METHOD FOR CONTROLLING HANDOVER, USER EQUIPMENT, BASE
5 STATION, AND RADIO COMMUNICATION SYSTEM
Technical Field
[0001]
The present invention relates to a method for controlling a handover, a user
10 equipment, a base station, and a radio communication system.
Background Art
[0002]
In Long Term Evolution-Advanced (LTE-A), which is the next-generation
15 cellular communication standard that is discussed in Third Generation Partnership
Project (3GPP), introduction of technology called carrier aggregation (CA) has been
studied. The carrier aggregation is technology that forms a communication channel
between a user equipment (UE) and a base station (BS, or evolved Node B (eNB)) by
aggregating a plurality of frequency bands that are supported in LTE, for example,
20 and thereby improves communication throughput. Each frequency band included in
one communication channel by the carrier aggregation is called a component carrier
(CC). The bandwidths of frequency bands that are available in LTE are 1.4 MHz,
3.0 MHz, 5.0 MHz, 10 MHz, 15 MHz, and 20 MHz. Accordingly, if five bands of
20 MHz are aggregated as component carriers, a communication channel of 100
25 MHz in total can be formed.
[0003]
Component carriers that are included in one communication channel in the
carrier aggregation are not necessarily contiguous to one another in the frequency
direction. The mode in which component carriers are arranged contiguous to one
30 another in the frequency direction is called a contiguous mode. On the other hand,
the mode in which component carriers are arranged not contiguous to one another is
2/41
called a non-contiguous mode.
[0004]
SP262630W000
Further, in the carrier aggregation, the number of component carriers in an
uplink and the number of component carriers in a downlink are not necessarily equal.
5 The mode in which the number of component carriers in an uplink and the number of
component carriers in a downlink are equal is called a symmetric mode. On the
other hand, the mode in which the number of component carriers in an uplink and the
number of component carriers in a downlink are not equal is called an asymmetric
mode. For example, in the case of using two component carriers in an uplink and
10 three component carriers in a downlink, it is asymmetric carrier aggregation.
[0005]
In radio communication of a conventional cellular system involving the
carrier aggregation, allocation information of communication resources (that is,
scheduling information) is transmitted from a base station from each user equipment
15 over a downlink control channel (for example, PDCCH: Physical Downlink Control
Channel). In radio communication not involving the carrier aggregation, the
scheduling information can be transmitted according to two kinds of methods. A
first method is a method in which a conventional method is applied to individual
component carriers as is. In other words, in the first method, a control channel for
20 transmitting scheduling information on data transmission in a certain component
carrier is set inside the corresponding component carrier. In this disclosure, the first
method is referred to as a straight scheduling method. On the other hand, in a
second method, a control channel for transmitting scheduling information on data
transmission in a certain component carrier is set inside a component carrier different
25 from the corresponding component carrier. According to the second method, when
communication resources used for transmission of scheduling information are
aggregated, a ratio of overhead occupied by communication resources is reduced.
Thus, the second method can achieve a higher throughput than the first method. In
this disclosure, the second method is referred to as a "cross scheduling method."
30 The straight scheduling method and the cross scheduling method can be complexly
used within one communication channel. In other words, one channel configuring a
3/41
SP262630W000
communication channel may be operated by the cross scheduling method, and
another channel may be operated by the straight scheduling method.
[0006]
A handover, which is a basic technique for achieving the mobility of a user
5 equipment in the cellular communication standard, is one of important subjects in
LTE-A. In LTE, a user equipment measures a communication quality over a
channel with a serving base station (a currently connected base station) and
communication qualities with peripheral base stations and transmits a measurement
report containing measurements to the serving base station . Receiving the
10 measurement report, the serving base station determines whether to execute a
handover based on the measurements contained in the report . Then, if it is
determined that a handover is to be executed, a handover is carried out among a
source base station (the serving base station before a handover ), the user equipment,
and a target base station (a serving base station after a handover) in accordance with
15 a prescribed procedure (e.g. cf. Patent Literature 1 below).
Citation List
Patent Literature
[0007]
20 Patent Literature 1:
Technical Problem
JP 2009-232293A
Summary of Invention
[0008]
25 However, no case has been reported where active consideration is given to
how to carry out a handover procedure in a radio communication involving the
carrier aggregation.
[0009]
In the existing handover procedure disclosed in Patent Literature 1,
30 processing such as a handover request, approval of the request, issuance of a
handover command, and random access to a target base station is performed under
4/41
SP262630 WO00
the assumption that one communication channel is configured with one component
carrier. When the carrier aggregation technique is introduced, since component
carriers are assumed to differ in the channel quality from each other, it is desirable to
execute a handover for each component carrier. However, under the circumstances
5 in which the cross scheduling method is employed, a data channel used to perform
data transmission and a control channel used to transmit scheduling information
related to data transmission can be located in different component carriers. For this
reason, when a handover procedure of each component carrier is not appropriately
controlled, data loss may occur due to loss or mismatching of scheduling information
10 or the like.
[0010]
In this regard, the present invention aims to provide a method for controlling
a handover, a user equipment, a base station, and a radio communication system,
which are novel and improved and are capable of performing a handover with no
15 data loss even under the circumstances in which the cross scheduling method is
employed.
Solution to Problem
[0011]
20 According to an aspect of the present invention, there is provided a method
for controlling a handover from a first base station to a second base station by a user
equipment that performs radio communication over a communication channel
formed by aggregating a plurality of component carriers, wherein scheduling
information on each component carrier is transmitted to the user equipment
25 according to either of a straight scheduling method and a cross scheduling method,
and the method includes, at the first base station, commanding first the user
equipment to perform a handover from the first base station to the second base
station on a second component carrier to be operated according to the straight
scheduling method in the second base station, when it is determined that a handover
30 on a first component carrier following the cross scheduling method is to be executed.
[0012]
5/41
SP262630W000
Further, the first base station may command the user equipment to perform a
handover on the second component carrier in which a channel for transmitting
scheduling information on the first component carrier is positioned before a handover
on the first component carrier.
5 [0013]
Further, the method may further include, at the first base station,
commanding the user equipment to perform a handover on the first component
carrier.
[0014]
10 Further, the first component carrier and the second component carrier may
be the same component carrier, and the method may further include, at the first base
station, changing a scheduling information transmission method on the first
component carrier from the cross scheduling method to the straight scheduling
method before a first handover is executed.
15 [0015]
Further, the first base station may change the scheduling information
transmission method on the first component carrier from the cross scheduling method
to the straight scheduling method according to a change request of the scheduling
information transmission method from a user equipment that has executed
20 measurement.
[0016]
Further, the first base station may change the scheduling information
transmission method on the first component carrier from the cross scheduling method
to the straight scheduling method after a handover request is confirmed by the second
25 base station.
[0017]
Further, the first component carrier and the second component carrier may
be the same component carrier, and the second component carrier may be operated
according to the straight scheduling method in the second base station after a
30 handover from the first base station to the second base station is performed.
[0018]
6/41
SP262630W000
Further, according to another aspect of the present invention, there is
provided a user equipment which includes a radio communication unit that performs
radio communication with a base station over a communication channel formed by
aggregating a plurality of component carriers, a control unit that controls a handover
5 from a first base station to a second base station by the radio communication unit,
and a quality measuring unit that measures a channel quality of the communication
channel between the user equipment and the first base station, wherein scheduling
information on each component carrier is transmitted according to either of a straight
scheduling method and a cross scheduling method, and when it is determined that a
10 handover on a first component carrier following the cross scheduling method is to be
executed, a handover from the first base station to the second base station on a
second component carrier to be operated according to the straight scheduling method
in the second base station is first executed according to a command from the first
base station.
15 [0019]
Further, according to another aspect of the present invention, there is
provided a base station which includes a radio communication unit that performs
radio communication with a user equipment over a communication channel formed
by aggregating a plurality of component carriers, and a control unit that controls a
20 handover to another base station by the user equipment, wherein scheduling
information on each component carrier is transmitted according to either of a straight
scheduling method and a cross scheduling method, and when it is determined that a
handover on a first component carrier following the cross scheduling method is to be
executed, the control unit commands first the user equipment to perform a handover
25 to the other base station on a second component carrier to be operated according to
the straight scheduling method in the other base station.
[0020]
Further, according to another aspect of the present invention, there is
provided a radio communication system which includes a user equipment that
30 performs radio communication over a communication channel formed by
aggregating a plurality of component carriers, a first base station that provides the
7/41
SP202630W000
user equipment with a service over the communication channel, and a second base
station that is a target of a handover from the first base station by the user equipment,
wherein scheduling information on each component carrier is transmitted according
to either of a straight scheduling method and a cross scheduling method, and when it
5 is determined that a handover on a first component carrier following the cross
scheduling method is to be executed, the first base station commands first the user
equipment to perform a handover on a second component carrier to be operated
according to the straight scheduling method in the second base station.
10 Advantageous Effects of Invention
[0021]
As described above, a method for controlling a handover, a user equipment,
a base station, and a radio communication system according to the present invention
can perform a handover with no data loss even under the circumstances in which
15 cross scheduling can be performed.
Brief Description of Drawings
[0022]
[Fig. 1] Fig. 1 is a sequence chart to describe a flow of a typical handover procedure.
20 [Fig. 2] Fig. 2 is an explanatory view to describe an example of a structure of
communication resources.
[Fig. 3] Fig. 3 is an explanatory view to describe an example of an arrangement of a
control channel included in communication resources.
[Fig. 4] Fig. 4 is an explanatory view to describe two kinds of scheduling
25 information transmission methods.
[Fig. 5] Fig. 5 is a schematic view showing an outline of a radio communication
system according to an embodiment of the present invention.
[Fig. 6] Fig. 6 is a block diagram showing an exemplary configuration of a user
equipment according to a first embodiment.
30 [Fig. 7] Fig. 7 is a block diagram showing an example of a more detailed
configuration of a radio communication unit according to the first embodiment.
8/41
SP262630WO00
[Fig. 8] Fig. 8 is a block diagram showing an exemplary configuration of a base
station according to the first embodiment.
[Fig. 9] Fig. 9 is a flowchart showing an example of the flow of a determination
process of a handover procedure by a base station according to the first embodiment.
5 [Fig. 10] Fig. 10 is a sequence chart showing an example of the flow of a handover
procedure according to the first embodiment.
[Fig. 11A] Fig. 11A is a first explanatory view to further describe a scenario
described with reference to Fig. 10.
[Fig. 11B] Fig. 11B is a second explanatory view to further describe a scenario
10 described with reference to Fig. 10.
[Fig. 11 C] Fig. II C is a third explanatory view to further describe a scenario
described with reference to Fig. 10.
[Fig. 11D] Fig. 11D is a fourth explanatory view to further describe a scenario
described with reference to Fig. 10.
15 [Fig. 12] Fig. 12 is a block diagram showing an exemplary configuration of a user
equipment according to a second embodiment.
[Fig. 13] Fig. 13 is a block diagram showing an exemplary configuration of a base
station according to the second embodiment.
[Fig. 14A] Fig. 14A is a sequence chart showing an example of the flow of a first
20 scenario of a handover procedure according to the second embodiment.
[Fig. 14B] Fig. 14B is a sequence chart showing an example of the flow of a second
scenario of a handover procedure according to the second embodiment.
[Fig. 15] Fig. 15 is a block diagram showing an exemplary configuration of a user
equipment according to a third embodiment.
25 [Fig. 16] Fig. 16 is a block diagram showing an exemplary configuration of a base
station according to the third embodiment.
[Fig. 17] Fig. 17 is a sequence chart showing an example of the flow of a handover
procedure according to the third embodiment.
30 Description of Embodiments
[0023]
9/41
SP262630WO00
Hereinafter, preferred embodiments of the present invention will be
described in detail with reference to the appended drawings. Note that, in this
specification and the drawings, elements that have substantially the same function
and structure are denoted with the same reference signs, and repeated explanation is
5 omitted.
[0024]
Preferred embodiments of the present invention will be described
hereinafter in the following order.
1. Description of Related Art
10 1-1. Handover Procedure
1-2. Structure of Communication Resources
1-3. Scheduling Information Transmission Method
2. Outline of Radio Communication System
3. Description of First Embodiment
15 3-1. Exemplary Configuration of User Equipment
3-2. Exemplary Configuration of Base Station
3-3. Flow of Process
3-4. Summary of First Embodiment
4. Description of Second Embodiment
20 4-1. Exemplary Configuration of User Equipment
4-2. Exemplary Configuration of Base Station
4-3. Flow of Process
4-4. Summary of Second Embodiment
5. Description of Third Embodiment
25 5-1. Exemplary Configuration of User Equipment
5-2. Exemplary Configuration of Base Station
5-3. Flow of Process
5-4. Summary of Third Embodiment
[0025]
30 <1. Description of Related Art>
(1-1. Handover Procedure)
10/41
SP262630W000
A technique related to the present invention is described hereinafter with
reference to Figs. 1 and 2. Fig. I shows a flow of a handover procedure in
conformity with LTE in a radio communication not involving the carrier aggregation
as an example of a typical handover procedure. In this example, a user equipment
5 (UE), a source base station (source eNB), a target base station (target eNB), and a
mobility management entity (MME) are involved in the handover procedure.
[0026]
As a preliminary step toward a handover, the user equipment first reports the
channel quality of a communication channel between the user equipment and the
10 source base station to the source base station (step S2). The channel quality may be
reported on a regular basis or when the channel quality falls below a predetermined
reference value. The user equipment can measure the channel quality of the
communication channel with the source base station by receiving a reference signal
contained in a downlink channel from the source base station.
15 [0027]
Then, the source base station determines the needs of measurement based on
the quality report received from the user equipment and, if measurement is necessary,
allocates measurement gaps to the user equipment (step S4).
[0028]
20 Then, the user equipment searches for a downlink channel from a peripheral
base station (i.e. performs cell search) during the periods of the allocated
measurement gaps (step S12). Note that the user equipment can recognize a
peripheral base station to search according to a list that is provided in advance from
the source base station.
25 [0029]
When the user equipment acquires synchronization with a downlink channel,
the user equipment performs measurement by using a reference signal contained in
the downlink channel (step S14). During this period, the source base station
restricts an allocation of data communication related to the user equipment so as to
30 avoid occurrence of data transmission by the user equipment.
[0030]
11/41
SP262630 WO00
Upon completion of the measurement, the user equipment transmits a
measurement report containing measurements to the source base station (step S22).
The measurements contained in the measurement report may be the average value or
the central value of measured values over a plurality of times of measurement or the
5 like. Further, the measurements may contain data about a plurality of frequency
bands.
[0031]
Receiving the measurement report, the source base station determines
whether or not to execute a handover based on the contents of the measurement
10 report. For example, when the channel quality of another base station in the
periphery is higher than the channel quality of the source base station by a
predetermined threshold or greater, it can be determined that a handover is necessary.
In this case, the source base station determines to carry out a handover procedure
with the relevant another base station as a target base station, and transmits a
15 handover request message to the target base station (step S24).
[0032]
Receiving the handover request message, the target base station determines
whether it is possible to accept the user equipment according to the availability of a
communication service offered by itself or the like. When it is possible to accept
20 the user equipment, the target base station transmits a handover request confirm
message to the source base station (step S26).
[0033]
Receiving the handover request confirm message, the source base station
transmits a handover command to the user equipment (step S28). Then, the user
25 equipment acquires synchronization with the downlink channel of the target base
station (step S32). After that, the user equipment makes a random access to the
target base station by using a random access channel in a given time slot (step S34).
During this period, the source base station forwards data addressed to the user
equipment to the target base station (step S36). i Then, after success in the random
30 access, the user equipment transmits a handover complete message to the target base
station (step S42).
12/41
[0034]
SP262630W000
Receiving the handover complete message, the target base station requests
the MME to perform route update for the user equipment (step S44). Upon
updating the route of user data by the MME, the user equipment becomes able to
5 communicate with another device through a new base station (i.e. the target base
station). Then, the target base station transmits acknowledgement to the user
equipment (step S46). A series of handover procedure thereby ends.
[0035]
(1-2. Structure of Communication Resource)
10 Fig. 2 shows a structure of communication resources in LTE as an example
of a structure of communication resources to which the present invention is
applicable. Referring to Fig. 2, the communication resources in LTE are segmented
in the time direction into radio frames each having a length of 10 msec. One radio
frame includes ten sub-frames, and one sub-frame is made up of two 0.5 ms slots.
15 Further, one 0.5 ms slot typically includes seven OFDM symbols in the time
direction. One unit of communication resources including seven OFDM symbols in
the time direction and 12 sub carriers in the frequency direction is referred to as a
resource block. In LTE, communication resources are allocated to each user
equipment in the time direction in units of sub frames or in units of resource blocks.
20 Further, one unit of communication resources corresponding to one OFDM symbol
in the time direction and one sub carrier in the frequency direction is referred to as a
resource element. In other words, one resource block corresponds 84 (=7x12)
resource elements. In conditions of the same bandwidth and the same time length,
as the number of resource blocks allocated for data communication increases, the
25 throughput of data communication increases.
[0036]
Further, a synchronization sequence is included in a resource block at a
predetermined position (typically, at the center of a band) in the frequency direction.
As the synchronization sequence, two kinds of synchronization sequences, that is, a
30 primary synchronization sequence (PSS) and a secondary synchronization sequence
(SSS), are used. A user equipment that has received the two kinds of
13/41
SP262630W000
synchronization sequences in a cell search may discriminate between base stations
and acquire synchronization with a specific base station. The two kinds of
synchronization sequences are arranged on sixth and seventh OFDM symbols #5 and
#6 of one sub fame in the time direction. Further, an OFDM symbol following the
5 synchronization sequences may be used as a broadcast channel for transmission of
system information.
[0037]
Further, a predetermined resource element in each resource block is used for
transmission of a reference signal. A user equipment that has received the reference
10 signal may measure the communication quality in units of resource blocks. Further,
a scheduler of a base station decides allocation of communication resources to a user
equipment according to the communication quality of each resource block that is
measured by a user equipment in the downlink and measured by a base station in the
uplink.
15 [0038]
(1-3. Scheduling Information Transmission Method)
Fig. 3 shows an arrangement of a control channel as an example of an
arrangement of a control channel included in communication resources. Unlike Fig.
2, in Fig. 3, a vertical axis represents a time direction, and a horizontal axis
20 represents a frequency direction. Referring to Fig. 3, a communication resource of
12 sub carriersx 1 sub frame is shown. 1 sub frame includes 14 OFDM symbols in
the time direction. In these communication resources, a control channel used to
transmit scheduling information, that is, a PDCCH, is arranged in a maximum of 3
OFDM symbols at the head of a sub frame. In addition to the scheduling
25 information, information used to designate a modulation scheme, power control
information, and the like may be transmitted over the PDCCH. A user equipment
recognizes communication resources used for each device to transmit or receive data
with reference to the scheduling information on the control channel. Transmission
and reception of data is performed over a physical downlink shared channel
30 (PDSCH) which is a data channel arranged in remaining OFDM symbols of the sub
frame.
14/41
[0039]
SP262630W000
Here, in radio communication involving the carrier aggregation, a plurality
of component carriers configure one communication channel. Typically, each
component carrier includes a control channel. However, in order to improve the
5 throughput by allocating more resource blocks for data communication (that is, by
reducing the overhead), a technique called cross scheduling (or cross carrier
scheduling) which will be described later with reference to Fig. 4 may be used.
[0040]
Fig. 4 is an explanatory view to describe two kinds of scheduling
10 information transmission methods in radio communication involving the carrier
aggregation. Referring to Fig. 4, 3 component carriers CCI to CC3 configure one
communication channel. Of these, each of the component carriers CCl and CC2
includes a control channel (PDCCH). Scheduling information for data
communication in the component carrier CCI is transmitted over the control channel
15 of the component carrier CC1. Scheduling information for data communication in
the component carrier CC2 is transmitted over the control channel of the component
carrier CC2. Meanwhile, the component carrier CC3 does not include a control
channel. Scheduling information for data communication in the component carrier
CC3 is transmitted over the control channel of the component carrier CC2. Thus, in
20 the example of Fig. 4, the component carriers CCI and CC2 follow the straight
scheduling method, and the component carrier CC3 follows the cross scheduling
method. The component carrier following the cross scheduling method is also
referred to as an extension carrier. Further, in this disclosure, a component carrier
including a control channel for an extension carrier is referred to as a master of the
25 extension carrier. In the example of Fig. 4, the component carrier CC2 is the master
of the component carrier CC3.
[0041]
<2. Outline of Radio Communication System>
Fig. 5 is a schematic view showing an outline of a radio communication
30 system 1 according to an embodiment of the present invention. Referring to Fig. 5,
the radio communication system 1 includes a user equipment 100, a base station
SP262630W000
200a and a base station 200b. It is assumed that the base station 200a is a serving
base station for the user equipment 100.
[0042]
The user equipment 100 is located inside a cell 202a where a radio
5 communication service is provided by the base station 200a. The user equipment
100 can perform a data communication with another user equipment (not shown) via
the base station 200a over a communication channel formed by aggregating a
plurality of component carriers (i.e. by carrier aggregation). However, because the
distance between the user equipment 100 and the base station 200a is not short, there
10 is a possibility that a handover is required for the user equipment 100. Further, the
user equipment 100 is located inside a cell 202b where a radio communication
service is provided by the base station 200b. Therefore, the base station 200b can
be a candidate for a target base station for a handover of the user equipment 100.
[0043]
15 The base station 200a can communicate with the base station 200b through
a backhaul link (e.g. X2 interface). Various kinds of messages in the handover
procedure as described with reference to Fig. 1, scheduling information related to the
user equipment belonging to each cell or the like, fors example, can be transmitted
and received between the base station 200a and the base station 200b. Further, the
20 base station 200a and the base station 200b can communicate with the MME, which
is an upper node, through S 1 interface, for example.
[0044]
r Here, it is assumed that a need to perform a handover to the base station
200b arises when the user equipment 100 performs radio communication involving
25 the carrier aggregation with the base station 200a. In this case, for example, an
attempt to perform a handover is made first on a component carrier having the worst
quality between the user equipment 100 and the base station 200a. At this time,
however, when the corresponding component carrier is an extension carrier, a
handover is performed before a component carrier of a master, and thus data loss
30 may occur due to loss or mismatching of scheduling information. For this reason, it
is desirable to control a handover procedure not to cause data loss under the
16/41
SP262630W000
circumstances in which the cross scheduling method is used as in first to third
embodiments of the present invention which will be described in detail in the next
section.
[0045]
5 It should be noted that, when there is no particular need to distinguish
between the base station 200a and the base station 200b in the following description
of the specification, they are collectively referred to as a base station 200 by omitting
the alphabetical letter at the end of the reference symbol. The same applies to the
other elements.
10 [0046]
<3. Description of First Embodiment>
Next, a first embodiment of the present invention will be described with
reference to Figs. 6 to IID.
[0047]
15 (3-1. Exemplary Configuration of User Equipment)
Fig. 6 is a block diagram showing an exemplary configuration of the user
equipment 100 according to the present embodiment. Referring to Fig. 6, the user
equipment 100 includes a radio communication unit 110, a signal processing unit 150,
a control unit 160, and a measurement unit 170.
20 [0048]
(Radio Communication Unit)
The radio communication unit 110 performs a radio communication with the
base station 200 over a communication channel formed by aggregating a plurality of
component carriers with use of the carrier aggregation technology.
25 [0049]
Fig. 7 is a block diagram showing an example of a more detailed
configuration of the radio communication unit 110. Referring to Fig. 7, the radio
communication unit 110 includes an antenna 112, a switch 114, a low noise amplifier
(LNA) 120, a plurality of down-converters 122a to 122c, a plurality of filters 124a to
30 124c, a plurality of analogue-to-digital converters (ADCs) 126a to 126c, a
demodulation unit 128, a modulation unit 130, a plurality of digital-to-analogue
SP262630WO00
converters (DACs) 132a to 132c, a plurality of filters 134a to 134c, a plurality of upconverters
136a to 136c, a combiner 138, and a power amplifier (PA) 140.
[0050]
The antenna 112 receives a radio signal transmitted from the base station
5 200 and outputs the received signal to the LNA 120 through the switch 114. The
LNA 120 amplifies the received signal. The down-converter 122a and the filter
124a separate a baseband signal of the first component carrier (CC1) from the
received signal amplified by the LNA 120. Then, the separated baseband signal is
converted to a digital signal by the ADC 126a and output to the demodulation unit
10 128. Likewise, the down-converter 122b and the filter 124b separate a baseband
signal of the second component carrier (CC2) from the received signal amplified by
the LNA 120. Then, the separated baseband signal is converted to a digital signal
by the ADC 126b and output to the demodulation unit 128. Further, the downconverter
122c and the filter 124c separate a baseband signal of the third component
15 carrier (CC3) from the received signal amplified by the LNA 120. Then, the
separated baseband signal is converted to a digital signal by the ADC 126c and
output to the demodulation unit 128. After that, the demodulation unit 128
generates a data signal by demodulating the baseband signals of the respective
component carriers and outputs the data signal to the signal processing unit 150.
20 [0051]
Further, when a data signal is input from the signal processing unit 150, the
modulation unit 130 modulates the data signal and generates baseband signals of the
respective component carriers. Among those baseband signals, the baseband signal
of the first component carrier (CC1) is converted to an analog signal by the DAC
25 132a. Then, a frequency component corresponding to the first component carrier in
a transmission signal is generated from the analog signal by the filter 134a and the
up-converter 136a. Likewise, the baseband signal of the second component carrier
(CC2) is converted to an analog signal by the DAC 132b. Then, a frequency
component corresponding to the second component carrier in the transmission signal
30 is generated from the analog signal by the filter 134b and the up-converter 136b.
Further, the baseband signal of the third component carrier (CC3) is converted to an
SP262630W000
analog signal by the DAC 132c. Then, a frequency component corresponding to the
third component carrier in the transmission signal is generated from the analog signal
by the filter 134c and the up-converter 136c. After that, the generated frequency
components corresponding to the three component carriers are combined by the
5 combiner 138, and the transmission signal is formed. The PA 140 amplifies the
transmission signal and outputs the transmission signal to the antenna 112 through
the switch 114. Then, the antenna 112 transmits the transmission signal as a radio
signal to the base station 200.
[0052]
10 Although the case where the radio communication unit 110 handles three
component carriers is described in Fig. 7, the number of component carriers handled
by the radio communication unit 110 may be two, or four or more.
[0053]
Further, instead of processing the signals of the respective component
15 carriers in the analog region as in the example of Fig. 7, the radio communication
unit 110 may process the signals of the respective component carriers in the digital
region. In the latter case, at the time of reception, a digital signal converted by one
ADC is separated into the signals of the respective component carriers by a digital
filter. Further, at the time of transmission, after digital signals of the respective
20 component carriers are frequency-converted and combined, the signal is converted
into an analog signal by one DAC. The load of the ADC and the DAC is generally
smaller when processing the signals of the respective component carriers in the
analog region. On the other hand, when processing the signals of the respective
component carriers in the digital region, a sampling frequency for AD/DA
25 conversion is higher, and the load of the ADC and the DAC can thereby increase.
[0054]
(Signal Processing Unit)
Referring back to Fig. 6, an example of a configuration of the user
equipment 100 is further described.
30 [0055]
The signal processing unit 150 performs signal processing such as
SP262630W000
deinterleaving, decoding or error correction on the demodulated data signal that is
input from the radio communication unit 110. Then, the signal processing unit 150
outputs the processed data signal to an upper layer. Further, the signal processing
unit 150 performs signal processing such as encoding or interleaving on the data
5 signal that is input from the upper layer. Then, the signal processing unit 150
outputs the processed data signals to the radio communication unit 110.
[0056]
(Control Unit)
The control unit 160 controls the overall functions of the user equipment
10 100 using a processing device such as a central processing unit (CPU) or a digital
signal processor (DSP). For example, the control unit 160 controls a timing of data
communication by the radio communication unit 110 for each component carrier
according to scheduling information which is received from the base station 200 by
the radio communication unit 110. More specifically, for example, the control unit
15 160 refers to scheduling information on a control channel of a component carrier
following the straight scheduling method among component carriers configuring a
communication channel between the upper equipment 100 and the base station 200.
This scheduling information may include information on an extension carrier
following the cross scheduling method in addition to information on a
20 communication resource of the same component carrier. Thus, when information
on an extension carrier is included in scheduling information, the control unit 160
controls a timing of data communication on a data channel of an extension carrier
according to the corresponding information. Further, the control unit 160 controls a
timing of data communication on a data channel of a component carrier following the
25 straight scheduling method according to information on communication resources of
the same component carrier as the control channel. In addition, the control unit 160
causes the user equipment 100 to operate in the same way as the user equipment in
the handover procedure described with reference to Fig. 1.
[0057]
30 (Measurement Unit)
The measurement unit 170 measures the channel quality for each of the
20/41
SP262630W000
component carriers by using a reference signal from the base station 200 according to
control from the control unit 160, for example. Further, the measurement unit 170
executes measurement for a handover with respect to each of the component carriers
by using the measurement gaps which are allocated by the base station 200. A
5 result of the measurement' executed by the measurement unit 170 is converted to a
predetermined format for a measurement report by the control unit 160 and
transmitted to the base station 200 through the radio communication unit 110. After
that, the base station 200 determines, based on the measurement report, whether a
handover should be executed or not for the user equipment 100.
10 [0058]
(3-2. Exemplary Configuration of Base Station)
Fig. 8 is a block diagram showing an exemplary configuration of the base
station 200 according to the embodiment. Referring to Fig. 8, the base station 200
includes a radio communication unit 210, an interface unit 250, a component carrier
15 (CC) management unit 260, and a control unit 280.
[0059]
(Radio Communication Unit)
A specific configuration of the radio communication unit 210 may be
similar to the configuration of the radio communication unit 110 of the user
20 equipment 100 which is described above with reference to Fig. 7, although the
number of component carriers to be supported, the requirements of processing
performance or the like are different. The radio communication unit 210 performs a
radio communication with the user equipment over a communication channel which
is formed by aggregating a plurality of component carriers with use of the carrier
25 aggregation technology.
[0060]
(Interface Unit)
The interface unit 250 mediates a communication between the radio
communication unit 210 or the control unit 280iand an upper node through the Si
30 interface illustrated in Fig. 5, for example. Further, the interface unit 250 mediates
a communication between the radio communication unit 210 or the control unit 280
21/41
SP262630W000
and another base station through the X2 interface illustrated in Fig. 5, for example.
[0061]
(CC Management Unit)
The CC management unit 260 holds data that indicates which component
5 carrier each user equipment is using for communication with respect to each of the
user equipments belonging to the cell of the base station 200. Such data can be
updated by the control unit 280 when an additional user equipment joins the cell of
the base station 200 or when a connected user equipment changes its component
carriers. Thus, the control unit 280 can recognize which component carrier the user
10 equipment 100 is using by referring to the data held by the CC management unit 260.
[0062]
(Control Unit)
The control unit 280 controls the overall functions of the base station 200
using the processing device such as a CPU or a DSP. For example, the control unit
15 280 allocates communication resources for data communication to the user
equipment 100 and another user equipment, and then transmits scheduling
information over a control channel of a component carrier corresponding to a
scheduling information transmission method.
More specifically, the control unit 280 transmits scheduling information on
20 communication resources in a component carrier following the straight scheduling
method over a control channel of the same component carrier. Further, the control
unit 280 transmits scheduling information on communication resources in an
extension carrier over a control channel of a different component carrier which is a
master.
25 [0063]
Further, the control unit 280 controls a handover to another base station by
the user equipment 100. More specifically, for example, when it is determined that
a handover on an extension carrier needs to be performed, the control unit 280 first
commands the user equipment 100 to perform a handover to a target base station on a
30 component carrier to be operated according to straight scheduling method in the
target base station. For example, it is assumed that the base station 200 and the
22/41
SP262630W000
target base station share a scheduling information transmission method for each
component carrier (for each operating frequency band). In this case, for example,
when it is determined that a handover on an extension carrier needs to be performed,
the control unit 280 commands the user equipment 100 to execute a handover on a
component carrier which is a master of the corresponding extension carrier before a
handover on the extension carrier. Then, after completing a handover on the
component carrier of the master, the control unit 280 commands the user equipment
100 to execute a,handover on the extension carrier. Further, when another available
component carrier is present, the control unit 280 may temporarily transmit
10 scheduling information on the extension carrier over a control channel of another
component carrier until the handover on the extension carrier is completed after the
handover on the component carrier of the master starts. In addition, the control unit
280 causes the base station 200 to operate in the same way as the source base station
or the target base station in the handover procedure described above with reference to
15 Fig. 1.
[0064]
(3-3. Flow of Process)
Fig. 9 is a flowchart showing an example of the flow of a determination
process of a handover procedure by the control unit 280 of the base station 200
20 according to the present embodiment.
[0065]
Referring to Fig. 9, the control unit 280 receives a measurement report from
the user equipment 100 through the radio communication unit 210 (step S102).
Next, the control unit 280 determines whether or not there is a component carrier
25 whose quality does not satisfy a predetermined criterion based on content of the
measurement report (step S104). Here, when there is no component carrier whose
quality does not satisfy a predetermined criterion, the process ends. However, when
there is a component carrier whose quality does not satisfy a predetermined criterion,
the process proceeds to step S106. Next, the control unit 280 determines whether or
30 not the component carrier whose quality does not satisfy a predetermined criterion is
a component carrier to be operated according to the cross scheduling method (step
23/41
SP262630W000
S 106). Here, when the corresponding component carrier is a component carrier to
be operated according to the cross scheduling method, the process proceeds to step
S108, However, when the corresponding component carrier is not a component
carrier to be operated according to the cross scheduling method, the process proceeds
5 to step 5110. In step S108, the control unit 280 decides to perform a handover on a
component carrier which is a master of the corresponding component carrier before
the component carrier to be operated according to the cross scheduling method (step
S108). Meanwhile, in step 5110, the control unit 280 decides a handover on a
component carrier determined as having a quality that does not satisfy a
10 predetermine criterion (step SI10).
[0066]
Fig. 10 is a sequence chart showing an example of the flow of a handover
procedure according to the present embodiment. In a scenario of Fig. 10, it is
assumed that a handover procedure is performed among the user equipment 100, the
15 base station 200a serving as the source base station, and the base station 200b serving
as the target base station. Further, a procedure (steps S2 to 514) up to the
measurement in the user equipment in the general handover procedure illustrated in
Fig. 1 is not particularly different, and thus a description thereof will not be made.
[0067]
20 Referring to Fig. 10, the user equipment 100 first transmits a measurement
report on a plurality of component carriers configuring a communication channel to
the base station 200a (step S120). Next, the base station 200a determines whether
or not.a handover is necessary and a handover procedure for each component carrier
based on the received measurement report as described above with reference to Fig.
25 9 (step S130).
[0068]
In the scenario of Fig. 10, for example, it is assumed that a handover on a
component carrier to be operated as an extension carrier is necessary. In this case,
the base station 200a transmits a handover request message for requesting a handover
30 on a component carrier which is a master of the corresponding component carrier to
the base station 200b (step S144). The base station 200b that has received the
24/41
SP262630WO00
handover request message determines whether or not the user equipment 100 can be
accepted, for example, based on availability of a communication service offered by
itself. Then, when it is determined that the user equipment 100 can be accepted, the
base station 200b transmits a handover request confirm message to the base station
5 200a (step 5146). The base station 200a that has received the handover request
confirm message transmits a handover command on a component carrier of a master
to the user equipment 100 (step S 148). Thus, a handover on a component carrier of
a master is executed among the user equipment 100 that has received the handover
command, the base station 200a, the base station 200b, and the MME (step S 150).
10 In step 5150, for example, synchronization with the target base station, random
access to the target base station, transmission of a handover complete message, a
route update, transmission of acknowledgement, and the like are performed, similarly
to the process described above with reference to Fig. 1.
[0069]
15 Next, the base station 200a transmits a handover request message for
requesting a handover on a component carrier to be operated as an extension carrier
to the base station 200b (step S 164). The base station 200b that has received the
handover request message determines whether or not the user equipment 100 can be
accepted, for example, based on availability of a communication service offered by
20 itself. Then, when it is determined that the user equipment 100 can be accepted, the
base station 200b transmits a handover request confirm message to the base station
200a (step S166). The base station 200a that has received the handover request
confirm message transmits a handover command on a component carrier to be
operated as an extension carrier to the user equipment 100 (step S168). Thus, a
25 handover on the corresponding component carrier is executed among the user
equipment 100 that has received the handover command, the base station 200a, the
base station 200b, and the MME (step S 170).
[0070]
Thereafter, when a handover on another component carrier is necessary, a
30 handover is performed on each component carrier in the same way as the abovedescribed
procedure.
25/41
[0071]
SP262630W000
Figs. 11A to 11D are explanatory views to further describe the scenario
described above with reference to Fig. 10.
[0072]
5 Referring to Fig. I1A, three component carriers CC1 to CC3 configuring a
communication channel between the user equipment 100 and the base station 200a
are depicted. At a point in time of Fig. 11A, the base station 200a functions as the
serving base station of the user equipment 100. Further, among the three
component carriers, the component carriers CC1 and CC2 are operated according to
10 the straight scheduling method. The component carrier CO is operated according
to the cross scheduling method. In this situation, when it is determined that a
handover to the base station 200b is necessary on the component carrier CC3, a
handover is first performed on the component carrier CC2 which is a master of the
component carrier CC3. This is the same even when it is determined that a
15 handover is necessary on the component carrier CC2.
[0073]
Fig. 11 B shows a state after the user equipment 100 has performed a
handover from the base station 200a to the base station 200b on the component
carrier CC2 (after step S 150 of Fig. 10 is completed). In Fig. 11 B, among the three
20 component carriers of the user equipment 100, the component carriers CC1 and CC3
remain connected to the base station 200a, and the component carrier CC2 remains
connected to the base station 200b. Further, the component carrier CC2 is operated
by the. straight scheduling method even between the user equipment 100 and the base
station 200b. Meanwhile, a master of the component carrier CC3 is temporarily
25 changed to the component carrier CCl. For example, the change of the master of
the extension carrier may be performed such that a change notice is transmitted from
the base station 200a to the user equipment 100 (and another user equipment), and
then the base station 200a changes a channel in which scheduling information on an
extension carrier is to be included.
30 [0074]
Further, Fig. I IC shows a state after the user equipment 100 has performed
26/41
SP262630W000
a handover from the base station 200a to the base station 200b on the component
carrier CO (after step 5170 of Fig. 10 is completed). In Fig. 11 C, among the three
component carriers of the user equipment 100, the component carrier CC1 remains
connected to the base station 200a, and the component carriers CC2 and CC3 remain
5 connected to the base station 200b. Further, the component carrier CC2 functions
as the master of the component carrier CC3 in the communication channel between
the user equipment 100 and the base station 200b.
[0075]
Further, Fig. 11D shows a state after the user equipment 100 has performed
10 a handover from the base station 200a to the base station 200b on the component
carrier CC 1. In Fig. I ID, all of the three component carriers of the user equipment
100 remain connected to the base station 200b.
[0076]
(3-4. Summary of First Embodiment)
15 The first embodiment of the present invention has been described so far
with reference to Figs. 6 to 11D. According to the present embodiment, in radio
communication involving the carrier aggregation, when it is determined that a
handover needs to be executed on an extension carrier following the cross scheduling
method, a handover is first executed on a component carrier to be operated according
20 to the straight scheduling method in the target base station. In this case; for
example, a component carrier on which a handover is first executed is a component
carrier functioning as a master of an extension carrier. Thereafter, a handover is
performed on a component carrier to be operated according to the cross scheduling
method in the target base station. In this sequence, a component carrier functioning
25 as a master of an extension carrier and the extension carrier are consecutively handed
over, and thus a risk that data loss will occur due to loss or mismatching of
scheduling information is reduced or eliminated. Accordingly, a seamless handover
can be implemented even under the circumstances, in which the cross scheduling
method is performed. Furthermore, in the present embodiment, a scheduling
30 information transmission method of each component carrier need not be changed for
a handover procedure, and thus the impact on a system is small.
27/41
[0077]
SP262630W000
<4. Description of Second Embodiment>
Next, a second embodiment of the present invention will be described with
reference to Figs. 12 to 14B.
5 [0078]
(4-1. Exemplary Configuration of User Equipment)
Fig. 12 is a block diagram showing an exemplary configuration of a user
equipment 300 according to the present embodiment. Referring to Fig. 12, the user
equipment 300 includes a radio communication unit 110, a signal processing unit 150,
10 a control unit 360, and a measurement unit 170.
[0079]
(Control Unit)
The control unit 360 controls the overall functions of the user equipment
300 using the processing device such as a CPU or a DSP. For example, the control
15 unit 360 controls a timing of data communication by the radio communication unit
110 for each component carrier according to scheduling information which is
received from a base station 400 by the radio communication unit 110, similarly to
the control unit 160 according to the first embodiment. Further, in the present
embodiment, for example, when it is determined that the quality of an extension
20 carrier operated by the cross scheduling method is being lowered based on the result
of measurement made by the measurement unit 170, the control unit 360 transmits a
change request of the scheduling information transmission method to the base station
400. This is done to prepare for a handover on a component carrier whose quality is
decreasing by changing the scheduling information transmission method of the
25 corresponding component carrier from the cross scheduling method to the straight
scheduling method. Further, even when the control unit 360 does not request a
change of the scheduling information transmission method, when a change of the
scheduling information transmission method is notified of by the base station 400,
the control unit 360 changes a component carrier,operating method according to the
30 corresponding notice. In addition, the control unit 360 causes the user equipment
300 to operate in the same way as the user equipment in the handover procedure
28/41
described above with reference to Fig. 1.
[0080]
SP262630W000
(4-2. Exemplary Configuration of Base Station)
Fig. 13 is a block diagram showing an exemplary configuration of the base
5 station 400 according to the present embodiment. Referring to Fig. 13, the base
station 400 includes a radio communication unit 210, an interface unit 250, a CC
management unit 260, and a control unit 480.
[0081]
(Control Unit)
10 The control unit 480 controls the overall functions of the base station 400
using the processing device such as a CPU or a DSP. For example, the control unit
480 allocates a communication resource for data communication to the user
equipment 300 and other user equipment, and then transmits scheduling information
over a control channel of a component carrier corresponding to a scheduling
15 information transmission method, similarly to the control unit 280 according to the
first embodiment.
[0082]
Further, the control unit 480 controls a handover to another base station by
the user equipment 300. For example, in the present embodiment, when it is
20 determined that a handover on a component carrier which is an extension carrier
needs to be executed, after the target base station confirms a request of a handover on
the corresponding component carrier, the control unit 480 changes the scheduling
information transmission method on the extension carrier from the cross scheduling
method to the straight scheduling method. Further, the control unit 480 notifies the
25 user equipment 300 of the change of the scheduling information transmission method.
Further, when the change request of the scheduling information transmission method
is received from the user equipment 300, the control unit 480 changes the scheduling
information transmission method according to the corresponding request. Further,
when the request from the user equipment 300 competes with another user
30 equipment (for example, when it leads to a reduction in the throughput of
communication of another user equipment with a high priority), the control unit 480
29/41
SP262630W000
may deny the request from the user equipment 300. Thereafter, the control unit 480
executes a handover on a component carrier on which it is determined that a
handover needs to be executed. In addition, the control unit 480 causes the base
station 400 to operate in the same way as the source base station or the target base
5 station in the handover procedure described above with reference to Fig. 1.
[0083]
(4-3. Flow of Process)
Next, two scenarios of handover procedures according to the present
embodiment will be described. In these scenarios, it is assumed that the handover
10 procedure is performed among the user equipment 300, a base station 400a serving
as the source base station, and a base station 400b serving as the target base station.
Further, a procedure (steps S2 to S14) up to the measurement in the user equipment
in the general handover procedure illustrated in Fig. 1 is not particularly different,
and thus a description thereof will not be made.
15 [0084]
Fig. 14A is a sequence chart showing an example of the flow of a first
scenario of a handover procedure according to the present embodiment.
[0085]
Referring to Fig. 14A, the user equipment 300 that has completed the
20 measurement first evaluates the quality of a communication channel between the user
equipment 300 and the base station 400a for each component carrier (step 5210).
Then, when it is determined that the quality of an extension carrier operated by the
cross scheduling method is being lowered, the user equipment 300 transmits a
change request to change the scheduling information transmission method from the
25 cross scheduling: method to the straight scheduling method to the base station 400a
(step 5212). Next, the base station 400a changes the scheduling information
transmission method on the extension carrier according to the request, and transmits
an acluiowledgement (ACK) to the user equipment 300 (step 5214). Next, the user
equipment 300 transmits a measurement report to the base station 400a (step 5222).
30 Next, the base station 400a transmits a handover request message for requesting a
handover on a component carrier on which it is determined that a handover is
30/41
SP262630W000
necessary based on the measurement report to the base station 400b (step S224).
Here, for example, the component carrier on which it is determined that a handover
is necessary is the component carrier whose scheduling information transmission
method has been changed from the cross scheduling method to the straight
5 scheduling method in steps S212 to 5214. The base station 400b that has received
the handover request message determines whether or not the user equipment 300 can
be accepted, for example, based on availability of a communication service offered
by itself Then, when it is determined that the user equipment 300 can be accepted,
the base station 400b transmits a handover request confirm message to the base
10 station 400a (step 5226). The base station 400a that has received the handover
request confirm message transmits a handover command to the user equipment 300
(step 5228). Thus, a handover is executed among the user equipment 300 that has
received the handover command, the base station 400a, the base station 400b, and the
MME (step 5230). In step S230, for example, synchronization with the target base
15 station, random access to the target base station, transmission of a handover complete
message, a route update, transmission of acknowledgement, and the like are
performed, similarly to the process described above with reference to Fig. 1.
[0086]
Fig. 14B is a sequence chart showing an example of the flow of a second
20 scenario of a handover procedure according to the present embodiment.
[0087]
Referring to Fig. 14B, the user equipment 300 that has completed the
measurement first transmits a measurement report to the base station 400a (step
5310). Next, the base station 400a evaluates the quality of a communication
25 channel between the user equipment 300 and the base station 400a for each
component carrier (step 5312). Next, the base station 400a transmits a handover
request message for requesting a handover on a component carrier on which it is
determined that a handover is necessary to the base station 400b (step 5324). The
base station 400b that has received the handover request message determines whether
30 or not the user equipment 300 can be accepted, for example, based on availability of
a communication service offered by itself. Then, when it is determined that the user
31/41
SP262630WO00
equipment 300 can be accepted, the base station 400b transmits a handover request
confirm message to the base station 400a (step S326). Next, when the component
carrier on which a handover request has been confirmed is an extension carrier
operated by the cross scheduling method, the base station 400a transmits a notice
5 representing that the scheduling information transmission method on the
corresponding extension carrier is to be changed from the cross scheduling method to
the straight scheduling method to the user equipment 300 (step 5330). Next, when
acknowledgement is received from the user equipment 300 (step 5332), the base
station 400a changes the scheduling information transmission method on the
10 extension carrier to the straight scheduling method. Then, the base station 400a
transmits a handover command to the user equipment 300 (step S334). Thus, a
handover is executed among the user equipment 300 that has received the handover
command, the base station 400a, the base station 400b, and the MME (step 5340).
[0088]
15 (4-4. Summary of Second Embodiment)
The second embodiment of the present invention has been described so far
with reference to Figs. 12 to 14B. According to the present embodiment, in radio
communication involving the carrier aggregation, when it is determined that a
handover needs to be executed on an extension carrier following the cross scheduling
20 method, the scheduling information transmission method on the corresponding
extension carrier is changed to the straight scheduling method before a handover is
executed. As a result, a component carrier on which a handover is first executed is
operated according to the straight scheduling method. Accordingly, a risk that data
loss will occur due to loss or mismatching of scheduling information is reduced or
25 eliminated. Furthermore, in the present embodiment, since an extension carrier and
a component carrier functioning as a master of the extension carrier need not be
consecutively handed over, for example, when the quality of the component carrier
of the master is good, a connection of the corresponding component carrier having a
good quality with the source base station can be maintained.
30 [0089]
<5. Description of Third Embodiment>
32/41
SP262630W000
Next, a third embodiment of the present invention will be described with
reference to Figs. 15 to 17.
[0090]
(5-1. Exemplary Configuration of User Equipment)
5 Fig. 15 is a block diagram showing an exemplary configuration of a user
equipment 500 according to the present embodiment. Referring to Fig. 15, the user
equipment 500 includes a radio communication unit 110, a signal processing unit 150,
a control unit 560,. and a measurement unit 170.
[0091]
10 (Control Unit)
The control unit 560 controls the overall functions of the user equipment
500 using the processing device such as a CPU or a DSP. For example, the control
unit 560 controls a timing of data communication by the radio communication unit
110 for each component carrier according to scheduling information which is
15 received from a base station 600 by the radio communication unit I10, similarly to
the control unit 160 according to the first embodiment. Further, in the present
embodiment, for example, when a handover command is received from the base
station 600 on a component carrier operated according to the cross scheduling
method, the control unit 560 performs access using a component carrier following
20 the straight scheduling method when performing access to the target base station
through the corresponding component carrier. In other words, the control unit 560
changes an operating method on an extension carrier from the cross scheduling
method to the straight scheduling method at the time of access to the target base
station. In addition, the control unit 560 causes the user equipment 500 to operate
25 in the same way as the user equipment in the handover procedure described above
with reference to Fig. 1.
[0092]
(5-2. Exemplary Configuration of Base Station)
Fig. 16 is a block diagram showing an exemplary configuration of the base
30 station 600 according to the present embodiment. Referring to Fig. 16, the base
station 600 includes a radio communication unit 210, an interface unit 250, a CC
33/41
management unit 260, and a control unit 680.
[0093]
SP262630WO00
(Control Unit)
The control unit 680 controls the overall functions of the base station 600
5 using the processing device such as a CPU or a DSP. For example, the control unit
680 allocates a communication resource for data communication to the user
equipment 500 and another user equipment, and then transmits scheduling
information over a control channel of a component carrier corresponding to a
scheduling information transmission method, similarly to the control unit 280
10 according to the first embodiment.
[0094]
Further, the control unit 680 controls a handover to another base station by
the user equipment 500. For example, in the present embodiment, when it is
determined that a handover on a component carrier which is an extension carrier
15 needs to be executed, the control unit 680 detects a component carrier operated
according to the straight scheduling method in the target base station. For example,
the component carrier operated according to the straight scheduling method in the
target base station can be detected by receiving system information which is
transmitted through an X2 interface illustrated in Fig. 5 or transmitted over a
20 broadcast channel from the target base station. Then, the control unit 680 transmits
a handover command for causing an extension carrier on which it is determined that
a handover needs to be executed to be handed over to a component carrier operated
according to the straight scheduling method in the target base station to the user
equipment 500. In addition, the control unit 680 causes the base station 600 to
25 operate in the same way as the source base station or the target base station in the
handover procedure described above with reference to Fig. 1.
[0095]
(5-3. Flow of Process)
Fig. 17 is a sequence chart showing an'example of the flow of a handover
30 procedure according to the present embodiment. In the scenario of Fig. 17, it is
assumed that the handover procedure is performed among the user equipment 500, a
34/41
SP262630W000
base station 600a serving as the source base station, and a base station 600b serving
as the target base station. Further, a procedure (steps S2 to S14) up to the
measurement in the user equipment in the general handover procedure illustrated in
Fig. 1 is not particularly different, and thus a description thereof will not be made.
5 [0096]
Referring to Fig. 17, the user equipment 500 first transmits a measurement
report on a plurality of component carriers configuring a communication channel to
the base station 600a (step S420). Next, when it is determined that a handover
needs to be executed on a component carrier which is an extension carrier based on
10 the measurement report, the base station 600a detects a component carder operated
according to the straight scheduling method in the base station 600b (step S430).
Next, the base station 600a transmits a handover request message for requesting a
handover to the detected component carrier to the base station 600b (step S444).
The base station 600b that has received the handover request message determines
15 whether or not the user equipment 500 can be accepted, for example, based on
availability of a communication service offered by itself. Then, when it is
determined that the user equipment 500 can be accepted, the base station 600b
transmits a handover request confirm message to the base station 600a (step S446).
The base station 600a that has received the handover request confirm message
20 transmits a handover command for causing an extension carrier on which it is
determined that a handover needs to be executed to be handed over to a component
carrier used in the base station 600b detected in step S430 to the user equipment 500
(step S448). Thus, a handover is executed among the user equipment 500 that has
received the handover command, the base station 600a, the base station 600b, and the
25 MME while changing the scheduling method from the cross scheduling method to
the straight scheduling method (step S450). More specifically, for example, the
user equipment 500 changes an operating frequency band of the extension carrier to a
frequency band of the component carrier designated in the handover command, and
makes an attempt to acquire synchronization with the base station 600b and make
30 random access to the base station 600b, Then, when random access is successfully
made, a handover complete message is transmitted from the user equipment 500 to
35/41
SP262630W000
the base station 600b, and a route is updated by the MME. Thereafter, the user
equipment 500 can perform communication with another device over a new
component carrier between itself and the base station 600b. At this time, since the
new component carrier follows the straight scheduling method, the user equipment
5 500 performs communication via the base station 600b according to scheduling
information on a control channel of the same component carrier.
[0097]
(5-4. Summary of Third Embodiment)
The third embodiment of the present invention has been described so far
10 with reference to Figs. 15 to 17. According to the present embodiment, in radio
communication involving the carrier aggregation, when it is determined that a
handover needs to be executed on a component carrier following the cross
scheduling method, a handover is executed on the corresponding component carrier.
Further, in the target base station, after a handover is completed, the corresponding
15 component carrier is operated according to the straight scheduling method.
Accordingly, a risk that data loss will occur due to loss or mismatching of scheduling
information is reduced or eliminated. Furthermore, in the present embodiment,
since an extension carrier and a component carrier functioning as a master of the
extension carrier need not be consecutively handed over, for example, when the
20 quality of the component carrier of the master is good, a connection of the
corresponding component carrier having a good quality with the source base station
can be maintained.
[0098].
As described above, according to the three embodiments described in this
25 disclosure, by appropriately controlling a handover procedure of each component
carrier, a handover can be performed with no data loss even under the circumstances
cross scheduling can be performed.
[0099]
The preferred embodiments of the present invention have been described
30 above with reference to the accompanying drawings, whilst the present invention is
not limited to the above examples, of course. A person skilled in the art may find
36/41
SP262630W000
various alternations and modifications within the scope of the appended claims, and
it should be understood that they will naturally come under the technical scope of the
present invention.
5 Reference Signs List
[0100]
I Radio communication system
100, 300, 500 User equipment
110 Radio communication unit (User equipment)
10 160, 360, 560 Control unit (User equipment)
200, 400, 600 Base station
210 Radio communication unit (Base station)
280, 480, 680 Control unit (Base station)
37/41
CLAIMS
SP262630W000
Claim 1
A method for controlling a handover from a first base station to a second
base station by a user equipment that performs radio communication over a
5 communication channel formed by aggregating a plurality of component carriers,
wherein scheduling information on each component carrier is transmitted to
the user equipment according to either of a straight scheduling method and a cross
scheduling method, and
the method includes
10 at the first base station, commanding first the user equipment to perform a
handover from the first base station to the second base station on a second
component carrier to be operated according to the straight scheduling method in the
second base station, when it is determined that a handover on a first component
carrier following the cross scheduling method is to be executed.
15
Claim 2
The method according to claim 1, wherein the first base station commands
the user equipment to perform a handover on the second component carrier in which
a channel for transmitting scheduling information on the first component carrier is
20 positioned before a handover on the first component carrier.
Claim 3
The method according to claim 2, further comprising:
at the first base station, commanding the user equipment to perform a
25 handover on the first component carrier.
Claim 4
The method according to claim 1, wherein the first component carrier and
the second component carrier are the same component carrier, and
30 the method further includes, at the first base station, changing a scheduling
information transmission method on the first component carrier from the cross
38/41
SP262630WO00
scheduling method to the straight scheduling method before a first handover is
executed.
Claim 5
5 The method according to claim 4, wherein the first base station changes the
scheduling information transmission method on the first component carrier from the
cross scheduling method to the straight scheduling method according to a change
request of the scheduling information transmission method from the user equipment
that has executed measurement.
10
Claim 6
The method according to claim 4, wherein the first base station changes the
scheduling information transmission method on the first component carrier from the
cross scheduling method to the straight scheduling method after a handover request
15 is confirmed by the second base station.
Claim 7
The method according to claim 1, wherein the first component carrier and
the second component carrier are the same component carrier, and
20 the second component carrier is operated according to the straight
scheduling method in the second base station after a handover from the first base
station to the second base station is performed.
Claim 8
25 A user equipment, comprising:
a radio communication unit that performs radio communication with a base
station over a communication channel formed by aggregating a plurality of
component carriers;
a control unit that controls a handover from a first base station to a second
30 base station by the radio communication unit; and
a quality measuring unit that measures a channel quality of the
39/41
SP262630W000
communication channel between the user equipment and the first base station,
wherein scheduling information on each component carrier is transmitted
according to either of a straight scheduling method and a cross scheduling method,
and
when it is determined that a handover on a first component carrier following
the cross scheduling method is to be executed, a handover from the first base station
to the second base station on a second component carrier to be operated according to
the straight scheduling method in the second base station is first executed according
to a command from the first base station.
10
Claim 9
A base station, comprising:
a radio communication unit that performs radio communication with a user
equipment over a communication channel formed by aggregating a plurality of
15 component carriers; and
a control unit that controls a handover to another base station by the user
equipment,
wherein scheduling information on each component carrier is transmitted
according to either of a straight scheduling method and a cross scheduling method,
20 and
when it is determined that a handover on a first component carrier following
the cross scheduling method is to be executed , the control unit commands first the
user equipment to perform a handover to the other base station on a second
component carrier to be operated according to the straight scheduling method in the
25 other base station.
Claim 10
A radio communication system, comprising:
a user equipment that performs radio communication over a communication
30 channel formed by aggregating a plurality of component carriers;
a first base station that provides the user equipment with a service over the
40/41
SP262630\WC00
communication channel; and
a second base station that is a target of a handover from the first base station
by the user equipment,
wherein scheduling information on each component carrier is transmitted
according to either of a straight scheduling method and a cross scheduling method,
and
when it is determined that a handover on a first component carrier following
the cross scheduling method is to be executed, the first base station commands first
the user equipment to perform a handover on a second component carrier to be
10 operated according to the straight scheduling method in the second base station.