Devices, methods, apparatuses, and computer readable media for timing advance

Abstract

Disclosed are devices, methods, apparatuses, and computer readable media for timing advance An example apparatus for a terminal device may include at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, may cause the apparatus at least to: receive from a source cell in preparation for a cell change, a message comprising a timing advance, TA, estimated by a target cell; track the TA; and update the TA according to the tracking of the TA.

Description

DEVICES, METHODS, APPARATUSES, AND COMPUTER READABLE MEDIA OR TIMING ADVANCETECHNICAL FIELD

[0001] Various example embodiments relate to devices, methods, apparatuses, and computer readable media for timing advance (TA).BACKGROUND

[0002] A TA is a value used by a user equipment (UE) to know the UE shall advance its uplink (UL) transmissions to ensure that network (NW) receives the UL transmissions from the UE within an expected reception window. UL transmissions without a correct TA will cause UL interference at the NW side and thus reduce an overall performance of communication systems. An early synchronization procedure, or referred to as an early TA acquisition procedure, has been introduced in a cell change, for example, a Layer 1 (LI) / Layer 2 (L2) cell switch, Layer 3 (L3) handover (HO), etc. Before the cell change, a target cell estimates the TA based on a received preamble from the UE and shares the TA with a current source cell of the UE, and the source cell transmits the TA to the UE. The estimated TA remains valid for a limited time, and the source cell has no means of checking the validity of the estimated TA. So, currently, the network relies on using the estimated TA immediately, for example, the source cell includes the estimated TA in a command for cell change right after receiving the estimated TA, and thus the network is forced to execute the cell change right after receiving the estimated TA from the target cell, which causes complexity and strict timing requirements to the network.SUMMARY

[0003] A brief summary of exemplary embodiments is provided below to provide basic understanding of some aspects of various embodiments. It should be noted that this summary is not intended to identify key features of essential elements or define scopes of the embodiments, and its sole purpose is to introduce some concepts in a simplified form as a preamble for a more detailed description provided below.

[0004] In a first aspect, disclosed is an apparatus for a terminal device. The apparatus mayinclude at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, may cause the apparatus at least to: receive from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; track the TA; and update the TA according to the tracking of the TA.

[0005] In a second aspect, disclosed is an apparatus for a network device. The apparatus may include at least one processor and at least one memory. The at least one memory may store instructions that, when executed by the at least one processor, may cause the apparatus as a source cell in preparation for a cell change of a terminal device at least to: transmit to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0006] In a third aspect, disclosed is a method performed by an apparatus for a terminal device. The method may comprise: receiving from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; tracking the TA; and updating the TA according to the tracking of the TA.

[0007] In a fourth aspect, disclosed is a method performed by an apparatus for a network device, the apparatus functioning as a source cell in preparation for a cell change of a terminal device. The method may comprise: transmitting to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0008] In a fifth aspect, disclosed is an apparatus for a terminal device. The apparatus may comprise: means for receiving from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; means for tracking the TA; and means for updating the TA according to the tracking of the TA.

[0009] In a sixth aspect, disclosed is an apparatus for a network device, the apparatus functioning as a source cell in preparation for a cell change of a terminal device. The apparatus may comprise: means for transmitting to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0010] In a seventh aspect, a computer-readable medium is disclosed. The computer-readable medium may comprise program instructions that, when executed by an apparatus for a terminaldevice, may cause the apparatus at least to: receive from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; track the TA; and update the TA according to the tracking of the TA.

[0011] In an eighth aspect, a computer-readable medium is disclosed. The computer-readable medium may comprise program instructions that, when executed by an apparatus for a network device, may cause the apparatus as a source cell in preparation for a cell change of a terminal device at least to: transmit to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0012] Other features and advantages of the example embodiments of the present disclosure will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of example embodiments of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Some example embodiments will now be described, by way of non-limiting examples, with reference to the accompanying drawings.

[0014] FIG. 1 shows an example sequence diagram according to the example embodiments of the present disclosure.

[0015] FIG. 2 shows a flow chart illustrating an example method 200 for TA according to the example embodiments of the present disclosure.

[0016] FIG. 3 shows a flow chart illustrating an example method 300 for TA according to the example embodiments of the present disclosure.

[0017] FIG. 4 shows a block diagram illustrating an example device 400 for TA according to the example embodiments of the present disclosure.

[0018] FIG. 5 shows a block diagram illustrating an example device 500 for TA according to the example embodiments of the present disclosure.

[0019] FIG. 6 shows a block diagram illustrating an example apparatus 600 for TA according to the example embodiments of the present disclosure.

[0020] FIG. 7 shows a block diagram illustrating an example apparatus 700 for TA accordingto the example embodiments of the present disclosure.

[0021] Throughout the drawings, same or similar reference numbers indicate same or similar elements. A repetitive description on the same elements would be omitted.DETAILED DESCRIPTION

[0022] Herein below, some example embodiments are described in detail with reference to the accompanying drawings. The following description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known circuits, techniques and components are shown in block diagram form to avoid obscuring the described concepts and features.

[0023] Example embodiments of the present disclosure provide solutions which can relax the strict timing requirements in a cell change using the early TA acquisition. The example embodiments of the present disclosure may apply in cell switch, handover, etc. The cell switch may comprise a lower layer, e.g., LI, L2, triggered mobility (LTM) cell switch, a conditional cell switch, a conditional LTM cell switch etc., and the handover may comprise a conventional L3 handover, a conditional handover, etc.

[0024] FIG. 1 shows an example sequence diagram according to the example embodiments of the present disclosure. Referring to FIG. 1, a UE 110 may represent any terminal device in a network, and a network device 150 may represent the network side serving the UE 110. The network device 150 may function as a source cell 155 in preparation for a cell change of the UE 110, and the network device 150 may be a base station (BS), such as an Evolved Node B (eNB), a next Generation Node B (gNB), etc. A cell 180 may represent a candidate cell and a target cell in the cell change of the UE 110.

[0025] In preparation for the cell change, it is assumed that the UE 110 is in radio resource control (RRC) connected mode with the source cell 155. The UE 110 may transmit a measurement report to the source cell 155, and the measurement report may comprise, for example, measured results for the candidate cell 180. Then, the source cell 155 and possibly the BS supporting the cell 180 prepares the candidate cell 180, and the source cell 155 may transmit to the UE 110 the configuration of the candidate cell 180, for example, using an RRCreconfiguration message. Receiving the configuration of the candidate cell 180, the UE 110 may acknowledge the configuration, for example, using an RRC reconfiguration complete message.

[0026] In an operation 114, the network, e.g., the source cell 155, may initiate an early TA acquisition, or referred to as early synchronization, for the candidate cell 180 towards the UE 110.

[0027] Before the UE 110 can perform the early TA acquisition, in an operation 116, the UE 110 may acquire downlink (DL) synchronization and proper time tracking of the candidate cell 180. For example, the UE 110 may receive one or more DL tracking reference signals from the candidate cell 180, and the DL tracking reference signals may be, for example, synchronization signal block (SSB) or referred to as synchronization signal and physical broadcast channel (PBCH) block (SSB). If the UE 110 has acquired the necessary DL tracking, the UE 110 may transmit, for example, a measurement report to the source cell 155. The measurement report may comprise measured results for the candidate cell 180. In an embodiment, the measurement report is a LI measurement report.

[0028] Assuming that the candidate cell 180 is determined to be the target cell of the cell change, in an operation 118, the UE 110 may acquire UL synchronization with the target cell 180. The source cell 155 may transmit to the UE 110, for example, a physical downlink control channel (PDCCH) order 156 ordering the UE 110 to transmit a preamble 120 to the target cell 180. Information on the target cell 180 and the preamble 120 are given in the PDCCH order 156. Then, the UE 110 may retune away from the source cell 155 (if needed) to the target cell 180 and transmit the preamble 120 to the identified target cell 180. When the preamble 120 has been transmitted, the UE 110 may retune back to the source cell 155 and continue operations. The target cell 180 may estimate / measure / determine (these terms for getting the TA 182 are interchangeable in the present disclosure, and this operation will be referred to as “estimate” hereinafter) a TA 182 based on the received preamble 120 and transmit the estimated TA 182, denoted as TAtarget cell, to the source cell 155.

[0029] As the source cell in preparation for the cell change of the UE 110, in case of using the early TA acquisition, the source cell 155 does not need to include the estimated TA 182 in the command for the cell change and transmit the command to the UE 110 immediately after receiving the estimated TA 182. According to the example embodiments of the present disclosure,the source cell 155 may transmit to the UE 110, a message 158 comprising the TA 182 estimated by the target cell 180. In some embodiments, the source cell 155 may transmit the message 158 via a medium access control (MAC) or RRC signaling, or other signaling.

[0030] Receiving the message 158, the UE 110 may transmit to the source cell 155 an acknowledgement in response to the message 158, and the acknowledgement may be transmitted on the same protocol layer as the message 158, such as MAC or RRC signaling, or other signaling. Receiving the message 158, in an operation 122, the UE 110 may track the TA 182. In some embodiments, the message 158 comprising the TA 182 may require the UE 110 to track the TA 182. In some embodiments, the message 158 may comprise a first indication 160 explicitly indicating the UE 110 to track the TA 182.

[0031] In some embodiments, the UE 110 may track the TA 182 by measuring one or more reference signals (RSs) for time tracking from the target cell 180. The RS may be SSB or other suitable DL RS. For example, the UE 110 may track the TA 182 based on DL frame timing from the target cell 180. After tracking the TA 182, in an operation 124, the UE 110 may update the TA 182 according to the tracking of the TA 182. The updated TA may be the TA 182 plus autonomous timing adjustment by the UE 110. The updated TA may be denoted as TAtarget cell tracked, and TAtarget cell tracked = TAtarget cell + UE autonomous timing adjustment. Note that the adjustment may be a reduction operation as well, depending on the measurement with respect to the current TA.

[0032] In some embodiments, the tracking of the TA by the UE 110 may be controlled via a duration or a number of times. The duration may be a (pre-)defined time period during which the UE 110 will track the TA, e.g. from the start of the tracking or from the start of the reception of the message 158. Alternatively, the UE 110 may perform the tracking of the TA, e.g. N times, and N is a positive integer. The duration or the number of times may be defined in standard specification. Alternatively or additionally, in some embodiments, the UE 110 may receive from the source cell 155, a second indication 162 indicating the duration or the number of times for the UE 110 to track the TA. The UE 110 may continue receiving the suitable DL RS from the target cell 180, and thus the UE 110 can keep tracking of and updating the TAtarget cell tracked. Those skilled in the art may understand that the initially TA to be tracked and updated is the TA 182, and the TA may be continuously tracked and updated in the UE 110. The second indication162 may be separate from the message 158 or comprised in the message 158.

[0033] In some embodiments, the UE 110 may transmit to the source cell 155, for example, an LI measurement report comprising measured results for the target cell 180, which may trigger the source cell 155 to request the cell change of the UE 110.

[0034] In some embodiments, in an operation 164, the source cell 155 may determine whether the TA is valid in the UE 110. For example, the source cell 155 may assume that the TA is valid in the UE 110 during the duration the UE 110 is required to track the TA.

[0035] In case of determining the TA is valid in the UE 110, the source cell 155 may transmit to the UE 110, a command 166, without a TA for the target cell 180, for the cell change to the target cell 180. The command 166 may comprise information for the UE 110 to identify the target cell 180 and does not need to comprise the TA for the target cell 180 since the UE 110 has a valid TA for the target cell 180. In some embodiments, the command 166 may comprise an indication explicitly indicating the UE 110 to use the updated TATAtarget cell tracked. The command 166 may be transmitted via, e.g., an MAC control element (MAC CE).

[0036] It may be noted that the command 166 is after the message 158, and thus the cell change according to the present disclosure allows more relaxed timing constraint. Receiving the command 166, the UE 110 may transmit to the source cell 155 an acknowledgement in response to the command 166.

[0037] In case the command 166 does not comprise the TA for the target cell 180 and the updated TAis valid, in an operation 128, the UE 110 may access the target cell 180 applying the updated TA. In some embodiments, the UE 110 may assume that the TA is valid in the UE 110 during the duration the UE 110 is required to track the TA. In case the UE 110 accesses the target cell 180 and applies the updated TA in the access, the UE 110 may access the target cell 180 not using random access channel (RACH), which means no preamble used and no random access procedure with TA estimation, and thus such cell change may be termed as RACH-less cell change.

[0038] In some embodiments, the command 166 may comprise a TA for the target cell 180. In case the command 166 comprises a TA 168 for the target cell 180, in an operation 130, the UE 110 may access the target cell 180 and apply in the access the TA 168 received in the command 166. In this case too, the UE 110 may access the target cell 180 using an RACH-less cell changesince the UE 110 has the TA 168 and needs not to perform the TA estimation via the random access procedure. In some embodiments, the UE 110 may apply the TA 168 received in the command 166, even if the updated TA is valid in the UE 110. In some embodiments, if the command 166 comprises the TA 168, the UE 110 may apply the TA 168 and does not need to determine whether the tracked and updated TA is valid or invalid.

[0039] In some embodiments, the command 166 may comprise a third indication 170 indicating the UE 110 to access the target cell 180 using an RACH-based cell change, and in this case, the UE 110 may access the target cell 180 using the RACH-based cell change. In some embodiments, receiving the third indication 170, the UE 110 may perform the RACH-based cell change, even if the tracked and updated TA is valid in the UE 110. In some embodiments, receiving the third indication 170, the UE 110 may perform the RACH-based cell change and estimates the TA via the random access procedure, and does not need to determine whether the updated TA is valid or invalid.

[0040] In some embodiments, the UE 110 may be configured with a conditional cell change, for example, a conditional LTM cell switch, or a conditional HO (CHO), etc. In case the cell change is the conditional cell change, the command 166 is not necessary, and after receiving the message 158 from the source cell 155, in an operation 126, the UE 110 may determine whether a condition for the conditional cell change is met. In case of determining the condition for the conditional cell change is met, the UE 110 perform the cell change without a cell change command to the target cell 180. In case the updated TA is valid in the UE 110, in the operation 128, the UE 110 may access the target cell 180 applying the updated TA. In this case, the UE 110 may access the target cell 180 using an RACH-less cell change.

[0041] No matter whether the cell change is based on the command 166 or is the conditional cell change, the UE 110 may fail to track the TA. In some embodiments, in case of failing to track the TA, the UE 110 may report to the source cell 155 that there is no valid TA in the UE 110. For example, the UE 110 may transmit to the source cell 155 a report 132 that there is no valid TA in the UE 110.

[0042] In response to the report 132, in an operation 172, the source cell 155 may initiate an early TA acquisition for the target cell 180 towards the UE 110. During the early TA acquisition, the source cell 155 may transmit to the UE 110 an RACH preamble 174 for the early TAacquisition for the target cell 180. After receiving from the source cell 155 the RACH preamble 174 in response to the reporting, by transmitting the RACH preamble 174 to the target cell 180, the UE 110 may get another TA estimated by the target cell 180.

[0043] In some embodiments, the UE 110 may track and update the TA and, when executing the cell change, access the target cell 180 using an RACH-less cell change. Alternatively, in some embodiments, in an operation 134, the UE 110 may access the target cell 180 using an RACH- based cell change.

[0044] Alternatively, in some embodiments, in case of failing to track the TA, the UE 110 may directly perform the operation 134. For example, when failing to track the TA, the UE 110 may access the target cell 180 using an RACH-based cell change without sending the report 132.

[0045] In some embodiments, the network may assume, or based on capability signaling, the UE 110 to have capability to support the tracking of the TA, and the source cell 155 may require the UE 110 to track and update the TA estimated by the target cell 180. Alternatively, in some embodiments, the UE 110 may transmit to the source cell 155, a fourth indication 112 indicating whether the UE 110 has the capability to support the tracking of the TA. In case the fourth indication 112 indicating the UE 110 has the capability to support the tracking of the TA, the UE 110 may transmit the message 158 indicating the UE 110 to track and update the TA estimated by the target cell 180.

[0046] After the cell change in which the UE 110 retunes from the current source cell 155 to the target cell 180 as a new cell, there may be an interruption period during which the UE 110 cannot be scheduled by the network. The actual interruption time depends on multiple parameters and UE conditions.

[0047] Taking the LTM cell switch as an example, the interruption time after the LTM cell switch is denoted as TLTM -interrupt, and TLTM -interrupt TLTM-RRC-processing TLTM-processing + Tfirst-RS +

[0048] TLTM-RRe-processing is the time for configuration processing, for example, abstract syntax notation one (ASN.l) decoding and validity / compliance check.

[0049] TLTM -processing is the time for UE processing, consisting of applying the target cell configuration parameters and L1 / L2 change.

[0050] Tfirst-RS is the time for fine time tracking and acquiring full timing information of thetarget cell.

[0051] TRs-proc is the time for SSB processing. TLTM-IU is the interruption uncertainty during LTM cell switch.

[0052] For RACH-based LTM cell switch, TLTM-IU is the interruption uncertainty in acquiring the first available physical random access channel (PRACH) occasion in the new cell.

[0053] For RACH-less LTM cell switch, TLTM-IU is the uncertainty on transmitting the first uplink transmission on the target cell.

[0054] Hence, whether the UE has a valid TA at the LTM switch has impact on TLTM-IU and has a larger impact in terms of not having to perform an RACH procedure in the target cell. Not having to perform an RACH procedure in accessing the target cell after the cell switch can reduce the interruption time.

[0055] Thus, according to the example embodiments of the present disclosure, the timing requirements in the cell change using the early TA acquisition can be relaxed. Further, because the UE performs a TA measurement towards the target cell before the cell change command and updates the initial TA accordingly, the UE can be in synchronization with the target cell, such that the interruption time can be reduced.

[0056] FIG. 2 shows a flow chart illustrating an example method 200 for TA according to the example embodiments of the present disclosure. The example method 200 may be performed, for example, by an apparatus for a terminal device, such as the UE 110 above mentioned.

[0057] Referring to FIG. 2, the example method 200 may comprise: an operation 210 of receiving from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; an operation 220 of tracking the TA; and an operation 230 of updating the TA according to the tracking of the TA.

[0058] In some embodiments, the message may comprise a first indication indicating the terminal device to track the TA.

[0059] In some embodiments, the example method 200 may comprise: receiving from the source cell, a second indication indicating a duration or a number of times for the terminal device to track the TA; and tracking the TA for the duration or the number of times.

[0060] In some embodiments, the example method 200 may comprise: tracking the TA by measuring one or more reference signals for time tracking from the target cell.

[0061] In some embodiments, the example method 200 may comprise: receiving after the message and from the source cell, a command for the cell change to the target cell.

[0062] In some embodiments, the example method 200 may comprise: in case the command does not comprise a TA for the target cell and the updated TA is valid, accessing the target cell applying the updated TA.

[0063] In some embodiments, the example method 200 may comprise: in case the command comprises a TA for the target cell, accessing the target cell applying the TA comprised in the command.

[0064] In some embodiments, the example method 200 may comprise: in case the command comprises a third indication indicating the terminal device to access the target cell using an RACH-based cell change, accessing the target cell using the RACH-based cell change.

[0065] In some embodiments, the cell change may be a conditional cell change, and the example method 200 may comprise: after receiving the message from the source cell, determining whether a condition for the conditional cell change is met; and performing the cell change without a cell change command to the target cell in case of determining the condition for the conditional cell change is met.

[0066] In some embodiments, the example method 200 may comprise: in case the updated TA is valid, accessing the target cell applying the updated TA.

[0067] In some embodiments, the example method 200 may comprise: in case of failing to track the TA, reporting to the source cell that there is no valid TA in the terminal device.

[0068] In some embodiments, the example method 200 may comprise: receiving from the source cell, an RACH preamble for an early TA acquisition for the target cell in response to the reporting.

[0069] In some embodiments, the example method 200 may comprise: in case of failing to track the TA, accessing the target cell using an RACH-based cell change.

[0070] In some embodiments, the example method 200 may comprise: transmitting to the source cell, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

[0071] In some embodiments, the cell change may be a cell switch.

[0072] FIG. 3 shows a flow chart illustrating an example method 300 for TA according to the nexample embodiments of the present disclosure. The example method 300 may be performed, for example, by an apparatus for a network device, such as the network device 150 above mentioned, the apparatus functioning as a source cell in preparation for a cell change of a terminal device.

[0073] Referring to FIG. 3, the example method 300 may comprise: an operation 310 of transmitting to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0074] In some embodiments, the example method 300 may comprise: transmitting to the terminal device, a second indication indicating a duration or a number of times for the terminal device to track the TA.

[0075] In some embodiments, the example method 300 may comprise: determining whether the TA is valid in the terminal device; and in case of determining the TA is valid in the terminal device, transmitting to the terminal device, a command, without a TA for the target cell, for cell change to the target cell.

[0076] In some embodiments, the example method 300 may comprise: in case of receiving from the terminal device a report that there is no valid TA in the terminal device, initiating an early TA acquisition for the target cell towards the terminal device in response to the report.

[0077] In some embodiments, the example method 300 may comprise: receiving from the terminal device, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

[0078] FIG. 4 shows a block diagram illustrating an example device 400 for TA according to the example embodiments of the present disclosure. The device, for example, may be at least part of an apparatus for a terminal device, such as the UE 110 in the above examples.

[0079] As shown in FIG. 4, the example device 400 may include at least one processor 410 and at least one memory 420 that may store instructions 430. The instructions 430, when executed by the at least one processor 410, may cause the device 400 at least to perform the example method 200 described above.

[0080] In various example embodiments, the at least one processor 410 in the example device 400 may include, but is not limited to, at least one hardware processor, including at least one microprocessor such as a central processing unit (CPU), a portion of at least one hardwareprocessor, and any other suitable dedicated processor such as those developed based on for example Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC). Further, the at least one processor 410 may also include at least one other circuitry or element not shown in FIG. 4.

[0081] In various example embodiments, the at least one memory 420 in the example device 400 may include at least one storage medium in various forms, such as a transitory memory and / or a non-transitory memory. The transitory memory may include, but is not limited to, for example, a random-access memory (RAM), a cache, and so on. The non-transitory memory may include, but is not limited to, for example, a read-only memory (ROM), a hard disk, a flash memory, and so on. 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). Further, the at least memory 420 may include, but is not limited to, an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[0082] Further, in various example embodiments, the example device 400 may also include at least one other circuitry, element, and interface, for example at least one I / O interface, at least one antenna element, and the like.

[0083] In various example embodiments, the circuitries, parts, elements, and interfaces in the example device 400, including the at least one processor 410 and the at least one memory 420, may be coupled together via any suitable connections including, but is not limited to, buses, crossbars, wiring and / or wireless lines, in any suitable ways, for example electrically, magnetically, optically, electromagnetically, and the like.

[0084] It is understood that the structure of the device on the side of the UE 110 is not limited to the above example device 400.

[0085] FIG. 5 shows a block diagram illustrating an example device 500 for TA according to the example embodiments of the present disclosure. The device, for example, may be at least part of an apparatus for a network device, such as the network device 150 in the above examples, the apparatus functioning as a source cell in preparation for a cell change of a terminal device.

[0086] As shown in FIG. 5, the example device 500 may include at least one processor 510 and at least one memory 520 that may store instructions 530. The instructions 530, when executedby the at least one processor 510, may cause the device 500 at least to perform the example method 300 described above.

[0087] In various example embodiments, the at least one processor 510 in the example device 500 may include, but is not limited to, at least one hardware processor, including at least one microprocessor such as a central processing unit (CPU), a portion of at least one hardware processor, and any other suitable dedicated processor such as those developed based on for example Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC). Further, the at least one processor 510 may also include at least one other circuitry or element not shown in FIG. 5.

[0088] In various example embodiments, the at least one memory 520 in the example device 500 may include at least one storage medium in various forms, such as a transitory memory and / or a non-transitory memory. The transitory memory may include, but is not limited to, for example, a random-access memory (RAM), a cache, and so on. The non-transitory memory may include, but is not limited to, for example, a read-only memory (ROM), a hard disk, a flash memory, and so on. 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). Further, the at least memory 520 may include, but is not limited to, an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[0089] Further, in various example embodiments, the example device 500 may also include at least one other circuitry, element, and interface, for example at least one I / O interface, at least one antenna element, and the like.

[0090] In various example embodiments, the circuitries, parts, elements, and interfaces in the example device 500, including the at least one processor 510 and the at least one memory 520, may be coupled together via any suitable connections including, but is not limited to, buses, crossbars, wiring and / or wireless lines, in any suitable ways, for example electrically, magnetically, optically, electromagnetically, and the like.

[0091] It is understood that the structure of the device on the side of the network device 150 is not limited to the above example device 500.

[0092] FIG. 6 shows a block diagram illustrating an example apparatus 600 for cellmeasurements according to the example embodiments of the present disclosure. The apparatus, for example, may be at least part of a terminal device, such as the UE 110 in the above examples.

[0093] As shown in FIG. 6, the example apparatus 600 may comprise: means 610 for receiving from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; means 620 for tracking the TA; and means 630 for updating the TA according to the tracking of the TA.

[0094] In some embodiments, the message may comprise a first indication indicating the terminal device to track the TA.

[0095] In some embodiments, the apparatus 600 may comprise: means for receiving from the source cell, a second indication indicating a duration or a number of times for the terminal device to track the TA; and means for tracking the TA for the duration or the number of times.

[0096] In some embodiments, the apparatus 600 may comprise: means for tracking the TA by measuring one or more reference signals for time tracking from the target cell.

[0097] In some embodiments, the apparatus 600 may comprise: means for receiving after the message and from the source cell, a command for the cell change to the target cell.

[0098] In some embodiments, the apparatus 600 may comprise: means for in case the command does not comprise a TA for the target cell and the updated TA is valid, accessing the target cell applying the updated TA.

[0099] In some embodiments, the apparatus 600 may comprise: means for in case the command comprises a TA for the target cell, accessing the target cell applying the TA comprised in the command.

[0100] In some embodiments, the apparatus 600 may comprise: means for in case the command comprises a third indication indicating the terminal device to access the target cell using an RACH-based cell change, accessing the target cell using the RACH-based cell change.

[0101] In some embodiments, the cell change may be a conditional cell change, and the apparatus 600 may comprise: means for after receiving the message from the source cell, determining whether a condition for the conditional cell change is met; and means for performing the cell change without a cell change command to the target cell in case of determining the condition for the conditional cell change is met.

[0102] In some embodiments, the apparatus 600 may comprise: means for in case the updatedTA is valid, accessing the target cell applying the updated TA.

[0103] In some embodiments, the apparatus 600 may comprise: means for in case of failing to track the TA, reporting to the source cell that there is no valid TA in the terminal device.

[0104] In some embodiments, the apparatus 600 may comprise: means for receiving from the source cell, an RACH preamble for an early TA acquisition for the target cell in response to the reporting.

[0105] In some embodiments, the apparatus 600 may comprise: means for in case of failing to track the TA, accessing the target cell using an RACH-based cell change.

[0106] In some embodiments, the apparatus 600 may comprise: means for transmitting to the source cell, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

[0107] In some embodiments, the cell change may be a cell switch.

[0108] In some example embodiments, examples of means in the example apparatus 600 may include circuitries. For example, an example of means 610 may include a circuitry configured to perform the operation 210 of the example method 200, an example of means 620 may include a circuitry configured to perform the operation 220 of the example method 200, and an example of means 630 may include a circuitry configured to perform the operation 230 of the example method 200.

[0109] The example apparatus 600 may further include means comprising circuitry configured to perform the example method 200. In some example embodiments, examples of means may also include software modules and any other suitable function entities.

[0110] FIG. 7 shows a block diagram illustrating an example apparatus 700 for cell measurements according to the example embodiments of the present disclosure. The apparatus, for example, may be at least part of a network device, such as the network device 150 in the above examples, the example apparatus 700 functioning as a source cell in preparation for a cell change of a terminal device.

[0111] As shown in FIG. 7, the example apparatus 700 may comprise: means 710 for transmitting to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0112] In some embodiments, the example method 300 may comprise: transmitting to theterminal device, a second indication indicating a duration or a number of times for the terminal device to track the TA.

[0113] In some embodiments, the apparatus 700 may comprise: means for determining whether the TA is valid in the terminal device; and means for in case of determining the TA is valid in the terminal device, transmitting to the terminal device, a command, without a TA for the target cell, for cell change to the target cell.

[0114] In some embodiments, the apparatus 700 may comprise: means for n case of receiving from the terminal device a report that there is no valid TA in the terminal device, initiating an early TA acquisition for the target cell towards the terminal device in response to the report.

[0115] In some embodiments, the apparatus 700 may comprise: means for receiving from the terminal device, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

[0116] In some example embodiments, examples of means in the example apparatus 700 may include circuitries. For example, an example of means 710 may include a circuitry configured to perform the operation 310 of the example method 300.

[0117] The example apparatus 700 may further include means comprising circuitry configured to perform the example method 300. In some example embodiments, examples of means may also include software modules and any other suitable function entities.

[0118] The example embodiments of the present disclosure also provide a computer-readable medium comprising program instructions that, when executed by an apparatus for a terminal device, such as the UE 110 in the above examples, may cause the apparatus at least to: receive from a source cell in preparation for a cell change, a message comprising a TA estimated by a target cell; track the TA; and update the TA according to the tracking of the TA.

[0119] In some embodiments, the message may comprise a first indication indicating the terminal device to track the TA.

[0120] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: receive from the source cell, a second indication indicating a duration or a number of times for the terminal device to track the TA; and track the TA for the duration or the number of times.

[0121] In some embodiments, the computer-readable medium may include instructions that,when executed by the apparatus, may cause the apparatus to: track the TA by measuring one or more reference signals for time tracking from the target cell.

[0122] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: receive after the message and from the source cell, a command for the cell change to the target cell.

[0123] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case the command does not comprise a TA for the target cell and the updated TA is valid, access the target cell applying the updated TA.

[0124] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case the command comprises a TA for the target cell, access the target cell applying the TA comprised in the command.

[0125] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case the command comprises a third indication indicating the terminal device to access the target cell using an RACH-based cell change, access the target cell using the RACH-based cell change.

[0126] In some embodiments, the cell change may be a conditional cell change, and the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: after receiving the message from the source cell, determine whether a condition for the conditional cell change is met; and perform the cell change without a cell change command to the target cell in case of determining the condition for the conditional cell change is met.

[0127] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case the updated TA is valid, access the target cell applying the updated TA.

[0128] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case of failing to track the TA, report to the source cell that there is no valid TA in the terminal device.

[0129] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: receive from the source cell, anRACH preamble for an early TA acquisition for the target cell in response to the reporting.

[0130] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case of failing to track the TA, access the target cell using an RACH-based cell change.

[0131] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: transmit to the source cell, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

[0132] In some embodiments, the cell change may be a cell switch.

[0133] The example embodiments of the present disclosure also provide a computer-readable medium comprising program instructions that, when executed by an apparatus for a network device, such as the network device 150 in the above examples, may cause the apparatus as a source cell in preparation for a cell change of a terminal device at least to: transmit to the terminal device, a message comprising a TA estimated by a target cell, wherein the message may comprise a first indication indicating the terminal device to track the TA.

[0134] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: transmit to the terminal device, a second indication indicating a duration or a number of times for the terminal device to track the TA.

[0135] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: determine whether the TA is valid in the terminal device; and in case of determining the TA is valid in the terminal device, transmit to the terminal device, a command, without a TA for the target cell, for cell change to the target cell.

[0136] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: in case of receiving from the terminal device a report that there is no valid TA in the terminal device, initiate an early TA acquisition for the target cell towards the terminal device in response to the report.

[0137] In some embodiments, the computer-readable medium may include instructions that, when executed by the apparatus, may cause the apparatus to: receive from the terminal device, a fourth indication indicating whether the terminal device has capability to support the tracking ofthe TA.

[0138] 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.

[0139] 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 is 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, vehiclemounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (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 above description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0140] The term “circuitry” throughout this disclosure 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); (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 orprocessor(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. This definition of circuitry applies to one or all uses of this term in this disclosure, including in any claims. As a further example, as used in this disclosure, 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 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.

[0141] Another example embodiment may relate to computer program codes or instructions which may cause an apparatus to perform at least the respective methods described above. Another example embodiment may be related to a computer-readable medium having such computer program codes or instructions stored thereon. In some embodiments, such a computer- readable medium may include at least one storage medium in various forms such as a volatile memory and / or a non-volatile memory. The volatile memory may include, but is not limited to, for example, a RAM, a cache, and so on. The non-volatile memory may include, but is not limited to, a ROM, a hard disk, a flash memory, and so on. The non-volatile memory may also include, but is not limited to, an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[0142] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but is not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the description using the singular or plural number may also include the plural or singular number respectively. The word “or” in referenceto a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0143] Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or states. Thus, such conditional language is not generally intended to imply that features, elements and / or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and / or states are included or are to be performed in any particular embodiment.

[0144] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, "determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0145] While some embodiments have been described, these embodiments have been presented by way of example, and are not intended to limit the scope of the disclosure. Indeed, the apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while blocks are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. At least one of these blocks may be implemented in a variety of different ways. The order of these blocks may also be changed. Any suitable combination of the elements and actions of the some embodiments described above can be combined to provide further embodiments. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.

[0146] Abbreviations used in the description and / or in the figures are defined as follows:ASN.1 abstract syntax notation oneBS base stationCHO conditional handoverDL downlink eNB Evolved Node B gNB next Generation Node BHO handoverLI layer 1L2 layer 2L3 layer 3LTM lower layer triggered mobilityMAC medium access controlMAC CE MAC control elementNW networkPRACH physical random access channelPDCCH physical downlink control channelRACH random access channelRRC radio resource controlRS reference signalPBCH physical broadcast channelSSB synchronization signal block synchronization signal and PBCH blockTA timing advanceTx transmitUE user equipmentUL uplink

Claims

CLAIMS:

1. An apparatus for a terminal device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive from a source cell in preparation for a cell change, a message comprising a timing advance, TA, estimated by a target cell; track the TA; and update the TA according to the tracking of the TA.

2. The apparatus of claim 1, wherein the message comprises a first indication indicating the terminal device to track the TA.

3. The apparatus of claim 1 or 2, wherein the apparatus is configured to: receive from the source cell, a second indication indicating a duration or a number of times for the terminal device to track the TA; and track the TA for the duration or the number of times.

4. The apparatus of any of claims 1 to 3, wherein the apparatus is configured to: track the TA by measuring one or more reference signals for time tracking from the target cell.

5. The apparatus of any of claims 1 to 4, wherein the apparatus is configured to: receive after the message and from the source cell, a command for the cell change to the target cell.

6. The apparatus of claim 5, wherein the apparatus is configured to: in case the command does not comprise a TA for the target cell and the updated TA is valid, access the target cell applying the updated TA.

247. The apparatus of claim 5, wherein the apparatus is configured to: in case the command comprises a TA for the target cell, access the target cell applying the TA comprised in the command.

8. The apparatus of claim 5, wherein the apparatus is configured to: in case the command comprises a third indication indicating the terminal device to access the target cell using a random access channel based, RACH-based, cell change, access the target cell using the RACH-based cell change.

9. The apparatus of any of claims 1 to 4, wherein the cell change is a conditional cell change, and the apparatus is configured to: after receiving the message from the source cell, determine whether a condition for the conditional cell change is met; and perform the cell change without a cell change command to the target cell in case of determining the condition for the conditional cell change is met.

10. The apparatus of claim 9, wherein the apparatus is configured to: in case the updated TA is valid, access the target cell applying the updated TA.

11. The apparatus of any of claims 1 to 10, wherein the apparatus is configured to: in case of failing to track the TA, report to the source cell that there is no valid TA in the terminal device.

12. The apparatus of claim 11, wherein the apparatus is configured to: receive from the source cell, an RACH preamble for an early TA acquisition for the target cell in response to the reporting.

13. The apparatus of any of claims 1 to 12, wherein the apparatus is configured to: in case of failing to track the TA, access the target cell using an RACH-based cell change.

14. The apparatus of any of claims 1 to 13, wherein the apparatus is configured to: transmit to the source cell, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

15. The apparatus of any of claims 1 to 14, wherein the cell change is a cell switch.

16. An apparatus for a network device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus as a source cell in preparation for a cell change of a terminal device at least to: transmit to the terminal device, a message comprising a timing advance, TA, estimated by a target cell, wherein the message comprises a first indication indicating the terminal device to track the TA.

17. The apparatus of claim 16, wherein the apparatus is configured to: transmit to the terminal device, a second indication indicating a duration or a number of times for the terminal device to track the TA.

18. The apparatus of claim 16 or 17, wherein the apparatus is configured to: determine whether the TA is valid in the terminal device; and in case of determining the TAis valid in the terminal device, transmit to the terminal device, a command, without a TA for the target cell, for cell change to the target cell.

19. The apparatus of any of claims 16 to 18, wherein the apparatus is configured to: in case of receiving from the terminal device a report that there is no valid TAin the terminal device, initiate an early TA acquisition for the target cell towards the terminal device in response to the report.

20. The apparatus of any of claims 16 to 19, wherein the apparatus is configured to: receive from the terminal device, a fourth indication indicating whether the terminal device has capability to support the tracking of the TA.

21. A method performed by an apparatus for a terminal device, comprising: receiving from a source cell in preparation for a cell change, a message comprising a timing advance, TA, estimated by a target cell; tracking the TA; and updating the TA according to the tracking of the TA.

22. The method of claim 21, wherein the message comprises a first indication indicating the terminal device to track the TA.

23. A method performed by an apparatus for a network device, as a source cell in preparation for a cell change of a terminal device, comprising: transmitting to the terminal device, a message comprising a timing advance, TA, estimated by a target cell, wherein the message comprises a first indication indicating the terminal device to track the TA.

24. An apparatus for a terminal device, comprising means for performing the method claim 21.

25. An apparatus for a network device, as a source cell in preparation for a cell change of a terminal device, comprising means for performing the method of claim 23.

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