Cell switching in a split gnb structure

Abstract

A distributed access network is disclosed in which a central unit (CU) of the access network receives, from a first distributed unit (DU) of the access network, a first notification indicating that a procedure to switch communication for a user equipment (UE) from a first cell provided via the first DU, to a second cell provided via a second DU of the access network, has been, or will be, initiated. The CU transmits, to the second DU of the access network, a second notification indicating that the procedure to switch communication for the UE, has been, or will be, initiated.

Description

CELL SWITCHING IN A SPLIT GNB STRUCTURE

[0001] The present disclosure relates to a communication system.

[0002] The disclosure has particular but not exclusive relevance to wireless communication systems and devices thereof operating according to the 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof (including LTE-Advanced, Next Generation or 5G networks, future generations, and beyond). The disclosure has particular, although not necessarily exclusive relevance to, inter-cell mobility triggered by L1 / L2 signalling.

[0003] Earlier developments of the 3GPP standards were referred to as the Long-Term Evolution (LTE) of Evolved Packet Core (EPC) network and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), also commonly referred as '4G'. More recently, the term '5G' and 'new radio' (NR) has started to be used to refer to an evolving communication technology that is expected to support a variety of applications and services. Various details of 5G networks are described in, for example, the 'NGMN 5G White Paper' V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, which document is available from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G by way of the so-called 3GPP Next Generation (NextGen) radio access network (RAN) and the 3GPP NextGen core network.

[0004] Under the 3GPP standards, a NodeB (or an eNB in LTE, and gNB in 5G) is the radio access network (RAN) node (or simply 'access node', 'access network node' or 'base station') via which communication devices (user equipment or 'UE') connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present application will use the term access network node, (R)AN node, RAN equipment or base station to refer to any such access nodes.

[0005] For simplicity, the present application will use the term mobile device, user device, or UE to refer to any communication device that is able to connect to the core network via one or more base stations. Although the present application may refer to mobile devices in the description, it will be appreciated that the technology described can be implemented on any communication devices (mobile and / or generally stationary) that can connect to a communications network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0006] In the current 5G architecture, the gNB structure may be split into two or more parts. In some RAN implementations there are two parts, known as the Central Unit (CU or gNB-CU) - sometimes referred to as a 'control unit' - and the Distributed Unit (DU or gNB-DU), connected by an F1 interface. This enables the use of a 'split' architecture in which the typically 'higher' CU layers (for example, but not necessarily or exclusively, Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers) and the, 'lower' DU layers (for example, but not necessarily or exclusively, Radio Link Control (RLC), Media Access Control (MAC), and Physical (PHY) layers) are separated between a particular CU, and one or more DUs that are connected to and controlled by that CU via the F1 interface. Thus, for example, the higher layer CU functionality for a number of gNBs may be implemented centrally (for example, by a single processing unit, or in a cloud-based or virtualised system), whilst retaining the lower layer DU functionality locally separately for each gNB.

[0007] NPL 1: The 'NGMN 5G White Paper' V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, available from https: / / www.ngmn.org / 5g-white-paper.html. NPL 2: "LTM procedure descriptions and stage 2 aspects", 3GPP DRAFT TYPE DISCUSSION, vol 3GPP RAN 2, DAVID LECOMPTE ET AL, available from https: / / www.3gpp.org / ftp / TSG_RAN / WG2_RL2 / TSGR2_121 / Docs / R2-2301358.zip NPL 3: "(TP for LlL2 Mob BLCR for TS 38.401) Discussion about the open issues for LlL2 mobility", 3GPP DRAFT TYPE DISCUSSION, vol 3GPP RAN 3, 2022, JIAYING SUN ET AL, available from https: / / www.3gpp.org / ftp / TSG_RAN / WG3_RL3 / TSGR3_119 / Docs / R3-230890.zip NPL 4: "(TP for LlL2MobBLCR for TS 38.401): Ll / L2 Mobility", 3GPP DRAFT, TYPE DISCUSSION, vol 3GPP RAN 3, 2023, HONGZHUO ZHANG ET AL, available from https: / / www.3gpp.org / ftp / TSG_RAN / WG3_RL3 / TSGR3_119 / Docs / R3-230580.zip NPL 5: "Rapporteur Update to TS 38.401", 3GPP DRAFT, vol RAN WG3, 2022, NEC(38 401 RAPPORTUER)

[0008] Historically, mobility between different cells in cellular communications has been based on communication at higher layers, such as layer 3 (e.g., the L3 or radio resource control (RRC) layer) signalling. More recently, with a view to providing enhanced mobility, consideration has given to developing and providing support for layer 1 (e.g., the L1 or physical (PHY) layer) and / or layer 2 (e.g., the L2 or media access control (MAC) layer) centric mobility (also referred to as L1 / L2 centric mobility) rather than at higher layers (e.g., the RRC layer). Such L1 / L2 centric mobility (also referred to as L1 / L2 triggered mobility or 'LTM') has prospects for improving mobility for devices operating both below 7 GHz and in mmWave bands, for example by supporting lower handover latency and improved robustness.

[0009] There is, therefore, a need for the development of communication devices (such as base stations and / or UEs) that support efficient / flexible mechanisms for supporting LTM.

[0010] The disclosure aims to provide one or more apparatus and / or one or more associated methods that at least partially addresses the above need.

[0011] In one aspect there is provided a method performed by a central unit (CU) of an access network, the method comprising: receiving, from a first distributed unit (DU) of the access network, a first notification indicating that a procedure to switch communication for a user equipment (UE) from a first cell provided via the first DU, to a second cell provided via a second DU of the access network, has been, or will be, initiated; and transmitting, to the second DU of the access network, a second notification indicating that the procedure to switch communication for the UE, has been, or will be, initiated.

[0012] The first notification may be received, and the second notification may be transmitted, no later than a message is transmitted, from the first DU to the UE, for initiating the procedure to switch communication for the UE. The first notification may include first information and the second notification may include second information that is different to the first information. The procedure to switch communication for the UE may be part of a layer 1 / layer 2 triggered mobility (LTM) procedure.

[0013] In another aspect there is provided a method performed by a second distributed unit (DU) of an access network, the method comprising: receiving, from a central unit (CU) of the access network, a notification indicating that a procedure to switch communication for a user equipment (UE) from a first cell provided via a first DU of the access network, to a second cell provided via the second DU, has been, or will be, initiated; and receiving, based on the notification, at least one uplink message from the UE.

[0014] The receiving, based on the notification, may comprise dynamically scheduling at least one resource for uplink communication based on the notification, and receiving the at least one uplink message from the UE using the at least one resource. The method may further comprise pre-configuring at least one resource for uplink communication prior to reception of the notification, and the receiving, based on the notification, may comprise decoding, based on the notification, the at least one uplink message received from the UE using the at least one resource.

[0015] In another aspect there is provided a method performed by a first distributed unit (DU) of an access network, the method comprising: determining that a procedure to switch communication for a user equipment (UE) from a first cell provided via the first DU, to a second cell provided via a second DU of the access network is to be initiated; transmitting, to a central unit (CU) of the access network, a notification indicating that the procedure to switch communication for the UE, has been, or will be, initiated; and transmitting, to the UE, a message for initiating the procedure to switch communication for the UE; wherein the notification is transmitted no later than the message for initiating the procedure to switch communication for the UE.

[0016] The notification may be transmitted upon determining that the procedure to switch communication for the UE is to be initiated. The notification may be transmitted at the time of transmitting the message for initiating the procedure to switch communication for the UE.

[0017] In another aspect there is provided a method performed by an access network node, the method comprising: transmitting, to each user equipment (UE) of a UE group, information for triggering a group procedure, at each UE of the UE group, to respectively switch communication from a first cell provided by the access network node to a second cell.

[0018] The information for triggering may be transmitted in common message for receipt by each UE of a UE group. The information for triggering may comprise an indication that the first cell is being switched to a network energy saving mode. The information for triggering may comprise a paging message. The paging message may include a field for triggering the group procedure. The information for triggering may comprise system information, or paging information, including a command for triggering the group procedure. The information for triggering may be provided using downlink control information (DCI) for triggering the group procedure. The information for triggering may be provided using at least one media access control (MAC) signal triggering the group procedure. The at least one MAC signal may be a MAC control element (MAC CE) or a MAC service data unit (MAC SDU). The information for triggering may be provided using a transport block (TB) carrying a respective MAC signal for each UE of the UE group, for triggering that UE to switch communication. The at least one MAC signal may include a respective command, for each UE of the UE group, for triggering that UE to switch communication. The information for triggering may include at least one UE group identifier for identifying the UE group. The information for triggering may include a list of UE group identifiers. The information for triggering may include a list including a respective identifier for each UE for which the group procedure is being triggered. The information for triggering may be configured for reception using a shared radio network temporary identifier. The information for triggering may be configured for reception, using the shared radio network temporary identifier, both by any UE in the first cell that is a member of the UE group and any UE in the first cell that is not a member of the UE group. The information for triggering may be configured for reception, using the shared radio network temporary identifier, by any UE in the first cell that is a member of the UE group but not by any UE in the first cell that is not a member of the UE group. The information for triggering may include layer 2 (L2) protocol handling information. The information for triggering may include information for identifying at least one target cell for the group procedure. The group procedure may be part of a layer 1 / layer 2 triggered mobility (LTM) procedure. The group procedure may be part of a conditional handover procedure.

[0019] In another aspect there is provided a method performed by a user equipment (UE), the method comprising: receiving, from an access network node, information for triggering a group procedure, at each UE of a UE group, to respectively switch communication from a first cell provided by the access network node to a second cell; and initiating a procedure to switch communication from the first cell provided by the access network node, to a second cell based on the information for triggering.

[0020] In another aspect there is provided a method performed by a user equipment (UE), the method comprising: monitoring at least one group triggering condition for triggering a group procedure, at each UE of a UE group of which the UE is a member, to respectively switch communication from a first cell to a second cell; and initiating a procedure to switch communication from the first cell to the second cell when the at least one group triggering condition is fulfilled.

[0021] The group triggering condition may be fulfilled when a predetermined time has been reached. The predetermined time may be based on a time when a non-terrestrial network (NTN) cell is going to stop serving an area in which the UE is located or is based on a time when network energy saving is going to be activated for the first cell.

[0022] In another aspect there is provided a method performed by a central unit (CU) of an access network, the method comprising: determining to initiate a procedure for preconfiguring a user equipment (UE) for switching communication from a serving cell provided via a serving distributed unit (DU) of the access network, to a target cell of a target DU of the access network; transmitting, to at least one candidate DU of the access network, via which at least one candidate cell is provided, a request for configuration of at least one candidate cell, wherein the at least one candidate DU is a candidate to be the target DU; receiving, from the at least one candidate DU, configuration information for at least one accepted candidate cell, wherein the at least one accepted candidate cell is a candidate to be the target cell; transmitting, to the serving DU, based on the communicating with the at least one candidate DU, second configuration information for configuring the UE for switching to the at least one accepted candidate cell; and transmitting, to at least one candidate DU, information identifying each accepted candidate cell of the at least one accepted candidate cell.

[0023] The information identifying each accepted candidate cell may be transmitted, after the UE has switched communication, to a candidate DU that was the target DU for the switched communication. The information identifying each accepted candidate cell may be respectively transmitted to each candidate DU, of the at least one candidate DU, after receiving from the serving DU an indication that the UE has successfully applied the second configuration information.

[0024] In another aspect there is provided a method performed by a candidate distributed unit (DU) of an access network, the method comprising: receiving from a central unit (CU) of the access network, as part of a procedure for preconfiguring a user equipment (UE) for switching communication from a serving cell provided via a serving DU of the access network to a target cell of a target DU of the access network, a request for configuration of at least one candidate cell, wherein the candidate DU is a candidate to be the target DU; transmitting, to the CU, configuration information for at least one accepted candidate cell, wherein the at least one accepted candidate cell is a candidate to be the target cell; and receiving, from the CU, information identifying at least one accepted candidate cell provided by at least one further candidate DU.

[0025] The information identifying each accepted candidate cell may be received, after the UE has switched communication, and the candidate DU was the target DU for the switched communication. The information identifying each accepted candidate cell may be received before switching communication to the target cell has commenced at the UE.

[0026] In another aspect there is provided a central unit (CU) for an access network, the CU comprising: means for receiving, from a first distributed unit (DU) of the access network, a first notification indicating that a procedure to switch communication for a user equipment (UE) from a first cell provided via the first DU, to a second cell provided via a second DU of the access network, has been, or will be, initiated; and means for transmitting, to the second DU of the access network, a second notification indicating that the procedure to switch communication for the UE, has been, or will be, initiated.

[0027] In another aspect there is provided a second distributed unit (DU) for an access network, the second DU comprising: means receiving, from a central unit (CU) of the access network, a notification indicating that a procedure to switch communication for a user equipment (UE) from a first cell provided via a first DU of the access network, to a second cell provided via the second DU, has been, or will be, initiated; and means for receiving, based on the notification, at least one uplink message from the UE.

[0028] In another aspect there is provided a first distributed unit (DU) for an access network, the first DU comprising: determining that a procedure to switch communication for a user equipment (UE) from a first cell provided via the first DU, to a second cell provided via a second DU of the access network is to be initiated; transmitting, to a central unit (CU) of the access network, a notification indicating that the procedure to switch communication for the UE, has been, or will be, initiated; and transmitting, to the UE, a message for initiating the procedure to switch communication for the UE; wherein the notification is transmitted no later than the message for initiating the procedure to switch communication for the UE.

[0029] In another aspect there is provided an access network node comprising: means for transmitting, to each user equipment (UE) of a UE group, information for triggering a group procedure, at each UE of the UE group, to respectively switch communication from a first cell provided by the access network node to a second cell.

[0030] In another aspect there is provided a user equipment (UE) comprising: means for receiving, from an access network node, information for triggering a group procedure, at each UE of a UE group, to respectively switch communication from a first cell provided by the access network node to a second cell; and means for initiating a procedure to switch communication from the first cell provided by the access network node, to a second cell based on the information for triggering.

[0031] In another aspect there is provided a user equipment (UE) comprising: means for monitoring at least one group triggering condition for triggering a group procedure, at each UE of a UE group of which the UE is a member, to respectively switch communication from a first cell to a second cell; and means for initiating a procedure to switch communication from the first cell to the second cell when the at least one group triggering condition is fulfilled.

[0032] In another aspect there is provided a central unit (CU) for an access network, the CU comprising: means for determining to initiate a procedure for preconfiguring a user equipment (UE) for switching communication from a serving cell provided via a serving distributed unit (DU) of the access network, to a target cell of a target DU of the access network; means for transmitting, to at least one candidate DU of the access network, via which at least one candidate cell is provided, a request for configuration of at least one candidate cell, wherein the at least one candidate DU is a candidate to be the target DU; means for receiving, from the at least one candidate DU, configuration information for at least one accepted candidate cell, wherein the at least one accepted candidate cell is a candidate to be the target cell; means for transmitting, to the serving DU, based on the communicating with the at least one candidate DU, second configuration information for configuring the UE for switching to the at least one accepted candidate cell; and means for transmitting, to at least one candidate DU, information identifying each accepted candidate cell of the at least one accepted candidate cell.

[0033] In another aspect there is provided a distributed unit (DU) for an access network, the DU comprising: means for receiving from a central unit (CU) of the access network, as part of a procedure for preconfiguring a user equipment (UE) for switching communication from a serving cell provided via a serving DU of the access network to a target cell of a target DU of the access network, a request for configuration of at least one candidate cell, wherein the candidate DU is a candidate to be the target DU; means for transmitting, to the CU, configuration information for at least one accepted candidate cell, wherein the at least one accepted candidate cell is a candidate to be the target cell; and means for receiving, from the CU, information identifying at least one accepted candidate cell provided by at least one further candidate DU.

[0034] Aspects of the disclosure extend to corresponding systems, apparatus, and computer program products such as computer readable storage media having instructions stored thereon which are operable to program a programmable processor to carry out a method as described in the aspects and possibilities set out above or recited in the claims and / or to program a suitably adapted computer to provide the apparatus recited in any of the claims.

[0035] Each feature disclosed in this specification (which term includes the claims) and / or shown in the drawings may be incorporated in the disclosure independently of (or in combination with) any other disclosed and / or illustrated features where it is technically feasible to do so. In particular but without limitation the features of any of the claims dependent from a particular independent claim may be introduced into that independent claim in any combination or individually wherever doing so does not cause a technical incompatibility or result in something that does not make technical sense.

[0036] Example embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings in which:

[0037] Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system;Fig. 2 illustrates a typical frame structure that may be used in the communication system of Fig. 1;Fig.3 illustrates an exemplary intra-CU L1 / L2 triggered mobility (LTM) cell switch scenario that may be used in the communication system of Fig. 1;Fig. 4 is a simplified sequence diagram illustrating, in overview, an LTM procedure that may occur in the communication system of Fig. 1;Fig. 5 is a simplified sequence diagram illustrating an LTM pre-configuration part of the LTM procedure of Fig. 4 in more detail;Fig. 6 is a simplified sequence diagram illustrating an LTM cell switch part of the LTM procedure of Fig. 4 in more detail;Fig. 7 is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system of Fig. 1;Fig. 8 is a simplified sequence diagram illustrating a number of procedures for supporting group LTM that may be used in the communication system of Fig. 1;Fig. 9 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system of Fig. 1;Fig. 10 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system of Fig. 1;Fig. 11 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system of Fig. 1;Fig. 12 illustrates a MAC signal that may be used to support group LTM in the communication system of Fig. 1;Fig. 13 illustrates another MAC signal that may be used to support group LTM in the communication system of Fig. 1;Fig. 14 illustrates other MAC signals that may be used to support group LTM in the communication system of Fig. 1;Fig. 15 is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system of Fig. 1;Fig. 16 is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system of Fig. 1;Fig. 17 is a schematic block diagram illustrating the main components of a UE for the communication system of Fig. 1; andFig. 18 is a schematic block diagram illustrating the main components of an access network for the communication system of Fig. 1.

[0038] Overview 　　An exemplary communication system will now be described in general terms, by way of example only, with reference to Figs. 1 to 6.

[0039] Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system 1 to which example embodiments of the present disclosure are applicable.

[0040] In the communication system 1 user equipment (UEs) 3-1, 3-2, 3-3 (e.g. mobile telephones and / or other mobile devices) can communicate with each other via a (radio) access network ((R)AN) node 5 (base station 5, RAN equipment 5) that operates according to one or more compatible radio access technologies (RATs). In the illustrated example, the (R)AN node 5 comprises a distributed NR / 5G base station 5 or 'gNB' 5 operating one or more associated cells 9. Communication via the (R)AN node 5 is typically routed through an associated core network 7 (e.g. a 5G core network or evolved packet core network (EPC)).

[0041] As those skilled in the art will appreciate, whilst three UEs 3, and one (R)AN node 5 are shown in Fig. 1 for illustration purposes, the system, when implemented, will typically include other (R)AN node 5 and UEs 3.

[0042] The (R)AN node 5 controls one or more associated cells either directly, or indirectly via one or more other nodes (such as home base stations, relays, remote radio heads, distributed units, and / or the like). It will be appreciated that the (R)AN node 5 may be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocols.

[0043] In this example the illustrated a (R)AN node 5 comprises a distributed base station 5 comprising at least one distributed unit (DU) 5b (e.g., a gNB-DU or the like), and a central unit (CU) 5c (e.g., a gNB-CU or the like). The CU 5c employs a separated control plane and user plane and so is, itself, split between a control plane function (CU-CP) and a user plane function (CU-UP) which respectively communicate, with the DU via an F1-C logical interface and an F1-U logical interface (together forming an F1 interface (or 'reference point')), and with one another via an E1 logical interface. It will be appreciated that while, in this example, the DU includes the physical and virtual elements required to provide the functionality of the lower parts of the PHY layer and hence communicate with the UEs 3 over the air interface, the RAN may alternatively (or additionally) include one or more separate radio units (RUs) (e.g., providing this functionality of the lower parts of the PHY layer). It will, nevertheless, be appreciated that whilst a distributed (R)AN node 5 is shown and described, the (R)AN node 5 may be provided in a non-distributed form, for example as an integrated gNB or eNB.

[0044] The UEs 3 and their serving (R)AN node 5 are connected via an appropriate air interface (for example the so-called 'Uu' interface and / or the like). Equipment of neighbouring (R)AN nodes 5 may be connected to each other via an appropriate base station to base station interface (such as the so-called 'X2' interface, 'Xn' interface and / or the like).

[0045] The core network 7 includes a number of logical nodes (or 'functions') for supporting communication in the communication system 1. In this example, the core network 7 comprises control plane functions (CPFs) 10 and one or more user plane functions (UPFs) 11. The CPFs 10 include one or more Access and Mobility Management Functions (AMFs) 10-1, one or more Session Management Functions (SMFs) 10-2 and a number of other functions 10-n (such as, for example, an Authentication Server Function (AUSF) which facilitates 5G security processes, a Unified Data Management (UDM) entity for managing user specific data (e.g., for access authorization, user registration, and data network profiles), a Policy Control Function (PCF), an Application Function (AF), and / or the like). It will be appreciated that the nodes or functions may have different names in different systems.

[0046] The (R)AN node 5 is connected to the core network nodes via appropriate interfaces (or 'reference points') such as an N2 reference point between the CU 5c (CU-CP) of the (R)AN node 5 and the AMF 10-1 for the communication of control signalling, and an N3 reference point between the CU 5c (CU-UP) of the (R)AN node 5 and each UPF 11 for the communication of user data. The UEs 3 are each connected to the AMF 10-1 via a logical non-access stratum (NAS) connection over an N1 reference point (analogous to the S1 reference point in LTE). It will be appreciated, that N1 communications are routed transparently via the (R)AN node 5.

[0047] One or more UPFs 11 are connected to an external data network (e.g. an IP network such as the internet) via reference point N6 for communication of the user data.

[0048] The AMF 10-1 performs mobility management related functions, maintains the NAS signalling connection with each UE 3 and manages UE registration. The AMF 10-1 is also responsible for managing paging.

[0049] The SMF 10-2 is connected to the AMF 10-1 via an N11 reference point. The SMF 10-2 provides session management functionality (that formed part of MME functionality in LTE) and additionally combines some control plane functions (provided by the serving gateway and packet data network gateway in LTE). The SMF 10-2 also allocates IP addresses to each UE 3. The SMF uses user information provided via the AMF to determine what session manager would be best assigned to the user. The SMF may be considered effectively to be a gateway from the user plane to the control plane of the network. The SMF 10-2 also allocates IP addresses to each UE 3.

[0050] The (R)AN node 5 is also configured for transmission of, and the UEs 3 are configured for the reception of, control information and user data via a number of downlink (DL) physical channels and for transmission of a number of physical signals. The DL physical channels correspond to resource elements (REs) carrying information originated from a higher layer, and the DL physical signals are used in the physical layer and correspond to REs which do not carry information originated from a higher layer.

[0051] The physical channels may include, for example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), and a physical downlink control channel (PDCCH). The PDSCH carries data sharing the PDSCH's capacity on a time and frequency basis. The PDSCH can carry a variety of items of data including, for example, user data, UE-specific higher layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) for supporting a number of functions including, for example, scheduling the downlink transmissions on the PDSCH and also the uplink data transmissions on a physical uplink shared channel (PUSCH). The PBCH provides UEs 3 with the Master Information Block, MIB. It also, in conjunction with the PDCCH, supports the synchronisation of time and frequency, which aids cell acquisition, selection and re-selection.

[0052] The DL physical signals may include, for example, reference signals (RSs) and synchronization signals (SSs). A reference signal (sometimes known as a pilot signal) is a signal with a predefined special waveform known to both the UE 3 and the (R)AN node 5. The reference signals may include, for example, cell specific reference signals, UE-specific reference signal (UE-RS), downlink demodulation signals (DMRS), and channel state information reference signal (CSI-RS).

[0053] Similarly, the UEs 3 are configured for transmission of, and the (R)AN node 5 is configured for the reception of, control information and user data via a number of uplink (UL) physical channels corresponding to REs carrying information originated from a higher layer, and UL physical signals which are used in the physical layer and correspond to REs which do not carry information originated from a higher layer. The physical channels may include, for example, the PUSCH, a physical uplink control channel (PUCCH), and / or a physical random-access channel (PRACH). The UL physical signals may include, for example, demodulation reference signals (DMRS) for a UL control / data signal, and / or sounding reference signals (SRS) used for UL channel measurement.

[0054] Frame Structure 　　Referring to Fig. 2, which illustrates the typical frame structure that may be used in the communication system 1, the (R)AN node 5 and UEs 3 of the communication system 1 communicate with one another using resources that are organised, in the time domain, into frames of length 10ms. Each frame comprises ten equally sized subframes of 1ms length. Each subframe is divided into one or more slots comprising 14 Orthogonal frequency-division multiplexing (OFDM) symbols of equal length.

[0055] As seen in Fig. 2, the communication system 1 supports multiple different numerologies (subcarrier spacing (SCS), slot lengths and hence OFDM symbol lengths). Specifically, each numerology is identified by a parameter, μ, where μ=0 represents 15 kHz (corresponding to the LTE SCS). Currently, the SCS for other values of μ can, in effect, be derived from μ=0 by scaling up in powers of 2 (i.e. SCS = 15 x 2μkHz). The relationship between the parameter, μ, and SCS (Δf) is as shown in Table 1:

[0056] Intra-CU LTM Cell Switches 　　Referring to Fig. 3, which illustrates an exemplary intra-CU L1 / L2 triggered mobility (LTM) cell switch scenario that may take place in the communication system 1. As seen in Fig. 3, a CU 5c may control a plurality of DUs 5b-1, 5b-2, 5b-3 and each DU 5b-1, 5b-2, 5b-3 may respectively operate a plurality of cells 9-1a to 9-1c, 9-2a to 9-2c, and 9-3a to 9-3c. (and / or beams). As a UE 3 moves through the cells (or beams), as illustrated by the dashed arrow A, it passes through a number of cells (in the example 9-1b ==> 9-1c ==> 9-2a ==> 9-2b ==> 9-3c ==> 9-3a) involving multiple cell-to-cell transitions (denoted 'X'). The cell transitions include intra-DU cell transitions (e.g., 9-1b ==> 9-1c; 9-2a ==> 9-2b; and 9-3c ==> 9-3a) and inter-DU cell transitions (e.g., 9-1c ==> 9-2a and 9-2b ==> 9-3c).

[0057] Beneficially, the UE 3 and a (R)AN node 5 (i.e., CU 5c and DUs 5b-1, 5b-2, 5b-3) are mutually configured for implementing an intra-CU LTM procedure in which the UE 3 is able to switch between pre-configured candidate LTM cells 9-1a to 9-1c, 9-2a to 9-2c, and 9-3a to 9-3c, based on the content of lower layer (L1 and / or L2) measurement reports, relatively swiftly (e.g., potentially without requiring any RRC reconfiguration). Accordingly, as the UE 3 moves around the pre-configured candidate LTM cells 9-1a to 9-1c, 9-2a to 9-2c, and 9-3a to 9-3c, it can execute fast cell switches, potentially without RRC reconfiguration.

[0058] It will be appreciated that while the cell switches in Fig. 3 are necessitated by movement of the UE 3 relative to the cells 9, cell switching of this type could be necessitated by movement of one or more cells 9 relative to the UE 3 (e.g., in a non-terrestrial network (NTN) where each cell is are provided via a moving satellite). Moreover, cell switching of this type could be necessitated by a change of cell size arising from a network energy saving (NES) mode being initiated in the RAN by / for one or more DUs. Moreover, cell switching of this type could be necessitated by a cell being turned off (or on) for energy saving (or load management) purposes.

[0059] General LTM procedure 　　An exemplary intra-CU LTM procedure will now be described, by way of example only, with reference to Figs. 4 to 6. Possible beneficial variations to these procedures are described later.

[0060] Fig. 4 is a simplified sequence diagram illustrating, in general overview, an LTM procedure that may be implemented in the communication system 1.

[0061] Referring to Fig. 4, the LTM procedure in this case concerns an intra-CU inter-DU cell switch between a cell (e.g., cell 9-1c in the scenario of Fig. 3) operated via a source DU 5b-1 (e.g., DU 5b-1 in the scenario of Fig. 3) controlled by a particular CU 5c and another cell (e.g., cell 9-1a in the scenario of Fig. 3) operated via a target DU 5b-2 (e.g., DU 5-2a in the scenario of Fig. 3) controlled by the same CU 5c.

[0062] Prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S402a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S404. This procedure typically involves the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0063] The CU 5c can then make a decision, at S406, to initiate an L1 / L2 inter-cell triggered mobility (pre) configuration.

[0064] The CU 5c, source DU 5b-1, target DU 5b-2, and UE 3 (and optionally one or more other 'candidate' DUs) then communicate with one another in pursuit of an LTM pre-configuration procedure at S410 (e.g., as described with reference to Fig. 5).

[0065] Following LTM pre-configuration at S410, the UE 3 and a (R)AN node 5 may engage in an LTM cell switch procedure as seen at S450 to switch to a cell of the target DU 5b-2 (e.g., as described with reference to Fig. 6). After the UE 3 accesses the new cell of the target DU 5b-2, and the target DU 5b-2 detects that access, the target DU 5b-2 can notify the CU 5c of the access success at S428. The UE 3 can then communicate user data via the target DU 5b-1 and associated CU 5c (as seen at S402b).

[0066] Fig. 5 is a simplified sequence diagram illustrating the LTM pre-configuration part of the LTM procedure of Fig. 4 in more detail. It will be appreciated that in Fig. 5 the steps shown in S510 correspond broadly to the procedure of step S410 in Fig. 4. Similarly steps S502a, S504, S506, S550, S528, and S502b correspond broadly to corresponding steps S402a, S404, S406, S450, S428, and S402b of Fig. 4.

[0067] As seen in Fig. 5, prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S502a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S504. This procedure typically involves the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0068] The CU 5c can then make a decision, at S1506, to initiate an L1 / L2 inter-cell triggered mobility (pre) configuration.

[0069] At S516-1, S516-2, the CU 5c sends one or more messages for requesting the setting up a context for the UE 3 (e.g., a UE Context Setup Request as shown in Fig. 5 or the like) to one or more candidate DUs 5b-3, 5b-2 containing (candidate) target cells. This message is, in effect, a request for LTM configuration at the recipient DU. If a candidate DU accepts the request for LTM configuration in one or more (candidate) target cells, it responds to the CU 5c with an appropriate response message (e.g., a UE Context Setup Response as shown in Fig. 5 or the like) including a generated lower layer configuration for one or more accepted target candidate cells at S518-1, S518-2. It will be appreciated that, potentially, either a single UE context setup procedure (i.e., one procedure per candidate DU to prepare one or multiple candidate cells of the DU) or one or multiple UE context setup procedures (i.e., one procedure per candidate cell) may be used at this stage. In the illustrated procedure, for example, at least the target DU 5b-2 responds with such a response message including the generated lower layer configuration for one or more accepted target candidate cells of the target DU 5b-2 at S518-2.

[0070] The CU 5c sends, at S520 an appropriate message to the source DU 5b-1, which includes a generated RRC reconfiguration message with the L1 / L2 triggered mobility configuration. This message may, for example, be a UE Context Modification Request as shown in Fig. 5 or another message such as, for example, a DL RRC Message Transfer message or the like.

[0071] The source DU 5b-1 forwards, at S522, the received RRC reconfiguration message to the UE 3 and the UE 3 responds, at S524 with an RRC reconfiguration complete message (effectively indicating that the RRC configuration for has been successfully applied at the UE).

[0072] The source DU 5b-1 forwards, at S526, the RRC reconfiguration complete message to the CU 5c (effectively indicating that the RRC configuration for has been successfully applied at the UE) using an appropriate message, corresponding to the message sent at S520. This message may, for example, be a UE Context Modification Response as shown in Fig. 5 or another message such as, for example, an UL RRC Message Transfer message or the like.

[0073] Following the LTM pre-configuration procedure (S510), the UE 3 and a (R)AN node 5 may engage in an LTM cell switch procedure as seen at S550 to switch to a cell of the target DU 5b-2 (e.g., as described with reference to Fig. 6). After the UE 3 accesses the new cell of the target DU 5b-2, and the target DU 5b-2 detects that access, the target DU 5b-2 can notify the CU 5c of the access success at S528. The UE 3 can then communicate user data via the target DU 5b-2 and associated CU 5c (as seen at S502b).

[0074] Fig. 6 is a simplified sequence diagram illustrating an LTM cell switch part of the LTM procedure of Fig. 4 in more detail.

[0075] It will be appreciated that in Fig. 6 the steps shown in S650 correspond broadly to the procedure of step S450 in Fig. 4 (and the corresponding part of the procedure of Fig. 5). Similarly steps S602a, S604, S606, S610, S628, and S602b correspond broadly to corresponding steps S402a, S404, S406, S410, S428, and S402b of Fig. 4 (and the corresponding parts of the procedure of Fig. 5).

[0076] As seen in Fig. 6, prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S602a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S604. This procedure typically involves the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0077] The CU 5c can then make a decision, at S606, to initiate an L1 / L2 inter-cell triggered mobility (pre) configuration.

[0078] The CU 5c, source DU 5b-1, target DU 5b-2, and UE 3 (and optionally one or more other 'candidate' DUs) then communicate with one another in pursuit of an LTM pre-configuration procedure at S610 (e.g., as described with reference to Fig. 5).

[0079] Following LTM pre-configuration at S610, the UE 3 and a (R)AN node 5 may engage in an LTM cell switch procedure as seen at S650 to switch to a cell of the target DU 5b-2.

[0080] Specifically, the UE 3 may send a lower layer measurement report (e.g., including one or more L1 / L2 measurement results) to the source DU 5b-1 (e.g., for the serving and / or one or more target / candidate cells) as seen at S652.

[0081] The source DU 5b-1 then decides to execute LTM to switch to a candidate target cell at S654. It will be appreciated that the source DU 5b-1 may also notify the LTM cell switch decision to the other nodes as well. The source DU 5b-1 sends, at S656, an LTM cell switch command to the UE 3. It will be appreciated that any notification of the LTM cell switch decision to other nodes at S658 may occur after the source DU 5b-1 sends, at S656, an LTM cell switch command to the UE 3 (e.g., using a MAC control element (CE) or the like).

[0082] The UE 3 is thus able to detach from the current cell of the source DU 5b-1 (and synchronise to the target cell of the target DU 5b-2 as necessary) at S660. The UE 3 may then engage, at S663, in a random access channel (RACH) based initial access procedure, or a RACH-less initial access procedure with the target DU 5b-2.

[0083] The source DU 5b-1 also notifies, at S658, the CU 5c about the initiation of LTM / the sending of the LTM command to the UE 3 (e.g., over the F1 interface using an F1 application protocol (F1AP) or the like). In this example, the notification occurs at some delay after the LTM command is sent at S656 and thus may be sent in parallel with (or even after) the UE 3 detaching from the current cell of the source DU 5b-1 / synchronising to the target cell of the target DU 5b-2 at S660.

[0084] The target DU 5b-2 detects the UE access at S664 and can notify the CU 5c of the access success at S628. The UE 3 can then communicate user data via the target DU 5b-2 and associated CU 5c (as seen at S602b).

[0085] It will be appreciated that, as a skilled person would understand, for inter-DU LTM, any release of resources of the source cell (and any prepared cell) in the source DU 5b-1, may be achieved in any appropriate manner (if at all).

[0086] It will be appreciated that the detailed steps of the procedures described with reference to Figs. 4 to 6 are exemplary and provided, for illustrative purposes, to how the procedures may be implemented. As those skilled in the art will be aware, there are a number of variations to the procedure and, in particular to the LTM pre-configuration part and / or the LTM cell switch part of the procedures.

[0087] Further LTM considerations 　　Beneficially, the communication system 1 includes one or more enhancements to the general LTM procedure described with reference to Figs 4 to 6 and / or more generally.

[0088] In one enhancement, for example, the communication system 1 supports early notification of LTM to a target cell. Specifically, the target DU 5b-2 is beneficially enabled to dynamically schedule the first / initial uplink grant to a UE 3 that has switched to a target cell 9-2 of the target DU 5b-2 by notifying the target DU 5b-2 when a UE 3 is going to switch to the target cell 9-2. This enhancement is particularly beneficial in the context of RACH-less initial access for LTM. It will be appreciated that providing an early notification to the target DU 5b-2, of when a UE 3 is going to switch to the target cell 9-2, also has potential benefits in the context of configured grant based initial access even if a dynamic grant procedure is not implemented.

[0089] In another enhancement, for example, the communication system 1 beneficially allows for LTM to triggered for a group of UEs 3 to cause that group of UEs 3 to switch to the same target cell (or possibly different target cells). Such group LTM is particularly beneficial in (but not limited to) the context of scenarios involving cell movement in an NTN arising from satellite movement and / or scenarios involving cell size changes / cell switch off for NES purposes.

[0090] In another enhancement, for example, a current serving (i.e., source) DU 5b-1 is informed of the candidate cells for which an LTM configuration has been pre-prepared. This is particularly beneficial for enable an efficient subsequent LTM cell switch after an earlier LTM cell switch.

[0091] These enhancements are described in more detail later. It will be appreciated that the enhancements are neither dependent on one another nor mutually exclusive from a technical perspective. They can each be implemented in the communication system 1 to achieve a commensurate benefit regardless of whether or not any of the other enhancements are implemented.

[0092] Early notification of LTM to target cell 　　As mentioned above, in one example, the communication system 1 supports early notification of LTM to a target cell.

[0093] A procedure for providing such a notification will now be described, by way of example only, with reference to Fig. 7, which is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system of Fig. 1.

[0094] As seen in Fig. 7, prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S702a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S704. This procedure might typically involve, for example, the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0095] The CU 5c, source DU 5b-1, target DU 5b-2, and UE 3 (and optionally one or more other 'candidate' DUs) then communicate with one another in pursuit of an LTM pre-configuration procedure at S710 (e.g., including the steps described in relation to the LTM pre-configuration procedure S510 with reference to Fig. 5).

[0096] Following LTM pre-configuration at S710, the UE 3 and a (R)AN node 5 may engage in an LTM cell switch procedure as seen at S750 to switch to a cell of the target DU 5b-2.

[0097] Specifically, the UE 3 may send a lower layer measurement report (e.g., including one or more L1 / L2 measurement results) to the source DU 5b-1 (e.g., for the serving and / or one or more target / candidate cells) as seen at S752.

[0098] The source DU 5b-1 then decides to execute LTM to switch to a candidate target cell at S754. It will be appreciated that the source DU 5b-1 may also notify the LTM cell switch decision to the other nodes as well. The source DU 5b-1 sends, at S756, an LTM cell switch command to the UE 3. It will be appreciated that the decision to switch to a particular candidate target cell at S674 (and any notification of the LTM cell switch decision to other nodes) may occur after the source DU 5b-1 sends, at S756, an LTM cell switch command to the UE 3 (e.g., in a MAC CE or the like).

[0099] The UE 3 is thus able to detach from the current cell of the source DU 5b-1 (and synchronise to the target cell of the target DU 5b-2 as necessary) at S760.

[0100] The source DU 5b-1 also notifies, at 758, the CU 5c about the initiation of LTM / the sending of the LTM command to the UE 3 (e.g., over the F1 interface using the F1AP or the like). In this example, the notification occurs at the same time, or even before where possible (e.g., upon or shortly after the LTM cell switch decision being made at S754) the LTM cell switch command is sent at S756.

[0101] In this example, following receipt of the LTM notification sent at S758, the CU 5c beneficially notifies, at S761, the target DU 5b-2 of the LTM cell switch. It will be appreciated that the content of the "LTM notify" message sent to the target DU 5b-2 at S761 need not be the same as the "LTM notify " message received by the CU 5c at S758.

[0102] Accordingly, the target DU 5b-2 is beneficially informed of the upcoming cell switch. This notification may be used, advantageously, to facilitate dynamic grant (DG) scheduling of the first / initial resources for the UE 3 in target cell (e.g., via DCI provided on a PDCCH as illustrated at S762). This notification may (alternatively or additionally) be used, advantageously, in the case of configured grant (CG) in which pre-allocated resources may be assigned periodically for one or more UEs (e.g., at LTM pre-configuration stage illustrated at S710). In this case, each UE with pre-allocated CG resources can respectively transmit using the pre-assigned resources without the need for a scheduling request, and or monitoring PDCCH. Specifically, in the CG case, the notification advantageously enables the target DU 5b-2 to know when the pre-allocated CG will be used by the UE, essentially in real-time, if RACH-less based initial access (also referred to as 'RACH-skip') with pre-allocated CG resources is preconfigured for the target cell. When the pre-allocated CG is not used by the UE, the resource can be scheduled to another UE or used for another purpose.

[0103] The UE 3 may thus engage, at S763, in a RACH-less initial access procedure with the target DU 5b-2 based on the dynamic grant (if provided at S762).

[0104] The target DU 5b-2 detects the UE access at S764 and can notify the CU 5c of the access success at S728. The UE 3 can then communicate user data via the target DU 5b-2 and associated CU 5c (as seen at S702b).

[0105] Configured Grant based RACH-less LTM 　　Considering the procedure of Fig. 7 in more detail for the case of Configured Grant based RACH less LTM (in which the target DU 5b-2 may pre-allocate periodical CG resources for one or more UEs), when the LTM Notify message is received by the target DU 5b-2, the target DU 5b-2 may assume that the UE 3 will attempt to access the target cell relatively soon via a pre-allocated CG resource. The target DU 5b-2 may then try to receive an uplink message sent using an indicated pre-allocated CG resource from the UE 3. Specifically, the (R)AN node 5 will assume that the uplink transmission over that CG resource is scrambled by a radio network temporary identifier (RNTI), such as a cell-RNTI (C-RNTI), for the incoming UE to which the LTM notification related and will attempt to decode an uplink transmission received using the pre-allocated CG resource based on this C-RNTI. The pre-allocated CG is released by UE and target DU 5b-2 after the initial access to the target DU using the pre-allocated CG is acknowledged (e.g., at S728).

[0106] Dynamic Grant based RACH-less LTM 　　Considering the procedure of Fig. 7 in more detail for the case of Dynamic Grant based RACH-less LTM, when the LTM Notify message is received by the target DU 5b-2 during an inter-DU cell switch procedure, the target DU 5b-2 may assume that the UE 3 will attempt to access the target cell relatively soon. The target DU 5b-2 can thus directly schedule a PDCCH transmission for the incoming UE 3 to which the LTM notification related. Specifically, a layer 1 (L1) message may be scrambled with the C-RNTI of the incoming UE 3. Thus, when the UE 3 receives the LTM Cell Switch command and starts to switch to the target cell, the UE 3 can monitor the PDCCH, and descramble and decode the L1 message using the C-RNTI for the UE 3. This L1 message can carry an uplink grant for at least the first uplink transmission of the UE 3 to the target cell. In this manner, therefore, the UE 3 can acquire a Dynamic Grant from the target cell without any uplink scheduling request or RACH signalling (assuming the UE 3 has acquired the timing advance (TA) already). When target DU 5b-2 receives the uplink transmission from the UE 3, the target DU 5b-2 can assume that the UE access has been successful.

[0107] Timeline for LTM Notify Considering the timing of the enhanced LTM notification procedure of Fig. 7 in more detail, there will be delays associated with the backhaul latency between source DU 5b-1 and CU 5c, and between CU 5c and target DU 5b-2. Accordingly, by ensuring that the source DU 5b-1 notifies the CU 5c (e.g., over the F1 interface using the F1AP) of the LTM handover of the UE 3 at substantially the same time as - or even before (if possible) - the source DU 5b-1 sends the LTM cell switch command (e.g., in a MAC CE) to the UE 3, the target DU 5b-2 can be well prepared before the UE 3 attempts to access the target cell. Here it will be appreciated that potentially, both the LTM notification by the source DU 5b-1 to the CU 5c, and the LTM notification by the CU 5c to the target DU 5b-2 may beneficially be timed to occur as early as possible - potentially before the source DU 5b-1 sends the LTM cell switch command to the UE 3.

[0108] Support for Group LTM 　　As mentioned above, in one example, the communication system 1 supports triggering of LTM for a group of UEs 3 to cause that group of UEs 3 to switch to the same target cell (or possibly different target cells).

[0109] A number of procedures for supporting such group LTM will now be described in more detail, by way of example only, with reference to Figs. 8 to 14.

[0110] In these procedures a group of UEs (which may be a subset of, or all, UEs in a cell) are instructed to execute LTM to switch cells. Such triggering of group LTM may be beneficial, for example, in a number of different scenarios in which a DU 5b wants all UEs, or a group of UEs, to move out of current serving cell in a relatively short time window. These scenarios include NES scenarios such as, for example, NES in which some or all connected UEs need to be moved out of a capacity booster cell when that capacity booster cell enters into an NES mode. These scenarios also include NTN scenarios such as, for example, when some or all UEs connected via an NTN cell need to be moved out of that NTN cell (e.g., due to an impending service link switch / satellite switch) to a replacement (NTN or other) cell. These scenarios also include load balancing scenarios such as, for example, a situation in which a cell becomes congested and some or all UEs in the congested cell need to be moved to one or more other cells to alleviate or eliminate that congestion.

[0111] It will be appreciated that while these procedures are described in the context of group LTM, similar procedures may be applied to support cell switching of a group of UEs in other mobility / handover scenarios such as, for example, conditional handover (CHO) scenarios.

[0112] Fig. 8 is a simplified sequence diagram illustrating a number of different procedures for supporting group LTM that may be used in the communication system 1.

[0113] In Fig. 8 each procedure represents a different way in which group LTM may be triggered for any capable UEs. These procedures include procedures in which a pre-defined condition is fulfilled and / or a common instruction is received from a node (e.g., a DU or integrated base station) of the (R)AN node 5 (e.g., when NES is activated, when a cell is turning off, when an NTN satellite switch occurs or is about to occur, and / or a common LTM indication is received at one or more UEs). It will be appreciated that while the procedures allow LTM for a group of more than one UE to be triggered this does not preclude the 'group' LTM being triggered for a single UE (e.g. when a single UE is being served in a cell and / or a particular condition only affects a single UE).

[0114] As seen at S812a, in one exemplary procedure, LTM for a group of UEs 3-1, 3-2, and 3-3 is triggered when a specific time associated with a particular event has been reached (or is approaching - e.g., the specific time minus a predefined 'delta' time / time period has been reached). The specific time may be a time when a current NTN serving cell will disappear (e.g., due to satellite switch / service link switch), for example, when a time measured at the UE 3 equals (or is approaching) 'T service' which is a parameter (e.g., included in system information such as SIB19) indicates the time information on when a cell provided via NTN quasi-Earth fixed system is going to stop serving the area it is currently covering. The specific time may be a time when a current cell (e.g., a capacity boosting cell) enters an NES mode / is switched off.

[0115] It will be appreciated that in the example of S812a, the target cell for the LTM switch may be indicated by the (R)AN node 5 separately and / or may be predefined. For example, the target cell may be the cell that is to replace the current serving cell in the NTN case or may be a cell which overlaps with the current serving cell in the NES case.

[0116] As seen at S812b, in another exemplary procedure, LTM for a group of UEs 3-1, 3-2, and 3-3 is triggered when the UEs 3-1, 3-2, and 3-3 are informed that the current serving cell has been (or will be) switched to an NES mode (e.g., by means of an indication provided by the (R)AN node 5 (e.g., by the DU 5b of the (R)AN node 5)).

[0117] As seen at S812c, in another exemplary procedure, LTM for a group of UEs 3-1, 3-2, and 3-3 is triggered when the UEs 3-1, 3-2, and 3-3 receive a paging short message (e.g., a message provided over DCI with a paging RNTI) in which a dedicated (potentially single bit) 'LTM' field is set to indicate that group LTM is being triggered (e.g., in which the LTM field is set to 'true' or '1').

[0118] As seen at S812d, in another exemplary procedure, LTM for a group of UEs 3-1, 3-2, and 3-3 is triggered when the UEs 3-1, 3-2, and 3-3 receive a general / common / group LTM command that is read from system information (or paging information) that includes the LTM command.

[0119] It will be appreciated that in the above procedures, described with reference to Fig. 8, the target cell may or may not be indicated / defined. If the target cell is not indicated / defined, then it is up to UE 3 to choose / select which cell out of all candidate LTM cells to switch to. The selected cell may, for example, be chosen to be a best ranked cell among a plurality of candidate cells.

[0120] Once group LTM has been triggered according to any of the procedures described with reference to Fig. 8, the affected UEs 3-1, 3-2, and 3-3 may execute an LTM procedure for switching to a candidate LTM cell (if the cell is detectable / available) as seen at S870.

[0121] Fig. 9 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system 1.

[0122] In the procedure of Fig. 9, a joint / group LTM command is sent via DCI provided in a PDCCH from a node (e.g., a DU or integrated base station) of the (R)AN node 5 as seen at S912. In this example the joint / group LTM command includes (or is provided with) a UE group identifier to allow the UEs 3-1, 3-2, and 3-3 to know that they are the intended recipients of the joint / group LTM command. It will be appreciated that the (R)AN node 5 may configure which UE group each UE 3 belongs by, for example, indicating one or more corresponding UE group identifiers for that UE as part of a dedicated configuration for that UE 3 (e.g., using dedicated / RRC signalling or the like) as seen at S910-1 to S910-3. It will be appreciated that a given UE could potentially form part of more than one group, each group being respectively identified by a respective group identifier configured to that UE.

[0123] Once group LTM has been triggered by the joint / group LTM command, the affected UEs 3-1, 3-2, and 3-3 may execute an LTM procedure for switching to a candidate LTM cell (if the cell is detectable / available) as seen at S970.

[0124] In the procedure of Fig. 9, the node (e.g., a DU or integrated base station) of the (R)AN node 5 may also pre-configure / pre-define a shared RNTI for all UEs served in the cell. In this example, when the network sends a joint / group LTM command via the PDCCH (at S912) the joint / group LTM command (indicating which one or more UE groups should execute an LTM cell switch procedure) may be identified by means of the shared RNTI (e.g., because the DCI has a cyclic redundancy check (CRC) field scrambled using the shared RNTI). Thus, all the UEs 3 in the cell (that have received the shared RNTI) may monitor and receive the PDCCH identified by the configured shared RNTI. However, only the UEs 3-1, 3-2, and 3-3 having a group identifier that matches the group identifier provided in / with the joint / group LTM command will proceed to execute LTM procedure for switching to a candidate LTM cell as seen at S970.

[0125] Fig. 10 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system 1.

[0126] In the procedure of Fig. 10, the UEs 3 in the cell are grouped by configuring a different shared RNTI to each UE group respectively. Specifically, a node (e.g., a DU or integrated base station) of the (R)AN node 5 may (pre)configure a first shared RNTI ('RNTI A' in the illustrated example) to a first group of UEs 3-1A, 3-2A, and 3-3A ('UE Group A' in the illustrated example) and may (pre)configure a second shared RNTI ('RNTI B' in the illustrated example) to a second group of UEs 3-1B, 3-2B, and 3-3B ('UE Group B' in the illustrated example). It will be appreciated that a given UE could potentially form part of more than one group each group being respectively identified by a different shared RNTI (pre)configured to that UE.

[0127] A UE group specific joint / group LTM command may then be sent via DCI provided in a PDCCH, that is scrambled (i.e., the CRC is masked) using the group specific RNTI (e.g., RNTI A or RNTI B) as seen at S1012A and S1012B.

[0128] The UEs 3 in the cell will monitor for, and attempt to decode, DCI sent by the (R)AN node 5 in the PDCCH that is scrambled using a group specific shared RNTI. Those UEs 3-1A, 3-2A, and 3-3A forming part of the first group (UE Group A) will be able to decode and hence receive the joint / group LTM command sent, at S1012A, using DCI scrambled using the first RNTI (RNTI A). Those UEs 3-1B, 3-2B, and 3-3B forming part of the second group (UE Group B) will be able to decode and hence receive the joint / group LTM command sent, at S1012B, using DCI scrambled using the second RNTI (RNTI B).

[0129] When group LTM has been triggered for the first group (UE Group A) by the corresponding joint / group LTM command at S1012A, the affected UEs 3-1A, 3-2A, and 3-3A may execute an LTM procedure for switching to a candidate LTM cell (if the cell is detectable / available) as seen at S1070A. If group LTM is triggered for the second group (UE Group B) by the corresponding joint / group LTM command at S1012B, then the affected UEs 3-1B, 3-2B, and 3-3B may execute an LTM procedure for switching to a candidate LTM cell (if the cell is detectable / available) as seen at S1070B.

[0130] It will be appreciated that further LTM configuration information may be included in the DCI that provides a joint / group LTM command (in either or both the procedures of Figs. 9 and 10). The further LTM configuration information may, for example, include target cell information for use in identifying the target cell. This target cell information may, for example, allow identification of the target cell in an indirect way (e.g., by providing a configuration identifier that corresponds to target cell) or may explicitly identify the target cell (e.g., by means of a physical cell identity (PCI), an associated carrier frequency, and / or a global cell identity (GCI) / cell global identifier (CGI)). In this case a UE 3, that decodes this group DCI, and has the identified target cell (pre)configured as an LTM candidate target cell, will cell switch to that target cell.

[0131] The further LTM configuration information may, for example, include UE identification information. This may, for example, comprise a selected list of one or more UE identifiers and / or one or more UE group identifiers. In this case a UE 3, that decodes this group DCI and finds that its own identity is present in the list, or that its UE group identity (which may be (pre)configured to the UE 3 as described with reference to Fig. 9) is present can then trigger LTM to switch away from the present cell.

[0132] The additional information may, for example, include other L2 protocol handling information indicating, for example: no, partial or full MAC reset; RLC reset; and / or PDCP data recovery etc.

[0133] Fig. 11 is a simplified sequence diagram illustrating another procedure for supporting group LTM that may be used in the communication system 1. In this example, as seen at S1112, a joint / group LTM command is sent from a node (e.g., a DU or integrated base station) of the (R)AN node 5 using a MAC CE rather than DCI. Once group LTM has been triggered by the joint / group LTM command, the affected UEs 3-1, 3-2, and 3-3 may execute an LTM procedure for switching to a candidate LTM cell (if the cell is detectable / available) as seen at S1170.

[0134] An example of a group LTM MAC CE that may be used in the communication system 1 (e.g., for the procedure of Fig. 11) will now be described, by way of example only, with reference to Fig. 12, which illustrates a MAC signal that may be used to support group LTM.

[0135] As seen in Fig. 12, the MAC CE has a subheader 1210 and a payload portion 1212 that carries the joint / group LTM command and any additional information 1214.

[0136] The subheader 1210 will typically include a length ('L') field to indicate the length in bytes of the MAC CE, a format ('F') field indicating a size of the length field, one or more reserved ('R') bits, and a logical channel identity field to identify the MAC CE as a specific (e.g., group LTM MAC CE).

[0137] The additional information may, for example, include target cell information 1214a for use in identifying the target cell. This target cell information 1214a may, for example, allow identification of the target cell in an indirect way (e.g., by providing a configuration identifier that corresponds to target cell) or may explicitly identify the target cell (e.g., by means of a physical cell identity (PCI), an associated carrier frequency, and / or a global cell identity (GCI) / cell global identifier (CGI)). In this case a UE 3, that decodes this group LTM MAC CE, and has the identified target cell (pre)configured as an LTM candidate target cell, will cell switch to that target cell.

[0138] The additional information may, for example, include UE identification information S1214b. This may, for example, comprise a selected list of one or more UE identifiers and / or one or more UE group identifiers. In this case a UE 3, that decodes this group LTM MAC CE and finds that its own identity is present in the list, or that its UE group identity (which may be (pre)configured to the UE 3 as described with reference to Fig. 9) is present can then trigger LTM to switch away from the present cell.

[0139] The additional information may, for example, include other L2 protocol handling information S1214c indicating, for example: no, partial or full MAC reset; RLC reset; and / or PDCP data recovery etc.

[0140] It will, nevertheless, be appreciated that group LTM MAC CE may not include any additional information. In this case a UE 3 that has decoded the received group LTM MAC CE, will need to trigger LTM to switch from the current serving cell. The UE 3 may then select which cell out of all candidate LTM cells to switch to. The selected cell may, for example, be chosen to be a best ranked cell among a plurality of candidate cells.

[0141] It will be appreciated that a shared RNTI may also be configured in a common search space (CSS) to all or a group of connected UEs in the cell. The shared RNTI may be configured and / or and used in conjunction with a group LTM MAC CE in a similar manner to the way the shared RNTI was described in relation to Fig. 9 (i.e., for all UEs 3) or the way the shared RNTI was described in relation to Fig. 10 (i.e., for a specific group of UEs 3).

[0142] Fig. 13 illustrates another MAC signal that may be used to support group LTM in the communication system of Fig. 1.

[0143] As seen in Fig. 13, the MAC CE has a subheader 1310 and a payload portion 1312 that carries a respective independent LTM command 1314a to 1314c for each UE of the UE group.

[0144] The subheader 1310 will typically include a length ('L') field to indicate the length in bytes of the MAC CE, a format ('F') field indicating a size of the length field, one or more reserved ('R') bits, and a logical channel identity field to identify the MAC CE as a specific (e.g., group LTM MAC CE).

[0145] Fig. 14 illustrates other MAC signals that may be used to support group LTM in the communication system 1.

[0146] As seen in Fig. 14, in this example a single transport block (TB) is provided which includes a respective MAC CE (or MAC SDU) 1412a to 1412c carrying a corresponding LTM command 1414a to 1414c for each UE of the UE group.

[0147] Each MAC CE (or MAC SDU) 1412a to 1412c has an associated subheader 1410a to 1410c corresponding to the MAC CE (or MAC SDU) 1412a to 1412c carrying the LTM commands 1414a to 1414c.

[0148] Each subheader 1410a to 14c will typically include a length ('L') field to indicate the length in bytes of the MAC CE (or MAC SDU), a format ('F') field indicating a size of the length field, one or more reserved ('R') bits, and a logical channel identity field to identify the MAC CE (MAC SDU) as a specific (e.g., group LTM MAC CE or MAC SDU).

[0149] It will be appreciated that, in respect of the MAC signalling described with reference to Fig. 13 or Fig. 14, a shared RNTI may also be configured in a common search space (CSS) to all or a group of connected UEs in the cell. The shared RNTI may be configured and / or and used in conjunction with the 'group' LTM commands in a similar manner to the way the shared RNTI was described in relation to Fig. 9 (i.e., for all UEs 3) or the way the shared RNTI was described in relation to Fig. 10 (i.e., for a specific group of UEs 3).

[0150] Support for a subsequent LTM procedure 　　As mentioned above, in one example, the communication system 1 provides support for enabling an efficient subsequent LTM cell switch after an earlier LTM cell switch.

[0151] In more detail, it is beneficial not only for the first serving DU 5b-1, but also any subsequent serving DU 5b-2, 5b-3, to be aware of all candidate target cells in order to facilitate continued subsequent cell switch management (e.g., to keep track of the cells to which the UE can move).

[0152] One procedure that provides support for support for enabling an efficient subsequent LTM cell switch will now be described, by way of example only, with reference to Fig. 15, which is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system 1.

[0153] In summary, in the procedure of Fig. 15, the CU 5c sends a list of the candidate cells to the new serving DU 5b-2 following the LTM cell switch (e.g., after an 'Access Success' is received). This procedure may be used for each cell switch and thus each new serving DU can be informed of the candidate LTM cells after each LTM cell switch.

[0154] It will be appreciated that in Fig. 15 the steps shown in S1510 correspond broadly to the procedure of step S410 in Fig. 4 (and corresponding steps of the other similar procedures described above), albeit with some differences as described below. Similarly steps S1502a, S1504, S1506, S1550, and S1528 correspond broadly to corresponding steps S1402a, S1404, S1406, S1450, and S1428 of Fig. 4 (and corresponding steps of the other similar procedures described above).

[0155] As seen in Fig. 15, prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S1502a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S1504. This procedure typically involves the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0156] The CU 5c can then make a decision, at S1506, to initiate an L1 / L2 inter-cell triggered mobility (pre) configuration.

[0157] At S1516-1, S1516-2, the CU 5c sends one or more messages for requesting the setting up a context for the UE 3 (e.g., a UE Context Setup Request as shown in Fig. 15 or the like) to one or more candidate DUs 5b-3, 5b-2 containing (candidate) target cells. This message is, in effect, a request for LTM configuration at the recipient DU. If a candidate DU accepts the request for LTM configuration in one or more (candidate) target cells, it responds to the CU 5c with an appropriate response message (e.g., a UE Context Setup Response as shown in Fig. 15 or the like) including a generated lower layer configuration for one or more accepted target candidate cells at S1518-1, S1518-2. It will be appreciated that, potentially, either a single UE context setup procedure (i.e., one procedure per candidate DU to prepare one or multiple candidate cells of the DU) or one or multiple UE context setup procedures (i.e., one procedure per candidate cell) may be used at this stage. In the illustrated procedure, for example, at least the target DU 5b-2 responds with such a response message including the generated lower layer configuration for one or more accepted target candidate cells of the target DU 5b-2 at S1518-2.

[0158] The CU 5c sends, at S1520 an appropriate message to the source DU 5b-1, which includes a generated RRC reconfiguration message with the L1 / L2 triggered mobility configuration. This message may, for example, be a UE Context Modification Request as shown in Fig. 15 or another message such as, for example, a DL RRC Message Transfer message or the like. In this example, the message sent at S1520 also includes a list of the LTM candidate cells thereby, advantageously, making the source (i.e., the current serving) DU 5b-1 aware of the LTM candidate cells.

[0159] The source DU 5b-1 forwards, at S1522, the received RRC reconfiguration message to the UE 3 and the UE 3 responds, at S1524 with an RRC reconfiguration complete message (effectively indicating that the RRC configuration for has been successfully applied at the UE).

[0160] The source DU 5b-1 forwards, at S1526, the RRC reconfiguration complete message to the CU 5c (effectively indicating that the RRC configuration for has been successfully applied at the UE) using an appropriate message, corresponding to the message sent at S1520. This message may, for example, be a UE Context Modification Response as shown in Fig. 15 or another message such as, for example, an UL RRC Message Transfer message or the like.

[0161] Following the LTM pre-configuration procedure (S1510), the UE 3 and a (R)AN node 5 may engage in an LTM cell switch procedure as seen at S1550 to switch to a cell of the target DU 5b-2 (e.g., as described with reference to Fig. 6). After the UE 3 accesses the new cell of the target DU 5b-2, and the target DU 5b-2 detects that access, the target DU 5b-2 can notify the CU 5c of the access success at S1528. The UE 3 can then communicate user data via the target DU 5b-2 and associated CU 5c as previously described.

[0162] Following receipt of the notification of access success at S1528, the CU 5c sends, at S1530 an appropriate message to the former target (i.e., the newly serving) DU 5b-2, which includes a list of the LTM candidate cells thereby, advantageously, making the former target (i.e., newly serving) DU 5b-2 aware of the LTM candidate cells. This message may, for example, be a UE Context Modification Request as shown in Fig. 15 or another suitable message. The former target (i.e., the newly serving) DU 5b-2 responds, at S1532 with an appropriate message, corresponding to the message sent at S1530. This message may, for example, be a UE Context Modification Response as shown in Fig. 15 or another suitable message.

[0163] Another procedure that provides support for support for enabling an efficient subsequent LTM cell switch will now be described, by way of example only, with reference to Fig. 16, which is a simplified sequence diagram illustrating another LTM procedure that may be used in the communication system 1.

[0164] In summary, in the procedure of Fig. 16, the CU 5c sends a list of the candidate cells to the new serving DU 5b-2 before the LTM cell switch.

[0165] It will be appreciated that in Fig. 16 the steps shown in S1610 correspond broadly to the procedure of step S410 in Fig. 4 (and corresponding steps of the other similar procedures described above), albeit with some differences as described below. Similarly steps S1602a, S1604, S1606, and S1650 correspond broadly to corresponding steps S1402a, S1404, S1406, and S1450 of Fig. 4 (and corresponding steps of the other similar procedures described above).

[0166] As seen in Fig. 16, prior to the LTM procedure being triggered, the UE 3 is communicating user data via the source DU 5b-1 and associated CU 5c (at S1602a). The UE 3, source DU 5b-1, and associated CU 5c engage in an L3 measurement control and reporting procedure at S1604. This procedure typically involves the UE 3 sending, to the source DU 5b-1, an L3 (e.g. RRC) measurement report (e.g., in a 'MeasurementReport' message or the like) containing the results of measurements for one or more cells (e.g., of measurements of reference signals in a serving cell and / or one or more neighbouring cells). The measurement results may include, for example, L3 filtered measurement results for a beam and / or cell (but this need not be the case). The source DU 5b-1 may then send an appropriate message (e.g., UL RRC Message Transfer message or the like) for conveying the received measurement report to the CU 5c.

[0167] User Equipment 　　Fig. 17 is a simplified block schematic illustrating the main components of a UE 3 for implementation in the system of Fig. 1.

[0168] signals from a (R)AN node 5 via an air interface 33 and one or more antennas.

[0169] The UE 3 has a controller 37 to control the operation of the UE 3. The controller 37 is associated with a memory 39 and is coupled to the transceiver circuit 31. Although not necessarily required for its operation, the UE 3 might, of course, have all the usual functionality of a conventional UE 3 (e.g. a user interface 35, such as a touch screen / keypad / microphone / speaker and / or the like for, allowing direct control by and interaction with a user) and this may be provided by any one or any combination of hardware, software, and firmware, as appropriate.

[0170] The controller 37 is configured to control overall operation of the UE 3 by, in this example, program instructions or software instructions stored within the memory 39. The software may be pre-installed in the memory 39 and / or may be downloaded via the communication system or from a removable data storage device (RMD), for example. As shown, these software instructions include, among other things, an operating system 41 and a communications control module 43.

[0171] The communications control module 43 is operable to control the communication between the UE 3 and one or more its serving (R)AN nodes 5 (and other communication devices connected to the (R)AN node 5, such as further UEs and / or core network nodes). The communications control module 43 is configured for the overall handling uplink communications via associated uplink channels (e.g. via a physical uplink control channel (PUCCH), random access channel (RACH), and / or a physical uplink shared channel (PUSCH)) including both dynamic and semi-static signalling (e.g., SRS). The communications control module 43 is also configured for the overall handling receipt of downlink communications via associated downlink channels (e.g. via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-static signalling (e.g., CSI-RS, SSBs etc.).

[0172] It will be appreciated that the communications control module 43 may include a number of sub-modules (or 'layers') to support specific functionalities. For example, the communications 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.

[0173] RAN (Distributed Type) 　　Fig. 18 is a simplified block schematic illustrating the main components of a distributed (R)AN node 5 comprising a distributed type of base station for implementation in the system of Fig. 1.

[0174] As shown, the (R)AN node 5 includes a central unit 5c and a distributed unit 5b (although it may include other DUs as described above). Each unit 5c, 5b includes respective transceiver circuitry 51c, 51b.

[0175] The distributed unit 5b transceiver circuitry 51b is operable to transmit signals to and to receive signals from UEs 3 via an air interface 53b and one or more antennas and is also operable to transmit signals to and to receive signals from the central unit 5c via an interface, for example the distributed unit side of an F1 interface (which may be provided over a satellite radio interface).

[0176] The central unit 5c transceiver circuitry 51c is operable to transmit signals to and to receive signals from functions of the core network 7 and / or other (R)AN nodes 5 via a network interface 55c. The network interface typically includes an N1, N2 and / or N3 interfaces for communicating with the core network and a base station to base station (e.g. Xn) interface for communicating with other (R)AN nodes 5. The central unit 5c transceiver circuitry 51c is also operable to transmit signals to and to receive signals from one or more distributed units 5b, for example the central unit side of the F1 interface provided.

[0177] Each unit 5c, 5b includes a respective controller 57c, 57b which controls the operation of the corresponding transceiver circuitry 51c, 51b in accordance with software stored in the respective memories 59c and 59b of the distributed unit 5b and the central unit 5c. The software of each unit may be pre-installed in the memory 59c, 59b and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example. The software of each unit includes, among other things, a respective operating system 61c, 61b and a respective communications control module 63c, 63b.

[0178] Each communications control module 63c, 63b is operable to control the communication of its corresponding unit 5c, 5b including the communication from one unit to the other. The communications control module 63b of the distributed unit 5b controls communication between the distributed unit 5b and the UEs 3, and the communications control module 63c of the central unit 5c controls communication between the central unit 5c and other network entities that are connected to the distributed (R)AN node 5.

[0179] The communications control modules 63c, 63b also respectively control the part played by the distributed unit 5b and central unit 5c in the flow of uplink and downlink user traffic and control data to be transmitted to the communications devices served by the (R)AN node 5 including, for example, control data for managing operation of the UEs 3. Each communication control module 63c, 63b is responsible, for example, for controlling the respective part played by the distributed unit 5b and central unit 5c in the reception and decoding of uplink communications, via associated uplink channels (e.g. via a physical uplink control channel (PUCCH), a random-access channel (RACH), and / or a physical uplink shared channel (PUSCH)) including both dynamic and semi-static signalling (e.g., SRS). Each communication control module 63c, 63b is responsible for controlling the respective part played by the distributed unit 5b and central unit 5c in the transmission of downlink communications via associated downlink channels (e.g. via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-static signalling (e.g., CSI-RS, SSBs etc.).

[0180] It will be appreciated that the communications control modules 63c, 63b may also include a number of sub-modules (or 'layers') to support specific functionalities for the corresponding unit 5c, 5b. The modules included will depend on how the corresponding unit 5c, 5b is configured (e.g., the precise CU-DU split). For example, the communications control modules 63c of the distributed unit 5b may include a PHY sub-module, a MAC sub-module, and an RLC sub-module, whereas the communications control modules 63c of the central unit 5c may include a PDCP sub-module, an SDAP sub-module, an IP sub-module, an RRC sub-module, etc.

[0181] Modifications and Alternatives 　　A detailed example embodiment has been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above example embodiments whilst still benefiting from the disclosure embodied therein.

[0182] It will be appreciated, for example, that whilst cellular communication generation (2G, 3G, 4G, 5G, 6G etc.) specific terminology may be used, in the interests of clarity, to refer to specific communication entities, the technical features described for a given entity are not limited to devices of that specific communication generation. The technical features may be implemented in any functionally equivalent communication entity regardless of any differences in the terminology used to refer to them.

[0183] In the above description, the UEs and the base station are described for ease of understanding as having a number of discrete functional components or modules. Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the disclosure, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities.

[0184] In the above example embodiments, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the base station or to the UE as a signal over a computer network, or on a recording medium. Further, the functionality 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 base station or the UE in order to update their functionalities.

[0185] Each controller may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs); input / output (IO) circuits; internal memories / caches (program and / or data); processing registers; communication buses (e.g. control, data and / or address buses); direct memory access (DMA) functions; hardware or software implemented counters, pointers and / or timers; and / or the like. Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0186] The base station may comprise a 'distributed' base station having a central unit 'CU' and one or more separate distributed units (DUs).

[0187] The User Equipment (or "UE", "mobile station", "mobile device" or "wireless device") in the present disclosure is an entity connected to a network via a wireless interface.

[0188] It should be noted that the present disclosure is not limited to a dedicated communication device and can be applied to any device having a communication function as explained in the following paragraphs.

[0189] The terms "User Equipment" or "UE" (as the term is used by 3GPP), "mobile station", "mobile device", and "wireless device" are generally intended to be synonymous with one another, and include standalone mobile stations, such as terminals, cell phones, smart phones, tablets, cellular IoT devices, IoT devices, and machinery. It will be appreciated that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for a long period of time.

[0190] A UE may, for example, be an item of equipment for production or manufacture and / or an item of energy related machinery (for example equipment or machinery such as: boilers; engines; turbines; solar panels; wind turbines; hydroelectric generators; thermal power generators; nuclear electricity generators; batteries; nuclear systems and / or associated equipment; heavy electrical machinery; pumps including vacuum pumps; compressors; fans; blowers; oil hydraulic equipment; pneumatic equipment; metal working machinery; manipulators; robots and / or their application systems; tools; molds or dies; rolls; conveying equipment; elevating equipment; materials handling equipment; textile machinery; sewing machines; printing and / or related machinery; paper converting machinery; chemical machinery; mining and / or construction machinery and / or related equipment; machinery and / or implements for agriculture, forestry and / or fisheries; safety and / or environment preservation equipment; tractors; precision bearings; chains; gears; power transmission equipment; lubricating equipment; valves; pipe fittings; and / or application systems for any of the previously mentioned equipment or machinery etc.).

[0191] A UE may, for example, be an item of transport equipment (for example transport equipment such as: rolling stocks; motor vehicles; motorcycles; bicycles; trains; buses; carts; rickshaws; ships and other watercraft; aircraft; rockets; satellites; drones; balloons etc.).

[0192] A UE may, for example, be an item of information and communication equipment (for example information and communication equipment such as: electronic computer and related equipment; communication and related equipment; electronic components etc.).

[0193] A UE may, for example, be a refrigerating machine, a refrigerating machine applied product, an item of trade and / or service industry equipment, a vending machine, an automatic service machine, an office machine or equipment, a consumer electronic and electronic appliance (for example a consumer electronic appliance such as: audio equipment; video equipment; a loud speaker; a radio; a television; a microwave oven; a rice cooker; a coffee machine; a dishwasher; a washing machine; a dryer; an electronic fan or related appliance; a cleaner etc.).

[0194] A UE may, for example, be an electrical application system or equipment (for example an electrical application system or equipment such as: an x-ray system; a particle accelerator; radio isotope equipment; sonic equipment; electromagnetic application equipment; electronic power application equipment etc.).

[0195] A UE may, for example, be an electronic lamp, a luminaire, a measuring instrument, an analyzer, a tester, or a surveying or sensing instrument (for example a surveying or sensing instrument such as: a smoke alarm; a human alarm sensor; a motion sensor; a wireless tag etc.), a watch or clock, a laboratory instrument, optical apparatus, medical equipment and / or system, a weapon, an item of cutlery, a hand tool, or the like.

[0196] A UE may, for example, be a wireless-equipped personal digital assistant or related equipment (such as a wireless card or module designed for attachment to or for insertion into another electronic device (for example a personal computer, electrical measuring machine)).

[0197] A UE may be a device or a part of a system that provides applications, services, and solutions described below, as to "internet of things (IoT)", using a variety of wired and / or wireless communication technologies.

[0198] Internet of Things devices (or "things") may be 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. IoT devices may comprise automated equipment that follow software instructions stored in an internal memory. IoT devices may operate without requiring human supervision or interaction. IoT devices might also remain stationary and / or inactive for a long period of time. IoT devices may be implemented as a part of a (generally) stationary apparatus. IoT devices may also be embedded in non-stationary apparatus (e.g. vehicles) or attached to animals or persons to be monitored / tracked.

[0199] It will be appreciated that IoT technology can be implemented on any communication devices that can connect to a communications network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0200] It will be appreciated that IoT devices are sometimes also referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be appreciated that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the following table. This list is not exhaustive and is intended to be indicative of some examples of machine type communication applications.

[0201] Applications, services, and solutions may be an MVNO (Mobile Virtual Network Operator) service, an emergency radio communication system, a PBX (Private Branch eXchange) system, a PHS / Digital Cordless Telecommunications system, a POS (Point of sale) system, an advertise calling system, an MBMS (Multimedia Broadcast and Multicast Service), a V2X (Vehicle to Everything) system, a train radio system, a location related service, a Disaster / Emergency Wireless Communication Service, a community service, a video streaming service, a femto cell application service, a VoLTE (Voice over LTE) service, a charging service, a radio on demand service, a roaming service, an activity monitoring service, a telecom carrier / communication NW selection service, a functional restriction service, a PoC (Proof of Concept) service, a personal information management service, an ad-hoc network / DTN (Delay Tolerant Networking) service, etc.

[0202] Further, the above-described UE categories are merely examples of applications of the technical ideas and example embodiments described in the present document. Needless to say, these technical ideas and example embodiments are not limited to the above-described UE and various modifications can be made thereto.

[0203] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0204] For example, the whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 　　　　(Supplementary note 1) 　　A method performed by a first unit of an access network, the method comprising: transmitting, to a second unit of the access network, capability information indicating a capability of the first unit, the information indicating the capability indicating at least one of: a capability of the first unit to communicate with a user equipment (UE) using a communication scheme in which at least one time resource is configured for uplink communication, at least one time resource is configured for downlink communication, and at least one time resource is configured both for downlink communication and for uplink communication; or a capability of the first unit to isolate downlink communication from uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 2) 　　A method according to supplementary note 1, wherein the capability information includes information indicating a respective isolation capability for each of a plurality of different isolation schemes. 　　　　(Supplementary note 3) 　　A method according to supplementary note 1, wherein the capability information includes information indicating a combined isolation capability for a plurality of different isolation schemes. 　　　　(Supplementary note 4) 　　A method according to supplementary note 3, wherein the capability information includes information identifying a configuration of the different isolation schemes used to determine the combined isolation capability. 　　　　(Supplementary note 5) 　　A method according to supplementary note 3 or 4, wherein the capability information includes information indicating a respective combined isolation capability for each a plurality of different configurations of the different isolation schemes. 　　　　(Supplementary note 6) 　　A method according to any one of supplementary notes 2 to 5, wherein the different isolation schemes include at least one of: a first isolation scheme in which at least one guard band is used to isolate downlink communication from uplink communication; a second isolation scheme in which different beams are used to isolate downlink communication from uplink communication; a third isolation scheme in which different antenna configurations are used to isolate downlink communication from uplink communication; or a fourth isolation scheme in which at least one cancellation mechanism is used to isolate downlink communication from uplink communication. 　　　　(Supplementary note 7) 　　A method according to any preceding supplementary note, further comprising receiving a request from the second unit, wherein the capability information is provided in response to the request. 　　　　(Supplementary note 8) 　　A method performed by a second unit of an access network, the method comprising: receiving, from a first unit of the access network, capability information indicating at least one of: a capability of the first unit to communicate with a user equipment (UE) using a communication scheme in which at least one time resource is configured for uplink communication, at least one time resource is configured for downlink communication, and at least one time resource is configured both for downlink communication and for uplink communication; or a capability of the first unit to isolate downlink communication from uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 9) 　　A method performed by a second unit of an access network, the method comprising: transmitting, to a first unit of the access network, configuration information for a communication scheme in which at least one time resource, of a plurality of time resources, is configured as a first type for uplink communication, at least one time resource, of the plurality of time resources, is configured as a second type for downlink communication, and at least one time resource, of the plurality of time resources, is configured as a third type for both downlink communication and uplink communication. 　　　　(Supplementary note 10) 　　10.　　A method according to supplementary note 9, wherein the configuration information is for configuring the first unit to communicate with at least one user equipment (UE) using the plurality of time resources in accordance with the communication scheme. 　　　　(Supplementary note 11) 　　A method according to supplementary note 9 or 10, wherein the configuration information includes information indicating, for each time resource of the plurality of time resources whether that time resource is: the first type, the second type, or the third type. 　　　　(Supplementary note 12) 　　A method according to supplementary note 9 or 10, wherein the first unit has an existing configuration of the plurality of time resources in which at least one time resource is configured as the first type and at least one time resource is configured as the second type, and wherein the configuration information includes information indicating which of the plurality of time resources of the existing configuration are to be modified from the first type, or from the second type, to the third type. 　　　　(Supplementary note 13) 　　13.　　A method according to supplementary note 9 or 10, wherein the configuration information includes: first information for respectively configuring each resource, of the plurality of time resources, to be the first type for uplink communication or the second type for downlink communication in a first frequency region; and second information for respectively configuring each resource, of the plurality of time resources, to be the first type for uplink communication or the second type for downlink communication in a second frequency region. 　　　　(Supplementary note 14) 　　A method according to any one of supplementary notes 9 to 13, further comprising transmitting, to the first unit, further information indicating: at least one time resource of the first type, and / or at least one time resource of the second type, to be modified dynamically to become a time resource of the third type; and / or at least one time resource of the third type to be modified dynamically to become a time resource of the first type or a time resource of the second type. 　　　　(Supplementary note 15) 　　A method according to supplementary note 14, wherein the transmitting of the further information is timed to be received by the first unit a minimum time before the first unit receives control information relating to transmission of data for at least one UE by the second unit. 　　　　(Supplementary note 16) 　　A method according to supplementary note 14, wherein the further information is transmitted with control information relating to transmission of data for at least one UE by the second unit. 　　　　(Supplementary note 17) 　　A method according to any one of supplementary notes 9 to 16, further comprising transmitting, to the first unit, an indication of a frequency region for at least one of: an uplink subband; a downlink subband; and / or a guard band. 　　　　(Supplementary note 18) 　　A method according to any one of supplementary notes 9 to 16, further comprising transmitting, to the first unit, an indication of a filter to be applied for time resources configured as the third type. 　　　　(Supplementary note 19) 　　A method according to supplementary note 9, wherein the configuration information includes at least one of: information indicating a configuration for the communication scheme for implementation at the first unit; information indicating an intended configuration for the communication scheme at the second unit; and / or information indicating a configuration for the communication scheme for a neighbouring unit of the access network or another access network. 　　　　(Supplementary note 20) 　　A method according to supplementary note 9 or 19, wherein the configuration information includes information, for configuring at least one time resource as the third type, that includes at least one of: an indication of frequency resources for at least one uplink subband; an indication of frequency resources for at least one downlink subband; an indication of frequency resources for at least one guard band; an indication of a time location for at least one uplink subband or downlink subband; and / or a time location for the at least one time resource of the third type. 　　　　(Supplementary note 21) 　　A method according to supplementary note 9, 19 or 20 wherein the configuration information is transmitted on condition that the first unit: supports reception of configuration information including information for configuring at least one time resource as the third type; or supports operation in accordance with a communication scheme in which at least one time resource is configured as the third type. 　　　　(Supplementary note 22) 　　A method according to supplementary note 9, 19 or 20, wherein the configuration information includes information for configuring at least one time resource as the third type on condition that the first unit: supports reception of configuration information including information for configuring at least one time resource as the third type; or supports operation in accordance with a communication scheme in which at least one time resource is configured as the third type. 　　　　(Supplementary note 23) 　　A method according to supplementary note 9 wherein the configuration information is second configuration information, and the transmitting includes transmitting first configuration information for configuring at least one time resource as the first type, and at least one time resource as the second type, without configuring a time resource as the third type. 　　　　(Supplementary note 24) 　　A method according to supplementary note 9 wherein the configuration information includes first configuration information for configuring at least one time resource as the first type, and at least one time resource as the second type, and second configuration information for configuring at least one time resource configured by the first configuration information as the first type or as the second type, as the third type. 　　　　(Supplementary note 25) 　　A method performed by a first unit of an access network, the method comprising: receiving, from a second unit of the access network, configuration information for a communication scheme in which at least one time resource, of a plurality of time resources, is configured as a first type for uplink communication, at least one time resource, of the plurality of time resources, is configured as a second type for downlink communication, and at least one time resource, of the plurality of time resources, is configured as a third type for both downlink communication and uplink communication. 　　　　(Supplementary note 26) 　　A method according to supplementary note 25, wherein the configuration information is for configuring the first unit to communicate with at least one user equipment (UE) using the plurality of time resources in accordance with the communication scheme. 　　　　(Supplementary note 27) 　　A method according to supplementary note 25 or 26, further comprising determining a filter to be applied between an uplink subband and a downlink subband based on a guard band configured by the second unit. 　　　　(Supplementary note 28) 　　A method according to supplementary note 25, wherein the configuration information is second configuration information, and the receiving includes receiving first configuration information for configuring at least one time resource as the first type, and at least one time resource as the second type, without configuring a time resource as the third type, the method further comprising: in a case where the first unit does not support reception of configuration information including information for configuring at least one time resource as the third type, or does not support operation in accordance with a communication scheme in which at least one time resource is configured as the third type: ignoring the second configuration information and using the first configuration information; and in a case where the first unit supports reception of configuration information including information for configuring at least one time resource as the third type, or supports operation in accordance with a communication scheme in which at least one time resource is configured as the third type: using the second configuration information. 　　　　(Supplementary note 29) 　　A method according to supplementary note 25, wherein the configuration information includes first configuration information for configuring at least one time resource as the first type, and at least one time resource as the second type, and second configuration information for configuring at least one time resource configured by the first configuration information as the first type or as the second type, as the third type, the method further comprising: in a case where the first unit does not support reception of configuration information including information for configuring at least one time resource as the third type, or does not support operation in accordance with a communication scheme in which at least one time resource is configured as the third type: ignoring the second configuration information and using the first configuration information; and in a case where the first unit supports reception of configuration information including information for configuring at least one time resource as the third type, or supports operation in accordance with a communication scheme in which at least one time resource is configured as the third type: using the first configuration information and the second configuration information. 　　　　(Supplementary note 30) 　　A method according to supplementary note 28 or 29, further comprising using a configuration of time resources based on whether the first configuration information and or second configuration is used, and transmitting an indication to the second unit to indicate: that the configuration of time resources used at the first unit is a configuration that includes at least one time resource that is configured as the third type; or that the configuration of time resources used at the first unit is a configuration that does not include at least one time resource that is configured as the third type. 　　　　(Supplementary note 31) 　　A method according to any one of supplementary notes 25 to 30, further comprising providing, to the second unit: an indication of whether the first unit does, or does not support reception of configuration information including information for configuring at least one time resource as the third type; or an indication of whether the first unit does, or does not support operation in accordance with a communication scheme in which at least one time resource is configured as the third type. 　　　　(Supplementary note 32) 　　A method according to any one of supplementary notes 25 to 30 further comprising, in a case where the first unit does not support reception of configuration information including information for configuring at least one time resource as the third type, or does not support operation in accordance with a communication scheme in which at least one time resource is configured as the third type: sending an error message to the second unit in response to receipt of the configuration information. 　　　　(Supplementary note 33) 　　A method performed by a first unit of an access network, the method comprising: transmitting, to a second unit of the access network, beam or antenna related information including at least one of: 　　first information indicating at least one first beam configuration for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam configuration for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　second information indicating at least one first beam pattern for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam pattern for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　third information indicating at least one first set of antenna components that can, or cannot, be used for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second set of antenna components that can, or cannot, be used for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication; and / or 　　fourth information indicating at least one first configuration for an antenna for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second configuration for an antenna for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 34) 　　A method performed by a second unit of an access network, the method comprising: receiving, from a first unit of the access network, beam or antenna related information including at least one of: 　　first information indicating at least one first beam configuration for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam configuration for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　second information indicating at least one first beam pattern for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam pattern for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　third information indicating at least one first set of antenna components that can, or cannot, be used for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second set of antenna components that can, or cannot, be used for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication; and / or 　　fourth information indicating at least one first configuration for an antenna for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second configuration for an antenna for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 35) 　　A method according to supplementary note 34, further comprising using the beam or antenna related information when identifying a beam to be used for at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 36) 　　A method according to supplementary note 34 or 35, further comprising using the beam or antenna related information when identifying at least one weight to be applied for beamforming for at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 37) 　　A first unit for an access network, the first unit comprising: means for transmitting, to a second unit of the access network, capability information indicating a capability of the first unit, the information indicating the capability indicating at least one of: a capability of the first unit to communicate with a user equipment (UE) using a communication scheme in which at least one time resource is configured for uplink communication, at least one time resource is configured for downlink communication, and at least one time resource is configured both for downlink communication and for uplink communication; or a capability of the first unit to isolate downlink communication from uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 38) 　　A second unit for an access network, the second unit comprising: means for receiving, from a first unit of the access network, capability information indicating at least one of: 　　a capability of the first unit to communicate with a user equipment (UE) using a communication scheme in which at least one time resource is configured for uplink communication, at least one time resource is configured for downlink communication, and at least one time resource is configured both for downlink communication and for uplink communication; or 　　a capability of the first unit to isolate downlink communication from uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 39) 　　A second unit for an access network, the second unit comprising: means for transmitting, to a first unit of the access network, configuration information for a communication scheme in which at least one time resource, of a plurality of time resources, is configured as a first type for uplink communication, at least one time resource, of the plurality of time resources, is configured as a second type for downlink communication, and at least one time resource, of the plurality of time resources, is configured as a third type for both downlink communication and uplink communication. 　　　　(Supplementary note 40) 　　A first unit for an access network, the first unit comprising: means for receiving, from a second unit of the access network, configuration information for a communication scheme in which at least one time resource, of a plurality of time resources, is configured as a first type for uplink communication, at least one time resource, of the plurality of time resources, is configured as a second type for downlink communication, and at least one time resource, of the plurality of time resources, is configured as a third type for both downlink communication and uplink communication. 　　　　(Supplementary note 41) 　　A first unit for an access network, the first unit comprising: means for transmitting, to a second unit of the access network, beam or antenna related information including at least one of: 　　first information indicating at least one first beam configuration for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam configuration for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　second information indicating at least one first beam pattern for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam pattern for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　third information indicating at least one first set of antenna components that can, or cannot, be used for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second set of antenna components that can, or cannot, be used for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication; and / or 　　fourth information indicating at least one first configuration for an antenna for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second configuration for an antenna for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication. 　　　　(Supplementary note 42) 　　A second unit for an access network, the second unit comprising: means for receiving, from a first unit of the access network, beam or antenna related information including at least one of: 　　first information indicating at least one first beam configuration for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam configuration for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　second information indicating at least one first beam pattern for at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second beam pattern for at least one time resource that is configured specifically for downlink communication or specifically for uplink communication; 　　third information indicating at least one first set of antenna components that can, or cannot, be used for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second set of antenna components that can, or cannot, be used for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication; and / or 　　fourth information indicating at least one first configuration for an antenna for uplink communication in at least one time resource that is configured both for downlink communication and for uplink communication, and at least one second configuration for an antenna for downlink communication in at least one time resource that is configured both for downlink communication and for uplink communication.

[0205] This application is based upon and claims the benefit of priority from Great Britain Patent Application No. 2305108.9, filed on April 5, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0206] 1 COMMUNICATION SYSTEM 3 USER EQUIPMENT 5 BASE STATION 5b DISTRIBUTED UNIT (DU) 5c CENTRAL UNIT (CU) 7 CORE NETWORK 9 CELL 10 CONTROL PLANE FUNCTIONS 11 USER PLANE FUNCTIONS 20 EXTERNAL DATA NETWORK 31 TRANSCEIVER CIRCUIT 33 ANTENNA 35 USER INTERFACE 37 CONTROLLER 39 MEMORY 41 OPERATING SYSTEM 43 COMMUNICATIONS CONTROL MODULE 51b TRANSCEIVER CIRCUIT (DU) 51c TRANSCEIVER CIRCUIT (CU) 53b AIR INTERFACE 55c NETWORK INTERFACE 57b DU CONTROLLER 57c CU CONTROLLER 59b DU MEMORY 59c CU MEMORY 61b DU OPERATING SYSTEM 61c CU OPERATING SYSTEM 63b DU COMMUNICATIONS CONTROL MODULE 63c CU COMMUNICATIONS CONTROL MODULE F1 INTERFACE

Claims

1. A method performed by a central unit (CU) of an access network, the method comprising: 　　receiving, from a first distributed unit (DU) of the access network, a first notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure f or a user equipment (UE) from a first cell operated by the first DU, to a second cell operated by a second DU of the access network, has been, or will be, initiated; and 　　transmitting, to the second DU, a second notification indicating that the LTM procedure for the UE, has been, or will be, initiated.

2. The method according to claim 1, wherein 　　the first notification is received, and the second notification is transmitted, no later than a message is transmitted, from the first DU to the UE, for initiating the LTM procedure for the UE.

3. The method according to claim 1 or 2, wherein 　　the LTM procedure is performed without using a random access channel (RACH).

4. The method according to any one of claims 1 to 3, wherein 　　the first notification and the second notification indicate when a resource of the second DU will be used by a communication with the UE.

5. The method according to any one of claims 1 to 4, wherein 　　the first notification includes first information and the second notification includes second information that is different from the first information.

6. A method performed by a second distributed unit (DU) of an access network, the method comprising: 　　receiving, from a central unit (CU) of the access network, a notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure for a user equipment (UE) from a first cell operated by a first DU of the access network, to a second cell operated by the second DU, has been, or will be, initiated; and 　　receiving, based on the notification, a uplink data from the UE.

7. The method according to claim 6, wherein 　　the receiving, based on the notification, is performed by: 　　　　dynamically scheduling a resource for the uplink data based on the notification; and 　　　　receiving the uplink data using the resource.

8. The method according to claim 6, further comprising: 　　pre-configuring a resource for the uplink data prior to the receiving the notification, and wherein 　　the receiving, based on the notification, is performed by decoding, based on the notification, the uplink data using the resource.

9. A method performed by a first distributed unit (DU) of an access network, the method comprising: 　　transmitting, to a central unit (CU) of the access network, a first notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure for a user equipment (UE) from a first cell operated by the first DU, to a second cell operated by a second DU of the access network, has been, or will be, initiated; and 　　transmitting, to the UE, a message for initiating the LTM procedure for the UE, 　　wherein a second notification indicating that the LTM procedure for the UE, has been, or will be, initiated, is transmitted from the CU to the second DU, upon the transmitting the first notification.

10. The method according to claim 9, wherein 　　the first notification and the second notification are transmitted no later than the message is transmitted.

11. A method performed by an access network node, the method comprising: 　　transmitting, to each of a plurality of user equipments (UEs) of a group, information for triggering a group procedure, at each of the plurality of the UEs of the group, to respectively switch from a first cell operated by the access network node to a second cell.

12. The method according to claim 11, wherein 　　the information is transmitted in a common message for receipt by each of the plurality of the UEs of the group.

13. The method according to claim 11 or 12, wherein 　　the information indicates that at least one of: 　　　　the first cell is being switched to a network energy saving mode, 　　　　the first cell is turning off, or 　　　　non-terrestrial network (NTN) satellite / service link switch will be occurred on the first cell.

14. The method according to any one of claims 11 to 13, wherein 　　the information is transmitted in a paging short message.

15. The method according to claim 14, wherein 　　the paging short message includes a field for triggering the group procedure.

16. The method according to any one of claims 11 to 13, wherein 　　the information is transmitted in system information, or paging information, including a command for triggering the group procedure.

17. The method according to any one of claims 11 to 13, wherein 　　the information is transmitted in downlink control information (DCI) for triggering the group procedure.

18. The method according to claim 11, or 12, wherein 　　the information is transmitted in a media access control (MAC) signaling for triggering the group procedure.

19. The method according to claim 18, wherein 　　the MAC signaling includes a MAC control element (MAC CE) or a MAC service data unit (MAC SDU).

20. The method according to claim 18 or 19, wherein 　　the information is transmitted in a transport block (TB) carrying a respective MAC signaling for one of the plurality of the UEs of the group, for triggering the one of the plurality of the UEs of the group to switch from the first cell to the second cell.

21. The method according to claim 18 or 19, wherein the MAC signaling includes a respective command, for each of the plurality of the UEs of the group, for triggering the each of the plurality of the UEs of the group to switch from the first cell to the second cell.

22. The method according to any one of claims 17 to 20, wherein 　　the information includes information identifying the group.

23. A method according to claim 22, wherein 　　the information identifying the group includes at least one of: 　　　　at least one UE group identifier, or 　　　　a Radio Network Temporary Identifier (RNTI) shared with the each of the plurality of the UEs of the group.

24. The method according to any one of claims 17 to 23, wherein 　　the information includes a list including a respective identifier for each of the plurality of the UEs for which the group procedure is being triggered.

25. The method according to any one of claims 17 to 24, wherein 　　the information is configured for reception using a shared radio network temporary identifier.

26. The method according to claim 25, wherein 　　the information is configured for reception, using the shared radio network temporary identifier, both by any UE in the first cell that is a member of the group and any UE in the first cell that is not a member of the group.

27. The method according to claim 25, wherein 　　the information is configured for reception, using the shared radio network temporary identifier, by any UE in the first cell that is a member of the group but not by any UE in the first cell that is not a member of the group.

28. The method according to any one of claims 17 to 27, wherein 　　the information includes layer 2 (L2) protocol handling information.

29. The method according to any one of claims 11 to 28, wherein 　　the information includes information for identifying at least one target cell for the group procedure.

30. The method according to any one of claims 11 to 29, wherein 　　the group procedure is part of a layer 1 / layer 2 triggered mobility (LTM) procedure.

31. The method according to any one of claims 11 to 29, wherein 　　the group procedure is part of a conditional handover procedure.

32. A method performed by a user equipment (UE), the method comprising: 　　receiving, from an access network node, information for triggering a group procedure, at each of a plurality of UEs of a group including the UE, to respectively switch from a first cell operated by the access network node to a second cell; and 　　initiating a procedure to switch from the first cell to the second cell based on the information.

33. A method performed by a central unit (CU) of an access network, the method comprising: 　　transmitting, to a distributed unit (DU) of the access network, information indicating at least one candidate target cell for a user equipment (UE) to perform a layer 1 / layer 2 triggered mobility (LTM) procedure; and 　　transmitting, to at least one further DU of the access network, the information indicating the at least one candidate target cell for the UE to perform a subsequent LTM procedure.

34. The method according to claim 33, further comprising; 　　receiving, from another DU out of the at least one further DU, information indicating that the LTM procedure from the first cell to a second cell operated by the another DU has been successful, and wherein 　　the transmitting, to the at least one further DU, the information indicating the at least one candidate target cell for the UE to perform a subsequent LTM procedure is performed by transmitting, to the another DU, the information indicating the at least one candidate target cell for the UE to perform a subsequent LTM procedure, upon receiving the information indicating the the LTM procedure has been successful.

35. The method according to claim 33, wherein 　　the transmitting, to the DU, the information indicating the at least one candidate target cell for the UE to perform the LTM procedure causes the DU to configure the UE with the information indicating the at least one candidate target cell for the UE to perform the LTM procedure, and the method comprises: 　　receiving, from the DU, a response message indicating that the UE has configured the at least one candidate target cell for the UE to perform the LTM procedure, and wherein 　　the transmitting, to the at least one further DU, the information indicating the at least one candidate target cell for the UE to perform a subsequent LTM procedure is performed upon receiving the response message.

36. A method performed by a candidate distributed unit (DU) of an access network, the method comprising: 　　receiving, from a central unit (CU) of the access network, as part of a procedure for preconfiguring, by a serving DU of the access network, a user equipment (UE) for a layer 1 / layer 2 triggered mobility (LTM) procedure from a serving cell operated by the serving DU to a target cell of a target DU of the access network, information indicating at least one candidate target cell, wherein the candidate DU is a candidate to be the target DU.

37. A central unit (CU) for an access network, the CU comprising: 　　means for receiving, from a first distributed unit (DU) of the access network, a first notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure for a user equipment (UE) from a first cell operated by the first DU, to a second cell operated by a second DU of the access network, has been, or will be, initiated; and 　　means for transmitting, to the second DU, a second notification indicating that the LTM procedure for the UE, has been, or will be, initiated.

38. A second distributed unit (DU) for an access network, the second DU comprising: 　　means receiving, from a central unit (CU) of the access network, a notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure for a user equipment (UE) from a first cell operated by a first DU of the access network, to a second cell operated by the second DU, has been, or will be, initiated; and 　　means for receiving, based on the notification, a uplink data from the UE.

39. A first distributed unit (DU) for an access network, the first DU comprising: 　　means for transmitting, to a central unit (CU) of the access network, a first notification indicating that a layer 1 / layer 2 triggered mobility (LTM) procedure for a user equipment (UE) from a first cell operated by the first DU, to a second cell operated by a second DU of the access network, has been, or will be, initiated; and 　　transmitting, to the UE, a message for initiating the LTM procedure for the UE, 　　wherein a second notification indicating that the LTM procedure for the UE, has been, or will be, initiated, is transmitted from the CU to the second DU, upon the transmitting the first notification.

40. An access network node comprising: 　　means for transmitting, to each of a plurality of user equipments (UEs) of a group, information for triggering a group procedure, at each of the plurality of the UEs of the group, to respectively switch from a first cell operated by the access network node to a second cell.

41. A user equipment (UE) comprising: 　　means for receiving, from an access network node, information for triggering a group procedure, at each of a plurality of UEs of a group including the UE, to respectively switch from a first cell operated by the access network node to a second cell; and 　　means for initiating a procedure to switch from the first cell to the second cell based on the information.

42. A central unit (CU) for an access network, the CU comprising: 　　means for transmitting, to a distributed unit (DU) of the access network, information indicating at least one candidate target cell for a user equipment (UE) to perform a layer 1 / layer 2 triggered mobility (LTM) procedure; and 　　means for transmitting, to at least one further DU of the access network, the information indicating the at least one candidate target cell for the UE to perform a subsequent LTM procedure.

43. A candidate distributed unit (DU) for an access network, the DU comprising: 　　means for receiving, from a central unit (CU) of the access network, as part of a procedure for preconfiguring, by a serving DU of the access network, a user equipment (UE) for a layer 1 / layer 2 triggered mobility (LTM) procedure from a serving cell operated by the serving DU to a target cell of a target DU of the access network, information indicating at least one candidate target cell, wherein the candidate DU is a candidate to be the target DU.

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