U.S. patent application number 11/039480 was filed with the patent office on 2005-12-29 for radio communication system and base station.
This patent application is currently assigned to Hitachi Communication Technologies, Ltd.. Invention is credited to Kawamoto, Kiyoshi, Mazawa, Shiro, Takahashi, Yosuke, Usuba, Keiji, Yoshida, Akihiko.
Application Number | 20050288025 11/039480 |
Document ID | / |
Family ID | 35506608 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050288025 |
Kind Code |
A1 |
Yoshida, Akihiko ; et
al. |
December 29, 2005 |
Radio communication system and base station
Abstract
A radio communication system includes a grouping unit for
grouping a plurality of base stations into a plurality of groups
(Soft Handoff Groups) and a determining unit for selecting base
stations belonging to one and the same group selected from the
groups produced by the grouping unit and for determining the base
stations as base stations to send communication packets to an
access terminal.
Inventors: |
Yoshida, Akihiko; (Yokohama,
JP) ; Mazawa, Shiro; (Yokohama, JP) ;
Kawamoto, Kiyoshi; (Yokohama, JP) ; Takahashi,
Yosuke; (Yokohama, JP) ; Usuba, Keiji;
(Yokohama, JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Hitachi Communication Technologies,
Ltd.
Tokyo
JP
|
Family ID: |
35506608 |
Appl. No.: |
11/039480 |
Filed: |
January 19, 2005 |
Current U.S.
Class: |
455/442 ;
455/525 |
Current CPC
Class: |
H04W 36/18 20130101 |
Class at
Publication: |
455/442 ;
455/525 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2004 |
JP |
2004-187223 |
Claims
1. A radio communication system including access terminals and a
plurality of base stations communicable with the access terminals,
comprising: grouping means for grouping the base stations into a
plurality of groups in association with Soft Handoff; and a
determining unit for selecting, from the base stations, base
stations belonging to one of the groups produced by the grouping
means, and for determining the base stations as base stations which
send communication packets to the access terminal.
2. A radio communication system including access terminals and a
plurality of base stations communicable with the access terminals,
comprising: a calculating unit for calculating distance between the
access terminal and a first base station selected from the base
stations, according to respective positional information of the
access terminal and the first base station; a comparing unit for
comparing a calculated result calculated by the calculating unit
with a predetermined parameter (Soft Combine Radius (SCR)); and a
requesting unit for requesting, according to a result of the
comparison by the comparing unit, a second base station selected
from the base stations to send a communication packet to the access
terminal.
3. A radio communication system according to claim 2, wherein the
requesting unit requests the second base station selected from the
base stations to send a communication packet to the access terminal
if the calculated result from the calculating unit is more than a
value of the parameter.
4. A radio communication system according to claim 3, wherein the
requesting unit requests the second base station to interrupt
transmission of a communication packet being transmitted to the
access terminal if the calculated result from the calculating unit
is equal to or less than the value of the parameter as a result of
movement of the access terminal.
5. A radio communication system including access terminals and a
plurality of base stations communicable with the access terminals,
comprising: a calculating unit for calculating distance between a
first base station selected from the base stations and a second
base station selected from the base stations, according to
respective positional information of the first and second base
stations; a comparing unit for comparing a calculated result
calculated by the calculating unit with a predetermined parameter
(Soft Combine Radius (SCR)); and a determining unit for
determining, according to a result of the comparison from the
comparing unit, the base station which sends communication packets
to the access terminal.
6. A radio communication system according to claim 5, wherein the
determining unit determines the second base station as a base
station to send a communication packet to the access station if the
calculated result from the calculating unit is equal to or less
than a value of the parameter.
7. A radio communication system including a plurality of access
terminals and a plurality of base stations communicable with the
access terminals, comprising: a power measuring unit for measuring
received power received from each of the base stations; a
collecting unit for comparing a measured result measured by the
power measuring unit with a predetermined power threshold value and
collecting information on the base stations being associated with
received power exceeding the power threshold value; and a
determining unit for determining, according to a collection result
collected by the collecting unit, the base stations to communicate
with the access terminals.
8. A radio communication system according to claim 7, wherein the
determining unit selects, from the base stations associated with
received power exceeding the power threshold value, n base stations
for communicating with the access terminals in descending order of
amount of information collected by the base stations.
9. In a radio communication system including a plurality of access
terminals and a plurality of base stations communicable with the
access terminals, each of the base stations comprises: a receiving
unit for receiving, from each of the access terminals, information
of the base stations associated with high received power; and a
determining unit for executing statistic processing for the
information of the base stations received by the receiving unit,
thereby producing statistic information and determining, according
to the statistic information, the base stations to communicate with
the access terminals.
10. A base station according to claim 9, wherein the determining
unit selects, from the base stations received from the access
terminals, n base stations to communicate with the access terminals
in descending order of amount of information received by the
receiving unit.
Description
INCORPORATION BY REFERENCE
[0001] The present application claims priority from Japanese
application JP2004-187223 filed on Jun. 25, 2004, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a radio communication
system and a base station in which a plurality of base stations
transmit the same communication information such as the same voice
and sound and data at same timing to an access terminal and the
access terminal combines the communication information with each
other to restore the original data stream.
[0003] In the field of communications in recent years, the
broadband communication has been broadly developed, routers have
been technically advanced, and a need of users to receive, for
example, streaming video images having a large capacity or
including a large amount of data is increasing. In association
therewith, attention has been attracted to a multicast
communication technique to broadcast data as well as voice and
sound having a large capacity using a few communication resources
as compared with a unicast communication technique. "Multicast" is
a technique to simultaneously transmit the same communication
information such as the same data and/or voice and sound to a
plurality of user terminals. "Unicast" is a technique to conduct
communication with each user terminal with a one-to-one
correspondence established therebetween.
[0004] Therefore, when plural access terminals have received the
same voice or data by using the multicast, the traffic on the
communication can be advantageously reduced when compared with the
case using the unicast.
[0005] Also, in the field of radio communication such as Evolution
Data Only (1xEVDO) using, for example, a Code Division Multiple
Access (CDMA), there has been discussed a communication technique
in which to improve efficiency of use of radio bands, one data
stream can be received by a plurality of access terminals.
Heretofore, a physical channel is assigned to each access terminal
to establish radio connection for communication therebetween. That
is, one-to-one unicast communication is carried out. By assigning
one particular channel one the physical channels as a multicast
channel, one data stream is sent to a plurality of access
terminals. This improves efficiency of use of radio bands.
[0006] For efficient use of frequencies, each of the base stations
constituting a radio communication system includes a plurality of
sectors. An electric wave receiving state of the access terminal
varies depending on a wave propagation environment between the
access terminal and the base stations. In the unicast, one-to-one
communication is conducted between an access terminal and a base
station (sector). Therefore, the base station (sector) can control
the communication. For example, the base station increases, for
each access terminal, a data rate of a data stream when the wave
propagation state is good for the access terminal and decreases the
data rate thereof when the wave propagation state is unsuitable or
is not good for the access terminal. In the multicast, it is
required for the access terminal to receive a data stream sent from
the base station (sector) at a particular data rate stipulated for
the multicast. Therefore, since the data rate of the data stream
received by the access terminal varies depending on the wave
propagation environment, when the data stream is sent from the base
station (sector) at a high data rate in the multicast, an access
terminal at a position in a deteriorated or bad wave propagation
environment cannot receive the data stream. When the data rate is
low, throughput of the communication is reduced.
[0007] Reception sensitivity of a signal received by the access
terminal depends on a ratio between an actual data signal level of
the received data signal and a noise signal level thereof.
Therefore, to enable the multicast data stream to be received by as
many access terminals as possible, it is only necessary to increase
the ratio of the actual data signal level to the noise signal
level.
[0008] However, since a base station (sector) in a best wave
propagation environment is selected for communication in the
conventional unicast communication, substantially all electric
waves sent from base stations (sectors) not selected as
communication targets become interference noise. The 3rd Generation
Partnership Project 2 (3GPP2) C.S0054 Version 1.0 describes a
method in which a plurality of base stations (sectors) transmit at
same timing the same data stream using the same frequency to the
access terminal. The access terminal combines data signals of the
data streams with each other to restore the original data stream to
thereby increases the ratio of the actual data signal level to the
noise signal level. As a result, an increased number of access
terminals can receive data streams multicast at a high data rate.
In a technique called Soft Combine, the same data streams sent from
a plurality of base stations (sectors) at same timing are combined
with each other and restored into the original data stream by the
access terminal. This increases the ratio of the actual data signal
level to the noise signal level of the signal received by the
access terminal to thereby improve data stream reception
quality.
[0009] Timing to transmit the data stream is sent from the base
stations (sectors) to the access terminals at a fixed interval of
time.
SUMMARY OF THE INVENTION
[0010] A data stream multicast from a base station (sector) to an
access terminal will be referred to as a BroadCast/MultiCast
Service (BCMCS) flow (hereinafter just represented as "flow"). As
described above, to achieve the Soft Combine, it is required for a
plurality of base stations (sectors) to transmit the same flows at
the same timing.
[0011] However, when all base stations (sectors) disposed in the
radio communication system send the same flows at the same timing
to access terminals, radio bands are not efficiently used. The
maximum number of base stations (sectors) from which an access
terminal can receive flows depends on performance of the access
terminal. Therefore, when flows are sent from base stations
(sectors) of which the number exceeds the maximum number, radio
bands are not efficiently used. It is necessary to determine the
number of base stations (sectors) to transmit flows so that
utilization efficiency of radio bands is kept optimized. However,
the 3GPP2 C.S0054 Version 1.0 does not describe any method of
implementing the optimization of radio band utilization
efficiency.
[0012] It is an object of the present invention to provide a radio
communication system and base stations which can dynamically
determine a sector to be communicated with an access terminal and
efficiently perform the soft combine in the radio communication
system under the unstable radio wave propagation environment.
[0013] To achieve the object, there is provided a radio
communication system according to the present invention. The system
includes an access terminal, a plurality of base stations
communicable with the access terminal, a grouping unit for grouping
the base stations into a plurality of groups in association with
Soft Handoff, and a determining unit for selecting, from the base
stations, base stations belonging to one of the groups produced by
the grouping unit, and for determining the base stations as base
stations which send communication packets to the access
terminal.
[0014] According to the present invention, there is provided a
radio communication system. The system includes an access terminal,
a plurality of base stations communicable with the access terminal,
a calculating unit for calculating distance between the access
terminal and a first base station selected from the base stations,
according to respective positional information of the access
terminal and the first base station; a comparing unit for comparing
a calculated result calculated by the calculating unit with a
predetermined parameter (Soft Combine Radius (SCR)), and a
requesting unit for requesting, according to a result of the
comparison by the comparing unit, a second base station selected
from the base stations to send a communication packet to the access
terminal.
[0015] According to the present invention, there is provided a
radio communication system. The system includes an access terminal,
a plurality of base stations communicable with the access terminal,
a calculating unit for calculating distance between a first base
station selected from the base stations and a second base station
selected from the base stations, according to respective positional
information of the first and second base stations; a comparing unit
for comparing a calculated result calculated by the calculating
unit with a predetermined parameter (Soft Combine Distance (SCD)),
and a determining unit for determining, according to a result of
the comparison from the comparing unit, base stations selected from
the base stations base stations which send communication packets to
the access terminal.
[0016] According to the present invention, there is provided a
radio communication system. The system includes a plurality of
access terminals, a plurality of base stations communicable with
the access terminals, a power measuring unit for measuring received
power received from each of the base stations, a collecting unit
for comparing a measured result measured by the power measuring
unit with a predetermined power threshold value and collecting
information from base stations selected from the base stations, the
base stations being associated with received power exceeding the
power threshold value; and a determining unit for determining,
according to a collection result collected by the collecting unit,
base stations selected from the base stations, the base stations
being to communicate with the access terminals.
[0017] According to the present invention, there are provided a
base stations for use in a radio communication system comprising a
plurality of access terminals and a plurality of base stations
communicable with the access terminals. Each of the base stations
includes a receiving unit for receiving, from each of the access
terminals, information of base stations selected from the base
stations, the base stations associated with high received power;
and a determining unit for executing statistic processing for the
information of the base stations received by the receiving unit,
thereby producing statistic information and determining, according
to the statistic information, base stations selected from the base
stations, the base stations being to communicate with the access
terminals.
[0018] According to the present invention implementing the
configurations described above, there can be provided a radio
communication system and a base station. Accordingly, in a radio
communication system in a wave propagation environment varying with
a lapse of time, base stations (sectors) to communicate with access
terminals are dynamically determined to efficiently achieve Soft
Combine.
[0019] Unnecessary use of the radio band can be prevented and hence
the radio resources can be efficiently used.
[0020] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram showing an overall configuration of a
first embodiment of a radio communication system 1.
[0022] FIG. 2 is a block diagram showing a configuration of a base
station.
[0023] FIG. 3 is a diagram showing a layout of a sector state
managing table 212 disposed in a base station.
[0024] FIG. 4 is a diagram showing a layout of a flow information
managing table 213 disposed in a base station.
[0025] FIG. 5 is a block diagram showing a configuration of a
communication controller 120.
[0026] FIG. 6 is a diagram showing a layout of an information
managing table 522 disposed in the communication controller.
[0027] FIG. 7 is a block diagram showing a configuration of a
contents server 140.
[0028] FIG. 8 is a sequence chart showing control operation of the
radio communication system 1 to start flow transmission.
[0029] FIG. 9 is a sequence chart showing control operation of the
radio communication system 1 to interrupt flow transmission.
[0030] FIG. 10 is a diagram showing an outline of operation in a
second embodiment of a radio communication system.
[0031] FIG. 11 is a diagram also showing an outline of operation in
the second embodiment of a radio communication system.
[0032] FIG. 12 is a block diagram showing a configuration of a
table 1200 disposed in a base station.
[0033] FIG. 13 is a sequence chart showing operation of the radio
communication system when a base station 1002 is added as a
communication target of an access terminal 100.
[0034] FIG. 14 is a sequence chart showing operation of the radio
communication system when the base station 1002 is removed from the
communication targets of an access terminal 100.
[0035] FIG. 15 is a diagram showing a configuration of a third
embodiment of the radio communication system.
[0036] FIG. 16 is a diagram showing a layout of a table 1600
disposed in the third embodiment of the communication controller
station.
[0037] FIG. 17 is a sequence chart showing operation of the third
embodiment of the radio communication system.
[0038] FIG. 18 is a diagram showing an outline of operation in a
fourth embodiment of the radio communication system.
[0039] FIG. 19 is a diagram also showing an outline of operation in
a fourth embodiment of the radio communication system.
[0040] FIG. 20 is a diagram showing a layout of a table 2100
disposed in an access terminal.
[0041] FIG. 21 is a diagram showing a layout of a table 2200
disposed in a base station.
[0042] FIG. 22 is a sequence chart showing operation of the fourth
embodiment of the radio communication system.
[0043] FIG. 23 is a sequence chart also showing operation of the
radio communication system when access terminals 101 and 102 move
to other positions.
[0044] FIG. 24 is a graph showing results of static information
collected by a base station.
[0045] FIG. 25 is a graph also showing results of static
information collected by the base station.
DESCRIPTION OF THE EMBODIMENTS
[0046] Description will now be given in detail of embodiments of
the present invention.
1. First embodiment
[0047] FIG. 1 shows an overall configuration of a first embodiment
of a radio communication system 1. The system 1 includes an access
terminal 100, a plurality of base stations 110-1 to 110-6, a
communication controller (packet communication controller) 120 to
control the base stations, a communication network such as an
Internet Protocol (IP) network connected to the communication
controller, and a contents server 140 connected to the IP network.
In the radio communication system 1, communication information and
control information are communicated in the form of packets.
Although the system 1 includes only one access terminal 100 for
convenience of description, a plurality of access terminals 100 are
actually installed in the system 1.
[0048] Each base station includes a plurality of sectors. The base
station 110-1 has an adjacent relationship with the base stations
(sectors) 110-2 and 110-3. In the embodiment, an adjacent base
station (sector) indicates a base station (sector) which is a
target of handoff of the access terminal 100.
[0049] Each base station conducts radio communication with the
access terminal 100. A flow (voice and sound as well as data) to be
multicast is transmitted from the base station (sector) via a
multicast channel to the access terminal. Each base station
(sector) periodically notifies control information including
information items such as transmission time and timing of a flow to
the access terminal.
[0050] The communication controller 120 controls communication of a
packet to be received and manages session information of the access
terminal. The controller 120 also manages information such as the
flow transmission time and timing of a flow sent from a plurality
of base stations (sectors) at the same timing.
[0051] The contents server 140 manages a flow (contents) delivered
to the access terminal.
[0052] FIG. 2 shows a configuration of the base station 110-1 in a
block diagram. The other base stations 110-2 to 110-6 are
configured also in a similar way. The base station 110-1 includes a
plurality of antennas 200-1 to 200-3, radio analog units 201-1 to
201-3 respectively connected to the antennas 200-1 to 200-3, a
digital signal processing unit 202 connected to the radio analog
units 201-1 to 201-3, a line interface unit 203 connected to the
communication controller 120, a call processing unit 204 connected
to the digital signal processing unit 202 and the line interface
unit 203, and a base station controller 205 connected to the call
processing unit 204.
[0053] The analog units 201-1 and 203-3 convert analog signals
received from the access terminal into digital signals and then
output the signals to the digital signal processing unit 202. The
units 201-1 and 203-1 also receive digital signals from the unit
202 to convert the signals into analog signals.
[0054] The digital signal processing unit 202 demodulates forward
digital signals received from the radio analog units 201-1 to 201-3
and modulates reverse signals to be sent to the access
terminal.
[0055] The line interface unit 203 communicates packets with the
communication controller 120.
[0056] The call processing unit 202 includes a processor 210, a
program storage memory 211 to store therein programs to be executed
by the processor 210, a sector state managing table 212 to manage
states of sectors, and a flow information managing table 213 to
manage information of a flow to be sent to the access terminal 100,
and an input/output (I/O) interface 214 to communicate signals with
the line interface unit 203 and the base station controller
205.
[0057] The controller 205 controls operation of the base station
110-1 in a unified way.
[0058] FIG. 3 shows a layout of the sector state managing table 212
disposed in the base station. The table 212 stores entries each of
which includes a sector number 212-1 to identify a sector and a
Soft Handoff group (SHOG) including information to identify a group
of sectors for which the same flow is transmitted at same timing,
with a correspondence established therebetween.
[0059] FIG. 4 shows a layout of the flow information managing table
213 disposed in the base station. The table 213 stores entries each
of which includes a flow ID 213-1 to identify a flow, a data rate
213-2 indicating a transmission data rate of the flow, transmission
time 213-3 indicating time to transmit the flow, and transmission
timing 213-4 to indicate timing to transmit the flow, with a
correspondence established therebetween.
[0060] FIG. 5 shows a configuration of the communication controller
120. The controller 120 includes a base station interface unit 500
to be connected to a base station, an IP network interface unit 501
to be connected to the IP network 130, a call processing unit 503
connected to the interface units 500 and 501, and a device
controller 502 connected to the call processing unit 503. Although
the embodiment includes only one base station interface unit, the
system may be configure to include a plurality of base station
interface units according to the number of base stations disposed
in the system.
[0061] The base station interface unit 500 communicates packets
with base stations. The IP network interface unit 501 communicates
packets with the IP network 130. The call processing unit 503
includes a processor 520, a program storage memory 521 to store
programs to be executed by the processor 520, an information
managing table 522 to store information necessary to achieve Soft
Combine according to the present invention, and an input/output
(I/O) interface 523 to communicate signals with the device
controller 502. The controller 502 controls the communication
controller 120 in a unified way.
[0062] FIG. 6 shows a layout of the information managing table 522
disposed in the communication controller. The table 522 stores
entries each of which includes a flow ID 522-1 to identify a flow,
a data rate 522-2 indicating a transmission data rate of the flow,
transmission time 522-3 indicating transmission time of the flow,
and transmission timing 522-4 indicating transmission timing of the
flow, with a correspondence established therebetween.
[0063] FIG. 7 shows a configuration of the contents server 140 in a
block diagram. The server 140 includes a processor 700, a program
storage memory 701 to store programs to be executed by the
processor 700, a contents storage database 702 to store flows
(contents) to be delivered to the access terminal 100, and an
input/output (I/O) interface 703 to be connected to the IP network
130.
[0064] Although not shown, the access terminal 100 includes a base
station interface unit to communicate packets with base stations, a
processor, a program storage memory to store programs to be
executed by the processor, and a unit to combine a plurality of
flows received from a plurality of base stations to restore the
original data stream.
[0065] FIG. 8 shows, in a sequence chart, control of the radio
communication system 1 to start flow transmission. Paying attention
to the base station (sector) 110-1, the base station (sector) 110-2
is an adjacent base station (sector) of the base station (sector)
110-1, and the base stations (sectors) 110-4 and 110-5 are adjacent
base stations (sectors) of the adjacent base stations (sectors)
110-2 and 110-3, respectively. In the embodiment, the base stations
(sectors) 110-2 and 110-3 are referred to as adjacent base stations
(sectors), and the base stations (sectors) 110-4 and 110-5 are
referred to as adjacent base stations (sectors) of adjacent base
stations (sectors).
[0066] The base station (sector) 110-1 having received a flow
viewing request from the access terminal 100 is referred to as a
base station in a "Main" state. The base stations (sectors) 110-2
and 110-3 having an adjacent relationship with the base station
(sector) 110-1 having received a flow viewing request are referred
to as base stations in a "Sub" state. The other base stations
(sectors) 110-4 and 110-5 are referred to as base stations in a
"Non" state.
[0067] According to the definitions, the initial state of each base
station (sector) is "Non" (steps S800 to S802) in which the base
station has not transmitted a flow to the access terminal 100. The
terminal 100 sends a flow viewing request to the base station
(sector) 110-1 (S803). The request is periodically sent thereto
during a period of time in which of the owner of the access
terminal is viewing the flow (S804).
[0068] When the flow viewing request is received from the access
terminal 100, the base station sector) 110-1 makes retrieval
through the sector state managing table 212 according to a sector
number of the sector from which the request is received to thereby
obtain information of an associated Soft Handoff group (SHOG;
S805). The base station sector) 110-1 sends a flow information
acquisition request including a flow ID of the requested flow
indicated by the request and the SHOG to the communication
controller 120 (S806).
[0069] Having received the request, the controller 120 sends a flow
transmission request including information of the flow ID to the
contents server 140 (S807). The controller 120 makes retrieval
through the information managing table 522 according to the flow ID
contained in the flow information acquisition request to obtain
therefrom a transmission data rate 522-2 of the flow and then sends
flow information including information of the transmission data
rate 522-2 to the base station (sector) 110-1 (S808). In this
operation, the controller 120 may send security information, not
shown, together with the flow information to the base station
(sector) 110-1.
[0070] When the flow transmission request is received, the contents
server 140 returns an ACK signal to the transmission controller 120
(S809). The server 140 makes retrieval through the contents storage
database 702 (FIG. 7) according to the flow ID contained in the
request to obtain an associated flow and sends the flow to the
controller 120 (S810).
[0071] Having received the flow information sent from the
transmission controller 120, the base station (sector) 110-1
carries out a control operation to establish a path to the
transmission controller 120 (S811). In the operation, the
controller 120 sends information items of transmission time 522-3
and transmission timing 522-4 obtained from the information
managing table 522 to the base station (sector) 110-1. For each
flow, the controller 120 beforehand stores information of a
physical data rate for radio communication between the access
terminal and the base station and information of required
throughput of an application in the access terminal in a storage
device such as a database, not shown. Using the information, the
controller 120 calculates the transmission time 522-3 and the
transmission timing 522-4 for the flow. The controller 120 may
transmit the transmission time 522-3 and the transmission timing
522-4 together with the contents information indicated in step S808
to the base station (sector) 110-1. After obtaining the
transmission time 522-3 and the transmission timing 522-4, the
transmission controller 120 stores these information items in the
information managing table 522 to resultantly update the table 522
(S812). The base station (sector) 110-1 starts transmitting the
flow delivered from the contents server 140 to the access terminal
100(S813, S814). The base station (sector) 110-1 controls the
operation thereof such that the own state makes a transition from
"Non" to "Main" after the transmission of the flow to the access
terminal 100 (S815). As a result, the base station (sector) 110-1
enters the Main state (S816). The base station (sector) 110-1 then
sends a flow transmission request including information items such
as a flow ID, own sector number, SHOG, and the transmission data
rate, transmission time, and transmission timing of the flow
received from the communication controller 120 to the adjacent base
stations (sectors) 110-2 and 110-3 (S817).
[0072] Having received the flow transmission request, each of the
adjacent base stations (sectors) 110-2 and 110-3 returns an ACK
signal to the base station (sector) 110-1 (S818). Thereafter, each
adjacent base station (sector) compares the SHOG sent from the base
station (sector) 110-1 with its own SHOG. If the SHOG is equal to
each other, the base station (sector) conducts control to establish
a path to the communication controller 120(S819). Next, each of the
adjacent base stations (sectors) 110-2 and 110-3 starts
transmitting the flow delivered from the contents server 140 to the
access terminal 100 (S820, S821, S822). The base station (sector)
then controls the operation thereof such that the own state makes a
transition from "Non" to "Sub" after the transmission of the flow
to the access terminal 100 (S823. As a result, each of the base
stations (sectors) 110-2 and 110-3 enters the Sub state (S824).
When flows are received from the base stations (sectors) 110-1 and
110-3, the access terminal 100 combines the flows with each other
to restore the original data stream (S825). In this regard, if the
SHOG of the access terminal 100 is different from the SHOGs of the
adjacent base stations (sectors) 110-2 and 110-3, the processing of
step S818 and subsequent steps is not executed. If the adjacent
base station (110-2, 110-3) is in the Main state or is already in
the Sub state when the flow transmission request is received from
the base station (sector) 110-1, the present state is kept retained
for the following reason. That is, the system is in a state in
which a path has already been established between the adjacent base
station (110-2, 110-3) and the communication controller 120 and the
adjacent base station (110-2, 110-3) is transmitting the flow
delivered from the contents server 140 to the access terminal
100.
[0073] FIG. 9 shows control operation of the radio communication
system 1 to interrupt flow transmission in a sequence chart. Assume
that the base station (sector) 110-1 is in the Main state, the
adjacent base stations (sectors) 110-2 and 110-3 are in the Sub
state, and the adjacent base stations (sectors) 110-4 and 110-5 of
the adjacent base stations (sectors) are in the Non state (steps
S900, S901, and S902).
[0074] The access terminal 100 periodically sends a flow viewing
request including a flow ID to the base station (sector) 110-1
(S903). When the access terminal 100 interrupts the transmission of
the flow viewing request to the base station (sector) 110-1 (S904),
the base station (sector) 110-1 detects expiration of a flow view
managing timer disposed therein and controls its own state to make
a transition from "Main" to "Sub" (S905) to resultantly enter the
Sub state (S906).
[0075] To confirm whether or not a sector in the Main state is
present, the base station (sector) 110-1 sends a sector state
confirmation request including information such as a sector number,
a flow ID, and SHOG to the adjacent base stations (sectors) 110-2
and 110-3 (S907).
[0076] When the request is received, each of the adjacent base
stations (sectors) 110-2 and 110-3 returns an ACK signal including
information of a flow ID, SHOG thereof, and a sector state to the
base station (sector) 110-1. Having received the ACK signal, the
base station (sector) 110-1 recognizes that the sector state
contained in the ACK signal is "Sub" and hence controls its own
state to make a transition from "Sub" to "Non" (S909) to thereby
enter the Non state (S910). If the sector state contained in the
ACK signal is "Main", the base station (sector) 110-1 keeps the
present state retained, i.e., "Sub".
[0077] Having received the sector state confirmation request from
the base station (sector) 110-1 (S907), the adjacent base stations
(sectors) 110-2 and 110-3 transfer the request to the adjacent base
stations (sectors) 110-4 and 110-5 thereof, respectively (S911).
The base stations (sectors) 110-4 and 110-5 return an ACK signal
including information such as a flow ID, SHOG thereof, and a sector
state to the base stations (sectors) 110-2 and 110-3, respectively
(S912). Having received the ACK signal, the base stations (sectors)
110-2 and 110-3 recognize that the sector state contained in the
ACK signal is "Non" and hence control the respective states to make
a transition from "Sub" to "Non" (S913) to thereby enter the Non
state (S914). If the sector state contained in the ACK signal is
"Main", the base stations (sectors) 110-2 and 110-3 keep the
present state retained, i.e., "Sub".
[0078] As indicated in step S910, when the own state is set to
"Non", the base station (sector) 110-1 releases the path to the
communication controller 120 (S915). The base stations (sectors)
110-2 and 110-3 also release the paths to the controller 120 when
the states thereof are set to "Non" (S916).
[0079] When it is recognized that the paths to all base stations
(sectors) under control of the communication controller 120 are
released, the controller 120 sends a flow interruption request
including a flow ID to the contents server 140 (S917).
[0080] Having received the request, the contents server 140 returns
an ACK signal to the communication controller 120 (S918).
[0081] As above, according to the first embodiment, the base
stations (sectors) to communicate with the access terminal 100 are
limited to the base station (sector) having received a flow viewing
request from the access terminal 100 and the adjacent base stations
(sectors) adjacent to the base station (sector) having received the
request. Therefore, the access terminal 100 receives flows from
base stations (sectors) of which the number is within performance
of the access terminal 100. The access terminal 100 does not
receive flows from a base station of which the received power is
weak. Therefore, it is possible to suppress useless flow
transmission. In a base station (sector) not required to send a
flow, a period of time not used for flow transmission can be
assigned to, for example, a unicast service for transmission of
voice and sound as wells as data. Therefore, the radio resources
can be efficiently used.
2. Second Embodiment
[0082] FIGS. 10 and 11 show an outline of operation in a second
embodiment of a radio communication system. Soft Combine Radius
(SCR) indicated in FIGS. 10 and 11 is a parameter stipulating a
range in which the operation of Soft Combine is not required. FIG.
10 shows a state in which a base station (sector) 1002 is
additionally disposed as a communication target of the access
terminal 100. When the access terminal 100 moves to a position
outside the SCR, the terminal 100 sends a flow addition request to
the base station (sector) 1001. Having received the request, the
base station (sector) 1001 sends a flow transmission request to the
base station (sector) 1002. The access terminal 100 then receives
flows from the base stations (sectors) 1001 and 1002 and combines
the flows with each other to restore the original data stream. FIG.
11 shows a situation in which the base station (sector) 1002 is
deleted from the communication targets of the access terminal 100.
When the access terminal 100 moves to a position in the SCR, the
terminal 100 sends a flow deletion request to the base station
(sector) 1001. Having received the request, the base station
(sector) 1001 sends a flow interruption request to the base station
(sector) 1002. The access terminal 100 then receives a flow only
from the base station (sector) 1001. FIG. 12 shows a configuration
of the table 1200 disposed in each of the base stations 1001 and
1002. The table 1200 stores entries each of which includes a sector
number 1201 and a Soft Combine Radius (SCR) 1202 with a
correspondence established therebetween.
[0083] FIG. 13 shows operation of the radio communication system in
a sequence chart in which the base station (sector) 1002 is added
to the communication targets of an access terminal 100.
[0084] In FIG. 13, the access terminal 100 is in a zone of the base
station (sector) 1002 and communicates signaling information with
the base station (sector) 1001.
[0085] The base station (sector) 1001 transmits a flow to the
access terminal 100 (step S1300). The base station (sector) 1001
also notifies a positional information thereof and information of
SCR stored in the table 1200 to the access terminal 100
(S1301).
[0086] The terminal 100 obtains positional information thereof
using, for example, a global positioning system (GPS; S1302). Next,
using the own positional information and the positional information
notified from the base station 1001, the terminal 100 obtains
distance between the terminal 100 and the base station 1001
(S1303). After the access terminal 100 moves to a position, when it
is recognized that the access terminal 100 is outside the SCR, the
terminal 100 compares the SCR value with the calculated value
obtained in step S1303 (S1304). If the SCR value is less than the
calculated value (SCR value<calculated value) as a result of the
comparison, the access terminal 100 sends a flow addition request
including a flow ID and a sector number of a base station (sector)
requested for flow transmission, e.g., the base station (sector)
1002 to the base station (sector) 1001 (S1305). When the flow
addition request is to be sent to a plurality of base stations
(sectors), it is also possible that the access terminal 100 selects
n base station which are n higher base stations with respect to
received power and which are in sectors other than the base station
(sector) 1001. The terminal 100 then sends the flow addition
request to the selected base stations (sectors). In step S1305,
when the flow addition request is to be sent to a plurality of base
stations (sectors), it is also possible that the access terminal
100 selects n nearer base stations with respect to the distance to
the terminal 100.
[0087] When the flow addition request is received from the access
terminal 100 (S1305), the base station (sector) 1001 makes
retrieval through the flow information managing table 213 (FIG. 4)
according to the flow ID contained in the request (S1306) and
sends, to the base station (sector) 1002, a flow ID, a data rate,
transmission time, and transmission timing associated with the flow
ID and a sector number of the base station (sector) 1001
(S1307).
[0088] Having received the request from the base station (sector)
1001, the base station (sector) 1002 starts flow transmission
(S1308).
[0089] The access terminal 100 receives flows sent respectively
from the base stations (sectors) 1001 and 1002 (S1300, S1308) and
combines the flows with each other to restore the original data
steam (S1309).
[0090] FIG. 14 shows, in a sequence chart, operation of the radio
communication system when the base station (sector) 1002 is removed
from the communication targets of an access terminal 100. In FIG.
14, a sequence from S1400 to S1403 is substantially equal to a
sequence from S1300 to S1303 shown in FIG. 13.
[0091] After the access terminal 100 moves to a position, when it
is recognized that the access terminal 100 is in the SCR, the
terminal 100 compares the SCR value with the calculated value
(S1404). If the SCR value is more than the calculated value (SCR
value>calculated value) as a result of the comparison, the
access terminal 100 sends a flow deletion request including a flow
ID and a sector number of a base station (sector) requested for
flow transmission interruption, e.g., the base station (sector)
1002 to the base station 1001 (S1405).
[0092] When the flow deletion request is received from the access
terminal 100, the base station (sector) 1001 makes retrieval
through the flow information managing table 213 (FIG. 4) according
to the flow ID contained in the request (S1406) to send information
such as an associated flow ID and a sector number of the base
station (sector) 1001 to the base station (sector) 1002
(S1407).
[0093] Having received the request, the base station (sector) 1002
makes a check to confirm whether or not a flow viewing request has
been received from any access terminal other than the access
terminal 100 for the flow. If such a flow viewing request has not
been received, the base station (sector) 1002 interrupts the flow
transmission (S1408).
[0094] To prevent addition and deletion of a flow from being
repeatedly conducted at an interval of quite a short period of
time, it is possible to provide a predetermined protection period
of time before a flow deletion request is transmitted. It is also
possible that by defining another SCR for a flow interruption
request in addition to the SCR for a flow transmission request such
that the flow interruption processing is executed using a
conditional expression of "SCR for flow transmission>SCR for
flow interruption".
[0095] For a flow viewing request periodically sent from access
terminals, a timer for flow interruption may be disposed in the
base station (sector). Using the timer, the base station interrupts
the flow transmission.
3. Third Embodiment
[0096] FIG. 15 shows a configuration of a third embodiment of the
radio communication system. In FIG. 15, Soft Combine Distance (SCD)
is a parameter stipulating a range in which a base station (sector)
sends a flow transmission request to an adjacent base station
(sector). A base station (sector) 1501 with which the access
terminal 100 is communicating signaling information transmits a
flow transmission request to adjacent base stations (sectors) 1502
and 1503. Since the base station (sector) 1505 is an adjacent base
station (sector) of the base station (sector) 1504, the base
station (sector) 1504 sends a flow transmission request to the base
station (sector) 1505. The operation will be described later in
detail.
[0097] FIG. 16 shows a layout of the table 1600 disposed in a base
station. The table 1600 stores entries each of which includes a
sector number 1601, an SCD 1602, positional information 1603, and
power information 1604 with a correspondence established
therebetween.
[0098] FIG. 17 shows, in a sequence chart, operation of the third
embodiment of the radio communication system. The base station
(sector) 1501 is transmitting a flow to the access terminal 100
(step S1701). When a flow viewing request is received from the
access terminal 100 (S1702), the base station (sector) 1501 sends a
flow transmission request including information such as its own
sector ID, a flow ID, transmission time, transmission timing, SCD,
positional information thereof, and a flow transmission request
count to the adjacent base stations (sectors) 1502 and 1504
(S1703). The flow transmission request count is used by the base
stations (sectors) to determine whether or not the flow
transmission is to be conducted. The base station (sector) 1501
stores the count in, for example, a memory, not shown (S1704). The
flow transmission request count is used by each of the base
stations (sectors) to determine whether or not the flow
transmission is to be conducted. The flow transmission request
count is used by each base station (sector) to determine whether or
not the flow transmission is to be conducted. For example, when a
flow transmission request is received from the base station
(sector) 1501, the base station (sector) 1502 sends the flow
transmission request to an adjacent base station thereof, i.e., the
base station (sector) 1503. Similarly, when the flow transmission
request is received from the base station (sector) 1502, the base
station (sector) 1503 sends the flow transmission request to an
adjacent base station thereof, i.e., the base station (sector)
1501. This forms a loop including the base stations (sectors) 1501,
1502, and 1503. To prevent this event, the flow transmission
request count is used.
[0099] Having received the request (S1703), each of the base
stations (sectors) 1502 to 1504 calculates distance between the
base station 1501 and the own base station (S1705). Next, the base
station (sector; 1502 to 1504) compares the calculated result with
the SCD value stored in the table 1600 (S1706). If the SCD value is
more than the calculated value (SCD>calculated value) as a
result of the comparison and it is recognized that the pertinent
base station is not transmitting the flow (S1706), the base station
starts transmitting the flow to the access terminal 100 (S1707).
Each base station (sector; 1502 to 1504) also stores the flow
transmission count in, for example, a memory, not shown (S1708). In
step S1706, each of the base stations (sectors) 1502 to 1504 keeps
the transmission state of the flow if the SCD value is equal to or
less than the calculated value (SCD<calculated value) as a
result of the comparison and it is recognized that the base station
is not transmitting the flow.
[0100] Next, each of the base stations (sectors) 1502 to 1504
compares the flow transmission count with a predetermined value
(S1709). If the count is less than the predetermined value, the
base station (sector) sends a flow transmission request to the base
station (sector) 1505 other than those having received the flow
transmission request. The base station (sector; 1502 to 1504)
updates the flow transmission request count stored in the memory
(S1711). That is, the base station (sector) having received the
flow transmission request adds one to the received transmission
request count to update the count if a predetermined period of time
has already lapsed after the last transmission of a flow
transmission request for the flow. The base station (sector) then
transmits the updated transmission request count together with the
flow transmission request to the adjacent base station (sector)
other than those having received the flow transmission request.
[0101] In step S1709, if the flow transmission request count is
more than the predetermined value, each of the base stations
(sectors) 1502 to 1504 does not transmit any flow transmission
request message.
[0102] The base station (sector) 1505 executes processing similar
to the processing of steps S1705 and S1706 (S1712 and S1713) to
transmit a flow to the access terminal 100 (S1714).
[0103] The base station (sector) 1501 sets a time limit to a timer
for the flow viewing request periodically sent from the access
terminal 100 to control the request. When the time limit thus set
to the timer expires (S1715), the base station (sector) 1501 sends
a flow interruption request including a flow ID for transmission
interruption and a message transmission request count to the
adjacent radio base stations (sectors) 1502 to 1504 (S1716). Having
received the request from the base station 1501, the base stations
1502 to 1504 transfer the request to the base station 1505
(S1717).
[0104] The base stations (sectors) 1502 to 1505 interrupt, if a
flow viewing request has not been received from other access
terminals, the flow transmission for the flow (S1718, S1719). If a
value obtained by adding one to the message transmission request
count contained in the flow interruption request is equal to or
less than a predetermined value, the base stations (sectors) 1502
to 1505 transmit a flow interruption request to the adjacent base
stations (sectors) other than those having received the flow
interruption request.
[0105] If the SCD value is changed according to the increase in the
number of access terminals in FIG. 15, operation similar to that
shown in FIG. 17 is conducted using the SCD changed as above. The
SCD value is changed as below. For example, when a small number of
access terminals are viewing multicast data, the SCD is set to a
small value (SCD1). When the number of such access terminals is
increasing, the SCD is set to a value (SCD2) larger than SCD1. When
the number becomes greater, the SCD is set to a value large than
SCD2.
4. Fourth Embodiment
[0106] FIGS. 18 and 19 show an outline of operation in a fourth
embodiment of the radio communication system. FIG. 20 shows a
layout of a table 2100 disposed in each access terminal. FIG. 21
shows a layout of a table 2200 disposed in each base station. FIG.
23 shows, in a sequence chart, operation in the fourth embodiment
of the radio communication system.
[0107] The access terminals 100, 101, and 102 are in the zone of a
base station (sector) 1900 and communicate signaling information
therewith. The base station 1900 is transmitting flows to the
access terminals 100 to 102 (step S2301).
[0108] When a signal is received from each base station (sector),
each of the access terminals 100 to 102 measures power of the
signal (step S2302) and stores the measured value of signal power
in the table 2100 (step S2303). Each access terminal (100, 101,
102) compares the measured power value with a predetermined power
threshold value to determine n base stations (sectors) (n=1, 2, . .
. ) in descending order of the received power, each of the n base
stations having a measured power value more than the predetermined
power threshold value (S2304). In the embodiment, the value of n is
set to a value within a range determined in consideration of
performance of the access terminals. That is, if the values are
within the range, the access terminals can combine received power
values with each other.
[0109] Next, each of the access terminals 100 to 102 sends a flow
viewing request including information of the base stations
(sectors) determined in step S2304 to the base station (sector)
1900 (S2305). In the embodiment, since the received power from the
base station (sector) 1901 has a high value, the access terminal
100 transmits a flow viewing request including information of the
base station (sector) 1901 to the base station (sector) 1900.
Similarly, the access terminal 101 transmits a flow viewing request
including information of the base station (sector) 1902 to the base
station (sector) 1900, and the access terminal 102 transmits a flow
viewing request including information of the base stations
(sectors) 1902 to 1904 to the base station (sector) 1900.
[0110] The base station (sector) 1900 collects information of a
sector contained in the request from each access terminal to
determine m high-order sectors (m=1, 2, . . . ) to which a flow
transmission request is to be transmitted (S2306). In the
embodiment, as can be seen from FIG. 24, the base station (sector)
1900 determines the base station (sector) 1902 as a base station
(sector) for the flow transmission request. The base station
(sector) 1900 then makes retrieval through the flow information
managing table according to a flow ID to send a flow transmission
request including a flow ID, a data rate, transmission time, and
transmission timing associated with the flow ID used in the
retrieval to the base station (sector) 1902 (S2308). When the
request is received therefrom, the base station (sector) 1902
transmits a flow to each of the access terminals 100 to 102
(S2309).
[0111] The access terminal 100 receives flows sent from the base
stations (sectors) 1900 and 1902 (S2301, S2309) and combines the
flows with each other to restore the original data stream
(S2310).
[0112] FIG. 23 shows, in a sequence chart, operation of the radio
communication system when the access terminals 101 and 102 move to
other positions as shown in FIG. 19. The base station 1900 is
transmitting a flow to the access terminals 100 to 102 (step
S2401).
[0113] Each of the access terminals 100 to 102 measures power of a
signal received from each base station (sector; step S2402) to
store a measured value of the power in the table 2100 (step S2403;
FIG. 20). Thereafter, each of the access terminals 100 to 102
compares the measured power value with a predetermined power
threshold value. The terminal (100, 101, 102) resultantly
determines n high-order base stations (sectors) with respect to the
received power (n=1, 2, . . . ), each of the n high-order base
stations having a measured power value more than the predetermined
power threshold value (S2404). Next, each of the access terminals
100 to 102 sends a flow viewing request including information of
the sectors determined in step S2404 to the base station (sector)
1900 (S2405). In the embodiment, the access terminal 101 sends,
according to the movement thereof, a flow viewing request including
information of the base station (sector) 1902 to the base station
1900. Similarly, the access terminal 102 transmits, according to
the movement thereof, a flow viewing request including information
of the base station (sector) 1903 to the base station (sector)
1900.
[0114] The base station (sector) 1900 collects information of
sectors contained in the flow viewing requests received from the
access terminals 100 to 102 and determines m high-order sectors
(m=1, 2, . . . ) to which a flow transmission request is to be
transmitted (S2406). As shown in FIG. 25, the base station (sector)
1900 determines the base station (sector) 1901 as a base station
(sector) for the flow transmission request. Next, the base station
(sector) 1900 makes retrieval through the flow information managing
table according to a flow ID to send a flow transmission request
including a flow ID, a data rate, transmission time, and
transmission timing associated with the flow ID used in the
retrieval to the base station (sector) 1901 (S2408). Thereafter,
the base station (sector) 1901 transmits a flow to each of the
access terminals 100 to 102 (S2409). The base station (sector) 1900
sends a flow interruption request to the base station (sector) 1902
(S2410). When the request is received from the base station
(sector) 1900, the base station (sector) 1902 interrupts
transmission of flows to the access terminals 100 to 102
(S2411).
[0115] According to the first to fourth embodiments described
above, there can be provided a radio communication system and a
base station. Using the system and the base station, it is
possible, in a radio communication system in which a wave
propagation environment varies, to dynamically determine base
stations (sectors) to be communicated with an access terminal to
efficiently conduct "Soft Combine".
[0116] Also, unnecessary use of radio bands can be prevented and
the radio resources can be efficiently used.
[0117] Although the base stations carry out the control operation
of flow transmission and interruption of the flow transmission in
the first to fourth embodiments, it is also possible that the
communication controller conducts the control operation.
[0118] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *