Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-08-31
2002-05-07
Ton, Dang (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000
Reexamination Certificate
active
06385181
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a wireless base station array antenna system in CDMA wireless communications. More particularly, the invention relates to an array antenna system for generating multiple beam signals split into an angle for each path of multipaths by an array antenna and beam former and combining the beam signals via a finger unit (despreader/delay-time adjustment unit) for each path to thereby demodulate received data.
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 such CDMA communications, transmission information from a plurality of channels or users is multiplexed by spreading codes that differ from one another and transmitted via a transmission path such as a wireless link.
In wireless communications, radio waves from a transmitter arrive at a receiver via several paths (multipaths) having different path lengths. The receiver combines the radio waves. However, the combining of the radio waves is not performed by coherent addition, as a result of which fading occurs. Various diversity schemes have been proposed to deal with such fading. One example is a Rake receiving scheme. Rake reception is a technique which involves identifying signals that have passed through multipaths and combining the signals (by maximum-ratio combining) upon weighting them for reliability, thereby improving the characteristic. A receiver employing such Rake reception in CDMA communication has been proposed as a Rake receiver.
FIG. 19A
is a block diagram showing the construction of the prior-art Rake receiver, and
FIG. 19B
is a diagram useful in describing the delay profile thereof.
Shown in
FIG. 19A
are a searcher
1
, fingers
2
1
-
2
3
each of which is provided for a path of multipaths, a Rake receiver antenna
3
, a Rake combiner
4
for combining the outputs of the fingers, and a decision unit
5
for deciding the “1”s and “0”s of received data based upon the output of the combiner
4
.
As shown in
FIG. 19B
, the reception level of the signal sent from a transmitter varies in the receiver in dependence upon each path of the multipaths, and the times of arrival at the receiver differ as well. The searcher
1
(1) measures the profile of the antenna reception level (the temporal transition characteristic of the level), (2) detects the multipaths from multipath signals MP
1
, MP
2
, MP
3
, which are higher than a threshold level, by referring to the profile, (3) identifies delay times from signal occurrence times t
1
, t
2
, t
3
of respective paths of the multipaths or from a reference time, and (4) inputs despreading start timings s
1
-S
3
and delay-time adjustment data d
1
-d
3
to the fingers
2
1
,
2
2
,
2
3
, respectively, that correspond to the respective paths.
The searcher
1
includes a matched filter
1
a
, which outputs the autocorrelation of a desired signal contained in the received signal.
FIG. 19A
illustrates the construction of one channel of a base station. That is, the reception output of the antenna
3
contains other channel components as well. The matched filter
1
a
uses the spreading code of its own channel to extract the signal component of its own channel from the antenna reception signal. The extracted signal component is delivered as the output. More specifically, when a direct sequence signal (DS signal) that has experienced multipath effects enters the matched filter
1
a,
the latter outputs a pulse train having a plurality of peaks conforming to arrival times and signal strengths and stores the pulse train in a RAM
1
c
via a low-pass filter
1
b.
A path detector
1
d
refers to the profile (
FIG. 19B
) that has been stored in the RAM
1
c
to detect each path constituting the multipaths as well as the delay times, and inputs the start signals s
1
-s
3
, which indicate the timings (chip synchronization timings) of the start of despreading, as well as the delay time adjustment data d
1
-d
3
, to the respective fingers
2
1
,
2
2
,
2
3
corresponding to the paths.
The fingers
2
1
,
2
2
,
2
3
corresponding to the respective paths are identically constructed and each includes a spreading code generator
2
a
for generating the spreading code assigned to its own channel, a multiplier
2
b
for multiplying the antenna reception signal by the spreading code to thereby despread the signal, a dump integrator
2
c
for performing dump integration, a delay time adjustment unit
2
d
for subjecting the despread signal to a time delay adjustment that conforms to the path, an arithmetic unit
2
e
which performs an operation for channel estimation, and a multiplier
2
f
for multiplying the input to the arithmetic unit
2
e
by the complex conjugate of the output thereof to estimate the channel and output a desired signal wave component corresponding to the channel. The complex conjugate is obtained by reversing the sign of the imaginary portion of the complex number. If the complex number is I+jQ, then the complex conjugate thereof is I−jQ.
FIG. 20
is a diagram useful in describing the channel estimation operation. Shown in
FIG. 20
is a transmitting antenna
3
′ of a mobile station, the antenna
3
of the base station, the arithmetic unit
2
e
that performs the operation for channel estimation of the finger, the multiplier
2
f,
and a complex conjugate arithmetic unit
2
f
′ for outputting the complex conjugate. Let's represent a signal transmitted from the transmitting antenna
3
′ to the destination of the base station,
the influence of the wireless path and r the reception output of the base station. The arithmetic unit
2
e
outputs the product rs* of the input signal r and desired signal s. Accordingly, the output of the arithmetic unit
2
e
is
rs
*
=
s
ξ
s
*
=
ξ
&LeftBracketingBar;
s
&RightBracketingBar;
2
∝
ξ
If there is no fluctuation in amplitude, the output of the complex conjugate arithmetic unit
2
f
′ becomes
*, and the output of the multiplier
2
f
becomes
r
ξ
*
=
s
ξξ
*
=
s
&LeftBracketingBar;
ξ
&RightBracketingBar;
2
∝
s
In other words, if the amplitude does not fluctuate, the signal s that was transmitted to itself is obtained from the multiplier
2
f.
Accordingly, the arithmetic unit
2
e
and multiplier
2
f
in
FIG. 19A
estimate and output the signal component of their own channel.
Thus, the fingers
2
1
-
2
3
corresponding to the respective multipaths despread the corresponding multipath signals MP
1
-MP
3
by multiplying them by the spreading codes allocated to the channels and adjust the delays of the despread signals by the path delay times to make the timings agree. The Rake combiner
4
performs maximum-ratio combining of the finger outputs, and the decision unit
5
decides the received data based upon the output of the combiner.
Base station antennas of DS-CDMA communications system currently employ sector antennas. As shown in
FIG. 21A
, the 360° perimeter of a base station is equally divided to split a cell into a plurality of sectors SC. A sector antenna is an antenna is that allocated to each sector SC. Since there is no directionality within a sector, the antenna is susceptible to interference from other users. Such interference from other users is the main cause of a decline in channel capacity and transmission quality. 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. If the multiple-beam approach is adopted, a directivity pattern is produced, as shown in
FIG. 21B
, to reduce the susceptibility to interference from other users and improve transmission quality.
As shown in
FIG. 22
, a multiple-beam antenna performs reception using an array antenna AAT
Kobayakawa Shuji
Tanaka Yoshinori
Tsutsui Masafumi
Fujitsu Limited
Rosenman & Colin LLP
Ton Dang
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