Communication system

Abstract

The communication system of the present invention includes: an anchor network, which is a network having user plane functionality that is directly connected to the data network of the data transmission and reception destination of the communication terminal; and a non-anchor network, which is a network connected to the data network via the anchor network. When the communication terminal switches the connected network, it uses multiple protocol stacks to transition to a state that is connected to both the anchor network and the non-anchor network and communicates with the data network, and then terminates the communication with the data network via the switching source network.

Description

Technical Field

[0001] This disclosure relates to wireless communication technology. Background Technology

[0002] Within the 3GPP (3rd Generation Partnership Project), the standardization organization for mobile communication systems, fifth-generation (hereinafter sometimes referred to as "5G") radio access systems were discussed as a successor to Long Term Evolution (LTE) and Long Term Evolution Advanced (LTE-A), one of the fourth-generation radio access systems (see Non-Patent Document 1) (e.g., Non-Patent Document 2). The technology for the 5G radio band is called "New Radio Access Technology" ("New Radio" is abbreviated as "NR"). NR systems are discussed based on LTE and LTE-A systems.

[0003] For example, in Europe, the organization METIS is summarizing the requirements for 5G (see Non-Patent Document 3). In 5G wireless access systems, for LTE systems, assuming a system capacity 1000 times greater, data transmission speed 100 times greater, data processing latency 1 / 5th, and simultaneous connection capacity of communication terminals 100 times greater, further reductions in power consumption and device cost can be listed as requirements (see Non-Patent Document 3).

[0004] To meet these requirements, discussions on 5G standards are ongoing within 3GPP (see Non-Patent Literature 4-23).

[0005] As an access method for NR, the downlink direction uses OFDM (Orthogonal Frequency Division Multiplexing), while the uplink direction uses OFDM and DFT-s-OFDM (Discrete Fourier Transform-spread-OFDM). Furthermore, similar to LTE and LTE-A, the 5G system does not include line switching; it uses only packet communication.

[0006] In NR, higher frequencies can be used compared to LTE to increase transmission speed and reduce processing latency.

[0007] In NR, which sometimes uses frequencies higher than LTE, a narrower beam-shaped transmit / receive range is formed (beamforming) and the direction of the beam is changed (beam scanning), thereby ensuring cell coverage through capability mapping.

[0008] use Figure 1 To explain the decisions regarding the frame structure of the NR system in 3GPP as described in Non-Patent Document 1 (Chapter 5). Figure 1 This is an explanatory diagram showing the structure of the wireless frame used in an NR communication system. Figure 1 In NR, a radio frame is 10 ms long. The radio frame is divided into 10 equal-sized subframes. The NR frame structure supports one or more numberologies, i.e., one or more subcarrier spacings (SCS). In NR, a subframe is 1 ms long, and a time slot consists of 14 symbols, regardless of the subcarrier spacing. Furthermore, the number of time slots in a subframe is one when the subcarrier spacing is 15 kHz; the number of time slots in other subcarrier spacings increases proportionally to the subcarrier spacing (see Non-Patent Document 11 (3GPP TS38.211)).

[0009] Non-Patent Document 2 (Chapter 5) and Non-Patent Document 11 record decisions made in 3GPP related to channel structure in NR systems.

[0010] The Physical Broadcast Channel (PBCH) is a channel used for downlink transmission from a base station (hereinafter sometimes referred to as a "base station") to a mobile terminal device (hereinafter sometimes referred to as a "mobile terminal") or other communication terminal device (hereinafter sometimes referred to as a "communication terminal" or "terminal"). The PBCH is transmitted together with the downlink synchronization signal.

[0011] In NR, the downlink synchronization signal consists of a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS). The synchronization signal is transmitted from the base station as a synchronization signal burst (hereinafter sometimes referred to as an SS burst), at a specified period for a specified duration. An SS burst consists of synchronization signal blocks (hereinafter sometimes referred to as SS blocks) for each beam of the base station.

[0012] During the duration of an SS burst, the base station changes its beam to transmit SS blocks for each beam. An SS block consists of P-SS, S-SS, and PBCH.

[0013] The Physical Downlink Control Channel (PDCCH) is the downlink transmission channel from the base station to the communication terminal. The PDCCH transmits Downlink Control Information (DCI). The DCI includes resource allocation information for the Downlink Shared Channel (DL-SCH), one of the transmission channels described later; resource allocation information for the Paging Channel (PCH), another transmission channel described later; and HARQ (Hybrid Automatic Repeat reQuest) information related to the DL-SCH. Additionally, the DCI sometimes includes Uplink Scheduling Grant. The DCI sometimes includes response signals for uplink transmissions, namely Ack (Acknowledgement) / Nack (Negative Acknowledgement). Furthermore, to allow for flexible DL / UL handover within time slots, the DCI sometimes includes Slot Format Indication (SFI). PDCCH or DCI is also known as the L1 / L2 control signal.

[0014] In NR, there are time-domain and frequency-domain regions that can serve as candidates for containing PDCCH. This region is called the Control Resource Set (CORESET). The communication terminal monitors the CORESET to acquire the PDCCH.

[0015] The Physical Downlink Shared Channel (PDSCH) is the downlink transmission channel from the base station to the communication terminal. The PDSCH maps to the Downlink Shared Channel (DL-SCH) used as the transport channel and the PCH used as the transport channel.

[0016] The Physical Uplink Control Channel (PUCCH) is the uplink transmission channel from the communication terminal to the base station. PUCCH transmits Uplink Control Information (UCI). UCI includes response signals (Ack / Nack) for downlink transmissions, CSI (Channel State Information), and Scheduling Requests (SRs). CSI is composed of RI (Rank Indicator), PMI (Precoding Matrix Indicator), and CQI (Channel Quality Indicator) reports. RI refers to the rank information of the channel matrix in MIMO (Multiple Input Multiple Output). PMI refers to the information of the precoding matrix used in MIMO. CQI is quality information indicating the quality of received data or the quality of the communication line. UCI is sometimes transmitted via PUSCH (described later). PUCCH or UCI is also referred to as L1 / L2 control signals.

[0017] The Physical Uplink Shared Channel (PUSCH) is the uplink transmission channel from the communication terminal to the base station. The PUSCH maps the Uplink Shared Channel (UL-SCH) as one of the transmission channels.

[0018] The Physical Random Access Channel (PRACH) is an uplink transmission channel from a communication terminal to a base station. PRACH transmits the random access preamble.

[0019] Downlink reference signals (RS) are symbols known in NR (Normally Injectable) communication systems. There are four types of downlink reference signals: UE-specific reference signals (DM-RS), phase tracking reference signals (PT-RS), positioning reference signals (PRS), and channel state information reference signals (CSI-RS). As physical layer measurements for communication terminals, there are measurements of the received power (RSRP) and received quality (RSRQ) of the reference signals.

[0020] The uplink reference signal is also a known symbol in NR communication systems. Three types of uplink reference signals are defined: Demodulation Reference Signal (DM-RS), Phase Tracking Reference Signal (PT-RS), and Sounding Reference Signal (SRS).

[0021] The transport channel described in Non-Patent Document 2 (Chapter 5) will be explained. The broadcast channel (BCH) in the downlink transport channel is broadcast to the entire coverage area of ​​its base station (cell). The BCH is mapped to the physical broadcast channel (PBCH).

[0022] HARQ-based retransmission control is applied to the Downlink Shared Channel (DL-SCH). The DL-SCH can broadcast to the entire coverage area of ​​the base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also known as semi-persistent scheduling. To reduce the power consumption of communication terminals, the DL-SCH supports discontinuous reception (DRX). The DL-SCH is mapped to the Physical Downlink Shared Channel (PDSCH).

[0023] The Paging Channel (PCH) supports DRX of communication terminals to reduce power consumption. The PCH is requested to broadcast over the entire coverage area of ​​the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH) that can be dynamically used for traffic.

[0024] HARQ-based retransmission control is applied to the Uplink Shared Channel (UL-SCH) in the uplink transport channel. UL-SCH supports dynamic or quasi-static resource allocation. Quasi-static resource allocation is also known as Configured Grant. UL-SCH is mapped to the Physical Uplink Shared Channel (PUSCH).

[0025] The Random Access Channel (RACH) is restricted to control information. RACH is subject to collision risks. RACH is mapped to the Physical Random Access Channel (PRACH).

[0026] The following explains HARQ. HARQ is a technique that improves the communication quality of a transmission line by combining Automatic Repeat Request (ARQ) and Forward Error Correction. HARQ has the following advantages: even for transmission lines where communication quality changes, retransmission can effectively enable error correction. In particular, during retransmission, the quality can be further improved by combining the initial received result with the retransmitted result.

[0027] Here's an example illustrating the retransmission method. When the receiving side cannot correctly decode the received data—in other words, when a CRC (Cyclic Redundancy Check) error occurs (CRC=NG)—a "Nack" is sent from the receiving side to the sending side. The sending side, upon receiving the "Nack," retransmits the data. When the receiving side can correctly decode the received data—in other words, when no CRC error occurs (CRC=OK)—a "ck" is sent from the receiving side to the sending side. The sending side, upon receiving the "Ack," sends the next data.

[0028] Other examples of retransmission methods are illustrated below. If a CRC error occurs at the receiving end, a retransmission request is sent from the receiving end to the sending end. The retransmission request is made via a switch of the NDI (New Data Indicator). The sending end, upon receiving the retransmission request, retransmits the data. If no CRC error occurs at the receiving end, no retransmission request is sent. If the sending end does not receive a retransmission request within a specified time, it is assumed that no CRC error occurred at the receiving end.

[0029] The logical channel described in Non-Patent Document 1 (Chapter 6) will be explained. The Broadcast Control Channel (BCCH) is a downlink channel used to broadcast system control information. The BCCH, as a logical channel, is mapped to either the broadcast channel (BCH) as a transmission channel or the downlink shared channel (DL-SCH).

[0030] The Paging Control Channel (PCCH) is a downlink channel used to transmit paging information and system information updates. The PCCH, as a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0031] The Common Control Channel (CCCH) is a channel used to transmit control information between a communication terminal and a base station. The CCCH is used when there is no RRC connection between the communication terminal and the network. In the downlink direction, the CCCH is mapped to the Downlink Shared Channel (DL-SCH) used as a transport channel. In the uplink direction, the CCCH is mapped to the Uplink Shared Channel (UL-SCH) used as a transport channel.

[0032] The Dedicated Control Channel (DCCH) is a channel used to transmit dedicated control information between a communication terminal and the network in a one-to-one manner. The DCCH is used when there is an RRC connection between the communication terminal and the network. In the uplink, the DCCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0033] A Dedicated Traffic Channel (DTCH) is a channel used for sending user information and conducting one-to-one communication with the communication terminal. DTCH exists in both the uplink and downlink. In the uplink, DTCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0034] Location tracking of a communication terminal is performed on a unit consisting of one or more cells. Location tracking is used to locate the communication terminal even in standby mode, enabling calls to the terminal; in other words, it is performed to enable calls to the communication terminal. The area used for location tracking of this communication terminal is called the Tracking Area (TA).

[0035] In NR, calls from communication terminals within a range smaller than the tracking area are supported. This range is called the RAN Notification Area (RNA). Paging of communication terminals in the RRC_INACTIVE state, as described later, occurs within this range.

[0036] In NR, to support wider transmission bandwidths, carrier aggregation (CA) has been studied, which involves combining two or more component carriers (CCs). CA is described in Non-Patent Literature 1.

[0037] In the case of a CA (Communication Terminal), the UE, as a communication terminal, has a unique RRC (Remote Reference Cell) connection with the network (NW). Within the RRC connection, a serving cell provides NAS (Non-Access Stratum) mobility information and security input. This cell is called the Primary Cell (PCell). Secondary serving cells (SCells) are formed based on the UE's capabilities, together with the PCell, to create a group of serving cells. For a single UE, a group of serving cells is formed consisting of one PCell and one or more SCells.

[0038] Furthermore, 3GPP includes dual connectivity (DC), where the UE communicates with two base stations to further increase communication capacity. DC is described in non-patent documents 1 and 22.

[0039] Sometimes, one of the base stations performing dual connectivity (DC) is called the "Master Node (MN)," and the other is called the "Secondary Node (SN)." The serving cells comprised of the Master Nodes are sometimes collectively referred to as the Master Cell Group (MCG), and the serving cells comprised of the Secondary Nodes are sometimes collectively referred to as the Secondary Cell Group (SCG). In DC, the Master Cell in the MCG or SCG is called a Special Cell (SpCell or SPCell). The Special Cell in the MCG is called a PCell, and the Special Cell in the SCG is called the Primary SCG Cell (PSCell).

[0040] In addition, in NR, the base station pre-defines a portion of the carrier frequency band for the UE (hereinafter sometimes referred to as the Bandwidth Part (BWP)). The UE transmits and receives data with the base station in this BWP, thereby reducing the power consumption in the UE.

[0041] Furthermore, 3GPP has explored services (or applications) that support sidelink (SL) communication (also known as PC5 communication) in both the EPS (Evolved Packet System) and 5G core systems (described later) (see Non-Patent Documents 1, 2, 26-28). SL communication involves communication between terminals. Examples of services using SL communication include V2X (Vehicle-to-everything) and proximity services. In SL communication, in addition to direct communication between terminals, communication between the UE and the NW via a relay has also been proposed (see Non-Patent Documents 26, 28).

[0042] The physical channel used for SL (refer to Non-Patent Documents 2, 11) is described below. The Physical Sidelink Broadcast Channel (PSBCH) transmits information related to system synchronization and is sent from the UE.

[0043] The Physical Sidelink Control Channel (PSCCH) transmits control information from the UE for sidelink communication and V2X sidelink communication.

[0044] The Physical Sidelink Shared Channel (PSSCH) transmits data from the UE for sidelink communication and V2X sidelink communication.

[0045] The Physical Sidelink Feedback Channel (PSFCH) transmits HARQ feedback from the sidelink from the UE that received the PSSCH to the UE that sent the PSSCH.

[0046] The transmission channel used for SL (refer to Non-Patent Document 1) will be described. The sidelink broadcast channel (SL-BCH) has a predetermined transmission format and is mapped to the PSBCH, which is the physical channel.

[0047] The Sidelink Shared Channel (SL-SCH) supports broadcast transmission. SL-SCH supports both UE autonomous resource selection and resource allocation scheduled by the base station. While UE autonomous resource selection carries a risk of conflict, there are no conflicts when the UE allocates dedicated resources through the base station. Furthermore, SL-SCH supports dynamic link adaptation by modifying transmit power, modulation, and coding. SL-SCH is mapped to the Physical Channel Sequential Channel (PSSCH).

[0048] The logical channels used for SL (refer to Non-Patent Document 2) will be described. The Sidelink Broadcast Control Channel (SBCCH) is a sidelink channel used to broadcast sidelink system information from one UE to other UEs. The SBCCH is mapped to the SL-BCH, which serves as the transport channel.

[0049] The Sidelink Traffic Channel (STCH) is a one-to-many traffic channel used to send user information from one UE to other UEs. The STCH is used only by UEs with sidelink communication capabilities and UEs with V2X sidelink communication capabilities. One-to-one communication between two UEs with sidelink communication capabilities is also achieved through the STCH. The STCH is mapped to the SL-SCH, which serves as the transport channel.

[0050] The Sidelink Control Channel (SCCH) is a control channel used to send control information from one UE to other UEs. The SCCH is mapped to the SL-SCH, which serves as the transport channel.

[0051] In LTE, SL communication only involves broadcast. In NR, in addition to broadcast, support for unicast and groupcast has also been studied for SL communication (see Non-Patent Document 27 (3GPP TS23.287)).

[0052] In SL's unicast and multicast communications, it supports HARQ feedback (Ack / Nack), CSI reports, and more.

[0053] In addition, 3GPP is studying Integrated Access and Backhaul (IAB), which uses wireless methods to serve as both access links between UEs and base stations and backhaul links between base stations (see Non-Patent Literature 2, 20, 29).

[0054] For mobile communication systems, some new technologies have been proposed. For example, to improve communication capacity and reliability, a technology has been proposed that allows one terminal to connect to multiple NWs simultaneously, thereby improving communication capacity and reliability (see Non-Patent Literature 30, 31).

[0055] Existing technical documents

[0056] Non-patent literature

[0057] Non-patent literature 1: 3GPP TS36.300 V17.5.0

[0058] Non-patent document 2: 3GPP TS38.300 V17.6.0

[0059] Non-patent literature 3: "Scenarios, requirements and KPIs for 5G mobile and wireless system", ICT-317669-METIS / D1.1

[0060] Non-patent literature 4: 3GPP TR23.799 V14.0.0

[0061] Non-patent literature 5: 3GPP TR38.801 V14.0.0

[0062] Non-patent document 6: 3GPP TR38.802 V14.2.0

[0063] Non-patent document 7: 3GPP TR38.804 V14.0.0

[0064] Non-patent document 8: 3GPP TR38.912 V16.0.0

[0065] Non-Patent Document 9: 3GPP RP-172115

[0066] Non-patent document 10: 3GPP TS23.501 V18.3.0

[0067] Non-patent document 11: 3GPP TS38.211 V18.0.0

[0068] Non-patent document 12: 3GPP TS38.212 V18.0.0

[0069] Non-patent document 13: 3GPP TS38.213 V18.0.0

[0070] Non-patent document 14: 3GPP TS38.214 V18.0.0

[0071] Non-patent document 15: 3GPP TS38.321 V17.6.0

[0072] Non-patent document 16: 3GPP TS38.322 V17.3.0

[0073] Non-patent document 17: 3GPP TS38.323 V17.5.0

[0074] Non-patent document 18: 3GPP TS37.324 V17.0.0

[0075] Non-patent document 19: 3GPP TS38.331 V17.6.0

[0076] Non-patent document 20: 3GPP TS38.401 V17.6.0

[0077] Non-patent document 21: 3GPP TS38.413 V17.6.0

[0078] Non-patent document 22: 3GPP TS37.340 V17.6.0

[0079] Non-patent document 23: 3GPP TS38.423 V17.6.0

[0080] Non-patent document 24: 3GPP TS38.305 V17.6.0

[0081] Non-patent document 25: 3GPP TS23.273 V18.3.0

[0082] Non-patent document 26: 3GPP TR23.703 V12.0.0

[0083] Non-patent document 27: 3GPP TS23.287 V18.1.0

[0084] Non-patent document 28: 3GPP TS23.303 V17.1.0

[0085] Non-patent document 29: 3GPP TS38.340 V17.5.0

[0086] Non-Patent Document 30: 3GPP SWS-230049

[0087] Non-patent document 31: 3GPP TS23.502 V18.3.0

[0088] Non-patent document 32: 3GPP TS23.503 V18.3.0

[0089] Non-patent document 33: 3GPP TR32.851 V12.2.0

[0090] Non-patent document 34: 3GPP TS28.537 V17.3.0 Summary of the Invention

[0091] The technical problem that the invention aims to solve

[0092] When a UE is simultaneously connected to multiple NWs, the NW that serves as the traffic path between the UE and the DN (Data Network) can be switched over. However, this can lead to the following problem: if the NW switchover occurs before all data from the previous NW has been delivered to the UE, the data may be lost.

[0093] In view of the above-mentioned issues, one of the objectives of this disclosure is to improve the reliability of data transmission and reception during network handover in a communication system in which the UE can connect to multiple networks simultaneously.

[0094] Technical means for solving technical problems

[0095] The communication system involved in this application is a communication system corresponding to a 5th generation wireless access system, which includes: an anchor network, which is a network with user plane functionality that is directly connected to the data network to which the communication terminal is destined for data transmission and reception; and a non-anchor network, which is a network connected to the data network via the anchor network. The communication system has multiple protocol stacks for communication between the communication terminal and the data network. When the communication terminal switches the connected network, it uses multiple protocol stacks to transition to a state of connection with both the anchor network and the non-anchor network and communication with the data network, and then terminates communication with the data network via the switching source network.

[0096] Invention Effects

[0097] According to this disclosure, in a communication system where the UE can connect to multiple networks simultaneously, the reliability of data transmission and reception during network handover can be improved.

[0098] The purpose, features, aspects, and advantages of this disclosure will become more apparent from the following detailed description and accompanying drawings. Attached Figure Description

[0099] Figure 1 This is an explanatory diagram showing the structure of a wireless frame used in an NR communication system.

[0100] Figure 2This is a block diagram showing the overall structure of a communication system 210 using the NR method discussed in 3GPP.

[0101] Figure 3 This is a structural diagram of a DC based on a base station connected to the NG core.

[0102] Figure 4 It is shown Figure 2 The diagram shows the structure of the mobile terminal 202.

[0103] Figure 5 It is shown Figure 2 The diagram shows the structure of base station 213.

[0104] Figure 6 This is a block diagram showing the structure of the 5GC section.

[0105] Figure 7 This is a flowchart illustrating the process from cell search to standby mode in a communication terminal (UE) in an NR-based communication system.

[0106] Figure 8 This is a diagram illustrating an example of cell structure in an NR system.

[0107] Figure 9 This is a connection structure diagram illustrating an example of the connection structure of a terminal in SL communication.

[0108] Figure 10 This is a connection structure diagram illustrating an example of a base station connection structure that supports integrated access and backhaul.

[0109] Figure 11 This is a structural diagram of implementation method 1, showing an example of a UE connected to multiple NWs.

[0110] Figure 12 This is a diagram illustrating an example of the protocol stack between the UE and the anchor point UPF in implementation method 1.

[0111] Figure 13 This is a diagram showing another example of the protocol stack between the UE and the anchor UPF in implementation 1.

[0112] Figure 14 This is a diagram showing another example of the protocol stack between the UE and the anchor UPF in implementation 1.

[0113] Figure 15 This is a diagram showing another example of the protocol stack between the UE and the anchor UPF in implementation 1.

[0114] Figure 16 This is a diagram showing the first half of a sequence of examples of NW switching actions that maintain the NW protocol between the two parties, according to implementation method 1.

[0115] Figure 17 This is a diagram showing the latter half of a sequence of examples of NW switching actions that maintain the NW protocol between the two parties, according to implementation method 1.

[0116] Figure 18 It is shown Figure 16 The sequence diagram of the process 1100 is an example.

[0117] Figure 19 It is shown Figure 16 The sequence diagram of an example of process 1111.

[0118] Figure 20 It is shown Figure 16 The sequence diagram of the example process 1120.

[0119] Figure 21 It is shown Figure 16 The sequence diagram of the example process 1130.

[0120] Figure 22 It is shown Figure 17 The sequence diagram of the example process 1255. Detailed Implementation

[0121] Implementation method 1.

[0122] Figure 2 This is a block diagram illustrating the overall structure of a communication system 210 using the NR method discussed in 3GPP. Figure 2 The following explanation is provided. The radio access network is referred to as NG-RAN (Next Generation Radio Access Network) 211. The communication terminal device, i.e., the mobile terminal device (hereinafter referred to as "User Equipment (UE)") 202, can wirelessly communicate with the base station device (hereinafter referred to as "NG-RAN NodeB (gNB)") 213, and uses wireless communication to transmit and receive signals. NG-RAN 211 consists of one or more NR base stations 213.

[0123] Here, "communication terminal device" includes not only mobile terminal devices such as mobile phone terminals, but also stationary devices such as sensors. In the following description, "communication terminal device" will sometimes be abbreviated as "communication terminal".

[0124] Between UE202 and NG-RAN 211, the AS (Access Stratum) protocol is terminated. AS protocols include, for example, RRC (Radio Resource Control), SDAP (Service Data Adaptation Protocol), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical Layer). RRC is used for the control plane (hereinafter sometimes referred to as C-plane, C-Plane, or CP), SDAP is used for the user plane (hereinafter sometimes referred to as U-plane, U-Plane, or UP), and PDCP, MAC, RLC, and PHY are used for both the C-plane and U-plane.

[0125] The Radio Resource Control (RRC) protocol between UE202 and NR base station 213 performs broadcasting, paging, and RRC connection management. The states between NR base station 213 and UE202 in RRC include RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0126] During RRC_IDLE, PLMN (Public Land Mobile Network) selection, System Information (SI) broadcasting, paging, cell re-selection, and mobility operations are performed. During RRC_CONNECTED, the mobile terminal has an RRC connection and can send and receive data with the network. Additionally, during RRC_CONNECTED, handover (HO) and neighbor cell determination (measurement) are performed. During RRC_INACTIVE, the connection between the 5G core unit 214 and the NR base station 213 is maintained while simultaneously performing System Information (SI) broadcasting, paging, cell re-selection, and mobility operations.

[0127] The gNB213 connects to the 5G core (hereinafter sometimes referred to as the "5GC unit") 214, which includes Access and Mobility Management Function (AMF), Session Management Function (SMF), or User Plane Function (UPF), via the NG interface. Control information and / or user data communication occurs between the gNB213 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB213 and AMF220, the N3 interface between the gNB213 and UPF221, the N11 interface between AMF220 and SMF222, and the N4 interface between UPF221 and SMF222. One gNB213 can connect to multiple 5GC units 214. The gNBs213 are connected to each other via the Xn interface, enabling communication of control information and / or user data between them.

[0128] The 5GC unit 214 is a host device, specifically a host node, that controls the connection between the NR base station 213 and the mobile terminal (UE) 202, and allocates paging signals for one or more NR base stations (gNB) 213 and / or LTE base stations (E-UTRAN NodeB: eNB). Additionally, the 5GC unit 214 performs mobility control in the idle state. The 5GC unit 214 manages the tracking area list when the mobile terminal 202 is in the idle state, and in the inactive and active states. The 5GC unit 214 initiates the paging protocol by sending paging messages to cells belonging to the registered tracking area of ​​the mobile terminal 202.

[0129] gNB213 can form one or more cells. When one gNB213 forms multiple cells, each cell is configured to communicate with UE202.

[0130] The gNB213 can be divided into a Central Unit (CU) 215 and a Distributed Unit (DU) 216. A CU 215 constitutes one unit within the gNB213. One or more DUs 216 constitute one or more cells within the gNB213. A single DU 216 constitutes one or more cells. The CU 215 connects to the DU 216 via an F1 interface, facilitating communication of control information and / or user data between the CU 215 and DU 216. The F1 interface consists of an F1-C interface and an F1-U interface. The CU 215 handles the functions of various protocols including RRC, SDAP, and PDCP, while the DU 216 handles the functions of various protocols including RLC, MAC, and PHY. One or more Transmission Reception Points (TRPs) 219 are sometimes connected to the DU 216. The TRP 219 transmits and receives radio signals with the UE.

[0131] CU215 can be divided into CU (CU-C) 217 ​​for the C-side and CU (CU-U) 218 ​​for the U-side. CU-C 217 is configured as one unit within CU215. CU-U 218 is configured as one or more units within CU215. CU-C 217 connects to CU-U 218 via an E1 interface, facilitating control information communication between CU-C 217 and CU-U 218. CU-C 217 connects to DU216 via an F1-C interface, facilitating control information communication between CU-C 217 and DU216. CU-U 218 connects to DU216 via an F1-U interface, facilitating user data communication between CU-U 218 and DU216.

[0132] 5G communication systems may include the Unified Data Management (UDM) function and Policy Control Function (PCF) described in Non-Patent Document 10 (3GPP TS23.501). UDM and / or PCF may be included in... Figure 2 In section 5GC214.

[0133] In a 5G communication system, a Location Management Function (LMF) as described in Non-Patent Document 24 (3GPP TS38.305) can be configured. As disclosed in Non-Patent Document 25 (3GPP TS23.273), the LMF can be connected to the base station via the AMF.

[0134] In 5G communication systems, the non-3GPP interworking function (N3IWF) described in Non-Patent Document 10 (3GPP TS23.501) may also be included. The N3IWF can terminate the access network (AN) between the user and the UE in non-3GPP access.

[0135] Figure 3 This is a diagram illustrating a structure based on a DC (dual-connection) linked to the NG core. Figure 3 In the diagram, solid lines represent U-Plane connections, and dashed lines represent C-Plane connections. Figure 3 In this configuration, the primary base station 240-1 can be either a gNB or an eNB. Similarly, the secondary base station 240-2 can also be either a gNB or an eNB. For example, in... Figure 3 In some contexts, the DC structure where the primary base station 240-1 is a gNB and the secondary base station 240-2 is an eNB is sometimes referred to as NG-EN-DC. Figure 3 The example shown illustrates a U-Plane connection between the 5GC unit 214 and the secondary base station 240-2 via the primary base station 240-1, but it can also be established directly between the 5GC unit 214 and the secondary base station 240-2. Additionally, Figure 3 In this configuration, the core network EPC (Evolved Packet Core) connected to the LTE and LTE-A systems can replace the 5GC unit 214 and connect to the main base station 240-1. The U-Plane connection between the EPC and the secondary base station 240-2 can be directly established.

[0136] Figure 4 It is shown Figure 2 The diagram shows the structure of the mobile terminal 202. Figure 4The transmission processing of the mobile terminal 202 shown will be described. First, control data from the control unit 310 and user data from the application unit 302 are sent to the protocol processing unit 301. Buffering of the control data and user data can be performed. This buffering can be set in the control unit 310, the application unit 302, or the protocol processing unit 301. The protocol processing unit 301 performs protocol processing such as SDAP, PDCP, RLC, and MAC, for example, determining the destination base station in DC and assigning headers to various protocols. The protocol-processed data is transmitted to the encoding unit 304 for error correction and other encoding processing. Alternatively, data may be output directly from the protocol processing unit 301 to the modulation unit 305 without encoding processing. The data encoded by the encoding unit 304 is modulated in the modulation unit 305. MIMO precoding may also be performed in the modulation unit 305. After the modulated data is converted into a baseband signal, it is output to the frequency conversion unit 306 and converted into a wireless transmission frequency. Subsequently, the transmitted signal was sent from antennas 307-1 to 307-4 to base station 213. Figure 4 The example shown has four antennas, but the number of antennas is not limited to four.

[0137] Furthermore, the receiving process of the mobile terminal 202 is performed as follows: Wireless signals from the base station 213 are received via antennas 307-1 to 307-4. The received signal is converted from the wireless receiving frequency to a baseband signal by the frequency conversion unit 306, and demodulation processing is performed in the demodulation unit 308. Waiting calculations and multiplication processes can be performed in the demodulation unit 308. The demodulated data is transmitted to the decoding unit 309 for error correction and other decoding processing. The decoded data is transmitted to the protocol processing unit 301, where protocol processing such as MAC, RLC, PDCP, and SDAP is performed, including actions such as header removal in each protocol. Of the data after protocol processing, control data is transmitted to the control unit 310, and user data is transmitted to the application unit 302.

[0138] The series of processes of the mobile terminal 202 are controlled by the control unit 310. Therefore, although in Figure 4 The details have been omitted, but the control unit 310 is also connected to each of the units 302, 304 to 309.

[0139] Each part of the mobile terminal 202, such as the control unit 310, protocol processing unit 301, encoding unit 304, and decoding unit 309, is implemented, for example, by a processing circuit comprising a processor and a memory. For example, the control unit 310 is implemented by the processor executing a program describing a series of processes of the mobile terminal 202. The program describing the series of processes of the mobile terminal 202 is stored in a memory. Examples of memory are non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), and flash memory. Each part of the mobile terminal 202, such as the control unit 310, protocol processing unit 301, encoding unit 304, and decoding unit 309, can be implemented by dedicated processing circuits such as FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), and DSP (Digital Signal Processor). Figure 4 In this context, the number of antennas used for transmitting and the number of antennas used for receiving in the mobile terminal 202 may be the same or different.

[0140] Figure 5 It is shown Figure 2 The diagram shows the structure of base station 213. Figure 5 The transmission processing of the base station 213 shown will be described. The EPC communication unit 401 transmits and receives data between the base station 213 and the EPC. The 5GC communication unit 412 transmits and receives data between the base station 213 and the 5GC (5GC unit 214, etc.). The other base station communication units 402 transmit and receive data with other base stations. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication units 402 exchange information with the protocol processing unit 403. Control data from the control unit 411, and user data and control data from the EPC communication unit 401, the 5GC communication unit 412, and the other base station communication units 402 are sent to the protocol processing unit 403. Buffering of control data and user data can be performed. This buffering can be provided in the control unit 411, the EPC communication unit 401, the 5GC communication unit 412, or the other base station communication units 402.

[0141] The protocol processing unit 403 performs protocol processing for SDAP, PDCP, RLC, MAC, etc., such as routing transmitted data in DC and assigning headers to various protocols. The protocol-processed data is transmitted to the encoding unit 405 for error correction and other encoding processing. Alternatively, data may be output directly from the protocol processing unit 403 to the modulation unit 406 without encoding processing. Furthermore, data can be transmitted from the protocol processing unit 403 to other base station communication units 402. For example, in DC, data transmitted from the 5GC communication unit 412 or the EPC communication unit 401 can be transmitted to other base stations, such as auxiliary base stations, via other base station communication units 402. The encoded data undergoes modulation processing in the modulation unit 406. Precoding for MIMO can also be performed in the modulation unit 406. After the modulated data is converted into a baseband signal, it is output to the frequency conversion unit 407 and converted into a wireless transmission frequency. Then, using antennas 408-1 to 408-4, the transmission signal is transmitted to one or more mobile terminals 202. Figure 5 The example shown has four antennas, but the number of antennas is not limited to four.

[0142] Furthermore, the reception processing of base station 213 is performed as follows: Wireless signals from one or more mobile terminals 202 are received by antennas 408-1 to 408-4. The received signals are converted from the wireless receiving frequency to a baseband signal by frequency conversion unit 407, and demodulated in demodulation unit 409. The demodulated data is transmitted to decoding unit 410 for error correction and other decoding processing. The decoded data is transmitted to protocol processing unit 403, where protocol processing such as MAC, RLC, PDCP, and SDAP is performed, including actions such as header removal in each protocol. Of the data after protocol processing, control data is transmitted to control unit 411, 5GC communication unit 412, EPC communication unit 401, or other base station communication unit 402, and user data is transmitted to 5GC communication unit 412, EPC communication unit 401, or other base station communication unit 402. Data sent from other base station communication units 402 can be transmitted to 5GC communication unit 412 or EPC communication unit 401. This data could be, for example, uplink data transmitted from the DC to the 5GC communication unit 412 or the EPC communication unit 401 via other base stations.

[0143] The series of processes of base station 213 are controlled by control unit 411. Therefore, although in Figure 5 The details have been omitted, but the control unit 411 is also connected to the various units 401, 402, 405 to 410, 412.

[0144] The various parts of base station 213, such as control unit 411, protocol processing unit 403, 5GC communication unit 412, EPC communication unit 401, other base station communication unit 402, encoding unit 405, and decoding unit 410, are implemented similarly to those of mobile terminal 202 by processing circuits comprising a processor and memory, or dedicated processing circuits such as FPGA, ASIC, and DSP. Figure 5 In this system, the number of antennas used for transmitting and the number of antennas used for receiving in base station 213 can be the same or different.

[0145] As Figure 2 The example of the structure of CU215 shown, except Figure 5 In addition to the encoding unit 405, modulation unit 406, frequency conversion unit 407, antennas 408-1 to 408-4, demodulation unit 409, and decoding unit 410 shown, a structure with a DU communication unit is sometimes used. The DU communication unit is connected to the protocol processing unit 403. The protocol processing unit 403 in CU215 performs protocol processing for PDCP, SDAP, etc.

[0146] As Figure 2 The example of the structure of DU216 shown, except Figure 5 In addition to the EPC communication unit 401, other base station communication units 402, and 5GC communication unit 412 shown, a structure with a CU communication unit is sometimes used. The CU communication unit is connected to the protocol processing unit 403. The protocol processing unit 403 in DU216 performs protocol processing for PHY, MAC, RLC, etc.

[0147] Figure 6 This is a block diagram showing the structure of the 5GC section. Figure 6 The above is shown in the figure. Figure 2 The structure of the 5GC section 214 shown. Figure 6 It shows in Figure 2 The 5GC section 214 shown includes the structures of AMF, SMF, and UPF. Figure 6In the example shown, the AMF can have the functions of the control plane control unit 525, the SMF can have the functions of the session management unit 527, and the UPF can have the functions of the user plane communication unit 523 and the data network communication unit 521. The data network communication unit 521 performs data transmission and reception between the 5GC unit 214 and the data network. The base station communication unit 522 performs data transmission and reception between the 5GC unit 214 and the base station 21 via the NG interface. User data sent from the data network is transmitted from the data network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523, and then sent to one or more base stations 213. User data sent from the base station 213 is transmitted from the base station communication unit 522 to the data network communication unit 521 via the user plane communication unit 523, and then sent to the data network.

[0148] Control data sent from base station 213 is transmitted from base station communication unit 522 to control plane control unit 525. Control plane control unit 525 can transmit control data to session management unit 527. Control data can be sent from data network. Control data sent from data network can be sent from data network communication unit 521 to session management unit 527 via user plane communication unit 523. Session management unit 527 can send control data to control plane control unit 525.

[0149] The user plane communication unit 523 includes a PDU processing unit 523-1, a mobility anchoring unit 523-2, etc., and performs overall processing for the user plane (hereinafter sometimes referred to as U-Plane). The PDU processing unit 523-1 processes data packets, such as sending and receiving packets with the data network communication unit 521 and sending and receiving packets with the base station communication unit 522. The mobility anchoring unit 523-2 is responsible for anchoring the data path when the UE moves.

[0150] The session management unit 527 manages the PDU sessions set up between the UE and the UPF. The session management unit 527 includes a PDU session control unit 527-1 and a UE IP address allocation unit 527-2. The PDU session control unit 527-1 manages the PDU sessions between the mobile terminal 202 and the 5GC unit 214. The UE IP address allocation unit 527-2 allocates IP addresses for the mobile terminal 202.

[0151] The control plane control unit 525 includes a NAS security unit 525-1, an idle state mobility management unit 525-2, etc., and performs overall processing for the control plane (hereinafter sometimes referred to as C-Plane). The NAS security unit 525-1 performs security protection for NAS (Non-Access Stratum) messages. The idle state mobility management unit 525-2 performs mobility management in standby state (idle state: RRC_IDLE state, or simply idle), generation and control of paging signals in standby state, addition, deletion, updating, retrieval of tracking areas for one or more mobile terminals 202 within the coverage area, and tracking area list management.

[0152] The series of processes in the 5GC unit 214 are controlled by the control unit 526. Therefore, although in Figure 6 The details are omitted, but the control unit 526 is connected to each of the units 521-523, 525, and 527. The units of the 5GC unit 214 are similar to the control unit 310 of the mobile terminal 202 described above, and are implemented, for example, by a processing circuit comprising a processor and a memory, or by a dedicated processing circuit such as an FPGA, ASIC, or DSP.

[0153] Next, an example of a cell search method in a communication system is shown. Figure 7 This is a flowchart illustrating the process of a communication terminal (UE) in an NR-based communication system from cell search to standby operation. If the communication terminal starts cell search, in step ST601, the first synchronization signal (P-SS) and the second synchronization signal (S-SS) sent from the surrounding base stations are used to obtain the synchronization of time slot timing and frame timing.

[0154] P-SS and S-SS are collectively referred to as Synchronization Signal (SS). The Synchronization Signal (SS) contains a synchronization code that corresponds one-to-one with the PCI (Physical Cell Identifier) ​​assigned to each cell. In this discussion, the number of PCIs is set to 1008. The communication terminal uses these 1008 PCIs to achieve synchronization and detects (determines) the PCIs of synchronized cells.

[0155] In step ST602, the communication terminal receives the PBCH for the next cell to be synchronized. The BCCH on the PBCH maps to the MIB (Master Information Block), which contains cell structure information. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. Information in the MIB includes, for example, the SFN (System Frame Number), scheduling information of SIB (System Information Block) 1, subcarrier spacing of SIB1, and DM-RS location information.

[0156] Additionally, the communication terminal obtains the SS block identifier via the PBCH. A portion of the bit string of the SS block identifier is contained in the MIB. The remaining bit string is contained in the identifier used to generate the DM-RS sequence accompanying the PBCH. The communication terminal uses the MIB contained in the PBCH and the DM-RS sequence accompanying the PBCH to obtain the SS block identifier.

[0157] Next, in step ST603, the communication terminal measures the received power of the SS block.

[0158] Next, in step ST604, the communication terminal selects the cell with the best reception quality from the more than one cell detected up to step ST603, for example, selecting the cell with the highest reception power, i.e., the optimal cell. Additionally, the communication terminal selects the beam with the best reception quality, for example, selecting the beam with the highest reception power in the SS block, i.e., the optimal beam. The selection of the optimal beam is, for example, using the reception power of the SS block identified by each SS block.

[0159] Next, in step ST605, the communication terminal receives the DL-SCH based on the scheduling information of SIB1 contained in the MIB, and obtains SIB1 (System Information Block) from the broadcast information BCCH. SIB1 contains information related to access to the cell, cell structure information, and scheduling information of other SIBs (SIBk: an integer k ≥ 2). In addition, SIB1 contains the Tracking Area Code (TAC).

[0160] Next, in step ST606, the communication terminal compares the TAC of SIB1 received in step ST605 with the TAC portion of the Tracking Area Identity (TAI) in the tracking area list already stored by the communication terminal. The tracking area list is also called the TAI list. TAI is identification information used to identify the tracking area, consisting of the MCC (Mobile Country Code), MNC (Mobile Network Code), and TAC (Tracking Area Code). MCC is the country code. MNC is the network code. TAC is the tracking area code number.

[0161] If the comparison result in step ST606 is the same as the TAC received in step ST605, and it is also included in the tracking area list, then the communication terminal enters standby mode in that cell. If the comparison shows that the TAC received in step ST605 is not included in the tracking area list, then the communication terminal requests a change of tracking area from the core network (EPC) containing the MME, etc., through that cell to perform a TAU (Tracking Area Update).

[0162] The apparatus constituting the core network (hereinafter sometimes referred to as "core network-side apparatus") updates the tracking area list based on the TAU request signal and the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal. The core network-side apparatus sends the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) its own TAC list based on the received tracking area list. Afterward, the communication terminal enters standby mode in the cell.

[0163] Next, examples of random access methods in a communication system are shown. In random access, 4-step random access and 2-step random access are used. Furthermore, for 4-step and 2-step random access, there are conflict-based random access, random access that may cause timing conflicts with other mobile terminals, and conflict-free random access.

[0164] An example of a conflict-based four-step random access method is shown. As step 1, the mobile terminal sends a random access preamble to the base station. The random access preamble can be selected by the mobile terminal from a predefined range, or it can be assigned separately to the mobile terminal and notified by the base station.

[0165] As a second step, the base station sends a random access response to the mobile terminal. The random access response includes uplink scheduling information used in the third step, and the terminal identifier used in the uplink transmission in the third step.

[0166] As step 3, the mobile terminal sends an uplink transmission to the base station. The mobile terminal uses the information obtained in step 2 in this uplink transmission. As step 4, the base station notifies the mobile terminal whether a conflict has been resolved. Mobile terminals notified of no conflict end the random access process. Mobile terminals notified of a conflict restart the process from step 1.

[0167] The conflict-free 4-step random access method differs from the conflict-based 4-step random access method in the following ways: First, before step 1, the base station pre-assigns a random access preamble and uplink scheduling to the mobile terminal. Second, notification regarding conflict resolution is not required in step 4.

[0168] An example of a collision-based two-step random access method is shown. In step 1, the mobile terminal sends a random access preamble and an uplink transmission to the base station. In step 2, the base station notifies the mobile terminal of whether a collision has occurred. Mobile terminals notified of no collision end the random access process. Mobile terminals notified of a collision restart the process from step 1.

[0169] The conflict-free two-step random access method differs from the conflict-based two-step random access method in the following way: Before step 1, the base station pre-assigns a random access preamble and uplink scheduling to the mobile terminal. Additionally, in step 2, the base station sends a random access response to the mobile terminal.

[0170] Figure 8 This illustrates an example of the structure of a cell in NR. In an NR cell, a narrow beam is formed and its direction is changed for transmission. Figure 8 In the example shown, base station 750 uses beam 751-1 to transmit and receive data with the mobile terminal at certain times. At other times, base station 750 uses beam 751-2 to transmit and receive data with the mobile terminal. Similarly, base station 750 uses one or more of beams 751-3 to 751-8 to transmit and receive data with the mobile terminal. Thus, base station 750 constitutes a wide-range cell 752.

[0171] exist Figure 8 The example shown depicts a base station 750 using 8 beams, but the number of beams can also be different from 8. Additionally, in Figure 8 In the example shown, the number of beams used simultaneously by base station 750 is set to one, but it can also be multiple.

[0172] Beam identification uses the concept of QCL (Quasi-CoLocation) (refer to Non-Patent Document 14 (3GPP TS 38.214)). That is, it is identified by information indicating which reference signal (e.g., SS block, CSI-RS) the beam can be considered to be the same as. This information sometimes includes the type of information about the viewpoints that can be considered the same beam, such as information about Doppler shift, Doppler shift spread, average delay, average delay spread, and spatial Rx parameters (refer to Non-Patent Document 14 (3GPP TS 38.214)).

[0173] In 3GPP, sidelinks (SL) are supported for D2D (Device to Device) communication and V2V (Vehicle to Vehicle) communication (see Non-Patent Document 1 and Non-Patent Document 16). SL is specified through the PC5 interface.

[0174] In SL communication, in addition to broadcasting, support for PC5-S signaling was studied to support unicast and groupcast (see Non-Patent Document 27 (3GPP TS23.287)). For example, PC5-S signaling was implemented to establish SL, i.e., the link used to implement PC5 communication. This link is implemented in the V2X layer and is also known as a Layer 2 link.

[0175] In addition, support for RRC signaling is being researched in SL communication (see Non-Patent Document 27 (3GPP TS23.287)). RRC signaling in SL communication is also referred to as PC5 RRC signaling. For example, the ability to notify UEs of each other during PC5 communication, and the notification of AS layer settings for using PC5 communication for V2X communication, have been proposed.

[0176] Figure 9 The diagram shows an example of the connection structure of a mobile terminal in SL communication. Figure 9 In the example shown, UE805 and UE806 exist within the coverage area 803 of base station 801. UL / DL communication 805 occurs between base station 801 and UE806. UL / DL communication 808 occurs between base station 801 and UE806. SL communication 810 occurs between UE805 and UE806. UE811 and UE812 exist outside the coverage area 803. SL communication 814 occurs between UE805 and UE811. Additionally, SL communication 816 occurs between UE811 and UE812.

[0177] As an example of communication between the UE and NW via relay in SL communication, Figure 9The UE805 shown relays the communication between UE811 and base station 801.

[0178] UEs that perform relays sometimes use with Figure 4 Same structure. Use Figure 4 The relay processing in the UE will be explained. The relay processing of UE805 in communication from UE811 to base station 801 will be explained. Radio signals from UE811 are received via antennas 307-1 to 307-4. The received signal is converted from the radio receiving frequency to a baseband signal by frequency conversion unit 306, and demodulation processing is performed in demodulation unit 308. In demodulation unit 308, waiting calculations and multiplication processes can be performed. The demodulated data is transmitted to decoding unit 309 for error correction and other decoding processing. The decoded data is transmitted to protocol processing unit 301, where protocol processing for communication with UE811, such as MAC, RLC, etc., is performed, including actions such as header removal in each protocol. Additionally, protocol processing for communication with base station 801, such as RLC, MAC, etc., is performed, including actions such as header assignment in each protocol. In the protocol processing unit 301 of UE811, PDCP and SDAP protocol processing are sometimes also performed. The data that has undergone protocol processing is transmitted to the encoding unit 304 for error correction and other encoding processing. Alternatively, data may be output directly from the protocol processing unit 301 to the modulation unit 305 without undergoing encoding processing. The data encoded by the encoding unit 304 is then modulated in the modulation unit 305. MIMO precoding may also be performed in the modulation unit 305. After the modulated data is converted into a baseband signal, it is output to the frequency conversion unit 306 and converted into a wireless transmission frequency. The transmission signal is then transmitted from antennas 307-1 to 307-4 to the base station 801.

[0179] The above content illustrates an example of UE805 relaying communication from UE811 to base station 801, but the same process is used in the relaying of communication from base station 801 to UE811.

[0180] 5G base stations can support Integrated Access and Backhaul (IAB) (see Non-Patent Documents 2, 20). An IAB-supporting base station (hereinafter sometimes referred to as an IAB base station) consists of a CU (IAB Host CU) acting as an IAB host, a DU (IAB Host DU) acting as an IAB host, and IAB nodes that connect to the IAB Host DU and the UE via radio interfaces. An F1 interface is provided between the IAB nodes and the IAB Host CU (see Non-Patent Document 2).

[0181] Figure 10The diagram illustrates an example of IAB base station connections. IAB host CU901 is connected to IAB host DU902. IAB node 903 connects to IAB host DU902 using a radio interface. IAB node 903 connects to IAB node 904 using a radio interface. That is, sometimes multiple levels of IAB node connections are made. UE905 connects to IAB node 904 using a radio interface. UE906 sometimes connects to IAB node 903 using a radio interface, and UE907 sometimes connects to IAB host DU902 using a radio interface. Multiple IAB host DU902s can connect to IAB host CU901, multiple IAB nodes 903 can connect to IAB host DU902, and multiple IAB nodes 904 can connect to IAB node 903.

[0182] In the connections between the IAB host DU and IAB nodes, and between IAB nodes, a BAP (Backhaul Adaptation Protocol) layer is set up (see Non-Patent Document 29). The BAP layer performs actions such as routing received data to the IAB host DU and / or IAB nodes, and mapping it to the RLC channel (see Non-Patent Document 29).

[0183] As an example of the structure of the IAB host CU, the same structure as CU215 is used.

[0184] As an example of the structure of the IAB host DU, it uses the same structure as DU216. In the protocol processing section of the IAB host DU, BAP layer processing is performed, such as assigning BAP headers to downlink data, routing for IAB nodes, and removing BAP headers from uplink data.

[0185] As an example of the structure of IAB nodes, sometimes in addition to Figure 5 The structure shown is excluding the EPC communication unit 401, other base station communication units 402, and 5GC communication unit 412.

[0186] use Figure 5 , Figure 10The transmit / receive processing in the IAB node will be explained. The transmit / receive processing of IAB node 903 in communication between IAB host CU901 and UE905 will be described. In uplink communication from UE905 to IAB host CU901, the radio signal from IAB node 904 is received through antenna 408 (part or all of antennas 408-1 to 408-4). The received signal is converted from the radio receiving frequency to a baseband signal by frequency conversion unit 407, and demodulation processing is performed in demodulation unit 409. The demodulated data is transmitted to decoding unit 410 for error correction and other decoding processing. The decoded data is transmitted to protocol processing unit 403, where protocol processing for communication with IAB node 904, such as MAC, RLC, etc., and actions such as header removal in each protocol, are performed. In addition, routing to the IAB host DU902 using the BAP header is performed, and protocol processing for communication with the IAB host DU902, such as assigning headers to each protocol, is carried out. The protocol-processed data is transmitted to the encoding unit 405 for error correction and other encoding processing. Alternatively, data may be output directly from the protocol processing unit 403 to the modulation unit 406 without encoding processing. The encoded data is modulated in the modulation unit 406. MIMO precoding may also be performed in the modulation unit 406. After the modulated data is converted into a baseband signal, it is output to the frequency conversion unit 407 and converted into a radio transmission frequency. Then, the transmission signal is transmitted to the IAB host DU902 using antennas 408-1 to 408-4. The same processing is performed in downlink communication from the IAB host CU901 to the UE905.

[0187] In IAB node 904, the same send and receive processing is performed as in IAB node 903. In the protocol processing unit 403 of IAB node 903, as part of the BAP layer processing, such as assigning BAP headers in uplink communication and routing to IAB node 904, and removing BAP headers in downlink communication, etc.

[0188] In a 3GPP mobile communication system, a UE can connect to multiple NWs. The connection between the UE and the data network (DN) can be made via an anchor UPF (a UPF directly connected to the DN). An anchor NW (a network with an anchor UPF, hereinafter the same) can connect to one or more of these NWs connected to the UE. In this specification, an NW without an anchor UPF is referred to as a non-anchor NW. Furthermore, the device constituting an anchor NW is referred to as an anchor NW device, and the device constituting a non-anchor NW is referred to as a non-anchor NW device.

[0189] Figure 11 This is a block diagram illustrating an example of a UE connecting to multiple NWs. Figure 11 In the example shown, the UE is connected to both NW1090 and NW1091. Figure 11 In the example shown, base station #1, AMF#1, UPF#1, SMF#1, SEPP (Security Edge Protection Proxy, see Non-Patent Document 10)#1, PCF#1, UDM#1, and anchor UPF all belong to NW1090, while base station #2, AMF#2, UPF#2, SMF#2, SEPP#2, PCF#2, and UDM#2 all belong to NW1091. The anchor UPF is connected to the DN.

[0190] The NW connected to the UE can be switched. For example, the NW used for transmission and reception between the UE and the DN can be switched from NW1090 to NW1091, from NW1091 to NW1090, or to other NWs. This switching can be performed on specific traffic. For example, if the UE communicates with application 1 via NW1090 and with application 2 via NW1091, the path for communication related to application 2 can be switched to NW1090.

[0191] The following problem arises during this handover: if the handover to the NW (Network Wireless Terminal) is performed before the data from the previously connected NW has been fully delivered to the UE, there is a risk of data loss.

[0192] This embodiment discloses a method for solving the aforementioned problems. Furthermore, in the following description, the NW to which the UE is connected before the handover is sometimes referred to as the handover source NW, and the NW to which the UE is connected after the handover is sometimes referred to as the handover destination NW. Additionally, the base station to which the UE is connected before the handover of the NW is sometimes referred to as the handover source base station, and the base station to which the UE is connected after the handover is sometimes referred to as the handover destination base station.

[0193] In this embodiment, a protocol stack is provided between the UE and multiple NWs. For example, the UE may have a protocol stack between itself and two NWs. For instance, the UE may have a protocol stack between itself and the source NW and the destination NW. The UE may also have protocol stacks from both NWs simultaneously.

[0194] A UE can simultaneously possess a protocol stack at the PDU (Protocol Data Unit) layer and below. For example, the UE's IP address can be changed. A UE can also have multiple IP addresses.

[0195] An anchor UPF can have two protocol stacks at or below the PDU layer. IP addresses within the anchor UPF can be changed. An anchor UPF can also have multiple IP addresses.

[0196] Figure 12 This is a diagram illustrating an example of the protocol stack between the UE and the anchor UPF. Figure 12 In the example shown, the UE has a protocol stack below multiple PDU layers. Figure 12 The diagram shows a method for connecting the UE to... Figure 11 The NW1090 shown communicates with the DN using the first protocol stack, and is used to connect the UE to... Figure 11 The example shown illustrates the configuration of the second protocol stack for the NW1091 communicating with the DN.

[0197] As another example of a protocol stack that a UE may also have, it could be a protocol stack at or below the SDAP layer. The anchor UPF can have multiple protocol stacks below GTP-U (GPRS (General Packet Radio Service) Tunneling Protocol for User Plane). Thus, for example, no IP address change is required during a UE's NW handover.

[0198] As another example of a protocol stack that a UE may possess, it could be a protocol stack below the PDCP layer. The anchor UPF can have multiple protocol stacks below GTP-U. This, for example, avoids the complexity associated with the correspondence between QoS (Quality of Service) flows and data in both parties' NWs.

[0199] Figure 13 This is a diagram illustrating other examples of the protocol stack between the UE and the anchor UPF. Figure 13 In the example shown, the UE has multiple protocol stacks below the SDAP layer. The anchor UPF has multiple protocol stacks below GTP-U.

[0200] As another example of a protocol stack that a UE may also have, it could be a protocol stack below the PDCP layer. The anchor UPF can have multiple protocol stacks below GTP-U. This, for example, can reduce memory usage in the UE.

[0201] Figure 14 This is a diagram illustrating other examples of the protocol stack between the UE and the anchor UPF. Figure 14 In the example shown, the UE has multiple protocol stacks below the PDCP layer. The anchor UPF has multiple protocol stacks below GTP-U.

[0202] As another example of a protocol stack that a UE may also have, it could be a protocol stack below the RLC layer. The anchor UPF can have multiple protocol stacks below GTP-U. This, for example, can reduce memory usage in the UE.

[0203] Figure 15 This is a diagram illustrating other examples of the protocol stack between the UE and the anchor UPF. Figure 15 In the example shown, the UE has multiple protocol stacks below the RLC layer. The anchor UPF has multiple protocol stacks below GTP-U.

[0204] For downlink data received from the DN via the anchor point UPF, the UE can notify the base station of the other NW of information related to the sequence number (hereinafter sometimes referred to as the PDCP SN) of the PDCP PDU received from the base station (gNB) of one of the NWs. This base station can be the handover source base station, the handover destination base station, or both. Thus, for example, the PDCP SN received by the UE can be shared between base stations of different NWs, resulting in the prevention of data stagnation awaiting reordering in the PDCP layer. This notification can, for example, be given as a PDCP status PDU. This notification can contain information representing downlink data.

[0205] For uplink data transmitted to the DN via the anchor UPF, the UE can notify the base station of the other NW of information related to the PDCP SN of the PDCP PDU already transmitted to the base station of one NW. This base station can be the handover source base station, the handover destination base station, or both. Thus, for example, the PDCP SN transmitted by the UE can be shared between base stations in different NWs, resulting in the prevention of data backlog awaiting reordering in the PDCP layer of the base station. This notification can, for example, be given as a PDCP status PDU. This information can include information representing uplink data.

[0206] The NW can configure the protocol stack for both the UE and the source NW. This configuration can be performed by the anchor NW, the handover source NW, or the handover destination NW. The Network Function (NF) used for this configuration can be either an AMF or an SMF. For example, this configuration may or may not be included in the NW handover instruction. For instance, the NW handover instruction could be a PDU session establishment instruction, a PDU session change instruction, or a PDU session release instruction. The UE can use this instruction as a trigger to maintain the protocol stack with the source NW, establish the protocol stack with the destination NW, and perform the aforementioned actions for both parties.

[0207] This setting can include NW-related information relative to the UE, information related to protocols with multiple protocol stacks (e.g., below PDU layer, below SDAP, below PDCP, below RLC), information related to the top-level protocol in multiple protocol stacks (e.g., PDU layer, SDAP, PDCP, RLC), and information related to settings within each protocol (e.g., PDCP setting information). The UE can use this information to generate protocol stacks and perform settings within each protocol.

[0208] The NF of the NW can determine whether to perform an NW handover to maintain the agreement between the two parties. This notification from the NW to the UE may include information indicating whether to perform an NW handover to maintain the agreement between the two parties. The UE can use this information to perform an NW handover to maintain the agreement between the two parties, or it can choose not to perform the NW handover.

[0209] The NF of the NW can determine whether to perform an NW handover to maintain the agreement between the two parties. This notification from the NW to the UE can include information indicating whether to perform an NW handover to maintain the agreement between the two parties. The UE can use this information to perform an NW handover to maintain the agreement between the two parties, or it can choose not to perform the NW handover. This, for example, improves the flexibility of the communication system.

[0210] The UE can contain information related to the configuration of the protocol stacks of both parties. This information can be configured as a UE capability, for example. The UE can notify the NF of the NW, such as the AMF. For example, the AMF can notify the SMF. The NF of the NW, such as the AMF and / or the SMF, can use this information to instruct the UE to perform a measurement. The measurement instructing the UE to perform can be a RAN-related measurement, a QoS (Quality of Service) monitoring (see Non-Patent Literature 10, 31), or a QoE (Quality of Experience) measurement (see Non-Patent Literature 2).

[0211] As an example of this information, the following (1) to (6) are disclosed.

[0212] (1) Information related to whether the UE can support the protocol stacks of both parties.

[0213] (2) Indicates which protocol stack the UE can have at the same time.

[0214] (3) Information related to the frequency bands that the UE can support.

[0215] (4) The amount of buffer that the UE can support for both protocol stacks.

[0216] (5) Information related to the switching destination NW and / or the switching source NW.

[0217] (6) The combination of (1) to (5) above.

[0218] Based on (1) above, for example, NW can quickly determine whether the relevant settings of the protocol stacks of both parties are feasible.

[0219] The above (2) could be, for example, a PDU layer, SDAP, PDCP, or RLC. Thus, for example, NW can quickly execute the relevant settings of both parties' protocol stacks.

[0220] Based on (3) above, for example, the NF that determines the NW switching destination can quickly decide the switching destination NW.

[0221] The above (4) can be, for example, the sum of the buffer amounts in both NWs, or the buffer amounts in the source NW and / or destination NW. The above (4) can be the buffer amount of the PDU layer, the buffer amount of SDAP, the buffer amount of PDCP, the buffer amount of RLC, the buffer amount of MAC, the buffer amount of HARQ, or a combination of multiple of the above. Thus, for example, judging the NF of NW handover can quickly determine the destination NW.

[0222] The above (5) could be, for example, information related to the settings of both parties' protocol stacks, indicating whether it pertains to information about the source NW or the destination NW. Thus, for example, the NF that determines the NW switch can quickly decide on the destination NW.

[0223] The NW can broadcast information related to the configuration of the protocol stack within the NW to the UE. This information may include, for example, the same information as described in (1) to (6) above. For example, this information may include the information obtained by replacing the UE with the NW described in (1) to (6) above. The UE can use this information to determine which NW to camp on. Thus, for example, the UE can connect to a more reliable NW.

[0224] The UE can establish a protocol stack with both NWs based on an NW handover indication from the NF of the NW. The UE can then respond to the NW in response to the handover indication, triggered by this protocol stack establishment. This response from the UE can be sent to the NF of the anchor NW, the NF of the handover destination NW, or the NF of the handover source NW. These NFs can be either SMFs or AMFs. The NF of the NW receiving this response can notify the NF of the handover destination NW of information related to the response from the UE. This notification can be sent via the SMF. The handover destination NW can then trigger this notification to begin receiving uplink data from the UE or to begin sending downlink data to the UE.

[0225] The handover source NW can send packets to the UE with an appended end marker. This end marker can be appended by the anchor UPF or by an intermediate UPF of the handover source NW (a UPF that is not the anchor UPF).

[0226] The UE can release the protocol stack with the handover source NW. This release can be triggered, for example, by receiving an end-of-time (OOT) packet, or by any packets received up to the end-of-time (OOT) packet. The UE can notify the NW's NF (Network Function) of this release. This notification from the UE can be made to the NF of the anchor NW, the NF of the handover destination NW, or the NF of the handover source NW. These NFs can be either SMFs (Self-Signaling Frames) or AMFs (Self-Signaling Frames). The NW's NF receiving this notification can notify the handover source NW's NF of the notification from the UE. The handover source NW can then release the protocol stack with the UE, triggered by this notification.

[0227] This notification can be sent as a response to an NW handover indication. For example, the UE can respond to an NW handover indication multiple times.

[0228] The UE can switch the destination of uplink data transmission from the handover source NW to the handover destination NW. This handover can be triggered by receiving a PDU session establishment request, receiving a PDU session change request, sending a signaling confirming the PDU session establishment request, sending a signaling confirming the PDU session change request, or establishing a protocol stack between the UE and both NWs.

[0229] Figure 16 and Figure 17 This is a sequence diagram illustrating an example of NW switching actions that maintain the agreement between the two NWs. Figure 16 The first half of the sequence is shown. Figure 17 This shows the latter half of the sequence. In Figure 16 and Figure 17 In the example shown, the UE's connection destination switches from NW1091, which is a non-anchor point NW, to NW1090, which is an anchor point NW. Figure 16 and Figure 17 The example shown illustrates an instance where the anchor SMF detects QoS degradation in NW1091, which is a non-anchor NW, and the anchor SMF makes an NW handover decision. Figure 16 and Figure 17 In the example shown, base station #1, AMF#1, UPF#1, SMF#1, PCF#1, UDM#1 and anchor point UPF belong to NW1090, while base station #2, AMF#2, UPF#2, SMF#2, PCF#2 and UDM#2 belong to NW1091.

[0230] exist Figure 16 In steps ST1196 to ST1199, data transmission and reception between the UE and DN via NW1091 are performed. Step ST1196 represents data transmission and reception between the UE and base station #2, step ST1197 represents data transmission and reception between base station #2 and UPF #2, step ST1198 represents data transmission and reception between UPF #2 and anchor point UPF, and step ST1199 represents data transmission and reception between anchor point UPF and DN.

[0231] exist Figure 16 In step ST1203 shown, SMF#1 detects QoS degradation. Figure 16 In the example shown, SMF#1 detects a QoS degradation associated with UPF#2. SMF#1 can detect this QoS degradation using both the QoS monitoring report from the anchor UPF and the QoS monitoring report from UPF#2.

[0232] exist Figure 16 In step ST1206 shown, SMF#1 decides to switch the NW as the data path. Figure 16 In the example shown, SMF#1 decides to switch the data path via UPF#2 to NW1090.

[0233] exist Figure 16 In step ST1206 shown, SMF#1 can choose whether to perform a NW handover to maintain the agreement between the two parties. Figure 16 In the example shown, SMF#1 decides that the UE will perform NW handover while maintaining the protocol stacks of both NW1090 and NW1091.

[0234] exist Figure 16In step ST1210, SMF#1 instructs SMF#2 to switch to the new device (NW). This instruction can use either PDU session release request signaling or PDU session change request signaling. The instruction can include information about the UE, information about the PDU session, information about QoS flows, information about QoS degradation, information about UPFs related to QoS degradation, the NW handover request, and information related to the NW after the path switch.

[0235] The instruction in step ST1210 may include information indicating the agreement to maintain the NW between the two parties, or information related to the maintained agreement. This information related to the maintained agreement may be below the PDU layer, below SDAP, below PDCP, or below RLC.

[0236] exist Figure 16 In process 1100 shown, the connection establishment process with the UPF in NW1090 is performed. Process 1100 will be described below. Figure 18 It means Figure 16 The sequence diagram of the process 1100 is an example.

[0237] exist Figure 18 In step ST1101 shown, SMF#1 selects UPF. In Figure 18 In the example shown, SMF#1 selects UPF#1 and decides to use UPF#1.

[0238] exist Figure 18 Step ST1102, as shown, involves establishing a session management policy association between SMF#1 and PCF#1. This process can be, for example, the process disclosed in section 4.16.4 of Non-Patent Document 31 (3GPP TS23.502). Step ST1102 can also include a process for changing the session management policy association. This process can be, for example, the process disclosed in section 4.16.5 of Non-Patent Document 31 (3GPP TS23.502).

[0239] exist Figure 18 In step ST1104, SMF#1 requests N4 session establishment from the anchor UPF. The anchor UPF initiates N4 session establishment based on step ST1104. In step ST1104, a change to the N4 session can also be requested. The anchor UPF can initiate or change the N4 session based on step ST1104. In step ST1105, the anchor UPF responds to SMF#1 in response to step ST1104.

[0240] exist Figure 18 In step ST1107, SMF#1 requests N4 session establishment from UPF#1. UPF#1 initiates N4 session establishment based on step ST1107. In step ST1108, UPF#1 responds to SMF#1 in response to step ST1107. Requests and responses regarding changes to the N4 session can also be made in steps ST1107 and ST1108.

[0241] return Figure 16 The explanation. In Figure 16 In procedure 1111 shown, a PDU session is established in NW1090. A PDU session change in NW1090 can also be performed. Procedure 1111 is described below. Figure 19 It means Figure 16 The sequence diagram of an example of process 1111.

[0242] exist Figure 19 In steps ST1113 and ST1114, the information required for establishing a PDU session for the UE is transmitted and received between SMF#1 and AMF#1. Information required for PDU session changes can also be transmitted and received. In step ST1113, an indication for establishing a PDU session from SMF#1 to AMF#1 can be given, or an indication for PDU session changes can be given. This indication can include the aforementioned information. This information can include information about the UE, information about the PDU session, information about QoS flows, and information about UPF. This information can also include information indicating the UE's maintenance of the NW protocol between the two parties.

[0243] exist Figure 19 In step ST1116, AMF#1 notifies base station #1 of a PDU session establishment request for the UE. A PDU session change request may also be notified. This notification may include information indicating that the UE maintains the agreement between the two NWs. In step ST1117, base station #1 notifies the UE of the PDU session establishment request. A PDU session change request may also be notified. RRC signaling, such as RRC establishment signaling or RRC resetting signaling, may be used in step ST1117. The notification in step ST1117 may include information indicating that the UE maintains the agreement between the two NWs. The UE can use the notification content in step ST1117 to process PDU session establishment, PDU session change, and maintain the agreement with NW1091.

[0244] exist Figure 19In step ST1118, the UE responds to base station #1 in response to step ST1117. This response may use RRC signaling, such as RRC establishment completion signaling or RRC reconfiguration completion signaling. In step ST1119, base station #1 responds to AMF #1 in response to step ST1116. This response in step ST1119 may contain N2 session management information.

[0245] exist Figure 19 In step ST1121, AMF#1 notifies SMF#1 of the N2 session management information from base station #1. This notification can be made, for example, using the signaling Nsmf_PDUSession_UpdateSMContext Request (refer to Non-Patent Document 31). In step ST1122, SMF#1 responds to AMF#1 in response to step ST1121. This response can also use, for example, the signaling Nsmf_PDUSession_UpdateSMContext Response (refer to Non-Patent Document 31).

[0246] exist Figure 19 In step ST1124, SMF#1 requests an N4 session change from the anchor UPF. This request may include, for example, QoS monitoring settings. The anchor UPF can use these settings to begin QoS monitoring. In step ST1125, the anchor UPF responds to SMF#1 in response to step ST1124.

[0247] exist Figure 19 In step ST1128, SMF#1 requests an N4 session change from UPF#1. This request may include, for example, QoS monitoring settings. UPF#1 can use these settings to start QoS monitoring. In step ST1129, UPF#1 responds to SMF#1 in response to step ST1128.

[0248] return Figure 16 The explanation. In Figure 16 In procedure 1120, the PDU session in NW1091 is released. Alternatively, the PDU session in NW1091 can be modified. Procedure 1120 is described below. Figure 20 It means Figure 16 The sequence diagram of the example process 1120.

[0249] exist Figure 20In step ST1156, SMF#2 requests N4 session release from UPF#2. This information may include information indicating that the UE maintains the agreement between the two parties. Alternatively, an announcement of N4 session release may be made. UPF#2 initiates N4 session release triggered by step ST1156. Preparation for N4 session release may also be initiated. In step ST1157, UPF#2 responds to SMF#2's response to step ST1156.

[0250] exist Figure 20 In steps ST1163 and ST1164, the information required for the release of the UE's PDU session is transmitted and received between SMF#2 and AMF#2. Information required for PDU session changes can also be transmitted and received. In step ST1163, an indication for the release of the PDU session from SMF#2 to AMF#2 can be given, or an indication for a PDU session change can be given. This indication can include the aforementioned information. This information can include information about the UE, information about the PDU session, information about QoS flows, and information about the UPF. This information can also include information indicating the protocol for the UE to maintain NW between the two parties.

[0251] exist Figure 20 In step ST1166, AMF#2 notifies base station #2 of the PDU session release request for the UE. It can also notify of a PDU session change request. This notification may contain information indicating that the UE maintains the agreement between the two NWs. In step ST1167, base station #2 notifies the UE of the PDU session release request. It can also notify of a PDU session change request. RRC signaling, such as RRC release signaling, or RRC reconfiguration signaling can be used in step ST1167. The notification in step ST1167 may contain information indicating that the UE maintains the agreement between the two NWs. The UE can use the notification content in step ST1167 to process PDU session release, PDU session change, or maintain the agreement with NW1091.

[0252] exist Figure 20 In step ST1168, the UE responds to base station #2 in response to step ST1167. This response may use RRC signaling, such as RRC reconfiguration completion signaling. In step ST1169, base station #2 responds to AMF #2 in response to step ST1166. This response in step ST1169 may contain N2 session management information.

[0253] exist Figure 20In step ST1172, AMF#2 notifies SMF#2 of the N2 session management information from base station #2. This notification can be made, for example, using the signaling Nsmf_PDUSession_UpdateSMContext Request (refer to Non-Patent Document 31). In step ST1174, SMF#2 responds to AMF#2 in response to step ST1172. This response can use, for example, the signaling Nsmf_PDUSession_UpdateSMContext Response (refer to Non-Patent Document 31).

[0254] exist Figure 19 In step ST1178, SMF#2 requests an N4 session change from UPF#2. This request may include, for example, QoS monitoring settings. In step ST1179, UPF#2 responds to SMF#2 in response to step ST1178.

[0255] return Figure 16 The following is an explanation. In step ST1225, SMF#2 notifies SMF#1 of its response to the NW handover indication. This notification can use signaling for a PDU session release request response or signaling for a PDU session change response. SMF#1, triggered by this signaling, acknowledges that the NW handover configuration in SMF#2 has been performed.

[0256] exist Figure 16 In step ST1227, the UE notifies base station #1 of a positive response to the PDU session establishment request. A positive response to a PDU session change request can also be notified. This notification can be triggered by the completion of PDU session establishment and / or change.

[0257] exist Figure 16 In process 1130 shown, the follow-up processing of PDU session establishment in NW1090 is performed. Follow-up processing of PDU session changes in NW1090 can also be performed. Process 1130 is described below. Figure 21 It means Figure 16 The sequence diagram of the example process 1130.

[0258] exist Figure 21 In step ST1132, base station #1 notifies AMF #1 of information related to the positive response in step ST1227. This notification in step ST1132 may include N2 session management information.

[0259] exist Figure 21 In steps ST1133 and ST1134 shown, the following steps are performed: Figure 19 The steps ST1121 and ST1122 shown are the same.

[0260] exist Figure 21 In steps ST1136 and ST1137 shown, the following steps are performed: Figure 19 The steps ST1124 and ST1125 shown are the same.

[0261] exist Figure 21 In steps ST1138 and ST1139 shown, the following steps are performed: Figure 19 The steps ST1128 and ST1129 shown are the same.

[0262] exist Figure 21 The step ST1140 shown is a process for changing the session management policy association between SMF#1 and PCF#1. This process can be, for example, the process disclosed in section 4.16.5 of non-patent document 31 (3GPP TS23.502).

[0263] Figure 17 Steps ST1230 to ST1233 show the transmission of uplink data from the UE via UPF#1. Step ST1230 shows the transmission of uplink data from the UE to base station #1, step ST1231 shows the transmission of uplink data from base station #1 to UPF#1, step ST1232 shows the transmission of uplink data from UPF#1 to the anchor UPF, and step ST1233 shows the transmission of uplink data from the anchor UPF to the DN.

[0264] exist Figure 17 In step ST1240, SMF#1 indicates to the anchor UPF that an end marker is added. This indication can, for example, use the signaling of an N4 session change request. For example, the request may include an indication to add an end marker. Step ST1240 can be triggered, for example, by the receipt of step ST1225, or by the completion of process 1130. In step ST1242, the anchor UPF notifies SMF#1 of its response to this indication. This notification can, for example, use the signaling of an N4 session change response.

[0265] Figure 17Steps ST1245–ST1248 illustrate the transmission of downlink data from the DN to the UE via UPF#2. Step ST1245 represents the transmission of downlink data from the DN to the anchor UPF, step ST1246 represents the transmission of downlink data from the anchor UPF to UPF#2, step ST1247 represents the transmission of downlink data from UPF#2 to base station #2, and step ST1248 represents the transmission of downlink data from base station #2 to the UE. In step ST1246, the anchor UPF may append an end marker to the downlink data from the DN and transmit it to UPF#2. The anchor UPF may forward downlink data received from the DN after the appended end marker packet to UPF#1. This action of the anchor UPF may be triggered by the transmission in step ST1242.

[0266] exist Figure 17 In step ST1251, the UE can notify base station #2 that it has received a packet with an end marker. This notification can indicate that all packets up to the end-marked packet have been received normally. The notification may also include information related to the release of the protocol stack. The UE can trigger the notification in step ST1251 by receiving data in step ST1248.

[0267] exist Figure 17 In procedure 1255, the PDU session in NW1091 is released. Alternatively, the PDU session in NW1091 can be modified. Procedure 1255 is explained below. Figure 22 It means Figure 17 The sequence diagram of the example process 1255.

[0268] exist Figure 22 In step ST1142, base station #2 notifies AMF #2 of information related to the UE having received a packet with an end marker. This notification in step ST1142 may include N2 session management information.

[0269] exist Figure 22 In steps ST1143 and ST1144 shown, the following steps are performed: Figure 19 The steps ST1121 and ST1122 are the same.

[0270] Figure 22 In steps ST1145 and ST1146, AMF#2 notifies SMF#2 of session management information, and SMF#2 responds to this notification from AMF#2 to AMF#2. This notification may include information related to the release of the PDU session.

[0271] exist Figure 22In step ST1148, SMF#2 requests N4 session release from UPF#2. UPF#2 initiates N4 session release triggered by step ST1148. In step ST1149, UPF#2 responds to SMF#2's response to step ST1148.

[0272] exist Figure 22 In step ST1150 shown, the process of ending the session management policy association between SMF#2 and PCF#2 is performed. This process can be, for example, the process disclosed in section 4.16.6 of non-patent document 31 (3GPP TS23.502).

[0273] return Figure 17 The following is an explanation. In step ST1260, base station #2 notifies SMF #1 of the completion of PDU session release.

[0274] exist Figure 17 In step ST1262, SMF#1 requests the anchor UPF to release the connection with UPF#2. This request can be made using the N4 Session Change Request signaling. The anchor UPF, triggered by this signaling, releases the connection with UPF#2. In step ST1264, the anchor UPF responds to SMF#1 in response to step ST1262.

[0275] exist Figure 17 In steps ST1266 to ST1269, data transmission and reception between the UE and DN via NW1090 are performed. Step ST1266 represents data transmission and reception between the UE and base station #1, step ST1267 represents data transmission and reception between base station #1 and UPF #1, step ST1268 represents data transmission and reception between UPF #1 and anchor UPF, and step ST1269 represents data transmission and reception between anchor UPF and DN.

[0276] The period associated with the release of the switching source NW can be set. For example, a timer associated with the release can be set. This timer can be set at the UE, for example. For example, the timer can be set with a PDU session release request (e.g. Figure 20 The step ST1167 shown can be triggered to start, or it can be triggered to stop upon receiving a packet with an end marker. For example, the UE can trigger the release of the handover source NW upon the expiration of this timer. Thus, for example, even if a packet with an end marker is not received, the NW can be released, thereby preventing malfunctions in the communication system.

[0277] The UE can perform NW handover while having protocol stacks between itself and multiple NWs. The UE can request a handover of the connection destination from an NW. This request can be made to the AMF. The AMF can forward the request to the SMF. The NW can be an anchor NW or a non-anchor NW, and can be a handover source NW or a handover destination NW. The NW handover processing on the NW side can adopt the same method as disclosed above.

[0278] The NW handover disclosed in Implementation 1 can be used for handover to a new NW. The UE can register with the new NW, and a PDU session can be established in the new NW. The registration can, for example, be performed using the method disclosed in section 4.2.2.2.2 of Non-Patent Document 31. The establishment of the PDU session can, for example, be performed using the method disclosed in section 4.3.2.2.1 of Non-Patent Document 31. Therefore, for example, flexibility in the communication system can be improved.

[0279] According to this embodiment 1, packet loss caused by NW handover can be prevented.

[0280] Implementation method 2.

[0281] Traffic can be split. For example, some packets of the same data traffic can pass through one NW, while the rest can pass through other NWs. When splitting traffic, a single PDU session can be split, or multiple PDU sessions can be established.

[0282] When configuring traffic splitting, the method disclosed in Implementation Method 1 can be appropriately applied. The same PDU session can be established and / or modified for multiple NWs. For example, the above method can be used when a PDU session is split.

[0283] As another example, information that links multiple PDU sessions together can be communicated. This information can be included in the signaling for PDU session establishment and / or PDU session changes. For example, this approach can be used in a traffic splitting configuration that utilizes multiple PDU sessions.

[0284] During uplink transmission from the UE, the buffer size of the PDCP layer and RLC layer can be used to determine which NW's base station to send data to. For example, if the buffer size is above a specified threshold, the UE can send data to either the primary RLC or the secondary RLC. If the buffer size is below the specified threshold, the UE can send data to the primary RLC.

[0285] The primary RLC can be, for example, the RLC layer corresponding to the RLC layer of the anchor base station (the base station of the anchor NW). As another example, the primary RLC layer corresponding to the RLC layer in which the base station of the NW is located can be determined separately. For example, this determination can be made by the NF of the anchor NW. This NF can be an SMF, an AMF, or a base station.

[0286] The above traffic splitting leads to the following problem: Even for the same traffic, the destination base station will differ depending on the packet, resulting in discontinuous SNs of the PDCP PDUs received by each base station. Consequently, the PDCP layer of each base station cannot complete reordering, leading to the inability to forward received data from the UE to the upper layer.

[0287] This embodiment discloses a method for solving the above-mentioned problems.

[0288] In this embodiment, the UE can notify the base station of information related to the PDCP SN of the transmitted PDCP PDU. This base station can be the handover source base station, the handover destination base station, or both of the above. This notification can, for example, be delivered as a PDCP status PDU. As other examples, this notification can be delivered using RRC signaling, as an RLC status PDU, as MAC signaling, or as L1 / L2 signaling.

[0289] As another example, the base station of one of the network worlds (NWs) to which the UE is connected can notify the base station of the other NW of information related to the PDCP SN received from the UE. This notification may include information related to the NW to which the base station belongs, information related to the base station's identifier, and information related to the base station's PDCP entity. Thus, for example, the target base station can quickly identify the base station from which the notification originated. This notification can be made, for example, via an inter-base station interface, via an AMF (Advanced Management Function), or via an SMF (Self-Managing Function). Thus, for example, the processing load in the UE can be reduced.

[0290] The notification may include information related to other NWs, information related to the identifiers of the base stations in other NWs, and information related to the PDCP entities of the base stations in other NWs. Thus, for example, other NW base stations can quickly determine that the notification is addressed to this base station.

[0291] The notification may include information related to the PDU session or information related to QoS flows. Thus, for example, the target base station can quickly grasp the traffic.

[0292] As another example, the notification can be made between base stations. For instance, it can be made via the AMF, the SMF, the SEPP, or a combination thereof. The notification can also be made directly between base stations. For example, a base station can query the DNS (Domain Name System) for information related to the base station of the target destination. The DNS can then notify the base station of this information. This, for example, can reduce the processing load in the UE.

[0293] Other solutions are disclosed. The application layer can route the NW to the destination. This, for example, improves routing flexibility.

[0294] The protocol stack can be configured to be split below the PDU layer. A UE can have multiple PDU layers. For example, a UE can have multiple IP addresses and multiple MAC addresses. The protocol stack can, for example, have... Figure 12 It has the same structure as the publicly available protocol stack.

[0295] Other solutions are disclosed. The UE's PDU layer can route the NW to the destination.

[0296] The protocol stack can be configured to be split below the SDAP layer. A UE can have multiple SDAP layers. This protocol stack can, for example, have... Figure 13 The protocol stack has the same structure as the publicly available protocol stack. Therefore, for example, the UE does not need to hold multiple IP addresses, resulting in reduced UE complexity compared to the above scenario.

[0297] The UE's PDU layer can, for example, perform routing based on the buffer size stored in its PDU layer. For instance, if the buffer size exceeds or exceeds a specified threshold, the UE can send data to either of the two NWs; if the buffer size is below or less than the specified threshold, the UE can send data to one of the NWs. Hereinafter, the NW that serves as the destination for uplink data transmission in the above scenario is sometimes referred to as the primary NW. As another example, if the buffer size exceeds or exceeds a specified threshold, the UE can send data to one of the NWs; if the buffer size is below or less than the specified threshold, the UE can send data to the other NW.

[0298] One of the aforementioned NWs can be either an anchor NW or a non-anchor NW. This, for example, improves flexibility in communication.

[0299] This cache size can include the cache size of lower layers. For example, it can include the cache size of the SDAP layer, the cache size of the PDCP layer, the cache size of the RLC layer, the cache size below the MAC layer, the cache size of the PHY layer, or multiple cache sizes mentioned above. Thus, for example, it is possible to perform routing that takes into account the overall cache size of the UE.

[0300] The above routing can use either the buffer size per PDU session or the buffer size per QoS flow. This allows for flexible routing, for example, on a per-traffic basis.

[0301] The UE's lower-level layer can notify the PDU layer of the buffer size at that lower-level layer. This lower-level layer can be SDAP, PDCP, RLC, or MAC. The buffer size can be the buffer size for each PDU session or the buffer size for each QoS flow. Thus, for example, the PDU layer can quickly ascertain the buffer size at the lower-level layer.

[0302] As another example, routing can employ QoS. For instance, a UE can send data to a network with good QoS. Thus, for example, QoS of uplink communication can be ensured.

[0303] The UE can perform QoS monitoring. The UE can use the results of the QoS monitoring for this routing. The QoS monitored by the UE may include, for example, information related to uplink and / or downlink packet delay, information related to congestion, data rate, packet delay dispersion, information related to round-trip packet delay, and information related to uplink delay in the UE (e.g., the difference between the time when uplink data should have been sent and the time when it was actually sent).

[0304] Routing using QoS can also employ thresholds. For example, if the QoS of one NW is better than or equal to a predetermined threshold, that NW can continue to be used; if the QoS of that NW is worse than or equal to the predetermined threshold, data can be sent to other NWs. One of these NWs can be either an anchor NW or a non-anchor NW. This ensures QoS during uplink transmission. The threshold can also have hysteresis. This, for example, can prevent frequent switching of the destination NW for uplink data transmission.

[0305] Routing using QoS flows can be performed on a per-QoS-flow basis. For example, a QoS flow requiring latency can pass through a lower-latency NW, while a QoS flow requiring reliability can pass through a higher-reliability NW. Thus, for example, the QoS of each QoS flow can be guaranteed.

[0306] The aforementioned threshold can be determined by the PCF. For example, it can be determined by the PCF of the anchor NW (hereinafter sometimes referred to as the anchor PCF). The anchor PCF can notify the anchor SMF of this threshold. The anchor SMF can then notify the UE of this threshold. This notification from the anchor SMF can be made via the anchor AMF or via the anchor base station.

[0307] As another example, the threshold mentioned above can be determined by the SMF. For instance, it can be determined by the anchor SMF. The anchor SMF can determine the threshold using a policy notified from the anchor PCF. The anchor SMF can then notify the UE of the threshold. This notification from the anchor SMF to the UE can be performed in the same manner as described above.

[0308] As another example, the threshold mentioned above can be determined by the AMF, such as the anchor AMF, or by the base station, such as the anchor base station. The AMF and / or base station can then notify the UE of this threshold.

[0309] As another example, the aforementioned threshold can be determined by the NWDAF (Network Data Analytics Function). Thus, for example, the threshold can be flexibly determined based on the state of the NW. The NWDAF can then notify the UE of this threshold. This notification can be made via the AMF, via the base station, or directly to the UE.

[0310] The method for determining which NW is one of the NWs described above can also be the same as the threshold method described above.

[0311] Other solutions are disclosed. The UE's SDAP layer can route to the NW of the transmission destination.

[0312] The protocol stack can be configured to be split below the PDCP layer. A UE can have multiple PDCP layers. This protocol stack can, for example, have... Figure 14 The protocol stack has the same structure as the one disclosed in the protocol stack. Thus, for example, the UE can reduce its complexity by having a PDCP layer corresponding to the base station of each NW, and can reduce the processing load of the UE by setting the SDAP layer to 1.

[0313] The UE's SDAP layer can, for example, perform routing based on the cache size stored in this SDAP layer. For instance, if the cache size exceeds or is above a specified threshold, the UE can send data to either of the two NWs; if the cache size is below or less than the specified threshold, the UE can send data to one of the NWs. As another example, if the cache size exceeds or is above a specified threshold, the UE can send data to one of the NWs; if the cache size is below or less than the specified threshold, the UE can send data to the other NW.

[0314] One of the aforementioned NWs can be either an anchor NW or a non-anchor NW. This, for example, improves flexibility in communication.

[0315] This cache size can include the cache size of lower layers. For example, it can include the cache size of the PDCP layer, the cache size of the RLC layer, the cache size below the MAC layer, the cache size of the PHY layer, or multiple cache sizes mentioned above. Thus, for example, it is possible to perform routing that takes into account the overall cache size of the UE.

[0316] The above routing can use either the buffer size per PDU session or the buffer size per QoS flow. This allows for flexible routing, for example, on a per-traffic basis.

[0317] The UE's lower-level layer can notify the SDAP layer of the buffer size at that lower-level layer. This lower-level layer can be the PDCP layer, the RLC layer, or the MAC layer. The buffer size can be the buffer size for each PDU session or the buffer size for each QoS flow. Thus, for example, the SDAP layer can quickly ascertain the buffer size at the lower-level layer.

[0318] As another example, routes can employ QoS. Routes using QoS can, for example, use the same methods as those exposed in the routing at the PDU layer described above. Thresholds can also be the same. The method for determining which NW one of the NWs is can also be the same.

[0319] A primary NW or a secondary NW can be set. For example, when the buffer size disclosed in this embodiment is above a specified threshold, the UE can send data to either the primary NW or the secondary NW. When the buffer size is below the specified threshold, the UE can send data to the primary NW.

[0320] The primary NW can be, for example, an anchor NW. The secondary NW can be, for example, a non-anchor NW.

[0321] As another example, the primary NW can be determined and notified to the UE. This determination can be made by the anchor NW, for example. The anchor NW can notify the UE of information indicating which NW is the primary NW. This notification can, for example, be performed together with the notification of the aforementioned threshold.

[0322] Regardless of the buffer size, the UE can send data to any NW. For example, by setting the aforementioned threshold to 0 or a negative value, the UE can send data to any NW. This, for example, improves the flexibility of the communication system.

[0323] According to this embodiment 2, once the reordering is completed in the base station, the received data from the UE can be quickly forwarded to the upper layer.

[0324] Variation 1 of Implementation Method 2.

[0325] The routing of uplink data in the UE can be triggered by an indication from the NW. This indication can be triggered, for example, by a failure and / or congestion of one of the NWs, or by a failure and / or congestion of the other NW.

[0326] This indication from the NW can be triggered by QoS meeting specified conditions. QoS monitoring can be performed in the NW. The specified conditions can be that the QoS monitoring result is better than, worse than, and / or equal to the specified threshold.

[0327] QoS monitoring can be performed at the UPF or at the base station. The QoS monitored by the UPF and / or base station may include, for example, information related to uplink and / or downlink packet delay, information related to congestion, data rate, packet delay dispersion, and information related to round-trip packet delay.

[0328] The threshold related to QoS monitoring can be determined, for example, at the application layer or by the PCF of one of the NWs. This NW can be, for example, an anchor NW, a non-anchor NW, or the NW to which the NF performing the QoS monitoring belongs.

[0329] This routing-related indication can be made by the NF of one of the NWs. This NW can be, for example, an anchor NW, a non-anchor NW, an NW that has detected a fault and / or congestion, or an NW that has not detected a fault and / or congestion.

[0330] The NF can be, for example, an SMF. The SMF can send the indication to the UE. This indication from the SMF to the UE can be done via the AMF or via the base station. As another example, the SMF can give the indication to the base station. This indication from the SMF to the base station can be done via the AMF.

[0331] The base station can notify the UE of routing-related information. This notification may, for example, use RRC signaling. Thus, for example, more information can be notified from the base station to the UE. As another example, the notification may use MAC signaling. Thus, for example, the base station can quickly notify the UE of this information. As another example, L1 / L2 signaling may be used in the notification. Thus, for example, the base station can further quickly notify the UE of this information. The UE can use this information to switch to its primary network router (NW).

[0332] As another example related to this NF, the NF could be an AMF. The AMF can give this instruction to the UE. This instruction from the AMF to the UE can be given via the base station. As another example, the SMF can give this instruction to the base station. Notification of routing-related information from the base station to the UE can be done in the same way as described above. The UE can use this information to switch the primary NW.

[0333] The instruction may include information related to the handover of the primary NW, or it may include threshold-related information disclosed in Implementation 2. The information related to the handover of the primary NW may, for example, include information indicating the handover of the primary NW. This, for example, can reduce the signaling size. As another example, the information may include information related to the NW after the handover. This, for example, allows the UE to quickly grasp the information about the NW after the handover.

[0334] This information may include traffic-related information associated with the handover of the primary NW. For example, it may include information related to PDU sessions or QoS flows.

[0335] According to this variation 1, rapid path switching can be achieved during NW splitting of traffic, resulting in rapid communication between the UE and DN.

[0336] Variation 2 of Implementation Method 2.

[0337] Routing can be performed on the C-side data.

[0338] This routing can, for example, use the method disclosed in Embodiment 2, or the method disclosed in Variation 1 of Embodiment 2. For example, in this routing, the cache size of the NAS layer can be used instead of the cache size of the PDU layer disclosed in Embodiment 2, or the cache size of the RRC layer can be used instead of the cache size of the SDAP layer.

[0339] Similar to implementation method 2, the cache size of the lower-level layer can also be used. For example, the RRC layer can notify the NAS layer of the cache size of the lower-level layer. This notification can be made by the PDCP layer, the RLC layer, the MAC layer, or the PHY layer. As another example, the PDCP layer can notify the RLC layer of the cache size of the lower-level layer. This notification can be made by the MAC layer or the PHY layer.

[0340] U-plane and C-plane data can use the same or different thresholds. Between U-plane and C-plane data, the destination NW for routes below or less than the threshold can be the same or different. Between U-plane and C-plane data, the primary NW can be the same or different.

[0341] The NF of the destination NW can forward C-plane data sent from the UE to the NFs of other NWs. This NF can be, for example, a base station, an AMF, an SMF, or an NWDAF.

[0342] According to this variation 2, even if one of the NWs fails or becomes congested, C-plane data can still be sent to that NW.

[0343] Implementation method 3.

[0344] The NW used as the data path can be switched. For example, when data is transmitted and received via a source NW, the data transmission path can be switched to a destination NW triggered by a failure and / or congestion in the source NW's NF (e.g., UPF). The source NW can be an anchor NW or a non-anchor NW. The destination NW can be a non-anchor NW or an anchor NW.

[0345] Traffic splitting (sometimes referred to as NW splitting) is possible. For example, some packets of the same data traffic can pass through one NW, while the remaining packets can pass through other NWs. Traffic splitting can be performed on a single PDU session or by establishing multiple PDU sessions.

[0346] However, during the NW switch, there is a problem that it takes time for the switch to be completed.

[0347] Furthermore, in NW splitting, resources related to the traffic need to be secured in the NF (e.g., UPF) of both the anchor NW and the non-anchor NW. This can lead to a waste of resources secured in NWs where no data passes through.

[0348] In this third embodiment, a method for solving the above-mentioned problems is disclosed.

[0349] In this embodiment, during NW handover, handover settings (hereinafter sometimes referred to as pre-settings) are pre-configured for each NF of the NW that serves as the handover destination. When the actual NW handover is performed, the handover settings are configured for the UE. NW handover settings for the base station can also be performed during the actual NW handover configuration. The actual NW handover can also be triggered by meeting specified conditions.

[0350] The specified conditions can be, for example, QoS-related conditions or QoE-related conditions. As an example of a specified condition, it could be that the QoS (e.g., latency) of a certain traffic is worse than a predetermined threshold. The specified conditions can be detected using QoS monitoring reports (see Non-Patent Documents 10, 31) or the results of QoE measurements (see Non-Patent Document 2).

[0351] For example, the NF of the anchor NW can initiate the switch of the NW that serves as the data path. This NF can be, for example, an SMF. The switch of the NW can be, for example, a switch from a non-anchor NW to an anchor NW.

[0352] The anchor SMF can notify the non-anchor NW of NW handover information. This notification can be made, for example, to the non-anchor SMF. The notification can be made, for example, as a request for PDU session modification or a request for PDU session release. The notification can use, for example, signaling such as Nsmf_PDUSession_Modification_Request (see Non-Patent Document 31) or Nsmf_PDUSession_Release_Request (see Non-Patent Document 31). The notification can include, for example, information indicating a pre-configured NW handover, information related to the UE, information related to the PDU session, and information related to QoS flows. The non-anchor NW can maintain its connection with the UE in its NW triggered by the information in the notification indicating a pre-configured NW handover.

[0353] A non-anchor SMF can request information related to pre-configurations for NW handover from a non-anchor AMF. This request may include a request for NAS signaling information for the UE. This NAS signaling may, for example, be NAS configuration information related to PDU session changes (e.g., NAS configurations to be released). A non-anchor AMF can notify a non-anchor SMF of this NAS signaling information. This notification from a non-anchor AMF to a non-anchor SMF can be triggered by this request from the non-anchor SMF to the non-anchor AMF.

[0354] The NAS signaling may contain information related to RRC signaling for the UE. This RRC signaling may, for example, be RRC setting information related to PDU session changes (e.g., AS settings to be released). A non-anchor AMF may request RRC signaling information from a non-anchor NW base station (hereinafter sometimes referred to as a non-anchor base station). The non-anchor base station may notify the non-anchor AMF of the RRC signaling information. This notification from the non-anchor base station to the non-anchor AMF may be triggered by this request from the non-anchor AMF to the non-anchor base station.

[0355] A non-anchor SMF can respond to an NW handover request to an anchor SMF. This response can be, for example, a response to a PDU session change request or a PDU session release request. The response can use, for example, signaling such as Nsmf_PDUSession_Modification_Response (see Non-Patent Document 31) or Nsmf_PDUSession_Release_Response (see Non-Patent Document 31). The response may contain, for example, information about NAS signaling. This NAS signaling can be, for example, the NAS signaling related to PDU session change described above. This NAS signaling can be, for example, NAS signaling obtained from a non-anchor AMF. This NAS signaling may contain RRC signaling. This RRC signaling can be, for example, the RRC signaling related to PDU session release described above. This RRC signaling can be, for example, RRC signaling obtained from a non-anchor base station.

[0356] The anchor point SMF can be preset in the anchor point NW. For example, a UPF setting can be performed. The UPF used for this setting can be, for example, an intermediate UPF of the anchor point NW or an anchor point UPF. In this UPF setting, for example, part or all of the processing disclosed in PDU session establishment (non-patent document 31 4.3.2) can be performed.

[0357] Anchor point SMFs can configure NW switching for anchor point UPFs. For example, an anchor point SMF can preset the release of the connection between an anchor point UPF and an intermediate UPF that is not an anchor point NW. The anchor point UPF can then use this setting as a trigger to prepare for the release of the connection with that intermediate UPF.

[0358] The anchor SMF can pre-configure PDU session changes for the anchor AMF. This pre-configuration may include NAS signaling information for the handover source NW (e.g., a non-anchor NW), or it may include RRC signaling information for the handover source NW (e.g., a non-anchor NW). The anchor AMF may request pre-RRC settings related to NW handover from the anchor base station, or it may choose not to make this request. The anchor AMF may notify the anchor base station of the RRC signaling information for the handover source NW (e.g., a non-anchor NW). This notification may, for example, be included in the aforementioned request.

[0359] Anchor point SMF can initiate NW switching by meeting the predetermined conditions.

[0360] An anchor point SMF can notify the anchor point AMF that the specified condition has been met. This notification from the anchor point SMF to the anchor point AMF can be triggered, for example, by the fulfillment of the specified condition, or by a response from a non-anchor point SMF to the anchor point SMF.

[0361] The anchor AMF can use this notification as a trigger to configure resources related to the UE. The anchor AMF can request the anchor base station to establish a PDU session related to the UE, or request to change the PDU session. This request may include NAS signaling and / or RRC signaling related to PDU session changes for non-anchor NWs, or NAS signaling related to pre-configured PDU session changes for anchor NWs. The anchor base station can use this request as a trigger to request the UE to establish a PDU session, or request to change the PDU session. This request can use RRC signaling. The RRC signaling may include NAS signaling and / or RRC signaling related to PDU session changes for non-anchor NWs, or NAS signaling and / or RRC signaling related to pre-configured PDU session changes for anchor NWs. The UE can use this RRC signaling as a trigger to establish a PDU session, or change the PDU session. The UE can send a response to the anchor base station for the PDU session establishment or change request. The anchor base station can notify the anchor AMF of this response from the UE.

[0362] The anchor AMF can notify the anchor SMF of this response from the UE.

[0363] Anchor SMFs can notify non-anchor SMFs that the specified conditions have been met. The non-anchor SMFs can then trigger an NW handover to the anchor NW based on this notification. For example, they can release the UPF on the non-anchor NW side. A non-anchor SMF can also request connection release from the UPF serving as the data transmission path. This request can, for example, use N4 session release signaling.

[0364] A non-anchor SMF can notify a non-anchor AMF that the specified condition has been met. The non-anchor AMF can then release resources associated with the UE based on this notification. The non-anchor AMF can also request the release of resources associated with the UE from a non-anchor base station. The non-anchor base station can then release resources associated with the UE based on this request.

[0365] A non-anchor SMF can notify an anchor SMF to release resources associated with the UE. This notification can, for example, be a response to a notification that a specified condition has been met.

[0366] A non-anchor AMF can notify a non-anchor SMF of the release of resources. This notification can be given as a response to a notification that the specified conditions have been met.

[0367] The method disclosed in this embodiment can also be applied to path switching from anchor point NW to non-anchor point NW. For example, the NF of anchor point NW can initiate the switching of NW as a data path. This NF can be, for example, an SMF.

[0368] Anchor SMFs can request NW handover presets from non-anchor SMFs. This request can be made, for example, as a PDU session change request or a PDU session establishment request. This notification can be made using, for example, the signaling `Nsmf_PDUSession_Modification_Request` (see Non-Patent Document 31) or the signaling `Nsmf_PDUSession_Establish_Request` (see Non-Patent Document 31). This notification can include, for example, information indicating the use of preset NW handover, information related to the UE, information related to the PDU session, and information related to QoS flows. The non-anchor NW can maintain its connection with the UE in its NW, triggered by the information in this notification indicating the use of preset NW handover.

[0369] The non-anchor SMF can perform presets in the non-anchor NW. For example, the non-anchor SMF can perform presets of the UPF. The UPF for which this preset is performed can be, for example, an intermediate UPF of the non-anchor NW. In the preset of this UPF, for example, part or all of the processing disclosed in PDU session establishment (not patent document 31 4.3.2) can be performed.

[0370] The non-anchor SMF can perform PDU session changes and / or establishment presets for the non-anchor AMF. The non-anchor SMF can request information related to NW handover presets from the non-anchor AMF. This request may include a request for NAS signaling information for the UE. This NAS signaling may, for example, be NAS setting information related to PDU session changes and / or establishment (e.g., NAS settings to be established). The non-anchor AMF can notify the non-anchor SMF of the NAS signaling information. This notification from the non-anchor AMF to the non-anchor SMF can be triggered by this request from the non-anchor SMF to the non-anchor AMF.

[0371] The NAS signaling may contain information related to RRC signaling for the UE. This RRC signaling may, for example, be RRC setting information related to PDU session changes and / or establishment (e.g., AS settings to be established). A non-anchor AMF may request RRC signaling information from a non-anchor base station. A non-anchor base station may notify a non-anchor AMF of the RRC signaling information. This notification from the non-anchor base station to the non-anchor AMF may be triggered by this request from the non-anchor AMF to the non-anchor base station.

[0372] The non-anchor SMF can respond to the pre-configured request to the anchor SMF. This response can be, for example, a response to a PDU session change request or a PDU session release request. The response can use, for example, the signaling of `Nsmf_PDUSession_Modification_Response` or `Nsmf_PDUSession_Release_Response`. The response may include, for example, information about NAS signaling. This NAS signaling can be, for example, the NAS signaling related to PDU session change and / or establishment mentioned above. This NAS signaling can be, for example, NAS signaling obtained from the non-anchor AMF. The NAS signaling may contain RRC signaling. This RRC signaling can be, for example, the RRC signaling related to PDU session change and / or establishment mentioned above. This RRC signaling can be, for example, RRC signaling obtained from the non-anchor base station.

[0373] The non-anchor SMF can pre-configure PDU session changes and / or PDU session establishment for the non-anchor AMF. This notification may include NAS signaling information for the UE's handover destination NW (e.g., a non-anchor NW), and may also include RRC signaling information for the handover destination NW (e.g., a non-anchor NW). The non-anchor AMF may request RRC pre-configuration related to NW handover from the non-anchor base station, or may not make this request. The non-anchor base station may notify the non-anchor AMF of the RRC signaling information for the handover destination NW (e.g., a non-anchor NW). This notification may, for example, be included in the aforementioned request.

[0374] An anchor SMF can initiate NW switching based on the fulfillment of a predetermined condition. An anchor SMF can also notify non-anchor SMFs that the specified condition has been met.

[0375] A non-anchor SMF can request a preset response from a non-anchor AMF. The non-anchor AMF can then respond to the preset response based on this request. A non-anchor AMF can also request a preset response from a non-anchor base station. The non-anchor base station can then respond to the preset response based on this request. The non-anchor base station can notify the non-anchor AMF of the completion of the preset response. The non-anchor AMF can also notify the non-anchor SMF of the completion of the preset response.

[0376] Non-anchor SMFs can notify anchor SMFs of the completion of preset responses.

[0377] The anchor SMF can notify the anchor AMF that the specified conditions have been met. The anchor AMF can then trigger this notification to perform changes and / or releases of resources associated with the UE. The anchor AMF can request the anchor base station to release the PDU session associated with the UE, or request to change the PDU session. This request may include NAS signaling and / or RRC signaling related to changes and / or established presets for PDU sessions with non-anchor NWs, or NAS signaling related to changes and / or releases of PDU sessions with anchor NWs. The anchor base station can trigger this request to request the UE to release the PDU session, or request to change the PDU session. This request may use RRC signaling. The RRC signaling may include NAS signaling and / or RRC signaling related to changes and / or established presets for PDU sessions with non-anchor NWs, or NAS signaling and / or RRC signaling related to changes and / or releases of PDU sessions with anchor NWs. The UE can use this RRC signaling as a trigger to establish and / or change a PDU session with a non-anchor NW, and can also release and / or change a PDU session with an anchor NW. The UE can send a response to the PDU session release or change request to the anchor base station. The anchor base station can notify the anchor AMF of this response from the UE.

[0378] The anchor AMF can notify the anchor SMF of this response from the UE.

[0379] Notifications from the NW to the UE can be made by the handover destination NW, such as a non-anchor NW. This, for example, can improve the reliability of signaling related to NW handover.

[0380] The NF for switching destination NW can initiate a path switch from anchor NW to non-anchor NW, or it can initiate a path switch from non-anchor NW to anchor NW. The destination NW can be either an anchor NW or a non-anchor NW. The method disclosed in this embodiment can be applied to the path switching described above. The NF can be, for example, a non-anchor SMF.

[0381] The specified conditions may include a validity period or a validity expiration date. This validity period or expiration date may be included within the specified conditions.

[0382] If the specified conditions are not met by the expiration of the validity period or validity period, the preset route switch can be cancelled. The NF (e.g., SMF) of the anchor point NW can notify the NF (e.g., SMF) of the candidate destination NW of information related to the expiration of the validity period or validity period, and can also notify information related to the cancellation of the preset. The NF of the candidate destination can release the preset upon triggering this notification.

[0383] The NF of the anchor NW can notify the NF (e.g., SMF) of the source NW of information related to the expiration of the validity period or validity period, and can also notify information related to the preset cancellation. The NF of the source NW can use this notification as a trigger to cancel the preset release of the NW. Thus, for example, the source NW can continue to communicate with the UE.

[0384] As an alternative solution, the UE can also determine the specified condition. This condition can be determined and notified to the UE by the NF of the anchor NW, the NF of a non-anchor NW, the NF of the handover source NW, or the NF of the handover destination candidate NW. This NF can be, for example, an SMF. This notification can be sent via the AMF or the base station. The UE can use this notification as a trigger to determine whether the specified condition is met.

[0385] The anchor AMF can notify the UE of pre-configured information related to NW handover. This notification can be made, for example, using NAS signaling. The UE can use this information for QoS monitoring and QoE measurement.

[0386] The UE can send a notification related to the specified condition to the NF of the NW. The NW can be an anchor NW or a non-anchor NW, a handover source NW or a handover destination NW. The NF can be, for example, an SMF. The notification can be, for example, a notification indicating that the specified condition has been met, or a notification indicating that the condition has not been met within the specified validity period. The notification can be sent via the base station or via the AMF. The NF can initiate an NW handover triggered by the notification, or it can cancel the preset setting. For example, an NW handover can be initiated by a notification indicating that the specified condition has been met, or a preset setting can be canceled by a notification indicating that the condition has not been met within the specified validity period. The execution of the NW handover can, for example, employ the method disclosed in the above solution. The cancellation of the preset setting can, for example, employ the method disclosed in the above solution.

[0387] According to implementation method 3, NW switching can be achieved in a short time, while saving NW resources, such as memory usage.

[0388] Variation 1 of Implementation Method 3.

[0389] Multiple NWs can be set as NW switching destination candidates. These candidates can be configured by the anchor NW. The anchor NW can preset multiple NWs.

[0390] For example, the anchor SMF can initiate this setting. The anchor SMF can instruct the SMF of a candidate NW to perform a pre-configuration. This instruction may include information related to handover conditions. These conditions may differ between different NWs. These conditions may be determined, for example, by the anchor PCF or by the anchor SMF. The candidate NW can use this information to perform a pre-configuration of its connection with the UE. This pre-configuration may be performed, for example, using the same method as disclosed in Embodiment 3.

[0391] The UE can initiate connection processing with a NW that meets the conditions. The UE can notify the NF (e.g., anchor SMF) of the anchor NW of information related to the NW that meets the conditions. As another example, the NW that meets the conditions can notify the NF (e.g., anchor SMF) of the anchor NW that a connection with the UE has started.

[0392] The anchor NW can notify the SMF of the NW that the conditions have been met. The NW that has met the conditions can then begin connection processing with the UE. The connection processing with the UE can be performed, for example, using the same method disclosed in Implementation 3.

[0393] Anchor NW can notify the SMF of candidate NWs other than those meeting the conditions that the conditions have not been met, or it can notify other NWs that the conditions have been met. The candidate NW can release connection preparation with the UE triggered by this notification from the anchor SMF. The candidate NW can also notify the anchor SMF that the release has ended.

[0394] A priority order can be set among multiple candidates. Thus, for example, when the conditions for multiple NWs are met simultaneously, the destination NW for switching can be uniquely determined, thereby preventing malfunctions of the communication system.

[0395] According to this variation 1, flexible switching of the communication system can be achieved.

[0396] The NW device in this disclosure can be an NF of an NW. For example, an anchor NW device can be an NF of an anchor NW. A non-anchor NW device can be an NF of a non-anchor NW. Thus, for example, the method shown in this disclosure can be applied even when multiple NFs of an NW are housed in the same device.

[0397] The method shown in this disclosure can be used in situations other than NW failure. For example, it can be used when QoS deteriorates. The NW failure detection shown in this disclosure can be QoS deterioration detection. Thus, for example, UPF handover and / or NW handover actions can be performed before communication is interrupted, resulting in improved availability of the communication NW.

[0398] As another example, the method shown in this disclosure can be used under specified conditions. These specified conditions could be, for example, an increase in the load on the UPF or the AMF. Thus, for example, further increases in the load on the UPF and / or AMF can be prevented, resulting in the prevention of NW failure.

[0399] In this disclosure, signaling between different NWs can be performed via SEPP (refer to Non-Patent Document 10). This, for example, ensures the security of the signaling.

[0400] In this disclosure, the IPUPS (Inter PLMN User Plane Security) function (refer to Non-Patent Document 10) can be used in the forwarding of user data between different NWs. Thus, for example, security in the forwarding of user data can be ensured.

[0401] Transmission and reception between the base station and CN nodes (excluding the AMF) can be performed via the AMF. Alternatively, transmission and reception between the base station and CN nodes (excluding the AMF) can be performed without going through the AMF. By bypassing the AMF, signaling traffic can be reduced, and the load on the AMF can be decreased.

[0402] In this specification, a node can be a function.

[0403] In the communication system disclosed herein, one gNB constitutes one or more cells. In this disclosure, it is referred to as gNB or cell, but unless otherwise specified, it can be either gNB or cell.

[0404] In this disclosure, gNB can be either MCG or SCG.

[0405] The above embodiments and their modifications are merely illustrative, and the embodiments and their modifications can be freely combined. Furthermore, any structural elements of the embodiments and their modifications can be appropriately modified or omitted.

[0406] For example, in the above embodiments and their variations, a time slot is an example of a time unit for communication in a fifth-generation communication system. A time slot can be a scheduling unit. In the above embodiments and their variations, processing can be performed by recording in time slot units, such as TTI units, subframe units, sub-time slot units, and micro-time slot units.

[0407] For example, the methods disclosed in the above embodiments and their variations can be applied to IABs. They can be applied to communication between the IAB host and IAB nodes. They can also be applied to the processing of Uu within an IAB.

[0408] Label Explanation

[0409] 202 Communication terminal device (mobile terminal)

[0410] 210 Communication System

[0411] 213, 240-1, 240-2, 750 Base Station Equipment (NR Base Station, Base Station)

[0412] 214 5G Core Unit

[0413] 215 Central Unit

[0414] 216 Distributed Units

[0415] 217 Control plane central unit

[0416] 218 User-facing Central Unit

[0417] 219 TRP

[0418] 301 and 403 Protocol Processing Department

[0419] 302 Application Department

[0420] 304 and 405 coding sections

[0421] Modulation sections 305 and 406

[0422] 306, 407 Frequency Conversion Section

[0423] Antennas 307-1 to 307-4 and 408-1 to 408-4

[0424] 308, 409 De-escalation Department

[0425] Decoding sections 309 and 410

[0426] Control Departments 310, 411, and 526

[0427] 401 EPC Communications Department

[0428] 402 Other Base Station Communications Department

[0429] 412 5GC Communications Department

[0430] 521 Data Network Communications Department

[0431] 522 Base Station Communications Department

[0432] 523 User Plane Communications Department

[0433] 523-1 PDU Processing Department

[0434] 523-2 Moving Anchoring Unit

[0435] 525 Control Panel Control Unit

[0436] 525-1 NAS Security Department

[0437] 525-2 Idle Status Mobility Management Department

[0438] 527 Session Management Department

[0439] 527-1 PDU Session Control Department

[0440] 527-2 UE IP Address Allocation Department

[0441] 751-1~751-8 Beams

[0442] 752 Community.

Claims

1. A communication system corresponding to a 5th generation wireless access system, characterized in that, It includes: an anchor network, which is a network with user plane functionality that is directly connected to the data network of the data transceiver destination of the communication terminal; and a non-anchor network, which is a network connected to the data network via the anchor network. It has multiple protocol stacks for enabling communication between the communication terminal and the data network. When the communication terminal switches the connected network, it uses multiple protocol stacks to transition to a state where it is connected to both the anchor network and the non-anchor network and communicates with the data network, and then terminates communication with the data network via the switched source network.

2. The communication system as described in claim 1, characterized in that, When the communication terminal sends data to the data network, it notifies the network at the data destination of information related to the sequence number of the uplink data being sent.

3. The communication system as described in claim 2, characterized in that, When the communication terminal is connected to both the anchor network and the non-anchor network and is communicating with the data network, it determines which of the anchor network and the non-anchor network to send the uplink data to, based on the uplink data buffer size of each of the multiple protocol stacks.

4. The communication system as described in claim 2, characterized in that, When the communication terminal is connected to both the anchor network and the non-anchor network and is communicating with the data network, the anchor network or the non-anchor network determines which of the anchor network and the non-anchor network to send the uplink data based on one or both of the fault detection and congestion detection of the anchor network and the non-anchor network, and indicates the sending destination to the communication terminal.

5. The communication system as described in any one of claims 1 to 4, characterized in that, For each function included in the candidate network for switching destination when the communication terminal switches connected networks, the settings used in communication with the communication terminal are made in advance.

6. The communication system as described in claim 5, characterized in that, There are multiple candidate networks, and for all of the multiple candidate networks, the functions contained in each network are preset.

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