Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-02-26
2002-12-10
Deppe, Betsy L. (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000, C375S347000, C370S342000, C342S378000
Reexamination Certificate
active
06493379
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an arrival direction estimation method using an array antenna for estimating an arrival direction of a desired signal. The present invention further relates to a DS-CDMA receiver unit in a Direct Sequence Code Division Multiple Access (DS-CDMA) system.
In a base station of a DS-CDMA communication system, signal reception is performed by utilizing an array antenna. Further, an arrival direction of a desired signal is estimated from signals received from the array antenna. By transmitting and receiving in a beam directed in the estimated arrival direction, it is possible to reduce both interference and required transmission power due to an increase in antenna gain. Therefore, it is desirable that the arrival direction of the desired signal is estimated accurately.
FIG. 7
is a diagram showing a receiver unit of a base station using an array antenna. In particular,
FIG. 7
shows array antenna elements
71
-
0
through
71
-(M−1) forming a receiving antenna, reception processors
72
-
0
to
72
-(K−1), despreading units
73
-
0
to
73
-(M−1), beam forming unit
74
, a channel receiver
75
, an arrival direction estimation unit
76
and a beam former
77
.
Received signals r
(0)
to r
(M−1)
from the array antenna elements
71
-
0
to
71
-(M−1) are input to the reception processors
72
-
0
through
72
-(K−1) corresponding to the different channels. In addition, the reception processor
72
-
0
carries out a despreading process with respect to the received signals by the despreading units
73
-
0
to
73
-(M−1), which are input with a spreading code C
0
. The despreading units
73
-
0
to
73
-(M−1) provide despread output signals x
(o)
to x
(M−1)
to the arrival direction estimation unit
76
and the beam former
77
of the beam forming unit
74
. The arrival direction estimation unit
76
estimates an arrival direction of a desired signal based on a cross-correlation function among the received signals received by adjacent antenna elements.
The beam former
77
multiplies a weighting coefficient obtained by estimating the arrival direction by the arrival direction estimation unit
76
to the despreading output signals x
(0)
through x
(M−1)
. Further, the beam former
77
then combines the products to provide an output signal to the channel receiver
75
.Therefore, received data of the kth channel is re-generated by the reception processors
72
-
0
to
72
-(K−1) corresponding to channels
0
through K−1.
FIG. 8
is a diagram showing a conventional beam forming unit
74
including the arrival direction estimation unit
76
. In particular,
FIG. 8
shows the beam forming unit
74
including an arrival direction estimation unit
76
and a beam former
77
having multipliers
78
-
0
to
78
-
3
and an adder
79
.
Received signals x
(0)
(n) to x
(3)
(n) from the antenna elements
71
-
0
to
71
-
3
(refer to
FIG. 7
) are input to the arrival direction estimation unit
76
and the beam former
77
. The arrival direction estimation unit
76
outputs to the beam former
77
weighting coefficients a
0
to a
3
obtained by the estimation of the arrival direction of the desired signal. The weighting coefficients a
0
to a
3
are respectively input to the multipliers
78
-
0
to
78
-
3
of the beam former
77
to be multiplied with signals x
(0)
(n) to x
(3)
(n) and then coherently summed by the adder
79
. An output signal y(n) of the adder
79
is then input to the channel receiver
75
(refer to FIG.
7
).
FIG. 9
is a diagram showing a conventional arrival direction estimation unit. In particular,
FIG. 9
shows an arrival direction estimation unit
76
including correlation calculators
81
-
0
through
81
-
2
, an adder
82
, and an array weighting coefficient calculator
83
. A correlation calculator
81
is shown in the lower part of
FIG. 9
, wherein each of the correlation calculators
81
-
0
to
81
-
2
include a multiplier
84
and an averaging filter
85
. Further, received signals x
(m)
(n) and x
(m+1)
(n) from mth and (m+1)th adjacent antenna elements are input to the multiplier
84
. In this case, one of the received signals is a complex conjugate (indicated by *), and a complex conjugate product between the received signals from the adjacent antenna elements (cross-correlation function of the zero lag) is obtained. A temporal average is also performed by the averaging filter
85
so that a cross-correlation function R
(m)
is output.
A received signal r
(m)
(t) from a mth antenna element at a time t satisfying (n−1)T≦t<nT is described by the following formula (1), where ø
i
(m)
for I=0 to N−1 in formula (1) is described by formula (2), N denotes a number of users, A
i
denotes a received amplitude of an ith user signal, c
i
(t) denotes a spreading code of the ith user, &tgr;
i
denotes a relative delay of the ith user, b
i
denotes an ith user transmission symbol, d denotes a distance between the antenna elements, &thgr;
i
denotes an arrival angle of the ith user signal, N
(m)
(t) denotes a noise signal, T denotes a symbol length, and a multipath is not taken into consideration for the sake of convenience.
r
(
m
)
(
t
)
=
∑
i
=
0
N
-
1
A
i
c
i
(
t
-
τ
I
)
b
(
t
-
τ
i
)
exp
(
-
j
φ
(
m
)
)
+
N
(
m
)
(
t
)
(
1
)
φ
i
(
m
)
=
2
π
md
sin
θ
i
(
2
)
A despreading output signal x
(k)
(m)
(n) which is obtained by subjecting the received signal r
(m)
(t) from the mth antenna element to a despreading process by the spreading code c
(k)
(t) of the kth user is described by the following formula (3), where w
ij
(n) in the formula (3) is described by the formula (4).
x
k
(
m
)
(
n
)
=
∫
(
n
-
1
)
T
n
T
r
(
m
)
(
t
)
c
k
*
(
t
-
τ
k
)
ⅆ
t
=
A
k
b
k
(
n
)
exp
(
-
j
φ
(
m
)
)
+
∫
(
n
-
1
)
T
n
T
[
∑
i
=
0
i
≠
k
N
-
1
A
i
c
i
(
t
-
τ
i
)
c
k
*
(
t
-
τ
k
)
b
i
(
t
-
τ
i
)
exp
(
-
j
φ
(
m
)
)
]
ⅆ
t
+
N
(
m
)
(
n
)
=
A
k
b
k
(
n
)
exp
(
-
j
φ
(
m
)
)
+
∑
i
=
0
i
≠
k
N
-
1
[
∫
(
n
-
1
)
T
n
T
c
i
(
t
-
τ
i
)
c
k
*
(
t
-
τ
k
)
b
i
(
t
-
τ
i
)
ⅆ
t
]
exp
(
-
j
φ
(
m
)
)
+
N
(
m
)
(
n
)
≅
A
k
b
k
(
n
)
exp
(
-
j
φ
(
m
)
)
+
∑
i
=
0
i
≠
k
N
-
1
[
A
i
w
ij
(
n
)
exp
(
-
j
φ
i
(
m
)
)
]
+
N
(
m
)
(
n
)
(
3
)
w
ij
(
n
)
≡
∫
(
n
-
1
)
T
n
T
c
I
(
t
-
τ
i
)
c
k
*
(
t
-
τ
k
)
bi
(
t
-
τ
i
)
ⅆ
t
(
4
)
In addition, the correlation calculator
81
of
FIG. 9
calculates a correlation R
k
(m)
between the received symbol x
(m)
(n) of the mth antenna element and the received s
Kobayakawa Shuji
Tanaka Yoshinori
Tsutsui Masafumi
Deppe Betsy L.
Fujitsu Limited
Katten Muchin Zavis & Rosenman
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