U.S. patent application number 15/089940 was filed with the patent office on 2016-07-28 for communication control method.
This patent application is currently assigned to KYOCERA CORPORATION. The applicant listed for this patent is KYOCERA CORPORATION. Invention is credited to Henry CHANG, Masato FUJISHIRO, Kugo MORITA, Yushi NAGASAKA, Fangwei TONG, Chiharu YAMAZAKI.
Application Number | 20160219604 15/089940 |
Document ID | / |
Family ID | 53757143 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160219604 |
Kind Code |
A1 |
FUJISHIRO; Masato ; et
al. |
July 28, 2016 |
COMMUNICATION CONTROL METHOD
Abstract
A communication control method pertaining to an embodiment of
the present invention is for controlling dual connectivity
communication which uses a master base station that establishes RRC
connection with a user terminal and a secondary base station that
provides a supplementary wireless resource to the user terminal.
The communication control method comprises: a step in which the
master base station receives, from the user terminal, a measurement
report which includes measurement results found for each cell in
the user terminal; and a step in which the secondary base station
receives, from the master base station, a supplementary request for
requesting the allocation of resources to the user terminal. In the
step for receiving a supplementary request, the master base station
includes, in the supplementary request, measurement results for a
cell of the secondary base station which is included in the
measurement results, and transmits the same.
Inventors: |
FUJISHIRO; Masato;
(Yokohama-shi, JP) ; NAGASAKA; Yushi;
(Yokohama-shi, JP) ; YAMAZAKI; Chiharu; (Tokyo,
JP) ; MORITA; Kugo; (Yokohama-shi, JP) ; TONG;
Fangwei; (Tokyo, JP) ; CHANG; Henry; (San
Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA CORPORATION |
Kyoto |
|
JP |
|
|
Assignee: |
KYOCERA CORPORATION
Kyoto
JP
|
Family ID: |
53757143 |
Appl. No.: |
15/089940 |
Filed: |
April 4, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2015/052591 |
Jan 29, 2015 |
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15089940 |
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62034678 |
Aug 7, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/04 20130101;
H04W 36/38 20130101; H04W 76/15 20180201; H04W 72/085 20130101;
H04W 72/0413 20130101; H04W 36/30 20130101; H04W 36/08 20130101;
H04W 92/20 20130101; H04W 36/0061 20130101; H04W 24/10
20130101 |
International
Class: |
H04W 72/08 20060101
H04W072/08; H04W 24/10 20060101 H04W024/10; H04W 76/02 20060101
H04W076/02; H04W 72/04 20060101 H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2014 |
JP |
2014-017980 |
Claims
1. A communication control method that controls communication by a
dual connectivity method using a master base station that
establishes an RRC connection with a user terminal, and a secondary
base station that provides an additional radio resource to the user
terminal, the communication control method comprising steps of; (a)
receiving, at the master base station, a measurement report from
the user terminal, the measurement report including a measurement
result obtained for each cell by the user terminal; (b)
transmitting, by the master base station, the received measurement
report to the secondary base station; and (c) selecting, by the
secondary base station, a special cell from among a plurality of
cells at the secondary base station in response to reception of the
measurement report, the plurality of cells being managed by the
secondary base station, and the special cell being a cell provided
with a Physical Uplink Control Channel of the user terminal.
2. The communication control method according to claim 1, wherein
the step (b) includes a step of notifying, by the master base
station, the secondary base station of a candidate of the special
cell based on the received measurement report.
3. The communication control method according to claim 1, wherein
the step (b) includes a step of notifying, by the master base
station, the secondary base station of a special cell selected
based on the received measurement report.
4. The communication control method according to claim 1, wherein
the step (c) includes a step of selecting the special cell based on
a capability and/or a load status of each of the plurality of
cells.
5. The communication control method according to claim 1,
comprising a step of: (d) transmitting information from the master
base station to the user terminal based on a capability and/or a
load status of each of the plurality of cells, the information
being used for controlling the transmission of the measurement
report.
6. The communication control method according to claim 1, wherein
the step (c) includes a step of reselecting, by the secondary base
station, the special cell from among the plurality of cells based
on a measurement report newly transmitted from the user
terminal.
7. The communication control method according to claim 1, wherein
the step (a) includes a step of receiving, by the master base
station, a failure notification from the user terminal, the failure
notification notifying of a radio link failure in the special cell,
and the step (b) includes a step of transmitting a replacement
request as a message including the received measurement report from
the master base station to the secondary base station, the
replacement request being a request for a replacement of the
special cell.
8. The communication control method according to claim 7, wherein
the failure notification includes a cause of the radio link failure
in the special cell.
9. The communication control method according to claim 7, wherein a
secondary cell group is managed by the secondary base station, the
secondary cell group including another special cell in which a
Physical Uplink Control Channel of the user terminal is set, and
the measurement report includes at least one of a first measurement
result and a second measurement result, the first measurement
result corresponding to a cell other than the another special cell
included in the secondary cell group, and the second measurement
result corresponding to the another special cell.
10. The communication control method according to claim 1, wherein
the step (b) includes a step of transmitting a replacement request
as a message including the received measurement report from the
master base station to the secondary base station, the replacement
request being a request for a replacement of the special cell, and
the communication control method comprising a step of:
transmitting, by the secondary base station, a response message for
the replacement request to the master base station in response to
reception of the replacement request.
11. The communication control method according to claim 10, wherein
a secondary cell group is managed by the secondary base station,
the secondary cell group including another special cell in which a
Physical Uplink Control Channel of the user terminal is set, and
the measurement report includes at least one of a first measurement
result and a second measurement result, the first measurement
result corresponding to a cell other than the another special cell
included in the secondary cell group, and the second measurement
result corresponding to the another special cell.
12. The communication control method according to claim 10, wherein
the response message includes information on a new cell, when the
new cell is selected as the special cell.
13. The communication control method according to claim 10, wherein
a secondary cell group is managed by the secondary base station,
the secondary cell group including a special cell in which a
Physical Uplink Control Channel of the user terminal is set, and
the response message includes information indicating a release of
the secondary cell group when a new cell is not selected as the
special cell.
14. A master base station that supports communication by dual
connectivity method with a secondary base station that provides an
additional radio resource to a user terminal, and establishes an
RRC connection with the user terminal, comprising: a receiver that
receives a measurement report from the user terminal, the
measurement report including a measurement result obtained for each
cell by the user terminal; and a transmitter that transmits the
received measurement report to the secondary base station; wherein
the received measurement report is used as a trigger to select a
special cell from among a plurality of cells managed by the
secondary base station, the special cell being a cell provided with
a Physical Uplink Control Channel of the user terminal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a communication control
method used in a mobile communication system.
BACKGROUND ART
[0002] In 3GPP (3rd Generation Partnership Project), which is a
project aiming to standardize a mobile communication system,
introduction of a dual connectivity method (Dual connectivity) in
Release 12 and thereafter is expected (see Non Patent Document 1).
In the dual connectivity method, a user terminal simultaneously
establishes a connection with a plurality of base stations. Because
a radio resource is assigned to the user terminal from each base
station, it is possible to expect an improvement in throughput.
[0003] In the dual connectivity method, of the plurality of base
stations that establish a connection with the user terminal, only
one base station (hereinafter, called "master base station")
establishes an RRC connection with the user terminal. On the other
hand, of the plurality of base stations, another base station
(hereinafter, called "secondary base station") provides an
additional radio resource to the user terminal without establishing
an RRC connection with the user terminal. It is noted that the dual
connectivity method may also be called an inter-base station
carrier aggregation (inter-eNB CA).
CITATION LIST
Non-Patent Literature
[0004] Non Patent Literature 1: 3GPP technical report "TR 36. 842
V12.0.0" Jan. 7, 2014
SUMMARY OF INVENTION
[0005] In order to appropriately perform communication by the dual
connectivity method, it is believed that an association between
base stations needs to be strengthened.
[0006] Thus, an object of the present invention is to provide a
communication control method that enables appropriately performing
communication by the dual connectivity method.
[0007] A communication control method according to a first feature
is a method for controlling communication by dual connectivity
method using a master base station that establishes an RRC
connection with a user terminal and a secondary base station that
provides an additional radio resource to the user terminal. The
communication control method includes a step that the master base
station receives a measurement report from the user terminal, the
measurement report including measurement result for each cell
obtained by the user terminal, and a step that the secondary base
station receives an addition request from the master base station,
the addition request being a request of a resource assignment for
the user terminal. In the step of receiving the addition request,
the master base station transmits the addition request while
including a measurement result into the addition request, said
measurement result corresponding to each cell of the secondary base
station included in the measurement rep ort.
[0008] A communication control method according to a second feature
is a method for controlling communication by dual connectivity
method using a master base station that establishes an RRC
connection with a user terminal and a secondary base station that
provides an additional radio resource to the user terminal, The
communication control method includes a step of transmitting an RRC
reconfiguration message from the master base station to the user
terminal, the RRC reconfiguration message is a message for
performing an RRC reconfiguration of the user terminal; and a step
of transmitting an RRC reconfiguration notification from the master
base station to the secondary base station, the RRC reconfiguration
notification notified in relationship with the RRC reconfiguration
message.
[0009] A communication control method according to a third feature
is a method for controlling communication by dual connectivity
method using a master base station that establishes an RRC
connection with a user terminal and a secondary base station that
provides an additional radio resource to the user terminal. The
communication control method includes a step that the master base
station receives a measurement report from the user terminal, the
measurement report including a measurement result obtained for each
cell by the user terminal; and a step of selecting a special cell
from among a plurality of cells managed by the secondary base
station based on the measurement report, the special cell being a
cell provided with a Physical Uplink Control Channel of the user
terminal.
[0010] A communication control method according to a fourth feature
includes a step of transmitting cell information from a first base
station to a second base station, the cell information indicating
whether or not at least one cell managed by the first base station
has a capability of operating as a special cell provided with a
Physical Uplink Control Channel of the user terminal.
[0011] A communication control method according to a fifth feature
is a method for a user terminal provided in a mobile communication
system supporting a dual connectivity method, the user terminal
that establishes an RRC connection with a master base station and
that is provided an additional radio resource from a secondary base
station. A secondary cell group is managed by the secondary base
station, the secondary cell group including a special cell that a
Physical Uplink Control Channel of the user terminal is set. The
communication control method includes a step of detecting a radio
link failure in the special cell; and a step of transmitting a
measurement result to the master base station upon the detection of
the radio link failure in the special cell, said measurement result
corresponding to the cell included in the secondary cell group.
[0012] A communication control method according to sixth feature is
a method for a master base station that performs communication by
dual connectivity method with a secondary base station that
provides an additional radio resource to a user terminal, and that
establishes an RRC connection with the user terminal. A secondary
cell group is managed by the secondary base station, the secondary
cell group including a special cell that a Physical Uplink Control
Channel of the user terminal is set. The communication control
method includes a step of receiving a failure notification from the
user terminal, the failure notification that notifies a radio link
failure in the special cell and includes a first measurement result
corresponding to a cell other than the special cell included in the
secondary cell group, and a step of transmitting a replacement
request to the secondary base station, the replacement request
being a request for a replacement of the special cell. In the step
of transmitting, the master base station transmits the replacement
request while including the first measurement result into the
replacement request.
[0013] A communication control method according to a seventh
feature is a method for a secondary base station that performs
communication by dual connectivity method with the master base
station that establishes an RRC connection with a user terminal,
and that provides an additional radio resource to the user
terminal. A secondary cell group is managed by the secondary base
station, the secondary cell group including a special cell that a
Physical Uplink Control Channel of the user terminal is set. The
communication control method includes: a step of receiving a
replacement request with a first measurement result from the master
base station, the replacement request being a request for a
replacement of the special cell, the first measurement result
corresponding to a cell other than the special cell included in the
secondary cell group; a step of making a determination whether or
not to replace the special cell with the other cell based on the
first measurement result; and a step of notifying a result of the
determination to the master base station.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a configuration diagram of an LTE system according
to a first embodiment to a third embodiment.
[0015] FIG. 2 is a block diagram of UE according to the first
embodiment to the third embodiment.
[0016] FIG. 3 is a block diagram of eNB according to the first
embodiment to the third embodiment.
[0017] FIG. 4 is a protocol stack diagram of a radio interface
according to the first embodiment to the third embodiment.
[0018] FIG. 5 is a configuration diagram of a radio frame according
to the first embodiment to the third embodiment.
[0019] FIGS. 6A and 6B are diagrams showing a first UP
architecture.
[0020] FIGS. 7A and 7B are diagrams showing a second UP
architecture.
[0021] FIG. 8 is a sequence diagram showing an operation of
starting a dual connectivity method.
[0022] FIG. 9 is a sequence diagram showing an operation when MeNB
200-1 performs an RRC reconfiguration for UE 100 with respect to UE
100.
[0023] FIG. 10 is a sequence diagram showing an operation sequence
according to the first embodiment.
[0024] FIG. 11 is a sequence diagram showing an operation pattern 1
according to a second embodiment.
[0025] FIG. 12 is a sequence diagram showing an operation pattern 2
according to the second embodiment.
[0026] FIG. 13 is a sequence diagram showing an operation pattern 3
according to the second embodiment.
[0027] FIG. 14 is an operation sequence diagram according to a
third embodiment.
[0028] FIG. 15 is a sequence diagram showing an operation pattern 1
according to a fourth embodiment.
[0029] FIG. 16 is a sequence diagram showing an operation pattern 2
according to the fourth embodiment.
[0030] FIG. 17 is a diagram showing a case that a release of
resources related to all cells included in SCG is not
preferred.
[0031] FIG. 18 is a diagram showing a case that a release of
resources related to all cells included in SCG is not
preferred.
DESCRIPTION OF EMBODIMENTS
Overview of Embodiment
[0032] A communication control method according to a second
embodiment is a method for controlling communication by dual
connectivity method using a master base station that establishes an
RRC connection with a user terminal and a secondary base station
that provides an additional radio resource to the user terminal.
The communication control method includes a step that the master
base station receives a measurement report from the user terminal,
the measurement report including measurement result for each cell
obtained by the user terminal, and a step that the secondary base
station receives an addition request from the master base station,
the addition request being a request of a resource assignment for
the user terminal. In the step of receiving the addition request,
the master base station transmits the addition request while
including a measurement result into the addition request, said
measurement result corresponding to each cell of the secondary base
station included in the measurement report.
[0033] A communication control method according to a first
embodiment is a method for controlling communication by dual
connectivity method using a master base station that establishes an
RRC connection with a user terminal and a secondary base station
that provides an additional radio resource to the user terminal,
The communication control method includes a step of transmitting an
RRC reconfiguration message from the master base station to the
user terminal, the RRC reconfiguration message is a message for
performing an RRC reconfiguration of the user terminal; and a step
of transmitting an RRC reconfiguration notification from the master
base station to the secondary base station, the RRC reconfiguration
notification notified in relationship with the RRC reconfiguration
message.
[0034] In the first embodiment, the transmission of the RRC
reconfiguration notification is performed before the transmission
of the RRC reconfiguration message.
[0035] In the first embodiment, the RRC reconfiguration
notification includes a content of the RRC reconfiguration.
[0036] In the first embodiment, the communication control method
includes a step that the secondary base station, which receives the
RRC reconfiguration notification, stops a transmission to the user
terminal based on the RRC reconfiguration notification.
[0037] In the first embodiment, the secondary base station stops
the transmission to the user terminal from a time of receiving the
RRC reconfiguration notification until a lapse of a predetermined
time. The predetermined time corresponds to a time from when the
user terminal receives the RRC reconfiguration message until when
the RRC reconfiguration message is reflected. The secondary base
station resumes the transmission to the user terminal after the
lapse of the predetermined time.
[0038] In the first embodiment, the communication control method
includes a step that the master base station receives an RRC
reconfiguration completion message from the user terminal, the RRC
reconfiguration completion message indicating a completion of the
RRC reconfiguration, a step of transmitting an RRC reconfiguration
completion notification from the master base station to the
secondary base station in response to the reception of the RRC
reconfiguration completion message; and a step that the secondary
base station, which receives the RRC reconfiguration completion
notification, resumes the transmission to the user terminal based
on the RRC reconfiguration completion notification.
[0039] In the first embodiment, the transmission stopped by the
secondary base station in the stopping step is a transmission on a
user dedicated channel.
[0040] A communication control method according to a second
embodiment is a method for controlling communication by dual
connectivity method using a master base station that establishes an
RRC connection with a user terminal and a secondary base station
that provides an additional radio resource to the user terminal.
The communication control method includes a step that the master
base station receives a measurement report from the user terminal,
the measurement report including a measurement result obtained for
each cell by the user terminal; and a step of selecting a special
cell from among a plurality of cells managed by the secondary base
station based on the measurement report, the special cell being a
cell provided with a Physical Uplink Control Channel of the user
terminal.
[0041] In the second embodiment, the step of selecting the special
cell includes a step that the master base station, which receives
measurement report, transfers the received measurement report to
the secondary base station, and a step that the secondary base
station, which receives the transferred measurement report, selects
the special cell.
[0042] In the second embodiment, the step of selecting the special
cell includes: a step that the master base station, which receives
the measurement report, notifies a candidate of the special cell to
the secondary base station based on the received measurement
report, a step that the secondary base station selects the special
cell based on the notified candidate.
[0043] In the second embodiment, the step of selecting the special
cell comprises: a step that the master base station, which receives
the measurement report, selects the special cell based on the
received measurement report; and a step that the master base
station notifies the selected special cell to the secondary base
station.
[0044] In the second embodiment, in the step of selecting the
special cell, the special cell is selected further based on a
capability and/or a load status of each of the plurality of cells
managed by the secondary base station.
[0045] In the second embodiment, the communication control method
includes a step of transmitting information from the master base
station to the user terminal based on a capability and/or a load
status of each of the plurality of cells managed by the secondary
base station, said information being used for controlling the
transmission of the measurement report.
[0046] In the second embodiment, the communication control method
includes a step of reselecting the special cell from among the
plurality of cells managed by the secondary base station based on a
measurement report transmitted newly from the user terminal.
[0047] A communication control method according to a third
embodiment includes a step of transmitting cell information from a
first base station to a second base station, the cell information
indicating whether or not at least one cell managed by the first
base station has a capability of operating as a special cell
provided with a Physical Uplink Control Channel of the user
terminal.
[0048] In the third embodiment, in the step of transmitting the
cell information, the first base station transmits the cell
information while including the cell information into a
configuration update message concerning an update of a
configuration of the first base station.
[0049] In the third embodiment, in the step of transmitting the
cell information, the first base station includes the cell
information in a negative response, when transmitting the negative
response to a request from the second base station.
[0050] A communication control method according to a fourth
embodiment is a method for a user terminal provided in a mobile
communication system supporting a dual connectivity method, the
user terminal that establishes an RRC connection with a master base
station and that is provided an additional radio resource from a
secondary base station. A secondary cell group is managed by the
secondary base station, the secondary cell group including a
special cell that a Physical Uplink Control Channel of the user
terminal is set. The communication control method comprising a step
of detecting a radio link failure in the special cell; and a step
of transmitting a measurement result to the master base station
upon the detection of the radio link failure in the special cell,
said measurement result corresponding to the cell included in the
secondary cell group.
[0051] In the fourth embodiment, in the step of transmitting, the
user terminal further transmits the measurement result to master
base station upon the detection of the radio link failure in the
special cell, said measurement result corresponding to a neighbor
cell.
[0052] In the fourth embodiment, said measurement result
corresponds to a cell other than the special cell included in the
secondary cell group.
[0053] In the fourth embodiment, the communication control method
includes a step of transmitting a failure notification to the
master base station, the failure notification notifying the radio
link failure upon the detection of the radio link failure in the
special cell. Said measurement result is included in the failure
notification.
[0054] In the fourth embodiment, the communication control method
includes a step of transmitting a measurement report of event
trigger type to the master base station upon occurrence of an event
designated by the master base station. The event is the detection
of the radio link failure in the special cell. Said measurement
result is included in the measurement report of event trigger
type.
[0055] A communication control method according to a fourth
embodiment is a method for a master base station that performs
communication by dual connectivity method with a secondary base
station that provides an additional radio resource to a user
terminal, and that establishes an RRC connection with the user
terminal. A secondary cell group is managed by the secondary base
station, the secondary cell group including a special cell that a
Physical Uplink Control Channel of the user terminal is set. The
communication control method includes a step of receiving a failure
notification from the user terminal, the failure notification that
notifies a radio link failure in the special cell and includes a
first measurement result corresponding to a cell other than the
special cell included in the secondary cell group, and a step of
transmitting a replacement request to the secondary base station,
the replacement request being a request for a replacement of the
special cell. In the step of transmitting, the master base station
transmits the replacement request while including the first
measurement result into the replacement request.
[0056] In the fourth embodiment, in the step of transmitting, the
master base station further transmits a cause of the radio link
failure in the special cell to the secondary base station.
[0057] In the fourth embodiment, in the step of receiving, the
master base station receives a second measurement result
corresponding to the special cell, in the step of transmitting, the
master base station transmits the replacement request while
including the first measurement result and the second measurement
result into the replacement request.
[0058] A communication control method according to a fourth
embodiment is a method for a secondary base station that performs
communication by dual connectivity method with the master base
station that establishes an RRC connection with a user terminal,
and that provides an additional radio resource to the user
terminal. A secondary cell group is managed by the secondary base
station, the secondary cell group including a special cell that a
Physical Uplink Control Channel of the user terminal is set. The
communication control method includes a step of receiving a
replacement request with a first measurement result from the master
base station, the replacement request being a request for a
replacement of the special cell, the first measurement result
corresponding to a cell other than the special cell included in the
secondary cell group; a step of making a determination whether or
not to replace the special cell with the other cell based on the
first measurement result; and a step of notifying a result of the
determination to the master base station.
[0059] In the fourth embodiment, in the step of receiving, the
secondary base station receives a second measurement result with
the first measurement result from the master base station, the
second measurement result corresponding to the special cell. In the
step of making the determination, the secondary base station makes
the determination based on the first measurement result and the
second measurement result.
[0060] In the fourth embodiment, in the step of notifying, the
secondary base station notifies the master base station of a new
special cell, when the new special cell is selected from among the
other cell.
[0061] In the fourth embodiment, in the step of notifying, the
secondary base station notifies the master base station of a
release of the secondary cell group, when a suitable cell for the
new special cell is not included in the other cell.
First Embodiment
[0062] Hereinafter, an embodiment in a case where the present
invention is applied to a LTE system will be described.
(System Configuration)
[0063] FIG. 1 is a configuration diagram of the LTE system
according to the first embodiment.
[0064] As shown in FIG. 1, the LTE system includes UEs (User
Equipments) 100, E-UTRAN (Evolved-UMTS Terrestrial Radio Access
Network) 10, and EPC (Evolved Packet Core) 20.
[0065] The UE 100 corresponds to the user terminal. The UE 100 is a
mobile communication device and performs radio communication with a
cell (a serving cell). A configuration of the UE 100 will be
described later.
[0066] The E-UTRAN 10 corresponds to a radio access network. The
E-UTRAN 10 includes eNBs 200 (evolved Node-Bs). The eNB 200
corresponds to a base station. The eNBs 200 are connected mutually
via an X2 interface. A configuration of the eNB 200 will be
described later.
[0067] The eNB 200 manages a cell or a plurality of cells, and
performs radio communication with the UE 100 that has established a
connection with the cell. The eNB 200 has a radio resource
management (RRM) function, a function of routing user data, and a
measurement control function for mobility control and scheduling.
It is noted that the "cell" is used as a term indicating a minimum
unit of a radio communication area, and is also used as a term
indicating a function of performing radio communication with the UE
100.
[0068] The EPC 20 corresponds to a core network. The EPC 20
includes MME (Mobility Management Entity)/S-GW (Serving-Gateway)
300. The MME is a network node that performs various mobility
controls and the like, for the UE 100. The S-GW performs control to
transfer user data. The MME/S-GW 300 is connected to the eNBs 200
via an S1 interface.
[0069] FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2,
the UE 100 includes a plurality of antennas 101, a radio
transceiver 110, a user interface 120, GNSS (Global Navigation
Satellite System) receiver 130, a battery 140, a memory 150, and a
processor 160. The memory 150 and the processor 160 configure a
control unit. The UE 100 may not have the GNSS receiver 130.
Furthermore, the memory 150 may be integrally formed with the
processor 160, and this set (that is, a chip set) may be called a
processor 160'.
[0070] The antenna 101 and the radio transceiver 110 are used to
transmit and receive a radio signal. The radio transceiver 110
converts a baseband signal (a transmitted signal) output from the
processor 160 into the radio signal, and transmits the radio signal
from the antenna 101. Furthermore, the radio transceiver 110
converts the radio signal received by the antenna 101 into the
baseband signal (a received signal), and outputs the baseband
signal to the processor 160.
[0071] The user interface 120 is an interface with a user carrying
the UE 100, and includes, for example, a display, a microphone, a
speaker, various buttons and the like. The user interface 120
receives an operation from a user and outputs a signal indicating
the content of the operation to the processor 160. The GNSS
receiver 130 receives a GNSS signal in order to obtain location
information indicating a geographical location of the UE 100, and
outputs the received signal to the processor 160. The battery 140
accumulates a power to be supplied to each block of the UE 100.
[0072] The memory 150 stores a program to be executed by the
processor 160 and information to be used for a process by the
processor 160. The processor 160 includes a baseband processor that
performs modulation and demodulation, encoding and decoding and the
like on the baseband signal, and a CPU (Central Processing Unit)
that performs various processes by executing the program stored in
the memory 150. The processor 160 may further include a codec that
performs encoding and decoding on sound and video signals. The
processor 160 executes various processes and various communication
protocols described later.
[0073] FIG. 3 is a block diagram of the eNB 200. As shown in FIG.
3, the eNB 200 includes a plurality of antennas 201, a radio
transceiver 210, a network interface 220, a memory 230, and a
processor 240. The memory 230 and the processor 240 constitute a
control unit. In addition, the memory 230 is integrated with the
processor 240, and this set (that is, a chipset) may be called a
processor.
[0074] The antenna 201 and the radio transceiver 210 are used to
transmit and receive a radio signal. The radio transceiver 210
converts the baseband signal (a transmitted signal) output from the
processor 240 into the radio signal, and transmits the radio signal
from the antenna 201. Furthermore, the radio transceiver 210
converts the radio signal received by the antenna 201 into the
baseband signal (a received signal), and outputs the baseband
signal to the processor 240.
[0075] The network interface 220 is connected to the neighboring
eNB 200 via the X2 interface and is connected to the MME/S-GW 300
via the S1 interface. The network interface 220 is used in
communication performed on the X2 interface and communication
performed on the S1 interface.
[0076] The memory 230 stores a program to be executed by the
processor 240 and information to be used for a process by the
processor 240. The processor 240 includes the baseband processor
that performs modulation and demodulation, encoding and decoding
and the like on the baseband signal and a CPU that performs various
processes by executing the program stored in the memory 230. The
processor 240 executes various processes and various communication
protocols described later.
[0077] FIG. 4 is a protocol stack diagram of a radio interface in
the LTE system. As shown in FIG. 4, the radio interface protocol is
classified into a layer 1 to a layer 3 of an OSI reference model,
wherein the layer 1 is a physical (PHY) layer. The layer 2 includes
MAC (Media Access Control) layer, RLC (Radio Link Control) layer,
and PDCP (Packet Data Convergence Protocol) layer. The layer 3
includes RRC (Radio Resource Control) layer.
[0078] The PHY layer performs encoding and decoding, modulation and
demodulation, antenna mapping and demapping, and resource mapping
and demapping. Between the PHY layer of the UE 100 and the PHY
layer of the eNB 200, user data and a control signal are
transmitted through the physical channel.
[0079] The MAC layer performs priority control of data, a
retransmission process by hybrid ARQ (HARQ), a random access
procedure at the time of the RRC connection establishment and the
like. Between the MAC layer of the UE 100 and the MAC layer of the
eNB 200, user data and a control signal are transmitted via a
transport channel. The MAC layer of the eNB 200 includes a
transport format of an uplink and a downlink (a transport block
size, a modulation and coding scheme) and a scheduler to decide a
resource block to be assigned for the UE 100.
[0080] The RLC layer transmits data to an RLC layer of a reception
side by using the functions of the MAC layer and the PHY layer.
Between the RLC layer of the UE 100 and the RLC layer of the eNB
200, user data and a control signal are transmitted via a logical
channel.
[0081] The PDCP layer performs header compression and
decompression, and encryption and decryption.
[0082] The RRC layer is defined only in a control plane managing a
control signal. Between the RRC layer of the UE 100 and the RRC
layer of the eNB 200, a control signal (an RRC message) for various
types of setting is transmitted. The RRC layer controls the logical
channel, the transport channel, and the physical channel in
response to establishment, re-establishment, and release of a radio
bearer. When a connection (the RRC connection) is established
between the RRC of the UE 100 and the RRC of the eNB 200, the UE
100 is in an RRC connected state, and when the connection (the RRC
connection) is not established, the UE 100 is in an RRC idle
state.
[0083] NAS (Non-Access Stratum) layer positioned above the RRC
layer performs session management, mobility management and the
like.
[0084] In the LTE system, OFDMA (Orthogonal Frequency Division
Multiple Access) is applied in a downlink, and SC-FDMA (Single
Carrier Frequency Division Multiple Access) is applied in an
uplink, respectively.
[0085] The radio frame is configured by 10 subframes arranged in a
time direction. Each subframe is configured by two slots arranged
in the time direction. Each subframe has a length of 1 ms and each
slot has a length of 0.5 ms. Each subframe includes a plurality of
resource blocks (RBs) in a frequency direction, and a plurality of
symbols in the time direction. E Each resource block includes a
plurality of subcarriers in the frequency direction. Among radio
resources (time-frequency resources) assigned to the UE 100, a
frequency resource can be designated by a resource block and a time
resource can be designated by a subframe (or slot).
[0086] In the downlink, an interval of several symbols at the head
of each subframe is a region mainly used as a physical downlink
control channel (PDCCH) for transmitting a control signal.
Furthermore, the remaining interval of each subframe is a region
that can be mainly used as a physical downlink shared channel
(PDSCH) for transmitting user data.
[0087] In the uplink, both end portions in the frequency direction
of each subframe are regions mainly used as a physical uplink
control channel (PUCCH) for transmitting a control signal. The
other portion in the frequency direction of each subframe is a
region that can be mainly used as a physical uplink shared channel
(PUSCH) for transmitting user data.
(Dual Connectivity Method)
[0088] An LTE system according to the first embodiment supports a
dual connectivity method. The dual connectivity method is expected
to be introduced in Release 12 and thereafter. In the dual
connectivity method, the UE 100 simultaneously establishes a
connection with a plurality of eNBs 200. Because a radio resource
is assigned to the UE 100 from each of the eNBs 200, it is possible
to expect an improvement in throughput. It is noted that the dual
connectivity method may be called an inter-eNB 200 carrier
aggregation (inter-eNB CA).
[0089] FIG. 5 is a diagram for describing an overview of the dual
connectivity method.
[0090] As shown in FIG. 5, in the dual connectivity method, of the
plurality of eNBs 200 that establish a connection with the UE 100,
only a master eNB (MeNB) 200-1 establishes an RRC connection with
the UE 100. On the other hand, of the plurality of eNBs 200, a
secondary eNB (SeNB) 200-2 provides an additional radio resource to
the UE 100 without establishing an RRC connection with the UE 100.
In other words, the MeNB 200-1 establishes not only a user plane
connection, but also a control plane connection with the UE 100. On
the other hand, the SeNB 200-2 establishes a user plane connection
with the UE 100, without establishing a control plane connection
with the UE 100. An Xn interface is set between the MeNB 200-1 and
the SeNB 200-2. The Xn interface is either an X2 interface or a new
interface.
[0091] In the dual connectivity method, the UE 100 is capable of
carrier aggregation using N number of cells managed by the MeNB
200-1 and M number of cells managed by the SeNB 200-2,
simultaneously. In the dual connectivity method, the maximum number
of serving cells of the UE 100, that is, the maximum number of
(N+M) is five, for example. Here, a group composed of N number of
cells managed by the MeNB 200-1 is called a master cell group
(MCG). Moreover, a group composed of M number of cells managed by
the SeNB 200-2 is called a secondary cell group (SCG). In the SCG,
a special cell provided with PUCCH of the UE 100 is set. The
special cell performs some of the functions of a primary cell
(PCell) in carrier aggregation. Hereinafter, the special cell will
be called a "DC special cell".
[0092] FIGS. 6A and 6B, and FIGS. 7A and 7B are diagrams for
illustrating a configuration format of the transfer route (data
path) of user data in a dual connectivity method. There are mainly
two types of user plane architecture (UP architectures)
constituting the transfer route (data path) of user data in the
dual connectivity method.
[0093] FIGS. 6A and 6B show a first UP architecture. As shown in
FIG. 6A, in the first UP architecture, an SI-U interface between
the MeNB 200-1 and S-GW 300U, and an S1-U interface between SeNB
200-2 and the S-GW 300U are used. An EPS bearer #1 between the UE
100 and the P-GW passes through the S1-U interface between the MeNB
200-1 and the S-GW 300U. An EPS bearer #2 between the UE 100 and
the P-GW passes through the S1-U interface between the SeNB 200-2
and the S-GW 300U. Thus, in the first UP architecture, the data
path between the SeNB 200-2 and S-GW 300U does not pass through the
MeNB 200-1. As shown in FIG. 6B, each of the MeNB 200-1 and the
SeNB 200-2 performs the processing of each layer of PDCP, RLC, and
MAC.
[0094] FIGS. 7A and 7B show a second UP architecture. As shown in
FIG. 7A, in the second UP architecture, the EPS bearer #2 between
the UE 100 and the P-GW is split in the MeNB 200-1, and while one
of the split parts (a split bearer) terminates in the UE 100 after
passing through the SeNB 200-2, the other split part (a split
bearer) terminates in the UE 100 without passing through the SeNB
200-2. Thus, in the second UP architecture, the data path between
the SeNB 200-2 and S-GW 300U passes through the MeNB 200-1. As
shown in FIG. 7B, in one of the divided parts (the split bearer) of
the EPS bearer #2, the processing of each layer is performed by the
PDCP of the MeNB 200-1, and the RLC and MAC of the SeNB 200-2. It
is noted that in the split bearer, the MeNB may take charge the
processing up to the RLC (or some functions of the RLC).
[0095] FIG. 8 is a sequence diagram showing an operation of
starting the dual connectivity method. In the initial state of FIG.
8, the UE 100 establishes an RRC connection with the MeNB
200-1.
[0096] As shown in FIG. 8, in step S11, the UE 100 transmits, to
the MeNB 200-1, a measurement report including the measurement
result obtained for each cell in the UE 100. The measurement result
includes a combination of identification information of the
measurement cell and the reference signal received power
(RSRP)/reference signal reception quality (RSRQ).
[0097] In step S12, the MeNB 200-1 having received the measurement
report, decides the use of an SeNB resource on the basis of the
received measurement report or another parameter.
[0098] In step S13, the MeNB 200-1 transmits, to the SeNB 200-2, an
SeNB addition request (SeNB Addition) for requesting resource
assignment to the UE 100. The SeNB addition request includes
various parameters concerning the UE 100.
[0099] In step S14, the SeNB 200-2 having received the SeNB
addition request, determines whether or not to authorize resource
assignment to the UE 100 on the basis of the received SeNB addition
request. When resource assignment to the UE 100 is authorized, the
SeNB 200-2 sets a radio resource (for example, the DC special cell)
for the UE 100. The SeNB 200-2 may select the random access
preamble to be assigned to the UE 100.
[0100] In step S15, the SeNB 200-2 transmits, to the MeNB 200-1, an
SeNB addition instruction for providing a new radio resource
configuration (for example, a configuration of the DC special cell,
or a random access preamble configuration).
[0101] In step S16, the SeNB 200-2 sets a parameter of a DC special
cell depending on the new radio resource configuration. It is noted
that the order of step S15 and step S16 may be reverse.
[0102] In step S17, the MeNB 200-1 having received the SeNB
addition instruction, generates an RRC message to be transmitted to
the UE 100 on the basis of the received SeNB addition
instruction.
[0103] In step S18, the MeNB 200-1 transmits, to the UE 100, the
generated RRC message (an RRC reconfiguration message).
[0104] In step S19, the UE 100 having received the RRC
reconfiguration message, generates a MAC entity corresponding to
the SCG on the basis of the received RRC reconfiguration message.
Here, the DC special cell included in the SCG is in an activated
state, and another cell included in the SCG is in a deactivated
state.
[0105] In step S21, the UE 100 transmits, to the MeNB 200-1, an RRC
reconfiguration completion message indicating the completion of RRC
reconfiguration.
[0106] In step S22, the UE 100 performs a random access to the SeNB
200-2.
[0107] In step S23, the SeNB 200-2 detects synchronization with the
UE 100, and transmits a notification (SeNB Addition complete), to
the MeNB 200-1, indicating that the new radio resource
configuration is available.
[0108] In step S24, the SeNB 200-2 uses the DC special cell to
transmit a downlink control signal to the UE 100 over the PDCCH,
and transmit downlink user data to the UE 100 over the PDSCH.
[0109] In step S25, the SeNB 200-2 decides to start the use of
other cells included in the SCG, in the MAC layer.
[0110] In step S26, the SeNB 200-2 transmits, to the UE 100, a MAC
control element indicating the activation of other cells included
in the SCG.
[0111] In step S27, the UE 100 having received the MAC control
element activates the other cells included in the SCG on the basis
of the received MAC control element.
Communication Control Method According to the First Embodiment
[0112] FIG. 9 is a sequence diagram showing an operation when the
MeNB 200-1 performs an RRC reconfiguration for the UE 100. The UE
100 is in a state in which a connection has been established
between the MeNB 200-1 and the SeNB 200-2 (step S101).
[0113] As shown in FIG. 9, in step S102, the MeNB 200-1 transmits,
to the UE 100, an RRC reconfiguration message for performing RRC
reconfiguration for the UE 100. For example, in the case of MCG:
three cells and SCG: two cells, it is assumed that the RRC
reconfiguration message indicates a change to MCG: four cells and
SCG: one cell.
[0114] Here, the time from when the UE 100 receives an RRC
reconfiguration message until when the RRC reconfiguration message
is reflected is approximately 15 ms (step S103). Until the RRC
reconfiguration message is reflected, the MeNB 200-1 stops the
PDSCH assignment to the UE 100 (step S104).
[0115] On the other hand, because the SeNB 200-2 does not know that
the UE 100 is in the process of RRC reconfiguration, the SeNB 200-2
continues the PDSCH assignment to the UE 100, transmits the
downlink control signal to the UE 100 over the PDCCH, and transmits
the downlink user data to the UE 100 over the PDSCH (steps S105 to
S108).
[0116] However, during the period in which the UE 100 is in the
process of RRC reconfiguration, the UE 100 is not capable of
receiving the downlink control signal and the downlink user data
from the SeNB 200-2, and as a result, the assignment and
transmission of steps S105 to S107 are wasted.
[0117] Thus, in the first embodiment, the problem described above
is resolved by the method shown below.
[0118] The communication control method according to the first
embodiment includes a step of transmitting, from the MeNB 200-1 to
the UE 100, an RRC reconfiguration message for performing an RRC
reconfiguration of the UE 100, and a step of transmitting, from the
MeNB 200-1 to the SeNB 200-2, an RRC reconfiguration notification
for notifying about the transmission of the RRC reconfiguration
message. The SeNB 200-2 having received the RRC reconfiguration
notification stops the transmission to the UE 100 on the basis of
the RRC reconfiguration notification. As a result, the MeNB 200-1
is capable of knowing that the UE 100 is in the process of RRC
reconfiguration, which enables the MeNB 200-1 to prevent the
wasteful assignment and transmission to the UE 100.
[0119] It is noted that the transmission stopped by the SeNB 200-2
is the transmission on a user dedicated channel (for example, DTCH:
Dedicated Traffic CHannel, and DCCH: Dedicated Control CHannel).
Thus, even though the SeNB 200-2 stops the transmission of the user
dedicated channel to the UE 100, the SeNB 200-2 may continue the
broadcast transmission, such as paging.
[0120] In the first embodiment, the transmission of the RRC
reconfiguration notification is performed before the transmission
of the RRC reconfiguration message. As a result, even when a
transmission delay occurs in a backhaul (the Xn interface), it is
possible that the timing of reception of the RRC reconfiguration
notification by the SeNB 200-2 matches with the transmission timing
of the RRC reconfiguration message.
[0121] In the first embodiment, the RRC reconfiguration
notification includes the contents of RRC reconfiguration. Thus,
the SeNB 200-2 is capable of knowing the contents of RRC
reconfiguration performed by the MeNB 200-1 for the UE 100, and
this enables the SeNB 200-2 to perform appropriate communication
control.
[0122] In the first embodiment, the SeNB 200-2 stops the
transmission to the UE 100 from the time of receiving the RRC
reconfiguration notification until the lapse of a predetermined
time. The predetermined time corresponds to the time from when the
UE 100 receives the RRC reconfiguration message until when the RRC
reconfiguration message is reflected. The SeNB 200-2 resumes the
transmission to the UE 100 after the lapse of the predetermined
time. Thus, the SeNB 200-2 is capable of resuming the transmission
to the UE 100 as soon as the RRC reconfiguration of the UE 100 is
complete.
[0123] Alternatively, rather than autonomously resuming the
transmission, the SeNB 200-2 may resume the transmission upon
receiving a notification from the MeNB 200-1. In such a case, the
communication control method includes a step of receiving, by the
MeNB 200-1 from the UE 100, an RRC reconfiguration completion
message indicating the completion of RRC reconfiguration, a step of
transmitting, from the MeNB 200-1 to the SeNB 200-2, an RRC
reconfiguration completion notification upon the reception of the
RRC reconfiguration completion message, and a step of resuming
transmission to the UE 100, by the SeNB 200-2 that receives the RRC
reconfiguration completion notification, on the basis of the RRC
reconfiguration completion notification.
Operation Sequence According to the First Embodiment
[0124] FIG. 10 is a sequence diagram showing an operation sequence
according to the first embodiment. The UE 100 is in a state in
which a connection has been established between the MeNB 200-1 and
the SeNB 200-2 (step S151).
[0125] As shown in FIG. 10, in step S152, the MeNB 200-1 transmits,
to the SeNB 200-2, an RRC reconfiguration notification (RRC
Connection Reconfiguration Initiation). The RRC reconfiguration
notification includes at least one of an RRC container for storing
the RRC configuration (RRC Configuration) and a flag indicating
start/end. Here, with the RRC container, the SeNB 200-2 is capable
of knowing the contents of the RRC configuration, and therefore,
the SeNB 200-2 is capable of determining whether to stop
transmission on the basis of the contents of the RRC configuration.
The RRC reconfiguration notification may include a threshold value
of the timer used in step S156 described later.
[0126] The RRC reconfiguration notification is preferably
transmitted at a timing that is earlier than the transmission
timing of the RRC reconfiguration message by only as much as the
transmission delay time of the backhaul (the Xn interface).
[0127] In step S153, the MeNB 200-1 transmits an RRC
reconfiguration message to the UE 100. The UE 100 having received
the RRC reconfiguration message starts the RRC reconfiguration on
the basis of the received RRC reconfiguration message.
[0128] In step S154, the MeNB 200-1 stops the PDSCH assignment to
the UE 100 until the RRC reconfiguration message is reflected.
[0129] In step S155, the SeNB 200-2 having received the RRC
reconfiguration notification stops the transmission to the UE 100
on the basis of the received RRC reconfiguration notification.
[0130] In step S156, the SeNB 200-2 starts a timer for clocking the
predetermined time. The predetermined time corresponds to the time
from when the UE 100 receives the RRC reconfiguration message until
when the RRC reconfiguration message is reflected.
[0131] In step S157, the UE 100 transmits an RRC reconfiguration
message to the MeNB 200-1.
[0132] In step S158, the MeNB 200-1 may transmit, to the SeNB
200-2, an RRC reconfiguration completion notification (RRC
Connection Reconfiguration complete) upon receiving the RRC
reconfiguration completion message.
[0133] In step S159, the SeNB 200-2 detects either the expiry of
the timer, or the reception of the RRC reconfiguration completion
notification.
[0134] In step S160, the SeNB 200-2 detects the expiry of the timer
or the reception of the RRC reconfiguration completion
notification, and resumes the transmission to the UE 100.
Second Embodiment
[0135] Hereinafter, a communication control method according to a
second embodiment will be described while focusing on the
differences from the first embodiment.
Communication Control Method According to the Second Embodiment
[0136] As described earlier, to the SCG, a DC special cell in which
PUCCH of the UE 100 is provided is set. Here, the DC special cell
is desired to be a cell having a favorable communication state as
compared to the other cells of the SCG. A cell having a favorable
communication state is, for example, a cell having a high received
power of a desired wave, a cell having a low interference power, or
a cell having a low load level. If the communication state is
unfavorable in the DC special cell, the uplink control signal is
not transmitted normally, thus making it difficult to appropriately
execute communication by the dual connectivity method.
[0137] Thus, in the second embodiment, the problem described above
is resolved by the method shown below.
[0138] The communication control method according to the second
embodiment includes a step of receiving, by the MeNB 200-1 from the
UE 100, a measurement report including a measurement result
obtained for each cell in the UE 100, and a step of selecting a DC
special cell in which a Physical Uplink Control Channel of the UE
100 is provided, from among a plurality of cells managed by the
SeNB 200-2 on the basis of the measurement report. This enables the
selection of a cell having a favorable communication state in the
UE 100 as a DC special cell, and thus making it possible to
appropriately execute communication by the dual connectivity
method.
[0139] In the second embodiment, the step of selecting the DC
special cell includes a step of transferring, by the MeNB 200-1
that receives the measurement report, to the SeNB 200-2, the
received measurement report, and a step of selecting the DC special
cell, by the SeNB 200-2 that receives the transferred measurement
report.
[0140] Alternatively, the step of selecting the DC special cell
includes a step of notifying, by the MeNB 200-1 that receives the
measurement report, to the SeNB 200-2, a candidate of the DC
special cell on the basis of the received measurement report, and a
step of selecting the DC special cell, by the SeNB 200-2 on the
basis of the notified candidate.
[0141] Alternatively, the step of selecting the DC special cell
includes a step of selecting the DC special cell, by the MeNB 200-1
that receives the measurement report on the basis of the received
measurement report, and a step of notifying the selected DC special
cell from the MeNB 200-1 to the SeNB 200-2.
[0142] In the second embodiment, in the step of selecting the DC
special cell, the DC special cell may be selected further on the
basis of the capability and/or the load status of each of the
plurality of cells managed by the SeNB 200-2.
[0143] The communication control method according to the second
embodiment may include a step of transmitting, from the MeNB 200-1
to the UE 100, information for controlling the transmission of the
measurement report on the basis of the capability and/or the load
status of each of the plurality of cells managed by the SeNB
200-2.
[0144] The communication control method according to the second
embodiment may further include a step of reselecting the DC special
cell from the plurality of cells managed by the SeNB 200-2 on the
basis of a measurement report newly transmitted from the UE
100.
Operation According to the Second Embodiment
(1) Operation Pattern 1
[0145] In an operation pattern 1 according to the second
embodiment, the SeNB 200-2 selects the DC special cell. FIG. 11 is
a sequence diagram showing the operation pattern 1 according to the
second embodiment. The UE 100 is in a state in which an RRC
connection has been established with the MeNB 200-1.
[0146] As shown in FIG. 11, in step S201, the UE 100 transmits, to
the MeNB 200-1, a measurement report including the measurement
result determined for each cell in the UE 100. The measurement
result includes a combination of identification information of the
measurement cell and the reference signal received power
(RSRP)/reference signal reception quality (RSRQ).
[0147] In step S202, the MeNB 200-1 having received the measurement
report decides the use of an SeNB resource on the basis of the
received measurement report.
[0148] In step S203, the MeNB 200-1 transmits, to the SeNB 200-2,
an SeNB addition request (SeNB Addition).
[0149] Here, the MeNB 200-1 includes the measurement report
received from the UE 100 in the SeNB addition request. That is, the
MeNB 200-1 transfers the measurement report received from the UE
100 to the SeNB 200-2. Of the measurement results included in the
measurement report received from the UE 100, the MeNB 200-1 may
extract the measurement result for a cell of the SeNB 200-2, and
transfer the same to the SeNB 200-2.
[0150] Alternatively, of the measurement results included in the
measurement report received from the UE 100, the MeNB 200-1 may
extract one or a plurality of cells of the SeNB 200-2 having a
favorable communication state, and may include (a list of) the
candidate cells which are extracted cells in the SeNB addition
request.
[0151] In step S204, the SeNB 200-2 having received the SeNB
addition request determines whether or not to authorize resource
assignment to the UE 100 on the basis of the received SeNB addition
request. When resource assignment to the UE 100 is authorized, the
SeNB 200-2 selects the DC special cell on the basis of information
included in the SeNB addition request.
[0152] In step S205, the SeNB 200-2 transmits, to the MeNB 200-1,
an SeNB addition instruction for providing a new radio resource
configuration (for example, a configuration of the DC special cell,
or a random access preamble configuration).
(2) Operation Pattern 2
[0153] In an operation pattern 2 according to the second
embodiment, the MeNB 200-1 selects the DC special cell. FIG. 12 is
a sequence diagram showing the operation pattern 2 according to the
second embodiment. The UE 100 is in a state in which an RRC
connection has been established with the MeNB 200-1.
[0154] As shown in FIG. 12, in step S231, the SeNB 200-2 transmits,
to the MeNB 200-1, information showing the load level of each cell
of the SeNB 200-2.
[0155] In step S232, the SeNB 200-2 transmits, to the MeNB 200-1,
information showing the class of each cell of the SeNB 200-2. The
details of the class (the type) of cells are provided in a third
embodiment.
[0156] It is noted that only one of step S231 and step S232 may be
provided.
[0157] In step S233, of the cells of the SeNB 200-2, the MeNB 200-1
selects the cells for which the measurement of the UE 100 is to be
performed. Of the cells of the SeNB 200-2, the MeNB 200-1 may
select a cell having a low load level, or a cell having a
capability of operating as a DC special cell as the measurement
target cell on the basis of information received from the SeNB
200-2.
[0158] In step S234, the MeNB 200-1 transmits, to the UE 100, a
measurement configuration (Measurement Config.) for setting the
measurement of the measurement target cell. The UE 100 having
received the measurement configuration performs measurement for
each cell of the SeNB 200-2 on the basis of the received
measurement configuration.
[0159] In step S235, the UE 100 transmits, to the MeNB 200-1, a
measurement report including the measurement result.
[0160] It is possible to apply the procedures of step S231 through
S235 to the aforementioned operation pattern 1.
[0161] In step S236, the MeNB 200-1 having received the measurement
report, decides the use of the SeNB resource on the basis of the
received measurement report. Moreover, of the measurement results
included in the measurement report received from the UE 100, the
MeNB 200-1 selects a cell of the SeNB 200-2 having a favorable
communication state as the DC special cell.
[0162] In step S237, the MeNB 200-1 transmits, to the SeNB 200-2,
an SeNB addition request (SeNB Addition). Here, the MeNB 200-1
includes the information on the selected DC special cell in the
SeNB addition request.
[0163] In step S238, the SeNB 200-2 having received the SeNB
addition request, determines whether or not to authorize resource
assignment to the UE 100 on the basis of the received SeNB addition
request. When resource assignment to the UE 100 is authorized, the
SeNB 200-2 sets the DC special cell on the basis of information on
the DC special cell included in the SeNB addition request.
[0164] In step S239, the SeNB 200-2 transmits, to the MeNB 200-1,
an SeNB addition instruction for providing a new radio resource
configuration (for example, a configuration of the DC special cell,
or a random access preamble configuration).
[0165] In step S240, the MeNB 200-1 having received the SeNB
addition instruction transmits an RRC reconfiguration message to
the UE 100. Here, the MeNB 200-1 may cancel the above-described
special measurement configuration (Measurement Config.) and make
new measurement configurations.
(3) Operation Pattern 3
[0166] In an operation pattern 3 of the second embodiment, after
selecting the DC special cell, the MeNB 200-1 or the SeNB 200-2
reselects the DC special cell on the basis of the measurement
report newly transmitted from the UE 100.
[0167] FIG. 13 is a sequence diagram showing an operation pattern 3
according to the second embodiment. The UE 100 is in a state in
which an RRC connection has been established with the MeNB
200-1.
[0168] In step S251, the MeNB 200-1 transmits, to the UE 100, a
measurement configuration (Measurement Config.) for setting the
measurement of the measurement target cell. The UE 100 having
received the measurement configuration performs measurement for
each cell of the SeNB 200-2 on the basis of the received
measurement configuration.
[0169] In step S252, the UE 100 transmits, to the MeNB 200-1, a
measurement report 1 including the measurement result.
[0170] In step S253, the MeNB 200-1 having received the measurement
report 1, decides the use of the SeNB resource on the basis of the
received measurement report 1. Moreover, of the measurement results
included in the measurement report 1 received from the UE 100, the
MeNB 200-1 selects a cell of the SeNB 200-2 having a favorable
communication state as a DC special cell 1.
[0171] In step S254, the MeNB 200-1 transmits, to the SeNB 200-2,
an SeNB addition request (SeNB Addition). Here, the MeNB 200-1
includes the information on the selected DC special cell 1 in the
SeNB addition request.
[0172] In step S255, the SeNB 200-2 having received the SeNB
addition request, determines whether or not to authorize resource
assignment to the UE 100 on the basis of the received SeNB addition
request. When resource assignment to the UE 100 is authorized, the
SeNB 200-2 sets the DC special cell 1 on the basis of information
on the DC special cell 1 included in the SeNB addition request.
[0173] In step S256, the SeNB 200-2 transmits, to the MeNB 200-1,
an SeNB addition instruction for providing a new radio resource
configuration (for example, a configuration of the DC special cell,
or a random access preamble configuration).
[0174] In step S257, the UE 100 transmits, to the MeNB 200-1, a
measurement report 2 including the measurement result.
[0175] In step S258, of the measurement results included in the
received measurement report 2, the MeNB 200-1 having received the
measurement report 2 selects a cell of the SeNB 200-2 having a
favorable communication state as a DC special cell 2. Also, the
MeNB 200-1 determines which of the DC special cell 1 selected
previously and the DC special cell 2 selected currently is optimum
as the DC special cell, and then reselects the DC special cell.
[0176] In step S259, the MeNB 200-1 transmits, to the SeNB 200-2,
an SeNB addition request (SeNB Addition). Here, the MeNB 200-1
includes the information on the selected DC special cell and
another cell (SCell) in the SeNB addition request.
[0177] In step S260, the SeNB 200-2 having received the SeNB
addition request sets the DC special cell on the basis of
information on the DC special cell included in the received SeNB
addition request.
[0178] In step S261, the SeNB 200-2 transmits, to the MeNB 200-1,
an SeNB addition instruction for providing a new radio resource
configuration (for example, a configuration of the DC special cell,
or a random access preamble configuration).
Third Embodiment
[0179] Hereinafter, a third embodiment will be described while
focusing on the differences from the first and the second
embodiments.
Communication Control Method According to Third Embodiment
[0180] As described below, in the recent years, special band
operation methods are being examined in addition to a usual band
operation methods (for example, the downlink/uplink pair
configuration). [0181] Supplemental DL: A downlink-dedicated band
[0182] Unlicensed band: It is a band for which a license is not
required, and is mainly used in best-effort type communications
[0183] Shared license band: It is a band in which a plurality of
operators exist in a single band, and is mainly used in best-effort
type communications [0184] White space: It is a band that reuses
the available time and location of the license band of another
company, and is mainly used in best-effort type communications
[0185] As a prerequisite, such special bands must be used as an
SCell. In other words, the following problems exist. [0186] A
handover request, even if performed, may be denied (not turned to a
PCell) [0187] An attempt of setting to a DC special cell may be
denied
[0188] Thus, in the third embodiment, unnecessary processing
(reject), and an increase in RLF/HOF (Handover Failure) and a
decline in QoE which are accompanied with this are avoided by the
following method.
[0189] The communication control method according to the third
embodiment includes a step of transmitting, from a first base
station to a second base station, cell information indicating
whether or not at least one cell managed by the first base station
has a capability of operating as a cell on which a Physical Uplink
Control Channel of the UE 100 (a PCell or a DC special cell) is
provided. The first base station may be the SeNB 200-2. Moreover,
the second base station may be the MeNB 200-1.
[0190] In the third embodiment, in the step of transmitting the
cell information, the first base station includes cell information
in the configuration update message concerning an update of the
configuration of the first base station, and then transmits the
cell information therein.
[0191] In the third embodiment, in the step of transmitting cell
information, when transmitting a negative response to a request
from the second base station, the first base station includes the
cell information into the negative response.
Operation Sequence According to Third Embodiment
[0192] FIG. 14 is an operation sequence diagram according to the
third embodiment.
[0193] As shown in FIG. 14, in step S300, eNB 1 transmits, to an
eNB 2, cell information indicating whether or not at least one cell
managed by the eNB 1 has a capability of operating as a cell (a
PCell or a DC special cell) on which a Physical Uplink Control
Channel of the UE 100 is provided.
[0194] As shown in Table 1, the cell information (HO possible) may
be included in Served Cell Information of an eNB Configuration
Update message concerning an update of the eNB configuration, or an
X2 setup message for establishing an X2 interface.
TABLE-US-00001 TABLE 1 IE/Group IE type and Semantics Name Presence
Range reference description PCI M INTEGER Physical (0 . . . Cell ID
503, . . .) Cell ID M ECGI 9.2.14 TAC M OCTET Tracking STRING(2)
Area Code [. . .] HO possible O ENUMERATED The cell can (Possible,
become PCell impossi- and/or Special ble, . . .) Cell for dual
connectivity.
[0195] Alternatively, as shown in Table 2, the cell information (HO
possible) may be included in the Cause in HO Preparation Failure,
which is a negative response to a handover request, or an SeNB
Addition/Modification failure, which is a negative response to an
SeNB Addition/Modification. The eNB 2 having received the Cause
stores that the cell does not have the capability of operating as a
PCell/DC special cell.
TABLE-US-00002 TABLE 2 IE/Group IE Type and Name Presence Range
Reference CHOICE Cause M Group >Radio Network Layer
>>Radio Network M ENUMERATED Layer Cause (Handover Desirable
for Radio Reasons, Time Critical Handover, Resource Optimisa- tion
Handover, Reduce Load in Serving Cell, . . . No PCell
functionality, No Special Cell functionality,) [. . .]
Fourth Embodiment
[0196] Hereinafter, a fourth embodiment will be described while
focusing on the differences from the first embodiment to the third
embodiment. The fourth embodiment is an embodiment concerning a
modification of the second embodiment. Therefore, the fourth
embodiment will be described while focusing on the differences from
the second embodiment.
Communication Control Method According to Fourth Embodiment
[0197] In the above-described second embodiment, S-RLF, which is a
radio link failure (RLF) in SCG was not particularly described. In
the fourth embodiment, mainly the operation during the occurrence
of the S-RLF will be described.
[0198] In the fourth embodiment, the UE 100 detects RLF for the DC
special cell in the SCG. Even when a plurality of cells are
included in the SCG, the UE 100 detects only the RLF of the DC
special cell among the plurality of cells. As described earlier,
the DC special cell is a special cell in the SCG on which PUCCH of
the UE 100 is provided. The DC special cell performs some of the
functions of a primary cell (PCell) in carrier aggregation. The DC
special cell may also be referred to as a primary secondary cell
(PSCell). Moreover, a cell other than the DC special cell in the
SCG may be referred to as secondary cell (SCell).
[0199] Upon detecting RLF of the DC special cell, the UE 100
transmits, to the MeNB 200-1, a failure notification for notifying
the S-RLF. Hereinafter, such a failure notification is referred to
as "S-RLF indication". Here, the two proposed operations described
below are assumed as operations of the UE 100 after the S-RLF
indication is transmitted. The first proposed operation is an
operation in which the UE 100 releases all secondary cells (that
is, the SCG) belonging to the SeNB 200-2. The second proposed
operation is an operation in which the UE 100 awaits an RRC
reconfiguration message (an RRC Connection Reconfiguration message)
from the MeNB 200-1, and follows the contents of the RRC
reconfiguration message.
[0200] However, the first proposed operation has the problem
described below. Even when RLF occurs in the DC special cell, it
may be possible to expect that the communication state of the
secondary cells other than the DC special cell is favorable.
However, the release of all secondary cells (the SCG) belonging to
the SeNB 200-2 may not be the most appropriate option.
[0201] The second proposed operation has the problem described
below. A precondition in the second proposed operation is that the
MeNB 200-1 determines whether the UE 100 should release all
secondary cells (the SCG) belonging to the SeNB 200-2, or the UE
100 should resume communication using the other secondary cells.
However, the MeNB 200-1 does not have the information for
appropriately performing the determination.
[0202] Thus, in the fourth embodiment, the UE 100, for example,
includes either the latest measurement results or information
corresponding thereto in the S-RLF indication. The MeNB 200-1
transfers the information to the SeNB 200-2 and requests the SeNB
200-2 to examine whether the DC special cell should be replaced, or
the SCG should be released. Upon receiving the result, the MeNB
200-1 decides the operation of the UE 100, and instructs the same
to the UE 100.
[0203] The communication control method according to the fourth
embodiment is a method in the UE 100 that establishes an RRC
connection with the MeNB 200-1 and in which additional radio
resources are provided from the SeNB 200-2, in a mobile
communication system supporting the dual connectivity method. The
SCG that includes the DC special cell in which PUCCH of the UE 100
is set is managed by the SeNB 200-2. The communication control
method includes a step of detecting the S-RLF in the DC special
cell, and a step of transmitting, to the MeNB 200-1, a first
measurement result for a cell other than the DC special cell in the
SCG, when S-RLF is detected in the DC special cell. This enables
the MeNB 200-1 to acquire information for determining whether all
secondary cells (the SCG) belonging to the SeNB 200-2 should be
released, or the communication should be resumed using the other
secondary cells. The first measurement result may include a
plurality of measurement results corresponding to a plurality of
cells.
[0204] In the fourth embodiment, when the UE 100 detects S-RLF in
the DC special cell, the UE 100 may further transmit, to the MeNB
200-1, the second measurement result for the DC special cell. Thus,
the MeNB 200-1 is capable of knowing the details of the S-RLF.
[0205] In an operation pattern 1 of the fourth embodiment, when the
UE 100 detects S-RLF in the DC special cell, the UE 100 transmits,
to the MeNB 200-1, an S-RLF indication for notifying the S-RLF. The
first measurement result and the second measurement result are
included in the S-RLF indication.
[0206] In an operation pattern 2 of the fourth embodiment, when an
event designated by the MeNB 200-1 occurs, the UE 100 transmits, to
the MeNB 200-1, an event trigger type measurement report. The event
indicates that S-RLF is detected in the DC special cell. The first
measurement result and the second measurement result are included
in the event trigger type measurement report.
[0207] According to such an operation pattern 1 or 2, the MeNB
200-1 is capable of knowing that S-RLF has occurred, and at the
same time, is capable of knowing a radio condition of each cell of
the SCG. It is possible to estimate the radio condition of the DC
special cell through the S-RLF indication or the event trigger type
measurement report. Thus, the second measurement result need not
necessarily be included in the S-RLF indication or the event
trigger type measurement report.
[0208] The communication control method according to the fourth
embodiment is a method in the MeNB 200-1 that performs
communication by the dual connectivity method along with the SeNB
200-2 that provides additional radio resources to the UE 100, and
also establishes an RRC connection with the UE 100. The
communication control method includes a step of receiving, from the
UE 100, an S-RLF indication for notifying the S-RLF, and a first
measurement result for a cell other than the DC special cell in the
SCG, and a step of transmitting, to the SeNB 200-2, along with the
first measurement result, a replacement request for requesting a
replacement of the DC special cell upon receiving the S-RLF
indication. This enables the SeNB 200-2 to appropriately determine
whether or not it is possible to replace the DC special.
[0209] The MeNB 200-1 may further receive the second measurement
result for the DC special cell from the UE 100. The MeNB 200-1 may
transmit, to the SeNB 200-2, the replacement request, along with
the first measurement result and the second measurement result.
Here, the SeNB 200-2 may notice that the S-RLF is detected in the
UE 100. Thus, by transmitting the second measurement result to the
SeNB 200-2, the SeNB 200-2 is capable of appropriately estimating
the occurrence of the S-RLF.
[0210] The communication control method according to the fourth
embodiment is a method in the SeNB 200-2 that performs
communication by the dual connectivity method along with the MeNB
200-1 that establishes an RRC connection with the UE 100, and also
provides additional radio resources to the UE 100. The
communication control method includes a step of receiving, from the
MeNB 200-1, along with the first measurement result for a cell
other than the DC special cell in the SCG, a replacement request
for requesting a replacement of the DC special cell, a step of
determining whether or not to replace the DC special cell with
another cell on the basis of the first measurement result, upon
receiving the replacement request, and a step of notifying the
determination result to the MeNB 200-1. This enables the MeNB 200-1
to know whether or not the replacement of the DC special cell is
possible in the SeNB 200-2.
[0211] The SeNB 200-2 may receive, from the MeNB 200-1, along with
the first measurement result, the second measurement result for the
DC special cell. The SeNB 200-2 may perform the determination on
the basis of the first measurement result and the second
measurement result.
[0212] When a new DC special cell is selected from another cell,
the SeNB 200-2 notifies, to the MeNB 200-1, the new DC special
cell. When a cell that is appropriate as a new DC special cell does
not exist in another cell, the SeNB 200-2 notifies the release of
the SCG to the MeNB 200-1.
Operation Sequence According to Fourth Embodiment
[0213] Hereinafter, an example of an operation sequence according
to the fourth embodiment will be explained.
(1) Operation Pattern 1
[0214] In the operation pattern 1 according to the fourth
embodiment, the first measurement result and the second measurement
result are included in the S-RLF indication. FIG. 15 is a sequence
diagram showing the operation pattern 1 according to the fourth
embodiment.
[0215] In the initial state of the present sequence, the
communication by the dual connectivity method is performed. The UE
100 performs radio link monitoring (RLM) for the DC special cell.
Moreover, the UE 100 performs measurement (RSRP measurement and
RSRQ measurement) for each cell of the SCG on the basis of the
measurement configuration (Measurement Config.) from the MeNB
200-1.
[0216] As shown in FIG. 15, in step S401, the UE 100 detects S-RLF.
The UE 100 may stop the uplink transmission to the SCG upon
detecting the S-RLF. Moreover, the UE 100 may stop the monitoring
of the PDCCH for the SCG upon detecting the S-RLF.
[0217] In step S402, the UE 100 transmits, to the MeNB 200-1, an
S-RLF indication for notifying the S-RLF. The UE 100 includes the
measurement result for the SCG (the first measurement result and
the second measurement result) in the S-RLF indication. Information
indicating the type of the S-RLF may be further included in the
S-RLF indication. Also, the UE 100 awaits an instruction from the
MeNB 200-1 without resuming the connection with the SCG. The MeNB
200-1 receives, from the UE 100, the S-RLF indication including the
first measurement result and the second measurement result.
[0218] In step S403, the MeNB 200-1 transmits, to the SeNB 200-2, a
replacement request for requesting a replacement of the DC special
cell upon receiving the S-RLF indication. Here, an example in which
the replacement request is SCG-ConfigInfo, which is a new X2
message, or an information element thereof, is explained. The
SCG-ConfigInfo includes the measurement result for the SCG (the
first measurement result and the second measurement result).
[0219] The SeNB 200-2 receives, from the MeNB 200-1, the
SCG-ConfigInfo (the replacement request) including the first
measurement result and the second measurement result. The SeNB
200-2 determines whether or not to replace the DC special cell with
another secondary cell upon receiving the SCG-ConfigInfo (the
replacement request). For example, the SeNB 200-2 compares the
first measurement result with a threshold value, and sets a cell
corresponding to the first measurement result that is more
favorable than the threshold value as a candidate of the new DC
special cell. Alternatively, the SeNB 200-2 compares the first
measurement result with the second measurement result, and sets a
cell corresponding to the first measurement result that is more
favorable than the second measurement result as a candidate of the
new DC special cell. Also, from the candidates, the SeNB 200-2
selects a new DC special cell in consideration of the cell load
status, etc. Moreover, when a candidate that is appropriate as a
new DC special cell does not exist, the SeNB 200-2 may determine to
release all secondary cells (SCGs).
[0220] In step S404, the SeNB 200-2 notifies the determination
result of the SeNB 200-2 to the MeNB 200-1. Here, an example in
which the notification is SCG-Configuration, which is a new X2
message, or an information element thereof, is explained. The MeNB
200-1 receives the SCG-Configuration (the determination
result).
[0221] In step S405, the MeNB 200-1 transmits, to the UE 100, an
RRC reconfiguration message (the RRCConnectionReconfiguration
message) concerning an update of the SCG configuration on the basis
of the SCG-Configuration (the determination result). The RRC
reconfiguration message includes information designating the new DC
special cell. Alternatively, the RRC reconfiguration message may
include information designating the release of the SCG.
[0222] Upon receiving the RRC reconfiguration message, the UE 100
applies the RRC reconfiguration designated by the RRC
reconfiguration message. However, when the UE 100 is not able to
perform at least a part of RRC reconfiguration designated by the
RRC reconfiguration message, the UE 100 may decide to deny the RRC
reconfiguration. Here, the explanation is proceeded with assuming
that the UE 100 is able to perform the RRC reconfiguration
designated by the RRC reconfiguration message.
[0223] In step S406, the UE 100 transmits, to the MeNB 200-1, an
RRC reconfiguration completion message (RRC
ConnectionReconfigurationComplete).
[0224] In step S407, the MeNB 200-1 transmits, to the SeNB 200-2,
an acknowledgment message (Inter eNB RRC message) for the
SCG-Configuration (the determination result).
(2) Operation Pattern 2
[0225] Next, an operation pattern 2 according to the fourth
embodiment will be described while focusing on the differences from
the operation pattern 1. In the operation pattern 2 according to
the fourth embodiment, the first measurement result and the second
measurement result are included in an event trigger type
measurement report. FIG. 16 is a sequence diagram showing the
operation pattern 2 according to the fourth embodiment.
[0226] In the initial state of the present sequence, the
communication by the dual connectivity method is performed. The UE
100 performs radio link monitoring (RLM) for the DC special
cell.
[0227] As shown in FIG. 16, in step S411, the MeNB 200-1 transmits,
to the UE 100, a measurement configuration (Measurement Config.)
for setting the event trigger type measurement report. The
measurement configuration includes information for designating the
event that acts as a trigger. The designated event is an event
indicating that S-RLF is detected in the DC special cell. The UE
100 performs measurement (RSRP measurement and RSRQ measurement)
for each cell in the SCG on the basis of the measurement
configuration.
[0228] In step S412, the UE 100 detects S-RLF.
[0229] In step S413, the UE 100 transmits, to the MeNB 200-1, an
S-RLF indication for notifying the S-RLF. Information indicating
the type of the S-RLF may be included in the S-RLF indication.
[0230] Moreover, in step S414, upon the fulfillment of the
designated event, the UE 100 transmits, to the MeNB 200-1, the
event trigger type measurement report (Measurement Report). The UE
100 includes the measurement result for the SCG (the first
measurement result and the second measurement result) in the
measurement report. Step S413 and step S414 may be performed
simultaneously. Also, the UE 100 awaits an instruction from the
MeNB 200-1 without resuming the connection with the SCG. The MeNB
200-1 receives, from the UE 100, the S-RLF indication, and the
measurement report including the first measurement result and the
second measurement result.
[0231] In step S415, the MeNB 200-1 transmits, to the SeNB 200-2, a
replacement request for requesting a replacement of the DC special
cell upon receiving the S-RLF indication. Here, an example in which
the replacement request is SCG-ConfigInfo, which is a new X2
message, or an information element thereof, is explained. The
SCG-ConfigInfo includes the measurement result for the SCG (the
first measurement result and the second measurement result). The
subsequent operations (steps S416 to S419) are the same as those in
the operation pattern 1.
Other Embodiments
[0232] The aforementioned first embodiment to the fourth embodiment
may be performed by combining at least two embodiments, rather than
performing each embodiment separately and independently.
[0233] In the aforementioned second embodiment, mainly an example
of selecting or reselecting a DC special cell on the basis of the
measurement report was explained. However, the second embodiment
obviously includes examples of selecting or reselecting an SCG
composed of a plurality of cells including the DC special cell, on
the basis of the measurement report. Moreover, the second
embodiment obviously includes examples of selecting or reselecting
an SCG cell other than the DC special cell, on the basis of the
measurement report.
[0234] The above-described third embodiment is not limited to the
dual connectivity method, and can be applied to a usual
handover.
[0235] In the aforementioned fourth embodiment, an example in which
when the UE 100 detects S-RLF, the UE 100 transmits, to the MeNB
200-1, the first measurement result for the cell other than the DC
special cell in the SCG was explained. However, the first
measurement result may further include the measurement result of a
cell that is not included in SCG (a non-serving cell of the UE 100)
from among the cells of the SeNB 200-2. That is, the first
measurement result may be the measurement result for the cells
having a frequency that is different from the frequency of the DC
special cell.
[0236] Moreover, in the aforementioned fourth embodiment, an
example in which the SeNB 200-2 selects a new DC special cell from
the secondary cells included in the SCG upon receiving the
SCG-ConfigInfo (the replacement request) was explained. However,
the SeNB 200-2 may select a new DC special cell from cells of the
SeNB 200-2 (a non-serving cell of the UE 100) that is not included
in the SCG.
[0237] In the embodiment described above, although an LTE system is
described as an example of a mobile communication system, it is not
limited to the LTE system, and the present invention may be applied
to a system other than the LTE system.
[Appendix 1]
(1) Introduction
[0238] According to the current agreements, upon the detection of
S-RLF, the UE shall report the cause of the S-RLF to MeNB (RLM, RA
or RLC failure) and suspend UL transmission and PDCCH monitoring on
the SCG. Upon receiving the S-RLF report from the UE, the MeNB has
the option to reconfigure the UE by releasing the SCG or by
resuming the UE's operation with the same SCG. However it is
unclear whether the MeNB can make the proper decision with only the
cause of the S-RLF.
[0239] This contribution discusses whether UE should also include
the latest measurement results in the S-RLF report.
(2) Discussion
[0240] During RAN2#85bis, the following agreements were
reached:
[0241] 1. UE shall perform radio link monitoring on the special
SCell (S-RLM) for the purpose of detecting L1 out-of-sync. S-RLM
specification should reuse the current RLM specification as much as
possible.
[0242] 1a. UE shall report S-RLF to MeNB (triggered by RLM, RA or
RLC) and indicates which of the triggers were met.
[0243] 1b. UE shall suspend UL transmissions to SCG upon S-RLF.
[0244] 2. UE is not required to monitor the PDCCH for the SCG upon
detecting S-RLF.
[0245] It has been explained that in many cases when S-RLF occur
the PSCell or even the SCG may need to be changed. And it would be
simpler for the UE to have the same UE behaviour as the RLF for MCG
by releasing all the resources associated with the SCG as opposed
to the suspension of UL transmission and PDCCH monitoring when it
detects S-RLF. However it isn't the best to release the resources
associated with all cells in SCG in some cases, e.g. if only PSCell
deteriorates and other SCells in SCG are still good enough.
Examples of such scenarios are shown in FIGS. 17 and 18. FIG. 17
shows S-RLF in PSCell triggered by interference from a neighbour
small cell on the same frequency layer while other cells in SCG
remain unaffected. FIG. 18 S-RLF in PSCell triggered by
interference from a MCG cell on the same frequency layer while
other cells in SCG remain unaffected.
[0246] In both cases, S-RLF is detected by UE because of the
interference although SCell(s) while other cells in SCG remain
unaffected. MeNB has the option to reconfigure the UE to resume
dual connectivity operation with the same SeNB. In order to avoid
the unnecessary complexity to establish a new connection to the
same SeNB, UE should not release the resources associated with the
SCG when S-RLF is triggered.
[0247] Proposal 1: UE should not release the all resources
associated with the SCG when S-RLF is triggered.
[0248] Assuming the UE remains suspended for UL transmission and
PDCCH monitoring when S-RLF is triggered, once the MeNB is notified
of the S-RLF condition, it should have the option to release or to
resume the SCG for the UE. However, in order for the MeNB to decide
whether to resume or release the SCG, it will need to know whether
any of the cells in SCG can be a candidate for the PSCell. Simply
knowing the cause of the S-RLF (i.e., RLF, RLM or RACH failure)
doesn't provide the MeNB with sufficient information to make the
proper decision. For the proper decision by MeNB, it should know
the measurement results.
[0249] Proposal 2: MeNB should be provided with measurement results
of serving cells in SCG upon S-RLF.
[0250] If Proposal 2 is agreeable, there are two potential
alternatives for the MeNB to obtain the measurement results of the
SCG.
[0251] 1. Reusing on the existing measurement report mechanism
which is based on the existing timeToTrigger criteria.
[0252] 2. The latest measurements results from the SCG cells, as
triggered by S-RLF, should be included as part of the contents in
the S-RLF report.
[0253] With alternative 1, it is up to the MeNB to configure the UE
with the appropriate measurements Events for SCG cells, and it is
also up to the MeNB whether the measurement reports are also shared
with the SeNB, to assist the SeNB in choosing the most appropriate
PSCell so that S-RLF may be prevented as much as possible. Since
the reporting of the measurements and events are based on
timeToTrigger, the MeNB may not know the latest measurement results
associated with the triggering of the S-RLF.
[0254] With alternative 2, the measurement reports of serving cells
of SCG are included as part of the S-RLF report sent to the MeNB.
It may be further discussed whether measurements from neighbour
cells also need to be included. With this alternative the latest
measurements corresponding to the cause of the S-RLF can be
reported to the MeNB. This is also consistent with the existing RLF
report for MCG which includes these types of measurements as part
of VarRLF-Rep ort.
[0255] Based on the above comparisons, alternative 2 would provide
a greater benefit to the MeNB for making appropriate decisions.
[0256] Proposal 3: The latest measurement results from the SCG
cells, as triggered by S-RLF, should be included in the S-RLF
report.
[0257] According to current agreements, the MeNB is allowed to
provide the latest measurement results of SCG cells when requesting
the SeNB to add an SCell or establish SCG. In the case of S-RLF, it
would be beneficial for the SeNB to obtain the latest measurement
results esp. if the MeNB chooses to resume the UE's operation with
the same SCG. However, this doesn't fall into the category of
adding an SCell or establishing a new SCG; therefore, further
clarification may be needed to allow the MeNB to provide the these
S-RLF related measurements to the SeNB. Additionally it may be
useful for the MeNB to inform the SeNB of the cause for the S-RLF
in case the MeNB chooses to resume the UE's operation with the same
SCG. In particular, it may be useful for the SeNB to know whether
the cause of the S-RLF is due to RACH or RLM failure to assist the
SeNB in choosing the most appropriate PSCell for the UE.
[0258] Proposal 4: If the MeNB chooses to resume the UE's operation
with the same SCG upon S-RLF, the MeNB can provide the latest
measurement reports and the cause of S-RLF to the SeNB.
(3) Conclusion
[0259] This contribution discusses the need for the UE to provide
additional information to the MeNB upon S-RLF. It is suggested that
the MeNB should be the entity to decide whether the SCG should be
released or resumed for the UE. The latest measurement reports
should be provided to the MeNB upon S-RLF in order to assist the
MeNB in making the proper decision. In case the MeNB decides to
resume the UE's operation with the same SCG, it would be helpful
for the MeNB to provide the measurement reports along with the
cause of the S-RLF to the SeNB.
[Appendix 2]
(1) Introduction
[0260] The cause values for dual connectivity may be borrowed from
the existing cause values used for S1AP, e.g., handovers. However,
the necessity of reusing the existing cause values and the
possibility of additional cause values for dual connectivity
required further discussion. In particular, the cause value "Radio
Connection With UE Lost" should be further clarified. Based on the
discussed proposal, this cause value seems to be only applicable
for the SeNB release message and it is unclear whether the cause
value is applicable for the MCG-RLF, SCG-RLF or both. Additionally,
it should be further considered whether this cause value is also
applicable for the MeNB initiated SeNB Modification preparation
procedure in case the MeNB decides not to release the SeNB upon
SCG-RLF. This contribution discusses how "Radio Connection With UE
Lost" should be handled in X2AP.
(2) Discussion
(SeNB Initiated SeNB Release)
[0261] "Radio Connection With UE Lost" is a cause value used for
informing another eNB of radio link failure. SeNB may include this
cause value in the SeNB initiated SeNB Release for informing MeNB
of SCG-RLF. However it is questionable if this cause value is
really needed since the UE sends SCGFailure report to the MeNB
immediately after the SCG-RLF occurrence. Additionally, an
agreement was reached that "There is no need to provide means for
SeNB to notify failure of SCG serving cells to the MeNB". So, at
least from RAN2's perspective, "Radio Connection With UE Lost" is
not needed in SeNB initiated SeNB Release.
[0262] Observation 1: "Radio Connection With UE Lost" is not needed
for the SeNB initiated SeNB Release procedure since the UE has
already reported the SCG-RLF condition to the MeNB.
(MeNB Initiated SeNB Release)
[0263] MeNB may initiate SeNB Release if it recognizes radio link
failure occurs. However there are two types of radio link failures,
i.e. RLF for MCG and for SCG. SeNB may not understand which it is.
Fundamental question here is if this cause value is needed for SeNB
Release since this message cannot be rejected. Otherwise, if SeNB
can utilize the cause value for e.g. parameter optimization, RAN3
should clarify the types of cause values. As a minimal expansion,
new cause value like "SeNB Radio Connection With UE" can be
introduced.
[0264] Proposal 1: RAN3 is kindly asked to discuss whether"Radio
Connection With UE Lost" is necessary for SeNB Release. If this
cause is useful for SeNB, the RLF type should be clarified.
(MeNB Initiated SeNB Modification Preparation)
[0265] According to the current specification, the UE provides the
SCGFailure report to the MeNB with up-to-date measurement
result.
[0266] The MeNB may use the reported measurement result to decide
whether the SeNB should be released or modified. In addition to the
measurement report, the SCGFailure report also includes details of
the cause of the SCG-RLF, i.e., physical layer issue, random access
failure or RLC failure. This information is also used by the MeNB
to determine whether the SeNB should be released or modified.
Clearly, there is no expectation that the MeNB will always release
the SeNB; hence the need to provide measurement report for all SCG
cells.
[0267] Of course, if the radio conditions of the reported
measurements of the SCG cells are poor, MeNB may decide to release
the SeNB using the MeNB initiated SeNB Release procedure.
Regardless of the indicated cause value, SeNB cannot reject the
SeNB Release request.
[0268] However, if one or more of the SCG cells are in good radio
condition, the MeNB has the option to initiate SeNB Modification
preparation for PSCell change since PSCell change can only be
performed in SCG change procedure and the SCG change procedure is
mapped to SeNB Modification.
[0269] Observation 2: MeNB may initiate SeNB Modification in order
to change PSCell upon reception of SCGFailure report from the
UE.
(Desired Action of SeNB)
[0270] Assuming the MeNB has decided not to release the SeNB upon
the reception of the SCGFailure report from the UE, the MeNB may
initiate the SeNB Modification preparation procedure which may
include the request to add new SCG cells as a candidate for a new
PSCell. However, unlike the case for the SeNB Release Request, the
SeNB is allowed to reject the MeNB Initiated SeNB Modification
preparation. Without the knowing the cause of such a modification
request (i.e., due to SCG-RLF), the SeNB may reject the
modification for the wrong reason which is undesirable.
[0271] Although it may be possible for the SeNB to detect the
occurrence of SCG-RLF, the detection of this failure may not be
immediate without feedback from the UE. This is precisely the
reason why the SCGFailure report is sent immediately to the MeNB
upon SCG-RLF. In turn, the SeNB should have the opportunity to
receive the same indication of this failure without delay.
[0272] Furthermore, since it isn't necessary for the MeNB to inform
the SeNB of MCG-RLF as part of the MeNB initiated SeNB Modification
procedure, there is no ambiguity to reuse the cause value "Radio
Connection With UE Lost" for this procedure as it can only be for
the occurrence of SCG-RLF.
[0273] Proposal 2: The cause value "Radio Connection With UE Lost"
should be included in the MeNB initiated SeNB Modification
procedure when SCG-RLF occurs.
(3) Conclusion
[0274] This contribution addresses the need for clarification of
the cause value "Radio Connection With UE Lost" used in SeNB
Release Request; whether it should be applicable for the occurrence
of MCG-RLF, SCG-RLF or both. In particular, the contribution
provided reasons why the same cause value should also be reused for
the MeNB Initiated SeNB Modification preparation procedure. We have
the following observation and proposals.
[0275] It is noted that the entire content of Japan Patent
Application No. 2014-017980 (filed on Jan. 31, 2014) and U.S.
Provisional Patent Application No. 62/034,678 (filed on Aug. 7,
2014) are incorporated in the present application by reference.
INDUSTRIAL APPLICABILITY
[0276] As described above, according to the communication control
method according to the embodiments, it is possible to
appropriately perform the communication by the dual connectivity
method, and it is useful in the mobile communication fields.
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