JP6376790B2 - Base station and transmission / reception start determination method - Google Patents

Description

  The present invention relates to a mobile station, a base station, and a transmission / reception start determination method.

  In the Long Term Evolution (LTE) system, the security function of the access layer (AS: Access-Stratum) and the security function of the non-access layer (NAS: Non-Access-Stratum) are separated, and the base station (eNB: evolved) The eNB manages security-related parameters (parameters for setting the security key) in the access layer between the Node B) and the mobile station (UE: User Equipment).

  FIG. 1 shows a security key generation procedure in the LTE system. In the LTE system, a security key is generated based on AKA (Authentication and Key Agreement).

The key K is shared in advance between USIM (Universal Subscriber Identity Module) and AuC (Authentication Center). Each time the network and user are mutually authenticated, keys CK and IK used for encryption and integrity assurance are generated. When the UE attaches to the network, the UE and HSS (Home Subscriber Service) generate K _ASME from the keys CK and IK. The key K _NASint for key K _NASenc and integrity guarantee for the encryption of NAS protocol between the UE and the MME (Mobility Management Entity) is generated from K _ASME. When the UE connects to the network, the MME generates a key K _eNB and passes it to the eNB. Also in handover, when RRC Connection Reconfiguration is completed, a new _KeNB is generated. This K _eNB, and K _UPenc a key for encryption of U-Plane data, K _RRCint and K _RRCenc are generated as a key for encryption and integrity protection for RRC (Radio Resource Control) . Note that K _UPint that is a key for guaranteeing the integrity of U-Plane data may not be generated (see Non-Patent Document 1).

3GPP TS 33.401 V11.7.0 (2013-06)

As described above, in the LTE system, the access layer security function is realized between the UE and the eNB. Further, the access layer security key K _eNB is updated by the trigger of the MME or eNB. For example, when a handover to E-UTRAN (Evolved Universal Terrestrial Radio Access Network) (Inter RAT HO to E-UTRAN) is performed, or for security reasons (for example, the UE is connected to the network longer than a predetermined time) The security key K _eNB is updated according to an instruction from the MME. For example, when the amount of transmitted / received data exceeds a threshold, the security key K _eNB is updated based on the eNB's determination.

  On the other hand, dual connectivity, in which a UE performs data communication using two or more eNB resources, has been studied. Dual Connectivity is a form of carrier aggregation (CA) that achieves high throughput using cell groups under different eNBs, and is also called inter eNB CA.

  In Dual Connectivity, it is assumed that each cell group of different eNBs uses different frequencies. In Dual Connectivity, a reliable master cell group (MCG: Master Cell Group) that ensures connectivity with the UE and a secondary cell group (SCG: Secondary) that is additionally set for the UE connected to the master cell group Cell Group) is set. A base station corresponding to MCG is called MeNB (Master eNB), and a base station corresponding to SCG is called SeNB (Secondary eNB).

FIG. 2 shows a conceptual diagram of Dual Connectivity. The connection form of Dual Connectivity shown in FIG. 2 is called Architecture option 1, and PDCP (Packet Data Convergence Protocol) entities exist in different eNBs. Accordingly, security-related parameters are also managed by each eNB. Furthermore, the security key for communication with the SCG (hereinafter referred to as the security key SK _eNB for SeNB) is updated as well as the update of the security key for communication with the MCG (hereinafter referred to as the security key for MeNB K _eNB ). There is a possibility that. For example, the SeNB security key SK _eNB is updated when the MeNB security key K _eNB is updated or when the amount of data transmitted and received by the SeNB exceeds a threshold.

  On the other hand, although a security related parameter is notified to UE by a RRC message, SeNB cannot transmit a RRC message to UE. For this reason, SeNB cannot grasp | ascertain the timing which UE updated the security key. If the UE and SeNB do not apply the security key at a predetermined timing, there is a possibility that the UE cannot correctly receive the data transmitted by the SeNB, and even if the SeNB can correctly receive the data transmitted by the UE, the S- There is a possibility of being discarded without being correctly transmitted to the GW (Serving Gateway).

  An object of the present invention is to appropriately determine the start of transmission / reception by grasping the update timing of a security key in dual connectivity.

In addition, a base station according to one aspect of the present invention is
A base station in a wireless system in which a mobile station communicates using a cell group under a different base station,
A receiving unit that receives an updated security key for the mobile station to communicate with the secondary cell group from the base station of the master cell group;
A security key setting unit that updates a security key for the mobile station to communicate with the secondary cell group;
A transmitting unit that transmits parameters for updating a security key for the mobile station to communicate with the secondary cell group to the mobile station via the base station of the master cell group;
After or the random access procedure after receiving the control message indicating the completion of updating of the security keys in the mobile station is completed, using the updated security key to start receiving the uplink data, the security keys in the mobile station Master response to setting change request before receiving control message indicating completion of update or before completion of random access procedure and including parameter for updating security key for mobile station to communicate with secondary cell group A transmission / reception start determination unit that starts transmission of downlink data using the updated security key after receiving from the base station of the cell group ;
Have

In addition, a transmission / reception start determination method according to an aspect of the present invention includes:
A transmission / reception start determination method in a base station in a wireless system in which a mobile station communicates using cell groups under different base stations,
Receiving an updated security key for the mobile station to communicate with the secondary cell group from a base station of the master cell group;
Updating a security key for the mobile station to communicate with the secondary cell group;
Transmitting the parameter for updating the security key for the mobile station to communicate with the secondary cell group to the mobile station via the base station of the master cell group;
Settings including parameters for updating the security key for the mobile station to communicate with the secondary cell group before receiving the control message indicating the completion of the security key update in the mobile station or before the random access procedure is completed After receiving a response to the change request from the base station of the master cell group, starting transmission of downlink data using the updated security key;
After or the random access procedure after receiving the control message indicating the completion of updating of the security keys in the mobile station is completed, and initiating the receiving of uplink data using the updated security keys,
Have

  According to the present invention, in the dual connectivity, it is possible to appropriately determine the start of transmission / reception by grasping the timing of updating the security key.

Diagram showing security key generation procedure in LTE system Conceptual diagram of Dual Connectivity Sequence diagram showing the security key update procedure for SeNB in Dual Connectivity Diagram showing key hierarchy in Dual Connectivity Configuration diagram of a mobile station according to an embodiment of the present invention Configuration diagram of a base station according to an embodiment of the present invention FIG. 7 is a sequence diagram showing a security key update procedure and a transmission / reception start determination procedure according to an embodiment of the present invention (when PDCP PDU or MAC CE is used). The figure which shows the example of PDCP PDU used in the Example of this invention FIG. 7 is a sequence diagram showing a security key update procedure and a transmission / reception start determination procedure according to an embodiment of the present invention (when using a random access procedure).

  Embodiments of the present invention will be described below with reference to the drawings.

  In an embodiment of the present invention, a case will be described in which carrier stations communicate with each other using a cell group under the control of a different base station in carrier aggregation (CA). Such a CA connection form is called Dual Connectivity.

  In the example illustrated in FIG. 2, the mobile station (UE) realizes dual connectivity by performing communication using cell groups having different frequencies under the control of two base stations (MeNB and SeNB). In Dual Connectivity, a highly reliable master cell group (MCG) that ensures connectivity with the UE and a secondary cell group (SCG) that is additionally set for the UE that is connected to the master cell group are set. . A base station corresponding to MSG is called MeNB, and a base station corresponding to SCG is called SeNB. In FIG. 2, two cell groups are set, but three or more cell groups may be set.

In Dual Connectivity, the bearer set to UE via SNB and MeNB may differ from the bearer set to UE via SNB and SeNB. In such a case, since PDCP (Packet Data Convergence Protocol) entities exist in different eNBs, security-related parameters are also managed by the respective eNBs. Further, the SeNB security key SK _eNB may be updated in the same manner as the MeNB security key K _eNB is updated. For example, the SeNB security key SK _eNB is updated when the MeNB security key K _eNB is updated or when the amount of data transmitted and received by the SeNB exceeds a threshold.

  On the other hand, although a security relevant parameter is notified to UE by a RRC message, since SeNB cannot transmit a RRC message to UE, the security relevant parameter of SeNB is notified to UE by the RRC message from MeNB. A specific example will be described below.

  In FIG. 3, the update procedure of the security key for SeNB in Dual Connectivity is shown.

When the MeNB security key K _eNB is updated, or when the amount of data transmitted / received by the SeNB exceeds the threshold, the MeNB determines to update the SeNB security key SK _eNB (S10). In addition, UE reports the measurement result (Meas Report) of signal quality to MeNB regularly (S11).

The MeNB generates a SeNB security key SK _eNB based on the MeNB security key K _eNB (S13). Specifically, as shown in FIG. 4, the SeNB security key SK _eNB is generated by SK _eNB = KDF (K _eNB , SCC). However, KDF is a hash function for generating a security key, and SCC (SK _eNB chaining count) is a counter for specifying the security key SK _eNB . With the update of the SeNB security key SK _eNB , SK _UPenc, which is a key for encrypting U-Plane data, is generated from this SK _eNB . Note that K _UPint, which is a key for guaranteeing the integrity of U-Plane data, may not be generated.

And MeNB transmits SCG (Secondary Cell Group) modification indication containing the information of the produced | generated security key SK _eNB to SeNB (S15). In response to the SCG modification indication, the SeNB updates the SeNB security key SK _eNB , and transmits an SCG modification request including the security key parameter notified to the UE to the MeNB (S17). At this time, SeNB can use SeNB security key SK _eNB (S19).

The MeNB transmits the security key parameter included in the SCG modification request to the UE by RRC Connection Reconfiguration (S21). The UE updates the SeNB security key SK _eNB and transmits RRC Connection Reconfiguration Complete to the MeNB in order to report that the setting of RRC Connection Reconfiguration has been completed (S23). At this point, the UE can use the SeNB security key SK _eNB (S25). And MeNB transmits SCG modification response to SeNB as a response with respect to SCG modification request (S27).

As described above, unlike the timing of SeNB is timing the UE to update the security key SK _eNB for SeNB updates the security key SK _eNB for SeNB, SeNB is directly know when the UE has updated the security keys for SeNB It is not possible. Furthermore, SeNB cannot grasp | ascertain whether UE updated the security key for SeNB normally. Therefore, in the embodiment of the present invention, in order to notify the update timing of the security key, a control message indicating the completion of the security key update or a random access procedure is used between the UE and the SeNB.

  Specific configurations and operations of the UE and eNB will be described below.

<Configuration of mobile station>
FIG. 5 shows a configuration diagram of a mobile station according to an embodiment of the present invention. The mobile station 10 includes a DL (Downlink) signal receiving unit 101, a UL (Uplink) signal transmitting unit 103, a signal measuring unit 105, a security key setting unit 107, a security key setting completion notification unit 109, and a UL data buffer. Unit 111 and transmission / reception start determination unit 113.

The DL signal receiving unit 101 receives downlink signals from MeNB and SeNB. Regarding the update of the SeNB security key, the DL signal receiving unit 101 receives a parameter for updating the SeNB security key from the MeNB. This parameter, for example, if the K _eNB is updated in MeNB, or may be included in the RRC Connection Reconfiguration sent from MeNB when the amount of data sent and received has exceeded a threshold SeNB. Also, the DL signal receiving unit 101 receives a signal for measuring signal quality for the base station. Furthermore, the DL signal receiving unit 101 receives a response message to the control message indicating completion of the security key update in the mobile station 10 or a message related to the random access procedure from the SeNB. The response message to the control message indicating completion of the security key update may be a PDCP layer message (PDCP PDU (PDCP Protocol Data Unit)) or MAC layer control information (MAC CE (MAC Control Element)).

  UL signal transmission section 103 transmits an uplink signal to MeNB and SeNB. Regarding the update of the security key for SeNB, UL signal transmission section 103 transmits RRC Connection Reconfiguration Complete, which is a response to RRC Connection Reconfiguration, to MeNB. Moreover, UL signal transmission part 103 transmits the measurement result of signal quality to MeNB. Furthermore, the UL signal transmission unit 103 transmits a control message indicating completion of the security key update in the mobile station 10 or a message regarding a random access procedure to the SeNB. The control message indicating completion of the security key update may be a PDCP layer message (PDCP PDU) or MAC layer control information (MAC CE).

  The signal measurement unit 105 measures the reception quality for the eNB based on the predetermined signal received by the DL signal reception unit 101. The measured reception quality is used to select an eNB to which the mobile station is connected.

  The security key setting unit 107 updates the SeNB security key using the SeNB security key parameter received by the DL signal receiving unit 101.

  The security key setting completion notifying unit 109 notifies the SeNB that the security key setting unit 107 has updated the security key. When the security key update is completed, the security key setting completion notification unit 109 may perform a control message transmission or random access procedure indicating the completion of the security key update to the SeNB.

  The UL data buffer unit 111 stores the uplink data until the transmission of the uplink data using the updated SeNB security key is started with the update of the SeNB security key.

  The transmission / reception start determination unit 113 determines the start of uplink data transmission and downlink data reception using the updated SeNB security key. The transmission / reception start determination unit 113 stops the transmission of the uplink data when receiving the parameter for updating the SeNB security key from the MeNB. The transmission / reception start determination unit 113 uses the updated SeNB security key when a response message to the control message transmitted by the security key setting completion notification unit 109 is received or when the random access procedure is completed. Start transmission of uplink data.

  In addition, when the update of the SeNB security key is completed, the transmission / reception start determination unit 113 starts receiving downlink data using the updated SeNB security key. Alternatively, as with the uplink, when the response message to the control message transmitted by the security key setting completion notification unit 109 is received or when the random access procedure is completed, the updated SeNB security key is used. You may start reception of link data.

<Base station configuration>
FIG. 6 shows a configuration diagram of a base station according to an embodiment of the present invention. FIG. 6 shows a base station 20 corresponding to SeNB. The base station 20 includes a UL signal receiving unit 201, a DL signal transmitting unit 203, a security key update request unit 205, a security key setting unit 207, a DL A data buffer unit 209, a transmission / reception start determination unit 211, and an inter-base station interface unit 213 are included.

  The UL signal receiving unit 201 receives a signal from the UE. Since SeNB cannot transmit and receive RRC messages, UL signal receiver 201 mainly receives data signals from UEs. Regarding the update of the SeNB security key, the UL signal reception unit 201 receives a control message indicating completion of the update of the security key in the UE or a message related to the random access procedure from the UE.

  The DL signal transmission unit 203 transmits a signal to the UE. Since SeNB cannot transmit and receive RRC messages, DL signal transmission section 203 mainly transmits data signals to UEs. Regarding the SeNB security key update, the DL signal transmission unit 203 transmits a response message to the control message indicating completion of the security key update in the UE or a message related to the random access procedure to the UE.

  When the amount of data transmitted / received at the base station 20 exceeds the threshold, the security key update request unit 205 requests the MeNB to update the SeNB security key. Note that the security key update request unit 205 may simply notify the MeNB of the data amount and determine whether or not the data amount exceeds the threshold in the MeNB.

  When MeNB decides to update the security key for SeNB, MeNB generates a security key for SeNB based on the security key for MeNB, puts the security key for SeNB in the SCG modification indication, and enters SeNB. Send. Note that the SeNB security key may be generated for each bearer or may be generated for each SCG.

  The security key setting unit 207 updates the SeNB security key using the security key information included in the SCG modification indication transmitted from the MeNB when the MeNB determines to update the SeNB security key.

  The DL data buffer unit 209 stores the downlink data until the start of transmission of the downlink data using the updated SeNB security key with the update of the SeNB security key.

  The transmission / reception start determination unit 211 determines the start of downlink data transmission and uplink data reception using the updated SeNB security key. The transmission / reception start determination unit 211 receives uplink data using the updated SeNB security key when a control message indicating completion of security key update in the UE is received or when the random access procedure is completed. To start.

  In addition, the transmission / reception start determination unit 211 stops transmission of the downlink data when the update of the security key is completed, and an SCG setting change request (SCG modification) including a parameter for updating the SeNB security key. When a response to the request (SCG modification response) is received from the MeNB, transmission of downlink data is started. Or, similar to the uplink, when the control message indicating completion of the security key update in the UE is received or when the random access procedure is completed, transmission of the downlink data is performed using the updated SeNB security key. Start.

  The inter-base station interface unit 213 is an interface for communicating with the MeNB. Regarding the update of the SeNB security key, the inter-base station interface unit 213 receives an SCG modification indication including information on the SeNB security key from the MeNB. Also, the inter-base station interface unit 213 transmits an SCG modification request including a security key parameter to notify the UE to the MeNB in response to the SCG modification indication. Further, the inter-base station interface unit 213 receives an SCG modification response, which is a response to the SCG modification request, from the MeNB.

<When using PDCP PDU or MAC CE>
When the SeNB security key is updated, PDCP PDU or MAC CE can be used as an opportunity for the UE to start transmitting uplink data.

  FIG. 7 shows a security key update procedure and a transmission / reception start determination procedure according to the embodiment of the present invention.

  SeNB requests MeNB to update the security key for SeNB when the amount of data transmitted / received by SeNB exceeds the threshold (S110). In addition, SeNB may notify data amount to MeNB and it may be determined whether data amount exceeded the threshold value in MeNB. Since the SeNB security key may be generated for each bearer, in this case, the data amount may be compared with a threshold value for each bearer. Moreover, since the security key for SeNB may be produced | generated for every SCG, the data amount of the whole SeNB may be compared with a threshold value in this case. Note that the UE periodically reports a signal quality measurement result (Meas Report) to the MeNB (S111).

  MeNB updates the security key for MeNB by the trigger of MME or eNB (S112). For example, when a handover to E-UTRAN is performed, when there is a security reason, or when the amount of data transmitted and received by the MeNB exceeds a threshold, the MeNB updates the MeNB security key.

When the SeNB security key needs to be updated in accordance with S110, or when the SeNB security key needs to be updated along with the update of the MeNB security key in S112, the MeNB updates the SeNB security key (S113). ). And SCG modification indication containing the information on the updated security key for SeNB is transmitted to SeNB (S115). The SCG modification indication includes a security key SK _eNB generated for each SCC and an SCC for specifying the security key SK _eNB . In response to the SCG modification indication, the SeNB updates the SeNB security key and transmits an SCG modification request to the MeNB (S117). The SCG modification request includes SCC, DRB ID (Data Radio Bearer ID) or SCG ID as a parameter of the security key notified to the UE. When the SeNB security key is generated for each bearer, the SCG modification request includes the DRB ID. When the SeNB security key is generated for each SCG, the SCG modification request includes the SCG ID. SeNB can use the SeNB security key at the point of time when the update of the SeNB security key is completed and the SCG modification request is transmitted (S119). At this time, SeNB stops transmission of downlink data (S120). Until the start of downlink data transmission, the downlink data is stored in the buffer. Data encrypted with the updated SeNB security key may be stored in the buffer.

The MeNB transmits the security key parameter included in the SCG modification request to the UE by RRC Connection Reconfiguration (S121). That is, RRC Connection Reconfiguration includes SCC, DRB ID, or SCG ID as a parameter of the security key notified to UE. Further, when the MeNB security key is also updated, the RRC Connection Reconfiguration includes a parameter eKSI (Key Set Identifier in E-UTRAN) for specifying the MeNB security key K _eNB . When the UE receives RRC Connection Reconfiguration, the UE stops transmitting uplink data (S122). Uplink data is stored in the buffer until the start of uplink data transmission. Data encrypted with the updated SeNB security key may be stored in the buffer.

The UE updates the MeNB security key K _eNB and / or the SeNB security key SK _eNB using the SCC, and transmits RRC Connection Reconfiguration Complete to the MeNB to report that the setting of the RRC Connection Reconfiguration is completed. (S123). The UE can use the SeNB security key when the update of the SeNB security key is completed and RRC Connection Reconfiguration is transmitted (S125). At this point, the UE may start receiving downlink data using the updated SeNB security key (S126).

  And MeNB transmits SCG modification response to SeNB as a response with respect to SCG modification request (S127). SeNB may start transmitting downlink data using the updated SeNB security key at the time of receiving the SCG modification response (S129).

  The UE notifies the SeNB of the completion of the SeNB security key update by means of PDCP PDU or MAC CE (S131). SeNB responds to the completion of the update of the security key from UE by PDCP PDU or MAC CE (S132).

  The UE starts transmission of uplink data using the updated SeNB security key when receiving a response message to the completion of the update of the SeNB security key from the SeNB (S133). Moreover, instead of S126, UE may start reception of downlink data using the updated security key for SeNB at this time.

  SeNB starts reception of uplink data using the updated security key for SeNB, when the completion of the update of the security key for SeNB is received from UE (S135). Moreover, instead of S129, SeNB may start transmission of downlink data using the updated security key for SeNB at this time.

  FIG. 8 shows an example of the PDCP PDU used in S131 and S132 of FIG. A PDCP PDU includes a field (D / C) indicating a data or PDCP layer control message, a field (PDU Type) indicating a PDU type, and an unused field (Reserved).

  To indicate the completion of the SeNB security key setting, information indicating that the control message of the PDCP layer is set in D / C, and the type indicating the completion of setting of the SeNB security key is set in PDU Type. May be. Different types of PDU Type may be set for the notification from the SeNB to the UE and the notification from the UE to the SeNB.

  Alternatively, four R bits may be used to indicate the completion of the SeNB security key setting. For example, in the case of 0001, the notification from the SeNB to the UE may be indicated, and in the case of 0010, the notification from the UE to the SeNB may be indicated.

  FIG. 8 is merely an example of the PDCP PDU used in the embodiment of the present invention, and other types of PDCP PDU or MAC CE may be used.

<When using random access procedure>
When the SeNB security key is updated, a random access procedure can be used as an opportunity for the UE to start transmitting uplink data.

  FIG. 9 shows a security key update procedure and a transmission / reception start determination procedure according to the embodiment of the present invention. S210 to S229 in FIG. 9 are the same as S110 to S129 in FIG.

  The UE notifies the SeNB of the completion of the SeNB security key update by a random access procedure (S231).

  When the random access procedure is completed, the UE starts transmission of uplink data using the updated SeNB security key (S233). Moreover, instead of S226, UE may start reception of downlink data using the updated security key for SeNB at this time.

  SeNB also starts receiving uplink data using the updated security key for SeNB when the random access procedure is completed (S235). Moreover, instead of S229, SeNB may start transmission of downlink data using the updated security key for SeNB at this time.

<Effect of the embodiment of the present invention>
According to the embodiment of the present invention, it is possible to appropriately determine the start of transmission / reception by grasping the update timing of the security key in dual connectivity.

  For this reason, it is possible to avoid a situation in which data is discarded due to a difference in security key update timing.

  In order to grasp the timing of updating the SeNB security key, a PDCP PDU or MAC CE may be used as shown in FIG. 7, or a random access procedure may be used as shown in FIG. When a security key for SeNB is generated for each bearer, use of PDCP PDU or MAC CE can avoid the situation that other bearers that have already been set are momentarily interrupted by the random access procedure. it can.

  For convenience of explanation, the base station and the mobile station according to the embodiment of the present invention are described using functional block diagrams, but the base station and the mobile station according to the embodiment of the present invention may be hardware, software, or A combination thereof may be realized. In addition, the functional units may be used in combination as necessary. In addition, the method according to the embodiment of the present invention may be performed in an order different from the order shown in the embodiment.

  As described above, in the dual connectivity, the method for appropriately determining the start of transmission / reception by grasping the timing of setting the security key has been described, but the present invention is not limited to the above-described embodiments, Various modifications and applications are possible within the scope of the claims.

DESCRIPTION OF SYMBOLS 10 Mobile station 101 DL signal reception part 103 UL signal transmission part 105 Signal measurement part 107 Security key setting part 109 Security key setting completion notification part 111 UL data buffer part 113 Transmission / reception start determination part 20 Base station 201 UL signal reception part 203 DL signal transmission unit 205 Security key update request unit 207 Security key setting unit 209 DL data buffer unit 211 Transmission / reception start determination unit 213 Interface unit between base stations

Claims (3)

A base station in a wireless system in which a mobile station communicates using a cell group under a different base station,
A receiving unit that receives an updated security key for the mobile station to communicate with the secondary cell group from the base station of the master cell group;
A security key setting unit that updates a security key for the mobile station to communicate with the secondary cell group;
A transmitting unit that transmits parameters for updating a security key for the mobile station to communicate with the secondary cell group to the mobile station via the base station of the master cell group;
After or the random access procedure after receiving the control message indicating the completion of updating of the security keys in the mobile station is completed, using the updated security key to start receiving the uplink data, the security keys in the mobile station Master response to setting change request before receiving control message indicating completion of update or before completion of random access procedure and including parameter for updating security key for mobile station to communicate with secondary cell group A transmission / reception start determination unit that starts transmission of downlink data using the updated security key after receiving from the base station of the cell group ;
Base station with Stop the transmission of downlink data, until the start of transmission of the downlink data, further comprising a downlink data storage unit for storing the downlink data, the base station according to claim 1. A transmission / reception start determination method in a base station in a wireless system in which a mobile station communicates using cell groups under different base stations,
Receiving an updated security key for the mobile station to communicate with the secondary cell group from a base station of the master cell group;
Updating a security key for the mobile station to communicate with the secondary cell group;
Transmitting the parameter for updating the security key for the mobile station to communicate with the secondary cell group to the mobile station via the base station of the master cell group;
Settings including parameters for updating the security key for the mobile station to communicate with the secondary cell group before receiving the control message indicating the completion of the security key update in the mobile station or before the random access procedure is completed After receiving a response to the change request from the base station of the master cell group, starting transmission of downlink data using the updated security key;
After or the random access procedure after receiving the control message indicating the completion of updating of the security keys in the mobile station is completed, and initiating the receiving of uplink data using the updated security keys,
A transmission / reception start determination method.

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