User terminal and communication control method

Abstract

When this user terminal is conducting a Multi-access PDU Session over a first radio access network of a PPLMN and a second radio access network of an SPLMN, the user terminal generates S-TFCL information indicating combinations of frequencies of the SPLMN available for use in an MA PDU Session using cells of the first radio access network, or P-TFCL information indicating combinations of frequencies of the PPLMN available for use in an MA PDU Session using cells of the second radio access network, and controls, on the basis of the S-TFCL information or the P-TFCL information, selection of a HO destination cell and selection of a frequency for DC or CA, with respect to a base station.

Description

User terminal and communication control method

[0001] The present invention relates to a user terminal and a communication control method.This application claims priority to Japanese Patent Application No. 2024-006292, filed on January 18, 2024, the contents of which are incorporated herein by reference.

[0002] Conventionally, a fifth-generation mobile communication system (5G system) standardized by "3GPP (registered trademark) (3rd Generation Partnership Project)" has been known (see, for example, Non-Patent Documents 1 and 2). FIG. 5 is a diagram showing a schematic architecture of a 5G system. In FIG. 5, the 5G system is composed of a UE (User Equipment), a RAN (Radio Access Network), a UPF (User Plane Function) of a CN (Core Network), and various NFs (Network Functions) of the CN control plane (C-plane). Examples of NFs of the CN C-plane include an AMF (Access and Mobility Management Function), an SMF (Session Management Function), and a PCF (Policy Control Function).

[0003] Here, a logical communication path established between a UE and a CN (UPF) to use a mobile communication service is referred to as a "session." A session established between a UE and a CN (UPF) using multiple wireless paths is referred to as a "multi-access session." Non-Patent Documents 1 and 2 specify a "Multi-access PDU (Packet Data Unit) Session (hereinafter referred to as an "MA PDU Session")" as an example of a multi-access session. Figure 6 shows an example configuration of an "MA PDU Session." As shown in Figure 6, a UE establishes an "MA PDU Session" with a CN (UPF) using a "3GPP access" wireless path via a RAN and a "non-3GPP access" wireless path via a wireless LAN (Local Area Network) such as Wi-Fi (registered trademark). "3GPP access" refers to an access network specified by 3GPP. "Non-3GPP access" refers to an access network other than "3GPP access." The UE uses the "MA PDU Session" to send and receive data between a DN (Data Network) such as the Internet outside the 5GC (CN of the 5G system). By using the "MA PDU Session", the UE can improve communication quality by expanding the communication bandwidth, reducing communication delays, and ensuring redundancy in the communication path.

[0004] Also, DC (Dual Connectivity) and CA (Carrier Aggregation) are known as communication methods in which one UE simultaneously uses multiple base stations that each use a different frequency (see, for example, Non-Patent Document 3). Also, HO (Handover) is known in which a UE switches the base station to which it is connected.

[0005] 3GPP, TS 23.501, V18.2.0, 2023-063GPP, TS 23.502, V18.2.0, 2023-063GPP, TS 36.300, V17.0.0, 2022-03

[0006] When a UE is performing a multi-access session (MA PDU Session With two 3GPP Access) with a UPF using multiple radio paths via each of two RANs (3GPP access), how to select an appropriate HO destination cell (base station) when HO is performed. Also, when a UE is performing DC or CA while performing "MA PDU Session With two 3GPP Access," how to select an appropriate target cell (base station) for DC or CA is also an issue.

[0007] The present invention has been made taking these circumstances into consideration, and its purpose is to appropriately select the cell (base station) to be HO'd and the cell (base station) to be targeted for DC or CA when a "Multi-access PDU Session" is being implemented.

[0008] One aspect of the present invention is a user terminal of a mobile communication system having a core network connected to a plurality of radio access networks, the user terminal comprising: a frequency combination information storage unit that stores frequency combination information indicating a combination of frequencies that can be used in a "Multi-access PDU Session" by the user terminal; a PLMN frequency information storage unit that stores PLMN frequency information indicating frequencies that can be used in each PLMN (Public Land Mobile Network); and, when a "Multi-access PDU Session" is being implemented between a first radio access network of a PPLMN (Primary PLMN) and a second radio access network of an SPLMN (Secondary PLMN), S-TFCL information indicating a combination of frequencies of an SPLMN that can be used in a "Multi-access PDU Session" using a cell of the first radio access network based on the frequency combination information and the PLMN frequency information. and a communication control unit that creates P-TFCL information indicating a combination of frequencies of PPLMNs that can be used in a "Multi-Session" and controls, based on the created S-TFCL information or P-TFCL information, the selection of a cell as a handover (HO) destination for the user terminal and the selection of frequencies to be used for DC (Dual Connectivity) or CA (Carrier Aggregation) for a base station to which the user terminal is connected. One aspect of the present invention is the user terminal described above, wherein, when a handover occurs for the user terminal or when DC or CA is enabled, the communication control unit determines whether or not terminal capability information of the user terminal held by a base station to which the user terminal is connected passes or fails based on the S-TFCL information or P-TFCL information, and if the result is unsuccessful, executes a frequency preference method for restricting the handover destination cell or frequencies to be used for DC or CA for the user terminal based on the S-TFCL information or P-TFCL information.In one aspect of the present invention, in the user terminal described above, the frequency preference method does not monitor frequencies other than those included in S-TFCL information or P-TFCL information, regardless of MC (Measurement Configure) from a base station.In another aspect of the present invention, in the user terminal described above, the frequency preference method does not include information about the designated frequency in the MR even when an opportunity to transmit an MR (Measurement Report) for a designated frequency that is a frequency other than those included in the S-TFCL information or P-TFCL information is detected.In another aspect of the present invention, in the user terminal described above, the frequency preference method is, when the user terminal receives from a base station a monitoring request for a designated frequency that is a frequency other than those included in the S-TFCL information or P-TFCL information, to transmit to the base station a signal rejecting the monitoring request for the designated frequency. In one aspect of the present invention, in the user terminal described above, the frequency preference method modifies terminal capability information of the user terminal previously transmitted to a base station to information that does not include frequencies other than those included in S-TFCL information or P-TFCL information, and transmits the modified terminal capability information of the user terminal to the base station. In another aspect of the present invention, in the user terminal described above, the frequency preference method is a method related to HO, and, if the user terminal supports CHO (Conditional HO), the user terminal excludes cells using frequencies other than those included in the S-TFCL information or P-TFCL information from the HO destination cells by CHO. In another aspect of the present invention, in the user terminal described above, the frequency preference method is a method related to DC and CA, and, when a base station instructs the user terminal to target cells using DC or CA with frequencies other than those included in the S-TFCL information or P-TFCL information, the user terminal rejects the instruction.

[0009] One aspect of the present invention is a communication control method executed by a user terminal of a mobile communication system having a core network connected to a plurality of radio access networks, the method comprising: a frequency combination information storage step of storing frequency combination information indicating a combination of frequencies available for use in a "Multi-access PDU Session" by the user terminal; a PLMN frequency information storage step of storing PLMN frequency information indicating frequencies available in each PLMN (Public Land Mobile Network); and, when a "Multi-access PDU Session" is being implemented between a first radio access network of a PPLMN (Primary PLMN) and a second radio access network of an SPLMN (Secondary PLMN), storing S-TFCL information indicating a combination of frequencies available for use in a "MA PDU Session" using a cell of the first radio access network based on the frequency combination information and the PLMN frequency information. and a communication control step of creating P-TFCL information indicating a combination of frequencies of PPLMNs that can be used in a "User Terminal Session," and controlling a base station to which the user terminal is connected to select a cell to which the user terminal will perform a Handover (HO) and a frequency to be used for Dual Connectivity (DC) or Carrier Aggregation (CA) based on the created S-TFCL information or P-TFCL information.

[0010] According to the present invention, when a "Multi-access PDU Session" is being implemented, the effect of being able to appropriately select the cell (base station) to be HO'd and the cell (base station) to be targeted for DC or CA is achieved.

[0011] FIG. 1 is a block diagram showing an example configuration of a mobile communication system according to an embodiment; FIG. 2 is a diagram showing a schematic configuration of a UE according to an embodiment; FIG. 3 is a diagram showing a schematic configuration of an AM (Access and Mobility) control device according to an embodiment; FIG. 4 is a flowchart showing an example procedure of a communication control method according to an embodiment; FIG. 5 is a diagram showing a schematic architecture of a conventional 5G system; and FIG. 6 is a diagram showing an example configuration of a conventional "MA PDU Session".

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of a mobile communication system according to one embodiment. In FIG. 1, a UE (user equipment) 10 is connectable to RANs (radio access networks) 30 (30_1, 30_2) that are "3GPP access." The RAN 30_1 is a RAN of a first PLMN (Public Land Mobile Network). The first PLMN is a PLMN (PPLMN (Primary PLMN)) that manages a base station of a PAN (Primary Access Network), which is a base station to which the UE 10 first connects. The RAN 30_2 is a RAN that is a candidate for a second PLMN. The second PLMN is a PLMN (SPLMN (Secondary PLMN)) that manages a base station of a SAN (Secondary Access Network), which is a base station to which the UE 10 connects after the base station of the PAN.

[0013] The first PLMN and the second PLMN may be the same PLMN (i.e., the same communication carrier) or different PLMNs (i.e., different communication carriers). The RANs 30 (30_1, 30_2) are connected to a UPF (User Plane Function) 60 of a CN (Core Network) of the mobile communication system 1. Hereinafter, the RANs 30_1 and 30_2 will be referred to as RAN 30 when there is no particular distinction between them.

[0014] Although only two RANs 30 (30_1, 30_2) are shown in FIG. 1 , the mobile communication system 1 may include three or more RANs 30 (30_1, 30_2, 30_3, ...) connected to the UPF 60, and the UE 10 may be connectable to three or more RANs 30 (30_1, 30_2, 30_3, ...). In this case, all of the RANs 30 (30_1, 30_2, 30_3, ...) may or may not be the same PLMN. Furthermore, all of the RANs 30 (30_1, 30_2, 30_3, ...) are connected to the UPF 60 of the mobile communication system 1. Furthermore, although only one UPF 60 is shown in FIG. 1 , the mobile communication system 1 may include multiple UPFs 60, and one RAN 30 may be connected to one or multiple UPFs 60.

[0015] The UE 10 is also connectable to a wireless LAN 80 that is "non-3GPP access." The wireless LAN 80 is connected to the UPF 60 of the mobile communication system 1. The wireless LAN 80 is an example of a wireless access network that is "non-3GPP access."

[0016] The UPF 60 is connected to a DN (data network) such as the Internet outside the CN of the mobile communication system 1 .

[0017] The UE 10 can establish a session with the UPF 60 using a wireless path via the RAN 30 or the wireless LAN 80, and can transmit and receive data to and from the DN using the established session. In addition, the UE 10 can establish a multi-access session with the UPF 60 using a wireless path via the RAN 30 and a wireless path via the wireless LAN 80, and can transmit and receive data to and from the DN using the established multi-access session.

[0018] In this embodiment, the UE 10 is further intended to be able to establish a multi-access session (MA PDU Session With two 3GPP Accesses) with the UPF 60 using multiple wireless paths via each of multiple RANs 30. The two "3gpp accesses" (base stations) for establishing the multi-access session are a PAN base station and a SAN base station.

[0019] Furthermore, in this embodiment, when UE 10 performs HO (Handover) while performing "MA PDU Session With two 3GPP Access", it is possible to appropriately select a cell (base station) as a HO destination. Furthermore, in this embodiment, when UE 10 performs "MA PDU Session With two 3GPP Access", it is possible to appropriately select a cell (base station) as a target of DC (Dual Connectivity) or CA (Carrier Aggregation).

[0020] The AM (Access and Mobility) control device 50 is a network device that realizes one NF (network function) of the control plane (C-plane) of the mobile communication system 1. The AM control device 50 is a network device that realizes an NF corresponding to the AMF of, for example, 5GC (CN of the 5G system). However, in this embodiment, the AM control device 50 is a network device that realizes a new additional NF in addition to the AMF of 5GC.

[0021] The AM control device 50 performs C-plane communication between the UE 10 and the RAN 30 .

[0022] 2 is a diagram showing a schematic configuration of a UE according to this embodiment. In FIG. 2, the UE 10 includes a control unit 110, a storage unit 120, a communication unit 130, a display unit 140, and an operation unit 150.

[0023] The control unit 110 is a CPU (Central Processing Unit) that calls and executes programs stored in the storage unit 120 to realize various functions.

[0024] The control unit 110 includes, as one of its functions, a communication control unit 1110. The communication control unit 1110 is realized by the CPU executing a communication control program 1210 stored in the storage unit 120.

[0025] 2 shows only a communication control unit 1110 related to functions added from the conventional UE 10 as a function of the control unit 110. Similarly, only a communication control program 1210 related to functions added from the conventional UE 10 as a program stored in the storage unit 120.

[0026] The storage unit 120 is configured by a storage medium, such as a hard disk drive (HDD), flash memory, electrically erasable programmable read-only memory (EEPROM), random access read / write memory (RAM), read-only memory (ROM), or any combination of these storage media. The storage unit 120 stores various programs, such as a communication control program 1210, executed by the control unit 110 (CPU), and various data.

[0027] The communication unit 130 connects to a base station of the RAN 30 and performs wireless communication via the connected base station. The communication unit 130 also connects to an access point of the wireless LAN 80 and performs wireless communication via the connected access point.

[0028] The display unit 140 includes a display element such as a liquid crystal display or an organic electroluminescence (EL) display, and displays display data output from the control unit 110. The operation unit 150 is configured with an input device such as a numeric keypad, and inputs data in response to user operations. Alternatively, the UE 10 may include a touch panel that can both input and display data.

[0029] The storage unit 120 stores SPLMN (Secondary PLMN) information 1202 , TFCL (Technical Frequency Combination List) information 1203 , and FPPP (Frequency party per PLMN) information 1204 .

[0030] The SPLMN information 1202 is information indicating PLMNs that are candidates for the second PLMN. The SPLMN information 1202 is provided, for example, by the CN of the mobile communication system 1. The SPLMN information 1202 may be, for example, information in the form of a list including multiple PLMNs. When the SPLMN information 1202 includes multiple PLMNs, a predetermined priority is set for each PLMN. Alternatively, the SPLMN information 1202 may be information that is a list of multiple PLMNs, with each PLMN assigned a priority.

[0031] The TFCL information 1203 is information (frequency combination information) indicating a combination of frequencies that the UE 10 can use in the "Multi-access PDU Session." The TFCL information 1203 is provided, for example, from the CN of the mobile communication system 1. The TFCL information 1203 is created, for example, by determining a combination of frequencies that the UE 10 can use in the "Multi-access PDU Session" through actual measurements, simulations, or the like, and the frequency combination resulting from this determination is included in the TFCL information 1203. Note that, although the TFCL information 1203 is created in a list format as an example of this embodiment, the format of the TFCL information 1203 is not limited as long as it is frequency combination information indicating a combination of frequencies that the UE 10 can use in the "Multi-access PDU Session."

[0032] The FPPP information 1204 is information indicating frequencies available in each PLMN (PLMN frequency information). The FPPP information 1204 is provided, for example, by the CN of the mobile communication system 1.

[0033] The communication control unit 1110 performs various communication controls of the UE 10. The communication control unit 1110 according to this embodiment has a function for appropriately selecting a cell (base station) as a HO destination when the UE 10 performs HO while performing "MA PDU Session With two 3GPP Access." The communication control unit 1110 also has a function for appropriately selecting a cell (base station) as a target of DC (Dual Connectivity) or CA (Carrier Aggregation) while the UE 10 performs "MA PDU Session With two 3GPP Access."

[0034] Fig. 3 is a diagram showing a schematic configuration of an AM control device according to this embodiment. The AM control device 50 shown in Fig. 3 is a device corresponding to the 5GC AMF. In this embodiment, the AM control device 50 includes, in addition to the functions of the 5GC AMF, an SPLMN control unit 501 as an additional part from the 5GC AMF. Note that Fig. 3 shows only the SPLMN control unit 501 added from the 5GC AMF as a function of the AM control device 50.

[0035] The SPLMN control unit 501 provides the SPLMN information 1202 to the UE 10. The SPLMN control unit 501 determines the appropriate SPLMN information 1202 for the UE 10.

[0036] In this embodiment, the AM control device 50 determines the SPLMN information 1202 of the UE 10, but this is not limiting. For example, the SMF, PCF, or the like may determine the SPLMN information 1202 of the UE 10.

[0037] Next, a communication control method according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a flowchart showing an example of the procedure of the communication control method according to this embodiment. Hereinafter, a base station of a PAN may be referred to as a PAN cell. Similarly, a base station of a SAN may be referred to as a SAN cell.

[0038] The communication control method according to this embodiment targets HO performed only in either a PAN cell or a SAN cell, and therefore targets HO from a PAN cell to a PAN cell and from a SAN cell to a SAN cell, but does not target HO from a PAN cell to a SAN cell and from a SAN cell to a PAN cell.

[0039] In addition, the communication control method according to this embodiment targets DC and CA executed only in either a PAN cell or a SAN cell. Therefore, the method targets selecting a target cell (base station) for DC or CA only in the PAN and selecting a target cell (base station) for DC or CA only in the SAN, and does not target selecting a target cell (base station) for DC or CA from both the PAN and the SAN.

[0040] (Step S11) The communication control unit 1110 of the UE 10 connects to a PAN cell, for example, when the UE 10 is powered on or airplane mode is turned off, performs network registration (NW registration) with the first PLMN (PPLMN) using the connected PAN cell, and establishes a PDU session with RAN 30_1 of the first PLMN (PPLMN). The PAN cell may be, for example, a base station of the PLMN to which the UE 10 was previously connected or a base station of a PLMN set as default for the UE 10. Here, for convenience of explanation, the PAN cell to which the UE 10 connects is PAN cell "n11" that uses frequency "n11." Therefore, the FPPP information 1204 related to the first PLMN (PPLMN) includes {n11}. Here, for convenience of explanation, the FPPP information 1204 relating to the first PLMN (PPLMN) is {n11, n12, n13, n14}.

[0041] The communication control unit 1110 of the UE 10 starts the procedure for establishing the "MA PDU Session With two 3GPP Access." The trigger for establishing the "MA PDU Session With two 3GPP Access" is not limited. One example of the trigger for establishing the "MA PDU Session With two 3GPP Access" may be when a request for packet communication requiring a high level of reliability is notified from a higher layer.

[0042] The communication control unit 1110 of UE 10 determines a second PLMN (SPLMN) based on the SPLMN information 1202, and determines a cell (SAN cell) to which RAN 30_2 (SAN) of SPLMN "2" is connected. Here, for convenience of explanation, the SAN cell to which UE 10 is connected is SAN cell "n21" that uses frequency "n21." Therefore, the FPPP information 1204 related to the second PLMN (SPLMN) includes {n21}. Here, for convenience of explanation, the FPPP information 1204 related to the second PLMN (SPLMN) is {n21, n22, n23, n24}.

[0043] (Step S12) When connecting to the SAN cell "n21", the communication control unit 1110 of the UE 10 notifies the SAN cell "n21" of the terminal capability information of the UE 10 itself, and performs "UE Capability" exchange. Below, examples 1 and 2 of the "UE Capability" exchange method according to this embodiment will be described.

[0044] (Example 1 of "UE Capability" Exchange Method) Communication control unit 1110 uses S-TFCL (Secondary-TFCL) information as terminal capability information of its own UE 10. A method of creating S-TFCL information will be described. S-TFCL information is information obtained by extracting all elements including the PAN cell frequency "n11" from TFCL information 1203, and extracting only frequencies {n21, n22, n23, n24} that can be used by the second PLMN (SPLMN) from the extracted elements. A specific example will be described.

[0045] The communication control unit 1110 extracts all elements that include the PAN cell frequency "n11" from the TFCL information 1203. Here, for convenience of explanation, eight elements {[n11], [n11, n12], [n11, n21], [n11, n13], [n11, n22] [n11, n12, n21], [n11, n12, n13], [n11, n21, n22]} are extracted from the TFCL information 1203. Next, the communication control unit 1110 extracts only the frequencies {n21, n22, n23, n24} available for use by the second PLMN (SPLMN) from the extracted eight elements {[n11], [n11, n12], [n11, n21], [n11, n13], [n11, n22], [n11, n12, n21], [n11, n12, n13], [n11, n21, n22]}. As a result, three elements {[n21], [n22], [n21, n22]} are extracted. The extracted three elements {[n21], [n22], [n21, n22]} constitute the S-TFCL information.

[0046] The S-TFCL information {[n21], [n22], [n21, n22]} is information indicating a combination of frequencies of the second PLMN (SPLMN) that can be used in the "MA PDU Session" in which UE 10 uses PAN cell "n11." As a result, SAN cell "n21" holds, as the terminal capability information of UE 10, only a combination of frequencies of the second PLMN (SPLMN) that can be used in the "MA PDU Session" in which UE 10 uses PAN cell "n11."

[0047] (Example 2 of "UE Capability" Exchange Method) The communication control unit 1110 uses the TFCL information 1203 as the terminal capability information of its own UE 10. As a result, the SAN cell "n21" holds only the combination of frequencies that the UE 10 can use in the "MA PDU Session" as the terminal capability information of the UE 10. This terminal capability information of the UE 10 is not limited to the combination of frequencies of the second PLMN (SPLMN) that can be used in the "MA PDU Session" using the PAN cell "n11". Therefore, the communication control unit 1110 executes a frequency preference method for the PAN cell "n11". This frequency preference method is a method for not selecting a cell of a specified frequency as a HO destination or for not selecting a specified frequency as a target for DC or CA. The designated frequencies are a set of frequencies remaining after deleting the set of frequencies included in the S-TFCL information {[n21], [n22], [n21, n22]} of the above-described example 1 of the "UE Capability" exchange method from the set of frequencies included in the TFCL information 1203. As a result, the PAN cell "n11" uses only the set of frequencies included in the S-TFCL information {[n21], [n22], [n21, n22]} to select a cell to be used as a HO destination for the UE 10 and to select a frequency to be used as a target for DC or CA. Details of the frequency preference method will be described later.

[0048] (Step S13) The communication control unit 1110 of the UE 10 creates P-TFCL (Primary-TFCL) information. The P-TFCL information is information obtained by extracting all elements including the SAN cell frequency "n21" from the TFCL information 1203, and extracting only the frequencies {n11, n12, n13, n14} that can be used by the first PLMN (PPLMN) from the extracted elements. A specific example will be described.

[0049] The communication control unit 1110 extracts all elements including the SAN cell frequency "n21" from the TFCL information 1203. Here, for convenience of explanation, six elements {[n21], [n11, n21], [n12, n21], [n21, n22], [n11, n12, n21], [n11, n21, n22]} are extracted from the TFCL information 1203. Next, the communication control unit 1110 extracts only the frequencies {n11, n12, n13, n14} that can be used by the first PLMN (PPLMN) from the extracted six elements {[n21], [n11, n21], [n12, n21], [n21, n22], [n11, n12, n21], [n11, n21, n22]}. As a result, three elements {[n11], [n12], [n11, n12]} are extracted. The extracted three elements {[n11], [n12], [n11, n12]} are the P-TFCL information.

[0050] The P-TFCL information {[n11], [n12], [n11, n12]} is information indicating the combination of frequencies of the first PLMN (PPLMN) that can be used in the "MA PDU Session" in which UE10 uses SAN cell "n21".

[0051] (Step S14) The communication control unit 1110 of the UE 10 checks whether the terminal capability information of the UE 10 held by the PAN cell "n11" matches the P-TFCL information {[n11], [n12], [n11, n12]}. The communication control unit 1110 holds the terminal capability information of the UE 10 notified to the PAN cell "n11" when connecting to the PAN cell "n11." The communication control unit 1110 checks whether the terminal capability information of the UE 10 notified to the PAN cell "n11" that it holds matches the P-TFCL information {[n11], [n12], [n11, n12]}. If the information matches, the process proceeds to the next step S15. On the other hand, if the information does not match, the process executes a frequency preference method for the PAN cell "n11" in the same manner as in the example 2 of the "UE Capability" exchange method described above. However, the specified frequencies here are the set of frequencies remaining after deleting the set of frequencies included in the P-TFCL information {[n11], [n12], [n11, n12]} from the set of frequencies included in the TFCL information 1203. As a result, the PAN cell "n11" uses only the set of frequencies included in the P-TFCL information {[n11], [n12], [n11, n12]} to select a cell to be the HO destination for UE 10 and to select frequencies to be subject to DC or CA.

[0052] (Step S15) The communication control unit 1110 of the UE 10 handles the occurrence of HO or activation of DC or CA in the SAN cell “n21” or the PAN cell “n11.” The following describes the SAN and the PAN separately.

[0053] (In the case of a SAN) When a handover occurs in a SAN, or when a DC or a CA is activated, the communication control unit 1110 executes steps S13 and S14 described above.

[0054] (In the case of PAN) When HO occurs in the PAN, or when DC or CA is activated, the communication control unit 1110 executes the above-described steps S13 and S14. However, in the case of a PAN, the above-described steps S13 and S14 are executed with PAN and SAN interchanged. That is, in step S13, S-TFCL information is created. In step S14, it is confirmed whether the terminal capability information of the own UE 10 held by the SAN cell "n21" matches the S-TFCL information, and if they do not match, the frequency preference method for the SAN cell "n21" is executed. The designated frequencies are the set of frequencies remaining after deleting the set of frequencies included in the S-TFCL information from the set of frequencies included in the TFCL information 1203.

[0055] Next, a frequency preference method according to this embodiment will be described.

[0056] The frequency preference method according to this embodiment has the following assumptions (1) and (2): (1) One or more frequencies are configured in the UE 10. For convenience of explanation, the configured frequencies are referred to as configured frequencies. (2) One or more of the configured frequencies are designated frequencies.

[0057] An example of a frequency preference method according to this embodiment will be given below.

[0058] (Example 1 of Frequency Preference Method) The UE 10 does not monitor the designated frequency regardless of the MC (Measurement Configure) from the base station, and therefore does not send an MR (Measurement Report) regarding the designated frequency to the base station.

[0059] (Example 2 of Frequency Preference Method) Even if the UE 10 detects an opportunity to transmit a Measurement Report (MR) regarding the designated frequency, the UE 10 does not include information regarding the designated frequency in the MR. Therefore, the UE 10 does not transmit the MR regarding the designated frequency to the base station.

[0060] (Example 3 of Frequency Preference Method) When the UE 10 receives a monitoring request for a designated frequency from a base station, the UE 10 transmits a signal to the base station rejecting the monitoring request for the designated frequency. Thus, the UE 10 does not monitor the designated frequency.

[0061] (Frequency Preference Method Example 4) The UE 10 amends its own terminal capability information previously transmitted to the base station to information that does not include the designated frequency, and transmits the amended terminal capability information of its own to the base station.

[0062] (Example 5 of Frequency Preference Method) Example 5 of the frequency preference method is a method related to HO. When the UE 10 supports conditional HO (CHO), the UE 10 excludes cells of a specified frequency from HO destination cells by CHO.

[0063] (Example 6 of Frequency Preference Method) Example 6 of the frequency preference method is a method related to DC and CA. When the base station instructs the UE 10 that a cell of a specified frequency is a target of DC or CA, the UE 10 rejects the instruction.

[0064] According to this embodiment, when a "Multi-access PDU Session" is being implemented, the effect is achieved of being able to appropriately select the cell (base station) to be HOed to and the cell (base station) to be targeted for DC or CA.

[0065] The above-described embodiment is applicable to mobile communication systems such as a 5G system, a B5G (Beyond 5G) system, and a sixth-generation mobile communication system (6G system).

[0066] This will enable, for example, improvements to the overall service quality of mobile communication systems, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0067] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present invention.

[0068] Furthermore, a computer program for implementing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read and executed by a computer system. Note that the term "computer system" may also include hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a DVD (Digital Versatile Disc), or a storage device such as a hard disk built into a computer system.

[0069] Furthermore, the term "computer-readable recording medium" also includes a storage medium that stores a program for a certain period of time, such as a volatile memory (e.g., a dynamic random access memory (DRAM)) within a computer system that serves as a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line. The program may also be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium or by transmission waves within the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be a program that realizes part of the aforementioned functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the aforementioned functions in combination with a program already stored in the computer system.

[0070] According to the present invention, it is possible to appropriately select a cell to be used as a HO destination or a cell to be used as a target for DC or CA when a "Multi-access PDU Session" is being implemented.

[0071] 1...mobile communication system, 10...UE, 30...RAN, 50...AM control device, 60...UPF, 70...DN, 80...wireless LAN, 110...control unit, 120...storage unit, 130...communication unit, 140...display unit, 150...operation unit, 1110...communication control unit, 501...SPLMN control unit

Claims

1. A user terminal of a mobile communication system comprising a core network connected to a plurality of radio access networks, a frequency combination information storage unit that stores frequency combination information indicating a combination of frequencies available in the "Multi-access PDU Session" for the user terminal, a PLMN frequency information storage unit that stores PLMN frequency information indicating frequencies available in each PLMN (Public Land Mobile Network), when the "Multi-access PDU Session" is being carried out between the first radio access network of the PPLMN (Primary PLMN) and the second radio access network of the SPLMN (Secondary PLMN), based on the frequency combination information and the PLMN frequency information, create S-TFCL information indicating a combination of frequencies of the SPLMN available in the "MA PDU Session" using the cell of the first radio access network, or P-TFCL information indicating a combination of frequencies of the PPLMN available in the "MA PDU Session" using the cell of the second radio access network, based on the created S-TFCL information or P-TFCL information, perform control of the selection of the cell of the HO (HandOver) destination and the selection of the frequencies for the DC (Dual Connectivity) or CA (Carrier Aggregation) target for the base station to which the user terminal is connected, A user terminal comprising:

2. The communication control unit, when HO occurs for the user terminal or when DC or CA is enabled, based on the S-TFCL information or P-TFCL information, determine whether the terminal capability information of the user terminal held by the base station to which the user terminal is connected is qualified, if it is unqualified, based on the S-TFCL information or P-TFCL information, execute a frequency preference method for restricting the cell of the HO destination or the frequencies for the DC or CA target for the user terminal. The user terminal according to claim 1.

3. The frequency preference method of the user terminal according to claim 2 is such that, regardless of the MC (Measurement Configure) from the base station, monitoring of frequencies other than the frequencies included in the S-TFCL information or P-TFCL information is not performed.

4. The frequency preference method of the user terminal according to claim 2 is such that, even if an opportunity to transmit an MR (Measurement Report) regarding a designated frequency, which is a frequency other than the frequencies included in the S-TFCL information or P-TFCL information, is detected, information regarding the designated frequency is not included in the MR.

5. The frequency preference method of the user terminal according to claim 2 is such that, when a monitoring request for a designated frequency, which is a frequency other than the frequencies included in the S-TFCL information or P-TFCL information, is received from the base station, a signal rejecting the monitoring request for the designated frequency is transmitted to the base station.

6. The frequency preference method of the user terminal according to claim 2 is such that the terminal capability information of the user terminal transmitted to the base station in the past is corrected to information not including frequencies other than the frequencies included in the S-TFCL information or P-TFCL information, and the corrected terminal capability information of the user terminal is transmitted to the base station.

7. The frequency preference method of the user terminal according to claim 2 is a method regarding HO, and when the user terminal supports CHO (Conditional HO), cells having frequencies other than the frequencies included in the S-TFCL information or P-TFCL information are excluded from the target cells for HO by CHO.

8. The frequency preference method of the user terminal according to claim 2 is a method regarding DC and CA, and when a cell having a frequency other than the frequencies included in the S-TFCL information or P-TFCL information is indicated as a target for DC or CA from the base station, the indication is rejected.

9. A communication control method executed by a user terminal of a mobile communication system including a core network connected to a plurality of radio access networks, the method comprising: a frequency combination information storage step of storing frequency combination information indicating a combination of frequencies available in a "Multi-access PDU Session" by the user terminal; a PLMN frequency information storage step of storing PLMN frequency information indicating frequencies available in each PLMN (Public Land Mobile Network); when a "Multi-access PDU Session" is being carried out between the first radio access network of the PPLMN (Primary PLMN) and the second radio access network of the SPLMN (Secondary PLMN), based on the frequency combination information and the PLMN frequency information, creating S-TFCL information indicating a combination of frequencies of the SPLMN available in a "MA PDU Session" using a cell of the first radio access network, or P-TFCL information indicating a combination of frequencies of the PPLMN available in a "MA PDU Session" using a cell of the second radio access network; and a communication control step of controlling, based on the created S-TFCL information or P-TFCL information, the selection of a cell of a HO (HandOver) destination for the user terminal and the selection of frequencies for DC (Dual Connectivity) or CA (Carrier Aggregation) for the base station to which the user terminal is connected.

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