U.S. patent application number 15/649219 was filed with the patent office on 2017-10-26 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 Miho MAEDA, Mitsuru MOCHIZUKI.
Application Number | 20170311314 15/649219 |
Document ID | / |
Family ID | 46969020 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170311314 |
Kind Code |
A1 |
MAEDA; Miho ; et
al. |
October 26, 2017 |
COMMUNICATION SYSTEM
Abstract
The present invention has an object to provide a communication
system of improving the communication quality in a case where a
plurality of communication devices having different sizes of ranges
coexist, in which communication with a terminal device is possible,
to thereby improve an entire throughput. In a case where a remote
radio head (RRH) is installed in a coverage of a macro cell, an
uplink resource transmitted from a user equipment (UE) to the macro
cell, that is, an uplink carrier frequency band UL1 of the macro
cell in a portion surrounded by a solid line is received not only
by the macro cell but also by the RRH. Then, the macro cell
combines a reception signal regarding the uplink resource of the
macro cell, which has been received by the macro cell, and a
reception signal regarding the uplink resource of the macro cell,
which has been received by the RRH.
Inventors: |
MAEDA; Miho; (Tokyo, JP)
; MOCHIZUKI; Mitsuru; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
46969020 |
Appl. No.: |
15/649219 |
Filed: |
July 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15181129 |
Jun 13, 2016 |
9730213 |
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15649219 |
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14009226 |
Oct 1, 2013 |
9392599 |
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PCT/JP2012/057735 |
Mar 26, 2012 |
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15181129 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 52/146 20130101;
H04W 56/0045 20130101; H04W 52/143 20130101; H04W 72/0426 20130101;
H04W 52/244 20130101; H04B 7/022 20130101; H04W 72/04 20130101;
H04W 52/40 20130101; H04B 17/327 20150115 |
International
Class: |
H04W 72/04 20090101
H04W072/04; H04W 52/40 20090101 H04W052/40; H04B 17/327 20060101
H04B017/327; H04W 52/14 20090101 H04W052/14; H04W 52/14 20090101
H04W052/14; H04W 72/04 20090101 H04W072/04; H04W 52/24 20090101
H04W052/24 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2011 |
JP |
2011-081799 |
Claims
1. A communication system comprising a movable terminal device and
a plurality of communication devices configured to perform radio
communication with said terminal device, wherein said plurality of
communication devices include a large-scale communication device
having a relatively large range in which communication with said
terminal device is possible and a small-scale communication device
having a relatively small range in which said communication is
possible, said terminal device is prohibited from a handover from
said large-scale communication device to said small-scale
communication device (a) when said small-scale communication device
is connected with said large-scale communication device by a
dedicated line, (b) when said small-scale communication device
shares functionality of said large-scale communication device, or
(c) when said small-scale communication device is located within a
range of said large-scale communication device, communicable with
said terminal device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
15/181,129, filed Jun. 13, 2016, which is a continuation of U.S.
patent application Ser. No. 14/009,226 (now U.S. Pat. No.
9,392,599), filed Oct. 10, 2013, which is a National Stage
Application of PCT Application No. PCT/JP12/057735, filed Mar. 26,
2012, which claims priority to Japanese Patent Application No.
2011-081799, filed Apr. 1, 2011. The entire content of U.S. patent
application Ser. No. 14/009,226 is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a communication system in
which a base station device performs radio communication with a
plurality of communication terminal devices.
BACKGROUND ART
[0003] Commercial service of a wideband code division multiple
access (W-CDMA) system among so-called third-generation
communication systems has been offered in Japan since 2001. In
addition, high speed downlink packet access (HSDPA) service for
achieving higher-speed data transmission using a downlink has been
offered by adding a channel for packet transmission (high
speed-downlink shared channel (HS-DSCH)) to the downlink (dedicated
data channel, dedicated control channel). Further, in order to
increase the speed of data transmission in an uplink direction,
service of a high speed uplink packet access (HSUPA) system has
been offered. W-CDMA is a communication system defined by the 3rd
generation partnership project (3GPP) that is the standard
organization regarding the mobile communication system, where the
specifications of Release 10 version are produced.
[0004] Further, new communication systems referred to as long term
evolution (LTE) regarding radio areas and system architecture
evolution (SAE) regarding the overall system configuration
including a core network (merely referred to as network as well) as
communication systems independent of W-CDMA is studied in 3GPP.
This communication system is also referred to as 3.9 generation
(3.9 G) system.
[0005] In the LTE, an access scheme, a radio channel configuration
and a protocol are totally different from those of the current
W-CDMA (HSDPA/HSUPA). For example, as to the access scheme, code
division multiple access is used in the W-CDMA, whereas in the LTE,
orthogonal frequency division multiplexing (OFDM) is used in a
downlink direction and single career frequency division multiple
access (SC-FDMA) is used in an uplink direction. In addition, the
bandwidth is 5 MHz in the W-CDMA, while in the LTE, the bandwidth
can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20
MHz per base station. Further, differently from the W-CDMA, circuit
switching is not provided but a packet communication system is only
provided in the LTE.
[0006] The LTE is defined as a radio access network independent of
the W-CDMA network because its communication system is configured
by a new core network different from a core network (general packet
radio service: GPRS) of the W-CDMA. Therefore, for differentiation
from the W-CDMA communication system, a base station that
communicates with a user equipment (UE) and a radio network
controller that transmits/receives control data and user data
to/from a plurality of base stations are referred to as an E-UTRAN
NodeB (eNB) and an evolved packet core (EPC) or access gateway
(aGW), respectively, in the LTE communication system.
[0007] Unicast service and evolved multimedia broadcast multicast
service (E-MBMS service) are provided in this LTE communication
system. The E-MBMS service is broadcast multimedia service, which
is merely referred to as MBMS in some cases. Bulk broadcast
contents such as news, weather forecast and mobile broadcast are
transmitted to a plurality of user equipments. This is also
referred to as point to multipoint service.
[0008] Non-Patent Document 1 (Chapter 4) describes the current
decisions by 3GPP regarding an overall architecture in the LTE
system. The overall architecture is described with reference to
FIG. 1. FIG. 1 is a diagram illustrating the configuration of the
LTE communication system. With reference to FIG. 1, the evolved
universal terrestrial radio access (E-UTRAN) is composed of one or
a plurality of base stations 102, provided that a control protocol
for a user equipment 101 such as a radio resource control (RRC) and
user planes such as a packet data convergence protocol (PDCP),
radio link control (RLC), medium access control (MAC) and physical
layer (PHY) are terminated in the base station 102.
[0009] The base stations 102 perform scheduling and transmission of
a paging signal (also referred to as paging messages) notified from
a mobility management entity (MME) 103. The base stations 102 are
connected to each other by means of an X2 interface. In addition,
the base stations 102 are connected to an evolved packet core (EPC)
by means of an S1 interface. More specifically, the base station
102 is connected to the mobility management entity (MME) 103 by
means of an S1_MME interface and connected to a serving gateway
(S-GW) 104 by means of an S1_U interface.
[0010] The MME 103 distributes the paging signal to a plurality of
or a single base station 102. In addition, the MME 103 performs
mobility control of an idle state. When the user equipment is in
the idle state and an active state, the MME 103 manages a list of
tracking areas.
[0011] The S-GW 104 transmits/receives user data to/from one or a
plurality of base stations 102. The S-GW 104 serves as a local
mobility anchor point in handover between base stations. Moreover,
a PDN gateway (P-GW) is provided in the EPC, which performs
per-user packet filtering and UE-ID address allocation.
[0012] The control protocol RRC between the user equipment 101 and
the base station 102 performs broadcast, paging, RRC connection
management and the like. The states of the base station and the
user equipment in RRC are classified into RRC_Idle and
RRC_CONNECTED. 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, is capable of
transmitting/receiving data to/from a network, and performs, for
example, handover (HO) and measurement of a neighbor cell.
[0013] The current decisions by 3GPP regarding the frame
configuration in the LTE system described in Non-Patent Document 1
(Chapter 5) are described with reference to FIG. 2. FIG. 2 is a
diagram illustrating the configuration of a radio frame used in the
LTE communication system. With reference to FIG. 2, 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 (SS) per each radio frame. The synchronization signals are
classified into a primary synchronization signal (P-SS) and a
secondary synchronization signal (S-SS).
[0014] Multiplexing of channels for multimedia broadcast multicast
service single frequency network (MBSFN) and for non-MBSFN is
performed on a per-subframe basis. MBSFN transmission is a
simulcast transmission technique realized by simultaneous
transmission of the same waveforms from a plurality of cells. The
MBSFN transmission from a plurality of cells in the MBSFN area is
seen as a single transmission by a user equipment. The MBSFN is a
network that supports such MBSFN transmission. Hereinafter, a
subframe for MBSFN transmission is referred to as MBSFN
subframe.
[0015] Non-Patent Document 2 describes a signaling example when
MBSFN subframes are allocated. FIG. 3 is a diagram illustrating the
configuration of the MBSFN frame. With reference to FIG. 3, a radio
frame including the MBSFN subframes is allocated per radio frame
allocation period. The MBSFN subframe is a subframe allocated for
the MBSFN in a radio frame defined by the allocation period and the
allocation offset (radio frame allocation offset), and serves to
transmit multimedia data. The radio frame satisfying Equation (1)
below is a radio frame including the MBSFN subframes.
SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset
(1)
[0016] The MBSFN subframe is allocated with six bits. The leftmost
bit defines the MBSFN allocation for the second subframe (#1). The
second bit, third bit, fourth bit, fifth bit, and sixth-bit define
the MBSFN allocation for the third subframe (#2), fourth subframe
(#3), seventh subframe (#6), eighth subframe (#7), and ninth
subframe (#8), respectively. The case where the bit indicates "one"
represents that the corresponding subframe is allocated for the
MBSFN.
[0017] Non-Patent Document 1 (Chapter 5) describes the current
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 cell (CSG cell) as that of a non-CSG
cell. Physical channels are described with reference to FIG. 4.
FIG. 4 is a diagram illustrating physical channels used in the LTE
communication system.
[0018] With reference to FIG. 4, a physical broadcast channel
(PBCH) 401 is a downlink channel transmitted from the base station
102 to the user equipment 101. A BCH transport block is mapped to
four subframes within a 40 ms interval. There is no explicit
signaling indicating 40 ms timing. A physical control format
indicator channel (PCFICH) 402 is transmitted from the base station
102 to the user equipment 101. The PCFICH notifies the number of
OFDM symbols used for PDCCHs from the base station 102 to the user
equipment 101. The PCFICH is transmitted in each subframe.
[0019] A physical downlink control channel (PDCCH) 403 is a
downlink channel transmitted from the base station 102 to the user
equipment 101. The PDCCH notifies the resource allocation of DL-SCH
(downlink shared channel that is one of the transport channels
shown in FIG. 5 described below) and PCH (paging channel that is
one of the transport channels shown in FIG. 5), and HARQ
information related to DL-SCH. The PDCCH carries an uplink
scheduling grant. The PDCCH carries acknowledgement (Ack)/negative
acknowledgement (Nack) that is a response signal to uplink
transmission. The PDCCH is referred to as an L1/L2 control signal
as well.
[0020] A physical downlink shared channel (PDSCH) 404 is a downlink
channel transmitted from the base station 102 to the user equipment
101. A DL-SCH (downlink shared channel) that is a transport channel
and a PCH that is a transport channel are mapped to the PDSCH. A
physical multicast channel (PMCH) 405 is a downlink channel
transmitted from the base station 102 to the user equipment 101. A
multicast channel (MCH) that is a transport channel is mapped to
the PMCH.
[0021] A physical uplink control channel (PUCCH) 406 is an uplink
channel transmitted from the user equipment 101 to the base station
102. 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). A physical uplink shared
channel (PUSCH) 407 is an uplink channel transmitted from the user
equipment 101 to the base station 102. A UL-SCH (uplink shared
channel that is one of the transport channels shown in FIG. 5) is
mapped to the PUSCH.
[0022] A physical hybrid ARQ indicator channel (PHICH) 408 is a
downlink channel transmitted from the base station 102 to the user
equipment 101. The PHICH carries Ack/Nack that is a response to
uplink transmission. A physical random access channel (PRACH) 409
is an uplink channel transmitted from the user equipment 101 to the
base station 102. The PRACH carries a random access preamble.
[0023] A downlink reference signal is a known symbol in a mobile
communication system. The physical layer measurement objects of a
user equipment include reference symbol received power (RSRP).
[0024] The transport channels described in Non-Patent Document 1
(Chapter 5) are described with reference to FIG. 5. FIG. 5 is a
diagram illustrating transport channels used in the LTE
communication system. FIG. 5(A) shows mapping between a downlink
transport channel and a downlink physical channel. FIG. 5(B) shows
mapping between an uplink transport channel and an uplink physical
channel.
[0025] Downlink transport channels are described. A broadcast
channel (BCH) is broadcast to the entire coverage of a base station
(cell). The BCH is mapped to the physical broadcast channel
(PBCH).
[0026] Retransmission control according to a hybrid ARQ (HARQ) is
applied to a downlink shared channel (DL-SCH). The DL-SCH enables
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
user equipment for enabling the user equipment to save power. The
DL-SCH is mapped to the physical downlink shared channel
(PDSCH).
[0027] The paging channel (PCH) supports DRX of the user equipment
for enabling the user equipment to save power. The PCH is required
to 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.
[0028] The multicast channel (MCH) is used for broadcast to the
entire coverage of the base station (cell). The MCH supports SFN
combining of MBMS service (MTCH and MCCH) in multi-cell
transmission. The MCH supports semi-static resource allocation. The
MCH is mapped to the PMCH.
[0029] Retransmission control according to a hybrid ARQ (HARQ) is
applied to an uplink shared channel (UL-SCH). The UL-SCH supports
dynamic or semi-static resource allocation. The UL-SCH is mapped to
the physical uplink shared channel (PUSCH).
[0030] A random access channel (RACH) shown in FIG. 5(B) is limited
to control information. The RACH involves a collision risk. The
RACH is mapped to the physical random access channel (PRACH).
[0031] The HARQ is described. The HARQ is the technique for
improving the communication quality of a channel by combination of
automatic repeat request and error correction (forward error
correction). The HARQ has an advantage 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.
[0032] An example of the retransmission method is described. In a
case where the receiver fails to successfully decode the received
data, in other words, in a case where 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. In a case where the receiver successfully decodes the
received data, in other words, in a case where 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.
[0033] Examples of the HARQ system include chase combining. In
chase combining, the same data is transmitted in the first
transmission and retransmission, which is the system for improving
gains by combining the data of the first transmission and the data
of the retransmission in retransmission. This is based on the idea
that correct data is partially included even if the data of the
first transmission contains an error, and highly accurate data
transmission is enabled by combining the correct portions of the
first transmission data and the retransmission data. Another
example of the HARQ system is incremental redundancy (IR). The IR
is aimed to increase redundancy, where a parity bit is transmitted
in retransmission to increase the redundancy by combining the first
transmission and retransmission, to thereby improve the quality by
an error correction function.
[0034] Logical channels described in Non-Patent Document 1 (Chapter
6) are described with reference to FIG. 6. FIG. 6 is a diagram
illustrating logical channels used in an LTE communication system.
FIG. 6(A) shows mapping between a downlink logical channel and a
downlink transport channel. FIG. 6(B) shows mapping between an
uplink logical channel and an uplink transport channel.
[0035] 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.
[0036] A paging control channel (PCCH) is a downlink channel for
transmitting changes of the paging information and system
information. The PCCH is used when the network does not know the
cell location of a user equipment. The PCCH that is a logical
channel is mapped to the paging channel (PCH) that is a transport
channel.
[0037] A common control channel (CCCH) is a channel for
transmission control information between user equipments and a base
station. The CCCH is used in a case where the user equipments have
no RRC connection with the network. In a downlink direction, the
CCCH is mapped to the downlink shared channel (DL-SCH) that is a
transport channel. In an uplink direction, the CCCH is mapped to
the uplink shared channel (UL-SCH) that is a transport channel.
[0038] 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 user equipment. The MCCH is used only by a user equipment
during reception of the MBMS. The MCCH is mapped to the multicast
channel (MCH) that is a transport channel.
[0039] A dedicated control channel (DCCH) is a channel for
point-to-point transmission of the dedicated control information
between a user equipment and a network. The DCCH is used when a
user equipment is in 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.
[0040] A dedicated traffic channel (DTCH) is a point-to-point
communication channel for transmission of the user information to a
dedicated user equipment. 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-SCH) in
downlink.
[0041] A multicast traffic channel (MTCH) is a downlink channel for
traffic data transmission from a network to a user equipment. The
MTCH is a channel used only by a user equipment during reception of
the MBMS. The MTCH is mapped to the multicast channel (MCH).
[0042] GCI represents a global cell identity. A closed subscriber
group cell (CSG cell) is introduced in the LTE, long term evolution
advanced (LTE-A) described below, and universal mobile
telecommunication system (UNITS). The CSG is described below (see
Chapter 3.1 of Non-Patent Document 3). The closed subscriber group
cell (CSG cell) is a cell in which subscribers who are allowed to
use are specified by an operator (hereinafter, referred to as "cell
for specific subscribers" in some cases).
[0043] The specified subscribers are allowed to access one or more
cells of a public land mobile network (PLMN). One or more cells in
which the specified subscribers are allowed access are referred to
as "CSG cell(s)". Note that access is restricted in the PLMN. The
CSG cell is part of the PLMN that broadcasts a specific CSG
identity (CSG ID; CSG-ID) and broadcasts "TRUE" by 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.
[0044] The CSG-TD is broadcast by the CSG cell or cells. A
plurality of CSG-TDs exist in a mobile communication system. The
CSG-IDs are used by user equipments (UEs) for making access from
CSG-related members easier.
[0045] The locations of user equipments are tracked based on an
area composed of one or more cells. The locations are tracked for
enabling tracking of the locations of user equipments and calling
(calling of user equipments) even in an idle state. An area for
tracking locations of user equipments is referred to as a tracking
area.
[0046] A CSG whitelist is a list that may be stored in a universal
subscriber identity module (USIM) in which all CSG IDs of the CSG
cells to which the subscribers belong are recorded. The CSG
whitelist is merely referred to as whitelist or is referred to as
an allowed CSG list in some cases. The MME performs access control
for the UEs accessing through CSG cells (see Chapter 4.3.1.2 of
Non-Patent Document 9). Specific examples of the access by user
equipments include attach, combined attach, detach, service
request, and tracking area update procedure (see Chapter 4.3.1.2 of
Non-Patent Document 9).
[0047] Service types of a user equipment in an idle state are
described below (see Chapter 4.3 of Non-Patent Document 3). The
service types of a user equipment in an idle state are classified
into a limited service (also referred to as closed service), a
normal service, and an operator service. The limited service
includes emergency calls, an earthquake and tsunami warning system
(ETWS), and a commercial mobile alert system (CMAS) on an
acceptable cell described below. The normal service (also referred
to as standard service) is the service for public use on a suitable
cell described below. The operator service is the service for
operators only on a reserved cell described below.
[0048] A "suitable cell" is described below. The "suitable cell" is
a cell on which a UE may camp to obtain a normal service. Such a
cell shall fulfill the following conditions (1) and (2).
[0049] (1) The cell is part of the selected PLMN or the registered
PLMN, or part of the PLMN of an "equivalent PLMN list".
[0050] (2) According to the latest information provided by a
non-access stratum (NAS), the cell shall further fulfill the
following conditions (a) to (d):
[0051] (a) the cell is not a barred cell;
[0052] (b) the cell is part of a tracking area (TA), not part of
the list of "forbidden LAs for roaming", where the cell needs to
fulfill (1) above;
[0053] (c) the cell shall fulfill the cell selection criteria;
and
[0054] (d) for a cell specified as CSG cell by system information
(SI), the CSG-ID is part of a "CSG whitelist" of the UE (contained
in the CSG whitelist of the UE).
[0055] An "acceptable cell" is described below. This is the cell on
which a UE may camp to obtain limited service. Such a cell shall
fulfill all the requirements of (1) and (2) below.
[0056] (1) The cell is not a barred cell. (2) The cell fulfills the
cell selection criteria.
[0057] "Barred cell" is shown in the system information. "Reserved
cell" is shown in the system information.
[0058] "Camping on a cell" represents the state where a UE has
completed the cell selection/reselection process and the UE has
selected a cell for monitoring the system information and paging
information. A cell on which the UE camps is referred to as
"serving cell" in some cases.
[0059] Base stations referred to as Home-NodeB (Home-NB; HNB) and
Home-eNodeB (Home-eNB; HeNB) are studied in 3GPP. HNB/HeNB is a
base station for, for example, household, corporation or commercial
access service in UTRAN/E-UTRAN. Non-Patent Document 4 discloses
three different modes of the access to the HeNB and HNB.
Specifically, those are an open access mode, a closed access mode
and a hybrid access mode.
[0060] The respective modes have the following characteristics. In
the open access mode, the HeNB and HNB are operated as a normal
cell of a normal operator. In the closed access mode, the HeNB and
HNB are operated as a CSG cell. The CSG cell is a cell where only
CSG members are allowed access. In the hybrid access mode, non-CSG
members are allowed access at the same time. In other words, a cell
in the hybrid access mode (also referred to as hybrid cell) is the
cell that supports both the open access mode and the closed access
mode.
[0061] According to 3GPP, there is a range of PCIs in all physical
cell identities (PCIs), which is reserved by the network for use by
CSG cells (see Chapter 10.5.1.1 of Non-Patent Document 1).
Splitting the range of PCIs is referred to PCI-split at times. The
PCI split information is broadcast in the system information from
the base station to the user equipments being served thereby.
Non-Patent Document 5 discloses the basic operation of a user
equipment using PCI split. The user equipment that does not have
the PCI split information needs to perform cell search using all
PCIs, for example, using all 504 codes. On the other hand, the user
equipment that has the PCI split information is capable of
performing cell search using the PCI split information.
[0062] Further, specifications standard of long term evolution
advanced (LTE-A) as Release 10 are pursued in 3GPP (see Non-Patent
Document 6 and Non-Patent Document 7).
[0063] As to the LTE-A system, it is studied that a relay and a
relay node (RN) are supported for achieving a high data rate, high
cell-edge throughput, new coverage area, and the like. The relay
node is wirelessly connected to the radio-access network via a
donor cell (Donor eNB; DeNB). The network (NW)-to-relay node link
shares the same frequency band (hereinafter, referred to as
"frequency band" in some cases) with the network-to-UE link within
the range of the donor cell. In this case, the UE in Release 8 can
also be connected to the donor cell. The link between a donor cell
and a relay node is referred to as a backhaul link, and the link
between the relay node and the UE is referred to as an access
link.
[0064] As the method of multiplexing a backhaul link in frequency
division duplex (FDD), the transmission from DeNB to RN is carried
out in a downlink (DL) frequency band, and the transmission from RN
to DeNB is carried out in an uplink (UL) frequency band. As the
method of dividing resources in relays, a link from DeNB to RN and
a link from RN to UE are time-division multiplexed in one frequency
band, and a link from RN to DeNB and a link from UE to RN are also
time-division multiplexed in one frequency band. This enables to
prevent, in a relay, the transmission of the relay from interfering
with the reception of the own relay.
[0065] Not only a normal eNB (macro cell) but also so-called local
nodes such as pico eNB (pico cell), HeNB (HNB, CSG cell), node for
hotzone cells, relay node, remote radio head (RRH) and repeater are
studied in 3GPP. The network composed of various types of cells as
described above is also referred to as a heterogeneous network
(HetNet) in some cases.
[0066] The frequency bands (hereinafter, referred to as "operating
bands" in some cases) usable for communication have been
predetermined in the LTE. Non-Patent Document 8 describes the
frequency bands. In the frequency division duplex (FDD)
communication, a frequency band for downlink (hereinafter, referred
to as "downlink frequency band" in some cases) and a frequency band
for uplink (hereinafter, referred to as "uplink frequency band" in
some cases) that is paired with the downlink frequency band have
been predetermined, where the uplink frequency band differs from
the downlink frequency band. This is because the downlink and
uplink are necessarily required for conventional communication such
as voice communication so that transmission/reception are enabled
at the same time by splitting the frequencies between downlink and
uplink in the FDD.
[0067] In the FDD, a default value of an interval (TX-RX frequency
separation) between a carrier frequency of resources for use in
downlink (hereinafter, referred to as "downlink carrier frequency"
in some cases) and a carrier frequency of resources for use in
uplink (hereinafter, referred to as "uplink carrier frequency" in
some cases) is determined per frequency band. Non-Patent Document 8
describes a default value at the TX-RX frequency separation.
[0068] In the LTE, a cell broadcasts, to UEs being served thereby,
the frequency band information and uplink carrier frequency
deployed by the own cell as broadcast information. Specifically,
the frequency band information is included in the SIB1. The uplink
carrier frequency is included in the SIB2. In a case where the
uplink carrier frequency is not included in the SIB2, the uplink
carrier frequency is derived from the downlink carrier frequency
using the default value at the TX-RX frequency separation. The UE
is capable of recognizing the downlink carrier frequency through
cell selection or reselection and is capable of obtaining the
frequency band and uplink carrier frequency deployed by the cell
through reception of the broadcast information from the cell.
[0069] As disclosed in Non-Patent Document 1, the development of
"long term evolution advanced (LTE-A)" specifications as Release 10
is pursued in 3GPP.
[0070] Carrier aggregation (CA) is studied in the LTE-A system, in
which two or more component carriers (CCs) are aggregated to
support wider transmission bandwidths up to 100 MHz.
[0071] A Release 8 or 9-compliant UE, which supports LTE, is
capable of transmission/reception on only the CC corresponding to
one serving cell. On the other hand, it is conceivable that a
Release 10-compliant UE may have the capability of
transmission/reception, only reception, or only transmission on the
CCs corresponding to a plurality of serving cells at the same
time.
[0072] Each CC employs the configuration of Release 8 or 9, and the
CA supports contiguous CCs, non-contiguous CCs, and CCs in
different frequency bandwidths. The UE cannot configure the number
of uplink CCs (UL CCs) equal to or more than the number of downlink
CCs (DL CCs). The CCs configured by the same eNBs do not need to
provide the same coverage. The CC is compatible with Release 8 or
9.
[0073] In CA, an independent HARQ entity is provided per serving
cell in uplink as well as downlink. A transport block is generated
per TTI for each serving cell. Each transport block and HARQ
retransmission are mapped to a single serving cell.
[0074] In a case where CA is configured, a UE has single RRC
connection with a NW. In RRC connection, one serving cell provides
NAS mobility information and security input. This cell is referred
to as 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).
[0075] A secondary cell (SCell) is configured to form a pair of a
PCell and a serving cell, 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).
[0076] A pair of one PCell and a serving cell configured by one or
more SCells is configured for one UE.
[0077] In each SCell, a UE is capable of using resources for uplink
(UL) in addition to resources for downlink (DL). The number of DL
SCCs is equal to or more than the number of UL SCCs. No SCell is
used for only resources for UL. Each resource for UL belongs to
only one serving cell for one UE. The number of serving cells
depends on the UE capability.
[0078] The PCell is changed through only a HO procedure. The PCell
is used for transmission of PUCCH. The PUCCH for HARQ of the DL-SCH
without UL-SCH is transmitted through only UL PCC. Differently from
SCells, the PCell is not de-activated.
[0079] Re-establishment is triggered when the PCell results in a
radio link failure (RLF). Re-establishment is not triggered in a
case of SCells. The NAS information is obtained from the PCell.
[0080] The SCells are reconfigured, added, or removed through RRC.
Also in handover within the LTE, the SCells used together with a
target PCell are added, removed, or reconfigured through RRC.
[0081] In a case of SCell addition, dedicated RRC signaling is used
to transmit the all system information (SI) required for the SCell.
That is, addition is performed in a connected mode, and the UE does
not have to receive the SI broadcast from the SCell.
[0082] It is studied that a PCell notifies user equipments of SCell
addition/modification using "RRC Connection Reconfiguration
message" of dedicated RRC signaling (see Non-Patent Document 2). It
is studied that SCell release is notified UEs by a PCell using "RRC
Connection Reconfiguration message" of dedicated RRC signaling or
is triggered by "RRC Connection re-establishment" (see Non-Patent
Document 2). "RRC Connection Reconfiguration message" of dedicated
RRC signaling contains "SCell To AddModList" and "SCell To
ReleaseList".
[0083] In each cell, the SIB2 represents a carrier frequency of a
resource for uplink.
[0084] Local nodes are installed for complementing a macro cell in
response to demands for various services such as high-speed and
high-capacity communication. Accordingly, the local node may be
installed within the coverage of the macro cell. In this case, an
interference may occur from a user equipment to the local node.
[0085] A case in which a local node is a remote radio head (RRH)
and the coverage of the macro cell is larger than the coverage of
the RRH, that is, a case in which the downlink transmission power
of the macro cell is larger than the downlink transmission power of
the RRH is considered here as a specific example. The downlink
reception power of the user equipment at each point becomes smaller
as the distance from each node increases. The uplink transmission
power of the user equipment to each node needs to be increased as
the distance from each node increases.
[0086] The user equipment according to the conventional technique
camps on a cell having the best downlink reception quality, and
thereafter, starts communication as required (see Non-Patent
Document 3). In areas where the downlink reception power from the
macro cell is larger than the downlink reception power from the
RRH, the user equipment camps on the macro cell and performs uplink
transmission to the macro cell.
[0087] In the area where the uplink transmission power from the
user equipment to the macro cell is larger than the uplink
transmission power from the user equipment to the RRH among the
above-mentioned areas, the link between the UE and RRH is better
than the other link in uplink, whereas the link between the UE and
macro cell is better than the other link in downlink. As described
above, an imbalance in link, that is, a link imbalance occurs.
[0088] When a link imbalance occurs, an interference occurs from
the user equipment to the RRH due to relatively large uplink
transmission power from the user equipment to the macro cell. Due
to this interference, the communication between the user equipment
and macro cell or the communication between the user equipment and
RRH is hindered, leading to a reduction in throughput of the entire
communication system. Therefore, there is required a method of
reducing an interference occurring in a HetNet being a
heterogeneous network in which a macro cell and a local node
coexist, to thereby improve a throughput of the entire
communication system.
[0089] Non-Patent Document 10 discloses a solution to the
inter-cell interference problem in a heterogeneous network.
Specifically, the use of a radio link exclusively in uplink and
downlink during the communication of a user equipment is disclosed
as a solution. In this solution, the same frequency is used in the
respective cells.
[0090] Non-Patent Document 11 also discloses a solution to the
inter-cell interference problem in a heterogeneous network.
Specifically, the following solutions are disclosed; carrier
aggregation is performed in each cell with different carrier
frequencies between the macro cell and pico cell, and the user
equipment accesses the pico cell when the user equipment comes
closer to the pico cell. However, Non-Patent Document 11 does not
disclose the details of the method in which the user equipment
accesses the pico cell when the user equipment comes closer to the
pico cell.
[0091] Non-Patent Document 1 discloses several scenarios regarding
carrier aggregation. Among the scenarios disclosed in Non-Patent
Document 1, scenario 4 discloses that the RRH operating on a
frequency 2 (F2) is aggregated with the macro cell operating on a
frequency 1 (F1).
PRIOR ART DOCUMENTS
Non-Patent Documents
[0092] Non-Patent Document 1: 3GPP TS 36.300 V10.2.0 [0093]
Non-Patent Document 2: 3GPP TS 36.331 V10.0.0 [0094] Non-Patent
Document 3: 3GPP TS 36.304 V10.0.0 Chapter 3.1, Chapter 4.3,
Chapter 5.2.4 [0095] Non-Patent Document 4: 3GPP S1-083461 [0096]
Non-Patent Document 5: 3GPP R2-082899 [0097] Non-Patent Document 6:
3GPP TR 36.814 V9.0.0 [0098] Non-Patent Document 7: 3GPP TR 36.912
V9.3.0 [0099] Non-Patent Document 8: 3GPP TS 36.101 V10.0.0 [0100]
Non-Patent Document 9: 3GPP TR 23.830 V9.0.0 [0101] Non-Patent
Document 10: 3GPP R1-094246 [0102] Non-Patent Document 11: 3GPP
R1-100061
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0103] As described above, Non-Patent Document 10 discloses, as a
solution to the inter-cell interference problem in a heterogeneous
network, the use of a radio link exclusively in uplink and downlink
during the communication of a user equipment. However, Non-Patent
Document 10 does not disclose the details of the method of using a
radio link exclusively in uplink and downlink.
[0104] Non-Patent Document 11 discloses the following as solutions
to the inter-cell interference problem in a heterogeneous network;
carrier aggregation is performed in respective cells with different
carrier frequencies between the macro cell and pico cell, and the
user equipment accesses the pico cell when the user equipment comes
closer to the pico cell. However, Non-Patent Document 11 does not
disclose the details of the method in which the user equipment
accesses the pico cell when the user equipment comes closer to the
pico cell. Besides, Non-Patent Document 11 does not disclose the
configuration for carrier aggregation between the macro cell and
pico cell.
[0105] Non-Patent Document 1 discloses the carrier aggregation
between the RRH operating on the frequency 2 (F2) and the macro
cell operating on the frequency 1 (F1). However, Non-Patent
Document 1 does not disclose the details of the method of carrier
aggregation between the RRH and macro cell.
[0106] An object of the present invention is to provide a
communication system capable of improving the communication quality
in a case where a plurality of communication devices having
different sizes of ranges coexist, in which communication with a
terminal device is possible, to thereby improve the entire
throughput.
Means to Solve the Problem
[0107] A communication system according to the present invention
includes a movable terminal device and a plurality of communication
devices configured to perform radio communication with the terminal
device. The plurality of communication devices include a
large-scale communication device having a relatively large range in
which communication with the terminal device is possible and a
small-scale communication device having a relatively small range in
which the communication is possible. The large-scale communication
device and the small-scale communication device are configured to
communicate with each other and are installed such that at least
parts of the ranges in which the communication is possible overlap
each other. The small-scale communication device is configured to
receive an uplink resource transmitted to the large-scale
communication device from the terminal device and, upon receipt of
the uplink resource, transmits a reception signal regarding the
uplink resource received to the large-scale communication device.
The large-scale communication device combines a reception signal
regarding the uplink resource transmitted from the terminal device
and received and the reception signal regarding the uplink resource
transmitted from the small-scale communication device and
received.
[0108] Further, a communication system according to the present
invention includes a movable terminal device and a plurality of
communication devices configured to perform radio communication
with the terminal device. The plurality of communication devices
include a large-scale communication device having a relatively
large range in which communication with the terminal device is
possible and a small-scale communication device having a relatively
small range in which the communication is possible. The large-scale
communication device and the small-scale communication device are
installed such that at least parts of the ranges in which the
communication is possible overlap each other. A first cell is
formed of a first large-scale downlink component carrier and a
large-scale uplink component carrier, the first large-scale
downlink component carrier being used in a downlink transmission
from the large-scale communication device to the terminal device,
the large-scale uplink component carrier being used in an uplink
transmission from the terminal device to the large-scale
communication device. A second cell is formed of a second
large-scale downlink component carrier and a small-scale uplink
component carrier, the second large-scale downlink component
carrier having a frequency different from that of the first
large-scale downlink component carrier and being used in a downlink
transmission from the large-scale communication device to the
terminal device, the small-scale uplink component carrier being
used in an uplink transmission from the terminal device to the
small-scale communication device. The terminal device sets a
transmission condition for performing the uplink transmission from
the terminal device to the large-scale communication device or the
small-scale communication device as a transmission condition set in
advance for any one of the first cell and the second cell that
includes a component carrier having higher reception quality with
respect to the reception signal received from the transmission from
the terminal device, to thereby perform the uplink
transmission.
Effects of the Invention
[0109] According to the communication system of the present
invention, the communication quality in a case where a large-scale
communication device and a small-scale communication device are
installed to coexist can be improved, to thereby improve the
throughput of the entire communication system. Further, an effect
of relatively large uplink transmission power from the terminal
device to the large-scale communication device can be prevented
from affecting the reception of uplink transmission in the
small-scale communication device, leading to a reduction in
interference as the entire communication system.
[0110] 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
[0111] FIG. 1 is a diagram illustrating the configuration of an LTE
communication system.
[0112] FIG. 2 is a diagram illustrating the configuration of a
radio frame used in the LTE communication system.
[0113] FIG. 3 is a diagram illustrating the configuration of an
MBSFN frame.
[0114] FIG. 4 is a diagram illustrating physical channels used in
the LTE communication system.
[0115] FIG. 5 is a diagram illustrating transport channels used in
the LTE communication system.
[0116] FIG. 6 is a diagram illustrating logical channels used in
the LTE communication system.
[0117] FIG. 7 is a block diagram showing the overall configuration
of an LTE mobile communication system currently under discussion of
3GPP.
[0118] FIG. 8 is a block diagram showing the configuration of a
user equipment (user equipment 71 of FIG. 7) according to the
present invention.
[0119] FIG. 9 is a block diagram showing the configuration of a
base station (base station 72 of FIG. 7) according to the present
invention.
[0120] FIG. 10 is a block diagram showing the configuration of an
MME (MME unit 73 of FIG. 7) according to the present invention.
[0121] FIG. 11 is a block diagram showing the configuration of a
HeNBGW 74 shown in FIG. 7 that is a HeNBGW according to the present
invention.
[0122] FIG. 12 is a flowchart showing an outline from a cell search
to an idle state operation performed by a user equipment (UE) in
the LTE communication system.
[0123] FIG. 13 is a diagram showing the concept of CA.
[0124] FIG. 14 is a block diagram showing an example of the
respective configurations of a remote radio head 1401 and a macro
cell 1402.
[0125] FIG. 15 is a block diagram showing an example of the
configuration in a case where a remote radio head is added to a
base station.
[0126] FIG. 16 is a diagram showing a situation in a case where an
RRH 1603 is installed in a coverage 1602 of a macro cell 1601.
[0127] FIG. 17 is a diagram showing the downlink reception power
and uplink transmission power of a user equipment at points between
the macro cell 1601 and RRH 1603.
[0128] FIG. 18 is a diagram for describing the concept of a
solution in a first embodiment.
[0129] FIG. 19 is a diagram showing an example of a sequence of a
communication system in the first embodiment.
[0130] FIG. 20 is a diagram showing an example of a sequence of a
communication system in a first modification of the first
embodiment.
[0131] FIG. 21 is a diagram for describing the concept of a
solution in a second embodiment.
[0132] FIG. 22 is a diagram showing an example of a sequence in a
case where a user equipment configures a path loss suitable for an
optimum node based on measurement results.
[0133] FIG. 23 is a diagram showing an example of a sequence in a
case where a macro cell obtains an offset value and notifies a user
equipment of the offset value to configure path loss suitable for
an optimum node.
[0134] FIG. 24 is a diagram showing an example of a sequence of a
communication system in a second embodiment.
[0135] FIG. 25 is a diagram for describing the concept of a
solution in a third embodiment.
[0136] FIG. 26 is a diagram showing an example of a sequence of a
communication system in the third embodiment.
[0137] FIG. 27 is a diagram for describing the concept of a
solution in a first modification of the third embodiment.
[0138] FIG. 28 is a diagram for describing a problem in a fifth
embodiment.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
First Embodiment
[0139] FIG. 7 is a block diagram showing an overall configuration
of an LTE mobile communication system, which is currently under
discussion of 3GPP. Currently, an overall system configuration
including closed subscriber group (CSG) cells (Home-eNodeBs
(Home-eNB; HeNB) of E-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG
cells (eNodeB (eNB) of E-UTRAN, NodeB (NB) of UTRAN, and BSS of
GERAN) is studied in 3GPP and, as to E-UTRAN, the configuration as
shown in FIG. 7 is proposed (see Chapter 4.6.1 of Non-Patent
Document 1).
[0140] FIG. 7 is described. A user terminal device (hereinafter,
referred to as "user equipment" or "UE") 71 is capable of
performing radio communication with a base station device
(hereinafter, referred to as "base station") 72 and
transmits/receives signals through radio communication. The user
terminal device is equivalent to a communication terminal device.
The base stations 72 are classified into an eNB 72-1 that is a
macro cell and a Home-eNB 72-2 that is a local node. The eNB 72-1
is equivalent to a large-scale base station device and has a
relatively large-scale coverage as the coverage in a range in which
communication with the user equipment (UE) 71 is possible. The
Home-eNB 72-2 is equivalent to a small-scale base station device
and has a relatively small-scale coverage as the coverage.
[0141] The eNB 72-1 is connected to an MME/S-GW unit (hereinafter,
referred to as an "MME unit" in some cases) 73 including an MME,
S-GW or MME and S-GW through an S1 interface, and control
information is communicated between the eNB 72-1 and the MME unit
73. A plurality of MME units 73 may be connected to one eNB 72-1.
The eNBs 72-1 are connected to each other by means of an X2
interface, and control information is communicated between the eNBs
72-1.
[0142] The Home-eNB 72-2 is connected to the MME unit 73 by means
of an S1 interface, and the control information is communicated
between the Home-eNB 72-2 and the MME unit 73. A plurality of
Home-eNBs 72-2 are connected to one MME unit 73. Also, the
Home-eNBs 72-2 are connected to the MME units 73 through a Home-eNB
Gateway (HeNBGW) 74. The Home-eNBs 72-2 are connected to the HeNBGW
74 by means of the S1 interface, and the HeNBGW 74 is connected to
the MME units 73 through an S1 interface. One or a plurality of
Home-eNB s 72-2 are connected to one HeNBGW 74, and information is
communicated therebetween through an S1 interface. The HeNBGW 74 is
connected to one or a plurality of MME units 73, and information is
communicated therebetween through an S1 interface. The MME unit 73
and HeNBGW 74 are equivalent to host node devices, and control the
connection between the user equipment (UE) 71 and each of the eNB
72-1 and Home-eNB 72-2 being a base station.
[0143] Further, the configuration below is currently studied in
3GPP. The X2 interface between the Home-eNBs 72-2 is supported.
That is, the Home-eNBs 72-2 are connected to each other by means of
the X2 interface, and control information is communicated between
the Home-eNBs 72-2. The HeNBGW 74 appears to the MME unit 73 as the
Home-eNB 72-2. The HeNBGW 74 appears to the Home-eNB 72-2 as the
MME unit 73. The interfaces between the Home-eNBs 72-2 and the MME
units 73 are the same, which are the S1 interfaces, in both of the
case where the Home-eNB 72-2 is connected to the MME unit 73
through the HeNBGW 74 and the case where the Home-eNB 72-2 is
directly connected to the MME unit 73. The HeNBGW 74 does not
support the mobility to the Home-eNB 72-2 or the mobility from the
Home-eNB 72-2 that spans the plurality of MME units 73. The
Home-eNB 72-2 supports a single cell.
[0144] FIG. 8 is a block diagram showing the configuration of the
user equipment (user equipment 71 of FIG. 7) according to the
present invention. The transmission process of the user equipment
71 shown in FIG. 8 is described. First, a transmission data buffer
unit 803 stores the control data from a protocol processing unit
801 and the user data from an application unit 802. The data stored
in the transmission data buffer unit 803 is transmitted to an
encoding unit 804 and is subjected to an encoding process such as
error correction. There may exist the data output from the
transmission data buffer unit 803 directly to a modulating unit 805
without the encoding process. The data encoded by the encoding unit
804 is modulated by the modulating unit 805. The modulated data is
output to a frequency converting unit 806 after being converted
into a baseband signal, and then is converted into a radio
transmission frequency. After that, a transmission signal is
transmitted from an antenna 807 to the base station 72.
[0145] The user equipment 71 executes the reception process as
follows. The radio signal is received through the antenna 807 from
the base station 72. The received signal is converted from a radio
reception frequency to a baseband signal by the frequency
converting unit 806 and is then demodulated by a demodulating unit
808. The demodulated data is transmitted to a decoding unit 809 and
is subjected to a decoding process such as error correction. Among
the pieces of decoded data, the control data is transmitted to the
protocol processing unit 801, while the user data is transmitted to
the application unit 802. A series of processes of the user
equipment 71 is controlled by a control unit 810. This means that,
though not shown in FIG. 8, the control unit 810 is connected to
the respective units 801 to 809.
[0146] FIG. 9 is a block diagram showing the configuration of the
base station (base station 72 of FIG. 7) according to the present
invention. The transmission process of the base station 72 shown in
FIG. 9 is described. An EPC communication unit 901 performs data
transmission/reception between the base station 72 and the EPCs
(such as MME unit 73 and HeNBGW 74). A communication with another
base station unit 902 performs data transmission/reception to/from
another base station. The EPC communication unit 901 and the
communication with another base station unit 902 respectively
transmit/receive information to/from a protocol processing unit
903. The control data from the protocol processing unit 903, and
the user data and control data from the EPC communication unit 901
and the communication with another base station unit 902 are stored
in a transmission data buffer unit 904.
[0147] The data stored in the transmission data buffer unit 904 is
transmitted to an encoding unit 905 and is then subjected to an
encoding process such as error correction. There may exist the data
output from the transmission data buffer unit 904 directly to a
modulating unit 906 without the encoding process. The encoded data
is modulated by the modulating unit 906. The modulated data is
output to a frequency converting unit 907 after being converted
into a baseband signal, and is then converted into a radio
transmission frequency. After that, a transmission signal is
transmitted to one or a plurality of user equipments 71 through an
antenna 908.
[0148] While, the reception process of the base station 72 is
executed as follows. Radio signals from one or a plurality of user
equipments 71 are received through the antenna 908. The received
signal is converted from a radio reception frequency into a
baseband signal by the frequency converting unit 907, and is then
demodulated by a demodulating unit 909. The demodulated data is
transmitted to a decoding unit 910 and is then subjected to a
decoding process such as error correction. Among the pieces of
decoded data, the control data is transmitted to the protocol
processing unit 903, EPC communication unit 901, or communication
with another base station unit 902, while the user data is
transmitted to the EPC communication unit 901 and the communication
with another base station unit 902. A series of processes by the
base station 72 is controlled by a control unit 911. This means
that, though not shown in FIG. 9, the control unit 911 is connected
to the respective units 901 to 910.
[0149] The functions of the Home-eNB 72-2 currently under
discussion of 3GPP are described below (see Chapter 4.6.2 of
Non-Patent Document 1). The Home-eNB 72-2 has the same function as
that of the eNB 72-1. In addition, the Home-eNB 72-2 has the
function of discovering a suitable serving HeNBGW 74 in a case of
connection to the HeNBGW 74. The Home-eNB 72-2 is connected only to
one HeNBGW 74. That is, in a case of the connection to the HeNBGW
74, the Home-eNB 72-2 does not use the Flex function in the S1
interface. When the Home-eNB 72-2 is connected to one HeNBGW 74, it
is not simultaneously connected to another HeNBGW 74 or another MME
unit 73.
[0150] The TAC and PLMN ID of the Home-eNB 72-2 are supported by
the HeNBGW 74. When the Home-eNB 72-2 is connected to the HeNBGW
74, selection of the MME unit 73 at "UE attachment" is performed by
the HeNBGW 74 instead of the Home-eNB 72-2. The Home-eNB 72-2 may
be deployed without network planning. In this case, the Home-eNB
72-2 is moved from one geographical area to another geographical
area. Accordingly, the Home-eNB 72-2 in this case is required to be
connected to a different HeNBGW 74 depending on its location.
[0151] FIG. 10 is a block diagram showing the configuration of the
MME according to the present invention. FIG. 10 shows the
configuration of an MME 73a included in the MME unit 73 shown in
FIG. 7 described above. A PDN GW communication unit 1001 performs
data transmission/reception between the MME 73a and a PDN GW. A
base station communication unit 1002 performs data
transmission/reception between the MME 73a and the base station 72
by means of the S1 interface. In the case where the data received
from the PDN GW is user data, the user data is transmitted from the
PDN GW communication unit 1001 to the base station communication
unit 1002 through a user plane communication unit 1003 and is then
transmitted to one or a plurality of base stations 72. In the case
where the data received from the base station 72 is user data, the
user data is transmitted from the base station communication unit
1002 to the PDN GW communication unit 1001 through the user plane
communication unit 1003 and is then transmitted to the PDN GW.
[0152] In the case where the data received from the PDN GW is
control data, the control data is transmitted from the PDN GW
communication unit 1001 to a control plane control unit 1005. In
the case where the data received from the base station 72 is
control data, the control data is transmitted from the base station
communication unit 1002 to the control plane control unit 1005.
[0153] A HeNBGW communication unit 1004 is provided in the case
where the HeNBGW 74 is provided, which performs data
transmission/reception by means of the interface (IF) between the
MME 73a and the HeNBGW 74 according to an information type. The
control data received from the HeNBGW communication unit 1004 is
transmitted from the HeNBGW communication unit 1004 to the control
plane control unit 1005. The processing results of the control
plane control unit 1005 are transmitted to the PDN GW through the
PDN GW communication unit 1001. The processing results of the
control plane control unit 1005 are transmitted to one or a
plurality of base stations 72 by means of the S1 interface through
the base station communication unit 1002, and are transmitted to
one or a plurality of HeNBGWs 74 through the HeNBGW communication
unit 1004.
[0154] The control plane control unit 1005 includes an NAS security
unit 1005-1, an SAE bearer control unit 1005-2, and an idle state
mobility managing unit 1005-3, and performs an overall process for
the control plane. The NAS security unit 1005-1 provides, for
example, security of a non-access stratum (NAS) message. The SAE
bearer control unit 1005-2 manages, for example, a system
architecture evolution (SAE) bearer. The idle state mobility
managing unit 1005-3 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 paging signaling in an idle
state, addition, deletion, update, and search of a tracking area
(TA) of one or a plurality of user equipments 71 being served
thereby, and tracking area list (TA list) management.
[0155] The MME 73a begins a paging protocol by transmitting a
paging message to the cell belonging to a tracking area (TA) with
which the UE is registered. The idle state mobility managing unit
1005-3 may manage the CSG of the Home-eNBs 72-2 to be connected to
the MME 73a, CSG-IDs, and a whitelist.
[0156] In the CSG-ID management, the relationship between a user
equipment corresponding to the CSG-ID and the CSG cell is managed
(added, deleted, updated or searched). For example, it may be the
relationship between one or a plurality of user equipments whose
user access has been registered with a CSG-ID and the CSG cells
belonging to this CSG-ID. In the whitelist management, the
relationship between the user equipment and the CSG-ID is managed
(added, deleted, updated, or searched). For example, one or a
plurality of CSG-IDs with which user registration has been
performed by a user equipment may be stored in the whitelist. The
above-mentioned management related to the CSG may be performed by
another part of the MME 73a. A series of processes by the MME 73a
is controlled by a control unit 1006. This means that, though not
shown in FIG. 10, the control unit 1006 is connected to the
respective units 1001 to 1005.
[0157] The function of the MME 73a currently under discussion of
3GPP is described below (see Chapter 4.6.2 of Non-Patent Document
1). The MME 73a performs access control for one or a plurality of
user equipments being members of closed subscriber groups (CSGs).
The MME 73a recognizes the execution of paging optimization as an
option.
[0158] FIG. 11 is a block diagram showing the configuration of the
HeNBGW 74 shown in FIG. 7 that is a HeNBGW according to the present
invention. An EPC communication unit 1101 performs data
transmission/reception between the HeNBGW 74 and the MME 73a by
means of the S1 interface. A base station communication unit 1102
performs data transmission/reception between the HeNBGW 74 and the
Home-eNB 72-2 by means of the S1 interface. A location processing
unit 1103 performs the process of transmitting, to a plurality of
Home-eNBs 72-2, the registration information or the like among the
data transmitted from the MME 73a through the EPC communication
unit 1101. The data processed by the location processing unit 1103
is transmitted to the base station communication unit 1102 and is
transmitted to one or a plurality of Home-eNBs 72-2 through the S1
interface.
[0159] The data only caused to pass through (to be transparent)
without requiring the process by the location processing unit 1103
is passed from the EPC communication unit 1101 to the base station
communication unit 1102, and is transmitted to one or a plurality
of Home-eNBs 72-2 through the S1 interface. A series of processes
by the HeNBGW 74 is controlled by a control unit 1104. This means
that, though not shown in FIG. 11, the control unit 1104 is
connected to the respective units 1101 to 1103.
[0160] The function of the HeNBGW 74 currently under discussion of
3GPP is described below (see Chapter 4.6.2 of Non-Patent Document
1). The HeNBGW 74 relays an S1 application. The HeNBGW 74
terminates the S1 application that is not linked to the user
equipment 71 though it is a part of the procedures toward the
Home-eNB 72-2 and towards the MME 73a. When the HeNBGW 74 is
deployed, the procedure that is not linked to the user equipment 71
is communicated between the Home-eNB 72-2 and the HeNBGW 74 and
between the HeNBGW 74 and the MME 73a. The X2 interface is not set
between the HeNBGW 74 and another node. The HeNBGW 74 recognizes
the execution of paging optimization as an option.
[0161] Next, an example of a typical cell search method in a mobile
communication system is described. FIG. 12 is a flowchart showing
an outline from a cell search to an idle state operation performed
by a user equipment (UE) in the LTE communication system. When
starting the cell search, in Step ST1201, the user equipment
synchronizes the slot timing and frame timing by a primary
synchronization signal (P-SS) and a secondary synchronization
signal (S-SS) transmitted from a neighbour base station.
Synchronization codes, which correspond to physical cell identities
(PCIs) assigned per cell one by one, are assigned to the
synchronization signals (SSs) including the P-SS and S-SS. The
number of PCIs is currently studied in 504 ways, and these 504 ways
are used for synchronization, and the PCIs of the synchronized
cells are detected (specified).
[0162] Next, in Step ST1202, the user equipment detects a reference
signal (RS) (cell-specific reference signal (CRS)) transmitted from
the base station per cell and measures the received power (also
referred to as RSRP). The code corresponding to the PCI one by one
is used for the reference signal (RS), and 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 ST1201, which
makes it possible to detect the RS and measure the RS received
power.
[0163] Next, in Step ST1203, the user equipment selects the cell
having the best RS reception quality, for example, cell having the
highest RS received power, that is, best cell from one or more
cells that have been detected up to Step ST1202.
[0164] In Step ST1204, 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 transmission
bandwidth configuration (dl-bandwidth)), transmission antenna
number, and system frame number (SFN).
[0165] In Step ST1205, 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
related to the access to the cell, information related to cell
selection, and scheduling information of other SIB (SIBk; k is an
integer equal to or larger than two). In addition, the SIB1
contains a tracking area code (TAC).
[0166] In Step ST1206, next, the user equipment compares the TAC of
the SIB1 received in Step ST1205 with the TAC in the tracking area
(TA) list that has been already possessed by the user equipment. In
a case where the TAC received in Step ST1205 is identical to the
TAC included in the tracking area (TA) list as a result of the
comparison, the user equipment enters an idle state operation in
the cell. In a case where the TAC received in Step ST1205 is not
included in the tracking area (TA) list as a result of the
comparison, the user equipment requires a core network (EPC)
(including MME and the like) to change a tracking area (TA) through
the cell for performing tracking area update (TAU). The core
network updates the tracking area (TA) list based on an
identification number (such as a UE-ID) of the user equipment
transmitted from the user equipment together with a TAU request
signal. The core network transmits the updated tracking area (TA)
list to the user equipment. The user equipment rewrites (updates)
the TAC list of the user equipment with the received tracking area
(TA) list. After that, the user equipment enters the idle state
operation in the cell.
[0167] As to the LTE, LTE-A, and universal mobile telecommunication
system (UMTS), the introduction of a closed subscriber group (CSG)
cell is studied. As described above, access is allowed for only one
or a plurality of user equipments registered with the CSG cell. A
CSG cell and one or a plurality of user equipments registered with
the CSG cell constitute one CSG. A specific identification number
referred to as CSG-ID is added to the thus constituted CSG. Note
that one CSG may contain a plurality of CSG cells. After being
registered with any one of the CSG cells, the user equipment can
access another CSG cell of the CSG to which the registered CSG cell
belongs.
[0168] Alternatively, the Home-eNB in the LTE and LTE-A or the
Home-NB in the UMTS is used as the CSG cell in some cases. The user
equipment registered with the CSG cell has a whitelist.
Specifically, the whitelist is stored in the subscriber identity
module (SIM)/USIM. The CSG information of the CSG cell with which
the user equipment has been registered is stored in the whitelist.
Specific examples of the CSG information include CSG-ID, tracking
area identity (TAI) and TAC. Any one of the CSG-ID and TAC is
adequate as long as they are associated with each other.
Alternatively, GCI is adequate as long as the CSG-ID and TAC are
associated with global cell identity (GCI).
[0169] As can be seen from the above, the user equipment that does
not have a whitelist (including a case where the whitelist is empty
in the present invention) is not allowed to access the CSG cell but
is allowed to access the non-CSG cell only. On the other hand, the
user equipment which has a whitelist is allowed to access the CSG
cell of the CSG-ID with which registration has been performed as
well as the non-CSG cell.
[0170] All physical cell identities (PCIs) are split into ones
reserved for CSG cells and the others reserved for non-CSG cells is
discussed in 3GPP (see Non-Patent Document 1). There is a range of
PCIs in all the PCIs, which is reserved by the network for use by
CSG cells (see Chapter 10.5.1.1 of Non-Patent Document 1).
Splitting the range of PCIs is referred to PCI-split as times. The
PCI split information is broadcast in the system information from
the base station to the user equipments being served thereby.
Non-Patent Document 5 discloses the basic operation of a user
equipment by PCI split. The user equipment that does not have the
PCI split information needs to perform cell search using all the
PCIs, for example, using all 504 codes. On the other hand, the user
equipment that has the PCI split information is capable of
performing cell search using the PCI split information.
[0171] Further, it has been determined that the PCIs for hybrid
cells are not contained in the PCI range for CSG cells in 3GPP (see
Chapter 10.7 of Non-Patent Document 1).
[0172] According to 3GPP, there are two modes in the method of
selecting or reselecting a CSG cell by a user equipment. One is an
automatic mode. The feature of the automatic mode is described
below. The user equipment performs selection or reselection with
the use of an allowed CSG list (allowed CSG ID list) in the user
equipment. After the completion of PLMN selection, the user
equipment camps on one cell in the selected PLMN only in a case of
a non-CSG cell or a CSG cell with a CSG ID present in the allowed
CSG list. The user equipment disables an autonomous search function
of the CSG cell if the allowed CSG list of the user equipment is
empty (see Chapter 5.2.4.8.1 of Non-Patent Document 3).
[0173] The second is a manual mode. The feature of the manual mode
is described below. The user equipment shows a list of available
CSGs in the currently selected PLMN to a user. The list of CSGs
provided to the user by the user equipment is not limited to the
CSGs included in the allowed CSG list stored in the user equipment.
The user selects the CSG based on the list of CSGs, and then, the
user equipment camps on the cell with the selected CSG ID, to
thereby attempt registration (see Non-Patent Document 3).
[0174] The HeNB and HNB are required to support various services.
For example, an operator causes the predetermined HeNB and HNB to
register user equipments therein and permits only the registered
user equipments to access the cells of the HeNB and HNB, which
increases radio resources available for the user equipments and
enables high-speed communication. In such a service, the operator
correspondingly sets a higher accounting fee compared with a normal
service.
[0175] In order to achieve the above-mentioned service, the closed
subscriber group cell (CSG cell) accessible only to the registered
(subscribed or member) user equipments is introduced. It is
required to install a large number of closed subscriber group cells
(CSG cells) in shopping malls, apartment buildings, schools,
companies and the like. For example, the following manner of use is
required; the CSG cells are installed for each store in shopping
malls, for each room in apartment buildings, for each classroom in
schools, and for each section in companies such that only the users
who have registered with the respective CSG cells are permitted to
use those CSG cells. The HeNB/HNB is required not only to
complement the communication outside the coverage of the macro cell
(area complementing HeNB/HNB) but also to support various services
as described above (service providing HeNB/HNB). This also leads to
a case where the HeNB/HNB is installed within the coverage of the
macro cell.
[0176] As described above, CA is studied in the LTE-A system, in
which two or more CCs are aggregated to support frequency
bandwidths up to 100 MHz, which are wider than the frequency
bandwidths of the LTE system.
[0177] FIG. 13 is a diagram showing the concept of CA. An eNB shown
in FIG. 13 configures a cell n configured by a DL CCn and a UL CCn
which is associated with the DL-CCn by a DL/UL link via SIB2. The
carrier frequency of the DL CCn is denoted by Fn (DL), and the
carrier frequency of the UL CCn is denoted by Fn (UL). Here, n is
an integer of one to five.
[0178] A UE camps on the cell 1 and performs RRC connection
indicated by an arrow 1301. As a result, the cell 1 becomes a
PCell.
[0179] After that, the eNB notifies the UE of the information
related to the CCs to be aggregated through dedicated RRC signaling
indicated by an arrow 1302. The information related to a cell m
configured by a DL CCm and a UL CCm, for example, system
information is notified as the information related to the CCs.
Here, m is an integer of two to five. The eNB notifies the UE of
the information related to the CCs in this manner, whereby the cell
2 to the cell 5 become SCells.
[0180] As described above, the eNB performs CA for the UE with the
cell 1 to the cell 5. Then, the UE performs communication with the
cell 1 to the cell 5 based on CA, as indicated by an arrow
1303.
[0181] A configuration example of a UE that supports CA is
described. It suffices that in the configuration shown in FIG. 8
described above, a part or the whole of the modulating unit 805,
frequency converting unit 806, antenna 807, and demodulating unit
808 is caused to support a wider bandwidth. In the transmitter, a
part or the whole of the modulating unit 805, frequency converting
unit 806, and antenna 807 may be caused to operate in a band
including a predetermined number of contiguous UL CCs. In the
receiver, a part or the whole of the antenna 807, frequency
converting unit 806, and demodulating unit 808 may be caused to
operate in a band including a predetermined number of contiguous DL
CCs. This enables to support CA by a predetermined number of
contiguous UL CCs or DL CCs.
[0182] As another method, it suffices that a plurality of a part or
the whole of the modulating unit 805, frequency converting unit
806, antenna 807, and demodulating unit 808 are provided in
parallel so as to operate in a band including a predetermined
number of non-contiguous UL CCs or DL CCs. In the transmitter, a
plurality of a part or the whole of the modulating unit 805,
frequency converting unit 806, and antenna 807 may be provided in
parallel so as to operate in a band including a predetermined
number of non-contiguous UL CCs. In the receiver, a plurality of a
part or the whole of the antenna 807, frequency converting unit
806, and demodulating unit 808 may be provided in parallel so as to
operate in a band including a predetermined number of
non-contiguous DL CCs. This enables to support CA with a
predetermined number of non-contiguous UL CCs or DL CCs.
Alternatively, the two configurations described above may be
appropriately combined.
[0183] A configuration example of an eNB that supports CA is
described. It suffices that in the configuration shown in FIG. 9
described above, the protocol processing unit 903 performs the
process for a UE for which CA is performed per cell configured by
an eNB, and the transmission data buffer unit 904, encoding unit
905, modulating unit 906, frequency converting unit 907, antenna
908, demodulating unit 909, and decoding unit 910 are configured
per cell. This enables to perform CA for a UE by cells configured
by an eNB.
[0184] The base station has a configuration as described above in
FIG. 9. The remote radio head (RRH) is described below. The base
station is composed of functional units below. The functional units
include a control unit, a baseband unit, a path interface unit, and
a radio functional unit. The correspondence between each functional
unit and units forming the base station 72 shown in FIG. 9 is
described.
[0185] The control unit includes a control unit 911 that controls
the whole of the base station and a protocol processing unit 903
that processes the protocol related to the control for calling. The
baseband unit includes a transmission data buffer unit 904 that
stores user data and control data, an encoding unit 905 that
performs encoding, and a decoding unit 910 that performs
decoding.
[0186] The path interface unit includes an EPC communication unit
901 that performs data transmission/reception with the EPC, and a
communication with another base station unit 902 that performs data
transmission/reception with another base station. The radio
function unit includes a modulating unit 906 that performs
modulation, a frequency converting unit 907, an antenna 908 through
which transmission/reception of radio signals are performed, and a
demodulating unit 909 that performs demodulation. The frequency
converting unit 907 converts a baseband frequency of a baseband
signal into a radio transmission frequency and converts a radio
transmission frequency into a baseband frequency of a baseband
signal.
[0187] It is possible not only to collectively install all the
functional units forming the base station at one place but also to
separately install them. On this occasion, the separation needs not
to be made in units of the functional units described above but may
be separated in units that form each functional unit. In a case
where the units of the functional units are separately installed,
the separated units are connected to each other through a dedicated
line for enabling high-speed communication.
[0188] In a case where the units of the functional units are
separately installed, the portion including a radio portion for
transmission/reception of radio signals, specifically, the portion
including the antenna 908, in the configuration of the base station
is referred to as "remote radio head (RRH)". The portion including
the configuration that is not included in the remote radio head,
that is, the portion that does not include the radio portion, in
the configuration of the base station may be referred to as "macro
cell".
[0189] FIG. 14 is a block diagram showing an example of the
configurations of a remote radio head 1401 and a macro cell 1402.
The respective configurations of the remote radio head 1401 and
macro cell 1402 shown in FIG. 14 are similar to the configuration
of the base station 72 shown in FIG. 9, and thus, the corresponding
portions are denoted by the same reference numbers and common
description is not given here.
[0190] The remote radio head 1401 shown in FIG. 14 includes the
antenna 908 and a frequency converting unit 907 that serve as a
radio functional unit. The macro cell 1402 includes the components
of the base station except for the components that are included in
the remote radio head 1401. In the example shown in FIG. 14, the
macro cell 1402 includes the EPC communication unit 901,
communication with another base station unit 902, protocol
processing unit 903, transmission data buffer unit 904, encoding
unit 905, modulating unit 906, demodulating unit 909, decoding unit
910, and control unit 911.
[0191] The remote radio head 1401 and macro cell 1402 are connected
to each other through a dedicated line 1403. Data
transmission/reception is performed between the remote radio head
1401 and macro cell 1402 by baseband signals.
[0192] There is a conceivable case in which the remote radio head
includes the antenna 908, frequency converting unit 907, modulating
unit 906, and demodulating unit 909, and the macro cell includes
the encoding unit 905, decoding unit 910, transmission data buffer
unit 904, EPC communication unit 901, communication with another
base station unit 902, protocol processing unit 903, and control
unit 911, though different from the present embodiment. In this
case, data transmission/reception is performed between the remote
radio head and macro cell through the data before modulation and
data after demodulation.
[0193] There is another conceivable case in which the remote radio
head includes the antenna 908, frequency converting unit 907,
modulating unit 906, demodulating unit 909, encoding unit 905, and
decoding unit 910, and the macro cell includes the transmission
data buffer unit 904, EPC communication unit 901, communication
with another base station unit 902, protocol processing unit 903,
and control unit 911. In this case, data transmission/reception is
performed between the remote radio head and macro cell through the
data before encoding and data after decoding.
[0194] There is still another conceivable case in which the remote
radio head includes the antenna 908 and the macro cell includes the
frequency converting unit 907, modulating unit 906, demodulating
unit 909, encoding unit 905, decoding unit 910, transmission data
buffer unit 904, EPC communication unit 901, communication with
another base station unit 902, protocol processing unit 903, and
control unit 911. In this case, data transmission/reception is
performed between the remote radio head and macro cell by radio
signals (RF signals).
[0195] As shown in FIG. 9 described above, the remote radio head is
not used solely in a case where the base station 72 including all
the functional units that are integrally formed is separately
installed. For example, it is conceivable that the remote radio
head being a portion including a radio portion may be added to the
base station.
[0196] FIG. 15 is a block diagram showing an example of the
configuration in which the remote radio head is added to the base
station. The configuration shown in FIG. 15 is similar to the
configuration shown in FIG. 9, and thus, the corresponding portions
are denoted by the same reference numbers and common description is
not given here.
[0197] The base station shown in FIG. 15 includes a macro cell 1501
corresponding to the base station 72 shown in FIG. 9 and two remote
radio heads 1502 and 1503. The remote radio heads 1502 and 1503
shown in FIG. 15 each include the antenna 908 and frequency
converting unit 907 that serve as the radio functional unit shown
in FIG. 14. The remote radio heads 1502 and 1503 are each connected
to the macro cell 1501 through a dedicated line 1504. While two
remote radio heads are provided in the example shown in FIG. 15,
one or a plurality of remote radio heads may be provided.
[0198] The problem to be solved in the first embodiment is
described below. The macro cell and a local node such as remote
radio head (RRH) are installed to coexist, which construct a
network referred to as a heterogeneous network. In the
heterogeneous network, the local node is installed to complement
the macro cell in response to demands for various services such as
high-speed and high-capacity communication. Therefore, the local
node may be installed in the coverage of the macro cell. In this
case, an interference may occur between the macro cell and local
node.
[0199] A specific example of the interference occurring in a case
where the local node is installed in the coverage of the macro cell
is described below with reference to FIGS. 16 and 17. FIG. 16 is a
diagram showing a situation in which an RRH 1603 is installed in a
coverage 1602 of a macro cell 1601. FIG. 17 is a diagram showing
the downlink reception power and uplink transmission power of a
user equipment at each point between the macro cell 1601 and RRH
1603. In FIG. 17, the macro cell 1601 and RRH 1603 shown in FIG. 16
are represented as antennas.
[0200] In FIG. 17, the vertical axis and horizontal axis represent
the power and position, respectively. In FIG. 17, the downlink
reception power from the macro cell 1601 at each point is indicated
by a solid line downward to the right. The downlink reception power
from the RRH 1603 at each point is indicated by a solid line
downward to the left. The uplink transmission power to the macro
cell 1601 at each point is indicated by a chain double-dashed line
upward to the right. The uplink transmission power to the RRH 1603
at each point is indicated by a chain double-dashed line upward to
the left.
[0201] In the example shown in FIG. 16, the RRH 1603 is installed
in the coverage 1602 of the macro cell 1601. The RRH 1603 has a
coverage 1604. Considered here is a case in which the coverage 1602
of the macro cell 1601 is larger than the coverage 1604 of the RRH
1603 as a comparison therebetween, as shown in FIG. 16. This means
that the downlink transmission power of the macro cell 1601 is
larger than the downlink transmission power of the RRH 1603 as a
result of the comparison of downlink transmission power.
[0202] As indicated by the solid line downward to the right and
solid line downward to the left in FIG. 17, the downlink reception
power of the user equipment at each point becomes smaller as the
distances from the nodes, that is, the macro cell 1601 and RRH 1603
increase. As indicated by the chain double-dashed line upward to
the right and chain double-dashed line upward to the left in FIG.
17, the uplink transmission power to the nodes of the user
equipment, that is, the macro cell 1601 and RRH 1603 being base
stations needs to be increased as the distances from the nodes
increase. These are affected by a propagation loss. This
propagation loss may be referred to as "path loss".
[0203] The user equipment according to the conventional technique
camps on a cell having the best downlink reception quality, and
thereafter, starts communication as required (see Non-Patent
Document 3). For example, a case in which the user equipment is
located at a point C is considered here. As indicated by the solid
line downward to the right in FIG. 17, the downlink reception power
from the macro cell 1601 at the point C has a value D. As indicated
by the solid line downward to the left, the downlink reception
power from the RRH 1603 at the point C has a value E. The value D
is larger than the value E as shown in FIG. 17, and accordingly,
the user equipment camps on the macro cell 1601, and thereafter,
starts communication as required. That is, the user equipment
performs uplink transmission to the macro cell 1601 at the point
C.
[0204] As indicated by the chain double-dashed line upward to the
right in FIG. 17, the uplink transmission power to the macro cell
1601 at the point C has the value E. As indicated by the chain
double-dashed line upward to the left, the uplink transmission
power to the RRH 1603 at the point C has a value F. That is, at the
point C, the transmission power required for the uplink
transmission from the user equipment to the macro cell 1601 is
larger than the transmission power required for the uplink
transmission from the user equipment to the RRH 1603.
[0205] Therefore, at the point C, the link between the user
equipment and RRH 1603 is good in uplink, and the link between the
user equipment and macro cell 1601 is good in downlink.
[0206] In an area Z between the point A and point B shown in FIG.
17, similarly to the point C, the downlink reception power from the
macro cell 1601 is larger than the downlink reception power from
the RRH 1603, and the uplink transmission power to the macro cell
1601 is larger than the uplink transmission power to the RRH 1603.
Therefore, in the area Z between the point A and point B, similarly
to the point C, the link between the user equipment and RRH 1603 is
good in uplink, and the link between the user equipment and macro
cell 1601 is good in downlink.
[0207] As described above, an imbalance in link, that is, link
imbalance occurs in the area Z between the point A and point B. In
this area Z where a link imbalance has occurred, the uplink
transmission power from the user equipment to the macro cell 1601
is larger than the uplink transmission power from the user
equipment to the RRH 1603, causing an interference from the user
equipment to the RRH 1603. This interference hinders the
communication between the user equipment and macro cell 1601 or the
communication between the user equipment and RRH 1603, leading to a
reduction in throughput of the entire communication system.
[0208] Therefore, there is a required method of reducing an
interference occurring in a heterogeneous network in which the
macro cell 1601 and the local node such as the RRH 1603 are
installed to coexist as shown in FIG. 16, that is, in a HetNet, to
thereby improve the throughput of the entire communication
system.
[0209] Therefore, the first embodiment aims to reduce interferences
occurring from a user equipment to a local node by relatively large
uplink transmission power from the user equipment to the macro cell
due to an occurrence of a link imbalance. The first embodiment also
aims to prevent a reduction in throughput of the entire system due
to communication being hindered by this interference.
[0210] A solution in the first embodiment is described below. The
present embodiment specifically describes the remote radio head
(RRH) as a representative example of the local node. In the present
embodiment, the carrier frequency of the RRH and the carrier
frequency of the macro cell are different from each other, and the
RRH is provided with a function of receiving the uplink resource of
the macro cell, specifically, uplink carrier frequency band. The
carrier frequency may be a frequency of a component carrier. The
uplink resource of the macro cell refers to an uplink resource from
a user equipment (UE) to a macro cell, that is, uplink resource
transmitted from a UE to a macro cell.
[0211] The carrier frequency of the RRH and the carrier frequency
of the macro cell are different from each other as in the present
embodiment, which enables to reduce interferences from a user
equipment (UE) to a local node that occurs due to relatively large
uplink transmission power from the UE to the macro cell.
[0212] A specific example of the solution in the first embodiment
is described with reference to FIG. 18. FIG. 18 is a diagram for
describing the concept of the solution of the first embodiment. The
downlink carrier frequency and uplink carrier frequency of the
macro cell are represented as DL_f1 and UL_f1, respectively. The
downlink carrier frequency band and uplink carrier frequency band
of the macro cell are represented as DL1 and UL1, respectively. The
downlink carrier frequency and uplink carrier frequency of the RRH
are represented as DL_f2 and UL_f2, respectively. The downlink
carrier frequency band and uplink carrier frequency band of the RRH
are represented as DL2 and UL2, respectively. The macro cell and
RRH are equivalent to a large-scale communication device and a
small-scale communication device, respectively. The downlink
carrier frequency and uplink carrier frequency of the macro cell
are equivalent to a first frequency, and the downlink carrier
frequency and uplink carrier frequency of the RRH are equivalent to
a second frequency.
[0213] In the present embodiment, the RRH is provided with a
function of receiving the UL1 being the uplink carrier frequency
band of the macro cell in addition to a function of receiving the
UL2 being the uplink carrier frequency band of the RRH. More
specifically, the RRH is provided with the function of receiving
the UL1 being the uplink carrier frequency band of the macro cell
in addition to a function of transmitting the DL2 being the
downlink carrier frequency band of the RRH and the function of
receiving the UL2 being the uplink carrier frequency band of the
RRH. That is, the RRH is provided with a function of receiving the
uplink carrier frequency band of the macro cell in a portion
surrounded by a solid line in addition to a function of
transmitting or receiving a carrier frequency band of the RRH in a
portion surrounded by a dashed line shown in FIG. 18.
[0214] Meanwhile, the macro cell is provided with a function of
receiving the UL1 being the uplink carrier frequency band of the
macro cell. More specifically, the macro cell is provided with a
function of transmitting the DL1 being the downlink carrier
frequency band of the macro cell and a function of receiving the
UL1 being the uplink carrier frequency band of the macro cell. That
is, the macro cell is provided with a function of transmitting or
receiving the carrier frequency band of the macro cell in the
portion surrounded by a broken line shown in FIG. 18.
[0215] While FIG. 18 shows a case in which the DL1 being the
downlink carrier frequency band of the macro cell and the DL2 being
the downlink carrier frequency band of the RRH are contiguous, the
downlink carrier frequency band of the macro cell and the downlink
carrier frequency band of the RRH may be non-contiguous. Also,
while FIG. 18 shows a case in which the UL1 being the uplink
carrier frequency band of the macro cell and the UL2 being the
uplink carrier frequency band of the RRH are contiguous, the uplink
carrier frequency band of the macro cell and the uplink carrier
frequency band of the RRH may be non-contiguous.
[0216] Here, the data in the uplink resource, which is transmitted
from the user equipment to the macro cell and is received by the
macro cell, and the data in the uplink resource of the macro cell,
which is received by the RRH, are the same.
[0217] Specific examples regarding which RRH is provided with a
function of receiving the uplink resource of the macro cell include
a case in which the RRH being served by the macro cell is provided
with a function of receiving the uplink resource of the macro
cell.
[0218] The following three (1) to (3) are disclosed as specific
examples of the RRH being served by the macro cell.
[0219] (1) RRH connected to the macro cell through a dedicated
line. It may be judged that the RRH connected to the macro cell
through a dedicated line receives the uplink resource of the macro
cell.
[0220] (2) RRH sharing the function of the macro cell, which is,
for example, RRH that processes a protocol by a control unit
located in the macro cell. The RRH sharing the function of the
macro cell may judge to receive the uplink resource of the macro
cell.
[0221] (3) RRH located in the coverage of the macro cell. The RRH
that has judged to be located in the coverage of the macro cell may
judge to receive the uplink resource of this macro cell. Specific
examples of the method in which the RRH judges whether or not it is
located in the coverage of the macro cell include the method in
which the RRH measures the surrounding radio wave environment, that
is, radio wave environment of a neighboring cell. The RRH measures
the surrounding radio wave environment in power-on, during
initialization, or while transmission is stopped. Also, the RRH
measures the reception power of the cell existing near itself and
obtains the PCI being a cell identity of a cell, to thereby detect
the cell. On this occasion, the RRH may detect a cell having
reception power equal to or larger than a predetermined threshold.
The RRH judges to be located in the coverage of a cell having
reception power equal to or larger than the threshold. The RRH
notifies a cell, in the coverage of which the own RRH has judged to
be located, that the own RRH is located in the coverage of the
cell.
[0222] The method disclosed in the present embodiment is
appropriately applicable also to a case in which the radio wave
environment between the macro cell and RRH changes or the coverage
area changes due to changes in transmission power of the macro cell
and antenna configuration of the macro cell.
[0223] The following two (a) and (b) are disclosed as specific
examples of the notification method in a case where there are a
plurality of cells that have been judged to have the reception
power equal to or higher than a threshold. (a) The RRH notifies all
the cells that the own RRH is located in the coverages of those
cells. (b) The RRH notifies a cell having the best measurement
results, that is, a cell having high reception power or small path
loss that the own RRH is located in the coverage of the cell.
[0224] A specific example of the process after the RRH has received
the uplink resource of the macro cell is disclosed below. The RRH
transmits a reception signal or reception data regarding the uplink
resource of the macro cell to the macro cell. The macro cell
combines the reception signal regarding the uplink resource of the
macro cell received by the macro cell and the reception signal
regarding the uplink resource of the macro cell received from the
RRH. This combining process improves the uplink reception quality
from the user equipment to the macro cell. As a result, the
throughput of the entire communication system can be improved.
[0225] The following two (1) and (2) are disclosed as specific
examples of the method of notifying a reception signal or reception
data from an RRH to a macro cell. (1) A dedicated line between the
macro cell and RRH is used. This achieves an effect that high-speed
communication is allowed. (2) An X2 interface is used. This
achieves an effect that in a case of the application to a local
node other than the RRH, the use of the X2 interface between the
macro cell and local node eliminates the need to newly provide an
interface.
[0226] The following two (1) and (2) are disclosed as specific
examples of the method of combining reception signals or pieces of
reception data in the macro cell. (1) Combining is performed by
simple addition. That is, reception powers are added together. (2)
Selective combining is performed. Selective combining refers to
that pieces of data received at the nodes, the macro cell and RRH,
are decoded separately, and then, the data having normal decoding
results is selected. In a case where the data received by the macro
cell and the data received by the RRH have normal decoding results,
any of the pieces of data is selected.
[0227] The following three (1) to (3) are disclosed as specific
examples of the signal or data to be transmitted from the RRH to
the macro cell.
[0228] (1) RF signal. In the case of the specific example (1), the
RRH needs not to recognize, for example, an identifier of a user
equipment being served by a macro cell, such as a cell radio
network temporary identifier (C-RNTI), and scheduling information
to the user equipment. This is more effective than the specific
example (3) described below in that a communication system can be
prevented from becoming complex.
[0229] Examples of the configurations of the remote radio head and
macro cell in the case where a signal or data to be transmitted
from the RRH to the macro cell is an RF signal include the
configurations in which the remote radio head includes the antenna
908 and the macro cell includes the frequency converting unit 907,
modulating unit 906, demodulating unit 909, encoding unit 905,
decoding unit 910, transmission data buffer unit 904, EPC
communication unit 901, communication with another base station
unit 902, protocol processing unit 903, and control unit 911, where
the reference numbers shown in FIG. 9 described above are used.
[0230] (2) Baseband signal, for example, analog baseband signal or
digital baseband signal. The specific example (2) has an effect
that a signal amount of the communication between the RRH and macro
cell is smaller compared with that of the specific example (1). In
the case of the specific example (2), the RRH needs not to
recognize, for example, an identifier of a user equipment being
served by a macro cell, such as C-RNTI, and scheduling information
to the user equipment. This is more effective than the specific
example (3) described below in that a communication system can be
prevented from becoming complex.
[0231] Examples of the configurations of the remote radio head and
macro cell in a case where the signal or data to be transmitted
from the RRH to the macro cell is a baseband signal include the
configurations in which the remote radio head 1401 includes the
antenna 908 and frequency converting unit 907, and the macro cell
1402 includes the EPC communication unit 901, communication with
another base station unit 902, protocol processing unit 903,
transmission data buffer unit 904, encoding unit 905, modulating
unit 906, demodulating unit 909, decoding unit 910, and control
unit 911, as shown in FIG. 14 described above.
[0232] (3) Demodulated data or decoded data. The specific example
(3) has an effect that a signal amount of the communication between
the RRH and macro cell is smaller compared with the specific
examples (1) and (2). In the case of the specific example (3), the
RRH needs to recognize, for example, an identifier of a user
equipment being served by a macro cell, such as C-RNTI, and
scheduling information to the user equipment.
[0233] Examples of the configurations of the remote radio head and
macro cell in a case where a signal or data to be transmitted from
the RRH to the macro cell is the demodulated data include the
configurations in which the remote radio head includes the antenna
908, frequency converting unit 907, modulating unit 906, and
demodulating unit 909, and the macro cell includes the encoding
unit 905, decoding unit 910, transmission data buffer unit 904, EPC
communication unit 901, communication with another base station
unit 902, protocol processing unit 903, and control unit 911, where
the reference numbers shown in FIG. 9 described above are used.
[0234] Examples of the configurations of the remote radio head and
macro cell in a case where a signal or data to be transmitted from
the RRH to the macro cell is the decoded data include the
configurations in which the remote radio head includes the antenna
908, frequency converting unit 907, modulating unit 906,
demodulating unit 909, encoding unit 905, and decoding unit 910,
and the macro cell includes the transmission data buffer unit 904,
EPC communication unit 901, communication with another base station
unit 902, protocol processing unit 903, and control unit 911, where
the reference numbers shown in FIG. 9 described above are used.
[0235] Specific examples of the method in which an RRH recognizes
an identifier of a user equipment being served by a macro cell and
scheduling information to the user equipment include the method in
which the macro cell notifies the RRH of the above through a
dedicated line. In a case where the method is applied to a local
node other than RRH, it is conceivable that the macro cell may
notify a local node of the above by means of an X2 interface.
[0236] The RRH may selectively modulate or decode only the
reception signal or reception data from a specific user equipment
being served by a macro cell and notify the macro cell of the
resultant. In that case, it suffices that the macro cell notifies
the RRH of, for example, only an identifier of the specific user
equipment being served thereby, such as C-RNTI, and scheduling
information to the specific user equipment. It suffices that the
RRH performs decoding using one or a plurality of received
identifiers, such as C-RNTIs, and scheduling information, and
notifies the macro cell of the resultant.
[0237] The following two (1) and (2) are disclosed as specific
examples of the method of making a hybrid automatic repeat request
(HARQ) in the present embodiment.
[0238] (1) A macro cell makes a HARQ. In this case, whether or not
the reception data has been successfully decoded can be judged
after combining the reception signal regarding the uplink resource
of the macro cell received by the macro cell and the reception
signal regarding the uplink resource of the macro cell received
from the RRH. The reception quality is improved, leading to a fewer
number of retransmission times. As a result, radio resources can be
used effectively, leading to an improvement in throughput as a
communication system.
[0239] (2) The RRH makes a HARQ. In this case, the RRH judges
whether or not the uplink resource of the macro cell has been
successfully decoded. In a case of judging that the uplink resource
has been successfully decoded, the RRH notifies the macro cell of
"Ack" together with the decoded data. In a case of judging that the
uplink resource has not been successfully decoded, the RRH notifies
the macro cell of "Nack". In a case of notifying "Nack", the RRH
needs not to notify the decoded data. This leads to an effect of a
fewer signal amount of the connection between the RRH and macro
cell than that of the specific example (1).
[0240] In a case where the macro cell does not combine the
reception signal regarding the uplink resource of the macro cell
received by the macro cell and the reception signal regarding the
uplink resource of the macro cell received from the RRH, the
specific example (2) is effectively used. This is because the use
of the specific example (1) cannot achieve the effects of
combining. The specific example (2) is effectively used also in a
case where the reception quality of the uplink resource of the
macro cell is good in the RRH. This is because the reception
quality of the uplink resource of the macro cell is good even
though the effects of combining with the use of the specific
example (1) are not expected.
[0241] A specific example in which an RRH knows the configuration
of an uplink resource of a macro cell is disclosed below. The macro
cell notifies the RRH of the configuration of the uplink resource
of the own cell. Specific examples of the configuration of the
uplink resource include a carrier frequency and a bandwidth. The
following three (1) to (3) are disclosed as specific examples of
the method in which a macro cell notifies an RRH of the
configuration of the uplink resource of the own cell.
[0242] (1) A dedicated line between a macro cell and an RRH is
used. The specific example (1) is effective in that high-speed
communication is allowed. (2) An X2 interface is used. In a case of
the application to a local node other than RRH, the use of the X2
interface between the macro cell and local node leads to an effect
that an interface needs not to be newly provided. (3) An operating
and maintenance tool (OMT) is used. This leads to an effect that an
interface needs not to be newly provided.
[0243] Next, a specific example of a sequence of a communication
system in the first embodiment is described with reference to FIG.
19. FIG. 19 is a diagram showing an example of the sequence of the
communication system in the first embodiment. This operation
example discloses a case in which an RRH is installed in the
coverage of the macro cell, and also discloses a case in which a
user equipment camps on the macro cell and a node optimum for
uplink is an RRH.
[0244] This operation example discloses, as a specific example
regarding which RRH is provided with a function of receiving an
uplink resource of a macro cell, the above-mentioned case in which
the function is provided to an RRH connected to the macro cell
through a dedicated line. The above-mentioned case in which a
dedicated line between the macro cell and RRH is used is disclosed
as a specific example of the method in which an RRH notifies a
macro cell of a reception signal. The above-mentioned case in which
combining is performed by simple addition is disclosed as a
specific example of the method of combining the reception signals
or pieces of reception data in the macro cell. The above-mentioned
case in which a baseband signal is used is disclosed as a specific
example of the signal to be transmitted from the RRH to the macro
cell. The above-mentioned case in which a dedicated line between
the macro cell and RRH is used is disclosed as a specific example
of the method in which an RRH knows the configuration of the uplink
resource of the macro cell.
[0245] In Step ST1901 the macro cell and RRH are connected through
a dedicated line. In Step ST1902, the macro cell notifies the RRH
of the configuration of the uplink resource of the macro cell. The
dedicated line is used in this notification.
[0246] In Step ST1903, the RRH judges whether or not it is
connected to the macro cell through the dedicated line. In a case
of judging that the RRH is connected to the macro cell through the
dedicated line in Step ST1903, the RRH moves to Step ST1904. Tn a
case of judging that the RRH is not connected to the macro cell
through the dedicated line in Step ST1903, the RRH ends the process
and moves to other process. The other process is not specific to
the present invention, which is not described here.
[0247] In Step ST1904, the RRH judges to receive the uplink
resource of the macro cell and then moves to Step ST1908.
[0248] In Step ST1905, the user equipment camps on the macro cell
as a cell having the best downlink reception quality. In Step
ST1906, the user equipment performs uplink transmission to the
macro cell.
[0249] In Step ST1907, the macro cell receives uplink transmission
from the user equipment, specifically, an uplink transmission
signal transmitted from the user equipment.
[0250] In Step ST1908, the RRH receives the uplink resource of the
macro cell. In a case of receiving the uplink resource of the macro
cell, the RRH uses the configuration of the uplink resource of the
macro cell received in Step ST1902. The RRH may perform the process
of Step ST1908 after receiving the configuration of the uplink
resource of the macro cell in Step ST1902.
[0251] In Step ST1909, the RRH notifies the macro cell of the
reception signal regarding the uplink resource of the macro cell
received by the RRH. A dedicated line is used in this
notification.
[0252] In Step ST1910, the macro cell combines the uplink
transmission signal transmitted from the user equipment, which has
been received in Step ST1907, and the reception signal regarding
the uplink resource of the macro cell received by the RRH, which
has been received in Step ST1909.
[0253] The first embodiment described above can achieve the
following effects. The carrier frequency of the RRH being a local
node and the carrier frequency of the macro cell are different from
each other, whereby relatively large uplink transmission power from
the user equipment (UE) to the macro cell can be prevented from
affecting the reception of uplink in the RRH. This enables to
reduce interferences as an entire communication system.
[0254] Further, the uplink transmission signals from a UE being
served by a macro cell to the macro cell are received by the macro
cell and RRH and are combined together, leading to an improvement
in communication quality of uplink transmission. This enables to
improve a throughput of the entire communication system.
[0255] According to the first embodiment, the uplink transmission
signals transmitted from the user equipment (UE) to the macro cell
are received by the macro cell and RRH and are combined together as
described above. Accordingly, the communication quality in a case
where the macro cell and the local node such as RRH are installed
to coexist is improved, which improves an entire throughput.
Additionally, the carrier frequency of the local node such as RRH
and the carrier frequency of the macro cell are different from each
other, which enables to prevent relatively large uplink
transmission power from the UE to the macro cell from affecting the
reception of uplink in the RRH. This achieves a reduction in
interference as an entire communication system.
[0256] In the solution of the first embodiment, the UE operates as
in the conventional uplink transmission. That is, the UE performs
uplink transmission to the macro cell on which it has camped.
Accordingly, the UE needs not to be additionally notified or be
additionally provided with a function. In this regard, the first
embodiment can construct a communication system having excellent
backward compatibility.
[0257] While the present embodiment has disclosed the case in which
the carrier frequency of the local node is different from the
carrier frequency of the macro cell, the present embodiment is also
applicable to a case in which the carrier frequency of the local
node is identical to the carrier frequency of the macro cell. This
achieves similar effects to those of the present embodiment.
[0258] While the present embodiment has described the configuration
of the communication system in a case where a remote radio head
(RRH) is used as a local node, the local node is not limited to the
RRH but may be a local node other than the RRH. Specific examples
of the local nodes other than the RRH include a pico eNB (pico
cell), HeNB (HNB, CSG cell), node for hotzone cells, relay node,
and repeater. The present embodiment is also applicable to local
nodes other than RRH, and thus, similar effects to those of the
present embodiment can be achieved.
First Modification of First Embodiment
[0259] While the first embodiment has mainly disclosed the solution
in a case where an RRH is used as a representative of the local
node, a first modification of the first embodiment discloses a case
in which the first embodiment is applied to a local node other than
RRH. The present modification mainly describes a portion different
from the solution of the first embodiment above, and a portion not
to be described is similar to the first embodiment.
[0260] The present modification describes a case of the application
to a local node having all the functions by itself, differently
from an RRH. Specific examples of the local node having all the
functions by itself include a pico eNB, HeNB, relay node, repeater,
and node for hotzone cells. The present modification describes a
case in which a HeNB is used as a representative of the local node
having all the functions by itself.
[0261] In the present modification, the carrier frequency of the
HeNB is different from the carrier frequency of the macro cell. The
HeNB processes the uplink resource for the own node by itself. In
addition, the HeNB is provided with a function of receiving the
uplink resource of the macro cell, specifically, uplink carrier
frequency.
[0262] Here, the data in the uplink resource which is transmitted
from a user equipment to a macro cell and is received by the macro
cell is identical to the data in the uplink resource of the macro
cell which is received by a HeNB.
[0263] A specific example of the process after the HeNB has
received the uplink resource of the macro cell is disclosed below.
The HeNB transmits a reception signal or reception data regarding
the uplink resource of the macro cell to the macro cell. The HeNB
does not process the reception signal or reception data regarding
the uplink resource of the macro cell by the own node.
[0264] The following two (1) and (2) are disclosed as specific
examples of the uplink resource of the macro cell received by the
HeNB.
[0265] (1) The HeNB receives all of the uplink resource of the
macro cell. This specific example (1) is more effective than the
specific example (2) described below in that control is more easily
made because a demand from the macro cell is not required.
[0266] (2) The HeNB receives an uplink resource of a macro cell,
reception of which is requested by the macro cell. Specific
examples of the uplink resource include a resource block (RB) unit
and a component carrier unit. In the specific example (2), an
uplink resource of a macro cell, which is received by a HeNB, is
fewer compared with the specific example (1) described above.
Accordingly, the processing load of the HeNB can be reduced, and
the communication amount from the HeNB to the macro cell can be
reduced.
[0267] The above-mentioned specific examples (1) and (2) regarding
the uplink resource of the macro cell received by the HeNB are also
applicable to the first embodiment described above.
[0268] The following three (1) to (3) are disclosed as specific
examples of the uplink resource, which the macro cell requests a
HeNB to receive.
[0269] (1) Resource of poor reception quality regarding an uplink
resource of a macro cell received by the macro cell. The HeNB is
requested to receive the resource of poor reception quality,
whereby an improvement in communication quality owing to the
combination with the uplink resource of the macro cell received by
the HeNB is expected.
[0270] (2) Resource having a high interference level at a macro
cell. The reception quality of the resource having a high
interference level is typically poor. Therefore, if the HeNB is
requested to receive a resource having a high interference level at
a macro cell, an improvement in communication quality owing to the
combination with the uplink resource of the macro cell received by
the HeNB is expected.
[0271] (3) Uplink resource in which a user equipment is scheduled.
If the HeNB is requested to receive the uplink resource,
unnecessary reception of the uplink resource in which a user
equipment has not been scheduled at a macro cell can be reduced in
the HeNB.
[0272] The specific examples (1) to (3) regarding the uplink
resource, which the macro cell requests a HeNB to receive, are also
applicable to the first embodiment described above.
[0273] The following two (1) and (2) are disclosed as specific
examples of the method in which a macro cell notifies a HeNB of an
uplink resource which is requested to be received.
[0274] (1) The macro cell notifies the HeNB of the uplink resource
which is requested to be received, using the X2 signaling or X2
message. The following two (a) and (b) are disclosed as specific
examples of the method in which a macro cell notifies a HeNB of the
uplink resource requested to be received by the HeNB, using X2
signaling or X2 message.
[0275] (a) X2 signaling or X2 message is newly provided. A
parameter to be mapped to the newly-provided X2 signaling is the
information indicating an uplink resource which is requested to be
received by a HeNB. The information indicating the uplink resource
which is requested to be received by the HeNB may be notified
together with the cell identifier of the macro cell. The cell
identifier of the macro cell is, for example, PCI or GCI.
[0276] (b) Existing X2 signaling or X2 message is used. The
specific example (b) is more effective than the specific example
(a) in that it is not necessary to provide new signaling. The use
of the specific example (b) enables to prevent a communication
system from becoming complex. A specific example of the method of
notifying a HeNB of an uplink resource which is requested to be
received using the existing X2 signaling is disclosed below. "LOAD
INFORMATION message" of X2 signaling, which is disclosed in Chapter
8.3.1.2 of TS 36.423 V10.0.0 (hereinafter, referred to as
"Non-Patent Document 12") by 3GPP, is used.
[0277] "UL Interference Overload Indication" in "LOAD INFORMATION
message" disclosed in Non-Patent Document 12 indicates an
interference level that source cell being a transmission source
receives per resource block on all the resource blocks. It suffices
that the resource block indicating a high interference level by "UL
Interference Overload Indication" in "LOAD INFORMATION message"
shows an uplink resource that a macro cell requests a HeNB to
receive. The reception quality in a resource having a high
interference level is typically poor. Therefore, if the HeNB is
requested to receive a resource having a high interference level,
an improvement in communication quality owing to the combination
with the uplink resource of the macro cell received by the HeNB is
expected.
[0278] An indicator showing what is indicated by "UL Interference
Overload Indication" may be newly added. The following three (A) to
(C) are disclosed as specific examples of the contents to be shown.
(A) An interference level is indicated as in a conventional case.
(B) A notification destination is requested to receive an uplink
resource of the own cell. In a case where an interference level
equal to or higher than a threshold is indicated, the notification
destination may be requested to receive an uplink resource of the
own cell. (C) Both (A) and (B) above are indicated.
[0279] "UL High Interference Indication" in "LOAD INFORMATION
message" disclosed in Non-Patent Document 12 indicates, per
resource block, the occurrence of the detection of high
interference sensitivity, as seen from a source cell being a
transmission source. It suffices that the resource block for which
the occurrence of detection of high interference sensitivity is
indicated by "UL High Interference Indication" in "LOAD INFORMATION
message" indicates an uplink resource that a macro cell requests
the HeNB to receive. The reception quality in the resource in which
high interference sensitivity has been detected is typically poor.
Therefore, if a HeNB is requested to receive the resource in which
high interference sensitivity has been detected, an improvement in
communication quality owing to the combination with the uplink
resource of the macro cell received by the HeNB is expected.
[0280] An indicator showing what is indicated by "UL High
Interference Indication" may be newly added. The following three
(A) to (C) are disclosed as specific examples of the contents to be
shown. (A) Interference sensitivity is shown as in a conventional
case. (B) A notification destination is requested to receive an
uplink resource of the own cell. In a case where interference
sensitivity equal to or higher than a threshold is indicated, the
notification destination may be requested to receive an uplink
resource of the own cell. (C) Both (A) and (B) above are
indicated.
[0281] "LOAD INFORMATION message" is a signal for controlling
intra-frequency neighboring cells (see Non-Patent Document 12).
Therefore, in the first modification of the first embodiment where
a carrier frequency of a local node is different from a carrier
frequency of a macro cell, in a case where "LOAD INFORMATION
message" is used as the method in which a macro cell notifies a
HeNB of an uplink resource which is requested to be received, it
suffices that "LOAD INFORMATION message" is extended as a signal
for controlling inter-frequency neighboring cells.
[0282] (2) The macro cell notifies the HeNB of the uplink resource
which is requested to be received, using a dedicated line.
[0283] The specific examples (1) and (2) of the method in which a
macro cell notifies a HeNB of an uplink resource which is requested
to be received are also applicable to the first embodiment
described above.
[0284] Next, a specific example of a sequence of a communication
system in the first modification of the first embodiment is
described with reference to FIG. 20. FIG. 20 is a diagram showing
an example of the sequence of the communication system in the first
modification of the first embodiment. The sequence shown in FIG. 20
is similar to the sequence shown in FIG. 19, and thus, the same
steps are denoted by the same step numbers and common description
is not given here.
[0285] This operation example discloses a case in which the HeNB is
installed in the coverage of the macro cell, and also discloses a
case in which the user equipment camps on the macro cell and a node
optimum for uplink is the HeNB.
[0286] This operation example discloses, as a specific example
regarding which HeNB is provided with a function of receiving an
uplink resource of a macro cell, the above-mentioned case in which
a HeNB located in the coverage of the macro cell is provided this
function. The above-mentioned case in which an X2 interface is used
is disclosed as a specific example of the method in which a HeNB
notifies a macro cell of a reception signal. The above-mentioned
case where combining is performed by simple addition is disclosed
as a specific example of the method in which a macro cell combines
reception signals or pieces of reception data. The above-mentioned
case in which a baseband signal is used is disclosed as a specific
example of the signal to be transmitted from the HeNB to the macro
cell.
[0287] The above-mentioned case in which an X2 interface is used is
disclosed as a specific example of the method in which a HeNB knows
the configuration of an uplink resource of a macro cell. The
above-mentioned case in which the HeNB receives an uplink resource
of the macro cell, whose reception is requested by the macro cell,
is disclosed as a specific example of the uplink resource of the
macro cell to be received by the HeNB. The above-mentioned case of
a resource having a high interference level in a macro cell is
disclosed as a specific example of the uplink resource that the
macro cell requests the HeNB to receive.
[0288] In Step ST2001, the HeNB measures a surrounding radio wave
environment, that is, measures a radio wave environment of a
neighboring cell.
[0289] In Step ST2002, the HeNB judges whether or not a cell having
reception power equal to or higher than a predetermined threshold
exists based on the measurement results of the surrounding radio
wave environment in Step ST2001. In a case of judging that a cell
having reception power equal to or higher than a predetermined
threshold exists in Step ST2002, the HeNB moves to Step ST2003. In
a case of judging that a cell having reception power equal to or
higher than a predetermined threshold does not exist in Step
ST2002, the HeNB ends the process and moves to other process. The
other process is not specific to the present invention, which is
not described here.
[0290] In a case of judging that a cell having reception power
equal to or higher than a predetermined threshold exists as a
result of the measurements of a surrounding radio wave environment,
the HeNB judges that the own HeNB is located in the coverage of
that cell. Meanwhile, in a case of judging that a cell showing a
value equal to or higher than a predetermined threshold does not
exist as a result of the measurement of a surrounding radio wave
environment, the HeNB judges that the own HeNB is not located in
the coverage of that cell. In this operation example, the HeNB
detects a macro cell as a cell having reception power equal to or
higher than a threshold.
[0291] In Step ST2003, the HeNB notifies the cell judged to have
reception power equal to or higher than a threshold in Step ST2002,
which is the macro cell in this operation example, that the own
HeNB is located in the coverage. An X2 interface or dedicated line
is used in this notification.
[0292] In Step ST1902, the macro cell notifies the HeNB of the
configuration of the uplink resource of the macro cell. An X2
interface is used in this notification. This notification is
performed on, for example, all the local nodes being served by the
macro cell, but may be performed on only a local node that has
notified that it is located in the coverage.
[0293] In Step ST1904, the HeNB judges to receive the uplink
resource of the macro cell and then moves to Step ST2006.
[0294] In Step ST1905, the user equipment camps on the macro cell
as a cell having the best downlink reception quality. In Step
ST1906, the user equipment performs uplink transmission to the
macro cell.
[0295] In Step ST2004, the macro cell judges whether or not there
is a resource having a high interference level in the uplink
resource of the own cell. In a case of judging that there is a
resource having a high interference level in Step ST2004, the macro
cell moves to Step ST2005. In a case of judging that there is no
resource having a high interference level in Step ST2004, the macro
cell ends the process and moves to other process. The other process
is not specific to the present invention, which is not described
here.
[0296] In Step ST2005, the macro cell notifies the HeNB of a
resource having a high interference level. Specifically, the macro
cell notifies the HeNB, which has notified the macro cell that it
is located in the coverage of the macro cell in Step ST2003, of the
resource having a high interference level. The macro cell may
notify the HeNB of the uplink resource requested to be received.
The X2 interface or dedicated line is used in this
notification.
[0297] In Step ST2006, the HeNB receives the uplink resource of the
macro cell having a high interference level which has been received
in Step ST2005. In a case of receiving the uplink resource of the
macro cell having a high interference level, the HeNB uses the
configuration of the uplink resource of the macro cell received in
Step ST1902.
[0298] In Step ST1907, the macro cell receives the uplink
transmission from the user equipment, specifically, the uplink
transmission signal transmitted from the user equipment.
[0299] In Step ST1909, the HeNB notifies the macro cell of a
reception signal regarding the uplink resource of the macro cell
received by the HeNB. The X2 interface or dedicated line is used in
this notification.
[0300] In Step ST1910, the macro cell combines the uplink
transmission signal transmitted from the user equipment, which has
been received in Step ST1907, and the reception signal regarding
the uplink resource of the macro cell received by the HeNB, which
has been received in Step ST1909.
[0301] The first modification of the first embodiment can achieve
the following effects in addition to the effects of the first
embodiment. In the present modification, the local node receives
the uplink resource of the macro cell, whose reception is requested
by the macro cell. This enables to reduce the processing load of a
local node and reduce the communication amount from the local node
to the macro cell.
[0302] While the present modification has disclosed the case in
which the carrier frequency of the local node is different from the
carrier frequency of the macro cell, the present modification is
also applicable to a case in which the carrier frequency of the
local node and the carrier frequency of the macro cell are
identical to each other, and similar effects to those of the
present modification can be achieved.
[0303] Also, while the present modification has described the
configuration of the communication system in a case where the HeNB
is used as a local node, the local node is not limited to a HeNB.
Local nodes other than HeNB may be used as long as the local nodes
have all the functions by themselves. The present modification is
also applicable to local nodes other than HeNB, and similar effects
to those of the present modification can be achieved.
Second Embodiment
[0304] A problem to be solved in a second embodiment is described
below. Even in cases where the first embodiment and the first
modification of the first embodiment are used, another problem may
occur. This problem is described with reference to FIG. 17
described above.
[0305] As described above, in the area Z between the point A and
point B shown in FIG. 17, a link between the user equipment (UE)
and RRH 1603 is good in uplink, and a link between the UE and macro
cell 1601 is good in downlink. An imbalance in link, that is, link
imbalance occurs as described above.
[0306] In the conventional technique, the user equipment camps on a
cell having the best downlink reception quality, and thereafter,
starts communication with the cell as required (see Non-Patent
Document 3). Accordingly, in the conventional technique, a
situation in which an optimum link is not used in uplink
communication occurs in, for example, the area Z between the point
A and point B shown in FIG. 17. In this case, the transmission
power required by the user equipment is larger than that in a case
where an optimum link is used. This causes a problem of increased
power consumption of the user equipment.
[0307] A solution in the second embodiment is described below. The
present embodiment mainly describes a portion different from the
solutions in the first embodiment and the first modification of the
first embodiment described above, and a portion not to be described
is similar to the first embodiment and the first modification of
the first embodiment.
[0308] In the present embodiment, a user equipment configures the
uplink transmission suitable for an optimum node. A user equipment
whose optimum node differs between uplink and downlink may
configure the uplink transmission suitable for a node optimum for
uplink. A user equipment whose optimum node differs between uplink
and downlink may configure the uplink transmission suitable for a
node optimum for uplink while camping on the optimum node in
downlink, as in the conventional technique. A user equipment whose
optimum node differs between uplink and downlink performs uplink
transmission to an optimum node in downlink as in the conventional
technique, where uplink transmission may be configured to be
suitable for a node optimum for uplink.
[0309] The concept of the solution in the second embodiment is
described with reference to FIG. 21. FIG. 21 is a diagram for
describing the concept of the solution in the second embodiment.
Considered here is a case in which a user equipment 2101 judges
that the downlink reception quality of a downlink 2104 of a macro
cell 2102 is the best and camps on the macro cell 2102. The user
equipment 2101 starts uplink communication with the macro cell 2102
using an uplink 2105 as required. The length of an arrow indicating
the uplink 2105 represents the uplink transmission power of the
user equipment 2101. That is, an uplink transmission signal
transmitted from the user equipment 2101 can be received within the
range of a circle indicated by reference numeral 2107 where the
length of the arrow indicating the uplink 2105 is a radius of the
circle.
[0310] An RRH 2103 is located near the user equipment 2101. The RRH
2103 is an optimum node in uplink of the user equipment 2101. In
the present embodiment, the user equipment 2101 configures the
uplink transmission suitable for an optimum node. That is, the user
equipment 2101 configures the uplink transmission suitable for the
RRH 2103 being an optimum node in uplink. As a specific example,
for example, the user equipment 2101 sets the uplink transmission
power to the transmission power for allowing the RRH 2103 to
receive the uplink transmission signal from the user equipment
2101. That is, the user equipment 2101 performs uplink transmission
to the macro cell 2102 using an uplink 2106 configured in the
uplink transmission suitable for the RRH 2103.
[0311] The length of an arrow indicating the uplink 2106 shows the
uplink transmission power after the uplink transmission is
configured to be suitable for the RRH 2103 being an optimum node
for the user equipment 2101. That is, an uplink transmission signal
transmitted from the user equipment 2101 can be received within the
range of a circle indicated by reference numeral 2108 where the
length of the arrow indicating the uplink 2106 is a radius. Also in
this case, a serving cell being a camp-on destination is not
changed to the RRH 2103, and thus, the uplink transmission
destination of the user equipment 2101 is still the macro cell
2102.
[0312] The following two (1) and (2) are disclosed as specific
examples of the method of determining a user equipment that needs
support or a method of determining a user equipment whose optimum
node differs between uplink and downlink. The method of determining
a node optimum for uplink is also described below.
[0313] (1) A macro cell determines a user equipment. The following
two (A) and (B) are disclosed as specific examples.
[0314] (A) Method in which a user equipment supports the
determination by a macro cell. The following two (A1) and (A2) are
disclosed as specific examples of the method in which a user
equipment supports the determination by a macro cell.
[0315] (A1) A user equipment measures a surrounding radio wave
environment, that is, measures a radio wave environment of a
neighboring cell. The user equipment performs a measurement for
changing the configuration of uplink transmission (hereinafter, may
be referred to as "uplink transmission configuration"). That is,
the user equipment measures a downlink resource of a neighboring
local node. This measurement may be performed while the user
equipment is in an idle state or is connected.
[0316] In a case of the measurement during an idle state, a
threshold different from the conventional threshold for starting a
measurement, which is disclosed in Non-Patent Document 3, is
provided. For example, a measurement threshold for changing the
uplink transmission configuration is provided. This enables to
start a measurement for changing the uplink transmission
configuration also in a case where the serving cell has good
downlink communication quality. The user equipment notifies the
macro cell of the measurement results.
[0317] In a case where there is a cell having better downlink
reception quality than the threshold, the macro cell determines the
user equipment that has performed a measurement as "user equipment
that needs support" and determines that cell as "optimum node for
uplink". Alternatively, in a case where there is a cell having
better downlink reception quality than the threshold as a result of
the measurement of a neighboring cell, the user equipment may
determine the own user equipment as "user equipment that needs
support" and determine that cell as "optimum node for uplink".
[0318] In a case of the measurement while the user equipment is
connected, a configuration different from the conventional
measurement configuration, measurement object, and reporting
configuration, which are disclosed in Non-Patent Document 2, is
provided. For example, a measurement configuration for changing an
uplink transmission configuration, a measurement object for
changing an uplink transmission configuration, and a reporting
configuration for changing an uplink transmission configuration are
provided. This allows the measurement for changing an uplink
transmission configuration and measurement reporting also in a case
where the serving cell has good downlink communication quality.
[0319] In a case where there is a cell having the downlink
reception quality better than the threshold, the macro cell
determines the user equipment that has performed a measurement as
"user equipment that needs support" and determines that cell as
"optimum node for uplink". Alternatively, in a case where there is
a cell having the better downlink reception quality than the
threshold as a result of the measurement of a neighboring cell, the
user equipment may determine the own user equipment as "user
equipment that needs support" and determine that cell as "optimum
node for uplink".
[0320] The measurement for a user equipment to change the uplink
transmission configuration can be switched on and off. That is, to
execute or not execute a measurement can be switched. The following
four (a) to (d) are disclosed as specific examples of the
conditions for switching on and off (a) The user equipment switches
on and performs a measurement if there is an RRH connected to the
macro cell through a dedicated line, or switches off and does not
perform a measurement if there is no such an RRH. (b) The user
equipment switches on and performs a measurement if there is an RRH
sharing the function of the macro cell, or switches off and does
not perform a measurement if there is no such an RRH. (c) The user
equipment switches on and performs a measurement if there is an RRH
located in the coverage of the macro cell, or switches off and does
not perform a measurement if there is no such an RRH. (d)
Combination of (a) to (c) above.
[0321] The following two (a) and (b) are disclosed as specific
examples of the method of notifying a user equipment of switching
on or off of the measurement for the user equipment to change the
uplink transmission configuration. (a) A notification is made in
the broadcast information. (b) A notification is made in the
dedicated information. For example, a notification is made by RRC
signaling or RRC message. Alternatively, a notification is made by
MAC signaling or MAC message. Still alternatively, a notification
is made by layer 1 signaling, as a specific example, using
PDCCH.
[0322] (A2) An indicator for notifying that the user equipment is
located near "optimum node for uplink" is provided. The macro cell
may notify a cell identifier such as PCI or GCI of a local node and
a downlink carrier frequency of a local node. As a result, a user
equipment can reduce measurement objects, leading to lower power
consumption of the user equipment.
[0323] When the downlink reception quality from the local node
becomes equal to or larger than a predetermined threshold
irrespective of the downlink reception quality of the serving cell,
the macro cell notifies that the user equipment is located near
"optimum node for uplink". This notification may contain a cell
identifier such as PCI or GCI, an identifier of a local node, and
reception quality such as downlink reception quality and path loss.
The identifier of local node may be broadcast from the local node.
The notification of the identifier of a local node may be
unnecessary as long as a cell identifier is associated with the
local node identifier by the macro cell.
[0324] The macro cell determines the user equipment that has
notified that it is located near "optimum node for uplink" as "user
equipment that needs support" and determines an object cell as
"optimum node for uplink". Alternatively, in a case of judging that
a user equipment is located near the optimum node for uplink, the
user equipment may determine the own user equipment as "user
equipment that needs support" and determine that cell as "optimum
node for uplink".
[0325] The function of the conventional proximity indication (see
Non-Patent Document 2) may be extended as described above. As a
result, it is not required to newly provide an indicator, which
enables to prevent a communication system from becoming
complex.
[0326] (B) Method in which an RRH supports the determination of a
macro cell. The macro cell makes a judgment based on the reception
quality of the uplink resource of the macro cell, which has been
received by the RRH and notified the macro cell. The RRH adds an
identifier of the own RRH when transmitting a reception signal or
reception data regarding the uplink resource of the macro cell to
the macro cell. This enables the macro cell to identify "optimum
node for uplink". The macro cell evaluates the uplink reception
quality at the RRH of each user equipment using the reception
signal or reception data of the uplink resource of the macro cell,
which has been notified from the RRH.
[0327] Examples of the signal for use in the evaluation of uplink
reception quality include reference signals. The reference signals
include a demodulation reference signal and a sounding reference
signal. In a case where there is a cell having the uplink reception
quality better than a threshold from the evaluation results about
the uplink reception quality at an RRH of each user equipment, the
macro cell determines this user equipment as "user equipment that
needs support" and determines that cell as "optimum node for
uplink".
[0328] The method (B) in which an RRH supports the determination of
a macro cell is more effective than the method (A) in which a user
equipment supports the determination of the macro cell in the
following respect. The above-mentioned method (A) is a method in
which a determination is made based on the downlink reception
quality. Meanwhile, the above-mentioned method (B) is a method in
which a determination is made based on the uplink reception
quality. In the present embodiment, the carrier frequency differs
between downlink and uplink. Each reception quality has different
frequency characteristics. Therefore, in selection of an optimum
node for uplink, fewer errors occur if a judgment is made in
uplink. The RRH needs an operation in downlink in the
above-mentioned method (A), whereas the RRH does not need an
operation in downlink in the above-mentioned method (B). As a
result, radio resources can be effectively used in the
above-mentioned method (B).
[0329] (2) An RRH determines a user equipment. The RRH makes a
judgment based on the reception quality of the received uplink
resource of the macro cell. The RRH evaluates the uplink reception
quality in the RRH of each user equipment using the reception
signal or reception data of the uplink resource of the macro cell.
Examples of the signals for use in the evaluation of uplink
reception quality include reference signals. The reference signals
include a demodulation reference signal and a sounding reference
signal.
[0330] In a case where there is a cell having better uplink
reception quality than a threshold from the evaluation results of
the uplink reception quality in the RRH of each user equipment, the
RRH determines that user equipment as "user equipment that needs
support" and determines the own cell as "optimum node for uplink".
The RRH notifies the macro cell of the identifier of the user
equipment, such as UE-ID or C-RNTI, as the information of "user
equipment that needs support". The RRH notifies the macro cell of
the identifier of the own RRH, such as PCI or GCI, as the
information of "optimum node for uplink".
[0331] The above-mentioned method of the specific example (2) in
which an RRH determines a user equipment is more effective in the
following point compared with the method (A) in which a user
equipment supports the determination of a macro cell in the
above-mentioned specific example (1) in which a macro cell
determines a user equipment. The method (A) of the specific example
(1) described above is a method in which a determination is made
based on the downlink reception quality. Meanwhile, the method of
the specific example (2) is a method in which a determination is
made based on the uplink reception quality. In the present
embodiment, the carrier frequency differs between downlink and
uplink. Each reception quality has different frequency
characteristics. Therefore, in the selection of an optimum node for
uplink, fewer errors occur in a case where a determination is made
in uplink. The RRH needs an operation in downlink in the method (A)
of the specific example (1) described above, whereas the RRH does
not need an operation in downlink in the method of the specific
example (2) described above. As a result, radio resources can be
effectively used in the method of the specific example (2)
described above.
[0332] The method of the specific example (2) in which an RRH
determines a user equipment has the following four problems (a) to
(d) in the reception of a reference signal. A solution to each
problem is disclosed as the method in which a local node receives a
reference signal from a user equipment to a macro cell.
[0333] (a) An uplink reference signal is scrambled with an
identifier of a user equipment (see TS 36.211 V10.0.0 (hereinafter,
referred to as "Non-Patent Document 13") by 3GPP). The RRH that is
not connected with the user equipment does not recognize the
identifier of the user equipment. Accordingly, the RRH cannot
evaluate the uplink reference signal transmitted from the user
equipment to the macro cell unless any improvement is made.
[0334] The solution to this problem (a) is disclosed below. A macro
cell notifies an RRH of the identifier of a user equipment being
served thereby, such as UE-ID or C-RNTI. The macro cell may notify
an RRH of the identifier of the user equipment during connection
which is being served thereby. For example, a dedicated line or X2
interface is used in this notification.
[0335] (b) The sequence of uplink reference signaling may depend on
an identifier of a cell (see Non-Patent Document 13). The RRH does
not recognize an identifier of a macro cell. Accordingly, at times,
the RRH cannot evaluate the uplink reference signal transmitted
from the user equipment to the macro cell unless any improvement is
made. The following two (b1) and (b2) are disclosed as solutions to
this problem (b).
[0336] (b1) The macro cell notifies an RRH of an identifier of a
cell such as PCI or GCI. The macro cell may notify the RRH of an
identifier of a cell as required. Specific examples of the case
where the notification is required include the case in which
hopping is applied for an uplink reference signal. For example, a
dedicated line or X2 interface is used in this notification.
[0337] (b2) The macro cell and RRH have the same cell identifier,
specifically, PCI. The macro cell and the RRH being served by the
macro cell may have the same cell identifier. A specific example of
the RRH being served by the macro cell is similar to that of the
first embodiment described above, which is not described here.
[0338] (c) A method of transmitting an uplink reference signal
depends on a user-equipment-specific parameters regarding the
method of transmitting a reference signal specified by higher
layers (see Non-Patent Document 13). Specific examples of the
parameters include "srs-bandwidth" indicating a bandwidth of a
sounding reference signal, "transmissionComb" indicating that the
sounding reference signal is periodic, and "transmissionComb-ap"
indicating that the sounding reference signal is aperiodic.
[0339] The RRH that is not connected with the user equipment does
not recognize a user-equipment-specific parameter regarding the
method of transmitting a reference signal specified by higher
layers. Accordingly, the RRH cannot evaluate the uplink reference
signal transmitted from the user equipment to the macro cell unless
any improvement is made.
[0340] A solution to this problem (c) is disclosed below. The macro
cell notifies the RRH of the user-equipment-specific parameter
regarding the method of transmitting a reference signal specified
by higher layers. The macro cell may notify the RRH of a
user-equipment-specific parameter regarding the method of
transmitting a reference signal specified by higher layers to a
user equipment during connection that is being served by the macro
cell. For example, a dedicated line or X2 interface is used in this
notification.
[0341] (d) The method of transmitting uplink reference signals
depends on a cell-specific parameter regarding the method of
transmitting reference signals specified by the higher layers (see
Non-Patent Document 13). Specific examples of the parameters
include "Group-hopping-enabled" indicating whether or not the
sequence of reference signaling is subjected to group hopping,
"srs-bandwidth" indicating the bandwidth for sounding reference
signals, and "MaxUpPts" regarding sounding reference signals. The
RRH does not recognize the cell-specific parameters regarding the
method of transmitting reference signals specified by higher
layers. Therefore, the RRH cannot evaluate the uplink reference
signals transmitted from the user equipment to the macro cell
unless any improvement is made. The following two (d1) and (d2) are
disclosed as solutions to the problem (d).
[0342] (d1) The macro cell notifies the RRH of the cell-specific
parameters regarding the method of transmitting reference signals
specified by the higher layers. The macro cell may notify the RRH
of identifier of a cell as required. For example, a dedicated line
or X2 interface is used in this notification.
[0343] (d2) The cell-specific parameters regarding the method of
transmitting reference signals specified by higher layers are the
same between the macro cell and RRH. The cell-specific parameters
regarding the method of transmitting reference signals specified by
higher layers may be the same between the macro cell and the RRH
being served by the macro cell. A specific example of the case
where the RRH is being served by the macro cell is as in the first
embodiment described above, which is not described here.
[0344] In a case where the demodulated data or decoded data in the
specific example (3) described above is used as a signal to be
transmitted from the RRH to the macro cell in the first embodiment
described above, the following problem arises as in the
above-mentioned case. That is, unless any improvement is made, the
RRH cannot receive and use the uplink reference signals transmitted
from the user equipment to the macro cell. Therefore, the RRH
cannot demodulate and decode the uplink data transmitted from the
user equipment to the macro cell. Also in that case, the problem
can be solved through application of the "method in which a local
node receives a reference signal from a user equipment to a macro
cell" described above.
[0345] In a case where the uplink transmission from a user
equipment is received at points other than the point targeted for
uplink communication, the following problem arises as described
above. That is, unless any improvement is made, uplink reference
signals cannot be received and used at points other than the point
targeted for uplink communication. Therefore, the uplink data
transmitted to points targeted for uplink communication, which has
been transmitted by the user equipment, cannot be demodulated and
decoded at points other than the point targeted for uplink
communication. Also in that case, the problem can be solved through
application of the "method in which a local node receives a
reference signal from a user equipment to a macro cell" described
above.
[0346] The following three (1) to (3) are disclosed as specific
examples of the configuration of the conventional uplink
transmission.
[0347] (1) The user equipment configures the uplink transmission
power based on a path loss (see Chapter 5.1 of TS 36.213 V10.0.1
(hereinafter, referred to as "Non-Patent Document 14") by
3GPP).
[0348] (2) Time alignment (TA) means that uplink transmission
timing is advanced or delayed. The time alignment (TA) is obtained
from a timing advance command. The time alignment (TA) indicates an
adjusted value relative to the uplink transmission timing at that
point in time. Upon receipt of a timing advance command, the user
equipment adjusts the uplink transmission timing of the PUCCH,
PUSCH, and sounding reference signal (SRS) (see Chapter 4.2.3 of
Non-Patent Document 14).
[0349] (3) The user equipment performs frequency synchronization
based on a downlink signal frequency (hereinafter, also referred to
as "reference frequency f") (see Non-Patent Document 1).
[0350] As the method of configuring an uplink transmission suitable
for an optimum node, the uplink transmission is configured using
the parameter suitable for an optimum node. The parameters are
equivalent to the transmission conditions. The uplink transmission
is configured by the conventional method using the parameters
suitable for an optimum node. The conventional method of
configuring an uplink transmission is used, which enables to
construct a communication system having excellent backward
compatibility. Specific examples of the parameters include a path
loss (PL), timing advance command, and reference frequency f Timing
advance command may be time alignment (TA).
[0351] The following two (1) and (2) are disclosed as the method of
configuring a path loss suitable for an optimum node.
[0352] (1) A path loss is configured by the user equipment based on
measurement results. The user equipment measures an optimum node,
for example, a downlink resource of the RRH to obtain a path loss,
and configures the obtained path loss as a path loss suitable for
an optimum node. This configuration method (1) is more advantageous
than the configuration method (2) described below in that an
optimum node, for example, a downlink resource of the RRH is
actually measured, leading to fewer errors.
[0353] A specific example of the sequence of the communication
system in the method (1) of configuring a path loss suitable for an
optimum node is described with reference to FIG. 22. FIG. 22 is a
diagram showing an example of the sequence in a case where the user
equipment configures a path loss suitable for an optimum node based
on the measurement results. This operation example discloses a case
in which an RRH is installed in the coverage of a macro cell, and
also discloses a case in which a user equipment camps on a macro
cell and the optimum node for uplink is an RRH.
[0354] In Step ST2201, the macro cell performs downlink
transmission to the user equipment (UE). The downlink transmission
may be the transmission dedicatedly to a user equipment or the
broadcast information.
[0355] In Step ST2202, the user equipment measures a downlink
resource of the macro cell from the downlink transmission
transmitted from the macro cell in Step ST2201, to thereby obtain a
path loss from the macro cell.
[0356] In Step ST2203, the user equipment configures an uplink
transmission suitable for the macro cell using the path loss
obtained in Step ST2202.
[0357] In Step ST2204, the RRH performs a downlink transmission to
the user equipment. The following two (1) and (2) are disclosed as
specific examples of the downlink transmission. (1) The
transmission power information of reference signals of the RRH are
transmitted by the broadcast information. (2) The reference signals
are transmitted. This transmission may be the transmission
dedicatedly to a user equipment or the broadcast information.
[0358] In Step ST2205, the user equipment measures a downlink
resource of the RRH from the downlink transmission transmitted from
the RRH in Step ST2204, to thereby obtain a path loss from the RRH.
A specific example of the method of obtaining a path loss is
disclosed below. The user equipment measures the reception power of
reference signals of the RRH. The user equipment receives the
broadcast information of the RRH to obtain the transmission power
information regarding the reference signals of the RRH. The user
equipment obtains a path loss from a difference between the
transmission power information regarding the reference signals of
the RRH and the actually-received reception power of the reference
signals of the RRH.
[0359] In Step ST2206, the user equipment configures the path loss
obtained in Step ST2205 as a path loss suitable for an optimum node
(RRH).
[0360] In Step ST2207, the user equipment configures the uplink
transmission suitable for an optimum node, as a specific example,
configures the uplink transmission power, using the path loss
configured in Step ST2206. In this operation example, an optimum
node is an RRH.
[0361] In Step ST2208, the user equipment performs an uplink
transmission to the macro cell based on the configuration of the
uplink transmission configured in Step ST2207.
[0362] However, the method (1) of configuring a path loss suitable
for an optimum node needs the downlink operation in the RRH, which
poses a problem in effective use of radio resources. Specific
examples of the problem include the need to transmit the reference
signals of the RRH and the transmission power information of the
reference signals by the RRH. The method (2) of configuring a path
loss suitable for an optimum node is disclosed below as the method
of solving this problem.
[0363] (2) The macro cell configures a path loss for the user
equipment. The following four (A) to (D) are disclosed as specific
examples of the value to be configured.
[0364] (A) The macro cell obtains a path loss from the user
equipment in the RRH and notifies the user equipment of the
resultant. As in the first embodiment described above, the RRH
receives the uplink resource transmitted from the user equipment to
the macro cell. The RRH notifies the macro cell of a reception
signal of the uplink resource of the macro cell received by the
RRH. The macro cell obtains the path loss from the user equipment
in the RRH, from the reception signal of the uplink resource of the
macro cell received by the RRH. The macro cell notifies the user
equipment of the path loss from the user equipment in the RRH. The
user equipment configures the received path loss from the user
equipment in the RRH as a path loss suitable for an optimum
node.
[0365] (B) The macro cell obtains an offset value and notifies the
user equipment of the obtained offset value. As in the first
embodiment described above, the RRH receives the uplink resource
transmitted from the user equipment to the macro cell. The RRH
notifies the macro cell of a reception signal of the uplink
resource of the macro cell received by the RRH. The macro cell
obtains a path loss from the user equipment in the RRH, from the
reception signal regarding the uplink resource of the macro cell
received by the RRH. The macro cell separately obtains a path loss
from the user equipment in the macro cell, from the reception
signal of the uplink resource of the macro cell received by the
macro cell. The macro cell calculates, as an offset value, a
difference between the path loss from the user equipment in the RRH
and the path loss from the user equipment in the macro cell. The
macro cell notifies the user equipment of this offset value. The
user equipment measures a downlink resource of the macro cell to
obtain a path loss, and adds the offset value received from the
macro cell to the obtained path loss, to thereby configure the
resultant as a path loss suitable for an optimum node.
[0366] A specific example of a sequence of a communication system
in a case where the macro cell obtains an offset value and notifies
the user equipment of the obtained offset value in (B) of the
method (2) of configuring a path loss suitable for an optimum node
is described with reference to FIG. 23. FIG. 23 is a diagram
showing an example of the sequence in a case where the macro cell
obtains an offset value and notifies the user equipment of the
obtained offset value to configure a path loss suitable for an
optimum node. The sequence shown in FIG. 23 is similar to the
sequences shown in FIGS. 19 and 22, and thus, the same steps are
denoted by the same step numbers and common description is not
given here. This operation example discloses a case in which an RRH
is installed in the coverage of the macro cell. Also disclosed is a
case in which the user equipment camps on the macro cell and an
optimum node for uplink is an RRH.
[0367] In Step ST2301, the user equipment (UE) performs an uplink
transmission to the macro cell based on the uplink transmission
configuration suitable for the macro cell, which has been
configured in Step ST2203.
[0368] In Step ST2302, the macro cell measures the uplink
transmission transmitted from the user equipment (UE) to the macro
cell in Step ST2301, that is, uplink resource of the macro cell
from the user equipment, to thereby obtain a path loss from the
user equipment to the macro cell.
[0369] In Step ST1908, the RRH receives the uplink resource of the
macro cell from the UE. In Step ST1909, the RRH notifies the macro
cell of the reception signal regarding the uplink resource of the
macro cell, which has been received by the RRH.
[0370] In Step ST2303, the macro cell obtains a path loss from the
user equipment to the RRH, from the reception signal regarding the
uplink resource from the UE to the macro cell received by the RRH,
which has been received in Step ST1909.
[0371] In Step ST2304, the macro cell obtains an offset value from
the path loss from the user equipment to the macro cell, which has
been obtained in Step ST2302, and the path loss from the user
equipment to the RRH, which has been obtained in Step ST2303.
Specific examples of the way of obtaining an offset value include
to obtain a difference between the path loss from the user
equipment to the macro cell, which has been obtained in Step
ST2302, and the path loss from the user equipment to the RRH, which
has been obtained in Step ST2303.
[0372] In Step ST2305, the macro cell notifies the user equipment
of the offset value obtained in Step ST2304. Dedicated transmission
to the user equipment may be used in this notification.
[0373] In Step ST2306, the user equipment configures a path loss
using the offset value received in Step ST2305, as a path loss
suitable for an optimum node. Specific examples of the method of
configuring a path loss using an offset value include the addition
of the offset value received in Step ST2305 to the path loss from
the user equipment to the macro cell, which has been obtained in
Step ST2202.
[0374] In Step ST2207, the user equipment configures an uplink
transmission suitable for an optimum node, as a specific example,
configures uplink transmission power, using the path loss
configured in Step ST2306. In this operation example, the optimum
node is an RRH.
[0375] In Step ST2208, the user equipment performs an uplink
transmission to the macro cell based on the configuration of the
uplink transmission configured in Step ST2207.
[0376] The specific examples (A) and (B) described above pose such
a problem that the path loss from the user equipment in the RRH
changes every time the user equipment moves, and accordingly, a
notification from the macro cell is required each and every time,
which complicates control.
[0377] Also, the specific examples (A) and (B) described above pose
such a problem that an uplink resource to be transmitted from the
user equipment to the macro cell is required, and the uplink
resource cannot be used for an initial uplink transmission, for
example, for RACH. Specific examples (C) and (D) are disclosed
below as the solutions to those problems.
[0378] (C) The macro cell obtains an offset value and notifies the
user equipment of the obtained offset value. The RRH notifies the
macro cell of the transmission power information of the RRH. The
macro cell calculates an offset value from a difference between the
transmission power from the macro cell and the transmission power
from the RRH. The macro cell notifies the user equipment of this
calculated offset value. The user equipment measures a downlink
resource of the macro cell to obtain a path loss, and adds the
offset value received from the macro cell to the obtained path
loss, to thereby configure the resultant as a path loss suitable
for an optimum node.
[0379] (D) A path loss suitable for an optimum node is
predetermined in a static or semi-static manner. In a case where,
for example, a local node has small coverage, it is conceivable
that the path loss of a constant value may pose no problem
regardless of a user equipment location. For example, in a case
where the RRH has small coverage, the path loss may be determined
as "0". Alternatively, a path loss may be determined per local
node. A path loss suitable for an optimum node may be notified from
the macro cell by the broadcast information or dedicated signaling.
The user equipment configures, as a path loss suitable for an
optimum node, the path loss received from the macro cell by the
broadcast information or dedicated signaling.
[0380] The uplink resource to be transmitted from the user
equipment to the macro cell is not required in the specific
examples (C) and (D) differently from the specific examples (A) and
(B) described above. Therefore, the specific examples (C) and (D)
are advantageously used also in the initial uplink transmission
from the user equipment. In the specific examples (C) and (D), the
notification of an offset value from the macro cell to the user
equipment is not required even in a case where the user equipment
moves. Therefore, in a case where the user equipment moves, the
specific examples (C) and (D) are more advantageous than the
specific examples (A) and (B) described above in easy control.
[0381] In the method (2) of configuring a path loss suitable for an
optimum node described above, downlink operation in the RRH is not
required. Accordingly, the method (2) of configuring a path loss is
more advantageous than the above-mentioned method (1) of
configuring a path loss in effective use of radio resources.
[0382] The above-mentioned configuration method (1) and
configuration method (2) can be used in combination. The following
two (a) and (b) are disclosed as specific examples of the
combination.
[0383] (a) The configuration method (1) described above is adopted
in a case where the RRH operates a downlink resource. Meanwhile,
the configuration method (2) is adopted in a case where the RRH
does not operate a downlink resource.
[0384] (b) The method (2) of configuring a path loss suitable for
an optimum node is adopted to configure a path loss. Even in this
case, overwriting is allowed based on the path loss in the method
(1) of configuring a path loss suitable for an optimum node.
[0385] The following two (b1) and (b2) are disclosed as specific
examples of the timing of overwriting in the specific example (b);
(b1) timing at which the RRH starts operation of a downlink
resource, and (b2) timing at which the user equipment starts
receiving the downlink resource of the RRH.
[0386] The specific examples (A) to (C) regarding the value to be
configured can be used in combination also in the configuration
method (2) above. A specific example of the combination is
disclosed below. The specific example (C) is used in the initial
uplink transmission, and the specific example (A) or specific
example (B) is used in the following uplink transmissions.
[0387] The method of configuring a timing advance command suitable
for an optimum node is disclosed below. The macro cell configures a
value for the user equipment. A specific example of the value to be
configured is disclosed below. A timing advance command suitable
for an optimum node is predetermined in a static or semi-static
manner. In a case where, for example, a local node has small
coverage, it is conceivable that the timing advance command of a
constant value will pose no problem regardless of a user equipment
location. For example, in a case where the RRH has small coverage,
the timing advance command may be determined as "0". Alternatively,
a timing advance command may be determined per local node. A timing
advance command suitable for an optimum node may be notified from
the macro cell by the broadcast information or dedicated
signaling.
[0388] In the configuration method described above, the RRH needs
not to perform downlink operation. Accordingly, radio resources can
be used effectively. In addition, an uplink resource to be
transmitted from the user equipment to the macro cell is not
required. Therefore, the uplink resource can be used also in the
initial uplink transmission from the user equipment.
[0389] The following two (1) and (2) are disclosed as the method of
configuring a reference frequency suitable for an optimum node. (1)
The user equipment configures a reference frequency based on the
measurement results. The user equipment measures the downlink
resource of the RRH and configures the downlink carrier frequency
as a reference frequency. The downlink resource of the RRH is
actually measured in this configuration method (1), and thus is
more effective than the configuration method (2) described below in
fewer errors.
[0390] A specific example of the method (1) of configuring a
reference frequency is described with reference to FIG. 18
described above. The downlink carrier frequency and uplink carrier
frequency of the macro cell are represented as DL_f1 and UL_f1,
respectively. The downlink carrier frequency and uplink carrier
frequency of the RRH are represented as DL_f2 and UL_f2,
respectively.
[0391] The user equipment measures a downlink resource of an RRH,
and recognizes and configures the downlink carrier frequency DL_f2
as a reference frequency.
[0392] However, the RRH needs to operate the downlink in the method
(1) of configuring a reference frequency, which poses a problem in
effective use of radio resources. The methods (2) and (3) of
configuring a reference frequency suitable for an optimum node are
disclosed below as the method of solving the problem.
[0393] (2) The RRH synchronizes reference frequencies with the
macro cell. The following three (a) to (c) are disclosed as
specific examples of the synchronization method.
[0394] (a) The macro cell notifies the RRH of the frequency
information. The frequency information may be a reference frequency
or downlink carrier frequency. The RRH that has received the
frequency information synchronizes the RRH frequency with the macro
cell frequency. The user equipment synchronizes frequencies based
on the downlink signal frequency of the macro cell. The RRH
frequency and macro cell frequency are in synchronization with each
other. Accordingly, the frequency of the user equipment is
synchronized with that of the macro cell, whereby the frequency of
the user equipment is synchronized with that of the RRH.
[0395] A specific example of the specific example (a) of the method
(2) of configuring a reference frequency is described with
reference to FIG. 18 described above. The downlink carrier
frequency and uplink carrier frequency of the macro cell are
represented as DL_f1 and UL_f1, respectively. The downlink carrier
frequency and uplink carrier frequency of the RRH are represented
as DL_f2 and UL_f2, respectively. The macro cell notifies the RRH
of the frequency information. The downlink carrier frequency DL_f1
or the uplink carrier frequency UL_f1 of the macro cell is
conceivable as the frequency information. The RRH synchronizes the
carrier frequencies DL_f2 and UL_f2 of the RRH to the frequency
information received from the macro cell. The user equipment
synchronizes frequencies based on the downlink carrier frequency
DL_f1 of the macro cell.
[0396] (b) The RRH receives a downlink signal from the macro cell
and synchronizes frequencies based on the frequency of the macro
cell. The user equipment synchronizes frequencies based on the
frequency of the downlink signal of the macro cell. The frequency
of the RRH and the frequency of the macro cell are in
synchronization with each other. Therefore, as a result of the
synchronization of the frequency of the user equipment with that of
the macro cell, the frequency of the user equipment is synchronized
with that of the RRH.
[0397] (c) The macro cell and the RRH configure a frequency using
the same reference signal source. Specific examples of the
reference signal source include a crystal unit, crystal oscillator,
and clock oscillator.
[0398] A specific example of the specific example (b) of the method
(2) of configuring a reference frequency is described with
reference to FIG. 18. The downlink carrier frequency and uplink
carrier frequency of the macro cell are represented as DL_f1 and
UL_f1, respectively. The downlink carrier frequency and uplink
carrier frequency of the RRH are represented as DL_f2 and UL_f2,
respectively. The RRH receives the downlink carrier frequency DL_f1
of the macro cell and synchronizes frequencies based on the
downlink carrier frequency DL_f1. The user equipment synchronizes
frequencies based on the frequency DL_f1 of the downlink signal of
the macro cell. The frequency of the RRH and the frequency of the
macro cell are in synchronization with each other. Therefore, as a
result of the synchronization of the frequency of the user
equipment with that of the macro cell, the frequency of the user
equipment is synchronized with that of the RRH.
[0399] The following three (1) to (3) are disclosed as specific
examples of the method of configuring a parameter suitable for an
optimum node.
[0400] (1) The macro cell notifies the user equipment of a
parameter by dedicated signaling. This notification may be
transmitted with an identifier of a target local node, for example,
with the PCI and GCI. This enables to configure a parameter
suitable for an optimum node per local node.
[0401] (2) The macro cell notifies the user equipment of a
parameter using paging. An indicator showing a notification of a
parameter suitable for an optimum node may be newly provided in a
paging message. The following two (a1) and (a2) are disclosed as
specific examples of the method of making a notification using
paging. (a1) "Parameter suitable for an optimum node" is mapped to
a paging message. As a specific example, "parameter suitable for an
optimum node" is mapped to the PCCH. (a2) Calling through paging
and RRC connection are performed, and then, "parameter suitable for
an optimum node" is notified using dedicated signaling.
[0402] (3) The macro cell notifies the user equipment of a
parameter using the broadcast information.
[0403] In the specific example (1) described above, a parameter is
notified by dedicated signaling, whereby the macro cell and user
equipment need to be in RRC connected. That is, in a case of an
idle state of the user equipment, a parameter suitable for an
optimum node cannot be configured. In addition, a parameter cannot
be used in the initial uplink transmission, for example, RACH.
[0404] Meanwhile, the macro cell and user equipment need not to be
in RRC connected in the specific examples (2) and (3) described
above, differently from the specific example (1) described above.
Therefore, a parameter suitable for an optimum node can also be
configured to a user equipment in an idle state. In addition, a
parameter suitable for an optimum node can also be used in the
initial uplink transmission from the user equipment.
[0405] The following two (1) and (2) are disclosed as specific
examples of the method in which a user equipment starts the use of
the configuration of an uplink transmission suitable for an optimum
node in uplink or the method in which a user equipment ends the use
of the configuration of an uplink transmission suitable for an
optimum node in uplink. In other words, the following two (1) and
(2) are disclosed as specific examples of the method in which a
user equipment switches from the configuration of the uplink
transmission suitable for an optimum node in downlink to the
configuration of the uplink transmission suitable for an optimum
node in uplink or the method in which a user equipment switches
from the configuration of the uplink transmission suitable for an
optimum node in uplink to the configuration of the uplink
transmission suitable for an optimum node in downlink.
[0406] (1) The macro cell notifies the user equipment that the use
of the configuration of an uplink transmission suitable for an
optimum node in uplink is started and that the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink is ended. The following two (a) and (b) are
disclosed as specific examples of the method of notifying the start
and end.
[0407] (a) The information indicating that the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink is started or the information "activation"
indicating that activation is notified by dedicated signaling. Or,
the information indicating that the use of the configuration of an
uplink transmission suitable for an optimum node in uplink is ended
or the information "deactivation" indicating deactivation is
notified. The following three (A) to (C) are disclosed as specific
examples of dedicated signaling. (A) The information is notified by
RRC signaling or RRC message. (B) The information is notified by
MAC signaling or MAC message. (C) The information is notified using
layer 1 signaling, as a specific example, PDCCH.
[0408] (b) The information indicating that the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink is started or the information "activation"
indicating activation is notified by paging. Or, the information
indicating that the use of the configuration of an uplink
transmission suitable for an optimum node in uplink is ended or the
information "deactivation" indicating deactivation is notified.
Indicator indicating a notification of the start and end may be
newly provided in the paging message.
[0409] (2) The macro cell notifies only the start. The macro cell
also notifies an effective period, and ends the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink after a lapse of the effective period from the
start. Also, the start of the use of the configuration of an uplink
transmission suitable for an optimum node in uplink may be notified
through a notification of a parameter suitable for an optimum node
in the specific examples (1) and (2).
[0410] The macro cell may interrupt the reception of an uplink
resource from the user equipment which has been notified that the
use of the configuration of an uplink transmission suitable for an
optimum node in uplink is started. The macro cell may restart the
reception of an uplink resource from the user equipment which has
been notified that the use of the configuration of an uplink
transmission suitable for an optimum node in uplink is ended.
[0411] Alternatively, the macro cell may interrupt the reception of
an uplink resource from the user equipment if the user equipment
has good reception quality regarding the uplink resource of the
macro cell in the RRH. The macro cell may restart the reception of
an uplink resource from the user equipment if the user equipment
has poor reception quality regarding the uplink resource of the
macro cell in the RRH. There may be provided a threshold of the
reception quality for judging an interruption or restart of the
reception.
[0412] Alternatively, the resource whose reception has been
interrupted may be scheduled to other user equipment. Specific
examples of the other user equipment include a user equipment that
is not located near the RRH and a user equipment that is located
near the macro cell.
[0413] Switching on and off the function of the RRH to receive an
uplink resource of a macro cell may be allowed.
[0414] Specific examples of the case in which the function to
receive an uplink resource is switched on include the case in which
there is a user equipment that selects the RRH as an optimum node.
A notification made by a macro cell in a case where there is a user
equipment that selects the RRH as an optimum node is conceivable as
a specific example of the method in which the RRH recognizes
on-timing.
[0415] Specific examples of the case in which the function to
receive an uplink resource is switched off include the case in
which there is no user equipment that selects the RRH as an optimum
node. A notification made by a macro cell in a case where there is
no user equipment that selects the RRH as an optimum node is
conceivable as a specific example of the method in which the RRH
recognizes off-timing.
[0416] In a case where the uplink transmission is configured
suitably for an optimum node, which is for a user equipment, the
macro cell may judge that there is a user equipment that selects
the RRH as an optimum node. Meanwhile, in a case where the uplink
transmission is not configured suitably for an optimum node, which
is for a user equipment, the macro cell may judge that there is no
user equipment that selects the RRH as an optimum node.
[0417] Next, a specific example of a sequence of a communication
system in the second embodiment is described with reference to FIG.
24. FIG. 24 is a diagram showing an example of the sequence of the
communication system in the second embodiment. The sequence shown
in FIG. 24 is similar to the sequences shown in FIGS. 19, 22, and
23, and thus, the same steps are denoted by the same step numbers
and common description is not given here.
[0418] This operation example discloses a case in which the RRH is
installed in the coverage of the macro cell, and also discloses a
case in which the user equipment camps on the macro cell and the
optimum node for uplink is an RRH.
[0419] This operation example discloses the case in which the RRH
determines a user equipment in the specific example (2) described
above, as a specific example of a method of determining a user
equipment whose optimum node differs between uplink and downlink.
This operation example discloses the case in which a macro cell
notifies a user equipment by dedicated signaling in the specific
example (1) described above, as a specific example of the method of
configuring a parameter suitable for an optimum node.
[0420] In Step ST2401, the macro cell notifies the RRH of the
information required for receiving a reference signal. Specific
examples of the information required for receiving a reference
signal include an identifier of a user equipment during connection
that is being served by the macro cell, a cell identifier of the
macro cell, a user-equipment-specific parameter regarding the
method of transmitting a reference signal specified from higher
layers to a user equipment during connection that is being served
by the macro cell, and a cell-specific parameter regarding the
method of transmitting a reference signal.
[0421] In Step ST2402, the RRH evaluates the uplink reception
quality of each user equipment at the RRH using the reception
signal or reception data regarding the uplink resource of the macro
cell.
[0422] In Step ST2403, the RRH judges whether or not there is a
user equipment having the uplink reception quality higher than a
threshold, based on the evaluation results of the uplink reception
quality in Step 2402. In a case of judging that there is a user
equipment having the uplink reception quality higher than the
threshold in Step ST2403, the RRH moves to Step ST2404. In a case
of judging there is no user equipment having the uplink reception
quality higher than the threshold in Step ST2403, the RRH ends the
process and moves to other process. The other process is not
specific to the present invention, which is not described here.
[0423] In Step ST2404, the RRH determines, as a user equipment that
needs support, the user equipment judged to have the uplink
reception quality higher than the threshold in Step ST2403.
[0424] In Step ST2405, the RRH notifies the macro cell of the
identifier of the user equipment that has been determined as a user
equipment that needs support in Step ST2404.
[0425] In Step ST2406, the RRH notifies the macro cell that the own
RRH is an optimum node in uplink for the user equipment that needs
support, which has been notified in Step ST2405. Specifically, the
RRH notifies the macro cell of the identifier of the own RRH.
[0426] In Step ST2407, the macro cell determines the configuration
of an uplink transmission suitable for a node optimum for the user
equipment received in Step ST2405. Specifically, the macro cell
determines the configuration of the uplink transmission suitable
for an optimum node in uplink, which has been received in Step
ST2406. Specific examples of the parameters of uplink transmission
include a path loss, timing advance command, and reference
frequency f.
[0427] In Step ST2408, the macro cell notifies the user equipment
of the configuration of an uplink transmission suitable for an
optimum node in uplink, which has been determined in Step
ST2407.
[0428] In Step ST2409, the user equipment reflects the
configuration of the uplink transmission suitable for an optimum
node in uplink, which has been received in Step ST2408.
[0429] In Step ST2410, the user equipment performs uplink
transmission to the macro cell, based on the uplink transmission
configuration suitable for an optimum node in uplink, which has
been reflected in Step ST2409.
[0430] In Step ST2411, the macro cell interrupts the reception of
the uplink resource of the user equipment that has been notified of
the configuration of the uplink transmission suitable for an
optimum node in uplink in Step ST2408. The macro cell may interrupt
the reception of an uplink resource scheduled to the user
equipment.
[0431] The second embodiment described above can achieve the
following effects in addition to the effects of the first
embodiment and the first modification of the first embodiment. As
described above, a link imbalance causes a situation in which an
optimum link is not used in uplink communication. In this case, the
transmission power required by the user equipment becomes larger
compared with the case in which an optimum link is used. This leads
to a problem of increased power consumption of a user
equipment.
[0432] In the present embodiment, the uplink transmission suitable
for a node optimum for uplink is configured. As a result, the
transmission power required by a user equipment is optimized. This
leads to a reduction in power consumption of the user equipment.
Additionally, unnecessary uplink transmission power from the user
equipment can be reduced, leading to a reduction in uplink
interference.
[0433] Meanwhile, in the solution of the second embodiment, the UE
performs uplink transmission persistently to the macro cell on
which the UE camps. The UE needs no additional notification or
additional function. In this respect, the second embodiment is
capable of constructing a communication system having excellent
backward compatibility.
[0434] While the present embodiment has disclosed the case in which
the carrier frequency of the local node differs from the carrier
frequency of the macro cell, the present embodiment is also
applicable to a case in which the carrier frequency of the local
node and the carrier frequency of the macro cell are identical to
each other. This enables to achieve similar effects to those of the
present embodiment.
[0435] While the present embodiment has described the configuration
of the communication system in a case where a remote radio head
(RRH) is used as a local node, the local node is not limited to an
RRH but may be a local node other than the RRH. The present
embodiment is also applicable to local nodes other than the RRH,
which enables to achieve similar effects to those of the present
embodiment.
[0436] While the present embodiment has mainly disclosed a case in
which an optimum node for uplink is a local node, the present
embodiment is also applicable if the optimum node for uplink is a
macro cell. This enables to achieve similar effects to those of the
present embodiment.
Third Embodiment
[0437] A third embodiment discloses another solution to the same
problem as that of the first embodiment and second embodiment
described above. The solution in the third embodiment is described
below. Carrier aggregation is performed using an uplink component
carrier of an optimum node in uplink without using downlink
component carriers thereof. Alternatively, carrier aggregation is
performed using a downlink component carrier and an uplink
component carrier of a macro cell and an uplink component carrier
of the optimum node in uplink. Still alternatively, a component
carrier of the optimum node for uplink is used in uplink of a
secondary cell (SCell).
[0438] The concept of the solution in the third embodiment is
described with reference to FIG. 25. FIG. 25 is a diagram for
describing the concept of the solution in the third embodiment.
[0439] A macro cell 2501 includes a DL_CC1 indicated by reference
numeral 2502 and a DL_CC2 indicated by reference numeral 2503 as
downlink component carriers. The macro cell 2501 also includes a
UL_CC1 indicated by reference numeral 2504 and a UL_CC2 indicated
by reference numeral 2505 as uplink component carriers.
[0440] An RRH 2506 includes a DL_CC3 indicated by reference numeral
2507 as a downlink component carrier. The RRH 2506 also includes a
UL_CC3 indicated by reference numeral 2508 as an uplink component
carrier. The macro cell 2501 and RRH 2506 are connected through a
dedicated line 2509.
[0441] A user equipment selects the DL_CC1 indicated by reference
numeral 2502 of the macro cell as a cell having the best downlink
reception quality, and then camps on the DL_CC1 (see Non-Patent
Document 3). That is, the DL_CC1 indicated by reference numeral
2502 of the macro cell serves as a downlink primary component
carrier of the PCell. The SIB2 in the broadcast information
notified by the downlink component carrier of the PCell shows a
carrier frequency of an uplink resource. Here, the UL_CC1 of the
macro cell 2501 is notified. That is, the PCell for the user
equipment, which is indicated by a broken line in FIG. 25, is
composed of the DL_CC1 and UL_CC1. The user equipment is located
nearer the RRH than the macro cell. In that case, an optimum node
in uplink is the RRH.
[0442] In the present embodiment, carrier aggregation is performed
using the uplink component carrier UL_CC3 indicated by reference
numeral 2508 of the RRH 2506 being an optimum node in uplink
without using the downlink component carrier DL_CC3 indicated by
reference numeral 2507 thereof.
[0443] Alternatively, carrier aggregation is performed using the
downlink component carriers of the macro cell 2501 being an optimum
node in downlink, which are specifically the DL_CC1 indicated by
reference numeral 2502 and the DL_CC2 indicated by reference
numeral 2503, the uplink component carriers of the macro cell 2501,
which is specifically the UL_CC1 indicated by reference numeral
2504, and the uplink component carrier of the RRH 2506 being an
optimum node in uplink, which is specifically the UL_CC3 indicated
by reference numeral 2508.
[0444] Still alternatively, in uplink of the SCell, the uplink
component carrier of the RRH 2506 being an optimum node in uplink,
specifically, the UL_CC3 indicated by reference numeral 2508 is
used. That is, the SCell for the user equipment indicated by a
chain double-dashed line in FIG. 25 is composed of the DL_CC2 and
UL_CC3.
[0445] Disclosed below is a specific example of the method of using
an uplink component carrier of an optimum node in uplink for
carrier aggregation. A PCell notifies a specific user equipment of
the uplink component carrier of the optimum node in uplink as the
addition or modification of a SCell. As described above, it is
studied that the PCell notifies the user equipment of the addition
or modification of the SCell using "RRC Connection Reconfiguration
message" of dedicated RRC signaling (see Non-Patent Document
2).
[0446] The method of using an uplink component carrier of an
optimum node in uplink for carrier aggregation is described with
reference to FIG. 25. Added to the DL_CC1 of the macro cell 2501
being a PCell as a SCell using dedicated RRC signaling are the
downlink component carrier DL_CC2 included in the macro cell 2501
being an optimum node in downlink and the uplink component carrier
UL_CC3 included in the RRH 2506 being an optimum node in
uplink.
[0447] This is characteristic in that the downlink component
carrier DL_CC2 and the uplink component carrier UL_CC3 are not
linked by the SIB2 in the broadcast information notified by the
downlink component DL_CC2. This is because an optimum node in
downlink serves as an optimum node in uplink in a case where, for
example, there is no local node in the coverage of the macro cell.
In a case where, for example, a user equipment is located nearer
the macro cell than the local node even if the local node is
located in the coverage of the macro cell, an optimum node in
downlink serves as an optimum node in uplink. Therefore, as
conventionally, the SIB2 in the broadcast information notified by
the downlink component DL_CC2 indicates the uplink resource carrier
UL_CC2 of the same node. A specific user equipment whose optimum
node differs between downlink and uplink is notified of the link
with the UL_CC3 using dedicated RRC signaling.
[0448] A specific example of the specific user equipment is a user
equipment located in the coverage of the RRH. A specific example of
the method of judging a user equipment located in the coverage of
the RRH is similar to the specific example of the method of
determining a user equipment that needs support in the second
embodiment described above, which is not described here. Note that
in the present embodiment, the function of receiving an uplink
component carrier of a macro cell is provided in the RRH, to
thereby realize (B) of the specific example (1) and the specific
example (2) described above.
[0449] A specific example of the method of selecting an optimum
node in uplink is disclosed below. (1) An optimum node is an RRH
being served by a macro cell. A specific example of the RRH being
served by the macro cell is similar to the specific example of the
first embodiment described above, which is not described here.
[0450] A problem of poor resource use efficiency arises in the
specific example (1) of the method of selecting an optimum node in
uplink. The specific example (2) of the method of selecting an
optimum node in uplink is disclosed below as the method of solving
the problem. (2) A different user equipment is scheduled for each
node. A specific example of the method of determining an optimum
node for uplink for each user equipment is similar to the specific
example of the method of determining an optimum node for uplink in
the second embodiment describe above, which is not described
here.
[0451] The user equipment configures an uplink transmission
suitable for an uplink component carrier of an optimum node. This
optimizes the transmission power required by the user. As a result,
the power consumption of the user equipment can be reduced. The
uplink transmission is configured using parameters suitable for an
optimum node, as the method of configuring an uplink transmission
suitable for an uplink component carrier of an optimum node.
Specific examples of the parameters include a path loss (PL),
timing advance command, and reference frequency f. The timing
advance command may be time alignment (TA).
[0452] The method of configuring a path loss suitable for an
optimum node is similar to that of the second embodiment described
above, which is not described here.
[0453] The method of configuring a timing advance command suitable
for an optimum node is disclosed below. In the conventional
technique, the uplink transmission timing for the PUSCH and SRS of
the SCell is identical to that of the PCell (see Chapter 4.2.3 of
Non-Patent Document 14). The present embodiment is also targeted
for, as an optimum node, a node installed at a place physically
remote from the node including the PCell.
[0454] The uplink component carrier of the optimum node is used for
the SCell in the present embodiment, which causes the following
problem in the conventional technique. Even if the user equipment
simultaneously performs the transmission using the uplink component
carrier of the PCell and the transmission using the uplink
component carrier of the SCell, the transmission arrives at each
node at different time. Therefore, the method of the conventional
technique in which the uplink transmission timing for the PUSCH and
SRS of the SCell is identical to that of the PCell poses a problem
that the uplink transmission of the SCell may fail to be received
normally. The method of configuring a timing advance command
suitable for an optimum node is similar to that of the second
embodiment described above, which is not described here.
[0455] The method of configuring a reference frequency suitable for
an optimum node is disclosed below.
[0456] (1) A user equipment configures a reference frequency based
on the measurement results. The user equipment measures the
downlink resource of the RRH, and recognizes and configures a
reference frequency. This configuration method (1) is more
effective than the configuration method (2) described below in
fewer errors because the downlink resource of the RRH is actually
measured.
[0457] A specific example of the method (1) of configuring a
reference frequency is described with reference to FIG. 25
described above. The carrier frequency of the downlink component
carrier DL_CC1, carrier frequency of the downlink component carrier
DL_CC2, carrier frequency of the uplink component carrier UL_1, and
carrier frequency of the uplink component carrier UL_2 of the macro
cell are represented as DL_f1, DL_f2, UL_f1, and UL_f2,
respectively. The carrier frequency of the downlink component
carrier DL_CC3 and carrier frequency of the uplink component
carrier UL_CC3 of the RRH are represented as DL_f3 and UL_f3,
respectively. The user equipment measures a downlink resource of
the RRH, and recognizes and configures the downlink carrier
frequency DL_f3 as a reference frequency.
[0458] Downlink operation needs to be performed in the RRH in the
method (1) of configuring a reference frequency suitable for an
optimum node, which poses a problem in effective use of radio
resources. Methods (2) and (3) of configuring a reference frequency
suitable for an optimum node are disclosed as the method of solving
the above-mentioned problem.
[0459] (2) The frequency of the RRH is synchronized with the
frequency of the macro cell. The following two (A) and (B) are
disclosed as specific examples of the method for
synchronization.
[0460] (A) The macro cell notifies the RRH of the frequency
information. The frequency information may be a reference frequency
or downlink carrier frequency. The RRH that has received the
frequency information synchronizes the frequency of the RRH with
the frequency of the macro cell. The user equipment synchronizes
the frequencies based on the frequency of the downlink signal of
the macro cell. The frequency of the RRH and the frequency of the
macro cell are in synchronization with each other. Therefore, the
frequency of the user equipment is synchronized with the frequency
of the RRH as a result of the synchronization of the frequency
between the user equipment and macro cell.
[0461] The following three (a1) to (a3) are disclosed as specific
examples of the downlink carrier frequency notified by the macro
cell in a case where there are a plurality of downlink component
carriers in the macro cell. (a1) Carrier frequency of the downlink
component carrier of the PCell. (a2) Carrier frequency of the
downlink component carrier of the macro cell linked with the uplink
component carrier of the RRH. (a3) Downlink carrier frequency of
the macro cell that is recognized as a reference frequency by the
user equipment.
[0462] The specific example (a1) of the specific example (A) in the
method (2) of configuring a reference frequency is described with
reference to FIG. 25 described above. The macro cell notifies the
RRH of the frequency information. The frequency information is the
downlink carrier frequency DL_f1 of the PCell. The RRH synchronizes
the carrier frequency DL_f3 of the downlink component carrier of
the RRH to the frequency information received from the macro cell.
The user equipment synchronizes frequencies based on the carrier
frequency DL_f1 of the downlink component carrier of the PCell or
the carrier frequency DL_f1 of the downlink component carrier of
the macro cell.
[0463] (B) The RRH receives a downlink signal of the macro cell and
synchronizes frequencies based on the frequency of the downlink
signal. The user equipment synchronizes frequencies based on the
frequency of the downlink signal of the macro cell. The frequency
of the RRH and the frequency of the macro cell are in
synchronization with each other. Therefore, the frequency of the
user equipment is synchronized with the frequency of the RRH as a
result of the synchronization of the frequency of the user
equipment with the frequency of the macro cell.
[0464] The following three (b1) to (b3) are disclosed as specific
examples of the downlink carrier frequency of the macro cell, which
is received by the RRH, in a case where there are a plurality of
downlink component carriers in a macro cell; (b1) carrier frequency
of a downlink component carrier of a PCell, (b2) carrier frequency
of a downlink component carrier of a macro cell linked with the
uplink component carrier of an RRH, and (b3) downlink carrier
frequency of a macro cell recognized as a reference frequency by a
user equipment.
[0465] The specific example (b1) of the specific example (B) in the
method (2) of configuring a reference frequency is described with
reference to FIG. 25 described above. The RRH receives the downlink
carrier frequency DL_f1 of the PCell of the macro cell and
synchronizes frequencies based on the downlink carrier frequency
DL_f1. The user equipment synchronizes frequencies based on the
frequency DL_f1 of the downlink signal of the macro cell. The
frequency of the RRH and the frequency of the macro cell are in
synchronization with each other. Therefore, the frequency of the
user equipment is synchronized with the frequency of the RRH as a
result of the synchronization of the frequency of the user
equipment with the frequency of the macro cell.
[0466] The following two (1) and (2) are disclosed as specific
examples of the method of configuring a parameter suitable for an
optimum node.
[0467] (1) A macro cell notifies a user equipment of a parameter
suitable for an optimum node by dedicated signaling. The
conventional addition or modification of a SCell may be used. This
enables to construct a communication system having excellent
backward compatibility. The notification by dedicated signaling may
be transmitted together with an identifier of a target local node,
for example, together with the PCI, GCI, and the like. As a result,
a parameter suitable for an optimum node can be configured per
local node.
[0468] (2) A macro cell notifies the user equipment of a parameter
suitable for an optimum node using the broadcast information.
[0469] The following two (1) and (2) are disclosed as specific
examples of the method in which a user equipment starts the use of
the configuration of an uplink transmission suitable for an optimum
node in uplink, or the method in which a user equipment ends the
use of the configuration of an uplink transmission suitable for an
optimum node in uplink.
[0470] (1) A macro cell notifies a user equipment that the use of
the configuration of an uplink transmission suitable for an optimum
node in uplink is started and that the use of the configuration of
an uplink transmission suitable for an optimum node in uplink is
ended. The macro cell notifies, by dedicated signaling, the
information indicating the start of the use of the configuration of
an uplink transmission suitable for an optimum node in uplink or
the information "activation" indicating activation. Or, the macro
cell notifies the information indicating the end of the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink or the information "deactivation" indicating
deactivation.
[0471] The conventional addition, modification, and removal of a
SCell, and activation and deactivation of a SCell may be used. For
example, in a case where the addition of a SCell is notified, in a
case where a SCell is added by modification, and in a case where
the activation of a SCell is notified, the start of the use of the
configuration of an uplink transmission suitable for an optimum
node in uplink may be notified. Meanwhile, in a case where the
removal of a SCell is notified and in a case where the deactivation
of a SCell is notified, the end of the use of the configuration of
an uplink transmission suitable for an optimum node in uplink may
be notified. This enables to construct a communication system
having excellent backward compatibility in that a conventional
message can also be used.
[0472] (2) A macro cell notifies only the start. The macro cell
also notifies an effective period, and after a lapse of the
effective period from the start, ends the use of the configuration
of an uplink transmission suitable for an optimum node in uplink.
Alternatively, in the specific examples (1) and (2), the macro cell
may notify the start of the use of the configuration of an uplink
transmission suitable for an optimum node in uplink based on the
notification of a parameter suitable for an optimum node.
[0473] Next, a specific example of a sequence of a communication
system in the third embodiment is described with reference to FIG.
26. FIG. 26 is a diagram showing an example of the sequence of the
communication system in the third embodiment. The sequence shown in
FIG. 26 is similar to the sequence shown in FIG. 24, and thus, the
same steps are denoted by the same step numbers and common
description is not given here.
[0474] This operation example discloses a case in which an RRH is
located in the coverage of a macro cell, and also discloses a case
in which a user equipment camps on the macro cell and an optimum
node for uplink is the RRH.
[0475] This operation example discloses the specific example (A1)
of the specific example (A) in the specific example (1) described
above, as a specific example of the method of judging a user
equipment located in the coverage of the RRH. This operation
example discloses, as a specific example of the method of
configuring a parameter suitable for an optimum node, a case of the
specific example (1) described above in which a macro cell notifies
a user equipment by addition of a SCell.
[0476] In Step ST2601, the user equipment camps on the DL_CC1 being
a downlink component carrier of the macro cell as a cell having the
best downlink reception quality. The carrier frequency of the
uplink resource is indicated by the SIB2 in the broadcast
information notified by the downlink component carrier DL_CC1.
Here, the UL_CC1 of the macro cell is notified. That is, the
downlink component carrier and uplink component carrier of the
PCell in the user equipment are DL_CC1 and UL_CC1,
respectively.
[0477] In Step ST2602, the user equipment configures an uplink
transmission suitable for the UL_CC1 of the macro cell being a
PCell.
[0478] In Step ST2603, the DL_CC1 of the macro cell performs a
downlink transmission to the user equipment.
[0479] In Step ST2604, the user equipment performs an uplink
transmission to the UL_CC1 of the macro cell based on the uplink
transmission configuration configured in Step ST2602.
[0480] In Step ST2605, the user equipment measures a neighboring
cell. The user equipment may measure a neighboring cell for judging
whether or not the own user equipment is a user equipment that
needs support, for judging whether or not the own user equipment is
located in the coverage of the RRH, or for determining an optimum
node for uplink.
[0481] In Step ST2606, the user equipment reports, to the PCell,
the measurement results of the neighboring cell performed in Step
ST2605. The user equipment reports the measurement results to a
control unit of the macro cell via the UL_CC1 of the macro
cell.
[0482] In Step ST2607, the control unit of the macro cell judges
whether or not there is a cell having downlink reception quality
higher than a threshold, based on the measurement results reported
from the user equipment in Step ST2606. In a case of judging that
there is a cell having downlink reception quality higher than the
threshold in Step ST2607, the control unit of the macro cell moves
to Step ST2608. In a case of judging that there is no cell having
downlink reception quality higher than the threshold in Step
ST2607, the control unit of the macro cell ends the process and
moves to other process. The other process is not specific to the
present invention, which is not described here.
[0483] In Step ST2608, the control unit of the macro cell
determines the user equipment that has reported the measurement
results in Step ST2606 as a user equipment that needs support, a
specific user equipment, or a user equipment located in the
coverage of the RRH.
[0484] In Step ST2609, the control unit of the macro cell
determines the cell that has been judged to have downlink reception
quality higher than the threshold in Step ST2607 as an optimum node
in uplink. In this operation example, the control unit determines
the UL_CC3 of the RRH as an optimum node in uplink.
[0485] In Step ST2407, the macro cell determines the configuration
of an uplink transmission suitable for an optimum node in uplink,
which has been determined in Step ST2609, of the user equipment
that has been determined as a user equipment located in the
coverage of the RRH in Step ST2608. Specific examples of the
parameters of uplink transmission include a path loss, timing
advance command, and reference frequency f.
[0486] In Step ST2610, the control unit of the macro cell notifies
the user equipment of the addition of a SCell via the PCell of the
macro cell. In notifying the addition of a SCell, the UL_CC3 of the
RRH being an optimum node in uplink, which has been determined in
Step ST2609, is configured as an uplink component carrier of the
SCell. The notification of the addition of a SCell includes the
configuration of an uplink transmission suitable for an optimum
node in uplink, which has been determined in Step ST2407. In
notifying the addition of a SCell, a cell having good downlink
reception quality is configured as a downlink component carrier. In
this operation example, the DL_CC2 of the macro cell is configured
as a downlink component carrier.
[0487] In Step ST2611, the user equipment configures an uplink
transmission suitable for an optimum node in uplink, which has been
received in Step ST2610. That is, the user equipment configures an
uplink transmission suitable for the SCell added in Step ST2610.
Specifically, the user equipment configures an uplink transmission
suitable for the UL_CC3 of the RRH.
[0488] In Step ST2612, the DL_CC1 of the macro cell performs a
downlink transmission to the user equipment. The DL_CC1 of the
macro cell performs communication as a PCell.
[0489] In Step ST2613, the DL_CC2 of the macro cell performs a
downlink transmission to the user equipment. The DL_CC2 of the
macro cell performs communication as a SCell.
[0490] In Step ST2614, the user equipment performs an uplink
transmission to the UL_CC1 of the macro cell based on the uplink
transmission configuration configured in Step ST2602. The UL_CC1 of
the macro cell performs communication as a PCell.
[0491] In Step ST2615, the user equipment performs an uplink
transmission to the UL_CC3 of the RRH based on the uplink
transmission configuration configured in Step ST2611. The UL_CC3 of
the RRH performs communication as a SCell.
[0492] The embodiment described above can achieve the following
effects. The uplink transmission suitable for an optimum node in
uplink is configured, which optimizes the transmission power
required by the user equipment. As a result, the power consumption
of the user equipment can be reduced. Besides, unnecessary uplink
transmission power from the user equipment can be reduced, leading
to a reduction in uplink interference.
[0493] While the present embodiment has described the configuration
of the communication system in a case where a remote radio head
(RRH) is used as a local node, the local node is not limited to the
RRH but may be a local node other than the RRH. The present
embodiment is also applicable to local nodes other than the RRH,
whereby similar effects to those of the present embodiment can be
achieved.
First Modification of Third Embodiment
[0494] A problem to be solved in a first modification of the third
embodiment is described below. Even in a case where the third
embodiment described above is used, the following problem occurs.
The PCell is used for transmission of the PUCCH from the user
equipment (see Chapter 7.5 of Non-Patent Document 1). If the third
embodiment is merely executed, the PUCCH cannot be transmitted
using an optimum node in uplink. Therefore, there still remains a
problem with the PUCCH, which has been yet to be solved in the
third embodiment.
[0495] The optimum node in uplink may be changed to a PCell by the
conventional carrier aggregation method. However, a PCell change
involves handover processing. In a case where an optimum node in
uplink is located in the coverage of the current node, two types of
measurement configurations, measurement objects, and reporting
configurations are respectively required. This is because the
following configurations are necessary; the conventional
configuration that supports handover out of the coverage of the
current node (see Non-Patent Document 2), and the configuration
that supports handover in a case where there is an optimum node in
the coverage of the current node in uplink. That is, the handover
method becomes complex, leading to a problem of an increased amount
of signaling. As described above, the solution to change an optimum
node in uplink to a PCell by the conventional carrier aggregation
method involves a problem.
[0496] A solution in the first modification of the third embodiment
is described below. The present modification mainly describes a
portion different from the solution in the third embodiment
described above, and a portion not to be described is similar to
the third embodiment.
[0497] In the present modification, carrier aggregation is
performed using downlink component carriers without uplink
component carriers of the optimum node in downlink, and also
carrier aggregation is performed using uplink component carriers
without using a downlink component carrier of the optimum node in
uplink.
[0498] Alternatively, carrier aggregation is performed using
downlink component carriers without using uplink component carriers
of a macro cell, and also carrier aggregation is performed using
uplink component carriers without using a downlink component
carrier of the optimum node in uplink. Still alternatively, in
uplink of a primary cell (PCell) and in uplink of a secondary cell
(SCell), component carriers of an optimum node in uplink are used.
Or, the RRH to be installed in the coverage of the cell is
dedicated to uplink reception. In the present modification, a SCell
needs not to be specifically configured.
[0499] The concept of the solution in the first modification of the
third embodiment is described with reference to FIG. 27. FIG. 27 is
a diagram for describing the concept of the solution in the first
modification of the third embodiment. The diagram shown in FIG. 27
is similar to the diagram shown in FIG. 25, and thus, portions
corresponding to those of FIG. 25 are denoted by the same reference
symbols and common description is not given here.
[0500] The macro cell 2501 includes the DL_CC1 denoted by reference
numeral 2502 and the DL_CC2 denoted by reference numeral 2503 as
downlink component carriers. The macro cell 2501 also includes the
UL_CC1 denoted by reference numeral 2504 and the UL_CC2 denoted by
reference numeral 2505 as uplink component carriers.
[0501] An RRH 2701 includes a DL_CC3 indicated by reference numeral
2507 as a downlink component carrier. The RRH 2701 also includes
the UL_CC3 indicated by reference numeral 2508 and a UL_CC4
indicated by reference numeral 2702 as uplink component carriers.
The macro cell 2501 and the RRH 2701 are connected through the
dedicated line 2509.
[0502] The user equipment selects the DL_CC1 indicated by reference
numeral 2502 of the macro cell as a cell having the best downlink
reception quality, and camps on the DL_CC1 (see Non-Patent Document
3). That is, the DL_CC1 indicated by reference numeral 2502 of the
macro cell serves as a downlink primary component carrier of a
PCell.
[0503] In the first modification of the third embodiment, carrier
aggregation is performed using the DL_CC1 and DL_CC2 being downlink
component carriers without using the UL_CC1 and UL_CC2 being uplink
component carriers of the macro cell 2501 being an optimum node in
downlink. Also, carrier aggregation is performed using the UL_CC3
and UL_CC4 being uplink component carriers without using the DL_CC3
being a downlink component carrier of the RRH 2701 being an optimum
node in uplink.
[0504] Alternatively, carrier aggregation is performed using the
DL_CC1 and DL_CC2 being downlink component carriers without using
the UL_CC1 and UL_CC2 being uplink component carriers of the macro
cell 2501. Also, carrier aggregation is performed using the UL_CC3
and UL_CC4 being uplink component carriers without using the DL_CC3
being a downlink component carrier of an optimum node in
uplink.
[0505] Still alternatively, in uplink of a primary cell (PCell) and
uplink of a secondary cell (SCell), the UL_CC3 and UL_CC4 being
uplink component carriers of the RRH 2701 being an optimum node in
uplink are used.
[0506] That is, the PCell for the user equipment, which is
indicated by a broken line in FIG. 27, is composed of the DL_CC1
and the UL_CC3. The SCell indicated by a chain double-dashed line
in FIG. 27 is composed of the DL_CC2 and the UL_CC4.
[0507] A specific example of the method of using the uplink
component carrier of the optimum node in uplink for carrier
aggregation is disclosed below. The uplink component carrier of the
optimum node in uplink is subjected to carrier aggregation for a
specific user equipment.
[0508] The method of selecting an uplink for carrier aggregation is
similar to a specific example of the method of determining an
optimum node for uplink in the second embodiment described above,
which is not described here.
[0509] A specific example of the method in which a PCell uses an
uplink component carrier of an optimum node in uplink for carrier
aggregation is disclosed below. The PCell notifies a specific user
equipment of the uplink component carrier of an optimum node in
uplink as a modification of the uplink component carrier of the
PCell. Similarly to the addition and modification of a SCell, "RRC
Connection Reconfiguration message" of dedicated RRC signaling is
used. This enables to construct a communication system having
excellent backward compatibility.
[0510] The present modification is characterized in that the uplink
component carrier of the PCell is not linked by the SIB2 of the
broadcast information. This is because in a case where, for
example, there is no local node in the coverage of the macro cell,
the optimum node in downlink serves as an optimum node in uplink.
Even if there is a local node in the coverage of the macro cell, in
a case where, for example, a user equipment is located nearer the
macro cell than the local node, an optimum node in downlink serves
as an optimum node in uplink. Therefore, the SIB2 shows the uplink
resource on the same node as in a conventional case. For example,
the uplink resource carrier UL_CC1 is shown by the SIB2 in the
broadcast information notified by the downlink component DL_CC1. As
in the present modification, a specific user equipment whose
optimum node differs between downlink and uplink, is notified of
the link with the UL_CC3 using dedicated RRC signaling.
[0511] The first modification of the third embodiment described
above can achieve the following effects in addition to the effects
of the third embodiment. As to the PUCCH, an uplink transmission
suitable for an optimum node in uplink is configured, which
optimizes the transmission power required by the user equipment. As
a result, the power consumption of the user equipment can be
reduced. In addition, unnecessary uplink transmission power from
the user equipment can be reduced, leading to a reduction in uplink
interference.
[0512] While the present modification has described the
configuration of the communication system in a case where a remote
radio head (RRH) is used as a local node, the local node is not
limited to the RRH but may be a local node other than the RRH. The
present modification is also applicable to local nodes other than
the RRH, whereby similar effects to those of the present
modification can be achieved.
Fourth Embodiment
[0513] A problem to be solved in a fourth embodiment is described
below. Non-Patent Document 11 discloses the solution to an
inter-cell interference problem in a heterogeneous network.
Specifically, it is described that a pico cell is installed in the
coverage of a macro cell, and a user equipment accesses the pico
cell when the user equipment comes closer to the pico cell.
[0514] The details disclosed in Non-Patent Document 11 are
described with reference to FIG. 16 described above. Description is
given here by replacing the RRH 1603 shown in FIG. 16 with a pico
cell. That is, a case in which the pico cell is installed in the
coverage of the macro cell is assumed. The pico cell 1603 is
installed in the coverage 1602 of the macro cell 1601. The pico
cell 1603 has the coverage 1604. A user equipment is located near
the macro cell 1601, and the user equipment communicates with the
macro cell 1601. In a case where the user equipment moves closer to
the pico cell 1603, the user equipment accesses the pico cell.
[0515] In a case where the optimum node in downlink is changed from
the macro cell 1601 to the local node installed in the coverage
1602 of the macro cell 1601, that is, to the pico cell 1603 as
described above, a handover occurs.
[0516] To allow the handover as described above, two types of
measurement configurations, measurement objects, and reporting
configurations are required respectively. This is because the
following configurations are necessary; the conventional
configuration that supports a handover out of the coverage of the
current node (see Non-Patent Document 2), and the configuration
that supports a handover in a case where there is an optimum node
in the coverage of the current node in uplink. That is, the
handover method becomes complex, leading to a problem of an
increased amount of signaling.
[0517] As described above, a PCell in carrier aggregation is
changed only through a handover. This causes a problem when an
optimum node is changed to a PCell in uplink, as described
above.
[0518] A solution in the fourth embodiment is described below. In
the present embodiment, a carrier frequency of an RRH is different
from a carrier frequency of a macro cell and a handover by a user
equipment from the macro cell to the RRH being served by the macro
cell is prohibited. Alternatively, a handover by a user equipment
to a cell being served by a serving cell is prohibited. That is,
even if the user equipment comes closer to the RRH being served by
the macro cell, a handover to the RRH is not allowed. A specific
example of the RRH being served by the macro cell and a specific
example of the cell being served by the serving cell are similar to
the specific examples of the RRH being served by the macro cell in
the first embodiment described above, which are not described
here.
[0519] A change of a PCell to an RRH being served by a macro cell
is prohibited. Alternatively, a change of a PCell to a component
carrier formed by a cell being served by a serving cell is
prohibited.
[0520] In the fourth embodiment, a handover is prohibited even in
the case where an optimum node in downlink is changed as described
above. In this case, the downlink reception quality may worsen and
a communication state in downlink may become worse, but a
characteristic point of the solution in the fourth embodiment is as
follows.
[0521] A cell to which a handover is prohibited in the fourth
embodiment is, for example, a cell being served by a serving cell.
The following three (1) to (3) are disclosed as specific examples
of the cell being served by a serving cell. (1) Cell connected with
the serving cell by a dedicated line. (2) Cell sharing the
functionality of the serving cell. (3) Cell located in the coverage
of the serving cell. Even if the solution in the fourth embodiment
is carried out, the carrier frequency of the macro cell being a
serving cell is different from the carrier frequency of the RRH,
and thus, the downlink reception quality is not degraded. In a case
where the RRH is located in the coverage of the serving cell, the
downlink reception quality is not degraded because the downlink
reception quality with respect to the serving cell is
satisfied.
[0522] Whether or not the fourth embodiment is performed may be
judged in accordance with the coverage size of the RRH being served
by a macro cell or the cell being served by a serving cell. In this
case, if, for example, the coverage of the RRH is larger than a
threshold, it is judged that the fourth embodiment is not
performed. Meanwhile, if the coverage of the RRH is smaller than
the threshold, it is judged that the fourth embodiment is
performed.
[0523] In the judgment of the coverage size, the downlink
transmission power of the RRH being served by the macro cell or the
cell being served by the serving cell may be used. In this case, it
is judged that the fourth embodiment is not performed in a case of,
for example, an RRH in high-power transmission. Meanwhile, it is
judged that the fourth embodiment is performed in a case of an RRH
not in high-power transmission.
[0524] The fourth embodiment described above can prevent the
handover method from becoming complex, which solves a problem of an
increased amount of signaling due to the complicated handover
method.
[0525] While the present embodiment has disclosed the case in which
the carrier frequency of the local node is different from the
carrier frequency of the macro cell, the present embodiment is also
applicable to a case in which the carrier frequency of the local
node is identical to the carrier frequency of the macro cell.
[0526] Further, while the present embodiment has described the
configuration of the communication system in a case where a remote
radio head (RRH) is used as a local node, the local node is not
limited to the RRH but may be a local node other than the RRH. The
present embodiment is also applicable to local nodes other than the
RRH, which enables to achieve similar effects to those of the
present embodiment.
First Modification of Fourth Embodiment
[0527] A problem to be solved in a first modification of the fourth
embodiment is described below. Even in a case where the fourth
embodiment described above is used, the same problem as those of
the first embodiment and second embodiment described above arises.
A solution in the first modification of the fourth embodiment is
described below.
[0528] In the present modification, the first embodiment, first
modification of the first embodiment, and second embodiment are
performed in addition to the fourth embodiment described above.
Alternatively, in the present modification, the third embodiment
described above is performed in addition to the fourth embodiment
described above.
[0529] The first modification of the fourth embodiment above can
achieve the following effects in addition to the effects of the
fourth embodiment. An uplink transmission suitable for an optimum
node in uplink is configured, which optimizes the transmission
power required by the user equipment. As a result, the power
consumption of the user equipment can be reduced. In addition,
unnecessary uplink transmission power from the user equipment can
be reduced, leading to a reduction in uplink interference.
Second Modification of Fourth Embodiment
[0530] A problem to be solved in a second modification of the
fourth embodiment is described below. Even in a case where the
third embodiment is performed in addition to the fourth embodiment
in the first modification of the fourth embodiment described above,
the same problem as that of the first modification of the third
embodiment described above arises. A solution in the second
modification of the fourth embodiment is described below.
[0531] In the present modification, the first modification of the
third embodiment described above is performed in addition to the
first modification of the fourth embodiment described above. Also,
the uplink component carrier of the RRH being served by a macro
cell can be used as an uplink component carrier of a PCell.
Alternatively, the uplink component carrier of a cell being served
by the serving cell can be used as an uplink component carrier of a
PCell.
[0532] The second modification of the fourth embodiment above can
achieve the following effects in addition to the effects of the
first modification of the fourth embodiment. As to the PUCCH, an
uplink transmission suitable for an optimum node in uplink is
configured, which optimizes the transmission power required by the
user equipment. As a result, the power consumption of the user
equipment can be reduced. In addition, unnecessary uplink
transmission power from the user equipment can be reduced, leading
to a reduction in uplink interference.
Third Modification of Fourth Embodiment
[0533] A third modification of the fourth embodiment discloses
another solution to the same problem as that of the second
modification of the fourth embodiment described above.
[0534] In the present modification, the RRH is provided with a
function of receiving an uplink component carrier of a macro cell
in addition to that of the first modification of the fourth
embodiment described above. Alternatively, the RRH may be provided
with a function of receiving an uplink component carrier of a PCell
of a macro cell. Still alternatively, the RRH may be only provided
with a function of receiving the PUCCH among the uplink component
carriers of the PCell of the macro cell.
[0535] The third modification of the fourth embodiment above can
achieve the following effects in addition to the effects of the
first modification of the fourth embodiment described above. As to
the PUCCH, an uplink transmission suitable for an optimum node in
uplink is configured, which optimizes the transmission power
required by the user equipment. As a result, the power consumption
of the user equipment can be reduced. In addition, unnecessary
uplink transmission power from the user equipment can be reduced,
leading to a reduction in uplink interference.
Fifth Embodiment
[0536] A problem to be solved in a fifth embodiment is described
below. The local node conceivably has a smaller coverage than that
of a macro cell. It is conceivable that in a case where the user
equipment is moving, the user equipment may pass through the
coverage of the local node in a short period of time. The following
problem arises in a case where an "uplink transmission suitable for
optimum node is configured" using the second embodiment, third
embodiment, first modification of the third embodiment, first
modification of the fourth embodiment, second modification of the
fourth embodiment, and third modification of the fourth embodiment
described above.
[0537] The problem to be solved in the fifth embodiment is
described with reference to FIG. 28. FIG. 28 is a diagram for
describing the problem of the fifth embodiment. The diagram shown
in FIG. 28 is similar to the diagram shown in FIG. 21, and thus,
the portions corresponding to those of FIG. 21 are denoted by the
same reference numerals and common description is not given
here.
[0538] An uplink transmission suitable for a local node being an
optimum node is configured. As a result, the uplink transmission
power of the user equipment serves as the uplink transmission power
suitable for the local node. The user equipment 2101 performs an
uplink transmission to the macro cell 2102 using the uplink 2106.
In FIG. 28, the magnitude of the uplink transmission power is
indicated by an arrow length of the uplink 2106. With reference to
FIG. 28, the uplink transmission from the user equipment 2101 can
be received in the range of a circle indicated by reference numeral
2108. That is, the macro cell 2102 cannot receive the uplink
transmission from the user equipment 2101 after the uplink
transmission power of the user equipment 2101 is adjusted to the
uplink transmission configuration suitable for a local node being
an optimum node. However, the RRH 2103 can receive the uplink
transmission from the user equipment 2101.
[0539] Next, a case in which the user equipment has moved out of a
coverage 2801 of the RRH 2103 is considered here. A user equipment
2101-2 performs an uplink transmission to the macro cell 2102 using
an uplink 2106-2. In FIG. 28, the uplink transmission power is
indicated by an arrow length of the uplink 2106-2. With reference
to FIG. 28, the uplink transmission of the user equipment 2101 can
be received in a range of a circle indicated by reference numeral
2108-2. That is, the macro cell 2102 cannot receive the uplink
transmission from the user equipment 2101-2 in a case where the
uplink transmission power of the user equipment 2101-2 has been
adjusted to the uplink transmission configuration suitable for a
local node being an optimum node and the user equipment has moved
out of the coverage of the optimum node. In addition, the RRH 2103
cannot receive the uplink transmission from the user equipment
2101-2.
[0540] In this case, it is conceivable that a reception error may
occur in the uplink transmission from the user equipment to the
macro cell as described above. This causes a problem of a
throughput reduction in uplink transmission.
[0541] The solution in the fifth embodiment is described below.
Whether or not an "uplink transmission suitable for an optimum
node" is configured is judged in accordance with a moving speed of
the user equipment. Specifically, whether or not to perform the
second embodiment, third embodiment, first modification of the
third embodiment, first modification of the fourth embodiment,
second modification of the fourth embodiment, and third
modification of the fourth embodiment is judged in accordance with
a moving speed of a user equipment. For example, in a case where
the moving speed of the user equipment is higher than a
predetermined threshold, an "uplink transmission suitable for an
optimum node" is not configured. Meanwhile, in a case where the
moving speed of the user equipment is lower than the predetermined
threshold, an "uplink transmission suitable for an optimum node" is
configured.
[0542] An effective period in which an "uplink transmission
suitable for an optimum node" is configured may be distinguished in
accordance with the moving speed of the user equipment. For
example, in a case where the moving speed of the user equipment is
higher than the predetermined threshold, an effective period in
which an "uplink transmission suitable for an optimum node" is
configured is set to be shorter than a predetermined reference
period. Meanwhile, in a case where the moving speed of the user
equipment is lower than the predetermined threshold, an effective
period in which an "uplink transmission suitable for an optimum
node" is configured is set to be equal to or longer than a
reference period.
[0543] A specific example of the method of recognizing the moving
speed of the user equipment is described below. It is possible to
apply, for example, the method of recognizing the moving speed
based on the number of cell reselections by a user equipment, whose
standardization is pursued by 3GPP, the method of recognizing the
moving speed based on Doppler frequency measurements, which is
described in R2-075149 by 3GPP, and the method of recognizing the
moving speed based on the positional information of a user
equipment, which is acquired using a global positioning system
(GPS).
[0544] The fifth embodiment above can achieve the following
effects. An uplink transmission suitable for an optimum node for
uplink is configured as in, for example, the third embodiment
described above, which optimizes the transmission power required by
the user equipment. As a result, the power consumption of the user
equipment can be reduced. In addition, unnecessary uplink
transmission power from the user equipment can be reduced, leading
to a reduction in uplink interference. Further, even in a case
where the local node has a relatively smaller coverage than that of
a macro cell and the user equipment is moving, an occurrence of
reception error in uplink transmission from the user equipment to
the macro cell can be prevented.
[0545] While the invention has been shown and 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.
DESCRIPTION OF REFERENCE SYMBOLS
[0546] 901 EPC communication unit, 902 communication with another
base station unit, 903 protocol processing unit, 904 transmission
data buffer unit, 905 encoding unit, 906 modulating unit, 907
frequency converting unit, 908 antenna, 909 demodulating unit, 910
decoding unit, 911 control unit, 1401, 1502, 1503, 1603 remote
radio head (RRH), 1402, 1501, 1601 macro cell, 1403, 1504 dedicated
line, 1602, 1604 coverage.
* * * * *