Method, mobile device, access network node

Abstract

A method performed by a mobile device is provided. The method includes: storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; receiving a latest condition of the SIB1; and determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

Description

METHOD, MOBILE DEVICE, ACCESS NETWORK NODE

[0001] The present disclosure relates to a communication system and to parts thereof. 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 / 6G networks, future generations, and beyond). The present disclosure in particular, but not exclusively, relates to the storage and re-using of SIB1 by a UE as it moves between different cells when the SIB1 is still valid and applicable.

[0002] 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) has started to be used to refer to an evolving communication technology that is expected to support a variety of applications and services. Various details of 5G networks are described in, for example, the 'NGMN 5G White Paper' V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, which document is available from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G by way of the so-called 3GPP Next Generation (NextGen) radio access network (RAN) and the 3GPP NextGen core network.

[0003] 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 will use the term access network node, RAN node or base station to refer to any such access nodes.

[0004] 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 RAN nodes. 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 network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0005] In the current 5G architecture, the gNB structure may be split into two or more parts. In some RAN implementations there are two parts, known as the Central Unit (CU or gNB-CU) - sometimes referred to as a 'control unit' - and the Distributed Unit (DU or gNB-DU), connected by an F1 interface. This enables the use of a 'split' architecture in which the typically 'higher' CU layers (for example, but not necessarily or exclusively, Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers) and the, 'lower' DU layers (for example, but not necessarily or exclusively, Radio Link Control (RLC), Media (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 gNBs may be implemented centrally (for example, by a single processing unit, or in a cloud-based or virtualised system), whilst retaining the lower layer DU functionality locally separately for each gNB.

[0006] With the increasing usage of mobile communications for a wide range of different use cases, additional frequencies and bands are needed to accommodate this increasing demand. Accordingly, a variety of different frequency bands are available for 5G NR. These frequency bands include many of the existing frequency bands used by previous generations of telecommunication technology and many new frequency bands including bands in the millimetre wave region. The bandwidth available for frequency bands in the millimetre wave region is very much higher than for frequency bands used by earlier generations and thus allow for greater data speeds to be achieved albeit at the expense of the range of the signals.

[0007] The available frequency bands are grouped into two different frequency ranges referred to as frequency range 1 (FR1) containing the lower frequency bands and frequency range 2 (FR2) containing the higher frequency bands. FR1 bands are likely to carry much of the traditional cellular mobile communications traffic whereas the FR2 bands are aimed at providing short range very high data rate capability for 5G radio. Originally the FR1 band was intended to define bands below 6 GHz, but with anticipated additional spectrum allocations, the FR1 range has now been extended to 7.125 GHz.

[0008] Further, as the usage of 5G mobile communications for a wide range of different use cases increases, their complexity and energy demands are also expected to increase. With this in mind, efforts are being made to enhance network energy saving (NES) approaches that afford significant power savings in an industry standardized manner. To that end, techniques / procedures have been evaluated that have shown to bring substantial NES gains. By way of example only, such techniques / procedures may include: * The adaption of transmission patterns; * The use of wake-up signals (WUS) to allow devices such as UEs to enter reduced transmission / reception modes, (for example discontinuous transmission / reception modes); * The use of on-demand synchronization signal / physical broadcast channel (PBCH) blocks (SSBs) (and possibly other DL signals) for camping onto secondary cells (SCells) by UEs configured to connect to, and use, such SCells; * The use of on-demand SSBs (and possibly other downlink (DL) signals) for camping onto non-serving cells by UEs configured to connect to, and use, such non-serving cells; and * The use of on-demand system information block 1 (SIB1) messages.

[0009] NPL 1: '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.

[0010] However, whilst energy savings may be achieved by implementing on-demand SIB1 messages, as a UE moves between different cells the need for a UE to (re)acquire SIB1 from the RAN node providing the cell that the UE has moved into requires associated signalling to (re)obtain the SIB1 in that cell. In some circumstances, this needs to always (re)acquire SIB1 and the resulting additional signalling can, in some circumstances, result in inefficiency in the system.

[0011] The present specification aims to disclose apparatus and methods that at least contribute to addressing one or more of the above needs and / or issues.

[0012] 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.

[0013] 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.

[0014] A method performed by a mobile device, the method comprises: 　　storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　receiving a latest condition of the SIB1; and 　　determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

[0015] A method performed by an access network node, the method comprises: 　　providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

[0016] A mobile device comprises: 　　means for storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　means for receiving a latest condition of the SIB1; and 　　means for determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

[0017] An access network node comprises: 　　means for providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　means for providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

[0018] Examples of apparatus and methods 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') communication system;Fig. 2 depicts a simplified sequence diagram illustrating a MIB / SIB acquisition procedure that may be used in the communication system of Fig. 1;Fig. 3A illustrates a mobility scenario involving a single RAN node of the communication system of Fig. 1;Fig. 3B illustrates a scenario involving four RAN nodes of the communication system of Fig. 1;Fig. 4 illustrates a scenario involving two RAN nodes of the communication system of Fig. 1;Fig. 5 depicts a simplified sequence diagram illustrating a procedure that may be used in the communication system of Fig. 1 to determine whether a SIB1 stored in the memory of a UE is still valid and usable for a cell that the UE has left and re-entered;Fig. 6A depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system of Fig. 1 to determine whether a SIB1 stored in the memory of a UE is still valid and usable for a cell that the UE has left and re-entered;Fig. 6B depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system of Fig. 1 to determine whether a SIB1 stored in the memory of a UE is still valid and usable for a cell that the UE has left and re-entered;Fig. 7 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE are still valid and usable for a cell that the UE has left and re-entered;Fig. 8 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE are still valid and usable for a cell that the UE has left and re-entered;Fig. 9 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE are still valid and usable for a cell that the UE has left and re-entered;Fig. 10A depicts a simplified sequence diagram illustrating yet another procedure that may be used in the communication system of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE are still valid and usable for a cell that the UE has left and re-entered;Fig. 10B depicts a simplified sequence diagram illustrating yet another procedure that may be used in the communication system of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE are still valid and usable for a cell that the UE has left and re-entered;Fig. 11 illustrates a scenario involving three RAN nodes of the communication system of Fig. 1;Fig. 12 depicts a simplified sequence diagram illustrating an example procedure that may be used in the communication system 1 of Fig. 1 to provide and use a common SIB1 for multiple cells.Fig. 13 depicts a simplified sequence diagram illustrating another example procedure that may be used in the communication system of Fig. 1 provide and use a SIB1 that is applicable to multiple cells.Fig. 14 is a simplified block schematic illustrating the main components of a UE for implementation in the system of Fig. 1; andFig. 15 is a simplified block schematic illustrating the main components of a RAN node for implementation in the system of Fig. 1.

[0019] Overview 　　An exemplary communication system will now be described in general terms, by way of example only, with reference to Fig. 1.

[0020] Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system 1 to which the examples described herein are applicable.

[0021] In the communication system 1 user equipments (UEs) 3-1, 3-2, 3-3 (e.g., mobile telephones and / or other mobile or stationary devices) can communicate with each other via a (radio) access network ((R)AN) node 5 that operates according to one or more compatible radio access technologies (RATs). In the illustrated example, the RAN node 5 comprises a base station 5 or 'gNB' 5 operating one or more associated cells 9. Communication via the RAN node 5 is typically routed through a core network 7 (e.g., a 5G / 6G or later generations core network or evolved packet core network (EPC)).

[0022] As those skilled in the art will appreciate, whilst three UEs 3 and one RAN node 5 are shown in Fig. 1 for illustration purposes, the system, when implemented, will typically include other RAN nodes 5 and UEs 3.

[0023] 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.

[0024] 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 base station to base station interface (such as the so-called 'X2' interface, 'Xn' interface and / or the like).

[0025] 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 (such as, for example an Authentication Server Function (AUSF) which facilitates security processes).

[0026] The RAN node 5 is 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.

[0027] Each UPF 11 is 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.

[0028] 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 AMF 10-1 receives user information sent through the network and forwards the information to the SMF 10-2.

[0029] 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 the UEs 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.

[0030] The RAN node 5 of the communication system 1 is configured to operate at least one cell 9 on an associated time-division duplex (TDD) carrier that operates in unpaired spectrum and / or at least one cell 9 on an associated frequency-division duplex (FDD) carrier that operates in paired spectrum.

[0031] The 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.

[0032] The DL physical channels may include, for example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), and a physical downlink control channel (PDCCH). The PDSCH carries data sharing the PDSCH's capacity on a time and frequency basis. The PDSCH can carry a variety of items of data including, for example, user data, UE-specific higher layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) for supporting a number of functions including, for example, scheduling the downlink transmissions on the PDSCH and also the uplink data transmissions on a physical uplink shared channel (PUSCH). The PBCH provides UEs 3 with the Master Information Block (MIB). It also includes the PSS / SSS and so supports the synchronisation of time and frequency, which aids cell acquisition, selection and re-selection.

[0033] The RAN node 5 also transmits DL physical signals that do not carry any data, such as, 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).

[0034] Similarly, the UEs 3 are configured for transmission of, and the RAN node 5 is configured for the reception of, control information and user data via a number of uplink (UL) physical channels corresponding to REs carrying information originated from a higher layer, and UL physical signals which are used in the physical layer and correspond to REs which do not carry information originated from a higher layer. The physical channels may include, for example, the PUSCH, a physical uplink control channel (PUCCH), and / or a physical random-access channel (PRACH). The UL physical signals may include, for example, demodulation reference signals (DMRS) for an UL control / data signal, and / or sounding reference signals (SRS) used for UL channel measurement.

[0035] Control Information 　　In the communication system 1, the RAN node 5 is configured to transmit control information to the UE 3 using one or more control resource sets (CORESETs). A CORESET is a set of time-frequency resources within which the UE 3 can search for DCI transmitted by a RAN node 5 on a PDCCH. A CORESET is analogous to the control region at the start of subframes in earlier generations of communication technology. Unlike earlier generations, however, in which the frequency domain of the control region typically corresponded to the total system bandwidth, the frequency domain location for CORESET is localised to a specific region in the frequency domain and has a variable width that can be set to any suitable value (typically in multiples of six resource blocks where each resource block comprises twelve subcarriers in the frequency domain).

[0036] A number of different DCI formats can be used by the RAN node 5, depending on requirements, for transmission on a PDCCH corresponding to one of the PDCCH candidates in one of the search spaces configured for a given UE 3. For example, the RAN node 5 may be able to transmit DCI using one or more of the currently standardised DCI formats as set out in Table 1.

[0037] Different DCI formats may or may not have the same DCI size. Moreover, DCI may be addressed (scrambled) using different radio network temporary identifiers (RNTIs) that a UE 3 may monitor for. Typically, the UE 3 is capable of monitoring up to three different DCI sizes for DCI formats using a cell RNTI (C-RNTI) - typically used as an identifier for scheduling purposes. Additionally, the UE 3 is typically capable of monitoring one additional DCI size using other RNTIs for specific purposes (e.g., a slot format indication RNTI (SFI-RNTI), interruption RNTI (INT-RNTI), or the like). This constraint is sometimes referred to as the "3+1" size budget and is imposed because a DCI scrambled with a C-RNTI is, generally, more time critical than a DCI scrambled with a RNTI used for another specific purpose, and so requires the UE 3 to decode it promptly in order to be able to process the scheduled data transmission.

[0038] To take account of the constraint imposed by the DCI size budget, the sizes of some DCI formats may be aligned by padding, truncation, and / or determining a frequency domain resource assignment field differently.

[0039] A UE 3 may monitor a set of PDCCH candidates in one or more control resource sets (CORESETs) on an active DL bandwidth part, where monitoring implies decoding each PDCCH candidate according to the monitored DCI formats. The number of blind decodes (BDs) may be restricted on a per carrier basis of a serving cell. The number of BDs may refer to the number of monitored PDCCH candidates or the number of PDCCH candidates the UE is capable of decoding within a certain time frame, such as a slot or span of consecutive symbols in a slot. As an example, at a 15 kHz subcarrier spacing (SCS), the maximum number of BDs per slot per serving cell supported by the UE 3 may be 44 BDs.

[0040]

[0041] Synchronisation Signal / Physical Broadcast Channel (PBCH) Blocks (SSBs) 　　The RAN node 5 is also configured to transmit synchronisation signal / Physical Broadcast Channel (PBCH) blocks (SSBs) periodically in the cell or cells 9 that it operates. The SSB includes both synchronisation signals (e.g., a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS)) and the PBCH carrying a MIB that provides at least part of the minimum system information for accessing the corresponding cell 9 (e.g., parameters required for acquiring system information block 1 (SIB1) which carries other minimum system information). The acquisition procedure for the MIB and SIB1 is described in more detail below.

[0042] Each UE 3 may receive an SSB, and the UE 3 may assume that reception occasions of a PBCH, PSS and SSS are in consecutive symbols from the SSB (also referred to as a SS / PBCH block). The PSS is a part of the SSB that aids in initial cell detection and synchronization. It provides coarse timing and frequency synchronization for UEs 3. The PSS consists of a predefined sequence of complex-valued symbols transmitted over a specific frequency range. The SSS is another component of the SSB that provides additional information for fine-grained synchronization and cell identification. It carries the cell identity group and provides the necessary information to determine the exact physical cell ID (PCI) of the serving cell (e.g., a unique identifier assigned to each cell within the network that helps UEs 3 differentiate between neighbouring cells and synchronize with the correct cell.

[0043] The RAN node 5 may transmit several SSBs corresponding to different DL beams. The total number of SSBs may be confined, for example, within a 5 ms duration as an SS burst. The periodicity of the SSB transmissions may be indicated to the UE 3 using any suitable signalling (e.g., per serving cell using ssb-periodicityServingCell). The periodicity value for the SSB may be, for example, greater than or equal to 20 ms. For initial cell selection, the UE 3 may be configured to assume that an SS burst occurs with a periodicity of 2 frames. The UE 3 may also be provided with an indication of which SSBs within a 5 ms duration are transmitted (e.g., using ssb-PositionsInBurst). The UE 3 may also be provided with an indication of an absolute transmit power value of the SSS (e.g., using ss-PBCH-BlockPower) which may range from -60 to 50 dBm. Furthermore, the UE 3 may also be provided with an indication of the subcarrier spacing (SCS) used for the SSB (e.g., using ssbSubcarrierSpacing). It will be appreciated that all indications to the UE 3 about the SSB may be indicated to the UE 3 via any appropriate information element (IE) (e.g., ServingCell ConfigCommon provided in a SIB1 message, or any other appropriate dedicated message).

[0044] Each UE 3 is configured to search for SSBs when scanning for an anchor cell to camp on and to decode the associated PBCH before proceeding to decode other system information transmitted on the PDSCH. Each UE 3 is also configured to perform measurements on specific resources configured for the SSBs, for example reference signal received power (RSRP), reference signal received quality (RSRQ), and / or signal to interference and noise ratio (SINR) measurements or the like. Each UE 3 may also be configured to perform radio resource management (RRM) measurements when triggered to do so by a RAN node 5.

[0045] MIB / SIB Acquisition 　　Fig. 2 depicts a simplified sequence diagram illustrating a MIB / SIB acquisition procedure that may be used in the communication system 1 of Fig. 1. As shown in Fig. 2, there is provided a UE 3 in communication with a RAN node 5 of the communication system 1 of Fig. 1.

[0046] At step S202, the RAN node 5 may transmit a MIB in a cell that may be received by one or more UEs 3 in that cell. The MIB is transmitted periodically on the PBCH as part of the SSB transmissions from the RAN node 5, which can be detected by the UE 3 during an initial cell selection procedure performed by the UE 3. The MIB comprises basic minimum system information (MSI) that the UE 3 needs to access a cell and to obtain other system information (SI). For example, the MIB may include cell barred status information for the cell provided by the RAN node 5, and essential physical layer information of the cell required to receive further SI. By way of example only, the MIB may include appropriate parameters (e.g., ssb-subcarrierOffset, pdsch-ConfigSIB1, searchSpaceZero, and the like) that indicate a core resource set 0 (CORESET#0) configuration that may be used to indicate the PDCCH resources for when scheduling PDSCH resources carrying SIB1 (as seen at step S204).

[0047] At step S204 the UE 3 may receive SIB1 according to the PDCCH received on the CORESET#0 resources. SIB1 is periodically broadcast on PDSCH or sent in a dedicated manner on PDSCH to UEs in RRC_CONNECTED mode. SIB1 includes appropriate information to allow the UE 3 to determine whether or not it has permission to access the cell. In addition, SIB1 carries other MSI (also referred to as Remaining Minimum SI (RMSI)) that defines the scheduling of other system information blocks and contains information required for initial access. For example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for other SI carrying other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo is outlined below in Table 2.

[0048]

[0049] In more detail, schedulingInfoList in SIB1 specifies the set of one or more other SI instances (SIm) which are available for transmission by the serving cell, wherein m = 1, 2, 3, …, 32.

[0050] sib-MappingInfo indicates one or multiple SIBx that may be mapped to and transmitted together in the form of a SIm, wherein x = 1, 2, 3, 4, 5, 6, 7, 8, or 9. Each SIm(and corresponding mapped SIBx) may be associated with an instance of si-BroadcastStatus which indicates whether the SImis to be broadcast using a regular periodic pattern or requires the UE 3 to request transmission of the SImusing an appropriate 'on-demand' procedure.

[0051] si-Periodicity defines a period between SImtransmissions and is used as an input when calculating the specific radio frames during which the RAN node 5 will transmit SIm.

[0052] Each SIBx, may also be associated with a valueTag and an areaScope.

[0053] valueTag is an integer value which is used by UE 3 to determine whether the content of a specific SIBx of a serving cell has changed compared to the SIBx of the serving cell that the UE 3 acquired in the past and stored in its memory, and whether the UE 3 should re-acquire the SIBx.

[0054] valueTag provides a version number of SIBx and is incremented by 1 each time the contents of SIBx is changed and allows the UE 3 to identify changes to the set of SIBs (e.g., SIB2, SIB3, SIB4, etc.) without having to decode and check each individual SIB transmission from the RAN node 5.

[0055] areaScope indicates appropriate area scope information pertaining to SIBx when the SIBx is applicable to a specific area, which may comprise more than one cell provided by more than one RAN node 5. For example, areaScope may be set to true or false to indicate whether a SIBx is area specific instead of cell specific. When areaScope is absent / excluded / false, then the corresponding SIBx has the scope of a single serving cell. This in turn means that the UE 3 must re-acquire SIBx when moving to a neighbouring cell. In this case, the UE 3 may use a combination of a PLMN identity, cell identity and valueTag to determine when the SIBx needs to be re-acquired i.e., the SIBx needs to be re-acquired if any of those values change. On the other hand, if areaScope is present / included / true, then the corresponding SIBx is applicable to a specific area larger than the serving cell, and the UE 3 need only re-acquire SIBx when moving outside that specific area i.e., the same SIBx content can be applied across a group of cells.

[0056] It will be appreciated that the IE areaScope that indicates appropriate area scope information pertaining to SIBx may be different for different SIBx. For example, within a SIB1, areaScope may be set to 'TRUE' for one SImthat is scheduling SIB2 and set to 'FALSE' for another SImthat is scheduling SIB3, and so on.

[0057] si-RequestConfig is included in SIB1 if the RAN node 5 supports 'on-demand' SIBx requests and transmissions.

[0058] systemInformationAreaID is included when areaScope is present / included / true and is used to identify the group of cells (i.e. the area) for which the corresponding SIBx is applicable. All cells that form a common area (i.e., a group of cells), and which share an area specific SIBx may broadcast the same systemInformationAreaID in their respective SIB1.

[0059] At step S206, the RAN node 5 broadcasts periodic SIBs (e.g., SIB2, SIB3, SIB4, etc) to the UE 3 using, by way of example, the periodicity indicated for each SIBx, wherein x = 1, 2, 3, 4, 5, 6, 7, 8, or 9, in si-Periodicity. Those SIBs may be periodically broadcast on the PDSCH. Currently standardised contents of a selection of such SIBs are outlined below in Table 3 by way of example only - it will be appreciated that this may represent only a subset of the possible SIBs that may be defined.

[0060]

[0061] At step S207, the UE 3 may decode all (or a subset of one or more) of the periodic SIBs broadcast by the RAN node 5. For example, during an initial cell selection procedure the UE 3 may decide to decode each relevant SIBx that it receives (each SIBx received during an initial cell selection procedure being the first such SIBx that the UE 3 has received for the cell that the UE 3 wishes to communicate over).

[0062] However, it will be appreciated that where the UE 3 is switching to a different cell or is moving back to a cell that it previously used, the UE 3 may decide not to decode some or all of the periodic SIBx broadcast by the RAN node 5 if the contents of the SIBx is unchanged across different cells (i.e., where a SIBx message is applicable to two or more cells and the UE 3 is moving between the those two or more cells), and / or the UE 3 has a valid version of SIBx for the cell to which it is moving stored in its memory (i.e., where a UE 3 moves from a first cell to a second cell and stores the SIBs associated with the first cell in its memory so that they can be accessed upon its return to the first cell). Thus, the UE 3 may use a valid stored version of the SIBx (e.g., SIB2, SIB3, SIB4, etc.) after cell re-selection if the SIBx in question is unchanged (i.e., its corresponding valueTag parameter in SIB1 is unchanged).

[0063] It will nevertheless be appreciated that for the UE 3 to be able to use valid stored versions of the SIBx (e.g., SIB2, SIB3, SIB4, etc.) in this manner, the UE 3 must perform appropriate SIB1 acquisition procedures as the valueTag parameter that indicates whether a specific SIBx have changed is provided in SIB1.

[0064] It will be appreciated that being able to use valid stored versions of SIBx (e.g., SIB2, SIB3, SIB4, etc.) in this manner reduces the number of times a UE 3 has to acquire SIBx. Being able to use a valid stored SIBx also reduces the number of on-demand SIBx requests that need to be sent by the UE 3.

[0065] At step S208, the UE 3 may send an appropriate request message to the RAN node 5 to request on-demand transmission of one or more SIBx. For example, where SIB1 includes si-RequestConfig to indicate to the UE 3 that the RAN node 5 supports on-demand SIBx requests and transmissions, the UE 3 may, when appropriate, request the transmission of a SIBx transmission. For example, the UE 3 may request on-demand transmission of one or more SIBx transmissions, upon cell selection (e.g. upon power on), upon cell-reselection, upon return from an 'out of coverage'' state, after reconfiguration with synchronisation completion, after entering the network from another RAT, upon receiving an indication that some or all of the information in SIBx has changed, upon receiving a public warning system (PWS) notification, and / or upon receiving an appropriate request from upper layers (e.g., a positioning request). At step S210, in response to receiving the appropriate request message at step S208, the RAN node 5 transmits SIBx (e.g., SIB2, SIB3, SIB4, etc) to the UE 3 based on the request message sent by the UE 3 to the RAN node 5. For example, the RAN node 5 may broadcast on-demand SIBx on the PDSCH upon request from the UE 3 in RRC_IDLE, RRC_INACTIVE, or RRC_CONNECTED.

[0066] Alternatively, the RAN node 5 may send on-demand SIBx in a dedicated manner on the PDSCH to the UE 3 in RRC_CONNECTED upon request, if configured by the network to do so. For example, the RAN node 5 may send on-demand SIBs in a dedicated manner on the PDSCH upon reception of an appropriate request message from the UE 3 in RRC_CONNECTED, or when the UE 3 has an active bandwidth part (BWP) with no common search space configured, or when the UE 3 is configured with inter-cell beam management and receives a PDSCH from a transmission-reception point (TRP) with a PCI different from serving cell's PCI. At step S211, having received the requested SIBx, the UE 3 decodes the on-demand SIBx transmitted by the RAN node 5.

[0067] Example scenarios where valid stored versions of the SIBx (e.g., SIB2, SIB3, SIB4, etc.) may be used will now be described in more detail.

[0068] areaScope IE absent / excluded / false 　　In one example, the UE 3 may use valid stored versions of SIBx (e.g., SIB2, SIB3, SIB4, etc.) after the UE 3 moves out and then back to the same cell 9 as depicted in Fig. 3A. As shown in Fig. 3A, the UE 3 may at a first time t1be located within the coverage area of a serving cell provided by RAN node 5. While in that coverage area, the UE 3 may communicate with the RAN node 5 over the serving cell 9 and may acquire from the RAN node 5 all necessary SI via appropriate MIB, SIB1, and SIBx transmissions in an appropriate SI acquisition procedure (e.g., such as that described above with reference to Fig. 2).

[0069] At some future time t2, the UE 3 may move out of the coverage area of the serving cell 9 for a period, before re-entering the coverage area of the serving cell 9 at a third time t3as shown by UE trajectory line 2 in Fig. 3A.

[0070] Upon re-entering the coverage area of the serving cell 9 at time t3, the UE 3 will begin to perform a SI acquisition procedure (e.g., the procedure of Fig. 2) to obtain and decode a MIB for the serving cell 9 to allow the UE 3 to subsequently acquire RMSI from SIB1. Upon reception of SIB1 from the RAN node 5, the UE 3 decodes the SIB1 to determine whether it requires other SI from SIBx transmissions.

[0071] For example, during the decoding and processing of SIB1, the UE 3 may respectively determine whether areaScope is present in the siSchedulingInfo of SIB1 for each SIBx. For each SIBx, if areaScope is absent / excluded / false then, if the UE 3 is non-public network (NPN) capable and the serving cell 9 is a NPN-only cell 9, the UE 3 may compare a first NPN identity in the NPN-IdentityInfoList, the cellIdentity and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the NPN identity, the cellIdentity and the valueTag associated with a stored version of that SIBx at the UE 3. Where it is determined that the corresponding parameters are identical the UE 3 may consider the stored SIBx to be valid for the cell 9 and thus may use the stored SIBx rather than acquiring a new SIBx from the RAN node 5.

[0072] Alternatively, if the UE 3 is not non-public network (NPN) capable, then the UE 3 may compare a first PLMN-Identity in the PLMN-IdentityInfoList, the cellIdentity and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the PLMN-Identity in the PLMN-IdentityInfoList, the cellIdentity and the valueTag associated with a stored version of that SIBx at the UE 3. Where it is determined that the corresponding parameters are identical the UE 3 may consider the stored SIBx to be valid for the cell and thus may use the stored SIBx rather than acquiring a new SIBx from the RAN node 5.

[0073] It will be appreciated that in the above scenario, it may be appropriate to apply, for each SIBx stored at the UE 3, an expiry deadline such that each SIBx is deleted from the memory of the UE 3 after an expiry deadline (e.g., after that SIBx has been stored at the UE 3 for 3 hours).

[0074] areaScope present / included / true 　　In another example, the UE 3 may use valid stored versions of the SIBx (e.g., SIB2, SIB3, SIB4, etc.) when the UE 3 moves between cells 9 that are part of a common coverage area that share the same SI as depicted in Fig. 3B.

[0075] As shown in Fig. 3B, the UE 3 may at a first time t1be located within the coverage area of a serving cell 9-1 provided by RAN node 5-1. While in that coverage area, the UE 3 may communicate with the RAN node 5-1 over the serving cell 9-1 and may acquire from the RAN node 5-1 all necessary SI via appropriate MIB, SIB1, and SIBx transmissions by an appropriate SI acquisition procedure (e.g., such as that described above with reference to Fig. 2).

[0076] Moving to another cell with a same systemInformationAreaID At some second time t2, the UE 3 may move out of the coverage area of the serving cell 9-1 to another cell 9-2 that is associated with a same systemInformationAreaID as the serving cell 9-1. For example, the serving cell 9-1 and the cell 9-2 may have the same systemInformationAreaID if the SI (one or multiple SIBx) needed to communicate over the cells 9-1, 9-2 is common between the two cells 9-1, 9-2.

[0077] Upon entering the cell 9-2, the UE 3 will begin to perform a SI acquisition procedure to obtain and decode a MIB for the cell 9-2 to allow the UE 3 to subsequently acquire RMSI from SIB1. Upon reception of SIB1 from the RAN node 5 the UE 3 decodes the SIB1 to determine whether it requires other SI from SIBx.

[0078] For example, during the decoding and processing of SIB1, the UE 3 may determine if areaScope is present / included in the siSchedulingInfo of SIB1 for each SIBx. For each SIBx, if areaScope is present / included in the siSchedulingInfo of SIB1, and the areaScope value is set to 'TRUE', and the areaScope value for the corresponding SIBx stored at the UE 3 is also set to 'TRUE' then, if the UE 3 is NPN capable and the serving cell 9-1 is a NPN-only cell 9-1, the UE 3 may compare a first NPN identity in the NPN-IdentityInfoList, the systemInformationAreaID and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the NPN identity, the systemInformationAreaID and the valueTag associated with a stored version of that SIBx at the UE 3 that was obtained over cell 9-1. Where it is determined that the corresponding parameters are identical the UE 3 may consider the stored SIBx obtained over cell 9-1 to be valid for the cell 9-2 and thus may use the stored SIBx rather than acquiring a new SIBx from the RAN node 5-2.

[0079] Alternatively, if the UE 3 is not NPN capable, then the UE 3 may compare a first PLMN-Identity in the PLMN-IdentityInfoList, the systemInformationAreaID and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the PLMN-Identity in the PLMN-IdentityInfoList, the systemInformationAreaID and the valueTag associated with a stored version of that SIBx at the UE 3 received over cell 9-1. Where it is determined that the corresponding parameters are identical the UE 3 may consider the stored SIBx obtained over cell 9-1 to be valid for the cell 9-2 and thus may use the stored SIBx rather than acquiring a new SIBx from the RAN node 5-2.

[0080] Moving to another cell with no common systemInformationAreaID At some third time t3, the UE 3 may move out of the coverage area of the serving cell 9-2 to another cell 9-3 that is associated with a different systemInformationAreaID than both the serving cell 9-1 and 9-2. For example, the serving cell 9-1 or 9-2 and the cell 9-3 may not have the same systemInformationAreaID if the SI needed to communicate over the cells is different between the two cells.

[0081] Upon entering the cell 9-3, the UE 3 will begin to perform the SI acquisition procedure (e.g., such as the procedure of Fig. 2) to obtain and decode a MIB for the cell 9-3 to allow the UE 3 to subsequently acquire RMSI from SIB1. Upon reception of SIB1 from the RAN node 5 the UE 3 decodes the SIB1 to determine whether it requires other SI from SIBx.

[0082] For example, during the decoding and processing of SIB1, the UE 3 may determine if areaScope is present in the siSchedulingInfo of SIB1 for each SIBx. For each SIBx, if areaScope is present in the siSchedulingInfo of SIB1, and the areaScope value is set to 'TRUE' and the areaScope value for the corresponding SIBx stored at the UE 3 is also set to 'TRUE' then, if the UE 3 is NPN capable and the serving cell 9-1 is a NPN-only cell 9-1, then the UE 3 may compare a first NPN identity in the NPN-IdentityInfoList, the systemInformationAreaID and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the NPN identity, the systemInformationAreaID and the valueTag associated with a stored version of that SIBx at the UE 3 that was obtained over cell 9-1.

[0083] Where it is determined that the corresponding parameters are not identical, the UE 3 may consider the stored SIBx obtained over cell 9-1 to be invalid for the cell 9-3 and thus the UE 3 may continue with the SI acquisition procedure; for example, the UE 3 may send appropriate request messages to the RAN node 5-3 to request on-demand SIB transmissions for the SIBx that it requires for the cell 9-3.

[0084] Alternatively, if the UE 3 is not NPN capable, then the UE 3 may compare a first PLMN-Identity in the PLMN-IdentityInfoList, the systemInformationAreaID and the valueTag that are included in the si-SchedulingInfo of SIB1 for the SIBx to determine if those parameters are identical to the PLMN-Identity in the PLMN-IdentityInfoList, the systemInformationAreaID and the valueTag associated with a stored version of that SIBx at the UE 3 received over cell 9-1.

[0085] Where it is determined that the corresponding parameters are not identical, the UE 3 may consider the stored SIBx obtained over cell 9-1 to be invalid for the cell 9-3 and thus the UE 3 may continue with the SI acquisition procedure; for example, the UE 3 may send appropriate request messages to the RAN node 5-3 to request on-demand SIB transmissions for the SIBx that it requires for the cell 9-3.

[0086] It will be appreciated that the procedures described above with reference to Figs. 2 and 3, help to minimise the overall signalling overhead of the communication system 1 as the UE 3 is able to use a valid stored version of the SIBs (e.g., SIB2, SIB3, SIB4, etc.) after cell re-selection, upon return from out of coverage stage, or after the reception of an indication of a change occurring in some of the SI if the SIBx in question is unchanged. Such reduction in signalling overhead in turn can beneficially translate into network energy savings (NES).

[0087] In the procedures described above with reference to Figs. 2 and 3 the UE 3 performs an acquisition procedure to acquire SIB1 as it moves between cells. SIB1 is (re)acquired in the procedures described above because SIB1 carries all the basic information needed by the UE 3 to perform initial access procedures at least up to RRCSetup, and also carries scheduling information for other SIBs. For example, as already outlined above, the IE SI-SchedulingInfo of SIB1 contains the information needed for acquisition of other SIB messages, as well as the information needed by the UE 3 to decide whether a stored version of a SIBx can be used, avoiding the need to acquire it.

[0088] It will be appreciated, however, that the necessity of repeatably acquiring SIB1 as a UE 3 moves between cells has the potential to result in unnecessary signalling / processing at the UE 3 and / or RAN node 5, because, in some instances, SIB1 may be unchanged. Beneficially, therefore, the UE3 and RAN node 5 of the communication system 1 are mutually configured to support one or more mechanisms / procedures for facilitating the storage of one or more versions of SIB1 at a UE 3 for potential later (re)use. Thus, when a SIB1 associated with a cell that the UE 3 enters is the same as a version of SIB1 stored at the UE 3, the stored version of SIB1 may be used rather than attempting to acquire a new SIB1.

[0089] In one or more aspects of the disclosure below, the communication system 1 is adapted to allow for the storage of SIB1 at a UE that it has previously acquired for a cell, and to allow the UE to determine, upon returning to that cell, whether the SIB1 in its storage for the cell remains valid and may be used.

[0090] In one or more other aspects of the disclosure below, the communication system 1 is adapted to allow for the storage of other system information at a UE that it has previously acquired for a cell, and to allow the UE to determine, upon returning to that cell, whether the system information in its storage for the cell remains valid and may be used.

[0091] In one or more other aspects of the disclosure below, the communication system 1 is adapted to allow for the storage of SIB1 (and other system information) for a cell at a UE to allow the UE to reuse that SIB1 (and other system information) for the cell at some future time, and it further indicate to the UE when that SIB1 (and other system information) has been updated even when the UE is not camped on the corresponding cell.

[0092] In one or more other aspects of the disclosure below, the communication system 1 is adapted to allow for the transmission and use of a common SIB1 that may be applicable to multiple cells provided by multiple different RAN nodes, and which may be used by a UE as it moves between those multiple cells.

[0093] Beneficially, therefore, if a UE has previously acquired a SIB1 for a cell, and / or if a SIB1 currently being used by a UE or stored in the memory of a UE is equally applicable to the cell it is moving into, the UE and RAN node can avoid additional signalling overhead, and associated energy consumption, which would otherwise arise from (re)acquiring SIB1 in the new cell.

[0094] Each of the mechanisms for storing a SIB1 and determining whether it can be re-used rather than acquiring a new SIB1 as outlined above will now be discussed in more detail with reference to Figs. 2 to 10.

[0095] Introducing a 'version number' IE for SIB1 　　Fig. 4 schematically illustrates a scenario involving two RAN nodes 5A, 5Bof the communication system 1.

[0096] As shown in Fig. 4, the RAN nodes 5A, 5Bare connected to the external data network 20 via the core network 7 and each provide one or more cells (e.g., cell A 9Aand cell B 9Brespectively).

[0097] As shown in Fig. 4, the UE 3 at time t1may be situated within the coverage area of the cell B 9Bprovided by the RAN node 5B. While in the coverage area of the cell B 9Bthe UE 3 may perform a MIB / SIB acquisition procedure (e.g., such as the procedure of Fig. 2) with the RAN node 5Bto acquire at least MIB and SIB1 for the cell B 9Bto allow the UE 3 to camp on the cell B 9B. The SIB1 received from the RAN node 5Bmay, in addition to the typical IEs contained within the SIB1, may also include a new IE indicating a version number, or the like, of the SIB1 (e.g., a 'valueTagOfSIB1' IE or the like). Having received SIB1 from the RAN node 5B, the UE 3 may store that SIB1 in its memory.

[0098] At time t2the UE 3 may have moved, as shown in Fig. 4, to a different cell (e.g., cell A 9A) provided by a different RAN node 5A. While in the coverage area of the different cell 9A, the UE 3 may perform another MIB / SIB acquisition procedure (e.g., such as the procedure of Fig. 2) with the RAN node 5Ato acquire at least MIB and SIB1 to allow the UE 3 to camp on the cell A 9A. The SIB1 received from the RAN node 5Amay, in addition to the typical IEs contained within the SIB1, also include the IE indicating a version number, or the like, of the SIB1. Having received SIB1 from the RAN node 5A, the UE 3 may store that SIB1 in its memory along with the SIB1 the UE 3 received earlier at time t1from the RAN node 5B.

[0099] At time t3the UE 3 may have moved, as shown in Fig. 4, back to the coverage area of the cell B 9Bprovided by the RAN node 5B. While in the coverage area of cell B 9Bthe UE 3 may perform a MIB / SIB acquisition procedure (e.g., such as the procedure of Fig. 2) with the RAN node 5Bto acquire at least the MIB and SIB1 for the cell B 9Bto allow the UE 3 to camp back onto the cell B 9B.

[0100] Nevertheless, rather than performing all of the steps of a typical MIB / SIB acquisition procedure (e.g., such as the procedure of Fig. 2) with the RAN node 5B, the UE 3, upon moving back to the coverage area of the cell B 9B, may first perform another procedure to determine whether there is any SIB1 stored in its memory that is still valid and usable for the cell B 9B. Having determined that at least one SIB1 stored in the memory of the UE 3 is still valid and usable for the cell B 9B, the UE 3 may use the stored SIB1 to camp back onto the cell B 9B(i.e., rather than reacquire SIB1). If however, the UE 3 determines that there is no SIB1 stored in the memory of the UE 3 that is valid and usable for the cell B 9B, then the UE 3 may (re)acquire the SIB1 for the cell B 9B, for example by performing a full MIB / SIB acquisition procedure such as that of Fig. 2 with the RAN node 5B.

[0101] A number of possible procedures for determining whether a SIB1 stored in the memory of the UE 3 is still valid and usable for a cell that the UE 3 is currently in will now be discussed in more detail with reference to Figs. 5 to 10.

[0102] SIB1 transmitted on initial serving cell and 'version number' indication transmitted on a different cell: Periodic SIB1 　　Fig. 5 depicts a simplified sequence diagram illustrating a procedure that may be used in the communication system 1 to determine whether a SIB1 stored in the memory of a UE 3 is still valid and usable for a cell that the UE 3 has left and re-entered.

[0103] As shown in Fig. 5, a RAN node 5Athat provides a first cell (cell A 9A), another RAN node 5Bthat provides a second cell (cell B 9B), and a UE 3 may be deployed in the communication system 1.

[0104] The UE 3 may initially attempt to camp on the cell B 9Bto allow communication with the RAN node 5Bat a time t1. For example, at step S502, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0105] Having received the SSB broadcasted transmissions at step S502, the UE 3 may await to receive periodic SIB1 transmissions from the RAN node 5Bat step S504 on resources indicated in the SSBs if there is no stored version yet.

[0106] Additionally, the SIB1 may include other appropriate information. For example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0107] Furthermore, SIB1 may also include the new version number IE (e.g., valueTagOfSIB1 IE or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That new IE allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5Bover time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31. For example, in the procedure of Fig. 5, the SIB1 transmitted to the UE 3 at step S504 has a version number of 8.

[0108] Having received the SIB1 at step S504, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S505).

[0109] At step S506, after having sent the SIB1 at step S504, the RAN node 5Bmay send an appropriate message to a neighbouring RAN node 5Athat provides a neighbouring cell (e.g., cell A 9A) with an indication of the version number of SIB1 for the cell B 9B. For example, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Aover the Xn interface to indicate to the neighbouring RAN node 5Athe version number value of the latest SIB1 sent by the RAN node 5Bin the cell B 9B. For example, in the procedure of Fig. 5, the appropriate message sent over the Xn interface by the RAN node 5Bindicates to the RAN node 5Athat the latest SIB1 sent by the RAN node 5Bhas a version number value of 8.

[0110] It will be appreciated that while it is described above that step S506 occurs after SSB transmissions at step S502, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Athat provides the neighbouring cell (e.g., cell A 9A) with an indication of the version number of SIB1 for the cell B 9B, prior to the SSB transmission, during the SSB transmissions (i.e., in parallel with the SSB transmissions), or after the SSB transmissions.

[0111] At step S508, the RAN node 5Bmay send an updated SIB1 in cell B 9Bvia periodic SIB1 transmissions. That updated SIB1 may include any number of updated / changed IEs, and in addition will also have an updated version number value to indicate that the SIB1 has changed or been updated. For example, in the procedure of Fig. 5, the SIB1 transmitted to at step S508 has an updated version number of 9.

[0112] If the UE 3 is still in cell B and receives the updated SIB1 sent at step S508, the UE 3 may store the updated SIB1 in its memory (at step S509). However, if the UE 3 has already moved out of cell B 9B, it will not receive the updated SIB1 and will, thus, not store the updated SIB1 in its memory.

[0113] At step S510, if the RAN node 5Bsent an updated SIB1 at step S508, then the RAN node 5Bmay send, via appropriate signalling means, an appropriate message to a neighbouring RAN node 5Ato indicate that the SIB1 provided to the UE 3 by the RAN node 5Bhas changed or been updated. For example, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Aover the Xn interface to indicate to the neighbouring RAN node 5Athe new updated version number value of the latest SIB1 sent at step S508. For example, in the procedure of Fig. 5, the appropriate message sent over the Xn interface by the RAN node 5Bindicates to the RAN node 5Athat the latest SIB1 sent by the RAN node 5Bhas a version number of 9.

[0114] It will be appreciated that while it is described above that step S508 occurs after SSB transmissions at step S502, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Athat provides the neighbouring cell (e.g., cell A 9A) with an indication of an updated version number of SIB1 for cell B 9Bwhenever such an update occurs. For example, where the update occurs, prior to the SSB transmissions at step S502, the RAN node 5Bmay send the appropriate message with the updated version number prior to sending the SSB transmissions. Similarly, where the update occurs, prior to the SSB transmissions at step S502, the RAN node 5Bmay send the appropriate message with the updated version number at the same time as the SSB transmissions at step S502.

[0115] At some time t2the UE 3 may move out of the cell coverage area of cell B 9Bprovided by RAN node 5Band into the cell coverage area of the neighbouring cell A 9A, provided by the neighbouring RAN node 5A.

[0116] Having moved into the cell coverage area of cell A 9A, the UE 3 may attempt to camp on cell A 9A. For example, the UE 3 may attempt to detect SSBs broadcast by RAN node 5A(not shown). Having received the SSBs broadcasted by RAN node 5A, the UE 3 may await to receive appropriate system information Blocks (SIBs) from the RAN node 5Ato enable the UE 3 to access the corresponding cell A 9A(e.g., a SIB1 from RAN node 5A, or the like and possibly other system information).

[0117] At step S512, the RAN node 5Amay broadcast such appropriate SIBs in cell A 9A, e.g., on resources indicated in the SSBs and the UE 3 may thus receive the broadcast SIBs. The SIBs broadcast at step S512 may include at least a SIB1 which the UE 3 may store in its memory. That SIB1 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which SIB1 is applicable.

[0118] Additionally, the SIB1 may include other appropriate information, for example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI containing other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0119] Furthermore, the SIB1 broadcast in cell A 9Amay also include the new version number IE which is incremented by 1 each time the contents of SIB1 for the cell A 9Ais changed and allows the UE 3 to identify whether changes to that SIB1 have occurred.

[0120] It will be appreciated nevertheless that the SIBs broadcast in the cell A 9Amay include more than just a SIB1. For example, the SI may also include other possible SIBs (e.g., SIB1, SIB2, SIB3, etc.) that may need to be transmitted to the UE 3 or otherwise broadcast by the RAN node 5A. For example, the SI broadcast in cell A 9Amay include appropriate SI pertaining to the cell B 9Bprovided by the RAN node 5Bto the RAN node 5A(e.g., over an Xn interface).

[0121] For example, the RAN node 5A, having received an indication of the latest version number value of the latest SIB1 sent in the cell B 9B(e.g., at step S508) by the RAN node 5B, may include an appropriate indication of that latest version number value in SIB sent in the cell A 9Aat step S512 and hence received by the UE 3 when it is in the cell A 9A. For example, in the procedure of Fig. 5, the SI transmitted at step S512 includes the version number value of the latest SIB1 sent by the RAN node 5Bin the cell B 9Bwhich, in this example, is a value of 9.

[0122] It will be appreciated that the indication of the latest version number of the latest SIB1 sent in the cell B 9Bat step S508 included in the SI sent at step S512, may be an indication provided in a SIB1, or another SIB, sent by the RAN node 5Ain the cell A 9A. For example, a new IE may be included in SIB1, or another SIB, to allow the indication of a latest version number indicated to a RAN node 5 by one of its neighbouring RAN nodes 5.

[0123] Alternatively, or additionally, the latest version number of the latest SIB1 sent in a neighbouring cell by a neighbouring RAN node 5 may be included in a dedicated SI message sent by a RAN node 5 serving the UE 3, for receipt by the UE 3, to indicate a latest version number indicated to that serving RAN node 5 by the neighbouring RAN node 5.

[0124] At some time t3the UE 3 may move out of the cell coverage area of the cell A 9Aprovided by the RAN node 5Aand may return to the cell coverage area of the cell B 9Bprovided by the neighbouring RAN node 5B.

[0125] Having moved back into the cell coverage area of the cell B 9B, the UE 3 may attempt to camp on the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (not shown). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0126] Having received the MIB for the cell B 9B, prior to attempting to receive and / or decode a SIB1 from the RAN node 5B, the UE 3 may check / determine whether a version number of SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to the latest version number of SIB1 for the cell B 9Bindicated to the UE 3 in the SI that it received from RAN node 5Aat step S512 while it was camped on the cell A 9A.

[0127] Where it is determined that the version number of SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to (i.e. matches) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 from the cell A 9A, (either it was camping in the cell A 9Abefore re-entering the cell B 9Bor It went back to the cell A 9Afor SIB validity purposes), the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is still valid and can be used. For example, where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3, rather than attempting to receive / decode a SIB1 from the RAN node 5B, may access that SIB1 from its memory, and use that SIB1 for continuing its camping procedure to camp on the cell B 9B. This in turn avoids the need for the UE 3 to unnecessarily monitor for and decode SIB1 for the cell B 9B.

[0128] Alternatively, where it is determined that the version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is not equal to (i.e. does not match) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 while it was camped on the cell A 9A, the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is not valid and cannot be used.

[0129] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid anymore, the UE 3 may attempt to receive a new SIB1 from the RAN node 5B(for example, as in the MIB / SIB acquisition procedure of Fig. 2). At the same time, the UE 3 may discard the invalid SIB1 for the cell B 9Bstored in its memory to make additional room for the storage of the new SIB1 it is to receive from the RAN node 5Bin the MIB / SIB acquisition procedure of Fig. 2.

[0130] It will be appreciated that to determine whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3 must first correctly identify the cell provided by the RAN node 5Bthat it is attempting to camp onto.

[0131] Typically, such cells are globally uniquely identified by a PLMN identifier and the cell's own unique identifier. Such indications however are typically obtained from a SIB1 transmitted over the cell, and thus in the procedure described above such indications will not be available to the UE 3 before the UE 3 either obtains a SIB1 from the RAN node 5Bor determines whether SIB1 stored in its memory is valid for the cell B 9B. Therefore, the cell B 9Bmay be identified by the UE 3 using its physical cell ID (PCI) in the SSB transmissions from the RAN node 5B. In addition, the version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 may also be associated with the PCI of the cell B 9B. However, where multiple cells are provided within a larger serving cell, those multiple cells may share a single PCI, and thus the UE 3 may not be able to identify the correct cell (i.e., cell B 9B) where there are multiple cells with the same PCI.

[0132] To assist the UE 3 to correctly identify the cell, in one example, the stored SIB1 in the memory of the UE 3 that was transmitted to the UE 3 by the RAN node 5Bwhen the UE 3 was initially camped on the cell B 9B, may include other appropriate information and parameters to assist in identifying that cell to which the SIB1 and version number of the SIB1 applies. For example, the UE will store a SIB1 of the cell B 9B, and the PCI together with following extra information of the cell B 9B: -　　Information of the frequency of the cell B 9Bto which the SIB1 is applicable (e.g., a frequency of the SSB provided over the cell and / or a frequency reference point for the cell B 9B); -　　Information of the subcarrier spacing (SCS) of the cell B 9Bto which the SIB1 is applicable; -　　An indication of which coverage area the cell B 9Bto which the SIB1 is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such an indication is provided, the UE 3, upon receiving the SIB1 may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A. -　　An indication of the best SSBs of which coverage area the cell B 9Bto which the SIB1 is applicable is whichin, and a (pre)configured RSRP threshold value for that coverage area.

[0133] It will be appreciated that where indications such as those listed above are identified by UE 3 (e.g., SSB of the cell A 9A) or provided in a stored SIB1 they may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the stored SIB1.may be used by the UE 3, in conjunction with a PCI, to correctly identify the cell B 9Bbeing provided by the RAN node 5B.

[0134] It will be appreciated that version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 may be associated with the PCI of cell B 9B, and furthermore associated with some / all of the above listed information, which may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the version number being provided by the RAN node 5A.

[0135] It will be appreciated that when determining whether the SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the stored SIB1 may only be considered valid if, in addition to having the correct version number, the stored SIB1 also has associated indications such as those listed above that match (correspond) with the cell B 9Bbeing provided by the RAN node 5Bat time t3.

[0136] In another example, rather than providing extra indications in SIB1 as indicated above, two new bits may be introduced in the SSBs that may be used in conjunction with the PCI in the SSB to assist the UE 3 in correctly identifying a cell being provided by the RAN node 5B.

[0137] SIB1 transmitted on initial serving cell and 'version number' indication transmitted on a different cell: On-demand SIB1　　Figs. 6A and 6B depict a simplified sequence diagram illustrating another procedure that may be used in the communication system 1 to determine whether a SIB1 stored in the memory of a UE 3 are still valid and usable for a cell that the UE 3 has left and re-entered.

[0138] As shown in Figs. 6A and 6B there is a RAN node 5Athat provides a first cell (cell A 9A), another RAN node 5Bthat provides a second cell (cell B 9B), and the UE 3 deployed in the communication system 1.

[0139] The UE 3 may initially attempt to camp on the cell B 9Bto allow communication with RAN node 5Bat a time t1. For example, at step S602, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0140] Having received the SSBs broadcasted by the RAN node 5Bat step S602, the UE 3 may perform an appropriate procedure to request the transmission of an on-demand SIB1 from the RAN node 5B(not shown). By way of example, the UE 3 may send one or more appropriate messages to the RAN node 5Bto indicate to the RAN node 5Bthat the UE 3 wishes to receive an on-demand SIB1 transmission over the cell B 9Bprovided by the RAN node 5Busing a specific set of resources (for example an appropriately formatted uplink WUS, an explicit on-demand SIB1 request, and / or the like). In response to that message, the RAN node 5Bmay transmit an on-demand SIB1 to the UE 3 over the cell B 9B. It will nevertheless be appreciated that the use of an explicit / implicit on-demand SIB request message as described above is by way of example only and that any appropriate on-demand SIB1 procedure may be performed between the UE 3 and the RAN node 5Bto facilitate the transmission of an on-demand SIB1 from the RAN node 5Bto the UE 3.

[0141] Having performed an appropriate on-demand SIB1 procedure to trigger the transmission of an on-demand SIB1, the UE 3 awaits to receive one or more on-demand SIB1 transmissions from the RAN node 5Bat step S604 on appropriate resources if there is no stored version of SIB1 in its memory yet. By way of example only, the appropriate resource may be indicated to the RAN node 5Bin an on-demand SIB1 request message or uplink WUS, or alternatively they may be preconfigured such that both the RAN node 5Band the UE 3 know which resources will be used for such on-demand SIB1 transmissions.

[0142] Additionally, the SIB1 may include other appropriate information, for example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0143] Furthermore, SIB1 may also include a new version number IE (e.g., valueTagOfSIB1 IE, or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That new IE allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version numbers the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31. For example, in the procedure of Fig. 6, the SIB1 transmitted to the UE 3 at step S504 has a version number value of 8.

[0144] Having received the SIB1 at step S604, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S605).

[0145] At step S606, after having sent the on-demand SIB1 at step S604, the RAN node 5Bmay send an appropriate message to a neighbouring RAN node 5Aproviding a neighbouring cell (e.g., cell A 9A) with an indication of the version number of SIB1 for the cell B 9B. For example, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Aover the Xn interface to indicate to the neighbouring RAN node 5Athe version number of the latest SIB1 sent by the RAN node 5Bin the cell B 9B. For example, in the procedure of Fig. 6, the appropriate message sent over the Xn interface by the RAN node 5Bindicates to the RAN node 5Athat the latest SIB1 sent by the RAN node 5Bhas a version number of 8.

[0146] It will be appreciated that while it is described above that step S606 occurs after SSB transmissions at step S602, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Athat provides the neighbouring cell (e.g., cell A 9A) with an indication of the version number of SIB1 for cell B 9B, prior to the SSB transmission, during the SSB transmissions (i.e., in parallel with the SSB transmissions), or after the SSB transmissions.

[0147] Additionally, at step S606, the RAN node 5Bmay also send, to the RAN node 5A, an appropriate wake-up signal (WUS) configuration that may be used for waking up the RAN node 5Bat some future time. For example, if at some future time the UE 3 were to move out of the coverage area of the cell B 9Band into the coverage area of the cell A 9A, the UE 3 will stop communicating with the RAN node 5B. In this instance the RAN node 5Bmay be configured to enter a 'sleep' or 'reduced transmission' mode to bring energy efficiency savings to the network. However, in this scenario, should the UE 3 ever move back into cell B 9Bit will need to be able to send an appropriate WUS message to the RAN node 5Bto wake the RAN node 5Bup so that it can begin broadcasting MIB / SIB messages again.

[0148] At step S608 the RAN node 5Bmay send an updated SIB1 via on-demand (or possibly a periodic) SIB1 transmission in the cell B 9B. It will be appreciated that an on-demand SIB may be triggered by / for the same or a different UE 3. That updated SIB1 may include any number of updated / changed IEs, and in addition will also have an updated version number to indicate that the SIB1 has changed or been updated. For example, in the procedure of Fig. 6, the SIB1 transmitted to the UE 3 at step S608 has an updated version number of 9.

[0149] If the UE 3 is still in the cell B 9Band receives the updated SIB1 sent at step S608, the UE 3 may store the updated SIB1 in its memory (at step S609). However, if the UE 3 has already moved out of the cell B 9B,it will not receive the updated SIB1 and will, thus, not store the updated SIB1 in its memory.

[0150] At step S610, if the RAN node 5Bsent an updated SIB1 at step S608, then the RAN node 5Bmay send an appropriate message to a neighbouring RAN node 5Avia appropriate signalling means to indicate that the SIB1 provided to the UE 3 by the RAN node 5Bhas changed or been updated. For example, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Aover the Xn interface to indicate to the neighbouring RAN node 5Athe new updated version number value of the latest SIB1 sent to the UE 3 at step S608. By way of example, in the procedure of Fig. 6, the appropriate message sent over the Xn interface by the RAN node 5Bindicates to the RAN node 5Athat the latest SIB1 sent by the RAN node 5Bhas a version number value of 9.

[0151] It will be appreciated that while it is described above that step S610 occurs after SSB transmissions at step S602, the RAN node 5Bmay send an appropriate message to the neighbouring RAN node 5Athat provides the neighbouring cell (e.g., cell A 9A) with an indication of an updated version number of SIB1 for the cell B 9Bwhenever such an update occurs. For example, where the update occurs, prior to the SSB transmissions at step S602, the RAN node 5Bmay send the appropriate message with the updated version number prior to sending the SSB transmissions. Similarly, where the update occurs, prior to the SSB transmissions at step S602, the RAN node 5Bmay send the appropriate message with the updated version number at the same time as the SSB transmissions at step S602.

[0152] At some time t2the UE 3 may move out of the cell coverage area of the cell B 9Bprovided by the RAN node 5Band into the cell coverage area of the neighbouring cell A 9Aprovided by the neighbouring RAN node 5A.

[0153] Having moved into the cell coverage area of the cell A 9A, the UE 3 may attempt to camp on the cell A 9A. For example, the UE 3 may attempt to detect SSBs broadcast by the RAN node 5A(not shown). Having received the SSB broadcasted transmissions, the UE 3 may await to receive appropriate SIBs from the RAN node 5Ato enable the UE 3 to access the corresponding cell A 9A(e.g., the SIB1 from the RAN node 5A, or the like, and possibly other system information).

[0154] At step S612, the RAN node 5Amay broadcast such appropriate SIBs in the cell A 9A, e.g., on resources indicated in the SSBs and the UE 3 may thus receive the broadcast SIBs. The SIBs broadcast at step S612 may include at least the SIB1 for the cell A 9Awhich the UE 3 may store in its memory. That SIB1 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which SIB1 is applicable.

[0155] Additionally, the SIB1 provided in the cell A 9Amay include other appropriate information, for example, the SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0156] Furthermore, the SIB1 broadcast in the cell A 9Amay also include the new version number IE which is incremented by 1 each time the contents of SIB1 for cell A 9Ais changed and allows the UE 3 to identify that changes to the SIB1 have occurred.

[0157] It will be appreciated nevertheless that the SIBs broadcast in the cell A 9Amay include more than just a SIB1. For example, the SI may also include all other possible SIBs (e.g., SIB1, SIB2, SIB3, etc.) that may need to be transmitted to the UE 3 or otherwise broadcast by the RAN node 5A. For example, the SIBs broadcast in the cell A 9Amay include appropriate SIBs pertaining to the cell B 9Bprovided by the RAN node 5Bto the RAN node 5A(e.g., over an Xn interface).

[0158] For example, the RAN node 5A, having received an indication of the latest version number of the latest SIB1 sent at step S608 by the RAN node 5B, in the cell B 9Bmay include an appropriate indication of that latest version number in the SI sent at step S612 in the cell A 9Aand hence received by the UE 3 when it is in the cell A 9A. For example, in the procedure of Fig. 6, the SI transmitted at step S612 includes the version number of the latest SIB1 sent by RAN node 5Bin the cell B 9Bwhich, in this example, is a value of 9.

[0159] It will be appreciated that the indication of the latest version number of the latest SIB1 sent in the cell B 9Bat step S608 included in the SIBs sent at step S612, may be an indication provided in a SIB1, or another SIB, sent by the RAN node 5Aover the cell A 9A. For example, a new IE may be included in the SIB1, or another SIB, to allow the indication of a latest version number indicated to a RAN node 5 by one of its neighbouring RAN nodes 5.

[0160] Alternatively, or additionally, the latest version number of the latest SIB1 sent in a neighbouring cell by a neighbouring RAN node 5 may be included in a dedicated SI message sent by a RAN node 5 serving the UE 3, for receipt by the UE 3 to indicate a latest version number indicated to that serving RAN node 5 by the neighbouring RAN node 5.

[0161] Additionally, at step S612, the RAN node 5Amay transmit, to the UE 3, the WUS configuration (or an indication of the WUS configuration) if the RAN node 5Areceived such a WUS configuration from the RAN node 5Bat step S606.

[0162] At some time t3the UE 3 may move out of the cell coverage area of cell A 9Aprovided by RAN node 5Aand may return to the cell coverage area of cell B 9Bprovided by the neighbouring RAN node 5B(possibly via one or more other 'intermediate' cells).

[0163] Having moved back into the cell coverage area of the cell B 9B, the UE 3 may attempt to camp on the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (not shown). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0164] Having received the MIB for the cell B 9B, prior to attempting to receive and / or decode a SIB1 from the RAN node 5B, the UE 3 may check / determine at step S614 whether a version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to the latest version number of SIB1 for the cell B 9Bindicated to the UE 3 in the SI that it received from the RAN node 5Aat step S612 while it was camped on the cell A 9A.

[0165] The remainder of the procedure is shown in Fig. 6B.

[0166] Where it is determined that the version number of SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to (i.e. matches) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S612 from the cell A 9A(either it was camping in the cell A 9Abefore re-entering the cell B 9Bor it went back to the cell A 9Afor SIB validity purposes), the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is still valid and can be used. For example, where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3, rather than attempting to receive / decode a SIB1 from RAN node 5B, may access that SIB1 from its memory, and use that SIB1 for continuing its camping procedure to camp onto the cell B 9B(at step S620). This in turn avoids the need for an on-demand SIB1 to be triggered by / for the UE 3 and transmitted by the RAN node 5Band avoids the need for the UE 3 to receive and decode a SIB1 transmitted in cell B 9B.

[0167] Alternatively, where it is determined that the version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is not equal to (i.e. does not match) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S612 while it was camped on the cell A 9A, the UE 3 may determine that the SIB1 stored in its memory is not valid and cannot be used.

[0168] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid anymore, the UE 3, at step S616 may send an appropriate SIB request message to the RAN node 5Bon configured PRACH resources to request the transmission of an on-demand SIB1. It will be appreciated that where the RAN node 5Bhas entered a 'sleep' state or reduced transmission state, the UE 3 may, prior to (or as an alternative to) sending an appropriate SIB1 request message, send a WUS message to the RAN node 5Bto trigger the RAN node 5Bto switch from a sleep' state or reduced transmission state to a normal transmission state. For example, where the RAN node 5Bis in a reduced signalling state (e.g., an energy saving mode), the UE 3 may send an appropriate uplink WUS message to the RAN node 5Bbased on the WUS configuration it received from the RAN node 5Ato 'wake-up' the RAN node 5B.

[0169] It will also be appreciated, that the WUS message, as well as triggering the RAN node 5Bto 'wake up', may also contain appropriate information to request that the RAN node 5Btransmit a SIB1 to the UE 3 either periodically or on an on-demand basis once it has woken up. In this scenario, it will be appreciated that a separate on-demand SIB1 request message may not need to be sent to the RAN node 5B.

[0170] The UE 3 may then attempt to receive a new SIB1 broadcast from the RAN node 5Bat step S618. At the same time, the UE 3 may discard the invalid SIB1 for the cell B 9Bstored in its memory to make additional room for the storage of the new SIB1 it is to receive from the RAN node 5B.

[0171] It will be appreciated that to determine whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3 must first correctly identify the cell B 9Bprovided by the RAN node 5Bthat it is attempting to camp on.

[0172] Typically, such cells are globally uniquely identified by an indication of a PLMN identifier and the cell's own unique identifier. Such indications however are typically obtained from a SIB1 transmitted over the cell, and thus in the procedure described above such indications will not be available to the UE 3 before the UE 3 either obtains a SIB1 from the RAN node 5B or determines whether SIB1 stored in its memory is valid for the cell B 9B. Therefore, the cell B 9Bmay be identified by the UE 3 using its physical cell ID (PCI) in the SSB transmissions from the RAN node 5B. In addition, the version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S612 may also be associated with the PCI of the cell B 9B. However, where multiple cells are provided within a larger serving cell, those multiple cells may share a single PCI, and thus the UE 3 may not be able to identify the correct cell (i.e., cell B 9B) where there are multiple cells with the same PCI.

[0173] To assist the UE 3 to correctly identify the cell, in one example, the stored SIB1 in the memory of the UE 3 that was transmitted to the UE 3 by the RAN node 5Bwhen the UE 3 was initially camped on the cell B 9B, may include other appropriate information and parameters to assist in identifying that cell to which the SIB applies. For example, the UE 3 will store a SIB1 of the cell B 9B, and the PCI together with following extra information of the cell B 9B: -　　Information of the frequency of cell B 9Bto which the SIB1 is applicable (e.g., a frequency of the SSB provided over the cell B 9Band / or a frequency reference point for the cell B 9B); -　　Information of the subcarrier spacing (SCS) of the cell B 9Bto which the SIB1 is applicable; -　　An indication of which coverage area the cell B 9Bto which the SIB1 is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such an indication is provided, the UE 3, upon receiving the SIB1 may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A. -　　An indication of the best SSBs of which coverage area the cell B 9Bto which the SIB1 is applicable is within, and a (pre)configured RSRP threshold value for that coverage area.

[0174] It will be appreciated that where indications such as those listed above are identified by the UE 3 (e.g., SSB of cell A 9A) or provided in a stored SIB1 they may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the stored SIB1 may be used by the UE 3, in conjunction with a PCI, to correctly identify the cell B 9Bbeing provided by the RAN node 5B.

[0175] It will be appreciated that version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S612 may be associated with the PCI of the cell B 9B, and furthermore associated with some / all of the above listed information, which may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the version number being provided by the RAN node 5A.

[0176] It will be appreciated that when determining whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the stored SIB1 may only be considered valid if, in addition to having the correct version number, the stored SIB1 also associated has indications such as those listed above that match (correspond) with the cell B 9Bbeing provided by the RAN node 5Bat time t3.

[0177] In another example, rather than providing extra indications in SIB1 as indicated above, two new bits may be introduced in the SSBs that may be used in conjunction with the PCI in the SSB to assist the UE 3 in correctly identifying a cell B 9Bbeing provided by the RAN node 5B.

[0178] Additionally, it will be appreciated that in the procedure of Fig. 6 the WUS configuration sent to the RAN node 5Aat step S606 and to the UE 3 at step S612 may include appropriate information and parameters to help identify for which RAN node 5 and thus which cell (e.g., cell B 9B) the WUS configuration is applicable. For example, the WUS configuration may include: -　　An indication of the PCI of the cell to which the WUS configuration is applicable; -　　Information of the frequency of the cell B 9Bfor which the WUS configuration is applicable (e.g., a frequency of the SSB provided over the cell and / or a frequency reference point for the cell); -　　Information of the subcarrier spacing (SCS) of cell B 9Bfor which the WUS configuration is applicable; -　　An indication of which coverage area the cell B 9Bfor which the WUS configuration is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such an indication is provided, the UE 3, upon receiving the WUS configuration may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A; -　　An indication of the best SSBs of which coverage area the cell B 9Bfor which the WUS configuration is applicable within, and a (pre)configured RSRP threshold value for that coverage area.

[0179] It will be appreciated that the WUS configuration may only be used by the UE 3 to send an appropriate WUS message to the RAN node 5Bif the WUS configuration has indications such as those listed above that match (correspond) with the cell B 9Bbeing provided by the RAN node 5Bat time t3.

[0180] It will also be appreciated that in the procedure of Fig. 6, the WUS configuration sent to the RAN node 5Aat step S606 and to the UE 3 at step S612 may be modified or updated at some time after the WUS configuration has been transmitted, but prior to the UE 3 using the WUS configuration to send a WUS message to the RAN node 5Bto wake-up the RAN node 5B. Therefore, appropriate mechanisms may also be incorporated into the procedure of Fig. 6 to allow for updated WUS configurations to be provided to the UE 3 as and when they are updated.

[0181] In one example, the UE 3 may always re-read the WUS configuration it received at S612 from the RAN node 5Aprior to using the WUS configuration to generate a WUS message for sending to the RAN node 5B. For example, having determined that the version number value for the SIB1 for the cell B 9Bstored in the memory of the UE 3 does not match the version number value indicated to the UE 3 at step S612, the UE 3 may return to the cell A 9Aprovided by the RAN node 5Ato receive a latest WUS configuration from the RAN node 5Aprior to generating a WUS message to send to the RAN node 5B. It will be appreciated that in this scenario, the WUS configuration may not be subject to normal system information modification procedures e.g., modification of the WUS configuration will not trigger paging, as the UE 3 always returns to receive the latest WUS configuration when it determines that the version number value for the SIB1 for the cell B 9Bstored in its memory does not match the version number value indicated to the UE 3 at step S612.

[0182] In another example, when the RAN node 5Bupdates its WUS configuration for the cell B 9Bnetwork-triggered paging may be used to signal to the UE 3 that the WUS configuration has been updated and that it needs to receive the latest WUS configuration to be able to generate an appropriate WUS message for waking up the RAN node 5Bat some later time. For example, the RAN node 5Bmay send a paging message to the UE 3 indirectly via the RAN node 5Ato indicate that its WUS configuration for cell B 9Bhas changed. In response to receiving that paging message, the UE 3 may return to the cell A 9Aprovided by the RAN node 5Ato receive a latest WUS configuration from the RAN node 5Aprior to generating a WUS message to send to the RAN node 5B.

[0183] In yet another example, to avoid the time interruptions and power consumption issues that may arise in the examples above, the WUS configuration provided to the RAN node 5A, and the UE 3 may be a common WUS configuration that is applicable to all, or a group of, on-demand cells e.g., all on-demand SIB1 cells under a same coverage cell. For example, the WUS configuration may be (pre)configured / predefined using e.g., a preamble over periodic PRACH occasions dedicated for on-demand SIB1 transmissions such that as soon as the UE 3 determines that a cell it is attempting to camp on is an on-demand SIB1 cell, and that it needs to acquire a SIB1 (e.g., because a stored SIB1 in the memory of the UE 3 is not valid), the UE 3 may use the (pre)configured / predefined WUS configuration to request a SIB1.

[0184] In yet another example, to avoid the time interruptions and power consumption issues that may arise in the examples above, the WUS configuration provided to the UE 3 may be a common WUS configuration provided to the UE 3 in SI of the neighbouring cell A 9A. That WUS configuration may be applicable to all, or a group of, on-demand cells e.g., cells under a same coverage cell as the cell that provided the WUS configuration i.e., cell A 9A.

[0185] It will be appreciated that in both the examples described above where a common WUS configuration is provided, the UE 3 may be told that the cell in question (e.g., cell B 9B) is an on-demand SIB1 cell, before using the common WUS to request SIB1.

[0186] In one example, to indicate to the UE 3 that the cell is an on-demand SIB1 cell, a spare bit, or a repurposed bit of a MIB received on an SSB of the cell may be used to indicate that the that the cell is an on-demand SIB1 cell. For example, where a spare bit or repurposed bit in the MIB is set to 1, that bit may indicate that the cell's SIB1 is only transmitted on an on-demand basis.

[0187] In another example, to indicate to the UE 3 that the cell is an on-demand SIB1 cell, a reserved bit in the PBCH channel may be used indicate that the that the cell is an on-demand SIB1 cell. In yet another example, to indicate to the UE 3 that the cell is an on-demand SIB1 cell, a special code value of the ssb-SubcarrierOffset IE may be used indicate that the that the cell is an on-demand SIB1 cell.

[0188] SIB1 and 'version number' indication transmitted on the same cell 　　Fig. 7 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system 1 of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE 3 are still valid and usable for a cell that the UE 3 has left and re-entered.

[0189] As shown in Fig. 7 there is a RAN node 5Bthat provides a cell (cell B 9B) and a UE 3 deployed in the communication system 1. Although not shown, it will be appreciated that there may also be another RAN node 5Athat provides another cell (e.g., cell A 9A) deployed in the communication system 1.

[0190] The UE 3 may initially attempt to camp on the cell B 9Bto allow communication with the RAN node 5Bat a time t1. For example, at step S702, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0191] Having broadcast the SSB transmissions at step S702, the RAN node 5B, at step S704, sends an appropriate indication to the UE 3 to indicate a current version number value (e.g., a valueTagOfSIB1 IE, or the like) for a SIB1 for the cell B 9Bthat the RAN node 5Bwill broadcast over the cell B 9B.

[0192] In one example, the current version number (e.g., valueTagOfSIB1 IE) may be indicated to the UE 3 using reserved bits in a MIB carried on the PBCH, or alternatively the current version number may be indicated to the UE 3 by re-purposing bits in a MIB carried on the PBCH that are not being used.

[0193] In another example, the current version number may be indicated to the UE 3 using new signalling. For example, the current version number may be indicated to the UE 3 using a new short periodic message / signalling sent by the RAN node 5Bto the UE 3 e.g., a new PDCCH message that provides the current version number to the UE 3.

[0194] In yet another example, the current version number may be indicated to the UE 3 using the PDCCH that is used to schedule the SIB1.

[0195] In yet another example, the current version number may be indicated to the UE 3 in an appropriate response message sent by the RAN node 5Bto the UE 3 in response to the UE 3 sending a WUS message to the RAN node 5B. For example, (not shown) upon initially attempting to camp on the cell B 9Bto allow communication with the RAN node 5Bat a time t1the RAN node 5Bmay be in a reduced energy state and may only broadcast SSBs for detection by the UE 3. Upon receiving those SSBs, the UE 3 may then send an appropriate WUS message to the RAN node 5Bbased on a WUS configuration preconfigured at the UE 3 or received by the UE 3 at some earlier time (not shown). In response to that WUS message, the RAN node 5Bmay send an appropriate WUS response message to confirm reception of the WUS message. The RAN node 5Bmay include the current version number for the SIB1 for the cell B 9Bin that WUS response message.

[0196] At step S706, the RAN node 5Bmay transmit periodic or on-demand SIB1 transmissions to the UE 3. It will be appreciated that where the transmissions are on-demand, the UE 3 may first perform an appropriate procedure to request the transmission of an on-demand SIB1 from the RAN node 5B(not shown).

[0197] By way of example only, where the SIB1 transmission is on-demand, the UE 3 may send an appropriate request message to the RAN node 5Bto indicate to the RAN node 5Bthat the UE 3 wishes to receive an on-demand SIB1 transmission in the cell B 9Bprovided by the RAN node 5Busing a specific set of resources. In response to that request message, the RAN node 5Bmay transmit an on-demand SIB1 to the UE 3 in the cell B 9B.

[0198] It will nevertheless be appreciated that the use of a request message as described above is by way of example only and that any appropriate on-demand SIB1 procedure may be performed between the UE 3 and the RAN node 5Bto facilitate the transmission of an on-demand SIB1 from the RAN node 5Bto the UE 3.

[0199] The periodic and / or on-demand SIB1 transmitted by the RAN node 5Bto the UE 3 at step S706 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which the SIB1 is applicable.

[0200] Additionally, the SIB1 may include other appropriate information, for example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0201] It will be appreciated that, SIB1 may also include the version number (e.g., in a valueTagOfSIB1 IE, or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That version number allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version numbers the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31.

[0202] Having received the SIB1 at step S706, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S707).

[0203] At some time t2the UE 3 may move out of the cell coverage area of the cell B 9Bprovided by RAN node 5Band into the cell coverage area of a neighbouring / overlapping cell (e.g., cell A 9A) provided by the same or another RAN node 5A.

[0204] At some time t3after t2, the UE 3 may return to the cell coverage area of cell B 9Bprovided by RAN node 5B.

[0205] Having moved back into the cell coverage area of the cell B 9B, the UE 3 may attempt to camp back onto the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (not shown). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0206] Having received the MIB for the cell B 9B, prior to attempting to receive and / or decode a SIB1 from the RAN node 5B, the UE 3 may receive from the RAN node 5Ban indication indicating the current version number (e.g. valueTagOfSIB1 value) of SIB1 for the cell B 9Bthat will be broadcast by the RAN node 5Bover the cell B 9B.

[0207] As described above with reference to step S704, in one example, the current version number of SIB1 may be indicated to the UE 3 using reserved bits in MIB carried on the PBCH, or alternatively it may be indicated to the UE 3 by re-purposing bits in MIB carried on the PBCH that are not being used.

[0208] In another example, the current version number of SIB1 may be indicated to the UE 3 using a new dedicated signalling. For example, it may be indicated to the UE 3 using a new short periodic message / signalling sent by the RAN node 5Bto the UE 3 e.g., a new PDCCH message that provides the current version number of SIB1 to the UE 3.

[0209] In another example, the current version number of SIB1 may be indicated to the UE 3 using the PDCCH that is used to schedule the SIB1.

[0210] In yet another example, the current version number of SIB1 may be indicated to the UE 3 in an appropriate response message sent by the RAN node 5Bto the UE 3 in response to the UE 3 sending a WUS message to the RAN node 5B. For example, (not shown) upon attempting to camp onto the cell B 9Bto allow communication with the RAN node 5Bat a time t1the RAN node 5Bmay be in a reduced energy state and may only broadcast SSBs for detection by the UE 3. Upon receiving those SSBs, the UE 3 may then send an appropriate WUS message to the RAN node 5B. In response to that WUS message, the RAN node 5Bmay send an appropriate WUS response message to confirm reception of the WUS message. The RAN node 5Bmay include in that WUS response message current version number of the SIB1 for the cell B 9B.

[0211] At step S710, having received the indication of the current version number of SIB1 for the cell B 9Bat step S708, the UE 3 may, prior to attempting to receive / decode a SIB1 from the RAN node 5B, check / determine whether the version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 message from the RAN node 5Bat step S708.

[0212] Where it is determined that the version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to (i.e. matches) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 at step S708, the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is still valid and can be used. For example, where it is determined that the SIB1 for cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3, rather than attempting to receive a SIB1 from RAN node 5B, may access that SIB1 from its memory, and use that SIB1 for continuing its camping procedure to camp onto cell B 9B(at step S716). This in turn avoids the need for the UE 3 to unnecessarily monitor for and decode a new SIB1 for the cell B 9B.

[0213] Alternatively, where it is determined that the version number value of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is not equal to (i.e. does not match) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 at step S708, the UE 3 may determine that the SIB1 stored in its memory is not valid and cannot be used.

[0214] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid, the UE 3 attempts to receive a new SIB1 from the RAN node 5B. For example, the UE 3 may send an appropriate SIB1 request message and / or WUS signalling at step S712 to request on-demand transmission of a SIB1 from the RAN node 5Band / or to 'wake-up' the RAN node 5Band trigger it to periodic and / or on-demand SIB1 transmissions to the UE 3 on configured PRACH resources.

[0215] It will also be appreciated, that the WUS message, as well as triggering the RAN node 5Bto 'wake up', may also contain appropriate information to request that the RAN node 5Btransmit a SIB1 to the UE 3 either periodically or on an on-demand basis once it has woken up. In this scenario, it will be appreciated that a separate on-demand SIB1 request message may not need to be sent to the RAN node 5B.

[0216] The UE 3 may then attempt to receive a new periodic SIB1 or on-demand SIB1 transmission from the RAN node 5Bat step S714. At the same time, the UE 3 may discard the invalid SIB1 for the cell B 9Bstored in its memory to make additional room for the storage of the new SIB1 it is to receive from the RAN node 5B.

[0217] It will be appreciated that to determine whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3 must first correctly identify the cell provided by the RAN node 5Bthat it is attempting to camp on.

[0218] Typically, such cells are globally uniquely identified by an indication of a PLMN identifier and the cell's own unique identifier. Such indications however are typically obtained from a SIB1 transmitted over the cell, and thus in the procedure described above such indications will not be available to the UE 3 before the UE 3 either obtains a SIB1 from the RAN node 5Bor determines whether SIB1 stored in its memory is valid for the cell B 9B. Therefore, the cell B 9Bmay be identified by the UE 3 using its physical cell ID (PCI) in the SSB transmissions from the RAN node 5B. In addition, the version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5A at step S712 may also be associated with the PCI of the cell B 9B. However, where multiple cells are provided within a larger serving cell, those multiple cells may share a single PCI, and thus the UE 3 may not be able to identify the correct cell (i.e., cell B 9B) where there are multiple cells with the same PCI.

[0219] To assist the UE 3 to correctly identify the cell, in one example, the stored SIB1 in the memory of the UE 3 that was transmitted to the UE 3 by the RAN node 5Bwhen the UE 3 was initially camped on cell B 9B, may include other appropriate information and parameters to assist in identifying that cell to which the SIB applies. For example, the SIB1 may include: -　　Information of the frequency of cell B 9Bto which the SIB1 is applicable (e.g., a frequency of the SSB provided over the cell and / or a frequency reference point for the cell); -　　Information of the subcarrier spacing (SCS) of the cell B 9Bto which the SIB1 is applicable; -　　An indication of which coverage area the cell B 9Bto which the SIB1 is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such an indication is provided, the UE 3, upon receiving the SIB1 may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A. -　　An indication of the best SSBs of which coverage area the cell B 9Bto which the SIB1 is applicable is within, and a (pre)configured RSRP threshold value for that coverage area.

[0220] It will be appreciated that where indications such as those listed above are identified by the UE 3 (e.g., SSB of cell A 9A) or provided in a stored SIB1 they may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the stored SIB1 may be used by the UE 3, in conjunction with a PCI, to correctly identify the cell B 9Bbeing provided by the RAN node 5B.

[0221] It will be appreciated that version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S712 may be associated with the PCI of the cell B 9B, and furthermore associated with some / all of the above listed information, which may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the version number being provided by the RAN node 5A.

[0222] It will be appreciated that when determining whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the stored SIB1 may only be considered valid if, in addition to having the correct version number, the stored SIB1 also has associated indications such as those listed above that match (correspond) with the cell B 9Bbeing provided by the RAN node 5Bat time t3.

[0223] In another example, rather than providing extra indications in SIB1 as indicated above, two new bits may be introduced in the SSBs that may be used in conjunction with the PCI in the SSB to assist the UE 3 in correctly identifying a cell B 9Bbeing provided by the RAN node 5B.

[0224] SIB1 and 'version number' indication transmitted on the same cell: On-demand 'version number' indication 　　Fig. 8 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system 1 of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE 3 are still valid and usable for a cell that the UE 3 has left and re-entered.

[0225] As shown in Fig. 8 there is a RAN node 5Bthat provides a cell (cell B 9B) and the UE 3 deployed in the communication system 1. Although not shown, it will be appreciated that there may also be another RAN node 5Athat provides another cell (e.g., cell A 9A) deployed in the communication system 1.

[0226] The UE 3 may initially attempt to camp onto the cell B 9Bto allow communication with RAN node 5Bat a time t1. For example, at step S802, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0227] At step S804, the RAN node 5Bmay broadcast periodic or on-demand SIB1 transmissions. It will be appreciated that where the transmissions are on-demand, the UE 3 may first perform an appropriate procedure to request the transmission of an on-demand SIB1 from the RAN node 5B(not shown). By way of example, the UE 3 may send an appropriate message (e.g., an explicit on-demand SIB request, a WUS, and / or the like) to the RAN node 5Bto indicate to the RAN node 5Bthat the UE 3 wishes to receive an on-demand SIB1 transmission over the cell B 9Busing a specific set of resources. In response to that message, the RAN node 5Bmay transmit an on-demand SIB1 over the cell B 9B. It will nevertheless be appreciated that the use of an explicit SIB1 request message as described above is by way of example only and that any appropriate on-demand SIB1 procedure may be performed between the UE 3 and the RAN node 5Bto facilitate the transmission of an on-demand SIB1 from the RAN node 5Bto the UE 3.

[0228] The periodic and / or on-demand SIB1 broadcast by the RAN node 5Bat step S804 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which the SIB1 is applicable.

[0229] Additionally, the SIB1 may include other appropriate information, for example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0230] Furthermore, SIB1 may also include the new version number IE (e.g., valueTagOfSIB1 IE or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That new IE allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31.

[0231] Having received the SIB1 at step S804, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S805).

[0232] At some time t2the UE 3 may move out of the cell coverage area of the cell B 9Bprovided by the RAN node 5Band into the cell coverage area of a neighbouring cell A 9Aprovided by a neighbouring RAN node 5A.

[0233] At some time t3after t2, the UE 3 may move out of the cell coverage area of the cell A 9Aprovided by the RAN node 5Aand may return to the cell coverage area of the cell B 9Bprovided by the RAN node 5B.

[0234] Having returned to the cell coverage area of the cell B 9B, the UE 3 may attempt to camp on the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (not shown). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0235] Having received the MIB for the cell B 9B, prior to attempting to receive and / or decode a SIB1 from the RAN node 5B, the UE 3 may send an appropriate request message (e.g., a SIB1 version number request message, or the like) to the RAN node 5Bto request that the RAN node 5Bsend the UE 3 the version number of the most recent SIB1 for the cell B 9B.

[0236] In response to the appropriate message sent at step S806, the RAN node 5Bmay respond to the message at step S808 by sending an appropriate response message to the UE 3. For example, the RAN node 5Bmay send a response message (e.g., a SIB1 version number message, or the like) indicating the version number of the most recent SIB1 for the cell B 9Bto the UE 3.

[0237] At step S810, the UE 3, having received the SIB1 version number message at step S808, may check / determine whether a version number of the latest SIB1 that will be provided by the RAN node 5Bover the cell B 9Bis equal to the version number of the SIB1 for the cell B 9Bstored in the memory of the UE 3.

[0238] Where it is determined that the version number of SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to (i.e. matches) the latest version number of the SIB1 for the cell B 9Bthat will be provided by the RAN node 5B, the UE 3 may determine that the SIB1 for cell B 9Bstored in its memory is still valid and can be used. For example, where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3, rather than attempting to receive / decode a SIB1 from the RAN node 5B, may access that SIB1 from its memory, and use that SIB1 for continuing its camping procedure to camp on the cell B 9B. For periodic SIB1 transmission, this avoids the need for the UE 3 to unnecessarily monitor for and decode a new SIB1 for the cell B 9B. For on-demand SIB1 transmission this avoids the need for an on-demand SIB1 to be triggered by / for the UE 3 and transmitted by the RAN node 5Band avoids the need for the UE 3 to receive and decode a SIB1 transmitted in the cell B 9B.

[0239] Alternatively, where it is determined that the version number of a SIB1 for cell B 9Bstored in the memory of the UE 3 is not equal to (i.e. does not match) the latest version number of the SIB1 for the cell B 9Bthat will be provided by the RAN node 5B, the UE 3 may determine that the SIB1 for cell B 9Bstored in its memory is not valid and cannot be used.

[0240] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid anymore, the UE 3 attempts to receive a new SIB1 from the RAN node 5B. For example, the UE 3 may monitor for periodic SIB1 transmissions in the cell B 9Band / or may send an appropriate SIB1 request message and / or WUS signalling at step S814 to request on-demand transmission of a SIB1 from the RAN node 5Band / or to 'wake-up' the RAN node 5Band trigger it to send on-demand SIB1 transmissions to the UE 3 on configured PRACH resources.

[0241] It will be appreciated that if the UE 3 does not have a stored SIB1 for cell B 9B, the UE 3 may skip step S806 and S808, directly go to step S812.

[0242] By way of example only, that WUS message, as well as triggering the RAN node 5Bto 'wake up', may also contain appropriate information to request that the RAN node 5Btransmit a SIB1 to the UE 3 either periodically or on an on-demand basis once it has woken up. Alternatively, a separate dedicated message may be transmitted to the RAN node 5Bafter the WUS message to request that the RAN node 5Btransmit a SIB1 to the UE 3 either periodically or on an on-demand basis once it has woken up (e.g., a SIB request message, or the like).

[0243] The UE 3 may then attempt to receive a new periodic SIB1 broadcast or on-demand SIB1 transmission from RAN node 5Bat step S814. At the same time, the UE 3 may discard the invalid SIB1 for the cell B 9Bstored in its memory to make additional room for the storage of the new SIB1 it is to receive from the RAN node 5B.

[0244] It will be appreciated that to determine whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3 must first correctly identify the cell 9Bprovided by the RAN node 5Bthat it is attempting to camp on.

[0245] Typically, such cells are globally uniquely identified by an indication of a PLMN identifier and the cell's own unique identifier. Such indications however are typically obtained from a SIB1 transmitted over the cell, and thus in the procedure described above such indications will not be available to the UE 3 before the UE 3 either obtains a SIB1 from the RAN node 5Bor determines whether SIB1 stored in its memory is valid for the cell B 9B. Therefore, the cell B 9Bmay be identified by the UE 3 using its physical cell ID (PCI) in the SSB transmissions from the RAN node 5B. In addition, the version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 may also be associated with the PCI of the cell B 9B. However, where multiple cells are provided within a larger serving cell, those multiple cells may share a single PCI, and thus the UE 3 may not be able to identify the correct cell (i.e., cell B 9B) where there are multiple cells with the same PCI.

[0246] To assist the UE 3 to correctly identify the cell, in one example, the stored SIB1 in the memory of the UE 3 that was transmitted to the UE 3 by the RAN node 5Bwhen the UE 3 was initially camped on the cell B 9B, may include other appropriate information and parameters to assist in identifying that cell to which the SIB applies. For example, the SIB1 may include: -　　Information of the frequency of the cell B 9Bto which the SIB1 is applicable (e.g., a frequency of the SSB provided over the cell B 9Band / or a frequency reference point for the cell B 9B); -　　Information of the subcarrier spacing (SCS) of the cell B 9Bto which the SIB1 is applicable; -　　An indication of which coverage area the cell B 9Bto which the SIB1 is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such an indication is provided, the UE 3, upon receiving the SIB1 may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A. -　　An indication of the best SSBs of which coverage area the cell B 9Bto which the SIB1 is applicable is within, and a (pre)configured RSRP threshold value for that coverage area.

[0247] It will be appreciated that where indications such as those listed above are identified by the UE 3 (e.g., SSB of cell A 9A) or provided in a stored SIB1 they may be used by the UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the stored SIB1 may be used by a UE 3, in conjunction with a PCI, to correctly identify the cell B 9Bbeing provided by the RAN node 5B.

[0248] It will be appreciated that version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 may be associated with the PCI of the cell B 9B, and furthermore associated with some / all of the above listed information, which may be used by a UE 3, in conjunction with a PCI, to correctly identify the associated cell B 9Bof the version number being provided by the RAN node 5A.

[0249] It will be appreciated that when determining whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the stored SIB1 may only be considered valid if, in addition to having the correct version number, the stored SIB1 also has indications such as those listed above that match (correspond) with the cell B 9Bbeing provided by the RAN node 5Bat time t3.

[0250] In another example, rather than providing extra indications in SIB1 as indicated above, two new bits may be introduced in the SSBs that may be used in conjunction with the PCI in the SSB to assist the UE 3 in correctly identifying the cell B 9Bbeing provided by the RAN node 5B.

[0251] SIB1 and 'version number' indication transmitted on the same cell: Network-side validity check 　　Fig. 9 depicts a simplified sequence diagram illustrating another procedure that may be used in the communication system 1 of Fig. 1 to determine whether one or more SIBs stored in the memory of a UE 3 are still valid and usable for a cell that the UE 3 has left and re-entered.

[0252] As shown in Fig. 9 there is a RAN node 5Bthat provides a cell (cell B 9B) and the UE 3 deployed in the communication system 1. Although not shown, it will be appreciated that there may also be another RAN node 5Athat provides another cell (e.g., cell A 9A) deployed in the communication system 1.

[0253] The UE 3 may initially attempt to camp onto the cell B 9Bto allow communication with the RAN node 5Bat a time t1. For example, at step S902, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0254] At step S904, the RAN node 5Bmay broadcast periodic or on-demand SIB1 transmissions. It will be appreciated that where the transmissions are on-demand, the UE 3 may first perform an appropriate procedure to request the transmission of an on-demand SIB1 from the RAN node 5B(not shown, but similar to steps S906, S908, and S910 where UE 3 indicates there is stored / valid SIB1 for the cell B 9B). By way of example, the UE 3 may send an appropriate message (e.g., an explicit on-demand SIB request, a WUS, and / or the like) to the RAN node 5Bto indicate to the RAN node 5Bthat the UE 3 does not have a stored SIB1 for the cell B 9Band wishes to receive an on-demand SIB1 transmission over the cell B 9Bprovided by the RAN node 5Busing a specific set of resources. In response to that request message, the RAN node 5Bmay transmit an on-demand SIB1 to the UE 3 over the cell B 9B. It will nevertheless be appreciated that the use of an explicit SIB1 request message as described above is by way of example only and that any appropriate on-demand SIB1 procedure may be performed between the UE 3 and the RAN node 5Bto facilitate the transmission of an on-demand SIB1 from the RAN node 5Bto the UE 3.

[0255] The periodic and / or on-demand SIB1 broadcast by the RAN node 5Bat step S904 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which the SIB1 is applicable.

[0256] Additionally, the SIB1 may include other appropriate information, for example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0257] Furthermore, SIB1 may also include the new version number IE (e.g., valueTagOfSIB1 IE or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That new IE allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31.

[0258] Having received the SIB1 at step S904, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S905).

[0259] At some time t2the UE 3 may move out of the cell coverage area of the cell B 9Bprovided by RAN node 5Band into the cell coverage area of a neighbouring / overlapping cell (e.g., cell A 9A) provided by the same or another RAN node 5A.

[0260] At some future time t3after t2the UE 3 may return to the cell coverage area of the cell B 9Bprovided by the RAN node 5B.

[0261] Having returned to the cell coverage area of the cell B 9B, the UE 3 may attempt to camp on the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (not shown). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0262] Having received the MIB for the cell B 9B, prior to attempting to receive and / or decode a SIB1 from the RAN node 5B, the UE 3 may send a WUS signal (e.g. on PRACH resources) to the RAN node 5Bto 'wake-up' the RAN node 5B.

[0263] In response to the WUS message, at step S908, the RAN node 5Bmay transmit an appropriate response message to the UE 3 to confirm receipt of the WUS message. For example, the RAN node 5Bmay send a random-access response (RAR) type message, or the like, to the UE 3 to indicate to the UE 3 that the RAN node 5Bhas successfully received the WUS message, and that the RAN node 5Bhas 'woken up' and is ready to receive and transmit other messages. It will be appreciated that the RAR-type message sent to the UE 3 at step S908 may also, where appropriate, include an indication of DL and / or UL resources that may be used for the transmission of further messages between the RAN node 5Band the UE 3.

[0264] At step S910, the UE 3 may send an indication of the version number of the SIB1 for the cell B 9Bstored in its memory which it received earlier at step S904. Alternatively, the UE may send a "no valid SIB1 / no stored SIB1" indication e.g., if the UE 3 initially attempts to camp onto the cell B 9Band does not have a stored SIB1 for the cell B 9B, or the stored SIB1 for the cell B 9Bhas been deleted after a defined time period - for example, a SIB1 may be deleted from the memory of the UE 3 where it is determined that the SIB1 has been stored at the UE 3 for a specified period of time / duration. It will be appreciated that the indication of the version number may be sent by the UE 3 in any appropriate message and / or signalling.

[0265] Having received the indication of the version number of the SIB1 for the cell B 9Bstored in the memory of the UE 3 or the "no valid SIB1 / no stored SIB1" indication, the RAN node 5Bmay, at step S912, check / determine whether the version number of the SIB1 for the cell B 9Bstored in the memory of the UE 3 that was indicated to it at step S910 is equal to the version number of the SIB1 for the cell B 9Bthat the RAN node 5Bwill send to the UE 3.

[0266] Where it is determined that the version number of the SIB1 for the cell B 9Bstored in the memory of the UE 3 that was indicated to it at step S910 is equal to (i.e. matches) the version number of the SIB1 for the cell B 9Bthat the RAN node 5Bwill send to the UE 3, the RAN node 5Bmay determine that the SIB1 stored in the memory of the UE 3 is a valid SIB1 for the cell B 9Band that the UE 3 does not need to require SIB1 for the cell B 9Bfrom the RAN node 5B.

[0267] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is valid, the RAN node 5Bat step S918 may send an indication to the UE 3 in an appropriate message to indicate that the SIB1 for the cell B 9Bstored in its memory still valid. In response to that message, the UE 3 may access that SIB1 for the cell B 9Bfrom its memory, and use that SIB1 for the cell B 9Bfor continuing its camping procedure to camp on the cell B 9B(at step S920). This in turn avoids the need for the UE 3 to unnecessarily monitor for and decode a new SIB1 for the cell B 9B.

[0268] It will be appreciated that the message to indicate that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is valid may be optional. For example, UE 3 may be (pre)configured to assume that the SIB1 for the cell B 9Bstored in its memory is valid if, having sent the indication of version number of the SIB1 for the cell B 9Bstored in its memory to the RAN node 5B, the UE 3 does not receive a response from the RAN node 5Bwithin a predefined period of time.

[0269] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid, or there is no stored SIB1 for the cell B 9B, the RAN node 5Bat step S914 may send an indication to the UE 3 in an appropriate message to indicate that the SIB1 for the cell B 9Bstored in its memory is no longer valid. In response to that message, the UE may await to receive a new SIB1 for the cell B 9Bfrom the RAN node 5Bat step S916.

[0270] It will be appreciated that the message to indicate that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid may be optional. For example, the UE 3 may be (pre)configured to assume that the SIB1 for the cell B 9Bstored in its memory is not valid if, having sent the indication of version number of the SIB1 for the cell B 9Bstored in its memory to the RAN node 5B, the UE 3 does not receive a response from the RAN node 5Bwithin a predefined period of time.

[0271] It will be appreciated that to determine whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3 must first correctly identify the cell provided by the RAN node 5Bthat it is attempting to camp on.

[0272] Typically, such cells are globally uniquely identified by an indication of a PLMN identifier and the cell's own unique identifier. Such indications however are typically obtained from a SIB1 transmitted over the cell, and thus in the procedure described above such indications will not be available to the UE 3 before the UE 3 either obtains a SIB1 from the RAN node 5Bor determines whether SIB1 stored in its memory is valid for the cell B 9B. Therefore, the cell B 9Bmay be identified by the UE 3 using its physical cell ID (PCI) in the SSB transmissions from the RAN node 5B. In addition, the version number of the SIB1 for the cell B 9Bindicated to the UE 3 in the SI it received from the RAN node 5Aat step S512 may also be associated with the PCI of the cell B 9B. However, where multiple cells are provided within a larger serving cell, those multiple cells may share a single PCI, and thus the UE 3 may not be able to identify the correct cell (i.e., cell B 9B) where there are multiple cells with the same PCI.

[0273] To assist the UE 3 to correctly identify the cell, in one example, the stored SIB1 in the memory of the UE 3 that was transmitted to the UE 3 by the RAN node 5Bwhen the UE 3 was initially camped on the cell B 9B, may include other appropriate information and parameters to assist in identifying that cell to which the SIB applies. For example: -　　A detected frequency of the cell B 9B(e.g., a frequency of the SSB provided over the cell B 9Band / or a frequency reference point for the cell B 9B); -　　A detected subcarrier spacing (SCS) of the cell B 9B; -　　A detected coverage area under which the cell B 9Bto which the SIB1 is applicable is within. For example, the indication may indicate that the cell B 9Bis within the coverage area of a larger cell A 9A. Where such a check is required, the UE 3 may be configured to check whether the RSRP value of the larger cell A 9Ais greater than a (pre)configured threshold value to determine whether the UE 3 is still under the coverage of the larger cell A 9A. -　　A detected best SSBs of the larger cell A 9Aunder which the cell B 9Bto which the SIB1 is applicable is within, and a (pre)configured RSRP threshold value for that coverage area.

[0274] It will be appreciated that where information such as that listed above requires checking by the UE 3 they may be used by the UE 3, in conjunction with a PCI, to correctly identify the cell B 9Bbeing provided by the RAN node 5B.It will be appreciated that when determining whether a SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the stored SIB1 may only be considered valid if, in addition to having the correct version number, the stored SIB1 also has indications such as those listed above that match (correspond) with the cell B 9Bbeing provided the by RAN node 5Bat time t3.

[0275] In another example, rather than providing extra indications in SIB1 as indicated above, two new bits may be introduced in the SSBs that may be used in conjunction with the PCI in the SSB to assist the UE 3 in correctly identifying a cell being provided by the RAN node 5B.

[0276] SIB1 and 'version number' indication both transmitted on a neighbouring cell 　　Fig. 10 depicts a simplified sequence diagram illustrating yet another procedure that may be used in the communication system 1 of Fig. 1 to determine whether one or more SIBs stored in the memory of the UE 3 are still valid and usable for a cell that the UE 3 has left and re-entered.

[0277] As shown in Fig. 10, a RAN node 5Athat provides a first cell (cell A 9A, which may be an anchor cell such as a neighbour / coverage cell), another RAN node 5Bthat provides a second cell (cell B 9B), and the UE 3 may be deployed in the communication system 1.

[0278] The UE 3 may initially attempt to camp on the cell B 9Bto allow communication with RAN node 5Bat a time t1. For example, at step S1002, the RAN node 5Bbroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell (cell B 9B) - e.g., parameters required for acquiring SIB1 which carries other minimum system information (i.e., RMSI).

[0279] At step S1004, the RAN node 5Bmay send a SIB1 for the cell B 9Bprovided by RAN node 5Bto the RAN node 5Aover the Xn interface between RAN node 5Band RAN node 5Ausing an appropriate Xn application protocol message, e.g., an XnAP setup request message or the like as part of an Xn setup procedure. Effectively, this message requests RAN node 5Ato broadcast SIB1 for cell B 9B. The recipient RAN node 5Amay decide to broadcast the received SIB1 for the cell B 9Beither periodically or on-demand.

[0280] The SIB1 for the cell B 9B.may include appropriate information. For example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0281] Furthermore, a version number (e.g., valueTagOfSIB1 IE or the like) of the SIB1 for cell B 9Bmay also be sent to the RAN node 5A, which is incremented by 1 each time the contents of SIB1 for the cell B 9Bis changed. The version number allows the UE 3 to identify whether changes to SIB1 for cell B 9Bhave occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31. For example, in the procedure of Fig. 10, the SIB1 transmitted to the UE 3 at step S1004 has a version number of 8.

[0282] In the example of Fig. 10, the MSI for accessing the corresponding cell 9 (e.g., cell B 9B) may include an indication that the SIB1 for the corresponding cell 9 (e.g., cell B 9B) will not be broadcast by the RAN node 5 (e.g., RAN node 5B) providing the corresponding cell, but that the SIB1 must be obtained from another RAN node 5 (e.g., RAN node 5A).

[0283] At step S1006, the RAN node 5Amay broadcast SIB1 for the cell A 9Awhich may be detected by the UE 3. The SIB1 for the cell A 9Abroadcast by the RAN node 5Aat step S1006 may contain appropriate information of the cell A 9Aand appropriate SI scheduling information (i.e. siSchedulingInfo) of Cell A's other SI.

[0284] Furthermore, SIB1 for the cell A 9Abroadcast by the RAN node 5Amay also include a version number (e.g., valueTagOfSIB1 IE or the like) which is incremented by 1 each time the contents of SIB1 for the cell A 9Ais changed. The version number allows the UE 3 to identify whether changes to SIB1 for the cell A 9Ahave occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different. The new version number IE may, by way of example only, have any value between 0 to 31.

[0285] In this example, the SIB1 for the cell A 9A(or another new SIB) broadcast by RAN node 5Amay also include a new IE to indicate information related to SIB1s associated with other cells provided by other RAN nodes 5 (e.g., IE otherCellSIB1SchedulingInfoList, or the like). For example, in the case of the procedure shown in Fig. 10, the new IE to indicate information related to SIB1s associated with other cells provided by other RAN nodes 5 may include appropriate information about the SIB1 for the cell B 9Bthat the RAN node 5Areceived from the RAN node 5Bat step S1004. In particular, the information related to each SIB1 associated with another cell in SIB1 for cell A 9Amay respectively include: a cell identity of the cell with which that SIB1 is associated; a version number (e.g., valueTagOfSIB1 IE or the like) associated with that SIB1; and corresponding scheduling information (e.g., mapping information for mapping each SIB1 to corresponding system information / a corresponding SI message to be transmitted by the RAN node 5Aand the BroadcastStatus (i.e. whether it is broadcast periodically or on-demand).

[0286] Having received the SIB1 for the cell A 9Afrom the RAN node 5Aat step S1006, the UE 3 may, at step S1007, store the SIB1 for the cell A 9Ain its memory.

[0287] At step S1008, the RAN node 5Amay broadcast, one or more periodic or on-demand SI messages comprising one or more appropriate containers (which may be a transparent container) for providing a respective SIB1 for each of one or more other cells (i.e., including SIB1 for the cell B 9Bthat was sent to the RAN node 5Aat step S1004 by the RAN node 5Bover the Xn interface).

[0288] Having received the one or more SI messages from the RAN node 5Aat step S1008, the UE 3 may, at step S1009, identify the SI message / container carrying SIB1 for the cell B 9Bbased on the associated mapping information and may store SIB1 for the cell B 9Bin its memory at step S1009.

[0289] At step S1010, the SIB1 for the cell B 9Bmay change. In response to the change of SIB1 for cell B 9Bthe corresponding version number for that SIB1 will be incremented by 1, and the RAN node 5Bmay send, at step S1012, the updated SIB1 for the cell B 9Bto the RAN node 5Avia an appropriate message over e.g., the Xn interface. For example, in the procedure of Fig. 10, the updated SIB1 for the cell B 9Btransmitted to the RAN node 5Aat step S1012 has an updated version number of 9.

[0290] Following the RAN node 5Bsending the updated SIB1 for the cell B 9Bto the RAN node 5A, the RAN node 5Bmay be triggered to send an appropriate paging message, at step S1014, to the UE 3 to indicate to the UE 3 that the system information of the cell A 9A(including SI containing the SIB1 for cell B 9B) has been updated. Additionally, or alternatively, at step S1016 the RAN node 5Amay be triggered (e.g., upon receiving the updated SIB1 for the cell B 9B) to send an appropriate paging message to the UE 3 to indicate to the UE 3 that the system information of cell B 9B(including SIB1 for the cell B 9B) has been updated.

[0291] At step S1018 the RAN node 5Amay broadcast an updated SIB1 for cell A 9Awhich may be detected by the UE 3.

[0292] The updated SIB1 for the cell A 9A(or a new SIB) broadcast by the RAN node 5Amay also include an updated version of the IE to indicate information related to SIB1s associated with other cells provided by other RAN nodes 5 (e.g., an updated version of the IE otherCellSIB1SchedulingInfoList, or the like). For example, in the case of the procedure shown in Fig. 10, the new IE to indicate SIB1s associated with other cells provided by other RAN nodes 5 may include appropriate updated information about the SIB1 for cell B 9Bthat the RAN node 5Areceived from the RAN node 5Bat step S1004. In particular, the updated information related to SIB1 for the cell B 9Bprovided in SIB1 for the cell A 9Amay include: the cell identity for the cell B 9B; an updated version number (e.g., valueTagOfSIB1 IE or the like) associated with SIB1 for the cell B 9B; and corresponding scheduling information (e.g., mapping information for mapping SIB1 for the cell B 9Bto corresponding system information / a corresponding SI message to be transmitted by the RAN node 5A).

[0293] Having received the updated SIB1 for the cell A 9A(or a new SIB) at step S1018, the UE 3 may store the updated SIB1 it received from the RAN node 5Ain its memory (not shown).

[0294] At step S1020, the RAN node 5Amay broadcast, one or more periodic or on-demand SI messages comprising one or more appropriate containers (which may be a transparent container) for providing a respective SIB1 for each of one or more other cells (i.e., including the updated SIB1 for the cell B 9Bthat was sent to the RAN node 5Aat step S1012 by the RAN node 5Bover the Xn interface).

[0295] Having received the one or more SI messages from the RAN node 5Aat step S1020, the UE 3 may identify the SI message / container carrying SIB1 for the cell B 9Bbased on the associated mapping information and may store the updated SIB1 for the cell B 9Bin its memory at step S1009.

[0296] The remainder of the procedure is shown in Fig. 10B.

[0297] At some time t2the UE 3 may move out of the cell coverage area of the cell B 9Bprovided by the RAN node 5B.

[0298] Then, at some time t3after t2the UE 3 may return to the cell coverage area of the cell B 9Bprovided by the RAN node 5B. Having returned to the cell coverage area of the cell B 9B, the UE 3 may attempt to camp on the cell B 9B. For example, the RAN node 5Bmay broadcast SSBs for detection by the UE 3 (at step S1022). As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell B 9B(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0299] As already indicated above in the example of Fig. 10, the MSI for accessing the corresponding cell 9 (e.g., cell B 9B) may include an indication that the SIB1 for the corresponding cell 9 (e.g., cell B 9B) will not be broadcast by the RAN node 5 (e.g., RAN node 5B) providing the corresponding cell, but that the SIB1 must be obtained from a neighbouring RAN node 5 (e.g., RAN node 5A). Therefore, having determined that the SIB1 for the cell B 9Bwill not be broadcast by the RAN node 5B, the UE 3, may monitor for broadcast periodic or on-demand transmissions of the SIB1 for cell A 9Afrom the RAN node 5A.

[0300] At step S1024 the RAN node 5Amay broadcast SIB1 for the cell A 9A(or a new SIB) which may be detected by the UE 3. As described above, that SIB1 for the cell A 9A(or the new SIB) may include the IE to indicate information related to SIB1s associated with other cells provided by other RAN nodes 5 (e.g., IE otherCellSIB1SchedulingInfoList, or the like). For example, the IE to indicate information related to SIB1s associated with other cells provided by other RAN nodes 5 may include appropriate information about the SIB1 for the cell B 9Bthat the RAN node 5Areceived from the RAN node 5Bwhile the UE 3 was out of the coverage of cell B 9B. In particular, the information related to each SIB1 associated with another cell in SIB1 for the cell A 9Amay respectively include: a cell identity of the cell with which that SIB1 is associated; a version number (e.g., valueTagOfSIB1 IE or the like) associated with that SIB1; and corresponding scheduling information (e.g., mapping information for mapping each SIB1 to corresponding system information / a corresponding SI message to be transmitted by the RAN node 5A).

[0301] Having received the SIB1 for the cell A 9Aand / or the new SIB from the RAN node 5Athe UE 3 may check / determine whether a version number of the SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to the latest version number of SIB1 for the cell B 9Bindicated to the UE 3 in the information related to SIB1s associated with other cells (e.g., in the IE otherCellSIB1SchedulingInfoList, or the like) that it received from RAN node 5Aat step S1024 (in the SIB1 for the cell A 9Aand / or the new SIB).

[0302] Where it is determined that the version number of SIB1 for the cell B 9Bstored in the memory of the UE 3 is equal to (i.e. matches) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in SIB1 for the cell A 9Areceived from the RAN node 5Aat step S1024 while it was camped on the cell A 9A, the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is still valid and can be used. For example, where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is still valid, the UE 3, rather than attempting to receive / decode a SIB1 for the cell B 9Bin an SI message received from RAN node 5A, may access that SIB1 from its memory, and use that SIB1 (at step S1032) for continuing its camping procedure to camp on the cell B 9B. This in turn avoids the need for the UE 3 to unnecessarily monitor for and decode SIB1 for the cell B 9B.

[0303] Alternatively, where it is determined that the version number of a SIB1 for the cell B 9Bstored in the memory of the UE 3 is not equal to (i.e. does not match) the latest version number of the SIB1 for the cell B 9Bindicated to the UE 3 in in SIB1 for the cell A 9Areceived from the RAN node 5Aat step S1024, the UE 3 may determine that the SIB1 for the cell B 9Bstored in its memory is not valid and cannot be used.

[0304] Where it is determined that the SIB1 for the cell B 9Bstored in the memory of the UE 3 is not valid, the UE 3 attempts to receive a new SIB1 for cell B from the RAN node 5A. For example, the UE 3 may obtain the SIB1 for the cell B 9Bfrom a periodic or on-demand SI message, comprising an appropriate container (which may be a transparent container) for providing SIB1 for the cell B 9B, sent at S1030 by the RAN node 5A.

[0305] It will be appreciated that, where the SI message sent at S1030 is provided on-demand, the UE 3 may send an appropriate SIB1 and / or SI request message, as indicated at step S1028 (e.g., using a configured PRACH channel or the like), to the RAN node 5Ato trigger transmission of the associated SI message.

[0306] The UE 3 may discard the invalid SIB1 for the cell B 9Bstored in its memory to make additional room for the storage of the new SIB1 it is to receive from the RAN node 5A.

[0307] SIB1 Sharing Across Multiple Cells 　　Common SIB1 across multiple cells: Provided over a single cell 　　In addition to the procedures described above with reference to Figs. 5 to 10, the SIB1 messages in those procedures may be configured to be common SIB1 messages that are applicable to multiple cells provided by multiple different RAN nodes 5 in a specific geographic area.

[0308] As shown in Fig. 11, a UE 3 may initially be located within the coverage area of a large serving cell A 9Aprovided by a RAN node 5A. Within that large serving cell A 9Athere may also be several smaller cells provided by other RAN nodes 5 (e.g., cell B 9Band cell C 9Cby RAN node 5Band RAN node 5Crespectively).

[0309] While in coverage area of the serving cell A 9A, the UE 3 may communicate with the RAN node 5Aover that cell and may acquire from the RAN node 5Aall necessary SI via appropriate MIB, SIB1, and SIBx transmissions via an appropriate SI acquisition procedure (e.g., the procedure of Fig 2, or any one of Figs. 5 to 10).

[0310] Where there are multiple small cells such as the cell B 9Band the cell C 9Cprovided by the RAN node 5Band the RAN node 5Crespectively within the coverage area of a larger serving cell such as the cell A 9Aprovided by the RAN node 5A, rather than each RAN node 5A, 5B, 5Cproviding a separate SIB1 containing appropriate system information for the UE 3 to access their corresponding cells (e.g., cell A 9A, cell B 9Band / or cell C 9C), a common SIB1 may beneficially be provided that is configured to be common across all the cells provided by a group of RAN nodes 5 (e.g., RAN nodes 5A, 5B, 5C).

[0311] For example, where there are multiple small cells (e.g., cell B 9Band cell C 9C) under a larger coverage cell (e.g., cell A 9A) as shown in Fig, 11, all those cells may have the same common configuration (except for some exception parameters such as each cell's respective cell identity, PCI, and / or PRACH configuration). In that scenario, the larger coverage cell (e.g., cell A 9A) may broadcast, periodically or on-demand, a common SIB1 applicable to all the cells (e.g., cell A 9A, cell B 9Band / or cell C 9C). That common SIB1 may include an appropriate IE to indicate that it is a common SIB1 and to indicate the cells to which the common SIB1 is applicable. Alternatively, separate dedicated signalling may be provided prior to, or after, the transmission of the common SIB1 to indicate that it is a common SIB1 and to indicate the cells to which it is applicable.

[0312] To support provision of a common SIB1, appropriate procedures / mechanism may be implemented in the communication system 1 to allow modifications / updates of the common SIB1 to be indicated to the UE 3 irrespective of which cell the UE 3 is within at any given time. For example, when the UE 3 is within large serving such as the cell A 9A(e.g., at a time t1as shown in Fig. 11), the RAN node 5Amay send an updated common SIB1 to the UE 3 to provide the UE 3 with a new common SIB1 that takes account of any modifications and / or updates. Nevertheless, the procedures / mechanisms also support the scenario in which, at some other time (e.g., a second time t2as shown in Fig. 11), the UE 3 is within the coverage area of one of the smaller cells (e.g., cell B 9B) and, accordingly, may not be monitoring for an updated SIB1 in the cell A 9A.

[0313] Fig. 12 depicts a simplified sequence diagram illustrating an example procedure that may be used in the communication system 1 of Fig. 1 to provide and use a common SIB1 for multiple cells.

[0314] As shown in Fig. 12 there is provided a RAN node 5Athat may provide a large serving cell A 9A, and a UE 3 deployed in the communication system 1 of Fig. 1. There is also provided a RAN node 5Band a RAN node 5Cthat provide smaller cells (e.g., cell B 9Band cell C 9C) respectively which are within the serving area of the large serving cell A 9Aas shown in Fig. 11.

[0315] The UE 3 may initially attempt to camp on the cell A 9Ato allow communication with the RAN node 5Aat a time t1. For example, at step S1202, the RAN node 5Abroadcasts SSBs for detection by the UE 3. As previously described, those SSBs include a PSS, a SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell A 9A(e.g., parameters required for acquiring SIB1 which carries other minimum system information).

[0316] Having broadcast the SSB transmissions at step S1202, the RAN node 5A, at step S1204, the UE 3 may await to receive periodic SIB1 transmissions from the RAN node 5Aon the resources indicated in the SSBs. That SIB1 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which the SIB1 is applicable.

[0317] Additionally, the SIB1 may include other appropriate information. For example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0318] Furthermore, SIB1 may also include the new version number IE (e.g., valueTagOfSIB1 IE or the like) which is incremented by 1 each time the contents of SIB1 itself is changed. That new IE allows the UE 3 to identify whether changes to SIB1 have occurred. For example, if the UE 3 receives multiple SIB1 from the RAN node 5 over time and those SIB1 have a different version number, the UE 3 can infer that the contents of those SIB1 are different.

[0319] Additionally, that SIB1 may also contain appropriate information to indicate that the SIB1 is common (i.e., applicable to multiple cells). For example, where the SIB1 is a common SIB1 applicable to multiple cells in a specific geographical area such as within the coverage area of the serving cell A 9A, the SIB1 may contain one or more appropriate IEs to indicate to the UE 3 that the SIB1 is a common SIB1 applicable to multiple cells (e.g., provided by multiple different RAN nodes 5). For example, the common SIB1 may include an IE that indicates to the UE 3 a list of cells provided by different RAN nodes 5 to which the SIB1 is applicable.

[0320] Having received the common SIB1 at step S1204, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S1205).

[0321] At step S1208, the RAN node 5Amay send an updated common SIB1 via periodic SIB1 transmissions to the UE 3. That updated common SIB1 may include any number of updated / changed IEs. For example, the common SIB1 may include an updated IE to indicate to the UE 3 an updated list of cells provided by different RAN nodes 5 to which the SIB1 is applicable.

[0322] Having received the updated common SIB1 at step S1208, the UE 3 may store the updated common SIB1 it received from the RAN node 5Ain its memory (at step S1209).

[0323] At some time t2the UE 3 may move out of the cell coverage area of cell A 9Aand into the cell coverage area of a neighbouring cell B 9Bprovided by a neighbouring RAN node 5B.

[0324] While camped on the cell B 9Bhowever, the common SIB1 may be modified / updated by the RAN node 5A(at step S1210). When the common SIB1 is updated, the RAN node 5Amay send an appropriate paging message to all of the RAN nodes 5 for which the common SIB1 is applicable to indicate to UEs 3 served by those RAN nodes 5 that the common SIB1 has been updated. For example, at step S1212, the RAN node 5Amay send an appropriate paging message to both the RAN node 5Band the RAN node 5Cto indicate that the common SIB1 applicable to the cells provided by both those RAN nodes 5 has been updated.

[0325] Following receipt of those paging messages, the RAN node 5Bcurrently in communication with the UE 3 may send / forward an appropriate paging message to the UE 3 to inform it that the common SIB1 has been updated. It will be appreciated that the any other RAN node 5 that also received the paging message may also send / forward an appropriate paging message to any UEs 3 that it serves.

[0326] At step S1216, the UE 3, having received an appropriate paging message indicating that the common SIB1 has been updated, may monitor for SIB1 transmissions from the RAN node 5Aand, at step S1218, may receive from the RAN node 5Aperiodic SIB1 transmissions of the updated common SIB1.

[0327] Common SIB1 across multiple cells: Provided over the multiple cells 　　Fig. 13 depicts a simplified sequence diagram illustrating another example procedure that may be used in the communication system 1 of Fig. 1 provide and use a SIB1 that is applicable to multiple cells.

[0328] As shown in Fig. 13 there is provided a RAN node 5Athat may provide a large serving cell A 9A, and a UE 3 deployed in the communication system 1 of Fig. 1. There is also provided a RAN node 5Band a RAN node 5Cthat provide smaller cells (e.g., cell B 9Band cell C 9C) respectively which are within the serving area of the large serving cell A 9Aas shown in Fig. 11.

[0329] The UE 3 may initially attempt to camp any one of cell A 9A, cell B 9B, or cell C 9cto allow communication with a corresponding RAN node 5 (e.g., RAN node 5A, 5B, or 5C). For example, at step S1202, the RAN nodes 5A, 5B, and 5Cbroadcast SSBs for detection by the UE 3. The SSBs broadcast by each corresponding RAN node 5 include a PSS, an SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the corresponding cell provided by the corresponding RAN node 5 - e.g., parameters required for acquiring SIB1 which carries other minimum system information. For example, the SSBs broadcast by the RAN node 5Ainclude a PSS, an SSS, and a PBCH carrying a MIB that provides at least part of the MSI for accessing the cell A 9A.

[0330] Having broadcast the SSB transmissions at step S1302, at step S1304a, S1304b, or S1304c the UE 3 may await to receive periodic SIB1 transmissions from the one of the RAN nodes 5A, 5B, 5C, on the resources indicated in the SSBs it measured (e.g., if the UE 3 measured the SSBs received from the RAN node 5A, then the UE 3 will await to receive periodic SIB1 transmissions from the RAN node 5A). That SIB1 may contain appropriate information to enable the UE 3 to identify the cell over which the SIB1 was sent, and the cell to which the SIB1 is applicable.

[0331] Additionally, the SIB1 may include other appropriate information. For example, SIB1 may include an appropriate IE (e.g., siSchedulingInfo) that indicates scheduling information for the scheduling of other SI received via other SIBs (e.g., SIB1, SIB2, SIB3, etc.). An example of some of the sub-IEs associated with siSchedulingInfo are outlined above in Table 2 and its corresponding description.

[0332] Furthermore, the SIB1 may include an appropriate IE to indicate other cells for which the SIB1 is applicable. For example, where the SIB1 is broadcast over the cell A 9A, that SIB1 may include an appropriate IE to indicate that the SIB1 is also applicable to the cell B 9Band / or the cell C 9C. Similarly, where the SIB1 is broadcast over the cell B 9B, that SIB1 may include an appropriate IE to indicate that the SIB1 is also applicable to the cell A 9Aand / or the cell C 9C, and where the SIB1 is broadcast over cell C 9A, that SIB1 may include an appropriate IE to indicate that the SIB1 is also applicable to the cell B 9Band / or the cell A 9A.

[0333] Having received the SIB1 at step S1304, the UE 3 may store the SIB1 it received from the RAN node 5Bin its memory (at step S1305).

[0334] At some time later, the UE 3 may move from the coverage of the cell A 9A, to the coverage of another cell such as the cell B 9Bor the cell C 9Cprovided by the RAN node 5Band RAN node 5C, respectively.

[0335] At step S1306, having moved to another cell, the UE 3, prior to attempting to obtain a new SIB1 for the cell that it has moved to, may determine whether one or more SIB1 stored in its memory are equally applicable to the cell to which it has moved. For example, if the UE 3 moves to the cell B 9Bthe UE 3 may determine whether a SIB1 stored in its memory that it received over a different cell (e.g., cell A 9A) is nevertheless applicable to the cell B 9Bbased on the IE in the SIB1 that indicates other cells for which the SIB1 is applicable. By way of example, where the IE in a SIB1 received over the cell A 9Aby the UE 3 and stored in its memory indicates that it is also applicable to e.g., the cell B 9B, the UE 3 may access and use that SIB1 after moving to the cell B 9Brather than attempting to obtain a new SIB1 for the cell B 9B, from the RAN node 5B.

[0336] SIB1AreaID 　　In the examples described above with reference to Figs. 12 and 13, the SIB1 broadcast by the RAN nodes 5 (e.g., RAN node 5A, 5Band / or 5C) may alternatively or additionally include other appropriate IEs to indicate a group and / or area of cells to which the SIB1 is applicable (e.g., a SIB1AreaID IE, or the like).

[0337] In that scenario, having received and stored a SIB1 in its memory when camped onto a cell (e.g., any one of cell A 9A, cell B 9B, or cell C 9Cof Figs. 11), when a UE 3 moves between cells, prior to receiving a new SIB1 for a corresponding cell to which the UE 3 has moved, the UE 3 may first receive an indication of an area ID (e.g., SIB1 area ID) of the corresponding cell. Having received the indication of the area ID (e.g., SIB1 area ID) of the corresponding cell, the UE 3 may then subsequently determine whether a SIB1 stored in its memory is applicable to the cell it has moved to, if the IEs to indicate a group and / or area of cells to which the SIB1 is applicable in said SIB1 (e.g., a SIB1AreaID IE, or the like). is equal to (i.e., matches) the indication of the area ID (e.g., SIB1 area ID) that the UE 3 received upon camping on the cell.

[0338] The area ID (e.g., SIB1 area ID) may be indicated to the UE 3 upon camping on a cell using reserved bits in a MIB carried on the PBCH, or alternatively 3 by re-purposing bits in a MIB carried on the PBCH that are not being used. Alternatively, the area ID (e.g., SIB1 area ID) may be indicated to the UE 3 using new dedicated signalling. For example, the area ID may be indicated to the UE 3 using a new short periodic message / signalling sent by the RAN node 5B to the UE 3 e.g., a new PDCCH message that provides the current version number to the UE 3. Alternatively, the area ID (e.g., SIB1 area ID) may be indicated to the UE 3 using the PDCCH that is used to schedule the SIB1.

[0339] Devices of the Communication System User Equipment 　　Fig. 14 is a simplified block schematic illustrating the main components of a UE 3 for implementation in the communication system 1 of Fig. 1.

[0340] 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 antenna 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 (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.

[0341] 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.

[0342] 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 communication 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 communication 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 communication (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 transmissions should be encoded and the like.

[0343] 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.

[0344] The communication control module 43 is configured, in particular, to control the UE's communication, in accordance with any of the methods described herein.

[0345] RAN node 　　Fig. 15 is a simplified block schematic illustrating the main components of a RAN node 5 for implementation in the communication system 1 of Fig. 1.

[0346] As shown, the RAN node 5 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 antenna 53 (e.g., a single or multi-panel antenna array / massive antenna), and a core network interface 55 for transmitting signals to and for receiving signals from network nodes in the core network 7. Although not shown, the RAN node 5 may also be coupled to other RAN nodes5 via an appropriate interface (e.g., the so-called 'X2' interface in LTE or the 'Xn' interface in NR). The RAN node 5 has a controller 57 to control the operation of the RAN node 5. 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 by, in this example, program instructions or software instructions stored within memory 59.

[0347] As shown, these software instructions include, among other things, an operating system 61, and a communication control module 63.

[0348] The communication control module 63 is operable to control the communication between the RAN node 5 and UEs 3 and other network entities (e.g., core network nodes) that communicate with the RAN node 5. The communication control module 63 is configured for the overall control of the reception and decoding of uplink communication, 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 control of the transmission of downlink communication 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-persistent scheduling (e.g., SPS). The communication control module 63 is responsible, for example: for determining where to configure the UE 3 to monitor for downlink control information (e.g., the location of search spaces, CORESETs, and associated PDCCH candidates to monitor); for determining the resources to be scheduled for UE transmission / reception of UL / DL communication (including interleaved resources and resources subject to frequency hopping); for managing frequency hopping at the RAN node side; for configuring slots / symbols appropriately (e.g., for UL, DL or full duplex communication, or the like); for configuring bandwidth parts for the UE 3; for providing related configuration signalling to the UE 3; and the like.

[0349] It will be appreciated that the communication control module 63 may include a number of sub-modules ('layers' or 'entities') to support specific functionalities. For example, the communication control module 63 may include, for communicating with a UE 3, a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc. Moreover, the communication control module 63 may include, for communicating with a core network entity such as an MME (or similar node such as an AMF 10-1), an S1 application protocol (S1-AP) sub-module, a stream control transmission protocol (SCTP) sub-module, an IP sub-module, a layer 1 (L1) sub-module, a layer 2 (L2) sub-module, etc (or corresponding sub-modules for communicating with an AMF 10-1).

[0350] The communication control module 63 is configured in particular, to control the RAN node's communication, in accordance with any of the methods described herein.

[0351] Modifications and Alternatives 　　Detailed examples been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above examples whilst still benefiting from the enhancements embodied therein.

[0352] It will also be appreciated, for example, that description of features of and actions performed by a RAN node / base station (or eNB or gNB), apply equally to distributed type RAN nodes / base stations as to non-distributed type RAN nodes / base stations.

[0353] It will also be appreciated that whilst information elements having specific names have been described differently named information elements but having a similar purpose may be used.

[0354] In the above description the UE and the RAN node 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 disclosed enhancements, 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.

[0355] In the above examples, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the UE or RAN node 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 UE or the RAN node in order to update their functionalities.

[0356] 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.

[0357] 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.

[0358] 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.

[0359] 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 an extended period of time.

[0360] 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; moulds 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.).

[0361] 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.).

[0362] 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.).

[0363] 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.).

[0364] 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.).

[0365] 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.

[0366] 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.

[0367] 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 an extended 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.

[0368] It will be appreciated that IoT technology can be implemented on any communication devices that can connect to a communication network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0369] It will be appreciated that IoT devices are sometimes also referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be appreciated that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the following table. This list is not exhaustive and is intended to be indicative of some examples of machine type communication applications.

[0370]

[0371] Further, the above-described UE categories are merely examples of applications of the technical ideas and exemplary examples described in the present document. Needless to say, these technical ideas and examples are not limited to the above-described UE and various modifications can be made thereto.

[0372] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0373] This application is based upon and claims the benefit of priority from British patent application No. 2405788.7, filed on April 24, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0374] The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes. (Supplementary note 1) 　　A method performed by a mobile device, the method comprising: 　　storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　receiving a latest condition of the SIB1; and 　　determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition. (Supplementary note 2) 　　The method according to supplementary note 1, wherein 　　the determining is performed in a case where the mobile device is moving around an area or moving out and in a cell. (Supplementary note 3) 　　The method according to supplementary note 1 or 2, wherein 　　the condition includes at least one of: 　　　　a version of the SIB1, or 　　　　an area in which the SIB1 is valid. (Supplementary note 4) 　　The method according to any one of supplementary notes 1 to 3, wherein 　　the receiving the latest condition of the SIB1 is performed by receiving at least one of: 　　　　a serving cell of the SIB1, or 　　　　a cell other than the serving cell of the SIB1. (Supplementary note 5) 　　The method according to any one of supplementary notes 1 to 4, further comprising: 　　receiving the SIB1 on at least one of: 　　　　a serving cell of the SIB1, or 　　　　a cell other than the serving cell of the SIB1. (Supplementary note 6) 　　The method according to any one of supplementary notes 1 to 5, further comprising: 　　transmitting a wakeup signal for requesting the SIB1, and wherein 　　the receiving the SIB1 is performed upon the transmitting the wakeup signal. (Supplementary note 7) 　　The method according to supplementary note 6, wherein 　　the transmitting the wakeup signal is performed in a case where the mobile device determines to reacquire the SIB1. (Supplementary note 8) 　　The method according to supplementary note 6 or 7, further comprising: 　　receiving configuration information for transmitting the wakeup signal, and 　　wherein the transmitting the wakeup signal is performed based on the configuration information. (Supplementary note 9) 　　The method according to supplementary note 6 or 7, wherein 　　the transmitting the wakeup signal is performed based on configuration information for transmitting the wakeup signal, and 　　the configuration information is predefined in the mobile device. (Supplementary note 10) 　　The method according to supplementary note 8 or 9, wherein 　　the configuration information is common among a group of cells. (Supplementary note 11) 　　The method according to supplementary note 8, wherein 　　the receiving the configuration information is performed in a case where at least one of: 　　　　the mobile device attempt to reselect a cell for receiving the SIB1, or 　　　　the configuration information is modified. (Supplementary note 12) 　　The method according to any one of supplementary notes 1 to 5, further comprising: 　　transmitting a wakeup signal for requesting the latest condition of the SIB1, and wherein 　　the receiving the latest condition of the SIB1 is performed upon the transmitting the wakeup signal. (Supplementary note 13) 　　The method according to any one of supplementary notes 1 to 12, wherein 　　the information indicating the condition under which the SIB1 is valid is received on at least one of: 　　　　a master information block (MIB), 　　　　another SIB1 of a cell other than the serving cell of the SIB1, 　　　　a short message, 　　　　a physical downlink control channel (PDCCH), or 　　　　a response message of a wakeup signal for requesting the SIB1. (Supplementary note 14) 　　The method according to supplementary note 13, wherein 　　the information indicating the condition under which the SIB1 is valid is received on the another SIB1 of the cell other than the serving cell of the SIB1, and the method comprising: 　　storing the another SIB1 and information indicating another condition under which the another SIB1 is valid; and 　　determining to reacquire the another SIB1 based on whether the another condition indicated by the information meets the latest condition, and wherein 　　the receiving the latest condition of the SIB1 is performed in a case where the mobile device determines to reacquire the another SIB1 including the information indicating the condition under which the SIB1 is valid. (Supplementary note 15) 　　The method according to any one of supplementary notes 1 to 14, further comprising: 　　deleting the SIB1 after a certain time elapsed from when determining not to reacquire the SIB1. (Supplementary note 16) 　　The method according to supplementary note 3, wherein 　　the area is represented by at least one cell. (Supplementary note 17) 　　The method according to supplementary note 16, wherein 　　determining whether the condition indicated by the information meets the latest condition is performed by determining whether a cell which is to transmit the SIB1 is in the area. (Supplementary note 18) 　　The method according to supplementary note 16 or 17, wherein 　　the at least one cell is represented by at least one of: 　　　　information indicating a group of the at least one cell, 　　　　information indicating a list of the at least one cell, or 　　　　an identifier which each of the at least one cell corresponds to. (Supplementary note 19) 　　The method according to any one of supplementary notes 1 to 18, wherein 　　the receiving the latest condition of the SIB1 is via at least one of: 　　　　a master system block (MIB), 　　　　another SIB1 of a cell other than a serving cell of the SIB1, 　　　　a short message, or 　　　　a physical downlink control channel (PDCCH). (Supplementary note 20) 　　The method according to any one of supplementary notes 1 to 19, further comprising: 　　storing information used for identifying a cell where the SIB1 is transmitted. (Supplementary note 21) 　　The method according to supplementary note 8, wherein 　　the configuration information includes information used for identifying a cell where the wakeup signal is to be transmitted. (Supplementary note 22) 　　The method according to supplementary note 20 or 21, wherein 　　the information used for identifying the cell indicates at least one of: 　　　　a frequency of synchronization signal / physical broadcast channel (PBCH) block (SSB) or a reference point of the cell, 　　　　a subcarrier spacing of the cell, 　　　　whether the mobile device is still under coverage area of the cell, 　　　　at least one best SSB of the cell, 　　　　a reference signal received power (RSRP) threshold of the cell, or 　　　　at least one bit added to an identity of the cell. (Supplementary note 23) 　　The method according to any one of supplementary notes 1 to 22, wherein 　　the SIB1 is transmitted on demand. (Supplementary note 24) 　　A method performed by an access network node, the method comprising: 　　providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition. (Supplementary note 25) 　　A mobile device comprising: 　　means for storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　means for receiving a latest condition of the SIB1; and 　　means for determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition. (Supplementary note 26) 　　An access network node comprising: 　　means for providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　means for providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

[0375] 1　　COMMUNICATION SYSTEM 3　　USER EQUIPMENT (UE) 5　　RAN NODE 7　　CORE NETWORK 9　　CELL 10　　CONTROL PLANE FUNCTION (CPF) 10-1　　ACCESS AND MOBILITY MANAGEMENT FUNCTION (AMF) 10-2　　SESSION MANAGEMENT FUNCTION (SMF) 10-N 　　OTHER FUNCTIONS 11　　USER PLANE FUNCTIONS (UPF) 20 　　EXTERNAL DATA NETWORK 31　　TRANSCEIVER CIRCUIT 33　　ANTENNA 35　　USER INTERFACE 37　　CONTROLLER 39　　MEMORY 41　　OPERATING SYSTEM 43　　COMMUNICATION CONTROL MODULE 51　　TRANSCEIVER CIRCUIT 53　　ANTENNA 55　　CORE NETWORK INTERFACE 57　　CONTROLLER 59　　MEMORY 61　　OPERATING SYSTEM 63　　COMMUNICATION CONTROL MODULE

Claims

1. A method performed by a mobile device, the method comprising: 　　storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　receiving a latest condition of the SIB1; and 　　determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

2. The method according to claim 1, wherein 　　the determining is performed in a case where the mobile device is moving around an area or moving out and in a cell.

3. The method according to claim 1 or 2, wherein 　　the condition includes at least one of: 　　　　a version of the SIB1, or 　　　　an area in which the SIB1 is valid.

4. The method according to any one of claims 1 to 3, wherein 　　the receiving the latest condition of the SIB1 is performed by receiving on at least one of: 　　　　a serving cell of the SIB1, or 　　　　a cell other than the serving cell of the SIB1.

5. The method according to any one of claims 1 to 4, further comprising: 　　receiving the SIB1 on at least one of: 　　　　a serving cell of the SIB1, or 　　　　a cell other than the serving cell of the SIB1.

6. The method according to any one of claims 1 to 5, further comprising: 　　transmitting a wakeup signal for requesting the SIB1, and wherein 　　the receiving the SIB1 is performed upon the transmitting the wakeup signal.

7. The method according to claim 6, wherein 　　the transmitting the wakeup signal is performed in a case where the mobile device determines to reacquire the SIB1.

8. The method according to claim 6 or 7, further comprising: 　　receiving configuration information for transmitting the wakeup signal, and 　　wherein the transmitting the wakeup signal is performed based on the configuration information.

9. The method according to claim 6 or 7, wherein 　　the transmitting the wakeup signal is performed based on configuration information for transmitting the wakeup signal, and 　　the configuration information is predefined in the mobile device.

10. The method according to claim 8 or 9, wherein 　　the configuration information is common among a group of cells.

11. The method according to claim 8, wherein 　　the receiving the configuration information is performed in a case where at least one of: 　　　　the mobile device attempt to reselect a cell for receiving the SIB1, or 　　　　the configuration information is modified.

12. The method according to any one of claims 1 to 5, further comprising: 　　transmitting a wakeup signal for requesting the latest condition of the SIB1, and wherein 　　the receiving the latest condition of the SIB1 is performed upon the transmitting the wakeup signal.

13. The method according to any one of claims 1 to 12, wherein 　　the information indicating the condition under which the SIB1 is valid is received on at least one of: 　　　　a master information block (MIB), 　　　　another SIB1 of a cell other than the serving cell of the SIB1, 　　　　a short message, 　　　　a physical downlink control channel (PDCCH), or 　　　　a response message of a wakeup signal for requesting the SIB1.

14. The method according to claim 13, wherein 　　the information indicating the condition under which the SIB1 is valid is received on the another SIB1 of the cell other than the serving cell of the SIB1, and the method comprising: 　　storing the another SIB1 and information indicating another condition under which the another SIB1 is valid; and 　　determining to reacquire the another SIB1 based on whether the another condition indicated by the information meets the latest condition, and wherein 　　the receiving the latest condition of the SIB1 is performed in a case where the mobile device determines to reacquire the another SIB1 including the information indicating the condition under which the SIB1 is valid.

15. The method according to any one of claims 1 to 14, further comprising: 　　deleting the SIB1 after a certain time elapsed from when determining not to reacquire the SIB1.

16. The method according to claim 3, wherein 　　the area is represented by at least one cell.

17. The method according to claim 16, wherein 　　determining whether the condition indicated by the information meets the latest condition is performed by determining whether a cell which is to transmit the SIB1 is in the area.

18. The method according to claim 16 or 17, wherein 　　the at least one cell is represented by at least one of: 　　　　information indicating a group of the at least one cell, 　　　　information indicating a list of the at least one cell, or 　　　　an identifier which each of the at least one cell corresponds to.

19. The method according to any one of claims 1 to 18, wherein 　　the receiving the latest condition of the SIB1 is via at least one of: 　　　　a master system block (MIB), 　　　　another SIB1 of a cell other than a serving cell of the SIB1, 　　　　a short message, or 　　　　a physical downlink control channel (PDCCH).

20. The method according to any one of claims 1 to 19, further comprising: 　　storing information used for identifying a cell where the SIB1 is transmitted.

21. The method according to claim 8, wherein 　　the configuration information includes information used for identifying a cell where the wakeup signal is to be transmitted.

22. The method according to claim 20 or 21, wherein 　　the information used for identifying the cell indicates at least one of: 　　　　a frequency of synchronization signal / physical broadcast channel (PBCH) block (SSB) or a reference point of the cell, 　　　　a subcarrier spacing of the cell, 　　　　whether the mobile device is still under coverage area of the cell, 　　　　at least one best SSB of the cell, 　　　　a reference signal received power (RSRP) threshold of the cell, or 　　　　at least one bit added to an identity of the cell.

23. The method according to any one of claims 1 to 22, wherein 　　the SIB1 is transmitted on demand.

24. A method performed by an access network node, the method comprising: 　　providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

25. A mobile device comprising: 　　means for storing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; 　　means for receiving a latest condition of the SIB1; and 　　means for determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

26. An access network node comprising: 　　means for providing a system information block 1 (SIB1) and information indicating a condition under which the SIB1 is valid; and 　　means for providing a latest condition of the SIB1, wherein 　　the providing the SIB1 and the information indicating the condition under which the SIB1 is valid is performed by providing to a mobile device directly or via another access network node, 　　the providing the latest condition of the SIB1 is performed by providing to the mobile device directly or via the another access network node, and 　　the information indicating the condition under which the SIB1 is valid is used by the mobile device in determining to reacquire the SIB1 based on whether the condition indicated by the information meets the latest condition.

Images