User terminal and communication control method

Abstract

This user terminal comprises a communication control unit that: specifies, when establishing a "multi-access PDU session" between a first wireless access network of PPLMN which has been already connected and a second wireless access network of SPLMN which is to be newly connected, a second frequency which is usable in the second wireless access network and is included in combinations of frequencies usable in the first wireless access network and the second wireless access network; and determines a base station which is a connection destination of the second wireless access network on the basis of the specified second frequency.

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. 2024-006291, 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).

[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] Generally, when a UE simultaneously uses multiple base stations that each use a different frequency, wireless interference due to intermodulation and harmonics may occur. To prevent performance degradation due to such wireless interference, it is desirable to be able to select the frequencies of each RAN so that the frequency combination is less susceptible to interference. In conventional DC and CA, the "Master RAN" exchanges the necessary information and selects the appropriate frequency combination.

[0007] On the other hand, when a UE performs a multi-access session (MA PDU Session With two 3GPP Access) with a UPF using multiple radio paths via two RANs (3GPP Access), the selection of a cell (base station) in a SAN (Secondary Access Network) can be performed by aggregating information on frequencies used by cells (base stations) in a PAN (Primary Access Network) and information on frequencies available to the UE in the CN. However, if signaling between the CN and the RAN for the "MA PDU Session" is defined in a standard specification, it would be difficult to achieve this because it would require functional upgrades to existing RAN base stations.

[0008] The present invention has been made in consideration of the above circumstances, and its object is to enable a user terminal to determine a cell (base station) to which the SAN is to be connected.

[0009] One aspect of the present invention is a user terminal of a mobile communication system having a core network connected to multiple radio access networks, the user terminal comprising: a frequency combination information storage unit that stores frequency combination information indicating a combination of frequencies that the user terminal can use in a "Multi-access PDU Session"; 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 a communication control unit that, when establishing a "Multi-access PDU Session" between a first radio access network of a PPLMN (Primary PLMN) to which the user terminal is already connected and a second radio access network of a SPLMN (Secondary PLMN) to which the user terminal is newly connected, identifies a second frequency that is included in the combination of frequencies that can be used in the first radio access network and the second radio access network based on the frequency combination information and the PLMN frequency information, and determines a base station to which the second radio access network will connect based on the identified second frequency. In one aspect of the present invention, in the user terminal, the communication control unit is configured to limit the second frequency available in the second radio access network in accordance with a predetermined frequency limiting condition, and the communication control unit is configured to determine whether to limit the second frequency available in the second radio access network based on information about an antenna used to connect to the first radio access network.

[0010] 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 multiple radio access networks, the communication control method including: a frequency combination information storage step of storing frequency combination information indicating a combination of frequencies that the user terminal can use in a "Multi-access PDU Session"; a PLMN frequency information storage step of storing PLMN frequency information indicating frequencies that can be used in each PLMN (Public Land Mobile Network); and a communication control step of, when a "Multi-access PDU Session" is to be established between a first radio access network of a PPLMN (Primary PLMN) to which the user terminal is already connected and a second radio access network of a SPLMN (Secondary PLMN) to which the user terminal is newly connected, identifying a second frequency that is included in the combination of frequencies that can be used in the first radio access network and the second radio access network based on the frequency combination information and the PLMN frequency information, and determining a base station to which the second radio access network is to be connected based on the identified second frequency.

[0011] According to the present invention, an effect is obtained in that a user terminal can determine a cell (base station) to which the SAN is to be connected.

[0012] 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".

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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."

[0017] The UPF 60 is connected to a DN (data network) such as the Internet outside the CN of the mobile communication system 1 .

[0018] 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.

[0019] 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 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. Here, in this embodiment, the UE 10 is enabled to determine the base station (cell) to which the SAN is connected.

[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 for the UE 10. The communication control unit 1110 according to this embodiment has a function of determining a cell (base station) of the SAN to which the UE 10 is to connect.

[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] (Step S1) 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) with the first PLMN (PPLMN) using the connected PAN cell, and establishes a PDU session with the 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 a 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) is {n11}.

[0039] (Step S2) 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.

[0040] (Step S3) The communication control unit 1110 of the UE 10 determines a second PLMN (SPLMN) based on the SPLMN information 1202. Here, for convenience of explanation, the SPLMN is "2".

[0041] (Step S4) The communication control unit 1110 of the UE 10 determines, as the SAN frequency candidate, the frequency candidate of the RAN 30_2 (SAN) of the SPLMN "2." A method for determining the SAN frequency candidate will be described below.

[0042] Here, for convenience of explanation, TFCL information 1203 is {[n11, n21], [n11, n22], [n11, n32]}. Also, FPPP information 1204 related to SPLMN "2" is {n21, n22, n23}. From the three elements [n11, n21], [n11, n22], and [n11, n32] of TFCL information 1203, communication control unit 1110 selects elements [n11, n21] and [n11, n22] that include both the PAN cell frequency "n11" and the SPLMN "2" frequency "n21," "n22," or "n23." Next, the communication control unit 1110 extracts "n21" and "n22", which are frequencies of SPLMN "2", from the two selected elements [n11, n21] and [n11, n22]. The communication control unit 1110 determines the extracted frequencies "n21" and "n22" as frequency candidates for RAN 30_2 (SAN) of SPLMN "2".

[0043] (Step S5) The communication control unit 1110 of the UE 10 determines the frequency to which RAN 30_2 (SAN) of SPLMN "2" will be connected from the frequency candidates "n21" and "n22" of RAN 30_2 (SAN) of SPLMN "2". Specifically, the communication control unit 1110 searches for each of the frequencies of the frequency candidates "n21" and "n22", and determines the frequency from the frequency candidates "n21" and "n22" to actually attempt connection based on the search results. The communication control unit 1110 connects to the SAN cell using the determined frequency.

[0044] As a result, the UE 10 connects to the SAN cell, performs network registration of the second PLMN (SPLMN) through the connected SAN cell, and establishes a PDU session with the RAN 30_2 of the second PLMN (SPLMN). After this, the UE 10 establishes "MA PDU Session With two 3GPP Access" using the PDU session with the RAN 30_1 of the first PLMN (PPLMN) and the PDU session with the RAN 30_2 of the second PLMN (SPLMN).

[0045] When determining SAN frequency candidates, the communication control unit 1110 may limit the SAN frequency candidates in accordance with predetermined SAN frequency limiting conditions. Examples of SAN frequency limiting conditions are given below.

[0046] (Example 1 of SAN Frequency Restriction Condition) As a SAN frequency restriction condition, a frequency that will not be used for "MA PDU Session With two 3GPP Access" is set in advance in the UE 10. In the above example, for example, frequency "n21" is a frequency that will not be used for "MA PDU Session With two 3GPP Access" and is set in advance in the UE 10. As a result, the communication control unit 1110 determines only frequency "n22" of frequencies "n21" and "n22" as a frequency candidate for RAN 30_2 (SAN) of SPLMN "2".

[0047] (Example 2 of SAN Frequency Restriction Condition) As a SAN frequency restriction condition, whether or not to restrict the frequencies available in the SAN cell is set in advance in UE 10 based on information about the antennas of UE 10 used to connect with the PAN cell. For example, as a SAN frequency restriction condition, if the number of antennas provided in UE 10 is two, when the number of antennas used to connect with the PAN cell is one, no restriction is imposed on the frequencies available in the SAN cell. On the other hand, when the number of antennas used to connect with the PAN cell is one, a restriction is imposed on the frequencies available in the SAN cell. When the number of antennas used to connect with the PAN cell is one, there is one unused antenna, so no restriction is imposed on the frequencies available in the SAN cell. On the other hand, when the number of antennas used to connect with the PAN cell is two, there are no unused antennas, so a restriction is imposed on the frequencies available in the SAN cell. When there are no unused antennas, for example, the frequencies used in the SAN cell are limited to frequencies that can be shared with the PAN cell.

[0048] According to this embodiment, an effect is obtained in which the UE 10 can determine the cell (base station) to which the SAN is connected.

[0049] 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).

[0050] 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."

[0051] 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.

[0052] 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.

[0053] 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.

[0054] According to the present invention, it is possible for a user terminal to determine a base station to which the SAN is to be connected.

[0055] 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 including 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 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); When establishing a "Multi-access PDU Session" between the first radio access network of the already-connected PPLMN (Primary PLMN) and the second radio access network of the newly-connected SPLMN (Secondary PLMN), Based on the frequency combination information and the PLMN frequency information, identify a second frequency available in the second radio access network included in the combination of frequencies available in the first radio access network and the second radio access network, Based on the identified second frequency, a communication control unit that determines a base station to which the second radio access network is connected. A user terminal comprising.

2. The communication control unit restricts a second frequency available in the second radio access network according to a predetermined frequency restriction condition. The user terminal according to claim 1.

3. The communication control unit determines whether to restrict the second frequency available in the second radio access network based on information on an antenna used for connection to the first radio access network. The user terminal according to claim 1.

4. 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 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 establishing a "Multi-access PDU Session" between a first radio access network of a PPLMN (Primary PLMN) already connected and a second radio access network of an SPLMN (Secondary PLMN) to be newly connected, based on the frequency combination information and the PLMN frequency information, identifying a second frequency available in the second radio access network included in a combination of frequencies available between the first radio access network and the second radio access network, a communication control step of determining a base station to which the second radio access network is to be connected based on the identified second frequency. A communication control method including the above steps.

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