User terminal and communication control method

Abstract

To make it possible to appropriately select an HO destination cell and a target cell for DC or CA when a "multi-access PDU session" is being performed.SOLUTION: When a "multi-access PDU session" is being performed using a first radio access network of a PPLMN and a second radio access network of a SPLMN, a user terminal creates S-TFCL information indicating a combination of SPLMN frequencies that can be used in a "MA PDU session" using a cell of the first radio access network, or P-TFCL information indicating a combination of PPLMN frequencies that can be used in a "MA PDU session" using a cell of the second radio access network, and controls a base station to select an HO destination cell and to select a target frequency for DC or CA based on the S-TFCL information or the P-TFCL information.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a user terminal and a communication control method.

Background Art

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

[0003] Here, the logical communication path established between the UE and the CN (UPF) for the UE to use the mobile communication service is referred to as a "session". Also, the session established between the UE and the CN (UPF) using multiple radio paths is referred to as a "multi-access session". Non-Patent Documents 1 and 2 define "Multi-access PDU (Packet Data Unit) Session" (hereinafter referred to as "MA PDU Session") as an example of a multi-access session. FIG. 6 is a diagram showing a configuration example of the "MA PDU Session". As shown in FIG. 6, the UE establishes a "MA PDU Session" with the CN (UPF) using a radio path via the RAN which is "3gpp access" and a radio path via a wireless LAN (Local Area Network) such as, for example, "Wi-Fi (registered trademark)" which is "non-3gpp access". "3gpp access" is an access network defined by 3GPP. "non-3gpp access" is an access network other than "3gpp access". The UE uses its "MA PDU Session" to transmit and receive data with a DN (Data Network, data network) such as the Internet outside the 5GC (CN of the 5G system). By using the "MA PDU Session", the UE can obtain the effect of improving communication quality, such as expanding the communication bandwidth, reducing communication delay, and ensuring communication path redundancy.

[0004] Also, as communication methods in which a single UE simultaneously uses a plurality of base stations that each use different frequencies, DC (Dual Connectivity) and CA (Carrier Aggregation) are known (see, for example, Non-Patent Document 3). Also, HO (HandOver) in which the base station to which the UE is connected is switched is known.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] When the UE performs handover (HO) while conducting a multi-access session (MA PDU Session With two 3GPP Access) with the UPF using multiple radio paths via two RANs (3gpp access) respectively, the problem is how to select an appropriate HO destination cell (base station). Also, when the UE performs dual connectivity (DC) or carrier aggregation (CA) while conducting "MA PDU Session With two 3GPP Access", the problem is how to select an appropriate cell (base station) for the DC or CA target.

[0007] The present invention has been made in consideration of such circumstances, and its object is to appropriately select the HO destination cell (base station) and the cell (base station) for the DC or CA target when conducting a "Multi-access PDU Session". [Means for Solving the Problems]

[0008] One aspect of the present invention is a user terminal of a mobile communication system including a core network connected to a plurality of radio access networks, the user terminal including: a frequency combination information storage unit that stores frequency combination information indicating a combination of frequencies available in a "Multi-access PDU Session"; a PLMN frequency information storage unit that stores PLMN frequency information indicating frequencies available in each PLMN (Public Land Mobile Network); and when a "Multi-access PDU Session" is being performed 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, 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 is created, and based on the created S-TFCL information or P-TFCL information, communication control is performed to control the selection of a target cell for HO (HandOver) related to 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. A user terminal comprising: a control unit. One aspect of the present invention is the above user terminal, wherein the communication control unit determines whether the terminal capability information of the user terminal held by the base station to which the user terminal is connected meets the requirements based on the S-TFCL information or the P-TFCL information when HO occurs or DC or CA is enabled for the user terminal, and when it fails, based on the S-TFCL information or the P-TFCL information, a frequency preference method for restricting the target cell for HO related to the user terminal or the frequencies for DC or CA is executed. A user terminal. One aspect of the present invention is a user terminal in which, regardless of MC (Measurement Configure) from a base station, the frequency preference method does not monitor frequencies other than those included in S-TFCL information or P-TFCL information. One aspect of the present invention is a user terminal in which, even if the user terminal detects an opportunity to transmit an MR (Measurement Report) regarding a designated frequency that is a frequency other than the frequencies included in S-TFCL information or P-TFCL information, the user terminal does not include information regarding the designated frequency in the MR. One aspect of the present invention is a user terminal in which, when the user terminal receives a monitoring request for a designated frequency that is a frequency other than the frequencies included in S-TFCL information or P-TFCL information from a base station, the user terminal transmits a signal to the base station rejecting the monitoring request for the designated frequency. One aspect of the present invention is a user terminal in which, regarding the frequency preference method in the user terminal, the terminal capability information of the user terminal transmitted to the base station in the past is corrected to information that does not include frequencies other than the frequencies included in S-TFCL information or P-TFCL information, and the corrected terminal capability information of the user terminal is transmitted to the base station. One aspect of the present invention is a user terminal in which the frequency preference method is a method related to HO. When the user terminal supports CHO (Conditional HO), the user terminal excludes a cell having a frequency other than the frequencies included in S-TFCL information or P-TFCL information from the target cell for HO by means of CHO. One aspect of the present invention is a user terminal in which the frequency preference method is a method related to DC and CA. When a cell having a frequency other than the frequencies included in S-TFCL information or P-TFCL information is designated as a target for DC or CA from a base station, the user terminal rejects the designation.

[0009] 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 including: 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 using a first radio access network of a PPLMN (Primary PLMN) and a second radio access network of an 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 based on the created S-TFCL information or P-TFCL information, performing control over the selection of a target cell of a HO (HandOver) destination cell related to the user terminal and the selection of frequencies for DC (Dual Connectivity) or CA (Carrier Aggregation) for a base station to which the user terminal is connected.

Effect of the Invention

[0010] According to the present invention, when a "Multi-access PDU Session" is being carried out, an effect can be obtained in that a target cell (base station) of a HO destination or a target cell (base station) of DC or CA can be appropriately selected.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a mobile communication system according to an embodiment. In FIG. 1, a UE (User Equipment) 10 can be connected to a RAN (Radio Access Network) 30 (30_1, 30_2) which is "3gpp access". RAN 30_1 is the RAN of the first PLMN (Public Land Mobile Network). The first PLMN is a PLMN (PPLMN (Primary PLMN)) that manages the base stations of the PAN (Primary Access Network), which is the base station to which the UE 10 first connects. RAN 30_2 is a candidate RAN of the second PLMN. The second PLMN is a PLMN (SPLMN (Secondary PLMN)) that manages the base stations of the SAN (Secondary Access Network), which is the base station to which the UE 10 connects next 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). RAN30 (30_1, 30_2) is connected to the UPF (User Plane Function) 60 of the CN (Core Network) of the mobile communication system 1. Hereinafter, when RAN30_1 and RAN30_2 are not particularly distinguished, they are referred to as RAN30.

[0014] Note that only two RAN30s (30_1, 30_2) are shown in FIG. 1, but the mobile communication system 1 may include three or more RAN30s (30_1, 30_2, 30_3, ···) connected to the UPF60, and the UE10 may be connectable to three or more RAN30s (30_1, 30_2, 30_3, ···). In this case, all the RAN30s (30_1, 30_2, 30_3, ···) may be the same PLMN or not. Also, all the RAN30s (30_1, 30_2, 30_3, ···) are connected to the UPF60 of the mobile communication system 1. Also, only one UPF60 is shown in FIG. 1, but the mobile communication system 1 may include a plurality of UPF60s, and one RAN30 may be connected to one or more UPF60s.

[0015] Also, the UE10 can be connected to a wireless LAN 80 which is a "non-3gpp access". The wireless LAN 80 is connected to the UPF60 of the mobile communication system 1. The wireless LAN 80 is an example of a wireless access network which is a "non-3gpp access".

[0016] The UPF60 is connected to a DN (Data Network) such as the Internet outside the CN of the mobile communication system 1.

[0017] UE10 can establish a session with UPF60 via a radio path through RAN30 or a wireless LAN80, and use the established session to send and receive data with the DN. Also, UE10 can establish a multi-access session with UPF60 using a radio path through RAN30 and a radio path through wireless LAN80, and use the established multi-access session to send and receive data with the DN.

[0018] In this embodiment, furthermore, it is intended that UE10 can establish a multi-access session (MA PDU Session With two 3GPP Access) with UPF60 using a plurality of radio paths respectively through a plurality of RAN30s. The two "3gpp accesses" (base stations) for establishing the multi-access session are a base station of a PAN and a base station of a SAN.

[0019] Also, in this embodiment, when UE10 performs HO (HandOver) while performing "MA PDU Session With two 3GPP Access", it is made possible to appropriately select the cell (base station) of the HO destination. Also, in this embodiment, when UE10 performs "MA PDU Session With two 3GPP Access", it is made possible to appropriately select the cells (base stations) for 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, for example, a network device that realizes an NF corresponding to the AMF of 5GC (the 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 communicates with the UE 10 and the RAN 30 on the C-plane.

[0022] FIG. 2 is a diagram showing a schematic configuration of a UE according to the present 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), and realizes various functions by calling and executing programs stored in the storage unit 120.

[0024] As its function, the control unit 110 includes 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] Note that FIG. 2 shows only the communication control unit 1110 related to additional functions from the conventional UE 10 as a function of the control unit 110. Similarly, as a program stored in the storage unit 120, only the communication control program 1210 related to additional functions from the conventional UE 10 is shown.

[0026] The storage unit 120 is composed of a storage medium, for example, an HDD (Hard Disk Drive), a flash memory, an EEPROM (Electrically Erasable Programmable Read Only Memory), a RAM (Random Access read / write Memory), a ROM (Read Only Memory), or an arbitrary combination of these storage media. Various programs such as the communication control program 1210 executed by the control unit 110 (CPU) and various data are stored in the storage unit 120.

[0027] The communication unit 130 connects to the base station of RAN 30 and communicates wirelessly via the connected base station. Also, the communication unit 130 connects to the access point of the wireless LAN 80 and communicates wirelessly via the connected access point.

[0028] The display unit 140 includes a display element such as a liquid crystal display or an organic EL (Electro Luminescence), and displays the display data output from the control unit 110. The operation unit 150 is composed of an input device such as a numeric keypad, and performs data input according to the user's operation. Alternatively, the UE 10 may be provided with a touch panel capable of both data input and data display.

[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 the candidate PLMNs of the second PLMN. The SPLMN information 1202 is provided, for example, from the CN of the mobile communication system 1. The SPLMN information 1202 may be information in a list format including a plurality of PLMNs, for example. When a plurality of PLMNs are included in the SPLMN information 1202, a predetermined priority is set for each PLMN. Alternatively, the SPLMN information 1202 may be information in the form of a list of a plurality of PLMNs with priorities assigned to each PLMN.

[0031] The TFCL information 1203 is information (frequency combination information) indicating a combination of frequencies available for the UE 10 in a "Multi-access PDU Session". The TFCL information 1203 is provided, for example, from the CN of the mobile communication system 1. The method for creating the TFCL information 1203 is, for example, to determine a combination of frequencies available for the UE 10 in a "Multi-access PDU Session" by actual measurement, simulation, etc., and include the combination of frequencies as the result of this determination in the TFCL information 1203. Note that the TFCL information 1203 is created in a list format as an example of this embodiment, but the format is not limited as long as it is frequency combination information indicating a combination of frequencies available for the UE 10 in a "Multi-access PDU Session".

[0032] The FPPP information 1204 is information (PLMN frequency information) indicating frequencies available in each PLMN. The FPPP information 1204 is provided, for example, from 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 target cell (base station) for HO when the UE 10 performs HO when it is implementing "MA PDU Session With two 3GPP Access". Also, the communication control unit 1110 has a function for appropriately selecting a target cell (base station) for DC (Dual Connectivity) or CA (Carrier Aggregation) when the UE 10 is implementing "MA PDU Session With two 3GPP Access".

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

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

[0036] Note that in the present embodiment, the AM control device 50 determines the SPLMN information 1202 of the UE 10, but it is not limited to this. For example, the SMF, PCF, etc. may determine the SPLMN information 1202 of the UE 10.

[0037] Next, the communication control method according to the present 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 the present embodiment. Hereinafter, the base station of the PAN may be referred to as a PAN cell. Similarly, the base station of the SAN may be referred to as a SAN cell.

[0038] Note that the communication control method according to the present embodiment targets the HO executed only in either the PAN cell or the SAN cell. Therefore, the HO from the PAN cell to the PAN cell and the HO from the SAN cell to the SAN cell are targeted, and the HO from the PAN cell to the SAN cell and the HO from the SAN cell to the PAN cell are not targeted.

[0039] Also, the communication control method according to the present embodiment targets the DC and CA executed only in either the PAN cell or the SAN cell. Therefore, selecting the cell (base station) targeted for DC or CA only in the PAN and selecting the cell (base station) targeted for DC or CA only in the SAN are targeted, and selecting the cell (base station) targeted for DC or CA from both the PAN and the SAN is not targeted.

[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, and performs network registration (NW registration) of the first PLMN (PPLMN) using the connected PAN cell, thereby establishing a PDU session with the RAN 30_1 of the first PLMN (PPLMN). The PAN cell may be, for example, a base station of a PLMN to which the UE 10 was previously connected, or a base station of a PLMN set as a default for the UE 10. Here, for convenience of explanation, it is assumed that 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, it is assumed that the FPPP information 1204 related 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 an upper layer.

[0042] The communication control unit 1110 of the UE 10 determines a second PLMN (SPLMN) based on the SPLMN information 1202, and determines a cell (SAN cell) to which the RAN 30_2 (SAN) of the SPLMN "2" is connected. Here, for convenience of explanation, the SAN cell to which the 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 the communication control unit 1110 of UE10 connects to the SAN cell "n21", it notifies the SAN cell "n21" of the terminal capability information of its own UE10 and performs "UE Capability" exchange. Hereinafter, Example 1 and Example 2 of the "UE Capability" exchange method according to the present embodiment will be described.

[0044] (Example 1 of the "UE Capability" exchange method) The communication control unit 1110 uses S-TFCL (Secondary-TFCL) information as the terminal capability information of its own UE10. The method for creating S-TFCL information will be described. The S-TFCL information is information obtained by extracting all elements including the frequency "n11" of the PAN cell from the TFCL information 1203 and then extracting only the frequencies {n21, n22, n23, n24} available for the second PLMN (SPLMN) from the extracted elements. This will be described with a specific example.

[0045] The communication control unit 1110 extracts all elements including the frequency "n11" of the PAN cell from the TFCL information 1203. Here, for the sake of convenience of explanation, 8 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 the second PLMN (SPLMN) from the 8 extracted elements {[n11], [n11, n12], [n11, n21], [n11,n13], [n11, n22] [n11, n12, n21], [n11, n12, n13], [n11, n21, n22]}. As a result, 3 elements {[n21], [n22], [n21, n22]} are extracted. The extracted 3 elements {[n21], [n22], [n21, n22]} are the S-TFCL information.

[0046] The S-TFCL information {[n21], [n22], [n21, n22]} indicates the combination of frequencies of the second PLMN (SPLMN) available in the "MA PDU Session" where UE10 uses the PAN cell "n11". Accordingly, the SAN cell "n21" will retain only the combination of frequencies of the second PLMN (SPLMN) available in the "MA PDU Session" where UE10 uses the PAN cell "n11" as the terminal capability information of UE10.

[0047] (Example 2 of the "UE Capability" exchange method) The communication control unit 1110 uses the TFCL information 1203 as the terminal capability information of its own UE10. Accordingly, the SAN cell "n21" will retain only the combination of frequencies available in the "MA PDU Session" of UE10 as the terminal capability information of UE10. This terminal capability information of UE10 is not limited to the combination of frequencies of the second PLMN (SPLMN) available 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 with a specified frequency as the HO destination or not selecting the specified frequency as the target for DC or CA. The specified frequency is the remaining set of frequencies obtained by deleting the set of frequencies included in the S-TFCL information {[n21], [n22], [n21, n22]} of Example 1 of the above-described "UE Capability" exchange method from the set of frequencies included in the TFCL information 1203. As a result, the PAN cell "n11" will use only the set of frequencies included in the S-TFCL information {[n21], [n22], [n21, n22]} for the selection of the HO destination cell regarding UE10 and the selection of the target frequency for DC or CA. The details of the frequency preference method will be described later.

[0048] (Step S13) The communication control unit 1110 of UE10 creates P-TFCL (Primary-TFCL) information. The P-TFCL information is the information obtained by extracting all elements including the frequency "n21" of the SAN cell from the TFCL information 1203 and then extracting only the frequencies {n11, n12, n13, n14} available to the first PLMN (PPLMN) from the extracted elements. This will be described with a specific example.

[0049] The communication control unit 1110 extracts all elements including the frequency "n21" of the SAN cell from the TFCL information 1203. Here, for the sake of explanation, 6 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} available to the first PLMN (PPLMN) from the 6 extracted elements {[n21], [n11, n21], [n12, n21], [n21, n22], [n11, n12, n21], [n11, n21, n22]}. As a result, 3 elements {[n11], [n12], [n11, n12]} are extracted. The extracted 3 elements {[n11], [n12], [n11, n12]} are the P-TFCL information.

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

[0051] (Step S14) The communication control unit 1110 of UE10 checks whether the terminal capability information of its own UE10 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 its own UE10 notified to the PAN cell "n11" when connecting to the PAN cell "n11". The communication control unit 1110 checks whether the held terminal capability information of its own UE10 notified to the PAN cell "n11" matches the P-TFCL information {[n11], [n12], [n11, n12]}. As a result of this check, if they match, it proceeds directly to the next step S15. On the other hand, if they do not match, similar to Example 2 of the above-described "UE Capability" exchange method, a frequency preference method for the PAN cell "n11" is executed. However, the designated frequency here is the remaining set of frequencies obtained by 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. Thereby, the PAN cell "n11" will use only the set of frequencies included in the P-TFCL information {[n11], [n12], [n11, n12]} for the selection of the target cell for handover regarding UE10 and the selection of frequencies for the target of DC or CA.

[0052] (Step S15) The communication control unit 1110 of UE10 takes measures when handover occurs or when DC or CA is activated in the SAN cell "n21" or the PAN cell "n11". This will be described separately for SAN and PAN below.

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

[0054] (In the case of PAN) In the PAN, when HO occurs, 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 the PAN, in the above-described steps S13 and S14, the PAN and the SAN are swapped and executed. That is, in step S13, S-TFCL information is created. In step S14, it is confirmed whether the terminal capability information of its own UE10 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. This designated frequency is the set of remaining frequencies obtained by deleting the set of frequencies included in the S-TFCL information from the set of frequencies included in the TFCL information 1203.

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

[0056] The frequency preference method according to this embodiment has the following premises (1) and (2). (1) One or more frequencies are configured in the UE10. For convenience of explanation, the configured frequencies are referred to as set frequencies. (2) One or more of the set frequencies are designated frequencies.

[0057] Examples of the frequency preference method according to this embodiment will be given below.

[0058] (Example 1 of the frequency preference method) Regardless of the MC (Measurement Configure) from the base station, the UE10 does not monitor the designated frequency. Therefore, the UE10 does not send an MR (Measurement Report) regarding the designated frequency to the base station.

[0059] (Example 2 of the frequency preference method) Even if the UE10 detects an opportunity to transmit an MR (Measurement Report) regarding the designated frequency, the UE10 does not include information regarding the designated frequency in the MR. Therefore, the UE10 does not send an MR regarding the designated frequency to the base station.

[0060] (Example 3 of Frequency Preference Method) When UE10 receives a monitoring request for a specified frequency from a base station, it transmits a signal to the base station rejecting the monitoring request for the specified frequency. Therefore, UE10 does not monitor the specified frequency.

[0061] (Example 4 of Frequency Preference Method) UE10 modifies its own terminal capability information transmitted to the base station in the past to information that does not include the specified frequency, and transmits the modified own terminal capability information 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 UE10 supports CHO (Conditional HO), CHO excludes the cell of the specified frequency from the target cell for HO.

[0063] (Example 6 of Frequency Preference Method) Example 6 of the frequency preference method is a method related to DC and CA. When UE10 is instructed by the base station that the cell of the specified frequency is the target of DC or CA, it rejects the instruction.

[0064] According to this embodiment, when "Multi-access PDU Session" is implemented, an effect can be obtained that an appropriate cell (base station) for HO destination or a cell (base station) that is the target of DC or CA can be selected.

[0065] The above-described embodiments are applicable to mobile communication systems such as, for example, 5G systems, B5G (Beyond 5G) systems, and sixth-generation mobile communication systems (6G systems).

[0066] In addition, since this can achieve, for example, an improvement in the overall service quality in a mobile communication system, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0067] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included.

[0068] Further, a computer program for realizing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the "computer system" may include hardware such as an OS and peripheral devices. Also, the "computer-readable recording medium" refers to a writable non-volatile memory such as a flexible disk, a magneto-optical disk, a ROM, a flash memory, a portable medium such as a DVD (Digital Versatile Disc), and a storage device such as a hard disk incorporated in a computer system.

[0069] Furthermore, the "computer-readable recording medium" shall include those that hold a program for a certain period of time, such as volatile memories (e.g., DRAM (Dynamic Random Access Memory)) inside a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. Also, the above program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication wire) such as a telephone line. Also, the above program may be for realizing a part of the aforementioned functions. Furthermore, it may be a so-called difference file (difference program) that can realize the aforementioned functions in combination with a program already recorded in the computer system.

Explanation of Signs

[0070] 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 for the user terminal in a "Multi-access PDU Session", a PLMN frequency information storage unit that stores 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, S-TFCL information indicating a combination of frequencies of the SPLMN available in a "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 a "MA PDU Session" using the cell of the second radio access network is created, Based on the created S-TFCL information or P-TFCL information, a communication control unit that controls the selection of a target cell for HO (HandOver) and the selection of frequencies for DC (Dual Connectivity) or CA (Carrier Aggregation) 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 activated, based on the S-TFCL information or P-TFCL information, it determines 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, it executes a frequency preference method for restricting the target cell for HO or the frequencies for DC or CA for the user terminal, The user terminal according to claim 1.

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

4. Even if the 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, the information regarding the designated frequency is not included in the MR. The user terminal according to claim 2.

5. When the frequency preference method receives 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, from the base station, the frequency preference method transmits a signal rejecting the monitoring request for the designated frequency to the base station. The user terminal according to claim 2.

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

7. The frequency preference method is a method related to HO. When the user terminal supports CHO (Conditional HO), CHO excludes cells with frequencies other than the frequencies included in the S-TFCL information or P-TFCL information from the target cells for HO. The user terminal according to claim 2.

8. The frequency preference method is a method related to DC and CA. When a cell with 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. The user terminal according to claim 2.

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, a frequency combination information storage step of storing frequency combination information indicating a combination of frequencies available in the "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 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 SPLMNs available for a "MA PDU Session" using the cell of the first radio access network, or P-TFCL information indicating a combination of frequencies of PPLMNs available for a "MA PDU Session" using the cell of the second radio access network. Based on the created S-TFCL information or P-TFCL information, perform a communication control step of controlling the selection of the target cell for HO (HandOver) and the selection of frequencies for DC (Dual Connectivity) or CA (Carrier Aggregation) for the base station to which the user terminal is connected with respect to the user terminal. A communication control method including the above steps.

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