Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2001-09-14
2003-04-22
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S372000, C342S422000
Reexamination Certificate
active
06552684
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a direction of arrival estimation method using an array antenna and a radio reception apparatus.
BACKGROUND ART
FIG. 1
is a block diagram showing a conventional radio reception apparatus using an array antenna. In
FIG. 1
, the conventional radio reception apparatus has units
10
-
1
to
10
-N corresponding in number to the channels received.
Reception units
10
-
1
to
10
-N each mainly comprise the same number of despreading sections
12
-
1
to
12
-M as the antenna elements of array antenna
11
, direction of arrival estimation section
13
for estimating the directions of arrival of signals based on the outputs of despreading sections
12
-
1
to
12
-M, beam former
14
for forming directivities in the directions of arrival estimated by direction of arrival estimation section
13
and letting the outputs of despreading sections
12
-
1
to
12
-M pass according to the formed directivities and channel reception section
15
for extracting a channel signal from the output of beam former
14
. The array antenna has a configuration of a plurality of antenna elements linearly spaced at intervals of half-wavelength of a carrier frequency.
Here, a beam search technique will be explained as an example of the direction of arrival estimation method. An input signal vector X(t) of the antenna is given by following expression (1).
X
(
t
)=[
x
0
(
t
),
x
1
(
t
), . . . ,
xn
(
t
)]
T
(1)
Furthermore, vector a(è) having a peak in a è direction (called a “steering vector”) is given by expression (2).
a
(
è
)=[
1
,exp(−
j
Π sin
è
), . . . ,exp(−
jn
Π sin
è
)]
T
(2)
By carrying out reception using the above expression, it is possible to observe power in the è direction included in X(t). That is, spatial profile H(è) can be determined by following expression (3).
H
(
è
)=
a
(
è
)
T·X
(
t
) (3)
From this, a spatial profile of X(t) over a 180° sector extending ahead can be determined. Here, è takes a value between −90° and 90°.
Beam forming in an array antenna is obtained by multiplying a reception signal from each antenna element by a complex amplitude and giving an arbitrary directivity using the result thereof.
An example of beam forming of the array antenna will be explained below.
FIG. 2
illustrates an example of beam forming of an array antenna. In
FIG. 2
, base station apparatus
21
has four antenna elements, forms directivities and performs communications with mobile stations
22
and
23
.
When base station apparatus
21
communicates with mobile station
22
located in the è direction, the input signal vector of the four antenna elements is given by expression (4) using expression (1).
X
(
t
)=[
x
0
(
t
),
x
1
(
t
),
x
2
(
t
),
x
3
(
t
)]
T
(4)
Then, when the directivity of the array antenna is directed to mobile station
22
at angle è from base station apparatus
21
, steering vector a(è) is given by expression (5).
a
(
è
)=[
1
,exp(−
j
Π sin
è
),exp(−
j
2
Π sin
è
)]
T
(5)
By carrying out a vector multiplication of expression (4) and expression (5) on the reception signal, the array antenna of base station apparatus
21
forms a directivity with a large gain in the è direction. For example, an array antenna with four linearly spaced antenna elements has a maximum gain in the è direction and the gain at an angle greater than 22.5° from the è direction is less than half the maximum gain.
Thus, beam forming forms directivities by phase-rotating signals received from the respective antennas of the array antenna by an arbitrary angle and then combining those signals. That is, by branching the signals received from the respective antenna elements to a plurality of groups and applying different ways of combination thereto, beam forming can form directivities with a high gain in a plurality of different directions. As a result, beam forming can form directivities appropriate for carrying out communications with a plurality of other parties of communication.
For example, it is possible to carry out processing of using beam
24
in the &thgr; direction for communication with mobile station
22
in the &thgr; direction and processing of using beam
25
in the &phgr; direction for communication with mobile station
23
in the &phgr; direction simultaneously.
Thus, base station apparatus
21
can receive signals of a plurality of other parties of communication individually by carrying out processing on signals output from the beam former through different reception units provided for the other parties of communication.
However, since the conventional radio reception apparatus estimates the directions of arrival of signals for their respective channels individually, it is not possible to achieve accuracy enough to estimate the directions of arrival due to interference received from other stations under circumstances in which many mobile stations exist adjacent to one another, hence it is not possible to form optimal antenna directivities for reception.
Moreover, to estimate the directions of arrival of radio signals for their respective channels, it is necessary to provide reception units
10
-
1
,
10
-
2
, . . . ,
10
-N for the respective channels, which requires the same number of direction of arrival estimation sections as channels received by reception units
10
-
1
,
10
-
2
, . . . ,
10
-N and despreading sections corresponding to (the number of channels×the number of antennas), increasing the scale of the circuit and costs.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a direction of arrival estimation method and a radio reception apparatus capable of reducing the scale of the circuit and preventing deterioration of reception quality even if many mobile stations exist adjacent to one another deteriorating the accuracy of direction of arrival estimations of signals.
This object is attained by calculating an intensity distribution of reception signals with respect to the directions of arrival of signals from the reception signals before they are separated according to their respective channels, estimating the directions of arrival of signals in band units (i. e., signals for each band) based on this intensity distribution, determining antenna directivities and receiving signals accordingly, grouping signals coming from quasi-identical directions and estimating the directions of arrival thereof, receiving radio signals with antenna directivities formed in the directions of arrival estimated in group units, and receiving the signals in group units and separating or extracting desired signals.
REFERENCES:
patent: 5936577 (1999-08-01), Shoki et al.
patent: 6061553 (2000-05-01), Matsuoka et al.
patent: 6188913 (2001-02-01), Fukagawa et al.
patent: 2337419 (1999-11-01), None
patent: 05259950 (1993-10-01), None
patent: 09219675 (1997-08-01), None
patent: 09261008 (1997-10-01), None
patent: 11251964 (1999-09-01), None
patent: 11331125 (1999-11-01), None
patent: 2001036451 (2001-02-01), None
International Search Report dated Apr. 3, 2001.
Hoshino Masayuki
Miya Kazuyuki
Mull Fred H
Stevens Davis Miller & Mosher LLP
Tarcza Thomas H.
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