Method and system for optimizing latency for L1 / L2 triggered mobility - Patents.com

Abstract

A method, system, and device for configuring an inter-cell change are provided. The method can be implemented by receiving, by a user equipment (UE), a downlink signal, where the downlink signal originates from a serving distribution unit (DU), and the downlink signal includes at least one of a scheduling gap duration value, a start time value, and a target cell index; and performing, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration, where the uplink synchronization includes sending, by the UE, a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, where the target DU is one of a plurality of neighbor cells to the serving DU.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from Indian Provisional Application No. 202241060061, filed with the Indian Patent Office on October 20, 2022, the entire disclosure of which is incorporated herein by reference for all purposes.

[0002] Systems and methods consistent with example embodiments of the present disclosure relate to optimizing latency in L1 / L2 triggered inter-cell changes in a decomposed telecommunications architecture. [Background technology]

[0003] The radio access network (RAN) is a critical component in telecommunications systems because it connects end-user devices (or user equipment (UE)) to the rest of the network. The RAN includes a combination of various network elements (NEs) that connect end-user devices to the core network. Traditionally, the hardware and / or software of a particular RAN is vendor-specific.

[0004] In recent years, advances in telecommunications technology have made it possible to virtually realize many telecommunication services in software. For example, a RAN, such as an open RAN (O-RAN) architecture, decomposes (de-aggregates) a network component into multiple functional elements. For example, a baseband unit (BBU) or a base station (i.e., an eNB or gNB) is decomposed into several functional elements, including a distributed unit (DU) and a centralized unit (CU), and the CU can be further decomposed into a centralized unit-control plane (CU-CP) and a centralized unit-user plane (CU-UP). The decomposition of network elements makes it possible to define and provide telecommunication services and related functions in software-based forms or virtual network services, such as virtualized network functions (VNFs), cloud-native network functions (CNFs), or software-defined networking (SDN), among others.

[0005] Figure 1 shows a decomposed gNB architecture of the related art in 3GPP. The gNB is decomposed into multiple logical entities. While two gNB-DU nodes are shown, it can be understood that there can be multiple gNB-DU nodes. It should also be noted that a single DU can host multiple cells. The gNB-DU node can communicate with the CU-CP via an F1-C interface and with the CU-UP via an F1-U interface. The CU-CP and CU-UP can communicate via an E1 interface. The gNB-CU-CP hosts the Packet Data Convergence Protocol (PDCP) layer and the Radio Resource Control (RRC) layer, while the gNB-DU hosts the Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and Physical (PHY) layer. Scheduling operations are performed in the gNB-DU.

[0006] To support L1 / L2-centric inter-cell change, since the RLC MAC and PHY layers are located in the gNB-DU, the cell change configuration should be performed in the gNB-CU-CP and the serving cell change should be performed autonomously by the gNB-DU without further interaction with higher layers. This operation may be referred to herein as L1 / L2 triggered mobility (LTM).

[0007] Specifically, LTM may be defined as a mobility procedure that enables the network to switch a UE from a source cell to a target cell without necessarily requiring a synchronous reconfiguration. In particular, the network may indicate in L2 signaling (e.g., MAC CE) beams belonging to LTM candidate cells on which the UE should perform the LTM cell switch procedure based on received L1 measurements. The UE is provided with at least one (or more) LTM candidate cell configurations by the network before performing the LTM cell switch procedure.

[0008] In related technology, a UE may periodically evaluate link quality between a serving cell and neighboring cells. To evaluate link quality, the UE may perform measurements (e.g., reference signal received power (RSRP) and reference signal received quality (RSRQ) of a synchronization signal block (SSB)) on the serving cell and neighboring cells relative to the UE. Such measurements may be processed (e.g., by L3 filtering) and reported to the serving cell based on a reporting configuration. If one of the neighboring cells meets a predetermined handover criterion, the serving cell may indicate to the UE that it should handover to that neighboring cell. The UE then uses a random access channel (RACH) in the new neighboring cell.

[0009] FIG. 2 illustrates a call flow for a typical Layer 3 handover procedure involving a UE, a source gNB node, and a target gNB node (i.e., the gNB-DU node described above) according to the related art. In this example, explicit radio resource control (RRC) signaling needs to be triggered, which may result in a handover. In a first step, the source gNB node can initiate the handover by issuing a handover request (e.g., over the Xn interface). In a second step, the target gNB node can perform admission control and provide a new RRC configuration by acknowledging (ACKing) the handover request. In a third step, the source gNB node can provide the RRC configuration to the UE by forwarding an RRC reconfiguration message received in the handover request ACK. The RRC reconfiguration message may include at least a cell ID and any information required to access the target cell (which may include beam-specific information, if present) so that the UE can access the target cell without reading system information. In some cases, information required for contention-based random access (CBRA) and contention-free random access (CFRA) may be included in the RRC reconfiguration message. In a fourth step, the UE moves the RRC connection to the target gNB node and can then respond to the target gNB node with an RRC reconfiguration complete message.

[0010] In the related art, another method for managing mobility can include inter-cell beam management (ICBM). Unlike the above method shown in FIG. 2, ICBM does not require explicit RRC signaling to be triggered. Instead, with ICBM, the UE may receive or transmit UE-dedicated channels / signals via a transmission / reception point (TRP) associated with a physical cell ID (PCI) different from the PCI of the serving cell, while non-UE-dedicated channels / signals can only be received via a TRP associated with the PCI of the serving cell. Generally, in the related art, a gNB node can provide a measurement configuration to the UE (via RRC signaling), which can include, for example, configuration of SSB and / or Channel State Information (CSI) resources and / or resource sets, reports, and trigger conditions for triggering channel and interference measurements and reports. In the case of ICBM, this can be a measurement configuration including SSB resources associated with a PCI different from the PCI of the serving cell. Beam-level mobility can then be handled at lower layers by physical layer and MAC layer control signaling, so that the RRC (hosted in the CU-CP) does not need to know which beam is being used by the UE at a given time. Other related similar methods can include, for example, SSB-based beam-level mobility based on an SSB associated with an initial downlink bandwidth part (DL BWP), and can be configured only for the initial DL BWP and the DL BWP that includes the SSB associated with the initial DL BWP. For other DL BWPs, beam-level mobility can be performed only based on a channel state information reference signal (CSI-RS).

[0011] In the related art, a potential problem with LTM occurs when a UE must perform a random access channel (RACH) when handing over to a new cell. In particular, the delay caused by the latency from the RACH procedure can increase. Specifically, during handover, the UE waits for a physical RACH (PRACH) opportunity to perform the RACH and synchronize to the target uplink. This is necessary because the UE's timing advance in the target cell (configured for handover) may differ from that of the serving cell. Therefore, the UE must wait for an available PRACH opportunity, send a preamble, and wait for a random access response (RAR). On average, this can cause a delay of 10 to 20 ms from the RACH procedure, which is suboptimal.

[0012] Additionally, although methods and systems related to beam-based inter-cell mobility (such as the ICBM described above) are known in the related art, the related art does not describe how to manage beam-based inter-cell mobility using handover. Therefore, there is a need to optimize / reduce delay in handover procedures while incorporating methods and systems for beam-based inter-cell mobility. Summary of the Invention

[0013] Exemplary embodiments of the present disclosure provide methods and systems for processing L1 / L2 triggered mobility (LTM) to reduce mobile latency. In particular, according to embodiments, the scheduling gap duration in a serving cell can be indicated to a user equipment (UE) so that preamble transmission and uplink synchronization with a target cell (target DU) can be performed during the scheduling gap. The uplink synchronization and preamble transmission, in which the UE acquires the target cell's timing advance, can be performed with respect to the target cell, and these discoveries can be indicated back to the serving cell (serving DU). Thus, exemplary embodiments can forgo performing random channel access (RACH) to perform serving cell change (SCC) handover (HO), such that mobile latency is reduced. Furthermore, exemplary embodiments can enable a UE to determine a preferred beam to be used by a neighboring target cell and indicate it to the serving cell / DU. Thus, embodiments of the present disclosure can provide a more optimal approach to processing LTM with reduced latency and enable beam-based inter-cell mobility.

[0014] According to an embodiment, there may be provided a method for configuring an inter-cell change, performed by at least one processor. The method may include receiving, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; and performing, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration, the uplink synchronization including sending, by the UE, a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, the target DU being one of a plurality of neighbor cells to the serving DU.

[0015] The method may also include obtaining, by the UE, a timing advance to use during transmission to or reception from the target cell, and reporting, by the UE, a result of the uplink synchronization and the obtained timing advance to the serving DU.

[0016] The preamble transmission and uplink synchronization may be performed while the UE is connected to the serving DU. The downlink signal may be one of the following: a Physical Downlink Control Channel (PDCCH) or a MAC Control Element (MAC CE) command.

[0017] Performing measurements based on the downlink signals further includes performing L1 measurements of the target cell. The method may further include sending, by the UE, the L1 measurements to a serving DU, where the serving DU can determine whether to perform a RACH-less LTM handover based on the L1 measurements based on a target cell timing advance reported by the UE.

[0018] Sending a preamble transmission to the target DU based on the downlink signal may further include sending a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble.

[0019] The method may further include performing, by the UE, uplink synchronization based on the measurements and the preamble transmission, and sending, by the UE, a status signal to the serving DU.

[0020] The L1 measurements are performed and reported aperiodically or event-based to one or more target cells, and the L1 measurements are sent aperiodically to the serving DU.

[0021] According to one embodiment, an apparatus for configuring an inter-cell change may be provided. The apparatus may include at least one memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to: receive, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; and perform, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration, the uplink synchronization including sending, by the UE, a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, the target DU being one of a plurality of neighbor cells to the serving DU.

[0022] The at least one processor may be further configured to execute computer-executable instructions to obtain, by the UE, a timing advance to use during transmission to or reception from the target cell, and to report, by the UE, a result of the uplink synchronization and the obtained timing advance to the serving DU.

[0023] The at least one processor may be further configured to execute the computer-executable instructions to perform the measurements by performing L1 measurements of the target cell based on the downlink signal, and the at least one processor may be further configured to execute the computer-executable instructions to send, by the UE, the L1 measurements to a serving DU, wherein the serving DU can decide, based on a target cell timing advance reported by the UE, whether to perform an LTM handover without RACH based on the L1 measurements.

[0024] The at least one processor may be further configured to execute computer-executable instructions to send a preamble transmission to the target DU based on the downlink signal by sending a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble.

[0025] The at least one processor may be further configured to execute computer-executable instructions to perform, by the UE, uplink synchronization based on the measurements and the preamble transmission, and to send, by the UE, a status signal to the serving DU.

[0026] Additional aspects will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the presented embodiments of the present disclosure. [Brief explanation of the drawings]

[0027] Features, aspects, and advantages of certain exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, in which like reference numerals refer to like elements.

[0028] [Figure 1] FIG. 1 illustrates a decomposed gNB architecture according to the related art. [Figure 2] A diagram showing a call flow for a typical handover procedure for LTM involving a UE, a source gNB node, and a target gNB node according to the related art. [Figure 3] FIG. 1 illustrates an inter-cell mobility scenario according to one embodiment. [Figure 4] FIG. 1 illustrates a handover procedure according to one embodiment. [Figure 5] FIG. 1 is a diagram of an example environment in which the systems and / or methods described herein may be implemented. [Figure 6] FIG. 2 is a diagram of exemplary components of a device, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following detailed description of the exemplary embodiments refers to the accompanying drawings.

[0030] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of implementations. Moreover, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Furthermore, in the flowcharts and operational descriptions provided below, it is understood that one or more operations may be omitted, one or more operations may be added, one or more operations may be performed (at least partially) concurrently, and the order of one or more operations may be swapped.

[0031] It will be apparent that the systems and / or methods described herein may be implemented in different forms of hardware, firmware, 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 implementation. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It will be understood that software and hardware can be designed to implement the systems and / or methods based on the description herein.

[0032] Although particular combinations of features are recited in the claims and / or disclosed herein, these combinations do not limit the disclosure of possible implementations. Indeed, many of these features can be combined in ways not specifically recited in the claims and / or disclosed herein. Although each dependent claim listed below may depend directly on only one claim, the disclosure of possible implementations includes each dependent claim in combination with every other claim in the claim set.

[0033] No element, act, or instruction used herein should be construed as critical or required unless explicitly stated 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." Where only one item is intended, the term "one" or similar language is used. Also, as used herein, terms such as "has," "have," "having," "include," and "including" are intended to be open-ended terms. Furthermore, the phrase "based on" is intended to mean "based at least in part on," unless expressly stated otherwise. Furthermore, phrases such as "at least one of [A] and [B]" or "at least one of [A] or [B]" should be understood to include A only, B only, or both A and B.

[0034] Furthermore, the described features, advantages, and characteristics of the present disclosure may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize, in light of the description herein, that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present disclosure.

[0035] Exemplary embodiments of the present disclosure provide methods and systems for handling L1 / L2 triggered mobility (LTM) to reduce mobile latency. In particular, according to embodiments, the scheduling gap duration in a serving cell can be indicated to a user equipment (UE) so that preamble transmission and uplink synchronization with a target cell (target DU) can be performed during the scheduling gap. The uplink synchronization and preamble transmission, in which the UE acquires the timing advance of the target cell, can be performed to the target cell, and these discoveries can be indicated back to the serving cell (serving DU). Thus, exemplary embodiments can forgo performing random channel access (RACH) to perform serving cell change (SCC) handover (HO), so that mobile latency is reduced. Furthermore, exemplary embodiments can enable a UE to determine a preferred beam to be used by a neighboring target cell and indicate it to the serving cell / DU.

[0036] Thus, embodiments of the present disclosure can provide a more optimal approach to processing LTM with reduced latency and enable beam-based inter-cell mobility.

[0037] 3 illustrates an exemplary inter-cell mobility scenario in accordance with one or more embodiments. A UE 300 is provided, as well as cell-1 310-1, cell-2 310-2, and cell-3 310-3. As shown in FIG. 3, UE 300 may be located in cell-1 310-1, which is the serving cell (i.e., serving DU). Cell-2 310-2 and cell-3 310-3 may be considered neighbor cells to cell-1 310-1.

[0038] According to some embodiments, the UE 300 may be configured with a measurement configuration including, for example, configurations for measuring SSB and / or CSI-RS resources, physical cell IDs, etc. The UE 300 may also be configured with a measurement reporting configuration. For example, such reporting configurations may include periodic and aperiodic reporting to a serving cell (e.g., cell-1 310-1), although it should be appreciated that other reporting schemes and scheduling configurations may be configured by the UE 300. The UE 300 may be configured to measure the signal quality of one or more of the cells (i.e., the serving cell cell-1 310-1 and neighboring cells cell-2 310-2 and cell-3 310-3).

[0039] The UE 300 may perform cell measurements while connected to cell-1 310-1, and the UE 300 may perform cell measurements during scheduling gaps indicated by cell-1 310-1 (scheduling gaps are described in more detail with reference to FIG. 4 below). For inter-frequency measurements, the UE 300 may be configured with measurement gaps. In other embodiments, the UE may be dynamically indicated the set of time resources on which the UE may perform measurements. Signaling for such indication may be in the form of a Physical Downlink Control Channel (PDCCH) or MAC Control Element (MAC CE) command.

[0040] According to one embodiment, the UE 300 may determine a preferred beam(s) to use while transmitting to or receiving from a neighboring cell. The UE 300 may also report to the serving cell Cell-1 310-1 (e.g., via an uplink MAC CE) the preferred beam to be used for that neighboring cell.

[0041] According to one embodiment, the UE 300 may be configured with a set of trigger states. In particular, each trigger state may include an offset value. For example, the offset value may be in slots. Each trigger state may also include a gap length. The trigger states may be configured in RRC, and at least one trigger state may be activated or deactivated in the MAC CE. The UE 300 may be indicated an index to the trigger state in Downlink Control Information (DCI). The offset value may indicate a time after a downlink signal (e.g., a PDCCH) is received at which the UE 300 may start performing measurements, and the gap value may indicate the length of a gap during which the UE 300 may continue performing measurements. As an example, if a downlink signal is received in slot n and the trigger state value includes an offset value of L slots and a gap value of M slots, the UE 300 may start performing measurements in slot n+L and finish in slot N+L+M−1. The UE 300 may also be indicated which cell(s) to measure as part of the trigger state. Alternatively, this may be indicated to the UE 300 using a separate entry in the control information. In yet another embodiment, the offset and / or gap values may be explicitly signaled in the DCI.

[0042] According to another embodiment, the UE 300 may be configured to receive a timing advance to use for transmissions to neighbor cell-2 310-2 and / or cell-3 310-3, which may be done proactively (i.e., before a handover request to the neighbor cell is received).

[0043] FIG. 4 illustrates an example timing diagram of an SCC / handover procedure according to one or more embodiments. A UE 400, a serving DU 410, a target DU 420, and a CU-CP 430 may be provided. It should be understood that, according to an embodiment, the UE 400 may be similar to the UE 300 described above, and the serving DU 410 may be similar to the cell-1 310-1 described above. The target DU 420 may be similar to either the cell-2 310-2 or the cell-2 310-3 described above. The UE 400 may be configured with lower layer (L1 / L2) triggered mobility (LTM) with one or more target cells within one or more DUs (e.g., the target DU 420). The CU-CP 430 may send an RRC reconfiguration message to the UE 400 to configure LTM in the target cell (the target DU 420). The UE 400 may then send an intra-frequency L1 measurement report to the serving DU 410.

[0044] 4, in operation S440, the serving DU 410 may detect that the target cell radio conditions exceed a predefined threshold. For example, this may be based on an L1 measurement report indicating that the UE 400 has a poor radio connection with the serving DU 410. Accordingly, the serving DU 410 may instruct the UE 400 to perform target cell measurements of the target DU 420 and / or an uplink synchronization procedure with the target DU 420 cell.

[0045] According to one embodiment, the instruction from the serving DU 410 to the UE 400 may be in the form of a downlink signal. The downlink signal may be in the form of a PDCCH or MAC CE command. The downlink signal may include a scheduling gap value, a start time value, and a target cell index. Specifically, a scheduling gap is a period of time during which the UE 400 does not schedule any packets in the downlink in all transmission time intervals (TTIs) by a packet scheduler (MAC PS) located in the serving DU 410 associated with the bearer. The scheduling gap may be in the form of a pre-configured index agreed by any known standard (e.g., 3GPP RAN2). Thus, different scheduling gap values may be represented using different indices. Based on this information from the downlink signal, the UE 400 can perform uplink measurements and / or uplink synchronization and / or preamble transmission during this scheduling gap. The downlink signal may include the physical cell ID (PCI) of a neighboring cell or the index of the neighboring cell. The PCI and / or index may be used to determine resource allocation for transmission (e.g., UE transmit beam, preamble index, random access time / frequency resource, etc.) Alternatively, the downlink signal may not include the PCI or cell index, but may include an index to the preamble and / or random access resource.

[0046] In operation S441, after receiving the command to perform target measurements in operation S440, the UE 400 may perform uplink (UL) synchronization with the target DU 420. The UL synchronization may include performing L1 measurements (e.g., RSRP and / or RSRQ) of neighboring target DUs 420, transmitting a preamble to the target DU 420, and obtaining a timing advance for the UE 400 in the target cell. Nevertheless, it should be noted that according to one embodiment, the UL synchronization may be performed with one or more neighboring cells other than the target DU 420. According to another embodiment, the L1 measurements of neighboring target DU cells 420, the timing advance obtained by the UE 400, and the result of the uplink synchronization may be signaled back to the serving DU 410 (e.g., via a MAC CE uplink). This report may be signaled to the serving DU 410 periodically or aperiodically (i.e., event-based). Based on these measurements, the serving DU 410 can instruct the UE to perform a RACH-less or RACH-based LTM handover / serving cell change (SCC) to the target DU 420 (operation S443, as described in more detail below). The UE 400 can also inform the serving DU 410 whether the UL synchronization and / or preamble transmission was successful (e.g., by sending a status signal). According to yet another embodiment, the UE 400 can proactively send a random access preamble for the indicated target DU 420 during the scheduling gap, so that the target DU 420 can determine a timing advance. The serving DU 410 can send the timing advance and the index of the cell corresponding to the timing advance to the UE 400.The timing advance information of the UE 400 can also be sent from the target DU 420 to the serving DU 410, for example through the CU-CP 430 (note that in this case it is assumed that the serving DU 410 and the target neighbor cell are associated with different gNB-DUs served by the same gNB-CU), or directly via the DU-DU interface if available.

[0047] According to one embodiment, the UE 400 may request a timing advance alignment applicable to the UE in the target DU 420 from the serving DU 410. The request may be sent to the serving DU 410 in the MAC CE. The request may include the PCI and / or index of the target DU 420. The serving DU 410 may send timing advance values applicable to neighboring cells to the UE 400, or may instruct the UE 400 to initiate the procedure disclosed above to obtain timing advance values (e.g., when the serving DU 410 does not have a timing advance value or the value is out of date).

[0048] The UE 400 may have been configured with random access resources before this operation (e.g., during target cell preparation), and these random access resources may be allocated exclusively for transmitting the random access preamble to the target DU 420. The resource configuration may include, but is not limited to, a preamble index, a time / frequency resource (e.g., a symbol / slot index, a resource block (RB) index), a transmit power, etc. The above measurements and preamble transmission may be performed while the UE 400 maintains an RRC connection to the serving DU 410.

[0049] In operation S443, the serving DU 410 may determine that the serving cell change radio conditions are met (e.g., based on L1 measurements of the target DU 420). Therefore, the serving DU 410 may instruct the UE 400 to perform an SCC handover to the target DU 420. According to one embodiment, this instruction may be sent via a MAC CE command. It should be understood that the system information of the target DU 420 may already be available for use by the UE 400 (e.g., from a previous configuration sent previously before the procedure). The serving DU 410 may also notify the CU-CP 430 of the change via an F1 message. Because the UE 400 has already acquired the timing advance of the target cell, the UE 400 can send a scheduling request directly to the target DU 420 without needing to perform a RACH. According to one embodiment, the scheduling request may utilize the previously acquired timing advance. The scheduling request configuration may also be available in the UE 400 from a previous configuration by the serving DU 410. Thus, when the UE 400 moves to the target DU 420, the target DU 420 can use a preferred beam to transmit to the UE, as this information may have been shared by the serving DU 410. Similarly, the UE 400 can also use a preferred / optimal transmit / receive beam. It should be understood that in an alternative embodiment, the UE 400 may instead send an RRC configuration request to the target DU 420. In this alternative embodiment, the resource allocation for the RRC configuration message may already be available to the UE 400 from a previous configuration by the serving DU 410.

[0050] Therefore, the above embodiments can forgo performing RACH to perform SCC / HO so that mobile latency is reduced. Furthermore, exemplary embodiments can enable a UE to determine a preferred beam to be used by a neighboring target cell and indicate it to the serving cell. Thus, embodiments of the present disclosure can provide a more optimal approach to handling LTM with reduced latency and enable beam-based inter-cell mobility.

[0051] FIG. 5 is a diagram of an example environment 500 in which the systems and / or methods described herein may be implemented. As shown in FIG. 5, environment 500 may include a user device 510, a platform 520, and a network 530. The devices in environment 500 may be interconnected via wired connections, wireless connections, or a combination of wired and wireless connections. In embodiments, any of the functions and operations described with reference to FIGS. 6-7 above may be performed by any combination of the elements shown in FIG. 5.

[0052] The user device 510 includes one or more devices capable of receiving, generating, storing, processing, and / or providing information related to the platform 520. For example, the user device 510 may include a computing device (e.g., a desktop computer, a laptop computer, a tablet computer, a handheld computer, a smart speaker, a server, etc.), a mobile phone (e.g., a smartphone, a wireless telephone, etc.), a wearable device (e.g., smart glasses or a smart watch), or a similar device. In some implementations, the user device 510 can receive information from the platform 520 and / or transmit information to the platform 520.

[0053] Platform 520 includes one or more devices capable of receiving, generating, storing, processing, and / or providing information. In some implementations, platform 520 may include a cloud server or a collection of cloud servers. In some implementations, platform 520 may be designed to be modular, such that certain software components can be swapped in or out depending on particular needs. Thus, platform 520 can be easily and / or quickly reconfigured for different uses.

[0054] In some implementations, as shown, platform 520 may be hosted in a cloud computing environment 522. In particular, although the implementations described herein describe platform 520 as being hosted within cloud computing environment 522, in some implementations platform 520 may not be cloud-based (i.e., may be implemented outside of a cloud computing environment) or may be partially cloud-based.

[0055] Cloud computing environment 522 includes an environment that hosts platform 520. Cloud computing environment 522 may provide services such as computing, software, data access, storage, etc. that do not require end-user (e.g., user device 510) knowledge of the physical location and configuration of the systems and / or devices that host platform 520. As shown, cloud computing environment 522 may include a collection of computing resources 524 (collectively referred to as “computing resources 524” and individually referred to as “computing resource 524”).

[0056] The computational resources 524 include one or more personal computers, clusters of computing devices, workstation computers, server devices, or other types of computational and / or communication devices. In some implementations, the computational resources 524 may host the platform 520. Cloud resources may include compute instances executing within the computational resources 524, storage devices provided within the computational resources 524, data transfer devices provided by the computational resources 524, etc. In some implementations, the computational resources 524 may communicate with other computational resources 524 via wired connections, wireless connections, or a combination of wired and wireless connections.

[0057] As further shown in FIG. 5, the computing resources 524 include a collection of cloud resources, such as one or more applications (“APP”) 524-1, one or more virtual machines (“VM”) 524-2, virtualized storage (“VS”) 524-3, and one or more hypervisors (“HYP”) 524-4.

[0058] The application 524-1 includes one or more software applications that may be provided to or accessed by the user device 510. The application 524-1 may eliminate the need to install and run software applications on the user device 510. For example, the application 524-1 may include software associated with the platform 520 and / or any other software that may be provided via the cloud computing environment 522. In some implementations, one application 524-1 may send information to or receive information from one or more other applications 524-1 via a virtual machine 524-2.

[0059] Virtual machine 524-2 includes a software-implemented machine (e.g., a computer) that executes programs like a physical machine. Virtual machine 524-2 can be either a system virtual machine or a process virtual machine, depending on the application and the degree to which virtual machine 524-2 matches any real machine. A system virtual machine may provide a complete system platform that supports the execution of a complete operating system (“OS”). A process virtual machine may execute a single program and support a single process. In some implementations, virtual machine 524-2 may run on behalf of a user (e.g., user device 510) and manage the infrastructure of cloud computing environment 522, such as data management, synchronization, or long-term data transfer.

[0060] Virtualized storage 524-3 includes one or more storage systems and / or one or more devices that use virtualization techniques within the storage systems or devices of the computing resources 524. In some implementations, types of virtualization in the context of storage systems may include block virtualization and file virtualization. Block virtualization may refer to the abstraction (or separation) of logical storage from physical storage such that the storage system can be accessed regardless of the physical storage or heterogeneous structure. The separation may allow administrators flexibility in how they manage the storage for end users. File virtualization can eliminate the dependency between data accessed at the file level and where the file is physically stored. This may enable optimization of storage usage, server consolidation, and / or the ability to perform non-disruptive file movements.

[0061] The hypervisor 524-4 may provide hardware virtualization technology that allows multiple operating systems (e.g., "guest operating systems") to run simultaneously on a host computer, such as the computing resource 524. The hypervisor 524-4 may present a virtual operating platform to the guest operating systems and may manage the execution of the guest operating systems. Multiple instances of different operating systems may share virtualized hardware resources.

[0062] Network 530 may include one or more wired and / or wireless networks. For example, network 230 may include a cellular network (e.g., a fifth-generation (5G) network, a long-term evolution (LTE) network, a third-generation (3G) network, a code division multiple access (CDMA) network, etc.), a public land mobile network (PLMN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), a telephone network (e.g., a public switched telephone network (PSTN)), a private network, an ad hoc network, an intranet, the Internet, an optical fiber-based network, etc., and / or a combination of these or other types of networks.

[0063] The number and arrangement of devices and networks shown in Figure 5 are provided as an example. In practice, there may be more, fewer, different, or differently arranged devices and / or networks than those shown in Figure 5. Furthermore, two or more devices shown in Figure 5 may be implemented within a single device, or a single device shown in Figure 5 may be implemented as multiple distributed devices. Additionally or alternatively, a set of devices (e.g., one or more devices) of environment 500 may perform one or more functions that are described as being performed by another set of devices of environment 500.

[0064] 6 is a diagram of example components of a device 600. The device 600 may correspond to a user device 510 and / or a platform 520. As shown in FIG. 6, the device 600 may include a bus 610, a processor 620, a memory 630, a storage component 640, an input component 650, an output component 660, and a communication interface 670.

[0065] The bus 610 includes components that enable communication between the components of the device 600. The processor 620 may be implemented in hardware, firmware, or a combination of hardware and software. The processor 620 may be a central processing unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU), a microprocessor, a microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or other type of processing component. In some implementations, the processor 620 includes one or more processors that can be programmed to perform functions. The memory 630 includes random access memory (RAM), read-only memory (ROM), and / or another type of dynamic or static storage device (e.g., flash memory, magnetic memory, and / or optical memory) that stores information and / or instructions for use by the processor 620.

[0066] The storage component 640 stores information and / or software related to the operation and use of the device 600. For example, the storage component 640 may include a hard disk (e.g., a magnetic disk, optical disk, magneto-optical disk, and / or solid-state disk), a compact disk, a digital versatile disk, a floppy disk, a cartridge, magnetic tape, and / or another type of non-transitory computer-readable medium, along with a corresponding drive. The input component 650 includes components that enable the device 600 to receive information, such as via user input (e.g., a touchscreen display, a keyboard, a keypad, a mouse, buttons, switches, and / or a microphone). Additionally or alternatively, the input component 650 may include sensors for sensing information (e.g., a global positioning system (GPS) component, an accelerometer, a gyroscope, and / or an actuator). The output component 660 includes components that provide output information from the device 600 (e.g., a display, a speaker, and / or one or more light-emitting diodes (LEDs)).

[0067] The communication interface 670 includes transceiver-like components (e.g., a transceiver and / or a separate receiver and transmitter) that allow the device 600 to communicate with other devices via a wired connection, a wireless connection, or a combination of wired and wireless connections, etc. The communication interface 670 may allow the device 600 to receive information from another device and / or provide information to another device. For example, the communication interface 670 may include an Ethernet interface, an optical interface, a coaxial interface, an infrared interface, a radio frequency (RF) interface, a universal serial bus (USB) interface, a Wi-Fi interface, a cellular network interface, etc.

[0068] Device 600 may perform one or more processes described herein. Device 600 may perform these processes in response to processor 620 executing software instructions stored by a non-transitory computer-readable medium, such as memory 630 and / or storage component 640. A computer-readable medium is defined herein as a non-transitory memory device. A memory device includes memory space within a single physical storage device or memory space spread across multiple physical storage devices.

[0069] The software instructions may be loaded into memory 630 and / or storage component 640 from another computer-readable medium or from another device via communication interface 670. When executed, the software instructions stored in memory 630 and / or storage component 640 may cause processor 620 to perform one or more processes described herein.

[0070] Additionally or alternatively, hardwired circuitry may be used in place of or in combination with software instructions to perform one or more of the processes described herein. Thus, implementations described herein are not limited to any specific combination of hardware circuitry and software.

[0071] The number and arrangement of components shown in Figure 6 are provided as an example. In practice, device 600 may include additional, fewer, different, or differently arranged components than the device shown in Figure 6. Additionally or alternatively, a set of components (e.g., one or more components) of device 600 may perform one or more functions that are described as being performed by another set of components of device 600.

[0072] In embodiments, any one of the operations or processes of Figure 4 may be implemented by or using any one of the elements shown in Figures 5 and 6. It will be appreciated that other embodiments may be implemented in a variety of different architectures (e.g., without limitation, a bare metal architecture, any cloud-based or deployment architecture such as Kubernetes, Docker, OpenStack, etc.).

[0073] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

[0074] Some embodiments may relate to systems, methods, and / or computer-readable media at any possible level of technical detail. Furthermore, one or more of the above components described above may be implemented as instructions stored on a computer-readable medium and executable by at least one processor (and / or may include at least one processor). The computer-readable medium may include a computer-readable non-transitory storage medium (or media) having computer-readable program instructions for causing a processor to perform operations.

[0075] A computer-readable storage medium may be a tangible device capable of retaining and storing instructions for use by an instruction-execution device. A computer-readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of computer-readable storage media includes portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital versatile disc (DVD), memory stick, floppy disk, mechanically encoded devices such as punch cards or ridge-in-groove structures having instructions recorded thereon, and any suitable combination of the foregoing. Computer-readable storage media, as used herein, should not be construed as a transitory signal per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission medium (e.g., light pulses passing through a fiber optic cable), or electrical signals transmitted through wires.

[0076] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to each computing / processing device or to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network, or a combination thereof. The network may include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers, or a combination thereof. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium in the respective computing / processing device.

[0077] The computer-readable program code / instructions for carrying out operations may be either source code or object code written in any combination of one or more programming languages, including assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, configuration data for integrated circuits, or object-oriented programming languages such as Smalltalk, C++, and procedural programming languages such as the "C" programming language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA) can execute computer-readable program instructions by utilizing state information of the computer-readable program instructions to personalize the electronic circuitry to perform aspects or operations.

[0078] These computer-readable program instructions may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, executed by the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams. These computer-readable program instructions may also be stored on a computer-readable storage medium that can instruct a computer, programmable data processing apparatus, and / or other device to function in a particular manner, such that the computer-readable storage medium having the instructions stored therein comprises an article of manufacture containing instructions that implement aspects of the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams.

[0079] The computer-readable program instructions may also be loaded into a computer, other programmable data processing apparatus, or other device to cause the computer, other programmable apparatus, or other device to perform a series of operational steps to generate a computer-implemented process, such that the instructions executing on the computer, other programmable apparatus, or other device implement the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams.

[0080] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer-readable media according to various embodiments. In this regard, each block in the flowcharts or block diagrams may represent a portion of a microservice(s), module, segment, or instruction set, which includes one or more executable instructions for implementing the specified logical function(s). The methods, computer systems, and computer-readable media may include additional, fewer, different, or differently arranged blocks than depicted in the figures. In some alternative implementations, the functions noted in the blocks may occur out of the order depicted in the figures. For example, two blocks shown in succession may actually be executed concurrently or substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the functionality involved. It should also be noted that each block of the block diagrams and / or flowchart diagrams, and combinations of blocks in the block diagrams and / or flowchart diagrams, may be implemented by a special-purpose hardware-based system that performs the specified functions or operations or executes a combination of special-purpose hardware and computer instructions.

[0081] It will be apparent that the systems and / or methods described herein may be implemented in different forms of hardware, firmware, 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 intended to limit the implementation. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code, and it will be understood that software and hardware can be designed to implement the systems and / or methods based on the description herein.

[0082] Various aspects of the embodiments

[0083] Various further respective aspects and features of embodiments of the present disclosure can be defined by the following clauses. Item [1]: A method, executed by at least one processor, for configuring an inter-cell change, comprising: receiving, by a user equipment (UE), a downlink signal, the downlink signal being originated from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; and performing, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration, wherein the uplink synchronization includes sending, by the UE, a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, wherein the target DU is one of a plurality of neighbor cells to the serving DU. Item [2]: The method according to item [1], further comprising: the UE obtaining a timing advance to be used during transmission to or reception from the target cell; and the UE reporting the result of uplink synchronization and the obtained timing advance to the serving DU. Item [3]: The method according to item [1] or [2], wherein preamble transmission and uplink synchronization are performed while the UE is connected to the serving DU. Item [4]: A method according to any one of items [1] to [3], wherein the downlink signal is one of a physical downlink control channel (PDCCH) or a MAC control element (MAC CE) command. Item [5]: A method according to any one of items [1] to [4], wherein performing measurements based on downlink signals further includes performing L1 measurements of the target cell, and the method further includes sending the L1 measurements by the UE to a serving DU, wherein the serving DU can determine whether to perform an LTM handover without RACH based on the L1 measurements based on a target cell timing advance reported by the UE. Item [6]. The method according to Item [5], wherein sending a preamble transmission to the target DU based on the downlink signal further includes sending a random access preamble to the target DU during a scheduling gap duration determined based on a scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble. Item [7]: A method according to any one of items [1] to [6], further comprising: performing uplink synchronization by the UE based on measurements and preamble transmission; and sending a status signal by the UE to the serving DU. Item [8]: A method according to item [5] or [6], in which L1 measurements are performed and reported aperiodically or based on events for one or more target cells, and the L1 measurements are sent aperiodically to the serving DU. Item [9]: An apparatus for configuring an inter-cell change, comprising: at least one memory storing computer-executable instructions; and at least one processor configured to execute the computer-executable instructions to: receive, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; and perform, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration; wherein the uplink synchronization includes, by the UE, sending a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, and the target DU is one of a plurality of neighbor cells to the serving DU. Item

[10] : The device described in Item [9], further configured to: execute computer-executable instructions by at least one processor to cause the UE to obtain a timing advance to be used during transmission to or reception from the target cell; and report, by the UE, the result of uplink synchronization and the obtained timing advance to the serving DU. Item

[11] : The apparatus described in Item [9] or

[10] , wherein preamble transmission and uplink synchronization are performed while the UE is connected to the serving DU. Item

[12] : The device described in any one of items [9] to

[11] , wherein the downlink signal is one of a physical downlink control channel (PDCCH) or a MAC control element (MAC CE) command. Item

[13] : The device described in any one of items [9] to

[12] , wherein at least one processor is further configured to execute computer-executable instructions to perform measurements by performing L1 measurements of the target cell based on the downlink signal, and the at least one processor is further configured to execute the computer-executable instructions to: send the L1 measurements by the UE to a serving DU, wherein the serving DU can determine whether to perform an LTM handover without RACH based on the L1 measurements based on a target cell timing advance reported by the UE. Item

[14] : The device described in Item

[13] , further configured to send a preamble transmission to the target DU based on a downlink signal by at least one processor executing computer-executable instructions to: send a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble. Item

[15] : The device described in any one of items [9] to

[14] , wherein at least one processor is further configured to execute computer-executable instructions to: perform uplink synchronization by the UE based on measurements and preamble transmission; and send a status signal to the serving DU by the UE. Item

[16] : The device described in Item

[13] or

[14] , wherein performing and reporting L1 measurements for one or more target cells is performed aperiodically or based on an event, and the L1 measurements are sent aperiodically to the serving DU. Item

[17] : A non-transitory computer-readable storage medium having instructions recorded thereon, the instructions being executable by at least one processor to cause the at least one processor to perform a method including: receiving, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; and performing, by the UE, uplink synchronization with the target cell based on the downlink signal during the scheduling gap duration, the uplink synchronization including, by the UE, sending a preamble transmission to the target cell based on the downlink signal to acquire a timing advance of the target cell, the target DU being one of a plurality of neighbor cells to the serving DU. Item

[18] : A non-transitory computer-readable recording medium as described in Item

[17] , wherein the method further includes: the UE obtaining a timing advance to use during transmission to or reception from the target cell; and the UE reporting the result of uplink synchronization and the obtained timing advance to the serving DU. Item

[19] : A non-transitory computer-readable recording medium according to Item

[17] or

[18] , wherein performing measurements based on the downlink signal further includes performing L1 measurements of the target cell, and the method further includes sending, by the UE, the L1 measurements to a serving DU, wherein the serving DU can determine whether to perform an LTM handover without RACH based on the L1 measurements based on a target cell timing advance reported by the UE. Item

[20] : A non-transitory computer-readable recording medium as described in Item

[19] , wherein sending a preamble transmission to the target DU based on the downlink signal further includes sending a random access preamble to the target DU during a scheduling gap duration determined based on a scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble.

[0084] It can be appreciated that many modifications and variations of the present disclosure are possible in light of the above teachings. It will be apparent that, within the scope of the appended clauses, the present disclosure may be practiced otherwise than as specifically described herein.

Claims

1. 1. A method executed by at least one processor for configuring inter-cell changes, comprising: receiving, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; performing, by the UE, uplink synchronization with a target cell based on the downlink signal during the scheduling gap duration; Including, The method, wherein the uplink synchronization includes sending a preamble transmission by the UE to a target cell to acquire a timing advance of the target cell based on the downlink signal, and the target DU is one of a plurality of neighbor cells to the serving DU.

2. The method comprises: obtaining, by the UE, a timing advance to use during transmission to or reception from the target cell; reporting, by the UE, the result of the uplink synchronization and the obtained timing advance to the serving DU; The method of claim 1 further comprising:

3. The method of claim 1 , wherein the preamble transmission and the uplink synchronization are performed while the UE is connected to the serving DU.

4. 2. The method of claim 1, wherein the downlink signal is one of a Physical Downlink Control Channel (PDCCH) or a MAC Control Element (MAC CE) command.

5. performing L1 measurements of the target cell based on the downlink signal; sending, by the UE, the L1 measurements to the serving DU, wherein the serving DU can determine whether to perform a RACH-less LTM handover based on the L1 measurements, based on the target cell timing advance reported by the UE. The method of claim 1 further comprising:

6. sending the preamble transmission to the target DU based on the downlink signal; sending a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble. The method of claim 5 further comprising:

7. The method comprises: performing, by the UE, uplink synchronization based on the measurements and the preamble transmission; sending, by the UE, a status signal to the serving DU; The method of claim 1 further comprising:

8. The method of claim 5 , wherein the performing and reporting of the L1 measurements is performed aperiodically or event-based to one or more target cells, and the L1 measurements are sent aperiodically to the serving DU.

9. 1. An apparatus for configuring an inter-cell change, comprising: at least one memory storing computer-executable instructions; at least one processor executing the computer-executable instructions to: receiving, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; performing, by the UE, uplink synchronization with a target cell based on the downlink signal during the scheduling gap duration; at least one processor configured to: Equipped with The apparatus, wherein the uplink synchronization includes sending, by the UE, a preamble transmission to a target cell to acquire a timing advance of the target cell based on the downlink signal, and the target DU is one of a plurality of neighbor cells to the serving DU.

10. The at least one processor executes the computer-executable instructions to obtaining, by the UE, a timing advance to use during transmission to or reception from the target cell; reporting, by the UE, the result of the uplink synchronization and the obtained timing advance to the serving DU; The apparatus of claim 9 , further configured to:

11. The apparatus of claim 9 , wherein the preamble transmission and the uplink synchronization are performed while the UE is connected to the serving DU.

12. 10. The apparatus of claim 9, wherein the downlink signal is one of a Physical Downlink Control Channel (PDCCH) or a MAC Control Element (MAC CE) command.

13. The at least one processor is further configured to execute the computer-executable instructions to perform the measurements by performing L1 measurements of the target cell based on the downlink signals, and the at least one processor is further configured to execute the computer-executable instructions to: sending, by the UE, the L1 measurements to the serving DU, wherein the serving DU can determine whether to perform a RACH-less LTM handover based on the L1 measurements, based on the target cell timing advance reported by the UE. The apparatus of claim 9 , further configured to:

14. The at least one processor executes the computer-executable instructions to sending a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble.

14. The apparatus of claim 13, further configured to send the preamble transmission to the target DU based on the downlink signal by:

15. The at least one processor executes the computer-executable instructions to performing, by the UE, uplink synchronization based on the measurements and the preamble transmission; sending, by the UE, a status signal to the serving DU; The apparatus of claim 9 , further configured to:

16. 14. The apparatus of claim 13, wherein the performing and reporting of the L1 measurements is performed aperiodically or event-based to one or more target cells, and the L1 measurements are sent aperiodically to the serving DU.

17. A non-transitory computer-readable storage medium having instructions stored thereon, the instructions being executable by at least one processor, the at least one processor comprising: receiving, by a user equipment (UE), a downlink signal, the downlink signal originating from a serving distribution unit (DU), the downlink signal including at least one of a scheduling gap duration value, a start time value, and a target cell index; performing, by the UE, uplink synchronization with a target cell based on the downlink signal during the scheduling gap duration; Including, the uplink synchronization includes sending, by the UE, a preamble transmission to the target cell to acquire a timing advance of the target cell based on the downlink signal, and the target DU is one of a plurality of neighbor cells to the serving DU. A non-transitory computer-readable storage medium for carrying out a method.

18. The method comprises: obtaining, by the UE, a timing advance to use during transmission to or reception from the target cell; reporting, by the UE, the result of the uplink synchronization and the obtained timing advance to the serving DU; 20. The non-transitory computer-readable storage medium of claim 17, further comprising:

19. performing L1 measurements of the target cell based on the downlink signal; sending, by the UE, the L1 measurements to the serving DU, wherein the serving DU can determine whether to perform a RACH-less LTM handover based on the L1 measurements, based on the target cell timing advance reported by the UE.

20. The non-transitory computer-readable storage medium of claim 17, further comprising:

20. sending the preamble transmission to the target DU based on the downlink signal; 20. The non-transitory computer-readable storage medium of claim 19, further comprising: sending a random access preamble to the target DU during a scheduling gap duration determined based on the scheduling gap duration value, wherein the target DU can determine a timing advance value for the UE based on receiving the random access preamble.

Images