COMMUNICATION DEVICE, BASE STATION, AND COMMUNICATION METHOD

Abstract

To allow a mobility management device controlling paging notifications to perform appropriate control.MEANS FOR SOLVING THE PROBLEM: A user device (100) that communicates with a first network (200A) using a first subscriber identity module (111) and communicates with a second network (200B) using a second subscriber identity module (112) includes: a control unit (130) that monitors a paging message notifying paging from a cell managed by a base station (200, 210B) of the second network (200B) during communication with the first network (200A); and a communication unit (120) that, when the cell does not support transmission of paging reason information indicating a reason for the paging by the paging message, transmits, to a mobility management device (221B) of the second network (200B), a NAS message indicating that the user device (100) is residing in a non-support cell that does not support transmission of the paging reason information.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a user equipment and a communication control method for use in a mobile communication system. [Background technology]

[0002] Release 17 of 3GPP (3rd Generation Partnership Project), a standardization project for mobile communication systems, has launched a work item to define a function that enables user equipment equipped with multiple subscriber identity modules to perform data communication while present in the networks of multiple telecommunications carriers.

[0003] At present, there is no provision in the standard specifications for a mechanism for a user device in the range of multiple networks to receive paging (i.e., incoming calls), and this is dependent on the implementation of the user device. However, if there is an incoming call from one network (hereinafter, "second network") while communicating with another network (hereinafter, "first network"), the user device will miss the incoming call. For this reason, a method for receiving incoming calls from multiple networks in cooperation with each network is being considered in the 3GPP standardization forum (see, for example, Non-Patent Document 1).

[0004] When a user device receives a paging from a second network while communicating with a first network, the user device is assumed to determine whether or not to prioritize communication with the first network over communication with the second network based on information indicating the reason for the paging (hereinafter, paging reason information). The paging reason information is included in a message for notifying paging (hereinafter, paging message). The user device can know the reason for the paging by receiving the paging message.

[0005] For example, when the user equipment determines that communication with the first network is to be prioritized over communication with the second network, the user equipment notifies the mobility management device of the second network that it is unable to respond to calls from the second network by sending a NAS message to the mobility management device of the second network, and the mobility management device controls paging (e.g., stops paging) in response to the NAS message. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP Technical Report: TR23.761 V1.4.0 Summary of the Invention [Problem to be solved by the invention]

[0007] Existing base stations do not support transmission of paging reason information to user equipment, and therefore it is assumed that the user equipment is present in a cell that does not support transmission of paging reason information (hereinafter, referred to as a non-support cell).

[0008] In this case, the mobility management device may operate on the assumption that the user equipment is in a cell that supports transmission of paging reason information to the user equipment, even though the user equipment is in a non-supported cell. As a result, there is a concern that the mobility management device may not be able to perform appropriate control over the user equipment in the non-supported cell.

[0009] Therefore, an object of the present invention is to provide a user equipment and a communication control method that enable a mobility management device that controls paging notifications to perform appropriate control. [Means for solving the problem]

[0010] A user equipment according to a first aspect is a user equipment that communicates with a first network using a first subscriber identity module and communicates with a second network using a second subscriber identity module, and includes: a control unit that monitors a paging message notifying of paging from a cell managed by a base station of the second network while communicating with the first network; and a communication unit that, when the cell does not support transmitting paging reason information indicating the reason for the paging via the paging message, transmits a NAS message to a mobility management device of the second network indicating that the user equipment is located in a non-support cell that does not support transmitting the paging reason information.

[0011] A communication control method according to a second aspect is a communication control method executed in a user equipment that communicates with a first network using a first subscriber identity module and communicates with a second network using a second subscriber identity module, and includes the steps of: monitoring a paging message notifying paging from a cell managed by a base station of the second network while communicating with the first network; and, if the cell does not support transmitting paging reason information indicating the reason for the paging via the paging message, transmitting a NAS message to a mobility management device of the second network indicating that the user equipment is located in a non-support cell that does not support transmitting the paging reason information. Effect of the Invention

[0012] According to one aspect of the present invention, it is possible to provide a user equipment and a communication control method that enable a mobility management device that controls paging notification to perform appropriate control. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a mobile communication system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of a protocol stack in the mobile communication system according to the embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a configuration example of a UE (user equipment) according to the embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration example of a base station according to the embodiment. [Diagram 5] FIG. 4 is a diagram illustrating a first operation example of the embodiment. [Figure 6] FIG. 11 is a diagram illustrating a second operation example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0015] [Embodiment] (System Configuration) A configuration of a mobile communication system 1 according to an embodiment will be described with reference to Fig. 1. In the following, an example in which the mobile communication system 1 is a 3GPP standard fifth generation system (5G / NR: New Radio) will be mainly described, but a fourth generation system (4G / LTE: Long Term Evolution) system and / or a sixth generation system may be at least partially applied to the mobile communication system 1.

[0016] As shown in FIG. 1, a mobile communication system 1 according to the embodiment includes a user equipment (UE) 100, a first network 200A, and a second network 200B.

[0017] The UE 100 is a mobile wireless communication device. The UE 100 may be any device used by a user, and may be, for example, a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0018] The UE 100 is a multi-SIM device that supports multiple subscriber identity modules (SIMs). The UE 100 communicates with multiple networks using multiple SIMs. In the following, an example in which the UE 100 supports two SIMs will be mainly described, but the UE 100 may support three or more SIMs. "Supporting multiple SIMs" means that the UE 100 has the ability to handle multiple SIMs, and the UE 100 does not necessarily have to be equipped with multiple SIMs. Such a UE 100 may be called a "UE that supports multiple SIMs." The SIM is not limited to a card-type SIM (a so-called SIM card), and may be an embedded SIM (a so-called eSIM) that is previously embedded in the UE 100. The SIM may be called a Universal Subscriber Identity Module (USIM).

[0019] The first network 200A is a network associated with one SIM of the UE 100. The second network 200B is a network associated with the other SIM of the UE 100. The UE 100 performs location registration to the first network 200A using one SIM, and performs location registration to the second network 200B using the other SIM. That is, the UE 100 is present in each of the first network 200A and the second network 200B. The first network 200A and the second network 200B may be networks of different telecommunications carriers. However, the first network 200A and the second network 200B may be networks of the same telecommunications carrier. The first network 200A and the second network 200B may be assigned different PLMN (Public Land Mobile Network) IDs.

[0020] The first network 200A includes a base station 210A constituting a radio access network, and a core network 220A. The core network 220A includes a mobility management device 221A and a gateway device 222A. Similarly, the second network 200B includes a base station 210B constituting a radio access network, and a core network 220B. The core network 220B includes a mobility management device 221B and a gateway device 222B. In the following, when the base stations 210A and 200B are not distinguished, they are simply called the base station 210, when the mobility management devices 221A and 221B are not distinguished, they are simply called the mobility management device 221, and when the gateway devices 222A and 222B are not distinguished, they are simply called the gateway device 222.

[0021] The base station 210 is a wireless communication device that performs wireless communication with the UE 100. The base station 210 manages one or more cells. The base station 210 performs wireless communication with the UE 100 that has established a connection with the base station 210 in a radio resource control (RRC) layer with the base station 210. The base station 210 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency. FIG. 1 shows an example in which the base station 210A manages a cell C1, and the base station 210B manages a cell C2. The UE 100 is located in an overlapping area of ​​the cells C1 and C2.

[0022] The base station 210 may be a gNB, which is a 5G / NR base station, or an eNB, which is a 4G / LTE base station. In the following, an example in which the base station 210 is a gNB will be mainly described. The base station 210 may be functionally divided into a CU (Central Unit) and a DU (Distributed Unit). The base station 210 may be a relay node such as an IAB (Integrated Access and Backhaul) node.

[0023] The mobility management device 221 is a device corresponding to the control plane, and is a device that performs various mobility management for the UE 100. The mobility management device 221 communicates with the UE 100 using NAS (Non-Access Stratum) signaling, and manages information of a tracking area in which the UE 100 is located. The mobility management device 221 performs paging through the base station 210 to notify the UE 100 of an incoming call. The mobility management device 221 may be an AMF (Access and Mobility Management Function) of 5G / NR, or an MME (Mobility Management Entity) of 4G / LTE.

[0024] The gateway device 222 is a device corresponding to the user plane and controls the transfer of data of the UE 100. The gateway device 222 may be a User Plane Function (UPF) of 5G / NR or a Serving Gateway (S-GW) of 4G / LTE.

[0025] (Example of protocol stack configuration) A configuration example of a protocol stack of the mobile communication system 1 will be described with reference to Fig. 2. As shown in Fig. 2, the protocol of the wireless section between the UE 100 and the base station 210 has a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) layer.

[0026] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the base station 210 via a physical channel.

[0027] The MAC layer performs data priority control, retransmission processing using hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the base station 210 via a transport channel. The MAC layer of the base station 210 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to the UE 100.

[0028] The RLC layer transmits data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the base station 210 via logical channels.

[0029] The PDCP layer performs header compression / decompression and encryption / decryption.

[0030] A Service Data Adaptation Protocol (SDAP) layer may be provided above the PDCP layer. The Service Data Adaptation Protocol (SDAP) layer maps IP flows, which are units for QoS control by the core network, to radio bearers, which are units for QoS control by the access stratum (AS).

[0031] The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. RRC signaling for various settings is transmitted between the RRC layer of the UE 100 and the RRC layer of the base station 210. When there is an RRC connection between the RRC of the UE 100 and the RRC of the base station 210, the UE 100 is in an RRC connected state. When there is no RRC connection between the RRC of the UE 100 and the RRC of the base station 210, the UE 100 is in an RRC idle state. When the RRC connection between the RRC of the UE 100 and the RRC of the base station 210 is suspended, the UE 100 is in an RRC inactive state.

[0032] The NAS layer, which is located above the RRC layer, performs session management and mobility management for the UE 100. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the mobility management device 221.

[0033] In addition, the UE 100 has an application layer and the like in addition to the protocol of the radio interface.

[0034] (Summary of selection behavior) The UE 100 can perform a cell selection operation or a cell reselection operation as a selection operation for selecting a camped-on cell. The UE 100 can perform the selection operation in any of the following cases, for example. When a new PLMN or a new SNPN (Stand-alone Non-Public Network) is selected When a USIM is inserted into the UE100 or an SNPN subscription is added If no suitable cell is found When transitioning from RRC connected state to RRC idle state or RRC inactive state

[0035] (A) Cell selection operation In the cell selection operation, UE 100 searches the frequency bands to identify the strongest cell for each frequency (e.g., the cell with the highest CD-SSB (cell-defining SS / PBCH Block) detection level, the cell with the highest CD-SSB received power (RSRP), or the cell with the highest CD-SSB received quality (RSRQ)). Next, UE 100 identifies a suitable cell from among the strongest cells. If UE 100 cannot identify a suitable cell (i.e., no suitable cell is found), UE 100 identifies an acceptable cell. If UE 100 can identify a suitable cell (i.e., a suitable cell is found), UE 100 selects the suitable cell as the camped-on cell. If UE 100 can identify only acceptable cells (i.e., an acceptable cell is found), UE 100 selects the acceptable cell as the camped-on cell.

[0036] Note that a suitable cell is one whose measured radio quality meets the cell selection criteria. A suitable cell's PLMN is one that is the selected PLMN, the registered PLMN or equal to these PLMNs. A suitable cell is not a forbidden or reserved cell and is not part of a tracking area included in the list of "forbidden tracking areas for roaming". An acceptable cell is one whose measured radio quality meets the cell selection criteria and is not a forbidden cell.

[0037] The cell selection criteria is, for example, Srxlev>0 and Squal>0. Srxlev represents the cell selection reception power. Srxlev is expressed as Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation -Qoffset temp It is calculated by Q rxlevmeas Q is the measured cell received power (RSRP). rxlevmin is the minimum required received power. Q rxlevminoffset is a constant applied predetermined offset. compensation is a parameter related to the uplink capability. tempis the offset applied temporarily. Squal represents the cell selection quality level. Squal=Q qualmeas -(Q qualmin +Q qualminoffset )-Qoffset temp It is calculated by Q qualmeas Q is the measured cell quality level (RSRQ). qualmin is the minimum required quality level. qualminoffset Qoffset is a constant offset. temp is the offset that is applied temporarily.

[0038] (B) Cell reselection operation In the cell reselection operation, the UE 100 measures the radio qualities of the serving cell and the neighboring cell. The UE 100 selects a camped-on cell to be used as a serving cell, for example, based on the following criteria. The UE 100 determines the priority of the selected cell based on the priority of the frequency. When one second or more has elapsed since the UE 100 camped on the current serving cell, the UE 100 may select a camped-on cell based on the following criteria.

[0039] (B1) The frequency priority of the neighboring cell is higher than the frequency priority of the current serving cell: The UE 100 is configured to transmit the received signal for a predetermined period (for example, Treselection RAT ) over Squal>Thresh X,HighQ or Srxlev>Thresh for a given period. X,HighP Select cells that satisfy the relationship Thresh X,HighP and Thresh X,HighQ Each of these is a predetermined threshold.

[0040] (B2) The frequency priority of the neighboring cell is the same as the frequency priority of the current serving cell: The UE 100 calculates a ranking Rs of a current serving cell and a ranking Rn of a neighboring cell, and selects a cell having a ranking Rn higher than Rs for a predetermined period as a camped-on cell.

[0041] Rs is Rs=Q meas,s +Q hyst -Qoffset temp Rn is calculated as Rn=Q meas,n -Qoffset-Qoffset temp It is calculated by Q meas,s Q is the received power (RSRP) of the current serving cell. meas,n is the received power (RSRP) of the neighboring cell. Q hyst Qoffset is a hysteresis value that makes it easier for the current serving cell to be reselected. temp is the offset that is applied temporarily.

[0042] (B3) The frequency priority of the neighboring cell is lower than the frequency priority of the current serving cell: The UE 100 is configured to <Thresh Serving,LowQ Or, Srxlev <Thresh Serving,LowP Under the assumption that the serving cell satisfies the relationship, Squal>Thresh X,LowQ or Srxlev>Thresh for a given period. X,LowP Select cells that satisfy the relationship Thresh X,LowP and Thresh X,LowQ Each of these is a predetermined threshold.

[0043] Various parameters used in cell selection are included in information (SIB: System Information Block) broadcast from the base station 210. The various parameters include frequency priority (e.g., cellReselectionPriority, cellReselectionSubPriority), a predetermined period (Treselection RAT ), various offsets (Qqualminoffset , Q rxlevminoffset , Q offsettemp , Q hyst , Q offset ), various thresholds (Thresh X,HighQ , Thresh X,HighP , Thresh Serving,LowQ , Thresh Serving,LowP , Thresh X,LowP , Thresh X,LowQ ) cellReselectionPriority indicates the priority of a frequency in eight stages, and cellReselectionSubPriority indicates the sub-priority of a frequency in four stages. This allows up to 32 stages of priority to be set for the frequency in UE 100. The frequency priority may be notified to UE 100 by an RRC release message. The frequency priority notified by the RRC release message can specify the priorities of multiple frequencies in a list format. The priority of the frequency takes precedence over the priority of the frequency that is broadcast. UE 100 performs a selection operation to select a camped-on cell based on the information received from base station 210.

[0044] The RRC release message may include carrier information (so-called redirectedCarrierInfo) that specifies a frequency. The carrier information takes precedence over the priority of the frequency. The UE 100 preferentially selects a cell that belongs to a frequency specified by the carrier information, regardless of the priority of the frequency.

[0045] (Example of UE configuration) A configuration example of the UE 100 will be described with reference to Fig. 3. As shown in Fig. 3, the UE 100 includes an antenna 101, an SIM 111, an SIM 112, a communication unit 120, and a control unit 130. The antenna 101 may be provided outside the UE 100. The SIM 111 and the SIM 112 are SIM cards or eSIMs.

[0046] The SIM 111 stores subscriber information and setting information necessary for the UE 100 to communicate with the first network 200A. The SIM 111 stores identification information of the UE 100 in the first network 200A, such as a telephone number and an International Mobile Subscriber Identity (IMSI).

[0047] The SIM 112 stores subscriber information and setting information necessary for the UE 100 to communicate with the second network 200B. The SIM 112 stores identification information of the UE 100 in the second network 200B, such as a telephone number and an IMSI.

[0048] The communication unit 120 performs wireless communication with the first network 200A and wireless communication with the second network 200B via the antenna 101 under the control of the control unit 130. The communication unit 120 may have only one receiving unit (RX: Receiver) 121. In this case, the communication unit 120 cannot simultaneously receive from the first network 200A and the second network 200B. The communication unit 120 may have only one transmitting unit (TX: Transmitter) 122. However, the communication unit 120 may have multiple transmitting units 122. The receiving unit 121 converts a radio signal received by the antenna 101 into a received signal that is a baseband signal, performs signal processing on the received signal, and outputs the signal to the control unit 130. The transmitting unit 122 performs signal processing on a transmission signal that is a baseband signal output by the control unit 130, converts the signal into a radio signal, and transmits the radio signal from the antenna 101.

[0049] The control unit 130 controls the communication unit 120 and performs various controls in the UE 100. The control unit 130 controls communication with the first network 200A using the SIM 111 and controls communication with the second network 200B using the SIM 112. The control unit 130 includes at least one processor and at least one memory. The memory stores a program executed by the processor and information used in processing by the processor. The memory may include at least one of a ROM, an EPROM, an EEPROM, a RAM, and a flash memory. The processor may include a digital signal processor (DSP) that performs digital processing of a digital signal, and a central processing unit (CPU) that executes a program. Note that a part of the memory may be provided in the communication unit 120. Also, the DSP may be provided in the communication unit 120.

[0050] The control unit 130 includes an RRC processing unit 131 and a NAS processing unit 132. The RRC processing unit 131 performs processing in the RRC layer. The NAS processing unit 132 performs processing in the NAS layer, which is a layer higher than the RRC layer. The RRC processing unit 131 and the NAS processing unit 132 may be configured by one processor or multiple processors.

[0051] The UE 100 thus configured communicates with the first network 200A using the SIM 111, and communicates with the second network 200B using the SIM 112. The control unit 130 monitors a paging message notifying paging from a cell managed by the base station 210B of the second network 200B during communication with the first network 200A. When the cell does not support transmission of paging reason information indicating the reason for paging by a paging message, the communication unit 120 transmits a NAS message indicating that the UE 100 is present in a non-support cell that does not support transmission of paging reason information to the mobility management device 221B of the second network 200B. This allows the mobility management device 221B to grasp that the UE 100 is present in a non-support cell. As a result, the mobility management device 221B does not operate on the assumption that the UE 100 is present in a supported cell, and therefore can perform appropriate control on the UE 100 present in a non-support cell.

[0052] The control unit 130 may have an RRC processing unit 131 that performs processing in a radio resource control (RRC) layer, and a NAS processing unit 132 that performs processing in a non-access stratum (NAS) layer that is a layer higher than the RRC layer. The RRC processing unit 131 may perform a process of providing support information indicating whether or not a cell supports transmission of paging reason information to the NAS processing unit 132 based on an RRC message from the base station 210B. The NAS processing unit 132 may perform a process of transmitting a NAS message to the mobility management device 221B via the communication unit 120 in response to the support information from the RRC processing unit 131. This allows the NAS processing unit 132 that performs a process of transmitting a NAS message to the mobility management device 221B to grasp whether or not a cell in which the UE 100 is present supports transmission of paging reason information. As a result, the mobility management device 221B can perform appropriate control on the UE 100 that is present in a non-support cell.

[0053] Furthermore, the RRC message may be a paging message. In this way, when paging for the UE 100 actually occurs, the NAS processing unit 132 can grasp whether the cell in which the UE 100 is located supports transmission of paging reason information.

[0054] When the identifier (ID) of the UE 100 and the paging reason information associated with the identifier are included in the paging message, the RRC processing unit 131 may provide support information indicating that the cell supports the transmission of the paging reason information to the NAS processing unit 132. This allows the NAS processing unit 132 to know whether the cell in which the UE 100 is located supports the transmission of the paging reason information without complicating the configuration of the paging message.

[0055] The RRC message may be a system information block (SIB) message broadcast from a cell. This allows the UE 100 to know in advance whether the cell in which the UE 100 is located supports transmission of paging reason information before receiving a paging message addressed to the UE 100. As a result, the UE 100 transmits a NAS message to the mobility management device 221B before a paging message is generated, so that the mobility management device 221B can know that the UE 100 is located in a non-supporting cell.

[0056] The NAS message may be at least one of a service request message for transitioning a mode in the NAS layer from an idle mode to a connected mode, and a registration request message for initial registration or registration update of the UE 100 in the second network 200B. This allows the mobility management device 221B to know that the UE 100 is present in a non-supported cell by the existing message, and can reduce the impact on the system. Also, when the NAS message is a registration request message, the mobility management device 221B can know that the UE 100 is present in a non-supported cell at the time of registration or registration update of the UE 100.

[0057] In addition, the operation of the functional units (specifically, at least one of antenna 101, SIM 111, SIM 112, communication unit 120, and control unit 130 (RRC processing unit 131 and NAS processing unit 132)) of UE 100 may be described as the operation of UE 100.

[0058] (Example of base station configuration) A configuration example of the base station 210A of the first network 200A will be described with reference to Fig. 4. Note that the base station 210B of the second network 200B has the same configuration as the base station 210A, so a description thereof will be omitted. As shown in Fig. 4, the base station 210A has an antenna 211, a communication unit 212, a network communication unit 213, and a control unit 214.

[0059] The communication unit 212 communicates with the UE 100 via the antenna 211 under the control of the control unit 214. The communication unit 212 has a receiving unit 212a and a transmitting unit 212b. The receiving unit 212a converts a radio signal received by the antenna 211 into a received signal which is a baseband signal, performs signal processing on the received signal, and outputs the signal to the control unit 214. The transmitting unit 212b performs signal processing on a transmission signal which is a baseband signal output by the control unit 214, converts the transmission signal into a radio signal, and transmits the radio signal from the antenna 211.

[0060] The network communication unit 213 is connected to the core network 220A. Under the control of the control unit 214, the network communication unit 213 performs network communication with the mobility management device 221A and the gateway device 222A.

[0061] The control unit 214 controls the communication unit 212 and performs various controls in the base station 210A. The control unit 214 includes at least one processor and at least one memory. The memory stores a program executed by the processor and information used in the processing by the processor. The memory may include at least one of a ROM, an EPROM, an EEPROM, a RAM, and a flash memory. The processor may include a digital signal processor (DSP) that performs digital processing of a digital signal, and a central processing unit (CPU) that executes the program. Note that a part of the memory may be provided in the communication unit 212. Also, the DSP may be provided in the communication unit 212.

[0062] The operation of the functional units (specifically, at least one of the antenna 211, the communication unit 212, the network communication unit 213, and the control unit 214) included in the base station 210A may be described as the operation of the base station 210A.

[0063] (Mobile communication system operation) The operation of the mobile communication system 1 will now be described.

[0064] (1) First operation example A first operation example of the mobile communication system 1 will be described with reference to Fig. 5. In the operation example shown in Fig. 5, the UE 100 communicates with the base station 210 of the first network 200A. A The mobile station 210 is present in a cell C1 managed by the base station 210B of the second network 200B, and is present in a cell C2 managed by the base station 210B of the second network 200B. Note that the following description will be given assuming that the mobility management device 221B of the second network 200B is an AMF.

[0065] In the following, the RRC processing unit 131 and the NAS processing unit 132 communicate with the second network 200B (specifically, transmission / reception / notification of messages, etc.) via the communication unit 120, but for ease of explanation, the explanation that the communication is via the communication unit 120 is omitted as appropriate. Also, the AMF 221B communicates with the UE 100 (specifically, the NAS processing unit 132) (transmission / reception / notification of messages, etc.) via the base station 210B, but for ease of explanation, the explanation that the communication is via the base station 210B is omitted as appropriate.

[0066] Step S101: The UE 100 and the second network 200B start a registration procedure. The UE 100 (NAS processing unit 132) transmits a registration request message to the AMF 221B. The AMF 221B receives the registration request message from the UE 100. The registration request message is a message for initially registering or updating the registration of the UE 100 in the second network 200B.

[0067] The NAS processing unit 132 may include the capability information of the UE 100 in the registration request message. The capability information may be, for example, information indicating that the UE 100 can grasp the paging reason from the paging reason information, or information indicating that the UE 100 can determine a communication to be prioritized based on the paging reason information. Thereby, the NAS processing unit 132 may transmit the capability information of the UE 100 to the second network 200B. The AMF 221B can grasp that the paging reason can be notified to the UE 100 based on the capability information.

[0068] Step S102: The AMF 221B transmits a registration approval message to the UE 100. The NAS processing unit 132 of the UE 100 receives the registration approval message from the AMF 221B. The registration approval message is a message indicating that registration or registration update to the second network 200B has been approved.

[0069] Step S103: The NAS processing unit 132 transmits a registration completion message to the AMF 221B. The AMF 221B receives the registration completion message from the UE 100. The registration completion message is, for example, a message indicating that the UE 100 has successfully completed the registration or registration update process to the second network 200B.

[0070] As shown in Fig. 5, the state of the UE 100 in the RRC layer thereafter is assumed to be an RRC connected state for the first network 200A and an RRC idle state for the second network 200B. The UE 100 is in communication with the first network 200A. The UE 100 is provided with a service such as a voice call from the first network 200A. Therefore, the UE 100 is in an RRC idle state for the second network 200B while communicating with the first network 200A.

[0071] In addition, the mode in the NAS layer of the UE 100 is a connected mode for the first network 200A and an idle mode for the second network 200B. The mode in the NAS layer may be a 5G Mobility Management (5GMM) mode. In this mode, the connected mode may be a 5GMM-connected mode, and the idle mode may be a 5GMM-idle mode.

[0072] The control unit 130 of the UE 100 monitors a paging message notifying of a paging from a cell C2 managed by a base station 210B of the second network 200B while communicating with the first network 200A.

[0073] Step S104: The AMF 221B transmits a paging request message addressed to the UE 100 to the base station 210B. B Receive from.

[0074] The paging request message includes paging reason information indicating the reason for paging. The AMF 221B may include the paging reason information in the paging request message based on the capability information from the UE 100. The paging reason information may indicate, for example, whether the reason for paging is a voice call.

[0075] Step S105: base station 210 B In response to receiving the paging request message, the communication unit 212 transmits a paging message notifying the UE 100 of a paging addressed to the UE 100, to the UE 100. The RRC processing unit 131 of the UE 100 receives the paging message addressed to the UE 100 from the base station 210B.

[0076] The paging message is used for notification to one or more UEs 100. The paging message is a message of the RRC layer. The paging message includes, for example, the ID of the UE 100. More specifically, for example, the paging message includes a list of paging records, and one paging record in the list includes the ID of the UE 100. For example, the ID is the 5G-S-TMSI or a full I-RNTI (Inactive Radio Network Temporary Identifier) ​​of the UE 100.

[0077] When transmission of paging reason information to the UE 100 is supported, the control unit 130 of the base station 210B transmits the paging reason information to the UE 100. For example, the control unit 130 of the base station 210B may associate the paging reason information with the ID of the UE 100 included in the paging message. The RRC processing unit 131 can grasp the reason for paging to the UE 100 based on the paging reason information associated with the ID of the UE 100.

[0078] Furthermore, the communication unit 212 of the base station 210B may associate paging reason information with each paging record. The RRC processing unit 131 can grasp the reason for paging to the UE 100 based on the paging reason information associated with the paging record including the ID of the UE 100.

[0079] Furthermore, the communication unit 212 of the base station 210B may transmit a paging message for each paging reason. The communication unit 212 of the base station 210B may transmit, for example, a first paging message for notifying paging whose paging reason is a voice call and a second paging message for notifying paging whose paging reason is not a voice call. The RRC processing unit 131 may grasp that the paging reason is a voice call by the fact that the first paging message includes an identifier of the UE 100. The RRC processing unit 131 may grasp that the paging reason is a reason other than a voice call by the fact that the second paging message includes an identifier of the UE 100.

[0080] Furthermore, the communication unit 212 of the base station 210B may transmit downlink control information (DCI) including paging reason information to the UE 100. The RRC processing unit 131 can grasp the reason for paging to the UE 100 based on the paging reason information included in the downlink control information.

[0081] By acquiring the paging reason information, the RRC processing unit 131 may determine that the cell C2 in which the UE 100 is located is a supporting cell that supports transmission of the paging reason information. Furthermore, when the RRC processing unit 131 can grasp the paging reason based on the paging message or the downlink control information, the RRC processing unit 131 may determine that the cell C2 in which the UE 100 is located is a supporting cell.

[0082] On the other hand, when the base station 210B does not support transmission of paging reason information to the UE 100, the base station 210B may not transmit the paging reason information to the UE 100. When the paging reason information is not included in the paging message, the RRC processing unit 131 may determine that the cell C2 in which the UE 100 is located is a non-support cell that does not support transmission of paging reason information. Furthermore, when the RRC processing unit 131 cannot grasp the paging reason based on the paging message or the downlink control information, the RRC processing unit 131 may determine that the cell C2 in which the UE 100 is located is a non-support cell.

[0083] In this operation example, the base station 210B is assumed to not support transmission of paging reason information to the UE 100. Therefore, the RRC processing unit 131 determines that the cell C2 in which the UE 100 is located is a non-supported cell.

[0084] Step S106: The RRC processing unit 131 provides a paging reception notification to the NAS processing unit 132. The NAS processing unit 132 receives the paging reception notification from the paging reception notification. The paging reception notification is for notifying that the UE 100 has received a paging. The RRC processing unit 131 may indicate to the NAS processing unit 132 that a paging message has been received by using the paging reception notification.

[0085] The RRC processing unit 131 provides, to the NAS processing unit 132, support information indicating whether or not the cell C2 in which the UE 100 is located supports transmission of paging reason information, based on the paging message.

[0086] When the RRC processing unit 131 determines that the cell C2 is a supporting cell, the RRC processing unit 131 may provide support information indicating that the cell C2 supports the transmission of the paging reason information to the NAS processing unit 132. For example, when the ID of the UE 100 and the paging reason information associated with the ID of the UE 100 are included in the paging message, the RRC processing unit 131 may provide the support information indicating that the cell C2 supports the transmission of the paging reason information to the NAS processing unit 132.

[0087] When the RRC processing unit 131 determines that the cell C2 is a non-supporting cell, the RRC processing unit 131 may provide support information indicating that the cell C2 does not support transmission of the paging reason information to the NAS processing unit 132. For example, when the paging reason information is not included in the paging message, the RRC processing unit 131 may provide support information indicating that the cell C2 does not support transmission of the paging reason information to the NAS processing unit 132.

[0088] For example, the RRC processing unit 131 may provide the paging reason information as the support information to the NAS processing unit 132. The RRC processing unit 131 may provide the NAS processing unit 132 with support information indicating that the paging reason information was not included in the paging message.

[0089] When the RRC processing unit 131 determines that the cell C2 is a supported cell, the RRC processing unit 131 may provide paging reason information to the NAS processing unit 132. This allows the NAS processing unit 132 to understand the paging reason and may also understand that the cell C2 is a supported cell. On the other hand, when the RRC processing unit 131 determines that the cell C2 is a non-supported cell, the RRC processing unit 131 may not provide paging reason information, but may indicate to the NAS processing unit 132 that a paging message has been received. The NAS processing unit 132 may understand that the cell C2 is a non-supported cell in response to the fact that the paging reason information has not been provided.

[0090] In this operation example, since the base station 210B does not support transmitting paging reason information to the UE 100, the explanation will proceed assuming that the RRC processing unit 131 provides support information indicating that the cell C2 does not support transmitting paging reason information to the NAS processing unit 132.

[0091] The NAS processing unit 132 may determine the priority in response to receiving the paging reception notification. The NAS processing unit 132 determines which of the communication with the first network 200 and the communication with the second network 200B corresponding to the paging is to be prioritized (or which is preferred).

[0092] For example, when the NAS processing unit 132 receives paging reason information, the NAS processing unit 132 determines whether to prioritize communication with the first network 200 or communication with the second network 200B corresponding to the paging, based on the paging reason indicated by the paging reason information. For example, when the NAS processing unit 132 does not know the reason for the paging from the second network 200B, the NAS processing unit 132 may determine that communication with the first network 200A is prioritized over communication with the second network 200B.

[0093] Step S107: The RRC processing unit 131 executes a process of establishing an RRC connection. The RRC processing unit 131 may execute an RRC setup procedure or may execute an RRC re-establishment procedure. As a result, an RRC connection is established between the UE 100 and the base station 210B. As a result, the state of the UE 100 in the RRC layer transitions to an RRC connected state for the second network 200B. Note that when the UE 100 is in an RRC inactive state, the UE 100 may transition to the RRC connected state by executing an RRC resume procedure.

[0094] Step S108: The NAS processing unit 132 transmits a NAS message indicating that the UE 100 is present in the non-supported cell to the AMF 221B. NAS A message is received from the UE 100.

[0095] For example, in response to receiving support information indicating that the cell C2 does not support transmission of paging reason information, the NAS processing unit 132 transmits a NAS message via the communication unit 120. For example, when the NAS processing unit 132 determines that the cell C2 is a non-supported cell, the NAS processing unit 132 may include serving cell information indicating that the UE 100 is serving a non-supported cell in the NAS message.

[0096] For example, in response to receiving support information indicating that the cell C2 supports transmission of the paging reason information, the NAS processing unit 132 transmits a NAS message via the communication unit 120. For example, when the NAS processing unit 132 determines that the cell C2 is a supporting cell, the NAS processing unit 132 may include serving cell information indicating that the UE 100 is serving the supporting cell in the NAS message.

[0097] When it is determined that the communication with the first network 200A is prioritized over the communication with the second network 200B, the NAS processing unit 132 may transmit a busy indicator to the AMF 221B using a service request message as a NAS message. The busy indicator is information indicating that the communication with the first network 200A is prioritized over the communication with the second network 200B when the priority of the communication with a network other than the second network 200B (the first network 200A) is higher than the priority of the communication with the second network 200B. The busy indicator may indicate that the UE 100 is busy.

[0098] The service request message is used to change the 5GMM mode from 5GMM-idle mode to 5GMM-connected mode. The service request message may include a service type. The service type is an information element for identifying the purpose of the service request procedure. The service type may indicate that the UE 100 is busy.

[0099] In this operation example, the explanation will be given on the assumption that the NAS processing unit 132 transmits a NAS message including a busy indicator and serving cell information to the AMF 221B.

[0100] Step S109: The AMF 221B determines whether the UE 100 is present in a non-supported cell. The AMF 221B may determine whether the UE 100 is present in a non-supported cell based on, for example, serving cell information. The AMF 221B may determine that the UE 100 is present in a non-supported cell based on serving cell information indicating that the UE 100 is present in a non-supported cell (YES). The AMF 221B may determine that the UE 100 is not present in a non-supported cell based on serving cell information indicating that the UE 100 is present in a supported cell (NO). Furthermore, when the serving cell information is not included in the NAS message, the AMF 221B may determine that the UE 100 is present in a non-supported cell (YES).

[0101] When the AMF 221B receives a busy indicator from the UE 100 existing in the non-supported cell, the AMF 221B may consider that the UE 100 has not correctly determined the priority of the communication. Therefore, when the AMF 221B determines that the UE 100 exists in the non-supported cell, the AMF 221B may execute the process of step S110. Note that when the priority of the communication of the second network 200B is high (for example, the paging reason is a voice call) and the AMF 221B determines that the UE 100 exists in the non-supported cell, the AMF 221B may execute the process of step S110.

[0102] When the AMF 221B receives a busy indicator from the UE 100 existing in the supported cell, the AMF 221B may consider that the UE 100 has correctly determined the priority of the communication. Therefore, when the AMF 221B determines that the UE 100 exists in the supported cell, the AMF 221B may execute the process of step S111. Note that even when the AMF 221B determines that the UE 100 exists in the non-supported cell, the AMF 221B may execute the process of step S111 if the priority of the communication of the second network 200B is low (for example, the paging reason is other than a voice call).

[0103] Step S110: The AMF 221B transmits a paging request message to the base station 210B, similarly to step S104. Note that, when the UE 100 is in the range of a non-supported cell, the AMF 221B does not need to include the paging reason information in the paging request message.

[0104] Thereafter, the base station 210B and the UE 100 may execute the same processes as steps S105, S106, and S108.

[0105] Step S111: In response to receiving the busy indicator, the AMF 221B stops further paging to the UE 100. More specifically, the AMF 221B stops paging escalation and paging repetition.

[0106] (2) Second operation example The second operation example will be described mainly with reference to Fig. 6, focusing on differences from the above-mentioned operation example. In the second operation example, a case will be described in which the UE 100 performs a selection operation to select a camped-on cell in the second network 200B.

[0107] In this operation example, the second network 200B includes a base station 210B and a base station 210C. Note that the UE 100 may be in an RRC connected state, an RRC idle state, or an RRC inactive state in the first network 200A.

[0108] Step S201: The communication unit 212 of the base station 210B transmits a system information block (SIB) message by broadcast. The communication unit 212 of the base station 210B transmits the SIB message via the cell C2. The communication unit 120 of the UE 100 receives the SIB message from the base station 210B (cell C2).

[0109] The SIB message may include, for example, cell support information indicating whether or not the cell that is the source of the SIB message supports transmission of paging reason information. Alternatively, if the control unit 214 of the base station 210B does not support transmission of paging reason information, the cell support information may not be included in the SIB message. The SIB message may be a type 1 SIB (SIB1) message or another SIB message. The other SIB message may be, for example, a type of SIB message newly defined for a UE that communicates with multiple networks using multiple SIMs (so-called Multi-SIM compatible UE).

[0110] The control unit 130 of the UE 100 determines whether the cell is a supported cell that supports transmission of paging reason information or a non-supported cell that does not support transmission of paging reason information based on the SIB message. The control unit 130 of the UE 100 may determine whether the cell that is the source of the SIB message is a supported cell or a non-supported cell based on, for example, cell support information. When the SIB message does not include cell support information, the control unit 130 of the UE 100 may determine that the cell is a non-supported cell.

[0111] The communication unit 212 of the base station 210C transmits the SIB message by broadcast, similar to the base station 210B. The communication unit 120 of the UE 100 receives the SIB message from (the cell of) the base station 210C.

[0112] In this operation example, the cell C2 of the base station 210C is a supporting cell that supports the transmission of paging reason information, and the cell of the base station 210C (hereinafter, appropriately referred to as cell C3) is a non-supporting cell that does not support the transmission of paging reason information. Therefore, the control unit 130 of the UE 100 determines that the cell C2 is a supporting cell based on the SIB message from the cell C2, and determines that the cell C3 is a non-supporting cell based on the SIB message from the cell C3.

[0113] Note that the control unit 130 of the UE 100 may store a cell identifier and whether the cell indicated by the cell identifier is a supported cell or a non-supported cell. The control unit 130 may determine whether the cell is a supported cell or not based on information stored in the past.

[0114] Step S202: The control unit 130 (the RRC processing unit 131) of the UE 100 performs a selection operation to select a camped-on cell in the second network 200B. Before selecting the camped-on cell, the RRC processing unit 131 measures radio quality for one or more cells of the second network 200B.

[0115] In the selection operation, the control unit 130 preferentially selects a supporting cell as a camped-on cell over a non-supporting cell. For example, the control unit 130 may select a supporting cell with the best measurement result of wireless quality from one or more cells as a camped-on cell. That is, the control unit 130 may select a supporting cell as a camped-on cell even if there is a non-supporting cell with a better measurement result of wireless quality than the supporting cell.

[0116] When the wireless quality of any of the supported cells does not satisfy the predetermined criterion, the control unit 130 may select a non-supported cell whose wireless quality satisfies the predetermined criterion from among one or more cells as the camped-on cell. When there are multiple non-supported cells that satisfy the predetermined criterion, the control unit 130 may select the non-supported cell whose wireless quality measurement result is the best as the camped-on cell. Note that the predetermined criterion is, for example, a cell selection criterion (Srxlev>0 and Squal>0).

[0117] In this operation example, the explanation will be given on the assumption that the wireless quality of cell C2, which is a supporting cell, does not satisfy the cell selection criterion, and the control unit 130 selects cell C3, which is a non-supporting cell, as the camped-on cell.

[0118] Step S203: The RRC processing unit 131 provides the support information to the NAS processing unit 132 .

[0119] The support information of the RRC processing unit 131 may be, for example, information related to whether or not cell support information indicating that the cell supports the transmission of paging reason information is included in the SIB message. For example, when cell support information indicating that the cell C3 is a non-supporting cell is included in the SIB message or when the cell support information is not included in the SIB message, the RRC processing unit 131 may provide support information indicating that the cell C3 does not support the transmission of paging reason information to the NAS processing unit 132. For example, when cell support information indicating that the cell C2 is a supporting cell is included in the SIB message, the RRC processing unit 131 may provide support information indicating that the cell C2 supports the transmission of paging reason information to the NAS processing unit 132.

[0120] Step S204: This is the same as step S107.

[0121] Step S205: When a non-supported cell is selected, the NAS processing unit 132 may transmit a NAS message indicating that the UE 100 is present in the non-supported cell to the AMF 221B. The AMF 221 may receive the NAS message from the UE 100. The NAS message may be a service request message or a registration request message.

[0122] The NAS processing unit 132 may include, in the NAS message, serving cell information indicating that the UE 100 is located in a non-supported cell, similarly to step S108. The AMF 221 may grasp that the UE 100 is located in a non-supported cell based on the serving cell information.

[0123] The NAS processing unit 132 may not include the serving cell information in the NAS message. The AMF 221B may know that the UE 100 is located in a non-supported cell because the NAS message does not include the serving cell information.

[0124] Step S206: AMF221B is a parameter that specifies the priority in the selection operation (Index to RAT / Frequency Selection Priority:R FS P index) to the base station 210C. The network communication unit 213 of the base station 210C receives the RSRP index from the AMF 221B.

[0125] The base station 210C generates frequency priority information (eg, cellReselectionPriority, cellReselectionSubPriority) based on the RSRP index such that the frequency priority of a supporting cell is higher than the frequency priority of a non-supporting cell.

[0126] Thereafter, the description will proceed on the assumption that the state of the UE 100 in the RRC layer is an RRC connected state with respect to the first network 200A, and the mode of the UE 100 in the NAS layer is a connected mode with respect to the first network 200A.

[0127] Step S207: The communication unit 212 of the base station 210C transmits an RRC release message to the UE 100. The communication unit 120 of the UE 100 receives the RRC release message. The RRC release message may include frequency priority information generated based on the RSRP index.

[0128] Since the RRC connection is released by the RRC release message, the state of the UE 100 in the RRC layer is the RRC idle state for the second network 200B, and the mode of the UE 100 in the NAS layer is the idle mode for the second network 200B.

[0129] Step S208: The control unit 130 performs a selection operation to select a camped-on cell in the second network 200B, similar to step S202. The control unit 130 preferentially selects a supporting cell over a non-supporting cell based on frequency priority information.

[0130] In this operation example, the explanation will be given on the assumption that the control unit 130 selects the cell C2, which is a supporting cell, as the camp-on cell.

[0131] Steps S209 and S210: The steps are the same as steps S104 and S105. Note that the communication unit 212 of the base station 210B ,sa The paging message including the paging cause information is transmitted to the UE 100 via the cell C2 which is a port cell.

[0132] Steps S211 to S213: The steps are the same as steps S106 to S108. Note that the UE 100 is a supporting cell. cell Since the mobile station is currently located in C2, paging is stopped as in step S111.

[0133] [Other embodiments] In the operation of the above-described embodiment, the NAS processing unit 132 of the UE 100 notifies the AMF 221 of whether the cell in which the UE 100 is present is a supported cell or a non-supported cell, but this is not limited to the above. For example, the base station 210 that manages a cell that does not support transmission of paging reason information may notify the AMF 221 that the Multi-SIM-compatible UE 100 is present in the cell.

[0134] In the operation of the above-described embodiment, the first network 200A and the base station 210A may be read as a cell C1 (first cell), and the first network 200A and the base station 210A may be read as a cell C2 (second cell).

[0135] The steps in the operations of the above-described embodiments do not necessarily have to be executed in chronological order according to the order described in the flow diagram or sequence diagram. For example, the steps in the operations may be executed in an order different from that described in the flow diagram or sequence diagram, or may be executed in parallel. Some of the steps in the operations may be deleted, and additional steps may be added to the process. Furthermore, each of the above-described operation flows is not limited to being executed separately and independently, but may be executed by combining two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0136] A program may be provided that causes a computer to execute each process performed by the UE 100 or the base station 210. The program may be recorded in a computer-readable medium. Using the computer-readable medium, it is possible to install the program in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. In addition, a circuit that executes each process performed by the UE 100 or the base station 210 may be integrated, and at least a part of the UE 100 or the base station 210 may be configured as a semiconductor integrated circuit (chip set, SoC).

[0137] In the above embodiment, "transmit" may mean performing processing of at least one layer in a protocol stack used for transmission, or may mean physically transmitting a signal wirelessly or by wire. Alternatively, "transmit" may mean a combination of performing processing of at least one layer and physically transmitting a signal wirelessly or by wire. Similarly, "receive" may mean performing processing of at least one layer in a protocol stack used for reception, or may mean physically receiving a signal wirelessly or by wire. Alternatively, "receive" may mean a combination of performing processing of at least one layer and physically receiving a signal wirelessly or by wire.

[0138] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes, etc. are possible without departing from the spirit of the invention. [Explanation of symbols]

[0139] 1: Mobile communication systems 100:UE 101: Antenna 120: Communications Department 121: Receiving unit 122: Transmitter 130: Control section 131: RRC processing unit 132: NAS processing unit 200A: First network 200B: Second network 210A:Base station 210B:Base station 210C: Base station 211: Antenna 212: Communications Department 212a: Receiving section 212b: Transmitter 213: Network interface 214: Control section 220A: Core Network 220B: Core Network 221A: Mobility management device 221B: Mobility management device 222A: Gateway device 222B: Gateway device

Claims

1. A communication device (100) for communicating with a plurality of networks including a first network (200A) and a second network (200B) using a plurality of subscriber identity modules (111, 112), comprising: a non-access stratum (NAS) processing unit (132) for performing processing to transmit a registration request message including capability information indicating that the communication device has a capability to support information indicating a paging cause to an access and mobility management function (AMF) (221B) of the second network; A radio resource control (RRC) processing unit (132) that performs processing to receive a paging message including a list of paging records and the paging reason associated with each of the paging records from a base station (210B) of the second network that supports information indicating the paging reason when a registration request message including the capability information is transmitted to an AMF of the second network, The capability information is used by a base station of the second network that supports the information indicating the paging reason to include the paging reason in the paging message based on the information indicating the paging reason from the AMF. Communications equipment.

2. The RRC processing unit provides the paging reason to the NAS processing unit based on the identifier of the communication device included in the paging record. The communication device according to claim 1 .

3. The paging reason indicates whether the reason for the paging message is a voice call or not.

3. A communication device according to claim 1 or 2.

4. A base station (210B) of a second network (200B) communicating with a communication device (100) that communicates with a plurality of networks including a first network (200A) and a second network (200B) using a plurality of subscriber identity modules (111, 112), comprising: A network communication unit (213) that receives information indicating a paging cause from an access and mobility management function (AMF) (221B) of the second network, the information being provided to a base station that supports the information indicating the paging cause based on a registration request message including capability information indicating that the communication device has a capability of supporting the information indicating the paging cause; and a communication unit (212) configured to transmit, based on reception of the information indicating the paging reason, a paging message including a list of paging records including an identifier of the communication device and the paging reason associated with each of the paging records to the communication device. Base station.

5. The paging reason indicates whether the reason for the paging message is a voice call or not. The base station according to claim 4.

6. A communication method for a communication device (100) that communicates with a plurality of networks including a first network (200A) and a second network (200B) using a plurality of subscriber identity modules (111, 112), comprising: sending a registration request message to an Access and Mobility Management Function (AMF) (221B) of the second network, the registration request message including capability information indicating that the communication device has a capability to support information indicating a paging cause; receiving a paging message including a list of paging records and the paging reason associated with each of the paging records from a base station (210B) of the second network that supports information indicating the paging reason when a registration request message including the capability information is sent to an AMF of the second network; The capability information is used by a base station of the second network that supports the information indicating the paging reason to include the paging reason in the paging message based on the information indicating the paging reason from the AMF. Communication methods.

7. providing the paging reason from a Radio Resource Control (RRC) layer to a Non-Access Stratum (NAS) layer based on an identifier of the communication device included in the paging record. The communication method according to claim 6.

8. The paging reason indicates whether the reason for the paging message is a voice call or not. A communication method according to claim 6 or 7.

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