U.S. patent application number 16/136469 was filed with the patent office on 2019-01-31 for mobile communication system, base station and user equipment.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. The applicant listed for this patent is MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Yasushi IWANE, Miho MAEDA, Mitsuru MOCHIZUKI, Taiga SAEGUSA.
Application Number | 20190036660 16/136469 |
Document ID | / |
Family ID | 43031898 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190036660 |
Kind Code |
A1 |
MOCHIZUKI; Mitsuru ; et
al. |
January 31, 2019 |
MOBILE COMMUNICATION SYSTEM, BASE STATION AND USER EQUIPMENT
Abstract
The present invention relates to a mobile communication system
having a coordinated communication mode in which radio
communication is performed between a user equipment and a plurality
of base stations in a coordinated manner and an uncoordinated
communication mode in which radio communication is performed
between a user equipment and a base station without coordinating
with another base station, in which radio communication is
performed by selectively using any of the coordinated communication
mode and the uncoordinated communication mode. The coordinated
communication in which radio communication is performed between a
user equipment and a plurality of base stations in a coordinated
manner and the uncoordinated communication in which radio
communication is performed between a user equipment and a base
station without coordinating with another base station are
selectively used in an appropriate manner, with the result that a
mobile communication system capable of exerting its performance in
accordance with a situation can be provided.
Inventors: |
MOCHIZUKI; Mitsuru; (Tokyo,
JP) ; MAEDA; Miho; (Tokyo, JP) ; SAEGUSA;
Taiga; (Tokyo, JP) ; IWANE; Yasushi; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI ELECTRIC CORPORATION |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Chiyoda-ku
JP
|
Family ID: |
43031898 |
Appl. No.: |
16/136469 |
Filed: |
September 20, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15617078 |
Jun 8, 2017 |
10110356 |
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16136469 |
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15073683 |
Mar 18, 2016 |
9705648 |
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15617078 |
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|
14534958 |
Nov 6, 2014 |
9438390 |
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15073683 |
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13264767 |
Oct 17, 2011 |
8953523 |
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PCT/JP2010/002020 |
Mar 23, 2010 |
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14534958 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0033 20130101;
H04W 88/02 20130101; H04W 72/0413 20130101; H04W 72/0406 20130101;
H04W 72/048 20130101; H04W 72/02 20130101; H04B 7/024 20130101;
H04W 88/08 20130101; H04W 88/16 20130101; H04W 72/0486 20130101;
H04B 7/0689 20130101; H04W 40/28 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 72/04 20090101 H04W072/04; H04W 40/28 20090101
H04W040/28; H04W 72/02 20090101 H04W072/02; H04B 7/024 20170101
H04B007/024 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2009 |
JP |
2009-109312 |
Claims
1. A mobile communication system, which has a coordinated
communication mode in which radio communication is performed
between a user equipment and a plurality of base stations in a
coordinated manner and an uncoordinated communication mode in which
radio communication is performed between a user equipment and a
base station without coordinating with another base station,
wherein radio communication is performed by selectively using any
of said coordinated communication mode and said uncoordinated
communication mode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation application of and
claims the benefit of priority under 35 U.S.C. .sctn. 120 from U.S.
application Ser. No. 15/617,078 filed Jun. 8, 2017, which is a
continuation of U.S. application Ser. No. 15/073,683 filed Mar. 18,
2016 (now U.S. Pat. No. 9,705,648 issued Jul. 11, 2017), which is a
divisional application of U.S. application Ser. No. 14/534,958
filed Nov. 6, 2014 (now U.S. Pat. No. 9,438,390 issued Sep. 6,
2016), which is a divisional application of U.S. application Ser.
No. 13/264,767 filed Oct. 17, 2011 (now U.S. Pat. No. 8,953,523
issued Feb. 10, 2015), the entire contents of each of which is
incorporated herein by reference. U.S. application Ser. No.
13/264,767 is a national stage of International Application No.
PCT/JP2010/002020 filed Mar. 23, 2010 which claims the benefit of
priority under 35 U.S.C. .sctn. 119 from prior Japanese Patent
Application No. 2009-109312 filed Apr. 28, 2009.
TECHNICAL FIELD
[0002] The present invention relates to a mobile communication
system in which a base station performs radio communication with a
plurality of user equipments.
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 down link packet access (HSDPA) service for
achieving higher-speed data transmission using a down link has been
offered by adding a channel for packet transmission high
speed-downlink shared channel (HS-DSCH)) to the down link
(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 up link packet access (HSUPA)
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 8 version are produced.
[0004] Further, 3GPP is investigating 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.
In the LTE, an access scheme, 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 for each base station. Further, differently from the W-CDMA,
circuit switching is not provided but a packet communication system
is only provided in the LTE.
[0005] The LTE is defined as a radio access network independent of
the W-CDMA network because its communication system is configured
with a new core network different from a core network (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: also referred to as access gateway
(aGW)), respectively, in the LTE communication system. 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 UEs. This is also referred to as point to multipoint
service.
[0006] Non-Patent Document 1 describes the current decisions by
3GPP regarding an overall architecture in the LTE system. The
overall architecture (Chapter 4 of Non-Patent Document 1) 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 example, radio resource
management (RRC)) and a user plane (for example, packet data
convergence protocol (PDCP), radio link control (RLC), medium
access control (MAC), and physical layer (PHY)) for a UE 101 are
terminated in the base station 102. The base stations 102 perform
scheduling and transmission of paging signaling (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, 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. The MME
103 distributes the paging signaling to multiple or a single base
station 102. In addition, the MME 103 performs mobility control of
an idle state. When the UE is in the idle state and an active
state, the MME 103 manages a list of tracking areas. 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, there is provided a
PDN gateway (P-GW), which performs per-user packet filtering and
UE-ID address allocation.
[0007] The current decisions by 3GPP regarding the frame
configuration in the LTE system are described in Non-Patent
Document 1 (Chapter 5), which 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 sub-frames. 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). Multiplexing of channels for multimedia broadcast
multicast service single frequency network (MBSFN) and for
non-MBSFN is performed on a per-subframe basis. Hereinafter, a
subframe for MBSFN transmission is referred to as an MBSFN
sub-frame. 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, the
MBSFN subframes are allocated for each MBSFN frame. An MBSFN frame
cluster is scheduled. A repetition period of the MBSFN frame
cluster is allocated.
[0008] Non-Patent Document 1 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 (CSG) cell as that of a non-CSG cell. A physical
channel (Chapter 5 of Non-Patent Document 1) is described with
reference to FIG. 4. FIG. 4 is a diagram illustrating physical
channels used in the LTE communication system. With reference to
FIG. 4, a physical broadcast channel 401 (PBCH) is a downlink
channel transmitted from the base station 102 to the UE 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 402 (PCFICH) is
transmitted from the base station 102 to the UE 101. The PCFICH
notifies the number of OFDM symbols used for PDCCHs from the base
station 102 to the UE 101. The PCFICH is transmitted in each
subframe. A physical downlink control channel 403 (PDCCH) is a
downlink channel transmitted from the base station 102 to the UE
101. The PDCCH notifies the resource allocation, HARQ information
related to DL-SCH (downlink shared channel that is one of the
transport channels shown in FIG. 5) and the PCH (paging channel
that is one of the transport channels shown in FIG. 5). The PDCCH
carries an uplink scheduling grant. The PDCCH carries ACK/Nack that
is a response signal to uplink transmission. The PDCCH is referred
to as an L1/L2 control signal as well. A physical downlink shared
channel 404 (PDSCH) is a downlink channel transmitted from the base
station 102 to the UE 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 405 (PMCH) is a
downlink channel transmitted from the base station 102 to the UE
101. A multicast channel (MCH) that is a transport channel is
mapped to the PMCH.
[0009] A physical uplink control channel 406 (PUCCH) is an uplink
channel transmitted from the UE 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 407
(PUSCH) is an uplink channel transmitted from the UE 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. A
physical hybrid ARQ indicator channel 408 (PHICH) is a downlink
channel transmitted from the base station 102 to the UE 101. The
PHICH carries ACK/Nack that is a response to uplink transmission. A
physical random access channel 409 (PRACH) is an uplink channel
transmitted from the UE 101 to the base station 102. The PRACH
carries a random access preamble.
[0010] A downlink reference signal which is a known symbol in a
mobile communication system is inserted in the first, third and
last OFDM symbols of each slot. The physical layer measurement
objects of a UE include, for example, reference symbol received
power (RSRP).
[0011] The transport channel (Chapter 5 of Non-Patent Document 1)
is 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.
A broadcast channel (BCH) is broadcast to the entire base station
(cell) regarding the downlink transport channel. The BCH is mapped
to the physical broadcast channel (PBCH). Retransmission control
according to a hybrid ARQ (HARQ) is applied to a downlink shared
channel (DL-SCH). Broadcast to the entire base station (cell) is
enabled. 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 UE for enabling the UE to save power. The
DL-SCH is mapped to the physical downlink shared channel (PDSCH).
The paging channel (PCH) supports DRX of the UE for enabling the UE
to save power. Broadcast to the entire base station (cell) is
required. The PCH is mapped to physical resources such as the
physical downlink shared channel (PDSCH) that can be used
dynamically for traffic or physical resources such as the physical
downlink control channel (PDCCH) of the other control channel. The
multicast channel (MCH) is used for broadcast to the entire 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.
[0012] 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). A random access channel
(RACH) shown in FIG. 5(b) is limited to control information. There
is a collision risk. The RACH is mapped to the physical random
access channel (PRACH). The HARQ is described.
[0013] The HARQ is the technique for improving the communication
quality of a channel by combination of automatic repeat request and
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.
An example of the retransmission method is described. In a case
where the receiver fails to successfully decode the received data
(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
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. Examples of the HARQ system
include "chase combining". In chase combining, the same data
sequence is transmitted in the first transmission and
retransmission, which is the system for improving gains by
combining the data sequence of the first transmission and the data
sequence of the 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.
[0014] A logical channel (Chapter 6 of Non-Patent Document 1) is
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. 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. A paging control channel (PCCH) is a
downlink channel for transmitting paging signals. The PCCH is used
when the network does not know the cell location of a UE. The PCCH
that is a logical channel is mapped to the paging channel (PCH)
that is a transport channel. A common control channel (CCCH) is a
channel for transmission control information between UEs and a base
station. The CCCH is used in a case where the UEs have no RRC
connection with the base station. In downlink, the CCCH is mapped
to the downlink shared channel (DL-SCH) that is a transport
channel. In uplink, the CCCH is mapped to the uplink shared channel
(UL-SCH) that is a transport channel.
[0015] A multicast control channel (MCCH) is a downlink channel for
point-to-multipoint transmission. The MCCH is a channel used for
transmission of MBMS control information for one or several MTCHs
from a network to a UE. The MCCH is a channel used only by a UE
during reception of the MBMS. The MCCH is mapped to the downlink
shared channel (DL-SCH) or multicast channel (MCH) that is a
transport channel. A dedicated control channel (DCCH) is a channel
that transmits dedicated control information between a UE and a
network. The DCCH is mapped to the uplink shared channel (UL-SCH)
in uplink and mapped to the downlink shared channel (DL-SCH) in
downlink. A dedicate traffic channel (DTCH) is a point-to-point
communication channel for transmission of user information to a
dedicated UE. 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. A
multicast traffic channel (MTCH) is a downlink channel for traffic
data transmission from a network to a UE. The MTCH is a channel
used only by a UE during reception of the MBMS. The MTCH is mapped
to the downlink shared channel (DL-SCH) or multicast channel
(MCH).
[0016] GCI represents a global cell identity. A closed subscriber
group (CSG) cell is introduced in the LTE and universal mobile
telecommunication system (UMTS). The CSG is described below
(Chapter 3.1 of Non-Patent Document 4). The closed subscriber group
(CSG) is a cell in which subscribers who are permitted to use are
identified by an operator (cell for identified subscribers). The
identified subscribers are permitted to access one or more E-UTRAN
cells of a public land mobile network (PLMN). One or more E-UTRAN
cells in which the identified subscribers are permitted to access
are referred to as "CSG cell(s)". Note that access is limited in
the PLMN. The CSG cell is part of the PLMN that broadcasts a
specific CSG identity (CSG ID, CSG-ID). The members of the
authorized subscriber group who have registered in advance access
the CSG cells using the CSG-ID that is the access permission
information. The CSG-ID is broadcast by the CSG cell or cells. A
plurality of CSG-IDs exist in a mobile communication system. The
CSG-IDs are used by UEs for making access from CSG-related members
easy. 3GPP discusses in a meeting that the information to be
broadcast by the CSG cell or cells is changed from the CSG-ID to a
tracking area code (TAC). The locations of UEs are traced based on
an area composed of one or more cells. The locations are traced for
enabling tracing of the locations of UEs and calling (calling of
UEs) even in an idle state. An area for tracing locations of UEs is
referred to as a tracking area. A CSG whitelist is a list stored in
the USIM containing all the CSG IDs of the CSG cells to which the
subscribers belong. The whitelist of the UE is provided by a higher
layer. By means of this, the base station of the CSG cell allocates
radio resources to the UEs.
[0017] A "suitable cell" is described below (Chapter 4. 3 of
Non-Patent Document 4). The "suitable cell" is a cell on which a UE
camps to obtain normal service. Such a cell shall fulfill the
following: (1) the cell is part of the selected PLMN or the
registered PLMN, or part of the PLMN of an "equivalent PLMN list";
and (2) according to the latest information provided by a
non-access stratum (NAS), the cell shall further fulfill the
following conditions: (a) the cell is not a barred cell; (b) the
cell is part of at least one tracking area (TA), not part of
"forbidden LAs for roaming", where the cell needs to fulfill (1)
above; (c) the cell shall fulfill the cell selection criteria; and
(d) for a cell identified 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).
[0018] An "acceptable cell" is described below (Chapter 4.3 of
Non-Patent Document 4). This is the cell on which a UE camps to
obtain limited service (emergency calls). Such a cell shall fulfill
all the following requirements. That is, the minimum required set
for initiating an emergency call in an E-UTRAN network are as
follows: (1) the cell is not a barred cell; and (2) the cell
fulfills the cell selection criteria.
[0019] 3GPP is studying base stations referred to as Home-NodeB
(Home-NB, HNB) and Home-eNodeB (Home-eNB, HeNB). HNB/HeNB is a base
station for, for example, household, corporation or commercial
access service in UTRAN/E-UTRAN. Non-Patent Document 6 discloses
three different modes of the access to the HeNB and HNB. Those are
an open access mode, a closed access mode and a hybrid access mode.
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, the HeNB and
HNB are CSG cells where non-CSG members are allowed access at the
same time. In other words, a cell in the hybrid access mode is the
cell that supports both the open access mode and the closed access
mode.
[0020] 3GPP is studying a further advanced new communication system
for radio areas referred to as LTE advanced (LTE-A) (Non-Patent
Document 5). The LTE-A is based on the communication system for
radio areas according to the LTE and is configured by addition of
several new techniques thereto. Examples of the new techniques
include the wider bandwidth extension for supporting a wider
bandwidth and the coordinated multiple point transmission and
reception (CoMP).
[0021] CoMP studied for LTE-A is the technique for increasing the
coverage of high data rates, improving the cell-edge throughput and
increasing the system throughput by transmission or reception among
multiple geographically separated points. The CoMP is classified
into downlink CoMP (DL CoMP) and uplink CoMP (UL CoMP).
[0022] In DL CoMP, the PDSCH for one user equipment (UE) is
transmitted among multiple points in a coordinated manner. The
PDSCH for one UE may be transmitted from one point among multiple
points, or may be transmitted from a plurality of points among
multiple points. In a case of the transmission from one point, it
is also referred to as coordinate scheduling (CS) or coordinate
beamforming (CB), where transmission is stopped or transmission
power is reduced in the physical resources to which the PDSCH is
allocated in down link from other point to the UE. This reduces
interference with the UE, leading to improvements in reception
quality of the PDSCH of the UE.
[0023] In the case of the transmission from a plurality of points
among multiple points, it is also referred to as joint processing
(JP) or joint transmission (JT), where the PDSCHs for the UE are
transmitted simultaneously from a plurality of points of the
multiple points. The PDSCHs transmitted from a plurality of points
among multiple points to the UE are identical to each other. This
enables the UE to combine a plurality of received PDSCHs and
accordingly improve the reception quality. The allocation
information of the physical channel PDSCH to physical resources
(resource blocks) is transmitted to a UE by being mapped on the
physical channel PDCCH.
[0024] As the units (cells) that perform transmission at multiple
points, base stations (NB, eNB, HNB, HeNB), a remote radio unit
(RRU), a remote radio equipment (RRE) and a relay are studied. The
unit (cell) that performs coordinated multiple point transmission
is referred to as a multi-point unit (multi-point cell).
[0025] In UL CoMP, the uplink data from one user equipment (UE) is
received by multiple points in a coordinated manner. The quality of
uplink reception from the UE can be improved by combination of
pieces of data received at multiple points.
[0026] As to UL CoMP, it is studied that the physical channel PUSCH
is received by multiple points in a coordinated manner. The
allocation information of the physical channel PUSCH to the
physical resources (resource blocks) is transmitted to the UE by
being mapped on the physical channel PDCCH.
[0027] As the units (cells) that perform reception at multiple
points, base stations (NB, eNB, HNB, HeNB), a remote radio unit
(RRU), a remote radio equipment (RRE) and a relay are studied. The
unit (cell) that performs coordinated multiple point reception is
referred to as a multi-point unit (multi-point cell).
PRIOR ART DOCUMENTS
Non-Patent Documents
[0028] Non-Patent Document 1: 3GPP TS36.300 V8.6.0 [0029]
Non-Patent Document 2: 3GPP R1-072963 [0030] Non-Patent Document 3:
TR R3.020 V0.6.0 [0031] Non-Patent Document 4: 3GPP TS36.304 V8.4.0
[0032] Non-Patent Document 5: 3GPP TR36.814 V0.2.0 [0033]
Non-Patent Document 6: 3GPP S1-083461 [0034] Non-Patent Document 7:
3GPP R1-090529 [0035] Non-Patent Document 8: 3GPP TS36.331 V8.4.0
[0036] Non-Patent Document 9: 3GPP TS36.211 V8.6.0 [0037]
Non-Patent Document 10: 3GPP TS36.213 V8.6.0
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0038] An object of the present invention is to provide a mobile
communication system capable of exerting its performance so as to
be suited for a situation by selectively using, in an appropriate
manner, coordinated communication in which radio communication is
performed between a user equipment and a plurality of base stations
in a coordinated manner and uncoordinated communication in which
radio communication is performed between a user equipment and a
base station without coordinating another base station.
Means to Solve the Problem
[0039] The present invention relates to a mobile communication
system, which has a coordinated communication mode in which radio
communication is performed between a user equipment and a plurality
of base stations in a coordinated manner and an uncoordinated
communication mode in which radio communication is performed
between a user equipment and a base station without coordinating
with another base station, wherein radio communication is performed
by selectively using any of the coordinated communication mode and
the uncoordinated communication mode.
Effects of the Invention
[0040] According to the present invention, radio communication is
performed by selectively using any of the coordinated communication
mode in which radio communication is performed between a user
equipment and a plurality of base stations in a coordinated manner
and the uncoordinated communication mode in which radio
communication is performed between a user equipment and a base
station without coordinating with another base station. Therefore,
it is possible to achieve a mobile communication system capable of
exerting its performance so as to be suited for a situation.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a diagram illustrating the configuration of an LTE
communication system. FIG. 1 is a diagram illustrating the
configuration of an LTE communication system.
[0042] FIG. 2 is a diagram illustrating the configuration of a
radio frame used in the LTE communication system.
[0043] FIG. 3 is a diagram illustrating the configuration of an
MBSFN frame.
[0044] FIG. 4 is a diagram illustrating physical channels used in
the LTE communication system.
[0045] FIG. 5 is a diagram illustrating transport channels used in
the LTE communication system.
[0046] FIG. 6 is a diagram illustrating logical channels used in
the LTE communication system.
[0047] FIG. 7 is a block diagram showing the overall configuration
of a mobile communication system currently under discussion of
3GPP.
[0048] FIG. 8 is a block diagram showing the configuration of a
user equipment 311 according to the present invention.
[0049] FIG. 9 is a block diagram showing the configuration of a
base station 312 according to the present invention.
[0050] FIG. 10 is a block diagram showing the configuration of an
MME according to the present invention.
[0051] FIG. 11 is a block diagram showing the configuration of a
HeNBGW according to the present invention.
[0052] FIG. 12 is a flowchart showing an outline of cell search
performed by a user equipment (UE) in the LTE communication
system.
[0053] FIG. 13 is a conceptual diagram of DL CoMP studied by
3GPP.
[0054] FIG. 14 is a diagram illustrating downlink physical
resources in LTE-A.
[0055] FIG. 15 is a diagram illustrating a case where a PDSCH to
which a BCCH has been mapped is subjected to CoMP.
[0056] FIG. 16 is a diagram illustrating allocation of downlink
physical resources of a cell that performs DL CoMP with neighboring
cells.
[0057] FIG. 17 is a diagram illustrating physical resource
allocation in a case of a BCCH on which a SIB1 of broadcast
information is mapped.
[0058] FIG. 18 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
for each logical channel.
[0059] FIG. 19 is a diagram illustrating operations of a serving
cell and another cell that performs DL-CoMP with the cell.
[0060] FIG. 20 is a sequence diagram in a case where discrimination
is made between support and non-support for DL CoMP for each
logical channel.
[0061] FIG. 21 is a sequence diagram in a case where, not limited
to an interface between cells, an interface between a core network
and a cell or an interface between MMES is used.
[0062] FIG. 22 is a sequence diagram in a case of notifying
physical resource information that cannot be allocated to cells
which may perform DL CoMP.
[0063] FIG. 23 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
for each information.
[0064] FIG. 24 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
in accordance with a state of a UE being a transmission target.
[0065] FIG. 25 is a conceptual diagram in a case where
discrimination between support and non-support for DL CoMP is set
for each cell.
[0066] FIG. 26 is a diagram illustrating a setting procedure in a
case where discrimination between support and non-support for DL
CoMP is set in a semi-static manner.
[0067] FIG. 27 is a conceptual diagram of UL CoMP.
[0068] FIG. 28 is a sequence diagram in a case of performing UL
CoMP.
[0069] FIG. 29 is a conceptual diagram of a method of transmitting
PUSCH allocation information from one cell in UL CoMP.
[0070] FIG. 30 is a sequence diagram of a method of transmitting
PUSCH allocation information or uplink HARQ judgment results from
one cell in UL CoMP.
[0071] FIG. 31 is a conceptual diagram in a case where the uplink
HARQ judgment results are transmitted from one cell in UL CoMP.
[0072] FIG. 32 is a sequence diagram in a case where the same
judgment results are transmitted from all cells that perform UL
CoMP.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
First Embodiment
[0073] FIG. 7 is a block diagram showing an overall configuration
of an LTE mobile communication system, which is currently under
discussion of 3GPP. Currently, 3GPP is studying an overall system
configuration including closed subscriber group (CSG) cells
(Home-eNodeBs (Home-eNB and 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) and, as to e-UTRAN, is proposing the
configurations of (a) and (b) of FIG. 7 (Non-Patent Document 1 and
Non-Patent Document 3). FIG. 7(a) is now described. A user
equipment (UE) 71 performs transmission/reception to/from a base
station 72. The base station 72 is classified into an eNB (non-CSG
cell) 72-1 and Home-eNBs (CSG cells) 72-2. The eNB 72-1 is
connected to MMEs 73 through interfaces S1, and control information
is communicated between the eNB and the MMEs. A plurality of MMEs
are connected to one eNB. The Home-eNB 72-2 is connected to the MME
73 through the interface S1, and control information is
communicated between the Home-eNB and the MME. A plurality of
Home-eNBs are connected to one MME.
[0074] Next, FIG. 7(b) is described. The UE 71 performs
transmission/reception to/from the base station 72. The base
station 72 is classified into the eNB (non-CSG cell) 72-1 and the
Home-eNBs (CSG cells) 72-2. As in FIG. 7(a), the eNB 72-1 is
connected to the MMEs 73 through the interface S1, and control
information is communicated between the eNB and the MMEs. A
plurality of MMEs are connected to one eNB. While, the Home-eNBs
72-2 are connected to the MMEs 73 through a Home-eNB Gateway
(HeNBGW) 74. The Home-eNBs are connected to the HeGW through the
interfaces S1, and the HeNBGW 74 is connected to the MMEs 73
through an interface S1_flex. One or a plurality of Home-eNBs 72-2
are connected to one HeNBGW 74, and information is communicated
therebetween through S1. The HeNBGW 74 is connected to one or a
plurality of MMEs 73, and information is communicated therebetween
through S1_flex.
[0075] With the configuration of FIG. 7(b), one HeNBGW 74 is
connected to the Home-eNBs belonging to the same CSG-ID. As a
result, in the case where the same information such as registration
information is transmitted from the MME 73 to a plurality of
Home-eNBs 72-2 belonging to the same CSG-ID, the information is
transmitted to the HeNBGW 74 and then transmitted to the plurality
of Home-eNBs 72-2, with the result that signaling efficiency is
enhanced more compared with the case where the information is
directly transmitted to each of the plurality of Horne-eNBs 72-2.
While, in the case where each Home-eNB 72-2 communicates dedicated
information with the MIME 73, the information is merely caused to
pass through the HeNBGW 74 (to be transparent) without being
processed, which allows communication in such a manner that the
Home-eNB 72-2 is directly connected to the MME 73.
[0076] FIG. 8 is a block diagram showing the configuration of the
UE (equipment 71 of FIG. 7) according to the present invention. The
transmission process of the UE 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 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 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 a base station 312. A UE 311
executes the reception process as follows. The antenna 807 receives
the radio signal from the base station 312. 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 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
process of the UE is controlled by a control unit 810. This means
that, though not shown, the control unit 810 is connected to the
respective units (801 to 809).
[0077] 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 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 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 the 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 the transmission data buffer unit 904. The data stored in the
transmission data buffer unit 904 is transmitted to an encoding
unit 905 and is then subjected to 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
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 from an antenna 908 to one or a
plurality of UEs 71. While, the reception process of the base
station 72 is executed as follows. A radio signal from one or a
plurality of UEs 311 is received by 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
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 communication
with another base station unit 902. A series of process by the base
station 72 is controlled by a control unit 911. This means that,
though not shown, the control unit 911 is connected to the
respective units (901 to 910).
[0078] FIG. 10 is a block diagram showing the configuration of a
mobility management entity (MME) according to the present
invention. A PDN GW communication unit 1001 performs data
transmission/reception between an MME 73 and a PDN GW. A base
station communication unit 1002 performs data
transmission/reception between the MME 73 and the base station 72
through 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 processing 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
processing unit 1003 and is then transmitted to the PDN GW.
[0079] 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. A
HeNBGW communication unit 1004 is provided in the case where the
HeNBGW 74 is provided, which performs data transmission/reception
by the interface (IF) between the MME 73 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 the S1
interface through the base station communication unit 1002, or are
transmitted to one or a plurality of HeNBGWs 74 through the HeNBGW
communication unit 1004.
[0080] The control plane control unit 1005 includes a NAS security
unit 1005-1, an SAE bearer control unit 1005-2 and an idle state
mobility managing unit 1005-3, and performs overall process for the
control plane. The NAS security unit 1005-1 provides, for example,
security of a non-access stratum (NAS) message. For example, the
SAE bearer control unit 1005-2 manages a system architecture
evolution (SAE) bearer. For example, the idle state mobility
managing unit 1005-3 performs 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 one or a plurality of UEs
71 being served thereby, and tracking area (TA) list management.
The MME begins a paging protocol by transmitting a paging message
to the cell belonging to a tracking area (TA) in 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, CSG-IDs
and a whitelist. In the CSG-ID management, the relationship between
a UE 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 UEs whose user access
registration has been performed with a CSG-ID and the CSG cells
belonging to this CSG-ID. In the whitelist management, the
relationship between the UE 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 UE may
be stored in the whitelist. Although other part of the MME 73 may
perform those types of CSG-related management, through execution by
the idle state mobility managing unit 1005-3, the method of using a
tracking area code in place of a CSG-ID, which is currently under
discussion of 3GPP meeting, can be efficiently performed. A series
of process by an MME 313 is controlled by a control unit 1006. This
means that, though not shown, the control unit 1006 is connected to
the respective units (1001 to 1005).
[0081] FIG. 11 is a block diagram showing the configuration of the
HeNBGW according to the present invention. An EPC communication
unit 1101 performs data transmission/reception between the HeNBGW
74 and the MME 73 by the S1_flex interface. A base station
communication unit 1102 performs data transmission/reception
between the HeNBGW 74 and the Home-eNB 72-2 by the S1 interface. A
location processing unit 1103 performs the process of transmitting,
to a plurality of Home-eNBs, the registration information or the
like among the data transmitted from the MME 73 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. 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 process by the HeNBGW 74 is
controlled by a control unit 1104. This means that, though not
shown, the control unit 1104 is connected to the respective units
(1101 to 1103).
[0082] 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 cell search to idle state operation performed by a
user equipment (UE) in the LTE communication system. When the cell
search is started by the UE, in Step ST1201, the slot timing and
frame timing are synchronized by a primary synchronization signal
(P-SS) and a secondary synchronization signal (S-SS) transmitted
from a nearby base station. Synchronization codes, which correspond
to physical cell identities (PCIs) assigned per cell one by one,
are assigned to the synchronization signals (SS) 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 (identified). Next, in Step ST1202,
a reference signal RS of the synchronized cells, which is
transmitted from the base station per cell, is detected and the
received power is measured. The code corresponding to the PCI one
by one is used for the reference signal RS, and separation from
other cell is enabled by correlation using the code. The code for
RS of the cell is derived from the PCI identified in ST1201, which
makes it possible to detect the RS and measure the RS received
power. Next, in ST1203, the cell having the best RS reception
quality (for example, cell having the highest RS received power;
best cell) is selected from one or more cells that have been
detected up to ST1202. In ST1204, next, the PBCH of the best cell
is received, and the BCCH that is the broadcast information is
obtained. A master information block (MIB) containing the cell
configuration information is mapped on the BCCH on the PBCH.
Examples of MIB information include the down link (DL) system
bandwidth, the number of transmission antenna and system frame
number (SFN).
[0083] In 1205, next, the DL-SCH of the cell is received 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 regarding access to the cell,
information regarding cell selection and scheduling information of
other SIB (SIBk; k is an integer equal to or larger than 2). In
addition, the SIB1 contains a tracking area code (TAC). In ST1206,
next, the UE compares the TAC received in ST1205 with the TAC that
has been already possessed by the UE. In a case where they are
identical to each other as a result of comparison, the UE enters an
idle state operation in the cell. In a case where they are
different from each other as a result of comparison, the UE
requires a core network (EPC) (including MIME and the like) to
change a TA through the cell for performing tracking area update
(TAU). The core network updates the TA based on an identification
number (such as a UE-ID) of the UE transmitted from the UE together
with a TAU request signal. The core network updates the TA, and
then transmits the TAU accept signal to the UE. The UE rewrites
(updates) the TAC (or TAC list) of the UE. After that, the UE
enters the idle state operation in the cell.
[0084] DL CoMP is studied as a new technique for LTE-A. FIG. 13 is
a conceptual diagram of DL CoMP currently studied by 3GPP. A
multi-point unit 1 (unit 1) 1301 and a multi-point unit 2 (unit 2)
1302 are units that perform DL CoMP, that is, downlink coordinated
multiple point transmission. 1304 denotes a cell 1 formed by the
unit 1, and 1305 denotes a cell 2 formed by the unit 2. 1303
denotes a user equipment (UE 1) that is a DL CoMP target. FIG. 13
shows DL CoMP in a case of joint processing. In DL CoMP, the PDSCHs
are transmitted from a plurality of points of multi-point cells to
one UE. That is, the same PDSCH is transmitted from the cell 1 and
the cell 2 to the UE 1 (1306, 1307). The reception quality of the
UE 1 can be improved by combination of the PDSCHs transmitted from
the cell 1 and the cell 2. The UE located at the cell edge is a
CoMP target for increasing the coverage of higher data rates,
improving the cell-edge throughput, and increasing the system
throughput, which are aimed in DL CoMP.
[0085] FIG. 14 is a diagram illustrating downlink physical
resources in LTE-A. A horizontal direction and a vertical direction
represent a frequency and time, respectively. The configuration of
downlink physical resources of LTE-A is basically identical to that
of LTE. In the diagram, one subframe is shown. In LTE (LTE-A), one
subframe corresponds to one transmission time interval (TTI). The
PDCCH, PHICH and PFICH are allocated to the first one, first two or
first three symbols of one subframe (1401). The PDSCH is allocated
to the remaining symbols except for the above-mentioned symbols
(1402). Therefore, the physical resources where DL CoMP, that is,
downlink coordinated multiple point transmission is performed
correspond to the physical resources of FIG. 14 to which the PDSCH
is allocated.
[0086] Synchronization is performed between cells (multi-point
cells) that perform DL CoMP, and the same physical resource
(resource block) is allocated to the PDSCHs transmitted from
respective cells (multi-point cells). This enables the UE 1 (1303)
to combine the received PDSCHs (1306, 1307) as shown in FIG.
13.
[0087] 3GPP is studying that a serving cell (or anchor cell)
allocates the PDSCH physical resources in a case where DL CoMP is
performed. DL CoMP is performed by a plurality of multi-point cells
including the serving cell. The allocation information of physical
resources to which the PDSCHs are allocated is transmitted to a UE
on the PDCCH of any one of cells. The serving cell is studied as
this any one of cells that perform DL CoMP. Alternatively, in a
case where an anchor cell is provided as the cell that schedules
the coordinated transmission of DL CoMP, it is studied that one
cell that transmits the allocation information is used as the
anchor cell.
[0088] The method of notifying the physical resource allocation
information of PDSCH has not been determined by 3GPP. It can be
realized that physical resource allocation of the PDSCH is
performed in advance from the serving cell (anchor cell) to the
other cell that performs DL CoMP by means of an interface X2 and/or
interface S1. The interface X2 is an interface between cells (base
stations), and the interface S1 is an interface between a cell and
a core network (such as MEE).
[0089] As shown in FIG. 5, the downlink transport channels mapped
to the PDSCH are classified into the DL-SCH and PCH. As shown in
FIG. 6, the downlink logical channels mapped to the DL-SCH are
classified into the BCCH, CCCH, DCCH, DTCH, MCCH and MTCH. On the
other hand, the downlink logical channel mapped to the PCH is the
PCCH as shown in FIG. 6.
[0090] Those logical channels each have a different number of
target UEs to be transmitted in accordance with a type thereof. For
example, the broadcast information is mapped on the BCCH, which is
broadcast to all UEs being served by a cell. While, the dedicated
data to one UE is mapped on the DTCH, which is transmitted only to
one UE being served by a cell.
[0091] Along with an increase in the number of target UEs to which
a logical channel is transmitted, the number of UEs targeted for DL
CoMP increases as well. This is because the existence probability
of UEs located at the cell edge also increases along with an
increase in the number of UEs being transmission targets. As a
result of an increase in the number of UEs to which DL CoMP is
applied, the radio resources required for DL CoMP increase, which
considerably reduces the usage efficiency of radio resources. The
throughput of the UE to which DL CoMP is applied increases, while
the throughput as a system decreases. An increase in the number of
UEs to which DL CoMP is applied causes a problem of an increase in
information amount of physical resource allocation information of
the PDSCH to the UEs to which DL CoMP is applied, the information
being notified from the cell that schedules coordinated
transmission of DL CoMP to the other cell that performs DL
CoMP.
[0092] The case where the BCCH is subjected to DL CoMP is described
as an example where the problem that the throughput as a system
decreases arises due to an increase in the number of UEs to which
DL CoMP is applied.
[0093] The information to be broadcast to all UEs being served by a
cell, such as system information of a cell, is mapped on the BCCH.
The BCCH is mapped to the transport channel DL-SCH and is further
mapped to the physical channel PDSCH, to thereby be transmitted to
all UEs being served by a cell. Scheduling such as physical
resource allocation of the PDSCH is set for each cell.
[0094] The case where any one of UEs whose serving cell is the cell
is located at the cell edge is taken as an example. When DL CoMP is
applied to the UE located at the cell edge, the PDSCH is also
transmitted from the other cell that performs CoMP, with the same
physical resource. Any one of UEs whose serving cell is the cell is
highly likely to be located at any cell edge, and it could be said
that it is located there almost all the time. As a result, the
PDSCH to which the BCCH of the cell is mapped is subjected to CoMP
with any neighboring cell in the vicinity thereof almost all the
time. This holds true for neighboring cells as well.
[0095] That is, taking one cell, the cell has to transmit not only
the PDSCH to which the BCCH of the cell is mapped but also the
PDSCH to which the BCCH of a neighboring cell is mapped, almost all
the time.
[0096] FIG. 15 is a diagram illustrating the case where the PDSCH
to which the BCCH is mapped is subjected to CoMP. 1501 denotes a
multi-point unit 1 (cell 1), and a multi-point unit 2 (cell 2)
(1502), a multi-point unit 3 (cell 3) (1503), a multi-point unit 4
(cell 4) (1504), a multi-point unit 5 (cell 5) (1505), a
multi-point unit 6 (cell 6) (1506) and a multi-point unit 7 (cell
7) (1507) are arranged in the vicinity thereof.
[0097] A UE 1 (1508) is a user equipment whose serving cell is the
cell 1. Similarly, a UE 2 (1509) is a UE targeted for DL CoMP
between the cell 2 and the cell 1, whose serving cell is the cell
2. A UE 3 (1510) is a UE targeted for DL CoMP between the cell 3
and the cell 1, whose serving cell is the cell 3. A UE 4 (1511) is
a UE targeted for DL CoMP between the cell 4 and the cell 1, whose
serving cell is the cell 4. A UE 5 (1512) is a UE targeted for DL
CoMP between the cell 5 and the cell 1, whose serving cell is the
cell 5. A UE 6 (1513) is a UE targeted for DL CoMP between the cell
6 and the cell 1, whose serving cell is the cell 6. A UE 7 (1514)
is a UE targeted for DL CoMP between the cell 7 and the cell 1,
whose serving cell is the cell 7.
[0098] 1515 denotes the PDSCH to which the BCCH to be transmitted
to the UE being served by the cell 1 is mapped. The UE 1 receives
the PDSCH (1515). 1522 denotes the PDSCH to which the BCCH to be
transmitted to the UE being served by the cell 2 is mapped. The UE
2 receives the PDSCH (1522). 1523 denotes the PDSCH to which the
BCCH to be transmitted to the UE being served by the cell 3 is
mapped. The UE 3 receives the PDSCH (1523). 1524 denotes the PDSCH
to which the BCCH to be transmitted to the UE being served by the
cell 4 is mapped. The UE 4 receives the PDSCH (1524). 1525 denotes
the PDSCH to which the BCCH to be transmitted to the UE being
served by the cell 5 is mapped. The UE 5 receives the PDSCH (1525).
1526 denotes the PDSCH to which the BCCH to be transmitted to the
UE being served by the cell 6 is mapped. The UE 6 receives the
PDSCH (1526). 1527 denotes the PDSCH to which the BCCH to be
transmitted to the UE being served by the cell 7 is mapped. The UE
7 receives the PDSCH (1527).
[0099] The PDSCH 1516 to which the BCCH is mapped is transmitted
from the cell 2 to the UE 2 and is also transmitted from the cell 1
to the UE 2 by DL CoMP. The same holds true for the cell 3 to the
cell 7, and the PDSCHs 1517 to 1521 to which the BCCH is mapped are
transmitted from the cell 3 to the cell 7 to the UE 3 to UE 7,
respectively, and are also transmitted from the cell 1 to the UE 3
to UE 7, respectively. In this case, accordingly, the cell 1 has to
transmit not only the PDSCH to which the BCCH of own cell (cell 1)
is mapped but also the PDSCH to which the BCCHs of the neighboring
cells are mapped.
[0100] FIG. 16 is a diagram illustrating downlink physical resource
allocation of the cell 1 that performs DL CoMP with a neighboring
cell. The horizontal axis and vertical axis represent a frequency
and time, respectively. In the diagram, a system band is shown in
the horizontal axis direction, and a plurality of subframes each
composed of 14 symbols are shown in the vertical axis direction.
One subframe is 1TTI.
[0101] The PDSCH to which the BCCH of the cell 1 (own cell) is
mapped is allocated to a partial domain 1601 of a subframe #n. The
PDSCH to which the BCCH of the cell 2 (neighboring cell) is mapped
is allocated to a partial domain 1602 of a subframe #n+1. The PDSCH
to which the BCCH of the cell 3 (neighboring cell) is mapped is
allocated to a partial domain 1603 of a subframe #n+2. The PDSCHs
to which the BCCHs of the cell 4 (neighboring cell) and the cell 5
(neighboring cell) are mapped are allocated to a partial domain
1604 and a partial domain 1605 of a subframe #n+3, respectively.
The PDSCH to which the BCCH of the cell 6 (neighboring cell) is
mapped is allocated to a partial domain 1606 of a subframe #n+5.
The PDSCH to which the BCCH of the cell 7 (neighboring cell) is
mapped is allocated to a partial domain 1607 of a subframe
#n+6.
[0102] As described above, the cell 1 has to allocate the PDSCHs to
which the BCCHs of own cell and the neighboring cells are mapped to
the physical resources and then transmit those, which considerably
decreases the usage efficiency of radio resources. This results in
an increase in throughput of the UE to which CoMP is applied, but
leads to a decrease in throughput as a system.
[0103] FIG. 17 is a diagram illustrating physical resource
allocation in a case of the BCCH on which a system information
block 1 (SIB1) of the broadcast information is mapped. A domain
1701 is a physical resource to which the PDSCH, to which the SIB1
of the cell 1 is mapped, is allocated. A domain 1702 is a physical
resource to which the PDSCH, to which the SIB1 of the cell 2 is
mapped, is allocated. A domain 1703 is a physical resource to which
the PDSCH, to which the SIB1 of the cell 3 is mapped, is allocated.
A domain 1704 is a physical resource to which the PDSCH, to which
the SIB1 of the cell 4 is mapped, is allocated. A domain 1705 is a
physical resource to which the PDSCH, to which the SIB1 of the cell
5 is mapped, is allocated. A domain 1706 is a physical resource to
which the PDSCH, to which the SIB1 of the cell 6 is mapped, is
allocated. A domain 1707 is a physical resource to which the PDSCH,
to which the SIB1 of the cell 7 is mapped, is allocated. The radio
frame number (system frame number (SFN)) and the subframe number
for transmitting the PDSCH to which the SIB1 is mapped are
determined in advance for all cells. The first transmission of the
SIB1 is the subframe number 5 of the SFN being a multiple of 8, and
its repetition is transmitted on the other all subframe numbers 5
of the SFNs being multiples of 2.
[0104] Accordingly, as shown in the diagram, on the subframe number
5 of the SFNs being multiples of 2, the physical resource
allocation is performed not only for the PDSCH to which the BCCH,
on which the SIB1 of own cell is mapped, is mapped but also for the
PDSCHs to which the BCCH, on which the SIB1 of the neighboring cell
that performs CoMP is mapped, is mapped.
[0105] This leads not only to a case where the usage efficiency of
radio resources decreases considerably, but also to a case where
the allocations of other PDSCHs cannot be made due to a shortage of
radio resources or a case where even the PDSCH of the neighboring
cell that performs CoMP cannot be allocated. This reduces the
throughput as a system as well as makes the operation as a system
unstable.
[0106] In order to solve the above-mentioned problem, the present
embodiment discloses the discrimination between support and
non-support for DL CoMP in accordance with the type of a logical
channel. Here, support for DL CoMP refers to the transmission using
DL CoMP, that is, the transmission by a plurality of base stations
in a coordinated manner. Non-support for DL CoMP refers to the
transmission without using DL CoMP, that is, the transmission by a
base station that is not coordinated with another base station.
[0107] As a result of the support/non-support for DL CoMP being
discriminated in accordance with the type of a logical channel as
described above, it is possible to set support/non-support for DL
CoMP in accordance with the number of UEs being transmission
targets on a logical channel. This solves, for example, the problem
that arises in the case of a large number of UEs being transmission
targets as described above. In addition, CoMP can be set finely in
accordance with a communication method, whereby it is possible to
improve the usage efficiency of radio resources as a system. This
increases the throughput as a system. Moreover, discrimination for
each logical channel achieves an effect that control at the base
station is made simpler and an effect that coordinated transmission
control between base stations is made simpler.
[0108] For example, discrimination is made between a logical
channel dedicatedly transmitted to a UE and other logical channel,
where the PDSCH to which the former logical channel is mapped is
made to support DL CoMP, whereas the PDSCH to which the latter
logical channel is mapped is made not to support DL CoMP.
[0109] Differently from the logical channel on which the
information so as to be broadcast to all UEs being served by a cell
is mapped, the logical channel dedicatedly transmitted to one UE is
transmitted only to the UE only in a case where the transmission
data for the UE is generated. Accordingly, the UE that transmits
the logical channel is seldom located at the cell edge. Therefore,
even when DL CoMP is performed on the UE located at the cell edge,
the usage efficiency of radio resources is not deteriorated
considerably as described above. Therefore, discrimination is made
between a logical channel dedicatedly transmitted to one UE and the
other logical channel, and the former logical channel is made to
support DL CoMP, whereas the latter logical channel is made not to
support DL CoMP. Accordingly, a throughput is increased by DL CoMP,
which makes it possible to increase the throughput as a system.
[0110] As another example, discrimination is made between the
dedicated logical channels (DTCH, DCCH) and other logical channels,
and the PDSCH to which the dedicated logical channels (DTCH, DCCH)
are mapped is made to support DL CoMP, whereas the PDSCH to which
the other logical channels are mapped is made not to support DL
CoMP.
[0111] The dedicated logical channels (DTCH, DCCH) are logical
channels dedicatedly transmitted to one UE, whereby similar effects
to those of the above-mentioned example can be achieved. In
addition, the logical channels supporting DL CoMP are limited to
the DTCH and DCCH, and accordingly the number of UEs to which DL
CoMP is applied is prevented from increasing, which makes it
possible to further increase the throughput as a system. Moreover,
the communication state of the UE to which DL CoMP is applied is
limited, whereby it is possible to make the DL CoMP control, that
is, coordinated transmission control between multi-cells,
simpler.
[0112] As another example, discrimination is made between the
logical channel for broadcast (BCCH) and other logical channels,
and the PDSCH to which the logical channel for broadcast (BCCH) is
mapped is made not to support DL CoMP, whereas the PDSCH to which
other logical channels are mapped is made to support DL CoMP.
[0113] The logical channel for broadcast (BCCH) is broadcast to all
UEs being served by a cell, which is a channel that causes the
above-mentioned problem most among the logical channels. Therefore,
when the PDSCH to which the channel (BCCH) is mapped is made not to
support DL CoMP, the usage efficiency of radio resources is
prevented from decreasing, and the throughput as a system can be
increased as a result of an increase in throughput by DL CoMP of
the PDSCH to which other logical channels are mapped.
[0114] As another example, discrimination is made between the
logical channels for MBMS (MTCH, MCCH) and other logical channels,
and the PDSCH to which the logical channels for MBMS (MTCH, MCCH)
are mapped is made not to support DL CoMP, whereas the PDSCH to
which other logical channels are mapped is made to support DL
CoMP.
[0115] The MBMS-related information used for MBMS, such as MBMS
data and control information, is mapped on the logical channels for
MBMS (MTCH, MCCH). In a case of single cell transmission in which
the MBMS-related information is transmitted from one cell, the
logical channels for MBMS are mapped to the DL-SCH and then mapped
to PDSCH, to be transmitted to the UE that is capable of receiving
MBMS and/or receives MBMS service. A plurality of UEs may receive
the MBMS service of the cell, and thus the number of UEs to which
the logical channels for MBMS (MTCH, MCCH) are transmitted is not
limited to one but may be multiple in some cases. The number of
target UEs increases, and accordingly the MBMS logical channels
(MTCH, MCCH) are apt to cause the above-mentioned problem.
Therefore, the PDSCH to which the channels (MTCH, MCCH) are mapped
is made not to support DL CoMP, and accordingly the usage
efficiency of radio resources can be prevented from decreasing, and
the throughput as a system can be increased as a result of an
increase in throughput by DL CoMP of the PDSCH to which other
logical channels are mapped.
[0116] As another example, discrimination is made between the
logical channel for paging message (PCCH) and other logical
channels, and the PDSCH to which the logical channel for paging
message (PCCH) is mapped is made not to support DL CoMP, whereas
the PDSCH to which the other logical channels are mapped is made to
support DL CoMP.
[0117] The paging message contains information related to paging
and/or information related to system information change (BCCH
modify information) and/or information related to earthquake and
tsunami warning system (ETWS) notification (ETWS indication). For
example, in a case where the ETWS notification is provided when an
earthquake occurs, the cell broadcasts a paging message to all UEs
being served thereby. The paging message is mapped on the PCCH, and
the PCCH is mapped to the PCH and is then mapped to the PDSCH to be
broadcast to all UEs being served. If the PDSCH to which the PCCH
is mapped is made to support DL CoMP in a case where the ETWS
notification needs to be transmitted also by the neighboring cells,
a large amount of radio resources is required for DL CoMP as
described above in ETWS notification. This makes it impossible to
secure radio resources for other PDSCH, for example, the PDSCH for
a call by a user in a critical situation, such as a user hit by an
earthquake. In order to solve the above-mentioned problem,
discrimination is made between the logical channel for paging
message (PCCH) and other logical channels, and the PDSCH to which
the logical channel for paging message (PCCH) is mapped is made not
to support DL CoMP. This prevents a decrease in usage efficiency of
radio resources, and the throughput as a system can be increased as
a result of an increase in throughput by DL CoMP of the PDSCH to
which the other logical channels are mapped.
[0118] As another example, discrimination is made between the
logical channels for broadcast, MBMS and paging message (BCCH,
MTCH, MCCH, PCCH) and other logical channels, and the PDSCH to
which the former logical channels (BCCH, MTCH, MCCH, PCCH) are
mapped may be made not to support DL CoMP and the PDSCH to which
the other logical channels are mapped may be made to support DL
CoMP. This enables to make the logical channels, where the number
of UEs being CoMP targets is large, not support CoMP, whereas the
other logical channels, where the number of UEs being CoMP targets
is few, support CoMP. This further prevents a decrease in usage
efficiency of radio resources, and the throughput as a system can
be further increased as a result of an increase in throughput by DL
CoMP of the PDSCH to which other logical channels are mapped.
[0119] Next, an operation is disclosed. The present embodiment
discloses that discrimination is made between support and
non-support for DL CoMP in accordance with the type of a logical
channel. What logical channel of the logical channels is made to
support/not to support CoMP is predefined.
[0120] As an example, description is given of a case where
discrimination is made between the dedicated logical channels
(DTCH, DCCH) and other logical channels such that the PDSCH to
which the dedicated logical channels (DTCH, DCCH) are mapped is
made to support DL CoMP, whereas the PDSCH to which the other
logical channels are mapped is made not to support DL CoMP.
[0121] FIG. 18 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
for each logical channel. 1801 to 1805 are similar to 1301 to 1305
of FIG. 13, and thus description thereof is omitted. The UE 1 takes
the cell 1 as a serving cell (or anchor cell). FIG. 18 shows the
case of joint processing. As shown in the diagram, the PDSCHs are
classified into the PDSCH to which the dedicated logical channels
(DTCH, DCCH) are mapped and the PDSCH to which the other logical
channels are mapped. The dedicated logical channels (DTCH, DCCH)
are made to support DL CoMP for the UE 1 being a DL CoMP target,
and the PDSCHs to which the logical channels are mapped are
transmitted from a plurality of multi-point cells (cell 1, cell 2)
that perform DL CoMP to the UE 1 (1806, 1807). On the other hand,
the other logical channels are made not to support DL CoMP for the
UE 1 being a DL CoMP target, and the PDSCH to which the logical
channels are mapped is transmitted only from the serving cell (cell
1) to the UE 1 (1808).
[0122] The UE 1 combines the PDSCHs to which the dedicated logical
channels (DTCH, DCCH) are mapped that have been transmitted from
the cell 1 and the cell 2, to thereby improve the reception
quality. On the other hand, the other logical channels do not
support DL CoMP and thus the UE 1 cannot improve the reception
quality. However, the usage efficiency of radio resources does not
decrease considerably as described above. This increases the
coverage of high data rates and improves the cell-edge throughput
for the dedicated logical channels (DTCH, DCCH), which are aimed in
DL CoMP, and further prevents a decrease in usage efficiency of
radio resources, leading to an increase of a throughput in a
system.
[0123] FIG. 19 shows an example of the operations of the serving
cell and the other cell that performs DL CoMP with the cell. In the
serving cell, when the procedure of transmitting the PDSCH to the
UE 1 is started in ST1901, the serving cell first maps the logical
channel for transmission to the transport channel corresponding to
the logical channel (ST1902). Next, the serving cell maps the
transport channel to the PDSCH (ST1903). Then, the serving cell
performs scheduling of physical resources of the PDSCH
(ST1904).
[0124] In ST1905, the serving cell judges whether the UE to which
the PDSCH is transmitted is the UE being a DL CoMP target. As
judgment criteria, for example, whether the UE is located at the
cell edge may be judged. Further, the serving cell determines with
which cell DL CoMP is performed for the UE. In the case where the
serving cell judges that the UE is not a DL CoMP target, the
serving cell transmits the scheduling information of the PDSCH
determined in ST1904 on the PDCCH and the PDSCH with the physical
resources indicated by the scheduling information (ST1908). On the
other hand, in a case where the serving cell judges that the UE is
a CoMP target in ST1905, in ST1906, the serving cell judges whether
the logical channel to be transmitted supports or does not support
DL CoMP.
[0125] In a case where the logical channel does not support DL
CoMP, the serving cell transmits the PDCCH and PDSCH in ST1908. In
a case where the serving cell judges that the logical channel to be
transmitted supports DL CoMP in ST1906, in ST1907, the serving cell
transmits the transmission data and PDSCH scheduling information to
the other cell that performs DL CoMP. After that, the serving cell
transmits the PDCCH and PDSCH in ST1908. The other cell that
performs DL CoMP receives the transmission data and PDSCH
scheduling information transmitted from the serving cell in ST1907
(ST1909). The other cell that performs DL CoMP may initiate DL CoMP
for the UE by reception of the above-mentioned pieces of
information or any piece thereof. The cell (other cell that
performs DL CoMP) that has initiated DL CoMP for the UE starts the
procedure of transmitting the PDSCH to the UE. In ST1910, the other
cell maps the transmission data for the UE to the PDSCH. In ST1911,
the other cell allocates the PDSCH to the same physical resource as
that of the serving cell based on the PDSCH scheduling information
for the UE, and then transmits the PDSCH. The UE being a DL CoMP
target receives the PDSCHs transmitted from the serving cell and
the other cell that performs DL CoMP.
[0126] Discrimination between support and non-support for DL CoMP
in accordance with the type of a logical channel allows to transmit
the data transmitted to the other cell that performs DL CoMP from
the serving cell in a format for each logical channel in ST1907.
Further, the received data has been in the format of a logical
channel, and thus the other cell that performs DL CoMP is capable
of mapping the received data to the PDSCH without any processing in
ST1910. Accordingly, there can be achieved an effect that control
in a base station is made simpler as well as an effect that
coordinated transmission control is made simpler between base
stations.
[0127] In this case, in ST1909, the cell that performs DL CoMP
receives a piece or a plurality of pieces of information for DL
CoMP, which have been transmitted from the serving cell, to thereby
initiate DL CoMP for the UE. However, in ST1905, when the serving
cell judges that the UE is a DL CoMP target, the serving cell may
transmit a signal for initiating DL CoMP to the cell that has been
determined to perform DL CoMP. The other cell that performs DL CoMP
receives the signal, to thereby initiate DL CoMP for the UE.
[0128] As a result, the other cell can explicitly receive the
signal for initiating DL CoMP, whereby an effect of preventing a
malfunction is achieved. How long before the signal for initiating
DL CoMP is transmitted prior to the subframe to which the PDSCH is
allocated, the time thereof, the number of subframes or the number
of radio frames may be predetermined. This allows the other cell to
recognize the radio frame for performing DL CoMP, which makes the
adjustment with scheduling for UEs being served by the other cell
simpler.
[0129] FIG. 20 is an example of the sequence diagram in a case
where discrimination is made between support and non-support for DL
CoMP for each logical channel. FIG. 20(a) shows the case where a
logical channel supporting DL CoMP is transmitted, and FIG. 20(b)
shows the case where a logical channel that does not support DL
CoMP is transmitted. Shown as an example is the case where
discrimination is made between the dedicated logical channels
(DTCH, DCCH) and other logical channels, and the PDSCH to which the
dedicated logical channels (DTCH, DCCH) are mapped is made to
support DL CoMP, whereas the PDSCH to which other logical channels
are mapped is made not to support DL CoMP.
[0130] As shown in FIG. 20(a), in a case where the logical channels
supporting DL CoMP are transmitted, the serving cell (cell 1)
transmits the DTCH, DCCH and PDSCH allocation scheduling
information to which the DTCH and DCCH are mapped to the other cell
that performs DL CoMP before transmitting the PDSCH to which the
DTCH and DCCH are mapped to the UE (UE 1) being a DL CoMP target
(ST2001). ST2001 may be performed by means of the interface X2
between cells. After that, the serving cell transmits the PDSCH
allocation information of the DTCH and DCCH to the UE 1 on the
PDCCH (ST2002). The serving cell transmits the PDSCH in accordance
with the PDSCH allocation information of the DTCH and DCCH
(ST2003). On the other hand, the other cell that performs DL CoMP
maps the DTCH and DCCH received in ST2001 to the PDSCH, allocates
the PDSCH to the physical resource in accordance with the PDSCH
allocation scheduling information to which the DTCH and DCCH are
mapped, which has been also received in ST2001, and transmits the
PDSCH to the UE 1 (ST2004). The UE 1 receives the PDCCH transmitted
from the serving cell in ST2002 to detect the physical resource
allocation information of the PDSCH for own UE (ST2005), and
receives the physical resource to which the PDSCH is allocated
based on the detected allocation information, to thereby detect the
DTCH and DCCH (ST2006). On this occasion, the UE 1 receives the
PDSCH allocated to the same physical resource from the other cell
that performs DL COMP with the serving cell, which improves the
reception quality.
[0131] As shown in FIG. 20(b), in a case where the other logical
channel that does not support DL CoMP is transmitted, the serving
cell (cell 1) does not need to transmit, to the other cell, the
logical channel and the PDSCH allocation scheduling information to
which the logical channel is mapped. Accordingly, the serving cell
transmits the PDSCH allocation information of the other logical
channel to the UE 1 on the PDCCH (ST2007). The serving cell
transmits the PDSCH in accordance with the PDSCH allocation
information of the other logical channel (ST2008). The UE 1
receives the PDCCH transmitted from the serving cell in ST2007 to
detect the physical resource allocation information of the PDSCH
for own UE (ST2009), and receives the physical resource to which
the PDSCH is allocated based on the detected allocation
information, to thereby detect the other logical channel
(ST2010).
[0132] In the example of FIG. 20, in the case where the logical
channel supporting DL CoMP is transmitted in ST2001, an interface
(X2) between cells is used for transmitting, by the serving cell
(cell 1), the DTCH, DCCH and the PDSCH allocation scheduling
information to which the DTCH and DCCH are mapped to the other cell
that performs DL CoMP.
[0133] Not only limited to an interface between cells, an interface
(S1) between the core network (MME) and the cell or an interface
between MMEs may be used, which are shown in ST2101 and ST2102 of
FIG. 21(a). First, the serving cell transmits the DTCH, DCCH and
the PDSCH allocation scheduling information to which the DTCH and
DCCH are mapped by means of the S1 interface for the MME (MME1)
that controls the serving cell (ST2101). Then, the MME1 transmits
those to the other cell that performs DL CoMP controlled by the
MME1 (ST2102). This allows the MME to determine a cell that
performs DL CoMP and, in such a case, DL CoMP can be performed even
if the serving cell does not recognize the other cell that performs
DL CoMP.
[0134] Alternatively, for example, ST2103, ST2104 and ST2105 of
FIG. 21(b) may be shown. First, the serving cell transmits the
DTCH, DCCH and the PDSCH allocation scheduling information to which
the DTCH and DCCH are mapped to the MME (MME1) that controls the
serving cell by means of the S1 interface (ST2103) Then, the MME1
transmits those to the MME2 that controls the cell that performs DL
CoMP by means of the interface between the MMEs (ST2104). Then, the
MME2 transmits those to the other cell that performs DL CoMP by
means of the S1 interface (ST2105). This allows the cell that
performs DL CoMP to perform DL CoMP even in a case where different
MMES control those cells. For example, DL CoMP is enabled by
applying the above-mentioned operation in a case where DL CoMP is
performed between cells belonging to different tracking areas. This
is because the MME is generally provided for each tracking area in
many cases.
[0135] In the present embodiment, in the case where logical
channels supporting DL CoMP are transmitted, the serving cell (cell
1) transmits the DTCH, DCCH and the PDSCH allocation scheduling
information to which the DTCH and DCCH are mapped to the other cell
that performs DL CoMP, before transmitting the PDSCH to which the
DTCH and DCCH are mapped to the UE (UE 1) being a DL CoMP target
(ST2001 of FIG. 20(a)). Before this is performed, physical resource
information that cannot be allocated (or can be allocated) may be
notified between neighboring cells that may perform DL CoMP.
[0136] FIG. 22(a) shows an example of a sequence diagram for
notifying the physical resource information required between the
neighboring cells that may perform DL CoMP. In ST2201, the physical
resource information that cannot be allocated or the physical
resource information that can be allocated is notified between the
neighboring cells that may perform DL CoMP. In a case where the
cell has already recognized a cell with which the UE being a DL
CoMP target performs DL CoMP, the physical resource information
that cannot be allocated may be notified to the UE being a DL CoMP
target only between the cells that perform DL CoMP. Alternatively,
the physical resource information that can be allocated may be
notified.
[0137] This allows the serving cell that performs DL CoMP to use
the information in scheduling of the PDSCH, which enables
scheduling in accordance with the physical resource usage situation
of the other cell. For example, in a case where the cell 2
periodically allocates any PDSCH to the same physical resource, the
cell 2 transmits the information on the above to the serving cell,
with the result that the serving cell can schedule the PDSCH for DL
CoMP while avoiding scheduling to the physical resource. This makes
coordinated transmission control between multiple points simpler
and prevents the generation of re-scheduling or a control delay
resulting from this.
[0138] As another method, the serving cell may transmit, to the
cell that may perform DL CoMP or the cell that performs DL CoMP, a
signal for requesting the physical resource information that cannot
be allocated. Alternatively, the serving cell may transmit a signal
for requesting the physical resource information that can be
allocated.
[0139] FIG. 22(b) shows an example of a sequence diagram for
transmitting, by the serving cell, a signal for requesting the
physical resource information that cannot be allocated (or can be
allocated). In ST2202, the serving cell transmits the signal for
requesting the physical resource information that cannot be
allocated (or can be allocated) to the cell that performs DL CoMP.
The cell that has received the signal from the serving cell
transmits, to the serving cell, the physical resource information
that cannot be allocated (or can be allocated) of own cell
(ST2203). In a case where the serving cell transmits the signal to
the cell that performs DL CoMP in ST2202 but does not recognize the
cell that performs DL CoMP, the serving cell may transmit the
signal to the cell that may perform DL CoMP. This allows the
serving cell that performs DL CoMP to use the information in
scheduling of the PDSCH and perform scheduling in accordance with
the physical resource usage situation of the other cell. Further,
the serving cell transmits the signal for requesting a physical
resource, and thus the signals shown in ST2202 and ST2203 are
transmitted as desired, which prevents an increase of signaling
capacity.
[0140] The interface (X2) between cells, the interface (S1) between
the MME and the cell or the interface between MMEs as described in
the first embodiment may be used for the notification of the
physical resource information that cannot be allocated (or can be
allocated) or the transmission of the signal for requesting the
physical resource information that cannot be allocated (or can be
allocated). Alternatively, the above may be performed via the MME,
so that the MME holds and manages the physical resource information
that cannot be allocated of each cell that may perform DL CoMP, and
that the serving cell of the UE being a DL CoMP target receives the
information from the MME.
[0141] While the physical resource information that cannot be
allocated (or can be allocated) is notified between the neighboring
cells that may perform DL CoMP in the example of FIG. 22, the
physical resource that cannot be allocated or physical resource
that can be allocated may be predetermined for DL CoMP. The
physical resource may be determined in a frequency domain or time
domain. The frequency domain and time domain may be both
determined. Alternatively, the physical resource may be on a
resource block basis. The method of deriving the physical resource
may be predetermined. It may be determined as a system. As a
result, the cell that may perform DL CoMP or the cell that performs
DL CoMP can share the physical resource information, and
accordingly mutual notification between the cells performed in
ST2201 or in ST2202 and ST2203 is not required, leading to a
reduction in signaling amount.
[0142] In a case where the method of deriving the physical resource
is predetermined, cell identifiers (cell-ID, PCI) may be used as
input parameters for derivation. In this case, notifications may be
performed mutually between the cells that perform DL CoMP for
recognizing the cell identifier information of the other cell that
performs DL CoMP. Alternatively, the MME may make a notification to
each cell as neighboring cell information. In any case, the
physical resource can be derived with signaling of a small amount
of information.
[0143] The physical resource that cannot be allocated or physical
resource that can be allocated for DL CoMP may be static or
semi-static. In a case where it is semi-static, the physical
resource information, information on application time (such as
start, stop and valid duration) and the like of the physical
resource information may be notified mutually between the cells
that may perform DL CoMP or the cells that perform DL CoMP. The
semi-static physical resource does not require the notifications
between the cells each time DL CoMP is performed, which reduces a
signaling amount and enables appropriate correspondence with the
radio wave propagation environment that varies in time or the
number of UEs being served by a cell.
[0144] As an example of the semi-static physical resource, several
types of physical resources that cannot be allocated or physical
resources that can be allocated for DL CoMP may be predetermined,
and a type thereof to be used may be notified mutually between the
cells that may perform DL CoMP or the cells that perform DL CoMP in
setting or changing of the physical resource. Alternatively, the
MME may notify each cell. This only requires that a signal of a
small amount of information, such as the information indicating a
type, be notified between the cells.
[0145] The above-mentioned information notification method may be
performed by means of the interface (X2) between cells, the
interface (S1) between an MME and a cell or the interface between
MMEs as described in the first embodiment. Alternatively, the above
may be performed via the MME, so that the MME holds and manages
those pieces of information. The serving cell of the UE being a DL
CoMP target may receive those pieces of information from the
MME.
[0146] While the present embodiment discloses that discrimination
is made between support and non-support for DL CoMP in accordance
with the type of a logical channel, discrimination may be made
between support and non-support for DL CoMP in accordance with the
type of a transport channel.
[0147] For example, discrimination is made between the DL-SCH and
other transport channel, and the PDSCH to which the former
transport channel is mapped is made to support DL CoMP, whereas the
PDSCH to which the latter transport channel is mapped is made not
to support DL CoMP.
[0148] Discrimination is made between support and non-support for
DL CoMP in accordance with the type of a transport channel as
described above, whereby it is possible to set support and
non-support for DL CoMP in accordance with the number of UEs being
transmission targets of a transport channel, which solves, for
example, a problem that arises in a case of a large number of UEs
being transmission targets. CoMP can be set finely in accordance
with a communication method, whereby it is possible to improve the
usage efficiency of radio resources as a system, leading to an
increase of the throughput as a system.
[0149] As an operation example in the cell, the judgment of ST1906
shown in FIG. 19 may be made by the transport channel, not by the
logical channel. Further, the transmission data transmitted, by the
serving cell, to the other cell that performs DL CoMP in ST1907 may
be on a data basis so as to be mapped on the transport channel. In
that case, in ST1908, the other cell that performs DL CoMP receives
the transmission data from the serving cell that has been
transmitted on a data basis so as to be mapped on the transport.
This achieves the effects that control at a base station is made
much simpler because the discrimination is made for each transport
channel, that coordinated transmission control between base
stations can be made simpler because the information
transmitted/received between base stations can be on a data basis
so as to be mapped on the transport channel, and that the period of
time required for mapping to the PDSCH or allocation to the
physical resource can be reduced at a base station that has
received the data on a transport channel basis from the serving
cell.
First Modification of First Embodiment
[0150] The first embodiment has disclosed that discrimination is
made between support and non-support for DL CoMP in accordance with
the type of a logical channel. In some cases, however, the number
of target UEs to be transmitted in accordance with the type of
information mapped on the logical channel varies even in a case of
the same type of logical channels.
[0151] One example thereof is the information mapped on the PCCH.
As described above, the paging message is mapped on the PCCH, and
the paging message contains the information related to paging
and/or the information related to system information change and/or
the information related to ETWS notification. The information
related to paging is transmitted to a UE that has received a call.
However, the information related to system information change and
the information related to ETWS notification are notified to all
UEs being served by a cell in a case where the system information
has been changed or in a case where an ETWS notification is made.
Therefore, in some cases, the number of target UEs to be
transmitted in accordance with the type of information mapped on a
logical channel varies even in a case of the same types of logical
channels.
[0152] The information related to paging is transmitted to the UE
that receives a call, and when the PCCH is made to support DL COMP,
the PCCH has to be broadcast to all UEs being served by a cell in a
case where the system information mapped on the PCCH has been
changed or in a case where an ETWS notification is made. The PCCH
is mapped to the PCH and is mapped to the PDSCH, to thereby be
broadcast to UEs being served. When the PDSCH to which the PCCH is
mapped is made to support DL CoMP in a case where, also in
neighboring cells, the system information has been changed or an
ETWS notification has to be transmitted, a large amount of radio
resources has to be used for DL CoMP. Accordingly, the usage
efficiency of radio resources decreases considerably, leading to a
problem that the throughput as a system decreases. Further, there
arises a problem that it is impossible to secure a radio resource
for a call by a user in a critical situation, such as a user hit by
an earthquake as described above.
[0153] On the other hand, when the PCCH is made not to support DL
CoMP, there arises a problem that the reception quality of the
information related to paging, which can be improved originally,
cannot be improved. That is, this is because the information
related to paging is transmitted only to the UE that receives a
call, and thus the above-mentioned problem does not arise
originally even when the PCCH is made to support DL CoMP, and the
PCCH can support DL CoMP.
[0154] In order to solve these problems, a first modification of
the present embodiment discloses that discrimination is made
between support and non-support for DL CoMP in accordance with the
type of information mapped to the PDSCH. As a result of
discrimination being made between support and non-support for DL
CoMP in accordance with the type of information as described above,
it is possible to set support/non-support for DL CoMP in accordance
with the number of UEs being transmission targets for each type of
information. Therefore, it is possible to set CoMP finely in
accordance with the number of UEs also in, for example, the
above-mentioned case including a case where the number of UEs being
transmission targets is large and a case where the number of UEs
being transmission targets is small (or in a case of only one UE)
as to the same type of logical channels. Further, setting can be
made for each type of information, which allows setting of
support/non-support for DL CoMP for each service. This allows the
use of radio resources to be flexibly controlled as a system, and
improves the usage efficiency of radio resources. Therefore, it is
possible to increase the throughput as a system.
[0155] For example, support and non-support for DL CoMP are
discriminated between the information required to be dedicatedly
transmitted to one UE being served by a cell and the other
information.
[0156] As a specific example, the dedicated UE user information,
dedicated UE control information, common control information and
paging information are made to support CoMP, whereas the other
information is made not to support CoMP. The dedicated UE user
information is mapped on the DTCH, and the dedicated UE control
information is mapped on the DCCH. The common control information
is mapped on the CCCH, is mapped to the DL-SCH, and is then mapped
to the PDSCH to be transmitted. The paging information is mapped on
the PCCH, is mapped to the PCH, and is then mapped to the PDSCH to
be transmitted. The other information, for example, broadcast
information, information indicating the system information change,
information related to ETWS notification or MBMS-related
information, is made not to support CoMP. The broadcast information
is mapped on the BCCH, is mapped to the DL-SCH, and is then mapped
to the PDSCH to be transmitted. The information indicating the
system information change and the information related to ETWS
notification are mapped on the PCCH, is mapped to the PCH, and is
then mapped to the PDSCH to be transmitted. The MBMS-related
information is mapped to the MTCH and MCCH, is mapped to the
DL-SCH, and is then mapped to the PDSCH to be transmitted.
Discrimination is made in accordance with the type of information
as described above, so that the PDSCH on which the dedicated UE
user information, dedicated UE control information, common control
information and paging information are mapped is made to support
CoMP, whereas the PDSCH on which the other information is mapped is
made not to support CoMP. This allows discrimination between
support and non-support for DL CoMP in accordance with the number
of UEs being DL CoMP targets for each type of information to be
transmitted or for each service, whereby it is possible to flexibly
control the use of radio resources as a system, leading to an
improvement in usage efficiency of radio resources. Accordingly, it
is possible to increase the throughput as a system.
[0157] Next, an operation is disclosed. This first modification has
disclosed that discrimination is made between support and
non-support for DL CoMP in accordance with the type of information
to be transmitted. What type of information to be transmitted is
made to support/not to support CoMP is predefined.
[0158] As an example, description is given of a case where
discrimination is made between the dedicated transmission
information and the other transmission information such that the
PDSCH to which the dedicated transmission information is mapped is
made to support DL CoMP and the PDSCH to which the other
transmission information is mapped is made not to support DL
CoMP.
[0159] FIG. 23 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
for each information. 2301 to 2305 are similar to 1301 to 1305 of
FIG. 13, and thus description thereof is omitted. As shown in the
diagram, the PDSCHs are classified into the PDSCH to which the
dedicated transmission information is mapped and the PDSCH to which
the other transmission information is mapped. The dedicated
transmission information is made to support DL CoMP for the UE 1
being a DL CoMP target, and the PDSCH to which the information is
mapped is transmitted from a plurality of multi-point cells (cell
1, cell 2) that perform DL CoMP to the UE 1 (2306, 2307). On the
other hand, the other transmission information is made not to
support DL DoMP for the UE 1 being a DL CoMP target, and the PDSCH
to which the information is mapped is transmitted only from the
serving cell (cell 1) to the UE 1 (2308).
[0160] The UE 1 combines the PDSCHs to which the dedicated
transmission information is mapped, which have been transmitted
from the cell 1 and the cell 2, to thereby improve the reception
quality. On the other hand, the other transmission information does
not support DL CoMP and thus the reception quality of the UE 1
cannot be improved, but the usage efficiency of radio resources
does not decrease considerably as described above. This increases
the coverage of high data rates and improves the cell-edge
throughput, which are aimed in DL CoMP for the dedicated
transmission information, and further prevents a decrease in usage
efficiency of radio resources by making the other transmission
information not support CoMP, leading to an increase of the
throughput in a system.
[0161] As to the operations of the serving cell and the other cell
that performs DL CoMP with the serving cell, it suffices that the
steps below are added and changed in the flowchart shown in FIG.
19. Added before ST1902 is the step of performing the process to
map the information on the logical channel corresponding to each
information to be transmitted. Further, the judgment regarding the
logical channel supporting CoMP is changed to the judgment
regarding the transmission information supporting CoMP. This allows
the transmission in which discrimination is made between support
and non-support for DL CoMP in accordance with the type of
information to be transmitted.
[0162] In some cases, the transmission information supporting DL
CoMP and the transmission information that does not support DL CoMP
are simultaneously mapped on the same logical channel. The
support/non-support for DL CoMP in such a case may be predefined.
In such a case, for example, non-support for DL CoMP is provided.
This prevents a significant decrease of radio resources, which
occurs in a case of a large number of UEs being DL CoMP targets as
described above.
[0163] As another example, the transmission information supporting
DL CoMP and the transmission information that does not support DL
CoMP may be mapped on different logical channels. Even in a case of
the same type of logical channels, those may be mapped on different
logical channels. For example, the paging information and the
information indicating the system information change are mapped on
different PCCHs to be transmitted. This allows the discrimination
between support and non-support for DL CoMP for each information
type.
[0164] Alternatively, the information indicating the type of
information mapped on the logical channel may be provided so as to
recognize what type of transmission information is mapped on the
logical channel.
[0165] As to one example of the sequence diagram of this first
modification, it suffices that "DTCH, DCCH" of FIG. 20 disclosed in
the first embodiment is changed to "logical channel on which the
information supporting CoMP is mapped", and that "other logical
channel" is changed to "logical channel on which other transmission
information is mapped".
Second Modification of First Embodiment
[0166] The first modification of the first embodiment discloses
that discrimination is made between support and non-support for DL
CoMP in accordance with the type of information to be transmitted.
However, the required reception quality may be different in
accordance with the state of the UE being a transmission target
even in a case of the same type of information.
[0167] In order to achieve the above-mentioned object, a second
modification of the present embodiment discloses that
discrimination is made between support and non-support for DL CoMP
in accordance with the state of a UE.
[0168] As an example, discrimination is made between support and
non-support for DL CoMP in accordance with the state of a UE, and
the PDSCH for a UE in RRC_Connected is made to support CoMP, while
the PDSCH for a UE in RRC_Idle is made not to support DL CoMP.
[0169] For example, the information required to be dedicatedly
transmitted to one UE being served by a cell is described. The
control information of the information required to be dedicatedly
transmitted to one UE has two types, the state in which the UE
being a transmission target is in an idle state (RRC_Idle) and the
state in which the UE is in a connected state (RRC_Connected). The
control information transmitted to the UE in RRC_Idle is common
control information, which is mapped to the common control channel
(CCCH) to be transmitted. On the other hand, the control
information transmitted to the UE in RRC_Connected is dedicated UE
control information, which is mapped to the dedicated control
channel (DCCH) to be transmitted. In a case where the request
reception quality is different in accordance with the state of a UE
being a transmission target, for example, in a case where high
reception quality is required for the RRC_Connected state and lower
reception quality than the above is required for the RRC_Idle
state, as disclosed in this modification, support for DL CoMP is
provided when the state of the UE being a transmission target is
RRC_Connected and non-support for DL CoMP is provided when the
state of the UE being a transmission target is RRC_Idle. This
allows to achieve the required reception quality that varies in
accordance with the state of a UE being a transmission target.
Further, discrimination can be made between support and non-support
for DL CoMP in accordance with the state of a UE, whereby it is
possible to prevent unnecessary DL CoMP for excessively obtaining
reception quality. As a result, the usage efficiency of radio
resources can be prevented from decreasing as described above.
[0170] FIG. 24 is a conceptual diagram in a case where
discrimination is made between support and non-support for DL CoMP
in accordance with the state of a UE being a transmission target.
2401 to 2405 are similar to 1301 to 1305 of FIG. 13, and thus
description thereof is omitted. As shown in the diagram,
discrimination is made between the PDSCH on which the information
where the UE being a transmission target is transmitted in the
RRC_Connected state is mapped and the PDSCH on which the
information where the UE being a transmission target is transmitted
in the RRC_Idle state is mapped. For the UE 1 being a DL CoMP
target, the PDSCH on which the information where the UE being a
transmission target is transmitted in the RRC_Connected state is
made to support DL CoMP. The PDSCH to which the information is
mapped is transmitted from a plurality of multi-point cells (cell
1, cell 2) that perform DL CoMP to the UE 1 (2406, 2407). On the
other hand, for the UE 1 being a DL CoMP target, the PDSCH on which
the information where the UE being a transmission target is
transmitted in the RRC_Idle state is mapped is made not to support
DL CoMP. The PDSCH to which the information is mapped is
transmitted only from the serving cell (cell 1) to the UE 1
(2408).
[0171] The UE 1 combines the PDSCHs on which the information
transmitted in the RRC_Connected state is mapped, which have been
transmitted from the cell 1 and the cell 2, to thereby improve the
reception quality. On the other hand, the information transmitted
in the RRC_Idle state does not support DL CoMP, and thus the UE 1
cannot improve the reception quality. However, the usage efficiency
of radio resources does not decrease considerably as described
above. This allows to obtain the reception quality in accordance
with the state of a UE described as the above-mentioned object,
with the result that the coverage of high data rates can be
increased and the cell-edge throughput can be improved in the state
where the UE supports DL CoMP. Further, a decrease in usage
efficiency of radio resources can be avoided in the state where the
UE does not support DL CoMP, leading to an increase of the
throughput in a system.
[0172] The operation or sequence in this second modification is
obtained by changing the operation or sequence of the first
embodiment such that discrimination is made between support and
non-support for DL CoMP and judged in accordance with the state of
a UE. Detailed description is omitted here.
[0173] As another example, discrimination between support and
non-support for DL CoMP may be set in accordance with a support
system (LTE-support, LTE-A-support or the like) of a UE, in
accordance with a support version (Release-8-support,
Release-10-support or the like) of a UE, or in accordance with the
capability of a UE. This makes it possible to set the number of UEs
being DL CoMP targets finely and flexibly in accordance with the
system or version that supports a UE, or UE capability. Therefore,
it is possible to increase the throughput as a system.
Third Modification of First Embodiment
[0174] In the first embodiment and the first modification and
second modification thereof, setting for discrimination between
support and non-support for DL CoMP is performed on any cell. A
third modification of the present embodiment discloses that setting
for discrimination between support and non-support for DL CoMP is
performed for each cell.
[0175] The communication situation differs for each cell in a
system. For example, the number of UEs being served, the number of
UEs in RRC_idle or RRC_Connected, and the number of UEs that
receive MBMS differ for each cell. It is conceivable in such a case
that the usage efficiency of radio resources may decrease as a
system if setting for discrimination between support and
non-support for DL CoMP is the same for all cells.
[0176] In order to solve the above-mentioned problem, a third
modification of the present embodiment discloses that the
discrimination between support and non-support for DL CoMP is set
for each cell.
[0177] This optimizes the usage efficiency of radio resources for
each cell, whereby it is possible to improve the throughput as a
system.
[0178] For example, the case where discrimination is made between
support and non-support for DL CoMP for each logical channel, which
has been disclosed in the first embodiment, is described. What
logical channel is made to support or not to support DL CoMP is set
for each cell.
[0179] FIG. 25 is a conceptual diagram in a case where
discrimination between support and non-support for DL CoMP is set
for each cell. 2501 to 2505 are similar to 1301 to 1305 of FIG. 13,
and thus description thereof is omitted. 2512 denotes a UE (UE 2)
being a DL CoMP target. As an example, in the cell 1, the DTCH and
DCCH are made to support DL CoMP, whereas other logical channels
are made not to support it. In the cell 2, the BCCH is made to
support DL CoMP, whereas other logical channels are made not to
support it.
[0180] The cell 1 transmits a PDSCH (2508) to which the DTCH and
DCCH of the UE 1 are mapped and a PDSCH (2509) to which other
logical channels are mapped to the UE 1 being a DL CoMP target,
whose serving cell is the cell 1. In addition, the cell 1 transmits
a PDSCH (2506) to which the BCCH of the cell 2 is mapped to the UE
2 being a DL CoMP target, whose serving cell is the cell 2.
Meanwhile, the cell 2 transmits a PDSCH (2507) to which the DTCH
and DCCH transmitted by the cell 1 are mapped to the UE 1 for
performing DL CoMP. In addition, the cell 2 transmits, to the UE 2,
a PDSCH (2511) to which the BCCH of the cell 2 is mapped and a
PDSCH (2510) to which other logical channels are mapped. The UE 1
whose serving cell is the cell 1 receives the PDSCHs to which the
DTCH and DCCH are mapped from the cell 1 and the cell 2, and
accordingly is capable of improving the reception quality of the
channels. Meanwhile, the UE 2 whose serving cell is the cell 2
receives the PDSCHs to which the BCCH is mapped from the cell 1 and
the cell 2, and accordingly is capable of improving the reception
quality of the channels.
[0181] As described above, the BCCH on which the broadcast
information is mapped only for one or several cells (in this case,
cell 2) is made to support DL CoMP, whereas the BCCH on which the
broadcast information is mapped for the other cell (in this case,
cell 1) is made not to support DL CoMP. This enables to prevent the
usage efficiency of physical resources from decreasing considerably
and the throughput as a system from decreasing which occur in a
case where the PDSCH on which the broadcast information is mapped
is subjected to DL CoMP for all cells as described above.
[0182] Further, in a case of, for example, poor reception quality
of the broadcast information at the cell edge or poor throughput in
a cell (in this case, cell 2) for some reason, a desired logical
channel is made to support DL CoMP only for the cell. Accordingly,
it is possible to improve the cell-edge reception quality or the
throughput in the cell without significantly affecting the
throughput of the entire system.
[0183] Although the case of a logical channel is described here,
not only limited to the logical channel, which can be, for example,
the type of information, the situation of a UE or the combination
thereof as long as discrimination between support and non-support
for DL CoMP can be set for each cell.
[0184] This allows flexible discrimination between support and
non-support for DL CoMP in accordance with a situation of each cell
in a system, which improves the throughput as an entire system and
improves the reception quality and the throughput of an individual
cell.
[0185] As another example, discrimination between support and
non-support for DL CoMP may be set for each cell in accordance with
the system bandwidth of a cell. Physical resource increases as the
system bandwidth is larger. The physical resource is small when the
bandwidth is narrow. Therefore, for example, setting is made such
that all PDSCHs are made to support DL CoMP in the cell having a
wide system bandwidth, and that only the PDSCH to which a logical
channel having a small number of UEs being DL CoMP targets or
information is mapped is made to support DL CoMP and other PDSCHs
are made not to support DL CoMP in the cell having a narrow system
bandwidth.
[0186] As a result, the physical resources required for DL CoMP can
be set in accordance with the physical resources of a cell, which
improves the throughput as a system without considerably decreasing
the usage efficiency of physical resources.
[0187] As to LTE-A, the technique for supporting a wider bandwidth
(wider bandwidth extension) is studied as a new technique. In order
to support a wider bandwidth, there is proposed the method of
aggregating bandwidths separated by a plurality of frequency axes.
Each individual separated bandwidth is referred to as a component
carrier. While it has been described that discrimination between
support and non-support for DL CoMP may be set for each cell in
accordance with the system bandwidth of a cell, as another example,
discrimination between support and non-support for DL CoMP may be
set for each component carrier. This achieves similar effects, and
besides, allows setting for discrimination between support and
non-support for DL CoMP in accordance with radio wave propagation
environment that varies depending on a frequency. Accordingly, it
is possible to use radio resources more efficiently in wider
bandwidth extension, leading to an improvement of the throughput of
a cell in which component carriers are aggregated.
[0188] As another example, discrimination between support and
non-support for DL CoMP may be set for each cell in accordance with
a cell-support system (LTE-support, LTE-A-support or the like) or
in accordance with a cell-support version (Release-8-support,
Release-10-support or the like). This enables to finely and
flexibly set the number of UEs being DL CoMP targets in accordance
with a support system or version. Therefore, it is possible to
increase the throughput as a system.
Fourth Modification of First Embodiment
[0189] In the first embodiment and the first modification to third
modification thereof, setting for discrimination between support
and non-support for DL CoMP is predefined. A fourth modification of
the present embodiment discloses that setting for discrimination
between support and non-support for DL CoMP is performed in a
semi-static manner.
[0190] The communication situation in a system varies not only for
each cell but also depending on time. For example, the number of
UEs being served, the number of UEs in RRC_idle or RRC_Connected,
and the number of UEs that receive the MBMS vary depending on time.
It is conceivable in such a case that the usage efficiency of radio
resources may decrease as a system if setting for discrimination
between support and non-support for DL CoMP is always the same
(static).
[0191] In order to solve the above-mentioned problem, this fourth
modification discloses that discrimination between support and
non-support for DL CoMP is performed in a semi-static manner.
[0192] This optimizes the usage efficiency of radio resources in
accordance with time, whereby it is possible to improve the
throughput as a system.
[0193] FIG. 26 shows an example of the setting procedure in a case
where setting for discrimination between support and non-support
for DL CoMP is performed in a semi-static manner. FIG. 26(a) shows
the case where determination is made by a cell, while FIG. 26(b)
shows the case where determination is made by a core network (MME).
FIG. 26(a) is described. In ST2601, as initialization, the cell
performs initialization of the discrimination between support and
non-support for DL CoMP in installation or resetting. The
initialization may be predetermined. In ST2602, the cell measures
the situation of own cell, for example, load situation. Examples of
the load situation include the number of UEs being served and/or
the number of UEs in RRC_idle or RRC_Connected and/or the number of
UEs that receive the MBMS. In ST2603, the cell derives setting for
the discrimination between support and non-support for DL CoMP with
the use of measurement results of the load situation of own cell.
Examples of the setting for discrimination between support and
non-support for DL CoMP include setting for discrimination for each
type of logical channel and setting for discrimination for each
information type, which have been disclosed in the first embodiment
and the first modification to third modification thereof. The use
of measurement results of the load situation of own cell allows
optimum setting at that point. In ST2604, the cell judges whether
to change the current setting to the setting for discrimination
between support and non-support for DL CoMP that has been derived.
In a case where no change is made, the cell does not change the
current setting and proceeds to ST2602 to measure the load
situation of own cell again. In a case where the cell judges to
make a change in ST2604, in ST2605, the cell changes the current
setting to the derived setting for discrimination between support
and non-support for DL CoMP. After changing, the cell proceeds to
ST2602 to measure the load situation of own cell again.
[0194] The measurement of a load situation in ST2602 may be
periodically performed or may be performed at an appropriate
timing. Alternatively, a threshold may be provided to the
measurement results of a load situation such that measurement is
performed in a case where the threshold is exceeded in a shift from
ST2602 to ST2603. Still alternatively, similarly, a threshold as to
whether or not change setting may be provided to the measurement
results of a load situation such that measurement is performed in a
case where the threshold is exceeded in the judgment of ST2604.
[0195] This allows to change the setting for discrimination between
support and non-support for DL CoMP in accordance with the
ever-changing load situation of a cell, which optimizes the usage
efficiency of radio resources in accordance with time. Accordingly,
it is possible to improve the throughput as a system.
[0196] Next, description is given of the case where core network
(MME) of FIG. 26(b) makes a determination.
[0197] In ST2606, the core network (MME) initializes the
discrimination between support and non-support for DL CoMP in cell
installation or resetting. The initialization may be predetermined.
In ST2607, the MME notifies the cell of the initialization. The
cell receives the initialization in ST2608 and sets the initial
value as initialization for discrimination between support and
non-support for DL CoMP for own cell in ST2609.
[0198] In ST2611, the cell measures the load situation of own cell.
The load situation may be measured periodically or at an
appropriate timing. Alternatively, the MME may transmit a request
for load situation measurement to the cell.
[0199] In ST2613, the cell that has measured the load situation of
own cell transmits the measurement results to the MME. In ST2612,
the MME that has received the measurement results from each cell in
ST2610 derives setting for discrimination between support and
non-support for DL CoMP for each cell. In ST2614, the MME judges
whether to change the current setting to the derived setting for
discrimination between support and non-support for DL COMP. In a
case where no change is made, the MME does not change the current
setting and proceeds to ST2610 to receive the load situation of
each cell again. In a case where it is determined that a change is
made in ST2614, in ST2616, the MME changes the current setting to
the derived setting for discrimination between support and
non-support for DL CoMP for each cell. After changing, in ST2618,
the MME transmits the setting for discrimination between support
and non-support for DL CoMP to each corresponding cell. In ST2617,
each cell that has received the setting in ST2615 changes the
setting for discrimination between support and non-support for DL
CoMP of own cell.
[0200] After that, the MME returns to the reception of a load
situation from each cell again, and each cell returns to
measurement of the load situation of own cell.
[0201] A threshold may be provided to the measurement results of a
load situation to serve as a threshold as to whether or not each
cell transmits the load situation to the MME in ST2613.
Alternatively, judgment may be performed in a case where the
threshold is exceeded in a shift from ST2610 to ST2612 in the MME.
Still alternatively, a threshold as to whether or not setting is
changed may be provided to the measurement results of a load
situation such that the judgment in ST2614 is performed in a case
where the threshold is exceeded.
[0202] The MME may perform the same setting for all cells
controlled by the MME without performing setting for each cell. By
doing this, it becomes possible not to have to perform different
controls from cell to cell, whereby an effect that DL CoMP control
is made simpler as a system can be achieved.
[0203] This allows to change the setting for discrimination between
support and non-support for DL CoMP in accordance with the
ever-changing load situation of a cell, which optimizes the usage
efficiency of radio resources in accordance with time. Accordingly,
it is possible to improve the throughput as a system.
[0204] Further, the MME can change the setting of each cell, which
allows optimum setting as a system. Accordingly, an effect that the
throughput as a system can be further improved is achieved.
[0205] The first embodiment and the first modification to fourth
modification thereof have described that the throughput as a system
can be increased by setting the discrimination between support and
non-support for DL CoMP depending on various cases.
[0206] However, even in a case where discrimination is made as
non-support for DL CoMP, there occurs a case where an increase of
the cell coverage, an improvement of the cell-edge reception
quality and an improvement of the throughput are desired
temporarily. It suffices that in such a case, the setting for
discrimination between support and non-support for DL CoMP, which
has been disclosed in the fourth modification of the first
embodiment, is performed in a semi-static manner. As another
method, the method below is disclosed. The information that
temporarily requires DL CoMP of the information set as not to
support DL CoMP is mapped on the logical channel supporting DL CoMP
and transmitted. As a result, DL CoMP is performed on the PDSCH to
which the logical channel is mapped, and thus the information is
subjected to DL CoMP in the UE being a DL CoMP target, which makes
it possible to improve the reception quality of the information.
This temporarily increases the cell coverage of the information,
improves the cell-edge reception quality and improves a throughput
even in the case of the information set not to support DL CoMP.
Differently from the case where the setting for discrimination
between support and non-support for DL CoMP is performed in a
semi-static manner, there is no need to change the setting of an
entire cell, which allows only the required information to
temporarily support DL CoMP. This improves the throughput as a
system more flexibly in accordance with a cell situation or system
situation.
[0207] In a case where, for example, the PCCH is made not to
support DL CoMP and the DCCH is made to support DL CoMP, the
information related to ETWS notification mapped on a paging message
is mapped to the DCCH, mapped to the PDSCH and is transmitted so as
to temporality support DL CoMP in the event of ETWS. This allows
the UE located at the cell edge to perform DL CoMP of the
information related to ETWS notification mapped on the DCCH, which
increases the cell coverage, improves the cell-edge reception
quality and improves a throughput for the information related to
ETWS notification. The information related to ETWS notification is
important information for cellular phone users, which is a matter
of life, if not being received. Therefore, it is effective to make
to support DL CoMP using the method disclosed here.
[0208] Besides, in a case where, for example, the PCCH is made not
to support DL CoMP and the DCCH is made to support DL CoMP, the
information indicating the system information change mapped on the
paging message is mapped on the DCCH, mapped to the PDSCH and then
transmitted so as to temporarily support DL CoMP in system
information change. This allows the UE located at the cell edge to
perform DL CoMP of the information indicating the system
information change mapped on the DCCH, which increases the cell
coverage, improves the cell-edge reception quality and improves a
throughput for the information indicating the system information
change. The information indicating the system information change is
important information for cellular phone users who cannot
communicate with the cell, if not being received. Therefore, it is
effective to support DL CoMP using the method disclosed here.
[0209] The matters disclosed in the first embodiment and the first
modification to fourth modification thereof are not required to be
used individually but may be used in combination. Setting can be
made by better combination as a system, and system design can be
made flexible for a communication load, whereby it is possible to
improve the throughput as a system.
[0210] While the first embodiment and the first modification to
fourth modification thereof have described the case of DL CoMP,
which are not limited to DL CoMP and may be applied to the case of
UL CoMP. Discrimination between support and non-support for UL CoMP
may be made in accordance with a logical channel, discrimination
between support and non-support for UL CoMP may be made in
accordance with an information type, discrimination between support
and non-support for UL CoMP may be made in accordance with a UE
state, setting for discrimination between support and non-support
for UL CoMP may be made for each cell, or setting for
discrimination between support and non-support for UL CoMP may be
made in a semi-static manner.
[0211] This allows to improve the usage efficiency of radio
resources as a system also in the UL as in the case of DL, which
increases the throughput as a system.
Second Embodiment
[0212] As a new technique for LTE-A, UL CoMP is studied. As
described above, in UL CoMP, uplink data from one user equipment
(UE) is received at multiple points in a coordinated manner. The
pieces of data received at the multiple points are combined, to
thereby improve the uplink reception quality from a UE. FIG. 27 is
a conceptual diagram of UL CoMP. A multi-point unit 1 (unit 1) 2701
and a multi-point unit 2 (unit 2) are units that perform UL CoMP,
that is, uplink coordinated multiple point reception. 2704 denotes
a cell formed by the unit 1, and 2705 denotes a cell formed by the
unit 2. 2703 denotes a user equipment (UE 1) being a UL CoMP
target. In UL CoMP, a plurality of multi-point cells receive the
PUSCH transmitted from one UE. That is, the UE 1 transmits the same
PUSCH to the cell 1 and the cell 2 (2708, 2709). The cell 1 and the
cell 2 are capable of improving the reception quality of the uplink
data from the UE by combination of the PUSCHs transmitted from the
UE 1. Accordingly, it is possible to increase the coverage of high
data rates, improve the cell-edge throughput and increase the
system throughput, which are aimed in UL CoMP.
[0213] The allocation information to the physical resources
(resource blocks) of the PUSCH, for example, the allocation
information in a frequency-time domain is transmitted to the UE on
the PDCCH that is a downlink physical channel. In general, cells
each have MAC having a scheduling function individually. Therefore,
different scheduling is performed in each cell, and the physical
resource allocation information of the PUSCH that varies for each
cell is transmitted on the PDCCH from each cell. However, in order
to perform UL CoMP, it is required to keep the reception timing of
the uplink PUSCH from the UE within a certain range in the
respective cells that perform UL CoMP. This is because the PUSCHs
from the UE, which have been received by the respective cells, have
to be combined between cells. Combination is performed after the
reception of the respective cells, and thus in a case where there
is a large difference between reception timings, a large delay is
generated between transmission and reception.
[0214] Therefore, respective cells that perform UL CoMP perform
scheduling allocation to UEs being UL CoMP targets through
adjustment therebetween such that the physical resource of the
PUSCH is kept in a certain time range. The UE, which has received
the information on physical resource allocation of the PUSCH
adjusted between the respective cells on PDCCHs (in FIGS. 27, 2707
and 2706) from the respective cells, maps the same PUSCH to those
physical resources and transmits the PUSCH. This enables UL
CoMP.
[0215] An example of a sequence diagram when UL CoMP is performed
is shown in ST2801 to ST2810 of FIG. 28. The cell 1 and the cell 2
adjust the timing of physical resource scheduling of the PUSCH to
the UE (UE 1) being a UL CoMP target by the above-mentioned method,
and each thereof transmits the PUSCH allocation information on the
PDCCH (ST2801, ST2802). In ST2803, the UE 1 allocates the PUSCH to
the physical resource in accordance with the allocation information
of the PUSCH that has been received from the cell 1 and transmits
the PUSCH in ST2804. Similarly, in ST2805, the UE 1 allocates the
same PUSCH as the PUSCH transmitted to the cell 1 to the physical
resource in accordance with the allocation information of the PUSCH
that has been received from the cell 2, and transmits the PUSCH in
ST2806. In ST2807 and ST2808, the cell 1 and cell 2 each receive
the PUSCH from the UE 1. In ST2809, the cell 2 transmits the
information received from the UE 1 to the cell 1. In ST2810, the
cell 1 combines the received information of the cell 1 and the
received information of the cell 2, which have been transmitted
from the UE 1. This improves the reception quality from the UE
1.
[0216] In the case of the above-mentioned method, however, the
timing of the physical resource for allocation of the PUSCH needs
to be adjusted in advance between the cell 1 and the cell 2 and be
scheduled, and the allocation information of the PUSCH has to be
transmitted to the UE 1 from each cell on the PDCCH. The UE 1 needs
to allocate, for each cell, the same PUSCH to the physical resource
in accordance with the allocation information of the PUSCH from
each cell. This means that the same PUSCH is allocated to the
physical resource in an overlapping manner, leading to a decrease
in usage efficiency of uplink radio resources. This increases the
transmission power of a UE as well, leading to an increase in power
consumption.
[0217] In order to solve the above-mentioned problem, the present
embodiment discloses that each cell that performs UL CoMP transmits
the same physical resource allocation information of the PUSCH to
the UE being a UL CoMP target. This allows the UE being a UL CoMP
target to receive the same PUSCH physical resource allocation
information transmitted on the PDCCH from each cell. The UE maps
the same uplink transmission data on the PUSCH to be transmitted to
each cell, allocates the PUSCH to the physical resource in
accordance with the received PUSCH physical resource allocation
information, and transmits the PUSCH to each cell. The conceptual
diagram in this case is the same as FIG. 27. While the sequence
diagram corresponds to ST2801 to ST2810 of FIG. 28, the PUSCH
allocation information transmitted from each cell in ST2801 and
ST2802 of FIG. 28 is the same between cells, and accordingly the UE
allocates the PUSCH for each cell to the same physical resource in
ST2803 and ST2805. As a result, in ST2804 and ST2806, the UE
transmits the PUSCH for each cell with the same physical
resource.
[0218] In this case, the physical resource allocation information
of the PUSCH needs to be shared in advance between cells that
perform UL CoMP. For this reason, it suffices that the physical
resource allocation information of the PUSCH is mutually notified
between the cells in ST2801 or before performing ST2801. The
physical resource of the PUSCH may be allocated by the serving cell
such that the serving cell notifies other cell that performs UL
CoMP of the allocation. Those notifications may be performed by
means of the interface (X2) between the cells, the interface (S1)
between the MME and cell, or the interface between the MMES as
described in the first embodiment.
[0219] As a result, the UE transmits the PUSCH with the same
physical resource to each cell that performs UL CoMP, which means
that only one uplink physical resource is required to be used for
one PUSCH. Therefore, it is possible to avoid a decrease in usage
efficiency of radio resources. Further, transmission is not
performed simultaneously with a plurality of physical resources,
leading to effects that the transmission power of a UE is prevented
from increasing and the power consumption is prevented from
increasing.
[0220] Further, it suffices that the PUSCH allocation information
is received from any one of cells without receiving the PUSCH
allocation information on the PDCCHs of all cells that perform UL
CoMP. On the contrary, the reception from a plurality of cells
achieves an effect that the reception quality of the information
can be improved.
[0221] In the case of the above-mentioned method, however, the
timing of the physical resource for allocating the PUSCH needs to
be adjusted in advance between the cell 1 and the cell 2 and be
scheduled, and the allocation information of the PUSCH has to be
transmitted to the UE 1 from each cell on the PDCCH. This means
that the PDCCH has to be transmitted to the UE being a UL CoMP
target from two cells, leading to an increase in signaling
capacity. Further, the UE needs to receive the PDCCH from two
cells, leading to an increase in size of a receiver circuit of a UE
and an increase in power consumption.
[0222] Disclosed here is that scheduling allocation of the PUSCH is
performed from one cell in UL CoMP for solving the above-mentioned
problems in addition to the problems of a decrease in usage
efficiency of uplink radio resources and an increase in power
consumption of a UE. The UE being a UL CoMP target complies with
the allocation information of the PUSCH from the one cell. The
serving cell of a UE being a UL CoMP target may be used as this one
cell. This does not require the UE to recognize whether or not own
UE is a UL CoMP target but requires to receive the PDCCH of only
the serving cell. This makes control for UL CoMP in the UE simpler
and also prevents an increase in size of the control circuit of the
UE. Moreover, it is possible to prevent an increase in power
consumption for UL CoMP.
[0223] FIG. 29 is a conceptual diagram of the method of
transmitting the PUSCH allocation information from one cell in UL
CoMP. 2901 to 2905 are similar to 2701 to 2705 of FIG. 27, and thus
description thereof is omitted. 2906 denotes the PDCCH on which the
PUSCH allocation information is mapped, which is transmitted from a
cell 1 to a UE 1. 2907 denotes the PUSCH allocated to a physical
resource in accordance with the PUSCH allocation information, which
is transmitted from the UE 1. On this occasion, the UE 1 does not
particularly need to transmit the PUSCH to a cell 2, and it
suffices that the cell 2 receives the PUSCH transmitted from the UE
1 (2908). The cell 1 and the cell 2 combine the PUSCHs transmitted
from the UE 1, and accordingly are capable of improving the
reception quality of the uplink data from the UE. It is possible to
increase the coverage of high data rates, improve the cell-edge
throughput and increase the system throughput, which are aimed in
UL CoMP.
[0224] ST3001 to ST3010 of FIG. 30 show an example of the sequence
diagram of the method of transmitting the PUSCH allocation
information from one cell in UL CoMP. The serving cell of the UE
(UE 1) being a UL CoMP target is the cell 1, and the cell that
performs UL CoMP is the cell 2. The cell 1 performs scheduling of
the physical resource of the PUSCH to the UE 1 and transmits the
PUSCH allocation information to the cell 2 (ST3001). In ST3002, the
cell 1 transmits the PUSCH allocation information to the UE 1 on
the PDCCH. In ST3003, the UE 1 receives the PDCCH from the cell 1
and performs allocation to a physical resource by the PUSCH
allocation information received from the cell 1 in ST3004. Then, in
ST3005, the UE 1 transmits the PUSCH. On this occasion, the UE 1
transmits the PUSCH to the cell 1, where the cell 1 and the cell 2
both receive the PUSCH transmitted from the UE 1 (ST3006). In
ST3007, the cell 1 receives the PUSCH from the UE 1. In ST3008, the
cell 2 receives the PUSCH from the UE 1 as well. On this occasion,
it suffices that the cell 2 receives the PUSCH from the UE 1 based
on the PUSCH allocation information for the UE 1, which has been
received from the cell 1 in ST3001. In ST3009, the cell 2 transmits
the information received from the UE 1 to the cell 1. In ST3010,
the cell 1 combines the information of the cell 1 and the
information of the cell 2, which have been received from the UE 1.
This allows to improve the reception quality from the UE 1.
[0225] The use of the method disclosed in the present embodiment
does not require the transmission of the PDCCH from two cells to a
UE being a UL CoMP target, which prevents an increase of signaling
capacity. In addition, the UE 1 is not required to allocate the
same PUSCH to physical resources of two cells in an overlapping
manner, which prevents a decrease in usage efficiency of uplink
radio resources. Further, this prevents an increase in transmission
power of a UE and an increase in power consumption. Further, it is
possible to increase the coverage of high data rates, improve the
cell-edge throughput and increase the system throughput, which are
aimed in UL CoMP.
[0226] While the description has been given of a fact that the UE
does not need to receive the allocation information of physical
resources of the PUSCH from all cells that perform CoMP, not
limited thereto, and it is not required to receive scrambling codes
of other cells of the serving cell and identifiers (UE-ID, C-RNTI)
of a UE in a cell. There is achieved an effect that control in UL
CoMP can be made much simpler.
[0227] While the description has been given of a fact that the cell
(in this case, serving cell, cell 1) that performs PUSCH allocation
transmits the PUSCH allocation information to the other cell (in
this case, cell 2) that performs CoMP in ST3001, the cell may
notify the information required for decoding of the PUSCH from the
UE. Examples of such information include UE identifiers (UE-ID,
C-RNTI) used by the cell 1 and/or a scrambling code for each UE
that is used by the cell 1. The above-mentioned information may be
notified by means of the interface (X2) between the cells or the
interface (S1) between the cell and the core network (MME).
Alternatively, notification may be made via the MME. This allows
the cell 2 to receive and decode the PUSCH from the UE 1.
Therefore, the transmission of the decoded information to the cell
1 enables the cell 1 to perform combining by the decoded
information.
[0228] It has been disclosed that the cell 1 transmits UE
identifiers (UE-ID, C-RNTI) used by the cell 1 and/or a scrambling
code for each UE used by the cell 1 to the cell 2. Alternatively,
as another method, UE identifiers (UE-ID, C-RNTI) used by a UE
being a UL CoMP target and/or a scrambling code for each UE may be
predetermined. Besides, the deriving method for the information may
be predetermined, and the deriving method may be shared by a cell
and a UE, so that the same results are individually derived by the
cell and UE. Examples of input parameters used in derivation
include a UE identifier (IMSI). As a result, the cell that performs
PUSCH allocation does not need to notify the other cell that
performs CoMP of the information necessary for decoding the PUSCH.
Accordingly, it is possible to reduce a signaling amount generated
between the cells (X2) or between the cell and the core network
(MME) (S1).
[0229] In the example above, the PDCCH from the other cell that
performs UL CoMP to the UE being a UL CoMP target has not been
described, and transmission is not necessarily required. The PDCCH
may not be transmitted from the other cell that performs UL CoMP to
the UE being a UL CoMP target. This eliminates the need for
allocating the UE identifiers (UE-TD, C-RNTT) to the UE by the
other cell. The UE identifiers can be used for the other cell,
which prevents the identifiers from being wasted. Further, the
PDCCH is not transmitted to the UE, whereby it is possible to
prevent a PDCCH physical resource from being wasted.
[0230] The other cell (cell 2) that performs UL CoMP may not
allocate, to the other cell whose serving cell is the cell 2, the
uplink physical resource to the UE being a UL CoMP target that has
been notified from the cell 1. As a result, transmission is not
performed from the other UE at the same frequency in the same time
domain as those of the PUSCH from the UE 1 being a UL CoMP target,
which eliminates the interference with the PUSCH by the UE 1 and
improves the reception quality in the cell 2. This further improves
the reception quality after combining, whereby it is possible to
increase the coverage of higher data rates, improve the cell-edge
throughput, and increase the system throughput.
[0231] In contrast, the other cell (cell 2) that performs UL CoMP
may permit the allocation of the uplink physical resource to the UE
being a UL CoMP target that has been notified from the cell 1 to
another UE whose serving cell is the cell 2. The PDSCH of the UE is
caused to be multiplied by the scrambling code for each UE, whereby
the cell is capable of detecting from which UE the PDSCH has been
transmitted. This achieves an improvement in usage efficiency of
physical resources of the PUSCH, for example, the same physical
resource as that of the PUSCH of the UE 1 is allocated to the UE
located at the center of the cell being served by the cell 2.
Third Embodiment
[0232] In general, the respective cells have MAC having a
scheduling function individually. In MAC, HARQ is performed on a
UE. In a case where UL CoMP is performed between such cells, one
MAC is composed for each cell, and HARQ is performed for each cell
by the MAC. The uplink (UL, uplink) HARQ is performed by the
following method using the PDCCH and PHICH (Non-Patent Document 1).
Ack/Nack is transmitted on the PHICH. In a case where there is the
PDCCH for the UE, the UE complies with a first transmission request
or a retransmission request of the PDCCH irrespective of the
contents of the PHICH. In this case, allocation of the physical
resources complies with the PDCCH. In a case where there is no
PDCCH for the UE, the UE complies with Ack/Nack transmitted on the
PHICH. In the case of Nack, the UE performs retransmission by the
same physical resource allocation as that of the former
transmission. In the case of Ack, the UE does not perform any
uplink transmission but complies with the PDCCH to be transmitted
later. By the above-mentioned method, the uplink HARQ is performed
on the PDCCH and PHICH for each cell (multi-point cell) that
performs UL CoMP.
[0233] ST2811 to ST2822 of FIG. 28 show an example of the sequence
diagram of the uplink HARQ in a case where UL CoMP is performed.
This is the case where the physical resource allocation of the
PUSCH that has been adjusted between cells is transmitted to the UE
being a UL CoMP target on the PDCCH from the respective cells and
the UE that has received the PDCCH from the respective cells maps
the same PUSCH to the physical resources of the respective cells
and transmits the PUSCH.
[0234] In ST2807, the cell 1 receives the PUSCH from the UE 1, and
performs the uplink HARQ based on the results thereof in ST2811, to
thereby judge as retransmission or first transmission to the UE 1
and/or Ack or Nack. In ST2813, the cell 1 transmits the PDCCH
and/or PHICH to the UE 1 based on the judgment results. While, the
cell 2 also receives the PUSCH from the UE 1 in ST2808, and
performs the uplink HARQ in ST2812 based on the results thereof, to
thereby judge as retransmission or first transmission to the UE 1
and/or Ack or Nack. In ST2814, the cell 2 transmits the PDCCH
and/or PHICH to the UE 1 based on the judgment results.
[0235] The UE 1 determines to perform retransmission or first
transmission, or transmit nothing based on the PDCCH and/or PHICH
received from the cell 1. In the case of retransmission or first
transmission, the UE 1 allocates the PUSCH for the cell 1 to the
physical resource in accordance with the contents transmitted on
the PDCCH and/or PHICH (ST2815). In ST2816, the UE 1 transmits the
PUSCH to the cell 1. Further, the UE 1 determines whether to
perform retransmission or first transmission, or transmit nothing
based on the PDCCH and/or PHICH received from the cell 2. In the
case of retransmission or first transmission, the UE 1 allocates
the PUSCH for the cell 2 to the physical resource in accordance
with the contents transmitted on the PDCCH and/or PHICH (ST2817).
In ST2818, the UE 1 transmits the PUSCH to the cell 2.
[0236] In ST2820, the cell 1 receives the PUSCH from the UE 1. In
ST2819, the cell 2 receives the PUSCH from the UE 1. In ST2821, the
cell 2 transmits the information received from the UE 1 to the cell
1. In ST2822, the cell 1 combines the information received from the
UE 1 by own cell and the information received from the UE 1 that
has been transmitted from the cell 2.
[0237] Even when the UE 1 transmits the same PUSCH to the cell 1
and the cell 2, however, the reception results differ between the
cell 1 and the cell 2 in some cases. This is because the radio wave
propagation environment differs for each cell. Accordingly, in some
cases, the results of judgment as retransmission or first
transmission to the UE 1 by the uplink HARQ and/or judgment as Ack
or Nack vary between cells. For example, judgment is made as first
transmission in the cell 1, whereas judgment is made as
retransmission in the cell 2. In this case, the UE 1 transmits the
PUSCH on which the first data is mapped to the cell 1 in ST2816,
and transmits the PUSCH on which the retransmission data is mapped
to the cell 2 in ST2818. That is, the state in which the uplink
HARQ is individually performed on each cell occurs, leading to a
state in which the UE 1 transmits different PDSCHs to the
respective cells. In such a case, even when the cell 1 combines the
information received from the UE 1 by own cell and the information
received from the UE 1 that has been transmitted from the cell 2,
it is useless. It is impossible to perform UL CoMP. As a result,
the coverage of high data rates cannot be increased, the cell-edge
throughput cannot be improved, and the system throughput cannot be
increased by UL CoMP.
[0238] In order to solve the above-mentioned problem, there is a
method in which the uplink HARQ is not performed on the UE being a
UL CoMP target in a case where UL CoMP is performed. The use of
this method solves a problem that UL CoMP cannot be performed,
which results from the application of uplink HARQ. However, the
uplink HARQ is not performed, whereby the uplink throughput
decreases. Therefore, the above is canceled by the effect of
improving an uplink throughput obtained in the case where UL CoMP
is performed, and thus the throughput cannot be improved
considerably as a system.
[0239] In the present embodiment, further, the uplink HARQ is
performed on a target UE in a case where UL CoMP is performed for
solving the above-mentioned problem.
[0240] Any one of cells that perform UL CoMP transmits the results
of the judgment as retransmission or first transmission to the UE
by the uplink HARQ and/or the judgment as Ack or Nack. The UE
receives the judgment results from any one of those cells and
complies with the judgment results.
[0241] This allows to perform the uplink HARQ on the UE being a UL
CoMP target. Therefore, owing to an improvement in uplink
throughput by the uplink HARQ and an improvement in uplink
throughput by UL CoMP, it is possible to increase the coverage of
higher data rates, improve the cell-edge throughput, and increase
the system throughput. Any one of the cells that transmit the
judgment results to a UE being a UL CoMP may be taken as a serving
cell. The UE receives the PDCCH from the serving cell for PUSCH
transmission. The physical resource allocation of the PHICH from
the serving cell is determined by a physical resource (resource
block) of the PUSCH to be allocated. The judgment results are
transmitted from the serving cell, with the result that the UE does
not need to receive PDCCH and/or PHICH from another cell other than
the serving cell for UL CoMP. This makes control of UL CoMP in the
cell and the UE simpler, which achieves a reduction in circuit size
and a reduction in power consumption of the cell and the UE.
[0242] The uplink HARQ for a UE being a UL CoMP target may be
performed by any one of cells. The uplink HARQ is performed by any
one of cells, and accordingly another cell does not need to perform
uplink HARQ for the UE, which eliminates wasteful processing in
another cell. The serving cell may be the above-mentioned any one
of cells. This allows the serving cell to perform scheduling of the
physical resource of the PUSCH in the first transmission up to
HARQ. In addition, when the serving cell is configured to transmit
the judgment results, the serving cell can consistently perform
scheduling of the physical resource of the PUSCH in the first
transmission up to HARQ, and further transmission of judgment
results by HARQ, which makes control of uplink HARQ in UL CoMP
simpler. It is only required for the UE to receive only the
scheduling information from the serving cell and comply with the
received results, whereby the uplink HARQ can be controlled easily
in a simple manner in UL CoMP. Further, it is possible to unify the
method of controlling the uplink HARQ regardless of whether or not
UL CoMP is performed, with the result that the size of a control
circuit can be reduced and control malfunctions can be reduced in
the cell and the UE.
[0243] FIG. 31 is a conceptual diagram in a case where the judgment
results of uplink HARQ are transmitted from one cell in UL CoMP.
3101 to 3105 are similar to 2701 to 2705 FIG. 27, and thus
description thereof is omitted. The cell 1 is a serving cell of the
UE 1. 3106 denotes the PDCCH transmitted from the cell 1 to the UE
1, on which the PUSCH allocation information, or the information
indicating whether retransmission or first transmission based on
the judgment results of uplink HARQ and the physical resource
allocation information of the PDSCH on which the retransmission or
first transmission is mapped are mapped. 3107 denotes the PUSCH
allocated to the physical resource in accordance with the PUSCH
allocation information, which is transmitted from the UE 1. In this
case, the UE 1 does not particularly need to transmit the PUSCH to
the cell 2, and it suffices that the cell 2 receives the PUSCH
transmitted from the UE 1 (3109). 3108 denotes the PHICH
transmitted from the cell 1 to the UE 1, on which Ack or Nack
information based on the judgment results of uplink HARQ is mapped.
The cell 1 and the cell 2 combine the PUSCHs transmitted from the
UE 1, and are accordingly capable of improving the reception
quality of the uplink data from the UE. This makes it possible to
increase the coverage of high data rates, improve the cell-edge
throughput and increase the system throughput, which are aimed in
UL CoMP, while improving a throughput due to the uplink HARQ.
[0244] The sequence diagram in a case where judgment results of
uplink HARQ are transmitted from one cell in UL CoMP is shown in
ST3011 to ST3020 of FIG. 30. The diagram shows, as an example, the
case where the serving cell (cell 1) performs the uplink HARQ and
the serving cell transmits the results of the HARQ to the UE (UE 1)
being a UL CoMP target. The serving cell of the UE (UE 1) being a
UL CoMP target is a cell 1, while the cell that performs UL CoMP is
a cell 2.
[0245] In ST3010, the cell 1 combines the information received from
the UE 1 by own cell and the information received from the UE 1
that has been transmitted from the cell 2. In ST3011, the cell 1
performs the uplink HARQ based on the combined received
information, to thereby make a judgment as retransmission or first
transmission to the UE 1 and/or Ack or Nack. In ST3012, the cell 1
transmits, to the cell 2, the next PUSCH allocation information for
the UE 1 and, in ST3013, transmits the PDCCH and/or PHICH to the UE
1.
[0246] The UE 1 determines whether to perform retransmission or
first transmission, or transmit nothing in accordance with the
contents of the PDCCH and/or the PHICH received from the cell 1. In
the case of retransmission or first transmission, the UE 1
allocates the PUSCH for the cell 1 to the physical resource in
accordance with the contents transmitted on the PDCCH and/or PHICH
(ST3014). In ST3015, the UE 1 transmits the PUSCH to the cell 1. In
this case, the UE 1 transmits the PUSCH to the cell 1, and besides,
the cell 1 and the cell 2 receive the PUSCH transmitted from the UE
1 (ST3016). In ST3017, the cell 1 receives the PUSCH from the UE 1.
In ST3018, the cell 2 receives the PUSCH from the UE 1 as well. In
this case, it suffices that the cell 2 receives the PUSCH from the
UE 1 based on the PUSCH allocation information for the UE 1 that
has been received from the cell 1 in ST3012. In ST3019, the cell 2
transmits the information received from the UE 1 to the cell 1. In
ST3020, the cell 1 combines the information of the cell 1 and the
information of the cell 2 that have been received from the UE
1.
[0247] This enables to improve the reception quality from the UE 1.
After that, the HARQ is performed again in the cell 1. In ST3012,
the cell 1 transmits the next PUSCH allocation information for the
UE 1 to the cell 2 based on the judgment results. In a case where
the judgment results indicate that the PDCCH is not transmitted,
however, it suffices that the cell 1 transmits the information
indicating the above, for example, the information indicating Ack
or Nack to the UE 1. In the case of Nack, the PDSCH on which
retransmission is mapped is allocated to the same physical resource
as that allocated last time. Accordingly, when the cell 2 holds the
physical resource allocated the last time, the cell 2 can receive
retransmission from the UE 1 in ST3018 even if the cell 1 transmits
only the information indicating Nack to the cell 2. In the case of
Ack, the UE does not perform any uplink transmission such as
retransmission or first transmission, and is accordingly not
required to transmit PDSCH allocation. The UE complies with PUSCH
allocation on the next PDCCH. For this reason, the cell 1 may
transmit only the information indicating Ack to the cell 2.
Further, it suffices that the UE receives, from the cell 1, the
PUSCH allocation information on the following PDCCH. This reduces a
signaling amount generated between the cells (X2) or between the
cell and the core network (MME) (S1).
[0248] The method disclosed above achieves an increase in coverage
of high data rates, an improvement in cell-edge throughput and an
increase in system throughput, which are aimed in UL CoMP, while
improving a throughput by uplink HARQ.
[0249] The description has been given of a fact that the UE is not
required to receive the PDCCH and/or PHICH from all cells that
perform UL CoMP. Besides, the UE is not required to receive a
scrambling code of another cell other than the serving cell and UE
identifiers (UE-ID, C-RNTI) in a cell for UL CoMP. There is
achieved an effect that control in UL CoMP in the UE can be made
much simpler.
[0250] While it has been described that the PUSCH allocation
information is transmitted in ST3012, as in the description of
ST3001, the information required for decoding the PUSCH from the UE
may be notified, or the deriving method may be predetermined. The
information between the cells that perform UL CoMP may be notified
by means of the interface (X2) between the cells or by means of the
interface (S1) between the cell and the core network (MME).
Notification may be made via the MME. The use of those methods
enable to achieve similar effects to those described in the second
embodiment.
[0251] The other cell (cell 2) that performs UL CoMP may not
allocate, to another UE whose serving cell is the cell 2, the
uplink physical resource to the UE being a UL CoMP target that has
been notified from the cell 1 in ST3012. Alternatively, allocation
may be permitted. Similar effects to those described in the second
embodiment are achieved.
[0252] In the method disclosed above, as the uplink HARQ, the cell
1 transmits the PDCCH and/or PHICH to the UE 1 based on the results
of the judgment as retransmission or first transmission to the UE 1
and/or the judgment as Ack or Nack. As another method, the judgment
results of retransmission or first transmission may be transmitted
to the UE being a UL CoMP target only on the PDCCH as the uplink
HARQ. As a result, the UE is not required to receive the PHICH,
which leads to less power consumption of the UE. In addition, even
the information indicating Ack or Nack does not need to be
transmitted between cells, whereby it is possible to reduce a
signaling amount generated between the cells (X2) or between the
cell and the core network (MME) (S1).
[0253] In the method disclosed above, the serving cell judges as
retransmission or first transmission and/or judges as Ack or Nack
as to the received results in which pieces of information received
from the cells that perform UL CoMP are combined. As another
method, each cell that performs UL CoMP may judge as retransmission
or first transmission and/or judge as Ack or Nack. Each cell
notifies the serving cell of the judgment results by own cell. The
serving cell determines the judgment as retransmission or first
transmission and/or judgment as Ack or Nack for the UE being a UL
CoMP target based on the judgment results from each cell, and
transmits the determination to the UE. The X2 interface or the S1
interface may be used for the judgment results notified from each
cell to the serving cell. The serving cell finally judges as
retransmission or first transmission and/or judges as Ack or Nack
for the UE being a UL CoMP target, whereby only X2 can be used. In
the case of using the X2 interface, there is achieved an effect
that control delays are reduced compared with the case of using the
S1 interface.
[0254] The core network (MME) may make a judgment without judging,
by the serving cell, as retransmission or first transmission and/or
judging as Ack or Nack for the UE being a UL CoMP target. Each cell
that performs UL CoMP notifies the MME of the judgment results by
own cell by means of the S1 interface. The MME finally judges as
retransmission or first transmission and/or judges as Ack or Nack
based on the judgment results from the cell that performs UL CoMP.
The MME notifies the serving cell of the judgment results by means
of the S1 interface. The serving cell that has received the
judgment results from the MME transmits the PDCCH and/or PHICH to
the UE 1 in accordance with the judgment results. The MME finally
judges as retransmission or first transmission and/or judges as Ack
or Nack, with the result that the judgments can be unified by the
MME regardless of which cell is a serving cell. This allows
flexible support for a change of a serving cell.
[0255] In the methods disclosed in the second embodiment and the
present embodiment, the information indicating which cell is a
serving cell may be transmitted between cells or via a MME, so that
each cell that performs UL CoMP recognizes which cell is a serving
cell. The information may be transmitted from the serving cell to
another cell that performs UL CoMP by means of the X2 interface or
may be transmitted from the MME to each cell that performs UL CoMP
by means of the S1 interface. Accordingly, only the serving cell
can transmit the PDCCH, judge as first transmission or
retransmission or judge as Ack or Nack, and transmit the PHICH, for
the UE being a UL CoMP target.
First Modification of Third Embodiment
[0256] In order to solve the problems described in the third
embodiment, this modification discloses another method of
performing the uplink HARQ on a UE being a target in a case where
UL CoMP is performed.
[0257] All cells that perform UL CoMP transmit, to the UE being a
UL CoMP target, the PDCCH and/or PHICH on which the same judgment
as retransmission or first transmission and/or Ack or Nack is
mapped. In a case where the retransmission information is mapped on
the PDCCH, all the cells transmit the PCCH on which the same
physical resource allocation information for retransmission is
mapped.
[0258] As an example, FIG. 32 is a sequence diagram in a case where
the same judgment results are transmitted from all the cells that
perform UL CoMP. FIG. 32 is identical to FIG. 28 in part, and thus
description of the identical parts is omitted. Steps from ST3201 to
ST3203 are added in FIG. 32. In ST2811 and ST2812, the respective
cells (cell 1, cell 2) that perform UL CoMP judge as retransmission
or first transmission and/or judge as Ack or Nack, and then in
ST3201, transmit/receive the judgment results between cells each
other. The respective cells derive one judgment result from the
combination of the received judgment results of the other cell that
performs UL CoMP and the judgment results of own cell (ST3202,
ST3203). The deriving method is predetermined such that the
judgment results are the same among all the cells that perform UL
CoMP. As a result, all the cells that perform UL CoMP transmit the
information based on the same judgment results on the PDCCH and/or
PHICH. This prevents retransmission or first transmission from
varying for each cell. Therefore, it is possible to perform UL
CoMP.
[0259] Accordingly, it is possible to further increase the coverage
of high data rates, improve the cell-edge throughput and increase
the system throughput, which are aimed in UL CoMP, while improving
a throughput by the uplink HARQ.
[0260] As the method of mutually transmitting/receiving the
judgment results between cells, the method disclosed in the second
embodiment or the third embodiment may be used. As the method of
deriving one judgment result from judgment results of the
respective cells, for example, first transmission is set in a case
where the judgment of any one of cells is first transmission. This
is because if any one of cells receives the judgment result
properly, reception is enabled by combination of pieces of received
information in UL CoMP. While, Ack is set in a case where there is
no judgment as retransmission or first transmission and any one of
cells is judged as Ack. This is for the same reason. In a case
where all the cells are judged as retransmission, retransmission is
set. Further, in a case where there is no judgment as first
transmission or retransmission and all the cells are judged as
Nack, Nack is set. This means that all the cells cannot have
performed reception, and thus all the cells have to perform
retransmission. As a result of the above-mentioned deriving method
being determined in advance, it is possible to derive one judgment
result while considering the radio wave propagation situations of
all the cells that perform UL CoMP. Accordingly, all the cells can
transmit first transmission and/or Ack if any one of the cells has
good reception quality even when any one of the cells has poor
reception quality. This allows to improve the throughput as a
system. In a case of this deriving method, the judgment results may
be transmitted/received between cells only in a case of first
transmission and/or Ack. This reduces a signaling amount between
cells or between the core network and the cell.
[0261] The method disclosed in this modification may be used in
combination with the method disclosed in the third embodiment. One
judgment result may be derived from the judgment results of all the
cells that perform UL CoMP, so that any one of cells that perform
UL CoMP transmits this one judgment result to the UE being a CoMP
target. As a result, all the cells can transmit first transmission
and/or Ack if any one of the cells has good reception quality even
when any of the cells has poor reception quality, which enables to
improve the throughput as a system. At the same time, it is
possible to increase the coverage of high data rates, improve the
cell-edge throughput and increase the system throughput owing to UL
CoMP. Alternatively, any one of the cells may be a serving cell.
This only requires that the UE consistently receive the control
information from the serving cell, leading to effects that the size
of a control circuit can be reduced and that control malfunctions
can be reduced in a cell and a UE.
[0262] The method disclosed in this modification may be used in
combination with the method disclosed in the second embodiment.
There can be achieved not only the effects described in this
modification but also the effects described in the second
embodiment.
Second Modification of Third Embodiment
[0263] In order to solve the problems described in the third
embodiment, this modification discloses another method of
performing uplink HARQ on a UE being a target in a case of
performing UL CoMP.
[0264] The UE being a UL CoMP target may derive one judgment result
based on the results of judgment as retransmission or first
transmission and/or judgment as Ack or Nack from the respective
cells in UL CoMP. The method disclosed in the first modification is
applicable as the deriving method. It suffices that each cell maps
the identification information indicating whether transmission is
the first one or how many times transmission has been performed,
such as a retransmission number or a first transmission number on
the retransmission or first transmission data transmitted from the
UE. Each cell performs the uplink HARQ based on the identification
information. Although this requires that the UE receive the results
of the judgment as retransmission or first transmission and/or
judgment as Ack or Nack from each cell, each cell is not required
to perform control for determining one judgment result for
transmission. This modification is applicable to persistent
scheduling or semi-persistent scheduling in which uplink
transmission is periodically allocated. The allocation timing of
first transmission has been determined, and thus even when
different judgment results are transmitted to the UE from the
respective cells, the respective cells can receive the transmission
data (PUSCH) from the UE by performing the next transmission at the
periodically-based transmission timing based on the judgment
results performed in the UE. This increases the coverage of high
data rates, improves the cell-edge throughput and increases the
system throughput, which are aimed in UL CoMP, while improving a
throughput by uplink HARQ.
Fourth Embodiment
[0265] PUSCH frequency hopping is performed in each cell in the LTE
(Non-Patent Document 9, Non-Patent Document 10). The PUSCH
frequency hopping pattern is derived using the cell identifiers
(Cell-ID, PCI) for each cell. Thus, the PUSCH frequency hopping
pattern varies among the cells (multi-point cells) that perform UL
CoMP. For example, in the case where the serving cell among the
cells that perform UL CoMP transmits the PUSCH allocation
information to the UE being a UL CoMP target, which has been
disclosed in the second embodiment to the second modification of
the third embodiment, the hopping pattern serves as a hopping
pattern used by the serving cell when frequency hopping is
performed on the PUSCH. This means that the hopping pattern is
different from a hopping pattern used by another cell that performs
UL CoMP. Accordingly, another cell that performs UL CoMP does not
recognize the frequency hopping pattern of the PUSCH of the UE, and
thus cannot receive the PUSCH from the UE. As a result, UL CoMP
cannot be performed.
[0266] In order to solve the above-mentioned problem, the serving
cell transmits, to another cell that performs UL CoMP, the
information regarding the frequency hopping pattern of the PUSCH
for the UE. The information may be transmitted before UL CoMP is
performed on the UE. For example, it may be transmitted as in
ST3001 of FIG. 30. Examples of the information regarding the PUSCH
frequency hopping pattern include the information indicating
whether or not frequency hopping is performed, the cell identifiers
(Cell-ID, PCI) of the serving cell, the system bandwidth of the
serving cell and the number of subblocks of the serving cell. Those
pieces of information are transmitted to another cell in advance,
whereby another cell can receive the PUSCH from the UE even if
PUSCH frequency hopping is performed. Accordingly, it is possible
to increase the coverage of high data rates, improve the cell-edge
throughput and increase the system throughput, which are aimed in
UL CoMP.
[0267] However, the control, in which the information regarding the
PUSCH frequency hopping pattern for the UE is transmitted from the
serving cell to another cell and the allocation of the physical
resource to which the PUSCH of the UE is transmitted is derived by
another cell, becomes complicated. This is because frequency
hopping is performed for each subframe or each slot. In order to
perform this, the information regarding frequency hopping needs to
be transmitted for each subframe or each slot, resulting in an
increase of the signaling amount from the serving cell to another
cell. Further, frequency hopping is controlled by another cell for
each subframe or each slot, and thus control becomes complicated,
resulting in an increase in size of the control circuit of the cell
and an increase in power consumption.
[0268] In order to solve the above-mentioned problem, PUSCH hopping
is not performed (is prohibited) for the UE being a UL CoMP target.
This may be predetermined. Alternatively, the serving cell may
transmit the information indicating whether or not to perform
(allow or prohibit) frequency hopping on the UE being a UL CoMP
target. This enables the serving cell not to perform PUSCH hopping
on the UE being a UL CoMP target, whereby it is possible to solve
the above-mentioned problem.
[0269] In a case of not performing PUSCH hopping on the UE being a
UL CoMP target, the serving cell may transmit the PUSCH allocation
information disclosed in ST3001 of FIG. 30 to another cell.
Alternatively, the serving cell may transmit the information
indicating whether or not to perform frequency hopping to another
cell. In a case of having transmitted the information indicating
that frequency hopping is not performed, the serving cell may
transmit the PUSCH allocation information disclosed in ST3001 of
FIG. 30. On the other hand, in the case of having transmitted the
information indicating that frequency hopping is performed, the
serving cell may transmit the information regarding the
above-mentioned PUSCH frequency hopping pattern. As a result,
whether or not frequency hopping is performed can be changed in a
dynamic manner, which allows flexible radio resource
allocation.
[0270] Frequency hopping is performed mainly in the case where
uplink transmission is periodically allocated, such as persistent
scheduling or semi-persistent scheduling. In such a case, while the
UE periodically transmits the PUSCH, it is a waste of radio
resources to transmit the PUSCH allocation information from the
serving cell to the UE in every transmission. If the PUSCH is
allocated in the same manner each time for avoiding this, the
reception quality of the PUSCH in the cell becomes deteriorated
continuously in a case where the radio wave propagation situation
of the physical resource for allocation, that is, frequency-time
domain becomes deteriorated. As a result of the PUSCH becoming
deteriorated continuously, a problem such as disconnection arises.
Therefore, in a case where the PUSCH is transmitted periodically,
frequency hopping is performed on the PUSCH, so that the reception
quality of the PUSCH is prevented from becoming deteriorated
continuously in the cell. In the case where the PUSCH is
transmitted periodically as described above, frequency hopping is
performed on the PUSCH in many cases.
[0271] However, no problem arises if the UE being a UL CoMP target
does not perform (stops) frequency hopping. This is because in UL
CoMP, a plurality of radio wave propagation paths are formed
between one UE and a cell that performs UL CoMP. Accordingly, even
when the radio wave propagation situation, with one cell, of the
PUSCH allocation physical resource, that is, the frequency-time
domain becomes deteriorated, the radio wave propagation situation
with another cell does not become deteriorated. Therefore, the
reception quality of the PUSCH is not degraded in another cell.
This allows to maintain the reception quality by combination of
pieces of received information by the cell that performs UL CoMP,
and thus communication is not prevented from being
disconnected.
[0272] Therefore, no problem arises even if the UE being a UL CoMP
target does not perform (prohibits) frequency hopping, whereby an
effect that control is prevented from becoming complicated can be
achieved.
[0273] Further, setting may be made as to whether or not PUSCH
hopping is performed (allowed or prohibited) for a UE being a UL
CoMP target in accordance with service. This setting may be
predetermined. For example, PUSCH hopping may not be performed (may
be prohibited) in a case where the transmission data of the UE
being a UL CoMP target is voice communication service. This is
because whether to perform persistent scheduling or semi-persistent
scheduling on the PUSCH is determined in accordance with service in
many cases, and accordingly whether to perform frequency hopping on
the PUSCH is determined in many cases. Therefore, it is possible to
prevent UL CoMP control from becoming complicated by setting
whether or not to perform PUSCH hopping in accordance with
service.
[0274] The method of predetermining a physical resource that cannot
be allocated for DL CoMP or a physical resource that can be
allocated therefor, which has been disclosed in the first
embodiment, may be applied to UL CoMP. For example, among the
physical resources to which the PDSCH can be allocated, the
frequency domain of a physical resource that can be allocated for
UL CoMP may be predetermined, while the other frequency domain may
be determined as a physical resource being a frequency hopping
target. As a result of the physical resources on which uplink
frequency hopping can be performed being divided into a physical
resource for UL CoMP and that for uplink frequency hopping, it is
possible to independently perform control of frequency hopping
performed for each cell and scheduling control of the physical
resource of the PUSCH, which has to be performed between the cells
that perform UL CoMP in a coordinated manner. This makes uplink
frequency hopping control as well as UL CoMP control simpler.
[0275] In a semi-static case, the physical resource information in
which frequency hopping is enabled or the physical resource
information in which frequency hopping is disabled may be notified
by being mapped on the broadcast information from each cell to the
UE. Change information of the physical resource may be notified by
being mapped on the broadcast information. All UEs being served by
a cell can recognize the physical resource where frequency hopping
of the cell can be performed, by being mapped on the broadcast
information to be notified from each cell to the UE. Therefore, it
is possible to determine a frequency hopping pattern in the
physical resource where frequency hopping can be performed.
[0276] While the case where UL CoMP is performed has been described
herein, the method disclosed in the present embodiment may be used
in DL CoMP. It is possible to achieve similar effects also in DL
CoMP when the above-mentioned method is used in DL CoMP.
[0277] While the LTE advanced system has been mainly described in
the present invention, the present invention is applicable to other
system using OFDM. Further, the present invention is applicable to
a mobile communication system to which a closed subscriber group
(CSG) is introduced, a communication system in which an operator
identifies a subscriber and the identified subscriber is allowed
access as in the case of CSG, and a communication system into which
a cell having a smaller cell radius compared with a normal cell is
introduced as in the case of HeNB.
* * * * *