Telecommunications – Radiotelephone system – Including private cordless extension system
Reexamination Certificate
2000-03-22
2003-11-11
Vo, Nguyen T. (Department: 2685)
Telecommunications
Radiotelephone system
Including private cordless extension system
C455S509000, C455S510000
Reexamination Certificate
active
06647271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transmission channel allocation methods and radio apparatuses using the same. More particularly, the present invention relates to a transmission channel allocation method and a radio apparatus using the same 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 a conventional portable telephone system such as PHS (Personal Handy phone System), when a plurality of users request connection to a base station, determination is made as to whether a user is connected in accordance with a desired wave level of a radio wave from the requesting user and an undesired wave level of a radio wave of the other user.
FIGS. 13 and 14
are schematic diagrams shown in conjunction with a channel allocation method of a conventional portable telephone system.
FIG. 13
relates to the case where the undesired wave level is too high to enable connection of the newly requesting user (hereinafter referred to as a newly requesting user) in the conventional portable telephone system.
First, for example, at a base station CS
1
, undesired wave levels (hereinafter referred to as U wave levels) to a slot which is not connected (not allocated to a user) at all frequencies are measured in advance. Then, a table showing a relationship between each of the frequencies and the U wave level is produced.
If a user PS
2
newly requests connection, base station CS
1
measures a desired wave level (hereinafter referred to as a D wave level) of user PS
2
. If a ratio of D wave level to the U wave level (hereinafter referred to as a D/U ratio) is equal to or smaller than a prescribed value at a given frequency (f
1
in FIG.
13
), that frequency cannot be used for communication with user PS
2
.
On the other hand,
FIG. 14
relates to the case where the U wave level is low enough to allow connection of the newly requesting user in the conventional portable telephone system. If the D/U ratio in the above mentioned table is at least the prescribed value, base station CS
1
uses the frequency for communication with newly requesting user PS
2
.
The above described communication channel allocation method suffers from the problem that communication cannot be established with the base station through a channel if the other user is in communication with another base station which is located near the present base station.
Recently, in the field of the mobile communication systems, various transmission channel allocation methods have been proposed to effectively use the frequencies. Some of the methods are actually in practice.
FIG. 15
is a diagram showing arrangements of channels in various communication systems of Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and PDMA.
Referring first to
FIG. 15
, the systems of FDMA, TDMA, and PDMA will be briefly described. FIG.
15
(
a
) relates to the FDMA system, where 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 users
1
-
4
are separated by frequency filters.
In the TDMA system shown in FIG.
15
(
b
), 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 are separated by frequency filters and by time synchronization between a base station and a mobile terminal device of each user.
Recently, the PDMA system has been proposed to improve the radio wave frequency usability to comply with the proliferation of portable telephones. In the PDMA system shown in FIG.
15
(
c
), one time slot of the same frequency is spatially divided to transmit data of a plurality of users. In this system, signals of respective users are separated by frequency filters, time synchronization between a base station and a mobile terminal device of each user, and interference canceller such as adaptive arrays.
FIG. 16
is a schematic block diagram showing a transmission/reception system
2000
of a conventional base station for PDMA.
In the structure shown in
FIG. 16
, four antennas #
1
to #
4
are provided to distinguish between users PS
1
and PS
2
.
In a reception operation, outputs of respective antennas are applied to RF circuit
101
, where they are amplified by a reception amplifier and subjected to frequency conversion by local oscillation signals. Thereafter, any unwanted frequency signal is eliminated by a filter. Further, the signals are subjected to A/D conversion to be applied to a digital signal processor
102
as digital signals.
Digital signal processor
102
includes a channel allocation standard calculator
103
, a channel allocation apparatus
104
, and an adaptive array
100
. Channel allocation standard calculator
103
preliminary calculates to determine if the signals from two users can be separated by the adaptive array. Based on the calculation result, channel allocation apparatus
104
provides to adaptive array
100
channel allocation information including user information for selection of the frequency and time. Adaptive array
100
separates the signal of a particular user by performing in real time a weighting operation on signals from four antennas #
1
to #
4
in accordance with the channel allocation information.
[Structure of Adaptive Array Antenna]
FIG. 17
is a block diagram showing a structure of a transmitting/receiving portion
100
a
corresponding to one user in adaptive array
100
. Referring to
FIG. 17
, n input ports
20
-
1
to
20
-n are arranged for extracting the signal of an intended user from input signals including a plurality of user signals.
The signals input to respective input ports
20
-
1
to
20
-n are applied to a weight vector controlling portion
11
and multipliers
12
-
1
to
12
-n through switch circuits
1
-
1
to
10
-n.
Weight vector controlling portion
11
calculates to obtain weight vectors w
1i
-w
ni
using the input signals, a training signal corresponding to a particular user signal which has preliminary been stored in a memory
14
, and an output from an adder
13
. Here, a subscript i indicates that the weight vector is used for transmission/reception with respect to the ith user.
Multipliers
12
-
1
to
12
-n respectively multiply the input signals from input ports
20
-
1
to
20
-n and weight vectors w
1i
-w
ni
for application to adder
13
. Adder
13
adds output signals from multipliers
12
-
1
to
12
-n for output as a reception signal S
RX
(t), which is also applied to weight vector controlling portion
11
.
Further, transmitting/receiving portion
100
a
includes multipliers
15
-
1
to
15
-n receiving an output signal R
TX
(t) from the adaptive array of the radio base station and multiplying it by each of w
1i
-w
ni
that have been applied from weight vector controlling portion
11
for output. Outputs form multipliers
15
-
1
to
15
-n are applied to switch circuits
10
-
1
to
10
-n. In other words, switch circuits
10
-
1
to
10
-n provide signals applied from input ports
20
-
1
to
20
-n to a signal receiving portion
1
R for signal reception, and provide signals from a signal transmitting portion IT to input/output ports
20
-
1
to
20
-n for signal transmission.
[Operation Principle of Adaptive Array]
Now, the operation principle of transmitting/receiving portion
100
a
shown in
FIG. 17
will be briefly described.
In the following, for simplification of the description, assume that four antenna elements are provided and two users PS are in connection at the same moment. Then, signals applied from respective antennas to receiving portion
1
R are represented by the following equations.
RX
1
(
t
)=
h
11
Srx
1
(
t
)+
h
12
Srx
2
(
t
)+
n
1
Armstrong Westerman & Hattori, LLP
Chow C.
Sanyo Electric Co,. Ltd.
Vo Nguyen T.
LandOfFree
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