JP2007013463A - Handover method and mobile terminal in radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute connection to an optimal radio base station according to circumstance change. <P>SOLUTION: After determining the start of a handover procedure, a host station 2 executes channel setting for one or more radio base stations 3b as handover destination candidates, and multi-casts a packet for radio base stations 3a and 3b as handover origin and handover destination candidates, and the host station 2 instructs the start of a handover procedure and the radio channel information of the handover destination candidates to a mobile terminal 4, and the mobile terminal 4 measures the radio line quality of the radio base station 3a as the handover origin and the radio base station 3b as the handover destination candidate corresponding to the instructed radio channel information, and determines a handover timing based on the measurement result, and switches it to a radio channel 3b as the handover destination, and notifies the host station 2 of handover completion, and when receiving handover completion, the host station 2 releases any radio resource other than the handover destination set for the radio base stations 3a and 3b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a handover method for a wireless communication system and a mobile terminal.

  Non-Patent Document 1 reports a measurement result of signal quality (wireless channel quality) received by a mobile terminal from surrounding radio base stations to an upper station, and the radio network controller as the upper station starts handover and handover timing. Has been shown to determine. That is, when the upper station decides to start handover, after setting the handover destination radio channel, the mobile terminal switches the radio channel by instructing the mobile terminal to reconfigure the radio channel, and the radio channel switching is completed. The mobile terminal notifies the upper station of the completion of the radio channel reconfiguration.

  Patent Document 1 discloses that in a mobile IP network, for real-time traffic, a home agent bicasts the same packet to a handover source and a handover destination radio base station in order to avoid communication interruption, non-real-time traffic Is shown that the wireless base station before the handover buffers the packet in order to avoid packet loss, and the buffered packet is transferred to the handover-destination wireless base station after the handover is completed.

JP, 2002-125254, A Claims 3 and 4 3GPP TR25.931 V6.1.0 (2005-03) "UTRAN Functions, Examples on Signaling Procedures", P63-68 (Section 7.11.1.3)

  However, in the handover method described in Non-Patent Document 1, since the upper station determines the handover start and the handover timing, the actual radio channel quality at the handover timing is reduced due to the control delay from the handover start time to the handover timing. There is a possibility that it is greatly different from the handover start time, and there is a problem that the mobile terminal cannot connect to the radio base station optimal as the radio channel quality for communication and fails in handover. Even if the mobile terminal frequently reports the measurement results of the radio channel quality to the upper station, there is a round trip delay with the upper station between the radio channel quality measurement timing and the handover timing. It was difficult to respond to the changes.

  Further, in the handover method described in Patent Document 1, for real-time traffic, the home agent multicasts to the handover source and handover destination radio base stations, and performs packet transmission from each radio base station to the radio channel. There is a problem that the use efficiency of radio resources deteriorates during handover. For non-real-time traffic, the handover source radio base station retransmits the packet in bursts regardless of the congestion state of the handover destination radio base station when the handover is completed. There was a high risk of packet discard.

  The present invention has been made in view of the above, and a handover method of a radio communication system capable of making a connection to an optimal radio base station according to a change in situation by a mobile terminal determining a handover timing And to obtain a mobile terminal.

  In addition, the present invention not only enables multicasting to the radio base station for non-real-time traffic, but also significantly reduces the risk of packet discard by performing multicast taking into account the congestion state of the radio base station. An object of the present invention is to provide a handover method of a radio communication system that can improve radio resource use efficiency by preventing unnecessary packet transmission to a radio channel at a radio base station as a handover destination candidate during multicast. And

  In order to solve the above-described problems and achieve the object, the present invention provides a multicast transmission of downlink packets to a plurality of radio base stations including a handover destination candidate by a higher-level apparatus that is a handover start decision source at the time of handover of a mobile terminal Thus, in a handover method of a radio communication system in which a plurality of radio base stations transmit packets including the same data to a mobile terminal, after the start of the handover procedure is determined, the higher-level apparatus can perform one or more radios serving as handover destination candidates Performs channel setting for the base station, multicasts packets to the handover source and handover destination candidate radio base stations, and the upper apparatus starts the handover procedure and sends the handover destination candidate radio channel information to the mobile terminal. The first step of instructing and the mobile terminal Measure the radio channel quality between the radio base station and the handover destination candidate radio base station corresponding to the instructed radio channel information, determine the handover timing based on the measurement result, and switch to the handover destination radio channel A second step of notifying the host device of the completion of handover, and a third step of releasing radio resources other than the handover destination set for the radio base station when the host device receives the handover completion. Features.

  According to the present invention, since the mobile terminal determines the handover timing based on the latest radio channel quality information, the possibility of successful handover increases. In addition, since the host device sets a plurality of handover destination candidate radio base stations that can be selected by the mobile terminal, it is possible for the mobile terminal to perform handover to the optimal handover destination for continuation of communication and succeed in handover. The property becomes extremely high.

  Hereinafter, a handover method of a radio communication system and an embodiment of a mobile terminal according to the present invention will be described in detail based on the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration of a wireless communication system to which the first embodiment is applied. In FIG. 1, a network 1 is a network constructed according to a communication system such as an IP network or an ATM network, and transmits / receives a packet to / from an upper station 2 as a handover start determination source. The radio base stations 3a and 3b are connected to the upper station 2 and transmit / receive packets to / from the upper station 2. Reference numeral 4 denotes a mobile terminal. In this case, the mobile terminal 4 transmits / receives a packet to / from the radio base station 3a through a radio channel, and represents handover to the radio base station 3b along with movement.

  Note that there may be a plurality of radio base stations serving as handover destination candidates, but here, for simplicity, it is assumed that only the radio base station 3b exists as a handover destination candidate. 5a to 5d represent downlink data packets, 6 is a packet holding unit held by the upper station 2, and 7a and 7b are packet holding units held by the radio base stations 3a and 3b, respectively.

  Next, a handover operation when the present invention is applied to, for example, a downlink packet channel (HS-DSCH) in HSDPA (High Speed Downlink Packet Access) which is a 3GPP standard will be described with reference to FIG. In this example, the upper station 2 corresponds to a radio network controller.

  As shown in FIG. 2, a packet addressed to the mobile terminal 4 is received by the upper station 2 via the network 1 from a partner device (not shown) communicating with the mobile terminal 4, and the upper station 2 The packet is transmitted to the mobile terminal 4 via the handover source radio base station 3a. At this time, the mobile terminal 4 periodically measures the radio channel quality of the connected radio base station 3a and the peripheral radio base station 3b, and sends the measurement result to the upper station 2 via the connected radio base station 3a. Reporting. When the upper station 2 determines the start of handover based on the measurement result or the like, the upper station 2 implements a packet channel setting procedure for the radio base station 3b that is a handover destination candidate. Note that there may be a plurality of handover destination candidate radio base stations.

  When the packet channel setting for the handover destination radio base station 3b is completed, the data packet 5a addressed to the mobile terminal 4 received by the upper station 2 via the network 1 is temporarily stored in the packet holding unit 6 of the upper station 2. After that, multicast transmission is performed to the radio base station 3a that is the handover source of the mobile terminal 4 and the radio base station 3b that is the handover destination candidate.

  In the first embodiment, a case where the radio base stations 3a and 3b transmit packets received from the upper station 2 to the radio channel will be described by taking as an example a case where real-time traffic is multicast.

  Next, the upper station 2 transmits a radio channel reconfiguration instruction, which is an instruction to start a handover procedure, to the mobile terminal 4 via the connected radio base station 3a in order to cause the mobile terminal 4 to execute a handover. The radio channel reconfiguration instruction includes radio channel information corresponding to handover destination candidates that can be selected by the mobile terminal 4.

  When receiving the radio channel reconfiguration instruction, the mobile terminal 4 measures the radio channel quality for all the radio base stations corresponding to the radio channel instructed by the radio channel reconfiguration and the currently connected radio base station 3a. Then, the necessity of handover is determined by comparing the latest radio channel quality information for each radio base station. For example, if it is determined that the radio channel quality of the currently connected radio base station 3a is better than the radio channel quality of the handover destination candidate and the handover is unnecessary, the handover is not performed at this stage, and the radio channel quality after the next time The necessity of handover is determined again at the time of measurement. In this way, the mobile terminal 4 receives the radio channel reconfiguration instruction from the upper station 2 and then measures the radio channel quality measurement of each radio base station, so that the exact timing at which the handover is actually required can be determined. Detected.

  After that, when it is determined that the handover is necessary, the mobile terminal 4 switches the radio channel to the radio base station 3b that is the handover destination, and after completion of the radio channel switching, the mobile terminal 4 completes the radio channel reconfiguration completion. Notification is made to the upper station 2 via the station 3b.

  The upper station 2 notified of the completion of the radio channel reconfiguration releases the packet channel set to other than the handover destination radio base station 3b. This completes the handover procedure.

  In the first embodiment, it is described on the assumption that the upper station performs packet multicast to one or more radio base stations. On the other hand, the present invention can be applied to a wireless communication system in which only a packet channel is secured.

  As described above, in Embodiment 1, since the mobile terminal determines the handover timing based on the latest radio channel quality information, there is a high possibility that the handover will be successful. In addition, since the upper station sets a plurality of handover destination candidate radio base stations that can be selected by the mobile terminal, the mobile terminal can be handed over to the optimum handover destination for continuation of communication, and the handover can succeed. The property becomes extremely high.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is based on the premise that the main part configuration of the first embodiment, that is, the mobile terminal 4 can finally select the handover destination radio base station, and the mobile station 4 moves with the upper station 2 that is the handover start decision source. A configuration and a procedure for dealing with a case where a radio channel reconfiguration instruction, which is information for handover control, does not arrive between the terminals 4 and the handover procedure fails or when the mobile terminal 4 does not perform a handover are added.

  FIG. 3 shows the handover control procedure of the second embodiment. Since the implementation configuration and the procedure before the upper station 2 transmits the radio channel reconfiguration are the same as those in the first embodiment, description thereof will be omitted.

  When the upper station 2 instructs the mobile terminal 4 to perform radio channel reconfiguration, the mobile terminal 4 sets handover deadline information to be handed over in the radio channel reconfiguration, and the mobile terminal 4 by the set handover deadline The upper station 2 sets a timer until the completion of radio channel reconfiguration completion in the hope that 4 will perform handover. As the handover deadline information, for example, a system frame number (SFN) is used.

  When the mobile terminal 4 receives the radio channel reconfiguration instruction including the handover deadline information, the mobile terminal 4 enters the handover timing determination operation as in the first embodiment, but the reason is that the radio channel quality at the handover source is sufficient. When the handover deadline set for the radio channel reconfiguration without performing the handover by elapses, the handover operation is stopped and the communication is continued at the handover source, and the upper station 2 is not notified of the completion of the radio channel reconfiguration.

  If the upper station 2 does not receive the completion of the radio channel reconfiguration before the set timer time-out, the upper station 2 stops the packet multicast and releases the packet channel to the handover destination candidate radio base station.

  As described above, in Embodiment 2, the handover deadline is indicated simultaneously with the handover instruction to the mobile terminal. Therefore, even when the mobile terminal determines the handover timing, the mobile terminal If the handover is not performed before, the handover destination candidate radio resource secured by the upper station can be released, and the radio resource in the system can be reused. Further, even when the handover instruction does not reach the mobile terminal due to the deterioration of the handover source radio channel quality, the radio resources can be released in the same procedure, so that the control at the host station is simplified.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, after the upper station 2 indicates the handover destination candidate to the mobile terminal 4, the handover is executed by explicitly specifying the handover destination, and the upper station 2 sets the radio base station. Radio resources are released.

  FIG. 4 shows the handover control procedure of the third embodiment. Since the implementation configuration and the procedure until the mobile terminal 4 receives the radio channel reconfiguration are the same as those in the first embodiment, description thereof will be omitted.

  After instructing the mobile terminal 4 to reconfigure the radio channel, the upper station 2 determines whether to immediately execute the handover of the mobile terminal 4. This determination is made from a specific radio base station, for example, due to the load state of the radio base stations 3a and 3b that are the handover source and handover destination candidates in the upper station 2 or for conservative reasons, such as rearrangement of radio resources. This is based on determining whether it is necessary to eliminate radio resources used by the user.

  When it is determined that the immediate execution of the handover is necessary, the upper station 2 selects one radio channel from the radio channels instructed by the radio channel reconfiguration, and issues an instruction to switch to the selected one radio channel. 4 is notified. The radio channel designated here may designate a handover source radio channel, and if a handover source radio channel is designated, it means cancellation of handover.

  The mobile terminal 4 that has received the radio channel switching designation cancels the handover timing determination, immediately switches to the designated radio channel, and then notifies the upper station 2 of the completion of the radio channel reconfiguration. The upper station 2 that has received the completion of radio channel reconfiguration performs packet multicast stop and packet channel release for the radio base station other than the handover destination.

  As described above, in the third embodiment, even when the handover timing is determined by a different algorithm for each mobile terminal, the upper station can forcibly execute or cancel the handover of the mobile terminal. There is an effect that the handover can be completed according to the use situation.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG. In the first to third embodiments, an example has been shown in which each radio base station can cope with real-time traffic by transmitting a packet multicast from the upper station 2 to the radio channel. However, in this fourth embodiment, It is possible to cope with communications in which packet loss is not desired, such as non-real-time traffic. Of course, application to real-time traffic is also possible.

  FIG. 5 shows the handover control procedure of the fourth embodiment. Since the implementation configuration and the procedure until the host station 2 determines the start of the handover procedure are the same as those in the first embodiment, the description thereof is omitted.

  The host station 2 that has decided to start handover performs packet channel setting for the radio base station 3b, which is a handover destination candidate, and at the same time, instructs to suspend packet transmission from the set channel. The hold instruction is included in the call control information when setting the packet channel.

  The data packet 5a addressed to the mobile terminal 4 received by the upper station 2 via the network 1 is temporarily stored in the packet holding unit 6 of the upper station 2, and then the radio base station 3a that is the handover source of the mobile terminal 4 and Multicast transmission is performed to the radio base station 3b which is a handover destination candidate. Here, when the upper station 2 multicasts the packet addressed to the mobile terminal 4, the packet is transmitted from the radio base station 3 a, but the radio base station 3 b packets the packet according to the hold instruction from the previous upper station 2. The data is buffered in the holding unit 7b and held without being transmitted to the wireless line.

  Next, as in the first embodiment, the upper station 2 instructs the mobile terminal 4 to reconfigure the radio channel via the radio base station 3a that is the handover source. In the fourth embodiment, when the mobile terminal 4 detects the handover timing in the same manner as in the first embodiment, before the mobile terminal 4 switches the radio channel to the handover destination, the mobile terminal 4 And notification of handover execution. This notification is performed by adding control information to an uplink channel such as an individual channel or HS-DPCCH, and notifies the radio base station 3a that the connection with the radio base station 3a that is the handover source is released by handover. . In addition, as a notification of handover execution to be performed for the radio base station 3a, the mobile terminal 4 may not perform explicit notification, but may simply switch the radio channel to the radio base station 3b. In this case, the handover of the mobile terminal 4 is detected when the radio synchronization state of the dedicated channel set in the mobile terminal 4 by the radio base station 3a is lost.

  Upon receiving the handover notification, the radio base station 3a immediately stops the packet transmission addressed to the mobile terminal 4 and notifies the upper station 2 of the index information of the untransmitted packet to the mobile terminal 4. The packet index information is a sequence number given to a transmission packet from the upper station 2 to the radio base stations 3a and 3b.

  The host station 2 notified of the index information immediately stops packet transmission to the radio base station 3a. On the other hand, after switching the radio channel to the handover destination, the mobile terminal 4 notifies the upper station 2 of the completion of the radio channel reconfiguration via the radio base station 3b that is the handover destination. Upon receiving the completion of radio channel reconfiguration from the mobile terminal 4, the upper station 2 instructs the handover destination radio base station 3b to start the pending packet transmission and then sets the radio base station other than the handover destination. Release the packet channel that was being used. In addition, in the packet transmission start instruction, index information of packets not yet transmitted to the mobile terminal 4 notified from the handover source radio base station 3a is given.

  Based on this index information, the radio base station 3b starts transmission to the mobile terminal 4 from untransmitted packets among the packets buffered in the packet holding unit 7b, and discards packets that have been transmitted to the mobile terminal 4. To do. When the mobile terminal 4 cancels without performing handover, the mobile base station 3a does not perform handover notification, and the radio base station 3a does not stop packet transmission and does not perform index information notification to the upper station 2. . When the host station 2 does not receive the index information from the radio base station 3a, it does not give a packet transmission start instruction to the handover destination radio base station 3b.

  As described above, in Embodiment 4, a multicast packet is held at the handover destination radio base station, transmission is stopped at the handover source radio base station immediately before the handover at the mobile terminal, and the handover destination Since the continuation packet can be received from the radio base station, communication by multicast can be applied to communication where packet loss is not desired, such as non-real-time traffic, so a handover method according to the nature of the traffic By switching between, there is an effect that the communication interruption time associated with the handover can be shortened for any communication.

Embodiment 5. FIG.
Next, a fifth embodiment of the present invention will be described with reference to FIGS. In the first to fourth embodiments, an example in which a packet is multicast from the upper station 2 regardless of the buffer state of each radio base station has been shown. However, in the fifth embodiment, the used buffer amounts of the handover source and the handover destination are set as follows. Multicasting is performed by the upper station in consideration. In this embodiment, it is assumed that a transmission packet is held at a handover destination candidate radio base station during a handover. That is, in the fifth embodiment, as described above, the upper station 2 that has decided to start handover performs packet channel setting for the radio base station that is a handover destination candidate, and at the same time, from the set channel. A radio base station that is a handover destination candidate is instructed to suspend packet transmission. Based on this instruction, the radio base station that is a handover destination candidate holds the transmission packet.

  FIG. 6 shows a system configuration and packet transmission / reception according to the fifth embodiment. The configurations and functions of the upper station 2, the radio base stations 3a and 3b, and the mobile terminal 4 are the same as those in FIG.

  When the upper station 2 decides to start the handover of the mobile terminal 4, as described above, the packet channel is set to the handover destination candidate radio base station 3b, and the suspension of the packet is instructed. In response, the handover destination candidate radio base station 3b notifies the upper station 2 of the allowable reception amount 8b for the downstream packet multicasted from the upper station 2 thereafter. On the other hand, the higher-level station 2 also notifies the handover source radio base station 3a that multicasting will be started. In response to this notification, the handover source radio base station 3a notifies the upper station 2 of the downlink packet reception allowable amount 8a. These downlink packet reception allowances are the number of packets that are allowed to be received during handover, and are determined based on the buffer free state of each radio base station.

  FIG. 7 shows a configuration example of each radio base station to which the fifth embodiment is applied. Packets received from the upper station 2 and addressed to the mobile terminal 4 are stored in the packet holding unit 7 via the packet transmitting / receiving unit 9. The packet holding unit 7 is provided with queues 7-1 to 7-m destined for each mobile terminal, and the packets stored in these queues 7-1 to 7-m are transmitted to the radio line in the order determined by the scheduler unit 11. Sent. The buffer usage management unit 12 manages the buffer amount used by the packet holding unit 7, calculates a downlink packet reception allowance as the number of receivable packets, and performs call control on the calculated downlink packet reception allowance. The data is sent to the upper station 2 through the unit 14.

  The upper station 2 determines the smallest downlink packet reception allowance as the number of packets to be multicast during handover based on the downlink packet reception allowance received from the handover source and handover destination candidate radio base stations, and transmits more packets. Do not do.

  As described above, in the fifth embodiment, in consideration of the buffer usage status of the radio base station that performs multicasting during handover, the upper station performs packet transmission in accordance with the radio base station with the smallest downlink packet reception allowance. As a result, packet discard due to buffer overflow in each radio base station is eliminated, packet loss associated with handover can be prevented, and retransmission in the upper layer also does not occur, thereby improving system throughput. .

Embodiment 6 FIG.
Next, a sixth embodiment of the present invention will be described with reference to FIG. In the sixth embodiment, the fifth embodiment is premised on, and during handover, the downlink packet reception allowance is updated from time to time and notified to the upper station at any time, and the upper station is based on this notification. The packet transmission amount to be multicast is updated.

  FIG. 8 shows a configuration example of each radio base station to which the sixth embodiment is applied. Since the operations of the constituent elements other than the buffer usage management unit 12, the reception allowable amount notification unit 13, and the timer 10 are the same as those in the fifth embodiment, the description thereof is omitted. The buffer usage management unit 12 periodically updates the downlink packet reception allowable amount using the timer 10. For example, the buffer usage management unit 12 updates the downlink packet reception allowable amount via the reception allowable amount notification unit 13 for each update. 2 is notified.

  As another example of the notification timing of the downlink packet reception allowance, there may be a case where there is a change from the previously notified downlink packet reception allowance, or a case where the value greatly varies from the previously notified downlink packet reception allowance. .

  The upper station 2 holds the smallest downlink packet reception allowance among the latest downlink packet reception allowances received from the handover source and handover destination candidate radio base stations as a packet transmission allowance, and a packet to be multicast during handover Packet transmission is performed so that the number does not exceed the packet transmission allowable amount. Each time the packet transmission allowable amount is updated, the number of packet transmissions is limited according to the latest value.

  The notification of the downlink packet reception allowance shown above can be substituted by the flow control implemented by Frame Protocol in the case of an HSDPA system. Further, the notification unit of the packet transmission allowable amount may be performed for each priority queue as in the HSDPA method, or may be performed collectively for each user.

  As described above, in the sixth embodiment, the upper station is constantly comparing and updating the downlink packet reception allowances of a plurality of radio base stations that perform multicasting during handover, so the period of the handover state becomes longer. However, since multicasting can be performed from the upper station to the handover source and handover destination candidate radio base stations based on the latest buffer usage status of each radio base station, packet discard due to buffer overflow at each radio base station The optimum throughput can be maintained without generating it.

Embodiment 7 FIG.
Next, a seventh embodiment of the present invention will be described with reference to FIG. In the seventh embodiment, as described in the sixth embodiment, the transmission amount of the multicast packet is changed based on the downlink received packet allowable amount from the handover destination radio base station, and the handover destination radio base station Packets that are no longer needed are discarded as needed. This Embodiment 7 is premised on that a transmission packet is held at a handover destination candidate radio base station during a handover. That is, in the seventh embodiment, as described above, the upper station 2 that has decided to start handover performs packet channel setting for a radio base station that is a handover destination candidate, and at the same time, from the set channel. A radio base station that is a handover destination candidate is instructed to suspend packet transmission. Based on this instruction, the radio base station that is a handover destination candidate holds the transmission packet.

  FIG. 9 shows a system configuration to which the seventh embodiment is applied and packet transmission / reception. 9, packet deletion information 15 is added to the configuration shown in FIG.

  When the handover is started and packets are multicast from the upper station 2 to the handover source candidate and handover destination candidate radio base stations, the handover destination candidate radio base station 3b internally stores the packet received from the upper station 2 It is on hold and is not transmitted to the mobile terminal 4. On the other hand, in the radio base station 3a as the handover source, communication is continued by transmitting packets to the mobile terminal 4 even during the handover.

  Here, the handover source radio base station 3 a notifies the handover destination candidate radio base station 3 b of the index information of the packet that has been transmitted to the mobile terminal 4 by the packet deletion information 15.

  This notification is possible because the radio base station 3a needs to recognize the handover destination candidate radio base station, so that it is possible to obtain a list of address information of the handover destination candidate from the upper station 2 in advance. 2 may be notified of the packet deletion information 15 to the handover destination candidate radio base station 3b via the higher-level station 2.

  In addition, for the notification timing of the packet deletion information 15, a method of notifying at a time when the number of packets transmitted from the handover source radio base station 3 a to the mobile terminal 4 has reached a certain value or at a certain time interval is adopted. Can do.

  The handover destination candidate radio base station 3b that has received the packet deletion information 15 discards unnecessary packets, that is, packets that have already been transmitted by the radio base station 3a from the buffer based on the index information of the packets to be deleted. During handover, packet deletion is repeated based on the above operation. When the handover is completed, the last packet deletion information 15 is notified from the handover source radio base station 3a to the handover destination radio base station 3b. This notification may be performed in the same manner as the packet deletion information notification performed as needed during the handover, but the index information notification and transmission start instruction shown in FIG. 5 of the fourth embodiment may be used. .

  In the handover destination radio base station 3b, after unnecessary packets are discarded, packet transmission to the mobile terminal 4 is started from a packet having index information following the index information received last. The upper station 2 deletes the packet addressed to the mobile terminal 4 staying in the radio base station by deleting the packet channel set in the radio base station 3a other than the handover destination.

  As described above, in the seventh embodiment, packets destined for the mobile terminal that have been transmitted at the handover source during handover can be discarded by the handover destination candidate radio base station, so that they can be used by the handover destination candidate radio base station. Since the free buffer amount increases, it is possible to increase the permissible downlink packet reception amount to be notified to the upper station, which has the effect of improving the throughput during the handover.

Embodiment 8 FIG.
Next, an eighth embodiment of the present invention will be described with reference to FIG. Embodiment 8 tries to cope with a case where a packet that has been transmitted only to the handover source radio base station before the start of handover is not completely transmitted to the mobile terminal at the handover source radio base station, and the handover is completed. Thus, a packet transmitted only to the handover source radio base station before the start of handover is transferred to the handover destination radio base station. This Embodiment 8 is also premised on holding a transmission packet at a handover destination candidate radio base station during a handover.

  FIG. 10 shows a system configuration to which the eighth embodiment is applied and packet transmission / reception. In FIG. 10, head index information 16 is notified from the upper station 2 to the handover source radio base station 3a at the start of multicasting, and is index information indicating the head of the multicast packet.

  The handover source notification 17 is notified from the upper station to the handover destination radio base station 3b, and is address information of the handover source radio base station 3a. This address information may be included in the transmission start instruction shown in FIG. 5, but here it will be described as being notified separately from the transmission start instruction.

  The packet 5e indicates that the packet transmitted only to the handover source radio base station 3a before the upper station 2 starts multicasting is transferred from the handover source radio base station 3a to the handover destination radio base station 3b. . Further, the downlink packet reception allowable amount 8c is notified from the handover destination radio base station 3b to the handover source radio base station 3a. The packet transfer completion notification 18 indicates that the handover source radio base station 3a notifies the upper station 2 that the packet transfer to the handover destination radio base station 3b has been completed. Since other configurations are the same as those in the sixth embodiment, description thereof is omitted.

  Next, the operation will be described. When multicasting of a packet is started by handover, head index information 16 that is index information indicating the head of the multicast packet is notified from the upper station 2 to the handover source radio base station 3a. The head index information 16 is shown separately from the packet 5b to be multicast, but may be notified by providing a flag indicating the head of the packet 5b. In the radio base station 3a, the head index information is stored, and when the packet transmission to the radio line is stopped by handover, for example, when the handover notification shown in FIG. 5 is received and the packet transmission is stopped. Compared with the index information of the packet that has been transmitted to the mobile terminal 4 during the handover.

  As a result of the comparison, if the head index information is larger than the transmission completion index information and the index information is not continuous, the packet transmitted from the upper station 2 only to the radio base station 3a is held in the radio base station 3a. Therefore, it prepares to transfer the packet before the packet indicated by the head index information to the handover destination radio base station 3b.

  On the other hand, when the upper station 2 recognizes that the radio channel switching in the mobile terminal 4 is completed, for example, when the radio channel reconfiguration completion shown in FIG. 5 is received, the handover source notification 17 is sent to the handover destination radio. The base station 3b is notified, and the packet channel set other than the handover destination and handover source radio base station is released.

  When the handover destination radio base station 3b receives the handover source notification 17, the radio base station 3b starts to notify the radio base station 3a of the downlink packet reception allowable amount 8c. The notification of the downlink packet reception allowance 8c is notified by updating the downlink packet reception allowance at the radio base station 3b as needed, as described in the sixth embodiment. The radio base station 3a that has received the downlink packet reception allowance 8c from the radio base station 3b recognizes that the packet transfer to the previously prepared radio base station is to be performed to the radio base station 3b, and has received the notified downlink packet reception. The packet is transferred to the radio base station 3b according to the allowable amount. Thereafter, when all packet transfers from the radio base station 3a to the radio base station 3b are completed, the packet transfer completion notification 18 is notified from the radio base station 3a to the upper station 2.

  Upon reception of the packet transfer completion notification 18, the upper station 2 releases the packet channel set in the handover source radio base station 3a. Further, the handover destination radio base station 3b sequentially starts packet transfer to the mobile terminal 4 while referring to the index of the packet transferred from the radio base station 3a, and all the packets before the packet received by multicast from the upper station 2 are all transmitted. When it is recognized that the packet is received, the notification of the downlink packet reception allowable amount 8c performed to the radio base station 3a is stopped, and the packet received by multicast from the upper station 2 is canceled to cancel the packet. Continue sending.

  As described above, in the eighth embodiment, when the packet transmitted only to the handover source radio base station before the start of the handover is transferred to the handover destination radio base station, the buffer status of the handover destination radio base station is taken into consideration. Since the packet can be transferred while being handed over, packet loss due to buffer overflow can be prevented at the handover destination radio base station, and packet delay and throughput reduction due to retransmission in the upper layer after handover is completed can be prevented. .

Embodiment 9 FIG.
In the above fifth to eighth embodiments, examples of the packet transmission method in consideration of the buffer state of the radio base station that receives the packet have been shown. However, regarding the determination of the handover start and the determination of the handover timing in these examples Is not limited to the mobile terminal 4 or the upper station 2, and can be performed even when the handover timing is determined by the upper station 2 as in the prior art.

Embodiment 10 FIG.
In the above first to ninth embodiments, examples where the present invention is applied to the HSDPA wireless communication system have been described. However, the present invention is not limited to the configuration of the wireless communication system, that is, the upper station 2, the wireless base station 3a, For example, the upper station 2 in FIG. 1 or the like is not limited to a W-CDMA radio network control device. Further, in FIG. 5 and the like, control of handover start and end, packet channel setting and release with the radio base stations 3a and 3b, and control information exchange regarding handover with the radio base stations 3a and 3b and the mobile terminal 4 are performed. Although implemented in the upper station 2, these control function units may be separated from the upper station 2 and provided as separate devices. In this case, a separate control channel is required for exchanging information between the functional unit separated from the upper station 2 and the upper station. Further, the present invention can be applied even when the function unit separated from the upper station 2 and the wireless base station are integrated. These higher-level stations 2 and other devices are referred to as higher-level devices.

  As described above, the handover method of the wireless communication system according to the present invention is useful for a wireless communication system such as the HSDPA method.

It is a figure which shows the structure of the radio | wireless communications system concerning this invention. 3 is a signal sequence diagram of the wireless communication system according to the first embodiment. FIG. FIG. 10 is a signal sequence diagram of the wireless communication system according to the second embodiment. FIG. 10 is a signal sequence diagram of the wireless communication system according to the third embodiment. FIG. 10 is a signal sequence diagram of the wireless communication system according to the fourth embodiment. FIG. 10 is a diagram illustrating a configuration of a wireless communication system according to a fifth embodiment and a packet flow. FIG. 10 is a block diagram showing an internal configuration of a radio base station when Embodiment 5 is applied. FIG. 10 is a block diagram showing an internal configuration of a radio base station when Embodiment 6 is applied. FIG. 10 is a diagram illustrating a configuration of a wireless communication system according to a seventh embodiment and a packet flow. FIG. 10 is a diagram illustrating a configuration of a wireless communication system and a packet flow according to an eighth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Network 2 Upper station 3a, 3b Wireless base station 4 Mobile terminal 6 Packet holding part 7, 7a, 7b Packet holding part 9 Packet transmission / reception part 10 Timer 11 Scheduler part 12 Buffer usage management part 13 Receiving capacity notification part 14 Call control Part

Claims (9)

When a higher-level apparatus that is a handover start decision source at the time of handover of a mobile terminal multicasts downlink packets to a plurality of radio base stations including handover destination candidates, the plurality of radio base stations transmit packets including the same data to the mobile terminal In a handover method of a wireless communication system for transmitting to
After deciding to start the handover procedure, the host device performs channel setting for one or more radio base stations that are handover destination candidates, and multicasts packets to the handover source and handover destination candidate radio base stations. A first step in which the higher-level device instructs the mobile terminal of the start of the handover procedure and the handover destination candidate radio channel information;
The mobile terminal measures the radio channel quality between the handover source radio base station and the handover destination candidate radio base station corresponding to the instructed radio channel information, determines the handover timing based on the measurement result, and performs handover. A second step of switching to the previous radio channel and notifying the host device of the completion of the handover;
A third step of releasing radio resources other than the handover destination set for the radio base station when the host apparatus receives the handover completion;
A handover method for a wireless communication system, comprising: When a higher-level apparatus that is a handover start decision source at the time of handover of a mobile terminal multicasts downlink packets to a plurality of radio base stations including handover destination candidates, the plurality of radio base stations transmit packets including the same data to the mobile terminal In a handover method of a wireless communication system for transmitting to
After deciding to start the handover procedure, the host device performs channel setting for one or more radio base stations that are handover destination candidates, and multicasts packets to the handover source and handover destination candidate radio base stations. A first step in which the higher-level device instructs the mobile terminal to start handover procedures, handover destination candidate radio channel information and handover timing deadline information;
The mobile terminal measures the radio channel quality between the handover source radio base station and the handover destination candidate radio base station corresponding to the instructed radio channel information, determines the handover timing based on the measurement result, and A second step of notifying the host device of the completion of handover by switching to the handover destination radio channel when the determined time is before the instructed handover timing deadline information;
If the host device receives the handover completion before the handover timing deadline information times out, it releases radio resources other than the handover destination set for the radio base station, and receives the handover completion by the timeout. If not, a third step of releasing radio resources of the handover destination candidate radio base station;
A handover method for a wireless communication system, comprising: When a higher-level apparatus that is a handover start decision source at the time of handover of a mobile terminal multicasts downlink packets to a plurality of radio base stations including handover destination candidates, the plurality of radio base stations transmit packets including the same data to the mobile terminal In a handover method of a wireless communication system for transmitting to
After deciding to start the handover procedure, the host device performs channel setting for one or more radio base stations that are handover destination candidates, and multicasts packets to the handover source and handover destination candidate radio base stations. A first step in which the higher-level device instructs the mobile terminal of the start of the handover procedure and the handover destination candidate radio channel information;
A second step in which a higher-level device determines whether or not to immediately perform handover of the mobile terminal, and designates one handover-destination radio channel including a handover source according to the determination result, and issues a handover instruction;
If the mobile terminal does not receive a handover instruction in which one radio channel is specified, the radio terminal quality of the handover source radio base station and the handover destination candidate radio base station corresponding to the instructed radio channel information When the handover timing is determined based on the measurement result, the handover channel is switched to the handover destination radio channel, the handover completion is notified to the host device, and a handover instruction in which one radio channel is specified is received. A third step of switching to the radio channel designated by the handover instruction and notifying the host device of the completion of handover;
When the host device receives the handover completion, a fourth step of releasing radio resources other than the handover destination set for the radio base station;
A handover method for a wireless communication system, comprising: When a higher-level device that is a handover start decision source at the time of handover of a mobile terminal multicasts downlink packets to a plurality of radio base stations including handover destination candidates, the plurality of radio base stations transmit packets including the same data to the mobile terminal In a handover method of a wireless communication system for transmitting to
A first step in which a higher-level device performs channel setting for one or more radio base stations that are candidates for a handover destination after the start of the handover procedure;
The host device multicasts the packet to the handover source candidate and handover destination candidate radio base stations, and instructs the handover destination candidate radio base station to hold the packet transmission to the mobile terminal with the channel set. A second step in which the radio base station that has received the hold of hold holds the packet transmission to the mobile terminal;
A third step in which the higher-level device instructs the mobile terminal to start the handover procedure and the handover destination candidate radio channel information;
The mobile terminal measures the radio channel quality between the handover source radio base station and the handover destination candidate radio base station corresponding to the instructed radio channel information, determines the handover timing based on the measurement result, and performs handover. A fourth step of notifying the original radio base station of the execution of the handover, then switching to the handover destination radio channel, and notifying the host device of the completion of the handover;
A fifth step of the handover source radio base station notified of the execution of the handover from the mobile terminal stopping the packet transmission addressed to the mobile terminal and notifying the host device of the index information of the packet that has not been transmitted; ,
When the host apparatus receives the handover completion from the mobile terminal, the host apparatus notifies the handover target radio base station of the packet transmission start and the index information of the packet that has not been transmitted, and the radio base station A sixth step of releasing radio resources other than the set handover destination;
A seventh step in which the wireless base station of the handover destination starts packet transmission to the mobile terminal based on the notified index information of the packet;
A handover method for a wireless communication system, comprising: At the time of handover of the mobile terminal, the host apparatus that is the handover start decision source multicasts downlink packets to a plurality of radio base stations including the handover destination candidate, and the host apparatus transmits the handover terminal candidate radio base station to the mobile terminal. In a handover method of a radio communication system in which packet transmission suspension is instructed, and a handover destination candidate radio base station suspends packet transmission to a mobile terminal based on the suspension instruction,
A plurality of radio base stations including the handover destination candidate, when starting handover, notifies the reception allowable amount of the downlink packet to the host device,
A handover method of a radio communication system, wherein a host device determines a transmission amount of a packet to be multicast based on a received allowable amount of the downlink packet and performs multicast transmission based on the determined transmission fee. A plurality of radio base stations including the handover destination candidate, after starting handover, sequentially update the downlink reception packet allowable amount and notify the upper device,
6. The handover method for a radio communication system according to claim 5, wherein the higher-level device updates the transmission amount of the multicast packet based on the allowable amount of the downlink reception packet sequentially received. The handover source radio base station notifies the handover destination candidate radio base station of the index information of the packet that has been transmitted to the mobile terminal during the handover and at the completion of the handover,
The handover destination candidate radio base station discards the held packet based on the received index information during handover and at the completion of handover, and transmits at the handover source radio base station based on the index information at the completion of handover. The wireless communication system handover method according to claim 5 or 6, wherein a packet after the completed packet is transmitted to the mobile terminal. At the time of handover of the mobile terminal, the host apparatus that is the handover start decision source multicasts downlink packets to a plurality of radio base stations including the handover destination candidate, and the host apparatus transmits the handover terminal candidate radio base station to the mobile terminal. In a handover method of a radio communication system in which packet transmission suspension is instructed, and a handover destination candidate radio base station suspends packet transmission to a mobile terminal based on the suspension instruction,
The host device notifies the handover source radio base station of the index information of the packet at the start of the multicast,
When the handover source radio base station completes the handover, based on the notified index information, forwards the packets before the start of multicast among the remaining packets to the handover destination radio base station,
After the handover is completed, the handover destination radio base station sequentially notifies the handover source radio base station of the reception allowable amount of the downlink packet,
The handover source radio base station changes the transmission amount of the packet to be transferred to the handover destination radio base station based on the notified reception allowance of the downlink packet,
After completion of handover, a radio communication system characterized in that a handover destination radio base station transmits a packet transferred from a handover source radio base station to a mobile terminal before the pending multicast packet Handover method. When a higher-level apparatus that is a handover start decision source at the time of handover of a mobile terminal multicasts downlink packets to a plurality of radio base stations including handover destination candidates, the plurality of radio base stations transmit packets including the same data to the mobile terminal In a mobile terminal applied to a wireless communication system transmitting to
Means for measuring the radio channel quality between the handover destination candidate radio base station corresponding to the radio channel information notified from the host device and the handover source radio base station, and determining the handover timing based on the measurement result;
Means for switching a radio channel to a handover destination radio channel based on the determined handover timing, and notifying completion of handover to a host device;
A mobile terminal comprising:

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