Method and apparatus for conditional low layer triggered mobility procedure

Abstract

A method for conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure is provided. The method is implemented by a user equipment (UE) and includes receiving a conditional LTM command from a source base station (BS), wherein the conditional LTM command comprises a first target cell configuration of a first target cell and an execution condition. The method includes receiving a first medium access control (MAC) control element (CE) associated with the first target cell from the source BS, wherein the first MAC CE comprises timing advance (TA) related information. The method includes switching to the first target cell by applying the first target cell configuration and the received TA related information when the execution condition is satisfied.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 567,479, filed March 20, 2024, entitled “Method and Apparatus for Conditional Lower Layer Triggered Mobility,” and U.S. Application No. 19 / 083,990, filed March 19, 2025, entitled “Method and Apparatus for Conditional Lower Layer Triggered Mobility Procedure,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to wireless communications. More specifically, aspects of this disclosure relate to a method and apparatus for a conditional Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) process. Background Technology

[0004] Unless otherwise stated herein, the methods described in this section are not prior art to the appended claims and are not acknowledged as prior art by virtue of their inclusion in this section.

[0005] A traditional handover (HO) procedure (i.e., Layer 3 / L3 mobility) is introduced to switch a User Equipment (UE) from a source serving cell to a target serving cell, for example, when the UE moves from the coverage area of ​​the source serving cell to the coverage area of ​​the target serving cell. The decision to perform a traditional HO is made by the current serving gNB (or source gNB) of the current serving cell (or source cell) based on measurements reported by the UE. If the source gNB determines that a handover is necessary, it sends an HO request message to the target gNB to request HO acceptance. If the target gNB accepts the HO request, it replies with an HO request confirmation message, which includes the necessary information / configuration for the UE to perform the traditional HO procedure to synchronize with the target gNB's target cell. Upon receiving the HO request confirmation message, the source gNB sends an HO command (or an RRC reconfiguration message with synchronization information for the target cell), which includes at least the target cell configuration, to instruct the UE to perform the traditional HO procedure to the target cell. Therefore, the traditional HO procedure is triggered by Layer 3 (L3) measurements and completed by instructing the UE to handover from the source cell to the target cell via RRC signaling. However, due to faster signal fading or higher UE speeds, the serving source gNB may not always receive measurement reports from the UE, or may fail to successfully send handover (HO) commands to the UE. This results in a higher HO failure rate. Furthermore, the traditional HO procedure involves a complete L2 (and L1) reset, leading to longer latency, greater overhead, and longer downtime compared to beam-switching mobility.

[0006] To reduce latency, overhead, and downtime, LTM (Local Time Management) was introduced in 3GPP Release 18 to improve HO latency and downtime compared to traditional HO procedures. By definition, LTM is a cell handover process triggered by the network through a Medium Access Control (MAC) Control Element (CE) based on L1 measurements. It should be noted that, based on the 5G protocol stack, L1 is the Physical Layer, and L3 is the Radio Resource Control (RRC) layer. L2 includes the MAC, Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Service Data Adaptation Protocol (SDAP) layers. As described in TS 38.300 of Release 18, LTM is a process in which the gNB receives an L1 measurement report from the UE, and based on this, the gNB changes the UE's serving cell via a cell handover command indicated by the MAC CE. The cell handover command indicates the LTM candidate configuration that the gNB previously prepared and provided to the UE via RRC signaling. The UE then switches to the target configuration according to the cell handover command.

[0007] Figure 1 Example scenario 100 of a signaling procedure for LTM, as described in TS 38.300 of Release 18, is shown. Scenario 100 involves a UE and a next-generation base station (gNB) (e.g., a base station (BS) or transmission and reception point (TRP)), which can be part of a wireless network (e.g., a 5G NR network, a 5G network, or a 6G network). Figure 1 As shown, when the UE is in the RRC_CONNECTED state, the signaling procedure for LTM is executed.

[0008] In step 101, the UE sends a Measurement Report message to the gNB. Upon receiving the Measurement Report message, the gNB decides to configure LTM and initiates LTM candidate preparation.

[0009] In step 102, the gNB sends an RRC Reconfiguration message to the UE, which includes the configuration of one or more LTM candidate cells.

[0010] In step 103, the UE stores the configuration of the LTM candidate cells and sends an RRC reconfiguration complete message to the gNB.

[0011] In step 104a, the UE may perform downlink (DL) synchronization with the candidate cell before receiving the LTM cell handover command.

[0012] In step 104b, the UE may perform uplink (UL) synchronization and timing advance (TA) acquisition with the candidate cell before receiving the LTM cell handover command. If UE-based TA measurement is configured (as introduced in TS 38.331 of Release 18), the UE uses the UE-based TA measurement to acquire the TA value of the candidate cell. Alternatively, the UE may perform early TA acquisition with the candidate cell at the request of the gNB before receiving the LTM cell handover command. This is accomplished via contention-free random access (CFRA) triggered by a Physical Downlink Control Channel (PDCCH) order from the source cell, after which the UE sends a preamble to the indicated candidate cell. To minimize source cell data interruption due to CFRA for the candidate cell, the UE does not receive a random access response from the gNB for acquiring the TA value, and the TA value of the candidate cell is indicated in the LTM cell handover command. The UE does not maintain a TA timer for the candidate cell and relies on the network implementation to guarantee the validity of the TA.

[0013] In step 105, the UE performs L1 measurements on the configured LTM candidate cells and sends an L1 measurement report to the gNB. L1 measurements should be performed whenever RRC reconfiguration (in step 102) is applicable. Upon receiving the L1 measurement report, the gNB can decide to perform an LTM cell handover to the target cell.

[0014] In step 106, the gNB decides to perform a handover to the target cell and sends a MAC control element (MAC-CE) that triggers the cell handover by including a candidate configuration index of the target cell. In response to the LTM cell handover trigger, the UE switches to the target cell and applies the configuration indicated by the candidate configuration index.

[0015] In step 107, as described in TS 38.321 of Release 18, if the UE does not have a valid TA for the target cell, the UE performs a random access procedure for the target cell.

[0016] In step 108, the UE completes the LTM cell handover process by sending an RRC reconfiguration complete message to the target cell. The UE considers the LTM cell handover process to be successfully completed when the UE has performed the RA procedure in step 107 and the random access procedure has successfully completed. For RACH-less LTM, the UE considers the LTM cell handover process to be successfully completed when it determines that the gNB has successfully received its first UL data. It should be noted that RACH-less LTM is an LTM cell handover process in which the UE skips the random access procedure.

[0017] In the Release 18 design, there is still room for further improvement in LTM. RP-234036 approved a new work project for further New Radio (NR) mobility enhancements. One of the goals of this new work project is to support conditional LTM by following the concept of conditional handover (CHO) to achieve greater robustness. As introduced in TS 38.300 v16.15.0, CHO is defined as a handover performed by the UE when one or more handover execution conditions are met, without prior signaling interaction with the source cell. By introducing a conditional LTM mechanism, UE mobility can enjoy both high robustness and short downtime.

[0018] However, many details of the entire conditional LTM design are not yet defined, such as: the related configuration design to support the conditional LTM design; the means to perform early UL synchronization (or obtain effective timing advance / TA value) for the target candidate cell for the conditional LTM design, considering that the UE intending to perform the conditional HO procedure may not receive the LTM cell handover command MACCE (as described in TS 38.321 of Release 18); and the corresponding UE behavior for performing the conditional LTM procedure, etc.

[0019] Therefore, how to design conditional LTM processes has become an important issue. Thus, appropriate solutions are needed to address this problem. Summary of the Invention

[0020] The following overview is for illustrative purposes only and is not intended to be limiting in any way. That is, it is provided to introduce the concepts, key points, benefits, and advantages of the novel and non-obvious techniques described herein. Some (but not all) implementations are further described in the detailed embodiments below. Therefore, the following overview is not intended to identify key features of the claimed subject matter, nor is it intended to determine the scope of the claimed subject matter.

[0021] Therefore, this disclosure provides a method and apparatus for a conditional Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) procedure. The main objective of this disclosure is to support the conditional LTM procedure, including: UE capability reporting to support the conditional LTM procedure; information required for conditional LTM configuration; steps for different types of conditional LTM procedures; a new MAC CE for providing TA values ​​for early UL synchronization to target candidate cells; overall TA management for performing the conditional LTM procedure; and cross-layer interactions.

[0022] In one exemplary embodiment, a method is provided for a conditional Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) procedure. The method is implemented by user equipment (UE) and includes receiving a conditional LTM command from a source base station (BS), wherein the conditional LTM command includes a first target cell configuration and execution conditions for a first target cell. The method includes receiving from the source BS a first Medium Access Control (MAC) control element (CE) associated with the first target cell, wherein the first MAC CE includes Timing Advance (TA) related information. The method includes, when the execution conditions are met, handing over to the first target cell by applying the first target cell configuration and the received TA related information.

[0023] In one exemplary embodiment, an apparatus is provided for a conditionally Layer 1 / L2 (L1 / L2) triggered mobility (LTM) procedure. The apparatus includes a transceiver and a processor. The transceiver wirelessly communicates with at least one network node during operation. The processor is communicatively coupled to the transceiver such that, during operation, the processor performs operations including generating a list of non-allowed cells for New Radio (NR) Standalone (SA) cells. The processor performs operations including receiving a conditional LTM command from a source base station (BS), wherein the conditional LTM command includes a first target cell configuration and execution conditions for a first target cell. The processor performs operations including receiving a first Media Access Control (MAC) control element (CE) associated with the first target cell from the source BS, wherein the first MAC CE includes timing advance (TA) related information. The processor performs operations including, when the execution conditions are met, switching to the first target cell by applying the first target cell configuration and the received TA related information.

[0024] In one exemplary embodiment, a method is provided for a conditionally Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) procedure. The method is implemented by a source base station (BS) and includes sending a conditional LTM command to a user equipment (UE), wherein the conditional LTM command includes a first target cell configuration and execution conditions for a first target cell; and sending a first media access control (MAC) control element (CE) associated with the first target cell to the UE, wherein the first MAC CE includes timing advance (TA) related information. Attached Figure Description

[0025] The accompanying drawings are included to provide a further understanding of this disclosure, and are incorporated in and constitute a part of this disclosure. The drawings illustrate embodiments of this disclosure and, together with the description, serve to explain the principles of this disclosure. It should be understood that the drawings are not necessarily drawn to scale, as some components may be displayed out of proportion in actual implementations, in order to clearly illustrate the concepts of this disclosure.

[0026] Figure 1 An example scenario of the signaling procedure used for LTM is shown.

[0027] Figure 2 The UE capability reporting process according to an embodiment of this disclosure is illustrated.

[0028] Figure 3 A conditional LTM process according to an embodiment of this disclosure is shown.

[0029] Figure 4A conditional LTM process according to an embodiment of this disclosure is shown.

[0030] Figure 5 A conditional LTM process according to an embodiment of this disclosure is shown.

[0031] Figure 6 A conditional LTM process according to an embodiment of this disclosure is shown.

[0032] Figure 7 An early UL TA acquisition process triggered by a PDCCH order is shown according to an embodiment of this disclosure.

[0033] Figure 8 An LTM TA command MAC according to an embodiment of this disclosure is shown.

[0034] Figure 9 A TA management flowchart for a conditional LTM process according to an embodiment of the present disclosure is shown.

[0035] Figure 10 This is a block diagram of an example communication system according to an embodiment of the present disclosure.

[0036] Figure 11 This is a flowchart of an example process according to an embodiment of the present disclosure. Detailed Implementation

[0037] The following description contains specific information relating to the exemplary embodiments in this disclosure. The accompanying drawings and detailed descriptions in this disclosure are only illustrative of exemplary embodiments. However, this disclosure is not limited to these exemplary embodiments only. Other variations and embodiments of this disclosure will occur to those skilled in the art. Unless otherwise stated, the same or corresponding elements in the drawings may be represented by the same or corresponding reference numerals. Furthermore, the drawings and illustrations in this disclosure are generally not drawn to scale and are not intended to correspond to actual relative dimensions.

[0038] For the sake of consistency and ease of understanding, similar features may be identified using the same reference numerals in the example figures (although not shown in some examples). However, features in different embodiments may differ in other respects, and therefore should not be narrowly limited to what is shown in the figures.

[0039] This specification uses the phrases "in one embodiment" or "in some embodiments," each of which may refer to one or more of the same or different embodiments. The term "coupled" is defined as a connection, whether direct or indirect through intermediate components, and is not necessarily limited to a physical connection. The term "comprising" is used to mean "including but not limited to"; it specifically refers to an open inclusion or membership in the described combinations, groups, series, and equivalents. The expression "at least one of A, B, and C" or "at least one of A, B, and C" means "only A, or only B, or only C, or any combination of A, B, and C."

[0040] Furthermore, for purposes of explanation rather than limitation, specific details (such as functional entities, technologies, protocols, standards, etc.) are described to provide an understanding of the technologies described. In other examples, detailed descriptions of well-known methods, technologies, systems, architectures, etc., are omitted to avoid unnecessary obfuscation.

[0041] Those skilled in the art will readily recognize that any network function or algorithm described in this disclosure can be implemented in hardware, software, or a combination of software and hardware. The described functions may correspond to modules that are software, hardware, firmware, or any combination thereof. Software implementations may include computer-executable instructions stored on a computer-readable medium such as memory or other types of storage devices. For example, one or more microprocessors or general-purpose computers with communication processing capabilities may be programmed to have corresponding executable instructions and execute the described network functions or algorithms. The microprocessor or general-purpose computer may consist of an application-specific integrated circuit (ASIC), a programmable logic array, and / or use one or more digital signal processors (DSPs). Although some of the exemplary embodiments described in this specification are directed to software installed on and executed on computer hardware, alternative exemplary embodiments implemented as firmware or as hardware or a combination of hardware and software are fully within the scope of this disclosure.

[0042] Computer-readable media include, but are not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, compact disc read-only memory (CD-ROM), magnetic tape cassette, magnetic tape, disk storage, or any other equivalent medium capable of storing computer-readable instructions.

[0043] Wireless communication network architectures (e.g., Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, LTE-Advanced Pro (LTE-Advanced Pro) systems, 5G New Radio (NR) radio access networks (RANs), or 6G NR RANs typically include at least one base station (BS), at least one user equipment (UE), and one or more optional network elements that provide connectivity to the network. The UE communicates with the network (e.g., a core network (CN), an evolved packet core (EPC) network, an evolved universal terrestrial radio access network (E-UTRAN), a 5G core network (5GC), or the Internet) through the RAN established by one or more BSs.

[0044] It should be noted that in this disclosure, the UE may include, but is not limited to, a mobile station, mobile terminal or device, or a user communication radio terminal. For example, the UE may be a portable wireless device, including but not limited to a mobile phone, tablet computer, wearable device, sensor, vehicle, or personal digital assistant (PDA) with wireless communication capabilities. The UE is configured to transmit and receive signals from one or more cells in a radio access network via an air interface.

[0045] The BS can be configured to provide communication services based on at least one of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile Communications (GSM, commonly referred to as 2G), GSM EDGE Radio Access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, commonly referred to as 3G) based on Wideband-Code Division Multiple Access (W-CDMA), High-Speed ​​Packet Access (HSPA), LTE, LTE-A, eLTE (evolved LTE, such as LTE connected to 5GC), NR (commonly referred to as 5G), 6G, and / or LTE-A Pro. However, the scope of this disclosure should not be limited to the protocols described above.

[0046] A BS can include, but is not limited to, a node B (NB) in UMTS, an evolved Node B (eNB) in LTE or LTE-A, a Radio Network Controller (RNC) in UMTS, a Base Station Controller (BSC) in GSM / GERAN, an ng-eNB in ​​an Evolved Universal Terrestrial Radio Access (E-UTRA) BS connected to 5GC, a next-generation Node B (gNB) in 5G-RAN, and any other device capable of controlling wireless communication within the cell and managing radio resources. A BS can serve one or more UEs through a radio interface.

[0047] A Base Station (BS) is operable to provide radio coverage to a specific geographic area using multiple cells forming a radio access network. The BS supports cell operation. Each cell is operable to serve at least one UE within its radio coverage area. More specifically, each cell (often referred to as the serving cell) provides service to one or more UEs within its radio coverage area (e.g., each cell schedules downlink resources and optional uplink resources for downlink packet transmission and optional uplink packet transmission to at least one UE within its radio coverage area). The BS can communicate with one or more UEs in a wireless communication system through multiple cells. Cells can allocate sidelink (SL) resources to support Proximity Service (ProSe) or Vehicle to Everything (V2X) services. Each cell can have overlapping coverage areas with other cells.

[0048] As mentioned above, the NR frame structure is designed to support flexible configuration to accommodate 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 meeting the requirements of high reliability, high data rate, and low latency. Orthogonal Frequency-Division Multiplexing (OFDM) technology, agreed upon in the 3rd Generation Partnership Project (3GPP), can serve as the basis for NR waveforms. A scalable OFDM parameter set (numerology) can also be used, such as adaptive subcarrier spacing, channel bandwidth, and cyclic prefix (CP). Furthermore, two coding schemes are considered for NR: (1) Low-Density Parity-Check (LDPC) codes and (2) Polar codes. The adaptive coding scheme can be configured based on channel conditions and / or service applications.

[0049] Furthermore, considering that the transmission time interval (TX) of a single NR frame should at least include downlink (DL) transmission data, guard interval, and uplink (UL) transmission data, the corresponding portions of the DL transmission data, guard interval, and UL transmission data should also be configurable, for example, based on the dynamic characteristics of the NR network. In addition, SL resources can also be provided in the NR frame to support ProSe services or V2X services.

[0050] Furthermore, the terms "system" and "network" are used interchangeably in this document. The term "and / or" is used only to describe the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone. Additionally, the character " / " in this document generally indicates that the objects preceding and following each other are in an "or" relationship.

[0051] UE capabilities

[0052] Figure 2 The UE capability reporting process according to an embodiment of this disclosure is illustrated. In step S205, when the network (NW) needs UE capability information, the NW can initiate the process with the UE in the RRC_CONNECTED state. That is, the NW can send a UE capability query message (i.e., a UECapabilityEnquiry message) to the UE, and then the UE can report the requested UE capability information in a UE capability information message (i.e., a UECapabilityInformation message) in step S210.

[0053] In one implementation, the UE can report its ability to support conditional LTM procedures to the NW. When the UE supports conditional LTM procedures, this means the NW can provide the UE with LTM candidate configurations and associated execution conditions. When the associated execution conditions are met, the UE can execute or apply the LTM candidate configuration itself without receiving any NW signaling instructing the UE to apply the LTM candidate configuration to handover or reshuffle to a new serving cell (or candidate target cell). In another implementation, when the UE reports its ability to execute conditional LTM procedures to the NW, the UE can also support the execution of subsequent LTM and / or subsequent conditional LTM. It should be noted that subsequent LTM can be accomplished by repeating the early synchronization, LTM cell handover execution, and / or LTM cell handover completion steps after each LTM cell handover completion without releasing other LTM candidate configurations. It should be noted that subsequent conditional LTM can be accomplished by repeating the early synchronization, execution condition evaluation, LTM cell handover execution, and / or LTM cell handover completion steps after each (conditional) LTM cell handover completion without releasing other conditional LTM candidate configurations. In one implementation, the UE may report one capability that supports subsequent LTM and another capability that supports subsequent conditional LTM.

[0054] In one implementation, the UE may report to the NW independent capabilities supporting a conditional LTM procedure, one for supporting a conditional LTM procedure and another for supporting subsequent LTM and / or subsequent conditional LTM. In another implementation, the UE may report a capability supporting an LTM procedure, a capability supporting a conditional LTM procedure, a capability supporting subsequent LTM, and a capability supporting subsequent conditional LTM.

[0055] In one implementation, the UE can report to the NW the independent capabilities supporting conditional LTM procedures: one for supporting intra-CU (intra-CU) conditional LTM procedures, and another for supporting inter-CU (inter-CU) conditional LTM procedures. For example, when the UE reports support for intra-CU conditional LTM procedures, the NW can configure intra-CU conditional LTM for the UE. Similarly, when the UE reports support for inter-CU conditional LTM procedures, the NW can configure inter-CU conditional LTM for the UE.

[0056] In one implementation, the UE can report its ability to support event-triggered L1 measurements for conventional LTM procedures. For example, when the UE reports support for event-triggered L1 measurements, the NW can configure the UE to perform SSB-based or CSI-RS-based L1 measurements by providing associated information of the synchronization signal block (SSB) or channel state information referenced signal (CSI-RS) and / or associated triggering conditions for measurement reporting (e.g., based on a certain measurement event).

[0057] In one implementation, the UE can report its ability to support conditional LTM configuration execution conditions based on L1 measurements. In another implementation, the UE can report its ability to support conditional LTM configuration execution conditions based on L3 measurements. In yet another implementation, when the UE reports its ability to support conditional LTM procedures to the NW, the UE can also support conditional LTM configuration execution conditions based on L1 and / or L3 measurements. It should be noted that whether the execution conditions are based on L1 or L3 measurements can depend on the NW configuration (e.g., based on the reporting configuration or measurement configuration associated with the received conditional LTM candidate configuration). That is, the NW can configure L1 or L3 execution conditions associated with the candidate target cell in the conditional LTM command.

[0058] In some implementations, capabilities can be differentiated between Time Division Duplex (TDD) and Frequency Division Duplex (FDD). For example, a UE may report one capability that supports performing a conditional LTM procedure in TDD and another capability that supports performing a conditional LTM procedure in FDD. In another example, a UE may report one capability that supports performing subsequent LTM and / or subsequent conditional LTM in TDD and another capability that supports performing subsequent LTM and / or subsequent conditional LTM in FDD.

[0059] In some embodiments, capabilities can be differentiated for Frequency Range 1 (FR1) and Frequency Range 2 (FR2). For example, a UE may report one capability that supports performing a conditional LTM procedure in FR1 and another capability that supports performing a conditional LTM procedure in FR2. In another example, a UE may report one capability that supports performing a subsequent LTM and / or a subsequent conditional LTM in FR1 and another capability that supports performing a subsequent LTM and / or a subsequent conditional LTM in FR2.

[0060] Figure 3 A conditional LTM process according to an embodiment of this disclosure is illustrated. It should be noted that... Figure 3 One or more steps in the process may or may not be performed. For example, the RACH procedure in step 307 may not be performed if UL synchronization in step 304b has been completed. Furthermore, the order of the steps is not mandatory. For example, the UE may begin evaluating the (configured) conditional LTM conditions before sending the RRC reconfiguration completion message in step 304.

[0061] In step 301, for a UE in the RRC_CONNECTED state, the serving gNB can configure the UE's measurement process, for example, by providing an L1 measurement configuration or an L3 measurement configuration, and the UE can report measurement results based on the L1 measurement configuration or the L3 measurement configuration. The L1 measurement configuration or L3 measurement configuration can be provided for measurements based on Channel State Information Reference Signal (CSI-RS) or Synchronization Signal Block (SSB) for a specific target candidate cell. Based on the received measurement configuration, the UE can periodically report measurement results to the serving gNB, or the measurement results can be reported via event triggering.

[0062] In step 302, the serving gNB can decide to use conditional LTM, for example, based on measurements received from the UE, UE speed, or current operating frequency. For intra-central unit (intra-CU) conditional LTM, the serving gNB (or the CU of the current serving cell) can prepare the configuration of candidate target cells for conditional LTM on its own and can send relevant information to the distributed unit (DU) of the current serving cell (or source cell) and / or the DU of the candidate target cells. For inter-CU (inter-CU) conditional LTM (or inter-gNB conditional LTM), the serving gNB can send conditional LTM requests for one or more candidate target cells belonging to one or more candidate gNBs. A conditional LTM request message can be sent to each candidate target cell (or its associated gNB). In one implementation, the request message may contain an indication (or relevant information) indicating whether the request message is for conditional LTM or conventional LTM. It should be noted that conventional LTM is a cell handover process triggered by the Medium Access Control (MAC) control element (CE) based on L1 measurements, as introduced in 3GPP Release 18. Therefore, there are no execution conditions for conventional LTM. In one example, when an indication (or related information) indicates that the request message is for conditional LTM, the candidate gNB may provide the execution conditions and / or candidate target cell configuration (or LTM candidate configuration) for conditional LTM in the request confirmation message. When an indication (or related information) indicates that the request message is for conventional LTM, the candidate gNB may provide the candidate target cell configuration in the request confirmation message without providing any execution conditions. In another example, when the request is for conditional LTM, the candidate gNB may provide CFRA resources / configuration and / or Contention-based Random Access (CBRA) resources / configuration for conditional LTM in the request confirmation message for the UE to perform the RA procedure to synchronize with the candidate target cell. In one implementation, the request message may contain an indication (or related information) indicating whether early UL synchronization is required for conditional LTM. In one example, when an indication (or related information) suggests whether conditional LTM requires early UL synchronization, the candidate gNB may provide CFRA resources / configuration and / or Contention-based random access (CBRA) resources / configuration for conditional LTM in a request confirmation message, allowing the UE to perform the RA procedure to synchronize with the candidate target cell before applying the candidate target cell configuration. In one implementation, a valid lifetime T1 may exist associated with the CFRA resources.When the effective timer T1 expires, the CFRA resource can be considered invalid, preventing the UE from using the CFRA resource to perform the RA procedure. Alternatively, the candidate gNB can also release the CFRA resource when the effective timer T1 expires, allowing the RA resource to be allocated to other UEs. In another example, when an indication (or related information) suggests that conditional LTM requires early UL synchronization, the candidate gNB can provide a Timing Advance (TA) value associated with the target candidate cell in the request confirmation message. For example, the TA value can be 0 or a configured value. In another implementation, an effective timer T2 can exist associated with the TA value. When the effective timer T2 expires, the TA value can be considered invalid, preventing the UE from using the TA value to perform RACH-less conditional LTM cell handover. It should be noted that the value of the effective timer T2 can be configured by the target gNB providing the CFRA resource or CFRA configuration.

[0063] It should be noted that in this disclosure, "candidate target cell configuration for conditional LTM", "candidate target cell configuration" and "LTM candidate configuration" are interchangeable.

[0064] In step 303, the serving gNB may send an RRC Reconfiguration message to the UE, which includes at least an LTM candidate configuration and a conditional LTM execution condition. It should be noted that the conditional LTM candidate configuration includes at least one LTM candidate configuration (of the target candidate cell) and at least one associated conditional LTM execution condition. The conditional LTM candidate configuration may also be identified by a (conditional) LTM ID. The (conditional) LTM ID may be assigned by the (source) serving gNB. The serving gNB can release the conditional LTM candidate configuration by indicating its associated (conditional) LTM ID in NW signaling. Furthermore, in this disclosure, "conditional LTM execution condition" and "execution condition" are interchangeable. In the case of Intra-CU conditional LTM, the execution condition may be generated by the original serving CU (or serving gNB). In the case of Inter-CU conditional LTM, the execution condition of the candidate target cell may be generated by the candidate gNB of the candidate target cell. Execution conditions can be associated with a measurement ID (e.g., measID) or an associated measurement report configuration. Associated measurement report configurations can be provided for SSB-based L1 measurements, CRI-RS-based L1 measurements, SSB-based L3 measurements, or CRI-RS-based L3 measurements. The associated measurement report configuration can be indicated for conditional LTM. When the associated measurement report configuration is indicated for conditional LTM (e.g., a specific information element exists in the measurement report configuration), the UE can evaluate the configured measurement event without reporting any measurement results to the gNB. In one implementation, whether to send measurement results associated with satisfied execution conditions to the gNB can be configured by the gNB.

[0065] In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include CFRA resources / configuration and / or contention-based random access (CBRA) resources / configuration for the UE to perform the RA procedure to synchronize with the corresponding candidate target cell. To avoid wasting RA resources, the RRC reconfiguration message or conditional LTM candidate configuration may include CFRA resources / configuration and an associated lifetime timer T1. The value of lifetime timer T1 may be provided by the gNB associated with the target candidate cell (e.g., in a request confirmation message). If lifetime timer T1 times out, the UE may release / suspend the CFRA resources / configuration. The lifetime timer T1 may be started when the UE receives the RRC reconfiguration message or conditional LTM candidate configuration.

[0066] In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include a TA value associated with a candidate target cell. The UE may apply this TA value to synchronize with the candidate target cell (in the uplink direction). For TA management, the RRC reconfiguration message or conditional LTM candidate configuration may include the TA value associated with the candidate target cell and an associated valid timer T2. The value of the valid timer T2 may be provided by the gNB associated with the target candidate cell (e.g., in a request confirmation message). If the valid timer T2 times out, the UE may consider the TA value associated with the candidate target cell invalid. That is, when the corresponding execution conditions of the conditional LTM candidate configuration are met, the UE may need to perform a RACH-based conditional LTM cell handover. When the valid timer T2 is running, the UE may consider the TA value associated with the candidate target cell valid, and when the corresponding execution conditions of the conditional LTM candidate configuration are met, the UE may perform a RACH-less conditional LTM cell handover. The valid timer T2 is started when the UE receives the RRC reconfiguration message or conditional LTM candidate configuration.

[0067] In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include an (explicit) indication (or related information) indicating whether a RA procedure is required for UL synchronization. For example, when the indication (or related information) is present or set to a specific value, the UE may perform an RA procedure to synchronize with the target candidate cell when applying the LTM candidate configuration. Conversely, when the indication (or related information) is absent or set to a specific value, the UE may not perform an RA procedure for synchronization with the target candidate cell when applying the LTM candidate configuration. Instead, the UE may utilize CFRA resources / configurations and / or Contention-based Random Access (CBRA) resources / configurations in the RRC reconfiguration message or conditional LTM candidate configuration to perform an RA procedure to synchronize with the target cell.

[0068] In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include an (explicit) indication (or related information) indicating whether an RA procedure is required for early UL synchronization. That is, the gNB can request the UE to perform early TA acquisition for the candidate cell before cell handover. For example, when the indication (or related information) is present or set to a specific value, the UE can perform an early UL synchronization procedure for the target candidate cell based on the RRC reconfiguration message, conditional LTM candidate configuration, CFRA resources / configuration provided in Downlink control information (DCI) or MAC CE, Contention-based random access (CBRA) resources / configuration, and / or PDCCH order.

[0069] In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include an (explicit) indication (or related information) indicating whether early DL synchronization is required. In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include Transmission Configuration Indication (TCI) status information of the target candidate cell in the conditional LTM candidate configuration. In one implementation, the network (or gNB) may activate the TCI status of the target candidate cell before the target candidate cell becomes the new serving cell. In one implementation, the RRC reconfiguration message, conditional LTM candidate configuration, DCI, or MAC CE may include TCI status information of the target candidate cell in the conditional LTM candidate configuration, and all TCI states are initially inactive. In one implementation, the RRC reconfiguration message, conditional LTM candidate configuration, DCI, or MAC CE may include TCI status information of the target candidate cell in the conditional LTM candidate configuration, and all TCI states are initially active. In one implementation, the RRC reconfiguration message, conditional LTM candidate configuration, DCI, or MAC CE may include TCI status information related to the target candidate cell of the conditional LTM candidate configuration, and the TCI status information indicates whether a TCI status is active or deactivated. For example, the network (or gNB) may configure TCI status #1 and TCI status #2 for the target candidate cell, with TCI status #1 configured as "active" and TCI status #2 configured as "deactivated".

[0070] In step 304a, the UE may perform an (early) DL synchronization procedure with the target candidate cell before applying the LTM candidate configuration of the target candidate cell. It should be noted that the LTM candidate configuration can be applied because the conditional LTM execution conditions associated with it are met. Whether the UE can perform an (early) DL synchronization procedure with the target candidate cell before applying the LTM candidate configuration may depend on network configuration or control signaling. In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include an indication (or related information) indicating whether an (early) DL synchronization procedure is required. If an (early) DL synchronization procedure is required / configured for the target candidate cell, the UE may perform an (early) DL synchronization procedure for the target candidate cell before applying the conditional LTM configuration associated with it. To perform the (early) DL synchronization procedure, the serving gNB may pre-activate the TCI state of the target candidate cell (e.g., via DCI or MAC CE) before applying the conditional LTM configuration associated with it.

[0071] In step 304b, the UE may perform an (early) UL synchronization procedure with the target candidate cell before applying the LTM candidate configuration of the target candidate cell. It should be noted that the LTM candidate configuration can be applied because the conditional LTM execution conditions associated with it are met. Whether the UE can perform an (early) UL synchronization procedure with the target candidate cell before applying the LTM candidate configuration may depend on network configuration or NW control signaling. In one implementation, the RRC reconfiguration message or conditional LTM candidate configuration may include an indication (or related information) indicating whether an (early) UL synchronization procedure is required. If an (early) UL synchronization procedure is required / configured for the target candidate cell, the UE may perform an (early) UL synchronization procedure for the target candidate cell before applying the conditional LTM configuration associated with it. To perform the (early) UL synchronization procedure, the serving gNB may pre-provide uplink resources (e.g., RA resources or PDCCH orders) before applying the conditional LTM configuration associated with the target candidate cell, allowing the UE to at least send a preamble. In another implementation, whether or how an (early) UL synchronization procedure is performed (e.g., an NW-triggered procedure or a UE-calculated procedure) can depend on the NW configuration or NW signaling. It should be noted that an NW-triggered procedure can be an (early) UL synchronization procedure, where the NW can provide the TA value of the target candidate cell to the UE (e.g., via RRC signaling or MAC CE). Furthermore, it should be noted that a UE-calculated procedure can be an (early) UL synchronization procedure, where the UE measures / calculates the TA value of the target candidate cell itself. For example, the UE can measure / calculate the TA value of the target candidate cell by deriving the TA based on the Rx timing difference between the current serving cell and the candidate cell, and the TA value of the current serving cell. In one implementation, timer T3 is started when the (early) UL synchronization procedure for the target candidate cell is successfully completed (e.g., a valid TA value is obtained from RRC signaling or MAC CE). For example, timer T3 is started when the UE receives a MAC CE that includes the TA value associated with the target candidate cell. While timer T3 is running, the TA value is considered valid and can be used to hand over to the target candidate cell. When timer T3 times out, the TA value is considered invalid and cannot be used for handover to the target candidate cell. For example, when timer T3 times out, the UE may consider the TA value associated with the target candidate cell invalid. In this case, another (early) UL synchronization procedure may be performed or triggered. In one implementation, when the UE is configured to measure / calculate the TA value of the target candidate cell itself, the UE may need to ensure that the measured / calculated TA value is valid. The value of timer T3 can be configurable (via RRC signaling, MAC CE, or DCI) or predefined.

[0072] In one implementation, if an (early) UL synchronization process (i.e., acquiring / storing a valid TA value for the target candidate cell) is completed before handover to the target candidate cell, and the execution conditions for the conditional LTM configuration of the target candidate cell are met, the UE can apply the TA and the LTM configuration of the target candidate cell without performing the RA process. If an (early) UL synchronization process is not completed before handover to the target candidate cell (or the acquired / stored TA value becomes invalid), and the execution conditions for the conditional LTM configuration of the target candidate cell are met, the UE can apply the LTM candidate configuration of the target candidate cell and perform the RA process for TA acquisition.

[0073] In step 305, the UE may begin evaluating the conditional LTM execution conditions upon receiving a conditional LTM candidate configuration. Once a handover is performed (e.g., performing traditional LTM, performing conditional LTM, performing traditional HO, or performing CHO), the UE may stop evaluating the conditional LTM execution conditions.

[0074] In step 306, the UE can maintain its connection with the current serving gNB after receiving the conditional LTM candidate configuration and can begin evaluating the conditional LTM execution conditions for the target candidate cell associated with the received conditional LTM candidate configuration. When at least one target candidate cell meets the corresponding conditional LTM execution conditions, the UE can detach from the current serving gNB, trigger an LTM cell handover process, and / or apply the stored LTM candidate configuration for the selected target candidate cell. In one implementation, when more than one target candidate cell meets the corresponding conditional LTM execution conditions (or triggers an LTM cell handover process), the UE can randomly select a target candidate cell to trigger the LTM cell handover process by applying the stored LTM candidate configuration for the selected target candidate cell. In another implementation, a priority value can be configured for each target candidate cell. When more than one target candidate cell meets the corresponding conditional LTM execution conditions, the UE can select the target candidate cell with the highest priority value to trigger the LTM cell handover process by applying the stored LTM candidate configuration for the selected target candidate cell. When there are more than one target candidate cell with the same highest priority value, the UE can randomly select one of these target candidate cells.

[0075] In step 307, when the UE does not have a valid TA for the target candidate cell or the early UL synchronization process has not been successfully completed, the UE may perform the RA process for the target cell.

[0076] In step 308, the UE can complete the conditional LTM procedure by sending an RRC reconfiguration complete message to the selected target candidate cell (or its associated gNB). After the UE has performed the RA procedure in step 307, the UE can consider the conditional LTM procedure to be successfully completed when the random access procedure is successfully completed. The RRC reconfiguration complete message may include an information element field indicating the LTM ID of the selected conditional LTM candidate configuration applied by the UE when performing conditional LTM. When the UE has a valid TA for the selected target candidate cell and does not need to perform the RA procedure, the UE can consider the conditional LTM procedure to be successfully completed when the UE determines that the network (or the new serving gNB) has successfully received the UE's first UL data.

[0077] In one implementation, when a subsequent conditional LTM is configured, (if there are conditional LTM candidate configurations associated with the new serving cell) the UE begins to evaluate the execution conditions of the conditional LTM candidate configurations associated with the new serving cell.

[0078] Signaling procedures for conditional LTM with UE notification and NW response

[0079] Figure 4 A conditional LTM procedure according to an embodiment of this disclosure is illustrated, wherein the UE sends a conditional LTM execution notification, and the NW responds to the conditional LTM execution notification by replying with a cell handover command. It should be noted that... Figure 4 One or more steps in the process may or may not be performed. Furthermore, the order of the steps is not mandatory.

[0080] like Figure 4 As shown, steps 401, 402, 403, 404, 404a, 404b, 405, 407, and 408 can respectively correspond to... Figure 3 Steps 301, 302, 303, 304, 304a, 304b, 305, 307, and 308 in the text will be omitted, and therefore details related to these steps will be omitted.

[0081] In step 405, the UE may maintain its connection with the current serving gNB after receiving the conditional LTM candidate configuration, and may begin evaluating the conditional LTM execution conditions for the target candidate cell associated with the received conditional LTM candidate configuration.

[0082] In step 405a, when at least one target candidate cell meets the corresponding conditional LTM execution conditions, the UE may send a conditional LTM execution notification message to the gNB. The conditional LTM execution notification message may include information related to the conditional LTM candidate configuration to be executed (e.g., its LTM ID), the latest L1 or L3 measurement results, beam information (e.g., the selected UL beam or the selected DL beam), and / or the applied TA value (e.g., a TA value calculated / measured by the UE itself), but is not limited thereto in this disclosure. It should be noted that the UE can maintain its connection with the current serving gNB after sending the conditional LTM execution notification message. Furthermore, even if the corresponding execution conditions are met, the UE may not detach from the current serving gNB and may not apply the stored LTM candidate configuration for the selected target candidate cell. In one implementation, when more than one target candidate cell meets the corresponding conditional LTM execution conditions, the conditional LTM execution notification message may include information (e.g., its LTM ID) related to the more than one conditional LTM candidate configuration to be executed, for NW reference.

[0083] In step 405b, in response to receiving a conditional LTM execution notification message from the UE, the gNB may reply with a cell handover command, which may be RRC signaling, MAC CE, or DCI. The cell handover command may include the conditional LTM candidate configuration to be executed (e.g., its LTM ID), response information (e.g., accept or reject), beam information (e.g., selected UL beam or selected DL beam), RA-related information (e.g., dedicated RA resource / preamble index), TCI status-related information (e.g., active TCI status for the target candidate cell), and / or the configuration TA value to be applied, but should not be limited thereto in this disclosure.

[0084] In step 406, upon receiving a cell handover command, the UE can execute relevant procedures accordingly. In one embodiment, when the cell handover command indicates a conditional LTM candidate configuration to be executed (e.g., by indicating an LTM ID), the UE can detach from the current serving gNB and apply the LTM candidate configuration indicated in the cell handover command. Furthermore, the UE can stop evaluating conditional LTM execution conditions. In one embodiment, when the cell handover command includes an acceptance response message, the UE can detach from the current serving gNB and apply the LTM candidate configuration indicated in the conditional LTM execution notification message. Furthermore, the UE can stop evaluating conditional LTM execution conditions. In one embodiment, when the cell handover command includes a rejection response message, the UE can choose not to detach from the current serving gNB and can choose not to apply the LTM candidate configuration indicated in the conditional LTM execution notification message. In one embodiment, when the cell handover command includes a rejection response message, the UE can stop evaluating conditional LTM execution conditions. In one embodiment, when the cell handover command includes a rejection response message, the UE can continue evaluating conditional LTM execution conditions. Based on the evaluation results, the UE can send another conditional LTM execution notification message to the gNB. The content of this conditional LTM execution notification message can be the same as or different from the content of the previously rejected conditional LTM execution notification message. In another implementation, when the cell handover command includes a rejection response, a prohibit timer T4 can be started, and while the prohibit timer T4 is running, the UE can be prevented from sending another conditional LTM execution notification message. The value of the prohibit timer T4 can be configurable (via RRC signaling, MAC CE, or DCI) or predefined.

[0085] In some implementations, a UE configured with a conditional LTM candidate configuration performs, for example... Figure 3 The conditional LTM procedure described in the document (i.e., without UE notification and NW response) is still executed. Figure 4 The conditional LTM procedure (i.e., with UE notification and NW response) can depend on the NW configuration and / or UE capabilities. For example, the NW can be configured for the UE to perform... Figure 4 The conditional LTM procedure (i.e., with UE notification and NW response) is because the UE reported the ability to send a conditional LTM execution notification message.

[0086] Signaling procedures for conditional LTM with UE notification and NW response

[0087] Figure 5A conditional LTM procedure according to an embodiment of this disclosure is illustrated, wherein the UE sends a conditional LTM execution notification but does not receive a cell handover command in response to the notification within the response time period. It should be noted that... Figure 5 One or more steps in the process may or may not be performed. Furthermore, the order of the steps is not mandatory.

[0088] and Figure 4 Compared to the conditional LTM process introduced in the article, Figure 5 The difference lies in the fact that the UE may not receive a cell handover command in response to a conditional LTM execution notification message within the response time period. In one implementation, the response timer T5 can be started when the conditional LTM execution notification message is sent. When the UE receives a cell handover command while the response timer T5 is running, the UE can perform the relevant procedures accordingly (e.g., such as...). Figure 4 (The actions and implementation methods described in step 406). When the response timer T5 times out and the UE does not receive a cell handover command, the UE can autonomously detach from the current serving gNB and apply the stored LTM candidate configuration for the selected target candidate cell. In one implementation, the value of the response timer T5 can be configurable (via RRC signaling, MAC CE, or DCI) or predefined.

[0089] Figure 6 A conditional LTM procedure according to an embodiment of this disclosure is illustrated, wherein the UE sends a conditional LTM execution notification, but applies the target cell configuration without any NW response. It should be noted that... Figure 6 One or more steps in the process may or may not be performed. Furthermore, the order of the steps is not mandatory.

[0090] and Figure 5 Compared to the conditional LTM process introduced in the article, Figure 6 The difference lies in that after sending the Conditional LTM Execution Notification Message, the UE can autonomously detach from the current serving gNB and apply the stored LTM candidate configuration for the selected target candidate cell. It should be noted that the order of steps 605a and 606 can be changed. When the serving gNB receives the Conditional LTM Execution Notification Message, the serving gNB can know that the Conditional LTM candidate configuration has been applied and can begin forwarding data to the DU or gNB of the target candidate cell to at least reduce data transmission latency.

[0091] UL Synchronization for Conditional LTM

[0092] For traditional LTM or conditional LTM processes, an early synchronization phase can be performed (e.g. Figure 3 Steps 304a and 304b in the process Figure 4 Steps 404a and 404b in Figure 5 Steps 504a and 504b in the process and Figure 6 Steps 604a and 604b in the process are used to shorten the delay and interruption time caused by HO (or LTM cell handover process).

[0093] In one implementation, the NW (or serving gNB, or serving DU) can be configured to allow the UE to initiate an (early) UL TA acquisition procedure for one or more target candidate cells. When a target candidate cell has the same TA value as the current serving cell, (early) UL TA acquisition may not be necessary. Whether a target candidate cell has the same TA value as the current serving cell can be notified by the NW (or serving gNB, or serving DU) via RRC signaling, MAC CE, or DCI. The NW (or serving gNB, or serving DU) can request the UE to perform early UL TA acquisition for the target candidate cell before cell handover to the target candidate cell.

[0094] In one implementation, the NW (or serving gNB, or serving DU) can send a DCI (or PDCCH order) to trigger the UE to perform an early ULTA acquisition by sending a preamble without receiving any RA response (RAR). Figure 7 An early ULTA acquisition process triggered by a PDCCH instruction according to an embodiment of this disclosure is illustrated. To provide appropriate PDCCH instruction information for the UE to transmit the preamble, the target gNB / DU can provide the source gNB / DU with the early RACH configuration of the target candidate cell, such as... Figure 7 As shown in step 701. Early RACH configuration may include a random access preamble index, an SS / PBCH index, and / or a PRACH mask index, but should not be limited to this in this disclosure. Upon receiving such... Figure 7Following the PDCCH instruction shown in step 702, the UE can transmit a preamble in step 703 based on the received PDCCH instruction. The received PDCCH instruction can indicate whether the UE transmits the preamble on a normal UL (NUL) carrier or a supplementary UL (SUL) carrier. In another implementation, the UE can use CBRA or CFRA resources provided by the NW (e.g., in RRC signaling or MAC CE) to transmit the preamble to the target candidate cell. Whether the UE uses CBRA or CFRA resources on an NUL carrier or an SUL carrier can depend on a configured threshold. For example, when the signal strength (e.g., the currently determined RSRP) is below or equal to the threshold, the UE can use RA resources on an SUL carrier. For another example, when the signal strength (e.g., the currently determined RSRP) is above or equal to the threshold, the UE can use RA resources on an NUL carrier. Upon successfully receiving the preamble from the UE, the target gNB / DU can send the TA value and / or associated information (e.g., preamble index, RA occasion information (RA-RNTI), or candidate cell identifier) ​​for the source gNB / DU to identify the UE, such as... Figure 7 As shown in step 704. When this information is received from the target gNB / DU, the source gNB / DU can send an LTM TA command MAC CE to the UE, as shown in step 704. Figure 7 As shown in step 705. In one embodiment, after sending a preamble to the target gNB / DU, the UE can receive an LTM TA command MAC CE from the source gNB / DU to complete early UL TA acquisition. In one embodiment, the LTM TA command MAC CE is identified by a MAC subheader with a specific extended Logical Channel ID (eLCID). The LTM TA command MAC CE may include fields indicating the target configuration ID (e.g., LTM ID), fields indicating the target candidate cell (e.g., cell ID), TA command fields indicating TA-related information (e.g., TA index value) to control timing adjustment amounts, fields indicating the Timing Advance Group (TAG), fields indicating and activating the TCI state of the target candidate cell, fields indicating and activating the uplink TCI state of the target candidate cell, and / or a validity timer field for the TA command, but should not be limited thereto in this disclosure.

[0095] Figure 8 An LTM TA command MAC according to an embodiment of this disclosure is shown. For example... Figure 8As shown, the LTM TA command MAC CE has a fixed size and contains the following fields:

[0096] R: Reserved bit, set to 0.

[0097] Target Configuration ID: This field indicates the index of the candidate target configuration to be applied to the conditional LTM. This field is 3 bits long. In another implementation, this field is N bits long, where N is predefined or configurable.

[0098] Timing Advance Command: This field indicates the TA value (or associated TA index) for the target candidate cell (i.e., the special primary cell (SpCell) corresponding to the target configuration indicated by the Target Configuration ID field). In one implementation, when the TA command is set to a specific value, it means that for the UE, there is no valid TA value available for the target candidate cell associated with the target configuration (identified by the Target Configuration ID).

[0099] Figure 9 A TA management flowchart 900 for a conditional LTM procedure according to an embodiment of this disclosure is shown. When the early UL TA acquisition procedure is applied, the UE can receive the TA value of the target candidate cell from the gNB (e.g., via LTM TA command MAC CE). Furthermore, the UE can receive the (valid) TA value of the target candidate cell in RRC signaling or in the associated conditional LTM candidate configuration. Figure 9 As shown, the UE can determine whether it has received a (valid) TA value for the target candidate cell from the gNB before applying the conditional LTM candidate configuration. For example, when the execution conditions of the conditional LTM candidate configuration are met, the UE can determine whether to perform a RACH-less LTM cell handover or a RACH-based LTM cell handover based on the condition that it has received a (valid) TA value for the target candidate cell from the gNB. It should be noted that a RACH-less LTM cell handover (or a RACH-less LTM cell handover procedure) means that the UE can directly apply the received TA value without performing an RA procedure and can apply the target candidate cell configuration (in the associated conditional LTM candidate configuration). Conversely, a RACH-based LTM cell handover (or a RACH-based LTM cell handover procedure) means that the UE can initiate an RA procedure to the target candidate cell and can apply the target candidate cell configuration (in the associated conditional LTM candidate configuration). When initiating an RA procedure, the UE can receive a TA command in the RAR of the RA procedure.

[0100] In one implementation, when the execution conditions of the conditional LTM candidate configuration are met in step S905, and the UE determines that the TA value of the target candidate cell is provided by the gNB (e.g., the UE determines that the TA value of the target candidate cell is stored and valid) ("Yes" in step S910), the UE can perform a RACH-free LTM cell handover in step S915 based on the provided TA value and the target candidate cell configuration (in the associated conditional LTM candidate configuration). In one implementation, when the received LTMTA command MAC CE includes a TA command field, the UE can apply the TA command (or TA-related information) to the primary timing advance group (pTAG) (or the associated cell group of the target candidate cell), and / or start (or restart) the time alignment timer (e.g., timer T3) associated with the pTAG (or the associated cell group of the target candidate cell). When the time alignment timer (e.g., timer T3) times out, the UE can consider the TA command (or TA-related information) invalid. It should be noted that the target candidate cell of the target configuration indicated in the received LTM TA command MAC CE, or the target candidate cell with the cell ID indicated in the received LTM TA command MAC CE, can belong to a pTAG (or an associated cell group of the target candidate cell). In one implementation, when a TA value is provided in RRC signaling or a conditional LTM candidate configuration, the UE can apply the TA value (or TA-related information) to the primary timing advance group (pTAG) (or an associated cell group of the target candidate cell), and / or start (or restart) the time alignment timer associated with the pTAG (or the associated cell group of the target candidate cell). When the time alignment timer (e.g., timer T3) times out, the UE can consider the TA command (or TA-related information) invalid. When the time alignment timer (e.g., timer T3) is running, the UE can consider the TA command (or TA-related information) still valid.

[0101] In another implementation, when the execution conditions of the conditional LTM candidate configuration are met in step S905, and the UE determines that the TA value of the target candidate cell is not provided by the gNB (e.g., the UE determines that the TA value of the target candidate cell is not stored or is invalid) ("No" in step S910), the UE can further determine in step S920 whether UE-based TA measurement is configured and the measured TA is available (e.g., the UE calculation process is successfully completed or a valid measured TA has been stored). In one implementation, when the execution conditions of the conditional LTM candidate configuration are met in step S905, and the UE determines that UE-based TA measurement is configured and the measured TA is available (e.g., the UE calculation process is successfully completed or a valid measured TA has been stored) ("Yes" in step S920), the UE can perform a RACH-free LTM cell handover in step S925 based on the measured TA value and the target candidate cell configuration (in the associated conditional LTM candidate configuration). In one implementation, when no LTM TA command MAC CE is received before applying the conditional LTM candidate configuration and the UE has successfully measured the TA, the UE can apply the measured timing advance to the pTAG (or the associated cell group of the target candidate cell) and / or start (or restart) the time alignment timer (e.g., timer T3) associated with the pTAG (or the associated cell group of the target candidate cell). When the time alignment timer (e.g., timer T3) times out, the UE can consider the TA command (or TA-related information) invalid. In one implementation, the gNB can configure / indicate whether the UE is allowed to apply its calculated / measured TA to synchronize with the target candidate cell. If the UE is not allowed to apply its calculated / measured TA to synchronize with the target candidate cell, the UE can skip steps such as... Figure 9 The flowchart shown includes the step of determining whether "UE-based TA measurement is configured and the measured TA is available".

[0102] In another implementation, when the execution conditions of the conditional LTM candidate configuration are met in step S905, but the UE determines that there is neither an available / valid TA value provided by the gNB nor a TA measurement based on the UE is configured (or the measured TA is unavailable) (e.g., the UE calculation process is not successfully completed or a valid measured TA is not stored), the UE may perform RACH-based LTM cell handover in step S930 based on the target candidate cell configuration (in the associated conditional LTM candidate configuration).

[0103] In some implementations, conditional LTM configuration can only be applied when the associated execution conditions are met and the TA (to the target cell) is available.

[0104] When the associated execution conditions of a conditional LTM configuration are met but the TA (to the target cell) is unavailable, the UE may not apply the conditional LTM candidate configuration, but instead report the L1 / L3 measurement results to the gNB.

[0105] In some implementations, whether a TA value (to the target cell) is required for applying conditional LTM configuration is based on NW configuration. For example, a TA required indication is included in the conditional LTM configuration to indicate whether a TA (to the target cell) is required for applying the conditional LTM configuration. For instance, when the TA required indication is absent (or set to a specific value, such as 0), the UE is allowed to apply conditional LTM configuration even if no available TA value (to the target cell) is currently available. In this case, the UE can apply the RA procedure to receive the TA value and complete UL synchronization to the target cell.

[0106] Cross-layer interaction

[0107] In one implementation, when the execution conditions of a conditional LTM candidate configuration are met (e.g., based on L1 measurements), a lower layer (e.g., the UE's PHY layer) can notify / inform a higher layer (e.g., the UE's MAC layer) that the execution conditions of the conditional LTM candidate configuration have been met (e.g., by providing the associated target configuration ID or other relevant information). Upon receiving the notification / information from the lower layer, the higher layer can execute an LTM cell handover procedure. The higher layer (e.g., the UE's MAC layer) can determine whether to execute a RACH-less LTM cell handover procedure or a RACH-based LTM cell handover procedure based on the availability of the TA value to the target candidate cell. For example, the higher layer (e.g., the MAC layer) can follow the following... Figure 9The flowchart 900 described herein illustrates this. For example, when the UE has a valid TA value received from the gNB, the UE can apply that TA value and perform a RACH-free LTM cell handover procedure (and no RA procedure is required). In this case, the RRC layer can be notified (e.g., by the MAC layer) that no RA procedure is required. For example, when the UE does not have a valid TA value received from the gNB, but the UE has a valid TA value that it has measured itself (when the UE is configured to measure TA values ​​itself), the UE can apply the measured TA value and perform a RACH-free LTM cell handover procedure. In this case, the RRC layer can be notified (e.g., by the MAC layer) that no RA procedure is required. In another example, when the UE does not have any valid TA value, the UE can accordingly perform a RACH-based LTM cell handover procedure. In this case, the RRC layer can be notified (e.g., by the MAC layer) that an RA procedure is required. In one implementation, a higher layer (e.g., the RRC layer) can notify / inform a lower layer (e.g., the MAC layer) whether the UE has configured UE-based TA measurements, enabling a RACH-free LTM cell handover process to be performed by synchronizing with the target candidate cell using its calculated / measured TA. It should be noted that the UE can evaluate whether the execution conditions of the LTM candidate configuration are met when the LTM candidate configuration's execution conditions are valid, active, enabled, or configured.

[0108] In one implementation, a lower layer (e.g., the MAC layer) may inform or notify a higher layer (e.g., the RRC layer) that an LTM cell handover procedure has been triggered (or successfully completed) and / or information related to the triggered conditional LTM candidate configuration (e.g., the associated target configuration ID). In one implementation, a lower layer (e.g., the MAC layer) may inform / notify a higher layer (e.g., the RRC layer) that an LTM cell handover procedure has been triggered (or successfully completed) due to conditional LTM and / or information related to the triggered conditional LTM candidate configuration (e.g., the associated target configuration ID). In one implementation, a lower layer (e.g., the MAC layer) may inform or notify a higher layer (e.g., the RRC layer) that an LTM cell handover procedure has been triggered due to conditional LTM and that an RA procedure is required. In one implementation, a lower layer (e.g., the MAC layer) may inform or notify a higher layer (e.g., the RRC layer) that an LTM cell handover procedure has been triggered and whether an RA procedure is not required. In one implementation, upon receiving notification / information from a lower layer (e.g., the MAC layer), a higher layer (e.g., the RRC layer) may apply a target candidate cell configuration (in the conditional LTM candidate configuration). In one implementation, upon receiving a notification from a lower layer, the higher layer can generate a conditional LTM execution notification message based on the information received from the lower layer, and instruct the lower layer to send the message and / or wait for a cell handover command from the gNB. When the conditional LTM execution notification message is sent, a response timer T5 is started. When the response timer T5 times out and no cell handover command is received, the UE (or its RRC layer) can directly apply the target candidate cell configuration (in the conditional LTM candidate configuration).

[0109] In one implementation, when the execution conditions of more than one conditional LTM candidate configuration are met (e.g., based on L1 measurement), the lower layer (e.g., the PHY layer) can inform / notify the higher layer (e.g., the MAC layer) of information about each met conditional LTM candidate configuration (e.g., by providing the associated target configuration ID). In another implementation, when the execution conditions of more than one conditional LTM candidate configuration are met (e.g., based on L1 measurement), the lower layer (e.g., the PHY layer) can inform / notify the higher layer (e.g., the MAC layer) of information about the selected conditional LTM candidate configuration (e.g., by providing the associated target configuration ID).

[0110] In one implementation, when a lower layer (e.g., the PHY layer or MAC layer) informs / notifies a higher layer (e.g., the MAC layer or RRC layer) of more than one satisfied conditional LTM candidate configuration, the higher layer may (randomly) select a satisfied conditional LTM to perform the LTM cell handover procedure (e.g., a RACH-free LTM cell handover procedure or a RACH-based LTM cell handover procedure). In another implementation, when a lower layer (e.g., the PHY layer) informs / notifies a higher layer (e.g., the MAC layer or RRC layer) of more than one satisfied conditional LTM candidate configuration, the higher layer may select the satisfied conditional LTM with the highest priority to perform the LTM cell handover procedure. When there are more than one satisfied conditional LTM candidate configuration with the same highest priority value, the UE may randomly select one satisfied conditional LTM candidate configuration.

[0111] Figure 10 An example communication system 1000 having an example communication device 1010 and an example network device 1020 according to an embodiment of the present disclosure is shown. Each of the communication device 1010 and the network device 1020 can perform various functions to implement the schemes, techniques, processes and methods related to conditional LTM process configuration described herein, including the scenarios / schemes described above and the process 1100 described below.

[0112] The communication device 1010 may be part of an electronic device, which may be a UE (User Equipment), such as a portable or mobile device, a wearable device, a wireless communication device, or a computing device. For example, the communication device 1010 may be implemented in a smartphone, smartwatch, personal digital assistant, digital camera, or computing device such as a tablet computer, laptop computer, or notebook computer. The communication device 1010 may also be part of a machine-type device, which may be an IoT, NB-IoT, or IIoT device, such as a fixed or stationary device, a home appliance, a wired communication device, or a computing device. For example, the communication device 1010 may be implemented in a smart thermostat, smart refrigerator, smart door lock, wireless speaker, or home control center. Alternatively, the communication device 1010 may be implemented as one or more integrated circuit (IC) chips, such as, but not limited to, one or more single-core processors, one or more multi-core processors, one or more reduced-instruction-set computing (RISC) processors, or one or more complex-instruction-set computing (CISC) processors. The communication device 1010 may include... Figure 10At least some of the components shown, such as processor 1012. Communication device 1010 may also include one or more other components (e.g., internal power supply, display device, and / or user interface device) unrelated to the scheme presented in this disclosure; therefore, for simplicity, such components of communication device 1010 are not described in... Figure 10 It is shown in the text and is not described in the following text.

[0113] Network device 1020 may be part of an electronic device, which may be a network node such as a BS, small cell, router, or gateway. For example, network device 1020 may be implemented in a gNB in ​​a 5G, B5G, 6G, IoT, NB-IoT, or IIoT network. Alternatively, network device 1020 may be implemented as one or more IC chips, such as, but not limited to, one or more single-core processors, one or more multi-core processors, or one or more RISC or CISC processors. Network device 1020 may include... Figure 10 At least some of the components shown, such as processor 1022. Network device 1020 may also include one or more other components (e.g., internal power supply, display device, and / or user interface device) unrelated to the scheme presented in this disclosure; therefore, for simplicity, such components of network device 1020 are not described in... Figure 10 It is shown in the text and is not described in the following text.

[0114] In one aspect, each of processors 1012 and 1022 may be implemented as one or more single-core processors, one or more multi-core processors, or one or more CISC processors. That is, even though the singular term "processor" is used herein to refer to processors 1012 and 1022, each of processors 1012 and 1022 may include multiple processors in some embodiments and a single processor in other embodiments, according to this disclosure. In another aspect, each of processors 1012 and 1022 may be implemented as hardware (and optionally firmware) having electronic components including, but not limited to, one or more transistors, one or more diodes, one or more capacitors, one or more resistors, one or more inductors, one or more memristors, and / or one or more varactor diodes, configured and arranged to achieve a specific purpose according to this disclosure. In other words, in at least some embodiments, each of processors 1012 and 1022 is a dedicated machine specifically designed, arranged and configured to perform specific tasks, including configuring conditional LTM procedures in a UE (e.g., represented by communication device 1010) and gNB (e.g., represented by network device 1020) according to various embodiments of this disclosure.

[0115] In some embodiments, the communication device 1010 may further include a transceiver 1016 coupled to the processor 1012 and capable of wirelessly transmitting and receiving control and data signals. In some embodiments, the transceiver 1016 is capable of wireless communication with different types of gNBs on different RATs. In some embodiments, the transceiver 1016 may be equipped with multiple antenna ports (not shown), such as four antenna ports. That is, the transceiver 1016 may be equipped with multiple transmit antennas and multiple receive antennas for multiple-input multiple-output (MIMO) wireless communication. In some embodiments, the network device 1020 may further include a transceiver 1026 coupled to the processor 1022 and capable of wirelessly transmitting and receiving control and data signals. In some embodiments, the transceiver 1026 is capable of wireless communication with different types of UEs on different RATs. In some embodiments, the transceiver 1026 may be equipped with multiple antenna ports (not shown), such as four antenna ports. That is, the transceiver 1026 may be equipped with multiple transmit antennas and multiple receive antennas for MIMO wireless communication. Therefore, the communication device 1010 and the network device 1020 can communicate wirelessly with each other via transceiver 1016 and transceiver 1026, respectively.

[0116] In some embodiments, the communication device 1010 may further include a memory 1014 coupled to and accessible by the processor 1012 and capable of storing data therein. In some embodiments, the network device 1020 may further include a memory 1024 coupled to and accessible by the processor 1022 and capable of storing data therein. Each of memories 1014 and 1024 may include some type of random-access memory (RAM), such as dynamic RAM (DRAM), static RAM (SRAM), thyristor RAM (T-RAM), and / or zero-capacitor RAM (Z-RAM). Alternatively, or further, each of memories 1014 and 1024 may include some type of read-only memory (ROM), such as mask ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), and / or electrically erasable programmable ROM (EEPROM). Alternatively, or further, each of memories 1014 and 1024 may include some type of non-volatile random-access memory (Non-volatile RAM). Random-access memory (NVRAM), such as flash memory, solid-state memory, ferroelectric RAM (FeRAM), magnetoresistive RAM (MRAM), and / or phase-change memory.

[0117] Each of the communication device 1010 and the network device 1020 can be a communication entity capable of communicating with each other according to the various schemes proposed in this disclosure. For illustrative purposes and not for limitation, the following provides an example in a UE (e.g., Figures 3-5 The communication device 1010 implemented in or as a UE in a gNB (e.g., Figures 3-5 Description of the operation, functions and capabilities of the network device 1020 implemented in or as a gNB (gNB).

[0118] According to certain embodiments of this disclosure, the processor 1012 of the communication device 1010 can receive a conditional LTM command from the network device 1020 via a transceiver 1016. Specifically, the conditional LTM command includes a first target cell configuration and execution conditions for a first target cell. The processor 1012 can then receive a first Media Access Control (MAC) control element (CE) associated with the first target cell from the network device 1020 via the transceiver 1016, wherein the first MAC CE includes timing advance (TA) related information. When the execution conditions are met, the processor 1012 can switch to the first target cell by applying the first target cell configuration and the received TA related information.

[0119] Figure 11 An example process 1100 according to an embodiment of this disclosure is shown. Process 1100 may be part or all of the above-described scenario / scheme regarding a conditionally triggered Level 1 / Level 2 (L1 / L2) mobility (LTM) process. Process 1100 may represent one aspect of an implementation of a feature of communication device 1010. Process 1100 may include one or more operations, actions, or functions as shown in one or more of blocks S1105, S1110, and S1115. Although shown as discrete blocks, the individual blocks of process 1100 may be divided into additional blocks, merged into fewer blocks, or eliminated, depending on the desired implementation. Furthermore, the blocks of process 1100 may be arranged in... Figure 11 The process 1100 may be executed in the order shown, or in a different order. Process 1100 may be implemented by communication device 1010 or any suitable UE. For illustrative purposes only and not as a limitation, process 1100 is described below in the context of communication device 1010 as a UE and network device 1020 as a gNB or BS. Process 1100 may begin at block 1105.

[0120] In S1105, process 1100 may involve the processor 1012 of communication device 1010 receiving a conditional LTM command from network device 1020 via transceiver 1016, wherein the conditional LTM command includes a first target cell configuration and execution conditions for a first target cell. Process 1100 may proceed from S1105 to S1110. The execution conditions may be configured as L1 execution conditions or L3 execution conditions.

[0121] In S1110, process 1100 may involve processor 1012 receiving a first Media Access Control (MAC) control element (CE) associated with a first target cell from network device 1020 via transceiver 1016, wherein the first MAC CE includes timing advance (TA) related information. Process 900 may proceed from 1110 to 1115. Furthermore, the first MAC CE may include a configuration ID (or configuration associated with the first target cell) associated with the first target cell. When the UE receives the first MAC CE associated with the first target cell (from the current serving cell or source BS), a time alignment timer (e.g., timer T3) starts or restarts. Process 1100 may proceed from S1110 to S1115.

[0122] In S1115, process 1100 may involve the processor 1012 switching to the first target cell by applying the first target cell configuration and the received TA-related information when the execution conditions are met.

[0123] While this disclosure has been described by way of example and in conjunction with preferred embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and similar arrangements (which will be apparent to those skilled in the art). Therefore, the scope of the appended claims should be given the broadest interpretation to cover all such modifications and similar arrangements.

Claims

1. A method for conditionally triggering a Layer 1 / Layer 2 (L1 / L2) mobility (LTM) procedure, wherein the method is implemented by a user equipment (UE), comprising: Receive a conditional LTM command from the source base station (BS), wherein the conditional LTM command includes a first target cell configuration and execution conditions for the first target cell; Receive a first medium access control (MAC) control element (CE) associated with the first target cell from the source BS, wherein the first MAC CE includes timing advance (TA) related information; as well as When the execution conditions are met, the system switches to the first target cell by applying the configuration of the first target cell and the received TA-related information.

2. The method for a conditional LTM process as described in claim 1, further comprising: Send the capability to the source BS to indicate at least one of the following: The UE supports the execution of conditional LTM procedures; The UE supports the execution of subsequent conditional LTM procedures; The UE supports evaluating the execution conditions using L1 measurements to perform an L1-based conditional LTM procedure; as well as The UE supports evaluating the execution conditions using Layer 3 (L3) measurements to perform an L3-based conditional LTM process.

3. The method for a conditional LTM process as described in claim 1, wherein upon receiving the conditional command, the method further comprises: Evaluate the execution conditions; The method further includes: Once the switching process is executed, the evaluation of the execution conditions is stopped.

4. The method for a conditional LTM process as described in claim 1, further comprising, when multiple conditional LTM commands are received from the source BS and the associated execution conditions of the multiple conditional LTM commands are all satisfied: A target conditional LTM command is randomly selected from the plurality of conditional LTM commands, and the user switches to the second target cell according to the second target cell configuration contained in the target conditional LTM command.

5. The method for a conditional LTM procedure as claimed in claim 1, wherein the UE sends a preamble to a first target BS of the first target cell before receiving the first MAC CE.

6. The method for a conditional LTM procedure as claimed in claim 1, wherein a timer associated with the TA-related information is started when the UE receives the first MAC CE.

7. The method for a conditional LTM process as described in claim 6, wherein the TA-related information is invalid when the timer times out.

8. The method for a conditional LTM procedure as claimed in claim 1, wherein when the UE does not have valid TA-related information, the UE performs a random access (RA) procedure for the first target cell.

9. The method for a conditional LTM procedure as claimed in claim 1, wherein the configuration ID associated with the first target cell is included in the first MAC CE.

10. An apparatus for a conditionally layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) process, comprising: A transceiver that communicates wirelessly with at least one network node during operation; as well as A processor, communicatively coupled to the transceiver, such that during operation, the processor performs operations including: Receive a conditional LTM command from the source base station (BS), wherein the conditional LTM command includes a first target cell configuration and execution conditions for the first target cell; Receive a first medium access control (MAC) control element (CE) associated with the first target cell from the source BS, wherein the first MAC CE includes timing advance (TA) related information; as well as When the execution conditions are met, the system switches to the first target cell by applying the configuration of the first target cell and the received TA-related information.

11. The apparatus for a conditional LTM process as claimed in claim 10, further comprising: Send the capability to the source BS to indicate at least one of the following: The UE supports the execution of conditional LTM procedures; The UE supports the execution of subsequent conditional LTM procedures; The UE supports evaluating the execution conditions using L1 measurements to perform an L1-based conditional LTM procedure; as well as The UE supports evaluating the execution conditions using Layer 3 (L3) measurements to perform an L3-based conditional LTM process.

12. The apparatus for a conditional LTM process as claimed in claim 10, wherein upon receiving the conditional LTM command, the method further comprises: Evaluate the execution conditions; The method further includes: Once the switching process is executed, the evaluation of the execution conditions is stopped.

13. The apparatus for a conditional LTM process as claimed in claim 10, wherein when a plurality of conditional LTM commands are received from the source BS and the associated execution conditions of the plurality of conditional LTM commands are all satisfied, the method further comprises: A target conditional LTM command is randomly selected from the plurality of conditional LTM commands, and the user switches to the second target cell according to the second target cell configuration contained in the target conditional LTM command.

14. The apparatus for a conditional LTM procedure as claimed in claim 10, wherein the apparatus sends a preamble to a first target BS of the first target cell before receiving the first MAC CE.

15. The apparatus for a conditional LTM process as claimed in claim 10, wherein a timer associated with the TA-related information is started when the apparatus receives the first MAC CE.

16. The apparatus for a conditional LTM process as claimed in claim 15, wherein the TA-related information is invalid when the timer times out.

17. The apparatus for a conditional LTM procedure as claimed in claim 10, wherein when the apparatus does not have valid TA-related information, the apparatus performs a random access (RA) procedure on the first target cell.

18. The apparatus for a conditional LTM procedure as claimed in claim 10, wherein the configuration ID associated with the first target cell is included in the first MAC CE.

19. A method for a conditionally Layer 1 / Layer 2 (L1 / L2) triggered mobility (LTM) procedure, wherein the method is implemented by a source base station (BS) and includes: Send a conditional LTM command to the user equipment (UE), wherein the conditional LTM command includes a first target cell configuration and execution conditions for the first target cell; as well as Send a first Media Access Control (MAC) control element (CE) associated with the first target cell to the UE, wherein the first MAC CE includes timing advance (TA) related information.

20. The method for a conditional LTM process as described in claim 19, further comprising: The UE receives a capability to indicate at least one of the following: The UE supports the execution of conditional LTM procedures; The UE supports the execution of subsequent conditional LTM procedures; The UE supports evaluating the execution conditions using L1 measurements to perform an L1-based conditional LTM procedure; as well as The UE supports evaluating the execution conditions using Layer 3 (L3) measurements to perform an L3-based conditional LTM process.

21. The method for a conditional LTM procedure as claimed in claim 19, wherein before sending the first MAC CE associated with the first target cell to the UE, the method further comprises: Receive the TA-related information from the target base station of the first target cell.

22. The method for a conditional LTM procedure as described in claim 19, wherein the configuration ID associated with the first target cell is included in the first MAC CE.

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