Apparatus and method for providing lower layer mobility in wireless communication systems

Abstract

Embodiments herein disclose a first apparatus that receives from a second apparatus, a radio resource control (RRC) message. The RRC message includes lower layer triggered mobility (LTM) cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of a third apparatus. The first apparatus evaluates one or more cell change conditions, based on the received LTM cell change configuration. The first apparatus reports to the second apparatus the evaluated one or more cell change conditions, and performs the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

Description

APPARATUS AND METHOD FOR PROVIDING LOWER LAYERMOBILITY IN WIRELESS COMMUNICATION SYSTEMSTechnical Field:

[0001] The present disclosure relates to the field of wireless communication, and more particularly relates to an apparatus and method for providing lower layer mobility in wireless communication systems.Background:

[0002] Certain abbreviations that may be found in the description and / or in the figures are herewith defined as follows.5G NR 5thGeneration New RadioCFRA Contention Free Random AccessCU Central UnitDU Distributed Unit gNB Next Generation Node BHO HandoverLTM Lower layer triggered switching or layer 1 / layer 2 triggered mobilityMAC CE Medium Access Control Control ElementPCell Primary CellPSCell Primary Secondary CellRRC Radio Resource ControlSCell Secondary CellSSB Synchronization Signal BlockTA Timing AdvanceUE User Equipment

[0003] Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) is a cell switch procedure, where a user equipment’s (UE) serving cell (Primary Cell (PCell) or PSCell) is switched by the network via an LTM cell switch command. The PCell is a primary cell in a master cell group (MCG) and the PSCell is a primary secondary cell in a secondary cell group (SCG). The LTM cell switch command can be delivered by Medium Access Control (MAC) signaling (i.e., L2 signaling) using a MAC CE (Control Element). Hence, not using Radio Resource Configuration (RRC) signaling as a layer 3 (L3) based handover, which is one of the current methods for changing between cells. LTM cell switch decision, is based on measurements (for example LI measurements) that are performed and reported (for example LI measurement report) by the UE. Measurements and reporting are based on the LTM candidate cell configuration provided by the network for one or more LTM candidate cells. An LTM candidate cell may be a UE’s neighboring cells and / or a UE’s current serving cells (e.g. SCells). In Release-18, LTM measurements on a neighboring candidate cell are performed using synchronization signal blocks (SSBs) transmitted by the candidate cell for which the SSB configuration is provided to the UE.

[0004] Before the UE undergoes the LTM cell switch, the network may optionally activate one or more transmission configuration indication (TCI) state(s) for one or more candidate cells. The TCI state is used to establish the quasi co-location (QCL) connection between a target reference signal and a source reference signal. Once a candidate cell’s TCI state is activated, the UE may start tracking the time / frequency synchronization using the reference signals associated with the activated TCI state(s). The UE may also perform early uplink (UL) synchronization before the cell switch if this is requested by the network.

[0005] Rel-18 LTM supports subsequent LTM, wherein after the UE has undergone the LTM cell switch procedure, the UE stores the LTM candidate cell configurations (i.e., the handover (HO)-related configurations that the UE received in the RRC Reconfiguration message) of the candidate cells and, after undergoing LTM cellchange, the UE re-uses the stored LTM candidate cell configurations when subsequently switching to one of the candidate cells. In other words, for a subsequent LTM candidate cell, the UE will continue to store the LTM configuration for the subsequent LTM candidate cell. Non-subsequent LTM candidate cells are those cells that the UE will not be switching to or switching back to, after undergoing LTM cell switch. Hence, it is not required for the UE to continue to store the LTM candidate configuration of the non-subsequent LTM candidate cells. Due to limited gNB / CU connectivity inside of radio access network (RAN), releasing of LTM configurations at the UE configured by a previous source gNB / CU may not be feasible or requires further signaling between the new source gNB / CU and the previous source gNB / CUSummary:

[0006] These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by advantageous embodiments of the present disclosure.

[0007] A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

[0008] In an embodiment, a first apparatus is provided. The first apparatus comprises at least one memory, storing a plurality of instructions, and at least one processor. The at least one processor, when executing the plurality of instructions, is configured to cause the first apparatus to receive from a second apparatus, a radio resource control (RRC) message. The RRC message includes lower layer triggered mobility (LTM) cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of a third apparatus. The first apparatus evaluatesone or more cell change conditions, based on the received LTM cell change configuration, The first apparatus reports the evaluated one or more cell change conditions to the second apparatus, and performs the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

[0009] In another embodiment disclosed herein, a second apparatus is provided. The second apparatus comprises at least one memory storing a plurality of instructions; and at least one processor, when executing the plurality of instructions, is configured to cause the second apparatus to perform the following. The second apparatus triggers a lower layer triggered mobility (LTM) cell change of a first apparatus to a third apparatus. The second apparatus receives, from the third apparatus, an allocation of LTM cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of the third apparatus. The second apparatus transmits, to the first apparatus, the LTM cell change configuration information, and wherein the first apparatus performs the LTM cell change to the third apparatus based on an evaluation of one or more cell change conditions.

[0010] In another embodiment disclosed herein, a method is provided. The method comprises receiving, from a second apparatus, a radio resource control (RRC) message. The RRC message includes lower layer triggered mobility (LTM) cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of a third apparatus. The method comprises evaluating one or more cell change conditions based on the received LTM cell change configuration information. The method comprises reporting to the second apparatus the evaluated one or more cell change conditions. The method comprises performing the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

[0011] In another embodiment disclosed herein, a method is provided. The method comprises triggering a lower layered mobility (LTM) cell change of a first apparatus to a third apparatus. The method comprises receiving, from the third apparatus, an allocation ofLTM cell change configuration information, comprising subsequent and non- subsequent LTM cell change configuration information, of the third apparatus. The method comprises transmitting, to the first apparatus, the LTM cell change configuration information, wherein the first apparatus performs the LTM cell change to the third apparatus based on an evaluation of one or more cell change conditions.

[0012] The details of the embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.Brief Description of Drawings:

[0013] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.FIG. 1 illustrates a message sequence chart for LTM procedure between a UE and a source network node;FIG. 2 illustrates a message sequence chart for a LTM procedure where the UE receives non-subsequent LTM indication, according to an embodiment of the present disclosure;FIG. 3 illustrates an environment with coexistence of non-subsequent inter-CU LTM and subsequent intra-CU LTM; according to an embodiment of the present disclosure;FIG. 4 illustrates a flowchart outlining a series of steps performed by a first apparatus, according to an embodiment of the present disclosure;FIG. 5 illustrates a flowchart outlining a series of steps performed by a second apparatus, according to an embodiment of the present disclosure; andFIG. 6 illustrates a block diagram of a device for implementing one or more embodiments of the present disclosure.Detailed Description

[0014] Exemplary embodiments now will be described with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey its scope to those skilled in the art. The terminology used in the detailed description of the particular exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting. In the drawings, like numbers refer to like elements. The term “exemplary embodiment” is meant to be interpreted as being an example embodiment and is not meant to be interpreted as a preferred embodiment.

[0015] The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

[0016] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless explicitly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and / or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, whenever the phrase “at least one of’ or “one or more of’ precedes a list of elements, wherein the elements are joined by “and” or “or”, it means that at least any one of the elements or at least all the elements are present. As used herein, whenever the phrase “one of’ precedes a list of elements, wherein the elements are joined by “and” or “or”, it means that only one of the elements are present at a given instant, unless the context permits a meaning that allows the inclusion of more than one element. The usage of the term “or” is to be understood as “inclusive or” instead of “exclusive or”, unless indicated otherwise by the relevant context. Conditional language, such as among others, “can” or “may”, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments may not include certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. As used herein, the term “and / or” includes any and all combinations and arrangements of one or more of the associated listed items.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0018] The figures depict a simplified structure only showing some elements and functional entities, all being logical units whose implementation may differ from what is shown. The connections shown are logical connections; the actual physical connections may be different. In addition, all logical units described and depicted in the figures include the software and / or hardware components required for the unit to function. Further, each unit may comprise within itself one or more components, which are implicitly understood. These components may be operatively coupled to each other and be configured to communicate with each other to perform the function of the said unit.

[0019] As used herein, the term “circuitry” may refer to at least one of the following: a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry); b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions); or c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0020] 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 particular claim element, a baseband integrated circuit orprocessor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0021] Before explaining in detail, the example embodiments of the present disclosure, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to FIG. 1 to assist in understanding the technology underlying the described examples.

[0022] In the following, different exemplifying embodiments will be described using, as an example of a communication network to which examples of embodiments may be applied, a communication network architecture based on 3 GPP standards for a communication network, such as 5G NR, without restricting the embodiments to such an architecture, however. It is apparent for a person skilled in the art that the embodiments may also be applied to other kinds of communication networks where mobile communication principles are integrated with a D2D (device-to-device) or V2X (vehicle to everything) configuration, such as SL (sidelink), e.g., Wi-Fi, worldwide interoperability for microwave access (WiMAX), Bluetooth, personal communications services, ZigBee, wideband code division multiple access (WCDMA), systems using ultra- wideband (UWB) technology, mobile ad-hoc networks (MANETs), wired access etc. Furthermore, without loss of generality, the description of some examples of embodiments is related to a mobile communication network, but principles of the disclosure can be extended and applied to any other type of communication network, such as a wired communication network.

[0023] A basic system architecture of a (tele)communication network including a mobile communication system, where some examples embodiments are applicable, may include an architecture of one or more communication networks including wireless access network subsystem(s) and core network(s). Such an architecture may include one or more communication network control elements or functions, access network elements, radio access network elements, access service network gateways or networknodes, such as a base station (BS), an access point (AP), a gNB, a distributed unit (DU) or a centralized / central unit (CU), which controls a respective coverage area or cell(s) and with which one or more communication stations such as communication elements or functions, like user devices or terminal devices, like a user equipment (UE), or another device having a similar function, such as a modern chipset, a chip, a module etc., which can also be part of a station, an element, a function or an application capable of conducting a communication, such as a UE, an element or function usable in a machine-to-machine communication architecture, or attached as a separate element to such an element, function or application capable of conducting a communication, or the like, are capable to communicate via one or more channels via one or more communication beams for transmitting several types of data in a plurality of access domains. Furthermore, core network elements or network functions, such as gateway network elements / functions, mobility management entities, a mobile switching center, servers, databases and the like, may be included.

[0024] The UE can be any device that is capable of sending and receiving radio signals. Nonlimiting examples of the UE comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, machine type devices or any combinations of these or the like.

[0025] The network node (e.g., a base station) can comprise a processor and associated circuitry to execute or direct the execution of computer-readable instructions to perform operations such as those further described herein. Briefly, the network node can retrieve and execute software from storage, which can include a disk drive, a flash drive, memory circuitry, or some other memory device, and which can be local or remotely accessible. The software may comprise computer programs, firmware, or some other form of machine-readable instructions, and may include an operating system, utilities, drivers, network interfaces, applications, or some other type ofsoftware, including combinations thereof. Further, the network node can receive instructions and other input at a user interface.

[0026] A gNB Central Unit (gNB-CU) comprises e.g., a logical node hosting e.g., RRC (Radio Resource Layer), SDAP (Service Data Adaptation Protocol) and PDCP (Packet Data Convergence Protocol) protocols of the gNB or RRC and PDCP protocols of the en- GNB that controls the operation of one or more gNB-DUs (gNB Distributed Units). The gNB-CU terminates the Fl interface connected with the gNB-DU. For the sake of simplicity, and because the embodiments disclosed herein may be applicable to an evolution system subsequent to the 5G NR system, the gNB-CU may be referred to as CU.

[0027] A gNB Distributed Unit (gNB-DU) comprises e.g., a logical node hosting e.g., RLC (Radio Link Control), MAC (Medium Access Control) and PHY (Physical) layers of the gNB or en-gNB, and its operation is partly controlled by the gNB-CU. One gNB- DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the Fl interface connected with the gNB-CU. A gNB-DU may support one or multiple cells, and could thus serve as, for example, a serving cell for a UE. The gNB CU and gNB DU parts may, for example, be co-located or physically separated. For the sake of simplicity, and because the embodiments disclosed herein may be applicable to an evolution system subsequent to the 5G NR system, the gNB- DU may be referred to as source DU or target DU.

[0028] The technical scheme described in the embodiment of the application can be applied to a 5G NR system and also can be applied to a subsequent evolution system of the 5G NR system. In this specification, a cell may refer to a component carrier having coverage of a signal transmitted from a transmission / reception point or a coverage of a signal transmitted from a transmission / reception point.

[0029] In this specification, a candidate cell (also referred to as “target cell” or “candidate target cell”) may refer to the cell that the UE considers for undergoing lower layer triggered mobility (LTM). A desired candidate cell (also referred to as “desiredcandidate target cell”) may refer to the cell that the UE switches to via the LTM switching command. In this specification, a source cell and a serving cell may be used synonymously. Similarly, a source network node and a serving network node may be used synonymously.

[0030] In a wireless communication network, there may be regions of radio coverage (referred to as a “cell”). Each cell may be supported by a network node (e.g., a base station). A user equipment may have a source cell, wherein it is associated with a network node (i.e., source network node) serving the source cell (also referred to as “serving cell”). When the cell quality of the source cell drops below a threshold, when compared to the cell quality of a target cell, a user equipment (UE) may undergo a mobility procedure (e.g., handover) to the target cell. The ability for a UE to communicate effectively with the wireless communication system as it moves through different cells, is typically referred to as mobility. One example of mobility is the layer 3 -triggered mobility (L3- triggered mobility, e.g., Radio Resource Control (RRC)), which involves L3 measurements and RRC signaling from the source network node to the UE to switch to the target cell. However, L3 -triggered mobility leads to layer 2 (L2, e.g., Medium Access Control (MAC) Control Element (CE)) and layer 1 (LI, e.g., Physical (PHY)) resets, resulting in increased latency, increased signaling overhead, and increased interruption time.

[0031] To overcome the issues with L3-triggered mobility, 3GPP (Third Generation Partnership Project) Release 18 (Rel-18) introduced LI / L2-triggered mobility, also referred to as lower-layer triggered mobility (LTM). LTM is a cell switch procedure, where the UE’s serving cell (PCell or PSCell) is switched as a result of the network sending an LTM cell switch command (e.g., via MAC CE signalling) to the UE. The LTM cell switch decision is based on measurements (e.g., LI measurements) that are performed and reported (e.g., LI measurement report) by the UE. The UE performs the measurements and reporting based on LTM candidate cell configuration provided by the network (in a RRC message) for one or more LTM candidate cells (also referred to as “LTM candidates”). The LTM candidate cell may be a neighbouring cell or a UE’scurrent serving cell (e.g. SCells). In Rel-18, the LTM measurements on the candidate cells can be performed based on synchronization signal blocks (SSBs) transmitted by the candidate cells for which the SSB configuration is provided to the UE.

[0032] Referring now to the drawings, and more particularly to FIGS. 1 to 5, where similar reference characters denote corresponding features used consistently throughout the figures relating to the example embodiments disclosed herein.

[0033] FIG. 1 illustrates a message sequence chart for LTM procedure between a UE and a source network node (e.g., Next Generation Node B (gNB)).

[0034] At step 1, the UE sends a MeasurementReport message to the gNB (i.e., the UE’s source network node). The measurement report includes L3 (RRC) measurements of a plurality of candidate cells. The gNB decides to configure LTM and initiates LTM candidate preparation.

[0035] At step 2, the gNB transmits an RRCReconfiguration message to the UE, the message including the LTM candidate configuration of the plurality of candidate cells.

[0036] At step 3, the UE stores the LTM candidate configuration (also referred to as “LTM candidate cell configuration”) of the plurality of candidate cells, and transmits an RRCReconfigurationComplete message to the gNB. The LTM candidate configuration can be a complete configuration (if there is no reference configuration), and if there is a reference configuration, the LTM candidate configuration is provided as delta configuration over the reference configuration. In the RRCReconfiguration message, the UE may receive the reference configuration (if present) and the LTM candidate configuration.

[0037] At step 4a, the UE performs downlink (DL) synchronization with the plurality of candidate cells before receiving the LTM cell switch command from the gNB. At step 4b, the UE performs early timing advance (TA) acquisition with the plurality of candidate cells, as requested by the network before receiving the cell switch command.This is done via contention free random access (CFRA) triggered by a physical downlink control channel (PDCCH) order from the serving cell, following which the UE sends a preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the plurality of candidate cell, the UE does not receive random access response from the network for the purpose of TA value acquisition. The TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity. It is to be noted that the UE may perform early TA acquisition only if requested by the network, and that in one or more embodiments disclosed herein, the UE may not perform early TA acquisition when undergoing LTM cell change.

[0038] At step 5, the UE performs LI measurements of the configured plurality of candidate cells, and transmits a measurement report, comprising the LI measurements, to the gNB. The LI measurement(s) should be performed as long as RRC reconfiguration (at step 2) is applicable.

[0039] At step 6, the gNB decides to execute cell switch to a desired candidate cell, from the plurality of candidate cells. The gNB transmits a cell switch command (e.g., a Medium Access Control (MAC) Control Element (CE) command) that triggers the cell switch, by including the candidate configuration index of the desired candidate cell in the cell switch command. The UE then switches to the desired candidate cell and applies the configuration indicated in the candidate configuration index.

[0040] At step 7, the UE performs the random access (RA) procedure towards the desired candidate cell, if the UE does have valid TA of the desired candidate cell.

[0041] At step 8, the UE completes the LTM cell switch, i.e., completes switch to the desired candidate cell, by sending RRCReconfigurationComplete message to the desired candidate cell. If the UE has performed a RA procedure in step 7, the UE considers that the LTM cell switch execution is successfully completed when the RA procedure is successfully completed. For RACH (random access channel)-less LTM, the UEconsiders that the LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first uplink (UL) data.

[0042] In the case of subsequent LTM, the steps 4-8 described above can be performed multiple times, wherein the UE can switch to other candidate cells (in the plurality of candidate cells) using the LTM candidate configuration provided in step 2. In the case of subsequent LTM, the UE continues to store the LTM candidate configuration of the candidate cells. In other words, after undergoing the LTM cell switch procedure, the UE does not release the LTM candidate configuration of the candidate cells (provided in step 2), thereby preventing the need for the gNB to send an additional RRCReconfiguration message with the LTM candidate configuration of the candidate cells.

[0043] According to Technical Specification (TS) 38.400 and 38.331, it is currently specified that the UE needs to store the LTM candidate cell configurations unless explicitly configured by the network to release these configurations (via an RRCReconfiguration message). Rel-18 LTM supports intra-CU (i.e., the UE’s serving cell and candidate cell belong to same central unit (CU)) LTM and inter-CU (i.e., the UE’s serving cell and candidate cell belong to different CUs) LTM. The main components of Intra-CU LTM, including early synchronization, would also be needed for inter-CU LTM. In case of inter-CU LTM, there might be a need to have a mix of both subsequent and non- subsequent LTM candidate cells (e.g., intra-CU LTM candidate cells can be subsequent, and inter-CU LTM candidate cells can be non-subsequent). For non- subsequent LTM candidate cells, it is not required for the UE to continue to store the LTM candidate configuration of the non-subsequent LTM candidate cells. Due to limited gNB / CU connectivity inside of radio access network (RAN), releasing of LTM configurations at the UE configured by a previous source gNB / CU may not be feasible or requires further signaling between the new source gNB / CU and the previous source gNB / CU.

[0044] The embodiments disclosed herein provide a solution to the above-mentioned issues.

[0045] In one embodiment, for one-way (non-subsequent) LTM for candidate cells, the LTM candidate configuration (also referred to as “LTM candidate cell configuration”) can be a delta configuration over a reference configuration. The reference configuration can be given by the network in the RRC Reconfiguration message. Alternatively, the reference configuration can be the UE’s serving sell configuration.. As part of the LTM handover preparation phase, the source CU can indicate which candidate cells are to be prepared as non-subsequent LTM cells. The target node (gNB2) can prepare the candidate cell configuration based on source configuration (from gNBl) instead of reference configuration. In other words, the UE applies a delta configuration of the candidate cell on top of the source configuration of the UE’s serving cell in order to switch to the candidate cell. One technical advantage of transmitting a delta configuration (in the RRC Reconfiguration message) instead of a complete configuration is the reduction in the size of the RRC Reconfiguration message.

[0046] The candidate RRC configuration may be exclusive of the LTM report config as there may not be subsequent LTM from the serving cell. In other words, it can be implicitly indicated that a candidate cell is configured as a non-subsequent LTM cell if the presence of the LTM report config is in the LTM candidate configuration instead of the LTM reference configuration. The LTM report config can refer to CSI-Reporting configuration to report LI measurements of the candidate cells, but is not limited to having the CSI-Reporting configuration. Towards the UE, the gNB2 includes an indication (e.g., a flag, number, or enumeration) in the LTM candidate configuration that ‘subsequent cell change disabled’.

[0047] Each candidate configuration is associated with a candidate cell identity (ID). Upon LTM execution to any candidate cell (either through the cell switch command (MAC CE) or in a UE autonomous manner through procedures like LTM recovery), the UE evaluates whether to maintain or release the current source cell LTM configuration. For example, if the source cell is an LTM candidate (e.g., a SCell), and if there is anindication that this is a non-subsequent LTM candidate, the LTM configuration of the source cell will be released in the UE and network / (CU+DU).

[0048] The LTM candidate configuration of non-subsequent LTM cells can include early-sync configuration, which is similar to other candidate cells. The LTM candidate configuration of non-subsequent LTM cells should not have LTM Report-config. Early RACH is triggered for the CFRA preamble. The target node can send TA information to the source CU / DU for the received preamble. The UE executes the HO in RACH- less manner via dynamic grant or configured grant. The UE then released the LTM config variable on execution.

[0049] FIG. 2 illustrates a message sequence chart for a LTM (e.g., L1 / L2 triggered mobility, i.e., LTM as referred to in TS 38.400) procedure where the UE receives non-subsequent LTM indication, according to an embodiment of the present disclosure. At steps 1-2, the UE sends an L3 measurement report to the source CU, via the source DU. At step 3, the source CU decides to configure for LTM.

[0050] At step 4, the source CU makes a handover request to a target CU. In an example embodiment, the source CU can already decide which candidate cells (covered by the target CU) should be configured as non-subsequent LTM cells (also referred to as “non- subsequent LTM candidate cells” and “non-subsequent LTM candidate”), and can inform the target CU of this in the form of a proposal or instruction in the handover request. Alternatively, the handover request can include a proposal or instruction from the source CU as to the number of candidate cells (covered by the target CU) to be configured as non-subsequent LTM cells.

[0051] At step 5, the target CU performs admission control, wherein if the handover request (from the source CU) includes the specific cells to be configured as non-subsequent LTM cells, the target CU can either accept or reject this instruction. In an embodiment where the handover request includes the number of candidate cells to be configured as non-subsequent LTM cells, the target CU may have already decided that certaincandidate cells should be configured as non-subsequent LTM cells and can indicate the specific candidate cells that should be configured this way. In the same embodiment, the target CU can otherwise indicate the number of candidate cells to be configured as non-subsequent LTM cells.

[0052] At step 6, the target CU sends a UE context setup request message to the target DU, wherein the UE context setup request message includes the target CU’s instructions, for the target DU, about the specific candidate cells to be configured as non-subsequent LTM cells or the number of candidate cells to be configured as non-subsequent LTM cells. The target DU can either accept or reject the instructions of the target CU. In another embodiment, the target DU can already decide which specific candidate cells are to be configured as non-subsequent LTM cells and indicate the specific candidate cells that are to be configured as non-subsequent LTM candidates. The target DU can also decide the number of candidate cells that are to be configured as non-subsequent LTM cells.

[0053] At step 7-8, the target DU sends the UE context setup response to the target CU, wherein the UE context setup response includes the list of cells configured as non- subsequent LTM cells. In embodiments where the target DU rejects the target CU’s instructions, the target DU can piggyback additional information clarifying why the instructions of the source CU or the target CU were rejected.

[0054] At step 9, the target CU sends a handover request acknowledgement message to the source CU, the message comprising the list of cells configured as non-subsequent LTM cells. The target CU can also piggyback additional information clarifying why the target CU rejected the instructions of the source CU, if this has occurred.

[0055] At steps 10-12, the source CU consolidates the RRC configuration containing the LTM configuration to be sent to the UE. The indication for the non-subsequent LTM candidate cells can be given as part of a candidate cell configuration and / or a reference configuration.

[0056] In the candidate cell configuration, there can be an indication to release only these LTM configurations (i.e., combination of the reference configuration (if present) and LTM candidate configuration). In another embodiment, the indication can be a list of LTM candidate cells and the reference configurations to be released. In another embodiment, the indication can be a list pointing to the identifiers of the LTM candidate cells and the reference configurations that should be released.

[0057] In an embodiment where the indication is provided in the reference configuration, if there are multiple reference configurations given to the UE, then the list of cells configured for non-subsequent LTM can be given as part of the reference configuration. This can happen in the following aspects. a. In a first aspect, there can be a CU-specific reference configuration containing the list of LTM candidate cells and / or reference configurations that should be released. In another example of the first aspect, the indication can be in the form of identifiers associated with the LTM candidate cells and / or the reference configurations that should be released. b. In a second aspect, the reference configuration might pertain to more than one CU. In this aspect, the list of LTM candidates for which subsequent LTM is not configured can be given as part of the reference configuration. In another example of the second aspect, the indication can be identifiers associated with the LTM candidate and / or the reference configurations that should be released. c. In a third aspect, the LTM reference configuration (either per CU or per multiple CUs) can contain a flag, based on which the UE releases all the non-subsequent LTM candidates at once. In one example of the third aspect, if the reference configuration is CU-specific, the UE may release all the LTM candidate cells under that CU. In another example of the third aspect, if the reference configuration spans more than one CU, this flag can indicate that the UE is torelease the LTM configuration of all the candidate cells that are linked to that reference configuration.

[0058] At steps 14-31 , the UE may perform early synchronization LTM execution procedures, which are similar to that outlined in FIG. 1. For the sake of brevity, the description of these steps is omitted.

[0059] At steps 32-33, upon successful LTM execution, the UE releases the LTM configurations (associated with each candidate cell) as provided by the network in the RRC Reconfiguration message, having the indication ‘subsequent cell change disabled’. The UE then sends the RRCReconfigurationComplete message to the target DU.

[0060] At steps 34-36, the target DU informs the target CU about the arrival of the UE. Then the path switch procedure takes place.

[0061] In an embodiment involving inter-CU (non-subsequent) and inter-CU (subsequent) LTM, the following may occur.

[0062] Each CU may prepare its own LTM configurations (for cells hosted by a CU). This can happen in the following aspects: a. In a first aspect, each CU uses its own reference configuration and provides the corresponding LTM candidate configuration. b. In a second aspect, different CUs negotiate a common reference configuration, and provide the LTM candidate configurations, for the different CUs, as delta configurations over the common reference configuration. c. In another implementation, where there is only one reference configuration across all LTM candidates or no reference configuration, each CU gives its own list of non-subsequent LTM candidates to the serving CU. If there would be asingle reference configuration across all CUs, this list of non-subsequent LTM candidates can be given as part of that reference configuration. As an example, the source CU would consolidate the list of non-subsequent LTM candidates which would then be forwarded to the UE.

[0063] Each candidate CU can inform the subsequent LTM groups (i.e., a list of cells, the cells hosted by the same or different gNB / DU / CU) to be maintained (or released) during preparation (indicated by ‘subsequent cell change is disabled’). This can happen in the following aspects: a. In a first aspect, wherein each CU has its own reference configuration, each CU can provide information on the subsequent LTM groups as part of the reference configuration, or it can include such group information in each of the LTM candidate configurations. This can mitigate any inter-operability issues which may arise due to the need for the source CU to decode the individual configurations coming from the different target CUs. b. In a second aspect, where a reference configuration is given across multiple CUs, the CUs which share a common reference configuration negotiate the list of subsequent and / or non-subsequent LTM candidates. The indication for the group of subsequent and / or non-subsequent LTM candidates can be given as part of the reference configuration (which would be common across multiple CUs), or as part of the candidate configurations. From the network’s perspective, this can avoid duplicate configurations, and allow each CU to be aware of the resources that will be released upon certain LTM execution. This way, should those CU become the source CU, they would be aware of the active configurations inside the UE, and if needed, can take faster actions to re-configure the UE. c. In a third aspect, where there is either only one reference configuration or no reference configuration at all, each CU sends the information of subsequent and non-subsequent LTM candidates to the source CU. The source CU then generatesthe LTM configuration which contains indicators for subsequent and non- subsequent LTM candidates and is sent to the UE.• If there is no reference configuration, then each LTM candidate cell configuration contains an indicator of non-subsequent LTM. In one implementation of the third aspect, the UE would only be able to release the configurations of the candidate cells which it has decoded. In another implementation, the source CU sends information about the groups of the subsequent and non-subsequent LTM candidates, outside the LTM candidate configurations. This would make it easier for the network to request the UE to release multiple candidate configurations at once, while saving the processing effort required from the UE side to decode those configurations. In another implementation of the third aspect, upon executing an inter-CU LTM handover, the UE releases the LTM configuration of the previous serving cell. In yet another implementation, upon executing an inter-CU LTM handover, the UE releases all the LTM candidate configurations pertaining to the previous source CU.• If there is a reference configuration (common across all CUs), then each LTM candidate configuration is given as delta over this reference configuration. This reduces the size of the RRC configuration message. Each LTM candidate configuration can contain an indicator of non- subsequent LTM. In another implementation, the source CU sends information about the groups of the subsequent and non-subsequent LTM candidates, as part of the reference configuration.

[0064] The UE is informed about the subsequent LTM groups to be maintained (or released) in the message including the LTM configuration. The candidate cells in each subsequent LTM group can have an identical type of LTM cell change (i.e., each cellin the subsequent LTM group can have an identical indication of whether ‘subsequence cell change is disabled’).

[0065] On switching to the new CU, the configurations of LTM candidates which are given as part of the subsequent-LTM groups are kept. Otherwise, the configurations of the LTM candidates which are not given as part of the subsequent LTM groups are released at the UE and NW (CU + DU) implicitly. This can be determined based on an indication of whether subsequent LTM is disabled.

[0066] FIG. 3 illustrates an environment with coexistence of non-subsequent inter-CU LTM and subsequent intra-CU LTM, according to an embodiment of the present disclosure. According to FIG. 3, cell 20 belongs to gNB2, whereas cells 10, 11, and 12 belong to gNBl. A mobility of the UE from cell 20 of gNB2 to cells 10 or 11 of gNBl, or vice versa, is non-subsequent inter-CU LTM. A mobility of the UE to different cells within gNBl, is subsequent intra-CU LTM.

[0067] In an embodiment involving intra-CU subsequent LTM combined with inter-CU non- subsequent LTM (with delta configuration), the following may occur.

[0068] The inter-CU candidates are prepared as delta-configuration with current serving cell configuration as basis. The UE maintains two configurations as reference configuration: the first reference configuration being the one provided in LTM configuration message, and the second reference configuration being the source configuration of the current source cell. The second reference configuration is maintained as the reference configuration for non-subsequent LTM.

[0069] Upon LTM execution, if the LTM candidate cell (i.e., the desired candidate cell / ) is intra-CU, then the UE uses the intra-CU reference configuration (i.e., the first configuration) and corresponding candidate configuration and executes intra-CU LTM. Consequently, in one example, the UE may automatically release the LTM configurations of non-subsequent LTM candidate cells. In a second example, the UE may release the non-subsequent LTM candidates only if there is an indication to releasethem. The indication can be provided via the RRC message, as previously explained herein. In a third example, the UE does not automatically release the LTM configurations of the non-subsequent LTM candidate cells.

[0070] Otherwise, if the desired candidate cell is in a different CU (i.e., inter-CU mobility), the UE may use the corresponding delta configuration (i.e., the candidate configuration) on top of the source cell configuration (i.e., the second reference configuration). If the previous serving cell was configured as subsequent LTM candidate, the UE does not release the LTM configurations of the previous serving cell. Otherwise, the UE releases the corresponding LTM configurations. In another example, if the previous serving CU was configured as a non-subsequent LTM candidate, then the UE releases the entire group of LTM candidate cells that were belonging to the previous serving CU.

[0071] The previously described embodiments cover a situation where the UE is explicitly indicated, via an indication in the RRC Reconfiguration message, about the non- subsequent LTM candidate cells. However, the UE may also be implicitly indicated of whether a candidate cell is a non-subsequent LTM candidate cell.

[0072] In one implementation, the behavior to release the candidate configurations is dependent on the serving cell from where the LTM cell switch is executed. If the serving cell is one of the candidate cells under the same CU, the non-subsequent LTM configurations are kept at the UE side. If the serving cell is not one of the candidate cells under the same CU, the non-subsequent LTM configurations are released. In other words, irrespective of whether the serving CU is a non-subsequent LTM candidate, if there is a change in the serving CU after undergoing LTM cell switch, the UE releases the LTM configuration of the previous serving CU. The UE can monitor through a variable it maintains to detect the CU or configuration group that the serving cell belongs to. For instance, if the UE has changed CUs, the UE might have to perform a PDCP reset and / or update the security keys. This way, the UE is able to determine if there has been a change in the serving CU.

[0073] In a second implementation for enabling implicit indication of subsequent and non- subsequent LTM candidate cells, the UE is provided with two candidate cell configurations: a first configuration for intra-CU LTM execution, and a second configuration for inter-CU LTM execution. If the UE applies the first configuration for intra-CU LTM execution to switch to candidate cell A, then it can be implicit that candidate cell A is a subsequent LTM cell. Upon switching to candidate cell A (i.e., the new serving cell of the UE), if the UE is to then switch to a candidate cell B, then the UE will retain the LTM configuration of candidate cell A even after switching to candidate cell B. When switching to candidate cell B, if the UE applies the second configuration for inter-CU LTM execution, then it can be implicit that candidate cell B is a non-subsequent LTM cell. After switching to candidate cell B (i.e., the new serving cell of the UE), if the UE then switches to candidate cell C, then the UE will release the LTM configuration of candidate cell B upon completing the switch to candidate cell C. By just transmitting two configurations, there is a reduction in the size of the RRC configuration message, and this ensures that there would be less signaling over the air interface, and at the same time, less processing effort on the UE side.

[0074] In another embodiment, the indication of a candidate cell being configured for non- subsequent LTM can be a timer, wherein if the UE does not use the LTM configuration (of any non-subsequent LTM candidate cell) for a threshold period of time (or expiry of the timer), the UE is to then release the LTM configuration(s) of the non-subsequent candidate cell(s). The timer can have any one of the following starting periods: a. When the UE decodes the entire LTM configuration (i.e., the reference configuration and the candidate cell configuration); b. When the UE decodes the LTM candidate cell configuration (i.e., there is no reference configuration); c. When the UE exits the serving cell, the serving cell being a non-subsequent LTM cell; and / or d. When the UE executes inter-CU LTM.

[0075] In a third implementation, the UE may convert the candidate configuration for intra- CU LTM and inter-CU LTM execution to each other through applying an additional configuration. Similar to the first and second implementation, such implicit indication of the subsequent and non-subsequent LTM candidates would result in reducing the size of the RRC configuration message, and ensure that there would be less signaling over the air interface, and at the same time, less processing effort on the UE side.

[0076] FIG. 4 illustrates a flowchart 400 outlining a series of steps performed by a first apparatus (e.g., the UE) as part of an LTM cell change procedure, according to an example embodiment disclosed herein. At step 402, the first apparatus receives from a second apparatus (e.g., serving network node or serving CU) a RRC message, the RRC message including LTM cell change configuration information of a third apparatus. This information can be allocated to the second apparatus by a third apparatus (e.g., a target network node or target CU), based on a trigger from the second apparatus to cause the first apparatus to undergo an LTM cell change to the third apparatus. Subsequently, at step 404, the first apparatus then evaluates one or more LTM cell conditions based on the received LTM cell change configuration. The purpose of the evaluation could be for undergoing the LTM cell change to the third apparatus. At step 406, the first apparatus reports to the second apparatus the evaluated one or more cell change conditions. In one embodiment, in response to this reporting, the first apparatus may receive an LTM cell switch command from the second apparatus. In other embodiments, the first apparatus may not receive the LTM cell switch command from the second apparatus upon the reporting. At step 408, the first apparatus performs the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

[0077] FIG. 5 illustrates a flowchart 500 outlining a series of steps performed by a second apparatus (e.g., serving network node or serving CU), according to an example embodiment disclosed herein. At step 502, the second apparatus triggers a LTM cell change of a first apparatus (e.g., a UE) to a third apparatus (e.g., a target network node1 or target CU). At step 504, the second apparatus receives, from the third apparatus, an allocation of LTM cell change configuration information of the third apparatus. At step 506, the second apparatus transmits to the first apparatus the LTM cell change configuration information, wherein the first apparatus performs the LTM cell change to the third apparatus based on an evaluation of one or more cell change conditions.

[0078] It is to be noted that in some embodiments, the flowcharts 400 and 500 can comprise additional steps or even omit one or more steps as mentioned in FIGS. 3 and 4.

[0079] FIG. 5 is a simplified block diagram of a device 600 for implementing the example embodiments of the present disclosure. The device 600 is an example of a device that may be configured to implement the various methods and processes described herein. The device 600 may be a network device (e.g., the source network node / source DU / CU / target network node / target CU / target DU) or a terminal device (e.g., the UE).

[0080] The device 600 comprises a processor 604 which can control the device’s operations. The processor 604 may also be referred to as a central processing unit (CPU). The memory 602, which may include both read-only memory (ROM) and random access memory (RAM), can provide instructions and data to the processor 604. The memory 602 and the processor 604 may be operatively coupled. The memory 602 may store computer readable instructions / computer program code. The computer readable instructions / computer program code may be pre-stored to the memory 602 or, alternatively or additionally, they may be received, by the device 600, via an electromagnetic carrier signal and / or may be copied from a physical entity such as a computer program product. Execution of the computer readable instructions by the processor 604, can cause the device 600 to carry out the example embodiments described herein, such as the steps in the flowcharts 400 and 500.

[0081] As referred to herein, “memory” (also referred to as “computer-readable media” or “computer-readable medium”) may be any non-transitory media or medium or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as acomputer. 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).

[0082] The transmitter / receiver (TX / RX) circuitry 606 may comprise a transmitter 608 and a receiver 612 that can enable the device 600 to transmit or receive data. The device 600 may comprise (not shown) multiple antennas, transmitters, and receivers.

[0083] In some example embodiments, the device 600 may comprise means that enable it to perform the steps / operations in FIGS. 4 and 5. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry (e.g., the memory 602 and processor 604) or a software module.

[0084] In the drawings and specification, there have been disclosed exemplary embodiments of the invention. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. It will be apparent to those having ordinary skill in this art that various modifications and variations may be made to the embodiments disclosed herein, consistent with the present invention, without departing from the spirit and scope of the present invention. Other embodiments consistent with the present invention will become apparent from consideration of the specification and the practice of the description disclosed herein.

Claims

29We Claim:

1. A first apparatus, comprising: at least one memory storing a plurality of instructions; and at least one processor, when executing the plurality of instructions, is configured to cause the first apparatus to: receive from a second apparatus, a radio resource control (RRC) message including lower layer triggered mobility (LTM) cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of a third apparatus; evaluate one or more cell change conditions, based on the received LTM cell change configuration information; report to the second apparatus the evaluated one or more cell change conditions; and perform the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

2. The first apparatus as claimed in claim 1, wherein the LTM cell change configuration information includes an indication of a type of the LTM cell change to the third apparatus, the type of LTM cell change comprising: subsequent LTM cell change; and non-subsequent LTM cell change.

3. The first apparatus as claimed in claim 2, wherein the third apparatus hosts a plurality of candidate cells, and wherein the first apparatus and the second apparatus release the stored LTM cell change configuration information of the plurality of candidate cells that are configured for non-subsequent LTM cell change, based on the indication in the LTM cell change configuration information.

304. The first apparatus as claimed in claim 1, wherein the LTM cell change configuration information comprises: a reference configuration for the LTM cell change; and / or an LTM configuration for the plurality of candidate cells.

5. The first apparatus as claimed in claim 1, wherein the allocation of the LTM cell change configuration information, by the third apparatus, is based on a request from the second apparatus.

6. The first apparatus as claimed in claim 1, wherein the allocation of the LTM cell change configuration information is based on a decision, by the third apparatus, on the request from the second apparatus.

7. The first apparatus as claimed in claim 1 , wherein the LTM cell change configuration information comprises one or more subsequent LTM groups, wherein each subsequent LTM group indicates one or more candidate cells from the plurality of candidate cells.

8. The first apparatus as claimed in claim 7, wherein the one or more candidate cells, in each subsequent LTM group, are configured to have an identical type of LTM cell change.

9. The first apparatus as claimed in claim 8, wherein the first apparatus and the second apparatus release the LTM configuration information of one or more candidate cells, in each subsequent LTM group, that are configured for non-subsequent LTM cell change.

10. The first apparatus as claimed in claim 1, wherein in the first apparatus is a terminal device.

11. The first apparatus as claimed in claim 1, wherein the second apparatus is one of: a source control unit; or a source network node.

12. The first apparatus as claimed in claim 1, wherein the third apparatus is one of: a target control unit; or a target network node.

13. The first apparatus as claimed in claim 2, wherein the indication is a timer, and wherein on either an expiry of a timer or a lapse of a threshold period of time, the first apparatus releases the LTM configuration information of the candidate cells configured for non- subsequent LTM cell change.

14. A second apparatus, comprising: at least one memory storing a plurality of instructions; and at least one processor, when executing the plurality of instructions, is configured to cause the second apparatus to: trigger a lower layer triggered mobility (LTM) cell change of a first apparatus to a third apparatus; receive, from the third apparatus, an allocation of LTM cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of the third apparatus; transmit, to the first apparatus, the LTM cell change configuration information; and wherein the first apparatus performs the LTM cell change to the third apparatus based on an evaluation of one or more cell change conditions.

15. The second apparatus as claimed in claim 14, wherein the LTM cell change configuration information includes an indication of a type of the LTM cell change to the third apparatus, the type of LTM cell change comprising:subsequent LTM cell change; and non-subsequent LTM cell change.

16. The second apparatus as claimed in claim 15, wherein the third apparatus hosts a plurality of candidate cells, and based on the indication of the type of LTM cell change in the LTM cell change configuration information, the first apparatus and the second apparatus release the stored LTM cell change configuration information of the plurality of candidate cells that are configured for non-subsequent LTM cell change.

17. The second apparatus as claimed in claim 14, wherein the LTM cell change configuration information comprises: a reference configuration for the LTM cell change; and / or an LTM configuration for the plurality of candidate cells.

18. The second apparatus as claimed in claim 14, wherein the allocation of the LTM cell change configuration information, by the third apparatus, is based on a request from the second apparatus.

19. The second apparatus as claimed in claim 14, wherein the allocation of the LTM cell change configuration information is based on a decision, by the third apparatus, on the request from the second apparatus.

20. The second apparatus as claimed in claim 15, wherein the LTM cell change configuration information comprises one or more subsequent LTM groups, wherein each subsequent LTM group indicates one or more candidate cells from the plurality of candidate cells.

21. The second apparatus as claimed in claim 20, wherein the one or more candidate cells, in each subsequent LTM group, are configured to have an identical type of LTM cell change3322. The second apparatus as claimed in claim 21, wherein the first apparatus and the second apparatus release the LTM configuration information of one or more candidate cells, in each subsequent LTM group, that are configured for non-subsequent LTM cell change.

23. The second apparatus as claimed in claim 14, wherein the second apparatus is one of: a source control unit; or a source network node24. The second apparatus as claimed in claim 14, wherein the first apparatus is a terminal device.

25. The second apparatus as claimed in claim 14, wherein the third apparatus is one of: a target control unit; or a target network node.

26. The second apparatus as claimed in claim 15, wherein the indication is a timer, and wherein on either an expiry of a timer or a lapse of a threshold period of time, the first apparatus releases the LTM configuration information of the candidate cells configured for non-subsequent LTM cell change.

27. A method, performed by a first apparatus, comprising: receiving, from a second apparatus, a radio resource control (RRC) message including lower layer triggered mobility (LTM) cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of a third apparatus; evaluating one or more cell change conditions, based on the received LTM cell change configuration information; reporting to the second apparatus the evaluated one or more cell change conditions; andperforming the LTM cell change to the third apparatus based on the evaluated one or more cell change conditions.

28. A method, performed by a second apparatus, comprising: triggering a lower layer triggered mobility (LTM) cell change of a first apparatus to a third apparatus; receiving, from the third apparatus, an allocation of LTM cell change configuration information, comprising subsequent and non-subsequent LTM cell change configuration information, of the third apparatus; transmitting, to the first apparatus, the LTM cell change configuration information; and wherein the first apparatus performs the LTM cell change based on an evaluation of one or more cell change conditions.

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