Communication system

Abstract

This communication system includes: an anchor network which is a network having a user plane function for direct connection with a data network of a data transmission / reception destination of a communication terminal; and a non-anchor network which is a network that connects to the data network via the anchor network. When switching a connected network to another network, the communication terminal uses a plurality of protocol stacks to connect to both the anchor network and the non-anchor network to transition to a state for communicating with the data network, and subsequently terminates communication with the data network via the connected network.

Description

communication systems

[0001] The present disclosure relates to wireless communication technology.

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

[0003] For example, in Europe, an organization called METIS has compiled 5G requirements (see Non-Patent Document 3). The requirements for a 5G wireless access system are that it must have 1000 times the system capacity, 100 times the data transmission speed, one-fifth the data processing delay, and 100 times the number of simultaneous connections of communication terminals compared to an LTE system, while also achieving further reductions in power consumption and cost reductions for the equipment (see Non-Patent Document 3).

[0004] In order to meet such demands, 3GPP is currently studying 5G standards (see Non-Patent Documents 4 to 23).

[0005] The NR access method uses OFDM (Orthogonal Frequency Division Multiplexing) in the downlink direction and OFDM and DFT-s-OFDM (Discrete Fourier Transform-spread-OFDM) in the uplink direction. Also, like LTE and LTE-A, the 5G system does not include circuit switching and is only a packet communication method.

[0006] NR allows the use of higher frequencies than LTE in order to improve transmission speeds and reduce processing delays.

[0007] In NR, which may use higher frequencies than LTE, cell coverage is ensured by forming a narrow beam-shaped transmission and reception range (beam forming) and changing the direction of the beam (beam sweeping).

[0008] The decisions made by 3GPP regarding the frame structure in an NR system, as described in Non-Patent Document 1 (Chapter 5), are explained using Figure 1. Figure 1 is an explanatory diagram showing the structure of a radio frame used in an NR communication system. In Figure 1, one radio frame is 10 ms. The radio frame is divided into 10 equally sized subframes. The NR frame structure supports one or more numerologies, i.e., one or more subcarrier spacings (SCSs). In NR, one subframe is 1 ms long, and one slot consists of 14 symbols, regardless of the subcarrier spacing. Furthermore, the number of slots included in one subframe is one when the subcarrier spacing is 15 kHz, and the number of slots at other subcarrier spacings increases in proportion to the subcarrier spacing (see Non-Patent Document 11 (3GPP TS38.211)).

[0009] 3GPP's decisions regarding channel configuration in NR systems are described in Non-Patent Document 2 (Chapter 5) and Non-Patent Document 11.

[0010] A physical broadcast channel (PBCH) is a channel for downlink transmission from a base station device (hereinafter sometimes simply referred to as a "base station") to a communication terminal device (hereinafter sometimes referred to as a "communication terminal" or "terminal") such as a mobile terminal device (hereinafter sometimes simply referred to as a "mobile terminal"). The PBCH is transmitted together with a downlink synchronization signal.

[0011] Downlink synchronization signals in NR include a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS). Synchronization signals are transmitted from base stations as synchronization signal bursts (hereinafter sometimes referred to as SS bursts) at predetermined intervals and for a predetermined duration. SS bursts are composed of synchronization signal blocks (hereinafter sometimes referred to as SS blocks) for each beam of the base station.

[0012] The base station transmits the SS block of each beam by changing the beam during the duration of the SS burst. The SS block consists of the P-SS, S-SS, and PBCH.

[0013] The Physical Downlink Control Channel (PDCCH) is a channel for downlink transmission from a base station to a communication terminal. The PDCCH carries downlink control information (DCI). The DCI includes resource allocation information for a Downlink Shared Channel (DL-SCH), which is one of the transport channels described below, resource allocation information for a Paging Channel (PCH), which is one of the transport channels described below, and Hybrid Automatic Repeat reQuest (HARQ) information related to the DL-SCH. The DCI may also include an uplink scheduling grant. The DCI may also include an acknowledgement (Ack) / negative acknowledgement (Nack), which is a response signal to the uplink transmission. In addition, in order to flexibly switch between DL and UL within a slot, the DCI may include a slot format indication (SFI). The PDCCH or the DCI is also called an L1 / L2 control signal.

[0014] In NR, a time-frequency region that is a candidate for including a PDCCH is provided. This region is called a control resource set (CORESET). A communication terminal monitors the CORESET and acquires a PDCCH.

[0015] The Physical Downlink Shared Channel (PDSCH) is a channel for downlink transmission from a base station to a communication terminal. The Downlink Shared Channel (DL-SCH), which is a transport channel, and the PCH, which is a transport channel, are mapped to the PDSCH.

[0016] The Physical Uplink Control Channel (PUCCH) is a channel for uplink transmission from a communication terminal to a base station. The PUCCH carries uplink control information (UCI). The UCI includes Ack / Nack, which is a response signal to a downlink transmission, CSI (Channel State Information), a scheduling request (SR), and the like. The CSI is composed of a Rank Indicator (RI), a Precoding Matrix Indicator (PMI), and a CQI (Channel Quality Indicator) report. The RI is rank information of a channel matrix in MIMO (Multiple Input Multiple Output). The PMI is information on a precoding weight matrix used in MIMO. The CQI is quality information indicating the quality of received data or the quality of a communication path. The UCI may be carried by the PUSCH, which will be described later. The PUCCH or UCI is also called an L1 / L2 control signal.

[0017] The Physical Uplink Shared Channel (PUSCH) is a channel for uplink transmission from a communication terminal to a base station. The Uplink Shared Channel (UL-SCH), which is one of the transport channels, is mapped to the PUSCH.

[0018] A physical random access channel (PRACH) is a channel for uplink transmission from a communication terminal to a base station. The PRACH carries a random access preamble.

[0019] A downlink reference signal (RS) is a known symbol in an NR communication system. The following four types of downlink reference signals are defined: a demodulation reference signal (DM-RS), which is a UE-specific reference signal, a phase tracking reference signal (PT-RS), a positioning reference signal (PRS), and a channel state information reference signal (CSI-RS). Measurements of the physical layer of a communication terminal include reference signal received power (RSRP) measurement and reference signal received quality (RSRQ) measurement.

[0020] Similarly, the uplink reference signal is a known symbol in an NR communication system. The following three types of uplink reference signals are defined: a data demodulation reference signal (DM-RS), a phase tracking reference signal (PT-RS), and a sounding reference signal (SRS).

[0021] The transport channels described in Non-Patent Document 2 (Chapter 5) will be described below. Among the downlink transport channels, a broadcast channel (BCH) is broadcast to the entire coverage of the base station (cell). The BCH is mapped to a physical broadcast channel (PBCH).

[0022] Retransmission control using HARQ is applied to the Downlink Shared Channel (DL-SCH). The DL-SCH can be broadcast to the entire coverage of the base station (cell). The DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called semi-persistent scheduling. The DL-SCH supports discontinuous reception (DRX) in communication terminals to reduce power consumption of the communication terminals. The DL-SCH is mapped to the Physical Downlink Shared Channel (PDSCH).

[0023] The Paging Channel (PCH) supports DRX of communication terminals to enable low power consumption of the communication terminals. The PCH is required to broadcast to the entire coverage 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] Among the uplink transport channels, the uplink shared channel (UL-SCH) is subject to retransmission control using HARQ. The UL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also called configured grant. The UL-SCH is mapped to the physical uplink shared channel (PUSCH).

[0025] The Random Access Channel (RACH) is limited to control information, has a risk of collision, and is mapped to the Physical Random Access Channel (PRACH).

[0026] The following describes HARQ. HARQ is a technology that improves the communication quality of a transmission path by combining Automatic Repeat reQuest (ARQ) and Forward Error Correction. HARQ has the advantage that error correction functions effectively through retransmission even for transmission paths whose communication quality varies. In particular, by combining the reception result of the initial transmission and the reception result of the retransmission when retransmitting, it is possible to obtain further quality improvement.

[0027] An example of a retransmission method will be described below. If the receiving side is unable to decode the received data correctly, in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC=NG), the receiving side will send a "Nack" to the transmitting side. The transmitting side, having received the "Nack", will retransmit the data. If the receiving side is able to decode the received data correctly, in other words, if no CRC error occurs (CRC=OK), the receiving side will send an "Ack" to the transmitting side. The transmitting side, having received the "Ack", will send the next data.

[0028] Another example of a retransmission method will be described. If a CRC error occurs on the receiving side, the receiving side requests a retransmission from the transmitting side. The retransmission request is made by toggling an NDI (New Data Indicator). The transmitting side, upon receiving the retransmission request, retransmits the data. If no CRC error occurs on the receiving side, no retransmission request is made. If the transmitting side does not receive a retransmission request for a predetermined period of time, it assumes that no CRC error occurred on the receiving side.

[0029] The logical channels described in Non-Patent Document 1 (Chapter 6) are explained below. The Broadcast Control Channel (BCCH) is a downlink channel for broadcasting system control information. The BCCH, which is a logical channel, is mapped to the broadcast channel (BCH) or the downlink shared channel (DL-SCH), which are transport channels.

[0030] The Paging Control Channel (PCCH) is a downlink channel for transmitting paging information and changes to system information. The PCCH, which is a logical channel, is mapped to the Paging Channel (PCH), which is a transport channel.

[0031] The Common Control Channel (CCCH) is a channel for transmitting control information between a communication terminal and a base station. The CCCH is used when the communication terminal does not have an RRC connection with the network. In the downlink direction, the CCCH is mapped to the Downlink Shared Channel (DL-SCH), which is a transport channel. In the uplink direction, the CCCH is mapped to the Uplink Shared Channel (UL-SCH), which is a transport channel.

[0032] A Dedicated Control Channel (DCCH) is a channel that transmits dedicated control information between a communication terminal and a network in a one-to-one relationship. The DCCH is used when the communication terminal has an RRC connection with the network. The DCCH is mapped to an uplink shared channel (UL-SCH) in the uplink and to a downlink shared channel (DL-SCH) in the downlink.

[0033] A Dedicated Traffic Channel (DTCH) is a point-to-point communication channel for transmitting user information to a communication terminal. DTCH exists in both uplink and downlink. In uplink, DTCH is mapped to an uplink shared channel (UL-SCH) and in downlink, it is mapped to a downlink shared channel (DL-SCH).

[0034] The location of a communication terminal is tracked in units of an area consisting of one or more cells. Location tracking is performed to track the location of the communication terminal even when it is in standby mode and to call the communication terminal, in other words, to enable the communication terminal to receive calls. The area for tracking the location of this communication terminal is called a Tracking Area (TA).

[0035] In NR, paging of communication terminals within a range that is smaller than a tracking area is supported. This range is called a RAN Notification Area (RNA). Paging of communication terminals in the RRC_INACTIVE state, which will be described later, is performed within this range.

[0036] In NR, in order to support wide frequency bandwidths (transmission bandwidths), carrier aggregation (CA) is being considered, which aggregates (also referred to as "aggregation") two or more component carriers (CCs). CA is described in Non-Patent Document 1.

[0037] When CA is configured, a communication terminal (UE) has only one RRC connection with the network (NW). In the RRC connection, one serving cell provides NAS (Non-Access Stratum) mobility information and security input. This cell is called a primary cell (PCell). Depending on the UE's capabilities, a secondary cell (SCell) is configured to form a serving cell set together with the PCell. A serving cell set consisting of one PCell and one or more SCells is configured for one UE.

[0038] In addition, in 3GPP, in order to further increase communication capacity, there is a dual connectivity (abbreviated as DC) in which a UE connects to two base stations to communicate. DC is described in Non-Patent Documents 1 and 22.

[0039] Of the base stations performing dual connectivity (DC), one may be referred to as a "master base station (Master Node: MN)" and the other as a "secondary base station (Secondary Node: SN)." Serving cells configured by the master base station may be collectively referred to as a master cell group (MCG), and serving cells configured by secondary base stations may be collectively referred to as a secondary cell group (SCG). In DC, the primary cell in the MCG or SCG is referred to as a special cell (SpCell or SPCell). The special cell in the MCG is referred to as a PCell, and the special cell in the SCG is referred to as a primary SCG cell (PSCell).

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

[0041] Additionally, 3GPP is considering supporting services (or applications) using side link (SL) communication (also referred to as PC5 communication) in both the Evolved Packet System (EPS) (described later) and the 5G core system (see Non-Patent Documents 1, 2, 26 to 28). SL communication involves communication between terminals. Services using SL communication include, for example, vehicle-to-everything (V2X) services and proximity services. In SL communication, not only direct communication between terminals but also communication between a UE and a network via a relay has been proposed (see Non-Patent Documents 26 and 28).

[0042] The physical channels used for SL (see Non-Patent Documents 2 and 11) are as follows: The physical sidelink broadcast channel (PSBCH) carries information related to the system and synchronization and is transmitted from the UE.

[0043] The physical sidelink control channel (PSCCH) carries control information from the UE for sidelink and V2X sidelink communications.

[0044] The physical sidelink shared channel (PSSCH) carries data from the UE for sidelink and V2X sidelink communications.

[0045] The physical sidelink feedback channel (PSFCH) carries HARQ feedback on the sidelink from a UE that received a PSSCH transmission to the UE that transmitted the PSSCH.

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

[0047] The Sidelink Shared Channel (SL-SCH) supports broadcast transmissions. The SL-SCH supports both UE autonomous resource selection and base station scheduled resource allocation. UE autonomous resource selection involves a collision risk, whereas when the UE is allocated dedicated resources by the base station, there is no collision. The SL-SCH also supports dynamic link adaptation by changing transmit power, modulation, and coding. The SL-SCH is mapped to the PSSCH, which is a physical channel.

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

[0049] The Sidelink Traffic Channel (STCH) is a point-to-multipoint traffic channel for transmitting user information from one UE to other UEs. The STCH is used only by UEs with sidelink communication capability and UEs with V2X sidelink communication capability. Point-to-point communication between two sidelink-capable UEs is also realized by the STCH. The STCH is mapped to the SL-SCH, a transport channel.

[0050] The Sidelink Control Channel (SCCH) is a control channel for transmitting control information from one UE to another UE. The SCCH is mapped to the SL-SCH, which is a transport channel.

[0051] In LTE, only broadcast was supported for SL communication. In NR, support for unicast and groupcast as SL communication in addition to broadcast is being considered (see Non-Patent Document 27 (3GPP TS23.287)).

[0052] In unicast communication and groupcast communication in SL, HARQ feedback (Ack / Nack), CSI reporting, etc. are supported.

[0053] In addition, 3GPP is considering integrated access and backhaul (IAB), which performs both the access link between a UE and a base station and the backhaul link between base stations wirelessly (see Non-Patent Documents 2, 20, and 29).

[0054] Several new technologies have been proposed for mobile communication systems, such as a technology that allows a single terminal to connect to multiple networks simultaneously to improve communication capacity and reliability (see Non-Patent Documents 30 and 31).

[0055] 3GPP TS36.300 V17.5.03GPP TS38.300 V17.6.0 “Scenarios, requirements and KPIs for 5G mobile and wireless system”, ICT-317669-METIS / D1.13GPP TR23.799 V14.0.03GPP TR38.801 V14.0.03GPP TR38.802 V14.2.03GPP TR38.804 V14.0.03GPP TR38.912 V16.0.03GPP RP-1721153GPP TS23.501 V18.3.03GPP TS38.211 V18.0.03GPP TS38.212 V18.0.03GPP TS38.213 V18.0.03GPP TS38.214 V18.0.03GPP TS38.321 V17.6.03GPP TS38.322 V17.3.03GPP TS38.323 V17.5.03GPP TS37.324 V17.0.03GPP TS38.331 V17.6.03GPP TS38.401 V17.6.03GPP TS38.413 V17.6.03GPP TS37.340 V17.6.03GPP TS38.423 V17.6.03GPP TS38.305 V17.6.03GPP TS23.273 V18.3.03GPP TR23.703 V12.0.03GPP TS23.287 V18.1.03GPP TS23.303 V17.1.03GPP TS38.340 V17.5.03GPP SWS-2300493GPP TS23.502 V18.3.03GPP TS23.503 V18.3.03GPP TR32.851 V12.2.03GPP TS28.537 V17.3.0

[0056] In a case where a UE is simultaneously connected to multiple networks, the network that serves as a route for traffic between the UE and a data network (DN) may be switched. However, if the network is switched before all data from the previous network has reached the UE, there is a risk that the data may be lost.

[0057] In view of the above-mentioned problems, one of the objectives of the present disclosure is to enable improvement in the reliability of data transmission and reception when a network switch occurs in a communication system configured to allow a UE to be simultaneously connected to multiple networks.

[0058] The communication system disclosed herein is a communication system compatible with a fifth-generation wireless access system, and includes an anchor network, which is a network having a user plane function that directly connects a communication terminal to a data network that is the destination of data transmission and reception, and a non-anchor network, which is a network that connects to the data network via the anchor network, and has multiple protocol stacks for communication between the communication terminal and the data network.When switching the network to which the communication terminal is connected, the communication terminal uses the multiple protocol stacks to connect to both the anchor network and the non-anchor network and transitions to a state in which it communicates with the data network, and then terminates communication with the data network via the source network.

[0059] According to the present disclosure, in a communication system configured so that a UE can be simultaneously connected to multiple networks, it is possible to improve the reliability of data transmission and reception when a network switch occurs.

[0060] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0061] 1 is an explanatory diagram showing the configuration of a radio frame used in an NR communication system. FIG. 2 is a block diagram showing the overall configuration of an NR communication system 210 being discussed in 3GPP. FIG. 3 is a configuration diagram of DC by a base station connected to an NG core. FIG. 4 is a block diagram showing the configuration of a mobile terminal 202 shown in FIG. 2. FIG. 5 is a block diagram showing the configuration of a base station 213 shown in FIG. 2. FIG. 6 is a block diagram showing the configuration of a 5GC unit. FIG. 7 is a flowchart showing an overview of operations from cell search to standby operation performed by a communication terminal (UE) in an NR communication system. FIG. 8 is a diagram showing an example of the configuration of a cell in an NR system. FIG. 9 is a connection configuration diagram showing an example of the connection configuration of a terminal in SL communication. FIG. 10 is a connection configuration diagram showing an example of the connection configuration of a base station that supports access / backhaul integration. FIG. 11 is a configuration diagram showing an example in which a UE connects to multiple NWs for the first embodiment. FIG. 12 is a diagram showing an example of a protocol stack between a UE and an anchor UPF for the first embodiment. FIG. 13 is a diagram showing another example of a protocol stack between a UE and an anchor UPF for the first embodiment. FIG. 14 is a diagram showing another example of a protocol stack between a UE and an anchor UPF for the first embodiment. 17 is a diagram showing the first half of a sequence illustrating an example of a NW switching operation maintaining the protocols of both NWs according to the first embodiment. FIG. 18 is a diagram showing the second half of a sequence illustrating an example of a NW switching operation maintaining the protocols of both NWs according to the first embodiment. FIG. 19 is a sequence diagram illustrating an example of a procedure 1100 of FIG. 16. FIG. 19 is a sequence diagram illustrating an example of a procedure 1111 of FIG. 16. FIG. 19 is a sequence diagram illustrating an example of a procedure 1120 of FIG. 16. FIG. 19 is a sequence diagram illustrating an example of a procedure 1130 of FIG. 16. FIG. 20 is a sequence diagram illustrating an example of a procedure 1255 of FIG.

[0062] Embodiment 1. Figure 2 is a block diagram showing the overall configuration of an NR communication system 210 being discussed in 3GPP. Figure 2 will be explained. The radio access network is called an NG-RAN (Next Generation Radio Access Network) 211. A mobile terminal device (hereinafter referred to as a "mobile terminal (User Equipment: UE)") 202, which is a communication terminal device, is capable of wireless communication with a base station device (hereinafter referred to as an "NR base station (NG-RAN NodeB: gNB)") 213, and transmits and receives signals via wireless communication. The NG-RAN 211 is composed of one or more NR base stations 213.

[0063] Here, the term "communication terminal device" includes not only mobile terminal devices such as mobile cell phone terminal devices, but also stationary devices such as sensors. In the following description, the term "communication terminal device" may be simply referred to as a "communication terminal."

[0064] An access stratum (AS) protocol is terminated between the UE 202 and the NG-RAN 211. Examples of AS protocols include radio resource control (RRC), service data adaptation protocol (SDAP), packet data convergence protocol (PDCP), radio link control (RLC), medium access control (MAC), and physical layer (PHY). RRC is used in the control plane (hereinafter sometimes referred to as the C-plane, C-Plane, or CP), SDAP is used in the user plane (hereinafter sometimes referred to as the U-plane, U-Plane, or UP), and PDCP, MAC, RLC, and PHY are used in both the C-plane and the U-plane.

[0065] The control protocol RRC (Radio Resource Control) between the UE 202 and the NR base station 213 performs broadcasting, paging, RRC connection management, etc. The states of the NR base station 213 and the UE 202 in RRC include RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE.

[0066] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can transmit and receive data with the network. In addition, in RRC_CONNECTED, handover (HO), measurement of neighbor cells, etc. are performed. In RRC_INACTIVE, the connection between the 5G core unit 214 and the NR base station 213 is maintained, and system information (SI) broadcast, paging, cell re-selection, mobility, etc. are performed.

[0067] The gNB 213 is connected to a 5G core unit (hereinafter sometimes referred to as the "5GC unit") 214, which includes an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a User Plane Function (UPF), via an NG interface. Control information and / or user data is communicated between the gNB 213 and the 5GC unit 214. The NG interface is a collective term for the N2 interface between the gNB 213 and the AMF 220, the N3 interface between the gNB 213 and the UPF 221, the N11 interface between the AMF 220 and the SMF 222, and the N4 interface between the UPF 221 and the SMF 222. Multiple 5GC units 214 may be connected to one gNB 213. The gNBs 213 are connected via an Xn interface, and control information and / or user data are communicated between the gNBs 213.

[0068] The 5GC unit 214 is a higher-level device, specifically a higher-level node, and controls the connection between the NR base station 213 and the mobile terminal (UE) 202, distributes paging signals to one or more NR base stations (gNB) 213 and / or LTE base stations (E-UTRAN NodeB: eNB), and performs other functions. The 5GC unit 214 also 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, in the inactive state, and in the active state. The 5GC unit 214 initiates a paging protocol by transmitting a paging message to a cell belonging to the tracking area in which the mobile terminal 202 is registered.

[0069] The gNB 213 may configure one or more cells. When one gNB 213 configures multiple cells, each cell is configured to be able to communicate with the UE 202.

[0070] The gNB 213 may be divided into a central unit (hereinafter, sometimes referred to as CU) 215 and a distributed unit (hereinafter, sometimes referred to as DU) 216. One CU 215 is configured within the gNB 213. One or more DUs 216 are configured within the gNB 213. One DU 216 configures one or more cells. The CU 215 is connected to the DU 216 via an F1 interface, and control information and / or user data is communicated between the CU 215 and the DU 216. The F1 interface consists of an F1-C interface and an F1-U interface. The CU 215 is responsible for the functions of the RRC, SDAP, and PDCP protocols, and the DU 216 is responsible for the functions of the RLC, MAC, and PHY protocols. One or more TRPs (Transmission Reception Points) 219 may be connected to the DU 216. The TRP 219 transmits and receives radio signals to and from the UE.

[0071] The CU 215 may be divided into a C-plane CU (CU-C) 217 ​​and a U-plane CU (CU-U) 218. One CU-C 217 is configured within the CU 215. One or more CU-Us 218 are configured within the CU 215. The CU-C 217 is connected to the CU-U 218 via an E1 interface, and control information is communicated between the CU-C 217 and the CU-U 218. The CU-C 217 is connected to the DU 216 via an F1-C interface, and control information is communicated between the CU-C 217 and the DU 216. The CU-U 218 is connected to the DU 216 via an F1-U interface, and user data is communicated between the CU-U 218 and the DU 216.

[0072] In a 5G communication system, a Unified Data Management (UDM) function and a Policy Control Function (PCF) described in Non-Patent Document 10 (3GPP TS23.501) may be included. The UDM and / or PCF may be included in the 5GC unit 214 in FIG. 2 .

[0073] In a 5G communication system, a Location Management Function (LMF) described in Non-Patent Document 24 (3GPP TS 38.305) may be provided. The LMF may be connected to a base station via an AMF as disclosed in Non-Patent Document 25 (3GPP TS 23.273).

[0074] A 5G communication system may include a Non-3GPP Interworking Function (N3IWF) described in Non-Patent Document 10 (3GPP TS23.501). The N3IWF may terminate an Access Network (AN) between the UE and the N3IWF in non-3GPP access between the UE and the N3IWF.

[0075] FIG. 3 is a diagram showing a DC (dual connectivity) configuration connected to an NG core. In FIG. 3, solid lines indicate U-Plane connections, and dashed lines indicate C-Plane connections. In FIG. 3, the master base station 240-1 may be a gNB or an eNB. Furthermore, the secondary base station 240-2 may be a gNB or an eNB. For example, in FIG. 3, a DC configuration in which the master base station 240-1 is a gNB and the secondary base station 240-2 is an eNB may be referred to as NG-EN-DC. In FIG. 3, an example is shown in which the U-Plane connection between the 5GC unit 214 and the secondary base station 240-2 is performed via the master base station 240-1, but it may also be performed directly between the 5GC unit 214 and the secondary base station 240-2. 3, an EPC (Evolved Packet Core), which is a core network connected to the LTE system and the LTE-A system, may be connected to the master base station 240-1 instead of the 5GC unit 214. A U-Plane connection may be directly established between the EPC and the secondary base station 240-2.

[0076] FIG. 4 is a block diagram showing the configuration of mobile terminal 202 shown in FIG. 2. The transmission process of mobile terminal 202 shown in FIG. 4 will be described. First, control data from control unit 310 and user data from application unit 302 are sent to protocol processing unit 301. Buffering of the control data and user data may be performed. Buffers for the control data and user data may be provided in control unit 310, application unit 302, or protocol processing unit 301. Protocol processing unit 301 performs protocol processing such as SDAP, PDCP, RLC, and MAC, for example, determining a destination base station in DC, and adding a header for each protocol. The protocol-processed data is passed to encoder unit 304, where it is subjected to encoding such as error correction. Some data may be output directly from protocol processing unit 301 to modulation unit 305 without being encoded. The data encoded by encoder unit 304 is modulated by modulation unit 305. Precoding in MIMO may be performed by modulation unit 305. The modulated data is converted into a baseband signal, and then output to frequency conversion section 306, where it is converted into a radio transmission frequency. Then, the transmission signal is transmitted from antennas 307-1 to 307-4 to base station 213. Although the example in FIG. 4 shows a case where the number of antennas is four, the number of antennas is not limited to four.

[0077] Furthermore, the reception process of the mobile terminal 202 is performed as follows. Radio signals from the base station 213 are received by the antennas 307-1 to 307-4. The received signals are converted from a radio reception frequency to a baseband signal by the frequency conversion unit 306, and demodulated by the demodulation unit 308. The demodulation unit 308 may also perform weight calculation and multiplication processing. The demodulated data is passed to the decoder unit 309, where decoding processes such as error correction are performed. The decoded data is passed to the protocol processing unit 301, where protocol processing such as MAC, RLC, PDCP, and SDAP is performed, for example, operations such as removing headers in each protocol. Of the data that has undergone protocol processing, the control data is passed to the control unit 310, and the user data is passed to the application unit 302.

[0078] A series of processes in the mobile terminal 202 is controlled by a control unit 310. Therefore, the control unit 310 is also connected to each of the units 302, 304 to 309, although this is omitted in FIG.

[0079] Each unit of the mobile terminal 202, such as the control unit 310, protocol processing unit 301, encoder unit 304, and decoder unit 309, is implemented by a processing circuit including, for example, a processor and memory. For example, the control unit 310 is implemented by a processor executing a program describing a series of processes performed by the mobile terminal 202. The program describing the series of processes performed by the mobile terminal 202 is stored in memory. Examples of memory include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), and flash memory. Each unit of the mobile terminal 202, such as the control unit 310, protocol processing unit 301, encoder unit 304, and decoder unit 309, may be implemented by a dedicated processing circuit such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a DSP (Digital Signal Processor). In FIG. 4, the number of antennas used by the mobile terminal 202 for transmission and the number of antennas used for reception may be the same or different.

[0080] 5 is a block diagram showing the configuration of the base station 213 shown in FIG. 2. The transmission process of the base station 213 shown in FIG. 5 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 (such as the 5GC unit 214). The other base station communication unit 402 transmits and receives data with other base stations. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402 each 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 unit 402 are sent to the protocol processing unit 403. Buffering of the control data and user data may be performed. Buffers for control data and user data may be provided in the control unit 411, the EPC communication unit 401, the 5GC communication unit 412, or the other base station communication unit 402.

[0081] The protocol processing unit 403 performs protocol processing such as SDAP, PDCP, RLC, MAC, etc., such as routing transmission data in DC, etc., and adding headers for each protocol. The protocol-processed data is passed to the encoder unit 405, where it is subjected to encoding processing such as error correction. Some data may be output directly from the protocol processing unit 403 to the modulation unit 406 without being encoded. Data may also be sent from the protocol processing unit 403 to the other base station communication unit 402. For example, in DC, data sent from the 5GC communication unit 412 or the EPC communication unit 401 may be sent to another base station, such as a secondary base station, via the other base station communication unit 402. The encoded data is modulated by the modulation unit 406. The modulation unit 406 may also perform MIMO precoding. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 407, where it is converted into a radio transmission frequency. Thereafter, the transmission signals are transmitted from antennas 408-1 to 408-4 to one or more mobile terminals 202. Although the number of antennas is four in the example shown in Fig. 5, the number of antennas is not limited to four.

[0082] Furthermore, the reception process of the base station 213 is performed as follows. Radio signals from one or more mobile terminals 202 are received by antennas 408-1 to 408-4. The received signals are converted from a radio reception frequency to a baseband signal by a frequency conversion unit 407, and demodulated by a demodulation unit 409. The demodulated data is passed to a decoder unit 410, where decoding processes such as error correction are performed. The decoded data is passed to a protocol processing unit 403, where protocol processes such as MAC, RLC, PDCP, and SDAP are performed, for example, operations such as removing headers in each protocol. Of the data that has undergone protocol processing, control data is passed to the control unit 411, 5GC communication unit 412, EPC communication unit 401, or other base station communication unit 402, and user data is passed to the 5GC communication unit 412, EPC communication unit 401, or other base station communication unit 402. Data sent from the other base station communication unit 402 may be sent to the 5GC communication unit 412 or the EPC communication unit 401. The data may be, for example, uplink data sent to the 5GC communication unit 412 or the EPC communication unit 401 via another base station in DC.

[0083] A series of processes in the base station 213 is controlled by a control unit 411. Therefore, the control unit 411 is also connected to each of the units 401, 402, 405 to 410, and 412, although this is omitted in FIG.

[0084] Each unit of the base station 213, for example, the control unit 411, the protocol processing unit 403, the 5GC communication unit 412, the EPC communication unit 401, the other base station communication unit 402, the encoder unit 405, and the decoder unit 410, is realized by a processing circuit including a processor and a memory, or a dedicated processing circuit such as an FPGA, an ASIC, or a DSP, similar to the above-mentioned mobile terminal 202. In Fig. 5, the number of antennas used by the base station 213 for transmission and the number of antennas used for reception may be the same or different.

[0085] As an example of the configuration of the CU 215 shown in Fig. 2, a configuration in which a DU communication unit is provided is sometimes used, excluding the encoder unit 405, modulation unit 406, frequency conversion unit 407, antennas 408-1 to 408-4, demodulation unit 409, and decoder unit 410 shown in Fig. 5. The DU communication unit is connected to a protocol processing unit 403. The protocol processing unit 403 in the CU 215 performs protocol processing such as PDCP and SDAP.

[0086] As an example of the configuration of the DU 216 shown in Fig. 2, a configuration in which a CU communication unit is provided may be used, excluding the EPC communication unit 401, other base station communication unit 402, and 5GC communication unit 412 shown in Fig. 5. The CU communication unit is connected to a protocol processing unit 403. The protocol processing unit 403 in the DU 216 performs protocol processing such as PHY, MAC, and RLC.

[0087] FIG. 6 is a block diagram showing the configuration of the 5GC unit. FIG. 6 shows the configuration of the 5GC unit 214 shown in FIG. 2 described above. FIG. 6 shows a case where the 5GC unit 214 shown in FIG. 2 includes an AMF configuration, an SMF configuration, and a UPF configuration. In the example shown in FIG. 6, the AMF may have the function of the control plane control unit 525, the SMF may have the function of the session management unit 527, and the UPF may have the functions of the user plane communication unit 523 and the Data Network communication unit 521. The Data Network communication unit 521 transmits and receives data between the 5GC unit 214 and the Data Network. The base station communication unit 522 transmits and receives data via the NG interface between the 5GC unit 214 and the base station 213. User data sent from the Data Network is passed from the Data Network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523, and then transmitted to one or more base stations 213. User data sent from the base station 213 is passed from the base station communication unit 522 to the Data Network communication unit 521 via the user plane communication unit 523, and then transmitted to the Data Network.

[0088] The control data sent from the base station 213 is passed from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 may pass the control data to the session management unit 527. The control data may be sent from the Data Network. The control data sent from the Data Network may be sent from the Data Network communication unit 521 to the session management unit 527 via the user plane communication unit 523. The session management unit 527 may send the control data to the control plane control unit 525.

[0089] The user plane communication unit 523 includes a PDU processing unit 523-1, a mobility anchoring unit 523-2, etc., and performs general processing for the user plane (hereinafter sometimes referred to as U-Plane). The PDU processing unit 523-1 processes data packets, for example, transmitting and receiving packets to and from the Data Network communication unit 521, and transmitting and receiving packets to and from the base station communication unit 522. The mobility anchoring unit 523-2 is responsible for anchoring the data path during UE mobility.

[0090] The session management unit 527 manages the PDU session established between the UE and the UPF. The session management unit 527 includes a PDU session control unit 527-1, a UE IP address allocation unit 527-2, etc. The PDU session control unit 527-1 manages the PDU session between the mobile terminal 202 and the 5GC unit 214. The UE IP address allocation unit 527-2 assigns an IP address to the mobile terminal 202, etc.

[0091] 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 the C-Plane). The NAS security unit 525-1 performs security for NAS (Non-Access Stratum) messages, etc. The idle state mobility management unit 525-2 performs mobility management in the standby state (idle state: also referred to as RRC_IDLE state or simply idle), generation and control of paging signals in the standby state, addition, deletion, update, search, tracking area list management, etc. for one or more mobile terminals 202 under its control.

[0092] A series of processes of the 5GC unit 214 is controlled by a control unit 526. Therefore, although the control unit 526 is omitted in Fig. 6, it is connected to each unit 521 to 523, 525, and 527. Like the control unit 310 of the mobile terminal 202 described above, each unit of the 5GC unit 214 is realized by, for example, a processing circuit configured to include a processor and memory, or a dedicated processing circuit such as an FPGA, ASIC, or DSP.

[0093] Next, an example of a cell search method in a communication system is shown. Fig. 7 is a flowchart showing an outline of the process from cell search to standby operation performed by a communication terminal (UE) in an NR communication system. When the communication terminal starts a cell search, in step ST601, it synchronizes slot timing and frame timing using a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS) transmitted from a surrounding base station.

[0094] P-SS and S-SS are collectively called a synchronization signal (SS). A synchronization code is assigned to the synchronization signal (SS) in one-to-one correspondence with a PCI (Physical Cell Identifier) ​​assigned to each cell. 1008 different PCIs are being considered. A communication terminal synchronizes using these 1008 different PCIs and detects (identifies) the PCI of the synchronized cell.

[0095] In step ST602, the communication terminal receives the PBCH for the next synchronized cell. A master information block (MIB) including cell configuration information is mapped to the BCCH on the PBCH. Therefore, the MIB can be obtained by receiving the PBCH and obtaining the BCCH. Examples of MIB information include a system frame number (SFN), scheduling information for system information block (SIB) 1, subcarrier spacing for SIB1 and the like, and information on the DM-RS position.

[0096] Furthermore, the communication terminal acquires an SS block identifier from the PBCH. A part of the bit string of the SS block identifier is included in the MIB. The remaining bit string is included in an identifier used to generate a sequence of DM-RS associated with the PBCH. The communication terminal acquires the SS block identifier using the MIB included in the PBCH and the sequence of DM-RS associated with the PBCH.

[0097] Next, in step ST603, the communication terminal measures the received power of the SS block.

[0098] Next, in step ST604, the communication terminal selects the cell with the best reception quality, for example, the cell with the highest reception power, that is, the best cell, from among the one or more cells detected up to step ST603. The communication terminal also selects the beam with the best reception quality, for example, the beam with the highest reception power of the SS block, that is, the best beam. The reception power of the SS block for each SS block identifier is used, for example, to select the best beam.

[0099] Next, in step ST605, the communication terminal receives DL-SCH based on the scheduling information of SIB1 included in the MIB, and obtains SIB (System Information Block) 1 in the broadcast information BCCH. SIB1 includes information on access to the cell, cell configuration information, and scheduling information of other SIBs (SIBk: k is an integer greater than or equal to 2). SIB1 also includes a tracking area code (TAC).

[0100] 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 held by the communication terminal. The tracking area list is also called a TAI list. The TAI is identification information for identifying a tracking area, and is composed of an MCC (Mobile Country Code), an MNC (Mobile Network Code), and a TAC (Tracking Area Code). The MCC is a country code. The MNC is a network code. The TAC is a tracking area code number.

[0101] If the comparison in step ST606 shows that the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters standby mode in the cell. If the comparison shows that the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a core network (EPC) including an MME and the like to change the tracking area through the cell in order to perform a Tracking Area Update (TAU).

[0102] An apparatus constituting a core network (hereinafter sometimes referred to as a "core network apparatus") updates the tracking area list based on the identification number (e.g., UE-ID) of a communication terminal sent from the communication terminal together with a TAU request signal. The core network apparatus transmits the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. Thereafter, the communication terminal enters standby mode in the cell.

[0103] Next, examples of random access methods in a communication system are shown. Four-step random access and two-step random access are used for random access. For each of the four-step and two-step random access methods, there is contention-based random access, i.e., random access in which timing collisions with other mobile terminals may occur, and contention-free random access.

[0104] An example of a collision-based four-step random access method is shown below. In the first step, the mobile terminal transmits a random access preamble to the base station. The random access preamble may be selected by the mobile terminal from a predetermined range, or may be individually assigned to the mobile terminal and notified by the base station.

[0105] In the second step, the base station transmits a random access response to the mobile terminal, which includes uplink scheduling information used in the third step, a terminal identifier used in the uplink transmission in the third step, and the like.

[0106] In the third step, the mobile terminal performs uplink transmission to the base station. The mobile terminal uses the information acquired in the second step for uplink transmission. In the fourth step, the base station notifies the mobile terminal whether or not the collision has been resolved. If the mobile terminal is notified that there is no collision, it ends the random access process. If the mobile terminal is notified that there is a collision, it starts the process over from the first step.

[0107] The contention-free four-step random access method differs from the contention-based four-step random access method in the following points: Prior to the first step, the base station pre-assigns a random access preamble and uplink scheduling to the mobile terminal, and the notification of whether or not contention has been resolved in the fourth step is not required.

[0108] An example of a collision-based two-step random access method is shown below. In the first step, the mobile terminal transmits a random access preamble and performs uplink transmission to the base station. In the second step, the base station notifies the mobile terminal whether there is a collision. If the mobile terminal is notified that there is no collision, it terminates the random access process. If the mobile terminal is notified that there is a collision, it restarts the process from the first step.

[0109] The contention-free two-step random access method differs from the contention-based two-step random access method in the following points: prior to the first step, the base station pre-assigns a random access preamble and uplink scheduling to the mobile terminal, and in the second step, the base station transmits a random access response to the mobile terminal.

[0110] FIG. 8 shows an example of a cell configuration in NR. In an NR cell, narrow beams are formed and transmitted in different directions. In the example shown in FIG. 8, at certain times, base station 750 transmits and receives signals to and from a mobile terminal using beam 751-1. At other times, base station 750 transmits and receives signals to and from a mobile terminal using beam 751-2. In a similar manner, base station 750 transmits and receives signals to and from a mobile terminal using one or more of beams 751-3 to 751-8. In this way, base station 750 forms a wide-area cell 752.

[0111] 8 shows an example in which the number of beams used by the base station 750 is 8, but the number of beams may be different from 8. Also, in the example shown in FIG. 8, the number of beams used simultaneously by the base station 750 is 1, but it may be multiple.

[0112] The concept of Quasi-CoLocation (QCL) is used to identify beams (see Non-Patent Document 14 (3GPP TS38.214)). That is, the beam is identified by information indicating which reference signal (e.g., SS block, CSI-RS) the beam can be considered to be the same as. The information may include types of information regarding the aspects of the beams that can be considered to be the same, such as Doppler shift, Doppler shift spread, mean delay, mean delay spread, and spatial Rx parameters (see Non-Patent Document 14 (3GPP TS38.214)).

[0113] In 3GPP, a side link (SL) is supported for D2D (Device to Device) communication and V2V (Vehicle to Vehicle) communication (see Non-Patent Document 1 and Non-Patent Document 16). The SL is defined by the PC5 interface.

[0114] In order to support unicast and groupcast in addition to broadcast in SL communication, support for PC5-S signaling is being considered (see Non-Patent Document 27 (3GPP TS23.287)). For example, PC5-S signaling is implemented to establish a link for implementing SL, i.e., PC5 communication. The link is implemented in the V2X layer and is also called a Layer 2 link.

[0115] Furthermore, support for RRC signaling in SL communication is being considered (see Non-Patent Document 27 (3GPP TS23.287)). RRC signaling in SL communication is also referred to as PC5 RRC signaling. For example, it has been proposed to notify UE capabilities between UEs performing PC5 communication, or to notify AS layer settings for performing V2X communication using PC5 communication.

[0116] An example of a connection configuration of mobile terminals in SL communication is shown in Fig. 9. In the example shown in Fig. 9, UE 805 and UE 806 exist within the coverage 803 of base station 801. UL / DL communication 807 is performed between base station 801 and UE 805. UL / DL communication 808 is performed between base station 801 and UE 806. SL communication 810 is performed between UE 805 and UE 806. UE 811 and UE 812 exist outside the coverage 803. SL communication 814 is performed between UE 805 and UE 811. In addition, SL communication 816 is performed between UE 811 and UE 812.

[0117] As an example of communication between a UE and a NW via a relay in SL communication, a UE 805 shown in FIG. 9 relays communication between a UE 811 and a base station 801.

[0118] A configuration similar to that shown in FIG. 4 may be used for a UE that performs relaying. The relaying process in the UE will be described using FIG. 4. The relaying process by UE 805 in communication from UE 811 to base station 801 will be described. A radio signal from UE 811 is received by antennas 307-1 to 307-4. The received signal is converted from a radio reception frequency to a baseband signal by frequency conversion unit 306, and demodulated by demodulation unit 308. Weight calculation and multiplication processing may also be performed by demodulation unit 308. The demodulated data is passed to decoder unit 309, where decoding processing such as error correction is performed. The decoded data is passed to protocol processing unit 301, where protocol processing such as MAC and RLC used for communication with UE 811 is performed, such as removing headers in each protocol. Protocol processing such as RLC and MAC used for communication with base station 801 is also performed, such as adding headers in each protocol. Protocol processing of PDCP and SDAP may be performed in protocol processing unit 301 of UE 811. The protocol-processed data is passed to encoder unit 304, where encoding such as error correction is performed. Some data may be output directly from protocol processing unit 301 to modulation unit 305 without being encoded. The data encoded by encoder unit 304 is modulated by modulation unit 305. Precoding in MIMO may be performed by modulation unit 305. The modulated data is converted into a baseband signal, and then output to frequency conversion unit 306, where it is converted into a radio transmission frequency. Thereafter, a transmission signal is transmitted to base station 801 from antennas 307-1 to 307-4.

[0119] In the above, an example of relaying by UE 805 in communication from UE 811 to base station 801 has been shown, but similar processing is also used in relaying communication from base station 801 to UE 811.

[0120] 5G base stations can support integrated access and backhaul (IAB) (see Non-Patent Documents 2 and 20). A base station supporting IAB (hereinafter sometimes referred to as an IAB base station) is composed of an IAB donor CU, which is a CU of the base station operating as an IAB donor that provides IAB functions, an IAB donor DU, which is a DU of the base station operating as an IAB donor, and an IAB node connected to the IAB donor DU and to a UE via a radio interface. An F1 interface is provided between the IAB node and the IAB donor CU (see Non-Patent Document 2).

[0121] An example of IAB base station connections is shown in Figure 10. IAB donor CU 901 is connected to IAB donor DU 902. IAB node 903 is connected to IAB donor DU 902 using a wireless interface. IAB node 903 is connected to IAB node 904 using a wireless interface. In other words, IAB nodes may be connected in cascade. UE 905 is connected to IAB node 904 using a wireless interface. UE 906 may be connected to IAB node 903 using a wireless interface, and UE 907 may be connected to IAB donor DU 902 using a wireless interface. Multiple IAB donor DUs 902 may be connected to an IAB donor CU 901, multiple IAB nodes 903 may be connected to an IAB donor DU 902, and multiple IAB nodes 904 may be connected to an IAB node 903.

[0122] A BAP (Backhaul Adaptation Protocol) layer is provided in the connection between the IAB donor DU and the IAB node and in the connection between the IAB nodes (see Non-Patent Document 29). The BAP layer performs operations such as routing received data to the IAB donor DU and / or the IAB node, and mapping to an RLC channel (see Non-Patent Document 29).

[0123] As an example of the configuration of the IAB donor CU, a configuration similar to that of CU 215 is used.

[0124] An example of the configuration of the IAB donor DU is the same as that of the DU 216. The protocol processing unit of the IAB donor DU performs BAP layer processing, such as adding a BAP header to downstream data, routing to an IAB node, and removing the BAP header from upstream data.

[0125] As an example of the configuration of an IAB node, a configuration excluding the EPC communication unit 401, other base station communication unit 402, and 5GC communication unit 412 shown in Figure 5 may be used.

[0126] The transmission and reception processing at the IAB node will be described using FIGS. 5 and 10 . The transmission and reception processing at the IAB node 903 in communication between the IAB donor CU 901 and the UE 905 will be described. In uplink communication from the UE 905 to the IAB donor CU 901, a radio signal from the IAB node 904 is received by the antenna 408 (some or all of the antennas 408-1 to 408-4). The received signal is converted from a radio reception frequency to a baseband signal by the frequency conversion unit 407, and demodulated by the demodulation unit 409. The demodulated data is passed to the decoder unit 410, where decoding processing such as error correction is performed. The decoded data is passed to the protocol processing unit 403, where protocol processing such as MAC and RLC used for communication with the IAB node 904 is performed, such as removing headers in each protocol. In addition, routing to the IAB donor DU 902 is performed using a BAP header, and protocol processing such as RLC and MAC used for communication with the IAB donor DU 902, such as adding headers for each protocol, is performed. The protocol-processed data is passed to the encoder unit 405, where it is subjected to encoding processing such as error correction. Some data may be output directly from the protocol processing unit 403 to the modulation unit 406 without being encoded. The encoded data is modulated by the modulation unit 406. The modulation unit 406 may also perform precoding in MIMO. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 407, where it is converted into a radio transmission frequency. Then, a transmission signal is transmitted to the IAB donor DU 902 from antennas 408-1 to 408-4. Similar processing is performed in downlink communication from the IAB donor CU 901 to the UE 905.

[0127] The IAB node 904 also performs the same transmission and reception processing as the IAB node 903. The protocol processing unit 403 of the IAB node 903 performs BAP layer processing, such as adding a BAP header and routing to the IAB node 904 in upstream communication, and removing the BAP header in downstream communication.

[0128] In a 3GPP mobile communication system, a UE may be connected to multiple NWs. The connection between the UE and a data network (DN) may be established via an anchor UPF (a UPF directly connected to the DN). An anchor NW (a network having an anchor UPF; the same applies hereinafter) may be connected to one or more NWs connected to the UE. In this specification, a NW that does not have an anchor UPF is referred to as a non-anchor NW. Furthermore, a device constituting an anchor NW is referred to as an anchor NW device, and a device constituting a non-anchor NW is referred to as a non-anchor NW device.

[0129] Fig. 11 is a configuration diagram showing an example in which a UE is connected to multiple networks. In the example shown in Fig. 11, the UE is connected to each of NW1090 and NW1091. In the example shown in Fig. 11, 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, and 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 a DN.

[0130] The network to which the UE is connected may be switched. For example, the network used for transmission and reception between the UE and the DN may be switched from NW1090 to NW1091, or the network may be switched from NW1091 to NW1090, or the network may be switched to another network. This switching may be performed for part of the traffic. For example, when the UE performs communication related to application 1 via NW1090 and communication related to application 2 via NW1091, the path for communication related to application 2 may be switched to NW1090.

[0131] In this switching, the following problem occurs: The switching of the network may be performed before all data from the network connected before the switching has reached the UE, and the data may be lost.

[0132] In this embodiment, a method for solving the above-mentioned problems is disclosed. In the following description, the NW to which the UE is connected before the NW to which the UE is connected is switched may be referred to as the source NW, and the NW to which the UE is connected after the NW is switched may be referred to as the destination NW. In addition, the base station to which the UE is connected before the NW to which the UE is connected is switched may be referred to as the source base station, and the base station to which the UE is connected after the NW is switched may be referred to as the destination base station.

[0133] In this embodiment, a protocol stack is provided between the UE and each of the multiple NWs. The UE may have a protocol stack between each of the two NWs, for example. For example, the UE has both a protocol stack between the UE and the source NW and a protocol stack between the UE and the target NW. The UE may have both protocol stacks simultaneously.

[0134] The protocol stacks that the UE both have may be protocol stacks below the PDU (Protocol Data Unit) layer. For example, the IP address of the UE may be changed. The UE may have multiple IP addresses.

[0135] The anchor UPF may have both protocol stacks below the PDU layer. The IP address of the anchor UPF may be changed. The anchor UPF may have multiple IP addresses.

[0136] Fig. 12 is a diagram showing an example of a protocol stack between a UE and an anchor UPF. In the example shown in Fig. 12, the UE has multiple protocol stacks below the PDU layer. Fig. 12 shows an example of the configuration of a first protocol stack for the UE to connect to the NW 1090 shown in Fig. 11 and communicate with a DN, and a second protocol stack for the UE to connect to the NW 1091 shown in Fig. 11 and communicate with a DN.

[0137] Another example of the protocol stacks that the UE has may be a protocol stack below the SDAP layer. The anchor UPF may have multiple protocol stacks below GTP-U (GPRS (General Packet Radio Service) Tunneling Protocol for User Plane). This eliminates the need to change the IP address associated with network switching of the UE, for example.

[0138] Another example of the protocol stacks that both UEs have may be a protocol stack below the PDCP layer. The anchor UPF may have multiple protocol stacks below GTP-U. This makes it possible to avoid, for example, the complexity of associating QoS (Quality of Service) flows and data in both networks.

[0139] 13 is a diagram showing another example of a protocol stack between a UE and an anchor UPF. In the example shown in FIG. 13, the UE has multiple protocol stacks below the SDAP layer. The anchor UPF has multiple protocol stacks below the GTP-U layer.

[0140] As another example of the protocol stacks that the UE has, the protocol stack may be a PDCP layer or lower. The anchor UPF may have multiple protocol stacks lower than GTP-U. This can reduce memory usage in the UE, for example.

[0141] 14 is a diagram showing another example of a protocol stack between a UE and an anchor UPF. In the example shown in FIG. 14, the UE has multiple protocol stacks below the PDCP layer. The anchor UPF has multiple protocol stacks below the GTP-U layer.

[0142] As another example of the protocol stacks that the UE has, the protocol stack may be a protocol stack below the RLC layer. The anchor UPF may have multiple protocol stacks below GTP-U. This can reduce memory usage in the UE, for example.

[0143] 15 is a diagram illustrating another example of a protocol stack between a UE and an anchor UPF. In the example shown in FIG. 15, the UE has multiple protocol stacks below the RLC layer. The anchor UPF has multiple protocol stacks below the GTP-U layer.

[0144] For downlink data received from a DN via the anchor UPF, the UE may notify a base station of one of the networks of information regarding the sequence number (hereinafter sometimes referred to as PDCP SN (Sequence Number)) of the PDCP PDU received from a base station (gNB) of the other network. The one of the base stations may be a source base station, a destination base station, or both of the above. This makes it possible, for example, to share the PDCP SN received by the UE between base stations of different networks, thereby preventing data from being accumulated while waiting for reordering in the PDCP layer. The notification may be performed, for example, as a PDCP Status PDU. The notification may include information indicating that the data is downlink data.

[0145] For uplink data to be transmitted to a DN via an anchor UPF, a UE may notify a base station of one of the networks of information regarding the PDCP SN of the PDCP PDU transmitted to the base station of the other network. The one of the base stations may be a source base station, a destination base station, or both of the above. This allows, for example, the PDCP SN transmitted by the UE to be shared between base stations of different networks, thereby preventing data from being accumulated while waiting for reordering in the PDCP layer of the base station. The notification may be performed, for example, as a PDCP Status PDU. The information may include information indicating that the data is uplink data.

[0146] The NW may configure both protocol stacks for the UE. The NW that performs the configuration may be an anchor NW, a source NW, or a destination NW. The NF (Network Function) that performs the configuration may be an AMF or an SMF. The configuration may or may not be included in, for example, an instruction for NW switching. The instruction for NW switching may be, for example, an instruction to establish a PDU session, an instruction to change a PDU session, or an instruction to release a PDU session. In response to the instruction, the UE may maintain the protocol stack with the source NW, establish a protocol stack with the destination NW, or perform both of the above-mentioned operations.

[0147] The setting may include information about the network with which the UE faces, information about a protocol having multiple protocol stacks (e.g., PDU layer and below, SDAP and below, PDCP and below, RLC and below), information about the highest protocol in multiple protocol stacks (e.g., PDU layer, SDAP, PDCP, RLC), or information about the setting in each protocol (e.g., PDCP setting information).The UE may use the information to generate a protocol stack or perform settings in each protocol.

[0148] The NF of the NW may determine whether to perform NW switching while maintaining both protocols. The notification from the NW to the UE may include information indicating whether to perform NW switching while maintaining both protocols. The UE may use the information to perform NW switching while maintaining both protocols, or may not perform NW switching.

[0149] The NF of the NW may determine whether to perform NW switching while maintaining both protocols. The notification from the NW to the UE may include information indicating whether to perform NW switching while maintaining both protocols. The UE may use the information to perform NW switching while maintaining both protocols, or may not perform NW switching. This makes it possible to improve flexibility in a communication system, for example.

[0150] Information about the configuration of both protocol stacks may be provided in the UE. The information may be provided, for example, as UE capabilities. The UE may notify the information to an NF in the NW, for example, an AMF. For example, the AMF may notify the information to an SMF. The NF in the NW, for example, the AMF and / or the SMF, may use the information to instruct the UE to perform measurements. The measurements instructed to the UE may be RAN-related measurements, QoS (Quality of Service) monitoring (see Non-Patent Documents 10 and 31), or QoE (Quality of Experience) measurements (see Non-Patent Document 2).

[0151] As examples of such information, the following (1) to (6) are disclosed.

[0152] (1) Information about whether the UE can support both protocol stacks.

[0153] (2) Information indicating which protocols and protocol stacks the UE can have in both.

[0154] (3) Information about frequency bands that the UE can support.

[0155] (4) The amount of buffering the UE can support for both protocol stacks.

[0156] (5) Information regarding the destination network and / or the source network.

[0157] (6) A combination of the above (1) to (5).

[0158] The above (1) enables the NW to quickly determine whether or not settings for both protocol stacks are possible, for example.

[0159] The above (2) may be, for example, a PDU layer, an SDAP, a PDCP, or an RLC, which enables the network to quickly perform settings related to both protocol stacks.

[0160] According to the above (3), for example, the NF that determines the NW switching can quickly determine the switching destination NW.

[0161] The above-mentioned (4) may be, for example, the sum of the buffer amounts in both NWs, or the buffer amount in the source NW and / or destination NW. The above-mentioned (4) may be the buffer amount in the PDU layer, the buffer amount in SDAP, the buffer amount in PDCP, the buffer amount in RLC, the buffer amount in MAC, the buffer amount in HARQ, or a combination of two or more of the above. This enables, for example, an NF that determines NW switching to quickly determine the destination NW.

[0162] The above-mentioned (5) may be information indicating whether the information on the settings of both protocol stacks is information on the source network or information on the destination network, for example. This allows, for example, an NF that determines network switching to quickly determine the destination network.

[0163] The network may notify the UE of information regarding the configuration of a protocol stack in the network. This information may include, for example, information similar to the above-mentioned (1) to (6). For example, the information may include information in which the UE is replaced with the network in the above-mentioned (1) to (6). The UE may use this information to determine the network to camp on. This allows the UE to connect to a highly reliable network, for example.

[0164] The UE may establish protocol stacks with both NWs in response to an instruction for NW switching from the NF of the NW. The UE may respond to the instruction for NW switching to the NW in response to the establishment of protocol stacks with both NWs. The response from the UE may be sent to the NF of the anchor NW, the NF of the switching destination NW, or the NF of the switching source NW. The NF may be an SMF or an AMF. The NF of the NW that receives the response may notify the NF of the switching destination NW of information regarding the response from the UE. The notification may be sent via the SMF. The switching destination NW may start receiving uplink data from the UE or starting transmitting downlink data to the UE in response to the notification.

[0165] The source network may send a packet with an end marker attached to it to the UE. The end marker may be attached by the anchor UPF or by an intermediate UPF (a UPF that is not the anchor UPF) in the source network.

[0166] The UE may release the protocol stack between itself and the source network. The release may be triggered, for example, by the reception of an end marker packet, or by the reception of packets up to the end marker packet. The UE may notify the NF of the NW of information regarding the release. The notification from the UE may be made to the NF of the anchor network, the NF of the switching destination network, or the NF of the source network. The aforementioned NF may be an SMF or an AMF. The NF of the NW that receives the notification may notify the NF of the source network of information regarding the notification from the UE. The source network may release the protocol stack between itself and the UE in response to the notification.

[0167] The notification may be made in response to the instruction for NW switching. For example, the UE may make a response to the instruction for NW switching multiple times.

[0168] The UE may switch the destination of uplink data from the source network to the target network. The switching may be triggered, for example, by receiving a PDU session establishment request, by receiving a PDU session modification request, by transmitting a signaling acknowledgement of a PDU session establishment request, by transmitting a signaling acknowledgement of a PDU session modification request, or by establishing a protocol stack between both networks.

[0169] 16 and 17 are sequence diagrams showing an example of NW switching operation while maintaining the protocols of both NWs. FIG. 16 shows the first half of the sequence, and FIG. 17 shows the second half of the sequence. In the examples shown in FIGS. 16 and 17, the UE's connection destination is switched from NW1091, which is a non-anchor NW, to NW1090, which is an anchor NW. In the examples shown in FIGS. 16 and 17, an example is shown in which the anchor SMF detects QoS deterioration in NW1091, which is a non-anchor NW, and the anchor SMF makes a decision to switch NWs. In the examples shown in FIGS. 16 and 17, base station #1, AMF #1, UPF #1, SMF #1, PCF #1, UDM #1, and anchor UPF belong to NW1090, and base station #2, AMF #2, UPF #2, SMF #2, PCF #2, and UDM #2 belong to NW1091.

[0170] 16, data is transmitted and received between the UE and the DN via the NW 1091. Step ST1196 indicates data transmission and reception between the UE and the base station #2, step ST1197 between the base station #2 and the UPF #2, step ST1198 between the UPF #2 and the anchor UPF, and step ST1199 between the anchor UPF and the DN.

[0171] In step ST1203 shown in Fig. 16 , SMF#1 detects QoS deterioration. In the example shown in Fig. 16 , SMF#1 detects QoS deterioration for UPF#2. SMF#1 may detect the QoS deterioration by using the QoS monitoring report from the anchor UPF and the QoS monitoring report from UPF#2.

[0172] 16, SMF#1 determines to switch the network that serves as the data path. In the example shown in FIG. 16, SMF#1 determines to switch the data path passing through UPF#2 to NW1090.

[0173] In step ST1206 shown in Fig. 16 , SMF#1 may select whether to perform NW switching while maintaining both protocols. In the example shown in Fig. 16 , SMF#1 determines that the UE will perform NW switching while maintaining the protocol stacks with both NW1090 and NW1091.

[0174] In step ST1210 shown in Fig. 16 , SMF #1 instructs SMF #2 to switch networks. The instruction may use signaling of a PDU session release request or signaling of a PDU session modification request. The instruction may include information about the UE, information about the PDU session, information about the QoS flow, information about QoS deterioration, information about the UPF related to QoS deterioration, a network switching request, or information about the network after path switching.

[0175] The instruction in step ST1210 may include information indicating that the protocols of both networks are to be maintained, or may include information on the protocols to be maintained. The information on the protocols to be maintained may be, for example, the PDU layer or lower, the SDAP or lower, the PDCP or lower, or the RLC or lower.

[0176] 16, a procedure 1100 is performed to establish a connection with the UPF in the NW 1090. The procedure 1100 will be described below. FIG. 18 is a sequence diagram showing an example of the procedure 1100 in FIG.

[0177] In step ST1101 shown in Fig. 18, SMF#1 selects a UPF. In the example shown in Fig. 18, SMF#1 selects UPF#1 and determines to use UPF#1.

[0178] In step ST1102 shown in FIG. 18 , a procedure for establishing a session management policy association is performed between SMF#1 and PCF#1. This procedure may be, for example, the procedure disclosed in clause 4.16.4 of non-patent document 31 (3GPP TS23.502). In step ST1102, a procedure for changing the session management policy association may be performed. The procedure for changing the session management policy association may be, for example, the procedure disclosed in clause 4.16.5 of non-patent document 31 (3GPP TS23.502).

[0179] In step ST1104 shown in FIG. 18 , SMF#1 requests the anchor UPF to establish an N4 session. The anchor UPF takes step ST1104 as an opportunity to establish the N4 session. In step ST1104, a request for changing the N4 session may be made. The anchor UPF may take step ST1104 as an opportunity to establish an N4 session or to change the N4 session. In step ST1105, the anchor UPF responds to step ST1104 to SMF#1.

[0180] In step ST1107 shown in Fig. 18, SMF#1 requests UPF#1 to establish an N4 session. Step ST1107 triggers UPF#1 to establish an N4 session. In step ST1108, UPF#1 responds to step ST1107 to SMF#1. In steps ST1107 and ST1108, a request to change the N4 session and a response may be made.

[0181] Returning to the description of Fig. 16 , in procedure 1111 shown in Fig. 16 , a PDU session is established in the NW 1090. A PDU session change may also be performed in the NW 1090. Procedure 1111 will be described below. Fig. 19 is a sequence diagram showing an example of procedure 1111 in Fig. 16 .

[0182] In steps ST1113 and ST1114 shown in FIG. 19 , information necessary for establishing a PDU session for the UE is transmitted and received between SMF#1 and AMF#1. Information necessary for modifying a PDU session may also be transmitted and received. In step ST1113, an instruction to establish a PDU session may be sent from SMF#1 to AMF#1, or an instruction to modify a PDU session may be sent. The instruction may include the above-mentioned information. The information may include information about the UE, information about the PDU session, information about the QoS flow, or information about the UPF. The information may include information indicating that the UE will maintain the protocols of both networks.

[0183] In step ST1116 shown in FIG. 19 , AMF #1 notifies base station #1 of a PDU session establishment request to the UE. The notification may be a PDU session modification request. The notification may include information indicating that the UE will maintain the protocols of both networks. In step ST1117, base station #1 notifies the UE of a PDU session establishment request. The notification may be a PDU session modification request. RRC signaling, for example, RRC establishment signaling or RRC reconfiguration signaling may be used in step ST1117. The notification in step ST1117 may include information indicating that the UE will maintain the protocols of both networks. The UE may perform a PDU session establishment process, a PDU session modification process, or maintain the protocol with NW 1091, using the content of the notification in step ST1117.

[0184] In step ST1118 shown in Fig. 19 , the UE sends a response to step ST1117 to the base station #1. For the response, RRC signaling, for example, signaling indicating RRC establishment completion or signaling indicating RRC reconfiguration completion may be used. In step ST1119, the base station #1 sends a response to step ST1116 to the AMF #1. The response in step ST1119 may include N2 session management information.

[0185] In step ST1121 shown in FIG. 19 , AMF#1 notifies SMF#1 of the N2 session management information from base station#1. This notification may be performed, for example, using signaling of Nsmf_PDUSession_UpdateSMContext Request (see Non-Patent Document 31). In step ST1122, SMF#1 responds to step ST1121 to AMF#1. This response may be performed, for example, using signaling of Nsmf_PDUSession_UpdateSMContext Response (see Non-Patent Document 31).

[0186] In step ST1124 shown in FIG. 19 , SMF#1 requests the anchor UPF to modify the N4 session. The request may include, for example, QoS monitoring configuration. The anchor UPF may start QoS monitoring using the configuration. In step ST1125, the anchor UPF sends a response to step ST1124 to SMF#1.

[0187] In step ST1128 shown in FIG. 19 , SMF#1 requests UPF#1 to modify an N4 session. The request may include, for example, QoS monitoring settings. UPF#1 may start QoS monitoring using the settings. In step ST1129, UPF#1 responds to step ST1128 to SMF#1.

[0188] Returning to the description of Fig. 16 , in procedure 1120 shown in Fig. 16 , a PDU session is released in NW 1091. A PDU session change may also be performed in NW 1091. Procedure 1120 will be described below. Fig. 20 is a sequence diagram showing an example of procedure 1120 in Fig. 16 .

[0189] In step ST1156 shown in FIG. 20 , SMF#2 requests UPF#2 to release the N4 session. This information may include information indicating that the UE will maintain both protocols. Instead of this request, a notice of the N4 session release may be sent. Step ST1156 triggers UPF#2 to release the N4 session. UPF#2 may also prepare for the N4 session release. In step ST1157, UPF#2 responds to step ST1156 to SMF#2.

[0190] In steps ST1163 and ST1164 shown in FIG. 20 , information required for releasing the PDU session of the UE is transmitted and received between SMF#2 and AMF#2. Information required for modifying the PDU session may also be transmitted and received. In step ST1163, an instruction to release the PDU session may be issued from SMF#2 to AMF#2, or an instruction to modify the PDU session may be issued. The instruction may include the above-mentioned information. The information may include information about the UE, information about the PDU session, information about the QoS flow, or information about the UPF. The information may include information indicating that the UE will maintain the protocols of both networks.

[0191] In step ST1166 shown in FIG. 20 , AMF#2 notifies base station#2 of a PDU session release request to the UE. The notification may be a PDU session modification request. The notification may include information indicating that the UE will maintain the protocols of both networks. In step ST1167, base station#2 notifies the UE of a PDU session release request. The notification may be a PDU session modification request. RRC signaling, for example, RRC release signaling or RRC reconfiguration signaling may be used in step ST1167. The notification in step ST1167 may include information indicating that the UE will maintain the protocols of both networks. The UE may perform a PDU session release process, a PDU session modification process, or maintain the protocol with NW 1091, using the content of the notification in step ST1167.

[0192] In step ST1168 shown in Fig. 20 , the UE sends a response to step ST1167 to the base station #2. The response may use RRC signaling, for example, signaling indicating completion of RRC reconfiguration. In step ST1169, the base station #2 sends a response to step ST1166 to the AMF #2. The response in step ST1169 may include N2 session management information.

[0193] In step ST1172 shown in FIG. 20 , AMF#2 notifies SMF#2 of the N2 session management information from base station#2. This notification may be performed, for example, using signaling of Nsmf_PDUSession_UpdateSMContext Request (see Non-Patent Document 31). In step ST1174, SMF#2 responds to step ST1172 to AMF#2. This response may be performed, for example, using signaling of Nsmf_PDUSession_UpdateSMContext Response (see Non-Patent Document 31).

[0194] In step ST1178 shown in FIG. 19 , the SMF#2 requests the UPF#2 to modify the N4 session. The request may include, for example, QoS monitoring configuration. In step ST1179, the UPF#2 responds to the request in step ST1178 to the SMF#2.

[0195] Returning to the description of Fig. 16 , in step ST1225, SMF #2 notifies SMF #1 of a response to the NW switching instruction. For this notification, signaling of a PDU session release request response or signaling of a PDU session modification response may be used. Triggered by this signaling, SMF #1 recognizes that NW switching configuration has been performed in SMF #2.

[0196] In step ST1227 shown in FIG. 16, the UE notifies the base station #1 of an acknowledgment to the PDU session establishment request. An acknowledgment to the PDU session modification request may also be notified. The notification may be triggered by the completion of the PDU session establishment and / or modification.

[0197] 16, the PDU session establishment in the NW 1090 is continued. The PDU session change in the NW 1090 may also be continued. The procedure 1130 will be described below. FIG. 21 is a sequence diagram showing an example of the procedure 1130 in FIG. 16.

[0198] 21, the base station #1 notifies the AMF #1 of information related to the acknowledgment in step ST1227. The notification in step ST1132 may include N2 session management information.

[0199] In steps ST1133 and ST1134 shown in FIG. 21, the same processes as those in steps ST1121 and ST1122 shown in FIG. 19 are performed.

[0200] In steps ST1136 and ST1137 shown in FIG. 21, the same processes as those in steps ST1124 and ST1125 shown in FIG. 19 are performed.

[0201] In steps ST1138 and ST1139 shown in FIG. 21, the same processes as those in steps ST1128 and ST1129 shown in FIG. 19 are performed.

[0202] In Step ST1140 shown in Fig. 21 , a procedure for changing a session management policy association is performed between the SMF #1 and the PCF #1. This procedure may be, for example, the procedure disclosed in Section 4.16.5 of Non-Patent Document 31 (3GPP TS23.502).

[0203] Steps ST1230 to ST1233 shown in Fig. 17 are transmission of uplink data from the UE via UPF #1. Step ST1230 indicates transmission of uplink data from the UE to base station #1, step ST1231 indicates transmission of uplink data from base station #1 to UPF #1, step ST1232 indicates transmission of uplink data from UPF #1 to the anchor UPF, and step ST1233 indicates transmission of uplink data from the anchor UPF to the DN.

[0204] In step ST1240 shown in FIG. 17 , SMF#1 instructs the anchor UPF to add an end marker. For example, the instruction may be sent using signaling of an N4 session modification request. For example, the request may include an instruction to add an end marker. Step ST1240 may be performed, for example, in response to reception of step ST1225 or in response to completion of procedure 1130. In step ST1242, the anchor UPF notifies SMF#1 of a response to the instruction. For example, signaling of an N4 session modification response may be used for the notification.

[0205] Steps ST1245 to ST1248 shown in FIG. 17 are for transmitting downlink data from the DN to the UE via UPF #2. Step ST1245 indicates transmission of downlink data from the DN to the anchor UPF, step ST1246 indicates transmission of downlink data from the anchor UPF to UPF #2, step ST1247 indicates transmission of downlink data from UPF #2 to base station #2, and step ST1248 indicates transmission of downlink data from base station #2 to the UE. In step ST1246, the anchor UPF may attach an end marker to the downlink data from the DN and transmit it to UPF #2. The anchor UPF may also forward downlink data received from the DN after the packet with the end marker to UPF #1. This operation of the anchor UPF may be triggered by the transmission of step ST1242.

[0206] In step ST1251 shown in FIG. 17, the UE may notify base station #2 that it has received a packet with an end marker. This notification may be a notification indicating that packets up to the packet with the end marker have been received normally. This notification may include information regarding the release of the protocol stack. The UE may perform the notification of step ST1251 upon receiving step ST1248.

[0207] In procedure 1255 shown in Fig. 17, a PDU session is released in NW 1091. A PDU session change may be performed in NW 1091. Procedure 1255 will be described below. Fig. 22 is a sequence diagram showing an example of procedure 1255 in Fig. 17.

[0208] 22 , the base station #2 notifies the AMF #2 of information indicating that the UE has received a packet with an end marker. The notification in step ST1142 may include N2 session management information.

[0209] In steps ST1143 and ST1144 shown in FIG. 22, the same processes as those in steps ST1121 and ST1122 in FIG. 19 are performed.

[0210] In steps ST1145 and ST1146 shown in Figure 22, AMF#2 notifies SMF#2 of session management information, and SMF#2 responds to the notification to AMF#2. The notification may include information related to PDU session release.

[0211] In step ST1148 shown in FIG. 22 , SMF#2 requests UPF#2 to release the N4 session. Taking step ST1148 as a trigger, UPF#2 releases the N4 session. In step ST1149, UPF#2 responds to step ST1148 to SMF#2.

[0212] In Step ST1150 shown in Fig. 22, a procedure for terminating a session management policy association is performed between the SMF#2 and the PCF#2. This procedure may be, for example, the procedure disclosed in Section 4.16.6 of Non-Patent Document 31 (3GPP TS23.502).

[0213] Returning to the description of Fig. 17, in step ST1260, base station #2 notifies SMF #1 of the completion of PDU session release.

[0214] In step ST1262 shown in FIG. 17 , SMF#1 requests the anchor UPF to release the connection with UPF#2. This request may be made using N4 session modification request signaling. The anchor UPF releases the connection with UPF#2 in response to this signaling. In step ST1264, the anchor UPF responds to step ST1262 to SMF#1.

[0215] 17, data is transmitted and received between the UE and the DN via the NW 1090. Step ST1266 indicates data transmission and reception between the UE and the base station #1, step ST1267 between the base station #1 and the UPF #1, step ST1268 between the UPF #1 and the anchor UPF, and step ST1269 between the anchor UPF and the DN.

[0216] A period related to the release of the source network may be provided. For example, a timer related to the release may be provided. The timer may be provided in, for example, a UE. For example, the timer may be started in response to a PDU session release request (e.g., step ST1167 shown in FIG. 20 ) or may be stopped in response to reception of a packet with an end marker. For example, the UE may perform a release operation from the source network in response to expiration of the timer. This makes it possible to release the network even in the case where, for example, a packet with an end marker is not received, thereby preventing malfunctions in the communication system.

[0217] The UE may initiate network switching while the UE has protocol stacks for each of the multiple networks. The UE may request a network to switch its connection destination. The request may be made to the AMF. The AMF may forward the request to the SMF. The network may be an anchor network, a non-anchor network, a source network, or a destination network. The network switching process on the network side may use a method similar to the method disclosed above.

[0218] The NW switching disclosed in the first embodiment may be used in switching to a new NW. A registration operation of the UE to the new NW may be performed, or a PDU session may be established in the new NW. For the registration operation, for example, the method disclosed in Section 4.2.2.2.2 in Non-Patent Document 31 may be used. For the establishment of the PDU session, for example, the method disclosed in Section 4.3.2.2.1 in Non-Patent Document 31 may be used. This, for example, can improve the flexibility of the communication system.

[0219] According to the first embodiment, it is possible to prevent packet loss due to NW switching.

[0220] Second Embodiment Traffic may be split. For example, some packets of the same data traffic may go through one network, and other packets may go through another network. In the traffic split, one PDU session may be split, or multiple PDU sessions may be established.

[0221] When configuring traffic branching, the method disclosed in the first embodiment may be applied as appropriate. The same PDU session may be established and / or changed for multiple networks. For example, when one PDU session branches, the above-described method may be used.

[0222] As another example, information associating multiple PDU sessions with each other may be notified. The information may be included in PDU session establishment and / or PDU session modification signaling. For example, the above method may be used in setting up traffic branching using multiple PDU sessions.

[0223] In uplink transmission from a UE, when determining which base station of a network to which the UE is connected should transmit data, the determination may be made using the buffer amounts of the PDCP layer and the RLC layer. For example, when the buffer amount is equal to or greater than a predetermined threshold, the UE may transmit data to the primary RLC or the secondary RLC. When the buffer amount is less than the predetermined threshold, the UE may transmit data to the primary RLC.

[0224] The primary RLC may be, for example, an RLC layer opposite to the RLC layer of the anchor base station (the base station of the anchor network). As another example, it may be separately determined which base station's RLC layer the primary RLC is opposite to. This determination may be made, for example, by the NF of the anchor network. The NF may be an SMF, an AMF, or a base station.

[0225] When the above-mentioned traffic branching is performed, the following problem occurs: Even if the traffic is the same, packets are sent to different base stations, and the SNs of the PDCP PDUs received by each base station become discontinuous. As a result, the PDCP layer of each base station cannot complete reordering, and the received data from the UE cannot be transferred to a higher layer.

[0226] In this embodiment, a method for solving the above-mentioned problems is disclosed.

[0227] In this embodiment, the UE may notify a base station of information regarding the PDCP SN of the PDCP PDU to be transmitted. The base station may be a source base station, a target base station, or both. The notification may be performed, for example, as a PDCP Status PDU. As another example, the notification may be performed using RRC signaling, an RLC Status PDU, MAC signaling, or L1 / L2 signaling.

[0228] As another example, a base station of one NW to which a UE is connected may notify a base station of the other NW of information about the PDCP SN received from the UE. The notification may include information about the NW to which the base station belongs, information about the identification of the base station, or information about the PDCP entity of the base station. This allows, for example, the other base station to quickly identify the base station that sent the notification. The notification may be performed, for example, using an inter-base station interface, via an AMF, or via an SMF. This may reduce, for example, the amount of processing in the UE.

[0229] The notification may include information about the other NW, information about the identification of the base station of the other NW, or information about the PDCP entity of the base station of the other NW. This allows, for example, the base station of the other NW to quickly understand that the notification is addressed to its own base station.

[0230] The notification may include information about the PDU session or information about the QoS flow, which allows, for example, the other base station to quickly understand the traffic.

[0231] As another example, the notification may be performed between base stations. For example, the notification may be performed via AMF, SMF, SEPP, or any of the above methods. The notification may be performed directly between base stations. For example, the base station may inquire about information about the corresponding base station from a Domain Name System (DNS). The DNS may notify the base station of the information about the corresponding base station. This may, for example, reduce the amount of processing in the UE.

[0232] Another solution is disclosed. The application layer may route the destination network. This allows, for example, improved flexibility in routing.

[0233] A protocol stack may be provided that branches below the PDU layer. A UE may have multiple PDU layers. For example, a UE may have multiple IP addresses or multiple MAC addresses. The protocol stack may have a configuration similar to the protocol stack disclosed in FIG. 12.

[0234] Another solution will be disclosed: The PDU layer of the UE may route the destination network.

[0235] A protocol stack may be provided that branches below the SDAP layer. A UE may have multiple SDAP layers. The protocol stack may have a configuration similar to the protocol stack disclosed in Figure 13. This may, for example, eliminate the need for the UE to have multiple IP addresses, thereby reducing the complexity of the UE compared to the previous case.

[0236] The PDU layer of the UE may perform routing based on, for example, the amount of buffer stored in its own PDU layer. For example, when the buffer amount is greater than or equal to a predetermined threshold, the UE may transmit data to either of the two networks. When the buffer amount is less than or equal to the predetermined threshold, the UE may transmit data to one of the networks. In the above case, the network to which uplink data is transmitted may be referred to as the main network. As another example, when the buffer amount is greater than or equal to a predetermined threshold, the UE may transmit data to either of the two networks. When the buffer amount is less than or equal to the predetermined threshold, the UE may transmit data to the other network.

[0237] The one of the networks may be an anchor network or a non-anchor network, which can improve flexibility in communication, for example.

[0238] The buffer amount may include the buffer amount of a lower layer. For example, it may include the buffer amount of the SDAP layer, the buffer amount of the PDCP layer, the buffer amount of the RLC layer, the buffer amount of the MAC layer or lower, the buffer amount of the PHY layer, or the above-mentioned multiple buffer amounts. This enables routing that takes into account the overall buffer amount of the UE, for example.

[0239] For the routing described above, the buffer amount for each PDU session or the buffer amount for each QoS flow may be used, which enables flexible routing for each traffic, for example.

[0240] A lower layer of the UE may notify the PDU layer of the buffer amount of the lower layer. The lower layer may be SDAP, PDCP, the RLC layer, or the MAC layer. The buffer amount may be the buffer amount per PDU session or per QoS flow. This allows, for example, the PDU layer to quickly grasp the buffer amount of the lower layer.

[0241] As another example, QoS may be used for routing. For example, a UE may transmit data to a network with good QoS. This makes it possible to ensure QoS for uplink communication, for example.

[0242] The UE may perform QoS monitoring. The UE may perform the routing using the results of the QoS monitoring. The QoS monitored by the UE may include, for example, information about uplink and / or downlink packet delay, information about congestion, data rate, packet delay variance, information about round-trip packet delay, and information about uplink delay at the UE (e.g., the difference between the time when uplink data should be sent and the time when it is actually sent).

[0243] A threshold may be used for routing using QoS. For example, if the QoS in one NW is better than or equal to a predetermined threshold, the NW may be continued to be used, or if the QoS is worse than or equal to the predetermined threshold, data may be transmitted to another NW. The one NW may be an anchor NW or a non-anchor NW. This makes it possible to ensure QoS in uplink transmission. Hysteresis may be provided to the threshold. This makes it possible to prevent, for example, frequent switching of the destination NW for uplink data.

[0244] Routing using QoS flows may be performed for each QoS flow. For example, a QoS flow requiring latency may be routed through a network with low latency, and a QoS flow requiring reliability may be routed through a network with high reliability. This makes it possible to ensure QoS for each QoS flow, for example.

[0245] The threshold value may be determined by the PCF. For example, the PCF of the anchor network (hereinafter, sometimes referred to as the anchor PCF) may determine the threshold value. The anchor PCF may notify the anchor SMF of the threshold value. The anchor SMF may notify the UE of the threshold value. The notification from the anchor SMF may be performed via the anchor AMF or the anchor base station.

[0246] As another example, the threshold may be determined by the SMF. For example, the anchor SMF may determine the threshold. The anchor SMF may determine the threshold using a policy notified by the anchor PCF. The anchor SMF may notify the UE of the threshold. The notification from the anchor SMF to the UE may be performed in the same manner as described above.

[0247] As another example, the threshold may be determined by an AMF, for example, an anchor AMF, or by a base station, for example, an anchor base station. The AMF and / or the base station may notify the threshold to the UE.

[0248] As another example, the threshold may be determined by a Network Data Analytics Function (NWDAF). This allows flexible threshold determination based on, for example, the status of the network. The NWDAF may notify the threshold to the UE. The notification may be performed via the AMF, via the base station, or directly to the UE.

[0249] The method of determining which NW is which NW may be the same as the threshold value described above.

[0250] Another solution will be disclosed: The SDAP layer of the UE may route the destination network.

[0251] A protocol stack branching below the PDCP layer may be provided. The UE may have multiple PDCP layers. The protocol stack may have a configuration similar to that of the protocol stack disclosed in FIG. 14. This reduces the complexity of the UE by having a PDCP layer facing each base station of each network, and reduces the amount of processing by the UE by using a single SDAP layer.

[0252] The SDAP layer of the UE may perform routing based on, for example, the amount of buffer data stored in its own SDAP layer. For example, if the buffer data amount is greater than or equal to a predetermined threshold, the UE may transmit data to either of the two NWs. If the buffer data amount is less than or equal to the predetermined threshold, the UE may transmit data to one of the NWs. As another example, if the buffer data amount is greater than or equal to a predetermined threshold, the UE may transmit data to either of the two NWs. If the buffer data amount is less than or equal to the predetermined threshold, the UE may transmit data to the other NW.

[0253] The one of the networks may be an anchor network or a non-anchor network, which can improve flexibility in communication, for example.

[0254] The buffer amount may include the buffer amount of a lower layer. For example, it may include the buffer amount of the PDCP layer, the buffer amount of the RLC layer, the buffer amount of the MAC layer or lower, the buffer amount of the PHY layer, or the above-mentioned multiple buffer amounts. This enables routing that takes into account the entire buffer amount of the UE, for example.

[0255] For the routing described above, the buffer amount for each PDU session or the buffer amount for each QoS flow may be used, which enables flexible routing for each traffic, for example.

[0256] A lower layer of the UE may notify the SDAP layer of the buffer volume of the lower layer. The lower layer may be the PDCP layer, the RLC layer, or the MAC layer. The buffer volume may be the buffer volume per PDU session or per QoS flow. This allows, for example, the SDAP layer to quickly grasp the buffer volume of the lower layer.

[0257] As another example, QoS may be used for routing. For routing using QoS, a method similar to the method disclosed in the routing by the PDU layer described above may be used. The same may also be used for thresholds. The same may also be used for a method for determining which NW is one of the NWs.

[0258] A primary NW or a secondary NW may be provided. For example, when the buffer amount disclosed in this embodiment is equal to or greater than a predetermined threshold, the UE may transmit data to the primary NW or the secondary NW. When the buffer amount is less than the predetermined threshold, the UE may transmit data to the primary NW.

[0259] The primary NW may be, for example, an anchor NW. The secondary NW may be, for example, a non-anchor NW.

[0260] As another example, which NW is the primary NW may be determined and notified to the UE. The determination may be made, for example, by the anchor NW. The anchor NW may notify the UE of information indicating which NW is the primary NW. The notification may be made, for example, together with the notification of the above-mentioned threshold.

[0261] Regardless of the buffer amount, data may be transmitted from the UE to either NW. For example, by setting the above-mentioned threshold value to 0 or a negative value, the UE may be allowed to transmit data to either NW. This, for example, can improve the flexibility of the communication system.

[0262] According to the second embodiment, reordering in the base station is completed, and data received from the UE can be quickly transferred to a higher layer.

[0263] Variation 1 of Embodiment 2. Routing of uplink data in a UE may be triggered by an instruction from a network. The instruction may be triggered, for example, by a failure and / or congestion in one network, or by a failure and / or congestion in the other network.

[0264] The instruction from the NW may be issued when the QoS satisfies a predetermined condition. QoS monitoring may be performed in the NW. The predetermined condition may be that the result of the QoS monitoring is better than, worse than, and / or equal to the predetermined threshold.

[0265] The QoS monitoring may be performed by the UPF or the base station. The QoS monitored by the UPF and / or the base station may include, for example, information about uplink and / or downlink packet delay, congestion, data rate, packet delay variance, and round-trip packet delay.

[0266] The threshold value for QoS monitoring may be determined, for example, in the application layer or by a PCF of one of the networks. The other network may be, for example, an anchor network, a non-anchor network, or a network to which an NF performing QoS monitoring belongs.

[0267] The instruction regarding routing may be given by an NF of one of the networks. The one of the networks may be, for example, an anchor network, a non-anchor network, a network that has detected a failure and / or congestion, or a network that has not detected a failure and / or congestion.

[0268] The NF may be, for example, an SMF. The SMF may issue the instruction to the UE. The instruction from the SMF to the UE may be issued via an AMF or via a base station. As another example, the SMF may issue the instruction to the base station. The instruction from the SMF to the base station may be issued via an AMF.

[0269] The base station may notify the UE of information related to routing. For example, RRC signaling may be used for the notification. This allows, for example, the base station to notify the UE of a large amount of information. As another example, MAC signaling may be used for the notification. This allows, for example, the base station to notify the information quickly. As another example, L1 / L2 signaling may be used for the notification. This allows, for example, the base station to notify the information even more quickly. The UE may use the information to switch the main NW.

[0270] As another example of the NF, the NF may be an AMF. The AMF may issue the instruction to the UE. The instruction from the AMF to the UE may be issued via a base station. As another example, the SMF may issue the instruction to the base station. Notification of routing information from the base station to the UE may be performed in the same manner as described above. The UE may use the information to switch the main NW.

[0271] The instruction may include information regarding the switching of the main NW, or may include information regarding the threshold disclosed in the second embodiment. The information regarding the switching of the main NW may include, for example, information indicating that the main NW will be switched. This makes it possible to reduce the size of signaling, for example. As another example, the information may include information regarding the post-switching NW. This makes it possible for the UE to quickly grasp the post-switching NW, for example.

[0272] The information may include information about traffic related to switching of the main NW. For example, information about PDU sessions or information about QoS flows may be included.

[0273] This first modification enables rapid route switching when traffic branches off into the network, thereby enabling rapid communication between the UE and the DN.

[0274] Modification 2 of the Second Embodiment Routing may be performed in the C plane data.

[0275] For example, the method disclosed in the second embodiment or the method disclosed in the first modification of the second embodiment may be used for the routing. For example, the buffer amount of the NAS layer may be used instead of the PDU layer disclosed in the second embodiment, or the buffer amount of the RRC layer may be used instead of the SDAP layer.

[0276] As in the second embodiment, the buffer amount of the lower layer may be used. For example, the RRC layer may notify the NAS layer of the buffer amount of the lower layer. The notification may be made by the PDCP layer, the RLC layer, the MAC layer, or the PHY layer. As another example, the PDCP layer may notify the RLC layer of the buffer amount of the lower layer. The notification may be made by the MAC layer or the PHY layer.

[0277] The same threshold value may be used between the U-plane data and the C-plane data, or different threshold values ​​may be used. The routing destination network when the U-plane data and the C-plane data are equal to or less than the threshold value may be the same or different. The primary network may be the same or different between the U-plane data and the C-plane data.

[0278] The NF of the routing destination network may forward the C-plane data transmitted from the UE to the NF of another network. The NF may be, for example, a base station, an AMF, an SMF, or an NWDAF.

[0279] According to the present modification 2, even if a failure, congestion, etc. occurs in one of the networks, it becomes possible to transmit C-plane data to that network.

[0280] Embodiment 3. A network serving as a data path may be switched. For example, in data transmission and reception via a source network, the path of the data transmission and reception may be switched to a destination network when a failure and / or congestion occurs in an NF (e.g., a UPF) of the source network. The source network may be an anchor network or a non-anchor network. The destination network may be a non-anchor network or an anchor network.

[0281] Traffic branching (hereinafter sometimes referred to as network branching) may be performed. For example, some packets of the same data traffic may go through one network, and other packets may go through another network. In traffic branching, one PDU session may branch, or multiple PDU sessions may be established.

[0282] However, when switching between networks, there is a problem that it takes time to complete the switching.

[0283] Furthermore, in network branching, resources related to the traffic need to be reserved in both the anchor network and the NF (e.g., UPF) of the non-anchor network, which creates the problem that the resources reserved in the network through which data does not pass are wasted.

[0284] In the third embodiment, a method for solving the above-mentioned problems will be disclosed.

[0285] In this embodiment, when switching between networks, switching is configured in advance in each NF of the network that is the switching destination (hereinafter, this may be referred to as pre-configuration). When actually performing network switching, switching is configured for the UE. The configuration of network switching for the base station may also be performed when actually configuring network switching. The actual network switching may be triggered by the satisfaction of predetermined conditions.

[0286] The predetermined condition may be, for example, a condition related to QoS or a condition related to QoE. An example of the predetermined condition may be that the QoS (e.g., latency) of a certain traffic is worse than a predetermined threshold. QoS monitoring reports (see Non-Patent Documents 10 and 31) or results of QoE measurements (see Non-Patent Document 2) may be used to detect the predetermined condition.

[0287] The switching of the NW serving as a data path may be initiated, for example, by an NF of the anchor NW. The NF may be, for example, an SMF. The switching of the NW may be, for example, switching from a non-anchor NW to an anchor NW.

[0288] The anchor SMF may notify the non-anchor NW of information regarding NW switching. The notification may be made to the non-anchor SMF, for example. The notification may be made, for example, as a request for PDU session modification or a request for PDU session release. For the notification, for example, Nsmf_PDUSession_Modification_Request signaling (see Non-Patent Document 31) or Nsmf_PDUSession_Release_Request signaling (see Non-Patent Document 31) may be used. The notification may include information indicating that NW switching is performed using pre-configuration, information about the UE, information about the PDU session, or information about the QoS flow. The non-anchor NW may maintain a connection with the UE in its own NW when the information indicating that NW switching is performed using pre-configuration is included in the notification.

[0289] The non-anchor SMF may request information related to NW switching pre-configuration from the non-anchor AMF. The request may include a request for NAS signaling information for the UE. The NAS signaling may be, for example, NAS configuration information related to PDU session modification (e.g., NAS configuration to be released). The non-anchor AMF may notify the non-anchor SMF of the NAS signaling information. The notification from the non-anchor AMF to the non-anchor SMF may be triggered by the request from the non-anchor SMF to the non-anchor AMF.

[0290] The NAS signaling may include information regarding RRC signaling for the UE. The RRC signaling may be, for example, RRC configuration information related to PDU session modification (e.g., AS configuration to be released). The non-anchor AMF may request RRC signaling information from a base station of a non-anchor NW (hereinafter, may be referred to as a non-anchor base station). The non-anchor base station may notify the non-anchor AMF of the RRC signaling information. The notification from the non-anchor base station to the non-anchor AMF may be triggered by the request from the non-anchor AMF to the non-anchor base station.

[0291] The non-anchor SMF may respond to the NW switching request to the anchor SMF. The response may be, for example, a response to a PDU session modification request or a response to a PDU session release request. For example, the response may use signaling of Nsmf_PDUSession_Modification_Response (see Non-Patent Document 31) or signaling of Nsmf_PDUSession_Release_Response (see Non-Patent Document 31). The response may include, for example, information on NAS signaling. The NAS signaling may be, for example, the above-mentioned NAS signaling related to PDU session modification. The NAS signaling may be, for example, NAS signaling acquired from the non-anchor AMF. The NAS signaling may include RRC signaling. The RRC signaling may be, for example, the above-mentioned RRC signaling related to PDU session release. The RRC signaling may be, for example, RRC signaling obtained from a non-anchor base station.

[0292] The anchor SMF may perform pre-configuration in the anchor NW, for example, UPF configuration. The UPF performing the configuration may be, for example, an intermediate UPF in the anchor NW or the anchor UPF. In the UPF configuration, for example, some or all of the processes disclosed in PDU session establishment (Section 4.3.2 of Non-Patent Document 31) may be performed.

[0293] The anchor SMF may configure the anchor UPF regarding network switching. For example, the anchor SMF may configure the anchor UPF in advance to release a connection with an intermediate UPF of a non-anchor network. The anchor UPF may prepare to release a connection with the intermediate UPF based on the configuration.

[0294] The anchor SMF may pre-configure the anchor AMF for PDU session modification. The pre-configuration may include NAS signaling information of the source network (e.g., non-anchor network) or RRC signaling information of the source network (e.g., non-anchor network). The anchor AMF may request the anchor base station to perform pre-RRC configuration related to network switching, or may not request this. The anchor AMF may notify the anchor base station of the RRC signaling information of the source network (e.g., non-anchor network). The notification may be included in the above-mentioned request, for example.

[0295] The anchor SMF may initiate NW switching when the predetermined conditions are met.

[0296] The anchor SMF may notify the anchor AMF that the predetermined condition is satisfied. The notification from the anchor SMF to the anchor AMF may be triggered, for example, by the satisfaction of the predetermined condition, or by the response from the non-anchor SMF to the anchor SMF.

[0297] The anchor AMF may configure resources for the UE based on the notification. The anchor AMF may request the anchor base station to establish a PDU session for the UE, or may request a PDU session change. The request may include NAS signaling and / or RRC signaling related to the PDU session change of the non-anchor NW, or may include NAS signaling related to pre-configuration of the PDU session change of the anchor NW. The anchor base station may request the UE to establish a PDU session or may request a PDU session change based on the request. RRC signaling may be used for the request. The RRC signaling may include NAS signaling and / or RRC signaling related to the PDU session change of the non-anchor NW, or may include NAS signaling and / or RRC signaling related to pre-configuration of the PDU session change of the anchor NW. The UE may establish a PDU session or modify the PDU session based on the RRC signaling. The UE may send a response to the PDU session establishment or modification request to the anchor base station. The anchor base station may notify the anchor AMF of the response from the UE.

[0298] The anchor AMF may notify the anchor SMF of the response from the UE.

[0299] The anchor SMF may notify the non-anchor SMF that the predetermined condition is satisfied. The non-anchor SMF may perform a network switching operation to the anchor network upon receiving the notification. For example, the non-anchor SMF may release the UPF on the non-anchor network side. The non-anchor SMF may request a connection release from the UPF that is the path for data transmission and reception. For example, the request may be made using N4 session release signaling.

[0300] The non-anchor SMF may notify the non-anchor AMF that the predetermined condition is met. The non-anchor AMF may release resources related to the UE based on the notification. The non-anchor AMF may request the non-anchor base station to release resources related to the UE. The non-anchor base station may release resources related to the UE based on the request.

[0301] The non-anchor SMF may notify the anchor SMF of the release of resources for the UE, for example, in response to a notification that the predetermined condition has been met.

[0302] The non-anchor AMF may notify the non-anchor SMF of the release of resources. The notification may be made in response to the notification that the predetermined condition has been met.

[0303] The method disclosed in this embodiment may also be applied to path switching from an anchor NW to a non-anchor NW. The switching of the NW serving as a data path may be initiated, for example, by an NF of the anchor NW. The NF may be, for example, an SMF.

[0304] The anchor SMF may request pre-configuration of NW switching from the non-anchor SMF. The request may be made, for example, as a request for PDU session modification or a request for PDU session establishment. For the notification, for example, Nsmf_PDUSession_Modification_Request signaling (see Non-Patent Document 31) or Nsmf_PDUSession_Establish_Request signaling (see Non-Patent Document 31) may be used. The notification may include information indicating that NW switching is using pre-configuration, information about the UE, information about the PDU session, or information about the QoS flow. The non-anchor NW may maintain a connection with the UE in its own NW when the information indicating that NW switching is using pre-configuration is included in the notification.

[0305] The non-anchor SMF may perform pre-configuration in the non-anchor NW. For example, the non-anchor SMF may perform pre-configuration of the UPF. The UPF performing the pre-configuration may be, for example, an intermediate UPF in the non-anchor NW. In the pre-configuration of the UPF, for example, some or all of the processes disclosed in PDU session establishment (Section 4.3.2 of Non-Patent Document 31) may be performed.

[0306] The non-anchor SMF may pre-configure the PDU session modification and / or establishment to the non-anchor AMF. The non-anchor SMF may request information related to NW switching pre-configuration from the non-anchor AMF. The request may include a request for NAS signaling information for the UE. The NAS signaling may be, for example, NAS configuration information related to the PDU session modification and / or establishment (e.g., NAS configuration to be established). The non-anchor AMF may notify the non-anchor SMF of the NAS signaling information. The notification from the non-anchor AMF to the non-anchor SMF may be triggered by the request from the non-anchor SMF to the non-anchor AMF.

[0307] The NAS signaling may include information about RRC signaling for the UE. The RRC signaling may be, for example, RRC configuration information related to PDU session modification and / or establishment (e.g., AS configuration to be established). The non-anchor AMF may request the RRC signaling information from the non-anchor base station. The non-anchor base station may notify the non-anchor AMF of the RRC signaling information. The notification from the non-anchor base station to the non-anchor AMF may be triggered by the request from the non-anchor AMF to the non-anchor base station.

[0308] The non-anchor SMF may respond to the pre-configuration request to the anchor SMF. The response may be, for example, a response to a PDU session modification request or a response to a PDU session release request. For example, the response may use signaling of Nsmf_PDUSession_Modification_Response or signaling of Nsmf_PDUSession_Release_Response. The response may include, for example, information on NAS signaling. The NAS signaling may be, for example, NAS signaling related to the above-mentioned PDU session modification and / or establishment. The NAS signaling may be, for example, NAS signaling acquired from the non-anchor AMF. The NAS signaling may include RRC signaling. The RRC signaling may be, for example, RRC signaling related to the above-mentioned PDU session modification and / or establishment. The RRC signaling may be, for example, RRC signaling obtained from a non-anchor base station.

[0309] The non-anchor SMF may pre-configure the non-anchor AMF for PDU session modification and / or PDU session establishment. The notification may include NAS signaling information of the target NW (e.g., non-anchor NW) for the UE, or may include RRC signaling information of the target NW (e.g., non-anchor NW). The non-anchor AMF may request the non-anchor base station to perform pre-RRC configuration related to NW switching, or may not make such a request. The non-anchor base station may notify the non-anchor AMF of the RRC signaling information of the target NW (e.g., non-anchor NW). The notification may be included in the above-mentioned request, for example.

[0310] The anchor SMF may initiate NW switching when the predetermined condition is satisfied. The anchor SMF may notify the non-anchor SMF that the predetermined condition is satisfied.

[0311] The non-anchor SMF may request the non-anchor AMF to reflect the pre-configuration. The non-anchor AMF may reflect the pre-configuration in response to the request. The non-anchor AMF may request the non-anchor base station to reflect the pre-configuration. The non-anchor base station may reflect the pre-configuration in response to the request. The non-anchor base station may notify the non-anchor AMF that the pre-configuration has been reflected. The non-anchor AMF may notify the non-anchor SMF that the pre-configuration has been reflected.

[0312] The non-anchor SMF may notify the anchor SMF of the completion of the pre-configuration update.

[0313] The anchor SMF may notify the anchor AMF that the specified condition has been met. The anchor AMF may use the notification as a trigger to modify and / or release resources for the UE. The anchor AMF may request the anchor base station to release the PDU session for the UE, or may request a PDU session modification. The request may include NAS signaling and / or RRC signaling related to pre-configuration of the PDU session modification and / or establishment of the non-anchor NW, or may include NAS signaling related to the PDU session modification and / or release of the anchor NW. The anchor base station may use the request as a trigger to request the UE to release the PDU session, or may request a PDU session modification. RRC signaling may be used for the request. The RRC signaling may include NAS signaling and / or RRC signaling related to pre-configuration of PDU session modification and / or establishment of the non-anchor NW, or may include NAS signaling and / or RRC signaling related to PDU session modification and / or release of the anchor NW. The UE may use the RRC signaling as a trigger to establish and / or modify a PDU session with the non-anchor NW, or may release and / or modify a PDU session with the anchor NW. The UE may send a response to the PDU session release or modification request to the anchor base station. The anchor base station may notify the anchor AMF of the response from the UE.

[0314] The anchor AMF may notify the anchor SMF of the response from the UE.

[0315] The notification from the NW to the UE may be performed from the target NW, for example, a non-anchor NW. This makes it possible to improve the reliability of signaling related to NW switching, for example.

[0316] An NF of a destination network may initiate path switching from an anchor network to a non-anchor network, or may initiate path switching from a non-anchor network to an anchor network. The destination network may be an anchor network or a non-anchor network. The method disclosed in this embodiment may be applied to the path switching. The NF may be, for example, a non-anchor SMF.

[0317] The predetermined condition may have a validity period or an expiration date. The validity period or expiration date may be included in the predetermined condition.

[0318] If the predetermined condition is not satisfied even after the validity period or expiration date has expired, the pre-configuration of the route switching may be canceled. The NF (e.g., SMF) of the anchor NW may notify the NF (e.g., SMF) of the switching destination candidate NW of information regarding the expiration of the validity period or expiration date, or may notify the NF (e.g., SMF) of the switching destination candidate NW of information regarding the cancellation of the pre-configuration. The NF of the switching destination candidate may release the pre-configuration in response to the notification.

[0319] The NF of the anchor network may notify the NF (e.g., SMF) of the source network of information about the expiration of the validity period or expiration date, or information about the cancellation of the pre-configuration. The NF of the source network may cancel the pre-configuration of the NW release in response to the notification. This allows, for example, the source network to continue communication with the UE.

[0320] As another solution, the UE may determine the predetermined condition. The condition may be determined by an NF of an anchor NW and notified to the UE, or may be determined by an NF of a non-anchor NW and notified to the UE, or may be determined by an NF of a handover source NW and notified to the UE, or may be determined by an NF of a handover destination candidate NW and notified to the UE. The NF may be, for example, an SMF. The notification may be performed via an AMF or a base station. The UE may measure whether the predetermined condition is met, triggered by the notification.

[0321] The anchor AMF may notify the UE of information related to the pre-configuration of NW switching. The notification may be performed, for example, by NAS signaling. The UE may perform QoS monitoring or QoE measurement using the notified information.

[0322] The UE may transmit a notification regarding the predetermined condition to the NF of the NW. The NW may be an anchor NW, a non-anchor NW, a source NW, or a target NW. The NF may be, for example, an SMF. The notification may be, for example, a notification that the predetermined condition has been satisfied, or a notification that the condition has not been satisfied within a predetermined validity period. The notification may be made via a base station or an AMF. The NF may perform NW switching or cancel pre-configuration in response to the notification. For example, the NF may perform NW switching in response to a notification that the predetermined condition has been satisfied, or may cancel pre-configuration in response to a notification that the condition has not been satisfied within a predetermined validity period. The NW switching may be performed, for example, using the method disclosed in the above-mentioned solution. The pre-configuration may be canceled, for example, using the method disclosed in the above-mentioned solution.

[0323] According to the third embodiment, it is possible to switch the network in a short time and to save network resources, for example, memory usage.

[0324] Modification 1 of the Third Embodiment: A plurality of NWs may be provided as candidate NWs for NW switching. The anchor NW may set the candidates. The anchor NW may perform pre-settings for a plurality of NWs.

[0325] The configuration may be initiated by, for example, the anchor SMF. The anchor SMF may instruct the SMF of the candidate network to perform pre-configuration. The instruction may include information on the switching conditions. The conditions may differ between networks. The conditions may be determined, for example, by the anchor PCF or the anchor SMF. The candidate network may use the information to pre-configure a connection with the UE. The pre-configuration may be performed, for example, by a method similar to that disclosed in the third embodiment.

[0326] The UE may start a connection process with the NW for which the condition is satisfied. The UE may notify the NF (e.g., anchor SMF) of the anchor NW of information about the NW for which the condition is satisfied. As another example, the NW for which the condition is satisfied may notify the NF (e.g., anchor SMF) of the anchor NW that it has started a connection with the UE.

[0327] The anchor NW may notify the SMF of the NW that satisfies the conditions that the conditions are satisfied. The NW that satisfies the conditions may start a connection process with the UE. The connection process with the UE may be performed, for example, in the same manner as the method disclosed in the third embodiment.

[0328] The anchor NW may notify the SMF of a candidate NW other than the NW that satisfied the conditions that the conditions were not satisfied, or may notify that another NW satisfied the conditions. The candidate NW may release the connection preparation with the UE in response to the notification from the anchor SMF. The candidate NW may notify the anchor SMF that the release has been completed.

[0329] A priority order may be set among the multiple candidates. This makes it possible to uniquely determine a switching destination network when, for example, conditions for multiple networks are simultaneously satisfied, thereby preventing malfunction of the communication system.

[0330] This first modification enables flexible switching of communication systems.

[0331] The network device in the present disclosure may be a network function (NF) of the network. For example, the anchor network device may be a network function (NF) of the anchor network. The non-anchor network device may be a network function (NF) of the non-anchor network. This makes it possible to apply the method described in the present disclosure even when, for example, multiple network functions of the network are accommodated in the same device.

[0332] The method described in the present disclosure may be used in situations other than a network failure. For example, the method may be used when QoS deteriorates. The network failure detection described in the present disclosure may be QoS deterioration detection. This makes it possible to perform UPF switching and / or network switching operations before communication is interrupted, thereby improving the availability of the communication network.

[0333] As another example, the method described in the present disclosure may be used in a predetermined situation. The predetermined situation may be, for example, an increase in the load of the UPF or the AMF. This may prevent a further increase in the load of the UPF and / or the AMF, and as a result, prevent a failure of the network.

[0334] In the present disclosure, signaling between different networks may be performed via SEPP (see Non-Patent Document 10), which makes it possible to ensure security in the signaling, for example.

[0335] In the present disclosure, the Inter PLMN User Plane Security (IPUPS) function (see Non-Patent Document 10) may be used for transferring user data between different networks. This makes it possible to ensure security in transferring user data, for example.

[0336] Transmission and reception between a base station and a CN node (excluding the AMF) may be performed via the AMF. Alternatively, transmission and reception between a base station and a CN node (excluding the AMF) may be performed without the AMF. By not using the AMF, the amount of signaling can be reduced and the load on the AMF can be reduced.

[0337] In this specification, a node may be a function.

[0338] In the communication system according to the present disclosure, one or more cells are configured in one gNB. In the present disclosure, although it is described as a gNB or a cell, it may be a gNB or a cell unless otherwise specified.

[0339] In the present disclosure, a gNB may be an MCG or an SCG.

[0340] The above-described embodiments and their modifications are merely examples, and the embodiments and their modifications can be freely combined. Furthermore, any of the components of the embodiments and their modifications can be modified or omitted as appropriate.

[0341] For example, in the above-described embodiments and their modifications, a slot is an example of a time unit for communication in a fifth-generation communication system. A slot may be a scheduling unit. In the above-described embodiments and their modifications, processing described as being performed in slot units may be performed in TTI units, subframe units, subslot units, or minislot units.

[0342] For example, the methods disclosed in the above-described embodiments and their modifications may be applied to the IAB, to communications between an IAB donor and an IAB node, or to processing using a Uu in the IAB.

[0343] 202 Communication terminal device (mobile terminal), 210 Communication system, 213, 240-1, 240-2, 750 Base station device (NR base station, base station), 214 5G core unit, 215 Central unit, 216 Distributed unit, 217 Central unit for control plane, 218 Central unit for user plane, 219 TRP, 301, 403 Protocol processing unit, 302 Application unit, 304, 405 Encoder unit, 305, 406 Modulation unit, 306, 407 Frequency conversion unit, 307-1 to 307-4, 408-1 to 408-4 Antenna, 308, 409 Demodulation unit, 309, 410 Decoder unit, 310, 411, 526 Control unit, 401 EPC communication unit, 402 Other base station communication unit, 412 5GC communication unit, 521 Data Network communication unit, 522 base station communication unit, 523 user plane communication unit, 523-1 PDU processing unit, 523-2 mobility anchoring unit, 525 control plane control unit, 525-1 NAS security unit, 525-2 idle state mobility management unit, 527 session management unit, 527-1 PDU session control unit, 527-2 UE IP address allocation unit, 751-1 to 751-8 beams, 752 cell.

Claims

1. A communication system corresponding to a fifth-generation wireless access system, comprising an anchor network which is a network having a user plane function that directly connects to a data network which is a data transmission / reception destination of a communication terminal, and a non-anchor network which is a network that connects to the data network via the anchor network, having a plurality of protocol stacks for communication between the communication terminal and the data network, wherein when the communication terminal switches the network to be connected, after migrating to a state where it connects to both the anchor network and the non-anchor network using the plurality of protocol stacks and communicates with the data network, it terminates communication with the data network via the source network to be switched. A communication system characterized by the above.

2. The communication system according to claim 1, wherein the communication terminal notifies a network of a data transmission destination of information regarding a sequence number of uplink data to be transmitted in data transmission to the data network.

3. The communication system according to claim 2, wherein when the communication terminal is in a state of connecting to both the anchor network and the non-anchor network and communicating with the data network, it determines which of the anchor network and the non-anchor network is to be the transmission destination of the uplink data based on the buffer amount of the uplink data in each of the plurality of protocol stacks.

4. The communication system according to claim 2, wherein when the communication terminal is in a state of connecting to both the anchor network and the non-anchor network and communicating with the data network, which of the anchor network and the non-anchor network is to be the transmission destination of the uplink data is determined by the anchor network or the non-anchor network based on one or both of failure detection and congestion detection of the anchor network and the non-anchor network, and the communication terminal is instructed of the transmission destination.

5. The communication system according to any one of claims 1 to 4, characterized in that, for each function included in a network that is a candidate for a switching destination when switching the network to which the communication terminal is connected, settings used for communication with the communication terminal are pre-performed.

6. The communication system according to claim 5, characterized in that there are a plurality of candidate networks, and the settings for each function included in the network are pre-performed for all of the plurality of candidate networks.

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