Distributed Unit, Central Unit, and Method

Abstract

A communication system is disclosed in which multicast and broadcast services (MBS) can be provided via multicast to inactive user equipment (UE). A distributed unit of a base station device receives, from a central unit of the base station device, information identifying at least one MBS session and information identifying that the at least one MBS session is provided in a cell via multicast to inactive UEs.

Description

[Technical field]

[0001] The present disclosure relates to wireless communication systems and devices. [Background technology]

[0002] This disclosure relates to wireless communication systems and devices thereof that operate in accordance with 3rd Generation Partnership Project (3GPP®) standards or equivalents or derivatives thereof. This disclosure has particular, but not exclusive, relevance to improvements relating to multimedia broadcast sessions in so-called "5G" (or "next generation") systems.

[0003] The latest evolution of the 3GPP standards is called "5G" or "New Radio" (NR). These terms refer to evolving communications technologies that support various applications and services. Various details of 5G networks are described, for example, in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, available at https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G by the so-called 3GPP NextGen Radio Access Network (RAN) and the 3GPP NextGen core network (NGC).

[0004] Under 3GPP standards, a base station (e.g., an "eNB" for 4G or a "gNB" for 5G) is a node through which communication devices (user equipment or "UE") connect to a core network and communicate with other communication devices or remote servers. For simplicity, this disclosure uses the term base station to refer to any such base station.

[0005] In the 5G architecture, the gNB internal structure may be split into two parts known as the Central Unit (CU) and the Distributed Unit (DU). In this "split" architecture, the generally "higher" CU layer (e.g., but not necessarily or exclusively, PDCP) and the generally "lower" DU layer (e.g., but not necessarily or exclusively, RLC / MAC / PHY) may be implemented separately. Thus, for example, in each of the gNBs, the higher layer CU functions of some gNBs may be implemented centrally (e.g., by a single processing unit or in a cloud-based or virtualized system), while the lower layer DU functions may be kept local.

[0006] For simplicity, this disclosure will use the terms mobile device, user device, or UE to refer to any communications device that can connect to a core network via one or more base stations, including distributed base stations and units thereof.

[0007] The communication devices may be mobile communication devices, such as, for example, mobile phones, smartphones, user equipment, personal digital assistants, laptop / tablet computers, web browsers, e-book readers, etc. Such mobile (or generally fixed) devices are typically operated by a user. However, the 3GPP standards also allow so-called "Internet of Things" (IoT) devices (e.g., Narrow-Band IoT (NB-IoT) devices) to be connected to the network, which typically includes various measurement equipment, telemetry equipment, monitoring systems, tracking and tracing devices, in-vehicle safety systems, vehicle maintenance systems, road sensors, digital billboards, point of sale (POS) terminals, remote control systems, and other automated equipment. In effect, the Internet of Things is a network of devices (or "things") equipped with appropriate electronics, software, sensors, network connectivity, and / or the like, which enable these devices to collect and exchange data with each other and with other communication devices. It will be appreciated that IoT devices may also be referred to as Machine-Type Communication (MTC) communication devices or Machine-to-Machine (M2M) communication devices.

[0008] For simplicity, this disclosure often refers to mobile devices in the description, however, it will be understood that the described techniques may be implemented on any communication device (mobile and / or generally fixed) capable of connecting to a communication network to transmit / receive data, regardless of whether such communication device is controlled by human input or by software instructions stored in memory.

[0009] The so-called Radio Resource Control (RRC) protocol is the control plane protocol between the UE and the radio access network (base station). RRC has three different states (in 5G): RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE. The functionality and state transitions in each state are defined in the 3GPP TS38.331 V16.7.0 standard (Release 17 version not yet published). In summary, in the RRC connected state, radio resources are allocated to the UE and there is usually an active (user plane or control plane) communication between the UE and the network. When the radio resources are no longer needed, the network can decide to release the RRC connection and move the UE to the RRC idle state. In the RRC idle state, there is no active communication between the UE and the network. A third RRC inactive state was introduced in 5G to provide an "always on" type of connection. Specifically, when the network decides to put the UE in an inactive state (rather than an idle state), the RRC connection can be resumed as needed without excessive signaling. This is achieved by (among other things) maintaining applicable radio and security configurations in the UE and the radio access network (base station). In the RRC connected state, UE mobility is controlled by the network via handovers between cells. In the RRC idle and inactive states, the UE performs measurements of nearby cells and performs cell reselection if necessary (based on the results of the measurements).

[0010] One of the recent features being developed on the existing 5G framework is called Multicast and Broadcast Services (MBS). This feature aims to enhance the capabilities of 5G New Radio and 5G Core Networks to deploy a variety of multicast and broadcast services reliably, with low latency, resource efficiency, and at scale. 3GPP is currently specifying the details of MBS for media distribution over mobile broadband networks. MBS (or "NR MBS" for 5G) aims to reuse cellular infrastructure such as the so-called Low Power Low Tower (LPLT) infrastructure. One of the main use cases is the distribution of linear / live media content to smartphones, tablets, vehicles, and other mobile (or fixed) devices. While MBS is designed to use the existing (or default) 3GPP infrastructure, MBS can provide more efficient delivery of multicast / broadcast traffic than unicast communication using the same infrastructure. Details of the MBS architectural enhancements are described in 3GPP Technical Specification (TS) 23.247V17.1.0, the contents of which are incorporated herein by reference.

[0011] MBS uses shared tunnels for delivering user plane data (e.g., F1 / NG user plane) to multiple UEs that have joined a particular service to benefit from more efficient delivery of multicast / broadcast traffic. Thus, a shared tunnel is established during session startup of the MBS, or if there is a shared tunnel already established for a given MBS, the tunnel is shared for the MBS session. When a UE joins an MBS service, an MBS session is established for that service on the user plane that is transmitted through the appropriate shared tunnel (using multicast). More specifically, the traffic of the MBS service is transmitted using multicast through the shared user plane tunnel of that MBS service via the serving base station or its distributed unit. Note that this is quite different from unicast, which uses a dedicated user plane tunnel for each UE.

[0012] In the current (Release 17) version of the 3GPP specification, MBS via multicast is supported for UEs in a Radio Resource Control (RRC) connected state. However, there is interest in extending multicast MBS support to UEs in an RRC inactive state. This, however, may impact RRC inactive state mobility and state transitions, since the current standard does not specify how to provide a UE with the necessary multicast configuration to receive multicast MBS data in the RRC inactive state. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] “NGMN 5G White Paper” V1.0, Next Generation Mobile Networks (NGMN) Alliance, https: / / www.ngmn.org / 5g-white-paper.html [Non-Patent Document 2] 3GPP TS38.331 V16.7.0 standard [Non-Patent Document 3] 3GPP Technical Specification (TS) 23.247 V17.1.0 Summary of the Invention [Problem to be solved by the invention]

[0014] The inventors have recognized that when using distributed base station units, it may be particularly difficult to provide MBS to UEs in RRC inactive state via multicast. Specifically, in Release 17, after a shared tunnel is established between the central unit and the distributed units for the MBS service, the central unit delivers the relevant data (PDCP PDUs) to the distributed units. However, it is up to the distributed units to decide whether to use unicast or multicast in the air interface. Since only RRC connected UEs are supported for receiving MBS (both unicast and multicast) in Release 17, the distributed units always have enough information (e.g., the number of UEs receiving or interested in a particular MBS session via the distributed unit) to decide whether to use unicast or multicast in the distributed unit's cell. However, the distributed units do not have accurate information (or any information) about the number of RRC inactive UEs camped in the distributed unit's cell or the number of RRC inactive UEs interested in a particular MBS session, even if such information is available in the central unit or core network nodes. For example, the UE can enter an RRC connected state and join an MBS session in the cell of the distributed unit. Thus, at this stage, the distributed unit is aware of the existence of the UE and the MBS session received by the UE in the cell. However, when the UE transitions to RRC inactive, the distributed unit no longer has this information (whether the UE performed cell reselection or not). In another example, the distributed unit may not have the correct MBS-related information due to mobility (cell reselection). Specifically, when the UE performs cell reselection to a cell of another base station (or distributed unit), neither the old nor the new base station can determine that the number of UEs camped in the respective cells has changed. Thus, they also cannot determine whether it is appropriate to use unicast or multicast in those cells.Furthermore, a UE that has performed cell reselection may want to continue receiving MBS multicast in the new cell without having to transition to an RRC connected. [Means for solving the problem]

[0015] SUMMARY Accordingly, the present disclosure seeks to provide a method, and associated apparatus, that addresses or at least alleviates (at least some of) the problems discussed above.

[0016] In one aspect, the present disclosure provides a method performed by a distributed unit of a base station device for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the method including receiving information from a central unit of the base station device in at least one of a UE context procedure and a multicast context procedure, identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast.

[0017] In one aspect, the present disclosure provides a method performed by a central unit of a base station device for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the method including transmitting information to a distributed unit of the base station device in at least one of a UE context procedure and a multicast context procedure, identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast.

[0018] In one aspect, the present disclosure provides a method performed by a distributed unit of a base station device for providing a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the method including receiving information from an associated central unit indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory.

[0019] In one aspect, the present disclosure provides a method performed by a central unit of a base station device for providing a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the method including transmitting information to a distributed unit of the base station device indicating that a point-to-multipoint transmission associated with the MBS session is no longer required.

[0020] In one aspect, the present disclosure provides a method performed by a user equipment (UE), the method including receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station device, performing cell reselection to a new cell, and transmitting information to a network node associated with the new cell indicating that the UE has performed cell reselection.

[0021] In one aspect, the disclosure provides a method performed by a network node, the method including receiving information from a user equipment (UE) indicating that the UE has performed cell reselection to a cell associated with the network node when, prior to the cell reselection, a multicast and broadcast service (MBS) session was provided to the UE in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus.

[0022] In one aspect, the present disclosure provides a method performed by a user equipment (UE), the method including receiving information indicating whether at least one multicast session is provided in a cell, and performing cell reselection based on the information to receive the multicast session in an inactive state.

[0023] In one aspect, the present disclosure provides a method performed by a base station, the method including transmitting information indicating whether at least one multicast session is provided in a cell, for use by a user equipment (UE) when performing cell reselection to receive at least one multicast session in an inactive state.

[0024] In one aspect, the present disclosure provides a distributed unit of a base station device for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the distributed unit comprising: means (e.g., a memory, a controller, and a transceiver) for receiving information from a central unit of the base station device in at least one of a UE context procedure and a multicast context procedure, the information identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell by multicast.

[0025] In one aspect, the present disclosure provides a central unit of a base station device for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the central unit comprising means (e.g., a memory, a controller, and a transceiver) for transmitting information to a distributed unit of the base station device in at least one of a UE context procedure and a multicast context procedure, identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell by multicast.

[0026] In one aspect, the present disclosure provides a distributed unit of a base station device for providing a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the distributed unit comprising means (e.g., a memory, a controller, and a transceiver) for receiving information from an associated central unit indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory.

[0027] In one aspect, the present disclosure provides a central unit of a base station device for providing a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the central unit comprising means (e.g., a memory, a controller, and a transceiver) for transmitting information to a distributed unit of the base station device indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory.

[0028] In one aspect, the present disclosure provides a user equipment (UE), the user equipment including: means (e.g., a memory, a controller, and a transceiver) for receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus; means for performing cell reselection to a new cell; and means for transmitting information indicating that the UE has performed cell reselection to a network node associated with the new cell.

[0029] In one aspect, the present disclosure provides a network node, comprising means (e.g., a memory, a controller, and a transceiver) for receiving information from a user equipment (UE) indicating that the UE has performed cell reselection to a cell associated with the network node when a Multicast and Broadcast Service (MBS) session was provided to the UE in an inactive state prior to the cell reselection using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus.

[0030] In one aspect, the present disclosure provides a user equipment (UE), the user equipment including means (e.g., a memory, a controller, and a transceiver) for receiving information indicating whether at least one multicast session is provided in a cell, and means for performing cell reselection based on the information for receiving the multicast session in an inactive state.

[0031] In one aspect, the present disclosure provides a base station, the base station comprising means (e.g., a memory, a controller, and a transceiver) for transmitting information indicating whether at least one multicast session is provided in a cell, for use by a user equipment (UE) when performing cell reselection to receive at least one multicast session in an inactive state.

[0032] Aspects of the present disclosure extend to corresponding systems, apparatus, and computer program products, such as computer readable storage media having instructions stored therein, the instructions being operable to program a programmable processor to perform the methods according to the aspects and possibilities set out above or recited in the claims, and / or to program a computer suitably adapted to provide an apparatus as recited in any of the claims.

[0033] Each feature disclosed in this specification (which term includes the claims) and / or shown in the drawings may be incorporated in the disclosure independently (or in combination) with any other disclosed and / or shown feature. In particular, but not by way of limitation, any feature of a claim depending from a particular independent claim may be incorporated in that independent claim in any combination or individually.

[0034] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0035] [Figure 1] 1 is a schematic diagram of a mobile (cellular or wireless) telecommunications system in which embodiments of the present disclosure may be applied; [Diagram 2] 1 is a schematic diagram of a mobile (cellular or wireless) telecommunications system in which embodiments of the present disclosure may be applied; [Diagram 3] 2 is a schematic block diagram of a mobile device forming part of the system shown in FIG. 1; [Figure 4] 2 is a schematic block diagram of an access network node (eg a base station) forming part of the system shown in FIG. 1; [Diagram 5] 2 is a schematic block diagram of an access network node (eg a base station) forming part of the system shown in FIG. 1; [Figure 6] FIG. 2 is a schematic block diagram of a core network node forming part of the system shown in FIG. 1; [Figure 7] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 8] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 9] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 10] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 11] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 12] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 13] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 14] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 15]FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 16A] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. [Figure 16B] FIG. 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] overview 1 and 2 illustrate diagrammatically a mobile (cellular or wireless) telecommunications system 1 in which embodiments of the present disclosure may be applied.

[0037] In this system 1, users of mobile devices 3 (UE) can communicate with each other and other users via base stations 5 (and other access network nodes) and a core network 7 using an appropriate 3GPP Radio Access Technology (RAT), such as Evolved Universal Terrestrial Radio Access (E-UTRA) and / or 5G RAT. It will be appreciated that multiple base stations 5 form a (Radio) Access Network or (R)AN. As will be appreciated by those skilled in the art, although one mobile device 3 and three base stations 5A-5C are shown in FIG. 1 for illustrative purposes, the system, when implemented, will typically include other base stations / (R)AN nodes and mobile devices (UE).

[0038] Each base station 5 controls (directly or via other nodes, such as home base stations, relays, remote radio heads, distributed units, and / or others) one or more associated cells. Base stations 5 supporting next generation / 5G protocols may be referred to as "gNBs". It will be appreciated that some base stations 5 may be configured to support both 4G and 5G protocols, and / or any other 3GPP or non-3GPP communication protocol.

[0039] It will be appreciated that the functionality of the gNB 5 (herein referred to as a "distributed" gNB) may be split between one or more distributed units (DUs) and a central unit (CU), where the CU typically performs higher level functions and communication with the next-generation core, and the DU performs lower level functions and communication over the air interface with nearby UEs (i.e., in the cell operated by the gNB). The distributed gNB includes the following functional units: The gNB Central Unit (gNB-CU) is a logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP) and Packet Data Convergence Protocol (PDCP) layers of the gNB (or the RRC and PDCP layers of an en-gNB) that controls the operation of one or more gNB-DUs. The gNB-CU terminates the so-called F1 interface connected to the gNB-DUs. The gNB distributed unit (gNB-DU) 5D is a logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC) and Physical (PHY) layers of a gNB or en-gNB, and the operation of the gNB-DU is partially controlled by the gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. The gNB-CU-Control Plane (gNB-CU-CP) 5C is a logical node that hosts the control plane part of the RRC and PDCP protocols of the gNB-CU for the en-gNB or gNB. The gNB-CU-CP terminates the so-called E1 interface connected to the gNB-CU-UP and the F1-C (F1 Control Plane) interface connected to the gNB-DU. The gNB-CU-User Plane (gNB-CU-UP) 5U is a logical node that hosts the user plane part of the PDCP protocol of the gNB-CU for the en-gNB and the user plane part of the PDCP protocol and SDAP protocol of the gNB-CU for the gNB. The gNB-CU-UP terminates the E1 interface connected to the gNB-CU-CP and the F1-U (F1 user plane) interface connected to the gNB-DU.

[0040] The mobile devices 3 and the base stations 5 are connected via suitable air interfaces (e.g. the so-called "NR" air interface, the "Uu" interface, and / or similar). Neighboring base stations 5 are connected to each other via suitable inter-base station interfaces (e.g. the so-called "Xn" interface, the "X2" interface, etc.). The base stations 5 are also connected to core network nodes via suitable interfaces (the so-called "NG-U" interface (for the user plane), the so-called "NG-C" interface (for the control plane), etc.).

[0041] The core network 7 (e.g. EPC in LTE or NGC in NR / 5G) typically includes logical nodes (or "functions") for supporting communications in the telecommunications system 1 and for, among other things, subscriber management, mobility management, charging, security, call / session management. For example, the core network 7 in a "next generation" / 5G system includes user plane entities and control plane entities, such as one or more Control Plane Functions (CPFs) and one or more User Plane Functions (UPFs). The so-called Access and Mobility Management Function (AMF) in 5G or Mobility Management Entity (MME) in 4G is responsible for handling connection and mobility management tasks for the mobile devices 3. The so-called Session Management Function (SMF) is responsible for handling communication sessions for the mobile devices 3, such as session establishment, modification and release. 1, the core network 7 includes one or more AMFs 9, one or more UPFs 10, and one or more SMFs 11. It will be appreciated that nodes or functions may have different names in different systems.

[0042] Further details of the core network 7 are shown in Figure 2, which also shows the interfaces between the respective network nodes or functions. As can be seen, the core network 7 may typically include, among others, an Authenticate Server Function (AUSF), a Unified Data Management (UDM) entity, a Policy Control Function (PCF), and an Application Function (AF). The core network 7 is coupled (via the UPF 10) to a Data Network (DN), such as the Internet or a similar Internet Protocol (IP) based network. The core network 7 may also be coupled to an Operation and Management (OAM) function (not shown). In this system 1, a multicast broadcast service (MBS) function is provided to the UE 3 via the UE's serving base station 5 and associated core network nodes such as a UPF 10 and an SMF 11. The UPF 10 may be an MBS-specific UPF, in which case the UPF 10 may be referred to as an MB-UPF 10M (e.g., dedicated to providing MBS function). Similarly, the SMF 11 may be an MBS-specific SMF, in which case the SMF 11 may be referred to as an MB-SMF 11M. However, it will be appreciated that any suitable UPF 10 / SMF 11 may be used for the MBS.

[0043] MBS traffic is distributed over shared user plane tunnels as needed. Specifically, MBS user plane data (e.g., F1-U / NG-U data) for a given MBS session is delivered to UEs that have joined that particular service over the associated shared tunnel using multicast transmission.

[0044] When a first UE joins an MBS service, an MBS session is established for that service on the user plane between the core network 7 and the UE's serving base station 5 (and, if applicable, between units of the distributed gNB that handle the user plane). For UEs (at least one UE) interested in that MBS service, MBS traffic may be transmitted via multicast via a given serving base station or its distributed units using a shared user plane tunnel.

[0045] To address various scenarios that may arise when a UE 3 in an inactive state receives or is interested in receiving an MBS session via multicast (point-to-multipoint: PTM) transmission, the following approach may be taken.

[0046] For example, in the first scenario, when UE 3 joins an MBS session in the cell of distributed unit 5D (or performs handover to the cell while UE 3 is receiving an MBS session), UE 3 may initially be in the RRC connected state. When UE 3 transitions to the RRC inactive state, distributed unit 5D no longer has information about the MBS session received by UE 3 in the cell of distributed unit 5D. Distributed unit 5D is also unaware of the current UE state (idle or inactive) or the cell selected by UE 3 while in the RRC inactive state.

[0047] Beneficially, the distributed unit 5D may be informed about the current RRC state of the UE and whether the UE 3 has performed cell reselection in order to determine whether to provide (continue to provide) PTM services to the RRC inactive UE 3 in a cell served by the distributed unit 5D. For example, the central unit 5C may inform the distributed unit 5D in a message for releasing the UE context associated with the UE 3 that the RRC inactive UE 3 is interested in (continues to receive) MBS services.

[0048] The central unit 5C can assist the distributed unit 5D in deciding to switch to PTM (unicast) transmission for inactive UEs in the cell of the distributed unit 5D. For example, the central unit 5C can inform the distributed unit 5D that an RRC inactive UE 3 is interested in an MBS service (or is interested in continuing to receive an MBS service) in a message for setting up or modifying a multicast context related to at least one MBS session. Effectively, the message can be used to configure the distributed unit 5D that an MBS session should turn on ("always on") or turn off PTM transmission for inactive UEs 3 in the cell of the distributed unit 5D.

[0049] In a second scenario, the UE 3 may be receiving an MBS session in an RRC inactive state in a first cell. When the UE 3 performs cell reselection to a second cell (which may be served by a nearby base station 5), the distributed unit 5D may be notified that the RRC inactive UE has performed cell reselection. This information may be used by the distributed unit 5D to determine whether to provide PTM transmission in the cell of the distributed unit 5D for the particular MBS session. For example, the UE 3 may be configured to perform a RAN notification area update procedure, a registration procedure, or a Small Data Transmission (SDT) to inform the new base station 5 about the cell reselection. The new base station 5 contacts the UE's access and mobility function, which may inform the old distributed unit 5D (via the central unit 5C) that the inactive UE 3 (previously served by the distributed unit 5D) has left the cell. The central unit 5C may instruct the distributed unit 5D to stop / deactivate multicast / PTM transmission in the cell of the distributed unit 5D.

[0050] In a third scenario, which can be combined with the first and / or second scenarios, the UE 3 is configured to obtain information related to the provision of MBS sessions in neighboring cells to assist the UE in cell reselection. For example, the serving base station 5 / distribution unit 5D can identify the frequencies used by the neighboring cells, and the UE 3 can obtain system information from the neighboring cells, such as an appropriate indication identifying whether PTM is always on in a particular neighboring cell, and information identifying any MBS services provided via multicast / PTM in that cell. Alternatively, this information may be provided by the serving base station 5 / distribution unit 5D (along with information identifying the frequencies used by the neighboring cells and / or the associated cell identifiers). Based on the indication that multicast / PTM is used in a cell, and based on the MBS services provided in that cell, the UE 3 can prioritize cells that provide multicast for MBS services of interest to the UE 3.

[0051] User Equipment (UE) FIG. 3 is a block diagram illustrating the main components of the mobile device (UE) 3 shown in FIG. 1. As shown, the UE 3 includes a transceiver circuit 31 operable to transmit signals to and receive signals from connected nodes via one or more antennas 33. Although not necessarily shown in FIG. 3, the UE 3 of course has all the usual features of a conventional mobile device (such as a user interface 35), which may be provided by any one or any combination of hardware, software, and firmware, as appropriate. A controller 37 controls the operation of the UE 3 according to software stored in a memory 39. The software may be pre-installed in the memory 39 and / or downloaded, for example, via the remote communication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 41, a communication control module 43, and an MBS module 45.

[0052] The communication control module 43 is responsible for handling (generating / sending / receiving) signaling messages and uplink / downlink data packets between the UE 3 and other nodes, including the (R)AN node 5 and the core network nodes. The signaling may include RRC signaling (to / from the (R)AN node 5) and / or NG-C / NG-U signaling (to / from the core network 7).

[0053] The MBS module 45 is responsible for handling signaling related to multimedia broadcast services (control signaling and / or MBS traffic), including signaling related to the provision of multimedia broadcast services via multicast for inactive UEs 3.

[0054] Access network node (base station) 4 and 5 are block diagrams showing the main components of the base station 5 (or a similar access network node) shown in FIG. 1. As shown in FIG. 4, the base station 5 comprises a transceiver circuit 51 for transmitting and receiving signals to and from user equipment (such as the mobile device 3) via one or more antennas 53, and a network interface 55 for transmitting and receiving signals to and from the core network 7 and neighboring base stations. The base station 5 comprises a control unit 57 for controlling the operation of the base station 5 according to software stored in a memory 59. The software may be pre-installed in the memory 59 and / or may be downloaded, for example, via the telecommunications network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and at least a communication control module 63. Although not shown in FIG. 4, the network interface 55 also typically comprises a base station-base station interface unit (such as, for example, Xn) and a core network interface unit (such as, for example, NG-C / NG-U / N2 / N3).

[0055] The communication control module 63 is responsible for processing (generating / sending / receiving) signaling between the base station 5 and other nodes, such as UEs 3 and core network nodes. Such signaling may include, for example, control data for managing the operation of the mobile device 3 (e.g., non-access stratum, radio resource control, system information, paging, etc.). The communication control module 63 is also responsible for processing signaling related to multimedia broadcast services (control signaling and / or MBS traffic), including signaling related to the provision of MBS by multicast for inactive UEs 3.

[0056] It will be appreciated that the communication control module 63 may include several sub-modules (or "layers") for supporting specific functions. For example, the communication control module 63 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an SDAP sub-module, an IP sub-module, an RRC sub-module, etc.

[0057] As shown in FIG. 5, if the base station 5 comprises a distributed gNB or en-gNB, the network interface 55 also comprises an E1 interface and an F1 interface (F1-C for control plane and F1-U for user plane) for communicating signals between the respective functions of the distributed gNB or en-gNB. In this case, the software also includes at least one of a gNB-CU-CP module 5C, a gNB-CU-UP module 5U, and a gNB-DU module 5D. If present, the gNB-CU-CP module 5C hosts the control plane portion of the RRC layer and the PDCP layer of the distributed gNB or en-gNB. If present, the gNB-CU-UP module 5U hosts the user plane portion of the PDCP and the SDAP layer of the distributed gNB or the user plane portion of the PDCP layer of the distributed en-gNB. If present, the gNB-DU module 5D hosts the RLC, MAC, PHY layers of the distributed gNB or en-gNB.

[0058] It will be appreciated by those skilled in the art that the central units (e.g., 5C and / or 5U) may be implemented and physically located with the base stations, or may be implemented remotely, as a single physical entity, or as a cloud-based or virtualized system. It will also be appreciated that a single central unit may serve multiple base stations 5.

[0059] Core Network Node FIG. 6 is a block diagram illustrating the main components of the core network node (e.g., AMF 9, UPF 10, or SMF 11) shown in FIG. 1. As shown, the core network node includes a transceiver circuit 71 operable to transmit signals to and receive signals from connected UEs 3 via one or more antennas 73, and to transmit signals to and receive signals from other network nodes (directly or indirectly) via a network interface 75. Signals may be transmitted to and received from UEs 3 directly and / or via base stations 5 or other (R)AN nodes, as required. The network interface 75 typically includes a suitable base station interface (S1 / NG-C / NG-U, etc.). The controller 77 controls the operation of the core network node according to software stored in memory 79. The software may be pre-installed in the memory 79 and / or downloaded, for example, via the remote communication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 81, a communication control module 83, and (optionally) an MBS module 85.

[0060] The communication control module 83 is responsible for handling (generating / sending / receiving) signaling between the core network nodes and other nodes such as UE 3, (R)AN nodes, and other core network nodes.

[0061] For example, when present in the MB-SMF or MB-UPF, the MBS module 85 is responsible for processing signaling related to multimedia broadcast services (control signaling and / or MBS traffic), including signaling related to the provision of MBS via multicast to inactive UEs 3.

[0062] Detailed Description The following is a description of some example procedures performed by nodes of the systems shown in FIGS. 1 and 2 to support MBS sessions for UEs in an RRC inactive state.

[0063] Before discussing these procedures in detail, a short overview of the Protocol Data Unit (PDU) Session Change procedure for a UE 3 participating in a multicast session MBS reception is given. The procedure is shown in Figures 7 and 8 and is based on Figure 7.2.1.3-1 of 3GPP TS 23.247 V17.2.0. This procedure may be followed, for example, when a UE 3 wants to receive an MBS service for the first time before entering an RRC inactive state. Although not shown, before a UE 3 requests to join an MBS session, An MBS session has been created in the core network 7; and The UE 3 knows at least the identifiers of the MBS sessions (MBS Session IDs) of the multicast groups that the UE can join (the identifiers may be provided to the UE 3, for example, via an appropriate service announcement); It will be appreciated that the UE 3 may be registered with the network and may have established a PDU session that may be associated with the multicast session, and that may be running.

[0064] When a first UE 3 in an RRC connected state joins an MBS session, the core network 7 (5GC) triggers an MBS session establishment procedure as specified in section 7.2.1 of 3GPP TS 23.247 (titled "MBS join and Session establishment procedure"). Using this procedure, the UE 3 informs the core network 7 of the UE's interest in joining a multicast MBS session. The first accepted UE join request triggers the establishment of a multicast MBS session to the radio access network (serving base station 5) and the UE 3. As can be seen in steps 15 to 18 of FIG. 8, the multicast data is delivered using an MBS-specific UPF called MB-UPF10M. Between the radio access network (serving base station 5) and the UE 3, the multicast data can be transmitted using either a point-to-point (PTP) bearer or a point-to-multipoint (PTM) bearer, as generally shown in step 18. If multicast delivery is not supported network-wide, the multicast data is sent using UE-specific PDU sessions via the associated UPF 10 as generally shown in steps 19 to 21. However, this delivery method is inefficient, especially when multiple UEs 3 are interested in the same MBS session, since the multicast data needs to be delivered to each UE 3 individually using their associated PDU sessions and UPFs 10, rather than using a shared tunnel (e.g. between the MB-UPF 10M and the base station 5 / distributed unit 5D) and a common (PTM) bearer.

[0065] Scenario 1 In this case, when UE 3 joins an MBS session in the cell of distributed unit 5D (or performs a handover to a cell while UE 3 is receiving an MBS session), UE 3 may initially be in RRC connected state. At this stage, distributed unit 5D is therefore aware of the presence of UE 3 and of the MBS session received by UE 3 in the cell managed by distributed unit 5D. When UE 3 moves to RRC inactive state, distributed unit 5D no longer has this information.

[0066] RRC is controlled by the central unit 5C, so that when the UE 3 transitions between RRC states, the central unit 5C is aware of the current UE state, however the distributed unit 5D is not aware of the current UE state nor the cell selected by the UE 3 while in the RRC inactive state.

[0067] The only thing the distributed unit 5D knows is that the UE context has been released by the central unit 5C, but it does not know whether the UE 3 has moved to an RRC idle state or to an RRC inactive state (where the UE 3 can still receive MBS using multicast).

[0068] Below is a description of several ways in which the distributed unit 5D can be informed regarding the UE's current RRC state and whether the UE 3 has performed cell reselection in order to determine whether to provide PTM service to an RRC inactive UE 3 in a cell served by the distributed unit 5D.

[0069] For example, if three UEs 3 are in RRC connected state and receiving an MBS service, the distributed unit 5D can decide to use a respective PTP bearer for each UE 3. When one of the UEs 3 that is still interested in the MBS session goes into RRC inactive state, the distributed unit 5D needs to know about the UE 3 that goes into RRC inactive state so that the distributed unit 5D can set up a PTM transmission for the RRC inactive UE 3.

[0070] 9 is a signalling (timing) diagram illustrating a schematic procedure for helping the distributed unit 5D decide to switch to PTM (unicast) transmission for inactive UEs in its cell. In this case, the central unit 5C informs the distributed unit 5D in a message for releasing the UE context associated with the UE 3 that the RRC inactive UE 3 is interested in (continues to receive) the MBS service.

[0071] In step 1, the central unit 5C sends a message to the distributed unit 5D for releasing the UE context associated with the UE 3. The message (e.g., UE context request) includes information identifying the UE 3 (UE ID), information identifying at least one MBS session in which the UE 3 is interested (MBS session ID / TMGI), and appropriate PTM multicast radio bearer (MRB) configuration for the MBS session. For example, the PTM MRB configuration may be included in the message for releasing the UE context associated with the UE 3 (e.g., UE context release message, and / or others). The RRC release message may be included in the message for releasing the UE context (shown in FIG. 9) or may be sent separately. Based on the MBS session information received from the central unit 5C, the distributed unit 5D knows which MBS service the UE 3 will (continue to) receive after the UE 3 transitions to the RRC inactive mode.

[0072] In step 2, an RRC release (including the appropriate PTM MRB configuration from the central unit 5C for the MBS session) is sent from the distributed unit 5D to the UE 3. The UE 3 obtains the PTM MRB configuration from the RRC release message. Note that the PTM MRB configuration for establishing the PTM MRB will typically include the appropriate PDCP, RLC, MAC, Multicast / MBS Control Channel (MCCH), and Multicast / MBS Traffic Channel (MTCH) configurations.

[0073] In step 3 (if the distributed unit 5D determines based on the information included in the UE context release message that there is at least one inactive UE in the cell of the distributed unit 5D), the distributed unit 5D decides that PTM transmission for at least one inactive UE 3 in the cell of the distributed unit 5D is always turned on. This decision may be based, for example, on the number of UE 3 reaching or exceeding an associated threshold (which may be "one" inactive UE). It will be appreciated that a different (higher) threshold may be used when deciding whether to use PTM for connected UE 3 in a cell.

[0074] FIG. 10 is a signalling (timing) diagram that illustrates, in schematic form, another procedure that assists the distributed unit 5D to decide to switch to PTM (unicast) transmission for inactive UEs in its cell.

[0075] In this case, the central unit 5C informs the distributed unit 5D that the RRC inactive UE 3 is interested in the MBS service (or is interested in continuing to receive the MBS service) in a message for setting up or modifying a multicast context associated with at least one MBS session. Such a message is illustrated in step 1 of FIG. 10. Essentially, the central unit 5C configures the distributed unit 5D that the MBS session should turn on PTM transmission for the inactive UE 3 in the cell of the distributed unit 5D. This is achieved by including appropriate information in the message transmitted in step 1. The information may be, for example, an indication related to PTM, such as an indication whether PTM should be turned on (always on) or an indication that PTM in the cell may be turned off. In the specific case illustrated in FIG. 10, the multicast context setup request is adapted to include an indication identifying whether PTM should be on or off. It will be understood that the multicast context modification request message may be adapted in a similar manner (if an existing multicast context exists).

[0076] The indication may be in the form of a "PTM always on" indication (or similar), where the distributed unit 5D knows that there is at least one UE 3 in RRC inactive mode that is interested in the MBS session, in other words, this type of indication may need to be sent at least to the first inactive UE 3 in the cell of the distributed unit 5D (although this type of indication may also be sent to any subsequent UEs).

[0077] The indication may be in the form of a "PTM can be off" indication, in which case the central unit 5C knows that there are no inactive UEs 3 in the cell of the distributed unit 5D that are still interested in receiving the MBS session, and therefore in this case the distributed unit 5D does not need to provide (or continue to provide) PTM transmission in its cell for that particular MBS service.

[0078] In this case, it will be appreciated that the base station 5 may provide the UE 3 with an appropriate PTM MRB configuration for the MBS session in an RRC release message, as described above with reference to Figure 9. Alternatively, the PTM MRB configuration may be provided using a system information block. For example, the system information may include the PTM MRB configuration itself, or may include information for receiving the MCCH, and for each MBS session, the relevant PTM MRB configuration (e.g., PDCP, RLC, MAC, MTCH configuration) may be signaled via the MCCH.

[0079] In summary, a distributed unit (providing MBS in its cell) receives from a central unit information identifying at least one MBS session and information identifying that the at least one MBS session is provided in the cell via multicast (using point-to-multipoint transmission) to a user equipment (UE) in inactive state. The information may be included in a suitably formatted UE context release message, which may also include a further message for releasing the UE to inactive state. The further message may include information for configuring a respective multicast radio bearer for the at least one MBS session. Alternatively, the information for configuring the multicast radio bearer may be included in a message for setting up or modifying a multicast context associated with the at least one MBS session. The distributed unit may transmit configuration information to the UE (e.g. in a message for releasing the UE's connection, in a system information block or via a multicast control channel) for configuring a respective multicast radio bearer for receiving the at least one MBS session in inactive state. The configuration information enables a UE in RRC inactive state to use multicast for receiving the at least one MBS session.

[0080] Scenario 2 The following is a description of another MBS-related scenario, specifically several ways in which an RRC inactive UE may inform the distributed unit 5D that it has performed cell reselection, which may be used by the distributed unit 5D to determine whether to provide a PTM transmission in its cell for a particular MBS session.

[0081] Initially, the UE 3 may be receiving an MBS session in the first cell in RRC inactive state. The UE 3 may have acquired the associated PTM MRB configuration as described above. At some point, the UE 3 may perform cell reselection to the second (which may be served by a nearby base station 5). Typically, the UE 3 does not perform a registration change procedure if the tracking area of ​​the second cell is within the UE's tracking area list. In other words, the UE 3 camps on the second cell and remains in RRC inactive state.

[0082] In this scenario, if this UE 3 is the last RRC inactive UE in the first (source) cell, the source distribution unit 5D does not know that there are no more RRC inactive UEs interested in the MBS service. The source distribution unit 5D has to keep PTM transmission running (always on) in the cell of the distribution unit 5D, which may result in a waste of resources. If there are only RRC connected UEs 3 interested in that particular MBS session, it may be more appropriate for the source distribution unit 5D to use PTP transmission for those UEs 3 (depending on the number of UEs and / or UE capabilities, among others).

[0083] Therefore, to help the distributed unit 5D make appropriate decisions regarding MBS multicast in its cell, the following procedures, which are described with reference to Figs. 11 to 16, may be used.

[0084] FIG. 11 is a signalling (timing) diagram that illustrates a schematic procedure for notifying the distributed unit 5D that an inactive UE (previously served by the distributed unit 5D) has left the cell of the distributed unit 5D.

[0085] More specifically, the UE 3 performs cell reselection to a cell served by another base station 5 (denoted as "new gNB" in FIG. 11) while receiving the MBS session via the cell of the distributed unit 5D (denoted as "old DU" in FIG. 11). Then, in step 1, the UE 3 informs the new base station 5 that the UE 3 has performed cell reselection. For example, information indicating that the UE 3 has performed cell reselection may be included in at least one of a registration request message, a resume request message, a radio access network (RAN) notification area update message, and a small data transmission message. In step 2, the new base station 5 informs the old base station (the central unit 5C of the old base station) via the base station-base station interface that the UE 3 has performed cell reselection to the cell of the new base station 5. The central unit 5C forwards this indication to the distributed unit 5D in step 3, so that the distributed unit 5D can make an appropriate decision on whether to maintain the multicast transmission for the associated MBS session or to release the associated MRB.

[0086] 12 is a signaling (timing) diagram illustrating an example of a procedure for notifying the distributed unit 5D that an inactive UE 3 has left its cell. In this case, the new base station 5 determines in the registration procedure initiated by the UE 3 that the UE 3 has performed cell reselection and notifies the distributed unit 5D. UE3 is initially in an RRC inactive state and receives the MBS session using the associated MRB configuration in the cell of distributed unit 5D (denoted as "old DU" in Fig. 12), which results in a multicast MBS transmission in the cell of distributed unit 5D.

[0087] The UE 3 performs cell reselection and then generates and sends in step 1 a suitably formatted message to register the UE 3's new cell with a mobility and access management function (in this case a new AMF 9' associated with the new cell). The new AMF 9' and the AMF 9 associated with the UE's old cell perform appropriate UE context transfer procedures as shown generally in steps 2 and 3. It will be appreciated that the new AMF 9' may be the same as the AMF 9 associated with the UE's old cell, in which case there is no need to perform a UE context transfer (i.e. steps 2 and 3 can be omitted). At this point, the UE's old distributed unit 5D does not know about the cell reselection.

[0088] Beneficially, the AMF 9 is configured to inform the central unit 5C that the UE 3 has performed a cell reselection and has left the cell of the distributed unit 5D associated to this central unit 5C. This notification can be sent when receiving the message in step 2 or when receiving the registration request in step 1 (in the absence of an AMF change).

[0089] In step 5, the central unit 5C informs the distributed units 5D that the PTM transmissions can be stopped. It will be appreciated that step 5 may be performed only after the central unit 5C has determined that there are no more inactive UEs 3 in the cell that are interested in the given MBS session.

[0090] If appropriate, based on the notification received in step 5, the source distribution unit 5D may determine in step 6 that the UE 3 in question was the last inactive UE 3 interested in the MBS service and the source distribution unit 5D may decide to turn off PTM transmissions in the cell.

[0091] 13 is a signaling (timing) diagram showing an example of a procedure for notifying the distributed unit 5D that the inactive UE 3 has left the cell of the distributed unit 5D. In this case, the new base station 5 determines that the UE 3 has performed cell reselection in the RAN notification area update procedure initiated by the UE 3, and notifies the distributed unit 5D.

[0092] As shown, UE3 is initially in an RRC inactive state and a connection management (CM) connected state while receiving an MBS session via PTM in the cell of distributed unit 5D (denoted as the “last serving gNB-DU” in FIG. 13).

[0093] In this case, following cell reselection to a new cell served by the new base station 5', the UE 3 performs an appropriate RAN notification area update procedure to inform the new base station 5' of the cell reselection. Thus, in step 1, the UE 3 generates and sends a properly formatted RRC resumption request (requesting to resume an inactive RRC connection with the new base station 5'). The request also includes a RAN notification area update. In step 2, the new base station 5' contacts the central unit 5C of the UE's old base station (denoted as "last serving gNB-CU" in Fig. 13) to obtain the UE context associated with the UE 3. Upon receiving this message, the central unit 5C generates and sends in step 4 a properly formatted multicast context setup request or multicast context modification request message (e.g. as described above with reference to Fig. 10) including an indication identifying whether PTM should be on or off in the cell of the distributed unit 5D.

[0094] 14 is a signalling (timing) diagram illustrating a schematic example of a procedure for informing the distributed unit 5D that an inactive UE 3 has left its cell, in which case the UE 3 does not need to perform a RAN notification area update procedure or a registration procedure (e.g. if the tracking area of ​​the new cell is in the tracking area list of the UE 3).

[0095] In this case, the UE 3 is configured to perform a small data transmission (SDT) to inform the new base station (new central unit 5C' in Fig. 14) of the cell reselection.

[0096] More specifically, prior to this procedure, UE3 is in an RRC inactive state and receives MBS sessions via PTM in the cell of distributed unit 5D (denoted as "old DU" in Fig. 14). When UE3 performs cell reselection, UE3 sends information identifying the MBS sessions (by their associated MBS session IDs and / or TMGI) to the new base station / central unit 5C' using an SDT message in step 1. Upon receiving this message, the new central unit 5C' contacts the central unit 5C of the UE's old base station (denoted as "old CU" in Fig. 14) in order to obtain the UE context associated with UE3 in step 2.

[0097] In step 3, the old central unit 5C determines, based on a message from the new central unit 5C', that the UE 3 in question has performed cell reselection to another cell.

[0098] If in step 4 the old central unit 5C determines that this particular UE 3 was the last inactive UE to receive the MBS session in the old distributed unit 5D's cell via multicast / PTM, the old central unit 5C instructs the old distributed unit 5D to deactivate the associated PTM transmission, if appropriate. However, it will be appreciated that there may be RRC connected UEs receiving the same session, in which case the distributed unit 5D may decide to continue using PTM transmission for those UEs.

[0099] If the old distributed unit 5D determines that the UE 3 was the last UE interested in the MBS service, the old distributed unit 5D may decide in step 5 to turn off the PTM in the cell.

[0100] Scenario 3 Referring again to FIG. 8, the central unit 5C sends a PDCP PDU to the distributed unit 5D, as shown in step 16. It is up to the distributed unit 5D to decide whether to map the received PDCP PDU to the PTM leg or the PTP leg (between the distributed unit 5D and the UE3), as shown in step 18. This is a dynamic decision of the distributed unit 5D, and the distributed unit 5D does not need to inform the central unit 5C of the decision. The decision varies from time to time, from UE to UE, and from MBS session to MBS session. Therefore, the UE3 having a control plane connection with the central unit 5C will also not be able to know whether a cell, e.g. a neighboring cell, uses PTM or PTP in the last leg for the MBS session that the UE3 is interested in.

[0101] Below are descriptions of some example ways this information can be provided to the UE 3.

[0102] In the first option shown in Fig. 15 and Fig. 16(a), the serving base station 5 (serving cell 500) indicates the frequency of the neighboring cell 501 to the UE 3. Specifically, as shown in step 1 of Fig. 15, the serving cell 500 transmits information identifying the neighboring frequency via the MCCH.

[0103] In step 2, the UE 3 monitors the identified frequency and obtains system information from the neighboring cell 501 or obtains at least a part of a system information block or a system information block related to the MCCH in the neighboring cell 501. The system information / MCCH of the neighboring cell 501 includes an appropriate indication identifying whether PTM is always on in the cell 501 and information identifying any MBS services provided via multicast / PTM. This information is shown in detail in Figure 16A.

[0104] Based on this indication and the identified MBS services, the UE 3 can prioritize cells 501 that provide multicast for the MBS services in which the UE 3 is interested.

[0105] It will be understood that if there are RRC inactive UEs receiving MBS services in the neighboring cell 501, the neighboring cell 501 will continue to transmit multicast data to those UEs via PTM and will continue to broadcast a PTM always-on indication associated with the MBS session ID or TMGI.

[0106] In another option shown in Figure 16B, the serving cell 500 may be configured to transmit PTM related information associated with neighboring cells 501. For example, for each neighboring cell 501, the serving cell 500 may broadcast an associated PTM always-on indication, an associated cell ID, information identifying the frequency used, and at least one MBS session ID or TMGI. This information may be transmitted in the MCCH or one or more system information blocks in the cell 500.

[0107] Modifications and Substitutions Detailed embodiments have been described above. As will be appreciated by those skilled in the art, several modifications and alternatives may be made to those embodiments while benefiting from the disclosure embodied in the above embodiments. By way of example, only some of these alternatives and modifications are described herein.

[0108] It will be appreciated that cell reselection may trigger either a RAN notification area update or a registration update depending on the selected cell. Thus, the UE may initiate either the procedure illustrated in Figure 12 or the procedure illustrated in Figure 13 depending on the selected cell.

[0109] Base stations in a 5G / NR communications system are typically referred to as new radio base stations ("NR-BS") or "gNBs," although it will be appreciated that they may also be referred to using the term "eNB" (or 5G / NReNB), which more typically relates to Long Term Evolution (LTE) base stations (also typically referred to as "4G" base stations). 3GPP TS 38.300V16.7.0 and 3GPP TS 37.340V16.7.0 define, among other things, the following nodes: gNB: A node that provides NR user plane and control plane protocol termination to the UE and is connected to the 5G core network (5GC) via the NG interface. The ng-eNB is a node that provides E-UTRA user plane and control plane protocol terminations to the UE and is connected to the 5GC via the NG interface. The En-gNB is a node that provides NR user plane and control plane protocol termination to the UE and functions as a secondary node in E-UTRA-NR dual connectivity (EN-DC). An NG-RAN node is either a gNB or a ng-eNB.

[0110] It will be appreciated that the above embodiments are applicable to 5G New Radio and LTE systems (E-UTRAN) and any future generation systems. A base station supporting E-UTRA / 4G protocols may be referred to as an "eNB" and a base station supporting NextGeneration / 5G protocols may be referred to as a "gNB". It will be appreciated that some base stations may be configured to support both 4G and 5G protocols and / or any other 3GPP or non-3GPP communication protocols.

[0111] In the above description, for ease of understanding, the UE, the access network node, and the data network node are described as having several separate modules (such as a communications control module). These modules may be provided in this manner in certain applications, for example where an existing system is modified to implement the present disclosure, but in other applications, for example where a system is designed from the beginning with the features of the present invention in mind, these modules may not be identifiable as separate entities, as they may be incorporated into an overall operating system or code. These modules may be implemented in software, hardware, firmware, or a combination thereof.

[0112] Each control unit may comprise any suitable form of processing circuitry including, for example (but not limited to), one or more hardware implemented computer processors, microprocessors, Central Processing Units (CPUs), Arithmetic Logic Units (ALUs), Input / Output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communications buses (e.g., control buses, data buses and / or address buses), Direct Memory Access (DMA) facilities, hardware or software implemented counters, pointers and / or timers, etc.

[0113] In the above embodiment, a number of software modules are described. Those skilled in the art will understand that the software modules may be provided in compiled or uncompiled form, and may be provided to the UE, the access network node, and the data network node as signals via a computer network or a recording medium. Furthermore, the functions performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the UE, the access network node, and the data network node to update their functions.

[0114] The above embodiments are also applicable to "non-mobile" or generally fixed user equipment.

[0115] The method performed by the distributed unit may further include, for reception of the at least one MBS session by the inactive UE, transmitting information for configuring the respective multicast radio bearers to the UE, where the transmitting may include transmitting information for configuring the respective multicast radio bearers using at least one of a message for releasing a connection of the UE, a system information block, and a multicast control channel.

[0116] The information for configuring each multicast radio bearer may include at least one configuration of a Packet Data Convergence Protocol (PDCP), a Radio Link Control (RLC), a Medium Access Control (MAC), a Multicast Control Channel (MCCH), and a Multicast Traffic Channel (MTCH) associated with the MBS session.

[0117] The distributed unit may receive a message from the central unit in a UE context procedure to release a UE context associated with the UE, the message including information identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast.

[0118] The method performed by the distributed unit may further include receiving a further message from the central unit for releasing the UE to an inactive state, the further message may include information for configuring respective multicast radio bearers for the at least one MBS session.

[0119] The distributed unit may receive a message from the central unit in a multicast context procedure for setting up or modifying a multicast context associated with at least one MBS session, the message for setting up or modifying the multicast context may include information identifying whether it is mandatory to turn on multicast for at least one MBS session in a cell.

[0120] The method performed by the distributed unit may further include transmitting data for the at least one MBS session in the cell via multicast based on information identifying the at least one MBS session and identifying that it is mandatory that the at least one MBS session be provided in the cell via multicast.

[0121] Multicast may include point-to-multipoint transmission between the distributed unit and multiple UEs.

[0122] The information received from the central unit with which the distributed unit is associated may include at least one of: information indicating that the UE has reselected for another cell; information identifying the at least one MBS session; and information identifying whether multicast should be turned on for the at least one MBS session in the cell of the distributed unit.

[0123] The method performed by the distributed unit may further include deactivating point-to-multipoint transmission associated with the MBS session or switching from point-to-multipoint transmission associated with the MBS session to point-to-point transmission based on the information.

[0124] The information that the network node receives from the UE may be included in at least one of a registration request message, a resume request message, a radio access network (RAN) notification area update message, and a small data transmission message, and may be used in controlling MBS sessions in cells served by the distributed unit.

[0125] The network node may be a base station or a core network node responsible for access and mobility of the UE.

[0126] The information indicating whether at least one multicast session is provided in the cell may be included in at least one of a message for releasing a UE connection, a system information block associated with the cell, and a multicast control channel associated with the cell, including at least one of information identifying that a multicast session is mandatory to be available in the cell, information identifying at least one Multicast and Broadcast Service (MBS) session provided in the cell, information identifying the cell, and information identifying a frequency associated with the cell.

[0127] Performing cell reselection based on the information may include prioritizing a cell if the information indicates that at least one multicast session is hosted in the cell.

[0128] The information identifying the at least one multicast session may include, for each multicast session, a respective multicast session identifier or a respective temporary mobile group identifier.

[0129] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0130] For example, all or a part of the exemplary embodiments disclosed above can be described as follows, but are not limited thereto. (Appendix 1) 1. A method for providing a multicast and broadcast service (MBS) to a user equipment (UE) in a cell, performed by a distributed unit of a base station apparatus, comprising: receiving information from a central unit of the base station device in at least one of a UE context procedure and a multicast context procedure, the information identifying the at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast; A method comprising: (Appendix 2) and transmitting, to the UE in an inactive state, information for configuring a respective multicast radio bearer for receiving at least one MBS session by the UE. The method described in Appendix 1. (Appendix 3) To send, A message to release the UE connection, System Information Block, and A multicast control channel; transmitting information for configuring each multicast radio bearer using at least one of The method described in Appendix 2. (Appendix 4) The information for configuring each multicast radio bearer is Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), Multicast Control Channel (MCCH), and A Multicast Traffic Channel (MTCH) associated with the MBS session;

[0033] The present invention relates to a method for producing a computer-implemented program for the purpose of the present invention. 4. The method according to claim 2 or 3. (Appendix 5) The receiving includes receiving, from the central unit, a message for releasing a UE context associated with the UE in a UE context procedure, the message including information identifying at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast. 5. The method according to any one of claims 1 to 4. (Appendix 6) receiving a further message from the central unit to release the UE to an inactive state; 6. The method of any one of claims 1 to 5. (Appendix 7) a further message including information for configuring a respective multicast radio bearer for the at least one MBS session; The method described in Appendix 6. (Appendix 8) The receiving includes receiving a message from the central unit in a multicast context procedure to set up or modify a multicast context associated with the at least one MBS session. 8. The method of any one of claims 1 to 7. (Appendix 9) a message for setting up or modifying a multicast context comprising information identifying whether multicast is mandatory to be turned on for at least one MBS session in the cell; The method described in Appendix 8. (Appendix 10) and transmitting data for the at least one MBS session within the cell via multicast based on the information identifying the at least one MBS session and identifying that the at least one MBS session is required to be provided in the cell via multicast. 10. The method of any one of claims 1 to 9. (Appendix 11) The multicast includes a point-to-multipoint transmission between the distributed unit and multiple UEs; 11. The method of any one of claims 1 to 10. (Appendix 12) 1. A method for providing a multicast and broadcast service (MBS) in a cell to a user equipment (UE), performed by a central unit of a base station apparatus, comprising: transmitting information to the distributed unit of the base station device in at least one of a UE context procedure and a multicast context procedure, the information identifying the at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast; A method comprising: (Appendix 13) 1. A method performed by a distributed unit of a base station apparatus for providing a multicast and broadcast service (MBS) session to an inactive user equipment (UE), comprising: receiving information from an associated central unit indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory; A method comprising: (Appendix 14) Information, Information indicating that the UE has reselected another cell; information identifying at least one MBS session; and information identifying whether multicast for at least one MBS session should be turned on in a cell of the distributed unit; At least one of 14. The method according to claim 13. (Appendix 15) and further comprising: deactivating a point-to-multipoint transmission associated with the MBS session or switching from a point-to-multipoint transmission associated with the MBS session to a point-to-point transmission based on the information. 15. The method according to claim 13 or 14. (Appendix 16) 1. A method performed by a central unit of a base station device for providing a Multicast and Broadcast Service (MBS) session for an inactive User Equipment (UE), comprising: transmitting information to the distributed unit of the base station device indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory; A method comprising: (Appendix 17) 1. A method performed by a user equipment (UE), comprising: receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by the distributed unit of the base station device; performing cell reselection to the new cell; and sending information to a network node associated with the new cell indicating that the UE has performed cell reselection; A method comprising: (Appendix 18) A method performed by a network node, comprising the steps of: receiving information from a user equipment (UE) indicating that the UE has performed cell reselection to a cell associated with a network node when a multicast and broadcast service (MBS) session is provided to the UE in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of the base station device prior to the cell reselection; A method comprising: (Appendix 19) The information includes: Registration request message, Resume request message, Radio Access Network (RAN) Notification Area Update messages, and Small data transmission message, At least one of the following is included: 19. The method according to claim 17 or 18. (Appendix 20) the information is used in controlling MBS sessions in cells served by the distributed unit; 20. The method of any one of claims 17 to 19. (Appendix 21) the network node is a base station or a core network node responsible for access and mobility of the UE, 21. The method of any one of claims 17 to 20. (Appendix 22) 1. A method performed by a user equipment (UE), comprising: receiving information indicating whether at least one multicast session is provided in a cell; performing cell reselection based on the information for receiving the multicast session in an inactive state; A method comprising: (Appendix 23) The information includes: A message to release the UE connection, a system information block associated with the cell; and a multicast control channel associated with the cell; At least one of the following is included: 23. The method according to claim 22. (Appendix 24) Information, information identifying that a multicast session is required to be available in the cell; information identifying at least one Multicast and Broadcast Service (MBS) session provided in the cell; Information identifying the cell; and information identifying a frequency associated with the cell; At least one of 24. The method according to claim 22 or 23. (Appendix 25) performing cell reselection based on the information includes prioritizing a cell if the information indicates that at least one multicast session is being provided in the cell. 25. The method of any one of claims 22 to 24. (Appendix 26) the information identifying the at least one multicast session includes, for each multicast session, a respective multicast session identifier or a respective temporary mobile group identifier; 25. The method of any one of claims 1, 5, 12, 14, and 24. (Appendix 27) 1. A method performed by a base station, comprising: Transmitting information indicating whether at least one multicast session is provided in a cell, the information being used by a user equipment (UE) when performing cell reselection to receive at least one multicast session in an inactive state. A method comprising: (Appendix 28) A distributed unit of a base station apparatus for providing a multicast and broadcast service (MBS) in a cell to a user equipment (UE), comprising: means for receiving information from a central unit of the base station device in at least one of a UE context procedure and a multicast context procedure, the information identifying the at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast; A distributed unit of a base station device comprising: (Appendix 29) A central unit of a base station device for providing a multicast and broadcast service (MBS) in a cell to a user equipment (UE), comprising: means for transmitting information to a distributed unit of the base station device in at least one of a UE context procedure and a multicast context procedure, the information identifying the at least one MBS session and identifying that the at least one MBS session is to be provided in the cell via multicast; A central unit of a base station device comprising: (Appendix 30) A distributed unit of a base station apparatus for providing a multicast and broadcast service (MBS) session to an inactive user equipment (UE), comprising: means for receiving information from an associated central unit indicating that a point-to-multipoint transmission associated with the MBS session is no longer mandatory; A distributed unit of a base station device comprising: (Appendix 31) A central unit of a base station device for providing a multicast and broadcast service (MBS) session for an inactive user equipment (UE), comprising: Means for transmitting information to a distributed unit of a base station device indicating that a point-to-multipoint transmission associated with an MBS session is no longer mandatory. A central unit of a base station device comprising: (Appendix 32) A user equipment (UE), means for receiving a Multicast and Broadcast Service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by the distributed unit of the base station device; means for performing cell reselection to a new cell; means for transmitting, to a network node associated with the new cell, information indicating that the UE has performed cell reselection; A user equipment (UE) comprising: (Appendix 33) A network node, Means for receiving information from a user equipment (UE) indicating that the UE has performed cell reselection to a cell associated with a network node when a multicast and broadcast service (MBS) session is provided to the UE in an inactive state prior to the cell reselection using point-to-multipoint transmission in a cell served by a distributed unit of the base station device. A network node including: (Appendix 34) A user equipment (UE), means for receiving information indicative of whether at least one multicast session is being offered in a cell; means for performing cell reselection based on information for receiving a multicast session in an inactive state; A user equipment (UE). (Appendix 35) A base station, Means for transmitting information indicating whether at least one multicast session is provided in a cell, for use by a user equipment (UE) when performing cell reselection for receiving at least one multicast session in an inactive state. A base station comprising:

[0131] This application claims the benefit of priority to UK patent application No. 2204294.9, filed March 25, 2022, the disclosure of which is incorporated herein by reference in its entirety. [Explanation of symbols]

[0132] 1. Telecommunications Systems 3. Mobile Devices 5 base station 7 Core Network 9. AMF 10 UPF 11 SMF 31 Transceiver Circuit 33 Antenna 35 User Interface 37 Control Unit 39 Memory 41 Operating Systems 43 Communication Control Module 45 MBS Module 51 Transceiver Circuit 53 Antenna 55 Network Interface 57 Control Unit 59 Memory 61 Operating Systems 63 Communication Control Module 5C gNB-CU-CP module 5U gNB-CU-UP module 5D gNB-DU module 71 Transceiver Circuit 75 Network Interface 77 Control Unit 79 Memory 81 Operating Systems 83 Communication Control Module 85 MBS Module

Claims

1. 1. A method for providing a Multicast and Broadcast Service (MBS) to a User Equipment (UE) in a cell, performed by a distributed unit of a base station, comprising: receiving MBS session information from a central unit of the base station, the MBS session information identifying whether at least one MBS session is to be provided or released in the cell by multicast for the UE; using the MBS session information to determine whether to provide the at least one MBS session in the cell by multicast or to release the at least one MBS session; A method comprising:

2. and transmitting configuration information to the UE for configuring a respective multicast radio bearer for the at least one MBS session. The method of claim 1.

3. The configuration information is a message for releasing a connection of the UE; a message for releasing a UE context associated with the UE; A message for transitioning the UE to a deactivation state; A message for setting up or modifying a multicast context associated with said at least one MBS session; System Information Block, and A multicast control channel; transmitted using at least one of The method of claim 2.

4. The configuration information is Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), A Multicast Control Channel (MCCH), and a Multicast Traffic Channel (MTCH) associated with said at least one MBS session; The present invention includes at least one of the following configurations: The method according to claim 2 or 3.

5. the receiving is performed in at least one of a UE context procedure, a multicast context procedure; 5. The method according to any one of claims 1 to 4.

6. receiving a further message from the central unit to release the UE to an inactive state; the further message includes the configuration information. The method of claim 2.

7. the MBS session information includes further information identifying whether turning on the multicast is mandatory for the at least one MBS session in the cell; 7. The method according to any one of claims 1 to 6.

8. transmitting data for the at least one MBS session in the cell via the multicast based on the MBS session information and further information.

8. The method according to any one of claims 1 to 7.

9. the multicast includes a point-to-multipoint transmission between the distributed unit and a plurality of UEs; 9. The method according to any one of claims 1 to 8.

10. the MBS session information indicates that a point-to-multipoint transmission associated with the at least one MBS session is no longer required. The method of claim 1.

11. The MBS session information is Information indicating that the UE has reselected another cell; Information identifying the at least one MBS session; and information identifying whether multicast should be turned on for the at least one MBS session in a cell of the distributed unit; At least one of the following: The method of claim 10.

12. deactivating the point-to-multipoint transmission associated with the MBS session or switching from the point-to-multipoint transmission associated with the MBS session to a point-to-point transmission based on the MBS session information; Further comprising:

12. The method according to claim 10 or 11.

13. 1. A method performed by a central unit of a base station for providing a multicast and broadcast service (MBS) to a user equipment (UE) in a cell, the method comprising: transmitting MBS session information to a distributed unit of the base station, which identifies to the UE whether at least one MBS session is to be provided in the cell by multicast or to be released; Including, the MBS session information is used by the distributed unit to determine whether to provide the at least one MBS session to the cell via multicast or to release the at least one MBS session. method.

14. 1. A method performed by a user equipment (UE), comprising: receiving a Multicast and Broadcast Service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by the distributed unit of the base station; performing cell reselection to the new cell; and sending, to a network node associated with the new cell, information indicating that the UE has performed the cell reselection; and Including, the information is used by the network node to transmit MBS session information to the distributed unit, the MBS session information identifying whether the MBS session should be released for the UE. method.

15. A method performed by a network node, comprising the steps of: receiving information from a User Equipment (UE) indicating that the UE has performed cell reselection to a cell associated with the network node prior to cell reselection when a Multicast and Broadcast Service (MBS) session is provided to the UE in an inactive state using a point-to-multipoint transmission in a cell served by a distributed unit of a base station; sending MBS session information to the distributed unit in response to the information from the UE, the MBS session information identifying whether the MBS session should be released for the UE; A method comprising:

16. The information is Registration request message, Resume request message, Radio Access Network (RAN) Notification Area Update Message, and Small data transmission message, At least one of 16. The method according to claim 14 or 15.

17. the information is used in controlling the MBS session in the cell served by the distributed unit; 17. The method according to any one of claims 14 to 16.

18. The network node is a base station or a core network node responsible for access and mobility of the UE, 18. The method according to any one of claims 14 to 17.

19. 1. A method performed by a user equipment (UE), comprising: receiving information indicating whether at least one Multicast and Broadcast Service (MBS) session is being provided in a cell; performing a cell reselection based on the information for receiving the at least one MBS session in an inactive state; A method comprising:

20. The information is a message for releasing a connection of the UE; A system information block associated with the cell; and a multicast control channel associated with the cell; At least one of the following:

20. The method of claim 19.

21. The information is Information identifying that it is mandatory for the at least one MBS session to be available in the cell; information identifying the at least one MBS session provided in the cell; information identifying the cell; and information identifying a frequency associated with the cell; At least one of the following:

21. The method of claim 19 or 20.

22. performing the cell reselection based on the information includes prioritizing the cell if the information indicates that the at least one MBS session is provided to the cell.

22. The method according to any one of claims 19 to 21.

23. the MBS session information including, for each of the at least one MBS session, a respective multicast session identifier or a respective temporary mobile group identifier; The method of claim 1.

24. 1. A method performed by a base station, comprising: transmitting information indicating whether at least one Multicast and Broadcast Service (MBS) session is provided in a cell for use by a user equipment (UE) when performing cell reselection to receive the at least one MBS session in an inactive state; A method comprising:

25. A distributed unit of a base station for providing a multicast and broadcast service (MBS) to a user equipment (UE) in a cell, comprising: means for receiving, from a central unit of the base station, MBS session information identifying, for the UE, whether at least one MBS session is to be provided in the cell by multicast or to be released; means for using the MBS session information to determine to provide the at least one MBS session in the cell via multicast or to release the at least one MBS session; A distributed unit comprising:

26. A central unit of a base station for providing a Multicast and Broadcast Service (MBS) to a User Equipment (UE) in a cell, comprising: means for transmitting MBS session information to a distributed unit of the base station, the MBS session information identifying whether at least one MBS session should be provided in the cell via multicast to be released for the UE; Equipped with the MBS session information is used by the distributed unit to determine whether to provide the at least one MBS session to the cell by multicast or to release the at least one MBS session; Central unit.

27. A user equipment (UE), means for receiving a Multicast and Broadcast Service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by the distributed unit of the base station; means for performing cell reselection to a new cell; means for transmitting, to a network node associated with the new cell, information indicating that the UE has performed the cell reselection; Equipped with the information is used by the network node to transmit MBS session information to the distributed unit, the MBS session information identifying whether the MBS session should be released for the UE. User Equipment (UE).

28. A network node, means for receiving information from a User Equipment (UE) indicating that the UE has performed cell reselection to a cell associated with the network node when a Multicast and Broadcast Service (MBS) session is provided to the UE in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station; sending MBS session information to the distributed unit in response to the information from the UE, the MBS session information identifying whether the MBS session should be released for the UE; A network node comprising:

29. means for receiving information indicating whether at least one Multicast and Broadcast Service (MBS) session is being provided in a cell; means for performing cell reselection based on the information for receiving the at least one MBS session in an inactive state; A user equipment (UE) comprising:

30. means for transmitting, in an inactive state, information indicating whether at least one Multicast and Broadcast Service (MBS) session is provided in a cell, for use by a User Equipment (UE) when performing cell reselection to receive said at least one MBS session; A base station comprising:

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