U.S. patent application number 17/723600 was filed with the patent office on 2022-08-04 for communication system.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Mitsuru MOCHIZUKI, Masayuki NAKAZAWA, Kuniyuki SUZUKI, Hideo UMEHARA.
Application Number | 20220248371 17/723600 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-04 |
United States Patent
Application |
20220248371 |
Kind Code |
A1 |
NAKAZAWA; Masayuki ; et
al. |
August 4, 2022 |
COMMUNICATION SYSTEM
Abstract
In a communication system, a plurality of base stations includes
an MeNB being a first base station, and a plurality of SeNBs to be
connected to the MeNB. At least one of control plane data about
control of communication and user plane data about a user is
transmitted to and received from a user equipment (UE) via the
first base station being the MeNB. The control plane data and the
user plane data are contained in information provided by a core
network about communication with the UE. The communication system
can simplify processing of at least one of control plane data and
user plane data when a communication terminal device communicates
with a plurality of base station devices.
Inventors: |
NAKAZAWA; Masayuki; (Tokyo,
JP) ; MOCHIZUKI; Mitsuru; (Tokyo, JP) ;
UMEHARA; Hideo; (Tokyo, JP) ; SUZUKI; Kuniyuki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Appl. No.: |
17/723600 |
Filed: |
April 19, 2022 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
17030045 |
Sep 23, 2020 |
11343798 |
|
|
17723600 |
|
|
|
|
16320119 |
Jan 24, 2019 |
10827462 |
|
|
PCT/JP2017/027597 |
Jul 31, 2017 |
|
|
|
17030045 |
|
|
|
|
International
Class: |
H04W 68/10 20060101
H04W068/10; H04W 76/15 20060101 H04W076/15; H04B 7/024 20060101
H04B007/024; H04W 72/00 20060101 H04W072/00; H04W 72/04 20060101
H04W072/04; H04W 16/32 20060101 H04W016/32 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2016 |
JP |
2016154272 |
Claims
1. A communication system comprising: a communication terminal
device; a plurality of base station devices configured to perform
radio communication with the communication terminal device; and a
core network configured to provide information about the
communication with the communication terminal device to the
plurality of base station devices, wherein the plurality of base
station devices include a master base station device configured to
perform main processing, and a plurality of secondary base station
devices to be connected to the master base station device, at least
one of control plane data about control of the communication and
user plane data about a user is transmitted to and received from
the communication terminal device via the master base station
device, the control plane data and the user plane data being
contained in the information provided by the core network about the
communication with the communication terminal device, one of the
plurality of secondary base station devices, being a specific
secondary base station device, performs radio resource control
processing on each of the plurality of secondary base station
devices, and after communication with the specific secondary base
station device is established, the communication terminal device
notifies the specific secondary base station device of a
measurement report for each of the secondary base station
devices.
2. The communication system according to claim 1 wherein before
communication with the specific secondary base station device is
established, the communication terminal device notifies the master
base station device of a measurement report for the specific
secondary base station device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
17/030,045, filed Sep. 23, 2020, which claims the benefit of
priority under 35 U.S.C. .sctn. 120 for U.S. Ser. No. 16/320,119,
filed Jan. 24, 2019, (U.S. Pat. No. 10,827,462), which is a
National Stage application of PCT/JP2017/027597, filed Jul. 31,
2017 and claims benefit of priority under 35 U.S.C. .sctn. 119 from
JP 2016-154272, filed Aug. 5, 2016, the entire contents of each of
which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a communication system in
which radio communication is performed between a communication
terminal device such as a user equipment device and a base station
device.
BACKGROUND ART
[0003] The 3rd generation partnership project (3GPP), the standard
organization regarding the mobile communication system, is studying
communication systems referred to as long term evolution (LTE)
regarding radio sections and system architecture evolution (SAE)
regarding the overall system configuration including a core network
and a radio access network, which will be hereinafter collectively
referred to as a network as well (for example, see Non-Patent
Documents 1 to 8). This communication system is also referred to as
3.9 generation (3.9 G) system.
[0004] As the access scheme of the LTE, orthogonal frequency
division multiplexing (OFDM) is used in a downlink direction and
single carrier frequency division multiple access (SC-FDMA) is used
in an uplink direction. Further, differently from the wideband code
division multiple access (W-CDMA), circuit switching is not
provided but a packet communication system is only provided in the
LTE.
[0005] The decisions by 3GPP regarding the frame configuration in
the LTE system described in Non-Patent Document 1 (Chapter 5) will
be described with reference to FIG. 1. FIG. 1 is a diagram
illustrating the configuration of a radio frame used in the LTE
communication system. With reference to FIG. 1, one radio frame is
10 ms. The radio frame is divided into ten equally sized subframes.
The subframe is divided into two equally sized slots. The first and
sixth subframes contain a downlink synchronization signal per radio
frame. The synchronization signals are classified into a primary
synchronization signal (P-SS) and a secondary synchronization
signal (S-SS).
[0006] Non-Patent Document 1 (Chapter 5) describes the decisions by
3GPP regarding the channel configuration in the LTE system. It is
assumed that the same channel configuration is used in a closed
subscriber group (CSG) cell as that of a non-CSG cell.
[0007] A physical broadcast channel (PBCH) is a channel for
downlink transmission from a base station device (hereinafter may
be simply referred to as a "base station") to a communication
terminal device (hereinafter may be simply referred to as a
"communication terminal") such as a user equipment device
(hereinafter may be simply referred to as a "user equipment"). A
BCH transport block is mapped to four subframes within a 40 ms
interval. There is no explicit signaling indicating 40 ms
timing.
[0008] A physical control format indicator channel (PCFICH) is a
channel for downlink transmission from a base station to a
communication terminal. The PCFICH notifies the number of
orthogonal frequency division multiplexing (OFDM) symbols used for
PDCCHs from the base station to the communication terminal. The
PCFICH is transmitted per subframe.
[0009] A physical downlink control channel (PDCCH) is a channel for
downlink transmission from a base station to a communication
terminal. The PDCCH notifies of the resource allocation information
for downlink shared channel (DL-SCH) being one of the transport
channels described below, resource allocation information for a
paging channel (PCH) being one of the transport channels described
below, and hybrid automatic repeat request (HARQ) information
related to DL-SCH. The PDCCH carries an uplink scheduling grant.
The PDCCH carries acknowledgement (Ack)/negative acknowledgement
(Hack) that is a response signal to uplink transmission. The PDCCH
is referred to as an L1/L2 control signal as well.
[0010] A physical downlink shared channel (PDSCH) is a channel for
downlink transmission from a base station to a communication
terminal. A downlink shared channel (DL-SCH) that is a transport
channel and a PCH that is a transport channel are mapped to the
PDSCH.
[0011] A physical multicast channel (PMCH) is a channel for
downlink transmission from a base station to a communication
terminal. A multicast channel (MCH) that is a transport channel is
mapped to the PMCH.
[0012] A physical uplink control channel (PUCCH) is a channel for
uplink transmission from a communication terminal to a base
station. The PUCCH carries Ack/Nack that is a response signal to
downlink transmission. The PUCCH carries a channel quality
indicator (CQI) report. The CQI is quality information indicating
the quality of received data or channel quality. In addition, the
PUCCH carries a scheduling request (SR).
[0013] A physical uplink shared channel (PUSCH) is a channel for
uplink transmission from a communication terminal to a base
station. An uplink shared channel (UL-SCH) that is one of the
transport channels is mapped to the PUSCH.
[0014] A physical hybrid ARQ indicator channel (PHICH) is a channel
for downlink transmission from a base station to a communication
terminal. The PHICH carries Ack/Nack that is a response signal to
uplink transmission. A physical random access channel (PRACH) is a
channel for uplink transmission from the communication terminal to
the base station. The PRACH carries a random access preamble.
[0015] A downlink reference signal (RS) is a known symbol in the
LTE communication system. The following five types of downlink
reference signals are defined: a cell-specific reference signal
(CRS), an MBSFN reference signal, a data demodulation reference
signal (DM-RS) being a UE-specific reference signal, a positioning
reference signal (PRS), and a channel state information reference
signal (CSI-RS). The physical layer measurement objects of a
communication terminal include reference signal received power
(RSRP).
[0016] The transport channels described in Non-Patent Document 1
(Chapter 5) will be described. A broadcast channel (BCH) among the
downlink transport channels is broadcast to the entire coverage of
a base station (cell). The BCH is mapped to the physical broadcast
channel (PBCH).
[0017] Retransmission control according to a hybrid ARQ (HARQ) is
applied to a downlink shared channel (DL-SCH). The DL-SCH can be
broadcast to the entire coverage of the base station (cell). The
DL-SCH supports dynamic or semi-static resource allocation. The
semi-static resource allocation is also referred to as persistent
scheduling. The DL-SCH supports discontinuous reception (DRX) of a
communication terminal for enabling the communication terminal to
save power. The DL-SCH is mapped to the physical downlink shared
channel (PDSCH).
[0018] The paging channel (PCH) supports DRX of the communication
terminal for enabling the communication terminal to save power. The
PCH is required to be broadcast to the entire coverage of the base
station (cell). The PCH is mapped to physical resources such as the
physical downlink shared channel (PDSCH) that can be used
dynamically for traffic.
[0019] The multicast channel (MCH) is used for broadcast to the
entire coverage of the base station (cell). The MCH supports SFN
combining of multimedia broadcast multicast service (MBMS) services
(MTCH and MCCH) in multi-cell transmission. The MCH supports
semi-static resource allocation. The MCH is mapped to the PMCH.
[0020] Retransmission control according to a hybrid ARQ (HARQ) is
applied to an uplink shared channel (UL-SCH) among the uplink
transport channels. The UL-SCH supports dynamic or semi-static
resource allocation. The UL-SCH is mapped to the physical uplink
shared channel (PUSCH).
[0021] A random access channel (RACH) is limited to control
information. The RACH involves a collision risk. The RACH is mapped
to the physical random access channel (PRACH).
[0022] The HARQ will be described. The HARQ is the technique for
improving the communication quality of a channel by combination of
automatic repeat request (ARQ) and error correction (forward error
correction). The HARQ is advantageous in that error correction
functions effectively by retransmission even for a channel whose
communication quality changes. In particular, it is also possible
to achieve further quality improvement in retransmission through
combination of the reception results of the first transmission and
the reception results of the retransmission.
[0023] An example of the retransmission method will be described.
If the receiver fails to successfully decode the received data, in
other words, if a cyclic redundancy check (CRC) error occurs
(CRC=NG), the receiver transmits "Nack" to the transmitter. The
transmitter that has received "Nack" retransmits the data. If the
receiver successfully decodes the received data, in other words, if
a CRC error does not occur (CRC=OK), the receiver transmits "AcK"
to the transmitter. The transmitter that has received "Ack"
transmits the next data.
[0024] The logical channels described in Non-Patent Document 1
(Chapter 6) will be described. A broadcast control channel (BCCH)
is a downlink channel for broadcast system control information. The
BCCH that is a logical channel is mapped to the broadcast channel
(BCH) or downlink shared channel (DL-SCH) that is a transport
channel.
[0025] A paging control channel (PCCH) is a downlink channel for
transmitting paging information and system information change
notifications. The PCCH is used when the network does not know the
cell location of a communication terminal. The PCCH that is a
logical channel is mapped to the paging channel (PCH) that is a
transport channel.
[0026] A common control channel (CCCH) is a channel for
transmission control information between communication terminals
and a base station. The CCCH is used in the case where the
communication terminals have no RRC connection with the network. In
the downlink direction, the CCCH is mapped to the downlink shared
channel (DL-SCH) that is a transport channel. In the uplink
direction, the CCCH is mapped to the uplink shared channel (UL-SCH)
that is a transport channel.
[0027] A multicast control channel (MCCH) is a downlink channel for
point-to-multipoint transmission. The MCCH is used for transmission
of MBMS control information for one or several MTCHs from a network
to a communication terminal. The MCCH is used only by a
communication terminal during reception of the MBMS. The MCCH is
mapped to the multicast channel (MCH) that is a transport
channel.
[0028] A dedicated control channel (DCCH) is a channel that
transmits dedicated control information between a communication
terminal and a network on a point-to-point basis. The DCCH is used
when the communication terminal has an RRC connection. The DCCH is
mapped to the uplink shared channel (UL-SCH) in uplink and mapped
to the downlink shared channel (DL-SCH) in downlink.
[0029] A dedicated traffic channel (DTCH) is a point-to-point
communication channel for transmission of user information to a
dedicated communication terminal. The DTCH exists in uplink as well
as downlink. The DTCH is mapped to the uplink shared channel
(UL-SCH) in uplink and mapped to the downlink shared channel
(DL-SCK) in downlink.
[0030] A multicast traffic channel (MTCH) is a downlink channel for
traffic data transmission from a network to a communication
terminal. The MTCH is a channel used only by a communication
terminal during reception of the MBMS. The MTCH is mapped to the
multicast channel (MCH).
[0031] CGI represents a cell global identifier. ECGI represents an
E-UTRAN cell global identifier. A closed subscriber group (CSG)
cell is introduced in the LTE, and the long term evolution advanced
(LTE-A) and universal mobile telecommunication system (UMTS)
described below.
[0032] The closed subscriber group (CSG) cell is a cell in which
subscribers who are allowed use are specified by an operator
(hereinafter, also referred to as a "cell for specific
subscribers"). The specified subscribers are allowed to access one
or more cells of a public land mobile network (PLMN). One or more
cells to which the specified subscribers are allowed access are
referred to as "CSG cell(s)". Note that access is limited in the
PLMN.
[0033] The CSG cell is part of the PLMN that broadcasts a specific
CSG identity (CSG ID) and broadcasts "TRUE" in a CSG indication.
The authorized members of the subscriber group who have registered
in advance access the CSG cells using the CSG ID that is the access
permission information.
[0034] The CSG ID is broadcast by the CSG cell or cells. A
plurality of CSG IDs exist in the LTE communication system. The CSG
IDs are used by communication terminals (UEs) for making access
from CSG-related members easier.
[0035] The locations of communication terminals are tracked based
on an area composed of one or more cells. The locations are tracked
for enabling tracking the locations of communication terminals and
calling communication terminals, in other words, incoming calling
to communication terminals even in an idle state. An area for
tracking locations of communication terminals is referred to as a
tracking area.
[0036] 3GPP is studying base stations referred to as Home-NodeB
(Home-NB; HNB) and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base
station for, for example, household, corporation, or commercial
access service in UTRAN/E-UTRAN. Non-Patent Document 2 discloses
three different modes of the access to the HeNB and HNB.
Specifically, an open access mode, a closed access mode, and a
hybrid access mode are disclosed.
[0037] Further, 3GPP is pursuing specifications standard of long
term evolution advanced (LTE-A) as Release 10 (see Non-Patent
Documents 3 and 4). The LTE-A is based on the LTE radio
communication system and is configured by adding several new
techniques to the system.
[0038] Carrier aggregation (CA) is studied for the LTE-A system, in
which two or more component carriers (CCs) are aggregated to
support wider transmission bandwidths up to 100 MHz. Non-Patent
Document 1 describes the CA.
[0039] In the case where CA is configured, a UE has a single RRC
connection with a network (NW). In RRC connection, one serving cell
provides NAS mobility information and security input. This cell is
referred to as a primary cell (PCell). In downlink, a carrier
corresponding to PCell is a downlink primary component carrier (DL
PCC). In uplink, a carrier corresponding to PCell is an uplink
primary component carrier (UL PCC).
[0040] A secondary cell (SCell) is configured to form a serving
cell group with a PCell, in accordance with the UE capability. In
downlink, a carrier corresponding to SCell is a downlink secondary
component carrier (DL SCC). In uplink, a carrier corresponding to
SCell is an uplink secondary component carrier (UL SCC).
[0041] A serving cell group of one PCell and one or more SCells is
configured for one UE.
[0042] The new techniques in the LTE-A include the technique of
supporting wider bands (wider bandwidth extension) and the
coordinated multiple point transmission and reception (CoMP)
technique. The CoMP studied for LTE-A in 3GPP is described in
Non-Patent Document 1.
[0043] The traffic flow of a mobile network is on the rise, and the
communication rate is also increasing. It is expected that the
communication rate will be further increased when the operations of
the LTE and the LTE-A are fully initiated.
[0044] Furthermore, 3GPP is studying the use of small eNBs
(hereinafter also referred to as "small-scale base station
devices") configuring small cells to satisfy tremendous traffic in
the future. In an example technique under study, etc., a large
number of small eNBs will be installed to configure a large number
of small cells, thus increasing spectral efficiency and
communication capacity. The specific techniques include dual
connectivity (abbreviated as DC) in which a UE communicates with
two eNBs through connection thereto. Non-Patent Document 1
describes the DC.
[0045] Among eNBs that perform dual connectivity (DC), one of them
may be referred to as a master eNB (abbreviated as MeNB), and the
other may be referred to as a secondary eNB (abbreviated as
SeNB).
[0046] For increasingly sophisticated mobile communications, the
fifth generation (hereinafter also referred to as "5G") radio
access system is studied, whose service is aimed to be launched in
2020 and afterward. For example, in the Europe, an organization
named METIS summarizes the requirements for 5G (see Non-Patent
Document 5).
[0047] Among the requirements in the 5G radio access system are a
system capacity 1000 times as high as, a data transmission rate 100
times as high as, a data latency one tenth ( 1/10) as low as, and
simultaneously connected communication terminals 100 times as many
as those in the LTE system, to further reduce the power consumption
and device cost.
[0048] To satisfy such requirements, increasing the transmission
capacity of data using broadband frequencies, and increasing the
transmission rate of data through increase in the spectral
efficiency are being studied. To realize these, the techniques
enabling the spatial multiplexing such as the Multiple Input
Multiple Output (MIMO) and the beamforming using a multi-element
antenna are being studied.
[0049] The MIMO is continuously studied also in LTE-A. From Release
13, full dimension (FD)-MIMO is studied as the extension of the
MIMO, which uses two-dimensional antenna array. Non-Patent Document
7 describes the FD-MIMO.
[0050] It is studied that the 5G radio access system will be
installed concurrently with the LTE system in the initial period of
the launch of its service, which is scheduled in 2020. The
following configuration is considered. Specifically, a base station
for the LTE system (hereinafter may be referred to as an "LTE base
station") and a base station for the 5G radio access system
(hereinafter may be referred to as a "5G base station") are
connected using the dual connectivity (DC) configuration, and the
LTE base station is used as an MeNB and the 5G base station as an
SeNB.
[0051] In this configuration, it is considered that the LTE base
station, which has a larger cell range, processes control plane
(C-plane) data, and the LTE base station and the 5G base station
process user plane (U-plane) data. Non-Patent Document 8 describes
an example of this configuration.
PRIOR ART DOCUMENTS
Non-Patent Documents
[0052] Non-Patent Document 1: 3GPP TS 36.300 V13.0.0 [0053]
Non-Patent Document 2: 3GPP S1-083461 [0054] Non-Patent Document 3:
3GPP TR 36.814 V9.0.0 [0055] Non-Patent Document 4: 3GPP TR 36.912
V10.0.0 [0056] Non-Patent Document 5: "Scenarios, requirements and
KPIs for 5G mobile and wireless system", [online], Apr. 30, 2013,
ICT-317669-METIS/D1.1, [Searched on Jul. 15, 2016], Internet
<https://www.metis2020.com/documents/deliverables/> [0057]
Non-Patent Document 6: 3GPP TS36.211 V13.0.0 [0058] Non-Patent
Document 7: 3GPP TR36.897 V13.0.0 [0059] Non-Patent Document 8:
3GPP R2-163702
SUMMARY
Problem to be Solved by the Invention
[0060] A DC configuration of using an LTE base station as an MeNB
and a 5G base station as an SeNB is considered for a case when the
5G radio access system is introduced and a plurality of 5G base
stations are installed in one location. In this case, the LTE base
station needs to process pieces of control plane (C-plane) data of
the plurality of 5G base stations.
[0061] In addition, when the split bearer configuration is
employed, in which a packet data convergence protocol (PDCP) is
collected in the MeNB, there is also a problem concerning
processing of user plane (U-plane) data as follows. That is, since
the data amount of a 5G base station is large, the load on an LTE
base station due to processing is increased when a plurality of 5G
base stations as SeNBs are connected to an LTE base station as an
MeNB.
[0062] The present invention has an object to provide a
communication system capable of simplifying processing of at least
one of control plane data and user plane data when a communication
terminal device communicates with a plurality of base station
devices.
Means to Solve the Problem
[0063] A communication system according to the present invention
includes a communication terminal device, a plurality of base
station devices, and a core network. The plurality of base station
devices are configured to perform radio communication with the
communication terminal device. The core network is configured to
provide information about the communication with the communication
terminal device to the plurality of base station devices. The
plurality of base station devices include a master base station
device configured to perform main processing, and a plurality of
secondary base station devices to be connected to the master base
station device. At least one of control plane data about control of
the communication and user plane data about a user is transmitted
to and received from the communication terminal device via the
master base station device. The control plane data and the user
plane data are contained in the information provided by the core
network about the communication with the communication terminal
device.
Effects of the Invention
[0064] According to the communication system of the present
invention, at least one of control plane data about control of
communication and user plane data about a user is transmitted to
and received from a communication terminal device via a master base
station device. The control plane data and the user plane data are
contained in information provided by a core network about
communication with the communication terminal device. This
configuration simplifies processing of at least one of control
plane data and user plane data when the communication terminal
device communicates with a plurality of base station devices.
[0065] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0066] FIG. 1 is a diagram illustrating the configuration of a
radio frame for use in an LTE communication system.
[0067] FIG. 2 is a block diagram showing the overall configuration
of an L1E communication system 200 under discussion of 3GPP.
[0068] FIG. 3 is a block diagram showing the configuration of a
user equipment 202 shown in FIG. 2, which is a communication
terminal according to the present invention.
[0069] FIG. 4 is a block diagram showing the configuration of a
base station 203 shown in FIG. 2, which is a base station according
to the present invention.
[0070] FIG. 5 is a block diagram showing the configuration of an
MME according to the present invention.
[0071] FIG. 6 is a flowchart showing an outline from a cell search
to an idle state operation performed by a communication terminal
(UE) in the LTE communication system.
[0072] FIG. 7 shows the concept of a cell configuration when macro
eNBs and small eNBs coexist.
[0073] FIG. 8 is a diagram showing the configuration of a
conventional communication system 10.
[0074] FIG. 9 is a diagram showing the configuration of a
communication system 20 according to a first embodiment of the
present invention.
[0075] FIG. 10 is a diagram showing one example of frequencies of
transmission and reception waves used by the communication system
20 according to the first embodiment of the present invention.
[0076] FIG. 11 is a diagram showing one example of transmission and
reception waveforms used by the communication system 20 according
to the first embodiment of the present invention.
[0077] FIG. 12 is a diagram showing one example of frequencies of
transmission and reception waves used in the example shown in FIG.
11.
[0078] FIG. 13 is a diagram showing one example of the flow of data
in the communication system 20 according to the first embodiment of
the present invention.
[0079] FIG. 14 is a diagram showing one example of the flow of data
in a communication system 20A as another example of the
communication system according to the first embodiment of the
present invention.
[0080] FIG. 15 is a diagram showing one example of a sequence of
processing before the start of communication in the communication
system according to the first embodiment of the present
invention.
[0081] FIG. 16 is a diagram showing the configuration of a
communication system 40 according to a first modification of the
first embodiment of the present invention.
[0082] FIG. 17 is a diagram showing one example of the flow of data
in the communication system 40 according to the first modification
of the first embodiment of the present invention.
[0083] FIG. 18 is a diagram showing one example of a layout of
cells in the communication system 40 according to the first
modification of the first embodiment of the present invention.
[0084] FIG. 19 is a diagram showing one example of a sequence of
processing before the start of communication in the communication
system 40 according to the first modification of the first
embodiment of the present invention.
[0085] FIG. 20 is a diagram showing one example of frequencies of
transmission and reception waves used by a communication system
according to a second modification of the first embodiment of the
present invention.
[0086] FIG. 21 is a diagram showing one example of frequencies of
transmission and reception waves used by the communication system
according to the second modification of the first embodiment of the
present invention.
[0087] FIG. 22 is a diagram showing one example of frequencies of
transmission and reception waves used by the communication system
according to the second modification of the first embodiment of the
present invention.
[0088] FIG. 23 is a diagram showing one example of a sequence of
processing to change an executor of an RRC processing function for
a second system from a BS #2 to a BS #1.
[0089] FIG. 24 is a diagram showing one example of a sequence of
processing to change an executor of the RRC processing function for
the second system from the BS #1 to the BS #2.
[0090] FIG. 25 is a diagram showing the configuration of a
communication system 60 according to a second embodiment of the
present invention.
[0091] FIG. 26 is a diagram showing one example of a sequence of
processing to acquire broadcast information in the communication
system 60 according to the second embodiment of the present
invention.
[0092] FIG. 27 is a diagram showing one example of a sequence of
processing to notify of broadcast information based on a request of
a UE.
[0093] FIG. 28 is a diagram showing another example of a sequence
of processing to notify of broadcast information based on a request
of the UE.
[0094] FIG. 29 is a block diagram showing the configuration of a
communication system 80 according to a third embodiment of the
present invention.
[0095] FIG. 30 is a block diagram showing the configuration of a
communication system 80A as another example of the communication
system according to the third embodiment of the present
invention.
[0096] FIG. 31 is a block diagram showing the configuration of a
communication system 90 as still another example of the
communication system according to the third embodiment of the
present invention.
[0097] FIG. 32 is a diagram showing one example of a sequence of
measurement report processing of a communication system according
to a fourth embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0098] FIG. 2 is a block diagram showing an overall configuration
of an LTE communication system 200, which is under discussion of
3GPP. FIG. 2 will be described. A radio access network is referred
to as an evolved universal terrestrial radio access network
(E-UTRAN) 201. A user equipment device (hereinafter, referred to as
a "user equipment (UE)") 202 that is a communication terminal
device is capable of radio communication with a base station device
(hereinafter, referred to as a "base station (E-UTRAN Node B:
eNB)") 203 and transmits and receives signals through radio
communication.
[0099] Here, the "communication terminal device" covers not only a
user equipment device such as a movable mobile phone terminal
device, but also an unmovable device such as a sensor. In the
following description, the "communication terminal device" may be
simply referred to as a "communication terminal".
[0100] The E-UTRAN is composed of one or a plurality of base
stations 203, provided that a control protocol for the user
equipment 202 such as a radio resource control (abbreviated as
RRC), and user planes such as a packet data convergence protocol
(PDCP), radio link control (RLC), medium access control (MAC), or
physical layer (PHY) are terminated in the base station 203.
[0101] The control protocol radio resource control (RRC) between
the user equipment 202 and the base station 203 performs broadcast,
paging, RRC connection management, and the like. The states of the
base station 203 and the user equipment 202 in RRC are classified
into RRC IDLE and RRC_CONNECTED.
[0102] In RRC IDLE, public land mobile network (PLMN) selection,
system information (SI) broadcast, paging, cell re-selection,
mobility, and the like are performed. In RRC_CONNECTED, the user
equipment has RRC connection and is capable of transmitting and
receiving data to and from a network. In RRC_CONNECTED, for
example, handover (HO) and measurement of a neighbor cell are
performed.
[0103] The base stations 203 are classified into eNBs 207 and
Home-eNBs 206. The communication system 200 includes an eNB group
203-1 including a plurality of eNBs 207 and a Home-eNB group 203-2
including a plurality of Home-eNBs 206. A system, composed of an
evolved packet core (EPC) being a core network and an E-UTRAN 201
being a radio access network, is referred to as an evolved packet
system (EPS). The EPC being a core network and the E-UTRAN 201
being a radio access network may be collectively referred to as a
"network".
[0104] The eNB 207 is connected to an MME/S-GW unit (hereinafter,
also referred to as an "MME unit") 204 including a mobility
management entity (MME), a serving gateway (S-GW), or an MME and an
S-GW by means of an S1 interface, and control information is
communicated between the eNB 207 and the MME unit 204. A plurality
of MME units 204 may be connected to one eNB 207. The eNBs 207 are
connected to each other by means of an X2 interface, and control
information is communicated between the eNBs 207.
[0105] The Home-eNB 206 is connected to the MME unit 204 by means
of an S1 interface, and control information is communicated between
the Home-eNB 206 and the MME unit 204. A plurality of Home-eNBs 206
are connected to one MME unit 204. Or, the Home-eNBs 206 are
connected to the MME units 204 through a Home-eNB gateway (HeNBGW)
205. The Home-eNB 206 is connected to the HeNBGW 205 by means of an
S1 interface, and the HeNBGW 205 is connected to the MME unit 204
by means of an S1 interface.
[0106] One or a plurality of Home-eNBs 206 are connected to one
HeNBGW 205, and information is communicated therebetween through an
S1 interface. The HeNBGW 205 is connected to one or a plurality of
MME units 204, and information is communicated therebetween through
an S1 interface.
[0107] The MME units 204 and HeNBGW 205 are entities of higher
layer, specifically, higher nodes, and control the connections
between the user equipment (UE) 202 and the eNB 207 and the
Home-eNB 206 being base stations. The MME units 204 configure an
EPC being a core network. The base station 203 and the HeNBGW 205
configure the E-UTRAN 201.
[0108] Further, 3GPP is studying the configuration below. The X2
interface between the Home-eNBs 206 is supported. In other words,
the Home-eNBs 206 are connected to each other by means of an X2
interface, and control information is communicated between the
Home-eNBs 206. The HeNBGW 205 appears to the MME unit 204 as the
Home-eNB 206. The HeNBGW 205 appears to the Home-eNB 206 as the MME
unit 204.
[0109] The interfaces between the Home-eNBs 206 and the MME units
204 are the same, which are the S1 interfaces, in both cases where
the Home-eNB 206 is connected to the MME unit 204 through the
HeNBGW 205 and it is directly connected to the MME unit 204.
[0110] The base station 203 may configure a single cell or a
plurality of cells. Each cell has a range predetermined as a
coverage in which the cell can communicate with the user equipment
202 and performs radio communication with the user equipment 202
within the coverage. In the case where one base station 203
configures a plurality of cells, every cell is configured so as to
communicate with the user equipment 202.
[0111] FIG. 3 is a block diagram showing the configuration of the
user equipment 202 of FIG. 2 that is a communication terminal
according to the present invention. The transmission process of the
user equipment 202 shown in FIG. 3 will be described. First, a
transmission data buffer unit 303 stores the control data from a
protocol processing unit 301 and the user data from an application
unit 302. The data stored in the transmission data buffer unit 303
is passed to an encoding unit 304 and is subjected to an encoding
process such as error correction. There may exist the data output
from the transmission data buffer unit 303 directly to a modulating
unit 305 without the encoding process. The data encoded by the
encoding unit 304 is modulated by the modulating unit 305. The
modulated data is converted into a baseband signal, and the
baseband signal is output to a frequency converting unit 306 and is
then converted into a radio transmission frequency. After that, a
transmission signal is transmitted from an antenna 307 to the base
station 203.
[0112] The user equipment 202 executes the reception process as
follows. The radio signal from the base station 203 is received
through the antenna 307. The received signal is converted from a
radio reception frequency into a baseband signal by the frequency
converting unit 306 and is then demodulated by a demodulating unit
308. The demodulated data is passed to a decoding unit 309 and is
subjected to a decoding process such as error correction. Among the
pieces of decoded data, the control data is passed to the protocol
processing unit 301, and the user data is passed to the application
unit 302. A series of processes by the user equipment 202 is
controlled by a control unit 310. This means that, though not shown
in FIG. 3, the control unit 310 is connected to the individual
units 301 to 309.
[0113] FIG. 4 is a block diagram showing the configuration of the
base station 203 of FIG. 2 that is a base station according to the
present invention. The transmission process of the base station 203
shown in FIG. 4 will be described. An EPC communication unit 401
performs data transmission and reception between the base station
203 and the EPC (such as the MME unit 204), HeNBGW 205, and the
like. A communication with another base station unit 402 performs
data transmission and reception to and from another base station.
The EPC communication unit 401 and the communication with another
base station unit 402 each transmit and receive information to and
from a protocol processing unit 403. The control data from the
protocol processing unit 403, and the user data and the control
data from the EPC communication unit 401 and the communication with
another base station unit 402 are stored in a transmission data
buffer unit 404.
[0114] The data stored in the transmission data buffer unit 404 is
passed to an encoding unit 405 and is then subjected to an encoding
process such as error correction. There may exist the data output
from the transmission data buffer unit 404 directly to a modulating
unit 406 without the encoding process. The encoded data is
modulated by the modulating unit 406. The modulated data is
converted into a baseband signal, and the baseband signal is output
to a frequency converting unit 407 and is then converted into a
radio transmission frequency. After that, a transmission signal is
transmitted from an antenna 408 to one or a plurality of user
equipments 202.
[0115] The reception process of the base station 203 is executed as
follows. A radio signal from one or a plurality of user equipments
202 is received through the antenna 408. The received signal is
converted from a radio reception frequency into a baseband signal
by the frequency converting unit 407, and is then demodulated by a
demodulating unit 409. The demodulated data is passed to a decoding
unit 410 and is then subjected to a decoding process such as error
correction. Among the pieces of decoded data, the control data is
passed to the protocol processing unit 403, the EPC communication
unit 401, or the communication with another base station unit 402,
and the user data is passed to the EPC communication unit 401 and
the communication with another base station unit 402. A series of
processes by the base station 203 is controlled by a control unit
411. This means that, though not shown in FIG. 4, the control unit
411 is connected to the individual units 401 to 410.
[0116] FIG. 5 is a block diagram showing the configuration of the
MME according to the present invention. FIG. 5 shows the
configuration of an MME 204a included in the MME unit 204 shown in
FIG. 2 described above. A PDN GW communication unit 501 performs
data transmission and reception between the MME 204a and the PDN
GW. A base station communication unit 502 performs data
transmission and reception between the MME 204a and the base
station 203 by means of the S1 interface. In the case where the
data received from the PDN GW is user data, the user data is passed
from the PDN GW communication unit 501 to the base station
communication unit 502 via a user plane communication unit 503 and
is then transmitted to one or a plurality of base stations 203. In
the case where the data received from the base station 203 is user
data, the user data is passed from the base station communication
unit 502 to the PDN GW communication unit 501 via the user plane
communication unit 503 and is then transmitted to the PDN GW.
[0117] In the case where the data received from the PDN GW is
control data, the control data is passed from the PDN GW
communication unit 501 to a control plane control unit 505. In the
case where the data received from the base station 203 is control
data, the control data is passed from the base station
communication unit 502 to the control plane control unit 505.
[0118] A HeNBGW communication unit 504 is provided in the case
where the HeNBGW 205 is provided, which performs data transmission
and reception between the MME 204a and the HeNBGW 205 by means of
the interface (IF) according to an information type. The control
data received from the HeNBGW communication unit 504 is passed from
the HeNBGW communication unit 504 to the control plane control unit
505. The processing results of the control plane control unit 505
are transmitted to the PDN GW via the PDN GW communication unit
501. The processing results of the control plane control unit 505
are transmitted to one or a plurality of base stations 203 by means
of the S1 interface via the base station communication unit 502,
and are transmitted to one or a plurality of HeNBGWs 205 via the
HeNBGW communication unit 504.
[0119] The control plane control unit 505 includes a NAS security
unit 505-1, an SAE bearer control unit 505-2, and an idle state
mobility managing unit 505-3, and performs an overall process for
the control plane. The NAS security unit 505-1 provides, for
example, security of a non-access stratum (NAS) message. The SAE
bearer control unit 505-2 manages, for example, a system
architecture evolution (SAE) bearer. The idle state mobility
managing unit 505-3 performs, for example, mobility management of
an idle state (LTE-IDLE state, which is merely referred to as idle
as well), generation and control of a paging signal in the idle
state, addition, deletion, update, and search of a tracking area of
one or a plurality of user equipments 202 being served thereby, and
tracking area list management.
[0120] The MME 204a distributes a paging signal to one or a
plurality of base stations 203. In addition, the MME 204a performs
mobility control of an idle state. When the user equipment is in
the idle state and an active state, the MME 204a manages a list of
tracking areas. The MME 204a begins a paging protocol by
transmitting a paging message to the cell belonging to a tracking
area in which the UE is registered. The idle state mobility
managing unit 505-3 may manage the CSG of the Home-eNBs 206 to be
connected to the MME 204a, CSG IDs, and a whitelist.
[0121] An example of a cell search method in a mobile communication
system will be described next. FIG. 6 is a flowchart showing an
outline from a cell search to an idle state operation performed by
a communication terminal (UE) in the LTE communication system. When
starting a cell search, in Step ST601, the communication terminal
synchronizes slot timing and frame timing by a primary
synchronization signal (P-SS) and a secondary synchronization
signal (S-SS) transmitted from a neighbor base station.
[0122] The P-SS and S-SS are collectively referred to as a
synchronization signal (SS). Synchronization codes, which
correspond one-to-one to PCIs assigned per cell, are assigned to
the synchronization signals (SSs). The number of PCIs is currently
studied in 504 ways. The 504 ways of PCIs are used for
synchronization, and the PCIs of the synchronized cells are
detected (specified).
[0123] In Step ST602, next, the user equipment detects a
cell-specific reference signal (CRS) being a reference signal (RS)
transmitted from the base station per cell and measures the
reference signal received power (RSRP). The codes corresponding
one-to-one to the PCIs are used for the reference signal RS.
Separation from another cell is enabled by correlation using the
code. The code for RS of the cell is derived from the PCI specified
in Step ST601, so that the RS can be detected and the RS received
power can be measured.
[0124] In Step ST603, next, the user equipment selects the cell
having the best RS received quality, for example, the cell having
the highest RS received power, that is, the best cell, from one or
more cells that have been detected up to Step ST602.
[0125] In Step ST604, next, the user equipment receives the PBCH of
the best cell and obtains the BCCH that is the broadcast
information. A master information block (MIB) containing the cell
configuration information is mapped to the BCCH over the PBCH.
Accordingly, the MIB is obtained by obtaining the BCCH through
reception of the PBCH. Examples of the MIB information include the
downlink (DL) system bandwidth (also referred to as a transmission
bandwidth configuration (dl-bandwidth)), the number of transmission
antennas, and a system frame number (SFN).
[0126] In Step ST605, next, the user equipment receives the DL-SCH
of the cell based on the cell configuration information of the MIB,
to thereby obtain a system information block (SIB) 1 of the
broadcast information BCCH. The SIB1 contains the information about
the access to the cell, information about cell selection, and
scheduling information on another SIB (SIBk; k is an integer equal
to or greater than two). In addition, the SIB1 contains a tracking
area code (TAC).
[0127] In Step ST606, next, the communication terminal compares the
TAC of the SIB1 received in Step ST605 with the TAC portion of a
tracking area identity (TM) in the tracking area list that has
already been possessed by the communication terminal. The tracking
area list is also referred to as a TM list. TM is the
identification information for identifying tracking areas and is
composed of a mobile country code (MCC), a mobile network code
(MNC), and a tracking area code (TAC). MCC is a country code. MNC
is a network code. TAC is the code number of a tracking area.
[0128] If the result of the comparison of Step ST606 shows that the
TAC received in Step ST605 is identical to the TAC included in the
tracking area list, the user equipment enters an idle state
operation in the cell. If the comparison shows that the TAC
received in Step ST605 is not included in the tracking area list,
the communication terminal requires a core network (EPC) including
MME and the like to change a tracking area through the cell for
performing tracking area update (TAU).
[0129] The device configuring a core network (hereinafter, also
referred to as a "core-network-side device") updates the tracking
area list based on an identification number (such as UE-ID) of a
communication terminal transmitted from the communication terminal
together with a TAU request signal. The core-network-side device
transmits the updated tracking area list to the communication
terminal. The communication terminal rewrites (updates) the TAC
list of the communication terminal based on the received tracking
area list. After that, the communication terminal enters the idle
state operation in the cell.
[0130] Widespread use of smartphones and tablet terminal devices
explosively increases traffic in cellular radio communications,
causing a fear of insufficient radio resources all over the world.
To increase spectral efficiency, thus, it is studied to downsize
cells for further spatial separation.
[0131] In the conventional configuration of cells, the cell
configured by an eNB has a relatively-wide-range coverage.
Conventionally, cells are configured such that
relatively-wide-range coverages of a plurality of cells configured
by a plurality of eNBs cover a certain area.
[0132] When cells are downsized, the cell configured by an eNB has
a narrow-range coverage compared with the coverage of a cell
configured by a conventional eNB. Thus, in order to cover a certain
area as in the conventional case, a larger number of downsized eNBs
than the conventional eNBs are required.
[0133] In the description below, a "macro cell" refers to a cell
having a relatively wide coverage, such as a cell configured by a
conventional eNB, and a "macro eNB" refers to an eNB configuring a
macro cell. A "small cell" refers to a cell having a relatively
narrow coverage, such as a downsized cell, and a "small eNB" refers
to an eNB configuring a small cell.
[0134] The macro eNB may be, for example, a "wide area base
station" described in Non-Patent Document 7.
[0135] The small eNB may be, for example, a low power node, local
area node, or hotspot. Alternatively, the small eNB may be a pico
eNB configuring a pico cell, a femto eNB configuring a femto cell,
HeNB, remote radio head (RRH), remote radio unit (RRU), remote
radio equipment (RRE), or relay node (RN). Still alternatively, the
small eNB may be a "local area base station" or "home base station"
described in Non-Patent Document 7.
[0136] FIG. 7 shows the concept of the cell configuration in which
macro eNBs and small eNBs coexist. The macro cell configured by a
macro eNB has a relatively-wide-range coverage 701. A small cell
configured by a small eNB has a coverage 702 whose range is
narrower than that of the coverage 701 of a macro eNB (macro
cell).
[0137] When a plurality of eNBs coexist, the coverage of the cell
configured by an eNB may be included in the coverage of the cell
configured by another eNB. In the cell configuration shown in FIG.
7, as indicated by a reference "704" or "705", the coverage 702 of
the small cell configured by a small eNB may be included in the
coverage 701 of the macro cell configured by a macro eNB.
[0138] As indicated by the reference "705", the coverages 702 of a
plurality of, for example, two small cells may be included in the
coverage 701 of one macro cell. A user equipment (UE) 703 is
included in, for example, the coverage 702 of the small cell and
performs communication via the small cell.
[0139] In the cell configuration shown in FIG. 7, as indicated by a
reference "706", the coverage 701 of the macro cell configured by a
macro eNB may overlap the coverages 702 of the small cells
configured by small eNBs in a complicated manner.
[0140] As indicated by a reference "707", the coverage 701 of the
macro cell configured by a macro eNB may not overlap the coverages
702 of the small cells configured by small eNBs.
[0141] Further, as indicated by a reference "708", the coverages
702 of a large number of small cells configured by a large number
of small eNBs may be configured in the coverage 701 of one macro
cell configured by one macro eNB.
[0142] In the fifth generation (5G), which is a forthcoming radio
access system aimed to be commercialized in 2018 to 2020, an
architecture of concurrently installing an LTE base station for the
LTE-A system and a 5G base station for the 5G system is
considered.
[0143] In LTE-A, the configuration of dual connectivity
(abbreviated as DC) establishes a master-subordinate relationship
of a master eNB (MeNB) and a secondary eNB (SeNB) between two base
stations. The MeNB corresponds to a master base station device, and
the SeNB corresponds to a secondary base station device. It is
considered that the control plane (C-plane) data is processed
solely by the MeNB, and the user plane (U-plane) data is processed
by the MeNB and the SeNB.
[0144] FIG. 8 is a diagram showing the configuration of a
conventional communication system 10. A first base station 11
(hereinafter may be referred to as a "BS #1") as an MeNB is
connected to a core network 15 by means of an S1 interface, and is
connected to a second base station 12 (hereinafter may be referred
to as a "BS #2") as an SeNB by means of an Xn interface. A third
base station 13 (hereinafter may be referred to as a "BS #3"),
which is installed independently of other base stations, is
connected to the core network 15 by means of the S1 interface.
[0145] In 5G, in addition to LTE-A, a plurality of base stations
using different frequencies are connected. Further, the data amount
of each base station is also large.
[0146] In view of this, a configuration of using LTE-A for the MeNB
11 is considered. The reason is that LTE-A can cover a relatively
wide cell radius. Specifically, the reason is that LTE-A can cover
a cell in a relatively wide range in a plan view due to its use of
low frequencies as well as a large number of already installed base
stations present because those base stations are the existing base
stations.
[0147] A base station of the 5G radio system is allocated to the
SeNB 12. In this case, it is likely that a base station
(hereinafter may be referred to as a "low SHF base station") that
uses low super high frequency (SHF) of frequencies of 6 GHz or
lower and a base station (hereinafter may be referred to as a "high
SHF base station") that uses high SHF of frequencies exceeding 6
GHz are installed concurrently.
[0148] In this case, the DC configuration allows only a single SeNB
12, e.g., only a single low SHF base station, to be allocated to
one MeNB 11. Another base station, e.g., a high SHF base station,
is only allowed to be installed as a standalone base station 13
that is independent of other base stations. That is, a
configuration in which a single MeNB 11 is connected to a plurality
of SeNBs 12 is not possible.
[0149] Accordingly, even when a user equipment (hereinafter may be
referred to as a "UE") 14 is capable of concurrently communicating
with three or more base stations, communication paths for pieces of
control plane (C-plane) information cannot be integrated into one.
Therefore, control is required such that mismatch between a
plurality of pieces of control plane (C-plane) information does not
occur in the UE 14.
[0150] Further, even if a plurality of SeNBs 12 are connected,
pieces of control plane (C-plane) information are concentrated at a
single MeNB 11, which may cause processing capacity of the MeNB 11
to be a bottleneck in the network.
[0151] The present embodiment has a configuration in which a single
base station corresponding to an MeNB is capable of executing
processing of pieces of control plane (C-plane) data of a plurality
of base stations that are connected as SeNBs. Further, the present
embodiment has a configuration in which a single base station
corresponding to an MeNB is also similarly capable of executing
processing of pieces of user plane (U-plane) data.
[0152] That is, in the present embodiment, control plane (C-plane)
data about control of communication, which is contained in
information provided by the core network about communication with
the UE, is transmitted to and received from the UE via a single
base station corresponding to an MeNB. This can simplify processing
of control plane (C-plane) data performed by a communication
terminal capable of concurrently communicating with a plurality of
base stations.
[0153] FIG. 9 is a diagram showing the configuration of a
communication system 20 according to a first embodiment of the
present invention. The communication system 20 includes a first
base station 21 (hereinafter may be referred to as a "BS #1"), a
second base station 22 (hereinafter may be referred to as a "BS
#2"), a third base station 23 (hereinafter may be referred to as a
"BS #3"), and a user equipment (UE) 24. The BS #1 is installed as
an MeNB. The BS #2 is installed as a first SeNB (hereinafter may be
referred to as a "SeNB #1"). The BS #3 is installed as a second
SeNB (hereinafter may be referred to as a "SeNB #2").
[0154] The MeNB corresponds to a master base station device. The
master base station device performs main processing. The main
processing is, for example, aggregation processing of the dual
connectivity (DC). The first SeNB and the second SeNB each
correspond to a secondary base station device. The first SeNB and
the second SeNB are each connected to the MeNB.
[0155] A single UE 24 concurrently communicates with the three base
stations 21 to 23, i.e., the BS #1, the BS #2, and the BS #3.
Concerning the three base stations, for example, the BS #1 is
considered to be a base station of LTE-A, the BS #2 to be a base
station of 5G, and the BS #3 to be a base station of 5G. An
interface allowing direct communication, i.e., an Xn interface in
this case, is provided between the BS #1 and the BS #2 and also
between the BS #1 and the BS #3.
[0156] The UE 24 communicates control plane (C-plane) data with the
BS #1. Further, the UE 24 communications user plane (U-plane) data
with each of the BS #1, the BS #2, and the BS #3.
[0157] FIG. 10 is a diagram showing one example of frequencies of
transmission and reception waves used by the communication system
20 according to the first embodiment of the present invention. In
FIG. 10, the horizontal axis represents frequency f. In the present
embodiment, for example, as shown in FIG. 10, the first base
station 21 installed as an MeNB, the second base station 22
installed as an SeNB #1, and the third base station 23 installed as
an SeNB #2 use transmission and reception waves of different
frequency bands.
[0158] FIG. 11 is a diagram showing one example of transmission and
reception waveforms used by the communication system 20 according
to the first embodiment of the present invention. FIG. 12 is a
diagram showing one example of frequencies of transmission and
reception waves used in the example shown in FIG. 11. FIG. 11 and
FIG. 12 show a case where the base stations 22 and 23 and the UE 24
each use an array antenna as their transmission and reception
antenna. In this case, as shown in FIG. 11, beam-shaped
transmission and reception waveforms 31 to 35 having directivity
are used. This configuration can improve spatial separation.
[0159] Accordingly, as shown in FIG. 12, a plurality of base
stations can be concurrently allocated to the same frequency band.
In the example shown in FIG. 12, one MeNB and two SeNBs use
transmission and reception waves of different frequency bands,
while the SeNB #1 and the SeNB #2 use transmission and reception
waves of the same frequency band.
[0160] FIG. 13 is a diagram showing one example of the flow of data
in the communication system 20 according to the first embodiment of
the present invention. As shown in FIG. 13, for example, user plane
(U-plane) data is transmitted and received through communication
between a core network device 25 as an upper layer device (a next
generation core network) and each of the base stations, i.e., the
first base station 21 (hereinafter may be referred to as a "BS
#1"), the second base station (hereinafter may be referred to as a
"BS #2"), and the third base station (hereinafter may be referred
to as a "BS #3"), and is also transmitted and received through
communication between each of the base stations and the UE 24.
[0161] The user plane (U-plane) data is not limited thereto, and
may be transmitted and received through communication between one
base station, e.g., the BS #1, and the core network device 25 as an
upper layer device, through communication between the BS #1 and the
UE 24, and through communication between the BS #1 and the UE 24
via the BS #2 or BS #3.
[0162] In the present embodiment, control plane (C-plane) data is
transmitted and received only through communication between the BS
#1 and the UE 24. The communication between the BS #1 and the UE 24
may be performed as direct communication between the BS #1 and the
UE 24, or may be performed via another base station, such as the BS
#3 or the BS #4.
[0163] FIG. 14 is a diagram showing one example of the flow of data
in a communication system 20A as another example of the
communication system according to the first embodiment of the
present invention. The communication system 20A shown in FIG. 14
includes the same components as those of the communication system
20 shown in FIG. 13, and therefore the same components are denoted
by the same reference symbols to omit common description.
[0164] As shown in FIG. 14, control plane (C-plane) data is
transmitted and received through communication between the core
network device 25 corresponding to an MME and the BS #1.
[0165] The control plane (C-plane) data may be transmitted and
received through communication between the BS #1 and the UE 24.
Further, as shown in FIG. 14, the control plane (C-plane) data may
be transmitted and received through communication with the UE 24
via radio resources of the BS #2 and the BS #3, in addition to the
communication between the BS #1 and the UE 24.
[0166] FIG. 15 is a diagram showing one example of a sequence of
processing before the start of communication in the communication
system according to the first embodiment of the present invention.
FIG. 15 shows a sequence of adding the BS #2 and the BS #3 in a
state where the BS #1 and the UE are connected.
[0167] In Step ST11, the BS #1, the BS #2, the BS #3, and the UE
are connected.
[0168] In Step ST12, the BS #1 notifies the BS #2 of a resource
allocation request. In Step ST13, the BS #2 notifies the BS #1 of a
request acknowledgement.
[0169] In Step ST14, the BS #1 notifies the UE of an addition
request of the BS #2. In Step ST15, the UE notifies the BS #1 of an
addition request acknowledgement. The UE measures a specified
synchronization signal of the BS #2.
[0170] In Step ST16, the UE synchronizes with a downlink (DL) of
the BS #2.
[0171] In Step ST17, the BS #2 notifies the UE of channel control,
such as a PDCCH.
[0172] In Step ST18, the UE starts communication of user plane
(U-plane) data based on a resource allocation condition of the
downlink signal specified by the PDCCH.
[0173] In Step ST19, the BS #1 notifies the BS #3 of a resource
allocation request. In Step ST20, the BS #3 notifies the BS #1 of a
request acknowledgement.
[0174] In Step ST21, the BS #1 notifies the UE of an addition
request of the BS #3. In Step ST22, the UE notifies the BS #1 of an
addition request acknowledgement. The UE measures a specified
synchronization signal of the BS #3.
[0175] In Step ST23, the UE synchronizes with a downlink (DL) of
the BS #3.
[0176] In Step ST24, the BS #3 notifies the UE of channel control,
such as a PDCCH.
[0177] In Step ST25, the UE starts communication of user plane
(U-plane) data based on a resource allocation condition of the
downlink signal specified by the PDCCH.
[0178] Deletion of a base station is executed similarly. Deletion
is executed based on a deletion command of the BS #1 transmitted to
the UE.
[0179] UEs and base stations compatible with the 5G standard may
use an array antenna as their transmission and reception antenna.
In such a case, the use of beam-shaped transmission and reception
waveforms having directivity can improve spatial separation.
Accordingly, a plurality of base stations may be concurrently
allocated to the same frequency band as shown in FIG. 13.
[0180] When beams are used, information as to which beam should be
selected, such as a beam ID, may be in some cases added to the
addition request signal of the BS #2 in Step ST14 and to the
addition request signal of the BS #3 in Step ST21 of FIG. 15. In
such a case, a beam for receiving PDCCH can be selected, and thus
the PDCCH information need not be transmitted via all of the beams,
which can lead to efficient use of channel resources.
[0181] Alternatively, information as to the selection of a beam can
be added to the PDCCH. In such a case, the BS #1 need not consider
beam control. Accordingly, when a plurality of base stations are
connected to the BS #1, resource allocation processing of the BS #1
is reduced, and the processing load can be distributed as a system.
Even if the BS #1 is a device having limited processing capacity,
e.g., an LTE-A base station, processing can be performed while such
limited processing capacity is prevented from turning into a
bottleneck.
[0182] According to the present embodiment as described above,
control plane (C-plane) data contained in information provided by
the core network about communication with the UE is transmitted to
and received from the UE via the MeNB. This can simplify processing
of control plane (C-plane) data when the UE communicates with a
plurality of base stations.
[0183] Specifically, in the embodiment, the core network provides
control plane (C-plane) data to the MeNB. The MeNB then provides
the control plane (C-plane) data provided by the core network to
the UE, and to the UE also via a plurality of SeNBs. This can
simplify processing of control plane (C-plane) data performed by a
UE capable of concurrently communicating with a plurality of base
stations.
First Modification of First Embodiment
[0184] As a first modification of the first embodiment, there is a
configuration in which part of processing of control plane
(C-plane) data is distributed to a base station other than the
MeNB, e.g., to a BS #2 described below. FIG. 16 is a diagram
showing the configuration of a communication system 40 according to
a first modification of the first embodiment of the present
invention. The communication system 40 includes a first base
station 41 (hereinafter may be referred to as a "BS #1"), a second
base station 42 (hereinafter may be referred to as a "BS #2"), a
third base station 43 (hereinafter may be referred to as a "BS
#3"), a fourth base station 44 (hereinafter may be referred to as a
"BS #4"), a user equipment (UE) 45, and a core network 46.
[0185] The present modification shows a case where the BS #1 is a
base station for LTE-A, and the BS #2, the BS #3, and the BS #4 are
each a base station for 5G. RRC messages for the 5G standard are
characterized in being transmitted and received collectively by the
BS #2.
[0186] The BS #1 and the BS #2 are connected by means of an
interface between base stations, specifically an Xn interface.
Further, the BS #2 and the BS #3 as well as the BS #2 and the BS #4
are connected by means of an interface between base stations,
specifically an Xn interface. The BS #1 and the core network 46 are
connected by means of an S1 interface.
[0187] The BS #1 handles RRC messages for the BS #1, and control
plane (C-plane) information for adding the BS #2.
[0188] Meanwhile, the BS #2 handles control plane (C-plane)
information for the BS #2, the BS #3, and the BS #4. The UE 45
transmits and receives the control plane (C-plane) information to
and from the BS #1 and the BS #2.
[0189] Adopting the configuration shown in FIG. 16, the BS #1 no
longer needs to handle RRC messages of a new system such as 5G.
Therefore, even in a system configuration where a new system such
as 5G is connected, a new system can be easily introduced.
[0190] FIG. 17 is a diagram showing one example of the flow of data
in the communication system 40 according to the first modification
of the first embodiment of the present invention. FIG. 17 shows an
example of a layout of RRC processing functions. The BS #1 employs
a first radio system (hereinafter may be referred to as a "first
system") of LTE-A, for example. The BS #2, the BS #3, and the BS #4
each employ a second radio system (hereinafter may be referred to
as a "second system") of 5G, for example.
[0191] The BS #1 has a function of RRC processing for the first
system. The BS #2 has a function of RRC processing for the second
system. The RRC messages for the first system may be transmitted
and received between the BS #1 and the UE, or may be communicated
to the UE via a radio resource of the BS #2.
[0192] Meanwhile, the BS #2 has a function of RRC processing for
the second system. RRC messages for the second system may be
transmitted and received between the BS #2 and the UE, or may be
communicated to the UE via radio resources of the BS #3 and the BS
#4. Control plane (C-plane) information for the second system is
transmitted and received through communication between the core
network 46 and the BS #2. The communication between the core
network 46 and the BS #2 may be performed as direct communication
between the core network 46 and the BS #2, or may be performed as
communication via the BS #1.
[0193] Separating the RRC processing functions for respective radio
systems can maintain independency of each of the radio systems.
Therefore, influence upon other radio systems can be reduced to the
extent possible even when a new system is introduced.
[0194] Further, connecting a plurality of base stations with
association between radio systems as in the dual connectivity can
improve connectivity of a UE, and can smoothly add and delete a
cell. The "connectivity of a UE" herein refers to the easiness of
connection between a UE and a base station.
[0195] FIG. 18 is a diagram showing one example of a layout of
cells in the communication system 40 according to the first
modification of the first embodiment of the present invention. The
connection between the BS #1 and the UE can be maintained in a wide
range in the case as shown in FIG. 18, for example. That is, the BS
#1 forms a macro cell 51 having a cell radius of 500 m, for
example, the BS #2 forms a micro cell 52 having a cell radius of
200 in, for example, and the BS #3 and the BS #4 respectively form
small cells 53 and 54 each having a cell radius of 50 m, for
example.
[0196] In the example shown in FIG. 18, a BS #2' as another second
base station 42A exists in the cell 51 of the BS #1. For example,
similarly to the BS #2, the BS #2' forms a micro cell 52A having a
cell radius of 200 m. In the cell 52A of the BS #2', a BS #5 as a
fifth base station 45 exists. For example, similarly to the BS #3
and the BS #4, the BS #5 forms a small cell 55 having a cell radius
of 50 m, for example.
[0197] Since such a large number of base stations 42, 42A, and 43
to 45 exist in the cell 51 of the BS #1, the BS #1 is subjected to
a large processing load if intending to process, for all of the
base stations 42, 42A, and 43 to 45, the pieces of control plane
(C-plane) data for a plurality of base stations described in the
first embodiment.
[0198] In view of this, in the present modification, the BS #2
executes processing of control plane (C-plane) data of the BS #2
and processing of control plane (C-plane) data of the BS #3 and the
BS #4 that are base stations running under the cell 52 of the BS
#2. This configuration can reduce the load on the BS #1 due to the
processing. Further, it is preferable that the BS #2' also executes
processing of control plane (C-plane) data of the BS #2' and
processing of control place (C-plane) data of the BS #5 that is a
base station running under the cell 52A of the BS #2'. This can
further reduce the load on the BS #1 due to the processing.
[0199] FIG. 19 is a diagram showing one example of a sequence of
processing before the start of communication in the communication
system 40 according to the first modification of the first
embodiment of the present invention. FIG. 19 shows an example of a
sequence for establishing connection with a plurality of base
stations. FIG. 19 shows a sequence of adding the BS #2, the BS #3,
and the BS #4 in a state where the BS #1 and the UE are
connected.
[0200] In Step ST31, the BS #1 and the UE are connected.
[0201] In Step ST32, the BS #1 notifies the BS #2 of a resource
allocation request. In Step ST33, the BS #2 notifies the BS #1 of a
request acknowledgement.
[0202] In Step ST34, the BS #1 notifies the UE of an addition
request of the BS #2. In Step ST35, the UE notifies the BS #1 of an
addition request acknowledgement. The UE measures a specified
synchronization signal of the BS #2.
[0203] In Step ST36, the UE synchronizes with a downlink (DL) of
the BS #2.
[0204] In Step ST37, the BS #2 notifies the UE of channel control,
such as a PDCCH.
[0205] In Step ST38, the UE starts communication of user plane
(U-plane) data based on a resource allocation condition of the
downlink signal specified by the PDCCH.
[0206] In Step ST39, the BS #2 notifies the BS #3 of a resource
allocation request. In Step ST40, the BS #3 notifies the BS #2 of a
request acknowledgement.
[0207] In Step ST41, the BS #2 notifies the UE of an addition
request of the BS #3.
[0208] In Step ST42, the UE notifies the BS #2 of an addition
request acknowledgement. The UE measures a specified
synchronization signal of the BS #3.
[0209] In Step ST43, the UE synchronizes with a downlink (DL) of
the BS #3.
[0210] In Step ST44, the BS #3 notifies the UE of channel control,
such as a PDCCH.
[0211] In Step ST45, the UE starts communication of user plane
(U-plane) data based on a resource allocation condition of the
downlink signal specified by the PDCCH.
[0212] In Step ST46, the BS #2 notifies the BS #4 of a recourse
allocation request. In Step ST47, the BS #4 notifies the BS #2 of a
request acknowledgement.
[0213] In Step ST48, the BS #2 notifies the UE of an addition
request of the BS #4.
[0214] In Step ST49, the UE notifies the BS #2 of an addition
request acknowledgement. The UE measures a specified
synchronization signal of the BS #3.
[0215] In Step ST50, the UE synchronizes with a downlink (DL) of
the BS #4.
[0216] In Step ST51, the BS #4 notifies the UE of control channel,
such as a PDCCH.
[0217] In Step ST52, the UE starts communication of user plane
(U-plane) data based on a resource allocation condition of the
downlink signal specified by the PDCCH.
[0218] Deletion of a base station is performed similarly to the
addition of a base station. Deletion of the BS #2 is performed
based on a command from the BS #1 to the UE. Further, deletion of
the BS #3 and the BS #4 is performed based on a command of the BS
#2.
[0219] When the BS #2 is deleted during connection between the BS
#3 and the BS #4, the following sequence may be employed. That is,
the BS #2 first issues a deletion command of base stations of the
BS #3 and the BS #4, and subsequently the BS #2 is deleted.
Alternatively, the BS #1 may issue a deletion command of the BS #2,
allowing the BS #3 and the BS #4 to be simultaneously deleted.
[0220] When the above-mentioned BS #2 is added, the addition
request command of the BS #2 that is to be notified of to the UE
contains a message indicating that the BS #2 is valid for the RRC
processing function of the second system. Further, the request
command of resource allocation from the BS #1 to the BS #2 contains
a message indicating the validity of the RRC processing function.
If the message indicates invalidity, the BS #2 is not valid for the
RRC processing function of the second system, thus playing the same
role as the BS #2 of the first embodiment shown in FIG. 9.
[0221] According to the present modification above, the sequence
shown in FIG. 19 is executed. Specifically, as shown in FIG. 19,
radio resource control (RRC) processing for the BS #2, the BS #3,
and the BS #4, each being an SeNB, is performed by one of the BS
#2, the BS #3, and the BS #4, e.g., performed by the BS #2. This
configuration can reduce the load on the BS #1 due to the
processing of control plane (C-plane) data. Accordingly, a time
period taken for sequence processing such as processing of adding a
base station can be reduced, which in turn can reduce delay of
processing.
Second Modification of First Embodiment
[0222] As a second modification of the first embodiment, one
example is given. Specifically, RRC messages are communicated using
a selected CC when a plurality of component carriers (CCs) exist in
the BS #2 in the configuration of the first modification of the
first embodiment shown in FIG. 16. A communication system of the
present modification has the same configuration as that of the
communication system 40 of the first modification of the first
embodiment shown in FIG. 16, and therefore illustration and common
description of the configuration are omitted.
[0223] FIG. 20 to FIG. 22 are each a diagram showing one example of
frequencies of transmission and reception waves used by a
communication system according to a second modification of the
first embodiment of the present invention. In FIG. 20 to FIG. 22,
the horizontal axis represents frequency f. FIG. 20 shows
frequencies of transmission and reception waves used by the BS #1.
FIG. 21 shows frequencies of transmission and reception waves used
by the BS #2. FIG. 22 shows frequencies of transmission and
reception waves used by the BS #3 and the BS #4.
[0224] As shown in FIG. 20, the BS #1 uses one type of transmission
and reception waves to transmit and receive RRC messages for the
first system. A bandwidth BW1 of the transmission and reception
waves used by the BS #1 is 20 MHz, for example.
[0225] As shown in FIG. 21, the BS #2 handles two CCs. Therefore,
in the present modification, RRC messages are transmitted using any
of CC #0 and CC #1. With this, the UE can obtain necessary RRC
information without performing modulation processing and
demodulation processing on all of the CCs.
[0226] A bandwidth BW2 of the transmission and reception waves used
by the BS #2 shown in FIG. 21 is 100 MHz, for example. In the
present modification, the CC #0, among the two CCs used by the BS
#2, is used to transmit and receive RRC messages for the second
system.
[0227] Further, in the present modification, the CC #1 of the BS
#2, to which RRC is not allocated, is treated equally with other BS
#3 and BS #4. This can simplify management of user plane (U-plane)
resources.
[0228] A bandwidth BW3 of the transmission and reception waves used
by the BS #3 shown in FIG. 22 is 100 MHz, for example. When the BS
#3 transmits and receives RRC messages for the second system, the
RRC messages are mapped to any CC of CC #0 to CC #7, or to a
plurality of CCs. Handling RRC using only a part of CCs can
simplify management of user plane (U-plane) resources of other CCs
to which RRC is not mapped.
Third Modification of First Embodiment
[0229] As a third modification of the first embodiment, one method
is given. Specifically, the configuration of the first embodiment
and the configuration of the first modification of the first
embodiment are combined. In the first embodiment, the BS #1
executes the RRC processing function for the second system. In
contrast, in the first modification of the first embodiment, the BS
#2 executes the RRC processing function for the second system.
[0230] FIG. 23 is a diagram showing one example of a sequence of
processing to change an executor of the RRC processing function for
the second system from the BS #2 to the BS #1.
[0231] In Step ST61, RRC communication for the second system is
performed between the BS #2 and the UE.
[0232] In Step ST62, the BS #1 notifies the BS #2 of a release
command of RRC processing for the second system.
[0233] In Step ST63, the BS #2 notifies the BS #1 of a positive
acknowledgement.
[0234] In Step ST64, the BS #1 notifies the UE of a change command
of the RRC processing for the second system. The change command of
RRC processing for the second system is a change command of the RRC
processing for the second system from the BS #2 to the BS #1.
Examples of specific command details include changing a radio
resource for handling RRC messages for the second system, and
changing a message format.
[0235] In Step ST65, RRC communication for the second system is
performed between the BS #1 and the UE.
[0236] FIG. 24 is a diagram showing one example of a sequence of
processing to change an executor of the RRC processing function for
the second system from the BS #1 to the BS #2.
[0237] In Step ST71, RRC communication for the second system is
performed between the BS #1 and the UE.
[0238] In Step ST72, the BS #1 notifies the BS #2 of an addition
command of RRC processing for the second system.
[0239] In Step ST73, the BS #2 notifies the BS #1 of a positive
acknowledgement.
[0240] In Step ST74, the BS #1 notifies the UE of a change command
of the RRC processing for the second system. The change command of
RRC processing for the second system is a change command of the RRC
processing for the second system from the BS #1 to the BS #2.
Examples of specific command details include changing a radio
resource for handling RRC messages for the second system, and
changing a message format.
[0241] In Step ST75, RRC communication for the second system is
performed between the BS #2 and the UE.
[0242] Enabling change of a base station and a resource to perform
RRC processing as described above in turn enables distribution of
the load of the RRC processing in accordance with a communication
condition of the UE, available functions of the UE, a loaded
condition of the base station, and the number of connected
terminals, for example.
[0243] Further, when high speed communication with low latency is
demanded in accordance with a communication condition of the UE,
the use of the BS #2 also enables execution of the RRC processing
for the second system with reduced latency.
[0244] In contrast, when the UE does not object to latency etc. and
is in power-saving usage such as by decreasing the number of RRC
messages, it is also effective to concentrate the RRC processing
for the first system and the RRC processing for the second system
at one entity, i.e., the BS #1, where the transmission and
reception of the RRC messages are performed.
Second Embodiment
[0245] In 5G, the concept of beam control may be added. Further,
the intervals at which base station are installed are reduced. This
may increase the number of base stations in one cell. Further,
various types of base stations may be installed concurrently. For
example, base stations of ultra-reliability and low latency
communication (URLLC) and a plurality of base stations of different
frequencies may be installed concurrently. In such a case,
information to be broadcast about base stations is increased. If
the information is transmitted by a single macro base station,
there is a problem in increasing the processing of the macro base
station.
[0246] In order to solve such a problem, in the present embodiment,
broadcast information is divided into basic information and
additional information. The basic information is transmitted from
the BS #1 having a large cell radius. The additional information is
transmitted from BS #2 that is installed inside the cell of the BS
#1 and has a cell radius smaller than that of the BS #1 or
equivalent to that of the BS #1.
[0247] This configuration can reduce the amount of broadcast
information transmitted from a single base station to distribute
the load. Further, the amount of information to be transmitted is
reduced by narrowing details of the broadcast information down to
information necessary for individual base stations. As a result,
the occupying proportion of the broadcast information with respect
to the entire radio resource can be reduced. Accordingly, the
system can be efficient.
[0248] FIG. 25 is a diagram showing the configuration of a
communication system 60 according to a second embodiment of the
present invention. The communication system 60 includes a first
base station 61 (hereinafter may be referred to as a "BS #1"), a
second base station 62 (hereinafter may be referred to as a "BS
#2"), a third base station 63 (hereinafter may be referred to as a
"BS #3"), a fourth base station 64 (hereinafter may be referred to
as a "BS #4"), and a user equipment (UE) 65.
[0249] The BS #1 forms a macro cell 71 having a cell radius of 500
m, for example. The BS #2 forms a micro cell 72 having a cell
radius of 200 m, for example. The BS #3 and the BS #4 respectively
form small cells 73 and 74 each having a cell radius of 50 m, for
example.
[0250] For example, if the base stations 61 to 64 are installed as
standalone base stations independently of other base stations,
pieces of broadcast information BrI #1 to BrI #3 are transmitted
from the respective base stations 61 to 64. Although FIG. 25 omits
illustration of broadcast information transmitted from the fourth
base station 64 for the sake of avoiding complexity and difficulty
in understanding the drawing, broadcast information is in actuality
also transmitted from the fourth base station 64.
[0251] The present embodiment, however, assumes a configuration in
which a plurality of base stations are connected to the UE 65 under
the cell of the BS #1 described in the first modification of the
first embodiment. Although it is possible that the BS #1 transmits
configuration information of all of the base stations as broadcast
information BrI #1 in the present configuration, the BS #1
transmits only configuration information of the BS #1 and
information necessary for initial connection of the BS #2 as
broadcast information BrI #1 in order to efficiently transmit
broadcast information. The BS #2 transmits pieces of broadcast
information other than the information necessary for the initial
connection of the BS #2 out of the broadcast information for the BS
#2, and pieces of broadcast information for the BS #3 and for the
BS #4.
[0252] In this manner, in the present embodiment, one of the
plurality of SeNBs, specifically the BS #2, at least partially
notifies the UE of pieces of broadcast information for each of
SeNBs, i.e., pieces of broadcast information for the BS #2, for the
BS #3, and for the BS #4.
[0253] Adopting the configuration, the BS #1 no longer needs to
transmit broadcast information for all of the base stations running
under the cell. Therefore, the amount of the data of the broadcast
information BrI #1 of the BS #1 can be reduced. With this, the
occupying proportion of the broadcast information BrI #1 with
respect to the radio resource of the BS #1 can be reduced. Further,
reducing the transmission cycle of the broadcast information BrI #1
of the BS #1 can reduce the period of time taken for the UE to
complete the initial connection to the BS #1.
[0254] The BS #2 may directly notify the UE of broadcast
information for each SeNB as shown in FIG. 26 to be described
later, or the BS #2 may notify the UE of broadcast information for
each SeNB via another base station as shown in FIG. 27 and FIG. 28
to be described later.
[0255] Examples of pieces of information necessary for the initial
connection of the BS #2 include SIB1 (cell access and cell
reselection related info, scheduling info list), and SIB2 (radio
resource configuration that is common for all UEs) of broadcast
information used in LTE-A. Further, information about transmission
and reception beams, being additional information, is considered to
be also added to a base station for 5G. The additional information
corresponds to pieces of broadcast information other than the
above-mentioned information necessary for the initial connection of
the BS #2.
[0256] FIG. 26 is a diagram showing one example of a sequence of
processing to acquire broadcast information in the communication
system 60 according to the second embodiment of the present
invention. FIG. 26 shows one example of a sequence of processing in
which the UE acquires pieces of broadcast information for the BS
#1, the BS #2, the BS #3, and the BS #4.
[0257] In Step ST81, the BS #1 notifies the UE of broadcast
information for the BS #1. The UE reads control information for the
BS #1 out of the broadcast information notified of from the BS
#1.
[0258] In Step ST82, communication is performed between the BS #1
and the UE.
[0259] In Step ST83, the BS #1 notifies the UE of basic information
of broadcast information for the BS #2. When the UE needs to be
connected to the BS #2, the UE reads the basic information of the
broadcast information for the BS #2 out of the broadcast
information of the BS #1, thereby obtaining information to access
the BS #2.
[0260] In Step ST84, the BS #2 notifies the UE of additional
information of the broadcast information for the BS #2. The UE
reads the additional information of the BS #2 out of the broadcast
information of the BS #2.
[0261] In Step ST85, communication is performed between the BS #2
and the UE.
[0262] In Step ST86, the BS #2 notifies the UE of broadcast
information for the BS #3 and broadcast information for the BS #4.
When the UE needs to be connected to the BS #3 or the BS #4, the UE
reads control information for the BS #3 or control information for
the BS #4 out of the broadcast information notified of from the BS
#2.
[0263] In Step ST87, communication is performed between the BS #3
and the UE. In Step ST88, communication is performed between the BS
#4 and the UE.
[0264] FIG. 27 is a diagram showing one example of a sequence of
processing to notify of broadcast information based on a request of
the UE. FIG. 27 shows an example where the BS #2 acknowledges a
broadcast information request of the UE.
[0265] In Step ST91, the BS #1 notifies the UE of broadcast
information for the BS #1.
[0266] In Step ST92, communication is performed between the BS #1
and the UE.
[0267] In Step ST93, the BS #1 notifies the UE of basic information
of broadcast information for the BS #2.
[0268] In Step ST94, the BS #2 notifies the UE of additional
information of the broadcast information for the BS #2.
[0269] In Step ST95, communication is performed between the BS #2
and the UE.
[0270] In Step ST96, the UE notifies the BS #2 of a broadcast
information request for the BS #3.
[0271] In Step ST97, the BS #2 notifies the UE of radio resource
allocation information for notifying of broadcast information.
[0272] In Step ST98, the BS #2 notifies the UE of broadcast
information for the BS #3 with the radio resource.
[0273] In Step ST99, communication is performed between the BS #3
and the UE.
[0274] Though the processing shown in FIG. 27, the occupying
proportion of broadcast information with respect to a radio
resource can be reduced. Particularly in 5G, base station
configuration information is increased due to beam control etc.,
and also base station configuration information is increased due to
coping with various scenarios such as massive machine type
connection (mMTC) and ultra-reliability and low latency
communication (URLLC). Accordingly, efficiency can be enhanced by
broadcasting only information necessary for initial connection, and
then individually transmitting the remaining information to the
UE.
[0275] FIG. 28 is a diagram showing another example of a sequence
of processing to notify of broadcast information based on a request
of the UE. FIG. 28 shows a method of notifying of broadcast
information requested by the UE by using a radio resource of a base
station, which is different from a radio resource of a base station
that has received the request.
[0276] In Step ST101, the BS #1 and the UE are communicated.
[0277] In Step ST102, the BS #2 and the UE are communicated.
[0278] In Step ST103, the BS #3 and the UE are communicated.
[0279] In Step ST104, the UE notifies the BS #2 of a broadcast
information request for the BS #4.
[0280] In Step ST105, the BS #2 notifies the BS #3 of a resource
securing request for broadcast information notification.
Specifically, the BS #2 notifies of broadcast information by using
a radio resource of the BS #3. The BS #2 informs the BS #3 of the
size of the broadcast information, information about radio resource
in use, etc.
[0281] In Step ST106, the BS #3 notifies the BS #2 of secured radio
information if the BS #3 succeeded in securing a radio
resource.
[0282] In Step ST107, the BS #2 notifies the UE of allocation
information of the broadcast information.
[0283] In Step ST108, the BS #3 notifies the UE of broadcast
information for the BS #4.
[0284] 5G is also considered to have a configuration in which, by
using an array antenna, beams are formed with transmission and
reception antenna waveforms so as to enhance directivity of the
antenna. This configuration enables spatial multiplexing. Such use
of a beam resource capable of enabling spatial multiplexing for
broadcast information can further reduce the occupying proportion
of broadcast information with respect to a radio resource.
[0285] Further, it is preferable to employ a configuration that
allows free selection of a base station that receives a broadcast
information request from the UE, and a base station that transmits
a broadcast information request from the UE. With this, radio
resources can be utilized further effectively.
[0286] In communication requiring high reliability, it is also
effective that a plurality of base stations transmit the same
broadcast information, as a way to enhance reliability of data.
[0287] Further, as in the second modification of the first
embodiment, it is preferable that a radio resource to transmit
broadcast information is determined per component carrier (CC) also
in the present embodiment. This can utilize an idle radio resource,
and thus spectral efficiency can be improved.
Third Embodiment
[0288] Regarding processing of user plane (U-plane) data, the
standard configuration for the split bearer configuration of dual
connectivity up to LTE-A is that the packet data convergence
protocol (PDCP) function is assigned to a master eNB (MeNB) so that
a secondary eNB (SeNB) performs processing of layers lower than the
RLC.
[0289] In such a configuration, ciphering of the PDCP is
concentrated at one entity, and therefore processing can be
simplified. In contrast, 5G is considered to have a configuration
in which a plurality of base stations communicate with one UE as in
the first embodiment. In this case, since the dual connectivity
configuration cannot be applied to three and more base stations,
the third and subsequent base stations need to be independent of
other base stations. Accordingly, there is a problem in that the
processing of the PDCP and the like cannot be simplified.
[0290] In order to solve the problem, in the present embodiment,
pieces of data split from the PDCP of the BS #1 are processed in
layers of the RLC and the lower layers of the BS #2 and the BS #3,
as a method of processing user plane (U-plane) data of the first
embodiment.
[0291] FIG. 29 is a block diagram showing the configuration of a
communication system 80 according to a third embodiment of the
present invention. The communication system 80 includes a first
base station 81 (hereinafter may be referred to as a "BS #1"), a
second base station 82 (hereinafter may be referred to as a "BS
#2"), a third base station 83 (hereinafter may be referred to as a
"BS #3"), a UE 84, and an upper layer device 85. The BS #1 includes
a PDCP processing unit, an RLC processing unit, a MAC processing
unit, and a PHY processing unit. The BS #2 and the BS #3 each
include an RLC processing unit, a MAC processing unit, and a PHY
processing unit. The UE 84 includes a PDCP processing unit, an RLC
processing unit, a MAC processing unit, and a PHY processing unit
for the BS #1, an RLC processing unit, a MAC processing unit, and a
PHY processing unit for the BS #2, and an RLC processing unit, a
MAC processing unit, and a PHY processing unit for the BS #3. The
upper layer device 85 includes a core network device and a serving
gateway (abbreviated as SGW).
[0292] The BS #1 and the BS #2, and the BS #1 and the BS #3 each
correspond to the configuration of the option 3C (split bearer) of
dual connectivity.
[0293] The BS #1 receives user plane (U-plane) data from the upper
layer device 85. The PDCP processing unit of the BS #1 performs
PDCP processing of robust header compression (ROHC) and ciphering
processing.
[0294] The data, to which a PDCP sequence number (SN) is attached,
is split into pieces to be transmitted to the RLC processing unit
of the BS #1, the RLC processing unit of the BS #2, and the RLC
processing unit of the BS #3.
[0295] The base stations each perform RLC processing, MAC
processing, and PHY processing on the split piece of data, and then
each transmit the processed piece of data to the UE 84. The UE 84
performs PHY processing, MAC processing, and RLC processing for
each of the base stations on the pieces of data. Subsequently, the
UE 84 collects the processed pieces of data into one PDCP. For
uplink data, the reverse procedures will be taken.
[0296] Such a configuration can simplify processing of the UE, such
as PDCP ciphering, even in a system where the UE is connected to a
plurality of base stations.
[0297] FIG. 30 is a block diagram showing the configuration of a
communication system 80A as another example of the communication
system according to the third embodiment of the present invention.
The communication system 80A shown in FIG. 30 includes the same
components as those of the communication system 80 shown in FIG.
29, and therefore the same components are denoted by the same
reference symbols to omit common description.
[0298] The communication system 80A includes a second base station
82A, instead of the second base station 82 shown in FIG. 29. The
second base station 82A further includes a data split processing
unit (also referred to as a "SPLIT processing unit") in addition to
the components of the second base station 82 of FIG. 29.
[0299] As shown in FIG. 30, the data split processing unit of the
BS #2 allows a configuration in which the BS #2 transfers, to the
BS #3, PDCP data from the BS #1. In this configuration, it is
sufficient that the BS #1 supports a user plane (U-plane) interface
that is only compatible with connection between the BS #1 and the
BS #2. Accordingly, the specifications of the option 3C of dual
connectivity of LTE can be supported without making changes
thereto.
[0300] According to the present embodiment as described above, user
plane (U-plane) data, which is contained in information provided by
the core network about communication with the UE, is transmitted to
and received from the UE via a single base station BS #1
corresponding to an MeNB. Specifically, the core network provides
user plane (U-plane) data to an MeNB. The MeNB then provides the
user plane (U-plane) data to the UE, and to the UE also via a
plurality of SeNBs. This can simplify processing of user plane
(U-plane) data when a UE communicates with a plurality of base
stations.
[0301] FIG. 31 is a block diagram showing the configuration of a
communication system 90 as still another example of the
communication system according to the third embodiment of the
present invention. The communication system 90 includes a first
base station 91 (hereinafter may be referred to as a "BS #1"), a
second base station 92 (hereinafter may be referred to as a "BS
#2"), a third base station 93 (hereinafter may be referred to as a
"BS #3"), a fourth base station 94 (hereinafter may be referred to
as a "BS #4"), a UE 95, a first core network 96, and a second core
network 97. The first core network 96 is a core network for LTE-A.
The second core network 97 is a core network for 5G.
[0302] The BS #1 and the BS #2 each include a PDCP processing unit,
an RLC processing unit, a MAC processing unit, and a PHY processing
unit. The BS #3 and the BS #4 each include an RLC processing unit,
a MAC processing unit, and a PHY processing unit. The UE 95
includes a PDCP processing unit, an RLC processing unit, a MAC
processing unit, and a PHY processing unit for the BS #1, a PDCP
processing unit, an RLC processing unit, a MAC processing unit, and
a PHY processing unit for the BS #2, an RLC processing unit, a MAC
processing unit, and a PHY processing unit for the BS #3, and an
RLC processing unit, a MAC processing unit, and a PHY processing
unit for the BS #4.
[0303] FIG. 31 shows the following configuration as a method of
processing user plane (U-plane) data of the first modification of
the first embodiment. That is, the BS #1 of LTE-A is connected to a
core network for LTE, for example, the BS #2 of 5G is connected to
a core network for 5G, for example, and the BS #3 and the BS #4 of
5G process pieces of user plane (U-plane) data split from the PDCP
processing unit of the BS #2, for example.
[0304] This is one example of a configuration where the BS #1 is a
base station for LTE-A, and the BS #2, the BS #3, and the BS #4 are
each of a base station for 5G.
[0305] The function of the PDCP processing unit for LTE-A and that
for 5G may be different. Even if the function of the PDCP
processing unit for LTE-A and that for 5G are the same, the data
amount of user plane (U-plane) data for 5G may be several tens of
times larger than the data amount of user plane (U-plane) data for
LTE, and thus performance of the PDCP processing unit of a
conventional base station of LTE-A may be a bottleneck. In such a
case, the PDCP processing for 5G needs to be executed by a base
station for 5G.
[0306] In order to solve the problem as above, the example shown in
FIG. 31 employs a configuration in which the BS #2 executes PDCP
processing of user plane (U-plane) data of the 5G system, and the
user plane (U-plane) data is then transmitted to the RLC processing
units of the BS #3 and the BS #4 that run under the BS #2.
[0307] The BS #1 is connected to the first core network 96 being a
core network for LTE-A. The BS #1 processes user plane (U-plane)
data received from the first core network 96 in the PDCP processing
unit, the RLC processing unit, the MAC processing unit, and the PHY
processing unit of the BS #1, and then transmits the processed data
to the UE 95.
[0308] The BS #2 is connected to the second core network 97 being a
core network (a next generation core network) for 5G. The BS #2
performs processing, such as ROHC, ciphering, and attaching a
sequence number (SN) of PDCP, on user plane (U-plane) data received
from the second core network 97 in the PDCP processing unit of the
BS #2.
[0309] The data subjected to the PDCP processing is split into
pieces to be transmitted to the RLC processing unit of the BS #2,
the RLC processing unit of the BS #3, and the RLC processing unit
of the BS #4. The base stations each perform processing on the
split piece of data in the RLC processing unit, the MAC processing
unit, and the PHY processing unit, and then each transmit the
processed piece of data to the UE 95.
[0310] The UE 95 performs PHY processing, MAC processing, and RLC
processing for each of the base stations on the pieces of data.
Subsequently, the UE 95 collects the processed pieces of data into
two PDCPs, i.e., a PDCP for LTE-A and a PDCP for 5G.
[0311] This configuration can simplify PDCP processing irrespective
of processing capacity of an LTE-A base station. Further, data of
5G can be transmitted and received without a problem even in a case
where a connection interface between the BS #1 and the BS #2
employs a so-called "non ideal network," which is a network that
does not guarantee provisions of latency in data processing.
[0312] In the example shown in FIG. 31 as above, user plane
(U-plane) data for the BS #2, the BS #3, and the BS #4, each being
an SeNB as well as being a second system, is transmitted to and
received from the UE via one of the BS #2, the BS #3, and the BS
#4, e.g., via the BS #2.
[0313] Specifically, the core network provides user plane (U-plane)
data of the second system to a representative SeNB (BS #2). The
representative SeNB then provides the user plane (U-plane) data of
the second system to the UE, and to the UE also via a plurality of
SeNBs of the same system.
[0314] This can simplify processing of user plane (U-plane) data
when a UE communicates with a plurality of base stations even in a
case where a network that does not guarantee provisions of latency
in data processing is employed between different communication
systems.
Fourth Embodiment
[0315] In the conventional dual connectivity configuration, a UE
notifies an MeNB of a measurement result of each base station as a
measurement report.
[0316] However, when a plurality of base stations form a
communication system as in the above first embodiment, notifying
only the BS #1 of measurement reports may cause processing
concentration at the BS #1.
[0317] Particularly in the 5G system, the use of an array antenna
having directivity may attach beam characteristics to a
transmission and reception signal, and therefore measurement
information about beam control etc. may be increased. Accordingly,
measurement processing is required more times, in comparison with
the conventional method.
[0318] In the present embodiment, in the configuration of the first
modification of the first embodiment, a measurement result for
connection to the BS #2 is reported to the BS #1 before
communication between the BS #2 and the UE is established.
[0319] After communication between the BS #2 and the UE is
established, the BS #1 is notified of a measurement report for the
BS #1, and the BS #2 is notified of measurement report for the BS
#2, the BS #3, and the BS #4.
[0320] FIG. 32 is a diagram showing one example of a sequence of
measurement report processing of a communication system according
to a fourth embodiment of the present invention.
[0321] When the UE is connected to the BS #1, in Step ST111, the UE
notifies the BS #1 of measurement information about the BS #1 and
the BS #2 as measurement reports.
[0322] In Step ST112, the BS #1 notifies the BS #2 of an addition
request of a base station in order to determine whether
communication between the BS #2 and the UE is possible based on the
measurement information about the BS #2. Specifically, the BS #1
notifies the BS #2 of an addition request of the BS #2.
[0323] In Step ST113, if the addition of a base station is
possible, the BS #2 notifies the BS #1 of an addition request
acknowledge (hereinafter may be referred to as an "addition request
Ack") as a positive response.
[0324] In Step ST114, the BS #1 notifies the UE of an RRC
connection reconfiguration message as an addition request of a base
station. Specifically, the BS #1 notifies the UE of an addition
request of the BS #2. The RRC connection reconfiguration message of
Step ST114 may contain information of a command to notify the BS #2
of measurement reports of the BS #2, the BS #3, and the BS #4.
[0325] In Step ST115, after completing establishment of
communication with the BS #2, the L1E notifies the BS #1 of an RRC
connection reconfiguration complete message as an addition complete
notification.
[0326] In Step ST116, after establishing communication with the BS
#2, the UE notifies the BS #1 of measurement information about the
BS #1 as a measurement report for the BS #1.
[0327] In Step ST117, the UE notifies the BS #2 of measurement
information about the BS #2, the BS #3, and the BS #4 as a
measurement report for the BS #2.
[0328] In Step ST118, the BS #2 notifies the BS #3 of an addition
request of a base station in order to determine whether
communication between the BS #3 and the UE is possible based on the
measurement information about the BS #3. Specifically, the BS #2
notifies the BS #3 of an addition request of the BS #3.
[0329] In Step ST119, if the addition of a base station is
possible, the BS #3 notifies the BS #2 of an addition request Ack
as a positive response.
[0330] In Step ST120, the BS #2 notifies the UE of an RRC
connection reconfiguration message as an addition request of a base
station. Specifically, the BS #2 notifies the UE of an addition
request of the BS #3.
[0331] In Step ST121, after completing establishment of
communication with the BS #3, the UE notifies the BS #2 of an RRC
connection reconfiguration complete message as an addition complete
notification.
[0332] In Step ST122, the BS #2 notifies the UE of measurement
information about the BS #2, the BS #3, and the BS #4 as a
measurement report.
[0333] In Step ST123, the BS #2 notifies the BS #4 of an addition
request of a base station in order to determine whether
communication between the BS #4 and the UE is possible based on the
measurement information about the BS #4. Specifically, the BS #2
notifies the BS #3 of an addition request of the BS #4.
[0334] In Step ST124, if the addition of a base station is
possible, the BS #4 notifies the BS #2 of an addition request Ack
as a positive response.
[0335] In Step ST125, the BS #2 notifies the UE of an RRC
connection reconfiguration message as an addition request of a base
station. Specifically, the BS #2 notifies the UE of an addition
request of the BS #4.
[0336] In Step ST126, after completing establishment of
communication with the BS #4, the UE notifies the BS #2 of an RRC
connection reconfiguration complete message as an addition complete
notification.
[0337] In Step ST127, after establishing communication with the BS
#4, the UE notifies the BS #1 of measurement information about the
BS #1 as a measurement report for the BS #1.
[0338] In Step ST128, the UE notifies the BS #2 of measurement
information about the BS #2, the BS #3, and the BS #4 as a
measurement report for the BS #2.
[0339] Through the above processing, measurement information can be
handled per radio system even if the radio system differs between
the BS #1 of LTE-A, for example, and the BS #2, the BS #3, and the
BS #4 of 5G, for example. Accordingly, a system can be constructed
without affecting the size of measurement information of other
radio systems etc.
[0340] Further, the UE may be capable of selecting a base station
used for the notification of a measurement report. For example, the
UE may use radio resources of the BS #3 and the BS #4 to notify of
measurement reports for the BS #2, the BS #3, and the BS #4.
[0341] In this configuration, examples of a method of configuring
the recipient of a measurement report include a method of using RRC
messages. With this method, a measurement report can be notified of
by using an idle radio resource even when pieces of measurement
information are increased due to beam control etc.
[0342] If communication with a base station as the notification
destination of a measurement report is deleted, with the
above-mentioned RRC messages, the notification destination of a
measurement report may be changed or may be returned to the
notification destination before the change.
[0343] The embodiments and the modifications are merely
illustrations of the present invention, and can be freely combined
within the scope of the present invention. Any constituent elements
of the embodiments and the modifications can be appropriately
modified or omitted.
[0344] While the invention has been described in detail, the
foregoing description is in all aspects illustrative and not
restrictive. It is therefore understood that numerous modifications
and variations can be devised without departing from the scope of
the invention.
EXPLANATION OF REFERENCE SIGNS
[0345] 20 communication system, 21 first base station (MeNB), 22
second base station (SeNB #1), 23 third base station (SeNB #2), 24
user equipment (UE), 25 core network
* * * * *
References