Description]
[Title of Invention]
MOBILITY CONTROL METHOD AND DEVICE IN MOBILE COMMUNICATION
NETWORK
[Technical Field]
[OOOI]
The present invention relates to mobility control in a mobile communication
network and, more particularly, to a mobility control method and device in a
heterogeneous network having multiple cells of different cell sizes.
[Background Art]
[0002]
In a mobile communication network for mobile telephones or the like, cells
managed by radio base stations have various sizes. These cells are named according
to the radiuses of cells; namely, cells not smaller than 1 km in radius are referred to as
macro cells, cells about 0.5 to 1.5 km in radius, pic0 cells, and cells about 10 to 500 m
in radius, femto cells. Of them, femto and pico cells are also referred to as small cells,
and hereinafter the term "small cell" will be used unless otherwise noted.
[0003]
The setup of a small cell makes it possible to achieve coverage compensation
and capacity increase. Coverage compensation is required to cover an area where
radio waves do not reach because of buildings and the like within a macro cell. For
example, sufficient mobile communication services can be provided by placing a small
cell base station inside a building where radio waves from a macro cell base station do
not reach due to penetration losses caused by building walls and the like. Moreover,
capacity increase is required to handle mobile traffic rapidly increasing due to the
popularization of mobile phones, particularly, smart phones. With small cells, the
number of users that can be accommodated per cell is lessened by shortening the cell
radius, whereby the overall capacity can be increased.
[0004]
As described above, the deployment of small cells makes it possible to achieve
coverage compensation and capacity increase. However, in a system where macro and
small cells coexist, a problem arises that the probability of radio wave interference
increases, leading to degradation in communication quality. To address such a problem,
heterogeneous networks employ such a configuration that small cells are entrusted with
hot spots and radio wave-unreachable areas while macro cells cover other areas, with
appropriate interference control, power control and the like being performed.
[0005]
Further, as to cell reselection control in mobile communication networks, NPLs
1 to 4 describe technologies for control at the times of cell reselection and handover.
NPLs 1 and 2 define T-reselection, which is a cell reselection timer value. NPL 3
defines 31 seconds as the maximum value of the T - reselection timer in 3G networks
and NPL 4 defines 7 seconds as the maximum value of the T-reselection timer in LTE
networks. Accordingly, in LIE networks, if the T-reselection timer is set to a maximum
value of 7 seconds, cell reselection determination can be performed by measuring radio
wave quality in another cell during 7 seconds, and if radio wave quality in the other cell
is good, cell reselection can be executed. Furthermore, if Speed dependent Scaling
Factor for Treselection defined in NPLs I and 3 is used, the determination time for cell
reselection, T-reselection, can be varied depending on the speed of a mobile station.
[0006]
Further, in inter-cell handover, the measurement time for measurement
reporting (Time To Trigger) can be varied by applying SpeedStateScaleFactors to a
mobile station moving at high speed (NPLs 3 and 4).
[Citation List]
[Non-patent Literature]
[0007]
[NPL I ]
3GPP TS25.304 Ver10.4.0
[NPL 21
3GPP TS36.304 Ver10.4.0
[NPL 31
3GPP TS25.331 Verl 1.0.0
[NPL 41
3GPP TS36.331 Ver10.5.0
[Summary of Invention]
[Technical Problem]
[OOOS]
However, in a system such as a heterogeneous network where macro and
small cells coexist, in general, the smaller the size of a cell, the shorter the duration of a
mobile station's stay therein. When a mobile station is moving, the duration of its stay
becomes shorter in proportion with the mobility speed. Accordingly, even if a mobile
station only passes through a small cell, location registration signaling is created both
when it enters the small cell and when it enters again a macro cell. Consequently, if a
number of mobile stations create such location registration signaling, a new problem
arises that an increase of location registration signals becomes more apparent as the
size of a small cell becomes smaller and/or more mobile stations move at high speed.
A more detailed description will be given of this problem of the frequent creation of
location registration signaling.
[0009]
First, in mobile communication, the locations of mobile terminals (User
Equipment; hereinafter, abbreviated to UE as appropriate) are managed on a location
registration area basis. In 3G networks, location areas are used for circuit switching
services, and routing areas are used for packet switching services. Moreover, in LIE
(Long Term Evolution), a TA list, which includes multiple tracking areas (TAs), is
assigned to each UE so that location registration timings can be staggered. Accordingly,
a TA list can be regarded as a location registration area.
[OO 1 01
Assuming that a UE moves at constant speed, the smaller a location
registration area, the shorter the duration of the UE's stay therein, and so the location
registration signaling of the UE greatly increases, as described above. Supposing a
scenario in which a user holding a UE passes through a small cell on foot, a location
registration procedure occurs in the small cell when shelhe moves from a macro cell to
the small cell, and a location registration procedure further occurs in the macro cell
when shethe moves from the small cell to the macro cell. Assuming that the small cell
is a femto cell, since a femto cell has a radius of a few tens meters, the user moves to
another cell only in a few tens seconds without making a call. In a few tens seconds, a
UE only can pass through a small cell even if it moves to the small cell and makes
location registration. It therefore can be thought that the number of UEs actually using
communication services such as voice and packet services shares only a few percent.
This only results in an increase in the number of location registrations in small and
macro cells.
[OOI I ]
Although the above-mentioned technologies for control at the times of cell
reselection and handover can also be applied to a heterogeneous network, any of them
has problems as will be described below and therefore cannot solve the abovedescribed
problem of the frequent creation of location registration signaling.
[OOI 21
(1) In NPLs 1 to 4, the cell reselection timer (T - reselection) is defined as
described above, but only one cell reselection timer is defined for the cell on which the
user is staying. That is, a change to a T-reselection for a macro cell affects not only
reselection from a macro cell to a small cell but also a time for reselection from a macro
cell to a macro cell. As a result, service quality may be degraded at the time of
reselection to a macro cell.
[00 1 31
(2) As defined in NPLs 1 and 3, the determination time at the time of high-speed
movement can be varied by multiplying T-reselection, which is the determination time
for cell reselection, by Speed dependent Scaling Factor for Treselection. However,
Speed dependent Scaling Factor for Treselection ranges from 0 to 1 in increments of
0. I , and the determination time for cell reselection only can be shortened but cannot be
extended. That is, it is impossible to allow a UE moving at high speed to delay starting
location registration.
[0014]
(3) The use of HCS (Hierarchical Cell Structure) defined in NPL 1 makes it
possible to allow a UE, when it is in high-speed state, to reselect a cell with a lower
HCS priority (HCS-PRIO). For example, in case where a micro cell is assigned
HCS - PRlO = I and a 3G small cell is assigned HCS-PRIO = 7, then a UE in still or
low-speed state preferentially selects the 3G small cell rather than the macro cell but,
when it is in high-speed state, can preferentially select the macro cell so that location
registration in the 3G small cell can be avoided.
[OOI 51
However, LTE does not define HCS and, instead, employs an absolute prioritybased
cell reselection mechanism. Accordingly, HCS cannot be applied to reduce
location registration signaling in LTE small cells and LTE macro cells. Further, to
accomplish mobility with LTE in a 3G network, an LTE-side frequency needs to be
broadcast by using broadcast information (SIB1 9: System Information Block type 19,
NPL 3) and the absolute priority-based cell reselection mechanism needs to be
introduced also in the 3G network, in which case HCS cannot be used concurrently
according to the existing technology (NPL 1). That is, HCS cannot be applied in a 3G
network that enables mobility with LTE, and so the problem of the frequent creation of
location registration signaling cannot be solved.
[00 1 61
As described above, according to the existing technologies described in NPLs 1
to 4, unrequired location registration signaling to small cells in a heterogeneous network
cannot be reduced.
[00 I 71
Accordingly, an object of the present invention is to provide a mobility control
method and device that can suppress an increase of location registration signaling.
[Solution to Problem]
[00 1 81
A mobility control method according to the present invention is a mobility control
method for a mobile terminal in a mobile communication network including cells of
multiple types differing in cell size, characterized by comprising: presetting priorities for
mobility control on individual neighbor cells or individual neighbor cell types; and
performing mobility control such as to select a neighbor cell with a priority lower than
that of a currently staying cell when the mobile terminal is moving faster than a
predetermined speed.
A mobility control device according to the present invention is a mobility control
device in a mobile communication network including cells of multiple types differing in
cell size, characterized by comprising: a priority assignment information storage means
for storing priorities for mobility control set on individual neighbor cells of a cell on which
a mobile terminal is currently staying or on individual neighbor cell types; and a mobility
determination control means for performing mobility control such as to select a neighbor
cell with a priority lower than that of the currently staying cell when the mobile terminal
is moving faster than a predetermined speed.
A mobility control system according to the present invention is a mobility control
system in a mobile communication network including cells of multiple types differing in
cell size, comprising: base stations managing the cells; and a mobile station that can
move between the cells, characterized in that the mobile station presets priorities for
mobility control on individual neighbor cells or individual neighbor cell types and, when
the mobile terminal is moving faster than a predetermined speed, performs mobility
control such as to select a neighbor cell with a priority lower than that of a currently
staying cell.
[Advantageous Effects of invention]
[OOI 91
According to the present invention, mobility control is performed such that a
neighbor cell with a priority lower than that of a currently staying cell is selected at the
time of high-speed movement, whereby an increase of location registration signaling
can be suppressed.
[Brief Description of Drawings]
[0020]
[FIG. I ]
FIG. 1 is a schematic diagram showing an example of a heterogeneous network
for implementing a mobility control system according to an exemplary embodiment of
the present invention.
[FIG. 21
FIG. 2 is a schematic block diagram showing a functional configuration of a
mobile terminal according to the present exemplary embodiment.
[FIG. 31
FIG. 3 is a schematic block diagram showing a functional configuration of a
base station according to the present exemplary embodiment.
[FIG. 41
FIG. 4 is a diagram showing an example of celllfrequency and priority
assignment information used in a mobility control method according to a first example of
the present invention.
[FIG. 51
FIG. 5 is a flowchart showing cell reselection control operation of a mobile
terminal according to the first example.
[FIG. 61
FIG. 6 is a diagram showing an example of cell type and priority assignment
information used in a mobility control method according to a second example of the
present invention.
[FIG. 71
FIG. 7 is a diagram showing an example of a neighbor cell list for describing a
first example of a method for deciding on a mobility determination time.
[FIG. 81
FIG. 8 is a flowchart showing the first example of the method for deciding on a
mobility determination time.
[FIG. 91
FIG. 9 is a diagram schematically showing the contents of the neighbor cell list
for describing the first example of the method for deciding on a mobility determination
time.
[FIG. 101
FIG. 10 is a diagram showing an example of broadcast information for
describing a second example of the method for deciding on a mobility determination
time.
[FIG. 111
FIG. 11A is a diagram showing an example of cell type estimation for describing
a third example of the method for deciding on a mobility determination time, and FIG.
11 B is a diagram showing an example of broadcast information in the third example.
[FIG. 121
FIG. 12 is a diagram showing an example of adjustment of a cell reselection
timer for describing the third example of the method for deciding on a mobility
determination time.
[Description of Embodiments]
[0021]
According to an exemplary embodiment of the present invention, in case where
priorities are set on individual neighbor cells or individual cell types, a mobile terminal
performs mobility control such as to select a neighbor cell with a lower mobility priority
than the mobility priority of a currently staying cell when it is moving faster than a
predetermined speed, whereby it is possible to avoid unrequired location registration.
[0022]
In case where a higher priority is preset on a cell of a smaller size, a mobile
terminal does not perform mobility control in accordance with the normal priorities but
performs mobility control such as to select a cell with a lower priority as the mobility
speed becomes higher. Thus, the mobile terminal is allowed to pass through a small
cell of a small size without performing cell reselection thereto, and consequently the
frequent creation of location registration signaling can be avoided. In this event, if a
neighbor cell is a macro cell, the mobile terminal is allowed to perform location
registration in accordance with the normal priorities, whereby cell reselection
performance is not affected. Hereinafter, a detailed description will be given of a mobile
communication network for implementing a mobility control system according to the
present exemplary embodiment, with reference to drawings. Here, to avoid
complication, a description will be given of a case as an example where in a
heterogeneous network in which macro and small cells neighbor on each other, a
mobile terminal located within the macro cell moves while passing through the small cell.
However, it is sufficient that the macro and small cells have different cell sizes and
neighbor on each other, and the cell deployment shown in FIG. 1 is not a restriction.
[0023]
Referring to FIG. I , the heterogeneous network for implementing the present
exemplary embodiment includes a mobile terminal 10, a macro cell base station 20a, a
small cell base station 20b, and a mobility management station 30. The mobility
management station 30 manages the macro cell base station 20a and small cell base
station 20b, and the macro cell base station 20a and small cell base station 20b control
a macro cell 21a and a small cell 21 b, respectively. Note that there may be a plurality of
mobile terminals 10, macro cell base stations 20a, and small cell base stations 20b,
respectively.
[0024]
Referring to FIG. 2, the mobile terminal 10 in the present exemplary
embodiment includes a radio transceiver section 101 and a control section 102 and, in
addition to them, has functions including a mobility determination control section 103, a
mobility determination timer 104, and a memory 105. The radio transceiver section 101
is capable of transmitting and receiving radio signals tolfrom the base stations (macro
cell base station 20a, small cell base station 20b) and, for example, receives broadcast
information from a base station and transmits a RRC (Radio Resource Control)
message and the like to a base station. The control section 102 performs control for
bearer establishment, radio quality measurement, handover and the like in accordance
with an instruction in a message (e.g., RRC message) from the network. According to
the present exemplary embodiment, the mobility determination control section 103
performs mobility determination control, using priority assignment information broadcast
from a base station and stored in the memory 105, which will be described later. Note
that the functions (such as under-mentioned cell reselection control and handover
control) of the control section 102, mobility determination control section 103, and
mobility determination timer 104 can also be implemented by executing programs
stored in a storage device (not shown) on a CPU (Central Processing Unit) of the
mobile terminal 10.
[0025]
The macro cell base station 20a and small cell base station 20b have the same
basic functional configuration as shown in FIG. 3 although some of their radio
characteristics such as maximum transmission power and cell radius are different.
Accordingly, a description will be given, collectively denoting these base stations 20a
and 20b as base station 20, and their radio areas, the cells 21a and 21 b, as cell 21.
[0026]
Referring to FIG. 3, the base station 20 includes a radio transceiver section 201
for performing radio communication with the mobile terminal 10, a control section 202
for performing overall control of the base station 20, a database 203 storing
configuration information and the like, and a transceiver section 204 for performing
communication with the mobility management station 30. The control section 202
performs control for RRC connection setup, bearer establishment, handover execution
and the like in accordance with a RRC message from the mobile terminal 10. Further,
the control section 202 transmits and receives messages tolfrom the higher-order
mobility management station 30 via the transceiver section 204. The database 203
stores office data as well as configuration information and the like set by an operator.
Note that when the mobile station 20 is the small cell base station 20b and the small cell
is a femto cell, then the femto cell may be in open mode, or hybrid access mode, or
closed mode. Note that the functionality of the control section 202 can also be
implemented by executing programs stored in a storage device (not shown) on a CPU
(Central Processing Unit) of the base station 20.
[0027]
Hereinafter, a detailed description will be given of a mobility control method and
system according to examples of the present invention with the above-described
configurations of the system, mobile terminal, and base station, with reference to
drawings.
[0028]
1. First example
According to a first example of the present invention, in the absolute prioritybased
frequency reselection mechanism, a mobile terminal moving at high speed
performs control such as to select a frequency (cell) with a lower priority, whereby the
possibility of reselecting a small cell at the time of high-speed movement can be
reduced.
[0029]
1.1) Broadcast information
In the absolute priority-based frequency reselection mechanism, freque~cies
differing with cell types are used, and different priorities are assigned to the different
frequencies (cell types). A method for assigning priorities depends on a policy of an
operator. For example, if an attempt is made to have mobile terminals gather in small
cells, a higher priority is assigned to a cell of a smaller size. The lowest priority 1 is
assigned to macro cells, and as for cells ranging from micro cell to femto cell, larger
priorities are assigned to them as they have smaller sizes, as shown in FIG. 4.
Accordingly, when a mobile terminal on a micro cell stays in the vicinity of a pic0 cell,
the mobile terminal performs cell reselection to the pico cell.
[0030]
However, when the mobile terminal 10 is moving at high speed, it only passes
through a cell of a small cell size in many cases as described already, in which case it is
preferable that cell reselection be avoided. Accordingly, the mobility determination
control section 103 of the mobile terminal according to the first example of the present
invention performs control such as not to select a high-priority cell (frequency) but to
select a lower-priority cell (frequency) at the time of high-speed movement, which will be
described next.
[0031]
1.2) Cell reselection control by mobile terminal
When receiving broadcast information as described above from the base station
20, the control section 102 of the mobile terminal 10 stores in the memory 105 a
neighbor cell list and frequency (cell type)-priority assignment information included in
the broadcast information and performs cell reselection control, which will be described
next. Hereinafter, cell reselection control will be described with reference to FIGS. 2
and 5.
[0032]
Referring to FIG. 5, the mobility determination control section 103 of the mobile
terminal 10, when detecting a timing of performing cell reselection (Operation 301; YES),
refers to the memory 105 and obtains the priorities of a currently staying cell and
neighbor cells (Operation 302). Subsequently, the mobility determination control
section 103 determines whether or not the mobile terminal 10 is moving at a speed
higher than a predetermined speed (Operation 303). When the mobile terminal 10 is
moving faster than the predetermined speed (Operation 303; YES), the mobility
determination control section 103 determines whether or not there is a cell (frequency)
with a priority lower than that of the currently staying cell (Operation 304) and, if there
are such lower-priority neighbor cells (Operation 304; YES), decides on, as a best cell,
a cell that has the best quality among the lower-priority neighbor cells (Operation 305).
Note that for a method for detecting high-speed movement and a timing thereof,
detection can be achieved by using the frequency of cell reselections performed within a
predetermined period of time or the like as an index, as described in NPL 1, 5.2.6.1 and
NPL 2, 5.2.4.3. If there is no lower-priority neighbor cell (Operation 304; NO), the
mobility determination control section 103 decides on, as a best cell, a cell that has the
best quality among those of the neighbor cells that have the lowest priority (Operation
306).
[0033]
When the mobile terminal 10 is at a stop or is moving at a speed not higher than
the predetermined speed (Operation 303; NO), the mobility determination control
section 103 decides on, as a best cell, a neighbor cell that has the highest priority
(Operation 307).
[0034]
Upon determining the best cell, the mobility determination control section 103
calculates a cell reselection timer (T-reselection) for the best cell by using a cell
reselection timer (t-ReselectionEUTRA) corresponding to this best cell and one speeddependent
scaling factor (t-ReselectionEUTRA-SF) corresponding to the mobility speed
of the mobile terminal, and sets it on the mobility determination timer 104.
Subsequently, the mobility determination control section 103 determines whether or not
the quality of the best cell exceeds the quality of the currently staying cell during the
calculated T-reselection (Condition I), and whether or not staying on the currently
staying cell lasts over a predetermined period of time (one second, according to 3GPP
TS36.304, 5.2.4.6) (Condition 2) (Operations 308 and 309). If both Conditions 1 and 2
are satisfied (Operation 308; YES, Operation 409; YES), the mobility determination
control section 103 performs cell reselection to this best cell (Operation 31 0) and
completes processing. Any one of Conditions 1 and 2 is not satisfied (Operation 308;
NO, or Operation 309; NO), the cell reselection control by the mobile terminal is
terminated.
[0035]
Note that the cell reselection timer (t-ReselectionEUTRA) can be configured to
be settable on each neighbor cell/cell type, as will be described in (first to third
examples of) a method for deciding on a mobility determination time, which will be
described later.
[0036]
1.3) Concrete example
Next, concrete operation of the mobile terminal 10 on a micro cell (with priority
3) will be described, taking a case as an example where broadcast information as
shown in FIG. 4 is broadcast. It is assumed that a macro cell, a pico cell, and a femto
cell exist, neighboring on this micro cell. A different frequency is used in the macro cell,
which is assigned priority 1 lower than the priority of the micro cell. The pic0 cell is
assigned priority 5, which is higher than the priority of the micro cell, while the femto cell
is assigned higher priority 7.
COO371
The mobile terminal 10 currently staying on the micro cell performs cell
reselection preferentially to the higher-priority pico cell or femto cell when it is not in
high-speed state (Operation 303; NO in FIG. 5). However, in high-speed movement
state (Operation 303; YES in FIG. 5), the mobile terminal 10 preferentially selects the
lower-priority macro cell. Thus, at the time of high-speed movement, the higher-priority
pic0 cell or femto cell is not selected, whereby the frequency of reselections to small
cells can be reduced, and on the whole, location registration signaling can be reduced.
[0038]
Note that although an example of frequency reselection within LTE (intra LTE)
is mainly described in FIGS. 4 and 5, similar effects can be obtained in cases of UTRA,
GERAN, and CDMA2000 cell reselection, by selecting a lower-priority frequency in
high-speed state. Moreover, although a case of LTE is descried in the present example,
the present example can be applied similarly to UTRA and other radio access systems.
Furthermore, a similar method can be applied by notifying priorities to each mobile
terminal individually by using a RRC message or the like other than broadcast
information.
[0039]
1.4) Effects
According to the first example of the present invention, in the absolute prioritybased
frequency reselection mechanism, a mobile terminal moving at high speed
performs control such as to select a lower-priority frequency (cell), whereby the
possibility of reselection to a small cell at the time of high-speed movement is lowered,
and a reduction of location registrations in small cells can be achieved.
[0040]
2. Second example
In the above-described first example, priorities assigned to individual
frequencies are used, as in the current absolute priority mechanism. According to a
second example of the present invention, however, in LTE, priorities are assigned to
individual cells, as in HCS (Hierarchical Cell Structure) introduced in 3G, and a mobile
terminal in high-speed state preferentially selects a cell with a priority lower than that of
a currently staying cell. In this case, a macro cell, a micro cell, and a small cell do not
need to use different frequencies but may use the same frequency. As described above,
HCS is introduced into LTE, and control is performed such that a mobile terminal
moving at high speed can select a lower-priority cell, whereby the possibility of
reselection to a small cell at the time of high-speed movement can be reduced.
[0041]
In LTE, different priorities are assigned to different cells, as shown in FIG. 6. A
method for assigning priorities depends on a policy of an operator. For example, if an
attempt is made to have mobile terminals gather in small cells, a higher priority is
assigned to a cell of a smaller size. The lowest priority 1 is assigned to macro cells, and
as for cells ranging from micro cell to femto cell, larger priorities are assigned to them as
they have smaller sizes, as shown in FIG. 6. Accordingly, when a low-speed mobile
terminal on a micro cell stays in the vicinity of a pic0 cell, the mobile terminal performs
cell reselection to the pic0 cell.
[0042]
However, when the mobile terminal 10 is moving at high speed, it only passes
through a cell of a small cell size in many cases as described already, in which case it is
preferable that cell reselection be avoided. Accordingly, the mobility determination
control section 103 of the mobile terminal according to the second example of the
present invention, at the time of high-speed movement (Operation 303; YES in FIG. 5),
performs control such as not to select a high-priority cell but to select a lower-priority
cell (Operation 305 in FIG. 5), as described using the flow in FIG. 5. If there is no
neighbor cell that has a lower priority than the currently staying cell, control is performed
such as to select a cell that has the best quality and has the lowest priority among
neighbor cells (Operation 306 in FIG. 5).
[0043]
According to the example shown in FIG. 6, the mobile terminal 10 is currently
staying on a micro cell (with priority 3), and a macro cell, a pico cell, and a femto cell
exist as neighbor cells of the micro cell. The same frequency is assigned to the macro
cell, which is assigned priority 1 lower than that of the micro cell. The pic0 cell is
assigned priority 5, which is higher than that of the micro cell, while the femto cell is
assigned higher priority 7.
[0044]
When the mobile terminal 10 on the micro cell is not in high-speed state
(Operation 303; NO in FIG. 5), it performs cell reselection preferentially to the higherpriority
pic0 cell or femto cell. However, in high-speed movement state (Operation 303;
YES in FIG. 5), the mobile terminal preferentially selects the lower-priority macro cell,
whereby it is possible to reduce the frequency of cell reselections. Thus, at the time of
high-speed movement, the higher-priority pic0 cell or femto cell is not selected, whereby
the frequency of reselections to small cells can be reduced, and on the whole, location
registration signaling can be reduced.
[0045]
As described above, according to the second example of the present invention,
priorities are introduced on individual neighbor cells in LTE as in HCS, whereby a
mobile terminal moving at high speed can perform control such as to select a lowerpriority
cell, whereby the possibility of reselection to a small cell at the time of highspeed
movement is lowered, and a reduction of location registrations in small cells can
be achieved.
[0046]
Note that the absolute priority, which is priority on each frequency defined by
3GPP, may be applied concurrently with priority on each cell.
LO0471
3. Method for deciding on mobility determination time
The cell reselection control according to the first and second examples of the
present invention described above, in case where mobility priorities are set, enables cell
reselection control which is not to follow mobility priorities, depending on the mobility
speed of a mobile terminal. In addition to this cell reselection control, it is also possible
to perform control such as to change a mobility determination time. That is, in addition
to mobility priorities, mobility determination times are set for individual neighbor cells or
individual cell types, whereby it is possible to avoid unrequired location registration in a
cell. The mobility determination time can be set to different values for different cells/cell
types, by changing a cell reselection timer (T-reselection), which indicates a
determination time for cell reselection, or the like.
[0048]
For example, the cell reselection timer is extended according to the mobility
speed of a mobile station, whereby, if a neighbor cell is a small cell of a small size,
location registration in this cell is delayed so that the mobile station is allowed to pass
through it, and consequently the frequent creation of location registration signaling can
be avoided. In this event, if a neighbor cell is a macro cell, location registration is
executed at normal timing, whereby cell reselection performance will not be affected.
[0049]
3.1) First example
According to a first example of a method for deciding on a mobility
determination time, a cell reselection timer T-reselection is set for each neighbor cell.
For example, cell reselection timers T-reselection that differ with cases where a
neighbor cell is a macro cell and where a neighbor cell is a small cell are broadcast, and
a mobile terminal applies a broadcast cell reselection timer T-reselection. Further,
according to the present example, the range of cell reselection timer T-reselection
values is extended, whereby the mobile terminal can determine a cell reselection timer
T-reselection according to the mobility speed. The cell reselection timer T-reselection
is thus set, whereby the start of location registration is delayed when a neighbor cell has
a small cell size andlor when a mobile terminal is moving at high speed, and location
registration signaling to small cells thus can be reduced. Hereinafter, the first example
will be described in detail.
[0050]
3.1 .I) Neighbor cell list
The base station 20 periodically broadcasts broadcast information, and the
mobile terminal 10 located within the relevant cell 21 performs cell reselection based on
cell reselection timer information included in the broadcast information. The broadcast
information includes a neighbor cell list, which indicates cell reselection timers
9-reselection for individual neighbor cells of the cell 21. In the present example, SIB4
(SystemInformationBlockType4), which is broadcast information for controlling samefrequency
cell reselection in a LTE network, includes a neighbor cell list
(IntraFreqNeighCelIlnfo) having a format as shown in FIG. 7.
[OOSI]
Referring to FIG. 7, introduced in the same-frequency neighbor cell list
(IntraFreqNeighCellInfo) are t-ReselectionEUTRAs, which are cell reselection timers,
and t-ReselectionEUTRA-SFs, which are speed-dependent scaling factors, in addition
to the identification information of neighbor cells and the like. Here, the t-
ReselectionEUTRA-SFs, the speed-dependent scaling factors, are an extended version
of SpeedStateScaleFactors-vabc, and their values range not only from 0 to 1, but the
range thereof is extended beyond 1. For example, the values of the speed-dependent
scaling factor t-ReselectionEUTRA-SF can be defined as values in increments of 0.25
within a range from a minimum of 0.25 to a maximum of 100. Thus, for the mobile
terminal I 0 moving at high speed, the cell reselection timer T-reselection can be
extended 100 times at maximum.
100521
Similarly, the above-described cell reselection timer and speed-dependent
scaling factor can also be introduced in SIB5, which includes a different-frequency cell
list, in SIB6, which includes a UTRA (Universal Terrestrial Radio Access, hereinafter,
abbreviated to UTRA) neighbor cell list, in SIB7, which includes a GERAN (GSMIEDGE
Radio Access Network) neighbor cell list, and in SIB8, which includes a CDMA2000
neighbor cell list.
[0053]
3.1.2) Mobility determination time decision control by mobile terminal
When receiving broadcast information (SIB4) including a neighbor cell list as
described above from the base station 20, the control section 102 of the mobile terminal
10 stores the neighbor cell list included in the broadcast information in the memory 105.
[0054]
Referring to FIG. 8, the mobility determination control section 103 of the mobile
terminal 10 refers to the memory 105 and determines a best cell by ranking the
neighbor cells in descending order of quality in accordance with criterion R (cell-ranking
criterion R defined in 3GPP TS36.304) (Operation 401).
[0055]
When determining the best cell, the mobility determination control section 103
reads from the neighbor cell list a cell reselection timer (t-ReselectionEUTRA)
corresponding to the best cell and one speed-dependent scaling factor (t-
ReselectionEUTRA-SF) corresponding to the mobility speed of the mobile terminal, and
calculates a cell reselection timer (T-reselection) for the best cell (Operation 402).
Specifically, a T-reselection for the best cell is calculated by multiplying the t-
ReselectionEUTRA by the t-ReselectionEUTRA-SF.
LO0561
Subsequently, the mobility determination control section 103 determines
whether or not the best cell satisfies a predetermined mobility criterion (Operations 403
and 404). That is, it is determined whether or not the quality of the best cell exceeds
the quality of a currently staying cell during the calculated T-reselection (Condition I),
and whether or not staying on the currently staying cell lasts over a predetermined
period of time (one second, according to 3GPP TS36.304, 5.2.4.6) (Condition 2)
(Operations 403 and 404). If both Conditions I and 2 are satisfied (Operation 403; YES,
Operation 404; YES), the mobility determination control section 103 sets the
T - reselection for the best cell determined in Operation 402 on the mobility
determination timer 104 (Operation 405) and completes processing.
[0057]
Any one of Conditions 1 and 2 is not satisfied (Operation 403; NO, or Operation
404; NO), the mobility determination control section I03 refers to a result of ranking the
neighbor cells and determines whether or not there is a neighbor cell having second
best quality (Operation 406). If there is such a neighbor cell (Operation 406; YES), this
neighbor cell is made to be a best cell (Operation 407), and the process goes back to
Operation 402 for determining a T-reselection. The above-described processing is
repeated until a T-reselection for a new best cell is set (Operation 405) or until all cells
in the neighbor cell list are subjected to determination (Operation 406; NO).
[0058]
Note that the procedure shown in FIG. 8 has been described taking a case of
broadcast information SIB4 shown in FIG. 7 as an example but can be similarly applied
even in case of broadcast information SIB5, SIB6, SIB or SIB 8.
[0059]
3.1.3) Concrete example
Next, concrete operation of the mobile terminal 10 located in the macro cell 21a
will be described, taking a case as an example where a neighbor cell list as shown in
FIG. 9 is broadcast.
[0060]
Referring to FIG. 9, it is assumed that macro cells 22a and 23a, micro cells 24b
and 25b, pic0 cells 26c and 27c, and femto cells 28d and 29d neighbor on the macro
cell 21a on which the mobile terminal 10 is currently staying. "PhysCellldl' is an
abbreviation of Physical Cell ID and is identification information (ID) for identifying a cell
at the physical channel level. "q-OffsetCell" is an offset to a cell and is for virtually
increasing the cell radius to thereby allow the mobile terminal 10 to easily reselect the
cell. Such technology is also referred to as Cell Range Expansion, which is a
technology for offloading user traffic in a macro cell. In this example, a q-Offsetcell for
the pic0 cells 26c and 27c is set to a large value for offloading. Note that a description
of the technology of Cell Range Expansion will be omitted because it is well known.
[006 1 1
Further, in the present example, t-ReselectionEUTRAs for the individual
neighbor cells are notified from the base station side to a mobile terminal. In the
example shown in FIG. 9, a t-ReselectionEUTRA value (7 seconds), which is longer
than a t-ReselectionEUTRA value (2 seconds) set for .the macro and micro cells, is set
for the pic0 and femto cells. That is, the cell reselection timer is set to a larger value for
a cell smaller than a micro cell, whereby the timing of a mobile terminal for reselection
to a small cell is delayed, and consequently it is possible to reduce location registration
signaling to small cells. The possibility of reselecting a pic0 cell or femto cell is reduced
as the mobility speed of the mobile terminal 10 increases. Conversely, for a mobile
terminal staying in the vicinity of a pico cell for a while (moving at low speed), it is
possible to achieve the traffic offloading effect of Cell Range Expansion because the q-
Offsetcell value is set large. Similarly, since a reselection timer for a femto cell is also
set long, only mobile terminals staying in the femto cell for a while are allowed for
location registration. As for mobile terminals that quickly pass through, location
registration signaling is not started because they pass through before the timeout of the
reselection timer for the femto cell occurs. Thus, it is possible to obtain the effect of a
reduction of location registrations in small cells such as femto cells and pic0 cells.
[0062]
Further, according to the present example, t-ReselectionEUTRA-SFs for the
individual neighbor cells are notified. According to the example shown in FIG. 6, tReselectionEUTRA-
SF = 0.5 is set for the micro cells, t-ReselectionEUTRA-SF = 5.0,
for the pico cells with a smaller size, and t-ReselectionEUTRA-SF = 10.0, for the femto
cells with a further smaller size. For example, in case of the mobile terminal 10 moving
at high speed in the micro cell 24b or 25b, the speed-dependent scaling factor is applied
so that the cell reselection timer is shortened to t-ReselectionEUTRA (2 seconds) x t-
ReselectionEUTRA-SF (0.5) = 1 second. In case of the mobile terminal 10 moving at
high speed in the pic0 cell 26c, if the speed-dependent scaling factor is applied, the cell
reselection timer is extended to t-ReselectionEUTRA (7 seconds) x t-
ReselectionEUTRA-SF (5.0) = 35 seconds. Accordingly, when moving at high speed in
the pico cell 26c or 27c, the mobile terminal is highly likely to pass through it before cell
reselection to the pico cell takes place, and consequently it is possible to reduce the
creation of location registration signaling. The speed-dependent scaling factors are set
for the individual neighbor cells in this manner, whereby the mobility speed-dependent
response performance of cell reselection can be changed only for a specific neighbor
cell.
100631
Note that although an example of same-frequency cell reselection within LTE
(intra LTE) is mainly described in FIG. 9, similar effects can be obtained in cases of
different-frequency cell reselection and UTRA, GERAN, and CDMA2000 cell reselection,
by using the respective broadcast information SIB5, SIB6, SIB7, and SIB8 and
introducing cell reselection timers T-reselection and/or speed-dependent scaling factors
for individual neighbor cells, as described already. Moreover, T-reselections andlor
speed-dependent scaling factors for individual neighbor cells may be introduced into
other broadcast information (SIB). Furthermore, T-reselections and/or speeddependent
scaling factors for individual neighbor cells may be notified to each mobile
terminal individually by using a RRC message or the like other than broadcast
information.
[0064]
As described above, according to the first example of the method for deciding
on a mobility determination time, cell reselection timers T-reselection and/or speeddependent
scaling factors for individual neighbor cells are introduced, whereby a
reduction of location registrations in small cells can be achieved without impairing the
effects of Cell Range Expansion and others. Further, it is possible to achieve cell
reselection following high-speed movement, targeting only a specific neighbor cell.
[0065]
3.2) Second example
In the above-described first example, a cell reselection timer T-reselection
and/or speed-dependent scaling factor is introduced for each neighbor cell. In a second
example of the method for deciding on a motility determination time, a cell reselection
timer T-reselection andlor speed-dependent scaling factor is introduced for each cell
type. Cell types can be classified on a cell size basis. The types have, as described
already, macro cell, micro cell, and small cell in descending order of cell size, and small
cells are further classified into the types of pico cell and femto cell.
100661
3.2.1) Broadcast information
The base station 20 periodically broadcasts broadcast information, and the
mobile terminal 10 having received the broadcast information performs cell reselection
based on cell reselection timer information on each cell type included in the broadcast
information. The broadcast information includes cell reselection timers T-reselection
and speed-dependent scaling factors set for individual cell types.
[0067]
FIG. 10 shows an example of the broadcast information in the second example
of the method for deciding on a mobility determination time. Similarly to the example
used in the first example (FIG. 9), a t-ReselectionEUTRA value (7 seconds), which is
longer than a t-ReselectionEUTRA value (2 seconds) set for macro cell and micro cell,
is set for pic0 cell and femto cell. Moreover, t-ReselectionEUTRA-SF = 0.5 is set for
micro cell, t-ReselectionEUTRA-SF = 2.0, for pico cell, which is smaller in size, and t-
ReselectionEUTRA-SF = 4.0, for femto cell, which is further smaller.
100681
3.2.2) Mobility determination time decision control by mobile terminal
When receiving broadcast information as described above from the base station
20, the control section 102 of the mobile terminal 10 stores the broadcast information in
the memory 105, and a mobility determination time is decided on through the
processing similar to that of FIG. 8. However, in the second example, only Operation
402 in FIG. 8 is different. The other Operations are the same as those of FIG. 8, and a
description thereof will be omitted.
[0069]
In Operation 402 in FIG. 8, the mobility determination control section 103 reads
from the memory 105 a cell reselection timer (t-ReselectionEUTRA) and one speeddependent
scaling factor (t-ReselectionEUTRA-SF) corresponding to the mobility speed
of the mobile terminal, based on to the cell type of the best cell, and calculates a cell
reselection timer (T-reselection) for the best cell. Specifically, a T-reselection for the
best cell is calculated by multiplying the t-ReselectionEUTRA by the t-
ReselectionEUTRA-SF. The Operations thereafter are as described in FIG. 8.
[0070]
3.2.3) Concrete example
Taking a case as an example where information as shown in FIG. 10 is
broadcast, for example, if the mobile terminal 10 stays in the vicinity of a micro cell
longer than its t-ReselectionEUTRA, 2 seconds, cell reselection to this micro cell is
performed and location registration procedure is executed, so that communication
services are allowed in the micro cell. However, in the vicinity of a small cell with a
smaller size than that of a micro cell, cell reselection to this pico cell is not performed
unless a stay there lasts over its t-ReselectionEUTRA, 7 seconds.
1007 1 ]
Moreover, for a mobile terminal moving at high speed, since a speed-dependent
scaling factor is applied as described already, cell reselection does not take place
unless the mobile terminal 10 stays in the vicinity of a small cell longer than 14 seconds
(= 7 seconds x 2.0). Accordingly, when moving in a small cell at high speed, a mobile
terminal is highly likely to pass through it before cell reselection to the small cell takes
place, and consequently it is possible to reduce the creation of location registration
signaling. Speed-dependent scaling factors are set for the individual cell types in this
manner, whereby the mobility speed-dependent response characteristic of cell
reselection can be changed only for a specific cell type.
[0072]
Note that although an example of same-frequency cell reselection within LTE
(intra LTE) is mainly described in FIG. 10, similar effects can be obtained in cases of
different-frequency cell reselection and UTRA, GERAN, and CDMA2000 cell reselection,
by using the respective broadcast information SIB5, SIB6, SIB7, and SIB8 and
introducing cell reselection timers T-reselection and/or speed-dependent scaling factors
for individual cell types, as described already. Moreover, T-reselections and/or speeddependent
scaling factors for individual cell types may be introduced into other
broadcast information (SIB). Furthermore, T-reselections and/or speed-dependent
scaling factors for individual cell types may be notified to each mobile terminal
individually by using a RRC message or the like other than broadcast information.
[0073]
According to the second example of the method for deciding on a mobility
determination time, since T-reselection timers and speed-dependent scaling factors can
be set for individual cell types, cell reselection to a small cell such as a pico cell, femto
cell or the like can be delayed without affecting cell reselection to, for example, a macro
cell. Accordingly, a reduction of location registrations in small cells can be achieved
without impairing the effects of Cell Range Expansion and others, as in the first example.
Further, it is possible to achieve cell reselection following high-speed movement,
targeting only a specific neighbor cell.
[0074]
Moreover, according to the second example, since cell reselection timers
T - reselection and speed-dependent scaling factors not for individual neighbor cells but
for individual cell types are broadcast, the size of broadcast information can be made
smaller, so that traffic volume is reduced to allow efficient transmission of broadcast
information.
[0075]
3.3) Third example
According to a third example of the method for deciding on a mobility
determination time, a base station broadcasts transmission power information or cell
sizes (cell radiuses), whereby a mobile terminal dynamically calculates a scaling factor
for each neighbor cell and applies them to a cell reselection timer T - reselection.
[0076]
3.3.1) Broadcast information
The base station 20 periodically broadcasts broadcast information, and the
mobile terminal 10 having received the broadcast information estimates a cell type from
the broadcast information and determines an adjustment factor. In case of LTE,
transmission power information (reference power information) is notified to a mobile
terminal as common radio resource information by using SIB2. In general, the larger
the radius of a cell, the stronger the transmission power (reference power) of a base
station. Accordingly, the mobile terminal side can estimate a cell type from reference
power information. An adjustment factor to be applied is determined based on the
estimated cell type, and a cell reselection timer T-reselection is adjusted. Note that it is
assumed that the reselection timer T-reselection is broadcast as 3 seconds in a macro
cell by using SIB2.
100771
It is assumed that neighbor cells of some macro cell have physical cell
identifiers (PhysCelllDs) 1000 to 1003 as shown in FIG. 11A and that their respective
transmission power (reference power) information is broadcast. In this case, the mobile
terminal 10 estimates the cell types of these neighbor cells based on the transmission
power (reference power). Here, a cell of 30 dBm, which is the largest transmission
power (reference power), is estimated to be a macro cell, a cell of 1 dBm, which is the
smallest transmission power (reference power), is estimated to be a femto cell, and a
cell of middle transmission power (reference power) therebetween is estimated to be a
pic0 cell.
[0078]
A cell type can also be estimated from a cell size when not transmission power
information (reference power information) but cell sizes are broadcast. Moreover, in
case of a femto cell, since CSG (Closed Subscriber Group) is applied in some cases,
the type "femto cell" can be determined if a CSG ID is assigned.
[0079]
A base station broadcasts combinations of cell types and adjustment factors as
shown in FIG. 11 B. If the mobile terminal 10 can estimate a cell type, it can obtain a
corresponding adjustment factor, which is applied to the broadcast cell reselection timer
T - reselection (here, 3 seconds), whereby a cell reselection timer suitable for the cell
type can be set.
[0080]
3.3.2) Mobility determination time decision control by mobile terminal
When receiving broadcast information as described above from the base station
20, the control section 102 of the mobile terminal 10 stores the broadcast information in
the memory 105, and a mobility determination time is decided on through the
processing similar to that of FIG. 8. However, in the third example, only Operation 402
in FIG. 8 is different. The other Operations are the same as those of FIG. 8, and a
description thereof will be omitted.
[0081]
In Operation 402 in FIG. 8, the mobility determination control section 103, from
the transmission power (reference power) information on the best cell, estimates its cell
type and adjusts a broadcast cell reselection timer (t-ReselectionEUTRA) by using an
adjustment factor corresponding to the estimated cell type, thereby calculating a cell
reselection timer (T-reselection) for the best cell (Operation 402). Specifically, a
T-reselection for the best cell is calculated by multiplying the t-ReselectionEUTRA by
the adjustment factor. Note that it is also possible that one speed-dependent scaling
factor (t-ReselectionEUTRA-SF) corresponding to the mobility speed of the mobile
terminal is read from the memory 105 and used to further change the cell reselection
timer (T-reselection) for the best cell, as described already. The Operations thereafter
are as described in FIG. 8.
[0082]
3.3.3) Concrete example
Next, concrete operation of the mobile terminal 10 will be described, taking a
case as an example where information as shown in FIG. 11 is broadcast.
[0083]
Referring to FIG. 12, it is assumed that four cells of PhysCelllds 1000 to 1003
neighbor on a cell on which the mobile terminal 10 is currently staying and that their cell
types estimated from their respective transmission power information are pico cell,
femto cell, femto cell, and macro cell, respectively. In this case, for the macro cell,
since the adjustment factor is 1, a broadcast t-ReselectionEUTRA = 3 seconds, as it is,
becomes its cell reselection timer (T-reselection). For the pico cell, since the
adjustment factor is 3, 3 seconds x 3 = 9 seconds is its cell reselection timer
(T-reselection) adjusted, and for the femto cells, since the adjustment factor is 10, 3
seconds x 10 = 30 seconds is their cell reselection timer (T-reselection) adjusted.
[0084]
Accordingly, for example, if the mobile terminal 10 stays in the vicinity of the
pic0 cell longer than 9 seconds, cell reselection to this pico cell takes place, and
location registration procedure is executed to allow communication services in the pic0
cell. However, in the vicinity of a femto cell with a smaller size than that of a pico cell,
cell reselection does not take place unless a stay there lasts over 30 seconds.
Accordingly, the response performance of cell reselection can be changed only for a cell
of a specific type by setting adjustment factors according to cell types.
[0085]
Moreover, for a mobile terminal moving at high speed, since a speed-dependent
scaling factor is applied as described already, cell reselection does not take place when
the mobile terminal 10 stays in the vicinity of a small cell unless the stay lasts a further
longer time. Accordingly, when moving in a small cell at high speed, a mobile terminal
is highly likely to pass through it before cell reselection to the small cell takes place, and
consequently it is possible to reduce the creation of location registration signaling.
Speed-dependent scaling factors are set for the individual cell types in this manner,
whereby the mobility speed-dependent response characteristic of cell reselection can
be changed only for a specific cell type.
[0086]
Note that although an example of same-frequency cell reselection within LTE
(intra LTE) is mainly described in FIG. 12, similar effects can be obtained in cases of
different-frequency cell reselection and UTRA, GERAN, and CDMA2000 cell reselection,
by using the respective broadcast information SIB5, SIB6, SIB7, and SIB8, estimating a
cell type based on reference power or a cell size in the broadcast information, and using
a corresponding adjustment factor, as described already. Further, the present example
can be applied similarly to UTRA and other radio access systems. Furthermore, a cell
type may be estimated based on reference power or a cell size by using a RRC
message or the like individually to each mobile terminal, other than broadcast
information.
[0087]
According to the third example of the method for deciding on a mobility
determination time, a cell type is estimated by using broadcast information including
transmission power information (or cell sizes), adjustment factors and the like from a
base station, and T-reselection timers andlor speed-dependent scaling factors can be
set by using the adjustment factors for individual cell types. Therefore, cell reselection
to a small cell such as a pico cell or femto cell can be delayed without affecting cell
reselection to, for example, a macro cell. Accordingly, a reduction of location
registrations in small cells can be achieved without impairing the effects of Cell Range
Expansion and others, as in the first example. Further, it is possible to achieve cell
reselection following high-speed movement, targeting only a specific neighbor cell.
[0088]
Moreover, according to the third example, since transmission power information
(or cell sizes) and adjustment factors not for individual neighbor cells but for individual
cell types are broadcast, the size of broadcast information can be made smaller, so that
traffic volume is reduced to allow efficient transmission of broadcast information.
[0089]
4. Other examples
For the priority on each frequency introduced in the first example and the
priority on each cell introduced in the second example, optimization may be performed
by Self Organization Network (SON) so that the number of location registration signaling
in a heterogeneous network falls within a given allowable range. In this case, a new
parameter introduced considering the handover success rate, system throughput or the
like other than location registration signaling may be optimized.
[Industrial Applicability]
[0090]
The present invention is applicable to cell reselection control in heterogeneous
networks.
[Reference Signs List]
[0091]
10 Mobile terminal
20 Base station
20a Macro cell base station
20b Small cell base station
30 Mobility management station
101 Radio transceiver section
102 Control section
103 Mobility determination control section
104 Mobility determination timer
105 Memory
201 Radio transceiver section
202 Control section
203 Database
204 Transceiver section

We Claim:
[Claim 1]
A mobility control method for a mobile terminal in a mobile communication
network including cells of multiple types differing in cell size, characterized by
comprising:
presetting priorities for mobility control on individual neighbor cells or individual
neighbor cell types; and
performing mobility control such as to select a neighbor cell with a priority lower
than that of a currently staying cell when the mobile terminal is moving faster than a
predetermined speed.
[Claim 2]
The mobility control method according to claim I, characterized in that the
priorities are broadcast from a base station of the currently staying cell.
[Claim 3]
The mobility control method according to claim 1 or 2, characterized in that the
priorities are set depending on cell sizes of the neighbor cells.
[Claim 4]
The mobility control method according to claim 3, characterized in that the
priorities are set in such manner that a higher priority is set on a neighbor cell having a
smaller size.
[Claim 5]
The mobility control method according to any one of claims 1 to 4, characterized
by further comprising:
setting mobility determination times for individual neighbor cells or individual
neighbor cell types,
wherein the mobility control is performed by determining whether or not a
predetermined mobility criterion remains satisfied during the mobility determination time
for a neighbor cell.
[Claim 6]
The mobility control method according to claim 5, characterized in that a
mobility determination time is set depending on at least one of a mobility speed of the
mobile terminal and a cell size of a neighbor cell.
[Claim 7]
The mobility control method according to claim 6, characterized in that the
mobility determination time is set by changing, depending on at least one of the mobility
speed and the cell size of the neighbor cell, a predetermined mobility determination time
broadcast from a base station to which the mobile terminal is connecting.
[Claim 8]
The mobility control method according to any one of claims 5 to 7, characterized
in that the types of the neighbor cells are estimated based on transmission power
information or the cell sizes of the neighbor cells broadcast from a base station to which
the mobile terminal is connecting.
[Claim 9]
A mobility control device in a mobile communication network including cells of
multiple types differing in cell size, characterized by comprising:
priority assignment information storage means for storing priorities for mobility
control set on individual neighbor cells of a cell on which a mobile terminal is currently
staying or on individual types of neighbor cell; and
mobility determination control means for performing mobility control such as to
select a neighbor cell with a priority lower than that of the currently staying cell when the
mobile terminal is moving faster than a predetermined speed.
[Claim 10]
The mobility control device according to claim 9, characterized in that the
priorities are broadcast from a base station of the currently staying cell.
[Claim 11]
The mobility control device according to claim 9 or 10, characterized in that the
priorities are set depending on cell sizes of the neighbor cells.
[Claim 12]
The mobility control device according to claim 3, characterized in that the
priorities are set in such manner that a higher priority is set on a neighbor cell having a
smaller size.
[Claim 13]
The mobility control device according to any one of claims 9 to 12,
characterized by further comprising:
mobility determination timer means for setting mobility determination times for
the individual neighbor cells of the cell on which the mobile terminal is currently camped
or for the individual neighbor cell types,
wherein the mobility determination control means performs the mobility control
by determining whether or not a predetermined mobility criterion remains satisfied
during the mobility determination time for a neighbor cell.
[Claim 14]
The mobility control device according to claim 13, characterized in that the
mobility determination timer means sets a mobility determination time depending on at
least one of a mobility speed of the mobile terminal and a cell size of a neighbor cell.
[Claim 15]
The mobility control device according to claim 14, characterized in that the
mobility determination timer means sets the mobility determination time by changing,
depending on at least one of the mobility speed and the cell size of the neighbor cell, a
predetermined mobility determination time broadcast from the base station.
[Claim 16]
The mobility control device according to any one of claims 13 to 15,
characterized in that the mobility determination control means estimates the types of the
neighbor cells based on transmission power information or the cell sizes of the neighbor
cells broadcast from a base station to which the mobile terminal is connecting.
[Claim 17]
A mobility control system in a mobile communication network including cells of
multiple types differing in cell size, comprising:
base stations managing the cells; and
a mobile station that can move between the cells,
characterized in that the mobile station presets priorities for mobility control on
individual neighbor cells or individual neighbor cell types and, when the mobile terminal
is moving faster than a predetermined speed, performs mobility control such as to select
a neighbor cell with a priority lower than that of a currently staying cell.
[Claim 18]
A base station in a mobile communication network including cells of multiple
types differing in cell size, the base station managing one of the cells, characterized by
comprising:
storage means for storing priority assignment information for mobility control,
which is set on individual neighbor cells of its own cell or on individual neighbor cell
types; and
broadcast means for broadcasting the priority assignment information to a
mobile terminal on its own cell.
[Claim 19]
A mobile terminal in a mobile communication network including cells of multiple
types differing in cell size, characterized by comprising:
priority assignment information storage means for storing priories for mobility
control set on individual neighbor cells of a cell on which the mobile terminal is currently
staying or on individual neighbor cell types; and
mobility determination control means for performing mobility control such as to
select a neighbor cell with a priority lower than that of the currently staying cell when the
mobile terminal is moving faster than a predetermined speed.
[Claim 20]
A program for causing a computer of a mobile terminal in a mobile
communication network including cells of multiple types differing in cell size to
implement mobility control functionality, characterized by causing the computer to
implement:
a function of setting priorities for mobility control on individual neighbor cells or
individual neighbor cell types; and
a function of performing mobility control such as to select a neighbor cell with a
priority lower than that of a currently staying cell when the mobility terminal is moving
faster than a predetermined speed.
[Claim 21]
A program for causing a computer to function as a mobility control device in a
mobile communication network including cells of multiple types differing in cell size,
characterized by causing the computer to implement:
a priority assignment information storage function of storing priorities for mobility
control set on individual neighbor cells of a cell on which a mobile terminal is currently
camped or on individual neighbor cell types; and
a mobility determination control function of performing mobility control such as
to select a neighbor cell with a priority lower than that of the currently staying cell when
the mobile terminal is moving faster than a predetermined speed.
[Claim 22]
A program for causing a computer to function as a base station in a mobile
communication network including cells of multiple types differing in cell size, the base
station managing one of the cells, characterized by causing the computer to implement:
a storage function of storing priority assignment information for mobility control,
which is set on individual neighbor cells of a cell of the own station or on individual
neighbor cell types; and
a broadcast function of broadcasting the priority assignment information to a
mobile terminal currently staying on the cell of the own station.