Timing advance optimization during uplink synchronization

Abstract

Embodiments disclosed herein 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 is performed by the UE (102) with the second DU. Further, the UE (102) receives a primary beam identifier and a secondary beam identifier associated with an associated timing advance (TA) from the second DU based on uplink synchronization. Accordingly, the UE (102) may determine a target beam of the target cell and perform a serving cell handover function to the target beam.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Indian Provisional Patent Application No. 202341024646 filed on March 31, 2023, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] The present disclosure relates generally to the field of wireless communications, and more particularly to timing advance optimization during uplink (UL) synchronization. Background Art

[0004] A cellular network is a telecommunications interconnection of user devices and cellular base stations (BSs), such as cell towers. A BS includes a service area divided into multiple cells. A cell defines the geographic area served by the transceiver antennas associated with the BS. Multiple user devices present in a particular cell (also called a serving cell) communicate with the BS's associated transceiver antennas over multiple frequencies and frequency channels.

[0005] The Radio Access Network (RAN) is part of a cellular network and is responsible for implementing radio access technologies. The RAN provides connectivity to user devices (such as mobile phones / devices, computers, or any remote control devices present in the network) through the Core Network (CN). User devices may be variously referred to as User Equipment (UE), Terminal Equipment, Mobile Station (MS), etc.

[0006] When a mobile device (such as a UE) is connected to a serving cell, the mobile device performs measurements of channel parameters and signal parameters related to the serving cell and neighboring cells within a predefined time period. In addition, when multiple UEs are connected to the serving cell, the distance between the serving BS and the UE can be derived by measuring the time it takes for radio waves to propagate from the UE to the serving BS (called timing advance (TA)). In addition, the value of TA may be affected by changes in the distance between the UE and the serving BS due to the movement of the UE. Similarly, at least one of the neighboring cells may have a TA associated with the UE being served in the neighboring cell.

[0007] During the movement of a mobile device, the TA, channel parameters and signal parameters associated with the serving cell and the neighboring cells are constantly changing. For example, if the UE moves from the coverage area of ​​the serving cell to the coverage area of ​​one of the neighboring cells (also called the target cell), the UE needs to connect to the neighboring cell and disconnect from the serving cell. This process is called handover (HO). The above-mentioned UE mobility that defines UE movement can be referred to as inter-cell mobility (LTM) centered around Layer 1 (L1) / Layer 2 (L2). However, it should be understood that UE mobility can also be implemented in an alternative manner to LTM, which is not discussed in this document for the sake of brevity. In LTM, based on UE movement, in order to perform a handover from the serving cell to the target cell, the UE needs to obtain knowledge of the TA associated with the target cell to implement the handover, and needs to continue communicating with the target cell. Knowledge of the TA is necessary for the UE to perform correct synchronization (also called UL synchronization) and connection with the target cell.

[0008] Conventional technology defines a decomposed BS architecture for cellular networks. For example, the Third Generation Partnership Project (3GPP) defines a decomposed next-generation Node B (gNB) architecture that decomposes the gNB into multiple logical entities. For example, a gNB may include a gNB Control Unit Control Plane (CU-CP) and a gNB Distributed Unit (DU). Similarly, a single DU can be responsible for hosting multiple cells. For example, in current 3GPP specifications, a single DU can be responsible for hosting up to 512 cells. The gNB-CU-CP can host the Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the gNB-DU hosts the Radio Link Control (RLC), Media Access Control (MAC), and Physical (PHY) layers. Furthermore, downlink (DL) scheduling operations can be performed at the gNB-DU. To support Layer 1 (L1) / Layer 2 (L2)-centric inter-cell mobility associated with serving cell changes, a mechanism is required in a decomposed gNB architecture where handover preparation is performed by the gNB-CU-CP, but handover is performed autonomously by the gNB-DU without further interaction with higher layers such as PDCP and RRC. Handover preparation can also be referred to as target cell configuration preparation. For example, a handover without further interaction with higher layers can be a Random Access Channel (RACH)-free L1 / L2 Triggered Mobility (LTM) handover (HO).

[0009] 3GPP Release 18 work items (WI) describe further New Radio (NR) mobility enhancements as follows:

[0010] Short name: NR_Mob_enh2-Core;

[0011] Main WG: RAN2;

[0012] 3GPP version: REL-18;

[0013] Work Item Description: RP-221799

[0014] The goals for the upcoming Mobility Enhancements Rel.18 work item can be found in RP-213565:

[0015] Specify mechanisms and procedures for L1 / L2-based inter-cell mobility to reduce mobility latency:

[0016] ○ Configuration and maintenance of multiple candidate cells to allow rapid application of candidate cell configurations [RAN2, RAN3]

[0017] Dynamic handover mechanism between candidate serving cells (including SpCell and SCell) based on potential applicable scenarios of L1 / L2 signaling [RAN2, RAN1]

[0018] ○ L1 enhancements for inter-cell beam management, including L1 measurement and reporting, and beam indication [RAN1, RAN2]

[0019] Comment 1: Early RAN2 engagement is necessary, including to further clarify the potential for interactions between this project and previous projects.

[0020] ○Timing advance management [RAN1, RAN2]

[0021] o CU-DU interface signaling, if required, to support L1 / L2 mobility [RAN3]

[0022] Note 2: FR2 specific enhancements (if any) are not excluded.

[0023] Note 3: The L1 / L2-based inter-cell mobility process is applicable to the following scenarios:

[0024] Standalone, Carrier Aggregation (CA), and NR Dual Connectivity (NR-DC) scenarios with serving cell change within one CG.

[0025] Intra-DU and intra-CU inter-DU scenarios (applicable to Standalone and CA: no new RAN interface is expected)

[0026] Both intra-frequency and inter-frequency

[0027] Both FR1 and FR2

[0028] • The source cell and the target cell may be synchronized or not.

[0029] Note: L1 / L2 triggered mobility is a mobility feature and can be considered as a basic UE capability (starting from R18).

[0030] According to conventional technology, the following is the RAN1 agreement reached at the RAN1#112 meeting:

[0031] For PDCCH orders RACH of candidate cell(s), RAR reception may be configured / indicated.

[0032] If RAR reception is not configured / indicated (no RAR)

[0033] o The TA value of the candidate cell is indicated in the cell handover command.

[0034] ○ FFS: When RAR reception is not configured / indicated, should the UE retransmit PRACH?

[0035] ○FFS: How does the UE determine the subsequent PRACH transmission triggered by the PDCCH command?

[0036] Transmission power

[0037] If reception of RAR is configured / indicated (with RAR), then FFS

[0038] ○ Whether RAR is received from the serving cell or candidate cell

[0039] If the RAR is received from the candidate cell, whether the Type 1-PDCCH CSS of the candidate cell is configured for the UE.

[0040] ○RAR content

[0041] FFS: Signaling used to configure / indicate whether RAR needs to be received

[0042] • The UE may report support combinations of only with RAR and only without RAR, where the baseline UE method of supporting one default solution is LTM.

[0043] Send LS to RAN2 and RAN3 to check the feasibility of the agreement.

[0044] Note: The definition of candidate cells depends on RAN2

[0045] Protocol If reception of RAR is configured / indicated, then the RAR contains at least the TA of the candidate cell.

[0046] • The maximum number of TA values ​​memorized by the UE is the UE capability.

[0047] FFS: Whether the RAR contains other parameters such as UEID, candidate cell ID, etc.

[0048] Conventional techniques obtain the target cell TA before a serving cell handover. This reduces handover delays during an LTM serving cell change (SCC) (hereinafter also referred to as a serving cell handover) because the TA is known to the UE and, therefore, TA acquisition during the actual SCC can be avoided. During the LTM, if the UE is configured to perform an UL synchronization procedure, there is a time window between obtaining the target cell TA and performing the LTM SCC. This duration can vary from one UE to another, or even from one UE to another. Therefore, the duration may not be accurately determined or predicted.

[0049] Because the UE may move during this duration, the UE's TA at the target cell may also change. For example, the TA acquired during UL synchronization may not be valid at the LTM SCC. Therefore, to acquire a valid TA at the LTM SCC and ensure RACH-free LTM handover, the serving gNB-DU requests the UE to perform repeated UL synchronization with the target gNB-DU to acquire an updated TA. However, performing UL synchronization again to acquire the updated TA affects the UE's data transmission at the serving gNB-DU and incurs overhead for the target gNB-DU. Alternatively, the serving gNB can request the UE to perform a RACH-based handover when issuing an LTM SCC command, which involves further interaction with higher layers.

[0050] Therefore, a technique is needed to perform RACH-free handover without the need to repeat UL synchronization when the UE undergoes mobility.

[0051] The information disclosed in the background of the disclosure is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgment or any form of suggestion that this information constitutes the prior art already known to those skilled in the art. Summary of the Invention

[0052] The present disclosure relates to an apparatus configured to receive, at a user equipment (UE), a request from a first distributed unit (DU) of a serving base station to perform uplink synchronization with a candidate cell of a second DU of a target base station. In addition, the apparatus is configured to perform uplink synchronization by the UE by sending a random access channel (RACH) request message to the second DU. In addition, the apparatus receives, by the UE based on uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA) from at least one of the first DU and the second DU, 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 associated one or more secondary TAs. The apparatus also receives, by the UE, a cell switching command indicating a target beam of a target cell from the first DU, wherein the target cell is selected from the primary candidate cell or one or more secondary candidate cells. The apparatus is also configured to perform, by the UE, a serving cell switching function to the target beam and apply a corresponding TA associated with the target beam.

[0053] The present disclosure also relates to a method for wireless communication at a user equipment (UE). The method includes receiving a request from a first distributed unit (DU) of a serving base station to perform uplink synchronization with a second DU of a target base station. In addition, the method includes performing uplink synchronization by sending a random access channel (RACH) request message to the second DU. In addition, the method includes receiving a main beam identifier of the second DU with an associated main TA from at least one of the first DU and the second DU based on uplink synchronization, and receiving one or more secondary beam identifiers of at least one of a primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs. In addition, the method includes receiving a cell switching command indicating a target beam of a target cell from the first DU. The target cell is selected from the primary candidate cell or one or more secondary candidate cells. The method also includes performing a serving cell switching function to the target beam and applying a corresponding TA associated with the target beam.

[0054] In addition, the present disclosure relates to an apparatus configured to determine, at a serving base station and a first distributed unit (DU) of the serving base station, 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. In addition, the apparatus is configured to send a request from the serving base station to a user equipment (UE) to perform uplink synchronization with the candidate cell. In addition, the apparatus is configured to receive, at the serving base station, from at least one of the UE and the second DU of the target base station, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA), and receive 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 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 received by the UE from the second DU based on uplink synchronization. In addition, the apparatus is configured to determine, at the serving base station, 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 a request from the serving base station to the UE to perform a serving cell handover function to the target beam and apply a corresponding TA associated with the target beam.

[0055] The foregoing summary is illustrative only and is not intended to be limiting in any way. In addition to the illustrative 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 DESCRIPTION OF THE DRAWINGS

[0056] The novel features and characteristics of the present disclosure are set forth in the appended claims. However, the disclosure itself, as well as the preferred mode of use, additional objects and advantages, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings. One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings, wherein like reference numerals represent like elements, and in which:

[0057] Figure 1 A schematic diagram illustrating random access resource configuration for a UE according to an embodiment disclosed herein is illustrated;

[0058] Figure 2 is a sequence diagram illustrating a scenario according to the embodiments disclosed herein, wherein the best beam belonging to a target gNB-DU is determined and the corresponding TA provided by the target gNB-DU is applied;

[0059] Figure 3is a sequence diagram illustrating another scenario according to embodiments disclosed herein, in which the best beam belonging to a target gNB-DU is determined and the corresponding TA provided by the target gNB-DU is applied;

[0060] Figure 4 illustrates a flow chart of a method for wireless communication at a UE according to embodiments disclosed herein; and

[0061] Figure 5 A detailed block diagram of a device in which the wireless communication method according to the embodiments disclosed herein may be implemented is illustrated.

[0062] Those skilled in the art will appreciate that any block diagrams herein represent conceptual diagrams of illustrative systems embodying the principles of the present subject matter. Similarly, it will be understood that any flow charts, flowcharts, state transition diagrams, pseudocode, etc. represent various processes that can be substantially represented 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

[0063] It should be understood that the present disclosure may assume various alternative variations and step sequences, unless expressly stated to the contrary. It should also be understood that the specific devices and processes shown in the drawings and described in the following description are merely illustrative and non-limiting embodiments or aspects. Therefore, specific dimensions and other physical characteristics related to the embodiments or aspects disclosed herein should not be considered limiting.

[0064] In this document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0065] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail below. However, it should be understood that it is not intended to limit the present disclosure to the specific forms disclosed, but rather, the present disclosure is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[0066] The terms "comprises," "comprising," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a device, apparatus, or method that comprises a list of components or steps includes not only those components or steps but may also include other components or steps not expressly listed or inherent to such device, apparatus, or method. In other words, a reference to one or more elements in a device, system, or apparatus beginning with "comprises ... a" does not, without more constraints, preclude the presence of other or additional elements in the device, system, or apparatus.

[0067] Unless expressly stated otherwise, the terms “an embodiment,” “embodiment,” “embodiments,” “the embodiment,” “the embodiments,” “one or more embodiments,” “some embodiments,” and “one embodiment” refer to “one or more (but not all) embodiments of the present disclosure.”

[0068] Unless expressly stated otherwise, the terms "including," "comprising," "having" and variations thereof mean "including but not limited to."

[0069] In the following detailed description of embodiments of the present disclosure, reference is made to the accompanying drawings which form a part hereof, in which are shown by way of illustration specific embodiments in which the present disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure, and it should be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present disclosure. Therefore, the following description should not be considered restrictive.

[0070] Embodiments disclosed herein provide a method and system for acquiring timing advance during UL synchronization and performing optimization to ensure that the acquired timing advance is valid and applicable for a longer duration. A UE sends an L1 measurement report (MR) to a serving gNB-DU for configured cells. The serving gNB-DU checks a set of radio resource management (RRM) criteria (e.g., predefined reference signal received power (RSRP) thresholds) and requests the UE to perform UL synchronization with one or more candidate / target cells using the configured physical random access channel (PRACH) preamble. The serving gNB-DU uses a physical downlink control channel (PDCCH) order to request the UE to perform UL synchronization. The UE performs UL synchronization and is configured to receive a random access response (RAR) from a target gNB-DU, which includes the timing advance of the candidate / target cell to be used by the UE.

[0071] In one embodiment, in addition to the TA of the UE's best beam at the candidate / target cell gNB-DU with RAR, the target gNB-DU also includes the TAs of the UE's neighboring beams. This ensures that when one of the neighboring beams becomes the best beam, the UE applies the corresponding TA. A neighboring beam is considered to be any neighboring beam that the UE is expected to subsequently access (i.e., any beam toward which the UE is expected to move in good radio conditions).

[0072] In one embodiment, after acquiring the target cell TA during UL synchronization, the UE reports the TAs of the best beam and neighboring beams to the serving gNB-DU. During LTM cell handover, the serving gNB-DU indicates the target cell beam to be used by the UE in a serving cell handover command (downlink media access control element (DL MAC CE)), and this command is sent to the UE. The UE uses the TA corresponding to the beam indicated during serving cell handover (provided by the candidate / target gNB-DU). Alternatively, the UE is autonomously configured to determine the best beam belonging to the candidate / target gNB-DU (based on L1 measurements) 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 is used to achieve RACH-free HO even in the event of UE mobility after UL synchronization, a change in the best beam, and better TA estimation.

[0073] Figure 1A diagram 100 illustrates a RAR configuration for a UE 102 according to embodiments disclosed herein. The UE 102 may communicate 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 PDCCH orders (RACHs) of candidate cell(s) 106A, 106B (hereinafter also referred to as target base stations 106A, 106B or target / candidate gNB-DUs 106A, 106B, as target / candidate gNB-DUs 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, in the absence of a configuration or indication to receive the RAR, the TA value of the candidate cell may be indicated in the cell handover command. In another embodiment, when reception of a RAR is configured / indicated and received from the candidate cells 106A, 106B, at least the TA may be included in the RAR.

[0074] In a conventional decomposed gNB architecture, as defined in 3GPP, a conventional gNB can be decomposed into multiple logical entities. For example, a conventional gNB can include a gNB Control Unit (CU-CP) (for simplicity, the gNB Control Unit (CU-CP) is also referred to as the gNB Centralized Unit (CU) below) and a gNB DU. Similarly, a single DU can be responsible for hosting multiple cells. For example, in current 3GPP specifications, a single DU can be responsible for hosting up to 512 cells. The gNB-CU-CP can 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 at the gNB-DU. To support L1 / L2-centric inter-cell changes associated with serving cell changes, a mechanism is implemented in the decomposed gNB architecture where scheduling operations / configuration occur at the gNB-CU-CP but are performed autonomously by the gNB-DU without any further interaction with higher layers. For example, the mechanism involves handover preparation being performed by the gNB-CU-CP, but handover being performed autonomously by the gNB-DU without further interaction with upper layers such as the PDCP and RRC layers.

[0075] In one embodiment, at link 108, UE 102 may transmit the target cell RSRP MR to serving cell 104 via link 108. In one embodiment, at link 110, serving cell 104 may configure UE 102 using a PDCCH order to perform UL synchronization by transmitting a PRACH preamble, so that UE 102 acquires the target cell TA.

[0076] In operation, a UE 102 may be configured to transmit measurement reports (MRs) associated with one or more signal and channel parameters of a plurality of candidate cells 106A, 106B of one or more neighboring base stations to a first distributed unit (DU) of a serving base station 104. In one example, the UE 102 may be configured to transmit L1 MRs associated with one or more signal and channel parameters 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 to the first DU. In one embodiment, the UE 102 may transmit Layer 1 (L1) MRs for the 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 MRs based on the UE's specifications and compatibility with defined UE capabilities, including only with and without RAR, where supporting a default solution may be a baseline UE 102 approach for LTM. In one example, the maximum number of TA values ​​that the UE 102 may be configured to memorize may define the UE's capabilities.

[0077] Furthermore, after sharing the MR with 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 also belong to the same base station as the serving cell. In one embodiment, the target base station may be the serving base station. In another embodiment, 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, after receiving the MR, the serving gNB-DU 104 may check a configured RRM criterion. In one example, the RRM criterion may be a predefined RSRP threshold. Based on the determination of the target base station 106A, 106B, the first DU may send a request to the UE to perform uplink synchronization with the determined candidate cell.

[0078] Thus, UE 102 may receive a request from a first DU of serving base station 104 to perform uplink synchronization with a candidate cell of a second DU associated with target base station 106A, 106B. In one example, the first DU of serving base station 104 may send a request to UE 102 to perform uplink synchronization using a PDCCH order. Furthermore, UE 102 may perform uplink synchronization by sending a random access channel (RACH) request message to the second DU. In one embodiment, in response to performing uplink synchronization, 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 corresponding signal quality metrics. For another example, UE 102 may be configured to receive the RAR as a subsequent message received from 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.

[0079] In one embodiment, based on uplink synchronization, the UE 102 may receive a primary beam identifier of the target base station 106A, 106B with an associated primary timing advance (TA) from the target base station 106A, 106B. Furthermore, the UE 102 may also receive one or more secondary beam identifiers of the target base station 106A, 106B with associated one or more secondary TAs. In an alternative embodiment, the first DU of the serving base station 104 may receive 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 one or more secondary candidate cells of the second DU with associated one or more secondary TAs from one of the UE 102 and the second DU of the target base station 106A, 106B.

[0080] In one embodiment, the UE 102 may include a best beam determination module 112A. The UE 102 may utilize the best beam determination module 112A to determine a best beam from a primary beam identifier and one or more secondary beam identifiers, and define the best beam as a target beam. In one embodiment, the best beam determination module 112A determines the best 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 best beam determination module 112A may determine the target beam from the primary beam identifier and the one or more secondary beam identifiers. Furthermore, the UE 102 may perform a serving cell handover function to the target beam and apply a corresponding TA associated with the target beam.

[0081] In another embodiment, the UE 102 may send a primary beam identifier of the target base station 106A, 106B with an associated primary timing advance (TA), and one or more secondary beam identifiers of the target base station 106A, 106B with associated one or more secondary TAs to the serving base station 104. In one example, the serving base station 104 may include a best beam determination module 112B. Thereafter, the serving base station 104 may utilize the best beam determination module 112B to determine a best beam from the primary beam identifier and the one or more secondary beam identifiers based on the associated one or more signal and channel parameters, and define the best beam as the target beam. In one example, to determine the best beam, the serving base station 104 may be configured to compare the one or more signal and channel parameters associated with the primary beam identifier with the corresponding one or more signal and channel parameters associated with at least one of the secondary beam identifiers. In one embodiment, serving base station 104 may be configured to, at a first DU of serving base station 104, determine a candidate cell for target base stations 106A and 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 base station and the target base station may also be the same base station. Furthermore, 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.

[0082] In one example, the best beam can be defined as the beam with the best TA during a specific time period. Therefore, by including the TAs of neighboring beams along with the target beam, UE 102 can be assured of applying the corresponding TA when any of the neighboring beams becomes the best beam. A neighboring beam can be considered any neighboring beam that UE 102 is expected to subsequently access. For example, a neighboring beam is a beam that UE 102 is expected to move toward and that has the best channel and signal characteristics.

[0083] Subsequently, serving base station 104 may request UE 102 to perform a serving cell handover 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 handover command to UE 102 indicating the target beam of the target cell. In one example, the cell handover command may be a Layer 1 / Layer 2 Triggered Mobility (LTM) cell handover command. In one example, the target cell may be selected from a primary candidate cell or one or more secondary candidate cells.

[0084] Subsequently, the serving gNB-DU 104 may request the UE 102 to perform UL synchronization with one or more target cells 106A, 106B using the configured PRACH preamble. The UE 102 may perform UL synchronization and receive an RAR from the target gNB-DU 106A, 106B including the candidate / target cell TA to be used by the UE 102. Thus, the UE 102 may perform a RACH-less LTM handover using the candidate / target cell TA.

[0085] Figure 2 is a sequence diagram illustrating a scenario according to the embodiments disclosed herein, where the UE 102 determines the best beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA provided by the target gNB-DU 106A, 106B.

[0086] refer to Figure 2 , the UE 102 is configured to determine the best beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and apply the corresponding TA.

[0087] In step S201, UE 102 is still connected to the serving gNB-DU 104 (before LTM serving cell handover).

[0088] In step S202, UE 102 uses an RRC connection with the gNB Centralized Unit (CU) (200) and sends L3 RRC measurements to gNB-CU 200.

[0089] In step S203, the gNB-CU 200 decides to prepare inter-gNB-DU LTM candidate cells.

[0090] In step S204, the gNB-CU 200 initiates a UE context establishment request message to the target gNB-DU 106A, 106B through the F1 interface to prepare inter-DU LTM candidate cells.

[0091] In step S205, the target gNB-DU 106A, 106B confirms with a UE Context Setup Response message via the F1 interface and provides candidate / target cell configuration.

[0092] In step S206, the gNB-CU 200 sends a DL RRC message transmission (RRC Reconfiguration (LTM Target Cell Configuration)) to the serving gNB-DU 104 via the F1 interface.

[0093] At step S207, the RRC reconfiguration message is delivered to the UE 102. The serving gNB-DU 104 checks the set of RRM criteria (e.g., predefined RSRP thresholds) that are set to trigger the sending of L1 measurements to the target gNB-DUs 106A, 106B.

[0094] In step S208, UE 102 sends L1 measurements of the configured cell to serving gNB-DU 104.

[0095] Based on step S208, in step S209, the serving gNB-DU 104 requests the UE 102 to perform UL synchronization with one or more target cells using the configured PRACH preamble.

[0096] In step S210, the serving gNB-DU 104 requests the UE 102 to perform UL synchronization using a PDCCH order.

[0097] In step S211, UE 102 performs UL synchronization and sends a RACH preamble to the target gNB-DU 106A, 106B cell.

[0098] At step S212, the UE 102 is configured to receive a RAR from the target gNB-DU 106A, 106B, which includes the candidate / target cell TA to be used by the UE 102. The target gNB-DU 106A, 106B also transmits multiple neighboring beams with timing advance in the RAR to the UE 102.

[0099] At step S213 , TAs corresponding to multiple beams of the candidate / target cell are available and stored at the UE 102 .

[0100] In step S214, UE 102 sends the TA of the target cell to serving gNB-DU 104 via an uplink media access control element (UL MAC CE).

[0101] At step S215, after receiving the RAR, UE 102 sends an intra-frequency L1 measurement report to serving gNB-DU 104. In one embodiment, UE 102 may send an L1 MR to serving gNB-DU 104 for the configured cell.

[0102] In step S216, the serving gNB-DU 104 determines the best beam of the target cell for the UE 102 using the corresponding TA.

[0103] In step S217, the serving gNB-DU 104 sends the best beam of the target cell to the UE 102 via MAC CE.

[0104] At step S218, UE 102 sends a RACH-less HO to the target gNB-DU 106A, 106B cell.

[0105] Figure 3 is a sequence diagram illustrating another scenario according to the embodiments disclosed herein, where the UE 102 determines the best beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA provided by the target gNB-DU 106A, 106B.

[0106] refer to Figure 3 , UE 102 determines the best beam belonging to the target gNB-DU 106A, 106B (based on L1 measurements) and applies the corresponding TA.

[0107] In step S301, UE 102 is still connected to the serving gNB-DU 104 (before LTM serving cell handover).

[0108] In step S302, UE 102 uses the RRC connection with gNB-CU 200 and sends L3 RRC measurements to gNB-CU 200.

[0109] In step S303, the gNB-CU 200 determines and prepares candidate cells for inter-gNB-DU LTM.

[0110] In step S304, the gNB-CU 200 initiates a UE context establishment request message to the target gNB-DU 106A, 106B to prepare inter-DU LTM candidate cells.

[0111] In step S305, the target gNB-DU 106A, 106B confirms with a UE Context Setup Response message and provides the candidate / target cell configuration.

[0112] In step S306, the gNB-CU 200 sends a DL RRC message (RRC Reconfiguration (LTM Target Cell Configuration)) to the serving gNB-DU 104 through the F1 interface.

[0113] At step S307, the RRC reconfiguration message is delivered to the UE 102. The serving gNB-DU 104 checks the set of RRM criteria (e.g., predefined RSRP thresholds) that are set to trigger the sending of L1 measurements to the target gNB-DUs 106A, 106B.

[0114] In step S308, UE 102 sends L1 measurements of the configured cell to serving gNB-DU 104.

[0115] Based on step S308, in step S309, the serving gNB-DU 104 requests the UE 102 to perform UL synchronization with one or more target cells using the configured PRACH preamble.

[0116] At step S310, the serving gNB-DU 104 requests the UE 102 to perform UL synchronization using a PDCCH order.

[0117] In step S311, UE 102 performs UL synchronization and sends a RACH preamble to the target gNB-DU cell.

[0118] At step S312, the UE 102 is configured to receive the RAR from the target gNB-DU 106A, 106B.

[0119] At step S313, the target gNB-DU 106A, 106B initiates a context modification procedure to inform the serving gNB-DU 104 of the candidate / target cell TA. An indication that a UE context modification is required is sent to the gNB-CU 200. This indication includes the candidate / target cell TA to be used by the UE 102. The target gNB-DU 106A, 106B also includes multiple beams with timing advance in the F1 message.

[0120] In step S314, based on the indication described in step S312, the gNB-CU 200 sends an acknowledgment related to the indication that UE context modification is required.

[0121] At step S315, the gNB-CU 200 initiates a UE Context Modification Request message to the serving gNB-DU 104. This includes the candidate / target cell TA to be used by the UE 102. The gNB-CU 200 also includes the multiple beams with timing advance sent by the target gNB-DU 106A, 106B to the serving gNB-DU 104 in the F1 message.

[0122] In step S316, the serving gNB-DU 104 confirms the request using the UE Context Modification Request message via the F1 interface.

[0123] In step S317, the TAs corresponding to the multiple beams of the target cell are available and stored at the serving gNB-DU 104.

[0124] In step S318, UE 102 sends an intra-frequency L1 measurement report to serving gNB-DU 104 based on the reception of the RAR.

[0125] In step S319, the serving gNB-DU 104 determines the best beam of the target cell for the UE 102 and uses the corresponding TA.

[0126] In step S320, the serving gNB-DU 104 sends the target beam of the target cell to the UE 102 via MAC CE based on the determination of the best beam.

[0127] In step S321, UE 102 sends a HO without RACH to the target gNB-DU 106A, 106B cell.

[0128] Figure 4 Illustrated is a flow chart of a method 400 for wireless communication at a UE according to embodiments disclosed herein.

[0129] like Figure 4 As shown, method 400 may include 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, and functions for performing specific functions or implementing specific abstract data types.

[0130] The order in which method 400 is described should not be construed as limiting, and any number of the described method blocks can be combined in any order to implement the method. Furthermore, individual blocks can be deleted from the method without departing from the scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or a combination thereof.

[0131] At step 402, UE 102 may receive a request from a first distributed unit (DU) of serving base station 104 to perform uplink synchronization with a second DU of target base stations 106A, 106B. In one embodiment, prior to receiving the request to perform uplink synchronization from serving base station 104, UE 102 may send a measurement report (MR) associated with one or more signal and channel parameters of a plurality of candidate cells of one or more neighboring base stations to serving base station 104. In one example, the plurality of candidate cells may include a plurality of non-serving cells. In one embodiment, UE 102 receives the request to perform uplink synchronization using a PDCCH order sent by serving base station 104.

[0132] At step 404, the UE 102 may perform uplink synchronization by sending 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.

[0133] At step 406, the UE 102 may receive, 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 associated one or more secondary TAs from one of the first DU and the second DU.

[0134] At step 408, the UE 102 may receive a cell switching command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or one or more secondary candidate cells. In another embodiment, the UE 102 may receive a target beam from a primary beam identifier and one or more secondary beam identifiers. In one embodiment, the determination of the target beam may be performed by comparing 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. Subsequently, the target beam may be determined from the primary beam identifier and the one or more secondary beam identifiers based on the comparison result. In one example, the one or more secondary beam identifiers are determined based on corresponding signal quality metrics. For example, based on a measurement of a signal quality metric associated with the beam compared to other beams present in the beam group, the beam may be selected as the secondary beam.

[0135] At step 410 , the UE 102 may perform a serving cell handover function to the target beam and apply a corresponding TA associated with the target beam.

[0136] In the proposed method, the target gNB-DU 106A, 106B adds the TA of the UE's best beam (the best beam or the DL beam corresponding to the UL beam used by UE 102 to perform UL synchronization operations) in the RAR. Furthermore, the target gNB-DU 106A, 106B includes the TAs of the UE's neighboring beams. This ensures that, in the event that any of the neighboring beams becomes the best beam, UE 102 can dynamically apply the corresponding TA to the best beam. Consequently, this dynamic application of the corresponding TA can reduce the overall time taken to perform a handover from a serving base station 104 or cell 104 to a target base station 106A, 106B or target cell 106A, 106B. This dynamic application of the corresponding TA also eliminates the need to repeatedly perform UL synchronization to obtain an updated TA due to UE mobility.

[0137] In one embodiment, a neighboring beam is considered to be any neighboring beam that the UE 102 may subsequently expect to access, such as any beam toward which the UE 102 is expected to move and that has the best channel and signal parameters or characteristics. In one example, the eligibility of a neighboring beam can be interpreted or calculated using artificial intelligence (AI) machine learning (ML) methods. For example, to determine the eligibility of a neighboring beam, a priority list can be generated by the UE 102 or the serving base station 104. In another example, a priority list of neighboring beams can be generated at the target base station 106A, 106B.

[0138] In one embodiment, a priority list of neighboring beams may be generated based on a target beam / beam group selected by UE 102 at one or more previous handover occasions. In one example, the priority 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 in the best beam or beam group, or RSRP metrics reported by UE 102 for different beams / beam groups. In another embodiment, the number of neighboring beam TAs may be determined by gNB-CU 200.

[0139] 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 corresponding to the beam indicated during the SCC command.

[0140] In another embodiment, the UE 102 is autonomously configured to determine the best 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).

[0141] In the proposed method and system, the serving gNB-DU 104 refines the optimal beam to correct for UE mobility and achieve better TA estimation. In one embodiment, the proposed method and system implements a receiver architecture associated with digital beamforming reception. In another embodiment, the proposed method and system implements analog beamforming reception. The proposed method is used to receive a physical random access channel (PRACH) signal, where multiple receive beams are processed (a set of adjacent beams, a list given by the serving cell 104, or a list selected by the target cells 106A, 106B).

[0142] Using at least one receive beam, the target gNB-DU 106A, 106B can calculate the TA. In one example, the serving cell 104 can share the TA using a UL MAC CE that includes both the beam index of the target cell 106A, 106B and the corresponding TA used by the UE 102.

[0143] Since the UE 102 will also have information about the TAs of the neighboring or secondary beams in addition to the TA information of the target beam, the UE 102 may be able to determine whether the target beam is the best beam for performing the handover. If the UE 102 determines that one of the secondary beams is the best beam for performing the handover, the UE 102 may select the secondary beam accordingly and replace it with the target beam. In an alternative embodiment, the serving base station 104 may also be configured to compare the target beam with the secondary beams to determine the best beam and send the best beam information to the UE accordingly. Thus, even when the UE 102 experiences mobility, the UE 102 may be able to perform a RACH-free LTM handover with the target base station 106A, 106B with the best beam that is valid for an extended period of time. For example, when the UE 102 travels from one location to another, resulting in a change in TA.

[0144] Figure 5 A detailed block diagram of an apparatus 500 is illustrated in which the method of wireless communication may be implemented. Figure 5A detailed block diagram of an apparatus 500 according to some embodiments of the present disclosure is illustrated. In one embodiment, it should be understood that the apparatus 500 is associated with the UE 102. In another embodiment, it should be understood that the apparatus 500 is associated with the serving base station 104. The apparatus 500 may include 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, and 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 the receiver 504 may be collectively implemented as a single transceiver module 506. In a non-limiting embodiment, the at least one processor 508 may be communicatively coupled with the transceiver module 506, the memory 510, the interface 512, and the antenna 514 to implement the aforementioned techniques for processing wireless communications, particularly techniques for performing RACH-less LTM HO.

[0145] The at least one processor 508 may include, but is not limited to, one or more of a microprocessor, a microcomputer, a microcontroller, a central processing unit, a state machine, a logic circuit system, and any device that manipulates signals based on operational instructions. A processor may also be implemented as a combination of computing devices, such as a combination of multiple microprocessors, or any other such configuration. At least one memory 510 may be communicatively coupled to the at least one processor 508 and may include various instructions, UE signal strength data, an initial bandwidth portion, one or more dedicated bandwidth portions, a predefined interval, and the like. 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 drive, a magnetic disk drive, a flash memory, an electrically erasable read-only memory (EEPROM), storage space on a server or cloud, and the like. The at least one processor 508 may be configured to execute one or more instructions stored in the memory 510.

[0146] The interface 512 may include various software and hardware interfaces, such as a network interface, a graphical user interface, an input device output device (I / O) interface, a network interface, etc. The I / O interface may allow the apparatus 500 to communicate with one or more nodes / devices directly or through other devices. The network interface may allow the apparatus 500 to interact with one or more networks directly or via any other network.

[0147] The apparatus 500 may further include a best beam determination module 112A, 112B configured to determine a best beam from the primary beam identifier and the one or more secondary beam identifiers based on one or more associated signal and channel parameters, and define the best beam as a target beam. In one example, the best beam is the target beam based on determining that the current target beam has the best characteristics compared to other beams or beam groups.

[0148] When provided with the TAs of neighboring beams as well as the TA of the target beam, the UE 102 is allowed to autonomously determine the best beam belonging to the target gNB-DU 106A, 106B. For example, the UE 102 may be autonomously configured to consider channel and signal parameters (such as L1 measurements) to determine the best beam belonging to the target gNB-DU 106A, 106B and then apply the corresponding TA provided by the target gNB-DU 106A, 106B.

[0149] In embodiment [1], an apparatus is configured to: at a user equipment (UE) 102, receive 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; at the UE 102, perform the uplink synchronization by sending a random access channel (RACH) request message to the second DU; at the UE 102, based on the uplink synchronization, receive 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 associated one or more secondary TAs from one of the first DU and the second DU; at the UE 102, receive a cell switching command indicating a target beam of a target cell from the first DU, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and at the UE 102, perform a serving cell switching function to the target beam and apply a corresponding TA associated with the target beam.

[0150] In embodiment [2], before receiving the request to perform the uplink synchronization from the first DU, the apparatus described in embodiment [1] is configured to: send, from the UE 102 to the first DU, a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to a plurality of candidate cells, the plurality of candidate cells being associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

[0151] In embodiment [3], in response to performing the uplink synchronization, the apparatus described in embodiment [1] is configured to: receive, at the UE 102, a random access response (RAR) from the second DU, wherein the RAR includes 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.

[0152] In embodiment [4], the cell handover command associated with the apparatus described in embodiment [1] is a layer 1 / layer 2 triggered mobility (LTM) cell handover command.

[0153] In embodiment [5], according to the apparatus described in embodiment [1], the one or more secondary beam identifiers are determined based on corresponding signal quality metrics.

[0154] In embodiment [6], according to the apparatus described in embodiment [1], at the UE 102, the request to perform the uplink synchronization is received using a physical downlink control channel (PDCCH) command, and wherein the serving base station is the target base station.

[0155] In embodiment [7], a method for wireless communication at a user equipment (UE) 102 is performed. The method includes: receiving a request from a first distributed unit (DU) of a serving base station 104 to perform uplink synchronization with a second 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; based on the uplink synchronization, receiving a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA) from at least one of the first DU and the second DU, 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 with associated one or more secondary TAs; receiving a cell handover command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and performing a serving cell handover function to the target beam and applying a corresponding TA associated with the target beam.

[0156] In embodiment [8], according to the method described in embodiment [7], before receiving the request to perform the uplink synchronization from the first DU, a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to multiple candidate cells is sent to the first DU, wherein the multiple candidate cells are associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the multiple candidate cells include multiple non-serving cells.

[0157] In embodiment [9], the method described in embodiment [7] further includes: receiving a random access response (RAR) from the second DU in response to performing the uplink synchronization, wherein the RAR includes 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.

[0158] In embodiment

[10] , the method described in embodiment [7] further comprises determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on corresponding signal quality metrics.

[0159] In embodiment

[11] , according to the method described in embodiment [7], receiving the request to perform the uplink synchronization includes: receiving the request to perform the uplink synchronization using a physical downlink control channel (PDCCH) command, and wherein the serving base station is the target base station.

[0160] In embodiment

[12] , an apparatus is configured to: determine, at a serving base station 104 and a first distributed unit (DU) of the serving base station 104, a candidate cell 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; send 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, receive a request from the UE 102 to perform uplink synchronization with the candidate cell; 102 and at least one of the second DUs of the target base station 106A, 106B receive a main beam identifier of a main candidate cell of the second DU with an associated main timing advance (TA), and receive one or more secondary beam identifiers of the main candidate cell and at least one of the one or more secondary candidate cells of the second DU with associated one or more secondary TAs, the main beam identifier, the main 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; at the serving base station 104, the target beam of the target cell is determined from the main beam identifier and the one or more secondary beam identifiers based on the associated one or more signal and channel parameters; and a request is sent from the serving base station 104 to the UE 102, the request being used to perform a serving cell switching function to the target beam and apply the corresponding TA associated with the target beam.

[0161] In embodiment

[13] , according to the apparatus described in embodiment

[12] , in order to determine the target beam, the apparatus is configured to: compare, at the serving base station 104, one or more signal and channel parameters associated with the main beam identifier and one or more corresponding signal and channel parameters associated with each of the one or more secondary beam identifiers; and based on the comparison, determine, at the serving base station 104, the target beam from the main beam identifier and the one or more secondary beam identifiers.

[0162] In embodiment

[14] , the apparatus described in embodiment

[12] is further configured to: before determining the second DU, receive, at the serving base station 104, from the UE 102, a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to the plurality of candidate cells, wherein the plurality of candidate cells are associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells include a plurality of non-serving cells.

[0163] In embodiment

[15] , the apparatus described in embodiment

[12] is configured to: send the request for performing the uplink synchronization from the serving base station 104 to the second DU, the request including a request for a random access channel request (RACH), wherein the request for the RACH triggers a random access response (RAR) from the 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.

[0164] In embodiment

[16] , according to the apparatus described in embodiment

[14] , the serving cell switching function is performed based on a layer 1 / layer 2 triggered mobility (LTM) cell switching command.

[0165] In embodiment

[17] , the apparatus described in embodiment

[12] determines the one or more secondary beam identifiers based on corresponding signal quality metrics.

[0166] In embodiment

[18] , the apparatus described in embodiment

[12] sends the request to perform the uplink synchronization to the UE (102) using a physical downlink control channel (PDCCH) command, and wherein the serving base station is the target base station.

[0167] In embodiment

[19] , a non-transitory computer-readable medium having program instructions stored thereon is disclosed, the program instructions being executed by an apparatus for wireless communication at a user equipment (UE) 102. The program instructions may include receiving a request from a first distributed unit (DU) of a serving base station 104 to perform uplink synchronization with a second 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, based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA) from one of the first DU and the second DU, 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 with associated one or more secondary TAs; receiving a cell handover command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and performing a serving cell handover function to the target beam and applying a corresponding TA associated with the target beam.

[0168] In embodiment

[20] , according to the non-transitory computer-readable medium described in embodiment

[19] , the program instructions may include determining the target beam including: comparing one or more signal and channel parameters associated with the main beam and corresponding one or more signal and channel parameters associated with each of the one or more auxiliary beams; and determining the target beam from the main beam and the one or more auxiliary beams based on the comparison.

[0169] In one embodiment

[21] , according to the non-transitory computer-readable medium described in embodiment

[19] , the program instructions may include: before receiving the request to perform the uplink synchronization from the first DU, sending a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to a plurality of candidate cells to the first DU, the plurality of candidate cells being associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells include a plurality of non-serving cells.

[0170] In embodiment

[22] , according to the non-transitory computer-readable medium described in embodiment

[19] , the program instructions may include: in response to performing the uplink synchronization, receiving a random access response (RAR) from the second DU, wherein the RAR includes 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.

[0171] In embodiment

[23] , according to the non-transitory computer-readable medium described in embodiment

[19] , the program instructions may include determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on corresponding signal quality metrics.

[0172] In embodiment

[24] , according to the non-transitory computer-readable medium described in embodiment

[19] , the program instructions may include receiving the request to perform the uplink synchronization including: receiving the request to perform the uplink synchronization using a PDCCH order. In a non-limiting embodiment, the apparatus 500 may be part of the serving base station 104, but is not limited thereto.

[0173] In another non-limiting embodiment, the apparatus 500 may be part of the UE 102, but is not limited thereto.

[0174] In a non-limiting embodiment of the present disclosure, one or more non-transient computer-readable media may be used to implement an embodiment consistent with the present disclosure. A computer-readable medium refers to any type of physical memory (such as memory 510) on which information or data readable by a processor can be stored. Therefore, a computer-readable medium can store one or more instructions executed 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, excluding carrier waves and transient signals. As an example and not limitation, such a computer-readable medium may include a random access memory (RAM), a read-only memory (ROM), a volatile memory, a non-volatile memory, a hard drive, a compact disc (CD) ROM, a digital video disc (DVD), a flash drive, a disk, and any other known physical storage medium.

[0175] Thus, certain aspects may include a computer program product for performing the operations described herein. For example, such a computer program product may include a computer-readable medium having stored (and / or encoded) thereon instructions, the instructions executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging materials.

[0176] The various illustrative logical blocks, modules, and operations described in conjunction with this disclosure may be implemented or performed using a general-purpose processor designed to perform the functions described herein, discrete gate or transistor logic, discrete hardware components, or any combination thereof. 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 computing devices, such as multiple microprocessors, or any other such configuration.

[0177] The above description of the specific embodiments will fully reveal the general nature of the embodiments herein so that others can easily modify or adapt the various applications of these specific embodiments by applying current knowledge without departing from the general concepts, and therefore, such adaptations and modifications should and are intended to be understood as being within the meaning and scope of equivalents of the disclosed embodiments. It should be understood that the words or terms used herein are for description and not limitation. Therefore, although the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced by making modifications within the scope of the embodiments described herein.

Claims

1. A device configured to: At a user equipment (UE) (102), a request is received 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, at the UE (102), the uplink synchronization by sending a random access channel (RACH) request message to the second DU; At the UE (102), based on the uplink synchronization, 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 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 with associated one or more secondary TAs; receiving, at the UE (102), a cell handover command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; as well as At the UE (102), a serving cell handover function to the target beam is performed and a corresponding TA associated with the target beam is applied.

2. The apparatus of claim 1 , wherein before receiving the request to perform the uplink synchronization from the first DU, the apparatus is configured to: send, from the UE (102) to the first DU, a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters of a plurality of candidate cells, the plurality of candidate cells being associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

3. The device according to claim 1, wherein In response to performing the uplink synchronization, the apparatus is configured to: At the UE (102), a random access response (RAR) is received from the second DU, wherein the RAR includes 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 handover command is a Layer 1 / Layer 2 Triggered Mobility (LTM) cell handover command.

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

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

7. A method comprising: receiving a request from a first distributed unit (DU) of a serving base station (104) to perform uplink synchronization with a second 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; Based on the uplink synchronization, 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 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 with associated one or more secondary TAs; receiving, from the first DU, a cell handover command indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; as well as A serving cell handover function to the target beam is performed and a corresponding TA associated with the target beam is applied.

8. The method according to claim 7, wherein the method further comprises: Before receiving the request to perform the uplink synchronization from the first DU, a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to a plurality of candidate cells is sent to the first DU, the plurality of candidate cells being associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

9. The method according to claim 7, wherein the method further comprises: In response to performing the uplink synchronization, a random access response (RAR) is received from the second DU, wherein the RAR includes 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.

10. The method according to claim 7, wherein the method comprises: The one or more secondary beam identifiers are determined by determining the one or more secondary beam identifiers based on corresponding signal quality metrics.

11. The method of claim 7, wherein receiving the request to perform the uplink synchronization comprises: The request to perform the uplink synchronization is received using a physical downlink control channel (PDCCH) order, and wherein the serving base station is the target base station.

12. An apparatus configured to: At a serving base station (104) and a first distributed unit (DU) of the serving base station (104), determining a candidate cell for 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 a plurality of 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; receiving, at the serving base station (104), a primary beam identifier of a primary candidate cell of a second DU having an associated primary timing advance (TA) from at least one of the second DU of the UE (102) and the target base station (106A, 106B), 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 having 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 being received from the second DU based on the uplink synchronization; At the serving base station (104), determining a target beam of a target cell from the primary beam identifier and the one or more secondary beam identifiers based on associated one or more signal and channel parameters; as well as A request is sent from the serving base station (104) to the UE (102), the request being to perform a serving cell handover function to the target beam and to apply a corresponding TA associated with the target beam.

13. The device according to claim 12, wherein In order to determine the target beam, the apparatus is configured to: comparing, at the serving base station (104), one or more signal and channel parameters associated with the primary beam identifier and corresponding one or more signal and channel parameters associated with each of the one or more secondary beam identifiers; as well as Based on the comparison, at the serving base station (104), the target beam is determined from the primary beam identifier and the one or more secondary beam identifiers.

14. The apparatus according to claim 12, wherein the apparatus is further configured to: Prior to determining the second DU, receiving, at the serving base station (104), from the UE (102), a layer 1 measurement report (L1 MR) associated with one or more signal and channel parameters corresponding to a plurality of candidate cells associated with the first DU and one or more DUs associated with one or more neighboring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

15. The apparatus of claim 12, wherein the apparatus is configured to: send the request to perform the uplink synchronization from the serving base station (104) to the second DU, the request comprising a request for a random access channel request (RACH), wherein the request for the RACH triggers a random access response (RAR) from the second DU, the RAR comprising at least: The primary beam identifier having the associated primary TA, and the one or more secondary beam identifiers having the associated one or more secondary TAs.

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

17. The apparatus of claim 12, wherein the apparatus determines the one or more secondary beam identifiers based on corresponding signal quality metrics.

18. The apparatus of claim 12, wherein the apparatus sends the request to perform the uplink synchronization to the UE (102) using a Physical Downlink Control Channel (PDCCH) command, and wherein the serving base station is the target base station.

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