Timing advance acquisition during cell switching

Abstract

The present disclosure relates to timing advance (TA) acquisition during cell switching. A method comprises receiving at a UE, LTM candidate cell configuration including an aperiodic NZP CSI-RS resource set configured as TRSs for TRPs associated with LTM candidate cells. The method includes receiving a DCI command to initiate delay offset reporting, computing a downlink delay offset value for each TRP based on the TRSs, and reporting the downlink delay offset value to the serving cell. The method includes receiving a cell switch command instructing the UE to switch from serving cell to target cell, the cell switch command indicating whether to use downlink delay offset values for computing an uplink TA value for the target cell. The method includes computing the uplink TA value based on the downlink delay offset values and performing RACH-less LTM cell switch to the target cell using the uplink TA value.

Description

[0001] TIMING ADVANCE ACQUISITION DURING CELL SWITCHING

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003]

[0001] This application claims priority to Indian Provisional Patent Application No.

[0004] 202541009518, filed on February 5, 2025, and Indian Non-Provisional Patent Application No.

[0005] 202541009518, filed on September 25, 2025, the entire contents of which are incorporated herein by reference.

[0006] FIELD

[0007]

[0002] The present disclosure relates to timing advance (TA) acquisition during cell switching.

[0008] BACKGROUND

[0009]

[0003] The information disclosed in this background section is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

[0010]

[0004] In Third Generation Partnership Project (3GPP), a disaggregated architecture of a base station is defined which includes partitioning the base station into multiple logical entities. In such an architecture, the base station is configured to provide wireless services within a defined service area, which is divided into multiple cells. Multiple User Equipment (UEs) may be active within a given cell. The UEs may transmit uplink (UL) signals (e.g.. Physical Uplink Shared Channel (PUSCH) signals) over different sets of subcarriers. The base station typically processes the received uplink signals jointly using a single Fast Fourier Transform (FFT) operation and converts the received uplink signals from time domain into frequency domain. For the FFT operation to be effective, it is necessary that the uplink signals from different UEsarrive at the base station in a synchronized manner, within the boundaries of the orthogonal frequency division multiplexing (OFDM) symbol duration.

[0011]

[0005] To maintain such synchronization, uplink transmissions across the different UEs need to be synchronized. This may be achieved by instructing each UE to adjust a start time of its uplink transmissions (e.g.. UL OFDM symbols) relative to its corresponding downlink (DL) transmissions (e.g., DL OFDM symbols). By adjusting the start timing, time differences of the uplink transmissions arriving at the base stations from the different UEs become sufficiently small. A parameter used to adjust the uplink transmission start timing of the UEs may be referred to as "‘Timing Advance” (TA). Typically, the base station transmits TA commands (TACs) to the UEs. The TACs inform the UEs about the respective times by which the UEs need to advance their uplink transmissions so that the uplink transmissions from multiple UEs reach the base station in a synchronized manner.

[0012]

[0006] When a UE moves from a coverage area of one cell (referred to as “serving cell” or “source cell”) to another cell (referred to as “target cell”), a handover (HO) process is triggered to change the serving cell for the UE. Traditionally, such handovers are coordinated through higher-layer signaling procedures. However, in order to reduce handover latency and improve mobility performance, the Third Generation Partnership Project (3GPP) has introduced a mechanism referred to as Lower-layer Triggered mobility (LTM) or Layer 1 / Layer 2 Triggered Mobility to change the serving cell of the UE through L1 / L2 signaling.

[0013]

[0007] In LTM, in order to effectuate more efficient cell switching, the UE is required to acquire the knowledge of the TA related to the target cell in advance of an actual switching to the target cell. The knowledge of the TA is necessary' for the UE to perform proper synchronization (also referred to as UL synchronization) with the target cell. Accordingly,acquisition of the TA related to the target cell is an essential requirement in enabling efficient and robust LTM-based handovers.

[0014] SUMMARY

[0015]

[0008] The present disclosure discloses techniques of optimizing Timing Advance (TA) acquisition during LTM cell switch procedures. In one example, the present disclosure addresses problems related to inefficient TA acquisition during Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch procedures. To address these problems, the present disclosure discloses mechanisms for efficiently provisioning TA information when a User Equipment (UE) performs LTM cell switching from a serving cell to a target cell. The techniques of the present disclosure utilize Tracking Reference Signals (TRS) based downlink delay offset measurements (originally used for multi-TRP CJT calibration) to derive TA values for use in LTM cell switch procedures.

[0016]

[0009] In one non-limiting embodiment, the present disclosure discloses a method which comprises receiving, at a User Equipment (UE) served by a serving cell, LTM candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The method comprises receiving, at the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs, computing, at the UE, a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell, and receiving, at the UE, a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells. Thecell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell. The method comprises responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: computing the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; and performing random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0017]

[0010] In one non-limiting embodiment, the present disclosure discloses a User Equipment (UE) which is configured to receive, at the UE served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The UE is further configured to receive a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; and receive a cell switch command instructing the UE to switch from the ser ing cell to a target cell of the one or more LTM candidate cells. The cell switch command indicating whether to use dow nlink delay offset values for computing an uplink timing advance (TA) value for the target cell. The UE is further configured to responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRPwhich is associated with the target cell; and perform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0018] [OH] In one non-limiting embodiment the present disclosure discloses a non-transitory computer readable media storing one or more computer executable instructions which, when executed by a User Equipment (UE) . cause the UE to receive, at the UE served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The one or more computer executable instructions further cause the UE to receive a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; receive a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells. The cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell. The one or more computer executable instructions further cause the UE to responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; and perform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0012] In one non-limiting embodiment, the present disclosure discloses a method which comprises transmitting, to a User Equipment (UE) served by a serving cell. Layer 1 / Layer 2 Tnggered Mobility (LTM) candidate cell configuration. The LTM candidate cell configuration comprising an apenodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The method further comprises transmitting, to the UE. a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; receiving, from the UE, a delay offset report comprising a downlink delay offset value for each of the one or more TRPs; transmitting, to the UE, a cell switch command instructing the UE to switch from the serving cell to the target cell of the one or more LTM candidate cells. The cell switch command indicating whether to use the downlink delay offset values for computing an uplink timing advance (TA) value for the target cell. The method further comprises facilitating a random access channel-less (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.

[0019]

[0013] In one non-limiting embodiment, the present disclosure discloses a base station which is configured to transmit, to a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility' (LTM) candidate cell configuration. The LTM candidate cell configuration comprises an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The base station is further configured to transmit, to the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or moreTRPs: receive, from the UE, a delay offset report comprising a downlink delay offset value for each of the one or more TRPs; transmit, to the UE, a cell switch command instructing the UE to switch from the serving cell to the target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use the downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and facilitate a random access channelless (RACEI-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.

[0020]

[0014] In one non-limiting embodiment, the present disclosure discloses a non-transitory computer readable media storing one or more computer executable instructions which, when executed by a base station . cause the base station to: transmit, to a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells. The instructions further cause the base station to transmit, to the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; receive, from the UE, a delay offset report comprising a downlink delay offset value for each of the one or more TRPs; transmit, to the UE, a cell switch command instructing the UE to sw itch from the serving cell to the target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use the downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and facilitate a random access channel-less (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0021]

[0015] Features, aspects, and advantages of embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and wherein:

[0022]

[0016] FIG. 1 illustrates a high-level block diagram 100 of a disaggregated architecture of an example communication system in which the techniques of TA acquisition during LTM cell switch procedures may be implemented.

[0023]

[0017] FIG. 2 illustrates an exemplary communication system 200 in which the techniques of TA acquisition during LTM cell switch procedures may be implemented.

[0024]

[0018] FIG. 3 illustrates an example signaling procedure 300 for TA acquisition during LTM cell switch procedures.

[0025]

[0019] FIG.4 illustrates a flowchart of an example method 400 of TA acquisition during LTM cell switch procedures.

[0026]

[0020] FIG.5 illustrates a flowchart of another example method 500 of TA acquisition during LTM cell switch procedures.

[0027]

[0021] FIG.6 illustrates a block diagram 600 of an apparatus or device.

[0028] DETAILED DESCRIPTION

[0029]

[0022] The following detailed description of example embodiments refers to the accompanying drawings. The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or morefeatures of another embodiment). Additionally, the flowchart and description of operations provided below relate to one of the various embodiments. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part).

[0030]

[0023] It will be apparent that systems and / or methods, described herein may be implemented in different forms of hardware, software, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and / or methods is not limiting of the implementations. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It is understood that software and hardware may be designed to implement the systems and / or methods based on the description herein.

[0031]

[0024] Even though particular combinations of features are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and / or disclosed in the specification. Although each dependent claim listed below' may directly depend on only one claim, the disclosure of implementations includes each dependent claim in combination with every' other claim in the claim set.

[0032]

[0025] No element, act, or instruction used herein should be constmed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and "an" are intended to include one or more items, and may be used interchangeably with “one or more.” Also, as used herein, the terms “has,” “have,” “having,” “include,” “including,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least inpart, on” unless explicitly stated otherwise. Furthermore, expressions such as ‘'at least one of [A] and [B],” “[A] and / or [B],” or “at least one of [A] or [B] ” are to be understood as including only A, only B, or both A and B.

[0033]

[0026] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

[0034]

[0027] In the present disclosure, the terms like "‘communication system”, “system”, and “wireless communication system” have been used interchangeably throughout the specification.

[0035]

[0028] In the context of present disclosure, the term “Timing Advance” (TA) or “Timing Advance Value” refers to a value sent by a base station to a User Equipment (UE) to adjust uplink transmissions i.e., the UE sends Uplink (UL) symbols in advance according to the TA for uplink transmissions such as Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH), and Sounding Reference Signal (SRS) transmissions. A Timing Advance Command (TAC) refers to a message sent by the base station to the UE, informing the UE to advance transmission timing of its UL transmissions by the amount specified by the TA value.

[0036]

[0029] When a User Equipment (UE) operates in a Radio Resource Control (RRC) connected state, the UE maintains an active connection with its associated serving cell. In the RRC connected state, uplink synchronization between the UE and the serving cell (or a base station providing wireless services w ithin the serving cell) is needed for reliable data transmission and to maintain orthogonality among uplink transmissions from multiple UEs. To achieve such synchronization, the base station may continuously monitor timing of uplink transmissionsfrom the UE. Such monitoring may be performed using configured uplink reference signals such as Sounding Reference Signals (SRSs), but not limited thereto.

[0037]

[0030] The SRS(s) may be transmitted either as a single instance or as a burst of multiple SRSs. The base station receives the SRS(s) and estimates timing offset between an expected arrival time of the SRS(s) and an actual arrival time. Based on this estimated timing offset, the base station determines whether the uplink transmissions of the UE are aligned within an acceptable timing window. If the base station determines that the uplink transmissions are misaligned, the base station may generate a TAC. The TAC specifies a value or amount informing the UE to advance the timing of its uplink transmissions by the specified value. In some cases, the TAC may be transmitted to the UE via a Medium Access Control (MAC) Control Element (CE). Upon receiving the TAC, e.g., via the MAC-CE, the UE may update the timings of its uplink transmissions.

[0038]

[0031] However, in certain scenarios the UE cannot use SRS(s) for time monitoring. One such scenario occurs when the UE is in a RRC idle state and intends to transition to the RRC connected state. In the idle state, the UE does not transmit uplink reference signals such as SRS(s), and therefore the base station cannot perform timing adjustment based on uplink reference signals such as SRS(s). Another scenario arises when the UE has lost uplink synchronization with the serving base station. In such scenario, previously established SRS-based timing information (e.g., TA) may become invalid, and the UE must obtain fresh timing information before resuming uplink data transmissions.

[0039]

[0032] A further scenario occurs when the UE in the RRC connected state undergoes a cell switch or handover procedure. During such procedures, the UE transitions from a source or serving cell to a target cell, which may belong to the same carrier frequency (intra-frequency handover) or a different carrier frequency (inter-frequency handover). Since the TA associatedwith the serving cell may not be directly applicable to the target cell, the UE acquires new timing information relative to the target cell for proper uplink synchronization after the handover.

[0040]

[0033] In such scenarios, where SRS-based time tracking cannot be utilized. Random Access Channel (RACH) preamble may be utilized for establishing uplink synchronization. The UE typically acquires timing information from the base station (e.g.. via a random access procedure) to achieve uplink synchronization with the target cell.

[0041]

[0034] Specifically, for handover (HO) related scenarios, when the UE is instructed to transition from the serving cell to the target cell, the TA value used in the serving cell may not be applicable for the target cell because the target cell may be geographically located at a different distance from the UE. may be served by a different Transmission and Reception Point (TRP), or may operate on a different carrier frequency.

[0042]

[0035] In tradition HO scenarios, the UE may perform a Physical Random Access Channel (PRACH) procedure upon accessing the target cell. The UE may wait for a PRACH occasion and may transmit a RACH preamble during the configured PRACH occasion. The target cell may detect the RACH preamble and determine a TA value based on a round-trip propagation delay between the UE and the target cell. The target cell may generate a TAC which is sent back to the UE e.g., in a Random Access Response (RAR) message. Upon receiving the TAC, the UE may adjust transmission timing of its UL transmissions by the amount specified in the TAC.

[0043]

[0036] It may be noted that the traditional handovers are generally coordinated through higher-layer signaling procedures. However, in order to reduce interruptions during handovers and improve mobility performance, the Third Generation Partnership Project (3GPP) has introduced various mobility enhancement features. One such feature is referred to as Lower-layer Triggered mobility (LTM) or Layer 1 / Layer 2 Triggered Mobility to provide more efficient UE movements across cells by reducing reliance on higher-layer signaling and leveraging lower-layer signaling.

[0044]

[0037] In LTM, the serving cell provides the UE with configurations of neighboring cells (e.g., RRC configurations) which are identified as candidate target cells for future handovers of the UE. Additionally, the serving cell may configure the UE with LTM report settings instructing the UE to measure and report Layer- 1 Received Signal Reference Power (Ll-RSRP) of one or more downlink reference signals transmitted by the candidate cells. The one or more downlink reference signals used for such measurements may include Synchronization Signal Blocks (SSBs) or Channel State Information Reference Signals (CSI-RSs), which are broadcasted from the candidate cells or associated Transmission and Reception Points (TRPs).

[0045]

[0038] The UE measures and reports signal quality measurements of the candidate cells in the form of periodic measurements or event triggered measurements. Additionally, the UE may acquire TA for a candidate cell based on a physical downlink control channel (PDCCH) order sent by the serving cell. Specifically, the serving cell may instruct the UE to initiate an uplink random access attempt toward the candidate cell by sending the PDCCH order. The UE may transmit RACH preamble to the candidate cell based on the PDCCH order. Upon receiving the RACH preamble from the UE, the candidate cell may estimate the TA value for the UE. The estimated TA value may then be forwarded from the candidate cell to the serving cell.

[0046]

[0039] In this manner, the serving cell obtains TA information for the UE relative to the candidate cell and conveys the same to the UE in the cell switch command. When the serving cell issues a cell switch command to the UE (e.g., via a MAC-CE) accompanying the TA information or when a pre-defined cell switch condition is met, the UE may switch to a target cell without w aiting for a new RRC configuration message from the target cell. Such pre-acquisition of the TA information accelerates LTM-based cell switch processes. Specifically, when the TA information of the target cell has already been determined and conveyed to the UE, the LTM cell switch may be executed in a RACH-less or RACH-free manner, thereby avoiding additional signaling delay associated with performing anew random access procedure in the target cell.

[0047]

[0040] An exemplary RACH-less LTM cell switch process is described herein. During preconfigured RACH opportunities, the UE which is served by the serving cell, may transmit a dedicated RACH preamble toward one or more candidate cells. Upon receiving the dedicated RACH preamble from the UE, each candidate cell may estimate an uplink TA value corresponding to the UE. The uplink TA value represents timing adjustment that the UE needs to apply in order to achieve uplink synchronization with the candidate cell. The estimated TA value is then transferred from each candidate cell to the serving cell. The serving cell maintains a record of such TA values for each candidate cell associated with the UE. When a cell switch decision is made and a candidate cell is identified as the target cell for the UE, the serving cell issues a cell switch command to the UE. The command includes the previously acquired TA value for the target cell. This allows the UE to quickly synchronize with the target cell without needing to perform a fresh random access procedure. In this manner, this RACH-less LTM cell switch process reduces signaling delay compared to traditional handover procedures. However, there are certain limitations associated with this procedure.

[0048]

[0041] In some deployments, the UE may have a large number of candidate cells and a time interval between successive RACH occasions for each candidate cell may be long. In such cases, if the UE is mobile or if there are variations in channel conditions between the UE and the candidate cell, the TA values stored at the serving cell may become outdated by the time the handover to the candidate target cell actually occurs, leading to inefficient uplinksynchronization at the target cell. In certain deployments, in cases of inter-gNB mobility cases, exchange of TA information between different base stations is dependent on the backhaul network. When the backhaul link is non-ideal (e.g., having high latency or limited capacity), the transfer of TA values may be delayed, preventing timely use of the TA information for the cell switch.

[0049]

[0042] Thus, although the RACH-less LTM cell switch process aim to achieve low-latency and efficient handovers, there are certain shortcomings, particularly the TA values may become outdated or may not be timely conveyed to the UE. Thus, there is a need of alternative approaches of TA acquisition in LTM cell switch procedures compared to the existing RACH based and RACH-less procedures.

[0050]

[0043] Modem cellular networks are evolving towards more distributed architectures to exploit macro-diversity. In such architectures, a single base station may utilize multiple Transmission and Reception Points (TRPs) to serve a single UE. In downlink, the transmission from multiple TRPs may be either non-coherent joint transmission (NCJT) or coherent joint transmission (CJT). In case of the NCJT, multiple TRPs may transmit different signals which may be different codewords or different redundancy versions of the same codeword. The NCJT mainly improves cell capacity' due to parallel utilization of multiple TRPs without necessitating synchronization across the multiple TRPs. In case of the CJT, multiple TRPs may transmit same version of the signal (i.e., same codeword and redundancy version) in a time-synchronized manner within the same OFDM symbol. The CJT improves coverage uniformity across a geographical area. In 3GPP Release 17 of New Radio (NR), NCJT of signals from different cells each assigned different physical cell identities (PCIs) is supported. In some cases, the CJT of signals from different cells may also be supported.

[0044] Unlike NCJT, the CJT requires coordination and synchronization across the multiple TRPs. Similar to the uplink synchronization, the CJT necessitates downlink time synchronization across the multiple TRPs. To achieve this synchronization, the base station relies on delay offset measurements which comprise relative propagation path delays from the multiple TRPs to the UE. The base station may configure the UE to perform measurements on Channel State Information Reference Signals (CSI-RSs) transmitted by the multiple TRPs. Upon receiving the CSI-RSs from the multiple TRPs. the UE may process the CSI-RSs to estimate the delay offsets among the TRPs and then report a quantized version of the delay offsets back to the base station. The reported delay offsets may be utilized by the base station to perform CJT calibration across the multiple TRPs (referred to as ’mulli-TRP CJT calibration”). Such mechanism of delay offset reporting has been standardized in 3GPP Release 19 of NR.

[0051]

[0045] In practice, uplink and downlink delays are closely correlated e.g., due to reciprocity of propagation channels between the UE and the base station. This property is well recognized and included in 3GPP specifications. For example, in 3GPP Release 17, the design of Fe-Type-II port selection codebook utilizes delay-angle symmetry between the uplink and downlink, thereby indicating that propagation delays measured in one link direction (DL or UL) can provide useful information about the other. Based upon this principle, the delay offset reporting standardized in the multi-TRP CJT calibration may be extended beyond downlink synchronization to also support uplink TA acquisition. Since the delay offset reflects the propagation path time from a TRP to the UE, the same may sen e as a basis for determining the TA required for uplink synchronization at the target cell or TRP.

[0052]

[0046] It may be noted that Synchronization Signal Blocks (SSBs) transmitted by different cells may be used for Received Signal Reference Power (RSRP) measurements, providinginformation useful for making cell-switch decision. However, the SSBs may not be suitable for propagation path delay measurements because of limited signal bandwidth of the SSBs. Thus, for multi-TRP CJT calibration, propagation path delays are measured using Tracking Reference Signals (TRSs).

[0053]

[0047] The TRSs are single-port CSI-RSs with high frequency density and are not subject to the bandwidth limitations like SSBs. making them suitable for delay offset measurements. Moreover, in certain scenarios, delay offsets measured using downlink reference signals (e.g., TRSs) may provide more accuracy than those derived from uplink reference signals (e.g., SRSs). One reason for more accuracy is that the UEs have limitations on the maximum transmission power, which restricts quality of SRS-based delay measurements, particularly in scenarios with large inter-site distances. In contrast, downlink reference signals transmitted by TRPs generally benefit from higher transmission pow er of TRPs, allowing for more accurate delay offset measurements at the UE.

[0054]

[0048] In the present disclosure, it is proposed that UEs configured with LTM are also configured with multi-Transmission and Reception Point (m-TRP) operations. In such configurations, the UEs can acquire TA values of candidate cells by leveraging TRSs that are configured for delay offset reporting in multi-TRP CJT calibration. Specifically, a UE is configured to measure delay offsets based on downlink reference signals (e.g., TRSs) transmitted from multiple TRPs across different cells including candidate cells identified for LTM-based handovers. The UE measures the delay offsets associated with each TRP based on the downlink reference signals and reports the measured delay offsets to the base station.

[0055]

[0049] The measured delay offsets may then be used by the UE to derive candidate TA values corresponding to the respective target cells served by the TRPs. Further, since the UE periodically transmits delay offset report to the serving (source) cell as part of the standardizedCJT calibration procedure, the serving cell may forward this information to the respective target cell(s). As a result, when a particular candidate cell is selected as the target cell for handover, the cell switch command issued by the serving cell may be supplemented with the TA value that was previously measured and derived from the delay offset reports of the UE. Thus, the target cell has immediate access to an accurate TA value already applied by the UE, thereby allowing the UE to perform uplink synchronization with the target cell without requiring a separate RACH procedure. Consequently, the proposed techniques facilitate efficient RACH-less LTM handovers by efficiently provisioning TA information when a UE performs LTM cell switching from the serving cell to the target cell, thereby reducing handover interruption time and improving overall performance of the communication system.

[0056]

[0050] FIG. 1 illustrates a high-level block diagram 100 of a disaggregated architecture of an example communication system comprising a Radio Access Network (RAN) node or a base station 102 configured to serve a geographical area or cell 104. The cell 104 may be an LTM cell and may comprise at least one UE 106. The base station 102 may be configured to provide wireless services to the at least one UE 106 served by the associated cell 104.

[0057]

[0051] The at least one UE 106 may be any mobile or non-mobile computing device including, but not limited to, a phone (e.g., a cellular phone or smart phone), a pager, a laptop computer, a desktop computer, a wireless handset, a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system device, or any other suitable computing device including a wired or wireless communications interface. In some embodiments of the present disclosure, the at least one UE 106 may be Intemet-of-Things (loT)-enabled device including, but not limited to, vehicles configured to communicate with the RAN node or a core network.

[0052] In a disaggregated architecture, the base station 102 may be implemented as a 5G NR base station (gNB) 102 and may be partitioned into multiple logical network entities. For instance, the base station 102 may be partitioned into a central unit (gNB-CU or CU) 108 and one or more distributed units (gNB-DUs or DUs) 110. In the embodiment of FIG. 1, the CU 108 may be further partitioned into a central unit control-plane entity 114 (gNB-CU-CP or CU-CP) and one or more central unit user-plane entities 116 (gNB-CU-Ups or CU-UPs) that may handle the control-plane and user-plane processing of the CU 108, respectively.

[0058]

[0053] The base station 102 may comprise one or more physical entities such as Radio Units (RUs) 112 including one or more antennas 118 for serving the at least one UE 106 in the associated cell. The CU 108 may be communicatively coupled with the one or more DUs 110 via an Fl interface. The DU 110 may be communicatively coupled with at least one RU 112 via a fronthaul interface 120. The CU-CP 114 may be communicatively coupled with each of the CU-UPs 116 via an El interface and may be further coupled with each of the DUs 110 via an Fl-C interface. Each of the DUs 110 may be communicatively coupled to each of the CU-UPs 116 via an Fl-U interface, as shown in FIG. 1.

[0059]

[0054] In one non-limiting embodiment, each DU 110 may host multiple cells. The CU-CP 114 may host one or more DUs 110 and one or more CU-UPs 116. In one example deployment, there may be one CU-CP 114 employed by the base station 102, and each DU 110 may be served by multiple CU-UPs 116. The CU-CP 114 is responsible for managing control plane protocols and procedures. For instance, the CU-CP 114 may host Packet Data Convergence Protocol - Control Plane (PDCP-C) layer and Radio Resource Control (RRC) layer, while the CU-UP 116 may host Packet Data Convergence Protocol - User Plane (PDCP-U) and Service Data Adaptation Protocol (SDAP) layers. The DU 110 may host lower layers such as Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers.

[0055] The CU 108 may be configured to communicate with a core network 122 using a backhaul network 124. In one non-limiting embodiment of the present disclosure, the core network 122 may be a 5G core network which may utilize cloud-aligned, service-based architecture that spans across all 5G functions and interactions including authentication, security, session management etc. It may be noted that for the sake of simplicity and explanation, the present disclosure is described considering Fifth Generation (5G) communication systems. However, the present disclosure is not limited thereto and in general, the techniques of the present disclosure are applicable to any type of communication systems such as 4G communication system, 6G communication system, and the like.

[0060]

[0056] It may be noted that a RU 112 may correspond to one or more Transmission and Reception Points (TRPs). A TRP may represent a logical or physical node within the communication system which is configured to transmit downlink signals and to receive uplink signals to / from UEs 106. In practice, a single RU 112 may correspond to a single TRP. In some cases, one RU 112 with multiple antenna panels / sectors may support multiple TRPs. In some cases, multiple RUs 112 may jointly form or support a single logical TRP. In some deployment scenarios, the UE 106 can be configured to communicate with multiple TRPs simultaneously, in accordance with a multi-TRP configuration. Such multi-TRP operation allows the UE 106 to receive and / or transmit data or reference signals from multiple geographically separated or co-located TRPs, thereby supporting CJT.

[0061]

[0057] Referring to FIG. 2, which shows an exemplary communication system 200 in which the techniques of TA acquisition during LTM cell switch procedures may be implemented, in accordance with some embodiments of the present disclosure. As shown in FIG. 2, the communication system 200 may comprise a CU 108 communicatively coupled with a plurality of DUs which comprises a source DU or serving DU 110-1 and a target DU 110-2. Each DUmay be similar to the DU 110 discussed in connection with FIG. 1 i.e., each DU 110 may be coupled with the CU 108 and may be configured to serve one or more LTM cells via one or more TRPs or RUs 112. For instance, the serving DU 110-1 may be configured to serve an LTM serving cell 104-1 (herein after referred to as “serving cell”). Likewise, the target DU 110-2 may be configured to serve an LTM target cell 104-2 (herein after referred to as “serving cell”). It may be worth noting here that only few relevant components / units of the communication system 100 are shown in FIG. 2 for the sake of simplicity. However, the present disclosure is not limited thereto and in general some or all component / units of the communication system 100 (shown in FIG. 1) may be a part of the communication system of FIG. 2

[0062]

[0058] The UE 106 represents end-user devices that access wireless services through a wireless network. The UE 106 is configured to connect to the CU 108 and the DUs 110 over the wireless network. The UE 106 may communicate with the CU 108 via the serving DU 110-1 over an Fl interface. The UE 106 may be configured with LTM with the serving DU 110-1. The LTM is a procedure in which a base station 102 receives LI measurement reports from the UE 106, and on their basis the base station 102 changes serving cell of the UE 106 using a Media Access Control (MAC) Control Element (CE). The UE 106 may switch from the LTM serving cell 104-1 to an LTM candidate / target cell 104-2 associated with the candidate / target DU 110-2.

[0063] Timing advance (TA) is used to control uplink transmission timing of the UE 106. The TA helps to ensure that uplink transmissions from all UEs are synchronized. The UE 106 needs to perform TA acquisition to acquire the TA of the LTM candidate / target cell 104-2 when there is a handover from the LTM serving cell 104-1 to the LTM candidate / target cell 104-2, as discussed in connection with FIG.3.

[0059] FIG. 3 illustrates an example signaling procedure 300 for TA acquisition during LTM cell switch procedures, in accordance with some embodiments of the present disclosure. The UE 106 is connected to or served by a serving cell 104-1 which belongs to the serving DU 110-1. There may be one or more LTM candidate cells 104-2 belonging to one or more candidate DUs which may be potential targets for handover of the UE 106. For example, the UE 106 may handover to a target cell 104-2 which belongs to a target DU 110-2. In some example, the serving DU 110-1 and the target DU 110-2 belong to a same base station. However, the present disclosure is not limited thereto and in one non-limiting embodiment, the serving DU 110-1 and the target DU 110-2 may belong to different base stations.

[0064]

[0060] When the UE 106 switches from the serving cell 104-1 to the target cell 104-2 of the one or more LTM candidate cells, the UE 106 needs to adjust uplink transmission timing to match the target cell 104-2. The techniques of the present disclosure utilize multi-TRP delay offset calibration to pre-acquire the TA of the target cell 104-2, as per the procedure outlined in FIG. 3

[0065]

[0061] In Step 1 (SI), the UE 106 is configured with LTM and also configured with multiTransmission and Reception Point (m-TRP or multi-TRP) operations. The UE may be configured to receive signals from one or more TRPs at the same time. Each of the one or more LTM candidate cells may be served by at least one TRP of the one or more TRPs. The UE 106 may maintain a list of Transmission Configuration Indicator (TCI) states. At least one TCI state (from the TCI state list) associated with the one or more LTM candidate cells state may be configured with the UE. The UE may be aware of which TCI state corresponds to which LTM candidate cell. Physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell 104-1. Specifically, each LTM candidate cell may have a uniquePCI which may be different from the PCI of the serving cell 104-1. Thus, the UE 106 may distinguish reference signals from different LTM candidate cells.

[0066]

[0062] In Step 2 (S2), the base station may transmit LTM candidate cell configuration(s) to the UE 106 and the UE 106 served by the serving cell 104-1 may receive the LTM candidate cell configuration(s) from the base station. In one implementation, the LTM candidate cell configuration may be generated by the CU 108 and delivered to the UE 106 via the serving DU 110-1 and the corresponding serving cell 104-1. The LTM candidate cell configuration comprises information associated with the one or more LTM candidate cells to which the UE 106 may potentially perform handover. Each candidate cell may be served by at least TRP of the one or more TRPs. The LTM candidate cell configuration comprises an aperiodic non-zeropower Channel State Information Reference Signal (NZP CSI-RS) resource set. The NZP CSI-RS resource set may be configured as one or more TRSs corresponding to the one or more TRPs associated with one or more LTM candidate cells. It may be noted that the NZP CSI-RS resource set refers to a predefined group of CSI-RS resources that are transmitted with nonzero power and may be activated / configured non-periodically, for example, upon a trigger from the base station. These CSI-RS resources are configured to act as TRSs that the UE 106 may use for delay offset measurements. Each TRP may have an associated TRS.

[0067]

[0063] In Step 3 (S3), the UE 106 may receive a downlink control information (DCI) command from the serving cell 104-1 to initiate aperiodic delay offset reporting of the one or more TRPs. Specifically, the base station (or the serving cell 104-1) may transmit the DCI command to the UE 106 over a Physical Downlink Control Channel (PDCCH). The DCI command may instruct the UE 106 to perform aperiodic delay offset reporting for the one or more TRPs that are associated with the one or more LTM candidate cells. In some implementations, the DCI command for delay offset reporting may be sent after the serving cell 104-1 has transmitted aPDCCH order for triggering Reference Signal Received Power (RSRP) measurement and reporting.

[0068]

[0064] In Step 4 (S4), after receiving the delay offset reporting request from the serving cell 104-1, the UE 106 may compute a downlink delay offset value for each TRP based on the one or more TRSs. Specifically, the UE 106 may process each TRS received from the one or more TRPs and may compute delay offset values for each TRP relative to a currently indicated downlink reference signal (e.g., TRS). The delay offset values represent differences in propagation delays of downlink reference signals received from the respective TRPs. In some cases, the UE 106 may receive the one or more TRSs from the one or more TRPs and compute the downlink delay offset value for each TRP based on the received one or more TRSs.

[0069]

[0065] In Step 5 (S5), after computing the downlink delay offset values, the UE 106 may report the computed downlink delay offset value for each TRP to the base station. Specifically, in Step 5.1 (S5.1), the UE 106 may transmit a delay offset report to the serving cell 104-1. The delay offset report may include the computed downlink delay offset value for each TRP. In Step 5.2 (S5.2), the serving cell 104-1 may forward or transmit the report to the CU 108 for further processing and coordination. The reported downlink delay offset values may be used by the CU 108 for multi-TRP CJT calibration. In Step S5, the base station receives, from the UE, the delay offset report comprising the downlink delay offset value for each of the one or more TRPs.

[0070]

[0066] In Step 5.3 (S5.3), the CU 108 may distribute relevant portions of the delay offset report to the respective candidate cells including the target cell 104-2. Thus, the candidate cells are aware of the measured timing differences of the UE 106 relative to their TRPs, which may be useful for synchronizing uplink and downlink transmissions when the UE 106 performs a cellswitch. For example, the target cell 104-2 may use the received delay offset value to determine uplink TA that the UE 106 is going to apply upon switching to the target cell 104-1.

[0071]

[0067] In Step 6 (S6), the base station may transmit a cell switch command to the UE 106 and the UE 106 which is served by the serving cell 104-1 may receive the cell switch command from the base station. In one implementation, the cell switch command may be generated by the CU 108 and delivered to the UE 106 via the serving DU 110-1 and the corresponding serving cell 104-1. The cell switch command provides instructions to the UE 106 to switch from the serving cell 104-1 to the target cell 104-2 which is one of the one or more LTM candidate cells. The cell switch command includes critical information, such as whether the UE 106 is allowed to use previously computed downlink delay offset values for computing an uplink TA value for the target cell 104-2.

[0072]

[0068] In some examples, the cell switch command is received by the UE 106 via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell 104-1 to the target cell 104-2. The MAC-CE is a signaling message defined in the MAC layer of the base station and serves as a low-latency mechanism to convey control information to the UE 106. The MAC-CE also comprises an indication regarding the use of dow nlink delay offset values for computing an uplink TA value for the target cell 104-2. Specifically, the MAC-CE informs the UE 106 whether the UE 106 is allowed to utilize previously computed downlink delay offset values for deriving the uplink TA value for the target cell. By providing such information, the MAC-CE helps the UE in determining whether the UE 106 can perform a RACH-less LTM cell switch using the pre-acquired TA or whether to perform a conventional RACH-based cell switch.

[0073]

[0069] At Step (S7), when the UE 106 receives the cell switch command from the serving cell 104-1, the cell switch command may indicate that the UE 106 is permitted to use the downlinkdelay offset values for computing the uplink TA for the target cell 104-2. In response, the UE 106 may compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell.

[0074]

[0070] At Step 8 (S8), after the uplink TA value for the target cell is acquired, the UE 106 may perform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value. The base station may also facilitate the RACH-less LTM cell switch procedure. By using the pre-computed uplink TA value, the UE 106 may synchronize uplink transmissions with the target cell 104-2 without performing traditional RACH-based procedures, thereby reducing handover latency, minimizing service interruption, and allowing for a seamless transition from the serving cell 104-1 to the target cell 104-2.

[0075]

[0071] In some cases, when the cell switch command indicates that the downlink delay offset values cannot be used for computing the uplink TA value for the target cell 104-2, the UE 106 may perform RACH-based cell switch to the target cell 104-2 and the base station may facilitate the RACH-based LTM cell switch to the target cell 104-2 (in Step S8).

[0076]

[0072] In some cases, the base station 102 may configure the UE 106 to automatically use downlink delay offset for computing the uplink TA value for the target cell 104-2, whenever a cell switch command is issued by the base station 102 (provided the UE 106 has a valid uplink TA value).

[0077]

[0073] In one example of Step S7, after computing the uplink TA value for the target cell 104-2 based on the downlink delay offset values, the UE 106 may determine a validity of the uplink TA value which was computed based on the downlink delay offset values. Specifically, the UE 106 may monitor a timer associated with the computed uplink TA value or the downlink delay offset values. The timer reflects freshness of the TA information.

[0074] In some cases, upon determining that the timer has expired (indicating that the computed TA value may no longer be valid due to potential changes in propagation conditions or due to UE mobility), the UE 106 performs a RACH-based cell switch from the serving cell 104-1 to the target cell 104-2. This approach ensures that the UE 106 synchronizes the uplink transmission with the target cell 104-2 even when the computed TA is outdated.

[0078]

[0075] In some cases, upon determining that the timer is active (i.e., indicating that the computed TA value is still valid), the UE 106 may perform the RACH-less cell switch from the serving cell 104-1 to the target cell 104-2 using the computed uplink TA value. This approach avoids delays and signaling overhead associated with the traditional RACH-based cell switch procedures, thereby providing a faster and seamless handover to the target cell 104-2. Thus, by monitoring the timer, the UE 106 dynamically selects between RACH-less and RACH-based LTM cell switch procedures, thereby providing reliable uplink synchronization in UE handovers.

[0079]

[0076] In some cases, the UE 106 may transmit and the base station 102 may receive an indication of validity of the uplink TA value. The base station 102 may facilitate a RACH-based cell switch from the serving cell 104-1 to the target cell 104-2, when the indication indicates that the uplink TA value is invalid. Further, the base station 102 may facilitate the RACH-less cell switch from the serving cell 104-1 to the target cell 104-2 using the uplink TA value, when the indication indicates that the uplink TA value is valid.

[0080]

[0077] In this manner, the techniques of the present disclosure optimize TA acquisition during LTM cell switch procedures The above discussed techniques allows the UE 106 to compute uplink TA values from downlink delay offset values measured during multi-TRP operations which results in implementing efficient RACH-less LTM cell switching procedures, thereby reducing handover latency and signaling overhead. Further, since the downlink delay offsetsare derived from high-density Tracking Reference Signals, the TA estimation is more accurate. The techniques of the present disclosure provide low-latency and reliable LTM cell switching by allowing the UE to pre-acquire accurate uplink TA from downlink delay offset measurements of multi-TRP reference signals.

[0081]

[0078] Referring now to FIG. 4, a flowchart is described illustrating an example method 400 performed by a UE 106 for TA acquisition during LTM cell switch procedures, according to an embodiment of the present disclosure.

[0082]

[0079] The method 400 may include, at block 402. receiving, at the UE 106 served by a serving cell 104-1, LTM candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic NZP CSI-RS resource set configured as one or more TRSs for one or more TRPs associated with one or more LTM candidate cells.

[0083]

[0080] At block 404, the method 400 may include receiving a DCI command to initiate aperiodic delay offset reporting of the one or more TRPs.

[0084]

[0081] At block 406, the method 400 may include computing a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell 104-1.

[0085]

[0082] At block 408, the method 400 may include receiving a cell switch command instructing the UE 106 to switch from the serving cell 104-1 to a target cell 104-2 of the one or more LTM candidate cells. The cell switch command indicates whether to use dow nlink delay offset values for computing an uplink TA value for the target cell 104-2.

[0086]

[0083] At block 410, the method 400 may include computing the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell 104-2, responsive to the cell switch command indicating that thedownlink delay offset values are to be used for computing the uplink TA value for the target cell.

[0087]

[0084] At block 412, the method 400 may include performing RACH-less LTM cell switch to the target cell 104-2 using the computed uplink TA value.

[0088]

[0085] Referring now to FIG. 5, a flowchart is described illustrating an example method 500 performed by a base station 102 for TA acquisition during LTM cell switch procedures, according to an embodiment of the present disclosure.

[0089]

[0086] The method 500 may include, at block 502, transmitting, to a UE 106 served by a serving cell 104-1. LTM candidate cell configuration. The LTM candidate cell configuration comprising an aperiodic NZP CSI-RS resource set configured as one or more TRSs for one or more TRPs associated with one or more LTM candidate cells.

[0090]

[0087] At block 504, the method 500 may include transmitting a DCI command to initiate aperiodic delay offset reporting of the one or more TRPs.

[0091]

[0088] At block 506, the method 500 may include transmitting a cell switch command instructing the UE 106 to switch from the serving cell 104-1 to a target cell 104-2 of the one or more LTM candidate cells. The cell switch command indicates whether to use downlink delay offset values for computing an uplink TA value for the target cell 104-2.

[0092]

[0089] At block 508, the method 500 may include initiating a random access channel-less (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell 104-2.

[0093]

[0090] FIG. 6 illustrates a block diagram 600 of an apparatus or device, in accordance with some embodiments of the present disclosure. As shown in FIG. 6, the apparatus 600 may include a processor 610, a memory 620, a storage component 630, an input component 640, an output component 650, a communication interface 660, a bus 670, but not limited thereto.

[0091] The processor 610, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 610 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and / or one or more single core processors, a distributed processing system, or the like. The processor 610 may be a Central Processing Unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU), an application-specific integrated circuit (ASIC), or another type of processing component.

[0094]

[0092] The memory 620 includes a non-transilory computer readable medium / media. The memory 620 includes a random- access memory (RAM), a read only memory (ROM), and / or another type of dynamic or static storage device (e.g., a flash memory’, a magnetic memory, and / or an optical memory’) that stores information and / or instructions for use by processor 610.

[0095] The memory 620 comprises machine-readable instructions which are executable by the processor 610. These machine-readable instructions when executed by the processor 610 cause the processor 610 to perform one or more method steps of an embodiment described in the present disclosure.

[0096]

[0093] The storage component 630 stores information and / or software related to the operation and use of the apparatus 600. For example, the storage component 630 may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, and / or a solid-state disk), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, a magnetic tape, and / or another ty pe of non-transitory computer-readable medium, along with a corresponding drive.

[0097]

[0094] The input component 640 is configured to receive information, such as user input. For example, the input component 640 may include, but not be limited to, a touch screen display, a keyboard, a keypad, a mouse, a button, a switch, and / or a microphone. Additionally, oralternatively, the input component 640 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0098]

[0095] The output component 650 is configured to provide output information from the apparatus 600. For example, the output component 650 may be, but not limited to, a display, a speaker, an instruction device to an external device, and / or one or more light-emitting diodes (LEDs).

[0099]

[0096] The communication interface 660 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 660 can be a wired connection, a wireless connection, or a combination of wired and wireless connections, and can be a direct connection or an indirect connection via a communication network that exists between the apparatus 600 and other devices. In other words, the standard of the communication interface 660 is not limited.

[0100]

[0097] The bus 670 acts as an interconnect between the processor 610, the memory 620, the storage component 630, the input component 640, the output component 650, and the communication interface 660 of the apparatus 600. The bus 670 may include a wired interconnection or a wireless interconnection.

[0101]

[0098] The number and arrangement of components shown in FIG. 6 are provided as an example. In practice, the apparatus 600 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 6.

[0102] Additionally, or alternatively, a set of components (e.g., one or more components) of the apparatus 600 may perform one or more functions described as being performed by another set of components of the apparatus 600. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of apparatuses 600 in communication with one another.

[0099] In one non-limiting embodiment, the apparatus 600 may be used to implement some or all functions of any entity including UEs 106, RUs 112, various network entities of the RAN (e.g., the CU 108, the DUs 110, the CU-CP 114, the CU-UP 116, etc.), various entities of the core network, but not limited thereto. In one example, the apparatus 600 may implement the functionalities of the UE 106. In another example, the apparatus 600 may implement the functionalities of the base station 102.

[0103]

[0100] Example Items:

[0104]

[0101] Item 1. A method comprising: receiving, at a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; receiving, at the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; computing, at the UE, a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; receiving, at the UE, a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: computing the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; and performingrandom access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0105]

[0102] Item 2. The method of item 1, further comprising: determining a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value; upon determining that the timer has expired, performing a RACH-based cell switch from the serving cell to the target cell; and upon determining that the timer is active, performing the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

[0106]

[0103] Item 3. The method of any of items 1-2, further comprising: responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, performing RACH-based LTM cell switch to the target cell.

[0107]

[0104] Item 4. The method of any of items 1-3, wherein receiving the cell switch command comprises: receiving the cell switch command via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

[0108]

[0105] Item 5. The method of any of items 1-4, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE, and wherein physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

[0109]

[0106] Item 6. The method of any of items 1-5, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

[0107] Item 7. The method of any of items 1-6, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to different base stations.

[0110]

[0108] Item 8. A User Equipment (UE) configured to: receive, at the User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; receive a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; receive a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; and perform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0111]

[0109] Item 9. The UE of item 8, further configured to: determine a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value; upon determining that the timer has expired, perform a RACH-based cell switch from the serving cell to the target cell; and upon determining that the timer is active,perform the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

[0112] [HO] Item 10. The UE of any of items 8-9, further configured to: responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, perform a RACH-based LTM cell switch to the target cell.

[0113] [Hl] Item 11. The UE of any of items 8-10, wherein to receive the cell switch command, the UE is configured to: receive the cell switch command via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

[0114]

[0112] Item 12. The UE of any of items 8-11, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE, and wherein physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

[0115]

[0113] Item 13. The UE of any of items 8-12, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

[0116]

[0114] Item 14. The UE of any of items 8-13, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to different base stations.

[0117]

[0115] Item 15. A non-transitory computer readable media storing one or more computer executable instructions which, when executed by a User Equipment (UE), cause the UE to: receive, at a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising anaperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; receive a downlink control information (DC1) command to initiate aperiodic delay offset reporting of the one or more TRPs; compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; receive a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and responsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell: compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; and perform random access channelless (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

[0118]

[0116] Item 16. The non-transitory computer readable media of item 15, wherein the one or more computer executable instructions further cause the UE to: determine a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value; upon determining that the timer has expired, perform a RACH-based cell switch from the serving cell to the target cell; and upon determining that the timer is active, perform the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

[0119]

[0117] Item 17. The non-transitory computer readable media of any of items 15-16, wherein the one or more computer executable instructions further cause the UE to: responsive to the cell switch command indicating that the downlink delay offset values are not be used forcomputing the uplink TA value for the target cell, perform a RACH-based LTM cell switch to the target cell.

[0120]

[0118] Item 18. The non-transitory computer readable media of any of items 15-17, wherein to receive the cell switch command, the one or more computer executable instructions cause the UE to: receive the cell switch command via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

[0121]

[0119] Item 19. The non-transitory computer readable media of any of items 15-18, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE, and wherein physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

[0122]

[0120] Item 20. The non-transitory computer readable media of any of items 15-19, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

[0123]

[0121] Item 21. A method comprising: transmitting, to a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; transmitting, to the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; receiving, from the UE, a delay offset report comprising a downlink delay offset valuefor each of the one or more TRPs; transmitting, to the UE, a cell switch command instructing the UE to switch from the serving cell to the target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use the downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and facilitating a random access channel-less (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.

[0124]

[0122] Item 22. The method of item 21. further comprising: responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, facilitating RACH-based LTM cell switch to the target cell.

[0125]

[0123] Item 23. The method of any of items 21-22, wherein transmitting the cell switch command comprises transmitting a Media Access Control-Control Element (MAC-CE) to the UE instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

[0126]

[0124] Item 24. The method of any of items 21-23, further comprising: configuring the UE to automatically use the downlink delay offset values for computing the uplink TA value for the target cell.

[0127]

[0125] Item 25. The method of any of items 21-24, further comprising: receiving, from the UE, an indication of validity7of the uplink TA value; facilitating a RACH-based cell switch from the serving cell to the target cell, when the indication indicates that the uplink TA value is invalid; and facilitating the RACH-less cell switch from the serving cell to the target cell using the uplink TA value, when the indication indicates that the uplink TA value is valid.

[0126] Item 26. A base station configured to: transmit, to a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CS1-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; transmit, to the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; receive, from the UE, a delay offset report comprising a downlink delay offset value for each of the one or more TRPs; transmit, to the UE, a cell switch command instructing the UE to switch from the serving cell to the target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use the downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and facilitate a random access channelless (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.

[0128]

[0127] Item 27. A non-transitory computer readable media storing one or more computer executable instructions which, when executed by a base station, cause the base station to: transmit, to a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells; transmit, to the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs; receive, from the UE, a delay offset report comprising a downlink delay offset value for each of the one or more TRPs; transmit, to the UE, a cellswitch command instructing the UE to switch from the serving cell to the target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use the dow nlink delay offset values for computing an uplink timing advance (TA) value for the target cell; and facilitate a random access channel-less (RACH-less) LTM cell switch procedure when the cell switch command indicates use of the downlink delay offset values for computing the uplink TA value for the target cell.

[0129]

[0128] It may be noted here that the subj ect matter of some or all embodiments described with reference to Figures 1-3 may be relevant for the methods 400.500 and the same is not repeated for the sake of brevity. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the embodiments of the present disclosure are intended to be illustrative, but not limiting, of the scope of the disclosure, which is set forth in the appended claims.

Claims

What is claimed is:

1. A method comprising:receiving, at a User Equipment (UE) served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells;receiving, at the UE, a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs;computing, at the UE, a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell; receiving, at the UE, a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; andresponsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell:computing the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; andperforming random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

2. The method of claim 1, further comprising:determining a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value;upon determining that the timer has expired, performing a RACH-based cell switch from the serving cell to the target cell; andupon determining that the timer is active, performing the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

3. The method of claim 1, further comprising:responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, performing RACH-based LTM cell switch to the target cell.

4. The method of claim 1, wherein receiving the cell switch command comprises:receiving the cell switch command via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

5. The method of claim 1, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE, and wherein physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

6. The method of claim 1. wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

7. The method of claim 1 , wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to different base stations.

8. A User Equipment (UE) configured to:receive, at the UE served by a serving cell. Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells;receive a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs;compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell;receive a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; andresponsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell:compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; andperform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

9. The UE of claim 8, further configured to:determine a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value;upon determining that the timer has expired, perform a RACH-based cell switch from the serving cell to the target cell; andupon determining that the timer is active, perform the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

10. The UE of claim 8. further configured to:responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, perform a RACH-based LTM cell switch to the target cell.

11. The UE of claim 8, wherein to receive the cell switch command, the UE is configured to:receive the cell switch command via a Media Access Control-Control Element (MAC-CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

12. The UE of claim 8, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE. and whereinphysical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

13. The UE of claim 8, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

14. The UE of claim 8, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to different base stations.

15. A non-transitory computer readable media storing one or more computer executable instructions which, when executed by a User Equipment (UE), cause the UE to:receive, at the UE served by a serving cell, Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configuration, the LTM candidate cell configuration comprising an aperiodic non-zero-power Channel State Information Reference Signal (NZP CSI-RS) resource set configured as one or more Tracking Reference Signals (TRSs) for one or more Transmission and Reception Points (TRPs) associated with one or more LTM candidate cells;receive a downlink control information (DCI) command to initiate aperiodic delay offset reporting of the one or more TRPs;compute a downlink delay offset value for each TRP based on the one or more TRSs and reporting the downlink delay offset value for each TRP to the serving cell;receive a cell switch command instructing the UE to switch from the serving cell to a target cell of the one or more LTM candidate cells, the cell switch command indicating whether to use downlink delay offset values for computing an uplink timing advance (TA) value for the target cell; andresponsive to the cell switch command indicating that the downlink delay offset values are to be used for computing the uplink TA value for the target cell:compute the uplink TA value for the target cell based on the downlink delay offset values corresponding to at least one TRP which is associated with the target cell; andperform random access channel-less (RACH-less) LTM cell switch to the target cell using the computed uplink TA value.

16. The non-transitory computer readable media of claim 15, wherein the one or more computer executable instructions further cause the UE to:determine a validity of the uplink TA value computed based on the downlink delay offset values, by monitoring a timer associated with the uplink TA value;upon determining that the timer has expired, perform a RACH-based cell switch from the serving cell to the target cell; andupon determining that the timer is active, perform the RACH-less cell switch from the serving cell to the target cell using the computed uplink TA value.

17. The non-transitory computer readable media of claim 15, wherein the one or more computer executable instructions further cause the UE to:responsive to the cell switch command indicating that the downlink delay offset values are not be used for computing the uplink TA value for the target cell, perform a RACH-based LTM cell switch to the target cell.

18. The non-transitory computer readable media of claim 15, wherein to receive the cell switch command, the one or more computer executable instructions cause the UE to:receive the cell switch command via a Media Access Control-Control Element (MAC- CE) instructing the UE to switch from the serving cell to the target cell, wherein the MAC-CE indicates whether to use the downlink delay offset values for computing the uplink TA value for the target cell.

19. The non-transitory computer readable media of claim 15, wherein at least one transmission configuration indicator (TCI) state associated with the one or more LTM candidate cells is configured with the UE, and wherein physical cell identifiers (PCIs) of the one or more LTM candidate cells differ from a PCI of the serving cell.

20. The non-transitory computer readable media of claim 15, wherein the serving cell is associated with a serving Distributed Unit (DU) and the target cell is associated with a target DU, and wherein the serving DU and the target DU belong to a same base station.

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