Communication methods, network nodes, user devices, chipsets, programs, and mobile communication systems

Abstract

The present invention provides an apparatus and method that enables improved multicast broadcast services (MBS). [Solution] In a mobile communication system, the user device 100 includes the steps of: receiving a multicast session from a network in an RRC (Radio Resource Control) idle state or an RRC inactive state; measuring the reception quality from the network in a multicast reception state in which a multicast session is being received; and, depending on whether the measured reception quality is worse than a threshold, performing a process to transition to an RRC connected state for multicast reception.

Description

Technical Field

[0001] The present disclosure relates to a communication method and a user device used in a mobile communication system.

Background Art

[0002] In the 3GPP (3rd Generation Partnership Project) standard, the technical specifications of NR (New Radio), which is the 5th generation (5G) radio access technology, are defined. NR has characteristics such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), which is the 4th generation (4G) radio access technology. In 3GPP, discussions are being held to formulate the technical specifications of the 5G / NR multicast broadcast service (MBS) (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] The communication method according to the first aspect is a method executed by a user device in a mobile communication system that provides a multicast broadcast service (MBS). The communication method includes receiving a multicast session from a network in the RRC idle state or the RRC inactive state, measuring the reception quality from the network in the multicast reception state in which the multicast session is being received, and performing a process of transitioning to the RRC connected state for multicast reception in response to the measured reception quality being worse than a threshold value.

[0005] The user device according to the second embodiment is a device used in a mobile communication system that provides a multicast broadcast service (MBS). The user device comprises a receiving unit that receives multicast sessions from the network in an RRC idle state or an RRC inactive state, and a control unit that measures the reception quality from the network in a multicast reception state in which the multicast session is being received. The control unit performs a process to transition to an RRC connected state for multicast reception depending on whether the measured reception quality is worse than a threshold. [Brief explanation of the drawing]

[0006] [Figure 1] This diagram shows the configuration of a mobile communication system according to an embodiment. [Figure 2] This diagram shows the configuration of the UE (User Equipment) according to the embodiment. [Figure 3] This diagram shows the configuration of the gNB (base station) according to the embodiment. [Figure 4] This diagram shows the protocol stack configuration of the user plane wireless interface that handles data. [Figure 5] This diagram shows the protocol stack configuration of the wireless interface of the control plane that handles signaling (control signals). [Figure 6] This diagram shows an overview of MBS traffic distribution according to the embodiment. [Figure 7] This figure shows the distribution mode according to the embodiment. [Figure 8] This figure shows an example of internal processing related to MBS reception in a UE according to the embodiment. [Figure 9] This figure shows another example of the internal processing related to MBS reception in the UE according to the embodiment. [Figure 10] This figure shows an example of the operation of the mobile communication system according to the embodiment. [Figure 11] This figure shows a first example of modification to the operation of the mobile communication system according to the embodiment. [Figure 12]This figure shows a second example of modification to the operation of the mobile communication system according to the embodiment. [Modes for carrying out the invention]

[0007] It is desirable that 5G / NR multicast broadcast services provide improved services compared to 4G / LTE multicast broadcast services.

[0008] Therefore, this disclosure aims to enable the realization of improved multicast broadcast services.

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals.

[0010] (Configuration of mobile communication systems) Figure 1 shows the configuration of a mobile communication system according to an embodiment. Mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following explanation, 5GS will be used as an example, but the mobile communication system may also have at least a portion of an LTE (Long Term Evolution) system. Furthermore, the mobile communication system may also have at least a portion of a 6th Generation (6G) system.

[0011] The mobile communication system 1 comprises User Equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as core network (CN) 20.

[0012] A UE100 is a mobile wireless communication device. A UE100 can be any device used by a user. For example, a UE100 can be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device attached to a sensor, a vehicle or a device attached to a vehicle (Vehicle UE), or an aircraft or a device attached to an aircraft (Aerial UE).

[0013] NG-RAN10 includes base stations (referred to as "gNBs" in 5G systems) 200. The gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with UEs 100 that have established a connection with its own cell. The gNB 200 has radio resource management (RRM) functions, user data routing functions (hereinafter simply referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to indicate the smallest unit of a wireless communication area. "Cell" is also used as a term to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] Furthermore, gNBs can also connect to the EPC (Evolved Packet Core), which is the core network of LTE. LTE base stations can also connect to 5GCs. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0015] 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls and the like for the UE100. The AMF manages the mobility of the UE100 by communicating with the UE100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB200 via the NG interface, which is an interface between the base station and the core network.

[0016] Figure 2 is a diagram showing the configuration of the UE100 (user device) according to the embodiment. The UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB200.

[0017] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0018] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0019] The control unit 130 performs various controls and processes in the UE100. Such processes include the processes of each layer described later. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of the baseband signal. The CPU executes the programs stored in the memory to perform various processes.

[0020] Figure 3 shows the configuration of the gNB200 (base station) according to the embodiment. The gNB200 comprises a transmitter 210, a receiver 220, a control unit 230, and a backhaul communication unit 240. The transmitter 210 and receiver 220 constitute a wireless communication unit that performs wireless communication with the UE100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN20.

[0021] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0022] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0023] The control unit 230 performs various control and processing in the gNB200. Such processing includes processing in each layer described later. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing.

[0024] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF300 via the NG interface, which is an inter-base station-core network interface. The gNB200 may consist of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally separated), and the two units may be connected by the F1 interface, which is a fronthaul interface.

[0025] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0026] The user plane radio interface protocol consists of a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the UE100's PHY layer and the gNB200's PHY layer via a physical channel. The UE100's PHY layer receives downlink control information (DCI) transmitted from the gNB200 over the physical downlink control channel (PDCCH). Specifically, the UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from the gNB200 has a CRC parity bit added, which is scrambled by the RNTI.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat request (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of the UE100 and the MAC layer of the gNB200 via the transport channel. The MAC layer of the gNB200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE100.

[0029] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the UE100's RLC layer and the gNB200's RLC layer via a logical channel.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0031] The SDAP layer maps IP flows, which are the units under which the core network performs QoS (Quality of Service) control, to wireless bearers, which are the units under which the AS (Access Stratum) performs QoS control. Note that if the RAN is connected to the EPC, the SDAP is not required.

[0032] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0033] The control plane's wireless interface protocol stack includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer, instead of the SDAP layer shown in Figure 4.

[0034] RRC signaling for various settings is transmitted between the RRC layer of the UE100 and the RRC layer of the gNB200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. If there is a connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC idle state. If the connection between the RRC of the UE100 and the RRC of the gNB200 is suspended, the UE100 is in the RRC inactive state.

[0035] The NAS layer, located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the UE100's NAS layer and the AMF300A's NAS layer. The UE100 also has application layers and other components in addition to its wireless interface protocol. Furthermore, layers below the NAS layer are called AS layers.

[0036] (Overview of MBS) An overview of the MBS according to this embodiment will be described. MBS is a service that enables broadcast or multicast, i.e., point-to-multipoint (PTM) data transmission from NG-RAN10 to UE100. Use cases (service types) of MBS are envisioned to include public security communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV (Internet protocol television), group communications, and software distribution.

[0037] The broadcast service provides service to all UE100s within a specific service area for applications that do not require high reliability QoS. The MBS session used for the broadcast service is called a broadcast session.

[0038] Multicast services provide services not to all UE100s, but to groups of UE100s participating in a multicast service (multicast session). The MBS session used for multicast services is called a multicast session. Multicast services allow the same content to be delivered to a group of UE100s in a more wirelessly efficient way compared to broadcast services.

[0039] Figure 6 shows an overview of MBS traffic distribution according to the embodiment.

[0040] MBS traffic (MBS data) is delivered from a single data source (application service provider) to multiple UEs. The 5G core network, 5G CN (5GC)20, receives MBS data from application service providers, creates copies of the MBS data (replication), and delivers them.

[0041] From the perspective of 5GC20, two multicast delivery methods are possible: 5GC Shared MBS Traffic delivery and 5GC Individual MBS Traffic delivery.

[0042] In the 5GC individual MBS traffic distribution method, the 5GC20 receives a single copy of MBS data packets and distributes individual copies of those MBS data packets to individual UE100s via a PDU session for each UE100. Therefore, one PDU session per UE100 needs to be associated with the multicast session.

[0043] In the 5GC shared MBS traffic distribution method, the 5GC20 receives a single copy of MBS data packets and distributes that single copy of MBS packets to the RAN nodes (i.e., gNB200). The gNB200 receives the MBS data packets via the MBS tunnel connection and distributes them to one or more UE100s.

[0044] From the perspective of RAN (5G RAN)10, two distribution methods are possible for transmitting MBS data wirelessly in the 5GC shared MBS traffic distribution method: PTP (Point-to-Point) and PTM (Point-to-Multipoint). PTP stands for unicast, while PTM stands for multicast and broadcast.

[0045] In the PTP distribution method, the gNB200 wirelessly distributes individual copies of MBS data packets to each UE100. On the other hand, in the PTM distribution method, the gNB200 wirelessly distributes a single copy of MBS data packets to a group of UE100s. The gNB200 can dynamically decide whether to use PTM or PTP as the method for distributing MBS data to a single UE100.

[0046] The PTP and PTM distribution methods primarily concern the user plane. There are two control modes for MBS data distribution: the first distribution mode and the second distribution mode.

[0047] Figure 7 shows a distribution mode according to an embodiment.

[0048] Delivery mode 1 (DM1) is a delivery mode available to UE100 in an RRC connected state and is a delivery mode for high QoS requirements. Delivery mode 1 is used for multicast sessions within MBS sessions. However, delivery mode 1 may also be used for broadcast sessions. Delivery mode 1 may also be available to UE100 in an RRC idle or RRC inactive state.

[0049] In the first distribution mode, MBS reception is configured via UE-dedicated signaling. For example, in the first distribution mode, MBS reception is configured via an RRC message (or RRC Release message), which is a unicast RRC message sent from gNB200 to UE100.

[0050] The MBS reception settings include MBS traffic channel configuration information (hereinafter referred to as "MTCH configuration information") relating to the settings of the MBS traffic channel that transmits MBS data. The MTCH configuration information includes MBS session information (including the MBS session identifier described later) relating to the MBS session, and scheduling information for the MBS traffic channel corresponding to this MBS session. The scheduling information for the MBS traffic channel may also include intermittent reception (DRX) settings for the MBS traffic channel. The intermittent reception settings may include one or more of the following parameters: an On Duration Timer that defines the On Duration (reception period), an Inactivity Timer that extends the On Duration, a Scheduling Period or DRX Cycle (Scheduling Period, DRX Cycle), an Offset value for the start subframe of the Scheduling or DRX Cycle (Start Offset, DRX Cycle Offset), a Slot Offset that starts the On Duration timer, a Retransmission Timer that defines the maximum time until retransmission, and a HARQ RTT Timer that defines the minimum interval until DL allocation for HARQ retransmission.

[0051] The MBS traffic channel is a type of logical channel and is sometimes called an MTCH. The MBS traffic channel is mapped to the Down Link-Shared Channel (DL-SCH), which is a type of transport channel.

[0052] Delivery mode 2 (DM2) is a delivery mode that can be used not only by UE100s in the RRC connected state, but also by UE100s in the RRC idle or RRC inactive state, and is a delivery mode for low QoS requirements. Delivery mode 2 is used for broadcast sessions within MBS sessions. However, delivery mode 2 may also be applicable to multicast sessions.

[0053] In the second distribution mode, MBS reception is configured via broadcast signaling. For example, in the second distribution mode, MBS reception is configured via a logical channel broadcast from the gNB200 to the UE100, such as a broadcast control channel (BCCH) and / or multicast control channel (MCCH). The UE100 can receive the BCCH and MCCH using a dedicated RNTI predefined in the technical specifications, for example. The RNTI for BCCH reception may be an SI-RNTI, and the RNTI for MCCH reception may be an MCCH-RNTI.

[0054] In the second distribution mode, UE100 may receive MBS data in the following three steps: First, UE100 receives MCCH configuration information via SIB (MBS SIB) transmitted over BCCH from gNB200. Second, UE100 receives MCCH from gNB200 based on the MCCH configuration information. MCCH transmits MTCH configuration information. Third, UE100 receives MTCH (MBS data) based on the MTCH configuration information. Hereinafter, MTCH configuration information and / or MCCH configuration information may be referred to as MBS reception settings.

[0055] In the first and second distribution modes, the UE100 may receive the MTCH using the group RNTI (G-RNTI) assigned by the gNB200. G-RNTI corresponds to the RNTI for MTCH reception. G-RNTI may be included in the MBS reception settings (MTCH setting information).

[0056] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of the following: TMGI (Temporary Mobile Group Identity), source-specific IP multicast address (consisting of a source unicast IP address such as an application function or application server, and an IP multicast address indicating the destination address), session identifier, and G-RNTI. At least one of the TMGI, source-specific IP multicast address, and session identifier is called the MBS session identifier. The TMGI, source-specific IP multicast address, session identifier, and G-RNTI together are called MBS session information.

[0057] Figure 8 shows an example of the internal processing related to MBS reception in the UE100 according to the embodiment. Figure 9 shows another example of the internal processing related to MBS reception in the UE100 according to the embodiment.

[0058] A single MBS radio bearer (MRB) is a single radio bearer that transmits either a multicast session or a broadcast session. That is, an MRB may be associated with a multicast session, or it may be associated with a broadcast session.

[0059] The MRB and its corresponding logical channel (e.g., MTCH) are configured from gNB200 to UE100 via RRC signaling. The MRB configuration procedure may be separate from the data radio bearer (DRB) configuration procedure. RRC signaling allows a single MRB to be configured as "PTM only," "PTP only," or "both PTM and PTP." The type of MRB can be changed via RRC signaling.

[0060] Figure 8 shows an example where MRB#1 is associated with a multicast session and a dedicated traffic channel (DTCH), MRB#2 is associated with a multicast session and MTCH#1, and MRB#3 is associated with a broadcast session and MTCH#2. In other words, MRB#1 is a PTP-only MRB, MRB#2 is a PTM-only MRB, and MRB#3 is a PTM-only MRB. Note that DTCH is scheduled using cell RNTI (C-RNTI), and MTCH is scheduled using G-RNTI.

[0061] The UE100's PHY layer processes user data (received data) received on the PDSCH, one of the physical channels, and sends it to the Downlink Shared Channel (DL-SCH), one of the transport channels. The UE100's MAC layer (MAC entity) processes data received on the DL-SCH and sends the received data to the corresponding logical channel (corresponding RLC entity) based on the logical channel identifier (LCID) contained in the header (MAC header) of the received data.

[0062] Figure 9 shows an example where DTCH and MTCH are associated with an MRB that is associated with a multicast session. Specifically, one MRB is split into two legs, one leg is associated with DTCH and the other leg is associated with MTCH. These two legs are joined at the PDCP layer (PDCP entity). In other words, this MRB is both a PTM and a PTP MRB. Such an MRB is sometimes called a split MRB.

[0063] (Operation of mobile communication systems) The operation of the mobile communication system 1 according to the embodiment will now be described. In the following, we will mainly assume a case where multicast distribution is performed using the first distribution mode (DM1) described above. As described above, the first distribution mode is a distribution mode that can be used by the UE100 in the RRC connected state and is a distribution mode for high QoS requirements.

[0064] In this embodiment, UE100 in the RRC idle state or RRC inactive state performs multicast session reception (i.e., multicast reception). For example, gNB200 starts multicast distribution to UE100 in the RRC connected state, and then continues multicast distribution while transitioning UE100 to the RRC idle state or RRC inactive state as the load on gNB200 increases. UE100 starts multicast reception in the RRC connected state, and then continues multicast reception in the RRC idle state or RRC inactive state.

[0065] The first distribution mode (DM1) may require ensuring high QoS requirements, and therefore, it may also be necessary to ensure high QoS requirements for UE100 in the RRC idle or RRC inactive state. While maintaining UE100 in the RRC connected state satisfies QoS requirements, it increases resource consumption on the network side and power consumption on the UE100 side. Transitioning UE100 to the RRC idle or RRC inactive state solves these problems, but may result in QoS not being met. Therefore, in this embodiment, UE100 performing multicast reception in the RRC idle or RRC inactive state is enabled to transition to the RRC connected state in response to deterioration of multicast reception quality.

[0066] In this embodiment, the UE100 first receives a multicast session from the network (gNB200) in the RRC idle state or RRC inactive state. Second, in the multicast reception state where the multicast session is being received, the UE100 measures the reception quality from the network (hereinafter also referred to as "multicast reception quality"). Third, depending on whether the measured reception quality is worse than a threshold, the UE100 performs a process to transition to the RRC connected state for multicast reception. By transitioning to the RRC connected state and continuing multicast reception, it becomes easier to ensure the QoS required for multicast reception.

[0067] The UE100 will not transition to the RRC Connected state for multicast reception if the multicast reception quality is above the threshold. In other words, the UE100 is prohibited from transitioning to the RRC Connected state for multicast reception if the multicast reception quality is above the threshold. This allows the RRC to remain idle or inactive, thereby reducing the load on the network side.

[0068] UE100 may receive configuration information from the network (gNB200) to set a threshold. UE100 may compare the measured reception quality with the threshold set according to the configuration information. In this way, the threshold that initiates the process of UE100 transitioning to the RRC connected state may be set by the network (gNB200) to UE100. This allows UE100 to transition to the RRC connected state under the management of the network.

[0069] Figure 10 shows an example of the operation of the mobile communication system 1 according to the embodiment.

[0070] In step S101, UE100 is in an RRC connected state in a cell of gNB200. Suppose UE100 has become interested in a multicast session (hereinafter referred to as the "target multicast session"). "Being interested in a multicast session" may mean that the upper layer of UE100 requests or desires to receive the multicast session. Here, the upper layer includes the NAS layer. The upper layer may further include applications. UE100 (the NAS entity) performs a multicast session join procedure to the network in order to join the target multicast session. For example, UE100 joins the target multicast session by sending a first NAS message to AMF300A requesting to join the target multicast session and receiving a second NAS message from AMF300A acknowledging its participation in the target multicast session. For example, the first NAS message is a PDU Session Modification Request, which may include the MBS session identifier and information about the join request. If the approval of the first NAS message is implicitly indicated by the MRB settings from gNB200, the second NAS message may be omitted. Also, "joining the target multicast session" may mean registering UE100 as a member of the UE group (multicast group) that receives multicast sessions with the CN device. The CN device may authenticate UE100 at the time of such registration. The CN device may also grant permission for UE100 to receive multicast sessions. Participation in a multicast session may be performed when the multicast session is active (transmitting) or when it is inactive (waiting to start transmission or transmission is suspended).

[0071] In step S102, the UE100, which is in the RRC connected state, begins receiving the target multicast session. Prior to this multicast reception, the gNB200 may configure the UE100 for multicast reception for the target multicast session. Multicast reception configuration may be performed, for example, by an RRC Reconfiguration message that includes MRB configuration.

[0072] In step S103, the UE100, which is in the RRC connected state, receives the target multicast session. Specifically, the UE100 receives MBS data belonging to the target multicast session from the gNB200.

[0073] In step S104, gNB200 decides to transition UE100 to the RRC idle state or RRC inactive state and sends an RRC Release message to UE100 to transition UE100 to the RRC idle state or RRC inactive state. gNB200 may also decide to transition UE100 to the RRC idle state or RRC inactive state in response to an increase in its own load (e.g., resource load). By transitioning UE100 to the RRC idle state or RRC inactive state, the load on gNB200 is reduced.

[0074] In one embodiment, the gNB200 sends an RRC Release message to the UE100 containing configuration information for setting the thresholds described above. The thresholds may be wireless quality thresholds, such as RSRP (Reference Signal Received Power) thresholds, RSRQ (Reference Signal Received Quality) thresholds, and / or SINR (Signal-to-Interference-plus-Noise Ratio) thresholds. The thresholds may also be demodulation quality thresholds, such as BER (Bit Error Rate) thresholds, BLER (Block Error Rate) thresholds, and / or PER (Packet Error Rate) thresholds. The thresholds may be set for each multicast session. That is, the thresholds may be set in association with the MRB setting (MRB ID) or multicast session ID (TMGI). Therefore, when the UE100 receives multiple multicast sessions, it may maintain multiple thresholds corresponding to multiple multicast sessions. The gNB200 may also send an RRC Release message to the UE100 containing configuration information for setting the duration (first predetermined time) of the threshold condition. By including this configuration information in the RRC Release message, UE-specific configuration information can be efficiently sent to UE100. Note that such configurations may also be sent in the RRC Reconfiguration in step S102. If the RRC Reconfiguration includes these configurations, UE100 may determine that it can receive multicast sessions in an RRC idle or inactive state (i.e., reception is permitted).

[0075] In step S105, upon receiving the RRC Release message, UE100 transitions to either the RRC idle state or the RRC inactive state. UE100 continues multicast reception in the RRC idle state or RRC inactive state using the multicast reception settings configured in the RRC connected state.

[0076] In step S107, the UE100 measures the multicast reception quality corresponding to the threshold set by the gNB200. For example, the UE100 may measure radio quality, e.g., RSRP, RSRQ, and / or SINR. The UE100 may also measure demodulation quality, e.g., BER, BLER, and / or PER.

[0077] In step S108, UE100 compares the multicast reception quality measured in step S107 with a threshold set by gNB200. If the measured multicast reception quality is better than the threshold (step S108: NO), UE100 returns to step S107. In this case, UE100 performs multicast reception while maintaining the RRC idle or RRC inactive state.

[0078] On the other hand, if the measured multicast reception quality is worse than the threshold (step S108: YES), in step S109, the UE100 initiates a process to transition to the RRC connected state, i.e., a random access procedure to the gNB200.

[0079] Note that multicast reception quality being worse than the threshold may also mean that the wireless quality (RSRP, RSRQ, and / or SINR) is lower than the threshold. Multicast reception quality being worse than the threshold may also mean that the error rate corresponding to demodulation quality (BER, BLER, and / or PER) is higher than the threshold.

[0080] In step S108, UE100 may determine whether the multicast reception quality has remained below a threshold for a first predetermined time. The first predetermined time may be set in UE100 by configuration information from gNB200. If the multicast reception quality remains below a threshold for a first predetermined time, UE100 may initiate a process to transition to the RRC connected state, i.e., a random access procedure to gNB200 (step S109). This makes it easier to exclude the effects of momentary degradation of multicast reception quality.

[0081] In step S109, UE100 performs a random access procedure. Here, the AS layer of UE100 may start RRC Resume if it is in the RRC inactive state. On the other hand, if it is in the RRC idle state, the AS layer of UE100 may start RRC Setup. The AS layer of UE100 may notify the NAS layer that the threshold condition has been met. Based on this notification, the NAS layer may instruct the AS layer to transition to the RRC connected state.

[0082] UE100 transitions to the RRC Connected state by performing the random access procedure in step S109. UE100 continues multicast reception in the RRC Connected state. While the RRC Connected state allows for individual scheduling from gNB200 to UE100, enabling the provision of high-quality service to UE100, it increases the load on gNB200.

[0083] Furthermore, if a predetermined event other than multicast reception occurs while UE100 is in the RRC idle or RRC inactive state, UE100 may be permitted to transition to the RRC connected state regardless of the above. The predetermined event may be the reception of paging from the network, i.e., the occurrence of MT (Mobile Terminated) traffic. The predetermined event may also be the need for uplink transmission, i.e., the occurrence of MO (Mobile Originated) traffic.

[0084] Furthermore, although the above embodiment describes an example of setting the threshold from gNB200 to UE100, the threshold may be pre-configured in UE100. UE100 may maintain pre-configured thresholds for each QoS level (5QI). UE100 may compare the pre-configured threshold corresponding to the QoS level of the target multicast session with the multicast reception quality.

[0085] (Example of first modification) As shown in Figure 11, the gNB200 may broadcast the configuration information described above in a System Information Block (SIB) (step S106). The UE100, which is in an RRC idle or RRC inactive state, may receive the SIB containing the configuration information from the gNB200 and apply the threshold (and first predetermined time) according to the received configuration information. Such an SIB may include individual configuration information for each bearer (MRB) (or each service) or for each QoS level (5QI). Alternatively, such an SIB may include configuration information common to all bearers.

[0086] For example, an SIB may contain multiple sets of bearer identifiers or 5QIs and configuration information associated with those bearer identifiers or 5QIs. Upon receiving an SIB, the UE100 may obtain configuration information from the SIB corresponding to the bearer or QoS level of the target multicast session and apply a threshold (and a first predetermined time) according to the obtained configuration information.

[0087] (Example of second modification) As shown in Figure 12, UE100 may be prohibited from transitioning to the RRC Connected state for multicast reception until a predetermined time (second predetermined time) has elapsed after transitioning to the RRC idle state or RRC inactive state. This prevents UE100 from transitioning to the RRC Connected state immediately after transitioning to the RRC idle state or RRC inactive state. The second predetermined time may be set from gNB200 to UE100 by an RRC Release message or SIB. The RRC Release message or SIB may include configuration information for setting the second predetermined time. This allows gNB200 to set an appropriate second predetermined time, for example, according to its own load status.

[0088] In step S201, the UE100, which has transitioned to the RRC idle state or RRC inactive state, starts a timer set to a second predetermined time (timer value). That is, the UE100 measures the elapsed time since transitioning to the RRC idle state or RRC inactive state. The second predetermined time (timer value) is set by, for example, the gNB200 and may be specified in seconds, subframes, wireless frames, or time units.

[0089] UE100 avoids performing the process of transitioning to the RRC Connected state for multicast reception (random access procedure) until the elapsed time since transitioning to the RRC Idle state or RRC Inactive state exceeds the second predetermined time. However, UE100 may be permitted to transition to the RRC Connected state regardless of the above if a predetermined event other than multicast reception occurs. The predetermined event may be the reception of Paging from the network, i.e., the occurrence of MT (Mobile Terminated) traffic. The predetermined event may also be the need for uplink transmission, i.e., the occurrence of MO (Mobile Originated) traffic.

[0090] After determining that the reception quality is worse than the threshold (step S108: YES), in step S202, UE100 determines whether the timer started in step S201 has expired, that is, whether the elapsed time since transitioning to the RRC idle state or RRC inactive state has exceeded the second predetermined time. If the timer has not expired (step S202: NO), UE100 returns to step S107. On the other hand, if the timer has expired (step S202: YES), in step S109, UE100 starts the process of transitioning to the RRC connected state, that is, the random access procedure to gNB200. In this way, UE100 performs the process of transitioning to the RRC connected state depending on whether the elapsed time since transitioning to the RRC idle state or RRC inactive state exceeds the second predetermined time, and the measured reception quality (multicast reception quality) is worse than the threshold.

[0091] (Other embodiments) Each of the above-described operation flows can be performed not only independently, but also in combination of two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0092] In the embodiments and examples described above, an example in which the base station is an NR base station (gNB) was described, but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, the base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of an IAB node. Furthermore, UE100 may be an MT (Mobile Termination) of an IAB node.

[0093] A program may be provided that causes a computer to execute each process performed by the UE100 or gNB200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM. Alternatively, the circuits that execute each process performed by the UE100 or gNB200 may be integrated, and at least a part of the UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0094] The terms "based on" and "depending on" used in this disclosure do not mean "based solely on" or "depending solely on" unless otherwise specified. The term "based on" means both "based solely on" and "at least partially on." Similarly, the term "depending on" means both "at least partially on" and "at least partially on." Also, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from other nodes, or obtaining information by generating it. The terms "include," "comprise," and their variations do not mean to include only the listed items, but may include only the listed items, or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to mean exclusive OR. Furthermore, any reference to elements using designations such as "first," "second," etc., used in this disclosure does not limit the quantity or order of those elements in general. These designations may be used herein as a convenient way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be employed therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated otherwise by the context.

[0095] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0096] This application claims priority to Japanese Patent Application No. 2022-005614 (filed on January 18, 2022), and all of its contents are incorporated into the specification of this application. [Explanation of Symbols]

[0097] 1: Mobile communication systems 10: RAN 20:CN 100 :UE 110: Receiver 120: Transmitter 130: Control Unit 200 :gNB 210: Transmitter 220: Receiving unit 230: Control Unit 240: Backhaul Communications Department

Claims

1. A communication method in a mobile communication system that provides multicast broadcast services (MBS), The network node sends a message to the user device that includes a threshold value defined for each of the multiple multicast sessions, and information relating the threshold value to the multicast session. The network node transmits the multicast session to the user device in an RRC inactive state. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. Communication method.

2. The aforementioned message is an RRC Release message for transitioning the user device from the RRC connected state to the RRC inactive state. The communication method according to claim 1.

3. A network node used in a mobile communication system that provides multicast broadcast services (MBS), The system includes a transmission unit that sends a message to a user device containing a threshold value defined for each of multiple multicast sessions, and information relating the threshold value to the multicast session. The transmitting unit transmits the multicast session to the user device in an RRC inactive state. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. Network node.

4. A user device used in a mobile communication system that provides multicast broadcast services (MBS), The system includes a receiving unit that receives messages from a network node, each containing a threshold value defined for each of multiple multicast sessions, and information relating the threshold value to the multicast session. The receiving unit receives the multicast session from the network node in the RRC inactive state. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. User device.

5. A chipset for user equipment used in a mobile communication system that provides multicast broadcast services (MBS), A process for receiving a message from a network node that includes a threshold defined for each of multiple multicast sessions, and information relating the threshold to the multicast session; The process of receiving the multicast session from the network node while the RRC is inactive is performed. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. Chipset.

6. User equipment used in mobile communication systems that provide multicast broadcast services (MBS): A process for receiving a message from a network node that includes a threshold defined for each of multiple multicast sessions, and information relating the threshold to the multicast session; The process of receiving the multicast session from the network node while the RRC is inactive is executed. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. program.

7. A mobile communication system that provides multicast broadcast services (MBS), Network nodes and A user device is provided, The aforementioned network node is A message is sent to the user device, which includes a threshold value defined for each of the multiple multicast sessions, and information relating the threshold value to the multicast session. The multicast session is transmitted to the user device in the RRC inactive state. The threshold is used in the process of transitioning from the RRC inactive state to the RRC connected state in the user device receiving the multicast session. Mobile communication system.

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