Description
Title of Invention
COMMUNICATION CONTROL DEVICE, COMMUNICATION CONTROL
METHOD, AND BASE STATION
Technical Field
[OOOl]
The present disclosure relates to coiml~unication control devices,
10 co~ninunicationc ontrol methods, and base stations.
Background At-t
[0002]
In recent years, it has become practical to use a high-speed cellular radio
15 con~nlunicatioat echnique, such as LTE (Long Term Evolution), WiMAX, etc., and
therefore, the communication rate of radio communications services enjoyable for
mobile users has been significarltly improved. Moreover, it is expected that the
introduction of the fourth-generation cellular radio communication technique, such
as LTE-A (LTE-Advanced) etc., would further improve the coinnlunication rate.
20 [0003]
On the other hand, there has beell a rapidly increasing number of mobile
users, and therefore, there has been increasing use of applications requiring a high
data rate. As a result, the cellular radio conlmunication technique has not yet been
developed to meet all needs of mobile users. Therefore, a small cell is beginning to
25 be introduced in order to supplen~ent a macro cell and thereby increase
colnmunication capacity. The concept of a small cell encompasses a ferntocell, a
nanocell, a picocell, a microcell, etc. A snlall cell is typically introduced by
providing a base station (also called an access point) wvl~ich is smaller than that (e.g.,
an eNB (evolved Node B) in LTE) of a macro cell. However, in an area where a
30 macro cell and a small cell overlap, there is a risk that a radio signal communicated
in the srnall cell may interfere with a terminal connected to the macro cell.
[0004]
As a technique for avoiding the risk of interference in the cellular radio
comtnunication system, a technique proposed by Patent Literature 1 below is known,
for example. According to the technique proposed by Patent Literature 1 below,
5 interference channel it~forniation is exchanged between adjacent macro cell base
stations, and based on the exchanged interference channel information, transmission
power is adjusted by these base stations.
Citation List
10 Patent Literature
[0005]
Patent Literature 1:
Sutninary of Invention
15 Technical Problem
[0006]
However, because a small cell has a role in supplementing a macro cell and
thereby increasing com~llunication capacity, it is not necessarily appropriate to
simply apply an arrangement for perfornling at1 interference control between macro
20 cells to an interference control between a macro cell and a small cell. For exatnple,
when there is a small cell which interferes with a macro cell terminal, then if the
macro cell ter~llinacl an be connected to the small cell which is an interference source:
to connect the macro cell ternlinal to the small cell is Inore beneficial than to reduce
the interference by reducing trans~nission power in terms of overall colllnlunicatiori
25 capacity.
[0007]
Therefore, it is desirable to provide an arrangement which is more suitable
for an interference control between a macro cell and a sniall cell.
30 Solution to Problem
[OOOS]
According to tlie present disclosure, there is provided a communication
control device including a determination unit which determines whether an access
type of a s~nall cell which at least partially overlaps a macro cell of a radio
communication system is a closed access type or an open access type, an
5 identification unit which, when it is determined that the access type of the small cell
is tlie closed access type, identifies a user terminal of the Inacro cell which should be
protected from interference caused by a radio signal fiom the stnall cell, and an
interference control unit which transnlits an interference control signal to a base
station of the small cell so that the interference on the user terminal identified by the
10 identification unit is reduced.
[0009]
According to another aspect of the present disclosure, there is provided a
co~mnunicationc ontrol method including determining whether an access type of a
small cell which at least partially overlaps a macro cell of a radio con~munication
16 system is a closed access type or an open access type, when it is determined that the
access type of the small cell is the closed access type, identifying a user terminal of
the macro cell which should be protected from interference caused by a radio signal
from the small cell, and transmitting an interference control signal to a base station of
the small cell so that the interference on the identified user terminal is reduced.
20 [OOlO]
According to another aspect of the present disclosure, there is provided a
base station of a sniall cell of a closed access type, the base station including a
control unit which, when the small ccll at least partially overlaps a macro cell of a
radio communication system, informs a control node which controls interference
25 between the macro cell and the small ccll that an access type of the base station is the
closed access type, and controls com~nunication in the stnall cell in accordance with
an interference control signal transmitted from the control node in response to the
informing to reduce interference on a user tennitla1 of the tnacro cell which should be
protected from interference caused by a radio signal from the small cell.
30 [ O O l l ]
According to another aspect of the present disclosure, there is provided a
communication control method perfornled by a base station of a small cell of a
closed access type, the method including, when the small cell at least partially
overlaps a macro cell of a radio co~l~municatiosny stem, informing a control node
which controls interference between the macro cell and the small cell that an access
5 type of the base station is the closed access type, and controlling comriiunication in
the small cell in accordance with an interference control signal transmitted fiom the
control node in response to the informing to reduce interference on a user terminal of
the macro cell which should be protected from interference caused by a radio signal
fro111 the small cell.
10
Advantageous Effects of Invention
[0012]
According to the technology of the present disclosure, an arrangement is
provided which is tilore suitable for an interference control between a macro cell and
15 a small cell.
Brief Description of Drawings
[00 131
[FIG. 11 FIG. 1 is a diagram for describing an overview of a system.
20 [FIG. 21 FIG. 2 is a diagram for describing some exatnple locations of a cooperation
manager for an interference control.
[FIG. 31 FIG. 3 is a block diagram showing an exatnple configuration of a
cooperation manager according to one embodiment.
[FIG. 41 FIG. 4 is a diagram for describing an example downlink frame format in LTE.
25 [FIG. 51 FIG. 5 is a diagram for describing an example uplink frame format in LTE.
[FIG. 6A] FIG. 6A is a diagram for describing first example scheduling information
which is transmitted to a small cell base station.
[FIG. 6B] FIG. 6B is a diagram for describing second example scheduling
information which is transmitted to a small cell base station.
30 [FIG. 71 FIG. 7 is a block diagram showing an example configuration of a small cell
base station according to one e~nbodiment.
[FIG. 8A] FIG. 8A is a sequence diagram showirig a first example general flow of a
co~linlunicationc ontrol process according to one embodiment.
[FIG. 8B] FIG. 8B is a sequence diagram showing a second example general flow of
a communication control process according to one embodiment.
5 [FIG. 91 FIG. 9 is a flowchart showing an exaniple flow of at1 interference control
process performed by a cooperation manager according to one embodiment.
[FIG. 101 FIG. 10 is a diagram for describing an example result of execution of a
communication control process according to one embodiment.
10 Description of Embodiments
[0014]
Hereinafter, preferred embodiments of the present invention will be
described in detail wit11 reference to the appended drawings. Note that, in this
specification and the drawings, elements that have substantially the same function
15 and structure are denoted wit11 the same reference signs, and repeated explanation is
omitted.
[OO 151
Also, the description will be given in the followirig order.
1. Oven~iewo f System
20 1-1.Example Small Cell
1-2. Location of Cooperation Manager (CM)
2. Configuration of Cooperation Manager
3. Configuration of Small Cell Base Station
4. Flow of Process
4-1. Process of Entire System
4-2. Communication Control Process by Cooperation Manager
5. Summa~y
[0016]
4 .O ve~vie\vo f System>
30 [l -1 . Example Small Cell]
Firstly, an oveiview of a system will be described with reference to FIGS. 1
and 2. FIG. 1 shows an exanlple radio comtnunication system 1. The radio
commu~~icatiosyns tem 1 may, for example, be a system based on any cellular radio
comnlunication sclleme, such as LTE, W-CDMA, CDMA2000, WiMAX, LTE-A, etc.
[00 171
5 Referring to FIG. 1, a base station 11 (e.g., an eNB in LTE) is shown which
provides a radio comnunications service to a terminal in a macro cell 10. The
radius of a nlacro cell is typically several hundreds of meters to a dozen or so
kilotneters. I-Iowever, a problem tilay occur that, in a space in the vicinity of the
boundary of a nlacro cell, behind a building, underground, indoors, etc., the intensity
10 of a radio signal from a base station of a macro cell decreases, so that
comn~unicationis not established or the data rate is insufficient. In such a situation,
a small cell may be introduced in order to supplement the macro cell and thereby
increase communicatio~c~ap acity. As described above, the concept of a sniall cell
includes a femtocell, a nanocell, a picocell, a microcell, etc. A small cell is
15 introduced by providing various types of smaller base stations. Table 1 illustrates
several types of snlall cell base stations.
[00 181
Place where
supposed to
be provided 1 Table 1. Types and Features of Small Cell Base Stations
ioutdoor
Type of base station
RRH (Remote Radio
Head)
Hot zone base station
Femtocell base station
Relay station
indoor
outdoor]
[0019]
IF type
Type 2
Type 2
Type 1
Type 1
20 In Table 1, the "IF type" refers to categories of interfaces between macro
Access type
open
open
closed
/open
open
cell base stations. RRHs and hot zone base stations, wvl~ich have the X2 interface
between macro cell base stations, may be categorized into Type 2. Femtocell base
stations and relay stations, which do not have the X2 interface, may be categorized
into Tj~pe 1. The "access type" refers to categories of acceptance of access from an
UE. In principle, every user ternlinal can be connected to a s~nallc ell of the open
access type. On the other hand, in principle, only limited user terminals can be
connected to a small cell of the closed access type. A small cell base station of the
5 closed access type may, for example, store a list of identification infornlation
(addresses, device IDS, user IDS, etc.) of user ternlinals for which connection is
acceptable, and based on the list, control access from a user terminal. I11 the
example of Table 1, a small cell which is operated by an RRH, a hot zone base
station, and a relay station has the open access type. On the other hand, a small cell
10 which is operated by a fe~ntocell base station has the closed or open access type.
Note that the categorization of the access types shown in Table 1 is only for
illustrative purposes.
[0020]
In FIG. 1, small cell base stations 16a, 16B, and 16c are shown. The stnall
15 cell base stations 16a, 16B, and 16c provide a radio conlnlunications sewice to
terminals in small cells 14a, 14b, and 14c, respectively, which at least partially
overlap the macro cell 10. In FIG. 1, a terminal connected to a macro cell
(hereinafter referred to as a macro cell tenninal) is indicated by a closed circle, and a
terminal connected to a slnall cell (hereinafter referred to as a small cell terniinal) is
20 indicated by an open circle.
[002 11
In such a case ~vlierea s~nalcl ell is provided in a macro cell, there is a risk
that a radio signal transmitted in the small cell may have interference on a macro cell
tenninal. In the example of FIG. 1, the macro cell tenninal 12a may be interfered
25 with by a radio signal transmitted in the small cell 14a. The macro cell terminals
12b and 12c may be interfered with by a radio signal transmitted in the small cell 14b.
Macro cell terminals 12d, 12e, 12f, and 12g may be interfered with a radio signal
transmitted from the small cell 14c. Among existing techniqnes for avoiding these
risks of interference is to control trans~nissionp ower. If the transmission power of a
30 small cell is reduced, the level of interference due to a radio signal transmitted in the
small cell is reduced. However, the reduction in transmission power means a
reduction in the commu~iicationc apacity of the small cell. 'll~ereforei,n order to
maintain or increase the overall conlmunication capacity of a syste~iii,t is desirable
to control the itlterfere~lceu sing a different approach if possible instead of reducing
transmission power. Therefore, in the tecl~nology of the present disclosure, a
6 cooperation manager (CM) described in detail in the following section is introduced.
[0022]
[I-2.L ocation of Cooperation Manager (CM)]
A cooperation manager may be provided at any communication node that
can comnunicate with a small cell base station. FIG. 2 is a diagram for describing
10 some example locations of a cooperation manager. In FIG. 2, an LTE-based
network architecture is shown as an example. I n the LTE-based network
architecture, a base station (eNB) 11 of a macro cell 10 is connected to a core
network 20. The core network 20 is, for example, imple~ilented as an EPC
(Evolved Packet Core) including a P-GW, an S-GW, and an MME. The core
15 network 20 is also connected to an external network 30. The external network 30 is
an IP (Internet Protocol) network which is also called a PDN (Packet Data Network).
Various application (AP) servers may be implemented on the external network 30.
LO0231
Nodes shown in FIG. 2 have the following respective functions. Although
20 only representative nodes are here shown, other nodes may be included in the
network architecture.
HSS (Home Subscriber Server): a server which manages identification
information, profile information, authentication information, etc. of subscribers.
MME (Mobility Management Entity): an entity ~vl~icchom municates a
25 NAS (Non Access Stratum) signal to and from an UE to perform mobility
management, session management, paging, etc. The entity is connected to a
plurality of eNBs.
P-GW (PDN-Gateway): a gateway which is located at a connection point
between an EPC and a PDN, and perfornls assignment of an IP address to an UE,
30 addition and deletion of an IP headel; etc. The gateway may also perform charging
S-GW (Senring-Gateway): a gateway which is located at a connection
point between an E-UTRAN and an EPC, and routes packets in the user plane.
Wl~ena n UE is handed over between eNBs or between UTRANs, an S-GW acts as
an anchor point.
5 eNB (evolved Node B): a base station which provides a radio link in a
tnacro cell, and performs radio resource nlarlagement (RRM), radio bearer control,
scheduling, etc.
[0024]
In a network architecture, such as that illustrated in FIG. 2, a cooperation
10 manager ]nay be provided as a new control node in the core network 20 (CMl).
Also, a cooperation manager may be provided as a new function on an existing
control node (e.g., an MME) in the core network 20 (CM2). Also, a cooperation
lnanager tnay be provided as a new function on a base station (eNB) of a macro cell
(CM3). Also, a cooperation manager may be provided as a new function on a small
15 cell base station (CM4). Also, a cooperation manager may be provided as a new
server device in the external network 30 (CM5).
[0025]
In any location, a cooperation manager co~n~nunicatewsi th a macro cell
base station and a small cell base station on a signaling channel including an X2
20 interface (or other logical/physical interfaces), the core network 20, the external
network 30, or the like. Also, the cooperation nlanager protects a macro cell
terminal from interference caused by a radio signal from a stnail cell while
minitnizing the reduction in communication capacity as much as possible.
[0026]
25 <2. Configuration of Cooperation Manager>
FIG. 3 is a block diagranl showing an exarnple configuration of a
cooperation manager 100. Referring to PIG. 3, the cooperation lnanager 100
includes a cornmunicatiot~u nit 110, a storage unit 120, and a control unit 130.
LO0271
30 (I) Communication Unit
The cornrnunication unit 110 is a communication nlodule for allowing the
cooperation manager 100 to communicate with another node. The comtnunication
unit 110 may include a radio co~~~rnunicatmioond ule including an antenna and an RF
(Radio Frequency) circuit, or a wired communication module, such as a LAN (Local
Area Network)-connected terminal etc.
5 [0028]
(2) Storage Unit
The storage unit 120 stores a program and data for operating the cooperation
manager 100, using a storage medium, such as a hard disk, a semiconductor memory,
etc. For example, the storage unit 120 stores snlall cell-related infor~nationr eceived
10 from a small cell base station. The s~nalcl ell-related information may include, for
example, identification infornlation, a location, etc. of a small cell base station. The
storage unit 120 may also store scl~eduling information received i?0111 a macro cell
base station.
[0029]
15 (3) Control Unit
The control unit 130 coi~espondsto a processor, such as a CPU (Central
Processing Unit), a DSP (Digital Signal Processor), etc. The control unit 130
executes a program stored in the storage unit 120 or another storage medium to cause
the cooperation manager 100 to perform various functions. In this embodiment, the
20 control unit 130 includes three functional modules, i.e., a determination unit 132, an
identification unit 134, and an interference control unit 136.
[0030]
(3-1) Determination Unit
M'hen a small cell is installed in a macro cell, initial setup of the small cell is
25 perfonned. In the initial setup procedure (or a subsequent stage), a small cell base
station registers s~nall cell-related infor~nation into the cooperation manager 100.
The deter~nination unit 132, when recognizing a new s~nall cell base station,
deter~nincs\ vl~etl~ethre access type of a s~nallc ell operated by the small cell base
station is the closed access type or the open access type. The determination of the
30 access type may be performed based on access type inforn~ation which may be
directly contained in the small cell-related information, or by querying a database
using identification information of the small cell base station as a key.
[003 11
When the determination unit 132 determines that the access type of the
small cell is the open access type, a macro cell terminal which is located in or near
5 the small cell can be connected to the small cell. Therefore, if the level of
interference from the small cell exceeds the allowable level, the macro cell terminal
changes the connection destination from the macro cell to a small cell of the open
access type (i.e., handover), and therefore, can avoid interference and continue the
desired communication. On the other hand, when the deternlination unit 132
10 deter~ninesth at the access type of the small cell is the closed access type, connection
from a macro cell ternlinal which is not previously registered to the small cell may be
rejected. Therefore, the identification unit 134, described next, identifies a macro
cell terminal which is likely to be interfered with by such a small cell of the closed
access type.
15 [0032]
(3-2) ldentificatio~Ui nit
The identification unit 134, when it is determined that the access type of a
sliiall cell is the closed access type, identifies a macro cell terminal wluch should be
protected from interhence caused by a radio signal from the small cell. More
20 specifically, in this enibodiment, the identification unit 134 identifies a macro cell
terminal which should be protected, based 011 the result of sensing received from a
small cell base station. Here, sensing typically refers to measurement of a signal
level of an uplink signal from a user terminal which is located around a small cell
(e.g., in or near a slnall cell). A small cell base station nay voluntarily perform
25 sensing. Instead, the identification unit 134 may request a small cell base station to
perform sensing.
[0033]
The sensing result provided fro111 the small cell base station may, for
exa~nple, indicate whether or not an uplink signal exceeding a predeter~nined level
30 has been detected ("1" when such an uplink signal has been detected, or "0"
othenvise, etc.) on a resource block-by-resource block basis or in groups of a
plurality of resource blocks. Instead, the sensing result may indicate the signal level
of the detected uplink signal on a resource block-by-resource block basis or in groups
of a plurality of resource blocks. Moreover, the identification unit 134 obtains
scheduling information of a macro cell from a macro cell base station (or other
5 control nodes). The scheduling illfor~llatiotlin dicates what macro cell terminal has
transmitted an uplink signal using what resource block. Thereaftel; the
identification unit 134 checks the se~lsitlgr esult obtained fiorn the small cell base
station against the scheduling information of the macro cell, to identify a macro cell
terminal which should be protected. For example, a macro cell terminal which has
10 been given an uplink grant (UL Grant) with respect to a resource block for which an
uplink signal exceeding the predetermined level has beell detected (i.e., for which
scheduling has been performed) may be identified as a target which should be
protected.
[0034]
15 The identification unit 134 outputs, to the interference control unit 136,
identification information of a macro cell termitla1 thus identified as a protection
target, and identification information of a corresponding snlall cell base station.
[0035]
(3-3) Interference Control Unit
20 In order to reduce interference on a tnacro cell terminal identified by the
ide~ltificationu nit 134, the interference co~~truonli t 136 controls interference caused
by a radio signal fiorn a corresponding small cell. For example, the interference
control unit 136 transmits scheduling information of a macro cell to a small cell base
station so that radio resources different fiom those allocated for a macro cell terminal
25 which should be protected are used in the small cell.
[0036]
FIG. 4 is a diagram for describing an example downlink kame format in
LTE. In an upper portion of FIG. 4, one radio frame having a length of 10 msec is
shown. One radio frame i~lcludes ten sub-fiaines each having a length of 1 msec.
30 One sub-fiame includes two 0.5-ms slots. One 0.5-111s slot typically includes seven
(six when extended cyclic prefixes are used) OFDM syn~bolsin the time direction.
Also, one OFDM sy~iiboal nd twelve sub-carriers in the frequency direction form one
resource block. Of such time-frequency resources, resources at a predetermined
locatio~i are used for control signaling. For exanlple, in some resource blocks
located at a middle of the band, a primary synchronization channel, a secondary
5 synchronization channel, and a broadcast cha~nlel are provided. The pritnary
synchronization channel arid the secondary synchronization channel are used for cell
search and synchronization. The broadcast cha~nlel is used to broadcast system
infor~nation,s uch as a system bandwidth, a MIMO antenna configuration, etc. The
other resource blocks may be used for downlink data transmission.
10 [0037]
FIG. 5 is a diagratn for describing an example uplink frame format in 1,TE.
Also in at1 uplink, one radio frame includes ten sub-frames each having a length of 1
msec. Of uplink resources, resources at a predetermined location are used for
control signaling. For example, a reference sequence for detnodulation of an uplink
15 signal is provided at a middle in the time direction of each 0.5-111s slot. A reference
sequence for CQI measurement may be provided at a head of the second sub-frame
( 1 A random access channel (PRACH) is used for random access from a user
terminal. A physical uplink shared channel (WSCH) may be used for uplink data
transmission.
20 [0038]
Allocation of resources to downlink data transmission to a macro cell
terminal and uplink data transmission to a macro cell terminal is determined by a
tnacro cell base station. Thereafter, the macro cell base station broadcasts
scheduling infoi~iiation indicating resource allocation to the macro cell terminal.
25 Moreover, in this emboditnent, a macro cell base station also provides the scheduling
itlfonnation to the cooperation lilanager 100. For example, the interference control
unit 136 tnay filter information about a resource block in which a macro cell terminal
which should be protected is involved, from scheduling infomlatioa provided from a
macro cell base station, and trans~nitt he filtered scheduling inforniation to a small
30 cell base station.
[0039]
FIG. 6A is a diagram for describing first example scheduling information
which is tra~lsmittedf rom the interference co~ltroul nit 136 to a small cell base station.
In the example of FIG. 6A, it is assumed that each square on the time-frequency
plane corresponds to a resource block (RB). Hatched squares are resource blocks
5 allocated to a macro cell terminal wl~ichs hould be protected. Non-hatched squares
are resource blocks which can be used by a small cell. Scheduling infonnation
transmitted from the interference control unit 136 to a small cell base station ntay be
information, such as a bitmap, wl~ichd istinguishes resource blocks the use of which
is restricted for a small cell from resource blocks which a small cell is allowed to use.
10 [0040]
Also, the interference control unit 136 may, for example, transmit, to a small
cell base station, scheduling infornlation which indicates resource blocks used by a
~leigllboring small cell in addition to resource blocks in which a macro cell terminal
which should be protected is involved.
15 [0041]
FIG. 6B is a diagram for describing second example scl~edulingin formation
which is transmitted from the interference co~~truonli t 136 to a small cell base station.
In the example of FIG. 6B, closed squares are resource blocks which are used by a
small cell located in the vicinity of a small cell base station which receives the
20 scheduling information. By providing such scheduling information, scheduling of a
plurality of neighboring small cells can be controlled so that interference between
these small cells is reduced.
[0042]
A small cell base station which has received the scheduling information
25 illustrated in FIG. 6A or 6B controls communication in the small cell so that only a
resource block(s) which the scheduling information indicates can be used is used by
a small cell terminal. Note that when there are a large number of macro cell
terminals, or when there is a macro cell ternlinal(s) which consulnes a large number
of resource blocks, it may i11 some cases be difficult to provide sufficient
30 communication opportunities in a small cell while appropriately reducing
i~lterfcrcncc0 11 a macro cell terminal. Therefore. the interference control unit 136
may, for exa~ilple, request a small cell base station to accept a handover of at least
one macro cell terminal to a small cell, based on the number of macro cell terminals
which should be protected or the proportion of radio resources which are used by the
macro cell ter~ninals. In this case, the handover acceptance request transmitted
5 from the interference control unit 136 may include identification information of a
macro cell terminal which is to be handed over. A small cell base station of tlie
closed access type, when receiving such a request, adds identification information of
the macro cell terminal to a list of user terminals which accept connection, and waits
for a handover from the terniinal.
10 [0043]
A macro cell terminal inay move after the interference control of the
cooperation manager 100 has begun. Therefore, it is desirable that a small cell base
station continue to perfor111 sensing on the surroundings. For example, when a
macro cell terminal which should be protected has moved far from a snlall cell, the
15 limitation on scl~edulingis no longer required, and therefore, resources avariable in
the small cell increase. Howevel; to continue to perform sensing on all resource
blocks in which an uplink signal may be transmitted is a great load on a small cell
base station and a small cell terminal. Therefore, the interference control unit 136
may, for example, inform a small cell base station of a location (at least one of a
20 timing and a frequency) of resources on which an uplink signal is transmitted by a
macro cell terminal which should be protected. Here, for example, an uplink signal
lnay include an aclu~owledge signal (ACK) with respect to a downlink signal. In
general, a terminal which has received a do\vrilink signal is supposed to return an
ACK (or an NACK) within a predetermined period of time (e.g., 8 msec).
25 Therefore, by narrowing locations of resources on which an uplink signal is
transmitted based on tlie period of time, the load of sensing on a small cell can be
reduced. Also, the upli~lks ignal may include a signal which carries a CQI (Channel
Quality Indicator) on a PUSCH. In particular, when a ternlinal downloads a file
having a large data size, or when a terminal receives streaming data, trans~nissioioi f
30 an uplink signal from the terminal is only performed at a considerably low frequency
cornpared to reception of a downlink signal. Therefore, it is usefill to infor~n a
small cell base station of locations of resources on which an uplink signal is
transmitted to allow the s~nalcl ell base station to narrow resource locatiotis at which
sensing should be perfornied. Also, the uplink signal may be an authentication
signal which is used when a niacro cell terminal which should be protected uses a
5 broadcast setvice (e.g., a signal transmitted for the purpose of handshake or
charging). A broadcast service is, for example, provided by using an MBMS
(Multimedia Broadcast Multicast Service) frame. A ternlinal which receives a
signal on an MBMS fsanle does not return an ACK. Therefore, by perfomi sensing
on the above authentication signal instead of an ACK signal, the movement of a
10 macro cell terminal can be detected with a sniall sensing load.
[0044]
<3. Configuration of Small Cell Base Station>
A small cell base station 200 and the above cooperation manager 100 form a
cotntnunication control system. FIG. 7 is a block diagram showing an example
15 configuration of the stnall cell base station 200 according to one embodiment.
Referring to FIG. 7, the small cell base station 200 includes a radio comtnunication
unit 210, a network communication unit 220, a storage unit 230, and a control unit
240.
[0045]
20 (1) Radio Comm~inication Unit
The radio comnlunication unit 210 is a radio com~nunication module for
providing a radio comnlunications service to a snlall cell terminal. The radio
comniunication unit 210 includes an antenna and an RF circuit. The radio
conl~nunicationu nit 210 co~mnunicatesa radio signal to and from one or more small
25 cell terminals in accordance wit11 scheduling by a co~nmunication control unit 246
described below.
[0046]
(2) Network Communication Unit
The network communication unit 220 is a communication module for
30 co~nmunicationb etween the small cell base station 200 and a control node, such as
the cooperation manager 100 etc. The network co~~~municatiuonni t 220 may
include a radio communication module which may be shared by the radio
colnmunication unit 210, or a wired comnlunicatio~i module, such as a LANconnected
terminal etc.
[0047]
5 (3) Storage Unit
The storage unit 230 stores a program and data for operating the stnail cell
base station 200, using a storage medium, such as a hard disk, a semiconductor
tnemory, etc. For example, when the access type of a small cell operated by the
small cell base station 200 is the closed access type, the storage unit 230 previously
10 stores a list of identification infonuation of user terminals which accept connection.
The storage unit 230 may also store scheduling information of a ll~acroc ell (and a
neighboring small cell) provided from the cooperation manager 100.
[0048]
The control unit 240 corresponds to a processor, such as a CPU, a DSP, etc.
15 The contsol unit 240 executes a progratn stored in the storage unit 230 or another
storage medium to cause the small cell base station 200 to perform various functions.
In this embodiment, the control unit 240 it~cludest hee functional n~odules,i .e., a
setting unit 242, a lneasurement unit 244, and a comn~unicatioct~on trol unit 246.
[0049]
20 (4-1) Setting Unit
The setting unit 242 sets up a radio communications service operated by the
stnall cell base station 200. For example, the setting unit 242, when the small cell
base station 200 has been installed in a macro cell, searcl~cs for a cooperation
tnanager 100, and transmits small cell-related information to the detected cooperation
26 manager 100. The stnall cell-related il~fortnation1 11ay, for example, include access
type infornlation indicating the access type of the small cell. When the access type
of the stnall cell is the closed access type, the colnrnunication control unit 246
described below reduces interferellce on a nlacro cell tern~inal under the control of
the cooperation manager 100.
30 [0050]
(4-2) Measuretnent Unit
The measurement unit 244 performs sensi~lgo n an uplink signal from a user
terminal around a small cell. The measuremellt unit 244 tnay voluntarily perform
sensing after the initial setup of a small cell has bee11 completed by the setting unit
242. Instead, the measure~nent unit 244 may perfornl sensing in response to a
5 request from the cooperation mauager 100. Also, the measurement unit 244 may
request a small cell tenninal connected to the small cell base station 200 to perfornl
sensing in addition to (or instead of) performing sensing on its own. The result of
sensing is collected and transmitted by the measurement unit 244 to the cooperation
manager 100.
10 [0051]
The measureme~lut nit 244 continues to perfornl sensing on an uplink signal
from a user terminal around a small cell even after the interference control of the
cooperation manager 100 has begun. Sensing for detecting movement of a macro
cell terminal which has already been identified as a target to be protected may be
15 perfor~ned o~lly at a resource location(s) recommended (narrowed) by the
cooperation manager 100. On the other hand, sensing for detecting appearance of a
new tnacro cell terminal which should be protected may be performed at a relatively
low frequency, within a wider target range of resource locations.
[0052]
20 (4-3) Conmunication Control Unit
The cotnmunication control unit 246 controls radio colllmunication between
the small cell base station 200 and a snlall cell terminal. For example, the
comnlunication control unit 246 broadcasts a synclu.onization signal for cell search
and synchronization, and system information, in accorda~lce with a setting by the
25 setting unit 242. The communication control unit 246 also allocates a resource
block on a data channel to each small cell terminal. Thereaftel; the cotnmunication
control unit 246 causes the radio communication unit 210 to receive an uplink signal
and transmit a downlink signal in accordance with the allocation. When the access
type of a stnall cell is the closed access type, the comtnunication control unit 246
30 accepts or rejects access from a user terminal using a previously stored list of user
ter~l~inals.
[0053]
The cotn~nunicationc ontrol unit 246, when receiving an interference control
signal from the cooperation manager 100, reduces interference on a macro cell
terminal in accordance with the received interference control signal. For example,
5 the interference control signal includes scheduling infornlation indicating radio
resources allocated to a macro cell ternlinal which should be protected. In this case,
the communication control unit 246 allocates, to a small cell ternlinal, radio
resources \vl~ich are different from those indicated by the scheduling information.
Such a simple resource separation scheme can appropriately protect a macro cell
10 ternlinal which may be interfered with by the small cell even wllen the small cell
base station 200 does not detect the identification info~nlation, location, etc, of a
macro cell terminal. When radio resources used in a neighboring small cell are also
indicated in the scheduling information, the communication control unit 246 nlay
remove the radio resources from those to be allocated.
15 [0054]
Also, mrllen the cooperation manager 100 requests the cotnmunication
control unit 246 to accept connection (i.e., a handover) of a specific macro cell
terminal to a cell to which the communication control unit 246 belongs, the
communication control unit 246 adds the macro cell te~minalto a list of allowable
20 user terminals. As a result, the macro cell terminal is allowed to be handed over
fio~na macro cell to a s~nallc ell (a cell to which the small cell base station 200
belongs). Note that the communication control unit 246 may reject a handover
acceptance request fiom the cooperation nlanager 100 when some condition (e.g.,
conditions related to a quality requirement, a location, a device type, etc.) is not
25 satisfied.
[OOS5]
<4. Flow of Process>
[4-1. Process of Entire Systern]
(1) First Example
30 FIG. 8A is a sequence diagram sl~owinga first example general flow of a
comnlunicatio~l control process according to this embodiment. In the
cotnmunication control process of FIG. 8A, the cooperation manager 100, the small
cell base station 200, a small cell terminal (UE), and a macro cell base station (eNB)
are i~ivolved.
[0056]
5 Initially, the cooperation manager 100 exchanges information with one or
more macro cell base stations periodically or as requested (step S100). Here, the
exchanged information may include scheduli~~ingf ormation of a macro cell.
[0057]
Next, when the small cell base station 200 is installed in any macro cell, an
10 initial setup procedure is performed between the small cell base station 200 and the
cooperation manager 100 (step S120). In the initial setup procedure, the setting unit
242 of the small cell base station 200 transmits small cell-related information which
may include access type information to the cooperation manager 100 (step SIZO).
[00.58]
15 In the exanlple of FIG, SA, next, a sensing request is transmitted f?om the
cooperatiot~m anager 100 to the small cell base station 200 (step S12.5). In response
to this, the small cell base station 200 (and a small cell terminal) performs sensing on
an uplink signal from a user tenninal around a small cell (step S130). Thereafter,
the measurexilent unit 244 of the sniall cell base station 200 reports the result of the
20 sensing to the cooperation manager 100 (step S135).
[0059]
Next, the determination unit 132 of the cooperation manager 100 determines
whether the access type of a small cell operated by the small cell base station 200 is
the closed access type or the open access type (step S140). Also, the identiiication
25 unit 134, when it is detertilined that tlie access type is the closed access type, checks
the xepol-ted sensing result against scheduling information provided from a macro
cell base station, to identify a macro cell terminal which should be protected (step
S150). Thereafter, the interference control unit 136 determines details of a control
for reducing interference from a small cell on tlie identified macro cell terminal (step
30 Sl6O). Note that an illterference control process of the cooperation manager 100
corresponding to steps S140 to Sl6O described here will be described in greater
detail below.
[0060]
Next, the cooperation manager 100 transmits an interference control signal
to the small cell base station 200 in accordance with the details of the control
5 determined in step S160 (step S170). Here, the transmitted interference control
signal may, for example, include scheduling information or a handover acceptance
request for a macro cell terminal which should be protected. Moreover, the
cooperation manager 100 may transmit, to the small cell base station 200,
reconitnended sensing information indicating the location of resources on which the
10 small cell base station 200 should perform serising (step S180).
[0061]
Thereafter, data is co~nlnunicated between the small cell base station 200
and one or more small cell ternlinals under the co~ltrool f the co~nmutlicationc ontrol
unit 246 of the small cell base station 200, and continual sensing is performed (step
15 S190).
[0062]
(2) Second Example
FIG. 8B is a sequence diagram showing a second example general flow of a
colnmunication control process according to this embodiment.
20 100631
Initially, the cooperation manager 100 exchanges infortnation with one or
more tmacro cell base stations periodically or as requested (step S100). Here, the
exchanged information may include scheduliag information of a macro cell.
[0064]
25 Next, when the small cell base station 200 is iristallcd in any lnacro cell, the
s~nalcl ell base station 200 detects a sy~lchonizationc ha~lnefl iom a nlacro cell base
station, and synchronizes with the macro cell (step S110). Thereaftel; the small cell
base station 200 (and a s~nallc ell ternlinal) perfor~nss ensing on an uplink signal
from a user terminal around a small cell (step S115). Here, if an uplink signal
30 exceeding a predeter~nined signal level is detected, the small cell base station 200
recognizes the ~iecessitpo f an interference control.
[0065]
Next, an initial setup procedure is perfomled between the small cell base
station 200 and the cooperation lnanager 100 (step S120). In the initial setup
procedure, the setting unit 242 of the small cell base station 200 transmits small cell-
5 related infornlation which nlay include access type infortnation to the cooperation
manager 100. Also, the measurement unit 244 of the small cell base station 200
reports the result of tlie sensing to tlie cooperation manager 100 (step S135).
[0066]
The subsequent process is similar to that of tlie first example of FIG. 8A and
10 will not be described. Note that, in any of the first and seeorid exanlples, tlie
identification of a macro cell terminal which should be protected in step S150 may
be performed by a macro cell base station instead of the cooperation manager 100.
[0067]
[4-2. Co~nnlunicationC ontrol Process of Cooperation Manager]
15 FIG. 9 is a flowc11a1-t showing an example flow of the interference control
process performed by the cooperation manager 100 of this embodiment.
[0068]
Referring to FIG. 9, initiallj: the deter~ninationu nit 132 determines whether
tlie access type of a small cell operated by the s~nall cell base station 200 is the
20 closed access type or the open access type (step S140). Here, if the access type of
the small cell is the open access type, a macro cell ternlinal can be handed over to tlie
snlall cell at any time, and therefore, the subsequent interference control process is
skipped.
[0069]
25 If the access type of the small cell is the closed access type, the
identification unit 134 obtains the result of sensing on an uplink signal, from the
small cell base station 200 (step S145). Thereafter, the identification unit 134
checks the obtained sensing result against the past scheduling inforniation of a macro
cell to identify a macro cell terminal which should be protected (step S150).
30 [0070]
Next, the interference control unit 136 determines whether or not sufficient
con~municationo pportunities can be provided to tlie small cell even if the scheduling
by the snlall cell is limited in order to protect a tnacro cell terminal (step S16O). For
example, when the number of macro cell terminals which should be protected
exceeds a predeternlined threshold, or when the proportion of resource blocks
5 consunled by a tnacro cell terniinal(s) which should be protected exceeds a
predetermined threshold, it may be determined that sufficient comnlunication
oppo~tunities cannot be provided to the small cell. The interference control unit
136, when detemiining that sufficient comlnunication oppo~tunitiesc an be provided
to the small cell, transmits scheduling information indicating a resource location at
10 which scheduling is limited to the small cell base station 200 (step S162). On the
other hand, the interference control unit 136, when determining that sufficient
communication opportunities cannot be provided to the small cell, requests tlie small
cell base station 200 to accept a handover of a macro cell terminal (step S164).
[0071]
15 [4-3. Example of Control Result]
FIG. 10 is a diagram for describing an example result of the process
described in this section which is performed after the situation illustrated in FIG. 1.
Referring to FIG 10, small cells 14a, 14b, and 14c which are operated by small cell
base stations 16a, 16b, and 16c, respectively, are shown again. Here, it is assumed
20 that tlie access types of the small cells 14a and 14c are the closed access type, and the
access type of tlie small cell 14b is the open access type. A closed circle in FIG. 10
is a macro cell terminal which is protected by a resource separation scheme.
LO0721
For the small cell 14a, the tilacso cell terminal 12a is identified as a terminal
25 which should be protected. Therefore, the snlall cell base station 16a allocates radio
resources different fiom those allocated to the macro cell terminal 12a to a small cell
ternlinal in the snlall cell 14a. As a result, there is not a macro cell terminal which
suffers fiom interference exceeding the allowable level from the small cell 14a.
[0073]
30 For the stnall cell 14b, the tei~nirials 12b and 12c which are connected to a
macro cell in the example of FIG. I is handed over to the sslnall cell 14b. Also, tlie
transmission power of the small cell base station 16B increases rather than decreases,
and the coverage of the small cell 14b slightly expands. As a result, there is not a
macro cell terminal which suffers from interference exceeding the allo\vable level
from the small cell 14b.
5 100741
For the small cell 14c, the terminals 12e and 12f which are connected to a
macro cell in the example of FIG. 1 are handed over to the small cell 14c. This is
because the small cell base station 16c approves a handover acceptance request from
the cooperation manager 100. On the other hand, the macro cell terminals 12d and
10 12g are identified as a terminal which should be protected. Therefore, the snlall cell
base station 16c allocates radio resources different from those allocated to the macro
cell terminal 12d or 12g to a small cell tenninal in the small cell 14c. As a result,
there is not a macro cell terminal which suffers from interference exceeding the
allowable level from the small cell 14c.
15 [0075]
Such an interference control can effectively reduce interference between a
macro cell and a small cell without impairing the overall communication capacity of
the system.
100761
20 15. Sunmla~y>
In the foregoing, enlbodiments of the technology of the present disclosure
have been described in detail with reference to FIGS. 1 to 10. According to the
above etl~bodiments, a cooperation manager determines the access type of a small
cell. Thereafter, wllen the access type is the closed access type, a macro cell
25 terminal which is likely to suffer from interference caused by a radio signal from a
small cell is identified, and the iuterference on the identified macro cell terminal is
reduced by a small cell base station. Thus, by limiting a small cell on which the
interference control is to be performed based on the access type, an unnecessary
reduction in the conullunication capacity of a snlall cell as a result of the interference
30 control can be avoided.
100771
Also, accordi~~tgo the above emboditnents, a macro cell terminal which
should be protected is identified by checking the result of sensing on an uplink sig~lal
from a user terminal around a s~nalcl ell against scheduli~igin formation of a macro
cell. With such a technique, even if a cooperation manager and a small cell base
5 station have not detected the location of each tenninal, a macro cell terminal which
should be protected can be appropriately identified. In this case, it is not necessary
to signal locatio~d~at a or calculate a parametel; such as a distance etc., in order to
identify a macro cell terminal which should be protected, and therefore, an overl~ead
for the interference control process is redaced, resulting in a reductio~in~ t he load on
10 the system.
[0078]
Also, according to the above embodiments, even if a small cell is of the
closed access type, connection of the small cell to a new terminal may be accepted,
depending on the number of macro cell terminals which should be protected or the
15 proportion of radio resources used by the terminals. Therefore, by positively
utilizing the functionality of a small cell supple~ne~~tota al macro cell, the overall
communication capacity of the system can be maintained while substantially
reducing adverse interference.
[0079]
20 Also, according to the above embodimettts, resource locations at which
collti~lual sensing should be perfortued in a small cell are :enaxowed based on
information which is sent from a cooperation manager. Therefore, the
con~munication capacity of a small cell can be prevented from decreasing due to
execution of sensing.
25 [0080]
Note that a series of co~ltropl rocesses performed by the devices described
herein may be in~plen~enteuds ing any of software, hardware, and a cornbinatio~o~f
software and hardware. A program included it1 software is, for example, previously
stored in each device or a storage medium externally provided. Thereafter, each
30 program is, for example, read into a RAM during execution, and executed by a
processor, such as a CPU etc.
[OOSl]
The preferred embodiments of the present invention have been described
above with reference to the accompanying drawings, whilst the present invention is
not limited to the above exatnples, of course. A person skilled in the art tnay find
5 various alterations and nlodifications within the scope of the appended claitns, and it
should be understood that they will naturally colne under the teclnlical scope of the
present invention.
[0082]
Additionally, the present technology may also be configured as below,
10 (1)
A cotnmunication control device including:
a determination unit which deternlines whether an access type of a small
cell which at least partially overlaps a macro cell of a radio communication system is
a closed access type or an open access type;
15 an identification unit which, when it is determined that the access type of
the small cell is the closed access type, identifies a user ternlinal of the macro cell
~vllichs l~ouldb e protected from interference caused by a radio signal from the small
cell; and
an interference control unit which transmits an interference control signal to
20 a base station of the small cell so that the interference on the user ternlinal identified
by the identification unit is reduced.
(2)
The communication control device according to (I), wherein
the identification unit identifies the user terminal of the tnacro cell which
25 should be protected, based on a result of sensing received from the base station of the
small cell, the result of sensing being related to an uplink signal from a user terminal
around the small cell.
(3)
The co~mlunicationc ontrol device according to (1) or (2), wherein
30 the interference control unit transmits scheduling information of the macro
cell to the base station of the s~nallc ell so that radio resources different from radio
resources allocated to the user terminal which should be protected are used in the
small cell.
(4)
The communication control device according to any one of (1) to (3),
5 wherein
the interference control unit requests the base station of the small cell to
accept connection to the small cell of at least one user terminal, depending on a
number of user terminals which should be protected or a propol-tion of radio
resources used by the user terminals.
10 (5)
The con~municationc ontrol device according to (2), \vherein
the interference control unit informs the base station of the small cell of a
resource location to which the user terminal which should bc protected tra~lsnlitst he
uplink signal.
15 (6)
The communication control device according to (5), wherein
the uplink signal includes an acknowledge signal with respect to a downlink
signal.
(7)
20 The co~unlunicationc ontrol device according to (5),w herein
the uplink signal includes an authet~tication signal which is used when the
user terminal which should be protected utilizes a broadcast service.
(8)
The con~n~unicatioconn trol device according to (2),w herein
25 the identification unit checks scheduling information of the macro cell
against the result of sensing to ideutify the user terminal of the macro cell ~vhich
should be protected.
(9)
A co~llnlunicationc ontrol method including:
30 deternlining whether an access type of a small cell which at least paltially
overlaps a macro cell of a radio colllnlunication system is a closed access type or an
open access type;
when it is determined that the access type of the small cell is the closed
access type, identifying a user ter~llinal of the macro cell which should be protected
from interference caused by a radio signal fro111 the small cell; and
5 transmitting an interference control signal to a base station of the small cell
so that the interference on the identified user terminal is reduced.
(10)
A base station of a small cell of a closed access type, the base station
including:
10 a control unit which
wl~e~lenth e s~ilallc ell at least partially overlaps a macro cell of a
radio communication system, i~iforms a control node which controls interference
between the macro cell and the small cell that an access type of the base station is the
closed access type, and
15 controls cornnlunication in the small cell in accordance with an
interference control signal transmitted from the control node in response to the
informing to reduce interference on a user terminal of the macro cell which should be
protected from interference caused by a radio signal from the small cell.
(11)
20 A comtnunication control method perfomled by a base station of a slllall cell
of a closed access type, the tllethod including:
when the small cell at least partially overlaps a macro cell of a radio
communication system, i~ifor~ninag control node which controls interference
between the macro cell and the small cell that an access type of the base station is the
25 closed access type, and
controlli~lg co~~ullunicationin the small cell in accordance with an
interference control signal transmitted from the control node in response to the
informing to reduce interference on a user terminal of the macro cell m~llichs hould be
protected from interference caused by a radio signal from the small cell.
30
Reference Signs List
[0083]
10 macro cell
11 macro cell base station
14a to 14c small cell
5 16ato16c small cell base station
100 cooperation manager (comtu~unicatiocno ntrol device)
132 determination unit
134 identificatior~u nit
136 interference control unit
10 200 small cell base station

CLAIMS
Claim 1
A cornm~~llicaticoo~nlt rol device co~nprising:
a deternlination unit which determines \vhetlier an access type of a small
5 cell which at least partially overlaps a macro cell of a radio conmunication system is
a closed access type or an open access type;
an identification unit which, when it is determined that the access type of
the s~nall cell is the closed access type, identifies a user terminal of the macro cell
which should be protected from interference caused by a radio signal from the small
10 cell; and
an interference control unit which transmits at1 interference control signal to
a base station of the small cell so that the interference on the user terminal identified
by tlie identification unit is reduced.
15 Claim 2
The conmunication control device according to claim 1, wherein
the identification unit identifies the user terminal of the macro cell which
should be protected, based on a result of sensing received from the base station of the
small cell, the result of sensing being related to an uplink signal from a user terminal
20 around the small cell.
Claim 3
The cotnmunication control device according to claim 1, wherein
the interference control unit tralismits scheduling information of the macro
25 cell to the base station of the sslnall cell so that radio resources different fio~n radio
resources allocated to the user tenninal \vhich should be protected are used in the
small cell.
Claim 4
30 The connnunication control device according to claiin 1, wherein
the interference control unit requests the base station of tlie small cell to
accept colmectiori to the slliall cell of at least one user temiitial, depending on a
number of user terminals which should be protected or a proportion of radio
resources used by tlie user terminals.
5 Clailil 5
The communication control device according to claitn 2, m41erein
the interference control unit informs the base station of the small cell of a
resource location to which the user terminal which should be protected transmits tlie
uplink signal.
10
Claim 6
The commnunication corltrol device accordillg to claim 5, wherein
the upli~lks ignal i~lcludesa n acknowledge signal with respect to a downlink
signal.
15
Claim 7
The communication coiitrol device according to claim 5, wherein
tlie uplink signal includes an authentication signal which is used when the
user terminal which should be protected utilizes a broadcast sewice.
20
Claim 8
The comnlutiication control device according to claim 2, wherein
tlie identification unit checks scheduling informatiori of the macro cell
against the result of sensing to identify the user ternlinal of the macro cell which
25 should be protected.
Claim 9
A communication control method co~liprising:
deterlniniiig whether an access type of a small cell \vliich at least partially
30 overlaps a macro cell of a radio co1n1llunicatio1i systelil is a closed access type or an
open access type;
when it is determined that the access type of the small cell is the closed '
access type, identifying a user terminal of the macro cell which should be protected
fiom interference caused by a radio signal from the small cell; and
transmitting an interference control signal to a base station of the small cell
5' so that the interference 011 the identified user terminal is reduced.
Claim 10
A base station of a small cell of a closed access type, the base station
comprising:
10 a control unit which
when the small cell at least partially overlaps a macro cell of a
radio communication system, informs a control node which co~ltrols interference
between the macro cell and the small cell that an access type of the base station is the
closed access type, and
15 controls communication in the small cell in accordance with an
interference control signal transmitted from tte control node in response to the
informing to reduce interference on a user termidal of the macro cell which should be
protected from interference caused by a radio signal from the small cell.
20 Claim 11
A commul~icationc ontrol method performed by a base station of a small cell
of a closed access type, the method comprising:
when the small cell at least partially overlaps a macro cell of a radio
communication system, informing a control node which controls interference
25 between the macro cell and the small cell that an access type of the base station is the
closed access type, and
controlling colnmunication in the small cell in accordance with an
interference control signal transmitted from the corrtrol node in response to the
informing to reduce interference on a user terminal of the macro cell which should be
30 protected from interference caused by a radio signal from the small cell.