System and method for direction finding and geolocation of emitters based on line-of-bearing intersections
View Patent ↗According to an embodiment of the present invention an emitter geolocation technique determines the geolocation of a radio frequency (RF) emitter using pair-wise line-of-bearing intersections that are derived from signal-to-noise ratios of transmitted signals received at a sensor. The technique may be employed with ground based vehicle or small unmanned air vehicles (UAV), and obtains reliable geolocation estimates of radio frequency (RF) emitters of interest.
1. A system for locating an emitter comprising:
a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern, wherein the first and second radiation patterns provide a received signal gain with respect to signals received from said emitter;
a receiver to receive signals from each of said plurality of antennas transmitted by said emitter and obtain received signal strength measurements of said received signals at a plurality of different locations; and
a processor to process said received signal strength measurements to locate said emitter, wherein said processor includes:
a location module to:
process said received signal strength measurements and determine lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations; and
determine a location of said emitter based on intersections of said lines-of-bearing to said emitter at said plurality of different locations.
2. The system of claim 1 , wherein said received signal strength measurements include signal-to-noise ratio measurements of said signals received at said plurality of antennas.
3. The system of claim 2 , wherein said location module determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements and determines a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.
4. The system of claim 2 , wherein said location module:
groups said received signal strength measurements into at least two clusters;
determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and
determines a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.
5. The system of claim 1 , wherein said location module determines said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.
6. The system of claim 5 , wherein said set of simultaneous equations includes:
(
x
ij
y
ij
)
=
(
-
m
i
1
-
m
j
1
)
-
1
(
y
i
-
m
i
x
i
y
j
-
m
j
x
j
)
and wherein x ij y ij represent said coordinates of said location of said emitter, and (x i , y i ), (x j , y j ), (for i, j=1 to N, i·j) represent coordinates of said locations for obtaining said received signal strength measurements, and N represents a quantity of said locations for obtaining said received signal strength measurements.
7. The system of claim 5 , wherein said location module computes a line-of-bearing from each of said plurality of different locations within to said emitter.
8. The system of claim 7 , wherein said location module computes a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.
9. The system of claim 8 , wherein said location module filters said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.
10. The system of claim 8 , wherein said location module determines one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.
11. The system of claim 10 , wherein said one or more geolocation centroids are determined using the set of equations:
x C =median( x 1 ,x 2 . . . x M )
y C =median ( y 1 ,y 2 . . . y M )
and wherein x C , y C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.
12. The system of claim 10 , wherein said location module computes a root-mean-square error of said one or more geolocation centroids.
13. The system of claim 12 , wherein said location module computes said root-mean-square error of said one or more geolocation centroids using the set of equations:
Std
R
=
1
M
-
1
∑
k
(
x
k
-
x
c
)
2
+
∑
k
(
y
k
-
y
c
)
2
Std
I
=
1
M
-
1
∑
k
(
x
k
′
-
x
c
)
2
+
∑
k
(
y
k
′
-
y
c
)
2
for k=1, 2 . . . M, and wherein Std R and Std I represent root-mean-square errors with respect to opposite sides of an axis of symmetry, x C , y C represent coordinates of said geolocation centroid, x k , y k represent line-of-bearing intersection coordinates on a side of a line of symmetry and (x′ k , y′ k ) represent line-of-bearing intersection coordinates on an opposite side of said line of symmetry, and M represents a quantity of said line-of-bearing intersections.
14. The system of claim 13 , wherein said location module filters said one or more geolocation centroids by comparing a ratio of Std R and Std I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.
15. The system of claim 1 , wherein said signals transmitted by said emitter include radio frequency signals.
16. The system of claim 1 , wherein said receiver is mounted on a mobile platform that traverses a pre-planned path to obtain said received signal strength measurements at said plurality of locations.
17. The system of claim 16 , wherein said mobile platform includes a terrain based vehicle or an unmanned aerial vehicle.
18. The system of claim 1 , further including a plurality of receivers each mounted on a stationary platform at a corresponding one of said plurality of locations to obtain said received signal strength measurements.
19. The system of claim 1 , wherein said first antenna comprises an omni-directional antenna and said second antenna comprises a directional antenna.
20. A method for locating an emitter comprising:
(a) receiving signals transmitted by said emitter via each of a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern, wherein the first and second radiation patterns provide a received signal gain with respect to signals received from said emitter, and obtaining received signal strength measurements of said received signals at a plurality of different locations; and
(b) processing said received signal strength measurements, via a processor, and determining lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations to determine a location of said emitter based on intersections of said lines-of-bearing to said emitter at said plurality of different locations.
21. The method of claim 20 , wherein step (b) further includes:
(b.1) determining said location using signal-to-noise ratio measurements of said signals received at said plurality of antennas.
22. The method of claim 21 , wherein step (b.1) further includes:
(b.1.1) determining a maximum signal-to-noise ratio from said signal-to-noise ratio measurements; and
(b.1.2) determining a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.
23. The method of claim 21 , wherein step (b.1) further includes:
(b.1.1) grouping said received signal strength measurements into at least two clusters;
(b.1.2) determining a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and
(b.1.3) determining a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.
24. The method of claim 20 , wherein step (b) further includes:
(b.1) determining said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.
25. The method of claim 24 , wherein said set of simultaneous equations includes:
(
x
ij
y
ij
)
=
(
-
m
i
1
-
m
j
1
)
-
1
(
y
i
-
m
i
x
i
y
j
-
m
j
x
j
)
and wherein x ij y ij represent said coordinates of said location of said emitter, and (x i , y i ), (x j , y j ), (for i, j=1 to N, i≠j) represent coordinates of said locations for obtaining said received signal strength measurements, and N represents a quantity of said locations for obtaining said received signal strength measurements.
26. The method of claim 24 , wherein step (b.1) further includes:
(b.1.1) computing a line-of-bearing from each of said plurality of different locations to said emitter.
27. The method of claim 26 , wherein step (b.1) further includes:
(b.1.2) computing a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.
28. The method of claim 27 , wherein step (b) further includes:
(b.2) filtering said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.
29. The method of claim 27 , wherein step (b) further includes:
(b.2) determining one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.
30. The method of claim 29 , wherein said one or more geolocation centroids are determined using the set of equations:
x C =median( x 1 ,x 2 . . . x M )
y C =median ( y 1 ,y 2 . . . y M )
and wherein x C , y C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.
31. The method of claim 30 , wherein step (b) further includes:
(b.3) computing a root-mean-square error of said one or more geolocation centroids.
32. The method of claim 31 , wherein step (b.3) computes said root-mean-square error of said one or more geolocation centroids using the set of equations:
Std
R
=
1
M
-
1
∑
k
(
x
k
-
x
c
)
2
+
∑
k
(
y
k
-
y
c
)
2
Std
I
=
1
M
-
1
∑
k
(
x
k
′
-
x
c
)
2
+
∑
k
(
y
k
′
-
y
c
)
2
for k=1, 2 . . . M, and wherein Std R and Std I represent root-mean-square errors with respect to opposite sides of an axis of symmetry, x C , y C represent coordinates of said geolocation centroid, x k , y k represent line-of-bearing intersection coordinates on a side of a line of symmetry and (x′ k , y′ k ) represent line-of-bearing intersection coordinates on an opposite side of said line of symmetry, and M represents a quantity of said line-of-bearing intersections.
33. The method of claim 32 , wherein step (b) further includes:
(b.4) filtering said one or more geolocation centroids by comparing a ratio of Std R and Std I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.
34. The method of claim 20 , wherein said first antenna comprises an omni-directional antenna and aid second antenna comprises a directional antenna.
35. A program product apparatus comprising a non-transitory computer readable memory device with computer program logic recorded thereon for locating an emitter, wherein a receiver receives signals transmitted by said emitter via each of a plurality of antennas including a first antenna with a first radiation pattern and a second different antenna with a second radiation pattern different from the first radiation pattern to obtain received signal strength measurements of said received signals at a plurality of different locations, said program product apparatus further comprising:
a location module to process said received signal strength measurements of signals transmitted by said emitter and obtained at a plurality of different locations, and determine lines-of-bearing to said emitter based on a combination of received signal strength measurements of a signal received by each of said first antenna and said second antenna at said plurality of different locations to determine a location of said emitter based on intersections of aid lines-of-bearing to said emitter at said plurality of different locations.
36. The apparatus of claim 35 , wherein said received signal strength measurements include signal-to-noise ratio measurements of said signals received at said plurality of antennas.
37. The apparatus of claim 36 , wherein said location module determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements and determines a line-of-bearing to said emitter based on said maximum signal-to-noise ratio.
38. The apparatus of claim 36 , wherein said location module:
groups said received signal strength measurements into at least two clusters;
determines a maximum signal-to-noise ratio from said signal-to-noise ratio measurements within each cluster; and
determines a line-of-bearing to said emitter based on each of said maximum signal-to-noise ratios.
39. The apparatus of claim 35 , wherein said location module determines said location by solving a set of simultaneous equations relating to said lines-of-bearing, wherein said set of simultaneous equations include unknown variables representing coordinates of said location of said emitter.
40. The apparatus of claim 39 , wherein said set of simultaneous equations includes:
(
x
ij
y
ij
)
=
(
-
m
i
1
-
m
j
1
)
-
1
(
y
i
-
m
i
x
i
y
j
-
m
j
x
j
)
and wherein x ij y ij represent said coordinates of said location of said emitter, and (x i , y i ), (x j , y j ), (for i, j=1 to N, i≠j) represent coordinates of said locations for obtaining said measurements, and N represents a quantity of said locations for obtaining said received signal strength measurements.
41. The apparatus of claim 39 , wherein said location module computes a line-of-bearing from each of said plurality of different locations to said emitter.
42. The apparatus of claim 41 , wherein said location module computes a plurality of line-of-bearing intersections that approximate said location of said emitter using line-of-bearing pairs.
43. The apparatus of claim 42 , wherein said location module filters said plurality of line-of-bearing intersections by comparing each individual line-of-bearing intersection to filtering criteria, wherein when said individual line-of-bearing intersection does not meet said filtering criteria said individual line-of-bearing intersection is discarded.
44. The apparatus of claim 42 , wherein said location module determines one or more arithmetic median value based geolocation centroids from selected ones of said plurality of line-of-bearing intersections.
45. The apparatus of claim 44 , wherein said one or more geolocation centroids are determined using the set of equations:
x C =median( x 1 ,x 2 . . . x M )
y C =median ( y 1 ,y 2 . . . y M )
and wherein x C , y C represent coordinates of said geolocation centroid, and M represents a quantity of said line-of-bearing intersections.
46. The apparatus of claim 44 , wherein said location module computes a root-mean-square error of said one or more geolocation centroids.
47. The apparatus of claim 46 , wherein said location module computes said root-mean-square error of said one or more geolocation centroids using the set of equations:
Std
R
=
1
M
-
1
∑
k
(
x
k
-
x
c
)
2
+
∑
k
(
y
k
-
y
c
)
2
Std
I
=
1
M
-
1
∑
k
(
x
k
′
-
x
c
)
2
+
∑
k
(
y
k
′
-
y
c
)
2
for k=1, 2 . . . M, and wherein Std R and Std I represent root-mean-square errors with respect to opposite sides of an axis of symmetry, x C , y C represent coordinates of said geolocation centroid, x k , y k represent line-of-bearing intersection coordinates on a side of a line of symmetry and (x′ k , y′ k ) represent line-of-bearing intersection coordinates on an opposite side of said line of symmetry, and M represents a quantity of said line-of-bearing intersections.
48. The apparatus of claim 47 , wherein said location module filters said one or more geolocation centroids by comparing a ratio of Std R and Std I to an error threshold, wherein when said ratio does not pass said error threshold a geolocation centroid used as a basis for said root-mean-square error computation is discarded.
49. The apparatus of claim 35 , wherein said first antenna comprises an omni-directional antenna and said second antenna comprises a directional antenna.