Adaptive array transmitter receiver

Details Adaptive array transmitter receiver Adaptive array transmitter receiver

1998-08-27

2001-06-05

Pham, Chi (Department: 2631)

Pulse or digital communications

Transceivers

C375S285000, C375S232000

Reexamination Certificate

active

06243412

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an adaptive array transmitter-receiver that suppresses degradation of the transmission performance due to interference signals and intersymbol interference in digital radio communications and, more particularly, to an adaptive array transmitter-receiver in a TDD system which uses the same carrier frequency in both uplink and downlink channels.
PRIOR ART
In digital mobile communications, the spatial reuse of the same frequency is adopted for the purpose of efficient utilization of frequency and one of significant challenges thereto is countermeasures against cochannel interference. An adaptive array, which is a kind of interference canceller, is one of promising techniques therefor; referring first to
FIG. 1
, its operation will be described, by way of example, in connection with reception by a base station under the uplink channel. With the adaptive array, it is possible to suppress interference signals through adaptive control of the directivity
10
of the array antenna
11
in its entirety by combining received signals from its plural antennas while controlling their phases and amplitudes. In the example of
FIG. 1
, in the case of receiving transmitted signals from a mobile station M
1
, a base station BS decreases the antenna gain of the array antenna
11
in the directions of interfering mobile stations M
2
and M
3
to suppress received signals therefrom, i.e. interference signals, while at the same time increasing the antenna gain in the direction of the mobile station M
1
to receive the desired signal at a sufficiently high level.
FIG. 2
depicts the frame structure in the TDD (Time Division Duplex) system. In the TDD system, as shown in FIG.
2
-Row A, for example, the mobile stations M
1
, M
2
and M
3
time-share carriers of the same frequency, besides each mobile station uses the same carrier frequency over its uplink UL and downlink DL. Accordingly, as shown in FIG.
2
-Row B, for example, the mobile station M
1
sends a signal in burst form to the base station over the uplink UL of a given time slot and receives a signal in burst form from the base station over the downlink DL. Each burst signal is composed of a training signal TR and a data signal DATA following it, and the uplink burst signal and the downlink burst signal are adjacent but separated by a guard time T
G
from each other. Hence, uplink and downlink channel impulse responses could be regarded as substantially the same unless they undergo sharp variations during the uplink and downlink burst. The guard time T
G
is determined taking into account a relatively long transmission delay of the channel.
In such a system that employs the same carrier frequency for the uplink and the downlink as in the TDD system, since adjoining uplink and downlink burst signals can be regarded as propagating over substantially the same channel, the uplink and downlink channel impulse responses can also be considered the same. Accordingly, if the pattern of a receiving antenna gain obtained over the uplink is used as a transmitting antenna pattern over the downlink, it is possible to reduce interference with reception at the mobile station in the downlink. This will be described with reference to
FIG. 1
; if the receiving antenna gain
10
is used as the transmitting antenna pattern, no radio waves are sent toward the mobile stations M
2
and M
3
but radio waves are sent in the direction of the mobile station M
1
, so that interference at the mobile stations M
2
and M
3
can be suppressed.
An adaptive array transmitter-receiver utilizing this transmission system is described, for example, in Shigeru TOMISATO and Tadashi MATSUMOTO, “Performances of Adaptive Transmission Array in TDD Mobile Communication Systems,” B-5-87, 1997 IEICE General Conference; its configuration is shown in
FIG. 3
with some parts supplemented. Incidentally, it is assumed in
FIG. 3
that the sampling period T
S
of a receiver baseband signal is equal to the modulation symbol duration T.
Having passed through duplexers
12
1
to
12
Q
from Q (where Q is an integer equal to or greater than 2) transmitting-receiving antennas forming the array antenna
11
, received signals are converted, by baseband signal generators
13
1
to
13
Q
respectively corresponding thereto, to baseband signals, which are fed as received baseband signals to output terminals
14
1
to
14
Q
. The received baseband signals each have an in-phase and a quadrature component, and the baseband signal generators
13
1
to
13
Q
shown in
FIG. 3
constitute a receiving part
13
. All the baseband signals will hereinafter be given in complex notation with the in-phase and quadrature components denoted as the real and imaginary parts, respectively. The received baseband signals x
1
(i) to x
Q
(i) corresponding to the high-frequency signals from the transmitting-receiving antennas
11
1
to
11
Q
are multiplied by weighting coefficients w
1
* to w
Q
* in complex multipliers
15
1
to
15
Q
, respectively, and the multiplier outputs are added together by a complex adder
16
, from which the resulting combined signal y(i) is output. By adaptive control of the weighting coefficients w
1
* to w
Q
*, the directivity of the receiving antenna gain of the array antenna
11
can be controlled, and consequently, the combined signal y(i) can be generated so that interference signals are suppressed. The complex multipliers
15
1
to
15
Q
and the complex adder
16
make up a linear combination part
20
. A decision unit
17
makes a hard decision on the combined signal y(i) and outputs a decision signal via an output terminal
18
.
Assume that a known training signal is used for initial convergence of parameter estimation and that the received signal is sent in burst form with the training signal followed by the data signal as referred to previously with reference to
FIG. 2. A
switching circuit
19
outputs the training signal from a training signal memory
21
during the training signal period, and during the following data signal period outputs the decision signal. A complex subtractor
22
outputs, as an error signal e(i), the difference between the output from the switching circuit
19
and the combined signal from the complex adder
16
. The decision unit
17
, the switching circuit
19
, the training signal memory
21
and the complex subtractor
22
make up a signal decision part
24
. A parameter estimation part
23
inputs thereinto the received baseband signals x
1
(i) to x
Q
(i) and the error signal e(i), and estimates the weighting coefficients w
1
* to w
Q
* through the use of a least mean squares algorithm so that a mean-squared value of the error signal e(i) is minimized.
On the other hand, a transmitted signal is input via an input terminal
25
and a hybrid
26
into complex multipliers
27
1
to
27
Q
. The complex multipliers
27
1
to
27
Q
multiply the transmitted signal by the abovementioned weighting coefficients w
1
* to w
Q
*, respectively. This is equivalent to an operation of matching the transmitting antenna pattern with the receiving antenna pattern. The hybrid
26
and the complex multipliers
27
1
to
27
Q
constitute a transmitted baseband generation part
30
. Q output signals from the complex multipliers
27
1
to
27
Q
are converted by RF modulated wave generators
28
1
to
28
Q
into RF frequency band signals, which are fed via the duplexers
12
1
to
12
Q
to the transmitting-receiving antennas
11
1
to
11
Q
respectively corresponding thereto, from which they are transmitted. The RF modulated wave generators
28
1
to
28
Q
make up a transmitting part
28
.
The received baseband signal generators
13
1
to
13
Q
and the RF modulated wave generators
28
1
to
28
Q
perform down-conversion and up-conversion of frequency using a carrier signal which is generated by a carrier signal generator
29
. In
FIG. 4
there is depicted the configuration of the received baseband signal generator
13
q
(q=1, . . . , Q). The received signal input via an input terminal
31
q is amplified by a low-

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