Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1998-07-10
2002-11-26
Nguyen, Chau (Department: 2663)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C375S227000, C455S069000
Reexamination Certificate
active
06487174
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transmitting electric power control apparatus used in a digital mobile communicating system.
In a digital mobile communicating system, transmitting electric power control is used for suppressing consumption of electric power at a mobile station while maintaining reception quality at a desired value, and for avoiding i,unnecessary interference with other mobile stations. Especially, in a CDMA (Code Division Multiple Access) system, due to the existence of common frequency interference (interference with other users) inherent in a multiple system, the transmitting electric power control is essential. In the CDMA system, generally, closed-loop type transmitting electric power control is used, in which a Signal-to-Noise Power Ratio (referred to as an S/N, hereinafter) is measured from a signal received and demodulated at a base station, instruction is sent to the mobile station so that this S/N value will be a value enough for desired reception quality, and transmitting electric power is sequentially controlled. A noise N used here includes a thermal noise and an interference signal. In order to conduct transmitting electric power control with good accuracy, it is necessary to correctly measure the S/N in a receiving device.
As an S/N measuring method, there is a technology shown in JP-B-50738/1992 (referred to as a first prior art, hereinafter).
FIG. 4
is a view showing an SIN measuring circuit of the first prior art. As shown in
FIG. 4
, an S/N measuring circuit
50
of the first prior art is constructed of a modulation removing circuit
3
connected to an analog-digital (A/D) converter
2
, a first averaging circuit
4
, a first square operating circuit
5
, a second square operating circuit
6
connected to the analog-digital (A/D) converter
2
, a second averaging circuit
7
, a subtracting circuit
8
, and a dividing circuit
9
.
In this first prior art, first, a demodulated reception signal is sampled at a modulation clock by the A/D converter
2
. In the S/N measuring circuit, after a modulated component of an output of the A/D converter
2
is removed in the modulation removing circuit
3
, the output is averaged over a plurality of symbol sections in the first averaging circuit
4
, and an amplitude value in which a noise component is suppressed is obtained. An output of the first averaging circuit
4
is squared by the first square operating circuit
5
, and desired signal power S is obtained.
On the other hand, an output of the A/D converter
2
is supplied to the second square operating circuit
6
, and is converted into time series having a dimension of electric power. Thereafter, the output is averaged over a plurality of symbol sections by the second averaging circuit
7
, and total electric power P of demodulated signals is obtained. The subtracting circuit
8
obtains noise electric power N by subtracting the desired signal power S from the total electric power P of the demodulated signals. The dividing circuit
9
receives the obtained S and N as above, and calculates a ratio S/N thereof.
If representing the above-mentioned operation by an equation, it is represented as an equation (1) below. A series of sampled values of demodulated signals are assumed as r
k
(k=1, 2, . . . , M, M is a positive integer.). If an amplitude of a signal point in which a noise is suppressed is A, the desired signal power S is shown by two equations described below.
A
=
1
M
∑
k
=
1
M
r
k
r
^
k
(
r
^
k
is a decision symbol.
)
(
1
)
S=|A
|
2
(2)
Hereupon, a noise component superimposed over a demodulated signal shows a Gaussian distribution of which center is at the amplitude A of the signal point in the absence of the noise, and the noise electric power N is given by the following equation (3):
N
=
1
M
∑
k
=
1
M
(
r
k
r
^
k
*
-
A
)
2
(
3
)
The above-described equation (3) can be transformed into the following equations (4) to (7):
N
=
1
M
∑
k
=
1
M
(
r
k
r
^
k
*
-
A
)
2
(
4
)
=
1
M
∑
k
=
1
M
&LeftBracketingBar;
r
k
r
^
k
*
&RightBracketingBar;
2
-
2
A
1
M
∑
k
=
1
M
r
k
r
^
k
*
+
A
2
(
5
)
=
1
M
∑
k
=
1
M
&LeftBracketingBar;
r
k
r
^
k
*
&RightBracketingBar;
2
-
A
2
(
6
)
=
P
-
S
(
7
)
In other words, by subtracting the desired signal power S from the total electric power P of the reception signals, the noise electric power N is obtained. Although the first prior art of
FIG. 4
is a simple arrangement based on the above-described equation (7), an arrangement based on the above-described equation (4) is naturally considered, and these arrangements are equal to each other in principle.
However, in this technology, in case that the received S/N is low, since there is an error in a decision signal and accuracy of inverse modulation by means of the decision signal deteriorates, a non-linear bias in which a measured S/N value appears higher is observed as the received S/N is lower.
FIG. 5
is a view showing a conventional transmitting electric power control apparatus using the S/N measuring circuit shown in FIG.
4
. In
FIG. 5
, a base station
51
includes a demodulator
11
connected to an antenna, a decoder
12
, a target S/N control circuit
52
, an adder
13
, a decision device
14
, a TPC bit generating circuit
15
, and a transmitter
16
connected to an antenna. The target S/N control circuit
52
includes a reception quality measuring circuit
61
, an adder
62
, a decision device
63
and a target S/N determining circuit
64
. Also, a mobile station
53
includes a demodulator
21
connected to an antenna, a TPC bit decoder
22
, a transmitting electric power determining circuit
23
, a transmitter
24
, and an encoder
25
.
In the transmitting electric power control apparatus of
FIG. 5
, demodulated signals demodulated by the demodulator
11
are sampled at a modulation clock by the A/D converter
2
. A series of sampled values of the demodulated signals that are outputs of the A/D converter
2
are input to the decoder
12
, and information signals after the decoding are obtained. On the other hand, an output of the A/D converter
2
is supplied to the S/N measuring circuit
50
. The S/N measuring circuit
50
has the same arrangement as the S/N measuring circuit
50
shown in
FIG. 4
, and in the S/N measuring circuit, a non-linear bias in which a measured S/N value appears higher is observed as the received S/N is lower. Accordingly, if transmitting electric power control is conducted using the measured S/N output from the S/N measuring circuit
50
, transmitting electric power of the mobile station is decreased more than it needs, and reception characteristic rapidly deteriorates. In order to solve this, a method of correcting a bias of the measured S/N value is proposed, in which reception quality such as a bit error ratio is monitored separately, and the control target S/N value itself is adaptively changed in accordance with the reception quality. This is generally called an outer-loop, and there is a literature “An Overview of the Application of Code Division Multiple Access (CDMA) to Digital Cellular Systems and Personal Networks” (Document EX60-10010, Qualcolm Incorporated, San Diego, May 1992.).
In the target S/N control circuit
52
shown in
FIG. 5
, the reception quality measuring circuit
61
receives an information signal decoded in the decoder
12
, and measures reception quality. The adder
62
obtains a difference between the reception quality measured by the reception quality measuring circuit
61
and target reception quality, and supplies the difference to the decision device
63
. The decision device
63
determines an amount of increase or decrease of the target S/N based on the output from the adder
62
. The target S/N determining circuit
64
determines the target S/N based on the amount of the increase or decrease of the
Mizuguchi Hironori
Ushirokawa Akihisa
Yoshida Shousei
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