Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-07-14
2002-10-15
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S341000, C370S437000, C370S439000, C455S063300, C455S450000, C455S509000
Reexamination Certificate
active
06466557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission channel allocation method and an apparatus thereof More particularly, the present invention relates to a transmission channel allocation method and apparatus for allocating a channel to be used for transmission to a user requesting connection in a PDMA (Path Division Multiple Access) communication system where a plurality of users transmit and receive data such as audio and video using channels of the same frequency and the same time.
2. Description of the Background Art
In the field of the 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. 46A-46C
show the channel arrangements 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. 46A-46C
. Referring to
FIG. 46A
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. 46B
corresponding to the TDMA system, the digitized signals of respective user 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 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. 46C
, one time slot of the same frequency is divided spatially to transmit data of a plurality of users. The signals of respective users are separated using frequency filters, time synchronization between a base station and each user's mobile terminal device, and a mutual interference removal apparatuses such as adaptive arrays.
FIG. 47
shows the reception system of a conventional base station for use in PDMA. Four antennas
3
-
6
are provided to distinguish between user
1
and user
2
. 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 the two users 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.
48
. The signal of each user can be separated by selecting only the signal of a particular user.
FIG. 48
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 corresponding to a plurality of user signals, 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 signals as well as a training signal corresponding to the signal of a certain user prestored in a memory
19
or the output of an adder
24
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 (or) weight vector calculator
18
.
The reception signal vector of the PDMA communication will be described briefly hereinafter. When signals As
1
(t) and Bs
1
(t) from user
1
are received on two antennas, the reception signals x
1
(t) and x
2
(t) of respective antennas are represented by the following equation.
x
1
(
t
)=
As
1
(
t
)+
n
1
(
t
)
x
2
(
t
)=
Bs
1
(
t
)+
n
2
(
t
)
In the above equations, A and B are coefficients of the signals sent from user
1
and received by respective antennas, and n
1
(t) and n
2
(t) are noise components. Here, reception signal vector U
1
of user
1
is represented by the following equation.
U1
=
[
A
B
]
When signals Cs
2
(t) and Ds
2
(t) from user
2
are received on the above two antennas, reception signals x
1
(t) and x
2
(t) of respective antennas are represented by the following equations.
x
1
(
t
)=
As
1
(
t
)+
Cs
2
(
t
)+
n
1
(
t
)
x
2
(
t
)=
Bs
1
(
t
)+
Ds
2
(
t
)+
n
2
(
t
)
Here, reception signal vector U
2
of user
2
is represented by the following equation.
U2
=
[
C
D
]
When there is only one user, reception signal vector U
1
can be obtained easily. However, when there are two users, it becomes difficult to separate respective signals since the signals will be mixed. Furthermore, a plurality of reception signals may be input from one user. If the correlation value of reception signal vectors U
1
and U
2
is a small value, the signals from two users can be separated with the adaptive arrays of FIG.
48
. Transmission can be carried out using channels of the same frequency and same time (time slot). However, when the correlation value of reception signal vectors U
1
and U
2
is a large value, it is difficult to separate the signals with the adaptive arrays. Therefore, communication cannot be carried out using channels of the same frequency and the same time (time slot).
The weight vector will be described hereinafter. When respective signals S
1
(t) and S
2
(t) from users
1
and
2
are received on the two antennas, reception signals x
1
(t) and x
2
(t) of respective antennas are represented by the following equations.
x
1
(
t
)=
As
1
(
t
)+
Cs
2
(
t
)+
n
1
(
t
)
x
2
(
t
)=
Bs
1
(
t
)+
Ds
2
(
t
)+
n
2
(
t
)
When the signal of user
1
is extracted by adaptive array
131
shown in
FIG. 47
in accordance with the information from channel allocation apparatus
122
, that is, when the signals x
1
(t) and x
2
(t) are input to input ports
14
and
15
and weight vector calculator
18
calculates ideal weights w
11
and w
12
to extract the signal transmitted from user
1
, an output signal y
1
(t) is represented by the following equation.
y
1
(
t
)=
w
11
(
t
)
x
1
(
t
)+
w
12
(
t
)
x
2
(
t
)=
s
1
(
t
)+
n
(
t
)
Thus, weight vector W
1
of user
1
is represented as follows.
W
1
=
[
w
11
w
12
]
When the signal of user
2
is extracted by adaptive array
132
shown in
FIG. 47
in accordance with the information from channel allocation apparatus
122
, on the other hand, an output signal y
2
(t) is represented by the following equation.
y
2
(
t
)=
w
21
(
t
)
x
1
(
t
)+
w
22
x
2
(
t
)=
s
2
(
t
)+
n
(
t
)
Thus, weight vector W
2
of user
2
is represented as follows.
W
2
=
[
w
21
w
22
]
If the correlation value of weight vectors of the two users is a large value, it is difficult to separate the signals transmitted from the two users with adaptive arrays
131
and
132
. As a result, communication can not be carried out using channels of the same frequency and same time.
The channel capacity of the communication system is coming to its limit by the rapid spread of portable telephones. In the future, it is expected tha
Hom Shick
Olms Douglas
Sanyo Electric Co,. Ltd.
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