Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1998-10-21
2002-09-10
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C455S272000
Reexamination Certificate
active
06449268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital radio communication system, a reception system for a PDMA radio base station, and a method of calculating a weight vector. More particularly, the present invention relates to a digital radio communication system of the PDMA (Path Division Multiple Access) system having the function to calculate a weight vector by which a reception signal is multiplied to separate a desired signal from the signal received at a base station from a mobile station, reception system thereof, and weight vector calculation method.
2. Description of the Background Art
In the field of mobile communication systems such as portable telephones that have become extremely popular recently, various transmission channel allocation methods have been proposed to effectively use the frequencies. Some thereof are actually in practice.
FIGS. 6A-6C
show the channel arrangement in various communication systems of Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and PDMA. The systems of FDMA, TDMA, and PDMA will be described briefly with reference to
FIGS. 6A-6C
.
Referring to
FIG. 6A
corresponding to the FDMA system, the analog signals of users
1
-
4
are frequency-divided to be transmitted in radio waves of different frequencies f
1
-f
4
. The signals of respective users
1
-
4
are separated by frequency filters.
Referring to
FIG. 6B
corresponding to the TDMA system, the digitized signals of respective users are time-divided and transmitted in radio waves of different frequencies f
1
-f
4
at every constant period of time (time slot). The signals of respective users
1
-
4
are separated by frequency filters and by time synchronization between a base station and each user's mobile terminal device.
Recently, the PDMA system has been proposed to improve the radio wave frequency usability to comply with the spread of portable telephones. In the PDMA system shown in
FIG. 6C
, one time slot of the same frequency is divided spatially to transmit data of a plurality of users. The signals of respective users
1
-
4
are separated using frequency filters, time synchronization between a base station and each user's mobile terminal device, and a mutual interference removal apparatus such as adaptive arrays.
FIG. 7
shows the reception system of a conventional base station for use in PDMA. Four antennas
3
-
6
are provided to distinguish between user a and user b. The outputs of respective antennas are applied to frequency conversion circuits
7
-
10
to be frequency-converted by a local oscillation signal Lo and then applied to an A/D converter
11
. The signals are converted into digital signals to be applied to a DSP (Digital Signal Processor)
12
.
DSP
12
includes a channel allocation standard calculator
121
, a channel allocation apparatus
122
, and adaptive arrays
131
and
132
. Channel allocation standard calculator
121
calculates data in advance to identify whether the signals of two users a and b can be separated by the adaptive arrays. In response to the calculation result, channel allocation apparatus
122
provides to each of adaptive arrays
131
and
132
the channel allocation information including user information that selects the frequency and the time. Each of adaptive arrays
131
and
132
is formed of, for example, a signal combine circuit as shown in FIG.
8
. The signal of each user can be separated by selecting only the signal of a particular user.
FIG. 8
is a block diagram of a conventional adaptive array. In this example, in order to extract the signal of a certain user from input signals of a plurality of users, four input ports
14
-
17
are provided. The signals applied to input ports
14
-
17
are provided to a weight vector calculator
18
as well as to respective multipliers
20
-
23
.
Weight vector calculator
18
uses the input signal as well as a training signal corresponding to the signal of a particular user prestored in a memory
19
or the output of an adder
24
that will be described afterwards to calculate weight vectors W
1
-W
4
. Multipliers
20
-
23
multiply the input signals of input ports
14
-
17
by weight vectors W
1
-W
4
, respectively. The multiplied results are sent to adder
24
. Adder
24
adds the output signals of multipliers
20
-
23
. The added result is output to an output port
25
and also to weight vector calculator
18
if necessary.
The weight vector will be described hereinafter.
Two signals X
1
(t) and X
2
(t) from a particular user are received at input ports
14
and
15
of the adaptive array of FIG.
8
. Assuming that the adaptive array operates in an ideal manner, the output signal of the adaptive array is represented by the following equation.
Y
(
t
)=
W
1
X
1
(
t
)+
W
2
X
2
(
t
)=
S
1
(
t
)+
n
(
t
)
Here, the weight vector W of that user is represented by the following equation.
W
=
[
W
1
W
2
]
FIGS. 9 and 10
schematically show the method of calculating a weight vector according to weight vector calculator
18
of the adaptive array of FIG.
8
.
FIG. 11
is a flow chart showing the procedure of signal extraction by the adaptive array of FIG.
8
. As shown in
FIG. 9
, one time slot includes a preamble and a channel control signal transmitted through a control channel of a frequency f
c
, and a preamble and-data transmitted through a conversation channel of a frequency f
T
.
The weight vector of a user signal is calculated using the preamble and the data of the data signal transmitted via the conversation channel of FIG.
9
.
The procedure of extracting a signal from a desired user using a weight vector will be described with reference to FIG.
11
.
When extraction of a signal Ua (t) of user a applied to, for example, input port
14
is requested at step SP
1
of
FIG. 11
, weight vector calculator
18
of
FIG. 8
sets the initial values P (
0
) and W (
0
) of a correlation matrix P and a weight vector W as in the following equation at step SP
2
.
P
(
0
)
=
δ
-
1
[
1
,
0
,
0
,
0
0
,
1
,
0
,
0
0
,
0
,
1
,
0
0
,
0
,
0
,
1
]
,
W
(
0
)
=
[
1
0
0
0
]
Here, &dgr; is a positive decimal, for example &dgr;=1.0
−10
.
At step SP
3
, time t=1 is set. At step SP
4
, the Kalman gain vector K (t) at time t is calculated according to the following equation.
T
(
t
)=&lgr;
−1
P(
t−
1 )
X
(
t
)
K
(
t
)
=
T
(
t
)
1
+
X
H
(
t
)
T
(
t
)
In the above equations, T (t) indicates the intermediate generated vector at time t.
At step SP
5
, determination is made whether the time length T
p
of the preamble shown in
FIG. 9
is smaller than t or not. When t≧T
p
, a standard signal d (t) is calculated according to the following equation at step SP
6
.
d
(
t
)=det[
W
(
t−
1)
T
X (
t
)]
X (t) indicates the reception signal vector at time t.
When not t≧T
p
at step SP
5
, control proceeds to step SP
7
to substitute a training signal d
Tr
(t) for standard signal d (t). At step SP
8
, error e (t) of time t is calculated according to the following equation.
e
(
t
)
=
d
(
t
)
-
[
W
1
(
t
)
,
W
2
(
t
)
,
W
3
(
t
)
,
W
4
(
t
)
]
[
X
1
(
t
)
X
2
(
t
)
X
3
(
t
)
X
4
(
t
)
]
At step SP
9
, weight vector W (t) at time t is calculated according to the following equation.
W
(
t
)=
W (
t
)+
e
(
t
)
K
(
t
)
At step SP
10
, correlation matrix P (t) at time t is calculated according to the following equation.
P
(
t
)=&lgr;
−1
P (
t
)−
K
(
t
) T
H
(
t
)
At step SP
11
, signal Ua (t) of user a at time t is calculated according to the following equation.
Ua
(
t
)
=
[
W
1
(
t
)
,
W
2
(
t
)
,
W
3
(
t
)
,
W
4
Armstrong Westerman & Hattori, LLP
Sanyo Electric Co,. Ltd.
Yao Kwang Bin
LandOfFree
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