U.S. patent application number 11/374140 was filed with the patent office on 2006-07-20 for wireless base station, wireless base station selection method, multicast signal transmission method, and wireless terminal.
This patent application is currently assigned to NTT DoCoMo, Inc.. Invention is credited to Hijin Sato, Kobaruto Shimada, Toshiaki Takao, Narumi Umeda.
Application Number | 20060160549 11/374140 |
Document ID | / |
Family ID | 26584758 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060160549 |
Kind Code |
A1 |
Sato; Hijin ; et
al. |
July 20, 2006 |
Wireless base station, wireless base station selection method,
multicast signal transmission method, and wireless terminal
Abstract
One preferred embodiment of the invention provides a wireless
base station which provides a multicasting service to
simultaneously transmit identical data to a plurality of wireless
terminals. A wireless base station is connected to a plurality of
wireless terminals and provides a multicasting service for a
plurality of wireless terminals. The wireless base station
determines autonomously whether it provides the multicasting
service for the plurality of wireless terminals. Another preferred
embodiment of the invention provides a method of selecting a
wireless base station for a wireless terminal, the wireless base
station providing a multicasting service for the wireless terminal.
When the wireless terminal can receive the same multicasting
information from a plurality of wireless base stations, the
wireless terminal selects one of the plurality of wireless base
stations so as to make the number of the wireless base stations
that send the same multicasting information as small as
possible.
Inventors: |
Sato; Hijin; (Yokohama-shi,
JP) ; Umeda; Narumi; (Yokohama-shi, JP) ;
Takao; Toshiaki; (Yokohama-shi, JP) ; Shimada;
Kobaruto; (Yokosuka-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
NTT DoCoMo, Inc.
Chiyoda-ku
JP
|
Family ID: |
26584758 |
Appl. No.: |
11/374140 |
Filed: |
March 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09926258 |
Jan 29, 2002 |
|
|
|
PCT/JP01/00748 |
Feb 2, 2001 |
|
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11374140 |
Mar 14, 2006 |
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Current U.S.
Class: |
455/503 |
Current CPC
Class: |
H04L 12/189 20130101;
H04W 48/20 20130101; H04W 72/005 20130101 |
Class at
Publication: |
455/503 |
International
Class: |
H04B 7/005 20060101
H04B007/005; H04B 15/00 20060101 H04B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2000 |
JP |
2000-025767 |
Feb 2, 2000 |
JP |
2000-025768 |
Claims
1. A wireless base station which is connected to a plurality of
wireless terminals and provides a multicasting service for the
plurality of wireless terminals, characterized in that the wireless
base station determines autonomously whether the wireless base
station provides the multicasting service for the plurality of
wireless terminals.
2. The wireless base station as claimed in claim 1, characterized
in that the determination as to whether the wireless base station
provides the multicasting service is made for each of a plurality
of multicasting service groups.
3. The wireless base station as claimed in claim 1, characterized
in that the determination as to whether the wireless base station
provides the multicasting service is made based on a magnitude of a
service area in which the wireless base station can provide the
multicasting service for the plurality of wireless terminals.
4. The wireless base station as claimed in claim 1, characterized
in that the determination as to whether the wireless base station
provides the multicasting service is made based on whether the
wireless base station has an overlapping service area.
5. The wireless base station as claimed in claim 1, characterized
in that the determination as to whether the wireless base station
provides the multicasting service is made based on a service state
of a neighboring wireless base station.
6. The wireless base station as claimed in claim 5, characterized
in that each of the wireless terminals which are connected to the
neighboring wireless base station sends a state signal indicating
the service state of the neighboring wireless base station.
7. The wireless base station as claimed in claim 1, characterized
in that the determination as to whether the wireless base station
provides the multicasting service is made based on a hop number of
the wireless base station.
8. The wireless base station as claimed in claim 1, characterized
in comprising: a transmitting means for transmitting a first state
signal to a neighboring wireless base station, the first state
signal indicating a multicasting service state of the wireless base
station; and a receiving means for receiving a second state signal
from the neighboring wireless base station, the second state signal
indicating a multicasting service state of the neighboring wireless
base station.
9. The wireless base station as claimed in claim 1, characterized
in comprising: a transmitter unit transmitting a first message; a
receiver unit receiving a second message; a message processing
unit-extracting a multicast-related control data from the second
message received by the receiver unit; a determination unit
determining whether the wireless base station provides the
multicasting service, based on the extracted multicast-related
control data; and a message generating unit generating the first
message that is indicative of the result of the determination by
the determination unit, and sending the first message to the
transmitter unit so that the transmitter unit transmits the first
message.
10. A wireless base station which is connected to a control station
and a plurality of wireless terminals and provides a multicasting
service for the plurality of wireless terminals, characterized in
comprising: a transmitting means for transmitting a first state
signal to the control station, the first state signal indicating a
multicasting service state of the wireless base station; and a
receiving means for receiving a second state signal from the
control station, the second state signal indicating a multicasting
service state of a neighboring wireless base station.
11. A wireless base station which is connected to a control station
and a plurality of wireless terminals and provides a multicasting
service for the plurality of wireless terminals, characterized in
that the wireless base station determines whether the wireless base
station provides the multicasting service, based on instructions
received from the control station.
12. A method of selecting a wireless base station for a wireless
terminal, the wireless base station providing a multicasting
service for the wireless terminal, characterized in that, when the
wireless terminal can receive same multicasting information from a
plurality of wireless base stations, the wireless terminal selects
one of the plurality of wireless base stations so as to make the
number of the wireless base stations that send the same
multicasting information as small as possible.
13. The method as claimed in claim 12, characterized in that, when
there is a first wireless base station which is connectable to the
wireless terminal and sending the same multicasting information to
the wireless terminal, the wireless terminal selects the first
wireless base station and is connected to the first wireless base
station.
14. The method as claimed in claim 12, characterized in that, when
there are a plurality of first wireless base stations which are
connectable to the wireless terminal and sending the same
multicasting information to the wireless terminal, the wireless
terminal selects one of the plurality of first wireless base
stations such that the selected first wireless base station has a
largest number of wireless terminals connected thereto, and the
wireless terminal being connected to the selected first wireless
base station.
15. The method as claimed in any of claims 12 to 14, characterized
in that the selected wireless base station provides the
multicasting service for the wireless terminal.
16. A wireless base station which provides a multicasting service
for a wireless terminal, characterized in that, when the wireless
terminal selects one of a plurality of wireless base stations so as
to make the number of the wireless base stations that send
identical multicasting information as small as possible, the
wireless base station determines that the wireless base station
provides a multicasting service for the wireless terminal.
17. A wireless base station which provides a multicasting service
for a wireless terminal, characterized in comprising a counter in
which a count value is incremented when a join message from the
wireless terminal is received at the wireless base station, and
decremented when a leave message from the wireless terminal is
received at the wireless base station, wherein the wireless base
station transmits the count value of the counter to the wireless
terminal.
18. The wireless base station as claimed in claim 17, characterized
in that the wireless base station transmits a renewed count value
of the counter to the wireless terminal each time the count value
is renewed.
19. The wireless base station as claimed in claim 17, characterized
in that the wireless base station stops providing the multicasting
service for the wireless terminal when the count value of the
counter is equal to zero.
20. A wireless terminal which receives a multicasting service
provided by a wireless base station, characterized in comprising:
an analysis unit determining the number of wireless terminals
connected to a multicast group, based on a received control data;
and a comparison unit determining whether the determined number is
larger than the number of wireless terminals currently connected to
the base station, wherein the wireless terminal selects one of
connection of the wireless terminal to the base station and
disconnection of the wireless terminal from the base station based
on the result of the determination of the comparison unit, so as to
make the number of wireless base stations that send identical
multicasting information as small as possible.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a wireless base station
which provides a multicasting service to simultaneously send
identical data to a plurality of wireless terminals, and relates to
a method of selecting a wireless base station, a method of
transmitting a multicast signal, and a wireless terminal.
BACKGROUND OF THE INVENTION
[0002] Generally, in a wireless communication system, a number of
wireless base stations have respective service areas to which the
service of each base station is provided, and the service areas of
the wireless base stations are overlapped each other.
[0003] In the IP (Internet protocol) network, there is an
increasing demand for broadcasting communication applications, such
as music or vide distributions. The studies of the protocols
suitable for such applications in the IP network have been carried
out. Hence, the wireless access communication system that supports
the multicasting service is the important issue.
[0004] Multicasting is the ability of one network node (for
example, a wireless base station) to send identical data to a
number of end-point terminals (for example, wireless terminals).
However, the service areas of wireless base stations are not
necessarily appropriate for providing the wireless terminals with
the multicasting services.
[0005] For example, it is often possible that multiple wireless
base stations cover the same service area, in order to avoid
network congestion.
[0006] FIG. 1 is a diagram for explaining a problem of a service
area of a conventional wireless base station. In the example of
FIG. 1, small service areas 3 through 6 are provided within a
larger service area 1, and small service areas 7 through 9 are
provided within a large service area 2.
[0007] FIG. 2 is an enlarged view of the large service area 1 of
the conventional wireless base station in FIG. 1. As shown, in the
large service area 1, a wireless base station B stands ready to
provide its service. In the small service area 3, a wireless base
station A stands ready to provide its service.
[0008] In the example of FIG. 2, a wireless terminal "a" exists in
the service area 3, and a wireless terminal "b" exists in the
service area 1. Each of the wireless base stations A and B provides
the multicasting service. In the present example, the wireless
terminal "a" can receive the multicasting service provided by the
wireless base station A, and the wireless terminal "b" can receive
the multicasting service provided by the wireless base station
B.
[0009] When providing the multicasting service in a wireless access
communication system in which the service areas of plural wireless
base stations overlap each other, it is likely that the plural
wireless base stations simultaneously send identical data to the
overlapping service area. For the example of FIG. 2, in such a
case, the wireless terminal "a" receives the multicasting service
from the wireless base station A, and, at the same time, it
receives the multicasting service from the wireless base station B.
Namely, the wireless terminal "a" receives identical data from both
the wireless base station A and the wireless base station B at the
same time.
[0010] In the present example, it is sufficient for the wireless
terminal "a" to receive the multicasting service from the wireless
base station B only. It is not necessary that the wireless terminal
"a" receive the multicasting service from the wireless base station
A.
[0011] Hence, in the present example, the multicasting service
provided to the wireless terminal "a" by the wireless base station
A is inefficient. The radio resources are utilized inefficiently in
the present example, and the efficiency of utilization of the radio
resources is lowered.
[0012] Further, conventionally, when the services supported by the
wireless base stations have to be changed in the individual base
stations, the scheduling of the service changes of the wireless
base stations is produced at another location other than the
wireless base stations, and the service changes are effected at the
respective base stations. Such conventional method requires high
cost from the standpoint of maintenance and operation.
[0013] In order to eliminate the above-mentioned problems, one
object of the present invention is to make efficient use of the
radio resources and lower the maintenance and operation cost.
[0014] Further, when the access communication network is based on
the IP network, the IGMP (Internet Group Management Protocol) can
be used as the multicasting protocol. According to the IGMP
protocol, it is determined whether the router sends the
multicasting messages to the sub-network, in order to avoid the
network congestion. When the access communication system is
connected to the IP network that supports the IGMP protocol, it is
preferred that the system employs the access control flow that is
compatible with the IGMP protocol.
[0015] According to the IGMP protocol, in order to prevent the
sending of unnecessary data to the sub-network, the multicasting is
not performed for the packets having a group address that is not
related to the sub-network. In addition, for the wireless access
system that supports the multicasting, the sending of unnecessary
data to the sub-network is avoided, and the radio resources are
saved.
[0016] However, when two different routers A and B receive the
packets having a same group address, the routers A and B perform
the multicasting to send identical data to the terminals of the
related group within the respective service areas thereof.
[0017] In a wireless access communication system in which the
service areas of plural wireless base stations overlap each other
and some wireless terminal can simultaneously receive the
multicasting services from the plural wireless base stations, it is
likely that the wireless terminal is connected to the wireless base
station that provides the highest level of communication quality
for the wireless terminal.
[0018] FIG. 3 is a diagram for explaining another problem of a
service area of a conventional wireless base station. As shown,
reference numeral 1 denotes the service area of the wireless base
station A, and reference numeral 2 denotes the service area of the
wireless base station B.
[0019] As indicated in (A) in FIG. 3, the wireless terminal "a" is
connected to the wireless base station A, and the wireless terminal
"b" can be connected to both the wireless base station A and the
wireless base station B. However, the wireless terminal "b" is
located at the place that is nearer to the wireless base station B
than the wireless base station A. As the wireless base station B
provides a higher level of communication quality for the wireless
terminal "b", the wireless terminal "b" is connected to the
wireless base station B and receives the service from the wireless
base station B.
[0020] As indicated in (B) in FIG. 3, when the service area 4 of
the wireless base station A is provided within the service area 3
of the wireless base station B, the wireless terminal "a" can be
connected to both the wireless base station A and the wireless base
station B. In the example of FIG. 3 (B), the wireless base station
A provides a higher level of communication quality for the wireless
terminal "a" than the wireless base station B, and the wireless
terminal "a" is connected to the wireless base station A and
receives the service from the wireless base station A.
[0021] However, conventionally, in the example of FIG. 3 (A), the
wireless terminal "a" is connected to the wireless base station A
according to the communication quality level, even when the
wireless terminals "a" and "b" belong to the same IGMP group (group
G1) and receive identical data. The wireless base station A sends
to the wireless terminal "a" the identical data that is the same as
that is sent to the wireless terminal "b".
[0022] If the connection of the wireless terminal "b" and the
wireless base station B is switched to the connection of the
wireless terminal "b" and the wireless base station A when the
wireless terminal "b" is the only terminal that belongs to the
group G1 and exists in the service area 2 of the wireless base
station B, the wireless base station B stops providing the
multicasting service to the wireless terminal "b". The radio
resources needed for the wireless base station B to transmit other
services to the group G1 terminals can be saved because of the
disconnection of the wireless terminal "b" from the wireless base
station B.
[0023] Further, in the example of FIG. 3 (B), the wireless terminal
"a" exists in the service area 3 of the wireless base station B,
and the wireless terminal "a" can communicate with the wireless
base station B as well. If the connection of the wireless terminal
"a" and the wireless base station A is switched to the connection
of the wireless terminal "a" and the wireless base station B, the
radio resources needed for the wireless base station A can be
saved.
[0024] In a conventional IGMP network, it is likely that, when
different wireless base stations provide the multicasting service
for the wireless terminals which belong to the same IGMP group and
exist in the overlapping service area, the wireless base stations
send identical data to the wireless terminals at the same time. The
radio resources are used unnecessarily in such a situation, and the
utilization of the radio resources is lowered.
[0025] In order to eliminate the above-mentioned problems, another
object of the present invention is to reduce the number of the
wireless base stations that send identical data to the wireless
terminals and increase the efficiency of utilization of the radio
resources.
SUMMARY OF THE INVENTION
[0026] In order to achieve the above-described objects, one
preferred embodiment of the present invention provides a wireless
base station which is connected to a plurality of wireless
terminals and provides a multicasting service for the plurality of
wireless terminals, the wireless base station determining
autonomously whether the wireless base station provides the
multicasting service for the plurality of wireless terminals. In
the preferred embodiment, the determination as to whether the
wireless base station provides the multicasting service may be made
for each of a plurality of multicasting service groups. The
determination as to whether the wireless base station provides the
multicasting service may be made based on a magnitude of a service
area in which the wireless base station can provide the
multicasting service for the plurality of wireless terminals. The
determination as to whether the wireless base station provides the
multicasting service may be made based on whether the wireless base
station has an overlapping service area. The determination as to
whether the wireless base station provides the multicasting service
may be made based on a service state of a neighboring wireless base
station. Each of the wireless terminals which are connected to the
neighboring wireless base station may send a state signal
indicating the service state of the neighboring wireless base
station. The determination as to whether the wireless base station
provides the multicasting service may be made based on a hop number
of the wireless base station.
[0027] Further, in order to achieve the above-described objects,
another preferred embodiment of the present invention provides a
method of selecting a wireless base station for a wireless
terminal, the wireless base station providing a multicasting
service for the wireless terminal, wherein, when the wireless
terminal can receive same multicasting information from a plurality
of wireless base stations, the wireless terminal selects one of the
plurality of wireless base stations so as to make the number of the
wireless base stations that send the same multicasting information
as small as possible. In the preferred embodiment, when there is a
first wireless base station which is connectable to the wireless
terminal and sending the same multicasting information to the
wireless terminal, the wireless terminal selects the first wireless
base station and is connected to the first wireless base station.
When there are a plurality of first wireless base stations which
are connectable to the wireless terminal and sending the same
multicasting information to the wireless terminal, the wireless
terminal selects one of the plurality of first wireless base
stations such that the selected first wireless base station has a
largest number of wireless terminals connected thereto, and the
wireless terminal being connected to the selected first wireless
base station.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Other objects, features and advantages of the present
invention will become apparent from the following detailed
description when read in conjunction with the accompanying
drawings.
[0029] FIG. 1 is a diagram for explaining a problem of a service
area of a conventional wireless base station.
[0030] FIG. 2 is an enlarged view of the service area of the
conventional wireless base station in FIG. 1.
[0031] FIG. 3 is a diagram for explaining another problem of a
service area of a conventional wireless base station.
[0032] FIG. 4 is a diagram for explaining a service area of one
preferred embodiment of the wireless base station of the
invention.
[0033] FIG. 5 is a diagram for explaining detection of an
overlapping service area by the wireless base station of the
present embodiment.
[0034] FIG. 6 is a diagram for explaining the case in which
wireless base stations having small service areas provide the
multicasting services.
[0035] FIG. 7 is a diagram for explaining the case in which
wireless base stations having large service areas provide the
multicasting services.
[0036] FIG. 8 is a diagram for explaining the case in which the
wireless base station provides the multicasting service based on
the service states of the neighboring wireless base stations.
[0037] FIG. 9 is a diagram for explaining the collection of the
service state data of the neighboring wireless base stations
performed by the wireless base station.
[0038] FIG. 10 is a diagram for explaining the collection of the
service state data of the neighboring wireless base stations
performed through the communication between the neighboring
wireless base stations.
[0039] FIG. 11 is a block diagram of the wireless base station in
the first preferred embodiment of the invention.
[0040] FIG. 12 is a diagram for explaining joining of a wireless
terminal to the multicasting service.
[0041] FIG. 13 is a diagram for explaining switching of the
connection of a wireless base station during the multicasting
service.
[0042] FIG. 14 is a diagram for explaining multicasting service
processing for the overlapping service area.
[0043] FIG. 15 is a flowchart for explaining a control process
performed by the wireless base station when a join message from the
wireless terminal is received.
[0044] FIG. 16 is a flowchart for explaining a control process
performed by the wireless base station when a leave message from
the wireless terminal is received.
[0045] FIG. 17 is a flowchart for explaining a control process
performed by the wireless terminal when sending a join message to a
wireless base station to join a multicasting service group.
[0046] FIG. 18 is a flowchart for explaining a control process
performed by the wireless terminal when the connection of the
wireless terminal is switched.
[0047] FIG. 19 is a block diagram of a wireless base station in a
second preferred embodiment of the invention.
[0048] FIG. 20 is a block diagram of a wireless terminal in the
second preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0049] A description will now be provided of preferred embodiments
of the present invention with reference to the accompanying
drawings.
[0050] FIG. 4 shows a service area of one preferred embodiment of
the wireless base station of the invention.
[0051] In the present embodiment, as shown in FIG. 4, a service
area 10.sub.A of a wireless base station A is provided within a
service area 10.sub.B of a wireless base station B. A wireless
terminal "a" exists in the service area 10.sub.A, and a wireless
terminal "b" exists in the service area 10.sub.B. Each of the
wireless base stations A and B stands ready to provide the
multicasting service.
[0052] A plurality of wireless terminals may exist in the service
area 10.sub.A or the service area 10.sub.B. However, the wireless
terminal "a" and the wireless terminal "b" are shown as the
representative one of the plural wireless terminals in each service
area, for the sake of convenience.
[0053] In the present example of FIG. 4, the wireless terminal "a"
can receive the multicasting service provided by the base station A
and the multicasting service provided by the base station B. The
wireless terminal "b" can receive the multicasting service provided
by the base station B.
[0054] As is apparent from the example of FIG. 4, the wireless
terminal "a" which is located within the overlapping service area
10.sub.A can receive the multicasting service from the base station
B as well. In the present embodiment, when the wireless base
stations A and B send the same multicasting information, the
wireless base stations A and B are controlled such that the base
station A does not provide the multicasting service for the service
area 10.sub.A, and only the base station B provides the
multicasting service for the service area 10.sub.B. According to
the present embodiment, the radio resources of the wireless base
station A can be allocated to other services than the multicasting
service. Hence, it is possible that the wireless base station of
the present embodiment make efficient use of the radio
resources.
[0055] Generally, in order to make efficient use of the radio
resources, the triggers that are needed for the wireless base
station to determine autonomously whether it provides the
multicasting service are as follows: [0056] 1) the magnitude of the
service area, [0057] 2) the presence of the overlapping service
area, [0058] 3) the service states of the neighboring wireless base
stations.
[0059] A description will now be given of the method of determining
whether the wireless base station provides the multicasting
service, based on the magnitude of the service area.
[0060] The magnitude of the service area depends on a transmission
power of the wireless base station. One of a plurality of levels of
the service area magnitude can be determined, in advance, for the
individual wireless base stations in accordance with their
transmission powers. Only the wireless base stations having a given
level of the service area magnitude are allocated to those
providing the multicasting service.
[0061] For example, suppose that wireless base stations having a
radius of the service area less than 100 meters are set to level 1,
wireless base stations having a radius of the service area ranging
from 100 meters to 200 meters are set to level 2, and wireless base
stations having a radius of the service area larger than 200 meters
are set to level 3. For the present case, it can be readily
understood that, according to the present embodiment, the wireless
base stations of level 1 and level 3 are arranged in a spot-like
coverage, and the wireless base stations of level 2 are arranged in
a wide-range coverage. In the above case, the wireless base
stations to which the wireless terminals are most likely to be
connected in the entire service area are the level-2 wireless base
stations. In such circumstances, the multicasting service is
provided by the level-2 wireless base stations only.
[0062] Hence, when the setting of the service area magnitude levels
is given, each wireless base station can determine autonomously
whether it provides the multicasting service, based on the
magnitude of the service area of the wireless base station. The
magnitude of the service area is derived from the transmission
power of the wireless base station. For example, when the level-2
wireless base stations are predetermined as providing multicasting
service, it can be autonomously determined that the wireless base
stations having the transmission power corresponding to the level-2
are those providing the multicasting service.
[0063] Alternatively, the wireless base stations with two or more
levels (for example, the wireless base stations of level 1 and
level 2 or the wireless base stations of level 2 and level 3) may
be predetermined as providing multicasting service.
[0064] Next, a description will be provided of the method of
determining whether the wireless base station provides the
multicasting service, based on the presence of the overlapping
service area, with reference to FIG. 5.
[0065] FIG. 5 shows a detection of an overlapping service area by
the wireless base station of the present embodiment.
[0066] As shown in FIG. 5, the presence of the overlapping service
area is detected by the wireless base station A based on the radius
D2 of the service area of the wireless base station A (derived from
a transmission power of the base station A), the receiving power R1
of a certain channel related to the neighboring wireless base
station B, and the transmission power T1 of the neighboring base
station B.
[0067] The distance D1 between the base station A and the base
station B is calculated from the transmission power T1 and the
receiving power R1.
[0068] The service area radius D2 and the distance D1 are compared
each other. When D1<D2 (the case indicated in (A) in FIG. 5),
the base station A detects that the service area of the neighboring
base station B is provided within the service area of the base
station A, and it is the overlapping area. In this case, the base
station A determines that it provides the multicasting service for
the overlapping service area.
[0069] When D1>D2, there are two different cases (the case
indicated in (B) in FIG. 5 and the case indicated in (C) in FIG.
5). The radius D3 of the service area of the neighboring base
station B is calculated from the transmission power T1 of the base
station B. Then, the distance D1 and the service area radius D3 are
also compared each other.
[0070] When D1>D3 (the case indicated in (C) in FIG. 5), there
is no overlapping service area. In this case, the base station A
determines that it provides the multicasting service for the
service area of the base station A. On the other hand, when
D1<D3 (the case indicated in (B) in FIG. 5), the base station A
detects that the service area of the base station A is provided
within the service area of the neighboring base station B, and it
is the overlapping service area. In this case, the base station A
determines that it does not provide the multicasting service for
the service area of the base station A.
[0071] Next, a description will be given of the relationship
between the multicasting service and the service area.
[0072] In the case indicated in (A) in FIG. 5, the service area of
the base station A is inclusive of the service area of the
neighboring base station B. If the base station A provides the
multicasting service for the service area of the base station A,
the neighboring base station B is not required to provide the
multicasting service for the service area of the base station B.
However, a wireless base station having a small service area
generally can easily increase the utilization of the radio
resources. If the matter is taken into consideration, an
alternative embodiment is possible in which the neighboring base
station B having a small service area provides the multicasting
service while the base station A having a large, inclusive service
area does not provide the multicasting service.
[0073] FIG. 6 is a diagram for explaining the case in which
wireless base stations having small service areas provide the
multicasting services. FIG. 7 is a diagram for explaining the case
in which wireless base stations having large service areas provide
the multicasting services.
[0074] In the case of FIG. 6, the base stations having the small
service areas cover a large service area. A wireless base station
having the large service area is installed when the necessity
arises, in order to avoid the congestion. In the present case, the
base stations having the small service areas provide their
multicasting services so as to cover the large service area. The
wireless base station having the large service area does not
provide the multicasting service. According to the present
embodiment, it is possible to avoid the redundancy of the
multicasting service provided for the overlapping service area.
[0075] Conversely to the case of FIG. 6, in the case of FIG. 7, the
base stations having the large service areas cover a wide-range
service area. Wireless base stations having small service areas are
installed when the necessity arises, in order to avoid the
congestion. In the present case, the base stations having the large
service areas provide their multicasting services so as to cover
the wide-range service area. The wireless base stations having the
small service areas do not provide their multicasting services.
According to the present embodiment, it is possible to avoid the
redundancy of the multicasting service provided for the overlapping
service area.
[0076] Next, a description will be given of the method of
determining whether the wireless base station provides the
multicasting service, based on the service states of the
neighboring wireless base stations.
[0077] FIG. 8 shows the case in which the wireless base station
provides the multicasting service based on the service states of
the neighboring wireless base stations.
[0078] As shown in FIG. 8, the multicasting service #1 is provided
by the wireless base station having the large service area, while
the multicasting service #2 is provided by each of the wireless
base stations having the small service areas. The load of the radio
resources used for the multicasting is controlled. In the present
embodiment, the radio resources used for the multicasting are
distributed, and it is possible to increase the utilization of the
radio resources used for the multicasting.
[0079] The method of collection of the service states of the
neighboring base stations will be described later. In the present
embodiment, the wireless base station determines whether it
provides the multicasting service, based on the service states of
the neighboring base stations. According to the present embodiment,
it is possible to avoid the redundancy of the multicasting service
provided for the overlapping service area. A different service
other than the multicasting service can be provided for the
overlapping service area.
[0080] The base stations which already provide the services are
excluded, and the different service may be provided so as to meet
the demands of the wireless terminals. The detection of the
overlapping service area may be performed according to the previous
embodiment of FIG. 5.
[0081] In applications which perform the multicasting to a
restricted local area, the multicasting information is effective
only in the restricted local area. In such a case, the multicasting
service is provided by only the wireless base stations which are
located near the information source. For this reason, the
determination as to whether the wireless base station provides the
multicasting service may be made based on a hop number of the
wireless base station in a wired or wireless communication network.
When the hop number is used, the present embodiment is more useful
in a wired communication network than a wireless communication
network.
[0082] In the present embodiment, the hop number is defined for a
wireless communication network as follows. The hop number 1 is
allocated for a wireless base station located nearest to the
information source, the hop number 2 is allocated for a wireless
base station neighboring the nearest base station, the hop number 3
is allocated for a wireless base station neighboring the second
nearest base station, and so on. As far as the hop number is
concerned, the wireless base stations correspond to the routers in
the IP (Internet protocol) network.
[0083] For example, suppose that a wireless base station located
near the information source has the hop number 3. When the base
station transmits control information, including the hop number 3,
to a neighboring wireless base station, the received hop number is
decremented to 2 at the neighboring base station. Further, when the
neighboring base station transmits control information, including
the hop number 2, to a next neighboring base station, the received
hop number is decremented to 1 at the next neighboring base
station. The same procedure is repeated. If the hop number that is
equal to 0 is received at a wireless base station, the wireless
base station determines that it does not provide the multicasting
service. If the hop number that ranges from 1 to 3 is received at a
wireless base station, the wireless base station determines that it
provides the multicasting service.
[0084] In the wireless communication network, the hop numbers of
the wireless base stations are managed for each of a plurality, of
multicast groups. According to the present embodiment, the
multicasting service is provided for a restricted local area in
accordance with each of the above-mentioned applications.
[0085] To realize the above-described embodiment, the wireless base
station collects the service states of the neighboring wireless
base stations, each service state including the hop number. The
method of collection of the service states of the neighboring
wireless base stations will now be explained.
[0086] FIG. 9 shows the collection of the service state data of the
neighboring wireless base stations performed by the wireless base
station. FIG. 10 shows the collection of the service state data of
the neighboring wireless base stations performed through the
communication between the neighboring wireless base stations.
[0087] As shown in FIG. 9, wireless base stations 31, 32, 33 and 34
are connected to a control station 30, and each base station is
capable of transmitting control information to and receiving
control information from the control station 30. As described
earlier, in the present example, each of the base stations 31-34
transmits the control information, including the multicast-related
data of the base station, to the control station 30, and one of the
base stations 31-34 receives the control information, including the
service state data of the neighboring base stations, from the
control station 30.
[0088] The above-described method is applicable to not only the
wireless communication network but also the wired communication
network. In alternative embodiment, the control station may
transmit total multicast instructions or individual multicast group
instructions to the neighboring wireless base stations, so that
each base station determines whether it provides the multicasting
service, based on the instructions received from the control
station.
[0089] As shown in FIG. 10, in the present embodiment, each of the
neighboring base stations receives the control information through
the communication between the neighboring base stations, instead of
the communication with the control station. The method of
collection of the service state data of the neighboring wireless
base stations in the present embodiment is also applicable to not
only the wireless communication network but also the wired
communication network.
[0090] All of the wireless base stations transmit the control
information by using a certain channel related to the neighboring
base station, and the neighboring base station may receive the
required control information from the required base station so as
to carry out the above-described method.
[0091] The wireless base station transmits the service state data,
related to the multicasting service of the wireless base station
itself, to the neighboring base station, and the neighboring base
station may determine whether it provides the multicasting service,
based on the received service state data. The wireless terminal
which receives the multicasting service can receive the service
state data of a wireless base station connectable to the terminal
by using a control channel or a certain channel. If the wireless
terminal sends the service state data of the connectable base
station to the currently connected base station, the currently
connected base station may determine whether it provides the
multicasting service, based on the received service state data.
[0092] FIG. 11 shows a configuration of the wireless base station
in the first preferred embodiment of the invention.
[0093] As shown in FIG. 11, in the present embodiment, a
transmitter unit 43 transmits a first message, including control
data of this base station, to a neighboring wireless base station,
and a receiver unit 40 receives a second message including control
data of a neighboring wireless base station. A message processing
unit 41 extracts a multicast-related control data from the second
message received by the receiver unit 40. The message processing
unit 41 sends the extracted multicast-related control data to a
determination unit 42. The determination unit 42 determines whether
the base station provides the multicasting service, based on the
extracted multicast-related control data from the message
processing unit 41. In a certain case, the determination unit 42
may determine that the base station does not provide the
multicasting service. The determination unit 42 sends the result of
the determination to a call processing unit 45. When a request from
a calling wireless terminal is received, the call processing unit
45 transmits the result of the determination to the calling
wireless terminal. Further, the determination unit 42 sends the
result of the determination to a message generating unit 44. The
message generating unit 44 generates the first message that is
indicative of the result of the determination by the determination
unit 42, and sends the first message to the transmitter unit 43 so
that the transmitter unit 43 transmits the first message to the
neighboring base station.
[0094] In the present embodiment, the transmission and receiving of
the control data may be performed by the wireless base station at
the time of power-on or periodically at the intervals of a certain
period. Each time a new control data of the neighboring wireless
base station is received, the message generating unit 44 and the
call processing unit 45 are notified of the new control data.
[0095] In the present embodiment, when the neighboring base station
provides the multicasting service for the multicasting group, the
determination unit 42 may determine that the wireless base station
of concern does not provide the multicasting service for the
multicasting group.
[0096] In the present embodiment, the wireless base station may
control the multicast-related control data (such as the in-service
state, the service disable state or the service enable state) for
each of the multicasting service types, and may transmit the
multicast-related control data to the neighboring wireless base
station or the control station.
[0097] According to the present embodiment, the wireless base
station collects the service states of the neighboring base
stations from the control station or the neighboring base stations,
and determines whether the wireless base station provides the
multicasting service, based on the service states of the
neighboring base stations. It is possible to avoid the redundancy
of the multicasting service provided for the overlapping service
area. It is possible for the wireless base station of the present
embodiment to make efficient use of the radio resources and lower
the maintenance and operation costs.
[0098] Next, a description will be given of a second preferred
embodiment of the invention.
[0099] FIG. 12 is a diagram for explaining joining of a wireless
terminal to the multicasting service. In FIG. 12, reference numeral
1 denotes the service area of the wireless base station A, and
reference numeral 2 denotes the service area of the wireless base
station B.
[0100] FIG. 12 (A) indicates the state before the wireless terminal
"b" joins the multicasting service provided by the base station A,
and FIG. 12 (B) indicates the state after the wireless terminal "b"
joins the multicasting service provided by the base station A
according to the present embodiment.
[0101] Initially, the wireless terminal "a" is connected to the
base station A to receive the multicasting service from the base
station A as the multicast group G1. As indicated in FIG. 12, in
such a state, the wireless terminal "b" is about to join the
multicast group G1. Suppose that the wireless terminal "b" exists
at the location where the terminal "b" is connectable to both the
base station A and the base station B.
[0102] In the above-described state, the wireless terminal "b"
according to the present embodiment detects that the base station A
is now providing the multicasting service for the multicast group
G1, by using a certain channel related to the neighboring base
station. The wireless terminal "b" selects the base station A which
is now providing the multicasting service, and receives the
multicasting service provided by the base station A, as indicated
in FIG. 12 (B).
[0103] According to the present embodiment, it is no longer
required that the base station B transmits identical multicasting
information to the multicast group G1. Hence, the base station B
stops providing the multicasting service for the multicast group
G1, and it is possible to allocate the radio sources of the base
station B to other services.
[0104] FIG. 13 is a diagram for explaining switching of the
connection of a wireless base station during the multicasting
service. In FIG. 13, reference numeral 1 denotes the service area
of the wireless base station A, and reference numeral 2 denotes the
service area of the wireless base station B.
[0105] FIG. 13 (A) indicates the state before the connection of the
wireless terminal "b" is switched, and FIG. 13 (B) indicates the
state after the connection of the wireless terminal "b" is switched
according to the present embodiment.
[0106] Initially, as indicated in FIG. 13 (A), the wireless
terminal "a" is connected to the base station A, and the wireless
terminals "b" and "c" are connected to the base station B. Suppose
that each of the wireless terminals "a", "b" and "c" receives
identical multicasting information of the multicast group G1.
[0107] In the above-described state, the terminal "c" moves away
from the service area of the base station B. In such a case, only
the terminal "b" in the service area of the base station B receives
identical multicasting information of the multicast group G1.
However, the wireless terminal "b" exists at the location where the
terminal "b" is connectable to both the base station A and the base
station B. The wireless terminal "b" according to the present
embodiment detects that the base station A is now providing the
multicasting service for the multicast group G1, by using a certain
channel related to the neighboring base station. The wireless
terminal "b" selects the base station A which is now providing the
multicasting service, and receives the multicasting service
provided by the base station A, as indicated in FIG. 13 (B).
[0108] According to the present embodiment, it is no longer
required that the base station B transmits identical multicasting
information to the multicast group G1. Hence, the base station B
stops providing the multicasting service for the multicast group
G1, and it is possible to allocate the radio sources of the base
station B to other services.
[0109] FIG. 14 is a diagram for explaining multicasting service
processing for the overlapping service area. In FIG. 14, reference
numeral 3 denotes the service area of the wireless base station B,
reference numeral 4 denotes the service area of the wireless base
station A, and the service area 4 of the base station A is provided
within the service area 3 of the base station B.
[0110] FIG. 14 (A) indicates the state before the connection of the
wireless terminal "a" is switched, and FIG. 14 (B) indicates the
state after the connection of the wireless terminal "a" is switched
according to the present embodiment.
[0111] Initially, as indicated in FIG. 14 (A), the wireless
terminal "a" is connected to the base station A, and the wireless
terminal "a" receives the multicasting service of the multicast
group GI provided by the base station A.
[0112] In the above-described state, the terminal "c" is newly
connected to the base station B and joins the multicast group G1.
In such a case, both the base station A and the base station B
transmit identical multicasting information of the multicast group
G1. However, the wireless terminal "a" exists at the location where
the terminal "a" is connectable to both the base station A and the
base station B. The wireless terminal "a" according to the present
embodiment detects that the base station B is now providing the
multicasting service for the multicast group G1, by using a certain
channel related to the neighboring base station.
[0113] Further, the wireless terminal "a" detects the number of
wireless terminals currently connected to the base station A (for
the multicast group G1) by using a certain channel related to the
base station A, and detects the number of wireless terminals
currently connected to the base station B (for the multicast group
G1) by using a certain channel related to the base station B. It is
determined at the wireless terminal "a" whether the latter number
is larger than the former number. The wireless terminal "a"
according to the present embodiment selects one of connection of
the terminal "a" to the base station A and disconnection of the
terminal "a" from the base station A based on the result of the
determination, so as to make the number of wireless base stations
that send identical multicasting information as small as
possible.
[0114] In the present example, the wireless terminal "a" selects
disconnection of the terminal "a" from the base station A, and
receives the multicasting service provided by the base station B,
as indicated in FIG. 14 (B).
[0115] Next, the notification of the number of the currently
connected wireless terminals which is sent from the wireless base
station to a wireless terminal for each multicast group will now be
explained.
[0116] It is necessary for the wireless base station to detect that
a certain wireless terminal terminates the receiving of the
multicasting service of that base station, or that only one
wireless terminal is left in the service area of that base station.
It is necessary for the wireless terminal to detect that the
terminal solely receives the multicasting service from the wireless
base station.
[0117] To resolve the above problems, when the wireless terminal is
about to receive the multicasting service of the wireless base
station, the wireless terminal sends a join message to the base
station. In addition, when the wireless terminal is about to leave
from the multicasting service of the wireless base station, the
wireless terminal sends a leave message to the base station. Each
time the join or leave message is received at the base station, the
count value, indicating the number of wireless terminals currently
connected to the base station for each multicast group, is
incremented or decremented. A broadcast message, including the
resulting count value, is transmitted from the base station to the
wireless terminal by using a certain channel related to the
neighboring base station.
[0118] In the above-described embodiment in FIG. 14, by receiving
the broadcast message from the base station, the wireless terminal
switches the connection of the wireless terminal to a new base
station, so as to make the number of wireless base stations that
send identical multicasting information as small as possible. When
it is detected that there is no wireless terminal receiving the
multicasting service, the base station stops providing the
multicasting service.
[0119] FIG. 15 shows a control process performed by the wireless
base station of the present embodiment when a join message from the
wireless terminal is received.
[0120] As shown in FIG. 15, when the wireless terminal is about to
receive the multicasting service of the wireless base station, the
wireless terminal sends a join message to the base station. At a
start of the control process, the base station receives the join
message from the terminal (S11). After the step S11 is performed,
the base station increments the count value of the internal counter
based on the received join message (S12). At the same time, the
base station updates the number of the currently connected wireless
terminals in a broadcast message to be transmitted (S13). After the
step S13 is performed, the base station transmits the broadcast
message (S14).
[0121] FIG. 16 shows a control process performed by the wireless
base station of the present embodiment when a leave message from
the wireless terminal is received.
[0122] As shown in FIG. 16, when the wireless terminal is about to
leave the multicasting service of the wireless base station, the
wireless terminal sends a leave message to the base station. At a
start of the control process, the base station receives the leave
message from the terminal (S21). After the step S21 is performed,
the base station decrements the count value of the internal counter
based on the received leave message (S22). At the same time, the
base station updates the number of the currently connected wireless
terminals in a broadcast message to be transmitted (S23).
[0123] After the step S13 is performed, the base station determines
whether the resulting count value is equal to 0 (S24). When the
count value is equal to 0, it indicates that there is no wireless
terminal receiving the multicasting service. The base station
notifies the radio resource scheduler that there is no wireless
terminal receiving the multicasting service (S25). The base station
causes the scheduler to stop the allocation of the radio resources
for the multicasting service, and causes the transmitter unit to
stop transmitting the multicasting service information (S26). After
the step S26 is performed, the control of the base station is
transferred to next step S27.
[0124] When the count value is not equal to 0 at the step S24, the
base station transmits the broadcast message including the
resulting count value (S27).
[0125] FIG. 17 shows a control process performed by the wireless
terminal of the present embodiment when sending a join message to a
wireless base station to join a multicast group.
[0126] As shown in FIG. 17, when the wireless terminal intends to
join the multicast group, the wireless terminal receives the
broadcast messages from the neighboring base stations A and B
(S31). After the step S31 is performed, the wireless terminal
detects the number of wireless terminals currently connected to the
base station A for the intended multicast group from the broadcast
message from the base station A, and detects the number of wireless
terminals currently connected to the base station B for the
intended multicast group from the broadcast message from the base
station B. If there is no information related to the intended
multicast group, it is determined that the number of wireless
terminals currently connected to the base station is equal to 0.
The wireless terminal determines whether the former number is
larger than the latter number (S32).
[0127] When the result at the step S32 is affirmative, the wireless
terminal sends a join message to the base station A (S33). The
wireless terminal receives the multicasting service provided by the
base station A (S34). On the other hand, when the result at the
step S32 is negative, the wireless terminal sends a join message to
the base station B (S35). The wireless terminal receives the
multicasting service provided by the base station B (S36). After
one of the steps S34 and S36 is performed, the control process of
FIG. 17 ends.
[0128] FIG. 18 shows a control process performed by the wireless
terminal when the connection of the wireless terminal is
switched.
[0129] In the present embodiment, the wireless terminal has been
connected to the base station B to receive the service from the
base station B, and the connection of the wireless terminal is
switched to the wireless base station A.
[0130] As shown in FIG. 18, at a start of the control process
(S40), the wireless terminal is now connected to the base station B
(S41). The wireless terminal intermittently receives broadcast
messages from the neighboring wireless base stations. The wireless
terminal is connectable to the base stations A and B. By using a
certain channel related to the neighboring wireless base stations,
the wireless terminal receives the service states of the base
stations A and B, and detects the number of wireless terminals
connected to the base station A and the number of wireless
terminals connected to the base station B from the received service
states of the base stations A and B. The wireless terminal
determines whether the number of the terminals of the base station
A is larger than the number of the terminals of the base station B
(S42).
[0131] When the result at the step S42 is affirmative, the wireless
terminal sends a leave message to the base station B (S43). After
the step S43. is performed, the wireless terminal sends a join
message to the base station A (S44). After the step S44 is
performed, the connection of the wireless terminal is switched to
the base station A, and the wireless terminal joins the multicast
group of the base station A and receives the multicasting service
provided by the base station A (S45).
[0132] When the result at the step S42 is negative, the control of
the wireless terminal is transferred to the step S41. The switching
of the connection of the wireless terminal to the base station A is
not performed in this case.
[0133] When the wireless terminal only leaves from the multicasting
group, it is adequate that the wireless terminal sends the leave
message to the base station B.
[0134] FIG. 19 shows a wireless base station in a second preferred
embodiment of the invention.
[0135] As shown in FIG. 19, in the wireless base station of the
present embodiment, a receiver unit 10 receives control data,
including a join message or a leave message, in addition to
communication data. A message analysis unit 11 extracts the
join/leave message from the control data received by the receiver
unit 10, and sends the extracted message to a counter 12. In the
counter 12, a count value is incremented or decremented, or remain
unchanged, in accordance with the extracted message from the
message analysis unit 11. When the count value of the counter 12 is
changed, the counter 12 notifies a message generating unit 13 of
the changed count value. The message generating unit 13 generates a
broadcast message based on the changed count value, and sends the
broadcast message to a transmitter unit 15 so that the transmitter
unit 15 transmits the broadcast message.
[0136] When the count value of the counter 12 is equal to zero, the
counter 12 notifies a radio resource scheduler 14. The resource
scheduler 14 in this case stops the allocation of the radio
resources to the wireless terminals. When a join message from the
wireless terminal to join a new multicasting group is received, the
count value of the counter 12 is changed from 0 to 1. The counter
12 notifies the resource scheduler 14 of the new join message. The
resource scheduler 14 allocates the radio resources to the new
multicasting group. In this case, the transmitter unit 15 transmits
the multicasting information related to the new multicasting
group.
[0137] FIG. 20 shows a wireless terminal in the second preferred
embodiment of the invention.
[0138] As shown in FIG. 20, in the wireless terminal of the present
embodiment, a receiver unit 20 receives control data, including a
broadcast message, in addition to communication data. A message
analysis unit 21 extracts the broadcast message from the control
data received by the receiver unit 20, determines the number of
wireless terminals connected to the multicast group from the
extracted message, and sends the number of wireless terminals to a
comparison unit 22. The comparison unit 22 determines whether the
received number is larger than the number of wireless terminals
currently connected to the base station. When the number of
wireless terminals connected to the multicast group is larger than
the number of wireless terminals currently connected to the base
station, the switching of the connection of the wireless terminal
of concern is needed. In this case, a join/leave message generating
unit 23 and a base station switching unit 24 are notified of the
need for the switching. Otherwise, no further processing is
performed.
[0139] The message generating unit 23 generates a leave message to
the current base station and a join message to a new base station
based on the result of the determination received from the
comparison unit 22. The message generating unit 23 sends the
join/leave messages to a transmitter unit 25 so that the
transmitter unit 25 transmits the messages. The base station
switching unit 24 controls the synchronization of the transmitter
unit 25 with the current base station (or the new base station) in
accordance with the result of the determination received from the
comparison unit 22.
[0140] The present invention is not limited to the above-described
embodiments, and variations and modifications may be made without
departing from the scope of the present invention.
* * * * *