Conditional layer 1 / layer 2 triggered mobility cell switch procedure

Abstract

Example embodiments of the present disclosure are directed to a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) cell switch procedure. A method comprising: receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and receiving, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

Description

CONDITIONAL LAYER 1 / LAYER 2 TRIGGERED MOBILITY CELL SWITCH PROCEDUREFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for event-triggered cell switch procedure.BACKGROUND

[0002] With the continuous development of mobile networks, managing and optimizing user mobility between different network nodes has become crucial. Modern mobile communication systems require seamless connectivity between various network nodes to ensure efficient and reliable handovers. In order to ensure the communication continuousness in the wireless communication system, multiple technologies are proposed, such as cell switch. During the cell switch, the terminal device may switch among different cells. Further, technology of layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) may be used for enabling the cell switch. LTM is a procedure in which the next generation node B (gNB) receives L1 and / or layer 3 (L3) measurement report(s) from a UE, and thus the gNB changes user equipment (UE) serving cell by a cell switch command signalled via a medium access control (MAC) control element (CE). Further, conditional LTM has be proposed as an enhancement of the network-triggered cell switch, which allows UE initiating the cell switch autonomously.SUMMARY

[0003] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmit, to the second apparatus, TA-related information comprising at least one of the following: a first indication indicating the TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, wherein the TA-related information is comprised in one of the following: a first message transmitted on a first resource indicated by the conditional LTM configuration, a measurement report, or a medium access control (MAC) control element (CE).

[0004] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, whenexecuted by the at least one processor, cause the second apparatus to: determine a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and at least one of the following: a first resource to be used by a first apparatus for transmitting a first message which comprises timing advance (TA)-related information comprising at least one of the following: a first indication indicating a TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, an event of TA invalidation that causes a TA of a candidate cell to become invalid, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid; and transmit the conditional LTM configuration to the first apparatus.

[0005] In a third aspect of the present disclosure, there is provided a first apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus, a conditional layer1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, wherein the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; perform measurements on the at least one candidate cell; and in accordance with a determination that the event of TA invalidation is detected for the TA of a candidate cell of the at least one candidate cell based at least in part on a measurement result of the candidate cell, transmit, to the second apparatus TA-related information indicating the TA of the candidate cell is invalid.

[0006] In a fourth aspect of the present disclosure, there is provided a second apparatus. The fourth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to: determine a conditional layer 1 / layer2 (L1 / L2) triggered mobility (LTM) for a first apparatus, wherein the conditional LTM configuration indicates at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, and the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; and transmit the conditional LTM configuration to the firstapparatus.

[0007] In a fifth aspect of the present disclosure, there is provided a first apparatus. The fifth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmit a random access (RA) preamble to a third apparatus providing the candidate cell; and receive, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

[0008] In a sixth aspect of the present disclosure, there is provided a second apparatus. The sixth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to: determine a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the conditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) preamble; and transmit the conditional LTM configuration to the first apparatus.

[0009] In a seventh aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting to the second apparatus, TA- related information comprising at least one of the following: a first indication indicating the TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, wherein the TA-related information is comprised in one of the following: a first message transmitted on a first resource indicated by the conditional LTM configuration, a measurement report, or a medium access control (MAC) control element (CE).

[0010] In an eighth aspect of the present disclosure, there is provided a method. The method comprises: determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and at least one of the following: a first resource to be used by a first apparatus for transmitting a first message which comprises timing advance (TA)-related information comprising at least one of the following: a first indication indicating a TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, an event of TA invalidation that causes a TA of a candidate cell to become invalid, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid; and transmitting the conditional LTM configuration to the first apparatus.

[0011] In a ninth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, wherein the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; performing measurements on the at least one candidate cell; and in accordance with a determination that the event of TA invalidation is detected for the TA of a candidate cell of the at least one candidate cell based at least in part on a measurement result of the candidate cell, transmitting to the second apparatus TA-related information indicating the TA of the candidate cell is invalid.

[0012] In a tenth aspect of the present disclosure, there is provided a method. The method comprises: determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) for a first apparatus, wherein the conditional LTM configuration indicates at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, and the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; and transmitting the conditional LTM configuration to the first apparatus.

[0013] In an eleventh aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and receiving, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

[0014] In a twelfth aspect of the present disclosure, there is provided a method. The method comprises: determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the conditional LTM configuration indicating at least one candidate cell and a condition for transmittingrandom access (RA) preamble; and transmitting the conditional LTM configuration to the first apparatus.

[0015] In a thirteenth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and means for based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting to the second apparatus, TA-related information comprising at least one of the following: a first indication indicating the TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, wherein the TA-related information is comprised in one of the following: a first message transmitted on a first resource indicated by the conditional LTM configuration, a measurement report, or a medium access control (MAC) control element (CE).

[0016] In a fourteenth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and at least one of the following: a first resource to be used by a first apparatus for transmitting a first message which comprises timing advance (TA)-related information comprising at least one of the following: a first indication indicating a TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, an event of TA invalidation that causes a TA of a candidate cell to become invalid, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid; and means for transmitting the conditional LTM configuration to the first apparatus.

[0017] In a fifteenth aspect of the present disclosure, there is provided a first apparatus. The third apparatus comprises means for receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, wherein the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; means for performing measurements on the at least one candidate cell; and means for in accordance with a determination that the event of TA invalidation is detected for the TA of a candidate cell of the at least one candidate cell based at least in part on a measurement result of the candidate cell, transmitting to the second apparatus TA-related information indicating the TA of the candidate cell is invalid.

[0018] In a sixteenth aspect of the present disclosure, there is provided a second apparatus. The fourth apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) for a first apparatus, wherein the conditional LTM configuration indicates at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, and the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; and means for transmitting the conditional LTM configuration to the first apparatus.

[0019] In a seventeenth aspect of the present disclosure, there is provided a first apparatus. The fifth apparatus comprises means for receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and means for based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and means for receiving, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

[0020] In an eighteenth aspect of the present disclosure, there is provided a second apparatus. The sixth apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the conditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) preamble; and means for transmitting the conditional LTM configuration to the first apparatus.

[0021] In a nineteenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the any of the seventh aspect to the twelfth aspect.

[0022] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Some example embodiments will now be described with reference to the accompanying drawings,where:

[0024] FIG. 1 illustrates a signaling flow for an overall procedure for LTM;

[0025] FIG. 2A and FIG. 2B illustrate example communication environments in which example embodiments of the present disclosure can be implemented, respectively;

[0026] FIG. 3A to FIG. 6C illustrate example signaling flows for communication in accordance with some example embodiments of the present disclosure;

[0027] FIG. 7 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0028] FIG. 8 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0029] FIG. 9 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0030] FIG. 10 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0031] FIG. 11 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0032] FIG. 12 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0033] FIG. 13 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0034] FIG. 14 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0035] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0036] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting anylimitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0037] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same mean as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0038] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0039] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0040] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0041] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0043] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0044] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0045] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-loT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1 G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0046] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer toa base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (I AB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0047] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customerpremises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0048] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some exampleembodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0049] As used herein, “inter-centralized unit (CU)” may refer to the interactions and handovers occurring between different centralized units within a mobile communication network. CUs are network nodes responsible for handling higher-layer functions such as radio resource control and mobility management. The term “inter-CU” specifically pertains to the processes, procedures, and mechanisms involved when a user equipment (UE) transitions from one CU to another, ensuring continuous and seamless connectivity during the handover.

[0050] As used herein, “intra-CU” may refer to the interactions and handovers occurring among different distributed units (DUs) or different gNBs of a same CU within a mobile communication network. The term “intra-CU” specifically pertains to the processes, procedures, and mechanisms involved when a UE transitions from one DU / gNB to another DU / gNB of a same CU, ensuring continuous and seamless connectivity during the handover.

[0051] As mentioned above, technologies such as cell switch are proposed to ensure the communication continuousness in the wireless communication system. For example, LTM may be used for enabling the cell switch to reduce the mobility latency. Reference is now made to FGI. 1, which illustrates a signaling flow for an overall procedure for LTM.

[0052] As illustrated in FIG. 1, at step 1 , the UE sends a MeasurementReport message to the gNB. Based on the measurement report, and / or other conditions, the gNB decides to configure LTM and initiates LTM preparation. At step 2, the gNB transmits an RRCReconfiguration message to the UE, and the RRCReconfiguration message includes the LTM candidate configurations. At step 3, the UE stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB.

[0053] At step 4a, the UE performs DL synchronization with the candidate cell(s) before receiving the cell switch command. At step 4b, when UE-based timing advance (TA) measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. UE performs early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command. This is done via contention free random access (CFRA) triggered by a physical downlink control channel (PDCCH) order from the source cell, following which the UE sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0054] At step 5, the UE performs L1 measurements on the configured candidate cell(s) and transmits L1 measurement reports to the gNB. L1 measurement should be performed as long as radio resource control (RRC) reconfiguration (step 2) is applicable.

[0055] At step 6, the gNB decides to execute cell switch to a target cell and transmits a medium access control (MAC) control element (CE) triggering cell switch by including the candidate configuration index of the target cell. The UE switches to the target cell and applies the configuration indicated by candidate configuration index.

[0056] At step 7, the UE performs the random access procedure towards the target cell, if UE does not have valid TA of the target cell. At step 8, the UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to target cell. If the UE has performed a random access (RA) procedure in step 7 the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RA channel (RACH)-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first uplink (UL) data.

[0057] In some mechanisms, a conditional LTM is supported. As used herein, a conditional LTM may be referred to as a UE triggered LTM or event-triggered LTM. For example, conditions for triggering LTM may be specified or configured. UE may evaluate the conditions for triggering the LTM. Conditional LTM may be supported including a subsequent LTM. In some cases, intra-CU LTM may be prioritized.

[0058] For release-19 (Rel-19) conditional LTM, procedures defined in release-18 (Rel-18) LTM, which was based on network-triggered cell switch, may have to be enhanced to support UE-autonomous cell switch triggering. One of the procedures to be considered for enhancement is early TA acquisition. In Rel-18, since the cell switch is network triggered, the TA is provided to the UE with the cell switch command. For conditional LTM, this would result in the TA never reaching the UE in case of a UE-autonomous conditional LTM cell switch and, as a result, LTM cell switch would always be random access channel (RACH)-based, which lack the benefit of reduced interruption time.

[0059] Therefore, for conditional LTM, a random access response (RAR) may be provided to the UE directly from the (candidate) target cell or TA information may be provided to the UE by the source cell (after being forwarded to it from the target DU via the CU). In both of these cases, the UE may be responsible for maintenance of the TA, i.e., the UE may be responsible to check whether the acquired TA is valid and potentially take action if the TA is invalid so as to obtain a new valid TA estimate.

[0060] That is, different from the TA maintaining mechanism of Rel-18 where the TA is acquired by PDCCHordered RACH and maintained by the network and provided to the UE at the cell switch command, in Rel- 19 conditional LTM, the exact time when the cell switch condition is met at the UE side is unknown to the network, which causes that UE cannot obtain TA via the network-triggered cell switch command.

[0061] In Rel-19 conditional LTM, the TA is expected to be available at the UE side, at the time when the UE autonomously evaluates the conditional cell switch condition, determines that at least one condition is satisfied, and performs cell switch to the cell where the condition was met. Therefore, different from that in Rel-18 LTM, in Rel-19 conditional LTM, it is expected that the TA could be provided to the UE by the network as soon as possible after its computation on the network side.

[0062] In a traditional solution, time alignment timer (TAT) may be used for controlling the validation of the TA, which is referred to as TAT-based validation. In the TAT-based validation, UE is configured with a TAT, an expiry of the TAT indicates that it is no longer in UL synchronization with the (serving) cell. After expiry of the TAT, UE has to perform random access to enable acquisition of a fresh TA. Following this simple approach for cell switch procedure (i.e., when the UE performs cell switch, it just checks if the TAT has expired. In a case that the TAT has expired, UE performs RA which could lead to many RACH-based cell switches and result in longer interruption time. Also, the drawback of validation based only on TAT is that it is a “blind” method, which means that the network can set the time that the TA remains valid based on past experience, but the actual channel conditions between the UE and the cell are not taken into account.

[0063] During the small data transmission (SDT) procedure, the measurement-based validation is used for controlling the validation of the TA. Specifically, for SDT, a UE in RRC inactive state, may use a configured grant (CG) which is provided to UE during transition from RRC connected state to RRC inactive state and a TA value obtained while being in RRC connected mode. More specifically, when the UE intends to perform SDT, UE measures the reference signal receiving power (RSRP) of the cell (such as, synchronization signal block, SSB) and if the difference compared to the RSRP measurement when the TA was obtained is smaller than a configured threshold and the TAT has not expired, the UE transmits on the CG using the obtained TA value. Otherwise, the UE performs random access. This approach too may lead to a large number of RACH-based cell switches, as the UE just checks the validity of the TA and does not take any actions to refresh the TA.

[0064] In summary, in the above solutions, the TA obtained by a UE may become invalid either due to expiry of the TAT or due to significant change of the RSRP of the candidate cell since TA acquisition. If the TAT is maintained on the UE side and / or the UE is not configured to report to the source the measurements used for TA validation, the serving / source cell cannot infer whether the TA is valid and, thus cannot determine there is a need to trigger a new PDCCH order-based TA acquisition process. Another problem isthat autonomous trigger of a new TA acquisition process by the UE (i.e. , RA preamble transmission) may not be desired, especially when CFRA preamble resources are shared among multiple UEs. As autonomous triggering by the UE is by definition uncoordinated, preamble sharing, which is intended to reduce the consumption of the scarce resource of dedicated RA preambles, would lead to collisions.

[0065] In order to solve at least part of the above problems or other potential problems, several solutions on conditional LTM-based cell switch procedure are proposed. Principle and implementations of the present disclosure will be described in detail below with reference to FIGS. 2A-12.Example Environment

[0066] FIG. 2A shows an example communication environment 200A in which example embodiments of the present disclosure may be implemented. The network communication 200A includes a first apparatus 210, a second apparatus 220 and a third apparatuses 230.

[0067] In some example embodiments, the first apparatus 210 may be comprised in a terminal device / apparatus and the second apparatus 220 / third apparatus 230 may be comprised in a network device / apparatus. Additionally, the second apparatuses 220 and the third apparatus 230 may provide one or more coverage areas, also called as cells. As illustrated in FIG. 2A, the communication environment 200A includes a cell 250 provided by the second apparatus 220 and a cell 260 provided by the third apparatus 230.

[0068] Further, in some example embodiments, the radio access network (RAN) architecture may include a centralized part, or central unit (CU), and a distributed part, or distributed unit (DU). The CU and the DU may be connected to one another by a so-called Fl interface. In the example of FIG. 2A, the second apparatus 220 may refer to a base station (such as, the next generation node B, gNB), a gNB-CU and / or a gNB-DU. Similarly, the third apparatus 230 also may refer to a base station (such as, a gNB), a gNB CU and / or a gNB DU.

[0069] In the example of FIG. 2A, the first apparatus 210 may move over time. As illustrated in FIG. 2A, the first apparatus 210 locates at different positions at different time points (T1 and T2). As moving, the first apparatus 210 may switch among different cells, i.e., a cell switch procedure. In the example of FIG. 2A, the first apparatus 210 may switch from cell 250 to cell 260. For a better discussion, the cell 250 may be called as the source cell 250 or the serving cell 250, and the cell 260 may be called as the candidate cell 260. Further, in a case that the cell 260 is selected as a target cell, the cell 260 also may be called as the target cell 260.

[0070] Reference is now made to FIG. 2B, which illustrates other example communication environments200B in which example embodiments of the present disclosure may be implemented. In the example (A) of FIG. 2B, the second apparatus 220 and the third apparatus 230 are gNB DUs, and both the second apparatus 220 and the third apparatus 230 are connected to a same gNB-CU. In the example (B) of FIG. 2B, the second apparatus 220 and the third apparatus 230 are gNB DUs, while the second apparatus 220 the third apparatus 230 are connected to two different gNB-CUs.

[0071] It should be noted examples (A) and (B) of FIG. 2B are two example communication environments of the present discourse which are illustrated only for the purpose of illustration without suggesting any limitations. In fact, the cell switch discussed herein may include at least one of the following: an inter-gNB cell switch, an intra-CU cell switch, or an inter-CU cell switch.

[0072] It is to be understood that the number of devices and their connections shown in FIG. 2A and FIG. 2B are only for the purpose of illustration without suggesting any limitation. The communication environments 200A and 200B may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the cell, and one or more additional cells may be deployed in the communication environments 200A and 200B. It is noted that although illustrated as a network device, the second apparatus 220 / the third apparatus 230 may be another device than a network device. Although illustrated as a terminal device, the first apparatus 210 may be another device than a terminal apparatus.

[0073] Communications in the communication environments 200A and 200B may be implemented according to any proper communication protocol (s), comprising, but not limited to, cellular communication protocols of the first generation (1 G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), 5.5G, the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple- Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future. l / l / br Principle and Example Signalling for Communication

[0074] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It is noted the order acts shown in FIGS. 3A-6C are only an example not limitation. Acts may be performed in any suitable manner. Example embodiments described with referenceto FIGS. 3A-6C may be implemented separately or combined in any manner. For example, one or more example embodiments shown in a single drawing may be combined with one or more example embodiments shown in one or more other drawings.

[0075] In the following discussion, a cell switch may comprise at least one of the following: an inter-gNB cell switch, an intra-CU cell switch, or an inter-CU cell switch.

[0076] Further, in the following discussions, the first apparatus 110 may comprise a terminal apparatus, the second apparatus 120 may comprise one of the following: a next generation node B (gNB) serving the first apparatus 110 (also called as a source gNB), a distributed unit (DU) connecting with the first apparatus 110 (also called as a source DU), or a centralized unit (CU) connecting with the source DU (also called as a source CU), and the third apparatus 130 may comprises one of the following: a target gNB (also called as a target gNB), a target DU, or a target CU.

[0077] According to some example embodiments of the present disclosure, the UE may be configured by the network with a TAT and / or a (newly-introduced) measurement-based event for TA invalidity (also called as event of TA invalidation). If the UE determines that the TA is invalid, UE may send information of TA invalidity (also called as TA-related information or indication of TA invalidation) to the source DU / source gNB to inform the source DU that the TA is invalid, such that the source DU / gNB may issue a new PDCCH order for early TA acquisition procedure.

[0078] In some example embodiments, the information of TA invalidity may be transmitted on a dedicated uplink (UL) resource(s). Alternatively, in some example embodiments, the information of TA invalidity may be provided in or together with a measurement report from UE to the source DU / gNB, which may be periodic, semi-persistent, event-triggered or aperiodic. Alternatively, in some example embodiments, the information of TA invalidity may be provided in one or more (new) MAC CEs. In a case of the new MAC CE(s), UE may transmit a scheduling request (SR) to obtain an UL resource / grant for transmitting the new MAC-CE(s).

[0079] Further, and new message format(s) may be introduced to transmit the information of TA invalidity. In some embodiments, the information of TA invalidity may comprise a first part indicating the LTM candidate cell and a second part indicating that the TA of the candidate cell is invalid. In some embodiments, since the maximum number of LTM candidates is 8 and at least 1 bit is needed to indicate the TA invalidity, therefor it may be: 1 bit for the TA invalidity and 3 bits for the candidate cell ID.

[0080] Additionally, if multi-transmission reception point (TRP) operation is needed, additional bits may be required, for example, 1 bit to support operations with 2 TRPs, 2 bits to support operations with 3 / 4 TRPs, and so on. In the following discussions, although 2 TRPs may be used as an example of multi-TRP, exampleembodiments discussed herein may be applicable to any multi-TRP setting.

[0081] In some embodiments, the information of TA invalidity may be indicated in a single message via a multi-bit (e.g., 4-bit or 5-bit) indication, which may be sufficient for directly indicating the TA invalidity event and candidate cell ID (and the TRP ID). Alternatively, in some embodiments, the information of TA invalidity may be indicated in more than one messages, for example, a first message comprising a single-bit for indicating the TA invalidity event, which is followed by an UL grant to the UE. The UE, then, uses the grant to indicate the candidate cell ID (and the TRP ID) for which the TA has become invalid.

[0082] In summary, the resources / manners for transmitting the information of TA invalidity is diversity, the number of messages carrying the information of TA invalidity is changeable.

[0083] Some example embodiments will be discussed with reference to FIG. 3A, which illustrates an example signaling flow 300A for communication in accordance with some example embodiments of the present disclosure. In operation, the second apparatus 220 determines (302) a conditional LTM configuration, and transmits (304-1) to the conditional LTM configuration the first apparatus 210. The first apparatus 210 receives (304-2) the conditional LTM configuration.

[0084] In some example embodiments, the conditional LTM configuration may comprise information for a cell switch (such as, intra-CU cell switch, inter-CU cell switch), for example, at least one candidate cell. In some example embodiments, the conditional LTM configuration may be comprised in an RRC reconfiguration message.

[0085] According to some example embodiments, more information may be indicated in the conditional LTM configuration as discussed below.

[0086] In some example embodiments, the conditional LTM configuration may indicate a configuration of a TAT associated with the TA. Alternatively, or in addition, in some example embodiments, the conditional LTM configuration may indicate an event of TA invalidation configured to the at least one candidate cell (more detail about how to define and detect the event of TA invalidation will be discussed in the following by referring to FIG. 3B).

[0087] Alternatively, or in addition, in some example embodiments, the conditional LTM configuration may indicate content to be reported by the first apparatus 210 based on a determination of a TA of a candidate cell is invalid.

[0088] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an event that causes a TA of a candidate cell to be invalid, information about a candidate cell for which a TA is invalid, or informationabout transmission reception point (TRP) identity of a candidate cell.

[0089] In FIG. 3A, the first apparatus 210 further determines (306) whether a TA of a candidate cell of the at least one candidate cell is invalid. In some example embodiments, the first apparatus 210 may determine the TA of the candidate cell is invalid based on a determination that a TAT associated with the TA of the candidate cell expires. Alternatively, or in addition, in some embodiments, the first apparatus 210 may determine the TA of the candidate cell is invalid upon detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid (will be discussed in the following by referring to FIG. 3B).

[0090] If the first apparatus 210 determine the TA of a candidate cell in invalid, the first apparatus 210 transmits (308-1 ) TA-related information to the second apparatus 220 and the second apparatus 220 receives (308-2) the TA-related information accordingly. Further, the TA-related information comprises a first indication indicating the TA of a candidate cell is invalid (such as, 1 -bit indication) and / or a second indication indicating an event that causes the invalidation of the TA (such as, an index of the event).

[0091] In some embodiments, the TA-related information is comprised in a first message which is transmitted on a first resource indicated by the conditional LTM configuration. That is, the TA-related information is transmitted on dedicated resources.

[0092] Alternatively, the TA-related information is comprised in a medium access control (MAC) control element (CE). Specifically, in some example embodiments, the first apparatus 210 may transmit an SR to the second apparatus 220. In response to the SR, the second apparatus 220 may respond the SR with a grant indicating a resource. Then, the first apparatus 210 may transmit the MAC CE on the resource to the second apparatus 220.

[0093] Alternatively, the TA-related information is comprised a measurement report, i.e., by reusing existing measurement report. In some example embodiments, the measurement report may be periodic, semi-persistent, event-triggered or aperiodic.

[0094] In some example embodiments, the first apparatus 210 may transmit the TA-related information in accordance with a determination that a current measurement result of the candidate cell is larger than or no smaller than a threshold. That is, only when there is a possibility that the candidate cell may be a target cell, the first apparatus 210 transmits the TA-related information. In this way, the unnecessary signalling transmission is avoided.

[0095] As discussed above, except for the TA-related information, other information, such as, candidate cell ID, TRP ID also may be reported by the first apparatus 210 to the second apparatus 220. Further, such information may be transmitted together with the TA-related information or transmitted separately from theTA-related information, as discussed below.

[0096] In some example embodiments, upon receiving the first message on the first uplink resource (i.e., dedicated resource) from the first apparatus 210, the second apparatus 220 may transmit a grant indicating a second resource to the first apparatus 210. Then, the first apparatus 210 may transmit a second message on the second resource, where the second message may indicate at least one of the following: the candidate cell ID, or a TRP ID in a case that the first apparatus 210 is configured with a multi-TRP configuration.

[0097] In some example embodiments, the first message or the MAC CE may comprise a multi-bit field. Further, a first part of the multi-bit field may indicate the TA-related information and the remaining part of the multi-bit field may indicate at least one of the following: an identity of a candidate cell (a TA of the candidate cell is invalid) or a TRP ID in a case that the first apparatus 210 is configured with a multi-TRP configuration.

[0098] In some example embodiments, the first message or the MAC CE comprise a first field indicating the TA-related information. Further, the first message or the MAC CE may comprise a second field indicating an identity of a candidate cell (a TA of the candidate cell is invalid), or a third field indicating a TRP ID in a case that the first apparatus 210 is configured with a multi-TRP configuration.

[0099] In some example embodiments, the measurement report may comprise a multi-bit field, and a first part of the multi-bit field may indicate the TA-related information and the remaining part of the multi-bit field may indicate a TRP identity in a case that the first apparatus 210 is configured with a multi-TRP configuration.

[0100] In some example embodiments, the measurement report may comprise a field indicating the TA- related information and a further field indicating a TRP identity in a case that the first apparatus 210 is configured with a multi-TRP configuration.

[0101] In the example of FIG. 3A, after receiving the TA-related information, the second apparatus 220 may determine whether to trigger an early TA acquisition.

[0102] As illustrated in FIG. 3A, after receiving the TA-related information, the second apparatus 220 may transmit (310-1 ) a PDCCH order for early TA acquisition to the first apparatus 210. After receiving (310-2) the PDCCH order, the first apparatus 210 may transmit (312-1 ) a random access (RA) preamble to a third apparatus providing the candidate cell (where the third apparatus and the second apparatus 220 may be a same apparatus or two different apparatuses). Then, the first apparatus 210 may receive (314-2) TA information of the candidate cell from the second apparatus 220 or the third apparatus, where the TA information may comprise at least one of the following: a TA value, a TA offset, or a configuration of a TAT.

[0103] In addition, according to some embodiments of the present disclosure, a new event for TAinvalidation may be introduced, where a measurement of a reference signal (e.g., SSB-based RSRP / signal to interference plus noise ratio (SINR)Zreceived signal strength indication (RSSI)Zreference signal receiving quality(RSRQ)) from a candidate cell is compared with another measurement of a reference signal at the same candidate cell which is temporally or causally associated with the TA acquisition process (e.g., latest SSB RSRP measurement of the candidate cell before transmission of the RA preamble to the candidate cell) and if their difference is above (or in some cases below) a configured threshold, the TA invalidation event occurs. The UE may then proceed with informing the NW about it as described above.

[0104] Some example embodiments will be discussed with reference to FIG. 3B, which illustrates an example signaling flow 300B for communication in accordance with some example embodiments of the present disclosure. In operation, the second apparatus 220 determines (322) a conditional LTM configuration, and transmits (324-1) to the conditional LTM configuration the first apparatus 210. The first apparatus 210 receives (324-2) the conditional LTM configuration. In some example embodiments, the conditional LTM configuration may be comprised in an RRC reconfiguration message.

[0105] In some example embodiments, the conditional LTM configuration may comprise information for a cell switch (such as, intra-CU cell switch, inter-CU cell switch), for example, at least one candidate cell and an event of TA invalidation.

[0106] In some example embodiments, the event of TA invalidation may be a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold.

[0107] Alternatively, or in addition, in some example embodiments, the event of TA invalidation may be a time length of a duration is larger than or no smaller than a threshold length (which may be defined as a default value in 3GPP specification, or configured by the second apparatus 220), wherein within the duration the difference is larger than or no smaller than the threshold. Further,

[0108] Alternatively, or in addition, in some example embodiments, the event of TA invalidation may be a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number (such as, 3).

[0109] In the example of FIG. 3B, the first apparatus 210 perform (325) measurements on the at least one candidate cell and detects (326) the event of TA invalidation based at least in part on a measurement result of the candidate cell.

[0110] In some example embodiments, the measurement result may comprise at least one of the following: a reference signal receiving power (RSRP) value, a signal to interference plus noise ratio (SINR) value, areceived signal strength indication (RSSI) value, or a reference signal receiving quality (RSRQ) value.

[0111] If the first apparatus 210 detects (326) the event of TA invalidation occurs on a candidate cell of the at least one candidate cell, the first apparatus 210 transmit (328-1) TA-related information to the second apparatus 220, and the second apparatus 220 may receive (328-2) the TA-related information accordingly, where the TA-related information indicates the TA of the candidate cell is invalid. As details about the TA- related information and how to transmit the TA-related information has been fully discussed above. Merely for brevity, the same or similar contents are omitted here.

[0112] In some example embodiments, the conditional LTM configuration may further comprise an event of cell switch. In this event, the first apparatus 210 may evaluate occurrence of the event of cell switch based at least in part on measurement results of the at least one candidate cell. Then if the first apparatus 210 determines that the event of cell switch is occurred on a candidate cell of the at least one candidate cell, the first apparatus 210 may start to determine validity of the TA of the candidate cell based at least in part on the measurement result of the candidate cell. In this way, the unnecessary TA invalidation evolution procedure is avoided.

[0113] In some example embodiments, if the event of cell switch is evaluated based on reference signals with a first type, and the event of TA invalidation is evaluated based on reference signals with the first type, the first apparatus 210 may determine the invalidity of the TA of the candidate cell based on at least one measurement sample of the reference signals with the first type.

[0114] Alternatively, in some example embodiments, if the event of cell switch is evaluated based on reference signals with a first type, and the event of TA invalidation is evaluated based on reference signals with a second type different from the first type, the first apparatus 210 may determine the invalidity of the TA of the candidate cell by starting measuring reference signals with the second type.

[0115] In some example embodiments, he first type may be one of the following: CSI-RS, SSB, TRS or DMRS, and the second type may be one of the following: CSI- RS, SSB, TRS or DMRS and different from the first type.

[0116] Similar with the example embodiments discussed with reference to FIG. 3A, in the example of FIG. 3B, after receiving the TA-related information, the second apparatus 220 may determine whether to trigger an early TA acquisition.

[0117] As illustrated in FIG. 3B, after receiving the TA-related information, the second apparatus 220 may transmit (330-1) a PDCCH order for early TA acquisition to the first apparatus. After receiving (330-2) the PDCCH order, the first apparatus 210 may transmit (332-2) a random access (RA) preamble to a thirdapparatus providing the candidate cell (where the third apparatus and the second apparatus 220 may be a same apparatus or two different apparatuses). Then, the first apparatus 210 may receive (334-2)TA information of the candidate cell from the second apparatus 220 or the third apparatus, where the TA information may comprise at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0118] For a better understanding about the above procedure, more example embodiments will be discussed with reference to FIG. 4A to FIG. 40, which illustrate example signaling flows 400A to 400C for communication in accordance with some example embodiments of the present disclosure. It should be noted that intra-CU cell switch is used as an example cell in FIG. 4A to FIG. 4G, which should not be interpreted as any limitation of the present disclosure.

[0119] In the example of FIG. 4A, the UE sends (step 1 and step 2) a measurement report to OU via source DU (S-DU), and OU decides (step 3) to prepare target DU (T-DU) / cell(s) for LTM. The OU proceeds with the UE context setup / modification procedures (steps 4-7).

[0120] In some example embodiments, in the UE Context Setup Response message sent (step 5) from the T-DU to the OU, the T-DU may include the configuration for TA invalidity indication (e.g., UL resources). OU may transmit (step 6) UE context modification request to S-DU and the S-DU may include the configuration for TA invalidity indication (e.g., UL resources) in the UE Context Modification Response message which is sent (step 7) from the S-DU to the OU.

[0121] In some example embodiments, the OU generates and sends (steps 8-10) the RRC reconfiguration message to the UE via the source DU. Further, the OU may include configuration of TA validity indication to the UE.

[0122] In some example embodiments, the configuration may comprise the TAT con configuration. Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration of the event for TA invalidation, where the event may be described as below: a current measurement of a reference signal from a candidate cell is compared to another measurement of a reference signal at the said candidate cell which is temporally or causally associated with the TA acquisition process (e.g., latest SSB RSRP measurement of the candidate cell before transmission of the RA preamble to the candidate cell) and if their difference is above a configured threshold, the TA invalidation event occurs. For example, if \RSRPcand 1D> current- RSRPcand lDi @TA acq| > or >~) threshold , then TA invalidation occurs. In some example embodiments, the definition of the event may be configured in the common configuration (e.g., in LTM-Config) or in the candidate configuration (e.g., in LTM-Candidate).

[0123] Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration indicating resources for transmitting information / indication of TA invalidity. Additionally, in some example embodiments, if the indication of TA invalidity is provided in dedicated resources, the configuration indicating resources for transmitting information / indication of TA invalidity is expected to be comprised.

[0124] Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration of TA invalidity indication content. For example, the UE may be configured to report that the TA of a candidate cell is invalid. Additionally, if the candidate cell has a multi-TRP configuration, the UE may be configured to report the TRP for which the TA is invalid. As one example, UE may be configured to report 1 bit for event indication, 3 bits for candidate ID indication and 1 bit for TRP indication.

[0125] In some example embodiments, UE sends (steps 11-12) the RRCReconfigurationComplete message to the CU via the source DU. In some example embodiments, UE performs (step 13) early DL synchronization with one or more candidate target cells. In some example embodiments, UE provides (step 14) either an L1-RSRP measurement report to the source DU or an L3 measurement report to the CU.

[0126] In some example embodiments, based on the measurement report, the source DU or the CU decides (step 15) to trigger early TA acquisition.

[0127] In some example embodiments, S-DU issues (steps 16-17) a PDCCH order for early TA acquisition to the UE and the UE performs msg1 transmission to the candidate target cell.

[0128] Depending on the mechanism used to provide the TA to the UE, below options may be implemented. In some example embodiments, the T-DU provides (step 18) the RAR to the UE, and the UE optionally informs (step 19) the S-DU about successful early TA acquisition, which is called as Case 1

[0129] In some example embodiments, the T-DU provides (step 20) the computed TA to the S-DU via the CU (which is called as Case 2). In another embodiment, T-DU also provides a timer that can be used to estimate the TA validity.

[0130] In some example embodiments, the S-DU provides (step 21 ) the TA to the UE. In another embodiment, S-DU also provides a timer that UE can use to estimate the TA validity. This timer can be provided through MAC CE. In one implementation, this would be the same MAC CE used to convey the TA value from S-DU to UE. In another implementation, this can be a different MAC CE (e.g., dedicated MAC CE) that S-DU sends to the UE. After some time, the TA obtained by the UE may become invalid.

[0131] Reference is now made to FIG. 4B. In some example embodiments, UE may determine (step 22) the TA is invalid.

[0132] In some example embodiments, UE is configured with conditional LTM based events (either LTM events or A-events). Once the conditional LTM event for the conditional LTM is triggered (i.e., UE will start to prepare for a cell switch), UE may perform measurement based validity evaluation to evaluate whether the UE needs to transmit the information of TA invalidation.

[0133] In some example embodiments, after the event condition is met at the measurement reference point, the UE may perform N number of measurements to fulfill the TA measurement criteria.

[0134] In some example embodiments, if the TA validity evaluation condition is configured with the same RS as the conditional event was triggered, the UE may use the same measurement samples to evaluate the TA validity. Alternatively, if the TA validity is configured to be performed with a different RS, meeting the event condition for conditional LTM will trigger the UE to start TA validity measurements for the configured reference signal (e.g., either CSI-RS or SSB).

[0135] In some example embodiments, if the TA is evaluated and the result is invalid, the UE may transmit information of TA invalidity. The network will then evaluate whether UE needs to perform RACH-less process or not, and transmits PDCCH ordered RACH to the UE if needed.

[0136] In some example embodiments, the transmission of the information that the TA is invalid from the UE to the source gNB / DU may be conditioned on an event based on the latest RSRP measurement of the candidate target cell. For example, if RSRPcand iD,current> (or >) threshold_B, which means that the candidate target cell is considered as likely to switch to, the indication is determined to be transmitted. Otherwise, the indication is not transmitted.

[0137] In some example embodiments, the obtained TA is found to be invalid with one of the following ways: the TAT has expired and / or measurement-based TA invalidation event (as configured in steps 8-10) has occurred. The UE indicates to the S-DU that the TA is invalid in one of the following options.

[0138] In one option (called as Option 1 ), the UE provides the TA invalidity indication in dedicated resources provided in steps 8-10. Further, the following two sub-options are proposed. In one sub-option (Option 1A), 1 bit indication of TA invalidity event (by using corresponding resources provided in steps 8-10) is sent (step 23) from the UE to the S-DU. Then, the S-DU provides (step 24) an UL grant to the UE, such that UE may provide details about the TA invalidity event. The UE indicates (step 25) the candidate ID and the TRP ID (if the candidate has a multi-TRP configuration). In one sub-option (Option 1 B), the UE provides (step 23) all the indications described in Option 1A in one step on the dedicated resources configured in steps 8-10. For example, in Option 1 B, the dedicated resources configured in steps 8-10 may be 5 bits (1 for event indication, 3 bits for candidate ID indication and 1 bit for TRP ID indication).

[0139] Alternatively, in another option (called as Option 2), the UE provides (step 26) the TA invalidity indication in the measurement report. For example, for a cell for which the TA has been found to be invalid, a 1 -bit indication may be added to the measurement report. Further, in case of multi-TRP configuration, an additional bit for indication of the TRP also may be included.

[0140] Alternatively, in another option (called as Option 3), the UE issues a scheduling request to the S- DU, and the S-DU provides (step 28) an UL grant to the UE. Then, the UE uses (step 29) the provided UL to send a new MAC-CE for TA invalidity indication. In one embodiment, the MAC-CE contains at least one of the following fields: event type (e.g., TAT expiry or measurement-based invalidity event), candidate ID indication and TRP indication.

[0141] In some example embodiments, the S-DU is informed (step 30) that the TA is invalid and issues a new PDCCH order to the UE, so that a fresh TA estimate can be acquired. In some example embodiments, early TA acquisition process continues (step 31) as in steps 18-21 and the UE obtains a fresh TA estimate.

[0142] Reference is now made to FIG. 4C. In some example embodiments, the UE determines (step 32) that the LTM cell switch condition is satisfied and initiates autonomous LTM cell switch. In some example embodiments, the UE determines (step 33) that a valid TA is available for the target cell, so a RACH-less LTM switch is performed. Then, the UE sends (step 34 and step 35) the RRCReconfigurationComplete message to the CU via the T-DU, Finally, the LTM cell switch completion phase is performed (steps 36-38).

[0143] According to some example embodiments of the present disclosure, the UE may determine whether to transmit RS preamble. Such example embodiments will be discussed with reference to FIG. 5, which illustrates an example signaling flow 500 for communication in accordance with some example embodiments of the present disclosure.

[0144] In operation, the second apparatus 220 determines (502) a conditional LTM configuration, and transmits (504-1 ) to the conditional LTM configuration the first apparatus 210. The first apparatus 210 receives (504-2) the conditional LTM configuration.

[0145] In some example embodiments, the conditional LTM configuration may be comprised in a radio resource control (RRC) reconfiguration message.

[0146] In some example embodiments, the conditional LTM configuration may comprise information for a cell switch (such as, intra-CU cell switch, inter-CU cell switch), for example, at least one candidate cell.

[0147] In some example embodiments, the conditional LTM configuration may further indicate information about a condition for transmitting RA preamble, such as, TAT configuration and / or event TA of invalidation (as discussed with reference to FIG. 3B).

[0148] In FIG. 5, the first apparatus 210 further determines 205 whether a TA of a candidate cell of the at least one candidate cell is invalid. In some example embodiments, the first apparatus 210 may determine the TA of the candidate cell is invalid based on a determination that a TAT associated with the TA of the candidate cell expires. Alternatively, or in addition, in some embodiments, the first apparatus 210 may determine the TA of the candidate cell is invalid upon detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid (as discussed in the example embodiments of FIG. 3B).

[0149] Then, if the first apparatus 210 determines (508) a TA of a candidate cell of the at least one candidate cell is invalid, the first apparatus 210 transmit (510-1) a random access (RA) preamble to a third apparatus providing the candidate cell. Next, the first apparatus 210 receives (514-2) a message comprising timing advance (TA) information of the candidate cell from the second apparatus 220 or the third apparatus.

[0150] In some example embodiments, the TA information may comprise at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0151] In some example embodiments, the TA information may be comprised in random access response (RAR).

[0152] In some example embodiments, in response to receiving the message comprising TA information from the third apparatus, the first apparatus 210 may transmit a message indicating a success of TA acquisition on the candidate cell to the second apparatus 220.

[0153] In some example embodiments, based on a determination that a TA of a candidate cell of the at least one candidate cell is invalid, the first apparatus 210 may transmit TA-related information to the second apparatus 220, where the TA-related information indicating the TA of the candidate cell is invalid. As details about the TA-related information and how to transmit the TA-related information has been fully discussed above. Merely for brevity, the same or similar contents are omitted here.

[0154] In some example embodiments, after transmitting the TA-related information, the first apparatus 210 may receive the TA information of the candidate cell from the second apparatus 220 or the third apparatus.

[0155] Such example embodiments will be discussed with reference to FIG. 6A to 6C, which illustrate example signaling flows 600A to 600C for communication in accordance with some example embodiments of the present disclosure. Example embodiments / processes should not be interpreted as any limitations on the present discourse.

[0156] In the example of FIG. 6A, the UE sends (step 1 and step 2) a (L3) measurement report to CU via source DU (S-DU), and CU decides (step 3) to prepare target DU (T-DU) / cell(s) for LTM. The CU proceedswith the UE context setup / modification procedures (steps 4-7).

[0157] In some example embodiments, in the UE Context Setup Response message sent (step 5) from the T-DU to the CU, the T-DU may include the configuration for TA invalidity indication (e.g., UL resources). CU may transmit (step 6) UE context modification request to S-DU and the S-DU may include the configuration for TA invalidity indication (e.g., UL resources) in the UE Context Modification Response message which is sent (step 7) from the S-DU to the CU.

[0158] In some example embodiments, the CU generates and sends (steps 8-10) the RRC reconfiguration message to the UE via the source DU. Further, the CU may include configuration of TA validity indication to the UE.

[0159] In some example embodiments, the configuration may comprise the TAT con configuration. Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration of the event for TA invalidation, where the event may be described as below: a current measurement of a reference signal from a candidate cell is compared to another measurement of a reference signal at the said candidate cell which is temporally or causally associated with the TA acquisition process (e.g., latest SSB RSRP measurement of the candidate cell before transmission of the RA preamble to the candidate cell) and if their difference is above a configured threshold, the TA invalidation event occurs. For example, if \RSRPcand 1D> current- RSRPcand lDi @TA acq| > or >~) threshold , then TA invalidation occurs. In some example embodiments, the definition of the event may be configured in the common configuration (e.g., in LTM-Config) or in the candidate configuration (e.g., in LTM-Candidate).

[0160] Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration indicating resources for transmitting information / indication of TA invalidity. Additionally, in some example embodiments, if the indication of TA invalidity is provided in dedicated resources, the configuration indicating resources for transmitting information / indication of TA invalidity is expected to be comprised.

[0161] Alternatively, or in addition, in some example embodiments, the configuration may comprise a configuration of TA invalidity indication content. For example, the UE may be configured to report that the TA of a candidate cell is invalid. Additionally, if the candidate cell has a multi-TRP configuration, the UE may be configured to report the TRP for which the TA is invalid. As one example, UE may be configured to report 1 bit for event indication, 3 bits for candidate ID indication and 1 bit for TRP indication.

[0162] Reference is now made to FIG. 6B. In some example embodiments, UE sends (steps 11 -12) the RRCReconfigurationComplete message to the CU via the source DU. In some example embodiments, UEperforms (step 13) early DL synchronization with one or more candidate target cells.

[0163] In some example embodiments, UE evaluates (step 14) the condition for sending RA preamble, such as, whether a TAT associated with the TA of the candidate cell expires, or whether UE has detected an event of TA invalidation that causes a TA of a candidate cell to become invalid. If the condition for sending RA preamble is met, UE transmits (step 15) RA preamble to the candidate DU.

[0164] Depending on the mechanism used to provide the TA to the UE, below options may be implemented. In some example embodiments, the T-DU provides (step 16) the RAR to the UE, and the UE may optionally inform the S-DU about successful early TA acquisition, which is called as Case 1 .

[0165] In some example embodiments, the T-DU may provide (step 17 and step 18) the computed TA to the S-DU via the CU (which is called as Case 2). In another embodiment, T-DU also may provide a timer that can be used to estimate the TA validity.

[0166] Optionally, in some example embodiments, UE may determine (step 19) the TA is invalid. In some example embodiments, the obtained TA is found to be invalid with one of the following ways: the TAT has expired and / or measurement-based TA invalidation event (as configured in steps 8-10) has occurred.

[0167] In the example of FIG. 6B, UE, the UE may (optionally) provide (step 20) the TA invalidity indication in the measurement report. For example, for a cell for which the TA has been found to be invalid, a 1 -bit indication may be added to the measurement report. Further, in case of multi-TRP configuration, an additional bit for indication of the TRP also may be included.

[0168] It should be understood that TA invalidity indication also may be provided on dedicated resource or MAC CE as discussed above.

[0169] According to some example embodiments of the present disclosure, as one optional processes, it may allow the source DU and candidate DU to recognize that TA is no longer applicable, which may result in a new round of TA acquisition is necessary for RACH-less LTM mobility. The CU may provide (steps 21 and 22) an indication for the cells for which TA is invalid to the source DU and candidate DU. Then a new round of TA acquisition may be performed (step 23).

[0170] Reference is now made to FIG. 6C. In some example embodiments, the UE determines (step 24) that the LTM cell switch condition is satisfied and initiates autonomous LTM cell switch. In some example embodiments, the UE determines (step 25) that a valid TA is available for the target cell, so a RACH-less LTM switch is performed. Then, the UE sends (step 26 and step 27) the RRCReconfigurationComplete message to the CU via the T-DU. Finally, the LTM cell switch completion phase is performed (steps 28-30).

[0171] FIG. FIG. 7 shows a flowchart of an example method 700 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the first apparatus 210 in FIG. 2A and FIG. 2B.

[0172] At block 710, the first apparatus receives, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell.

[0173] At block 720, based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, the first apparatus transmits to the second apparatus, TA-related information comprising at least one of the following: a first indication indicating the TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, wherein the TA- related information is comprised in one of the following: a first message transmitted on a first resource indicated by the conditional LTM configuration, a measurement report, or a medium access control (MAC) control element (CE).

[0174] In some example embodiments, after transmitting the first message on the first uplink resource, the first apparatus may receive, from the second apparatus, a grant indicating a second resource; and transmit, to the second apparatus, a second message on the second resource, the second message indicating at least one of the following: the candidate cell, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0175] In some example embodiments, the first message or the MAC CE comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates at least one of the following: an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0176] In some example embodiments, the first message or the MAC CE comprises a first field indicating the TA-related information and at least one of the following: a second field indicating an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a third field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0177] In some example embodiments, the measurement report comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi- TRP configuration.

[0178] In some example embodiments, the measurement report comprises a field indicating the TA-relatedinformation and a further field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0179] In some example embodiments, the first apparatus may transmit a scheduling request (SR) to the second apparatus; receive, from the second apparatus, a grant indicating a resource; and transmit, to the second apparatus, the MAC CE on the resource.

[0180] In some example embodiments, the first apparatus may determine the TA of the candidate cell is invalid based on at least one of the following: a determination that a time alignment timer (TAT) associated with the TA of the candidate cell expires, or detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid.

[0181] In some example embodiments, the first apparatus may transmit the TA-related information in accordance with a determination that a current measurement result of the candidate cell is larger than or no smaller than a threshold.

[0182] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), an event of TA invalidation configured to the at least one candidate cell, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid.

[0183] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an event that causes a TA of a candidate cell to be invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0184] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0185] In some example embodiments, the first apparatus may receive, from the second apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; transmit a random access (RA) preamble to a third apparatus providing the candidate cell, wherein the third apparatus and the second apparatus is a same apparatus or two different apparatuses; and receive, from the second apparatus or the third apparatus, timing advance (TA) information of the candidate cell, wherein the TA information comprises at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0186] In some example embodiments, the measurement report is periodic, semi-persistent, event- triggered or aperiodic.

[0187] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0188] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0189] FIG. 8 shows a flowchart of an example method 800 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the second apparatus 220 in FIG. 2A and FIG. 2B.

[0190] At block 810, the second apparatus determines a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and at least one of the following: a first resource to be used by a first apparatus for transmitting a first message which comprises timing advance (TA)-related information comprising at least one of the following: a first indication indicating a TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, an event of TA invalidation that causes a TA of a candidate cell to become invalid, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid.

[0191] At block 820, the second apparatus transmits the conditional LTM configuration to the first apparatus.

[0192] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an even that causes a TA of a candidate cell is invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0193] In some example embodiments, the second apparatus may receive, from the first apparatus, the TA-related information which is comprised in one of the following: the first message transmitted on the first resource, a measurement report, or a medium access control (MAC) control element (CE).

[0194] In some example embodiments, after receiving the first message on the first uplink resource, the second apparatus may transmit, to the first apparatus, a grant indicating a second resource; and receive, from the first apparatus, a second message on the second resource, the second message indicating at least one of the following: the candidate cell for which the TA is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0195] In some example embodiments, the first message or the MAC CE comprises a multi-bit field, anda first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates at least one of the following: an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0196] In some example embodiments, the first message or the MAC CE comprises a first field indicating the TA-related information and at least one of the following: a second field indicating an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a third field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0197] In some example embodiments, the measurement report comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi- TRP configuration.

[0198] In some example embodiments, the measurement report comprises a field indicating the TA-related information and a further field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0199] In some example embodiments, the second apparatus may receive a scheduling request (SR) from the first apparatus; transmit, to the first apparatus, a grant indicating a resource; and receiving, from the first apparatus, the MAC CE on the resource.

[0200] In some example embodiments, the second apparatus may transmit, to the first apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; receive a random access (RA) preamble from the first apparatus; and transmit, to the first apparatus, timing advance (TA) information of the candidate cell.

[0201] In some example embodiments, the measurement report is periodic, semi-persistent, event- triggered or aperiodic.

[0202] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0203] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0204] In some example embodiments, the first apparatus comprises a terminal apparatus and the secondapparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0205] FIG. 9 shows a flowchart of an example method 900 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the first apparatus 210 in FIG. 2A and FIG. 2B.

[0206] At block 910, the first apparatus receives, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, wherein the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number.

[0207] At block 920, the first apparatus performs measurements on the at least one candidate cell.

[0208] At block 930, in accordance with a determination that the event of TA invalidation is detected for the TA of a candidate cell of the at least one candidate cell based at least in part on a measurement result of the candidate cell, the first apparatus transmits to the second apparatus TA-related information indicating the TA of the candidate cell is invalid.

[0209] In some example embodiments, the conditional LTM configuration further comprises an event of cell switch, and the first apparatus may evaluate occurrence of the event of cell switch based at least in part on measurement results of the at least one candidate cell; and in accordance with a determination that the event of cell switch is occurred on a candidate cell of the at least one candidate cell, start to determine validity of the TA of the candidate cell based at least in part on the measurement result of the candidate cell.

[0210] In some example embodiments, the event of cell switch is evaluated based on reference signals with a first type, and in accordance with a determination that the event of TA invalidation is evaluated based on reference signals with the first type, the first apparatus may determine the invalidity of the TA of the candidate cell based on at least one measurement sample of the reference signals with the first type; and in accordance with a determination that the event of TA invalidation is evaluated based on reference signals with a second type different from the first type, the first apparatus may determine the invalidity of the TA of the candidate cell by starting measuring reference signals with the second type.

[0211] In some example embodiments, the first type is one of the following: channel state information(CSI)-reference signal (RS), synchronization signal and physical broadcast channel (PBCH) block (SSB), CSI-RS for tracking (TRS) or demodulation reference signal (DMRS), and the second type is one of the following: CSI- RS, SSB, TRS or DMRS and different from the first type.

[0212] In some example embodiments, the measurement result comprises at least one of the following: a reference signal receiving power (RSRP) value, a signal to interference plus noise ratio (SINR) value, a received signal strength indication (RSSI) value, or a reference signal receiving quality (RSRQ) value.

[0213] In some example embodiments, the first apparatus may transmit the TA-related information in accordance with a determination that the current measurement result is larger than or no smaller than a threshold.

[0214] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid.

[0215] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an event that causes a TA of a candidate cell to be invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0216] In some example embodiments, the first apparatus may receive, from the second apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; transmit a random access (RA) preamble to a third apparatus providing the candidate cell, wherein the third apparatus and the second apparatus is a same apparatus or two different apparatuses; and receiving, from the second apparatus or the third apparatus, timing advance (TA) information of the candidate cell.

[0217] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0218] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0219] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0220] FIG. 10 shows a flowchart of an example method 1000 implemented at a second apparatus inaccordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the second apparatus 220 in FIG. 2A and FIG. 2B.

[0221] At block 1010, the second apparatus determines a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) for a first apparatus, wherein the conditional LTM configuration indicates at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, and the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number.

[0222] At block 1020, the second apparatus transmits the conditional LTM configuration to the first apparatus.

[0223] In some example embodiments, the measurement result comprises at least one of the following: a reference signal receiving power (RSRP) value, a signal to interference plus noise ratio (SINR) value, a received signal strength indication (RSSI) value, or a reference signal receiving quality (RSRQ) value.

[0224] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), content to be reported by the first apparatus based on a determination that a TA of a candidate cell is invalid.

[0225] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an even that causes a TA of a candidate cell is invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0226] In some example embodiments, the second apparatus may transmit, to the first apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; receiving a random access (RA) preamble from the first apparatus; and transmitting, to the first apparatus, timing advance (TA) information of the candidate cell.

[0227] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0228] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch,or an inter-CU cell switch.

[0229] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0230] FIG. 11 shows a flowchart of an example method 1100 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the first apparatus 210 in FIG. 2A and FIG. 2B.

[0231] At block 1110, the first apparatus receives, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell.

[0232] At block 1120, based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, the first apparatus transmits a random access (RA) preamble to a third apparatus providing the candidate cell.

[0233] At block 1130, the first apparatus receives, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

[0234] In some example embodiments, in response to receiving the message comprising TA information from the third apparatus, the first apparatus may transmit to the second apparatus, a message indicating a success of TA acquisition on the candidate cell.

[0235] In some example embodiments, the TA information is comprised in random access response (RAR).

[0236] In some example embodiments, the TA information comprises at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0237] In some example embodiments, the first apparatus may determine the TA of the candidate cell is invalid based on at least one of the following: a determination that a time alignment timer (TAT) associated with the TA of the candidate cell expires, or detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid.

[0238] In some example embodiments, based on a determination that a TA of a candidate cell of the at least one candidate cell is invalid, the first apparatus may transmit to the second apparatus, TA-related information indicating the TA of the candidate cell is invalid.

[0239] In some example embodiments, after transmitting the TA-related information, the first apparatus may receive the TA information of the candidate cell from the second apparatus or the third apparatus.

[0240] In some example embodiments, the conditional LTM configuration further indicates information about a condition for transmitting RA preamble.

[0241] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0242] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0243] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a distributed unit (DU) connecting with the first apparatus.

[0244] FIG. 12 shows a flowchart of an example method 1200 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1200 will be described from the perspective of the second apparatus 220 in FIG. 2A and FIG. 2B.

[0245] At block 1210, the second apparatus determines a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the conditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) preamble.

[0246] At block 1220, the second apparatus transmits the conditional LTM configuration to the first apparatus.

[0247] In some example embodiments, the second apparatus may receive timing advance (TA) information of a candidate cell; transmit the TA information of the candidate cell to the first apparatus.

[0248] In some example embodiments, the second apparatus may receive, from the first apparatus, a message indicating a success of TA acquisition on the candidate cell.

[0249] In some example embodiments, the second apparatus may receive, from the first apparatus, TA- related information indicating a TA of a candidate cell of the at least one candidate cell is invalid.

[0250] In some example embodiments, the second apparatus is a centralized unit (CU), and the second apparatus is further caused to: in response to receiving the TA-related information, transmitting to a distributed unit (DU) providing the candidate cell and / or a DU providing a serving cell of the first apparatus, a message indicating the TA of the candidate cell is invalid.

[0251] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch,or an inter-CU cell switch.

[0252] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0253] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a distributed unit (DU) connecting with the first apparatus.

[0254] Example Apparatus, Device and Medium

[0255] In some example embodiments, a first apparatus capable of performing any of the method 700 (for example, the first apparatus 210 in FIG. 2A and FIG. 2B) may comprise means for performing the respective operations of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 210 in FIG. 2A and FIG. 2B.

[0256] In some example embodiments, the first apparatus comprises means for receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and means for based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting to the second apparatus, TA-related information comprising at least one of the following: a first indication indicating the TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, wherein the TA-related information is comprised in one of the following: a first message transmitted on a first resource indicated by the conditional LTM configuration, a measurement report, or a medium access control (MAC) control element (CE).

[0257] In some example embodiments, the first apparatus further comprises: means for after transmitting the first message on the first uplink resource, receive, from the second apparatus, a grant indicating a second resource; and means for transmitting, to the second apparatus, a second message on the second resource, the second message indicating at least one of the following: identity of the candidate cell, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0258] In some example embodiments, the first message or the MAC CE comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates at least one of the following: an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configuredwith a multi-TRP configuration.

[0259] In some example embodiments, the first message or the MAC CE comprises a first field indicating the TA-related information and at least one of the following: a second field indicating an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a third field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0260] In some example embodiments, the measurement report comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi- TRP configuration.

[0261] In some example embodiments, the measurement report comprises a field indicating the TA-related information and a further field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0262] In some example embodiments, the first apparatus further comprises: means for transmitting a scheduling request (SR) to the second apparatus; means for receiving, from the second apparatus, a grant indicating a resource; and means for transmitting, to the second apparatus, the MAC CE on the resource.

[0263] In some example embodiments, the first apparatus further comprises: means for determining the TA of the candidate cell is invalid based on at least one of the following: a determination that a time alignment timer (TAT) associated with the TA of the candidate cell expires, or detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid.

[0264] In some example embodiments, the first apparatus further comprises: means for transmitting the TA-related information in accordance with a determination that a current measurement result of the candidate cell is larger than or no smaller than a threshold.

[0265] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), an event of TA invalidation configured to the at least one candidate cell, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid.

[0266] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an event that causes a TA of a candidate cell to be invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0267] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0268] In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; means for transmitting a random access (RA) preamble to a third apparatus providing the candidate cell, wherein the third apparatus and the second apparatus is a same apparatus or two different apparatuses; and means for receiving, from the second apparatus or the third apparatus, timing advance (TA) information of the candidate cell, wherein the TA information comprises at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0269] In some example embodiments, the measurement report is periodic, semi-persistent, event- triggered or aperiodic.

[0270] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0271] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0272] In some example embodiments, a second apparatus capable of performing any of the method 800 (for example, the second apparatus 220 in FIG. 2A and FIG. 2B) may comprise means for performing the respective operations of the method 800. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 220 in FIG. 2A and FIG. 2B.

[0273] In some example embodiments, the second apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and at least one of the following: a first resource to be used by a first apparatus for transmitting a first message which comprises timing advance (TA)-related information comprising at least one of the following: a first indication indicating a TA of a candidate cell is invalid or a second indication indicating an event that causes the invalidation of the TA, an event of TA invalidation that causes a TA of a candidate cell to become invalid, or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid; and means for transmitting the conditional LTM configuration to the first apparatus.

[0274] In some example embodiments, the content to be reported comprises at least one of the following:information about whether a TA of a candidate cell is invalid, information about an even that causes a TA of a candidate cell is invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0275] In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, the TA-related information which is comprised in one of the following: means for the first message transmitted on the first resource, a measurement report, or a medium access control (MAC) control element (CE).

[0276] In some example embodiments, the second apparatus further comprises: means for after receiving the first message on the first uplink resource, transmit, to the first apparatus, a grant indicating a second resource; and means for receiving, from the first apparatus, a second message on the second resource, the second message indicating at least one of the following: an identity of the candidate cell for which the TA is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0277] In some example embodiments, the first message or the MAC CE comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates at least one of the following: an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0278] In some example embodiments, the first message or the MAC CE comprises a first field indicating the TA-related information and at least one of the following: a second field indicating an identity of a candidate cell, wherein a TA of the candidate cell is invalid, or a third field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0279] In some example embodiments, the measurement report comprises a multi-bit field, and a first part of the multi-bit field indicates the TA-related information and the remaining part of the multi-bit field indicates a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi- TRP configuration.

[0280] In some example embodiments, the measurement report comprises a field indicating the TA-related information and a further field indicating a transmission reception point (TRP) identity in a case that the first apparatus is configured with a multi-TRP configuration.

[0281] In some example embodiments, the second apparatus further comprises: means for receiving a scheduling request (SR) from the first apparatus; means for transmitting, to the first apparatus, a grantindicating a resource; and means for receiving, from the first apparatus, the MAC CE on the resource.

[0282] In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; means for receiving a random access (RA) preamble from the first apparatus; and means for transmitting, to the first apparatus, timing advance (TA) information of the candidate cell.

[0283] In some example embodiments, the measurement report is periodic, semi-persistent, event- triggered or aperiodic.

[0284] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0285] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0286] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0287] In some example embodiments, a first apparatus capable of performing any of the method 900 (for example, the first apparatus 210 in FIG. 2A and FIG. 2B) may comprise means for performing the respective operations of the method 900. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the first apparatus 210 in FIG. 2A and FIG. 2B.

[0288] In some example embodiments, the first apparatus comprises means for receiving, from a second apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, wherein the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold, or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; means for performing measurements on the at least one candidate cell; and means for in accordance with a determination that the event of TA invalidation is detected for the TA of a candidate cell of the at least one candidate cell based at least in part on a measurement result of thecandidate cell, transmitting to the second apparatus TA-related information indicating the TA of the candidate cell is invalid.

[0289] In some example embodiments, the conditional LTM configuration further comprises an event of cell switch, and the first apparatus may further comprise: means for evaluating occurrence of the event of cell switch based at least in part on measurement results of the at least one candidate cell; and means for in accordance with a determination that the event of cell switch is occurred on a candidate cell of the at least one candidate cell, starting to determine validity of the TA of the candidate cell based at least in part on the measurement result of the candidate cell.

[0290] In some example embodiments, the event of cell switch is evaluated based on reference signals with a first type, and the first apparatus may further comprise: means for in accordance with a determination that the event of TA invalidation is evaluated based on reference signals with the first type, determining the invalidity of the TA of the candidate cell based on at least one measurement sample of the reference signals with the first type; and means for in accordance with a determination that the event of TA invalidation is evaluated based on reference signals with a second type different from the first type, determining the invalidity of the TA of the candidate cell by starting measuring reference signals with the second type.

[0291] In some example embodiments, the first type is one of the following: channel state information (CSI)-reference signal (RS), synchronization signal and physical broadcast channel (PBCH) block (SSB), CSI-RS for tracking (TRS) or demodulation reference signal (DMRS), and the second type is one of the following: CSI- RS, SSB, TRS or DMRS and different from the first type.

[0292] In some example embodiments, the measurement result comprises at least one of the following: a reference signal receiving power (RSRP) value, a signal to interference plus noise ratio (SINR) value, a received signal strength indication (RSSI) value, or a reference signal receiving quality (RSRQ) value.

[0293] In some example embodiments, the first apparatus may further comprise: means for transmitting the TA-related information in accordance with a determination that the current measurement result is larger than or no smaller than a threshold.

[0294] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), or content to be reported by the first apparatus based on a determination of a TA of a candidate cell is invalid.

[0295] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an event that causes a TA of a candidate cell to be invalid, information about a candidate cell for which a TA is invalid, or informationabout transmission reception point (TRP) identity of a candidate cell.

[0296] In some example embodiments, the first apparatus may further comprise: means for receiving, from the second apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; means for transmitting a random access (RA) preamble to a third apparatus providing the candidate cell, wherein the third apparatus and the second apparatus is a same apparatus or two different apparatuses; and means for receiving, from the second apparatus or the third apparatus, timing advance (TA) information of the candidate cell.

[0297] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0298] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0299] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0300] In some example embodiments, a second apparatus capable of performing any of the method 1000 (for example, the second apparatus 220 in FIG. 2A and FIG. 2B) may comprise means for performing the respective operations of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The fourth apparatus may be implemented as or included in the second apparatus 220 in FIG. 2A and FIG. 2B.

[0301] In some example embodiments, the second apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) for a first apparatus, wherein the conditional LTM configuration indicates at least one candidate cell and an event of timing advance (TA) invalidation configured for the at least one candidate cell, and the event of TA invalidation is one of that: a difference between a current measurement result of a candidate cell and a measurement result associated with a latest TA acquisition process of the candidate cell is larger than or no smaller than a threshold, a time length of a duration is larger than or no smaller than a threshold length, wherein within the duration the difference is larger than or no smaller than the threshold or a number of times that the difference is larger than or no smaller than the threshold is larger than or no smaller than a threshold number; and means for transmitting the conditional LTM configuration to the first apparatus.

[0302] In some example embodiments, the measurement result comprises at least one of the following: areference signal receiving power (RSRP) value, a signal to interference plus noise ratio (SINR) value, a received signal strength indication (RSSI) value, or a reference signal receiving quality (RSRQ) value.

[0303] In some example embodiments, the conditional LTM configuration further indicates at least one of the following: a configuration of a time alignment timer (TAT), content to be reported by the first apparatus based on a determination that a TA of a candidate cell is invalid.

[0304] In some example embodiments, the content to be reported comprises at least one of the following: information about whether a TA of a candidate cell is invalid, information about an even that causes a TA of a candidate cell is invalid, information about a candidate cell for which a TA is invalid, or information about transmission reception point (TRP) identity of a candidate cell.

[0305] In some example embodiments, the second apparatus may further comprise: means for transmitting, to the first apparatus, a physical downlink control channel (PDCCH) order for early TA acquisition; means for receiving a random access (RA) preamble from the first apparatus; and means for transmitting, to the first apparatus, timing advance (TA) information of the candidate cell.

[0306] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0307] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0308] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, a distributed unit (DU) connecting with the first apparatus, or a centralized unit (CU) connecting with the DU.

[0309] In some example embodiments, a first apparatus capable of performing any of the method 1100 (for example, the first apparatus 210 in FIG. 2A and FIG. 2B) may comprise means for performing the respective operations of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The fifth apparatus may be implemented as or included in the first apparatus 210 in FIG. 2A and FIG. 2B.

[0310] In some example embodiments, the fifth apparatus comprises means for receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; and means for based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and means for receiving,from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

[0311] In some example embodiments, the first apparatus may further comprise: means for in response to receiving the message comprising TA information from the third apparatus, transmitting to the second apparatus, a message indicating a success of TA acquisition on the candidate cell.

[0312] In some example embodiments, the TA information is comprised in random access response (RAR).

[0313] In some example embodiments, the TA information comprises at least one of the following: a TA value, a TA offset, or a configuration of a time alignment timer (TAT).

[0314] In some example embodiments, the first apparatus may further comprise: determining the TA of the candidate cell is invalid based on at least one of the following: a determination that a time alignment timer (TAT) associated with the TA of the candidate cell expires, or detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid.

[0315] In some example embodiments, the first apparatus may further comprise: means for based on a determination that a TA of a candidate cell of the at least one candidate cell is invalid, transmitting to the second apparatus, TA-related information indicating the TA of the candidate cell is invalid.

[0316] In some example embodiments, the first apparatus may further comprise: means for after transmitting the TA-related information, receive the TA information of the candidate cell from the second apparatus or the third apparatus.

[0317] In some example embodiments, the conditional LTM configuration further indicates information about a condition for transmitting RA preamble.

[0318] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0319] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0320] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a distributed unit (DU) connecting with the first apparatus.

[0321] In some example embodiments, a second apparatus capable of performing any of the method 1200 (for example, the second apparatus 220 in FIG. 2A and FIG. 2B) may comprise means for performing therespective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The sixth apparatus may be implemented as or included in the second apparatus 220 in FIG. 2A and FIG. 2B.

[0322] In some example embodiments, the second apparatus comprises means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the conditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) preamble; and means for transmitting the conditional LTM configuration to the first apparatus.

[0323] In some example embodiments, the second apparatus may further comprise: means for receiving timing advance (TA) information of a candidate cell; means for transmitting the TA information of the candidate cell to the first apparatus.

[0324] In some example embodiments, the second apparatus may further comprise: means for receiving, from the first apparatus, a message indicating a success of TA acquisition on the candidate cell.

[0325] In some example embodiments, the second apparatus may further comprise: means for receiving, from the first apparatus, TA-related information indicating a TA of a candidate cell of the at least one candidate cell is invalid.

[0326] In some example embodiments, the second apparatus is a centralized unit (CU), and the second apparatus may further comprise: means for in response to receiving the TA-related information, transmitting to a distributed unit (DU) providing the candidate cell and / or a DU providing a serving cell of the first apparatus, a message indicating the TA of the candidate cell is invalid.

[0327] In some example embodiments, the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter-CU cell switch.

[0328] In some example embodiments, the conditional LTM configuration is comprised in a radio resource control (RRC) reconfiguration message.

[0329] In some example embodiments, the first apparatus comprises a terminal apparatus and the second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a distributed unit (DU) connecting with the first apparatus.

[0330] FIG. 13 is a simplified block diagram of a device 1300 that is suitable for implementing example embodiments of the present disclosure. The device 1300 may be provided to implement a communication device, for example, the first apparatus 210 or the second apparatus 220 as shown in FIG. 2A and FIG. 2B.As shown, the device 1300 includes one or more processors 1310, one or more memories 1320 coupled to the processor 1310, and one or more communication modules 1340 coupled to the processor 1310.

[0331] The communication module 1340 is for bidirectional communications. The communication module 1340 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1340 may include at least one antenna.

[0332] The processor 1310 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1300 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0333] The memory 1320 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1324, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 1322 and other volatile memories that will not last in the power-down duration.

[0334] A computer program 1330 includes computer executable instructions that are executed by the associated processor 1310. The instructions of the program 1330 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1330 may be stored in the memory, e.g., the ROM 1324. The processor 1310 may perform any suitable actions and processing by loading the program 1330 into the RAM 1322.

[0335] The example embodiments of the present disclosure may be implemented by means of the program 1330 so that the device 1300 may perform any process of the disclosure as discussed with reference to FIG. 2A to FIG. 12. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0336] In some example embodiments, the program 1330 may be tangibly contained in a computer readable medium which may be included in the device 1300 (such as in the memory 1320) or other storage devices that are accessible by the device 1300. The device 1300 may load the program 1330 from the computer readable medium to the RAM 1322 for execution. In some example embodiments, the computerreadable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0337] FIG. 14 shows an example of the computer readable medium 1400 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1400 has the program 1330 stored thereon.

[0338] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0339] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0340] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partlyon a remote machine or entirely on the remote machine or server.

[0341] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0342] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0343] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0344] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

I / We Claim:1 . A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) gered mobility (LTM) configuration indicating at least one candidate cell; and based on a determination that a timing advance (TA) of a candidate cell is invalid, transmit a random access (RA) amble to a third apparatus providing the candidate cell; and receive, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of candidate cell.

2. The first apparatus of claim 1, wherein the first apparatus is further caused to: in response to receiving the message comprising TA information from the third apparatus, transmit, to the second paratus, a message indicating a success of TA acquisition on the candidate cell.

3. The first apparatus of claim 1 , wherein the TA information is comprised in random access response (RAR).

4. The first apparatus of claim 1 , wherein the TA information comprises at least one of the following: a TA value, a TA set, or a configuration of a time alignment timer (TAT).

5. The first apparatus of claim 1 , wherein the first apparatus is further caused to: determine the TA of the candidate ll is invalid based on at least one of the following: a determination that a time alignment timer (TAT) associated with the TA of the candidate cell expires, or detecting an event of TA invalidation that causes a TA of a candidate cell to become invalid.

6. The first apparatus of any of claims 1 to 5, wherein the first apparatus is further caused to: based on a determination that a TA of a candidate cell of the at least one candidate cell is invalid, transmit, to the cond apparatus, TA-related information indicating the TA of the candidate cell is invalid.

7. The first apparatus of claim 6, wherein the first apparatus is further caused to: after transmitting the TA-related information, receive the TA information of the candidate cell from the second apparatus the third apparatus.

8. The first apparatus of any of claims 1 to 7, wherein the conditional LTM configuration further indicates information about a condition for transmitting RA preamble.

9. The first apparatus of any of claims 1 to 8, wherein the conditional LTM configuration comprises information for a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an inter- cell switch.

10. The first apparatus of any of claims 1 to 9, wherein the conditional LTM configuration is comprised in a radio ource control (RRC) reconfiguration message.11 . The first apparatus of any of claims 1 to 10, wherein the first apparatus comprises a terminal apparatus and the cond apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a distributed it (DU) connecting with the first apparatus.

12. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second paratus to: determine a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the nditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) amble; and transmit the conditional LTM configuration to the first apparatus.

13. The second apparatus of claim 12, wherein the second apparatus is further caused to: receiving timing advance (TA) information of a candidate cell; transmit the TA information of the candidate cell to the first apparatus.

14. The second apparatus of claim 12, wherein the second apparatus is further caused to: receive, from the first apparatus, a message indicating a success of TA acquisition on the candidate cell.

15. The second apparatus of any of claims 12 to 14, wherein the second apparatus is further caused to: receive, from the first apparatus, TA-related information indicating a TA of a candidate cell of the at least one candidate ll is invalid.

16. The second apparatus of claim 15, wherein the second apparatus is a centralized unit (CU), and the second apparatus is further caused to: in response to receiving the TA-related information, transmit, to a distributed unit (DU) providing the candidate cell and / or a DU providing a serving cell of the first apparatus, a message indicating the TA of the candidate cell is invalid.

17. The second apparatus of any of claims 12 to 16, wherein the conditional LTM configuration comprises information a cell switch, and the cell switch comprises at least one of the following: an intra-centralized unit (CU) cell switch, or an er-CU cell switch.

18. The second apparatus of any of claims 12 to 17, wherein the conditional LTM configuration is comprised in a radio ource control (RRC) reconfiguration message.

19. The second apparatus of any of claims 12 to 18, wherein the first apparatus comprises a terminal apparatus and second apparatus comprises one of the following: a next generation node B (gNB) serving the first apparatus, or a tributed unit (DU) connecting with the first apparatus.

20. A method comprising: receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer 2 (L1 / L2) gered mobility (LTM) configuration indicating at least one candidate cell; based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, nsmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and receiving, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information the candidate cell.

21. A method comprising: determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, the nditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) amble; and transmitting the conditional LTM configuration to the first apparatus.

22. A first apparatus comprising: means for receiving, from a second apparatus providing a serving cell of the first apparatus, a conditional layer 1 / layer L1 / L2) triggered mobility (LTM) configuration indicating at least one candidate cell; andmeans for based on a determination that a timing advance (TA) of a candidate cell of the at least one candidate cell is invalid, transmitting a random access (RA) preamble to a third apparatus providing the candidate cell; and means for receiving, from the second apparatus or the third apparatus, a message comprising timing advance (TA) information of the candidate cell.

23. A second apparatus comprising: means for determining a conditional layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) configuration for a first apparatus, conditional LTM configuration indicating at least one candidate cell and a condition for transmitting random access (RA) amble; and means for transmitting the conditional LTM configuration to the first apparatus.

24. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform method of claim 20 or the method of claim 21 .

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