U.S. patent application number 16/902683 was filed with the patent office on 2020-10-01 for radio communication system, base station apparatus, radio terminal, and communication control method.
This patent application is currently assigned to NEC Corporation. The applicant listed for this patent is NEC Corporation. Invention is credited to Hiroaki AMINAKA, Hisashi FUTAKI, Hiroto SUGAHARA.
Application Number | 20200314839 16/902683 |
Document ID | / |
Family ID | 1000004897009 |
Filed Date | 2020-10-01 |
View All Diagrams
United States Patent
Application |
20200314839 |
Kind Code |
A1 |
FUTAKI; Hisashi ; et
al. |
October 1, 2020 |
RADIO COMMUNICATION SYSTEM, BASE STATION APPARATUS, RADIO TERMINAL,
AND COMMUNICATION CONTROL METHOD
Abstract
A radio communication system includes a first base station (11)
that manages a first cell (110), a second base station (12) that
manages a second cell (120), and a radio terminal (2). The radio
terminal (2) supports dual connectivity involving a bearer split in
which a first network bearer between the radio terminal (2) and a
core network (3) is split over the first base station (11) and the
second base station (12). The first base station (11) receives,
from the second base station (12), bearer split status information
about communication of the first network bearer in the second base
station (12), and performs control of an access stratum related to
the first network bearer. It is thus possible to contribute, for
example, to an improvement in control of an access stratum when
dual connectivity involving a bearer split is performed.
Inventors: |
FUTAKI; Hisashi; (Tokyo,
JP) ; SUGAHARA; Hiroto; (Tokyo, JP) ; AMINAKA;
Hiroaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
NEC Corporation
Tokyo
JP
|
Family ID: |
1000004897009 |
Appl. No.: |
16/902683 |
Filed: |
June 16, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15028915 |
Apr 12, 2016 |
10721728 |
|
|
PCT/JP2014/002423 |
May 7, 2014 |
|
|
|
16902683 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 28/08 20130101;
H04L 5/0091 20130101; H04W 16/32 20130101; H04W 28/085 20130101;
H04W 24/10 20130101; H04W 72/085 20130101; H04L 5/001 20130101;
H04W 92/20 20130101; H04W 52/146 20130101; H04W 88/06 20130101;
H04W 76/15 20180201; H04W 52/367 20130101; H04B 7/02 20130101; H04W
72/12 20130101; H04W 52/365 20130101; H04W 72/0426 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04B 7/02 20060101 H04B007/02; H04W 28/08 20060101
H04W028/08; H04L 5/00 20060101 H04L005/00; H04W 76/15 20060101
H04W076/15; H04W 16/32 20060101 H04W016/32; H04W 92/20 20060101
H04W092/20; H04W 24/10 20060101 H04W024/10; H04W 52/36 20060101
H04W052/36; H04W 72/08 20060101 H04W072/08; H04W 72/12 20060101
H04W072/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2013 |
JP |
2013-227473 |
Claims
1-43. (canceled)
44. A first radio station, comprising: a memory storing
instructions; and at least one processor configured to process the
instructions to: serve a first cell; control a radio terminal to
cause the radio terminal to perform dual connectivity using the
first cell and a second cell served by a second radio station;
receive a first Power Headroom on the first cell and a second Power
Headroom on the second cell from at least the radio terminal; and
transmit the first Power Headroom on the first cell and the second
Power Headroom on the second cell to at least the second radio
station.
45. A second radio station, comprising: a memory storing
instructions; and at least one processor configured to process the
instructions to: serve a second cell; communicate with a radio
terminal configured to perform dual connectivity using a first cell
served by a first radio station and the second cell; and receive a
first Power Headroom on the first cell and a second Power Headroom
from at least the first radio station.
46. A radio communication system comprising: a first radio station
configured to serve a first cell; a second radio station configured
to serve a second cell; and a radio terminal configured to perform
dual connectivity using the first cell and the second cell, wherein
the radio terminal is configured to transmit a first Power Headroom
on the first cell and a second Power Headroom on the second cell to
at least the first radio station, and the first radio station is
configured to transmit the first Power Headroom on the first cell
and the second Power Headroom on the second cell to at least the
second radio station.
47. A control method for a first radio station, comprising: serving
a first cell; controlling a radio terminal to cause the radio
terminal to perform dual connectivity using the first cell and a
second cell served by a second radio station; receiving a first
Power Headroom on the first cell and a second Power Headroom on the
second cell from at least the radio terminal; and transmitting the
first Power Headroom on the first cell and the second Power
Headroom on the second cell to at least the second radio
station.
48. A control method for a second radio station, comprising:
serving a second cell; communicating with a radio terminal
configured to perform dual connectivity using the first cell and a
second cell served by a second radio station; and receiving a first
Power Headroom on the first cell and a second Power Headroom on the
second cell from at least the first radio station.
Description
TECHNICAL FIELD
[0001] This application relates to a radio communication system in
which base stations communicate with the same radio terminal in
their respective cells.
BACKGROUND ART
[0002] To improve deterioration in communication quality due to the
recent rapid increase in mobile traffic and to achieve higher-speed
communication, 3GPP Long Term Evolution (LTE) specifies a carrier
aggregation (CA) function to allow a radio base station (eNode B
(eNB)) and a radio terminal (User Equipment (UE)) to communicate
with each other using a plurality of cells. The cells which can be
used by the UE in the CA are limited to cells of one eNB (i.e.,
cells that are served or managed by the eNB). The cells used by the
UE in the CA are classified into a primary cell (PCell) that is
already used as a serving cell when the CA is started and a
secondary cell(s) (SCell(s)) that is used additionally or
subordinately. In the PCell, Non Access Stratum (NAS) mobility
information (NAS mobility information) and security information
(security input) is sent and received during radio connection
(re)-establishment (RRC Connection Establishment, RRC Connection
Re-establishment) (see Section 7.5 in Non-Patent Literature 1).
[0003] In the CA, SCell configuration information transmitted from
the eNB to the UE includes SCell radio resource configuration
information common to UEs (RadioResourceConfigCommonSCell) and
SCell radio resource configuration information dedicated to a
specific UE (RadioResourceConfigDedicatedSCell). The latter
information mainly indicates a dedicated configuration
(PhysicalConfigDedicated) for a physical layer. When cells
(carriers) having different transmission timings (Timing Advance:
TA) are aggregated in an uplink, configuration information
(MAC-MainConfigSCell) about a Medium Access Control (MAC) sublayer
is also transmitted from the eNB to the UE. However, the
configuration information about the MAC sublayer includes only an
STAG-Id, which is an index of TA Group (TAG) representing a set of
cells included in the same TA (see Section 5.3.10.4 in Non-Patent
Literature 2). The other configurations for the MAC sublayer in the
SCell are the same as those in the PCell.
[0004] One of the ongoing study items in the LTE standardization
related mainly to a Heterogeneous Network (HetNet) environment is
dual connectivity in which the UE performs communication using a
plurality of cells of a plurality of eNBs (see Non
Patent-Literature 3). Dual connectivity is a process to allow an UE
to perform communication simultaneously using both radio resources
(i.e., cells or carriers) provided (or managed) by a main base
station (master base station, Master eNB (MeNB)) and a sub base
station (secondary base station, Secondary eNB (SeNB)). Dual
connectivity enables inter-eNB CA in which the UE aggregates a
plurality of cells managed by different eNBs. Since the UE
aggregates radio resources managed by different nodes, dual
connectivity is also called "inter-node radio resource
aggregation". The MeNB is connected to the SeNB through an
inter-base-station interface called Xn. The MeNB maintains, for the
UE in dual connectivity, the connection (S1-MME) to a mobility
management apparatus (Mobility Management Entity (MME)) in a core
network (Evolved Packet Core (EPC)). Accordingly, the MeNB can be
called a mobility management point (or mobility anchor) of the UE.
For example, the MeNB is a Macro eNB, and the SeNB is a Pico eNB or
Low Power Node (LPN).
[0005] Further, in dual connectivity, a bearer split for splitting
a network bearer (EPS bearer) over the MeNB and the SeNB has been
studied. The term "network bearer (EPS Bearer)" used in this
specification means a virtual connection that is configured between
a UE and an endpoint (i.e., Packet Data Network Gateway (P-GW)) in
a core network (EPC) for each service provided to the UE. In an
alternative of the bearer split, for example, both a radio bearer
(RB) in a cell of the MeNB and a radio bearer in a cell of the SeNB
are mapped to one network bearer. The radio bearer (RB) described
herein refers mainly to a data radio bearer (DRB). The bearer split
will contribute to a further improvement in user throughput.
CITATION LIST
Non Patent Literature
[0006] [Non-Patent Literature 1] 3GPP TS 36.300 V11.5.0 (2013
March), "3rd Generation Partnership Project; Technical
Specification Group Radio Access Network; Evolved Universal
Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial
Radio Access Network (E-UTRAN); Overall description; Stage 2
(Release 11)", March, 2013 [0007] [Non-Patent Literature 2] 3GPP TS
36.331 V11.4.0 (2013 June), "3rd Generation Partnership Project;
Technical Specification Group Radio Access Network; Evolved
Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control
(RRC); Protocol specification (Release 11)", June, 2013 [0008]
[Non-Patent Literature 3] 3GPP TR 36.842 V0.2.0 (2013 May), "3rd
Generation Partnership Project; Technical Specification Group Radio
Access Network; Evolved Universal Terrestrial Radio Access
(E-UTRA); Study on Small Cell Enhancements for E-UTRA and
E-UTRAN--Higher layer aspects (Release 12)", May, 2013
SUMMARY OF INVENTION
Technical Problem
[0009] In the LTE, an UE generates an uplink (UL) Medium Access
Control Protocol Data Unit (MAC PDU) to be transmitted using
available resources (Uplink Grant) allocated from an eNB. One MAC
PDU is also called a transport block. In the generation of an UL
MAC PDU, logical channels configured in the UE are multiplexed on
one MAC PDU. At this time, it is necessary to guarantee the QoS of
each EPS bearer configured in the uplink. Accordingly, the UE
generates an UL MAC PDU in accordance with a Logical Channel
Prioritization (LCP) procedure. In the Logical Channel
Prioritization (LCP) procedure, a priority and a Prioritized Bit
Rate (PBR) are given to each logical channel. The PBR is a bit rate
which is provided to one logical channel before allocating any
resource to a logical channel having a lower priority. The PBR is
configured by the eNB for each logical channel. In the LCP
procedure, first, all logical channels are guaranteed to be
allocated resources corresponding to respective PBRs in descending
order of their priorities. Next, if there are still any available
resources left after all logical channels have been served up to
their PBR, the remaining resources are allocated to the logical
channels in a descending order of priorities of the logical
channels until there is no data of logical channels, or until the
allocated resources are used up.
[0010] However, in dual connectivity involving a bearer split, it
is considered that the MeNB and the SeNB each independently perform
Radio Resource Management (RRM). Accordingly, there is a
possibility that the MeNB and the SeNB each independently perform
the above-mentioned LCP procedure, which may lead to an unfairness
between resources (i.e., effective bit rate) allocated to a logical
channel (or EPS bearer, radio bearer) which is not subjected to a
bearer split and is transmitted only in the PCell and resources
allocated to a logical channel (or EPS bearer, radio bearer) which
is subjected to a bearer split and is transmitted in the PCell and
the SCell. In other words, the balance of resource allocation
between a logical channel which is not subjected to a bearer split
and a logical channel which is subjected to a bearer split may be
lost, and consequently, the LCP procedure may not function as
intended.
[0011] In the case of performing dual connectivity involving a
bearer split, there is a possibility that expected performance
cannot be obtained not only in the generation of MAC PDUs (i.e.,
the LCP procedure) described above, but also in other Layer 1/Layer
2 control in an access stratum. For example, in uplink transmission
power control (PC), there is a possibility that the distribution of
transmission power between the uplink transmission in the PCell and
the uplink transmission in the SCell may not be performed as
intended. Further, in the case of performing dual connectivity
involving a bearer split, there is a possibility that expected
performance cannot be obtained not only in the uplink Layer 1/Layer
2 control, but also in the downlink Layer 1/Layer 2 control. It is
also possible that expected performance cannot be obtained in
control of layer 3 of the Access stratum (i.e., Radio Resource
Control (RRC)) in the uplink or the downlink or both.
[0012] Accordingly, one object to be achieved by embodiments
disclosed in the specification is to contribute to an improvement
in control of an access stratum when dual connectivity involving a
bearer split is performed. Other objects and novel features will
become apparent from the following description and the accompanying
drawings.
Solution to Problem
[0013] In an embodiment, a radio communication system includes a
first base station that manages a first cell, a second base station
that manages a second cell, and a radio terminal. The radio
terminal supports dual connectivity involving a bearer split in
which a first network bearer between the radio terminal and a core
network is split over the first base station and the second base
station. The first base station is configured to receive, from the
second base station, bearer split status information about
communication of the first network bearer in the second base
station, and to perform control of an access stratum related to the
first network bearer.
[0014] In an embodiment, a base station apparatus includes a
communication control unit configured to control dual connectivity
involving a bearer split in which a first network bearer between a
radio terminal and a core network is split over the base station
apparatus and a neighbor base station. The communication control
unit is configured to receive, from the neighbor base station,
bearer split status information about communication of the first
network bearer in the neighbor base station, and to perform control
of an access stratum related to the first network bearer.
[0015] In an embodiment, a base station apparatus includes a
communication control unit configured to control dual connectivity
involving a bearer split in which a first network bearer between a
radio terminal and a core network is split over the base station
apparatus and a neighbor base station. The communication control
unit is configured to transmit, to the neighbor base station,
bearer split status information about communication of the first
network bearer in the base station apparatus. The bearer split
status information triggers the neighbor base station to perform
control of an access stratum related to the first network
bearer.
[0016] In an embodiment, a radio terminal is used in the radio
communication system described above and includes a communication
control unit configured to control dual connectivity involving a
bearer split in which the first network bearer is split over first
and second base stations. The communication control unit is
configured to perform control of an access stratum related to the
first network bearer based on an instruction from the first base
station.
[0017] In an embodiment, a control method includes: (a) starting,
by a first base station, communication of dual connectivity
involving a bearer split in which a first network bearer between a
radio terminal and a core network is split over the first base
station and a second base station; and (b) receiving, by the first
base station from the second base station, bearer split status
information about communication of the first network bearer in the
second base station, and performing, by the first base station,
control of an access stratum related to the first network
bearer.
[0018] In an embodiment, a control method includes: (a) starting,
by a second base station, communication of dual connectivity
involving a bearer split in which a first network bearer between a
radio terminal and a core network is split over a first base
station and the second base station; and (b) transmitting, to the
first base station, bearer split status information about
communication of the first network bearer in the second base
station. The bearer split status information triggers the first
base station to perform control of an access stratum related to the
first network bearer.
[0019] In an embodiment, a program includes instructions (software
codes) for causing a computer to perform the above-described method
when the program is loaded into the computer.
Advantageous Effects of Invention
[0020] According to the embodiments described above, it is possible
to contribute to an improvement in control of an access stratum
when dual connectivity involving a bearer split is performed.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1A is a diagram showing an example of a user plane
protocol stack in a downlink direction of LTE Layer 2 related to
dual connectivity involving a bearer split;
[0022] FIG. 1B is a diagram showing another example of the user
plane protocol stack in the downlink direction of LTE Layer 2
related to dual connectivity involving a bearer split;
[0023] FIG. 2A is a diagram showing an example of a user plane
protocol stack in an uplink direction of LTE Layer 2 related to
dual connectivity involving a bearer split;
[0024] FIG. 2B is a diagram showing another example of the user
plane protocol stack in the uplink direction of LTE Layer 2 related
to dual connectivity involving a bearer split;
[0025] FIG. 3 is a diagram showing a configuration example of a
radio communication system according to first to fourth
embodiments;
[0026] FIG. 4 is a diagram showing a LogicalChannelConfig
information element specified in 3GPP TS 36.331;
[0027] FIG. 5A is a diagram showing UplinkPowerControl information
elements specified in 3GPP TS 36.331;
[0028] FIG. 5B is a diagram showing UplinkPowerControl information
elements specified in 3GPP TS 36.331;
[0029] FIG. 6 is a sequence diagram showing an example of a control
procedure regarding dual connectivity involving a bearer split
according to the first embodiment;
[0030] FIG. 7 is a sequence diagram showing an example of a control
procedure regarding dual connectivity involving a bearer split
according to the second embodiment;
[0031] FIG. 8A is a schematic diagram showing an example of
generating an uplink MAC PDU when no bearer split is performed;
[0032] FIG. 8B is a schematic diagram showing an example of
generating uplink MAC PDUs when bearer split is performed;
[0033] FIG. 8C is a schematic diagram showing an example of
generating uplink MAC PDUs when bearer split is performed;
[0034] FIG. 9 is a sequence diagram showing an example of a control
procedure regarding dual connectivity involving a bearer split
according to the third embodiment;
[0035] FIG. 10 is a block diagram showing a configuration example
of an MeNB according to the first to fourth embodiments;
[0036] FIG. 11 is a block diagram showing a configuration example
of an SeNB according to the first to fourth embodiments; and
[0037] FIG. 12 is a block diagram showing a configuration example
of a UE according to the first to fourth embodiments.
DESCRIPTION OF EMBODIMENTS
[0038] Specific embodiments will hereinafter be described in detail
with reference to the drawings. The same or corresponding elements
are denoted by the same reference symbols throughout the drawings,
and repeated descriptions thereof are omitted as appropriate for
clarity of the explanation.
First Embodiment
[0039] First, with regard to some embodiments including this
exemplary embodiment, several examples of dual connectivity (e.g.,
inter-node radio resource aggregation) involving a bearer split are
described. FIGS. 1A and 1B show two alternatives of a user plane
protocol stack in a downlink direction of LTE Layer 2 related to
dual connectivity involving a bearer split. In the bearer split, a
network bearer (EPS bearer) configured between a UE and an endpoint
(i.e., P-GW) of a core network (EPC) is split over an MeNB 11 and
an SeNB 12. In the alternatives shown in FIGS. 1A and 1B, an EPS
bearer #2 is split over the MeNB 11 and the SeNB 12. An EPS bearer
#1 shown in FIGS. 1A and 1B is a normal bearer which is not
subjected to a bearer split. Accordingly, the EPS bearer #1 is
mapped in a one-to-one correspondence to the radio bearer in a cell
of the MeNB 11.
[0040] In the alternatives shown in FIGS. 1A and 1B, one data radio
bearer (DRB), which has a one-to-one association with the EPS
bearer #,2 is split over the MeNB 11 and the SeNB 12 in a Packet
Data Convergence Protocol (PDCP) sublayer, a Radio Link Control
(RLC) sublayer, or a MAC sublayer of Layer-2. Specifically, in the
alternative shown in FIG. 1A, a PDCP entity of the MeNB 11
terminates the S1-U of the EPS bearer #2. In other words, one S1
bearer and one data radio bearer (DRB) which are mapped to the EPS
bearer #2 are terminated at the PDCP sublayer of the MeNB 11.
Further, in the alternative shown in FIG. 1A, the MeNB 11 and the
SeNB 12 have independent RLC entities for bearer split, and one DRB
(or PDCP bearer) terminated at the MeNB 11 is split into the RLC
bearer of the MeNB 11 and the RLC bearer of the SeNB 12. Note that,
the term "PDCP bearer" means a connection terminated at the PDCP
sublayers of the eNB and the UE. The PDCP bearer can also be called
a PDCP Protocol Data Unit (PDCP PDU). In the example shown in FIG.
1A, there is one PDCP bearer related to the EPS bearer #2 to be
split, and this PDCP bearer is terminated at the MeNB 11 and the UE
2. On the other hand, the term "RLC bearer" means a connection
terminated at the RLC sublayers of the eNB and the UE. The RLC
bearer can also be called an RLC PDU or a logical channel. In the
example shown in FIG. 1, there are two independent RLC bearers
associated with the EPS bearer #2. One of the two RLC bearers is
terminated at the MeNB 11 and the UE 2, and the other one is
terminated at the SeNB 12 and the UE 2. Accordingly, in the
architecture shown in FIG. 1A, the UE 2 is required to have two
independent RLC entities associated with the EPS bearer #2 to be
split.
[0041] Like in the alternative shown in FIG. 1A, in the alternative
shown in FIG. 1B, a PDCP entity of the MeNB 11 terminates the S1-U
of the EPS bearer #2. Further, as for the EPS bearer #2 to be
split, the MeNB 11 has a master RLC entity and the SeNB 12 has a
slave RLC entity. In the alternative shown in FIG. 1B, the UE 2 is
required to have only one RLC entity associated with the EPS bearer
#2 to be split. In the downlink, the slave RLC entity of the SeNB
12 receives, from the master RLC entity of the MeNB 11, RLC PDUs
that has already been generated by the master RLC entity and
allocated to the slave RLC for transmission.
[0042] The following description is based on an assumption that a
cell of the MeNB 11 can be called a PCell and a cell of the SeNB 12
can be called an SCell from the viewpoint of the conventional
Carrier Aggregation (CA). However, the scope of this embodiment is
not limited to this. For example, when the radio terminal (UE)
performs the CA (Intra-SeNB CA) on a plurality of cells of the SeNB
12 (i.e., at least a plurality of downlink Component Carriers
(CCs)) during dual connectivity, one of the cells of the SeNB 12
subjected to the CA may be defined as a PCell or a pseudo PCell
which functions similarly to a PCell. The pseudo PCell can also be
called an Anchor cell, a Master cell, a Control cell, or the like.
In the CA of the cells of the SeNB 12, the former cell (the PCell
of the SeNB 12) has a role similar to that of the PCell in the
conventional CA. In the PCell of the SeNB 12, for example, the eNB
(SeNB) carries out SCell configuration or SCell
activation/deactivation for the CA, and the UE carries out Radio
Link Monitoring (RLM)/Radio Link Failure (RLF) detection. Further,
the UE may perform, for example, transmission of L1/L2 control
information (e.g., CQI, CSI, HARQ feedback, Scheduling Request) in
an uplink control channel (PUCCH), transmission of (a preamble of)
a Contention-based Random Access Channel (RACH), and reception of a
response (Random Access Response (RAR)) to the RACH Preamble. The
latter cell (the Pseudo PCell of the SeNB 12) has a role as a cell
having a PCell function regarding the control of a User Plane (UP)
in the conventional CA. In the Pseudo PCell of the SeNB 12, the UE
may perform, for example, transmission of L1/L2 control information
in the uplink control channel (PUCCH), transmission of (a preamble
of) a Contention-based RACH, and reception of a response (RAR) to
the RACH Preamble. Furthermore, in the UE, the cells of the MeNB 11
and the cells of the SeNB 12 need not necessarily have a
hierarchical relationship (PCell and SCell) or a master-slave
relationship.
[0043] The user plane protocol stack for dual connectivity
involving a bearer split is not limited to the alternatives shown
in FIGS. 1A and 1B. In the bearer split, for example, two radio
bearers may be mapped to one network bearer (EPS bearer). When the
terms in FIGS. 1A and 1B are used, it can be expressed that the EPS
bearer #2 is mapped to both the radio bearer (RB) in the cell
(PCell) of the MeNB 11 and the radio bearer in the cell (SCell) of
the SeNB 12. For convenience of explanation, the radio bearer in
the cell (PCell) of the MeNB 11 is defined herein as a Primary RB
(P-RB) and the radio bearer (RB) in the cell (SCell) of the SeNB is
defined herein as a Secondary RB (S-RB). Since the bearer split is
mainly applied to data radio bearers (DRBs), the P-RB and the S-RB
can also be called P-DRB and S-DRB, respectively. For example, the
MeNB 11 may terminate the S1-U of the EPS bearer #2, and the MeNB
11 and the SeNB 12 may have independent PDCP entities. Further, in
a new layer higher than the PDCP entity of the MeNB 11, a downlink
S1-U packet stream of the EPS bearer #2 may be split over the PDCP
entity of the MeNB 11 and the PDCP entity of the SeNB 12. In this
case, there are two independent PDCP bearers related to the EPS
bearer #2. One of the two PDCP bearers is terminated at the MeNB 11
and the UE 2, and the other one is terminated at the SeNB 12 and
the UE 2.
[0044] The user plane protocol stack in the uplink direction of LTE
Layer 2 related to dual connectivity involving a bearer split is
similar to that in the downlink direction described above. FIGS. 2A
and 2B show two alternatives of the user plane protocol stack in
the uplink direction of the UE 2, and correspond to FIG. 1A and
FIG. 1B, respectively. In the alternative shown in FIG. 2A, one
PDCP entity of the UE 2 receives user data of the EPS bearer #2
from an upper layer. The PDCP entity of the UE 2 distributes PDCP
PDUs between a MAC entity to transmit to the MeNB 11 and a MAC
entity to transmit to the SeNB 12, and sends the MAC entities. In
other words, the PDCP PDUs (i.e., PDCP bearer) are split over an
RLC bearer to be transmitted to the MeNB 11 and an RLC bearer to be
transmitted to the SeNB 12. Like in the alternative shown in FIG.
1B, in the alternative shown in FIG. 2B, the UE 2 has a master RLC
entity (RLC entity for the MeNB 11 shown in the left side of FIG.
2B) and a slave RLC entity (RLC entity for the SeNB 12 shown in the
right side of FIG. 2B). The slave RLC entity of the UE 2 receives,
from the master RLC entity, the RLC PDUs which are already
generated by the master RLC entity and allocated to the slave RLC
for transmission. The alternatives shown in FIGS. 2A and 2B are
only illustrative and other architectures can also be employed. For
example, in the alternatives shown in FIG. 2A and FIG. 2B, the UE 2
has the MAC entity for the MeNB 11 and the MAC entity for the SeNB
12. However, the UE 2 may have only one MAC entity for uplink
transmission.
[0045] FIG. 3 shows a configuration example of a radio
communication system according to some embodiments including this
embodiment. The radio communication system includes a radio access
network (RAN) 1, a radio terminal (UE) 2, and a core network 3. In
the EPS, the RAN 1 is an Evolved UMTS Terrestrial Radio Access
Network (E-UTRAN), and the core network 3 is an Evolved Packet Core
(EPC). The E-UTRAN 1 includes base stations (evolved NodeBs (eNBs))
11 and 12. The eNB 11 manages a cell 110, and the eNB 12 manages a
cell 120. The UE 2 is connected to the eNBs 11 and 12 by means of a
radio access technology. The EPC 3 is accessed from the UE 2
through the E-UTRAN 1, and provides the UE 2 with a connection
service (e.g., Internet Protocol (IP) connection service) for
connecting to an external network (Packet Data Network (PDN)). In
addition, FIG. 3 shows a HetNet environment. Specifically, the cell
110 shown in FIG. 3 has a coverage area larger than that of the
cell 120. FIG. 3 also shows a hierarchical cell configuration in
which the cell 120 is located within the cell 110. However, the
cell configuration shown in FIG. 3 is merely an example. For
example, the cells 110 and 120 may have the same degree of
coverage. In other words, the radio communication system according
to this embodiment may be applied to a homogeneous network
environment.
[0046] The E-UTRAN 1 and the UE 2 according to this embodiment
support dual connectivity involving a bearer split. Specifically,
while using the cell 110 of the eNB (i.e., MeNB) 11 as a primary
cell (PCell), the UE 2 can use the cell 120 of the eNB (i.e., SeNB)
12 as a secondary cell (SCell). The UE 2 can receive and/or
transmit data of one EPS bearer subjected to a bearer split through
the PCell 110 and the SCell 120.
[0047] In order to improve the Layer 1/Layer 2 control of an access
stratum in the case of performing dual connectivity involving a
bearer split, the MeNB 11 and the SeNB 12 according to this
embodiment carry out a control procedure or signalling as described
below. The SeNB 12 is configured to transmit, to the MeNB 11,
bearer split status information about communication in the SeNB 12
(i.e., SCell 120) of the EPS bearer to be subjected to a bearer
split (hereinafter referred to as a split EPS bearer). The MeNB 11
is configured to perform control of the access stratum related to
the split EPS bearer in response to receiving the bearer split
status information from the SeNB 12.
[0048] The bearer split status information may include, for
example, at least one of communication status information, radio
resource control information, and admission control
information.
[0049] The communication status information indicates a
communication status of the split EPS bearer in the SeNB 12 (i.e.,
SCell 120). The communication status of the split EPS bearer in the
SeNB 12, which is indicated by the communication status information
and sent to the MeNB 11 from the SeNB 12, may be a communication
status in Layer 1 or Layer 2 of the SCell 120. More specifically,
the communication status of the split EPS bearer in the SeNB 12 may
include at least one of the following items (1) to (6):
(1) Statistics of throughput; (2) Statistics of allocated radio
resources; (3) Statistics of packet losses; (4) Statistics of power
headroom; (5) Information about retransmission control in the Radio
Link Control (RLC) sublayer; and (6) Information about packet
discarding in the Radio Link Control (RLC) sublayer.
[0050] The statistics of throughput may be, for example, at least
one of an average value, a minimum value, and a maximum value of a
data rate (e.g., transmission rate or data rate of PDCP SDU, PDCP
PDU, RLC PDU, or MAC PDU (i.e., Transport Block)) of the UE 2 in
the SeNB 12. The statistics of allocated radio resources may be,
for example, at least one of an average value, a minimum value, and
a maximum value of radio resources allocated to the UE 2 in the
SeNB 12. In this case, the radio resources may be, for example,
resource blocks. When the SeNB 12 transmits data of the split EPS
bearer to the UE 2 by using a plurality of cells, the statistics of
throughput and the statistics of radio resources may be a value in
each of the plurality of cells, or the total value of the plurality
of cells.
[0051] The statistics of packet losses may be, for example, the
number or ratio of discarded packets in a radio interface (LTE-Uu
interface) between the SeNB 12 and the UE 2, or in an
inter-base-station interface (Xn interface) between the MeNB 11 and
the SeNB 12. In this case, the packets may be, for example, PDCP
SDUs, PDCP PDUs, RLC PDUs, or MAC PDUs (i.e., Transport Blocks).
The statistics of packet losses may be statistics observed not for
the Xn interface, but for an X2 interface or an S1 interface.
[0052] The statistics of uplink power headroom indicate, for
example, an average value of power headroom of the UE 2 for the
SCell 120 (in a predetermined period). The power headroom indicates
a difference (i.e., surplus transmission power) between the uplink
maximum transmission power of the UE 2 and the transmission power
of a Physical Uplink Shared channel (PUSCH) in the present
subframe. The UE 2 reports the power headroom for the SCell 120 to
the SeNB 12. The UE 2 may report the power headroom for the PCell
110 and the power headroom for the SCell 120 to the SeNB 12.
[0053] The information about retransmission control in the RLC
sublayer may indicate a NACK ratio of Automatic Repeat Request
(ARQ) for RLC PDUs (i.e., logical channel) of the split EPS bearer
(i.e., a ratio of NACKs with respect to the total of ACKs and
NACKs), the number of retransmissions in the ARQ, or a frequency of
occurrence of retransmission in the ARQ.
[0054] The information about packet discarding in the RLC sublayer
may indicate the rate or number of discarded RLC SDUs of the split
EPS bearer, or the data amount of discarded RLC SDUs. Packet
discarding in the RLC sublayer (i.e., discarding of RLC SDUs) may
be executed in response to an instruction from the PDCP sublayer of
the MeNB 11. Alternatively, the RLC sublayer of the SeNB 12 may
independently determine whether to perform packet discarding.
[0055] The communication status information transmitted from the
SeNB 12 to the MeNB 11 may indicate, for example, a communication
status monitored for each split EPS bearer, monitored for each
ratio bearer mapped to the split EPS bearer, monitored for each
SCell 120, or monitored for each SeNB 12. The communication status
monitored for each SCell 120 may be obtained by observation of each
SCell 120 and each radio terminal (UE) which performs a bearer
split, or may be obtained by observation of each SCell 120 and a
plurality of radio terminals which perform a bearer split in the
SeNB 12. The same is true of the communication status monitored for
each SeNB 12.
[0056] Next, the control of the access stratum performed by the
MeNB 11 is described. The control of the access stratum may be, for
example, a Layer 1 control, a Layer 2 control, a Layer 3 control,
or any combination thereof. Several examples of the Layer 1/Layer 2
control of the access stratum are given below. Note that, the Layer
1/Layer 2 control of the access stratum may be a Layer 3 (RRC)
control or signalling regarding functions in Layer 1 (PHY)/Layer 2
(MAC, RLC, and PDCP). For example, the MeNB 11 may perform at least
one of the following controls (a) to (c) in response to receiving
from the SeNB 12 the communication status of the split EPS bearer
in the SeNB 12.
(a) Control for Generation of Uplink (UL) MAC PDUs
[0057] Even during execution of the bearer split, the UE 2 should
generate MAC PDUs in consideration of an EPS bearer QoS (QoS class
identifier (QCI), a guaranteed bit rate (GBR), an aggregate maximum
bit rate (AMBR), etc.) for each of all EPS bearers including a
split EPS bearer and a non-split EPS bearer. Accordingly, if the
uplink LCP procedure does not function as intended due to, for
example, the excess uplink throughput of the split EPS bearer in
the SCell 120, the MeNB 11 may adjust an uplink Prioritized Bit
Rate (PBR) or Bucket Size Duration (BSD) or both of them, which are
applied to the split EPS bearer or the non-split EPS bearer or both
of them, so that the LCP procedure functions as intended. For
example, when the throughput of the split EPS bearer in the SCell
120 is excessive, the MeNB 11 may decrease the uplink PBR applied
to the split EPS bearer in the PCell 110 and may increase the
uplink PBR applied to the non-split EPS bearer in the PCell 110. In
this case, the PBR can also be called a prioritized resource
amount. For example, the RRC layer in the MeNB 11 may determine the
PBR applied to the split EPS bearer and the PBR applied to the
non-split EPS bearer, and may notify the UE 2 of the determined PBR
values by RRC signalling. The PBR applied to the split EPS bearer
in the PCell 110 may be the same as or different from that in the
SCell 120. Further, the MeNB 11 may determine the BSD for each of
the split EPS bearer and the non-split EPS bearer, and may notify
the UE 2 of the obtained BSD values. The BSD of the split EPS
bearer in the PCell 110 may be the same as or different from that
in the SCell 120. Non-Patent Literature 2 (3GPP TS 36.331)
specifies parameters regarding the LCP including the PBR and the
BSD (see FIG. 4). The parameters shown in FIG. 4, including the PBR
and the BSD, may be adjusted in the control of the access stratum
according to this embodiment. The parameters shown in FIG. 4 may be
set separately for the split EPS bearer and the non-split EPS
bearer. The parameters set for the split EPS bearer in the cell 110
of the MeNB 11 may be the same or different from the parameters set
for the split EPS bearer in the cell 120 of the SeNB 12.
(b) Uplink (UL) Transmission Power Control
[0058] The MeNB 11 may adjust the transmission power of the UE 2 to
achieve intended distribution of transmission power between uplink
transmission in the PCell 110 and uplink transmission in the SCell
120. For example, in response to determining, based on the
communication status information received from the SeNB 12, that
the power headroom of the UE 2 in the PCell 110 is less than the
power headroom of the UE 2 in the SCell 120 by more than a
predetermined amount, the MeNB 11 may adjust a parameter(s) used
for a formula for calculating P.sub.CMAX so as to increase the
configured maximum transmission power P.sub.CMAX, PCELL in the
PCell 110 of the UE 2 and to decrease the configured maximum
transmission power P.sub.CMAX, SCELL in the SCell 120 of the UE 2.
The formula for calculating P.sub.CMAX is specified in 3GPP TS
36.301. Specifically, the MeNB 11 may adjust the maximum
transmission power (i.e., transmit power limit) P.sub.EMAX, PCELL,
which is allowed for the UE 2 in the PCell 110, or the maximum
transmission power P.sub.EMAX, SCELL, which is allowed for the UE 2
in the SCell 120, or both of them. Non-Patent Literature 2 (3GPP TS
36.331) specifies parameters regarding the UL transmission power
control (see FIGS. 5A and 5B). The parameters shown in FIGS. 5A and
5B may be adjusted in the control of the access stratum according
to this embodiment. The parameters set to the cell 110 of the MeNB
11 may be the same or different from the parameters set to the cell
120 of the SeNB 12.
(c) Control for Generation of Downlink (DL) MAC PDUs
[0059] The MeNB 11 may perform control regarding the downlink
similar to the above-described control for generation of uplink MAC
PDUs. Specifically, in response to determining, based on the
communication status information received from the SeNB 12, that
the downlink LCP procedure does not function as intended, the MeNB
11 may adjust the downlink PBR for the split EPS bearer or the
downlink PBR for the non-split EPS bearer or both of them, so that
the LCP procedure functions as intended. For example, when the
downlink throughput of the split EPS bearer in the SCell 120 is
excessive, the MeNB 11 may decrease the downlink PBR applied to the
split EPS bearer in the PCell 110 and may increase the downlink PBR
applied to the non-split EPS bearer in the PCell 110. In this case,
the PBR can also be called a prioritized resource amount.
[0060] The above description concentrates on an example in which
the SeNB 12 reports to the MeNB 11 the communication status
regarding the split EPS bearer in the SeNB 12 (SCell 120) and the
MeNB 11 performs the Layer 1/Layer 2 control of the access stratum.
However, it should be noted that the roles of the MeNB 11 and the
SeNB 12 are interchangeable. Specifically, the MeNB 11 may report
to the SeNB 12 the communication status related to the split EPS
bearer in the MeNB 11 (PCell 110). The SeNB 12 may perform the
Layer 1/Layer 2 control of the access stratum related to the split
EPS bearer in response to receiving the communication status
information from the MeNB 11 (PCell 110).
[0061] Next, a specific example of the control procedure according
to this embodiment is described. FIG. 6 is a sequence diagram
showing an example of the control procedure regarding dual
connectivity involving a bearer split. In step S11, the control
procedure for starting the dual connectivity involving a bearer
split is performed among the MeNB 11, the SeNB 12, and the UE 2.
Accordingly, in step S12, the UE 2 performs uplink, downlink, or
bidirectional communication of the split EPS bearer with the MeNB
11 and the SeNB 12.
[0062] In step S13, the MeNB 11 sends a bearer split status request
to the SeNB 12. In step S14, in response to receiving the bearer
split status request, the SeNB 12 sends a bearer split status
response to the MeNB 11. The bearer split status response includes
the bearer split status information. Note that steps S13 and S14
are only illustrative. For example, the SeNB 12 may send the bearer
split status information periodically or non-periodically,
regardless of the request from the MeNB 11.
[0063] In step S15, the MeNB 11 performs control (e.g., Layer
1/Layer 2 control) of the access stratum related to the split EPS
bearer based on the bearer split status information received from
the SeNB 12. As described above, the MeNB 11 may perform control
for generation of uplink MAC PDUs (e.g., adjustment of PBR), uplink
transmission power control (e.g., adjustment of P.sub.EMAX), or
control for generation of downlink MAC PDUs (e.g., adjustment of
PBR). In the example shown in FIG. 6, the MeNB 11 transmits to the
UE 2 an RRC Connection Reconfiguration message that contains
updated configuration information about uplink transmission
(updated UL Tx configuration) regarding the Layer 1/Layer 2
control. The UE 2 performs the Layer 1/Layer 2 control of the
access stratum in accordance with the updated configuration
information received from the MeNB 11. Accordingly, in step S16,
the UE 2 performs uplink, downlink, or bidirectional communication
of the split EPS bearer with the MeNB 11 and the SeNB 12 in
accordance with the Layer 1/Layer 2 control by the MeNB 11.
[0064] In FIG. 6, the roles of the MeNB 11 and the SeNB 12 are
interchangeable. Specifically, the MeNB 11 may send to the SeNB 12
the bearer split status information related to the split EPS bearer
in the MeNB 11 (PCell 110). Further, the SeNB 12 may perform
control of the access stratum in response to receiving the bearer
split status information from the MeNB 11 (PCell 110).
[0065] As can be seen from the above description, according to this
embodiment, the MeNB 11 (or SeNB 12) is configured to receive the
bearer split status information from the SeNB 12 (or MeNB 11) and
to perform control of the access stratum. In some implementations,
the bearer split status information includes communication status
information indicating communication status of the split EPS bearer
in the SeNB 12. In this case, according to this embodiment, the
Layer 1/Layer 2 control of the access stratum is performed based on
the communication status information between the MeNB 11 and the
SeNB 12. Thus, in this embodiment, when dual connectivity involving
a bearer split is performed, unfairness between communication of
the split EPS bearer and that of the non-split EPS bearer can be
corrected, and generation of MAC PDUs, transmission power control,
and the like can be optimized so that they can be performed as
intended.
Second Embodiment
[0066] In this embodiment, a specific example of the Layer 1/Layer
2 control for uplink transmission, which is included in the control
of the access stratum based on sharing of the bearer split status
information between the MeNB 11 and the SeNB 12 according to the
first embodiment, is described. A configuration example of a radio
communication system according to this embodiment is similar to
that shown in FIG. 3.
[0067] FIG. 7 is a sequence diagram showing an example of the
control procedure regarding dual connectivity (e.g., inter-node
radio resource aggregation) involving a bearer split according to
this embodiment. The processing of step S21 may be performed in the
same manner as the processing of step S11 shown in FIG. 6.
Specifically, in step S21, the control procedure for starting dual
connectivity involving a bearer split is performed among the MeNB
11, the SeNB 12, and the UE 2.
[0068] In step S22, the MeNB 11 transmits a control message for
controlling uplink communication of an EPS bearer(s) that is
configured in the UE 2 and includes a split EPS bearer. In the
example shown in FIG. 7, the MeNB 11 transmits the control message
to the UE 2 by using an RRC Connection Reconfiguration message. The
control message may include a parameter(s) related to the LCP
procedure for generating UL MAC PDUs (e.g., PBR). The control
message may also include a control parameter(s) related to the
uplink transmission power (e.g., maximum transmission power
P.sub.EMAX allowed for the UE 2 in the PCell 110 or SCell 120).
[0069] In step S23, the UE 2 performs uplink communication of a
split EPS bearer with the MeNB 11 and the SeNB 12 in accordance
with the control by the MeNB 11 in step S22. Step S23 may include
uplink communication of a non-split EPS bearer in the PCell
110.
[0070] The processing of steps S24 and S25 may be performed in the
same manner as the processing of steps S13 and S14 shown in FIG. 6.
Specifically, in step S24, the MeNB 11 sends a bearer split status
request to the SeNB 12. In step S25, in response to receiving the
bearer split status request, the SeNB 12 sends a bearer split
status response including the bearer split status information to
the MeNB 11. Instead of performing steps S24 and S25, the SeNB 12
may send the bearer split status information periodically or
non-periodically, regardless of the request from the MeNB 11.
[0071] In step S26, the MeNB 11 performs uplink Layer 1/Layer 2
control for the split EPS bearer based on the bearer split status
information received from the SeNB 12. In the example shown in FIG.
7, the MeNB 11 transmits to the UE 2 an RRC Connection
Reconfiguration message containing an updated control message for
controlling the uplink communication. The updated control message
is generated in consideration of the bearer split status
information received from the SeNB 12. For example, the MeNB 11 may
update a parameter(s) related to the LCP procedure applied to
generation of uplink MAC PDUs (e.g., PBR), or may update a control
parameter(s) related to the uplink transmission power (e.g.,
P.sub.EMAX) so as to correct the unfairness between communication
of the split EPS bearer and communication of the non-split EPS
bearer.
[0072] In step S27, the UE 2 performs uplink communication of the
split EPS bearer with the MeNB 11 and the SeNB 12 in accordance
with the control by the MeNB 11 in step S26. Step S26 may include
uplink communication of the non-split EPS bearer in the PCell
110.
[0073] In FIG. 7, the roles of the MeNB 11 and the SeNB 12 are
interchangeable. Specifically, the MeNB 11 may report to the SeNB
12 the bearer split status information related to the split EPS
bearer in the MeNB 11 (PCell 110). Further, the SeNB 12 may perform
uplink Layer 1/Layer 2 control in response to receiving the bearer
split status information from the MeNB 11 (PCell 110).
[0074] Next, a specific example of the control for generation of
uplink MAC PDUs is described with reference to FIGS. 8A to 8C. FIG.
8A is a schematic diagram showing an example of generating an
uplink MAC PDU in the MeNB 11 (PCell 110) when no bearer split is
performed. FIG. 8A shows an example in which data from two logical
channels (i.e., LCH #1 and LCH #2) is multiplexed on available
resources (MAC PDU) indicated by an Uplink Grant from the MeNB 11.
The LCH #1 is assigned a highest priority (first priority) and
PBR1. The LCH #2 is assigned a second priority and PBR2. In
accordance with the uplink PBR procedure specified in the LTE
standards, resources up to the PBR1 are first allocated to the LCH
#1 which is of the highest priority, and then resources up to the
PBR2 are allocated for the LCH #2. After that, the remaining room
in the available resources (MAC PDU) is filled with data from the
LCH #1 until there is no further data from the LCH #1 which is of
the highest priority or there is no further room in the MAC
PDU.
[0075] FIG. 8B shows a case where a bearer split is performed on
the EPS bearer corresponding to the logical channel LCH #2. In the
SCell 120, only the logical channel LCH #2 is configured to the UE
2. Accordingly, uplink resources of the SCell 120 granted to the UE
2 by the SeNB 12 can be used mainly for transmission of data from
the logical channel LCH #2. However, in the example shown in FIG.
8B, the PBRs for the logical channels LCH #1 and LCH #2 are the
same as those in the example shown in FIG. 8A (i.e., PBR1 and
PBR2), and the logical channel LCH #2 of the split EPS bearer is
provided with the PBR2 in each of the PCell 110 and the SCell 120.
Accordingly, in the example shown in FIG. 8B, the bit rate of the
logical channel LCH #2 which is of the second priority is higher
than the bit rate of the logical channel LCH #1 which is of the
highest priority. This state shows a situation where there is
unbalanced resource allocation between the logical channel LCH #1
which is not subjected to a bearer split and the logical channel
LCH #2 which is subjected to a bearer split and the LCP procedure
does not function as intended.
[0076] To overcome the undesirable situation shown in FIG. 8B, the
SeNB 12 reports to the MeNB 11 the communication status of the
logical channel LCH #2 in the SeNB 12 (SCell 120) or the
communication status of the split EPS bearer (or the radio bearer)
associated with the logical channel LCH #2. The SeNB 12 may report
to the MeNB 11, for example, the throughput of the logical channel
LCH #2 in the SeNB 12 (e.g., transmission rate or data rate of PDCP
SDUs, PDCP PDUs, RLC PDUs, or MAC PDUs (i.e., Transport Blocks)).
The SeNB 12 may report to the MeNB 11 the total uplink throughput
of the UE 2 in the SCell 120, instead of the throughput per logical
channel (or EPS bearer, radio bearer). The MeNB 11 determines that
the throughput of the logical channel LCH #2 related to the split
EPS bearer is excessive upon considering the PCell 110 and the
SCell 120 as a whole, and thus controls the LCP procedure to
correct the excessive throughput of the logical channel LCH #2.
Specifically, the MeNB 11 may increase the PBR1 of the logical
channel LCH #1 which is not subjected to a bearer split, or may
decrease the PBR2 of the logical channel LCH #2 which is subjected
to a bearer split, or may perform both increase of the PBR1 and
decrease of the PBR2.
[0077] FIG. 8C is a schematic diagram showing an example of
generating uplink MAC PDUs after the adjustment of the PBRs. In the
example shown in FIG. 8C, the PBR1 of the logical channel LCH #1
which is not subjected to a bearer split is increased to PBR1'.
Further, the PBR2 of the logical channel LCH #2 which is subjected
to a bearer split is decreased to PBR2'. Accordingly, the bit rate
of the logical channel #1 in the PCell 110 increases and the bit
rate of the logical channel #2 in the PCell 110 decreases. Thus,
upon viewing the PCell 110 and the SCell 120 as a whole, the
balance of resource allocation between the logical channel LCH #1
and the logical channel LCH #2 can be brought closer to the
intended state. When only data of a radio bearer (RB) associated
with one EPS Bearer is transmitted in the SCell 120, all the
available resources may be simply allocated to the data of the RB,
without executing the LCP algorithm.
[0078] The uplink Layer 1/Layer 2 control performed in this
embodiment may be uplink transmission power control. In this case,
the SeNB 12 may report, to the MeNB 11, information about the power
headroom of the UE 2 in the SCell 120 as the communication status
information. The information about the power headroom may be
statistics, such as an average value of the power headroom, or
other information indicating the size of the power headroom. The
MeNB 11 may adjust the transmission power of the UE 2 by taking
into account both the power headroom of the UE 2 in the PCell 110
and the power headroom of the UE 2 in the SCell 120. For example,
as described above, the MeNB 11 may adjust one or both of
P.sub.EMAX,PCELL and P.sub.EMAX,SCELL when it is determined that
the power headroom of the UE 2 in the PCell 110 is less than the
power headroom of the UE 2 in the SCell 120 by more than a
predetermined amount. Specifically, the MeNB 11 may increase
P.sub.EMAX,PCELL and decrease P.sub.EMAX,SCELL. P.sub.EMAX,PCELL
represents the maximum transmission power (i.e., transmit power
limit) allowed for the UE 2 in the PCell 110, and P.sub.EMAX,SCELL
represents the maximum transmission power allowed for the UE 2 in
the SCell 120. P.sub.EMAX, PCELL and P.sub.EMAX,SCELL are used to
determine the configured maximum transmission power
P.sub.CMAX,PCELL in the PCell 110 and P.sub.CMAX,SCELL in the SCell
120. P.sub.CMAX,PCELL and P.sub.CMAX,SCELL may be determined
according to the calculation formulas (P.sub.CMAX,C) specified in
3GPP TS 36.301.
[0079] Also in the example of the uplink transmission power
control, the roles of the MeNB 11 and the SeNB 12 are
interchangeable. Specifically, the MeNB 11 may report, to the SeNB
12, the information about the power headroom of the UE 2 in the
PCell 110. Further, the SeNB 12 may adjust the uplink maximum
transmission power of the UE 2 in one or both of the PCell 110 and
the SCell 120 in consideration of the power headroom of the UE 2 in
the PCell 110.
Third Embodiment
[0080] In this embodiment, a specific example of the Layer 1/Layer
2 control for downlink transmission, which is included in the
control of the access stratum based on sharing of the bearer split
status information between the MeNB 11 and the SeNB 12 according to
the first embodiment, is described. A configuration example of a
radio communication system according to this embodiment is similar
to that shown in FIG. 3.
[0081] FIG. 9 is a sequence diagram showing an example of the
control procedure regarding dual connectivity involving a bearer
split according to this embodiment. The processing of step S31 may
be performed in the same manner as the processing of step S11 shown
in FIG. 6. Specifically, in step S31, the control procedure for
starting dual connectivity involving a bearer split is performed
among the MeNB 11, the SeNB 12, and the UE 2.
[0082] In step S32, the MeNB 11 and the SeNB 12 perform downlink
communication of a split EPS bearer with the UE 2. Step S32 may
include downlink communication of a non-split EPS bearer in the
PCell 110.
[0083] The processing of steps S33 and S34 may be performed in the
same manner as the processing of steps S13 and S14 shown in FIG. 6.
Specifically, in step S33, the MeNB 11 sends a bearer split status
request to the SeNB 12. In step S34, in response to receiving the
bearer split status request, the SeNB 12 sends a bearer split
status response including the bearer split status information to
the MeNB 11. Instead of performing steps S33 and S34, the SeNB 12
may send the bearer split status information periodically or
non-periodically, regardless of the request from the MeNB 11.
[0084] The bearer split status information sent in step S34 may
indicate information relating to the downlink communication of the
UE 2 in the SCell 120, including communication status information,
radio resource control information, or admission control
information, or any combination thereof. The communication status
information may indicate statistics (e.g., average value) of radio
resources (i.e., the number of resource blocks) allocated to the UE
2 in the SCell 120. The communication status information may
indicate statistics (e.g., average value) of the throughput (e.g.,
transmission rate or data rate of PDCP SDUs, PDCP PDUs, RLC PDUs,
or MAC PDUs (Transport Blocks)) of the UE 2 in the SCell 120. The
communication status information may also indicate a packet loss
rate, information about retransmission control in the RLC sublayer,
information about packet discarding in the RLC sublayer, and the
like.
[0085] The radio resource control information may be information
about radio resources used in the SCell 120 for data (service) from
the split EPS bearer. More specifically, the radio resource control
information in the SeNB 12 may include at least one of the
following information items (1) to (3):
(1) Information about an increase or decrease in radio resources;
(2) Information about available radio resources; and (3)
Information about surplus radio resources.
[0086] The information about an increase or decrease in radio
resources may indicate, for example, that the number of radio
resources can be increased (or a request to increase the number of
radio resources can be made), or the number of radio resources can
be reduced (or a request to reduce the number of radio resources
can be made), according to the use status or the like of radio
resources used for a bearer split (i.e., split EPB bearer) in the
SeNB 12.
[0087] The information about available radio resources may
indicate, for example, radio resources which can be allocated to
the data (service) of the split EPS bearer in the SeNB 12.
[0088] The information about surplus radio resources may indicate,
for example, radio resources which are not used in the SeNB 12
(i.e., radio resources which can be used for data transmission or
the like). Examples of the radio resources may include the number
of resource blocks, the number of packets (PDCP PDUs, PDCP SDUs,
RLC PDUs, RLC SDUs, MAC PDUs (TBs), etc.), and the number of cells
(i.e., the number of downlink and/or uplink carriers).
[0089] The admission control information may be information
relating to admission executed in the SeNB 12 on data (service) of
the split EPS bearer (i.e., information about whether a bearer
split can be accepted). More specifically, the admission control
information in the SeNB 12 may include at least one of the
following information items (1) to (5):
(1) Information about whether or not to admit a new bearer split;
(2) Information about a wait time until a new bearer split is
acceptable; (3) Information about a wait time until a request for a
new bearer split is made; (4) Information about estimated
(expected) throughput (data rate); and (5) Information about an
estimated (expected) amount of radio resources to be allocated.
[0090] The information about whether or not to admit a new bearer
split may indicate, for example, whether a new bearer split is
allowed in the SeNB 12, or the number of new bearer splits that can
be allowed in the SeNB 12 (i.e., the number of EPS bearers
transmitted by radio bearers (RBs) in a cell of the SeNB 12 in the
case of a bearer split).
[0091] The information about a wait time until a new bearer split
is acceptable may indicate, for example, an expected minimum wait
time until a bearer split is acceptable in the SeNB 12, or a wait
time until a bearer split is acceptable.
[0092] The information about a wait time until a request for a new
bearer split is made may indicate, for example, a prohibited time
during which sending (by the MeNB 11) a request for a bearer split
to the SeNB 12, i.e., sending a request for transmitting data
(service) of the split EPS bearer in a cell of the SeNB 12, is
prohibited.
[0093] The information about an estimated (expected) data rate
(throughput) may indicate, for example, an estimated (expected)
data rate (e.g., throughput) in the SeNB 12, or a level of a data
rate (e.g., throughput) (e.g., an index value indicating one of
several predetermined levels of data rates).
[0094] The information about an estimated (expected) amount of
radio resources to be allocated may indicate, for example, an
estimated (expected) amount of radio resources to be allocated in
the SeNB 12, or a level of an amount of radio resources (e.g., an
index value indicating one of several predetermined levels of the
amount of radio resources). Examples of the radio resources may
include the number of resource blocks, the number of packets (PDCP
PDUs, PDCP SDUs, RLC PDUs, RLC SDUs, MAC PDUs (TBs), etc.), and the
number of cells (i.e., the number of downlink and/or uplink
carriers).
[0095] In step S35, the MeNB 11 may perform the downlink Layer
1/Layer 2 control for the split EPS bearer based on the bearer
split status information received from the SeNB 12. As shown in
FIG. 9, if necessary, the MeNB 11 may transmit, to the UE 2, an
updated control message for controlling the downlink communication,
for example, by using the RRC Connection Reconfiguration message.
Further, if necessary, the MeNB 11 may transmit the updated control
message for controlling the downlink communication to the SeNB
12.
[0096] In the downlink Layer 1/Layer 2 control in step S35, the
MeNB 11 may update a parameter(s) related to the LCP procedure
applied to generation of downlink MAC PDUs (e.g., PBR). For
example, when the average value of radio resources allocated to the
UE 2 in the SCell 120 is equal to or greater than a predetermined
value, the MeNB 11 may decrease the downlink PBR (i.e., prioritized
resource amount) for the logical channel of the split EPS bearer of
the UE 2 in the PCell 110. Further, the MeNB 11 may increase the
downlink PBR for the non-split EPS bearer of the UE 2 in the PCell
110. Accordingly, when dual connectivity involving a bearer split
is performed, the unfairness between downlink communication of the
split EPS bearer and downlink communication of the non-split EPS
bearer can be corrected, and thus generation of MAC PDUs,
transmission power control, and the like can be optimized so that
they can be performed as intended.
[0097] In step S36, the MeNB 11 and the SeNB 12 perform downlink
communication of the split EPS bearer with the UE 2 in accordance
with the control by the MeNB 11 in step S35. Step S36 may include
downlink communication of a non-split EPS bearer in the PCell
110.
[0098] In FIG. 9, the roles of the MeNB 11 and the SeNB 12 are
interchangeable. Specifically, the MeNB 11 may report to the SeNB
12 the bearer split status information related to the split EPS
bearer in the MeNB 11 (PCell 110). Further, the SeNB 12 may perform
downlink Layer 1/Layer 2 control in response to receiving the
bearer split status information from the MeNB 11 (PCell 110).
Fourth Embodiment
[0099] In this embodiment, modified examples of the first to third
embodiments are described. A configuration example of a radio
communication system according to this embodiment is similar to
that shown in FIG. 3. In this embodiment, the SeNB 12 is configured
to send to the MeNB 11 a request for a bearer split as described
below. According to this configuration, dual connectivity involving
a bearer split can be used more effectively.
[0100] For example, the SeNB 12 may request the MeNB 11 to
increase, decrease, or update the amount of downlink data (e.g.,
PDCP PDU) on the split EPS bearer that is split in the MeNB 11 and
is transmitted to the SeNB 12.
[0101] In another alternative, the SeNB 12 may request the MeNB 11
to adjust the maximum transmission power allowed for the UE 2 in
the PCell 110 or the SCell 120.
[0102] In still another alternative, the SeNB 12 may request the
MeNB 11 to adjust the Prioritized Bit Rate (PBR) which is applied
to the logical channel of the split EPS bearer when the UE 2
generates the uplink MAC PDUs for the PCell 110 or the SCell
120.
[0103] In yet another alternative, the SeNB 12 may request the MeNB
11 to stop the dual connectivity involving a bearer split related
to the UE 2.
[0104] These requests from the SeNB 12 to the MeNB 11 may be sent
periodically or non-periodically (by event-triggered) according to
the load of the SeNB 12 (SCell 120), or the characteristics of a
physical channel (e.g., Physical Downlink Shared Channel (PDSCH)),
a transport channel (e.g., Downlink Shared channel (DL-SCH)), or a
logical channel (e.g., Dedicated Traffic channel (DTCH)).
[0105] Next, configuration examples of the MeNB 11, the SeNB 12,
and the UE 2 according to the first to fourth embodiments described
above are described. FIG. 10 is a block diagram showing a
configuration example of the MeNB 11. A radio communication unit
111 receives an uplink signal transmitted from the UE 2 via an
antenna. A received data processing unit 113 recovers the received
uplink signal. Obtained received data is transferred to other
network nodes, such as Serving Gateway (S-GW) or MME of the EPC 3,
or another eNB, via a communication unit 114. For example, uplink
user data received from the UE 2 is transferred to the S-GW within
the EPC 3. NAS control data contained in control data received from
the UE 2 is transferred to the MME within the EPC 3. Further, the
received data processing unit 113 receives control data to be sent
to the SeNB 12 from a communication control unit 115, and sends the
received control data to the SeNB 12 via the communication unit
114.
[0106] A transmission data processing unit 112 receives user data
addressed to the UE 2 from the communication unit 114, and performs
error correction coding, rate matching, interleaving, or the like,
to thereby generate a transport channel. Further, the transmission
data processing unit 112 adds control information to a data
sequence of the transport channel, to thereby generate a
transmission symbol sequence. The radio communication unit 111
generates a downlink signal by performing processing including
carrier wave modulation based on the transmission symbol sequence,
frequency conversion, and signal amplification, and transmits the
generated downlink signal to the UE 2. The transmission data
processing unit 112 receives control data to be transmitted to the
UE 2 from the communication control unit 115, and transmits the
received control data to the UE 2 via the radio communication unit
111.
[0107] The communication control unit 115 controls dual
connectivity involving a bearer split. In some implementations, the
communication control unit 115 may generate configuration
information and control information necessary for dual connectivity
involving a bearer split, and may transmit the generated
information to the SeNB 12 and the UE 2. Further, the communication
control unit 115 may perform control of the access stratum in
response to receiving from the SeNB 12 the bearer split status
information (e.g., communication status information) related to the
split EPS bearer. The communication control unit 115 may send to
the SeNB 12 the bearer split status information (e.g.,
communication status information) related to the split EPS bearer
to trigger the control of the access stratum in the SeNB 12.
[0108] FIG. 11 is a block diagram showing a configuration example
of the SeNB 12. The functions and operations of a radio
communication unit 121, a transmission data processing unit 122, a
received data processing unit 123, and a communication unit 124,
which are shown in FIG. 11, are the same as those of the
corresponding elements, i.e., the radio communication unit 111, the
transmission data processing unit 112, the received data processing
unit 113, and the communication unit 114 in the MeNB 11 shown in
FIG. 10.
[0109] A communication control unit 125 of the SeNB 12 controls
dual connectivity involving a bearer split. The communication
control unit 125 may send to the MeNB 11 the bearer split status
information (e.g., communication status information) related to the
split EPS bearer to trigger the control of the access stratum in
the MeNB 11. Further, the communication control unit 125 may
perform control of the access stratum in response to receiving from
the MeNB 11 the bearer split status information (e.g.,
communication status information) related to the split EPS
bearer.
[0110] FIG. 12 is a block diagram showing a configuration example
of the UE 2. A radio communication unit 21 is configured to support
dual connectivity and to communicate simultaneously in a plurality
of cells (PCell 110 and SCell 120) served by different eNBs (MeNB
11 and SeNB 12). Specifically, the radio communication unit 21
receives a downlink signal from one or both of the MeNB 11 and the
SeNB 12 via an antenna. A received data processing unit 22 recovers
received data from the received downlink signal, and sends the
recovered data to a data control unit 23. The data control unit 23
uses the received data according to the intended use. A
transmission data processing unit 24 and the radio communication
unit 21 generate an uplink signal by using data for transmission
supplied from the data control unit 23, and transmit the generated
uplink signal to one or both of the MeNB 11 and the SeNB 12.
[0111] A communication control unit 25 of the UE 2 controls dual
connectivity involving a bearer split. The communication control
unit 25 performs control of the access stratum relating to the
split EPS bearer based on an instruction from the MeNB 11 or the
SeNB 12.
Other Embodiments
[0112] The communication control processes in the MeNB 11, the SeNB
12, and the UE 2 in association with dual connectivity involving a
bearer split as described in the first to fourth embodiments may be
implemented by a semiconductor processing device including an
Application Specific Integrated Circuit (ASIC). These processes may
be implemented by causing a computer system including at least one
processor (e.g., a microprocessor, a Micro Processing Unit (MPU),
or a Digital Signal Processor (DSP)) to execute a program.
Specifically, one or more programs including instructions for
causing the computer system to perform algorithms described above
with reference to sequence diagrams and the like may be created,
and the program(s) may be supplied to a computer.
[0113] The program(s) can be stored and provided to a computer
using any type of non-transitory computer readable media.
Non-transitory computer readable media include any type of tangible
storage media. Examples of non-transitory computer readable media
include magnetic storage media (such as flexible disks, magnetic
tapes, hard disk drives, etc.), optical magnetic storage media
(e.g. magneto-optical disks). Compact Disc Read Only Memory
(CD-ROM), CD-R, CD-R/W, and semiconductor memories (such as mask
ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flash ROM,
Random Access Memory (RAM), etc.). The program(s) may be provided
to a computer using any type of transitory computer readable media.
Examples of transitory computer readable media include electric
signals, optical signals, and electromagnetic waves. Transitory
computer readable media can provide the program to a computer via a
wired communication line, such as electric wires and optical
fibers, or a wireless communication line.
[0114] In the first to fourth embodiments, the LTE system is mainly
described. However, as described above, these embodiments may be
applied to radio communication systems other than the LTE system,
such as a 3GPP UMTS, a 3GPP2 CDMA2000 system (1.times.RTT, HRPD), a
GSM/GPRS system, or a WiMAX system.
[0115] Further, the above embodiments are only illustrative of the
application of the technical idea obtained by the present inventor.
That is, the technical idea is not limited only to the above
embodiments and can be modified in various ways as a matter of
course.
[0116] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2013-227473, filed on
Oct. 31, 2013, the disclosure of which is incorporated herein in
its entirety by reference.
REFERENCE SIGNS LIST
[0117] 1 EVOLVED UTRAN (E-UTRAN) [0118] 2 USER EQUIPMENT (UE)
[0119] 3 EVOLVED PACKET CORE (EPC) [0120] 11 MASTER eNodeB (MeNB)
[0121] 12 SECONDARY eNodeB (SeNB) [0122] 25 COMMUNICATION CONTROL
UNIT [0123] 110 PRIMARY CELL (PCell) [0124] 120 SECONDARY CELL
(SCell) [0125] 115 COMMUNICATION CONTROL UNIT [0126] 125
COMMUNICATION CONTROL UNIT
* * * * *