Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-02-12
2003-12-16
Trost, William (Department: 2683)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S335000, C455S025000, C455S276100
Reexamination Certificate
active
06665286
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an adaptive receiving device removing interference from other users by an antenna directivity control, more particularly to an adaptive receiving device for a CDMA (Code Division Multiple Assess).
In such a cellular mobile communication system, interference from other users and interference by delay waves are the dominant factors which determine a receiving quality. Methods for removing these interference by employing adaptive antennas are considered. On the other hands, a CDMA method which can be expected for capacity acceptable for a large subscribership is noted as a wireless transmission method. A method utilizing a spread process gain is proposed as a receiving device employing an adaptive antenna which is suitable for a CDMA method.
Conventionally, for this type of an adaptive receiving device for a CDMA, as indicated, for example, in Oh, Kohno and Imai: “An TDL adaptive array antenna using spread process gain for spectrum spread multi-dimension connections”, Communication Engineering Theory, Vol.J75-BII No. 11, pp. 815-825, 1992, and in Tanaka, Miki and Sawahashi: “Characteristic of decision feedback-type coherent adaptive diversity in DS-CDMA”, Communication Engineering Technical Report, RCS96-102, 1996-11, the effect of SINR improvement due to process gain in an adaptive control is obtained by utilizing weight control error signal taken after de-spreading upon an antenna weight controlling.
FIG. 7
is a block diagram showing an example of conventional CDMA adaptive receiving devices, and
FIG. 8
is a block diagram showing an adaptive receiving sub-block
27
m
for the m-th path in an adaptive receiving device for a CDMA of FIG.
7
. Here, an adaptive receiving device for a CDMA is represented in the case where the number of receiving antennas is N (N is an integer more than 1), the number of users is K (K is an integer more than 1), and the number of multi-path is M (M is an integer more than 1).
Each of receiving antenna
1
1
~
1
n
made of N pieces receives solicitation wave signals and a plurality of interference wave signals which are code-multiplexed. Receiving antenna
1
1
~
1
n
are arranged closely so that each receiving signal has the correlation with each other. The first adder
5
adds outputs of adaptive receiving sub-blocks
27
1
~
27
M
for the first~the M-th path, and outputs the k-th user demodulation signal. The decision circuit
6
performs hard decision for the first adder
5
, outputs the k-th user decision symbol.
The adaptive receiving sub-block for the m-th path is composed of the weighted synthesis circuit
7
, the first delay circuit
10
, the de-spreading circuit
11
, the demodulation circuit
12
, the third complex multiplier
15
, the error detection circuit
16
, the fourth complex multiplier
17
, the second delay circuit
18
, the third delay circuit
19
and the antenna weight control circuit
20
.
The adaptive receiving sub-block
27
m
for the m-th path inputs antenna receiving signal
1
~antenna signal N and the k-th user decision symbol which is an output outputted from the decision circuit
6
.
The weighted synthesis circuit
7
is composed of the first
10
complex multiplier
8
1
~
8
N
and the second adder
9
. A signal received by the m-th path inherent antenna directivity pattern is generated by multiplying antenna receiving signal
1
~antenna receiving signal N by antenna weight W
m1
antenna W
mN
and by adding them.
The first delay circuit
10
delays an output outputted from the weighted synthesis circuit
7
on the basis of path delay of an separately required solicitation wave signal corresponding to multi-path. The de-spreading circuit
11
computes the correlation between an output of the weighted synthesis circuit
7
and a spread code C
k
of the k-user. The modulation circuit
12
is composed of the transmission path estimate circuit
13
and the second complex multiplier
14
. An output which is multiplied the de-spreading circuit
11
by a complex conjugate of transmission estimate output becomes an output of adaptive receiving sub-block
27
m
for the m-th path.
The third complex multiplier
15
multiplies the k user decision symbol by a transmission path estimate output. The error detection circuit
16
computes the difference between an output of the third complex multiplier
15
and an output of the de-spreading circuit
11
, and detects detection errors. The fourth complex multiplier
17
multiplies a decision error by the k-user spread code C
k
, and generates a weight control error signal. The delay circuit
18
delays weight control error signals on the basis of path delay of the foregoing separately required solicitation signal so as to cancel out the effect of the first delay circuit
10
.
The third delay circuit
19
delays antenna receiving signal
1
~antenna receiving signal N in accordance with the processing time of the weighted synthesis
7
, the de-spreading circuit
11
, the demodulation circuit
12
, the error detection circuit
16
and the like. The antenna weight control circuit
20
computes antenna weight W
m1
~W
mN
from a weight control error signal which is an output of the second delay circuit
18
and an output of the delay circuit
19
.
By assuming a spread code C
k
as a complex code composed of a code of C
kI
and a code of C
kQ
which are in an orthogonal relationship of the two (2) affiliations, the de-spreading circuit
11
can be realized by one-piece of complex multiplier and an averaging circuit over a symbol interval. Moreover, the de-spreading circuit
11
can be also realized by a transversal filter component in the case of assuming C
k
as a tap weight.
In receiving signals from receiving antenna
1
1
~
N
of N pieces, a solicitation wave signal component, an interference wave signal component and thermal noise are included. Moreover, multi-path component exists in a solicitation wave signal component and in an interference wave signal component respectively. Conventionally, those signal components arrive from different directions.
A conventional adaptive receiving device for a CDMA shown in
FIGS. 7 and 8
, prepares adaptive receiving sub-block
27
1
~
27
M
for the first~the M-th path independently with respect to multi-path components and performs weighted synthesis of a receiving signal in each weighted synthesis circuit
7
so as to make solicitation wave signal-to-interference wave signal power rate (SIR) of signal components of each path to be the maximum value. As a result, as for antenna gain with respect to the arrival directions (directivity pattern) of adaptive receiving sub-block
27
1
~
27
M
for the first~the M-th path, it is formed so that it becomes larger with respect to the respective arrival directions of path signal components and becomes smaller with respect to other delay wave signal components and interference wave signal components
In order to improve the deterioration of adaptive control characteristic of a conventional adaptive receiving device for a CDMA shown in
FIGS. 7 and 8
in the case where the number of paths are large, the authors previously proposed an adaptive receiving device for a CDMA adding weight control error of all paths for each user (Japanese Patent Application No. H9-210336). This adaptive receiving device for a CDMA prepares a weighted synthesis circuit with respect to each user, and performs weighted synthesis of antenna weight and antenna receiving signal so as to make synthesis weight control error signal adding weight control error signal of all paths for each user to be the minimum value. As a result, one directivity pattern for each user is formed, antenna gain becomes larger with respect to the arrival directions of signal components of each path, and it becomes smaller with respect to the interference components. Since this method adds weight control error signals of all paths for each user, information of adaptive control becomes increasing, and its adaptive control characteristic is excellent even in the case where the number of paths is large.
Since a
Maruta Yasushi
Ushirokawa Akihisa
Yoshida Shousei
Torres Marcos L.
Trost William
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