SP353224WO00 1/74
Description
Title of Invention
COMMUNICATION CONTROL APPARATUS, COMMUNICATION CONTROL
5 METHOD, RADIO COMMUNICATION SYSTEM AND TERMINAL
APPARATUS
Technical Field
[0001]
10 The present disclosure relates to a communication control apparatus, a
communication control method, a radio communication system and a terminal apparatus.
Background Art
15 [0002]
A traffic amount handled in cellular communication sei^vice such as third generation mobile phone service has rapidly increased under encouragement of introduction of a higli speed packet communication protocol such as high speed packet access (HSPA), or the like. A user now can download large data such as
20 music data and video streaming data from a network via cellular communication service. Long term evolution (LTE) which has been put into practical use in recent years is high speed cellular communication semce also referred to as 3.9 generation mobile phone service. In the LTE, for example, by using orthogonal frequency division muUiple access (OFDMA) in downlink, a peak data rate of 100 Mbps or
25 higher can be realized. In the fourth generation mobile phone service which is to be put into practical use in around 2015, it is expected that a data rate of 1 Gbps at a maximum can be realized in a semi-fixed enviromnent, and 100 Mbps at a maximum can be realized in a mobile environment. [0003]
30 However, such development of cellular communication service does not
catch up with increase of data traffic, and there still remains a risk of local

SP353224WO00 2/74
degradation of a data rate and occurrence of a network failure due to increase of system load. One measure against such a risk is introduction of a small cell. The small cell which is, for example, disposed so as to cover a hot spot where traffic is concentrated, can be used to complement radio communication service of a macro 5 cell or provide specific semce. A network formed by disposing a plurality of different types of cells such as macro cells and small cells in an overlapped manner is also referred to as a heterogeneous network. Patent Literature 1 discloses a technique of resting a small cell base station when there is no terminal in the vicinit>^ and activating a resting small cell when there is a terminal in the vicinity for the 10 purpose of saving power in the heterogeneous network.
Citation List
Patent Literature
[0004]
15 Patent Literature 1: JP2011-91748A
Summaiy of Invention Technical Problem [0005]
20 However, with a method in which an operation mode of a small cell base
station is passively controlled depending on presence of a terminal in the vicinity, it is difficult to say that sufficient power saving is achieved. For example, in a situation where load of a macro cell is not verj' high, if a small cell base station is made to operate in an active mode while a very few terminal exists in the vicinity, it
25 is not efficient in terms of power consumption of the whole system. [0006]
Therefore, it is desirable to realize a mechanism which enables further power saving in a heterogeneous network.
30 Solution to Problem [0007]

SP353224WO00 3/74
According to the present disclosure, there is provided a coininunication control apparatus including: a radio communication unit configured to provide second radio communication sei^vice within a cell in which a first base station provides first radio communication sen'ice; and a control unit configured to, when an 5 operation mode of the radio communication unit is made to transition from a first mode to a second mode in which power is less consumed than in the first mode, switch the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted from the radio communication unit. [0008]
10 According to the present disclosure, there is provided a communication
control method including: providing second radio communication service by a second base station within a cell in which a first base station provides first radio communication service; and switching, when an operation mode of the second base station is made to transition fi*om a first mode to a second mode in which power is
15 less consumed than in the fii'st mode, the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted fi'om the second base station. [0009]
According to the present disclosure, there is provided a radio
20 communication system including: a first base station configured to provide first radio communication semee; and a second base station including a radio communication unit configured to provide second radio communication sei^vice within a cell of the first radio communication service, and a control unit configured to, when an operation mode of the radio communication unit is made to transition from a first
25 mode to a second mode in which power is less consumed than in the first mode, switch the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmhted from the radio communication unit. [0010]
According to the present disclosure, there is provided a terminal apparatus
30 including: a radio communication unit configured to utilize second radio communication service provided by a second base station within a cell in which a

SP353224WO00
4/74
first base station provides first radio communication service; and a control unit configured to switch a connection destination of the radio communication unit from the second base station to another base station while transmission power of a reference signal received by the radio communication unit is reduced stepwisely in 5 the process in which an operation mode of the second base station transitions from a first mode to a second mode in which power is less consumed than in the first mode. [0011]
According to the present disclosure, there is provided a communication control apparatus including: a radio communication unit configured to provide first
10 radio communication service within a cell; and a control unit configured to, when an operation mode of a second base station which provides second radio communication service within the cell is made to transition from a first mode to a second mode in which power is less consumed than in the first mode, made the second base station switch the operation mode to the second mode after stepwisely reducing transmission
15 power of a reference signal to be transmitted fi*om the second base station.
Advantageous Effects of Invention [0012]
According to the present disclosure, it is possible to realize fiaither power 20 saving in a heterogeneous network.
It should be noted that the above-described advantageous effect is not
necessarily limited, and any advantageous effect described in the present
specification or other advantageous effects which can be understood from the present
specification may be provided in addition to the above-described advantageous effect
25 or in place of the above-described advantageous effect.
Brief Description of Drawings [0013]
[FIG. lA] FIG. lA is a first explanatory diagram for explaining outline of a radio 30 communication system to which a technique according to the present disclosure is applied.

SP353224WO00 5/74
[FIG. IB] FIG. IB is a second explanatory diagram for explaining outline of a radio
communication system to which a technique according to the present disclosure is
applied.
[FIG. IC] FIG. IC is a third explanatoiy diagram for explaining outline of a radio 5 communication system to which a technique according to the present disclosure is
applied.
[FIG. 2] FIG. 2 is a block diagram illustrating an example of a configuration of a
macro cell base station according to a first embodiment.
[FIG. 3A] FIG. 3A is a block diagram illustrating a first example of a detailed 10 configuration of a load monitoring unit illustrated in FIG. 2.
[FIG. 3B] FIG. 3B is a block diagram illustrating a second example of a detailed
configuration of a load monitoring unit illustrated in FIG. 2.
[FIG. 3C] FIG. 30 is a block diagram illustrating a third example of a detailed
configuration of a load monitoring unit illustrated in FIG. 2. 15 [FIG. 4A] FIG. 4A is an explanatory diagram for explaining a first example of
transition between operation modes of a small cell base station.
[FIG. 4B] FIG. 4B is an explanatory diagram for explaining a second example of
transition between operation modes of a small cell base station.
[FIG. 4C] FIG 4C is an explanatory diagram for explaining a third example of 20 transition between operation modes of a small cell base station.
[FIG 4D] FIG. 4D is an explanatory diagram for explaining a fourth example of
transition between operation modes of a small cell base station.
[FIG. 5] FIG. 5 is a block diagram illustrating an example of a configuration of a
small cell base station according to the first embodiment. 25 [FIG. 6A] FIG. 6A is a flowchart illustrating an example of flow in first scenario of
communication control processing executed by a macro cell base station according to
the first embodiment.
[FIG 6B] FIG. 6B is a flowchart illustrating an example of flow in second scenario of
communication control processing executed by a macro cell base station according to 30 the first embodiment.
[FIG. 7A] FIG. 7A is a flowchart illustrating an example of flow in first scenario of

SP353224WO00 6/74
communication control processing executed by the small cell base station according
to the first embodiment.
[FIG. 7B] FIG. 7B is a flowchart illiTStrating an example of flow in second scenario of
communication control processing executed by the small cell base station according 5 to the first embodiment.
[FIG 8A] FIG. 8A is a flowchart illustrating an example of detailed flow of
processing for transition to an operation mode in which power is less consumed in
the first scenario.
[FIG. 8B] FIG. 8B is a flowchart ilhistrating an example of detailed flow of 10 processing for transition to an operation mode in which power is less consumed in
the second scenario.
[FIG. 9] FIG 9 is a block diagi'am illustrating an example of a configuration of a
macro cell base station according to a second embodiment.
[FIG. lOA] FIG. lOA is a block diagram illustrating a first example of a detailed 15 configuration of an information managing unit illustrated in FIG. 9.
[FIG. lOB] FIG. 1 OB is a block diagram illustrating a second example of a detailed
configumtion of an information managing unit illustrated in FIG. 9.
[FIG. IOC] FIG. IOC is a block diagram illustrating a third example of a detailed
configuration of an information managing unit illustrated in FIG. 9. 20 [FIG. 11] FIG. 11 is a block diagram illustrating an example of a configuration of a
small cell base station according to the second embodiment.
[FIG. 12A] FIG. 12A is a block diagram illustrating a first example of a detailed
configuration of an operation mode setting unit illustrated in FIG. 11.
[FIG. 12B] FIG 12B is a block diagi-am illustrating a second example of a detailed 25 configuration of an operation mode setting unit illustrated in FIG 11.
[FIG. 12C] FIG. 12C is a block diagram illustrating a third example of a detailed
configuration of an operation mode setting unit illustrated in FIG 11.
[FIG. 13] FIG. 13 is a flowchart illustrating an example of flow of communication
control processing executed by the macro cell base station according to the second 30 embodiment.
[FIG. 14A] FIG. 14A is a flowchart illustrating an example of flow in first scenario of

SP353224WO00 7/74
communication control processing executed by the small cell base station according to the second embodiment.
[FIG. 14B] FIG. 14B is a flowchart illustrating an example of flow in second scenario of communication control processing executed by the small cell base station 5 according to the second embodiment.
[FIG. 15] FIG. 15 is a block diagram illustrating a first example of a schematic configuration of an eNB.
[FIG. 16] FIG. 16 is a block diagram illustrating a second example of a schematic configuration of an eNB. 10 [FIG 17] FIG. 17 is a block diagram illustrating an example of a schematic configuration of a smailphone.
[FIG. 18] FIG. 18 is a block diagram illustrating an example of a schematic configuration of a car navigation apparatus.
15 Description of Embodiments
[0014]
Hereinafter, (a) preferred embodiment(s) of the present disclosure will be described in detail with reference to the appended drawings. In this specification and the drawings, elements that have substantially the same function and stmcture 20 are denoted with the same reference signs, and repeated explanation is omitted. [0015]
Further, explanation will be provided in the following order.
1. Outline of system
2. First embodiment
25 2-1. Configuration example of macro cell base station
2-2. Configuration example of small cell base station
2-3. Configuration example of terminal apparatus
2-4. Processing flow (macro cell base station)
2-5. Processing flow (small cell base station)
30 3. Second embodiment
3-1. Configuration example of macro cell base station

SP353224WO00 8/74
3-2. Configuration example of small cell base station
3-3. Configuration example of terminal apparatus
3-4. Processing flow (macro cell base station)
3-5. Processing flow (small cell base station)
5 4. Application example
5. Conclusion [0016] <1. Outline of system>
FIG. lA to FIG. IC are explanatoiy diagrams for explaining outline of a 10 radio communication system 1 to which a technique according to the present disclosure is applied. Referring to FIG. lA, the radio communication system 1 includes a macro cell base station 10, small cell base stations 20b and 20c, and terminal apparatuses 30a, 30b and 30c. It should be noted that the number of macro cell base stations, the number of small cell base stations and the number of terminal 15 apparatuses included in the radio communication system 1 are not limited to the example of FIG. lA. For example, the radio communication system 1 may include two or more macro cell base stations. [0017]
The macro cell base station 10 is a base station which provides first radio 20 communication service within a macro cell 11. The macro cell base station 10 can operate the macro cell 11 by utilizing, for example, a fi'equency channel legally permitted or authorized. The macro cell base station 10 may operate the macro cell 11 using a frequency division duplex (FDD) or may operate the macro cell 11 using a time division duplex (TDD). The terminal apparatuses located within the macro 25 cell 11 can be connected to the macro cell base station 10. In the example of FIG. lA, thi'ee terminal apparatuses 30a are connected to the macro cell base station 10. [0018]
The small cell base stations 20b and 20c are base stations which
respectively provide second radio communication service within the macro cell 11.
30 In the present specification, the small cell is concept including a femto cell, a nano
cell, a pico cell, a micro cell, or the like. The second radio conmiunication service

SP353224WO00 9/74
may be radio communication sei-vice which, for example, increases capacity of the first radio communication service at a hot spot, and which is substantially equal to the first radio communication sei^vice,. Alternatively, the second radio communication service may be radio communication service different from the first 5 radio communication service (for example, in terms of a frequency band to be used, a radio access technique, a provider, or the like). The second radio communication service may be pro^'ided by secondarily utilizing a frequency channel for the first radio communication service. The terminal apparatuses located within a small cell 21b can be comiected to the small cell base station 20c. In the example of FIG. lA,
10 two teiminal apparatuses 30b are connected to the small cell base station 20b, and three terminal apparatuses 30c are connected to the small cell base station 20c. [0019]
It should be noted that in the present specification, when it is not necessaiy to distinguish between the small cell base stations 20b and 20c, a letter of the
15 alphabet at the end of the reference numeral will be omitted, and they are collectively referred to as a small cell base station 20. The same applies to other components such as the small cells 21b and 21c (which will be referred to as a small cell 21), and the terminal apparatuses 30a, 30b and 30c (which will be referred to as a terminal apparatus 30).
20 [0020]
The small cell base station 20 is connected to the macro cell base station 10 via a backhaul link. The backhaul link may be a wired link or a radio link. The macro cell base station 10 is connected to a core network 5. The core network 5 includes a plurality of control nodes respectively having roles such as management
25 of user information, management of mobility of terminals, transfer of packets and a gateway. The small cell base station 20 may be also comiected to the core network 5. It should be noted that the small cell base station 20 may be connected to the core network 5 and the macro cell base station 10 via the Internet 7. [0021]
30 In some embodiments, the small cell base station 20 can operate at least in a
first mode and in a second mode in which power is less consumed than in the first

SP353224WO00 10/74
mode. In the simplest example, the first mode is an active mode. The second mode is an idle mode. In the active mode, the small cell base station 20 continuously supplies power to hardware of the small cell base station 20 including a radio communication circuit and a control circuit, so that the whole small cell base 5 station 20 is powered "on". In the idle mode, the small cell base station 20 intermittently supplies power to at least the radio coimnunication circuit, so that a radio communication function of the small cell base station 20 is powered "off' while power is not supplied. The second mode may be a sleep mode. In the sleep mode, the small cell base station 20 intermittently supplies power to the radio
10 communication circuit and the control circuit, so that various functions of the small ceil base station 20 including the radio communication function are powered "off' while power is not supplied. In the example of FIG. lA, the small cell base stations 20b and 20c both operate in the active mode. [0022]
15 It should be noted that the technique according to the present disclosure can
be applied to combination of operation modes other than the modes described herein. For example, in the idle mode or the sleep mode, any function block may be powered "on" or "ofP'. Further, for example, when the small cell base station 20 operates using an LTE-Advanced (LTE-A) scheme, the small cell base station 20 can provide
20 high rate radio communication service on an integrated channel formed by integrating a plurality of component carriers (CCs). As will be described later, the operation mode may support the number of CCs in such a carrier aggregation technique. For example, the first mode may be an operation mode in which more CCs are used than in the second mode. Further, as will be described later, there can
25 be a terminal apparatus which has both ftmctionality of a mobile station and ftmctionalit)' of a small cell base station (or a radio access point). Such a terminal apparatus operates as the small cell base station (or the radio access point) in one operation mode (hereinafter, referred to as a base station mode), and operates only as a mobile station in the other operation mode (hereinafter, referred to as a terminal
30 mode). The above-described first mode and second mode may respectively coiTespond to the base station mode and terminal mode.

SP353224WO00 11/74
[0023]
In a situation in FIG. lA, for example, when the operation mode of the small cell base station 20b suddenly transitions to the idle mode or the sleep mode, the terminal apparatus 30b cannot perform communication due to absence of a serving 5 base station until connection to another base station (for example, the macro cell base station 10) is completed. To avoid such a situation, according to the existing method, the small cell base station 20 is allowed to transition to the idle mode or the sleep mode only when there remains no terminal connected to the small cell base station 20. Referring to FIG. IB, as a result of the terminal apparatus 30b located in
10 the vicinity of the small cell base station 20b moving away or being powered off, no terminal connected to the small cell base station 20b exists. The operation of the small cell base station 20b thus transitions to the idle mode. [0024]
However, with a method of passively controlling the operation mode of the
15 small cell base station 20 depending on presence of a terminal in the vicinity, it is difficult to say that sufficient power saving is achieved. In the example of FIG. IB, only one terminal apparatus 30a is connected to the macro cell base station 10. Therefore, at this time, only low load falling below the capacity is applied to the macro cell base station 10. It is not efficient to keep the small cell base station 20c
20 in the active mode under such a situation, in teims of power consumption of the whole system. [0025]
In embodiments which will be described later, when it is determined that load of first radio communication sei"vice provided by the macro cell base station 10
25 is low, the operation mode of the small cell base station 20 is made to transition to the idle mode or the sleep mode even when there is a terminal coimected to the small cell base station 20. The small cell base station 20 reduces transmission power stepwisely before the operation mode transitions so as to avoid the terminal being connected from being unable to perform communication. By this means, the
30 terminal located in the vicinity of the small cell base station 20 can switch a comiection destination to another base station through execution of handover, or cell

SP353224WO00 12/74
selection or cell reselection. Referring to FIG. IC, the terminal apparatus 30c located in the vicinity of the small cell base station 20c is comiected to the macro cell base station 10, and the operation mode of the small cell base station 20c transitions to the idle mode. As a result of the operation modes of the small cell base stations 5 20b and 20c both transitioning to the idle mode in the radio communication system 1 in this manner, power consumed in the whole system can be largely reduced. Two illustrative embodiments for realizing such a mechanism will be described in detail in the following sections. [0026]
10 <2. First embodiment>
In the first embodiment described in this section, the macro cell base station 10 monitors load of the first radio communication semce and determines necessity of change of the operation mode. The small cell base station 20 makes the operation mode of the small cell bases station 20 transition among a plurality of
15 modes according to an instruction from the macro cell base station 10. [0027]
[2-1. Configuration example of macro cell base station] FIG. 2 is a block diagram illustrating an example of a configuration of the macro cell base station 10 according to the first embodiment. Referring to FIG. 2,
20 the macro cell base station 10 includes a radio communication unit 110, a network communication unit 120, a storage unit 130 and a control unit 140. [0028]
(1) Radio communication unit
The radio communication unit 110 provides the first radio communication
25 service to the terminal apparatus 30 located within the macro cell 11. For example, the radio communication unit 110 transmits a reference signal (also referred to as a beacon signal, a pilot signal or a synchronization signal) on a downlink channel. The reference signal is searched by the terminal apparatus 30 during procedure of cell selection or cell reselection. Further, the terminal apparatus 30 derives
30 communication quality for each cell which becomes a base of handover determination bj' executing measurement for the reference signal. The radio

SP353224WO00 13/74
communication unit 110 establishes a radio bearer (or a radio access bearer) for each of the terminal apparatuses 30 connected to the macro cell base station 10. The radio bearer receives uplink traffic from the terminal apparatus 30 on an uplink channel and transmits downlink traffic to the terminal apparatus 30 on the downlink 5 channel. [0029]
(2) Network communication unit
The network communication unit 120 relays communication between the
macro cell base station 10, and a control node whhin the core network 5, another
10 macro cell base station and the small cell base station 20. As an example, when the
macro cell base station 10 operates using an LTE scheme or an LTE-A scheme, the
network communication unit 120 establishes a communication link respectively
referred to as an Sl-U interface and an Sl-MME interface between a serving-
gateway (S-GW) within the core network 5 and mobility management entity (MME).
15 Further, the network communication unit 120 establishes a communication link
referred to as an X2 interface with another macro cell base station. Still further, the
net\vork communication unit 120 establishes the above-described backliaul link with
the small cell base station 20 which operates within the macro cell 11.
[0030]
20 (3) Storage unit
The storage unit 130 stores a program and data for operation of the macro cell base station 10 using a storage medium such as a hard disc and a semiconductor memory. The data stored in the storage unit 130 can include, for example, an index of load for the first radio communication service which will be described later and a 25 set of thi-esholds to be compared with the load. [0031]
(4) Control unit
The control unit 140 controls the whole operation of the macro cell base
station 10 using a processor such as a central processing unit (CPU) and a digital
30 signal processor (DSP). In the present embodiment, the control unit 140 includes a
communication control unit 142, a load monitoring unit 144 and a small cell control

SP353224WO00 14/74
unit 146. [0032]
(4-1) Communication control unit
The communication control unit 142 controls provision of the first radio 5 communication service. For example, the communication control unit 142 transfers uplink data traffic received by the radio communication unit 110 from the network communication unit 120 to the core network 5 or another macro cell base station or the small cell base station 20 according to the address. Further, the communication control unit 142 transmits downlink data traffic received from other nodes by the
10 network communication unit 120 from the radio communication unit 110 to the terminal apparatus 30 to which the downlink data traffic is addressed. Further, the communication control unit 142 performs control so that the radio communication unit 110 receives a report (for example, a measurement report or a channel quality indicator (CQI)) indicating downlink communication quality measured by the
15 terminal apparatus 30. Further, the communication control unit 142 performs control so that the radio communication unit 110 measures uplink communication quality. [0033]
(4-2) Load monitoring unit
20 The load monitoring unit 144 monitors load of the first radio
communication service provided by the macro cell base station 10. The load monitoring unit 144 then determines whether the load of the first radio communication service satisfies conditions defined in advance for transition of the operation mode of the small cell base station 20. Determination of the conditions is
25 typically executed periodically. Determination of the conditions may be separately performed for each of partial regions included in the macro cell 11. Here, thi*ee methods for monitoring the load of the first radio conmiunication service will be described using FIG. 3A to FIG. 3C. [0034]
30 (4-2-1) First method
FIG. 3A is a block diagram illustrating a first example of a detailed

SP353224WO00 15/74
configuration of the load monitoring unit 144 illustrated in FIG. 2. Referring to FIG.
3A, the load monitoring unit 144 has a traffic amount calculating unit 151, a
threshold setting unit 152 and a determining unit 153.
[0035]
5 The traffic amount calculating unit 151 calculates amounts of uplink traffic
and downlink traffic processed by the radio communication unit 110 for each time window. A length of the time window may be defined in advance, for example, in terms of a slot, a subfi'ame or a radio frame. The calculated traffic amount may be a total value, a time average, a moving average or a maximum value. The traffic
10 amount calculating unit 151 typically normalizes the latest calculation result of the ti'affic amount at a maximum value corresponding to the capacity of the macro cell 11 and outputs the normalized traffic amount to the determining unit 153. [0036]
The thieshold setting unit 152 sets a threshold constituting the determination
15 conditions for determimng the load of the first radio communication service at the determining unit 153. The thieshold setting unit 152 may set a fixed thieshold. Alternatively, the threshold setting unit 152 may set a thi'eshold designated by a control message received fi*om other nodes (for example, a control node within the core network 5) via the network communication unit 120 at the determining unit 153.
20 When the traffic amount is normalized as described above, a thi-eshold to be compared with the normalized traffic amount falls within a range fi*om 0 to 1. A first thi'eshold to be compared with the traffic amount of the first radio communication sei-vice for switching from the first mode (for example, the active mode) to the second mode (for example, the idle mode) may be a value lower than a
25 second threshold for switching fi*om the second mode to the first mode. As an example, when the first thi*eshold is 0.4 (40% of the maximum value of the capacity) and an offset between tlu'csholds is 0.1, the second thi*eshold is 0.5 (50% of the maximum value of the capacity). With such hysteresis control, it is possible to avoid a risk that the operation mode is excessively frequently switched between the
30 two modes when the value of the traffic amount is close to the threshold. [0037]

SP353224WO00 16/74
The determining unit 153 determines whether the determination conditions for transition of the operation mode of the small cell base station 20 by comparing the traffic amount inputted from the traffic amount calculating unit 151 with the tlii'cshold set by the tlu'eshold setting unit 152. For example, the determining unit 5 153 can determine whether the latest traffic amount of the macro cell 11 falls below a first thi'eshold to determine whether to make the operation mode of the small cell base station 20 transition to the second mode in which power is less consumed in the case where the small cell base station 20 operates in the first mode. When the latest traffic amount falls below the first threshold, because the load of the first radio
10 communication service is sufficiently low, it is possible to reduce power consumption of the whole system by making the operation mode of the small cell base station 20 transition to the second mode. Further, the determining unit 153 can determine whether the latest traffic amount of the macro cell 11 exceeds a second threshold to determine whether to make the operation mode of the small cell base
15 station 20 transition to the first mode in the case where the small cell base station 20 operates in the second mode. When the latest traffic amount exceeds the second thi'eshold, because the load of the first radio communication service is considerably high, it is possible to distribute the load (partially off-loads traffic) by making the operation mode of the small cell base station 20 transition to the first mode. When
20 determining that the determination conditions are satisfied, the determination unit 153 outputs the determination result to the small cell conti'ol unit 146. [0038]
(4-2-2) Second method
FIG. 3B is a block diagram illustrating a second example of a detailed
25 configuration of the load monitoring unit 144 illustrated in FIG. 2. Referring to FIG. 3B, the load monitoring unit 144 has a bearer number calculating unit 154, a thi-eshold setting unit 155 and a determining unit 156. [0039]
The bearer number calculating unit 154 calculates the number of active
30 radio bearers established by the radio communication unit 110 for each time windo\\'. A length of the time window may be defined in advance, for example, in terms of a

SP353224WO00
17/74
slot, a subframe or a radio frame. The calculated number of bearers may be a time average, a moving average or a maximum value in each time window. The bearer number calculating unit 154 typically normalizes the latest calculation result of the number of radio bearers with a maximum value corresponding to the capacity of the 5 macro cell 11 and outputs the normalized number of bearers to the determining unit 156. It should be noted that the number of radio bearers practically becomes larger when the number of terminals being connected to the macro cell base station 10 is larger. Therefore, in place of the number of radio bearers, it is also possible to use the number of terminals being connected.
10 [0040]
The threshold setting unit 155 sets a threshold constituting determination conditions for determining the load of the first radio communication service at the determining unit 156. The threshold setting unit 155 may set a fixed threshold. Alternatively, the threshold setting unit 155 may set a thi'eshold designated by a
15 control message received from other nodes via the network communication unit 120 at the determining unit 156. When the number of radio bearers is normalized as described above, a threshold to be compared with the normalized number of radio bearers falls within a range from 0 to 1. A first tlii'eshold to be compared with the number of radio bearers of the first radio communication service for switching fi'om
20 the first mode (for example, the active mode) to the second mode (for example, the idle mode) may be a value lower than a second threshold for switching fi-om the second mode to the first mode. [0041]
The determining unit 156 determines whether the determination conditions
25 for transition of the operation mode of the small cell base station 20 by comparing the number of radio bearers inputted from the bearer number calculating unit 154 with the thi-eshold set by the thi'eshold setting unit 155. For example, the determining unit 156 can determine whether the latest number of radio bearers of the macro cell 11 falls below a first thi-eshold to determine whether to make the
30 operation mode of the small cell base station 20 transition to the second mode in which power is less consumed in the case where the small cell base station 20

SP353224WO00 18/74
operates in the first mode. When the latest number of radio bearers falls below the first threshold, because the load of the first radio communication service is sufficiently low, it is possible to reduce power consumption of the whole system by making the operation mode of the small cell base station 20 transition to the second 5 mode. Further, the determining unit 156 can deteiinine whether the latest numbrt of radio bearers of the macro cell 11 exceeds a second tlii-eshold to determine whether to make the operation mode of the small cell base station 20 transition to the first mode in the case where the small cell base station 20 operates in the second mode. When the latest number of radio bearers exceeds the second threshold, because the
10 load of the first radio communication semce is considerably high, it is possible to disti'ibute the load by making the operation mode of the small cell base station 20 transition to the first mode. When determining that the determination conditions are satisfied, the determination unit 156 outputs the determination result to the small cell control unit 146.
15 [0042]
(4-2-3) Third method
FIG. 3C is a block diagram illustrating a third example of a detailed configuration of the load monitoring unit 144 illustrated in FIG. 2. Referring to FIG. 3C, the load monitoring unit 144 has a CQI acquiring unit 157 and a determining unit
20 158. [0043]
The CQI acquiring unit 157 acquires a measurement result of communication quality measured in the first radio communication service fi'om the radio communication unit 110. The measurement result of the communication
25 quality acquired by the CQI acquiring unit 157 may be, for example, a CQI. When the communication quality indicated by the CQI is more favorable, the radio communication unit 110 can perform coimnunication with the terminal using a higher-order modulation scheme at a higher coding rate (as an example, in the LTE scheme, 16 types of values of the CQI are defined). Therefore, when an average
30 value of CQIs reported fi'om one or more terminals within a certain area is sufficiently high, excessive load is less likely to be applied to the first radio

SP353224WO00 19/74
communication service even when the small cell base station 20 is not utilized in the area. The CQI acquiring unit 157, for example, calculates the communication quality indicated by the CQIs reported from the terminals for each time window. A length of the time window may be defined in advance, for example, in terms of a slot, 5 a subframe or a radio frame. The calculated communication quality may be an average value in each time window. The CQI acquiring unit 157 outputs the calculated value of the communication quality or the acquired CQI itself to the determining unit 158. [0044]
10 The determining unit 158 determines whether the determination conditions
for making the operation mode of the small cell base station 20 transition are satisfied based on an index relating to the communication quality inputted from the CQI acquiring unit 157. For example, the determining unit 158 can determine whether the inputted communication quality exceeds a predetermined threshold to
15 determine whether to make the operation mode of the small cell base station 20 transition to the second mode in which power is less consumed in the case where the small cell base station 20 operates in the first mode. The determining unit 158 may compare the number or a ratio of terminals which experience poor communication quality with a thi'eshold. Wlien the determination conditions based on such
20 communication quality are satisfied, the determining unit 158 can determine whether to make the operation mode of the small cell base station 20 transition to the second mode. Meanwhile, in the case where the small cell base station 20 operates in the second mode, the determining unit 158 can determine that the operation mode of the small cell base station 20 should be made to transition to the first mode when the
25 inputted communication quality falls below a predetermined threshold or the number or a ratio of terminals which experience poor communication quality exceeds a predetermined threshold. When determining that the determination conditions are satisfied, the determining unit 158 outputs the determination result to the small cell control unit 146.
30 [0045]
(4-3) Small cell control unit

SP353224WO00 20/74
The small cell control unit 146 controls operation of one or more small cell base stations 20 located witliin the macro cell 11. For example, the small cell control unit 146 controls an operation mode of each of the small cell base stations 20 based on the load of the first radio communication sendee monitored by the load 5 monitoring unit 144. The small cell control unit 146 may dynamically control the operation mode of each of the small cell base stations 20, for example, in units of an arbiti'ary time period such as a slot, a subframe and a radio frame. Further, the small cell control unit 146 can control transmission power of each of the small cell base stations 20. For example, the small cell control unit 146 can stepwisely reduce
10 transmission power of the reference signal to be transmitted from the small cell base station 20 when making the operation mode of the small cell base station 20 transition from the first mode to the second mode in which power is less consumed than in the first mode. [0046]
15 FIG. 4A to FIG. 4D respectively illustrate examples of transition between the
operation modes of the small cell base station 20. In the first example illustrated in FIG. 4A, the small cell base station 20 can operate in the active mode Mil and the idle mode M12. While, in the active mode Mil, the whole circuit of the small cell base station 20 continuously operates, because, in the idle mode M12, at least a
20 circuit for radio communication of the small cell base station 20 intermittently operates, power consumption in the idle mode M12 is smaller than that in the active mode Mil. When the operation mode of the small cell base station 20 ti'ansitions from the active mode Mil to the idle mode Ml2 (thick arrow in the figure), the small cell base station 20 stepwisely reduces transmission power of the reference
25 signal to be transmitted from the small cell base station 20 to enable smooth handover of terminals being coimected to the small cell base station 20, cell selection or cell reselection. Meanwhile, when the operation mode of the small cell base station 20 transitions from the idle mode M12 to the active mode Mil (thin arrow in the figure), the small cell base station 20 may increase transmission power of the
30 reference signal in a non-stepwise mamier (until a setting value aimed in one step). [0047]

SP353224WO00 21/74
In the second example illustrated in FIG. 4B, the small cell base station 20 can operate in the active mode Mil, the idle mode M12 and the sleep mode M13. In the sleep mode Ml3, because a circuit for control as well as a circuit for radio communication intermittently operate, power consumption in the sleep mode Ml 3 is 5 lower than that in the active mode Mil and the idle mode M12. When the operation mode of the small cell base station 20 transitions from the active mode Mil to the idle mode M12 or the sleep mode M13 (thick arrow in the figure), the small cell base station 20 stepwisely reduces transmission power of the reference signal to be transmitted from the small cell base station 20 to enable smooth
10 handover of terminals being connected to the small cell base station 20, cell selection or cell reselection. [0048]
In the third example illustrated in FIG. 4C, Ncc means the number of component carriers constituting an integrated channel formed by the small cell base
15 station 20. Ncc may be an arbitrary integer of one or greater. The small cell base station 20 can operate in a high aggi'egation mode M21 with greater Ncc and a low aggregation mode M22 with smaller Ncc- While, in the high aggregation mode M21, a radio signal is transmitted over a wider frequency band, because, in the low aggregation mode M22, a radio signal is transmitted over a narrower frequency band,
20 power consumption in the low aggregation mode M22 is smaller than that in the high aggregation mode M21. When the operation mode of the small cell base station 20 transitions from the high aggregation mode M21 to the low aggregation mode M22 (thick arrow in the figure), the small cell base station 20 stepwisely reduces transmission power of the reference signal of a component carrier to be removed to
25 enable smooth handover of terminals being connected to the small cell base station 20 on the component carrier to be removed, cell selection or cell reselection. Meanwhile, when the operation mode of the small cell base station 20 transitions from the low aggregation mode M22 to the high aggregation mode M21 (thin arrow in the figure), the small cell base station 20 may reduce transmission power of the
30 reference signal of the component carrier to be added in a non-stepwise manner. [0049]

SP353224WO00
22/74
In the fourth example illustrated in FIG. 4D, the small cell base station 20 can operate in the high aggregation mode M21, the low aggregation mode M22 and the idle mode M23. In the idle mode M21, because no component carrier is activated, power consumption in the idle mode M23 is smaller than that in other two 5 operation modes. When the operation mode of the small cell base station 20 transitions from the high aggregation mode M21 to the low aggregation mode M22, the small cell base station 20 stepwisely reduces transmission power of a reference signal of a component carrier to be removed to enable smooth handover of terminals being connected to the small cell base station 20 on the component earner to be
10 removed, cell selection or cell reselection. Further, when the operation mode of the small cell base station 20 transitions from the low aggregation mode M22 to the idle mode M23, the small cell base station 20 stepwisely reduces the transmission power of the reference signal of the component carrier to be removed in a similar manner. [0050]
15 Stepwise reduction of the transmission power of the reference signal from
the small cell base station 20 as described using FIG. 4A to FIG. 4D may be realized through tight transmission power control by the small cell control unit 146. Alternatively, the small cell control unit 146 may provide only a control message giving an instmction of transhion of the operation mode, and the small cell base
20 station 20 receiving the control message may autonomously reduce the transmission power stepwisely. When the control message giving an insti^uction of transmission of the operation mode is generated by the small cell control unit 146, the generated control message is transmitted to a target small cell base station 20 via the network communication unit 120 and the backhaul link.
25 [0051]
[2-2. Configuration example of small cell base station] FIG. 5 is a block diagiam illustrating an example of the configuration of the small cell base station 20 according to the first embodiment. Referring to FIG. 5, the small cell base station 20 includes a radio communication unit 210, a network
30 communication unit 220, a storage unit 230 and a control unit 240. [0052]

SP353224WO00
23/74
(1) Radio communication unit
The radio communication unit 210 provides second radio communication seiTice to the terminal apparatus 30 located within the small cell 21 provided so as to overlap with the macro cell 11. For example, the radio communication unit 210 5 transmits a reference signal on a downlink channel. The reference signal is searched by the terminal apparatus 30 during procedure of cell selection or cell reselection. Further, the terminal apparatus 30 derives communication quality for each cell which becomes a base of handover determination by executing measurement for the reference signal. 10 [0053]
(2) Network communication unit
The network communication unit 220 establishes a backhaul link with the macro cell base station 10 and relays communication between the small cell base station 20 and the macro cell base station 10. 15 [0054]
(3) Storage unit
The storage unit 230 stores a program and data for operation of the small cell base station 20 using a storage medium such as a hard disc and a semiconductor memory. 20 [0055]
(4) Control unit
The control unit 240 controls the whole operation of the small cell base station 20 using a processor such as a CPU and a DSP. In the present embodiment, the control unit 240 includes a communication control unit 242 and an operation
25 mode setting unit 244. [0056]
The communication control unit 242 conti'ols provision of the second radio communication ser\'ice. For example, the coimminication control unit 242 performs control so that uplink data traffic received by the radio conmiunication unit
30 210 is transferred from the network communication unit 220 to the macro cell base station 10 according to the address. Further, the communication control unit 242

SP353224WO00 24/74
performs control so that downlink data- traffic received from other nodes by the network communication unit 220 is transmitted from the radio communication unit 210 to the terminal apparatus 30 to which the downlink data traffic is addressed. Further, the communication control unit 242 performs control so that the radio 5 communication unit 210 receives a report (for example, a measurement report or a CQI report) indicating downlink communication quality measured by the terminal apparatus 30. Further, the communication control unit 242 performs control so that the radio communication unit 210 measures uplink communication quality. [0057]
10 The operation mode setting unit 244 sets an operation mode which can be
selected from a set of the operation modes illustrated in FIG. 4A to FIG. 4D at the small cell base station 20. In the present embodiment, when the network communication unit 220 receives a control message which gives an instruction of transition of the operation mode from the macro cell base station 10, the operation
15 mode setting unit 244 makes the operation mode of the small cell base station 20 transition according to the control message. [0058]
When the operation mode setting unit 244 makes the operation mode of the radio communication unit 210 transition from a first mode to a second mode in
20 which power is less consumed than in the first mode, the communication control unit 242 stepwisely reduces transmission power of a reference signal to be transmitted from the radio communication unit 210. When the second mode is a low aggregation mode as described using FIG. 4C, the reference signal described here may be a reference signal of a component carrier to be removed. The
25 communication control unit 242 then stands by over a predetermined time period every time the transmission power of the reference signal is reduced by one step. A duration of the standby period here may be, for example, a duration corresponding to a transmission cycle corresponding to several times of transmission of the reference signal. During this standby period, the terminal apparatus 30 connected to the
30 second radio communication sen'ice executes handover, cell selection or cell reselection to switch a connection destination from the small cell base station 20 to

SP353224WO00
25/74
another base station (or from a component carrier to be removed to another component earner). The communication control unit 242 confirms tlie number of the terminal apparatuses 30 which utilize the second radio communication service while stepwisely reducing transmission power of the reference signal, and, after the 5 number of the terminal apparatuses 30 becomes 0, the communication control unit 242 switches the operation mode of the radio communication unit 210 to the second mode. Through such procedure, the small cell base station 20 can switch the operation mode to a mode in which power is less consumed without passively waiting until there remains no active terminals being connected, and without making
10 the terminals being connected unable to perform communication. The terminals can sense a situation as if the small cell base station 20 moved away (as if the terminals moved away from the small cell base station 20). Such a mechanism does not depend on whether handover, cell selection or cell reselection is voluntarily executed at a terminal side or controlled at a network side. Therefore, for example,
15 compared to a method in which the small cell base station 20 issues a mandatory handover instruction to the terminal apparatus 30, the above-described mechanism is beneficial. [0059]
Reduction of the transmission power of the reference signal in one step may
20 be a fixed value such as, for example, 5 dB. Alternatively, the reduction may be a value changing depending on an absolute value of the transmission power (for example, when the transmission power falls witliin a range from -20 dBm to 0 dBm, the value may be 5 dB, and, when the transmission power falls within a range from -60 dBm to -20 dBm, the value may be 2 dB). Further, the communication control
25 unit 242 may dynamically set reduction of the transmission power in one step according to a parameter such as, for example, the number of terminals being connected and communication quality. By this means, it is possible to achieve optimal balance between smooth transition of the operation mode and a period required for completing transition of the mode.
30 [0060]
As described above, in the present embodiment, the communication control

SP353224WO00 26/74
unit 242 switches the operation mode according to an instruction included in the control message received from the macro cell base station 10 which monitors the load of the first radio communication service. When the radio communication unit 210 operates in the first mode, and it is determined that the load of the first radio 5 communication service is low, the operation mode is switched to the second mode. When the radio communication unit 210 operates in the second mode, and it is determined that the load of the first radio communication service is high, the operation mode is switched to the first mode. According to this configuration, it is not necessary to transmit an index relating to the load of the first radio
10 communication service from the macro cell base station 10 to the small cell base station 20, so that it is possible to reduce overhead of signaling required for control of the operation mode. Further, because a logic for conditions determination relating to the load of the first radio communication service is only required to be implemented at the macro cell base station 10, it is possible to realize the above-
15 described mechanism at relatively low cost. [0061]
It should be noted that, regardless of the load of the first radio communication service, when it is determined that communication quality measured for the second radio communication service within the small cell 21 can be further
20 reduced, the communication control unit 242 may reduce the transmission power of the reference signal to be transmitted from the radio communication unit 210 without making the operation mode transition. For example, when the communication quality reported fi'om the terminal apparatus 30 cormected to the small cell base station 20 is well above a desired quality level, it can be determined that the
25 communication quality can be fiuther reduced. In such a case, it is possible to reduce power consumed by the small cell base station 20 also by reducing the transmission power of the reference signal. Further, interference between the small cell and a cell in the vicinity can be reduced. [0062]
30 [2-3. Configuration example of terminal apparatus]
After the radio communication unit of the terminal apparatus 30 is powered

SP353224WO00 27/74
on or restored from the idle mode or the sleep mode to the active mode, the radio communication unit selects a cell of a connection destination by executing cell selection procedure. Typically, in the cell selection procedure, all the frequency channels are searched, and identification of a cell and measurement of reception 5 power are performed for each of the detected reference signals. When reception power of a reference signal received from the macro cell base station 10 is the largest, the terminal apparatus 30 utilizes the first radio communication sei^vice provided by the macro cell base station 10. Wlien reception power of a reference signal of the small cell base station 20 is larger than the reception power of the reference signal
10 fi'om the macro cell base station 10, the terminal apparatus 30 utilizes the second radio communication service provided by the small cell base station 20. The terminal apparatus 30 may periodically measure communication quality for the cell of the connection destination and one or more cells in the vicinity and execute cell reselection. Further, when the communication quality which is measured for the
15 cell of the connection destination and one or more cells in the vicinity while the terminal apparatus 30 operates in the active mode satisfies predetermined handover conditions, the terminal apparatus 30 may switch the cell of the connection destination by executing handover procedure. The control unit of the terminal apparatus 30 controls execution of such cell selection, cell reselection and handover.
20 [0063]
Here, it is assumed that the terminal apparatus 30 is currently cormected to the small cell base station 20. In the present embodiment, during process in which the operation mode of the small cell base station 20 transitions from the first mode to the second mode in which power is less consumed than in the first mode,
25 transmission power of the reference signal received by the terminal apparatus 30 is reduced stepwisely. The terminal apparatus 30 continuously measures reception power (and communication quality depending on the reception power) of the reference signal from the small cell base station 20 also while the transmission power is reduced. The terminal apparatus 30 then switches the connection destination of
30 the radio communication unit from the small cell base station 20 which is a current serving base station to another base station at a certain timing (or switches a primary

SP353224WO00 28/74
CC to another CC). During such procedure, the terminal apparatus 30 neither loses
packets, nor is put into a state where communication is impossible.
[0064]
[2-4. Processing flow (macro cell base station)]
5 In this section, an example of processing flow executed by the macro cell
base station 10 in the first embodiment will be described. In first scenario, the small ceil base station 20 can operate in the active mode and the idle mode. In second scenario, the small cell base station 20 can operate in the high aggregation mode, the low aggregation mode, and the idle mode.
10 [0065]
(1) First scenario
FIG. 6A is a flowchart illustrating an example of flow in the first scenario of communication control processing executed by the macro cell base station 10 according to the first embodiment. The communication control processing
15 illustrated in FIG 6A is processing which can be periodically executed for one small cell base station 20. Actually, the communication control processing described here may be executed for each of one or more small cell base stations 20. [0066]
First, the load monitoring unit 144 calculates the latest load of the first radio
20 communication service provided in the macro cell 11 (step SllO). The load of the first radio commutiication service may be calculated in terms of any of a traffic amount, the number of radio bearers, the number of terminals being connected and communication quality. [0067]
25 The processing thereafter branches depending on whether the small cell
base station 20 currently operates in the active mode or in the idle mode (step SI20). When the small cell base station 20 currently operates in the active mode, the load monitoring unit 144 compares the load of the macro cell 11 calculated in step SllO with a first threshold (step S130). When the load of the macro cell 11 falls below
30 the first threshold, the small cell control unit 146 instructs the small cell base station 20 to make the operation mode transition to the idle mode (step S135).

SP353224WO00 29/74
[0068]
When the small cell base station 20 currently operates in the idle mode, the load monitoring unit 144 compares the load of the macro cell 11 calculated in step SllO with a second thi'eshold which is greater than the first tlireshold (step S140). 5 When the load of the macro cell 11 exceeds the second thi'eshold, the small cell control unit 146 instructs the small cell base station 20 to make the operation mode transition to the active mode (step S145). [0069]
(2) Second scenario
10 FIG. 6B is a flowchart illustrating an example of flow in the second scenario
of communication control processing executed by the macro cell base station 10 according to the first embodiment. The communication control processing illush'ated in FIG. 6B is processing which can be periodically executed for one small cell base station 20. Actually, the communication control processing described here
15 may be executed for each of one or more small cell base stations 20. [0070]
First, the load monitoring unit 144 calculates the latest load of the first radio communication service provided in the macro cell 11 (step SllO). The load of the first radio communication sei^vice may be calculated in terms of any of a traffic
20 amount, the number of radio bearers, the number of terminals being connected and communication quality. [0071]
The processing thereafter branches depending on whether the small cell base station 20 currently uses one or more component carriers (step S150). When
25 the small cell base station 20 currently uses one or more component carriers, the load monitoring unit 144 compares the load of the macro cell 11 calculated in step SllO with a first tlireshold corresponding to the number of CCs at that time (step S155). When the load of the macro cell 11 falls below the first tlueshold, the small cell control unit 146 instructs the small cell base station 20 to reduce the number of CCs
30 (remove any CC) (step S160). By this means, the operation mode of the small cell base station 20 transitions fiom the high aggregation mode to the low aggregation

SP353224WO00 30/74
mode, or transitions from the low aggregation mode to the idle mode. It should be
noted that a determination tin'eshold for the former transition may be different from a
determination thi'cshold for the latter transition.
[0072]
5 When the load of the macro cell 11 does not fall below the first thi'eshold,
the load monitoring unit 144 compares the load of the macro cell 11 with a second threshold which is greater than the first thi-eshold (step SI 65). When the load of the macro cell 11 exceeds the second threshold, the small cell control unit 146 instmcts the small cell base station 20 to increase the number of CCs (add a new CC) (step
10 SI75). By this means, the operation mode of the small cell base station 20 transitions from the low aggregation mode to the high aggregation mode. It should be noted that when the small cell base station 20 has already operated in the high aggregation mode, determination in step SI65 may be skipped. [0073]
15 When the small cell base station 20 cunently operates in the idle mode, the
small cell base station 20 does not use any CC. In this case, the load monitoring unit 144 compares the load of the macro cell 11 with a third threshold (step SI40). When the load of the macro cell 11 exceeds the third threshold, the small cell control unit 146 instructs the small cell base station 20 to increase the number of CCs (add a
20 new CC) (step SI75). By this means, the operation mode of the small cell base station 20 transitions from the idle mode to the low aggregation mode or the high aggregation mode. [0074]
[2-5. Processing flow (small cell base station)]
25 In this section, an example of processing flow executed by the small cell
base station 20 in the first embodiment will be described. First scenario and second scenario in this section respectively coirespond to the first scenario and the second scenario in the previous section. [0075]
30 (1) First scenario
FIG. 7A is a flowchart illustrating an example of flow of the first scenario of

SP353224WO00 31/74
communication control processing executed by the small cell base station 20
according to the first embodiment.
[0076]
First, the operation mode setting unit 244 waits for reception of a control 5 message from the macro cell base station 10 (step S210). When the control message giving an instruction to make the operation mode transition is received by the network eomiminication unit 220 fi'om the macro cell base station 10, processing proceeds to step S220. [0077]
10 The processing thereafter branches depending on in which of the active
mode and the idle mode, the small cell base station 20 currently operates (step S220). When the small cell base station 20 currently operates in the active mode, the operation mode setting unit 244 determines whether an instruction to transition to the idle mode is issued by the control message (step S225). When an instruction to
15 transition to the idle mode is issued, the communication control unit 242 stepwisely reduces transmission power of a reference signal to be transmitted from the radio communication unit 210 (step S230). The operation mode setting unit 244 then sets the operation mode of the small cell base station 20 to the idle mode (step S235). [0078]
20 When the small cell base station 20 currently operates in the idle mode, the
operation mode setting unit 244 determines whether an insti'uction to transition to the active mode is issued by the control message (step S240). When an instmetion to transition to the active mode is issued, the operation mode setting unit 244 sets the operation mode of the small cell base station 20 to the active mode (step S245).
25 [0079]
FIG. 8 A is a flowchart illustrating an example of detailed flow of processing corresponding to step S230 in FIG. 7A. [0080]
Referring to FIG. 8A, first, the communication control unit 242 determines
30 whether there is a terminal apparatus 30 which utilizes the second radio communication service in the small cell 21 (step S231). Here, when there is no

SP353224WO00
32/74
terminal apparatus 30 which utilizes the second radio communication service, the
communication control unit 242 reduces transmission power of a reference signal to
be transmitted from the radio communication unit 210 to 0 (step S236).
[0081]
5 When there is a terminal apparatus 30 which utilizes the second radio
communication service, the communication control unit 242 reduces the transmission power of the reference signal to be transmitted from the radio communication unit 210 by one step (step S232). The communication control unit 242 then stands by over a predetermined period to switch the connection destination of the terminal
10 apparatus 30 (step S233). During this period, the terminal apparatus can execute cell selection or cell reselection. Further, when a terminal apparatus 30 which satisfies handover conditions occurs as a result of reduction of the transmission power (step S234), the communication control unit 242 executes handover to a target base station in collaboration with the terminal apparatus 30 (step S235). Handover
15 procedure can include, for example, reception of a measurement report from the terminal apparatus 30, handover determination, transmission of an RRC connection reconfiguration message, and reception of an RRC connection reconfiguration complete message. [0082]
20 Subsequently, the processing returns to step S231, and the above-described
processing is repeated until there remains no terminal apparatus 30 which utilizes the second radio communication service. [0083]
(2) Second scenario
25 FIG. 7B is a flowchart illustrating an example of flow of the second scenario
of communication control processing executed by the small cell base station 20 according to the first embodiment. [0084]
First, the operation mode setting unit 244 waits for reception of a control
30 message from the macro cell base station 10 (step S250). When the control message giving an instruction to change the number of CCs is received by the

SP353224WO00
33/74
network communication unit 220 from the macro cell base station 10, the processing
proceeds to step S255.
[0085]
The processing thereafter branches depending on whether an instruction to 5 reduce the number of CCs is issued or an instruction to increase the number of CCs
is issued (step S255). When an instruction to reduce the number of CCs is issued,
the communication control unit 242 stepwisely reduces transmission power of a
reference signal to be transmitted in a CC to be removed (step S260). The
operation mode setting unit 244 then makes the operation mode of the small cell base 10 station 20 transition from the high aggregation mode to the low aggregation mode, or
transition from the low aggregation mode to the idle mode by removing the CC (step
S265).
[0086]
When an instruction to increase the number of CCs is issued, the operation 15 mode setting unit 244 makes the operation mode of the small cell base station 20
transition from the low aggregation mode to the high aggiegation mode or transition
fi-om the idle mode to the low aggregation mode by adding a new CC (step S270).
[0087]
It should be noted that change of the number of CCs in step S265 and step 20 S270 is, for example, signaled thi'ough transmission of the RRC connection
reconfiguration message from the communication control unit 242 to the terminal
apparatus 30. The RRC connection reconfiguration message can include system
information relating to a component carrier to be removed or to be added.
[0088]
25 FIG. 8B is a flowchart illustrating an example of detailed flow of processing
corresponding to step S260 in FIG. 7B.
[0089]
Referring to FIG. 8B, first, the communication control unit 242 determines
whether there is a terminal apparatus 30 connected to a CC to be removed in the 30 small cell 21 (step S261). Here, when there is no terminal apparatus 30 connected
to a CC to be removed, the communication control unit 242 reduces transmission

SP353224WO00
34/74
power of a reference signal to be transmitted in the CC to 0 (step S266).
[0090]
When there is a terminal apparatus 30 coimected to the CC to be removed,
the communication control unit 242 reduces transmission power of a reference signal 5 to be transmitted in the CC by one step (step S262). The communication control
unit 242 then stands by over a predetermined period to switch the connection
destination of the terminal apparatus 30 (step S263). During this period, the
terminal apparatus 30 can execute cell selection or cell reselection. Further, when a
terminal apparatus 30 which satisfies handover conditions occurs as a result of 10 reduction of the transmission power (step S264), the communication control unit 242
executes handover between CCs or handover to a target base station in collaboration
with the terminal apparatus 30 (step S265).
[0091]
Subsequently, the processing returns to step S261, and the above-described 15 processing is repeated until there remains no terminal apparatus 30 which is
connected to the CC to be removed.
[0092]
<3. Second embodiment>
In the second embodiment described in this section, the macro cell base 20 station 10 provides an index regarding the load of the first radio commimication
sei^vice to the small cell base station 20, and the small cell base station 20 determines
necessity of change of the operation mode.
[0093]
[3-1. Configuration example of macro cell base station]
25 FIG. 9 is a block diagram illustrating an example of a configuration of the
macro cell base station 10 according to the second embodiment. Referring to FIG. 9,
the macro cell base station 10 includes a radio communication unit 110, a network
communication unit 120, a storage unit 130 and a control unit 160.
[0094]
30 The control unit 160 controls the whole operation of the macro cell base
station 10 using a processor such as a CPU and a DSP. In the present embodiment,

SP353224WO00
35/74
the control unit 160 includes a communication control unit 162 and an information
managing unit 166.
[0095]
(1) Communication control unit
5 The conmiunication control unit 162 controls provision of the first radio
coimnunication service. For example, the communication control unit 162 transfers uplink data traffic received by the radio communication unit 110 from the network communication unit 120 to the core network 5 or another macro cell base station or the small cell base station 20 according to the address. Further, the commumcation
10 control unit 162 transmits downlink data traffic received ffom other nodes by the network communication unit 120 from the radio communication unit 110 to the terminal apparatus 30 to which the downlink data traffic is addressed. Further, the communication control unit 162 performs control so that the radio communication unit 110 receives a report (for example, a measurement report or a CQI) indicating
15 downlink communication quality measured by the terminal apparatus 30. Further, the communication control unit 162 performs control so that the radio communication unit 110 measures uplink communication quality. [0096]
(2) Information managing unit
20 The information managing unit 166 manages information to be provided
from the macro cell base station 10 to one or more small cell base stations 20. For example, the information managing unit 166 generates information regarding the load of the first radio communication semee to be provided by the macro cell base station 10 and transmits a control message indicating the generated information to
25 the small cell base station 20 via the network communication unit 120 and the backhaul link. Here, tln-ee methods for generating the information regarding the load of the first radio communication service will be described using FIG. lOA to FIG. IOC. [0097]
30 (2-1) First method
FIG. lOA is a block diagram illustrating a first example of a detailed

SP353224WO00 36/74
configuration of the information managing imit 166 illustrated in FIG. 9. Referring
to FIG. lOA, the information managing unit 166 has a traffic information generating
unit 171 and a signaling imit 172.
[0098]
5 The traffic information generating unit 171 calculates an amount of uplink
traffic and downlink traffic to be processed by the radio communication unit 110 for each time window. A length of the time window may be defined in advance, for example, in terms of a slot, a subfranie or a radio frame. The calculated traffic amount may be a total value of the traffic amount, a time average, a moving average
10 or a maximum value in each time window. The traffic information generating unit 171 typically normalizes the latest calculation result of the traffic amount with a maximum value corresponding to the capacity of the macro cell 11 and outputs an index indicating the normalized traffic amount to the signaling unit 172. [0099]
15 The signaling unit 172 executes signaling with the small cell base station 20.
For example, when the index indicating the traffic amount is inputted from the tiaffic information generating unit 171, the signaling unit 172 generates a conti'ol message indicating the index and transmits the generated control message to the small cell base station 20. The control message may be transmitted in response to a request
20 from the small cell base station 20. [0100]
(2-2) Second method
FIG. lOB is a block diagram illustrating a second example of the detailed configuration of the information managing unit 166 illustrated in FIG. 9. Referring
25 to FIG. lOB, the information managing unit 166 has a bearer information generating unit 174 and a signaling unit 175. [0101]
The bearer information generating unit 174 calculates the number of active radio bearers established by the radio communication unit 110 for each time window.
30 A length of the time window may be defined in advance, for example, in terms of a slot, a subfi'ame or a radio frame. The calculated number of bearers may be a time

SP353224\VO00 37/74
average, a moving average or a maximum value in each time window. The bearer information generating unit 174 typically normalizes the latest calculation result of the number of radio bearers with a maximum valne corresponding to the capacity of the macro ceU 11 and outputs an index indicating the normalized number of bearers 5 to the signaling unit 175. It should be noted that it is also possible to use the number of terminals being connected in place of the number of radio bearers. [0102]
The signaling unit 175 executes signaling with the small cell base station 20. For example, when the index indicating the number of radio bearers is inputted fi*om
10 the bearer information generating unit 174, the signaling unit 175 generates a control message indicating the index and ti'ansmits the generated control message to the small cell base station 20. The control message may be transmitted in response to a request from the small cell base station 20. [0103]
15 (2-3) Third method
FIG IOC is a block diagram illustrating a third example of the detailed configuration of the information managing unit 166 illustrated in FIG. 9. Referring to FIG IOC, the information managing unit 166 has a quality information generating unit 177 and a signaling unit 178.
20 [0104]
The quality information generating unit 177 acquires a measurement result of communication quality measured in the first radio communication service fi'om the radio communication unit 110. For example, the measurement result of the communication quality acquired by the quality information generating unit 177 may
25 be a CQI. The qualit)' information generating unit 177 calculates the communication quality indicated by the CQI reported from the terminal for each time window. A length of the time window may be defined in advance, for example, in terms of a slot, a subfi'ame or a radio fiame. The calculated communication quality may be an average value in each time window. The quality' information generating
30 unit 177 then outputs an index indicating the calculated communication quality or the acquired CQI itself to the signaling unit 178.

SP353224WO00 38/74
[0105]
The signaling unit 178 executes signaling with the small cell base station 20. For example, when the index indicating the conmiunication quality is inputted fi*om the bearer information generating unit 177, the signaling unit 178 generates a control 5 message indicating the index and transmits the generated control message to the small cell base station 20. The control message may be transmitted in response to a request from the small cell base station 20. [0106]
In any example of FIG. lOAto FIG. IOC, the index regarding the load of the 10 first radio communication seivice provided to the small cell base station 20 can be used by the small cell base station 20 to control the operation mode of the small cell base station 20. Also in the present embodiment, the small cell base station 20 may be able to operate in the operation modes as described using FIG. 4A to FIG. 4D or in other arbitrary operation modes. 15 [0107]
[3-2. Configuration example of small cell base station] FIG. 11 is a block diagram illustrating an example of a configuration of the small cell base station 20 according to the second embodiment. Referring to FIG. 11, the small cell base station 20 includes a radio cormnunication unit 210, a network 20 communication unit 220, a storage unit 235 and a control unit 260. [0108]
(1) Storage unit
The storage unit 235 stores a program and data for operation of the small cell base station 20 using a storage medium such as a hard disc and a semiconductor 25 memory. The data stored in the storage unit 235 can include, for example, the index of the load of the first radio communication service received from the macro cell base station 10 and a set of thresholds to be compared with the load. [0109]
(2) Control unit
30 The control unit 260 controls the whole operation of the small cell base
station 20 using a processor such as a CPU and a DSP. In the present embodiment,

SP353224WO00 39/74
the control unit 260 includes a communication control unit 262 and an operation
mode setting unit 264.
[0110]
(2-1) communication control unit
5 The" communication control unit 262 controls provision of the second radio
communication service. For example, the conmiunication control unit 262 performs control so that uplink data traffic recei^'ed by the radio communication unit 210 is ti'ansferred from the network communication unit 220 to the macro cell base station 10 according to the address. Further, the communication control unit 262
10 performs control so that downlink data ti'affic received from other nodes by the network communication unit 220 is transmitted from the radio communication unit 210 to the terminal apparatus 30 to which the downlink data traffic is addressed. Further, the communication control unit 262 performs conti'ol so that the radio communication unit 210 receives a report (for example, a measurement report or a
15 CQI report) indicating downlink communication quality measured by the tenninal apparatus 30. Further, the communication control unit 262 performs control so that the radio communication unit 210 measures uplink communication quality. [0111]
(2-2) Operation mode setting unit
20 The operation mode setting unit 264 sets an operation mode which can be
selected from a set of the operation modes illustrated in FIG. 4A to FIG. 4D at the small cell base station 20. In the present embodiment, the operation mode setting unit 264 makes the operation mode of the small cell base station 20 transition based on the index regarding the load of the first radio communication sei-vice indicated by
25 the control message received from the macro cell base station 10. Here, thi-ee methods for making the operation mode transition based on the index regarding the load of the first radio communication semce will be described using FIG. 12A to FIG. 120. [0112]
30 (2-2-1) First method
FIG. 12A.is a block diagram illustrating a first example of a detailed

SP353224WO00 40/74
configuration of the operation mode setting unit 264 illustrated in FIG 11. Referring to FIG. 12A, the operation mode setting unit 264 has a determining unit 271, a threshold setting unit 272 and a mode setting unit 273. In the first example, the load of the first radio communication service is determined based on the traffic 5 amount of the first radio communication service. [0113]
The determining unit 271 acquires the index indicating the traffic amount included in the control message received from the macro cell base station 10. The determining unit 271 then determines whether determination conditions for making
10 the operation mode of the small cell base station 20 transition are satisfied by comparing the traffic amount indicated by the acquired index with the threshold set by the thi*eshoId setting unit 272. For example, the determining unit 271 can determine whether the latest tiaffic amount of the macro eel! 11 falls below a first threshold to determine whether to make the operation mode of the small cell base
15 station 20 transition to the second mode in which power is less consumed in the case where the small cell base station 20 operates in the first mode. When the latest traffic amount falls below the first threshold, because the load of the first radio communication service is sufficiently low, it is possible to reduce power consumption of the whole system by making the operation mode of the small ceil
20 base station 20 transition to the second mode. Further, the determining unit 271 can determine whether the latest traffic amount of the macro cell 11 exceeds a second threshold to determine whether to make the operation mode of the small cell base station 20 transition to the first mode in the case where the small cell base station 20 operates in the second mode. When the latest traffic amount exceeds the second
25 thi-eshold, because the load of the first radio communication service Is considerably high, it is possible to distribute the load by making the operation mode of the small cell base station 20 transition to the first mode. When determining that the determination conditions are satisfied, the determination unit 271 outputs the determination result to the mode setting unit 273.
30 [0114]
The thi'eshold setting unit 272 sets a threshold constituting the determination

SP353224WO00 41/74
conditions for determining the load of the first radio communication service at the determining unit 271. The tlii*eshold setting iniit 272 may set a fixed threshold. Alternatively, the thi'eshold setting unit 272, for example, may set a thi'eshold designated by a control message received from other nodes (for example, a macro 5 cell base station 10 or a control node within the core network 5) via the network communication unit 220 at the determining unit 271. When the traffic amount is normalized as described above, a tlii'eshold to be compared with the normalized traffic amount falls within a range from 0 to 1. A first threshold to be compared with the traffic amount of the first radio communication sei^vice for switching from
10 the first mode (for example, the active mode) to the second mode (for example, the idle mode) may be a value lower than a second threshold for switching from the second mode to the first mode. With such hysteresis control, it is possible to avoid a risk that the operation mode is excessively frequently switched between the two modes when the value of the traffic amount is close to the threshold.
15 [0115]
The mode setting unit 273 makes the operation mode of the small cell base station 20 transition according to the determination result for the transition of the operation mode inputted from the determining unit 271. Wlien the mode setting unit 273 makes the operation mode of the radio communication unit 210 transition
20 from a first mode to a second mode in which power is less consumed than in the first mode, the communication control unit 262 stepwisely reduces transmission power of a reference signal to be transmitted from the radio communication unit 210. When the second mode is a low aggregation mode as described using FIG. 4C, the reference signal described here may be a reference signal of a component carrier to be removed.
25 The communication control unit 262 then stands by over a predetermined time period every time the transmission power of the reference signal is reduced by one step. A duration of the standby period here may be, for example, a duration corresponding to a transmission cycle corresponding to several times of transmission of the reference signal. During this standby period, the terminal apparatus 30 connected to the
30 second radio conmumication sei-vice executes handover, cell selection or cell reselection to switch a connection destination fi*om the small cell base station 20 to

SP353224WO00
42/74
another base station (or from a component carrier to be removed to another component canier). The communication control unit 262 confirms the number of the terminal apparatuses 30 which utilize the second radio conmiunication sei-vice while stepwisely reducing transmission power of the reference signal, and, after the 5 number of the terminal apparatuses 30 becomes 0, the communication control unit 242 switches the operation mode of the radio communication unit 210 to the second mode. [0116]
(2-2-2) Second method
10 FIG. 12B is a block diagram illustrating a second example of the detailed
configuration of the operation mode setting unit 264 illustrated in FIG. 11. Referring to FIG. 12B, the operation mode setting unit 264 has a determining unit 274, a threshold setting unit 275 and a mode setting unit 273. In the second example, the load of the first radio communication service is determined based on
15 the number of radio bearers in the first radio communication semce. It should be noted that it is also possible to use the number of terminals being coimected in place of the number of radio bearers. [0117]
The determining unit 274 acquires an index indicating the number of bearers
20 included in the control message received from the macro cell base station 10. Subsequenty, the determining unit 274 determines whether the determination conditions for transition of the operation mode of the small cell base station 20 by comparing the number of radio bearers indicated by the acquired index with the thi'eshold set by the threshold setting unit 275. For example, the determining unit
25 274 can determine whether the latest number of radio bearers of the macro cell 11 falls below a first thi'eshold to determine whether to make the operation mode of the small cell base station 20 transition to the second mode in which power is less consumed in the case where the small cell base station 20 operates in the first mode. When the latest number of radio bearers falls below the first thieshold, because the
30 load of the fust radio communication semce is sufficiently low, it is possible to reduce power consumption of the whole system by making the operation mode of the

SP353224WO00 43/74
small cell base station 20 transition to the second mode. Further, the determining unit 274 can determine whether the latest numbrt of radio bearers of the macro cell 11 exceeds a second threshold to determine whether to make the operation mode of the small cell base station 20 transition to the first mode in the case where the small 5 cell base station 20 operates in the second mode. When the latest number of radio bearers exceeds the second threshold, because the load of the first radio communication service is considerably high, it is possible to distribute the load by making the operation mode of the small cell base station 20 transition to the first mode. When determining that the determination conditions are satisfied, the
10 determination unit 274 outputs the determination result to the mode setting unit 273. [0118]
The thi-eshold setting unit 275 sets a thi-eshold constituting determination conditions for determining the load of the first radio communication service at the determining unit 274. The thi-eshoId setting unit 275 may set a fixed thi'eshold.
15 Alternatively, the threshold setting unit 275, for emxaple, may set a threshold designated by a control message received fi*om other nodes via the network communication unit 220 at the determining unit 274. When the number of radio bearers is normalized as described above, a threshold to be compared with the normalized number of radio bearers falls within a range from 0 to 1. A first
20 threshold to be compared with the number of radio bearers of the first radio communication sei'vice for switching from the first mode (for example, the active mode) to the second mode (for example, the idle mode) may be a value lower than a second thieshold for switching fi'om the second mode to the first mode. [0119]
25 (2-2-3) Third method
FIG. 12C is a block diagram illustrating a tliird example of the detailed configuration of the operation mode setting unit 264 illustrated in FIG. 11. Referring to FIG. 12C, the operation mode setting unit 264 has a determining unit 277, a threshold setting unit 278 and a mode setting unit 273. In the third example,
30 the load of the first radio communication service is determined based on the communication quality measured in the first radio communication service.

SP353224WO00 44/74
[0120]
The determining unit 277 acquires an index indicating the communication quality included in the control message received from the macro cell base station 10. The determining unit 277 then determines whether determination conditions for 5 making the operation mode of the small cell base station 20 transition are satisfied by comparing the communication quality indicated by the acquired index with the threshold set by the threshold setting unit 278. For example, when the small cell base station 20 operates in the first mode, the determining unit 277 can determine whether the communication quality of the first radio conmiunication service exceeds
10 a predetermined threshold to determine whether to make the operation mode of the small cell base station 20 transition to the second mode in which power is less consumed. The determining unit 277 may compare the number or a ratio of terminals which experience poor communication quality with the thi*eshold. When the determination conditions based on the communication quality are satisfied, the
15 determining unit 277 can detennine that the operation mode of the small cell base station 20 should be made to transition to the second mode. Meanwhile, when the small cell base station 20 operates in the second mode, the detennining unit 277 can determine that the operation mode of the small cell base station 20 should be made to ti'anshion to the first mode when the communication qualit}' of the first radio
20 communication service falls below a predetermined threshold, or when the number or a ratio of terminals which experience poor communication quality exceeds a predetermined tln'eshold. When determining that the determination conditions are satisfied, the determining unit 277 outputs the determination result to the mode setting unit 273.
25 [0121]
The threshold setting unit 278 sets a tlii'eshoid constituting determination conditions for determining the load of the first radio communication service at the determining unit 277. The thi-eshold setting unit 278 may set a fixed thi'eshold. Alternatively, the threshold setting unit 278, for emxaple, may set a thi'eshold
30 designated by a control message received fi'om other nodes via the network communication unit 220 at the determining unit 277.

SP353224WO00 45/74
[0122]
According to a configuration in which the small cell base station 20 voluntarily determines whether to make the operation mode of the small cell base station 20 transition as in the present embodiment, it is possible to flexibly control 5 the operation mode according to the requirements of individual small cell base stations 20. Further, because it is not necessary to implement a logic for conditions determination for transition of the operation mode at the macro cell base station 10, it is possible to introduce the above-described mechanism to the radio communication system 1 while minimizing impact on the existing system.
10 [0123]
It should be noted that, also in the present embodiment, regardless of the load of the first radio communication service, when it is determined that the communication quality measured for the second radio communication service within the small cell 21 can be further reduced, the communication control unit 262 may
15 reduce the transmission power of the reference signal to be transmitted from the radio communication unit 210 without making the operation mode transition. [0124]
[3-3. Configuration example of terminal apparatus]
The configuration of the terminal apparatus 30 in the present embodiment
20 may be the same as the configuration of the terminal apparatus 30 described in association with the first embodiment. That is, also in the present embodiment, during process in which the operation mode of the small cell base station 20 transitions &om the first mode to the second mode in which power is less consumed than in the first mode, the transmission power of the reference signal received by the
25 terminal apparatus 30 is reduced stepwisely. The terminal apparatus 30 switches the cormection destination of the radio communication unit from the small cell base station 20 which is a current sen'ing base station to another base station (or switches a primary CC to another CC) at a timing during the process. During such procedure, the terminal apparatus 30 neither loses a packet, nor is put into a state where
30 communication is impossible. [0125]

SP353224WO00 46/74
[3-4. Processing flow (macro cell base station)]
In this section, an example of flow of processing executed by the macro cell base station 10 in the second embodiment will be described. The processing executed by the macro cell base station 10 does not depend on types of the operation 5 modes in which the small cell base station 20 can operate. [0126]
FIG. 13 is a flowchart illustrating an example of flow of communication control processing executed by the macro cell base station according to the second embodiment. 10 [0127]
First, the information managing unit 166 calculates the latest load of the first radio communication service provided in the macro cell 11 (step S310). The load of the first radio communication sei-vice may be calculated in terms of any of a traffic amount, the number of radio bearers, the number of terminals being connected and 15 communication quality. [0128]
Next, the information managing unit 166 generates a control message including an index regarding the load of the first radio communication service (step S320). 20 [0129]
The information managing unit 166 then transmits the generated control
message to the small cell base station 20 via the network communication unit 120
and the backhaul link (step S330).
[0130]
25 Subsequently, the processing returns to step S310, and the above-described
processing can be repeated in a fixed cycle. It should be noted that the processing
illustrated in FIG 13 may be at least partially executed in response to a request
received from the small cell base station 20.
[0131]
30 [3-5. Processing flow (small ceil base station)]
In this section, an example of processing flow executed by the small cell

SP353224WO00 47/74
base station 20 in the second embodiment will be described. In first scenario, the small cell base station 20 can operate in the active mode and the idle mode. In second scenario, the small cell base station 20 can operate in the high aggregation mode, the low aggregation mode, and the idle mode. 5 [0132]
(1) First scenario
FIG. 14A is a flowchart illustrating an example of flow in the first scenario of communication control processing executed by the small cell base station 20 according to the second embodiment.
10 [0133]
First, the operation mode setting unit 264 acquires an index regarding the latest load of the first radio communication service provided in the macro cell 11 from the control message received from the macro cell base station 10 (step S410). The load of the first radio communication service may be determined in terms of any
15 of a traffic amount, the number of radio bearers, the number of terminals being connected and communication quality. [0134]
The processing thereafter branches depending on whether the small cell base station 20 currently operates in the active mode or in the idle mode (step S420).
20 When the small cell base station 20 currently operates in the active mode, the operation mode setting unit 264 compares the load of the macro cell 11 indicated by the index acquired in step S410 with a first thi*eshold (step S430). When the load of the macro cell 11 falls below the first tlireshold, the communication control unit 262 stepwisely reduces transmission power of a reference signal to be transmitted from
25 the radio conmiunication unit 210 (step S435). Here, the transmission power may be reduced stepwisely as described using FIG. 8A. The operation mode setting unit 264 then sets the operation mode of the small cell base station 20 to the idle mode (step S437). [0135]
30 When the small cell base station 20 currently operates in the idle mode, the
operation mode setting unit 264 compares the load of the macro cell 11 calculated in

SP353224WO00 48/74
step S410 with a second threshold which is greater than the first threshold (step S440). When the load of the macro cell 11 exceeds the second tlii'eshold, the operation mode setting unit 264 sets the operation mode of the small ceil base station 20 to the active mode (step S445). 5 [0136]
(2) Second scenario
FIG. 14B is a flowchart illustrating an example of flow in the second scenario of communication control processing executed by the small cell base station 20 according to the second embodiment.
10 [0137]
First, the operation mode setting unit 264 acquires an index regarding the latest load of the first radio communication service provided in the macro cell 11 from the control message received from the macro cell base station 10 (step S410). The load of the first radio communication service may be determined in terms of any
15 of a traffic amount, the number of radio bearers, the number of terminals being connected and communication quality. [0138]
The processing thereafter branches depending on whether the small cell base station 20 currently uses one or more component carriers (step S450). When
20 the small cell base station 20 cun*ently uses one or more component carriers, the operation mode setting unit 264 compares the load of the macro cell 11 indicated by the index acquired in step S410 with a first threshold corresponding to the number of CCs at that time (step S455). When the load of the macro cell 11 falls below the first thi'cshold, the conmiunication control unit 262 stepwisely reduces the
25 transmission power of the reference signal to be transmitted in a CC to be removed (step S460). Here, the transmission power may be reduced stepwisely as described using FIG. 8B. The operation mode setting unit 264 then makes the operation mode of the small cell base station 20 transition from the high aggregation mode to the low aggregation mode or transition from the low aggregation mode to the idle mode by
30 removing the CC (step S462). It should be noted that a determination tlir'eshold for the former ti'ansition may be different from a determination thi'eshold for the latter

SP353224WO00 49/74
transition. [0139]
When the load of the macro cell 11 does not fall below the first threshold, the operation mode setting unit 264 compares the load of the macro cell 11 with a 5 second threshold which is greater than the first threshold (step S465). When the load of the macro cell 11 exceeds the second thi'eshold, the operation mode setting unit 264 makes the operation mode of the small cell base station 20 ti-ansition from the low aggi'egation mode to the high aggregation mode by adding a new CC (step S475). It should be noted that when the small cell base station 20 has already
10 operated in the high aggregation mode, determination in step S465 may be skipped. [0140]
Wlien the small cell base station 20 currently operates in the idle mode, the small ceil base station 20 does not use any CC. In this case, the operation mode setting unit 264 compares the load of the macro cell 11 with a third threshold (step
15 S470). When the load of the macro cell 11 exceeds the third thieshold, the operation mode setting unit 264 makes the operation mode of the small cell base station 20 transition fi-om the idle mode to the low aggregation mode or the high aggregation mode by adding a new CC (step S475). [0141]
20 <4. Application example>
The technique according to the present disclosure can be applied to various products. For example, the macro cell base station 10 and the small cell base station 20 can be implemented as evolved node B (eNB) of an LTE scheme or the LTE-A scheme. Alternatively, the macro cell base station 10 and the small cell base
25 station 20 can be implemented as other types of base stations such as Node B or base transceiver station (BTS). The macro cell base station 10 may include a body (also referred to as a base station apparatus) which controls radio communication, and one or more remote radio heads (RRHs) disposed at positions dijRferent from the body. The small cell base station 20 may be implemented as a smaller-scale base station,
30 radio access point or mobile router. [0142]

SP353224WO00 50/74
For example, a terminal apparatus 30 may be realized as a mobile terminal such as a smartphone, a tablet personal computer (PC), a notebook PC, a portable game terminal, a portable/dongle type mobile router, and a digital camera, or an in-vehicle terminal such as a car navigation apparatus. The terminal apparatus 30 may 5 also be realized as a terminal (that is also referred to as a machine type communication (MTC) terminal) that performs machine-to-machine (M2M) conmiunication. Furthermore, the terminal apparatus 30 may be a radio communication module (such as an integrated circuit module including a single die) mounted on each of the terminals. 10 [0143]
[4-1. Application Examples Regarding Base Station] (First Application Example)
FIG. 15 is a block diagram illustrating a fust example of a schematic configuration of an eNB to which the technology of the present disclosure may be 15 applied. An eNB 800 includes one or more antennas 810 and a base station apparatus 820. Each antenna 810 and the base station apparatus 820 may be comiected to each other via an RF cable. [0144]
Each of the antennas 810 includes a single or muhiple antenna elements 20 (such as multiple antemia elements included in an MIMO antenna), and is used for the base station apparatus 820 to transmit and receive radio signals. The eNB 800 may include the muhiple antennas 810, as illustrated in FIG 15. For example, the multiple antennas 810 may be compatible with multiple frequency bands used by the eNB 800. Although FIG. 15 illustrates the example in which the eNB 800 includes 25 the multiple anteimas 810, the eNB 800 may also include a single antenna 810. [0145]
The base station apparatus 820 includes a controller 821, a memory 822, a
network interface 823, and a radio communication interface 825.
[0146]
30 The controller 821 may be, for example, a CPU or a DSP, and operates
various fimctions of a higher layer of the base station apparatus 820. For example,

SP353224WO00 51/74
the controller 821 generates a data packet from data in signals processed by the radio communication interface 825, and transfers the generated packet via the network interface 823. The controller 821 may bundle data from multiple base band processors to generate the bundled packet, and transfer the generated bundled packet. 5 The controller 821 may have logical functions of performing control such as radio resource control, radio bearer control, mobility management, admission control, and scheduling. The control may be performed in corporation with an eNB or a core network node in the vicinity. The memoiy 822 includes RAM and ROM, and stores a program that is executed by the controller 821, and various types of control data
10 (such as a terminal list, transmission power data, and scheduling data). [0147]
The network interface 823 is a communication interface for connecting the base station apparatus 820 to a core network 824. The controller 821 may communicate with a core network node or another cNB via the network interface 823.
15 hi that case, the cNB 800, and the core network node or the other eNB may be connected to eacli other through a logical interface (such as an SI interface and an X2 interface). The network interface 823 may also be a wired communication interface or a radio communication interface for radio backhaul. If the network interface 823 is a radio communication interface, the network interface 823 may use
20 a higher frequency band for radio communication than a frequency band used by the radio communication interface 825. [0148]
The radio communication interface 825 supports any cellular communication scheme such as LTE and LTE-A, and provides radio connection to a
25 terminal positioned in a cell of the eNB 800 via the antenna 810. The radio
communication interface 825 may typically include, for example, a baseband (BB)
processor 826 and an RF circuit 827. The BB processor 826 may perform, for
example, encoding/decoding, modulating/demodulating, and
multiplexing/demultiplexing, and performs various t)'pes of signal processing of
30 layers (such as LI, medium access control (MAC), radio link control (RLC), and a packet data convergence protocol (PDCP)). The BB processor 826 may have a part

SP353224WO00 52/74
or all of the above-described logical functions instead of the controller 821. The BB processor 826 may be a memory that stores a communication control program, or a module that includes a processor and a related circuit configured to execute the program. Updating the program may allow the functions of the BB processor 826 5 to be changed. The module may be a card or a blade that is inserted into a slot of the base station apparatus 820. Alternatively, the module may also be a chip that is mounted on the card or the blade. Meanwhile, the RF circuit 827 may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna 810.
10 [0149]
The radio communication interface 825 may include the multiple BB processors 826, as illustrated in FIG. 15. For example, the multiple BB processors 826 may be compatible with multiple frequency bands used by the eNB 800. The radio communication interface 825 may include the multiple RF circuits 827, as
15 illustiated in FIG. 15. For example, the multiple RF circuits 827 may be compatible with multiple antenna elements. Although FIG. 15 illustrates the example in which the radio communication interface 825 includes the multiple BB processors 826 and the multiple RF circuits 827, the radio communication interface 825 may also include a single BB processor 826 or a single RF circuit 827.
20 [0150]
(Second Application Example)
FIG. 16 is a block diagram illustrating a second example of a schematic configuration of an eNB to which the technology of the present disclosure may be applied. An eNB 830 includes one or more antennas 840, a base station apparatus
25 850, and an RRH 860. Each antenna 840 and the RRH 860 may be connected to each other via an RF cable. The base station apparatus 850 and the RRH 860 may be connected to each other via a high speed line such as an optical fiber cable. [0151]
Each of the antennas 840 includes a single or multiple antenna elements
30 (such as multiple anteima elements included in an MIMO antemia), and is used for the RRH 860 to transmit and receive radio signals. The eNB 830 may include the

SP353224WO00 53/74
mukiple antennas 840, as illustrated in FIG. 16. For example, the multiple antemias 840 may be compatible with multiple frequency bands used by the cNB 830. Although FIG 16 illustrates the example in which the eNB 830 includes the multiple antennas 840, the eNB 830 may also include a single antenna 840. 5 [0152]
The base station apparatus 850 includes a controller 851, a memory 852, a network interface 853, a radio communication interface 855, and a connection interface 857. The controller 851, the memory 852, and the network interface 853 are the same as the controller 821, the memory 822, and the network interface 823
10 described with reference to FIG 15. [0153]
The radio communication interface 855 supports any cellular communication scheme such as LTE and LTE-A, and provides radio communication to a terminal positioned in a sector corresponding to the RRH 860 via the RRH 860
15 and the antenna 840. The radio communication inteiface 855 may typically include, for example, a BB processor 856. The BB processor 856 is the same as the BB processor 826 described with reference to FIG 15, except the BB processor 856 is connected to the RF circuit 864 of the RRH 860 via the connection interface 857. The radio communication interface 855 may include the muhiple BB processors 856,
20 as illustrated in FIG 16. For example, the multiple BB processors 856 may be compatible with multiple frequency bands used by the eNB 830. Although FIG 16 illustrates the example in which the radio communication interface 855 includes the multiple BB processors 856, the radio communication interface 855 may also include a single BB processor 856.
25 [0154]
The connection interface 857 is an interface for connecting the base station apparatus 850 (radio communication interface 855) to the RRH 860. The connection interface 857 may also be a communication module for communication in the above-described high speed line that comiects the base station apparatus 850
30 (radio communication interface 855) to the RRH 860. [0155]

SP353224WO00 54/74
The RRH 860 includes a coimection interface 861 and a radio communication interface 863. [0156]
The connection interface 861 is an interface for connecting the RRH 860 5 (radio communication interface 863) to the base station apparatus 850. The connection interface 861 may also be a communication module for communication in the above-described high speed line. [0157]
The radio comiminication interface 863 transmits and receives radio signals
10 via the antenna 840. The radio communication interface 863 may typically include, for example, the RF circuit 864. The RF circuit 864 may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna 840. The radio communication interface 863 may include multiple RF circuits 864, as illustrated in FIG. 16. For example, the multiple RF circuits 864
15 may support multiple antenna elements. Although FIG 16 illustrates the example in which the radio communication interface 863 includes the multiple RF circuits 864, the radio communication interface 863 may also include a single RF circuit 864. [0158]
In the eNB 800 and the eNB 830, the function relating to small cell control
20 of the macro cell base station 10 described using FIG. 2 and FIG. 9 may be implemented in the radio cormnunication interface 825", the radio conmiunication interface 855 or the radio communication interface 863. Further, the function relating to small cell control of the macro cell base station 10 may be implemented in the controller 821 or the controller 851. For example, when the operation mode of
25 the small cell disposed within a cell of the eNB 800 is made to transition to the idle mode, the controller 821 may stepwisely reduce the transmission power of the reference signal from the small cell. By tliis means, it is possible to actively reduce power consumption of the small cell without making the terminal located in the vicinity of the small cell unable to perform communication.
30 [0159]
Further, in the eNB 800, the function relating to operation mode control of

SP353224WO00 55/74
the small cell base station 20 described using FIG. 5 and FIG. 11 may be implemented in the radio communication interface 825 or maj^ be implemented in the controller 821. For example, when the small cell base station is implemented as the eNB 800, the controller 821 may make the operation mode of the radio 5 communication interface 825 transition to the idle mode after stepwisely reducing the transmission power of the reference signal from the eNB 800. By this means, it is possible to actively reduce power consumption of the eNB 800 without making the terminal located in the vicinity of the eNB 800 unable to perform communication. [0160]
10 [4-2. Application Examples Regarding Terminal Apparatus]
(First Application Example)
FIG. 17 is a block diagram illustrating an example of a schematic configuration of a smartphone 900 to which the technology of the present disclosure may be applied. The smartphone 900 includes a processor 901, a memory 902, a
15 storage 903, an external connection interface 904, a camera 906, a sensor 907, a microphone 908, an input device 909, a display device 910, a speaker 911, a radio coiumunlcation interface 912, one or more antenna switches 915, one or more antennas 916, a bus 917, a battery 918, and an auxiliaiy controller 919. [0161]
20 The processor 901 may be, for example, a CPU or a system on a chip (SoC),
and controls functions of an application layer and another layer of the smartphone 900. The memory 902 includes RAM and ROM, and stores a program that is executed by the processor 901, and data. The storage 903 may include a storage medium such as a semiconductor memory and a hard disk. The external connection
25 interface 904 is an interface for connecting an external device such as a memory card and a universal serial bus (USB) device to the smartphone 900. [0162]
The camera 906 includes an image sensor such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS), and generates a
30 captured image. The sensor 907 may include a group of sensors such as a measurement sensor, a gyro sensor, a geomagnetic sensor, and an acceleration sensor.

SP353224WO00 56/74
The microphone 908 converts sounds that are input to the smartphone 900 to audio signals. The input device 909 includes, for example, a touch sensor configured to detect touch onto a screen of the display device 910, a keypad, a keyboard, a button, or a switch, and receives an operation or an information input from a user. The 5 display device 910 includes a screen such as a liquid crystal display (LCD) and an organic light-emitting diode (OLED) display, and displays an output image of the smartphone 900. The speaker 911 converts audio signals that are output from the smartphone 900 to sounds. [0163]
10 The radio communication interface 912 supports any cellular
communication scheme such as LTE and LTE-Advanced, and performs radio communication. The radio communication interface 912 may typically include, for example, a BB processor 913 and an RF circuit 914. The BB processor 913 may perform, for example, encoding/decoding, modulating/demodulating, and
15 multiplexing/demultiplexing, and perfoitns various types of signal processing for radio communication. Meanwhile, the RF circuit 914 may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna 916. The radio communication interface 912 may also be a one chip module that has the BB processor 913 and the RF circuit 914 integrated thereon.
20 The radio communication interface 912 may include the multiple BB processors 913 and the multiple RF circuits 914, as illusti'ated in FIG. 17. Ahhough FIG 17 illusti'ates the example in which the radio communication interface 912 includes the multiple BB processors 913 and the multiple RF circuits 914, the radio communication interface 912 may also include a single BB processor 913 or a single
25 RF circuit 914. [0164]
Furthermore, in addition to a cellular communication scheme, the radio communication interface 912 may support another type of radio communication scheme such as a short-distance wireless communication scheme, a near field
30 communication scheme, and a radio local area network (LAN) scheme. In that case, the radio communication interface 912 may include the BB processor 913 and the RF

SP353224WO00 57/74
circuit 914 for each radio communication scheme.
[0165]
Each of tlie antenna switches 915 switches connection destinations of the
antennas 916 among multiple circuits (such as circuits for different radio 5 communication schemes) included in the radio communication interface 912.
[0166]
Each of the anteimas 916 includes a single or multiple antenna elements
(such as multiple antenna elements included in an MIMO antenna), and is used for
the radio communication interface 912 to transmit and receive radio signals. The 10 smartphone 900 may include the multiple antennas 916, as iUustrated in FIG. 17.
AUhough FIG. 17 illusti'ates the example in which the smartphone 900 includes the
multiple antennas 916, the smartphone 900 may also include a single antenna 916.
[0167]
Furthermore, the smartphone 900 may include the antenna 916 for each 15 radio communication scheme. In that case, the antenna switches 915 may be
omitted fiom the configuration of the smartphone 900.
[0168]
The bus 917 connects the processor 901, the memory 902, the storage 903,
the external connection interface 904, the camera 906, the sensor 907, the 20 microphone 908, the input device 909, the display device 910, the speaker 911, the
radio communication interface 912, and the auxiliary controller 919 to each other.
The battery 918 supplies power to blocks of the smartphone 900 illustrated in FIG. 17
via feeder lines, which are partially shown as dashed lines in the figure. The
auxiliary controller 919 operates a minimum necessary function of the smartphone 25 900, for example, in a sleep mode.
[0169]
The radio communication interface 912 of the smartphone 900 illustrated in
FIG. 17 may have functions for executing the above-described cell selection, cell
reselection and handover of the terminal apparatus 30. Further, at least part of these 30 ftmctions may be implemented in the processor 901 or the auxiliary controller 919.
For example, by the smartphone 900 performing handover to another base station

SP353224WO00 58/74
while the transmission power of the reference signal from the small cell base station
is reduced stepwisely, it is possible to make the operation mode of the small cell base
station smoothly transition to the idle mode.
[0170]
5 It should be noted that the smartphone 900 may operate as the small cell
base station by the processor 901 executing an access point function. Further, the radio communication interface 913 may have a function as the small cell base station. [0171]
(Second Application Example)
10 FIG. 18 is a block diagram illustrating an example of a schematic
configuration of a car navigation apparatus 920 to which the technology of the present disclosure may be applied. The car navigation apparatus 920 includes a processor 921, a memoiy 922, a global positioning system (GPS) module 924, a sensor 925, a data interface 926, a content player 927, a storage medium interface
15 928, an input device 929, a display device 930, a speaker 931, a radio communication interface 933, one or more antenna switches 936, one or more antennas 937, and a battery 938. [0172]
The processor 921 may be, for example, a CPU or a SoC, and controls a
20 navigation function and another function of the car navigation apparatus 920. The memory 922 includes RAM and ROM, and stores a program that is executed by the processor 921, and data. [0173]
The GPS module 924 uses GPS signals received from a GPS satellite to
25 measure a position (such as latitude, longitude, and altitude) of the car navigation apparatus 920. The sensor 925 may include a group of sensors such as a gyro sensor, a geomagnetic sensor, and an air pressure sensor. The data interface 926 is coimected to, for example, an in-vehicle network 941 via a terminal that is not shown, and acquires data generated by the vehicle, such as vehicle speed data.
30 [0174]
The content player 927 reproduces content stored in a storage medium (such

SP353224WO00 59/74
as a CD and a DVD) that is inserted into the storage medium interface 928. The input device 929 includes, for example, a touch sensor configured to detect touch onto a screen of the display device 930, a button, or a switch, and receives an operation or an information input from a user. The display device 930 includes a 5 screen such as a LCD or an OLED display, and displays an image of the navigation function or content that is reproduced. The speaker 931 outputs sounds of the navigation function or tlie content that is reproduced. [0175]
The radio communication interface 933 supports any cellular
10 communication scheme such as LET and LTE-A, and performs radio communication.
The radio communication interface 933 may typically include, for example, a BB
processor 934 and an RF circuit 935. The BB processor 934 may perform, for
example, encoding/decoding, modulating/demodulating, and
multiplexing/demultiplexing, and performs various types of signal processing for
15 radio communication. Meanwhile, the RF circuit 935 may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna 937. The radio communication interface 933 may be a one chip module having the BB processor 934 and the RF circuit 935 integrated thereon. The radio communication interface 933 may include the multiple BB processors 934 and the
20 multiple RF circuits 935, as illustrated in FIG. 18. Although FIG. 18 illustrates the example in which the radio communication interface 933 includes the multiple BB processors 934 and the multiple RF circuits 935, the radio communication interface 933 may also include a single BB processor 934 or a single RF circuit 935. [0176]
25 Furthermore, in addition to a cellular communication scheme, the radio
communication interface 933 may support another type of radio communication scheme such as a short-distance wireless communication scheme, a near field communication scheme, and a radio LAN scheme. In that case, the radio communication interface 933 may include the BB processor 934 and the RF circuit
30 935 for each radio communication scheme. [0177]

SP353224WO00 60/74
Each of the antenna switches 936 switches connection destinations of the
antennas 937 among multiple circuits (such as circuits for different radio
communication schemes) included in the radio communication interface 933.
[0178]
5 Each of the antennas 937 includes a single or multiple antenna elements
(such as muUiple antenna elements included in an MIMO antenna), and is used for the radio communication interface 933 to transmit and receive radio signals. The car navigation apparatus 920 may include the multiple antennas 937, as illustrated in FIG. 18. Although FIG. 18 illustrates the example in which the car navigation
10 apparatus 920 includes the multiple antennas 937, the car navigation apparatus 920 may also include a single antenna 937. [0179]
Furthermore, the car navigation apparatus 920 may include the antenna 937 for each radio communication scheme. In that case, the anteima switches 936 may
15 be omitted from the configuration of the car navigation apparatus 920. [0180]
The batteiy 938 supplies power to blocks of the car navigation apparatus 920 illustrated in FIG. 18 via feeder lines that are partially shown as dashed lines in the figure. The battery 938 accumulates power supplied form the vehicle.
20 [0181]
The radio communication interface 933 of the car navigation apparatus 940 illustrated in FIG. 18 may have functions of executing the above-described cell selection, cell reselection and handover of the terminal apparatus 30. Further, at least part of these functions may be implemented in the processor 921. For example,
25 by the car navigation apparatus 940 performing handover to another base station while the transmission power of the reference signal fi-om the small cell base station is reduced stepwisely, it is possible to make the operation mode of the small cell base station smoothly transition to the idle mode. [0182]
30 Further, the teclmique according to the present disclosure may be
implemented as a vehicle system (or a vehicle) 940 including one or more blocks of

SP353224WO00 61/74
the above-described car navigation apparatus 920, the iii-vehicle network 941 and a vehicle side module 942. The veliicle side module 942 generates vehicle side data such as vehicle speed, engine speed and failure information and outputs the generated data to the in-vehicle network 941. 5 [0183]
<5. Conclusion>
Some embodiments of the teclinique according to the present disclosure have been described in detail above using FIG. 1 to FIG. 18. According to the above-described embodiments, in a situation where the second base station provides
10 the second radio communication sewice within a cell where the first base station provides the first radio communication service, when the operation mode is made to transition from the first mode to the second mode in which power is less consumed than in the first mode, the second base station switches the operation mode to the second mode after stepwisely reducing the transmission power of the reference signal
15 to be transmitted to the terminal apparatus. Therefore, the second base station can smoothly switch the operation mode to a mode in which power is less consumed without passively waiting until there remains no active terminal being connected to the second base station. That is, it is possible to realize ftirther power saving in a heterogeneous network.
20 [0184]
Further, according to the above-described embodiments, the second base station stands by for a period required for the terminal apparatus connected to the second radio communication service to switch the connection destination, every time the transmission power is reduced by one step. That is, the terminal apparatus is
25 provided with a period for executing handover, cell selection or cell reselection by evaluation the reduced reception power of the reference signal. By this means, it is possible to prevent the terminal apparatus connected to the second base station from being unable to perform communication due to transition of the operation mode of the second base station.
30 [0185]
Further, according to the abo^'e-described embodiments, when the second

SP353224WO00 62/74
base station operates in the first mode, and if it is determined that the load of the first radio communication service is low, the operation mode of the second base station is switched to the second mode. Therefore, it is possible to avoid a situation where the second base station (for example, the small cell base station) is made to operate 5 in the first mode in which power is more consumed while the load of the first base station (for example, the macro cell base station) is not so high, which is not efficient in terms of power consumption of the whole system. [0186]
As an example, the first mode is the active mode in which the radio
10 communication unit continuously operates, and the second mode is the idle mode or the sleep mode in which the radio communication unit at least intermittently operates. In this case, as a result of a period during which power is supplied to the radio communication unit of the second base station being reduced, power saving of the second base station or as the whole system is realized.
15 [0187]
As another example, the first mode is a mode in which a plurality of component carriers for the second radio communication sei-vice are used, and the second mode is a mode in which component carriers fewer than the first mode are used. In this case, as a result of power consumed in the radio communication unit
20 of the second base station being reduced, power saving of the second base station or as the whole system is realized. [0188]
Note that the series of control processing by the respective apparatuses described herein may be implemented by using any of software, hardware, and a
25 combination of software and hardware. Programs constituting the software are previously stored in, for example, a recording medium (or a non-transitory recording medium) provided in the inside or the outside of the respective apparatuses. And the respective programs are, for example, read into a random access memory (RAM) during execution and executed by the processor such as the CPU.
30 [0189]
The processing described with reference to the flowcharts in this

SP353224WO00 63/74
specification does not necessarily need to be executed in order shown in the
flowcharts. Some processing steps may be executed in parallel. Additional
processing step may be employed and some processing steps may be omitted.
[0190]
5 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 examples, of course. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the
10 present invention. [0191]
In addition, the effects described in the present specification are merely illustrative and demonsti*ative, and not limitative. In other words, the technology according to the present disclosure can exhibit other effects that are evident to those
15 skilled in the art along with or instead of the effects based on the present specification. [0192]
Additionally, the present technology may also be configured as below.
(1)
20 A communication control apparatus including:
a radio communication unit configured to provide second radio communication service within a cell in which a first base station provides first radio communication service; and
a control unit configured to, when an operation mode of the radio
25 communication unit is made to transition from a first mode to a second mode in
which power is less consumed than in the first mode, switch the operation mode to
the second mode after stepwisely reducing transmission power of a reference signal
to be transmitted fi*om the radio communication unit.
(2)
30 The communication control apparatus according to (1),
wherein, when the operation mode is made to transition from the first mode

SP353224WO00 64/74
to the second mode, the control unit stands by for a period required for a terminal apparatus connected to the second radio communication service to switch a connection destination every time the transmission power is reduced by one step.
(3)
5 The communication control apparatus according to (2),
wherein the control unit switches the operation mode to the second mode after the number of terminal apparatuses utilizing the second radio communication semce becomes zero.
(4)
10 The communication control apparatus according to any one of (1) to (3),
wherein, in a case where the radio communication unit operates in the fust mode, when it is determined that load of the first radio communication service is low, the control unit switches the operation mode to the second mode.
(5)
15 The communication control apparatus according to (4),
wherein the control unit switches the operation mode to the second mode
according to an instruction from the first base station which determines that the load
of the first radio communication seivice is low.
(6)
20 The communication control apparatus according to (4),
wherein, when an index acquired fi'om the first base station indicates that
the load of the first radio communication service is low, the control unit switches the
operation mode to the second mode.
(7)
25 The communication control apparatus according to (5) or (6),
wherein the load of the first radio communication sei-vice is determined based on a traffic amount of the fir*st radio communication semce.
(8)
The communication control apparatus according to (5) or (6),
30 ^^'herein the load of the first radio communication service is determined
based on the number of radio bearers or the number of terminals being connected in

SP353224WO00 65/74
the first radio communication sendee.
(9)
The communication control apparatus according to (5) or (6), wherein the load of the first radio communication service is determined 5 based on communication quality measured In the first radio communication service. (10)
The communication control apparatus according to any one of (1) to (9), wherein, in the case where the radio communication control unit operates in the second mode, when it is determined that the load of the first radio communication 10 service is high, the control unit switches the operation mode to the first mode.
(11)
The communication control apparatus according to (10),
wherein a first threshold to be compared with the load of the first radio
communication service for switching from the first mode to the second mode is 15 lower than a second threshold to be compared with the load of the first radio
communication service for switching from the second mode to the first mode.
(12)
The communication control apparatus according to any one of (1) to (11), wherein the first mode is a mode in which the radio communication unit 20 continuously operates, and
the second mode is a mode in which the radio communication unit
intermittently operates.
(13)
The communication control apparatus according to (12),
25 wherein, in the second mode, the control unit also intermittently operates.
(14)
The communication control apparatus according to any one of (1) to (13), wherein the first mode is a mode in which a plurality of component carriers
are used for the second radio communication service, and
30 the second mode is a mode in which component carriers fewer than the first
mode are used for the second radio communication service.

SP353224WO00 66/74
(15)
The communication control apparatus according to (14), wherein, when the operation mode is made to transition from the fust mode to the second mode, the control unit stepwisely reduces the transmission power of the 5 reference signal of a component carrier to be removed. (16)
The communication control apparatus according to any one of (1) to (15), wherein, when it is determined that communication quality measured in the second radio communication service is able to be fiirther reduced, the control unit 10 reduces the transmission power of the reference signal. (17)
A communication control method including:
providing second radio communication semce by a second base station within a cell in which a first base station provides first radio communication sei-vice; 15 and
switching, when an operation mode of the second base station is made to transition from a first mode to a second mode in which power is less consumed than in the first mode, the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted from the second base 20 station. (18)
A radio communication system including:
a first base station configured to provide first radio communication semce;
and
25 a second base station including
a radio communication unit configured to provide second radio communication semce within a cell of the first radio communication service, and
a control unit configured to, when an operation mode of the radio
communication unit is made to transition fr'om a first mode to a second mode in
30 whicii power is less consumed than in the first mode, switch the operation mode to
tlie second mode after stepwisely reducing transmission power of a reference signal

SP353224WO00 67/74
to be transmitted from the radio communication unit. (19)
A terminal apparatus including:
a radio communication unit configured to utilize second radio 5 communication service provided by a second base station within a cell in which a first base station provides first radio communication sen'ice; and
a control unit configured to switch a connection destination of the radio communication unit fi*om the second base station to another base station while transmission power of a reference signal received by the radio communication unit is 10 reduced stepwisely in the process in which an operation mode of the second base station transitions from a first mode to a second mode in which power is less consumed than in the first mode. (20)
A communication conti'ol apparatus including:
15 a radio communication unit configured to provide first radio communication
service within a cell; and
a control unit configured to, when an operation mode of a second base station which provides second radio communication sei-vice within the cell is made to transition from a first mode to a second mode in which power is less consumed 20 than in the first mode, made the second base station switch the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted fi'om the second base station.
Reference Signs List 25 [0193]
1 radio communication system
10 first base station (macro cell base station)
110 radio communication unit
140, 160controlunit
30 20 second base station (small cell base station)
210 radio communication unit

240, 260contro! ruiit
30 terminal apparatus

SP353224WO00 68/74

SP353224WO00 69/74

CLAIMS
1. A communication control apparatus comprising:
a radio communication unit configured to provide second radio 5 communication service within a ceil in which a first base station provides first radio communication service; and
a control unit configured to, when an operation mode of the radio
communication unit is made to transition fi'om a first mode to a second mode in
which power is less consumed than in the first mode, switch the operation mode to
10 the second mode after stepwisely reducing transmission power of a reference signal
to be transmitted from the radio communication unit.
Claim 2
The communication control apparatus according to claim 1,
15 wherein, when the operation mode is made to transition from the first mode
to the second mode, the control unit stands by for a period required for a terminal apparatus connected to the second radio communication service to switch a connection destination every time the transmission power is reduced by one step.
20 Claim 3
The communication control apparatus according to claim 2, wherein the control unit switches the operation mode to the second mode after the number of terminal apparatuses utilizing the second radio communication service becomes zero. 25
Claim 4
The conmiunication control apparatus according to claim 1, wherein, in a case where the radio communication unit operates in the first mode, when it is determined that load of the first radio communication sei-vice is low, 30 the control unit switches the operation mode to the second mode.

SP353224WO00 70/74
Claim 5
The communication control apparatus according to claim 4,
wherein the control unit switches the operation mode to the second mode
according to an instruction from the first base station which determines that the load 5 of the first radio commimication service is low.
Claim 6
The communication control apparatus according to claim 4, wherein, when an index acquired fi*om the first base station indicates that 10 the load of the first radio communication semce is low, the control unit switches the
operation mode to the second mode.
Claim 7
The communication control apparatus according to claim 5,
15 wherein the load of the first radio communication sei-vice is determined
based on a traffic amount of the first radio communication semce.
Claim 8
The communication control apparatus according to claim 5,
20 wherein the load of the first radio communication sei"vice is determined
based on the number of radio bearers or the number of terminals being connected in the first radio communication sei^vice.
Claim 9
25 The communication control apparatus according to claim 5,
wherein the load of the first radio communication sendee is determined based on communication qualit)' measured in the first radio coimnunication semce.
Claim 10
30 The communication control apparatus according to claim 1,
wherein, in the case where the radio communication control unit operates in

. SP353224WO00 71/74
the second mode, when it is determined that the load of the first radio communication service is high, the control unit switches the operation mode to the first mode.
Claim 11
The communication control apparatus according to claim 10, wherein a first threshold to be compared with the load of the first radio communication service for switching from the first mode to the second mode is lower than a second threshold to be compared with the load of the first radio communication service for switching from the second mode to the first mode.
10
Claim 12
The communication control apparatus according to claim I,
wherein the first mode is a mode in which the radio communication unit
continuously operates, and
15 the second mode is a mode in which the radio communication unit
intermittently operates.
Claim 13
The commumcation control apparatus according to claim 12,
20 wherein, in the second mode, the control unit also intermittently operates.
Claim 14
The communication control apparatus according to claim 1, wherein the first mode is a mode in which a pluralit>' of component carriers 25 are used for the second radio communication sei-vice, and
the second mode is a mode in which component caniers fewer than the first
mode are used for the second radio communication service.
Claim 15
30 The communication control apparatus according to claim 14,
wherein, ^^'hen the operation mode is made to transition fiom the first mode

SP353224WO00 72/74
to the second mode, the control unit stepwisely reduces tlie transmission power of the reference signal of a component carrier to be removed.
Claim 16
5 The communication control apparatus according to claim 1,
wherein, when it is determined that communication quality measured in the second radio communication service is able to be fijrther reduced, the control unit reduces the transmission power of the reference signal.
10 Claim 17
A communication control method comprising:
providing second radio communication service by a second base station
within a cell in which a fust base station provides first radio communication service;
and
15 switching, when an operation mode of the second base station is made to
transhion &om a first mode to a second mode in which power is less consumed than in the first mode, the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted fi*om the second base station. 20
Claim 18
A radio communication system comprising:
a first base station configured to provide first radio communication semce;
and
25 a second base station including
a radio communication unit configured to provide second radio communication semce within a cell of the first radio communication service, and
a control unit configured to, when an operation mode of the radio
communication unit is made to transition from a first mode to a second mode in
30 which power is less consumed than in the first mode, switch the operation mode to
the second mode after stepwisely reducing transmission power of a reference signal

73/74

SP353224VVO00

to be transmitted from the radio conmumication unit.

10

Claim 19 1
A terminal apparatus comprising:
a radio coimnunication unit configured to utilize second radio coimminication service provided by a second base station witliin a cell in which a first base station provides fnst radio conmiunication service; and
a control unit configured to switch a connection destination of the radio communication unit firom the second base station to another base station while transmission power of a reference signal recei^^ed by the radio communication unit is reduced stepwisely in the process in which an operation mode of the second base station transitions from a first mode to a second mode in which power is less consumed than! in the first mode.

15
20

Claim 20 ;
A communication control apparatus comprismg:
i
a radio conmiunication unit configured to provide first radio communication ser\'ice within a cell; and
a control unit configured to, when an operation mode of a second base station which |)rovides second radio communication ser^'ice within the cell is made to transition fi-dm a first mode to a second mode in wluch power is less consumed than in the first mode, made the second base station switch the operation mode to the second mode after stepwisely reducing transmission power of a reference signal to be transmitted from the second base station.

25

I III
Dated tliis 4'" day of February, 2016

RANJNA MEHTA DUTT
i [IN/PA-190A]
OF REK^RY AND SAGAR
ATTORNEY FOR THE APPLICANT(S)

SP353224WO00
74/74
ABSTRACT
[Object] To enable further power saving in a heterogeneous network.
[Solution] Provided is a communication control apparatus including: a radio
5 communication unit configured to provide second radio communication service within a cell in which a first base station provides first radio communication service; and a control unit configured to, when an operation mode of the radio communication unit is made to transition from a first mode to a second mode in which power is less consumed than in the first mode, switch the operation mode to 10 the second mode after stepwisely reducing transmission power of a reference signal to be transmitted from the radio communication unit.
Representative Drawing FIG. 5 15