MCG (de) activation during MCG failure

Abstract

Described herein is a user equipment (UE) configured for operation in dual connectivity, where the UE is served by a primary cell group (MCG) and a secondary cell group (SCG), the MCG is configured by a primary node (MN), and the SCG is configured by a secondary node (SN), the UE comprising: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, transmit the instructions to the at least one processor; causing the UE to at least: detect an MCG link failure; starting a timer for deactivating the MCG; and deactivating the MCG.

Description

Technical Field

[0001] This disclosure relates to the failure of the MCG link in dual connectivity, and particularly to the deactivation of the MCG in the case of an MCK link failure. Background Art

[0002] Any discussion of background art throughout the specification should not be construed as an admission that such art is widely known or forms part of the common general knowledge in the art.

[0003] Due to the rapid degradation of the PCell (Primary Cell) link, the UE (User Equipment) may not receive the handover command in time, or may not have time to report the PCell measurement. In this case, the UE may experience RLF (Radio Link Failure) or MCG (Master Cell Group) link failure in the dual connectivity scenario.

[0004] Even if the UE has sent a measurement report, the UE may still experience RLF or MCG link failure. In this scenario, there are two possible cases:

[0005] Case 1: The UE is configured to measure all frequency layers. The MN (Master Node) does not find a suitable cell on any frequency layer based on the measurement report provided by the UE. In other words, the UE is in a coverage hole.

[0006] Case 2: The UE is configured to measure some frequency layers. The MN does not find a suitable cell on the frequency layers that the UE is configured to measure, only because the network does not configure some inter-frequency measurements at the UE. In other words, the MN does not have all the information it can trigger for inter-frequency handover.

[0007] According to the traditional process (up to version 17), once the UE detects RLF or MCG link failure in dual connectivity, the process of UE reconstruction or MCG failure recovery (if configured) is triggered.

[0008] This means that in Case 1 above, the UE RRC (Radio Resource Control) reconstruction or UE RRC release (if MCG failure recovery is configured, but the MN cannot find any neighboring cells for handover or changing the bearer configuration) will be immediately executed. If the UE returns within the coverage area of the serving PCell, the UE must perform RRC reconstruction after cell selection. This process results in unnecessary delays.

[0009] Problem 1: Coverage holes / gaps may cause the UE to trigger RRC reconstruction, resulting in additional interruption time due to cell selection and RRC reconstruction in addition to the interruption caused by the coverage gap.

[0010] Similarly, in the above Case 2, the UE will be released, and it will perform cell selection to another frequency other than the frequency of the serving PCell and reconstruct the link, resulting in additional latency. A simple solution for Case 2 is to configure all inter-frequency measurements from the beginning, but this solution is neither resource-efficient nor energy / cost-efficient due to the need for measurement gaps, as multiple active RF (radio frequency) chains are required.

[0011] Problem 2: To avoid coverage gaps, the UE has to perform inter-frequency measurements, resulting in unnecessary throughput loss, latency, and higher energy consumption and device cost.

[0012] Traditional procedures (up to Release 17) do not solve this problem, and there is no solution for the above cases in the conventional art. Moreover, following the traditional procedures results in additional latency, which is not optimal for latency-critical applications.

[0013] Therefore, in a dual-connectivity scenario where, for example, handover or cell selection for the MCG is to be performed, in the case of RLF or MCG link failure, especially for latency-critical applications, it is necessary to reduce the latency and signaling overhead caused by, for example, UE RRC reconstruction or release. In the above scenarios, in the case of RLF or MCG link failure, it is also necessary to reduce throughput loss, energy consumption, and device cost. Summary of the Invention

[0014] An object of the present disclosure is to provide a user equipment UE and a master node MN for reducing latency and signaling overhead, as well as throughput loss, energy consumption, and device cost in the case of RLF or MCG link failure in dual connectivity.

[0015] Another object of the present disclosure is to provide a system comprising at least the UE and the MN for reducing latency and signaling overhead, as well as throughput loss, energy consumption, and device cost in the case of RLF or MCG link failure in dual connectivity.

[0016] Another object of the present disclosure is to provide methods for the UE, the MN, and the system, configured to reduce latency and signaling overhead, as well as throughput loss, energy consumption, and device cost in the case of RLF or MCG link failure in dual connectivity.

[0017] According to one aspect of the present disclosure, there is provided a user equipment UE configured to operate in a dual connection, where the UE is served by a master cell group MCG and a secondary cell group SCG, the MCG is configured by a master node MN, and the SCG is configured by a secondary node SN. The UE includes: at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the UE to at least: detect an MCG link failure; start a timer for deactivating the MCG; and deactivate the MCG.

[0018] In the present disclosure, "MN" and "source MN" are used interchangeably to refer to the MN that configures the MCG currently serving the UE, that is, the MN that serves the UE before performing a handover to a target MN or before performing a selective activation of a candidate target cell.

[0019] According to the present disclosure, in the case of an MCG link failure, a timer is started at the UE during which the MCG is deactivated. Therefore, in the case of an MCG link failure, UE RRC reconstruction or release is not immediately performed, thus avoiding unnecessary delays and signaling overhead.

[0020] In some examples, the UE is further caused to: send an (extended) measurement report to the MN while the timer is running.

[0021] Wherein, the UE providing an extended measurement report preferably means that the UE performs network measurements during the period when the MCG is deactivated.

[0022] According to the present disclosure, when the MCG is deactivated, the UE continues to provide measurements, that is, extended measurement reports, so that the measurements can be directly applied to, for example, MCG activation, selective activation of candidate target cells, handover for the MCG, etc. Therefore, the delays for MCG activation, selective activation of candidate target cells, and handover for the MCG can be reduced (for example, after the timer expires or when a candidate target cell is selected), because there is no need to provide measurements from scratch, but they are ready for use at the UE.

[0023] In some examples, the extended measurement report is periodic, event-triggered, or event-triggered periodic.

[0024] In some examples, the extended measurement report includes at least the latest in-band measurement report and at least one of the following: inter-band measurement report and radio access technology RAT inter-band measurement report.

[0025] In some examples, the UE being caused to deactivate the MCG includes: the UE being caused to: suspend MCG transmissions for all radio bearers while the timer is running, maintain the measurement configuration for the MCG, and continue to measure the MCG based on the maintained MCG measurement configuration.

[0026] According to the present disclosure, during the operation of the timer, the measurement configuration for the MCG is maintained so that measurements can be continuously obtained at the UE even during MCG deactivation. Thus, the obtained measurements can be directly applied to, for example, MCG activation, selective activation of candidate target cells, handover for the MCG, etc. Therefore, the latency of MCG activation, selective activation of candidate target cells, and handover for the MCG can be reduced (e.g., after the timer expires or when a candidate target cell is selected), because there is no need to provide measurements from scratch, but they are ready for use at the UE.

[0027] In some examples, the UE is further configured to: in response to detecting an MCG failure and preferably before starting the timer, preferably send an MCG (link) failure indication message to the MN via the SN, for indicating to the MN the detected MCG link failure.

[0028] According to the present disclosure, the MN is notified of the MCG link failure so that the MN can prepare for MCG deactivation in response to receiving the MCG link failure indication message, e.g., provide the UE with an MCG deactivation configuration (e.g., timer configuration) for deactivating the MCG during the operation of the timer.

[0029] In some examples, the UE is further configured to: directly start the timer after detecting the MCG link failure, where the UE is configured with an MCG deactivation configuration that is to be enabled by the UE when the UE detects the MCG link failure.

[0030] According to the present disclosure, deactivation of the MCG is provided at the UE as a default or fallback step once the UE detects an MCG link failure, because the UE has been provided with the MCG deactivation configuration before detecting the MCG link failure. For example, the UE notifies the network of the MCG deactivation capability configured at the UE, and preferably, the network provides the UE with the MCG deactivation configuration after being notified of the UE's MCG deactivation capability. Thus, MCG deactivation can be directly performed immediately after detecting the MCG link failure, further reducing latency and signaling overhead.

[0031] Wherein, the MCG deactivation configuration preferably refers to the timer configuration, and more preferably refers to whether the UE should apply the timer. Preferably, this is part of the general RRC reconfiguration message provided to the UE.

[0032] In some examples, the UE is further configured to: start the timer in response to receiving an MCG deactivation signaling message.

[0033] Among them, the MCG deactivation signaling message is also referred to as the MCG deactivation command message, which is preferably provided by the MN (preferably via the SN) to trigger MCG deactivation. Preferably, the MCG deactivation signaling message includes MCG deactivation configuration (for example, timer configuration including the length of the time period set for the timer). Additionally or alternatively, the MCG deactivation configuration is sent to the UE via a separate message.

[0034] In some examples, the UE is also made to: in response to receiving a first radio resource control (RRC) reconfiguration message, start a timer, where the first RRC reconfiguration message preferably includes a command for the UE to perform inter-frequency measurement and configuration related to performing inter-frequency measurement.

[0035] Among them, the first RRC reconfiguration message is preferably provided by the MN (preferably via the SN) to trigger MCG deactivation. Preferably, the first RRC reconfiguration message includes MCG deactivation configuration (for example, timer configuration including the length of the time period set for the timer). Additionally or alternatively, the MCG deactivation configuration is sent to the UE via a separate message.

[0036] In some examples, the UE is also made to: in response to a first radio condition, start a timer, where the first radio condition includes radio link failure (RLF) through the start of T310 or the UE receiving X or N310 consecutive different synchronization OoS indications from the physical layer.

[0037] Among them, 5G NR timers include, for example, T304 timer, T310 timer, and T311 timer used for various functions in 5G NR (New Radio), where constants such as N310 and N311 are used, which is a traditional RLF process. For example, when N310 consecutive OoS indications are provided, RLF is declared at the UE. The RLF timer T310 is also triggered.

[0038] In some examples, the UE is also made to: in response to a second radio condition, start a timer, where the second radio condition includes detecting that the frequency layer of the MCG or the measurement on the frequency for all configurations of the MCG is below a threshold.

[0039] Among them, the threshold is preferably configured by the network.

[0040] In some examples, the UE is also made to: in response to receiving a second radio resource control (RRC) reconfiguration message for performing a handover to the MCG, stop the timer; and perform the handover.

[0041] Among them, the second RRC reconfiguration message is preferably provided by the MN (preferably via the SN) to instruct the UE to perform a handover. Among them, preferably, "handover to the MCG" refers to the handover from the (source) MN to the target MN. Therefore, the UE performs a handover and stops the timer.

[0042] In some examples, the UE is also caused to: in response to receiving the MCG activation command message, stop the timer; and activate the deactivated MCG.

[0043] Among them, the MCG activation message is also referred to as the MCG activation signaling message to instruct the UE to activate the activated MCG. The MCG activation message is preferably provided by the MN (preferably via the SN). Therefore, the UE activates the MCG and stops the timer.

[0044] Preferably, when the network indicates the MCG activation command, the transmission on the suspended bearer is restarted, which is more preferably configured by the network.

[0045] In some examples, the UE is also caused to: when the timer expires, perform radio resource control (RRC) reconstruction.

[0046] Among them, preferably, the network configures the length of the time period set for the timer. According to the present disclosure, the delay for UE RRC reconstruction can thus be set to, for example, 10 milliseconds to 200 milliseconds, which is significantly shorter compared to the conventional process in the case of MCG failure.

[0047] In some examples, the UE is also caused to, in the scenario of conditional handover (CHO) and / or selective activation for the MCG, where the UE is configured with candidate target cell configurations for CHO and / or selective activation: when sending an MCG link failure indication message to the MN, start a timer for deactivating the MCG; and keep the MCG in the deactivated state.

[0048] According to the present disclosure, the solution for setting and starting the timer at the UE preferably also applies to the scenario of CHO and / or selective activation for the MCG. That is, when an MCG failure is detected and / or when a corresponding MCG link failure indication message is sent from the UE to the MN, the MCG is deactivated. Therefore, before performing the handover and before selecting a candidate target cell, the MCG remains in the deactivated state. Therefore, once the conditions for CHO or the candidate target cell are selected, the timer can be stopped and CHO recovery can be performed instead of RRC reconstruction. This significantly reduces the delay that would otherwise be caused by RRC reconstruction. In the case of the timer expiring, preferably RRC reconstruction is performed.

[0049] In some examples, the UE is further caused to: perform measurements on the MCG while the timer is running; select a target cell for serving the UE based on the performed measurements; and if the selected target cell is a candidate target cell for CHO and / or selective activation, apply the configuration of the selected candidate target cell stored at the UE and stop the timer.

[0050] Wherein, when applying the timer to CHO and selective activation, measurements on the MCG are maintained during the running of the timer, such that a target cell can be selected based on the provided measurements. In this case, if the selected target cell is a candidate target cell whose configuration has been stored at the UE, the stored configuration can be immediately applied to selective activation, and the timer is stopped.

[0051] According to the present disclosure, by using the timer, the delays required for CHO and selective activation can be controlled in the order of the length of the timer.

[0052] In some examples, the UE is further caused to: resume transmission on the suspended bearer when the timer expires and the UE measurement indicates MCG link recovery.

[0053] In some examples, the UE is further caused to: trigger cell selection and radio resource control (RRC) reestablishment when the timer expires and an MCG link recovery is not detected.

[0054] Preferably, the UE is further caused to provide MCG deactivation configuration via an MCG failure recovery configuration message (as part of the MCG failure recovery configuration).

[0055] Preferably, the UE is further caused to set the timer to a length of 10 milliseconds to 200 milliseconds.

[0056] In some examples, the UE is further caused to set the timer to a length of 0.

[0057] That is to say, in the case of an MCG link failure, the MCG is not deactivated, and once an MCG link failure is detected at the UE and / or an MCG link failure indication message is signaled to the MN, MCG link recovery is performed.

[0058] According to another aspect of the present disclosure, a master node MN is provided for serving a user equipment UE together with a secondary node SN. The MN configures a master cell group MCG, and the SN configures a secondary cell group SCG. The MN includes: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the MN to at least: preferably send a MCG deactivation indication message to the UE via the SN, for instructing the UE to start a timer for deactivating the MCG in response to the UE detecting a MCG link failure.

[0059] Wherein, in dual connectivity, the MCG is configured by the (source) MN and the SCG is configured by the SN serving the UE.

[0060] In the present disclosure, "MN" and "source MN" can be used interchangeably, while "target MN" is used in the scenario of handover from the (source) MN.

[0061] Preferably, the MCG deactivation indication message includes a MCG deactivation configuration (for example, the timer configuration preferably includes the length of the timer, and more preferably includes an indication as to whether the UE should apply the configured timer), which is provided to the UE for the UE to deactivate the MCG in response to detecting a MCG link failure. Additionally or alternatively, the MCG deactivation configuration is provided to the UE via a separate message.

[0062] According to the present disclosure, the MN instructs the UE to start a timer for deactivating the MCG in the case of a MCG link failure via the MCG deactivation indication message. Thus, the UE can deactivate the MCG accordingly instead of immediately performing RRC reestablishment or release, thereby avoiding unnecessary delay and signaling overhead.

[0063] In some examples, the MN is further caused to: detect a MCG link failure by receiving a MCG link failure indication message; and trigger MCG deactivation by sending a MCG deactivation indication message to the UE in response to detecting the MCG link failure.

[0064] Wherein, preferably, the MN preferably receives the MCG link failure indication message from the UE via the SN.

[0065] According to the present disclosure, the MN is notified of the MCG link failure, such that the MN prepares for MCG deactivation by, for example, providing the MCG deactivation configuration to the UE.

[0066] In some examples, the MCG deactivation indication message includes a first radio resource control RRC reconfiguration message, and the first RRC reconfiguration message preferably includes a command for the UE to perform inter-frequency measurement and configurations related to performing the inter-frequency measurement.

[0067] That is, the MN triggers the deactivation of the MCG and, via a first RRC reconfiguration message (preferably via the SN), instructs the UE to deactivate the MCG and start a timer. Preferably, the first RRC reconfiguration message includes MCG deactivation configuration (e.g., a timer configuration including the length of the timer period set for the timer, for example).

[0068] In some examples, the MCG deactivation indication message includes an MCG deactivation signaling message.

[0069] That is, the MN triggers the deactivation of the MCG and, via an MCG deactivation signaling message (also referred to as an MCG deactivation command message) (preferably via the SN), instructs the UE to deactivate the MCG and start a timer. Preferably, the MCG deactivation signaling message includes MCG deactivation configuration (e.g., a timer configuration including the length of the timer period set for the timer, for example).

[0070] In some examples, the MCG deactivation indication message includes a third Radio Resource Control (RRC) reconfiguration message, and the MN is further caused to: send a third RRC reconfiguration message to the UE, the third RRC reconfiguration message including a configuration for MCG deactivation to be enabled by the UE when the UE detects an MCG link failure.

[0071] Preferably, the MN receives an indication from the UE that the UE is provided with MCG deactivation capability, such that the MN provides the UE with an MCG deactivation configuration for the UE to deactivate the MCG once an MCG link failure is detected at the UE.

[0072] In some examples, the MN is further caused to: determine, based on a received extended measurement report, to perform a handover to the MCG; and for instructing the UE to stop the timer: preferably send a second Radio Resource Control (RRC) reconfiguration message to the UE via the SN for performing the handover to the MCG.

[0073] Wherein, when the timer is running, the MN preferably continuously receives extended measurement reports from the UE, and based on the received measurements provided together with the extended measurement reports, the MN determines to perform a handover to the MCG. Accordingly, the MN instructs the UE to stop the timer and perform the handover.

[0074] In some examples, the MN is further caused to: determine, based on a received extended measurement report, to activate the deactivated MCG; and for instructing the UE to stop the timer: preferably send an MCG activation command message to the UE via the SN.

[0075] Among them, when the timer is running, the MN preferably continuously receives extended measurement reports from the UE, and based on the received measurements provided together with the extended measurement reports, the MN determines to activate the activated MCG. Therefore, the MN instructs the UE to stop the timer and activate the deactivated MCG.

[0076] Preferably, the MN is also caused to: provide MCG deactivation configuration via an MCG failure recovery configuration message (as part of the MCG failure recovery configuration).

[0077] Preferably, the MN is also caused to set the timer to a length of 10 milliseconds to 200 milliseconds.

[0078] In some examples, the MN is also caused to set the timer to a length of 0.

[0079] That is, in the case of an MCG link failure, the MCG is not deactivated, and once an MCG link failure is detected at the UE and / or an MCG link failure indication message is signaled to the MN, MCG link recovery is performed.

[0080] According to another aspect of the present disclosure, a system is provided, the system includes: a user equipment UE according to any one of the above examples, a master node MN according to any one of the above examples, and a secondary node SN, configuring a secondary cell group SCG, where the UE is served by the MN and the SN.

[0081] According to another aspect of the present disclosure, a method for a user equipment UE is provided, configured to operate in a dual connection, where the UE is served by a master cell group MCG and a secondary cell group SCG, the MCG is configured by a master node MN, and the SCG is configured by a secondary node SN, the method includes: detecting an MCG link failure; starting a timer for deactivating the MCG; and deactivating the MCG.

[0082] According to another aspect of the present disclosure, a method for a master node MN is provided, the MN is used to serve a user equipment UE together with a secondary node SN, the MN configures a master cell group MCG, and the SN configures a secondary cell group SCG, the method includes: preferably sending an MCG deactivation indication message to the UE via the SN, for instructing the UE to start a timer for deactivating the MCG in response to the UE detecting an MCG link failure.

[0083] In addition, according to some example embodiments, a computer program is provided, the computer program includes instructions for causing a device to execute the method according to any one of the above examples and / or the method executed by the device and system according to any one of the above examples.

[0084] In addition, according to some example embodiments, a memory is provided that stores computer-readable instructions for causing a device to perform the method according to any one of the above examples and / or the method performed by a device and a system according to any one of the above examples.

[0085] In addition, according to some other example embodiments, for example, a computer program product for a wireless communication device including at least one processor is provided, including software code portions for performing the corresponding steps disclosed in the present disclosure when the product runs on the device. The computer program product may include a computer-readable medium on which the software code portions are stored. In addition, the computer program product may be directly loadable into the internal memory of a computer and / or may be sent via a network by means of at least one of uploading, downloading, and pushing processes.

[0086] Although some example embodiments will be specifically described herein with reference to the above applications, it should be understood that the present disclosure is not limited to such fields of use and is applicable to a broader context.

[0087] It should be noted that it should be understood that the method according to the present disclosure relates to a method of operating a device according to the above example embodiments and their variations, and the corresponding statements regarding the device equally apply to the corresponding method, and vice versa, such that for the sake of brevity, similar descriptions may be omitted. Additionally, the above aspects may be combined in many ways even if not explicitly disclosed. Those skilled in the art will understand that these combinations of aspects and features / steps are possible unless they result in contradictions that are explicitly excluded.

[0088] Embodiments of the disclosed device may include, but are not limited to, one or more processors, one or more application-specific integrated circuits (ASICs), and / or one or more field-programmable gate arrays (FPGAs). Embodiments of the device may also include the use of other conventional and / or custom hardware, such as software-programmable processors, such as graphics processing unit (GPU) processors.

[0089] During the following discussion and by reference to the accompanying drawings, other and further example embodiments of the present disclosure will become apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Example embodiments of the present disclosure will now be described by way of example only with reference to the accompanying drawings, in which:

[0091] Figure 1 An example of a reconstruction process initiated by a UE is schematically shown;

[0092] Figure 2 An example of a fast MCG recovery process in the case where the network decides to perform a handover according to an example embodiment of the present disclosure is schematically shown;

[0093] Figure 3 Schematically shows an example of a signaling diagram for an MCG deactivation procedure according to an example embodiment of the present disclosure;

[0094] Figure 4 Schematically shows an example of a signaling procedure for MCG activation and / or RRC reconfiguration according to an example embodiment of the present disclosure;

[0095] Figure 5 Schematically shows an example of an MCG deactivation procedure according to an example embodiment of the present disclosure; and

[0096] Figure 6 Schematically shows an example of a procedure for CHO / selective activation according to an example embodiment of the present disclosure. Detailed Description

[0097] However, hereinafter, a communication network architecture based on the 3GPP standard for a communication network (such as 5G / NR), as an example of a communication network to which the embodiments can be applied, will be used to describe different exemplary embodiments, without limiting the embodiments to such an architecture. It will be apparent to those skilled in the art that the embodiments can also be applied to other types of communication networks, where the mobile communication principle is integrated with D2D (device-to-device) or V2X (vehicle-to-everything) configurations, such as SL (sidelink), for example Wi-Fi, Worldwide Interoperability for Microwave Access (WiMAX), Personal Communication Service (PCS), Wideband Code Division Multiple Access (WCDMA), systems using Ultra-Wideband (UWB) technology, Mobile Ad-hoc NETwork (MANET), wired access, etc. In addition, without loss of generality, the description of some examples of the embodiments relates to mobile communication networks, but the principles of the present disclosure can be extended and applied to any other type of communication network, such as a wired communication network.

[0098] The following examples and embodiments are to be understood only as illustrative examples. Although the specification may refer to "one", "a", or "some" example or embodiment in several places, this does not necessarily mean that each such reference relates to the same example or embodiment, or that the feature applies only to a single example or embodiment. The individual features of different embodiments can also be combined to provide other embodiments. In addition, terms similar to "including" and "comprising" should be understood not to limit the described embodiments to only those features already mentioned; such examples and embodiments can also include features, structures, units, modules, etc. that have not been specifically mentioned.

[0099] The basic system architecture of a (remote) communication network, including a mobile communication system (to which some examples of embodiments may apply), may include the architecture of one or more communication networks (including a radio access network subsystem and a core network). Such an architecture may include one or more communication network control elements or functions, access network elements, radio access network elements, access service network gateways, or base station transceivers, such as base stations (BSs), access points (APs), NodeBs (NBs), eNBs, or gNBs, distributed units (DUs), or centralized / central units (CUs), which control corresponding coverage areas or cells; and one or more communication stations, such as communication elements or functions, like user equipment or terminal devices, such as user equipment (UEs), or another device with similar functions, such as a modem chipset, chip, module, etc., which may also be part of a station, element, function, or application capable of communication, such as a UE, an element or function usable in a machine-to-machine communication architecture, or attached as a separate element to such an element, function, or application capable of communication, etc., capable of communicating via one or more communication beams via one or more channels for transmitting several types of data in multiple access domains. In addition, core network elements or network functions may be included, such as gateway network elements / functions, mobility management entities, mobile switching centers, servers, databases, etc.

[0100] The following description may provide further details of alternatives, variations, and variants: The gNB includes, for example, a node that provides NR user plane and control plane protocol terminations to the UE and is connected to the 5GC via the NG interface, for example, according to Section 3.2 of 3GPP TS38.300 V16.6.0 (2021-06) incorporated by reference.

[0101] The gNB central unit (gNB-CU) includes, for example, a logical node that hosts, for example, the RRC, SDAP, and PDCP protocols of the gNB or controls the operation of one or more gNB-DUs, such as the RRC and PDCP protocols of the en-gNB. The gNB-CU terminates the F1 interface connected to the gNB-DU.

[0102] The gNB distributed unit (gNB-DU) includes, for example, a logical node that hosts, for example, the RLC, MAC, and PHY layers of the gNB or en-gNB, and whose operation is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU.

[0103] The gNB-CU control plane (gNB-CU-CP) includes, for example, a logical node hosting the RRC and control plane parts that manage, for example, the PDCP protocol for the gNB-CU of an en-gNB or gNB. The gNB-CU-CP terminates the E1 interface connected to the gNB-CU-UP and the F1-C interface connected to the gNB-DU.

[0104] The gNB-CU user plane (gNB-CU-UP) includes, for example, a logical node hosting the user plane part of the PDCP protocol for the gNB-CU of an en-gNB and the user plane parts of the PDCP protocol and SDAP protocol for the gNB-CU of a gNB. The gNB-CU-UP terminates the E1 interface connected to the gNB-CU-CP and the F1-U interface connected to the gNB-DU, for example, according to Section 3.1 of 3GPP TS 38.401 V16.6.0 (2021-07) incorporated by reference.

[0105] Different functional divisions between the central and distributed units are possible, for example, referred to as options: Option 1 (similar to the 1A division): · The functional division in this option is similar to the 1A architecture in DC. RRC is in the central unit. PDCP, RLC, MAC, physical layer, and RF are in the distributed unit. Option 2 (similar to the 3C division): · The functional division in this option is similar to the 3C architecture in DC. RRC and PDCP are in the central unit. RLC, MAC, physical layer, and RF are in the distributed unit. Option 3 (division within RLC): · Low RLC (part of the functions of RLC), MAC, physical layer, and RF are in the distributed unit. PDCP and high RLC (another part of the functions of RLC) are in the central unit. Option 4 (RLC-MAC division): · MAC, physical layer, and RF are in the distributed unit. PDCP and RLC are in the central unit. Or, for example, according to Section 11 of 3GPP TR 38.801 V14.0.0 (2017-03) incorporated by reference.

[0106] The gNB supports different protocol layers, for example, Layer 1 (L1) - physical layer.

[0107] The Layer 2 (L2) of NR is divided into the following sub-layers: Media Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Service Data Adaptation Protocol (SDAP), where, for example: · The physical layer provides transport channels to the MAC sublayer; · The MAC sublayer provides logical channels to the RLC sublayer; · The RLC sublayer provides RLC channels to the PDCP sublayer; · The PDCP sublayer provides radio bearers to the SDAP sublayer; · The SDAP sublayer provides 5GC QoS flows; · Comp. refers to header compression and Segm. refers to segmentation; · Control channels include (BCCH, PCCH).

[0108] Layer 3 (L3) includes, for example, radio resource control (RRC), for example, according to Section 6 of 3GPP TS38.300 V16.6.0 (2021-06) incorporated by reference.

[0109] A RAN (radio access network) node or a network node (such as a gNB, a base station, a gNB CU or a gNB DU or a part thereof) can be implemented using, for example, a device having at least one processor and / or at least one memory (with computer-readable instructions (computer programs)), the device being configured to support and / or provide and / or process CU- and / or DU-related functions and / or features, and / or at least one protocol (sub)layer of the RAN (radio access network), such as layer 2 and / or layer 3.

[0110] The gNB CU and gNB DU parts can be, for example, co-located or physically separated. The gNB DU can even be further divided into, for example, two parts, for example, one part including a processing device and one part including an antenna. The central unit (CU) can also be referred to as BBU / REC / RCC / C-RAN / V-RAN, O-RAN or a part thereof. The distributed unit (DU) can also be referred to as RRH / RRU / RE / RU or a part thereof. Hereinafter, in various example embodiments of the present disclosure, the CU-CP (or more generally, the CU) can also be referred to as the (first) network node supporting at least one of the central unit control plane functions or the layer 3 protocol of the radio access network; and similarly, the DU can be referred to as the (second) network node supporting at least one of the distributed unit functions or the layer 2 protocol of the radio access network.

[0111] The gNB-DU supports one or more cells and can thus be used as, for example, a serving cell for a user equipment (UE).

[0112] A User Equipment (UE) may include a wireless or mobile device, a device with a radio interface for interacting with a RAN (Radio Access Network), a smart phone, a vehicle-mounted device, an IoT device, an M2M device, etc. Such a UE or device may include: at least one processor; and at least one memory including computer program code; wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device to perform at least certain operations, such as an RRC connection to the RAN. The UE is configured, for example, to generate a message to be sent to the RAN via radio (e.g., including a cell ID) (e.g., to reach and communicate with a serving cell). The UE may generate and send and receive RRC messages containing one or more RRC PDUs (Packet Data Units).

[0113] The UE may have different states (e.g., according to Sections 4.2.1 and 4.4 of 3GPP TS 38.331 V16.5.0 (2021-06) incorporated by reference).

[0114] For example, when an RRC connection has been established, the UE is in the RRC_CONNECTED state or the RRC_INACTIVE state.

[0115] In the RRC_CONNECTED state, the UE may: · Store the AS context; · Transmit unicast data to / from the UE; · Monitor the control channel associated with the shared data channel to determine whether data is scheduled for the data channel; · Provide channel quality and feedback information; · Perform neighbor cell measurements and measurement reporting.

[0116] The RRC protocol includes, for example, the following main functions: · RRC connection control; · Measurement configuration and reporting; · Establishment / modification / release of measurement configuration (e.g., intra-frequency, inter-frequency, and inter-RAT measurements); · Setting and releasing measurement gaps; · Measurement reporting.

[0117] The general functionality and interconnections of the described elements and functions, which also depend on the actual network type, are known to those skilled in the art and are described in the corresponding specifications, such that for the sake of brevity, their detailed description may be omitted herein. However, it should be noted that several additional network elements and signaling links may be used for communication to or from elements, functions, or applications, such as communication endpoints, communication network control elements (such as servers, gateways, radio network controllers), and other elements of the same or other communication networks other than those described in detail below in this document.

[0118] The communication network architecture considered in the example of the embodiment may also be capable of communicating with other networks, such as the public switched telephone network or the Internet. The communication network is also capable of supporting the use of cloud services for virtual network elements or their functions, where it should be noted that the virtual network part of the telecommunication network may also be provided by non-cloud resources, such as internal networks, etc. It should be understood that the network elements and / or corresponding functions of the access system of the core network, etc., may be implemented by using any node, host, server, access node, or entity suitable for such use. Generally, network functions may be implemented as network elements on dedicated hardware, software instances running on dedicated hardware, or virtualized functions instantiated on a suitable platform (e.g., cloud infrastructure).

[0119] In addition, network elements as described herein, such as communication elements, e.g., a UE, a terminal device, a control element or function, such as an access network element, e.g., a base station / BS, gNB, radio network controller, a core network control element or function, such as a gateway element or other network element or function, and any other element, function or application can be implemented by software (e.g., by a computer program product for a computer) and / or by hardware. To perform their respective processing, the correspondingly used devices, nodes, functions or network elements can include several components, modules, units, assemblies, etc. (not shown) required for control, processing and / or communication / signaling functions. Such components, modules, units and assemblies can include, for example, one or more processors or processor units, which include: one or more processing parts for executing instructions and / or programs and / or for processing data; a storage or memory unit or component (e.g., ROM, RAM, EEPROM, etc.) for storing instructions, programs and / or data, for serving as a working area for the processor or processing part, etc.; an input or interface component (e.g., a floppy disk, CD-ROM, EEPROM, etc.) for inputting data and instructions by software; a user interface (e.g., a screen, a keyboard, etc.) for providing the user with possibilities for monitoring and manipulation; other interfaces or components for establishing links and / or connections under the control of the processor unit or part (e.g., wired and wireless interface components, a radio interface component including, for example, an antenna unit, etc.; components for forming a radio communication part, etc.), etc., where the corresponding components forming an interface such as a radio communication part can also be located at a remote site (e.g., a radio head or a radio station, etc.). It should be noted that in this specification, the processing part should not only be considered as representing a physical part of one or more processors, but also can be considered as a logical division of the referenced processing tasks executed by one or more processors. It should be understood that according to some examples, a so-called "liquid" or flexible network concept can be adopted, where the operations and functions of network elements, network functions or another entity of a network can be executed in a flexible manner in different entities or functions, such as being executed in a node, a host or a server. In other words, the "division of labor" among the involved network elements, functions or entities can vary according to the situation.

[0120] As described above, the present disclosure generally attempts to provide apparatuses (including a user equipment UE and / or a master node MN) for reducing latency, signaling overhead, throughput loss, energy consumption and device cost in case of RLF or MCG link failure in dual connectivity, and to provide methods for implementing the same executed by these apparatuses.

[0121] Summarizing the example embodiments provided in this disclosure, a new timer "T" is defined during which the MCG is considered to be deactivated. This means that while the timer is running, the UE maintains the current measurement configuration and continues to measure based on the MCG measurement configuration (e.g., intra-frequency / inter-frequency / RAT-inter). In addition, the UE maintains the timing advance for the MCG (i.e., the UE maintains its uplink synchronization, the UE maintains the timer related to timing advance, etc.). However, the UE pauses the MCG transmission for all radio bearers (i.e., the UE does not monitor the PDCCH (Physical Downlink Control Channel), pauses the transmission on the PUSCH (Physical Uplink Shared Channel), and there is also no transmission on the SCell).

[0122] In addition, this disclosure provides different alternatives regarding the trigger conditions of the timer.

[0123] In one alternative, when the UE receives the MCG deactivation signaling from the MN, the timer starts.

[0124] In another alternative, when the UE receives an RRC reconfiguration message from the MN (including a command and related configuration for performing inter-frequency measurements), the timer starts.

[0125] In a third alternative, the UE is configured to start the timer after special radio conditions: The radio conditions can be RLF, i.e., the UE receives a T310 start or X (or N310) number of OoS indications from the lower layer. Among them, 5G NR timers include, for example, T304 timer, T310 timer, and T311 timer used for various functions in 5G NR (New Radio), where constants such as N310 and N311 are used, which is the traditional RLF process. For example, when N310 consecutive OoS indications are provided, RLF is declared at the UE. The RLF timer T310 is also triggered. For details regarding the relevant background information, for example, refer to https: / / www.rfwireless-world.com / 5G / 5G-NR-timers-T304-T310-T311.html.

[0126] In yet another alternative, the UE is configured to start the timer after special radio conditions: The radio conditions can also be the case if the strongest measurement on the frequency layer of the serving cell or on the configured frequency is below a certain threshold that requires the UE to wait until it moves to an area with better / suitable radio coverage or performs new measurements on a different frequency (to find a cell on a different layer). Among them, the threshold (value) is preferably configured by the network.

[0127] According to this disclosure, when the timer is running, the UE can send an additional (extended) measurement report to the MN in the case of dual connectivity.

[0128] The present disclosure also provides example embodiments for scenarios of MCG-enabled CHO or selective activation: When the UE is configured with candidate target cell configurations for conditional handover or selective activation of a cell group (fast handover between cells without reconfiguration), the UE may start a timer when sending an MCG failure indication to the source MN, and trigger a cell selection process, keeping the MCG in a deactivated state. If the UE finds a suitable selected cell of a cell that is already ready, the UE may directly trigger a CHO recovery to the ready cell. Among them, the source MN may instruct the target MN to maintain resource reservation until the UE completes the CHO recovery or an extended duration. This is because if the UE does not access the target cell after a period of time, i.e., depending on the implementation of the target MN, the target MN may cancel the CHO preparation (and release the reserved resources).

[0129] Among them, the source MN (primary node) refers to the MN that configures the MCG that is currently serving the UE, i.e., before handover, and the target MN refers to the MN that configures the MCG and is to perform a handover from the source MN to the MCG.

[0130] Before providing a detailed description of the example embodiments provided by the present disclosure, the following relevant background information and / or basic knowledge are introduced.

[0131] The following objectives are discussed as part of Release 18WI (RP-213565):

[0132] Objective 1: Specify the mechanisms and procedures for NR-DC (New Radio Dual Connectivity), where cell groups (at least for SCG, secondary cell group) are selectively activated via L3 enhancements; and allow subsequent cell group changes after changing the CG without reconfiguring and restarting CPC / CPA (Conditional PScell Change / Add) [RAN2, RAN3, RAN4]. Note that a coordinated RRC modeling method for Objectives 1 and 2 can be considered to minimize the workload in RAN2.

[0133] Objective 2: Include CHO (Conditional Handover) for the target MCG and target SCG [RAN3, RAN2]. Note that this has been for Release 17, so this objective will be reviewed at RAN#95-e.

[0134] Objective 3: Specify CHO for the target MCG and candidate SCG including for CPC / CPA [RAN3, RAN2], where the CHO including the target MCG and target SCG is used as a baseline.

[0135] Objectives 1 and 3 are particularly relevant to the present disclosure.

[0136] In addition, the present disclosure may also be related to general enhancements of mobility procedures in versions 19 and above.

[0137] In the following, the RRC reestablishment procedure is described (refer to TS 38.300, section 9.2.3.3):

[0138] When a failure condition occurs (e.g., radio link failure, reconfiguration failure, integrity check failure, etc.), the UE in RRC_CONNECTED may initiate the reestablishment procedure to continue the RRC connection.

[0139] Figure 1 The reestablishment procedure initiated by the UE is described below:

[0140] Step S11: The UE reestablishes the connection and provides the UE identifier (PCI + C-RNTI) to the gNB where the trigger for reestablishment occurs. Here, PCI refers to the physical cell identifier, and C-RNTI refers to the cell radio network temporary identifier.

[0141] Step S12: If the UE context is not locally available, the gNB requests the last serving gNB to provide the context data to the UE.

[0142] Step S13: The last serving gNB provides the context data to the UE.

[0143] Step 14 / 14a: The gNB continues the reestablishment of the RRC connection. This message is sent on SRB1, where SRB refers to the signaling radio bearer. Note that the configuration of the signaling radio bearer can be found in, for example, TS 38.331.

[0144] Step 15 / 15a: When the reestablishment procedure is in progress, the gNB may perform reconfiguration to reestablish SRB2 and DRB (data radio bearer).

[0145] Step 16 / 17: If the loss of user data cached in the last serving gNB can be prevented, the gNB provides a forwarding address, and the last serving gNB provides the SN status to the gNB.

[0146] Step 18 / 19: The gNB performs a path switch.

[0147] Step 110, the gNB triggers the release of the UE resources at the last serving gNB.

[0148] In the following, the UE reestablishment delay requirement is described (refer to TS 38.133, section 6.2.1.2.1):

[0149] The UE re-establishment delay requirement is defined in clause 6.2.1.2.1 of TS 38.133, and it is the time between the moment when the UE detects any condition requiring RRC re-establishment as defined in clause 5.3.7 of TS 38.331 and the moment when the UE sends a PRACH (Physical Random Access Channel) to the target PCell. According to the specific definition of the UE re-establishment delay, the UE re-establishment delay (TUE_re-establish) requirement should be less than the corresponding value.

[0150] The UE re-establishment delay can be defined as the time to identify the NR cell within the target frequency, and it depends on whether the target NR cell is a known cell or an unknown cell and on the FR of the target NR cell. If the UE is not configured with an intra-frequency NR carrier for RRC re-establishment, the UE re-establishment delay = 0; otherwise, the UE re-establishment delay should not exceed the value defined in Table 6.2.1.2 of TS 38.133.

[0151] The UE re-establishment delay can be defined as the time to identify the target inter-frequency NR cell on the inter-frequency carrier configured for RRC re-establishment, and it depends on whether the target NR cell is a known cell or an unknown cell and on the FR of the target NR cell. The UE re-establishment delay should not exceed the value defined in Table 6.2.1.2 of TS 38.133.

[0152] The UE re-establishment delay can be defined as the time required to receive all relevant system information according to the reception process of the system information block and the RRC process delay defined for the target NR cell in TS 38.331.

[0153] The UE re-establishment delay can be defined as the delay uncertainty to obtain the first available PRACH opportunity in the target NR cell, and it can reach the sum of the SSB (Synchronization Signal Block) to PRACH timing association period and 10 ms. Among them, the SSB to PRACH timing association period is defined in Table 8.1-1 of TS38.213.

[0154] The UE re-establishment delay can be defined as the total number of NR frequencies to be monitored for RRC re-establishment; if the NR cell within the target frequency is known, the UE re-establishment delay = 1, otherwise the UE re-establishment delay = 2, and if the inter-frequency NR cell is known.

[0155] It can be observed that the UE re-establishment delay can easily be on the order of seconds.

[0156] To reduce the UE re-establishment delay in the case of the dual-connectivity (DC) scenario, fast MCG failure recovery (so-called network-controlled recovery) was specified in Release 16. Its details are given below, as also shown in Figure 2 shown.

[0157] Figure 2 Shows the fast MCG recovery process in the case where the network decides to perform a handover according to an exemplary embodiment provided by the present disclosure.

[0158] For MCG failure recovery, refer to TS 37.340.

[0159] In a multi-RAT (radio access technology) (MR)-DC deployment, the UE may be configured to perform fast MCG failure recovery via the existing SN when detecting an RLF for the PCell. Figure 2 The signaling diagram for fast MCG failure recovery is shown in.

[0160] As Figure 2 shown, the UE is in an MCG link failure scenario.

[0161] Step S21: The UE sends an MCG failure indication message to the SN (secondary node). Herein, the SN is a network node or network element configured in the SCG (secondary cell group) for serving the UE. In dual connectivity, the SCG and the MCG (primary cell group) serve the UE together.

[0162] Step S22: The SN forwards the received MCG failure indication message to the source MN, where the forwarded MCG failure indication message includes the measurements provided by the UE.

[0163] Step S23: The source MN sends a handover request message to the target MN.

[0164] Step S24: The target MN sends a handover request confirmation message to the source MN in response to the received handover request message.

[0165] Step S25: The source MN sends a handover command message to the SN.

[0166] Step S26: The SN forwards the received handover command message to the UE.

[0167] Step S27: The UE performs a handover in response to the received handover command message, where the handover includes the UE sending a random access channel (RACH) message to the target MN.

[0168] It can be observed that the fast MCG recovery process uses the active SCG link to notify the source MN of the failure and measurement information. Based on this information, the source MN decides to perform an RRC reconfiguration (changing the bearer configuration), an RRC release (releasing the bearer), or a handover to a neighboring cell (as Figure 2 shown).

[0169] In this way, in a normal handover, the RRC reconstruction delay of several hundred milliseconds is reduced to several tens of milliseconds.

[0170] In the following, a description of UE measurements is provided with reference to Section 9.1 of TS 38.300.

[0171] The measurements to be performed by the UE for connected-mode mobility are classified into at least four measurement types: - Intra-frequency NR measurements; - Inter-frequency NR measurements; - Inter-RAT measurements for E-UTRA; - Inter-RAT measurements for UTRA.

[0172] For each measurement type, one or more measurement objects can be defined (the measurement object definition, for example, the carrier frequency to be monitored).

[0173] For each measurement object, one or more reporting configurations can be defined (the reporting configuration defines the reporting criteria). Three reporting criteria are used: event-triggered reporting, periodic reporting, and event-triggered periodic reporting.

[0174] The association between the measurement object and the reporting configuration is created by a measurement identity (the measurement identity links a measurement object and a reporting configuration of the same RAT). By using several measurement identities (one measurement identity per measurement object, reporting configuration pair), it is possible to: - Associate several reporting configurations with one measurement object; and - Associate one reporting configuration with several measurement objects.

[0175] The measurement identity is also used when reporting the measurement results.

[0176] The measurement quantities are considered separately for each RAT.

[0177] The network uses a measurement configuration to configure the UE to start, modify, or stop measurements.

[0178] According to the fast MCG recovery process of Release 16, the UE notifies the MN of a link failure (e.g., RLF) using the active SCG link by triggering an MCG link failure indication to the MN. The MCG failure information message contains the cause of the failure and a measurement report. Based on these measurement reports, the MN can perform an appropriate recovery process, such as RRC reconfiguration, RRC release, or handover. This process is not optimal in the case of a coverage hole (such as Case 1 discussed in the Background section above) or in the case of unavailability of inter-frequency / inter-RAT measurement reports from the UE (such as Case 2 discussed in the Background section above). This is because, according to this process, the UE will be released from the network and will have to perform an RRC reconstruction process, which results in additional and unnecessary delays in the case of a coverage hole (Case 1) and in the case of unavailability of inter-frequency / inter-RAT measurement reports (Case 2).

[0179] Therefore, to avoid unnecessary delays, the present disclosure proposes to perform MCG deactivation during an MCG failure controlled by a timer. In other words, when the UE maintains measurements on the MCG, the transmission on the MCG bearers is suspended. Once the MCG link is restored (i.e., the UE returns to coverage) or the MN has received measurement reports for a different frequency layer or RAT, the MN triggers an appropriate action. The action can be MCG activation (in the case where the UE returns to coverage) or inter-frequency / inter-RAT handover (in the case where new inter-frequency / inter-RAT measurement reports are received).

[0180] Figure 3 A signaling diagram for the above MCG deactivation process according to an example embodiment of the present disclosure is shown.

[0181] As Figure 3 shown, in step S31, the UE is operating in dual connectivity.

[0182] Further, according to Figure 3 the following steps are performed:

[0183] Steps S32 / S33: The UE detects an MCG failure and indicates an MCG failure indication message to the MN via the SN.

[0184] Steps S34 / S35 / S36: The MN triggers MCG deactivation and indicates a first RRC reconfiguration message for MCG deactivation to the UE via the SN by signal transmission. Preferably, the first RRC reconfiguration message includes a command for the UE to perform inter-frequency measurements and configurations related to performing inter-frequency measurements.

[0185] Step S37: The UE deactivates the MCG and starts a timer. When the MCG is deactivated, there is: · No PDCCH monitoring · No PUSCH (configured grant released / suspended) · No CSI report · No PHR (Power Headroom Report) is reported (triggered when SCG is activated), and · The SCell of MCG is deactivated (hibernation not supported) · RRM (Radio Resource Management) measurements continue. · Radio link and beam monitoring is enabled / disabled by RRC.

[0186] Step S38 / 39: Send an RRC reconfiguration confirmation to the MN via the SN. Among them, send a (first) RRC reconfiguration complete (message) to the MN.

[0187] As described above, when the timer is running, the measurements at the UE continue, so that an extended measurement report is provided and can be directly applied to perform a handover or selective activation or activation of the MCG.

[0188] According to the present disclosure and as Figure 3 shown, a timer is started when receiving an RRC reconfiguration for MCG deactivation from the MN (via the SN) (e.g., using a (first) RRC reconfiguration message), and / or a timer is started when receiving an MCG deactivation command from the MN (via the SN) (e.g., using an MCG deactivation signaling message). However, the timer is stopped when receiving an RRC reconfiguration from the MN (via the SN) to perform a handover (e.g., using a (second) RRC reconfiguration message), and / or the timer is stopped when receiving an MCG activation command from the MN (via the SN). In the case where the timer expires, the UE performs an RRC reconstruction.

[0189] Figure 4 Shows a signaling procedure for MCG activation and / or RRC reconfiguration according to an exemplary embodiment of the present disclosure.

[0190] As Figure 4 shown, in step S41, the MCG is deactivated.

[0191] According to Figure 4 the following steps are performed:

[0192] Step S41: The UE sends a measurement report to the MN via the SN (based on the extended measurement report).

[0193] Step S42 / S43: The MN enables the activation of deactivating the MCG and transmits it to the UE via the SN by signaling. This can be done using a second RRC reconfiguration message including an RRC reconfiguration to perform a handover. Additionally or alternatively, this can be done using an MCG activation command message (or MCG activation signaling message).

[0194] Step S44: The MCG is activated and / or the handover is executed and the timer is stopped.

[0195] Step S45: The (second) RRC reconfiguration complete (message) is sent to the target MN for handover or to the source MN for reactivation.

[0196] As an alternative to the above method for MCG deactivation (in Figure 3 ), according to an exemplary embodiment of the present disclosure, when detecting an RLF (e.g., T310 starts or consecutive N310 out-of-sync indications are received from the physical layer) or when the measurement on the frequency layer of the serving cell or all configured frequencies is below a threshold (preferably configured by the network), the MCG can be deactivated as the default behavior of the UE. As an example, this method is illustrated for the RLF scenario in Figure 5 .

[0197] As Figure 5 shown, in step S51, the UE operates in dual connectivity.

[0198] Further, according to Figure 5 the following steps are performed:

[0199] Step S51: The UE indicates the MCG deactivation capability to the network.

[0200] Steps S52 / S53: Once an MCG failure is detected, the network can configure the MCG deactivation measurement configuration (or the entire configuration) to be enabled (by the UE) for the UE. This can be done using the (third) Radio Resource Control RRC reconfiguration message, which includes the configuration for MCG deactivation to be enabled by the UE when the UE detects an MCG link failure.

[0201] Step S54: Once an MCG failure is detected, the UE applies the stored MCG deactivation configuration: The UE places the MCG in the deactivated state and starts the measurement for the extended measurement report for the MCG failure procedure.

[0202] Step S55: The UE sends an extended measurement report to the MN via the SN.

[0203] According to the present disclosure, as provided by the above exemplary embodiment shown in, for example, Figures 2 to 5 , the following advantages are achieved: Avoiding unnecessary delays and signaling overhead due to RRC release and RRC reconstruction from scratch; and allowing the network to trigger an inter-frequency handover / inter-RAT handover without enabling inter-frequency / inter-RAT measurements from the beginning.

[0204] Basically, the present disclosure achieves the above advantages by delaying the triggering of UE reconstruction and / or fast MCG recovery processes by using a newly defined timer "T". In particular, while the timer T is running, the UE keeps providing measurements to the network, and all transmissions on the MCG bearers are suspended, such that the MCG is deactivated for the period set for the timer. The UE performs RRC reconstruction when the timer expires and / or immediately after the MCG is activated, because the extended measurement reports provided by the UE while the timer T is running can be directly provided to the source MN. Thus, the network can set the timer to a length of, for example, 10 milliseconds to 200 milliseconds, which is shorter compared to the (conventional) fast MCG recovery process.

[0205] Furthermore, the above solution according to the present disclosure can be used as a solution for CHO recovery, or when selective activation is enabled for the MCG. For example, in the case where the UE is configured with CHO or selective activation of the MCG, the UE starts the timer when sending an MCG failure indication to the source MN, and triggers a cell selection process to keep the MCG in a deactivated state. If the UE finds a suitable selected cell that has been ready within the timer duration, the UE can directly trigger CHO recovery to the ready cell (i.e., handover instead of RRC reconstruction). In the case where the timer expires, RRC reconstruction is performed.

[0206] Figure 6 A process for CHO / selective activation according to an example embodiment of the present disclosure is shown, applying the above solution using the timer T for MCG deactivation.

[0207] As Figure 6 shown, at step S61, the UE is operating in dual connectivity.

[0208] Further, according to Figure 6 the following steps are performed:

[0209] Steps S62 / S63: Perform an RRC reconfiguration procedure, i.e., the UE is provided with MCG deactivation configuration (e.g., timer configuration, whether the UE should apply the timer, etc.) and conditional configuration (e.g., candidate PCell and handover conditions).

[0210] Step S64: The UE detects an MCG (link) failure, deactivates the MCG (directly in response to detecting the MCG link failure), and starts the timer T.

[0211] Step S65: During the timer, the UE performs measurements, and if the selected cell is one of the candidate target cells, it applies the configuration of the (selected) candidate target cell that has been stored at the UE and stops the timer. Wherein, if the timer expires, the UE performs an RRC reconstruction procedure.

[0212] Note that conditional handover (CHO) is a Release 16 procedure and CHO recovery is also defined.

[0213] However, according to the present disclosure, CHO is related to a newly defined timer.

[0214] Note that selective activation means that the UE stores the configurations of all candidate target cells, and whenever the corresponding conditions are met, the UE applies the configuration of the (selected) cell that has been stored at the UE. This is specified in Release 18.

[0215] However, Release 18 is for selective activation of the SCG (Secondary Cell Group). Here, according to the present disclosure, the use of the newly defined timer is related to the selective activation of the MCG (Master Cell Group).

[0216] According to the present disclosure, as provided by the above example embodiments as shown, for example, Figure 6 the same advantages as those achieved by the example embodiments as shown, for example, Figures 2 to 5 are achieved: namely, unnecessary delays and signaling overheads due to RRC release and RRC reconstruction from scratch are avoided; and the network is allowed to trigger a handover to the MCG or selective activation of the MCG without having to provide UE measurements from scratch.

[0217] Basically, the present disclosure achieves the above advantages by delaying the triggering of a handover to the MCG or selective activation of the MCG by using the newly defined timer "T". In particular, while the timer T is running, the UE keeps providing measurements to the network, while all transmissions on the MCG bearer are suspended, such that the MCG is deactivated for the period set for the timer. If the cell selected by the UE based on the measurements performed during the timer is one of the candidate target cells, the UE directly applies the configuration of the selected cell that has been stored at the UE and stops the timer. Accordingly, the network can set the timer to a length of, for example, 10 milliseconds to 200 milliseconds, which is shorter compared to the (conventional) CHO and selective activation procedures.

[0218] In summary, according to the present disclosure, an MCG deactivation procedure in case of an MCG link failure is provided, wherein when the MN (via the SN) receives an MCG failure indication message, the MN does not immediately perform an RRC release or a handover. Instead, the MN sends an MCG deactivation command or a corresponding RRC reconfiguration (to configure inter-frequency / inter-RAT measurements) to the UE via the SN. Upon receiving the MCG deactivation command or the corresponding RRC reconfiguration message (e.g., Figure 3 the first RRC reconfiguration message as shown) or directly in response to detecting an MCG link failure, a new timer T is started on the UE side, and transmissions on the MCG bearer are suspended while the timer is running.

[0219] According to an example embodiment, the configuration of the timer is performed as part of the MCG failure recovery configuration.

[0220] According to an example embodiment, in response to an MCG failure indication message from the UE, the configuration of the timer is performed (preferably at the MN).

[0221] According to an example embodiment, the network decides not to trigger the timer. This can be achieved by configuring the value of the timer to zero. In this case, once the MCG failure indication is signaled to the MN, the MCG is not deactivated and the MCG link recovery is performed.

[0222] According to an example embodiment, the UE provides an extended measurement report while the timer is running. The extended measurement report can at least include the latest in - frequency measurement report. The report can also include inter - frequency and inter - RAT measurement reports.

[0223] According to an example embodiment, the extended measurement report can be periodic or aperiodic (based on events and in response to a request from the network). In the case of event - based, an example is to trigger the report when the MCG coverage is restored (i.e., the UE is outside the coverage hole of the Pcell).

[0224] According to an example embodiment, when the UE receives an MCG activation command, the timer stops. The MCG activation command can be signaled as an RRC message or a MAC control element.

[0225] According to an example embodiment, when the UE receives an RRC reconfiguration message to perform a handover, the timer stops.

[0226] According to an example embodiment, the UE performs an RRC reconstruction when the timer expires.

[0227] According to an example embodiment, after receiving the start of T310 or N310 consecutive out - of - sync indications from the physical layer or detecting that the measurements on the frequency layer of the serving cell or all configured frequencies are below a threshold and deactivating the MCG during this timer, the timer is always used as a fallback / default operation. This also applies to the single - connection case where the start of the timer is the default process at RLF. Once the timer expires and the UE measurement indicates the recovery of the link, the UE can resume its transmission on the suspended bearers. This can also be indicated to the network using a newly defined RRC message. In the case where the timer expires and the link is not recovered, the UE triggers cell selection and RRC establishment.

[0228] According to an example embodiment, when the MCG is configured or selectively activated in a CHO, a timer is started when indicating an MCG failure to the MN. As part of this embodiment, the UE triggers cell selection, and if the newly selected cell is one of the already prepared / configured cells while the timer is running, the UE triggers a handover procedure (CHO recovery) instead of RRC reconstruction. In some example embodiments, the source MN may instruct the target MN to maintain resource reservation until the UE completes CHO recovery or an extended duration. This is because if the UE does not access the target cell after a period of time, i.e., depending on the implementation of the target MN, the target MN may cancel the CHO preparation (and release the reserved resources).

[0229] It should be noted that although in the above example embodiments (with reference to the accompanying drawings), the messages communicated / exchanged between network components / elements may appear to have specific / explicit names, depending on various implementations (e.g., underlying technologies), these messages may have different names and / or be communicated / exchanged in different forms / formats, as can be understood and appreciated by those skilled in the art.

[0230] According to some example embodiments, corresponding methods suitable for being executed by the devices (network elements / components) as described above (such as UE, MN, SN, etc.) are also provided.

[0231] List of abbreviations: MN Master Node SN Secondary Node MCG Master Cell Group SCG Secondary Cell Group DC Dual Connectivity MR-DC Multi-RAT Dual Connectivity RLF Radio Link Failure RRC Radio Resource Control UE User Equipment RAT Radio Access Technology PDCCH Physical Downlink Control Channel PUSCH Physical Uplink Shared Channel CHO Conditional Handover PCell Primary Cell SCell Secondary Cell

[0232] However, it should be noted that for the sake of brevity, the above device (equipment) features correspond to the corresponding method features that may not be explicitly described. The disclosure of this document is considered to also extend to such method features. In particular, the present disclosure is understood to relate to methods of operating the above devices, and / or to methods of providing and / or arranging the corresponding elements of these devices.

[0233] In addition, according to some further example embodiments, a corresponding apparatus (e.g., implementing the UE, MN, SN, etc. as described above) is also provided, which includes at least one processing circuit and at least one memory for storing instructions to be executed by the processing circuit, wherein the at least one memory and the instructions are configured to, together with the at least one processing circuit, cause the corresponding apparatus to at least perform the corresponding steps as described above.

[0234] In some other example embodiments, a corresponding apparatus (e.g., implementing the UE, MN, SN, etc. as described above) is provided, which includes corresponding components configured to at least perform the corresponding steps as described above.

[0235] It should be noted that the examples of the embodiments of the present disclosure are applicable to various different network configurations. In other words, the examples shown in the above figures (which serve as the basis for the above examples) are merely illustrative and do not limit the present disclosure in any way. That is, based on the defined principles, additional existing and proposed new functions available in the corresponding operating environment can be used in combination with the examples of the embodiments of the present disclosure.

[0236] It should also be noted that the disclosed example embodiments can be implemented in many ways using hardware and / or software configurations. For example, the disclosed embodiments can be implemented using dedicated hardware and / or hardware associated with software executable thereon. The components and / or elements in the figures are merely examples and do not limit the use or the scope of the functions of any hardware, software combined with hardware, firmware, embedded logic components, or a combination of two or more such components for implementing the specific embodiments of the present disclosure.

[0237] It should further be noted that the specification and the figures only illustrate the principles of the present disclosure. Those skilled in the art will be able to implement various arrangements, which, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope. In addition, all the examples and embodiments outlined in the present disclosure are mainly intended explicitly for explanatory purposes only to help the reader understand the principles of the proposed methods. Moreover, all statements of the principles, aspects, and embodiments of the present disclosure provided herein, as well as their specific examples, are intended to cover their equivalents.

Claims

1. A user equipment (UE) configured to operate in dual connectivity, where the UE is served by a master cell group (MCG) and a secondary cell group (SCG), the MCG is configured by a master node (MN), and the SCG is configured by a secondary node (SN), the UE comprises: at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the UE to at least: detect an MCG link failure; start a timer for deactivating the MCG; and deactivate the MCG.

2. The UE according to claim 1, wherein the UE is further caused to: send a measurement report to the MN while the timer is running.

3. The UE according to claim 2, wherein the measurement report is periodic, event-triggered, or event-triggered periodic.

4. The UE according to claim 2 or 3, wherein the measurement report at least includes the latest in-band measurement report and at least one of the following: an inter-band measurement report and an inter-radio access technology (RAT) measurement report.

5. The UE according to any one of claims 1 to 4, wherein the UE is caused to deactivate the MCG, comprises: the UE is caused to: while the timer is running, suspend MCG transmissions for all radio bearers, maintain the measurement configuration for the MCG, and continue to measure the MCG based on the maintained MCG measurement configuration.

6. The UE according to any one of claims 1 to 5, wherein the UE is further caused to: in response to detecting an MCG failure and preferably before starting the timer, preferably send an MCG link failure indication message to the MN via the SN, for indicating the detected MCG link failure to the MN.

7. The UE according to any one of claims 1 to 6, wherein the UE is further caused to: directly start the timer after detecting the MCG link failure, where the UE is configured with an MCG deactivation configuration for being enabled by the UE when the UE detects the MCG link failure.

8. The UE according to any one of claims 1 to 7, wherein the UE is further caused to: start the timer in response to receiving an MCG deactivation signaling message.

9. The UE according to any one of claims 1 to 8, wherein the UE is further caused to: start the timer in response to receiving a first radio resource control (RRC) reconfiguration message, the first RRC reconfiguration message preferably includes a command for the UE to perform inter-band measurements and a configuration related to performing the inter-band measurements.

10. The UE according to any one of claims 1 to 9, wherein the UE is further caused to: start the timer in response to a first radio condition, the first radio condition includes a radio link failure (RLF) indicated by the start of T310 or the UE receiving X or N310 consecutive out-of-sync OoS indications from the physical layer.

11. The UE according to any one of claims 1 to 10, wherein the UE is further caused to: Start the timer in response to a second radio condition, the second radio condition including detecting that a frequency layer of the MCG or measurements on all configured frequencies for the MCG are below a threshold.

12. The UE according to any one of claims 1 to 11, wherein the UE is further caused to: Stop the timer in response to receiving a second radio resource control (RRC) reconfiguration message for performing a handover to the MCG; and Perform the handover.

13. The UE according to any one of claims 1 to 12, wherein the UE is further caused to: Stop the timer in response to receiving an MCG activation command message; and Activate the deactivated MCG.

14. The UE according to any one of claims 1 to 13, wherein the UE is further caused to: Perform radio resource control (RRC) reconstruction when the timer expires.

15. The UE according to any one of claims 1 to 14, wherein the UE is further caused, in a scenario of conditional handover (CHO) and / or selective activation for the MCG, where the UE is configured with candidate target cell configurations for CHO and / or selective activation: Start the timer for deactivating the MCG when sending an MCG link failure indication message to the MN; and Keep the MCG in a deactivated state.

16. The UE according to claim 15, wherein the UE is further caused to: Perform measurements on the MCG while the timer is running; Select a target cell for serving the UE based on the performed measurements; and If the selected target cell is a candidate target cell for CHO and / or selective activation, apply the configuration of the selected candidate target cell stored at the UE and stop the timer.

17. The UE according to claim 15 or 16, wherein the UE is further caused to: Resume transmission on a suspended bearer when the timer expires and the UE measurement indicates that the MCG link has recovered.

18. The UE according to any one of claims 15 to 17, wherein the UE is further caused to: Trigger cell selection and radio resource control (RRC) reconstruction when the timer expires and it is detected that the MCG link has not recovered.

19. The UE according to any one of claims 1 to 18, wherein the UE is further caused to set the timer to a length of 0.

20. A master node (MN) for serving a user equipment (UE) together with a secondary node (SN), the MN configuring a master cell group (MCG), the SN configuring a secondary cell group (SCG), the MN comprises: At least one processor, and At least one memory storing instructions which, when executed by the at least one processor, cause the MN to at least: Preferably, send an MCG deactivation indication message to the UE via the SN, for instructing the UE to start a timer for deactivating the MCG in response to the UE detecting an MCG link failure.

21. The MN according to claim 20, wherein the MN is further configured to: Detect the MCG link failure by receiving an MCG link failure indication message; and In response to detecting the MCG link failure, trigger MCG deactivation by sending the MCG deactivation indication message to the UE.

22. The MN according to claim 20 or 21, wherein the MCG deactivation indication message includes a first Radio Resource Control (RRC) reconfiguration message, and the first RRC reconfiguration message preferably includes a command for the UE to perform inter-frequency measurement and configurations related to performing the inter-frequency measurement.

23. The MN according to any one of claims 20 to 22, wherein the MCG deactivation indication message includes an MCG deactivation signaling message.

24. The MN according to any one of claims 20 to 23, wherein the MCG deactivation indication message includes a third Radio Resource Control (RRC) reconfiguration message, and the MN is further configured to: Send the third RRC reconfiguration message to the UE, and the third RRC reconfiguration message includes configurations for MCG deactivation to be enabled by the UE when the UE detects the MCG link failure.

25. The MN according to any one of claims 20 to 24, wherein the MN is further configured to: Determine to perform a handover to the MCG based on a received measurement report; and For instructing the UE to stop the timer: preferably send a second Radio Resource Control (RRC) reconfiguration message to the UE via the SN for performing a handover to the MCG.

26. The MN according to any one of claims 20 to 25, wherein the MN is further configured to: Determine to activate the deactivated MCG based on a received measurement report; and For instructing the UE to stop the timer: preferably send an MCG activation command message to the UE via the SN.

27. The MN according to any one of claims 20 to 26, wherein the MN is further configured to set the timer to a length of 0.

28. A system comprising: A user equipment (UE) according to any one of claims 1 to 19, A master node (MN) according to any one of claims 20 to 27, and A secondary node (SN) configured to configure a secondary cell group (SCG), wherein the UE is served by the MN and the SN.

29. A method for a user equipment (UE), configured to operate in a dual connection, wherein the UE is served by a master cell group (MCG) and a secondary cell group (SCG), the MCG is configured by a master node (MN), and the SCG is configured by a secondary node (SN), the method comprises: Detecting an MCG link failure; Starting a timer for deactivating the MCG; and Deactivating the MCG.

30. A method for a master node MN, where the MN is used to serve a user equipment UE together with a secondary node SN, the MN configures a master cell group MCG, the SN configures a secondary cell group SCG, the method comprises: Preferably sending a deactivation indication message of the MCG to the UE via the SN, for instructing the UE to start a timer for deactivating the MCG in response to the UE detecting an MCG link failure.

31. A computer program comprising instructions for causing an apparatus to perform the method according to claim 29 or claim 30.

32. A memory storing computer-readable instructions for causing an apparatus to perform the method according to claim 29 or claim 30.

Images