JP2012034054A - Radio communication system, radio base station, radio terminal, and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent interruption of packet reproduction.SOLUTION: An S-eNB, which is a handover source base station, includes information on transfer delay time as well as on transfer preparation time, which is a period (first communication interruption time) during which a UE 60 cannot receive a packet containing user data either from the S-eNB or from a T-eNB, which is a handover destination base station, in the handover destination information and sends the information to the UE 60. On the other hand, the UE 60 regulates the reproduction speed of packets in a jitter buffer according to the amount of stored packets in the jitter buffer 270 of its own terminal and second communication interruption time estimated on the basis of the first communication interruption time, before the first communication interruption time arrives.

Description

  The present invention relates to a wireless communication system in which a packet is transferred from a handover source base station that is a handover source to a handover destination base station that is a handover destination at the time of handover of the wireless terminal, the wireless base station and the wireless terminal in the wireless communication system, and communication control. Regarding the method.

    Conventionally, a wireless terminal that performs real-time communication (for example, VoIP or the like) with a communication terminal (partner terminal) via a network is known (for example, Patent Document 1). In order to absorb the delay time of the network, a jitter buffer for temporarily storing packets is provided in the wireless terminal. The packet playback speed in the wireless terminal is controlled according to the packet reception speed and the amount of packets stored in the jitter buffer. The network delay time is a concept that includes not only the time during which a packet from a communication terminal (partner terminal) that is a communication partner of the wireless terminal stays in the network (retention time) but also a variation (jitter) in the residence time. .

  In 3GPP (Third Generation Partnership Project), in a wireless communication system corresponding to LTE (Long Term Evolution) currently being developed, when a handover of a wireless terminal (UE) occurs, a handover source base station (Source-eNB) ) And a handover destination base station (Target-eNB) and a wireless terminal exist during which communication is not possible. For this reason, the handover source base station transfers packets that could not be transmitted to the wireless terminal to the handover destination base station. The handover destination base station transmits the transferred packet to the wireless terminal. Even when the wireless terminal performs VoIP communication, packet transfer is performed in the same manner, and packet loss at the wireless terminal is prevented.

JP 2008-14266 A

  However, as described above, even when a handover occurs while the wireless terminal is performing VoIP communication, a time zone during which the packet does not arrive at the wireless terminal even if the packet is transferred between base stations (reception interruption) Time zone) occurs. This is because during a handover, there is a period during which the wireless terminal cannot communicate with both the handover source base station and the handover destination base station, or it takes time for the packet transfer preparation and transfer itself. This is because the delay time until arrival at the wireless terminal becomes long. When the reception interruption time zone occurs in the wireless terminal, all the packets in the jitter buffer are reproduced, causing interruption of packet reproduction (sound interruption in VoIP communication).

  In particular, in LTE, the base station is designed to transmit a packet to a wireless terminal every 20 [msec] by scheduling, so that the jitter buffer capacity in the wireless terminal is designed to be small. For this reason, it is expected that the reception interruption time zone is vulnerable.

  In view of the above problems, an object of the present invention is to provide a wireless communication system, a wireless base station, a wireless terminal, and a communication control method that can prevent interruption of packet reproduction.

  In order to solve the above-described problems, the present invention has the following features. The first feature of the present invention is that a packet is transferred from a handover source base station (S-eNB), which is a handover source, to a handover destination base station (T-eNB), which is a handover destination, when a radio terminal (UE 60) is handed over. In the wireless communication system (wireless communication system 1), the handover source base station is a time during which the wireless terminal cannot receive a packet from either the handover source base station or the handover destination base station in the handover. A transmission unit (handover destination information providing unit 128) that transmits information on one communication interruption time, and the wireless terminal receives a reception unit (handover information acquisition unit 264) that receives information on the first communication interruption time; Before the first communication interruption time arrives, the packet in the buffer in its own terminal A reproduction control unit (reproduction rate calculation unit) that controls the reproduction rate of the packets in the buffer according to the accumulation amount and the predicted communication interruption time that is a communication interruption time predicted based on the first communication interruption time 273, jitter buffer control unit 274).

  In such a wireless communication system, the handover source base station transmits information on the first communication interruption time, which is a time during which the wireless terminal cannot receive packets from both the handover source base station and the handover destination base station. On the other hand, before the first communication interruption time arrives, the wireless terminal responds to the accumulated amount of packets in the buffer in its own terminal and the predicted communication interruption time predicted based on the first communication interruption time. Thus, the packet reproduction is prevented from being interrupted by controlling the reproduction speed of the packet in the buffer.

  The second feature of the present invention relates to a second communication interruption time in which the wireless terminal cannot receive a packet from either the handover source base station or the handover destination base station in the handover. A holding unit (handover preparation time storage unit 214) that holds information, and the reproduction control unit determines the larger of the first communication interruption time and the second communication interruption time as the predicted communication interruption time. It is a summary.

  The third feature of the present invention is that the first communication interruption time includes a packet transfer delay time between the handover source base station and the handover destination base station, and a transfer preparation time required for transfer preparation. The gist is the added time.

  According to a fourth aspect of the present invention, the transmission unit transmits information on the first communication interruption time corresponding to the handover destination base station, and the reproduction control unit corresponds to the handover destination base station. The gist is to control the reproduction rate of the packet in the buffer according to the predicted communication interruption time predicted based on the first communication interruption time.

  According to a fifth feature of the present invention, the transmission unit transmits information on the first communication interruption time corresponding to a plurality of base stations that are handover destination candidates, and the reproduction control unit includes the plurality of base stations. The gist is to control the reproduction rate of the packets in the buffer according to the predicted communication interruption time predicted based on the average value of the first communication interruption times corresponding to the stations.

  A sixth feature of the present invention is summarized in that the reproduction control unit weights the first communication interruption time according to a radio state between the corresponding base station.

  A seventh feature of the present invention is that the transmission unit is a time before the first communication interruption time, wherein the wireless terminal can receive a packet only from the handover source base station in the handover. Transmits information on preparation time, the receiving unit receives information on the handover preparation time, and the reproduction control unit determines a reproduction rate of the packet in the buffer at a predetermined standard in the handover preparation time. The gist is to lower the playback speed than the above.

  According to an eighth feature of the present invention, the reproduction control unit is configured so that the accumulated amount of packets in the buffer becomes a predetermined first predetermined value at the end of the predicted communication interruption time. The gist of this is to control the playback speed of the packets inside.

  According to a ninth feature of the present invention, the reproduction control unit, based on the packet reception speed from the handover destination base station and the accumulated amount of packets in the buffer, after the predicted communication interruption time has elapsed, The gist is to control the reproduction speed of the packet in the buffer.

  A tenth feature of the present invention is a radio base station that receives a packet from another radio base station that is a handover source at the time of handover of the radio terminal, and in which the radio terminal The gist of the present invention is to include a transmitter that transmits information related to a first communication interruption time, which is a time during which packets cannot be received from the own radio base station and the other radio base station.

  An eleventh feature of the present invention is a wireless terminal that switches a connection destination from a handover source base station that is a handover source to a handover destination base station that is a handover destination at the time of handover, and is transmitted by the handover source base station, A receiving unit that receives information about a first communication interruption time, which is a time during which a terminal cannot receive a packet from either the handover source base station or the handover destination base station in a handover; and the first communication interruption time Before arrival, according to the accumulated amount of packets in the buffer in its own terminal and the predicted communication interruption time that is the communication interruption time predicted based on the first communication interruption time, The gist of the present invention is to provide a playback control unit that controls the playback speed.

  A twelfth feature of the present invention is a communication control method in a radio base station that receives a packet from another radio base station that is a handover source at the time of handover of a radio terminal. The gist of the invention is that the wireless terminal includes a step of transmitting information related to a first communication interruption time which is a time during which a packet cannot be received from the own wireless base station and the other wireless base station.

  A thirteenth feature of the present invention is a communication control method in a radio terminal in which a connection destination is switched from a handover source base station that is a handover source to a handover destination base station that is a handover destination at the time of handover, and transmitted by the handover source base station Receiving the information on the first communication interruption time, which is a time during which the terminal itself cannot receive a packet from either the handover source base station or the handover destination base station in the handover, and the first communication Depending on the accumulated amount of packets in the buffer in its own terminal and the predicted communication interruption time that is predicted based on the first communication interruption time before the interruption time arrives, And a step of controlling the reproduction speed of the packet.

  According to the present invention, interruption of packet reproduction in a wireless terminal can be prevented.

1 is an overall schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. It is a sequence diagram which shows operation | movement of the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows the structure of the LTE base station which concerns on embodiment of this invention. It is a flowchart which shows operation | movement when the LTE base station which concerns on embodiment of this invention becomes a handover origin. It is a flowchart which shows operation | movement when the LTE base station which concerns on embodiment of this invention becomes a hand-over destination. It is a figure which shows the structure of the radio | wireless terminal which concerns on embodiment of this invention. It is a figure which shows the structure of the softphone in the radio | wireless terminal which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the wireless-communications function part in the wireless terminal which concerns on embodiment of this invention. It is a flowchart which shows 1st operation | movement of the softphone in the radio | wireless terminal which concerns on embodiment of this invention. It is a flowchart which shows the 2nd operation | movement of the softphone in the radio | wireless terminal which concerns on embodiment of this invention. It is a figure which shows the time transition of the sequence number of the received packet in the radio | wireless terminal which concerns on embodiment of this invention, the number of received packets of unit time, a reproduction speed, and the packet accumulation amount in a buffer.

  Next, an embodiment of the present invention will be described with reference to the drawings. Specifically, (1) schematic configuration and operation of wireless communication system, (2) configuration and operation of LTE base station, (3) configuration and operation of wireless terminal, (4) action and effect, (5) other Embodiments will be described. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Schematic Configuration and Operation of Radio Communication System (1.1) Schematic Configuration of Radio Communication System FIG. 1 is an overall schematic configuration diagram of a radio communication system. The wireless communication system 1 shown in FIG. 1 is configured by adopting LTE technology in a wireless section. The radio communication system 1 illustrated in FIG. 1 includes an LTE base station 10-1 (eNB) and an LTE base station 10-2 (hereinafter referred to as “LTE base station 10” when they are not distinguished from each other). S-GW (Serving Gateway) 20-1 and S-GW 20-2 (hereinafter referred to as “S-GW 20” where appropriate) and P-GW (PDN Gateway) 30 MME (Mobile Management Entity) 40-1 and MME 40-2 (hereinafter referred to as “MME 40” where appropriate), an upper network IMS (IP Multimedia Subsystem) 50, and a wireless terminal (UE) 60 and the communication apparatus (CN) 70 are comprised.

  UE60 communicates with the communication apparatus 70 via eNB10, S-GW20, P-GW30, and IMS50. In LTE, VoIP (Voice over Internet Protocol) is adopted for voice communication between the UE 60 and the communication device 70. The radio terminal 60 performs handover for switching the connection destination eNB 10 as it moves.

  In handover, there are the following two methods for exchanging control messages between the eNBs 10. In the first technique, control messages are directly exchanged between the eNBs 10 via the X2 interface between the eNBs 10. The handover in this case is referred to as X2 handover. In the second method, control messages are exchanged between the eNBs 10 via the S1 interface via the S-GW 20 and the P-GW 30. The handover in this case is referred to as S1 handover.

  In handover, the handover source eNB (S (Source) -eNB) 10 arrives at the S-eNB 10 and transmits a packet that has not been transmitted to the UE 60 to the handover destination eNB (T (Target) -eNB). Forward to 10. The T-eNB 10 transmits the received packet to the UE 60. The following two methods exist as the transfer method. In the first technique, packets are directly exchanged between the eNBs 10 via the X2 interface between the eNBs 10. This transfer method is called direct transfer. In the second method, packets are exchanged between the eNBs 10 via the S1 interface via the S-GW 20 and the P-GW 30. This transfer method is called indirect transfer. Note that in indirect transfer, the P-GW 20 that is passed through may or may not change.

(1.2) Operation of Radio Communication System FIG. 2 is a sequence diagram showing message exchange during handover. FIG. 2 is an example when the eNB 10-1 is a handover source (S-eNB) and the eNB 10-2 is a handover destination (T-eNB).

  In step S1, when the connection between the S-eNB 10-1 and the UE 60 is established, in step S2, the S-eNB 10-1 sends an information (handover destination candidate information) message indicating an eNB that is a handover destination candidate to the UE 60. Send. The UE 60 receives the handover destination candidate information message.

  Thereafter, in step S3, the UE 60 transmits a Measurement Reports message including the communication quality with the S-eNB 10-1 and the communication quality with the handover destination candidate eNB to the S-eNB 10-1. The S-eNB 10-1 receives the Measurement Reports message.

  In step S4, the S-eNB 10-1 determines a handover destination (here, the T-eNB 10-2) of the UE 60 based on the Measurement Reports message. In step S5, the S-eNB 10-1 transmits an information (handover destination information) message indicating the T-eNB 10-2 to the UE 60. The UE 60 receives the handover destination information message.

  In step S <b> 6, the S-eNB 10-1 requires Handover Required to request a handover from the MME 40-1 and the MME 40-2 to the MME (S (Source) -MME) 40-1 that performs control related to the UE 60 before the handover. Send a message. The Handover Required message includes a cell ID that is identification information of the T-eNB 10-2 that is the handover destination. The S-MME 40-1 receives the Handover Required message.

  In step S7, the S-MME 40-1 transmits a Forward Relocation Request message for requesting a packet transfer change to the MME (T (Target) -MME) 40-2 that performs control related to the UE 60 after the handover. The T-MME 40-2 receives the Forward Relocation Request message.

  In step S8, the T-MME 40-2 transmits a Create Bearer Request message for requesting generation of a bearer to the T-SGW 20-2. The T-SGW 20-2 receives the Create Bearer Request message.

  In step S9, the T-SGW 20-2 transmits a Create Bearer Response message indicating that a bearer has been generated to the T-MME 40-2. The T-MME 40-2 receives the Create Bearer Response message.

  In step S10, the T-MME 40-2 transmits a Handover Request message for requesting a handover to the T-eNB 10-2. The T-eNB 10-2 receives the Handover Request message.

  In step S11, the T-eNB 10-2 transmits a Handover Request Acknowledge message indicating acceptance of the handover to the T-MME 40-2. The T-MME 40-2 receives the Handover Request Acknowledge message.

  In step S12, the T-MME 40-2 requests Create of a bearer from the SGW 20-1 and the SGW 20-2 to the SGW (T (Target) -SGW) 20-2 that performs control related to the UE 60 after the handover. Send a Bearer Request message. The T-SGW 20-2 receives the Create Bearer Request message.

  In step S13, the T-SGW 20-2 transmits a Create Bearer Response message indicating that a bearer has been generated to the T-MME 40-2. The T-MME 40-2 receives the Create Bearer Response message.

  In step S14, the T-MME 40-2 transmits a Forward Relocation Response message that is a response to the Forward Relocation Request message to the S-MME 40-1. The S-MME 40-1 receives the Forward Relocation Response message.

  In step S15, the S-MME 40-1 requests the generation of a bearer from the SGW 20-1 and the SGW 20-2 to the SGW (S (Source) -SGW) 20-1 that performs control related to the UE 60 before the handover. Send Create Bearer Request message. The T-SGW 20-1 receives the Create Bearer Request message.

  In step S16, the T-SGW 20-1 transmits a Create Bearer Response message indicating that a bearer has been generated to the S-MME 40-1. The S-MME 40-1 receives the Create Bearer Response message.

  In step S17, the S-MME 40-1 transmits a Handover Command message to the S-eNB 10-1. The Handover Command message includes a cell ID that is identification information of the T-eNB 10-2 that is the handover destination. The S-eNB 10-1 receives the Handover Command message.

  The time from when the S-eNB 10-1 transmits the Handover Required message in step S6 to the reception of the Handover Command message in step S17 is a time during which a packet can be received only from the S-eNB 10-1, This is the time required for preparation (handover preparation time).

  In step S18, the S-eNB 10-1 transmits a Handover Command message to the UE 60. The UE 60 receives the Handover Command message. At this time, the connection between the UE 60 and the S-eNB 10-1 ends.

  In step S19, the S-eNB 10-1 transmits an eNB Status Transfer message indicating a packet transmitted from the S-eNB 10-1 to the UE 60 to the S-MME 40-1. The S-MME 40-1 receives the eNB Status Transfer message.

  In step S20, the S-MME 40-1 transmits a Forward SRNS Context message to the T-MME 40-2. The T-MME 40-2 receives the Forward SRNS Context message.

  In step S21, the T-MME 40-2 transmits a Forward SRNS Context Ack message to the S-MME 40-1. The S-MME 40-1 receives the Forward SRNS Context Ack message.

  In step S22, the T-MME 40-2 transmits an eNB Status Transfer message to the T-eNB 10-2. The T-eNB 10-2 receives the eNB Status Transfer message.

  Thereafter, in the case of X2 handover, in step S23, the S-eNB 10-1 arrives at the S-eNB 10 and transmits a packet that has not been transmitted to the UE 60 to the T-eNB 10-2 via the X2 interface. Direct forwarding of data. The T-eNB 10 receives the packet.

  On the other hand, in the case of the S1 handover, in step S24, the S-eNB 10-1 arrives at the S-eNB 10 and transmits a packet that has not been transmitted to the UE 60 to the T-eNB 10-2 via the S1 interface. Indirect forwarding of data. The packet is transferred to the T-eNB 10-2 via the S-SGW 20-1 and the T-SGW 20-2. The T-eNB 10 receives the packet.

  In step S25, the UE 60 transmits a Handover Confirm message indicating that the handover has been established to the T-eNB 10-2. The T-eNB 10-2 receives the Handover Confirm message. At this time, the connection between the UE 60 and the T-eNB 10-2 is started.

  The time from when the S-eNB 10-1 transmits the Handover Command message to the UE 60 at step S18 until the T-eNB 10-2 receives the packet at step S23 or step S24 is in preparation for packet transfer. It is the time (first communication interruption time) obtained by adding the time required (transfer preparation time) and the transfer delay time of the packet between the S-eNB 10-1 and the T-eNB 10-2.

  The time from when the UE 60 receives the Handover Command message at Step S18 to when the Handover Confirm message is transmitted to the T-eNB 10-2 at Step S25 is the time when the connection is interrupted at the UE 60 (second communication interruption time). ).

  In step S <b> 26, the T-eNB 10-2 transmits a downlink packet (Downlink Data) to the UE 60. The UE 60 receives a downlink packet. In step S27, the UE 60 transmits an uplink packet (Uplink User Plane data) to the T-eNB 10-2. The uplink packet is sent to the PGW 30 via the T-eNB 10-2 and the T-SGW 20-2.

  In step S28, the S-eNB 10-1 transmits a Handover Notify message to the S-MME 40-1. The S-MME 40-1 receives the Handover Notify message.

  In step S29, the S-MME 40-1 transmits a Forward Relocation Complete Notification message indicating that the packet transfer change has been completed to the T-eNB 10-2. The T-eNB 10-2 receives the Forward Relocation Complete Notification message.

  In step S30, the T-eNB 10-2 transmits a Forward Relocation Complete Acknowledge that is a response to the Forward Relocation Complete Notification message to the S-MME 40-1. The S-MME 40-1 receives the Forward Relocation Complete Acknowledge message.

  In step S31, the S-MME 40-2 transmits a Modify Bearer Request message for requesting correction of a bearer to the S-SGW 20-1. The S-SGW 20-1 receives the Modify Bearer Request message.

  In step S <b> 32, the S-SGW 20-1 transmits a Modify Bearer Request message to the PGW 30. The PGW 30 receives the Modify Bearer Request message.

  In step S33, the PGW 30 transmits a Modify Bearer Response message indicating that the bearer has been modified to the S-SGW 20-1. The S-SGW 20-1 receives the Modify Bearer Response message.

  In step S34, the S-SGW 20-1 transmits a Modify Bearer Response message to the S-MME 40-1. The S-MME 40-1 receives the Modify Bearer Response message.

  Thereafter, in step S35, the T-SGW 20-2 transmits a downlink packet (Downlink User Plane data) to the T-eNB 10-2 via the S-SGW 20-1. The T-eNB 10-2 receives a downlink packet.

  In step S <b> 36, the T-eNB 10-2 transmits a downlink packet and a transfer end notification message indicating that the packet transfer has ended to the UE 60. The UE 60 receives the downlink packet and the transfer end notification message.

(2) Configuration and operation of LTE base station (2.1) Configuration of LTE base station FIG. 3 is a diagram illustrating a configuration of the eNB 10-1. The eNB 10-2 has a similar configuration. The eNB 10-1 illustrated in FIG. 3 includes an eNB communication processing unit 102 that performs communication processing with other eNBs (other cells), an MME communication processing unit 104 that performs communication processing with the MME 40, and an SGW 30. Communication processing unit 106 for performing communication processing with UE, communication processing unit 108 for performing communication processing with UE 60, UE connection control unit 110 for controlling connection of UE 60, and communication of user data A user data control unit 112 that performs control is included.

  In addition, the eNB 10-1 includes an NRT management unit 122, a transfer delay time acquisition unit 124, a handover candidate information acquisition unit 126, a handover destination information provision unit 128, and a call data path monitoring unit 130. Among these, the UE connection control unit 110 and the handover destination information providing unit 128 constitute a UE connection control function unit, the user data control unit 112 and the call data route monitoring unit 130 constitute a user data processing function unit, The NRT management unit 122, the transfer delay time acquisition unit 124, and the handover candidate information acquisition unit 126 constitute an automatic adjacency related function unit. The UE connection control function unit, the user data processing function unit, and the automatic adjacency related function unit are configured by a CPU and a memory.

  The NRT management unit 122 manages a Neighbor Relation Table (NRT). The NRT includes, for each other eNB (other cell), as information related to the other eNB, a cell ID, information about availability of Neighbor Relation at the time of handover, and information about availability of the X2 interface.

  Further, in the present embodiment, the NRT includes information on the packet transfer delay time between the own eNB (own cell) and the other eNB and the time required for preparation for packet transfer for each other eNB. Information on transfer preparation time and information on handover preparation time, which is time required for preparation for handover, are included.

  The transfer delay time acquisition unit 124 has information on transfer delay times corresponding to each of the S1 interface and the X2 interface. The transfer delay time acquisition unit 124 corresponds to the X2 interface if the X2 interface is usable with the other eNB based on the information on the availability of the X2 interface corresponding to the other eNB in the NRT. The transfer delay time information is output to the NRT management unit 122. If the X2 interface cannot be used with the other eNB, the transfer delay time information corresponding to the S1 interface is output to the NRT management unit 122. Thereby, the NRT management part 122 can acquire the transfer delay time information corresponding to another eNB, and can add it to NRT.

  Note that the transfer delay time acquisition unit 124 can use the X2 interface with another eNB, and the eNB communication processing unit 102 can transmit a ping command to the other eNB. For example, a transmission round-trip time that is a time from when the ping command is transmitted until a response is received may be measured, and ½ of the measured time may be used as a transfer delay time corresponding to the X2 interface.

  In addition, when the X2 interface cannot be used with another eNB, the transfer delay time acquisition unit 124 uses the call data path at the time of handover in which the own eNB is the handover destination and the other eNB is the handover destination. Sequence numbers and reception of packets transferred from the other eNB to the own eNB and packets transmitted on the new route after the handover (route not passing through the other eNB of the handover source) acquired from the monitoring unit 130 The transfer delay time corresponding to the S1 interface may be predicted from the time obtained and the difference in the reception timing of these two types of packets.

  The handover candidate information acquisition unit 126 acquires information on other eNBs that are the handover source and the handover destination of the UE 60 in the past from the UE connection control unit 110. When the acquired information on the other eNB is not registered in the NRT, the handover candidate information acquisition unit 126 outputs the information on the other eNB to the NRT management unit 122. The NRT management unit 122 adds the input information of the other eNB to the NRT.

  In addition, when the own eNB is a handover source, the UE connection control unit 110 transmits a Handover Required message, and further transmits a Handover Command message, the handover candidate information acquisition unit 126 receives a Handover from the UE connection control unit 110. Receive notification of required message transmission and handover command message transmission. The handover candidate information acquisition unit 126 measures the time from the notification of transmission of the Handover Required message to the notification of transmission of the Handover Command message, and uses the measured time as the handover preparation time corresponding to the other eNB of the handover destination. To do. Further, the handover candidate information acquisition unit 126 outputs information on other eNBs to be handed over and information on handover preparation time to the NRT management unit 122. Thereby, the NRT management unit 122 can acquire the handover preparation time information and add it to the NRT.

  In addition, when the own eNB is a handover source, the UE connection control unit 110 transmits a Handover Command message, and when the packet transfer is further started, the handover candidate information acquisition unit 126 receives a handover from the UE connection control unit 110. Receives a command message transmission notification and packet transfer notification. The handover candidate information acquisition unit 126 measures the time from the notification of the Handover Command message transmission to the notification of the packet transfer, and sets the measurement time as the transfer preparation time corresponding to the other eNB of the handover destination. Furthermore, the handover candidate information acquisition unit 126 outputs information of other eNBs to be handed over and transfer preparation time information to the NRT management unit 122. Thereby, the NRT management part 122 can acquire transfer preparation time information, and can add it to NRT. In addition, when the transfer preparation time information corresponding to the other eNB of the handover destination is already included in the NRT, the NRT management unit 122 weights the plurality of transfer preparation time information corresponding to the other eNB of the handover destination. An average is calculated, and the calculated value is used as transfer preparation time information.

  After the handover preparation time information, transfer preparation time information, and transfer delay time information are added to the NRT by the above-described processing, the following processing is performed.

  When the UE 60 is connected, the UE connection control unit 110 outputs a notification indicating that the UE 60 is connected to the handover destination information providing unit 128. The handover destination information providing unit 128 associates the cell ID, the transfer preparation time information, and the transfer delay time information among the information of each other eNB included in the NRT, and serves as a handover destination candidate information message to the UE communication processing unit. It transmits to UE60 via 108.

  Furthermore, the UE connection control unit 110 determines the handover destination of the UE 60 based on the Measurement Reports message from the UE 60. Furthermore, the UE connection control unit 110 outputs the cell ID of another eNB that is a handover destination to the handover destination information providing unit 128.

  When the cell ID is input, the handover destination information providing unit 128 specifies the information of another eNB including the same cell ID as the input cell ID among the information of each other eNB included in the NRT. Further, the handover destination information providing unit 128 uses the input cell ID and the handover preparation time information, the transfer delay time information, and the handover preparation time information included in the specified other eNB information as a handover destination information message. It transmits to UE60 via UE communication processing part 108.

  If there is no information on other eNBs including the same cell ID as the input cell ID among the information on each other eNB included in the NRT, X2 is exchanged with other eNBs at the handover destination. If the handover is possible, the handover destination information providing unit 128 transfers the average value of the handover preparation time information in the information of the other eNBs capable of X2 handover among the information of the other eNBs included in the NRT, the transfer The average value of the delay time information and the average value of the handover preparation time information are included in the handover destination information message. Also, if X2 handover is not possible with another eNB to be handed over, the handover destination information providing unit 128 of other eNBs included in the NRT, of other eNBs that are not capable of X2 handover The average value of the handover preparation time information, the average value of the transfer delay time information, and the average value of the handover preparation time information in the information are included in the handover destination information message.

  On the other hand, when the own eNB is a handover destination and the SGW 30 is not changed by the handover, the UE connection control unit 110 transmits a packet (transfer) from the other eNB to the handover destination own eNB from the SGW 30 The end marker message indicating that the transmission of the packet) has ended is received. In this case, the UE connection control unit 110 outputs a notification indicating that the end marker message has been received to the handover destination information providing unit 128. When receiving the notification indicating that the end marker message has been received, the handover destination information providing unit 128 outputs a notification to that effect when transmission of the transfer packet to the UE 60 is completed to the call data path monitoring unit 130. To request.

  Further, when the own eNB is the handover destination and the SGW 30 is changed by the handover, the handover destination information providing unit 128 notifies the call data path monitoring unit 130 of the completion of reception of the transfer packet. Is requested to be output.

  When the call data path monitoring unit 130 receives a request for outputting a notification that the reception of the transfer packet from the handover destination information providing unit 128 is completed, the call data route monitoring unit 130 passes the user data control unit 112 (a packet to be transmitted to the UE 60). ) And the sequence number of the packet are monitored.

  Here, the route through which the packet to be transmitted to the UE 60 has passed is the route from the other eNB of the handover source to the eNB of the handover destination, and the new route after the handover (not via the other eNB of the handover source) Route). The call data path monitoring unit 130 includes the initial sequence number of a packet that has passed through a new path after handover, and the sequence of the latest packet that has passed through the path from the other eNB of the handover source to the eNB of the handover destination. When the difference is less than or equal to 1, a notification that the reception of the transfer packet is completed is output to the handover destination information providing unit 128.

  When the handover destination information providing unit 128 receives the notification that the reception of the transfer packet is completed, the handover destination information providing unit 128 outputs a notification to that effect to the call data path monitoring unit 130 when the transmission of the transfer packet to the UE 60 is completed. To request.

  When the call data path monitoring unit 130 receives a request for output indicating that the transmission of the transfer packet to the UE 60 is completed, the call data path monitoring unit 130 monitors the transfer packet passing through the user data control unit 112 and transmits all the transfer packets to the UE 60. At that time, a notification that the transmission of the transfer packet to the UE 60 is completed is output to the handover destination information providing unit 128.

  When the handover destination information providing unit 128 receives a notification that transmission of the transfer packet to the UE 60 has ended, the handover destination information providing unit 128 sends a transfer end notification message indicating that transmission of the transfer packet to the UE 60 has ended to the UE communication processing unit 106. To the UE 60.

(2.2) Operation of LTE Base Station FIG. 4 is a flowchart showing an operation when the eNB 10-1 is a handover source.

  In step S101, the eNB 10-1 connects the UE 60. In step S102, the eNB 10-1 transmits a handover destination candidate information message to the UE 60.

  Thereafter, in step S103, the eNB 10-1 receives the Measurement Reports message from the UE 60. In step S104, the eNB 10-1 determines another eNB that is the handover destination of the UE 60 based on the Measurement Reports message. In step S <b> 105, the S-eNB 10-1 transmits a handover destination information message to the UE 60.

  In step S106, the eNB 10-1 transmits a Handover Required message to another eNB that is a handover destination. Thereafter, in step S107, the eNB 10-1 determines whether or not a Handover Command message has been received from another eNB serving as a handover destination. When the Handover Command message is received, the eNB 10-1 transmits the Handover Command message to the UE 60 in Step S108. In step S109, the eNB 10-1 disconnects communication with the UE 60.

  FIG. 5 is a flowchart illustrating an operation when the eNB 10-1 is a handover destination.

  In step S151, the eNB 10-1 transmits a packet (transfer packet) from the other eNB of the handover source to the UE 60. In step S152, the eNB 10-1 determines whether or not the SGW 30 has been changed by the handover.

  When SGW30 is changed, in step S153, eNB10-1 monitors the completion | finish of reception of the transfer packet from other eNB of a handover origin. Furthermore, in step S154, the eNB 10-1 determines whether or not reception of the transfer packet has ended.

  On the other hand, when SGW30 is not changed, in step S155, eNB10-1 determines whether the end marker message from SGW30 was received.

  If it is determined in step S154 that reception of the transfer packet has ended, or if it is determined in step S155 that the end marker message has been received, in step S156, the eNB 10-1 has finished transmitting the transfer packet to the UE 60 It is determined whether or not. When the transmission of the transfer packet to the UE 60 ends, the eNB 10-1 transmits a transfer end notification message to the UE 60 in step S157.

(3) Configuration and operation of radio terminal (3.1) Configuration of radio terminal FIG. 6 is a diagram illustrating a configuration of the UE 60. 6 includes a control message communication unit 202, a data communication unit 204, a radio information acquisition unit 206, a handover control unit 212, a handover preparation time storage unit 214, a handover destination information acquisition unit 216, and a soft phone 250. Among these, the control message communication unit 202, the data communication unit 204, the radio information acquisition unit 206, the handover control unit 212, the handover preparation time storage unit 214, and the handover destination information acquisition unit 216 constitute a radio communication function unit. The wireless communication function unit includes a CPU and a memory. The soft phone 250 is realized by the CPU executing a predetermined program.

  The data communication unit 204 communicates packets including user data with the S-eNB 10-1. Further, the data communication unit 204 performs communication of packets including user data with the softphone.

  In the handover preparation time storage unit 214, in the past handover, the handover control unit 212 receives the Handover Command message from the S-eNB 10-1 via the control message communication unit 202, and receives the Handover Command message via the control message communication unit 202. -When Handover Confirm message is transmitted to eNB10-2, the information of the connection interruption time (2nd communication interruption time) which is the time from reception of Handover Command message to transmission of Handover Confirm message is memorized. Further, the handover preparation time storage unit 214 stores the cell ID of the T-eNB 10-2 included in the Handover Command message in association with the second communication interruption time information, and is acquired by the radio information acquisition unit 206. -The information of the reception intensity | strength of the electromagnetic wave from the said T-eNB10-2 which is a radio | wireless state between eNB10-2 is memorize | stored.

  As described above, after the second communication interruption time information, the cell ID, and the reception strength information are stored in the handover preparation time storage unit 214 in the past handover, the UE 60 performs the following processing.

  After connecting to the S-eNB 10-1, the handover destination information acquisition unit 216 receives the handover destination candidate information message from the S-eNB 10-1 via the control message communication unit 202. Further, the handover destination information acquisition unit 216 includes information on the first communication interruption time that is a value obtained by adding the transfer preparation time and the transfer delay time included in the handover destination candidate information message, and the handover included in the handover destination candidate information message. The cell ID of the previous candidate (here, eNB 10-2) is associated and stored in the handover preparation time storage unit 214.

  Furthermore, the radio information acquisition unit 206 starts monitoring the reception intensity of radio waves from the surrounding eNB that is in a radio state with the surrounding eNB, and receives the reception intensity information from time to time as information on the reception intensity. And stored in the handover preparation time storage unit 214 in association with the cell ID of the eNB corresponding to.

  When handover occurs after receiving the handover destination candidate information message, the handover destination information acquisition unit 216 receives the handover destination information message from the S-eNB 10-1 via the control message communication unit 202. Furthermore, the handover destination information acquisition unit 216 stores the handover preparation time information included in the handover destination information message in the handover preparation time storage unit 214 in association with the cell ID of the T-eNB 10-2.

  The UE 60 performs the following first process before receiving the Handover Command message from the S-eNB 10-1, and after receiving the Handover Command message from the S-eNB 10-1, Perform the process.

(First process)
The handover destination information acquisition unit 216 determines whether or not the radio state with the S-eNB 10-1 has deteriorated. Specifically, the handover destination information acquisition unit 216 obtains the latest reception strength information associated with the cell ID of the S-eNB 10-1 among the reception strength information stored in the handover preparation time storage unit 214. When the reception intensity indicated by the read and reception intensity information is less than a predetermined first threshold, it is determined that the radio state with the S-eNB 10-1 has deteriorated.

  When the radio state with the S-eNB 10-1 deteriorates, the handover destination information acquisition unit 216 includes the cell ID of the handover destination candidate among the first communication interruption time information stored in the handover preparation time storage unit 214. The first communication interruption time information and a plurality of reception intensity information corresponding to are read out. The handover destination information acquisition unit 216 weights the read first communication interruption time according to the average value of the reception strengths indicated by the read plurality of reception strength information. Specifically, in consideration of the fact that the communication interruption time tends to increase as the reception strength indicated by the reception strength information decreases, the handover destination information acquisition unit 216 receives the reception strength indicated by the plurality of read reception strength information. The weighting is performed so that the first communication interruption time becomes longer as the average value of becomes smaller. The handover destination information acquisition unit 216 stores the weighted first communication interruption time information (hereinafter, first predicted communication interruption time information) in the handover preparation time storage unit 214 in association with the cell ID of the handover destination candidate. Further, the handover destination information acquisition unit 216 includes the first predicted communication interruption time information for the softphone 250, and information indicating that the radio state with the S-eNB 10-1 has deteriorated (radio state deterioration information) Is output.

  After the deterioration of the radio state with the S-eNB 10-1 is notified, the handover destination information acquisition unit 216 determines whether or not the radio state with the S-eNB 10-1 has been recovered. Specifically, the handover destination information acquisition unit 216 obtains the latest reception strength information associated with the cell ID of the S-eNB 10-1 among the reception strength information stored in the handover preparation time storage unit 214. When the reception strength indicated by the read-out reception strength information is equal to or greater than a predetermined second threshold, it is determined that the radio state with the S-eNB 10-1 has been recovered. Here, the second threshold value is larger than the first threshold value.

  When the radio state with the S-eNB 10-1 is recovered, the handover destination information acquisition unit 216 informs the softphone 250 that the radio state with the S-eNB 10-1 has been recovered (wireless Status recovery information) is output.

(Second process)
When receiving the Handover Command message from the S-eNB 10-1 via the control message communication unit 202, the handover control unit 212 ends the connection with the S-eNB 10-1 according to the Handover Command message. Thereby, UE60 will be in the state of the communication interruption which cannot communicate the packet containing user data with any of S-eNB10-1 and T-eNB10-2. Next, the handover control unit 212 outputs a communication interruption start notification indicating that communication interruption has started to the softphone 250.

  In addition, when the handover control unit 212 receives the Handover Command message, the T-eNB 10 that is the handover destination included in the Handover Command message among the first predicted communication interruption time information stored in the handover preparation time storage unit 214. The first predicted communication interruption time information associated with the cell ID of -2. Further, the handover control unit 212 includes the second communication associated with the cell ID of the T-eNB 10-2 included in the Handover Command message among the second communication interruption time information stored in the handover preparation time storage unit 214. Read interruption time information. Furthermore, the handover control unit 212 sets the larger one of the read first predicted communication interruption time and second communication interruption time as the second predicted communication interruption time.

  The handover control unit 212 reads out handover preparation time information associated with the cell ID of the T-eNB 10-2 included in the Handover Command message from among the handover preparation time information stored in the handover preparation time storage unit 214. Furthermore, the handover control unit 212 outputs handover determination information including information on the second predicted communication interruption time and the read handover preparation time information to the softphone 250.

  Thereafter, the handover control unit 212 transmits a Handover Confirm message to the T-eNB 10-2 via the control message communication unit 202. Next, the handover control unit 212 is connected to the T-eNB 10-2 and starts communication of a packet including user data with the T-eNB 10-2. At this time, the handover control unit 212 outputs a communication interruption end notification indicating that the communication interruption has ended to the softphone 250.

  Further, when the handover control unit 212 receives the transfer completion notification message from the T-eNB 10-2 via the control message communication unit 202, the handover control unit 212 outputs the transfer completion notification message to the softphone 250.

  FIG. 7 is a diagram illustrating a configuration of the softphone 250. 7 includes a button input unit 252, a screen display unit 254, a microphone 256, an encoder 258, a packet transmission unit 260, a packet reception unit 262, a handover information acquisition unit 264, an overall control unit 266, and a SIP control unit 268. A jitter buffer 270, a jitter buffer monitoring unit 272, a jitter buffer control unit 274, a decoder 276, and a speaker 278.

  The overall control unit 266 acquires user operation information from the button input unit 252 and the screen display unit 254, and controls the entire softphone 250 according to the operation information. The SIP control unit 268 performs SIP procedures at the start and end of a call. The encoder 258 encodes the audio data acquired from the microphone 256 and inserts it into the payload portion of the packet (RTP packet). Furthermore, the encoder 258 outputs the packet to the data communication unit 204 via the packet transmission unit 260.

  The jitter buffer 270 acquires and stores a packet (RTP packet) from the data communication unit 204 via the packet receiving unit 262. The decoder 276 reads the RTP packet stored in the jitter buffer 270. Further, the decoder 276 decodes the payload portion of the read RTP packet and causes the speaker 278 to output reproduced sound.

  The jitter buffer monitoring unit 272 monitors the current packet amount (current packet accumulation amount) stored in the jitter buffer 270. Further, the jitter buffer monitoring unit 272 outputs information on the current packet accumulation amount as a monitoring result to the jitter buffer control unit 274 and the reproduction speed calculation unit 273 at a predetermined time interval (for example, 20 [msec] interval).

  The playback speed calculation unit 273 calculates the playback speed. Specifically, when the playback speed calculation unit 273 receives the wireless state deterioration information via the handover information acquisition unit 264, in other words, the wireless state with the S-eNB 10-1 has deteriorated. In the case, the following third process is performed. In addition, when the playback speed calculation unit 273 receives the handover determination information via the handover information acquisition unit 264, the playback speed calculation unit 273 performs the following fourth process.

(Third process)
When receiving the wireless state deterioration information, the playback speed calculation unit 273 sets a playback speed lower than the standard playback speed. Further, the playback speed calculation unit 273 outputs low playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs low-speed reproduction by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed according to the acquired low-speed reproduction speed information. The low playback speed is preferably 90% or more of the standard playback speed, and the high speed playback speed described below is preferably 110% or less of the standard playback speed at the maximum.

  When the low speed reproduction is being executed, the reproduction speed calculation unit 273 has received the current packet accumulation amount in advance until the reproduction speed calculation unit 273 receives the wireless state recovery information via the handover information acquisition unit 264. It is determined whether or not a predetermined target amount has been reached. When the current packet accumulation amount reaches the target amount, the reproduction speed calculation unit 273 sets a standard reproduction speed. Further, the playback speed calculation unit 273 outputs standard playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs reproduction at the standard speed by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed corresponding to the acquired standard reproduction speed information.

  When the above-described low-speed playback is being performed or when the above-described standard-speed playback is being performed, when the playback speed calculation unit 273 receives the radio state recovery information via the handover information acquisition unit 264, Then, when the radio state with the S-eNB 10-1 is recovered, the playback speed calculation unit 273 determines whether or not the current packet accumulation amount is larger than the standard packet accumulation amount (standard amount). judge.

  When the current packet accumulation amount is equal to or less than the standard amount, the reproduction speed calculation unit 273 sets a standard reproduction speed. Further, the playback speed calculation unit 273 outputs standard playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs reproduction at the standard speed by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed corresponding to the acquired standard reproduction speed information.

  On the other hand, when the current packet accumulation amount is larger than the standard amount and the radio state with the S-eNB has deteriorated again, the reproduction speed calculation unit 273 sets a low reproduction speed. Further, the playback speed calculation unit 273 outputs low playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs low-speed reproduction by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed according to the acquired low-speed reproduction speed information.

  In addition, when the current packet accumulation amount is larger than the standard amount and the wireless state with the S-eNB 10-1 is not deteriorated, the reproduction speed calculation unit 273 is faster than the standard reproduction speed. Set the playback speed. Further, the playback speed calculation unit 273 outputs high speed playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs high-speed reproduction by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed corresponding to the acquired high-speed reproduction speed information.

  When playback at high speed is being performed and the current packet accumulation amount is below the standard amount, the playback speed calculation unit 273 sets the standard playback speed. Further, the playback speed calculation unit 273 outputs standard playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs reproduction at the standard speed by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed corresponding to the acquired standard reproduction speed information.

(Fourth process)
When receiving the handover determination information, the playback speed calculation unit 273, based on the second predicted interruption time information, the handover preparation time information, and the current packet accumulation amount information included in the handover determination information, Is calculated.

  Specifically, the playback speed calculation unit 273 decreases the playback speed as the current packet storage amount indicated by the current packet storage amount information decreases, and plays back as the second predicted interruption time or handover preparation time decreases. Reduce speed. Note that the playback speed calculation unit 273 may determine a playback speed at the time of low speed playback and a playback speed at the time of high speed playback in advance, and may select a low speed playback speed when receiving the handover determination information. In addition, the playback speed calculation unit 273 performs a predetermined standard packet accumulation amount Pn [msec], a current packet accumulation amount Pc [msec], an estimated reception interruption time Td [msec], and a handover preparation time Tp [msec]. Based on this, the playback speed S [msec / msec] may be calculated by S = (Pc−Pn + Tp) / (Td + Tp). The playback speed calculation unit 273 outputs the acquired low speed playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 274 performs low-speed reproduction by outputting the RTP packet in the jitter buffer 270 to the decoder 276 at the extraction speed corresponding to the acquired low-speed reproduction speed information.

  When the low speed reproduction is being executed, the reproduction speed calculation unit 273 receives the communication interruption start notification via the handover information acquisition unit 264, and the reproduction speed calculation unit 273 indicates that the current packet accumulation amount is the target. Determine if the amount has been reached. When the current packet accumulation amount reaches the target amount, the reproduction speed calculation unit 273 sets a standard reproduction speed. Further, the playback speed calculation unit 273 outputs standard playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs reproduction at the standard speed by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed corresponding to the acquired standard reproduction speed information.

  When the playback speed calculation unit 273 receives the communication interruption start notification via the handover information acquisition unit 264, the playback speed calculation unit 273 receives the communication interruption end notification via the handover information acquisition unit 264 during the standard speed playback. And whether or not the second predicted reception interruption time has elapsed since the reception of the communication interruption start notification is determined.

  When the second predicted reception interruption time has elapsed since the reception of the communication interruption start notification, the reproduction speed calculation unit 273 sets a low reproduction speed. Further, the playback speed calculation unit 273 outputs low playback speed information to the jitter buffer control unit 274. The jitter buffer control unit 273 performs low-speed reproduction by causing the RTP packet in the jitter buffer 270 to be output to the decoder 276 at the extraction speed according to the acquired low-speed reproduction speed information.

  When the slow playback is being executed and the playback speed calculation unit 273 receives the communication interruption start notification or when the second predicted reception interruption time has elapsed since the reception of the communication interruption start notification, If it is being executed, the playback speed calculation unit 273 determines whether or not a communication interruption end notification has been received.

  When receiving the communication interruption end notification, the reproduction speed calculation unit 273 determines whether or not the packet reception speed is equal to or less than the threshold and the current packet accumulation amount is equal to or less than the standard packet accumulation amount. When the packet reception speed is less than or equal to the threshold and the current packet accumulation amount is less than or equal to the standard packet accumulation amount, standard reproduction rate information is output to the jitter buffer control unit 274. Here, the reception speed is calculated by calculating the difference between two current packet accumulation amounts with different acquisition times, and subtracting the value obtained by multiplying the interval between the acquisition times of the two current packet accumulation amounts by the reproduction speed, The value obtained by subtraction is divided by the interval between the acquisition times of the two current packet accumulation amounts. The jitter buffer control unit 274 reproduces at the standard speed by outputting the RTP packet in the jitter buffer 270 to the decoder 276 at the extraction speed corresponding to the acquired standard reproduction speed information.

  When the playback speed calculation unit 273 acquires the transfer completion notification message via the handover information acquisition unit 264 during execution of the standard speed playback, the standard speed playback is continued. On the other hand, until the transfer completion notification message is acquired, the playback speed calculation unit 273 again determines whether or not the packet reception speed is equal to or less than the threshold value and the current packet accumulation amount is equal to or less than the standard packet accumulation amount. judge.

  On the other hand, when the packet reception rate is greater than the threshold value or the current packet accumulation amount is greater than the standard packet accumulation amount, high-speed reproduction rate information is output to the jitter buffer control unit 274. The jitter buffer control unit 274 performs high-speed reproduction by outputting the RTP packet in the jitter buffer 270 to the decoder 276 at the extraction speed corresponding to the high-speed reproduction speed information.

(3.2) Operation of Radio Terminal FIG. 8 is a flowchart showing the operation of the radio communication function unit in the UE 60.

In step S201, the wireless communication function unit receives the handover destination candidate information message from the S-eNB. In step S202, the wireless communication function unit starts monitoring the wireless state with the S-eNB 10-1.
In step S203, the radio communication function unit determines whether or not a Handover Command message from the S-eNB 10-1 has been received. When the Handover Command message has not been received, in step S204, the wireless communication function unit determines whether the wireless state with the S-eNB 10-1 has deteriorated. When the radio state with the S-eNB 10-1 has not deteriorated, the operation after step S203 is repeated again.

  On the other hand, when the radio state with the S-eNB 10-1 deteriorates, in step S205, the radio communication function unit calculates the first predicted communication interruption time. Furthermore, the wireless communication function unit outputs wireless state deterioration information including the first predicted communication interruption time information to the softphone 250.

  In step S206, the radio communication function unit determines whether or not a Handover Command message from the S-eNB 10-1 has been received. When the Handover Command message has not been received, in step S207, the wireless communication function unit determines whether the wireless state with the S-eNB 10-1 has been recovered. When the radio state with the S-eNB 10-1 has not recovered, the operations after step S206 are repeated again.

  When the wireless state with the S-eNB 10-1 is recovered, the wireless communication function unit outputs the wireless state recovery information to the softphone 250 in step S208. Thereafter, the operation after step S203 is repeated again.

  After it is determined in Step S203 or Step S206 that the Handover Command message has been received, in Step S209, the wireless communication function unit calculates a second predicted communication interruption time. Further, the wireless communication function unit outputs handover determination information including the second predicted communication interruption time information to the softphone 250.

  In step S210, the radio communication function unit determines whether a transfer end notification message from the T-eNB 10-2 has been received. When the transfer end notification message is received, the wireless communication function unit outputs the transfer end notification message to the softphone 250 in step S211.

  FIG. 9 is a flowchart showing a first operation of the softphone 250 in the UE 60. The operation shown in FIG. 9 shows the operation when the softphone 250 receives the wireless state deterioration information.

  In step S301, the softphone 250 determines whether or not the radio state with the S-eNB 10-1 has deteriorated.

  When the radio state with the S-eNB 10-1 deteriorates, the softphone 250 performs low-speed playback in step S302.

  In step S303, the softphone 250 determines whether or not the radio state with the S-eNB 10-2 has been recovered.

  If the wireless state with the S-eNB 10-2 has not recovered, in step S304, the softphone 250 determines whether or not the current packet accumulation amount has reached the target amount.

  When the current packet accumulation amount does not reach the target amount, the operations after step S302 are repeated. On the other hand, when the current packet accumulation amount reaches the target amount, the softphone 250 performs standard speed reproduction in step S305.

  In step S306, the softphone 250 determines whether or not the radio state with the S-eNB 10-2 has been recovered. When it is determined in step S303 or step S306 that the radio state with the S-eNB 10-2 has been recovered, in step S307, the softphone 250 determines whether or not the current packet accumulation amount exceeds the standard packet accumulation amount. Determine.

  If the current packet accumulation amount exceeds the standard packet accumulation amount, in step S308, the softphone 250 determines whether or not the radio state with the S-eNB 10-1 has deteriorated. When the radio state with the S-eNB 10-1 deteriorates, the softphone 250 performs high-speed playback in step S309.

  In step S310, the softphone 250 determines whether or not the current packet accumulation amount is equal to or less than the standard packet accumulation amount.

  If the current packet accumulation amount exceeds the standard packet accumulation amount, the operations in and after step S308 are repeated. On the other hand, when it is determined in step S307 or step S310 that the current packet accumulation amount is equal to or less than the standard packet accumulation amount, the softphone 250 performs standard speed reproduction in step S311. Specifically, the softphone 250 controls the playback speed so that the current packet accumulation amount becomes the standard packet accumulation amount. Softphone 250 also controls the playback speed so that the current packet accumulation amount changes according to the jitter with the received packet. Thereafter, the operations after step S301 are repeated.

  FIG. 10 is a flowchart showing a second operation of the softphone 250 in the UE 60. The operation illustrated in FIG. 10 illustrates an operation when the softphone 250 receives handover determination information.

  In step S401, the softphone 250 calculates a playback speed (slow playback speed) during low speed playback. In step S402, the softphone 250 performs low speed playback.

  In step S403, the softphone 250 determines whether or not a communication interruption start notification has been received, in other words, whether or not reception interruption during handover has started. If reception interruption at the time of handover has not started, the softphone 250 determines in step S404 whether the current packet accumulation amount has reached the target amount. If the current packet accumulation amount does not reach the target amount, the operations after step S402 are repeated.

  On the other hand, when the current packet accumulation amount reaches the target amount, the softphone 250 performs standard speed reproduction in step S405. In step S406, the softphone 250 determines whether reception interruption at the time of handover has started. If reception interruption at the time of handover has not been started, the operations after step S405 are repeated.

  On the other hand, when reception interruption at the time of handover is started, in step S407, the softphone 250 determines whether or not the communication interruption end notification has been received, in other words, whether or not the reception interruption at the time of handover has ended. To do.

  If the reception interruption at the time of handover has not ended, the softphone 250 determines in step S408 whether the second predicted communication interruption time has elapsed. If the second predicted communication interruption time has not elapsed, the operations after step S407 are repeated. On the other hand, when the second predicted communication interruption time has elapsed, the softphone 250 performs low-speed playback in step S409.

  After it is determined in step S403 that reception interruption at the time of handover has started, or after low-speed playback in step S409, in step S410, the softphone 250 determines whether or not the reception interruption at the time of handover has ended. To do. When the reception interruption at the time of the handover is not finished, the operations after step S409 are repeated.

  On the other hand, if it is determined that the reception interruption at the time of handover has ended, in step S411, the softphone 250 determines whether the reception speed is equal to or less than a threshold value and the current packet accumulation amount is equal to or less than the standard packet accumulation amount. To do. If the reception speed is equal to or less than the threshold value and the current packet accumulation amount is equal to or less than the standard packet accumulation amount, the softphone 250 performs standard rate reproduction in step S412. On the other hand, if the reception speed is equal to or lower than the threshold and the current packet accumulation amount is not equal to or less than the standard packet accumulation amount, the softphone 250 performs high-speed playback in step S413.

  After the standard speed reproduction in step S413, in step S414, the softphone 250 determines whether or not a transfer end notification message has been received. If the transfer end notification message is received, the softphone 250 performs standard speed playback in step S415.

  On the other hand, when the transfer end notification message has not been received, or when high-speed playback has been performed in step S413, the operations after step S411 are repeated.

(4) Operation / Effect In the wireless communication system 1 described above, the S-eNB that is the handover source base station transmits a packet including user data from both the S-eNB and the T-eNB that is the handover destination base station. Information on transfer preparation time and transfer delay time, which is a time during which reception is not possible (first communication interruption time), is included in the handover destination information and transmitted to the UE 60. On the other hand, before the first communication interruption time arrives, the UE 60 sets the accumulated amount of packets in the jitter buffer 270 in the own terminal and the second predicted communication interruption time predicted based on the first communication interruption time. Accordingly, the playback speed of the packet in the jitter buffer can be controlled. For this reason, interruption of packet reproduction can be prevented.

  In addition, the S-eNB is a time during which a packet can be received only from the S-eNB, and information on a time required for handover preparation (handover preparation time) is included in the handover destination information and transmitted to the UE 60. On the other hand, the UE 60 can recognize the time until the first communication interruption time comes based on the handover preparation time, and can set the reproduction speed in consideration of the time.

  FIG. 11 is a diagram showing the time transition of the received packet sequence number, the number of received packets per unit time, the playback speed, and the buffered packet accumulation amount in the UE 60.

  As illustrated in FIGS. 11A to 11D, the UE 60 cannot receive a packet from either the S-eNB or the T-eNB during the communication interruption time. For this reason, as shown in FIG. 11 (c), the UE 60 performs low-speed playback at the time (T1) when the wireless state (the reception strength of the radio wave in the S-eNB) deteriorates while receiving the packet from the S-eNB. Transition to. After that, when reception of a packet from the T-eNB is started, the packet is transferred from the S-eNB to the T-eNB and further transmitted to the UE 60. Therefore, as shown in FIG. The reception speed increases, and the sequence number of the packet increases rapidly as shown in FIG. For this reason, as shown in FIG.11 (c), high speed reproduction is performed for a while after the reception of the packet from T-eNB is started, and standard speed reproduction is performed after that.

  By appropriately controlling the reproduction speed in this way, as shown in FIG. 11D, the packet in the jitter buffer 270 is maintained at a predetermined amount or more and is prevented from overflowing.

(5) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above-described embodiment, the handover preparation time information is included in the handover destination information, but may be included in the handover destination candidate information. In this case, the UE 60 can recognize the handover preparation time at an earlier stage, and can provide a time margin for the playback control process.

  In the above-described embodiment, the LTE radio communication system 1 has been described. However, the present invention can be similarly applied to other radio communication systems.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 10-1, 10-2 ... e-NB, 20-1, 20-2 ... SGW, 30 ... PGW, 40-1, 40-2 ... MME, 50 ... IMS, 60 ... UE, 70 ... CN, 102 ... to eNB communication processing unit, 104 ... to MME communication processing unit, 106 ... to SGW communication processing unit, 108 ... to UE communication processing unit, 110 ... UE connection control unit, 112 ... user data control unit, 202 ... control message communication unit, 204 ... data communication unit, 206 ... wireless information acquisition unit, 212 ... handover control unit, 214 ... handover preparation time storage unit, 216 ... handover destination information acquisition unit, 250 ... softphone, 252 ... button Input unit, 254 ... screen display unit, 256 ... microphone, 258 ... encoder, 260 ... packet transmission unit, 262 ... packet reception unit, 264 ... handover information Acquisition unit, 266 ... overall control unit, 268 ... SIP control unit, 270 ... jitter buffer, 272 ... jitter buffer monitoring unit, 274 ... jitter buffer control unit, 276 ... decoder, 278 ... speaker

Claims (13)

A wireless communication system in which a packet is transferred from a handover source base station that is a handover source to a handover destination base station that is a handover destination at the time of handover of a wireless terminal,
The handover source base station is
A transmitter that transmits information related to a first communication interruption time that is a time during which the wireless terminal cannot receive a packet from either the handover source base station or the handover destination base station in the handover;
The wireless terminal is
A receiving unit for receiving information on the first communication interruption time;
Before the first communication interruption time arrives, according to the accumulated amount of packets in the buffer in the terminal and the predicted communication interruption time that is the communication interruption time predicted based on the first communication interruption time And a reproduction control unit that controls a reproduction rate of the packet in the buffer. The wireless terminal is
A holding unit that holds information about a second communication interruption time that is a time during which the wireless terminal cannot receive a packet from either the handover source base station or the handover destination base station in the handover;
The wireless communication system according to claim 1, wherein the reproduction control unit sets a larger one of the first communication interruption time and the second communication interruption time as the predicted communication interruption time.   The first communication interruption time is a time obtained by adding a transfer delay time of a packet between the handover source base station and the handover destination base station and a transfer preparation time required for transfer preparation. The wireless communication system according to 2. The transmitting unit transmits information on the first communication interruption time corresponding to the handover destination base station;
2. The reproduction control unit controls a reproduction rate of packets in the buffer according to the predicted communication interruption time predicted based on the first communication interruption time corresponding to the handover destination base station. The wireless communication system according to any one of 1 to 3. The transmission unit transmits information on the first communication interruption time corresponding to a plurality of base stations that are candidates for a handover destination,
The reproduction control unit controls the reproduction rate of packets in the buffer according to the predicted communication interruption time predicted based on an average value of the first communication interruption times corresponding to the plurality of base stations. The wireless communication system according to any one of claims 1 to 3.   The radio communication system according to any one of claims 1 to 5, wherein the reproduction control unit weights the first communication interruption time according to a radio state with the corresponding base station. The transmitter transmits information related to a handover preparation time that is before the first communication interruption time and is a time during which the wireless terminal can receive a packet only from the handover source base station in the handover;
The receiving unit receives information related to the handover preparation time,
The wireless communication system according to any one of claims 1 to 6, wherein the reproduction control unit reduces the reproduction rate of the packet in the buffer to be lower than a predetermined standard reproduction rate during the handover preparation time.   The reproduction control unit controls the reproduction speed of the packet in the buffer so that the accumulated amount of the packet in the buffer becomes a predetermined first predetermined value at the end of the predicted communication interruption time. The wireless communication system according to claim 1.   The reproduction control unit determines a packet reproduction rate in the buffer based on a reception rate of packets from the handover destination base station and an accumulated amount of packets in the buffer after the predicted communication interruption time elapses. The radio | wireless communications system in any one of Claim 1 thru | or 8 to control. At the time of handover of a wireless terminal, a wireless base station that receives a packet from another wireless base station that is a handover source as a handover destination,
A radio base station comprising: a transmitter that transmits information related to a first communication interruption time, which is a time during which the radio terminal cannot receive a packet from its own radio base station and the other radio base station in the handover. A wireless terminal whose connection destination is switched from a handover source base station that is a handover source to a handover destination base station that is a handover destination during handover,
Received by the handover source base station for receiving information on the first communication interruption time, which is a time during which the own terminal cannot receive a packet from either the handover source base station or the handover destination base station in the handover. And
Before the first communication interruption time arrives, according to the accumulated amount of packets in the buffer in the terminal and the predicted communication interruption time that is the communication interruption time predicted based on the first communication interruption time And a reproduction control unit that controls a reproduction rate of the packet in the buffer. A communication control method in a radio base station that receives a packet from another radio base station that is a handover source during handover of the radio terminal,
A communication control method comprising a step of transmitting information on a first communication interruption time, which is a time during which the wireless terminal cannot receive a packet from its own wireless base station and the other wireless base station in the handover. A communication control method in a radio terminal in which a connection destination is switched from a handover source base station that is a handover source to a handover destination base station that is a handover destination during handover,
A step of receiving information related to a first communication interruption time, which is transmitted by the handover source base station, during which the terminal itself cannot receive a packet from either the handover source base station or the handover destination base station. When,
Before the first communication interruption time arrives, according to the accumulated amount of packets in the buffer in the terminal and the predicted communication interruption time that is the communication interruption time predicted based on the first communication interruption time And a step of controlling the reproduction speed of the packet in the buffer.

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