TECHNOLOGY

[0001] The present disclosure relates to MCG link failure in dual connectivity, in particular to MCG deactivation in a case of MCK link failure.

BACKGROUND

[0002] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

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

[0004] RLF or MCG link failure can also be experienced by the UE even if the UE has sent the measurement report. In such a scenario, there are two possible cases:

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

[0006] Case 2: UE is configured to measure some frequency layers. MN does not find a suitable cell on the frequency layer that UE is configured to measure, only because some interfrequency measurement is not configured at the UE by the network. In other words, the MN does not have all the information based on which it can trigger an inter-frequency handover.

[0007] According to the legacy procedure (up to Release 17), the procedure of UE reestablishment or MCG failure recovery (if configured) is triggered as soon as UE detects the RLF or MCG link failure in dual connectivity.

[0008] That means, in case 1 above, UE RRC (Radio Resource Control) re-establishment or UE RRC release (if MCG failure recovery is configured, but MN could not find any neighboring cell for handover or change the bearer configuration) will be performed immediately. If the UE returns within the coverage of the serving PCell, the UE has to perform RRC re-establishment after performing cell selection. This procedure causes unnecessary delay. [0009] Issue 1 : Coverage holes/gaps may cause UE to trigger RRC re-establishment, causing extra interruption time due to cell selection and RRC re-establishment on top of the interruption caused by the coverage gap.

[0010] Similarly, in Case 2 above, the UE will be released and it performs cell selection to another frequency than that of the serving PCell and re-establishes the link resulting in extra delay. One simple solution to case 2 is to configure all the inter-frequency measurements from the beginning, but such solution is neither resource efficient due to the need of measurement gaps, nor energy/cost efficient due to the need of active multiple RF (Radio Frequency) chains. [0011] Issue 2: In order to avoid the coverage gaps, the UE has to be doing inter-frequency measurements, causing unnecessary throughput loss, delay, as well as higher energy consumption and device cost.

[0012] The legacy procedure (up to Release 17) does not tackle this problem and in the conventional art there are no solutions which targets the cases described above. Furthermore, following the legacy procedure results in extra delay which is not optimum for latency-critical applications.

[0013] It is therefore necessary to reduce delay and signalling overhead caused by for instance UE RRC re-establishement or release in a case of RLF or MCG link failure in a dual connectivity scenario where for instance handover or cell selection for MCG is to be carried out, in particular for latency-critical applications. It is also necessary to reduce throughput loss, energy consumption and device cost in a case of RLF or MCG link failure in the aforementioned scenario.

SUMMARY

[0014] Object of the present disclosure is to provide a User Equipment, UE, and a Master Node, MN, for reducing delay and signalling overhead, as well as throughput loss, energy consumption and device cost in a case of RLF or MCG link failure in dual connectivity.

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

[0016] Object of the present disclosure is also to provide methods of the UE, the MN and the system being configured for reducing delay and signalling overhead, as well as throughput loss, energy consumption and device cost in a case of RLF or MCG link failure in dual connectivity. [0017] In accordance with an aspect of the present disclosure, there is provided a User Equipment, UE, configured for operating in dual connectivity in which the UE is served by a Master Cell Group, MCG and a Secondary Cell Group, SCG, the MCG being configured by a Master Node, MN and the SCG being 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, cause the UE at least to: 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 for referring to an MN configuring the MCG that is currently serving the UE, i.e., serving the UE before handover to a Target MN is carried out or before selective activation of a candidate target cell is carried out.

[0019] According to the present disclosure, in a case of MCG link failure, a timer is started at the UE, during which the MCG is deactivated. As a result, UE RRC re-establishment or realease is not immediately carried out in a case of MCG link failure, thereby avoiding unnecessary delay und signalling overhead.

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

[0021] Therein, that the UE provides an extended measurement report preferably refers to that measurements of the network are carried out by the UE during the time period of the MCG being deactivated.

[0022] According to the present disclosure, while the MCG is deactivated, the UE keeps on providing measurements, i.e., an extended measurement report, such that the measurements can be directly applied for e.g., MCG activation, selective activation of a candidate target cell, handover for the MCG and etc. As a result, delay in MCG activation, selective activation of a candidate target cell and handover for the MCG ( for instance, after the timer expires or when a candidate target cell is selected) can be reduced since the measurements do not have to be provided from scratch, but instead are ready at the UE for being used.

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

[0024] In some examples, the extended measurement report comprises at least the latest intra-frequency measurements reports and at least one of inter-frequency measurement reports and inter-RAT, Radio Access Technology, measurement reports. [0025] In some examples, that the UE is caused to deactivate the MCG comprises that: the UE is caused to: while the timer is running, suspend MCG transmissions for all radio bearers, maintain measurement configurations for the MCG, and continue measurements on the MCG based on the maintained MCG measurement configurations.

[0026] According to the present disclosure, during the timer running, measurement configurations are maintained for the MCG, such that the measurements can be continuously obtained at the UE even during MCG deactivation. Thereby, the obtained measurements can be directly applied for e.g., MCG activation, selective activation of a candidate target cell, handover for the MCG and etc. As a result, delay in MCG activation, selective activation of a candidate target cell and handover for the MCG ( for instance, after the timer expires or when a candidate target cell is selected) can be reduced since the measurements do not have to be provided from scratch, but instead are ready at the UE for being used.

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

[0028] According to the present disclosure, the MN is informed of the MCG link failure, such that the MN can prepare for MCG deactivation in response to receving the MCG link failure indication message, for instance, provide the UE with MCG deactivation configurations (e.g., timer configuration) for deactivating the MCG during the timer running.

[0029] In some examples, the UE is further caused to: start the timer directly after detecting the MCG link failure, wherein the UE is configured with MCG deactivation configurations for being initiated by the UE upon the UE detecting 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 to be carried out as soon as the UE detects an MCG link failure since the UE is already provided with MCG deactivation configurations before detecting the MCG link failure. For instance, the UE informs the network of the MCG deactivation capabilities configured at the UE, and preferably the network provides the UE with the MCG deactivation configurations after being informed of the MCG deactivation capabilities of the UE. As a result, MCG deactivation can be immediately carried out directly after detecting an MCG link failure, further reducing delay and signalling overhead. [0031 ] Therein, MCG deactivation configurations preferably refer to timer configuration and more preferably whether or not the UE should apply the timer. Preferably this is part of general RRC Reconfiguration message provided to the UE.

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

[0033] Therein, the MCG deactivation signalling message is also referred to as an MCG deactivation command message, which is preferably provided by the MN (preferably via the SN) for triggering the MCG deactivation. Preferably, the MCG deactivation signalling message comprises MCG deactivation configurations (e.g., timer configuration including length of the time period set for the timer). Additionally or alternatively, the MCG deactivation configurations are transmitted to the UE via a separate message.

[0034] In some examples, 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 comprising a command for the UE to perform inter-frequency measurements and configurations related to performing the inter-frequency measurements.

[0035] Therein, the first RRC reconfiguration message is preferably provided by the MN (preferably via the SN) for triggering the MCG deactivation. Preferably, the first RRC reconfiguration message comprises MCG deactivation configurations (e.g., timer configuration including length of the time period set for the timer). Additionally or alternatively, the MCG deactivation configurations are transmitted to the UE via a separate message.

[0036] In some examples, the UE is further caused to: start the timer in response to a first radio condition, the first radio condition comprising a radio link failure, RLF, with start of T310, or X, or N310 consecutive out-of-sync, OoS, indications being received by the UE from the physical layer.

[0037] Therein, 5G NR timers include for instance T304 timer, T310 timer and T311 timer used in 5G NR (New Radio) for various functions, with usage of for instance constants N310 and N311, which is the legacy RLF procedure. For instance, RLF is declared at the UE when N310 consecutive OoS indication is provided. RLF timer T310 is also triggered.

[0038] In some examples, the UE is further caused to: start the timer in response to a second radio condition, the second radio condition comprising a detection that a measurement on a frequency layer of the MCG or on all configured frequencies for the MCG is below a threshold. [0039] Therein, the threshold is preferably configured by the network. [0040] In some examples, the UE is further caused to: stop the timer in response to receiving a second Radio Resource Control, RRC, reconfiguration message for performing handover to the MCG; and perform the handover.

[0041] Therein, the second RRC reconfiguration message is preferably provided by the MN (preferably via the SN) for indicating the UE to perform the handover. Therein, preferably “handover to the MCG” refers to a handover to a Target MN from the (Source) MN. Accordingly, the UE performs the handover and stops the timer.

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

[0043] Therein, the MCG activation message is also referred to as an MCG activation signalling message, for indicating the UE to activate the deactivated MCG. The MCG activation message is preferably provided by the MN (preferably via the SN). Accordingly, the UE activates the MCG and stops the timer.

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

[0045] In some examples, the UE is further caused to: perform Radio Resource Control, RRC, re-establishment upon expiry of the timer.

[0046] Therein, preferably the network configures the length of the time period set for the timer. According to the present disclosure, the delay for UE RRC reestablishment can therefore be set to for instance 10 to 200 milliseconds, which is considerably shortened in comparision with conventional procedures in case of MCG failure.

[0047] In some examples, the UE is further caused to, 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 at the time of transmitting an MCG link failure indication message to the MN; and keep the MCG in deactivated state.

[0048] According to the present disclosure, the solution of setting and starting a timer at the UE is preferably also applicable to scenarios of CHO and/or selective activation for the MCG. That is, the MCG is deactivated when an MCG failure is detected and/or when a corresponding MCG link failure indication message is transmitted from the UE to the MN. Therefore, before handover is performed and before a candidate target cell is selected, the MCG is kept in deactivated state. Accordingly, as soon as a condition for CHO or a candidate target cell is selected, the timer can be stopped and CHO recovery can be carried out instead of RRC reestablishment. This significantly reduces the delay which would otherwise be caused by RRC reestablishment. In case of the timer expiry, RRC reestablishement is preferably performed.

[0049] In some examples, the UE is further caused to: while the timer is running, perform measurements on the MCG; 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 configuration of the selected candidate target cell stored at the UE and stop the timer.

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

[0051] According to the present disclosure, with the timer, the delay necessary for CHO and selective activation can be controlled to be in the order of the length of the timer.

[0052] In some examples, the UE is further caused to: upon the timer expiring and UE measurements indicating recovery of the MCG link, restart transmissions on suspended bearers. [0053] In some examples, the UE is further caused to: upon the timer expiring and detecting the MCG link not recovered, trigger cell selection and Radio Resource Control, RRC, reestablishment.

[0054] Preferably, the UE is further caused to: provide MCG deactivation configurations 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 have a length of 10 to 200 milliseconds.

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

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

[0058] In accordance with another aspect of the present disclosure, there is provided a Master Node, MN, configuring a Master Cell Group, MCG, for serving a User Equipment, UE, together with a Secondary Node, SN, configuring a Secondary Cell Group, SCG, the MN comprising: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the MN at least to: transmit an MCG deactivation indication message to the UE, preferably via the SN, for indicating the UE to start a timer for deactivating the MCG in response to the UE detecting an MCG link failure.

[0059] Therein, in dual connectivity, the MCG configured by the (Source) MN and the SCG configured by the SN serve the UE.

[0060] In the present disclosure, “MN” and “Source MN” are used interchangeably, whereas “Target MN” is used in a scenario of handover from the (Source) MN.

[0061] Preferably, the MCG deactivation indication message comprises MCG deactivation configurations (e.g., timer configurations preferably including length of the timer and more preferably an indication as to whether the UE should apply the configured timer) which are provided to the UE for the UE to deactivate the MCG in response to detecting an MCG link failure. Additional or alternatively, the MCG deactivation configurations are provided to the UE via a separate message.

[0062] According to the present disclosure, the MN indicates the UE, via the MCG deactivation indication message, to start the timer for deactivating the MCG in a case of MCG link failure. As a result, the UE can accordingly deactivate the MCG instead of immediatey carrying out RRC re-establishment or realease, thereby avoiding unnecessary delay und signalling overhead.

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

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

[0065] According to the present disclosure, the MN is informed of the MCG link failure, such that the MN prepares for the MCG deactivation by for instance providing the UE with the MCG deactivation configurations.

[0066] In some examples, the MCG deactivation indication message comprises a first Radio Resource Control, RRC, reconfiguration message, the first RRC reconfiguration message preferably comprising a command for the UE to perform inter-frequency measurements and configurations related to performing the inter-frequency measurements.

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

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

[0069] That is, the MN triggers the MCG deactivation and indicates the UE to deactivate the MCG and to start the timer via the MCG deactivation signaling message, also referred to as the MCG deactivation command message, (preferably via the SN). Preferably, the f MCG deactivation signaling message comprises the MCG deactivation configurations (e.g., the timer configuration including for instance length of the timer period set for the timer).

[0070] In some examples, the MCG deactivation indication message comprises a third Radio Resource Control, RRC, reconfiguration message, and the MN is further caused to: transmit to the UE the third RRC reconfiguration message comprising configurations for MCG deactivation for being initiated by the UE upon the UE detecting the MCG link failure.

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

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

[0073] Therein, while the timer is running, the MN preferably receives continuously from the UE an extended measurement report, and based on the received measurements provided with the extended measurement report, the MN determines to perform handover to the MCG. Accordingly, the UE is indicated by the MN to stop the timer and to perform the handover.

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

[0075] Therein, while the timer is running, the MN preferably receives continuously from the UE an extended measurement report, and based on the received measurements provided with the extended measurement report, the MN determines to activate the deactivated MCG. Accordingly, the UE is indicated by the MN to stop the timer and to activate the deactivated MCG.

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

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

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

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

[0080] In accordance with yet another aspect of the present disclosure, there is provided a system, comprising: a User Equipment, UE, according to any one of the above described examples, a Master Node, MN, according to any one of the above described examples, and a Secondary Node, SN, configuring a Secondary Cell Group, SCG, wherein the UE is served by the MN and the SN.

[0081] In accordance with yet another aspect of the present disclosure, there is provided a method of a User Equipment, UE, being configured for operating in dual connectivity in which the UE is served by a Master Cell Group, MCG and a Secondary Cell Group, SCG, the MCG being configured by a Master Node, MN and the SCG being configured by a Secondary Node, SN, the method comprising: detecting an MCG link failure; starting a timer for deactivating the MCG; and deactivating the MCG.

[0082] In accordance with yet another aspect of the present disclosure, there is provided a method of a Master Node, MN, configuring a Master Cell Group, MCG, for serving a User Equipment, UE, together with a Secondary Node, SN, configuring a Secondary Cell Group, SCG, the method comprising: transmitting an MCG deactivation indication message to the UE, preferably via the SN, for indicating the UE to start a timer for deactivating the MCG in response to the UE detecting an MCG link failure.

[0083] Furthermore, according to some example embodiments, there is provided a computer program comprising instructions for causing an apparatus to perform the method according to any one of the above described examples, and/or the method carried out by the apparatuses and system according to any one of the above described examples. [0084] Furthermore, according to some example embodiments, there is provided a memory storing computer readable instructions for causing an apparatus to perform the method according to any one of the above described examples, and/or the method carried out by the apparatuses and system according to any one of the above described examples.

[0085] In addition, according to some other example embodiments, there is provided, for example, a computer program product for a wireless communication device comprising at least one processor, including software code portions for performing the respective steps disclosed in the present disclosure, when said product is run on the device. The computer program product may include a computer-readable medium on which said software code portions are stored. Furthermore, the computer program product may be directly loadable into the internal memory of the computer and/or transmittable via a network by means of at least one of upload, download and push procedures.

[0086] While some example embodiments will be described herein with particular reference to the above application, it will be appreciated that the present disclosure is not limited to such a field of use, and is applicable in broader contexts.

[0087] Notably, it is understood that methods according to the present disclosure relate to methods of operating the apparatuses according to the above example embodiments and variations thereof, and that respective statements made with regard to the apparatuses likewise apply to the corresponding methods, and vice versa, such that similar description may be omitted for the sake of conciseness. In addition, the above aspects may be combined in many ways, even if not explicitly disclosed. The skilled person will understand that these combinations of aspects and features/steps are possible unless it creates a contradiction which is explicitly excluded.

[0088] Implementations of the disclosed apparatuses may include using, but not limited to, one or more processor, one or more application specific integrated circuit (ASIC) and/or one or more field programmable gate array (FPGA). Implementations of the apparatus may also include using other conventional and/or customized hardware such as software programmable processors, such as graphics processing unit (GPU) processors.

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

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

[0091] Figure 1 schematically illustrates an example of a re-establishment procedure started by the UE;

[0092] Figure 2 schematically illustrates an example of a fast MCG recovery procedure in case network decides to perform handover according to an example embodiment of the present disclosure;

[0093] Figure 3 schematically illustrates an example of the signalling diagram for the MCG de-activation procedure according to an example embodiment of the present disclosure;

[0094] Figure 4 schematically illustrates an example of the signalling procedure for MCG activation and/or RRC reconfiguration according to an example embodiment of the present disclosure;

[0095] Figure 5 schematically illustrates an example of MCG de-activation procedure according to an example embodiment of the present disclosure; and

[0096] Figure 6 schematically illustrates an example of a procedure for CHO/selective activation in accordance with an example embodiment of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

[0097] In the following, different exemplifying embodiments will be described using, as an example of a communication network to which examples of embodiments may be applied, a communication network architecture based on 3 GPP standards for a communication network, such as a 5G/NR, without restricting the embodiments to such an architecture, however. It is apparent for a person skilled in the art that the embodiments may also be applied to other kinds of communication networks where mobile communication principles are integrated with a D2D (device-to-device) or V2X (vehicle to everything) configuration, such as SL (side link), e.g. Wi-Fi, worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, mobile ad-hoc networks (MANETs), wired access, etc. Furthermore, without loss of generality, the description of some examples of embodiments is related to a mobile communication network, but principles of the 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 “an”, “one”, or “some” example(s) or embodiment(s) in several locations, this does not necessarily mean that each such reference is related to the same example(s) or embodiment(s), or that the feature only applies to a single example or embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, terms like “comprising” and “including” should be understood as not limiting the described embodiments to consist of only those features that have been mentioned; such examples and embodiments may also contain features, structures, units, modules, etc., that have not been specifically mentioned.

[0099] A basic system architecture of a (tele)communication network including a mobile communication system where some examples of embodiments are applicable may include an architecture of one or more communication networks including wireless access network subsystem(s) and core network(s). 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 transceiver stations, such as a base station (BS), an access point (AP), a NodeB (NB), an eNB or a gNB, a distributed unit (DU) or a centralized/central unit (CU), which controls a respective coverage area or cell(s) and with which one or more communication stations such as communication elements or functions, like user devices or terminal devices, like a user equipment (UE), or another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a station, an element, a function or an application capable of conducting a 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 conducting a communication, or the like, are capable to communicate via one or more channels via one or more communication beams for transmitting several types of data in a plurality of access domains. Furthermore, core network elements or network functions, such as gateway network elements/functions, mobility management entities, a mobile switching center, servers, databases and the like may be included.

[00100] The following description may provide further details of alternatives, modifications and variances: a gNB comprises e.g., a node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC, e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2 incorporated by reference. [00101] A gNB Central Unit (gNB-CU) comprises e.g., a logical node hosting e.g., RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the Fl interface connected with the gNB-DU.

[00102] A gNB Distributed Unit (gNB-DU) comprises e.g., a logical node hosting e.g., RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by the gNB- CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the Fl interface connected with the gNB-CU.

[00103] A gNB-CU-Control Plane (gNB-CU-CP) comprises e.g., a logical node hosting e.g., the RRC and the control plane part of the PDCP protocol of the gNB-CU for an en-gNB or a gNB. The gNB-CU-CP terminates the El interface connected with the gNB-CU-UP and the Fl-C interface connected with the gNB-DU.

[00104] A gNB-CU-User Plane (gNB-CU-UP) comprises e.g., a logical node hosting e.g., the user plane part of the PDCP protocol of the gNB-CU for an en-gNB, and the user plane part of the PDCP protocol and the SDAP protocol of the gNB-CU for a gNB. The gNB-CU-UP terminates the El interface connected with the gNB-CU-CP and the Fl-U interface connected with the gNB-DU, e.g., according to 3GPP TS 38.401 V16.6.0 (2021-07) section 3.1 incorporated by reference.

[00105] Different functional splits between the central and distributed unit are possible, e.g., called options:

Option 1 (lA-like split):

• The function split in this option is similar to the 1 A architecture in DC. RRC is in the central unit. PDCP, RLC, MAC, physical layer and RF are in the distributed unit.

Option 2 (3C-like split):

• The function split 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 (intra RLC split):

• Low RLC (partial function of RLC), MAC, physical layer and RF are in the distributed unit. PDCP and high RLC (the other partial function of RLC) are in the central unit.

Option 4 (RLC-MAC split): • MAC, physical layer and RF are in the distributed unit. PDCP and RLC are in the central unit.

Or else, e.g., according to 3GPP TR 38.801 V14.0.0 (2017-03) section 11 incorporated by reference.

[00106] A gNB supports different protocol layers, e.g., Layer 1 (LI) - physical layer.

[00107] The layer 2 (L2) of NR is split into the following sublayers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP), where e.g. :

• The physical layer offers to the MAC sublayer transport channels;

• The MAC sublayer offers to the RLC sublayer logical channels;

• The RLC sublayer offers to the PDCP sublayer RLC channels;

• The PDCP sublayer offers to the SDAP sublayer radio bearers;

• The SDAP sublayer offers to 5GC QoS flows;

• Comp, refers to header compression and Segm. To segmentation;

• Control channels include (BCCH, PCCH).

[00108] Layer 3 (L3) includes e.g., Radio Resource Control (RRC), e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 6 incorporated by reference.

[00109] A RAN (Radio Access Network) node or network node like e.g. a gNB, base station, gNB CU or gNB DU or parts thereof may be implemented using e.g. an apparatus with at least one processor and/or at least one memory (with computer-readable instructions (computer program)) configured to support and/or provision and/or process CU and/or DU related functionality and/or features, and/or at least one protocol (sub-)layer of a RAN (Radio Access Network), e.g. layer 2 and/or layer 3.

[00110] The gNB CU and gNB DU parts may e.g., be co-located or physically separated. The gNB DU may even be split further, e.g., into two parts, e.g., one including processing equipment and one including an antenna. A Central Unit (CU) may also be called BBU/REC/RCC/C- RAN/V-RAN, 0-RAN, or part thereof. A Distributed Unit (DU) may also be called RRH/RRU/RE/RU, or part thereof. Hereinafter, in various example embodiments of the present disclosure, the CU-CP (or more generically, the CU) may also be referred to as a (first) network node that supports at least one of central unit control plane functionality or a layer 3 protocol of a radio access network; and similarly, the DU may be referred to as a (second) network node that supports at least one of distributed unit functionality or the layer 2 protocol of the radio access network. [00111] A gNB-DU supports one or multiple cells, and could thus serve as e.g., a serving cell for a user equipment (UE).

[00112] A user equipment (UE) may include a wireless or mobile device, an apparatus with a radio interface to interact with a RAN (Radio Access Network), a smartphone, an in-vehicle apparatus, an loT device, a M2M device, or else. Such UE or apparatus may comprise: 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, with the at least one processor, cause the apparatus at least to perform certain operations, like e.g. RRC connection to the RAN. A UE is e.g., configured to generate a message (e.g., including a cell ID) to be transmitted via radio towards a RAN (e.g., to reach and communicate with a serving cell). A UE may generate and transmit and receive RRC messages containing one or more RRC PDUs (Packet Data Units).

[00113] The UE may have different states (e.g., according to 3GPP TS 38.331 V16.5.0 (2021- 06) sections 42.1 and 4.4, incorporated by reference).

[00114] A UE is e.g., either in RRC CONNECTED state or in RRC INACTIVE state when an RRC connection has been established.

[00115] In RRC CONNECTED state a UE may:

• store the AS context;

• transfer unicast data to/from the UE;

• monitor control channels associated with the shared data channel to determine if data is scheduled for the data channel;

• provide channel quality and feedback information;

• perform neighboring cell measurements and measurement reporting.

[00116] The RRC protocol includes e.g. the following main functions:

• RRC connection control;

• measurement configuration and reporting;

• establishment/modification/release of measurement configuration (e.g. intrafrequency, inter-frequency and inter-RAT measurements);

• setup and release of measurement gaps;

• measurement reporting.

[00117] The general functions 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 described in corresponding specifications, so that a detailed description thereof may omitted herein for the sake of conciseness. However, it is to be noted that several additional network elements and signaling links may be employed for a communication to or from an element, function or application, like a communication endpoint, a communication network control element, such as a server, a gateway, a radio network controller, and other elements of the same or other communication networks besides those described in detail herein below.

[00118] A communication network architecture as being considered in examples of embodiments may also be able to communicate with other networks, such as a public switched telephone network or the Internet. The communication network may also be able to support the usage of cloud services for virtual network elements or functions thereof, wherein it is to be noted that the virtual network part of the telecommunication network can also be provided by non-cloud resources, e.g. an internal network or the like. It should be appreciated that network elements of an access system, of a core network etc., and/or respective functionalities may be implemented by using any node, host, server, access node or entity etc. being suitable for such a usage. Generally, a network function can be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure.

[00119] Furthermore, a network element, such as communication elements, like a UE, a terminal device, control elements or functions, such as access network elements, like a base station / BS, a gNB, a radio network controller, a core network control element or function, such as a gateway element, or other network elements or functions, as described herein, and any other elements, functions or applications may be implemented by software, e.g., by a computer program product for a computer, and/or by hardware. For executing their respective processing, correspondingly used devices, nodes, functions or network elements may include several means, modules, units, components, etc. (not shown) which are required for control, processing and/or communication/signaling functionality. Such means, modules, units and components may include, for example, one or more processors or processor units including one or more processing portions for executing instructions and/or programs and/or for processing data, storage or memory units or means for storing instructions, programs and/or data, for serving as a work area of the processor or processing portion and the like (e.g. ROM, RAM, EEPROM, and the like), input or interface means for inputting data and instructions by software (e.g. floppy disc, CD-ROM, EEPROM, and the like), a user interface for providing monitor and manipulation possibilities to a user (e.g. a screen, a keyboard and the like), other interface or means for establishing links and/or connections under the control of the processor unit or portion (e.g. wired and wireless interface means, radio interface means including e.g. an antenna unit or the like, means for forming a radio communication part etc.) and the like, wherein respective means forming an interface, such as a radio communication part, can be also located on a remote site (e.g. a radio head or a radio station etc.). It is to be noted that in the present specification processing portions should not be only considered to represent physical portions of one or more processors, but may also be considered as a logical division of the referred processing tasks performed by one or more processors. It should be appreciated that according to some examples, a so-called “liquid” or flexible network concept may be employed where the operations and functionalities of a network element, a network function, or of another entity of the network, may be performed in different entities or functions, such as in a node, host or server, in a flexible manner. In other words, a “division of labor” between involved network elements, functions or entities may vary case by case.

[00120] As illustrated above, the present disclosure generally seeks to provide apparatuses (including a User Equipment, UE, and/or a Master Node, MN) for reducing delay and signalling overhead, as well as throughput loss, energy consumption and device cost in a case of RLF or MCG link failure in dual connectivity, and to provide methods carried out by these apparatuses for achieving the same.

[00121] To summarize the example embodiments provided in the present discloure, a new timer “T” is defined during which MCG is considered to be de-activated. That means, while the timer is running, the UE maintains the current measurement configurations and continues measurements (e.g. intra-frequency/inter-frequency/inter-RAT) based on the MCG measurement configuration. Also, the UE maintains the timing advance for the MCG (that is, the UE keeps its uplink synchronization, the UE keeps the time advance related timers, and etc.). However, the UE suspends MCG transmissions for all radio bearers (i.e. UE does not monitor PDCCH (Physical Downlink Control Channel), suspends transmission on PUSCH (Physical Uplink Shared Channel), and there is no transmission on SCells either).

[00122] Further, the present disclosure provides different alternatives on the trigger condition of the timer.

[00123] In one alternative, the timer starts when UE receives the MCG deactivation signalling from the MN.

[00124] In another alternative, the timer starts when UE receives RRC reconfiguration message (including a command to perform inter-frequency measurements and the related configurations) from the MN. [00125] In a third alternative, UE is configured to start the timer after a special radio condition: The radio condition can be RLF i.e. T310 start or X (or N310) number of OoS indications are received by the UE from lower layer. Therein, 5G NR timers include for instance T304 timer, T310 timer and T311 timer used in 5G NR (New Radio) for various functions, with usage of for instance constants N310 and N311, which is the legacy RLF procedure. For instance, RLF is declared at the UE when N310 consecutive OoS indication is provided. RLF timer T310 is also triggered. For details relate to the relevant background information, reference is made to for instance: https://www.rfwireless-world.com/5G/5G-NR-timers-T304-T310-T 311.html.

[00126] In a yet further alternative, UE is configured to start the timer after a special radio condition: The radio condition can also be the case if the strongest measurement on the frequency layer of the serving cell or on the configured frequencies is below a certain threshold requiring the UE to wait until it moves to an area with better/suitable radio coverage or to perform new measurements on different frequencies (to find a cell on a different layer). Therein, the threshold (value) is preferably configured by the network.

[00127] According to the present disclosure, when the timer is running, the UE may send an additional (extended) measurement report to the MN in case of dual connectivity.

[00128] The present disclosure further provides example embodiments for scenario with CHO or selective activation enabled for MCG: When a UE is configured with candidate target cell configurations for conditional handover or selective activation of cell group (fast swithing between cells without reconfiguration), the UE may start the timer at the time of sending MCG failure indication to Source MN and trigger cell selection procedure keeping the MCG in deactivated state. If the UE finds a suitable selected cell that is already prepared cell, the UE can trigger CHO recovery directly to this prepared cell. Therein, Source MN may indicate the Target MN to keep the resource reservations until the UE complete CHO recovery or for the extended duration. This is because the Target MN may cancel the CHO preparation (and release the reserved resources) if the UE does not access the target cell after some time, i.e., depends on the implementation of the Target MN.

[00129] Therein, the Source MN (Master Node) refers to an MN configuring the MCG that is currently serving the UE, i.e., before the handover, whereas a Target MN refers to an MN configuring the MCG, to which the handover from the Source MN is to be carried out.

[00130] Before a detailed description regarding the example embodiments provided by the present disclosure is provided, it is introduced in the following the relevant background information and/or basic knowledge. [00131] The following objectives are discussed as part of Rel. 18 WI (RP -213565):

[00132] Objective 1 : To specify mechanism and procedures of NR-DC (New Radio Dual Connectivity) with selective activation of the cell groups (at least for SCG, Secondary Cell Group) via L3 enhancements; and to allow subsequent cell group change after changing CG without reconfiguration and re-initiation of CPC/CPA (Conditional PScell Change/Addition) [RAN2, RAN3, RAN4], Note that a harmonized RRC modelling approach for objectives 1 and 2 could be considered to minimize the workload in RAN2.

[00133] Obj ctive 2 : To specify CHO (Conditional Handover) including target MCG and target SCG [RAN3, RAN2], Note that this is already being targeted for Rel-17, so this objective will be reviewed at RAN#95-e.

[00134] Object 3 : To specify CHO including target MCG and candidate SCGs for CPC/CPA [RAN3,RAN2], wherein CHO including target MCG and target SCG is used as the baseline. [00135] Objectives 1 and 3 are particularly relevant to the present disclosure.

[00136] Furthermore, the present disclosure could also be relevant as general enhancement to mobility procedure in Rel. 19 and beyond.

[00137] In the following, RRC re-establishment procedure (referring to TS 38.300, Section 9.2.3.3) is described:

[00138] A UE in RRC CONNECTED may initiate the re-establishment procedure to continue the RRC connection when a failure condition occurs (e.g. radio link failure, reconfiguration failure, integrity check failure and etc.).

[00139] Figure 1 below describes the re-establishment procedure started by the UE:

[00140] Step SI 1 : The UE re-establishes the connection, providing the UE Identity (PCI+C- RNTI) to the gNB where the trigger for the re-establishment occurred. Therein, PCI refers to Physical Cell Identity and C-RNTI refers to Cell Radio Network Temporary Identifier.

[00141] Step S12: If the UE Context is not locally available, the gNB requests the last serving gNB to provide the UE with context data.

[00142] Step S13: The last serving gNB provides the UE with the context data.

[00143] Step 14/14a: The gNB continues the re-establishment of the RRC connection. The message is sent on SRB1, wherein SRB refers to Signalling Radio Bearer. Note that configurations of signalling radio bearers are to be found in for instance TS 38.331.

[00144] Step 15/15a: The gNB may perform the reconfiguration to re-establish SRB2 and DRBs (Data Radio Bearers) when the reestablishment procedure is ongoing. [00145] Step 16/17: If loss of user data buffered in the last serving gNB shall be prevented, the gNB provides forwarding addresses, and the last serving gNB provides the SN status to the gNB.

[00146] Step 18/19: The gNB performs path switch.

[00147] Step 110: The gNB triggers the release of the UE resources at the last serving gNB.

[00148] In the following, UE re-establishment delay requirement is described (referring to TS 38.133, Section 6.2.1.2.1):

[00149] The UE re-establishment delay requirement is defined in TS 38.133, section 6.2.1.2.1 and it is the time between the moments when any of the conditions requiring RRC reestablishment as defined in clause 5.3.7 in TS 38.331 is detected by the UE and when the UE sends PRACH (Physical Random Access Channel) to the target PCell. The UE reestablishment delay (TUE re-establish delay) requirement shall be less than a corresponding value depending on the specific definition of the UE reestablishment delay.

[00150] The UE reestablishment delay may be defined as the time to identify the target intrafrequency NR cell and it depends on whether the target NR cell is known cell or unknown cell and on the FR of the target NR cell. If the UE is not configured with intra-frequency NR carrier for RRC re-establishment, then the UE reestablishment delay = 0; otherwise the UE reestablishment delay shall not exceed the values defined in Table 6.2.1.2 of TS 38.133.

[00151] The UE reestablishment delay may be defined as the time to identify the target interfrequency NR cell on inter-frequency carrier configured for RRC re-establishment and it depends on whether the target NR cell is known cell or unknown cell and on the FR of the target NR cell. The UE reestablishment delay shall not exceed the values defined in Table 6.2.1.2 of TS 38.133.

[00152] The UE reestablishment delay may be defined as the time required for receiving all the relevant system information according to the reception procedure and the RRC procedure delay of system information blocks defined in TS 38.331 for the target NR cell.

[00153] The UE reestablishment delay may be defined as the delay uncertainty in acquiring the first available PRACH occasion in the target NR cell, and can be up to the summation of SSB (Synchronization Signal Block) to PRACH occasion association period and 10 ms. Therein, SSB to PRACH occasion associated period is defined in the table 8.1-1 of TS 38.213. [00154] The UE reestablishment delay may be defined as the total number of NR frequencies to be monitored for RRC re-establishment; the UE reestablishment delay =1 if the target intra- frequency NR cell is known, else =2 and if the target inter-frequency NR cell is known. [00155] It can be observed that the UE re-establishment delay can easily be in the order of seconds.

[00156] In order to reduce the UE re-establishment delay in case of dual connectivity (DC) scenarios, fast MCG failure recovery (the so-called network controlled recovery) is specified in Release 16. The detail of which is given below, as illustrated also in Figure 2.

[00157] Figure 2 shows a fast MCG recovery procedure in case network decides to perform handover in accordance with example embodiments provided by the present disclosure.

[00158] For MCG Failure Recovery, reference is made to TS 37.340.

[00159] In (MR)-DC deployment, MR referring to Multi-RAT (Radio Access Technology), the UE can be configured to perform a fast MCG failure recovery via the existing SN when a RLF is detected for PCell. The signalling diagram for fast MCG failure recovery is shown in Figure 2.

[00160] As shown in Figure 2, the UE is in a MCG link failure scenario.

[00161] Step S21 : the UE transmits to the SN (Secondary Node) an MCG failure indication message. Therein, the SN is a network node or network element configured in an SCG (Secondary Cell Group) for serving the UE. In dual connectivity, the SCG and an MCG (Master Cell Group) together serve the UE.

[00162] Step S22: the SN forwards the received MCG failure indication message to the Source MN, wherein the forwarded MCG failure indication message includes measurements provided by the UE.

[00163] Step S23 : the Source MN transmits a handover request message to the Target MN.

[00164] Step S24: the Target MN transmits, in response to the received handover request message, a handover request acknowledgement message to the Source MN.

[00165] Step S25: the Source MN transmits a handover command message to the SN.

[00166] Step S26: the SN forwards the received handover command message to the UE.

[00167] Step S27: the UE executes the handover in response to the received handover command message, wherein the handover includes transmitting by the UE a Random Access Channel (RACH) message to the Target MN.

[00168] It can be observed that fast MCG recovery procedure makes use of the active SCG link to inform the Source MN about the failure, together with the measurement information. Based on this information, the Source MN decides to perform either RRC reconfiguration (changing the bearer configurations), RRC release (releasing the bearers) or handover to neighboring cell (as shown in the Figure 2). [00169] In this way, the RRC re-establishment delay of several hundreds of milliseconds is reduced to a few tens of milliseconds as in normal handover.

[00170] In the following, it is provided a description as to UE measurements, with reference being made to TS 38.300, Section 9.1.

[00171] Measurements to be performed by a UE for connected mode mobility are classified in at least four measurement types:

- Intra-frequency NR measurements;

- Inter-frequency NR measurements;

- Inter-RAT measurements for E-UTRA;

- Inter-RAT measurements for UTRA.

[00172] For each measurement type, one or several measurement objects can be defined (a measurement object defines e.g. the carrier frequency to be monitored).

[00173] For each measurement object, one or several reporting configurations can be defined (a reporting configuration defines the reporting criteria). Three reporting criteria are used: event triggered reporting, periodic reporting and event triggered periodic reporting.

[00174] The association between a measurement object and a reporting configuration is created by a measurement identity (a measurement identity links together one measurement object and one reporting configuration of the same RAT). By using several measurement identities (one for each measurement object, reporting configuration pair) it is then possible to:

- Associate several reporting configurations to one measurement object and;

- Associate one reporting configuration to several measurement objects.

[00175] The measurements identity is used as well when reporting results of the measurements.

[00176] Measurement quantities are considered separately for each RAT.

[00177] Measurement configurations are used by the network to configure the UE to start, modify or stop measurements.

[00178] According to Rel. 16 fast MCG recovery procedure, a UE makes use of the active SCG link to inform the MN about the link failure (e.g. RLF) by triggering the MCG link failure indication to the MN. The MCG failure information message contains the cause of failure as well as the measurement reports. Based on these measurement reports, MN can perform an appropriate recovery procedure e.g. RRC reconfiguration, RRC release or handover. This procedure is not optimum in case of the coverage hole (case 1 as discussed above in the background section) or unavailability of inter-frequency/inter-RAT measurement reports from the UE (case 2 as discussed above in the background section). This is because, according to the procedure, the UE will be released from the network and will have to perform RRC reestablishment procedure which results in extra and unnecessary delay in case of coverage hole (case 1) and non-availability of interfrequency/inter-RAT measurement reports (case 2).

[00179] Therefore, in order to avoid the unnecessary delay, the present disclosure proposes to perform MCG deactivation during the MCG failure which is controlled by a timer. In other words, transmissions on MCG bearers are suspended while the UE maintains the measurements on the MCG. Once the MCG link is recovered (i.e. UE returns within the coverage) or the MN has received the measurement report for different frequency layer or RAT, the suitable action is triggered by the MN. This action can be MCG activation (in case of UE returning within the coverage) or inter-frequency/inter-RAT handover (in case of new inter-frequency/inter-RAT measurement reports are received).

[00180] Figure 3 shows the signalling diagram for the MCG de-activation procedure described above according to an example embodiment of the present disclosure.

[00181] As shown in Figure 3, at Step S31, the UE is operating in dual connectivity.

[00182] Further, the following steps are executed according to Figure 3:

[00183] Step S32/S33: the UE detects an MCG failure and indicates it to the MN via the SN with an MCG failure indication message.

[00184] Step S34/S35/S36: the MN triggers MCG deactivation and signals it to the UE via the SN with a first RRC reconfiguration message indicating MCG deactivation. Preferably, the first RRC reconfiguration message comprises a command for the UE to perform inter-frequency measurements and configurations related to performing the inter-frequency measurements.

[00185] Step S37: the UE deactivates the MCG and starts the timer. When MCG is deactivated, there is:

• No PDCCH monitoring

• No PUSCH (configured grants released/suspended)

• No CSI reporting

• no PHR (Power Headroom Report) reported (triggered when SCG is activated), and

• SCells of MCG are deactivated (dormancy not supported)

• RRM (Radio Resources Management) measurements continue

• Radio Link and Beam monitoring is enabled/disabled by RRC.

[00186] Step S38/39: Confirmation of RRC reconfiguration is sent to the MN via the SN. Therein, a (first) RRC reconfiguration complete (message) is sent to the MN. [00187] As described above, while the timer is running, measurements at the UE continue, such that an extended measurement report is provided, and can be directly applied for performing handover or selective activation or activation of the MCG.

[00188] In accordance with the present disclosure and as shown in Figure 3, the timer is started upon the reception of the RRC reconfiguration for MCG deactivation (for instance with an (first) RRC reconfiguration message) from the MN (via the SN), and/or the timer is started upon the reception of an MCG de-activation command (for instance with an MCG deactivation signalling message) from the MN (via the SN). Whereas, the timer is stopped upon receiving the RRC reconfiguration to perform the handover (for instance with an (second) RRC reconfiguration message) from the MN (via SN), and/or the timer is stopped upon receiving an MCG activation command from the MN (via SN). In case the timer expires, the UE performs RRC re-establishment.

[00189] Figure 4 shows the signalling procedure for MCG activation and/or RRC reconfiguration according to an example embodiment of the present disclosure.

[00190] As shown in Figure 4, at step S41, the MCG is deactivated.

[00191] The following steps are executed according to Figure 4:

[00192] Step S41 : the UE sends the measurement report to the MN over the SN (based on the extended measurement report).

[00193] Step S42/S43: the MN initiates the activation of the de-activated MCG and signals it to UE via SN. This may be done with the second RRC reconfiguration message comprising the RRC reconfiguration to perform the handover. Additionally or alternatively, this may be done with an MCG activation command message (or an MCG activation signalling message).

[00194] Step S44: the MCG is activated and/or handover is performed and the timer is stopped.

[00195] Step S45: a (second) RRC reconfiguration complete (message) is sent to the Target MN for handover or to the Source MN for reactivation.

[00196] As an alternative to the above described method for MCG de-activation (in Figure 3), in accordance with an example embodiment of the present disclosure, the MCG can be deactivated as a default behaviour of a UE upon the detection of RLF (e.g. T310 starts or consecutive N310 out-of-sync indications are received from the physical layer) or the detection that the measurement on the frequency layer of the serving cell or all configured frequency is below a threshold (preferably configured by the network). This method is illustrated in Figure 5 for the RLF case, as an example. [00197] As shown in Figure 5, at step S51, the UE is operating in dual connectivity.

[00198] Further, the following steps are executed according to Figre 5:

[00199] Step S51 : The UE indicates the MCG de-activation capability to the network.

[00200] Step S52/S53: The network may configure the UE with MCG de-activation measurement configuration (or entire configuration) to be initiated (by the UE) once the MCG failure is detected. This may be done with a (third) Radio Resource Control, RRC, reconfiguration message comprising configurations for MCG deactivation for being initiated by the UE upon the UE detecting the MCG link failure.

[00201] Step S54: Once the MCG failure is detected, UE applies the stored MCG deactivation configuration: UE puts the MCG into de-activated state and starts measurement for extended measurement reporting for MCG failure procedure.

[00202] Step S55: The UE sends the extended measurement report to the MN via the SN.

[00203] In accordance with the present disclosure, as provided for instance with the above described example embodiments as illustrated in Figures 2 to 5, the following advantages are achieved: Avoid unnecessary delay and signalling overhead due to RRC release and RRC reestablishment from the scratch; and Allow network to trigger a handover to an inter- frequency/inter-RAT handover without enabling inter-frequency/inter-RAT measurements from the start.

[00204] Essentially, the present disclosure achieves the above advantages by delaying the trigger of UE re-establishment and/or fast MCG recovery procedure using the newly defined timer “T”. In particular, while the timer T is running, the UE keeps providing measurements of the network, whereas all transmissions on MCG bearers are suspended, such that the MCG is deactivated within the time period set for the timer. The UE performs RRC reestablishment immediately upon expiry of the timer and/or after activation of the MCG since the extended measurement report provided by the UE during running of the timer T can be directly provided to the Source MN. Therefore, the network can set the timer to have a length of for instance 10 to 200 milliseconds, which is shorter compared with the (conventional) fast MCG recovery procedure.

[00205] Furthermore, the above described solution in accordance with the present discloure can be used as a solution to CHO recovery or when selective activation is enabled for MCG. For example, in case a UE is configured with CHO or selective activation of MCG, the UE starts the timer at the time of sending the MCG failure indication to source MN and trigger cell selection procedure keeping the MCG in de-activated state. If the UE finds a suitable selected cell that is already prepared cell within the timer duration, the UE can trigger CHO recovery (i.e. handover instead of RRC re-establishment) directly to this prepared cell. In case of the timer expiry, RRC reestablishment is performed.

[00206] Figure 6 shows a procedure for CHO/selective activation, applying the abovedescribed solution using the timer T for MCG deactivation, in accordance with an example embodiment of the present disclosure.

[00207] As shown in Figure 6, at step S61, The UE is operating in dual connectivity.

[00208] Further, the following steps are executed according to Figure 6:

[00209] Step S62/S63 : the RRC reconfiguration procedure is executed, i.e. the UE is provided with the MCG deactivation configuration (e.g. timer configuration, whether or not UE should apply the timer, and etc.) and conditional configurations (e.g. candidate PCells and the switching conditions).

[00210] Step S64: the UE detects MCG (link) failure, deactivates the MCG (directly in response to detecting the MCG link failure) and starts the timer T.

[00211] 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 already stored at the UE and stops the timer. Therein, if the timer expires, the UE performs RRC re-establishment procedure.

[00212] Note that Conditional handover (CHO) is a Rel. 16 procedure and CHO recovery is also defined.

[00213] However, in accordance with the present disclosure, CHO is related to the newly defined timer.

[00214] Note that Selective Activation means that the UE stores all the candidate target cells’ configurations and whenever the respective conition is fulfilled, the UE applies the configuration of the (selected) cell already stored at the UE. This is being specified in Rel. 18. [00215] However, Rel. 18 is targeting selective activation of SCG (secondary cell group). Here, in accordance with the present disclosure, the use of a newly defined timer is related to selective activation of MCG (master cell group).

[00216] In accordance with the present disclosure, as provided for instance with the above described example embodiment as illustrated in Figure 6, it is achieved the same advantages as achieved with the example embodiments as shown in for instance Figures 2 to 5: Namely avoid unnecessary delay and signalling overhead due to RRC release and RRC reestablishment from the scratch; and Allow network to trigger a handover to MCG or selective activation of MCG without having to provide UE measurements from the scratch.

[00217] Essentially, the present disclosure achieves the above advantages by delaying the trigger of a handover to MCG or selective activation of MCG using the newly defined timer “T”. In particular, while the timer T is running, the UE keeps providing measurements of the network, whereas all transmissions on MCG bearers are suspended, such that the MCG is deactivated within the time period set for the timer. If a 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 already stored at the UE and stops the timer. Therefore, the network can set the timer to have a length of for instance 10 to 200 milliseconds, which is shorter compared with the (conventional) CHO and selective activation procedures.

[00218] To summarize, it is provided according to the present disclosure a MCG deactivation procedure in a case of MCG link failure, wherein when an MCG failure indication message is received by the MN (via the SN), the MN does not perform RRC release or handover immediately. Instead, the MN sends the MCG deactivation command or the corresponding RRC reconfiguration (to configure inter-frequency/inter-RAT measurements) to the UE via the SN. On reception of the MCG deactivation command or the corresponding RRC reconfiguration message (for instance, the first RRC reconfiguration message shown in Figure 3) or directly in response to detection of the MCG link failure, a new timer T is started at the UE side and the transmissions on MCG bearers are suspended while the timer is running.

[00219] According to one example embodiment, the configuration of the timer is performed as part of the MCG failure recovery configuration.

[00220] According to one example embodiment, the configuration of the timer is performed (preferably at the MN) as a response to the MCG failure indication message from the UE.

[00221] According to one example embodiment, the network decides not to trigger the timer. It can be implemented by configuring the value of the timer to be zero. In this case, MCG is not deactivated and MCG link recovery is performed as soon as MCG failure indication is signalled to the MN.

[00222] According to one example embodiment, the UE provides extended measurement reports while the timer is running. The extended measurement reports may include at least the latest intra-frequency measurement reports. This report may also include inter-frequency as well as inter-RAT measurement reports. [00223] According to one example embodiment, the extended measurement reports can be periodic or aperiodic (event-based as well as in response to the request from the network). In case of event based, one example is the triggering of the report when MCG coverage is restored (i.e. UE is out of coverage hole of Pcell).

[00224] According to one example embodiment, the timer is stopped when the UE received MCG activation command. MCG activation command can be signalled as RRC message or MAC control element.

[00225] According to one example embodiment, the timer is stopped when the UE received the RRC reconfiguration message to perform the handover.

[00226] According to one example embodiment, UE performs RRC re-establishment upon expiry of the timer.

[00227] According to one example embodiment, the timer is always used as a fall- back/default operation after the start of T310 or N310 consective out-of-sync indications are received from the physical layer or the detection that the measurement on the frequency layer of the serving cell or all configured frequency is below a threshold and MCG is deactivated during this timer. This is also applicable in case of single connectivity where the start of the timer is a default procedure upon RLE Once the timer expires and UE measurements indicate the recovery of the link, UE may restart its transmissions on the suspended bearers. This can also be indicated to the network using a new defined RRC message. In case the timer expires and the link is not recovered, UE triggers the cell selection and RRC eestablishment.

[00228] According to one example embodiment, the timer is started at the time of MCG failure indication to the MN in case CHO or selective activation of MCG is configured. As a part of this embodiment, the UE triggers cell selection and if the new selected cell while the timer is running is one of the already prepared/configured cells, UE triggers a handover procedure (CHO recovery) instead of RRC reestablishment. In some example embodiments, the source MN may indicate the Target MN to keep the resource reservations until the UE complete CHO recovery or for the extended duration. This is because the target MN may cancel the CHO preparation (and release the reserved resources) if the UE does not access the target cell after some time, i.e., depends on the implementation of the target MN.

[00229] It is noted that, although in the above-illustrated example embodiments (with reference to the figures), the messages communi cated/exchanged between the network components/elements may appear to have specific/explicit names, depending on various implementations (e.g., the underlining technologies), these messages may have different names and/or be communi cated/exchanged in different forms/formats, as can be understood and appreciated by the skilled person.

[00230] According to some example embodiments, there are also provided corresponding methods suitable to be carried out by the apparatuses (network elements/components) as described above, such as the UE, the MN, the SN, etc.

[00231] 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

[00232] It should nevertheless be noted that the apparatus (device) features described above correspond to respective method features that may however not be explicitly described, for reasons of conciseness. The disclosure of the present document is considered to extend also to such method features. In particular, the present disclosure is understood to relate to methods of operating the devices described above, and/or to providing and/or arranging respective elements of these devices.

[00233] Further, according to some further example embodiments, there is also provided a respective apparatus (e.g., implementing the UE, the MN, the SN, etc., as described above) that comprises at least one processing circuitry, and at least one memory for storing instructions to be executed by the processing circuitry, wherein the at least one memory and the instructions are configured to, with the at least one processing circuitry, cause the respective apparatus to at least perform the respective steps as described above. [00234] Yet in some other example embodiments, there is provided a respective apparatus (e.g., implementing the UE, the MN, the SN, etc., as described above) that comprises respective means configured to at least perform the respective steps as described above.

[00235] It is to be noted that examples of embodiments of the disclosure are applicable to various different network configurations. In other words, the examples shown in the above described figures, which are used as a basis for the above discussed examples, are only illustrative and do not limit the present disclosure in any way. That is, additional further existing and proposed new functionalities available in a corresponding operating environment may be used in connection with examples of embodiments of the disclosure based on the principles defined.

[00236] It should also to be noted that the disclosed example embodiments can be implemented in many ways using hardware and/or software configurations. For example, the disclosed embodiments may be implemented using dedicated hardware and/or hardware in association with software executable thereon. The components and/or elements in the figures are examples only and do not limit the scope of use or functionality of any hardware, software in combination with hardware, firmware, embedded logic component, or a combination of two or more such components implementing particular embodiments of the present disclosure.

[00237] It should further be noted that the description and drawings merely illustrate the principles of the present disclosure. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in the present disclosure are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed method. Furthermore, all statements herein providing principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.