U.S. patent application number 14/616875 was filed with the patent office on 2015-06-04 for mobile communication system, core network node selection method, and base station and mobile station used therefor.
This patent application is currently assigned to Lenovo Innovations Limited (Hong Kong). The applicant listed for this patent is Sadafuku HAYASHI. Invention is credited to Sadafuku HAYASHI.
Application Number | 20150156691 14/616875 |
Document ID | / |
Family ID | 38792234 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150156691 |
Kind Code |
A1 |
HAYASHI; Sadafuku |
June 4, 2015 |
MOBILE COMMUNICATION SYSTEM, CORE NETWORK NODE SELECTION METHOD,
AND BASE STATION AND MOBILE STATION USED THEREFOR
Abstract
A mobile communication system in which a plurality of base
stations and a plurality of core network nodes are distributed in a
plurality of areas, wherein a source base station or a mobile
station in a handover procedure of the mobile station transmits
information for selecting a core network node to a target base
station.
Inventors: |
HAYASHI; Sadafuku; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HAYASHI; Sadafuku |
Tokyo |
|
JP |
|
|
Assignee: |
Lenovo Innovations Limited (Hong
Kong)
Quarry Bay
HK
|
Family ID: |
38792234 |
Appl. No.: |
14/616875 |
Filed: |
February 9, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13303354 |
Nov 23, 2011 |
|
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14616875 |
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Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 36/0033 20130101;
H04W 36/0016 20130101; H04W 36/08 20130101; H04W 36/12 20130101;
H04W 92/20 20130101 |
International
Class: |
H04W 36/08 20060101
H04W036/08 |
Claims
1. A core network node in a mobile communication system comprising
a target base station, a source base station, and a mobile station,
the core network node comprising: a unit which receives a first
identifier from the target base station when the mobile station
performs handover from the source base station to the target base
station; wherein the first identifier identifies the core network
node to which the source base station is connected.
2. The core network node according to claim 1, wherein the first
identifier is included in a message related to Path Switch.
3. A target base station in a mobile communication system
comprising a source base station, a core network node, and a mobile
station, the target base station comprising: a unit which transmits
a first identifier to the core network node when the mobile station
performs handover from the source base station to the target base
station; wherein the first identifier identifies the core network
node to which the source base station is connected.
4. The target base station according to claim 3, wherein the first
identifier is included in a message related to Path Switch.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation of U.S. application Ser.
No. 13/303,354, filed Nov. 23, 2011, which is a Divisional
application of U.S. application Ser. No. 11/829,644 filed Jul. 27,
2007, which is based upon and claims the benefit of priority from
Japanese Patent Application No. 2006-225967 filed on Aug. 23, 2006,
the contents of all of which are incorporated herein by reference
in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a mobile communication
system, a core network node selection method, and a base station
and a mobile station used therefor, and more particularly, to a
method for selecting a core network node at the time of a handover
associated with the movement of a mobile station.
[0004] 2. Description of Related Art
[0005] A mobile communication system based on Long Term Evolution
(LTE) of 3GPP aims at such architecture as shown in FIG. 8. This
architecture is intended to build a system that can realize data
transfer of higher throughput, for example, than existing systems
by reducing transmission delay in a control plane and a user
plane.
[0006] In this architecture, when cells of base stations (eNodes
B21 to 23) are small, e.g., in a metropolitan area, it is possible
that movement of a mobile station (User Equipment or UE) between
base stations significantly increases handover signals transmitted
from a base station to a core network node (CN Node 11 or 12,
hereinafter abbreviated as CN node). Consequently, excess signal
load would be placed on a Core Network (CN). To reduce load of
handover signals on the CN node, direct exchange of handover
signals between a source base station (Source eNode B) and a target
base station (Target eNode B) is under consideration.
[0007] Also, as shown in the sequence diagram of FIG. 9 that shows
operations during a handover, when a mobile station moves from a
cell covered by a source base station to a cell covered by a target
base station and the source base station carries out a handover
(S1), if a handover is successful by using a handover signal
("Handover Request" message) S2 which the target base station
receives from the source base station, that is, if the target base
station establishes a communication connection with the mobile
station (S3 to S7), the handover procedure can be completed just by
the target base station transmitting one signal S8 called "Handover
Complete" to a CN node.
[0008] The signal name "Handover Complete" is just an example: the
signal is also called "Path Switch", "Binding Update" etc., all of
which are supposed to mean the same signal.
[0009] Upon receipt of the "Handover Complete" signal, the CN node
switches the path for the mobile station from the source base
station to the target base station. In this way, the loads of
signals and processing on CN nodes due to a handover can be
reduced.
[0010] Describing this further in detail with reference to FIG. 9,
S9 denotes a process for the CN node 11 having received the
"Handover Complete" signal S8 to switch the path for the mobile
station from the source base station to the target base station.
After this process, the CN node 11 transmits "Handover Complete Ack
(Acknowledge)" signal S10 to the target base station. Upon
receiving the signal S10, the target base station transmits
"Release Resource" signal S11 to the source base station, and in
response to the signal S11, the source base station releases a
radio resource allocated for the UE. The release of resource is
notified to the CN node 11 with "Release Resource Indication"
signal S12 to complete the handover process. In this manner, loads
of signals and processing on CN nodes due to a handover can be
reduced.
[0011] In a hierarchical structure of CN nodes and base stations,
to prevent service unavailability in a wide area covered by one CN
node in a core network due to its system failure, for example, such
a configuration has been proposed in which CN nodes 11, 12 and
eNode Bs 21 to 23, which are base stations, are connected with one
another in a mesh configuration so that even if one of the CN nodes
fails, the other CN node replaces it to continue to provide
services, as shown in FIG. 8. This mesh configuration is called
"S1-Flex", which is known from 3GPP TR 23.236 V6. 3.0 (2006-03)
(Non-Patent Document 1). The "S1" denotes S1 interface which is an
interface between CN nodes and base stations (eNode B), and
"S1-Flex" used to be called "Iu-Flex" in mobile communication
systems prior to the LTE system.
[0012] In the LTE-based mobile communication system having the
S1-Flex configuration, once a mobile station is connected to a CN
node, it is basically desirable not to change the CN node as long
as the communication continues. This is because it is possible to
reduce interruption of communication due to a handover by
minimizing handovers between CN nodes that are performed along with
the movement of the mobile station, and also because maintaining a
communication path for a long time period is desirable for a
non-real-time service communication such as data communication.
[0013] Existing systems have the soft handover function, which can
prevent discontinuity or interruption of audio even when the mobile
station moves between base stations. However, the new LTE system
mentioned above is designed to build architecture without soft
handover because the system is complicated by maintaining the soft
handover function.
[0014] The new LTE system also aims at the effect of reducing
signal load on CN nodes by reducing handovers between CN nodes so
that fewer signals are exchanged between CN nodes when a mobile
station moves.
[0015] However, in the S1-Flex configuration shown in FIG. 8, it is
sometimes impractical not to change the CN node with which a mobile
station should communicate when the mobile station moves. This is
because, by way of example, if a mobile station as a user terminal
starts communication in Tokyo and continues to be connected to a CN
node in Tokyo even after its user travels to Osaka by Shinkansen,
the communication path gets long and transmission delay will
significantly increase. In such a case, it is therefore required to
change the CN node as the mobile station moves. Consequently, the
function to change or not to change a CN node as appropriate when a
mobile station moves is required for the S1-Flex configuration.
[0016] However, at present, there is no means or way for a target
base station to select a CN node at the time of a handover in the
LTE system. In the existing system, a CN node receives a handover
request signal from a source RNC (radio network controller) and the
CN node itself can judge whether to change the CN node.
SUMMARY
[0017] An exemplary object of the invention is to provide a mobile
communication system and a CN node selection method that enable a
target base station to select an appropriate CN node when a mobile
station moves, as well as a base station and a mobile station used
for the same.
[0018] A base station according to an exemplary aspect of the
invention is a source base station in a mobile communication system
in which a plurality of base stations and a plurality of core
network nodes are distributed in a plurality of areas, the source
base station including:
[0019] a wireless communication unit that performs wireless
communication with a mobile station that performs handover from the
source base station to a target base station in a handover
procedure; and
[0020] a communication unit that transmits, to the target base
station, a first identifier of a core network node to which the
source base station is connected and a second identifier of an area
to which the source base station belongs, in the handover
procedure.
[0021] A base station according to an exemplary aspect of the
invention is a target base station in a mobile communication system
in which a plurality of base stations and a plurality of core
network nodes are distributed in a plurality of areas, the target
base station including:
[0022] a wireless communication unit that performs wireless
communication with a mobile station that performs handover from a
source base station to the target base station in a handover
procedure;
[0023] a communication unit that receives, from the source base
station, a first identifier of a core network node to which the
source base station is connected and a second identifier of an area
to which the source base station belongs, in the handover
procedure.
[0024] A system according to an exemplary aspect of the invention
is a mobile communication system in which a plurality of base
stations and a plurality of core network nodes are distributed in a
plurality of areas, the mobile communication system including;
[0025] a mobile station; a source base station; and a target base
station, wherein
[0026] the mobile station that performs handover from the source
base station to the target base station in a handover
procedure;
[0027] the source base station that transmits a first identifier of
a core network node to which the source base station is connected
and a second identifier of an area to which the source base station
belongs, in the handover procedure; and
[0028] the target base station that receives the first identifier
and the second identifier from the source base station.
[0029] A method according to an exemplary aspect of the invention
is a method for a mobile communication system in which a plurality
of base stations and a plurality of core network nodes are
distributed in a plurality of areas, the method including:
[0030] in a source base station, performing wireless communication
with a mobile station that performs handover from the source base
station to a target base station in a handover procedure; and
[0031] in the source base station, transmitting, to the target base
station, a first identifier of a core network node to which the
source base station is connected and a second identifier of an area
to which the source base station belongs, in the handover
procedure.
[0032] A mobile station according to an exemplary aspect of the
invention is a mobile station in a mobile communication system in
which a plurality of base stations and a plurality of core network
nodes are distributed in a plurality of areas, the mobile station
including:
[0033] a handover processing unit that performs handover from a
source base station to a target base station in a handover
procedure;
[0034] a wireless communication unit that performs wireless
communication with the source base station and the target base
station; and
[0035] a communication unit that transmits, to the target base
station, an identifier of a core network node to which a source
base station is connected and an identifier of an area to which the
source base station belongs, in the handover procedure.
[0036] A base station according to an exemplary aspect of the
invention is a target base station in a mobile communication system
in which a plurality of base stations and a plurality of core
network nodes are distributed in a plurality of areas, the target
base station including:
[0037] a wireless communication unit that performs wireless
communication with a mobile station that performs handover from a
source base station to the target base station in a handover
procedure;
[0038] the communication unit that receives, from a mobile station,
a first identifier of a core network node to which the source base
station is connected and a second identifier of an area to which
the source base station belongs, in the handover procedure.
[0039] A system according to an exemplary aspect of the invention
is a mobile communication system in which a plurality of base
stations and a plurality of core network nodes are distributed in a
plurality of areas, the mobile communication system including:
[0040] a source base station;
[0041] a target base station; and
[0042] a mobile base station that performs handover from the source
base station to the target base station in a handover procedure and
transmits, to the target base station, a first identifier of a core
network node to which a source base station is connected and a
second identifier of an area to which the source base station
belongs, in the handover procedure.
[0043] A method according to an exemplary aspect of the invention
is a method for a mobile communication system in which a plurality
of base stations and a plurality of core network nodes are
distributed in a plurality of areas, the method including:
[0044] in a mobile station, performing handover from a source base
station to a target base station in a handover procedure; and
[0045] in the mobile station, transmitting, to the target base
station, a first identifier of a core network node to which the
source base station is connected and a second identifier of an area
to which the source base station belongs, in the handover
procedure.
[0046] A system according to an exemplary aspect of the invention
is a mobile communication system in which a plurality of base
stations and a plurality of core network nodes are distributed in a
plurality of areas, wherein
[0047] a target base station in a handover procedure of a mobile
station selects a core network node to which the target base
station connects based on information for selecting a core network
node transmitted from a source base station or a mobile
station.
[0048] A system according to an exemplary aspect of the invention
is a mobile communication system in which a plurality of base
stations and a plurality of core network nodes are distributed in a
plurality of areas, wherein
[0049] a source base station or a mobile station in a handover
procedure of the mobile station transmits information for selecting
a core network node to a target base station.
[0050] A base station according to an exemplary aspect of the
invention is a source base station in a mobile communication system
including a target base station and a mobile station, the source
base station including:
[0051] a wireless communication unit that performs wireless
communication with the mobile station that performs handover from
the source base station to the target base station in a handover
procedure; and
[0052] a communication unit that transmits an identifier of a core
network node to which the source base station is connected to the
target base station in the handover procedure.
[0053] A system according to an exemplary aspect of the invention
is a mobile communication system including a source base station, a
target base station and a mobile station, wherein
[0054] the mobile station performs handover from the source base
station to the target base station in a handover procedure,
[0055] the source base station performs wireless communication with
the mobile station and transmits an identifier of a core network
node to which the source base station is connected to the target
base station in the handover procedure, and
[0056] the target base station receives the identifier of the core
network.
[0057] A method according to an exemplary aspect of the invention
is a method for a communication system, the system including a
source base station, a target base station and a mobile station,
the method including:
[0058] performing, in the source base station, wireless
communication with the mobiles station that performs handover from
the source base station to the target base station in a handover
procedure; and
[0059] transmitting, in the source base station, an identifier of a
core network node to which the source base station is connected, to
the target base station in the handover procedure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] FIG. 1 is a system diagram showing a configuration of pool
areas to which the exemplary embodiments of the invention are
applied;
[0061] FIG. 2 is a functional block diagram of a base station
according to a first exemplary embodiment of the invention;
[0062] FIG. 3 is a functional block diagram of a mobile station
according to a first exemplary embodiment of the invention;
[0063] FIG. 4 is a sequence diagram showing operations in the first
exemplary embodiment of the invention;
[0064] FIG. 5 is a flowchart illustrating the algorithm for
selecting a CN node for communication executed at a target base
station in the first exemplary embodiment of the invention;
[0065] FIG. 6 is a flowchart illustrating the algorithm for
selecting a CN node for communication executed at a target base
station in the second exemplary embodiment of the invention;
[0066] FIG. 7 is a functional block diagram of a mobile station
according to a third exemplary embodiment of the invention;
[0067] FIG. 8 illustrates the existing S1-Flex configuration among
eNode Bs and CN nodes; and
[0068] FIG. 9 is a sequence diagram showing an example of a
handover procedure in the configuration of FIG. 8.
EXEMPLARY EMBODIMENT
[0069] The present invention will be described below with reference
to drawings. FIG. 1 is a system configuration diagram for
illustrating the principle of the exemplary embodiments of the
invention, showing an example of a mobile communication system that
uses the concept of "Pool Area" which is defined in the Non-patent
Document 1. In FIG. 1, components corresponding to the ones shown
in FIG. 8 are denoted with the same reference numerals as in FIG.
8.
[0070] A CN is responsible for call control, location control,
service control and the like, and sometimes collectively refers to
an Access Gateway (ASGW) and/or an Access Anchor. CN nodes 11 to 13
are nodes constituting a Core Network (CN). The CN nodes may be
nodes having known functions, such as MSC (Mobile Switching
Center), SGSN (Serving GPRS (General Packet Radio Service) Support
Node) and HLR (Home Location Register). A "CN" sometimes refers to
a CN node itself. A certain area covered by the CN nodes 11 to 13
and base stations 21 to 24 is segmented into pool areas 41 and 42,
each of which has assigned thereto a pool area ID for identifying
the area. It is assumed that the pool areas 41 and 42 are defined
in advance by an operator. Each of the CN nodes 11 to 13 and base
stations 21 to 24 has a pool area ID of the pool area to which it
belongs. To each of the CN nodes, a CN node ID is assigned, and to
each of the base stations, a base station ID is assigned.
[0071] In FIG. 1, in the pool area 41, the CN nodes 11 and 12, and
the base stations 21 to 23 are located, and in the pool area 42,
the CN node 13 and the base station 24 are located. It is assumed
that a mobile station not shown is now in communication with the
base station 21 and the base station 21 is being connected to and
communicating with the CN node 11. In this situation, when the
mobile station moves to a cell of the base station 22, the base
station 22 remains to be connected to the CN node 11 and does not
change the CN node for connection because the base station 22 is
still able to connect to the CN node 11.
[0072] It is assumed that the mobile station moves from the base
station 22 to the base station 23 while still in communication. At
this time, since the distance between the base station 23 and the
CN node 11 is still short enough not to affect delay in
communication, the base station 23 remains to be connected to the
CN node 11 and does not change the CN node for connection.
[0073] It is assumed that the mobile station further moves from the
base station 23 to the base station 24 while in communication.
Then, the distance between the target base station 24 and the CN
node 11 in the pool area 41 becomes long enough to affect delay in
communication, so that the target base station 24 determines
whether to change the CN node in accordance with the type of
communication performed by the mobile station. If the communication
is of a type that is not sensitive to delay, e.g., a non-real-time
service (NRT) type, the base station 24 continues to communicate
with the CN node 11.
[0074] However, if the communication performed by the mobile
station is of a real-time (RT) service type that is sensitive to
delay, the base station 24 selects the CN node 13 belonging to the
pool area 42, to which the base station 24 belongs, as a CN node
for communication (connection), and continues communication. Here,
the non-real-time service may be data communication, for example,
and the real-time service may be audio communication and/or
streaming, for instance.
[0075] Based on the principle described above, a first exemplary
embodiment of the invention can be provided as follows. FIG. 2 is a
functional block diagram of a base station according to the first
exemplary embodiment of the invention. The base station according
to the first exemplary embodiment of the invention includes a
wireless communication unit 31, a communication unit 32, a handover
processing unit 33, a CN node selection unit 34, a notification
information generating unit 35, a control unit (CPU) 36, and a
memory 37.
[0076] The wireless communication unit 31 performs communication
with mobile stations. The communication unit 32 performs
communication with CN nodes and/or other base stations. The
handover processing unit 33 performs handover processing. The CN
node selection unit 34 selects a CN node for a mobile station to
communicate with (or connect to) when the base station becomes a
target base station at the time of a handover of the mobile
station. The notification information generating unit 35 generates
notification information for a target base station when the base
station becomes a source base station at the time of a handover.
The control unit (CPU) 36 controls the units 31 to 35. The memory
37 functions as work memory for the control unit 36 and also as ROM
in which the control operations of the control unit 36 are
prestored as a control procedure program.
[0077] FIG. 3 is a functional block diagram of a mobile station
according to the first exemplary embodiment of the invention. The
mobile station of the first exemplary embodiment of the invention
includes a wireless communication unit 51, a handover processing
unit 52, a control unit (CPU) 53, and a memory 54. The wireless
communication unit 51 performs communication with a base station.
The handover processing unit 52 performs handover processing. The
control unit (CPU) 53 controls the units 51 and 52. The memory 54
functions as work memory for the control unit 53 and also as ROM in
which the control operations of the control unit are prestored as a
control procedure program.
[0078] FIG. 4 is a sequence diagram showing operations in the first
exemplary embodiment of the invention, wherein signals and
processing corresponding to the ones shown in FIG. 9 are denoted
with the same reference numerals as in FIG. 9. When the mobile
station moves from a cell of a source base station to a cell of a
target base station and the source base station performs a handover
(S1), the source base station transmits "Handover Request" message
S2 as a handover request signal to the target base station. The
message S2 contains information for selecting a CN node, such as
the type of communication performed by the mobile station, the ID
of a CN node with which the source base station has been
communicating, and the ID of a pool area (PA) to which the source
base station belongs. The information for selecting a CN node is
generated by the notification information generating unit 35 shown
in FIG. 2.
[0079] After the handover succeeds and the target base station
establishes a communication connection with the mobile station (S3
to S7), the target base station selects a CN node to which it
should be connected in accordance with a CN node selection
algorithm at the CN node selection unit 34 (see FIG. 2) (S21). The
flowchart shown in FIG. 5 illustrates an example of this CN node
selection algorithm. Referring to FIG. 5, the type of communication
performed by the mobile station which will undergo a handover is
first determined (step S31). Specifically, it is determined whether
the communication type is a real-time service or a non-real-time
service. This determination is made by using communication type
information contained in the "Handover Request" signal S2.
[0080] If the communication type is a non-real-time service, the
target base station selects the CN node with which the source base
station has been communicating (been connected to), that is to say,
does not change the CN node (step S33). In this case, subsequent
processing will be the same as processing S8 to S12 of FIG. 9. On
the other hand, if the communication type is a real-time service
such as audio communication, it is determined whether the pool area
ID of the source base station is the same as that of the target
base station (step S32).
[0081] This determination is made with information on the ID of a
pool area to which the source base station belongs that is
contained in the "Handover Request" signal S2. If the pool area ID
of the source base station is the same as that of the target base
station (Yes at step S32), processing at step S33 is performed,
that is, the CN node is not changed.
[0082] On the other hand, if the pool area ID of the source base
station is different from that of the target base station,
processing at step S34 is performed. In this processing, a CN node
that is closer to the target base station than the CN node with
which the source base station has been communicating (or connected
to) (generally, a CN node within a pool area to which the target
base station belongs) is selected as the node for connection. This
can prevent information delay that results from a long
communication path. Here, the target base station can also select a
CN node that is closest to it. When selecting a CN node, the target
base station may be configured to select one with reference to a
table showing the positional relationship between the target base
station and CN nodes which is prepared in each base station.
[0083] Referring back to FIG. 4, after step S34 of FIG. 5, the
target base station transmits "Handover Complete" message S22 to
the selected CN node. Assuming that the target base station is the
base station 24 in the system of FIG. 1, the selected CN node is
the CN node 13 within the same pool area 42. Therefore, the
sequence of FIG. 4 shows that the signal S22 is transmitted to the
CN node 13.
[0084] After the CN node 13 receives the "Handover Complete"
message S22 from the target base station, the CN node 13 asks the
source CN node (CN node 11 in this example) for information on the
mobile station, that is, "UE Context" ("Context Request" signal
S23), because the CN node 13 does not have control information for
the mobile station. The target CN node 13 can get the destination
of the "Context Request" signal S23 from the ID of the source CN
node 11 contained in the "Handover Complete" message S22 received
from the target base station. Then, the CN node 13 receives the "UE
Context" information through "Context Response" signal S24 from the
CN node 11, sets the target base station and a path, and continues
communication (S25, S11, and S12).
[0085] The selection of a CN node at the target base station shown
in FIG. 5 can be represented as the rules below:
If QoS=NRT (if Quality of Service (QoS) is a non-real-time
service), then, target eNode B chooses same CN Node. If QoS=RT and
PA=own PA (if the QoS is a real-time service and the pool area ID
is the same as its own pool area ID), then, target eNode B chooses
same CN Node, else, if QoS=RT and PA.noteq.own PA (if the QoS is a
real-time service and the pool area ID is not the same as its own
pool area ID), then, target eNode B chooses target CN Node.
[0086] By selecting a CN node based on a communication type and a
pool area, the first exemplary embodiment provides the effects of
reducing the frequency of CN node switching and lessening the
influence of information delay resulting from a long communication
path on the quality of a service which is sensitive to delay, such
as a real-time service.
[0087] The first exemplary embodiment described above focuses
attention to delay of information resulting from a long
communication path and determines whether the communication type is
a real-time service (RT) or a non-real-time service (NRT), and
changes the CN node if the communication type is a real-time
service which is sensitive to delay and if the pool ID is
different. Next, a second exemplary embodiment will be described
below as illustration of a case that focuses on discontinuity (or
interruption) of information due to CN node switching and controls
CN node switching by determining whether the communication type is
an audio communication service which is sensitive to discontinuity
of information or a data communication service which tolerates
discontinuity of information.
[0088] As the system configuration, and the configurations of a
base station and a mobile station of the second exemplary
embodiment are the same as those of the first exemplary embodiment,
description of them is omitted. The operation sequence diagram of
this exemplary embodiment is the same as the operation sequence of
FIG. 4 except for the algorithm for CN node selection processing
S21 at the target base station in FIG. 4.
[0089] FIG. 6 is a flowchart showing the CN node selection
algorithm in this exemplary embodiment, wherein steps corresponding
to the ones FIG. 5 are denoted with the same reference numerals as
in FIG. 5. In FIG. 6, the type of communication performed by the
mobile station which is to undergo a handover is determined (step
S31). Specifically, at step S31, it is determined whether the
communication type is an audio communication service which is
sensitive to discontinuity of information or a data communication
service which tolerates discontinuity of information.
[0090] If the communication type is an audio communication service,
the target base station selects the CN node with which the source
base station has been communicating, that is, does not change the
CN node (step S33). This can prevent discontinuity of information
due to switching of a CN node. On the other hand, if the
communication type is a data communication service, it is
determined whether the pool area ID of the source base station is
the same as that of the target base station (step S32). If the pool
area ID of the source base station is the same as that of the
target base station, processing at step S33 is performed, i.e., the
CN node is not changed. If the pool area ID is different,
processing at step S34 is performed, where a CN node which is
closer to the target base station than the CN node with which the
source base station has been communicating (or connected to)
(generally, a CN node within the pool area to which the target base
station belongs) is selected as a node for connection.
[0091] As in the first exemplary embodiment, the target base
station may be configured to reference a table showing the
positional relationship between it and CN nodes which is prepared
in each base station when selecting a CN node closest to it (target
base station) and/or a CN node.
[0092] In this case, a CN node is selected at the target base
station in accordance with the rules below:
If QoS=Audio (if the QoS is an audio service), then, target eNode B
chooses same CN Node. If QoS=Data and PA=own PA (if the QoS is data
communication and the pool area ID is the same as its own pool area
ID), then, target eNode B chooses same CN Node, else, if QoS=DATA
and PA.noteq.own PA (if the QoS is data communication and the pool
area ID is not the same as its own pool area ID), then, target
eNode B chooses target CN Node.
[0093] According to the second exemplary embodiment, by selecting a
CN node based on a communication type and a pool area, there can be
provided an effect of lessening the influence of information
discontinuity due to switching of a CN node on the quality of
communication that is sensitive to discontinuity of information,
such as audio communication, while presupposing switching of a CN
node according to movement of a mobile station.
[0094] Which of the CN node selection algorithm of the first
exemplary embodiment (FIG. 5) and that of the second exemplary
embodiment (FIG. 6 to adopt can depend on the system in question.
For example, for a system which puts emphasis on the reduction of
influence of information delay resulting from a long communication
path on communication quality, the CN node selection algorithm of
the first exemplary embodiment may be adopted. For a system which
puts emphasis on the reduction of influence of information
discontinuity due to CN node switching on communication quality,
the CN node selection algorithm of the second exemplary embodiment
may be adopted.
[0095] As has been described, according to the first or second
exemplary embodiment, when the "Handover Request" message contains
CN node ID information and pool area ID information, the target
base station can use those pieces of information with communication
type information to decide an optimum CN node.
[0096] The communication types (QoS) in the first and second
exemplary embodiments described above are merely examples and are
not limited to the ones described: the communication type (QoS)
information may also be a guaranteed bit rate, maximum bit rate,
delay, error rate, traffic class (e.g., audio, streaming,
background, interactive), for example. A CN node selection
algorithm appropriately defined to such communication types can be
applied to the first and second exemplary embodiments.
[0097] It is also possible to define an information set which
consists of elements of information on a plurality of communication
types (QoS) (e.g., guaranteed bit rate, maximum bit rate, delay,
error rate, and traffic class). It is also possible to define a
label for indicating a combination of values of elements in such an
information set (e.g., combination of guaranteed bit rate=A (bps),
maximum bit rate=B (bps) and traffic class=audio). In this case,
information on communication type (QoS) may be transmitted as a
label (e.g., one-byte information) from a CN node to an eNode
B.
[0098] The label can also be used as the communication type
contained in the "Handover Request" message in the sequence of FIG.
4 which is transmitted from a source base station to a target base
station. In this case, the target base station can select an
appropriate piece of communication type (QoS) information (element)
(e.g., traffic class=audio) from the elements of an information set
about communication type (QoS) received as a label, and use the
selected communication type information in the CN node selection
algorithm.
[0099] In such a way, even in a system that has many pieces of
communication type (QoS) information, there is provided an effect
of allowing a target base station to select an appropriate CN node
while suppressing the amount or duration of communication between
the source base station and the target base station.
[0100] In the exemplary embodiments described above, the target
base station receives the communication type of the mobile station,
the ID of a CN node with which the source base station is
communicating, and a pool area ID to which the source base station
belongs, which are information necessary for CN node selection, in
the "Handover Request" message S2 (see FIG. 4) from the source base
station. On the other hand, in a third exemplary embodiment of the
invention, the target base station receives such information (i.e.,
information for CN node selection) through the "Handover Complete"
message S7 shown in FIG. 4 from a mobile station.
[0101] The system configuration and mobile station configuration of
the third exemplary embodiment are the same as those shown in FIGS.
1 and 2. FIG. 7 shows the configuration of a mobile station,
wherein units corresponding to the ones shown in FIG. 3 are denoted
with the same reference numerals as in FIG. 3. As shown in FIG. 7,
the mobile station of the third exemplary embodiment has a
notification information storing unit 55 for storing notification
information for a target base station in addition to the
configuration of FIG. 3. The notification information storing unit
55 stores the communication type, the CN node ID with which the
source base station is communicating, and the pool area ID of the
source base station. The mobile station includes the information
stored in the notification information storing unit 55 in the
"Handover Complete" message S7 for transmission to the target base
station. The target base station receives the information and
decides a CN node to which it should connect in accordance with the
CN node selection algorithm shown in FIG. 5 or 6.
[0102] In the third exemplary embodiment, the mobile station
transmits information for CN node selection (communication type,
and the ID and the pool area ID of the CN node with which the
source base station is communicating) to the target base station in
the "Handover Complete" message S7. However, the message used by
the mobile station for transmitting the information for CN node
selection to the target base station is not limited to the
"Handover Complete" message. In a system where a mobile station,
not the source base station, requests a handover, for example, the
mobile station can also use the "Handover Request", which is a
handover request signal, to transmit the information for CN node
selection to the target base station.
[0103] In the exemplary embodiments described above, the target
base station makes determination based on the pool area ID of the
source base station (step S32) after determination based on
communication type (step S31). However, the target base station can
also make determination based on communication type (step S31)
after determination based on the pool area ID of the source base
station (step S32). In other words, step S31 and step S32 can also
be interchanged in FIGS. 5 and 6.
[0104] In the exemplary embodiments described above, the target
base station selects or decides a CN node with which it will
communicate based on the communication type, the ID of the CN node
with which the source base station is communicating, and the ID of
the pool area to which the source base station belongs. However,
the target base station can also decide a node for communication
based on the CN node with which the source base station is
communicating and the ID of the pool area to which the source base
station belongs. In this case, the target base station determines
whether the ID of the pool area to which the source base station
belongs is the same as its pool area ID without considering the
communication type. In other words, step S31 is removed from the CN
selection algorithms shown in FIGS. 5 and 6.
[0105] This has the effect of allowing the target base station to
select a CN node while suppressing the amount of processing
performed by the target base station. In addition, the source base
station and/or the mobile station may also be configured not to
send a communication type to the target base station. This provides
the effect of allowing the target base station to select a CN node
while suppressing the amount or duration of communication between
the source base station or the mobile station and the target base
station.
[0106] In the exemplary embodiments described above, the target
base station decides appropriately a CN node for communication by
using the communication type, the ID of the CN node with which the
source base station is communicating, and the ID of the pool area
to which the source base station belongs. However, it is also
possible to arrange the source base station and/or the mobile
station to send only the CN node ID to the target base station. In
this case, the target base station can also receive the CN node ID
from the source base station and/or the mobile station and connect
to a CN node which has the CN node ID received.
[0107] This provides the effect of allowing the target base station
to select a CN node while suppressing the amount or duration of
communication between the source base station or the mobile station
and the target base station. It also has the effect of enabling the
target base station to select a CN node while suppressing the
amount of processing to be performed by the target base
station.
[0108] Further, the source base station and/or the mobile station
may also decide a CN node to which the target base station should
connect taking into consideration the communication type and/or the
pool area ID of CN nodes in advance and send the ID of the CN node
decided to the target base station. This provides the effect of
enabling the source base station and/or the mobile station to
select a CN node to which the target base station should
connect.
[0109] In addition, when executing the CN node selection algorithm
shown in FIG. 5 or 6, the target base station can select a CN node
also in consideration of information indicating load on CN nodes.
In this case, if the load on a CN node decided or selected for
connection is large (i.e., the amount of load is large), the target
base station may also select another CN node in its vicinity which
is under less load. This provides the effect of allowing the target
base station to select an appropriate CN node also in consideration
of load distribution among CN nodes in addition to information such
as the pool area ID.
[0110] It will be apparent that the operation procedure of the base
station and/or the mobile station in the exemplary embodiments can
be stored as programs in a recording medium such as a ROM, which
are read and executed by a computer (CPU).
[0111] Further, a fourth exemplary embodiment of the invention is a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, wherein a target base station at the time of a
handover of a mobile station selects a core network node to which
the target base station should connect based on information for
selecting a core network node transmitted from a source base
station or the mobile station.
[0112] A fifth exemplary embodiment of the invention is a mobile
communication system in which a plurality of base stations and a
plurality of core network nodes are distributed in a plurality of
areas, wherein a source base station or a mobile station at the
time of a handover of the mobile station transmits information for
selecting a core network node to a target base station.
[0113] A sixth exemplary embodiment of the invention is a mobile
communication system in which a plurality of base stations and a
plurality of core network nodes are distributed in a plurality of
areas, the mobile communication system comprising:
[0114] in a source base station at the time of a handover of a
mobile station,
[0115] a message generating unit for generating a handover request
message which includes an identifier of a core network node to
which the source base station is connected and an identifier of an
area to which the source base station belongs,
[0116] and a transmitting unit for transmitting the message to a
target base station.
[0117] A seventh exemplary embodiment of the invention is a mobile
communication system in which a plurality of base stations and a
plurality of core network nodes are distributed in a plurality of
areas, the mobile communication system comprising:
[0118] in a mobile station,
[0119] a message generating unit for generating a handover request
message which includes an identifier of a core network node to
which a source base station is connected and an identifier of an
area to which the source base station belongs,
[0120] and a transmitting unit for transmitting the message to a
target base station at the time of a handover.
[0121] A eighth exemplary embodiment of the invention is, in a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, a method for selecting a core network node to
which a target base station should connect at the time of a
handover of a mobile station, comprising:
[0122] in a source base station,
[0123] generating a handover request message which includes an
identifier of a core network node to which the source base station
is connected and an identifier of an area to which the source base
station belongs,
[0124] and transmitting the message to a target base station.
[0125] A ninth exemplary embodiment of the invention is, in a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, a method for selecting a core network node to
which a target base station should connect at the time of a
handover of a mobile station, comprising:
[0126] in the mobile station, including an identifier of a core
network node to which a source base station is connected and an
identifier of an area to which the source base station belongs into
a message to a target base station at the time of a handover, and
transmitting the message.
[0127] A tenth exemplary embodiment of the invention is a source
base station at the time of a handover of a mobile station in a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, the source base station comprising:
[0128] a message generating unit for generating a handover request
message which includes an identifier of a core network node to
which the source base station is connected and an identifier of an
area to which the source base station belongs,
[0129] and a transmitting unit for transmitting the message to a
target base station.
[0130] A eleventh exemplary embodiment of the invention is a target
base station at the time of a handover of a mobile station in a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, the target base station comprising:
[0131] a selection unit for selecting a core network node to which
the target base station should connect based on an identifier of a
core network node to which a source base station is connected and
an identifier of an area to which the source base station belongs,
which are contained in a handover request message from the source
base station.
[0132] A twelfth exemplary embodiment of the invention is a target
base station at the time of a handover of a mobile station in a
mobile communication system in which a plurality of base stations
and a plurality of core network nodes are distributed in a
plurality of areas, the target base station comprising:
[0133] a selection unit for selecting a core network node to which
the target base station should connect based on an identifier of a
core network node to which a source base station is connected and
an identifier of an area to which the source base station belongs,
which are contained in a message at the time of the handover from
the mobile station.
[0134] A thirteenth exemplary embodiment of the invention is a
mobile station in a mobile communication system in which a
plurality of base stations and a plurality of core network nodes
are distributed in a plurality of areas, the mobile station
comprising:
[0135] a message generating unit for generating a message which
includes an identifier of a core network node to which a source
base station is connected and an identifier of an area to which the
source base station belongs,
[0136] and a transmitting unit for transmitting the message to a
target base station at the time of a handover.
[0137] An exemplary advantage according to the invention is that a
target base station itself can appropriately select a CN node with
which it should communicate by receiving information necessary for
selecting a CN node from a source base station or a mobile station
at the time of the handover of the mobile station.
[0138] While the invention has been particularly shown and
described with reference to exemplary embodiments thereof, the
invention is not limited to these embodiments. It will be
understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the claims.
* * * * *