LTM fault handling using a fallback configuration for either a user equipment (UE) wireless link fault (RLF) or handover (HO) fault.

Abstract

A fallback configuration is prepared for either a radio link failure (RLF) or a handover (HO) failure of the user equipment (UE). Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) candidate cells for fallback are identified. An HO failure or RLF is predicted for the LTM target cell, and at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration is prepared for the target cell selected from one or more LTM candidate cells. The UE is provided with at least one of the prepared fallback LTM configurations or fallback CHO configurations for the target cell. Based on at least one of the prepared fallback LTM configurations or fallback CHO configurations for the target cell, control information is sent to the UE to initiate a cell switch from the serving cell to the target cell.

Description

Technical Field

[0001] This description relates to LTM failure handling using a fallback configuration for one of radio link failure (RLF) or handover (HO) failure of a user equipment (UE), and a method of using the same.

Background Art

[0002] Layer 1 / Layer 2 triggered mobility (LTM) is fundamentally different from traditional or legacy layer 3 mobility with respect to its execution. The concept of layer 3 mobility or baseline mobility or legacy mobility is centered around a network that configures a user equipment (UE) with radio resource control (RRC) measurement results or layer 3 measurement results, uses those measurement results for the preparation of a target cell, and subsequently sends a handover command to the UE. The target cell configuration and the handover command are provided to instruct the UE to hand over to the target cell. For LTM, the UE may be configured for lower layer mobility such as layer 1 (L1) / layer 2 (L2) triggered mobility, where the UE may dynamically execute handover procedures for different cells in the same or neighboring base stations, and may also execute lower layer handover procedures.

[0003] The difference between L3 mobility and L1 / L2 triggered mobility is that in L3 mobility, the UE is configured to provide RRC measurement results. As usual, the UE provides them in L3 messages going to the gNB's aggregation unit (CU) using the RRC protocol, and the CU determines the candidate / target cells (i.e., one or more target / candidate cells) to be prepared for mobility, which may be legacy L3 HO or advanced L3 HO such as conditional HO (CHO) or dual active protocol stack (DAPS HO), and the CU contacts the corresponding DU to prepare the target cell configuration. The target cell configuration and L3 HO commands are obtained by the CU and sent to the UE. In the case of CHO, there are no HO commands from the gNB, but HO criteria are sent to the UE, and whenever the HO criteria are satisfied, the UE autonomously executes the HO. The fundamental difference with L1 / L2 HO is that, following the existing principles of baseline handover, the execution of the handover is performed using the L1 / L2 protocol while the preparation for the handover is being performed. In other words, L1 / L2 cell-centric mobility involves a UE receiving L1 / L2 signaling during cell switching, instead of RRC signaling as in the case of L3. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] For example, in response to an LTM handover (HO) failure due to a sudden wireless link failure (RLF), configuration failure, or non-delivery of Media Access Control (MAC) control element (CE) HO commands, RRC re-establishment is performed, as in any other mobility procedure. However, RRC re-establishment is a costly procedure for the network and the UE. The UE loses its user plane session, and data transfer is interrupted. For this reason, RRC re-establishment should be avoided whenever possible.

[0005] In the event of an LTM HO failure, as a fallback to prevent the UE from performing RRC re-establishment, the UE may consider one of the LTM candidate cells and autonomously perform RACH to gain access to the candidate cell (without an explicit HO command from the network). Of course, such a scenario is based on the candidate / target cell being visible to the UE and satisfying certain predetermined radio conditions. However, multiple LTM candidate cells may be configured to be fully reserved and used for UEs without resources. That is, resource reservation is delayed until a candidate cell with good radio conditions is reported by the UE in an L1 measurement report for serving or target gNB-DU. For candidate cells with other resources reserved, the RACH resource may not need to be reserved at the time of target cell configuration preparation, as it may depend on the UE's beam / beam group, which may change by the time the UE arrives at the target cell.

[0006] The reservation of the RACH preamble ensures that the correct RACH preamble corresponding to the UE's best beam in the candidate cell can be reserved later as the UE moves closer to the candidate cell boundary. Under these conditions, the UE cannot autonomously or arbitrarily select an LTM candidate cell. [Means for solving the problem]

[0007] In at least one embodiment, a method for preparing a fallback configuration for one of a user equipment (UE) radio link failure (RLF) or handover (HO) failure is to identify one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, predict at least one HO failure or RLF for one or more LTM target cells, and, in response to predicting at least one RLF or HO failure for one or more LTM target cells, to prepare a fallback configuration for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells. The process includes preparing at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration; providing the UE with at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the target cells; and sending control information to the UE to initiate a cell switch by the UE from the serving cell to at least one of the LTM target cells based on at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the LTM target cells.

[0008] In at least one embodiment, a radio access network (RAN) node includes a memory for storing computer-readable instructions and a processor connected to the memory, which identifies one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, predicts at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, and, in response to predicting at least one HO failure or RLF for one or more LTM target cells, configures a fallback LTM configuration or fallback for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells. The system includes a processor configured to execute computer-readable instructions to perform the following: prepare at least one back-conditional handover (CHO) configuration; provide a user device (UE) with at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells; and send control information to the UE to initiate a cell switch by the UE from a serving cell to at least one of the one or more LTM target cells based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells.

[0009] In at least one embodiment, a non-transient computer-readable medium, depending on what is performed by the processor, identifies one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback for a user device (UE), predicts at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, and, depending on what is performed, for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells, a fallback LTM configuration or fallback conditional handover configuration is applied. The system stores computer-readable instructions causing the processor to perform an operation that includes preparing at least one crossover (CHO) configuration, providing the UE with at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the LTM target cells, and sending control information to the UE to initiate a cell switch by the UE from the serving cell to at least one of the LTM target cells, based on at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the LTM target cells. [Brief explanation of the drawing]

[0010] Aspects of this disclosure are best understood from the following detailed description, when read in conjunction with the accompanying drawings. Note that, in accordance with industry practice, various features are not depicted to actual size. In fact, the dimensions of various features may be increased or decreased for the sake of clarity in the discussion.

[0011] Figure 1 illustrates a fragmented radio access network (RAN) architecture according to at least one embodiment.

[0012] Figure 2 illustrates the entire procedure for LTM according to at least one embodiment.

[0013] Figures 3A and 3B illustrate a process for handling LTM failures according to at least one embodiment.

[0014] Figure 4 is a flowchart of a method for handling LTM handover failures or wireless link failures according to at least one embodiment.

[0015] Figure 5 is a high-level functional block diagram of a processor-based system according to at least one embodiment. [Modes for carrying out the invention]

[0016] The embodiments described herein describe examples for implementing different features of the subject matter provided. Examples of components, values, operations, materials, arrangements, etc., are described below for the sake of simplicity of this disclosure. These are, needless to say, examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, etc., are also conceivable. For example, the formation of a first feature above or on a second feature in the following descriptions includes embodiments in which the first and second features are formed in direct contact, and embodiments in which an additional feature is formed between the first and second features so that the first and second features are not in direct contact. In addition, this disclosure repeats reference numbers and / or letters in various examples. This repetition is for simplicity and clarity and does not indicate relationships between the various embodiments and / or configurations discussed.

[0017] Furthermore, spatially relative terms such as "beneath," "below," "lower," "above," and "upper" are used here for ease of description in describing the relationship between one element or feature to other elements or features, as illustrated in the diagram. The spatially relative terms are intended to encompass different orientations of the device during use or operation, in addition to the orientation shown in the diagram. The device may be oriented in other directions (rotated 90 degrees or in other directions), and the spatially relative descriptors used here are interpreted accordingly.

[0018] Terms such as "user equipment," "mobile station," "mobile," "mobile device," "subscriber station," "subscriber equipment," "access terminal," "terminal," and "handset," and similar terms, refer to wireless devices used by subscribers or users of wireless communication services to receive or transmit data, control, voice, video, sound, gaming, data streaming, or signaling streaming. The above terms are used interchangeably in the subject matter specification and related drawings. Terms such as "access point," "base station," "Node B," "evolved Node B (eNode B)," "next generation Node B (gNB)," "enhanced gNB (en-gNB)," "home Node B (HNB)," and "home access point (HAP)" refer to wireless network components or devices that provide and receive data, control, voice, video, sound, gaming, data streaming, or signaling streaming to and from the UE.

[0019] In at least one embodiment, a method for preparing a fallback configuration for one of a user equipment (UE) radio link failure (RLF) or handover (HO) failure is to identify one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, predict at least one HO failure or RLF for one or more LTM target cells, and, in response to predicting at least one RLF or HO failure for one or more LTM target cells, to prepare a fallback configuration for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells. The process includes preparing at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration; providing the UE with at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the target cells; and sending control information to the UE to initiate a cell switch by the UE from the serving cell to at least one of the LTM target cells based on at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the LTM target cells.

[0020] The embodiments described herein provide a method that offers one or more advantages. For example, RRC re-establishment can be avoided during a radio link failure (RLF) or LTM handover (HO) failure.

[0021] Figure 1 illustrates a fragmented wireless access network (RAN) architecture 100 according to at least one embodiment.

[0022] In Figure 1, UE1 (User Equipment 1) 110, UE2 112, UE3 114, and UE4 116 access the mobile network via RAN 100. The wireless access network 100 includes wireless towers 120, 123, and 125. Wireless towers 120, 123, and 125 are associated with RU (Radio Unit) 1 122, RU2 124, and RU3 126, respectively.

[0023] RU1 122, RU2 124, and RU3 126 handle the digital front end (DFE), the PHY layer portion, and digital beamforming functionality. RU1 122 and RU2 124 are associated with the gNB-DU1 130, and RU3 126 is associated with the gNB-DU2 132. The gNB-DU1 130 and gNB-DU2 132 are responsible for real-time Layer 1 and Layer 2 scheduling functions. For example, in 5G, Layer 1 is the physical layer, Layer 2 includes the Media Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers, and Layer 3 (Network Layer) is the Radio Resource Control (RRC) layer. Layer 2 is the data link or protocol layer that determines how data packets are encoded and decoded and how data is transferred between adjacent network nodes. Layer 3 is the network routing layer, which defines how data moves across the physical network.

[0024] gNB-DU1 130 is coupled to RU1 122 and RU2 124, and gNB-DU2 132 is coupled to RU3 126. gNB-DU1 130 and gNB-DU2 132 perform the Radio Link Control (RLC), MAC, and Physical (PHY) layer portions. gNB-DU1 130 and gNB-DU2 132 include a subset of eNB / gNB functions depending on the function split option, and the operation of gNB-DU1 130 and gNB-DU2 132 is controlled by the Aggregation Unit (CU) 140. gNB-CU 140 is responsible for non-real-time, higher L2 and L3 network layer functions. The server and associated software for gNB-CU 140 may be hosted on-site or in an edge cloud (data center or central office), depending on the transport availability and interfaces for fronthaul connections 150, 152, and 154. The gNB-CU140 server and associated software can be located in the same location as the gNB-DU1 130 or gNB-DU2 132, or they can be hosted in a regional cloud data center.

[0025] The gNB-CU140 handles the RRC and PDCP layers. The gNB-CU140 includes a gNB-CU-Control Plane (CU-CP) 142 and one or more gNB-CU-User Plane (CU-UP) 144 respectively. The gNB-CU-CP142 is a logical node that hosts the RRC and control plane parts of the PDCP protocol for the gNB100. The gNB-CU-UP144 is a logical node that hosts the user plane part of the PDCP protocol of the gNB-CU140 and the SDAP protocol of the gNB-CU142. The gNB-DU1 130 and gNB-DU1 132 are connected to the gNB-CU-CP142 via the Fs-C160, and the gNB-DU1 130 and gNB-DU1 132 are connected to one or more gNB-CU-UP via the Fs-U162 interface. The split architecture enables the 5G network to utilize different distributions of the protocol stack among the gNB-CU140, gNB-DU1 130, and gNB-DU2 132 according to the network design and the availability of the midhole connection 156. The gNB-CU-CP142 is coupled to one or more gNB-CU-UP144 via one or more E1 interfaces 170.

[0026] In FIG. 1, two connections between the gNB-CU140, gNB-DU1 130, and gNB-DU2 132 are shown. The gNB-CU140 can implement additional connections to other gNB-DUs (not shown). The gNB-CU140 can implement, for example, 256 endpoints or gNB-DUs in 5G. The gNB-CU140 supports gNB functions such as user data transfer, mobility control, RAN sharing (MORAN), positioning, session management, etc. However, one or more functions can be assigned to the gNB-DU1 130 and gNB-DU2 132. The gNB-CU140 controls the operations of the gNB-DU1 130 and gNB-DU2 132 on the midhole interface 156.

[0027] FIG. 2 illustrates an overall procedure 200 for LTM according to at least one embodiment.

[0028] In FIG. 2, UE 210 and gNB 220 are shown. gNB 220 includes one or more DUs 222 and CUs 224. Mobility enhancement 3rd Generation Partnership Project (3GPP) Release 18, RP-213565 defines L1 / L2-based inter-cell mobility mechanisms and procedures for mobility latency reduction. L1 / L2-based inter-cell mobility involves stand-alone, carrier aggregation (CA), and New Radio dual connectivity (NR-DC) cases with serving cell changes within one cell group (CG), in-DU cases, and in-CU DU-to-DU cases (applicable for stand-alone and CA: no new radio access network (RAN) interface is assumed), applicable within and between frequencies, and the frequency range 1 (FR1) and FR2 source and target cells may or may not be synchronized.

[0029] The execution of the LTM handover (HO) occurs at DU222. Information regarding which target cell or candidate cell is configured for the LTM is provided to UE210 and serving gNB220. A candidate cell is a cell prepared for future mobility executions. A target cell is an LTM candidate cell selected for the LTM serving cell change or handover. According to the embodiments described herein, candidate cell and target cell are used as common terms. Also, handover, cell switch, and serving cell change are used synonymously in the embodiments described herein. Thus, LTM handover or LTM serving cell change has the same meaning as used herein. The serving gNB is the cell that UE210 uses for service and has a radio link to the serving cell. The corresponding DU associated with that cell is called serving DU222. Information regarding which other cells are configured as LTM candidate cells is provided to serving DU222 and UE210.

[0030] The UE210 is configured to report L1 measurement results for candidate cells. The UE210 continues to periodically report these L1 measurement results to the serving DU222, and based on these L1 measurement results, the serving DU222 makes a decision regarding the LTM serving cell based on the time and threshold at which the UE210 should hand over to one of the other candidate cells (which will become the target cell). Candidate cells may be within the same DU222 or within another DU (not shown) of the same gNB220. However, since 3GPP Release 18 limits LTM functionality to one gNB, candidate cells must not be outside of the gNB220. For inter-gNB mobility, the L3 mobility procedure is used.

[0031] While it is not yet codified that the number of candidate cells is limited to eight, there can be, for example, up to eight candidate cells. However, previous 3GPP releases agreed to limit the number of candidate cells for a UE to eight. For example, a feature called conditional handover can be used to provide a target cell configuration to the UE. Based on this agreement, eight candidate cells is a reasonable assumption, however the number may be expanded. Thus, UE210 can be configured with eight candidate cells, one of which can be selected as the target cell. The target cell is selected by the serving gNB-DU222 based on periodic measurements received from UE210 or measurements based on events.

[0032] In Figure 2, the first phase is LTM preparation 230. UE210 is in RRC connection state 232. UE210 sends an L3 measurement report message 234 to gNB220. In Figure 2, CU224 and DU222 are shown as parts of the same gNB220.

[0033] After receiving the L3 measurement report 234, gNB220 decides to use LTM for the UE and initiates LTM candidate cell preparation 236 (for example, gNB220 prepares one or more candidate cells). This involves CU224 sending an F1 message to DU222, and DU222 responding with the candidate cell configuration.

[0034] The gNB220 sends an RRC reconfiguration message 237 to the UE210, which includes the configuration of one or more LTM candidate target cells.

[0035] UE210 stores the configuration 238 of the LTM candidate target cell and sends an RRC reconfiguration complete message 239 to gNB220 to indicate that the RRC reconfiguration procedure is complete.

[0036] Early synchronization 240 can be performed using DL synchronization and TA acquisition with candidate cell 240, and UL synchronization and TA acquisition with candidate cell 244, while UE210 is still connected to the old serving cell. DL synchronization for candidate cell 242 before the cell switch command is supported based on at least SSB. TA acquisition of candidate cells before the LTM cell switch command is supported based on at least PDCCH order RACH, where the PDCCH order is triggered by the source cell.

[0037] Subsequently, when the cell switch criteria are satisfied, LTM execution 250 is performed. UE210 performs an L1 measurement on the configured LTM candidate target cell and sends an L1 measurement report 252 to gNB220. The L1 measurement report 252 is provided to DU222 but not to CU224. Then, gNB220 makes an LTM cell switch decision 254 to initiate the LTM cell switch to the target cell by selecting one of the candidate configurations in the target configuration for LTM and sending a MAC CE message accompanied by an LTM cell switch command 256 containing the candidate configuration index of the target cell.

[0038] After receiving MAC CE256, UE210 applies target cell configuration 258 to leave the serving cell and switch to the configuration of the LTM candidate / target cell. Candidate cell configurations may be added, modified, or released by the network via RRC signaling.

[0039] The optional RACH procedure 260 is executed (as indicated by the dotted line). For example, the RACH procedure is used depending on whether a TA is available. Depending on whether a target cell TA is available, the RACH-less HO procedure is not executed. Not all LTM HO procedures use the RACH procedure 260.

[0040] Once the LTM execution is complete and the LTM cell switch to the UE's target cell is successful, the LTM completion stage 270 begins. An RRC configuration complete message 272 is sent from the UE210 to the gNB220. The RRC configuration complete message 272 indicates that the previously sent RRC configuration has been successfully applied. Subsequent LTMs are executed by repeating the early synchronization, LTM execution, and LTM completion steps without releasing any other candidates after the LTM completion.

[0041] However, LTM handover failures or serving cell LTM switch failures may occur. Failures may occur, for example, due to RLF or LTM HO failures for failure to receive RRC message 237 carrying the LTM candidate configuration to UE210, failure to receive MAC CE 256 by UE210, loss of radio link, or configuration failure. For example, the LTM candidate configuration 237 sent to UE210 for the target cell may not be properly decoded or recognized. Decoding failures can also occur due to failure to deliver MAC CE handover command 256. In the case of an RLF in the context of an LTM HO failure, RRC re-establishment occurs, as in the case of any other mobility procedure.

[0042] RRC re-establishment is a costly procedure for the network and UE because it results in the loss of user plane sessions and longer interpretation times for data transfers. However, the goal is to avoid RRC re-establishment whenever possible.

[0043] The fallback mechanism allows the UE210 to autonomously execute RACH procedure 260 (without an explicit HO command received from the network) to consider one of the LTM candidate cells and gain access if the candidate cell is visible to the UE210 and satisfies certain predetermined radio conditions. In such a scenario, one of the LTM candidate cells is autonomously selected by the UE210, and RACH procedure 260 is executed to gain network access. Such a solution has been considered in the past for conditional handover (CHO). CHO is a UE-based handover where the target cell configuration and conditions are provided to the UE210. Depending on whether the conditions provided by the network are satisfied in the UE210, the UE210 autonomously performs the handover, which does not depend on a handover command, or even on a MAC CE from the network side. Thus, the UE performs the handover without the network instructing the UE210 to perform the handover.

[0044] Thus, based on these principles, a fallback may be considered when one of the LTM candidates is selected to run RACH260 without an explicit handover command. There may be multiple LTM candidate cells configured for UE210 without requiring resources to be reserved and used for the network to gain access. However, considering multiple cells, resource reservations in those cells, thousands of UEs residing in those cells, and numerous resource reservations would be too costly for the operator.

[0045] Therefore, for all cells and cell sizes involving thousands of UEs, it is impossible to reserve candidate cell resources for a single UE210. Such a process is extremely cumbersome and involves many repercussions for the network and the UE210, as the UE210 must store the configuration, continuously receive timing alignment timing advances (TAs), and also report measurement results for the configured cells. Thus, the CHO is very complex, and an alternative is to ensure that the target configuration is sent to the UE210.

[0046] As a result, not all resources are reserved during LTM target cell preparation. Resources are reserved as the UE210 approaches one of the candidate cells. The likelihood of the UE210 experiencing a HO failure while going to a particular cell or one or more candidate cells is determined. For example, if there are eight candidate cells and the UE moves from the serving cell to one of the candidate / target cells based on a cell switch command, a fallback configuration must be prepared for the candidate cell where the UE has a high probability of experiencing an LTM cell switch failure. Two cells may be predicted based on measurement results or radio conditions, or an AI-ML-based prediction algorithm. The prediction identifies which of the eight LTM candidate cells is more susceptible to handover failures based on the UE210 approaching a candidate cell, or by transmitting measurement results from a neighboring cell, which the serving DU222 then communicates to the target cell. Such handover failures can be predicted based on historical data. Based on this handover failure prediction, candidate and resource reservations may only be made if the UE210 reports good wireless conditions for a given candidate cell. Resource reservations are delayed until good wireless conditions are reported by the UE. In the L1 measurement report for serving DU222, resources for candidate cells are not reserved until the UE210 reports a candidate cell with good wireless conditions. However, this may differ for candidate cells susceptible to LTM cell switch failures, as they require a fallback configuration.

[0047] For candidate cells where other Radio Resource Management (RRM) resources are reserved, such as those for critical UEs, the RACH preamble cannot be reserved to ensure that the correct RACH preamble corresponding to the best beam for UE210 in the candidate cell can be reserved later, depending on UE210's proximity to the candidate cell boundary. Pre-reserving the RACH preamble would, in a sense, also mean determining a beam or beamgroup for UE210, but this is highly speculative, or at least suboptimal, because the beamgroup to which UE210 should be associated is not known in advance. Determining the actual beamgroup and performing the correct RACH preamble assignment is more appropriate than pre-performing the correct RACH preamble assignment.

[0048] In these situations, UE210 does not know which resources are reserved, whether the RACH preamble is reserved, etc., and therefore cannot select an LTM candidate cell for fallback from among the eight candidate cells to autonomously or arbitrarily perform RACH operation 260.

[0049] Figures 3A and 3B illustrate a process 300 for LTM fault handling according to at least one embodiment.

[0050] In Figures 3A-B, process 300 for LTM failure handling includes preparing a fallback handover configuration for autonomous execution by UE310 and a process for performing cell selection. UE310 is configured with LTM candidate cells in one or more distributed units (DUs) 312 (320). Periodic resource status update (RSU) messages 322 are provided to the aggregate unit (CU) 316 from the serving / candidate DUs 312 / 314 / 318 via the F1 interface. However, according to at least one embodiment, RLF and LTM HO failure data 323 are added to the periodic resource status update message 322 so that RLF and LTM HO failure data 323 are periodically collected for gNB-DU in-situations. CU316 also stores RLF and LTM HO failure data 323 for gNB-DU inter-scenarios, which are provided to CU316 from neighboring / target cells (DU2 314) (324) and from candidate cells, DU3 318 (326). In this way, CU316 can identify one or more LTM candidate cells 314, 318 for fallback by identifying LTM candidate cells that are susceptible to cell switch / handover failures. Identifying one or more LTM candidate cells 314, 318 for fallback involves identifying which of the LTM candidate cells 314, 318 of the configured UE310 are eligible to be configured for fallback. One or more LTM candidate cells 314, 318 can be identified by receiving periodic resource status updates 322 from one or more gNB distributed units (DUs) 312, 314, 318. Here, the periodic resource status update 322 includes HO failure data 323 for one or more LTM candidate cells 314, 318. The HO failure data 323 for one or more LTM candidate cells 314, 318 includes data 323 indicating RLF or LTM HO failures associated with one or more LTM candidate cells 314, 318.HO failure data 323 for one or more LTM candidate cells 314, 318 of one or more gNB-DUs is accumulated over a period of 328.

[0051] Next, the RRC measurement result 330 is received by CU316 from UE310, and it is determined that a candidate cell for inter-DU LTM should be prepared (332). CU316 checks whether the candidate cell is susceptible to RLF or LTM HO failure 332. Depending on whether the candidate cell is susceptible to RLF or LTM HO failure 332, CU316 predicts at least one HO failure or RLF for one or more LTM target cells in candidate DU314, 318. CU316 determines full resource reservation and prepares fallback configurations for the identified candidate cells.

[0052] CU316 sends a UE310 context setup request 334, a full resource reservation, and flags indicating a fallback CHO configuration request to a neighbor / target cell (e.g., DU2 314) via the F1 interface. The neighbor / target cell (e.g., DU2 314) responds via the F1 interface with a UE context setup response 336. The UE context setup response 336 provides the cell group configuration to CU316. Subsequently, CU316 prepares and sends the fallback CHO configuration along with the LTM candidate configuration (338). At least one of the fallback LTM configuration or fallback conditional handover (CHO) configuration 338 is prepared for at least one target cell 314, 318 selected from one or more LTM candidate cells (332). Preparing the fallback CHO configuration for at least one target cell (332) may include obtaining the fallback CHO configuration from the target distribution unit (DU) 314. A fallback CHO configuration includes a delta and / or rule for converting an LTM target cell configuration to a fallback CHO configuration, or receiving a full fallback CHO configuration from target DU314. At least one fallback LTM configuration for at least one target cell may also include at least one fallback LTM configuration with full resource reservation, where the fallback CHO configuration includes at least fallback CHO criteria added to the LTM configuration. Preparing at least one fallback LTM configuration or fallback CHO configuration for at least one target cell (332) may further include determining, based on HO failure data 323, whether a handover to at least one target cell is susceptible to an HO failure.Depending on whether at least one target cell (e.g., DU2 314) is susceptible to HO failure, at least one neighboring candidate cell (e.g., candidate cell 318) of the target cell 314 is determined, and at least one fallback LTM configuration or fallback CHO configuration is prepared for the neighboring candidate cell 318 (332).

[0053] The downlink (DL) RRC message forwarding message 340, including the RRC reconfiguration with the prepared LTM target cell configuration and / or the fallback CHO configuration, is sent by CU316 to the serving DU (e.g., DU1 312). The RRC message 340 is the container inside the F1 message.

[0054] The serving DU (DU1 312) sends an RRC reconfiguration message 342 to the UE310, which includes the LTM target cell configuration and the fallback CHO configuration. In this way, the UE310 may be provided with a prepared fallback LTM configuration 342.

[0055] UE310 stores the LTM target cell configuration and fallback CHO configuration 344. The serving DU (DU1 312) sends a PDCCH order message 350, which includes at least the target cell PCI, to UE310.

[0056] The PDCCH order message 350 instructs the UE310 to perform UL synchronization using a random access message 352 to obtain the timing advance for one or more candidate cells. The UE310 sends a random access request message 352 containing the RACH preamble to the candidate DU (DU2 314).

[0057] The candidate DU (DU2 314) responds with a Random Access Response (RAR) message 354 that includes a timing advance (TA) for the candidate DU (DU2 314). The Random Access Response (RAR) message 354 carrying the TA for the candidate cell (DU2 314) can be sent directly from the candidate DU to the UE, but alternatively (360) it can be sent from the candidate DU (DU2 314) to CU316 (362), and then from CU316 to the serving DU (DU1 312) (364) for a subsequent transmission to the UE310 (366).

[0058] The UE310 acquires the target cell TA so that it can execute RACH-less HO370 when the LTM cell switch command is issued by the gNB-DU.

[0059] The in-frequency L1 measurement report 372 is sent from UE310 to the serving DU (DU1 312). The serving DU (DU1 312) determines the best target cell for UE310 to perform LTM HO to the cell of DU2 314, for example (374).

[0060] The DL MAC CE376 is sent from the serving DU (DU1 312) to the UE310. The MAC CE376 carries an LTM cell switch command that includes at least the target cell PCI and the target cell's beam identifier.

[0061] UE310 performs a RACH-less handover 378 to the target cell (DU2 314), which is expected to fail here.

[0062] UE310 detects an RLF or LTM HO failure 380. Depending on whether the CHO criteria are met, UE310 activates a fallback CHO configuration 382 and performs a fallback CHO to a selected fallback candidate cell 314.

[0063] Depending on whether the CHO criteria are met, UE310 performs a CHO to cell 314 by executing RACH384 based on how the network configured UE310. In this way, UE310 can autonomously perform cell switching 382 in the event of detecting a handover failure 380 without sending additional signaling.

[0064] As described herein, the fallback handover configuration is either an LTM handover configuration or a conditional handover (CHO) configuration 344. The LTM candidate cell configuration can be converted to a CHO autonomous configuration or target cell configuration in which the UE310 performs the target cell configuration without further signaling assistance from the network.

[0065] CU316 prepares a fallback CHO configuration by using the LTM candidate cell configuration and adding at least the CHO criteria and other necessary elements. CU316 transforms the LTM candidate cell configuration in response to the detection of an RLF or LTM HO failure (380), and UE310 is configured with either the LTM candidate cell configuration or the CHO configuration. For example, the CHO criteria are conditions that must be met before a handover can be performed. If the conditions are not met, UE310 cannot perform a CHO handover. The CHO criteria are provided with the configuration. Thus, the fallback configuration 344 may be the prepared LTM handover configuration, the prepared CHO configuration, or both, provided to UE310.

[0066] As previously mentioned, UE310 can be configured with multiple LTM candidate cells. In such a scenario, CU316 is configured to select target cells 314, 318 to which a fallback configuration should be applied, depending on whether resources have been reserved and whether a fallback configuration has been prepared or requested from target DU314, 318. Depending on the selection of a cell for the CHO fallback configuration from among the LTM candidate cells 314, 318, a full resource reservation is performed for that cell in the target gNB-DU. To assist or support such cell identification, AI-ML-assisted cell identification is used by CU316 to identify the cell and determine whether a full resource reservation should be applied rather than a partial or delayed resource reservation.

[0067] Serving DU312 and / or CU316 can perform RLF and HO handover failure data collection over a period of time to identify a given LTM target cell experiencing an RLF or HO failure. RLF and LTM HO failure data collection is accumulated for different DU312, 314, and 318. For example, in response to a handover from A (LTM serving cell) to B (LTM target cell), DU312 and CU316 prepare a list of serving cell 312 and target cells 314 and 318 that will suffer an RLF or LTM handover failure.

[0068] In response to gNB-CU316 performing gNB-DU inter-LTM candidate cell preparation for UE310 and recognizing that UE310 currently has serving cell A 312 and candidate cell B 314 must be prepared as the LTM target cell (i.e., UE310 has suffered an RLF or LTM HO failure from cell A 312 to cell B 314), CU316 checks the RLF and LTM HO failure data collected for the HO from cell A 312 to cell B 314.

[0069] In response to an RLF or LTM HO failure from cell A 312 to cell B 314, CU316 ensures that neighboring cells of candidate cell B 314 (e.g., candidate cell 318) are appropriately prepared for the fallback configuration, depending on whether cell B 314 is prepared or selected for the LTM HO. For example, depending on whether cells C and D (e.g., candidate cell 318) are neighboring cells of candidate cell B 314, and cells C and D (e.g., candidate cell 318) are also prepared as LTM candidate cells for the same UE310, CU316 requests an LTM target cell configuration with full resource reservation and prepares LTM and / or CHO fallback configurations for cells C and D (e.g., candidate cell 318).

[0070] In the case of inter-DU, serving DU 312 is unaware that an RLF or LTM HO failure has occurred, and CU 316 performs RLF and LTM HO failure data collection. For example, if UE 310 experiences an RLF while moving from serving cell A 312 to a cell belonging to a different DU (e.g., DU2 314), CU 316 performs RLF and LTM HO failure data collection. In the case of intra-DU, the DU is aware of both the source and target cells. Therefore, the DU can detect HO failures. This data is periodically reported to CU 316 by UE 310 and accumulated for different DUs 312, 314, and 318. This provides insight into which cells are susceptible to RLF or LTM HO failures and which cells are potentially resilient to handover failures or RLFs.

[0071] Thus, when CU316 performs inter-DU LTM candidate cell preparation for UE310 and determines that UE310 currently has serving cell A 312 and candidate cell B 314 should be prepared as the LTM target cell, CU316 checks whether RLF and LTM HO failures from cell A 312 to cell B 314 have occurred in the past. If CU316 determines that RLF and LTM HO failures from cell A 312 to cell B 314 have occurred in the past, CU316 ensures that neighboring cells of cell B (e.g., candidate DU3 318) are properly prepared for fallback, depending on whether cell B 314 is prepared or selected for the LTM handover.

[0072] CU316 requests an LTM target cell configuration with full resource reservation and also prepares LTM and / or CHO fallback configurations for cells C and D (e.g., candidate DU3 318). Thus, full resources are reserved for cells C and D (e.g., candidate DU3 318) and LTM or CHO fallback configurations are prepared for cells C and D (e.g., candidate DU3 318) so that UE310 has cells C and D (e.g., candidate DU3 318) as fallbacks in response to a cell switch failure while UE310 is moving to cell B 314. Cells C and D are used here as examples. Those skilled in the art will understand that the cells may be any other cells, including the previous serving cell.

[0073] Thus, according to at least one embodiment, a fallback configuration is prepared for either a radio link failure (RLF) or a handover (HO) failure of the user equipment (UE). One or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells are identified for fallback. At least one of a handover (HO) failure or a radio link failure (RLF) is predicted for one or more LTM target cells. In response to the prediction of at least one RLF or HO failure for one or more LTM target cells, at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration is prepared for at least one target cell selected from the one or more LTM candidate cells. The UE is provided with at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one target cell. Control information is sent to the UE based on at least one of the fallback LTM configurations or fallback CHO configurations for at least one target cell in order to initiate a cell switch by the UE from the serving cell to at least one target cell.

[0074] Figure 4 is a flowchart 400 of a method for handling LTM handover failures or wireless link failures according to at least one embodiment.

[0075] In Figure 4, the method is initiated (S402), and one or more L1 / L2 trigger mobility (LTM) candidate cells are identified for fallback (S410). Referring to Figure 3A, identifying one or more LTM candidate cells for fallback involves identifying which of the configured UE's LTM candidate cells are eligible to be configured for fallback. One or more LTM candidate cells may be identified by receiving periodic resource status updates 322, 323, 326 from one or more gNB distributed units (DUs) 312, 314, 318, where the periodic resource status update 322 includes HO failure data 323 for one or more LTM candidate cells. The HO failure data 323 for one or more LTM candidate cells includes data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells. The HO failure data 323 for one or more LTM candidate cells of one or more gNB-DUs is accumulated over period 328.

[0076] At least one HO failure or RLF for one or more LTM target cells is predicted (S414). The HO failure or RLF for one or more LTM target cells is predicted based on the accumulation of HO failure data 328 and RRC measurement results (L3) 330.

[0077] In response to the prediction of at least one RLF or HO failure for one or more LTM target cells, at least one fallback LTM configuration or fallback conditional handover (CHO) configuration is prepared for at least one target cell selected from one or more LTM candidate cells (S418). Referring to Figure 3A, at least one fallback LTM configuration or fallback conditional handover (CHO) configuration 338 is prepared for at least one target cell selected from one or more LTM candidate cells (332). Preparing a fallback CHO configuration for at least one target cell (332) may include obtaining a fallback CHO configuration from a target distribution unit (DU) 314. The fallback CHO configuration includes a delta for converting an LTM target cell configuration to a fallback CHO configuration, or receiving a fallback CHO configuration from the target DU 314. At least one fallback LTM configuration for at least one target cell may also include at least one fallback LTM configuration with full resource reservation. Here, the fallback CHO configuration includes at least the fallback CHO criteria added to the LTM configuration. Preparing at least one fallback LTM configuration or fallback CHO configuration for at least one target cell (332) may further include determining, based on HO failure data 323, whether a handover to at least one target cell is susceptible to an HO failure. Depending on whether at least one target cell is susceptible to an LTM cell switch HO failure, at least one neighbor candidate cell for the target cell 314 is determined, and at least one fallback LTM configuration or fallback CHO configuration is prepared for the neighbor candidate cell (332).

[0078] The UE is provided with at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one target cell (S422). Referring to Figure 3A, the UE 310 may be provided with a prepared fallback LTM configuration 342. Referring to Figure 3B, the UE 310 can autonomously perform cell switching 382 without transmitting additional signaling in the event of detecting a handover failure or radio link failure (RLF) 380.

[0079] Control information is sent to the UE (S426) based on at least one of a fallback LTM configuration or fallback CHO configuration for at least one target cell in order to initiate a cell switch by the UE from the serving cell to at least one target cell. Referring to Figure 3A, DL MAC CE376 is sent from the serving DU (DU1 312) to the UE310. MAC CE376 carries an LTM cell switch command including the target cell PCI and beam identifier. Referring to Figure 3B, the UE310 can autonomously perform the cell switch 382 without sending additional signaling in the event of a handover failure or RLF380 detection.

[0080] Next, the process terminates at S430.

[0081] According to at least one embodiment, a method for preparing a fallback configuration for one of a radio link failure (RLF) or handover (HO) failures of a user device (UE) includes: identifying one or more L1 / L2 trigger mobility (LTM) candidate cells for fallback; predicting at least one HO failure or RLF for one or more LTM target cells; preparing at least one fallback LTM configuration or fallback conditional handover (CHO) configuration for at least one of the LTM target cells selected from one or more LTM candidate cells in response to the prediction of at least one RLF or HO failure for one or more LTM target cells; providing the UE with at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the target cells; and transmitting control information to the UE for initiating a cell switch by the UE from a serving cell to at least one of the LTM target cells based on at least one of the prepared fallback LTM configurations or fallback CHO configurations for at least one of the LTM target cells.

[0082] Figure 5 is a high-level functional block diagram of a processor-based system 500 according to at least one embodiment.

[0083] In at least one embodiment, the processing circuit 500 provides radio link fault (RLF) or LTM handover fault handling. The processing circuit 500 implements the RLF or LTM handover fault handling using a processor 502. The processing circuit 500 also includes a non-transient computer-readable storage medium 504 used to implement the RLF or LTM handover fault handling. The non-transient computer-readable storage medium 504 is, in particular, encoded with (i.e., stores) instructions 506 (i.e., computer program code executed by the processor 502) that cause the processor 502 to perform operations for RLF or LTM handover fault handling. The execution of instructions 506 by the processor 502 represents (at least in part) an application that implements at least a portion of the method described herein (hereinafter referred to as process and / or method) according to one or more embodiments.

[0084] The processor 502 is electrically coupled to the non-temporary computer-readable storage medium 504 via the bus 508. The processor 502 is electrically coupled to the input / output (I / O) interface 510 via the bus 508. The network interface 512 is also electrically connected to the processor 502 via the bus 508. The network interface 512 is connected to the network 514, and the processor 502 and the non-temporary computer-readable storage medium 504 can be connected to external elements via the network 514. The processor 502 is configured to execute instructions 506 encoded in the non-temporary computer-readable storage medium 504 so that the processing circuit 500 can be used to execute at least a portion of a process and / or method. In one or more embodiments, the processor 502 is a central processing unit (CPU), a multiprocessor, a distributed processing system, an ASIC (Application Specific Integrated Circuit), and / or a suitable processing unit.

[0085] The processing circuit 500 includes an I / O interface 510. The I / O interface 510 is coupled to an external circuit. In one or more embodiments, the I / O interface 510 includes a keyboard, keypad, mouse, trackball, trackpad, touchscreen, and / or cursor directional keys for transmitting information and commands to the processor 502.

[0086] The processing circuit 500 also includes a network interface 512 coupled to the processor 502. The network interface 512 enables the processing circuit 500 to communicate with a network 514 to which one or more other computer systems are connected. The network interface 512 includes wireless network interfaces such as Bluetooth, Wi-Fi, Worldwide Interoperability for Microwave Access (WiMAX), General Packet Radio Service (GPRS), or Wideband Code Division Multiple Access (WCDMA), or wired network interfaces such as Ethernet, Universal Serial Bus (USB), or Institute of Electrical and Electronics Engineers (IEEE) 864.

[0087] The processing circuit 500 is configured to receive information through the I / O interface 510. The information received through the I / O interface 510 includes one or more instructions, data, design rules, cell libraries, and / or other parameters for processing by the processor 502. The information is transferred to the processor 502 via the bus 508. The processing circuit 500 is configured to receive information about the user interface (UI) through the I / O interface 510. The information is stored as the UI 520 in a non-temporary computer-readable storage medium 504. The user interface 520 is used to process network data 522, such as L1 / L2 / L3 RRC measurement results, for handling RLF or LTM handover failures.

[0088] In one or more embodiments, one or more non-temporary computer-readable storage media 504 store instructions 506, which may be used to program a computer, processor, or other electronic device to perform the processes or methods described herein (in compressed or uncompressed form). One or more non-temporary computer-readable storage media 504 include one or more electronic storage media, magnetic storage media, optical storage media, quantum storage media, etc.

[0089] For example, the non-temporary computer-readable storage medium 504 may include, but is not limited to, a hard drive, a floppy diskette, an optical disk, read-only memory (ROM), random access memory (RAM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, a magnetic or optical card, a solid-state memory device, or other types of physical media suitable for storing electronic instructions. In one or more embodiments using an optical disk, one or more non-temporary computer-readable storage medium 504 include a compact disk read-only memory (CD-ROM), a compact disk read / write (CD-R / W), and / or a digital video disc (DVD).

[0090] In one or more embodiments, the non-transient computer-readable storage medium 504 stores instructions 506 configured to cause the processor 502 to execute at least a portion of a process and / or method for handling an RLF or LTM handover failure. In one or more embodiments, the non-transient computer-readable storage medium 504 also stores information such as algorithms that facilitate the execution of at least a portion of the process and / or method for handling an RLF or LTM handover failure.

[0091] Thus, in at least one embodiment, the processor 502 executes instructions 506 stored on one or more non-temporary computer-readable storage media 504 to implement RLF or LTM handover fault handling. Handover fault data, such as radio link fault (RLF) or LTM HO fault data 540, is received by the gNB via resource status updates. The handover fault data 540 is received from one or more candidate cells 542, neighbor cells 544, or target cells 546. Here, the handover fault data from one or more candidate cells 542, neighbor cells 544, or target cells 546 is accumulated over a predetermined period. Based on the handover fault data, a list of cells that will suffer a fault, including the serving cell 548 and the target cell 546, is prepared. Based on the handover failure data 540, a fallback LTM configuration 530, such as an LTM candidate cell configuration, is prepared for the LTM target cell 546, and a fallback CHO configuration 532 is prepared for at least one alternative candidate cell 552. The prepared fallback LTM configuration 530 may include a full resource reservation. The fallback CHO configuration 532 can be generated by converting the fallback LTM configuration 530 into a fallback CHO configuration 532 by adding a CHO criterion 550. The fallback CHO configuration 532 is initiated by performing an autonomous CHO with at least one alternative candidate cell 552 of the target cell 546.The processor 502 can identify one or more lower-level trigger mobility (LTM) candidate cells 542, 552 for fallback, predict at least one of HO failures or RLFs for one or more LTM target cells based on accumulated handover failure data 540, prepare at least one of fallback LTM configurations 530 or fallback CHO configurations 532 for at least one target cell 546 selected from the one or more LTM candidate cells 542, 552, provide the UE with at least one of the fallback LTM configurations 530 or fallback CHO configurations 532 prepared for at least one target cell 546, and send control information to the UE to initiate a cell switch by the UE from the serving cell 548 to at least one target cell 546 based on at least one of the fallback LTM configurations 530 or fallback CHO configurations 532 prepared for at least one target cell 546. The display 570 includes a user interface (UI) 572 for displaying network data 574, including identification of different cells, CHO criteria, and handover failure data.

[0092] The embodiments described herein provide a method that offers one or more advantages. For example, RRC re-establishment can be avoided during a radio link failure (RLF) or LTM handover (HO) failure.

[0093] This description focuses on methods related to the following items. Item 1: A method for preparing a fallback configuration for either a wireless link failure (RLF) or a handover (HO) failure of user equipment (UE), Identifying one or more Layer 1 (L1) / Layer 2 (L2) Trigger Mobility (LTM) candidate cells for fallback, To predict at least one of the HO failures or RLFs for one or more LTM target cells, In response to predicting at least one of the RLF or HO failures for the one or more LTM target cells, prepare at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells, To provide the UE with at least one of the fallback LTM configuration or the fallback CHO configuration prepared for at least one of the one or more target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to at least one of the one or more LTM target cells to the UE for initiating cell switching by the UE. A method that includes this.

[0094] Item 2: The method of item 1, wherein providing the prepared fallback LTM configuration to the UE is to provide the prepared fallback LTM configuration to the UE without sending additional signaling for the UE to autonomously perform the cell switch in the event of at least one of the HO failure or RLF.

[0095] Item 3: Preparing the fallback CHO configuration for at least one of the one or more LTM target cells includes obtaining the fallback CHO configuration from a target distribution unit (DU), Obtaining the fallback CHO configuration includes receiving a delta from the target DU for converting the LTM target cell configuration to the fallback CHO configuration, or receiving the fallback CHO configuration from the target DU. The method described in item 1 or 2.

[0096] Item 4: Identifying the one or more LTM candidate cells for fallback is a method of any one of items 1 to 3, which includes identifying which of the configured LTM candidate cells of the UE is eligible to be configured for fallback.

[0097] Item 5: Preparing the at least one fallback LTM configuration for at least one of the one or more target cells includes preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, Preparing the aforementioned fallback CHO configuration includes adding at least a fallback CHO criterion to the LTM configuration. The method described in any of items 1 through 4.

[0098] Item 6: Identifying the one or more LTM candidate cells means that Receiving periodic resource status updates, including HO failure data for one or more LTM candidate cells, from one or more gNB distributed units (DUs), The HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs is accumulated over a period of time. Includes, Preparing at least one of the fallback LTM configurations or fallback CHO configurations for at least one of the one or more LTM target cells is: Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, including, The method described in any of items 1 through 5.

[0099] Item 7: Receiving the periodic resource status update, which includes the HO failure data for one or more LTM candidate cells, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. including, The method described in any of items 1 through 6.

[0100] This description is directed towards wireless access network (RAN) nodes relating to the following items. Item 8: A Wireless Access Network (RAN) node, Memory for storing computer-readable instructions, A processor connected to the aforementioned memory, Identifying one or more Layer 1 (L1) / Layer 2 (L2) Trigger Mobility (LTM) candidate cells for fallback, To predict at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, In response to predicting at least one of the HO failures or RLFs for the one or more LTM target cells, prepare at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells, To provide the user equipment (UE) with at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to the UE to initiate a switch by the UE to at least one of the one or more LTM target cells. A processor configured to execute computer-readable instructions in order to perform an operation to perform the above, A RAN node that includes this node.

[0101] Item 9: The RAN node according to item 8, wherein the processor is configured to provide the UE with the prepared fallback LTM configuration and / or at least one of the prepared fallback CHO configurations for at least one of the one or more LTM target cells, by providing the UE with the prepared fallback LTM configuration and / or at least one of the prepared fallback LTM configurations for at least one of the one or more LTM target cells, without sending additional signaling for the UE to autonomously execute the cell switch in the event of the HO failure or the RLF.

[0102] Item 10: The RAN node according to item 8 or 9, wherein the processor is further configured to prepare the fallback CHO configuration for at least one of the one or more LTM target cells by receiving a delta from a target distributed unit (DU) for converting the LTM target cell configuration to the fallback CHO configuration, or by receiving the fallback CHO configuration from the target DU.

[0103] Item 11: The RAN node according to any one of items 8 to 10, wherein the processor is configured to identify one or more LTM candidate cells for fallback by identifying which of the configured LTM candidate cells of the UE are eligible to be configured for fallback.

[0104] Item 12: The aforementioned processor, By preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, the at least one fallback LTM configuration is prepared for at least one of the one or more LTM target cells. The configuration is set up to prepare the fallback CHO configuration by adding at least a fallback CHO criterion to the LTM configuration. A RAN node listed in any of items 8 through 11.

[0105] Item 13: The aforementioned processor, Periodic resource status updates, including HO failure data for the one or more LTM candidate cells, are received from one or more gNB distributed units (DUs). The system is configured to accumulate the HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs over a period of time. Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, This is configured to prepare at least one of the fallback LTM configuration or the fallback CHO configuration for at least one of the one or more LTM target cells. A RAN node listed in any of items 8 through 12.

[0106] Item 14: The aforementioned processor, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. The system is configured to receive the periodic resource status updates, which include the HO failure data for one or more LTM candidate cells. A RAN node listed in any of items 8 through 13.

[0107] This description focuses on non-temporary computer-readable media containing computer-readable instructions relating to the following items. Item 15: When executed by the processor, For user equipment (UE), identify one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, To predict at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, In response to predicting at least one of the RLF or HO failures for the aforementioned UE, prepare at least one of the fallback LTM configuration or fallback conditional handover (CHO) configuration for at least one of the aforementioned LTM target cells selected from one or more LTM candidate cells, To provide the UE with at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to the UE to initiate a switch by the UE to at least one of the one or more LTM target cells. A non-temporary computer-readable medium containing computer-readable instructions that cause the processor to perform an operation including the above.

[0108] Item 16: Providing the prepared fallback LTM configuration to the UE is a non-transient computer-readable medium as described in item 15, which includes providing the prepared fallback LTM configuration to the UE without sending additional signaling for the UE to autonomously perform the cell switch in the event of at least one of the HO failures or RLFs.

[0109] Item 17: Preparing the fallback CHO configuration for at least one of the one or more LTM target cells includes obtaining the fallback CHO configuration from a target distribution unit (DU), Obtaining the fallback CHO configuration includes receiving a delta from the target DU for converting the LTM target cell configuration to the fallback CHO configuration, or receiving the fallback CHO configuration from the target DU. Non-temporary computer-readable media as described in item 15 or 16.

[0110] Item 18: Preparing the at least one fallback LTM configuration for at least one of the one or more LTM target cells includes preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, Preparing the aforementioned fallback CHO configuration includes adding at least a fallback CHO criterion to the LTM configuration. A non-temporary computer-readable medium as described in any of items 15 through 17.

[0111] Item 19: Identifying the one or more LTM candidate cells means that Receiving periodic resource status updates, including HO failure data for one or more LTM candidate cells, from one or more gNB distributed units (DUs), The HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs is accumulated over a period of time. Includes, Preparing at least one of the fallback LTM configurations or fallback CHO configurations for at least one of the one or more LTM target cells is: Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, including, A non-temporary computer-readable medium as described in any of items 15 through 18.

[0112] Item 20: Receiving the periodic resource status update, which includes the HO failure data for one or more LTM candidate cells, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. including, A non-temporary computer-readable medium as described in any of items 15 through 19.

[0113] Other instances of these programs may run on or distributed across any number of other computer systems. Thus, while certain steps are described as being performed by a specific device, software program, process, or entity, this is not required. Various alternative implementations will be understood by those skilled in the art.

[0114] In addition, those skilled in the art will readily recognize that the aforementioned technologies can be used in a variety of devices, environments, and situations. Although the embodiments have been described in terms specific to structural features or methodological actions, the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described. Rather, specific features and actions are disclosed as exemplary forms that implement the claims.

Claims

1. A method for preparing a fallback configuration for either a radio link failure (RLF) or a handover (HO) failure of a user equipment (UE), Identifying one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, To predict at least one of the HO failures or RLFs for one or more LTM target cells, In response to predicting at least one of the RLF or HO failures for the one or more LTM target cells, prepare at least one of a fallback LTM configuration or a fallback conditional handover (CHO) configuration for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells, To provide the UE with at least one of the fallback LTM configuration or the fallback CHO configuration prepared for at least one of the one or more target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to at least one of the one or more LTM target cells to the UE for initiating cell switching by the UE. A method for providing this.

2. The method according to claim 1, wherein providing the prepared fallback LTM configuration to the UE is provided to the UE without sending additional signaling for the UE to autonomously perform the cell switch in the event of at least one of the HO failure or RLF.

3. Preparing the fallback CHO configuration for at least one of the one or more LTM target cells includes obtaining the fallback CHO configuration from a target distribution unit (DU). Obtaining the fallback CHO configuration includes receiving a delta from the target DU for converting the fallback LTM configuration to the fallback CHO configuration, or receiving the fallback CHO configuration from the target DU. The method according to claim 1.

4. The method according to claim 1, wherein identifying the one or more LTM candidate cells for fallback includes identifying which of the configured LTM candidate cells of the UE is eligible to be configured for fallback.

5. Preparing the at least one fallback LTM configuration for at least one of the one or more target cells includes preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, Preparing the aforementioned fallback CHO configuration includes adding at least a fallback CHO criterion to the LTM configuration. The method according to claim 1.

6. Identifying the one or more LTM candidate cells means that Receiving periodic resource status updates, including HO failure data for one or more LTM candidate cells, from one or more gNB distributed units (DUs), The HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs is accumulated over a period of time. Includes, Preparing at least one of the fallback LTM configurations or fallback CHO configurations for at least one of the one or more LTM target cells is: Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, including, The method according to claim 1.

7. Receiving the periodic resource status update, which includes the HO failure data for one or more LTM candidate cells, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. including, The method according to claim 6.

8. A Wireless Access Network (RAN) node, Memory for storing computer-readable instructions, A processor connected to the aforementioned memory, Identifying one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, To predict at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, In response to predicting at least one of the HO failures or RLFs for the one or more LTM target cells, prepare at least one of the fallback LTM configurations or fallback conditional handover (CHO) configurations for at least one of the one or more LTM target cells selected from the one or more LTM candidate cells, To provide the user equipment (UE) with at least one of the fallback LTM configuration or the fallback CHO configuration prepared for at least one of the one or more target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to at least one of the one or more LTM target cells to the UE for initiating cell switching by the UE. A processor configured to execute computer-readable instructions in order to perform an operation to perform the above, A RAN node equipped with the following features.

9. The RAN node according to claim 8, wherein the processor is configured to provide the UE with the prepared fallback LTM configuration and / or at least one of the prepared fallback LTM configurations for at least one of the one or more LTM target cells, by providing the UE with the prepared fallback LTM configuration and / or the fallback CHO configuration for at least one of the one or more LTM target cells, without sending additional signaling for the UE to autonomously execute the cell switch in the event of the HO failure or the RLF.

10. The RAN node according to claim 8, wherein the processor is configured to prepare the fallback CHO configuration for at least one of the one or more LTM target cells by receiving a delta from a target distributed unit (DU) for converting the fallback LTM configuration to the fallback CHO configuration, or by receiving the fallback CHO configuration from the target DU.

11. The RAN node according to claim 8, wherein the processor is configured to identify one or more LTM candidate cells for fallback by identifying which of the configured LTM candidate cells of the UE are eligible to be configured for fallback.

12. The aforementioned processor, By preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, the at least one fallback LTM configuration is prepared for at least one of the one or more LTM target cells. The configuration is set up to prepare the fallback CHO configuration by adding at least a fallback CHO criterion to the LTM configuration. The RAN node according to claim 8.

13. The aforementioned processor, Periodic resource status updates, including HO failure data for the one or more LTM candidate cells, are received from one or more gNB distributed units (DUs). The system is configured to accumulate the HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs over a period of time. Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, This is configured to prepare at least one of the fallback LTM configuration or the fallback CHO configuration for at least one of the one or more LTM target cells. The RAN node according to claim 8.

14. The aforementioned processor, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. The system is configured to receive the periodic resource status updates, which include the HO failure data for one or more LTM candidate cells. The RAN node according to claim 13.

15. When executed by the processor, For user equipment (UE), identify one or more Layer 1 (L1) / Layer 2 (L2) trigger mobility (LTM) candidate cells for fallback, To predict at least one handover (HO) failure or radio link failure (RLF) for one or more LTM target cells, In response to predicting at least one of the RLF or HO failures for the UE, prepare at least one of the fallback LTM configuration or fallback conditional handover (CHO) configuration for at least one of the one or more LTM target cells selected from one or more LTM candidate cells, To provide the UE with at least one of the fallback LTM configuration or the fallback CHO configuration prepared for at least one of the one or more target cells, Based on at least one of the fallback LTM configurations or fallback CHO configurations prepared for at least one of the one or more LTM target cells, control information is transmitted from the serving cell to at least one of the one or more LTM target cells to the UE for initiating cell switching by the UE. A non-temporary computer-readable medium containing computer-readable instructions that cause the processor to perform an operation comprising the above.

16. The non-transient computer-readable medium according to claim 15, wherein providing the prepared fallback LTM configuration to the UE includes providing the prepared fallback LTM configuration to the UE without transmitting additional signaling for the UE to autonomously perform the cell switch in the event of at least one of the HO failure or RLF.

17. Preparing the fallback CHO configuration for at least one of the one or more LTM target cells includes obtaining the fallback CHO configuration from a target distribution unit (DU). Obtaining the fallback CHO configuration includes receiving a delta from the target DU for converting the fallback LTM configuration to the fallback CHO configuration, or receiving the fallback CHO configuration from the target DU. The non-temporary computer-readable medium according to claim 15.

18. Preparing the at least one fallback LTM configuration for at least one of the one or more target cells includes preparing the at least one fallback LTM configuration with full resource reservation in at least one of the one or more LTM target cells, Preparing the aforementioned fallback CHO configuration includes adding at least a fallback CHO criterion to the LTM configuration. The non-temporary computer-readable medium according to claim 15.

19. Identifying the one or more LTM candidate cells means that Receiving periodic resource status updates, including HO failure data for one or more LTM candidate cells, from one or more gNB distributed units (DUs), The HO failure data for the one or more LTM candidate cells of the one or more gNB-DUs is accumulated over a period of time. Includes, Preparing at least one of the fallback LTM configurations or fallback CHO configurations for at least one of the one or more LTM target cells is: Based on the HO failure data, determine whether the handover to at least one of the one or more LTM target cells is susceptible to the HO failure. In accordance with the fact that at least one of the one or more LTM target cells is susceptible to the effects of an LTM cell switch HO failure, a neighboring candidate cell for at least one of the one or more LTM target cells is determined. To prepare at least one fallback LTM configuration or fallback CHO configuration for the neighboring candidate cell, including, The non-temporary computer-readable medium according to claim 15.

20. Receiving the periodic resource status update, which includes the HO failure data for one or more LTM candidate cells, Receiving data indicating an RLF or LTM HO failure associated with one or more LTM candidate cells, The data indicating RLF or LTM HO failures associated with the one or more LTM candidate cells belonging to the one or more gNB-DUs is accumulated over a predetermined period of time. including, The non-temporary computer-readable medium according to claim 19.

Images