Handling radio link failure while performing lower layer triggered mobility in telecommunications network

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method performed by a user equipment (UE) associated with a first group of cells and a second group of cells in a wireless communication system, the UE comprising: receiving a control message from a base station, the control message comprising an LTM configuration for performing lower layer triggered mobility (LTM) measurements and a timer for supervising LTM cell handover; detecting a radio link failure of a first cell group of the first cell group and the second cell group while performing the LTM cell handover; identifying whether a timer for supervising LTM cell handover is running on a second cell group; and transmitting a radio resource control (RRC) reestablishment message to the base station if the timer for supervising LTM cell handover is running on the second cell group.

Description

Technical Field

[0001] The present disclosure relates to the field of wireless communications, and more particularly, to handling radio link failure while performing lower layer triggered mobility in a telecommunication network. Background Art

[0002] Fifth-generation (5G) mobile communication technology defines a wide frequency band, enabling high transmission rates and new services, and can be implemented not only in "sub-6 gigahertz (GHz)" frequency bands such as 3.5 GHz, but also in "above 6 GHz" frequency bands, known as millimeter waves (mmWave), including 28 GHz and 39 GHz. Furthermore, in order to achieve transmission rates fifty times faster than 5G mobile communication technology and ultra-low latency one-tenth that of 5G mobile communication technology, consideration has been given to implementing sixth-generation (6G) mobile communication technology (referred to as a "super 5G system") in the terahertz frequency band (e.g., the 95 GHz to 3 THz band).

[0003] Since the initial development of 5G mobile communication technology, in order to support services and meet performance requirements related to enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine-type communications (mMTC), standardization has been underway on the following technologies: beamforming and massive multiple-input multiple-output (MIMO) for mitigating radio wave path loss and increasing radio wave transmission range in mmWave, support for dynamic operation of parameter sets (e.g., operating multiple subcarrier spacings) and time slot formats for efficient utilization of mmWave resources, initial access technology supporting multi-beam transmission and wideband, definition and operation of bandwidth parts (BWPs), new channel coding methods (such as low-density parity-check (LDPC) codes for large-scale data transmission and polar codes for highly reliable transmission of control information), L2 preprocessing, and network slicing for providing dedicated networks dedicated to specific services.

[0004] Currently, discussions are underway on improvements and performance enhancements to initial 5G mobile communication technologies in view of the services they are to support, and there is already standardization of physical layers for technologies such as Vehicle-to-Everything (V2X) for assisting driving determination of autonomous vehicles based on information about the position and status of vehicles transmitted by the vehicles and for enhancing user convenience, New Radio Unlicensed (NR-U) designed to enable system operation in unlicensed bands to comply with various regulatory requirements, New Radio (NR) User Equipment (UE) power saving, Non-Terrestrial Network (NTN) for UE-satellite direct communication for providing coverage in areas where communication with terrestrial networks is unavailable, and positioning.

[0005] In addition, in terms of air interface architecture / protocols, standardization is also underway on technologies such as the Industrial IoT (IIoT) for supporting new services through interoperability and integration with other industries, Integrated Access and Backhaul (IAB) for providing nodes for network service area expansion by integrating wireless backhaul links and access links, mobility enhancements including conditional handover and dual-active protocol stack (DAPS) handover, and two-step random access (NR's two-step random access channel (RACH)) for simplifying the random access process. In terms of system architecture / services, standardization is also underway on the following: a 5G baseline architecture (e.g., a service-based architecture or service-based interface) for combining network function virtualization (NFV) and software-defined networking (SDN) technologies, and mobile edge computing (MEC) for receiving services based on UE location.

[0006] With the commercialization of 5G mobile communication systems, the number of devices that will be connected to the communication network is expected to grow exponentially, and therefore it is expected that enhanced functionality and performance of 5G mobile communication systems and the integrated operation of connected devices will be necessary. To this end, new research is planned related to: extended reality (XR) for effectively supporting augmented reality (AR), virtual reality (VR), mixed reality (MR), etc.; improving 5G performance and reducing 5G complexity by utilizing artificial intelligence (AI) and machine learning (ML); AI service support; metaverse service support; and drone communications.

[0007] Furthermore, such developments in 5G mobile communication systems will serve as the foundation for the development of not only new waveforms for providing terahertz band coverage for 6G mobile communication technology, multi-antenna transmission technologies (such as full-dimensional MIMO (FD-MIMO), array antennas, and massive antennas), metamaterial-based lenses and antennas for improving terahertz band signal coverage, high-dimensional spatial multiplexing technologies using orbital angular momentum (OAM), and reconfigurable smart surfaces (RIS), but also full-duplex technologies for increasing the frequency efficiency of 6G mobile communication technology and improving system networks, AI-based communication technologies for achieving system optimization by leveraging satellites and AI from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technologies for implementing services at a complexity level that exceeds the operational capability limits of UEs by utilizing ultra-high-performance communication and computing resources.

[0008] In wireless technologies such as 5G New Radio, mobility is achieved through cell reselection in RRC_IDLE mode. Prior to NR Release 17, handover was the preferred method in RRC_CONNECTED mode, requiring explicit RRC signaling triggered by the gNB. This network-controlled mobility involves a three-step handover process: preparation, execution, and completion. The gNB can configure the UE to report measurements or use its understanding of the network topology to send an RRC reconfiguration message to handover the UE to the target cell. Alternatively, in NR Release 16, the gNB can configure the UE with execution conditions for triggering handover and an RRC reconfiguration message to be executed when the execution conditions are met. Once these conditions are met, the UE can move to the target cell, apply the RRC reconfiguration message, and send an RRC reconfiguration complete message. 3GPP also introduced new handover methods in NR Release 16, known as dual-active protocol stack handover. However, these methods rely on Layer 3 (RRC) messages, which can result in significant signaling overhead and latency. Therefore, there is a growing need to address these issues and reduce signaling overhead and latency. Summary of the Invention

[0009] Technical issues

[0010] The present disclosure relates to wireless communication systems, and more particularly, to handling radio link failure while performing lower layer triggered mobility in a telecommunication network.

[0011] It would be desirable to address the above-mentioned or other disadvantages or at least provide a useful alternative.

[0012] A primary object of embodiments herein is to provide a method and UE for handling cell group failure while performing lower layer triggered mobility in a telecommunication network.

[0013] Another object of embodiments herein is to receive, from a network device in a telecommunications network, an LTM configuration for performing LTM measurements and a timer for supervising LTM cell switching.

[0014] Another object of embodiments herein is to determine whether a timer for supervising the LTM cell switching process is running on other cell groups.

[0015] Additionally, another object of the embodiments herein is to send an RRC re-establishment message to a network device when a timer for supervising an LTM cell switching process is running on another cell group.

[0016] Additionally, another object of embodiments herein is to send a cell group failure information message to a network device when a timer for supervising an LTM cell switching process is not running.

[0017] Additionally, another object of embodiments herein is to store the LTM configuration of at least one cell group and the current LTM candidate cell configuration of at least one candidate cell belonging to the at least one cell group in a memory of the UE.

[0018] In addition, another object of the embodiments herein is to stop LTM measurement of at least one cell group based on LTM configuration when cell group failure information is transmitted by determining the content of the cell group failure information.

[0019] Additionally, another object of embodiments herein is to handle SCG and MCG failures when the UE is configured to perform LTM measurements or when a cell handover for LTM is received.

[0020] Solution to the problem

[0021] Therefore, embodiments herein provide a method for handling radio link failure (RLF) while performing lower layer triggered mobility (LTM) in a telecommunications network. The method includes receiving, by a UE, an LTM configuration for performing LTM measurements and a timer for supervising LTM cell handovers from a network device in the telecommunications network. Furthermore, the method includes detecting, by the UE, RLF in at least one cell group. Furthermore, the method includes determining, by the UE, whether a timer for supervising the LTM cell handover process is running in another cell group. Furthermore, the method includes performing, by the UE, one of the following: sending an RRC re-establishment message to the network device when the timer for supervising the LTM cell handover process is running in another cell group, and sending a cell group failure information message to the network device when the timer for supervising the LTM cell handover process is not running.

[0022] In an embodiment, the cell group is at least one of a master cell group (MCG) and a secondary cell group (SCG).

[0023] In an embodiment, the network device is one of a Master Node (MN) and a Secondary Node (SN).

[0024] In an embodiment, the timer for supervising the LTM cell switching process is T304, and when the cell group is MCG, the cell group failure information is MCGFailureInformation, and when the cell group is SCG, the cell group failure information is SCGFailureInformation.

[0025] In an embodiment, sending the cell group failure information message to the network device includes creating, by the UE, a cell group failure information message by including LTM measurements, wherein the LTM measurements include a candidate cell identifier and L1 measurements of at least one candidate cell belonging to at least one cell group, and sending, by the UE, the cell group failure information message including the LTM measurements to the network device.

[0026] In an embodiment, the LTM measurement is the latest LTM measurement of at least one cell group.

[0027] In an embodiment, the LTM measurement is one of periodic measurement, aperiodic measurement, semi-periodic measurement, and event-based measurement performed by the UE configured by the network device for LTM.

[0028] In an embodiment, the LTM measurement is one of: a reference signal received power (RSRP) measurement, a signal to interference and noise ratio (SINR) measurement, and a reference signal received quality (RSRQ) measurement.

[0029] In an embodiment, the method includes storing, by a UE, an LTM configuration for at least one cell group and a current LTM candidate cell configuration for at least one candidate cell belonging to the at least one cell group in a memory of the UE. The method also includes receiving the current LTM candidate cell configuration for the at least one candidate cell from a network device. Furthermore, the method includes, when transmitting cell group failure information by determining content of the cell group failure information, stopping, by the UE, LTM measurement of the at least one cell group based on the LTM configuration.

[0030] Therefore, embodiments herein provide a UE for handling radio link failures while performing LTM in a telecommunications network. The UE includes an LTM and a cell group failure controller coupled to a memory and a processor. The LTM and cell group failure controller is configured to receive an LTM configuration for performing LTM measurements and a timer for supervising LTM cell handovers from a network device in the telecommunications network. Furthermore, the LTM and cell group failure controller is configured to detect RLF in at least one cell group. Furthermore, the LTM and cell group failure controller is configured to determine whether a timer for supervising the LTM cell handover process is running on another cell group. In one embodiment, the LTM and cell group failure controller is configured to send an RRC reestablishment message to the network device when the timer for supervising the LTM cell handover process is running on another cell group. In another embodiment, the LTM and cell group failure controller is configured to send a cell group failure information message to the network device when the timer for supervising the LTM cell handover process is not running.

[0031] Therefore, embodiments herein provide a method for handling radio link failures while performing LTM in a telecommunications network. The method includes receiving, by a network device, one of MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements from a UE. Furthermore, the method includes the network device performing one of the following: sending an MCG reconfiguration message based on the MCGFailureInformation to restore the MCG link, and sending an SCG reconfiguration message based on the SCGFailureInformation to restore the SCG link.

[0032] In an embodiment, when the timer for supervising the LTM cell switching procedure is not running, the network device receives from the UE one of: MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements.

[0033] Therefore, an embodiment of the present invention is to provide a network device for handling radio link failures while performing LTM in a telecommunications network. The network device includes an LTM and a cell group fault controller coupled to a memory and a processor. The LTM and the cell group fault controller are configured to receive one of MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements from a UE. In an embodiment, the LTM and the cell group fault controller are configured to send an MCG reconfiguration message based on the MCGFailureInformation to restore the MCG link. In another embodiment, the LTM and the cell group fault controller are configured to send an SCG reconfiguration message based on the SCGFailureInformation to restore the SCG link.

[0034] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and accompanying drawings. However, it should be understood that the following description, while indicating preferred embodiments and many specific details thereof, is given by way of illustration and not limitation. Many changes and modifications may be made within the scope of the embodiments herein, and the embodiments herein include all such modifications.

[0035] In an embodiment, a method performed by a user equipment (UE) associated with a first cell group and a second cell group in a wireless communication system includes: receiving a control message from a base station, the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurement and a timer for supervising LTM cell switching; detecting a radio link failure of a first cell group among the first cell group and the second cell group while performing LTM cell switching; identifying whether the timer for supervising LTM cell switching is running on the second cell group; and sending a radio resource control (RRC) re-establishment message to the base station if the timer for supervising LTM cell switching is running on the second cell group.

[0036] In another embodiment, a method performed by a base station in a wireless communication system includes: sending a control message to a user equipment (UE), the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching; and receiving a radio resource control (RRC) re-establishment message from the UE in a case where the timer for supervising LTM cell switching is running on the second cell group, wherein the UE is associated with a first cell group and a second cell group, wherein the UE detects a radio link failure of a first cell group among the first cell group and the second cell group while performing the LTM cell switching, wherein the UE identifies whether the timer for supervising LTM cell switching is running on the second cell group.

[0037] In yet another embodiment, a user equipment (UE) is associated with a first cell group and a second cell group in a wireless communication system, the UE including: a transceiver; and a processor configured to: receive a control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching from a base station, detect a radio link failure of a first cell group in the first cell group and the second cell group while performing LTM cell switching, identify whether the timer for supervising LTM cell switching is running on the second cell group, and send a radio resource control (RRC) re-establishment message to the base station if the timer for supervising LTM cell switching is running on the second cell group.

[0038] In yet another embodiment, a base station in a wireless communication system includes: a transceiver; and a processor configured to: send a control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching to a user equipment (UE), and receive a radio resource control (RRC) re-establishment message from the UE if the timer for supervising LTM cell switching is running on a second cell group, wherein the UE is associated with a first cell group and a second cell group, wherein the UE detects a radio link failure of a first cell group out of the first cell group and the second cell group while performing the LTM cell switching, and wherein the UE identifies whether the timer for supervising LTM cell switching is running on the second cell group.

[0039] Advantageous Effects of the Invention

[0040] Advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The method and UE are shown in the accompanying drawings, and the same reference numerals indicate corresponding parts throughout the drawings. The embodiments of the present invention will be better understood from the following description with reference to the accompanying drawings, in which:

[0042] Figure 1 A block diagram illustrating a telecommunications network for handling radio link failure while performing LTM according to embodiments disclosed herein;

[0043] Figure 2 shows various hardware components of a UE according to embodiments disclosed herein;

[0044] Figure 3 is a flow chart illustrating a method implemented by a UE for handling a radio link failure while performing LTM in a telecommunications network according to an embodiment disclosed herein;

[0045] Figure 4 is a flow chart illustrating fault information initiation using a tcellswitch according to an embodiment disclosed herein;

[0046] Figure 5 is a flow chart illustrating MCG fault information transmission when LTM is configured according to an embodiment disclosed herein;

[0047] Figure 6 is a flow chart illustrating SCG fault information initiation using Tcellswitch according to an embodiment disclosed herein;

[0048] Figure 7is a flow chart illustrating SCG fault information transmission when LTM is configured according to an embodiment as disclosed herein;

[0049] Figure 8 illustrates various hardware components of a network device according to embodiments disclosed herein; and

[0050] Figure 9 is a flow chart illustrating a method implemented by a network device for handling radio link failure while performing LTM in a telecommunications network according to embodiments disclosed herein.

[0051] It may be noted that, to the extent possible, identical reference numerals have been used to denote identical elements in the accompanying drawings. Furthermore, one of ordinary skill in the art will appreciate that the elements in the accompanying drawings are illustrated for simplicity and may not necessarily be drawn to scale. For example, the dimensions of some elements in the accompanying drawings may be exaggerated relative to other elements to help improve understanding of various aspects of the present invention. Furthermore, one or more elements may have been represented in the accompanying drawings by conventional symbols, and the accompanying drawings may show only those specific details relevant to understanding embodiments of the present invention, so as not to obscure the drawings with details that would be readily apparent to one of ordinary skill in the art having the benefit of the description herein. DETAILED DESCRIPTION

[0052] The embodiments of this document and their various features and advantageous details are explained more fully with reference to the non-limiting embodiments shown in the accompanying drawings and described in detail in the following description. Descriptions of well-known components and processing technologies are omitted so as not to unnecessarily obscure the embodiments of this document. In addition, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. Unless otherwise indicated, the term "or" as used herein refers to a non-exclusive or. The examples used herein are intended only to facilitate understanding of the manner in which the embodiments of this document can be practiced, and further enable those skilled in the art to practice the embodiments of this document. Therefore, the examples should not be interpreted as limiting the scope of the embodiments of this document.

[0053] As is conventional in the art, embodiments may be described and illustrated in terms of blocks that perform one or more of the described functions. These blocks, which may be referred to herein as managers, units, modules, hardware components, etc., are physically implemented by analog and / or digital circuitry (such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hard-wired circuitry, etc.) and may optionally be driven by firmware and software. The circuitry may, for example, be embodied in one or more semiconductor chips or on a substrate support such as a printed circuit board. The circuitry comprising a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware that performs some of the block's functions and a processor that performs other functions of the block. Each block of an embodiment may be physically separated into two or more interacting and discrete blocks without departing from the scope of this disclosure. Similarly, the blocks of an embodiment may be physically combined into more complex blocks without departing from the scope of this disclosure.

[0054] Layer 3 mobility is represented by handover and conditional handover (CHO). In the case of dual connectivity, the UE can perform a PSCellChange or a conditional PSCellChange. This patent disclosure describes PSCellChange or conditional PSCellChange as a form of Layer 3 mobility within the context of dual connectivity. This means that handover, conditional handover, PSCellChange, conditional PSCellChange, and other similar actions all fall under the category of L3 mobility. In the context of dual connectivity, this disclosure also refers to PSCellChange or conditional PSCellChange as secondary cell group (SCG) Layer 3 mobility, and handover and CHO as primary cell group (MCG) Layer 3 mobility. Upon receiving an RRC reconfiguration message requesting the UE to perform a handover or perform a conditional reconfiguration (CHO CPA or CPC), the UE can perform L3 mobility.

[0055] In conventional methods, a user equipment (UE) is provided with a radio resource control (RRC) configuration to facilitate updating of certain security parameters. This patent disclosure considers relevant background information, including 3GPP specifications such as TS38300, TS38331, TS38321, and V1720.

[0056] 3GPP Release 18 is exploring the implementation of Lower Layer Triggered Mobility (LTM) (also known as the L1 / L2 layer) as a solution to issues related to latency, signaling overhead, and other issues associated with Layer 3 mobility. According to 3GPP, the primary goal of LTM is to facilitate seamless transitions between serving cells through L1 / L2 signaling, minimizing latency and disruption. To achieve this, the network (such as a gNB or similar entity) can configure multiple candidate cells for the UE, enabling rapid application of configurations for these cells. Each of these candidate cells can be assigned a candidate cell identifier and a candidate cell configuration, which can include an RRC reconfiguration message to be executed when the network moves the UE to that candidate cell via LTM. Additionally, the network can send a Media Access Control Element (MAC CE) or Layer 1 signaling to dynamically handover the UE from the source cell to one of the configured candidate cells. Notably, LTM is triggered based on Layer 1 measurements, not Layer 3 measurements.

[0057] 3GPP has proposed a method for performing LTM that avoids resetting lower layers, such as the MAC, to prevent data loss and minimizes additional data recovery delay. Alternatively, the gNB can configure LTM candidate cells via a single RRCReconfiguration message for the candidate target cell, via a CellGroupConfig for each candidate target cell, or via any similar RRC structure or IE containing similar fields. For example, a new IE, LTM-CandidateConfig, can be defined as an ASN1 sequence containing the CellGroupConfig and other information elements in the RRCReconfiguration message. The gNB can also modify or release the candidate configuration, while the UE can store the LTM configuration for other candidate cells even after moving to a candidate cell via LTM. Furthermore, the gNB can provide the UE with configuration for performing LTM measurements for different candidate frequencies and candidate cells and reporting based on the performed LTM measurements. Therefore, performing LTM involves various steps, such as receiving LTM configuration, performing the measurements required for LTM, reporting the measurements to the network, receiving a MAC CE (such as a cell handover command) from the network, and performing a cell handover.

[0058] Measurement configuration : For NR R17, the UE may be configured with a MeasConfig IE for performing layer 3 measurements. The NR R17v17.2.0 NR specification defines MeasConfig as follows.

[0059] MeasConfig ::= SEQUENCE {

[0060] measObjectToRemoveList MeasObjectToRemoveList OPTIONAL, -- Need N

[0061] measObjectToAddModList MeasObjectToAddModList OPTIONAL, -- Need N

[0062] reportConfigToRemoveList ReportConfigToRemoveList OPTIONAL, -- Need N

[0063] reportConfigToAddModList ReportConfigToAddModList OPTIONAL, -- Need N

[0064] measIdToRemoveList MeasIdToRemoveList OPTIONAL, -- Need N

[0065] measIdToAddModList MeasIdToAddModList

[0066] OPTIONAL, -- Need N

[0067] s-MeasureConfig CHOICE {

[0068] ssb-RSRP RSRP-Range,

[0069] csi-RSRP RSRP-Range

[0070] }

[0071] OPTIONAL, -- Need M

[0072] quantityConfig QuantityConfig

[0073] OPTIONAL, -- Need M

[0074] measGapConfig MeasGapConfig

[0075] OPTIONAL, -- Need M

[0076] measGapSharingConfig MeasGapSharingConfig OPTIONAL, -- Need M

[0077] ..., [[

[0079] interFrequencyConfig-NoGap-r16 ENUMERATED {true} OPTIONAL -- Need R ]]

[0081] }

[0082] Additional details and definitions of all parameters of MeasConfig are presented in TS 38.331 V17.2.0.

[0083] LTM measurement: The gNB has the ability to configure various measurement configurations for UEs for both Layer 3 mobility (using the MeasConfig IE in Release 17 NR) and LTM. A UE that has been configured with measurement configurations for Layer 3 mobility (commonly referred to as L3 measurements, configured via the Release 17 MeasConfig IE) as well as LTM (referred to as LTM measurements) performs both types of measurements. It is important to note that LTM measurements are considered Layer 1 measurements.

[0084] L1 measurement reports for LTM are reported periodically via the Physical Uplink Control Channel (PUCCH), semi-persistently via the PUCCH / Physical Uplink Shared Channel (PUSCH), and aperiodically on the PUSCH. MAC CEs can also be used to report L1 measurements. These reports can be scheduled by the gNB or initiated by the UE. Furthermore, the gNB can determine LTM based on uplink (UL) measurements.

[0085] Cell switching command: The gNB instructs the UE to perform LTM, prompting it to switch to the target candidate cell via a downlink (DL) MAC CE or L1 signaling. The MAC CE triggering the cell handover carries key LTM-related information, including the cell identifier. The process of initiating a cell change using the LTM feature is called cell handover. This procedure supports both RACH-based (contention-free random access (CFRA) and contention-based random access (CBRA)) and RACH-free methods for cell handover. RACH-free cell handover is suitable when the UE does not require timing advance (TA) during cell handover. RACH resources for CFRA in cell handover can be provided to the UE in the RRC configuration.

[0086] LTM cell handovers are supervised by a timer, denoted as Tcellswitch in this patent disclosure. The network is notified of the UE's arrival at the target cell via uplink signaling, either via MAC or RRC signaling. Upon receipt of a cell handover command, the timer is started and stopped once the cell handover is complete. One option is to designate Tcellswitch as a novel timer, while another option involves leveraging the existing NR RRC R17 timer T304 to monitor LTM cell handovers. When used for LTM, all embodiments described in this disclosure for Tcellswitch also relate to T304, including supervision of LTM cell handovers.

[0087] Once the UE successfully completes random access for RACH-based cell handover, the cell handover is complete. For RACH-less cell handover, the cell handover is complete once the UL transmission is successful (e.g., a UL transmission indicating the target cell). In Release 18 NR, LTM is supported in dual connectivity, such as in NR-DC, where both the mobile node and the network node are NR nodes (gNBs).

[0088] Dual Connection: 3GPP specifies dual connectivity or more technically multi-radio dual connectivity in specifications such as TS 37.340. An overview of the details of dual connectivity and measurement gap operation with dual connectivity is given below.

[0089] NG-RAN facilitates Multi-Radio Dual Connectivity (MR-DC) operation, in which an RRC_CONNECTED UE is configured to utilize radio resources provided by two different schedulers located in separate NG-RAN nodes. These nodes are connected via a non-ideal backhaul, with one providing access to NR (New Radio) and the other providing access to E-UTRA (Evolved UMTS Terrestrial Radio Access) or NR. One node serves as a Master Node (MN), while the other serves as a Secondary Node (SN). These nodes are linked via a network interface, with at least the MN connected to the core network. The cell group associated with the MN may be referred to as an MCG, and the cell group associated with the SN may be referred to as an SCG.

[0090] NG-RAN also supports NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC), in which the UE is connected to an ng-eNB (E-UTRA base station capable of connecting to the 5G core) operating as a mobile node and a gNB (5G base station) acting as a network node. Additionally, NG-RAN implements NR-E-UTRA Dual Connectivity (NE-DC), in which the UE is connected to a gNB acting as a mobile node and an ng-eNB acting as a network node.

[0091] From R17 onwards, the gNB can use RRC messages to activate or deactivate SCG. Based on certain conditions, the UE can perform random access during SCG activation.

[0092] SCG troubleshooting: The UE sends the RRC message SCGFailureInformation to report an SCG failure to the mobile node. The purpose of this procedure is to inform the mobile node of the SCG failure that the UE has experienced, namely, SCG radio link failure, failure of SCG reconfiguration with sync, SCG configuration failure of RRC messages over SRB3, SCG integrity check failure, and consistent uplink LBT failure for shared spectrum channel access operations on the PSCell. SCG failures are described in detail in 3GPP specifications (such as TS 37.340, TS 38.300, TS 38.331, etc.).

[0093] According to TS 37.340 v17.2.0, the UE supports the following SCG failures.

[0094] SCG RLF;

[0095] SCG beam failure when SCG is deactivated;

[0096] SN addition / change failure;

[0097] For EN-DC, NGEN-DC and NR-DC, SCG configuration failure or CPC (Conditional PSCell Change) configuration failure (for messages on signalling radio bearer SRB3 only);

[0098] SCG RRC integrity check failure (on signaling radio bearer SRB3) for EN-DC (dual connectivity, where the mobile node is an LTE node connected to the LTE core network), NGEN-DC (dual connectivity, where the mobile node is an LTE node connected to the NR core network), and NR-DC;

[0099] Consistent UL Listen Before Send (LBT) failure on PSCell for EN-DC, NGEN-DC, and NR-DC;

[0100] For IAB-MT, receive BH RLF indication from SCG; and

[0101] CPA / CPC execution failure.

[0102] In the event of an SCG failure, if MCG transmission of radio bearers is not suspended, that is, when the UE can send information to the MN on the MCG radio bearers, the UE suspends SCG transmission of all radio bearers and, if the SCG failure is not triggered by an SCG beam failure, also suspends transmission on any configured backhaul radio link control (BH RLC) channels and reports SCGFailureInformation to the MN instead of triggering re-establishment. If an SCG failure is detected while MCG transmission of all radio bearers is suspended, the UE initiates the RRC connection re-establishment procedure.

[0103] SCGFailureInformation is defined in TS38.331 v17.2.0 as follows.

[0104] ASN1START

[0105] TAG-SCGFAILUREINFORMATION-START

[0106] SCGFailureInformation ::= SEQUENCE {

[0107] criticalExtensions CHOICE {

[0108] scgFailureInformation SCGFailureInformation-IEs,

[0109] criticalExtensionsFuture SEQUENCE {}

[0110] }

[0111] }

[0112] SCGFailureInformation-IEs ::= SEQUENCE {

[0113] failureReportSCG FailureReportSCG OPTIONAL,

[0114] nonCriticalExtension SCGFailureInformation-v1590-IEs OPTIONAL

[0115] }

[0116] SCGFailureInformation-v1590-IEs ::= SEQUENCE {

[0117] lateNonCriticalExtension OCTET STRING OPTIONAL,

[0118] nonCriticalExtension SEQUENCE {} OPTIONAL

[0119] }

[0120] FailureReportSCG ::= SEQUENCE {

[0121] failureType ENUMERATED {

[0122] t310-Expiry, randomAccessProblem,

[0123] rlc-MaxNumRetx,

[0124] synchReconfigFailureSCG, scg-ReconfigFailure,

[0125] srb3-IntegrityFailure, other-r16, spare1},

[0126] measResultFreqList MeasResultFreqList OPTIONAL,

[0127] measResultSCG-Failure OCTET STRING (CONTAINING MeasResultSCG-Failure)OPTIONAL,

[0128] ..., [[

[0130] locationInfo-r16 LocationInfo-r16 OPTIONAL,

[0131] failureType-v1610 ENUMERATED {scg-lbtFailure-r16,beamFailureRecoveryFailure-r16,

[0132] t312-Expiry-r16, bh-RLF-r16, beamFailure-r17, spare3, spare2, spare1}OPTIONAL

[0133] ]], [[

[0135] previousPSCellId-r17 SEQUENCE {

[0136] physCellId-r17 PhysCellId,

[0137] carrierFreq-r17 ARFCN-ValueNR

[0138] } OPTIONAL,

[0139] failedPSCellId-r17 SEQUENCE {

[0140] physCellId-r17 PhysCellId,

[0141] carrierFreq-r17 ARFCN-ValueNR

[0142] } OPTIONAL,

[0143] timeSCGFailure-r17 INTEGER (0..1023) OPTIONAL,

[0144] perRAInfoList-r17 PerRAInfoList-r16 OPTIONAL ]]

[0146] }

[0147] MeasResultFreqList ::= SEQUENCE (SIZE (1..maxFreq)) OF MeasResult2NR

[0148] TAG-SCGFAILUREINFORMATION-STOP

[0149] ASN1STOP

[0150] Fast MCG link recovery:The NR UE sends MCGFailureInformation to report an MCG failure, i.e., an MCG radio link failure, to the SCG. This patent disclosure generally refers to MCGFailureInformation as any RRC message sent by the UE to the network to notify the MCG RLF through the SCG, i.e., in new wireless technologies, the message may be different. The fast MCG link recovery procedure may be performed by the network after receiving MCGFailureInformation. The network sends an MCG reconfiguration message through the SCG to restore the MCG. The UE starts a timer called the T316 timer after initiating MCGFailureInformation. If the UE does not receive the MCG reconfiguration before the timer expires, the UE initiates the RRC reestablishment procedure. Fast MCG link recovery is explained in detail in 3GPP specifications such as TS 38.331. This patent disclosure is based on v17.2.0 of TS38.331. MCGFailureInformation is defined in TS38.331 v17.2.0 as follows.

[0151] MCGFailureInformation: The MCGFailureInformation message is used to provide information about NR MCG failure detected by the UE.

[0152] Signaling Radio Bearer: SRB1

[0153] RLC-SAP:AM

[0154] Logical channel: DCCH

[0155] Direction: UE to network

[0156] MCGFailureInformation message

[0157] ASN1START

[0158] TAG-MCGFAILUREINFORMATION-START

[0159] MCGFailureInformation-r16 ::= SEQUENCE {

[0160] criticalExtensions CHOICE {

[0161] mcgFailureInformation-r16 MCGFailureInformation-r16-IEs,

[0162] criticalExtensionsFuture SEQUENCE {}

[0163] }

[0164] }

[0165] MCGFailureInformation-r16-IEs ::= SEQUENCE {

[0166] failureReportMCG-r16 FailureReportMCG-r16 OPTIONAL,

[0167] lateNonCriticalExtension OCTET STRING

[0168] OPTIONAL,

[0169] nonCriticalExtension SEQUENCE {}

[0170] OPTIONAL

[0171] }

[0172] FailureReportMCG-r16 ::= SEQUENCE {

[0173] failureType-r16 ENUMERATED {t310-Expiry, randomAccessProblem, rlc-MaxNumRetx,

[0174] t312-Expiry-r16, lbt-Failure-r16, beamFailureRecoveryFailure-r16,

[0175] bh-RLF-r16, spare1}

[0176] OPTIONAL,

[0177] measResultFreqList-r16 MeasResultList2NR

[0178] OPTIONAL,

[0179] measResultFreqListEUTRA-r16 MeasResultList2EUTRA OPTIONAL,

[0180] measResultSCG-r16 OCTET STRING (CONTAINING MeasResultSCG-Failure)OPTIONAL,

[0181] measResultSCG-EUTRA-r16 OCTET STRING OPTIONAL,

[0182] measResultFreqListUTRA-FDD-r16 MeasResultList2UTRA OPTIONAL, ...

[0184] }

[0185] MeasResultList2UTRA ::= SEQUENCE (SIZE (1..maxFreq)) OFMeasResult2UTRA-FDD-r16

[0186] MeasResult2UTRA-FDD-r16 ::= SEQUENCE {

[0187] carrierFreq-r16 ARFCN-ValueUTRA-FDD-r16,

[0188] measResultNeighCellList-r16 MeasResultListUTRA-FDD-r16

[0189] }

[0190] MeasResultList2EUTRA ::= SEQUENCE (SIZE (1..maxFreq)) OFMeasResult2EUTRA-r16

[0191] TAG-MCGFAILUREINFORMATION-STOP

[0192] ASN1STOP

[0193] Therefore, embodiments herein provide a method for handling radio link failures while performing LTM in a telecommunications network. The method includes receiving, by a UE, an LTM configuration for performing LTM measurements and a timer for supervising LTM cell handover from a network device in the telecommunications network. When the UE receives a MAC control element (CE) for LTM cell handover from a gNB, the UE may start the timer for supervising LTM cell handover. Furthermore, the method includes detecting, by the UE, a RLF in at least one cell group. Furthermore, the method includes determining, by the UE, whether a timer for supervising the LTM cell handover process is running for another cell group. Furthermore, the method includes performing, by the UE, one of the following: sending an RRC re-establishment message to the network device if the timer for supervising the LTM cell handover process is running for another cell group, and sending a cell group failure information message to the network device if the timer for supervising the LTM cell handover process is not running.

[0194] The method is able to effectively manage SCG and MCG failures in situations where the UE is set up for LTM measurements or receives a cell handover for the same purpose. By doing so, the UE significantly minimizes bandwidth inefficiencies in the telecommunications network.

[0195] This method involves verifying the status of the Tcellswitch for the Master Cell Group (MCG). If the Tcellswitch is active for the MCG, the UE initiates RRC reestablishment or transmission of SCG Failure Information. However, the SCG Failure Information procedure is only initiated if a cell handover procedure is not currently running for the MCG. In an embodiment, the UE triggers the SCG Failure Information procedure only if a cell handover procedure is not active for the SCG.

[0196] Referring now to the drawings and more particularly to Figures 1 to 9 , wherein like reference numerals indicate corresponding features consistently throughout the drawings, there is shown a preferred embodiment.

[0197] Figure 1 A block diagram of a telecommunication network (1000) for handling radio link failure while performing LTM according to an embodiment disclosed herein is shown. The telecommunication network (1000) may be, for example, but not limited to, a fourth generation (4G) network, a fifth generation (5G) network, an open radio access network (ORAN), etc. The UE (100) may be, for example, but not limited to, a laptop, a smartphone, a desktop computer, a notebook, a device-to-device (D2D) device, a vehicle-to-everything (V2X) device, a foldable phone, a smart TV, a tablet, an immersive device, and an Internet of Things (IoT) device.

[0198] The UE (100) receives an LTM configuration for performing LTM measurement and a timer for supervising LTM cell switching from a network device (200). The network device (200) is one of a mobile node (MN) and a network node (SN). In addition, the LTM measurement is one of periodic measurement, aperiodic measurement, semi-periodic measurement, and event-based measurement performed by the UE (100) configured by the network device (200) for LTM. The LTM measurement is related to one of the following: RSRP measurement, SINR measurement, and RSRQ measurement. The timer for supervising the LTM cell switching process may be an NR timer T304.

[0199] Furthermore, the UE (100) detects a radio link failure (RLF) in at least one cell group. In an embodiment, the cell group may be an MCG or an SCG. Furthermore, the UE (100) determines whether a timer for supervising a long term evolution (LTE) cell handover procedure is active on another cell group. In an embodiment, if the timer is active on the other cell group, the UE (100) sends a radio resource control (RRC) reestablishment message to the network device (200). Alternatively, in another embodiment, if the timer is not active, the UE (100) sends a cell group failure information message to the network device (200). In this embodiment, the UE (100) creates the cell group failure information message by merging LTM measurements, the LTM measurements including a candidate cell identifier and the LTM measurements of at least one candidate cell belonging to the cell group. The LTM measurements are the latest LTM measurements of the cell group. The term "latest" refers to the last measurement performed before the failure information is sent. The UE (100) then sends the cell group failure information message including the LTM measurements to the network device (200). The LTM measurements reported in the cell group fault information may be the LTM measurements of the cell group or the LTM measurements configured for all cell groups.

[0200] In an embodiment, when the fault cell group is an MCG, the cell group fault information is MCGFailureInformation. The SN sends the received MCGFailureInformation including the LTM measurement to the MN. By using the identifier(s) of the LTM candidate cell(s) reported in the MCGFailureInformation and the LTM measurement, the MN identifies a suitable LTM candidate cell to which the UE (100) can move so that the MCG link can be restored. In an embodiment, when the fault cell group is an SCG, the cell group fault information is SCGFailureInformation. By using the identifier(s) of the LTM candidate cell(s) reported in the SCGFailureInformation and the LTM measurement of the SCG, the MN identifies a suitable LTM candidate cell to which the UE (100) can move so that the SCG link can be restored.

[0201] Furthermore, the UE (100) retains in its memory an LTM configuration for a specified cell group and a current LTM candidate cell configuration for at least one potential cell belonging to the same group. The network device (200) provides the UE with the current LTM candidate cell configuration for the aforementioned candidate cells. When evaluating the content of the cell group failure information, the UE (100) stops LTM measurements for a specific cell group according to the LTM configuration. Stopping LTM measurements for a specific cell group upon cell group failure helps the UE (100) save power. This also helps avoid unnecessary cell handovers that could interfere with the cell group recovery process.

[0202] Figure 2 Various hardware components of a UE (100) according to an embodiment disclosed herein are shown. In an embodiment, the UE (100) includes a processor (110), a communicator or transceiver (120), a memory (130), and an LTM and cell group failure controller (140). The processor (110) is coupled to the communicator or transceiver (120), the memory (130), and the LTM and cell group failure controller (140).

[0203] The LTM and cell group failure controller (140) receives an LTM configuration for performing LTM measurements and a timer for supervising LTM cell switching from a network device (200). In addition, the LTM and cell group failure controller (140) detects RLF of at least one cell group. In an embodiment, the cell group is at least one of an MCG and an SCG. In addition, the LTM and cell group failure controller (140) determines whether a timer for supervising the LTM cell switching process is running on another cell group. In an embodiment, when the timer for supervising the LTM cell switching process is running on another cell group, the LTM and cell group failure controller (140) sends an RRC reestablishment message to the network device (200). In another embodiment, when the timer for supervising the LTM cell switching process is not running, the LTM and cell group failure controller (140) sends a cell group failure information message to the network device (200). In an embodiment, the LTM and cell group failure controller (140) creates the cell group failure information message by including the LTM measurements. The LTM measurements include a candidate cell identifier of at least one candidate cell belonging to the at least one cell group. Furthermore, the LTM and cell group failure controller (140) sends a cell group failure information message including the LTM measurements to the network device (200).

[0204] Furthermore, the LTM and cell group failure controller (140) stores an LTM configuration for at least one cell group and a current LTM candidate cell configuration of at least one candidate cell belonging to the at least one cell group in a memory (130) of the UE (100). The current LTM candidate cell configuration of the at least one candidate cell is received from the network device (200). Furthermore, the LTM and cell group failure controller (140) stops LTM measurement of the at least one cell group based on the LTM configuration when the cell group failure information is sent by determining the content of the cell group failure information.

[0205] The LTM and cell group fault controller (140) is implemented by analog and / or digital circuits (such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hard-wired circuits, etc.) and may optionally be driven by firmware.

[0206] The processor (110) may include one or more processors. The one or more processors may be general-purpose processors (such as a central processing unit (CPU), an application processor (AP), etc.), graphics processing units (such as a graphics processing unit (GPU), a visual processing unit (VPU)), and / or AI-specific processors (such as a neural processing unit (NPU)). The processor (110) may include multiple cores and be configured to execute instructions stored in the memory (130).

[0207] Furthermore, the processor (110) is configured to execute instructions stored in the memory (130) and perform various processes. The communicator (120) is configured to communicate internally between internal hardware components and with external devices via one or more networks. The memory (130) also stores instructions to be executed by the processor (110). The memory (130) may include a non-volatile storage element. Examples of such non-volatile storage elements may include a magnetic hard disk, an optical disk, a floppy disk, a flash memory, or a form of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). Additionally, in some examples, the memory (130) may be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or propagating signal. However, the term "non-transitory" should not be interpreted as meaning that the memory (130) is non-removable. In some instances, a non-transitory storage medium may store data that may change over time (e.g., in random access memory (RAM) or cache memory).

[0208] In an embodiment, the communicator (120) includes electronic circuitry dedicated to implementing standards for wired or wireless communication. The communicator (120) is configured to communicate internally between internal hardware components of the user device (100) and to communicate internally with external devices via one or more networks.

[0209] although Figure 2 Various hardware components of the UE (100) are shown, but it should be understood that other embodiments are not limited thereto. In other embodiments, the UE (100) may include fewer or greater numbers of components. Furthermore, the labels or names of the components are for illustrative purposes only and do not limit the scope of the present invention. One or more components may be combined to perform the same or substantially similar functions in the UE (100).

[0210] Figure 3 1 is a flow chart (S300) illustrating a method for handling radio link failure while performing LTM in a telecommunications network (1000) according to an embodiment disclosed herein. Operations (S302-S310) are handled by the LTM and cell group failure controller (140).

[0211] At S302, the method includes receiving an LTM configuration for performing LTM measurements and a timer for supervising LTM cell switching from a network device (200). At S304, the method includes detecting an RLF of at least one cell group. At S306, the method includes determining whether a timer for supervising the LTM cell switching process is running on another cell group. At S308, the method includes sending an RRC reestablishment message to the network device (200) when the timer for supervising the LTM cell switching process is running on another cell group. At S310, the method includes sending a cell group failure information message to the network device (200) when the timer for supervising the LTM cell switching process is not running.

[0212] The proposed method can be used to handle SCG and MCG failures when the UE is configured to perform LTM measurements or when a cell handover is received for which LTM is received. As a result, the UE (100) reduces bandwidth waste and saves power in the telecommunications network (1000). The network device (200) is able to identify a suitable cell for restoration, and the UE's service is immediately restored.

[0213] Figure 4 4 is a flow chart illustrating MCG fault information initiation using a tcellswitch according to an embodiment disclosed herein ( S400 ).

[0214] MCG fault information process initiated: In an embodiment, upon detecting a radio link failure of an MCG (e.g., according to Section 5.3.10.3 of TS 38.331), a UE (100) configured for fast MCG recovery according to TS 38.331 determines whether the Tcellswitch is operating for an SCG. If the Tcellswitch is operating for an SCG, the UE (100) initiates RRC reestablishment. Otherwise, the UE (100) initiates transmission of MCGFailureInformation (if other conditions required for MCGFailureInformation initiation are met). In other words, the MCG Failure Information procedure (e.g., as specified in Section 5.7.3b of NR TS 38.331) is initiated only when the cell handover procedure is not operating for an SCG.

[0215] Below is an example specification excerpt from TS 38.331 with reference to v17.2.0: 5> If neither PSCell change, PSCell add, nor cell switch is in progress (i.e., timer T304 for the NR PSCell is not running in the case of NR-DC, or timer T307 for the E-UTRA PSCell is not running in NE-DC as specified in TS 36.331 section 5.3.10.10, or timer Tcellswitch is running). 6> Initiate the MCG Failure Information procedure as specified in 5.7.3b to report an MCG radio link failure. 5> Otherwise: 6> Initiate the connection re-establishment procedure as specified in 5.3.7.

[0216] like Figure 4 As shown, operations (S402-S408) are handled by the LTM and cell group failure controller (140). At S402, the method includes detecting an MCG RLF. At S404, the method includes determining whether the Tcellswitch for the SCG is running. In response to determining that the Tcellswitch for the SCG is running, at S406, the method includes sending an RRC Reestablishment. At S408, in response to determining that the Tcellswitch for the SCG is not running, the method includes: sending an MCGFailureInformation if other conditions are also met. The other conditions include that there is no ongoing L3 mobility for the SCG, the SCG is not deactivated, and a timer (such as T316) in the NR is configured.

[0217] Figure 5 is a flowchart ( S500 ) illustrating MCG fault information transmission when LTM is configured according to an embodiment disclosed herein.

[0218] In an embodiment, the content of the MCG failure information is determined, and the UE (100) indicates that the MCG has failed due to Tcellswitch expiration in the RRC message MCGFailureInformation to indicate that the MCG has failed. If the UE (100) is initiating the MCG failure information procedure due to Tcellswitch expiration, the UE (100) sets the failureType (failureType field in the RRCMCGFailureInformation message) to tcellswitch-Expiry. Alternatively, a flag may be included in the MCGFailureInformation to indicate that the tcellswitch has failed.

[0219] In an embodiment, a UE (100) configured for LTM measurements (L1 measurements for LTM) and initiating transmission of a MCGFailureInformation message includes the LTM measurements, i.e., a cell identifier and L1 measurements, in the MCGFailureInformation message. In an embodiment, the UE (100) includes the latest LTM measurements in the MCGFailureInformation message. In an embodiment, the UE (100) sends an average value of the LTM measurements over a specific time period to a network device (200) via the MCGFailureInformation message. In an embodiment, the time period for performing the averaging is received from the network device (200). In an embodiment, the LTM measurement may be one of a periodic measurement, an aperiodic measurement, a semi-periodic measurement, or an event-based measurement performed by the UE (100) configured by the gNB for LTM.

[0220] In an embodiment, the LTM measurement included in MCGFailureInformation is an RSRP (Reference Signal Received Power) measurement. In an embodiment, the LTM measurement included in MCGFailureInformation is an SINR (Signal to Interference and Noise Ratio) measurement. In an embodiment, the LTM measurement included in MCGFailureInformation is an RSRQ (Reference Signal Received Quality) measurement.

[0221] In an embodiment, the UE (100) includes LTM measurements of both MCG and SCG in MCGFailureInformation.

[0222] In an embodiment, the included cell identifier is a physical cell identifier.In an embodiment, the included cell identifier is a candidate cell identifier configured for LTM.In an embodiment, the included cell identifier is a temporary cell identifier configured for LTM.

[0223] In an embodiment, the UE (100) includes LTM measurements only for the MCG and not for the SCG in the MCGFailureInformation.

[0224] In an embodiment, the UE (100) skips filtering the LTM measurements included in the MCGFailureInformation according to L3 filtering rules.

[0225] In an embodiment, a UE (100) configured with both L1 and L3 measurements for the same cell includes only the L3 measurements in the MCG failure information. In an alternative embodiment, a UE (100) configured with both L1 and L3 measurements for the same cell includes both L1 and L3 measurements in the MCG failure information. The gNB may use the received L1 measurements and the cell identifier to identify a cell to which the UE may move during the MCG recovery procedure.

[0226] In an embodiment, the UE (100) includes LTM measurement results available based on the current LTM measurement configurations of both the MN and the SN. Once fast MCG link recovery is triggered, the UE (100) maintains the current LTM measurement configurations from both the MN and the SN. The UE (100) stops LTM measurements based on the configuration from the MN. This will ensure that the UE does not unnecessarily waste its battery power with respect to MN operations. In an embodiment, the UE (100) stops LTM measurements based on the configuration from the SN. This will ensure that the UE (100) does not unnecessarily waste its battery power with respect to SN operations. This also prevents cell handover at a faulty SN that may lead to MCG recovery. The UE (100) also maintains the current LTM candidate cell configurations from both the MN and the SN, thereby avoiding the need to reconfigure the LTM configuration again.

[0227] In an alternative embodiment, once fast MCG link recovery is triggered, the UE (100) continues measurements based on the LTM configuration from the MN. This implementation helps the UE (100) to quickly perform LTM cell handover of the MCG when the MCG link recovery is successful.

[0228] In yet another embodiment, once fast MCG link recovery is triggered, the UE (100) continues measurements based on the LTM configuration from the SN. This will help the UE (100) to quickly perform LTM cell handover of the SCG when the MCG link recovery is successful.

[0229] In an alternative embodiment, once fast MCG link recovery is triggered, the UE (100) clears the LTM candidate cell configuration from the MN. The MN's new reconfiguration for fast MCG link recovery may establish LTM candidates according to its updated requirements.

[0230] In yet another embodiment, once fast MCG link recovery is triggered, the UE (100) clears the LTM candidate cell configuration from the SN. The new reconfiguration of the MN for fast MCG link recovery can establish the SCG and SCG LTM candidates according to its updated requirements.

[0231] An example specification excerpt for a MCGFailureInformation report with LTM measurements according to TS 38.331 is given below.

[0232] FailureReportMCG-r16 ::= SEQUENCE {

[0233] failureType-r16 ENUMERATED {t310-Expiry, randomAccessProblem, rlc-MaxNumRetx,

[0234] t312-Expiry-r16, lbt-Failure-r16, beamFailureRecoveryFailure-r16,

[0235] bh-RLF-r16, spare1}

[0236] OPTIONAL,

[0237] measResultFreqList-r16 MeasResultList2NR OPTIONAL,

[0238] measResultFreqListEUTRA-r16 MeasResultList2EUTRA OPTIONAL,

[0239] measResultSCG-r16 OCTET STRING (CONTAINING MeasResultSCG-Failure)OPTIONAL,

[0240] measResultSCG-EUTRA-r16 OCTET STRING OPTIONAL,

[0241] measResultFreqListUTRA-FDD-r16 MeasResultList2UTRA OPTIONAL, [[

[0243] ltmMeasResults-r18LtmMeasResults-r18 OPTIONAL ]] ...

[0246] }

[0247] LtmMeasResults-r18 SEQUENCE {

[0248] ltmRSRPMeasResults-r18LTMRSRPMeasResults-r18 OPTIONAL,

[0249] ltmRSRQMeasResults-r18LTMRSRPMeasResults-r18 OPTIONAL,

[0250] ltmSINRMeasResults-r18LTMSINRMeasResults-r18 OPTIONAL,

[0251] }

[0252] The LTM measurement results are included in the FailureReportMCG sequence.

[0253] In an embodiment, the MN is a gNB and the DC is an NR-NR DC, i.e., the SN is also a gNB.

[0254] In an embodiment, a UE (100) configured for LTM measurements (L1 measurements for LTM) and initiating transmission of a MCGFailureInformation message skips including LTM measurements, i.e., cell identifiers and L1 measurements, in the MCGFailureInformation message. The UE (100) includes only L3 measurements in the MCG FailureInformation message. In an embodiment, the UE (100) may include cell identifiers for which measurements are performed / measurements are available, but not L1 measurements of LTM candidate cells.

[0255] In an embodiment, after sending MCGFailureInformation, based on the received LTM measurement results, the MN decides whether there is an available MCG cell that the UE (100) can move to. If so, the MN can send an RRC reconfiguration message.

[0256] In an embodiment, upon receiving the MCGFailureInformation message, the MN may send an RRCConnectionReconfiguration message, an RRCReconfiguration message, a MobilityFromNRCommand message, a MobilityFromUTRACommand message, an RRCConnectionRelease message, or an RRCRecrelease message to the UE (100) using a detached SCG branch of SRB1 or SRB3. When the UE (100) receives any of these messages, the fast MCG failure is completed. Upon receiving the RRCReconfiguration message, if the MN and SN LTM measurements were stopped while the fast MCG link recovery was triggered, the UE (100) resumes the MN and SN LTM measurements (and if the measurement configuration allows).

[0257] Cell handover during fast MCG link recovery: In an embodiment, if the UE (100) receives a cell handover command (e.g., for SCG) while T316 is running, T316 is stopped (T316 is defined in TS 38.331, version V17.2.0 of the specification to which the proposed invention refers) and an RRC Reestablishment is sent. If a cell handover command for SCG is received while the fast MCG link recovery procedure is not completed, the UE (100) considers that the fast MCG link recovery has failed. This will help the UE (100) to recover via RRC Reestablishment because during cell handover, downlink SCG transmission may be stopped and the recovery message may not reach the UE (100) until the recovery is complete.

[0258] In an embodiment, if the UE (100) receives a cell handover command (e.g., for SCG) while T316 is running and the cell handover is unsuccessful, T316 is stopped (T316 is defined in TS 38.331, the proposed invention refers to version V17.2.0 of the specification) and RRC Reestablishment is sent. If a cell handover command for SCG is received while the fast MCG link recovery process is not completed and the cell handover command is unsuccessful (e.g., due to T316 expiration), the UE (100) for fast MCG link recovery is considered to have failed.

[0259] like Figure 5As shown, operations (S502-S508) are handled by the LTM and cell group fault controller (140). At S502, the method includes receiving an LTM configuration for L1 measurement and performing L1 measurement. At S504, the method includes detecting an MCG RLF and sending an MCGFailureInformation. At S506, the method includes creating an MCGFailureInformation message including the L1 measurement. The method includes maintaining the L1 measurement configuration and candidate cell configuration for the LTM. The method includes stopping the LTM measurement. At S508, the method includes sending the MCGFailureInformation to the network device (200).

[0260] Figure 6 6 is a flowchart illustrating SCG fault information initiation using a Tcellswitch according to an embodiment disclosed herein ( S600 ).

[0261] SCG fault information process initiated: In an embodiment, upon detecting a radio link failure for an SCG (e.g., in accordance with Section 5.3.10.3 of TS 38.331), the UE (100) determines whether the Tcellswitch is operating for the MCG. If the Tcellswitch is operating for the MCG, the UE (100) initiates RRC reestablishment. Otherwise, the UE (100) initiates transmission of SCGFailureInformation (if other conditions required for SCGFailureInformation initiation are met). In other words, the SCG failure information procedure (e.g., as specified in Section 5.7.3 of NR TS 38.331) is initiated only when the cell handover procedure is not operating for the MCG. In an embodiment, the UE (100) initiates the SCG failure information procedure only when the cell handover procedure is not operating for the SCG. In an embodiment, the UE (100) may send SCGFailureInformation without checking whether the Tcellswitch for the MCG is operating. In another embodiment, the UE (100) may postpone sending SCGFailureInformation until the Tcellswitch for the MCG stops.

[0262] like Figure 6As shown, operations (S602-S608) are handled by the LTM and cell group failure controller (140). At S602, the method includes detecting an SCG RLF. At S604, the method includes determining whether the Tcellswitch for the MCG is running. In response to determining that the Tcellswitch for the MCG is running, at S606, the method includes sending an RRC Reestablishment. In response to determining that the Tcellswitch for the MCG is not running, at S608, the method includes: sending an SCGFailureInformation if other conditions are also met. The other conditions include that MCG and SCG transmissions are not suspended.

[0263] Figure 7 is a flow chart ( S700 ) illustrating SCG fault information transmission when LTM is configured according to an embodiment as disclosed herein.

[0264] Determine the content of the SCG fault message: The UE (100) indicates that the SCG has failed due to Tcellswitch expiration in an RRC message sent to indicate that the SCG has failed (e.g., SCGFailureInformation). That is, the UE (100) sends information in SCGFailureInformation that the SCGFailure is due to Tcellswitch. If the UE (100) is initiating the SCG failure information procedure due to Tcellswitch expiration, the UE (100) sets the failureType to tcellswitch-Expiry in SCGFailureInformation. Alternatively, a flag may be included in the SCGFailureInformation message to indicate that the SCGFailureInformation is initiated due to Tcellswitch expiration.

[0265] In an embodiment, a UE (100) is configured for LTM measurements (L1 measurements for LTM) and is initiating transmission of an SCGFailureInformation message including LTM measurements (i.e., a cell identifier and L1 measurements in the SCGFailureInformation message). In an embodiment, the UE (100) includes the latest LTM measurements in the SCGFailureInformation message. In an embodiment, the UE (100) sends an average of the LTM measurements over a specific time period to the network in the SCGFailureInformation message. The time period for averaging may be communicated to the UE (100) by the gNB. In an embodiment, the LTM measurements may be one of periodic measurements, aperiodic measurements, semi-periodic measurements, or event-based measurements performed by the UE (100) as configured by the gNB for LTM. The gNB (MN) may use the received L1 measurements and cell identifier to identify an SCG cell to which the UE may move to continue SCG operation. The received measurements may also be used by various network entities to drive self-optimization and minimization for testing purposes.

[0266] In an embodiment, the LTM measurement included in SCGFailureInformation is an RSRP (Reference Signal Received Power) measurement. In an embodiment, the LTM measurement included in SCGFailureInformation is an SINR (Signal to Interference and Noise Ratio) measurement. In an embodiment, the LTM measurement included in SCGFailureInformation is an RSRQ (Reference Signal Received Quality) measurement.

[0267] In an embodiment, the UE (100) includes LTM measurements of both MCG and SCG in SCGFailureInformation.

[0268] In an embodiment, the included cell identifier is a physical cell identifier. In an embodiment, the included cell identifier is a candidate cell identifier configured for LTM. In an embodiment, the included cell identifier is a temporary cell identifier configured for LTM.

[0269] In an embodiment, even if both LTM measurements for SCG and LTM measurements for MCG are configured in SCGFailureInformation, the UE (100) includes LTM measurements for SCG instead of MCG. LTM measurements are included only when LTM measurements for SCG are configured and available.

[0270] In an embodiment, the UE skips filtering the LTM measurements included in the SCGFailureInformation according to L3 filtering rules.

[0271] In an embodiment, a UE (100) configured with both L1 and L3 measurements for the same cell includes only the L3 measurements in the SCG failure information. In an alternative embodiment, a UE (100) configured with both L1 and L3 measurements for the same cell includes both the L1 and L3 measurements in the SCG failure information. In an alternative embodiment, a UE (100) configured with both L1 and L3 measurements for the same cell includes both the L1 and L3 measurements in the SCG failure information.

[0272] In an embodiment, the UE (100) includes LTM measurement results available based on the current LTM measurement configuration of both the MN and the SN. Once the SCGFailureInformation message is triggered, the UE (100) maintains the current LTM measurement configuration from both the MN and the SN. In an embodiment, the UE (100) stops LTM measurement based on the configuration from the SN. This will help save power at the UE (100). In an embodiment, the UE (100) continues LTM measurement based on the configuration from the MN. This will help perform any MN-triggered cell handover regardless of a failure at the SCG. In an embodiment, the UE (100) maintains the current LTM candidate cell configuration from both the MN and the SN. This will help the UE and the gNB quickly recover the LTM configuration without additional signaling overhead.

[0273] In an alternative embodiment, even after sending SCGFailureInformation, the UE (100) continues measuring based on the LTM configuration from the SN. Such an implementation helps to quickly perform LTM after the SCG link is restored at the expense of some power consumption.

[0274] In yet another embodiment, once the SCGFailureInformation is sent, the UE (100) stops the measurement based on the LTM configuration from the SN.

[0275] In an alternative embodiment, once the SCGFailureInformation is sent, the UE (100) clears the LTM candidate cell configuration from the MN.

[0276] In yet another embodiment, once the SCGFailureInformation is sent, the UE (100) clears the LTM measurement configuration from the SN. Once the SCG is restored, the gNB can configure the UE (100) with the new configuration.

[0277] In an embodiment, the dual-connectivity deployment scenario of SCGFailureInformation in this patent disclosure is NR-NRDC.

[0278] like Figure 7 As shown, operations (S702-S708) are handled by the LTM and cell group fault controller (140). At S702, the method includes receiving an LTM configuration for L1 measurement and performing L1 measurement. At S704, the method includes detecting an SCG RLF and sending SCGFailureInformation. At S706, the method includes creating an SCGFailureInformation message including the L1 measurement. The method includes maintaining the L1 measurement configuration and candidate cell configuration for the LTM. In addition, the method includes stopping the LTM measurement. At S708, the method includes sending SCGFailureInformation to the network device (200).

[0279] Figure 8 Various hardware components of a network device (200) according to an embodiment disclosed herein are shown. In an embodiment, the network device (200) includes a processor (210), a communicator or transceiver (220), a memory (230), and an LTM and cell group failure controller (240). The processor (210) is coupled to the communicator or transceiver (220), the memory (230), and the LTM and cell group failure controller (240).

[0280] The LTM and cell group failure controller (240) receives one of MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements from the UE (100). In an embodiment, when a timer for supervising the LTM cell switching process is not running in the UE (100), the network device receives one of the following from the UE: MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements. In an embodiment, the LTM and cell group failure controller (240) sends an MCG reconfiguration message based on the MCGFailureInformation to restore the MCG link. In another embodiment, the LTM and cell group failure controller (240) sends an SCG reconfiguration message based on the SCGFailureInformation to restore the SCG link.

[0281] The LTM and cell group fault controller (240) is implemented by analog and / or digital circuits (such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hard-wired circuits, etc.) and may optionally be driven by firmware.

[0282] The processor (210) may include one or more processors. The one or more processors may be general-purpose processors (such as a central processing unit (CPU), an application processor (AP), etc.), graphics processing units (such as a graphics processing unit (GPU), a visual processing unit (VPU)), and / or AI-specific processors (such as a neural processing unit (NPU)). The processor (210) may include multiple cores and be configured to execute instructions stored in the memory (230).

[0283] In addition, the processor (210) is configured to execute instructions stored in the memory (230) and perform various processes. The communicator (220) is configured to communicate internally between internal hardware components and with external devices via one or more networks. The memory (230) also stores instructions to be executed by the processor (210). The memory (230) may include a non-volatile storage element. Examples of such non-volatile storage elements may include a magnetic hard disk, an optical disk, a floppy disk, a flash memory, or a form of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). In addition, in some examples, the memory (230) may be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or propagating signal. However, the term "non-transitory" should not be interpreted as meaning that the memory (230) is non-removable. In some instances, a non-transitory storage medium may store data that may change over time (e.g., in random access memory (RAM) or cache memory).

[0284] In an embodiment, the communicator (220) includes electronic circuitry dedicated to implementing standards for wired or wireless communication. The communicator (220) is configured to communicate internally between internal hardware components of the user equipment (100) and with external devices via one or more networks.

[0285] although Figure 8 Various hardware components of the network device (200) are shown, but it should be understood that other embodiments are not limited thereto. In other embodiments, the network device (200) may include fewer or greater numbers of components. Furthermore, the labels or names of the components are for illustrative purposes only and do not limit the scope of the present invention. One or more components may be combined to perform the same or substantially similar functions in the network device (200).

[0286] Figure 9 The present invention is a flowchart (S900) illustrating a method implemented by a network device (200) for handling radio link failure when performing LTM in a telecommunications network (1000) according to an embodiment disclosed herein. Operations (S902-S906) are handled by the LTM and cell group failure controller (240).

[0287] At S902, the method includes receiving one of MCGFailureInformation including LTM measurements and SCGFailureInformation including LTM measurements from the UE (100). At S904, the method includes sending an MCG reconfiguration message based on the MCGFailureInformation to restore the MCG link. At S906, the method includes sending an SCG reconfiguration message based on the SCGFailureInformation to restore the SCG link.

[0288] The various actions, blocks, steps, etc. in the flowcharts (S300-S700 and S900) may be performed in the order presented, in a different order, or simultaneously. In addition, in some embodiments, some of the actions, blocks, steps, etc. may be omitted, added, modified, skipped, etc. without departing from the scope of the present invention.

[0289] This invention proposes an innovative method and UE for managing SCG and MCG failures when the UE is configured to implement Long Term Evolution (LTM) measurements or has received a cell handover request for LTM. The invention encompasses various related embodiments for configuring LTM, releasing LTM, and regulating the interaction of LTM with other features and conditions. The proposed invention is used to conserve overall UE resources, such as battery, performance, and cost.

[0290] The foregoing description of the specific embodiments will fully reveal the general nature of the embodiments herein so that others can easily modify and / or adapt such specific embodiments for various applications by applying current knowledge without departing from the general concepts, and therefore, such adjustments and modifications should and are intended to be understood as being within the meaning and range of equivalents of the disclosed embodiments. It should be understood that the wording or terminology employed herein is for purposes of description and not limitation. Therefore, although the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein may be practiced by modification within the scope of the embodiments as described herein.

Claims

1. A method performed by a user equipment (UE) associated with a first cell group and a second cell group in a wireless communication system, the method comprising: receiving a control message from a base station, the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching; while performing LTM cell handover, detecting a radio link failure of the first cell group among the first cell group and the second cell group; identifying whether a timer for supervising LTM cell switching is running on the second cell group; as well as In a case where the timer for supervising the LTM cell switching is running on the second cell group, a radio resource control (RRC) re-establishment message is sent to the base station.

2. The method according to claim 1, further comprising: In a case where the timer for supervising the LTM cell switching is not running on the second cell group, a first cell group failure information message is sent to the base station.

3. The method according to claim 2, in, The timer for supervising the LTM cell switching includes T304, The first cell group fault information message includes an MCG fault information message, and The first cell group includes a master cell group (MCG) associated with a primary node, and the second cell group includes a secondary cell group (SCG) associated with a secondary node.

4. The method according to claim 1, further comprising: identifying whether the timer for supervising the LTM cell switching of the second cell group has expired based on detecting a radio link failure (RLF) of the second cell group; as well as When the timer for supervising the LTM cell switching of the second cell group expires, sending a second cell group failure information message to the base station, The failure type field is included in the second cell group failure information message, and the failure type field is used to indicate that the second cell group fails due to the expiration of the timer used to supervise the LTM cell switching of the second cell group.

5. The method according to claim 4, in, The timer for supervising the LTM cell switching includes T304, The second cell group fault information message includes a secondary cell group (SCG) fault information message, and The first cell group includes a master cell group (MCG) associated with a master node, and the second cell group includes an SCG associated with a secondary node.

6. A method performed by a base station in a wireless communication system, the method comprising: sending a control message to a user equipment (UE), the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching; and receiving a radio resource control (RRC) re-establishment message from the UE in a case where the timer for supervising the LTM cell switching is running on a second cell group, The UE is associated with a first cell group and a second cell group, The UE detects a radio link failure of the first cell group among the first cell group and the second cell group while performing LTM cell handover. The UE identifies whether the timer for supervising the LTM cell switching is running on the second cell group.

7. The method according to claim 6, further comprising: In a case where the timer for supervising the LTM cell switching is not running on the second cell group, a first cell group failure information message is received from the UE.

8. The method according to claim 6, further comprising: receiving a second cell group failure information message from the UE in a case where the timer for supervising the LTM cell switching of the second cell group expires, The UE identifies whether the timer for supervising the LTM cell switching of the second cell group has expired based on detecting a radio link failure (RLF) of the second cell group. The failure type field is included in the second cell group failure information message, and the failure type field is used to indicate that the second cell group fails due to the expiration of the timer used to supervise the LTM cell switching of the second cell group.

9. A user equipment (UE) associated with a first cell group and a second cell group in a wireless communication system, the UE comprising: transceiver; as well as The processor is configured to: receiving a control message from a base station, the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching, while performing LTM cell handover, detecting a radio link failure of the first cell group among the first cell group and the second cell group; identifying whether the timer for supervising the LTM cell handover is running on the second cell group, and In a case where the timer for supervising the LTM cell switching is running on the second cell group, a radio resource control (RRC) re-establishment message is sent to the base station.

10. The UE according to claim 9, wherein the processor is further configured to: In a case where the timer for supervising the LTM cell switching is not running on the second cell group, a first cell group failure information message is sent to the base station.

11. The UE according to claim 10, in, The timer for supervising the LTM cell switching includes T304, The first cell group fault information message includes an MCG fault information message, and The first cell group includes a master cell group (MCG) associated with a primary node, and the second cell group includes a secondary cell group (SCG) associated with a secondary node.

12. The UE according to claim 9, wherein the processor is further configured to: identifying whether the timer for supervising the LTM cell switching of the second cell group has expired based on detecting a radio link failure (RLF) of the second cell group, and When the timer for supervising the LTM cell switching of the second cell group expires, sending a second cell group failure information message to the base station, in, A failure type field is included in the second cell group failure information message, the failure type field being used to indicate that a failure occurs in the second cell group due to expiration of the timer for supervising the LTM cell switching of the second cell group.

13. The UE according to claim 12, in, The timer for supervising the LTM cell switching includes T304, The second cell group fault information message includes a secondary cell group (SCG) fault information message, and The first cell group includes a master cell group (MCG) associated with a master node, and the second cell group includes an SCG associated with a secondary node.

14. A base station in a wireless communication system, the base station comprising: transceiver; as well as The processor is configured to: sending a control message to a user equipment (UE), the control message including a lower layer triggered mobility (LTM) configuration for performing LTM measurements and a timer for supervising LTM cell switching, and receiving a radio resource control (RRC) re-establishment message from the UE in a case where the timer for supervising the LTM cell switching is running on a second cell group, The UE is associated with a first cell group and a second cell group, The UE detects a radio link failure of the first cell group among the first cell group and the second cell group while performing LTM cell handover. The UE identifies whether the timer for supervising the LTM cell switching is running on the second cell group.

15. The base station according to claim 14, wherein the processor is further configured to: In a case where the timer for supervising the LTM cell switching is not running on the second cell group, a first cell group failure information message is received from the UE.

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