LTM recovery procedure in dual connectivity system

Abstract

A method includes detecting a low-tier triggered mobility (LTM) execution failure of a LTM cell handover of a user equipment (UE), the LTM execution failure being for a target cell hosted by a first distributed unit; receiving, from the UE via a second distributed unit from a centralized unit, a measurement report of a plurality of LTM candidate cells belonging to a cell group associated with the failure, wherein the centralized unit is connected to the first distributed unit and the second distributed unit; identifying, based on the measurement report, a new target cell for the LTM cell handover, wherein the new target cell exists in the plurality of LTM candidate cells belonging to the cell group associated with the failure; and sending, via the centralized unit and the second distributed unit, information of the new target cell to the UE for performing the LTM cell handover.

Description

Cross-reference to related applications

[0001] This application claims priority to Indian patent application IN 2024-41036176, filed on 7 May 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to a low-level triggered mobility (LTM) recovery process in a dual-connectivity system. Background Technology

[0003] Handover is a process in mobile communications where a cellular transmission is transferred from one cell in a network to another neighboring cell without losing connectivity. In other words, handover (mobility) is the process of transferring an ongoing communication session of a User Equipment (UE) from one cell (i.e., a base station or gNodeB (gNB)) to another. Release 18 of the 3GPP introduced Low Layer Triggered Mobility (LTM), or L1 / L2-based mobility. LTM enables serving cell changes via L1 / L2 signaling while preserving upper-layer configurations and / or minimizing lower-layer configuration changes. Compared to Layer 3-based mobility, LTM offers improvements in handover latency and downtime. However, the LTM introduced in Release 18 has several limitations compared to Layer 3 mobility.

[0004] In 3GPP, the decomposed architecture of a gNodeB (gNB) is defined as breaking down the gNB into multiple logical entities. The gNB is split into three logical nodes: the Centralized Unit (CU), the Distributed Unit (DU), and the Radio Unit (RU). A single DU can host multiple cells. For example, 3GPP specifies that a DU can host up to 512 cells. The CU (also known as gNB-CU) hosts upper layers such as the Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the DU (also known as gNB-DU) hosts lower layers such as Radio Link Control (RLC), Media Access Control (MAC), and Physical (PHY) layers. Scheduling operations are performed at the gNB-DU.

[0005] The information disclosed in this Background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] In one embodiment, this disclosure discloses a method. The method includes: detecting an LTM execution failure of a low-level triggered mobility (LTM) cell handover between a user equipment (UE) configured with dual connectivity and a target cell. The target cell is hosted by a first distributed unit. Furthermore, the method includes: receiving, via a centralized unit and a second distributed unit, measurement reports from the UE of a plurality of LTM candidate cells belonging to a cell group associated with the failure. The centralized unit is connected to both the first and second distributed units. Additionally, the method includes: identifying a new target cell for LTM cell handover based on the measurement reports, the new target cell existing among the plurality of LTM candidate cells belonging to the cell group associated with the failure. Thereafter, the method includes: sending information about the new target cell to the UE via the centralized unit and the second distributed unit. The information about the new target cell is sent for performing an LTM cell handover.

[0007] In one embodiment, this disclosure discloses a first distributed unit. The first distributed unit is configured to: detect an LTM execution failure for an LTM cell handover of a UE configured with dual connectivity, the LTM execution failure being for a target cell. The target cell is managed by the first distributed unit. Furthermore, the first distributed unit is configured to: receive measurement reports from the UE via a centralized unit and a second distributed unit, representing multiple LTM candidate cells belonging to the cell group associated with the failure. The centralized unit is connected to both the first and second distributed units. Additionally, the first distributed unit is configured to: identify a new target cell for the LTM cell handover based on the measurement reports, the new target cell existing among the multiple LTM candidate cells belonging to the cell group associated with the failure. Subsequently, the first distributed unit is configured to: send information about the new target cell to the UE via the centralized unit and the second distributed unit. The information about the new target cell is sent for performing the LTM cell handover.

[0008] In one embodiment, this disclosure discloses a non-transitory computer-readable medium including instructions for performing an operation. The operation includes: detecting an LTM execution failure of a low-level triggered mobility (LTM) cell handover between a user equipment (UE) configured with dual connectivity and a target cell. The target cell is hosted by a first distributed unit. Furthermore, the operation includes: receiving measurement reports from the UE via a centralized unit and a second distributed unit, representing a plurality of LTM candidate cells belonging to a cell group associated with the failure. The centralized unit is connected to both the first and second distributed units. Additionally, the operation includes: identifying a new target cell for LTM cell handover based on the measurement reports, the new target cell existing among the plurality of LTM candidate cells belonging to the cell group associated with the failure. Thereafter, the operation includes: sending information about the new target cell to the UE via the centralized unit and the second distributed unit. The information about the new target cell is sent for performing the LTM cell handover. Attached Figure Description

[0009] The features, aspects, and advantages of embodiments of the present disclosure will now be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and in the drawings:

[0010] Figure 1A The diagram illustrates the traditional decomposed gNodeB (gNB) architecture;

[0011] Figure 1B and Figure 1C The illustration shows an exemplary environment for performing a low-level triggered mobility (LTM) recovery procedure according to some embodiments of the present disclosure;

[0012] Figure 2 Detailed diagrams of a first distributed unit according to some embodiments of the present disclosure are illustrated;

[0013] Figure 3A and Figure 3B An exemplary flowchart for performing an LTM recovery process according to some embodiments of the present disclosure is illustrated;

[0014] Figure 4 and Figure 5 Exemplary flowcharts according to some embodiments of the present disclosure are illustrated, illustrating method steps for performing an LTM recovery process; and

[0015] Figure 6 A schematic diagram of an example component of a first distributed unit for performing an LTM recovery process according to an embodiment of the present disclosure is shown. Detailed Implementation

[0016] The following detailed description of exemplary embodiments is provided with reference to the accompanying drawings. The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations are possible based on the foregoing disclosure, or may be obtained from the practice of implementation. Furthermore, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowcharts and operational descriptions provided below relate to one of various embodiments. It should be noted that other embodiments may be made that do not perfectly match the flowcharts and their descriptions. It should be understood that in other embodiments, one or more operations may be omitted, one or more operations may be added, and one or more operations may be performed simultaneously (at least partially).

[0017] It is evident that the systems and / or methods described herein can be implemented in various forms of hardware, software, or combinations of hardware and software. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit their implementation. Therefore, since the operation and behavior of systems and / or methods are described herein without reference to specific software code, it should be understood that software and hardware can be designed to implement these systems and / or methods based on the descriptions herein.

[0018] Even if specific combinations of features are listed in the claims and / or disclosed in this specification, these combinations are not intended to limit the disclosure of implementation. In fact, many of these features can be combined in ways not specifically listed in the claims and / or not disclosed in the specification. Although each dependent claim listed below may depend directly on only one claim, the disclosure of implementation includes a combination of each dependent claim with every other claim in the claim set.

[0019] Unless explicitly stated otherwise, no element, action, or instruction used herein should be construed as critical or necessary. Furthermore, as used herein, the terms “a” and “an” are intended to include one or more items and may be used interchangeably with “one or more.” Additionally, as used herein, the terms “has,” “have,” “having,” “include,” “including,” etc., are intended to be open-ended terms. Furthermore, unless explicitly stated otherwise, the word “based on” means “at least partially based on.” Moreover, expressions such as “at least one of [A] and [B],” “[A] and / or [B],” or “at least one of [A] or [B]” should be understood to include only A, only B, or both A and B.

[0020] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations are possible or can be derived from the practice of implementation based on the foregoing disclosure.

[0021] The Lower Layer Triggered Mobility (LTM) introduced in Release 18 of the 3GPP program enables serving cell changes via L1 / L2 signaling while maintaining upper-layer configurations and / or minimizing changes to lower-layer configurations. However, LTM introduced in Release 18 has several limitations compared to Layer 3 mobility.

[0022] In 3GPP, the decomposition architecture of gNodeB (gNB) is defined as decomposing the gNB into multiple logical entities, such as... Figure 1AAs shown, the gNB is split into three logical nodes: the Centralized Unit (CU) (also known as gNB-CU), the Distributed Unit (DU) (also known as gNB-DU), and the Radio Unit (RU). To support L1 / L2-centric inter-cell changes (i.e., changes in serving cell) / LTM within the decomposed gNB architecture, a new mechanism is needed where configuration occurs in the gNB-CU but is autonomously executed by the gNB-DU without further interaction with upper layers.

[0023] In version 18, LTM was limited to within a CU and a single connection. In version 19, LTM supports the new Wireless Dual Connectivity (NR-DC), as described below: Specify support for Layer 2 Mobility (LTM) between CUs [RAN2, RAN3] ○ When the DC is not configured, the CU should be considered as the MN. ○ As a secondary priority, it supports the case where NR-DC is configured, CU acts as SN, and MCG remains unchanged. ○ As a secondary priority, it supports the case where NR-DC is configured and CU acts as MN, and SCG remains unchanged or SCG is released. Note: This excludes cases where LTM is configured in both MCG and SCG. ○ Specifies support for subsequent LTM mobility procedures, based on Rel-18 LTM, designed to avoid handover during cell transfers. Configure RRC during the process. Coordination with SA3 is required in terms of secure key processing. Note: Version 18 of the intra-CU LTM procedure is considered the baseline for adding inter-CU support. Measurement-related enhancements to support LTM: [RAN2, RAN1] ○ Measurement-related enhancement is applicable to MCG / SCG LTM within CU and MCG / SCG-LTM between CUs. ○ Specify the necessary components to support event-triggered L1 measurement reporting [RAN2, RAN1] RAN1 and RAN2 are performed independently on their respective MIMO and mobility-enhanced WI event-triggered measurement targets. Check the progress at RAN#105 to see if any modifications to the objectives are needed to avoid / manage any overlap in the work. ○ Specify support for CSI-RS measurements during the LTM procedure, and enable candidate cells based on LTM prior to LTM. CSI-RS beam management and / or other necessary physical layer operations [RAN1] Specify support for conditional LTM [RAN2, RAN3, RAN1] ○ Prioritize LTM within CU ○ Checkpoint at RAN#105 where the target is reviewed. The RAN working group cannot start before this checkpoint. Specify RRM requirements [RAN4] related to the above objectives as necessary.

[0024] The LTM used for NR-DC can be described in two variations, such as Figure 1B and Figure 1C As shown in the figure, in the first variant, the gNB comprises multiple distributed units that respectively host the primary cell group (MCG) and the secondary cell group (SCG). The centralized unit hosts both the primary node (MN) and the secondary node (SN). In the second variant, the gNB is divided into multiple distributed units and centralized units. The distributed units respectively host the MCG and SCG. Furthermore, the centralized units respectively host the MN and SN.

[0025] In LTM, the gNB receives multiple L1 measurement reports from the UE, and changes the UE's serving cell based on these reports by signaling a cell handover command. LTM failure occurs when the UE does not receive a cell handover command or fails to connect to the target cell identified by the gNB. In this case, the UE performs LTM failure recovery. 3GPP Release 18 defines the following in TS38.300: NR supports a timer-based handover failure procedure. The RRC connection rebuild procedure is used to recover from handover failures. However, certain CHO, DAPS handover, or LTM cell handover scenarios are exceptions: - When DAPS handover fails, the UE falls back to the source cell configuration, restores the connection with the source cell, and if If the source link has not been released, the DAPS handover failure will be reported via the source without triggering RRC connection reconstruction. - When the initial CHO execution attempt fails or the HO fails, the UE performs cell selection, and if the selected cell fails... The selected cell is a CHO candidate, and if the network is configured for the UE to attempt CHO after a handover / CHO failure, the UE will attempt CHO execution. Once, otherwise rebuild. - When the initial LTM execution attempt fails or the HO fails, the UE performs cell selection, and if the selected cell is selected... The selected cell is an LTM candidate cell, and if the network configures the UE to try LTM after LTM execution fails, then the UE will try... LTM is executed once; otherwise, a rebuild is performed.

[0026] The above statement indicates that whenever an LTM cell handover failure occurs, the UE performs cell selection based on the current radio conditions. If the selected cell happens to be one with an LTM candidate cell configuration, the UE performs another LTM execution after the failure (only if the network is already configured). This is only attempted once, and if the failure occurs again, an RRC reconstruction is initiated. During the RRC reconstruction, both the MCG and SCG bearers need to be released. LTM failure recovery is inherently autonomous and does not require an LTM handover command (Downlink MAC Control Element (DL MAC CE)) from the gNB. However, the overall goal of failure recovery is to avoid RRC reconstruction. Furthermore, in the context of NR-DC, i.e., when both SCG and MCG are present, LTM failure recovery needs to be addressed differently.

[0027] This disclosure provides methods and apparatus for performing an LTM recovery process. When an initial LTM execution attempt or handover fails, the UE performs cell selection, and if the selected cell is an LTM candidate SCG cell, and if the network has configured the UE to attempt LTM after an LTM execution failure, the UE attempts an LTM execution. This is referred to as an LTM recovery attempt or autonomous LTM execution. This disclosure enables a UE configured with dual connectivity to send a measurement report to a distributed unit (or gNB-DU) via a centralized unit (gNB-CU). The distributed unit checks whether the radio conditions of any cell indicated in the measurement report are suitable for LTM cell handover. When the radio conditions are satisfactory and the cell is ready for LTM, the distributed unit sends a DL MAC CE to perform an LTM cell handover. In this way, this disclosure enables LTM cell handover to be performed without RRC reconstruction. Furthermore, this disclosure describes such methods and apparatus for both NR-DC variants 1 and 2 as described above. Therefore, this disclosure defines an LTM recovery process for a DC scenario.

[0028] Figure 1A The diagram illustrates a traditional decomposed gNodeB (gNB) architecture. In fifth-generation (5G) networks, the base station or gNB is divided into three distinct components: the Centralized Unit (CU) (also referred to as gNB-CU in this specification), the Distributed Unit (DU) (also referred to as gNB-DU in this specification), and the Remote Radio Unit (RU) (not shown in the diagram). The gNB-CU acts as the central intelligent device, skillfully handling complex and centralized network functions. These functions include, but are not limited to, skillful radio resource management, effective network control, and seamless coordination with the 5GC. The gNB-DU is responsible for managing data plane processing, including critical tasks such as data transmission and reception with user equipment (UE) (not shown in Figure 1). The gNB-DU seamlessly interfaces with the gNB-CU via the F1 interface. Figure 1A The separation of the control plane and user plane (i.e., gNB-CU-CP and gNB-CU-UP) of the gNB-CU is further illustrated. The gNB-CU-CP is connected to the gNB-DU via the F1-C interface. The gNB-CU-UP is connected to the gNB-DU via the F1-U interface. The gNB-CU-CP is connected to (multiple) gNB-CU-CPs via the E1 interface. The RU handles physical layer functions, housing antennas and radio transceivers to facilitate the actual transmission and reception of radio signals. The description of this disclosure is interpreted only with consideration for fifth-generation (5G) networks. However, this disclosure applies to any type of network, such as fourth-generation (4G) networks, 6G networks, etc.

[0029] Figure 1B and Figure 1CAn exemplary environment for performing an LTM recovery process according to an embodiment of the present disclosure is illustrated. Figure 1B An implementation of this disclosure according to a first variant 102 of NR-DC is shown. In the first variant 102, the gNB includes distributed units, namely gNB-DU1 1061 and gNB-DU2 1062, connected to a single centralized unit gNB-CU 104. In one embodiment, gNB-DU1 1061 hosts the SCG, and gNB-DU2 1062 hosts the MCG (such as...). Figure 1B (As shown). In another embodiment, gNB-DU1 1061 hosts the MCG, and gNB-DU1 1061 hosts the SCG (not shown in the figure). The centralized unit gNB-CU 104 hosts both MN and SN. Figure 1B The illustration shows UE 108. UE 108 represents an end-user equipment that accesses services and applications via a wireless network. UE 108 is configured to connect to both centralized and distributed units via a wireless network. Examples of UE 108 include, but are not limited to, any device used by a user to communicate via a wireless network, such as, but not limited to, mobile phones, smartphones, laptops, wearable devices, Internet of Things (IoT), etc. UE 108 communicates with centralized unit gNB-CU 104 via the F1 interface, through gNB-DU1 1061 and gNB-DU2 1062.

[0030] In the second variant 110, the gNB includes distributed units, namely gNB-DU1 1061 and gNB-DU2 1062. gNB-DU1 1061 is connected to gNB-CU1 1041, and gNB-DU2 1062 is connected to gNB-CU2 1042. gNB-DU1 1061 and gNB-DU2 1062 host SCG and MCG, respectively. Furthermore, gNB-CU1 1041 and gNB-CU2 1042 host MN and SN, respectively. In one embodiment, gNB-DU1 1061 hosts SCG and also hosts MCG. gNB-CU1 1041 hosts SN, and gNB-CU2 1042 hosts MN (e.g., ...). Figure 1C(As shown). In another embodiment, gNB-DU1 1061 hosts the MCG and gNB-DU1 1061 hosts the SCG. gNB-CU1 1041 hosts the MN and gNB-CU2 1042 hosts the SN (not shown). UE 108 communicates with gNB-CU1 1041 and gNB-CU2 1042 via the F1 interface, through gNB-DU1 1061 and gNB-DU2 1062. gNB-CU1 1041 and gNB-CU2 1042 communicate via the Xn interface. This disclosure is explained with respect to NR-DC. However, this should not be considered as limiting. This disclosure applies to any other dual-connectivity system. Hereinafter, gNB-DU1 1061 is referred to as the first distributed unit 1061. gNB-DU2 1062 is referred to as the second distributed unit 1062. gNB-CU2 104 is referred to as the centralized unit 104. gNB-CU11041 is referred to as the first centralized unit 1041, and gNB-CU2 1042 is referred to as the second centralized unit 1042.

[0031] In this disclosure, a first distributed unit 1061 is configured to perform an LTM recovery procedure in a dual-connectivity system. Here, the first distributed unit 1061 detects an execution failure of an LTM cell handover for a UE 108 configured with dual connectivity, the LTM execution failure targeting a target cell managed by the first distributed unit 1061. In this case, this disclosure enables the UE 108 to send a measurement report to the first distributed unit 1061 upon such a failure. According to a first variant 102, the first distributed unit 1061 receives measurement reports from the UE 108 via a centralized unit 104 and a second distributed unit 1062, representing multiple LTM candidate cells belonging to the cell group associated with the failure. The first distributed unit 1061 uses the measurement reports to identify the availability of a new target cell for LTM cell handover among the configured LTM candidate cells belonging to the cell group associated with the failure. The first distributed unit 1061 then sends information about such a target cell to the UE 108 to perform an LTM cell handover in the dual-connectivity system. According to the first variant 102, the information is sent to the UE 108 via the centralized unit 104 and the second distributed unit 1062.

[0032] According to the second variation 110, this disclosure also enables the first distributed unit 1061 to perform the LTM recovery procedure in a dual-connectivity system. According to the second variation 110, the first distributed unit 1061 receives a measurement report from the UE 108 from the first centralized unit 1041 via the second centralized unit 1042 and the second distributed unit 1062. According to the second variation 110, this information is transmitted from the first centralized unit 1041 to the UE 108 via the second centralized unit 1042 and the second distributed unit 1062.

[0033] Figure 2 A detailed diagram of a first distributed unit 1061 according to some embodiments of the present disclosure is illustrated. The first distributed unit 1061 may include an input / output (I / O) interface 202, a memory 204, and a central processing unit (also referred to as a "CPU" or "processor 206"). In some embodiments, the memory 204 may be communicatively coupled to the processor 206. The memory 204 stores instructions executable by the processor 206. The processor 206 may include at least one data processor for executing program components to perform user- or system-generated requests. The memory 204 may be communicatively coupled to the processor 206. The memory 204 stores instructions executable by the processor 206 that, when executed, cause the processor 206 to perform an LTM recovery process. The I / O interface 202 is coupled to the processor 206, through which input signals and / or output signals can be transmitted. For example, the first distributed unit 1061 may receive measurement reports from a UE 108 via the I / O interface 202. In one embodiment, the first distributed unit 1061 can be implemented in various computing systems, such as servers, web servers, cloud-based servers, etc.

[0034] In one embodiment, memory 204 may include one or more modules 210 and data 208. The one or more modules 210 may be configured to perform the steps of this disclosure using data 208. In one embodiment, each of the one or more modules 210 may be a hardware unit that may be external to memory 204 and coupled to the first distributed unit 1061. As used herein, the term module 210 refers to an application-specific integrated circuit (ASIC), electronic circuitry, a field-programmable gate array (FPGA), a programmable system-on-a-chip (PSoC), combinational logic circuitry, and / or other suitable components that provide the described functionality. When configured with the functionality defined in this disclosure, the one or more modules 210 will produce novel hardware.

[0035] In one implementation, module 210 may include, for example, a detection module 222, a receiving module 224, an identification module 226, a transmission module 228, and other modules 230. It should be understood that the above modules may be represented as a single module or a combination of different modules. In one implementation, data 208 may include, for example, detection data 212, measurement data 214, identification data 216, transmission data 218, and other data 220.

[0036] First, let’s explain module 210 and data 208 for the first variant 102 of NR-DC.

[0037] In one embodiment, the detection module 222 can be configured to detect an LTM execution failure of an LTM cell handover for a UE 108 configured with dual connectivity, the LTM execution failure being for a target cell. The target cell can be hosted by a first distributed unit 1061. The first distributed unit 1061 can host multiple cells. For example, the first distributed unit 1061 can host up to 512 cells. The UE 108 can currently camp on the serving cell of the first distributed unit 1061. The UE 108 can attempt to connect to the target cell hosted by the first distributed unit 1061 by performing an LTM cell handover. Here, the first distributed unit 1061 can send an LTM serving cell handover command to the UE 108 to switch from the serving cell to the target cell. The LTM cell handover can fail for several reasons. In one example, consider that the UE 108 does not receive an LTM serving cell handover command indicating the target cell from the first distributed unit 1061 due to a radio link failure at the source or a handover failure at the target. In this case, the LTM cell handover fails. In another example, consider UE 108 receiving an LTM serving cell handover command from the first distributed unit 1061; however, UE 108 is unable to connect to the target cell. In this case, the LTM cell handover fails. UE 108 can then perform an LTM recovery attempt according to conventional procedures; that is, UE 108 can perform cell reselection, and if the selected cell is an LTM candidate cell, UE 108 will attempt an LTM execution once. Detection module 222 can detect failures in the LTM recovery attempt.

[0038] Considering the failure of LTM execution during LTM cell handover at SCG, Figure 2 and Figure 3A Let's explain together. gNB-DU1 1061 hosts the SCG, and gNB-DU2 1062 hosts the MCG. gNB-CU hosts both MN and SN (represented as MN / SN). Reference Figure 3AUE108 performs SCG LTM cell handover, as shown in steps 1-3. The SCG LTM cell handover fails, as shown in steps 4 and 5. UE108 then performs cell reselection and attempts to resume LTM, as shown in step 6. The LTM resumption attempt fails, as shown in step 7. (Refer to step 7 again.) Figure 2 Data related to the detection of LTM execution failure during SCG LTM cell handover of UE 108 can be stored in memory 204 as detection data 212. In one embodiment, receiving module 224 can be configured to receive detection data 212 from detection module 222. Furthermore, receiving module 224 can be configured to receive measurement reports from UE 108 for multiple LTM candidate cells belonging to the cell group associated with failure. UE 108 can perform measurements based on the LTM configuration received from first distributed unit 1061. UE 108 can generate Layer 1 (L1) and Layer 3 (L3) measurement reports based on the measurements. The measurement reports may include information about SCG LTM candidate cells. UE 108 can send a measurement report including L1 and L3 measurement reports to first distributed unit 1061. According to first variant 102, first distributed unit 1061 can receive measurement reports from UE 108 via centralized unit 104 and second distributed unit 1062. Here, second distributed unit 1062 can receive measurement reports from UE 108 because no link is established between UE 108 and first distributed unit 1061 due to LTM execution failure. The second distributed unit 1062 can send measurement reports to the centralized unit 104. The centralized unit 104 can receive measurement reports including L3 and L1 measurement reports. In one example, the L1 measurement report can be received as a container. The centralized unit 104 can send the L1 measurement report (received as a payload) to the receiving module 224 of the first distributed unit 1061 via the F1 interface.

[0039] Refer again Figure 3A The centralized unit 104 (MN+SN) can receive measurement reports, i.e., RRC measurement reports, from UE108 via the second distributed unit 1062 (MCG), as shown in step 8. The centralized unit 104 (MN+SN) checks the measurement reports used for LTM cell preparation, as shown in step 9, which will be explained in detail in later paragraphs of this specification. The receiving module 224 of the first distributed unit 1061 (SCG) can receive L1 measurement reports from the centralized unit 104 (MN+SN), as shown in step 11. (See again...) Figure 2The measurement reports received by UE 108 can be stored in memory 204 as measurement data 214. This disclosure enables UE 108 to send measurement reports to the network (centralized unit 104 and first distributed unit 1061 (SCG)) in the event of an LTM recovery attempt failure. The network performs LTM cell handover based on the measurement reports. Therefore, LTM cell handover is performed, and RRC reconstruction is avoided in the event of failure.

[0040] In one embodiment, the identification module 226 may be configured to receive measurement data 214 from the receiving module 224. Furthermore, the identification module 226 may be configured to, based on the measurement report, identify a new target cell among multiple LTM candidate cells belonging to the cell group associated with the failure for LTM cell handover. The measurement report received by the identification module 226 may include multiple LTM candidate cells. These multiple LTM candidate cells may be cells already configured by the network (i.e., the first distributed element 1061). The identification module 226 may determine the availability of the new target cell from among the multiple LTM candidate cells. Here, the identification module 226 may determine whether the radio conditions of any cell indicated in the measurement report are suitable / applicable for LTM cell handover.

[0041] exist Figure 3A In the illustrated embodiment, the first distributed unit 1061 manages the SCG, and the second distributed unit 1062 manages the MCG. The centralized unit 104 manages both the MN and SN. In this case, the measurement report received from UE 108 may include the configuration of the SCG LTM candidate cell. In another embodiment (not shown), the first distributed unit 1061 manages the MCG, and the second distributed unit 1062 manages the SCG. In this case, the measurement report received from UE 108 may include the configuration of the MCGLTM candidate cell. (Refer to...) Figure 3A In step 12, the identification module 226 can determine whether LTM cell handover can be performed on different cells / at least one candidate / target cell.

[0042] Refer again Figure 2 In one embodiment, the identification module 226 can determine that the new target cell does not exist among multiple configured LTM candidate cells. In this case, the identification module 226 can receive information about at least one new candidate / target cell from the centralized unit 104 for performing LTM candidate / target cell preparation and cell handover. Here, the centralized unit 104 identifies at least one new candidate / target cell for LTM cell handover based on the L3 measurement report received from the UE 108. (Refer to again...) Figure 3ACentralized unit 104 (MN+SN) prepares new candidate cells for SCG LTM cell handover based on the L3 measurement report, as shown in step 9. Centralized unit 104 (MN+SN) can send information about the new candidate / target cell to identification module 226 via the F1 interface in the UE context modification request. (See again...) Figure 2 Information about at least one newly identified candidate / target cell can be stored in memory 204 as identification data 216. This disclosure enables the network to perform LTM cell handover based on the measurement report of UE 108. Therefore, LTM cell handover is performed, and RRC reconstruction in case of failure is avoided.

[0043] In one embodiment, transmission module 228 can be configured to receive identification data 216 from identification module 226. Furthermore, transmission module 228 can be configured to send information about a new target cell to UE 108. Here, transmission module 228 can be configured to send information about a new target cell when the radio conditions of the new target cell are satisfactory and the new target cell is ready for LTM. In one embodiment, transmission module 228 can send information about the new target cell in an LTM serving cell handover command or a DLMAC CE to perform an LTM cell handover. The DL MAC CE can be sent as a payload. The DL MAC CE may also include the target cell beam, a random access channel (RACH) preamble (if required for contention-free random access (CFRA)), and a corresponding timing advance (TA).

[0044] The transmission module 228 can send information about a new target cell to the UE 108 via the F1 interface, through the centralized unit 104 and the second distributed unit 1062. When a new target cell is unavailable, information about at least one new candidate / target cell can be sent to the UE 108 via the F1 interface, through the centralized unit 104 and the second distributed unit 1062. (See again...) Figure 3A Information on at least one new candidate / target cell can be sent to UE 108, as shown in steps 13-16. SCG LTM cell handover can be performed as shown in steps 17-21. (Refer again...) Figure 2 The information sent to UE 108 can be stored in memory 204 as transmission data 218.

[0045] Considering the failure of LTM execution during LTM cell handover at SCG, Figure 2 and Figure 3ALet's explain together. Here, gNB-DU1 1061 manages the SCG, and gNB-DU2 1062 manages the MCG. A similar procedure applies when LTM execution failure during LTM cell handover occurs at the MCG, with gNB-DU1 1061 managing the MCG and gNB-DU2 1062 managing the SCG. For simplicity, an explanation of MCGLTM execution failure is not provided.

[0046] This disclosure enables UE 108 and the network to perform LTM cell handover without RRC reconstruction in the event of a failed LTM recovery attempt. Following both the LTM cell handover failure and the LTM recovery attempt failure at the first distributed unit 1061, UE 108 does not need to initiate RRC reconstruction because the second distributed unit 1062 remains active. The centralized unit 104 configures UE 108 to perform the LTM recovery process using new RRC parameters (RRC measurement reports). This saves network resources by avoiding the release of MCG / SCG bearers. This disclosure enables the provision of information about a new target cell to UE 108. In the event of an LTM cell handover failure due to UE 108 not receiving an LTM serving cell handover command, UE 108 can use the information about the new target cell to perform the LTM cell handover. In another scenario, when UE 108 cannot connect to the target cell, UE 108 can use the information about the new target cell to perform the LTM cell handover without performing RRC reconstruction.

[0047] Other data 220 may store data generated by one or more modules 210 for performing various functions of the first distributed unit 1061, including temporary data and temporary files. Other data 220 may be stored in memory 204. One or more modules 210 may also include other modules 230 to perform various other functions of the first distributed unit 1061.

[0048] Now, for the second variant 110 of NR-DC, interpret module 210 and data 208.

[0049] The detection module 222, which is configured to perform the LTM recovery process for the second variant 110, is configured similarly to the first variant 102, and therefore will not be explained further for the sake of brevity.

[0050] In one embodiment, receiving module 224 can be configured to receive detection data 212 from detection module 222. Furthermore, receiving module 224 can be configured to receive measurement reports from UE 108. UE 108 can send a measurement report including L1 and L3 measurement reports to first distributed unit 1061. According to the second variant 110, receiving module 224 of first distributed unit 1061 can receive measurement reports from UE 108 via first centralized unit 1041, second centralized unit 1042, and second distributed unit 1062. Here, due to LTM execution failure, no link is established between UE and first distributed unit 1061, therefore second distributed unit 1062 can receive measurement reports from UE 108. Second distributed unit 1062 can send measurement reports to second centralized unit 1042. Second centralized unit 1042 can receive measurement reports including L3 and L1 measurement reports. The second centralized unit 1042 can send an L1 measurement report (received as a payload) to the first centralized unit 1041 via the Xn interface. The L1 measurement report is then forwarded to the receiving module 224 of the first distributed unit 1061 via the F1 interface.

[0051] Given the failure of LTM execution during LTM cell handover at SCG, the explanation is as follows: Figure 3B . refer to Figure 3B Steps 1-7 illustrate LTM execution failure and LTM recovery attempt failure. The receiving module 224 of the first distributed unit 1061 (SCG) can receive measurement reports of multiple LTM candidate cells belonging to the cell group associated with the failure from the first centralized unit 1041 (SN) via the Xn+F1 interface, through the second centralized unit 1042 (MN) and the second distributed unit 1062 (MCG), as shown in steps 8, 11, and 12. The second centralized unit 1042 (MN) checks the measurement reports for LTM cell preparation, as shown in step 9. (Refer again...) Figure 2 The measurement reports received by UE 108 can be stored in memory 204 as measurement data 214.

[0052] The configuration of the identification module 226, which is configured to perform the LTM recovery process of the second variant 110, is similar to that of the first variant 102, and therefore will not be explained further for the sake of brevity.

[0053] In one embodiment, the transmission module 228 can be configured to receive identification data 216 from the identification module 226. Furthermore, the transmission module 228 can be configured to send information about a new target cell to the UE 108. Here, the transmission module 228 can be configured to send the information about the new target cell when the radio conditions of the new target cell are satisfactory and the new target cell is ready for LTM. In one embodiment, the transmission module 228 can send the information about the new target cell in an LTM serving cell handover command or a DLMAC CE to perform an LTM cell handover.

[0054] The transmission module 228 can transmit information about a new target cell from the first centralized unit 1041 via the Xn+F1 interface, through the second centralized unit 1042 and the second distributed unit 1062. When a new target cell is unavailable, information about at least one new candidate / target cell can be transmitted from the first centralized unit 1041 via the Xn+F1 interface, through the second centralized unit 1042 and the second distributed unit 1062. (See again...) Figure 3B Information about the new target cell can be sent from the first centralized unit 1041 (SN) to the UE 108 via the second centralized unit 1042 (MN) and the second distributed unit 1062 (MCG), as shown in steps 14-17. SCG LTM cell handover can be performed as shown in steps 18-22. (Refer again...) Figure 2 The information sent to UE 108 can be stored in memory 204 as transmission data 218.

[0055] Considering the failure of LTM execution during LTM cell handover at SCG, Figure 2 and Figure 3B Let's explain together. Here, gNB-DU1 1061 hosts the SCG, and gNB-DU2 1062 hosts the MCG; gNB-CU1 1041 hosts the SN, and gNB-CU2 1042 hosts the MN. A similar procedure applies when LTM handover failure occurs at the MCG, gNB-DU1 hosts the SCG and gNB-DU2 hosts the MCG, or gNB-CU1 1041 hosts the MN and gNB-CU2 1042 hosts the SN. For simplicity, an explanation of MCGLTM failure is not provided.

[0056] Other data 220 may store data generated by one or more modules 210 for performing various functions of the first distributed unit 1061, including temporary data and temporary files. Other data 220 may be stored in memory 204. One or more modules 210 may also include other modules 230 to perform various other functions of the first distributed unit 1061.

[0057] Figure 4 Exemplary flowcharts according to some embodiments of the present disclosure are illustrated, illustrating method steps for performing an LTM recovery process. 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. Typically, computer-executable instructions may include routines, programs, objects, components, data structures, procedures, modules, and functions that perform a particular function or implement a particular abstract data type.

[0058] The order in which method 400 is described should not be construed as limiting, and any number of described method blocks can be combined in any order to implement the method. Furthermore, individual blocks can be removed from the method without departing from the scope of the subject matter herein. Moreover, the method can be implemented in any suitable hardware, software, firmware, or a combination thereof.

[0059] In step 402, an LTM execution failure can be detected for LTM cell handover of the UE 108 configured with dual connectivity. The LTM execution failure pertains to the target cell. The target cell can be managed by the first distributed unit 1061. The first distributed unit 1061 can manage multiple cells. The UE 108 can perform an LTM recovery attempt when an LTM cell handover failure occurs; that is, the UE 108 can perform cell reselection, and when the selected cell is an LTM candidate cell, the UE 108 attempts an LTM execution once. The first distributed unit 1061 can detect failures in the LTM recovery attempt.

[0060] In step 404, measurement reports of multiple LTM candidate cells belonging to the cell group associated with failure can be received from UE 108. UE 108 can send a measurement report including L1 and L3 measurement reports to the first distributed unit 1061. According to the first variant 102, the first distributed unit 1061 can receive the measurement report from UE 108 via the centralized unit 104 and the second distributed unit 1062.

[0061] In step 406, based on the measurement report, a new target cell may be identified among multiple LTM candidate cells whose LTM cell handover identifier belongs to the cell group associated with failure. The multiple LTM candidate cells may be cells already configured by the network (i.e., the first distributed element 1061). Here, the first distributed element 1061 may determine whether the radio conditions of any cell indicated in the measurement report are suitable / applicable for LTM cell handover.

[0062] In step 408, information about a new target cell can be sent to UE 108. Here, the first distributed unit 1061 can be configured to send information about a new target cell when the radio conditions of the new target cell are satisfactory and the new target cell is ready for LTM. In one embodiment, the first distributed unit 1061 can send information about the new target cell in an LTM serving cell handover command or DL ​​MAC CE to perform LTM cell handover. The first distributed unit 1061 can send information about the new target cell to UE 108 via the F1 interface, through the centralized unit 104 and the second distributed unit 1062. When a new target cell is unavailable, information about at least one new candidate / target cell can be sent to UE 108 via the F1 interface, through the centralized unit 104 and the second distributed unit 1062.

[0063] Figure 5 Exemplary flowcharts according to some embodiments of the present disclosure are illustrated, illustrating method steps for performing an LTM recovery process. Figure 5 As shown, method 500 may include one or more steps. Method 500 may be described in the general context of computer-executable instructions. Typically, computer-executable instructions may include routines, programs, objects, components, data structures, procedures, modules, and functions that perform a particular function or implement a particular abstract data type.

[0064] The order in which method 500 is described should not be construed as limiting, and any number of described method blocks can be combined in any order to implement the method. Furthermore, individual blocks can be removed from the method without departing from the scope of the subject matter herein. Moreover, the method can be implemented in any suitable hardware, software, firmware, or a combination thereof.

[0065] Step 502 is similar to step 402, and will not be repeated for the sake of brevity.

[0066] In step 504, a measurement report from UE 108 can be received. UE 108 can send a measurement report including L1 and L3 measurement reports to the first distributed unit 1061. According to the second variant 110, the first distributed unit 1061 can receive the measurement report from UE 108 via the first centralized unit 1041, the second centralized unit 1042, and the second distributed unit 1062. Here, due to LTM execution failure, no link is established between the UE and the first distributed unit 1061, therefore the second distributed unit 1062 can receive the measurement report from UE 108. The second distributed unit 1062 can send the measurement report to the second centralized unit 1042. The second centralized unit 1042 can receive the measurement report including L3 and L1 measurement reports. The second centralized unit 1042 can send the L1 measurement report (received as a payload) to the first centralized unit 1041 via the Xn interface, and the L1 measurement report is then forwarded to the first distributed unit 1061 via the F1 interface.

[0067] Step 506 is similar to step 406, and will not be repeated for the sake of brevity.

[0068] In step 508, information about a new target cell can be sent to UE 108. Here, the first distributed unit 1061 can be configured to send information about a new target cell when the radio conditions of the new target cell are satisfactory and the new cell is ready for LTM. In one embodiment, the first distributed unit 1061 can send information about the new target cell in an LTM serving cell handover command or DLMAC CE to perform an LTM cell handover. The first distributed unit 1061 can send information about the new target cell from the first centralized unit 1041 via the Xn+F1 interface, through the second centralized unit 1042 and the second distributed unit 1062. When the new target cell is unavailable, information about at least one candidate / new target cell can be sent from the first centralized unit 1041 via the Xn+F1 interface, through the second centralized unit 1042 and the second distributed unit 1062.

[0069] Figure 6 An embodiment of the first distributed unit 600 is shown. For example... Figure 6 As shown, the first distributed unit 600 includes a processor 602, a memory 604, a storage component 606, an input component 608, an output component 610, a communication interface 612, and a bus 614. The first distributed unit 600 can be used to implement... Figure 2 The first distributed unit 1061. Therefore, according to embodiments of this disclosure, the first distributed unit 600 can be used to perform the LTM recovery process.

[0070] As used herein, processor 602 refers to any type of computing circuit that may include hardware and software elements. Processor 602 may be embodied as a multi-core processor, a single-core processor, or a combination of one or more multi-core processors and / or one or more single-core processors, a distributed processing system, etc. Processor 602 may be a central processing unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU), an application-specific integrated circuit (ASIC), or another type of processing component. Processor 602 can be used to implement... Figure 2 The processor 206 is described in the document.

[0071] Memory 604 includes a non-transitory computer-readable medium. Memory 604 includes random access memory (RAM), read-only memory (ROM), and / or another type of dynamic or static storage device (e.g., flash memory, magnetic storage, and / or optical storage) that stores information and / or instructions for use by processor 602. Memory 604 includes machine-readable instructions executable by processor 602. When executed by processor 602, these machine-readable instructions cause processor 602 to perform one or more method steps of the above embodiments. Memory 604 can be used to implement... Figure 2 The memory 604 is described in the present disclosure. The memory 604 is communicatively coupled to the processor 602. According to embodiments of the present disclosure, the memory 604 stores instructions executable by one or more processors 602, which, when executed, cause the processor 602 to perform an LTM recovery process.

[0072] Storage component 606 stores information and / or software related to the operation and use of the first distributed unit 600. For example, storage component 606 may include a hard disk (e.g., a magnetic disk, optical disk, magneto-optical disk, and / or solid-state disk), an optical disk (CD), a digital versatile disk (DVD), a floppy disk, a cassette tape, a magnetic tape, and / or another type of non-transitory computer-readable medium, and a corresponding drive.

[0073] Input component 608 is configured to receive information, such as user input. For example, input component 608 may include, but is not limited to, a touchscreen display, keyboard, keypad, mouse, button, switch, and / or microphone. Additionally or alternatively, input component 608 may include sensors for sensing information (e.g., Global Positioning System (GPS), accelerometer, gyroscope, and / or actuator).

[0074] Output component 610 is configured to provide output information from the first distributed unit 600. For example, output component 610 may be, but is not limited to, a display, a speaker, instructions to external devices, and / or one or more light-emitting diodes (LEDs).

[0075] Communication interface 612 provides a communication connection to other devices, such as external and internal devices. The connection implemented by communication interface 612 can be a wired connection, a wireless connection, or a combination of wired and wireless connections, and can be a direct or indirect connection via a communication network existing between the first distributed unit 600 and other devices. In other words, the standard of communication interface 612 is not limited. Computer system 600 can communicate with second distributed unit 1062, centralized unit 104, and UE via communication network 609.

[0076] Bus 614 serves as an interconnect between the processor 602, memory 604, storage component 606, input component 608, output component 610, and communication interface 612 of the first distributed unit 600. Bus 614 may include wired or wireless interconnects.

[0077] Figure 6 The number and arrangement of components shown are provided as an example. In practice, with Figure 6 Compared to the examples shown, the first distributed unit 600 may include more components, fewer components, different components, or components arranged differently. Additionally or alternatively, a set of components of the first distributed unit 600 (e.g., one or more components) may perform one or more functions described as being performed by another set of components of the first distributed unit 600. Furthermore, one or more method steps described in any embodiment may be performed using multiple first distributed units 600 communicating with each other.

[0078] In one embodiment, this disclosure discloses a method comprising: detecting an LTM execution failure of a low-level triggered mobility (LTM) cell handover for a user equipment (UE) (108) configured with dual connectivity, the LTM execution failure being for a target cell hosted by a first distributed unit (1061). The method includes: receiving from the UE (108) a measurement report of a plurality of LTM candidate cells belonging to a cell group associated with the failure via a centralized unit (104) and a second distributed unit (1062). The centralized unit (104) is connected to the first distributed unit (1061) and the second distributed unit (1062). Furthermore, the method includes: identifying a new target cell for the LTM cell handover based on the measurement report, wherein the new target cell exists among the plurality of LTM candidate cells belonging to the cell group associated with the failure. Thereafter, the method includes: sending information about the new target cell to the UE (108) via the centralized unit (104) and the second distributed unit (1062) from the first distributed unit (1061) for performing the LTM cell handover.

[0079] In one embodiment, the measurement report received from the UE (108) is an L1 measurement report.

[0080] In one embodiment, the method further includes: determining that the new target cell does not exist among multiple LTM candidate cells belonging to a cell group associated with failure; and receiving information on at least one new candidate / target cell from a centralized unit (104) for performing LTM candidate / target cell preparation and cell handover. The centralized unit (104) prepares at least one new candidate / target cell for LTM cell handover based on an L3 measurement report received from the UE (108). Information on at least one new candidate / target cell is transmitted to the UE (108) via the centralized unit (104) and the second distributed unit (1062).

[0081] In one embodiment, the method includes: detecting a failure in an LTM recovery attempt when LTM execution fails.

[0082] In one embodiment, a first distributed unit (1061) hosts the primary cell group (MCG), and a second distributed unit (1062) hosts the secondary cell group (SCG). In another embodiment, the first distributed unit (1061) hosts the SCG, and the second distributed unit (1062) hosts the MCG.

[0083] In one embodiment, information about the new target cell is transmitted to the UE (108) via the F1 interface through the centralized unit (104) and the second distributed unit (1062).

[0084] In one embodiment, this disclosure discloses a first distributed unit (1061). The first distributed unit (1061) detects a low-level triggered mobility (LTM) cell handover failure of a user equipment (UE) (108) configured with dual connectivity, the LTM execution failure being for a target cell hosted by the first distributed unit (1061). Furthermore, the first distributed unit (1061) receives measurement reports from the UE (108) via a centralized unit (104) and a second distributed unit (1062) for multiple LTM candidate cells belonging to the cell group associated with the failure. The centralized unit (104) is connected to the first distributed unit (1061) and the second distributed unit (1062). Additionally, based on the measurement reports, the first distributed unit (1061) identifies a new target cell for the LTM cell handover, wherein the new target cell exists among the multiple LTM candidate cells belonging to the cell group associated with the failure. The first distributed unit (1061) sends information about the new target cell to the UE (108) via the centralized unit (104) and the second distributed unit (1062) for performing LTM cell handover.

[0085] In one embodiment, a first distributed unit (1061) is configured to determine that a new target cell does not exist among multiple LTM candidate cells belonging to a cell group associated with failure. The first distributed unit (1061) receives information about at least one new candidate / target cell from a centralized unit (104) for performing LTM candidate / target cell preparation and cell handover. The centralized unit (104) prepares at least one new candidate / target cell for LTM cell handover based on an L3 measurement report received from the UE (108). Information about at least one new candidate / target cell is transmitted to the UE (108) via the centralized unit (104) and the second distributed unit (1062).

[0086] In one embodiment, the first distributed unit (1061) detects the failure of LTM execution between the UE (108) and the target cell by: detecting the failure in the LTM recovery attempt when LTM execution fails.

[0087] In one embodiment, the first distributed unit (1061) transmits information about the new target cell to the UE (108) via the F1 interface, through the centralized unit (104) and the second distributed unit (1062).

[0088] In one embodiment, this disclosure discloses a non-transitory computer-readable medium including instructions for performing operations including: detecting an LTM execution failure of a low-level triggered mobility (LTM) cell handover for a user equipment (UE) (108) configured with dual connectivity, the LTM failure being for a target cell hosted by a first distributed unit (1061). Furthermore, the operation includes: receiving from the UE (108) a measurement report of a plurality of LTM candidate cells belonging to a cell group associated with the failure via a centralized unit (104) and a second distributed unit (1062), wherein the centralized unit (104) is connected to the first distributed unit (1061) and the second distributed unit (1062). Furthermore, the operation includes: identifying a new target cell for the LTM cell handover based on the measurement reports, wherein the new target cell exists among the plurality of LTM candidate cells belonging to the cell group associated with the failure. Thereafter, the operation includes: sending information about the new target cell to the UE (108) via the centralized unit (104) and the second distributed unit (1062) for performing the LTM cell handover.

Claims

1. A method comprising: The first distributed unit detects a low-level triggered mobility (LTM) cell handover failure of a user equipment (UE) configured with dual connectivity, the LTM execution failure being for a target cell hosted by the first distributed unit; The first distributed unit receives measurement reports of multiple LTM candidate cells belonging to the cell group associated with the failure from the UE via a centralized unit and a second distributed unit, wherein the centralized unit is connected to the first distributed unit and the second distributed unit. Based on the measurement report, the first distributed unit identifies a new target cell for the LTM cell handover, wherein the new target cell exists among the plurality of LTM candidate cells belonging to the cell group associated with the failure; as well as The first distributed unit sends information about the new target cell to the UE via the centralized unit and the second distributed unit to perform the LTM cell handover.

2. The method of claim 1, wherein the measurement report received from the UE is an L1 measurement report.

3. The method according to claim 1, further comprising: It is determined that the new target cell does not exist among the plurality of LTM candidate cells belonging to the cell group associated with the failure; as well as The centralized unit receives information on at least one new candidate / target cell for performing LTM candidate / target cell preparation and cell handover, wherein the centralized unit prepares the at least one new candidate / target cell for the LTM cell handover based on the L3 measurement report received from the UE. The information of at least one new candidate / target cell is transmitted to the UE via the centralized unit and the second distributed unit.

4. The method of claim 1, wherein detecting the LTM execution failure for the UE in the target cell comprises: When the LTM execution fails, the failure in the LTM recovery attempt is detected.

5. The method according to claim 1, wherein the first distributed unit hosts the primary cell group (MCG), and the second distributed unit hosts the secondary cell group (SCG).

6. The method of claim 1, wherein the first distributed unit hosts the SCG, and the second distributed unit hosts the MCG.

7. The method according to claims 1 and 3, wherein the information of the new target cell is transmitted to the UE via the F1 interface, through the centralized unit and the second distributed unit.

8. A first distributed unit, configured as follows: The LTM execution failure of a low-layer triggered mobility (LTM) cell handover of a user equipment (UE) configured with dual connectivity is detected, the LTM execution failure being for a target cell hosted by the first distributed unit; Measurement reports of multiple LTM candidate cells belonging to the cell group associated with the failure are received from the UE via a centralized unit and a second distributed unit, wherein the centralized unit is connected to the first distributed unit and the second distributed unit. Based on the measurement report, a new target cell is identified for the LTM cell handover, wherein the new target cell exists among the plurality of LTM candidate cells belonging to the cell group associated with the failure; as well as The information of the new target cell is sent to the UE via the centralized unit and the second distributed unit to perform the LTM cell handover.

9. The first distributed unit of claim 8, wherein the measurement report received from the UE is an L1 measurement report.

10. The first distributed unit according to claim 8 is further configured as follows: It is determined that the new target cell does not exist among the plurality of LTM candidate cells belonging to the cell group associated with the failure; and The centralized unit receives information on at least one new candidate / target cell for performing LTM candidate / target cell preparation and cell handover, wherein the centralized unit prepares the at least one new candidate / target cell for the LTM cell handover based on the L3 measurement report received from the UE. The information of at least one new candidate / target cell is transmitted to the UE via the centralized unit and the second distributed unit.

11. The first distributed unit according to claim 8, detecting LTM execution failure for the UE in the target cell by: When the LTM execution fails, the failure in the LTM recovery attempt is detected.

12. The first distributed unit according to claim 8, wherein the first distributed unit hosts the primary cell group (MCG) and the second distributed unit hosts the secondary cell group (SCG).

13. The first distributed unit according to claim 8, wherein the first distributed unit hosts the SCG and the second distributed unit hosts the MCG.

14. The first distributed unit according to claims 8 and 10, transmits the information of the new target cell to the UE via the centralized unit and the second distributed unit through the F1 interface.

15. A non-transitory computer-readable medium comprising instructions for performing operations, the operations including: The LTM execution failure is detected for a user equipment (UE) configured with dual connectivity, and the LTM execution failure is for a target cell hosted by the first distributed unit; Measurement reports of multiple LTM candidate cells belonging to the cell group associated with the failure are received from the UE via a centralized unit and a second distributed unit, wherein the centralized unit is connected to the first distributed unit and the second distributed unit. Based on the measurement report, a new target cell is identified for the LTM cell handover, wherein the new target cell exists among the plurality of LTM candidate cells belonging to the cell group associated with the failure; as well as The information of the new target cell is sent to the UE via the centralized unit and the second distributed unit to perform the LTM cell handover.

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