Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
1998-08-31
2002-02-12
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S134000, C455S135000, C370S320000
Reexamination Certificate
active
06347220
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a wireless base station multiple-beam antenna system in DS-CDMA wireless communications. More particularly, the invention relates to a multiple-beam antenna system having an uplink beam forming function for performing reception upon applying uplink beam forming to signals that have been received by a plurality of antenna elements, and a downlink beam forming function for applying downlink beam forming to transmission signals in order to form a transmission beam in a prescribed direction.
Digital cellular wireless communication systems using DS-CDMA (Direct Sequence Code Division Multiple Access) technology have been developed as next-generation mobile communications systems for implementing wireless multimedia communication. In a communications system using DS-CDMA, interference between users is the main cause of a decline in channel capacity and transmission quality of cells. Research and development in regard to multiple-beam antennas and adaptive array antennas is being carried out in an effort to discover techniques for reducing such interference and improving transmission quality.
As shown in
FIG. 10
, a multiple-beam antenna performs reception using an array antenna AAT consisting of a plurality of element antennas AT
1
-AT
N
, and applies beam forming to antenna output signals by means of a beam former BMF to electrically form multiple beams B
1
-B
M
of prescribed directivity. Each beam of the multiple-beam antenna possesses a directivity pattern of the kind shown in FIG.
11
. Accordingly, radio waves emitted from an ith user (mobile station) residing in the directivity direction of beam
2
, for example, are received by the array antenna AAT and the beam former BMF outputs the beams B
1
-B
M
. The power of beam B
2
, however, is greater than that of the other beams B
1
, B
3
-B
M
. Data is subsequently demodulated by performing despreading using the beam B
2
. Thus, in accordance with a multiple-beam antenna, reception is performed upon selecting the optimum beam on a per-user (channel) basis, whereby there are obtained such effects as a reduction in interference between channels, an improvement in reception SN ratio owing to a higher antenna gain and a reduction in terminal transmission power.
The foregoing relates to a reception beam former which electrically forms the plurality of uplink reception beams B
1
-B
M
by applying uplink reception beam forming to the signals received by the plurality of antenna elements AT
1
-AT
N
of the array antenna AAT. However, a transmission beam former can be provided as well. More specifically, it is possible to provide a transmission beam former in such a manner that downlink transmission beam forming is applied to transmission signals to generate antenna element input signals and the signals are input to individual antenna elements, whereby beams having directivities in prescribed directions are output from the antenna.
FIG. 12
is a diagram showing the construction of a wireless base station using a transceiving multiple-beam antenna. An array antenna AAT
1
on the receiving side has a plurality of antenna elements ATR
1
-ATR
N
. An array antenna AAT
2
on the transmitting side has a plurality of antenna elements ATT
1
-ATT
N
. A reception beam former RBF electrically forms M-number of uplink reception beams B
1
-B
M
by applying uplink reception beam forming to signals that have been received by the N-number of antenna elements ATR
1
-ATR
N
. Channel receivers CHR
1
-CHR
K
are provided for respective channels (users or mobile units) and are equipped with despreading circuits, synchronous detection circuits and data identification circuits, etc. The output signals of the reception beam former RBF enter each of the channel receivers CHR
1
-CHR
K
. Channel transmitters CHT
1
-CHT
K
are provided for respective channels and are equipped with spreading circuits and quadrature modulation circuits, etc. Transmission data on respective channels enter respective ones of the channel transmitters CHT
1
-CHT
K
. A transmission beam former TBF generates antenna element input signals by applying downlink transmission beam forming to transmission signals (transmission beams) output from the channel transmitters.
As illustrated in
FIG. 13
, the reception beam former RBF multiplies output signals x
1
-x
N
of the respective antenna elements by weights W
k,i
to thereby implement phase rotation, and sums the products to electrically form M-number of uplink reception beams 1−M each having a prescribed directivity. If x
k
(nT
c
) represents the reception signals of N-number of antenna elements and W
k,i
represents a conversion coefficient of the beam former, then a signal y
i
(nT
c
) of an ith beam (i=1−M) will be expressed by the following:
y
i
(
nT
c
)=&Sgr;
W
k,i
·
x
k
(
nT
c
)(k=1−
N
) (1)
The direction (directivity) of each of the M beams can be applied to the array antenna by deciding the conversion coefficient W
k,i
. As a result, a transmission signal from a user (mobile station) in a prescribed ith directivity direction can be obtained from a terminal, e.g., the ith terminal, that corresponds to the ith directivity direction of the reception beam former RBF.
As illustrated in
FIG. 14
, the transmission beam former TBF splits a transmission signal (transmission beam) y
i
that enters an ith input terminal into N branches and multiplies each branch signal Y
i
by the weight W
k,i
(k=1−N) to implement phase rotation and generate a signal x
k
(k=1−N) that is input to a respective one of the N transmitting antennas. In this case, x
k
is represented by the following:
x
k
=W
k,i
·
y
i
(2)
The direction (directivity) of each of the M beams can be applied to the array antenna by deciding the conversion coefficient W
k,i
. As a result, if it is desired to make a transmission to a user (mobile station) in an ith transmission beam direction, the transmission signal y
i
should be input to the ith input terminal of the transmission beam former TBF.
Thus, multiple beams produced by the reception beam former RBF and multiple beams produced by the transmission beam former TBF are made to coincide. Consequently, in order to communicate with a user (mobile station) in the ith beam direction, it will suffice to despread the beam output by the ith output terminal of the reception beam former RBF and demodulate the data. In order to transmit data, it will suffice to input the transmission signal to the ith input terminal of the transmission beam former TBF. More specifically, reception signals x
i
(nT
c
) (i=1−N) from N-number of antenna elements ATR
1
-ATR
N
are amplified, detected and subjected to an A/D conversion by means that are not shown. The reception beam former RBF then digitally forms M-number of beams. That is, the reception beam former RBF obtains the signal y
i
(nT
c
) of each beam through the conversion expressed by Equation (1). Next, the reception beam former RBF performs despreading on a per-channel basis in regard to the plurality of beams formed and carries out uplink reception upon selecting the beam for which signal power after despreading is largest or the beam for which the correlation power between a pilot signal after despreading and a reference signal is largest. In case of downlink transmission, a transmission signal is input to the ith input terminal of the transmission beam former TBF in such a manner that the direction obtained will be the same as that of the beam that was selected at the time of uplink reception. As a result, the transmission array antenna AAT
2
radiates the transmission signal toward the user (mobile station) in the ith beam direction.
FIG. 15
shows another example of a beam former. This is a diagram showing the construction of the well-known Butler matrix (in the case of an 8-beam antenna).
FIG. 16
is a diagram useful in describing multiple beams formed by the Butler matrix.
The transmission beam former TBF in
FIG. 15
is obt
Kobayakawa Shuji
Tanaka Yoshinori
Tsutsui Masafumi
Rosenman & Colin LLP
Tran Conguan
Trost William
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