Communication control method, base station, user equipment, and processor

Abstract

To provide a communication control method, a base station, user equipment, and a processor in which the base station notifies the user equipment of a cell that provides a multicast / broadcast service (MBS).SOLUTION: A communication control method used in a mobile communication system that provides an MBS includes: that a base station transmits MBS data to user equipment UE, in a first cell C1; that the base station transmits, to the user equipment, a notification message indicating that an MBS cell, which is a cell used for transmitting or receiving the MBS data, is changed from the first cell C1 to a second cell C2; and that the user equipment that receives the MBS data from the base station receives the notification message from the base station.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a communication control method used in a mobile communication system. [Background technology]

[0002] In recent years, the fifth generation (5G) mobile communication system has been attracting attention. NR (New Radio), the radio access technology (RAT) of the 5G system, has features such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), the fourth generation radio access technology. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP technical specification "3GPP TS 38.300 V16.2.0 (2020-07)" Summary of the Invention

[0004] A communication control method according to a first aspect is a communication control method used in a mobile communication system that provides a multicast broadcast service (MBS), and includes the steps of: a base station transmitting MBS data to a user device in a first cell; the base station transmitting a notification message to the user device indicating that the MBS cell used for transmitting or receiving the MBS data will be changed from the first cell to a second cell; and the user device receiving the MBS data from the base station receiving the notification message from the base station.

[0005] A communication control method according to a second aspect is a communication control method used in a mobile communication system that provides a multicast broadcast service (MBS), and includes a base station managing a first cell transmitting a notification message regarding MBS transmission in a second cell different from the first cell to a user device in the first cell, wherein the notification message includes at least one of radio access technology information indicating the radio access technology used by the second cell for the MBS transmission and bandwidth portion information indicating the bandwidth portion used by the second cell for the MBS transmission.

[0006] A communication control method according to a third aspect is a communication control method used in a mobile communication system that provides a multicast broadcast service (MBS), and includes a user device that supports multiple radio access technologies selecting a radio access technology from the multiple radio access technologies that the user device will use to receive MBS data, and the user device transmitting a message to a base station indicating the selected radio access technology. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Figure 3] A diagram showing the configuration of a gNB (base station) according to an embodiment. [Figure 4] FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 5] FIG. 1 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 6] FIG. 2 is a diagram illustrating a correspondence relationship between downlink logical channels and transport channels according to the embodiment. [Figure 7]FIG. 1 is a diagram illustrating an example of an operating environment according to an embodiment. [Figure 8] FIG. 10 is a diagram illustrating another example of an operating environment according to an embodiment. [Figure 9] FIG. 2 is a diagram illustrating a first example of operation of the mobile communication system according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating a second example of the operation of the mobile communication system according to the embodiment. [Figure 11] FIG. 10 is a diagram illustrating an operation according to the first modification. [Figure 12] FIG. 1 is a diagram illustrating an example of a BWP. [Figure 13] FIG. 10 is a diagram illustrating an operation according to a second modified example. [Figure 14] FIG. 10 is a diagram illustrating an operation according to a third modified example. [Figure 15] FIG. 11 is a diagram illustrating a configuration example of an MBS indication according to a third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] The introduction of multicast and broadcast services into the 5G system (NR) is being considered. The NR multicast and broadcast services are expected to provide improved services compared to the LTE multicast and broadcast services.

[0009] Therefore, an object of the present disclosure is to realize an improved multicast / broadcast service.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (Configuration of a mobile communication system) First, the configuration of a mobile communication system according to an embodiment will be described. Fig. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. This mobile communication system complies with the 5th Generation System (5GS) of the 3GPP (registered trademark) standard. In the following, 5GS will be described as an example, but the LTE (Long Term Evolution) system may also be applied at least in part to the mobile communication system.

[0012] As shown in FIG. 1, the mobile communication system includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20.

[0013] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user, and may be, for example, a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0014] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0015] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

[0016] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0017] FIG. 2 is a diagram showing a configuration of the UE 100 (user equipment) according to the embodiment.

[0018] As shown in FIG. 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit .

[0019] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0020] 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 a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0021] The control unit 130 performs various controls in the UE 100. 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 in processing 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 baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0022] FIG. 3 is a diagram showing the configuration of a gNB200 (base station) according to the embodiment.

[0023] As shown in FIG. 3, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240.

[0024] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0025] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0026] The control unit 230 performs various controls in the gNB 200. 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 in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0027] The backhaul communication unit 240 is connected to neighboring base stations via an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and both units may be connected via an F1 interface.

[0028] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0029] As shown in Figure 4, the user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0030] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the gNB 200 via a physical channel.

[0031] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via a transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE 100.

[0032] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via logical channels.

[0033] The PDCP layer performs header compression / decompression and encryption / decryption.

[0034] The SDAP layer maps IP flows, which are the units for QoS control by the core network, to radio bearers, which are the units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, SDAP is not necessary.

[0035] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0036] As shown in FIG. 5, the protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in FIG.

[0037] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0038] The NAS layer, which is positioned above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300.

[0039] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0040] (MBS) Next, an MBS according to an embodiment will be described. The MBS is a service for broadcasting or multicasting, i.e., point-to-multipoint (PTM) data transmission, from the NG-RAN 10 to the UE 100. The MBS is sometimes called an MBMS (Multimedia Broadcast and Multicast Service).

[0041] MBS use cases include public safety communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV, group communications, and software distribution.

[0042] There are two types of MBS transmission methods in LTE: MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. Fig. 6 is a diagram showing the correspondence relationship between downlink logical channels and transport channels according to an embodiment.

[0043] As shown in Figure 6, the logical channels used for MBSFN transmission are the MTCH (Multicast Traffic Channel) and the MCCH (Multicast Control Channel), and the transport channel used for MBSFN transmission is the MCH (Multicast Control Channel). MBSFN transmission is designed primarily for multi-cell transmission, and in an MBSFN area consisting of multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0044] The logical channels used for SC-PTM transmission are the Single Cell Multicast Traffic Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH), and the transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission, transmitting data by broadcast or multicast on a cell-by-cell basis. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Control Channel (PDSCH), which enable dynamic resource allocation.

[0045] In the following, an example in which an MBS is provided using the SC-PTM transmission method will be mainly described, but the MBS may also be provided using the MBSFN transmission method. Also, an example in which an MBS is provided by multicast will be mainly described, but the MBS may also be provided by broadcast. In the following, MBS data refers to data transmitted by MBS transmission, and MBS transmission refers to multicast or broadcast. The multicast control channel refers to the MCCH or SC-MCCH, and the multicast traffic channel refers to the MTCH or SC-MTCH.

[0046] The network can deliver different MBS data for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identity (TMGI), a session identifier, and a Group Cell Radio Network Temporary Identifier (G-RNTI). Hereinafter, at least one of these identifiers is referred to as an MBS session identifier. The MBS session identifier may also be referred to as an MBS group identifier (or multicast group identifier).

[0047] FIG. 7 is a diagram illustrating an example of an operating environment according to the embodiment.

[0048] As shown in FIG. 7, the gNB 200 manages a cell C1 (first cell) and a cell C2 (second cell). Although an example in which the cell sizes of the cells C1 and C2 are equal is illustrated, the cell sizes of the cells C1 and C2 may be different from each other. The cell C1 operates at a frequency F1, and the cell C2 operates at a frequency F2. That is, the frequencies (carrier frequencies) of the cells C1 and C2 are different from each other. The geographical areas of the cells C1 and C2 at least partially overlap. Such a relationship between the cells may be referred to as neighboring cells. The UE 100 is located in the overlapping area of ​​the cells C1 and C2.

[0049] FIG. 8 is a diagram showing another example of the operating environment according to the embodiment.

[0050] As shown in Figure 8, this differs from Figure 7 in that cells C1 and C2 are managed by different base stations. Specifically, gNB200A manages cell C1, and gNB200B manages cell C2. Figure 8 shows an example in which the two base stations managing cells C1 and C2 are base stations of the same radio access technology, NR. However, the two base stations managing cells C1 and C2 may use different radio access technologies. For example, one of the two base stations managing cells C1 and C2 may be an NR base station (gNB) and the other an LTE base station (eNB).

[0051] (Mobile communication system operation) Next, an operation according to one embodiment will be described, assuming the above-described mobile communication system and MBS.

[0052] An operation according to one embodiment relates to an operation of changing the MBS cell used for transmitting or receiving MBS data from cell C1 to cell C2 when UE 100 is receiving MBS data transmitted in cell C1 in an operating environment such as that shown in Figures 8 and 9. For example, gNB 200 managing cell C1 determines to change the MBS cell from cell C1 to cell C2 in response to an increase in load due to congestion in cell C1. This enables load balancing between cells.

[0053] A communication control method according to one embodiment includes the steps of: a gNB200 transmitting MBS data to a UE100 in a cell C1; a gNB200 transmitting a notification message to the UE100 indicating that an MBS cell used for transmitting or receiving the MBS data will be changed from cell C1 to cell C2; and a UE100 receiving the MBS data from the gNB200 receiving the notification message from the gNB200. By transmitting such a notification message to the UE100, the UE100 is aware that the MBS cell will be changed, making it easier for the UE100 to continue receiving the MBS data.

[0054] The gNB 200 may transmit the notification message to the UE 100 as a control message transmitted on a multicast control channel or as system information (SIB: System Information Block) transmitted on a broadcast control channel (BCCH). The gNB 200 may transmit the notification message as a MAC CE (Control Element), which is a control message of the MAC layer, or as an RRC message.

[0055] The notification message includes at least one of an information element indicating the timing to change the MBS cell, an identifier (cell identifier) ​​indicating cell C2, an identifier (frequency identifier) ​​indicating the frequency to which cell C2 belongs, and an identifier (MBS session identifier) ​​indicating the MBS session for which the MBS cell is to be changed. In the notification message, at least one of the information element indicating the timing to change the MBS cell, the cell identifier, and the frequency identifier may be associated with the MBS session identifier. However, when the notification message is transmitted by MAC CE and the multicast traffic channel and MAC CE are multiplexed, the MBS session identifier is self-evident, and therefore there is no need to explicitly notify the MBS session identifier.

[0056] The notification message may include an information element indicating whether MBS transmission in cell C1 is to be stopped. The information element indicating the change of the MBS cell from cell C1 to cell C2 and the information element indicating whether MBS transmission in cell C1 is to be stopped may be a common information element, and the content of this information element may indicate "change" or "stop."

[0057] The notification message may be a message notifying that the MBS cell will be changed within a certain period of time, or may be a message including the notification as an information element. The certain period of time may be 0 (zero: immediately), the period of an SC-MCCH modification boundary (or SIB modification boundary), or any period set by the gNB 200. The time unit of the certain period of time may be an SC-MCCH (or SIB) modification boundary unit, a radio frame unit, a subframe unit, or minutes or seconds.

[0058] The notification message may be a message notifying that a transmission cell will be changed at a certain time, or may be a message containing the notification as an information element. The time may be expressed by a system frame number (SFN) or a hyper system frame number (H-SFN).

[0059] The notification message may be a message notifying that the MBS session currently transmitting MBS data is also transmitting in another cell, or may be a message including the notification as an information element. When MBS transmission of the same MBS session is being performed in multiple cells, the notification message may be a message notifying information indicating a cell that is recommended for reception. In this case, since the same MBS session is being transmitted simultaneously (double) in other cells, UE 100 can smoothly change the destination cell at any timing.

[0060] The notification message may be a message notifying that a change of cell is recommended (or instructed) for the MBS session currently transmitting MBS data, or may be a message including the notification as an information element.

[0061] 9 is a diagram showing operation example 1. In operation example 1, it is assumed that the UE 100 is in an RRC connected state.

[0062] 9, in step S101, the gNB 200 starts transmitting MBS data of a certain MBS session (here, assumed to have MBS session identifier #1) in cell C1. The UE 100 receives the MBS data from cell C1. Thereafter, it is assumed that the gNB 200 decides to change the MBS cell that transmits the MBS data corresponding to MBS session identifier #1 from cell C1 to cell C2.

[0063] In step S102, the gNB 200 transmits, in the cell C1, a notification message indicating that the MBS cell that transmits the MBS data corresponding to the MBS session identifier #1 is changed from the cell C1 to the cell C2. The UE 100 receives the notification message.

[0064] In step S103, based on the notification message received in step S102, the UE 100 transmits an indication (hereinafter referred to as an MBS indication) for the UE 100 to perform handover from the cell C1 to the cell C2 to the gNB 200. The handover is a cell switching operation of the UE 100 in the RRC connected state.

[0065] The MBS indication may be an RRC message. The MBS indication includes an identifier of a cell C2 from which the UE 100 wishes to receive MBS data and / or an identifier of its frequency (frequency F2). The MBS indication may include an information element indicating whether the UE 100 prioritizes MBS reception over unicast reception.

[0066] The MBS indication may be a message requesting the setting of an MBS reception period for the UE 100 to receive MBS data from cell C2 while maintaining connection to cell C1, or a message including the request as an information element. The MBS reception period is a period during which the UE 100 does not communicate with cell C1, and may be called an MBS reception gap.

[0067] The MBS indication may be transmitted based on a condition related to switching of an MBS cell, or may be transmitted based on other conditions. Only in the latter case, the UE 100 may operate a prohibition timer to restrict repeated transmission of the MBS indication. Specifically, the UE 100 starts the prohibition timer when transmitting the MBS indication, and transmission of the next MBS indication is prohibited until the prohibition timer expires. On the other hand, when the UE 100 transmits the MBS indication based on a condition related to switching of an MBS cell, the prohibition timer is not applied (ignored).

[0068] Based on the MBS indication from the UE 100, the gNB 200 determines that the UE 100 wishes to receive an MBS from the switching destination cell C2 (is interested in receiving an MBS). In step S104, the gNB 200 transmits a configuration message, which is an RRC message, to the UE 100 in the cell C1. The configuration message may be an RRC Reconfiguration message. The configuration message may be a message that configures (instructs) the UE 100 to perform a handover to the cell C2. The configuration message may be a message that configures the UE 100 to measure cell C2 (frequency F2) and report the measurements prior to the handover. In this case, the UE 100 is instructed to perform a handover after the measurement report. The configuration message may be a message that configures the UE 100 with the above-mentioned MBS reception period.

[0069] If the setting message is a message instructing a handover, in step S105, the UE 100 performs a handover from the cell C1 to the cell C2.

[0070] In step S106, the gNB 200 starts transmitting MBS data of the MBS session identifier #1 in the cell C2. The UE 100 receives the MBS data from the cell C2. When an MBS reception period is set in the UE 100, the UE 100 receives the MBS data from the cell C2 in the set MBS reception period.

[0071] In step S107, the gNB 200 stops transmitting the MBS data of the MBS session identifier #1 in the cell C1. Step S107 may be performed simultaneously with step S106.

[0072] 10 is a diagram showing an operation example 2. In the operation example 2, it is assumed that the UE 100 is in an RRC idle state or an RRC inactive state.

[0073] As shown in FIG. 10, steps S201 and S202 are similar to steps S101 and S102 described above.

[0074] In step S203, UE 100 performs cell reselection from cell C1 to cell C2 based on the notification message received from gNB 200 (cell C1) in step S202. Cell reselection is a cell switching operation of UE 100 in an RRC idle state or an RRC inactive state. Here, UE 100 may perform cell reselection from cell C1 to cell C2 by setting cell C2 or frequency F2 to which cell C2 belongs as the highest priority for cell reselection.

[0075] In step S204, the gNB 200 starts transmitting the MBS data of the MBS session identifier #1 in the cell C2. The UE 100 receives the MBS data from the cell C2.

[0076] In step S205, the gNB200 stops transmitting the MBS data of the MBS session identifier #1 in the cell C1. Step S205 may be performed simultaneously with step S204.

[0077] (Change example 1) Next, the operation according to Modification 1 of the above-described embodiment will be described, focusing on differences from the above-described embodiment. In Modification 1, a scenario in which NR cells and LTE cells coexist is assumed.

[0078] In the above-described embodiment, it is assumed that cell C2 is an NR cell. However, cell C2 may be an LTE cell. UE 100 that supports both NR and LTE radio access technologies (RATs) can receive MBS from NR cells and transmit MBS from LTE cells. On the other hand, UE 100 that supports only NR can receive MBS from NR cells but cannot receive MBS from LTE cells. For this reason, in Modification 1, the RAT of cell C2 is notified in the notification message.

[0079] The notification message according to the first modification may have at least one of the functions of the notification message described above. However, the notification message according to the first modification may not have the function of indicating that the MBS cell is changed from cell C1 to cell C2. In the first modification, cell C1 and cell C2 may transmit MBS data of different MBS sessions. This premise also applies to each modification described below.

[0080] FIG. 11 is a diagram illustrating the operation according to the first modification.

[0081] As shown in Fig. 11, in step S401, gNB200 managing cell C1 transmits a notification message regarding MBS transmission in cell C2 to UE100 in cell C1. The notification message according to Modification 1 includes RAT information indicating the RAT used by cell C2 for MBS transmission. The RAT information indicates whether the RAT used by cell C2 for MBS transmission is LTE or NR. The notification message according to Modification 1 may be an SIB transmitted on the BCCH or a message transmitted on the multicast control channel.

[0082] When a neighboring cell (cell C2) is transmitting an MBS, the gNB 200 (cell C1) includes in the notification message transmitted by cell C1 the MBS session identifier of the MBS transmission, the cell ID of the neighboring cell, and at least one of the frequencies to which the neighboring cell belongs, as well as RAT information that identifies whether the MBS transmission is performed in LTE or NR. The RAT information is, for example, an information element such as "ratType ENUM(lte,nr)".

[0083] In the first modification, when the UE 100 in the RRC connected state receives a notification message from the gNB 200 (cell C1), the UE 100 controls the transmission of the above-mentioned MBS indication based on the RAT information included in the notification message, the RATs that the UE 100 supports, and the MBS sessions that the UE 100 is interested in receiving. The sequence of such operations is the same as that of the above embodiment (see FIG. 9).

[0084] For example, UE 100 may determine, based on the RAT information included in the notification message, that an MBS session, cell, or frequency where MBS transmission is performed using a RAT different from the RAT that UE 100 supports is not capable of receiving MBS, and may exclude the MBS session, cell, or frequency that UE 100 is interested in. UE 100 may determine, based on the RAT information included in the notification message, that an MBS session, cell, or frequency where MBS transmission is performed using a RAT that UE 100 supports is capable of receiving MBS, and may set the MBS session, cell, or frequency as a candidate for an MBS session, cell, or frequency that UE 100 is interested in.

[0085] In Modification 1, when UE 100 in the RRC idle state or the RRC inactive state receives a notification message from gNB 200 (cell C1), UE 100 controls the above-mentioned cell reselection based on the RAT information included in the notification message, the RATs it supports, and the MBS sessions it is interested in receiving. The sequence of such operations is the same as in the above-mentioned embodiment (see FIG. 10).

[0086] (Change example 2) Next, the operation of the first modification of the above-described embodiment will be described, focusing mainly on the differences from the above-described embodiment and its modifications.

[0087] Modification example 2 assumes a scenario in which cell C2, which is a neighboring cell, is an NR cell. When cell C2 is an NR cell, a bandwidth part (BWP) that limits the transmission and reception band of UE 100 may be set in cell C2. Figure 12 is a diagram showing an example of the BWP.

[0088] As shown in Figure 12, a BWP is a frequency portion of the entire band of a cell. Figure 12 illustrates BWP1 with a bandwidth of 40 MHz and a subcarrier spacing of 15 kHz, BWP2 with a bandwidth of 10 MHz and a subcarrier spacing of 15 kHz, and BWP3 with a bandwidth of 20 MHz and a subcarrier spacing of 60 kHz. The BWPs are configured to the UE 100 by the gNB 200, and switching from one BWP to another is controlled by the gNB 200. For example, when multiple BWPs are configured to the UE 100, and some BWPs are active and others are inactive, the gNB 200 can control the active BWP to be switched to another BWP. In addition, the subcarrier spacing and cyclic prefix can be variably configured for each BWP.

[0089] Under such a premise, the gNB 200 may set a BWP for MBS transmission. Here, it is preferable that the UE 100 located in the cell C1 knows in advance the setting of the BWP for MBS transmission of the cell C2. This allows the UE 100 to quickly receive MBS data from the cell C2 upon switching from the cell C1 to the cell C2.

[0090] FIG. 13 is a diagram illustrating an operation according to the second modification.

[0091] As shown in FIG. 13, in step S401, gNB200 managing cell C1 transmits a notification message regarding MBS transmission in cell C2 to UE100 in cell C1. The notification message according to modification 2 includes BWP information indicating the BWP used by cell C2 for MBS transmission. The notification message according to modification 2 may include RAT information, as with the notification message according to modification 1. In this case, the BWP information may be included in the notification message only when the RAT information in the notification message indicates NR. Note that the notification message according to modification 2 may be an SIB transmitted on a BCCH or a message transmitted on a multicast control channel.

[0092] When a neighboring cell (cell C2) is transmitting an MBS, gNB200 (cell C1) includes in the notification message transmitted by cell C1 at least one of the MBS session identifier of the MBS transmission, the cell ID of the neighboring cell, and the frequency to which the neighboring cell belongs, as well as BWP information indicating the BWP to be used for the MBS transmission.

[0093] The BWP information may include information (BWP identifier) ​​that identifies which BWP is being transmitted. The BWP information may include at least one of BWP setting information, such as information indicating the frequency location and bandwidth of the BWP, information indicating the subcarrier spacing of the BWP (e.g., 15 kHz, 30 kHz, 60 kHz, 120 kHz, or 240 kHz), and information indicating the cyclic prefix length used in the BWP (e.g., normal length or extended length).

[0094] For example, the BWP information includes the first PRB (Physical Resource Block) position and bandwidth, and may also include an index value associated with the first PRB position and bandwidth.

[0095] Furthermore, the BWP information may include at least one of PDCCH configuration information and PDSCH configuration information for the corresponding BWP. The BWP information may include at least one of SIB configuration information and multicast control channel configuration information (scheduling information) for the corresponding BWP.

[0096] (Change example 3) Next, the operation according to Modification 3 of the above-described embodiment will be described, focusing on differences from the above-described embodiment. In Modification 3, a scenario in which NR cells and LTE cells coexist is assumed, similar to Modification 1.

[0097] When the UE 100 supports multiple RATs (NR and LTE), the above-mentioned MBS indication does not allow the gNB 200 to determine which RAT the UE 100 desires to receive MBS on. In particular, when NR cells and LTE cells coexist on the same frequency, it is difficult to identify the RAT from the frequency identifier included in the MBS indication.

[0098] Furthermore, if the UE 100 can transmit both the NR MBS indication and the LTE MBS indication, there is a concern that an unexpected error may occur in the gNB 200. For this reason, a RAT can be selected so that the NR MBS indication and the LTE MBS indication are not transmitted in duplicate.

[0099] FIG. 14 is a diagram illustrating an operation according to the third modification.

[0100] 14, in step S501, UE 100, which supports multiple RATs, selects a RAT to be used by itself to receive MBS data from among the multiple RATs, and transmits a message indicating the selected RAT (MBS indication) to gNB 200. For example, if UE 100 selects NR, it transmits an NR MBS indication to gNB 200, and if UE 100 selects LTE, it transmits an LTE MBS indication to gNB 200.

[0101] Fig. 15 is a diagram showing a configuration example of an MBS indication according to Modification 3. As shown in Fig. 15, the MBS indication (MBSInterestIndication-r17) is configured to allow selection (CHOICE) between an LTE MBS indication (LTE-MBMSInterestIndication) and an NR MBS indication (NR-MBSInterestIndication).

[0102] Alternatively, the UE 100 may include an explicit information element (e.g., ENUM(lte,nr)) indicating the selection result in the MBS indication. For example, the UE 100 may transmit an NR MBS indication to the gNB 200 when it selects NR, and may transmit an NR MBS indication including information indicating LTE to the gNB 200 when it selects LTE.

[0103] (Other embodiments) The above-described modifications are not limited to being implemented independently, but may be implemented in combination of two or more modifications.

[0104] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0105] In addition, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0106] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0107] This application claims priority from Japanese Patent Application No. 2020-131728 (filed August 3, 2020), the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method used in a mobile communication system that provides a multicast broadcast service (MBS), comprising: a network node managing a first cell and a second cell different from the first cell transmitting a notification message regarding MBS transmission in the second cell to a user equipment in the first cell; the network node transmitting the MBS in the second cell while maintaining a connection between the user equipment and the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. Communication control method.

2. The notification message further includes information indicating the position and bandwidth of a first PRB (Physical Resource Block) used to receive the MBS in the second cell. The communication control method according to claim 1 .

3. receiving, by the network node, an indication from the user equipment based on the notification message; and starting the MBS transmission in the second cell and stopping the MBS transmission in the first cell based on the indication. The communication control method according to claim 1 .

4. The network node may further configure, based on the indication, an MBS reception period for the user equipment during which no communication with the first cell is performed; The MBS reception period is a period during which the user equipment receives the MBS transmission from the second cell. The communication control method according to claim 3.

5. A network node for providing a multicast and broadcast service (MBS), comprising: a control unit that manages a first cell and a second cell different from the first cell; a transmitter configured to transmit a notification message regarding MBS transmission in the second cell to a user equipment in the first cell; The transmitter performs the MBS transmission in the second cell while maintaining a connection between the user equipment and the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. Network node.

6. A user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising: A receiving unit that receives a notification message regarding MBS transmission in the second cell from a network node that manages a first cell and a second cell different from the first cell, via the first cell; The receiver receives the MBS transmission in the second cell while maintaining a connection with the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. User equipment.

7. A chipset for controlling user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising: receiving, via the first cell, a notification message regarding MBS transmission in the second cell from a network node managing a first cell and a second cell different from the first cell; receiving the MBS transmission in the second cell while maintaining a connection with the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. Chipset.

8. A user device in a mobile communication system providing a multicast broadcast service (MBS) receiving, via the first cell, a notification message regarding MBS transmission in the second cell from a network node managing a first cell and a second cell different from the first cell; receiving the MBS transmission in the second cell while maintaining a connection with the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. program.

9. A mobile communication system providing a multicast broadcast service (MBS), comprising: a network node that manages a first cell and a second cell different from the first cell; The network node Sending a notification message regarding the MBS transmission in the second cell to a user equipment in the first cell; transmitting the MBS in the second cell while maintaining a connection between the user equipment and the first cell; The notification message includes a cell identifier that identifies the second cell, information that indicates a frequency of the second cell, and bandwidth portion information in the second cell. Mobile communication system.

Images