Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
TITLE OF THE INVENTION
RADIO CHANNEL ASSIGNMENT AND SELECTION METHOD
TECHNICAL FIELD
The present invention relates to a radio channel
1o assignment method and an assigned radio channel
selection method, which are applied to a mobile radio
communications system employing simultaneous
multiple radio channels.
BACKGROUND ART
In order to improve the frequency utilization
efficiency of a mobile radio communications system,
some radio channel assignment methods of the mobile
radio communications system have been researched up
2o to now: a method of fixedly assigning radio channels
to each zone (Fixed Channel Assignment: FCA); and a
method of dynamically assigning radio channels to a
plurality of zones (Dynamic Channel Assignment: DCA)
are known. In addition, a radio channel assignment
method of simultaneously using the two methods are
proposed.
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The FCA has already come into practice in the
mobile communications system: an analog NTT system
and a digital mobile communications method (personal
digital cellular : PDC ) are typical examples . As for
the DCA, it has been put to practical use in a digital
cordless form until now.
In such an FCA mobile communications system, a
radio channel is conventionally established between
a base station and a mobile station by selecting an
1o idle radio channel from among radio channels assigned
to the base station in the zone visited by the mobile
station, thereby setting up a mobile radio channel with
that radio channel. Although the radio channels
assigned to each base station are decided such that
interference with the other base stations does not
exceed a predetermined cochannel interference level,
it is mainly assumed that only a single channel is used
in the mobile radio communications system.
In contrast with this, a mobile radio
2o communications method has emerged recently which
assigns multiple radio channels to a mobile station.
In the communications system that employs the multiple
radio channels, a mobile station uses two or more
channels assigned to the base station in the zone
(visited zone) that the mobile station is present so
as to implement high-speed or high-quality
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transmission.
This method, however, is essentially the same as
the radio channel assignment method within a cluster
of cells in that although it employs multiple channels,
it only utilizes radio channels assigned to the visited
zone to be used precedently.
Thus , as compared with the method of using a single
radio channel, the method of using simultaneous
multiple channels has a problem of reducing the total
1o frequency utilization efficiency (a product of the
utilization efficiency on the frequency axis and the
utilization efficiency on the spatial axis).
Therefore, an object of the present invention is
to provide a radio channel assignment and selection
method without involving degradation in the total
frequency utilization efficiency as compared with the
method of using the single radio channel, even if a
mobile station employs multiple radio channels
simultaneously.
DISCLOSURE OF THE INVENTION
To achieve the object, in a first aspect of the
present invention, there is provided a radio channel
assignment method which is associated with a plurality
of zones constituting a cluster based on frequency
reuse of radio channels , in order to implement a mobile
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radio communications system by employing multiple
radio channels in each one of the plurality of zones ,
the radio channel assignment method comprising the
steps of
assigning to at least one of the multiple radio
channels a radio channel over which the one of the
plurality of zones itself has priority; and
assigning to a remainder of the multiple radio
channels a radio channel available in a zone adjacent
1o to the one of the plurality of zones.
By thus assigning the radio channel in the mobile
ratio communications system, a radio channels over
which the visited zone has priority can be assigned
to at least one of the multiple radio channels the
mobile station uses simultaneously, and an idle radio
channel selected from radio channels precedently
available in zones adjacent to the visited zone can
be used as the remainder of the multiple radio
channels.
2o This makes it possible to prevent reduction in the
frequency utilization efficiency in the cluster in
spite of the simultaneous use of the multiple radio
channels.
The radio channel assignment method in accordance
with the present invention can be applied
independently of whether the radio channels are
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established bythe frequency division multiple access,
time division multiple access or code division
multiple access, or by any combination of them.
If the transmission quality is degraded because
of cochannel interference during the use of the radio
channel over which an adjacent zone has priority, the
mobile device can utilize an idle radio channel over
which another zone has priority by carrying out
handover to that idle radio channel. This enables a
1o continuous use of the multiple channels.
In a second aspect of the present invention, there
is provided a radio channel selection method which is
carried out by a mobile station visiting one of a
plurality of zones constituting a cluster for
frequency reuse of radio channels, in order to
implement a mobile radio communications system by
employingsimultaneousmultiple radio channels in each
one of the plurality of zones, the radio channel
selection method comprising the steps of:
2o selecting at least one of the multiple radio
channels from radio channels assigned to the zone
visited by the mobile station; and
selecting a remainder of the multiple radio
channels from radio channels assigned to a plurality
of zones adjacent to the zone visited by the mobile
station, and using the selected radio channel in the
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VlSl.ted zone .
Here, the radio channel selection method as
claimed in claim 9, wherein selection of the radio
channel of one of the adjacent zones by the mobile
station may comprise the steps of:
detecting a received level of a radio channel in the
adjacent zones;
measuring cochannel interference from the received
level detected;
Zo comparing the received level detected with a
predetermined level;
setting up the radio channel as a radio channel between
the mobile station and a base station in the visited
zone when the received level compared is less than the
predetermined level; and
selecting another radio channel of the adjacent zones
by returning to the step ( 1 ) when the received level
compared is greater than the predetermined level.
The radio channel selection method as claimed in
2o claim 10 , wherein the selection of the radio channel
of one of the adjacent zones by the mobile station may
further comprise the step of:
controlling transmission power of the base station
and mobile station connected to the radio channel setup
between the visited zone base station and the mobile
station such that the transmission power approach a
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predetermined receiving sensitivity.
The radio channel selection method as claimed in
any one of claims 9-12, wherein the mobile station that
implements the radio channel selection method may be
a mobile device.
The radio channel assignment method and selection
method in accordance with the present invention have
the following advantages of:
(1) Improving the frequency utilization efficiency
1o as compared with the conventional radio channel
assignment method in the mobile communications
employing multiple radio channels;
(2) Enabling high speed transmission;
(3) Applicable to an existing mobile radio
communications method using a single carrier; and
(4) Applicable to an existing mobile station by a
simple expansion of channel control of the existing
mobile station.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a diagram showing a radio zone
configuration for illustrating a radio channel
assignment method in accordance with the present
invention;
Fig. 2 is a diagram showing a zone configuration
simplifying the embodiment in Fig. 1;
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Fig. 3 is a~diagram illustrating the relationship
between Figs. 3A and 3B;
Figs. 3A and 3B are block diagrams showing a
configuration of a mobile station associated with the
radio channel assignment in accordance with the
present invention;
Fig. 4 is a flowchart illustrating a selection
processing by the mobile station for explaining the
radio channel selection method in accordance with the
1o present invention;
Fig. 5 is a flowchart illustrating remaining steps
of the selection method of Fig. 4;
Figs. 6A and 6B are diagrams illustrating the
application of the radio channel assignment to
frequency division multiple access;
Figs. 7A and 7B are diagrams illustrating the
application of the radio channel assignment to time
division multiple access;
Figs. 8A and 8B are diagrams illustrating the
2o application of the radio channel assignment to code
division multiple access;
Figs . 9A and 9B are diagrams illustrating a method
of carrying out the radio channel assignment by
simultaneous use of the frequency division multiple
access and time division multiple access;
Figs. 10A and 10B are diagrams illustrating a
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method of carrying out the radio channel assignment
by simultaneous use of the time division multiple
access and code division multiple access;
Figs. 11A and 11B are diagrams illustrating a
method of carrying out the radio channel assignment
by simultaneous use of the code division multiple
access and frequency division multiple access; and
Figs. 12A and 12B are diagrams illustrating a
method of carrying out the radio channel assignment
1o by simultaneous use of the frequency division multiple
access, time division multiple access and code
division multiple access.
BEST MODE FOR CARRYING OUT THE INVENTION
The radio channel assignment in accordance with
invention will now be described with reference to the
accompanying drawings from the following point of
view: a method of assigning channels by dividing them
into channels over which the current zone has priority,
2o and channels over which the other zones have priority;
and a method for a visitor mobile station to select
multiple channels from among a plurality of channels
assigned to individual zones in accordance with the
present invention.
Fig . 1, relating to the radio channel assignment ,
shows a switching center 108 , base stations ( 101-107 )
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connected the switching center, and interconnection
between switching centers, in which the switching
center 108 functions as a regional center of a cluster
100 consisting of seven zones each including its own
base station.
In Fig . 1, the switching center 108 is connected
with the base stations (101-107) in the individual
zones through dedicated lines 109 consisting of common
communications channels. In the radio channel
to assignment method in accordance with the present
invention, the switching center 108 instructs the base
stations ( 101-107 ) of available radio channel numbers
through the dedicated lines 109 according to a
predetermined radio channel assignment scheme.
Fig. 1 illustrates a case in which the radio
channels are assigned by frequency division multiple
access (FDMA).
For example, in an 800 MHz band FDMA system with
60 radio channels, the radio channel numbers assigned
2o to respective zones are as shown in table 1, in which
the radio channels each have a 25 kHz bandwidth with
a frequency interval of 50 kHz. For example, if the
radio channel No. 1 is assigned to 800.050 MHz, the
radio channel No. 60 becomes 803.000 MHz.
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Table 1
Base station Assigned radio channel numbers
numbers
1 1, 2, 4, 5
3,
2 10,11, 12, 13,14, 15,16, 17,18, 19, 20
3 30,31, 32, 33,34, 35,36, 37
4 6, 7, 9, 21,22, 23,24, 25,26, 27, 28,
8, 29
38,39, 40, 41,42, 43,44, 45,46
6 50,51, 52, 53,54, 55,56, 57,58, 59, 60
7 47,48,
49
According to Table 1, radio channels 1-5 are
5 assigned to the base station 1. This means that five
carries from 800.050 MHz to 800.250 MHz are assigned.
As for the assignment of the radio channels to the
individual zones, the switching center of Fig. 1
includes a cross-reference table as Table 1. The
to assignment table stored in the switching center 108
can be stored instead in a higher rank switching center
that carries out the overall control of a plurality
of switching centers. As a method for storing the
table, for example, it is implemented in the form of
software stored in a base station controller in the
switching center.
A method will now be described for establishing
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a channel between a mobile station and the base station
by effectively selecting multiple radio channels from
the channels assigned to the zones with maintaining
the frequency utilization efficiency. Referring Fig.
2, a method will be described, for the purpose of
simplicity, which selects only two simultaneous radio
channels from the radio channels assigned to the zones
by the frequency division multiple access.
As shown in Fig. 2, as the radio communications
to zones, there are seven zones ( zones 1-7 ) constituting
a cluster 8 with zone 1 being adjacent to zones 2-
7. Frequencies fl-f7 are respectively assigned to the
base stations of the respective zones : there are one
radio channel which the visitor mobile station can use
precedently, and six radio channels over which the
other zones have priority. For example, as for zone
1, the radio channel of the frequency f 1 is assigned
as a channel over which zone 1 has priority, and the
channels of the frequencies f2-f7 are assigned as
2o channels over which the other zones ( zones 2-7 ) have
priority, and a base station 10 of zone 1 has equipment
enabling the communications using these radio channels .
The mobile station in each individual zone not only
can communicate through the radio channel over which
the visited zone has priority, but also has a function
to communicate through one of the channels over which
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the other zones have priority.
As a method of identifying the radio channel over
which the visited zone has priority, because the base
station broadcasts its own identification number
through a control channel, the mobile station can
identify the radio channel over which it has priority
from the identification number by receiving the
control channel containing the identification number.
Next , taking an example in which a mobile station
to in a certain zone establishes two simultaneous
channels , a method a mobile station uses to select the
channels from the plurality of radio channels thus
assigned will be described in connection with a
conf igurat ion .
A mobile station as shown in Figs . 3A and 3B has
in its radio stage a couple of transmitting and
receiving sections. A first receiving section 110 and
a second receiving section 120 comprise RF (radio
frequency) amplifiers 112 and 122, receiving mixers
114 and 124, IF amplifiers 116 and 126 and demodulators
118 and 128, respectively, and convert received radio
channels with different frequencies to baseband
signals . A first transmitting section 130 and a second
transmitting section 140 comprise modulators 136 and
146 , transmitting mixers 134 and 144 , and RF amplifiers
132 and 142. The first transmitting section 130 and
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second transmitting section 140 transmit transmitted
signals fed from a baseband signal processor 150
through radio channels with different frequencies . A
frequency synthesizer 103 supplies the receiving
mixers 114 and 124 in the first and second receiving
sections ( 110 and 120 ) and the transmitting mixers 134
and 144 in the first and second transmitting sections
(130 and 140) with corresponding frequencies, thus
determining the receiving frequencies and
to transmitting frequencies.
The received signals from the radio stage and the
transmitted signals to the radio stage are processed
by a received signal processor 152 and a transmitted
signal processor 154 in the baseband signal processor
150. A signal from the received signal processor 152
is fed to a user of the mobile station through a
telephone receiver 170. A signal from a telephone
transmitter 180 is processed by the transmitted signal
processor 154 and transferred to the radio stage . A
2o controller, which consists of a controller 160
including key pad 190 and a CPU, controls the baseband
signal processor 150 and the radio section. The
baseband signal processor comprises a
transmitting/receiving timing controller that
supplies the controller with timing signals.
Next, referring to Fig. 2, first, the steps of
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making effective use of the radio channels will be
described briefly which are taken by the mobile station
with the foregoing configuration and by the base
station in the visitor location of the mobile station.
The mobile station 10 visiting zone 1 establishes
in zone 1 the first radio channel of the frequency fl
over which the mobile station has priority. The
establishment of the channel is carried out in the same
manner as the establishment of a conventional radio
to channel between a mobile station and a base station
in an ordinary visited zone.
Subsequently, the mobile station 10 observes the
cochannel interference of the other radio channels,
and sets up a channel with a radio channel whose
interference level is less than a predetermined level.
The radio channel setup can utilize the radio channels
over which the other zones have priority.
Thus, the mobile station 10 establishes between
it and the base station in its visited zone 1 the second
2o radio channel of the frequency f2 over which zone 2
has priority. In this case, the mobile station
notifies the base station in the visited zone 1 of using
the second radio channel, first . The base station in
zone 1 sets up the channel to the mobile station in
zone 1 using the second radio channel.
The mobile station 10 uses the first and second
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radio channels. The mobile station continually
observes the cochannel interference of the second
radio channel. If the channel quality of the second
radio channel degrades during the communication, the
mobile station performs handover to a radio channel
over which another zone has priority. For example,
it performs handover to a radio channel over which the
third zone has priority. In this case also, the mobile
station notifies the base station in the visited zone
of the radio channel to be handed over, so that the
base station can set up a channel using the radio
channel over which zone 3 has priority.
The reason for observing the degradation of the
channel quality will now be described. The radio
channels over which other zones have priority can be
precedently used by these zones . If two or more zones
including the current zone and another zone use a
particular radio channel over which the another zone
has priority, the quality of that channel is degraded
2o because of the cochannel interference. Detecting the
degradation in the channel quality due to the cochannel
interference, the mobile station using the radio
channel over which the visited zone does not have
priority relinquishes the second channel and performs
handover to another radio channel.
These operations enable the mobile station to
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continually use two radio channels.
Although the case of establishing two simultaneous
radio channels is described above, three or more
simultaneous radio channels can be set up.
Next, the channel selection operation by the
mobile station will be described in more detail.
As described above, the mobile station 10 selects
the radio channel of the frequency f 1, f first , which
is assigned to the base station of zone 1, as the first
1o radio channel. Then, the mobile station communicates
with the base station to establish the radio channel,
and controls the frequency synthesizer 103 to tune the
first transmitting section 130 and first receiving
section 110 of Figs. 3A and 3B to that frequency.
Subsequently, the mobile station 10 detects an
idle radio channel in one of the adjacent zones with
a frequency different from the frequency of the visited
zone . This is carried out by the second transmitting
section 140 and second receiving section 120 of Figs .
3A and 3B. Assume that the radio channel of the
adjacent zone 2 with the frequency f2 as illustrated
in Fig. 2 is detected to be idle. The mobile station
selects it as the second radio channel, and notifies
the visitor location base station of the radio channel
selected, thereby establishing the radio channel
between the visitor location base station and the
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mobile station l Thus , the mobile station can use the
two radio channels simultaneously as the visited zone
radio channels . Because the idle channel is used, the
frequency utilization efficiency of the mobile radio
communication system is not reduced.
The simultaneous use of the radio channel in the
visited zone of the mobile station and the radio
channel in the adjacent zone enables the efficient
channel selection.
io Thus, in the radio channel selection method, the
radio channel that is assigned in advance to the
visited zone of the mobile station is selected first .
Then, the radio channel that is assigned in advance
to one of the adjacent zones is selected as the radio
channel of the visited zone.
The second selection of the radio channel, however,
causes the cochannel interference mentioned above,
which becomes a major factor of degrading the quality
in the radio channel between the visited zone and the
2o adjacent zone. To avoid the cochannel interference
in the radio channel selection method in accordance
with the present invention when the visited zone base
station and the mobile station establish, as the radio
channel of the visited zone, the radio channel using
the idle channel of one of the adjacent zones, the
mobile station and the base station can carry out the
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transmission power control to reduce the cochannel
interference to the adjacent zone.
Afterward, if the second radio channel selected
undergoes the degradation in the channel quality due
to the cochannel interference, the mobile station
immediately performs the handover to another radio
channel of one of the adjacent zones.
The series of the foregoing processes in
accordance with the present invention has an advantage
to of being able to achieve the mobile radio
communications using simultaneous multiple radio
channels without reducing the frequency utilization
efficiency, with circumventing the effect of the
cochannel interference.
z5 The series of the foregoing operations will now
be described with reference to Fig. 4, and particularly
the selection of the second radio channel will be
described in more detail . Here , as in Fig . 2 , the radio
channel selection of two simultaneous radio channels
2o by the mobile station will be described.
Fig. 4 illustrates the processing of the second
selection by the mobile station 10 after the first
channel selection. Since the first radio channel is
the radio channel that is assigned to the visited zone,
25 and is selected in the same manner as a conventional
radio channel, description thereof is omitted here.
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First , the mobile station 10 detects , as the second
radio channel , an idle radio channel of one of the zones
adjacent to the visited zone ( S202 ) . Then, the mobile
station measures the cochannel interference to the
idle channel from the base station ( S204 ) , and makes
a decision as to whether the power ratio to the measured
value is greater than or less than the predetermined
value (S206).
If the decision result indicates that the
1o predetermined value is exceeded, the mobile station
notifies the visitor location base station of the idle
channel (S208). The mobile station carries out
subsequent communication with the visitor location
base station. Then, the mobile station and the visited
zone base station carries out the transmission power
control of the second channel with each other ( S210 ) ,
thereby adjusting the transmission power to about a
required receiving sensitivity (S212). In this case,
the controller 160 performs the transmission power
2o control of the RF amplifier 142 of Fig. 3B at the mobile
station side . This control can be low-speed control
at every several second interval. Although the
transmission power control requires a wide dynamic
range from the maximum transmission power to around
the required receiving sensitivity, the accuracy of
a few decibels is enough as the accuracy of the
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transmission power control because the purpose of the
transmission control is to reduce the cochannel
interference . Thus , the selection of the second radio
channel is completed (S214).
If the decision result at step S206 indicates that
the predetermined level is not exceeded, the mobile
station detects another radio channel of one of the
adjacent zones (S202). Subsequently, the mobile
station selects the radio channel to be used through
1o the foregoing radio channel selection processing.
As for the second radio channel, the interference
measurement is continued even during the
communications, the processing of which will now be
described with reference to the flowchart of Fig. 5.
In the flowchart of Fig. 5, the mobile station carries
out the cochannel interference measurement ( 5220 ) in
conjunction with the transmission power control after
the selection. If the measurement result of the
interference is less than the predetermined level, it
2o continues to use the radio channel (YES at step S222) .
On the contrary, if the interference exceeds the
predetermined level, the handover is performed to an
idle channel of another adjacent zone. The processing
of selecting the idle channel is the same as the channel
selection as illustrated in Fig. 4.
The foregoing processing is described taking an
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example of carrying out the communications with the
base station through the two radio channels as
described above in connection with Fig. 4. When the
mobile station requires three or more radio channels ,
it carries out the foregoing idle radio channel
selection processing by the number of required radio
channels after the second radio channel selection,
thereby achieving the radio channel selection in the
same manner. This makes it possible to assign multiple
io radio channels to the mobile station without impairing
the frequency utilization efficiency.
So far, the method of assigning the radio channels
and selecting the radio channels from among the
channels assigned in accordance with the present
invention is described in connection with the example
in which the radio channels are mainly configured by
the frequency division multiple access. The channel
assignment in accordance with the present invention,
however, is not limited to this. The radio channel
2o assignment in accordance with the present invention
is also applicable to other radio communications
systems like various types of multiplexing systems
such as a TDMA ( time division multiple access ) system
in which channels consist of slots based on the time
division multiple access, and a CDMA (code division
multiple access) system with its channel configured
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using orthogonal codes.
Applications of the radio channel assignment
method in accordance with the present invention will
now be described for each radio channel configuration
including the foregoing configuration based on the
frequency division multiple access.
[Frequency Division Multiple Access]
Figs . 6A and 6B show an example in which the present
invention is applied to frequency division radio
1o channels. Fig. 6A shows an example of forming one
cluster from seven zones as in Fig. 2. As shown in
Fig. 6B, the radio channels are established by dividing
the frequency band . In Fig . 6B , the radio channel of
a particular frequency band is precedently assigned
to the first zone, and the mobile station roaming in
the first zone has priority over that radio channel.
The mobile station tries to use two radio channels
simultaneously. First, as the first radio channel,
the mobile station uses a particular carrier over which
2o zone 1 has priority. As the second radio channel, it
selects, for example, a carrier over which zone 3 has
priority, that is , the channel with low interference
so as to be used by zone 1. If the channel quality
of the second radio channel degrades, the mobile
station performs handover to a carrier over which zone
6 has priority, for example.
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[ Time Divisionf Multiple Access ]
Figs . 7A and 7B show an example in which the present
invention is applied to time division radio channels .
Fig. 7A shows an example of forming one cluster from
seven zones as in Fig. 6A. As shown in Fig. 7B, the
radio channels consist of time slots, and the
individual zones have time slots over which they have
priority.
The mobile station tries to use two radio channels
1o simultaneously. First, as the first radio channel,
the mobile station uses a particular time slot over
which zone 1 has priority. As the second radio channel,
it uses in zone 1 a time slot over which zone 3 has
priority. If the channel quality of the second radio
channel degrades , the mobile station performs handover
to a time slot over which another zone has priority
(for example, to a radio channel of zone 6).
[Code Division Multiple Access]
Figs . 8A and 8B show an example in which the present
2o invention is applied to code division radio channels .
Fig. 8A shows an example of forming one cluster from
seven zones as in Fig. 6A. As shown in Fig. 8B, the
radio channels are configured using multiple
orthogonal codes, and by spreading a signal by
multiplying the signal by the orthogonal codes.
The mobile station tries to use two radio channels
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simultaneously. First, as the first radio channel,
the mobile station uses a particular orthogonal code
over which zone 1 has priority. As the second radio
channel, it uses in zone 1 an orthogonal code over which
zone 3 has priority. If the channel quality of the
second radio channel degrades, the mobile station
performs handover to a radio channel over which another
zone has priority (for example, to a radio channel of
zone 6).
1o [ Frequency Division Multiple Access and Time Division
Multiple Access]
Figs . 9A and 9B show an example in which the present
invention is applied to radio channels established by
using both the frequency division multiple access and
time division multiple access at the same time. Fig.
9A shows an example of forming one cluster from seven
zones as in Fig. 6A. As shown in Fig. 9B, the radio
channels are established by dividing according to
frequencies and time slots.
2o The mobile station tries to use two radio channels
simultaneously. First, as the first radio channel,
the mobile station uses a particular carrier and time
slot over which zone 1 has priority. As the second
radio channel, it uses in zone 1 a radio channel
consisting of a carrier and time slot over which zone
3 has priority. If the channel quality of the second
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radio channel degrades, the mobile station performs
handover to another radio channel over which another
zone has priority (for example, to a radio channel of
zone 6).
[Time Division Multiple Access and Code Division
Multiple Access]
Figs. 10A and 10B show an example in which the
present invention is applied to radio channels
established by using both the time division multiple
io access and code division multiple access. Fig. 10A
shows an example of forming one cluster from seven
zones as in Fig. 6A. As shown in Fig. lOB, the radio
channels are established by dividing according to time
slots and orthogonal codes.
The mobile station tries to use two radio channels
simultaneously. First, as the first radio channel,
the mobile station uses a particular time slot and
orthogonal code over which zone 1 has priority. As
the second radio channel, it uses in zone 1 a time slot
2o and orthogonal code over which zone 3 has priority.
If the channel quality of the second radio channel
degrades, the mobile station performs handover to a
radio channel over which another zone has priority ( for
example, to a radio channel of zone 6).
[ Code Division Multiple Access and Frequency Division
Multiple Access]
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Figs. 11A and 11B show an example in which the
present invention is applied to radio channels
established by using both the code division multiple
access and frequency division multiple access. Fig.
11A shows an example of forming one cluster from seven
zones as in Fig . 6A . As shown in Fig . 11B , the radio
channels are established by dividing according to
orthogonal codes and frequencies.
The mobile station tries to use two radio channels
1o simultaneously. First, as the first radio channel,
the mobile station uses a particular orthogonal code
and carrier over which zone 1 has priority. As the
second radio channel, it uses in zone 1 an orthogonal
code and carrier over which zone 3 has priority. If
the channel quality of the second radio channel
degrades, the mobile station performs handover to a
radio channel over which another zone has priority ( for
example, to a radio channel of zone 6).
[Frequency Division Multiple Access, Time Division
2o Multiple Access and Code Division Multiple Access]
Figs. 12A and 12B show an example in which the
present invention is applied to radio channels
established by using the frequency division multiple
access, time division multiple access and code
division multiple access simultaneously. Fig. 12A
shows an example of forming one cluster from seven
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CA 02281578 1999-08-19
zones as in Fig-. 6A . As shown _ in Fig . 12B , the radio
channels are established by dividing according to
frequencies, time slots and orthogonal codes.
The mobile station tries to use two radio channels
simultaneously. First, as the first radio channel,
the mobile station uses a particular carrier, time slot
and orthogonal code over which zone 1 has priority.
As the second radio channel, it uses in zone 1 a carrier,
time slot and orthogonal code over which zone 3 has
to priority. If the channel quality of the second radio
channel degrades, the mobile station performs handover
to a radio channel over which another zone has priority
(for example, to a radio channel of zone 6).
As described above, the radio channel assignment
method in accordance with the present invention is
applicable independently of the way the radio channels
are established, that is, independently of whether
they are established by any one of the frequency
division multiple access, time division multiple
2o access and code division multiple access, or by their
combinations.
Furthermore, since the mobile station can
establish multiple radio channels using one or more
radio channels other than the radio channel
precedently assigned to the visited zone, the
frequency utilization efficiency can be improved.
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