1. A wireless communication system in which each of a plurality of base stations that manage cells is capable of communication with base stations that manage cells that are adjacent to the cell that said base station manages, wherein each of said plurality 5 of base stations has a control unit that: when assigning to a cell that said base station manages a cell identifier that identifies the cell, supplies to peripheral base stations that are base stations that manage cells that are adjacent to said cell a determination request regarding whether or not to 10 assign the cell identifier that is intended to be assigned, and when, in response to said determination request, permission to assign said cell identifier that is intended to be assigned is supplied from said peripheral base stations, assigns said cell identifier that is intended to be assigned to said cell that said base station manages; and when a determination request whether or not to assign a cell identifier that is 15 intended to be assigned is supplied from said peripheral base station, determines whether or not to assign said cell identifier that is intended to be assigned according to the state of assignment of cell identifiers to cells that are adjacent to said cell that said base station manages, and supplies the result of determination to said peripheral base station to said peripheral base station that originated said determination request. 20

2. The wireless communication system as set forth in claim 1, wherein said control unit: supplies to said peripheral base stations cell information that indicates the cell identifier that is assigned to said cell that said base station manages; and 25 upon supply of a determination request whether or not to assign said cell identifier that is intended to be assigned, permits assignment when the cell identifier that is intended to be assigned does not match a cell identifier that is indicated in cell information that was supplied from said peripheral base stations or does not match the cell identifier for which determination whether or not to assign the PCI was requested 30 from a peripheral base station other than the base station that originated the request.

3. The wireless communication system as set forth in claim 1 or 2, wherein said control unit determines a cell identifier that is intended to be assigned to said cell that said base station manages based on cell identifier information that is supplied from said 19 peripheral base stations.

4. A base station that manages a cell and that is capable of communication with peripheral base stations that are base stations that manage cells that are adjacent to said cell, wherein said base station has a control unit tha5 t: when assigning to said cell that said base station manages a cell identifier that identifies the cell, supplies to said peripheral base stations a determination request whether or not to assign the cell identifier that is intended to be assigned, and when, in response to said determination request, an indication of permission to assign said cell 10 identifier that is intended to be assigned is supplied from said peripheral base stations, assigns said cell identifier that is intended to be assigned to said cell that said base station manages; and when a determination request whether or not to assign a cell identifier that is intended to be assigned is supplied from a said peripheral base station, determines 15 according to the state of assignment of cell identifiers to cells that are adjacent to said cell that said base station manages whether said cell identifier that is intended to be assigned can be assigned, and supplies the determination result to said peripheral base station to said peripheral base station that originated said determination request. 20 5. The base station as set forth in claim 4, wherein said control unit: supplies to said peripheral base stations cell information that indicates the cell identifier that is assigned to said cell that said base station manages; and when a determination request whether or not to assign said cell identifier that is intended to be assigned is supplied, permits assignment when the cell identifier that is 25 intended to be assigned does not match with cell identifiers that are indicated in cell information that was supplied from said peripheral base stations or does not match the cell identifier for which determination whether or not to assign the PCI was requested from a peripheral base station other than the base station that originated the request. 30 6. The base station as set forth in claim 4 or 5, wherein said control unit determines a cell identifier that is intended to be assigned to said cell that said base station manages based on cell identifier information that is supplied from said peripheral base stations.

7. A control method of a base station that manages a cell and that is capable of 20 communication with peripheral base stations that are base stations that manage cells that are adjacent to said cell, wherein: when a cell identifier that identifies the cell is to be assigned to said cell that is managed, a determination request whether or not to assign the cell identifier that is intended to be assigned is supplied to said peripheral base stations, and 5 d when, in response to said determination request, permission to assign said cell identifier that is intended to be assigned is supplied from said peripheral base stations, said cell identifier that is intended to be assigned is assigned to said cell that is managed; and when a determination request whether or not to assign a cell identifier that is 10 intended to be assigned is supplied from said peripheral base station, said peripheral base station, determining whether or not to assign said cell identifier that is intended to be assigned is made according to the state of assignment of cell identifiers to cells that are adjacent to said cell that is managed, and the result of determination is supplied to said peripheral base station that originated said determination request. 15

8. The control method as set forth in claim 7, wherein: cell information that indicates a cell identifier that is assigned to said cell that is managed is supplied to said peripheral base stations; and when a determination request whether or not to assign said cell identifier that is 20 intended to be assigned is supplied, the assignment is permitted when the cell identifier that is intended to be assigned does not match cell identifiers that are indicated in cell information that is supplied from said peripheral base stations or does not match the cell identifier for which determination whether or not to assign the PCI was requested from a peripheral base station other than the base station that originated the request. 25

9. The control method as set forth in claim 7 or 8, wherein a cell identifier that is intended to be assigned to said cell that is managed is determined based on cell identifier information that is supplied from said peripheral base stations.

Wireless Communication System, Base Station, and Control Method Therefor
Technical Field
[5 0001]
The present invention relates to a wireless communication system, a base station, and a
control method of the base station.
Background Art
10 [0002]
In order to identify each of the cells that are managed by a base station in a
cellular wireless communication system such as an LTE (Long Term Evolution) system,
a Physical Cell Identity (PCI) is assigned to each cell (for example, refer to Patent
Document 1 (Japanese Unexamined Patent Application Publication No. 2013-021450)).
15 A PCI is used for identifying cells at the time of, for example, performing handover that
switches the cells to which a mobile station is connected. As a result, a PCI must be
assigned to each cell to prevent the occurrence of PCI Collision in which the same PCI
is assigned to a plurality of cells that are arranged in proximity.
[0003]
20 In the following explanation, the operation of a base station according to a
typical method of assigning PCI is described with reference to the sequence chart shown
in FIG. 2 taking as an example a case in which cell #19 is newly arranged in a state in
which a plurality of cells, to which PCI have been assigned (cells #1–#18), are arranged
as shown in FIG. 1. In the following explanation, the base station that manages cell #19
25 is referred to as the newly-established base station, and the base stations that manage
adjacent cells (cells #1–#6) that are adjacent to cell #19 are referred to as peripheral
base stations.
[0004]
The peripheral base stations acquire cell information that indicates the PCI
30 assigned to the adjacent cells from base stations that manage the adjacent cells of the
cells they manage (Step S11). For example, the base station that manages cell #6
acquires cell information from the base stations that manage cells #1, #5, #7, #17, and
#18.
[0005]
3
The peripheral base stations next, upon receiving an inquiry from the
newly-established base station, regarding the adjacent cells of cell #19 create adjacent
cell lists that indicate the PCI assigned to the adjacent cells based on the acquired cell
information and supply the adjacent cell lists to the newly-established base station (Step
S5 12).
[0006]
The newly-established base station determines a candidate of the PCI that is
intended to be assigned to cell #19 based on the adjacent cell lists (Step S13). Here, the
newly-established base station determines a PCI other than the PCI indicated in the
10 adjacent cell lists as the assignment candidate PCI. PCI (PCI #0–#17) that have been
assigned cells that are adjacent to cell #19 (cells #1–#6) and the cells that are adjacent to
these adjacent cells (cells #7–#18) are included in the adjacent cell lists that were
acquired from the peripheral base stations. Accordingly, the newly-established base
station determines, for example, PCI #18, that has not been assigned to cells #1–#18, as
15 the assignment candidate PCI.
[0007]
The newly-established base station then assigns PCI #18, that was determined as
the assignment candidate, to cell #19 (Step S14) and supplies to the peripheral base
stations a PCI assignment notification that indicates that PCI #18 has been assigned to
20 cell #19 (Step S15).
[0008]
By thus assigning a PCI, that is not contained in the adjacent cell lists acquired
from the peripheral base stations, to the cell that is the object of assignment, the
newly-established base station is able to prevent the occurrence of a PCI collision
25 between cells that are adjacent to cell that is the object of assignment and the cells that
are adjacent to these adjacent cells.
[0009]
Although this explanation used an example in which cell #19 is newly arranged
in FIG. 1 and FIG. 2, the base station that changes the PCI of cell #19 (hereinbelow
30 referred to as the “altering base station”) is also able to change the PCI by the using
same process as that of the newly-established base station shown in FIG. 2 in a case in
which cell #19 has already been arranged and the PCI of cell #19 is to be changed.
Literature of the Prior Art
4
Patent Documents
[0010]
Patent Document 1: Japanese Unexamined Patent Application Publication No.
2013–21450
5
Summary of the Invention
Problem to be Solved by the Invention
[0011]
In the typical PCI assignment method described hereinabove, when base stations
10 assign PCI to the cells they manage, each base station determines the PCI that is
assigned to the cell it manages based on adjacent cell lists that are acquired from
peripheral base stations. In addition, this process may consume a time interval of several
hours from the time the base stations begin assignment to cells that they manage until
the PCI are actually assigned. The problem therefore arises that a PCI collision will
15 occur in which the same PCI (PCI #17) is assigned to cell #18 and cell #20 that are
adjacent, as shown in FIG. 3.
[0012]
When a PCI collision occurs, the PCI that is assigned to the cell where the PCI
collision occurred is altered. For example, in FIG. 3, the PCI assigned to cell #18 is
20 altered. In the following explanation, the PCI assigned to cell #18 is assumed to be
altered from PCI #17 to PCI #18.
[0013]
In the typical PCI assignment method described above, there is a further problem
that, with the alteration of the PCI assigned to cell #18, a PCI collision will again occur.
25 This problem is described hereinbelow with reference to FIG. 3.
[0014]
In FIG. 3, due to a PCI collision between cell #18 and cell #20, it is assumed that
the base station that manages cell #18 will attempt to alter the PCI assigned to cell # 18
from PCI #17 to PCI # 18.
30 [0015]
Here, PCI #17 is assigned to cell #18 at the time at which the base station that
manages cell #6 acquires cell information of cell #18, and the PCI that is assigned to
cell #18 is PCI #17 in the adjacent cell list that is produced by the base station that
manages cell #6. As a result, when the newly-established/altering base station (the base
5
station that manages cell #19) assigns PCI #18 to cell #19 based on this adjacent cell
list, a PCI collision occurs between cell #18 and cell #19 due to the alteration of the PCI
assigned to cell #18 by the base station that manages cell #18.
[0016]
Thus, in the typical PCI assignment method described 5 d above, the
newly-established/altering base station assigns PCI to the cell that is the object of
assignment without checking with the peripheral base stations regarding whether or not
to assign the PCI that was determined as an assignment candidate, and as a result, the
potential exists for the occurrence of a PCI collision.
10 [0017]
It is an object of the present invention to provide a wireless communication
system, a base station, and a control method that can reduce the possibility of a PCI
collision.
15 Means for Solving the Problem
[0018]
The wireless communication system of the present invention for achieving the
above-described object is a wireless communication system in which each of a plurality
of base stations that manage cells is capable of communication with base stations that
20 manage cells that are adjacent to the cell that the base station manages, wherein each of
the plurality of base stations has a control unit that:
when assigning a cell identifier that identifies the cell to the cell that the base
station manages, supplies to peripheral base stations that are base stations that manage
cells that are adjacent to the cell a determination request regarding whether or not to
25 assign the cell identifier that is intended to be assigned, and when, in response to the
determination request, permission to assign the cell identifier that is intended to be
assigned is supplied from the peripheral base stations, assigns the cell identifier that is
intended to be assigned to the cell that the base station manages; and
when a determination request regarding whether or not to assign a cell identifier
30 that is intended to be assigned is supplied from a peripheral base station, determines
whether or not to assign the cell identifier that is intended to be assigned according to
the state of assignment of cell identifiers to cells that are adjacent to the cell that the
base station manages, and supplies the result of determination to the peripheral base
station that is the request origin of the determination request.
6
[0019]
The base station of the present invention for achieving the above-described
object is a base station that manages a cell and that is able to communicate with
peripheral base stations that are base stations that manage cells that are adjacent to the
cell, the base station including a control unit tha5 t:
when assigning to the cell that the base station manages a cell identifier that
identifies the cell, supplies to the peripheral base stations a determination request
regarding whether or not to assign the cell identifier that is intended to be assigned, and
when, in response to the determination request, permission to assign the cell identifier
10 that is intended to be assigned is supplied from the peripheral base stations, assigns the
cell identifier that is intended to be assigned to the cell that the base station manages;
and
when a determination request regarding whether or not to assign a cell identifier
that is intended to be assigned is supplied from a peripheral base station, determines,
15 according to the state of assignment of cell identifiers to cells that are adjacent to the
cell that the base station manages, whether the cell identifier that is intended to be
assigned can be assigned, and supplies the determination result to the peripheral base
station that is the request origin of the determination request.
[0020]
20 The control method of the present invention for achieving the above-described
object is a control method of a base station that manages a cell and that is capable of
communication with peripheral base stations that are base stations that manage cells that
are adjacent to the cell, wherein:
when a cell identifier, that identifies the cell, is to be assigned to the cell that the
25 base station manages, a determination request regarding whether or not to assign the cell
identifier that is intended to be assigned is supplied to the peripheral base stations, and
when, in response to the determination request, permission to assign the cell identifier
that is intended to be assigned is supplied from the peripheral base stations, the cell
identifier that is intended to be assigned is assigned to the cell that the base station
30 manages; and
when a determination request regarding whether or not to assign a cell identifier
that is intended to be assigned is supplied from a peripheral base station, the
determination whether or not to assign the cell identifier that is intended to be assigned
is made according to the state of assignment of cell identifiers to cells that are adjacent
7
to the cell that the base station manages, and the result of determination is supplied to
the peripheral base station that is the request origin of the determination request.
[0021]
According to the present invention, the potential for of a PCI collision to occur
can be reduce5 d.
Brief Description of the Drawings
[0022]
FIG. 1 shows an example of the assignment of PCI by a related PCI assignment
10 method.
FIG. 2 is a sequence chart showing an example of the operation of a base station
when assigning PCI by a related PCI assignment method.
FIG. 3 shows an example of the assignment of PCI by a related PCI assignment
method.
15 FIG. 4 shows the principal configuration of a wireless communication system of
an exemplary embodiment of the present invention.
FIG. 5 is a block diagram showing the principal configuration of the base station
shown in FIG. 4.
FIG. 6 is a sequence chart that shows an example of the operation of the base
20 station shown in FIG. 4 at the time of assigning PCI.
FIG. 7 is a sequence chart showing an example of the operation of the base station
shown in FIG. 4 at the time of assigning PCI.
FIG. 8 is a sequence chart showing an example of the operation of the base
station shown in FIG. 4 at the time of assigning PCI.
25 FIG. 9 shows an example of the assignment of PCI in the wireless
communication system shown in FIG. 4.
FIG. 10 shows an example of the assignment of PCI in the wireless
communication system shown in FIG. 4.
30 Mode for Carrying Out the Invention
[0023]
An exemplary embodiment of the present invention is next described with
reference to the accompanying drawings.
[0024]
8
FIG. 4 shows the principal configuration of wireless communication system 10
of an exemplary embodiment of the present invention.
[0025]
Communication system 10 shown in FIG. 4 is provided with a plurality of base
stations (eNodeB) 5 ) 100.
[0026]
Base stations 100 manage cells 100A that are predetermined communication
areas and carry out wireless communication with mobile stations (not shown in the
figure) that are in the range of cells 100A. FIG. 4 shows an example in which base
10 stations 100 each manage one cell 100A, but base stations 100 may each manage a
plurality of cells 100A.
[0027]
Base stations 100 are able to communicate with other base stations 100 by way
of an X2 interface. In addition, base stations 100 are connected to a host device (not
15 shown) on the network side.
[0028]
FIG. 5 is a block diagram showing the principal configuration of base station
100. FIG. 5 omits any description of the configuration by which base station 100 carries
out wireless communication with mobile station 100 or the configuration by which base
20 station 100 carries out communication with the host device.
[0029]
Base station 100 shown in FIG. 5 includes communication unit 101 and control
unit 102.
[0030]
25 Communication unit 101 carries out communication with other base stations 100
by way of an X2 interface.
[0031]
Control unit 102 assigns PCI to cells that base station 100 manages. In addition,
control unit 102 both supplies cell information, that indicates PCI that is assigned to the
30 cell that base station 100 manages by way of communication unit 101, to peripheral
base stations that manage cells that are adjacent to this cell and receives the input of cell
information from peripheral base stations.
[0032]
When newly assigning a PCI to the cell that it manages, control unit 102 further
9
communicates to peripheral base stations a determination request that requests
determination regarding whether or not to assign the PCI, and when, in response to the
determination request, a determination request response is communicated from the
peripheral base stations that indicates that assignment of the PCI is permitted, assigns
the PCI to the cell that it manage5 s.
[0033]
Upon communication from another base station 100 indicating for a request to
determine whether or not to assign a PCI to a cell that that base station 100 manages,
control unit 102 further determines whether to permit assignment of the PCI and
10 communicates the result of determination to base station 100 that is the origin of the
determination request.
[0034]
The operation of base station 100 is next described.
[0035]
15 As shown in FIG. 1, the following explanation takes as an example a case in
which cell #19 is newly arranged in a state in which a plurality of cells (cell #1–#18) to
which PCI have been assigned are arranged or a case in which the PCI of cell #19 is to
be altered in a state in which cells #1–#19 have already been arranged. In this case, base
station 100 that manages cell #19 is the newly-established/altering base station, and
20 base stations 100 that manage cells #1–#6 that are adjacent to cell #19 are the peripheral
base stations.
[0036]
FIG. 6 is a sequence chart showing the operations of base stations 100.
[0037]
25 Control unit 102 of a peripheral base station acquires cell information that
indicates the PCI that have been assigned to adjacent cells from the base stations that
manage the cells that are adjacent to the cell that it manages (Step S101). The
acquisition of the cell information is carried out by the transmission and reception of
eNB Configuration Update messages by way of the already existing X2 interface.
30 [0038]
Control unit 102 of a peripheral base station, upon receiving an inquiry
regarding the adjacent cells that are adjacent to cell #19 from the
newly-established/altering base station, creates an adjacent cell list that indicates the
PCI that have been assigned to cells that are adjacent to the cell it manages based on cell
10
information that has been acquired and supplies the adjacent cell list to the
newly-established/altering base station (Step S102).
[0039]
Based on the adjacent cell list, control unit 102 of the newly-established/altering
base station determines a candidate PCI that is intended to be assigned to the cell 5 that is
the object of PCI assignment (Step S103). Control unit 102 determines, as the
assignment candidate PCI, a PCI other than the PCI that are indicated in the adjacent
cell list. In the following explanation, control unit 102 is assumed to determine PCI #A
as the assignment candidate.
10 [0040]
Control unit 102 of new-established/altering base station next supplies a
request to the peripheral base station, by way of communication unit 101 (Step S104),
to determine whether or not to assign the PCI that was determined as the assignment
candidate (PCI #A).
15 [0041]
When the request to determine whether or not to assign PCI #A is supplied,
control unit 102 of each peripheral base station checks the state of assignment of PCI
#A in cells that are adjacent to the cell that it manages (Step S105) and decided whether
or not to assign PCI #A. More specifically, control unit 102 permits the assignment of
20 PCI #A when PCI #A has not been assigned to adjacent cells, and further, when the
assignment of PCI #A has not been reserved. In other words, control unit 102 permits
the assignment of PCI #A when PCI #A, concerning which a request was made whether
or not to assign it, does not match PCI are indicated in the cell information of cells that
are adjacent to the cell that it manages and permits assignment of the PCI, concerning
25 which a request was made whether or not to assign it from base stations other than the
base station that originated the determination request. Control unit 102 is able to
check whether or not the assignment of PCI #A is reserved according to whether a
determination request to determine whether or not to assign PCI #A is output from base
stations 100 other than base station 100 that supplied the request to determine whether
30 or not to assign PCI #A.
[0042]
In the following explanation, it will be assumed that PCI #A is not assigned to a
cell that is adjacent to the cells that the peripheral base stations manage and that the
assignment of PCI #A has not been reserved.
11
[0043]
Control unit 102 of each peripheral base station, having permitted the
assignment of PCI #A, reserves the assignment of PCI #A (Step S106) and supplies a
determination request response (to the newly-established/altering base station (Step
S107)) indicating that the assignment of PCI #A is permitted (assignment OK)5 .
[0044]
Upon being supplied with the determination request responses indicating that the
assignment of PCI #A is permitted from all peripheral base stations, control unit 102 of
the newly-established/altering base station assigns PCI #A to the cell that is the object
10 of assignment (Step S108) and supplies notification of the PCI assignment, that
indicates that PCI #A was assigned to the assignment object cell (cell #19), to the
peripheral base stations (Step S109). The notification of PCI assignment is realized by
the transmission and reception of eNB Configuration Update messages by way of the
existing X2 interface.
15 [0045]
Upon being supplied with the notification of PCI assignment indicating that PCI
#A was assigned to cell #19, control unit 102 of each peripheral base station updates the
cell information of cell #19 (Step S110), cancels the reservation of PCI #A (Step S111),
and ends the process.
20 [0046]
The operation that is performed when the assignment of an assignment candidate
PCI is not permitted by a peripheral base station is next described with reference to FIG.
7. In FIG. 7, processes identical to those of FIG. 6 are given the same reference numbers
and redundant explanation is omitted.
25 [0047]
When PCI #A has been assigned to a cell that is adjacent to the cell it manages
or when the assignment of PCI #A has been reserved, control unit 102 of the peripheral
base station determines not to permit the assignment of PCI #A and supplies a
determination request response indicating that the assignment of PCI #A is not
30 permitted (assignment NG) (Step S201).
[0048]
Newly-established/altering base station 102, having been supplied with the
determination request response from the peripheral base station indicating that the
assignment of PCI #A is not permitted, again determines an assignment candidate PCI
12
based on the adjacent cell lists (Step S202). Here, control unit 102 determines a
candidate of the assignment candidate PCI while excluding PCI #A. In the following
explanation, it is assumed that control unit 102 determines PCI#B as the assignment
candidate.
[5 0049]
Control unit 102 of the newly-established/altering base station next supplies to
the peripheral base stations a determination request a determination request whether or
not to assign PCI #B (Step S203).
[0050]
10 Control unit 102 of each peripheral base station, having been supplied with the
determination request a determination request whether or not to assign PCI #B, checks
the state of assignment of PCI #B cells that are adjacent to the cell it manages (Step
S204) and determines whether PCI #B can be assigned. In the following explanation, it
is assumed that PCI #B is not assigned to cells that are adjacent to the cells managed by
15 the peripheral base stations and that the assignment of PCI #B is not reserved.
[0051]
When PCI #B is not assigned to cells that are adjacent to the cells managed by
the peripheral base stations and the assignment of PCI #B is not reserved, control unit
102 of each peripheral base station determines to permit assigning of PCI #B and then
20 both reserves the assignment of PCI #B (Step S205) and supplies a determination
request response indicating that the assignment of PCI #B is permitted (Step S206).
[0052]
Control unit 102 of the newly-established/altering base station, having been
supplied with determination request responses from all peripheral base stations
25 indicating that the assignment of PCI #B is permitted, assigns PCI #B to the assignment
object cell (Step S207), and supplies PCI assignment notification to the peripheral base
stations indicating that PCI #B was assigned to the assignment object cell (cell #19)
(Step S208).
[0053]
30 Control unit 102 of the peripheral base station, having been supplied with the
PCI assignment notification indicating that PCI #B was assigned to cell #19, updates the
cell information of cell # 19 (Step S209), cancels the reservation of PCI #B (Step S210),
and ends processing.
[0054]
13
The operation that is performed when the assignment of the assignment
candidate PCI is permitted by a particular peripheral base station but not permitted by
another peripheral base station is described with reference to FIG. 8. In FIG. 8,
processes that are identical to those of FIGs. 6 and 7 are given the same reference
numbers and redundant explanation is here omitte5 d.
[0055]
Even when a determination request response indicating that the assignment of
PCI #A is permitted is supplied from a particular peripheral base station, when a
determination request response, indicating that the assignment of PCI #A is permitted,
10 is supplied from another peripheral base station (Step S301), control unit 102 of the
newly-established/altering base station again determines an assignment candidate PCI
based on the adjacent cell lists (Step S302). Here, control unit 102 determines
assignment candidate PCI while excluding PCI #A. In the following explanation, it is
assumed that control unit 102 determines PCI#B as the assignment candidate.
15 [0056]
Control unit 102 of the newly-established/altering base station next supplies to
the peripheral base stations a determination request whether or not to assign PCI #B
(Step S303).
[0057]
20 Upon supply of the determination request regarding whether or not to assign PCI
#B, control unit 102 of each peripheral base station checks the assignment state of PCI
#B in adjacent cells of the cells it manages (Step S304) and judges whether or not to
assign PCI #B. In the following explanation, it is assumed that PCI #B is not assigned to
cells that are adjacent to the cells managed by the peripheral base stations, and further,
25 that the assignment of PCI #B is not reserved.
[0058]
If PCI #B is not assigned to cells that are adjacent to the cells managed by a
peripheral base station and the assignment of PCI #B is not reserved, control unit 102 of
the peripheral base station determines to permit the assigning of PCI #B and both
30 cancels the reservation of PCI #A (Step S305) and reserves the assignment of PCI #B
(Step S306).
[0059]
Control unit 102 of the peripheral base station next supplies a determination
request response indicating permission to assign PCI #B (Step S307).
14
[0060]
When determination request responses indicating that the assignment of PCI #B
is permitted have been supplied from all peripheral base stations, control unit 102 of the
newly-established/altering base station assigns PCI #B to the assignment object cell
(Step S308) and proceeds to the process of Step 5 tep S208.
[0061]
An example of the assignment of PCI to cells in wireless communication system
10 is next described.
[0062]
10 FIG. 9 shows an example of the assignment of PCI to a plurality of cells in
wireless communication system 10 of the present exemplary embodiment. In FIG. 9, an
example is described in which cell #19 is to be newly disposed in a state in which PCI
are assigned to each of cells #1–#18, or in which cell #19 has already been disposed but
in which the PCI assigned to cell #19 is to be altered. Accordingly, cell #19 is the
15 assignment object cell, base station 100 that manages cell #19 is the
newly-established/altering base station, and base stations 100 that manage cells #1–#6
that are adjacent to cell #19 are peripheral base stations.
[0063]
It is further assumed in FIG. 9 that the assignment of PCI #18 is not reserved in
20 any base station.
[0064]
Each of base stations 100 that manage cells #1–#6 acquires cell information of
the cells that are adjacent to the cell it manages.
[0065]
25 Upon receiving an inquiry regarding cells that are adjacent to cell #19 from base
station 100 that manages cell #19, each of base stations 100 that manage cells #1–#6
creates an adjacent cell list based on the cell information that it has acquired and
supplies the created adjacent cell list to base station 100 that manages cell #19.
Accordingly, PCI (PCI #0–#17) that have been assigned to cells that are adjacent to cell
30 #19 (cells #1–#6) and the cells that are adjacent to these adjacent cells (cells #7–#18)
are included in some of the adjacent cell lists supplied from each of base stations 100
that manage cells #1–#6.
[0066]
Base station 100 that manages cell #19 determines PCI #18 that is not included
15
in the adjacent cell list as an assignment candidate and supplies to the peripheral base
stations a determination request regarding whether or not to assign PCI #18.
[0067]
PCI #18 is not assigned to cells that are adjacent to cells #1–#6. In addition, as
described hereinabove, the assignment of PCI #18 is not reserved in any of the 5 base
stations. As a result, each of base stations 100 that manage cells #1–#6 supplies a
determination request response indicating permission to assign PCI #18 to base station
100 that manages cell #19.
[0068]
10 Upon supply of determination request responses from all of the peripheral base
stations, indicating permission to assign PCI #18 base station 100 that manages cell #19
assigns cell #18.
[0069]
FIG. 10 shows another example of the assignment of PCI to a plurality of cells
15 in wireless communication system 10. Compared with FIG. 9, cell #20 that is adjacent
to cell #18 is added in FIG. 10. It is here assumed that PCI #17 that is the same as for
cell #18, has been assigned to cell #20.
[0070]
In addition, because a PCI collision occurs between cell #18 and cell #20, base
20 station 100 that manages cell #18 is assumed to supply, to base station 100 that manages
cell #6 that is adjacent to cell #18, a determination request regarding whether or not to
assign PCI #18 in order to alter the PCI, that is assigned to cell #18, from PCI #17 to
PCI #18.
[0071]
25 Because PCI #18 has not been assigned to adjacent cells of cell #6, when the
determination request whether or not to assign PCI #18 is supplied from base station
100 that manages cell #18, base station 100 that manages cell #6 supplies, to base
station 100 that manages cell #18, a determination request response that indicates
permission to assign PCI #18. Base station 100 that manages cell #6 further reserves the
30 assignment of PCI #18.
[0072]
In this state, base station 100 that manages cell #19 determines PCI #18 that is
not included in the adjacent cell lists that were reported from the peripheral base stations
as an assignment candidate, and upon supplying a determination request whether or not
16
to assign PCI #18, base station 100 that manages cell #6 supplies to base station 100
that manages cell #19 a determination request response indicating that the assigning of
PCI #18 is not permitted because the assignment of PCI #18 has been reserved.
[0073]
Because a determination request response indicating that the assignment of PC5 I
#18 is not permitted has been supplied, base station 100 that manages cell #19 again
determines an assignment candidate PCI. Base station 100 that manages cell #19 here
determines, as an assignment candidate PCI, a PCI other than PCI included in the
adjacent cell lists and PCI #18, for example, PCI #19.
10 [0074]
Base station 100 that manages cell #19 next supplies to the peripheral base
stations a determination request regarding whether or not to assign PCI #19.
[0075]
PCI #19 is not assigned to cells that are adjacent to each of cells #1–#6. The
15 assignment of PCI #19 is not reserved in any of the base stations. As a result, base
stations 100 that manage cells #1–#6 each supply to base station 100 that manages cell
#19 a determination request response that indicates permission to assign PCI #19.
[0076]
If determination request responses indicating that the assignment of PCI #19 is
20 permitted are supplied from all of the peripheral base stations, base station 100 that
manages cell #19 assigns cell #18 to cell #19.
[0077]
If base station 100 that manages cell #19 here assigns PCI #18 that was
determined as an assignment candidate to cell #19 without checking with the peripheral
25 base stations whether or not to assign PCI #18, a PCI collision will occur between cell
#18 and cell #19. However, due to the output to the peripheral base stations of a
determination request whether or not to assign the assignment candidate PCI by base
station 100 that manages the assignment object cell and the determination that is made
by the peripheral base stations whether or not to assign the assignment candidate PCI,
30 based on the state of assignment of PCI in cells that are adjacent to the cells that they
manage as in the present exemplary embodiment, the potential for the occurrence of PCI
collisions can be reduced.
[0078]
Thus, according to wireless communication system 10 of the present exemplary
17
embodiment, when base station 100 assigns a cell identifier to the cell that it manages, it
supplies to peripheral base stations a determination request regarding whether or not to
assign the cell identifier that is intended to be assigned, and when, in response to the
determination request, permission to assign the cell identifier that is intended to be
assigned is supplied from the peripheral base stations, base station 100 assigns the ce5 ll
identifier that is intended to be assigned to the cell that it manages. Further, when a
determination request whether or not to assign a cell identifier that is intended to be
assigned is supplied from a peripheral base station, base station 100 determines whether
or not to assign the cell identifier that is intended to be assigned according to the state of
10 assignment of cell identifiers to cells that are adjacent to the cell it manages and
supplies the determination result to base station 100 originated of the request.
[0079]
As a result, the potential for PCI collisions to occur can be reduced.
[0080]
15 The invention of the present application has been described hereinabove with
reference to an exemplary embodiment, but the present invention is not limited to the
above-described exemplary embodiment. The configuration and details of the invention
of the present application are open to various modifications within the scope of the
invention of the present application that will be clear to one of ordinary skill in the art.
20 [0081]
This application claims the benefits of priority based on Japanese Patent
Application No. 2013-112632 for which application was submitted on May 29, 2013
and incorporates by citation all of the disclosures of that application.

We Claim:
1. A wireless communication system in which each of a plurality of base stations
that manage cells is capable of communication with base stations that manage cells that
are adjacent to the cell that said base station manages, wherein each of said plurality 5 of
base stations has a control unit that:
when assigning to a cell that said base station manages a cell identifier that
identifies the cell, supplies to peripheral base stations that are base stations that manage
cells that are adjacent to said cell a determination request regarding whether or not to
10 assign the cell identifier that is intended to be assigned, and when, in response to said
determination request, permission to assign said cell identifier that is intended to be
assigned is supplied from said peripheral base stations, assigns said cell identifier that is
intended to be assigned to said cell that said base station manages; and
when a determination request whether or not to assign a cell identifier that is
15 intended to be assigned is supplied from said peripheral base station, determines
whether or not to assign said cell identifier that is intended to be assigned according to
the state of assignment of cell identifiers to cells that are adjacent to said cell that said
base station manages, and supplies the result of determination to said peripheral base
station to said peripheral base station that originated said determination request.
20
2. The wireless communication system as set forth in claim 1, wherein said control
unit:
supplies to said peripheral base stations cell information that indicates the cell
identifier that is assigned to said cell that said base station manages; and
25 upon supply of a determination request whether or not to assign said cell
identifier that is intended to be assigned, permits assignment when the cell identifier
that is intended to be assigned does not match a cell identifier that is indicated in cell
information that was supplied from said peripheral base stations or does not match the
cell identifier for which determination whether or not to assign the PCI was requested
30 from a peripheral base station other than the base station that originated the request.
3. The wireless communication system as set forth in claim 1 or 2, wherein said
control unit determines a cell identifier that is intended to be assigned to said cell that
said base station manages based on cell identifier information that is supplied from said
19
peripheral base stations.
4. A base station that manages a cell and that is capable of communication with
peripheral base stations that are base stations that manage cells that are adjacent to said
cell, wherein said base station has a control unit tha5 t:
when assigning to said cell that said base station manages a cell identifier that
identifies the cell, supplies to said peripheral base stations a determination request
whether or not to assign the cell identifier that is intended to be assigned, and when, in
response to said determination request, an indication of permission to assign said cell
10 identifier that is intended to be assigned is supplied from said peripheral base stations,
assigns said cell identifier that is intended to be assigned to said cell that said base
station manages; and
when a determination request whether or not to assign a cell identifier that is
intended to be assigned is supplied from a said peripheral base station, determines
15 according to the state of assignment of cell identifiers to cells that are adjacent to said
cell that said base station manages whether said cell identifier that is intended to be
assigned can be assigned, and supplies the determination result to said peripheral base
station to said peripheral base station that originated said determination request.
20 5. The base station as set forth in claim 4, wherein said control unit:
supplies to said peripheral base stations cell information that indicates the cell
identifier that is assigned to said cell that said base station manages; and
when a determination request whether or not to assign said cell identifier that is
intended to be assigned is supplied, permits assignment when the cell identifier that is
25 intended to be assigned does not match with cell identifiers that are indicated in cell
information that was supplied from said peripheral base stations or does not match the
cell identifier for which determination whether or not to assign the PCI was requested
from a peripheral base station other than the base station that originated the request.
30 6. The base station as set forth in claim 4 or 5, wherein said control unit determines
a cell identifier that is intended to be assigned to said cell that said base station manages
based on cell identifier information that is supplied from said peripheral base stations.
7. A control method of a base station that manages a cell and that is capable of
20
communication with peripheral base stations that are base stations that manage cells that
are adjacent to said cell, wherein:
when a cell identifier that identifies the cell is to be assigned to said cell that is
managed, a determination request whether or not to assign the cell identifier that is
intended to be assigned is supplied to said peripheral base stations, and 5 d when, in
response to said determination request, permission to assign said cell identifier that is
intended to be assigned is supplied from said peripheral base stations, said cell identifier
that is intended to be assigned is assigned to said cell that is managed; and
when a determination request whether or not to assign a cell identifier that is
10 intended to be assigned is supplied from said peripheral base station, said peripheral
base station, determining whether or not to assign said cell identifier that is intended to
be assigned is made according to the state of assignment of cell identifiers to cells that
are adjacent to said cell that is managed, and the result of determination is supplied to
said peripheral base station that originated said determination request.
15
8. The control method as set forth in claim 7, wherein:
cell information that indicates a cell identifier that is assigned to said cell that is
managed is supplied to said peripheral base stations; and
when a determination request whether or not to assign said cell identifier that is
20 intended to be assigned is supplied, the assignment is permitted when the cell identifier
that is intended to be assigned does not match cell identifiers that are indicated in cell
information that is supplied from said peripheral base stations or does not match the cell
identifier for which determination whether or not to assign the PCI was requested from
a peripheral base station other than the base station that originated the request.
25
9. The control method as set forth in claim 7 or 8, wherein a cell identifier that is
intended to be assigned to said cell that is managed is determined based on cell
identifier information that is supplied from said peripheral base stations.