercepted audio band transmissions from unknown sources frequently contain modulations other than those associated with voice. These modulations can be generated by propulsion systems, transmitters, heating and cooling equipment, or other systems associated with the transmitting platform, and are unintentional. Such unintentional modulations can permit platform identification when properly detected, analyzed, and interpreted.
Various governmental and industrial organizations have signal collection activities which gather massive amounts of voice channel data. This data is or is not of interest, depending on the information contained in the voice signal and any additional information that might be gleaned from the channel itself. Additional data from unintentional modulations can be used to assist in culling uninteresting data and as a means of providing “external” cues to the identity or location of the transmitting device. Such information is of value in search and rescue missions. Exploring possible analysis techniques for exploiting unintentional modulations is a continuing activity of these organizations.
Some of these organizations are interested in the use of passive devices to detect, select, and identify signal sources of interest. Since the activities of the signal sources frequently are accompanied by radio transmissions, it was deemed possible to identify the emitting platform by detecting and identifying unintentional modulations imposed on the transmission. In addition, classifying emitters based on unintentional modulations can enhance the correlation of identification data from other, usually known reliable, sources.
SUMMARY OF THE INVENTION
The principal object of this invention is to provide a feasible method of using non-speech audio band information to obtain identification information pertaining to the emitting platform.
A further object of the invention is to provide a method for identification of the emitting platform by detecting and identifying unintentional modulations imposed on the transmission.
Still a further object of the invention is to provide a method for classifying emitters based on unintentional modulations to enhance the correlation of identification data from other sources.
Still another object of the invention is to provide a method to identify the emitting platform based on its unique normalized energies in seven bandpass filters, which are feature signatures of unintentional modulations.
Another object of this invention is to provide an algorithm to automatically detect gaps in speech transmissions, and to analyze unique spectral features present in the gaps, the accuracy of the resulting algorithm performance being based on the “ground truth” associated with several emitting platforms.
Other objects, features and advantages of the invention will be apparent to those skilled in the art from the following description of the preferred embodiments.
In a first aspect of this invention, a system for emitter identification of a transmitting platform using spectral energy analysis, comprises a means to process recorded transmission activity on a radio channel in the audio frequency range with a fast fourier transform algorithm; a means to detect gaps in speech in said processed transmission data; and a means to process said gaps to extract spectral features characteristic of said transmitting platform from said gaps. It then processes the results to execute a decision function based on said extracted characteristic features to identify the platform of said transmitter based on said features.
In a second aspect of this invention, the system also includes a means to detect transmission activity on a radio channel in the audio frequency range and a means to detect the boundaries of transmitter keyclicks at the beginning and end of said transmission. It further includes means to extract keying envelopes from said detected keyclick boundaries and means to analyze said keying envelopes to extract features characteristic of said keyclicks. Finally, the system has means to execute a decision function based on correlating both sets of said extracted characteristic features to identify the platform of said transmitter based on the features of said keyclick.
In a third aspect of the invention, a method of emitter identification comprises the steps of: processing audio transmission data using a fast fourier transform; detecting gaps in said processed transmission data; extracting spectral features consisting of normalized energy per unit frequency; extracting spectral features of each transmission from said gaps; and executing a decision function for identification of said emitter platforms based on said extracted spectral features
In a fourth aspect of the invention, the method of emitter identification of a transmitting platform further includes using microphone keyclick analysis, comprising the steps of: 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; and executing a decision function correlating the identification of said emitter platforms based on said extracted keyclick features and said extracted characteristic spectral features to identify the platform of said transmitter.
Other objects, features and advantages of the invention will be apparent to those skilled in the art from the following description of the preferred embodiments.
REFERENCES:
patent: 3924182 (1975-12-01), Jensen
patent: 4885586 (1989-12-01), Hoover et al.
Geldart Timothy A.
Goodman Fred J.
Martin Alvin F.
Mosko James D.
General Dynamics Government Systems Corporation
Hellner Mark
Jenner & Block
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