Multicast service providing system, multicast service providing method, information distributor, radio terminal, and radio base station

The present invention is configured such that, in a multicast service providing system in which multicast information distribution service is made from an information distributing apparatus to radio terminals present within a service area via a radio section, the radio terminal has service continuation request signal transmitting a service continuation request signal for requesting continuation of the multicast information distribution service to the information distributing apparatus, the information distributing apparatus has service continuation management means managing as to whether or not request for the service continuation has been made by the radio terminal for the multicast information distribution service, and the information distributing apparatus transmits information indicating as to whether or not continuation request has been made for the multicast information distribution service managed by the service continuation management means.

TECHNICAL FIELD

The present invention relates to a multicast service providing method and system, and, in particular, a multicast service providing method and system by which, to radio terminals present in a service area, multicast information (multicast data) distribution service is performed via a radio section.

Furthermore, the present invention relates to an information distributing apparatus, a radio terminal and a radio base station applied to the above-mentioned multicast service providing system.

BACKGROUND ART

An IGMP (Internet Group Management Protocol) is known as a multicast communication protocol realizable in an IP network. The IGMP is a protocol for determining whether or not a router sends out multicast information to a sub-network, for the purpose of avoiding congestion of a network. An access communication system connected to the network which supports the IGMP should employ a control procedure which has an affinity with the IGMP.

In a communication system according to the IGMP, while the router distributes (broadcasts) multicast information to each host in the sub-network, the router broadcasts query periodically. The host which received the query monitors as to whether a response from another host is received within a random time. When a response from another host is received by the host, this host maintains a reception condition for multicast information. However, no response from another host is received by the host, this host transmits a response (report) to the router and the other host so as to continue reception of multicast information. Then, when the router receives a response (report) from any host in response to the periodically broadcast query, the router continues distribution (broadcast) of the multicast information to each host.

Such a processing procedure may be applied to a radio section as it is. In this case, as shown inFIG. 1, a message corresponding to the above-mentioned query is transmitted to all the radio terminals present in a service area by a radio base station. The radio terminal which has received the message transmits a request for the service continuation as a response thereto to the radio base station after a random time has elapsed, when desiring continuation of multicast information distribution service. When receiving a response to the above-mentioned query from any radio terminal, the radio base station continues the multicast information distribution service.

Thus, in case the processing procedure of IGMP is applied to the radio section, when receiving the message corresponding to the query from the radio base station, the radio terminal can transmit a response thereto to the radio base station. However, it is not possible to transmit another radio terminal in case of IP network. If the above-mentioned response transmitted from the radio terminal could not be received by all the other radio terminals which receive multicast information in the same service area, the response would be returned to the radio base station from all the radio terminals which desire continuation of receiving the multicast information. Thereby, congestion is likely to occur in the radio section.

Further, an access to a channel transmitting the above-mentioned request for service continuation occurs randomly from a plurality of radio terminals. However, in case the permissible number of the accesses is limited for this channel, collision occurs when many radio terminals simultaneously transmit the requests for service continuation by chance. Thereby, as shown inFIG. 1, the request for service continuation does not reach the radio base station (see a sign ×). When the radio base station operates in accordance with a protocol such as IGMP, the radio station terminates multicast information distribution service after a predetermined time has elapsed without transmission of a request for service continuation made from any radio terminal after transmitting the query. Thereby, the service would be interrupted even though there are the radio terminals which request service of distributing multicast information in the service area if the request for service continuation made from the many radio terminals simultaneously by chance collided as mentioned above.

Further, recently, verification for a multicast application performing broadcast-like distribution of music or movies via the Internet employing a cable network, or performing cooperative works or remote meeting by a plurality of users has been performed by using IGMP performing group management of various multicast service.

On the other hand, through spread of portable telephone terminals such as cellular phones, PHS terminals, or the like, or portable information terminals such as so-called notebook personal computers, it is expected that a demand of radio provision of multicast service increases. When an PC terminal of an end user of a network and a router of a sub-network in which this PC terminal exists can operate in accordance with IGMP, provision of multicast service can be made whether the channel is of cable or radio.

Therefore, a system such as that shown inFIG. 2can be assumed as a system performing the above-mentioned provision of multicast service, for example. This example employs a radio base station220which can operate in accordance with IGPM which acts as an access point for a radio LAN. In this case, multicast information A, B and C provided by various servers251,252and253via an IP network NW and a router230is distributed from the radio base station220.

For example, when radio terminals210(1),210(2) and210(3) including radio LAN connection communication devices belonging to a service area Es (LAN) of radio LAN and PC terminals request multicast information A, B and C different from each other, the radio base station220broadcasts all the multicast information A, B and C thus requested. Then, each of the radio terminals210(1),210(2) and210(3) receives all the multicast information A, B and C. Then, in each radio terminal (PC terminal), necessary multicast information is extracted from the thus-received information to be used.

In case the radio base station220distributes multicast information in the service area Es (LAN) of radio LAN, no individual radio channel is set for each radio terminal. However, a data stream including the plurality of sets of multicast information broadcast from the radio base station220mixed therein is received by each radio terminal (cellular phone and PC terminal), and is stored thereby, and, then, only necessary information is extracted therefrom. Therefore, when each radio terminal receives a large amount of multicast information, a heavy burden is loaded thereon for buffering it.

Furthermore, a system such as that shown inFIG. 3can also be assumed as a system performing the above-mentioned radio provision of multicast service, for example. This example performs multicast service by using a radio base station220connected to a public network NW such as an existing PDC (Personal Digital Cellular) or PHS. In this case, multicast information A provided from a server250via the public network NW is distributed from the radio base station220to respective radio terminals210(1),210(2) and210(3) belonging to a service area Es thereof. In distributing the multicast information A, an individual channel is set between each of the radio terminals210(1),210(2) and210(3), and the radio base station220.

In such a system in which multicast service is performed by using the base station220connected to the public network NW, the individual radio channel should be set for each radio terminal even for transmitting the same multicast information within the same service area Es. Accordingly, it is not possible to effectively utilize the radio resources.

Furthermore, a system shown inFIG. 4can also be assumed for performing the above-mentioned radio provision of multicast information, for example. This example performs multicast service in an advanced radio calling system (FLEX-TD). In this system, a radio base station220transmits multicast information provided from various servers251,252and253via a public network NW by using a radio channel set for each set of multicast information regardless of whether or not radio terminals which desire the service belonging to a service area (radio zone) Es exist, in a broadcast-like manner. Each of the radio terminals210(1),210(2) and210(3) can receive multicast information for which contract has been made previously. For example, the radio terminal210(1) which made a contract for multicast information A can receive only the multicast information A from among multicast information A, B and C, the radio terminal210(2) which made a contract for multicast information A and C can receive only the multicast information A and C, and the radio terminal210(3) which made a contract for multicast information C can receive only the multicast information C.

However, in such a system, each radio terminal can receive only multicast information for which a contract has been made. However, even when the radio terminal which made a contract of receiving multicast information does not exist within the service area Es, the radio base station220should perform continues transmission of the multicast information. Thus, it is not possible to effectively utilize the radio resources.

Furthermore, when information multicast distribution service is realized in a radio communication system, in particular, in a mobile communication system, smooth switching of base station from which information is received by a mobile set is needed when the mobile set which is a radio terminal moves across service areas (in case of handoff) while receiving the multicast distribution of the information.

Thus, in case information multicast distribution service is applied to a radio communication system, various problems should be solved.

DISCLOSURE OF THE INVENTION

A general object of the present invention is to provide a new and useful multicast service providing system, method and, information distributing apparatus, radio terminal and radio base station by which the above-described problems of the prior art can be solved.

A detailed object of the present invention is to provide a multicast service providing system, method and, information distributing apparatus, radio terminal and radio base station by which radio resources can be effectively utilized, and, also, it becomes possible to properly perform multicast information distribution service via a radio section to radio terminals present within a service area.

The objects of the present invention can be attained by configuring a radio terminal to have service continuation requesting means transmitting to an information distributing apparatus a service continuation request signal for requesting continuation of multicast information distribution service, in a multicast service providing system for performing multicast information distribution service to the radio terminal present within a service area via a radio section from the information distributing apparatus, and, by configuring the information distributing apparatus to have a service continuation management means managing as to whether or not the above-mentioned request for service continuation from the radio terminal for the multicast information distribution service has been made, the information distributing apparatus transmitting information managed by the service continuation management means to the radio terminal information indicating whether or not the continuation request for the multicast information distribution service has been made.

In this multicast service providing system, the radio terminal can determine whether or not the service continuation request signal is to be transmitted thereby, based on the information indicating whether or not continuation request for the multicast information distribution service has been made transmitted from the information distributing apparatus. Then, when this information indicating whether or not continuation request for the multicast information distribution service has been made indicates a state that this continuation request has not been made, the service continuation requesting means of the radio terminal can transmit the service continuation request signal to the information distributing apparatus.

Further, the information distributing apparatus can determine whether or not the multicast information distribution service should be continued, based on the management state of the service continuation management means.

In the above-mentioned multicast information distributing system, the service management means may be configured to have management state resetting means resetting the management state into a state that no request for continuation of the multicast information distribution service has been made from the radio terminal.

In this multicast service providing system, the information distributing apparatus can positively determines whether or not the radio terminal requesting the multicast information distribution service is present within the service area. That is, when the service continuation request signal is transmitted from the radio terminal after the management state of the service management means is reset to a state that no request for continuation of the multicast information distribution service has been made, the information distributing apparatus can determine that the radio terminal which requests the multicast information distribution service is present within the service area.

Furthermore, in the above-mentioned multicast information distributing system, the above-mentioned management state resetting means may be configured to perform the resetting operation for the management state every predetermined period.

In this multicast information distributing system, the above-mentioned positive determination made by the information distribution apparatus can be made periodically.

Furthermore, in the above-mentioned multicast information distributing system, the radio terminal may have continuation request control means performing control such that, when the information indicating whether or not continuation request for the multicast information distribution service has been made transmitted from the information distribution apparatus indicates a state that the request has not been made, the service continuation requesting means transmits the service continuation request signal to the information distributing apparatus.

In this multicast service providing system, the request for multicast information distribution service continuation can be properly transmitted according to the management state of the information distributing apparatus.

Further, in the above-mentioned multicast service providing system, the above-mentioned continuation request control means may be configured to control the above-mentioned service continuation requesting means so that the above-mentioned service continuation request signal is transmitted after a first random time has elapsed since the information indicating the state that no continuation request has been made for the multicast information distribution service was received.

In this multicast service providing system, in case a plurality of radio terminals requesting continuation of the multicast information distribution service exist within the service area, it is possible to reduce a probability of collision of the service continuation request signals transmitted to the information distributing apparatus from the respective radio terminals. That is, in the case where the plurality of radio terminals requesting continuation of the multicast information distribution service exist within the service area, each radio terminal transmits the above-mentioned service continuation request signal at a random timing after receiving from the information distributing apparatus the information indicating the state that no continuation request has been made for the multicast information distribution service. Thereby, a probability that each radio terminal simultaneously transmits the service continuation request signal to the information distributing apparatus is made smaller.

Further, in the above-mentioned multicast service providing system, the radio terminal may be configured to have re-transmission control means performing a control such that the above-mentioned service continuation requesting means re-transmits the service continuation request signal to the information distributing apparatus when the information indicating as to whether or not continuation request has been made for the multicast information distribution service has not been changed into information indicating that the request has been made within a predetermined time after the service continuation requesting means transmute the service continuation request signal.

In this multicast service providing method, even when the service continuation request signal transmitted from the radio terminal has not been received by the information distributing apparatus by some reason, it is possible to prevent the multicast information distribution service from being terminated for the radio terminal.

Further, in the above-mentioned multicast service providing system, the above-mentioned re-transmission control means may be configured to control the above-mentioned service continuation requesting means so that the above-mentioned service continuation request signal may be transmitted again after a second random time has elapsed after the above-mentioned predetermined time had elapsed since the service continuation requesting means transmitted the service continuation request signal.

In this multicast service providing system, in case a plurality of radio terminals exist within the service area, it is possible to prevent the service continuation request signals re-transmitted from the respective radio terminals from colliding.

Further, in the above-mentioned multicast service providing system, a setting may be made such that a time elapsing since the above-mentioned management state resetting means reset the management state of the service request management means into a state that no request for continuation of the multicast information distribution service until the above-mentioned service continuation request means re-transmits the service continuation request signal may be shorter than a time elapsing since the above-mentioned management state was reset to a state that continuation for a service has not been made from the radio terminal for the multicast information distribution service until resetting is made subsequently.

In this multicast service providing system, it is possible to positively change the management state of the information distributing apparatus by the above-mentioned service continuation request signal re-transmitted.

Further, in the above-mentioned multicast service providing system, the above-mentioned service continuation management means may be configured to manage as to whether or not continuation request has been made for the multicast information distribution service by using a flag which is made to be ON when the service continuation request signal is received from the radio terminal.

In this multicast service providing system, it is possible to easily perform management performed by the service continuation management means in the above-mentioned information distributing apparatus.

Further, the above-mentioned object of the present invention may be attained as a result of the above-mentioned information distributing apparatus which performs multicast information distribution service to radio terminals present within a service area via a radio section having service continuation management means managing as to whether or not request for service continuation from the radio terminals for the multicast information distribution service has been made, and being configured so that information managed by the service continuation management means indicating whether or not the continuation request for the multicast information distribution service has been made may be transmitted to the radio terminals.

Further, the above-mentioned object of the present invention may be attained as a result of a radio terminal which receives multicast information distribution service from an information distributing apparatus via a radio section having service continuation requesting means transmitting a service continuation signal for requesting provision of the multicast information distribution service to the information distributing apparatus, and continuation request control means performing control such that the above-mentioned service continuation requesting means may transmit the service continuation request signal to the information distributing apparatus when information, transmitted from the information distributing apparatus managing as to whether or not a request for service continuation has been made by the radio terminal for the multicast information distribution service, indicating whether or not service continuation request has been made from the radio terminal for the multicast information distribution service indicates a state that the request has not been made.

Further, the above-mentioned object of the present invention may be attained as a result of, in a multicast service providing method by which multicast information distribution service is performed by an information distributing apparatus via a radio section on a radio terminal present in a service area thereof, the information distributing apparatus informing all the radio terminals present in the service area of information for identifying multicast information on distribution service and radio channels used for the distribution of the multicast information by using a predetermined radio channel, and the respective radio terminals within the service area receiving the multicast information distribution service from the information distributing apparatus via the thus-informed radio channels.

In this multicast service providing method, the radio terminal receives the multicast information distribution service by using the radio channel informed of by the information distributing apparatus. Accordingly, the radio channel used for the multicast information distribution service can be made to be only the radio channel informed of by the information distributing apparatus, and, also, the distribution service made via the radio channel can be made to be only of multicast information corresponding to the informed radio channel.

The above-mentioned information for identifying the multicast information informed of by the information distributing apparatus is not particularly limited as long as it can be used for identifying the multicast information provided based on this information at the radio terminal, and, may be information identifying a type of the multicast information, the channel providing it (multicast group address), information identifying a server which originally provides the information, a title of the multicast information, or the like.

Further, in the above-mentioned multicast service providing method, the information distributing apparatus may be configured to manage correspondence relationship between the information for identifying multicast information on distribution service and the radio channels used for distributing the multicast information, informs all the radio terminals present within the service area management information indicating the correspondence relationship by using the above-mentioned predetermined radio channel, and, each of the radio terminals present within the service area receives the desired multicast information distribution services by using the corresponding radio channels based on the management information.

In this multicast service providing method, it is possible to inform the radio terminals of relationship between the information for identifying a plurality of sets of multicast information on distribution service and the radio channels used for distributing the respective sets of multicast information without error.

Further, in the above-mentioned multicast service providing method, the radio terminal transmits a service request signal for requesting distribution service for multicast information not included in the above-mentioned management information, and, when receiving the above-mentioned service request signal from the radio terminal, the information distributing apparatus adds to the above-mentioned management information correspondence relationship between information for identifying the multicast information concerning this request and a radio channel used for distributing this multicast information, and, also, starts distribution service of the multicast information concerning the request by using this radio channel.

In this multicast service providing method, the radio terminal can receive distribution service of the new multicast information other than the multicast information which is currently on distribution service.

Further, the above-mentioned object of the present invention may be attained as a result of, in an information distributing apparatus which performs multicast information distribution service for radio terminals present within a service area via a radio section, a configuration being made such as to have informing control means for informing of all the radio terminals present within the service area information for identifying multicast information on distribution service and radio channels used for distributing the multicast information by using a predetermined radio channel, and, such that each of the radio terminals present within the service area can receive the multicast information distribution service via the thus-informed radio channels.

Further, the above-mentioned object of the present invention may be attained as a result of, in a radio terminal which receives multicast information distribution service via a radio section from an information distributing apparatus, a configuration being made such as to have service state reception control means receiving from the information distributing apparatus management information indicating correspondence relationship between information for identifying multicast information on distribution service and radio channels used for distributing the multicast information, such as to receive from the information distributing apparatus the desired multicast information distribution service via the corresponding radio channel based on the management information received by the service state reception control means.

Further, the above-mentioned object of the present invention may be attained as a result of, in a multicast service providing method by which multicast data is distributed to radio terminals from a radio base station, a configuration being made such that the radio terminal receiving the multicast data may transmit a distribution request for the multicast data to the radio base station on movement destination in case a necessity arises such that the other party of communication be switched from the radio base station on movement origin to the radio base station on movement destination, the radio base station on movement destination may transmit information of a radio channel used for distributing the multicast data to the above-mentioned radio terminal in response to the distribution request given from the above-mentioned radio terminal, the radio terminal may switch the radio channel based on the information of the radio channel given from the above-mentioned radio base station on movement destination so as to receive the multicast data from the radio base station on movement destination.

In this multicast service providing method, when a necessity arises such that the other party of communication be switched from the radio base station on movement origin to the radio base station on movement destination, the radio terminal should merely transmit a distribution request to the radio base station on movement destination, and, thereby, in response to the distribution request, information of the radio channel used for distributing the multicast data is transmitted from the radio base station on movement destination. Therefore, the radio terminal receives the multicast data by switching the radio channel based on this information of the radio channel. Accordingly, it is possible to switch the radio base station acting as the other party of communication, rapidly than in a case, as in the prior art, the radio terminal again receives a perch channel from the radio base station on movement destination, further receives a multicast management table based on information included in the perch channel, then, recognizes a radio channel to be used for transmission from the management table, and, thus, receives the multicast data.

Further, in the above-mentioned multicast service providing method, a configuration may be made such that the radio terminal may transmit the above-mentioned distribution request for the multicast data to the radio base station on movement origin, and the above-mentioned distribution request for the multicast data may be transmitted to the radio base station on movement destination via this radio base station on movement origin.

In this multicast service providing method, the distribution request given from the radio terminal can be made to be positively received by the radio base station on movement destination.

Further, in the above-mentioned multicast service providing method, a configuration may be made such that, in case the radio terminal cannot receive information of a radio channel to be used for distributing multicast data within a predetermined time after transmitting the distribution request, the radio terminal may transmit the distributing request again.

Also by this multicast service providing method, the distribution request given from the radio terminal can be made to be positively received by the radio base station on movement destination.

Further, in the above-mentioned multicast service providing method, a configuration may be made such that the radio terminal may transmit the distribution request several times.

Also by this multicast service providing method, the distribution request given from the radio terminal can be made to be positively received by the radio base station on movement destination.

Further, in the above-mentioned multicast service providing method, a configuration may be made such that the radio base station on movement origin may obtain information concerning multicast data distributed by an adjacent radio base station, and transmit the information concerning the multicast data, and, in case the radio terminal determines that the radio base station on movement destination does not distribute the desired multicast data based on the information concerning the multicast data thus given from the radio base station on movement origin, the radio terminal may transmit the distribution request to the radio base station on movement destination or the radio base station on movement origin so that the above-mentioned distribution request may be received by the radio base station on movement destination.

In this multicast service providing method, the multicast data which the radio base station on movement destination distributes is made to be previously recognized by the radio terminal, and, when the radio base station on movement destination distributes the desired multicast data, the multicast data can be received by the radio terminal immediately without transmission of distribution request. Accordingly, reception of the multicast data at a time of movement can be made rapidly.

Further, for example, the information concerning the multicast data includes information for identifying the multicast data on distribution, and information of radio channels by which the multicast information is distributed.

Further, the object of the present invention may be attained in a radio base station which transmits multicast data to a radio terminal, as a result of a configuration being made such as to have distribution request receiving means receiving a distribution request for multicast data transmitted from the radio terminal, and radio channel information transmitting means transmitting information of a radio channel used for distributing multicast data in response to the distributing request for the multicast data given from the radio terminal.

In this case, a configuration may be made such that the above-mentioned distribution request receiving means may receive the distribution request for the multicast data transmitted from the radio terminal via another radio base station. Further, a configuration may be made such that the above-mentioned distribution request receiving means may have information obtaining means obtaining information concerning multicast data transmitted from a radio base station adjacent to the own station, and multicast information transmitting means transmitting the information concerning the multicast information.

Further, the above-mentioned object of the present invention may be attained, as a result of, in a radio terminal which receives multicast data distributed by a radio base station, a configuration being made such as to have distribution request transmitting means transmitting a distribution request for multicast data to the radio base station on movement destination in case a necessity arises such that the other party of communication be switched from the radio base station on movement origin to the radio base station on movement destination, and multicast data reception control means switching the radio base station based on information concerning a radio channel used for distributing the multicast data transmitted from the radio base station on movement destination in response to the distribution request so as to receive the multicast data distributed from the radio base station on movement destination.

In this case, a configuration may be made such that the above-mentioned distribution request transmitting means may transmit the above-mentioned distribution request for the multicast data to the radio base station on movement origin, and, then, the above-mentioned distribution request for the multicast data may be transmitted to the radio base station on movement destination via the radio base station on movement origin. Further, a configuration may be made such that the above-mentioned distribution request transmitting means may transmit the distribution request again in case information concerning a radio channel to be used for distributing the multicast data cannot be received thereby. Further, a configuration may be made such that the above-mentioned distribution request transmitting means may transmit the distribution request several times. Further, a configuration may be made such that the above-mentioned distribution request transmitting means may transmit the distribution request to the radio base station on movement destination or the radio base station on destination origin so that the above-mentioned distribution request for the multicast data may be received by the radio base station on movement destination in case the distribution request transmitting means determines that the radio base station on movement destination does not distribute the desired multicast data based on information, received from the radio base station on movement origin, concerning multicast information distributed from the radio base station adjacent to the station.

Other objects, features, and advantages of the present invention may become apparent from the following detailed description made together with attached drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, embodiments of the present invention will be described based on the drawings.

First, a multicast service providing system in a first embodiment of the present invention will be described.

This system is configured as shown inFIG. 5.

InFIG. 5, a radio base station20broadcasts information A (henceforth, referred to as multicast information) provided, for example, through a public network, etc. to a service area Es. Radio terminals10(cellular phones, personal computers which have a communication function, or the like) present in this service area Es can receive the multicast information A broadcast by the radio base station20.

The radio base station20is configured as shown inFIG. 6.

InFIG. 6, this radio base station20has a transmitting/receiving unit21, a multicast information storing part22, a network control part23, and an information distribution control part24. The transmitting/receiving unit21performs radio communications with each radio terminal10present in the service area Es. The multicast information storing part22stores multicast information to be distributed which the network control part23receives from the network. The information distribution control part24performs control for distributing the multicast information stored in the multicast information storing part22through the transmitting/receiving unit21to each radio terminal10present in the service area Es.

The information distribution control part24has a management table as shown inFIG. 7. This management table is used for managing as to whether requests for continuation have been made for various distribution services of multicast information. InFIG. 7, when continuation requests for various distribution services (multicast groups) of multicast information are made, flags (#1, #2, #3, and #4, referred to also as received flags) corresponding to the services are made to be ON, and, when no continuation requests for distribution services of multicast information are made, the flags corresponding to the services are made to be OFF.

Moreover, the radio base station20(information distribution control part24) resets (makes to be OFF) all the flags in the above-mentioned management table at a predetermined timing. Then, the state (ON/OFF) of each flag managed in the above-mentioned management table is broadcast from the radio base station immediately after the flag reset timing (after a predetermined time). Such a state of the radio base station20is managed by a reset state flag of a reset state item in the above-mentioned management table. Namely, the reset state flag is made to be ON (ON) together with resetting (OFF) of the flags corresponding to the above-mentioned various distribution services, and the reset state flag is made to be OFF (OFF) from a timing immediately after that (after a predetermined time) at which each flag state is broadcast until all the flags are subsequently reset. Therefore, the state of the radio base station20changes by turn between a state where the reset state flag is made to be ON (ON), and a state where the reset state flag is made to be OFF (OFF), as shown inFIG. 8.

In case the various distribution services of multicast information are provided from the radio base station20, processing is performed by the radio base station20according to a procedure shown inFIG. 9, and the radio terminal10which receives the multicast information performs processing according to a procedure shown inFIG. 10.

InFIG. 9, the radio base station20resets the flags (#1, #2, #3, #4) corresponding to all the distribution services in the above-mentioned management table (seeFIG. 6) at a predetermined timing (S1). The reset state flag is made to be ON at this time. The reset state flag is made to be OFF immediately after that (after the predetermined time). Thus, a signal showing the reset state flag which is made to be ON or made to be OFF is broadcast using a different channel from a channel used for the various distribution services of multicast information. Moreover, when the above-mentioned reset state flag is switched to OFF, a signal showing the states of the flags corresponding to the various distribution services managed in the above-mentioned management table are broadcast using the predetermined channel.

When the flags corresponding to all distribution services are reset as mentioned above, it is determined (S3) whether it is the subsequent timing of flag reset, while it is determined (S2) whether the radio base station20has received a service continuation request signal (which will be described later in details) from any one of the radio terminals10. In this process, in response to reception of the service continuation request signal from any one of the radio terminals10(YES at S2), the flag corresponding to the relevant service is made to be ON in the management table (S4).

When it becomes the subsequent timing of flag reset (YES at S3), it is determined whether the flag corresponding to each service of the management table has been made to be ON (S5). Then, the distribution service corresponding to the flag which has been made to be ON is continued, the distribution service corresponding to the flag which has been made to be OFF is terminated (S6), and then, the series of processing is finished (YES at S5). Then, again, while all the flags corresponding to distribution services of multicast information are reset, and, also, the series of processing is started from the processing (S1) at which the reset state flag is made ON.

Each radio terminal10which receives distribution service of multicast information performs processing according to a procedure shown inFIG. 10, while the radio base station20performs the above-describe processing and provides the various distribution services of multicast information.

InFIG. 10, the radio terminal10receives a signal indicating the reset state flag broadcast by using the predetermined channel, and, in this process, it determines (S12) whether or not this reset state flag is made to be ON, i.e., whether the flags corresponding to the multicast information distribution services are reset. When it is determined that the reset state flag is made to be ON (YES at S12), a random time R1is calculated based on a random number generated by a random number generator (S13). Then, a timer in which the random time R1is set starts operation. After that, it is determined (S14) whether or not the timer has reached the random time R1which is the set time thereof.

When the timer has reached the time R1(time out), a signal showing the flag corresponding to the multicast information distribution service which the radio base station20broadcasts is received from the timing at which the reset state flag is made to be OFF, and it is determined whether the flag corresponding to the service which the radio terminal10receives is made to be ON (S15). There, when the relevant flag (received flag) is made to be OFF (NO at S15), as management is made by the radio base station20such that it is recognized that the service continuation signal for the corresponding service has not been received, the radio terminal10transmits the service continuation signal to the radio base station20in case it desires continuation of the service (S16).

Then, Twait which is a random time is calculated (S17), and reception of the signal showing the states of the flags corresponding to the various multicast information distribution services broadcast from the radio base station20is started (S18). Then, it is determined whether or not the random time Twait has been reached (S19), while it is determined whether the flag (received flag) corresponding to the distribution service which the radio terminal10receives is made to be ON (S20). There, in case the flag corresponding to the relevant service has been already made to be ON (see the processing at S2and S4inFIG. 9) in response to the service continuation request signal transmitted from the relevant radio terminal10as mentioned above (see the processing in S16), the radio terminal10finishes the series of processing, and repeats the processing of determining whether or not the reset state flag is made to be ON (the flags corresponding to the services are made to be OFF) again (S11, S12).

In a condition where the random time R1has elapsed from the timing of detection of ON of the reset state flag, when the flag corresponding to the relevant service has been already made to be ON in the radio base station20in response to the service continuation request signal from another radio terminal10which receives the service (YES at S15), the radio terminal10finishes the series of processing, and repeats the processing of determining whether or not the reset state flag is made to be ON (the flags corresponding to the services are made to be OFF) again (S11, S12).

As a result of the processing being performed in accordance with the above-described procedure by the radio base station20and radio terminals10, a communication according to a sequence shown inFIG. 11is performed between the radio base station20and the radio terminals10, for example.

In the process in which the multicast information distribution service is made on the radio terminal10by the radio base station20, when the reset state flag is made to be ON by the radio base station20({circle around (1)}), that is, the flags (received flags) corresponding to the respective services are made to be OFF, the signal indicating the flags corresponding to the various services are transmitted to the radio terminal10by the radio base station20at predetermined timing repeatedly (see broken line inFIG. 11). In this process, when receiving the signal indicating the reset state flag having the ON state (the flags corresponding to the services are made to be OFF) from the radio base station20({circle around (1)}), the radio terminal10transmits the service continuation request signal to the radio base station20after elapse of a random time R1({circle around (2)}). Then, the radio terminal10monitors as to whether the flag corresponding to the relevant service is made to be ON during a random time Twait.

When receiving the above-mentioned service continuation request signal from the relevant radio terminal10or another radio terminal10, the radio base station20makes the flag corresponding to the service to be ON. When detecting that the flag corresponding to the service has been made to be ON ({circle around (1)}), the radio terminal10monitors the reset state flag being made to be ON ({circle around (4)}). Then, each time the reset state flag is made to be ON, communication is performed between the radio base station20and radio terminal10in accordance with the above-mentioned procedure.

By the above-mentioned processing, the radio base station20resets (makes to be OFF) the flags corresponding to the various multicast information distribution services at predetermined timing, and, also, after the resetting, when receiving the service continuation request signal from any radio terminal10, the radio base station20makes the flag corresponding to the service to be ON. Accordingly, the radio base station20can determine continuation and termination of the services based on the flags corresponding to the respective services managed by the management table (seeFIG. 7) without managing the number of the radio terminals20which receive the multicast information distribution services in the service area Es, or the like.

Moreover, each radio terminal10can check whether another radio terminal10which requires the same service as that of itself exists in the same service area Es by monitoring the states of the flags (received flags) corresponding to the respective services broadcast from the radio base station20. Then, when the relevant flag is made to be OFF, the radio terminal10which desires the service transmits the service continuation request signal to the radio base station20, as recognizing that no other radio terminal10which requires the same service as that of itself exists. On the other hand, when the relevant flag is made to be ON, the radio terminal10that desires the service does not transmit the service continuation request signal, as recognizing that another radio terminal10which requires the same service as that of itself exists.

Thus, the service continuation request signals are not transmitted from a plurality of radio terminals10, respectively, which desire the same service in the same service area Es, and thus congestion is not likely to occur in the radio section.

In case the service continuation request signal is transmitted from the radio terminal10which processes according to the above-described procedure (seeFIG. 10), the service continuation request signal may be unable to be received by the radio base station20due to interference of signals, collision with the service continuation request signal simultaneously transmitted by chance from another radio terminal, or the like in the radio channel. In such a case, as will be described below, the radio terminal10performs re-transmission of the service continuation request signal.

After transmitting the service continuation request signal to the radio base station20(S16), the radio terminal10which processes in accordance with the above-described procedure shown in theFIG. 10further calculates a random time R2again (S21) after a random time Twait has elapsed, in case the OFF state of the flag corresponding to the service received from the radio base station20is maintained during the random time Twait (NO at S19, and also, YES at S20). Then, after the random time R2elapsed (YES at S22), it determines again whether or not the flags (received flags) corresponding to the services broadcast by the radio base station20are made to be ON (S23). Then, when the flag corresponding to the service has the ON state, the radio terminal10finishes the series of processing while receiving the multicast information distribution service broadcast by the radio base station20.

The radio terminal10re-transmits the service continuation request signal, as recognizing that the service continuation request signal (see S16) transmitted last time has not been received by the radio base station20, when the flag corresponding to the service received has the OFF state (S24). Then, after finishing re-transmitting of the service continuation request signal, the radio terminal10finishes the series of processing.

Between the radio base station20and the radio terminal10, as a result of the processing according to the above-described procedure being performed by he radio terminal10, communication according to a sequence shown inFIG. 12is performed.

In the process in which the radio base station20is performing multicast information distribution service on the radio terminal10, when the reset state flag is made to be ON by the radio base station20({circle around (1)}), same as in the case described above (seeFIG. 11), that is, when the flags corresponding to the respective services (received flags) are made to be OFF, the signal indicating the states of the flags corresponding to the respective services is repeatedly transmitted to the radio terminal10from the radio base station20at predetermined timing (see the broken line inFIG. 12). In this process, when receiving the signal indicating the reset state flag having the ON state (the flags corresponding to the services are made to be OFF) ({circle around (1)}), the radio terminal10transmits the service request continuation signal to the radio base station20after elapse of a random time R1({circle around (2)}). Then, the radio terminal10monitors, during a random time Twait, whether the flag corresponding to the relevant service is made to be ON.

In case the above-mentioned service request signal is not received by the radio base station20by some reason such as signal interference or collision (× mark), and the flag corresponding to the service given from the radio base station20is not made to be ON during the random time Twait, the radio terminal10re-transmits the service request continuation signal ({circle around (3)}) after further elapse of the random time R2after elapse of the random time Twait. When the flag corresponding to the relevant service managed by the radio base station20is made to have the ON state by this service continuation request signal re-transmitted by the radio terminal10, after receiving this flag in the ON state ({circle around (4)}), the radio terminal10monitors that the reset state flag is made to be ON ({circle around (5)}).

Since the service continuation request signal is re-transmitted from the radio terminal10when the service continuation request signal transmitted from the radio terminal10is not received by some reason by the radio base station20, the flag corresponding to the relevant service managed by the radio base station20can be positively made into the ON state.

In the above-mentioned system, relationship between the reset period Treset, that is, the period at which the flags corresponding to all the multicast information distribution services are reset, the above-mentioned random times R1and R2, and the random time Twait are set as follows, for example.

When making the random time Twait constant, it is set as follows:
Twait=Treset−R1max−R2max  (1)
Moreover, when making the random time Twait variable, it is set as follows:
Twait=(Treset−R1max)×RATE  (2)

When making the Twait constant and applying the same value for every Treset cycle, the maximum time of Twait is calculated according to the above-mentioned formula (1). Accordingly, calculation of Twait is realizable by setting up a value smaller than Treset−R1as the maximum (R2max) of R2, and then using the above-mentioned formula (1).

Moreover, when making the Twait variable and changing it for every Treset, it is also possible to use a value acquired by multiplying (Treset−R1) by a fixed coefficient RATE. In this case, since R1is a random value, Twait can be made variable. As RATE becomes larger in the above-mentioned formula (2), the maximum of R2becomes smaller, and probability of collision at the time of re-transmitting becomes higher. However, since the probability that the service continuation request signal from another radio terminal which receives the same multicast information distribution service is transmitted becomes higher, there is an advantage that the necessity of re-transmission becomes lower.

On the other hand, when RATE is smaller in the above-mentioned formula (2), the probability of collision with the service continuation request signal from another radio terminal which receives the same multicast information distribution service becomes higher. However, since R2can be made larger, there is an advantage that the probability of the collision with the service continuation request signal from another radio terminal which receives the same multicast information distribution service becomes lower, at the time of re-transmitting the service continuation request signal.

Moreover, the probability of collision of the service continuation request signals can be reduced by making RATE in the above-mentioned formula (2) have a unique value for every radio terminal.

Although, in the above-mentioned example, re-transmitting of the service continuation request signal is made once, it is easily realizable to change respective parameters so that re-transmitting of the service continuation request signal may be performed several times.

Namely, Twait and R2max may be set such that:
Treset=A×(Twait+R2max)  (3)
‘A’ is an integer and expresses the number of times of retransmissions.

As, for the radio base station connected to the network which supports the version 1 of IGMP, the maximum time for which an IGMP router waits for a report from a host is 10 seconds, and, thereby, it is reasonable to set the Treset period of the radio base station equal to or shorter than 10 seconds. Since the maximum time for which the IGMP router waits for the report from the host is specified in a message in the case of the network corresponding to the version 2, it is reasonable to set the Treset period to be equal to or shorter than the specified time. However, as for this Treset period, it is also possible to set it regardless of the parameter of IGMP, and, then, for the router, the radio base station may perform operation in accordance with IGMP. Furthermore, in case multicast information distribution service in a network which does not support IGMP is carried out, this Treset period may be set as a value original for the radio base station.

In each above-mentioned example, the radio base station acts as an information distributing apparatus.

In this embodiment, a radio channel used for distribution of each multicast information is informed of to each radio terminal of a service area. Thereby, each radio terminal can receive the desired multicast information by using the radio channel corresponding to the multicast information.

A basic configuration of a multicast service providing system in the second embodiment is configured as shown inFIG. 5, same as the above-described embodiment, and, also, a radio base station is configured as shown inFIG. 6.

In the present invention embodiment, an information distribution control part24manages multicast service by a multicast information channel table as shown inFIG. 13. In this multicast information channel table, relationship between multicast group addresses for identifying multicast information channels for performing distribution services, transmission channels used for transmitting the multicast information corresponding to the respective multicast information channels, and information channel numbers managed by a radio base station20is described.

The multicast group addresses for identifying the multicast information channels for providing the distribution services are used for identifying the contents of distribution services, and, are the same as multicast addresses, for example, used by IGMP (Internet Group Management Protocol) which is the multicast protocol of IP (Internet Protocol) network. However, in case the radio base station20is connected with a network other than the IP network, any addresses which can be used for identifying servers and the networks providing the multicast services can be used as the multicast group addresses.

The transmission channels are expressed by channel identifiers by which the radio base station20and each radio terminal10can use for identification, and indicate channels for transmitting the multicast information corresponding to the multicast information channels. In case the access type is, for example, a time division multiple access type (TDMA), channel identifiers include time slot numbers in radio frames and frequency numbers. There may also be a system which requires neither frequencies nor time slots for identifying the radio channels, and a system which requires another identifiers. In such a case, any type of identifiers which are used for identifying the radio channels according to an identification method suitable for the system may be used.

In case transmission channels are changed according to a situation of channel allocation in a radio section between the radio base station20and each radio terminal, the item of the transmission channel of this multicast information channel table is updated.

An information channel number is a number which the radio base station20gives for a multicast group address. The information channel numbers are numbers unique only to the service area Es of the radio base station20, and, when the radio terminal10moves to another service area by handoff, etc., and connection switching to another radio base station is made, information channel numbers managed by the newly connected radio base station are used.

These information channel numbers correspond to the multicast group addresses, as described above, and may be used as the multicast information channels between the radio base station20and each radio terminal10, i.e., simple identifiers for the contents of distribution services.

The radio base station20which provides the multicast services processes in accordance with a procedure shown inFIG. 14. This processing is mainly performed by the information distribution control part24of the radio base station20.

The radio base station20enters one state of state of providing multicast service and a state of not doing so. InFIG. 14, it is determined whether the radio base station20is performing multicast service (S31). When the multicast service is performed (YES at S31), it is monitored whether it is a transmission timing for the multicast information channel table (seeFIG. 13) which shows information concerning the multicast information channels under the service (S32), and, when it is the timing, the multicast information channel table is informed of to all the radio terminals10in the service area Es (S33).

Then, it is determined whether a multicast service request signal is received from anyone of the radio terminals10(S34). When the multicast service request signal is received by none of the radio terminals10(NO at S34), the series of processing is finished. After that, as long as the multicast service request signal from the radio terminal10is not received, processing (S31through S34) described above is performed repeatedly. Consequently, each radio terminal10in the service area Es can know the contents of services distributed at the time, and the radio channels for receiving the contents of the services, by receiving the multicast information table transmitted from the radio base station20.

The above-mentioned transmission (S33) of the multicast information table is made by using a radio channel which can be used by the radio base station20. The radio channel which can be used should be a radio channel determined according to a channel allocation method which the radio base station20employs. The radio channel used for transmission of this multicast information channel table is informed of to each radio terminal10present in the service area Es from the radio base station20using a perch channel, for example. Each radio terminal10receives the multicast information table from the radio base station20using the informed radio channel.

In addition, it is also possible to transmit the multicast information channel table from the radio base station20periodically at fixed intervals. In this case, control information concerning the transmission period can also be informed of by using the perch channel.

Moreover, the radio channel used for transmission of the multicast information channel table may also be fixed. In this case, when the radio channel known between the radio base station20and each radio terminal10is previously fixed therebetween, it is not necessary to include the information concerning the radio channel used for transmission of the multicast information channel in the perch channel.

Returning toFIG. 14, in a state in which the radio base station20does not perform multicast service (NO at S31), or when, in the above-described process (S31through S34), a multicast service request signal (including the above-mentioned multicast group address) is received by the radio base station20from the radio terminal which newly desires a service (YES at S34), the above-mentioned multicast information channel table (seeFIG. 13) is referred to, and it is determined (S35) whether or not the service concerning the request has been already provided. When the service has been already provided (YES at S35), the series of processing is finished, and, the above-described processing (S31through S34) is repeatedly performed, until a multicast service request signal is received subsequently.

When the service concerning the request has not been provided yet (NO at S35), the multicast information channel table is updated by newly registering into the multicast information channel table the multicast group address which identifies the multicast service concerning the request, the radio channel (transmission channel) used for the service, and an information channel therefor (S36). Then, the radio base station20starts transmission of the multicast information corresponding to the service concerning the above-mentioned request using the thus-determined radio channel (S37). After that, the above-described processing (S31through S34) is performed repeatedly. In this process, the multicast information channel table updated as mentioned above is transmitted to each radio terminal10present in the service area Es from the radio base station20(S32, S33).

In the process in which the radio base station20performs processing in accordance with the above-described procedure, and provides the multicast services, each radio terminal10performs processing in accordance with a procedure shown inFIG. 15.

InFIG. 15, the radio terminal10receives the perch channel first (S41). The radio base station20transmits, by using this perch channel, various control information concerning the system, also, information indicating whether or not the radio base station20is providing multicast service, and, in case of providing the multicast service, transmits information concerning the radio channel used for transmitting the multicast information channel table, transmission period therefor, and so forth.

When reception of multicast service is desired by the radio terminal10(YES at S42), it is determined whether the own terminal has already received a certain multicast service from the radio base station20(S43). When the own terminal has not received multicast service from the radio base station20yet (NO at S43), it is determined whether, based on the information informed of by the above-mentioned perch channel, the radio base station20is providing multicast service (S44). When the radio base station20is providing multicast service (YES at S44), it is determined, based on the transmission period for the multicast information channel table informed of by the above-mentioned perch channel, whether or not it is a timing of receiving the multicast information channel table (S45). When it is the timing, the multicast information channel table transmitted from the radio base station20will be received (S46) using the radio channel informed of by the above-mentioned perch channel.

The radio terminal10determines whether or not the multicast information channel (multicast group) which the own terminal desires is registered in the multicast information table, when the multicast information channel table is received thereby (S47). When this multicast information channel desired is registered there (YES at S47), i.e., when distribution service of the desired multicast information has been already performed, the radio terminal10receives the distribution information (multicast information) of the multicast information channel using the transmission channel corresponding to the desired multicast information channel in the multicast information channel table (S48).

In the above-mentioned process, when the radio terminal10already receives some multicast service (YES at S43), while the above-mentioned service is received thereby, the distribution information of the multicast information channel concerning the relevant new request is received thereby by using the radio channel for receiving the multicast information according to the above-described procedure (S45through S48).

On the other hand, when the radio base station20is not providing multicast service (NO at S44), or, when the radio base station20is providing multicast service, but is not providing a service of the desired multicast information channel (NO at S47), the radio terminal10transmits a multicast service request signal for the desired multicast information channel to the radio base station20(S49), and waits for the radio base station20to start the service of the desired multicast information channel. Then, when the multicast information channel table updated by this multicast service request signal (see S34through S36inFIG. 14) is received from the radio base station20(S46), the radio terminal10receives the distribution information of the new multicast information using the radio channel (transmission channel) specified by the multicast information channel table (S47, S48).

As mentioned above, since the radio terminal10receives the multicast information channel table from the radio base station20by the radio channel informed of by using the perch channel, even when the radio channel by which the multicast information channel table should be transmitted by the radio base station20changes, the radio terminal10can always receive the multicast information channel table. Moreover, even when the transmission channel by which the information of the multicast information channel (multicast information) is transmitted by the radio base station20is changed, since the change is reflected by the multicast information channel table, the radio terminal10can receive the distribution information of the desired multicast information channel by the radio channel specified in the relevant multicast information channel table.

In the processing according to the procedure shown inFIG. 15, when the radio terminal10does not desire multicast service (NO at S42), the series of processing is finished. Consequently, the radio terminal10which does not particularly desire multicast service continues the state of receiving the perch channel (S41, S42).

In the above-mentioned system, multicast information will be distributed to the radio terminal10from the radio base station20through the processing by the radio terminal10according to the procedure shown in the processing ofFIG. 15and the processing by the radio base station20according to the procedure shown inFIG. 14, as shown inFIG. 16.

That is, the multicast information channel table is transmitted to the radio terminal using the transmission channel {circle around (1)} informed of by the perch channel, and, further, the distribution information of the multicast information channel (multicast group) registered in the multicast information channel table is transmitted to the radio terminal10using the transmission channel {circle around (2)} registered in the multicast information channel table.

In the above system, during provision of the multicast service, when all the radio terminals that receive the multicast information corresponding to a multicast information channel in the service area Es stop desiring continuation of the relevant multicast service, the radio base station20which provides the multicast service processes according to the procedure shown inFIG. 17, for example, in order to stop the multicast service.

In this processing, a service continuation check signal corresponding to the flag state reset signal and a response signal corresponding to the service continuation request signal, described above for the first embodiment, are transmitted and received between the radio base station20and the radio terminal10.

InFIG. 17, it is determined whether it is a timing of transmitting the service continuation check signal (S51). When it is determined that it is the transmitting timing for the service continuation check signal, the service continuation check signal is transmitted to each radio terminal10present in the service area Es from the radio base station20(S52). Then, a timer at which a response waiting time is set starts operation (S53). In this state, it is determined whether or not the response signal in response to the service continuation check signal is received from anyone of the radio terminals (S55), while it is determined whether or not the relevant timer has reached a time-out state (S54). There, when the response signal is received from any one of the radio terminals before the time-out of the above-mentioned timer, the radio base station20enters a state where distribution service of the multicast information channel concerning the response signal is continued (S56). Whenever it receives the response signal in response- to the service continuation check signal for each service from the radio terminal until the above-mentioned timer reaches the time-out state, a state is entered where distribution service of the multicast information channel concerning the response signal is continued (S54, S55, S56).

On the other hand, when the above-mentioned timer reaches the time-out state (YES at S54), distribution service of the multicast information channel for which no response signal is returned in response to the service continuation check signal is terminated (S57). Then, the relevant multicast information channel table is updated by deleting the information concerning this terminated multicast information channel from the multicast information channel table (seeFIG. 13) (S58).

Transmission of the above-mentioned service continuation check signal by the radio base station20can be performed as follows.

For example, in the perch channel, the multicast group address for which continuation of service is to be checked can be described as the service continuation check signal. In this case, the radio terminal receives the perch channel for every transmission period of this service continuation check signal.

Moreover, the service continuation check signal can be transmitted using the same transmission channel as the transmission channel of the multicast information channel table. In this case, the service continuation check signal is transmitted at the same period as the transmission period of the multicast information channel table. Moreover, as shown inFIG. 18; in this case, a flag as the service continuation check signal can be included in the multicast information channel table. When the multicast information channel table is transmitted, the flag corresponding to the multicast group for which it is the timing for checking continuation of the service is set to “1”, and the flag corresponding to the multicast group for which it is not the timing is reset into “0.”

Thus, similar to the first embodiment, in case of transmitting to each radio terminal the multicast information channel table including the above-mentioned flag information as the service continuation check signal, when each radio terminal continues reception of the multicast information, it can be determined whether it is necessary to transmit the service continuation request signal, based on the state of the flag information.

Furthermore, the service continuation check signal can also be transmitted by using a different radio channel independently from the multicast information table. In this case, the transmission period of the service continuation check signal can also be set independently, for example, information of the transmission channel for this service continuation check signal is given by using the perch channel.

Each radio terminal which receives the service continuation check signal transmitted from the radio base station as mentioned above processes in accordance with a procedure shown inFIG. 19.

InFIG. 19, when the service check signal is received (YES at S61), in case continuation of the multicast service currently received is desired (YES at S62), the radio terminal starts a random timer in which a random time setting is possible (S63). Then, when the random timer by which the random time is set reaches a time-out state (YES at S64), a response signal is transmitted to the radio base station20.

Even when the service continuation check signal transmitted from the radio base station20is a signal for a specific multicast information channel, even when it is a signal for all the multicast information channels under service by the radio base station20, the identifies (multicast group addresses, information channel numbers or the like) for indicating all the multicast information channels for which service is desired are contained in the response signal.

Furthermore, when the radio terminal which has received the multicast service positively terminates reception of the service, it processes in accordance with a procedure shown inFIG. 20. That is, reception of the multicast information corresponding to the multicast information channel transmitted from the radio base station20is interrupted (S71), and a service reception termination signal is transmitted to the radio base station20(S72). The identifiers (multicast group addresses, information channel numbers or the like) which indicate all the multicast information channels for which reception of service be terminated are included in this service reception termination signal.

The radio base station20which has received the service reception termination signal from any one of the radio terminals transmits a service continuation check signal for the multicast information channels indicated by the identifiers (multicast group addresses, information channel numbers or the like) contained in the service reception termination signal, to each radio terminal present in the service area Es, and determines the necessity of continuation of the service in accordance with the procedure shown inFIG. 17. Then, when no response signal is received from any of the radio terminals, the radio base station20terminates the service of these multicast information channels.

In the example described above, the control signals transmitted to the radio base station20from the radio terminal10are three, the service request signal, response signal, and service reception termination signal. These signals can be transmitted by a random access channel which is used for accessing the radio base station20first, at a time of turning on of the power supply of the radio terminal, or by using user data included in a packet or a control information transmission channel in case during uni-cast communication.

Moreover, in the above-described example, the time division multiple access type (TDMA) is used as an access type for downlink signals from the radio base station20to the radio terminal10. However, a code division multiple access type (CDMA) is also applicable in the above-mentioned example, by a similar manner only by replacing the identifiers by spread codes, etc.

In addition, also in this embodiment, the radio base station20acts as an information distributing apparatus.

A third embodiment of the present invention will now be described.

According to this embodiment, in case a mobile set used as a radio terminal moves across service areas (in case of handoff) while receiving multicast distribution of information, switching of base station which acts as a distribution origin for the mobile set can be made smoothly.

A system to which a multicast service providing method in the present embodiment is applied is configured as shown inFIG. 21.

The multicast service providing system shown in this figure includes a radio base station110and a radio terminal120. The radio base station110transmits (distributes) information (multicast data) provided via a root network, such as an IP network, to the radio terminal120present in a radio area. The radio terminal120is, for example, a cellular phone, or a personal computer terminal (PC terminal) which has a telecommunication function, the radio terminal120receives multicast data distributed from the radio base station, and when a movement arises, the radio base station acting as the other party of communicative is rapidly switched.

The radio base station110has a network interface111, a radio link control device112, a transmitting/receiving unit113, an antenna114, a radio base station side multicast control device115, a radio base station side handoff control device116, and an input/output device117.

The network interface111performs control concerning the third layer of OSI reference model. Specifically, when TCP/IP is used as a communication protocol, the network interface111performs composition/decomposition of IP packets, and extraction/insertion of multicast addresses.

The radio link control device112performs control concerning the second layer of OSI reference model. Specifically, the radio link control device112performs composition/decomposition of radio frames which include data channels to which multicast data is inserted, and various control channels, in a combined manner.

The transmitting/receiving unit113performs control concerning the first layer of OSI reference model. Specifically, the transmitting/receiving unit113transmits and receives radio signals by converting a base-band signal from the radio link control device12into radio signal, and transmitting it through the antenna114or converting a radio signal given through the antenna114into a base-band signal.

The radio base station side multicast control device115performs control for multicast cooperatively with a multicast control device of the radio terminal120described later. Moreover, the radio base station side multicast control device115produces a multicast management table which is information required in order that the radio terminal120can receive multicast data. Details of the multicast management table will be described later.

The radio base station side handoff control device116gives instructions of distribution of multicast data to the radio base station side multicast control device115, and performs control of informing the radio terminal120of radio channels used for distributing the multicast data to the radio terminal120. Specifically, based on multicast addresses obtained from the root network via the network interface, and/or information concerning link control obtained from the radio link control device112, the radio base station side handoff control device116performs handoff control for the radio terminal to switch the radio base station acting as the other party of communication, and, also, gives radio channels used for the multicast to the transmitting/receiving unit113.

Moreover, the radio base station side handoff control device116exchanges the multicast management table between the network interface111and a radio base station adjacent thereto via the root network connected with the network interface111, and in order to inform the radio terminal120of the multicast management tables of the own station and the adjacent radio base station, it controls the radio link control device112.

On the other hand, the radio terminal120has an antenna121, a transmitting/receiving unit122, a radio link control device123, a user interface124, an input/output device125, a radio terminal side multicast control device126, and a radio terminal side handoff control device127.

The transmitting/receiving unit122and the radio link control device123perform operation equivalent to the transmitting/receiving unit113and the radio link control device112of the radio base station110, respectively. However, the transmitting/receiving unit122also performs measurement of electric field intensity of a signal transmitted from the radio base station110.

The user interface124terminates the TCP/IP protocol for the signal given from the radio link control device123, and performs interface with an input/output device125. The input/output device125outputs and inputs a sound, a picture, etc., and includes a display, a speaker, a microphone, various keyboards, an external connection terminals, etc.

The radio terminal side multicast control device126performs control for the multicast while communicating with the radio base station side multicast control device115via the radio link control device123based on the information acquired through the user interface124.

The radio terminal side handoff control device127detects an opportunity of handoff, selects a radio base station to which a movement is made, performs request to the radio base station to which the movement is made for distribution of multicast data, and acquires the multicast management table.

Specifically, based on the information concerning electric field intensity obtained from the transmitting/receiving unit122, and the information concerning the link control obtained from the radio link control device123, the radio terminal side handoff control device127performs synchronization with the radio base station side handoff control device116and performs handoff. Moreover, the radio terminal side handoff control device127gives the radio channel used for multicast to the transmitting/receiving unit122.

As embodiments realizing the above-mentioned functions will now be described. A first embodiment is such that the radio terminal requests to the radio base station for which the radio terminal moves, for distribution of multicast data, directly, or, via the radio base station at the movement origin, further acquires information for identifying the radio channel used for the multicast, so that switching of the radio base station which acts as the other party of communication at the time of movement can be made rapidly. A second embodiment is such that the radio base station informs the radio terminal of the multicast management table of the own station and also the multicast management table of an adjacent radio base station, the radio terminal previously determines multicast data which the radio base station on the movement destination distributes, and thus, the radio base station which acts as the other party of communication can be switched rapidly at the time of movement.

First, the first example of operation will now be described.FIG. 22(a) and (b) shows a conceptual diagram, andFIG. 23shows an operation flow of the first example of operation. It is assumed that, as shown inFIG. 22(a), a radio terminal120-1in a radio zone Z1of a radio base station110-1on movement origin moves to a radio zone Z2of a radio base station110-2on movement destination, while receiving multicast data given by the radio base station110-1on movement origin.

In this case, as shown in the operation flow ofFIG. 23, when the radio terminal120-1moves into the radio zone Z2from the radio zone Z1(S82) while receiving multicast data (S81), in the radio terminal120-1, the signal reception intensity from the radio base station110-2on movement destination becomes larger than the signal reception intensity from the radio base station110-1on movement origin. At this time, the radio terminal side handoff control device127built in the radio terminal120-1determines (S83), as an opportunity of handoff, the time of the reception intensity of the perch channel from the radio base station110-2on movement destination becoming larger than the reception intensity of the perch channel from the radio base station110-1on movement origin, based on the reception intensity of the perch channel received periodically.

In case of the opportunity of handoff, the radio terminal side handoff control device127transmits a switching request signal for switching the radio base station to be communicated, from the radio base station110-1on movement origin to the radio base station110-2on movement destination, to the radio base station on movement destination via the radio link control device123(S84).

Information which indicates the radio base station110-2on movement destination determined from the electric field intensity, information which indicates multicast data which the radio terminal120-1desires to receive, information which indicates the radio terminal120-1of transmission origin, and so forth, are included in the switching request signal.

A random access channel which the radio base station110-2on movement destination which is a transmission origin provides is used for transmission of this switching request signal. Information concerning the random access channel can be acquired from the perch channel from the radio base station110-2on movement destination.

The radio base station side handoff control device116built in the radio base station110-2on movement destination receives the switching request signal from the radio terminal110-1, and, when the multicast data indicated by the switching request signal is not distributed by the radio base station110-2, it controls the radio base station side multicast control device115to newly distribute the multicast data. The radio base station side multicast control device115starts distribution of the multicast data which the radio terminal120-1desires to receive, under such control (S85). When the multicast data indicated by the switching request signal is already distributed by the radio base station110-2, such control to the radio base station side multicast control device115by the radio base station side handoff control device116is not performed.

Furthermore, the radio base station side handoff control device116transmits, via the radio link control device112, a switching response signal including information which indicates multicast data desired by the radio terminal120-1and started to be distributed or already distributed, and information indicating a radio channel used for distributing this multicast data, to the radio terminal120-1which has transmitted the switching request signal (S86).

The radio terminal side handoff control device127built in the radio terminal120-1controls switching of the radio channel according to this switching response signal. Thereby, the radio terminal side handoff control device127starts reception of the multicast data from the radio base station110-2on movement destination (S87).

By the above-described series of operation, even when the radio terminal120-1moves into the radio zone Z2of the radio base station110-2on movement destination from the radio zone Z1of the radio base station110-1on movement origin, the radio base station to be communicated with can be quickly switched.

In S84of the flow of operation shown inFIG. 23, the radio terminal120-1may transmit the switching request signal to the radio base station110-1on movement origin. Further, in order for the radio base station110-2to increase opportunities to receive the switching request signal so as to receive it positively, the radio terminal120-1may transmit the switching request signal to both the radio base station110-1on movement origin and radio base station110-2on movement destination.

When transmitting the switching request signal to the radio base station110-1on movement origin from the radio terminal, it is necessary to include information which indicates the radio base station110-2on movement destination in the switching request signal. In this case, when the radio base station110-1on movement origin receives the switching request signal, the radio base station side handoff control device116built therein transfers the switching request signal to the radio base station110-2on movement destination via the network interface110and root network, according to the switching request signal. When the radio terminal120-1transmits the switching request signal to both the radio base station110-1on movement origin and the radio base station on movement destination, the radio base station110-2on movement destination needs to select one of the two received switching request signals. There is a method of selecting one having a lower bit error rate between those two received switching request signals as a specific method of selection.

Further, in order for the radio base station to increase opportunities to receive the switching request signal so as to receive it positively, after the radio terminal120-1transmits the switching request signal, when the switching response signal is not able to be received thereby even when a predetermined time has elapsed, the switching request signal may be transmitted again. Further, the radio terminal120-1may previously transmits the switching request signal several times. Furthermore, the radio terminal120-1may transmit the switching request signal several times, and, when the switching response signal is not able to be received thereby even when a predetermined time has elapsed after the several times of transmission, the switching request signal may transmitted again several times.

Thus, according to this example of operation, in case the radio terminal120-1moves across radio zones, by transmitting the distribution request to the radio base station110-2on movement destination, in response thereto, the radio base station110-2on movement destination transmits the multicast data, and the switching request signal including the information indicating this multicast data and information indicating the radio channel used for distributing the relevant multicast data. Thereby, the radio base station to be communicated with can be switch rapidly at the time of movement.

In this example of operation, when a plurality of radio terminals transmit the switching request signals simultaneously, in order to prevent that these signals collide, the radio terminal knows a timing of a multicast management table being informed of from the perch channel of the radio base station on movement destination, and, in case the multicast management table is inform of within a predetermined time, the radio terminal receives the multicast management table. Then, the radio terminal may transmit the switching request signal only when the contents of the multicast management table do not include the multicast data which it desires to continuously receive. On the other hand, in case the multicast data which it desires to receive continuously is included in the contents of the multicast management table, the radio terminal receives the multicast data in accordance with the contents, without transmitting the switching request signal.

Next, the second example of operation will now be described. A conceptual diagram of the operation of the second example is shown inFIG. 24(a) and (b). Moreover, an example of a multicast management table used in the operation example is shown inFIG. 25, and an example of an operation flow thereof is shown inFIG. 26.

First, the multicast management table used in this embodiment will now be described. InFIG. 24(a), the radio base station110-1on movement origin receives information concerning multicast data distributed by radio base stations110-2through110-7adjacent to the own station from the relevant radio base stations110-2through110-7, and, informs to a radio zone Z1at a period T1the multicast management table including this information and information concerning multicast data distributed by the own station. The radio terminals120-1through120-3receive this information transmitted from the radio base station110-1on movement origin.

In the multicast management table shown inFIG. 25, the radio base station number on first column is information which indicates the radio base stations110-1through110-7. The radio base station numbers1through7are related with the respective radio base stations110-1through110-7. The program name on second column is information which indicates each multicast data. The IP address (multicast address) particular to a program name is related with each multicast data. In the example ofFIG. 25, the radio base station110-1distributes three sorts of multicast data, and the radio base station110-7distributes two sorts of multicast data.

The radio channel number on third column is information identifying radio channels, such as a career frequencies, radio slots, and spread codes, used for distribution of the multicast data identified by the program names on second column. The particular radio channel number is related with each radio channel.

The distribution check1on fourth column and the distribution check2on fifth column are used in order that the radio base station110inquires for termination of distribution of multicast data to the radio terminals120present in the radio zone on the own station.

Specifically, when multicast data which becomes unnecessary to distribute is included in multicast data distributed from the radio base station110, the radio terminal120transmits a distribution unnecessary notice including information which indicates the multicast data which became unnecessary for the radio base station110. In order to inquire for permission of distribution termination to the radio terminals120present in the radio zone on the own station, the radio base station110which has received the distribution unnecessary notice informs the multicast management table in which the value on the distribution check1for the multicast data indicated by the distribution unnecessary notice is set as “1”, and the values on the distribution check1for the other multicast data are set as “0”.

When the value on the distribution check1for the multicast data which is under reception by itself is “1” in the received multicast management table, the radio terminal120sets any value within a predetermined time in a random timer, and, at a timing at which the random timer reaches the time-out state, transmits a response signal including information which indicates the multicast data under reception to the radio base station110.

When receiving the response signal within a predetermined response interval, the radio base station110continues distribution of the multicast data corresponding to the response signal, i.e., continues distribution of the multicast data for which the value “1” is set on the distribution check1, but terminates the distribution when not receiving the response signal therefor.

There is a case the radio base station110cannot receive the distribution unnecessary notice from the radio terminal120due to degradation of propagation environment, power supply termination on the radio terminal, or the like. In this case, distribution of unnecessary multicast data is continued and thus effective use of the radio resources cannot be attained. Therefore, the radio base station110inquires for permission of distribution termination to the radio terminals120present in the radio zone for all the multicast data distributed thereby.

Specifically, the radio base station110informs the multicast data in which the value on the distribution check2is set as “1” at period Tq which is N times the period Tt of informing of the multicast management table. When the value on the distribution check2of the received multicast data is “1” and, also, the multicast data is under reception thereby, the radio terminal120sets any value shorter than Tq in a random timer, and, at a timing at which the random timer reaches the time-out state, transmits a response signal including information indicating the multicast data which is under reception thereby.

The radio base station110continues distribution for the multicast data indicated by the response signal until the subsequent period Tq has elapsed. On the other hand, when the subsequent period Tq has elapsed from the notice of the multicast data for which the value on the distribution check2is set as “1”, the radio base station10terminates distribution of the multicast data for which no indication has been made until then.

The multicast management table shown inFIG. 25is produced by the radio base station side handoff control device116built in the radio base station110periodically transmitting and receiving the multicast management table with the adjacent radio base stations110via the network interface11, and inserting in the multicast management table on the own station the thus-obtained multicast management tables on the adjacent radio base stations110.

Next, specific operation will now be described. As shown inFIG. 24(a), it is assumed that a radio terminal120-1in a radio zone Z1of a radio base station110-1on movement origin moves to a radio zone Z1of a radio base station110-2on movement destination.

In this case, as shown in the operation flow ofFIG. 26, while the radio terminal120-1receives the multicast data A and also receives the multicast management table at a period Tt (S91), it moves into the radio zone Z2from the radio zone Z1(S92), in the radio terminal120-1, the signal reception intensity from the radio base station110-2on movement destination becomes larger than the signal reception intensity from the radio base station110-1on movement origin. At this time, the radio terminal side handoff control device127built in the radio terminal120-1determines (S93), as an opportunity of handoff, the time of the reception intensity of the perch channel from the radio base station110-2on movement destination becoming larger than the reception intensity of the perch channel from the radio base station110-1on movement origin, based on the reception intensity of the perch channel received periodically.

In case of the opportunity of handoff, the radio terminal side handoff control device127refers to the latest multicast management table, and determines as to whether or not the multicast data A under reception thereby is distributed into the radio zone Z2on the radio base station110-2on movement destination.

When the multicast data A under reception thereby is not distributed into the radio zone Z2(NO at S94), the radio terminal side handoff control device127transmits a switching request signal for switching the radio base station to be communicated from the radio base station110-1on movement origin to the radio base station110-2on movement destination to the radio base station on movement destination via the radio link control device123(S95). At this time, the radio terminal side handoff control device127may transmit the switching request signal directly to the radio base station110-2on movement destination, or to the radio base station110-2on movement destination via the radio base station110-1on movement origin.

As shown inFIG. 24(b), the radio base station side handoff control device116built in the radio base station110-2on movement destination receives the switching request signal from the radio terminal110-1, and, controls the radio base station side multicast control device115on the own station so as to distribute the multicast data A, according to the switching request signal. Under the control, the radio base station side multicast control device115starts distribution of the multicast data A (S96). Furthermore, the radio base station side handoff control device116transmits a switching response signal to the radio terminal120-1which has transmitted the switching request signal, via the radio link control device112(S97).

The radio terminal side handoff control device127built in the radio terminal120-1controls switching of the radio channel according to this switching response signal. Thereby, the radio terminal side handoff control device127starts reception of the multicast data A from the radio base station110-2on movement destination (S98).

Further, when the multicast data A under reception is distributed into the radio zone Z2(YES at S94), the radio terminal side handoff control device127built in the radio terminal120-1controls switching of the radio channel according to the multicast management table. Thereby, the radio terminal side handoff control device127starts reception of the multicast data A from the radio base station110-2on movement destination (S99).

By the series of operation described above, even when the radio terminal120-1moves into the radio zone Z2on the radio base station110-2on movement destination from the radio zone Z1on the radio base station110-1on movement origin, the radio base station to be communicated with can be rapidly switched.

Further, same as in the first embodiment, in S95of the operation flow shown inFIG. 26, the radio terminal120-1may transmit the switching request signal to the radio base station110-1on movement origin. Further, the radio terminal120-1may transmit the switching request signal to both the radio base station110-1on movement origin and the radio base station110-2on movement destination.

Further, after the radio terminal120-1transmits the switching request signal, when the switching response signal is not able to be received even when a predetermined time has elapsed, the switching request signal may be transmitted again. Further, the radio terminal120-1may previously transmits the switching request signal several times. Furthermore, the radio terminal120-1may transmit the switching request signal several times, and, when the switching response signal is not able to be received even when a predetermined time has elapsed after the several times of transmission, the switching request signal may transmitted again several times.

Thus, according to this example of operation, in case the radio terminal120-1moves across radio zones, information concerning the multicast data which the radio base station110-2on movement destination distributes is included in the multicast management table informed of from the radio base station110-1on movement origin. Thereby, the radio terminal120-1can previously recognize the multicast data which the radio base station110-2on movement destination distributes, and it receives the multicast data immediately without transmitting the distribution request, in case the radio base station110-2on movement destination distributes the desired multicast data. Accordingly, the radio terminal120-1can rapidly switch the radio base station to be communicated with at a time of movement.

Thus, according to the present invention, a radio terminal can determine whether or not to transmit a service continuation request signal to an information distributing apparatus based on informational indicating as to whether continuation request having been made for multicast information distribution service. Moreover, an information distributing apparatus can determine whether or not multicast information distribution service should be continued, based on a management state of service continuation management means. Thereby, the information distributing apparatus can provide multicast information distribution service properly via a radio section to radio terminals present within the service area.

Moreover, according to the present invention, radio channels used for multicast information distribution service can be limited only to radio channels which are informed of by an information distributing apparatus. Further, distribution services made by these radio channels can be limited only to multicast information corresponding to the radio channels informed of. Accordingly, it is possible to utilize the radio resources effectively, and, also, each radio terminal can receive only the necessary multicast information distribution services.

Furthermore, according to the present invention, in case necessity arises for a radio terminal to switch the other party to be communicated, from a radio base station on movement origin to a radio base station on movement destination, information of a radio channel used for distributing multicast data is transmitted from the radio base station on movement destination to the radio terminal, only as a result of the radio terminal transmitting a distribution request to the radio base station on movement destination. Thereby, it is possible to rapidly switch the radio base station to be communicated with at a time of movement, more rapidly than the prior art.