Timing advance validity

Abstract

Example embodiments of the present disclosure are directed to timing advance (TA) validity. A method comprises receiving, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; determining, from the mapping, a first TAT value mapped to a first TAT index for a first cell; in accordance with reception of first timing advance, TA, information of the first cell from a second network node, start a TA timer with the first TAT value for the first TA information of the first cell; and performing access to the first cell based on whether the TA timer is expired or not.

Description

TIMING ADVANCE VALIDITYFIELD

[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 timing advance (TA) validity in access to a cell.BACKGROUND

[0002] A communication network may serve as a facility that enables communications between two or more communication devices or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network. A communication device may be provided with a service by an application server.

[0003] The communication network may operate in accordance with standards such as those provided by Third Generation Partnership Project (3 GPP) or European Telecommunications Standards Institute (ETSI). Examples of standards provided by 3 GPP are the so-called 3 GPP standards for cellular technology generations, such as 3 GPP standards for 4G technology, 5G technology, 6G technology etc.SUMMARY

[0004] 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 at least to: receive, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; determine, from the mapping, a first TAT value mapped to a first TAT index for a first cell; in accordance with reception of first timing advance, TA, information of the first cell from a second network node, start a TA timer with the first TAT value for the first TA information of the first cell; and perform access to the first cell based on whether the TA timer is expired or not.

[0005] 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 storinginstructions that, when executed by the at least one processor, cause the second apparatus at least to: determine a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; determine, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell; and transmit, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

[0006] In a third aspect of the present disclosure, there is provided a third 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 third apparatus at least to: determine a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; and transmit, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

[0007] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; determining, from the mapping, a first TAT value mapped to a first TAT index for a first cell; in accordance with reception of first timing advance, TA, information of the first cell from a second network node, start a TA timer with the first TAT value for the first TA information of the first cell; and performing access to the first cell based on whether the TA timer is expired or not.

[0008] In a fifth aspect of the present disclosure, there is provided a method. The method comprises: determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; determining, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell; and transmitting, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

[0009] In a sixth aspect of the present disclosure, there is provided a method. The method comprises: determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; and transmitting, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

[0010] In a seventh aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a first network node,configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; means for determining, from the mapping, a first TAT value mapped to a first TAT index for a first cell; means for in accordance with reception of first timing advance, TA, information of the first cell from a second network node, starting a TA timer with the first TAT value for the first TA information of the first cell; and means for performing access to the first cell based on whether the TA timer is expired or not.

[0011] In an eighth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; means for determining, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell; and means for transmitting, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

[0012] In a ninth aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; and means for transmitting, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

[0013] In a tenth 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 fourth aspect.

[0014] In an eleventh 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 fifth aspect.

[0015] In a twelfth 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 sixth aspect.

[0016] 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

[0017] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0018] FIG. 1 illustrates a signaling flow for an example LTM procedure in a communication system;

[0019] FIG. 2 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0020] FIG. 3 illustrates a signaling flow for TA validity according to some example embodiments of the present disclosure;

[0021] FIG. 4A and 4B illustrates signaling flows for example processes for TA validity in the conditional LTM according to some example embodiments of the present disclosure;

[0022] FIG. 5 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0023] FIG. 6 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0024] FIG. 7 illustrates a flowchart of a method implemented at a third apparatus in accordance with some example embodiments of the present disclosure;

[0025] FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0026] FIG. 9 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0027] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0028] 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 any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0029] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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., butdo not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0035] 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.

[0036] 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.

[0037] 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-IoT) 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 generationcommunication protocols, including, but not limited to, the first generation (1G), 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.

[0038] 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 to a 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 (IAB) 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.

[0039] 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-mountedequipment (LME), USB dongles, smart devices, wireless customer-premises 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.

[0040] 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 example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0041] Layer 1 or Layer 2 (L1 / L2) triggered mobility (LTM) is a cell switch procedure, where a UE’s serving cell (primary cell (PCell) or primary secondary cell (PSCell)) is switched by the network by sending an LTM cell switch command. An LTM switch command is currently assumed delivered by medium access control (MAC) signaling using an MAC control element (CE). Hence, radio resource control (RRC) signaling is not used as a Layer 3 (L3) based handover which is one of the current methods for changing between cells. An LTM cell switch decision is based on measurements (for example LI measurements) that are performed and reported (for example LI measurement report) by the UE. Measurements and reporting are based on an LTM candidate cell configuration provided by the network for one or more LTM candidate cells. An LTM candidate cell may be a neighboring cell or a UE’s current serving cell (e.g., SCell). In Release-18, LTM measurements on a neighboring candidate cell areperformed using synchronization signal and physical broadcast channel (PBCH) blocks (SSBs) transmitted by the candidate cell for which the SSB configuration is provided to the UE. This is being extended to channel state information-reference signal (CSI-RS) based measurements in Release-19.

[0042] Before the cell switch, the network may optionally activate one or more transmission configuration indication (TCI) state(s) for one or more candidate cells. Once a candidate cell TCI state is activated the UE may start tracking the time / frequency synchronization using the reference signals associated with the activated TCI state(s). The UE may also perform early uplink (UL) synchronization before the cell switch if this is requested by the network.

[0043] FIG. 1 illustrates a signaling flow 100 for an LTM procedure in a communication system. Without loss of generality, the signaling flow 100 involves a terminal device 150 and a network node 152 (e.g., a gNB) which serves the terminal device 150. As shown in FIG. 1, an LTM procedure may split in four phases, including an LTM preparation phase 103, an early synchronization phase 107, an LTM execution phase 111, and an LTM completion phase 116.

[0044] During the LTM preparation phase 103, at 101, the terminal device 150 is in a radio resource control (RRC) connected (RRC Connected) state. At 102, the terminal device 150 transmits a measurement report to the network node 152 containing the measurement results for neighboring cells. At 103, the network node 152 (e.g., the serving CU of the network node) decides to configure LTM and initiates LTM candidate preparation. The network node 152 performs the LTM candidate preparations by identifying the potential targets based on the measurement report and preparing candidate target cells (or referred to as “target cells” for short). At 105, the network node 152 shares the LTM candidate configuration (which includes target cell configurations) with the terminal device 150. The network node 152 transmits an RRCReconfiguration message to the terminal device 150 including the LTM candidate configurations. At 106, the terminal device 150 stores the LTM candidate configurations and transmits a RRC reconfiguration complete message to the network node 152.

[0045] During the early synchronization phase 107, at 108a, the terminal device 150 performs downlink (DL) synchronization with the candidate cell(s) before receiving the cell switch command. At 108a, the terminal device 150 performs early TA acquisitionwith 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 a 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 doesn’t receive a 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 may not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0046] During the LTM execution phase 111, at 110, the terminal device 150 performs LI measurements on the configured candidate cell(s) and transmits a LI measurement report to the network node 152. The LI measurements should be performed as long as RRC reconfiguration (at 105) is applicable. At 112, the network node 152 (e.g., the serving DU) makes an LTM decision on a target cell by considering the LI measurements on the target cell) and requests, at 113, the terminal device 150 to switch to that target cell by transmitting a cell switch command to the terminal device 150. The cell switch command may be transmitted in a medium access control (MAC) control element (CE). In other words, the network node 152 decides to execute a cell switch to a target cell and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell. At 114, the terminal device 150 detaches from the source cell and applies the target configuration corresponding to the target cell that is received previously. At 115, if the terminal device 150 does not have a valid TA of the target cell, the terminal device 150 switches to that target cell through a random access channel (RACH) procedure and starts receiving data from the target cell.

[0047] During the completion phase 116, the terminal device 150 completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to target cell. If the terminal device 150 has performed an RA procedure at 115, the terminal device 150 considers that the LTM cell switch execution is successfully completed when the RA procedure is successfully completed. For RACH-less LTM, the terminal device 150 considers that the LTM cell switch execution is successfully completed when the terminal device 150 determines that the network has successfully received its first UL data.

[0048] It is noted that in case the terminal device 150 maintains the configurations ofthe target cell it is allowed to perform multiple / sub sequent LTM operations. This may be referred to as a subsequent LTM procedure.

[0049] As can be seen from the signaling flow 100 of FIG. 1, in the Release- 18 LTM procedure, the UE receives the UL sync information (i.e., a TA value) in the cell switch command. However, the cell switch command does not indicate whether the TA value is valid or not. In Release-18 it is left to the network to maintain the validity of the TA value and indicate the TA value to the UE at the time of cell switch. In this document cell switch and handover may be used inter-changeably, unless otherwise specified. Following the 3GPP terminology, the handover is generally used in connection with Layer 3 handover and conditional handover, while cell switch is generally used in connection with LTM and conditional LTM. Basically, both relate to the same concept of switching the UE from one cell to another, and 3 GPP specifies the various procedures for that.

[0050] Compared to the LTM procedure illustrated in FIG. 1, in the conditional LTM, the UE may or may not receive the cell switch command (CSC) from the serving cell. In the conditional LTM as execution happens at the UE side, the TA value may be given beforehand. This may create the situation that the execution may happen after some time passes after the UE receives the TA value. So there needs to be a mechanism to monitor the validity of the TA value given beforehand. In other words, it is not clear how can the UE monitor the validity of the TA value that is given to the UE earlier than the cell switch operation.

[0051] Currently, a timing alignment timer (TAT) has been used for TA validity in a RACH-less mobility procedure. The UE can receive a time alignment timer (TAT) from the network to determine the validity of the TA value. In case the TAT expires, the UE will consider that the TA value is not valid. In that case the UE will perform a RACH based handover. This is signaled to the UE in the handover command or a cell switch command.

[0052] However, in the conditional LTM, the handover command or the cell switch command is provided to the UE in the LTM candidate configuration (similar to the LTM candidate configuration at 105 in FIG. 1) and there is no TAT value included in the configuration. The network dynamically determines whether a conditional LTM procedure can be RACH based or RACH-less. As it is not clear whether a conditional LTM procedure can be RACH-less or not, the TAT value cannot be included in the RRCconfiguration like in prior art.

[0053] Example embodiments of the present disclosure propose a solution for TA validity. With this solution, a terminal device is configured with a mapping of TAT values to TAT indices, e.g. via RRC reconfiguration. The mapping may map each of multiple TAT indices to one of multiple TAT values. Accordingly, there may be one-to-one mapping between multiple TAT indices and multiple TAT values. The number of TAT indices may be equal to the number of TAT values, and the number of TAT indices / values may be fixed or variable. The terminal device may then use the mapping to determine one of the TAT values mapped to a TAT index for a cell and start a TA timer with the determined TAT value. In some embodiments, the network device may validate the TAT value while providing the TA information for the cell by transmitting an index mapped to the TAT value to the terminal device.

[0054] When performing access to the corresponding cell, the terminal device may validate whether the TA information for a cell is valid or not depending on whether the TA timer is expired or not. This validation may then be used to determine how the terminal device shall access the cell in the cell switch, e.g. via RACH-less or RACH- based access.

[0055] In some example embodiments, the TA validity mechanism may enable the terminal device to use the conditional LTM procedure in a RACH-less manner if the TA value is valid. This may also ensure that the terminal device uses a RACH-based conditional LTM procedure if the TA value is not valid. Moreover, in some example embodiments, the network device may use a mapping of a TAT configuration provided to the terminal device, to indicate different TAT values in the cell switch command. Longer TAT values may indicate a TA value that is valid for a longer duration due to slow change of the propagation delay (e.g., fixed multi-path environment) or due to low mobility of the terminal device.

[0056] It is to be noted that the solution for configuring dynamic TAT values may be implemented in cell switches in various scenarios including the LTM procedure, the conditional LTM procedure, radio link failure and recovery procedure, and so on.

[0057] FIG. 2 illustrates an example communication environment 200 in which example embodiments of the present disclosure can be implemented. As shown in FIG. 2, the communication environment 200 comprises one or more network devices, such as anetwork device 210-1, a network device 210-2, and one or more terminal devices such as a terminal device 220. For purpose of discussion, the network device 210-1 and network device 210-2 are collectively or individually referred to as network devices 210.

[0058] In some example embodiments, the network device 210-1 may be a RAN network device of a serving cell 240, for example, a gNB of the serving cell 240 for the terminal device 220. The network device 210-2 may be a RAN network device of a neighbor cell 250, for example, a gNB of the cell 250. In some embodiments, the cell 250 may be a candidate for LTM of the terminal device 220. The terminal device 220, for example, may be a UE served by the serving cell 240. The cell 250 may be a potential candidate to become a new serving cell for the terminal device 220.

[0059] In some example embodiments, a network device of a serving cell for a terminal device may include one or more distributed units (DUs), e.g., one or more gNB-DUs, and one or more central units (CUs), e.g., one or more gNB-CUs. For example, the network device 210 may include a CU 212-1, a DU 214-1 and a DU 214-2. The network device 210-2 may include a CU 212-2 and a DU 214-3. The CU 212-1 and CU 212-2 are collectively or individually referred to as CUs 212. The DU 214-1, 214-2, 214-3 are collectively or individually referred to as DUs 214. In some example embodiments,

[0060] A DU may be connected to the terminal device 220, and each DU may serve one or more cells. Depending on whether the serving cell and a candidate target cell are associated with the same CU, the LTM procedure may include an intra-CU LTM procedure or an inter-CU LTM procedure. If the candidate target cell(s) and the serving cell are associated with the same CU, the intra-CU LTM procedure is applied. If the candidate target cell(s) and the serving cell are associated with different CUs, the inter- CU LTM procedure is applied.

[0061] In the following, for the purpose of illustration, some example embodiments may be described with the network device 210-1 or the network device 210-2 operating as a network device. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

[0062] In some example embodiments, a communication direction from a network device 210 to the terminal device 220 is referred to as a downlink (DL), and acommunication direction from the terminal device 220 to a network device 210 is referred to as an uplink (UL). In DL, the network device 210 is a transmitting (TX) device (or a transmitter) and the terminal device 220 is a receiving (RX) device (or a receiver). In UL, the terminal device 220 is a TX device (or a transmitter) and the network device 210 is a RX device (or a receiver).

[0063] Communications in the communication environment 200 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols, 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.

[0064] FIG. 3 illustrates a signaling flow 300 for TA validity according to some example embodiments of the present disclosure. Without loss of generality, the signaling flow 300 involves the terminal device 220, and one or more network nodes including a CU 212 and a DU 214 in a RAN network device 210. In some example embodiments, the RAN network device 210 may be a serving RAN network device 210 for the terminal device 220. In some example embodiments, the RAN network device 210 may include one or more DU and the DU 214 may be corresponding to a serving cell of the terminal device 220. As such, the DU 214 may also be referred to as a source DU for the terminal device 220. In some examples, the RAN network device 210 may include more than one DU 214 each serving one cell.

[0065] In the signaling flow 300, the DU 214 or the CU 212 determines (340) a mapping of TAT values to TAT indices for the terminal device 220.

[0066] In some example embodiments, the DU 214 and the CU 212 may determine an LTM preparation for the terminal device 220 based on a measurement report (e.g., L3 measurement report) received from the terminal device 220. The measurement report mayindicate that neighbor cells of the current serving cell of the terminal device 220 may be considered as candidate cells for handover. The CU 212 may perform preparation of one or more candidate cells, e.g., for LTM.

[0067] In some example embodiments, the DU 214 may receive a candidate cell configuration from the CU 212 and may determine to configure a conditional handover procedure (for example, a conditional LTM procedure) for one or more candidate cells.

[0068] In some example embodiments, if a conditional handover procedure is determined to be configured for the terminal device 220, the DU 214 may determine the mapping of TAT values to TAT indices for the terminal device 220. In some example embodiments, if the conditional handover procedure is configured for a certain candidate cell, the DU 214 may determine the mapping of TAT values to TAT indices for the candidate cell. A TAT value may indicate a timer value or a duration of validity of TA information (e.g., TA value) of a cell for the terminal device 220.

[0069] In some example embodiments, in addition to the handover procedure, the DU 214 may determine the mapping of TAT values to TAT indices for use in a recovery procedure for the terminal device 220 when the terminal device 220 experience radio link failure (RLF).

[0070] In some example embodiments, with the mapping of TAT values to TAT indices determined, the DU 214 may transmit the determined mapping to the CU 212, e.g., for early UL synchronization in the LTM procedure or the conditional LTM procedure.

[0071] In some example embodiments, the mapping of TAT values to TAT indices may be determined by the CU 212. The DU 214 may receive the mapping of TAT values to TAT indices from the CU 212.

[0072] The CU 212 transmits (352), to the terminal device 220, configuration information indicating the mapping of TAT values to TAT indices. It would be appreciated that in some other cases, it may be the DU 214 other than the CU 212 which transmits the configuration information indicating the mapping of TAT values to TAT indices to the terminal device 220. The terminal device 220 receives (354) the configuration information and may store the mapping(s) of TAT values to TAT indices.

[0073] In some example embodiments, for the LTM procedure or the conditional LTM procedure, the mapping of TAT values to TAT indices may be included in an LTMconfiguration (also referred to as an LTM candidate configuration) transmitted to the terminal device 220. The LTM configuration may be included in early UL synchronization configuration of the corresponding candidate cell. In some example embodiments, the CU 212 may generate the RRC configuration to include the LTM configuration and transmit the RRC configuration to the terminal device 220.

[0074] In some example embodiments, for the LTM procedure or the conditional LTM procedure, the mapping of TAT values to TAT indices may be included in a serving cell configuration, or a serving cell group configuration.

[0075] In some example embodiments, different mappings of TAT values to TAT indices may be configured for different cells, so that a respective mapping of TAT values to TAT indices may be associated with a cell. The configuration information may include one or more mappings of TAT values to TAT indices associated with one or more corresponding cells. In some other example embodiments, a single mapping of TAT values to TAT indices may be applicable for a plurality of cells.

[0076] In some example embodiments, the mapping of TAT values to TAT indices may be pre-configured to the terminal device 220, and the network may not need to signal the mapping to the terminal device 220. The pre-configured mapping of TAT values to TAT indices may be applied for multiple candidate cells.

[0077] In some example embodiments, a large mapping table of TAT values to TAT indices may be pre-configured to the terminal device 220, and the network may indicate that some of the TAT indices in the mapping table are enabled for a specific candidate cell. The indication of the enabled TAT indices may be transmitted to the terminal device 220.

[0078] The DU 214 may determine (356), from the mapping of TAT values to TAT indices configured for the terminal device 220, a first TAT value for first TA information of a first cell. The first cell may be a candidate cell for cell switch.

[0079] The DU 214 may receive the first TA information for the first cell and transmit (358) the first TA information to the terminal device 220. In some example embodiments, the DU 214 may also transmit, to the terminal device 220, a first TAT index mapped to the determined first TAT value in the configured mapping. The terminal device 220 may receive (360), from the DU 214, the first TA information of the first cell and optionally,receive the first TAT index.

[0080] In some example embodiments, the DU 214 may transmit a PDCCH order to the terminal device 220 to indicate a candidate cell, i.e., the first cell. In this case, the terminal device 220 may transmit a preamble towards the first cell. The network node of the first cell, e.g., the DU of the RAN network device corresponding to the first cell, may use the preamble to determine the first TA information of the first cell for the terminal device 220. The first TA information, for example, may include a TA value for the terminal device 220. Such TA information may be transmitted by the DU of the first cell to the CU 212 which may then forward it to the DU 214.

[0081] Upon reception of the first TA information of the first cell, the DU 214 may determine a TAT value for the first TAT information. In some example embodiments, the DU 214 may determine a validity duration of the first TA information of the first cell based on a mobility status of the terminal device 220. For example, due to low mobility of the terminal device 220, a large TAT value may be determined to indicate that the first TAT information of the first cell may be considered as valid for a long time. As an opposite, if the terminal device 220 is in high mobility, a short TAT value may be determined to indicate that the first TAT information may be considered as valid for a relatively short time.

[0082] Alternatively or in addition, the DU 214 may determine the validity duration of the first TA information further based on a propagation path between the terminal device 220 and the first cell. For example, if the propagation path between the terminal device 220 and the first cell is detected to have a slow change of the propagation delay, which means there is a fixed multi-path environment of the terminal device 220 in the first cell, then a large TAT value may be determined to indicate that the first TAT information of the first cell may be considered as valid for a long time.

[0083] In some example embodiments, the DU 214 may determine the validity duration of the first TA information for the terminal device 220 using the last measurements received from the terminal device 220. The measurements, e.g., LI measurements, may indicate whether the terminal device 220 moves towards the first cell, which may indicate the potential change in the timing advance value for the first cell. The CU 212 may determine the mobility status and / or the propagation path for the terminal device 220 based on the received measurements.

[0084] With the first TAT value for the first TA information of the first cell determined, the DU 214 may determine, from the mapping for the first cell, the first TAT value associated with the determined validity duration. The first TAT value may indicate a time duration that approximates to the determined validity duration. With the first TAT value determined, the DU 214 may further determine a first TAT index that is mapped to the determined first TAT value in the configured mapping for the first cell. The DU 214 may thus transmit the first TAT index to the terminal device 220.

[0085] At the terminal side, the terminal device 220 determines (362), from the mapping, a first TAT value mapped to the first TAT index for the first cell. As discussed above, in some example embodiments, the terminal device 220 may receive, from the DU 214, the first TAT index for the first cell.

[0086] In some other example embodiments, if no TAT index is indicated by the network for the first cell, the terminal device 220 may determine a default TAT value or use a default TAT index to determine a default TAT value from the configured mapping.

[0087] In some examples, the default TAT value or the default TAT index may be preconfigured to the terminal device 220, e.g. in the RRC reconfiguration in step 105, 354, or may be specified in communication specifications to which the terminal device 220 conforms.

[0088] In some example embodiments, the first TAT index may be determined by the terminal device 220 itself in a similar way as by the DU 214, for example, based on the mobility of the terminal device 220, or based on measured signal propagation properties between the terminal device 220 to the first cell.

[0089] In some example embodiments, if no TAT index is indicated by the network for the first cell, the terminal device 220 may be able to fall back to the conventional solution and utilize for the first cell a fixed (default) TAT value.

[0090] In some example embodiments, the TAT index for the candidate cell may not be transmitted to the terminal device 220 each time when the TA information of the candidate cell is transmitted or updated to the terminal device 220. For example, the TAT index of the candidate cell may be transmitted to the terminal device 220 if the PDCCH order indicating the candidate cell or the TA information of the candidate cell is provided to the terminal device 220 for the first time.

[0091] In some example embodiments, in the case where the TAT index for a candidate cell is transmitted from the network, the TAT index may be received from the DU 214 in association with the TA information for the candidate cell. In some example embodiments, the TAT index may be appended to a cell switch command for an LTM procedure or a conditional LTM procedure for the candidate cell. The cell switch command may be included in a medium access control (MAC) control element (CE). In some example embodiments, with the TAT index received, the terminal device 220 may infer that the MAC CE or the cell switch command is for conditional LTM and is to provide TA information to the terminal device 220 for a later use in a conditional LTM procedure.

[0092] In some example embodiments, in the case where the TAT index is transmitted from the network, the TAT index may be received from the DU 214 in association with a PDCCH order. The PDCCH order may be transmitted to the terminal device 220 in an earlier stage than the first TA information for the candidate cell. The PDCCH order may indicate the candidate cell as a target candidate cell for handover or cell switch.

[0093] Still referring to FIG. 3, in accordance with reception of the first TA information of the first cell from the DU 214, the terminal device 220 starts (364) a TA timer with the first TAT value for the first TA information of the first cell. The TA timer may sometimes be referred to as a TAT or a TAT timer. The TA timer is configured to indicate the remaining validity duration of the TA information for a certain cell. That is, the TAT information of the candidate cell is considered as valid while the corresponding TA timer is running.

[0094] The terminal device 220 performs (366) access to the first cell based on whether the TA timer is expired or not. In some example embodiments, the access to a candidate cell may be include sending a first UL message or listening to downlink signaling for receiving an UL grant for the candidate cell.

[0095] In some example embodiments, while the TA timer is running, the terminal device 220 may perform a handover to the candidate cell without initiating a RACH procedure towards the candidate cell. As such, the terminal device 220 may get access to the candidate cell in a fast way with low resource cost. In some example embodiments, the handover may be a conditional handover or an LTM procedure (e.g., a conditional LTM procedure). The handover without initiating RACH procedure may also be referred to as a RACH-less handover procedure or a RACH-less LTM procedure.

[0096] In some example embodiments, upon an expiry of the TA timer, the terminal device 220 may perform a handover to the candidate cell by initiating a RACH procedure towards the candidate cell. If the handover is a conditional handover or an LTM procedure, the handover with the RACH procedure initiated may also be referred to as a RACH- based handover procedure or a RACH-based LTM procedure.

[0097] In some example embodiments, the terminal device 220 may start evaluation for a conditional LTM procedure start after receiving the TAT index. With the TA timer set to the TAT index, the terminal device 220 may determine whether a condition for handover (e.g., an LTM condition) to the candidate cell is fulfilled or not. If the condition for handover to the candidate cell is fulfilled and the TA timer for the TA information of the candidate cell is still running, the terminal device 220 may execute the RACH-less handover procedure or the RACH-less LTM procedure.

[0098] In some cases, if the TA timer has expired before the condition for handover to the candidate cell is fulfilled, the terminal device 220 may perform a handover to the candidate cell by initiating the RACH procedure and get the valid TA information in the RACH procedure.

[0099] In some example embodiments, for the case of radio link failure, to recovery from radio link failure, the terminal device 220 may start a TA timer for the candidate cell after receiving TA information of the candidate cell. The terminal device 220 may perform access to the candidate cell while the TA timer is running, without initiating the RACH procedure. Otherwise, if the TA timer has been expired, the terminal device 220 may perform a RACH procedure towards the candidate cell to get access to the candidate cell.

[0100] In some example embodiments, if different mappings of TAT values to TAT indices are configured for different cells, and a second cell is indicated for handover or recovery, the terminal device 220 may determine, from a second mapping of TAT values to TAT indices, a second TAT value mapped to a second TAT index for the second cell. The second TAT index for the second cell may be a default TAT index, may be determined by the terminal device 220 for the second cell, or may be received from the DU 214.

[0101] Similarly, if the terminal device 220 receives second TA information of a second cell, the terminal device 220 may start a second TA timer for the second TA information of the second cell with the second TAT value, and perform access to the second cell basedon whether the second TA timer is expired or not. The access to the second cell is not repeated here for brevity.

[0102] FIG. 4A and 4B illustrates signaling flows for example processes 401 and 405 for TA validity in the conditional LTM according to some example embodiments of the present disclosure. As illustrated in the processes 401 and 405, a UE 410, a DU1 420, a CU 430 and a DU2 440 are involved in the process. The process in FIG. 4A and 4B may be deemed as a detailed example of the process illustrated in FIG. 3. The UE 410 may be an example of the terminal device 220 in FIG. 2, the DU1 420, CU 430 and DU2 440 may be respective examples of the DU 214-1, CU 212-1 and DU 214-2 in FIG. 2. In the processes 401 and 405, the DU1 420 may be also referred to as a source DU and the DU2 440 may be also referred to as a target DU.

[0103] As illustrated in FIG. 4 A, at step 1, the UE 410 sends an L3 measurement report to the DU1 420. The DU1 420 at step 2 sends the L3 measurement report to the CU 430 to indicate that a neighbor cell can be a good LTM candidate cell. At step 3, the network (CU 430) uses those measurements to determine that an LTM preparation can take place, e.g., decides to prepare a cell (e.g., cell 2 and / or cell 3) in DU2 440 for LTM. Then, the network does preparation of one or more LTM candidate cells. For example, at step 4, the CU 430 sends a UE context setup request for LTM preparation to the DU 440. At step 5, the DU2 440 sends a UE context setup response to the CU 430.

[0104] At step 6, the CU 430 sends a candidate LTM configuration to the source DU, e.g., in a UE context modification request. At step 7, the source DU (i.e., DU1 420) determines that the conditional LTM may be configured and configures conditional LTM conditions for the LTM candidate cell. The source DU further determines and includes a TAT configuration for the conditional LTM. The TAT configuration may indicate or comprise a mapping of TAT values to TAT indices (also referred to as a TAT value-to- index mapping) for the candidate cell.

[0105] At step 8, the source DU sends, to the CU 430, a UE context modification response for conditional LTM configuration. The UE context modification response includes the mapping of the TAT values to TAT indices for early UL synchronization. As discussed above, alternatively, the TAT value-to-index mapping may be determined by the CU 430 and indicated to source DU.

[0106] At step 9, the CU 430 sends a UE context modification request to the target node,i.e., DU2 440, to inform of the conditional LTM conditions and also the TAT value-to- index mapping. At step 10, the DU2 440 sends a UE context modification response to the CU 430. In one alternative embodiment, the target DU node (e.g., DU2 440) may use this mapping to indicate the validity duration of the TA value to the source DU (i.e., DU1 420) over source CU. In another alternative embodiment, the validity duration of the TA value for the UE 410 may be indicated to the source DU (i.e., DU1 420) irrespectively.

[0107] At step 11, the CU 430 generates an RRC configuration including an LTM configuration. The network (CU 430) may include the TAT value-to-index mapping of the corresponding candidate cell in the LTM configuration, e.g., in earlyUL-SyncConfig of the corresponding candidate cell. The mapping may be included in an LTM-candidate information element (IE) in the LTM configuration. Alternatively, the TAT value-to- index mapping may be included in a serving cell configuration. Alternatively, the mapping may be included in the serving cell group configuration. At step 12, the CU 430 sends the RRC configuration indicating the TAT value-to-index mapping to the UE 410. At step 13, the UE 410 stores the TAT value-to-index mapping. The mapping is to be used when a TA value is indicated by the source DU. The UE 410 may store the mapping until receiving a further TAT value-to-index mapping. At step 14, the UE 410 sends an RRC reconfiguration complete message to the CU 430 to acknowledge reception of the configuration.

[0108] Continuing referring to the process 405 illustrated in FIG. 4B, at step 15, the UE 410 sends a LI measurement report for the candidate cell to the DU1 420. At step 16, the network (DU1 420) determines that the UE 410 should acquire a TA value for the candidate cell and triggers acquisition of a TA value of the candidate cell. At step 17, the DU1 420 sends a PDCCH order to the UE 410. As discussed above, in one example, the TA validity (represented by the TAT index) may be indicated with the PDCCH order to the UE 410. In another example, the mapping of TAT values to TAT indices may be configured towards different candidate cells. The UE 410 may have a TAT value for each candidate cell that it can infer over the PDCCH order. For example, the mapping may be specific to each candidate cell. Alternatively, the mapping may be common to the candidate cells but different indices may be configured for different candidate cells.

[0109] At step 18, the UE 410 sends a preamble towards the candidate cell, i.e., to the target DU (DU2 440). At step 19, the DU2 440 sends a TA value that it calculates for theUE 410 over the CU 430 to source DU.

[0110] At step 20, the source DU estimates validity, i.e., a validity duration of the TA value of the UE 410 using UE mobility from the last measurements received from the UE 410. The measurements may indicate the UE movement towards the target cell, which may indicate a potential change in the TA value for the target cell. As discussed above, the propagation delay between the UE 410 and the target cell may also be used for determination of the validity duration of the TA value.[OHl] At step 21, the source DU indicates the TA value and a TAT index to the UE 410. The TAT index may be appended to an existing MAC CE cell switch command for LTM. In other words, in some examples, the cell switch command may include both the TA value and the TAT index for the UE 410. Alternatively, as discussed above, the TA value and the TAT index may be sent separately. For example, the TA value may be sent in the cell switch command for the LTM and the TAT index may be sent in association with the PDCCH order.

[0112] At step 22, upon receiving the TAT index, the UE 410 may infer that the MAC CE cell switch command is for the conditional LTM and is to provide the TA value to the UE 410 for a later use in the conditional LTM procedure. The UE 410 uses the TAT index to map to the related TAT value, and starts the TAT timer for the received TA value for the related cell. In other words, the UE 410 uses that TAT index to extract the right TAT value from the mapping that was provided in step 12 and stored in step 13, and starts the TA timer according to the value it mapped. If receiving the TAT index and the TA value in the cell switch command, the UE 410 may determine that the TA value may be used in the conditional LTM procedure. Upon receiving the TA value, the UE 410 starts the timer for the TA value to monitor the validity of the TA value.

[0113] If the TAT timer expired before the LTM condition is fulfilled, at step 23, the UE executes a RACH-based LTM. In other words, the received TA value is not valid anymore before the LTM condition is fulfilled, such that a RACH-based LTM is needed for uplink synchronization. If the TAT timer is running when the LTM condition is fulfilled, at step 24, the UE 410 executes a RACH-less LTM. In this case, since the TAT time is still running, the received TA value is valid for use.

[0114] With the processes 401 and 405 illustrated in FIG. 4A and 4B, a TAT timer is maintained at the UE side and dynamic TAT indices (and thus TAT values) can beconfigured for the UE. Longer TAT values may indicate that the TA value is valid for a longer period due to slow change of the propagation delay (fixed multi-path environment) or due to low mobility of the UE. Moreover, with the TAT value, the UE can monitor the validity of the TA value received earlier and decide to perform a RACH-less LTM or RACH-based LTM accordingly.

[0115] FIG. 5 shows a flowchart of an example method 500 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the first apparatus may be or may be included in the terminal device 220 in FIG. 2.

[0116] At block 510, the first apparatus receives, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices.

[0117] At block 520, the first apparatus determines, from the mapping, a first TAT value mapped to a first TAT index for a first cell.

[0118] At block 530, in accordance with reception of first timing advance, TA, information of the first cell from a second network node, the first apparatus starts a TA timer with the first TAT value for the first TA information of the first cell.

[0119] At block 540, the first apparatus performs access to the first cell based on whether the TA timer is expired or not.

[0120] In some example embodiments, the method 500 further comprises: receiving, from the second network node, the first TAT index for the first cell.

[0121] In some example embodiments, the first TAT index is received from the second network node in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is received from the second network node in association with the first TA information.

[0122] In some example embodiments, the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

[0123] In some example embodiments, the configuration information comprises: an LTM configuration, a serving cell configuration, or a serving cell group configuration.

[0124] In some example embodiments, the method 500 further comprises: determining, from the second mapping, a second TAT value mapped to a second TAT index for the second cell; in accordance with reception of second TA information of a second cell from the second network node, starting a second TA timer for the second TA information of the second cell with the second TAT value; and performing access to the second cell based on whether the second TA timer is expired or not.

[0125] In some example embodiments, the first apparatus is caused to perform access to the first cell by: while the TA timer is running, performing access to the first cell without initiating a random access channel (RACH) procedure towards the first cell; or upon an expiry of the TA timer, performing access to the first cell by initiating a RACH procedure towards the first cell.

[0126] In some example embodiments, the access is performed through a conditional handover or an LTM procedure.

[0127] In some example embodiments, the method 500 further comprises: starting evaluation for a conditional LTM procedure after receiving the first TAT index.

[0128] In some example embodiments, the first apparatus is or is comprised in a terminal device, and / or wherein the first network node comprises a centralized unit of a radio access network (RAN) network device, and / or wherein the second network node comprises a source distributed unit of the RAN network device for the terminal device.

[0129] FIG. 6 shows a flowchart of an example method 600 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the second apparatus may be or may be included in the DU 214 in FIG. 2.

[0130] At block 610, the second apparatus determines a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device.

[0131] At block 620, the second apparatus determines, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell.

[0132] At block 630, the second apparatus transmits, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

[0133] In some example embodiments, the second apparatus is caused to determine themapping by: in accordance with a determination that a conditional handover procedure is configured for the terminal device, determining the mapping of TAT values to TAT indices for the terminal device.

[0134] In some example embodiments, the method 600 further comprises: transmitting the determined mapping to the centralized unit of the RAN network device for the terminal device.

[0135] In some example embodiments, the method 600 further comprises: determining a validity duration of the first TA information of the first cell based on at least one of: a mobility status of the terminal device, or a propagation path between the terminal device and the first cell; and determining the first TAT value associated with the determined validity duration.

[0136] In some example embodiments, the first TAT index is transmitted to the terminal device in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is transmitted to the terminal device in association with the first TA information.

[0137] In some example embodiments, the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

[0138] In some example embodiments, the method 600 further comprises: determining a second mapping of TAT values to TAT indices associated with a second cell; determining, from the second mapping of TAT values to TAT indices, a second TAT value for second TA information of a second cell, wherein the second TAT value indicates a validity duration of the second TA information of the second cell; and transmitting, to the terminal device, the second TA information and a second TAT index mapped to the second TAT value in the second mapping.

[0139] FIG. 7 shows a flowchart of an example method 700 implemented at a third apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the third apparatus may be or may be included in the CU 212 in FIG. 3.

[0140] At block 710, the third apparatus determines a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device.

[0141] At block 720, the third apparatus transmits, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

[0142] In some example embodiments, the third apparatus is caused to transmit the configuration information by: in accordance with a determination that a conditional handover procedure is configured for the terminal device, transmitting, to the terminal device, the configuration information indicating the mapping of TAT values to TAT indices.

[0143] In some example embodiments, the third apparatus is caused to determine the mapping by: receiving the mapping from a distributed unit of a radio access network (RAN) network device for the terminal device.

[0144] In some example embodiments, the configuration information comprises: an LTM configuration, a serving cell configuration, or a serving cell group configuration.

[0145] In some example embodiments, the mapping of TAT values to TAT indices is a first mapping of TAT values to TAT indices associated with the first cell, and the configuration information further indicates a second mapping of TAT values to TAT indices associated with a second cell.

[0146] In some example embodiments, a first apparatus capable of performing any of the method 500 (for example, the terminal device 220 in FIG. 3) may comprise means for performing the respective operations of the method 500. 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 terminal device 220 in FIG. 3.

[0147] In some example embodiments, the first apparatus comprises means for receiving, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; means for determining, from the mapping, a first TAT value mapped to a first TAT index for a first cell; means for in accordance with reception of first timing advance, TA, information of the first cell from a second network node, starting a TA timer with the first TAT value for the first TA information of the first cell; and means for performing access to the first cell based on whether the TA timer is expired or not.

[0148] In some example embodiments, the first apparatus further comprises: means forreceiving, from the second network node, the first TAT index for the first cell.

[0149] In some example embodiments, the first TAT index is received from the second network node in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is received from the second network node in association with the first TA information.

[0150] In some example embodiments, the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

[0151] In some example embodiments, the configuration information comprises: an LTM configuration, a serving cell configuration, or a serving cell group configuration.

[0152] In some example embodiments, the first apparatus further comprises: means for determining, from the second mapping, a second TAT value mapped to a second TAT index for the second cell; means for in accordance with reception of second TA information of a second cell from the second network node, starting a second TA timer for the second TA information of the second cell with the second TAT value; and means for performing access to the second cell based on whether the second TA timer is expired or not.

[0153] In some example embodiments, the means for performing access to the first cell may comprise means for while the TA timer is running, performing access to the first cell without initiating a random access channel (RACH) procedure towards the first cell; or means for upon an expiry of the TA timer, performing access to the first cell by initiating a RACH procedure towards the first cell.

[0154] In some example embodiments, the access is performed through a conditional handover or an LTM procedure.

[0155] In some example embodiments, the first apparatus further comprises: means for starting evaluation for a conditional LTM procedure after receiving the first TAT index.

[0156] In some example embodiments, the first apparatus is or is comprised in a terminal device, and / or wherein the first network node comprises a centralized unit of a radio access network (RAN) network device, and / or wherein the second network node comprises a source distributed unit of the RAN network device for the terminal device.

[0157] In some example embodiments, a second apparatus capable of performing any of the method 600 (for example, the DU 214 in FIG. 3) may comprise means for performing the respective operations of the method 600. 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 DU 214 in FIG. 3.

[0158] In some example embodiments, the second apparatus comprises means for determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; means for determining, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell; and means for transmitting, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

[0159] In some example embodiments, the means for determining the mapping may comprise means for in accordance with a determination that a conditional handover procedure is configured for the terminal device, determining the mapping of TAT values to TAT indices for the terminal device.

[0160] In some example embodiments, the second apparatus may further comprise means for transmitting the determined mapping to the centralized unit of the RAN network device for the terminal device.

[0161] In some example embodiments, the second apparatus may further comprise: means for determining a validity duration of the first TA information of the first cell based on at least one of a mobility status of the terminal device, or a propagation path between the terminal device and the first cell; and means for determining the first TAT value associated with the determined validity duration.

[0162] In some example embodiments, the first TAT index is transmitted to the terminal device in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is transmitted to the terminal device in association with the first TA information.

[0163] In some example embodiments, the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

[0164] In some example embodiments, the second apparatus further comprises: means for determining a second mapping of TAT values to TAT indices associated with a second cell; means for determining, from the second mapping of TAT values to TAT indices, a second TAT value for second TA information of a second cell, wherein the second TAT value indicates a validity duration of the second TA information of the second cell; and means for transmitting, to the terminal device, the second TA information and a second TAT index mapped to the second TAT value in the second mapping.

[0165] In some example embodiments, a third apparatus capable of performing any of the method 700 (for example, the CU 212 in FIG. 3) 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 third apparatus may be implemented as or included in the CU 212 in FIG. 3.

[0166] In some example embodiments, the third apparatus comprises means for determining a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; and means for transmitting, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

[0167] In some example embodiments, the means for transmitting the configuration information may comprise means for in accordance with a determination that a conditional handover procedure is configured for the terminal device, transmitting, to the terminal device, the configuration information indicating the mapping of TAT values to TAT indices.

[0168] In some example embodiments, the means for determining the mapping may comprise means for receiving the mapping from a distributed unit of a radio access network (RAN) network device for the terminal device.

[0169] In some example embodiments, the configuration information comprises: an LTM configuration, a serving cell configuration, or a serving cell group configuration.

[0170] In some example embodiments, the mapping of TAT values to TAT indices is a first mapping of TAT values to TAT indices associated with the first cell, and the configuration information further indicates a second mapping of TAT values to TAT indices associated with a second cell.

[0171] FIG. 8 is a simplified block diagram of a device 800 that is suitable forimplementing example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the terminal device 220 or the network device 210 as shown in FIG. 1. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

[0172] The communication module 840 is for bidirectional communications. The communication module 840 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 840 may include at least one antenna.

[0173] The processor 810 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 800 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.

[0174] The memory 820 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) 824, 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 randomaccess memory (RAM) 822 and other volatile memories that will not last in the powerdown duration.

[0175] A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The instructions of the program 830 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 830 may be stored in the memory, e.g., the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

[0176] The example embodiments of the present disclosure may be implemented bymeans of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIG. 3 to FIG. 7. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0177] In some example embodiments, the program 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 for execution. In some example embodiments, the computer readable 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).

[0178] FIG. 9 shows an example of the computer readable medium 900 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 900 has the program 830 stored thereon.

[0179] 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.

[0180] 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.

[0181] 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 partly on a remote machine or entirely on the remote machine or server.

[0182] 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.

[0183] 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 randomaccess memory (RAM), a read-only memory (ROM), an erasable programmable readonly memory (EPROM or Flash memory), an optical fiber, a portable compact disc readonly memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0184] 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 desirableresults. 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.

[0185] 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

WHAT IS CLAIMED IS1. 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 at least to: receive, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; determine, from the mapping, a first TAT value mapped to a first TAT index for a first cell; in accordance with reception of first timing advance, TA, information of the first cell from a second network node, start a TA timer with the first TAT value for the first TA information of the first cell; and perform access to the first cell based on whether the TA timer is expired or not.

2. The first apparatus of claim 1, wherein the first apparatus is further caused to: receive, from the second network node, the first TAT index for the first cell.

3. The first apparatus of claim 2, wherein the first TAT index is received from the second network node in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is received from the second network node in association with the first TA information.

4. The first apparatus of claim 2 or 3, wherein the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

5. The first apparatus of any of claims 1 to 4, wherein the configuration information comprises: an LTM configuration,35a serving cell configuration, or a serving cell group configuration.

6. The first apparatus of any of claims 1 to 5, wherein the mapping of TAT values to TAT indices is a first mapping of TAT values to TAT indices associated with the first cell, and the configuration information further indicates a second mapping of TAT values to TAT indices associated with a second cell, and wherein the first apparatus is further caused to: determine, from the second mapping, a second TAT value mapped to a second TAT index for the second cell; in accordance with reception of second TA information of a second cell from the second network node, start a second TA timer for the second TA information of the second cell with the second TAT value; and perform access to the second cell based on whether the second TA timer is expired or not.

7. The first apparatus of any of claims 1 to 6, wherein the first apparatus is caused to perform access to the first cell by: while the TA timer is running, performing access to the first cell without initiating a random access channel (RACH) procedure towards the first cell; or upon an expiry of the TA timer, performing access to the first cell by initiating a RACH procedure towards the first cell.

8. The first apparatus of claim 7, wherein the access is performed through a conditional handover or an LTM procedure.

9. The first apparatus of any of claim 1 to 8, wherein the first apparatus is further caused to: start evaluation for a conditional LTM procedure after receiving the first TAT index.

10. The first apparatus of any of claims 1 to 9, wherein the first apparatus is or is comprised in a terminal device, and / or wherein the first network node comprises a centralized unit of a radio access36network (RAN) network device, and / or wherein the second network node comprises a source distributed unit of the RAN network device for the terminal device.

11. 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 apparatus at least to: determine a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; determine, from the mapping of TAT values to TAT indices, a first TAT value for first TA information of a first cell; and transmit, to the terminal device, the first TA information and a first TAT index mapped to the first TAT value in the mapping.

12. The second apparatus of claim 11, wherein the second apparatus is caused to determine the mapping by: in accordance with a determination that a conditional handover procedure is configured for the terminal device, determining the mapping of TAT values to TAT indices for the terminal device.

13. The second apparatus of claim 11 or 12, wherein the second apparatus is caused to determine the mapping by: receiving the mapping from a centralized unit of a radio access network (RAN) network device for the terminal device, or wherein the second apparatus is further caused to: transmit the determined mapping to the centralized unit of the RAN network device for the terminal device.

14. The second apparatus of any of claims 11 to 13, wherein the second apparatus is further caused to: determine a validity duration of the first TA information of the first cell based on at least one of: a mobility status of the terminal device, or a propagation path between the terminal device and the first cell; and determine the first TAT value associated with the determined validity duration.

15. The second apparatus of any of claims 11 to 14, wherein the first TAT index is transmitted to the terminal device in association with a physical downlink control channel, PDCCH, order, or wherein the first TAT index is transmitted to the terminal device in association with the first TA information.

16. The second apparatus of any of claims 11 to 15, wherein the first TAT index is appended to a cell switch command for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) procedure or a conditional LTM procedure.

17. The second apparatus of any of claims 11 to 16, wherein the mapping of TAT values to TAT indices is a first mapping of TAT values to TAT indices associated with the first cell, and wherein the second apparatus is further caused to: determine a second mapping of TAT values to TAT indices associated with a second cell; determine, from the second mapping of TAT values to TAT indices, a second TAT value for second TA information of a second cell, wherein the second TAT value indicates a validity duration of the second TA information of the second cell; and transmit, to the terminal device, the second TA information and a second TAT index mapped to the second TAT value in the second mapping.

18. A third apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: determine a mapping of timing alignment timer, TAT, values to TAT indices for a terminal device; and transmit, to the terminal device, configuration information indicating the mapping of TAT values to TAT indices.

19. The third apparatus of claim 18, wherein the second apparatus is caused to transmit the configuration information by: in accordance with a determination that a conditional handover procedure isconfigured for the terminal device, transmitting, to the terminal device, the configuration information indicating the mapping of TAT values to TAT indices.

20. The third apparatus of claim 18 or 19, wherein the second apparatus is caused to determine the mapping by: receiving the mapping from a distributed unit of a radio access network (RAN) network device for the terminal device.

21. The third apparatus of any of claims 18 to 20, wherein the configuration information comprises: an LTM configuration, a serving cell configuration, or a serving cell group configuration.

22. The third apparatus of any of claims 18 to 21, wherein the mapping of TAT values to TAT indices is a first mapping of TAT values to TAT indices associated with the first cell, and the configuration information further indicates a second mapping of TAT values to TAT indices associated with a second cell.

23. A method comprising: receiving, from a first network node, configuration information indicating a mapping of timing alignment timer, TAT, values to TAT indices; determining, from the mapping, a first TAT value mapped to a first TAT index for a first cell; in accordance with reception of first timing advance, TA, information of the first cell from a second network node, start a TA timer with the first TAT value for the first TA information of the first cell; and performing access to the first cell based on whether the TA timer is expired or not.

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