Description
Title of Invention
COMMUNICATION CONTROL METHOD AND SMALL-OR-MEDIUM-SCALE
---*-* ' 5 -~ " BASE STATION
Technical Field
[0001]
The present invention relates to a communication control method and a
10 small-or-medium-scale base station.
Background Art
[0002]
Recently, a heterogeneous network has been suggested as the next-
15 generation communication network. This heterogeneous network is a network in
which a plurality of kinds of small-or-medium-scale base stations coexist in a macrocell
by performing overlay transmission or spectrum sharing. A Remote RadioHead
(RRH) cell base station, a hot zone base station (Pico/micro-ceil eNB), a femto-cell
base station (Home eNB), a relay device (relay base station), and the like are referred
20 to as small-or-medium-scale base stations.
[0003]
Each small-or-medium-scale base station described above, for example, can
perform an operation for reinforcing link quality between a communication terminal
and a friacro-cell base station, an operation for increasing an area capacity, an
25 operation for extending communication coverage, or an operation for operating an
independent cell.
[0004]
There are many technologies for controlling an operation of the abovedescribed
small-or-medium-scale base station from a fixed network side. For
30 example, the''fixed network side can reduce power consumption of the small-ormedium-
scale base station by managing a sleep mode of the small-or-medium-scale
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base station. As an example of the small-or-medium-scale base station, a relay
apparatus is disclosed, for example, in Non-Patent Literature 1.
Citation List
••-"-*• 5 - Non-Patent Literature
[0005] :
Non-Patent Literature 1: Rl-090015, "Consideration on Relay.ppt", China
Potevio, CATT, Jan 2009
10 Summary of Invention
Technical Problem
[0006]
Here, the case in which a function for executing a plurality of types of
operations is implemented in one small-or-medium-scale base station is assumed.
15 For example, a small-or-medium-scale base station corresponding to both an
operation for reinforcing link quality between a communication terminal and a
macro-cell base station- and an operation for increasing an area capacity is assumed to
be developed. However, when the operation of the small-or-medium-scale base
station is controlled from the fixed network side as described above, it is difficult for
20 the small-or-medium-scale base station corresponding to a plurality of types of
operations to immediately execute an appropriate operation corresponding to a
situation.
[0007]
The present invention has been made in view of the above-described
25 problems, and an object of the present invention is to provide a novel and improved
communication control method and small-or-medium-scale base station, which can
autonomously select an operation range in the small-or-medium-scale base station
and perform communication in accordance with the selected operation range.
30 Solution to Problem
[0008]
%
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According to the first aspect of the present invention in order to achieve the
above-mentioned object, there is provided a communication control method for use
in a small-or-medium-scale base station including the steps of: receiving a radio
signal transmitted from a communication terminal or a large-scale base station;
5 acquiring information of the communication terminal or the large-scale base station
by analyzing the radio signal; selecting one operation range among a plurality of
types of operation ranges based on the information of the communication terminal or
the large-scale base station; and communicating with the communication terminal in
accordance with the operation range selected from among the plurality of types of
10 operation ranges.
[0009]
The plurality of types of operation ranges may include: a first operation
range for link reinforcement between the communication terminal and the large-scale
base station; a second operation range for improving a capacity; a third operation
15 range for extending communication coverage; and a fourth operation range in which
the small-or-medium-scale base station operates a cell.
[0010]
' The step of selecting the operation range may be a step of selecting the first
operation range when link quality between the communication terminal and the
20 large-scale base station is less than a predetermined standard.
[0011]
The step of selecting the operation range may be a step of selecting the
second operation range when a degree of congestion of traffic in the large-scale base
station is greater than an upper limit.
25 [0012]
The[step of selecting the operation range may be a step of selecting the third
operation range when a distribution of the communication terminals is biased toward
a cell edge of thq large-scale base station.
[0013]
30 The-step of selecting the operation range may be a step of selecting the
fourth operation range when the small-or-medium-scale base station and the
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communication terminal are out of a cell area of the large-scale base station.
[0014]
The first operation range may include a relay operation of communication
between the large-scale base station and the communication terminal or a CoMP
%,, 5 .operation. The second operation range may include an overlay transmission
operation. The third operation range may include the relay operation or an
operation of operating a cell.
[0015]
The step of selecting the operation range may be a step of selecting the
10 operation range from the first operation range and the fourth operation range when a
connection between the large-scale base station or a network, which manages the
large-scale base station, and the small-or-medium-scale base station is only a wired
connection.
J [0016]
I 15 The step of selecting the operation range may be a step of selecting the
operation range from the first operation range, the second operation range, and the
| third operation range when the connection between the large-scale base station or the
j network^ which manages the large-scale base station, and the small-or-medium-scale
base station is only a wireless connection. l 20 [0017] j
The step of selecting the operation range may be a step of selecting the
I operation range from the first operation range, the second operation range, the third
l operation range, and the fourth operation range when the connection between the j
\ •• large-seale base station or the network, which manages the large-scale base station,
j 25 and the small-or-medium-scale base station is the wireless connection and the wired
connection. ' ;
if | [0018]
: The large-scale base station or the network, which manages the large-scale
I base station, may perform interference avoidance control for avoiding interference
I 30 caused due to-cbmmunication by the small-or-medium-scale base station.
[0019]
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According to the second aspect of the present invention in order to achieve
the above-mentioned object, there is provided a small-or-medium-scale base station
including: a reception unit for receiving a radio signal transmitted from a
communication terminal or a large-scale base station; an information acquisition unit
.--*_*, 5 ."for acquiring information of the communication terminal or the large-scale base
station by analyzing the radio signal; a selection unit for selecting one operation
range among a plurality of types of operation ranges based on the information of the
communication terminal or the large-scale base station; and a communication control
unit for controlling communication with the communication terminal in accordance
10 with the operation range selected from among the plurality of types of operation
ranges.
Advantageous Effects of Invention
[0020]
15 According to the present invention as described above, a small-or-mediumscale
base station can autonomously select an operation range and perform
communication in accordance with the selected operation range.
Brief Description of Drawings 20 [0021]
[Fig. 1] Fig. 1 is an explanatory diagram illustrating a configuration of a
communication system according to an embodiment of the present invention.
[Fig. 2] Fig. 2 is an explanatory diagram illustrating a configuration example of a
small-or-medium-scale base station according to the embodiment of the present
25 invention.
[Fig. 3] Fig! 3 is a sequence diagram illustrating the entire operation in the
communication system according to the embodiment of the present invention.
[Fig. 4] Fig. 4 is an explanatory diagram illustrating an example of interference to be
considered during overlay transmission.
30 [Fig. 5] Fig/ 5 is an explanatory diagram illustrating a method of selecting an
operation range.
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[Fig. 6] Fig. 6 is an explanatory diagram illustrating a method of selecting an
operation range.
[Fig. 7] Fig. 7 is an explanatory diagram illustrating a method of selecting an
operation range.
..-.X* 5 -iFig. 8] Fig. 8 is an explanatory diagram illustrating a method of selecting an
operation range.
[Fig. 9] Fig. 9 is an explanatory diagram illustrating a specific example of
interference that occurs due to a coverage extension.
[Fig. 10] Fig. 10 is an explanatory diagram illustrating an adjustable SESFR range.
10
Description of Embodiments
[0022]
Hereinafter, preferred embodiments of the present invention will be
described in detail with reference to the appended drawings. Note that, in this
15 specification and the drawings, elements that have substantially the same function
and structure are denoted with the same reference signs, and repeated explanation is
omitted.
[0023]
In addition, in this specification and the drawings, a plurality of elements
20 having substantially the same functional configuration may be distinguished from
each other by each having a different letter added to the same reference numeral.
For example, a plurality of elements having substantially the same functional
configuration are distinguished from each other as communication terminals 20A,
20B, and 20C, if necessary. However, if it is not particularly necessary to
25 distinguish each of a plurality of elements having substantially the same functional
configuration^ only the same reference numeral is assigned. For example, if it is not
particularly necessary to distinguish the communication terminals 20A, 20B, and
20C, they are simply referred to as the communication terminal 20.
[0024]
30 In addition, "Description of Embodiments" will be given in the following
item order.
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1. Overview of Embodiments of Present Invention
2. Information to Be Used for Selection of Operation Range
3. Content of Operation Ranges
4. Method of Selecting Operation Range
5 5. Monitoring by Management Server
6. Summary
[0025]
<1. Overview of Embodiments of Present Invention>
First, a configuration of a communication system 1 according to an
10 embodiment of the present invention will be described with reference to Fig. 1. Fig.
1 is an explanatory diagram illustrating the configuration of the communication
system 1 according to the embodiment of the present invention. As illustrated in
Fig. 1, the communication system 1 according to the embodiment of the present
invention includes a macro-cell base station 10, a management server 16,
15 communication terminals 20A to 20D, and small-or-medium-scale base stations 30A
to 30D.
[0026]
The macro-cell base station 10 is a large-scale base station that manages
scheduling information of a small-or-medium-scale tbase station 30 and a
20 communication terminal 20, which are present within a macro cell, and
communicates with the small-or-medium-scale base station 30 and the
communication terminal 20 according to the scheduling information.
[0027]
The management server 16 receives management information indicating a
25 state of a cell formed by the macro-cell base station 10 from each base station 10,
and controls, communication in the cell formed by the macro-cell base station 10
based on the management information. A function of the management server 16
may be implemented in the macro-cell base station 10 or either small-or-mediumscale
base station. In addition, the management server 16 may have a function as a
30 mobile management entity (MME) or gateway apparatus.
[0028]
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The communication terminal 20 is a user terminal that communicates with
the small-or-medium-scale base station 30 or the macro-cell base station 10. This
communication terminal 20, for example, may be a portable phone or a personal
computer (PC).
J „ 5 -t0029]
The small-or-medium-scale base station 30 autonomously selects an
operation range suitable for a current situation from a plurality of operation ranges,
and communicates with the communication terminal 20 in accordance with the
selected operation range.
10 [0030]
For example, when a communication link between the macro-cell base
station 10 and the communication terminal 20A is less than a predetermined quality,
the small-or-medium-scale base station 30A performs communication in accordance
with an operation range (operation range A) for reinforcing the communication link
15 between the macro-cell base station 10 and the communication terminal 20A as
illustrated in Fig. 1.
[0031] -
In addition, when a degree of congestion of a macro cell is greater than a ;
predetermined standard, the small-or-medium-scale base station 30B communicates
20 with the communication terminal 20B in accordance with an operation range
(operation range B) for increasing an area capacity as illustrated in Fig. 1.
[0032]
In addition, when a distribution of communication terminals is biased
toward a cell edge of the macro cell, the small-or-medium-scale base station 30C
25 communicates with the communication terminal 20C in accordance with an >
operation rarige (operation range C) for extending coverage as illustrated in Fig. 1.
[0033] :
In addition, when the small-or-medium-scale base station 30D and the
communication terminal 20D are out of a range of the macro cell the small-or-
30 medium-scale base station 30D provides a communication opportunity to the
communication terminal 20D by operating an independent cell (operation range D)
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as illustrated in Fig. 1.
[0034]
Hereinafter, the entire operation in the above-described communication
system 1 will be described along with a configuration of the small-or-medium-scale
5 base station 30.
[0035]
FIG. 2 is an explanatory diagram illustrating an example of the
configuration of the small-or-medium-scale base station 30 according to the
embodiment of the present invention. As illustrated in Fig. 2, the small-or-medium-
10 scale base station 30 includes a wireless communication unit 310, a network
communication unit 320, an information acquisition unit 330, an operation-range
selection unit 340, and a communication control unit 350. The wireless
communication unit 310 is configured for wirelessly communicating with the
communication terminal 20, and the network communication unit 320 is configured
15 for performing wired communication and/or wireless communication with a network
side such as the macro-cell base station 10 or the management server 16.
[0036]
Fig. 3 is a sequence diagram illustrating the entire operation in the
communication system 1 according to the embodiment of the present invention. As
20 illustrated in Fig. 3, the macro-cell base station 10 acquires macro-cell operation ;
information, and reports the macro-cell operation information to the management
server 16 (SI04). For example, a BER/PER, the number of retransmissions, a statistical value such as an average value of throughput, traffic information, or the
like corresponds to the macro-cell operation information.
25 [0037]
i
Subsequently, the management server 16 determines whether or not to start
an operation of the small-or-medium-scale base station 30 (S108). Specifically,
position information of each small-or-medium-scale" base station 30 is registered in
the management server 16, and the management server 16 determines to start the
30 operation of-the small-or-medium-scale base station 30 when the communication
terminal 20 has moved to a communication area of a certain small-or-medium-scale
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base station 30. The management server 16 instructs the small-or-medium-scale
base station 30 to start the operation (S112).
[0038]
Thereafter, the wireless communication unit 310 of the small-or-medium-
5 ."scale base station 30 receives radio signals (for example, a preamble, a pilot signal,
and a reference signal) transmitted from the communication terminal 20 or the
macro-cell base station 10 (SL16 and SI20). The information acquisition unit 330
acquires information to be used to select an operation range by analyzing the radio
signals received by the wireless communication unit 310 (S124). In addition, the
10 information acquisition unit 330 may acquire information from the management
server 16 via the network communication unit 320.
[0039]
Subsequently, the operation-range selection unit 340 of the small-ormedium-
scale base station 30 selects one operation range of operation ranges A to D
15 based on the information acquired by the information acquisition unit 330 (S128).
Thereafter, the small-or-medium-scale base station 30 notifies the management
server 16 of the selected operation range, and acquires operation parameters (for
example, transmission power, a slot, and a transmission rate) from the management ;
server 16 (SI32). 20 [0040] I
The communication control unit 350 of the small-or-medium-scale base
station 30 starts control of the wireless communication unit 310 using the operation
parameters acquired from the management server 16 in accordance with the
operation range selected by the operation-range selection unit 340 (SI36).
25 Thereafter, the management server 16 monitors communication by the small-ormedium-
scale base station 30, issues an instruction for a change in an operation
parameter, for example, when communication by the small-or-medium-scale base
station 30 leads tp interference, and instructs the small-or-medium-scale base station
30 to stop an operation when interference is not removed (SI40).
30 [0041]
As described above, the small-or-medium-scale base station 30 according to
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the embodiment of the present invention autonomously selects an operation range
suitable for a current situation. Therefore, the small-or-medium-scale base station
30 can immediately reflect the fluctuation in a communication environment in the
operation range. Hereinafter, particulars related to the above-described
5 "embodiment of the present invention will be described in detail.
[0042]
<2. Information to Be Used for Selection of Operation Range>
In the embodiment of the present invention, the small-or-medium-scale base
station 30 uses the following information (1) to (6) for selection of the operation
10 range.
[0043]
Information (1): Operation Information of Macro Cell
Information (2): Position Information of Macro-Cell Base Station 10
Information (3): Communication-Path Environment between Macro-Cell
15 Base Station 10 and Small-or-Medium-Scale Base Station 30
Information (4): Position Information of Communication Terminal 20
Information (5): Pairing between Communication Terminal 20 and Macro-
Cell Base Station 10
Information (6): Quality of Communication Link between Communication
20 Terminal 20 and Macro-Cell Base Station 10
[0044] i
Hereinafter, methods of acquiring the above-described information will be
sequentially described.
[0045]-
25 Information (1): Operation Information of Macro Cell
The ^operation information of the macro cell corresponds to system
information indicating a cell ID of the macro cell, a cell search list, a center
frequency, or a bandwidth, uplink/downlink traffic information, and the like.
[0046]
30 When a wired connection to the management server 16 is established, the
small-or-medium-scale base station 30 acquires the operation information of the
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macro cell from the management server 16. On the other hand, when the wired
connection to the management server 16 is not established, the small-or-mediumscale
base station 30 acquires the operation information of the macro cell by
decoding a physical broadcast channel (PBCH), a physical downlink control channel
--•*.*. 5 - (PDCCH), or the like transmitted from the macro-cell base station 10. In addition,
the small-or-medium-scale base station 30 appropriately updates system information,
if necessary, using frequency information or the like acquired during previous
communication and stored in a memory as system information.
[0047]
10 When the small-or-medium-scale base station 30 can also acquire the
operation information of the macro cell by one of wired communication with the
management server 16 and wireless communication with the macro-cell base station
10, the operation information of the macro cell may be acquired by one type of
communication according to a predetermined standard. For example, the small-or-
15 medium-scale base station 30 may use the wired communication when it is difficult
to decode a radio signal because of bad characteristics of the wireless connection, use
the wireless communication when the latency of the wired communication is large,
and use communication having low power consumption when the reduction of power
consumption is desired. 20 [0048]
Information (2): Position Information of Macro-Cell Base Station 10
The small-or-medium-scale base station 30 acquires the position
information of the macro-cell base station 10 from the macro-cell base station 10 or
the management server 16. Alternatively, the small-or-medium-scale base station
25 30 may estimate the position information of the macro-cell base station 10 based on a
reference signal received from the macro-cell base station 10.
[0049]
Information (3): Communication-Path Environment between Macro-Cell
Base Station 10 and Small-or-Medium-Scale Base Station 30
30 The - small-or-medium-scale base station 30 estimates the information
indicating the communication-path environment between the macro-cell base station
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10 and the small-or-medium-scale base station 30 from an SINR or signal strength of
a downlink reference signal or the like transmitted from the macro-cell base station
10.
[0050]
: 5 Information (4): Position Information of Communication Terminal 20
The small-or-medium-scale base station 30 acquires the position
information of the communication terminal 20 from the management server 16 in a
fixed network.
[0051]
10 Alternatively, the small-or-medium-scale base station 30 receives a uplink
reference signal transmitted from the communication terminal 20, and estimates a
positional relationship between the small-or-medium-scale base station 30 and the
communication terminal 20 according to reception power. For example, when the
small-or-medium-scale base station 30 can recognize transmission power of the
15 communication terminal 20, the small-or-medium-scale base station 30 may estimate
a distance from the communication terminal 20 based on the transmission power of
the communication terminal 20, path loss, and reception power. The small-ormedium-
scale base station 30 may recognize the transmission power of the
communication terminal 20 by referring to transmission power control information
20 of a physical downlink shared channel (PDSCH) or a physical uplink shared channel
(PUSCH) described in the PDCCH transmitted from the macro-cell base station 10.
[0052]
Alternatively, the small-or-medium-scale base station 30 receives a
transmission signal of a RACH transmitted from the communication terminal 20, and
25 estimates a positional relationship between the small-or-medium-scale base station
30 and the communication terminal 20 according to reception power. For example,
when the small-or-medium-scale base station 30 can recognize transmission power
of the communication terminal 20, the small-or-medium-scale base station 30 may
estimate a distance from the communication terminal 20 based on the transmission
30 power of the communication terminal 20, path loss, and reception power. The
small-or-medium-scale base station 30 may recognize the transmission power of the
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communication terminal 20 by referring to transmission power control information
transmitted from the macro-cell base station 10 to the communication terminal 20 in
a process of a physical random access channel (PRACH).
[0053]
•-•;.:- 5 Information (5): Pairing between Communication Terminal 20 and Macro-
Cell Base Station 10
The small-or-medium-scale base station 30 acquires the information
indicating the pairing between the communication terminal 20 and the macro-cell
base station 10 from the management server 16 in the fixed network.
10 [0054]
Alternatively, the small-or-medium-scale base station 30 may determine
which macro-cell base station 10 is being connected to the communication terminal
20 by decoding the PBCH and the PDCCH transmitted from the macro-cell base
station 10. i
15 [0055] i
Information (6): Quality of Communication Link between Communication
Terminal 20 and Macro-Cell Base Station 10
The small-or-medium-scale base station 30 acquires the information
indicating the quality of the communication link between the communication
20 terminal 20 and the macro-cell base station 10 from the management server 16 in the
fixed network. ?
[0056]
Alternatively, because PUSCH or RACH retransmission is considered to be
iteratedvvhen a signal of the same pattern is transmitted from the communication
25 terminal 20 at a plurality of times, the small-or-medium-scale base station 30 may
determine that the communication link between the communication terminal 20 and
the macro-cell base station 10 is bad in such a case.
[0057]
Alternatively, the small-or-medium-scale base station 30 may determine the
30 link quality between the communication terminal 20 and the macro-cell base station
10 based on a physical uplink control channel (PUCH) and a signal level of a UL
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reference signal transmitted from the communication terminal 20 to the macro-cell
base station 10.
[0058]
<3. Content of Operation Ranges>
'• 5 * Examples of methods of acquiring the information (1) to (6) to be used for
the small-or-medium-scale base station 30 to select an operation range have been
described. Next, content of each of the operation ranges A to D will be described.
[0059]
(Operation Range A)
10 Communication for reinforcing a communication link between the macrocell
base station 10 and the communication terminal 20A is included in the operation
range A as described above. Examples of the above-described communication are
relay communication and coordinated multiple (CoMP) transmission/reception
to/from the macro-cell base station 10.
15 [0060] J
Therefore, when a resource (time - frequency slot) different from that of the
macro-cell base station 10 is acquirable, the small-or-medium-scale base station 30, •
which operates according to the operation range A, performs relay communication of
transmission/reception data of a link to be '• reinforced or CoMP
20 transmission/reception in a state of carrier aggregation. On the other hand, when a
resource different from that of the macro-cell base station 10 is not acquired, the
small-or-medium-scale.base station 30, which operates according to the operation
range A, performs CoMP transmission/reception of transmission/reception data of a
link to be reinforced to/from the macro-cell base station 10.
25 [0061]
The small-or-medium-scale base station 30 can cooperate with the macrocell
base station 10 using a wired interface such as radio on fiber or X2_IF or a
wireless interface.
[0062]
30 (Operation Range B)
Communication for increasing an area capacity is included in the operation
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range B as described above. An example of the above-described communication is
overlay transmission (or underlay transmission). Here, the overlay transmission is a
normal base-station operation, which is performed using the same time - frequency
slot as in the macro-cell base station 10 or either small-or-medium-scale base station
.- . .?.*. 5 - within the macro cell. The overlay transmission is an operation different from relay
communication or a CoMP operation. For a slot for the overlay transmission, it is
preferable that the macro-cell base station 10 allocate a slot different from slots to be
used for transmission of the PBCH, a Sync, ch, and a PUCCH/PDCCH so as to
secure the quality of the macro-cell base station 10.
10 [0063]
However, because the overlay transmission leads to interference with other
communication within the macro cell, it is important that the small-or-medium-scale
base station 30 appropriately control transmission power when the overlay
transmission is performed.
15 [0064]
FIG. 4 is an explanatory diagram illustrating an example of interference to
be considered during the overlay transmission. As illustrated in Fig. 4, if the smallor-
medium-scale base station 3 0B performs overlay transmission for communicating j
with the communication terminal 20B, a radio signal transmitted from the small-or-
20 medium-scale base station 30B reaches the macro-cell base station 10 and a
communication terminal 20X as an interference wave.
[0065] ,
Here, the small-or-medium-scale base station 30B can calculate a level of
interference given by the small-or-medium-scale base station 30B to the macro-cell
25 base station 10 by subtracting path loss from transmission power based on path loss
(transmission path) information with the macro-cell base station 10. Likewise, the
small-or-medium-scale base station 30B can calculate a level of interference given
by the small-or-medium-scale base station 30B to the communication terminal 20X
by subtracting path loss from transmission power based on path loss with the
30 communication terminal 20X.
[0066]
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Therefore, the small-or-medium-scale base station 3OB can perform overlay
transmission by controlling transmission power so that levels of interference given to
the macro-cell base station 10 and the communication terminal 20X are less than
permissible interference amounts of the macro-cell base station 10 and the
5 • communication terminal 20X.
[0067]
The small-or-medium-scale base station 30 acquires information regarding a
peripheral communication terminal 20 when performing the overlay transmission.
For example, the small-or-medium-scale base station 30 may acquire information
10 (position information, an ID, reserved-slot information of UL transmission, and the
like) regarding the peripheral communication terminal 20 from the macro-cell base
station 10. Alternatively, the small-or-medium-scale base station 30 may acquire
the reserved-slot information of the communication terminal 20 by receiving the
PDCCH, and estimate position information of the communication terminal 20 based
15 on reference of the PUSCH. Alternatively, the small-or-medium-scale base station
30 may estimate a communication-path environment between the small-or-mediumscale
base station 30 and the communication terminal 20 based on the reference of
the PUSCH after acquiring the reserved-slot information of the communication
terminal 20.
20 [0068]
(Operation'Range C)
Communication for extending coverage is included in the operation range C
as described above. Examples of the above-described communication are relay
communication and overlay transmission.
25 [0069]
Therefore, when a resource (time - frequency slot) different from that of the
macro-cell base station 10 is acquirable, the small-or-medium-scale base station 30,
which operates according to the operation range C, performs relay communication of
transmission/reception data of a link to be reinforced or an operation of an
30 independent cell. On the other hand, when a resource different from that of the
macro-cell base station 10 is not acquirable, the small-or-medium-scale base station
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30, which operates according to the operation range C, performs the overlay
transmission to the macro cell. The small-or-medium-scale base station 30 may
prevent interference by performing transmission power control or beam steering
during overlay transmission.
' 5 "[0070]
(Operation Range D)
Communication for operating an independent cell is included in the
operation range D as described above. Therefore, the small-or-medium-scale base
station 30, which operates according to the operation range D, operates the
10 independent cell by controlling a transmission parameter such as maximum
transmission power using an acquired resource.
[0071]
<4. Method of Selecting Operation Range>
The operation ranges A to D assumed to be implemented in the small-or-
15 medium-scale base station 30 have been described above. Next, a method in which I
the small-or-medium-scale base station 30 selects the operation range will be i
described. '
[0072]
As illustrated in Fig. 5, the operation-range selection unit 340 of the small-
20 or-medium-scale base station 30 first checks a connection relationship between the {
macro-cell base station 10 or the management server 16 and the small-or-mediumscale
base station 30. When a connection between the macro-cell base station 10 or
the management server 16 and the small-or-medium-scale base station 30 is only the i
wired connection, the operation-range selection unit 340 selects the operation range
25 from the operation ranges A and D (S408). A method of selecting the operation
range from the operation ranges A and D will be described later with reference to Fig.
6.
[0073]
On the other hand, when the connection between the macro-cell base station
30 10 or the management server 16 and the small-or-medium-scale base station 30 is :
both the wired connection and the wireless connection (S412), the operation-range
^ SP262744WO00
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selection unit 340 selects the operation range from among the operation ranges A to
D (S416). A method of selecting the operation range from among the operation
ranges A to D will be described later with reference to Fig. 8.
[0074]
•-'••:. 5 In addition, when the connection between the macro-cell base station 10 or
the management server 16 and the small-or-medium-scale base station 30 is only the
wireless connection (S412), the operation-range selection unit 340 selects the
operation range from among the operation ranges A, B, and C (S420). A method of
selecting the operation range from among the operation ranges A, B, and C will be
10 described later with reference to Fig. 7.
[0075]
Fig. 6 is a flowchart illustrating a method in which the small-or-medium- I
scale base station 30 selects the operation range from the operation ranges A and D.
As illustrated in Fig. 6, when the above-described information (1) to (6) is acquirable
15 (S504), the operation-range selection unit 340 of the small-or-medium-scale base
station 30 determines whether or not link quality between the peripheral
communication terminal 20 and the macro-cell base station 10 is bad based on the
above-described information (S508). When the link quality between the peripheral
communication terminal 20 and the macro-cell base station 10 is bad, the operation-
20 range selection unit 340 selects the operation range A so as to improve the link
quality (S512).
[0076]
On the other hand, when the information (1) and (6) is not acquirable but the
information (1), (2), and (4) is acquirable (S516), the operation-range selection unit
25 340 determines whether or not both the small-or-medium-scale base station 30 and
the communication terminal 20 are out of the range of the macro cell based on the
above-described information (S520). When both the small-or-medium-scale base
station 30 and the, communication terminal 20 are out of the range of the macro cell,
the operation-range selection unit 340 selects the operation range D so as to provide
30 a communication opportunity to the communication terminal 20 (S524).
[0077]
4 | SP262744WO00
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When the information (1), (2), and (4) is determined not to be acquirable in
S516.and at least one of the small-or-medium-scale base station 30 and the
communication terminal 20 is determined to be in the range of the macro cell in S520,
the operation-range selection unit 340 does not select any operation range. In this
5 - case, the small-or-medium-scale base station 30 transitions to an initial state without
performing an operation of transmission to the communication terminal 20 (S528).
[0078] ;
Fig. 7 is a flowchart illustrating a method in which the small-or-mediumscale
base station 30 selects the operation range from among the operation ranges A,
10 B, and C. As illustrated in Fig. 7, when a slot different from that of the macro-cell
base station 10 is securable (S604) and the information (1) and (6) is acquirable
(S608), the operation-range selection unit 340 of the small-or-medium-scale base ;
station 30 determines whether or not the link quality between the peripheral :
communication terminal 20 and the macro-cell base station 10 is bad based on the
15 above-described information (S612). When the link quality between the peripheral
communication terminal 20 and the macro-cell base station 10 is bad, the operation- frange
selection unit 340 selects the operation range A (S616). [0079]
On the other hand, when the link quality is determined not to be bad in S612
20 and the information (1) and (6) is acquirable (S620), the operation-range selection
unit 340 determines whether or not a distribution of communication terminals 20 is
biased toward a cell edge of the macro cell based on the above-described information
(S624). For example, when an average value of distances of a plurality of
communication terminals 20 from the macro-cell base station 10 within the macro
25 cell is greater than a predetermined value, the operation-range selection unit 340 may
determine that the distribution of the communication terminals 20 is biased toward
the cell edge of the macro cell. When the distribution of the communication
terminals 20 is biased toward the cell edge of the macro cell, the operation-range
selection unit 340 selects the operation range C so as to extend the coverage (S628).
30 [0080]
In addition, when the slot different from that of the macro-cell base station
£ SP262744WO00
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10 is not securable and the information (1) to (6) is acquirable (S636), the operationrange
selection unit 340 determines whether or not a degree of congestion of the
macro cell is greater than a predetermined standard based on the above-described
information (S640). When the degree of congestion of the macro cell is greater
5 'than the predetermined standard, the operation-range selection unit 340 selects the
operation range B so as to increase the area capacity (S644).
[0081]
On the other hand, when the degree of congestion of the macro cell is not
greater than the predetermined standard, the operation-range selection unit 340
10 determines whether or not the distribution of the communication terminals 20 is
biased toward the cell edge of the macro cell (S648). When the distribution of the
communication terminals 20 is biased toward the cell edge of the macro cell, the
operation-range selection unit 340 selects the operation range C so as to extend the
coverage (S628).
15 [0082]
When the information (1) to (6) is determined not to be acquirable in S620
or S636 and when the distribution of the communication terminals 20 is determined
not to be biased toward the cell edge of the macro, cell in S624 or S648, the
operation-range selection unit 340 does not select any operation range. In this case,
20 the small-or-medium-scale base station 30 transitions to the initial state without
performing an operation of transmission to the communication terminal 20 (S632).
[0083] , . .
_ Fig. 8 is a flowchart illustrating a method in which the small-or-mediumscale
base station 30 selects the operation range from among the operation ranges A
25 to D. As illustrated in Fig. 8, when a slot different from that of the macro-cell base
station 10 is securable (S704) and the information (1) and (6) is acquirable (S708),
the operation-range selection unit 304 of the small-or-medium-scale base station 30
determines whether or not link quality between the peripheral communication
terminal 20 and the macro-cell base station 10 is bad based on the above-described
30 information (§712). When the link quality between the peripheral communication
terminal 20 and the macro-cell base station 10 is bad, the operation-range selection
4}- SP262744WO00
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unit 340 selects the operation range A (S716).
[0084]
On the other hand, when the information (1) and (6) is not acquirable but the
information (1), (2), and (4) is acquirable (S720), the operation-range selection unit
5 340 determines whether or not both the small-or-medium-scale base station 30 and
the communication terminal 20 are out of the range of the macro cell based on the
above-described information (S724). When both the small-or-medium-scale base
station 30 and the communication terminal 20 are out of the range of the macro cell,
the operation-range selection unit 340 selects the operation range D so as to provide
10 a communication opportunity to the communication terminal 20 (S728). On the
other hand, when at least one of the small-or-medium-scale base station 30 and the
communication terminal 20 is in the range of the macro cell, a determination of S752
is made.
[0085]
15 In addition, when a slot different from that of the macro-cell base station 10
is not securable and the information (1) to (6) is acquirable (S740), the operationrange
selection unit 340 determines whether or not a degree of congestion of the
macro cell is greater than a predetermined standard based on the above-described
information (S744). When the degree of congestion of the macro cell is greater
20 than the predetermined standard, the operation-range selection unit 340 selects the
operation range B so as to increase the area capacity (S748).
[0086]
_ On the other hand, when the degree of congestion of the macro cell is not
greater" than the predetermined standard, the operation-range selection unit 340
25 determines whether or not a distribution of the communication terminals 20 is biased
toward the cell edge of the macro cell (S752). When the distribution of the
communication terminals 20 is biased toward the cell edge of the macro cell, the
operation-range selection unit 340 selects the operation range C so as to extend the
coverage (S748). _ ...
30 [0087]
When the information (1) to (6) is determined not to be acquirable in S732
^ SP262744WO00
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or S740, when the distribution of the communication terminals 20 is determined not
to be biased toward the cell edge of the macro cell in S752, and the like, the
operation-range selection unit 340 does not select any operation range. In this case,
the small-or-medium-scale base station 30 transitions to the initial state without
5 - performing an operation of transmission to the communication terminal 20 (S736),
[0088]
<5. Monitoring and Control by Management Server>
The small-or-medium-scale base station 30 selects the operation range by
the above-described method, and starts communication according to the selected
10 operation range. If the small-or-medium-scale base station 30 starts the
communication, the management server 16 monitors the communication of the
small-or-medium-scale base station 30, and performs interference avoidance control,
if necessary. Hereinafter, corresponding particulars will be described in detail.
[0089]
15 (When Small-or-Medium-Scale Base Station 30 Performs Overlay
Transmission)
The management server 16 monitors a report regarding a communication
situation from the small-or-medium-scale base station 30, which performs overlay
transmission according to the operation range B or C. \The report regarding the
20 communication situation, for example, includes a BER/PER, the number of
retransmissions, a statistical value such as an average value of throughput, traffic
information, or the like.
[0090]
Here, when the small-or-medium-scale base station 30, which performs the
25 overlay transmission, is in proximity of another small-or-medium-scale network and
an index value such as area throughput is lower than a constant level or rapidly
decreases, interference may be caused due to the overlay transmission. In this case,
the management, server 16 determines whether of not another resource for the
overlay transmission is allocated to the small-or-medium-scale base station 30.
30 [0091]
When the other resource is allocated, the management server 16 notifies the
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small-or-medium-scale base station 30 of the other resource and a change of an
interference subject. The interference subject after the change newly performs
sensing or information acquisition, and executes transmission power control. On
the other hand, when another resource is not allocated, the management server 16
••-'••'• 5 instructs the small-or-medium-scale base station 30 to stop the operation.
[0092]
(When Small-or-Medium-Scale Base Station 30 Performs Cell-Area
Extension Operation)
When the small-or-medium-scale base station 30 has extended a cell area by
10 relay communication or an operation of an independent cell, it is difficult for the
small-or-medium-scale base station 30 to check interference with other
communication. For example, if the small-or-medium-scale base station 30
performs communication for extending the cell area with the communication
terminal 20A as illustrated in Fig. 9, the small-or-medium-scale base station 30 may
15 interfere with a communication terminal 20Y, which communicates with the macrocell
base station 10B.
[0093]
In this case, the management server 16 determines whether or not another
resource is allocated to the small-or-medium-scale base station 30. When the other
20 resource is allocated, the management server 16 notifies the small-or-medium-scale
base station 30 of the other resource and a change of an interference subject. On the
other hand, when jio other resource is allocated, the management server 16 instructs
the small-or-medium-scale base station 30 to stop the operation.
[0094]"
25 (When Small-or-Medium-Scale Base Station 30A, which Performs Link
Reinforcement Operation, Is Adjacent to Small-or-Medium-Scale Base Station 30B,
which Performs Overlay Transmission)
In a communication link reinforced by the small-or-medium-scale base -
station 30A, an SINR range adjustable by transmission power control becomes larger
30 than usual as* illustrated in Fig. 10. In this case, the management server 16 notifies
the small-or-medium-scale base station 30B of an update value of a permissible
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interference amount by link reinforcement, and the small-or-medium-scale base
station 30B, which performs overlay transmission, can set transmission power based
on the update value of the notification. Thus, an increase in the area capacity is
further expected.
5 * [0095]
<6. Summary>
As described above, the small-or-medium-scale base station 30 according to
the embodiment of the present invention can autonomously select an operation range
suitable for a current situation. Therefore, the small-or-medium-scale base station
10 30 can immediately reflect the fluctuation in a communication environment in the
operation range.
[0096]
The preferred embodiments of the present invention have been described
above with reference to the accompanying drawings, whilst the present invention is
15 not limited to the above examples, of course. A person skilled in the art may find
various alternations 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
present invention. •
[0097]
20 For example, the steps in the process of the small-or-medium-scale base »
station 30 of this specification are not necessarily processed in time series in the
order described as.the flowchart. For example, the steps in the process of the smallor-
medium-scale base station 30 may be processed in an order different from the
order described in the flowchart or processed in parallel. In addition, it is possible
25 to create a computer program for causing hardware such as a CPU, ROM and RAM
embedded in;the small-or-medium-scale base station 30 to have the same functions
as the configurations of the small-or-medium-scale base station 30 described above.
In addition, a storage medium recording the computer program is also provided.
[0098] _ -
30 In addition, the macro-cell base station according to the embodiment of the
present invention may dynamically change a coverage area of a macro cell, an
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amount of resources to be used, or the number of communication terminals or smallor-
medium-scale base stations capable of being accommodated according to an
amount of communication traffic within the macro cell or a distribution of
communication terminals 20 or small-or-medium-scale base stations 30.
" "" 5 "Accordingly, the small-or-medium-scale base station may dynamically change a
control operation. For example, a coverage area of the macro cell of the macro-cell
base station is dynamically reduced, so that the small-or-medium-scale base station
30B, which performs communication for an increase in an area capacity in Fig. 1,
may be dynamically switched to an operation of the small-or-medium-scale base
10 station 30D, which performs communication for operating an independent cell.
Reference Signs List
[0099]
10 Macro-cell base station
15 20 Communication terminal
30 Small-or-medium-scale base station
310 Wireless communication unit
320 Network communication unit
330 Information acquisition unit
20 340 Operation-range selection unit
350 Communication control unit

CLAIMS
Claim 1
A communication control method for use in a small-or-medium-scale base
station, comprising the steps of:
' • 5 receiving a radio signal transmitted from a communication terminal or a
large-scale base station;
acquiring information of the communication terminal or the large-scale base
station by analyzing the radio signal;
selecting one operation range among a plurality of types of operation ranges
10 based on the infonnation of the communication terminal or the large-scale base
station; and
communicating with the communication terminal in accordance with the
operation range selected from among the plurality of types of operation ranges.
15 Claim 2
The communication control method according to claim 1,
wherein the plurality of types of operation ranges include a first operation
range for link reinforcement between the communication terminal and the large-scale
base station, a second operation range for improving a capacity, a third operation
20 range for extending communication coverage, and a fourth operation range in which
the small-or-medium-scale base station operates a cell.
Claim 3
" The communication control method according to claim 2,
25 wherein the step of selecting the operation range is a step of selecting the
first operation range when link quality between the communication terminal and the
large-scale base station is less than a predetermined standard.
Claim 4
30 The communication control method according to claim 3,
wherein the step of selecting the operation range is a step of selecting the
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second operation range when a degree of congestion of traffic in the large-scale base
station is greater than an upper limit.
Claim 5
5 • The communication control method according to claim 4,
wherein the step of selecting the operation range is a step of selecting the
third operation range when a distribution of the communication terminals is biased
toward a cell edge of the large-scale base station.
10 Claim 6
The communication control method according to claim 5,
wherein the step of selecting the operation range is a step of selecting the
fourth operation range when the small-or-medium-scale base station and the
communication terminal are out of a cell area of the large-scale base station.
15
Claim 7
The communication control method according to claim 6,
wherein the first operation range includes a relay operation of
communication between the large-scale base station and the communication terminal
20 or a CoMP operation.
Claim 8 . .
The communication control method according to claim 7,
wherein the second operation range includes an overlay transmission
25 operation.
i
Claim 9
The communication control method according to claim 8,
wherein the third operation range includes the relay operation or an
30 operation ofbperating a cell.
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Claim 10
The communication control method according to claim 9,
wherein the step of selecting the operation range is a step of selecting the
operation range from the first operation range and the fourth operation range when a
' ' 5 ' connection between the large-scale base station or a network, which manages the
large-scale base station, and the small-or-medium-scale base station is only a wired
connection.
Claim II
10 The communication control method according to claim 10,
wherein the step of selecting the operation range is a step of selecting the
operation range from the first operation range, the second operation range, and the
third operation range when the connection between the large-scale base station or the
network, which manages the large-scale base station, and the small-or-medium-scale
15 base station is only a wireless connection.
Claim 12
The communication control method according to claim 11,
wherein the step of selecting the operation range is a step of selecting the
20 operation range from the first operation range, the second operation range, the third
operation range, and the fourth operation range when the connection between the
large-scale base station or the network, which manages the large-scale base station,
and thfi. small-or-medium-scale base station is the wireless connection and the wired
connection.
25
Claim 13 '
The communication control method according to claim 12,
wherein the large-scale base station or the network, which manages the
large-scale base station, performs interference avoidance control for avoiding
30 interference caused due to communication by the small-or-medium-scale base station.
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Claim 14-
A small-or-msdium-scale base station comprising:
: " a reception unit for receiving ' a radio ' signal transmitted from a
-' - '"-^ co'fnmunication terminal or a large-scale base station; - ' - ' ~ ',
5 an information -acquisition unit for acquiring information of the
communication terminal or the large-scale base station by analyzing the radio signal;
a selection unit for selecting one operation range among a plurality of types
of operation ranges based on the information of the communication terminal or the
large-scale base station; and
10 a communication control unit for controlling communication with the
communication terminal in accordance with the operation range selected from among
the plurality of t}pes of operation ranges.