CBRA and CFRA L1 / L2 trigger mobility improvements

Abstract

A method and system for handling L1 / L2 triggered mobility (LTM) to reduce mobile latency is provided. The method may include transmitting a request by a serving distribution unit (DU) to a user equipment (UE) to perform uplink synchronization with a target cell of a target distribution unit (DU). Upon receiving the request, the UE performs uplink synchronization with the target DU, including transmitting a preamble signal to the target DU, and upon receiving the preamble signal, the target DU determines a best beam group (BG) for the UE. The method may include receiving, by the serving DU, a random access channel (RACH) preamble from the target DU based on the best BG, and performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority from Indian Provisional Application IN202221062661, filed with the Indian Patent Office on November 2, 2022, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0002] [Technical field] Systems and methods consistent with embodiments of the present disclosure relate to L1 / L2 triggered inter-cell transitions in a fragmented communication architecture. [Background technology]

[0003] The Radio Access Network (RAN) is a critical component in a communication system that connects end-user devices (or user equipment (UE)) to the rest of the network. The RAN includes a combination of various network elements (NEs) that connect end-user devices to the core network. Traditionally, the hardware and / or software of a particular RAN has been vendor-specific.

[0004] In recent years, advances in communications technology have enabled many communication services to be virtually realized in software. A RAN, such as the Open RAN (O-RAN) architecture, subdivides a network component into multiple functional elements. For example, a baseband unit (BBU) or base station (i.e., eNB or gNB) is subdivided into many functional elements, including a distributed unit (DU) and an aggregation unit (CU). The CU can be further subdivided into an aggregation unit control plane (CU-CP) and an aggregation unit user plane (CU-UP). This subdivision of network elements allows communication services and related functions to be defined and provided in software-based forms or virtual network services, such as virtualized network functions (VNFs), cloud-native network functions (CNFs), or software-defined networking (SDN), among others.

[0005] Figure 1 illustrates a related technology of a fragmented gNB architecture in 3GPP. The gNB is fragmented into multiple logical entities. Two gNB-DU nodes are illustrated, but it can be understood that multiple gNB-DU nodes may exist. Note that a single DU may host multiple cells. The gNB-DU node may communicate with the CU-CP via an F1-C interface and with the CU-UP via an F1-U interface. The CU-CP and CU-UP may communicate via an E1 interface. The gNB-CU-CP hosts 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.

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

[0007] L1 / L2 Triggered Mobility (LTM) is a mobility procedure that allows the network to switch a UE from a source cell to a target cell without necessarily requiring synchronization and reconfiguration. In particular, the network can indicate in L2 signaling (e.g., MAC CE) beams belonging to LTM candidate cells on which the UE should perform the LTM cell switch procedure based on received L1 measurement results. The UE is provided with at least one (or multiple) LTM candidate cell configurations by the network before performing the LTM cell switch procedure.

[0008] The first challenge in LTM in the related art is that the LTM target cell is prepared for contention-based random access (CBRA) (i.e., this configuration may be the result of a lack of random access channel (RACH) preamble resources in the target cell). However, during the lead time (between LLM preparation and execution), if the resource situation in the target cell (target DU) changes, the UE must perform CBRA even if the resource situation in the target cell has changed since handover (HO) preparation. In this situation, performing CBRA again is not ideal. This challenge may be referred to as "Scenario 1" below.

[0009] A second challenge in the LTM of the related art is that the LTM target cell configuration is prepared for contention-free random access (CFRA) mapped to a given beam group (BG), but the UE undergoes mobility during the lead time, resulting in the RACH preamble / resources allocated at the target DU not being optimized. This challenge may be referred to as "Scenario 2" below.

[0010] FIG. 2 illustrates a typical deployment scenario in the related art in which a CU-CP serves multiple DUs. A UE may be located at positions A and B in gNB-DU1 in beam group 1 (BG1). At position A, an LTM target cell has been prepared in target gNB-DU2. The best radio connection / conditions for position A are beam group 2 (BG2) in target gNB-DU2. Referring to scenario 1, no RACH preamble is assigned to the UE because the load does not allow it in this case. Referring to scenario 2, a RACH preamble corresponding to BG2 is reserved and sent to the UE in the target cell configuration (i.e., by an RRC reconfiguration message).

[0011] The UE may move to position B in gNB-DU1 when an LTM serving cell transition (SCC) is sent from the serving DU to the UE. This causes the best beam group to no longer be BG2 but to become beam group 3 (BG3). Therefore, as described above with reference to scenario 1, this forces the UE to perform contention-based RACH access (CBRA) even though the resource situation in the target cell has changed since HO preparation. This is not ideal. With reference to scenario 2, UE mobility during LTM preparation and execution means that the RACH preamble assigned during preparation is not optimal. Since resources in the target cell are not reserved for BG3, a serving cell transition (SCC) or radio link failure (RLF) may occur immediately afterward.

[0012] FIG. 3 illustrates a typical SCC / handover procedure performed in the related art using CBRA, without any problems. The UE may be configured for lower layer mobility / LTM with one or more target cells in one or more DUs. RRC (L3) measurements may be performed, which are sent from the UE to the CU-CP. The CU-CP may communicate with the target cell (target DU) using the F1:UE context setup procedure. The target DU may determine that the RACH preamble is not available and may indicate to the CU-CP that a CBRA configuration is prepared and should be used by the UE. The CU-CP may then send an LTM target cell configuration to the UE by using RRC reconfiguration. The UE may then perform an L1 intra-frequency measurement report and send it to the serving DU. At the same time, the target cell (target DU) may determine that the resource conditions in the target cell have changed to "available." Upon receiving the L1 measurement report, the serving DU may determine that the target cell radio conditions are satisfied and may instruct the execution of HO. Therefore, SCC may be performed using CBRA, which is not ideal because although the resource conditions in the target cell have changed, the UE is still forced to perform CBRA without being configured with contention-less RACH access (CFRA).

[0013] Figure 4 illustrates the SCC / handover procedure performed in the related art for scenario 2. Description of operations similar to those in Figure 3 is redundant and therefore omitted for simplicity. After receiving the L1 measurement report, the serving DU may determine that the target cell radio conditions exceed a predetermined threshold (i.e., the connection is not optimal) and instruct the UE to perform SCC. However, after performing SCC, the target cell discovers that the reserved preamble (sent during preparation) is not optimal due to UE mobility (i.e., movement from position A to position B in Figure 2 described above). This may lead to an immediate SCC or RLF, as described above.

[0014] FIG. 5 illustrates an SCC / handover procedure performed in the related art to resolve Scenario 2. The description of operations similar to those in FIGS. 3 and 4 is redundant and therefore omitted for simplicity. After receiving the L1 measurement report, the serving DU may compare the BG / preamble associated with the UE report (taking into account the L1 measurement report) with the BG / preamble assigned by the CU during preparation (received in the F1 message). If they differ, the serving DU may ask the CU to update the preamble, which is then routed to the target DU. This can be done by initiating an F1 procedure so that the serving DU receives a message from the target DU via the CU containing the updated RACH preamble for the best BG. However, this is too slow for LTM. In particular, it requires many F1 messages between the serving DU and target DU via the CU (which may result in a latency of at least 20 ms), and the UE must wait for the delivery of the SCC command. This may lead to RLF because the UE may move. Generally, the solution illustrated in FIG. 5 may not be acceptable in light of the low latency requirements of LTM. Summary of the Invention [Problem to be solved by the invention]

[0015] For CBRA and situation 1, it is necessary to avoid the UE retrying uplink synchronization (UL synchronization) if it fails, especially to avoid the scenario where CBRA occurs during LTM SCC. For CFRA and situation 2, it is necessary to deliver a reconstructed RACH preamble to the UE. [Means for solving the problem]

[0016] The embodiments of the present disclosure provide a method and system for handling L1 / L2 triggered mobility (LTM) to reduce mobile latency. In particular, according to the embodiments, preamble resource reservation in a target cell (target DU) is performed based on uplink synchronization (UL synchronization) during inter-cell mobility, rather than after a serving cell transition (SCC) command is issued. Because UL synchronization is performed substantially before SCC, updating a random access channel (RACH) preamble does not consume additional latency during handover (HO). In other words, the serving DU does not need to wait for the transmission of an SCC command.

[0017] In this manner, embodiments of the present disclosure may provide a more ideal approach for dealing with LTM.

[0018] According to an embodiment, a method may be provided that may be executed by at least one processor for configuring an inter-cell transition. The method may include: sending, by a serving distribution unit (DU), a request to a user equipment (UE) to perform uplink synchronization with a target cell of a target distribution unit (DU), where the UE performs uplink synchronization with the target DU including transmitting a preamble signal to the target DU upon receiving the request, and the target DU determines a best beam group (BG) for the UE upon receiving the preamble signal; receiving, by the serving DU, a random access channel (RACH) preamble from the target DU based on the best BG; and performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble.

[0019] The preamble signal used during UL synchronization may include a contention-based random access (CBRA) preamble, and the UE may be configured to determine whether uplink synchronization is successful, and based on the determination that uplink synchronization is successful, the target DU may be configured to determine that no preamble is assigned to the UE during a handover (HO) preparation phase, and based on the determination that no preamble is assigned to the UE, the target DU may be configured to assign and transmit a RACH preamble to the serving DU to configure contention-free random access (CFRA) for the UE with the best BG for the UE.

[0020] The preamble signal used during UL synchronization may include a contention-based random access (CBRA) preamble, and the UE may be configured to determine whether uplink synchronization is successful, and based on a determination that uplink synchronization is not successful, the UE may be configured to prevent further attempts at uplink synchronization.

[0021] The UE may be configured to determine whether the RACH preamble received from the serving DU has arrived at the UE or not before the serving DU has performed SCC, and based on a determination that the RACH preamble has not arrived at the serving DU before performing SCC, the UE is configured to perform CBRA during the performance of SCC by the serving DU.

[0022] The preamble signal may include a contention-free random access (CFRA) preamble, wherein the target DU is configured to determine whether a preamble has already been assigned to the UE, and based on a determination that a preamble has already been assigned to the UE, the target DU is configured to determine whether the preamble to be assigned to the UE is associated with a best BG for the UE, and based on a determination that the preamble to be assigned to the UE is not associated with the best BG for the UE, the target DU is configured to assign a RACH preamble to be a new preamble associated with the best BG for the UE, and further comprising transmitting the newly assigned RACH preamble to the serving DU, wherein the transmitting to the serving DU is performed via a control unit (CU) or directly on the DU-DU interface.

[0023] The serving DU may perform SCC for the UE by sending a Downlink MAC Control Element (DL MAC CE) to the UE, which includes the RACH preamble received from the target DU by the serving DU.

[0024] The target DU may be configured to estimate the timing advance (TA) of the UE based on the preamble signal received from the UE and share it with the serving DU, and the DL MAC CE sent from the serving DU to the UE includes the estimated TA.

[0025] According to an embodiment, a method executed by at least one processor for configuring an inter-cell transition may be provided. The method may include receiving, by a serving distribution unit (DU), a random access channel (RACH) preamble from a target distribution unit (DU), and performing, by the serving DU, a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble, wherein the UE is not configured to perform uplink synchronization by the serving DU, the UE is not configured with a CFRA RACH preamble by the target DU, the target DU is configured to determine whether RACH resource availability may change between the target cell configuration preparation and the execution of the serving cell transition, and based on the determination that RACH resources have become available, the target DU is configured to allocate the RACH preamble and transmit the RACH preamble to the serving DU to configure a contention-free random access (CFRA) for the UE with a best beam group (BG) for the UE.

[0026] According to an embodiment, an apparatus for configuring inter-cell transition may be provided, the apparatus may include at least one memory storing computer-executable instructions, and at least one processor configured to execute the computer-executable instructions to perform: sending, by a serving distribution unit (DU), a request to a user equipment (UE) to perform uplink synchronization with a target cell of a target distribution unit (DU), where the UE performs uplink synchronization with the target DU including transmitting a preamble signal to the target DU upon receiving the request, and the target DU determines a best beam group (BG) for the UE upon receiving the preamble signal; receiving, by the serving DU, a random access channel (RACH) preamble from the target DU based on the best BG; and performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble.

[0027] According to an embodiment, an apparatus for configuring inter-cell transition may be provided, the apparatus may include at least one memory storing computer-executable instructions and at least one processor configured to execute the computer-executable instructions to: receive, by a serving distribution unit (DU), a random access channel (RACH) preamble from a target distribution unit (DU); and perform, by the serving DU, a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble, wherein the UE is not configured to perform uplink synchronization by the serving DU, the UE is not configured with a CFRA RACH preamble by the target DU, the target DU is configured to determine whether RACH resource availability may change between the target cell configuration preparation and the execution of the serving cell transition, and based on the determination that RACH resources have become available, the target DU is configured to allocate a RACH preamble and transmit the RACH preamble to the serving DU to configure a contention-free random access (CFRA) for the UE with a best beam group (BG) for the UE.

[0028] The RACH preamble may be received when the resource situation at the target DU changes. The SCC may include transmitting the RACH preamble to the UE via a downlink MAC control element (DL MAC CE). The target DU may be configured to estimate a timing advance (TA), and the DL MAC CE includes the estimated TA. The RACH preamble may be transmitted to the serving DU via a control unit (CU) or directly over the DU-DU interface.

[0029] Additional aspects will be set forth in part in the description that follows, and in part will be obvious from the description, or may be realized by practice of presented embodiments of the disclosure. [Brief explanation of the drawings]

[0030] Features, aspects, and advantages of certain exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, in which like numerals represent like elements.

[0031] FIG. 1 illustrates a fragmented gNB architecture according to the related art.

[0032] FIG. 2 illustrates an exploded view of a gNB architecture according to the related art.

[0033] FIG. 3 illustrates an SCC / handover procedure performed in the related art using CBRA.

[0034] FIG. 4 illustrates the SCC / handover procedure performed in the related art for Situation 2.

[0035] FIG. 5 illustrates another SCC / handover procedure performed in the related art for Situation 2.

[0036] FIG. 6 illustrates an SCC / handover procedure for CFRA, according to one embodiment.

[0037] FIG. 7 illustrates an SCC / handover procedure for CBRA, according to one embodiment.

[0038] FIG. 8 is a diagram of an example environment in which the systems and / or methods described herein may be implemented.

[0039] FIG. 9 is a diagram of example components of a device, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] The following detailed description of the embodiments refers to the accompanying drawings.

[0041] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit implementations to the precise form disclosed. Modifications and variations are possible in light of the foregoing disclosure or may be acquired from practice of the implementations. Furthermore, one or more features or components of one embodiment may be combined or combined with other embodiments (or one or more features of other embodiments). Additionally, in the flowcharts and operational descriptions provided below, it is understood that one or more operations may be omitted, one or more operations may be added, one or more operations may be performed concurrently (at least in part), and the order of one or more operations may be rearranged.

[0042] It will be apparent that the systems and / or methods described herein may be implemented in different forms of hardware, firmware, or a combination of hardware and software. The actual specific control hardware or software code used to implement these systems and / or methods is not a limitation of the implementation. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It will be understood that software and hardware may be designed to implement the systems and / or methods based on the description herein.

[0043] Although particular feature combinations are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of possible implementations. Indeed, many of these features may be combined in ways other than those specifically recited in the claims and / or specifically disclosed in the specification. Although each dependent claim listed below may depend directly on only one claim, the disclosure of possible implementations includes each dependent claim in combination with all other claims in the claim group.

[0044] No element, act, or instruction used herein should be construed as critical or required unless explicitly stated otherwise. Also, as used herein, the articles "a" and "an" are intended to include one or more items and may be used interchangeably with "one or more." Where only one item is intended, the term "one" or similar words are used. Also, as used herein, the terms "has," "have," "having," "include," "including," etc. are intended to be open-ended terms. Furthermore, the phrase "based on" is intended to mean "based, at least in part, on," unless expressly stated otherwise. Furthermore, phrases such as "at least one of A and B" or "at least one of A or B" are understood to include A only, B only, or both A and B.

[0045] Furthermore, the described features, advantages, and characteristics of the present disclosure may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize, in light of the description herein, that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in a particular embodiment that may not be present in all embodiments of the present disclosure.

[0046] The embodiments of the present disclosure provide a method and system for handling L1 / L2 triggered mobility (LTM) to reduce mobile latency. In particular, according to the embodiments, preamble resource reservation in a target cell (target DU) is performed based on uplink synchronization (UL synchronization) during inter-cell mobility, rather than after a serving cell transition (SCC) command is issued. Because UL synchronization is performed substantially before SCC, updating a random access channel (RACH) preamble does not consume additional latency during handover (HO). In other words, the serving DU does not need to wait for the transmission of an SCC command.

[0047] In this manner, embodiments of the present disclosure may provide a more ideal approach for dealing with LTM.

[0048] FIG. 6 shows an example timing diagram for an SCC / handover procedure using CBRA, according to one or more embodiments. A UE 600, a serving DU 610, a target DU 620, and a CU-CP 630 may be provided. The UE 600 may be configured for lower layer (L1 / L2) triggered mobility (LTM) with one or more target cells in one or more DUs (e.g., target DU 620). The UE 600 may first provide RRC measurement results (L3) to the CU-CP 630. The CU-CP 630 may perform an F1:UE context setup procedure by sending a request to the target DU 620 and may receive a response therefrom. Subsequently, the CU-CP 630 may send an RRC reconfiguration message to the UE 600 to configure for LTM in the target cell (target DU 620) using CBRA. The UE 600 may then send an intra-frequency L1 measurement report to the serving DU 610.

[0049] 6, in operation S640, the serving DU 610 may detect that the target cell radio conditions exceed a predetermined threshold. For example, this may be based on an L1 measurement report that suggests that the UE 600 has a poor radio connection with the serving DU 620. Thus, the serving DU 610 may instruct the UE 600 to perform uplink synchronization and / or RACH procedures with the target DU 620.

[0050] In operation S641, after receiving the instruction to perform uplink synchronization sent in operation S640, the UE 600 performs uplink synchronization, which may include sending a preamble to the target DU 620. The UE 600 may send uplink measurement results and a CBRA preamble to the target DU 620.

[0051] In operation S642, after receiving the preamble signal from the UE 600, the target DU 620 may determine the best beam group (BG) and may determine that RACH resources are available for the best BG. Based on this determination, the CU-CP 630 may send a RACH preamble to the serving DU 610 based on the best BG (e.g., via an F1:UE context modification procedure). The CU-CP 630 may send another RRC configuration message to the UE 600 to configure LTM in the target cell (target DU 620) using CFRA. The UE 600 may then again send an intra-frequency L1 measurement report to the serving DU 610.

[0052] In operation S643, the serving DU 610 may detect that the target cell radio conditions are satisfied after receiving the intra-frequency L1 measurement report from the UE 600. Therefore, the serving DU 610 may instruct the UE 600 to perform SCC using a RACH preamble. The RACH preamble may be transmitted to the UE 600 using a downlink MAC control element (DL MAC CE) according to an embodiment.

[0053] According to one embodiment, the UE 600 may be configured to determine whether the UL synchronization performed in operation S641 is successful. If successful, the target DU 620 may be configured to determine that there are no preambles assigned by the target DU to the UE 600. If it is determined that there are no preambles assigned to the UE 600, the target DU 620 may be configured to assign a RACH preamble and send it to the serving DU 610 to configure a CFRA for the UE 600 with the best BG for the UE 600.

[0054] According to one embodiment, the UE 600 may determine that the UL synchronization performed in operation S641 is not successful, and the UE 600 may be configured to stop further attempts of uplink synchronization. The UE 600 may then determine whether the RACH preamble received by the serving DU 610 has reached the UE 600 or not before the serving DU 610 performs SCC in operation S643. If it is determined that the RACH preamble has not been received before the serving DU 610 performs SCC, the UE may be configured to perform CBRA during the performance of SCC by the serving DU.

[0055] Based on the above embodiment, preamble resource reservation is performed based on UL synchronization before an SCC command is issued. Furthermore, referring to Situation 1, UE 600 can detect when UL synchronization fails (e.g., due to a CBRA failure), so that it can specifically avoid further UL synchronization and perform CBRA only when it is really necessary. In this way, the above embodiment can achieve an ideal low-latency LTM and can avoid repeated CBRA unless it is really necessary.

[0056] It should be noted that although the above embodiments are described including UL synchronization, other embodiments are not necessarily limited thereto. In particular, according to one embodiment, the UE 600 may not be configured to perform uplink synchronization, and the UE 600 may not be configured with a CFRA RACH preamble by the target DU 620. In this case, the target DU 620 may be configured to determine whether the availability of RACH resources may change between the time of target cell configuration preparation and the execution of the SCC (i.e., operation S643). Based on the determination that RACH resources have become available, the target DU 620 may be configured to allocate a RACH preamble and transmit the RACH preamble to the serving DU 610 to configure a CFRA for the UE 600 with the best BG for the UE 600.

[0057] FIG. 7 illustrates an example timing diagram for an SCC / handover procedure using CFRA, according to one or more embodiments.

[0058] A UE 700, a serving DU 710, a target DU 720, and a CU-CP 730 may be provided. Note that these elements may be similar to the UE 600, serving DU 610, target DU 620, and CU-CP 630 described above in FIG. 6. The UE 700 may be configured for lower layer (L1 / L2) triggered mobility (LTM) with one or more target cells in one or more DUs (e.g., target DU 720). The UE 700 may first provide RRC measurement results (L3) to the CU-CP 730. The CU-CP 730 may perform an F1:UE context setup procedure by sending a request to the target DU 720 and may receive a response therefrom. Subsequently, the CU-CP 730 may send an RRC reconfiguration message to the UE 700 to configure for LTM in the target cell (target DU 720) using CFRA. The UE 700 may then send an intra-frequency L1 measurement report to the serving DU 710.

[0059] 7, in operation S740, the serving DU 710 may detect that the target cell radio conditions exceed a predetermined threshold. For example, this may be based on an L1 measurement report that suggests that the UE 700 has a poor radio connection with the serving DU 720. As such, the serving DU 710 may instruct the UE 700 to perform uplink synchronization and / or RACH procedures with the target DU 720.

[0060] In operation S741, after receiving the instruction to perform uplink synchronization sent in operation S740, the UE 700 performs uplink synchronization, which may include sending a preamble to the target DU 720. The UE 700 may send uplink measurement results and a CBRA preamble to the target DU 720.

[0061] In operation S642, after receiving the preamble signal from the UE 700, the target DU 720 may determine that there is already a preamble assigned to the UE 700 and that this preamble is not associated with the best beam group (BG). This may be performed by comparing the BG associated with the preamble with the best BG. Based on this comparison, the target DU 720 may determine that the RACH preamble should be updated so that the target DU 720 can assign the updated RACH preamble to the UE 700. Based on this determination, the CU-CP 730 may send the updated RACH preamble to the serving DU 710 based on the best BG (via the F1: UE Context Modification procedure). According to some embodiments, sending the updated RACH preamble may be performed over the DU-DU interface. The CU-CP 730 may send another RRC configuration message to the UE 700 to configure for LTM in the target cell (target DU 720) using CFRA. Then, the UE 700 may again send an intra-frequency L1 measurement report to the serving DU 710.

[0062] In operation S743, the serving DU 710 may detect that the target cell radio conditions are satisfied after receiving the intra-frequency L1 measurement report from the UE 700. Therefore, the serving DU 710 may instruct the UE 700 to perform SCC using a RACH preamble. The RACH preamble may be transmitted to the UE 700 using a downlink MAC control element (DL MAC CE) according to an embodiment.

[0063] Based on the above embodiment, preamble resource reservation is performed based on UL synchronization before an SCC command is issued. Furthermore, referring to Situation 2, even if the UE undergoes mobility, the target DU 720 compares the best BG for the UE 700 with the one initially prepared for the UE 700 and proactively sends it to the serving DU 710, so that the UE 700 can perform SCC using the best BG. In this way, the above embodiment can achieve ideal low-latency LTM even if the UE undergoes mobility.

[0064] According to one embodiment, the target DU 620, 720 may be configured to estimate the timing advance (TA) of the UE 600, 700 based on a preamble signal received from the UE 600, 700. The estimated TA may be indicated to the serving DU via the CU or by the serving DU 610, 710 to the UE via a downlink MAC control element (DL MAC CE). An indication may be sent to the UE 600, 700 within, together with, or before the cell switch command. The estimated TA may be sent to the UE 600, 700 within a time interval after the preamble is sent by the UE 600, 700. The UE may monitor the PDCCH for a TA message within this time interval.

[0065] According to one embodiment, if the UE 600, 700 does not receive a TA message within the time interval in which the TA message is expected, the UE 600, 700 may retransmit the same preamble or another preamble. The maximum number of times the UE attempts to transmit a preamble (the same or a different preamble) may be fixed and configurable. The maximum number may be set to 1.

[0066] According to other embodiments, the UE 600, 700 may expect to receive a TA message within or along with the cell switch command message. In one case, the cell switch message may not include a valid TA value (or a valid TA value may not be received within or outside the cell switch command), for example, due to failure of reception of the preamble at the target cell (target DU 620, 720).

[0067] According to one embodiment, if the UE 600, 700 is not indicated a valid TA value (e.g., before, within, or together with the cell switch message), the UE 600, 700 performs RACH in the target cell (target DU 620, 720) after it receives the cell switch message and performs the cell switch. This may be referred to as a fallback to the conventional RACH mechanism. For the RACH procedure, it may use the configuration indicated during LTM preparation. If the UE 600, 700 is indicated a valid TA value, it may adjust its transmission and start transmitting to the target cell (target DU 620, 720) after the cell switch command is received and the cell switch is performed.

[0068] According to one embodiment, the serving cell (serving DU 610, 710) may send to the UE 600, 700 a first TA value and an indication of whether the UE 600, 700 should perform another RACH after the cell switch command is executed. The additional RACH may be a CFRA, and resources for it may also be indicated in the DL MAC CE. This is useful if the target cell (target DU 620, 720) wants to increase the reliability of the calculated TA. The UE 600, 700 may use the first TA value to adjust its uplink timing when transmitting after the cell switch command is executed.

[0069] When the UE 600, 700 receives the TA value, it may start a timer. The timer may start at a predetermined time (e.g., the nth (e.g., n=1) slot after the slot containing the message in which the TA value is transmitted). The timer may be expressed in seconds, milliseconds, slots, etc. If a cell switch command is not received until the timer expires, the UE 600, 700 may perform a RACH after the cell switch command is executed. This may mean that the indicated TA value is discarded. Alternatively, the TA value applicable in a particular cell may be valid for a predetermined (e.g., configured, signaled) validity period, and the UE 600, 700 may store and use the TA value within the last updated validity period.

[0070] FIG. 8 is a diagram of an example environment 800 in which the systems and / or methods described herein may be implemented. As shown in FIG. 8, environment 800 may include a user device 810, a platform 820, and a network 830. The devices of environment 800 may be interconnected via wired connections, wireless connections, or a combination of wired and wireless connections. In an embodiment, any of the functions and operations described above with reference to FIGS. 6-7 may be performed by any combination of elements illustrated in FIG. 8.

[0071] User device 810 includes one or more devices capable of receiving, generating, storing, processing, and / or providing information related to platform 820. For example, user device 810 may include a computing device (e.g., a desktop computer, a laptop computer, a tablet computer, a handheld computer, a smart speaker, a server, etc.), a mobile phone (e.g., a smartphone, a wireless phone, etc.), a wearable device (e.g., smart glasses or a smart watch), or a similar device. In some implementations, user device 810 may receive information from and / or send information to platform 820.

[0072] Platform 820 includes one or more devices capable of receiving, generating, storing, processing, and / or providing information. In some implementations, platform 820 may include a cloud server or a group of cloud servers. In some implementations, platform 820 may be designed to be modular, such that particular software components may be swapped in or out depending on particular needs. In this manner, platform 820 may be easily and / or quickly reconfigured for different uses.

[0073] In some implementations, as shown, platform 820 may be hosted in a cloud computing environment 822. Note that although the implementations described herein describe platform 820 as being hosted in a cloud computing environment 822, in some implementations platform 820 may not be cloud-based (i.e., may be implemented outside of a cloud computing environment) or may be partially cloud-based.

[0074] Cloud computing environment 822 includes an environment that hosts platform 820. Cloud computing environment 822 may provide services such as computation, software, data access, storage, etc. that do not require end-user (e.g., user device 810) knowledge of the physical location and configuration of the systems and / or devices that host platform 820. As shown, cloud computing environment 822 may include a group of computing resources 824 (collectively referred to as “computing resources 824” and individually referred to as “computing resource 824”).

[0075] Computing resources 824 include one or more personal computers, clusters of computing devices, workstation computers, server devices, or other types of computation and / or communication devices. In some implementations, computing resources 824 may host platform 820. Cloud resources may include compute instances executing on computing resources 824, storage devices provided on computing resources 824, data transfer devices provided by computing resources 824, etc. In some implementations, computing resources 824 may communicate with other computing resources 824 via wired connections, wireless connections, or a combination of wired and wireless connections.

[0076] As further shown in FIG. 8, computing resources 824 include a group of cloud resources such as one or more applications (“APP”) 824-1, one or more virtual machines (“VM”) 824-2, virtualized storage (“VS”) 824-3, and one or more hypervisors (“HYP”) 824-4.

[0077] Applications 824-1 include one or more software applications that may be provided to or accessed by user device 810. Applications 824-1 may obviate the need to install and run software applications on user device 810. For example, applications 824-1 may include software associated with platform 820 and / or any other software that may be provided via cloud computing environment 822. In some implementations, one application 824-1 may send and receive information to one or more other applications 824-1 via virtual machine 824-2.

[0078] Virtual machine 824-2 includes a software implementation of a device (e.g., a computer) that executes programs like a physical device. Virtual machine 824-2 may be a system virtual machine or a process virtual machine, depending on the use by virtual machine 824-2 and the degree of correspondence with any real-world device. A system virtual machine may provide a complete system platform that supports the execution of a complete operating system (“OS”). A process virtual machine may execute a single program or support a single process. In some implementations, virtual machine 824-2 may execute on behalf of a user (e.g., user device 810) and manage the infrastructure of cloud computing environment 822, such as data management, synchronization, or long-term data transfer.

[0079] Virtualized storage 824-3 includes one or more storage systems and / or one or more devices or computing resources 824 that use virtualization technology within a storage system. In some implementations, within the context of a storage system, types of virtualization may include block virtualization and file virtualization. Block virtualization may represent the abstraction (or separation) of logical storage from physical storage so that the storage system may be accessed without consideration of the physical storage or heterogeneous structure. The separation may provide storage system administrators with flexibility in managing storage for end users. File virtualization may remove the dependency between data accessed at the file level and where the file is physically stored. This may enable storage usage optimization, server consolidation, and / or non-disruptive file migration performance.

[0080] The hypervisor 824-4 may provide hardware virtualization technology that allows multiple operating systems (e.g., "guest operating systems") to run simultaneously on a host computer, such as the computing resource 824. The hypervisor 824-4 may present a virtual operating platform to the guest operating systems and may manage the execution of the guest operating systems. Multiple instances of different operating systems may share virtualized hardware resources.

[0081] Network 830 may include one or more wired and / or wireless networks. For example, network 830 may include a cellular network (e.g., a fifth-generation (5G) network, a long-term evolution (LTE) network, a third-generation (3G) network, a code division multiple access (CDMA) network, etc.), a public land mobile network (PLMN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), a telephone network (e.g., a public switched telephone network (PSTN), a private network, an ad hoc network, an intranet, the Internet, an optical fiber-based network, etc.), and / or a combination of these or other types of networks.

[0082] The number and arrangement of devices and networks shown in Figure 8 are provided as an example. In practice, there may be additional, fewer, different, or differently arranged devices and / or networks than those shown in Figure 8. Furthermore, two or more devices shown in Figure 8 may be implemented within a single device, and a single device shown in Figure 8 may be implemented as multiple distributed devices. Additionally or alternatively, a set of devices in environment 800 (e.g., one or more devices) may perform one or more functions that are described as being performed by other sets of devices in environment 800.

[0083] 9 is a diagram of example components of a device 900. The device 900 may correspond to a user device 810 and / or a platform 820. As shown in FIG. 9, the device 900 may include a bus 910, a processor 920, a memory 930, a storage component 940, an input component 950, an output component 960, and a communication interface 970.

[0084] The bus 910 includes components that enable communication between the components of the device 900. The processor 920 may be implemented in hardware, firmware, or a combination of hardware and software. The processor 920 may be a central processing unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU), a microprocessor, a microcontroller, a digital signal processor (DSP), a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or other type of processing component. In some implementations, the processor 920 includes one or more processors that are programmable to perform functions. The memory 930 includes random access memory (RAM), read-only memory (ROM), and / or other types of dynamic or static storage devices (e.g., flash memory, magnetic memory, and / or optical memory) that store information and / or instructions for use by the processor 920.

[0085] The storage component 940 stores information and / or software related to the operation and use of the device 900. For example, the storage component 940 may include a hard disk (e.g., a magnetic disk, optical disk, magneto-optical disk, and / or solid-state disk), a compact disk (CD), a digital versatile disk (DVD), a floppy disk, a cartridge, a magnetic tape, and / or other type of non-transitory computer-readable medium, along with a corresponding drive. The input component 950 includes components that enable the device 900 to receive information, such as via user input (e.g., a touchscreen display, a keyboard, a keypad, a mouse, buttons, switches, and / or a microphone). Additionally or alternatively, the input component 950 may include sensors for measuring information (e.g., a global positioning system (GPS) component, an accelerometer, a gyroscope, and / or an actuator). The output component 960 includes components that provide output information from the device 900 (e.g., a display, a speaker, and / or one or more light-emitting diodes (LEDs)).

[0086] The communication interface 970 includes transceiver-like components (e.g., a transceiver and / or a separate receiver and transmitter) that allow the device 900 to communicate with other devices, such as via a wired connection, a wireless connection, or a combination of wired and wireless connections. The communication interface 970 allows the device 900 to receive information from and / or provide information to other devices. For example, the communication interface 970 may include an Ethernet interface, an optical interface, a coaxial interface, an infrared interface, a radio frequency (RF) interface, a universal serial bus (USB) interface, a Wi-Fi interface, a cellular network interface, etc.

[0087] Device 900 may perform one or more processes described herein. Device 900 may perform these processes in response to processor 920 executing software instructions stored by a non-transitory computer-readable medium, such as memory 930 and / or storage component 940. The computer-readable medium is defined herein as a non-transitory memory device. A memory device includes memory space within a single physical storage device or memory space distributed across multiple physical storage devices.

[0088] The software instructions may be loaded into memory 930 and / or storage component 940 from other computer-readable media or other devices via communication interface 970. When executed, the software instructions stored in memory 930 and / or storage component 940 may cause processor 920 to perform one or more of the processes described herein.

[0089] Additionally or alternatively, hardwired circuitry may be used in place of, or in combination with, software instructions to implement one or more processes described herein. Thus, implementations described herein are not limited to any specific combination of hardware circuitry and software.

[0090] The number and arrangement of components shown in Figure 9 is provided as an example. In practice, device 900 may include additional, fewer, different, or differently arranged components than those shown in Figure 9. Additionally or alternatively, a set of components (e.g., one or more components) of device 900 may perform one or more functions that are described as being performed by other sets of components of device 900.

[0091] In embodiments, any operation or process of Figures 6-7 may be implemented by or using any of the elements illustrated in Figures 8 and 9. It is understood that other embodiments are not so limited and may be implemented in a variety of different architectures (e.g., bare metal architectures, any cloud-based architectures or deployment architectures such as Kubernetes, Docker, OpenStack, etc.).

[0092] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit implementations to the precise form disclosed. Modifications and variations are possible in light of the foregoing disclosure or may be acquired from practice of the implementations.

[0093] Some embodiments may relate to systems, methods, and / or computer-readable media at any possible level of technical detail of integration. Furthermore, one or more of the above-described components may be implemented as instructions stored on a computer-readable medium and executable by at least one processor (and / or may include at least one processor). The computer-readable medium may include a computer-readable non-transitory storage medium (or medium) having computer-readable program instructions stored thereon for causing a processor to perform operations.

[0094] A computer-readable storage medium may be a tangible device that can hold and store instructions for use by an instruction execution device. The computer-readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. A non-exhaustive list of more specific examples of computer-readable storage media includes the following: portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disk read-only memory (CD-ROM), digital versatile disk (DVD), memory sticks, floppy disks, mechanically encoded devices such as punch cards or raised structures in grooves in which instructions are recorded, and any suitable combination thereof. As used herein, computer-readable storage medium is not to be understood as a transitory signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse passing through a fiber optic cable), or an electrical signal transmitted over a wire.

[0095] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium into each computing / processing device, or may be downloaded to an external computer or external storage device over a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and transfers the computer-readable program instructions for storage in a computer-readable storage medium within the respective computing / processing device.

[0096] The computer-readable program code / instructions for carrying out operations may be assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, configuration data for an integrated circuit, or source or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and procedural programming languages ​​such as the "C" programming language, or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, partially on the user's computer, partially on a remote computer, or entirely on a remote computer or server, as a standalone software package. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be to an external computer (e.g., through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), may execute computer-readable program instructions by utilizing state information of the computer-readable program instructions to personalize the electronic circuitry to perform a certain aspect or operation.

[0097] These computer-readable program instructions may be provided to a processor of a general-purpose computer, special-purpose computer, or other programmable data processing apparatus to produce an apparatus, such that the instructions, when executed by the processor of the computer or other programmable data processing apparatus, produce means for implementing the functions / acts set forth in the flowcharts and / or block diagrams (one or more blocks). These computer-readable program instructions may be stored on a computer-readable storage medium that can direct a computer, programmable data processing apparatus, and / or other device to function in a particular manner, such that the computer-readable storage medium on which the instructions are stored comprises an article including instructions that implement aspects of the functions / acts set forth in the flowcharts and / or block diagrams (one or more blocks).

[0098] The computer-readable program instructions may be loaded onto a computer, other programmable data processing apparatus, or other device such that a series of operational steps are performed on the computer, other programmable apparatus, or other device to generate a computer-implemented process such that the instructions, executed on the computer, other programmable apparatus, or other device, implement the functions / acts described in the flowcharts and / or block diagrams (one or more blocks).

[0099] The illustrated flowcharts and block diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer-readable media according to various embodiments. Each block in a flowchart or block diagram may represent a microservice, module, segment, or portion of instructions, comprising one or more executable instructions for implementing specific logical functions. The methods, computer systems, and computer-readable media may include additional, fewer, different, or differently arranged blocks than those shown in the figures. In some alternative implementations, the functions shown in the blocks may occur out of the order shown in the figures. For example, two blocks shown in succession may, in fact, be executed concurrently or substantially concurrently, depending on the functionality involved, or the blocks may be executed in the reverse order. Note that each block of the block diagram and / or flowchart illustrations, and combinations of blocks in the block diagram and / or flowchart illustrations, may be implemented by a dedicated hardware-based system that performs specific functions or acts, or by executing a combination of dedicated hardware and computer instructions.

[0100] It will be apparent that the systems and / or methods described herein may be implemented in different forms, such as hardware, firmware, or a combination of hardware and software. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit the implementation. As such, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It will be understood that software and hardware may be designed to implement the systems and / or methods based on the description herein.

[0101] Various aspects of the embodiments

[0102] Various further respective aspects and features of embodiments of the present disclosure may be defined by the following items. Item 1: 1. A method executed by at least one processor for configuring inter-cell transitions, comprising: Sending a request by a serving distribution unit (DU) to a user equipment (UE) to perform uplink synchronization with a target cell of a target distribution unit (DU), Upon receiving the request, the UE performs the uplink synchronization with the target DU, including transmitting a preamble signal to the target DU; Upon receiving the preamble signal, the target DU determines the best beam group (BG) for the UE. sending the request to perform the uplink synchronization with the target DU; receiving, by the serving DU, a random access channel (RACH) preamble originating from the target DU based on the best BG for the UE; performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble; A method for providing Item 2: the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble, and the UE is configured to determine whether the uplink synchronization is successful; Based on determining that the uplink synchronization is successful, the target DU is configured to determine that there is no preamble assigned to the UE during a handover (HO) preparation phase; and Based on the determination that there is no preamble assigned to the UE, the target DU is configured to assign and transmit a RACH preamble to the serving DU to configure a contention-free random access (CFRA) for the UE with the best BG for the UE. The method according to item 1. Item 3: the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble; The UE is configured to determine whether the uplink synchronization is successful; and upon determining that the uplink synchronization is not successful, the UE is configured to prevent further attempts of uplink synchronization. The method according to item 1. Item 4: The UE is configured to determine whether the RACH preamble received from the serving DU has reached the UE or not before the serving DU has performed the SCC; Based on a determination that a RACH preamble has not arrived at the serving DU before performing the SCC, the UE is configured to perform CBRA during the performance of the SCC by the serving DU. The method according to item 3. Item 5: The preamble signal includes a contention-free random access (CFRA) preamble, and the target DU is configured to determine whether there is a preamble already assigned to the UE; Based on a determination that there is a preamble already assigned to the UE, the target DU is configured to determine whether the preamble to be assigned to the UE is associated with the best BG for the UE; based on determining that the preamble assigned to the UE is not associated with the best BG for the UE, the target DU is configured to assign the RACH preamble to be a new preamble associated with the best BG for the UE; transmitting the newly assigned RACH preamble to the serving DU; The sending to the serving DU is performed via a control unit (CU) or directly on a DU-DU interface. The method according to item 1. Item 6: Item 1, the method further comprising: the serving DU executing the SCC for the UE transmitting, to the UE, a downlink MAC control element (DL MAC CE) including the RACH preamble received by the serving DU from the target DU. Item 7: The target DU is configured to estimate a timing advance (TA) of the UE based on the preamble signal received from the UE; The DL MAC CE includes the estimated TA. The method according to item 6. Item 8: 1. A method executed by at least one processor for configuring inter-cell transitions, comprising: receiving, by a serving distribution unit (DU), a random access channel (RACH) preamble originating from a target distribution unit (DU); performing a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble by the serving DU; Equipped with The UE is not configured to perform uplink synchronization with the serving DU, and the UE is not configured with a CFRA RACH preamble with the target DU; The target DU is configured to determine whether availability of RACH resources may change between target cell configuration preparation and execution of the serving cell transition; A method in which, based on a determination that the RACH resource has become available, the target DU is configured to allocate a RACH preamble to configure a contention-free random access (CFRA) for the UE with the best beam group (BG) for the UE, and to transmit the RACH preamble to the serving DU. Item 9: 1. An apparatus for configuring inter-cell transitions, comprising: at least one memory storing computer-executable instructions; Sending a request by a serving distribution unit (DU) to a user equipment (UE) to perform uplink synchronization with a target cell of a target distribution unit (DU), Upon receiving the request, the UE performs the uplink synchronization with the target DU, including transmitting a preamble signal to the target DU; Upon receiving the preamble signal, the target DU determines the best beam group (BG) for the UE. sending the request to perform the uplink synchronization with the target DU; receiving, by the serving DU, a random access channel (RACH) preamble originating from the target DU based on the best BG; performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble; at least one processor configured to execute the computer-executable instructions to perform the An apparatus comprising: Item 10: the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble, and the UE is configured to determine whether the uplink synchronization is successful; Based on determining that the uplink synchronization is successful, the target DU is configured to determine that there is no preamble assigned to the UE during a handover (HO) preparation phase; and Based on the determination that there is no preamble assigned to the UE, the target DU is configured to assign and transmit a RACH preamble to the serving DU to configure a contention-free random access (CFRA) for the UE with the best BG for the UE. Item 9. The device according to item 9. Item 11: the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble; The UE is configured to determine whether the uplink synchronization is successful; and upon determining that the uplink synchronization is not successful, the UE is configured to prevent further attempts of uplink synchronization. Item 9. The device according to item 9. Item 12: The UE is configured to determine whether the RACH preamble received from the serving DU has reached the UE or not before the serving DU has performed the SCC; Based on a determination that a RACH preamble has not arrived at the serving DU before performing the SCC, the UE is configured to perform CBRA during the performance of the SCC by the serving DU. Item 12. The device according to item 11. Item 13: The preamble signal includes a contention-free random access (CFRA) preamble, and the target DU is configured to determine whether there is a preamble already assigned to the UE; Based on a determination that there is a preamble already assigned to the UE, the target DU is configured to determine whether the preamble to be assigned to the UE is associated with the best BG for the UE; based on determining that the preamble assigned to the UE is not associated with the best BG for the UE, the target DU is configured to assign the RACH preamble to be a new preamble associated with the best BG for the UE; the at least one processor is further configured to execute the computer-executable instructions to: transmit the newly assigned RACH preamble to the serving DU; The sending to the serving DU is performed via a control unit (CU) or directly on a DU-DU interface. Item 9. The device according to item 9. Item 14: Item 10. The apparatus of item 9, wherein the at least one processor is further configured to execute the computer-executable instructions to execute the SCC for the UE by transmitting, by the serving DU, a downlink MAC control element (DL MAC CE) including the RACH preamble received from the target DU to the UE. Item 15: The target DU is configured to estimate a timing advance (TA) of the UE based on the preamble signal received from the UE; The DL MAC CE includes the estimated TA. Item 15. The device according to item 14. Item 16: 1. An apparatus for configuring inter-cell transitions, comprising: at least one memory storing computer-executable instructions; receiving, by a serving distribution unit (DU), a random access channel (RACH) preamble originating from a target distribution unit (DU); performing a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble by the serving DU; at least one processor configured to execute the computer-executable instructions to perform the Equipped with The UE is not configured to perform uplink synchronization with the serving DU, and the UE is not configured with a CFRA RACH preamble with the target DU; The target DU is configured to determine whether availability of RACH resources may change between target cell configuration preparation and execution of the serving cell transition; An apparatus configured to, based on a determination that the RACH resource has become available, the target DU allocates a RACH preamble to configure a contention-free random access (CFRA) for the UE with the best beam group (BG) for the UE, and transmits the RACH preamble to the serving DU. Item 17: 17. The apparatus of claim 16, wherein the RACH preamble is received when a resource situation at the target DU changes. Item 18: Item 17. The apparatus of item 15 or 16, wherein performing the SCC comprises transmitting the RACH preamble to the UE via a downlink MAC control element (DL MAC CE). Item 19: the target DU is configured to estimate a timing advance (TA); The DL MAC CE includes the estimated TA. Item 19. The device according to item 18. Item 20: 20. The apparatus according to any one of items 17 to 19, wherein the RACH preamble is transmitted to the serving DU via a control unit (CU) or directly on a DU-DU interface.

[0103] It will be appreciated that many modifications and variations of the present disclosure are possible in light of the above teachings. It will be apparent that, within the scope of the appended claims, the present disclosure may be practiced otherwise than as specifically described herein.

Claims

1. 1. A method for configuring inter-cell transitions, comprising: Sending a request by a serving distribution unit (DU) to a user equipment (UE) to perform uplink (UL) synchronization with a target cell of a target distribution unit (DU), Upon receiving the request, the UE performs the uplink synchronization with the target DU, including transmitting a preamble signal to the target DU; Upon receiving the preamble signal, the target DU determines the best beam group (BG) for the UE. sending the request to perform the uplink synchronization with the target DU; receiving, by the serving DU, a random access channel (RACH) preamble originating from the target DU based on the best BG for the UE; performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the received RACH preamble; A method for providing the above.

2. the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble, and the UE is configured to determine whether the uplink synchronization is successful; Based on determining that the uplink synchronization is successful, the target DU is configured to determine that no preamble is assigned to the UE during a handover (HO) preparation phase; and Based on the determination that there is no preamble assigned to the UE, the target DU is configured to assign a RACH preamble to the UE and transmit it to the UE via the serving DU to configure a contention-free random access (CFRA) for the UE with the best BG for the UE. The method of claim 1.

3. the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble; The UE is configured to determine whether the uplink synchronization is successful; and upon determining that the uplink synchronization is not successful, the UE is configured to prevent further attempts of uplink synchronization. The method of claim 1.

4. The UE is configured to determine whether the RACH preamble received from the serving DU has reached the UE or not before the serving DU has performed the SCC; Based on a determination that a RACH preamble has not arrived at the serving DU before performing the SCC, the UE is configured to perform CBRA during the performance of the SCC by the serving DU. The method of claim 3.

5. The preamble signal includes a contention-free random access (CFRA) preamble, and the target DU is configured to determine whether there is a preamble already assigned to the UE; Based on a determination that there is a preamble already assigned to the UE, the target DU is configured to determine whether the preamble to be assigned to the UE is associated with the best BG for the UE; based on determining that the preamble assigned to the UE is not associated with the best BG for the UE, the target DU is configured to assign the RACH preamble to be a new preamble associated with the best BG for the UE; transmitting the newly assigned RACH preamble to the serving DU; The sending to the serving DU is performed via a control unit (CU) or directly on a DU-DU interface. The method of claim 1.

6. 2. The method of claim 1, further comprising: the serving DU that performs the SCC for the UE transmitting, to the UE, a downlink MAC control element (DL MAC CE) including the RACH preamble received by the serving DU from the target DU.

7. The target DU is configured to estimate a timing advance (TA) of the UE based on the preamble signal received from the UE and shared with the serving DU; The DL MAC CE transmitted by the serving DU to the UE includes the estimated TA. The method of claim 6.

8. 1. A method for configuring inter-cell transitions, comprising: receiving, by a serving distribution unit (DU), a random access channel (RACH) preamble originating from a target distribution unit (DU); performing a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble by the serving DU; Equipped with The UE is not configured to perform uplink synchronization with the serving DU, and the UE is not configured with a CFRA RACH preamble with the target DU; The target DU is configured to determine whether availability of RACH resources may change between target cell configuration preparation and execution of the serving cell transition; A method in which, based on a determination that the RACH resource has become available, the target DU is configured to allocate a RACH preamble to configure a contention-free random access (CFRA) for the UE with the best beam group (BG) for the UE, and to transmit the RACH preamble to the serving DU.

9. 1. An apparatus for configuring inter-cell transitions, comprising: Sending a request by a serving distribution unit (DU) to a user equipment (UE) to perform uplink (UL) synchronization with a target cell of a target distribution unit (DU), Upon receiving the request, the UE performs the uplink synchronization with the target DU, including transmitting a preamble signal to the target DU; Upon receiving the preamble signal, the target DU determines the best beam group (BG) for the UE. sending the request to perform the uplink synchronization with the target DU; receiving, by the serving DU, a random access channel (RACH) preamble originating from the target DU based on the best BG; performing, by the serving DU, a serving cell transition (SCC) for the UE to one of the prepared target cells based on the RACH preamble; 20. An apparatus configured to:

10. the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble, and the UE is configured to determine whether the uplink synchronization is successful; Based on determining that the uplink synchronization is successful, the target DU is configured to determine that no preamble is assigned to the UE during a handover (HO) preparation phase; and Based on the determination that there is no preamble assigned to the UE, the target DU is configured to assign and transmit a RACH preamble to the serving DU to configure a contention-free random access (CFRA) for the UE with the best BG for the UE.

10. The apparatus of claim 9.

11. the preamble signal used during the UL synchronization includes a contention-based random access (CBRA) preamble; The UE is configured to determine whether the uplink synchronization is successful; and upon determining that the uplink synchronization is not successful, the UE is configured to prevent further attempts of uplink synchronization.

10. The apparatus of claim 9.

12. The UE is configured to determine whether the RACH preamble received from the serving DU has reached the UE or not before the serving DU has performed the SCC; Based on a determination that a RACH preamble has not arrived at the serving DU before performing the SCC, the UE is configured to perform CBRA during the performance of the SCC by the serving DU.

12. The apparatus of claim 11.

13. The preamble signal includes a contention-free random access (CFRA) preamble, and the target DU is configured to determine whether there is a preamble already assigned to the UE; Based on a determination that there is a preamble already assigned to the UE, the target DU is configured to determine whether the preamble to be assigned to the UE is associated with the best BG for the UE; based on determining that the preamble assigned to the UE is not associated with the best BG for the UE, the target DU is configured to assign the RACH preamble to be a new preamble associated with the best BG for the UE; The apparatus is further configured to perform transmitting the newly assigned RACH preamble to the serving DU; The sending to the serving DU is performed via a control unit (CU) or directly on a DU-DU interface.

10. The apparatus of claim 9.

14. The apparatus of claim 9 , further configured to: transmit, by the serving DU, to the UE, a Downlink MAC Control Element (DL MAC CE) including the RACH preamble received from the target DU.

15. The target DU is configured to estimate a timing advance (TA) of the UE based on the preamble signal received from the UE; The DL MAC CE includes the estimated TA.

15. The apparatus of claim 14.

16. 1. An apparatus for configuring inter-cell transitions, comprising: receiving, by a serving distribution unit (DU), a random access channel (RACH) preamble originating from a target distribution unit (DU); performing a serving cell transition (SCC) for a user equipment (UE) to one of the prepared target cells based on the RACH preamble by the serving DU; configured to run The UE is not configured to perform uplink synchronization with the serving DU, and the UE is not configured with a CFRA RACH preamble with the target DU; The target DU is configured to determine whether availability of RACH resources may change between target cell configuration preparation and execution of the serving cell transition; An apparatus configured to, based on a determination that the RACH resource has become available, the target DU allocates a RACH preamble to configure a contention-free random access (CFRA) for the UE with the best beam group (BG) for the UE, and transmits the RACH preamble to the serving DU.

17. The apparatus of claim 16, wherein the RACH preamble is received when a resource situation at the target DU changes.

18. 17. The apparatus of claim 16, wherein performing the SCC comprises transmitting the RACH preamble to the UE via a downlink MAC control element (DL MAC CE).

19. the target DU is configured to estimate a timing advance (TA); The DL MAC CE includes the estimated TA.

20. The apparatus of claim 18.

20. 17. The apparatus of claim 16, wherein the RACH preamble is transmitted to the serving DU via a control unit (CU) or directly over a DU-DU interface.

Images