L1 / l2 triggered mobility

Abstract

A User Equipment, UE, configured to: receiving configuration information associated with CLTM, the configuration information indicative of an indication associated with network based TA precedence, and an indication associated with early UE based TA estimation; estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a RACH procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information; starting a timer associated with disabling use of the UE estimated TA information; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information.

Description

[0001] TITLE

[0002] L1 / L2 TRIGGERED MOBILITY

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to L1 / L2 triggered mobility (LTM). Some relate to conditional LTM (CLTM).

[0005] BACKGROUND

[0006] A wireless network comprises a plurality of network nodes including terminal nodes and access nodes. Communication between the terminal nodes and the access nodes is wireless.

[0007] A terminal node, such as a user equipment (UE) can be configured to perform L1 / L2 triggered mobility (LTM) from a first cell to a second, different cell. In some circumstances, it may be desirable to improve or enhance how LTM is performed. BRIEF SUMMARY

[0008] According to various, but not necessarily all, examples there is provided a User Equipment, UE, comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the UE to perform at least: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with early UE based TA estimation; estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information; starting a timer associated with disabling use of the UE estimated TA information; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

[0009] In some examples, the indication associated with network based TA precedence comprises information to configure the UE to give precedence to valid TA information provided by an access node over UE estimated TA information, andwherein the indication associated with early UE based TA estimation comprises information to configure determining of TA information by the UE.

[0010] In some examples, the configuration information associated with CLTM is received via at least one radio resource control, RRC, reconfiguration message.

[0011] In some examples, starting the timer associated with disabling use of the UE estimated TA information comprises starting the timer based, at least in part, on transmitting physical random access channel, PRACH, preamble after receiving the information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM.

[0012] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: determining that valid TA information provided by an access node is unavailable at the UE when the CLTM condition or conditions for the first candidate access node has been met; and wherein triggering RACH-less CLTM towards the first candidate access node is based, at least in part, on the timer associated with disabling use of the UE estimated TA information and determining that valid TA information provided by an access node is unavailable at the UE.

[0013] In some examples, determining that valid TA information provided by an access node is unavailable at the UE comprises: receiving, from the source access node, information indicative of TA information and an associated timer value for a timer associated with TA information validity; starting a timer associated with TA information validity having the timer value; and determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node has been met.

[0014] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: stopping the timer associated with disabling use of the UE estimated TA information based, at least in part, on determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node.

[0015] In some examples, determining that valid TA information provided by an access node is unavailable at the UE comprises: determining that information indicative of TAinformation has not been received from the source access node when the CLTM condition or conditions for the first candidate access node has been met.

[0016] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: determining that the timer associated with disabling use of the UE estimated TA information has expired when the CLTM condition or conditions for the first candidate access node has been met and information indicative of TA information has not been received from the source access node; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node based, at least in part, on determining that the timer associated with disabling use of the UE estimated TA information has expired.

[0017] According to various, but not necessarily all, examples there is provided a method comprising: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with Early UE based TA estimation; estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information; starting a timer associated with disabling use of the UE estimated TA information; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

[0018] In some examples, the indication associated with network based TA precedence comprises information to configure the UE to give precedence to valid TA information provided by an access node over UE estimated TA information, and wherein the indication associated with early UE based TA estimation comprises information to configure determining of TA information by the UE.

[0019] In some examples, starting the timer associated with disabling use of the UE estimated TA information comprises starting the timer based, at least in part, on transmitting physical random access channel, PRACH, preamble after receiving theinformation configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM.

[0020] In some examples, the method comprises: determining that valid TA information provided by an access node is unavailable at the UE when the CLTM condition or conditions for the first candidate access node has been met; and wherein triggering RACH-less CLTM towards the first candidate access node is based, at least in part, on the timer associated with disabling use of the UE estimated TA information and determining that valid TA information provided by an access node is unavailable at the UE.

[0021] According to various, but not necessarily all, examples there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with early UE based TA estimation; estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information; starting a timer associated with disabling use of the UE estimated TA information; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

[0022] According to various, but not necessarily all, examples there is provided a network node comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network node to perform at least: receiving information associated with conditional L1 / L2 triggered mobility, CLTM; determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information.In some examples, transmitting the configuration information comprises transmitting at least one radio resource control, RRC, reconfiguration message.

[0023] According to various, but not necessarily all examples, there is provided a method comprising: receiving information associated with conditional L1 / L2 triggered mobility, CLTM from a source access node; determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information towards the source access node.

[0024] In some examples, transmitting the configuration information comprises transmitting at least one radio resource control, RRC, reconfiguration message.

[0025] According to various, but not necessarily all, examples there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information associated with conditional L1 / L2 triggered mobility, CLTM from a source access node; determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information towards the source access node.

[0026] According to various, but not necessarily all, embodiments there is provided an apparatus comprising at least one processor; and at least one memory; the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least a part of one or more methods described herein.

[0027] According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein.

[0028] The description of a function and / or action should additionally be considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method.

[0029] According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function.

[0030] BRIEF DESCRIPTION

[0031] Some examples will now be described with reference to the accompanying drawings in which:

[0032] FIG. 1 shows an example of the subject matter described herein;

[0033] FIG. 2A shows another example of the subject matter described herein;

[0034] FIG. 2B shows another example of the subject matter described herein;

[0035] FIG. 2C shows another example of the subject matter described herein;

[0036] FIG. 2D shows another example of the subject matter described herein;

[0037] FIG. 2E shows another example of the subject matter described herein;

[0038] FIG. 2F shows another example of the subject matter described herein;

[0039] FIG. 2G shows another example of the subject matter described herein;

[0040] FIG. 3 shows another example of the subject matter described herein;

[0041] FIG. 4 shows another example of the subject matter described herein;

[0042] FIG. 5 shows another example of the subject matter described herein;

[0043] FIG. 6 shows another example of the subject matter described herein;

[0044] FIG. 7 shows another example of the subject matter described herein;

[0045] FIG. 8 shows another example of the subject matter described herein;

[0046] FIG. 9 shows another example of the subject matter described herein;

[0047] FIG. 10A shows another example of the subject matter described herein; and FIG. 10B shows another example of the subject matter described herein.

[0048] The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar referencenumerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures.

[0049] DETAILED DESCRIPTION FIG 1 illustrates an example of a communications network 100 such as a 5G network or a 6G network or any other suitable type of network. The network 100 comprises a plurality of network nodes including terminal nodes 110, access nodes 120 and one or more core nodes 129. The access nodes 120 and core node 129 can be considered network nodes.

[0050] The terminal nodes 110 and access nodes 120 communicate with each other. The one or more core nodes 129 communicate with the access nodes 120. In some examples, the core nodes 129 communicate with the terminal nodes 110.

[0051] The network 100 is in this example a radio telecommunications network, in which at least some of the terminal nodes 110 and access nodes 120 communicate with each other using transmission / reception of radio waves / signals.

[0052] The one or more core nodes 129 may, in some examples, communicate with each other. The one or more access nodes 120 may, in some examples, communicate with each other.

[0053] The network 100 may be a cellular network comprising a plurality of cells 122 each served by an access node 120. In this example, the interface between the terminal nodes 110 and an access node 120 defining a cell 122 is a wireless interface 124.

[0054] The access nodes 120 can comprise at least one cellular radio transceiver. The terminal nodes 110 can comprise at least one cellular radio transceivers.

[0055] In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE), and the access nodes 120 are base stations. The terminal nodes 110 can comprise any other suitable type of device or devices. The access nodes 120 can be any suitable type of base station.

[0056] The access node 120 can be a network entity responsible for radio transmission and reception in one or more cells to or from terminal nodes 110. The access node 120 can be a network element in a Radio Access Network (RAN), or any other suitable type of network.

[0057] The core network nodes 129 can be part of a core network. The core network nodes 129 can be configured to manage functions relating to connectivity for theterminal nodes 110. For example, the core network nodes 129 can be configured to manage functions such as connectivity, mobility, authentication, authorization and / or other suitable functions.

[0058] In the example of Fig. 1 the core network node 129 is shown as a single entity. In some examples the core network node 129 could be distributed across multiple entities. For example, the core network node 129 could be cloud based or distributed in any other suitable manner.

[0059] In examples the network 100 is an Evolved Universal Terrestrial Radio Access network (E-UTRAN). The E-UTRAN consists of E-UTRAN NodeBs (eNBs) 120, providing the E-UTRA user plane and control plane (RRC) protocol terminations towards the UE. The eNBs 120 are interconnected with each other by means of an X2 interface 126. The eNBs are also connected by means of the S1 interface 128 to the Mobility Management Entity (MME) 129.

[0060] In other examples the network 100 is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs) 120, providing the user plane and control plane (RRC) protocol terminations towards the UE 110. The gNBs 120 are interconnected with each other by means of anXn interface 126. The gNBs are also connected by means of the N2 interface 128 to the Access and Mobility management Function (AMF).

[0061] In some examples, the access nodes 120 can comprise at least one wireless edge computing server.

[0062] A user equipment (UE) can comprise a mobile equipment. Where reference is made to user equipment that reference includes and encompasses, wherever possible, a reference to mobile equipment.

[0063] An access node 120, for example a gNB, can comprise a central unit (CU) and at least one distributed unit (DU). In examples, a central unit can be an access node 120. In examples, a distributed unit can be an access node 120. In examples, action(s) performed by a CU can be action(s) performed by an access node. In examples, action(s) performed by a DU can be action(s) performed by an access node.

[0064] The network 100 can comprise a combination of E-UTRAN and NG-RAN. The network 100 can comprise a 6thgeneration radio access network, 6GRAN. A terminal node 110, such as a user equipment (UE), can be configured to perform L1 / L2 triggered mobility (LTM) to perform a handover procedure. For example, a terminal node 110 can be connected to a first access node 110 and can beconfigured to perform LTM to instead be connected to a second, different access node 110.

[0065] In examples, a terminal node 110 can be connected to a first distributed unit (DU) of a central unit (CU) and can be configured to perform LTM to instead be connected to a different DU of the CU.

[0066] In examples, a terminal node 110 can be connected to a first cell of an access node 110, and can be configured to perform LTM to instead be connected to a second, different cell of the access node 120.

[0067] A terminal node 110 can be configured to perform conditional LTM (CLTM). A terminal node 110 configured to perform CLTM can be configured with at least one condition associated with at least one candidate access node 110, and can perform handover to a candidate access node 110 when the associated condition(s) for a candidate access node 110 are fulfilled.

[0068] A candidate access node 110 can be the access node 110 with which the terminal node 110 is connected (source access node), as the CLTM can be configured in relation to a different cell of the source access node.

[0069] In examples, a terminal node 110 that is configured to perform CLTM can be instructed, for example using a physical downlink control channel (PDCCH) order, to perform early synchronization and acquire timing advance (TA) information for at least one candidate access node.

[0070] In examples, information is provided to the terminal node 110 that is configured to perform CLTM, to control use of TA information by the terminal node 110 during CLTM. In some examples, information is provided to the terminal node 110 that is configured to perform CLTM, to control use of network provided TA information and terminal node estimated TA information at the terminal node during CLTM.

[0071] In some examples, information is provided to the terminal node 110 that is configured to perform CLTM, to control estimation of TA information by the terminal node 110.

[0072] At least some examples of the disclosure relate to at least one of the following: apparatuses, methods, or computer programs for performing CLTM.

[0073] At least some examples of the disclosure relate to at least one of the following: apparatuses, methods, or computer programs for use of TA information at a terminal node 110, such as a UE.At least some examples of the disclosure relate to at least one of the following: apparatuses, methods, or computer programs for enabling random access channel (RACH)-less CLTM.

[0074] FIGS. 2A to 2G illustrates an example of signaling between entities. FIGS. 2A to 2G also illustrate an example of at least one method 200. In some, but not necessarily all, examples FIGS. 2B to 2D illustrate at least one method associated with a first alternative and FIGS. 2E to 2G illustrate at least one method associated with a second alternative.

[0075] FIGS. 2A to 2G illustrate methods performed by a system comprising interaction between different system entities. FIGS. 2A to 2G also illustrates a collection of separate methods performed separately by the different system entities.

[0076] In some examples, FIGS. 2A, 2B, 2C, 2D illustrate first methods. In some examples, FIGS. 2A, 2E, 2F, 2G illustrate second methods.

[0077] One or more of the features discussed in relation to FIGS. 2A to 2G can be found in one or more of the other FIGS.

[0078] In the examples of FIGS. 2A to 2G, a plurality of apparatuses transmit and / or receive one or more signals and / or messages across and / or via and / or using a network. In examples, any suitable form of communication in any suitable network can be used. For example, at least a portion of the network 100 of FIG. 1 can be used.

[0079] In the examples of FIGS. 2A to 2G, a terminal node 110, a first access node 120A, a second access node 120B, and a third access node 120C transmit and / or receive one or more signals and / or one or more messages.

[0080] In the examples of FIGS. 2A to 2G, the terminal node is a UE 164, the first access node 120A is a source access node 173 and, in the illustrated example, is a source DU.

[0081] In the examples of FIGS. 2A to 2G, the second access node 120B is a first candidate access node 174A and, in the illustrated example, is a candidate DU. The candidate DU can be referred to as a target DU.

[0082] In the examples of FIGS. 2A to 2G, the third access node 120C is a CU associated with the source DU and candidate DU. Accordingly, FIGS. 2A to 2G illustrate examples of intra-CU mobility.

[0083] However, examples of the disclosure are applicable to any suitable arrangement of access nodes. For example, examples of the disclosure are applicableto inter-CU mobility, and therefore, in examples, the first candidate access node 174 can be associated with a different CU than the source access node 120.

[0084] Examples of the disclosure are also applicable to non-distributed access node examples. For example, the first access node 120A can be non-distributed and therefore actions performed by the first access node 120A (source DU) and third access node 120C (CU 165) in the illustrated examples can be performed by a nondistributed access node 120.

[0085] Similarly, examples of the disclosure are applicable to intra-DU examples. For example, the first access node 120A, and the second access node 122B can be the same DU, and the mobility can be between different cells of a DU.

[0086] In examples, transmissions between entities illustrated in FIGS. 2A to 2G can proceed via any number of intervening entities, including no intervening entities.

[0087] Although a single terminal node 110 is illustrated in the example of FIGS. 2A to 2G, in examples any suitable number of terminal nodes 110 can be included. Similarly, any suitable number of access nodes 120 can be included.

[0088] The preceding statements concerning FIGS. 2A to 2G should be understood to apply to other FIGs described herein, for example FIGS. 8 and 9.

[0089] As used herein, a description of an apparatus, such as a terminal node 110 or an access node 120, performing an action should also be considered to disclose at least one controller of the apparatus performing at least one of the following: enabling the apparatus to perform the action, causing the apparatus to perform the action, or controlling the apparatus to perform the action. For example, a description of an apparatus transmitting information should also be considered to disclose at least one controller of the apparatus performing at least one of the following: enabling the apparatus to transmit the information, causing the apparatus to transmit the information, or controlling the apparatus to transmit the information.

[0090] In examples, at least part of method 200 can be considered a method of performing CLTM.

[0091] Additionally, or alternatively, in examples, at least part of method 200 can be considered a method of controlling TA information use at a terminal node 110, such as a UE.

[0092] Additionally, or alternatively, in examples, at least part of method 200 can be considered a method of enabling random access channel (RACH)-less CLTM.In the illustrated examples, the location of blocks indicates the entity or entities performing the function(s) / action(s). For example, block 208 is performed by the source access node (transmitting) and the terminal node 110 (receiving). For example, block 204 is performed by the central unit 165.

[0093] As used herein, the term ‘block’ is intended to refer to an action of actions indicated in a FIG. For example, the term ‘block’ can refer to the action of transmitting / receiving indicated by, for example, reference numeral 208 in FIG. 2, and can also refer to the action of determining indicated by reference numeral 204 and so on.

[0094] For the purposes of clarity, in the following description of FIGS. 2A to 2G the first access node 120A will be referred to as a source access node 173, the second access node 120B will be referred to as a first candidate access node 174A, and the third access node 120C will be referred to as a CU 165. However, as set out above, any suitable combination of any suitable type or types of access nodes 120 can be used in examples of the disclosure.

[0095] In the example of FIG. 2A, the terminal node 110, which in the illustrated example is a UE 164, is in a connected mode with the source access node 120A, which in the illustrated example is a DU. In examples, information is being transmitted between the terminal node 110 and the source access node 120A.

[0096] At block 202, method 200 comprises transmitting information 184 associated with CLTM. In the illustrated example, the information 184 is transmitted towards a CU 165.

[0097] As FIGS. 2A to 2G illustrate one or more functions / actions of transmitting, FIGS. 2A to 2G also illustrate the corresponding receiving and causing / enabling / controlling receiving. For example, from the point of view of the CU 165, at block 202, method 200 comprises receiving information 184 associated with CLTM.

[0098] In the illustrated example, the information 184 associated with CLTM is received from the source access node 173, which is a DU, but in examples, the information 184 associated with CLTM can be received from any suitable source.

[0099] The information 184 associated with CLTM can comprise any suitable information. For example, the information associated with CLTM can comprise any suitable information 184 to enable the CU 165 to determine configuration information 186 associated with CLTM.In examples, the information 184 associated with CLTM comprises at least one CLTM execution condition. In examples, the information 184 associated with CLTM comprises at least one layer 1 (L1) measurement reporting configuration. The at least one L1 measurement reporting configuration can comprise at least one pruned L1 measurement reporting configuration.

[0100] In some, but not necessarily all, examples the information 184 associated with CLTM can be CLTM information.

[0101] In examples, block 202 can comprise transmitting / receiving any suitable message or messages. In some examples, block 202 comprises transmitting / receiving at least one UE Context Modification Response message.

[0102] At block 204, method 200 comprises determining configuration information 186 associated with CLTM, the configuration information indicative of an indication 168 associated with network based TA precedence, and an indication 170 associated with UE based TA estimation. In some examples the configuration information 186 comprises information indicative of an indication 168 associated with network based TA precedence, and information indicative of an indication 170 associated with UE based TA estimation.

[0103] The configuration information 186 associated with CLTM can comprise any suitable information. In examples, the configuration information 186 associated with CLTM can comprise information to configure CLTM at a terminal node or terminal nodes 110.

[0104] In some examples, the configuration information 186 comprises an LTM configuration of at least one candidate access node 174 and the CLTM execution condition or conditions for the at least one candidate access node 174.

[0105] Any suitable information indicative of an indication 168 associated with network based TA precedence can be used. For example, any suitable flag in at least one message, for example at least one radio resource control (RRC) reconfiguration message, indicating ‘enabled’ or ‘disabled’ (for example set to T or ‘0’).

[0106] For example, any suitable indication can be included as a field within the LTM-candidate information element (IE) in cell-specific examples.

[0107] Any suitable information indicative of an indication 170 associated with UE based TA estimation can be used. For example, any suitable flag in at least one message, for example at least one radio resource control (RRC) reconfiguration message, indicating ‘enabled’ or ‘disabled’ (for example set to T or ‘0’).For example, any suitable indication can be included as a field within the LTM-candidate information element (IE) in cell-specific examples.

[0108] An indication 170 associated with UE based TA estimation can be applicable to any suitable terminal node 110, whether a UE 164 or not. Accordingly, in examples, an indication 170 associated with UE based TA estimation can be referred to as an indication associated with terminal node based TA estimation.

[0109] Different types of indications 170 associated with UE based TA estimation can be used. For example, the configuration information 186 can comprise information indicative of an indication 170A associated with early UE based TA estimation. This will be discussed further in relation to FIGS. 2B to 2D. For example, the configuration information 186 can comprise information indicative of an indication 170B associated with delayed UE based TA estimation. This will be discussed further in relation to FIGS. 2E to 2G.

[0110] In some, but not necessarily all, examples the configuration information 186 associated with CLTM can be CLTM configuration information.

[0111] In some, but not necessarily all, examples the indication 168 associated with network based TA precedence can be a network based TA precedence indication 168.

[0112] In some, but not necessarily all, examples the indication 170 associated with UE based TA estimation can be a UE based TA estimation indication 170.

[0113] In examples, the indication 168 associated with network based TA precedence comprises information to configure at least one UE 164 to give precedence to valid TA information 172 provided by an access node 120 over UE estimated TA information, and the indication 170 associated with UE based TA estimation comprises information to configure determining of TA information 172 by at least one UE 164.

[0114] In some, but not necessarily all examples, the configuration information 168 does not comprise information indicative of an indication associated with network based TA precedence.

[0115] In examples, block 204 comprises determining a TA management policy comprising information indicative of an indication 168 associated with network based TA precedence, and information indicative of an indication 170 associated with UE based TA estimation. In examples, the configuration information 168 can comprise information indicative of the TA management policy.

[0116] In some examples, network based TA information 172 is TA information provided to a UE 164 by the network, for example by the source access node 173.At block 206, method 200 comprises transmitting the configuration information 186.

[0117] Consequently, FIG. 2A illustrates a method 200 comprising: receiving information 184 associated with conditional L1 / L2 triggered mobility (CLTM); determining configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information 186.

[0118] In the example of FIG. 2A, the configuration information 186 is transmitted towards the source access node 173.

[0119] In examples, block 206 can comprise transmitting / receiving any suitable message or messages. In some examples, block 206 comprises transmitting / receiving at least one radio resource control (RRC) reconfiguration message. Accordingly, in examples, transmitting the configuration information 186 comprises transmitting at least one RRC reconfiguration message.

[0120] At block 208, method 200 comprises transmitting the configuration information towards at least one UE 164.

[0121] Consequently, from the point of view of the source access node 173, FIG. 2A illustrates a method 200 comprising: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information towards at least one user equipment (UE) 164.

[0122] In examples, block 208 can comprise transmitting / receiving any suitable message or messages. In some examples, block 208 comprises transmitting / receiving at least one radio resource control (RRC) reconfiguration message. Accordingly, in examples, transmitting the configuration information 186 comprises transmitting at least one RRC reconfiguration message.

[0123] From the pointof viewof the terminal node 110, which in the illustrated example is a UE 164, block 208 comprises receiving configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based TA precedence, and an indication 170 associated with UE based TA estimation.In examples, the configuration information 186 associated with CLTM is received via at least one RRC reconfiguration message.

[0124] As discussed in relation to block 204, in examples, the indication 168 associated with network based TA precedence comprises information to configure the UE 164 to give precedence to valid TA information 172 provided by an access node 120 over UE estimated TA information, and the indication 170 associated with UE based TA estimation comprises information to configure determining of TA information 172 by the UE 164.

[0125] Accordingly, in some examples, after the UE 164 has processed the configuration information 186 associated with CLTM, the UE 164 is configured to give precedence to valid network based TA information. For example, if the source access node 173 provides TA information 172 to the UE 164, the UE 164 will use the TA information 172 from the source access node 173 ahead of TA information 172 determined by the UE 164.

[0126] Accordingly, in some examples, after the UE 164 has processed the configuration information 186 associated with CLTM, the UE 164 is configured to determine TA information 172. For example, the UE 164 can be configured to determine TA information 172 to enable TA information 172 to be available for the first candidate access node 174A when valid network based TA information 172 is unavailable at the UE 164.

[0127] As discussed in relation to block 204, in examples, different types of indications 170 associated with UE based TA estimation can be used. In examples, different UE behavior associated with TA estimation can be configured based, at least in part, on the type of indication 170 associated with UE based TA estimation indicated in the configuration information 186 associated with CLTM.

[0128] In some examples, an indication 170A associated with early UE based TA estimation can be indicated in the configuration information 186 associated with CLTM. See, for example, FIGS. 2A to 2D.

[0129] In some examples, an indication 170B associated with delayed UE based TA estimation can be indicated in the configuration information 186 associated with CLTM. See, for example, FIGS 2A and 2E to 2G.

[0130] In examples, the CU 165 determines what type of indication 170 associated with UE based TA estimation is to be used at block 204, and includes informationindicative of the determined type of indication 170 associated with UE based TA estimation in the configuration information 86 associated with CLTM.

[0131] In examples, block 204 comprises determining what type of indication 170 associated with UE based TA estimation to configure at the terminal node 110, which in the illustrated examples is a UE 164.

[0132] Determining what type of indication 170 associated with UE based TA estimation to configure at the terminal node 110 can be based, at least in part, on any suitable information. For example, determining what type of indication 170 associated with UE based TA estimation to configure at the terminal node 110 can be based, at least in part, on at least one of: information associated with terminal node position, information associated with at least one terminal node measurement report, information associated with terminal node mobility, information associated with terminal node capability, synchronization signal block (SSB) signal strength, for example reference signal received power (RSRP) / reference signal received quality (RSRQ), channel state information reference signal (CSI-RS), for example (RSRP / RSRQ), and so on.

[0133] In some, but not necessarily all, examples, at least one of the following: information associated with terminal node position can be referred to as terminal node position information, information associated with at least one terminal node measurement report can be referred to as terminal node measurement report information, or information associated with terminal node capability can be referred to as terminal node capability information.

[0134] In examples, terminal node position information can be used to determine a relative position of the terminal node 110 with respect to the source access node 173 and candidate access node 174. In examples, the type of indication 170 associated with UE based TA estimation to be configured at the terminal node 110 is based, at least in part, on the determined relative position.

[0135] In examples, a terminal node 110, such as a UE 164, can transmit measurement report information, for example, at least one of L1 measurement reports or L3 measurement reports towards the source access node 173 which can provide information indicative of the received measurement report information to the CU 165. In examples, the type of indication 170 associated with UE based TA estimation to be configured at the terminal node 110 is based, at least in part, on the measurement report information.In examples, SSB signal strength, for example at least one of reference signal RSRP or RSRQ can be reported to the CU 165. In examples, the type of indication 170 associated with UE based TA estimation to be configured at the terminal node 110 is based, at least in part, on the SSB signal strength.

[0136] In examples, CSI-RS information, for example at least one of RSRP or RSRQ can be reported to the CU 165. In examples, the type of indication 170 associated with UE based TA estimation to be configured at the terminal node 110 is based, at least in part, on the CSI-RS information.

[0137] In examples, mobility information of the terminal node 110, such as how quickly the terminal node 110 is moving, can be provided to the CU 165 by, for example, the source access node 173. In examples, the type of indication 170 associated with UE based TA estimation to be configured at the terminal node 110 is based, at least in part, on the mobility information of the terminal node 110.

[0138] For example, if the CU 165 determines, based, at least in part, on the mobility information of the terminal node 110 that it is likely that the network will have to transmit information 176 configured to instruct the terminal node 110 to initiate a randomaccess channel, RACH, procedure to acquire early TA information for CLTM, for example using a PDCCH order, the CU 165 can determine to configure the terminal node 110 with an indication 170A associated with early UE based TA estimation.

[0139] In examples, capability information of the terminal node 110 can be provided to the CU 165 by, for example, the source access node 173. Capability information of the terminal node 110 can comprise any suitable information of the capability or capabilities of the terminal node 110. For example, capability information of the terminal node 110 can indicate whether the terminal node 110 is resource constrained (limited terminal node capability). In examples, if the CU 165 determines, based, at least in part, on the terminal node capability information that the terminal node is resource constrained, the CU 165 can determine to configure the terminal node 110 with an indication 170B associated with delayed UE based TA estimation.

[0140] In examples, the CU 165 can determine to configure the terminal node 110 with an indication 170A associated with early UE based TA estimation when it is determined that the terminal node 110 should begin estimating TA information 172 based, at least in part, on receiving the configuration information 186 associated with CLTM.

[0141] In some examples, the CU 165 can determine to configure the terminal node 110 with an indication 170A associated with early UE based TA estimation when it isdetermined that the terminal node 110 should begin estimating TA information 172 in response to receiving the configuration information 186 associated with CLTM.

[0142] In examples, the CU 165 can determine to configure the terminal node 110 with an indication 170B associated with delayed UE based TA estimation when it is determined that the terminal node 110 should delay estimating TA information 172 after processing the configuration information 186 associated with CLTM.

[0143] In examples, configuring the terminal node 110, which in the illustrated example is a UE 164, with an indication 170 associated with UE based TA estimation comprises including information indicative of the indication 170 in the configuration information 186 associated with CLTM.

[0144] As discussed above in relation to the example of FIG. 2A, in some, but not necessarily all, examples, the configuration information 186 associated with CLTM is indicative of an indication associated with network based TA precedence, and an indication 170A associated with early UE based TA estimation.

[0145] Reference is made to the example of FIG. 2B. The example of FIG. 2B carries on from the example of FIG. 2A. However, in the example of FIG. 2B, the configuration information 186 associated with CLTM comprises information indicative of an indication associated with network based TA precedence, and information indicative of an indication 170A associated with early UE based TA estimation.

[0146] For the purposes of clarity, block 208 is shown again in the example of FIG. 2B to indicate the use of information indicative of the indication 170A associated with early UE based TA estimation. It is not intended to indicate that block 208 is performed twice.

[0147] Accordingly, FIG. 2B illustrates an example where the UE 164 is configured for early UE based TA estimation.

[0148] At block 210, method 200 comprises estimating TA information 172 for at least one candidate access node 174. The at least one candidate access node 174 comprises the first candidate access node 174A.

[0149] In examples, the UE 164 begins estimating TA information 172 based, at least in part, on receiving the configuration information 186 associated with CLTM.

[0150] In some examples, the UE 164 begins estimating TA information 172 based, at least in part, on receiving the configuration information 186 because early UE TA information estimation is enabled by the indication 170A associated with early UE based TA estimation. Accordingly, in example, block 210 comprises estimating TAinformation 172 for at least one candidate access node 174 based, at least in part, on the indication OA associated with early UE based TA estimation.

[0151] The UE 164 can, in some examples, start estimating TA information 172 for at least one candidate access node 174 as soon as the UE 164 receives the configuration information 186 and checks that the UE 164 is configured with UE based TA estimation.

[0152] In examples, the UE 164 estimates, maintains and updates the UE estimated TA information 172.

[0153] In examples, the UE 164 estimates TA information 172 for at least one candidate access node 174, the at least one candidate access node 174 comprising the first candidate access node 174A.

[0154] At block 212, method 200 comprises, from the point of view of the terminal node 110, receiving information 176 configured to instruct the UE 164 to initiate a randomaccess channel (RACH) procedure to acquire early TA information for CLTM.

[0155] The information 176 configured to instruct the UE 164 to initiate a RACH procedure to acquire early TA information for CLTM can comprise any suitable information. In some examples, the information 176 configured to instruct the UE 164 to initiate a RACH procedure to acquire early TA information for CLTM comprises a PDCCH order. Accordingly, in examples, from the point of view of the UE 164, block 212 comprises receiving a PDCCH order.

[0156] In examples, the information 176 configured to instruct the UE 164 to initiate a RACH procedure to acquire early TA information for CLTM can be considered information to instruct the UE 164 to initiate early synchronization (uplink (UL) synch) to acquire early TA information.

[0157] In examples, the UE 164 transmits information associated with at least one measurement report, which can, in examples, be referred to as measurement report information, towards the source access node 173 and block 212 is performed based, at least in part, on the measurement report information.

[0158] The measurement report information can comprise at least one of at least one L1 measurement report, or at least one L3 measurement report.

[0159] At block 214, method 200 comprises disabling, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172.In examples, at block 214, the UE 164 performs at least one action to temporarily prevent the UE 164 from using the UE estimated TA information 172.

[0160] The UE 164 can perform any suitable action or actions to disable use of the UE estimated TA information 172. For example, the UE can set at least one indicator, such as at least one flag, configured to indicate that the UE 164 should not use the UE estimated TA information 172 while the indicator is set.

[0161] In some examples, the information indicative of the indication OA associated with early UE based TA estimation triggers at least one procedure at the UE 164 that stops UE based TA information estimation.

[0162] In examples, block 214 is performed based, at least in part, on block 212. Accordingly, in some examples, block 214 comprises setting at least one indicator, such as at least one flag, to disable use of the UE estimated TA information 172 based, at least in part, on receiving information 176 configured to instruct the UE 164 to initiate a RACH procedure to acquire early TA information for CLTM.

[0163] At block 216, method 200 comprises starting a timer associated with disabling use of the UE estimated TA information 172. In examples, use of the UE estimated TA information 172 is disabled while the timer associated with disabling use of the UE estimated TA information 172 is running. For example, the UE 164 may maintain the indicator that is set to disable use of the UE estimated TA information 172 while the timer associated with disabling use of the UE estimated TA information 172 is running.

[0164] The timer associated with disabling use of the UE estimated TA information 172 can have any suitable duration. For example, the timer associated with disabling use of the UE estimated TA information 172 can have a duration in the range 50ms to 350ms. For example, the timer associated with disabling use of the UE estimated TA information 172 can have a duration in the range 100ms to 300ms. For example, the timer associates with disabling use of the UE estimated TA information 172 can have a duration of 100ms, 200ms, or 300ms.

[0165] The duration of the timer associated with disabling use of the UE estimated TA information 172 can be configured at the UE 164 in any suitable way using any suitable method. In some examples, the duration for the timer can be preconfigured at the UE 164, for example during manufacture, and the duration for the timer can be retrieved from at least one memory of the UE 164.

[0166] In some examples, the duration for the timer associated with disabling use of the UE estimated TA information 172 can be configured at the UE 164 by the network.For example, the source access node 173 can transmit information indicative of the duration for the timer associated with disabling use of the UE estimated TA information 172.

[0167] The timer associated with disabling use of the UE estimated TA information 172 can be referred to as a disablement timer.

[0168] In examples, block 216 comprises starting the timer based, at least in part, on transmitting physical random access channel (PRACH) preamble after receiving the information configured to instruct the UE 164 to initiate a RACH procedure to acquire early TA information for CLTM.

[0169] In some examples, the UE 164 starts the timer associated with disabling use of the UE estimated TA information upon transmission of the PRACH preambles towards the first candidate access node 174A.

[0170] In examples, use of the UE estimated TA information is disabled while the timer associated with disabling use of the UE estimated TA information 172 is running. Accordingly, in examples, block 216 can be an action to disable use of the UE estimated TA information 172 at block 214.

[0171] In examples, suspension can be beam-specific, for example, only for UE expects to do LTM cell change on beam(s) used for NW-based TA acquisition.

[0172] At block 218, method 200 comprises determining that a CLTM condition or conditions for a first candidate access node 174A has been met.

[0173] In examples, the UE 164 evaluates the CLTM condition or conditions associated with at least one candidate access node 174. For example, the UE 164 can perform at least one measurement in relation to at least one candidate access node 174 to determine that a CLTM condition or conditions for a first candidate access node 174A has been met.

[0174] In some examples, the UE 164 begins to evaluate the condition or conditions for CLTM after the processing of the configuration information 168 is complete. For example, the UE 164 can begin evaluating the condition or conditions for CLTM based, at least in part, on transmitting an RRC Reconfiguration Complete message towards the source access node 173 following receiving the configuration information 168 associated with CLTM.

[0175] At block 220, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, atleast in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0176] Consequently, FIGS. 2A and 2B illustrate a method 200 comprising: receiving configuration information 168 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 168 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170A associated with early UE based TA estimation; estimating TA information for at least one candidate access node 174; receiving information 176 configured to instruct the UE 164 to initiate a random-access channel (RACH) procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172; starting a timer associated with disabling use of the UE estimated TA information 172; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0177] In some examples, block 220 comprises performing RACH-less CLTM towards the first candidate access node 174A.

[0178] In some examples, block 220 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, at least in part on the timer associated with disabling use of the UE estimated TA information 172 and the indication OA associated with early UE based TA estimation.

[0179] At block 222, method 200 comprises determining that valid TA information provided by an access node 120 is unavailable at the UE 164 when the CLTM condition or conditions for the first candidate access node 174A has been met, and triggering RACH-less CLTM towards the first candidate access node 174A is based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172 and determining that valid TA information provided by an access node 120 is unavailable at the UE 164.

[0180] Determining that valid TA information provided by an access node 120 is unavailable can comprise determining that valid network based TA information is unavailable at the UE 164.Determining that valid TA information provided by an access node 120, for example the source access node 173, is unavailable can be performed in any suitable way, using any suitable method. In some examples, determining that valid TA information provided by an access node 120 is unavailable comprises determining that TA information provided by an access node 120 has become invalid. In some examples, determining that valid TA information provided by an access node 120 is unavailable comprises determining that TA information has not been provided by the network, for example by an access node 120, such as the source access node 173.

[0181] As discussed above, in some examples, determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises determining that TA information provided by an access node 120 has become invalid. By way of example, reference is made to the example of FIG. 2C.

[0182] FIG. 2C illustrates blocks that in some, but not necessarily all, examples are part of method 200.

[0183] Some of the blocks illustrated in the example of FIG. 2C are indicated as 222A, 222B, 222C. This is intended to indicate that in some examples these blocks can form part of block 222. However, in examples at least one of blocks 222A, 222B, 222C can be block(s) separate from block 222.

[0184] At block 222A, method 200 comprises, from the point of view of the terminal node 110, which in the illustrated example is a UE 164, receiving, from the source access node 173, information 180 indicative of TA information and information indicative of an associated timer value 182 for a timer associated with TA information validity. A timer value can be an indication of a duration for a timer.

[0185] In examples, the CU 165 determines the information 180 indicative of TA information and the associated timer value 182 for a timer associated with TA information validity, and the information 180 and timer value 182 is received by the source access node 173 from the CU 165.

[0186] In examples, block 222A can comprise transmitting / receiving any suitable message or messages. In some examples, block 222A comprises transmitting / receiving at least one medium access control (MAC) control element (CE) message. Accordingly, in examples, transmitting the information 180 indicative of TA information and an associated timer value 182 for a timer associated with TA information validity comprises transmitting at least one MAC CE message.In examples, the MAC CE transmitted at block 222 can be considered a new MAC CE. For example, the MAC CE transmitted at block 222 can be a MAC CE that does not contain a cell switch command CSC.

[0187] Information 180 indicative of TA information can be referred to as TA information. In examples, the information 180 indicative of TA information comprises information 180 indicative of TA information for the first candidate access node 174A.

[0188] In examples, the information 180 indicative of TA information and the associated timer value 182 can be received separately. For example, the information 180 indicative of TA information can be received at block 222A, and the associated timer value can be received with configuration information, for example in an RRC reconfiguration message, for example at block 208.

[0189] At block 222B, method 200 comprises starting a timer associated with TA information validity having the timer value 182. In examples, the TA information received from the source access node 173 is considered valid while the timer associated with TA information validity is running / has not expired.

[0190] The timer associated with TA information validity can be considered at least one of a TA information validity timer, or a network based TA information validity timer.

[0191] At block 222C, method 200 comprises determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met. For example, block 222C can be performed when block 218 has been performed.

[0192] In some examples, block 222A and 222B can be performed before block 218 so that the timer associated with TA information validity started at block 222B has expired when block 218 is performed and at block 222C it is determined that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0193] In examples, as the timer associated with TA information validity has expired when the CLTM condition or conditions has been met, the TA information of block 222A is considered invalid when the CLTM condition or conditions has been met.

[0194] Consequently, in examples such as examples illustrated by FIG. 2C, determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises: receiving, from the source access node 173, information 180 indicative of TA information and an associated timer value 182 for a timer associated with TA information validity, starting a timer associated with TA information validityhaving the timer value, and determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0195] At block 224, method 200 comprises stopping the timer associated with disabling use of the UE estimated TA information 172 based, at least in part, on determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0196] In examples, at block 224, the UE 164 determines that the CLTM condition(s) for the first candidate access node 174A has been met but the UE 164 does not have valid TA information for the first candidate access node 174A that has been provided by the network. This is because, in the example of FIG. 2C, the timer associated with TA information validity has expired and the TA information provided at block 222A is no longer valid.

[0197] In examples, at block 224, the UE 164 therefore stops the timer associated with disabling use of the UE estimated TA information 172 to re-enable use of the UE estimated TA information 172. This enables the UE 164 to have TA information for RACH-less CLTM towards the first candidate access node 174A even when the network provided TA information has become invalid.

[0198] In some examples, block 224 comprises enabling use of the UE estimated TA information 172.

[0199] At block 220, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 for the first candidate access node 174A.

[0200] Consequently, FIG. 2C illustrates a method 200 comprising: stopping the timer associated with disabling use of the UE estimated TA information based, at least in part, on determining that the timer associated with TA information validity has expired when CLTM condition or conditions for the first candidate access node 174A has been met, and triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information for the first candidate access node 174A.

[0201] Block 220 is shown in both the example of FIG. 2A and the example of FIG. 2C for the purposes of clarity. It is not intended to indicate that block 220 is performed twice.FIG. 20 illustrates examples where the network provided TA information expires and use of UE estimated TA information is controlled based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

[0202] In examples, the UE 164 is configured to perform such behavior by the indication 170A associated with early UE based TA estimation, and therefore examples illustrated by FIG. 20 can also be based, at least in part, on the indication 170A associated with early UE based TA estimation.

[0203] As discussed above, in some examples, determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises determining that TA information has not been provided by the network, for example by an access node 120, such as the source access node 173. By way of example, reference is made to the example of FIG. 2D.

[0204] FIG. 2D illustrates blocks that in some, but not necessarily all, examples are part of method 200.

[0205] A block illustrated in the example of FIG. 2D is indicated as 222D. This is intended to indicate that in some examples this block can form part of block 222. However, in examples block 222D can be separate from block 222.

[0206] As indicated by a crossed arrow from the source access node 173 to the UE 164, in the example of FIG. 2D, TA information has not been provided from the network to the UE 164.

[0207] In examples, the network, for example the source access node 173, decides not to provide TA information to the UE 164. In some examples, the network, for example the source access node 173 is unable to provide TA information to the UE 164. For example, the source access node 173 can be unable to provide TA information to the UE due to link problems. This can mean that the source access node 173 is unable to successfully transmit the information at block 222A of FIG. 2C towards the UE 164.

[0208] At block 222D, method 200 comprises determining that information 180 indicative of TA information has not been received from the source access node 173 when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0209] In examples, block 222D can be performed when block 218 has been performed. In examples, block 222D can be performed based, at least in part, on performing block 218.Consequently, in examples such as examples illustrated by FIG. 2D, determining that valid TA information provided by an access node 120 is unavailable at the UE comprises: determining that information 180 indicative of TA information has not been received from the source access node 173 when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0210] At block 226, method 200 comprises determining that the timer associated with disabling use of the UE estimated TA information 172 has expired when the CLTM condition or conditions for the first candidate access node 174 has been met and information 180 indicative of TA information has not been received from the source access node 173.

[0211] As the timer associated with disabling use of the UE estimated TA information 172 has expired, the UE 164 can re-enable use of the UE estimated TA information 172. In examples, block 226 comprises enabling use of the UE estimated TA information 172 based, at least in part, on determining that the timer associated with disabling use of the UE estimated TA information 172 has expired.

[0212] In examples, the timer associated with disabling use of the UE estimated TA information 172 can expire before, during, or after block 222D.

[0213] At block 220, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 for the first candidate access node 174A based, at least in part, on determining that the timer associated with disabling use of the UE estimated TA information has expired.

[0214] Block 220 is shown in both the example of FIG. 2A and the example of FIG. 2C for the purposes of clarity. It is not intended to indicate that block 220 is performed twice.

[0215] As discussed above in relation to the example of FIG. 2A, in some, but not necessarily all, examples, the configuration information 186 associated with CLTM is indicative of an indication associated with network based TA precedence, and an indication 170B associated with delayed UE based TA estimation.

[0216] Reference is made to the example of FIG. 2E. The example of FIG. 2E carries on from the example of FIG. 2A. However, in the example of FIG. 2E, the configuration information 186 associated with CLTM comprises information 168 indicative of an indication associated with network based TA precedence, and information indicative of an indication 170B associated with early UE based TA estimation.For the purposes of clarity, block 208 is shown again in the example of FIG. 2E to indicate the use of information indicative of the indication 170B associated with delayed UE based TA estimation. It is not intended to indicate that block 208 is performed twice.

[0217] Accordingly, FIG. 2E illustrates an example where the UE 164 is configured for delayed UE based TA estimation.

[0218] In some, but not necessarily all, examples FIGS 2A and 2E are alternatives. In examples, if the UE 164 is configured for both early UE based TA estimation and delayed UE based TA estimation the UE 164 determines that an error in configuration has occurred and informs the network, for example the source access node 173.

[0219] At block 230, method 200 comprises delaying TA information estimation based, at least in part, on the indication 170B associated with delayed UE based TA estimation.

[0220] In examples, without the indication 170B associated with delayed UE based TA estimation, the UE 164 can start estimating TA information after block 208. See, for example, FIG. 2B.

[0221] In some examples, block 230 comprises disabling estimating of TA information at the UE 164 based, at least in part, on the indication 170B associated with delayed UE based estimation.

[0222] In examples, the UE 164 performs at least one action to temporarily disable estimating TA information at the UE 164.

[0223] The UE 164 can perform any suitable action or actions to disable estimating TA information 172 by the UE 164. For example, the UE can set at least one indicator, such as at least one flag, configured to indicate that the UE 164 should not estimate TA information 172 while the indicator is set.

[0224] In some examples, the information indicative of the indication 170B associated with delayed UE based TA estimation triggers at least one procedure at the UE 164 that temporarily disables UE based TA information estimation.

[0225] In examples, block 230 is performed based, at least in part, on block 208. Accordingly, in some examples, block 230 comprises setting at least one indicator, such as at least one flag, to disable estimating TA information 172 by the UE 164 based, at least in part, on receiving the configuration information 186.

[0226] At block 232, method 200 comprises starting a timer associated with delaying TA information estimation based, at least in part, on the indication associated withdelayed UE based TA estimation. In examples, estimation of TA information 172 by the UE 164 is disabled while the timer associated with delaying TA information estimation is running. For example, the UE 164 may maintain the indicator that is set to disable estimation of TA information 172 by the UE 164 while the timer associated with delaying TA information estimation is running.

[0227] The timer associated with delaying TA information estimation can have any suitable duration. For example, the timer associated with delaying TA information estimation can have a duration in the range 100ms to 600ms. For example, the timer associated with delaying TA information estimation can have a duration in the range 200ms to 500ms. For example, the timer associated with delaying TA information estimation can have a duration greater than or equal to 400ms. For example, the timer associated with delaying TA information estimation can have a duration in the range 400ms to 600ms.

[0228] In examples, the duration of the timer associated with delaying TA information estimation is configured to be longer than a duration of a timer associated with TA validity and an estimated time taken for the UE 164 to estimate TA information 172.

[0229] The duration of the timer associated with delaying TA information estimation can be configured at the UE 164 in any suitable way using any suitable method. In some examples, the duration for the timer can be preconfigured at the UE 164, for example during manufacture, and the duration for the timer can be retrieved from at least one memory of the UE 164.

[0230] In some examples, the duration for the timer associated with delaying TA information estimation can be configured at the UE 164 by the network. For example, the source access node 173 can transmit information indicative of the duration for the timer associated with delaying TA information estimation.

[0231] The timer associated with delaying TA information estimation can be referred to as a delay timer.

[0232] In examples, block 232 comprises starting the timer based, at least in part, on receiving the configuration information 186. In some examples, the UE 164 starts the timer associated with delaying TA information estimation upon receiving the configuration information 186.

[0233] In examples, estimation of TA information is disabled at the UE 164 while the timer associated with delaying TA information estimation is running. Accordingly, inexamples, block 232 can be an action to disable estimating of TA information 172 by the UE 164 at block 230.

[0234] At block 234, method 200 comprises transmitting towards a source access node 173 information 190 indicative of an estimated time for the UE 164 to perform TA estimation to enable determining of a duration for a timer associated with TA information validity.

[0235] In examples, an estimated time for the UE 164 to perform TA estimation is a duration that it is estimated the UE 164 will take to estimate TA information 172. The estimated time for the UE 164 to perform TA estimation can be the time that is required by the UE 164 for estimating TA information 172.

[0236] In examples, the UE 164 determines the estimated time for the UE 164 to perform TA estimation. In some examples, the estimated time for the UE 164 to perform TA estimation is determined based, at least in part, on at least one of: transmission time of synchronization signal blocks (SSBs), the number of SSB measurements to be made, the propagation time, or the processing time for computing a time difference of arrival.

[0237] In examples, block 234 can comprise transmitting / receiving any suitable message or messages. In some examples, block 234 comprises transmitting / receiving at least one RRC reconfiguration complete message. In some examples, block 234 comprises transmitting the information 190 indicative of an estimated time for the UE 164 to perform TA estimation as part of UE capability reporting.

[0238] At block 236, method 200 comprises, from the point of view of the source access node 173, transmitting towards a CU 165 the information 190 indicative of an estimated time for the UE 164 to perform TA estimation.

[0239] In examples, block 236 can comprise transmitting / receiving any suitable message or messages. In some examples, block 236 comprises transmitting / receiving at least one RRC reconfiguration complete message.

[0240] Accordingly, from the point of view of the CU 165, block 236 comprises receiving information 190 indicative of an estimated time for a UE 164 to perform TA estimation.

[0241] At block 238, method 200 comprises determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE to perform TA estimation.In some examples, determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation comprises determining a duration of the timer that is greater than the estimated time for a UE 164 to perform TA estimation.

[0242] Accordingly, in examples, at block 238 it can be ensured that the determined duration for a timer associated with TA information validity is longer than the estimated time for a UE 164 to perform TA estimation.

[0243] At block 240, method 200 comprises transmitting information 192 indicative of the duration for a timer associated with TA information validity. In examples, the duration for a timer can be considered a timer value.

[0244] Consequently, FIG. 2E illustrates a method 200 comprising: receiving information 190 indicative of an estimated time for a UE 164 to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation; and transmitting information 192 indicative of the duration for a timer associated with TA information validity.

[0245] In examples, the CU 165 transmits information 180 indicative of TA information for at least one candidate access node 174, including the first candidate access node 174A towards the source access node 173. The information 180 can be sent together with the information 192 or separately from the information 192.

[0246] In some, but not necessarily all examples, the source access node 173 transmits the information 192 indicative of the duration for a timer associated with TA information validity and the information 180 indicative of TA information towards the UE 164.

[0247] At block 242, method 200 comprises from the point of view of the terminal node 110, which in the illustrated example is a UE 164, receiving, from the source access node 173, information 180 indicative of TA information and information 192 indicative of the duration for a timer associated with TA information validity.

[0248] In some examples, the information 192 indicative of the duration for a timer associated with TA validity can be referred to as information 192 indicative of a timer value for a timer associated with TA information validity. In examples, the information 192 indicative of the duration for a timer associated with TA information validity can beequivalent to the information indicative of the timer value 182 discussed in relation to FIG. 2C.

[0249] In examples, block 242 can comprise transmitting / receiving any suitable message or messages. In some examples, block 242 comprises transmitting / receiving at least one MAC CE message. Accordingly, in examples, receiving the information 180 indicative of TA information and information 192 indicative of the duration for a timer associated with TA validity comprises transmitting at least one MAC CE message.

[0250] In examples, the MAC CE transmitted at block 242 can be considered a new MAC CE. For example, the MAC CE transmitted at block 242 can be a MAC CE that does not contain a cell switch command CSC.

[0251] Information 180 indicative of TA information can be referred to as TA information. In examples, the information 180 indicative of TA information comprises information 180 indicative of TA information for the first candidate access node 174A.

[0252] In examples, the information 180 indicative of TA information and the information 192 indicative of the duration for a timer associated with TA validity can be received separately. For example, the information 180 indicative of TA information can be received at block 242, and the associated timer value can be received with configuration information, for example in an RRC reconfiguration message.

[0253] In some examples, the information at block 242 is successfully received at the UE 164. See, for example, FIG. 2F. In some examples, the information at block 242 is not successfully received at the UE 164, or is not provided to the UE 164. See, for example, FIG. 2G.

[0254] At block 244, method 200 comprises determining that a CLTM condition or conditions for a first candidate access node 174A has been met.

[0255] In examples, the UE 164 evaluates the CLTM condition or conditions associated with at least one candidate access node 174. For example, the UE 164 can perform at least one measurement in relation to at least one candidate access node 174 to determine that a CLTM condition or conditions for a first candidate access node 174A has been met.

[0256] In some examples, the UE 164 begins to evaluate the condition or conditions for CLTM after the processing of the configuration information 168 is complete. For example, the UE 164 can begin evaluating the condition or conditions for CLTM based, at least in part, on transmitting an RRC Reconfiguration Complete message towardsthe source access node 173 following receiving the configuration information 168 associated with CLTM.

[0257] At block 246, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0258] Consequently, FIGS. 2A and 2E illustrate a method 200 comprising: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170B associated with delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0259] In some examples, block 246 comprises performing RACH-less CLTM towards the first candidate access node 174A.

[0260] In some examples, block 246 comprises triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part on the timer associated with delaying TA information estimation and the indication 170B associated with delayed UE based TA estimation.

[0261] At block 248, method 200 comprises determining that valid TA information provided by an access node 120 is unavailable at the UE 164 when the CLTM condition or conditions for the first candidate access node 174A has been met, and triggering RACH-less CLTM towards the first candidate access node 174A is based, at least in part, on the timer associated with delaying TA information estimation and determining that valid TA information provided by an access node 120 is unavailable at the UE 164.

[0262] Determining that valid TA information provided by an access node 120 is unavailable can comprise determining that valid network based TA information is unavailable at the UE 164.

[0263] Determining that valid TA information provided by an access node 120, for example the source access node 173, is unavailable can be performed in any suitableway, using any suitable method. In some examples, determining that valid TA information provided by an access node 120 is unavailable comprises determining that TA information provided by an access node 120 has become invalid. In some examples, determining that valid TA information provided by an access node 120 is unavailable comprises determining that TA information has not been provided by the network, for example by an access node 120, such as the source access node 173.

[0264] As discussed above, in some examples, determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises determining that TA information provided by an access node 120 has become invalid. By way of example, reference is made to the example of FIG. 2F.

[0265] FIG. 2F illustrates blocks that in some, but not necessarily all, examples are part of method 200.

[0266] Some of the blocks illustrated in the example of FIG. 2F are indicated as 248A, 248B. This is intended to indicate that in some examples these blocks can form part of block 248. However, in examples at least one of blocks 248A, 248B can be block(s) separate from block 248.

[0267] The example of FIG. 2F comprises block 242 of FIG. 2E. In the example of FIG. 2F the information 180 indicative of TA information and information 192 indicative of the duration for a timer associated with TA information validity is successfully received by the UE 164 at block 242.

[0268] Block 242 is included in the example of FIG. 2F for the purposes of clarity, to indicate that, in the example of FIG. 2F, the information is successfully received by the UE 164. It is not intended to indicate that block 242 is performed twice.

[0269] In some examples, block 242 can be considered to be part of block 248.

[0270] At block 248A, method 200 comprises starting a timer associated with TA information validity having the timer duration received at block 242 as described above. In examples, the TA information received from the source access node 173 is considered valid while the timer associated with TA information validity is running / has not expired.

[0271] The timer associated with TA information validity can be considered at least one of a TA information validity timer, or a network based TA information validity timer.

[0272] At block 250, method 200 comprises stopping the timer associated with delaying TA information estimation based, at least in part, on receiving the information 180 indicative of TA information.In examples, at block 250, the UE 164 stops the timer associated with delaying TA information estimation to re-enable estimating TA information at the UE 164. This enables the UE 164 to estimate TA information for RACH-less CLTM towards the first candidate access node 174A in case the network provided TA information becomes invalid.

[0273] In examples, estimating TA information 172 at the UE 164 is delayed, based, at least in part, on the indication 170B associated with delayed UE based TA estimation until the information 180 indicative of TA information has been received from the network, for example the source access node 173.

[0274] In some examples, block 250 comprises enabling use of the UE estimated TA information 172.

[0275] At block 252, method 200 comprises starting estimating TA information 172 for at least the first candidate access node 174A prior to expiry of the timer associated with TA information validity.

[0276] In examples, the UE 164 estimates TA information 172 for at least one candidate access node 174, the at least one candidate access node 174 comprising the first candidate access node 174A.

[0277] In examples, the UE 164 estimates, maintains and updates the UE estimated TA information 172.

[0278] In examples, the UE 164 begins estimating TA information 172 after the timer associated with delaying TA information estimation is stopped at block 240 and prior to expiry of the timer associated with TA information validity.

[0279] In examples, the UE 164 begins estimating TA information at a time to enable estimated TA information to be available when the timer associated with TA information validity expires and the TA information received from the source access node 173 becomes invalid.

[0280] In some examples, method 200 comprises starting estimating TA information 172 at a time determined by the value of the timer associated with TA information validity minus an estimated time for the UE 164 to perform TA estimation.

[0281] In examples, the UE 164 starts estimating TA information 172 so that the estimating of TA information 172 will be complete substantially as the timer associated with TA information validity expires.In some examples, the UE 164 starts estimating TA information 172 after a period of (duration of timer associated with TA validity - estimated time for UE 164 to perform TA estimation) from receiving the information 180 indicative of TA information.

[0282] At block 248B, method 200 comprises determining that the timer associated with TA information validity (started at block 248A) has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0283] In examples, blocks 248A, 250, and 252 are performed before block 244 so that the timer associated with TA information validity started at block 248A has expired when block 244 is performed, and at block 248B it is determined that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0284] Accordingly, in examples, the UE 164 starts estimating TA information before the CLTM condition or conditions for the first candidate access node 174A has been met.

[0285] In examples, as the timer associated with TA information validity has expired when the CLTM condition or conditions has been met, the TA information of block 242 is considered invalid when the CLTM condition or conditions has been met.

[0286] Consequently, in examples such as the examples illustrated by FIG. 2F determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises: receiving, from a source access node 173, information 180 indicative of TA information and an associated timer value for a timer associated with TA information validity, starting a timer associated with TA information validity having the timer value, and determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node 174A has been met.

[0287] At block 246, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 for the first candidate access node 174A.

[0288] Consequently, FIG. 2F illustrates a method 200 comprising: stopping the timer associated with delaying TA information estimation based, at least in part, on receiving the information 180 indicative of TA information, estimating TA information 172 for at least the first candidate access node 174A prior to expiry of the timer associated with TA information validity, and triggering RACH-less CLTM towards the first candidateaccess node 174A using the estimated TA information for the first candidate access node 174A.

[0289] Block 246 is shown in both the example of FIG. 2E and the example of FIG. 2F for the purposes of clarity. It is not intended to indicate that block 246 is performed twice.

[0290] FIG. 2F illustrates examples where the network provided TA information expires and the UE estimating TA information is controlled based, at least in part, on the timer associated with delaying TA information estimation.

[0291] In examples, the UE 164 is configured to perform such behavior by the indication 170B associated with delayed UE based TA estimation, and therefore examples illustrated by FIG. 2F can also be based, at least in part, on the indication 170A associated with delayed UE based TA estimation.

[0292] As discussed above, in some examples, determining that valid TA information provided by an access node 120 is unavailable at the UE 164 comprises determining that TA information has not been provided by the network, for example by an access node 120, such as the source access node 173. By way of example, reference is made to the example of FIG. 2G.

[0293] FIG. 2G illustrates blocks that in some, but not necessarily all, examples are part of method 200.

[0294] A block illustrated in the example of FIG. 2G is indicated as 248C. This is intended to indicate that in some examples this block can form part of block 248. However, in examples block 248C can be separate from block 248.

[0295] As indicated by a crossed arrow from the source access node 173 to the UE 164, in the example of FIG. 2G, TA information has not been provided from the network to the UE 164.

[0296] In examples, the network, for example the source access node 173, decides not to provide TA information to the UE 164. In such examples, block 242 in FIG. 2E does not occur, or the information indicative of TA information is not provided at block 242.

[0297] In some examples, the network, for example the source access node 173 is unable to provide TA information to the UE 164. For example, the source access node 173 can be unable to provide TA information to the UE due to link problems. This can mean that the source access node 173 is unable to successfully transmit the information at block 242 of FIG. 20 towards the UE 164.At block 248C, method 200 comprises determining that information 180 indicative of TA information has not been received from the source access node 173 prior to expiry of the timer associated with delaying TA information estimation.

[0298] Accordingly, in examples, the UE 164 determines that TA information has not been received from the source access node 173 before estimating TA information can be re-enabled at the UE 164.

[0299] At block 254, method 200 comprises stopping the timer associated with delaying TA information estimation based, at least in part, on determining that information 180 indicative of TA information has not been received from the source access node 173.

[0300] In examples, at block 254, the UE 164 stops the timer associated with delaying TA information estimation to re-enable estimating TA information at the UE 164. This enables the UE 164 to estimate TA information for RACH-less CLTM towards the first candidate access node 174A so that the estimated TA information 172 is available when the timer associated with delaying TA information estimation would have expired if it were not stopped at block 254.

[0301] In examples, estimating TA information 172 at the UE 164 is delayed, based, at least in part, on the indication 170B associated with delayed UE based TA estimation until it is determined that information 180 indicative of TA information has not been received from the source access node 173 and the timer associated with delaying TA information estimation is about to expire.

[0302] In examples the timer associated with delaying TA information estimation is stopped if the timer reaches almost towards the timer expiry so that the UE 164 can estimate TA information in case the information 180 indicative of TA information is not received from the source access node 173.

[0303] In some examples, block 254 comprises enabling use of the UE estimated TA information 172.

[0304] At block 256, method 200 comprises starting estimating TA information 172 for at least the first candidate access node 174A.

[0305] In examples, the UE 164 estimates TA information 172 for at least one candidate access node 174, the at least one candidate access node 174 comprising the first candidate access node 174A.

[0306] In examples, the UE 164 estimates, maintains and updates the UE estimated TA information 172.In examples, the UE 164 begins estimating TA information 172 after the timer associated with delaying TA information estimation is stopped at block 254 and prior to when the timer associated with delaying TA information estimation would have expired if it were not stopped.

[0307] In examples, the UE 164 begins estimating TA information at a time to enable estimated TA information to be available when the timer associated with delaying TA information estimation would have expired if it were not stopped.

[0308] In some examples, method 200 comprises starting estimating TA information at a time determined by the value of the timer associated with delaying TA information estimation minus an estimated time for the UE to perform TA estimation.

[0309] In examples, the UE 164 starts estimating TA information 172 so that the estimating of TA information 172 will be complete substantially as the timer associated with delaying TA information estimation would have expired if it were not stopped.

[0310] At block 246, method 200 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 for the first candidate access node 174A.

[0311] Consequently, FIG. 2G illustrates a method 200 comprising: determining that information 180 indicative of TA information has not been received from the source access node 173 prior to expiry of the timer associated with delaying TA information estimation, stopping the timer associated with delaying TA information estimation based, at least in part, on determining that information indicative of TA information has not been received from the source access node 173, estimating TA information for at least the first access node, and triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 for the first candidate access node 174A.

[0312] Block 246 is shown in both the example of FIG. 2E and the example of FIG. 2G for the purposes of clarity. It is not intended to indicate that block 246 is performed twice.

[0313] In examples, the UE 164 is configured to perform the behavior associated with delayed UE based TA information estimation by the indication 170B associated with delayed UE based TA estimation.

[0314] Examples of the disclosure are advantageous and / or provide technical benefits.For example, examples of the disclosure ensure that TA information for CLTM is available at a UE 164.

[0315] For example, examples of the disclosure help to ensure that a UE can perform RACH-less CLTM towards a candidate access node.

[0316] For example, examples of the disclosure enable the network to control UE based TA estimation, for example based on circumstances of the UE.

[0317] For example, examples of the disclosure enable UE TA information estimation to be started when the UE can be confident the network is delaying provision of TA information, or is not able to provide TA information, benefitting, for example, UEs having limited capabilities

[0318] FIG. 3 illustrates an example of a method 300. Method 300 can be performed by any suitable apparatus comprising any suitable means for performing method 300, for example an apparatus as described in relation to FIG. 10A and / or 10B.

[0319] In examples, method 300 can be performed by a terminal node 110, such as a UE 164, or by at least one control device configured to control the functioning thereof.

[0320] At block 302, method 300 comprises receiving configuration information 168 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 168 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170A associated with early UE based TA estimation.

[0321] At block 304, method 300 comprises estimating TA information for at least one candidate access node 174.

[0322] At block 306, method 300 comprises receiving information 176 configured to instruct the UE 164 to initiate a random-access channel (RACH) procedure to acquire early TA information for CLTM.

[0323] At block 308, method 300 comprises disabling, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172.

[0324] At block 310, method 300 comprises starting a timer associated with disabling use of the UE estimated TA information 172.

[0325] At block 312, method 300 comprises determining that a CLTM condition or conditions for a first candidate access node 174A has been met.At block 314, method 300 comprises triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0326] Consequently, FIG. 3 illustrates a method 300 comprising: receiving configuration information 168 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 168 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170A associated with early UE based TA estimation; estimating TA information for at least one candidate access node 174; receiving information 176 configured to instruct the UE 164 to initiate a random-access channel (RACH) procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172; starting a timer associated with disabling use of the UE estimated TA information 172; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0327] FIG. 4 illustrates an example of a method 400. Method 400 can be performed by any suitable apparatus comprising any suitable means for performing method 400, for example an apparatus as described in relation to FIG. 10A and / or 10B.

[0328] In examples, method 400 can be performed by a terminal node 110, such as a UE 164, or by at least one control device configured to control the functioning thereof.

[0329] At block 402, method 400 comprises receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170B associated with delayed UE based TA estimation.

[0330] At block 404, method 400 comprises delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation.At block 406, method 400 comprises starting a timer associated with delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation.

[0331] At block 408, method 400 comprises determining that a CLTM condition or conditions for a first candidate access node 174A has been met.

[0332] At block 410, method 400 comprises triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0333] Consequently, FIG. 4 illustrates a method 400 comprising: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170B associated with delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0334] FIG. 5 illustrates and example of a method 500. Method 500 can be performed by any suitable apparatus comprising any suitable means for performing method 500, for example an apparatus as described in relation to FIG. 10A and / or 10B.

[0335] In examples, method 500 can be performed by an access node 120, such as a CU 165, or by at least one control device configured to control the functioning thereof.

[0336] At block 502, method 500 comprises receiving information 184 associated with conditional L1 / L2 triggered mobility (CLTM).

[0337] At block 504, method 500 comprises determining configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation.

[0338] At block 506, method 500 comprises transmitting the configuration information 186.Consequently, FIG. 5 illustrates a method 500 comprising: receiving information 184 associated with conditional L1 / L2 triggered mobility (CLTM); determining configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information 186.

[0339] FIG. 6 illustrates and example of a method 600. Method 600 can be performed by any suitable apparatus comprising any suitable means for performing method 600, for example an apparatus as described in relation to FIG. 10A and / or 10B.

[0340] In examples, method 600 can be performed by an access node 120, such as a CU 165, or by at least one control device configured to control the functioning thereof.

[0341] At block 602, method 600 comprises receiving information 190 indicative of an estimated time for a UE 164 to perform TA estimation.

[0342] At block 604, method 600 comprises determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation.

[0343] At block 606, method 600 comprises transmitting information 192 indicative of the duration for a timer associated with TA information validity.

[0344] Consequently, FIG. 6 illustrates a method 600 comprising: receiving information 190 indicative of an estimated time for a UE 164 to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation; and transmitting information 192 indicative of the duration for a timer associated with TA information validity.

[0345] FIG. 7 illustrates and example of a method 700. Method 700 can be performed by any suitable apparatus comprising any suitable means for performing method 700, for example an apparatus as described in relation to FIG. 10A and / or 10B.

[0346] In examples, method 700 can be performed by an access node 120, such as a DU, or by at least one control device configured to control the functioning thereof.

[0347] At block 702, method 700 comprises receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation.At block 702, method 700 comprises transmitting the configuration information towards at least one user equipment (UE) 164.

[0348] Consequently, FIG. 7 illustrates a method 700 comprising: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information towards at least one user equipment (UE) 164.

[0349] In examples of the disclosure a method based on signalling and procedural enhancements is described which would define the UE behaviour when UE based TA is initially configured for C-LTM and network (NW) in the meanwhile decides to provide the early TA and transmit a PDCCH order to the UE. In examples, it is assumed in general that the TA value provided by the network shall be more reliable compared to the UE estimated TA.

[0350] Example hereinafter referred to as Emb#1: NW sends indications to the UE along with the RRC Reconfiguration message during the preparation phase as part of the TA management policy. In examples, it includes the first indication as NW based TA precedence indication, the second indication as Early UE based TA estimation indication and third one is Delayed UE based TA estimation.

[0351] In examples, these indications can be given as part of the LTM configuration, either inside the candidate configuration, or outside the candidate configuration (for example as part of the reference configuration). In examples, if Early UE based TA estimation is enabled, then Delayed UE based TA estimation will be disabled and vice versa. In examples, if NW configures both, UE understands that this is an erroneous configuration and informs the NW about it.

[0352] In examples, these new indications can be part of the evaluation conditions for C-LTM as well. If these new indications are enabled, the UE behavior upon reception of these two additional indications are as follows:

[0353] NW based TA precedence indication

[0354] If NW-given TA is valid, UE uses it.

[0355] If no NW-given TA, or the NW-given TA has become invalid, UE uses its own TA estimate acquired through the UE-based TA estimation procedures (if configured by the NW).If no valid TA is available (for example, NW-given TA has expired, UE-based TA estimate has expired or the UE is not configured with UE-based TA estimation for the selected cell), UE does RACH. In some examples, this can be contention-based random access (CBRA). In some examples, this can be contention free random access (CFRA).

[0356] In examples, the above solution may also be applied to the following case: A candidate cell is configured both for C-LTM and LTM, and the UE receives the TA for the candidate cell in a MAC CE before the reception of the cell switch command. Later the UE receives a cell switch command for the same candidate cell without a valid TA (or TAC = FFF), then the above procedure may be followed, that is, network provided TA, given that its valid, may be used instead of a UE-based TA for the indicated candidate cell.

[0357] In examples, the cell switch command may contain an indication which tells the UE to use the TA it received in the new MAC CE previously instead of UE-based TA.

[0358] Early UE based TA estimation indication

[0359] In examples, UE can start estimating the TA for the LTM candidates as soon as it receives the RRC Reconfiguration message and checks that it is configured with UE based TA estimation This UE estimated TA is stored, maintained and updated by the UE.

[0360] In examples, if UE has received the PDCCH order for early sync, UE will temporarily suspend the use of the UE estimated TA. The duration for which UE suspends the use of the estimated and stored TA depends on the value of the proposed UE based TA de-activation timer (explained in example labelled Emb#2). Suspension can be beam-specific, that is, only for UE expects to do LTM cell change on beam(s) used for NW-based TA acquisition. In examples, UE may still perform UE-based TA estimation in parallel to executing the procedures required for the early TA estimation procedure.

[0361] In examples, UE can use the TA value it has estimated itself only if the networkgiven TA is invalid (for example, timer associated with the network given TA has expired).

[0362] In examples, UE can use the TA value it has estimated itself only if the new MAC CE containing the TA value is not received at the UE and the proposed UE based TA de-Activation timer expires while the C-LTM execution conditions are met.Delayed UE based TA estimation indication

[0363] In examples, UE reports the UE based TA estimation time (as part of UE capability reporting or through RRC Reconfiguration Complete) to the S-CU. The UE-based TA estimation time is the time that is required by the UE for estimating the TA and it may be impacted by the transmission time of SSBs, the required number of SSB measurements, the propagation time and / or the processing time for computing a time difference of arrival.

[0364] In examples, UE can start estimating the TA for the candidates indicated in the PDCCH order. In examples, this procedure can start (Absolute max. value of new TA maintenance timer - UE based TA estimation time) seconds upon receiving the new MAC CE containing the TA+ new TA maintenance timer value.

[0365] In examples, if the conditions for C-LTM cell switch execution is met while the new TA maintenance timer has expired (TA has become invalid), UE can use the UE based TA for RACH-less C-LTM cell switch.

[0366] In examples, if UE has not received the new MAC CE containing the TA and the new TA maintenance timer value, UE can start estimating the TA for the candidates specified in the PDCCH order, (Absolute max. value of UE based TA estimation suspension timer - UE based TA estimation time) seconds after starting the new proposed time, so that by the time when the timer expires, UE has completed the estimation of the TA.

[0367] In examples, if UE begins the estimation of the UE-based TA estimation after the triggering condition for CLTM execution is meet, that is, if there is an empty MAC CE and the conditions for triggering CLTM are meet, that is, “if no TA has been received in a MAC CE from the NW and the condition for executing CLTM cell switch towards the LTM candidate is met, UE begins the TA estimation process.

[0368] In examples, if this indication is configured, after a PDCCH order is received for a candidate cell, UE stops UE based TA estimation for a fixed amount of time. During this fixed amount of time, the UE expects a MAC CE to send the TA value for the candidate cell. After the expiry of the timer, UE re-starts the UE based TA procedure for the candidate cell.

[0369] Example hereinafter referred to as Emb#2: UE based TA de-activation timer In examples, UE can start this timer in case if UE has received Early UE based TA estimation indication along with the RRC reconfiguration message.In examples, UE can start the newly proposed UE based TA de-activation timer upon transmission of the PRACH preambles after receiving the PDCCH order during the Early Synch Phase.

[0370] In examples, if UE receives the new MAC CE with (TA+ TA maintenance timer), the new proposed UE based TA de-Activation timer is stopped. If the TA maintenance timer has expired (TA has become invalid) when the conditions for C-LTM is met, UE can use the UE based TA to execute RACH-less C-LTM.

[0371] In examples, if the UE based TA de-Activation timer expires and the UE doesn't receive the new MAC CE, then UE can re-use the estimated UE based TA and initiate RACH-less C-LTM when the conditions are met.

[0372] Example hereinafter referred to as Emb#3: UE based TA estimation suspension timer

[0373] In examples, UE can start this timer in case if UE has received Delayed UE based TA estimation indication along with the RRC reconfiguration message.

[0374] In examples, this new timer is started upon receiving the RRC Reconfiguration message and a relatively larger value is set for the maximum absolute value of this timer.

[0375] In examples, the timer is stopped if UE has received the new MAC CE containing the TA and the new TA maintenance timer.

[0376] In examples, this timer can also be stopped by the UE if it reaches almost towards the timer expiry (few seconds before the expiry so that UE can estimate the TA) in case if no new MAC CE containing the TA and the new TA maintenance timer has been received by UE from the network.

[0377] FIG. 8 illustrates an example of signaling between entities. FIG. 8 also illustrates a method 800. FIG. 8 is similar to the examples of FIGS. 2A to 2G, and can therefore illustrate multiple methods performed by individual actors.

[0378] Example hereinafter referred to as Solution#1: Early UE based TA estimation In the example of FIG. 8, UE estimates the TA but if PDCCH order for early synchronization is received from the network, UE will temporarily suspend the UE of the TA it estimated and wait to receive a valid TA from the network. In examples, if the network provided TA becomes invalid by the time C-LTM conditions for cell switch execution is met or for any reason if the new MAC CE containing the TA is not received at the UE, this example proposed handling of the stored UE estimated TA.

[0379] Block 1: UE transmit L3 measurements to the serving DU.Block 2: Serving DU forwards the L3 measurements to the source-CU.

[0380] Block 3: Source-CU decides to configure candidate cell(s) for L1 / L2 triggered mobility for intra-CU LTM

[0381] Block 4 and Block 5: Source CU sends UE Context Set-up Request to the candidate cell(s) belonging to a candidate DU different from the serving DU but under the same CU (gNB). The Source CU then receives UE Context Set-up Response from the candidate DU.

[0382] Block 6: Source-CU sends UE Context Modification Request to the serving DU which contains the CSI-Resource Configuration Request for LTM reporting configuration for the selected list of Candidate IDs.

[0383] Block 7: Serving DU decides it can trigger conditional LTM and includes execution conditions for conditional-LTM in reporting configuration.

[0384] Block 8: Serving DU then send the UE Context Modification Response to the source-CU which indicates the conditional-LTM executions conditions in case of reporting configurations and some pruned L1 measurement reporting configuration as necessary.

[0385] Block 9 and Block 10: Source-CU now prepares the RRC Reconfiguration Message which contains the LTM configuration of the selected candidate cell(s) including the conditional-LTM execution conditions which it has received from the serving DU and transmit it to the serving-DU as a transparent container. In examples, the RRC Reconfiguration message may also contain the proposed TA management policy which includes NW based TA precedence indication and Early UE based TA estimation indication as per example of Emb#1. In examples, the serving DU then forwards the RRC Reconfiguration message along with the newly proposed TA management policy containing the new indications to the UE.

[0386] Block 11: UE reads the RRC Reconfiguration message and finds that UE is configured with UE based TA estimation. It also reads the new indications contained within the RRC Reconfiguration message.

[0387] Block 12: UE starts estimating the TA. It is up to the UE to estimate, maintain and update the UE estimated TA.

[0388] Block 13: UE sends RRC Reconfiguration Complete message to the S-DU. Block 14: UE starts evaluating the conditional LTM cell switch execution conditions.

[0389] Block 15: S-DU sends the RRC Reconfiguration Complete to the S-CU.Block 16 and Block 17: UE continues reporting L1 measurements to the serving DU. However, there will be no explicit cell switch command from the network.

[0390] Block 18: UE receives the PDCCH order from the serving DU to initiate early synchronization (UL synch) to acquire early timing advance (TA).

[0391] Block 19: Based on the UE behaviour described in the Early UE based TA estimation indication; UE will temporarily suspend the use of the TA it estimated.

[0392] Block 20: As per example of Emb#2, UE will now initiate the UE based TA deActivation timer (As long as the timer is running, UE will suspend using the UE estimated TA).

[0393] Block 21, block 22 and block 23: UE send the PRACH preamble to the candidate cell. Candidate cell provides the Timing Advance (TA) to the S-CU which then shares the TA of the candidate cell along with the new TA maintenance timer to the S-DU.

[0394] Block 24: UE receives the TA and the absolute value of the new TA maintenance timer over the new MAC CE.

[0395] Scenario#1: TA obtained from the network has become invalid.

[0396] Block 25: UE determines that when the conditions for the C-LTM cell switch execution towards the best candidate cell is met, the new TA maintenance timer has expired (which implies that the TA provided by the network has become invalid).

[0397] Block 26: As per example of Emb#1, UE now decides to use the UE estimated TA which is maintained and updated by the UE.

[0398] Block 27: As per example of Emb#2, UE stops the UE based TA de-Activation Timer.

[0399] Block 28: UE checks the validity of the UE estimated and finds that the TA estimated by the UE is valid.

[0400] Block 29: UE triggers C-LTM cell switch towards the candidate cell.

[0401] Scenario#2: New MAC CE with TA is not received at the UE or the new MAC CE doesn’t contain the TA.

[0402] Block 30: S-DU couldn’t send the new MAC CE to the UE due to link problems between the S-DU and the UE.

[0403] Block 31: UE finds the UE based TA de-Activation timer has expired.

[0404] Block 32: As per example of Emb#1, UE now decides to use the UE estimated TA which is maintained and updated by the UE.Block 33: UE checks the validity of the UE estimated and finds that the TA estimated by the UE is valid.

[0405] Block 34: UE triggers C-LTM cell switch towards the candidate cell.

[0406] FIG. 9 illustrates an example of signaling between entities. FIG. 9 also illustrates a method 900. FIG. 9 is similar to the examples of FIGS. 2A to 2G, and can therefore illustrate multiple methods performed by individual actors.

[0407] Example hereinafter referred to as Solution#2: Delayed UE based TA estimation.

[0408] In examples, UE decides to have a delayed estimation of the TA if UE based TA estimation is configured. The time instant when to start the TA estimation is defined by the new UE based TA estimation suspension timer introduced.

[0409] Block 1: UE transmit L3 measurements to the serving DU.

[0410] Block 2: Serving DU forwards the L3 measurements to the source-CU.

[0411] Block 3: Source-CU decides to configure candidate cell(s) for L1 / L2 triggered mobility for intra-CU LTM.

[0412] Block 4 and block 5: Source CU sends UE Context Set-up Request to the candidate cell(s) belonging to a candidate DU different from the serving DU but under the same CU (gNB). The Source CU then receives UE Context Set-up Response from the candidate DU.

[0413] Block 6: Source-CU sends UE Context Modification Request to the serving DU which contains the CSI-Resource Configuration Request for LTM reporting configuration for the selected list of Candidate IDs.

[0414] Block 7: Serving DU decides it can trigger conditional LTM and includes execution conditions for conditional-LTM in reporting configuration.

[0415] Block 8: Serving DU then send the UE Context Modification Response to the source-CU which indicates the conditional-LTM executions conditions in case of reporting configurations and some pruned L1 measurement reporting configuration as necessary.

[0416] Block 9 and Block 10: Source-CU now prepares the RRC Reconfiguration Message which contains the LTM configuration of the selected candidate cell(s) including the conditional-LTM execution conditions which it has received from the serving DU and transmit it to the serving-DU as a transparent container. In examples, the RRC Reconfiguration message may also contain the proposed TA management policy which includes NW based TA precedence indication and Delayed UE based TAestimation indication as per example of Emb#1. In examples, the serving DU then forwards the RRC Reconfiguration message along with the newly proposed TA management policy containing the new indications to the UE.

[0417] Block 11: UE reads the RRC Reconfiguration message and finds that UE is configured with UE based TA estimation. It also reads the new indications contained within the RRC Reconfiguration message.

[0418] Block 12: Based on the Delayed UE based TA estimation indication, UE decides to have a delayed start of TA estimation and starts the UE based TA estimation suspension timer as described in example of Emb#3. In examples, the maximum duration of this timer value set longer ensuring that it is more than the expected maximum value of the new TA maintenance timer and the UE based TA estimation time.

[0419] Block 13: UE sends RRC Reconfiguration Complete message to the S-DU along with UE based TA estimation time.

[0420] Block 14: UE starts evaluating the conditional LTM cell switch execution conditions.

[0421] Block 15: S-DU sends the RRC Reconfiguration Complete to the S-CU along with UE based TA estimation time.

[0422] Block 16 and Block 17: UE continues reporting L1 measurements to the serving DU. However, there will be no explicit cell switch command from the network.

[0423] Block 18: UE receives the PDCCH order from the serving DU to initiate early synchronization (UL synch) to acquire early timing advance (TA).

[0424] Block 19, block 20 and block 21: UE send the PRACH preamble to the candidate cell. Candidate cell provides the Timing Advance (TA) to the S-CU which then shares the TA of the candidate cell along with the new TA maintenance timer to the S-DU.

[0425] Block 22: UE receives the TA and the absolute value of the new TA maintenance timer over the new MAC CE.

[0426] Scenario#1: TA obtained from the network has become invalid.

[0427] Block 23: UE stops the UE based TA estimation suspension timer.

[0428] Block 24: UE starts estimating the TA UE starts TA estimation after (TA maintenance timer - UE based TA estimation time) seconds upon receiving the new MAC CE containing the TA and the new TA maintenance timer (C-LTM conditions not yet met).Block 25: UE determines that the C-LTM conditions are met but the new TA maintenance timer has expired (TA became invalid).

[0429] Block 26: As per example of Emb#1, UE now decides to use the UE estimated TA which has been just evaluated maintained at the UE.

[0430] Block 27: UE triggers C-LTM cell switch towards the candidate cell.

[0431] Scenario#2: New MAC CE with TA is not received at the UE, or the new MAC CE doesn’t contain the TA.

[0432] Block 28: S-DU couldn’t send the new MAC CE to the UE due to link problems between the S-DU and the UE.

[0433] Step-29: UE stops the UE based TA estimation suspension timer few seconds before it expires. The stopping time depends on the time required by the UE to estimate the TA which means that the timer should be stopped (Maximum absolute value of UE based TA estimation suspension timer - UE based TA estimation time) seconds after the UE based TA estimation suspension timer was started.

[0434] Block 30: UE estimates the TA.

[0435] Block 31: C-LTM cell switch execution conditions are met.

[0436] Block 32 In examples, validity check for the UE estimated TA.

[0437] Block 33: UE triggers C-LTM cell switch towards the candidate cell According to various, but not necessarily all, examples there is provided a User Equipment, UE, comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the UE to perform at least: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with Delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using estimated TA information based, at least in part, on the timer associated with delaying TA information estimation.In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: transmitting towards a source access node information indicative of an estimated time for the UE to perform TA estimation to enable determining of a duration for a timer associated with TA information validity.

[0438] In some examples, the indication associated with network based TA precedence comprises information to configure the UE to give precedence to valid TA information provided by an access node over UE estimated TA information, and wherein the indication associated with delayed UE based TA estimation comprises information to configure determining of TA information by the UE.

[0439] In some examples, the configuration information associated with CLTM is received via at least one radio resource control, RRC, reconfiguration message.

[0440] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: determining that valid TA information provided by an access node is unavailable at the UE when the CLTM condition or conditions for the first candidate access node has been met; and wherein triggering RACH-less CLTM towards the first candidate access node is based, at least in part, on the timer associated with delaying TA information estimation and determining that valid TA information provided by an access node is unavailable at the UE.

[0441] In some examples, determining that valid TA information provided by an access node is unavailable at the UE comprises: receiving, from a source access node, information indicative of TA information and an associated timer value for a timer associated with TA information validity; starting a timer associated with TA information validity having the timer value; and determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node has been met.

[0442] In some examples, the associated timer value is determined based, at least in part, on information indicative of an estimated time for the UE to perform TA estimation transmitted by the UE towards the source access node.

[0443] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: stopping the timer associated with delaying TA information estimation based, at least in part, on receiving the information indicative of TA information; startingestimating TA information for at least the first candidate access node prior to expiry of the timer associated with TA information validity; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node.

[0444] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: starting estimating TA information at a time determined by the value of the timer associated with TA information validity minus an estimated time for the UE to perform TA estimation. In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: determining that information indicative of TA information has not been received from the source access node prior to expiry of the timer associated with delaying TA information estimation; stopping the timer associated with delaying TA information estimation based, at least in part, on determining that information indicative of TA information has not been received from the source access node; starting estimating TA information for at least the first candidate access node; and triggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node.

[0445] In some examples, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least: starting estimating TA information at a time determined by the value of the timer associated with delaying TA information estimation minus an estimated time for the UE to perform TA estimation.

[0446] According to various, but not necessarily all, examples there is provided a method comprising: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with Delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node has been met; andtriggering RACH-less CLTM towards the first candidate access nodeusing estimated TA information based, at least in part, on the timer associated with delaying TA information estimation.

[0447] According to various, but not necessarily all, examples there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with Delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication associated with delayed UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node has been met; and triggering RACH-less CLTM towards the first candidate access node using estimated TA information based, at least in part, on the timer associated with delaying TA information estimation.

[0448] According to various, but not necessarily all, examples there is provided a network node comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network node to perform at least: receiving information associated with conditional L1 / L2 triggered mobility, CLTM; determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with delayed UE based TA estimation; and transmitting the configuration information.

[0449] According to various, but not necessarily all, examples there is provided a method comprising: receiving information associated with conditional L1 / L2 triggered mobility, CLTM; determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with delayed UE based TA estimation; and transmitting the configuration information.

[0450] According to various, but not necessarily all, examples there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information associated with conditional L1 / L2 triggered mobility, CLTM; determining configuration information associated with CLTM, the configuration information indicative of an indicationassociated with network based timing advance, TA, precedence, and an indication associated with delayed UE based TA estimation; and transmitting the configuration information.

[0451] According to various, but not necessarily all, examples there is provided a network node comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network node to perform at least: receiving information indicative of an estimated time for a UE to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information indicative of an estimated time for a UE to perform TA estimation; and transmitting information indicative of the duration for a timer associated with TA information validity.

[0452] In some examples, determining a duration for a timer associated with TA information validity based, at least in part, on the information indicative of an estimated time for a UE to perform TA estimation comprises determining a duration of the timer that is greater than the estimated time for a UE to perform TA estimation.

[0453] According to various, but not necessarily all, examples there is provided a method comprising: receiving information indicative of an estimated time for a UE to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information indicative of an estimated time for a UE to perform TA estimation; and transmitting information indicative of the duration for a timer associated with TA information validity.

[0454] According to various, but not necessarily all, examples there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving information indicative of an estimated time for a UE to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information indicative of an estimated time for a UE to perform TA estimation; and transmitting information indicative of the duration for a timer associated with TA information validity.

[0455] FIG. 10A illustrates an example of a block diagram of an apparatus 130. The apparatus 130 may be a controller of an apparatus or device such as a terminal node 110, for example a UE 164, or an access node 120. The apparatus 130 may be considered a controller or controller device.Implementation of a controller 130 may be as controller circuitry. The controller 130 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

[0456] As illustrated in Fig 10A the controller 130 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions 136 in a general-purpose or special-purpose processor 132 that may be stored on a machine readable storage medium (disk, memory etc.) to be executed by such a processor 132.

[0457] The processor 132 is configured to read from and write to the memory 134. The processor 132 may also comprise an output interface via which data and / or commands are output by the processor 132 and an input interface via which data and / or commands are input to the processor 132.

[0458] The memory 134 stores instructions, program, or code 136 that controls the operation of the apparatus 130 when loaded into the processor 132. The instructions, program, or code 136, provide the logic and routines that enables the apparatus 130 to perform the methods illustrated in the accompanying FIGs. The processor 132 by reading the memory 134 is configured to load and execute the instructions, program, or code 136.

[0459] The apparatus 130 comprises: at least one processor 132; and at least one memory 134 storing instructions that, when executed by the at least one processor 132, cause the apparatus at least to: receive configuration information 168 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 168 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170A associated with early UE based TA estimation; estimate TA information for at least one candidate access node 174; receiving information 176 configured to instruct the UE 164 to initiate a random-access channel (RACH) procedure to acquire early TA information for CLTM; disable, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172; start a timer associated with disabling use of the UE estimated TA information 172; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and trigger RACH-less CLTM towards the first candidate access node 174A using theestimated TA information 172 based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0460] The apparatus 130 comprises: at least one processor 132; and at least one memory 134 storing instructions that, when executed by the at least one processor 132, cause the apparatus at least to: receive configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170B associated with delayed UE based TA estimation; delay TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; start a timer associated with delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and trigger RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0461] The apparatus 130 comprises: at least one processor 132; and at least one memory 134 storing instructions that, when executed by the at least one processor 132, cause the apparatus at least to: receive information 184 associated with conditional L1 / L2 triggered mobility (CLTM); determining configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information 186.

[0462] The apparatus 130 comprises: at least one processor 132; and at least one memory 134 storing instructions that, when executed by the at least one processor 132, cause the apparatus at least to: receive information 190 indicative of an estimated time fora UE 164 to perform TA estimation; determine a duration fora timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation; and transmit information 192 indicative of the duration for a timer associated with TA information validity.

[0463] The apparatus 130 comprises: at least one processor 132; and

[0464] at least one memory 134 storing instructions that, when executed by the at least one processor 132, cause the apparatus at least to: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configurationinformation 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information towards at least one user equipment (UE) 164.

[0465] As illustrated in Fig 10A, the instructions, program, or code 136 may arrive at the apparatus 130 via any suitable delivery mechanism 162. The delivery mechanism 162 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a solid-state memory, an article of manufacture that comprises or tangibly embodies the instructions 136. The delivery mechanism may be a signal configured to reliably transfer the instructions 136. The apparatus 130 may propagate or transmit the instructions 136 as a data signal.

[0466] The term “non-transitory” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0467] The instructions 136 cause an apparatus to perform at least the following: receiving configuration information 168 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 168 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170A associated with early UE based TA estimation; estimating TA information for at least one candidate access node 174; receiving information 176 configured to instruct the UE 164 to initiate a random-access channel (RACH) procedure to acquire early TA information for CLTM; disabling, based at least in part on the indication 170A associated with early UE based TA estimation and receiving the information 176 configured to instruct the UE 164 to initiate a RACH procedure, use of the UE estimated TA information 172; starting a timer associated with disabling use of the UE estimated TA information 172; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using the estimated TA information 172 based, at least in part, on the timer associated with disabling use of the UE estimated TA information 172.

[0468] The instructions 136 cause an apparatus to perform at least the following: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associatedwith network based timing advance (TA) precedence, and an indication 170B associated with delayed UE based TA estimation; delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; starting a timer associated with delaying TA information estimation based, at least in part, on the indication 170B associated with UE based TA estimation; determining that a CLTM condition or conditions for a first candidate access node 174A has been met; and triggering RACH-less CLTM towards the first candidate access node 174A using estimated TA information 172 based, at least in part, on the timer associated with delaying TA information estimation.

[0469] The instructions 136 cause an apparatus to perform at least the following: receiving information 184 associated with conditional L1 / L2 triggered mobility (CLTM); determining configuration information 186 associated with CLTM, the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information 186.

[0470] The instructions 136 cause an apparatus to perform at least the following: receiving information 190 indicative of an estimated time for a UE 164 to perform TA estimation; determining a duration for a timer associated with TA information validity based, at least in part, on the information 190 indicative of an estimated time for a UE 164 to perform TA estimation; and transmitting information 192 indicative of the duration for a timer associated with TA information validity.

[0471] The instructions 136 cause an apparatus to perform at least the following: receiving configuration information 186 associated with conditional L1 / L2 triggered mobility (CLTM), the configuration information 186 indicative of an indication 168 associated with network based timing advance (TA) precedence, and an indication 170 associated with UE based TA estimation; and transmitting the configuration information towards at least one user equipment (UE) 164.

[0472] The instructions 136 may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the instructions 136 may be distributed over more than one computer program.

[0473] Although the memory 134 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of whichmay be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0474] In examples the memory 134 comprises a random-access memory 158 and a read only memory 160. In examples the computer program 136 can be stored in the read only memory 158. See, for example, Fig. 10B.

[0475] Although the processor 132 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 132 may be a single core or multi-core processor.

[0476] References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry including quantum processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

[0477] As used in this application, the term ‘circuitry’ may refer to one or more or all the following: (a) hardware-only circuitry implementations (such as implementations in analog, digital and / or quantum circuitry) and (b) combinations of hardware circuit(s) and software, such as (as applicable):

[0478] i. a combination of analog, digital and / or quantum hardware circuit(s) with software / firmware and

[0479] ii. any or all portions of hardware processor(s) (including digital and / or quantum processor(s)) with software, and memory(ies) that work together to cause an apparatus, such as a mobile device, computing device or server, to perform various functions and

[0480] (c) any or all portions of hardware circuit(s), such as a microprocessor(s) and / or quantum processors, that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0481] The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the instructions 136. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

[0482] Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

[0483] In examples, an apparatus can comprise means for performing one or more methods, or at least part of one or more methods, as disclosed herein.

[0484] In examples, an apparatus can be configured to perform one or more methods, or at least a part of one or more methods, as disclosed herein.

[0485] The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

[0486] The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certainimplementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility.

[0487] The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’

[0488] In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components.

[0489] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database, or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0490] In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a propertyof only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

[0491] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or” mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0492] Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0493] Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

[0494] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0495] The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus.

[0496] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0497] The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates thatX may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

[0498] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent featuresinclude, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0499] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

[0500] As used herein, the terms “the at least one” and “the one or more” mean “any one of the at least one” and “any one of the one or mor” respectively.

[0501] The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0502] Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon.

[0503] l / we claim:

Claims

67CLAIMS1. A User Equipment, UE, comprising:at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the UE to perform at least:receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with early UE based TA estimation;estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM;disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information;starting a timer associated with disabling use of the UE estimated TA information;determining that a CLTM condition or conditions for a first candidate access node has been met; andtriggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

2. A UE as claimed in claim 1, wherein the indication associated with network based TA precedence comprises information to configure the UE to give precedence to valid TA information provided by an access node over UE estimated TA information, and wherein the indication associated with early UE based TA estimation comprises information to configure determining of TA information by the UE.

3. A UE as claimed in claim 1 or 2, wherein the configuration information associated with CLTM is received via at least one radio resource control, RRC, reconfiguration message.

684. A UE as claimed in any preceding claim, wherein starting the timer associated with disabling use of the UE estimated TA information comprises starting the timer based, at least in part, on transmitting physical random access channel, PRACH, preamble after receiving the information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM.

5. A UE as claimed in any preceding claim, any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least:determining that valid TA information provided by an access node is unavailable at the UE when the CLTM condition or conditions for the first candidate access node has been met; and wherein triggering RACH-less CLTM towards the first candidate access node is based, at least in part, on the timer associated with disabling use of the UE estimated TA information and determining that valid TA information provided by an access node is unavailable at the UE.

6. A UE as claimed in claim 5, wherein determining that valid TA information provided by an access node is unavailable at the UE comprises:receiving, from the source access node, information indicative of TA information and an associated timer value for a timer associated with TA information validity;starting a timer associated with TA information validity having the timer value; anddetermining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node has been met.

7. A UE as claimed in claim 6, wherein any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least:stopping the timer associated with disabling use of the UE estimated TA information based, at least in part, on determining that the timer associated with TA information validity has expired when the CLTM condition or conditions for the first candidate access node has been met; and69triggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node.

8. A UE as claimed in claim 5, wherein determining that valid TA information provided by an access node is unavailable at the UE comprises:determining that information indicative of TA information has not been received from the source access node when the CLTM condition or conditions for the first candidate access node has been met.

9. A UE as claimed in claim 8, wherein any one of the at least one memory storing instructions that, when executed by any one of the at least one processor, cause the UE to perform at least:determining that the timer associated with disabling use of the UE estimated TA information has expired when the CLTM condition or conditions for the first candidate access node has been met and information indicative of TA information has not been received from the source access node; andtriggering RACH-less CLTM towards the first candidate access node using the estimated TA information for the first candidate access node based, at least in part, on determining that the timer associated with disabling use of the UE estimated TA information has expired.

10. A method comprising:receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with Early UE based TA estimation;estimating TA information for at least one candidate access node; receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM;disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information;starting a timer associated with disabling use of the UE estimated TA information;70determining that a CLTM condition or conditions for a first candidate access node has been met; andtriggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

11. A method as claimed in claim 10, wherein the indication associated with network based TA precedence comprises information to configure the UE to give precedence to valid TA information provided by an access node over UE estimated TA information, and wherein the indication associated with early UE based TA estimation comprises information to configure determining of TA information by the UE.

12. A method as claimed in claim 10 or 11, wherein starting the timer associated with disabling use of the UE estimated TA information comprises starting the timer based, at least in part, on transmitting physical random access channel, PRACH, preamble after receiving the information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM.

13. A method as claimed in any of claims 10 to 12, comprising:determining that valid TA information provided by an access node is unavailable at the UE when the CLTM condition or conditions for the first candidate access node has been met; and wherein triggering RACH-less CLTM towards the first candidate access node is based, at least in part, on the timer associated with disabling use of the UE estimated TA information and determining that valid TA information provided by an access node is unavailable at the UE14. A computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following:receiving configuration information associated with conditional L1 / L2 triggered mobility, CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with early UE based TA estimation;estimating TA information for at least one candidate access node;71receiving information configured to instruct the UE to initiate a random-access channel, RACH, procedure to acquire early TA information for CLTM;disabling, based at least in part on the indication associated with early UE based TA estimation and receiving the information configured to instruct the UE to initiate a RACH procedure, use of the UE estimated TA information;starting a timer associated with disabling use of the UE estimated TA information;determining that a CLTM condition or conditions for a first candidate access node has been met; andtriggering RACH-less CLTM towards the first candidate access node using the estimated TA information based, at least in part, on the timer associated with disabling use of the UE estimated TA information.

15. A network node comprising:at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network node to perform at least:receiving information associated with conditional L1 / L2 triggered mobility, CLTM;determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information.

16. A network node as claimed in claim 15, wherein transmitting the configuration information comprises transmitting at least one radio resource control, RRC, reconfiguration message.

17. A method comprising:receiving information associated with conditional L1 / L2 triggered mobility, CLTM from a source access node;determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information towards the source access node.7218. A method as claimed in claim 17, wherein transmitting the configuration information comprises transmitting at least one radio resource control, RRC, reconfiguration message.

19. A computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following:receiving information associated with conditional L1 / L2 triggered mobility, CLTM from a source access node;determining configuration information associated with CLTM, the configuration information indicative of an indication associated with network based timing advance, TA, precedence, and an indication associated with UE based TA estimation; and transmitting the configuration information towards the source access node.

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