Patent Issued for Systems and Methods for Direct Emitter Geolocation (USPTO 9377520)

By a News Reporter-Staff News Editor at Electronics Newsweekly -- L-3 Communications Integrated Systems LP (Greenville, TX) has been issued patent number 9377520, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Westcott, Bryan L. (Rockwall, TX); Stanners, Steven P. (Rowlett, TX).

This patent was filed on May 31, 2013 and was published online on June 28, 2016.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Emitter geolocation methods exist that rely either on use of multiple separate simultaneous signal collection platforms (e.g., separate aircraft), or rely on knowledge of the signal modulation structure of an emitter signal. For example, a direct approach to geolocation that requires knowledge of emitter signal modulation has been conventionally employed. Such a direct approach does not require determination of an intermediate geolocation observable measurement such as from time difference of arrival (TDOA), frequency difference of arrival (FDOA), direction of arrival (DOA), etc. However, such a conventional direct geolocation approach requires and relies on prior knowledge of some or all of the emitted signal (e.g., a known reference signal embedded in the full emitted signal), i.e., some or all of the modulation applied to the emitted signal must be known in advance at the collection platform. Conventional array-based multi-emitter geolocation techniques also exist that rely on use of multiple separate simultaneous collection platforms such as separate aircraft.

"Other existing array-based direction finding systems exist that can locate multiple cochannel emitters using intermediate geolocation observable measurements. One conventional geolocation approach generates multiple line-of-bearing (LOB) measurements (hard decisions), and then estimates position based on these observables. Several algorithms exist to generate LOBs in a co-channel environment (e.g., such as MUSIC, MVDR). Conventional observable-based geolocation techniques typically become impossible with low-SNR emitters and overloaded environments (i.e., environments with more signals than antenna elements). Conventional observable-based geolocation techniques are also sub-optimal in the sense that hard decisions are made on small blocks of data, without considering the spatial correlation of the emitters."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Disclosed herein are systems and methods for locating signal wave (SW) emitter/s using at least a single moving signal collection platform. The disclosed systems and methods may be employed in one embodiment to estimate the signal energy transmitted from a grid of locations (such as a map) using collected IQ data (or other raw-data representations such as a IQ data covariance matrix), and without requiring computation of any intermediate geolocation-observable measurements (such as angle-of-arrival, direction-of-arrival, line-of-bearing, time-of-arrival, frequency-of-arrival, frequency-difference-of-arrival and time-difference of arrival). In a further embodiment, the disclosed systems and methods may be implemented in a blind manner (i.e., transmitted emitter signal/s are unknown and processed blindly) to geolocate SW emitters using a single SW signal collection platform (e.g., at relatively large standoff distances in some implementations) without relying on a known signal modulation or operation of multiple simultaneous SW signal collection platforms. In one further embodiment the final SW location estimate may be combined with additional geolocation observables if available.

"In a further embodiment, partial timing structure and/or frequency structure information may be known about the signal modulation (e.g., if a SW is known to be active only at a discrete set of times or if a SW is known to move in frequency in a deterministic pattern) and may be employed to improve geolocation accuracy (e.g., if data is only collected at times and frequencies when the SW is known to be active, the interference of cochannel emitters may be reduced) without requiring a known reference emitter signal or complete knowledge of the signal modulation or transmitted SW (e.g., a SW emitter may be known to employ a time-division-multiple-access scheme, which may provide information on when a signal is active but not what signal is being transmitted when the SW emitter is active).

"The energy collected from a set of discrete blocks of data may be projected onto all points on the grid, and then the resulting surface may be decomposed in order to separate (and geolocate) multiple emitters if they exist. In one embodiment, both the presence and geolocation of an unknown emitter may be simultaneously detected. Examples of some of the features that may be advantageously achieved individually or in combination in various embodiments of the disclosed systems and methods include, but are not limited to, an entire collection system based on this technique may be implemented with a relatively-small amount of code (e.g., allowing the geolocation system to be highly portable where desired); implementation of the disclosed geolocation solution techniques using field programmable gate array (FPGA) and/or graphics processing unit (GPU) acceleration; and/or use of geolocations to task additional collect resources for low-signal to noise ratio (SNR) or very wideband emitters (i.e., not relying on an observable power spectrum).

"The disclosed systems and methods may be implemented in one exemplary embodiment using a standard interferometry array for coherent collection of SW signals from an aircraft or other single mobile and moving SW signal collection platform, although it is also possible to implement the disclosed systems and methods using multiple SW signal collection platforms, e.g., by using additional stationary and/or moving platform/s. Unknown emitters of interest may be located by measuring temporal variation of collected SW signals and decomposing multiple blocks of raw multi-channel array data collected from at least one SW signal collection platform. The SW signal data may be collected and/or processed across defined periods of time (e.g., such as in multiple data collection bursts or in a single defined collection time period to produce window/s of data for processing), or may be collected on a continuous basis with no pre-defined collection time period (in which case the collected data may be buffered and the collection data set continues to grow over time). Emitters of interest may be located using a variety of processing methods, including iterative methods or with single pass sparse reconstruction techniques. The disclosed systems and methods may also be extended to location of wide-bandwidth emitters and may incorporate other information about the emitters and/or environment, where available. In one embodiment, moving-target (emitter) geolocation may be performed by further statistically processing collected data projected onto all points on a grid, e.g., using a moving vector of the collected data. Although the interferometry array may be used in one embodiment, it will be understood that it is possible that other embodiments of the disclosed systems and methods may be implemented using a single antenna element on a single platform or single antenna elements on respective multiple platforms for location of SW emitters.

"Unlike conventional techniques that require LOBs to be calculated for a given emitter, the disclosed systems and methods may be implemented to individually calculate the magnitude of the potential for each of many different defined points on the ground (or other range or set of potential emitter locations) to be the source of the emission/s received at the signal collection platform at a given time from a given emitter. The magnitude of the calculated potential for each given different point at a given time may be assigned to each point, e.g., by color coding on a display (e.g., video display) or using any other suitable point-weighting or value assignment methodology. As the signal collection platform moves relative to the emitter source/s, multiple values of cumulative emitter potential may be integrated over time (e.g., dynamically in real time) for each given point to result in a matrix of integrated point values that indicates actual emitter location/s. For example, in one exemplary embodiment, a displayed map of possible emitter locations that is color coded according to calculated magnitude of emitter source potential may be seen to transition from lines to peaks as cumulative emitter location potential is integrated over time in a manner that visually indicates actual emitter location/s. The disclosed systems and methods may be implemented in one embodiment to use covariance data directly in order to support single-collection platform operation (i.e., SW data collection occurring at only one platform such as one aircraft) while still obtaining most of the benefit from not using hard decisions (LOBs).

"The disclosed systems and methods may be advantageously implemented using a variety of types of signal collection platforms under a variety of different operating environments including, for example, using large-standoff platforms and low space weight and power (SWAP) commutated array platforms. Greatly simplified (and highly portable) collection systems may also be achieved in one embodiment. The disclosed systems and methods may utilize one or more processing devices may be utilized to perform direct IQ emitter geolocation, e.g., such as microprocessor, central processing unit (CPU), field gate programmable array (FPGA), application specific integrated circuit (ASIC), etc. In one embodiment, FPGA-based implementation may be employed in order to achieve a relatively small signal location system.

"Advantageously, in one exemplary embodiment, the disclosed systems and methods may be implemented to locate one or more low power emitters (e.g., having an emitter power that is lower than or under the noise floor throughout the integration) using a single SW signal collection platform (e.g., aircraft or other suitable mobile platform such as spacecraft, satellite, ship, wheeled vehicle, submarine, etc.) that moves relative to the emitter location/s. In another exemplary embodiment, the disclosed systems and methods may be implemented to locate multiple cochannel (or co-frequency) emitters that all simultaneously transmit on the same frequency. The disclosed systems and methods may be further employed in another exemplary embodiment to detect multiple emitters in a manner that is not limited by the number of antenna elements, e.g., by using overloaded array processing to locate more SW signal emitters than the number of elements present in an interferometry array of a SW signal collection platform. These features may be combined in one exemplary embodiment to achieve overloaded array cochannel processing to locate multiple low-power SW emitters. In a further embodiment, more than one SW signal collection platform may be employed to further enhance location of unknown emitter/s.

"In another exemplary embodiment, direct geolocation of multiple emitters of unknown location may be achieved by performing an iterative serial nulling or cancellation process. Such a serial nulling process may include using an interferometer array on a moving signal collection platform to collect SW signal data that includes signals received from multiple cochannel emitters transmitting from unknown locations along the path of the moving collection platform (e.g., along an aircraft flight path). The collected SW data may be processed and mapped (or otherwise digitized and/or stored) in a manner that facilitates visual identification of signal peaks that represent potential emitter locations. Geolocations of the multiple emitters may be sequentially identified and determined.

"Using a serial nulling processing technique embodiment, the geolocation of the strongest emitter (i.e., the overall peak in the collected data) of a group of multiple emitters of interest may be first identified. Then, the contribution of this identified emitter may be surgically subtracted from the overall data set to result in a new data set that includes all but the signal contribution of the removed strongest emitter. Then, the next strongest emitter peak (i.e., the overall peak in the remaining collected data) may be identified and located, and surgically subtracted as before. This identification and subtraction process may be repeated for each additional emitter, e.g., until a greater number of emitters have been located than the number of antenna elements in the array so as to achieve overloaded array processing. In one embodiment, the location of each identified emitter may be optionally indicated and displayed (e.g., on a graphical user interface or GUI) in real time by unique color code and/or symbol. Once all unknown SW signal emitters of interest have been located using this approach, the actual location (e.g., ground truth) of each of the multiple emitters is known, and may be displayed (e.g., as a complex map showing several potential peaks) and/or may be otherwise digitized, processed and/or stored for later use. In a further embodiment, the disclosed serial nulling emitter location processing may be simultaneously performed in parallel on a large number of different frequencies, allowing for simultaneous cochannel/low power emitter geolocation in multiple SW bands.

"As described above, direct geolocation of multiple emitters may be solved in one exemplary embodiment using an iterative technique (i.e., select a signal, cancel or subtract the signal, and repeat). However, it is possible to use other suitable techniques to process array information of a single moving signal collection platform to solve for the geolocations of multiple emitters, including single-pass techniques. For example, in one exemplary embodiment, a sparse reconstruction technique may be employed to process SW signal information received at the array of a single moving collection platform, e.g., using a framework that exploits the spatial sparsity of the emitters which may be characterized as a statistical estimation problem formulation. Such sparse reconstruction techniques may be used to take advantage of the fact that the number of emitter locations is small, and may be applied in one embodiment to stationary or fixed emitter locations where location of the emitters does not change over time during at least a portion of the duration of a SW data collection time. Further numerical refinement of the accuracy of one or more selected geolocations may also be optionally performed using any technique or combination of techniques suitable for increasing confidence of geolocation solutions obtained using the disclosed systems and methods.

"In one respect, disclosed herein is a method for locating at least one signal wave (SW) emitter of unknown modulation using a single moving signal collection platform, including: collecting a raw data representation of SW signal emissions within a SW emissions environment only at the single moving collection platform, the raw data representation of SW signal emissions including SW emissions of unknown modulation from the SW emitter, and the raw data representation including data samples having magnitudes that are characteristic of received signal energy of the SW emitter; estimating the signal energy transmitted within the SW emissions environment from a two or three dimensional grid of locations using the raw data representation collected only at the single moving signal collection platform; and determining the location of the SW emitter on the two dimensional or three dimensional grid from an estimated signal energy distribution across the two or three dimensional grid without knowledge of the modulation of the SW emissions from the SW emitter and without determining any intermediate geolocation observable measurement.

"In another respect, disclosed herein is a signal wave (SW) emitter location system, including a single mobile signal collection platform including at least one antenna element coupled to signal processing circuitry and configured to receive SW signal emissions within a SW emissions environment as the signal collection platform is moving. The signal processing circuitry may be configured to: use the at least one antenna element to collect a raw data representation of the SW signal emissions within the SW emissions environment as the signal collection platform is moving, the raw data representation of SW signal emissions including SW emissions from at least one SW emitter of unknown modulation, and the raw data representation including data samples having magnitudes that are characteristic of received signal energy of the SW emitter; estimate the signal energy transmitted within the SW emissions environment from a two or three dimensional grid of locations using the raw data representation collected only at the single moving signal collection platform; and determine the location of the SW emitter on the two dimensional or three dimensional grid from an estimated signal energy distribution across the two or three dimensional grid without knowledge of the modulation of the SW emissions from the SW emitter and without determining any intermediate geolocation observable measurement.

"In another respect, disclosed herein is a method for locating at least one signal wave (SW) emitter using at least a single moving signal collection platform. The method may include: collecting a raw data representation of SW signal emissions within a SW emissions environment at the single moving collection platform, the raw data representation of SW signal emissions including SW emissions from the SW emitter, and the raw data representation including data samples having magnitudes that are characteristic of received signal energy of the SW emitter; estimating the signal energy transmitted within the SW emissions environment from a two or three dimensional grid of locations using the collected raw data representation; and determining the location of the SW emitter on the two dimensional or three dimensional grid from an estimated signal energy distribution across the two or three dimensional grid. The collected raw data representation of SW signal emissions may include SW emissions from multiple SW emitters; where the raw data representation includes data samples having magnitudes that are characteristic of received signal energy of each of the SW emitters. The method may further include: decomposing and separating the received signal energy of the raw data representation into the signal energy contributions for each of the multiple SW emitters at a single location on the grid, and determining a location of each of the multiple SW emitters on the grid based at least in part on the received signal energy contribution of each SW emitter, where each SW emitter remains stationary on the grid at the same time that the signal collection platform moves relative to the SW emitter and collects the raw data representation of SW signal emissions. The method may also further include decomposing and separating the received signal energy of the raw data representation into the signal energy contributions for each of the multiple SW emitters using at least one of single pass sparse reconstruction that jointly and simultaneously estimates the contribution of each emitter; iterative serial nulling or cancellation that separately and sequentially estimates the contribution of each emitter; or a combination thereof.

"In another respect, disclosed herein is a SW emitter location system, including at least one mobile signal collection platform including at least one antenna element coupled to signal processing circuitry and configured to receive SW signal emissions within a SW emissions environment as the signal collection platform is moving. The signal processing circuitry may be configured to: use the at least one antenna element to collect a raw data representation of the SW signal emissions within the SW emissions environment as the signal collection platform is moving, the raw data representation of SW signal emissions including SW emissions from the SW emitter, and the raw data representation including data samples having magnitudes that are characteristic of received signal energy of the SW emitter; estimate the signal energy transmitted within the SW emissions environment from a two or three dimensional grid of locations using the collected raw data representation; and determine the location of the SW emitter on the two dimensional or three dimensional grid from an estimated signal energy distribution across the two or three dimensional grid. The collected raw data representation of SW signal emissions may include SW emissions from multiple SW emitters; where the raw data representation includes data samples having magnitudes that are characteristic of received signal energy of each of the SW emitters. The signal processing circuitry may be further configured to: decompose and separate the received signal energy of the raw data representation into the signal energy contributions for each of the multiple SW emitters at a single location on the grid, and determine a location of each of the multiple SW emitters on the grid based at least in part on the received signal energy contribution of each SW emitter, where each SW emitter remains stationary on the grid at the same time that the signal collection platform moves relative to the SW emitter and collects the raw data representation of SW signal emissions. The signal processing circuitry may be further configured to decompose and separate the received signal energy of the raw data representation into the signal energy contributions for each of the multiple SW emitters using at least one of single pass sparse reconstruction that jointly and simultaneously estimates the contribution of each emitter; iterative serial nulling or cancellation that separately and sequentially estimates the contribution of each emitter, or a combination thereof."

For the URL and additional information on this patent, see: Westcott, Bryan L.; Stanners, Steven P.. Systems and Methods for Direct Emitter Geolocation. U.S. Patent Number 9377520, filed May 31, 2013, and published online on June 28, 2016. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9377520.PN.&OS=PN/9377520RS=PN/9377520

Keywords for this news article include: Electronics, Signal Processing, L-3 Communications Integrated Systems LP.

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