Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2001-05-16
2002-10-01
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S450000
Reexamination Certificate
active
06459409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to method and device that uses an array antenna to locate the near-field source of a signal that falls incident on the array antenna.
2. Description of the Related Art
FIG. 1
shows a uniform linear array ULA with elements 0 to 6 receiving a signal from a source in the far field of the array ULA. When a transmission source is in the far field, it is assumed to be an infinite distance from the array, so that the received signal has a plane wavefront PW. Because the wavefront is plane, the incident signal has the same incident angle &thgr;
farfield
at each element. Direction of Arrival (DOA) estimation algorithms such as MUSIC and ESPIRIT perform DOA estimation with great accuracy when the transmission source is in the far field of the array. For example, U.S. Pat. No. No. 5,854,612 (based on foreign priority of Japanese Patent Application No. 9-042877) describes that it is a relatively easy task to obtain the angle of the incident signal by calculating the phase difference of the signal received at the different antenna elements.
However, in most indoor applications, such as Wireless LAN, the source is in the near field. As shown in
FIG. 2
, when the transmission source S in the near field of the reception array, propagation waves from the transmission source have a spherical wavefront SW. The arrival angle is different at each element, for example, angles &thgr;
0
, &thgr;
4
, and &thgr;
6
at elements 0, 4 and 6, respectively. When the above-described DOA estimation algorithms are used for near field sources, the estimate of the source location, and consequentially the radiation diagram, can be distorted.
Attempts have been made to improve results of DOA estimation performed for near field sources using far field DOA estimation algorithms. For example Kennedy et al disclose such a method in “Broadband Near field Beamforming Using a Radial Beam pattern Transformation”, IEEE Trans. on Signal Proc., vol. 46, no 8, August 1998. However, this method requires a previous precise knowledge of the distance from the source to each element of the array.
Asano et al disclose another method in “Source separation using subspace method and spatial inverse filter”, IEICE Technical Report, EA 99-22, pp. 1-7, June 1996. This method estimates not only DOA, but also distance to the source. However, without some general knowledge of the source's location, the distance to the source can be any value from 0 to infinity. Therefore, a range domain with essentially no bounds must be searched to find the source.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above-described problems, and to provide a source location estimation device capable of estimating source location in the near field using far field DOA estimation algorithms, with only a limited domain search even when source location is completely unknown.
To achieve the above-described objective, a source location estimation device according to the present invention includes an array antenna, first and second samplers, a direction-of-arrival estimator, a source location estimator, and a sampling adjuster.
The array antenna includes two sub-arrays. Each sub-array has at least three elements with at least one uncommon element. The first sampler samples elements of one sub-array, and the second sampler samples elements of the other sub-array. The direction-of-arrival estimator uses samples from the samplers to make a separate direction-of-arrival estimate for each sub-array for direction of arrival of a signal from a source. The source location estimator estimates distances from the source to each element based on the separate direction-of-arrival estimates from the direction-of-arrival estimator. The sampling adjuster adjusts timing of sampling performed by the samplers based on the distances from the source location estimator.
With this configuration, the sampling timing of the sampler is synchronized to follow the sphericity of the incoming wavefront. The near field distortion is gradually removed with each iteration, so that the source is located with increasingly higher precision. No previous knowledge of the source location is needed, because only a simple angle-domain is searched, limited to the interval between 0 (0 degrees) and &pgr; (180 degrees).
According to another aspect of the present invention, the sampling adjuster adjusts timing of sampling by the first sampler based on the following formula:
Δτ
&RightBracketingBar;
i
θ
0
=
(
d
^
i
-
d
0
^
)
c
-
i
λΔ
e
c
cos
(
θ
0
^
)
wherein i represents the target element of sampling from elements 0 to Ls−1, element 0 being the optimum referential element of the one sub-array;
&Dgr;&tgr;|
i
&thgr;
0
represents the error between the far-field delay and the near-field delay with respect to the element 0 and the target element;
{circumflex over (d)}
i
represents the distance between the source and the target element estimated by the source location estimator;
{circumflex over (d)}
0
represents the distance between the source and the element 0 estimated by the source location estimator;
c represents the speed of light;
&lgr;&Dgr;e represents inter-element distance; and
{circumflex over (&thgr;)}
0
represents direction of arrival estimated for the element 0 of the one sub-array by the direction-of-arrival estimator.
Further, the sampling adjuster adjusts timing of sampling by the second sampler based on the following formula:
Δτ
&RightBracketingBar;
i
θ
L
-
1
=
(
d
^
i
-
d
0
^
)
c
-
i
λΔ
e
c
cos
(
θ
^
L
-
1
)
wherein i represents the target element of sampling from elements L-Ls to L-1, the element L-1 being the optimum referential element of the other sub-array;
&Dgr;&tgr;|
i
&thgr;
L-1
represents the error between the far-field delay and the near-field delay with respect to the element L-1 and the target element; and
{circumflex over (&thgr;)}
L-1
represents the direction of arrival estimated for the element L-1 by the direction-of-arrival estimator.
With this configuration, the sampling adjuster can adjust timing of sampling for elements using a relatively simple algorithm.
According to another aspect of the present invention, the array antenna includes elements 0 to L-1 for a total of L elements. One sub-array includes elements 0 to L
s
-1, wherein L
s
<L. Element 0 is an optimum referential element of the one sub-array. The other sub-array is obtained by a shift of L-Ls elements, and so includes elements L-L
s
to L-1. The element L-1 is an optimum referential element of the other sub-array.
Further, the source location estimator estimates distances between the source and each of the elements 0 to L-1 based on the following formulas:
d
^
0
=
(
L
-
1
)
Δ
e
λ
&LeftBracketingBar;
sin
(
θ
^
0
)
sin
(
θ
^
L
-
1
)
cos
(
θ
^
L
-
1
)
-
cos
(
θ
^
0
)
&RightBracketingBar;
and
d
^
i
>
0
=
(
d
0
cos
(
θ
^
0
)
+
i
Δ
e
λ
)
2
+
(
d
0
sin
(
θ
^
0
)
2
)
wherein i represents a target element of sampling from elements 0 to L-1;
{circumflex over (d)}
0
represents the distance between the source and the element 0 estimated by the source location estimator;
&lgr;&Dgr;e represents the inter-element distance;
{circumflex over (&thgr;)}
0
represents the direction of arrival estimated for the element 0 by the direction-of-arrival estimator:
{circumflex over (&thgr;)}
L-1
represents the direction of arrival estimated for the element L-1 by the direction-of-arrival estimator; and
{circumflex over (d)}
i
represents the distance between the source and the target element estimated by the source location estimator.
With this configuration, the source location estimator can estimate distanc
Giuseppe Abreu
Kohno Ryuji
Frommer William S.
Frommer & Lawrence & Haug LLP
Mull Fred H
Sony Corporation
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