Method and apparatus for layer1 / layer2 triggered mobility (LTM) operation

Abstract

A method performed by a User Equipment (UE) for performing a Layer1 / Layer2 Triggered Mobility (LTM) operation is provided. The method receives, from a Base Station (BS), a first Medium Access Control (MAC) Control Element (CE) including a first Timing Advance (TA) value for a first CLTM candidate cell. The method stores the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE. The method starts or restarts a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE. The method considers the first TA value for the first CLTM candidate cell as valid until the first timer expires.　

Description

METHOD AND APPARATUS FOR LAYER1 / LAYER2 TRIGGERED MOBILITY (LTM) OPERATION

[0001] The present disclosure is related to wireless communication and, more specifically, to a User Equipment (UE), Base Station (BS), and method for Conditional Layer1 / Layer2 Triggered Mobility (CLTM) operations in the wireless communication networks.

[0002] Various efforts have been made to improve different aspects of wireless communication for the cellular wireless communication systems, such as the 5thGeneration (5G) New Radio (NR), by improving data rate, latency, reliability, and mobility. The 5G NR system is designed to provide flexibility and configurability to optimize network services and types, accommodating various use cases, such as enhanced Mobile Broadband (eMBB), massive Machine-Type Communication (mMTC), and Ultra-Reliable and Low-Latency Communication (URLLC). As the demand for radio access continues to grow, however, there exists a need for further improvements in the next-generation wireless communication systems, such as improvements in CLTM operations.

[0003] The present disclosure is related to a UE, a BS, and a method for a CLTM operation in the wireless communication networks.

[0004] In a first aspect of the present disclosure, a UE for performing a CLTM operation is provided. The UE includes at least one processor and at least one non-transitory computer-readable medium that is coupled to the at least one processor and that stores one or more computer-executable instructions. The computer-executable instructions, when executed by the at least one processor, cause the UE to: receive, from a BS, a first Medium Access Control (MAC) Control Element (CE) including a first Timing Advance (TA) value for a first CLTM candidate cell; store the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE; start or restart a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE; and consider the first TA value for the first CLTM candidate cell as valid until the first timer expires.

[0005] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: receive, from the BS, a second MAC CE including a second TA value for a second CLTM candidate cell; store the second TA value for the second CLTM candidate cell in response to receiving the second MAC CE; start or restart a second timer that is associated with the second CLTM candidate cell in response to receiving the second MAC CE; and consider the second TA value for the second CLTM candidate cell as valid until the second timer expires.

[0006] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: receive, from the BS, a first Radio Resource Control (RRC) message indicating an initial value for the first timer; and set the first timer to the initial value when starting or restarting the first timer.

[0007] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: perform a CLTM cell switch procedure to switch to the first CLTM candidate cell; and keep the first timer running upon switching to the first CLTM candidate cell.

[0008] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: perform a CLTM cell switch procedure to switch to a second CLTM candidate cell other than the first CLTM candidate cell; and keep the first timer running upon switching to the second CLTM candidate cell.

[0009] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: perform an early synchronization procedure with the first CLTM candidate cell.

[0010] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: receive, from the BS, a Physical Downlink Control Channel (PDCCH) order that initiates the early synchronization procedure.

[0011] In some implementations of the first aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: activate or deactivate at least one Transmission Configuration Indicator (TCI) state of the first CLTM candidate cell.

[0012] In a second aspect of the present application, a BS for configuring a CLTM operation is provided. The BS includes at least one processor and at least one non-transitory computer-readable medium that is coupled to the at least one processor and that stores one or more computer-executable instructions. The computer-executable instructions, when executed by the at least one processor, cause the BS to: transmit, to a UE, a first MAC CE including a first TA value for a first CLTM candidate cell. The UE stores the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE. The UE starts or restarts a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE. The UE considers the first TA value for the first CLTM candidate cell as valid until the first timer expires.

[0013] In some implementations of the second aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: transmit, to the UE, a second MAC CE including a second TA value for a second CLTM candidate cell. The UE stores the second TA value for the second CLTM candidate cell in response to receiving the second MAC CE. The UE starts or restarts a second timer that is associated with the second CLTM candidate cell in response to receiving the second MAC CE. The UE considers the second TA value for the second CLTM candidate cell as valid until the second timer expires.

[0014] In some implementations of the second aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: transmit, to the UE, a first RRC message indicating an initial value for the first timer. The UE sets the first timer to the initial value when starting or restarting the first timer.

[0015] In some implementations of the second aspect, the UE performs a CLTM cell switch procedure to switch to the first CLTM candidate cell, and the UE keeps the first timer running upon switching to the first CLTM candidate cell.

[0016] In some implementations of the second aspect, the UE performs a CLTM cell switch procedure to switch to a second CLTM candidate cell other than the first CLTM candidate cell, and the UE keeps the first timer running upon switching to the second CLTM candidate cell.

[0017] In some implementations of the second aspect, the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: transmit, to the UE, a PDCCH order that initiates an early synchronization procedure. The UE performs the early synchronization procedure with the first CLTM candidate cell.

[0018] In a third aspect of the present application, a method performed by a UE for performing a CLTM operation is provided. The method includes receiving, from a BS, a first MAC CE including a first TA value for a first CLTM candidate cell; storing the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE; starting or restarting a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE; and considering the first TA value for the first CLTM candidate cell as valid until the first timer expires.

[0019] Aspects of the present disclosure are best understood from the following detailed disclosure when read with the accompanying drawings. Various features are not drawn to scale. Dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

[0020] FIG. 1 is a flowchart illustrating a method / process performed by a UE for a CLTM operation, according to an example implementation of the present disclosure.

[0021] FIG. 2 is a block diagram illustrating a node for wireless communication, according to an example implementation of the present disclosure.

[0022] The following contains specific information related to implementations of the present disclosure. The drawings and their accompanying detailed disclosure are merely directed to implementations. However, the present disclosure is not limited to these implementations. Other variations and implementations of the present disclosure will be obvious to those skilled in the art.

[0023] Unless noted otherwise, like or corresponding elements among the drawings may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations in the present disclosure are generally not to scale and are not intended to correspond to actual relative dimensions.

[0024] For the purposes of consistency and ease of understanding, like features may be identified (although, in some examples, not illustrated) by the same numerals in the drawings. However, the features in different implementations may be different in other respects and may not be narrowly confined to what is illustrated in the drawings.

[0025] References to “one implementation,” “an implementation,” “example implementation,” “various implementations,” “some implementations,” “implementations of the present application,” etc., may indicate that the implementation(s) of the present application so described may include a particular feature, structure, or characteristic, but not every possible implementation of the present application necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “In some implementations,” or “in an example implementation,” “an implementation,” do not necessarily refer to the same implementation, although they may. Moreover, any use of phrases like “implementations” in connection with “the present application” are never meant to characterize that all implementations of the present application must include the particular feature, structure, or characteristic, and should instead be understood to mean “at least some implementations of the present application” includes the stated particular feature, structure, or characteristic. The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the equivalent.

[0026] The expression “at least one of A, B and C” or “at least one of the following: A, B and C” means “only A, or only B, or only C, or any combination of A, B and C.” The terms “system” and “network” may be used interchangeably. The term “and / or” is only an association relationship for describing associated objects and represents that three relationships may exist such that A and / or B may indicate that A exists alone, A and B exist at the same time, or B exists alone. The character “ / ” generally represents that the associated objects are in an “or” relationship.

[0027] For the purposes of explanation and non-limitation, specific details, such as functional entities, techniques, protocols, and standards, are set forth for providing an understanding of the disclosed technology. In other examples, detailed disclosure of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the present disclosure with unnecessary details.

[0028] Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) disclosed may be implemented by hardware, software, or a combination of software and hardware. Disclosed functions may correspond to modules which may be software, hardware, firmware, or any combination thereof.

[0029] A software implementation may include computer-executable instructions and / or Artificial Intelligence (AI) / Machine Learning (ML) module(s) stored on a computer-readable medium, such as memory or other type of storage devices. One or more microprocessors or general-purpose computers with communication processing capability may be programmed with corresponding computer-executable instructions and perform the disclosed network function(s), AI / ML module(s), or algorithm(s). The AI / ML module(s) may be implemented with a supervised learning approach, a semi-supervised learning approach, an unsupervised learning approach (e.g., Transductive approach and Inductive approach), a federated learning approach, or a reinforcement learning (RL) approach, but the present disclosure is not limited thereto. The computer-executable instructions associated with the AI module(s) and / or the ML module(s) may include but are not limited to, data management instructions (e.g., collection instructions, validation instructions…etc.), model monitoring and management instructions (e.g., NW key performance indicators (KPIs) monitoring, model input / output monitoring, model selection / switching / update / upload / download, model (de)activation, model identification, functionality selection…etc.), and / or pre-process input instructions.

[0030] The microprocessors or general-purpose computers may include Application-Specific Integrated Circuits (ASICs), programmable logic arrays, Central Processing Units (CPUs), Tensor Processing Units (TPUs), Graphics Processing Units (GPUs), General-purpose computing on GPUs (GPGPU, or less often GPGP), and / or using one or more Digital Signal Processors (DSPs). Although some of the disclosed implementations are oriented to software installed and executing on computer hardware, alternative implementations implemented as firmware, as hardware, or as a combination of hardware and software are well within the scope of the present disclosure. The computer-readable medium may include, but is not limited to, Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), High Bandwidth Memory (HBM), Magnetoresistive Random Access Memory (MRAM), Ferroelectric Random Access Memory (FRAM), Resistive Random Access Memory (RRAM), Read-Only Memory (ROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory (or other memory technology), Compact Disc Read-Only Memory (CD-ROM) , Digital Versatile Disks (DVD) (or other optical disk storage), magnetic cassettes, magnetic tape, magnetic disk storage (or other magnetic storage devices), or any other equivalent medium capable of storing computer-readable instructions.

[0031] A radio communication network architecture such as a Long-Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system, an LTE-Advanced Pro system, or a 5G NR Radio Access Network (RAN), 5G-Advanced (5G-A) system, or an open radio access network (O-RAN) may typically include at least one base station (BS), at least one UE, and one or more optional network elements that provide connection within a network. The BS and one or more optional network elements enable the UE to access a radio network. The UE may communicate with the network, such as a Core Network (CN), an Evolved Packet Core (EPC) network, an Evolved Universal Terrestrial RAN (E-UTRAN), a Next-Generation Core (NGC), a 5G Core (5GC), or an internet via a RAN established by one or more BSs and the network elements / functions.

[0032] A UE may include, but is not limited to, a mobile station, a mobile terminal or device, or a user communication radio terminal. The UE may be a portable radio equipment that includes, but is not limited to, a mobile phone, a tablet, a wearable device, a sensor, a vehicle, a virtual reality (VR) device, an augmented (AR) device, an Internet of Things (IoT) device, an unmanned aerial vehicle (UAV), or a Personal Digital Assistant (PDA) with wireless communication capability. The UE may be configured to receive and transmit signals over an air interface to one or more cells in a RAN. In some implementations, the UE may be an AI / ML-enabled device and / or an AI / ML capable device that is equipped with AI module(s) and / or ML module(s).

[0033] The BS may be configured to provide communication services according to at least a Radio Access Technology (RAT), such as Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM) that is often referred to as 2G, GSM Enhanced Data rates for GSM Evolution (EDGE) RAN (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunication System (UMTS) that is often referred to as 3G based on basic Wideband-Code Division Multiple Access (W-CDMA), High-Speed Packet Access (HSPA), LTE, LTE-A, evolved / enhanced LTE (eLTE) that is LTE connected to 5GC, NR (often referred to as 5G), 5G-A, and / or LTE-A Pro. However, the scope of the present disclosure is not limited to these protocols.

[0034] The BS may include, but is not limited to, a node B (NB) in the UMTS, an evolved node B (eNB) in LTE or LTE-A, a radio network controller (RNC) in UMTS, a BS controller (BSC) in the GSM / GERAN, a next-generation eNB (ng-eNB) in an Evolved Universal Terrestrial Radio Access (E-UTRA) BS in connection with 5GC, a next-generation Node B (gNB) in the 5G-RAN or in the 5G Access Network (5G-AN), or any other apparatus capable of controlling radio communication and managing radio resources within a cell. The BS may serve one or more UEs via a radio interface. Although the gNB is used as an example in some implementations within the present disclosure, it should be noted that the disclosed implementations may also be applied to other types of base stations. In some implementations, the BS may be an AI / ML-enabled device and / or an AI / ML capable device that is equipped with AI module(s) and / or ML module(s).

[0035] The BS may be operable to provide radio coverage to a specific geographical area using multiple cells forming the RAN. The BS may support the operations of the cells. Each cell may be operable to provide services to at least one UE within its radio coverage.

[0036] Each cell (may often referred to as a serving cell) may provide services to one or more UEs within the cell’s radio coverage, such that each cell schedules the downlink (DL) (and optionally uplink (UL) resources) to at least one UE within its radio coverage for DL (and optionally UL packet transmissions from the UE). The BS may communicate with one or more UEs in the radio communication system via the cells.

[0037] A cell may allocate sidelink (SL) resources for supporting the Proximity Services (ProSe), LTE SL services, LTE / NR sidelink communication services, LTE / NR sidelink discovery services, and / or LTE / NR Vehicle-to-Everything (V2X) services. In addition, a cell may allocate DL and / or UL resources for supporting Multicast / Broadcast Service (MBS) services, Non-Terrestrial Networks (NTN) services, positioning services, power serving services and / or Network Energy Saving (NES) services.

[0038] In Multi-RAT Dual Connectivity (MR-DC) cases, the primary cell of a Master Cell Group (MCG) or a Secondary Cell Group (SCG) may be referred to as a Special Cell (SpCell). A Primary Cell (PCell) may include the SpCell of an MCG. A Primary SCG Cell (PSCell) may include the SpCell of an SCG. MCG may include a group of serving cells associated with the Master Node (MN), including the SpCell and optionally one or more Secondary Cells (SCells). An SCG may include a group of serving cells associated with the Secondary Node (SN), including the SpCell and optionally one or more SCells.

[0039] As discussed above, the frame structure for NR may support flexible configurations for accommodating various next generation (e.g., 5G) communication requirements, such as Enhanced Mobile Broadband (eMBB), Massive Machine Type Communication (mMTC), and Ultra-Reliable and Low-Latency Communication (URLLC), while fulfilling high reliability, high data rate, and low latency requirements. The Orthogonal Frequency-Division Multiplexing (OFDM) technology in the third generation partnership project (3GPP) may serve as a baseline for an NR waveform. The scalable OFDM numerology, such as adaptive sub-carrier spacing, channel bandwidth, and Cyclic Prefix (CP), may also be used.

[0040] Two coding schemes may be considered for NR, specifically, Low-Density Parity-Check (LDPC) code and Polar Code. The coding scheme adaption may be configured based on channel conditions and / or service applications.

[0041] At least the DL transmission data, a guard period, and UL transmission data should be included in a transmission time interval (TTI) of a single NR frame. The respective portions of the DL transmission data, the guard period, and the UL transmission data should also be configurable based on, for example, the network dynamics of NR. SL resources may also be provided in an NR frame to support ProSe services or V2X services.

[0042] Any two or more than two of the following paragraphs, (sub)-bullets, points, actions, behaviors, terms, or claims described in the present disclosure may be combined logically, reasonably, and properly to form a specific method.

[0043] Any sentence, paragraph, (sub)-bullet, point, action, behaviors, terms, or claims described in the present disclosure may be implemented independently and separately to form a specific method.

[0044] Dependency, e.g., “based on”, “more specifically”, “preferably”, “in one embodiment”, “in some implementations”, etc., in the present disclosure is just one possible example which would not restrict the specific method.

[0045] In some implementations, all the designs / embodiment / implementations introduced within this disclosure are not limited to be applied for dealing with the problems discussed within this disclosure. For example, the described embodiments may be applied to solve other problems that exist in the RAN of wireless communication systems. In some implementations, all of the numbers listed within the designs / embodiment / implementations introduced within this disclosure are just examples and for illustration, for example, of how the described methods are executed.

[0046] The terms, definitions, and abbreviations given in the present disclosure are either imported from existing documentation (e.g., European Telecommunications Standards Institute (ETSI), International Telecommunication Union (ITU), or elsewhere) or newly created by 3GPP experts whenever the need for precise vocabulary is identified.

[0047] Examples of some selected terms in the present disclosure are provided as follows.

[0048] The network (NW), cell, camped cell, serving cell, base station, gNB, eNB, and ng-eNB may be interchangeably in the present disclosure. In some implementations, some of these items may refer to the same network entity.

[0049] The Radio Access Technology (RAT) may include, but not limited to, New Radio (NR), Long Term Evolution (LTE), Evolved Universal Terrestrial Radio Access (E-UTRA) connected to 5G Core Network (5GC), LTE connected to 5GC, E-UTRA connected to Evolved Packet Core (EPC), and LTE connected to EPC. The proposed mechanism may be applied for UEs in public networks or in private networks, such as non-public network (NPN), standalone NPN (SNPN), and public network integrated NPN (PNI-NPN).

[0050] The proposed mechanism may be used for licensed frequency and / or unlicensed frequency. In addition, the proposed mechanism of conditional configuration selection may be applied to cases in which a UE experiences a radio link failure when configured with conditional configurations.

[0051] System information (SI) may refer to Master Information Block (MIB), System Information Block 1 (SIB1), and other SI. Minimum SI may include MIB and SIB1. Other SI may refer to SIB3, SIB4, SIB5, and other SIB(s).

[0052] Dedicated signaling may refer to (but not limited to) RRC message(s). For example, RRC (Connection) Setup Request message, RRC (Connection) Setup message, RRC (Connection) Setup Complete message, RRC (Connection) Reconfiguration message, RRC Connection Reconfiguration message including the mobility control information, RRC Connection Reconfiguration message without the mobility control information inside, RRC Reconfiguration message including the configuration with sync, RRC Reconfiguration message without the configuration with sync inside, RRC (Connection) Reconfiguration Complete message, RRC (Connection) Resume Request message, RRC (Connection) Resume message, RRC (Connection) Resume Complete message, RRC (Connection) Reestablishment Request message, RRC (Connection) Reestablishment message, RRC (Connection) Reestablishment Complete message, RRC (Connection) Reject message, RRC (Connection) Release message, RRC System Information Request message, UE Assistance Information message, UE Capability Enquiry message, and UE Capability Information message.

[0053] The RRC_CONNECTED UE, RRC_INACTIVE UE, and RRC_IDLE UE may apply the proposed implementations.

[0054] The source cell may be a suitable cell or an acceptable cell.

[0055] A suitable cell is a cell on which a UE may camp. The UE may consider a cell as suitable if the following conditions are fulfilled: (1) The cell is part of either the selected Public Land Mobile Network (PLMN) or the registered PLMN or PLMN of the Equivalent PLMN list, and (2) The cell criteria of the cell are fulfilled. Furthermore, according to the latest information provided by Non-Access Stratum (NAS), the suitable cell is not barred. The suitable cell is part of at least one Tracking Area (TA) that is not part of the list of “Forbidden Tracking Areas”, which belongs to a PLMN that fulfils the condition (1).

[0056] An acceptable cell is a cell on which the UE may camp to obtain limited service, such as originating emergency calls and receiving Earthquake and Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) notifications. An acceptable cell may fulfil the following requirements, which is the minimum set of requirements to initiate an emergency call and to receive ETWS and CMAS notification in an NR network: (1) the cell is not barred, and / or (2) the cell selection criteria are fulfilled.

[0057] Primary Cell (PCell): The MCG cell, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure may be referred to as a primary cell.

[0058] Primary SCG Cell (PSCell): For dual connectivity operation, the SCG cell in which the UE performs random access when performing the Reconfiguration with Sync procedure.

[0059] Serving Cell: For a UE in the RRC_CONNECTED state, that is not configured with Carrier Aggregation (CA) or Dual Connectivity (DC), there is only one serving cell which is a primary cell. For a UE in the RRC_CONNECTED state, that is configured with CA / DC, the term ‘serving cells’ is used to denote a set of cells including the Special Cell(s) and all secondary cells. The serving cell may include a PCell, a PSCell, or an SCell.

[0060] Secondary Cell: For a UE configured with CA, a cell that provides additional radio resources on top of the special cell may be referred to as a secondary cell.

[0061] Special Cell (SpCell): For a Dual Connectivity operation, the term Special Cell may include the PCell of the MCG or the PSCell of the SCG depending on whether the MAC entity is associated with the MCG or the SCG, respectively. Otherwise, the term Special Cell may include the PCell.

[0062] Master Cell Group (MCG): In MR-DC, a group of serving cells associated with the master node, including the SpCell (e.g., PCell) and optionally one or more SCells.

[0063] Master node: In MR-DC, the radio access node that provides the control plane connection to the core network. It may be a Master eNB (in E-UTRA-NR Dual Connectivity (EN-DC)), a Master ng-eNB (in NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC)), or a Master gNB (in NR-NR Dual Connectivity (NR-DC) and NR-E-UTRA Dual Connectivity (NE-DC)).

[0064] Secondary Cell Group (SCG): In MR-DC, a group of serving cells associated with the secondary node, including the SpCell (e.g., PSCell) and optionally one or more SCells.

[0065] Secondary node: In MR-DC, the radio access node, with no control plane connection to the core network, providing additional resources to the UE. It may be an en-gNB (in EN-DC), a Secondary ng-eNB (in NE-DC), or a Secondary gNB (in NR-DC and NGEN-DC).

[0066] The serving cell in the implementations may be a PCell, SCell or PSCell.

[0067] Source node: The node from which the UE receives a Cell Switch Command (CSC). The source node may be interpreted as a source MN, a source SN, a source PCell, a source PSCell, or a source gNB.

[0068] Source cell: The cell from which the UE receives a CSC. The source cell may be interpreted as a source PCell, or a source PSCell.

[0069] Candidate node: The node that is associated with the LTM candidate configuration stored by the UE. The candidate node may be interpreted as a candidate MN, a candidate SN, a candidate PCell, a candidate PSCell, or a candidate gNB.

[0070] Candidate cell: The cell that is associated with the LTM candidate configuration stored by the UE. The candidate cell may be interpreted as a candidate PCell, or a candidate PSCell.

[0071] Target node: The node that is associated with the LTM candidate configuration ID in the CSC received by the UE. The target node may be interpreted as a target MN, a target SN, a target PCell, a target PSCell, or a target gNB.

[0072] Target cell: The cell that is associated with the LTM candidate configuration ID in the CSC received by the UE. The target cell may be interpreted as a target PCell, or a target PSCell.

[0073] In the present disclosure, the system information may be associated with the serving cell and / or the candidate / target cell.

[0074] Multiple PLMNs may operate on the unlicensed spectrum. Multiple PLMNs may share the same unlicensed carrier. The PLMNs may be public or private. Public PLMNs may include, but not limited to, the operators or virtual operators that provide radio services to the public subscribers. Public PLMNs may own the licensed spectrum and support the radio access technology on the licensed spectrum as well. Private PLMNs may include, but not limited to, the micro-operators, factories, or enterprises that provide radio services to private users (e.g., employees or machines). In some implementations, public PLMNs may support more deployment scenarios (e.g., carrier aggregation between licensed band NR (PCell) and NR-U (SCell), dual connectivity between licensed band LTE (PCell) and NR-U (PSCell), stand-alone NR-U, an NR cell with DL in unlicensed band and UL in licensed band, dual connectivity between licensed band NR (PCell) and NR-U (PSCell)). In some implementations, private PLMNs may mainly support, but not limited to, the stand-alone unlicensed radio access technology (e.g., stand-alone NR-U).

[0075] In the wireless cellular network, mobile devices (e.g., UE) may move from the coverage area of one cell to another cell. To avoid the connection interruption and ensure the service continuity, a handover procedure may be applied for the mobile devices when the handover procedure is triggered under certain conditions, e.g., when the signal quality of the source cell becomes poorer than a threshold for a period.

[0076] A handover procedure may be triggered by Layer 3 (L3) measurements and completed through RRC signaling, which triggers Reconfiguration with Synchronization to change the PCell and PSCell, as well as to release and add SCells. In addition, a conditional handover (CHO) may enhance robustness by allowing the mobile device to receive the target cell configuration in advance, for example, when the signal quality between the mobile device and the source cell is stable. Dual Active Protocol Stack (DAPS) handover may reduce the interruption time because the mobile device may maintain two protocol stacks for simultaneous connections with the source cell and the target cell during handover. For example, one protocol stack is associated with the source cell and the other one is associated with the target cell. These handover procedures, including the conditional handover and the DAPS handover, may require a complete Layer 2 (L2) reset and Layer 1 (L1) reset. L2 may refer to the Medium Access Control (MAC) layer, Radio Link Control (RLC) layer, and Packet Data Convergence Protocol (PDCP) layer, and L1 may refer to the Physical (PHY) layer. Complete L1 / L2 reset may result in longer latency, larger overhead and longer interruption time than beam switch mobility. Thus, L1 / L2 triggered mobility (LTM) has been proposed to enable a serving cell change via L1 / L2 signaling, which may reduce the latency, overhead and interruption time during the handover procedures.

[0077] In addition, LTM may allow the UE to perform early downlink and uplink synchronization to shorten the possible experience of interruption. For early downlink synchronization, the UE may activate the downlink beam of the candidate cell in advance. For early uplink synchronization, the UE may obtain the timing advance (TA) by itself or upon the reception of a cell switch command (CSC) to skip the lengthy random access (RA) procedure.

[0078] To enable faster execution of LTM with reduced signaling overhead, the concept of Conditional LTM (CLTM) has been proposed. However, the details of CLTM remain unclear. For example, it is not yet specified how the UE performs early UL synchronization (e.g., early TA acquisition) and obtains a TA value associated with a candidate cell before executing the CLTM. In addition, after obtaining the TA value, the procedure by which the UE maintains or updates this value is still undefined. Furthermore, it is uncertain whether the CLTM configuration may be utilized to support Radio Link Failure (RLF) recovery. The conditions that trigger CLTM are also not precisely defined, and the specific timing and manner in which the UE evaluates these conditions require further clarification. Accordingly, this disclosure proposes methods for the UE to perform the CLTM procedure, including TA maintenance, RLF recovery, and condition evaluation.

[0079] Scenarios

[0080] The following scenarios may be considered in the present disclosure. A network may include multiple cells, and a UE may or may not support the MR-DC configuration. That is, the UE may receive services from at least two Radio Access Network (RAN) nodes or from only one RAN node. The RAN node may be an evolved node B (eNB) or a next generation node B (gNB). The at least two RAN nodes may include an MN associated with an MCG and at least one SN associated with an SCG. The UE may be equipped with multiple receivers and transmitters, and the UE may be capable of supporting the MR-DC dedicated configurations. The network, having the information that the UE is capable of supporting the MR-DC, may configure the UE with the MR-DC configuration (e.g., the SCG configuration), which may be encapsulated in an RRC Reconfiguration message and transmitted from the serving RAN node to the UE.

[0081] In addition, the involved cells may belong to the same gNB distributed unit (gNB-DU) or to different gNB-DUs. Likewise, the involved gNB-DUs may belong to the same gNB centralized unit (gNB-CU) or to different gNB-CUs. It should be noted that, in an MR-DC operation, the UE may transmit or receive signaling (e.g., RRC signaling) to or from the source PCell, where the signaling may include configuration information of the SCG. Similarly, the UE may transmit or receive signaling to or from the source PSCell, where the signaling may include configuration information of the MCG and / or SCG.

[0082] In some implementations, the UE may perform early TCI activation / deactivation for a beam in a candidate cell. In some implementations, the UE may activate / deactivate the beam in response to signaling from the network, where the signaling may be a MAC CE. In some implementations, the UE may activate / deactivate the beam when a preconfigured condition (e.g., the LTM3-like, LTM5-like event) is satisfied. In some implementations, the UE may activate / deactivate the beam by the UE’s implementation.

[0083] In some implementations, the UE may perform early TA acquisition toward a candidate cell. It should be noted that, in this disclosure, “early TA acquisition” and “early UL synchronization” may refer to the same procedure. In some implementations, the UE may obtain a TA value associated with the candidate cell.

[0084] In some implementations, the UE may initiate the early TA acquisition procedure in response to signaling from the network, where the signaling may be Downlink Control Information (DCI). In some implementations, the UE may initiate the early TA acquisition procedure when a preconfigured condition (e.g., the LTM3-like, LTM5-like event) is satisfied. In some implementations, the UE may initiate the early TA acquisition procedure by the UE’s implementation. In some implementations, the UE may obtain the TA value by a measurement performed by the UE (e.g., a UE-based TA measurement). In some implementations, the UE may obtain the TA value via signaling from the serving cell, where the signaling may be a MAC CE. In some implementations, the UE may obtain the TA value via signaling from the candidate cell, where the signaling may be a MAC CE or an RA response.

[0085] In some implementations, an early TA procedure may be initiated by the UE or by the network in a CLTM procedure to enable the UE to obtain, in advance, a TA value associated with a candidate cell before establishing a connection with the candidate cell.

[0086] In some implementations, the early TA procedure may be initiated by the network via DCI (e.g., PDCCH-order RA). For example, the UE may receive, from the BS, a PDCCH order that initiates the early TA procedure. In some implementations, the DCI may indicate the ID of the candidate configuration associated with the candidate cell, the preamble index, and / or the Contention-Free Random Access (CFRA) resource information. In some implementations, upon receiving the DCI, the UE may transmit a preamble on a CFRA resource towards the candidate cell according to the DCI. In some implementations, upon receiving the preamble transmitted from the UE, the candidate cell may obtain a TA value and send the TA value to the serving cell (e.g., via XnAP signaling). In some implementations, upon receiving the TA value from the candidate cell, the serving cell may transmit the TA value to the UE (e.g., via a MAC CE).

[0087] In some implementations, the early TA procedure may be performed by the UE itself. For example, the UE may measure the TA value associated with a candidate cell by its implementation. More specifically, whether the UE is allowed to measure the TA value associated with the candidate cell by its implementation may be configured by the network.

[0088] In some implementations, the early TA procedure may be initiated by the UE. In some implementations, the UE may transmit an early TA request to the serving cell. In some implementations, the early TA request may be transmitted via Uplink Control Information (UCI) or a MAC CE. In some implementations, the early TA request may include an ID associated with the candidate cell, and / or the information of the activated beams or beams with good quality. In some implementations, upon receiving the TA request, the serving cell may transmit DCI to indicate the information of the early TA. In some implementations, upon receiving the DCI, the UE may transmit a preamble on a CFRA resource towards the candidate cell according to the DCI. In some implementations, upon receiving the preamble transmitted from the UE, the candidate cell may obtain a TA value and send the TA value to the serving cell (e.g., via XnAP signaling). In some implementations, upon receiving the TA value from the candidate cell, the serving cell may transmit the TA value to the UE (e.g., via a MAC CE).

[0089] In some implementations, the early TA procedure may be initiated by the UE. In some implementations, the UE may transmit a preamble to the candidate cell. In some implementations, the preamble index of the transmitted preamble may be preconfigured in the LTM configuration (e.g., ltm-Config or ltm-Candidate) and may be determined by the UE according to the activated beams or beams with good quality. In some implementations, after transmitting the preamble, the UE may wait for a period (e.g., an RA-window) for the RA response from the candidate cell. In some implementations, the RA response may include at least the TA value.

[0090] In some implementations, the UE may monitor the PDCCH associated with the RA response according to the search space and Control Resource Set (CORESET) information in the SIB1 of the candidate cell. In some implementations, the UE may monitor the PDCCH associated with the RA response according to the search space and CORESET information in the LTM configuration (e.g., the ltm-Config or the ltm-Candidate).

[0091] NW-based TA Maintenance

[0092] In some implementations, the network may ensure that the TA value associated with a candidate cell is valid when the UE is storing the TA value.

[0093] In some implementations, when the network considers that the TA value associated with a candidate cell is invalid, the network may initiate a PDCCH-order RA procedure towards the UE to update the TA value.

[0094] In some implementations, when the UE receives a TA value, the UE may assume that the TA value is valid for the associated candidate cell when executing the CLTM configuration associated with that candidate cell. In some implementations, Time Alignment Timer (TAT) mechanism may be applied, in which a timer may be started by the UE upon receiving the TA value from the serving cell. When the timer expires and the UE does not receive any CSC MAC CE or does not trigger the CLTM to connect with a candidate cell, the UE may determine that the received TA value is invalid. The timer may be restarted by the UE if (1) the UE receives a new TA from the serving cell, (2) the TA acquisition procedure is completed, or (3) the UE performs the CLTM and acquires a TA from a new serving cell. Before the expiration of the TAT, the UE may treat the stored TA as valid.

[0095] In some implementations, the UE may stop the timer when the timer expires. In some implementations, the UE may stop the timer when the UE completes the CLTM procedure, for example, when the UE transmits an RRCReconfigurationComplete message to the target cell. In some implementations, the initial value of the TA timer may be configured via an RRC message, such as an RRCReconfiguration message including the CLTM configuration.

[0096] In some implementations, the UE may store multiple TA values for the CLTM procedure, where each of the TA values may be associated with a candidate cell. In some implementations, upon receiving a TA value associated with a candidate cell, if the UE is not storing a TA value associated with that candidate cell, the UE may store the received TA value associated with the candidate cell. In some implementations, upon receiving a TA value associated with a candidate cell, if the UE is storing a TA value associated with that candidate cell, the UE may replace the stored TA value with the received TA value associated with the candidate cell.

[0097] In some implementations, the UE may store multiple TA values for the CLTM procedure, where multiple TA values may be associated with a candidate cell.

[0098] In some implementations, the UE may store a single TA value for the CLTM procedure. If the UE is storing a first TA value associated with a first candidate cell, when the UE receives a second TA value associated with a second candidate cell, the UE may release the stored first TA value and store the received second TA value. The first candidate cell and the second candidate cell may be the same or different cells.

[0099] In some implementations, the UE may receive a TA invalidity indication from the network indicating that the stored TA value associated with a candidate cell is invalid. Upon receiving the TA invalidity indication, the UE may consider that the stored TA value associated with the candidate cell is invalid and may release the stored TA value associated with the candidate cell.

[0100] In some implementations, the TA invalidity indication may be provided via DCI.

[0101] In some implementations, the DCI may include a field indicating a TA value and a field indicating an LTM candidate cell. In some implementations, upon receiving the DCI, if the TA value is a first value (e.g., 0xFFF in hexadecimal notation), the UE may consider that the stored TA value associated with the LTM candidate cell indicated by the DCI is invalid. Otherwise (e.g., the TA value is not the first value), the UE may consider that the TA value indicated by the DCI is valid and may store or update the TA value associated with the LTM candidate cell indicated by the DCI.

[0102] In some implementations, the DCI may include a field indicating one or more LTM candidate cells. In some implementations, upon receiving the DCI, if the scrambling Radio Network Temporary Identifier (RNTI) is a specific value, the UE may consider the stored TA values associated with the candidate cells indicated by the DCI to be invalid and may release the indicated TA values.

[0103] In some implementations, the field indicating the LTM candidate cell in the DCI may indicate the ID of the LTM candidate configuration associated with the LTM candidate cell.

[0104] In some implementations, the TA invalidity indication may be provided via a MAC CE.

[0105] In some implementations, the MAC CE may include a field indicating a TA value and a field indicating an LTM candidate cell. In some implementations, upon receiving the MAC CE, if the TA value is a first value (e.g., 0xFFF in hexadecimal notation), the UE may consider that the stored TA value associated with the LTM candidate cell indicated by the MAC CE is invalid. Otherwise (e.g., the TA value is not the first value), the UE may consider that the TA value indicated by the MAC CE is valid and may store or update the TA value associated with the LTM candidate cell indicated by the MAC CE.

[0106] In some implementations, the MAC CE may include a field indicating one or more LTM candidate cells. In some implementations, upon receiving the MAC CE, if the logical channel ID (LCID) is a specific value, the UE may consider the stored TA values associated with the candidate cells indicated by the MAC CE to be invalid and may release the indicated TA values.

[0107] In some implementations, the field indicating the LTM candidate cell in the MAC CE may indicate the ID of the LTM candidate configuration associated with the LTM candidate cell.

[0108] In some implementations, the TA invalidity indication may be provided via an RRC message.

[0109] In some implementations, the TA invalidity indication may be an implicit indication. When a specific measurement event is fulfilled, the UE may recognize that the stored TA is invalid. For example, if a change in the Reference Signal Received Power (RSRP) of the candidate cell (e.g., the difference between the RSRP measured when the UE received the TA and the current measured RSRP) is greater than a threshold, the UE may determine that the stored TA is invalid.

[0110] UE-based TA Maintenance

[0111] In some implementations, the UE may maintain an LTM TA timer for early TA acquisition operation in CLTM. Upon obtaining a TA value associated with a candidate cell, the UE may initialize / re-initialize the LTM TA timer to an initial value and start the LTM TA timer. When the LTM TA timer expires, the UE may consider that the TA value is invalid. In some implementations, the UE may obtain the TA value by receiving the TA value from the network.

[0112] In some implementations, the UE may obtain the TA value by measuring and calculating the TA value by its implementation. In some implementations, the UE may measure and calculate a TA value associated with a candidate cell according to a candidate cell group ID and a stored group ID. The UE may measure and calculate a TA value associated with the candidate cell if the candidate cell group ID associated with the candidate cell is equal to the stored group ID. The candidate cell group ID may be included in the LTM-Candidate associated with the candidate cell. Upon an LTM execution toward a first cell, the UE may release the stored group ID and store the candidate cell group ID associated with the first cell.

[0113] In some implementations, the LTM TA timer may be commonly applied to all candidate cells, and the initial value of the LTM TA timer may be common to all the candidate cells. For example, upon obtaining a first TA value associated with a first candidate cell, the UE may initialize the LTM TA timer to an initial value and may start the LTM TA timer. Upon obtaining a second TA value associated with a second candidate cell, the UE may reinitialize the LTM TA timer to the initial value and may restart the LTM TA timer.

[0114] In some implementations, the first candidate cell and the second candidate cell may be the same cell. In some implementations, the initial value may be configured in an Information Element (IE) common to all the CLTM configurations. For example, the initial value may be configured in the ltm-Config. In some implementations, when the UE possesses a first TA value associated with the first candidate cell and the LTM TA timer is running, upon receiving a second TA value associated with the first candidate cell, the UE may initialize the LTM TA timer to the initial value and may restart the LTM TA timer. In some implementations, the initial value may be predefined or preconfigured to a fixed value.

[0115] In some implementations, the LTM TA timer may be commonly applied to all candidate cells, while the initial value of the LTM TA timer may depend on the respective candidate cell. For example, upon obtaining a first TA value associated with a first candidate cell, the UE may initialize the LTM TA timer to a first initial value and may start the LTM TA timer. Upon obtaining a second TA value associated with a second candidate cell, the UE may reinitialize the LTM TA timer to a second initial value and may restart the LTM TA timer.

[0116] In some implementations, the first candidate cell and the second candidate cell may be the same cell. In this case, the first initial value may be the same as the second initial value. In some implementations, the initial value may be configured in an IE specific to the CLTM configuration, such as the ltm-Candidate. For example, the first initial value may be configured in a first ltm-Candidate associated with the first candidate cell and the second initial value may be configured in a second ltm-Candidate associated with the second candidate cell. In some implementations, the initial value may be indicated in the signaling indicating the TA value from the network. For example, the first initial value may be indicated by the first signaling indicating the first TA value, and the second initial value may be indicated by the second signaling indicating the second TA value. In some implementations, the initial value may be predefined or preconfigured to a fixed value in CLTM.

[0117] In some implementations, the LTM TA timer may be operated separately for each candidate cell, while the initial value of the LTM TA timer may be common to all candidate cells. For example, upon obtaining a first TA value associated with a first candidate cell, the UE may initialize a first LTM TA timer to an initial value and may start the first LTM TA timer. Upon obtaining a second TA value associated with a second candidate cell, the UE may initialize a second LTM TA timer to the same initial value and may start the second LTM TA timer. In some implementations, the initial value may be configured in an IE common to all the CLTM configurations. For example, the initial value may be configured in the ltm-Config.

[0118] In some implementations, the LTM TA timer may be operated separately for each candidate cell, and the initial value of the LTM TA timer may depend on the corresponding candidate cell. For example, upon obtaining a first TA value associated with a first candidate cell, the UE may initialize a first LTM TA timer to a first initial value and may start the first LTM TA timer. Upon obtaining a second TA value associated with a second candidate cell, the UE may initialize a second LTM TA timer to a second initial value and may start the second LTM TA timer.

[0119] In some implementations, the first candidate cell and the second candidate cell may be the same cell. In some implementations, the initial value may be configured in an IE specific to the CLTM configuration, such as the ltm-Candidate. For example, the first initial value may be configured in a first ltm-Candidate associated with the first candidate cell, and the second initial value may be configured in a second ltm-Candidate associated with the second candidate cell. In some implementations, the initial value may be indicated in the signaling indicating the TA value from the network. For example, the first initial value may be indicated by the first signaling indicating the first TA value, and the second initial value may be indicated by the second signaling indicating the second TA value.

[0120] In some implementations, the TAT and the LTM TA timer(s) may be operated separately, where the TAT may correspond to the TA timer associated with the serving cell, and the LTM TA timer(s) may correspond to the TA timer(s) associated with the candidate cell(s). When the TAT expires, the LTM TA timer(s) may continue running, and vice versa. Moreover, when the UE successfully completes the RRCConnectionReconfiguration procedure with one of the candidate cells, which may become the new serving cell, the LTM TA timer and its running value may be inherited or continued as the TA timer for the new serving cell.

[0121] In some implementations, the UE may stop the LTM TA timer when the UE receives an RRC Reconfiguration associated with a cell other than the serving cell, or when the UE receives an LTM CSC MAC CE that indicates an LTM candidate cell.

[0122] In some implementations, the UE may stop the LTM TA timer when the UE applies an RRC Reconfiguration associated with a cell other than the serving cell, where the RRC Reconfiguration may be included in a conditional configuration (e.g., CHO, Conditional PSCell Addition or Change (CPAC)) or a CLTM configuration.

[0123] In some implementations, the UE may maintain only one timer for the candidate cell that meets the cell switching condition(s) and stop other running timers.

[0124] In some implementations, when the UE considers a TA value to be invalid, the UE may check a condition. If the condition is satisfied, the UE may trigger an early TA request procedure to obtain a new TA value. Conversely, if the condition is not satisfied, the UE may not trigger the early TA request procedure to obtain a new TA value. In some implementations, the condition may be specific to early TA acquisition. In some implementations, the condition may be referred to as one or more of the conditions described in the section “Conditions for CLTM.”

[0125] In some implementations, the checking procedure may be common to all candidate cells. For example, when the UE considers the TA value associated with a first candidate cell to be invalid, if the UE considers one or more conditions associated with one or more candidate cells to be satisfied, the UE may initiate the early TA procedure. In some implementations, the one or more candidate cells may include the first candidate cell. In some implementations, the UE may select a cell from the one or more candidate cells and initiate the early TA procedure toward the selected cell. In some implementations, the UE may initiate the early TA procedure toward the one or more candidate cells.

[0126] In some implementations, the checking procedure may be performed on a per-candidate cell basis. For example, when the UE considers the TA value associated with a first candidate cell to be invalid, if the UE considers one or more conditions associated with the first candidate cell to be satisfied, the UE may initiate the early TA procedure toward the first candidate cell.

[0127] In some implementations, when the UE considers a TA value to be invalid, the UE may check whether there is an activated beam associated with the candidate cells. If there is at least one activated beam associated with the candidate cells, the UE may trigger an early TA request procedure to obtain a new TA value. Conversely, if there is no activated beam associated with the candidate cells, the UE may not trigger the early TA request procedure to obtain a new TA value.

[0128] In some implementations, the checking procedure may be common to all the candidate cells. For example, when the UE considers the TA value associated with a first candidate cell to be invalid, if there is one or more activated beams associated with one or more candidate cells, the UE may initiate the early TA procedure. In some implementations, the one or more candidate cells may include the first candidate cell. In some implementations, the UE may select a cell from the one or more candidate cells and initiate the early TA procedure toward the selected cell. In some implementations, the UE may initiate the early TA procedure toward the one or more candidate cells.

[0129] In some implementations, the checking procedure may be performed on a per-candidate cell basis. For example, when the UE considers the TA value associated with a first candidate cell to be invalid, if there is one or more activated beams associated with the first candidate cell, the UE may initiate the early TA procedure toward the first candidate cell.

[0130] In some implementations, when a condition associated with a cell switch towards a candidate cell is satisfied, if the UE considers the TA value associated with the candidate cell to be invalid, the UE may perform one of the following actions:

[0131] - The UE may perform a Random Access Channel (RACH)-based LTM cell switch towards the candidate cell. In some implementations, if the UE has activated one or more beams associated with the candidate cell, the UE may select the RACH Occasion and / or the preamble index according to the activated one or more beams associated with the candidate cell.

[0132] - The UE may trigger an early TA acquisition procedure to obtain a valid TA value associated with the candidate cell. In some implementations, upon obtaining the TA value, the UE may perform a RACH-less LTM cell switch towards the candidate cell using the TA value.

[0133] In some implementations, upon a CLTM execution (e.g., the UE is applying the stored RRC configuration associated with the candidate cell triggering the condition), an LTM execution (e.g., the UE is applying the stored RRC configuration associated with the candidate cell indicated by the CSC MAC CE), a handover execution (e.g., the UE is applying an RRC configuration received from the network), or a CHO execution (e.g., the UE is applying the stored RRC configuration associated with the candidate cell triggering the condition), if an LTM TA timer is running, the UE may perform one of the following actions:

[0134] - If the UE maintains a single LTM TA timer for all the candidate cells, the UE may stop the LTM TA timer.

[0135] - If the UE maintains a single LTM TA timer for all the candidate cells, the UE may keep running the LTM TA timer.

[0136] - If the UE maintains separate LTM TA timers for different candidate cells, the UE may keep running all the currently running LTM TA timers.

[0137] - If the UE maintains separate LTM TA timers for different candidate cells, the UE may stop all the currently running LTM TA timers.

[0138] - If the UE maintains separate LTM TA timers for different candidate cells, the UE may keep running the LTM TA timer associated with the target cell, and the UE may stop all the LTM TA timers that are not associated with the target cell.

[0139] - If the UE maintains separate LTM TA timers for different candidate cells, the UE may keep running the LTM TA timer associated with the candidate cells fulfilling the conditions, and the UE may stop all the LTM TA timers that are associated with the cells that are not fulfilling the conditions.

[0140] In some implementations, the UE may consider that the TA value is valid if the measurement quantity does not change over a threshold. In some implementations, the UE may consider that the TA value is invalid if the measurement quantity changes over the threshold. The measurement may be based on Synchronization Signal Block (SSB) or Channel State Information Reference Signal (CSI-RS). The measurement quantity may be RSRP, Reference Signal Received Quality (RSRQ), or Signal to Interference plus Noise Ratio (SINR).

[0141] In some implementations, the change of the measurement quantity may be the difference between a first measurement quantity value obtained at a first timestamp and a second measurement quantity value obtained at a second timestamp. In some implementations, the first timestamp may correspond to the time when the UE obtains the TA value. In some implementations, the second timestamp may correspond to any time after the UE obtains the TA value and when the UE considers the TA value to be valid. The second timestamp may correspond to the time when the UE executes the CLTM, such as when the UE considers that the cell switch condition of the CLTM candidate cell is satisfied or when the UE performs the cell switch to the CLTM candidate cell.

[0142] In some implementations, when the UE maintains a single TA value for all the candidate cells and the TA value is associated with a first cell, the UE may consider that the TA value to be invalid if at least one of the following conditions is satisfied: the measurement quantity of the first cell changes more than a threshold, or the measurement quantity of a candidate cell other than the first cell changes more than a threshold.

[0143] In some implementations, when the UE maintains a first TA value associated with a first cell and a second TA value associated with a second cell, if the measurement quantity of the second cell changes more than a threshold, the UE may perform at least one of the following actions: the UE may consider that the first TA value is valid and that the second TA value is invalid, or the UE may consider that both the first TA value and the second TA value are invalid.

[0144] In some implementations, the threshold may be configured by the network (e.g., via an RRC message).

[0145] In some implementations, the threshold may be configured as a common value for all the candidate cells. In some implementations, the threshold may be configured in an IE common to all the candidate cells (e.g., the ltm-Config). For example, the UE may consider a first condition associated with a first candidate cell to be satisfied if the measurement quantity value of the first candidate cell changes more than the threshold, and the UE may consider a second condition associated with a second candidate cell to be satisfied if the measurement quantity value of the second candidate cell changes more than the same threshold.

[0146] In some implementations, the threshold may be configured on a per-candidate cell basis. In some implementations, the threshold may be configured in an IE specific to a candidate cell. For example, the UE may consider a first condition associated with a first candidate cell to be satisfied if the measurement quantity value of the first candidate cell changes more than a first threshold associated with the first candidate cell, and the UE may consider a second condition associated with a second candidate cell to be satisfied if the measurement quantity value of the second candidate cell changes more than a second threshold associated with the second candidate cell.

[0147] In some implementations, the threshold may be configured on a per-candidate cell group basis. In some implementations, the threshold may be configured in an IE specific to a candidate cell group. For example, the UE may consider a first condition associated with a first candidate cell to be satisfied if the measurement quantity value of the first candidate cell changes more than a first threshold associated with a first candidate cell group, and the UE may consider a second condition associated with a second candidate cell to be satisfied if the measurement quantity value of the second candidate cell changes more than a second threshold associated with a second candidate cell group.

[0148] In some implementations, the first candidate cell group and the second candidate cell group may be the same candidate cell group. In this case, the first threshold and the second threshold may have the same value. In some implementations, the first candidate cell group and the second candidate cell group may be different candidate cell groups. In this case, the first threshold and the second threshold may be the same or different.

[0149] In some implementations, the UE may maintain the TA value based on the UE’s implementation. For example, after the UE has obtained and stored a TA value associated with a candidate cell, the UE may determine that the stored TA value is invalid based on the UE’s implementation. The network may configure (e.g., via an RRC message) an indication that allows the UE to determine whether the TA value associated with a candidate cell is valid. In some implementations, the indication may be configured in an IE common to the candidate cells, such as the ltm-Config. In some implementations, the indication may take the value ENUMERATED {‘true’}. In some implementations, if the indication is present, the UE may determine that the TA value is invalid based on the UE’s implementation; if the indication is absent, the UE may not determine that the TA value is invalid based on the UE’s implementation.

[0150] CLTM Configuration for RLF Recovery

[0151] In some implementations, when the UE declares the RLF, the UE may initiate an RRC re-establishment procedure. In the beginning of the RRC re-establishment procedure, the UE may perform cell reselection. If the (re)selected cell is a CLTM candidate cell, the UE may apply the CLTM configuration associated with the cell.

[0152] In some implementations, if the (re)selected cell is associated with a CLTM configuration, and if the UE has activated at least one beam associated with the candidate cell, and if the UE has a valid TA value upon the completion of the cell reselection, the UE may perform RACH-less cell switch towards the candidate cell by using the TA value and the activated beam.

[0153] In some implementations, if the (re)selected cell is associated with a CLTM configuration, and if the UE has activated at least one beam associated with the candidate cell, the UE may perform RACH-based cell switch towards the candidate cell by using the activated beam.

[0154] The RACH-less cell switch may include the UE, having a valid TA value, transmitting a PUSCH via a configured grant or a dynamic grant towards the candidate cell without performing an RA procedure. In some implementations, the UE may determine the uplink resource of the configured grant or the dynamic grant based on the activated beam. The RACH-based cell switch may include the UE performing an RA procedure towards the candidate cell before transmitting a PUSCH to the candidate cell.

[0155] In some implementations, if the (re)selected cell is associated with a CLTM configuration and at least one of an LTM configuration or a CHO configuration, the UE may perform one or more of the following actions:

[0156] - The UE may prioritize the CLTM configuration over other configurations. For example, the UE may apply the CLTM configuration associated with the (re)selected cell. In some implementations, the UE may prioritize the CLTM configuration over other configurations if the UE has a valid TA value associated with the (re)selected cell. In some implementations, the UE may prioritize the CLTM configuration over other configurations if the UE has at least one activated beam associated with the (re)selected cell.

[0157] - The UE may select one of the CLTM configuration, the LTM configuration, and the CHO configuration. The UE may apply the selected configuration.

[0158] Conditions for CLTM

[0159] In some implementations, the UE may evaluate the condition during the CLTM procedure. If a set of conditions are considered to be satisfied, the UE may perform corresponding actions.

[0160] In some implementations, when an action is associated with more than one conditions, the UE may perform the action if all of the conditions are considered to be satisfied.

[0161] In some implementations, the action may be that the UE activates the measurement of a reference signal (RS) resource set. For example, the UE may start measuring the RS resource set. The RS resource set may include one or more SSB resources and / or one or more CSI-RS resources.

[0162] In some implementations, the actions may be that the UE activates one or more beams associated with one or more candidate cells.

[0163] In some implementations, the actions may be that the UE triggers an early TA acquisition procedure.

[0164] In some implementations, the actions may be that the UE performs a cell switch. For example, the UE may apply the stored RRC configuration associated with a candidate cell.

[0165] In some implementations, the condition may be configured on a per-action basis. For example, the UE may be configured with a first condition associated with a first candidate cell and a first action, a second condition associated with the first candidate cell and a second action, and a third condition associated with the second candidate cell and the first action. If the UE considers that the first condition is satisfied, the UE may perform the first action towards the first candidate cell; if the UE considers that the second condition is satisfied, the UE may perform the second action towards the first candidate cell; if the UE considers that the third condition is satisfied, the UE may perform the first action towards the second candidate cell.

[0166] In some implementations, when the UE is performing a first action toward a first candidate cell triggered by its associated condition, the UE may skip or postpone performing a second action toward the first candidate cell, a first action toward a second candidate cell, or a second action toward a second candidate cell that is triggered by another associated condition.

[0167] In some implementations, the UE may postpone performing a second action toward the first candidate cell by performing the second action toward the first candidate cell upon the completion of the first action towards the first candidate cell. In some implementations, the UE may postpone performing the second action if the second action is not a cell switch. In some implementations, the UE may stop or postpone the first action and perform the second action if the second action is a cell switch. In some implementations, the UE may stop or postpone the first action and perform the second action if the second action is indicated by the network. For example, the second action may correspond to one of the following actions: the UE receives a TCI state activation MAC CE, the UE receives a PDCCH-order for early TA acquisition, the UE receives a MAC CE activating the measurement of a RS resource set, or the UE receives a CSC MAC CE.

[0168] In some implementations, the condition may be based on the beam level or be based on the cell level. In some implementations, a beam-level condition may be based on the measured qualities of one or more beams in one or more cells. In some implementations, the measured qualities may be based on RSRP, RSRQ, or SINR. A beam-level condition may be one of the following conditions:

[0169] - The measured quality of the serving beam is lower than a threshold for a time-to-trigger (TTT) period.

[0170] - The measured quality of a candidate beam is offset higher than the measured quality of the serving beam for a TTT period.

[0171] - The measured quality of a candidate beam is higher than a threshold for a TTT period.

[0172] - The measured quality of a candidate beam is higher than a first threshold and the measured quality of the serving beam is lower than a second threshold for a TTT period.

[0173] The candidate beam may be a beam configured in the ltm-Config. The serving beam may be the beam currently used for uplink / downlink transmission or the beam with the best measured quality in the serving cell.

[0174] In some implementations, the threshold, the first threshold, the second threshold, the offset, and the TTT period may be configured on a per-beam basis. For example, the threshold, the first threshold, the second threshold, the offset, and the TTT period may be applied to a specific candidate beam. For example, different beams may be configured with different thresholds, different first thresholds, different second thresholds, different offsets, and different TTT periods. In some implementations, the threshold, the first threshold, the second threshold, the offset, and the TTT period may be configured on a per-cell basis.

[0175] In some implementations, a cell-level condition may be based on the measured qualities of one or more cells. The one or more cells may include a serving cell or one or more candidate cells. In some implementations, the UE may derive the measured quality of a cell from a set of measured qualities of one or more beams in the cell. For example, the UE may derive the measured quality of a cell by averaging the measured qualities of a number of beams whose measured qualities are higher than a threshold.

[0176] In some implementations, the measured quality of a beam may be obtained via the measurement of an SSB or a CSI-RS. In some implementations, the threshold and the maximum number of beams whose measured qualities are to be averaged may be configured by the network (e.g., via an RRC signaling) to the UE.

[0177] In some implementations, the UE may be configured with two sets of cell-quality derivation parameters (e.g., the threshold and the maximum number of beams (e.g., N)), where a first set of cell-quality derivation parameters may be used for Layer-3 measurement, and a second set of cell-quality derivation parameters may be used for LTM measurement. For example, the UE may average the measured qualities of one or more (at most N1) beams whose measured qualities are higher than a first threshold to obtain a first cell-level quality for the Layer-3 measurement. The UE may average the measured qualities of one or more (at most N2) beams whose measured qualities are higher than a second threshold to obtain a second cell-level quality for the LTM measurement.

[0178] In some implementations, the first set of cell-quality derivation parameters may be configured in the IE indicating the Layer-3 measurement object (e.g., the measObjectNR). In some implementations, the second set of cell-quality derivation parameters may be configured in the IE indicating the LTM measurement object (e.g., the ltm-Config or ltm-CSI-ResourceConfig).

[0179] In some implementations, a cell-level condition may include one of the following conditions:

[0180] - The measured quality of the serving cell is lower than a threshold for a TTT period.

[0181] - The measured quality of a candidate cell is offset higher than the measured quality of the serving cell for TTT period.

[0182] - The measured quality of a candidate cell is higher than a threshold for a TTT period.

[0183] - The measured quality of a candidate cell is higher than a first threshold and the measured quality of the serving cell is lower than a second threshold for a TTT period.

[0184] In some implementations, a cell-level condition may be based on the consolidation of a set of beam-level conditions. The cell-level condition may include one of the following conditions:

[0185] - For a candidate cell, the number of beams whose beam-level conditions are considered to be satisfied is larger than or equal to a threshold for a TTT period.

[0186] - For a candidate cell, the number of beams whose beam-level sub-conditions, which may be also referred to as sub-beam-level conditions, are considered to be satisfied is larger than or equal to a threshold for a TTT period.

[0187] In some implementations, a beam-level sub-condition associated with a beam may be a condition that is the same type of the beam-level condition associated with the beam and whose one or more parameter values (e.g., the threshold, the offset, the first threshold, the second threshold, and the TTT period) are different from the beam-level condition associated with the beam. For example, given that a beam-level condition associated with a beam is that the measured quality of the beam is higher than a first threshold for a first TTT period, the sub-beam-level condition associated with the beam may be that the measured quality of the beam is higher than a second threshold for the first TTT period; alternatively, the sub-beam-level condition associated with the beam may be that the measured quality of the beam is higher than the first threshold for a second TTT period.

[0188] In some implementations, the parameters of the sub-beam-level condition associated with the beam may be configured by the network (e.g., via an RRC signaling).

[0189] In some implementations, the parameters of the sub-beam-level condition associated with the beam may be configured on a per-beam basis. For example, the parameters of the sub-beam-level condition associated with the beam may be applied to the beam and may not be applied to other beams.

[0190] In some implementations, the parameters of the sub-beam-level condition associated with the beam may be configured on a per-cell basis. For example, the parameters of the sub-beam-level condition associated with the cell may be applied to the beams associated with the cell and may not be applied to the beams not associated with the cell.

[0191] In some implementations, the parameters of the sub-beam-level condition may be configured as a separate set from the parameters of the beam-level condition. For example, the UE may be configured with a first set of parameters for the beam-level condition associated with a beam and a second set of parameters for the sub-beam-level condition associated with the beam. For example, the UE may be configured with a first threshold, a first TTT period, a second threshold, and a second TTT period. The UE may consider that the first threshold and the first TTT period are used for the beam-level condition associated with the beam, and that the second threshold and the second TTT period are used for the sub-beam-level condition associated with the beam.

[0192] In some implementations, the parameters of the sub-beam-level condition may be configured as a partially separate set from the parameters of the beam-level condition. For example, the UE may be configured with a threshold, a first TTT period, and a second TTT period. The UE may consider that the threshold and the first TTT period are used for the beam-level condition associated with the beam, and that the threshold and the second TTT period are used for the sub-beam-level condition associated with the beam.

[0193] In some implementations, the parameters of the sub-beam-level condition may be configured as a difference value. For example, the UE may be configured with a threshold, a TTT period, and a TTT difference. The UE may consider that the threshold and the TTT period are used for the beam-level condition associated with the beam, and that the threshold and the TTT period plus / minus the TTT difference are used for the sub-beam-level condition associated with the beam.

[0194] In some implementations, an action towards a candidate cell may be associated with one or more conditions. In some implementations, an action towards a candidate cell may be associated with a cell-level condition and a beam-level condition. In some implementations, an action towards a candidate cell may be associated with one or more cell-level conditions and one or more beam-level conditions.

[0195] In some implementations, the UE may start evaluating the condition upon receiving signaling from the network, where the signaling may be DCI, MAC CE, or RRC signaling. The evaluated conditions may include one or more cell-level conditions and / or one or more beam-level conditions.

[0196] In some implementations, the signaling associated with the start of condition evaluation may be DCI. The DCI may be the DCI used to trigger an early TA acquisition. In some implementations, the DCI may include a field indicating the candidate cell (or the candidate configuration) with the candidate cell ID (or the candidate configuration ID). In some implementations, the DCI may include a field indicating that the UE starts evaluating the condition. For example, if the field is a first value (e.g., 1), the UE may start the evaluation of the conditions; if the field is a second value (e.g., 0), the UE may not start the evaluation of the conditions.

[0197] In some implementations, upon receiving the DCI, the UE may start evaluating all the conditions associated with LTM procedure. For example, upon receiving the DCI, the UE may start evaluating the conditions associated with cells that are configured with conditions. In some implementations, upon receiving the DCI, the UE may start evaluating the conditions associated with the candidate cell (or the candidate configuration) indicated by the DCI. In some implementations, upon receiving the DCI, the UE may start evaluating the cell-level conditions. The cell-level conditions may be associated with the cell indicated by the DCI.

[0198] In some implementations, a DCI field may be used to indicate whether the UE applies cell level conditions or beam level conditions. For example, if the field is set to 0, the cell level condition may be applied. If the field is set to 1, the beam level condition may be applied.

[0199] In some implementations, if the UE is not evaluating the condition before receiving the DCI, the UE may start evaluating the condition upon receiving the DCI. In some implementations, if the UE is evaluating the condition before receiving the DCI, the UE may keep evaluating the condition upon receiving the DCI.

[0200] In some implementations, the signaling associated with the start of condition evaluation may be a MAC CE. The MAC CE may be the MAC CE used to activate / deactivate the TCI states of a candidate cell. In some implementations, if the MAC CE is used to activate the TCI states of a candidate cell, the UE may start the evaluation of the conditions. In some implementations, if the MAC CE is used to deactivate the TCI states of a candidate cell, the UE may stop the evaluation of the conditions. In some implementations, the MAC CE may be the CSC MAC CE.

[0201] In some implementations, the MAC CE may include a field indicating the candidate cell (or the candidate configuration) with candidate cell ID (or the candidate configuration ID). In some implementations, the MAC may include a field indicating that the UE starts evaluating the condition. For example, if the field is a first value (e.g., 1), the UE may start the evaluation of the conditions. If the field is a second value (e.g., 0), the UE may not start the evaluation of the conditions.

[0202] In some implementations, upon receiving the MAC CE, the UE may start evaluating all the conditions associated with LTM procedure. For example, upon receiving the MAC CE, the UE may start evaluating the conditions associated with cells that are configured with conditions. In some implementations, upon receiving the MAC CE, the UE may start evaluating the conditions associated with the candidate cell (or the candidate configuration) indicated by the MAC CE.

[0203] In some implementations, a MAC CE field may be used to indicate whether the UE applies cell level conditions or beam level conditions. For example, if the field is set to 0, the cell level condition may be applied. If the field is set to 1, the beam level condition may be applied. In some implementations, upon receiving the MAC CE, the UE may start evaluating the cell-level conditions. The cell-level conditions may be associated with the cell indicated by the MAC CE. In some implementations, upon receiving the MAC CE, the UE may start evaluating the beam-level conditions. The beam-level conditions may be associated with the beams indicated by the MAC CE.

[0204] In some implementations, if the UE is not evaluating the condition before receiving the MAC CE, the UE may start evaluating the condition upon receiving the MAC CE. In some implementations, if the UE is evaluating the condition before receiving the MAC CE, the UE may keep evaluating the condition upon receiving the MAC CE.

[0205] In some implementations, the signaling associated with the start of condition evaluation may be RRC signaling. The RRC signaling may be the RRC signaling used to configure the LTM configuration.

[0206] In some implementations, upon receiving the RRC signaling, the UE may start evaluating all the conditions associated with LTM procedure. For example, upon receiving the RRC signaling, the UE may start evaluating the conditions associated with cells that are configured with conditions. In some implementations, if the UE is not evaluating the condition before receiving the RRC signaling, the UE may start evaluating the condition upon receiving the RRC signaling. In some implementations, if the UE is evaluating the condition before receiving the RRC signaling, the UE may keep evaluating the condition upon receiving the RRC signaling.

[0207] In some implementations, the UE may keep evaluating the conditions by evaluating the conditions without resetting the associated TTT.

[0208] In some implementations, the UE may receive an indication that indicates which signaling triggers the start of condition evaluation. In some implementations, the indication may be configured in RRC signaling, such as the ltm-Config.

[0209] In some implementations, the indication may take ENUMERATED format with value ‘true’. In some implementations, if the indication is present in the RRC signaling, the UE may consider that DCI is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling, the UE may consider that a MAC CE is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling, the UE may consider that an RRC signaling is used to trigger the evaluation of conditions.

[0210] In some implementations, the indication may take ENUMERATED format. In some implementations, if the indication is present in the RRC signaling with a first value (e.g., ‘dci’), the UE may consider that DCI is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling with a second value (e.g., ‘pdcch-order’), the UE may consider that DCI triggering an early TA acquisition is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling with a third value (e.g., ‘mac’), the UE may consider that a MAC CE is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling with a fourth value (e.g., ‘tci-activation’), the UE may consider that a MAC CE triggering the activation of TCI states is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling with a fifth value (e.g., ‘csc’), the UE may consider that a Cell Switch Command MAC CE is used to trigger the evaluation of conditions. In some implementations, if the indication is present in the RRC signaling with a sixth value (e.g., ‘rrc’), the UE may consider that RRC signaling is used to trigger the evaluation of conditions.

[0211] In some implementations, when the UE starts the evaluation of conditions, the UE may stop transmitting a measurement report to the network. When the UE stops the evaluation of conditions, the UE may start transmitting a measurement report to the network. In some implementations, the measurement report may be transmitted to the serving cell. In some implementations, stopping the transmission of the measurement report may include skipping the transmission or postponing the transmission.

[0212] In some implementations, when the UE starts the evaluation of conditions associated with one or more beams, the UE may stop transmitting the measurement report associated with the one or more beams. When the UE stops the evaluation of conditions associated with the one or more beams, the UE may start transmitting the measurement report associated with the one or more beams. In some implementations, when the UE starts the evaluation of conditions associated with one or more RS resource sets, the UE may stop transmitting the measurement report associated with the one or more RS resource sets. When the UE stops the evaluation of conditions associated with the one or more RS resource sets, the UE may start transmitting the measurement report associated with the one or more RS resource sets.

[0213] In some implementations, the behavior related to the condition evaluation and the report transmission may be configured by the network (e.g., via RRC signaling). In some implementations, the behavior may be indicated in an indicator configured in the ltm-Config, ltm-Candidate, or ltm-CSI-ResourceConfig. In some implementations, the indication may take ENUMERATED format with value ‘true’.

[0214] For example, if the indication is present in the ltm-Config, when the UE starts the evaluation of conditions associated with one or more RS resource sets, the UE may stop transmitting the measurement report associated with the one or more RS resource sets. When the UE stops the evaluation of conditions associated with the one or more RS resource sets, the UE may start transmitting the measurement report associated with the one or more RS resource sets.

[0215] For example, if the indication is present in the ltm-Candidate, when the UE starts the evaluation of conditions associated with one or more RS resource sets associated with the ltm-Candidate, the UE may stop transmitting the measurement report associated with the one or more RS resource sets. When the UE stops the evaluation of conditions associated with the one or more RS resource sets associated with the ltm-Candidate, the UE may start transmitting the measurement report associated with the one or more RS resource sets.

[0216] For example, if the indication is present in the ltm-CSI-ResourceConfig, when the UE starts the evaluation of conditions associated with one or more RS resource sets associated with the ltm-CSI-ResourceConfig, the UE may stop transmitting the measurement report associated with the one or more RS resource sets. When the UE stops the evaluation of conditions associated with the one or more RS resource sets associated with the ltm-CSI-ResourceConfig, the UE may start transmitting the measurement report associated with the one or more RS resource sets.

[0217] FIG. 1 is a flowchart illustrating a method / process 100 performed by a UE for a CLTM operation, according to an example implementation of the present disclosure. In the action 102, the process 100 may start by receiving, from a BS, a first MAC CE including a first TA value for a first CLTM candidate cell. In some implementations, the UE may receive, from the BS, an LTM configuration or a CLTM configuration that indicates multiple candidate cells, which may include the first CLTM candidate cell, a second CLTM candidate cell, and so on. It should be noted that the first TA value may be specific to the first CLTM candidate cell.

[0218] In some implementations, the first MAC CE may correspond to an LTM candidate Timing Advance Command MAC CE. In some implementations, the first CLTM candidate cell may obtain the first TA value and then send the TA value to the BS (e.g., via XnAP signaling), and then the BS may transmit the first TA value to the UE via the first MAC CE.

[0219] In the action 104, the process 100 may store the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE. In the action 106, the process 100 may start or restart a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE. In some implementations, the UE may start or restart the first timer when receiving the first MAC CE. In some implementations, the first timer may correspond to a Time Alignment Timer (TAT) associated with the first CLTM candidate cell. It should be noted that the first timer may be specific to the first CLTM candidate cell. In some implementations, the UE may maintain a timer (e.g., a TAT) for each CLTM candidate cell.

[0220] In the action 108, the process 100 may consider the first TA value for the first CLTM candidate cell as valid until the first timer expires. If the first timer associated with the first CLTM candidate cell is running, the UE may consider the first TA value for the first CLTM candidate cell as valid. If the first timer associated with the first CLTM candidate cell expires, the UE may consider the first TA value for the first CLTM candidate cell as invalid. The process 100 may then end.

[0221] The steps / actions shown in FIG. 1 should not be construed as necessarily order dependent. The order in which the process is described is not intended to be construed as a limitation. Moreover, some of the actions shown in FIG. 1 may be omitted in some implementations and one or more actions shown in FIG. 1 may be combined.

[0222] The technical problem addressed by the method illustrated in FIG. 1 relates to the validity of the TA value and the maintenance of the associated timer for CLTM operations. In the method illustrated in FIG. 1, the UE may maintain a separate timer for each candidate cell, and the validity of the TA value for each candidate cell may be determined based on the expiration of the corresponding timer. By managing timers on a per-candidate-cell basis, the UE may independently control the validity duration of each stored TA value, thereby avoiding the use of outdated TA values, improving uplink timing alignment, enhancing mobility performance during CLTM operation, and reducing signaling overhead for TA updates.

[0223] In some implementations, the UE may receive, from the BS, a second MAC CE including a second TA value for a second CLTM candidate cell. The second TA value may be specific to the second CLTM candidate cell The second MAC CE may correspond to an LTM candidate Timing Advance Command MAC CE. The UE may store the second TA value for the second CLTM candidate cell in response to receiving the second MAC CE. The UE may start or restart a second timer that is associated with the second CLTM candidate cell in response to receiving the second MAC CE. The second timer may correspond to a TAT associated with the second CLTM candidate cell. The second timer may be specific to the second CLTM candidate cell. The UE may consider the second TA value for the second CLTM candidate cell as valid until the second timer expires.

[0224] In some implementations, the UE may receive, from the BS, a first RRC message indicating an initial value for the first timer. The UE may set the first timer to the initial value when starting or restarting the first timer. In some implementations, the first RRC message may include an RRC Reconfiguration message including the CLTM configuration.

[0225] In some implementations, the UE may perform a CLTM cell switch procedure to switch to the first CLTM candidate cell. The UE may keep the first timer running upon switching to the first CLTM candidate cell. In other words, the UE may keep running the timer (e.g., the TAT) associated with the target candidate cell.

[0226] In some implementations, the UE may perform a CLTM cell switch procedure to switch to a second CLTM candidate cell other than the first CLTM candidate cell. The UE may keep the first timer running upon switching to the second CLTM candidate cell. In other words, upon CLTM execution, the UE may keep the first timer running even if the first CLTM candidate cell is not the target candidate cell of the CLTM execution. In some implementations, for any candidate cell other than the targe candidate cell, the UE may keep the corresponding timer (e.g., the corresponding TAT) running upon CLTM execution to switch to the target candidate cell.

[0227] In some implementations, the UE may maintain separate timers respectively for different candidate cells. For example, the UE may maintain an individual TAT for each candidate cell. In some implementations, upon CLTM execution, the UE may keep running all the timers regardless of which cell is the target candidate cell.

[0228] In some implementations, the UE may perform an early synchronization procedure with the first CLTM candidate cell. The early synchronization procedure may also be referred to as an early TA acquisition procedure or an early TA procedure in the present disclosure. In some implementations, the UE may obtain a TA value associated with the first CLTM candidate cell based on the early synchronization procedure. The UE may perform the early synchronization procedure before the CLTM execution. In some implementations, the UE may autonomously initiate the early synchronization procedure. In some implementations, the UE may be instructed by the BS (e.g., the serving cell) to perform the early synchronization procedure.

[0229] In some implementations, the UE may receive, from the BS, a PDCCH order that initiates the early synchronization procedure. For example, the early synchronization procedure may be initiated by the network via DCI (e.g., PDCCH-order RA).

[0230] In some implementations, the UE may activate or deactivate at least one TCI state of the first CLTM candidate cell. The UE may perform early TCI activation / deactivation for a beam in the first CLTM candidate cell, for example, before the CLTM execution. In some implementations, the UE may activate / deactivate the beam in response to signaling from the network.

[0231] FIG. 2 is a block diagram illustrating a node 200 for wireless communication, according to an example implementation of the present disclosure. As illustrated in FIG. 2, a node 200 may include a transceiver 220, a processor 228, a memory 234, one or more presentation components 238, and at least one antenna 236. The node 200 may also include a radio frequency (RF) spectrum band module, a BS communications module, a network communications module, and a system communications management module, Input / Output (I / O) ports, I / O components, and a power supply (not illustrated in FIG. 2).

[0232] Each of the components may directly or indirectly communicate with each other over one or more buses 240. The node 200 may be a UE or a BS that performs various functions disclosed with reference to FIG. 1.

[0233] The transceiver 220 has a transmitter 222 (e.g., transmitting / transmission circuitry) and a receiver 224 (e.g., receiving / reception circuitry) and may be configured to transmit and / or receive time and / or frequency resource partitioning information. The transceiver 220 may be configured to transmit in different types of subframes and slots including, but not limited to, usable, non-usable, and flexibly usable subframes and slot formats. The transceiver 220 may be configured to receive data and control channels.

[0234] The node 200 may include a variety of computer-readable media. Computer-readable media may be any available media that may be accessed by the node 200 and include volatile (and / or non-volatile) media and removable (and / or non-removable) media.

[0235] The computer-readable media may include computer-storage media and communication media. Computer-storage media may include both volatile (and / or non-volatile media), and removable (and / or non-removable) media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, AI / ML module(s), or data.

[0236] Computer-storage media may include RAM, ROM, EPROM, EEPROM, flash memory (or other memory technology), CD-ROM, Digital Versatile Disks (DVD) (or other optical disk storage), magnetic cassettes, magnetic tape, magnetic disk storage (or other magnetic storage devices), etc. Computer-storage media may not include a propagated data signal. Communication media may typically embody computer-readable instructions (e.g., computer-readable instructions related to AI module(s) and / or the ML module(s)), data structures, program modules, or other data in a modulated data signal, such as a carrier wave, or other transport mechanisms and include any information delivery media.

[0237] The term “modulated data signal” may mean a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Communication media may include wired media, such as a wired network or direct-wired connection, and wireless media, such as acoustic, RF, infrared, and other wireless media. Combinations of any of the above listed components should also be included within the scope of computer-readable media.

[0238] The memory 234 may include computer-storage media in the form of volatile and / or non-volatile memory. The memory 234 may be removable, non-removable, or a combination thereof. Example memory may include solid-state memory, hard drives, optical-disc drives, etc. As illustrated in FIG. 2, the memory 234 may store a computer-readable and / or computer-executable instructions 232 (e.g., software codes) that are configured to, when executed, cause the processor 228 to perform various functions disclosed herein, for example, with reference to FIG. 1. Alternatively, the instructions 232 may not be directly executable by the processor 228 but may be configured to cause the node 200 (e.g., when compiled and executed) to perform various functions disclosed herein.

[0239] The processor 228 (e.g., having processing circuitry) may include an intelligent hardware device, e.g., a Central Processing Unit (CPU), a microcontroller, an ASIC, etc. The processor 228 may include memory. The processor 228 may process the data 230 and the instructions 232 received from the memory 234, and information transmitted and received via the transceiver 220, the baseband communications module, and / or the network communications module. The processor 228 may also process information to send to the transceiver 220 for transmission via the antenna 236 to the network communications module for transmission to a CN.

[0240] One or more presentation components 238 may present data indications to a person or another device. Examples of presentation components 238 may include a display device, a speaker, a printing component, a vibrating component, etc.

[0241] In view of the present disclosure, it is obvious that various techniques may be used for implementing the disclosed concepts without departing from the scope of those concepts. Moreover, while the concepts have been disclosed with specific reference to certain implementations, a person of ordinary skill in the art may recognize that changes may be made in form and detail without departing from the scope of those concepts. As such, the disclosed implementations are to be considered in all respects as illustrative and not restrictive. It should also be understood that the present disclosure is not limited to the particular implementations disclosed and many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure.

Claims

1. A User Equipment (UE) for performing a Conditional Layer 1 / Layer 2 Triggered Mobility (CLTM) operation, the UE comprising: 　　　　at least one processor; and 　　　　at least one non-transitory computer-readable medium coupled to the at least one processor and storing one or more computer-executable instructions that, when executed by the at least one processor, cause the UE to: 　　　　　　　　receive, from a Base Station (BS), a first Medium Access Control (MAC) Control Element (CE) comprising a first Timing Advance (TA) value for a first CLTM candidate cell; 　　　　　　　　store the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE; 　　　　　　　　start or restart a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE; and 　　　　　　　　consider the first TA value for the first CLTM candidate cell as valid until the first timer expires.

2. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　receive, from the BS, a second MAC CE comprising a second TA value for a second CLTM candidate cell; 　　　　store the second TA value for the second CLTM candidate cell in response to receiving the second MAC CE; 　　　　start or restart a second timer that is associated with the second CLTM candidate cell in response to receiving the second MAC CE; and 　　　　consider the second TA value for the second CLTM candidate cell as valid until the second timer expires.

3. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　receive, from the BS, a first Radio Resource Control (RRC) message indicating an initial value for the first timer; and 　　　　set the first timer to the initial value when starting or restarting the first timer.

4. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　perform a CLTM cell switch procedure to switch to the first CLTM candidate cell; and 　　　　keep the first timer running upon switching to the first CLTM candidate cell.

5. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　perform a CLTM cell switch procedure to switch to a second CLTM candidate cell other than the first CLTM candidate cell; and 　　　　keep the first timer running upon switching to the second CLTM candidate cell.

6. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　perform an early synchronization procedure with the first CLTM candidate cell.

7. The UE of claim 6, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　receive, from the BS, a Physical Downlink Control Channel (PDCCH) order that initiates the early synchronization procedure.

8. The UE of claim 1, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to: 　　　　activate or deactivate at least one Transmission Configuration Indicator (TCI) state of the first CLTM candidate cell.

9. A Base Station (BS) for configuring a Conditional Layer 1 / Layer 2 Triggered Mobility (CLTM) operation, the BS comprising: 　　　　at least one processor; and 　　　　at least one non-transitory computer-readable medium coupled to the at least one processor and storing one or more computer-executable instructions that, when executed by the at least one processor, cause the BS to: 　　　　　　　　transmit, to a User Equipment (UE), a first Medium Access Control (MAC) Control Element (CE) comprising a first Timing Advance (TA) value for a first CLTM candidate cell, wherein: 　　　　the UE stores the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE, 　　　　the UE starts or restarts a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE, and 　　　　the UE considers the first TA value for the first CLTM candidate cell as valid until the first timer expires.

10. The BS of claim 9, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: 　　　　transmit, to the UE, a second MAC CE comprising a second TA value for a second CLTM candidate cell, wherein: 　　　　the UE stores the second TA value for the second CLTM candidate cell in response to receiving the second MAC CE, 　　　　the UE starts or restarts a second timer that is associated with the second CLTM candidate cell in response to receiving the second MAC CE, and 　　　　the UE considers the second TA value for the second CLTM candidate cell as valid until the second timer expires.

11. The BS of claim 9, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: 　　　　transmit, to the UE, a first Radio Resource Control (RRC) message indicating an initial value for the first timer, wherein: 　　　　the UE sets the first timer to the initial value when starting or restarting the first timer.

12. The BS of claim 9, wherein: 　　　　the UE performs a CLTM cell switch procedure to switch to the first CLTM candidate cell, and 　　　　the UE keeps the first timer running upon switching to the first CLTM candidate cell.

13. The BS of claim 9, wherein: 　　　　the UE performs a CLTM cell switch procedure to switch to a second CLTM candidate cell other than the first CLTM candidate cell, and 　　　　the UE keeps the first timer running upon switching to the second CLTM candidate cell.

14. The BS of claim 9, wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the BS to: 　　　　transmit, to the UE, a Physical Downlink Control Channel (PDCCH) order that initiates an early synchronization procedure, wherein: 　　　　the UE performs the early synchronization procedure with the first CLTM candidate cell.

15. A method performed by a User Equipment (UE) for performing a Conditional Layer 1 / Layer 2 Triggered Mobility (CLTM) operation, the method comprising: 　　　　receiving, from a Base Station (BS), a first Medium Access Control (MAC) Control Element (CE) comprising a first Timing Advance (TA) value for a first CLTM candidate cell; 　　　　storing the first TA value for the first CLTM candidate cell in response to receiving the first MAC CE; 　　　　starting or restarting a first timer that is associated with the first CLTM candidate cell in response to receiving the first MAC CE; and 　　　　considering the first TA value for the first CLTM candidate cell as valid until the first timer expires.

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