Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
2002-02-04
2003-12-30
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C342S375000
Reexamination Certificate
active
06670919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an adaptive antenna receiving apparatus and, more particularly, to an adaptive antenna receiving apparatus which receives a CDMA (Code Division Multiple Access) signal and adaptively forms an antenna directional beam to receive a desired wave and also removes interference.
2. Description of the Prior Art
CDMA is expected as a radio access scheme for a mobile communication cellular system of next generation because of its capability of increasing the subscriber capacity. However, on the base station receiving side, simultaneously accessing user signals interfere with each other. To remove interference between user signals, an adaptive array antenna has been proposed.
An adaptive array antenna receives signals using a plurality of antennas, and weights and combines the received signals using complex numbers. Next, the adaptive array antenna forms a directional beam by controlling the amplitude and phase of the reception signal of each antenna. With this operation, only a desired user signal can be received. Additionally, any other user interference signal can be suppressed.
Two methods of determining the antenna weight of an adaptive antenna have been generally known.
As one method, a weight is determined by feedback control using an adaptive update algorithm such as LMS (Least Mean Square) or RLS in accordance with the MMSE (Minimum Mean Square Error) (feedback control method).
The other is an open loop control method in which the direction of arrival of a desired wave is estimated from an antenna reception signal by using an arrival direction estimating algorithm such as MUSIC or ESPRIT, and a beam is directed to that direction.
This open loop control method has an advantage that the antenna weight can be accurately calculated even from a short reception signal sequence, unlike the feedback control method. However, the arithmetic amount becomes large.
Japanese Unexamined Patent Publication No. 11-274976 has proposed “Array Antenna System at Radio Base Station” which uses a method of easily determining an antenna weight without using any complex arrival direction estimating algorithm in the open loop control method.
FIG. 1
shows an adaptive antenna receiving apparatus according to this prior art. This adaptive antenna receiving apparatus has L (L is a positive integer) path signal processing means
101
-
1
to
101
-L. As the number L, a number corresponding to a multipath transmission path in a mobile communication environment, i.e., the number of paths is employed such that the path signal processing means receive and demodulate CDMA signals.
The path signal processing means
101
-
1
to
101
-L have antenna weight calculation means
102
-
1
to
102
-L, beam formers
103
-
1
to
103
-L, and RAKE combining/weighting means
104
-
1
to
104
-L, respectively. The path #
1
signal processing means
101
-
1
will be described below. The description also applies to the path #
2
signal processing means
101
-
2
to path #L signal processing means
101
-L.
The antenna weight calculation means
102
-
1
has an antenna signal in-phase averaging means
106
-
1
, correlation-to-reference-antenna detection means
107
-
1
, and time averaging means
108
-
1
.
The antenna signal in-phase averaging means
106
-
1
improves the SINR by matching the phases of despread symbols of the respective paths and adding their vectors.
This operation cannot be performed when the symbols are modulated. However, in-phase addition can be done after modulation is canceled by a known pilot symbol using a pilot signal. The larger the number of symbols for in-phase averaging becomes, the more the SINR can be improved. However, it is limited if a quick phase variation is present due to fading or the like.
The antenna signal in-phase averaging means
106
-
1
can employ an arbitrary number of symbols to be averaged and an arbitrary method of weighting each symbol.
The correlation-to-reference-antenna detection means
107
-
1
detects the correlation between a reference antenna reception signal and the remaining antenna reception signals. More specifically, the correlation-to-reference-antenna detection means
107
-
1
multiplies the reception signal of another antenna by the complex conjugate signal of the reference antenna reception signal.
For example, antenna No.
1
is defined as a reference antenna. The output from the correlation-to-reference-antenna detection means
107
-
1
is given by
R
(
i,j,m
)=
Z
EL
(
i,j,m
)
Z*
EL
(
i
,1,
m
) (1)
where i (i is an integer; 1≦i≦L) is the path number, j (j is an integer; 2≦j≦N) is the antenna number, and m (m is a positive integer) is the output number of an output Z
EL
(i,j,m) from the antenna signal in-phase averaging means
106
-
1
.
FIG. 6
shows signals received by array antennas
61
-
1
to
61
-N (N is a positive integer). The signal received by each antenna has a phase lag depending on its direction of arrival. For example, the signal received by the antenna element
61
-
1
(reference antenna element) has a phase lag of (j−1)(2&pgr;d/&lgr;)sin &phgr;
0
with respect to the signal received by the jth antenna element
61
-j (j is an integer; 1<j≦N). In this case, &phgr;
0
is the direction of signal arrival, d is the interval between adjacent antennas, and &lgr; is the signal wavelength.
Hence, the phase of R(i, j, m) is ideally detected as (j−1)(2&pgr;d/&lgr;)sin &phgr;
0
.
The time averaging means
108
-
1
averages a plurality of outputs from the correlation-to-reference-antenna detection means
107
-
1
. An arbitrary time and method can be employed as an averaging time and weighting method to be used for this averaging. An output from the time averaging means
108
-
1
is an antenna weight w(i,j,m).
The beam former
103
-
1
weights and combines the respective antenna reception signal using the antenna weights w(i,j,m) output from the time averaging means
108
-
1
. That is, using the antenna weights calculated by the antenna weight calculation means
102
-
1
, despread signals are received by antenna directional beams for the respective paths.
FIG. 4
shows the arrangement of the beam former
103
-
1
of path #
1
. The number of antennas is N (N is a positive integer).
The beam formers
103
-
1
to
103
-L have complex conjugate means (
41
-
1
-
1
to N) to (
41
-L-
1
to N), multipliers (
42
-
1
-
1
to N) to (
42
-L-
1
to N), and combiners
43
-
1
to
43
-L, respectively.
Each of the complex conjugate means
41
-
1
-
1
to
41
-
1
-N calculates a complex conjugate w*(i, j, m) of the antenna weight w(i,j,m) (j in the antenna weight w and its complex conjugate w* is an integer; j≧1).
Each of the multipliers
42
-
1
-
1
to
42
-
1
-N multiplies a corresponding despread input in path #
1
by the complex conjugate w*(i, j, m) of the antenna weight.
The combiner
43
-
1
adds the outputs from the multipliers
42
-
1
-
1
to
42
-
1
-N, thereby calculating the beam former output.
The phase of the complex conjugate w*(i,j,m) of the antenna weight is ideally −(j−1)(2&pgr;d/&lgr;)sin &phgr;
0
. Hence, the beam former
103
-
1
acts to combine signals that have arrived from the direction &phgr;
0
such that the reception signals of the respective antennas and the reception signal of the reference antenna element
61
-
1
are in phase. In addition, since a signal that has arrived from a direction different from the direction &phgr;
0
is not in phase, a beam that has a gain in the direction &phgr;
0
and reduces gains in directions other than &phgr;
0
can be formed.
The RAKE combining/weighting means
104
-
1
compensates for a variation in phase of the output from the beam former
103
-
1
, i.e., phase of the reference antenna and weights the output to combine the paths (RAKE combining). That is, the RAKE combining/weighting means
104
-
1
weights the beam output of each path. This weighting is executed such that the SINR (Signal to Interference and Noise Ratio) after combining is maximized
NEC Corporation
Phan Dao
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