Mobile access node

Abstract

A method for a mobile access node (e.g. a mobile IAB node (mIAB)) in a network. The method comprises broadcasting system information, wherein the system information comprises two or more tracking area

Description

BACKGROUND Field Certain examples of the present disclosure provide one or more techniques for a mobile access node. For example, certain examples of the present disclosure provide one or more techniques for a mobile Integrated Access and Backhaul (IAB) node, in a 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) network. Description of the Related Art Overview of Integrated Access and Backhaul (IAB) In 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR), Integrated Access and Backhaul (IAB) is a technique for providing wireless backhaul as an alternative to a fibre backhaul network. An IAB network comprises IAB nodes, at which wireless resources are shared between wireless backhaul and access links. By means of such a configuration, it is possible to install nodes without the necessity of providing a fibre data connection, thereby allowing speedy and simple roll out of network coverage to locations where no such data connection is available or possible. Due to the limited coverage area of an IAB node, the backhaul network is typically implemented as a multi-hop network with backhaul traffic traversing multiple IAB nodes. Figure 1 shows a two-hop IAB network as described in 3GPP NR Rel-16 and further enhanced in Rel-17. 3GPP 5G Release 16 was the first release comprising the IAB feature. Release 17 comprised enhancements on top of the Release 16 baseline and is now frozen. Work on Release 18 is currently underway to develop and improve features relating to IAB relative to previous Releases, most notably the mobility of IAB nodes. Assumption in previous Releases was that IAB nodes are stationary. Overview of Mobile IAB As noted in the original Release 18 IAB 3GPP Work Item Description (WID), “At the beginning of the work period, RAN3, RAN2 should discuss the potential complexity of a scenario where a mobile IAB node connects to a stationary (intermediate) IAB node, with respect to the scenario where a mobile IAB node connects directly to an lAB-donor.” This topic was discussed in RAN2#119-e and the following was agreed: R2 assumes that Mobile IAB connecting to a stationary (intermediate) IAB node is / can be supported. R2 assumes this can be supported with no (or limited) impact. The assumption in Release 18 is therefore that a mobile IAB node connects to the gNB (Donor DU) either directly or via other IAB nodes which are stationary. There is therefore multi-hop support in Release 18 but the assumption is that intermediate nodes (if any) are stationary. Overview of Radio Resource Control (RRC) idle / inactive idle mode procedures The procedures for a UE in RRC idle mode are illustrated in Figure 2 (which is Figure 5.2.2-1 from 3GPP TS 38.304, V17.2.0). The idle mode procedures include: Public Land Mobile Network (PLMN) selection o The UE scans and reports detected PLMNs to Non Access Stratum (NAS). A PLMN is reported as a high quality PLMN if the measured Reference Signal Received Power (RSRP) value is greater than -110 dBm. - Cell selection o UE selects an (possibly initial) cell based on two criteria known as the cell selection criteria. The UE selects a cell that fulfils the criteria, but if multiple cells satisfy the criteria, it is not specified which of those cells the UE shall select. The criteria are based on the received power level as well as the quality of the signal, which are in turn based on signalled thresholds and measurements. - Cell reselection o Cell reselection is performed for the UE to camp on the most suitable cell. In addition to the cell selection criteria, the UE also ranks different cells of the same priority to choose the best cell. The UE also measures on different frequencies that have either higher or lower priority, which ensures that the UE always camps on the best cell with the highest priority. Location registration and Radio Access Network (RAN) Area Registration o Tracking Area registration - The UE reports the tracking area information to NAS. If a UE camps on a new tracking area, a Tracking Area Update (TAU) is triggered. This can also be done periodically. o RAN Area Registration - The UE performs a RAN-based notification area update when the UE camps on a new cell that does not belong to the current RAN Notification Area (RNA). This can also be done periodically. Overview of RANAC and TAC and related procedures Tracking Areas are utilized by a (core) network to allow for a network to be able to reach a UE when it is idle mode. A UE can in general perform idle mode mobility without indicating to a new cell that it is camping on it. Whenever a UE has entered a new Tracking Area, it will be required to announce its presence using a so-called Tracking Area Update (sometimes also referred to as a mobility registration). This allows the (core) network to be aware within which cell is located in to remain reachable. The Tracking Area Codes are signalled in a cell. What is signalled is the following: -------------------------3GPPTS 38.331 V17.3.0------------------------- - PLMN-ldentitylnfoList The IE PLMN-ldentitylnfoList includes a list of PLMN identity information. PLMN-ldentitylnfoList information element gBBgiBBBOiisTOsisssssssssssssssssssssssiiM SEggggCE (S1PE (1. .mazPLMH) ) PLM'I-Ige-ntitg, tl 4 21 111 1 Till! lllglHdl , issssTSggSsssssssssssssssss IIPij- P ( r¢--5:¢-lived, riutReser.-T-d), Eti iab-Supf-'i-rt-vlg ilsSiTT®gsSi:LLigig{iiigSgjggggg iililililililililill t rstckirigAreaList-rl^ gHSggSggeSggSggggs i iiiiiiiiiiiiiiiiiiiiiii / ii _________________________________PLMN-ldentitylnfo field descriptions_________________________________ cellReservedForOperatorUse Indicates whether the cell is reserved for operator use (per PLMN), as defined in TS 38.304

[20] , This field is ignored by IAB-MT.____________________________________________________________________________________ gNB-ID-Length Indicates the length of the gNB ID out of the 36-bit long cellldentity._____________________________________________ iab-Support This field combines both the support of IAB and the cell status for IAB. If the field is present, the cell supports IAB and the cell is also considered as a candidate for cell (re)selection for lAB-node; if the field is absent, the cell does not support IAB and / or the cell is barred for lAB-node._________________________________________________ trackingAreaCode Indicates Tracking Area Code to which the cell indicated by cellldentity field belongs. The absence of the field indicates that the cell only supports PSCell / SCell functionality (per PLMN) or is an NTN cell.____________________ trackingAreaList List of Tracking Areas to which the cell indicated by cellldentity field belongs. If this field is present, network does not configure trackingAreaCode. Total number of different TACs across different PLMN-ldentitylnfos shall not exceed maxTAC. This field is only present in an NTN cell. -------------------------3GPPTS 38.331 V17.3.0------------------------- When the UE receives reads the SIB1 containing the Tracking Area, the UE will forward the Tracking Areas to upper layers (NAS), which then decides on the course of action according to the following (with emphasis added): -------------------------3GPPTS 38.331 V17.3.0------------------------- 5.2.2.4.2 Actions upon reception of the SIB1 Upon receiving the SIB1 the UE shall: 1> store the acquired SI BL <0MITTED> 1> if the cellAccessRelatedlnfo contains an entry of a selected SNPN or PLMN and in case of PLMN the UE is either allowed or instructed to access the PLMN via a cell for which at least one CAG ID is broadcast: 2> in the remainder of the procedures use npn-IdentityList, trackingAreaCode, and cellldentity for the cell as received in the corresponding entry of npn-IdentitylnfoList containing the selected PLMN or SNPN; 1> else if the cellAccessRelatedlnfo contains an entry with the PLMN-Identity of the selected PLMN: 2> in the remainder of the procedures use plmn-IdentityList, trackingAreaCode, trackingAreaList, and cellldentity for the cell as received in the corresponding PLMN-Identitylnfo containing the selected PLMN; <OMITTED> 1> else: <OMITTED> 2> iffrequencyShift7p5khz is present and the UE supports corresponding 7.5kHz frequency shift on this band; or frequencyShift7p5khz is not present: 3> if neither trackingAreaCode nor trackingAreaList is provided for the selected PLMN nor the registered PLMN nor PLMN of the equivalent PLMN list: 4> consider the cell as barred in accordance with TS 38.304

[20] ; 4> perform cell re-selection to other cells on the same frequency as the barred cell as specified in TS 38.304

[20] ; 3> else if UE is IAB-MT and if iab-Support is not provided for the selected PLMN nor the registered PLMN nor PLMN of the equivalent PLMN list nor the selected SNPN nor the registered SNPN: 4> consider the cell as barred for IAB-MT in accordance with TS 38.304

[20] ; 3> else: 4> apply a supported uplink channel bandwidth with a maximum transmission bandwidth which - is contained within the carrier Bandwidth indicated in uplinkConfigCommon for the SCS of the initial uplink B WP or, for RedCap UEs, RedCap-specific initial uplink B WP, if configured, and which - is wider than or equal to the bandwidth of the initial BWP for the uplink or, for a RedCap UE, of the RedCap-specific initial uplink BWP if configured; 4> apply a supported downlink channel bandwidth with a maximum transmission bandwidth which - is contained within the carrierBandwidth indicated in downlinkConfigCommon for the SCS of the initial downlink B WP or, for RedCap UEs, RedCap-specific initial downlink B WP, if configured, and which - is wider than or equal to the bandwidth of the initial B WP for the downlink or, for a RedCap UE, of the RedCap-specific initial downlink BWP if configured; 4> select the first frequency band in the frequencyBandList, for FDD from frequencyBandList for uplink, or for TDD from frequencyBandList for downlink, which the UE supports and for which the UE supports at least one of the additionalSpectrumEmission values in nr-NS-PmaxList, if present; 4> forward the cellidentity to upper layers; 4> forward the trackingAreaCode to upper layers; 4> forward the trackingAreaList to upper layers, if included; 4> forward the received posSIB-Mappinglnfo to upper layers, if included; 4> forward the PLMN identity or SNPN identity or PNI-NPN identity to upper layers; 4> if in RRCINACTIVE and the forwarded information does not trigger message transmission by upper layers: 5> if the serving cell does not belong to the configured ran-NotificationArealnfo'. 6> initiate anRNA update as specified in 5.3.13.8; 4> forward the ims-EmergencySupport to upper layers, if present; 4> forward the eCallOverlMS-Support to upper layers, if present; 4> forward the UAC-AccessCategoryl-SelectionAssistancelnfo or UAC-ACl-SelectAssistlnfo for the selected PLMN / SNPN to upper layers, if present and set to a, b or c; 4> if the UE is in SNPN access mode: 5> forward the imsEmergencySupportForSNPN indicators with the corresponding SNPN identities to upper layers, if present; 4> apply the configuration included in the servingCellConfigCommon', 4> apply the specified PCCH configuration defined in 9.1.1.3; -------------------------3GPPTS 38.331 V17.3.0------------------------- Overview of RRC idle and RRC inactive procedures RRC inactive is a state in which the UE may move faster to connected mode compared to RRC idle, for example to perform data transmission. The transition to connected mode is faster because the gNB maintains the UE context when the UE is in inactive mode. This means that the UE does not need to re-initiate security and the UE does not need to be fully re-configured whenever the UE re-connects. This mechanism is enabled by the UE being configured with a RAN Notification Area (RNA) where the UE may camp within without having to notify RAN. The UE may perform RRC Resume for Mobile Originated data as long as the RNA remains the same. The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention. SUMMARY It is an aim of certain examples of the present disclosure to address, solve and / or mitigate, at least partly, at least one of the problems and / or disadvantages associated with the related art, for example at least one of the problems and / or disadvantages described herein. It is an aim of certain examples of the present disclosure to provide at least one advantage over the related art, for example at least one of the advantages described herein. The present invention is defined in the independent claims. Advantageous features are defined in the dependent claims. Embodiments or examples disclosed in the description and / or figures falling outside the scope of the claims are to be understood as examples useful for understanding the present invention. Other aspects, advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 (from 3GPP TR 38.874 V16.0.0) illustrates a two-hop IAB network; Figure 2 is Figure 5.2.2-1 from 3GPP TS 38.304, V17.2.0; Figure 3 is Figure 5.3.1-1 from 3GPP TR 23.700-05 V18.0.0; Figure 4 illustrates a scenario resulting in a so-called TAU storm due to updated TAs; Figures 5a and 5b illustrate first and second examples of the present disclosure for signalling tracking areas by a mobile IAB; Figure 6 illustrates a third example of the present disclosure for signalling tracking areas by a mobile IAB; Figures 7a and 7b are flow diagrams of two examples of the present disclosure for handling signalled tracking areas by a UE. Figure 8 is a flow diagram of an example of the present disclosure for selecting a signalled tracking area by a UE; Figures 9a and 9b are signal flow diagrams of examples of the present disclosure for setting up or updating a tracking area by a gNB; and Figure 10 is a block diagram of an exemplary network entity that may be used in certain examples of the present disclosure. DETAILED DESCRIPTION The following description of examples of the present disclosure, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of the present invention, as defined by the claims. The description includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the examples described herein can be made without departing from the scope of the invention. The same or similar components may be designated by the same or similar reference numerals, although they may be illustrated in different drawings. Detailed descriptions of techniques, structures, functions, operations or processes known in the art may be omitted for clarity and conciseness, and to avoid obscuring the subject matter of the present invention. The terms and words used herein are not limited to the bibliographical or standard meanings, but, are merely used to enable a clear and consistent understanding of the invention. Throughout the description and claims of this specification, the words “comprise”, “include” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and / or groups thereof. Throughout the description and claims of this specification, the singular form, for example “a”, “an” and “the”, encompasses the plural unless the context otherwise requires. For example, reference to “an object” includes reference to one or more of such objects. Throughout the description and claims of this specification, language in the general form of “X for Y” (where Y is some action, process, operation, function, activity or step and X is some means for carrying out that action, process, operation, function, activity or step) encompasses means X adapted, configured or arranged specifically, but not necessarily exclusively, to do Y. Features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and / or groups thereof described or disclosed in conjunction with a particular aspect, embodiment, example or claim are to be understood to be applicable to any other aspect, embodiment, example or claim described herein unless incompatible therewith. The skilled person will appreciate that the techniques described herein may be used in any suitable combination. Certain examples of the present disclosure provide one or more techniques for a mobile access node. For example, certain examples of the present disclosure provide one or more techniques for a mobile IAB node, in a 3GPP 5G NR network. However, the skilled person will appreciate that the present invention is not limited to these examples, and may be applied in any suitable system or standard, for example one or more existing and / or future generation wireless communication systems or standards, including any existing or future releases of the same standards specification, for example 3GPP 5G. The functionality of the various network entities and other features disclosed herein may be applied to corresponding or equivalent entities or features in the same or any other suitable communication systems or standards. Corresponding or equivalent entities or features may be regarded as entities or features that perform the same or similar role, function or purpose within the network. For example, the functionality of a base station or the like (e.g. eNB, gNB, NB, RAN node, access point, wireless point, transmission / reception point, central unit, distributed unit, radio unit, remote radio head, etc.) in the examples herein may be applied to any other suitable type of entity performing RAN functions, the functionality of an IAB or the like in the examples herein may be applied to any other suitable type of entity performing a relay, and the functionality of a UE or the like (e.g. electronic device, user device, mobile station, subscriber station, customer premises equipment, terminal, remote terminal, wireless terminal, vehicle terminal, etc.) in the examples herein may be applied to any other suitable type of device. The skilled person will appreciate that the various examples disclosed herein may be implemented using existing messages (e.g. RRC messages) or any other suitable messages. The skilled person will appreciate that the names of messages may vary across different RATs, for example NR and LTE (Evolved Universal Terrestrial Radio Access Network (E-UTRAN)). The skilled person will appreciate that examples disclosed herein referring to message names in one particular RAT (e.g. E-UTRAN) are not limited to that RAT, but may be applied to other RATs (e.g. NR). Certain examples of the present disclosure may be provided in the form of an apparatus / device / network entity configured to perform one or more defined network functions and / or a method therefor. Certain examples of the present disclosure may be provided in the form of a system (e.g. network or wireless communication system) comprising one or more such apparatuses / devices / network entities, and / or a method therefor. A particular network entity may be implemented as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and / or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure. The skilled person will appreciate that the present invention is not limited to the specific examples disclosed herein. For example: • The techniques disclosed herein are not limited to 3GPP 5G. • One or more entities in the examples disclosed herein may be replaced with one or more alternative entities performing equivalent or corresponding functions, processes or operations. • One or more of the messages in the examples disclosed herein may be replaced with one or more alternative messages, signals or other type of information carriers that communicate equivalent or corresponding information. • One or more further elements or entities may be added to the examples disclosed herein. • One or more non-essential elements or entities may be omitted in certain examples. • The functions, processes or operations of a particular entity in one example may be divided between two or more separate entities in an alternative example. • The functions, processes or operations of two or more separate entities in one example may be performed by a single entity in an alternative example. • Information carried by a particular message in one example may be carried by two or more separate messages in an alternative example. • Information carried by two or more separate messages in one example may be carried by a single message in an alternative example. • The order in which operations are performed and / or the order in which messages are transmitted may be modified, if possible, in alternative examples. At least the following problem exist in view of the related art. In the Work Item Description [RP-220843, “Mobile IAB (Integrated Access and Backhaul) for NR”, RAN-P, Qualcomm, March 2022] the following problem statement is included: • Define Procedures for migration / topology adaptation to enable lAB-node mobility, including inter-donor migration of the entire mobile lAB-node (full migration) [RAN3, RAN2] • Enhancements for mobility of an lAB-node together with its served UEs, including aspects related to group mobility. No optimizations for the targeting of surrounding UEs. [RAN3, RAN2] Furthermore, in the SA2 Technical Report 23.700-05 (V18.0.0), Study on architecture enhancements for vehicle-mounted relays, the following Key Issue is stated: -----------------3GPP TR 23.700-05, V18.0.0----------------- 5.3 Key Issue #3: Efficient mobility and service continuity when served by mobile base station relay 5.3.1 General description When the moving vehicles are equipped with mobile base station relays (i.e. lAB-node), the mobile base station relays can provide 5G coverage and communication to UEs (inside the vehicle and / or in its vicinity), and connected wirelessly to the 5G network via lAB-donor gNB. When one or a group of UEs are already served by the mobile base station relay, there are two mobility scenarios to be studied as the following: - Scenario A (mobility within the same lAB-donor gNB): When the UEs are continuously served by a mobile base station relay (e.g. inside the vehicle and / or in its vicinity), this mobile base station relay within the vehicle is moving around within a limited geographical area while keeping connecting with the same lAB-donor gNB. In this case, the UE keeps the connection with the same mobile base station relay (i.e. lAB-node), and there is no change of the lAB-donor gNB as in figure 5.3.1-1. - Scenario B (mobility between different lAB-donor gNBs): When the UEs are continuously served by a mobile base station relay (e.g. inside the vehicle and / or in its vicinity), this mobile base station relay within the vehicle is moving around over a long distance. The mobile base station relay node connects with a different lAB-donor gNB if the vehicle keeps moving. In this case, the UE keeps the connection with the same mobile base station relay (i.e. lAB-node), but there is change of the lAB-donor gNB. NOTE 1: For the above scenarios, whether the cell information in the System Information Broadcast (e.g. Cell ID, TAC) changes has RAN dependency. NOTE 2: For the above scenarios, whether UE needs to perform the legacy handover procedures has RAN dependency. Figure 5.3.1-1: Scenarios for efficient mobility and service continuity The following aspects need to be studied for UEs served by the mobile base station relay in the case of mobility within the same lAB-donor gNB and mobility between different lAB-donor gNBs: - Whether and how to enhance current procedures of mobility and service continuity for a UE or a group of UEs, to efficiently deliver the data. Following aspects need to be considered in potential solutions: - If the TAC in the System Information Broadcast changes, whether and how to enhance the NAS mobility procedure. - If the handover is needed due to cell changes, whether and how to enhance the mobility for group UEs (e.g. during handover). NOTE 3: Mechanisms related to mobility management and service continuity have RAN dependency and should align with the progress of RAN WGs. -----------------3GPP TR 23.700-05, V18.0.0----------------- In the conclusion the following is stated: -----------------3GPP TR 23.700-05, V18.0.0----------------- 8.3 Conclusions for Kl#3 For KI#3, the interim conclusions are as follows: - The UE's mobility management is performed using the legacy mechanism as defined in the TS 23.501 [2] and TS 23.502 [5], The UE in CM-Idle shall follow legacy procedure when detecting a TAC which is not in the TA list. - The TAC broadcasted by the MB SR cell(s) is configured by the Donor gNB and whether this is the same as the one of the cell of the Donor gNB serving the MB SR, or not, will be based on alignment with RAN WGs and SA2 may align specifications if SA WG2 specifications impact is identified. NOTE: Normative work will be based on RAN decisions. - Each UE connected via the MBSR may have different serving AMFs e.g., due to slicing and individual PDU sessions / QoS service flows configured. UE context handling and path switching would be handled per each individual UE. - No normative work for Group mobility of the UEs served by the MBSR. Alignment of specifications may be done only if RAN WGs decide to support this. -----------------3GPP TR 23.700-05, V18.0.0----------------- In RAN3#118 the following was agreed: • Static TAC solution is not pursued. • RAN3 assumes that dynamic TAC solution should be supported. • RAN3 to continue discussions on impacts (if any) of dynamic TAC solutions on RAN3 specs The notion of a dynamic TAC as opposed to a static TAC is that the Tracking Area can be changed for a cell and by extension the mobile IAB. The purpose of this is to ensure that the Tracking Area remains geographically fixed (i.e. fixed with respect to the ground) while the mobile IAB moves around. This is opposed to static TAC, where the TAC would remain with the mobile IAB as it moves around. One problem with having a dynamic TAC is that when the Tracking Area changes, the UEs all have to perform Tracking Area Updates at the same time when the cell changes its Tracking Area. This might be challenging for a network to handle, causing core network congestion and potentially loss of service. An example of this problem can be seen in Figure 4. Another issue is that in the 3GPP work, the following is one of the guiding principles [RP-220843, Mobile IAB Integrated Access and Backhaul for NR, Qualcomm, RAN#95-e, March 2022]: The following principles should be respected: Mobile lAB-nodes should be able to serve legacy UEs. This means that the network will still have to support UEs that are not enhanced, thus any enhancements introduced should not “break” the supported of non-enhanced UEs. Certain examples of the present disclosure provide one or more techniques for alleviating Tracking Area Update storms by signalling multiple Tracking Area Fields that may be utilized by different UEs. Various techniques disclosed herein may be applied, for example, to lAB-MTs &UEs, and gNBs, such as NG-RAN gNBs (for example in split CU / DU configuration), to which they connect. Various techniques disclosed herein may also be applied to lAB-MTs in EN-DC. Various techniques disclosed herein may be configured via RRC, for example through System Information via SIBs such as SIB1, SIB2, SIB3, etc. In a typical scenario, there may exist a number of fixed cells, for example corresponding to donor gNBs. Each fixed cell may correspond to a fixed geographical area, and each may have a corresponding tracking area code (TAG) assigned to it. A mobile IAB (mlAB) node may move through the fixed cells. One or more UEs may be continuously attached to the mlAB as it moves through the fixed cells. In this case, as the mlAB node moves through the fixed cells, the mlAB may broadcast the TAG of the fixed cell in which the mlAB is currently located. As the mlAB moves from a first fixed cell (e.g. cell#1 with TAC=TA1) to a second fixed cell (e.g. cell#2 with TAC=TA2), the TAG broadcast by the mlAB may change from TA1 to TA2 at the boundary between cell#1 and cell#2. At this time, each UE attached to the mlAB may have to perform a Tracking Area Update procedure. If many UEs are (continuously) attached to the mlAB then many TAUs occur at the same time, possibly causing network congestion. On the other hand, in the scenario described above, in certain examples of the present disclosure, as the mlAB node moves through the fixed cells, the mlAB may broadcast two (or more) separate TACs, for example in two (or more) fields. The first TAG field may be used by legacy UEs while the other TAG field may be used by enhanced UEs. Figure 5a illustrates an example in which, when the mlAB moves from a first fixed cell (e.g. cell#1 with TAC=TA1) to a second fixed cell (e.g. cell#2 with TAC=TA2), the two TACs broadcast by the mlAB both change from TA1 to TA2 at the boundary between cell#1 and cell#2. However, the TAG broadcast in the first field changes before (or after) the TAG broadcast in the second field. This means that the TAUs of the legacy UEs are performed before the TAUs of the enhanced UEs. This in turn distributes the TAUs over a time window reducing the risk of network congestion. Figure 5b illustrates an example similar to Figure 5a in which the second field may signal more than one TAC, and in which TACs signalled in the same field may change at different times. The skilled person will appreciate that the mobile IAB does not necessarily need to broadcast the same TAC of its parent Donor gNB when TA1 and TA2 is different. Figure 6 illustrates an example in which, when the mlAB moves through a number of fixed cells with two different TACs, these two TACs are broadcast by the mlAB in the first and second fields. For example, in the scenario of Figure 6, the mlAB moves through cells with TACs that constantly alternate between TA#1 and TA#2. The broadcast TACs may be “semistatic” in the sense that they are at least temporarily static (e.g. temporarily do not change). For example, in the case of Figure 6, while the mlAB traverses the path indicated, TA#1 is always broadcast in the first field and TA#2 is always broadcast in the second field so that there are no TAlls along the entire mlAB path. Accordingly, in this example, the TA#1 and TA#2 as broadcasted by the mobile IAB cell may remain the same (static) at least for a while. Without this technique, the TAC would change a lot in the scenario of Figure 6. In certain examples, the first TAC field may change along with the fixed cells, whereas the second TAC field (TAC2) may remain static in this limited space (semi-static). In certain examples, the TAC broadcast in one of the fields (e.g. the second field) may be a static TAC assigned to the mlAB which remains fixed when the mlAB moves through fixed cells (possibly having different TACs). This static TAC may be clearly separated / different from the TACs of the nearby fixed cells. The TAC broadcast in the other field (e.g. the first field) may be configured to change in a manner as described herein. Certain examples of the present disclosure provide a method, for a mobile access node (e.g. a mobile IAB node) in a network, the method comprising: broadcasting system information, wherein the system information comprises two or more Tracking Area Codes (TACs). In certain examples, the two or more TACs may comprise at least a first TAC signalled in a first field, and at least a second TAC signalled in a second field. In certain examples, a first subset of the TACs (e.g. a TAC signalled in the first field) may be utilised by a first group of UEs connected to the mobile IAB node, and a second subset of the TACs (e.g. a TAC signalled in the second field) may be utilised by a second group of UEs connected to the mobile IAB node. In certain examples, one of the first and second groups of UEs may be legacy UEs (e.g. UEs having a first level of capability), and the other of the first and second groups of UEs may be modified or enhanced UEs (e.g. UEs having a second level of capability different from or higher than the first level). In certain examples, when the mobile IAB node is located in an area corresponding to (e.g. overlapping with) a first fixed cell, at least some of the TACs in the system information may be set to be the same as a TAC associated with the first fixed cell, or a TAC associated with a fixed cell adjacent / near to the first fixed cell. In certain examples, when the mobile IAB node moves from an area corresponding to (e.g. overlapping with) a first fixed cell to an area corresponding to (e.g. overlapping with) a second fixed cell, at least some of the TACs in the system information may change from a first TAC to a second TAC. In certain examples, the first TAC may be a TAC associated with the first fixed cell or a TAC associated with a fixed cell adjacent / near to the first fixed cell, and the second TAC may be a TAC associated with the second fixed cell or a TAC associated with a fixed cell adjacent / near to the second fixed cell. In certain examples, at least some of the TACs broadcast in the system information may change at different times. In certain examples, a TAC signalled in a first field of the system information may change at a different time to a TAC signalled in a second field of the system information. In certain examples, a TAC signalled in a second field of the system information may change at a different time to another TAC signalled in the second field of the system information. In certain examples, the system information may include two or more semi-static TACs (e.g. included in at least one of the first and second fields) respectively set to be the same as two or more TACs respectively associated with two or more sets of fixed cells, each set of fixed cells being associated with the same TAC, and the semi-static TACs may remain fixed while the mobile IAB moves within areas corresponding to (e.g. overlapping with) the two or more sets of fixed cells. In certain examples, the method may further comprise: predicting a path of the mobile IAB node; determining, based on the predicted path, two or more sets of fixed cells along the predicted path, each set of fixed cells being associated with the same TAC; identifying two or more TACs associated with the determined cells; and setting the semi-static TACs as the identified TACs. In certain examples, the system information may include at least one static TAC (e.g. included in at least one of the first and second fields) associated with the mobile IAB node that remains fixed. In certain examples, the system information may be included in a system information block (e.g. SIB1). Certain examples of the present disclosure provide a mobile access node (e.g. a mobile IAB node) configured to perform a method according to any example, aspect, embodiment and / or claim disclosed herein. Certain examples of the present disclosure provide a network (or wireless communication system) comprising a mobile access node (e.g. a mobile IAB node) and one or more UEs according to any example, aspect, embodiment and / or claim disclosed herein. Certain examples of the present disclosure provide a computer program comprising instructions which, when the program is executed by a computer or processor, cause the computer or processor to carry out a method according to any example, aspect, embodiment and / or claim disclosed herein. Certain examples of the present disclosure provide a computer or processor-readable data carrier having stored thereon a computer program according to any example, aspect, embodiment and / or claim disclosed herein. The skilled person will appreciate that, in various examples, the two or more TACs may be broadcast simultaneously, or substantially simultaneously (e.g. sequentially but in relatively quick succession, for example with a small time delay less than a certain threshold). Various examples and aspect will now be described in more detail. Network Signalling (to UE) In certain examples, a mobile IAB may signal two different Tracking Area fields, for example one using legacy tracking area for legacy UEs (first tracking area field) and one using a new field (second tracking area field) that could potentially be utilized by an enhanced UE. These Tracking Areas may change at different times as the mlAB node moves, which means that different UEs camping on the same cell may camp on different Tracking Areas depending on capability. This can smooth out the transition of moving in between two different Tracking areas. An example of this is illustrated in Figure 5a. In certain examples, the mobile IAB may signal tracking areas that are adjacent to current tracking areas. In certain examples, multiple tracking areas may be included in the new field (second tracking area field, as illustrated in Figure 5b). This may also be used to smooth out the transition of moving in between two different tracking areas. Figure 6 illustrates a scenario in which a UE attaching to an mlAB node moves (together with the mlAB node) for a long time in between multiple cells belonging to two different tracking areas. In this case, the tracking areas signalled in the first and second tracking area fields are semi-static in that they remain fixed for a certain time (e.g. during traversal of the path illustrated in Figure 6). Without this technique, there would be constant tracking area updates in the scenario of Figure 6. In certain examples, the network may broadcast, in one of the tracking area fields (e.g. the second tracking area field), a static tracking area that is associated with the mlAB cell. This static tracking area is not changed when the mlAB cell moves around. For example, this technique may be applicable to future mobile networks. The above information may be broadcast in any suitable way, for example in SystemlnformationBlocks, such as SIB1. In certain examples, the signalled information may be signalled in a mobile lAB-specific System Information Block. UE Actions A UE may handle the multiple broadcast tracking areas in any suitable way. In certain examples, all of the information may be relayed to NAS, where the NAS makes the decision whether to camp on one Tracking Area as opposed to another. Alternatively, the decision may be made at RRC level, in which case only one of the tracking areas is sent to the NAS. Examples of these two scenarios are illustrated in Figures 7a and 7b. In Figure 7a, RRC receives broadcast first (e.g. legacy) and second (e.g. new) TACs from a mlAB. Next, RRC selects one of the TAs and forwards the corresponding TAC to NAS. Next, NAS receives the selected TAC and performs further action(s) as appropriate. For example, next, NAS performs a TAU. In Figure 7b, RRC receives broadcast first (e.g. legacy) and second (e.g. new) TACs from a mlAB. Next, RRC forwards both TACs to NAS. Next, NAS receives both TACs and selects one of them. Next, NAS performs further action(s) as appropriate. For example, NAS may perform a TAU. As described above, in certain examples, the RRC layer may forward one of the signalled tracking areas to NAS, which then makes the appropriate decision. This may be done in a number of ways, including one or more of the following: - The enhanced mobile IAB capable UE only forwards the new field to NAS, if the new field is present. - The enhanced mobile IAB capable UE selects one of the new and legacy fields to forward to NAS. This may be done in a number of ways, including one or more of the following: o UE selects one field at random. o UE is aware of it being on a moving platform (or not) and selects one of the fields, otherwise the legacy field is forwarded to NAS. This may ensure onboard UEs do not perform cell reselection to stationary cells. Determining being on a moving platform may for instance be done by utilizing Mobility States of a UE whether the UE is in a High-Mobility State, which may be decided via idle mode specification. An example of this is illustrated in Figure 8 and in specification example 4 further below. Mobility States are used in idle mode to scale cell reselection rules based on whether the UE is High / Medium / Normal mobile. The state is determined according to rules on how many cell reselections are performed over a time-period. Movement may also be determined via additional signalling from the network indicating access point (mlAB node) speed and / or direction of movement, which the UE could compare to its own to infer its status. As described above, in certain examples, the RRC layer may forward all of the signalled fields (e.g. legacy and new fields) and the NAS may take the appropriate decisions. This may be done in a number of ways, including one or more of the following: - The NAS only uses the new field if present. NAS selects any of the new or legacy field. This may be done in a number of ways, including one or more of the following. o Select a field at random. o NAS is aware of the UE being a mobile UE and can thus select the appropriate TAG. o NAS uses previous TAG history. Network Signalling (e.g. to AMF) In certain examples, when communicating the user location (User Location Information), for example to the AMF, a mobile IAB gNB may signal one or more of the following: - Which specific Tracking Area the UE is located in, depending on whether the UE is an enhanced mobile IAB. o If UE is an enhanced mobile IAB UE, the network sends the second Tracking Area Code field. o If UE is not an enhanced mobile IAB UE, the network sends the first Tracking Area Code field. Both tracking areas (e.g. the legacy and the new tracking areas) if the UE is an enhanced mobile IAB UE. Inter-Node Signalling to Support TAC Handling To enable a gNB CU to setup its mobile cell or a mobile gNB DU according to the techniques disclosed herein, certain examples use signalling indicating which TACs to signal in the different fields. In certain example, the gNB CU may, in addition to indicating legacy TAC field for a mobile cell (a first TAC field), also indicate which new TAC field to use (a second TAC field) in the same mobile cell. This can for instance be signalled in the F1AP message F1 SETUP REQUEST or in the field Served Cell Information. An example of this is illustrated in Figure 8. In certain examples where the above information needs to be updated quickly, a new message specifically for the update may be introduced. Further Examples In certain examples, a timer or a timestamp may be included to indicate when the new tracking area field will change is included. This may also be considered a validity time to ensure that the UE will keep updated on the system information when connected to a mobile IAB cell. In certain examples, the UE may be paged, for example via Short Message paging (the same as used for emergency notifications and system modification procedures) when the new tracking area field has changed. This paging may only be considered by the mobile IAB enhanced UEs. This may for instance be achieved by introducing a new field in Short Message (which is only interpreted by mobile IAB enhanced UEs) mlAB-trackingAreaUpdate. In certain examples, the UE may be considered an enhanced mobile IAB UE if it supports TA enhancements above (i.e. that the UE is capable of choosing multiple TAs). gNB-CU TAC Signalling As described above, TACs may be broadcast by a mobile IAB, which may then be applied by a UE. In certain examples, TACs for an IAB-MT part of the mobile IAB may be handled. Accordingly, in certain examples, the techniques disclosed herein may be extended to a gNB(-CU) signalling multiple tracking areas, which are applied by a mobile IAB-MT. For instance the IAB-MT may only apply the new tracking area field. Various examples have been disclosed herein relating to a mobile IAB node. However, the skilled person will appreciate that the present disclosure is not limited to this example. For example, the techniques disclosed herein may be applied to any other suitable type of mobile relay node. More broadly, the techniques described herein may be applied to any suitable type of mobile access node. Even more broadly, the techniques disclosed herein may be applied to non-mobile (e.g. stationary or fixed) nodes. For example, the techniques may be applied in the case of a fixed access node in a Non-Terrestrial Network (NTN) in which the cells of the NTN move, for example due to movement of the satellites providing the cell coverage. In this case, a fixed node corresponds to an mlAB node in the above examples, and a moving NTN cell corresponds to a fixed cell in the above examples. The skilled person will appreciate that the techniques disclosed herein may be applied when an access node needs to change TAC. The skilled person will appreciate that the identification of a tracking area is not limited to a TAC, and that any suitable type and / or format of identification may be used. The skilled person will also appreciate that when two or more TACs are included in system information, at least some of the TACs may be the same (i.e. have the same value). For example, a first TAC in a first field may have the same value as a second TAC in a second field, or two TACs in the same field may have the same value. Specification Examples Example 1 -------------------------3GPPTS 38.331 V17.3.0------------------------- 5.2.2.4.2 Actions upon reception of the SIB1 Upon receiving the SIB1 the UE shall: 1> store the acquired SI BL 1> if the UE is a RedCap UE and it is in RRC IDLE or in RRCIN ACTIVE, or if the RedCap UE is in RRCCONNECTED while T311 is running: 2> if intraFreqReselectionRedCap is not present in SIBk 3> consider the cell as barred in accordance with TS 38.304

[20] ; 3> perform barring as if intraFreqReselectionRedCap is set to allowed; 2> else: 3> if the cellBarredRedCaplRx is present in the acquired SIB1 and is set to barred and the UE is equipped with 1 Rx branch; or 3> if the cellBarredRedCap2Rx is present in the acquired SIB1 and is set to barred and the UE is equipped with 2 Rx branches; or 3> if the halfDuplexRedCapAllowed is not present in the acquired SIB1 and the UE supports only half-duplex FDD operation: 4> consider the cell as barred in accordance with TS 38.304

[20] ; 4> perform barring based on intraFreqReselectionRedCap as specified in TS 38.304

[20] ; 1> if the cellAccessRelatedlnfo contains an entry of a selected SNPN or PLMN and in case of PLMN the UE is either allowed or instmcted to access the PLMN via a cell for which at least one CAG ID is broadcast: 2> in the remainder of the procedures use npn-IdentityList, trackingAreaCode, and cellldentity for the cell as received in the corresponding entry of npn-IdentitylnfoList containing the selected PLMN or SNPN; 1> else if the cellAccessRelatedlnfo contains an entry with the PLMN-Identity of the selected PLMN: 2> in the remainder of the procedures use plmn-IdentityList, trackingAreaCode, trackingAreaList, and cellldentity for the cell as received in the corresponding PLMN-Identitylnfo containing the selected PLMN; 1> if in RRC CONNECTED while T311 is not running: 2> disregard the frequencyBandList, if received, while inRRC CONNECTED; 2> forward the cellldentity to upper layers; 3> forward the trackingAreaCode to upper layers, if included; 3> forward the trackingAreaList to upper layers, if included; 2> forward the received posSIB-Mappinglnfo to upper layers, if included; 2> apply the configuration included in the servingCellConfigCommon', 2> if the UE has a stored valid version of a SIB or posSIB, in accordance with clause 5.2.2.2.1, that the UE requires to operate within the cell in accordance with clause 5.2.2.1: 3> use the stored version of the required SIB or posSIB; 2> else: 3> acquire the required SIB or posSIB requested by upper layer as defined in clause 5.2.2.3.5; NOTE: Void. -------------------------3GPPTS 38.331 V17.3.0------------------------- -------------------------3GPPTS 38.331 V17.3.0------------------------- - PLMN-ldentitylnfoList The IE PLMN-ldentitylnfoList includes a list of PLMN identity information. PLMN-ldentitylnfoList information element FLMbl-Id^iTtityliTfoLi^t : : = FLMH-Identitylnfo ::= plhin^IdentityLiM t r a c k 1 it g Ar e a Co d e c o11Ro a o rvod Fo rOyo rat o rU a o ' i . (1..111-1 FLUID ) \ PL1 III —I iMitit Iiif Th -1 D Hi , DDL illRAT-1u {reserved, notR^^rved} f _________________________________PLMN-ldentitylnfo field descriptions_________________________________ cellReservedForOperatorUse Indicates whether the cell is reserved for operator use (per PLMN), as defined in TS 38.304

[20] , This field is ignored by IAB-MT.____________________________________________________________________________________ gNB-ID-Length Indicates the length of the gNB ID out of the 36-bit long cellldentity._____________________________________________ iab-Support This field combines both the support of IAB and the cell status for IAB. If the field is present, the cell supports IAB and the cell is also considered as a candidate for cell (re)selection for lAB-node; if the field is absent, the cell does not support IAB and / or the cell is barred for lAB-node._________________________________________________ trackingAreaCode Indicates Tracking Area Code to which the cell indicated by cellldentity field belongs. The absence of the field indicates that the cell only supports PSCell / SCell functionality (per PLMN) or is an NTN cell. For a mobile IAB enhanced / capable UE, this field together with frac / sngAreaijsf is considered to be the tracking areas of ths ceil._________________________________________________________________________________________ trackingAreaList List of Tracking Areas to which the cell indicated by cellldentity field belongs. If this field is present, network does not configure trackingAreaCode. Total number of different TACs across different PLMN-ldentitylnfos shall not exceed maxTAC. For a mobile IAB capable UE, this field together with tracfengAreaCod® is considered the tracking areas of the -------------------------3GPPTS 38.331 V17.3.0------------------------- 5.2.2.4.2 Actions upon reception of the SIB1 Upon receiving the SIB1 the UE shall: 1> store the acquired SIBP, 1> if the UE is a RedCap UE and it is in RRC IDLE or in RRCIN ACTIVE, or if the RedCap UE is in RRCCONNECTED while T311 is running: 2> if intraFreqReselectionRedCap is not present in SIBk 3> consider the cell as barred in accordance with TS 38.304

[20] ; 3> perform barring as if intraFreqReselectionRedCap is set to allowed; 2> else: 3> if the cellBarredRedCaplRx is present in the acquired SIB1 and is set to barred and the UE is equipped with 1 Rx branch; or 3> if the cellBarredRedCap2Rx is present in the acquired SIB1 and is set to barred and the UE is equipped with 2 Rx branches; or 3> if the halfDuplexRedCapAllowed is not present in the acquired SIB1 and the UE supports only half-duplex FDD operation: 4> consider the cell as barred in accordance with TS 38.304

[20] ; 4> perform barring based on intraFreqReselectionRedCap as specified in TS 38.304

[20] ; 1> if the cellAccessRelatedlnfo contains an entry of a selected SNPN or PLMN and in case of PLMN the UE is either allowed or instructed to access the PLMN via a cell for which at least one CAG ID is broadcast: 2> in the remainder of the procedures use npn-IdentityList, trackingAreaCode, and cellldentity for the cell as received in the corresponding entry of npn-IdentitylnfoList containing the selected PLMN or SNPN; 1> else if the cellAccessRelatedlnfo contains an entry with the PLMN-Identity of the selected PLMN: 2> in the remainder of the procedures use plmn-IdentityList, trackingAreaCode, trackingAreaList, and cellldentity for the cell as received in the corresponding PLMN-Identitylnfo containing the selected PLMN; 1> if in RRC CONNECTED while T311 is not running: 2> disregard the frequencyBandList, if received, while inRRC CONNECTED; 2> forward the cellldentity to upper layers; 3> forward either trackingAreaCode or trackingAreaList to upper savers, if included; 3> forward the trackingAreaCode to upper layers, if included; 3> forward the trackingAreaList to upper layers, if included; 2> forward the received posSIB-Mappinglnfo to upper layers, if included; 2> apply the configuration included in the servingCellConfigCommon', 2> if the UE has a stored valid version of a SIB or posSIB, in accordance with clause 5.2.2.2.1, that the UE requires to operate within the cell in accordance with clause 5.2.2.1: 3> use the stored version of the required SIB or posSIB; 2> else: 3> acquire the required SIB or posSIB requested by upper layer as defined in clause 5.2.2.3.5; NOTE: Void. 3GPPTS 38.331 V17.3.0 3GPPTS 38.331 V17.3.0 PLMN-ldentitylnfoList The IE PLMN-ldentitylnfoList includes a list of PLMN identity information. PLMN-ldentitylnfoList information element PLI- IM -1 d e n t i t yl n f 0 L i a t FLl'dl-Identitylnfo plmri-IdaTit it yList: 11R^ 3 Pr e v~d Fo EOya rat o eU £ .pRQG-Gii F (31R1F (1. . manFLI Ihl) ) GF FLI Ihl-Ident it y, IGidi iRRAT-LG {reserved, notR^^ETed} , {true} t ueckiugAi'e aLiat-rl7 gllE-IP'-Lengt h-rl7 _________________________________PLMN-ldentitylnfo field descriptions______________________________ cellReservedForOperatorUse Indicates whether the cell is reserved for operator use (per PLMN), as defined in TS 38.304

[20] , This field is ignored by IAB-MT.__________________________________________________________________________________ gNB-ID-Length Indicates the length of the gNB ID out of the 36-bit long cellldentity.____________________________________________ iab-Support This field combines both the support of IAB and the cell status for IAB. If the field is present, the cell supports IAB and the cell is also considered as a candidate for cell (re)selection for lAB-node; if the field is absent, the cell does not support IAB and / or the cell is barred for lAB-node.________________________________________________ trackingAreaCode Indicates Tracking Area Code to which the cell indicated by cellldentity field belongs. The absence of the field indicates that the cell only supports PSCell / SCell functionality (per PLMN) or is an NTN cell. trackingAreaList List of Tracking Areas to which the cell indicated by cellldentity field belongs. If this field is present, network does not configure trackingAreaCode. Total number of different TACs across different PLMN-ldentitylnfos shall not exceed maxTAC. -------------------------3GPPTS 38.331 V17.3.0------------------------- PLMN-ldentitylnfoList The IE PLMN-ldentitylnfoList includes a list of PLMN identity information. FLMH-IdentitylnfoList; PLMN-ldentitylnfoList information element RLMH-Id^ntitylnfo ::= t rsckiiTykreaCode c-llR-c-.r'-dFprOp-ratprU.?- i ah-Support-rl 6: trackingAresLict-rib gnE-ID-Length-rl" {t rue} ELI itylnfo RLMbl-Identity. (1. .mar.TAC-El" ) ) _________________________________PLMN-ldentitylnfo field descriptions______________________________ cellReservedForOperatorUse Indicates whether the cell is reserved for operator use (per PLMN), as defined in TS 38.304

[20] , This field is ignored by IAB-MT.__________________________________________________________________________________ gNB-ID-Length Indicates the length of the gNB ID out of the 36-bit long cellldentity.____________________________________________ iab-Support This field combines both the support of IAB and the cell status for IAB. If the field is present, the cell supports IAB and the cell is also considered as a candidate for cell (re)selection for lAB-node; if the field is absent, the cell does not support IAB and / or the cell is barred for lAB-node.________________________________________________ trackingAreaCode Indicates Tracking Area Code to which the cell indicated by cellldentity field belongs. The absence of the field indicates that the cell only supports PSCell / SCell functionality (per PLMN) or is an NTN cell. trackingAreaList List of Tracking Areas to which the cell indicated by cellldentity field belongs. If this field is present, network does not configure trackingAreaCode. Total number of different TACs across different PLMN-ldentitylnfos shall not exceed maxTAC. -------------------------3GPPTS 38.331 V17.3.0------------------------- -------------------------3GPPTS 38.331 V17.3.0------------------------- 5.2.2.4.2 Actions upon reception of the SIB1 Upon receiving the SIB1 the UE shall: 1> store the acquired SIB I'. 1> if the UE is a RedCap UE and it is in RRC IDLE or in RRCIN ACTIVE, or if the RedCap UE is in RRCCONNECTED while T311 is running: 2> if intraFreqReselectionRedCap is not present in SIBk 3> consider the cell as barred in accordance with TS 38.304

[20] ; 3> perform barring as if intraFreqReselectionRedCap is set to allowed; 2> else: 3> if the cellBarredRedCaplRx is present in the acquired SIB1 and is set to barred and the UE is equipped with 1 Rx branch; or 3> if the cellBarredRedCap2Rx is present in the acquired SIB1 and is set to barred and the UE is equipped with 2 Rx branches; or 3> if the halfDuplexRedCapAllowed is not present in the acquired SIB1 and the UE supports only half-duplex FDD operation: 4> consider the cell as barred in accordance with TS 38.304

[20] ; 4> perform barring based on intraFreqReselectionRedCap as specified in TS 38.304

[20] ; 1> if the cellAccessRelatedlnfo contains an entry of a selected SNPN or PLMN and in case of PLMN the UE is either allowed or instructed to access the PLMN via a cell for which at least one CAG ID is broadcast: 2> in the remainder of the procedures use npn-IdentityList, trackingAreaCode, and cellldentity for the cell as received in the corresponding entry of npn-IdentitylnfoList containing the selected PLMN or SNPN; 1> else if the cellAccessRelatedlnfo contains an entry with the PLMN-Identity of the selected PLMN: 2> in the remainder of the procedures use plmn-IdentityList, trackingAreaCode, trackingAreaList, and cellldentity for the cell as received in the corresponding PLMN-Identitylnfo containing the selected PLMN; 1> if in RRC CONNECTED while T311 is not running: 2> disregard the frequencyBandList, if received, while inRRC CONNECTED; 2> forward the cellldentity to upper layers; 3> forward the trackingAreaCode to upper layers, if included; 3> forward the trackingAreaList to upper layers, if included; 2> forward the received posSIB-Mappinglnfo to upper layers, if included; 2> apply the configuration included in the servingCellConfigCommon', 2> if the UE has a stored valid version of a SIB or posSIB, in accordance with clause 5.2.2.2.1, that the UE requires to operate within the cell in accordance with clause 5.2.2.1: 3> use the stored version of the required SIB or posSIB; 2> else: 3> acquire the required SIB or posSIB requested by upper layer as defined in clause 5.2.2.3.5; NOTE: Void. -------------------------3GPPTS 38.331 V17.3.0------------------------- Figure 10 is a block diagram of an exemplary network entity that may be used in examples of the present disclosure. For example, the UE, gNB, IAB and / or other NFs in the examples of Figures 1-9 may be provided in the form of the network entity illustrated in Figure 10. The skilled person will appreciate that a network entity may be implemented, for example, as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and / or as a virtualised function instantiated on an appropriate platform (e.g. on a cloud infrastructure). The entity 1000 comprises a processor (or controller) 1001, a transmitter 1003 and a receiver 1005. The receiver 1005 is configured for receiving one or more messages from one or more other network entities, for example as described above. The transmitter 1003 is configured for transmitting one or more messages to one or more other network entities, for example as described above. The processor 1001 is configured for performing one or more operations, for example according to the operations as described above. The techniques described herein may be implemented using any suitably configured apparatus and / or system. Such an apparatus and / or system may be configured to perform a method according to any aspect, embodiment, example or claim disclosed herein. Such an apparatus may comprise one or more elements, for example one or more of receivers, transmitters, transceivers, processors, controllers, modules, units, and the like, each element configured to perform one or more corresponding processes, operations and / or method steps for implementing the techniques described herein. For example, an operation / function of X may be performed by a module configured to perform X (or an X-module). The one or more elements may be implemented in the form of hardware, software, or any combination of hardware and software. It will be appreciated that examples of the present disclosure may be implemented in the form of hardware, software or any combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, 5 RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement certain examples of the present disclosure. 10 Accordingly, certain examples provide a program comprising code for implementing a method, apparatus or system according to any example, embodiment, aspect and / or claim disclosed herein, and / or a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium, for example a communication signal carried over a wired or wireless connection. 15 While the invention has been shown and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention, as defined by the appended claims. Abbreviations / Definitions In the present disclosure, the following acronyms / definitions are used. 3GPP 5G 3rd Generation Partnership Project 5th Generation 5 AMF Access and Mobility management Function AS Access Stratum BWP Bandwidth Part GAG Closed Access Group CM Connected Mode 10 CU Central Unit dBm decibel-milliwatts DU Distributed Unit eNB Base Station EN-DC E-UTRA NR Dual Connectivity 15 E-UTRAN Evolved Universal Terrestrial Radio Access Network F1 Interface between gNB-CU and gNB-DU F1AP F1 Application Protocol FDD Frequency Division Duplex gNB 5G NR Base Station 20 IAB Integrated Access and Backhaul ID Identity / ldentification IE Information Element IMS IP Multimedia Subsystem LTE Long Term Evolution 25 MBSR Mobile Base Station Relay mlAB Mobile IAB MT Mobile Termination NAS Non Access Stratum NB Base Station 30 NF Network Function NG Next Generation NR New Radio NTN Non-Terrestrial Network PDU Protocol Data Unit 35 PLMN Public Land Mobile Network PSCell Primary and Secondary Cell QoS Quality of Service RAN Radio Access Network RANAC RAN Area Code 40 RAT Radio Access Technology Rei Release RNA RAN Notification Area RRC Radio Resource Control RSRP Reference Signal Received Power 45 Rx Receive SCell Secondary Cell SCS Sub-Carrier Spacing SIB System Information Block SNPN Standalone Non-Public Network 50 TA Tracking Area TAG Tracking Area Code TAG Timing Advance Group TAU Tracking Area Update TR Technical Report TS Technical Specification Txxx Timer xxx UE User Equipment WG Working Group WID Work Item Description

Claims

23 06 251. A method, for a mobile access node in a network, the method comprising: broadcasting system information, wherein the system information comprises two or more Tracking Area Codes (TACs)5 wherein a first subset of the TACs are utilised by a first group of UEs connected to themobile access node, and a second subset of the TACs are utilised by a second group of UEs connected to the mobile access node.

2. A method according to claim 1, wherein the two or more TACs comprise at least a first 10 TAC signalled in a first field, and at least a second TAC signalled in a second field.

3. A method according to claim 2, wherein the first subset of the TACs are signalled in the first field, and the second subset of the TACs are signalled in the second field.15 4. A method according to any preceding claim, wherein one of the first and second groupsof UEs are legacy UEs (e.g. UEs having a first level of capability), and the other of the first and second groups of UEs are modified or enhanced UEs (e.g. UEs having a second level of capability different from or higher than the first level).20 5. A method according to any preceding claim, wherein, when the mobile access node islocated in an area corresponding to (e.g. overlapping with) a first fixed cell, at least some of the TACs in the system information are set to be the same as a TAC associated with the first fixed cell, or a TAC associated with a fixed cell adjacent / near to the first fixed cell.25 6. A method according to any preceding claim, wherein, when the mobile access nodemoves from an area corresponding to (e.g. overlapping with) a first fixed cell to an area corresponding to (e.g. overlapping with) a second fixed cell, at least some of the TACs in the system information change from a first TAC to a second TAC.30 7. A method according to claim 6,wherein the first TAC is a TAC associated with the first fixed cell or a TAC associated with a fixed cell adjacent / near to the first fixed cell, andwherein the second TAC is a TAC associated with the second fixed cell or a TAC associated with a fixed cell adjacent / near to the second fixed cell.3523 06 258. A method according to claim 6 or 7, wherein at least some of the TACs broadcast in the system information change at different times.

9. A method according to claim 8, wherein a TAC signalled in a first field of the system 5 information changes at a different time to a TAC signalled in a second field of the system information.

10. A method according to claim 8 or 9, wherein a TAC signalled in a second field of the system information changes at a different time to another TAC signalled in the second field of 10 the system information.

11. A method according to any preceding claim, wherein the system information includes two or more semi-static TACs (e.g. included in at least one of the first and second fields) respectively set to be the same as two or more TACs respectively associated with two or more 15 sets of fixed cells, each set of fixed cells being associated with the same TAC, wherein the semi-static TACs remain fixed while the mobile access node moves within areas corresponding to (e.g. overlapping with) the two or more sets of fixed cells.

12. A method according to claim 11, further comprising:20 predicting a path of the mobile access node;determining, based on the predicted path, two or more sets of fixed cells along the predicted path, each set of fixed cells being associated with the same TAC;identifying two or more TACs associated with the determined cells; and setting the semi-static TACs as the identified TACs.2513. A method according to any preceding claim, wherein the system information includes at least one static TAC (e.g. included in at least one of the first and second fields) associated with the mobile access node that remains fixed.30 14. A method according to any preceding claim, wherein the system information is includedin a system information block (e.g. SIB1).

15. A method according to any preceding claim, wherein the mobile access node is a mobile Integrated Access and Backhaul (IAB) node.3516. A mobile access node configured to perform the method of any of claims 1 to 15.

17. A network (or wireless communication system) comprising a mobile access node according to claim 16 and one or more UEs.

18. A computer program comprising instructions which, when the program is executed by 5 a computer or processor, cause the computer or processor to carry out a method according to any of claims 1 to 15.

19. A computer or processor-readable data carrier having stored thereon a computer program according to claim 18.23 06 25

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