Connection of repeater node to network

Abstract

A Network Control Repeater (NCR) is a relay or repeater node deployed between a radio access network (RAN) node and a user equipment (UE) in a 5G network. At step 1, the NCR determines that a connecti

Description

BACKGROUND Field Certain examples of the present disclosure provide one or more techniques for handling a connection of a repeater node to a network. For example, certain examples of the present disclosure provide one or more techniques for handling connection of a Network Controlled Repeater (NCR) to a Radio Access Network (RAN) node in a 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) network following Radio Link Failure (RLF). Description of the Related Art In order to provide enhanced network coverage, a variety of different types of network nodes have been developed. For example, a Radio Frequency (RF) repeater may be deployed to amplify and forward any signal that it receives to supplement coverage provided by a regular cell. An enhanced type of repeater node, called a Network-Controlled Repeater (NCR), is currently underdevelopment and is a Release 18 Study Item / Work Item (3GPP RP-213700). Figure 1 illustrates the network architecture of NCR communication. As shown, the NCR receives and forwards signals from gNB to UE via an NCR-Fwd link. The NCR also receives control signals from gNB via a NCR-Mobile Termination (MT) link, which are used to configure the NCR. Once configured, the NCR provides an amplify-and-forward function that is transparent to the UE. Accordingly, gNB may communicate with UE directly or through an NCR. To enable easy deployment of NCR nodes, an NCR is configured to be transparent to a UE whether it is communicating through an NCR or not. For example, when an NCR is deployed, to make the NCR transparent to the UE for a random access procedure, the gNB may allocate a set of SSB indices to the NCR when the NCR registers to the network (while other SSB indices remain with gNB), for example as described in 3GPP R1-2203741, Section 5. The UE may then perform the random access procedure via SSBs transmitted via SSB indices allocated to the NCR as though the random access procedure was performed via the gNB. The NCR-MT part of the NCR is expected to function almost like a normal UE, meaning that the NCR configurations are signalled similar to a normal UE. This means that NCR-MT will have a full protocol stack, but it is expected that some functionality that is normally used by a UE may not be applicable and will not be implemented by the NCR-MT and / or configured by the network. Radio Link Failure (RLF) procedures have been introduced to allow a UE to regain its radio link to a base station (or another base station) in case the UE’s radio link fails. After RLF is triggered, the UE performs Radio Resource Control (RRC) Re-establishment. In this procedure, the UE performs cell selection to select a cell (either a new cell or possibly the same cell) and connects to the selected cell. The RLF may be declared in a number of cases, for example including the following: • UE out of sync o The UE measures the cell strength through Radio Link Monitoring. If the cell strength is below a certain threshold a certain number of times, the UE triggers a timer (T310) for the UE to recover. If it does not recover, the UE declares a RLF. • RLC PDUs are re-transmitted a number of times o The network configures a number of times (maxRetxThreshold) that retransmission of an RLC PDU may be attempted. • Random access problems o This can occur when the UE is in connected mode and the UE is trying to resynchronize, for instance after losing uplink synchronization. • Backhaul (BH) RLF (IAB related) o Failure of backhaul links. • Uplink Listen Before Talk (LBT) failure o This is when the UE fails LBT when on unlicensed band. As part of performing the RLF procedure, the UE may be configured to gather an RLF-Report which contains information regarding the RLF, which then can be reported to the gNB where it occurred or any other gNB. The RRC Re-establishment procedure (along with RLF) is illustrated in Figure 2. The steps are as follows: 1. RLF between a UE and a gNB (‘old’ gNB) is declared. This may also be a Handover failure. 2. UE performs Idle mode cell selection (in this example selecting ‘new’ gNB). 3. UE sends an RRC Re-establishment request to the selected new gNB (after first performing random access). 4. New gNB requests the UE context from old gNB (if new gNB is not the same as old gNB). 5. Old gNB provides the requested UE context to new gNB. 6. New gNB replies to the RRC Re-establishment request in step 3 with a RRC Reestablishment message. New gNB may potentially reconfigure UE if needed, or continue using the same previous RRC configuration. If reconfiguring the UE, new gNB replies with RRCSetup message. 7. UE responds with RRC Re-establishment Complete message. To indicate to an old gNB that a UE previously associated / connected to it has failed, a new gNB may signal an RLF indication to the old gNB via the Xn interface. The RLE indication may include, for example, an RLF-Report compiled by the UE. This procedure is illustrated in Figure 3. In some circumstances, such as when RRC Re-establishment fails, or if the UE has not yet activated AS security, the UE may have to leave connected mode under the release cause ‘RRC Connection Failure’. The release cause is relayed to upper layers of the UE - NAS in this case. The action in NAS upon entering RRC idle mode with this release cause is to trigger a Tracking Area Update to any cell according to idle mode procedures. 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 illustrates an exemplary NCR communication architecture in which NCR-MT is the control link to control the NCR-Fwd link at the NCR; Figure 2 illustrates an example of a RRC Re-establishment procedure after RLF; Figure 3 illustrates an example of a failure indication procedure with an accompanying RLF and RRC re-establishment procedure, as well as RLF Report transmission; Figure 4a illustrates an example of an RLF procedure in which cell reselection is not performed, and Figure 4b illustrates an example of an RLF procedure in which cell selection is performed to fallback gNBs; Figure 5 illustrates an example of transmission of an NCR indication to the UE and transmission of an NCR recovery indication to the UE once NCR has re-established to a new Donor gNB; Figure 6 illustrates an example of transmission of an NCR indication in an RLF Report; Figure 7 illustrates an example of transmission of an NCR failure indication to Core Network or 0AM; Figure 8 illustrates an example of transmission of an NCR-specific RLF report; Figure 9 illustrates an example of an NCR return procedure; 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, constructions, functions 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 handling a connection of a repeater node to a network. For example, certain examples of the present disclosure provide one or more techniques for handling connection of a NCR to a RAN node in a 3GPP 5G NR network following RLF. 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 following examples are applicable to, and use terminology associated with, 3GPP 5G. However, the skilled person will appreciate that the techniques disclosed herein are not limited to 3GPP 5G. For example, the functionality of the various network entities and other features disclosed herein may be applied to corresponding or equivalent entities or features in other 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. 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. 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. At least the following problem exist in view of the related art: When a NCR detects / declares RLF compared to when a UE detects / declares RLF, various behaviour / requirements are currently undefined, for example including the following: • How does an NCR perform cell selection during Re-establishment. For example, can the NCR freely connect to any cell? • How should NCR-MT RLF be indicated to a UE connecting through an NCR? • How should an NCR failure be indicated to the network, to a new gNB, to the old gNB, to the core network and / or to the GAM, so that the network may perform appropriate actions? • What is reported in an NCR RLF report? What is reported to the gNB and what is reported to UEs attaching to the NCR? • What action(s) should be taken when an NCR fails the Re-establishment procedure? Certain examples of the present disclosure provide one or more techniques, for an NCR (e.g. NCR-MT) and / or a UE attaching to the network via an NCR, for performing RLF and RRC Reestablishment. The skilled person will appreciate that the techniques disclosed herein may be applied to gNBs, for example, NG-RAN gNB. The skilled person will also appreciate that the techniques disclosed herein may also be applied to NCR-MTs in EN-DC. Various techniques will now be described in more detail. The skilled person will appreciate that these techniques may be applied in any suitable combination. 1. Fallback (Donor-)gNB When an NCR (e.g. NCR-MT) declares RLF, the NCR selects a cell with which to perform RRC Re-establishment. In certain examples, the NCR may select the same cell with which the NCR was previously connected prior to RLF. That is, in the cell selection mechanism, the NCR does not select a cell that is different from the previously connected cell. This may be advantageous in cases in which an NCR is pre-configured in advance regarding which donor gNB it should be connected to, such that the NCR may not be allowed to attempt to connect to any cell. For example, in some cases a donor gNB shall only have a single NCR, for example due to the bandwidth usage of having an NCR connected to it. An example of this technique is illustrated in Figure 4a. In certain examples, the NCR may be pre-configured with a number of potential fallback Donor gNBs from which a cell may be selected. This may be advantageous in cases in which the donor gNBs can be both macro and smaller cells. An example of this technique is illustrated in Figure 4b. In certain examples, the NCR may be pre-configured with a number of potential fallback Donor gNBs, and the NCR may select a cell from among these candidate gNBs when one or more criteria are satisfied. For example, if the frequency of occurrence of RLF when connecting (and re-connecting) to a given cell is greater than a threshold, the NCR may instead select a (different) cell from among a set of pre-configured cells. In certain examples, the candidate cells may be configured in multiple NCRs through a broadcast message, or may be configured in one or more specific NCR through one or more NCR-specific messages, for example through dedicated RRC signalling. In certain examples, the candidate cells may be configured through CAM in advance, or during the initial NCR connection and set-up. In one example, the above technique may be implemented by configuring the NCR with one or more NCR-specific cell (re-)selection parameters to be used in case of RLF or Reestablishment. This could for instance be achieved by transmitting, via RRC, a dedicated SIB2 (SystemlnformationBlock containing one or more cell (re-)selection parameters) that (only) concerns parameters to be used for NCR when performing RLF and Re-establishment. Example 1 In the following example of the above techniques, with underlined modifications to 3GPP TS 38.331 V17.2.0, the NCR-MT re-selects the same Donor gNB and does not perform cell selection. -----------------IS 38.331 VIZ.2.0................................... 5.3.7 RRC connection re-establishment 5.3.7.1 General 10 Upon initiation of the procedure, the UE shall: 1> stop timer T310, if running: 1> stop timer T312, if running: 1> stop timer T304, if running; 1> start timer T311; 15 1 >stop timer T316, if running: CM CM . f .f f. d 1> release sl-L2RelayUE-Conjig, if configured; 1-- 1> release sl-L2RemoteUE-Config, if configured; 1> release the SRAP entity, if configured; 20 1> if the UE is acting as L2 U2N Remote UE: 2> if the PC5-RRC connection with the U2N Relay UE is determined to be released: 3> indicate upper layers to trigger PC5 unicast link release; 3> perform either cell selection in accordance with the cell selection process as specified in TS 38.304

[20] , or relay selection as specified in clause 5.8.15.3, or both; 25 2> else (i.e., maintain the PC5 RRC connection): 3> consider the connected L2 U2N Relay UE as suitable and perform actions as specified in clause 5.3.7.3a; NOTE 1: It is up to Remote UE implementation whether to release or keep the current PC5 unicast link. 1> else: 30 2> if the UE is acting as mt NCR-MT: 3 >consider the same cell to have been selected and follow procedures as specified in 5.3.7.3 2> else: 3> perform cell selection in accordance with the cell selection process as specified in TS 38.304

[20] , Example 2 In the following example of the above techniques, with underlined modifications to 3GPP TS 38.331 V17.2.0, the network configures NCR-specific cell reselection parameters via dedicated delivery of SIB2. - RRCReconfiguration The RRCReconfiguration message is the command to modify an RRC connection. It may convey information for measurement configuration, mobility control, radio resource configuration (including RBs, MAC main configuration and physical channel configuration) and AS security configuration. Signalling radio bearer: SRB1 or SRB3 RLC-SAP: AM Logical channel: DCCH Direction: Network to UE RRCReconfiguration message -«.RFR=r uf 1-pii a ti . :: = rrc-Traii acti ...F a=. =if i = r uritiu alEr.tu rrcRecii.f i a. a .-a ion criticalZaiaaaLina Future c .:. ( RRCRtucnficurati RRCReconfiguration-IEs field descriptions dedica tedSys temlnforma tionDelivery This field is used to transfer SIB6, SIB7, SIB8, SIB19, SIB21 to the UE with an active BWP with no common search space configured or the L2 U2N Remote UE in RRC_CONNECTED. ForUEs in RRC_CONNECTED (including L2 U2N Remote UE), this field is used to transfer the SIBs requested on-demand FoLNCR jhk; fie is used to transfer SIB2 dedicated for use in NCR RIF case bv listinq. ceil fallback options. ........................................................................................................................................................ 2. NCR indicating failure to UE In certain examples, the NCR may send to UEs connecting to it an indication that RLF was detected on the NCR-MT to gNB link, for example through specific L1 / L2 signalling. In certain examples, this indication may be in a form such that it appears from the UE’s point of view to come from Donor gNB. For example, the indication may be in the form of existing gNB signalling, for example instructing the UE to look for alternative cells (e.g. an RRC Release message). The UE may then take any suitable action according to receipt of RLF indication from gNB. This technique maintains NCR transparency, such that the UE is not aware that it is connecting to the network via an NCR. In certain examples, when receiving an RLF indication from an NCR (or from a Donor gNB where the RLF indication refers to the NCR-to-gNB link), a UE may not actually treat this as an indication of RLF with the Donor gNB in terms of what action to take in response, but may take alternative action. For example, as illustrated in Figure 5, when receiving an NCR failure indication from the NCR, the UE may wait for completion of an RRC Re-establishment procedure between the NCR and Donor gNB and then perform an NCR recovery procedure. In certain examples, the gNB may configure the NCR according to the above technique when the NCR declares an RLF. In certain examples an RLF detection indication (indicating RLF has been detected but not declared) and / or an RLF declared indication may be sent to a UE. In certain examples, after NCR has detected RLF on the link between the NCR and the gNB, the NCR may send a message, for example RRC Release, to UEs associated with the NCR. The NCR may also provide an indication to the Donor gNB, for example during the Reestablishment procedure. For example, this may be indicated in the NCR Failure report. In certain examples, an RLF detection indication may be sent to UE(s) attaching to the NCR. Once a new link is established between the NCR and either the old Donor gNB or a new Donor gNB, an indication of RLF recovery may be sent to the UEs. For example, if the NCR reconnects to an old gNB, the indication may be a PDCCH-ordered Random access in order to bring all the UEs back into synchronization. The PDCCH-ordered Random access may trigger the UEs to perform random access so that any lost synchronization can be re-gained. On the other hand, if the NCR re-connects to a new gNB, then a reconfiguration with sync procedure (a handover) may be performed to ensure that UEs connect to the new Donor gNB. Since it would be the NCR that sends the reconfiguration with sync (a handover), this behaviour can be configured by the Donor gNBs or other network elements. 3. NCR RLF indication and re-establishment In certain examples, if the NCR performs an RLF procedure and then connects to another Donor gNB, the new gNB may send an indication to the old Donor gNB that the NCR has failed. For example, this may be achieved by sending an indication in the RLF Indication that the RLF Report is for an NCR. In certain examples the NCR-MT may include a flag in the RLF Report indicating to the network that the “UE” is an NCR node. In other examples the NCR-MT may be identified as NCR without this flag, for example based on its C-RNTI or other radio / CN identifiers. In certain examples, the new Donor gNB may include an NCR indication in the RLF indication itself. An example of this technique is illustrated in Figure 6. In certain examples, if the NCR is unable to find a suitable NCR-capable donor gNB when performing the Re-establishment procedure, the NCR may be configured to connect to a gNB that is not NCR capable. Then, the NCR (acting as a UE to the gNB) may signal, for example to the Core Network or the 0AM, that a failure has occurred. This allows the Core Network or 0AM to reconfigure the NCR, or allows reporting to an operator that there is a problem with the NCR setup, configuration or deployment. An example of this technique is illustrated in Figure 7. In certain examples, the method described above in which a flag is included in the RLF report to indicate NCR identity may be used. The report may then be sent to the previous gNB, which may then properly interpret the signalled flag. 4. NCR RLF report In certain examples, the NCR report may provide NCR specific failure information to the donor gNB. An example of this technique is illustrated in Figure 8. The NCR report may include any suitable information, for example one or more of the following: • Whether the UE was in NCR Fwd on / off mode. • Buffer data occupancy at NCR-Fwd, the volume of packets transmitted whose reception status is unconfirmed and / or are awaiting retransmission, or any other suitable indicators of data to / from UEs which have not been successfully delivered. • Load indicators, for example how much of the NCR bandwidth is being used and / or how many UEs attach to the NCR and / or channel conditions / link status updates on access links. • Any NCR specific configuration that the NCR was configured with, for example the configurations of the NCR-Fwd such as whether the NCR-Fwd was ON / OFF, which beams that were being utilized or any other NCR-Fwd configuration or state. • How many UEs connected through the NCR. 5. NCR Re-establishment procedure In certain examples, when an NCR node performs RLF or fails Re-establishment, the NCR may not indicate to upper layers that the release cause is for ‘RRC Connection Failure’. In this case, the NCR node will not be configured to perform a Tracking Area Update. This may be important as an NCR node may not be configured to perform any Tracking Area Updates, for example since it may be a stationary node, and / or a network may not be configured to handle a Tracking Area Update from an NCR. In certain examples, if the NCR is unable to find any suitable donor gNBs with NCR support, the NCR may perform a Tracking Area Update as a normal UE, and may indicate, for example to the Core Network or CAM, transparently to a gNB. 6. NCR return procedure In some cases, if RLF occurs between an NCR and a first gNB, and then the NCR performs Re-establishment with a second gNB, then a problem may occur if the second gNB accepts and continues the connection with the NCR. For example, if an operator has configured the first gNB to operate the NCR (e.g. based on using 0AM or manual configurations), then it may be preferable to provide a mechanism to regain the NCR connection with the first gNB, or to avoid the NCR connection with the second gNB. In certain examples, if RLF occurs, the first gNB may indicate that it requires the NCR to rereconnect to the first gNB. For example, this may be achieved by the first gNB indicating to the second gNB that it requires the NCR to be handed back to the first gNB. In certain examples, a suitable indication to the second gNB may be sent in any suitable message, for example a separate (e.g. newly defined) message, or any suitable pre-existing message, for example RETRIEVE UE CONTEXT FAILURE / RETRIEVE UE CONTEXT RESPONSE. In certain examples the indication may be provided in the form of a flag, for example returnNCR-Request. In certain examples, the return of the NCR may be done via handover through RRCReconfiguration with sync, which is connected mode handover, or via RRC Release with redirection. The indication to first gNB that the NCR has connected to the second gNB may be done through any suitable technique, for example any of the techniques disclosed above (e.g. under Item 3 above). An example of this technique is illustrated in Figure 9. Figure 10 is a block diagram of an exemplary network entity that may be used in examples of the present disclosure. 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, 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. 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. Certain examples of the present disclosure provide a method, for a Network Control Repeater (NCR), the method comprising: determining that a connection between the NCR and a first Radio Access Network (RAN) node has been terminated (e.g. due to RLF or handover); selecting a RAN node for performing an RRC connection procedure with the NCR; and performing the connection procedure with the selected RAN node. In certain examples, selecting the RAN node may comprise selecting the first RAN node based on a configuration of the NCR. In certain examples, selecting the RAN node may comprise selecting a RAN node other than the first RAN node. In certain examples, the RAN node other than the first RAN node may be selected if one or more certain criteria are satisfied. In certain examples, the one or more criteria may comprise: termination of the connection between the NCR and the first RAN node has occurred a number of times above a certain threshold within a certain time window. In certain examples, the method may further comprise obtaining a list of RAN nodes, and wherein selecting the RAN node comprises selecting the RAN node from among the list of RAN nodes. In certain examples, the list of RAN nodes may be obtained according to one or more of: a configuration (e.g. via OAM / RRC / NAS signalling); a pre-configuration (e.g. via CAM); through a broadcast signal; and through a SIB2 in an RRC message. In certain examples, the method may further comprise transmitting, to one or more UEs connected to the NCR, an indication that the connection between the NCR and the first RAN node has been terminated. In certain examples, the indication may be transmitted in a message of a type (e.g. RRC Release message) transmitted by the first RAN node to a UE for indicating that a connection between the first RAN node and the UE has been terminated. In certain examples, the indication may indicate that termination of the connection has been detected but not declared. In certain examples, the method may further comprise: when a connection between the NCR and the selected RAN node is established, transmitting, to the one or more UEs, an indication that the connection is established. In certain examples, the method may further comprise transmitting, to the selected RAN node, information relating to the terminated connection (e.g. an RLF report). In certain examples, the method may further comprise transmitting, by the selected RAN node, to the first RAN node, information relating to the terminated connection (e.g. an RLF report). In certain examples, the information transmitted by the selected RAN node may include an indication that the terminated connection was a connection to the NCR. In certain examples, the information relating to the terminated connection may comprise information indicating one or more of: how many UEs were connected through the NCR; whether the NCR was in NCR Fwd on / off mode; a buffer data occupancy of the NCR; a volume of data to / from a UE which have not been successfully delivered; a load indicator relating to the NCR; and one or more NCR configurations the NCR was configured with. In certain examples, when no RAN node capable of supporting the NCR is available, the selected RAN node may be a RAN node not capable of supporting the NCR, and the method may further comprise transmitting, to a core network entity, a message indicating that a connection has been terminated. In certain examples, when a connection cannot be established between the NCR and a RAN node, the NCR may not perform either or both of a Tracking Area Update and RAN Based Notification Area Update. In certain examples, the method may further comprise: when no RAN node capable of supporting the NCR is available, performing a Tracking Area Update as a UE. Certain examples of the present disclosure provide an apparatus (e.g. a Network Control Repeater) configured to perform a method according to any aspect, example, claim or embodiment disclosed herein. Certain examples of the present disclosure provide a network (or wireless communication system) comprising an apparatus according to any aspect, example, claim or embodiment 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 aspect, example, claim or embodiment disclosed herein. 5 Certain examples of the present disclosure provide a computer or processor-readable data carrier having stored thereon a computer program according to any aspect, example, claim or embodiment disclosed herein. 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 10 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 AS Access Stratum nil Drl Backhaul BWP Bandwidth Part CN Core Network C-RNTI Cell Radio Network Temporary Identifier 10 eNB Base Station EN-DC E-UTRA NR Dual Connectivity E-UTRA Evolved Universal Terrestrial Radio Access Fwd Forward gNB 5G NR Base Station 15 IAB Integrated Access and Backhaul L1 / L2 Layer 1 / Layer 2 LBT Listen Before Talk MAC Medium Access Control MT Mobile Termination 20 NAS Non Access Stratum NCR Network-Controlled Repeater NG Next Generation NR New Radio OAM Operations, Administration and Maintenance 25 PDCCH Physical Downlink Control Channel PDU Protocol Data Unit RAN Radio Access Network RF Radio Frequency RLF Radio Link Failure 30 RRC Radio Resource Control SIB2 System Information Block 2 SSB Synchronization Signal Block TAG Timing Advance Group TS Technical Specification 35 UE User Equipment Xn Interface between RAN nodes 28 04 25

Claims

1. A method, for a Network Control Repeater (NCR) in a 3rd Generation Partnership Project (3GPP) 5th Generation (5G) network, the method comprising:being configured, via at least one of Operations, Administration and Maintenance5 (OAM) signalling, Radio Resource Control (RRC) signalling, or Non Access Stratum (NAS) signalling, with a list of fallback cells from which a cell may be selected in case a connection between the NCR and a first cell is terminated (e.g. due to RLF or handover);determining that a connection between the NCR and a first cell has been terminated;selecting, from among the configured list of fallback cells, a cell for performing an RRC10 connection procedure with the NCR; andperforming the connection procedure with the selected cell.

2. A method according to claim 1, wherein selecting the cell comprises selecting the first cell based on a configuration of the NCR.

153. A method according to claim 1, wherein selecting the cell comprises selecting a cell other than the first cell.

4. A method according to claim 3, wherein the cell other than the first cell is selected if 20 one or more certain criteria are satisfied.

5. A method according to claim 4, wherein the one or more criteria comprise: termination of the connection between the NCR and the first cell has occurred a number of times above a certain threshold within a certain time window.

256. A method according to claim 1, wherein the NCR is further configured with the list of fallback cells via one or more of:a broadcast signal; anda SIB2 in an RRC message.

307. A method according to any preceding claim, further comprising transmitting, to one ormore UEs connected to the NCR, an indication that the connection between the NCR and the first cell has been terminated.28 04 258. A method according to claim 7, wherein the indication is transmitted in a message of a type (e.g. RRC Release message) transmitted by the first cell to a UE for indicating that a connection between the first cell and the UE has been terminated.5 9. A method according to claim 7, wherein the indication indicates that termination of theconnection has been detected but not declared.

10. A method according to claim 7, 8, or 9, further comprising: when a connection between the NCR and the selected cell is established, transmitting, to the one or more UEs, an 10 indication that the connection is established.

11. A method according to any preceding claim, further comprising transmitting, to the RAN node of the selected cell, information relating to the terminated connection (e.g. an RLE report).1512. A method according to claim 11, further comprising transmitting, by the RAN node of the selected cell, to the RAN node of the first cell, information relating to the terminated connection (e.g. an RLF report).20 13. A method according to claim 12, wherein the information transmitted by the RAN nodeof the selected cell includes an indication that the terminated connection was a connection to the NCR.

14. A method according to claim 11, 12, or 13, wherein the information relating to the 25 terminated connection comprises information indicating one or more of:how many UEs were connected through the NCR;whether the NCR was in NCR Fwd on / off mode;a buffer data occupancy of the NCR;a volume of data to / from a UE which have not been successfully delivered;30 a load indicator relating to the NCR; andone or more NCR configurations the NCR was configured with.

15. A method according to any preceding claim,wherein, when no cell capable of supporting the NCR is available, the selected cell is35 a cell not capable of supporting the NCR, andwherein the method further comprises transmitting, to a core network entity, a message indicating that a connection has been terminated.

16. A method according to any preceding claim, wherein, when a connection cannot be established between the NCR and a cell, the NCR does not perform either or both of a Tracking Area Update and RAN Based Notification Area Update.

517. A method according to any preceding claim, further comprising: when no cell capable of supporting the NCR is available, performing a Tracking Area Update as a UE.

18. An apparatus (e.g. a Network Control Repeater) configured to perform the method of 10 any of claims 1 to 17.

19. A network (or wireless communication system) comprising an apparatus according to claim 18.15 20. A computer program comprising instructions which, when the program is executed bya computer or processor, cause the computer or processor to carry out a method according to any of claims 1 to 17.

21. A computer or processor-readable data carrier having stored thereon a computer20 program according to claim 20.28 04 25

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