U.S. patent application number 16/884516 was filed with the patent office on 2021-12-02 for multiple long baseline interferometry geolocation.
This patent application is currently assigned to BAE Systems Information and Electronic Systems Integration Inc.. The applicant listed for this patent is BAE Systems Information and Electronic Systems Integration Inc.. Invention is credited to Eleanna Georgiadis, Richard Schiffmiller.
Application Number | 20210373114 16/884516 |
Document ID | / |
Family ID | 1000005968544 |
Filed Date | 2021-12-02 |
United States Patent
Application |
20210373114 |
Kind Code |
A1 |
Schiffmiller; Richard ; et
al. |
December 2, 2021 |
MULTIPLE LONG BASELINE INTERFEROMETRY GEOLOCATION
Abstract
Techniques are provided for emitter geolocation. A methodology
implementing the techniques according to an embodiment includes
measuring phase differences between radar signals received at one
or more pairs of antennas. The method also includes calculating
hypothesized phase differences based on ray tracings from
hypothesized emitter locations at a first set of grid points, to
the antennas. The method further includes generating scores based
on correlations between the measured phase differences and the
hypothesized phase differences. The method further includes
generating an error ellipse based on candidate grid points
associated with scores that are above a threshold. The process may
be repeated on a second set of grid points, bounded by the error
ellipse, to generate a second set of scores. The grid point, from
the second set of grid points, that is associated with the highest
of the second set of scores is selected as the estimated emitter
geolocation.
Inventors: |
Schiffmiller; Richard;
(Teaneck, NJ) ; Georgiadis; Eleanna; (Franklin
Square, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BAE Systems Information and Electronic Systems Integration
Inc. |
Nashua |
NH |
US |
|
|
Assignee: |
BAE Systems Information and
Electronic Systems Integration Inc.
Nashua
NH
|
Family ID: |
1000005968544 |
Appl. No.: |
16/884516 |
Filed: |
May 27, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 3/42 20130101 |
International
Class: |
G01S 3/42 20060101
G01S003/42 |
Claims
1. A system for emitter geolocation, the system comprising: a delta
phase measurement circuit to measure a phase difference between
radar signals received at a pair of antennas; a ray tracing circuit
to calculate hypothesized phase differences based on ray tracings
from a hypothesized emitter location at each of a first set of grid
points to the pair of antennas; a score calculation circuit to
generate scores based on correlation between the measured phase
difference and the hypothesized phase differences; a confidence
calculation circuit to generate an error ellipse based on candidate
grid points of the first set of grid points, the candidate grid
points of the first set of grid points associated with a subset of
the scores, the subset including scores greater than a threshold
percentage of a highest of the scores; the ray tracing circuit
further to repeat the calculation of hypothesized phase differences
using a second set of grid points bounded by the error ellipse; the
score calculation circuit further to repeat the generation of
scores based on the hypothesized phase differences using the second
set of grid points; and the confidence calculation circuit further
to select one of the second set of grid points as the estimated
emitter geolocation, the selected grid point associated with a
highest of the scores generated during the repetition of the
generation of scores.
2. The system of claim 1, further comprising a search grid
generation circuit to generate the first set of grid points bounded
by a search area, the search area based on an estimated angle and
range to the emitter as provided by a radar warning receiver.
3. The system of claim 2, wherein the search grid generation
circuit is further to space the grid points of the first set of
grid points so that a difference in path length between the ray
tracings associated with adjacent grid points is less than one
wavelength of the radar signal.
4. The system of claim 2, wherein the search grid generation
circuit is further to space the grid points of the second set of
grid points as less than the spacing between the grid points of the
first set of grid points.
5. The system of claim 1, wherein generating the error ellipse
further comprises calculating a covariance matrix based on
coordinates of the candidate grid points of the first set of grid
points.
6. The system of claim 5, wherein the covariance matrix is a first
covariance matrix and the threshold percentage is a first threshold
percentage, and the score calculation circuit is further to:
generate a second covariance matrix based on coordinates of
candidate grid points of the second set of grid points, the
candidate grid points of the second set of grid points associated
with a subset of the scores generated during the repetition of the
generation of the scores including scores greater than a second
threshold percentage of the highest of the scores generated during
the repetition of the generation of the scores; and generate a
confidence value based on a size of the second covariance
matrix.
7. A computer program product including one or more
machine-readable mediums encoded with instructions that when
executed by one or more processors cause a process to be carried
out for emitter geolocation, the process comprising: measuring a
phase difference between radar signals received at a pair of
antennas; calculating hypothesized phase differences based on ray
tracings from a hypothesized emitter location at each of a first
set of grid points to the pair of antennas; generating scores based
on correlation between the measured phase difference and the
hypothesized phase differences; generating an error ellipse based
on candidate grid points of the first set of grid points, the
candidate grid points of the first set of grid points associated
with a subset of the scores, the subset including scores greater
than a threshold percentage of a highest of the scores; repeating
the process of calculating hypothesized phase differences and
generating scores using a second set of grid points bounded by the
error ellipse; and selecting one of the second set of grid points
as the estimated emitter geolocation, the selected grid point
associated with a highest of the scores generated during the
repetition of the process.
8. The computer program product of claim 7, wherein the first set
of grid points is bounded by a search area, the search area based
on an estimated angle and range to the emitter as provided by a
radar warning receiver.
9. The computer program product of claim 7, wherein spacing between
the grid points of the first set of grid points is selected so that
a difference in path length between the ray tracings associated
with adjacent grid points is less than one wavelength of the radar
signal.
10. The computer program product of claim 7, wherein spacing
between the grid points of the second set of grid points is less
than spacing between the grid points of the first set of grid
points.
11. The computer program product of claim 7, wherein generating the
error ellipse further comprises calculating a covariance matrix
based on coordinates of the candidate grid points of the first set
of grid points.
12. The computer program product of claim 11, wherein the
covariance matrix is a first covariance matrix and the threshold
percentage is a first threshold percentage, and the process further
comprises: generating a second covariance matrix based on
coordinates of candidate grid points of the second set of grid
points, the candidate grid points of the second set of grid points
associated with a subset of the scores generated during the
repetition of the process including scores greater than a second
threshold percentage of the highest of the scores generated during
the repetition of the process; and generating a confidence value
based on a size of the second covariance matrix.
13. The computer program product of claim 12, further comprising
repeating the process using additional measured phase differences
if the confidence value is less than a threshold confidence
value.
14. The computer program product of claim 7, wherein the process is
performed as a multi-threaded process comprising a first thread to
perform the process to geolocate a first emitter and a second
thread to perform the process to geolocate a second emitter.
15. A method for emitter geolocation, the method comprising:
measuring, by a processor-based system, phase differences between
radar signals received at one or more pairs of antennas;
calculating, by the processor-based system, a first plurality of
hypothesized phase differences based on ray tracings from
hypothesized emitter locations at each of a first set of grid
points to the one or more pairs of antennas; generating, by the
processor-based system, a first plurality of scores based on
correlations between the measured phase differences and the first
plurality of hypothesized phase differences; generating, by the
processor-based system, an error ellipse based on candidate grid
points of the first set of grid points, the candidate grid points
of the first set of grid points associated with a subset of the
first plurality of scores, the subset including scores greater than
a threshold percentage of a highest score of the first plurality of
scores; calculating, by the processor-based system, a second
plurality of hypothesized phase differences based on ray tracings
from hypothesized emitter locations at each of a second set of grid
points to the one or more pairs of antennas, the second set of grid
points bounded by the error ellipse; generating, by the
processor-based system, a second plurality of scores based on
correlations between the measured phase differences and the second
plurality of hypothesized phase differences; and selecting, by the
processor-based system, one of the second set of grid points, that
is associated with a highest of the second plurality of scores, as
the estimated emitter geolocation.
16. The method of claim 15, wherein the first set of grid points is
bounded by a search area, the search area based on an estimated
angle and range to the emitter as provided by a radar warning
receiver.
17. The method of claim 15, wherein spacing between the grid points
of the first set of grid points is selected so that a difference in
path length between the ray tracings associated with adjacent grid
points is less than one wavelength of the radar signal.
18. The method of claim 15, wherein spacing between the grid points
of the second set of grid points is less than spacing between the
grid points of the first set of grid points.
19. The method of claim 15, wherein generating the error ellipse
further comprises calculating a covariance matrix based on
coordinates of the candidate grid points of the first set of grid
points.
20. The method of claim 19, wherein the covariance matrix is a
first covariance matrix and the threshold percentage is a first
threshold percentage, and the process further comprises: generating
a second covariance matrix based on coordinates of candidate grid
points of the second set of grid points, the candidate grid points
of the second set of grid points associated with a subset of the
second plurality of scores, the subset including scores greater
than a second threshold percentage of a highest score of the second
plurality of scores; generating a confidence value based on a size
of the second covariance matrix; and repeating the method using
additional measured phase differences if the confidence value is
less than a threshold confidence value.
Description
FIELD OF DISCLOSURE
[0001] The present disclosure relates to geolocation of ground
based emitters, and more particularly, to geolocation of emitters
using multiple long baseline interferometry (LBI) antennas and
correlation of measured and hypothesized phase differences.
BACKGROUND
[0002] Long baseline interferometry (LBI) is a technique that may
be used to perform geolocation of stationary targets from a single
moving platform. Traditional LBI systems perform geolocation by
flying the interferometer for a period of time with changing
orientations of the interferometer axis with respect to the
emitter. This constrains the possible locations of the emitter that
will produce a set of measured phase differences. Typically, the
time required to achieve less than a 10 percent error in range and
a two degree error in azimuth, is on the order of 30 to 60 seconds,
depending on antenna configuration and geometry, speed of flight,
changes in orientation of the interferometer axis, and measurement
errors. This time can be too long for many applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 illustrates a deployment of a geolocation system on
an airborne platform, configured in accordance with an embodiment
of the present disclosure.
[0004] FIG. 2 is a block diagram of the airborne platform including
geolocation system and associated components, configured in
accordance with an embodiment of the present disclosure.
[0005] FIG. 3 is a block diagram of the geolocation system,
configured in accordance with an embodiment of the present
disclosure.
[0006] FIG. 4 illustrates grid patterns of hypothesized emitter
geolocations, in accordance with an embodiment of the present
disclosure.
[0007] FIG. 5 is a flowchart illustrating operation of the
geolocation system, configured in accordance with an embodiment of
the present disclosure.
[0008] FIG. 6 illustrates ray tracing geometry, in accordance with
an embodiment of the present disclosure.
[0009] FIG. 7 illustrates grid point spacing calculation, in
accordance with an embodiment of the present disclosure.
[0010] FIG. 8 illustrates a correlation surface of scores, in
accordance with an embodiment of the present disclosure.
[0011] FIG. 9 is a flowchart illustrating a methodology for emitter
geolocation, in accordance with an embodiment of the present
disclosure.
[0012] FIG. 10 is a block diagram schematically illustrating a
platform employing the disclosed geolocation system, in accordance
with certain embodiments of the present disclosure.
[0013] Although the following Detailed Description will proceed
with reference being made to illustrative embodiments, many
alternatives, modifications, and variations thereof will be
apparent to those skilled in the art.
DETAILED DESCRIPTION
[0014] Techniques are provided for geolocation of ground based
emitters. The geolocation is based on correlation scores calculated
from measured and hypothesized phase differences between radar
signals received at multiple LBI antennas. In more detail, and
according to one such embodiment, a search grid is established over
an area in which the emitter is believed to be transmitting and the
hypothesized phase differences are calculated based on ray tracings
between the LBI antennas and hypothesized emitter locations at each
grid point in the search grid. A correlation surface is formed from
the scores, and a region surrounding a peak in the correlation
surface is selected as a new and refined search grid. The process
is repeated on the refined search grid and a new peak is selected
as the estimated geolocation of the emitter. As will be
appreciated, the disclosed techniques can be used to reduce the
time needed to estimate a geolocation of the emitter and provide
increased accuracy of that estimate compared to traditional LBI
methods.
[0015] The disclosed techniques can be implemented, for example, in
a computing system or a software product executable or otherwise
controllable by such systems, although other embodiments will be
apparent. In accordance with an embodiment, a methodology to
implement these techniques includes measuring a phase difference
between radar signals received at one or more pairs of antennas.
The use of multiple antenna pairs helps to decrease ambiguity in
the results. The method also includes calculating hypothesized
phase differences based on ray tracings from a hypothesized emitter
location at each of a first set of grid points to the pairs of
antennas. The method further includes generating scores based on
correlation between the measured phase difference and the
hypothesized phase differences. The method further includes
generating an error ellipse based on candidate grid points of the
first set of grid points, the candidate grid points of the first
set of grid points associated with a subset of the scores, the
subset including scores greater than a threshold percentage of a
highest of the scores. The process is repeated on a second set of
grid points, which are bounded by the error ellipse, to generate a
second set of scores. The grid point, from the second set of grid
points, that is associated with the highest of the second set of
scores, is selected as the estimated emitter geolocation.
[0016] It will be appreciated that the techniques described herein
may provide improved geolocation capabilities including faster
estimation time and increased accuracy compared to existing
techniques that rely on a large number of phase measurements
obtained over a relatively long period of flight. These techniques
may further be implemented in hardware or software or a combination
thereof. Additionally, the disclosed techniques lend themselves to
multi-threaded processing which can further improve efficiency.
[0017] FIG. 1 illustrates a deployment 100 of a geolocation system
on an airborne platform 110, such as an aircraft, drone, unmanned
aerial vehicle, or projectile, configured in accordance with
certain embodiments of the present disclosure. The airborne
platform 110, or aircraft, is shown to host a geolocation system
120 coupled to an interferometer comprising two LBI antennas 130a
and 130b that are separated by a distance or baseline D. In this
example the LBI antennas 130a and 130b are depicted running a
longitudinal length along the fuselage of the aircraft however the
antennas can also be located with a horizontal orientation or any
other suitable orientation. The geolocation system 120 is
configured to locate a ground-based radar emitter 140 based on the
measured phase differences of the emitted radar signals 150 at the
two antennas 130a and 130b, as will be explained in greater detail
below. The radar signal may be a pulsed radar signal or a
continuous wave (CW) radar signal.
[0018] FIG. 2 is a block diagram of the airborne platform 110
including geolocation system and associated components, configured
in accordance with certain embodiments of the present disclosure.
In this example, six antennas are shown: forward right 130a,
forward left 130d, mid-ship right 130b, mid-ship left 130e, aft
right 130c, and aft left 130f. Other configurations are possible
depending on the type and size of the platform. Numerous
interferometer baselines may be formed out of various pairs of
these antennas. For example: 130d-130a, 130a-130b, 130b-130c,
130e-130f, etc. Depending on the orientation of the platform 110
with respect to the emitter 150, two, three or four antennas may
simultaneously detect the radar signals from the emitter. In the
case of four antennas, three interferometer baselines may be
formed. In some embodiments, measured signal to noise ratio may be
used to determine which antennas are employed to form
interferometers. In general, an increase in the number of usable
interferometers will result in an increase in the accuracy of the
geolocation and the speed with which the emitter geolocation is
achieved. In some embodiments, spacing between antenna pairs of an
interferometer may be on the order of 30 to 40 feet depending upon
the platform.
[0019] Platform 110 is also shown to include a radar warning
receiver (RWR) 260, or other suitable digital receiver, and an
inertial navigation system (INS) 270. The RWR 260 is configured to
collect and buffer raw data samples from the antennas 130 and to
provide phase and frequency data associated with the raw data
samples (e.g., radar signal segments or pulses 300), for processing
by the geolocation system 120. INS 270 is configured to provide
platform position and orientation 305, which is used for
determining the location of the antennas 130 for use in the ray
tracing calculations, as will be described in greater detail
below.
[0020] FIG. 3 is a block diagram of the geolocation system 120,
configured in accordance with certain embodiments of the present
disclosure. The geolocation system 120 is shown to include a search
grid generation circuit 310, a delta phase measurement circuit 320,
a ray tracing circuit 330, a score calculation circuit 340, and a
confidence calculation circuit 350. Radar signals 300 are provided
to the geolocation system 120 from LBI antennas, and in some
embodiments, it is provided through RWR 260. The radar signals may
be processed as pulses from a pulsed emitter or as segments of a
continuous wave from a CW emitter. INS 270 is also shown to provide
platform and orientation data 305 to the geolocation system
120.
[0021] Search grid generation circuit 310 is configured to generate
a first set of grid points in a search grid (e.g., bounded by a
search area) in which the emitter is believed to be transmitting.
In some embodiments, the grid points may be specified by latitude
and longitude. The search area is based on an estimated angle and
range to the emitter which, in some embodiments, may be provided by
the RWR 260 based on signal strength and coarse angle of arrival
measurements. For example, the swath of search area may cover from
one-half to double the estimated range in the radial direction from
the aircraft, and the angular extent of the swath may span plus or
minus twenty degrees from the coarse angle of arrival measurement.
An example of this search grid, labeled "first pass grid" 410 is
provided in FIG. 4 and is shown to comprise grid points illustrated
by dots. The grid points of the first set of grid points are spaced
so that the difference in path lengths between the ray tracings
associated with adjacent grid points is less than one wavelength of
the radar signal, as will be explained in greater detail below in
connection with FIG. 7.
[0022] Delta phase measurement circuit 320 is configured to measure
phase differences between radar signals received at one or more
pairs of antennas using any suitable measurement technique. The
measured phase is designated as .DELTA..phi..sub.meas.
[0023] Ray tracing circuit 330 is configured to calculate a first
set of hypothesized phase differences based on ray tracings from
hypothesized emitter locations at each of the first set of grid
points to the one or more pairs of antennas. This is shown in FIG.
6, which illustrates ray tracing geometry 600 for the case of two
antennas 130a and 130b and one grid point 610. The locations of the
antennas are known, based on data provided by INS 270 specifying
the position and orientation 305 of the platform, combined with the
known layout of the antenna installations on the platform. The
locations of the grid points are also known since they are created
by search grid generation circuit 310, as described above.
Therefore, rays R.sub.1 and R.sub.2 can be drawn from each antenna
to each grid point 610 and a path length can be calculated for each
ray. A hypothesized phase difference can then be calculated from
the difference in path lengths of the rays, for example, using the
following formula:
.DELTA..phi. h .times. y .times. p = ( 2 .times. .pi. .lamda. )
.times. ( R 1 - R 2 ) ##EQU00001##
where .lamda. is the wavelength of the radar signal. This provides
an unwrapped phase which may then be converted into a wrapped phase
by taking the modulo 2.pi. radians of the unwrapped phase. This
allows for proper comparison with the measured phase, which is a
wrapped phase.
[0024] Thus, if the emitter happened to be located at one of the
grid points, then the measured phase would be substantially equal
to the hypothesized phase computed for that grid point
(disregarding measurement errors and the like).
[0025] The use of ray tracing offers an advantage over traditional
methods which rely on an assumption that the wavefront impinging on
the interferometer is planar. In actuality, for frequencies of
interest at near-field distances (typically less than 20 nautical
miles), the emitted spherical electromagnetic wave of the radar
signal is not sufficiently planar and can introduce an error in the
phase calculation of several degrees. The use of ray tracing to
compute the hypothesized phases does not introduce an error at any
range, since no assumption is made as to the curvature of the
wavefront.
[0026] Score calculation circuit 340 is configured to generate a
first set of scores based on correlations between the measured
phase differences and the first set of hypothesized phase
differences. A score is calculated for the radar signals received
at a given interferometer, for a given grid point. The score may be
calculated as the sum of the magnitudes of
e.sup.-j.DELTA..phi..sup.mease.sup.j.DELTA..phi..sup.hyp normalized
by the number of phase differences. This normalized sum is referred
to as g.sub.k, where k is an index for the k.sup.th interferometer.
The sum over all interferometers (e.g., pairs on antennas) of the
magnitudes of each g.sub.k score is computed and normalized by
dividing by the number of interferometers and is referred to as f.
A correlation score f is calculated for every grid point. A
3-dimensional correlation surface 800 of scores f is illustrated in
FIG. 8.
[0027] Confidence calculation circuit 350 is configured to generate
an error ellipse based on candidate grid points of the first set of
grid points. The candidate grid points are those points that are
associated with a subset of the first set of scores that include
scores greater than a threshold percentage of a highest score. In
some embodiments, the threshold may be selected heuristically or
experimentally, and may be on the order of 90 percent. The
two-dimensional northing and easting coordinates of each candidate
grid point are calculated. A covariance matrix is created using the
following equation, where x.sub.i and y.sub.i are the
two-dimensional coordinates of the i.sup.th candidate grid
point:
covariance = [ i .times. ( x i - x ) 2 N i .times. ( x i - x )
.times. ( y i - y ) N i .times. ( x i - x ) .times. ( y i - y ) N i
.times. ( y i - y ) 2 N ] ##EQU00002##
where N is the number of candidate grid points, and x and y are the
means of the x and y candidate grid point coordinates,
respectively.
[0028] The covariance matrix may be converted into a
two-dimensional error ellipse (see, for example, 430 of FIG. 4)
based on the eigenvalues and eigenfunctions of the matrix. If the
size of the ellipse is less than a threshold value, the center may
be reported as the estimate of the emitter location, along with the
covariance matrix as a confidence indicator. Otherwise, the bounds
of the error ellipse are used as the limits for a new grid, which
is typically smaller than the original grid, and a second pass of
processing is performed on the new grid. An example of this new
search grid, labeled "second pass grid" 420 is also shown in FIG.
4.
[0029] For the second pass, the ray tracing circuit 330 is
configured to calculate a second set of hypothesized phase
differences based on ray tracings from hypothesized emitter
locations at each of a second set of grid points to the one or more
pairs of antennas, as described previously for the first pass. The
grid points of the second set of grid points are typically spaced
closer together than the grid points of the first set of grid
points.
[0030] The score calculation circuit 340 is further configured to
generate a second set of scores based on correlations between the
measured phase differences and the second set of hypothesized phase
differences, as described previously for the first pass.
[0031] The confidence calculation circuit 350 is further configured
to generate a second covariance matrix based on coordinates of
candidate grid points of the second set of grid points. The
confidence calculation circuit 350 is further configured to
generate a confidence value based on a size of the second
covariance matrix. The confidence calculation circuit 350 is
further configured to select one of the second set of grid points
that is associated with a highest of the second set of scores, as
the estimated emitter geolocation. This second pass result is shown
as 450 in FIG. 4 alongside the true emitter location 440. Although
additional passes (e.g., a third pass, fourth pass, etc.) are
possible, in general, two passes are sufficient, with additional
passes providing little or no improvement in geolocation
accuracy.
[0032] FIG. 5 is a flowchart illustrating operation of the
geolocation system, configured in accordance with certain
embodiments of the present disclosure. Prior to operation, an
initialization is performed in which the antenna and interferometer
configuration is established (e.g., locations of antennas are noted
and pairings of antennas into interferometers are determined).
Additionally, measured sensor data (radar signal phase and
frequency, and INS data) is collected and stored.
[0033] At operation 500, a first pass search grid is generated. The
grid points are bounded by a search area in which the emitter is
believed to be transmitting. The search area is based on an
estimated angle and range to the emitter, derived from any suitable
source.
[0034] The process then proceeds with three nested loops. The
innermost loop is performed for each radar pulse or segment, the
next outer loop is performed for each interferometer (e.g., antenna
pair), and the outermost loop is performed for each grid point.
Thus, at operation 510, a grid point is selected, an interferometer
(antenna pair) is selected, and a radar pulse or segment is
selected.
[0035] At operation 520, a measured delta phase is determined for
the radar signal received at the two antennas of the current
interferometer. A hypothesized delta phase is also calculated based
on ray tracing from the current interferometer to the current grid
point. A correlation score is calculated based on the measured and
hypothesized delta phases, and the process loops back to operation
510 for the next radar pulse or segment.
[0036] At operation 530, after all radar signals have been
processed for the current interferometer, a normalized score (g) is
computed as the sum of the scores over all radar pulses/segments
divided by the number of radar pulses/segments. The process then
loops back to operation 510 for the next interferometer (e.g., the
next pair of antennas).
[0037] At operation 540, after all interferometers have been
processed for the current grid point, a normalized score (f) is
computed as the sum of the g scores over all interferometers
divided by the number of interferometers. The process then loops
back to operation 510 for the next grid point.
[0038] At operation 550, after all grid points have been processed,
candidate grid points associated with the highest scores (f) are
identified. In some embodiments, these may include all scores that
are within a threshold percentage of the highest score.
[0039] At operation 560, an error ellipse is generated, based on
the candidate scores, and a confidence value is calculated, as
previously described.
[0040] At operation 570, if the confidence exceeds a threshold
value, then the grid point with the highest score is selected as
the estimated emitter location. Otherwise, at operation 580, a new
search grid is generated, bounded by the error ellipse, and the
process repeats, at operation 510.
[0041] If, after the second pass with the new search grid, the
confidence value still fails to exceed the desired threshold, and
if a processing timer has not yet expired, additional radar signal
data may be collected and appended to the existing data, and the
process repeated to generate a new geolocation estimate. In some
embodiments, the expiration of time may be based on communication
with a threat warning system which may provide an indication that
an incoming missile or other threat is imminent, and thus no
further time may be spent refining the geolocation estimate.
[0042] FIG. 7 illustrates grid point spacing calculation 700, in
accordance with certain embodiments of the present disclosure.
Three adjacent grid points 710, 712, and 714, are shown to be
spaced at a distance B. The antennas are located at an approximate
distance R from the grid points, where R is much greater than D,
the distance between the antennas 130a and 130b.
[0043] As previously explained, the grid points, in both the first
search grid and the second search grid, should be spaced at
distance B such that the difference in path lengths between the ray
tracings associated with adjacent grid points is less than one
wavelength A of the radar signal. This distance B can be determined
according to the following equation:
B .apprxeq. R .function. ( acos .function. ( cos .times. .times. (
.theta. 1 ) - .lamda. D ) - .theta. 1 ) ##EQU00003##
where .theta..sub.1 is the orientation angle of the interferometer
relative to a grid point, as shown in FIG. 7. This equation can be
derived from the requirement that D cos(.theta..sub.1)-D
cos(.theta..sub.2).ltoreq..DELTA., where .theta..sub.2 is the
orientation angle of the interferometer relative to the adjacent
grid point. From this it follows that
.theta. 2 .apprxeq. acos .function. ( cos .times. .times. ( .theta.
1 ) - .lamda. D ) , ##EQU00004##
and B.apprxeq.R(.theta..sub.2-.theta..sub.1).
[0044] FIG. 8 illustrates a correlation surface 800 of scores, in
accordance with certain embodiments of the present disclosure. The
correlation surface (for the first pass or the second pass) is made
up of the computed correlation scores 810 (for the first pass or
the second pass, respectively), as a function of latitude and
longitude. The peak score 820 is shown to lie relatively close to
the true emitter location 440.
[0045] Methodology
[0046] FIG. 9 is a flowchart illustrating a methodology for emitter
geolocation, in accordance with certain other embodiments of the
present disclosure. As can be seen, example method 900 includes a
number of phases and sub-processes, the sequence of which may vary
from one embodiment to another. However, when considered in the
aggregate, these phases and sub-processes form a process for
geolocation of ground based emitters, in accordance with certain of
the embodiments disclosed herein. These embodiments can be
implemented, for example using the system architecture illustrated
in FIGS. 1-3, and 5, as described above. However other system
architectures can be used in other embodiments, as will be apparent
in light of this disclosure. To this end, the correlation of the
various functions shown in FIG. 9 to the specific components
illustrated in FIGS. 1-3, and 5, is not intended to imply any
structural and/or use limitations. Rather other embodiments may
include, for example, varying degrees of integration wherein
multiple functionalities are effectively performed by one system.
Numerous variations and alternative configurations will be apparent
in light of this disclosure.
[0047] As illustrated in FIG. 9, in one embodiment method 900
commences, at operation 910, by measuring phase differences between
radar signals received at pairs of antennas of one or more
interferometers. The radar signals are transmitted from the
ground-based emitter.
[0048] Next, at operation 920, hypothesized phase differences are
calculated based on ray tracings from hypothesized emitter
locations at each of a first set of grid points to the one or more
pairs of antennas. The first set of grid points is bounded by a
search area that may be based on an estimated angle and range of
the emitter. In some embodiments, the estimate may be provided by a
radar warning receiver. The spacing between the grid points of the
first set of grid points is selected so that a difference in path
length between the ray tracings associated with adjacent grid
points is less than one wavelength of the radar signal.
[0049] At operation 930, a first set of scores is generated based
on correlations between the measured phase differences and the
hypothesized phase differences.
[0050] At operation 940, an error ellipse is generated based on
candidate grid points of the first set of grid points. The
candidate grid points are associated with a subset of the first set
of scores, the subset including scores greater than a threshold
percentage of the highest of the scores. The generation of the
error ellipse further comprises calculating a covariance matrix
based on coordinates of the candidate grid points.
[0051] At operation 950, new hypothesized phase differences are
generated based on ray tracings from hypothesized emitter locations
at each of a second set of grid points to the one or more pairs of
antennas. The area of the second set of grid points is bounded by
the error ellipse and is subdivided by the same number of grid
points as in the first search area grid. Therefore the spacing
between the grid points of the second set of grid points is
generally less than the spacing between the grid points of the
first set of grid points since the error ellipse is typically a
smaller region located within the first set of grid points,
potentially providing a greater geolocation accuracy.
[0052] At operation 960, a second set of scores is generated based
on correlations between the measured phase differences and the new
hypothesized phase differences.
[0053] At operation 970, one of the second set of grid points, that
is associated with a highest of the second set of scores, is
selected as the estimated emitter geolocation. A confidence value
may be associated with the estimated emitter geolocation, based on
a size of a second covariance matrix calculated from points of the
second set of grid points that are associated with scores greater
than a threshold percentage of the highest of the second set of
scores.
[0054] Of course, in some embodiments, additional operations may be
performed, as previously described in connection with the system.
These additional operations may include, for example, repeating the
process using additional measured phase differences if the
confidence value is less than a threshold confidence value. The
process may be repeated until a process timer exceeds a duration
threshold. In some embodiments, the process may be performed as a
multi-threaded process comprising a first thread to perform the
process to geolocate a first emitter, a second thread to perform
the process to geolocate a second emitter, and so forth. In some
embodiments, the threads may be executed on multiple
processors.
[0055] Example Platforms
[0056] FIG. 10 is a block diagram 1000 schematically illustrating a
processing platform 1010 employing the disclosed geolocation
system, in accordance with certain embodiments of the present
disclosure. In some embodiments, platform 1010, or portions
thereof, may be hosted on, or otherwise be incorporated into an
aircraft, the electronic systems of the aircraft, a ground station,
or any other suitable platform.
[0057] In some embodiments, platform 1010 may comprise any
combination of a processor 1020, a memory 1030, an input/output
(I/O) system 1060, a user interface 1062, a display element 1064, a
storage system 1070, geolocation system 120, radar warning receiver
260, antennas (including interferometer antennas), and inertial
navigation system 270. As can be further seen, a bus and/or
interconnect 1090 is also provided to allow for communication
between the various components listed above and/or other components
not shown. Other componentry and functionality not reflected in the
block diagram of FIG. 10 will be apparent in light of this
disclosure, and it will be appreciated that other embodiments are
not limited to any particular hardware configuration.
[0058] Processor 1020 can be any suitable processor, and may
include one or more coprocessors or controllers, such as an audio
processor, a graphics processing unit, or hardware accelerator, to
assist in control and processing operations associated with
platform 1010. In some embodiments, the processor 1020 may be
implemented as any number of processor cores. The processor (or
processor cores) may be any type of processor, such as, for
example, a micro-processor, an embedded processor, a digital signal
processor (DSP), a graphics processor (GPU), a network processor, a
field programmable gate array or other device configured to execute
code. The processors may be multithreaded cores in that they may
include more than one hardware thread context (or "logical
processor") per core. Processor 1020 may be implemented as a
complex instruction set computer (CISC) or a reduced instruction
set computer (RISC) processor.
[0059] Memory 1030 can be implemented using any suitable type of
digital storage including, for example, flash memory and/or random
access memory (RAM). In some embodiments, the memory 1030 may
include various layers of memory hierarchy and/or memory caches as
are known to those of skill in the art. Memory 1030 may be
implemented as a volatile memory device such as, but not limited
to, a RAM, dynamic RAM (DRAM), or static RAM (SRAM) device. Storage
system 1070 may be implemented as a non-volatile storage device
such as, but not limited to, one or more of a hard disk drive
(HDD), a solid-state drive (SSD), a universal serial bus (USB)
drive, an optical disk drive, tape drive, an internal storage
device, an attached storage device, flash memory, battery backed-up
synchronous DRAM (SDRAM), and/or a network accessible storage
device.
[0060] Processor 1020 may be configured to execute an Operating
System (OS) 1080 which may comprise any suitable operating system,
such as Google Android (Google Inc., Mountain View, Calif.),
Microsoft Windows (Microsoft Corp., Redmond, Wash.), Apple OS X
(Apple Inc., Cupertino, Calif.), Linux, or a real-time operating
system (RTOS). As will be appreciated in light of this disclosure,
the techniques provided herein can be implemented without regard to
the particular operating system provided in conjunction with
platform 1010, and therefore may also be implemented using any
suitable existing or subsequently-developed platform.
[0061] I/O system 1060 may be configured to interface between
various I/O devices and other components of platform 1010. I/O
devices may include, but not be limited to, user interface 1062 and
display element 1064. User interface 1062 may include other devices
(not shown) such as a touchpad, keyboard, mouse, microphone and
speaker, trackball or scratch pad, and camera. I/O system 1060 may
include a graphics subsystem configured to perform processing of
images for rendering on the display element 1064. Graphics
subsystem may be a graphics processing unit or a visual processing
unit (VPU), for example. An analog or digital interface may be used
to communicatively couple graphics subsystem and the display
element. For example, the interface may be any of a high definition
multimedia interface (HDMI), DisplayPort, wireless HDMI, and/or any
other suitable interface using wireless high definition compliant
techniques. In some embodiments, the graphics subsystem could be
integrated into processor 1020 or any chipset of platform 1010.
[0062] It will be appreciated that in some embodiments, some of the
various components of platform 1010 may be combined or integrated
in a system-on-a-chip (SoC) architecture. In some embodiments, the
components may be hardware components, firmware components,
software components or any suitable combination of hardware,
firmware or software.
[0063] Geolocation system 120 is configured to perform geolocation
of ground based emitters using multiple long baseline
interferometry based on measured and hypothesized phase
differences, as described previously. Geolocation system 120 may
include any or all of the circuits/components illustrated in FIGS.
1-3, and 5, as described above. These components can be implemented
or otherwise used in conjunction with a variety of suitable
software and/or hardware that is coupled to or that otherwise forms
a part of platform 1010. These components can additionally or
alternatively be implemented or otherwise used in conjunction with
user I/O devices that are capable of providing information to, and
receiving information and commands from, a user.
[0064] In one example, the emitter location is detected and
communicated to a pilot or base station so that evasive maneuvers
can be conducted to avoid or minimize detection by the emitter.
Other measures may include using the emitter location for jamming,
signal intelligence, spoofing or other countermeasure techniques.
The emitter location can also be targeted for destruction.
[0065] Various embodiments of platform 1010 may be implemented
using hardware elements, software elements, or a combination of
both. Examples of hardware elements may include processors,
microprocessors, circuits, circuit elements (for example,
transistors, resistors, capacitors, inductors, and so forth),
integrated circuits, ASICs, programmable logic devices, digital
signal processors, FPGAs, logic gates, registers, semiconductor
devices, chips, microchips, chipsets, and so forth. Examples of
software may include software components, programs, applications,
computer programs, application programs, system programs, machine
programs, operating system software, middleware, firmware, software
modules, routines, subroutines, functions, methods, procedures,
software interfaces, application program interfaces, instruction
sets, computing code, computer code, code segments, computer code
segments, words, values, symbols, or any combination thereof.
Determining whether an embodiment is implemented using hardware
elements and/or software elements may vary in accordance with any
number of factors, such as desired computational rate, power level,
heat tolerances, processing cycle budget, input data rates, output
data rates, memory resources, data bus speeds, and other design or
performance constraints.
[0066] The various embodiments disclosed herein can be implemented
in various forms of hardware, software, firmware, and/or special
purpose processors. For example, in one embodiment at least one
non-transitory computer readable storage medium has instructions
encoded thereon that, when executed by one or more processors,
causes one or more of the methodologies disclosed herein to be
implemented. Other componentry and functionality not reflected in
the illustrations will be apparent in light of this disclosure, and
it will be appreciated that other embodiments are not limited to
any particular hardware or software configuration. Thus, in other
embodiments platform 1010 may comprise additional, fewer, or
alternative subcomponents as compared to those included in the
example embodiment of FIG. 10.
[0067] Some embodiments may be described using the expression
"coupled" and "connected" along with their derivatives. These terms
are not intended as synonyms for each other. For example, some
embodiments may be described using the terms "connected" and/or
"coupled" to indicate that two or more elements are in direct
physical or electrical contact with each other. The term "coupled,"
however, may also mean that two or more elements are not in direct
contact with each other, but yet still cooperate or interact with
each other.
[0068] The aforementioned non-transitory computer readable medium
may be any suitable medium for storing digital information, such as
a hard drive, a server, a flash memory, and/or random access memory
(RAM), or a combination of memories. In alternative embodiments,
the components and/or modules disclosed herein can be implemented
with hardware, including gate level logic such as a
field-programmable gate array (FPGA), or alternatively, a
purpose-built semiconductor such as an application-specific
integrated circuit (ASIC). In some embodiments, the hardware may be
modeled or developed using hardware description languages such as,
for example Verilog or VHDL. Still other embodiments may be
implemented with a microcontroller having a number of input/output
ports for receiving and outputting data, and a number of embedded
routines for carrying out the various functionalities disclosed
herein. It will be apparent that any suitable combination of
hardware, software, and firmware can be used, and that other
embodiments are not limited to any particular system
architecture.
[0069] Some embodiments may be implemented, for example, using a
machine readable medium or article which may store an instruction
or a set of instructions that, if executed by a machine, may cause
the machine to perform a method and/or operations in accordance
with the embodiments. Such a machine may include, for example, any
suitable processing platform, computing platform, computing device,
processing device, computing system, processing system, computer,
process, or the like, and may be implemented using any suitable
combination of hardware and/or software. The machine readable
medium or article may include, for example, any suitable type of
memory unit, memory device, memory article, memory medium, storage
device, storage article, storage medium, and/or storage unit, such
as memory, removable or non-removable media, erasable or
non-erasable media, writeable or rewriteable media, digital or
analog media, hard disk, floppy disk, compact disk read only memory
(CD-ROM), compact disk recordable (CD-R) memory, compact disk
rewriteable (CD-RW) memory, optical disk, magnetic media,
magneto-optical media, removable memory cards or disks, various
types of digital versatile disk (DVD), a tape, a cassette, or the
like. The instructions may include any suitable type of code, such
as source code, compiled code, interpreted code, executable code,
static code, dynamic code, encrypted code, and the like,
implemented using any suitable high level, low level, object
oriented, visual, compiled, and/or interpreted programming
language.
[0070] Unless specifically stated otherwise, it may be appreciated
that terms such as "processing," "computing," "calculating,"
"determining," or the like refer to the action and/or process of a
computer or computing system, or similar electronic computing
device, that manipulates and/or transforms data represented as
physical quantities (for example, electronic) within the registers
and/or memory units of the computer system into other data
similarly represented as physical quantities within the registers,
memory units, or other such information storage transmission or
displays of the computer system. The embodiments are not limited in
this context.
[0071] The terms "circuit" or "circuitry," as used in any
embodiment herein, are functional and may comprise, for example,
singly or in any combination, hardwired circuitry, programmable
circuitry such as computer processors comprising one or more
individual instruction processing cores, state machine circuitry,
and/or firmware that stores instructions executed by programmable
circuitry. The circuitry may include a processor and/or controller
configured to execute one or more instructions to perform one or
more operations described herein. The instructions may be embodied
as, for example, an application, software, firmware, or one or more
embedded routines configured to cause the circuitry to perform any
of the aforementioned operations. Software may be embodied as a
software package, code, instructions, instruction sets and/or data
recorded on a computer-readable storage device. Software may be
embodied or implemented to include any number of processes, and
processes, in turn, may be embodied or implemented to include any
number of threads or parallel processes in a hierarchical fashion.
Firmware may be embodied as code, instructions or instruction sets
and/or data that are hard-coded (e.g., nonvolatile) in memory
devices. The circuitry may, collectively or individually, be
embodied as circuitry that forms part of a larger system, for
example, an integrated circuit (IC), an application-specific
integrated circuit (ASIC), a system-on-a-chip (SoC), computers, and
other processor-based or functional systems. Other embodiments may
be implemented as software executed by a programmable control
device. In such cases, the terms "circuit" or "circuitry" are
intended to include a combination of software and hardware such as
a programmable control device or a processor capable of executing
the software. As described herein, various embodiments may be
implemented using hardware elements, software elements, or any
combination thereof. Examples of hardware elements may include
processors, microprocessors, circuits, circuit elements (e.g.,
transistors, resistors, capacitors, inductors, and so forth),
integrated circuits, application specific integrated circuits
(ASIC), programmable logic devices (PLD), digital signal processors
(DSP), field programmable gate array (FPGA), logic gates,
registers, semiconductor device, chips, microchips, chip sets, and
so forth.
[0072] Numerous specific details have been set forth herein to
provide a thorough understanding of the embodiments. It will be
understood by an ordinarily-skilled artisan, however, that the
embodiments may be practiced without these specific details. In
other instances, well known operations, components and circuits
have not been described in detail so as not to obscure the
embodiments. It can be appreciated that the specific structural and
functional details disclosed herein may be representative and do
not necessarily limit the scope of the embodiments. In addition,
although the subject matter has been described in language specific
to structural features and/or methodological acts, it is to be
understood that the subject matter defined in the appended claims
is not necessarily limited to the specific features or acts
described herein. Rather, the specific features and acts described
herein are disclosed as example forms of implementing the
claims.
Further Example Embodiments
[0073] The following examples pertain to further embodiments, from
which numerous permutations and configurations will be
apparent.
[0074] One example embodiment of the present disclosure provides a
system for emitter geolocation, the system comprising: a delta
phase measurement circuit to measure a phase difference between
radar signals received at a pair of antennas; a ray tracing circuit
to calculate hypothesized phase differences based on ray tracings
from a hypothesized emitter location at each of a first set of grid
points to the pair of antennas; a score calculation circuit to
generate scores based on correlation between the measured phase
difference and the hypothesized phase differences; a confidence
calculation circuit to generate an error ellipse based on candidate
grid points of the first set of grid points, the candidate grid
points of the first set of grid points associated with a subset of
the scores, the subset including scores greater than a threshold
percentage of a highest of the scores; the ray tracing circuit
further to repeat the calculation of hypothesized phase differences
using a second set of grid points bounded by the error ellipse; the
score calculation circuit further to repeat the generation of
scores based on the hypothesized phase differences using the second
set of grid points; and the confidence calculation circuit further
to select one of the second set of grid points as the estimated
emitter geolocation, the selected grid point associated with a
highest of the scores generated during the repetition of the
generation of scores.
[0075] In some cases, the system further comprises a search grid
generation circuit to generate the first set of grid points bounded
by a search area, the search area based on an estimated angle and
range to the emitter as provided by a radar warning receiver. In
some such cases, the search grid generation circuit is further to
space the grid points of the first set of grid points so that a
difference in path length between the ray tracings associated with
adjacent grid points is less than one wavelength of the radar
signal. In some such cases, the search grid generation circuit is
further to space the grid points of the second set of grid points
as less than the spacing between the grid points of the first set
of grid points. In some cases, generating the error ellipse further
comprises calculating a covariance matrix based on coordinates of
the candidate grid points of the first set of grid points. In some
such cases, the covariance matrix is a first covariance matrix and
the threshold percentage is a first threshold percentage, and the
score calculation circuit is further to: generate a second
covariance matrix based on coordinates of candidate grid points of
the second set of grid points, the candidate grid points of the
second set of grid points associated with a subset of the scores
generated during the repetition of the generation of the scores
including scores greater than a second threshold percentage of the
highest of the scores generated during the repetition of the
generation of the scores; and generate a confidence value based on
a size of the second covariance matrix.
[0076] Another example embodiment of the present disclosure
provides a computer program product including one or more
machine-readable mediums encoded with instructions that when
executed by one or more processors cause a process to be carried
out for emitter geolocation, the process comprising: measuring a
phase difference between radar signals received at a pair of
antennas; calculating hypothesized phase differences based on ray
tracings from a hypothesized emitter location at each of a first
set of grid points to the pair of antennas; generating scores based
on correlation between the measured phase difference and the
hypothesized phase differences; generating an error ellipse based
on candidate grid points of the first set of grid points, the
candidate grid points of the first set of grid points associated
with a subset of the scores, the subset including scores greater
than a threshold percentage of a highest of the scores; repeating
the process of calculating hypothesized phase differences and
generating scores using a second set of grid points bounded by the
error ellipse; and selecting one of the second set of grid points
as the estimated emitter geolocation, the selected grid point
associated with a highest of the scores generated during the
repetition of the process.
[0077] In some cases, the first set of grid points is bounded by a
search area, the search area based on an estimated angle and range
to the emitter as provided by a radar warning receiver. In some
cases, spacing between the grid points of the first set of grid
points is selected so that a difference in path length between the
ray tracings associated with adjacent grid points is less than one
wavelength of the radar signal. In some cases, spacing between the
grid points of the second set of grid points is less than spacing
between the grid points of the first set of grid points. In some
cases, generating the error ellipse further comprises calculating a
covariance matrix based on coordinates of the candidate grid points
of the first set of grid points. In some such cases, the covariance
matrix is a first covariance matrix and the threshold percentage is
a first threshold percentage, and the process further comprises:
generating a second covariance matrix based on coordinates of
candidate grid points of the second set of grid points, the
candidate grid points of the second set of grid points associated
with a subset of the scores generated during the repetition of the
process including scores greater than a second threshold percentage
of the highest of the scores generated during the repetition of the
process; and generating a confidence value based on a size of the
second covariance matrix. In some such cases, the computer program
product further comprises repeating the process using additional
measured phase differences if the confidence value is less than a
threshold confidence value. In some cases, the process is performed
as a multi-threaded process comprising a first thread to perform
the process to geolocate a first emitter and a second thread to
perform the process to geolocate a second emitter.
[0078] Another example embodiment of the present disclosure
provides a method for emitter geolocation, the method comprising:
measuring, by a processor-based system, phase differences between
radar signals received at one or more pairs of antennas;
calculating, by the processor-based system, a first plurality of
hypothesized phase differences based on ray tracings from
hypothesized emitter locations at each of a first set of grid
points to the one or more pairs of antennas; generating, by the
processor-based system, a first plurality of scores based on
correlations between the measured phase differences and the first
plurality of hypothesized phase differences; generating, by the
processor-based system, an error ellipse based on candidate grid
points of the first set of grid points, the candidate grid points
of the first set of grid points associated with a subset of the
first plurality of scores, the subset including scores greater than
a threshold percentage of a highest score of the first plurality of
scores; calculating, by the processor-based system, a second
plurality of hypothesized phase differences based on ray tracings
from hypothesized emitter locations at each of a second set of grid
points to the one or more pairs of antennas, the second set of grid
points bounded by the error ellipse; generating, by the
processor-based system, a second plurality of scores based on
correlations between the measured phase differences and the second
plurality of hypothesized phase differences; and selecting, by the
processor-based system, one of the second set of grid points, that
is associated with a highest of the second plurality of scores, as
the estimated emitter geolocation.
[0079] In some cases, the first set of grid points is bounded by a
search area, the search area based on an estimated angle and range
to the emitter as provided by a radar warning receiver. In some
cases, spacing between the grid points of the first set of grid
points is selected so that a difference in path length between the
ray tracings associated with adjacent grid points is less than one
wavelength of the radar signal. In some cases, spacing between the
grid points of the second set of grid points is less than spacing
between the grid points of the first set of grid points. In some
cases, generating the error ellipse further comprises calculating a
covariance matrix based on coordinates of the candidate grid points
of the first set of grid points. In some such cases, the covariance
matrix is a first covariance matrix and the threshold percentage is
a first threshold percentage, and the process further comprises:
generating a second covariance matrix based on coordinates of
candidate grid points of the second set of grid points, the
candidate grid points of the second set of grid points associated
with a subset of the second plurality of scores, the subset
including scores greater than a second threshold percentage of a
highest score of the second plurality of scores; generating a
confidence value based on a size of the second covariance matrix;
and repeating the method using additional measured phase
differences if the confidence value is less than a threshold
confidence value.
[0080] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described (or
portions thereof), and it is recognized that various modifications
are possible within the scope of the claims. Accordingly, the
claims are intended to cover all such equivalents. Various
features, aspects, and embodiments have been described herein. The
features, aspects, and embodiments are susceptible to combination
with one another as well as to variation and modification, as will
be understood by those having skill in the art. The present
disclosure should, therefore, be considered to encompass such
combinations, variations, and modifications. It is intended that
the scope of the present disclosure be limited not by this detailed
description, but rather by the claims appended hereto. Future filed
applications claiming priority to this application may claim the
disclosed subject matter in a different manner, and may generally
include any set of one or more elements as variously disclosed or
otherwise demonstrated herein.
* * * * *