Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-09-02
2004-09-14
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S347000
Reexamination Certificate
active
06792033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an array antenna reception apparatus installed in a base station for removing another user interference under antenna directivity control and, more particularly, to an array antenna having antenna elements linearly laid out on each side of a polygon.
2. Description of the Prior Art
In a cellular mobile communication system and the like, the following method is examined. A directional pattern which maximizes the reception gain in a desired signal arrival direction is formed using an adaptive antenna made up of a plurality of antenna elements, and interference from another user and interference by a delayed wave are removed in reception. As a radio transmission method expected for a large subscriber capacity, the CDMA method receives a great deal of attention.
FIG. 1
is a block diagram showing an example of a conventional array antenna reception apparatus using the CDMA method.
The conventional array antenna reception apparatus is constituted by an antenna
20
having a plurality of antenna elements
21
1
to
21
M
laid out circularly, one adaptive receiver
22
, and a determination circuit
5
.
The antenna
20
is made up of the M antenna elements
21
1
to
21
M
laid out circularly. Each of the antenna elements
21
1
to
21
M
is not particularly limited in horizontal plane directivity and may take omnidirectivity or dipole directivity. The M antenna elements
21
1
to
21
M
are close to each other so as to establish correlations between antenna reception signals, and receive signals obtained by code-multiplexing a desired signal and a plurality of interference signals. In the following processing, since signals are digitally processed in the baseband, M antenna reception signals S
1
to S
M
are frequency-converted from the radio band to the baseband and A/D-converted.
The determination circuit
5
receives a demodulated signal for a user as an output from the adaptive receiver
22
and performs hard determination for the demodulated signal, thereby outputting a user determination symbol. Here, it should be noted that only one of the determination circuit
5
is shown in
FIG. 1
, but other circuits are omitted.
FIG. 2
is a block diagram showing the adaptive receiver
22
in the conventional array antenna reception apparatus.
The adaptive receiver
22
is constituted by despread circuits
6
1
to
6
M
, weighting synthesizer
7
, demodulator
10
, complex multiplier
13
, subtracter
14
, delay circuit
15
, and antenna weight control circuit
16
. The adaptive receiver
22
receives the antenna reception signals S
1
to S
M
received by the M antenna elements
21
1
to
21
M
laid out circularly, and the user determination symbol as an output from the determination circuit
5
, and outputs a demodulated signal for a user.
The despread circuits
6
1
to
6
M
calculate correlations between the antenna reception signals S
1
to S
M
and a user spread code C. Assuming that the spread code C is a complex code made up of two quadrature codes C
I
and C
Q
, the despread circuits
6
1
to
6
M
can be realized by one complex multiplier and averaging circuits over the symbol section. The despread circuits
6
1
to
6
M
can also be realized by a transversal filter arrangement with a tap weight C.
The weighting synthesizer
7
comprises complex multipliers
8
1
to
8
M
and adder
9
. The weighting synthesizer
7
multiplies outputs from the despread circuits
6
1
to
6
M
by antenna weights W
r1
to W
rM
, and adds them to generate a signal received with a directional pattern unique to a desired signal.
The demodulator
10
comprises a transmission path estimation circuit
11
and complex multiplier
12
. The product of an output from the weighting synthesizer
7
and the complex conjugate of a transmission path estimation output is the demodulated signal for a user as an output from the adaptive receiver
22
.
The complex multiplier
13
multiplies the user determination symbol by the transmission path estimation output. In multiplying the user determination symbol by the transmission path estimation output, only a component about the phase of the estimation value can be multiplied, and an amplitude obtained by another means can be multiplied. This another means is one for obtaining the amplitude by measuring reception power or the like.
The subtracter
14
calculates the difference between an output from the complex multiplier
13
and an output from the weighting synthesizer
7
, and detects an antenna weight control error e.
The delay circuit
15
delays outputs from the despread circuits
6
1
to
6
M
in accordance with the processing times of the weighting synthesizer
7
, demodulator
10
, subtracter
14
, and the like.
The antenna weight control circuit
16
calculates the antenna weights W
r1
to W
rM
from the antenna weight control error e and outputs from the delay circuit
15
. The antenna weight control circuit
16
adaptively controls the antenna weights W
r1
to W
rM
based on the MMSE standard so as to minimize the mean square value of the antenna weight control error e. When the LMS algorithm is employed as an update algorithm with a small arithmetic amount, the antenna weights W
r1
to W
rM
are given by
W
r
(
i+
1)=
W
r
(
i
)+&mgr;
r
(
i−D
dem
)
e
*(
i
) (1)
where W
r
(i) (column vector having M elements) is the antenna weight of the ith symbol, r(i) (column vector having M elements) is the antenna reception signal, &mgr; is the step size, D
dem
is a delay time given by the delay circuit
15
, and * is the complex conjugate. From equation (1), the antenna weights W
rl
to W
rM
are updated every symbol. The adaptive control convergence step may use a known symbol instead of the determination symbol.
The M antenna reception signals S
1
to S
M
contain desired (user) signal components, interference signal components, and thermal noise. Each of the desired signal component and interference signal component contains a multipath component. In general, these signal components arrive from different directions. In forming a reception directional pattern, the conventional array antenna reception apparatus shown in
FIG. 1
uses an antenna having antenna elements laid out circularly. Thus, a directional pattern with almost uniform reception gains in all the signal arrival directions can be formed.
However, first, the conventional array antenna reception apparatus shown in
FIG. 1
cannot attain a high reception gain proportional to the number of antenna elements.
This is because the directional pattern with almost uniform reception gains in all the signal arrival directions is formed by circularly laying out antenna elements, and the reception gain cannot be optimized.
Second, as the number of antenna elements increases, the conventional array antenna reception apparatus shown in
FIGS. 1 and 2
decreases in adaptive convergence and stability in forming a directional pattern in the desired user direction.
This is because in the antenna having antenna elements laid out circularly, all the antenna elements must be simultaneously adaptively controlled.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation in the prior art, and has as its object to provide an array antenna reception apparatus which can attain a high reception gain proportional to the number of antenna elements and is excellent in adaptive control convergence and stability in forming a directional pattern in the user direction.
To achieve the above object, an array antenna reception apparatus according to the main aspect of the present invention is constituted as follows. Antenna elements are linearly laid out on each side (sector) of a polygon, a directional pattern for suppressing interference with another user or multipath is independently formed for each sector, and weighting synthesis is done between sectors. More specifically, the array antenna reception apparatus comprises an array antenna having M (M is an integer of not less
Maruta Yasushi
Yoshida Shousei
Dickstein , Shapiro, Morin & Oshinsky, LLP
NEC Corporation
Vo Don N.
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