Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2000-02-22
2002-02-26
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S417000
Reexamination Certificate
active
06351238
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a direction of arrival (herein after recited as DOA) estimation apparatus to estimate a direction of an arrival wave using an array antenna, and a variable directional signal receiving apparatus to vary directional characteristics of an antenna basing on a result of a direction estimation of the DOA estimation apparatus.
BACKGROUND OF THE INVENTION
As one of a method of estimating a direction of an arriving wave with high accuracy using an array antenna composed of plurality of antenna elements, the MUSIC (Multiple Signal Classification) described in a paper “Multiple emitter Location and Signal Parameter Estimation”, IEEE Trans., AP-34, 3, pp.276-280 (1986) by R. O. Schmidt has been known. The method is an algorithm that estimates a direction of multiple waves in a same frequency band simultaneously with high accuracy. With reference to
FIGS. 15 and 16
, the DOA estimation apparatus using the conventional MUSIC method will now be described.
FIG. 15
is a block diagram showing a composition of a DOA estimation apparatus. A signal
102
-
1
. . .
102
-M received by antenna elements
101
-
1
. . .
101
-M, where M is the number of elements (M>1), is converted at frequency converters
103
-
1
. . .
103
-M connected to each antenna elements
101
-
1
. . .
101
-M and the signals are phase detected and then are converted to complex base band signals
104
-
1
. . .
104
-M composed of an orthogonal I, Q signals.
The each complex base band signals
104
-
1
. . .
104
-M are converted from analog signals to complex digital signals
106
-
1
. . .
106
-M by an analog/digital converters (A/D converters)
105
-
1
. . .
105
-M.
A data transfer section
107
transfers data of each complex digital signals x
1
(k),x
2
(k), . . . ,xM(k) obtained from the complex digital signals
106
-
1
. . .
106
-M at a sample time of k&Dgr;T (&Dgr;T is a sample interval) to a DOA estimation processing section
108
in a lump at a specified timing after storing specified sample time temporarily.
A DOA processing section
108
performs a computation from the output data of the data transfer section
107
basing on the MUSIC method and estimates a direction.
FIG. 16
is a block diagram of a conventional DOA processing section
108
. A computation of covariance matrix means
109
makes a receiving vector X(k) expressed with formula 1 using the complex digital signals
106
-
1
. . .
106
-M obtained from the data transfer section
107
and makes a covariance matrix R shown in formula 2 using the receiving vector X(k) of the sample time k=1 . . . N. The T indicates transposition, and the H exhibits complex conjugate transposition.
X(k)=[x
1
(k), x
2
(k), . . . ,x
M
(k)]
T
(formula 1)
R
=
∑
k
=
1
N
X
(
k
)
X
(
k
)
H
/
N
(
formula
2
)
An eigenvalue computation means
110
gets eigenvalues &lgr;1 . . . &lgr;M by computing the eigenvalues of the covariance matrix R in descending order.
An eigenvector computation means
111
computes eigenvectors e
1
. . . ,e
M
corresponding to the eigenvalues &lgr;1 . . . &lgr;M. In a case, a number of arriving waves is S, a DOA evaluation function computation means
112
uses (M . . . S) number of eigenvector matrix E
N
=[e
s+1
, . . . ,e
M
] belonging to a subspace spanned by noise eigenvector (hereinafter noise subspace) relative to formula 3 and utilizes an orthogonal characteristics between a subspace spanned by signal eigenvector (hereinafter signal subspace) Es=[e
1
, . . . ,e
M
] spread by eigenvector e
1
, . . . ,e
M
and E
N
. Namely, the DOA estimation function F(&thgr;) is defined as formula 4, that evaluates an orthogonal characteristics with E
N
at the time when&thgr; is rotated from 0 to 360°, wherein a(&thgr;) (steering vector) indicates complex response of an array antenna against the direction&thgr;.
&lgr;
1
≧&lgr;
2
≧
. . .
≧&lgr;
S
>&lgr;
S
+1=&lgr;
S
+2=
- - -
=&lgr;
M
(Formula 3)
F(&thgr;)={a
H
(&thgr;)E
N
E
N
H
a (&thgr;)}
−1
(formula 4)
In a case when &thgr; equals to an arriving angle, the DOA estimation function F(&thgr;) idealistically becomes infinite value. Therefore, the direction of peak value from the result of the computation of F(&thgr;) at the time of angle &thgr; is regarded as the DOA estimation of an arriving wave.
In general, since the number of arriving waves S is unknown, a judgement is made to determine the number of waves by distribution of eigenvalue or by setting a signal number judgement reference described in the paper M. Wax and T. Kailath, “Detection of Signals by Information Theoretic Criteria”, IEEE Trans. On Acoustics, Speech and Signal Processing, Vol. ASSP33(2), pp.387-392, February (1985).
With such DOA estimation apparatus using above MUSIC method, that estimates the DOA accurately by signal processing using an algorithm of eigenvalue decomposition, an reciprocally correlative value of the receiving signals between the antenna elements is obtained with the covariance matrix. And, statistically, the accuracy becomes higher when the observation time is longer. As a result, the higher accuracy of the DOA estimation is obtained. In order to secure certain accuracy level of the DOA estimation, it has been a problem that an amount of memory storing the temporary data at the data transfer section becomes larger, since the amount of receiving data used for the DOA estimation becomes larger due to handling a large amount of receiving signal data from each antenna elements converted to digital signals by A/D converters.
And also, it is required to secure transferring speed at a data transfer section and computation ability of signal processing apparatus corresponding to the moving speed of the estimating object when estimating the DOA of an transmitter loaded on a moving object.
With such DOA estimation apparatus using MUSIC method, that estimates the DOA accurately by signal processing using an algorithm eigenvalue decomposition of array receiving signals of a covariance matrix, it has been a problem that arriving waves cannot be separated with high accuracy when reciprocal delay time between the multiple waves reflected from the earth or buildings is shorter than a symbol length since the rank of the covariance matrix is decreased due to the high correlation between the multiple waves.
In order to deal with this problem, the Spatial Smoothing method has been proposed in the paper of Pillai et al, “Forward/Backward Spatial Smoothing Techniques for Coherent Signal Identification”, IEEE Trans. On Acoustics, speech and signal processing, VOL.37, NO.1, 1989.
With the spatial smoothing method, however, it has been a problem that substantial effects can not be obtained since the freedom of array is decreased further than sub-arrayed in a case of a four-element circular array antenna or so due to taking the averaging processing of a covariance matrix from sub-arrayed linear array.
The purpose of the present invention is to simplify the composition of the DOA estimation apparatus, and to provide an apparatus that enables to decrease the transfer speed of a data transfer section to signal processing apparatus and at the same time to decrease the memory capacity for accumulation and to alleviate the computation capacity of signal processing apparatus by decreasing the amount of computation.
And also, in a case when application is not to estimate directions of all the multiple arriving waves but limited to estimate the direction of the maximum level among the multiple arriving waves, the present invention is to provide an DOA estimation apparatus to detect accurately an DOA of the maximum level among multiple waves, even when the number of antenna elements is small and the correlation between the arriving waves is high.
Furthermore, utilizing a result of estimation by a DOA estimation apparatus, the present invention is to provide a variable directional signal receiv
Fukagawa Takashi
Hasegawa Makoto
Kishigami Takaaki
Matsushita Electric - Industrial Co., Ltd.
Phan Dao
Ratner & Prestia P.C.
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