DESCRIPTION
BASE STATION, TERMINAL DEVICE, CONTROL CHANNEL ASSIGNMENT
METHOD, AND REGION SIZE DETERMINATION METHOD
TECHNICAL FIELD
[0001] The present invention relates to a base station,
a terminal device, a control channel assignment method, and
a region size determination method.
BACKGROUND ART
[0002] In these years, 3GPP (Third Generation
Partnership Project) completes the standardization of LTE
(Long Time Evolution) that is one of high-speed data
communication specifications and starts the standardization
of LTE-Advanced that is an evolved system. The LTE-
Advanced system targets the further increase of throughput.
In other words, the LTE-Advanced system can perform
communication by using a maximum bandwidth of 100MHz when
the LTE system performs communication by using a maximum
system bandwidth of 20MHz.
[0003] Moreover, the LTE-Advanced system is required to
have compatibility with the LTE system, and a terminal
device that employs the LTE system is required to be
connected to a network of the LTE-Advanced system. To meet
these demands, some consider forming one LTE-Advanced
system band by bundling LTE system bands.
[0004] An example of a radio format of the LTE system is
illustrated in FIG. 20. As illustrated in FIG. 20, an LTE
system band 600 is divided into a control channel region
610 and a data channel region 620. The control channel
region 610 includes therein a control channel 611. A
terminal device transmits and receives various types of

data at a predetermined resource location in the date,
channel region 620 on the basis of the control channel 611.
[0005] For example, when the control channel 611 is a
control channel for downlink data assignment, the terminal
device receives a data channel in the data channel region
620 which is located at a resource location designated by
the control channel 611. On the other hand, when the
control channel 611 is a control channel for uplink data
assignment, the terminal device transmits data in the data
channel region 620, at a resource location designated by
the control channel,
[0006] Next, an example of a radio format of an LTE-
Advanced system obtained by bundling three system bands of
the LTE system is illustrated in FIG. 21 as an example of
the LTE-Advanced system. Hereinafter, LTE system bands of
the LTE-Advanced system are referred to as component
carriers. As illustrated in FIG. 21, component carriers
700a to 700c respectively have control channel regions 710a
to 710c and data channel regions 720a to 720c.
[0007] In the LTE-Advanced system, a terminal device
transmits and receives data on the basis of a control
channel similarly to the LTE system. In this case, in the
LTE-Advanced system, control channels corresponding to the
component carriers are included in the control channel
region of one component carrier. For example, as
illustrated in FIG. 21, a control channel 730a
corresponding to the component carrier 700a, a control
channel 730b corresponding to the component carrier 700b,
and a control channel 730c corresponding to the component
carrier 700c are all included in the control channel region
710b of the component carrier 700b.
[0008] In this way, the LTE-Advanced system previously
decides one component carrier among the component carriers

700 as the one which has all the control channels 73C to be
acquired by a certain terminal device. As a result, the
terminal device can acquire control channels that
correspond to all the component carriers 700 only by
accessing the control channel region 710 of one of the
component carriers 700 (see Non-Patent Document 1).
[0009] Non-Patent Document 1: 3GPP TSG-RM WGl#53fcis,
R1-082468, "Carrier aggregation in LTS-Advanced"
DISCLOSURE OF INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0010] When the LTE-Advanced system as described above
is employed, the control channel has to carry information
indicating which of the component carriers corresponds to
this control channel, and therefore an amount of
information included in the control channel increases. As
a result, there is a possibility that an utilizable data
channel region decreases and thus frequency use efficiency
decreases as the whole system.
[0011] According to an aspect of the present invention,
an object of the invention is to provide a base station, a
terminal device, a control channel assignment method, and a
region size determination method that are used for
improving frequency use efficiency of the overall system.
MEMS FOR SOLVING PROBLEM
[0012] As one embodiment according to the first aspect
of the present invention, in a base station that performs
radio data communication with terminal devices by using a
plurality of bands of which each has a data channel region
to which a data channel is assigned and a control channel
region to which a control channel is assigned, the bc.se
station includes a control channel assigning unit that

assigns a control channel for the terminal device at a
location in the control channel region of any band of the
plurality of bands according to a band to which a data
channel assigned to the terminal device belongs, and a
control channel transmitting unit that transmits the
control channel to the terminal device at the location
assigned by the control channel assigning unit.
[0013] According to the second aspect of the present
invention, in a terminal device that performs radio data
communication with a base station by using a plurality of
bands of which each has a data channel region to which a
data channel is assigned and a control channel region to
which a control channel is assigned, the terminal device
includes a control channel receiving unit that receives,
from the base station, a control channel assigned to a
control channel region of the band to which a control
channel for the device itself is assigned, a band
specifying unit that specifies, on the basis of an
assignment location in the control channel region of the
control channel received by the control channel receiving
unit, a band to which a data channel corresponding to the
control channel is assigned, and a data channel receiving
unit that receives the data channel at an assignment
location of the data channel indicated by the control
channel in a data channel region of the band specified by
the band specifying unit.
[0014] According to the third aspect of the present
invention, in a method for assigning a control channel to a
control channel region by using a plurality of bands of
which each has a data channel region to which a data
channel is assigned and a control channel region to which a
control channel is assigned when radio data communication
is performed between a base station and a terminal device,

the method includes assigning, by the base station, a
control channel for the terminal device at a location in
the control channel region of any band of the plurality of
bands according to the band to which a data channel
assigned to the terminal device belongs.
[0015] According to the fourth aspect of the present
invention, in a base station that performs radio data
communication with terminal devices by using a plurality of
bands of which each has a data channel region to which a
data channel is assigned and a control channel region to
which a control channel is assigned, the base station
includes a region setting unit that sets a size of the
control channel region for each of the bands.
(0016) According to the fifth aspect of the present
invention, the base station further includes a storage unit
that stores therein as a main band of the terminal device,
among the plurality of bands, a band to which the control
channel for the one terminal device is assigned in
association with the terminal device, and the region
setting unit sets a size of a control channel region of a
band other than the main band to a value smaller than that
of the control channel region of the band to which the
control channel for the terminal device is assigned.
[0017] According to the sixth aspect of the present
invention, in a method for setting a region size of s.
control channel region when radio data communication is
performed between a base station and terminal devices, by
using a plurality of bands of which each has a data channel
region to which a data channel is assigned and a control
channel region to which a control channel is assigned, the
method includes setting by the base station, a size of the
control channel for each of the bands.

EFFECT OF THE INVENTION
[0018] Because the reduction of a data channel region
can be prevented, frequency use efficiency can be improved,
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a schematic diagram explaining a radio
communication system according to a first embodiment.
FIG, 2 is a diagram illustrating a configuration
example of a radio format according to the first embodiment.
FIG. 3 is a block diagram illustrating the
configuration of a base station according to the first
embodiment.
FIG. 4 is a diagram illustrating an example of a main
carrier association table according to the first embodiment.
FIG. 5 is a diagram explaining a control channel
assignment method according to the first embodiment.
FIG. 6 is a block diagram illustrating the
configuration of a terminal device according to the first
embodiment.
FIG. 7 is a flowchart illustrating an example of
processing procedures performed by the base station
according to the first embodiment.
FIG, 8 is a flowchart illustrating an example of
processing procedures of a schedule process according to
the first embodiment.
FIG. 9 is a flowchart illustrating an example of
processing procedures performed by the terminal device
according to the first embodiment.
FIG. 10 is a diagram explaining a modification process
of a component carrier to which a data channel is assigned
according to a second embodiment.
FIG. 11 is a diagram explaining a control -channel

assignment method according to a third embodiment.
FIG. 12 is a diagram illustrating information included
in a main control channel and a sub control channel
according to a fourth embodiment.
FIG. 13 is a diagram explaining an example of a
control channel assignment method according to the fourth
embodiment.
FIG. 14 is a block diagram illustrating the
configuration of a base station according to a fifth
embodiment.
FIG. 15 is a diagram explaining a control channel
region setting method according to the fifth embodiment.
FIG. 16 is a diagram explaining a control channel
region setting method according to a sixth embodiment.
FIG. 17 is a diagram explaining a control channel
region setting method according to a seventh embodiment.
FIG. 18 is a diagram explaining a control channel
region setting method according to an eighth embodiment.
FIG. 19 is a flowchart illustrating an example of
processing procedures performed by a terminal device
according to the eighth embodiment.
FIG. 20 is a diagram illustrating an example of a
radio format of an LTE system..
FIG. 21 is a diagram illustrating an example of a
radio format of an LTE-Advanced system that is made by
bundling three system bands of the LTE system.
EXPLANATIONS OF LETTERS OR NUMERALS
[0020] S Radio communication system
1 Base station
2 Terminal device

10 Antenna
11 Storage unit

12 Control unit
13 Transmitting unit
14 Data channel receiving unit
110 Main carrier association table

120 Carrier determining unit
121 Control channel assigning unit
300 Component carrier

310 Control channel region
311 Control channel region identifier
312 Search space
313 Control channel

320 Data channel region
321 Assignment location of data channel
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0021] Exemplary embodiments of a base station, a
terminal device, a control channel assignment method, and a
region size determination method according to the present
invention will be explained below in detail with reference
to the accompanying drawings.
First Embodiment
[0022] First, it will be explained about the
configuration of a radio communication system including a
base station according to the first embodiment with
reference to the drawings. FIG. 1 is a schematic diagram
explaining a radio communication system according to the
first embodiment. As illustrated in FIG. 1, the radio
communication system S according to the first embodiment
includes a base station 1 and a plurality of terminal
devices 2a to 2c. The base station 1 performs radio data
communication, such as downlink, communication transmitting
signals from the base station 1 to each of the terminal
devices 2a to 2c and uplink communication transmitting

signals from each of the terminal devices 2a to 2c to the
base station 1, with the terminal devices 2a to 2c located
in a cell C that is a communication range.
[0023] In the first embodiment, radio data communication
between the base station 1 and the terminal devices 2 is
performed by using different frequency bands. Specifically,
the radio communication system S according to the first
embodiment performs radio data communication that uses
three LTE system bands. Hereinafter, it will be explained
about the configuration of a radio format that is used in
the radio communication system S according to the first
embodiment. FIG. 2 is a diagram illustrating a
configuration example of a radio format according to the
first embodiment.
(0024] As illustrated in FIG, 2, the radio format that
is used in the radio communication system S is formed by
bundling three system bands 300a to 300c of the LTE system.
Hereinafter, the system bands 300a to 300c of the-LTE
system are respectively referred to as component carriers
300a to 300c. In this case, the number of the component
carriers 300 is not limited to three.
[0025] The format of each of the component carriers 300a
to 300c is defined by one subframe unit. The component
carriers respectively include control channel regions* 310a
to 310c and data channel regions 320a to 320c. The control
channel regions 310 are regions to which control channels
are assigned, and the data channel regions 320 are regions
to which data channels are assigned.
[0026] A data channel is a divided area (channel)
obtained by dividing the data channel region 320 by a
predetermined time interval and is assigned to each of the
terminal devices 2. Moreover, a control channel includes
information that indicates the assignment location of data

channel in the data channel region 320. The terminal
device 2 transmits and receives data by using a data
channel for itself that is assigned in the data channel
region 320. The control channel according to the first
embodiment does not include information that indicates
which of the three component carriers 300a to 300c a data
channel is assigned to,
[0027] In the radio communication system S according to
the first embodiment, the component carriers 300a to 300c
have high frequency bands in the order of the component
carrier 300c → the component carrier 300b → the component
carrier 300a. Each of the component carriers 300a to 300c
independently forms one LTE system. The radio
communication system S can also perform radio data
communication that uses one of the component carriers 300.
[0028] Next, it will be explained about the
configuration of the base station 1 according to the first
embodiment. FIG. 3 is a block diagram illustrating the
configuration of the base station 1 according to the first
embodiment. FIG. 4 is a diagram illustrating an example of
a main carrier association table according to the first
embodiment. As illustrated in FIG. 3, the base station 1
according to the first embodiment includes an antenna 10, a
storage unit 11, a control unit 12, a transmitting unit 13,
and a data channel receiving unit 14.
[0029] The antenna 10 is used for transmitting and
receiving various types of data. In the first embodiment,
the antenna 10 is particularly used when transmitting a
control channel or a data channel to the terminal device 2
or when receiving a data channel from the terminal device 2.
[0030] The storage unit 11 stores therein the device
names of the terminal devices 2, the frequency bands of the
component carriers 300a to 300c, and the like, as various

types of information that is used for radio data
communication with the terminal devices 2. The storage
unit 11 particularly stores a main carrier association
table 110, The main carrier association table 110 stores
the component carriers 300 of the component carriers 300a
to 300c, to which the control channels for the terminal
devices 2 are respectively assigned, in association with
the terminal devices 2.
[0031] In other words, in the first embodiment, the
terminal devices 2a to 2c do not detect all the control
channel regions 310a to 310c of the component carriers 300a
to 300c but detect only the one predetermined control
channel region 310. Therefore, the base station 1 sets the
component carrier 300 having a control channel, to which
the control channel for the certain terminal device 2 is
assigned, as the main carrier of this terminal device 2,
and manages a correspondence relationship between the
terminal devices 2 and main carriers by using the main
carrier association table 110.
[0032] For example, as illustrated in FIG. 4, the main
carrier of the terminal device 2a is the component carrier
300a. In other words, the terminal device 2a receives only
the control channel assigned to the control channel region
310a of the component carrier 300a. Similarly, the main
carrier of the terminal device 2b is the component carrier
300b and the main carrier of the terminal device 2c is the
component carrier 300c.
[0033] The control unit 12 controls the whole of the
base station 1. The control unit 12 includes a carrier
determining unit 120 and a control channel assigning unit
121. The carrier determining unit 120 determines whih
location of which component carrier 300 a data channel for
the certain terminal device 2 is assigned at. Specifically,

the carrier determining unit 120 determines, from the
component carriers 300a to 300c, the component carriers 300,
to which data channels for each of the terminal devices 2
are assigned, in an ascending order of frequency bands of
the component carriers 300 by using the main carrier of the
terminal device 2 as a starting point.
[0034] For example, when transmitting one data to the
terminal device 2c, the carrier determining unit 120
assigns a data channel for the terminal device 2c to the
data channel region 320c of the component carrier 300c that
is the main carrier of the terminal device 2c. Moreover,
when transmitting two data to the terminal device 2c, the
carrier determining unit 120 determines, as the component
carriers 300 to which data channels corresponding to these
data are assigned, the component carrier 300c that is the
main carrier of the terminal device 2c and the component
carrier 300b that has a high frequency band next to the
component carrier 300c.
[0035] The control channel assigning unit 121 assigns a
control channel corresponding to a data channel for the
terminal device 2 at a location corresponding to the
component carrier 300 to which the data channel is assigned,
in the control channel region 310 of the main carrier of
this terminal device 2. Specifically, the control channel
assigning unit 121 determines the assignment location of a
control channel on the basis of the frequency band of the
component carrier 300 to which a data channel corresponding
to this control channel is assigned.
[0036] Hereinafter, it will be explained about a
specific assignment method of a control channel according
to the first embodiment. FIG. 5 is a diagram explaining a
control channel assignment method according to the first
embodiment. In this case, a control channel 313a

corresponds to a data channel assigned at an assignment
location 321b in the component carrier 300b and a control
channel 313b corresponds to a data channel assigned at an
assignment location 321a in the component carrier 300a.
Moreover, a control channel 313c corresponds to a data
channel assigned at an assignment location 321c in the
component carrier 300c.
[0037] As illustrated in FIG. 5, the control channels
313a to 313c for the terminal device 2b that uses the
component carrier 300b as a main carrier are assigned in
the control channel region 310b of the component carrier
300b. Moreover, a control channel region identifier 311
that is information that indicates a boundary location
between the control channel region 310b and the data
channel region 320b is assigned to the head of the centrol
channel region 310b.
[0038] When communicating with the base station 1, the
terminal device 2b first decodes the control channel region
identifier 311 located in the control channel region 310b
of the main carrier of the device itself in order to
identify the size of the control channel region 310b, the
starting position of the data channel region 320b, and the
like. In the first embodiment, the control channel region
identifier 311 assigned to the control channel region 310b
is applied to all the component carriers 300a to 300c. In
other words, the terminal device 2b decodes the control
channel region identifier 311 located at the control
channel region 310b in order to identify boundary locations
between the control channel regions 310a to 310c and the
data channel regions 320a to 320c of all the component
carriers 300a to 300c.
[0039] Moreover, one or a plurality of search spaces
different for each terminal device 2 is assigned in the

control channel region 310. A search space is a region in
the control channel region 310 and is arranged to be
detected (received) by a certain terminal device 2. For
example, as illustrated in FIG. 5, search spaces 312a to
312c are assigned in the control channel region 310b as
regions to be detected by the terminal device 2b.
[0040] The control channel assigning unit 121 assigns
the control channels 313a to 313c corresponding to the data
channels for the terminal device 2b (including the
assignment location information of the data channels) to
the search spaces 312a to 312c, In this case, the control
channel assigning unit 121 determines which of the search
spaces 312 which control channel is assigned to on the
basis of the frequency band of the component carrier 300 to
which the data channel is assigned.
[0041] In other words, the control channel assigning
unit 121 first assigns the control channel 313a
corresponding to the data channel assigned to the main
carrier (the component carrier 300b) of the terminal device
2b to the search space 312a first detected by the terminal
device 2b among the search spaces 312a to 312c. Next, the
control channel assigning unit 121 assigns a control
channel, which corresponds to the data channel assigned to
the component carrier 300a having a high frequency band
next to the component carrier 300b, to the search space
312b next detected by the terminal device 2b.
[0042] Because the component carrier 300 having a higher
frequency band than that of the component carrier 300a does
not exist, the control channel assigning unit 121 assigns
the control channel 313c corresponding to the component
carrier 300c having the lowest frequency band to the search
space 312c next detected by the terminal device 2b.
[0043] In this way, the control channel assigning unit

121 first sets the control channel 313 first detected, by
the terminal device 2 as a control channel corresponding to
the data channel assigned to the main carrier. Then, the
control channel assigning unit 121 assigns the other
control channels 313 at locations at which the sequence of
detection of the control channels 313 of the terminal
device 2 is associated with in the ascending order of
frequency bands of the component carriers 300 corresponding
to the control channels 313.
[0044] The transmitting unit 13 transmits the control
channel and the data channel to the terminal device 2 via
the antenna 10. The transmitting unit 13 includes a
control channel transmitting unit 130 and a data channel
transmitting unit 131. The control channel transmitting
unit 130 transmits the control channel 313 to the terminal
device 2 at the location assigned by the control channel
assigning unit 121. Moreover, the data channel
transmitting unit 131 transmits the data channel to the
terminal device 2 at the determined assignment location of
the component carrier 300 determined by the carrier
determining unit 120.
[0045] The data channel receiving unit 14 receives the
data channel transmitted from the terminal device 2 via the
antenna 10 at the determined assignment location of the
component carrier 300 determined by the carrier determining
unit 120,
[0046] Next, it will be explained about the
configuration of the terminal device 2 according to the
first embodiment. FIG. 6 is a block diagram illustrating
the configuration of the terminal device 2 according to the
first embodiment. As illustrated in FIG. 6, the terminal
device 2 according to the first embodiment includes an
antenna 20, a data channel transmitting unit 21, a

receiving unit 22, a storage unit 23, and a control unit 24.
[0047] The antenna 20 is used for transmitting and
receiving various types of data. In the first embodiment/
the antenna 20 is particularly used when a control channel
or a data channel is received, from the base station 1 or
when a data channel is transmitted to the base station 1.
[0048] The receiving unit 22 receives a control channel
and a data channel from the base station 1 via the antenna
20. The receiving unit 22 includes a control channel
receiving unit 220 that receives a control channel and a
data channel receiving unit 221 that receives a data
channel.
[0049] The storage unit 23 stores therein various bypes
of information that is used for radio data communication
with the base station 1. The storage unit 23 particularly
stores a mapping information management table 230. The
mapping information management table 230 stores a main
carrier of the device itself and a correspondence
relationship between the component carrier 300 and the
assignment location of a control channel in the control
channel region 310 of the main carrier. For example, the
mapping information management table 230 stored in the
storage unit 23 of the terminal device 2b stores, as the
information on the main carrier, that a main carrier is the
component carrier 300b. Moreover, the mapping information
management table 230 of the terminal device 2b stores that
the sequence of detection of control channels is associated
with the ascending order of frequency bands of the
component carriers 300 corresponding to the control
channels.
[0050] The control unit 24 controls the whole of the
terminal device 2. The control unit 24 includes a table
updating unit 240 and a carrier specifying unit 241. The

table updating unit 240 corresponds to an information
updating unit, and modifies the information of the mapping
information management table 230 in accordance with the
request of the base station 1. Specifically, the table
updating unit 240 modifies a correspondence relationship
between the component carrier and the assignment location
of a control channel in the control channel region 310 of
the main carrier of the device itself.
[0051] The carrier specifying unit 241 corresponds to a
band specifying unit, and specifies the component carrier
300 to which a data channel corresponding to this control
channel is assigned on the basis of the assignment location
of the received control channel in the control channel
region and the mapping information management table 230.
For example, the carrier specifying unit 241 of the
terminal device 2b specifies that the control channel 313a
in the search space 312a first: detected by the terminal
device 2b, among the search spaces 312a to 312c in the
control channel region 310b of the main carrier, is a
control channel corresponding to the data channel assigned
to the main carrier.
[0052] Next, the carrier specifying unit 241 specifies
that the control channel 313b in the next search space 312b
is a control channel corresponding to the data channel
assigned to the component carrier 300a that has a high
frequency band next to the main carrier. Moreover, because
a component carrier having a frequency band higher than
that of the component carrier 300a does not exist, the
carrier specifying unit 241 specifies that the control
channel 313c in the next search space 312c is a control
channel corresponding to the data channel assigned to the
lowest component carrier 300c in the system.
[0053] Next, it will be explained about specific

operations of the base station 1 according to the first
embodiment with reference to the drawing. FIG. 7 is a
flowchart illustrating an example of processing procedures
performed by the base station 1 according to the first
embodiment. In FIG. 7, among the processing procedures
that are performed by the base station 1, only processing
procedures on the transmission of a control channel and the
transmission and reception of a data channel to and from
the one terminal device 2 are illustrated.
[0054] As illustrated in FIG. 7, the control unit 12 of
the base station 1 first performs a schedule process (Step
S11). The schedule process for performing scheduling on a
transmission timing etc. of a control channel or a data
channel for the terminal device 2 will be described below.
Next, the control unit 12 transmits a control channel to
the terminal device 2 on the basis of the scheduling result
at Step Sll (Step S12).
[0055] Next, the control unit 12 determines whether the
control channel transmitted at Step S12 is a downlink
control channel from the base station 1 to the terminal
device 2 (Step S13). In the process, when it is determined
that the control channel transmitted at Step S12 is a
downlink control channel (Step S13: YES), the control unit
12 transmits data to the terminal device 2 at an assignment
location based on the scheduling result at Step Sll (3tep
S14). On the other hand, when the control channel
transmitted at Step S12 is not a downlink control channel,
in other words, when the control channel is an uplink
control channel (Step S13: NO), the control unit 12
receives a data channel at the assignment location based on
the scheduling result (Step S15).
[0056] Next, it will be explained about the schedule
process at Step Sll with reference to the drawing. FIG. 8

is a flowchart illustrating an example of processing
procedures of the schedule process according to the first
embodiment.
[0057] As illustrated in FIG. 8, the carrier determining
unit 120 determines the component carrier 300 that
transmits a data channel (Step S21). Specifically, the
carrier determining unit 120 determines, from the component
carriers 300a to 300c, the component carrier 300 to which a
data channel for each of the terminal devices 2 is assigned
in an ascending order of frequency bands of the component
carriers 300 by using the main carrier of this terminal
device 2 as a starting point.
[0058] Next, the carrier determining unit 120 determines
whether the component carrier 300 for transmission is
decided for all the data channels (Step S22). In the
process, when there is a data channel on which the decision
of the component carrier 300 for transmission is not yet
performed (Step S22: NO), the carrier determining unit 120
shifts the process to Step S21, On the other hand, when it
is determined that the decision o£ the component carrier
300 for transmission has been performed on all the data
channels (Step S22: YES), the carrier determining unit 120
shifts the process to Step S23.
[0059] At Step S23, the control channel assigning unit
121 assigns the control channel corresponding to the data
channel assigned to the main carrier of the terminal device
2 in the search space 312 first detected by the terminal
device 2 among the search spaces 312 assigned to the
terminal device 2 in the control channel region 310 of the
main carrier (Step S23). Next, the control channel
assigning unit 121 assigns the control channel
corresponding to the component carrier 300 having a high
frequency band next to the main carrier in the search space

312 next detected by the terminal device 2 (Step S24).
[0060] Next, the control channel assigning unit 121
determines whether the assignment to the search space 312
has been performed on all the control channels (Step S25).
In the process, when there is a control channel on which
the assignment to the search space 312 is not yet performed
(Step S25: NO), the control channel assigning unit 121
shifts the process to Step S26.
[0061] At Step S26, the control channel assigning unit
121 determines whether the control channel corresponding to
the component carrier having the highest frequency band has
been assigned in the search space 312. In the process,
when the control channel is not assigned in the search
space 312 (Step S26: NO), the control channel assigning
unit 121 shifts the process to Step S24. On the other hand,
when it is determined that the control channel is assigned
in the search space 312 (Step S26: YES), the control
channel assigning unit 121 shifts the process to Step S27.
[0062] At Step S27, the control channel assigning unit
121 assigns the remaining control channels to the search
space 312 in sequence from the control channel that has the
lowest frequency band of the corresponding component
carrier 300. When the process is finished or when it is
determined at Step S25 that the assignment to the search
space 312 is already performed on all the control channels
(Step S25: YES), the control channel assigning unit 121
terminates the schedule process.
[0063] Next, it will be explained about specific
operations of the terminal device 2 according to the first
embodiment. FIG. 9 is a flowchart illustrating an example
of processing procedures performed by the terminal device
according to the first embodiment. In FIG. 9, only
processing procedures on the reception of a control channel

and the transmission and reception of a data channel are
illustrated among the processing procedures that are
performed by the terminal device 2.
[0064] As illustrated in FIG. 9, the control unit 24 of
the terminal device 2 detects the control channel region
identifier 311 located in the control channel region 310 of
the main carrier of the device itself and decodes the
control channel region identifier 311 (Step S31). Next,
the control unit 24 receives all the control channels in
the search spaces 312 assigned to the device itself and
decodes all the control channels (Step S32).
[0065] Next, the control unit 24 determines whether a
control channel for data assignment exists among the
control channels decoded at Step S32 (Step S33). In the
process, when it is determined that a control channel for
data assignment exists (Step S33: YES), the control unit 24
shifts the process to Step $34,
[0066] At Step S34, the control unit 24 determines
whether the nnmber of control channels for data assignment
is two or more or not. In the process, when it is
determined that the number of control channels for data
assignment is two or more (Step S34: YES), the control unit
24 shifts the process to Step S35.
[0067] At Step S35, the carrier specifying unit 241
specifies the component carrier 300 to which the data
channel corresponding to each control channel is assigned
on the basis of the mapping information stored in the
mapping information management table 230. Specifically,
the carrier specifying unit 241 specifies the control
channel 313 located in the search space 312, first detected
by the device itself, among the search spaces 312 in the
control channel region 310 of the main carrier as a control
channel corresponding to the data channel assigned to the

main carrier.
[0068] The carrier specifying unit 241 specifies the
control channel 313 in the next search space 312 as a
control channel corresponding to the data channel assigned
to the component carrier 300 that has a high frequency band
next to the main carrier. Moreover, when specifying the
control channel corresponding to the component carrier that
has the highest frequency band, the carrier specifying unit
241 specifies the control channel 313 in the next search
space 312 as a control channel corresponding to the data
channel assigned to the lowest component carrier 300 in the
system.
[0069] When the process of Step S35 is finished or when
the number of control channels for data assignment is not
two or more at Step $34 (Step S34: NO), the control unit 24
determines whether the control channel is a downlink
control channel (Step S36). In the process, when it is
determined that the control channel is a downlink control
channel (Step S36: YES), the control unit 24 receives a
data channel for the device itself at the assignment
location indicated by the control channel in the component
carrier 300 specified at Step S35 (Step S37). On the other
hand, when the control channel is not a downlink control
channel (Step S36: NO), in other words, when the control
channel is an uplink control channel, the control unit 24
transmits data at the assignment location indicated by the
control channel in the specified component carrier 300
(Step S38) .
[0070] When the process of Steps S37 and S38 is finished
or when there is not a control channel for data assignment
at Step S33 (Step 333: NO), the control unit 24 terminates
the process on the transmission and reception of the
control channel and the data channel.

[0071] As described above, according to the first
embodiment, the base station 1 assigns a control channel at
a location according to the component carrier 300 to which
a data channel corresponding to this control channel is
assigned. Therefore, because the terminal device 2 can
identify which of the component carriers 300 the control
channel corresponds to in accordance with the assignmsnt
location of the control channel, an amount of information
of the control channel can be decreased. As a result,
because the reduction of a data channel region can be
prevented/ frequency use efficiency can be improved.
[0072] when radio data communication is performed by
using only one LTE system band in the LTE-Advanced sy.stem
that performs communication by using a plurality of LTE
system bands, a terminal device combines (blind decode)
both of a control channel for LTE and a control channel for
LTE-Advanced. By doing so, because a throughput increases
and thus power consumption increases, a circuit for
parallel processing can be separately provided in the
terminal device in some cases. However, because one blind
decode pattern is used by using the radio communication
system S according to the first embodiment, a throughout
can be reduced and also a circuit for parallel processing
may not be provided in the terminal device.
[0073] Because information included in the control
channel is similar to that of the conventional LTE system,
the LTE-Advanced system has compatibility with a device
that performs communication by using only one component
carrier and thus a development overhead can be reduced when
various types of devices according to the first embodiment
are developed from these devices.
[0074] In the first embodiment, it has been explained
about the case where the assignment of control channels to

the control channel regions 310 is performed in an
ascending order of frequency bands of the component
carriers 300 corresponding to the control channels.
However, the present invention is not limited to this. The
assignment may be performed in a descending order to obtain
a similar effect.
Second Embodiment
[00753 According to the second embodiment, a
correspondence relationship between the assignment location
of a control channel and the component carrier 300 is
changed in response to the request of the base station 1.
As a result, even when data to be transmitted or received
is concentrated on terminal devices that use a certain
component carrier 300 as a main carrier, a wider range of
the component carriers 300 can be used. It will be below
explained about the flow of a modification process of a
correspondence relationship between the assignment location
of a control channel and a component carrier. PIG. 10 is a
diagram explaining a modification process of a component
carrier to which a data channel is assigned according to
the second embodiment. In this case, the same
configuration as that explained already has the same
reference numbers, and their descriptions will not be
repeated.
[0076] In the first embodiment, it has been explained
about the case where the terminal device that receives the
control channel of the component carrier #3 assigns only
consecutive component carriers, which begin with the
component carrier #3, such as "the component carrier #3",
"the component carriers #3 and #4", and "the component
carriers #3, #4, and #5". However, when data assignment is
concentrated on, for example, the terminal device that uses
the component carrier #3 as a main carrier, the component

carrier #2 will not be effectively used even if the
terminal device to which the component carrier #2 is
assigned does not exist. Therefore, when transmission data
is concentrated on the terminal device that uses a certain
component carrier as a main carrier, the base station 1
performs signaling and modifies the assignment sequence of
the data channels.
[0077] Specifically, as illustrated in FIG. 10, the
carrier determining unit 120 of the base station 1 changes
the component carrier 300 to which each data channel is
assigned in accordance with a communication situation of
each of the component carriers 300 to which a data channel
is assigned (Step S51).
[0078] In other words, when data transmission is
concentrated on, for example, the terminal device 2 that
uses the component carrier #3 as a main carrier, the
carrier determining unit 120 changes the component carriers
#3, #4, and #5, to which the data channel of the certain
terminal device 2 is assigned, to the component carrisrs #0,
#1, and #2.
[0079] When a correspondence relationship between the
assignment location of the control channel and the
component carrier is modified by the carrier determining
unit 120, the base station 1 transmits mapping information
that indicates a correspondence relationship after
modification to the terminal device 2.
[0080] When the mapping information is acquired, in
other words, when information indicating the correspondence
relationship after modification is acquired from the base
station 1, the table updating unit 240 of the terminal
device 2 updates the mapping information management table
230 on the basis of the information (Step S52).
[0081] Next, the control unit 12 of the base station 1

performs a schedule process on the basis of the
correspondence relationship modified at Step S51 (Step S53),
and transmits a control channel at an assignment location
according to the scheduling result (Step S54). On the
other hand, upon receiving the control channel, the carrier
specifying unit 241 of the terminal device 2 specifies the
component carrier 300 corresponding to each control channel
on the basis of the mapping information updated at Step S52
(Step S54) .
[008?] The control unit 12 of the base station 1
performs data transmission at a predetermined assignment
location of each of the component carriers 300 determined
as the component carrier 300 to which the data channel is
assigned at Step S51 (Step S55), Then, the control unit 24
of the terminal device 2 receives a data channel for the
device itself at the assignment location indicated by the
acquired control channel in the data channel region 320 of
the component carrier 300 specified at Step S54 (Step S56).
In this case, the process of Steps S53 to S56 is repeatedly
performed every subframe.
[0083] As described above, according to the second
embodiment, because the correspondence relationship batween
the assignment location of a control channel and a
component carrier is modified, the component carrier 300
can be more widely used even when data to be transmitted or
received is concentrated on the plurality of terminal
devices 2 that uses the certain component carrier 300 as a
main carrier.
[0084] The above-described method is a solution whan
data transmission is concentrated in the short term. For
example, the number of the terminal devices 2 that use the
certain component carrier 300 as a main carrier may be
largely different between the component carriers 300. In

this case, a correspondence relationship may be modified
between each of the terminal devices 2 and the component
carrier 300 that is a main carrier.
Third Embodiment
[0085] In the first embodiment, it has been explained
about the case where the terminal device 2 receives only a
control channel in the search space 312. According to the
third embodiment, a control channel is assigned to a space
other than the search space 312. Hereinafter, it will be
- pecifically explained about a control channel assignment
method according to the third embodiment. FIG. 11 is a
diagram explaining a control channel assignment method
according to the third embodiment. In this case, the same
configuration as that explained already has the same
reference numbers, and their descriptions will not be
repeated.
[0086] In the third embodiment, when a plurality of
control channels is assigned as a control channel for the
certain terminal device 2, the control channel assigning
unit 121 of the base station 1 assigns each.control channel
a consecutive location in the control channel region 310 of
the main carrier of the terminal device 2. For example,
when the control channels 313a to 313c for the terminal
device 2b are assigned, the control channel assigning unit
121 assigns the control channel 313a corresponding to the
main carrier of the terminal device 2b in the search space
312a of the terminal device 2b.
[0087] Next, the control channel assigning unit 121
assigns the control channel 313b corresponding to the
component carrier 300a having a high frequency band next to
the main carrier, not in the search space 312b, but a
continued location next to the control channel 313a.
Moreover, the control channel assigning unit 121 assigns

the control channel 313c corresponding to the component
carrier 300c a continued location next to the control
channel 313b. In this case, the control channel 3131: can
be larger than the search space 312a. The control channel
assigning unit 121 assigns each of the control channels
313a to 313c in the control channel region 310 irrespective
of the size of the search space 312.
[0088] On the other hand, the terminal device 2b first
decodes the control channel in the search space 312a of the
device itself similarly to the first embodiment. Then,
upon detecting the control channel 313a for data assignment,
the terminal device 2b decodes the control channel located
at a continued location next to the control channel 313a.
[O'J-,,9] At this time, the size of each control channel
313 may be previously set to the same value as that of the
first detected control channel 313a. Generally, the more
the number of the search spaces 312, the more false
detection caused by blind decode. However, because the
control channel 313 can be assigned to a space other than
the search space 312 by using the aforementioned method,
the assignment region of the control channel 313 is
increased and thus a false detection probability of blind
decode can be reduced.
[0090] There is a high possibility that the other
control channel 313 exists at a continued location next to
the control channel 313 that has been already detected.
Therefore, the reception success probability of the control
channel 313 can be raised by determining presence/abssnce
thresholds of the control channel 313 when the terminal
device 2 detects the control channel 313 on the assumption
that the possibility of the presence of the control channel
313 is high (by determining that the control channel exists
even if a signal level is low).

Fourth Embodiment
[0091] According to the fourth embodiment, main and sub
control channels are provided and have the different
numbers of bits. Hereinafter, it will be specifically
explained about the configuration of main and sub control
channels according to the fourth embodiment. FIG, 12 is a
diagram illustrating information included in a main control
channel and a sub control channel according to the fourth
embodiment. FIG. 13 is a diagram explaining an example of
a control channel assignment method according to the fourth
embodiment. In this case, the same configuration as that
explained already has the same reference numbers, and their
descriptions are omitted.
[0092] As illustrated in FIG. 12, a main control channel
314 includes all information for data channel reception in
addition to data channel assignment location information.
For example, there are the number of bits of data, a
modulation method, retransmission information, power
control information, and the like as the other information.
Moreover, sub control channels 315a and 315b include only
data channel assignment information. The terminal device 2
uses the other information included in the main control
channel 314 as information of the sub control channels 315a
and 315b.
[0093] In this case, the main control channel 314 is
assigned at the location first detected by the terminal
device 2 in the control channel region 310 of the component
carrier 300. As a result, the terminal device 2 first
detects the main control channel 314, and uses the other
information included in the main control channel 314 for
the sub control channels 315a and 315b that are detected
afterwards.
[0094] As described above, according to the fourth

embodiment, because the sub control channel 315 includes
only the data channel assignment location information and
the other information included in the main control channel
314 is used for the sub control channel 315,, the total
number of bits of the control channel can be reduced.
[0095] For example, as illustrated in FIG. 13, the main
control channel 314 and the sub control channel 315 can be
assigned at continued locations in the control channel
region 310 by previously setting the size of the main
control channel 314 to two times of the size of the sub
control channel 315. As a result, the same effect as that
of the third embodiment can be obtained.
Fifth Embodiment
[0096] According to the first to fourth embodiments
described above, it has been explained about the case where
it is previously decided that the component carriers 300
have the same control channel region identifier 311. This
method is effective in that the operation of the terminal
device 2 is simple. However, it is not possible to adjust
the size of the control channel region 310 for each of the
component carriers 300. Therefore, the component carrier
300 having few control channels for transmission includes
an useless area and thus frequency use efficiency decreases.
Therefore, the fifth embodiment changes the size of the
control channel region 310 among the component carriers 300.
[0097] Hereinafter, it will be specifically explained
about a control channel region setting method according to
the fifth embodiment. FIG. 14 is a block diagram
illustrating the configuration of the base station
according to the fifth embodiment. FIG. 15 is a diagram
explaining a control channel region setting method
according to the fifth embodiment. In this case, the same
configuration as that explained already has the same

reference numbers, and their descriptions will not be;
repeated..
[0098] As illustrated in FIG. 14, the control unit. 12 of
the base station 1 of the fifth embodiment includes a
region setting unit 122. The region setting unit 122 sets
the size of the control channel region 310 for each cf the
component carriers 300. In the fifth embodiment, the
region setting unit 122 particularly sets the size of the
control channel region of the component carrier 300 other
than the main carrier to a value smaller than that of the
control channel region 310 of the main carrier.
[0099] Specifically, the size of the control channel
region 310 of each of the component carriers 300 can be
modified stepwise. The region setting unit 122 sets the
size of the control channel region 310 of the component
carrier 300 other than the main carrier to the minimum
value of the several steps.
[0100] For example, as illustrated in FIG. 15, when the
component carrier 300b is a main carrier, a control channel
corresponding to the component carrier 300a is assigned to
the control channel region 310b of the component carrier
300b that is a main carrier. Therefore, the size of the
control channel region 310a of the component carrier 300a
may be smaller than that of the control channel region 310b
of the component carrier 300b.
[0101] In this way, a useless area can be reduced by
setting the size of the control data channel region of the
component carrier 300 other than the main carrier to the
minimum value. Moreover, because the data channel region
320 of the component carrier 300 other than the main
carrier can be increased, frequency use efficiency is
raised.
Sixth Embodiment

[0102] According to the sixth embodiment, a data channel
region is determined on the assumption that the possible,
maximum value of the sizes of the control channel regions
310 is selected as the size of the control channel region
310 of the component carrier 300 to which a control channel
is not assigned. Hereinafter, it is specifically explained
about the setting method of the control channel region 310
according to the sixth embodiment. FIG. 16" is a diagram
explaining a control channel region setting method
according to the sixth embodiment. The same configuration
as that explained already has the same reference numbers,
and their descriptions will not be repeated,
[0103] In the sixth embodiment, the carrier determining
unit 120 of the base station 1 determines the assignment
location of a data channel in the data channel region 320
of each of the component carriers 300, assuming that the
size of the control channel region 310 of the component
carrier 300 other than the main carrier is set to the
maximum size of the sizes that can be taken by the control
channel regions 310.
[0104] For example, as illustrated in FIG. 16, when the
component carrier 300b is a main carrier, the size of the
control channel region 310b of the component carrier 300b
is identified by the control channel region identifier 311.
On the other hand, the sizes of the control channel rsgions
310a and 310c of the component carriers 300a and 300c are
set to the maximum size of the sizes that can be taken by
the control channel regions 310,
[0105] At this time, there is a high possibility t.nat
the sizes of the control channel regions 310a and 310z of
the component carriers 300a and 300c are actually smaller
than the set size. Therefore, for example, when data
transmission is performed on the terminal device 2a that

uses the component carrier 300a as a main carrier by using
only the component carrier 300a, the size of a control
channel region 410 can be determined in accordance with the
size of the control channel for the terminal device 2a, and
thus frequency use efficiency can be raised.
Seventh Embodiment
[0106] Hereinafter, it is specifically explained aoout
the setting method of the control channel region 310
according to the seventh embodiment. FIG. 17 is a diagram
explaining a control channel region setting method
according to the seventh embodiment. The same
configuration as that explained already has the same
reference numbers, and their descriptions will not be
repeated. In the seventh embodiment, data channel
assignment is performed on the assumption that the control
channel region 310 having the same size as that of the main
carrier is assigned to the other component carriers 300.
[0107] In the seventh embodiment, the carrier
determining unit 120 determines the assignment location of
a data channel in the data channel region of each of the
component carriers 300, assuming that the sizes of the
control channel regions 310 of the component carriers 300
other than the main carrier are the same as that of the
control channel region 310 of the main carrier.
[0108] For example, as illustrated in FIG. 17, when the
component carrier 300b is a main carrier, the size of the
control channel region 310b of the component carrier 300b
is identified by the control channel region identifier 311.
On the other hand, the sizes of the control channel regions
310a and 310c of the component carriers 300a and 300c are
set to the same as that of the control channel region 310b
of the component carrier 300b.
[0109] As a result, when data, transmission is performed

on, for example, the terminal device 2a that uses the
component carrier 300a as a main carrier by using only the
component carrier 300a, the size of the control channel
region 410 can be determined in accordance with the size of
the control channel for the terminal device 2a and thus
frequency use efficiency can be raised. Moreover, there is
a high possibility that the sizes of the control channel
regions 310 of the component carriers 300 other than the
main carrier are smaller than that of the control channel
region 310 of the main carrier. Therefore, it may be
assumed that the sizes of the control channel regions 310
are not the maximum value like the sixth embodiment. The
data channel region can be increased that much.
Eighth Embodiment
[0110] Hereinafter, it is specifically explained about
the setting method of the control channel region 310
according to the eighth embodiment. FIG. 18 is a diagram
explaining a control channel region setting method
according to the eighth embodiment.
[0111) In the eighth embodiment, each of the component
carriers 300 independently sets the control channel rogion
310 and uses a remaining portion as the data channel region
320. Specifically, as illustrated in FIG. 18, control
channel region identifiers 311a to 311c are respectively
assigned to the control channel regions 310a to 310c of the
component carriers 300a to 300c.
[0112] It will be explained about the specific
operations of the terminal device 2 according to the eighth
embodiment. FIG. 19 is a flowchart illustrating an example
of processing procedures performed by the terminal device 2
according to the eighth embodiment. The processing
procedures other than Step S76 among the processing
procedures of the terminal device 2 according to the eighth

embodiment are similar to those of the terminal device 2
according to the first embodiment illustrated in FIG. 9,
and their descriptions will not be repeated.
[0113] As illustrated in FIG. 19, when the component
carrier 300 corresponding to each control channel is
specified at Step S75, the control unit 24 of the terminal
device 2 decodes the control channel region identifier 311
that is assigned to the control channel region 310 of each
of the component carriers 300 (Step S76). As a result, the
terminal device 2 can identify the size of the control
channel region 310 of each of the component carriers 300.
[0114] Although the invention has been described with
respect to specific embodiments for a complete and clear
disclosure, the appended claims are not to be thus limited
but are to be construed as embodying all modifications and
alternative constructions that may occur to one skilled in
the art that fairly fall within the basic teaching herein
set forth.
[0115] For example, it has been mainly explained about
the assignment of a downlink data channel in the firs': to
eighth embodiments described above. However, the present
invention is applied to the assignment of an uplink data
channel.

WE CLAIM:
1. A base station that performs radio data
communication with terminal devices by using a
plurality of bands of which each has a data channel
region to which a data channel is assigned and a
control channel region to which a control channel
is assigned, the base station comprising :
A control channel assigning unit that assigns a
control channel for the terminal device at a
location corresponding to a band to which a data
channel assigned to the terminal device belongs, in
the control channel region of any band of the
plurality of bands; and
a control channel transmitting unit that transmits
the control channel to the terminal device at the
location assigned by the control channel assigning
unit.
2. The base station according to claim 1, wherein the
control channel assigning unit assigns the control channel
for the terminal device to the control channel region in
any one of the plurality of bands in such a manner that a
detection sequence of the control channels performed by the
terminal device is identical to a sequence of frequency
bands of the bands corresponding to the control channels.
3. The base station according to claim 2, wherein the
control channel assigning unit sets the sequence of
frequency bands of the bands corresponding to the control
channels as an ascending order or a descending order of the
frequency bands of the bands by using the band to whc.ch the
control channel for the terminal device is assigned as a
starting point.

4. The base station according to claim 3, wherein the
control channel assigning unit sets a control channel
detected by the terminal device next to the control channel
corresponding to a band having the highest/lowest frequency
band to a control channel corresponding to a band having
the lowest/highest frequency band, as the detection
sequence of the control channels performed by the terminal
device.
5. The base station according to claim 1, further
comprising a carrier determining unit that determine.?,
among the plurality of bands, bands to which the data
channel for each of the terminal devices is assigned in an
ascending order or a descending order of frequency bands of
the bands by using the band to which the control channel
for the terminal device is assigned as a starting point.
6. The base station according to claim 5, wherein the
carrier determining unit modifies a band to which the data
channel is assigned in accordance with a communication
situation of each of the bands to which the data channel is
assigned.
7. The base station according to claim 2, wherein the
control channel assigning unit assigns the control channels
corresponding to the data channels at consecutive locations
in the control channel region of the band to which the
control channel for the terminal device is assigned.
8. The base station according to claim 1, wherein a
control channel other than the control channel assigned at
a location first detected by the terminal device, in the
control channel region of the band to which the control
channel for the terminal device is assigned, includes only
information that indicates an assignment location of the
data channel.

9. A terminal device that performs radio data
communication with a base station by using a
plurality of bands of which each has a data
channel region to which a data channel is
assigned and a control channel region to which
a control channel is assigned, the terminal
device comprising:
a control channel receiving unit that receives,
from the base station, a control channel
assigned to a control channel region of a band
to which a control channel for the terminal
device is assigned; and
a data channel receiving unit that receives a
data channel at an assignment location
indicated by the control channel in a data
channel region of a band corresponding to a
location to which the control channel received
by the control channel receiving unit is
assigned in the control channel region.
10. The terminal device according to claim 9, further
comprising:
a storage unit that stores therein a band to which the
control channel for the device itself is assigned among the
plurality of bands and a correspondence relationship
between the band and an assignment location of the control
channel in the control channel region of the band; and
an information updating unit that modifies, in
accordance with a request of the base station, the
correspondence relationship between the band and the
assignment location of the control channel in the control
channel region of the band stored in the storage unit to
which the control channel for the device itself is assigned.

11. The terminal device according to claim 9, wherein the
control channel receiving unit determines/ upon receiving
the control channel, that another control channel is
assigned at an assignment location continued next to the
assignment location of the control channel and receives the
control channel at the continued assignment location.
12. A method for assigning a control channel to a control
channel region by using a plurality of bands of which each
has a data channel region to which a data channel is
assigned and a control channel region to which a control
channel is assigned when radio data communication is
performed between a base station and a terminal device, the
method comprising
assigning, by the base station, a control
annel for the terminal device at a location corresponding
a band to which a data channel assigned to the terminal
ice belongs, in the control channel region of any band
the plurality of bands.
13. A base station that performs radio data communication
with terminal devices by using a plurality of bands of
which each has a data channel region to which a data
channel is assigned and a control channel region to which a
control channel is assigned, the base station comprising
a region setting unit that sets a size of the control
channel region for each of the bands.
14. The base station according to claim 13, wherein
the base station further comprises a storage unit that
stores therein, among the plurality of bands, a band to
which the control channel for one terminal device is

assigned in association with the one terminal device, and
the region setting unit sets a size of a control
channel region of a band other than the band to which the
control channel for the one terminal device is assigned to
a value smaller than that of the control channel region of
the band to which the control channel for the one terminal
device is assigned.
15. The base station according to claim 14, wherein
the base station further comprises a carrier
determining unit that determines, among the plurality of
bands, one or a plurality of bands including the band to
which the control channel for the one terminal device is
assigned as a band to which a data channel for the one
terminal device is assigned and determines an assignment
location of the data channel in the data channel region of
each of the bands, and
the carrier determining unit determines the assignment
location of the data channel in the data channel region of
each of the bands assuming that the size of the control
channel region of the band other than the band to which the
control channel for the one terminal device is assigned is
set to a maximum size of sizes that can be taken by the
control channel regions.
16. The base station according to claim 14, wherein the
carrier determining unit determines the assignment lccation
of the data channel in the data channel region of each of
the bands assuming that the size of the control channel
region of the band other than the band to which the control
channel for the one terminal device is assigned is a same
as that of the control channel region of the band to which
the control channel for the one terminal device is assigned.

17. A method for setting a region size of a control
channel region when radio data communication is performed
between a base station and terminal devices by using a
plurality of bands of which each has a data channel region
to which a data channel is assigned and a control channel
region to which a control channel is assigned, the method
comprising
setting by the base station, a size of the control
channel for each of the bands.

It is an object to improve the frequency use
efficiency of the overall system. In order to solve the
object, a base station that performs radio data
communication with terminal devices by using a plurality of
bands of which each has a data channel region to which a
data channel is assigned and a control channel region to
which a control channel is assigned. The base station
includes a control channel assigning unit that assigns a
control channel for the terminal device at a location in
the control channel region of any band of the plurality of
bands according to a band to which a data channel assigned
to the terminal device belongs, and a control channel
transmitting unit that transmits the control channel to the
terminal device at the location assigned by the control
channel assigning unit.