U.S. patent application number 10/778106 was filed with the patent office on 2004-11-04 for system for and its method of controlling handover, mobile terminal, and apparatus for controlling handover.
This patent application is currently assigned to NTT DoCoMo, Inc.. Invention is credited to Hirata, Shoichi, Ihara, Takeshi, Kakishima, Jun.
Application Number | 20040219918 10/778106 |
Document ID | / |
Family ID | 32767730 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219918 |
Kind Code |
A1 |
Kakishima, Jun ; et
al. |
November 4, 2004 |
System for and its method of controlling handover, mobile terminal,
and apparatus for controlling handover
Abstract
A system for controlling handover is disclosed that includes a
mobile terminal that enables communications with multiple wireless
systems having wireless access stations, and a handover-controlling
apparatus that executes control of handover for the mobile
terminal, which travels among multiple types of wireless systems.
The mobile terminal includes a destination wireless system
determining unit that receives downlink signals from the
corresponding wireless access stations so as to determine which
wireless system accommodates a destination wireless access station
based on reception quality of downlink signals. The mobile terminal
also includes a destination wireless system reporting unit that
sends information indicating the determined wireless system to the
handover-controlling apparatus. The handover-controlling apparatus
includes a handover-controlling unit that controls handover
operations for the mobile terminal based on the information
indicating the determined wireless system, which is sent from the
destination wireless system reporting unit.
Inventors: |
Kakishima, Jun;
(Yokohama-shi, JP) ; Ihara, Takeshi;
(Yokosuka-shi, JP) ; Hirata, Shoichi; (Tokyo,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
NTT DoCoMo, Inc.
11-1, Nagatacho 2-chome Chiyoda-ku
Tokyo
JP
100-6150
|
Family ID: |
32767730 |
Appl. No.: |
10/778106 |
Filed: |
February 17, 2004 |
Current U.S.
Class: |
455/436 ;
455/424 |
Current CPC
Class: |
H04W 36/14 20130101;
H04W 36/0055 20130101; H04W 36/30 20130101; H04W 36/0058 20180801;
H04W 36/36 20130101 |
Class at
Publication: |
455/436 ;
455/424 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2003 |
JP |
2003-047761 |
Claims
What is claimed is:
1. A system for controlling handover, comprising: a mobile terminal
which enables communication with a plurality of wireless systems
having wireless access stations; and a handover-controlling
apparatus which executes control of handover for said mobile
terminal which travels among a plurality of types of the wireless
systems, wherein said mobile terminal comprises: a destination
wireless system determining unit which receives downlink signals
from two or more of the wireless access stations so as to determine
which of the corresponding wireless systems accommodates a
destination wireless access station based on reception quality of
the downlink signals; and a destination wireless system reporting
unit which sends information indicating said determined wireless
system to said handover-controlling apparatus, and said
handover-controlling apparatus comprises a handover-controlling
unit which controls handover operations for said mobile terminal
based on the information indicating the determined wireless system
which is sent from said destination wireless system reporting
unit.
2. The system for controlling handover as claimed in claim 1,
wherein said handover-controlling apparatus is connected to the two
or more wireless access stations via a plurality of connecting
access routers; and said handover-controlling unit comprises: a
database which manages corresponding relationships between said
wireless access stations and said access routers; a router
compatibility determination unit which makes a determination by
referring to said database, at the time the information indicating
the wireless system which accommodates said destination wireless
access station is reported, as to whether the access router which
is connected to the destination wireless access station differs
from the access router which is connected to the currently
connecting wireless access station; a handover method determining
unit which determines a handover method based on the wireless
system which accommodates the destination wireless access station
in the case that said determination is affirmative; and a handover
processing executing unit which executes handover processing based
on said determined handover method.
3. The system for controlling handover as claimed in claim 1,
wherein said mobile terminal further comprises: a travelling speed
projecting unit which projects the travelling speed of the mobile
terminal based on received power characteristics of the downlink
signals from the two or more wireless access stations; and a
travelling speed reporting unit which sends the information
indicating said projected travelling speed of the mobile terminal
to said handover-controlling apparatus.
4. An apparatus for controlling handover which executes control of
handover for a mobile terminal that travels among a plurality of
types of wireless systems, comprising a handover-controlling unit
which controls handover operations for said mobile terminal based
on information indicating a wireless system which is sent from said
mobile terminal.
5. The apparatus for controlling handover as claimed in claim 4,
which is connected to corresponding wireless access stations within
said wireless systems via connecting access routers, wherein said
handover-controlling unit comprises: a database which manages
corresponding relationships between said wireless access stations
and said access routers; a router compatibility determination unit
which makes a determination by referring to said database, at the
time that information indicating the wireless system which
accommodates a destination wireless access station is reported, as
to whether the access router which is connected to the destination
wireless access station differs from the access router which is
connected to the currently connecting wireless access station; a
handover method determining unit which determines a handover method
based on the wireless system which accommodates the destination
wireless access station in the case that said determination is
affirmative; and a handover processing executing unit which
executes the handover processing based on said determined handover
method.
6. The apparatus for controlling handover as claimed in claim 5,
wherein said handover method determining unit determines one of a
hard-handover method, a soft-handover method, and an
IP-packet-buffering method as the handover method based on the
wireless system which accommodates the destination wireless access
station.
7. The apparatus for controlling handover as claimed in claim 5,
wherein said handover method determining unit comprises: a
high-speed handover method selecting unit which determines based on
travelling speed information of the mobile terminal which is
reported by a travelling speed information reporting unit, whether
the handover of said mobile terminal is executed by a high-speed
handover method; and a high-speed handover method selection
reporting unit which reports said determination result to said
handover processing executing unit, and said handover processing
executing unit comprises a high-speed handover method executing
unit which executes the high-speed handover method in response to
said reported determination result.
8. A mobile terminal which enables communication with a plurality
of wireless systems having wireless access stations and handover to
a plurality of types of the wireless systems, comprising: a
destination wireless system determining unit which receives
downlink signals from two or more of the wireless access stations
so as to determine which of the corresponding wireless systems
accommodates a destination wireless access station based on
reception quality of the received downlink signals; and a
destination wireless system reporting unit which sends to an
apparatus for controlling handover at the network side the
information indicating said determined wireless system.
9. The mobile terminal as claimed in claim 8, comprising: a
travelling speed projecting unit which projects a travelling speed
of the mobile terminal based on received power characteristics of
the downlink signals from the two or more wireless access stations;
and a travelling speed information reporting unit which sends
information indicating said projected travelling speed of said
mobile terminal to the apparatus for controlling handover which
executes control of handover for said mobile terminal travelling
among the types of wireless systems.
10. The mobile terminal as claimed in claim 8, wherein the wireless
system which is determined at said destination wireless system
determining unit is one of a homogeneous system and a heterogeneous
system.
11. A method of controlling handover in a system for controlling
handover which comprises a mobile terminal that enables
communication with a plurality of wireless systems having wireless
access stations and an apparatus for controlling handover that
executes control of the handover for said mobile terminal that
travels among a plurality of types of the wireless systems, said
method comprising the steps of: receiving, at said mobile terminal,
downlink signals from two or more wireless access stations so as to
determine which of the corresponding wireless systems accommodates
a destination wireless access station based on reception quality of
received downlink signals; and sending, from said mobile terminal,
information indicating said determined wireless system to said
apparatus for controlling handover, and controlling, by said
apparatus, handover operations for said mobile terminal based on
the information indicating said reported wireless system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a system for and
its method of controlling handover, a mobile terminal, and an
apparatus for controlling handover, and particularly relates to a
system for and its method of controlling handover between
homogeneous or heterogeneous wireless systems at the network side
so as to enable a reduction in the throughput of the mobile
terminal.
[0003] Furthermore, the present invention relates to the mobile
terminal and the apparatus for controlling handover which are used
in such a system for controlling handover.
[0004] 2. Description of the Related Art
[0005] In recent years, the Wireless Local Area Network (WLAN) has
been spreading rapidly and also has been watched with keen interest
as means for connecting to the Internet.
[0006] In the WLAN, when changing on the move from one connecting
access point to another, the IP address of the mobile terminal
changes so that a problem of intermittent data flow arises in a
case such as streaming. To this end, as a method of solving this
problem, the "Mobile IP" has been proposed. In the Mobile IP,
having a home address and an agent address enables the mobile
terminal to retain connectivity even when the connecting access
point changes from one to another.
[0007] Furthermore, although the transmission data rate of the WLAN
is higher than that of a mobile telephone network, in order for the
WLAN to achieve the same level of ease-of-use as the mobile
telephone network, the problem of handover needs to be solved so as
to be able to use the WLAN consistently without a break in data
communications even when the mobile terminal is on the move. In
order to respond to this problem, the Hierarchical Mobile IP (HMIP)
which is based on the Mobile IP has been proposed. This HMIP
enables the enhancement in the speed of handover as registration at
the home agent is not performed every time a location is
registered. More specifically, a server called the Mobility Anchor
Point (MAP) having a function similar to that of the home agent is
provided within a foreign network, and the location information is
registered within the MAP so as to implement the enhancement in the
handover speed.
[0008] Non-Patent Document 1
[0009] Hesham Soliman, Claude Castelluccia, Karim El-Malki, Ludovic
Bellier, "Hierarchical MIPv6 mobility management", Internet draft,
draft-ietf-mobileip-hmipv6-03.txt., 2001
[0010] However, as seen in the HMIP described above, in the
handover using the WLAN, the terminal itself needs to designate a
route in the network. An IP (Internet Protocol)-centric network
(the so-called IP network) is layered so that the own layer number
and the IP address are provided as broadcast information to the
terminal. At the terminal side, its own optimal route (which does
not produce redundant routes) is determined using the broadcast
information.
[0011] Now it is expected that, in the next generation mobile
telephone system which follows the current mobile telephone system,
a wide variety of wireless systems including the mobile telephone
and the WLAN systems will be interconnected via the IP network. For
example, in the case of accommodating such a wide variety of
wireless systems in a common IP network, the development of
handover technology to seamlessly connect the wide variety of
wireless systems in response to the location and the taste of the
user, the communications content, etc., will become quite
important.
[0012] Furthermore, at the terminal side, although study on a
software-defined radio that enables the handling of a variety of
wireless methods and protocols is underway, it is expected that the
amount of processing at the terminal side will increase in order to
achieve such greater functionality. Therefore, if the HMIP of the
Mobile IP as described above is implemented as it is in the
software-defined radio, a problem arises such that there will be a
further increase in the amount of processing at the terminal so as
to make minituarization difficult.
SUMMARY OF THE INVENTION
[0013] It is a general object of the present invention to provide a
system for and its method of controlling handover, a mobile
terminal, and an apparatus for controlling handover that
substantially obviate one or more problems caused by the
limitations and disadvantages of the related art.
[0014] In light of the problems as described above, it is a more
particular object of the present invention to provide a system for
and its method of controlling handover between homogeneous or
heterogeneous wireless systems at the network side so as to enable
the seamless implementation of handover between homogeneous or
heterogeneous wireless systems while seeking a reduction in the
amount of processing at the mobile terminal for controlling
handover in the case of accommodating multiple types of wireless
networks in the common network.
[0015] Furthermore, the present invention relates to the mobile
terminal and the apparatus for controlling handover which are used
in such a system for controlling handover.
[0016] According to the invention, a system for controlling
handover includes a mobile terminal which enables communication
with a plurality of wireless systems having wireless access
stations, and a handover-controlling apparatus which executes
control of handover for the mobile terminal which travels among a
plurality of types of the wireless systems, wherein the mobile
terminal includes a destination wireless system determining unit
which receives downlink signals from the respective wireless access
stations so as to determine a wireless system which accommodates a
destination wireless access station based on reception quality of
the downlink signals, and a destination wireless system reporting
unit which sends information indicating said determined wireless
system to said handover-controlling apparatus, and said
handover-controlling apparatus includes a handover-controlling unit
which controls handover operations for said mobile terminal based
on the information indicating the wireless system which is sent
from said destination wireless system reporting unit.
[0017] The system for controlling handover as described above
enables the reduction of handover control processing at the mobile
terminal side as the apparatus for controlling handover at the
network side selects the handover method which fulfills the request
of the mobile terminal based on the wireless system type
information which is provided from the mobile terminal. This
enables the simplification of said apparatus even in such a case as
a software-defined radio in which the mobile terminal is enabled to
conduct communications with the wireless systems.
[0018] According to another aspect of the invention, an apparatus
for controlling handover which executes control of handover for a
mobile terminal that travels among a plurality of types of wireless
systems includes a handover-controlling unit which controls
handover operations for said mobile terminal based on the
information indicating a wireless system which is sent from said
mobile terminal.
[0019] The apparatus for controlling handover as described above
enables the reduction of handover control processing at the mobile
terminal side as said apparatus at the network side selects the
handover method which fulfills the request of the mobile terminal
based on the wireless system type information which is provided
from the mobile terminal.
[0020] According to another aspect of the invention, a mobile
terminal enables communication with a plurality of wireless systems
having wireless access stations and the handover to a plurality of
types of the wireless systems includes a destination wireless
system determining unit which receives downlink signals from
respective wireless access stations so as to determine the wireless
system which accommodates the destination wireless access station
based on the reception quality of the received downlink signals,
and a destination wireless system reporting unit which sends to
said apparatus at the network side the information indicating said
determined wireless system.
[0021] The mobile terminal as described above enables the reduction
of handover control processing at said terminal side as the
apparatus for controlling handover at the network side selects the
handover method which fulfills the request of said terminal based
on the wireless system type information which is provided from said
terminal. This enables the simplification of the apparatus even in
such a case as a software-defined radio in which said terminal is
enabled to conduct communications with the wireless systems.
[0022] According to another aspect of the invention, a method of
controlling handover in the system for controlling handover which
includes the mobile terminal that enables the communication with
the plurality of wireless systems having wireless access stations
and the apparatus for controlling handover that executes control of
handover for said mobile terminal that travels among the plurality
of types of wireless systems, said method including the steps of
receiving, at said mobile terminal, the downlink signals from the
respective wireless access stations so as to determine the wireless
system which accommodates the destination wireless access station
based on the reception quality of the received downlink signals and
sending, from said mobile terminal, information indicating said
determined wireless system to said apparatus for controlling
handover, and controlling, by said apparatus, handover operations
for said mobile terminal based on the information indicating said
reported wireless system.
[0023] The method of controlling handover as described above
enables the reduction of handover control processing at the mobile
terminal side as the apparatus for controlling handover at the
network side selects the handover method which fulfills the request
of the mobile terminal based on the wireless system type
information which is provided from the mobile terminal. This
enables the simplification of the apparatus even in such a case as
a software-defined radio in which the mobile terminal is enabled to
conduct communications with the wireless systems.
[0024] Other objects and further features of the present invention
will be apparent from the following detailed description when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a block diagram of a system for controlling
handover which is concerned with a working form of the
invention;
[0026] FIG. 2 is a block diagram of an IP network as illustrated in
FIG. 1;
[0027] FIG. 3 is a block diagram of a mobile terminal as
illustrated in FIG. 1;
[0028] FIG. 4 is a schematic diagram which illustrates a state of
communications for describing handover operations of a system for
controlling handover according to the working form of the
invention;
[0029] FIG. 5 is the first part of a sequence diagram which
illustrates handover operations of a system for controlling
handover according to the working form of the invention;
[0030] FIG. 6 is the second part of the sequence diagram which
illustrates handover operations of a system for controlling
handover according to the working form of the invention; and
[0031] FIG. 7 is a table which illustrates an exemplary structure
of an AP-AR management database.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] In the following, embodiments of the present invention are
described with reference to the accompanying drawings.
[0033] FIG. 1 is a block diagram of a system for controlling
handover which is concerned with a working form of the
invention.
[0034] In FIG. 1, this handover control system 100 comprises a
WCDMA (Wideband Code Division Multiple Access)/WLAN
multi-functional wireless communications terminal (hereinafter
abbreviated as the mobile terminal) 10 which handles both the WCDMA
method based on the IMT-2000 standards specifications and the WLAN
method, a WCDMA access point 20 (for example, a wireless base
station), a WLAN access point 30, and an IP network 40, the mobile
terminal 10 being enabled for connection to the Internet 50 via the
IP network 40.
[0035] FIG. 2 is a block diagram of the IP network 40 which is
illustrated in FIG. 1.
[0036] In FIG. 2, this IP network 40 comprises access routers 41
through 45 which connect to the WLAN access point 30 and the WCDMA
access point 40, a handover method selector 46, a handover method
effector 47, and a database 48 which manages the corresponding
relationships between the access routers and the access points (or
an AP-AR management database).
[0037] The handover method selector 46 refers to the AP-AR
management database 48 based on the information provided from the
mobile terminal 10 so as to select an optimal handover method and
notifies the handover method effector 47 of the selection. The
handover method effector 47 performs the handover processing
according to the handover method as provided from the handover
method selector 46. The specific processing procedures are
described below.
[0038] FIG. 3 is a block diagram of a mobile terminal 10 as
illustrated in FIG. 1.
[0039] In FIG. 3, this mobile terminal 10 comprises an antenna 11
which receives a WCDMA wireless or a WLAN wireless signal, a
multi-band RF/IF unit 12 which switches to a filter that is
relevant to the corresponding wireless methods of said received
signal so as to convert the wireless signal to an IF signal, an ADC
(Analog-to-Digital Converter) and DAC (Digital-to-Analog Converter)
13 which performs conversion processing between an analog IF signal
and a digital. IF signal, a signal processor 14 which performs
signal processing that is relevant to the method (for example,
despreading processing, modulation/demodulation processing), an
external interface unit 16 which is provided with an interface
function for outputting to an external Ethernet (a registered
trademark), etc., the output received from the signal processor 14,
a Central Processing Unit (CPU) 15 which is in charge of
controlling the overall system and determines a destination
wireless system based on the received input signal output from the
multi-band RF/IF unit 12, and the network interface cards (NICs) 17
and 18 which accommodate, for example, the communications protocols
for performing wireless connections according to said corresponding
wireless methods.
[0040] The mobile terminal 10 as described above comprises, for
example, a software-defined radio which enables the operation, by
downloading to the multi-band RF/IF unit 12, the ADC and DAC 13,
and the signal processor 14, the software of the communications
method accommodated in NIC 17 or NIC 18, as an apparatus at the
terminal side for the corresponding methods. Besides, the software
of the corresponding methods may be accommodated in one NIC, or one
NIC may be provided per wireless method. In the present embodiment,
a NIC is provided per wireless method so that a WLAN NIC 17 and a
WCDMA NIC 18 are implemented in the mobile terminal 10.
[0041] Besides, the example described above is an example in which
the NIC and the antenna 11 are separately configured, but there may
be a case in which a NIC includes an antenna. In such a case, such
antenna serves the function of the antenna 11 as described
above.
[0042] Referring to FIG. 4 through FIG. 6, the handover operations
of the system for controlling handover which is configured as
described above are described.
[0043] FIG. 4 is a diagram which illustrates a state of
communications so as to describe the handover operations of a
system for controlling handover according to a working form of the
invention.
[0044] FIG. 5 and FIG. 6 are sequence diagrams which illustrate the
handover operations of a system for controlling handover according
to a working form of the invention.
[0045] In FIG. 4, the example is intended to represent a case in
which the mobile terminal 10 is located in the vicinity of the
boundary between a wireless zone that comprises a WLAN access point
AP-LAN 30 and a wireless zone that comprises a WCDMA access point
AP-WCDMA 20 and in which the mobile terminal 10 is seeking a
handover from a WLAN wireless system to a WCDMA wireless
system.
[0046] Moreover, taking an access router that is proximate to the
WLAN access point AP-LAN 30 as AR-A 101 and an access router that
is proximate to the WCDMA access point AP-WCDMA 20 as AR-B 102, the
access routers AR-A 101 and AR-B 102 are connected to a router R-A
103, the handover method selector 46, and the handover method
effector 47 so as to form the respective communications routes.
Furthermore, a transmitting mobile terminal 70 which transmits a
packet to the mobile terminal 10 conducts wireless communications
with an access point AP-TX 60 which is currently communicating so
that a packet which is received at the AP-TX 60 is transferred via
a proximate router R-B 104.
[0047] Now referring to FIG. 5 and FIG. 6, the handover operations
of a system for controlling handover according to a working form of
the invention are described in detail.
[0048] A user packet which is transmitted at the transmitting
mobile terminal 70 is received at the wireless system access point
AP-TX 60 and then is sequentially transferred in the order of R-B
104, R-A 103, AR-A 101, and AP-LAN 30 so as to be converted to a
wireless signal at the AP-LAN 30 and sent to the mobile terminal 10
(S1). The wireless signal which transmits said user packet is input
to the multi-band RF/IF unit 12 of the mobile terminal 10, which
measures the received input value. The measured value is converted
to a predetermined signal format at the W-LAN NIC 17 so as to be
sent to the CPU 15. Furthermore, as the mobile terminal 10 is then
in the vicinity of the boundary of the wireless zone which
comprises the WCDMA access point AP-WCDMA 20, the wireless signal
which is being transmitted from said AP-WCDMA 20 is also received.
Therefore, as described above, the measurement result of the
received input of the wireless signal which is transmitted from
AP-WCDMA 20 is also sent to the CPU 15 (S3).
[0049] The CPU 15 of the mobile terminal 10 compares the received
input value from AP-LAN 30 and that from AP-WCDMA 20 so as to
determine the wireless system with the higher received input value
as the destination wireless system. Here it is assumed that the
WCDMA wireless system is determined as the destination wireless
system. Also, then, the CPU 15 detects a change in the respective
received inputs at AP-LAN 30 and at AP-WCDMA 20 so as to estimate
from said detected amount of change the travelling speed of the
mobile terminal 10. For example, the Doppler velocity is calculated
based on the distribution of the received power so as to assume the
Doppler velocity as the travelling speed of the mobile terminal
(S4).
[0050] The CPU 15, as described above, determines the WCDMA
wireless system as the destination wireless system and, when the
projection of the travelling speed is completed, a startup
instruction which triggers the startup of WCDMA wireless
communications is output to NIC 17 (S5). Upon receiving this
startup instruction, the WCDMA NIC 18 outputs and sets up at the
signal processor 14, the ADC/DAC 13, and the multi-band RF/IF unit
12, the software in which various parameters (such as modulation
parameters) for receiving the WCDMA wireless signal are stated so
as to enable the reception of the broadcast information which is
periodically broadcast from the AP-WCDMA 20. This broadcast
information is received at the CPU 15 via the multi-band RF/IF unit
12, the ADC/DAC 13 and the signal processor 14 (S6), said CPU 15
determining the destination access point (hereinafter abbreviated
as the destination AP) according to the address information of the
access router which is included in this broadcast information (in
this case, determined as AR-B 102) (S7).
[0051] The CPU 15 outputs to the signal processor 14 the
information of the destination AP which is determined in said
manner (1), the travelling speed information of the mobile terminal
10 which is previously predicted (2) and the information on the
wireless communications system previously determined (to be called
the wireless system type information (3)). A set of information
items comprising (1), (2) and (3) as described above which is input
to the signal processor 14, after undergoing modulation processing,
etc., is converted to an analog signal at the DAC portion of the
ADC/DAC 13 and then is converted to a wireless signal at the
multi-band RF/IF unit 12 so as to be transmitted to the AP-WCDMA
20. Subsequently, the information set is sent to the handover
method selector 46 via the AR-B 102 within the IP network 40
(S8).
[0052] The handover method selector 46, upon receiving the set of
information items (1), (2) and (3), or the destination AP
information, the speed information of the mobile terminal 10, and
the wireless system type information, accesses the AP-AR management
database 48 so as to determine whether the access router which is
in the proximity of the destination access point differs from the
access router which is in the proximity of the access point prior
to travelling (in this case, referred to as the determination on
the compatibility of the access routers) (S9).
[0053] More specifically, the compatibility of the access routers
is determined as described below. FIG. 7 is a table which
illustrates an exemplary structure of the AP-AR management
database. This AP-AR management database is a database for
registering and/or inquiring about the corresponding relationships
between the access points and the access routers per user and may
be a database server, for example.
[0054] In FIG. 7, this AP-AR management database 48 manages per
user the Access Point address (the AP address), the Access Router
address (the AR address), the wireless QoS parameter which
corresponds to the required QoS class, the wireless system type
information and the wireless quality condition information.
[0055] Hereupon, it is assumed that a user A of the mobile terminal
10 is currently conducting wireless communications with the AP-LAN
30 so as to transfer a user packet via AR-A 101. Therefore, in the
AP-AR management database 48, the AP-LAN 30 address as the AP
address for the user A and the AR-A 101 address as the AR address
are registered.
[0056] The handover method selector 46, upon receiving the wireless
system type information and the notification of AP-WCDMA 20 as the
destination AP, refers to the AP-AR management database 48 so as to
retrieve the AP address which corresponds to the AP address of the
AP-WCDMA 20, the destination access point. In this example, the
fact that the AR address which corresponds to the AP address of the
AP-WCDMA 20 is AR-B 102 may be determined from the same database.
In this connection, this AR-B 102 is used for transferring the user
packet from the mobile terminal of a certain user x.
[0057] The handover method selector 46 upon identifying the
destination access router as described above determines whether
this destination access router and the access router prior to
travelling are compatible.
[0058] As described below, there are, for example, two methods of
determining this compatibility of access routers.
[0059] Method 1
[0060] Method 1 is a method which corresponds to a handover between
heterogeneous wireless systems in which the compatibility of the
access routers is determined based on the wireless system type
information. For example, in the example as described above, the
wireless system type information of AR-A 101 and the wireless
system type information of AR-B 102 are compared so as to determine
whether there is compatibility of the access points in the case
that the types are different.
[0061] Method 2
[0062] Method 2 is a method which corresponds to a handover between
homogeneous wireless systems in which a prefix is set up per access
router so as to determine whether there is compatibility of the
access routers in the case that the prefixes are different.
[0063] The handover method selector 46, upon completing the
determination of the compatibility of the access routers as
described above, transmits to the mobile terminal 10 a request for
setting up a WCDMA wireless link (S10). Thereafter, a predetermined
process to set up a wireless link between the AP-WCDMA 20 and the
mobile terminal 10 is executed (S11) so that a wireless link setup
completion notification is sent from the mobile terminal 10 to the
handover method selector 46 upon completing this setup process.
[0064] The handover method selector 46, upon receiving the wireless
link set-up completion notification (S12), determines a handover
method based on the wireless characteristics of the destination
wireless system (S13). More specifically, a network method is
selected (or a handover algorithm is determined) based on the
wireless system type information sent from the mobile terminal 10,
and then a determination is made as to whether a high-speed
handover is to be performed based on the information of the
travelling speed of the mobile terminal.
[0065] Selection of Handover Method
[0066] The handover method selector 46 selects a handover algorithm
based on the destination wireless system according to the criteria
as described below.
[0067] Selection Criteria of Handover Method
[0068] (1) In the case of WCDMA: the soft-handover method
[0069] (2) In the case of HSDPA (High Speed Downlink Packet
Access), an enhanced WCDMA method: the IP-packet-buffering
method
[0070] (3) In the case of WLAN: the IP-packet-buffering method
[0071] (4) In the case of PDC (Personal Digital Cellular): the
hard-handover method
[0072] Below, the respective handover methods as listed above
according to an embodiment of the invention are described.
[0073] The soft-handover method of (1) refers to a method in which
the same packet is sent at the time of handover to the router of
the destination and the router prior to travelling.
[0074] The IP-packet-buffering method of (2) and (3) refers to a
method in which an IP packet is buffered temporarily at the time of
handover, the buffering being completed at the time the mobile
terminal changes over to the destination router.
[0075] The hard-handover method of (4) refers to a method in which
at the time of handover a routing cache table is newly created
while the routing cache table of the router prior to travelling is
deleted.
[0076] In the case of the present embodiment, since WCDMA is
selected as the destination wireless system based on the wireless
system type information, the soft-handover method (1) is
selected.
[0077] Then, the handover method selector 46 selects whether a
high-speed handover is to be performed based on the criteria as
described below.
1 Selection Criteria of High-speed Handover High-speed handover
Speed of terminal 10 selection High speed Required Medium speed Not
required Low speed Not required
[0078] Herein, the high-speed handover method refers to a method in
which the signaling procedure (referring to a signal procedure to
set up a communications channel with the other party before
starting communications and to carry out the connection with the
other party) of the wireless link is simplified, or to multicasting
to the candidate destination routers at the network side, in order
to enable, at the time the mobile terminal 10 is travelling at high
speed, the accomplishment of the handover for the mobile
terminal.
[0079] Based on the travelling speed information from the mobile
terminal 10, the handover method selector 46 selects the high-speed
handover method in the case where the mobile terminal 10 is
determined to be travelling at high speed while the high-speed
handover method is not selected in the cases where the mobile
terminal 10 is determined to be travelling at either low speed or
medium speed.
[0080] As described above, the handover method selector 46 selects
a handover method according to the type of the wireless system and
determines whether the high-speed handover method is required so
that the result (for example, a combination of the handover method
and a determination as to whether the high-speed handover method is
required) is provided to the handover method effector 47 (S14). The
handover effector 47 performs processing for the mobile terminal 10
to make the handover based on the provided result (S15). More
specifically, the handover method effector 47 transfers the user
packet which is transmitted from the transmitting mobile terminal
70 to AP-WCDMA 20 and an access point which neighbors said AP-WCDMA
(tentatively referred to herein as the AP-WCDMA2) via R-A 103 and
AR-B 102 (S16). In the case where the mobile terminal 10 is located
in the vicinity of the boundary of the wireless zones comprising
the respective access points, the mobile terminal 10 receives and
modulates the user packets which are transmitted from the
respective access points. Furthermore, the mobile terminal 10, in
the case where the terminal is not located in the vicinity of the
boundary, receives and modulates the user packet which is received
from either access point. Besides, in the case that the handover
method selector 46 determines that the high-speed handover method
is required, a further transfer of the user packet is performed,
omitting the signaling procedure as described above.
[0081] As described above, according to the present working form,
the handover method selector 46 at the network side selects a
handover method which fulfills the requirement of the mobile
terminal 10 based on the destination AP information, the wireless
system type information and the travelling speed information which
are provided by the mobile terminal 10 so that the selection of the
handover method at the side of the mobile terminal 10 is not
required. In other words, the identification of the handover method
at the mobile terminal 10 is not required so as to enable a
reduction in the amount of handover control processing at the
mobile terminal. Therefore, even in the case of the mobile terminal
10 in which the handover between homogeneous or heterogeneous
wireless systems is implemented by a software-defined radio, the
configuration of the apparatus at the mobile side does not become
complex, enabling the simplification of the apparatus.
[0082] Although the embodiment describes an example in which the
handover method selector 46 and the handover method effector 47 are
configured separately, they do not necessarily have to be set up
separately and may be configured in one server unit which includes
both functions.
[0083] Moreover, although the embodiment describes a case in which
the handover method selector 46 selects the handover method based
on the wireless system type information which is received from the
mobile terminal 10, the present invention is not limited to that
case. For example, it may take a form in which the mobile terminal
10 monitors the wireless link quality conditions prior to and after
travelling, and the monitoring results are provided to the handover
method selector 46 at the network side so that the selector selects
the handover method based on the wireless link quality conditions.
In this case, the mobile terminal 10 calculates the BER (Bit Error
Rate) or the S/N (Signal-to-Noise ratio) using the received inputs
from the access point prior to travelling (the WLAN system in the
case of the present embodiment) and the access point after
travelling (the WCDMA system in the case of the present embodiment)
so as to provide the calculation results as the wireless link
quality conditions to the handover method selector 46 at the
network side. The handover method selector 46 performs the
selection of the handover method according to the criteria as
described below:
2 Handover method Wireless link before/after quality conditions
travelling Good/good Hard-handover method Good/bad Soft-handover
method Bad/good IP-packet buffering method Bad/bad Soft-handover
method
[0084] For example, in the case such that the BER is good before
travelling and bad after travelling, the soft-handover method in
which the packets are sent from two or more access points is
selected as the handover method to obtain a predetermined reception
quality. This enables the execution of handover without degrading
the reception quality at the mobile terminal 10.
[0085] Moreover, although the AP-AR management database 48 in the
embodiment described above assumes a database server which is
connected externally to the handover method selector 46, the
configuration is not limited to this form, but may take, for
example, a form such that the functions of the AP-AR management
database 48 are provided within the handover method selector
46.
[0086] Furthermore, although the example as described thus far
indicates a case in which communications with multiple wireless
systems is enabled by having the mobile terminal 10 either to
switch NICs which store the respective wireless system
communications protocols or to implement multiple NICs, the present
invention is not limited to this form. For example, it may take a
form in which the software which is stored in the NICs is
downloaded from a server, etc., that is provided externally. In
such a case, as the software in which a wireless protocol most
suitable for the location as stated is automatically downloaded to
the mobile terminal 10, the user of the mobile terminal 10 does not
have to keep possession of multiple NICs, thus improving the
ease-of-use for the user. Also, although the embodiment describes a
case in which the mobile terminal 10 is a multi-functional
WCDMA/WLAN terminal which handles both WCDMA and WLAN
communications methods, it is possible as a matter of course to
apply to the present invention a multi-functional terminal which
handles more than two types of wireless systems.
[0087] The present application is based on Japanese Priority Patent
Application No. 2003-047761 filed Feb. 25, 2003, with the Japanese
Patent Office, the entire contents of which are hereby incorporated
by reference.
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