Timing advance optimization during uplink synchronization

Abstract

The presently disclosed embodiments provide a method and system for performing TA optimization during uplink synchronization. A request is received at a user equipment (UE) 102 from a first distributed unit (DU) of a serving base station 104 to perform uplink synchronization with a candidate cell of a second DU of a target base station 106A, 106B. Further, uplink synchronization with the second DU is performed by the UE 102. Furthermore, the UE 102 receives a primary beam identifier and a secondary beam identifier with an associated timing advance (TA) from the second DU based on the uplink synchronization. Thus, the UE 102 may determine a target beam of the target cell and perform a serving cell switch function for the target beam.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to Indian Provisional Patent Application No. 202341024646, filed on March 31, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present disclosure relates generally to the field of wireless communications, and more particularly to timing advance optimization during uplink (UL) synchronization. [Background technology]

[0003] A cellular network is a communication interconnection of user devices and cellular base stations (BSs), such as cell towers. A BS includes a service area that is divided into multiple cells. A cell defines a geographic area served by a BS and its associated transceiver antenna. Multiple user devices residing within a particular cell, also referred to as a serving cell, communicate with the BS's associated transceiver antenna over multiple frequencies and frequency channels.

[0004] The Radio Access Network (RAN) is the part of a cellular network that is responsible for implementing radio access technologies. The RAN provides connectivity to the Core Network (CN) for user devices, such as mobile phones / devices, computers, or remotely controlled devices present in any network. User devices may also be known as User Equipment (UE), Terminal Equipment, Mobile Station (MS), etc.

[0005] While a mobile device, such as a UE, is connected to a serving cell, the mobile device performs measurements of channel and signal parameters for the serving cell and neighboring cells over a predetermined period of time. In addition, when multiple UEs are connected to a serving cell, the distance between the serving BS and the UE can be obtained through measurements of the time it takes for a radio wave to travel from the UE to the serving BS, known as the timing advance (TA). Furthermore, the value of the TA can be affected by changes in the distance between the UE and the serving BS due to UE movement. Similarly, at least one of the neighboring cells can have an associated TA for the UEs served by the neighboring cell.

[0006] During the movement of a mobile device, the TA, channel parameters, and signal parameters for the serving cell and neighboring cells constantly change. For example, when a UE moves from the coverage area of ​​a serving cell to the coverage area of ​​one of the neighboring cells, also referred to as a target cell, the UE needs to connect to the neighboring cell and disconnect from the serving cell. This procedure is known as handover (HO). The aforementioned UE mobility, which defines UE movement, may also be referred to as Layer 1 (L1) / Layer 2 (L2) inter-cell mobility (LTM). However, it should be understood that UE mobility may be realized in alternative ways to LTM, which are not discussed here for brevity. In LTM, to perform a handover from a serving cell to a target cell based on UE movement, the UE needs to acquire TA knowledge for the target cell to implement it and continue communication with the target cell. TA knowledge is necessary for the UE to perform proper synchronization, also referred to as UL synchronization, and connection with the target cell.

[0007] In the prior art, a separated BS architecture has been defined for cellular networks. For example, a separated Next Generation Node B (gNB) architecture that decomposes the gNB into multiple logical entities has been defined in the 3rd Generation Partnership Project (3GPP). For example, a gNB may include a gNB-CU-CP (Control Unit-Control Plane) and a gNB-Distributed Unit (DU). Similarly, a single DU may host multiple cells. As an example, in the current 3GPP specification, a single DU may host up to 512 cells. The gNB-CU-CP may host the Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the gNB-DU hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers. Furthermore, downlink (DL) scheduling operations may occur in the gNB-DU. To support Layer 1 (L1) / Layer 2 (L2) inter-center cell mobility for serving cell changes, a separated gNB architecture requires handover preparation to be performed by the gNB-CU-CP, but a mechanism is required for handover to be performed autonomously by the gNB-DU without further interaction with higher layers such as the PDCP and RRC layers. Handover preparation may also be referred to as target cell configuration preparation. For example, handover without further interaction with higher layers may be a random access channel (RACH)-less L1 / L2 triggered mobility (LTM) handover (HO).

[0008] 3GPP Release 18 work items (WI) describe further New Radio (NR) mobility improvements as described below: Short name:NR_Mob_enh2-Core; Reading WG:RAN2; 3GPP Release: REL-18; Work Item Description: RP-221799 The objectives of the upcoming Mobility Improvements Release 18 work item can be found in RP-213565: Define mechanisms and procedures for L1 / L2 based inter-cell mobility to reduce mobility latency: Configuration and maintenance of multiple candidate cells to enable rapid application of configuration to candidate cells [RAN2, RAN3] Dynamic switching mechanism between candidate serving cells (including SpCell and SCell) for potentially applicable scenarios based on L1 / L2 signaling [RAN2, RAN1] L1 improvements for inter-cell beam management including L1 measurement and reporting, beam suggestion [RAN1, RAN2] Note 1: Early RAN2 engagement is needed, including potentially further clarification of the interplay between this bullet and the previous one. Timing Advance Management [RAN1, RAN2] CU-DU interface signaling to support L1 / L2 mobility, if required [RAN3] Note 2: FR2 specific improvements (if any) are not excluded. Note 3: The L1 / L2 based inter-cell mobility procedures are applicable to the following scenarios: Standalone, CA and NR-DC cases with serving cell change within one CG Intra-DU case and intra-CU inter-DU case (applicable for standalone and CA: no new RAN interface is assumed) Both intra- and inter-frequency · Both FR1 and FR2 · The source and target cells can be synchronous or asynchronous. Note: L1 / L2 triggered mobility is a mobility feature and can be interpreted as a basic UE capability (starting from R18).

[0009] According to the prior art, the following is the agreement in RAN1 from the RAN1#112 meeting: RAR reception may be configured / indicated for the RACH with PDCCH order for the candidate cell. If RAR reception is not configured / indicated (no RAR) The TA value of the candidate cell is indicated in the cell switch command. FFS: Should the UE retransmit the PRACH when reception of the RAR is not configured / indicated? FFS: How the UE determines the transmit power of the subsequent PRACH triggered by the PDCCH order. If RAR reception is configured / indicated (RAR present), FFS Whether the RAR is received from the serving cell or the candidate cell If an RAR is received from a candidate cell, is the Type1-PDCCH CSS of the candidate cell configured for the UE? RAR content FFS: Signaling for configuration / indication of whether RAR needs to be received The UE can report support for one default scheme, a combination of RAR only and RAR only, which is the baseline UE approach to LTM. Send LS to RAN2 and RAN3 to check the feasibility of this agreement. Note: Candidate cell definition is based on RAN2 agreement If reception of RAR is configured / indicated, the RAR contains at least the TA of the candidate cell. The maximum number of TA values ​​stored by the UE is the UE capability. FFS: Are other parameters such as UE ID, candidate cell ID, etc. included in the RAR? Summary of the Invention [Problem to be solved by the invention]

[0010] In the prior art, acquiring the target cell TA before the serving cell switch reduces handover latency during an LTM serving cell change (SCC) (hereinafter also referred to as a serving cell switch) because the TA is already known to the UE and acquiring the TA can be avoided during the actual SCC. During LTM, if the UE is configured to perform a UL synchronization process, there is a time window between acquiring the target cell TA and performing the LTM SCC. The duration may vary from UE to UE and even for the same UE depending on the situation. Therefore, the duration cannot be accurately determined or predicted.

[0011] The UE may undergo mobility during this time, which may result in a change in the UE's TA in the target cell. For example, the TA acquired during the UL synchronization process may not be valid at the time of the LTM SCC. Therefore, to acquire a valid TA at the time of the LTM SCC and ensure RACH-less LTM handover, the serving gNB-DU requests that the UE perform repeated UL synchronization with the target gNB-DU to obtain an updated TA. However, performing UL synchronization again to obtain an updated TA impacts the UE's data transmission at the serving gNB-DU and results in overhead for the target gNB-DU. Alternatively, the serving gNB may request that the UE perform a RACH-based handover when issuing the LTM SCC command, resulting in additional interactions with higher layers.

[0012] Therefore, there is a need for a technique to perform RACH-less handover without the need to repeat UL synchronization when the UE undergoes mobility.

[0013] The information disclosed in this Background of the Disclosure section is intended only to facilitate understanding of the general background of the present disclosure and should not be construed as an admission or any form of suggestion that this information constitutes prior art already known to those skilled in the art. [Means for solving the problem]

[0014] The present disclosure relates to an apparatus configured to receive, in a user equipment (UE), a request to perform uplink synchronization with a candidate cell of a second DU of a target base station from a first distributed unit (DU) of a serving base station. The apparatus is further configured to perform uplink synchronization by transmitting, by the UE, a random access channel (RACH) request message to the second DU. The apparatus further receives, by the UE, from at least one of the first DU and the second DU, a primary beam identifier of a primary candidate cell of the second DU along with an associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU along with an associated one or more secondary TAs, based on the uplink synchronization. The apparatus is further configured to receive, by the UE, a cell switch command from the first DU indicating a target beam of the target cell selected by the UE from the primary candidate cell or the one or more secondary candidate cells. The apparatus is further configured to perform, by the UE, a serving cell switch function on the target beam and apply a corresponding TA associated with the target beam.

[0015] The present disclosure also relates to a method for wireless communication in a user equipment (UE). The method comprises receiving, from a first distributed unit (DU) of a serving base station, a request to perform uplink synchronization with a second DU of a target base station. The method further comprises performing uplink synchronization by transmitting a random access channel (RACH) request message to the second DU. The method further comprises receiving, from at least one of the first DU and the second DU, a primary beam identifier of a primary candidate cell of the second DU along with an associated primary timing advance (TA) based on the uplink synchronization, and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU along with associated one or more secondary TAs. The method further comprises receiving, from the first DU, a cell switch command indicating a target beam of the target cell. The target cell is selected from the primary candidate cell or one or more secondary candidate cells. The method further comprises performing a serving cell switch function on the target beam and applying a corresponding TA associated with the target beam.

[0016] The present disclosure further relates to an apparatus configured in a serving base station and a first distributed unit (DU) of the serving base station to determine a candidate cell of a target base station from one or more DUs of one or more candidate base stations based on one or more signal and channel parameters of multiple candidate cells of one or more neighboring base stations. The apparatus is further configured to transmit, from the serving base station, a request to a user equipment (UE) to perform uplink synchronization with the candidate cell. The apparatus is further configured in the serving base station to receive, from at least one of the UE and a second DU of the target base station, a primary beam identifier of the primary candidate cell of the second DU with an associated primary timing advance (TA) and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with an associated one or more secondary TAs. The primary beam identifier, the primary TA, the one or more secondary beam identifiers, and the one or more secondary TAs are received by the UE from the second DU based on the uplink synchronization. Furthermore, the apparatus is configured to, at the serving base station, determine a target beam of the target cell from the primary beam identifier and the one or more secondary beam identifiers based on the associated one or more signal and channel parameters. The apparatus is further configured to send, from the serving base station to the UE, a request to perform a serving cell switch function on the target beam and apply a corresponding TA associated with the target beam.

[0017] The foregoing summary is for purposes of illustration only and is not intended to be limiting in any way. In addition to the exemplary aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. [Brief explanation of the drawings]

[0018] The novel features and characteristics of the present disclosure are set forth in the appended claims. However, the disclosure itself, its preferred mode of use, further objects and advantages, will best be understood by reference to the following detailed description of illustrative embodiments when read in connection with the accompanying drawings. One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings in which like reference numerals represent like elements.

[0019] FIG. 1 illustrates a schematic representation of a random access resource configuration for a UE according to an embodiment as disclosed herein.

[0020] Figure 2 is a sequence diagram illustrating a scenario in which an optimal beam belonging to a target gNB-DU is determined and the corresponding TA provided by the target gNB-DU is applied, according to this embodiment as disclosed herein.

[0021] Figure 3 is a sequence diagram illustrating another scenario in which an optimal beam belonging to a target gNB-DU is determined and the corresponding TA provided by the target gNB-DU is applied, according to the present embodiment as disclosed herein.

[0022] FIG. 4 illustrates a flowchart of a method for wireless communication in a UE according to an embodiment as disclosed herein.

[0023] FIG. 5 illustrates a detailed block diagram of an apparatus in which a method for wireless communication may be implemented according to an embodiment as disclosed herein.

[0024] Any block diagrams herein should be understood by those skilled in the art to represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, any flowcharts, flow diagrams, state transition diagrams, pseudocode, etc., will be understood to represent various processes that may be substantially embodied in a computer-readable medium and executed by a computer or processor (whether or not such a computer or processor is explicitly shown). DETAILED DESCRIPTION OF THE INVENTION

[0025] It is understood that the present disclosure contemplates various modifications and step sequences unless otherwise specified. The specific devices and processes illustrated in the accompanying drawings and described in the following specification are also understood to be merely exemplary and non-limiting embodiments or aspects. Hence, specific dimensions and other physical characteristics related to the embodiments or aspects disclosed herein are not to be construed as limiting.

[0026] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0027] While the present disclosure embraces various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are described in detail below. However, it is not intended to limit the disclosure to the particular forms disclosed, but rather the disclosure should be understood to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

[0028] The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a setup, device, or method comprising a list of components or steps does not include only those components or steps, but may also include other components or steps not expressly listed or inherent in such setup or device or method. In other words, one or more elements in a device or system or apparatus with "comprises... a" does not, unless there are more constraints, exclude the presence of other or additional elements in the device or system or apparatus.

[0029] The terms "one embodiment," "embodiment," "(embodiments)," "this embodiment," "(the) present embodiments," "one or more embodiments," "some embodiments," and "one embodiment" mean "one or more (but not all) embodiments of the present disclosure," unless otherwise specified.

[0030] The terms "including," "comprising," "having," and variations thereof mean "including, but not limited to," unless otherwise specified.

[0031] In the following detailed description of the present embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown, by way of illustration, specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it being understood that other embodiments may be utilized and changes may be made without departing from the scope of the disclosure. Accordingly, the following description is not to be construed as limiting.

[0032] The presently disclosed embodiments provide a method and system for acquiring timing advances during UL synchronization and performing optimization to ensure that the acquired timing advances are valid and applicable for a longer duration. A UE transmits an L1 measurement report (MR) for a configured cell to a serving gNB-DU. The serving gNB-DU checks set radio resource management (RRM) criteria (e.g., a predefined reference signal received power (RSRP) threshold) and requests that the UE perform UL synchronization with one or more candidate / target cells using a configured physical random access channel (PRACH) preamble. The serving gNB-DU uses a physical downlink control channel (PDCCH) order to request that the UE perform UL synchronization. The UE is configured to perform UL synchronization and receive a random access response (RAR) from the target gNB-DU, which includes the timing advances of the candidate / target cells to be used by the UE.

[0033] In one embodiment, the target gNB-DU, together with the RAR, includes the UE's TA of the neighboring beams in addition to the UE's TA of the optimal beam in the candidate / target cell gNB-DU. This ensures that when one of the neighboring beams becomes the optimal beam, the UE applies the corresponding TA. A neighboring beam is qualified as any nearby beam that is expected to be accessed next by the UE (i.e., any beam with good radio conditions that the UE is expected to be heading towards).

[0034] In one embodiment, after acquiring the target cell TA during the UL synchronization procedure, the UE reports the TAs of the optimal beam and neighboring beams to the serving gNB-DU. At the time of an LTM cell switch, the serving gNB-DU indicates the target cell beam to be used by the UE in a serving cell switch command (downlink media access control element (DL MAC CE)), which is sent to the UE. The UE uses the TA (provided by the candidate / target gNB-DU) corresponding to the beam indicated during the serving cell switch. Alternatively, the UE is configured to autonomously determine the optimal beam (based on L1 measurements) belonging to the candidate / target gNB-DU and apply the corresponding TA (provided by the candidate / target gNB-DU). In this alternative, the serving gNB-DU may not provide the target beam ID. Thus, the proposed method can be used to achieve RACH-less HO with UE mobility after UL synchronization, optimal beam changes, and better TA estimation.

[0035] 1 illustrates a schematic representation 100 of an RAR configuration for a UE 102 according to an embodiment as disclosed herein. The UE 102 may be in communication with a serving cell 104 (hereinafter also referred to as a serving base station 104, or a serving gNB distributed unit (DU) 104 as a serving gNB-DU 104 may include one or more serving cells 104). RAR reception is configured / indicated for a RACH via a PDCCH order for a candidate cell 106A, 106B (hereinafter also referred to as a target base station 106A, 106B, or a target / candidate gNB-DU 106A, 106B as a target / candidate gNB-DU 106A, 106B may include one or more target / candidate cells 106A, 106B). The RAR configuration may be received at the UE 102, and the RAR may be received from the candidate / target cell 106A, 106B or the serving cell 104. In one embodiment, if reception of the RAR is not configured or indicated, the TA value of the candidate cell may be indicated in the cell switch command. In other embodiments, when reception of the RAR is configured / indicated and received from the candidate cell 106A, 106B, at least the TA may be included in the RAR.

[0036] In a conventional separated gNB architecture, as defined in 3GPP, a conventional gNB may be decomposed into multiple logical entities. For example, a conventional gNB may include a gNB-CU-CP (Control Unit-Control Plane) (hereinafter, the gNB-CU-CP is also referred to as a gNB-CU (aggregation unit) for simplicity) and a gNB DU. Similarly, a single DU may host multiple cells. As an example, in the current 3GPP specification, a single DU may host up to 512 cells. The gNB-CU-CP may host the Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the gNB-DU hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers. Scheduling operations occur in the gNB-DU. To support L1 / L2 inter-center cell changes, with respect to serving cell changes, the separated gNB architecture implements a mechanism whereby scheduling operations / configurations occur in the gNB-CU-CP but are executed autonomously by the gNB-DU without further interaction with higher layers. For example, the mechanism involves handover preparation being performed by the gNB-CU-CP but handover being executed autonomously by the gNB-DU without further interaction with higher layers such as the PDCP and RRC layers.

[0037] In one embodiment, on link 108, the UE 102 may send a target cell RSRP MR to the serving cell 104 over link 108. In one embodiment, on link 110, the serving cell 104 may use a PDCCH order to configure the UE 102 to perform UL synchronization by sending a PRACH preamble to enable the UE 102 to acquire the TA of the target cell.

[0038] In operation, the UE 102 may be configured to transmit, to a first distributed unit (DU) of the serving base station 104, a measurement report (MR) associated with one or more signal and channel parameters for each of a plurality of candidate cells 106A, 106B of one or more neighboring base stations. In one example, the UE 102 may be configured to transmit, to the first DU, an L1 MR associated with one or more signal and channel parameters for each of a plurality of candidate cells 106A, 106B associated with the first DU and one or more DUs associated with one or more neighboring base stations. In one embodiment, the UE 102 may transmit Layer 1 (L1) MRs for a plurality of candidate cells 106A, 106B to the serving gNB-DU 104. In one example, the plurality of candidate cells may include a plurality of non-serving cells. In one example, the UE 102 may transmit the MRs based on UE specifications and compatibility defining UE capabilities with RAR only and without RAR only, where support for one default scheme may be the baseline UE 102 approach to LTM. In one example, the maximum number of TA values ​​that the UE 102 may be configured to store may define the capabilities of the UE.

[0039] Furthermore, upon sharing the MR to the serving base station 104, the first DU of the serving base station 104 may determine a candidate cell for the target base station 106A, 106B from one or more DUs of one or more candidate base stations. Note: The candidate cell may belong to the same base station as the serving cell. In one embodiment, the target base station may be the serving base station. In other embodiments, the candidate cell determination may be based on one or more signal and channel parameters of multiple candidate cells of one or more neighboring base stations. In one embodiment, upon receiving the MR, the serving gNB-DU 104 may check a set RRM criterion. In one example, the RRM criterion may be a predetermined RSRP threshold. Based on the target base station 106A, 106B's determination, the first DU may send a request to the UE to perform uplink synchronization with the determined candidate cell.

[0040] In this manner, the UE 102 may receive a request from the first DU of the serving base station 104 to perform uplink synchronization with a candidate cell of a second DU associated with the target base station 106A, 106B. In one example, the first DU of the serving base station 104 may transmit the request to perform uplink synchronization to the UE 102 using a PDCCH order. Furthermore, the UE 102 may perform uplink synchronization by transmitting a random access channel (RACH) request message to the second DU. In one embodiment, in response to performing uplink synchronization, the UE 102 may be configured to receive a random access response (RAR) from one of the first DU and the second DU. For example, the RAR may include at least a primary beam identifier of a primary candidate cell of the second DU with an associated primary TA and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with one or more associated secondary TAs. The secondary beam identifiers may be determined or selected based on respective signal quality metrics. As another example, the UE 102 may be configured to receive a RAR as a subsequent message received from the target base station 106A, 106B. The RAR may include at least a primary beam identifier with an associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

[0041] In one embodiment, based on uplink synchronization, the UE 102 may receive from the target base station 106A, 106B a primary beam identifier of the target base station 106A, 106B along with an associated primary timing advance (TA). Additionally, the UE 102 may receive one or more secondary beam identifiers of the target base station 106A, 106B along with one or more associated secondary TAs. In an alternative embodiment, the first DU of the serving base station 104 may receive from the UE 102 and one of the second DUs of the target base station 106A, 106B a primary beam identifier of a primary candidate cell of the second DU along with an associated primary TA and one or more secondary beam identifiers of one or more secondary candidate cells of the second DU along with an associated secondary TA.

[0042] In one embodiment, the UE 102 may include an optimal beam determination module 112A. The UE 102 may utilize the optimal beam determination module 112A to determine an optimal beam from a primary beam identifier and one or more secondary beam identifiers and define the optimal beam as a target beam. In one embodiment, the optimal beam determination module 112A determines the optimal beam based on a comparison between one or more signal and channel parameters associated with the primary beam identifier and one or more corresponding signal and channel parameters associated with at least one of the secondary beam identifiers. Based on the comparison, the optimal beam determination module 112A may determine a target beam from the primary beam identifier and one or more secondary beam identifiers. Furthermore, the UE 102 may perform a serving cell switch function for the target beam and apply a corresponding TA associated with the target beam.

[0043] In another embodiment, the UE 102 may transmit to the serving base station 104 the primary beam identifier of the target base station 106A, 106B along with an associated primary timing advance (TA) and one or more secondary beam identifiers of the target base station 106A, 106B along with the associated one or more secondary TAs. In one example, the serving base station 104 may include an optimal beam determination module 112B. The serving base station 104 may then utilize the optimal beam determination module 112B to determine an optimal beam from the primary beam identifier and one or more secondary beam identifiers based on the associated one or more signal and channel parameters and define the optimal beam as the target beam. In one example, to determine the optimal beam, the serving base station 104 may be configured to compare one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with at least one of the secondary beam identifiers. In one embodiment, the serving base station 104 may be configured to determine, at a first DU of the serving base station 104, a candidate cell for the target base station 106A, 106B from one or more DUs of one or more candidate base stations based on one or more signal and channel parameters of multiple candidate cells of one or more neighboring base stations. The serving and target base stations may be the same base station. Further, the serving base station 104 may be configured to determine a target beam from a primary beam identifier and one or more secondary beam identifiers based on the comparison result.

[0044] In one example, an optimal beam may be defined as a beam with the best TA for a particular period of time. Thus, including the TAs of neighboring beams along with the target beam ensures that the UE 102 applies the corresponding TA when one of the neighboring beams becomes the optimal beam. The neighboring beams may be qualified as nearby beams that may be expected to be accessed next by the UE 102. For example, a nearby beam is a beam with the best channel and signal characteristics that the UE 102 may be expected to be directed toward.

[0045] The serving base station 104 may then request that the UE 102 perform a serving cell switch function to the target beam based on the corresponding TA associated with the target beam. In one example, the first DU may send a cell switch command to the UE 102 indicating the target beam of the target cell. In one example, the cell switch command may be a Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command. In one example, the target cell may be selected from a primary candidate cell or one or more secondary candidate cells.

[0046] The serving gNB-DU 104 may then request that the UE 102 perform UL synchronization with one or more target cells 106A, 106B using the configured PRACH preamble. The UE 102 may perform UL synchronization and may receive an RAR from the target gNB-DU 106A, 106B that includes the TA of the candidate / target cell to be used by the UE 102. Thus, the UE 102 may use the TA of the candidate / target cell to perform a RACH-less LTM handover.

[0047] Figure 2 is a sequence diagram illustrating a scenario in which UE 102 determines the optimal beam belonging to target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA provided by target gNB-DU 106A, 106B, according to this embodiment as disclosed herein.

[0048] Referring to Figure 2, the UE 102 is configured to determine the optimal beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and apply the corresponding TA.

[0049] In step S201, the UE 102 is still connected to the serving gNB-DU 104 (before the LTM serving cell switch).

[0050] In step S202, the UE 102 uses an RRC connection with the gNB aggregation unit (CU) (200) to transmit L3 RRC measurement results to the gNB-CU 200.

[0051] In step S203, gNB-CU200 decides to prepare an inter-gNB-DU LTM candidate cell.

[0052] In step S204, the gNB-CU 200 initiates a UE context setup request message to the target gNB-DU 106A, 106B over the F1 interface to prepare an inter-DU LTM candidate cell.

[0053] In step S205, the target gNB-DU 106A, 106B confirms with a UE context setup response message over the F1 interface and provides the candidate / target cell configuration.

[0054] In step S206, the gNB-CU200 sends a DL RRC message transfer (RRC reconfiguration (LTM target cell configuration)) to the serving gNB-DU104 via the F1 interface.

[0055] In step S207, an RRC reconfiguration message is passed to the UE 102. The serving gNB-DU 104 checks a set of RRM criteria (e.g., a pre-defined RSRP threshold) to trigger the transmission of L1 measurements to the target gNB-DU 106A, 106B.

[0056] In step S208, the UE 102 transmits the L1 measurement results of the configured cells to the serving gNB-DU 104.

[0057] Based on step S208, in step S209, the serving gNB-DU 104 requests that the UE 102 perform UL synchronization with one or more target cells using the configured PRACH preamble.

[0058] In step S210, the serving gNB-DU 104 uses a PDCCH order to request that the UE 102 perform UL synchronization.

[0059] In step S211, the UE 102 performs UL synchronization and transmits a RACH preamble to the cell of the target gNB-DU 106A, 106B.

[0060] In step S212, the UE 102 is configured to receive an RAR from the target gNB-DU 106A, 106B, which includes the TA of the candidate / target cell to be used by the UE 102. The target gNB-DU 106A, 106B also transmits multiple neighboring beams along with a timing advance to the UE 102 in the RAR.

[0061] In step S213, the TAs corresponding to multiple beams of the candidate / target cell are available and stored in the UE 102.

[0062] In step S214, the UE 102 transmits the TA of the target cell to the serving gNB-DU 104 via an uplink media access control element (UL MAC CE).

[0063] In step S215, after receiving the RAR, the UE 102 sends an intra-frequency L1 measurement report to the serving gNB-DU 104. In one embodiment, the UE 102 may send an L1 MR to the serving gNB-DU 104 for configured cells.

[0064] In step S216, the serving gNB-DU 104 determines the optimal beam of the target cell for the UE 102 using the corresponding TA.

[0065] In step S217, the serving gNB-DU 104 transmits the optimal beam of the target cell via MAC CE to the UE 102.

[0066] In step S218, the UE 102 transmits a RACH-less HO to the cells of the target gNB-DUs 106A and 106B.

[0067] Figure 3 is a sequence diagram illustrating another scenario in which UE 102 determines the optimal beam belonging to target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA provided by target gNB-DU 106A, 106B, according to this embodiment as disclosed herein.

[0068] Referring to Figure 3, the UE 102 determines the optimal beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA.

[0069] In step S301, the UE 102 is still connected to the serving gNB-DU 104 (before the LTM serving cell switch).

[0070] In step S302, UE102 uses an RRC connection with gNB-CU200 to transmit L3 RRC measurement results to gNB-CU200.

[0071] In step S303, gNB-CU200 decides to prepare an inter-gNB-DU LTM candidate cell.

[0072] In step S304, the gNB-CU 200 initiates a UE context setup request message to the target gNB-DU 106A, 106B to prepare an inter-DU LTM candidate cell.

[0073] In step S305, the target gNB-DU 106A, 106B confirms with a UE context setup response message and provides the candidate / target cell configuration.

[0074] In step S306, the gNB-CU200 sends a DL RRC message (RRC reconfiguration (LTM target cell configuration)) to the serving gNB-DU104 via the F1 interface.

[0075] In step S307, an RRC reconfiguration message is passed to the UE 102. The serving gNB-DU 104 checks a set of RRM criteria (e.g., a pre-defined RSRP threshold) to trigger the transmission of L1 measurements to the target gNB-DU 106A, 106B.

[0076] In step S308, the UE 102 transmits the L1 measurement results of the configured cells to the serving gNB-DU 104.

[0077] Based on step S308, in step S309, the serving gNB-DU 104 requests that the UE 102 perform UL synchronization with one or more target cells using the configured PRACH preamble.

[0078] In step S310, the serving gNB-DU 104 uses a PDCCH order to request that the UE 102 perform UL synchronization.

[0079] In step S311, UE102 performs UL synchronization and transmits a RACH preamble to the cell of the target gNB-DU.

[0080] In step S312, the UE 102 is configured to receive the RAR from the target gNB-DU 106A, 106B.

[0081] In step S313, the target gNB-DU 106A, 106B initiates a context modification procedure to inform the serving gNB-DU 104 of the TA of the candidate / target cell. An indication that a UE context modification is required is sent to the gNB-CU 200. Such indication includes the TA of the candidate / target cell to be used by the UE 102. The target gNB-DU 106A, 106B also includes multiple beams with timing advance in the F1 message.

[0082] In step S314, based on the indication described in step S312, gNB-CU200 sends a confirmation regarding the indication that a UE context change is required.

[0083] In step S315, the gNB-CU 200 initiates a UE context modification request message to the serving gNB-DU 104, which includes the TA of the candidate / target cell to be used by the UE 102. The gNB-CU 200 also includes multiple beams with timing advances sent by the target gNB-DUs 106A, 106B to the serving gNB-DU 104 in an F1 message.

[0084] In step S316, the serving gNB-DU104 acknowledges with a UE context modification request message over the F1 interface.

[0085] In step S317, TAs corresponding to multiple beams of the target cell are available and stored in the serving gNB-DU104.

[0086] In step S318, the UE 102 transmits an intra-frequency L1 measurement report to the serving gNB-DU 104 based on the reception of the RAR.

[0087] In step S319, the serving gNB-DU 104 determines the optimal beam of the target cell for the UE 102 and uses the corresponding TA.

[0088] In step S320, the serving gNB-DU 104 transmits the target beam of the target cell via MAC CE to the UE 102 based on the determination of the optimal beam.

[0089] In step S321, UE 102 transmits a RACH-less HO to the cells of target gNB-DUs 106A and 106B.

[0090] FIG. 4 illustrates a flowchart of a method 400 for wireless communication in a UE, according to an embodiment as disclosed herein.

[0091] 4, method 400 may comprise one or more steps. Method 400 may be described in the general context of computer-executable instructions. Generally, computer-executable instructions may include routines, programs, objects, components, data structures, procedures, modules, or functions that perform particular functions or implement particular abstract data types.

[0092] The order in which method 400 is described is not intended to be limiting, as any number of the described method blocks may be combined in any order to implement the method. Additionally, individual blocks may be deleted from the method without departing from the scope of the subject matter described herein. Furthermore, the method may be implemented in any suitable hardware, software, firmware, or combination thereof.

[0093] In step 402, the UE 102 may receive a request from a first distributed unit (DU) of the serving base station 104 to perform uplink synchronization with a second DU of the target base station 106A, 106B. In one embodiment, before receiving the request to perform uplink synchronization from the serving base station 104, the UE 102 may transmit to the serving base station 104 a measurement report (MR) associated with one or more signal and channel parameters for each of multiple candidate cells of one or more neighbor base stations. In one example, the multiple candidate cells may include multiple non-serving cells. In one embodiment, the UE 102 receives the request to perform uplink synchronization using a PDCCH order transmitted by the serving base station 104.

[0094] In step 404, the UE 102 may perform uplink synchronization by transmitting a random access channel (RACH) request message to the second DU. In one embodiment, the UE 102 may receive a random access response (RAR) from the target base station 106A, 106B in response to performing uplink synchronization. For example, the RAR may include at least a primary beam identifier with an associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

[0095] In step 406, UE 102 may receive, from one of the first DU and the second DU, based on uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with one or more associated secondary TAs.

[0096] In step 408, the UE 102 may receive a cell switch command from the first DU indicating a target beam for the target cell. The target cell may be selected from a primary candidate cell or one or more secondary candidate cells. In other embodiments, the UE 102 may receive the target beam from a primary beam identifier and one or more secondary beam identifiers. In one embodiment, determining the target beam may be performed by comparing one or more signal and channel parameters associated with the primary beam identifier with one or more corresponding signal and channel parameters associated with at least one of the secondary beam identifiers. The target beam may then be determined from the primary beam identifier and one or more secondary beam identifiers based on the comparison results. In one example, the one or more secondary beam identifiers are determined based on respective signal quality metrics. For example, a beam may be selected as a secondary beam based on a measurement of a signal quality metric associated with the beam compared to other beams present in a beam group.

[0097] In step 410, the UE 102 may perform a serving cell switch function for the target beam and may apply a corresponding TA associated with the target beam.

[0098] In the proposed method, the target gNB-DU 106A, 106B adds the UE's TA of the optimal beam (the optimal beam or DL ​​beam corresponding to the UL beam used by the UE 102 to perform UL synchronization operation) to the RAR. Furthermore, the target gNB-DU 106A, 106B includes the UE's TA of neighboring beams. This ensures that if one of the neighboring beams becomes the optimal beam, the UE 102 may dynamically apply the corresponding TA to the optimal beam. Therefore, such dynamic application of the corresponding TA can reduce the total time required to perform a handover from the serving base station 104 or cell 104 to the target base station 106A, 106B or target cell 106A, 106B. Such dynamic application of the corresponding TA also eliminates the need to repeatedly perform UL synchronization to obtain an updated TA due to the UE's mobility.

[0099] In one embodiment, a neighboring beam is qualified as any nearby beam that may be expected to be accessed next by the UE 102, such as any beam with optimal channel and signal parameters or characteristics toward which the UE 102 is expected to be headed. In one example, artificial intelligence (AI) machine learning (ML) methods may be used to interpret or compute the eligibility of a neighboring beam. For example, a priority list may be generated by the UE 102 or the serving base station 104 to determine the eligibility of a neighboring beam. In another example, a priority list of neighboring beams may be generated at the target base station 106A, 106B.

[0100] In one embodiment, a prioritized list of neighboring beams may be generated based on target beams / beam groups selected by the UE 102 during one or more previous handovers. In one example, the prioritized list may be generated based on one or more of the beamforming structure implemented in the cell, the total number of neighboring target beams / beam groups available from the optimal beam or beam group, and RSRP metrics reported by the UE 102 for different beams / beam groups. In other embodiments, the number of neighboring beams TA may be determined by the gNB-CU 200.

[0101] In one embodiment, the serving gNB-DU 104 may indicate the target cell beam to be used by the UE 102 in an SCC command, such as a downlink (DL) MAC CE, sent to the UE 102. The UE 102 may use the TA provided by the target gNB-DU 106A, 106B that corresponds to the beam indicated in the SCC command.

[0102] In another embodiment, the UE 102 is configured to autonomously determine the optimal beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and apply the corresponding TA (provided by the target gNB-DU 106A, 106B).

[0103] In the proposed method and system, the serving gNB-DU 104 improves the optimal beam to compensate for UE mobility and implement better TA estimation. In one embodiment, digital beamforming reception and related receiver architectures are implemented by the proposed method and system. In another embodiment, analog beamforming reception is implemented by the proposed method and system. The proposed method is used to receive physical random access channel (PRACH) signals, and multiple receive beams (a list of which is provided by the serving cell 104 or a set of beams that are close to each other, selected by the target cells 106A, 106B) are processed.

[0104] For at least one of the receive beams, the target gNB-DU 106A, 106B may calculate a TA. In one example, the serving cell 104 may share the TA with the UE 102 using a UL MAC CE that includes both the beam index and the corresponding TA of the target cell 106A, 106B.

[0105] Because the UE 102 has information about the TAs of neighboring or secondary beams, separate from the TA of the target beam, the UE 102 can determine whether the target beam is the optimal beam for performing a handover. If the UE 102 determines that one of the secondary beams is the optimal beam for performing a handover, the UE 102 can select the secondary beam to replace the target beam. In an alternative embodiment, the serving base station 104 may be configured to compare the target beam with the secondary beams to determine the optimal beam and transmit optimal beam information to the UE. This allows the UE 102 to perform a RACH-less LTM handover with the target base station 106A, 106B on an optimal beam that remains valid for an extended period of time, even if the UE 102 undergoes mobility, for example, when the UE 102 moves from one location to another, resulting in a change in TA.

[0106] FIG. 5 illustrates a detailed block diagram of an apparatus 500 in which a method for wireless communication may be implemented. FIG. 5 illustrates a detailed block diagram of the apparatus 500, according to some embodiments of the present disclosure. In one embodiment, the apparatus 500 is understood to be associated with the UE 102. In another embodiment, the apparatus 500 is understood to be associated with the serving base station 104. The apparatus 500 may comprise at least one transmitter 502, at least one receiver 504, at least one processor 508, at least one memory 510, at least one interface 512, and at least one antenna 514. The at least one transmitter 502 may be configured to transmit data / information to one or more nodes / devices using the antenna 514. The at least one receiver 504 may be configured to receive data / information from one or more nodes / devices using the antenna 514. The at least one transmitter 502 and receiver 504 may be collectively implemented as a single transceiver module 506. In one non-limiting embodiment, at least one processor 508 may be communicatively coupled to the transceiver module 506, memory 510, interface 512, and antenna 514 to process wireless communications and, in particular, to implement the techniques described above for performing RACH-less LTM HO.

[0107] The at least one processor 508 may include one or more of, but are not limited to, a microprocessor, a microcomputer, a microcontroller, a central processing unit, a state machine, a logic circuit, or any device that manipulates signals based on operational instructions. The processor may also be implemented as a combination of computing devices, such as a combination of multiple microprocessors, or any other such configuration. The at least one memory 510 may be communicatively coupled to the at least one processor 508 and may comprise various instructions, UE signal strength data, an initial bandwidth portion, one or more dedicated bandwidth portions, predetermined intervals, etc. The at least one memory 510 may include one or more of a random access memory (RAM) unit and a non-volatile memory unit such as a read-only memory (ROM), an optical disk drive, a magnetic disk drive, a flash memory, an electrically erasable read-only memory (EEPROM), memory space on a server or cloud, etc. The at least one processor 508 may be configured to execute one or more instructions stored in the memory 510.

[0108] The interface 512 may include various software and hardware interfaces, such as a web interface, a graphical user interface, an input / output device (I / O) interface, a network interface, etc. The I / O interface may enable the apparatus 500 to communicate with one or more nodes / devices directly or through other devices. The network interface may enable the apparatus 500 to interact with one or more networks, either directly or via any other network.

[0109] The apparatus 500 may further include an optimal beam determination module 112A, 112B for determining an optimal beam from the primary beam identifier and one or more secondary beam identifiers based on one or more associated signal and channel parameters and defining the optimal beam as a target beam. In one example, the optimal beam is a target beam based on a determination that the current target beam has optimal characteristics compared to other beams or beam groups.

[0110] When the UE 102 is provided with the TA of a neighboring beam along with the TA of the target beam, the UE 102 can autonomously determine the optimal beam belonging to the target gNB-DU 106A, 106B. For example, the UE 102 may be configured to autonomously consider channel and signal parameters, such as L1 measurement results, to determine the optimal beam belonging to the target gNB-DU 106A, 106B and subsequently apply the corresponding TA provided by the target gNB-DU 106A, 106B.

[0111] In embodiment 1, the device comprises: receiving, at a user equipment (UE) 102, a request from a first distributed unit (DU) of a serving base station 104 to perform uplink synchronization with a candidate cell of a second DU of a target base station 106A, 106B; performing the uplink synchronization at the UE 102 by sending a random access channel (RACH) request message to the second DU; receiving, from one of the first DU and the second DU, at the UE 102, based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU together with an associated primary timing advance (TA), and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU together with an associated one or more secondary TAs; receiving, at the UE 102, a cell switch command from the first DU indicating a target beam of a target cell selected from the primary candidate cell or the one or more secondary candidate cells; performing, at the UE 102, a serving cell switch function for the target beam and applying a corresponding TA associated with the target beam; is configured to execute

[0112] In embodiment 2, the device of embodiment 1 further comprises: The UE 102 is configured to transmit, from the first DU to the first DU before receiving the request to perform the uplink synchronization, Layer 1 measurement reports (L1 MRs) associated with each of one or more signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations.

[0113] In embodiment 3, the device of embodiment 1 further comprises: In response to performing the uplink synchronization, the UE 102 is configured to receive a random access response (RAR) from the second DU, the random access response including at least the primary beam identifier with the associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

[0114] In embodiment 4, the cell switch command associated with the device of embodiment 1 is a Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command.

[0115] In embodiment 5, the device of embodiment 1 further comprises: The one or more secondary beam identifiers are determined based on respective signal quality metrics.

[0116] In embodiment 6, the device of embodiment 1 further comprises: the request to perform the uplink synchronization is received at the UE 102 using a Physical Downlink Control Channel (PDCCH) order; The serving base station is the target base station.

[0117] In embodiment 7, a method for wireless communication in a user equipment (UE) 102 is performed. The method is: receiving a request from a first distributed unit (DU) of the serving base station 104 to perform uplink synchronization with a second DU of the target base station 106A, 106B; performing the uplink synchronization by sending a random access channel (RACH) request message to the second DU; receiving, from at least one of the first DU and the second DU, a primary beam identifier of a primary candidate cell of the second DU together with an associated primary Timing Advance (TA) based on the uplink synchronization, and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the primary candidate cell and the second DU together with one or more associated secondary TAs; receiving a cell switch command from the first DU indicating a target beam of a target cell selected from the primary candidate cell or the one or more secondary candidate cells; performing a serving cell switch function on the target beam and applying a corresponding TA associated with the target beam; Equipped with.

[0118] In embodiment 8, the method of embodiment 7, further comprising: Before receiving the request to perform the uplink synchronization from the first DU, transmit to the first DU Layer 1 measurement reports (L1 MRs) associated with each one or more signals and channel parameters of multiple candidate cells, including multiple non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations.

[0119] In embodiment 9, the method of embodiment 7 further comprises: The method further comprises receiving a random access response (RAR) from the second DU in response to performing the uplink synchronization, the RAR including at least the primary beam identifier with the associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

[0120] In embodiment 10, the method of embodiment 7 further comprises: The method further comprises determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on respective signal quality metrics.

[0121] In embodiment 11, the method of embodiment 7 further comprises: receiving the request to perform uplink synchronization includes receiving the request to perform uplink synchronization using a Physical Downlink Control Channel (PDCCH) order; The serving base station is the target base station.

[0122] In embodiment 12, the apparatus comprises: In a serving base station 104 and a first distributed unit (DU) of the serving base station 104, determining candidate cells of the target base station 106A, 106B from one or more DUs of one or more candidate base stations based on one or more signal and channel parameters of multiple candidate cells of one or more neighboring base stations; sending a request from the serving base station 104 to a user equipment (UE) 102 to perform uplink synchronization with the candidate cell; At the serving base station 104, receiving from at least one of the second DUs of the UE 102 and the target base stations 106A, 106B a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA) and one or more secondary beam identifiers of the primary candidate cell and at least one of one or more secondary candidate cells of the second DU with associated one or more secondary TAs, wherein the primary beam identifier, the primary TA, the one or more secondary beam identifiers, and the one or more secondary TAs are received from the second DU based on the uplink synchronization; determining, at the serving base station 104, a target beam for a target cell from the primary beam identifier and the one or more secondary beam identifiers based on one or more associated signal and channel parameters; sending a request from the serving base station 104 to the UE 102 to perform a serving cell switch function for the target beam and apply a corresponding TA associated with the target beam; is configured to execute

[0123] In embodiment 13, the device of embodiment 12 further comprises: To determine the target beam: comparing, at the serving base station 104, one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with each of the one or more secondary beam identifiers; determining, at the serving base station 104, the target beam from the primary beam identifier and the one or more secondary beam identifiers based on the comparison; is configured to execute

[0124] In embodiment 14, the device of embodiment 12 further comprises: Prior to determining the second DU, the serving base station 104 is further configured to receive from the UE 102 Layer 1 Measurement Reports (L1 MRs) associated with each of the one or more signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations.

[0125] In embodiment 15, the device of embodiment 12 further comprises: configured to transmit, from the serving base station 104, the request to perform the uplink synchronization to the second DU, the request comprising a request for a random access channel (RACH); The request for the RACH triggers a random access response (RAR) from the second DU, which includes at least the primary beam identifier with the associated primary TA and the one or more secondary beam identifiers with the associated one or more secondary TAs.

[0126] In embodiment 16, the device of embodiment 14, further comprising: The serving cell switch function is performed based on a Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command.

[0127] In embodiment 17, the device of embodiment 12 further comprises: The one or more secondary beam identifiers are determined based on respective signal quality metrics.

[0128] In embodiment 18, the device of embodiment 12 further comprises: sending the request to perform the uplink synchronization to the UE 102 using a Physical Downlink Control Channel (PDCCH) order; The serving base station is the target base station.

[0129] In embodiment 19, a non-transitory computer-readable medium storing program instructions executed by an apparatus for wireless communication in a user equipment (UE) 102 is disclosed. The program instructions are receiving a request from a first distributed unit (DU) of the serving base station 104 to perform uplink synchronization with a second DU of the target base station 106A, 106B; performing the uplink synchronization by sending a random access channel (RACH) request message to the second DU; receiving, from one of the first DU and the second DU, a primary beam identifier of a primary candidate cell of the second DU together with an associated primary Timing Advance (TA) based on the uplink synchronization, and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the primary candidate cell and the second DU together with one or more associated secondary TAs; receiving a cell switch command from the first DU indicating a target beam of a target cell selected from the primary candidate cell or the one or more secondary candidate cells; performing a serving cell switch function on the target beam and applying a corresponding TA associated with the target beam; may also be provided.

[0130] In embodiment 20, the non-transitory computer-readable medium of embodiment 19, wherein the program instructions are: comparing one or more signal and channel parameters associated with the primary beam with corresponding one or more signal and channel parameters associated with each of the one or more secondary beams; determining the target beam from the primary beam identifier and the one or more secondary beam identifiers based on the comparison; and and determining the target beam comprising:

[0131] In embodiment 21, in the non-transitory computer-readable medium of embodiment 19, the program instructions include: Before receiving the request to perform the uplink synchronization from the first DU, the method may include transmitting to the first DU Layer 1 measurement reports (L1 MRs) associated with each of the one or more signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations.

[0132] In embodiment 22, the non-transitory computer-readable medium of embodiment 19, wherein the program instructions are: In response to performing the uplink synchronization, the method may include receiving a random access response (RAR) from the second DU, the random access response including at least the primary beam identifier with the associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

[0133] In embodiment 23, in the non-transitory computer-readable medium of embodiment 19, the program instructions include: The method may further comprise determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on respective signal quality metrics.

[0134] In embodiment 24, the non-transitory computer-readable medium of embodiment 19, Receiving the request to perform uplink synchronization includes receiving the request to perform uplink synchronization using a PDCCH order. In one non-limiting embodiment, the apparatus 500 may be part of the serving base station 104, but is not limited to such.

[0135] In other non-limiting embodiments, the device 500 may be part of the UE 102, but is not limited to such.

[0136] In non-limiting embodiments of the present disclosure, one or more non-transitory computer-readable media may be utilized to implement embodiments consistent with the present disclosure. A computer-readable medium represents any type of physical memory (such as memory 510) in which information or data readable by a processor may be stored. As such, a computer-readable medium may store one or more instructions for execution by at least one processor 508, including instructions for causing at least one processor 508 to perform steps or stages consistent with the embodiments described herein. The term "computer-readable medium" should be understood to include tangible items and exclude carrier waves and transitory signals. By way of non-limiting example, such computer-readable media may comprise random access memory (RAM), read-only memory (ROM), volatile memory, non-volatile memory, a hard drive, a compact disc (CD) ROM, a digital video disc (DVD), a flash drive, a disk, or any other known physical storage medium.

[0137] As such, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored thereon (and / or encoded thereon). The instructions are executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging materials.

[0138] The various illustrative logical blocks, modules, and operations described in connection with this disclosure may be implemented or performed by a general-purpose processor, discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. A general-purpose processor may include a microprocessor, but in the alternative, the processor may include any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of multiple microprocessors, or any other such configuration of computing devices.

[0139] The above description of specific embodiments fully reveals the general nature of the present embodiments herein, and third parties, by applying current knowledge, can easily modify or adapt such specific embodiments for various applications without departing from the general concept. Therefore, such adaptations and modifications should be understood to be within the meaning and range of equivalents of the disclosed embodiments. The expressions or terms used herein are understood to be for non-limiting descriptive purposes. Thus, although the present embodiments herein have been described with reference to preferred embodiments, those skilled in the art will recognize that the present embodiments herein can be practiced with modifications within the scope of the present embodiments as described herein.

Claims

1. receiving, at a user equipment (UE) (102), from a first distributed unit (DU) of a serving base station (104) a request to perform uplink synchronization with a candidate cell of a second distributed unit (DU) of a target base station (106A, 106B); performing the uplink synchronization by transmitting a random access channel (RACH) request message to the second DU in the UE (102); receiving, from at least one of the first DU and the second DU, at the UE (102), based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU together with an associated primary timing advance (TA), and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU together with an associated one or more secondary TAs; receiving, in the UE (102), from the first DU, a cell switch command indicating a target beam of a target cell selected from the primary candidate cell or the one or more secondary candidate cells; In the UE (102), performing a serving cell switch function on the target beam and applying a corresponding TA associated with the target beam; 20. An apparatus configured to:

2. 2. The apparatus of claim 1, further comprising: a first DU configured to transmit, from the UE (102) to the first DU, Layer 1 measurement reports (L1 MRs) associated with one or more respective signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations, before receiving the request to perform the uplink synchronization from the first DU.

3. The device of claim 1, configured to receive, in response to performing the uplink synchronization, a random access response (RAR) from the second DU, the RAR including at least the primary beam identifier with the associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs.

4. The apparatus of claim 1 , wherein the cell switch command is a Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command.

5. The apparatus of claim 1 , wherein the one or more secondary beam identifiers are determined based on respective signal quality metrics.

6. The request to perform the uplink synchronization is received at the UE (102) using a Physical Downlink Control Channel (PDCCH) order; the serving base station is the target base station; 10. The apparatus of claim 1.

7. receiving a request from a first distributed unit (DU) of a serving base station (104) to perform uplink synchronization with a second distributed unit (DU) of a target base station (106A, 106B); performing the uplink synchronization by sending a random access channel (RACH) request message to the second DU; receiving, from at least one of the first DU and the second DU, a primary beam identifier of a primary candidate cell of the second DU together with an associated primary timing advance (TA) based on the uplink synchronization, and receiving one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU together with one or more associated secondary TAs; receiving a cell switch command from the first DU indicating a target beam of a target cell selected from the primary candidate cell or the one or more secondary candidate cells; performing a serving cell switch function on the target beam and applying a corresponding TA associated with the target beam; A method for providing

8. 8. The method of claim 7, further comprising, before receiving the request to perform the uplink synchronization from the first DU, transmitting to the first DU Layer 1 Measurement Reports (L1 MRs) associated with respective one or more signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations.

9. 8. The method of claim 7, further comprising receiving, from the second DU, a random access response (RAR) including at least the primary beam identifier with the associated primary TA and one or more secondary beam identifiers with one or more associated secondary TAs in response to performing the uplink synchronization.

10. 8. The method of claim 7, comprising determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on respective signal quality metrics.

11. receiving the request to perform uplink synchronization includes receiving the request to perform uplink synchronization using a Physical Downlink Control Channel (PDCCH) order; the serving base station is the target base station; The method of claim 7.

12. In a serving base station (104) and a first distributed unit (DU) of the serving base station (104), determining candidate cells of a target base station (106A, 106B) from one or more DUs of one or more candidate base stations based on one or more signal and channel parameters of multiple candidate cells of one or more neighboring base stations; sending a request from the serving base station (104) to a user equipment (UE) (102) to perform uplink synchronization with the candidate cell; In the serving base station (104), receiving from at least one of the second DUs of the UE (102) and the target base station (106A, 106B) a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA) and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with an associated one or more secondary TAs, wherein the primary beam identifier, the primary TA, the one or more secondary beam identifiers, and the one or more secondary TAs are received from the second DU based on the uplink synchronization; determining, at the serving base station (104), a target beam for a target cell from the primary beam identifier and the one or more secondary beam identifiers based on one or more associated signal and channel parameters; sending a request from the serving base station (104) to the UE (102) to perform a serving cell switch function for the target beam and apply a corresponding TA associated with the target beam; 20. An apparatus configured to:

13. To determine the target beam: comparing, at the serving base station (104), one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with each of the one or more secondary beam identifiers; determining, at the serving base station (104), the target beam from the primary beam identifier and the one or more secondary beam identifiers based on the comparison; The apparatus of claim 12 configured to perform the following:

14. 13. The apparatus of claim 12, further configured to receive, from the UE (102), Layer 1 measurement reports (L1 MRs) associated with each of the one or more signals and channel parameters of a plurality of candidate cells, including a plurality of non-serving cells, associated with the first DU and one or more DUs associated with one or more neighbor base stations, before determining the second DU.

15. configured to transmit, from the serving base station (104) to the second DU, the request to perform the uplink synchronization comprising a request for a random access channel (RACH); the request for the RACH triggers a Random Access Response (RAR) from a second DU, the RAR including at least the primary beam identifier with the associated primary TA and the one or more secondary beam identifiers with the associated one or more secondary TAs.

13. The apparatus of claim 12.

16. The apparatus of claim 12 , wherein the serving cell switch function is performed based on a Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command.

17. The apparatus of claim 12 , further comprising: determining the one or more secondary beam identifiers based on respective signal quality metrics.

18. Sending the request to perform the uplink synchronization to the UE (102) using a Physical Downlink Control Channel (PDCCH) order; the serving base station is the target base station; 13. The apparatus of claim 12.

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