Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
2000-04-04
2001-09-18
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C342S378000
Reexamination Certificate
active
06292135
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an adaptive array antenna system in radio communication system for directivity control and waveform equalization.
An adaptive array antenna system controls directivity of an antenna system so that received waves which have high correlation with a desired signal are combined, and received waves which have low correlation with a desired signal are suppressed.
In an adaptive array antenna system, a directivity is controlled so that the square of an error between a receive signal and a reference signal is the minimum. If a directivity control of an adaptive array antenna system is ideally carried out, transmission quality is highly improved even under multi-path environment such as out of line-of-sight.
For comparison between a receive signal and a reference signal, synchronization of a receive signal must first be established. If synchronization is unstable, the operation of an adaptive array antenna itself becomes unstable. Therefore, the stable operation of synchronization is essential under severe environment with degraded transmission quality.
A prior adaptive array antenna system is shown in FIG.
34
. This is for instance shown in R. A. Monzingo and T. W. Miller, Introduction to Adaptive Arrays, John Wiley & Sons, Inc. 1980.
An adaptive array antenna system comprises N number of antenna elements A
511
through A
51
N, N number of complex weight means A
521
through A
52
N for giving a weight to an output of each antenna element, a weight control A
53
for control a weight of said complex weight means, a reference signal generator A
54
, and a combiner A
55
for combining weighted signals.
A value of weight (W
opt
) for forming directivity so that the square of error between a desired signal and a receive signal is the minimum, is expressed in the equation (1), where signals received in N number of antennas are x
1
through xN, weights in weight means A
521
through A
52
N are w
1
through wN, and d is a desired signal.
w
opt
=R
xx
−1
r
xd
(1)
where
R
xx
=E(x*x
T
) (2)
r
xd
=
(
x1
d
*
_
|
|
|
|
|
xn
d
*
_
)
(
3
)
x
=
(
x1
|
|
|
|
|
xN
)
W
opt
=
(
w1
|
|
|
|
|
wN
)
(
4
)
In equations (2) and (3), R
x
is correlation matrix between antenna elements, E(P) is expected value of (P). The symbols x* and d* are conjugate of x and d, respectively. x
T
is transposed matrix of matrix x in the equation (4), and R
xx
−1
is inverse matrix of R
xx
. The equation (2) shows that the correlation matrix R
xx
between antenna elements is a product of a conjugate of a matrix x and a transposed matrix x
T
of a matrix x. In the equation (3), the value r
xd
is a matix of average of a product of a receive signal x
1
through xN received by each antenna elements, and a conjugate of a desired signal component d.
In an adaptive array antenna system, a directivity is controlled so that an error between an output signal and a desired signal is the minimum. Therefore, the error is not the minimum until the directivity converges, and in particular, the error is large during the initial stage of the directivity control. when the error in the initial stage is large, carrier synchronization and timing synchronization are unstable, so that a frequency error and a timing error from a desired signal can not be detected. Thus, the value r
xd
might have large error, and an adaptive array antenna system does not operate correctly.
FIG. 35
shows a block diagram of a prior adaptive array antenna system having N number of antenna elements, and forming a directivity beam before synchronization is established. This is described in “Experiment for Interference Suppression in a BSCMA Adaptive Array Antenna”, by Tanaka, Miura, and Karasawa, Technical Journal of Institute of Electronics, Information and Communication in Japan, Vol. 95, No. 535, pages 49-54, Feb. 26, 1996.
In the figure, the symbols A
611
through A
61
N are a plurality of antenna elements, A
621
through A
62
N are A/D converters each coupled with respective antenna element, A
63
is an FFT (Fast Fourier Transform) multibeam forming means for forming a plurality of beams through FFT process by using outputs of the A/D converters A
621
through A
62
N, A
64
is a beam selection means for selecting a beam which is subject to weighting among the beams thus formed, and A
65
is an adaptive beam control means for controlling a selected beam. The beam selection means A
64
selects a beam which exceed a predetermined threshold, then, a directivity of an antenna is directed to a direction of a receive signal having high power. Thus, synchronization characteristcs are improved.
However, when signal quality is degraded because of long delay longer than one symbol length, and/or interference, no correlation is recognized between signal quality and receive level. In that environment, the prior art which forms a plurality of beams through FFT process, and selects a beam which exceeds a threshold, is not practical.
Further, the prior art which forms a plurality of beams through FFT process, and selects a beam which exceeds a threshold, needs much amount of calculation for measuring signal quality. Further, it has the disadvantage that an adaptive array antenna does not operate correctly because of out of synchronization in an indoor environment which generates many multi-paths.
Next, a prior art for establishing synchronization is described.
FIG. 36
shows a block diagram of a prior adaptive array antenna which uses a transversal filter. This is described in “Dual Diversity and Equalization in Digital Cellular Mobile Radio”, Transaction on VEHICULAR TECHNOLOGY, VOL. 40, No. 2, May 1991.
In the figure, the numerals
14011
through
1401
N are antenna elements,
1402
is a beam forming circuit,
14031
through
1403
N are first weight means,
1404
is a first combiner,
1405
is a transversal filter,
14061
through
1406
M are delay elements,
14070
through
1407
M are second weight means,
1408
is a second combiner,
1412
is an automatic frequency control,
1413
is a timing regeneration circuit,
14141
through
1414
N are A/D (analog to digital) converters.
FIG. 37
shows a detailed block diagram of first weight means
14031
through
1403
N, and second weight means
14070
through
1407
M. In the figure,
14091
through
14094
are multipliers for real values,
1410
is a subtractor for real values, and
1411
is an adder for real values.
1415
is a clock generator.
The timing regeneration circuit
1413
regenerates a clock signal which is the same as that of a receive signal. The A/D converters
14141
through
1414
N carry out the A/D conversion of a receive signal by using the regenerated clock signal, and the converted signal is applied to the beam forming circuit
1402
.
Assuming that an output signal of the beam forming circuit
1402
is y
b
(t), the weights cO through cM of the second weight means
10470
through
1047
M are determined so that the following equation is satisfied.
C=R
t
−1
r
txd
(5)
where R
t
is matrix having (M+1) columns and (M+1) lines, having an element on i'th line and j'th column;
E[y
b
(t−(i−1)(T
S
/a)y
b
(t−(j−1)(T
S
/a)*] (6)
and r
txd
is a vector of (M+1) dimensions, having i'th element;
E[y
b
(t−(i−1)(T
S
/a)d(t)*]
where Ts is symbol length of a digital signal, and (a) is an integer larger than 2.
In the above prior art, a signal at each antenna elements is essential, and therefore, a receive signal at an antenna element is converted to digital form by using an A/D converter. However, if sampling rate in A/D conversion differs from receive signal rate, the algorithm of minumum mean square error can not be used at a beam forming network, since a beam forming circuit would be controlled by a data with no timing compensation.
Further, the prior art has the disadvantage that the operation is unstable, since waveform equalization is carried ou
Cho Keizo
Hori Toshikazu
Nishimori Kentaro
Takatori Yasushi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Nippon Telegraph and Telephone Corporation
Phan Dao
LandOfFree
Adaptive array antenna system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Adaptive array antenna system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive array antenna system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2439503