JP5412566B1 - Handover source radio base station, handover destination radio base station, radio communication system, and radio communication method - Google Patents

Abstract

When a voice default bearer for a general call is established for an emergency call of VoLTE and a handover is to be performed before a voice default bearer for an emergency call is established, the handover of the emergency call is performed. to be certain.
A radio base station determines whether a VoLTE call transmitted from a user apparatus is an emergency call based on a message at the time of transmission from the user apparatus. The radio base station includes a handover request transmitter that transmits a handover request to another radio base station, and the handover request transmitter transmits voice for an emergency call after a voice default bearer for a general call is established. If the call is determined to be an emergency call when the handover request is transmitted before the default bearer is established, the handover request includes information indicating that the call is an emergency call.
[Selection] Figure 5

Description

  The present invention relates to a handover source radio base station, a handover destination radio base station, a radio communication system, and a radio communication method.

  When performing Voice over LTE (VoLTE) in LTE (Long Term Evolution) of 3GPP (Third-Generation Partnership Project), the UE (user equipment, user equipment, mobile station) must first connect to the wireless network. A bearer called (default bearer) is established, signaling according to the SIP (Session Initiation Protocol) procedure is performed via the default bearer, and then, for voice communication called a dedicated bearer (dedicated bearer) Is established.

  FIG. 1 is a schematic diagram illustrating various bearers established for a UE that can use VoLTE. As shown in FIG. 1, various bearers are established between an access point (AP) and a UE via an eNB (base station). The access points include an access point for SP mode (smart phone mode), an IMS (IP Multimedia Subsystem) access point, and an IMS emergency call access point. An SP mode access point is used for data communication, and an IMS or IMS emergency call access point is used for voice data communication, that is, VoLTE. VoLTE uses IMS.

  For VoLTE general calls, a default bearer is first established between the UE and the IMS access point. The default bearer is a bearer that is initially set between a certain UE and a certain access point. SIP signaling is performed using the default bearer, and then a dedicated bearer is established between the UE and the IMS access point. A dedicated bearer is a bearer set second or later between a certain UE and a certain access point. By establishing this dedicated bearer, voice data is communicated.

  For VoLTE emergency calls (calls to police agencies, fire departments or emergency medical institutions), a default bearer is first established between the UE and the IMS emergency call access point. SIP signaling is performed using the default bearer, and then a dedicated bearer is established between the UE and the IMS emergency call access point. By establishing this dedicated bearer, the voice data of the emergency call is communicated.

  For data communication, a default bearer is first established between the UE and the IMS access point. Thereafter, a default bearer is established between the UE and the SP mode access point, and data is communicated via the default bearer.

  In LTE, a general call and a preferential call are distinguished by an information element called Allocation and Retention Priority (ARP) (see Non-Patent Document 1). Sec. 9.2.31 of Non-Patent Document 1 describes that a general call and a priority call are identified using ARP. Specifically, if the priority level (Priority Level) included in the ARP is 15, the call is a general call, and if the priority level is 1 to 14, the call is a priority call. In addition, when data communication is transmitted in a state where a priority voice call bearer exists, 15 may be used as the priority level for the data communication call.

ARP is sent with the following message attached.
S1-AP (application protocol): Initial Context Setup Request
S1-AP: E-RAB Setup Request
S1-AP: E-RAB Modify Request
S1-AP: Handover Request
X2-AP: Handover Request

  Further, the priority calls identified by the ARP priority levels 1 to 14 are classified into priority user calls and emergency calls. The priority user call is, for example, a call originated by an important subscriber's UE. The eNB and MME (Mobility Management Entity) can determine whether the call is a priority user call or not by IMSI (International Mobile Subscriber Identity) transmitted from the UE. Thus, the eNB and MME can distinguish between priority user calls and emergency calls. Unlike emergency calls, priority user calls are always handled preferentially in the wireless communication network.

  FIG. 2 is a sequence diagram showing a control procedure in a wireless communication network in outgoing VoLTE general call. When a general call is transmitted in the UE, the UE and the eNB execute RRC Connection establishment processing Step1. In RRC Connection establishment process Step1, UE transmits RRC Connection Request to eNB, eNB transmits RRC Connection Setup to UE, and UE transmits RRC Connection Setup Complete to eNB.

  Next, voice default bearer establishment processing Step2 is executed. Here, eNB sends Initial UE Message to MME, MME sends Initial Context Setup Request to eNB, eNB sends Security Mode Command and RRC Connection Reconfiguration to UE, and UE sends Security Mode Complete and RRC to eNB. Connection Reconfiguration Complete is transmitted, and eNB transmits Initial Context Setup Response to MME. By this process, a default bearer is established between the UE and the IMS access point.

  Next, SIP procedure Step3 is executed using a default bearer set between the UE and the IMS access point. Further, the voice dedicated bearer establishment process Step 4 is executed. Here, MME sends E-RAB Setup Request to eNB, eNB sends RRC Connection Reconfiguration to UE, UE sends RRC Connection Reconfiguration Complete to eNB, and eNB sends E-RAB Setup Response to MME To do. Through this process, a dedicated bearer is established between the access point of the UE and the IMS. Thereafter, voice communication by VoLTE is started (Step 5).

  In the default bearer establishment process Step 2 for voice, the Initial Context Setup Request transmitted from the MME to the eNB includes an information element ARP. In this ARP, the priority level is set to 15 (that is, a general call). This is regardless of the fact that the actual call is a general call or an emergency call, and if the Initial UE Message that the eNB sends to the MME contains an information element called Service Request, the MME will have a priority level. This is because it is specified to notify 15 to the eNB.

  In the voice dedicated bearer establishment process Step 4, the E-RAB Setup Request transmitted from the MME to the eNB also includes the information element ARP, and the priority level is set to 15 (that is, a general call) even in this ARP. This is because the MME is specified to notify the eNB of the priority level 15 unless an emergency call is notified from the UE to the MME by NAS (Non-Access Stratum).

  FIG. 3 is a sequence diagram showing a control procedure in the wireless communication network in making an emergency call of VoLTE. When an emergency call is transmitted in the UE, the UE and the eNB execute the RRC connection establishment process Step1 as in the control procedure of FIG.

  Next, voice default bearer establishment processing Step2 is executed. This voice default bearer establishment process Step2 is similar to the voice default bearer establishment process Step2 of FIG. 2, and a default bearer is established between the UE and the IMS access point.

  Even in the control procedure for an emergency call, priority level 15 (that is, a general call) is set in the ARP included in the Initial Context Setup Request transmitted from the MME to the eNB in the voice default bearer establishment process Step2. This is regardless of the fact that the actual call is a general call or an emergency call, and if the Initial UE Message that the eNB sends to the MME contains an information element called Service Request, the MME will have a priority level. This is because it is specified to notify 15 to the eNB. When an emergency call is transmitted, as described in Sec. 5.10.2 of Non-Patent Document 2, the MME performs a Service Request procedure before connecting to the IMS emergency call access point.

  After the voice default bearer establishment process Step 2 enables data exchange between the UE and the MME (after the Active transition), the emergency call notification process Step 6 is executed. In the emergency call notification process Step6, the UE transmits UL Information Transfer to the eNB, and the eNB transmits Uplink NAS Transfer to the MME. UL Information Transfer and Uplink NAS Transfer are PDN Connectivity Requests using NAS. In this way, the UE is notified that the call is an emergency call via the NAS.

  When the emergency call notification process Step6 ends, the emergency voice default bearer establishment process Step7 is executed. Here, MME sends E-RAB Setup Request to eNB, eNB sends RRC Connection Reconfiguration to UE, UE sends RRC Connection Reconfiguration Complete to eNB, and eNB sends E-RAB Setup Response to MME To do. In the emergency voice default bearer establishment process Step 7, the priority level is set to other than 15 (that is, emergency call) in the information element ARP included in the E-RAB Setup Request transmitted from the MME to the eNB. By the emergency voice default bearer establishment process Step 7, a default bearer is established between the UE and the IMS emergency call access point.

  Next, SIP procedure Step8 is executed using the default bearer set between the UE and the IMS emergency call access point. Further, the emergency bear dedicated bearer establishment process Step 9 is executed. Here, MME sends E-RAB Setup Request to eNB, eNB sends RRC Connection Reconfiguration to UE, UE sends RRC Connection Reconfiguration Complete to eNB, and eNB sends E-RAB Setup Response to MME To do. In the emergency voice dedicated bearer establishment process Step 9, the priority level is set to other than 15 (that is, emergency call) in the information element ARP included in the E-RAB Setup Request transmitted from the MME to the eNB. By the emergency voice dedicated bearer establishment process Step 9, a dedicated bearer is established between the UE and the IMS emergency call access point. Thereafter, voice communication by VoLTE is started (Step 10).

3GPP TS 36.423 V11.1.0 (2012-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); "X2 application protocol (X2AP) (Release 11)", 2012 June 3GPP TS 23.401 V11.2.0 (2012-06), 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access (Release 11 ) ", June 2012

  As described above, in the case of VoLTE emergency call transmission, the voice default bearer establishment process Step 2 for establishing a default bearer between the UE and the IMS access point is executed as in the case of transmission of a general call. Even in the control procedure for an emergency call, the priority level 15 (that is, general call) is set in the ARP included in the Initial Context Setup Request sent by the MME to the eNB in the voice default bearer establishment process Step2, and the call is sent to the eNB. It is notified that it is a general call. For this reason, there is a possibility that a problem may occur in the handover accompanying the movement of the UE.

  FIG. 4 is a sequence diagram showing a problem of handover in originating a VoLTE emergency call. Two eNBs (eNB1 and eNB2) are shown to illustrate the handover problem. The UE first attaches to eNB1. Therefore, UE and eNB1 perform RRC Connection establishment process Step1, and UE, eNB1, and MME perform voice default bearer establishment process Step2.

  After Active transition in the voice default bearer establishment process Step2, communication is possible between the UE and the eNB1, and the UE can transmit a Measurement Report to the eNB1. The Measurement Report is a signal indicating reception quality of radio waves from the eNB to which the UE is attached and reception quality of radio waves from other eNBs. If the UE communicates with eNB2 better than eNB1 and the reception quality at the UE improves, eNB1 determines the handover of the UE and transmits a Handover Request to eNB2 for that UE. The Handover Request includes an information element ARP. Since the eNB is notified of the general call by the Initial Context Setup Request, the priority level is set to 15 (that is, the general call) in the ARP included in the Handover Request.

  However, it is assumed that the eNB 2 has decided not to accept a general call in CAC (Call Admission Control) due to congestion before receiving a Handover Request. In this case, the eNB 2 that has received the Handover Request does not accept the call (“CAG NG” in the figure), and the handover fails. Eventually, the radio wave between the UE and the eNB 1 is weakened, and the UE and the eNB 1 become unable to communicate (call loss occurs).

  This problem can occur, for example, during an earthquake disaster. It is assumed that eNB2 where many users use congestion and eNB1 used by few users are close to each other, and a certain user calls a fire engine. If the user's UE can use VoLTE and attaches to eNB1 first, the call will continue if the user does not move, but the UE moves with the user and needs to be handed over to eNB2 Call loss occurs.

  If the emergency call notification process Step6 is executed and the emergency voice default bearer establishment process Step7 is executed, this problem does not occur. However, this problem occurs when a Handover Request is transmitted before the emergency voice default bearer establishment process Step 7 is executed.

  Therefore, the present invention relates to an emergency call when a voice default bearer for a general call is established for an emergency call of VoLTE and a handover is to be executed before a voice default bearer for an emergency call is established. A handover source radio base station, a handover destination radio base station, a radio communication system, and a radio communication method are provided.

  The handover source radio base station according to the present invention determines whether a VoLTE (Voice over LTE) call transmitted from a user apparatus is an emergency call based on a message at the time of transmission from the user apparatus In response to a first bearer establishment request message sent from a mobility management entity indicating that the call is a general call, regardless of whether the call is actually a general call or an emergency call. Responding to a general voice default bearer establishment unit for establishing a voice default bearer for a general call and a second bearer establishment request message transmitted from the mobility management entity indicating that the call is actually an emergency call Then, an emergency voice default bearer establishment unit for establishing a voice default bearer for an emergency call with respect to the call, and another report based on a report from the user device A handover determination unit that determines whether or not the call of the user apparatus should be handed over to a radio base station, and the handover determination unit that determines that the call of the user apparatus should be handed over, A handover request transmission unit configured to transmit a handover request to a radio base station, wherein the handover request transmission unit includes the emergency request bearer after the voice default bearer for the general call is established by the general voice default bearer establishment unit. Before the voice default bearer for the emergency call is established by the voice default bearer establishment unit, the emergency call determination unit determines that the call is an emergency call when transmitting the handover request. The handover request includes information indicating that the call is an emergency call. That.

  The wireless communication method according to the present invention determines whether a VoLTE (Voice over LTE) call transmitted from a user apparatus is an emergency call based on a message at the time of transmission from the user apparatus at a handover source wireless base station. In response to a first bearer establishment request message sent from a mobility management entity indicating that the call is a general call, regardless of whether the call is actually a general call or an emergency call; The handover source radio base station establishes a voice default bearer for a general call with respect to the call, and the handover source radio base station determines another radio base based on a report from the user apparatus. Determining whether to hand over the call of the user equipment to a station, and determining that the call of the user equipment should be handed over, Transmitting a handover request to the other radio base station at a base radio base station, wherein the handover request is transmitted after a voice default bearer for the general call is established. If the call is determined to be an emergency call when the handover request is transmitted before the voice default bearer for the emergency call is established, the call is included in the emergency call when the call is determined to be an emergency call. Information indicating that it is included.

  In the present invention, regardless of whether the call is actually a general call or an emergency call, in response to the first bearer establishment request message transmitted from the mobility management entity (MME) indicating that the call is a general call. In the handover source radio base station, a voice default bearer for a general call is established for the call. However, the handover source radio base station determines whether or not a VoLTE (Voice over LTE) call transmitted from the user apparatus is an emergency call based on a message at the time of transmission from the user apparatus. Then, after the voice default bearer for the general call is established and before the voice default bearer for the emergency call is established, it is determined that the call is an emergency call when a handover request is transmitted. The handover source radio base station includes information indicating that the call is an emergency call in the handover request. The handover destination radio base station can recognize from the information included in the handover request that the call to be handed over is an emergency call. When the call to be handed over is an emergency call, the handover destination radio base station can accept the handover of the emergency call even if congestion occurs. In this way, in the present invention, emergency call handover can be ensured.

It is the schematic which shows the various bearers established with respect to UE which can utilize VoLTE. It is a sequence diagram which shows the control procedure in the radio | wireless communication network in transmission of the general call of VoLTE. It is a sequence diagram which shows the control procedure in the radio | wireless communication network in the transmission of the emergency call of VoLTE. It is a sequence diagram which shows the problem of the hand-over in transmission of the emergency call of VoLTE. It is a sequence diagram which shows a part of control procedure in the radio | wireless communication network in the transmission of the call of VoLTE which concerns on the 1st Embodiment of this invention, and the procedure of a hand-over. It is a block diagram which shows the structure of the wireless base station which concerns on the 1st Embodiment of this invention. It is a sequence diagram which shows the problem of the handover which can be assumed in the 1st Embodiment of this invention. It is a sequence diagram which shows the control procedure in the radio | wireless communication network in the handover of the emergency call of VoLTE which concerns on the 2nd Embodiment of this invention.

  Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings. In order to simplify the description, one UE, two eNBs, and one MME are shown in the drawing. However, the wireless communication network, of course, has a larger number of eNBs and a larger number of MMEs, and can communicate with a larger number of UEs.

First Embodiment FIG. 5 is a sequence diagram showing a part of a control procedure and a handover procedure in a wireless communication network in a VoLTE call transmission according to a first embodiment of the present invention. As shown in FIG. 5, when a call is transmitted in the UE, the UE first attaches to the eNB 1. UE and eNB1 perform RRC Connection establishment process Step11. In RRC Connection establishment process Step11, UE transmits RRC Connection Request to eNB1, eNB1 sends RRC Connection Setup to UE, and UE transmits RRC Connection Setup Complete to eNB1.

  Unlike the RRC Connection establishment process Step1 shown in FIG. 2 and FIG. 3, in the RRC Connection establishment process Step11 of FIG. 5, the eNB1 is based on the RRC Connection Request (message at the time of transmission from the user apparatus) that the UE sends to the eNB1 Then, it is determined whether or not the VoLTE call transmitted from the UE is an emergency call ("emergency call determination" in the figure). Specifically, when the information element Establishment Cause included in the RRC Connection Request indicates that the call is an emergency call, the eNB 1 determines that the call is an emergency call. In other cases, the eNB 1 It is determined that the call is a general call.

  Next, regardless of whether the call is actually a general call or an emergency call, the UE, eNB1, and MME execute voice default bearer establishment processing Step2. The contents of the voice default bearer establishment process Step2 are the same as those of the voice default bearer establishment process Step2 of the control procedure shown in FIGS. In other words, regardless of whether the call is actually a general call or an emergency call, an Initial Context Setup Request (including a general call) is sent from the MME and includes an information element ARP with a priority level set to 15 (that is, a general call). In response to the first bearer establishment request message indicating that the call is a call, the eNB 1 establishes a voice default bearer for the general call regarding the call.

  After Active transition in the voice default bearer establishment process Step2, communication is possible between the UE and the eNB1, and the UE can transmit a Measurement Report to the eNB1. The Measurement Report is a signal indicating reception quality of radio waves from the eNB to which the UE is attached and reception quality of radio waves from other eNBs. If the UE communicates with eNB2 better than eNB1 and the reception quality at the UE improves, eNB1 (handover source base station) determines the handover of the UE, and sends a Handover Request (handover request) to eNB2 for the UE. ). That is, the eNB 1 determines whether or not to hand over the call of the UE to another eNB based on the report from the UE, and transmits a handover request to the other eNB when determining that the handover should be performed. .

  When the eNB 1 does not transmit a Handover Request immediately after the Active transition, a dedicated bearer for the call is established through normal procedures, and voice communication is started. That is, if the call is a general call, the SIP procedure Step3, the voice dedicated bearer establishment process Step4, and the voice communication start Step5 are executed as in the control procedure of FIG. In the voiced dedicated bearer establishment process Step4, regardless of whether the call is actually a general call or an emergency call, the information element ARP with a priority level set to 15 (that is, a general call) is sent from the MME. In response to the included E-RAB Setup Request (bearer establishment request message indicating that the call is a general call), the eNB 1 establishes a voice dedicated bearer for the general call regarding the call.

  If the eNB1 does not transmit a Handover Request immediately after the Active transition, if the call is an emergency call, the emergency call notification process Step6, the emergency voice default bearer establishment process Step7, as in the control procedure of FIG. SIP procedure Step 8, emergency voice dedicated bearer establishment processing Step 9 and voice communication start Step 10 are executed. In the default voice bearer establishment process Step7 for emergency voice, the E-RAB Setup Request (call is actually an emergency call) that includes the information element ARP that is sent from the MME and has a priority level other than 15 (that is, an emergency call) is set. In response to the second bearer establishment request message indicating that the eNB 1 establishes a voice default bearer for an emergency call regarding the call. In the emergency bearer dedicated bearer establishment process Step9, the E-RAB Setup Request including the information element ARP that is sent from the MME and whose priority level is set to other than 15 (that is, emergency call) In response to a bearer establishment request message indicating that the call is a call, the eNB 1 establishes a voice dedicated bearer for an emergency call regarding the call.

  After the voice default bearer for the general call is established (voice default bearer establishment process Step2), and before the voice default bearer for the emergency call is established (emergency voice default bearer establishment process Step7), When eNB1 transmits a Handover Request and eNB1 determines that the call is an emergency call in the emergency call determination, eNB1 clearly indicates that the call is an emergency call in the Handover Request. Include information. The information that clearly indicates that the call is an emergency call may be a flag, for example, and the type of the information is not limited. However, this information is different from the information element ARP (indicating the priority level) that can be included in the Handover Request, and the eNB that receives the Handover Request has a priority level of 15 in the ARP included in the Handover Request. Even if the call is set to be a general call (ie, a general call), if the information indicating that the call is an emergency call is included in the Handover Request, the call is recognized as an emergency call.

  It is assumed that eNB2 (handover destination radio base station) has decided not to accept a general call in CAC due to congestion of eNB2 before receiving a Handover Request. However, the eNB 2 can recognize that the call to be handed over is an emergency call from the information included in the Handover Request. When the call to be handed over is an emergency call, the eNB 2 can accept the handover of the emergency call even if congestion occurs ("CAC OK" in the figure). And eNB2 starts communication with UE according to Handover Request. In this way, this embodiment can ensure emergency call handover.

  When the eNB 1 determines that the call is a general call in the emergency call determination, the eNB 1 may include, in particular, information indicating that the call is a general call in the Handover Request. Such information may not be included. That is, if the call is a general call, the Handover Request may indicate or imply that the call is a general call.

  When eNB2 that has decided not to accept a general call in CAC receives a Handover Request that does not include information that clearly indicates that the call is an emergency call (expressly or implies that the call is a general call) The acceptance of the general call handover is rejected. In this way, depending on whether the call is actually an emergency call or a general call, the eNB 2 that is the handover destination radio base station can appropriately determine whether or not to accept the call handover.

  FIG. 6 is a block diagram showing a configuration of radio base station (eNB) 10 according to the first embodiment of the present invention. The radio base station 10 can function as both the handover source radio base station (eNB1) and the handover destination radio base station (eNB2). The radio base station 10 includes a radio transmission unit 12, a radio reception unit 14, an inter-base station communication interface 16, an access point interface 18, an MME interface 20, and a control unit 22.

  The wireless transmission unit 12 is a wireless transmission circuit that transmits a wireless signal to the UE, and the wireless reception unit 14 is a wireless reception circuit that receives a wireless signal from the UE. The inter-base station communication interface 16 is an interface for communicating with other eNBs. The access point interface 18 is an interface for communicating with an SP mode access point, an IMS access point, and an IMS emergency call access point. The MME interface 20 is an interface for communicating with the MME.

  The control unit 22 includes an emergency call determination unit 220, a handover determination unit 222, a handover request transmission unit 224, a congestion determination unit 226, and a handover control unit 228. The control unit 22 is a CPU (central processing unit), for example, and operates according to a computer program. The emergency call determination unit 220, the handover determination unit 222, the handover request transmission unit 224, the congestion determination unit 226, and the handover control unit 228 are functional blocks realized by the control unit 22 functioning according to the computer program.

  When the radio base station 10 is a handover source radio base station, the emergency call determination unit 220 determines that the VoLTE call transmitted from the UE is based on the information element Establishment Cause included in the RRC Connection Request transmitted from the UE to the eNB 1. Determine if it is an emergency call.

  When the radio base station 10 is a handover source radio base station, the handover determination unit 222 determines whether or not to hand over the call of the UE to another eNB based on a report (Measurement Report) from the UE. When the radio base station 10 is a handover source radio base station, when the handover determination unit 222 determines that the UE call should be handed over, the handover request transmission unit 224 passes through the inter-base station communication interface 16. A Handover Request is transmitted to other eNBs. After the voice default bearer for the general call is established (voice default bearer establishment process Step2), and before the voice default bearer for the emergency call is established (emergency voice default bearer establishment process Step7), When the handover request transmission unit 224 transmits a Handover Request and the emergency call determination unit 220 determines that the call is an emergency call, the handover request transmission unit 224 indicates that the call is an emergency call in the Handover Request. Include information indicating

  The congestion determination unit 226 determines whether this eNB is in a congestion state. When it is determined that the eNB is in a congestion state, the congestion determination unit 226 determines that the CAC does not accept a general call.

  The inter-base station communication interface 16 functions as a handover request receiving unit that receives a Handover Request from another eNB. When the radio base station 10 is a handover destination radio base station, the handover control unit 228 functions. When the congestion determination unit 226 determines that this eNB is in a congestion state, and when the inter-base station communication interface 16 receives a Handover Request including information indicating that the call is an emergency call from another eNB, the handover is performed. The control unit 228 starts communication with the UE according to the Handover Request. When the congestion determination unit 226 determines that this eNB is in a congestion state, and when the inter-base station communication interface 16 receives a Handover Request that does not include information indicating that the call is an emergency call from another eNB, The handover control unit 228 rejects the Handover Request.

  Moreover, the control part 22 performs the bearer establishment process for UE in cooperation with another element. In the default bearer establishment process Step2 for voice, regardless of whether the call is actually a general call or an emergency call, the initial including the information element ARP that is sent from the MME and has a priority level set to 15 (that is, a general call) In response to the Context Setup Request (first bearer establishment request message indicating that the call is a general call), the control unit 22, the radio transmission unit 12, the radio reception unit 14, and the access point interface 18 A voice default bearer for the call is established between the IMS access point and the UE. That is, the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 function as a general voice default bearer establishment unit.

  In the voiced dedicated bearer establishment process Step4, regardless of whether the call is actually a general call or an emergency call, the information element ARP with a priority level set to 15 (that is, a general call) is sent from the MME. In response to the included E-RAB Setup Request (bearer establishment request message indicating that the call is a general call), the control unit 22, the radio transmission unit 12, the radio reception unit 14, and the access point interface 18 A voice dedicated bearer for the call is established between the IMS access point and the UE. That is, the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 function as a general voice dedicated bearer establishment unit.

  In the default voice bearer establishment process Step7 for emergency voice, the E-RAB Setup Request (call is actually an emergency call) that includes the information element ARP that is sent from the MME and has a priority level other than 15 (that is, an emergency call) is set. In response to the second bearer establishment request message indicating that the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 have set a voice default bearer for an emergency call regarding the call. Established between IMS emergency call access point and UE. That is, the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 function as an emergency voice default bearer establishment unit.

  In the emergency bearer dedicated bearer establishment process Step9, the E-RAB Setup Request including the information element ARP that is sent from the MME and whose priority level is set to other than 15 (that is, emergency call) In response to the bearer establishment request message indicating that the call is a call, the control unit 22, the radio transmission unit 12, the radio reception unit 14, and the access point interface 18 perform a voice dedicated bearer for an emergency call regarding the call. Is established between the IMS emergency call access point and the UE. That is, the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 function as an emergency voice dedicated bearer establishment unit.

  In the above configuration, in response to the first bearer establishment request message indicating that the call transmitted from the mobility management entity (MME) is a general call regardless of whether the call is actually a general call or an emergency call, The general voice default bearer establishment unit of the handover source radio base station establishes a voice default bearer for a general call regarding the call. However, the emergency call determination unit 220 of the handover source radio base station determines whether or not the VoLTE call transmitted from the user apparatus is an emergency call based on a message (RRC Connection Request) at the time of transmission from the user apparatus. . Then, after the voice default bearer for the general call is established and before the voice default bearer for the emergency call is established, it is determined that the call is an emergency call when the Handover Request is transmitted. The handover request transmitting unit 224 of the handover source radio base station includes information indicating that the call is an emergency call in the Handover Request. The handover control unit 228 of the handover destination radio base station can recognize that the call to be handed over is an emergency call from the information included in the Handover Request. If the call to be handed over is an emergency call, the handover control unit 228 of the handover destination radio base station can accept the handover of this emergency call even if congestion occurs. In this way, emergency call handover can be ensured.

Problems that may occur in the first embodiment FIG. 7 is a sequence diagram illustrating a handover problem that can be assumed in the first embodiment of the present invention. As described above, it is assumed that a Handover Request including information indicating that a call is an emergency call is transmitted from eNB1 to eNB2, and a VoLTE call that is an emergency call is handed over from eNB1 to eNB2. Then, it is assumed that the emergency call is terminated at the UE while the eNB 2 has information indicating that the call is an emergency call.

  The end of the call at the UE and the release of the call at the wireless communication network are not simultaneous. In a wireless communication network, even if a call is terminated at the UE, the call is maintained for a certain period without being released. The length of this period depends on the operator of the wireless communication network, but can be for example several minutes. When the call ends at the UE, the MME transmits an E-RAB Release Request to the eNB (eNB2) to which the UE is attached, the eNB2 transmits an RRC Connection Reconfiguration to the UE, and the UE eNB2 to release the call. RRC Connection Reconfiguration Complete is transmitted to eNB2 and E-RAB Release Response is transmitted to MME.

  However, suppose that before the call is released, the UE initiates a data transmission or a general voice call. In this case, since the call is not released, the eNB 2 accepts a new call even if the call is terminated. Furthermore, since communication is possible between UE and eNB2, UE can transmit Measurement Report to eNB2. When the UE communicates with another eNB (for example, eNB1) rather than eNB2 and the reception quality at the UE improves, the eNB2 determines the handover of the UE, and the other eNB (for example, eNB1) for the UE A Handover Request is transmitted. If eNB1 accepts the Handover Request, the UE attaches to eNB1 and the call continues.

  It is assumed that eNB1 has decided not to accept a general call in CAC due to congestion of eNB1 before receiving a Handover Request. If this Handover Request contains information indicating that the call to be handed over is an emergency call, even if this call is actually a data call or a general voice call ENB1 treats this call as an emergency call, UE attaches to eNB1, and the call continues. In other words, when the eNB always holds information indicating that it is an emergency call and includes information indicating that it is an emergency call in the Handover Request, even if the call related to the Handover Request is not actually an emergency call, Handover is established.

  In practice, such a call is not an emergency call, so this handling is unfair to other users. Emergency calls should be preferential, but not data calls or general voice calls that are made immediately after the emergency call is terminated. If such handling is allowed, a call can be established if the user makes an emergency call, terminates the emergency call, and immediately sends a data call or a general voice call. The second embodiment described below solves this problem.

Second Embodiment FIG. 8 is a sequence diagram showing a control procedure in a radio communication network in VoLTE emergency call handover according to a second embodiment of the present invention. As in the first embodiment, after the voice default bearer establishment process Step2 in FIG. 5, in order to hand over the VoLTE call that is an emergency call from eNB1 to eNB2, the call from eNB1 to eNB2 is an emergency call. Assume that a Handover Request including the indicated information is transmitted.

  Thereafter, emergency voice default bearer establishment processing Step 17 is executed. Here, MME transmits E-RAB Setup Request to eNB2, eNB2 transmits RRC Connection Reconfiguration to UE, UE transmits RRC Connection Reconfiguration Complete to eNB2, and eNB2 transmits E-RAB Setup Response to MME. To do. By the emergency voice default bearer establishment process Step7, a default bearer is established between the UE and the IMS emergency call access point via the eNB2. In the emergency voice default bearer establishment process Step17, the priority level is set to other than 15 (that is, emergency call) in the information element ARP included in the E-RAB Setup Request (third bearer establishment request message) sent by the MME to the eNB2. Has been. This is because the MME and higher-level devices already know whether the call to be handed over is actually an emergency call or a general call.

  When the E-RAB Setup Request is received in the emergency voice default bearer establishment process Step 17, the eNB 2 invalidates information indicating that the call is an emergency call. As a mode of invalidation, for example, deleting the information stored in the memory (not shown) of the eNB 2 and other invalidations can be considered.

  Next, SIP procedure Step18 is performed using the default bearer set up between UE and the access point of an IMS emergency call via eNB2. Further, the emergency bear dedicated bearer establishment process Step 19 is executed. Here, MME transmits E-RAB Setup Request to eNB2, eNB2 transmits RRC Connection Reconfiguration to UE, UE transmits RRC Connection Reconfiguration Complete to eNB2, and eNB2 transmits E-RAB Setup Response to MME. To do. The priority level of the information element ARP included in the E-RAB Setup Request (fourth bearer establishment request message) sent from the MME to the eNB 2 in the emergency bearer dedicated bearer establishment process Step 19 is other than 15 (that is, an emergency call) Is set to In the emergency voice dedicated bearer establishment process Step 19, a dedicated bearer is established between the UE and the IMS emergency call access point via the eNB2. Thereafter, voice communication by VoLTE becomes possible via eNB2. In this way, the VoLTE call that is an emergency call is handed over from eNB1 to eNB2.

  Then, it is assumed that the emergency call is ended at the UE. When the call ends at the UE, the MME transmits an E-RAB Release Request to the eNB (eNB2) to which the UE is attached, the eNB2 transmits an RRC Connection Reconfiguration to the UE, and the UE eNB2 to release the call. RRC Connection Reconfiguration Complete is transmitted to eNB2 and E-RAB Release Response is transmitted to MME.

  Assume that before the call is released, the UE makes a data call or a general voice call. In this case, since the call is not released, the eNB 2 accepts a new call even if the call is terminated. Furthermore, since communication is possible between UE and eNB2, UE can transmit Measurement Report to eNB2. When the UE communicates with another eNB (for example, eNB1) rather than eNB2 and the reception quality at the UE improves, the eNB2 determines the handover of the UE, and the other eNB (for example, eNB1) for the UE A Handover Request (second handover request) is transmitted. If eNB1 accepts the Handover Request, the UE attaches to eNB1 and the call continues.

  It is assumed that eNB1 has decided not to accept a general call in CAC due to congestion of eNB1 before receiving a Handover Request. If this Handover Request contains information indicating that the call to be handed over is an emergency call, even if this call is actually a data call or a general voice call ENB1 treats this call as an emergency call, UE attaches to eNB1, and the call continues.

  However, in this embodiment, in the emergency voice default bearer establishment process Step 17, when the E-RAB Setup Request already received indicates that the immediately preceding call is actually an emergency call, the eNB 2 The information indicating that the call is an emergency call is invalidated. Since eNB2 invalidates emergency call information, when transmitting a Handover Request (second handover request) after the previous call is terminated, eNB2 returns a Handover Request (second handover request). Do not include information indicating that the new call is an emergency call. The eNB 2 may include information clearly indicating that the call is a general call in the Handover Request. That is, the Handover Request may be specified or implied that it is a general call.

  When eNB1 that has decided not to accept a general call in CAC receives a Handover Request that does not include information that clearly indicates that the call is an emergency call (expressly or implies that the call is a general call) The acceptance of the handover of this new call (data call or general voice call) is rejected. Therefore, according to the second embodiment, it is possible to eliminate the possibility that a data call or a general voice call sent immediately after an emergency call is terminated will be preferentially performed in the handover.

  When eNB2 handles an emergency call that has been handed over, eNB2 establishes a third bearer for a voice default bearer indicating that the call (previous call) is an emergency call in emergency voice default bearer establishment processing Step 17 A request message (E-RAB Setup Request) is received from the MME, and in the emergency voice dedicated bearer establishment process Step 19, for the voice dedicated bearer indicating that the call (previous call) is an emergency call. A fourth bearer establishment request message (E-RAB Setup Request) is received from the MME. The trigger for invalidating the information indicating that the call is an emergency call may be reception of a third bearer establishment request message or reception of a fourth bearer establishment request message.

  However, before the emergency bearer dedicated bearer establishment process Step19 and after the emergency voice default bearer establishment process Step17, the eNB2 sends a Handover Request for handover of a new call (data call or general voice call). There can be a situation of transmission. In order to prevent this Handover Request from including information indicating that the new call is an emergency call, the third bearer establishment request message (E-RAB Setup message) received in the emergency voice default bearer establishment process Step 17 is used. In response to (Request), it is preferable to invalidate information indicating that the call is an emergency call.

  The configuration of the radio base station (eNB) according to the second embodiment may be the same as the configuration shown in FIG. The radio base station 10 can function as both the handover source radio base station (eNB1) and the handover destination radio base station (eNB2).

  When the radio base station 10 is a handover destination radio base station, the inter-base station communication interface 16 functions as a handover request receiving unit that receives a Handover Request from the handover source radio base station. When the radio base station 10 is a handover destination radio base station, the MME interface 20 receives a Handover Request from the handover request receiver, and then receives a bearer establishment request message (emergency voice default bearer establishment process Step 17 and It functions as a bearer establishment request message receiving unit for receiving the emergency bearer dedicated bearer establishment process Step 19 E-RAB Setup Request).

  In the emergency voice default bearer establishment process Step 17, in response to the third bearer establishment request message (E-RAB Setup Request), the control unit 22, the radio transmission unit 12, the radio reception unit 14, and the access point interface 18 A voice default bearer for an emergency call is established between the IMS access point and the UE for the call. In the emergency voice dedicated bearer establishment process Step 19, in response to the fourth bearer establishment request message (E-RAB Setup Request), the control unit 22, the radio transmission unit 12, the radio reception unit 14, and the access point interface 18 The voice dedicated bearer for the emergency call is established between the IMS access point and the UE. That is, the control unit 22, the wireless transmission unit 12, the wireless reception unit 14, and the access point interface 18 function as a bearer establishment unit.

  The control unit 22 functions as a new call accepting unit that accepts a new call when a new call is transmitted from the UE related to the terminated call even after the previous call is terminated. The handover determining unit 222 functions as a second handover determining unit that determines whether or not to hand over a new call of the UE to another eNB based on a report from the UE. The handover request transmission unit 224 transmits a Handover Request (second handover request) to another eNB when the second handover determination unit determines that the new call of the UE should be handed over It functions as a handover request transmission unit.

  The handover determination unit 222 as the second handover request transmission unit receives the bearer establishment request message reception unit (MME interface 20) from the MME when transmitting the second handover request after the previous call is terminated. If the bearer establishment request message (E-RAB Setup Request, particularly preferably E-RAB Setup Request in Step 17 for emergency voice default bearer establishment) indicates that the previous call is actually an emergency call, The information indicating that the new call is an emergency call is not included in the second handover request. For this purpose, the control unit 22 determines that the bearer establishment request message (E-RAB Setup Request, particularly preferably the E-RAB Setup Request in the emergency bearer default bearer establishment process Step 17) received from the MME is the previous call. Information indicating that the call is an emergency call is invalidated.

  When the radio base station 10 is a handover destination radio base station, the congestion determination unit 226 functions as a first congestion determination unit that determines whether or not the handover destination radio base station is in a congestion state. The handover control unit 228 follows the Handover Request when the first congestion determination unit determines that the handover destination radio base station is congested and when the Handover Request includes information indicating that the call is an emergency call. When communication with the UE is started and the first congestion determination unit determines that the handover destination radio base station is in a congestion state, and when the Handover Request does not include information indicating that the call is an emergency call, It functions as a first handover control unit that rejects a Handover Request.

  When the radio base station 10 is another radio base station, the congestion judgment unit 226 functions as a second congestion judgment unit that judges whether or not this radio base station is in a congestion state, and the inter-base station communication interface 16 functions as a second handover request receiving unit that receives a second handover request (Handover Request) from the handover destination radio base station (eNB2). When the second congestion determination unit determines that the radio base station is in a congestion state and the second handover request includes information indicating that the new call is an emergency call, the handover control unit 228 includes: When communication with the UE is started according to the second handover request, the second congestion determination unit determines that the radio base station is in a congestion state, and information indicating that the new call is an emergency call is second Function as a second handover control unit that rejects the second handover request when the second handover request is not included.

  In the above configuration, the same effect as in the first embodiment is achieved. In addition, even after the previous call is terminated, when the eNB accepts a new call transmitted from the UE and the eNB transmits a second handover request to another eNB, the bearer establishment request message received from the MME. ENB indicates that the previous call is actually an emergency call, the eNB does not include information indicating that the new call is an emergency call in the second handover request. The handover control unit 228 of the radio base station that receives the second handover request can recognize from the second handover request that the call to be handed over is a general call. Therefore, it is possible to eliminate the possibility that a data call or a general voice call transmitted immediately after the emergency call is terminated is preferentially performed in the handover.

Other variants
In the eNB, each function executed by the CPU may be executed by hardware instead of the CPU, or executed by a programmable logic device such as an FPGA (Field Programmable Gate Array) or DSP (Digital Signal Processor). Also good.

1, 2, 10 eNB (radio base station),
12 wireless transmission unit (general voice default bearer establishment unit, emergency voice dedicated bearer establishment unit, bearer establishment unit),
14 wireless receiver (general voice default bearer establishment unit, emergency voice dedicated bearer establishment unit, bearer establishment unit),
16 Communication interface between base stations (handover request receiving unit, second handover request receiving unit),
18 access point interface (general voice default bearer establishment unit, emergency voice dedicated bearer establishment unit, bearer establishment unit),
20 MME interface (bearer establishment request message receiver),
22 control unit (general voice default bearer establishment unit, emergency voice dedicated bearer establishment unit, bearer establishment unit, new call reception unit),
220 Emergency call determination unit,
222 handover determination unit (second handover determination unit),
224 handover request transmission unit (second handover request transmission unit),
226 congestion determination unit (first congestion determination unit, second congestion determination unit),
228 Handover control unit (first handover control unit, second handover control unit).

Claims (7)

An emergency call determination unit that determines whether a call of VoLTE (Voice over LTE) transmitted from the user apparatus is an emergency call based on a message at the time of transmission from the user apparatus;
In response to a first bearer establishment request message sent from a mobility management entity indicating that the call is a general call, whether the call is actually a general call or an emergency call, A general voice default bearer establishment unit for establishing a voice default bearer for
Responsive to a second bearer establishment request message sent from the mobility management entity indicating that the call is actually an emergency call, an emergency voice for establishing a voice default bearer for the emergency call with respect to the call A default bearer establishment unit;
A handover determining unit that determines whether or not to hand over the call of the user apparatus to another radio base station based on a report from the user apparatus;
A handover request transmitter for transmitting a handover request to the other radio base station when the handover determination unit determines that the call of the user apparatus should be handed over,
After the voice default bearer for the general call is established by the general voice default bearer establishment unit, the handover request transmission unit receives a voice default bearer for the emergency call by the emergency voice default bearer establishment unit. If the emergency call determination unit determines that the call is an emergency call when transmitting the handover request before being established, the handover request indicates that the call is an emergency call. A handover source radio base station characterized by including information to indicate. A handover request receiving unit configured to receive the handover request from the handover source radio base station according to claim 1;
A bearer establishment request message receiving unit that receives a bearer establishment request message transmitted from the mobility management entity after the handover request receiving unit receives the handover request;
A bearer establishment for establishing a bearer for an emergency call with respect to the call when the bearer establishment request message received by the bearer establishment request message receiving unit from the mobility management entity indicates that the call is actually an emergency call. And
Even after the previous call that is the call is terminated, when a new call is transmitted from the user device, a new call accepting unit that accepts the new call;
A second handover determining unit that determines whether or not to hand over the new call of the user apparatus to another radio base station based on a report from the user apparatus;
A second handover request transmitting unit that transmits a second handover request to another radio base station when the second handover determining unit determines that the new call of the user apparatus should be handed over; With
The second handover request transmission unit receives the bearer establishment request received from the mobility management entity by the bearer establishment request message reception unit when transmitting the second handover request after the previous call is terminated. When the message indicates that the immediately preceding call is actually an emergency call, the second handover request does not include information indicating that the new call is an emergency call. Handover destination radio base station. The bearer establishment request message reception unit includes a third bearer establishment request message for a voice default bearer transmitted from the mobility management entity indicating that the immediately preceding call is an emergency call, and the immediately preceding call Receiving a fourth bearer establishment request message for the voice dedicated bearer sent from the mobility management entity indicating an emergency call;
When the bearer establishment request message receiving unit receives the third bearer establishment request message, the bearer establishment unit establishes a voice default bearer for an emergency call with respect to the immediately preceding call, and receives the bearer establishment request message When the unit receives the fourth bearer establishment request message, it establishes a voice dedicated bearer for an emergency call with respect to the immediately preceding call,
The second handover request transmission unit receives the third handover request received from the mobility management entity when the bearer establishment request message reception unit transmits the second handover request after the immediately preceding call is terminated. When the bearer establishment request message indicates that the immediately preceding call is actually an emergency call, the handover request does not include information indicating that the new call is an emergency call. The handover destination radio base station according to claim 2. A handover source radio base station according to claim 1 and another radio base station,
The other radio base station is
A congestion determination unit that determines whether or not the other radio base station is in a congestion state;
A handover request receiver for receiving the handover request from the handover source radio base station;
When the congestion determination unit determines that the other radio base station is congested, and when the handover request includes the information indicating that the call is an emergency call, the user apparatus according to the handover request When the congestion determination unit determines that the other radio base station is in a congestion state, and when the handover request does not include the information indicating that the call is an emergency call And a handover control unit that rejects the handover request. A handover destination radio base station according to claim 2, and another radio base station that receives the second handover request from the handover destination radio base station,
The handover destination radio base station is
A first congestion determination unit for determining whether or not the handover destination radio base station is in a congestion state;
When the first congestion determination unit determines that the handover destination radio base station is congested, and when the handover request includes the information indicating that the call is an emergency call, according to the handover request The communication with the user apparatus is started, and when the first congestion determination unit determines that the handover destination radio base station is in a congestion state, the information indicating that the call is an emergency call is sent to the handover A first handover controller that rejects the handover request when the request is not included,
The other radio base station is
A second congestion determination unit that determines whether or not the other radio base station is in a congestion state;
A second handover request receiver for receiving the second handover request from the handover destination radio base station;
When the second congestion determination unit determines that another radio base station is congested, and when the second handover request includes the information indicating that the new call is an emergency call, Communication with the user apparatus is started in accordance with a second handover request, and when the second congestion determination unit determines that the other radio base station is in a congestion state, and the new call is an emergency call And a second handover control unit that rejects the second handover request when the second handover request does not include the information indicating the wireless communication system. Determining whether a VoLTE (Voice over LTE) call originating from the user apparatus is an emergency call based on a message at the time of transmission from the user apparatus at the handover source radio base station;
In response to a first bearer establishment request message sent from a mobility management entity indicating that the call is a general call, regardless of whether the call is actually a general call or an emergency call, the handover source radio base Establishing a voice default bearer for a general call at the station for the call;
In the handover source radio base station, based on a report from the user apparatus, determining whether to hand over the call of the user apparatus to another radio base station;
When it is determined that the call of the user apparatus should be handed over, the handover source radio base station comprises a handover request to the other radio base station,
When the handover request is transmitted, after the voice default bearer for the emergency call is established after the voice default bearer for the general call is established, When it is determined that the call is an emergency call, information indicating that the call is an emergency call is included in the handover request. In the handover destination radio base station, receiving the handover request including the information indicating that the call is an emergency call from the handover source radio base station;
Receiving a bearer establishment request message transmitted from the mobility management entity at the handover destination radio base station;
When the bearer establishment request message received from the mobility management entity indicates that the previous call is actually an emergency call, the handover target radio base station establishes a bearer for the emergency call with respect to the call To do
Even after the previous call that is the call is terminated, when a new call is transmitted from the user apparatus, the handover destination radio base station accepts the new call;
In the handover destination radio base station, based on a report from the user apparatus, determining whether to hand over the new call of the user apparatus to another radio base station;
When determining that the new call of the user apparatus should be handed over, the handover destination radio base station transmits a second handover request to another radio base station, and
Transmitting the second handover request means that the bearer establishment request message received from the mobility management entity is transmitted when the second handover request is transmitted after the previous call is terminated. 7. The method according to claim 6, further comprising not including, in the handover request, information indicating that the new call is an emergency call in a case where the actual call is an emergency call. Wireless communication method.

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