WO2025187366A1

WO2025187366A1 - Method performed by first access network node, method performed by second access network node, first access network node, and second access network node

Info

Publication number: WO2025187366A1
Application number: PCT/JP2025/005013
Authority: WO
Inventors: Hui Ma; Sadafuku Hayashi
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2024-03-08
Filing date: 2025-02-14
Publication date: 2025-09-12
Anticipated expiration: 2026-09-08
Also published as: WO2025187366A8; GB202403408D0

Abstract

A method performed by a first access network node is disclosed. The method includes: receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode; transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.

Description

METHOD PERFORMED BY FIRST ACCESS NETWORK NODE, METHOD PERFORMED BY SECOND ACCESS NETWORK NODE, FIRST ACCESS NETWORK NODE, AND SECOND ACCESS NETWORK NODE

　　The present disclosure relates to a communication system. 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 Long Term Evolution (LTE)-Advanced, Next Generation or 5G networks, future generations, and beyond). The disclosure has particular, although not necessarily exclusive, relevance to providing for the exchange of appropriate information between nodes of different radio access networks, and/or different nodes of the same radio access network, related to the triggering of a system information block 1 (SIB1) transmission and/or to the activation and/or deactivation of on-demand SIB1 transmission or SIB1-less operation in one or more cells.

　　Earlier developments of the 3GPP standards were referred to as the Long-Term Evolution (LTE) of Evolved Packet Core (EPC) network and Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), also commonly referred as '4G'. More recently, the term '5G' and 'new radio' (NR) is used to refer to an evolving communication technology that supports 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.

　　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 equipments or 'UEs') connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present application may use the term access network node, RAN node (or simply RAN) or base station to refer to any such access nodes.

　　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 communication system for sending/receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

　　In the current 5G architecture, the RAN architecture may be distributed with the base station structure 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 (sometimes referred to as 'Medium') 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 base stations 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 base station.

　　In more recently proposed RAN distributed architectures, in addition to the CU and DU, the concept of a Radio Unit (RU) - sometimes referred to as a 'remote unit' - has been introduced. In this architecture the RU is responsible for handling the digital front end (DFE), digital beamforming functionality and, typically, the functionality of the lower parts of the PHY layer, whilst the DU typically handles the higher parts of the PHY layer and the RLC and MAC layers. The CU in this architecture continues to be responsible for controlling one or more DUs (each DU corresponding to a different respective gNB) and to handle higher layer signalling (typically RRC and PDCP layers).

　　The actual functional split between the CU and DUs (and potentially RUs where applicable) of these distributed architectures is flexible allowing the functionality to be optimised for different use cases. Effectively, the split architecture enables a 5G network to use a different distribution of protocol stacks between CU and DUs (and potentially RUs) depending on, for example, midhaul availability and network design.

　　In 5G, core network entities comprise logical nodes (or 'functions') including control plane functions (CPFs) and one or more user plane functions (UPFs). The CPFs include, amongst other things, one or more Access and Mobility Management Functions (AMFs), a session management function (SMF), an Authentication Server Function (AUSF), a Unified Data Management (UDM) entity for managing user specific data, a Policy Control Function (PCF), an Application Function (AF), a Security Anchor Function (SEAF), an Authentication credential Repository and Processing Function (ARPF), and/or the like. The AMF generally corresponds to the mobility management entity (MME) in 4G and performs many of the functions performed by the MME. Each UPF combines functionality of both the S-GW and P-GW - specifically user plane functionality of the S-GW (SGW-U) and user plane functionality of the P-GW (PGW-U). The SMF provides session management functionality (that formed part of MME functionality in 4G). The SMF also combines the some of the functionality provided by the S-GW and P-GW - specifically control plane functionality of the S-GW (SGW-C) and control plane functionality of the P-GW (PGW-C). The SMF also allocates IP addresses to each UE.

　　As cellular communication systems evolve, there is an increasing need for wireless communication networks having improved energy efficiency. This need is being driven, for example, by the fact that 5G (and beyond) communication systems are becoming more pervasive across industries and geographical areas, handling more advanced services and applications requiring very high data rates. Moreover, networks are becoming denser, use more antennas, larger bandwidths, and more frequency bands.

　　A reduction in the amount of energy needed to operate a communication network beneficially reduces both the operational expenditure (OPEX) and the environmental impact, of operating the system. Moreover, for battery-powered devices (for example, UEs) reduced power consumption extends the battery life of the device. However, more recent developments of cellular communication systems (for example to implement wide channel bandwidths, to enable operations at significantly higher frequencies than previously, to provide improved capacity, and the like) tend to increase, rather than reduce, power demand and thus present significant challenges when it comes to energy saving.

　　In this context, a number of network energy saving (NES) techniques are typically implemented in cellular communication systems, and improvements to those NES techniques and completely new techniques are being developed. The NES techniques being considered include time, frequency, spatial, and power domain adaptation techniques.

　　One method of achieving energy savings in a cellular communication system is to reduce the energy requirements associated with communication between a UE and an associated RAN node. The energy consumption arising from such communication includes a dynamic part that is associated with data transmission and reception, and a static part that is associated with operations of the UE, and the RAN node, that are performed even when there is no ongoing data transmission or reception. The static part may include, for example, the power required to operate a UE in a mode in which the UE is able to receive and decode a physical downlink control channel (PDCCH) transmitted by a RAN node.

　　Energy saving modes may be configured for one or more devices in the system (e.g., a UE). For example, a UE may be configured to operate in an energy saving mode (which may also be referred to as a sleep mode) in which the UE performs a reduced number of transmissions, or in which the UE is configured not to attempt to transmit and/or to receive signals during a particular time period. Such operation is commonly referred to as DRX/DTX which stands for Discontinuous Reception (DRX) and Discontinuous Transmission (DTX). DRX for a UE includes idle mode DRX and connected mode DRX (C-DRX). In idle mode DRX, the UE periodically wakes up to monitor for paging messages and goes back to a sleep mode if paging message is not intended for it. In C-DRX, the UE powers down most of its circuitry when there are no packets to be received or transmitted. During this time, the UE nevertheless still monitors for a physical downlink control channel (PDCCH) occasionally during a DRX 'active' state, or DRX 'ON' period. The time during which UE does not monitor the PDCCH is often called a DRX 'sleep' or 'inactive' state, or DRX 'OFF' period.

　　However, most of the energy consumption (and associated OPEX), comes from the radio access network. In view of this, therefore, there remains an ongoing need to develop techniques for achieving more efficient operation (dynamically and/or semi-statically) at the RAN side, and potentially adaptation of transmissions and/or receptions for NES in time, frequency, spatial, and/or power domains with a finer granularity than is currently possible.

　　One NES technique that is being developed to help address this involves discontinuous operation of the cell or cells provided by a RAN node in a similar manner to DTX/DRX at the UE. This is often referred to as 'cell DTX/DRX'. With cell DTX/DRX, the RAN node operating a cell stops transmitting and receiving in that cell during certain periods of time. The UEs that are served by the cell may be provided with information that allows them to determine when the RAN node is in an active or 'ON' state (and is therefore able to communicate with the UE) and when it is in an inactive or 'OFF' state (and is therefore not able to communicate with the UE).

　　Currently, cell DTX/DRX is applied to at least UEs in an RRC connected state. A periodic cell DTX/DRX pattern (i.e., active and non-active periods) for cell DTX/DRX is typically configured by a RAN node using UE specific RRC signalling in a serving cell. The pattern configuration for cell DTX/DRX is, nevertheless, common for the UEs configured with the cell DTX/DRX functionality in the cell. A cell DTX/DRX configuration typically defines a periodicity, start slot/offset, on duration, and a configuration type (i.e., whether the configuration applies to cell DTX only, cell DRX only, or cell DTX and cell DRX jointly). An activation status for cell DTX/DRX indicates whether the UE shall activate the configuration according to the received parameters. The cell DTX/DRX mode may, for example, be activated/de-activated via dynamic layer 1 (L1)/ layer 2 (L2) signalling and/or UE-specific RRC signalling.

　　Previous NES development has also focused, primarily, on NES enhancements aimed at reducing energy associated with connected mode UEs during a low cell load scenario. These enhancements deliberately avoided any impact on idle or legacy UE operation and focused on reducing energy associated with user specific signals and channels. However, this focus has limited the NES gains that are potentially achievable, especially in the RAN.

　　More recently, therefore, a number of procedures have been developed to reduce the amount of energy expenditure associated with idle/inactive mode UEs selecting, camping on, and/or reselecting cells. Much of the energy expenditure associated with these procedures arises from the transmission, reception, and processing of the minimum system information that a RAN node periodically sends to provide a UE with the parameters required for initial access to the cell and acquisition of any other system information.

　　Part of the minimum system information is carried by synchronisation signal / physical broadcast channel (PBCH) blocks (SSBs) which are periodically in the cells of the communication system. Each SSB includes both synchronisation signals (SSs) - e.g., a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS) - and the PBCH. SSBs are, therefore, sometimes referred to as an 'SS/PBCH blocks'. The PBCH in the SSB carries a master information block (MIB) that provides an initial part of the minimum system information. The MIB typically includes, for example, information identifying whether the cell is or is not barred for access, and information allowing subsequent acquisition of the remaining minimum system information (carried by a system information block 1 (SIB1)). The minimum system information carried by the MIB and SIB1 effectively provides the UE with the parameters required for initial access to the cell and acquisition of any other system information.

　　To help reduce energy expenditure associated with the transmission, reception, and processing of the minimum system information, therefore, techniques/procedures are being developed to avoid unnecessary SSB and/or SIB1 transmission. By way of example, such techniques/procedures may include:
-　　The application of 'SSB-less' or 'SIB1-less' operation in certain 'non-anchor' cells, which involves not transmitting SSBs or SIB1s in those cells. Instead, a UE may rely on an SSB or SIB1 transmission in a different 'anchor' cell for acquiring synchronisation and/or minimum system information.
-　　The use of on-demand transmission, rather than automatic (periodic) transmission, of SSBs for camping onto certain cells (e.g., secondary cells (SCells) and/or non-serving cells) by UEs configured to connect to, and use, such cells; and
-　　The use of on-demand transmission, rather than automatic (periodic) transmission, of system information block 1 (SIB1) for certain cells in which a UE is able to retrieve the system information carried by SIB1 by sending an uplink wake-up signal (WUS) to a corresponding RAN node and can perform synchronization based on another cell in which SIB1 is transmitted.

　　There is, nevertheless, still further development required to optimise the use of such NES techniques/procedures to ensure UEs can receive the required minimum system information whilst also minimising the unnecessary transmissions of minimum system information in order to maximise the available energy saving benefits.

　　The disclosure aims to provide one or more apparatus and/or one or more associated methods that at least partly contributes meeting the above need.

NPL 1: NGMN 5G White Paper' V1.0

　　In the present disclosure, one or more apparatus and/or one or more associated methods are disclosed that aim to at least partially contribute to implementing one or more of the above mentioned possible enhancements.

　　In one aspect there is provided a method performed by a first access network node, the method comprising:
　　receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.

　　In one aspect there is provided a method performed by a second access network node, the method comprising:
　　in a case where a mobile device requests a first access network node to transmit a system information block 1 (SIB1) on a cell operated by the second access network node, receiving, from the first access network node, information for requesting the second access network node to transmit the SIB1; and
　　transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.

　　In one aspect there is provided a first access network node comprising:
　　means for receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　means for transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.

　　In one aspect there is provided a second access network node comprising:
　　means for receiving, from a first access network node, information for requesting the second access network node to transmit a system information block 1 (SIB1), in a case where a mobile device requests the first access network node to transmit the SIB1 on a cell operated by the second access network node; and
　　means for transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.

　　The various functional means described below that are part of the UE may be provided by a memory and one or more processors that execute instructions stored in the memory. Similarly, the various functional means described below that are part of the access network node may be provided by a memory and one or more processors that execute instructions stored in the memory.

　　Various example described below may be implemented by means of a computer program product comprising computer implementable instructions for causing a programmable computer to carry out the any of the methods described below. The computer implementable instructions may be provided as a signal or on a tangible computer readable medium.

　　According to the present disclosure, it is possible to provide a method performed by a mobile terminal, a method performed by an access network node, a mobile terminal, and an access network node.

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

Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') telecommunication system; Fig. 2 is a simplified sequence diagram illustrating different inter-node procedures for triggering SIB1 transmission that may be implemented in the communication system of Fig. 1; Fig. 3 is a simplified sequence diagram illustrating further inter-node procedures for triggering SIB1 transmission that may be implemented in the communication system of Fig. 1; Fig. 4 is a simplified sequence diagram different intra-RAN, inter-node, information exchange procedures for informing a central unit of a distributed RAN node of the transmission status for SIB1 transmission that may be implemented in the communication system of Fig. 1; Fig. 5 is a simplified sequence diagram different intra-RAN, inter-node, procedures for triggering activation/deactivation of on-demand SIB1 transmission or SIB1-less operation that may be implemented in the communication system of Fig. 1; Fig. 6 is a schematic block diagram illustrating the main components of a UE the communication system of Fig. 1; Fig. 7 is a schematic block diagram illustrating the main components of a non-distributed RAN node for the communication system of Fig. 1; and Fig. 8 is a schematic block diagram illustrating the main components of a distributed RAN node for the communication system of Fig. 1.

　　< Overview >
　　An exemplary communication system will now be described in general terms, by way of example only, with reference to Fig. 1.

　　Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system (e.g. communication system 1) to which examples of the present disclosure are applicable.

　　In the communication system 1, user equipments (UEs) 3 (3-1, 3-2, 3-3) (e.g. mobile telephones and/or other mobile devices) can communicate with each other via a corresponding (radio) access network ((R)AN) node 5-1, 5-2 that operates according to one or more compatible radio access technologies (RATs). In the illustrated example, each RAN node 5 (5-1, 5-2) comprises a base station 5 or 'gNB' that respectively operates one or more associated cells 9 (9-1, 9-2). In the illustrated communication system 1, the coverage provided by each RAN node 5 may be by means of a plurality of beams B (B₁, B₂ … B_r, B_r+1 … B_N). It will be appreciated that while, for clarity of illustration, only a selection of possible beams B are shown for one of the RAN nodes 5, the set of beams may include any suitable number of beams and each RAN node 5 may operate a respective set of beams or may provide coverage in a non-beamformed manner.

　　Communication via each RAN node 5 is typically routed through a core network 7 (e.g. a 5G or later generations core network or evolved packet core network (EPC)).

　　As those skilled in the art will appreciate, whilst three UEs 3 and two RAN nodes 5 are shown in Fig. 1 for illustration purposes, the system, when implemented, will typically include one or more other RAN nodes 5 and UEs 3.

　　Each RAN node 5 controls one or more associated cells 9 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 RAN nodes 5 may be configured to support 4G, 5G, 6G, and/or later generations and/or any other 3GPP or non-3GPP communication protocols.

　　In this example one of the illustrated RAN nodes 5 is a RAN node 5-2 that forms part of a distributed RAN (which may be referred to as a 'distributed base station' or distributed 'RAN node'). The RAN node 5-2 of a distributed RAN comprises at least one distributed unit (DU) 5-2_DU (e.g., a gNB-DU or the like), and a central unit (CU) 5-2_CU (e.g., a gNB-CU or the like). The CU 5-2_CU 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 5-2_DU via an appropriate interfaces (e.g. an F1-C interface and an F1-U interface (together forming an F1 interface (or 'reference point'))), and with one another via an appropriate interface (e.g. an E1 interface). It will be appreciated that while, in this example, the DU 5-2_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 distributed RAN node 5-2 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).

　　Whilst one non-distributed ('integrated') RAN node 5-1 and one distributed RAN node 5-2 are shown, it will, nevertheless, be appreciated that either (or both) of the RAN nodes 5 may be provided in a distributed or non-distributed form. It will also be appreciated that whilst the term 'RAN node' is generally used herein to refer to a whole base station, the CU 5-2_CU and DU 5-2_DU are also both parts of a corresponding distributed RAN and are therefore each a distinct 'RAN node' albeit that they each form part of the same RAN, and that each may have only a subset of the functionality provided by a whole base station. References to a RAN node as used herein should, therefore, be understood, accordingly.

　　The UEs 3 and their serving RAN node 5 are connected via an appropriate air interface (for example the so-called 'Uu' interface and/or the like). Neighbouring RAN nodes 5 may be connected to each other via an appropriate RAN node to RAN node interface (such as the so-called 'X2' interface, 'Xn' interface and/or the like).

　　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 network node entities for the communication of user data (e.g. user plane functions (UPFs) 11). The CPFs 10 include one or more network node entities for the communication of control signalling (e.g. Access and Mobility Management Functions (AMFs) 10-1), one or more network node entities for session management (e.g. Session Management Functions (SMFs) 10-2) and a number of other functions 10-n. Additional functions may include, for example: an Authentication Server Function (AUSF) which facilitates 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); a Security Anchor Function (SEAF) which is in a serving network and acts as a "middleman" during an authentication process between a UE 3 and its home network; an Authentication credential Repository and Processing Function (ARPF) which maintains the authentication credentials; and/or the like. It will be appreciated that the nodes or functions may have different names in different systems.

　　The communication system 1 also includes an Operations, Administration and Maintenance (OAM) 14 comprising one or more OAM functions for provisioning and managing network or elements within the wider communication system 1. The OAM 14 may be responsible for the storage and analysis of some radio-related measurements and may perform some data analytics functions including some RAN analytics. The OAM 14 may, for example, communicate with one or more of the core network CPFs 10 via a network data analytics function (NWDAF) or the like (not shown).

　　Each RAN node 5 is respectively connected to the core network nodes via appropriate interfaces (or 'reference points') such as an N2 reference point between the RAN node 5 and the AMF 10-1 for the communication of control signalling, and an N3 reference point between the RAN 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 non-access stratum (NAS) connection over an appropriate interface (e.g. an N1 reference point (analogous to the S1 reference point in LTE)). It will be appreciated, that N1 communications are routed transparently via the RAN node 5.

　　Each UPF 11 is respectively connected to an external data network 20 (e.g. an IP network such as the internet) via an appropriate interface (e.g. an N6 reference point) for communication of the user data.

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

　　The SMF 10-2 is connected to the AMF 10-1 via an appropriate interface (e.g. 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 10-2 uses user information provided via the AMF 10-1 to determine what session manager would be best assigned to the user. The SMF 10-2 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.

　　Each RAN 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.

　　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 at least the 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. Specifically, a UE 3 may receive a Synchronization Signal / Physical Broadcast Channel (PBCH) Block (SSB) (also referred to as an 'SS/PBCH block'), and the UE 3 may assume that reception occasions of a PBCH, primary synchronization signal (PSS) and secondary synchronization signal (SSS) are in consecutive symbols and form that SSB. The RAN node 5 may transmit a number of SSBs corresponding to different DL beams. The total number of SSBs may be confined, for example, within a 5ms duration as an SS burst.

　　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 RAN 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).

　　Similarly, the UEs 3 are configured for transmission of, and the RAN node 5-1 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.

　　When the UE 3 initially establishes a radio resource control (RRC) connection with a RAN node 5 via a cell 9 it registers with an appropriate core network node (e.g., AMF 10-1, MME). The UE 3 is in the so-called RRC connected state and an associated UE context is maintained by the network. When the UE 3 is in the so-called RRC idle state, or is in the RRC inactive state, it selects an appropriate cell 9 for camping so that the network is aware of the approximate location of the UE 3 (although not necessarily on a cell level).

　　< Carrier Aggregation (CA) >
　　In the communication system 1, increases in bandwidth, and thereby bitrate can be achieved through carrier aggregation (CA), whereby multiple frequency blocks, i.e., component carriers (CCs), are assigned to the same UE 3 for use. Each CC in turn serves a cell 9 which provides a particular bandwidth and set of services to the UE 3. For example, in CA each UE 3 has a first CC that provides a primary cell (PCell) that carries traffic and RRC signalling messages and may additionally any number of other CCs that each provide their own corresponding secondary cell (SCell) which carry traffic alone. The SCells are optional, and are added, removed, and/or reconfigured are required by the UE 3 and the network.

　　In CA, when initially scanning for a cell to camp on each UE 3 scans for a PCell. The PCell is serves as the main point of communication between the UE 3 and the RAN node 5 and is responsible for all control information signalling (e.g., RRC Configuration signalling), non-access stratum (NAS) signalling, and the like, between the UE 3 and the network, as well as initial data transmissions. The PCell typically offers a high bandwidth for low latency data transmission. It will be appreciated that when initially scanning for a PCell to camp on each UE 3 searches for SSB as described previously to enable efficient cell searching for, and initial access to the PCell.

　　As and when required, the UE 3 may be triggered to search for, and camp on one or more secondary cells (SCells) to provide additional capacity and adaptability in the network. For example, the UE 3 may be triggered to search for, and camp on one or more SCells to provide extra bandwidth when the network is experiencing high data traffic or congestion. Additionally, or alternatively, SCells may be camped on to provide specific specialist services, for example, the UE 3 may camp onto a SCell that caters for Internet-of-Things (IoT) devices, high-definition data streaming, or the like.

　　< Dual Connectivity (DC) >
　　The UEs 3 and RAN nodes 5 of the communication system 1 are also mutually configured for dual connectivity in which the UE 3 can be configured to connect and communicate via (at least) two different RAN nodes 5 known as a master RAN node 5 and a secondary RAN node 5 that are themselves interconnected via an appropriate RAN node to RAN node interface (e.g., Xn or X2). It will be appreciated that, in dual connectivity, the master RAN node 5 and the secondary RAN node 5 may be configured to use the same, or a different, radio access technology (e.g., the RAN nodes may each use a different one of a 4G, 5G, 6G (or other) radio access technology).

　　CA can also be used by a UE 3, in the context of dual connectivity. For example, the UE 3 may be configured to communicate via one, or multiple (carrier aggregated) cells 9 of the master RAN node 5 and via one, or multiple (carrier aggregated) cells of the secondary RAN node 5.

　　A group of serving cells associated with the master RAN Node 5 may be referred to as a master cell group (MCG). The MCG typically comprises a so called special cell (SpCell) which is the PCell (Primary Cell), and one or more SCells. A group of serving cells associated with the secondary RAN Node 5 may be referred to as a secondary cell group (SCG). The SCG typically comprises an SpCell, which is known as a primary SCell (PSCell) in this case, and one or more SCells.

　　It will be appreciated that whilst CA and DC are conceptually similar, there are a number of differences. For example, in CA the user traffic is typically split between different carriers at the MAC layer, whereas in DC user traffic is typically split at the PDCP layer.

　　< Network Energy Saving (NES) >
　　The UEs 3 and RAN nodes 5 of the communication system 1 are mutually configured to be able to coordinate with one another appropriately to implement one or more NES techniques. The NES techniques may include, for example, conventional DTX/DRX at the UE 3, cell DTX/DRX at the RAN node 5, the use of SSB-less cells in which SSBs are not transmitted, the use of SIB1-less cells in which SIB1s are not transmitted, the provision of SSBs on-demand in one or more cells 9, and/or the provision of one remaining minimum system information (SIB1) transmission on-demand in one or more cells 9.

　　The communication system 1 may, for example, support SSB-less/SIB1-less operation for intra-band CA scenarios, for example, where the UE 3 is able to retrieve system information from, and can perform synchronisation based on, another intra-band cell that transmits SSB and SIB1. For the non-CA scenario, the UE 3 may obtain system information from other associated carriers/cells and synchronise from other associated carriers/cells and/or synchronise from other signals transmitted in the cell 9. A cell 9 in which the RAN node 5 transmits, and the UE 3 is capable of receiving, an SSB, system information and paging may be referred to as an anchor cell. Access may occur only via an anchor cell, or directly via the non-anchor NES cell if supported. Where access directly via a non-anchor NES cell is supported, system information transmitted in the anchor cell may also include the necessary information to access the non-anchor NES cell. The UE 3 will camp on an anchor cell rather than a non-anchor NES cell in which there is no SIB1 transmission (or no SSB or SIB1 transmission).

　　The communication system 1 may nevertheless support on-demand SSB/SIB1 transmission (e.g., in an otherwise SSB-less or SIB1-less cell) to enable longer periods of cell inactivity to achieve network energy saving. SSB/SIB1 transmission in a serving cell 9 may, for example, be triggered on-demand, for example by the UE 3 (or RAN node 5). The UE 3 and RAN node 5 of the communication system 1 may, for example, be mutually configured to support the transmission of dedicated SSBs and/or SIB1s in (non-anchor NES) SCells on-demand.

　　The triggering of an on-demand SSB/SIB1 may, for example, be facilitated by the transmission, by the UE 3, of an appropriate trigger signal (or 'wake-up' signal (WUS)) in the uplink to cause the RAN node 5 to 'wake-up' from its current sleep state (or at least transition into a more awake / higher power level sleep state) and begin to transmit SSBs in the corresponding non-anchor/secondary cell. The configuration of the WUS, for example, the configuration of when and/or where in frequency the WUS can be transmitted, may be predefined or may be configured by the RAN node 5 (e.g., via system information and/or DCI).

　　A WUS may, for example be configured by appropriate common radio resource configuration information, comprising WUS configuration information (e.g., in a dedicated WUS configuration information element), provided as part of system information.

　　On-demand SSB/SIB1 transmission may, for example, be enabled semi-statically or dynamically. For example, common channel adaptation and/or on-demand SSB may be enabled via dedicated RRC signalling on a PCell and/or PSCell if the UE 3 has a PCell and/or PSCell connection. On-demand SSB/SIB1 may be enabled via system information (e.g., where the content of system information includes a carrier indication field to indicate the applicable carrier/cell for the enabling of on-demand SSB transmission). On-demand SSB/SIB1 may be enabled via a DCI with an appropriate DCI format.

　　At the RAN node 5, depending on what energy saving technique is being implemented, and how that technique is being implemented, the RAN node 5 (and/or a specific subset of one or more cells that it operates) may be operated in one of a number of different NES modes or states. The possible NES modes may include, for example, simple 'on' or 'off' states. Nevertheless, the possible NES modes may include different predefined energy/power consumption states for the RAN node 5 (or one or more cells 9 operated by that RAN node 5) including: a number of different 'sleep' states in which the RAN node 5 is at least partially off / not fully on but may perform certain operations. These sleep states may be characterised, for example, by different relative power levels, for example: 'deep' sleep (lowest power); 'light' sleep (higher power relative to deep sleep); and micro sleep (higher power relative to both deep and light sleep). Moreover, the possible NES modes may include an active uplink state and an active downlink state in which the RAN node 5 is respectively 'on' for communication in the uplink direction only, or for communication in the downlink direction only.

　　It will be appreciated that whilst a number of specific techniques are described, a given UE 3 or RAN node 5 need not implement every NES technique mentioned, and or may implement one or more other such NES techniques.

　　< Inter-node configuration exchange for NES >
　　Beneficially, as described in more detail later, the communication system 1 is configured to support one or more techniques for inter-node triggering of system information block 1 (SIB1) transmission and/or the activation and/or deactivation of on-demand SIB1 transmission or SIB1-less operation in one or more cells 9. The different nodes involved may be different RAN nodes 5 of different RANs, or different nodes (e.g., DU and CU) of the same RAN.

　　The techniques that may be supported include one or more techniques that extend support for on-demand SIB1 transmission, and thereby enable longer periods of cell inactivity to achieve network energy saving, to provide for inter RAN node triggering of SIB1 transmission.

　　The techniques that may be supported include one or more techniques that extend support for on-demand SIB1 transmission, and thereby enable longer periods of cell inactivity to achieve network energy saving, to provide for inter RAN node exchange of SIB1 to allow transmission of SIB1 for one cell 9 (e.g., a SIB1-less cell, which might, for example, be a non-anchor cell) in a different cell 9 (e.g., an anchor cell, a PCell, or the like).

　　The techniques that may be supported also include one or more techniques to support the provision of a SIB1 transmission status (e.g., whether SIB1-less transmission and/or on-demand SIB1 transmission is activated/deactivated), for each of one or more identified cells, from a DU to a CU of a distributed RAN node 5. One of these techniques may, for example, be used when the DU is responsible for deciding whether to operate a given cell as a SIB1-less cell, as a cell in which SIB1 is transmitted on-demand, or as a cell in which SIB1 is transmitted periodically in a conventional manner.

　　The techniques that may be supported also include one or more techniques by which a CU may request activation (or deactivation), of a particular type of SIB1 transmission operation in each of one or more identified cells (e.g., SIB1-less operation, transmission of SIB1 on-demand, or transmission of SIB1 in a conventional manner), at a DU via which the identified cell or cells are provided. One of these techniques may, for example, be used when the CU is responsible for deciding whether to operate a given cell as a SIB1-less cell, as a cell in which SIB1 is transmitted on-demand, or as a cell in which SIB1 is transmitted periodically in a conventional manner.

　　< Inter-RAN Node On-Demand SIB1 Transmission >
　　As mentioned above, the communication system 1 may support one or more techniques that extend support for on-demand SIB1 transmission to provide for inter RAN node triggering of SIB1 transmission.

　　It will be appreciated that each technique potentially provides for a beneficial extension to known techniques for SIB1 adaptation for NES, including on-demand SIB1 transmission to enable longer periods of cell inactivity, and hence achieve more flexible and/or additional energy savings.

　　A number of techniques/procedures for inter RAN node triggering of SIB1 transmission will now be described, by way of example only, with reference to Fig. 2, which is a simplified sequence diagram illustrating different inter-node procedures for triggering SIB1 transmission that may be implemented in the communication system 1.

　　In the examples illustrated in Fig. 2, the RAN nodes 5 include a first RAN node 5-1 and a second (e.g., neighbouring) RAN node 5-2 that are interconnected by an appropriate RAN node (base station) to RAN node (base station) interface (e.g., an X2 or Xn interface and/or the like). It will be appreciated that the RAN nodes 5 may each use the same, or a different, one of a 4G, 5G, 6G (or other) radio access technology. Moreover, the first RAN node 5-1 and the second RAN node 5-2 may each be configured to provide carrier aggregation for one or more UEs 3 in the communication system 1 and/or may each be configured to, together, provide dual connectivity (e.g., acting as a master node and secondary node respectively) for one or more UEs 3 in the communication system 1.

　　< General RAN Node Configuration Update Procedure >
　　In a first example illustrated in Fig. 2, the RAN nodes 5 are configured to engage in a general RAN node configuration update procedure 210a to provide a SIB1 transmission trigger from the first RAN node 5-1 to the second RAN node 5-2. This procedure may, for example, be a modified form of a conventional Xn application protocol (XnAP) based RAN node configuration update procedure. As those skilled in the art will appreciate, the RAN node configuration update procedure is specified for 5G (or later generations) systems, for updating application level configuration data needed for two RAN nodes 5 (e.g., gNBs) to interoperate correctly over the Xn control plane (Xn-C) interface.

　　As part of the RAN node configuration update procedure 210a the first RAN node 5-1 sends to the second RAN node 5-2, at S212a, a request to transmit SIB1 in at least one cell 9 operated by the second RAN node 5-2 using an appropriate RAN node configuration update message (for example a RAN node configuration update message). The SIB1 transmission request may be accompanied, for example by a list of one or more cells 9 (e.g. indicated by their respective global cell-ID or physical cell ID) to which the SIB1 transmission request relates. The granularity of the SIB1 request can be at a per cell level (or at a cell group level), e.g., the first RAN node 5-1 can issue a SIB1 request relating to each cell listed (or each of one or more groups of cells listed) in the list of (e.g., serving non-anchor) cells 9 provided via the second RAN node 5-2 within which to transmit SIB1.

　　The RAN node configuration update message including the SIB1 transmission request may be triggered at the first RAN node 5-1, for example, when the first RAN node 5-1 receives appropriate signalling from the UE 3 to request transmission of SIB1 of one or more cells 9 other than an anchor cell operated by the first RAN node 5-1.

　　If any of the listed cells are configured for on-demand SIB1 transmission then, on receipt of the SIB1 transmission request, the second RAN node 5-2 may (if SIB1 is not currently being, or has not already been, transmitted in at least some of the indicated cells) initiate transmission of the respective SIB1 of each of the indicated cells (or group of cells) for which that SIB1 is not, or has not been, already transmitted. If any of the listed cells are configured for SIB1-less operation then, on receipt of the SIB1 transmission request, the second RAN node 5-2 may switch back to normal (or possibly on-demand) SIB1 transmission for each cell (or group of cells) that are configured for SIB1-less operation, and hence begin (possibly temporary) SIB1 transmission (possibly for a (pre)configured period of time).

　　Where SIB1 is then successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 indicates this success appropriately, at S214a, by sending an appropriate RAN node configuration update acknowledge message (for example an NG-RAN node configuration update acknowledge message). Effectively, this acknowledgement message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1: that the second RAN node 5-2 has successfully reactivated to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured); and/or that the second RAN node 5-2 has successfully reverted to normal (or on-demand) SIB1 transmission in the indicated cell or cells (e.g., where SIB1-less operation is configured). It will be appreciated that the success may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 is only successfully transmitted in a subset of the originally indicated cells.

　　Where SIB1 is not successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 may indicate this lack of success appropriately, at S216a, by sending an appropriate RAN node configuration update failure message (for example an NG-RAN node configuration update failure message). Effectively, this failure message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1: that the second RAN node 5-2 has failed to reactivate to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured); and/or that the second RAN node 5-2 has failed to revert to normal (or on-demand) SIB1 transmission in the indicated cell or cells (e.g., where SIB1-less operation is configured). The failure message may include an indication of a reason for or cause of the failure (e.g., "function not supported", "temporary failure to transmit SIB1", and/or the like). It will be appreciated that the failure may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 has not been successfully transmitted in only a subset of the originally indicated cells.

　　< Dedicated Activation of Transmission Request Procedure >
　　In a second example illustrated in Fig. 2, the RAN nodes 5 are configured to engage in a dedicated activation of transmission request procedure 210b to provide a SIB1 transmission trigger from the first RAN node 5-1 to the second RAN node 5-2.

　　As part of the dedicated activation of transmission request procedure 210b the first RAN node 5-1 sends to the second RAN node 5-2, at S212b, a request to transmit SIB1 in at least one cell operated by the second RAN node 5-2 using an appropriate dedicated message for requesting activation of transmission in one or more cells 9 (for example an 'activation transmission request' message, a 'transmission activation request' message, an 'activate transmission request' message, or the like). The SIB1 transmission request may be accompanied, for example by a list of one or more cells 9 (e.g. indicated by their respective global cell-ID or physical cell ID) to which the SIB1 transmission request relates. The granularity of the SIB1 request can be at a per cell level (or at a cell group level), e.g., the first RAN node 5-1 can issue a SIB1 request relating to each cell listed (or each of one or more groups of cells listed) in the list of (e.g., serving non-anchor) cells provided via the second RAN node 5-2 within which to transmit SIB1.

　　The activation of transmission request message including the SIB1 transmission request may be triggered at the first RAN node 5-1, for example, when the first RAN node 5-1 receives appropriate signalling from the UE 3 to request transmission of SIB1 of one or more cells 9 other than an anchor cell operated by the first RAN node 5-1.

　　Where SIB1 is then successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 indicates this success appropriately, at S214b, by sending an appropriate dedicated message for acknowledging the request for activation of transmission in one or more cells 9 (for example an 'activation transmission acknowledge' message, a 'transmission activation acknowledge' message, an 'activate transmission acknowledge' message, or the like). Effectively, this acknowledgement message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1: that the second RAN node 5-2 has successfully reactivated to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured); and/or that the second RAN node 5-2 has successfully reverted to normal (or on-demand) SIB1 transmission in the indicated cell or cells (e.g., where SIB1-less operation is configured). It will be appreciated that the success may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 is only successfully transmitted in a subset of the originally indicated cells.

　　Where SIB1 is not successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 may indicate this lack of success appropriately, at S216b, by sending an appropriate dedicated message for indicating failure of activation of transmission in one or more cells 9 (for example an 'activation transmission failure' message, a 'transmission activation failure' message, an 'activate transmission failure' message, or the like). Effectively, this failure message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1: that the second RAN node 5-2 has failed to reactivate to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured); and/or that the second RAN node 5-2 has failed to revert to normal (or on-demand) SIB1 transmission in the indicated cell or cells (e.g., where SIB1-less operation is configured). The failure message may include an indication of a reason for or cause of the failure (e.g., "function not supported", "temporary failure to transmit SIB1", and/or the like). It will be appreciated that the failure may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 has not been successfully transmitted in only a subset of the originally indicated cells.

　　< Inter-RAN Node Procedure in the Context of SIB1-less Operation >
　　As mentioned above, the communication system 1 may support one or more techniques that extend support for on-demand SIB1 transmission to provide for inter RAN node exchange of SIB1 to allow transmission of SIB1 for one cell 9 (e.g. a cell that is configured for SIB1-less operation), in a different cell 9.

　　It will be appreciated that each technique potentially provides for a beneficial extension to known techniques for SIB1 adaptation for NES, including SIB1-less operation to enable longer periods of cell inactivity, and hence achieve more flexible and/or additional energy savings.

　　A number of techniques/procedures for inter RAN node triggering of SIB1 transmission will now be described, by way of example only, with reference to Fig. 3, which is a simplified sequence diagram illustrating further inter-node procedures for triggering SIB1 transmission that may be implemented in the communication system 1.

　　In the examples illustrated in Fig. 3, the RAN nodes 5 include a first RAN node 5-1 and a second (e.g., neighbouring) RAN node 5-2 that are interconnected by an appropriate RAN node (base station) to RAN node (base station) interface (e.g., an X2 or Xn interface and/or the like). It will be appreciated that the RAN nodes 5 may each use the same, or a different, one of a 4G, 5G, 6G (or other) radio access technology. Moreover, the first RAN node 5-1 and the second RAN node 5-2 may each be configured to provide carrier aggregation for one or more UEs 3 in the communication system 1 and/or may each be configured to, together, provide dual connectivity (e.g., acting as a master node and secondary node respectively) for one or more UEs 3 in the communication system 1.

　　In the examples illustrated in Fig. 3, when the first RAN node 5-1 receives signalling from a UE 3 to request transmission of SIB1 of one or more cells 9 other than an anchor cell operated by the first RAN node 5-1, the first RAN node 5-1, may send to the second RAN node 5-2, an appropriate signalling message using a RAN node to RAN node interface based application protocol ('AP', e.g., XnAP), to request SIB1 transmission. In these examples, if SIB1 cannot be transmitted in one or more indicated cells (e.g., cells configured for SIB1-less operation), upon request from the first RAN node 5-1, then the second RAN node 5-2 may forward the SIB1 for the corresponding indicated cell or cells to the first RAN node 5-1. The first RAN node 5-1 can then send the received SIB1 to the UE 3 on behalf of the second RAN node 5-2.

　　< General RAN Node Configuration Update Procedure >
　　In a first example illustrated in Fig. 3, the RAN nodes 5 are configured to engage in a general RAN node configuration update procedure 310a to provide a SIB1 transmission trigger from the first RAN node 5-1 to the second RAN node 5-2. This procedure may, for example, be a modified form of a conventional Xn application protocol (XnAP) based RAN node configuration update procedure. As those skilled in the art will appreciate, the RAN node configuration update procedure is specified for 5G (or later generations) systems, for updating application level configuration data needed for two RAN nodes 5 (e.g., gNBs) to interoperate correctly over the Xn control plane (Xn-C) interface.

　　As part of the RAN node configuration update procedure 310a the first RAN node 5-1 sends to the second RAN node 5-2, at S312a, a request to transmit SIB1 in at least one cell 9 operated by the second RAN node 5-2 using an appropriate RAN node configuration update message (for example an NG-RAN node configuration update message). The SIB1 transmission request may be accompanied, for example by a list of one or more cells 9 (e.g. indicated by their respective global cell-ID or physical cell ID) to which the SIB1 transmission request relates. The granularity of the SIB1 request can be at a per cell level (or at a cell group level), e.g., the first RAN node 5-1 can issue a SIB1 request relating to each cell listed (or each of one or more groups of cells listed) in the list of (e.g., serving non-anchor) cells provided via the second RAN node 5-2 within which to transmit SIB1.

　　If any of the listed cells are configured for on-demand SIB1 transmission then, on receipt of the SIB1 transmission request, the second RAN node 5-2 may (if SIB1 is not currently being, or has not already been, transmitted in at least some of the indicated cells) initiate transmission of the respective SIB1 of each of the indicated cells (or group of cells) for which that SIB1 is not, or has not been, already transmitted.

　　Where SIB1 is then successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 indicates this success appropriately, at S314a, by sending an appropriate RAN node configuration update acknowledge message (for example an NG-RAN node configuration update acknowledge message). Effectively, this acknowledgement message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1 that the second RAN node 5-2 has successfully reactivated to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured). It will be appreciated that the success may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 is only successfully transmitted in a subset of the originally indicated cells.

　　Nevertheless, if any of the listed cells are configured for SIB1-less operation, then, on receipt of the SIB1 transmission request, the second RAN node 5-2 may not be able to transmit SIB1 in the corresponding cell or cells. When SIB1 cannot be transmitted for a listed cell (or group of cells), the second RAN node 5-2 may provide, to the first RAN node 5-1, the SIB1 for each corresponding indicated cell (or group of cells). The first RAN node 5-1 can then send the received SIB1 (or SIB1s) to the UE 3 on behalf of the second RAN node 5-2.

　　The second RAN node 5-2 may provide the SIB1 (or SIB1s) for a corresponding cell (or group of cells), as indicated at S316a, by sending an appropriate RAN node configuration update failure message (for example an NG-RAN node configuration update failure message) including the SIB1 (or SIB1s).

　　Nevertheless it will be appreciated that, as an alternative to providing SIB1 (or SIB1s) in such a failure message, the second RAN node 5-2 may forward the SIB1 (or SIB1s) for a corresponding cell (or group of cells) in an appropriate transfer message using the RAN node to RAN node interface based application protocol (e.g., XnAP), for example, an RRC transfer message that is used to transfer RRC messages and/or information elements via the RAN node to RAN node interface. Such a transfer message may be sent in addition to (or as an alternative to) sending a RAN node configuration update failure message. It will also be appreciated that the SIB1 (or SIB1s) could potentially be provided in the RAN node configuration update acknowledge message (e.g., the presence of the SIB1/SIB1s could implicitly indicate that the SIB1/SIB1s require transmission to the UE 3 by the first RAN node 5-1).

　　Regardless of the message used to provide the SIB1 (or SIB1s) to the first RAN node 5-1, the second RAN node 5-2 may provide the SIB1 (or SIB1s) in that message using any appropriate information element. An exemplary information element that may be used for cells 9 is illustrated in Table 1 below by way of example only.

Table 1 - SIB1 IE for providing SIB1 for one or more cells

　　It will be appreciated that, whilst the example illustrated in Table 1 is for cells 9 a similar information element could be used for cells associated with other cellular technologies (e.g., 6G, or beyond cellular technologies). It will also be appreciated that, in Table 1, the parameter 'maxnoNRcells' represents a maximum number of cells that can be served by a RAN node 5 (specifically an NG-RAN node in the illustrated example). The value of maxnoNRcells is typically 64 for NR but may be different (e.g., for other, more advanced, cellular technologies e.g., more advanced 5G and/or 6G technologies).

　　If the second RAN node 5-2 fails to transmit a SIB1 on request by the first RAN node 5-1 (or to provide the SIB1 to the first RAN node 5-1), then the second RAN node 5-2 may send an appropriate RAN node configuration update failure message (for example an NG-RAN node configuration update failure message). The failure message may include an indication of a reason for or cause of the failure (e.g., "function not supported", "temporary failure to transmit SIB1", and/or the like). It will be appreciated that the failure may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 has not been successfully transmitted in only a subset of the originally indicated cells.

　　< Dedicated SIB1 Request Procedure >
　　In a second example illustrated in Fig. 3, the RAN nodes 5 are configured to engage in a dedicated SIB1 request procedure 310b to provide a SIB1 transmission trigger from the first RAN node 5-1 to the second RAN node 5-2.

　　As part of the dedicated SIB1 request procedure 310b the first RAN node 5-1 sends to the second RAN node 5-2, at S312b, a dedicated request message (for example a 'SIB1 request' or the like). The SIB1 request message may include, for example a list of one or more cells 9 (e.g. indicated by their respective global cell-ID or physical cell ID) to which the SIB1 transmission request relates. The granularity of the SIB1 request can be at a per cell level (or at a cell group level), e.g., the first RAN node 5-1 can issue a SIB1 request relating to each cell listed (or each of one or more groups of cells listed) in the list of (e.g., serving non-anchor) cells provided via the second RAN node 5-2 within which to transmit SIB1.

　　Transmission of the SIB1 request message may be triggered at the first RAN node 5-1, for example, when the first RAN node 5-1 receives appropriate signalling from the UE 3 to request transmission of SIB1 of one or more cells 9 other than an anchor cell operated by the first RAN node 5-1.

　　If any of the listed cells are configured for on-demand SIB1 transmission then, on receipt of the SIB1 request, the second RAN node 5-2 may (if SIB1 is not currently being, or has not already been, transmitted in at least some of the indicated cells) initiate transmission of the respective SIB1 of each of the indicated cells (or group of cells) for which that SIB1 is not, or has not been, already transmitted.

　　Where SIB1 is then successfully transmitted for a listed cell (or group of cells), the second RAN node 5-2 indicates this success appropriately, at S314b, by sending an appropriate response message (for example a 'SIB1 Response', 'SIB1 Request Response', 'SIB1 Request Acknowledge' or the like). Effectively, this response message may serve to explicitly, or implicitly, indicate to the first RAN node 5-1 that the second RAN node 5-2 has successfully reactivated to transmit SIB1 in the indicated cell or cells (e.g., where on-demand SIB1 is configured). It will be appreciated that the success may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 is only successfully transmitted in a subset of the originally indicated cells.

　　Nevertheless, if any of the listed cells are configured for SIB1-less operation, then, on receipt of the SIB1 request, the second RAN node 5-2 may not be able to transmit SIB1 in the corresponding cell or cells. When SIB1 cannot be transmitted for a listed cell (or group of cells), the second RAN node 5-2 may provide, to the first RAN node 5-1, the SIB1 for each corresponding indicated cell (or group of cells). The first RAN node 5-1 can then send the received SIB1 (or SIB1s) to the UE 3 on behalf of the second RAN node 5-2.

　　The second RAN node 5-2 may provide the SIB1 (or SIB1s) for a corresponding cell (or group of cells), as indicated at S316b, by sending an appropriate failure message (for example a 'SIB1 Failure', 'SIB1 Request Failure' or the like) including the SIB1 (or SIB1s).

　　Nevertheless it will be appreciated that, as an alternative to providing SIB1 (or SIB1s) in such a failure message, the second RAN node 5-2 may forward the SIB1 (or SIB1s) for a corresponding cell (or group of cells) in an appropriate transfer message using the RAN node to RAN node interface based application protocol (e.g., XnAP), for example, an RRC transfer message that is used to transfer RRC messages and/or information elements via the RAN node to RAN node interface. Such a transfer message may be sent in addition to (or as an alternative to) sending a RAN node configuration update failure message. It will also be appreciated that the SIB1 (or SIB1s) could potentially be provided in a response message (e.g., as sent at S314b) (e.g., the presence of the SIB1/SIB1s could implicitly indicate that the SIB1/SIB1s require transmission to the UE 3 by the first RAN node 5-1).

　　Regardless of the message used to provide the SIB1 (or SIB1s) to the first RAN node 5-1, the second RAN node 5-2 may provide the SIB1 (or SIB1s) in that message using any appropriate information element. For example, the exemplary information element illustrated in Table 1 above is equally applicable here. Nevertheless, it will be appreciated that, whilst the example illustrated in Table 1 is for NR cells a similar information element could be used for cells 9 associated with other cellular technologies (e.g., 6G, or beyond cellular technologies).

　　If the second RAN node 5-2 fails to transmit a SIB1 on request by the first RAN node 5-1 (or to provide the SIB1 to the first RAN node 5-1), then the second RAN node 5-2 may send an appropriate failure message (for example a 'SIB1 Failure', 'SIB1 Request Failure' or the like). The failure message may include an indication of a reason for or cause of the failure (e.g., "function not supported", "temporary failure to transmit SIB1", and/or the like). It will be appreciated that the failure may be indicated at a per cell (or per group of cells) level of granularity to cater for scenarios where SIB1 has not been successfully transmitted in only a subset of the originally indicated cells.

　　< Indicating SIB1-less / On-Demand SIB1 Operation Status Over F1 interface >
　　As mentioned above, the communication system 1 may support one or more techniques to support the provision of a SIB1 transmission status, for each of one or more identified cells, from a DU to a CU of a distributed RAN node 5.

　　Specifically, in a CU-DU split deployment, if the activation/deactivation of SIB1-less operation and/or on-demand SIB1 transmission is decided by the DU itself, then when the DU decides to activate/deactivate the SIB1-less operation and/or on-demand SIB1 transmission, the communication system 1 may support one or more techniques by which the DU can inform the CU of the associated SIB1 transmission status. This may be notified, for example, by providing one or more lists of one or more cells (e.g. indicated by their respective global cell-ID or physical cell ID) where the indicated cells have been activated (or deactivated) for SIB1-less operation and/or for on-demand SIB1 transmission.

　　It will be appreciated that the deactivation of SIB1-less transmission and/or on demand SIB1 transmission for a given cell effectively means that the SIB1 transmission (broadcasts) revert to 'normal' operation in accordance with a 'normal' SIB1 transmission configuration that is different to a SIB1 transmission configuration that may have been configured initially. For example, the periodicity of the SIB1 transmission/broadcasting may be shorter than for transmission of SIB1 in an anchor cell on behalf of a non-anchor cell configured for SIB1-less operation.

　　A number of techniques/procedures by which the DU can inform the CU of the associated SIB1 transmission status will now be described, by way of example only, with reference to Fig. 4, which is a simplified sequence diagram different intra-RAN, inter-node, information exchange procedures for informing a central unit of a distributed RAN node of the transmission status for SIB1 transmission that may be implemented in the communication system 1.

　　In the examples illustrated in Fig. 4, the RAN nodes 5 include a DU 5-2_DU and a CU 5-2_CU that are interconnected by an appropriate DU to CU interface (e.g., an F1 interface and/or the like).

　　< General DU Configuration Update Procedure >
　　In a first example illustrated in Fig. 4, the DU 5-2_DU and CU 5-2_CU are configured to engage in a general DU configuration update procedure 410a to support notification of the SIB1 transmission status for one or more cells 9. This procedure may, for example, be a modified form of a conventional F1 application protocol (F1AP) based gNB-DU configuration update procedure. As those skilled in the art will appreciate, the gNB-DU configuration update configuration procedure is specified for 5G (or later generations) systems, for updating application level configuration data needed for a gNB-DU and a gNB-CU to interoperate correctly on the F1 interface.

　　As part of the DU configuration update procedure 410a the DU 5-2_DU sends, at S412a, information for notifying the SIB1 transmission status for one or more cells 9 to the CU 5-2_CU in an appropriate DU configuration update message (for example a gNB-DU configuration update message).

　　As seen in Fig. 4, the DU configuration update message may, for example, include: a list of one or more cells 9 for which SIB1-less operation has been activated; a list of one or more cells 9 for which SIB1-less operation has been deactivated; a list of one or more cells 9 for which on-demand SIB1 transmission has been activated; and/or a list of one or more cells 9 for which on-demand SIB1 transmission has been deactivated. It will, nevertheless, be appreciated that a combined list of cells may be provided with the activation/deactivation status for SIB1-less operation and/or on-demand SIB1 transmission respectively indicated for each cell (or for each group of a plurality of groups of cells).

　　Moreover, a configuration for SIB1-less operation transmission may be indicated to the CU 5-2_CU at the same time as activating the SIB1-less operation and/or on-demand SIB1 transmission. For example, a SIB1 transmission configuration comprising a SIB1 broadcast periodicity for transmission, in the anchor cell, of SIB1 for each cell of a (further) list of cells (e.g. indicated by global cell ID or Physical Cell ID) may be included. Nevertheless, it will be appreciated that the DU 5-2_DU may inform the CU 5-2_CU of the (or an initial) SIB1 transmission configuration for SIB1-less operation during a procedure to set up communication via the DU to CU interface (e.g., an F1 setup procedure via the F1 interface), and any further updates to the SIB1 transmission configuration may be provided using a DU configuration update procedure (e.g., a gNB-DU Configuration Update procedure).

　　When the CU 5-2_CU has successfully received the DU configuration update message and is able to provide the necessary functionality to support the activation/deactivation of SIB1-less operation and/or on-demand SIB1 transmission indicated for the corresponding cell or cells, the CU 5-2_CU may acknowledge this. Specifically, the CU 5-2_CU may acknowledge successful receipt of the DU configuration update message, at S414a, by sending an appropriate DU configuration update acknowledge message (for example a gNB-DU configuration update acknowledge message).

　　Alternatively, in the event of a failure, the CU 5-2_CU may indicate this to the DU 5-2_DU, at S416a, by sending an appropriate DU configuration update failure message (for example a gNB-DU configuration update failure message).

　　< Dedicated SIB Transmission Status Indication Procedure >
　　In a second example illustrated in Fig. 4, the DU 5-2_DU and CU 5-2_CU are configured to engage in a dedicated SIB transmission status indication procedure 410b to support notification of the SIB1 transmission status for one or more cells 9.

　　As part of the dedicated SIB transmission status indication procedure 410b the DU 5-2_DU sends, at S412b, information for notifying the SIB1 transmission status for one or more cells 9 to the CU 5-2_CU in a dedicated message for notifying the SIB1 transmission status (e.g., a 'SIB transmission status indication' message as illustrated, or a 'SIB1 transmission status indication' message, or the like).

　　As seen in Fig. 4, the message for notifying the SIB1 transmission status may, for example, include: a list of one or more cells 9 for which SIB1-less operation has been activated; a list of one or more cells 9 for which SIB1-less operation has been deactivated; a list of one or more cells 9 for which on-demand SIB1 transmission has been activated; and/or a list of one or more cells 9 for which on-demand SIB1 transmission has been deactivated. It will, nevertheless, be appreciated that a combined list of cells may be provided with the activation/deactivation status for SIB1-less operation and/or on-demand SIB1 transmission respectively indicated for each cell (or for each group of a plurality of groups of cells).

　　Moreover, a configuration for SIB1-less operation transmission may be indicated to the CU 5-2_CU at the same time as activating the SIB1-less operation and/or on-demand SIB1 transmission. For example, a SIB1 transmission configuration comprising a SIB1 broadcast periodicity for transmission, in the anchor cell, of SIB1 for each cell of a (further) list of cells (e.g. indicated by global cell ID or Physical Cell ID) may be included. Nevertheless, it will be appreciated that the DU 5-2_DU may inform the CU 5-2_CU of the (or an initial) SIB1 transmission configuration for SIB1-less operation during a procedure to set up communication via the DU to CU interface (e.g., an F1 setup procedure via the F1 interface), and any further updates to the SIB1 transmission configuration may be provided using a DU configuration update procedure (e.g., a gNB-DU Configuration Update procedure) and/or via the message for notifying the SIB1 transmission status (when sent).

　　When the CU 5-2_CU has successfully received the message for notifying the SIB1 transmission status and is able to provide the necessary functionality to support the activation/deactivation of SIB1-less operation and/or on-demand SIB1 transmission indicated for the corresponding cell or cells, the CU 5-2_CU may acknowledge this. Specifically, the CU 5-2_CU may acknowledge successful receipt of the message for notifying the SIB1 transmission status, at S414b, by sending an appropriate message for acknowledging receipt of the SIB1 transmission status message (e.g., a 'SIB transmission status indication acknowledge' message as illustrated, or a 'SIB1 transmission status indication acknowledge' message, or the like).

　　Alternatively, in the event of a failure, the CU 5-2_CU may indicate this to the DU 5-2_DU, at S416b, by sending an appropriate message for indicating a failure related to receipt of the SIB1 transmission status message (e.g., a 'SIB transmission status indication failure' message as illustrated, or a 'SIB1 transmission status indication failure' message, or the like).

　　< Activation of SIB1-less / On-Demand SIB1 Operation over F1 interface >
　　As mentioned above, the communication system 1 may support one or more techniques by which a CU 5-2_CU may request activation (or deactivation), of a particular type of SIB1 transmission operation in each of one or more identified cells, at a DU 5-2_DU via which the identified cell or cells are provided.

　　Specifically, in a CU-DU split deployment, if the activation/deactivation of SIB1-less operation and/or on-demand SIB1 transmission is decided by the CU 5-2_CU itself, then when the CU 5-2_CU decides to activate/deactivate the SIB1-less operation and/or on-demand SIB1 transmission, the communication system 1 may support one or more techniques by which the CU 5-2_CU can indicate, to the DU 5-2_DU, the associated SIB1 transmission operation that is to be employed in one or more cells provided via the DU 5-2_DU. This may be notified, for example, by providing one or more lists of one or more cells (e.g. indicated by their respective global cell-ID or physical cell ID) where the indicated cells are to be activated (or deactivated) for SIB1-less operation and/or for on-demand SIB1 transmission.

　　It will be appreciated that the deactivation of SIB1-less transmission and/or on demand SIB1 transmission for a given cell effectively means that the SIB1 transmissions (broadcasts) revert to 'normal' operation in accordance with a 'normal' SIB1 transmission configuration that is different to a SIB1 transmission configuration that may have been configured initially. For example, the periodicity of the SIB1 transmission/broadcasting may be shorter than for transmission of SIB1 in an anchor cell on behalf of a non-anchor cell configured for SIB1-less operation.

　　A number of techniques/procedures by which the CU 5-2_CU can inform the DU 5-2_DU of the associated SIB1 transmission operation to implement will now be described, by way of example only, with reference to Fig. 5, is a simplified sequence diagram different intra-RAN, inter-node, procedures for triggering activation/deactivation of on-demand SIB1 transmission or SIB1-less operation, in one or more cells 9 of the DU 5-2_DU of a distributed RAN, that may be implemented in the communication system 1.

　　In the examples illustrated in Fig. 5, the nodes of the RAN include a DU 5-2_DU and a CU 5-2_CU that are interconnected by an appropriate DU to CU interface (e.g., an F1 interface and/or the like).

　　< General DU Configuration Update Procedure >
　　In a first example illustrated in Fig. 5, the DU 5-2_DU and CU 5-2_CU are configured to engage in a general CU configuration update procedure 510a to support notification of the required SIB1 transmission operation for one or more cells 9. This procedure may, for example, be a modified form of a conventional F1 application protocol (F1AP) based CU configuration update procedure. As those skilled in the art will appreciate, the CU configuration update configuration procedure is specified for 5G (or later generations) systems, for updating application level configuration data needed for a DU 5-2_DU and a CU 5-2_CU to interoperate correctly on the F1 interface.

　　As part of the CU configuration update procedure 510a the CU 5-2_CU sends, at S512a, information for notifying the SIB1 transmission operation to be employed for one or more cells to the DU 5-2_DU in an appropriate CU configuration update message (for example a gNB-CU configuration update message).

　　As seen in Fig. 5, the CU configuration update message may, for example, include: a list of one or more cells 9 for which SIB1-less operation is to be activated; a list of one or more cells 9 for which SIB1-less operation is to be deactivated; a list of one or more cells 9 for which on-demand SIB1 transmission is to be activated; and/or a list of one or more cells 9 for which on-demand SIB1 transmission is to be deactivated. It will, nevertheless, be appreciated that a combined list of cells may be provided with an indication of the activation/deactivation to be employed for SIB1-less operation and/or on-demand SIB1 transmission respectively indicated for each cell (or for each group of a plurality of groups of cells).

　　Moreover, a configuration for SIB1-less operation transmission may be indicated to the DU 5-2_DU at the same time as activating the SIB1-less operation and/or on-demand SIB1 transmission. For example, a SIB1 transmission configuration comprising a SIB1 broadcast periodicity for transmission, in the anchor cell, of SIB1 for each cell of a (further) list of cells (e.g. indicated by global cell ID or Physical Cell ID) may be included. Nevertheless, it will be appreciated that the CU 5-2_CU may inform the DU 5-2_DU of the (or an initial) SIB1 transmission configuration for SIB1-less operation during a procedure to set up communication via the DU to CU interface (e.g., an F1 setup procedure via the F1 interface), and any further updates to the SIB1 transmission configuration may be provided using a CU configuration update procedure (e.g., a gNB-CU Configuration Update procedure).

　　When the DU 5-2_DU has successfully received the CU configuration update message and is able to successfully activate/deactivate the SIB1-less operation and/or on-demand SIB1 transmission indicated for the corresponding cell or cells, the DU 5-2_DU may acknowledge this. Specifically, the DU 5-2_DU may acknowledge successful receipt of the CU configuration update message, at S514a, by sending an appropriate CU configuration update acknowledge message (for example a gNB-CU configuration update acknowledge message).

　　Alternatively, in the event of a failure, the DU 5-2_DU may indicate this to the CU 5-2_CU, at S516a, by sending an appropriate CU configuration update failure message (for example a gNB-CU configuration update failure message).

　　< Dedicated SIB Transmission Status Indication Procedure >
　　In a second example illustrated in Fig. 5, the DU 5-2_DU and CU 5-2_CU are configured to engage in a dedicated SIB transmission status indication procedure 510b to support notification of the required SIB1 transmission operation for one or more cells 9.

　　As part of the dedicated SIB transmission status indication procedure 510b the CU 5-2_CU sends, at S512b, information for notifying the SIB1 transmission operation to be employed for one or more cells 9 to the DU 5-2_DU in a dedicated message for notifying the SIB1 transmission status (e.g., a 'SIB transmission status indication' message as illustrated, or a 'SIB1 transmission status indication' message, or the like).

　　As seen in Fig. 5, the message for notifying the SIB1 transmission status may, for example, include: a list of one or more cells 9 for which SIB1-less operation is to be activated; a list of one or more cells 9 for which SIB1-less operation is to be deactivated; a list of one or more cells 9 for which on-demand SIB1 transmission is to be activated; and/or a list of one or more cells 9 for which on-demand SIB1 transmission is to be deactivated. It will, nevertheless, be appreciated that a combined list of cells may be provided with an indication of the activation/deactivation to be employed for SIB1-less operation and/or on-demand SIB1 transmission respectively indicated for each cell (or for each group of a plurality of groups of cells).

　　Moreover, a configuration for SIB1-less operation transmission may be indicated to the DU 5-2_DU at the same time as activating the SIB1-less operation and/or on-demand SIB1 transmission. For example, a SIB1 transmission configuration comprising a SIB1 broadcast periodicity for transmission, in the anchor cell, of SIB1 for each cell of a (further) list of cells (e.g. indicated by global cell ID or Physical Cell ID) may be included. Nevertheless, it will be appreciated that the CU 5-2_CU may inform the DU 5-2_DU of the (or an initial) SIB1 transmission configuration for SIB1-less operation during a procedure to set up communication via the DU to CU interface (e.g., an F1 setup procedure via the F1 interface), and any further updates to the SIB1 transmission configuration may be provided using a CU configuration update procedure (e.g., a gNB-CU Configuration Update procedure) and/or via the message for notifying the SIB1 transmission status (when sent).

　　When the DU 5-2_DU has successfully received the message for notifying the SIB1 transmission status and is able to successfully activate/deactivate the SIB1-less operation and/or on-demand SIB1 transmission indicated for the corresponding cell or cells, the DU 5-2_DU may acknowledge this. Specifically, the DU 5-2_DU may acknowledge successful receipt of the message for notifying the SIB1 transmission status, at S514b, by sending an appropriate message for acknowledging receipt of the SIB1 transmission status message (e.g., a 'SIB transmission status indication acknowledge' message as illustrated, or a 'SIB1 transmission status indication acknowledge' message, or the like).

　　Alternatively, in the event of a failure, the DU 5-2_DU may indicate this to the CU 5-2_CU, at S516b, by sending an appropriate message for indicating a failure related to receipt of the SIB1 transmission status message (e.g., a 'SIB transmission status indication failure' message as illustrated, or a 'SIB1 transmission status indication failure' message, or the like).

　　< User Equipment >
　　Fig. 6 is a schematic block diagram illustrating the main components of a UE 3 as shown in Fig. 1.

　　As shown, the UE 3 has a transceiver circuit 31 that is operable to transmit signals to and to receive signals from a RAN node 5 via one or more antennas 33 (e.g., comprising one or more antenna elements). 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. Software may be pre-installed in the memory 39 and/or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example.

　　The controller 37 is configured to control overall operation of the UE 3 by, in this example, program instructions or software instructions stored within memory 39. As shown, these software instructions include, among other things, an operating system 41, and a communication control module 43.

　　The communication control module 43 is operable to control the communication between the UE 3 and its serving RAN node or RAN nodes 5 (and other communication devices connected to the RAN node 5, such as further UEs 3 and/or core network nodes). The communication control module 43 is configured for the overall handling of 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 communication control module 43 is also configured for the overall handling of receipt of downlink communications via associated downlink channels (e.g., of DCI via a physical downlink control channel (PDCCH) and/or a physical downlink shared channel (PDSCH)) including both dynamic and semi-persistent scheduling (e.g., SPS). The communication control module 43 is responsible, for example: for determining where to monitor for downlink control information; for determining the resources to be used by the UE 3 for transmission/reception of UL/DL communications (including interleaved resources and resources subject to frequency hopping); for managing frequency hopping at the UE side; for determining how slots/symbols are configured (e.g., for UL, DL or full duplex communication, or the like); for determining which bandwidth parts are configured for the UE 3; for determining how uplink transmission should be encoded and the like.

　　It will be appreciated that the communication control module 43 may include a number of sub-modules ('layers' or 'entities') to support specific functionalities. For example, the communication control module 43 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc.

　　The communication control module 43 is configured, in particular, to control the UE's communications, where applicable, in accordance with any of the methods described herein.

　　< RAN node (non-distributed) >
　　Fig. 7 is a schematic block diagram illustrating the main components of a RAN node 5-1 for the communication system 1 shown in Fig. 1. As shown, the RAN node 5-1 has a transceiver circuit 51 for transmitting signals to and for receiving signals from the communication devices (such as UEs 3) via one or more antennas 53 (e.g. a single or multi-panel antenna array / massive antenna), and a core network interface 55 (e.g. comprising the N2, N3 and other reference points/interfaces) for transmitting signals to and for receiving signals from network nodes in the core network 7. Although not shown, the RAN node 5-1 may also be coupled to other RAN nodes via an appropriate interface (e.g. the so-called 'Xn' interface in NR). The RAN node 5-1 has a controller 57 to control the operation of the RAN node 5-1. The controller 57 is associated with a memory 59. Software may be pre-installed in the memory 59 and/or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example. The controller 57 is configured to control the overall operation of the RAN node 5-1 by, in this example, program instructions or software instructions stored within memory 59.

　　As shown, these software instructions include, among other things, an operating system 61, and a communication control module 63.

　　The communication control module 63 is operable to control the communication between the RAN node 5-1 and UEs 3 and other network entities that are connected to the RAN node 5-1. The communication control module 63 is configured for the overall control of 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). The communication control module 63 is also configured for the overall handling 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.). The communication control module 63 is also responsible, for example, for determining and scheduling the resources to be used by the UE 3 for receiving in DL / transmitting in UL, for configuring slots/symbols appropriately (e.g., for UL, DL, flexible, full duplex communication, or the like), for configuring one or more bandwidth parts for the UE 3, and for providing related configuration signalling to the UE 3.

　　It will be appreciated that the communications control module 63 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.

　　The communication control module 63 is configured, in particular, to control the RAN node's communications, where applicable, in accordance with any of the methods described herein.

　　< RAN node (distributed) >
　　Fig. 8 is a simplified block schematic illustrating the main components of a distributed RAN node 5-2 comprising a distributed type of base station for implementation in the system of Fig. 1. As shown, the RAN node 5-2 includes a central unit 5-2_CU and a distributed unit 5-2_DU (although it may include other DUs as described above). Each unit 5-2_CU, 5-2_DU includes respective transceiver circuit 51c, 51d.

　　The transceiver circuit 51d of the distributed unit 5-2_DU is operable to transmit signals to and to receive signals from UEs 3 via an air interface 53d and one or more antennas and is also operable to transmit signals to and to receive signals from the central unit 5-2_CU via an interface, for example the distributed unit side of an F1 interface (which may be provided over a satellite radio interface).

　　The transceiver circuit 51c of the central unit 5-2_CU is operable to transmit signals to and to receive signals from functions of the core network 7 and/or other RAN nodes 5 via a network interface 55c. The network interface typically includes an N2 and/or N3 interfaces for communicating with the core network 7 and a RAN node to RAN node (e.g. Xn) interface for communicating with other RAN nodes 5. The transceiver circuit 51c of the central unit 5-2_CU is also operable to transmit signals to and to receive signals from one or more distributed units 5-2_DU, for example the central unit side of the F1 interface provided.

　　Each unit 5-2_CU, 5-2_DU includes a respective controller 57c, 57d which controls the operation of the corresponding transceiver circuit 51c, 51d in accordance with software stored in the respective memories 59c and 59d of the central unit 5-2_CU and the distributed unit 5-2_CU. The software of each unit may be pre-installed in the memory 59c, 59d 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, 61d, and a respective communications control module 63c, 63d.

　　Each communications control module 63c, 63d is operable to control the communication of its corresponding unit 5-2_CU, 5-2_DU including the communication from one unit to the other. The communications control module 63d of the distributed unit 5-2_DU controls communication between the distributed unit 5-2_DU and the UEs 3, and the communications control module 63c of the central unit 5-2_CU controls communication between the central unit 5-2_CU and other network entities that are connected to the distributed RAN node 5-2.

　　The communications control modules 63c, 63d also respectively control the part played by the central unit 5-2_CU and distributed unit 5-2_DU in the flow of uplink and downlink user traffic and control data to be received from and transmitted to the communications devices served by the RAN node 5-2 including, for example, control data for managing operation of the UEs 3. Each communication control module 63c, 63d is responsible, for example, for controlling the respective part played by the central unit 5-2_CU and distributed unit 5-2_DU 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, 63d is responsible, for example, for controlling the respective part played by the central unit 5-2_CU and distributed unit 5-2_DU in the overall handling 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.). Each communication control module 63c, 63d is responsible, for example, for controlling the respective part played by the central unit 5-2_CU and distributed unit 5-2_DU in determining and scheduling the resources to be used by the UE 3 for receiving in DL / transmitting in UL, for configuring slots/symbols appropriately (e.g., for UL, DL, flexible, full duplex communication, or the like), for configuring one or more bandwidth parts for the UE 3, and for providing related configuration signalling to the UE 3.

　　It will be appreciated that each communication control module 63c, 63d may include a number of sub-modules (or 'layers') to support specific functionalities supported by the by the central unit 5-2_CU and distributed unit 5-2_DU. For example, a communications 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 may be distributed between the central unit 5-2_CU and distributed unit 5-2_DUappropriately depending on where the functional split is configured between the central unit 5-2_CU and distributed unit 5-2_DU.

　　Each communication control module 63c, 63d is configured, in particular, to control the respective communications of the central unit 5-2_CU and distributed unit 5-2_DU, where applicable, in accordance with any of the methods described herein.

　　< Modifications and Alternatives >
　　As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above embodiments whilst still benefiting from the disclosure embodied therein.

　　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.

　　In the above description, the UEs and the RAN nodes 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.

　　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 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 RAN node or the UE in order to update their functionalities.

　　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.

　　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.

　　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.

　　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.

　　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.).

　　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.).

　　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.).

　　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.).

　　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.).

　　A UE may, for example, be an electronic lamp, a luminaire, a measuring instrument, an analyser, 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.

　　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)).

　　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.

　　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.

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

　　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 2. This list is not exhaustive and is intended to be indicative of some examples of machine type communication applications.
Table 2 - MTC applications list

　　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.

　　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.

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

　　Although the present disclosure has been described with reference to the example embodiments, the present disclosure is not limited to the above. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the disclosure.

　　This application is based upon and claims the benefit of priority from UK patent application No. 2403408.4, filed on March 8, 2024, the disclosure of which is incorporated herein in its entirety by reference.

　　The program can be stored and provided to the computer device using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). The program may be provided to the computer device using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to the computer device via a wired communication line, such as electric wires and optical fibers, or a wireless communication line.

　　For example, the whole or part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes.
(Supplementary note 1)
　　A method performed by a first access network node, the method comprising:
　　receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.
(Supplementary note 2)
　　The method according to supplementary note 1, wherein
　　the information for requesting to transmit the SIB1 causes the second access network node to move from the NES mode to a normal mode to transmit the SIB1 on the cell.
(Supplementary note 3)
　　The method according to supplementary note 1, further comprising:
　　in a case where the second access network node cannot transmit the SIB1 on the cell, receiving, from the second access network node, the SIB1; and
　　transmitting, to the mobile device; the SIB1 on another cell operated by the first access network node.
(Supplementary note 4)
　　The method according to any one of supplementary notes 1 to 3, wherein
　　the information for requesting to transmit the SIB1 is includes in at least one of:
　　　　a XnAP signaling message,
　　　　a NG-RAN node configuration update message, or
　　　　an activation transmission request message.
(Supplementary note 5)
　　The method according to any one of supplementary notes 1 to 4, further comprising:
　　in a case where the second access network node fails to transmit the SIB1 or fails to move to the normal mode to transmit the SIB1, receiving, from the second access network node, a failure message to indicate a reason of failure.
(Supplementary note 6)
　　The method according to any one of supplementary notes 1 to 5, further comprising:
　　transmitting, to the second access network node, information for activating/deactivating the NES mode for not transmitting the SIB1.
(Supplementary note 7)
　　The method according to any one of supplementary notes 1 to 6, further comprising:
　　receiving, from the second access network node, information for activating/deactivating the NES mode for not transmitting the SIB1.
(Supplementary note 8)
　　The method according to supplementary note 6 or 7, wherein
　　the first access network node includes a distributed unit of a distributed base station, and
　　the second access network node includes a central unit of the distributed base station.
(Supplementary note 9)
　　A method performed by a second access network node, the method comprising:
　　in a case where a mobile device requests a first access network node to transmit a system information block 1 (SIB1) on a cell operated by the second access network node, receiving, from the first access network node, information for requesting the second access network node to transmit the SIB1; and
　　transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.
(Supplementary note 10)
　　A first access network node comprising:
　　means for receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　means for transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.
(Supplementary note 11)
　　A second access network node comprising:
　　means for receiving, from a first access network node, information for requesting the second access network node to transmit a system information block 1 (SIB1), in a case where a mobile device requests the first access network node to transmit the SIB1 on a cell operated by the second access network node; and
　　means for transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.

1　　communication system
3　　UEs
5, 5-1, 5-2　　radio access network (RAN) node
5-2_CU　　DU
5-2_DU　　CU
7　　core network
9, 9-1, 9-2　　cells
10　　control plane functions (CPFs)
10-1　　Access and Mobility Management Functions (AMFs)
10-2　　session management function (SMF)
11　　user plane functions (UPFs)
14　　Operations, Administration and Maintenance (OAM)
20　　external data network
31, 51　　transceiver circuit
33, 53　　antenna
35　　user interface
37, 57　　controller
39, 59　　memory
41, 61　　operating system
43, 63　　communication control module
55　　core network interface
51c, 51d　　　　transceiver circuit
53d　　air interface
55c　　network interface
57c, 57d　　　　controller
59c, 59d　　　　memory
61c, 61d　　　　operating system
63c, 63d　　　　communication control module

Claims

　　A method performed by a first access network node, the method comprising:
　　receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.
　　The method according to claim 1, wherein
　　the information for requesting to transmit the SIB1 causes the second access network node to move from the NES mode to a normal mode to transmit the SIB1 on the cell.
　　The method according to claim 1, further comprising:
　　in a case where the second access network node cannot transmit the SIB1 on the cell, receiving, from the second access network node, the SIB1; and
　　transmitting, to the mobile device; the SIB1 on another cell operated by the first access network node.
　　The method according to any one of claims 1 to 3, wherein
　　the information for requesting to transmit the SIB1 is includes in at least one of:
　　　　a XnAP signaling message,
　　　　a NG-RAN node configuration update message, or
　　　　an activation transmission request message.
　　The method according to any one of claims 1 to 4, further comprising:
　　in a case where the second access network node fails to transmit the SIB1 or fails to move to the normal mode to transmit the SIB1, receiving, from the second access network node, a failure message to indicate a reason of failure.
　　The method according to any one of claims 1 to 5, further comprising:
　　transmitting, to the second access network node, information for activating/deactivating the NES mode for not transmitting the SIB1.
　　The method according to any one of claims 1 to 6, further comprising:
　　receiving, from the second access network node, information for activating/deactivating the NES mode for not transmitting the SIB1.
　　The method according to claim 6 or 7, wherein
　　the first access network node includes a distributed unit of a distributed base station, and
　　the second access network node includes a central unit of the distributed base station.
　　A method performed by a second access network node, the method comprising:
　　in a case where a mobile device requests a first access network node to transmit a system information block 1 (SIB1) on a cell operated by the second access network node, receiving, from the first access network node, information for requesting the second access network node to transmit the SIB1; and
　　transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.
　　A first access network node comprising:
　　means for receiving, from a mobile device, a request for transmitting a system information block 1 (SIB1) of a cell operated by a second access network node which is in a network energy saving (NES) mode;
　　means for transmitting, to the second access network node, information for requesting the second access network node to transmit the SIB1, and
　　wherein the information for requesting to transmit the SIB1 causes the second access network node to transmit the SIB1.
　　A second access network node comprising:
　　means for receiving, from a first access network node, information for requesting the second access network node to transmit a system information block 1 (SIB1), in a case where a mobile device requests the first access network node to transmit the SIB1 on a cell operated by the second access network node; and
　　means for transmitting, to the mobile device, the SIB1 based on the information for requesting to transmit the SIB1.