Failure of a layer 1 / layer 2 triggered mobility (LTM) procedure

Abstract

There is provided a method performed by a user equipment (UE) The UE is operating with multi- radio dual connectivity (MR-DC) with a first cell group and a second cell group. The method comprises detecting (1101) a failure of a Layer 1 / Layer 2 Triggered Mobility (LTM) procedure; and sending (1103), to a first network node associated with the first cell group, a notification message that comprises information relating to the failure.

Description

[0001] Failure of a Layer 1 / Layer 2 Triggered Mobility (LTM) procedure

[0002] Technical Field

[0003] This disclosure relates to failure of a Layer 1 / Layer 2 Triggered Mobility (LTM) procedure.

[0004] 3GPP Dual Connectivity

[0005] In 3rdGeneration Partnership Project (3GPP) Release 12 (Rel-12), the Long Term Evolution (LTE) feature Dual Connectivity (DC) was introduced, to enable the User Equipment (UE) to be connected in two cell groups, each controlled by an LTE access node, eNBs, labelled as the Master eNB (MeNB) and the Secondary eNB (SeNB). The UE still only has one Radio Resource Control (RRC) connection with the network. In 3GPP, the Dual Connectivity (DC) solution has since then been evolved and is now also specified for New Radio (NR) as well as between LTE and NR. With the introduction of 5thGeneration (5G), the term Multi-Radio Dual Connectivity (MR-DC) was defined as a generic term for all dual connectivity options which includes at least one NR access node. This is described further in 3GPP Technical Standard (TS) 37.340 v17.4.0. Using the MR-DC generalised terminology, the UE is connected in a Master Cell Group (MCG), controlled by the Master Node (MN), and in a Secondary Cell Group (SCG) controlled by a Secondary Node (SN).

[0006] Further, in MR-DC, when dual connectivity is configured for the UE, within each of the two cell groups, MCG and SCG, carrier aggregation may be used as well. In this case, within the Master Cell Group (MCG) controlled by the master node (MN), the UE may use one Primary Cell (PCell) and one or more Secondary Cells (SCell(s)). Within the Secondary Cell Group (SCG) controlled by the secondary node (SN), the UE may use one Primary SCell (PSCell, also known as the Primary SCG cell in NR) and one or more SCell(s). This combined case (dual connectivity combined with carrier aggregation in MR-DC) is illustrated in Fig. 1.

[0007] In NR, the primary cell of a master or secondary cell group is sometimes also referred to as the Special Cell (SpCell). Hence, the SpCell in the MCG is the PCell and the SpCell in the SCG is the PSCell.

[0008] There are different ways to deploy a 5G network with or without interworking with LTE (also referred to as Evolved Universal Terrestrial Radio Access (E-UTRA)) and Evolved Packet Core (EPC). These different ways to deploy 5G are also known as architecture options. In principle, NR and LTE can be deployed without any interworking, denoted by NR stand-alone (SA) operation, also known as architecture option 2, that is gNB in NR can be connected to 5G core network (5GC) and eNB in LTE can be connected to EPC with no interconnection between the two, also known as architecture option 1.

[0009] On the other hand, the first supported version of NR uses dual connectivity, denoted as EN- DC (E-UTRA Network-NR Dual Connectivity), also known as architecture option 3, as depicted in Fig. 2. In such a deployment, dual connectivity between NR and LTE is applied, where the UE is connected with both the LTE radio interface (LTE Uu in Fig. 2) to an LTE access node and the NR radio interface (NR Uu in Fig. 2) to an NR access node. Further, in EN-DC, the LTE access node acts as the master node (in this case known as the Master eNB (MeNB)), controlling the master cell group (MCG), and the NR access node acts as the secondary node (in this case sometimes also known as the Secondary gNB (SgNB)), controlling the secondary cell group (SCG). The SgNB has a user plane (UP) connection S1-U to the core network (EPC). The control plane (CP) connection S1-C to the core network (EPC) is instead provided by the MeNB. This is also called “Non-standalone NR” (NSA NR). It should be noted that in this case the functionality of an NR cell is limited and would be used for connected mode UEs as a booster and / or diversity leg, but an RRCJDLE UE cannot camp on these NR cells. In EN-DC, there is no connection to the 5G core network (5GC).

[0010] With the introduction of 5GC, other options may be also valid. As mentioned above, option 2 supports stand-alone NR deployment where the gNB is connected to 5GC. Similarly, LTE can also be connected to 5GC using option 5 (also known as eLTE, E-UTRA / 5GC, or LTE / 5GC and the node can be referred to as a Next Generation-eNB (ng-eNB)). In these cases, both NR and LTE are seen as part of the Next Generation-Radio Access Network (NG-RAN), and both the ng- eNB and the gNB can be referred to as NG-RAN nodes.

[0011] It is worth noting that there are also other variants of dual connectivity between LTE and NR which have been standardised as part of NG-RAN connected to 5GC. Under the MR-DC umbrella there is:

[0012] • EN-DC (also known as architecture option 3): LTE is the master node and NR is the secondary node (EPC Core Network (CN) employed, as depicted in Fig. 4);

[0013] • NR-E-UTRA Dual Connectivity (NE-DC) (also known as architecture option 4): NR is the master node and LTE is the secondary (5GC employed);

[0014] • NG-RAN - E-UTRA Dual Connectivity (NGEN-DC) (also known as architecture option 7): LTE is the master node and NR is the secondary (5GC employed);

[0015] • New Radio-Dual Connectivity (NR-DC) (variant of architecture option 2): Dual connectivity where both the master node (MN) controlling the MCG and the secondary node (SN) controlling the SCG are NR (5GC employed, as depicted in Fig. 3).

[0016] In NR-DC, which is depicted in Fig. 3, the secondary node (NR SN) is a gNB, providing NR radio interface NR Uu to the UE and has a user plane connection NG-U to the 5G core network (5GC). The master node (NR MN) is also a gNB, providing NR radio interface NR Uu to the UE and has the control plane connection NG-C as well as a user plane connection NG-U to the 5G core network (5GC). Between the MN and SN the Xn interface is used.

[0017] As migration for these options may differ from different operators, it is possible to have deployments with multiple options in parallel in the same network. For example, there could be an eNB base station supporting architecture options 3, 5 and 7 in the same network as a NR base station supporting architecture options 2 and 4. In combination with dual connectivity solutions between LTE and NR it is also possible to support Carrier Aggregation (CA) in each cell group (i.e. MCG and SCG) and dual connectivity between nodes on same Radio Access Technology (RAT) (e.g. NR-NR DC). For the LTE cells, a consequence of these different deployments is the co-existence of LTE cells associated to eNBs connected to EPC, 5GC, or both EPC and 5GC.

[0018] As noted above, DC is standardised for both LTE and E-UTRA-NR DC (EN-DC).

[0019] LTE DC and EN-DC are designed differently when it comes to which nodes control what. Basically, there are two options:

[0020] 1. Centralised solution (like LTE-DC),

[0021] 2. Decentralised solution (like EN-DC).

[0022] Fig. 4 shows the schematic control plane architecture for LTE DC, EN-DC and NR-DC. The main difference here is that in EN-DC and NR-DC, the Secondary Node (SN) has a separate NR RRC entity. This means that the SN can also control the UE; sometimes using the NR radio interface NR Uu directly to the UE without the knowledge of the MN, but often the SN needs to coordinate with the Master Node (MN). The UE has an LTE RRC state in EN-DC and an NR RRC state in NR-DC. Further, in LTE-DC and EN-DC, the control plane interface between MN and SN is X2-C. In LTE-DC, the RRC decisions are always coming from the MN (MN uses the LTE radio interface LTE Uu to the UE). Note however, the SN still decides the configuration of the SN, since it is only the SN itself that has knowledge of what kind of resources, capabilities, etc. it has. Further, in LTE-DC, the UE has an LTE RRC state. Further, in NR-DC, the control plane interface between MN and SN is Xn-C.

[0023] For EN-DC and NR-DC, the major changes compared to LTE DC are:

[0024] • The introduction of a split data radio bearer (DRB) from the SN (known as SN terminated split DRB);

[0025] • The introduction of split signalling radio bearer (SRB) for RRC;

[0026] • The introduction of a direct SRB from the SN (also referred to as SCG SRB or SRB3).

[0027] Fig. 5 shows, from a network perspective, the user plane protocol architecture in MR-DC with EPC (EN-DC). A bearer may be categorised into a bearer type. Each bearer type is characterised by which radio resources that are involved. For an MCG bearer, only MCG radio resources and RLC + Medium Access Control (MAC) layer entities for the MCG are involved. For an SCG bearer, only SCG radio resources and RLC+MAC layer entities for the SCG are involved. For a split bearer, both MCG and SCG radio resources as well as RLC+MAC layer entities for both the MCG and SCG are involved. Further, a bearer may also be categorised into MN terminated bearers and SN terminated bearers depending on which network node they are terminated at. For MN terminated bearers, the Packet Data Convergence Protocol (PDCP) layer entity and the user plane connection to the core network is terminated in the MN. For SN terminated bearers, the PDCP layer entity and the user plane connection to the core network is terminated in the SN.

[0028] The network can configure either a E-UTRA PDCP layer or a NR PDCP layer for MN terminated MCG bearers, while a NR PDCP layer is always used for all other bearers. In this case, the network can configure either E-UTRA PDCP or NR PDCP for MN terminated MCG DRBs, while NR PDCP is always used for all other DRBs.

[0029] Fig. 6 shows, from a network perspective, the user plane protocol architecture in MR-DC with 5GC (NGEN-DC, NE-DC and NR-DC). In MR-DC with 5GC, NR PDCP is always used for all DRB types. In NGEN-DC, E-UTRA Radio Link Control (RLC) / MAC is used in the MN while NR RLC / MAC is used in the SN. In NE-DC, NR RLC / MAC is used in the MN while E-UTRA RLC / MAC is used in the SN. In NR-DC, NR RLC / MAC is used in both MN and SN.

[0030] L1 / L2 based inter-cell mobility in Rel-18

[0031] In 3GPP Release 18 (Rel-18), a work item known as Further NR mobility enhancements has been agreed. This work item includes a technical area entitled Layer 1 (L1) / Layer 2 (L2) based inter-cell mobility. According to the Work Item Description (WID) (RP-223520, 3GPP work item description: Further NR mobility enhancements; MediaTek Inc, Apple; 3GPP TSG RAN Meeting #98-e, Electronic Meeting, December 12-16, 2022), when the UE moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently serving cell change is triggered by Layer 3 (L3) measurements and is done by RRC signalling triggered Reconfiguration with Synchronisation for change of PCell and PSCell, as well as releasing or adding SCells when applicable. All cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead and longer interruption time than beam switch mobility. The goal of L1 / L2 based inter-cell mobility is to enable a serving cell change via L1 / L2 signalling, in order to reduce the latency, overhead and interruption time.

[0032] In 3GPP, L1 is a Physical (PHY) layer and L2 is a Medium Access Control (MAC) layer.

[0033] According to the above WID, the following is included as one objective of the work:

[0034] (in the above, CU is Central Unit, DU is Distributed Unit, FR1 is Frequency Range 1 and FR2 is Frequency Range 2) In 3GPP, discussions have started on solutions for L1 / L2 based inter-cell mobility (sometimes also referred to as L1 / L2-triggered mobility (LTM) or lower layer-triggered mobility).

[0035] A basic principle with L1 / L2 -triggered mobility is that the UE is pre-configured, by the network, with an RRC configuration per LTM candidate cell, which is also known as a LTM candidate cell configuration. Such a LTM candidate cell configuration may be an RRCReconfiguration message or one or more lEs / fields / parameters such as CellGroupConfig.

[0036] The UE performs measurements on these LTM candidate cells and transmits corresponding measurement reports to the network. The network then triggers the execution of the LTM cell switch in the UE by transmitting a lower layer signal (such as a MAC Control Element (CE) or Downlink Control Information (DCI)), sometimes also referred to as a LTM cell switch command, to the UE, which then connects to the target cell and switches to a configuration of an LTM candidate cell. At the 3GPP meetings, there were multiple agreements made on L1 / L2-triggered mobility, and among these are the following:

[0037] Support NR-DC scenario in L1L2 based mobility, at least for the PSCell change without MN involvement case, i.e. intra-SN.

[0038] Following behaviors of LTM supervisor timer are agreed:

[0039] - 1: The UE starts the LTM supervisor timer, upon reception of the LTM cell switch MAC CE;

[0040] - 2: The UE stops the LTM supervisor timer, upon successful completion of LTM cell switch;

[0041] - 3: If the LTM supervisor timer for MCG expires, as baseline, the UE considers LTM failure and initiates RRC re-establishment. (SCG switch case FFS)

[0042] At RLF or LTM execution failure (for MCG), RAN2 intend to support fast recovery to a candidate cell by LTM execution.

[0043] The UE may perform early decoding and early validity check. FFS whether Early validity check triggers early re-establishment. FFS the possible timing, FFS subset of cells, FFS if need to specify anything or just up to UE impl, FFS if other signalling to notify network is needed.

[0044] Summary

[0045] There currently exist certain challenge(s). Many details of the procedures for L1 / L2- triggered mobility (LTM) are still open in 3GPP.

[0046] One aspect that has not yet been agreed is failure recovery. In the RAN2#121bis meeting there was a high level agreement to support fast recovery to a candidate cell by LTM execution, but no details have been agreed yet.

[0047] When UE is configured for dual connectivity, such as MR-DC or NR-DC, failure handling procedures are defined. The failure handling will be different for MCG and SCG. For SCG, the UE currently triggers a SCG Failure Information procedure, but the message lacks information related to possible failed LTM execution or other LTM-related failures. For MCG, the UE may trigger an MCG Failure Information procedure when timer T316 (as defined in 3GPP 38.331 v17.4.0) has been configured, but also in this case there is lack of information regarding LTM- relating failures.

[0048] It has not yet been agreed whether these failure handling procedures for dual connectivity can be used when the UE is configured with LTM, and at the same time configured with dual connectivity.

[0049] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. In particular, this disclosure proposes different methods for recovery from LTM related failures for a UE configured with multi-radio dual connectivity (MR-DC), such as NR-DC, EN-DC or NE-DC, and at the same time being configured with L1 / L2-triggered mobility (LTM). The disclosed method relates to a UE that is configured with multi-radio dual connectivity (MR-DC) with a first cell group controlled by a first network node and a second cell group controlled by a second network node. When this UE detects a LTM related failure, the UE transmits, to a first network node, a message including LTM related failure information. The first network node may then transmit, to the second network node, a message including LTM related failure information. The first network node may transmit the message to the second node if the detected LTM related failure related to the second cell group.

[0050] In some embodiments, when the UE detects a LTM related failure relating to the Secondary Cell Group (SCG) controlled by the Secondary Node (SN), the UE transmits, to the Master Node (MN), a message, such as SCGFailurelnformation, including LTM related failure information. The MN can then transmit, to the SN, a message indicating an LTM related failure including LTM related failure information.

[0051] In some embodiments, when the UE detects a LTM related failure relating to the Master Cell Group (MCG) controlled by the Master Node (MN), the UE transmits, to the Secondary Node (SN), a message, such as MCGFailurelnformation, including LTM related failure information. The SN can then transmit, to the MN, a message indicating an LTM related failure including LTM related failure information.

[0052] In yet other embodiments, when the UE detects a LTM related failure relating to the Master Cell Group (MCG) controlled by the Master Node (MN), the UE transmits, to the MN, a message, such as an RRC message or a MAC CE, including LTM related failure information.

[0053] In yet other embodiments, when the UE detects a LTM related failure relating to the Secondary Cell Group (SCG) controlled by the Secondary Node (SN), the UE transmits, to the SN, a message, such as an RRC message or a MAC CE, including LTM related failure information.

[0054] In another set of embodiments, when the UE detects a LTM related failure relating to the Master Cell Group (MCG) controlled by the Master Node (MN), the UE initiates RRC Reestablishment and transmits, to a network node, an RRC Re-establishment request message, which may include LTM related failure information.

[0055] The LTM related failure described herein may be one of:

[0056] • a failure to execute LTM cell switch for the MCG,

[0057] • a failure to execute LTM cell switch for the SCG,

[0058] • a validity / compliance check failure for an LTM candidate cell configuration.

[0059] The LTM related failure information that the UE includes in the message may include one or more of the following: the LTM candidate configuration identity (ID) of the cell toward which the LTM cell switch has previously failed;

[0060] L1 measurements; a new failure cause; an indication whether the UE has released a cell group to which the LTM related failure relates; an indication whether the failure relates to the first cell group or the second cell group.

[0061] According to a first aspect, there is provided a method performed by a UE that is operating with MR-DC with a first cell group and a second cell group. The method by the UE comprises: detecting a failure of a LTM procedure; and sending, to a first network node associated with the first cell group, a notification message that comprises information relating to the failure.

[0062] According to a second aspect, there is provided a method performed by a first network node that is associated with a first cell group for a UE that is operating with MR-DC. The method comprises: receiving, from the UE, a notification message that comprises information relating to a failure of a LTM procedure.

[0063] According to a third aspect, there is provided a method performed by a second network node that is associated with a second cell group for a UE that is operating with MR-DC. The method comprises: receiving, from a first network node, a notification message that comprises information relating to a failure of a LTM procedure.

[0064] According to a fourth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of the first to third aspects.

[0065] According to a fifth aspect, there is provided a UE that is configurable for operation with MR-DC with a first cell group and a second cell group, and the UE is configured to perform the method according to the first aspect or any embodiments thereof.

[0066] According to a sixth aspect, there is provided a UE that is configurable for operation with MR-DC with a first cell group and a second cell group. The UE comprises a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative to perform the method according to the first aspect or any embodiments thereof.

[0067] According to a seventh aspect, there is provided a network node configured to perform the method according to the second aspect, the third aspect, or any embodiments thereof.

[0068] According to an eighth aspect, there is provided a network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to perform the method according to the second aspect, the third aspect, or any embodiments thereof. Certain embodiments may provide one or more of the following technical advantage(s). The solutions proposed herein enable the UE to recover from, and report, an LTM related failure when configured with multi-radio dual connectivity (MR-DC). The solutions avoid a re-establishment, and therefore a faster recovery can be performed also for LTM related failures.

[0069] The solutions also enable the network to receive further information about the LTM related failure in order to take further actions, such as initiate a new LTM cell switch procedure for the UE or perform UE reconfiguration, such as reconfiguration of LTM candidate cells for the UE.

[0070] Brief Description of the Drawings

[0071] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings, in which:

[0072] Fig. 1 is an illustration of dual connectivity combined with carrier aggregation in MR-DC;

[0073] Fig. 2 is an illustration of EN-DC;

[0074] Fig. 3 is an illustration of NR-DC;

[0075] Fig. 4 illustrates a Control Plane architecture for Dual Connectivity in LTE DC, EN-DC and NR-DC;

[0076] Fig. 5 illustrates network side protocol termination options for MCG, SCG and split DRBs in MR-DC with EPC (EN-DC);

[0077] Fig. 6 illustrates network side protocol termination options for MCG, SCG and split DRBs in MR-DC with 5GC (NGEN-DC, NE-DC and NR-DC);

[0078] Fig. 7 illustrates a system structure according to embodiments of the present disclosure;

[0079] Fig. 8 is an exemplary signalling diagram for one example of the described techniques;

[0080] Fig. 9 is an exemplary signalling diagram for another example of the described techniques;

[0081] Fig. 10 is a flow chart illustrating an exemplary method in a UE;

[0082] Fig. 11 is a flow chart illustrating another exemplary method in a UE;

[0083] Fig. 12 is a flow chart illustrating yet another exemplary method in a UE;

[0084] Fig. 13 is a flow chart illustrating an exemplary method in a first network node;

[0085] Fig. 14 is a flow chart illustrating an exemplary method in a second network node;

[0086] Fig. 15 shows an example of a communication system in accordance with some embodiments;

[0087] Fig. 16 shows a UE in accordance with some embodiments;

[0088] Fig. 17 shows a RAN network node in accordance with some embodiments; and

[0089] Fig. 18 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized. Detailed Description

[0090] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0091] This disclosure refers to the term “L1 / L2 based inter-cell mobility” as used in the Work Item Description in 3GPP, though it interchangeably also uses the terms L1 / L2 mobility, L1-mobility, L1 based mobility, L1 / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility L1 / L2-Triggered Mobility, Lower-layer triggered Mobility or LTM. The basic principle is that the UE receives lower layer signalling from the network indicating to the UE a change (or switch or activation) of its serving cell (e.g. a change of PCell, from a source PCell to a target PCell). The lower layer signalling is a message / signalling of a lower layer protocol, which may be referred as a “L1 / L2 inter-cell mobility execution” command or “LTM cell switch” command. L1 can refer to a Physical (PHY) layer and L2 can refer to a Medium Access Control (MAC) layer. The lower layer signalling can be signalling in a Physical Layer and / or signalling in a Medium Access Control (MAC) Layer. More generally, “lower layer signalling” as used herein refers to Layer 1 and / or Layer 2 signalling. Lower layer signalling can mean signalling in a layer below a Radio Resource Control (RRC) layer. The change of serving cell (e g. change of PCell) may also lead to a change in SCell(s) for the same cell group, e g. in case the command triggers the UE to change to another cell group configuration of the same type (e.g. another MCG configuration). Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more LTM candidate cell configurations (e.g. reception of an RRC Reconfiguration message, with at least one LTM candidate cell configuration). A LTM candidate cell configuration may include parameters in the Information Element (IE) CellGroupConfig per candidate cell and / or an embedded RRC Reconfiguration per LTM candidate cell.

[0092] The term “LTM cell switch procedure” refers to the process of a UE switching (or changing) its cell from a source cell to a target cell (which may be called here an LTM candidate cell or a neighbour cell), using L1 / L2-triggered mobility (LTM). In the context of L1 / L2-triggered mobility (LTM), an LTM cell switch procedure may sometimes also be known as L1 / L2 based inter-cell mobility execution, LTM execution, dynamic switch, LTM switch, (LTM) cell switch, (LTM) serving cell change or (LTM) cell change. In the context of the techniques described herein, switching to the LTM candidate cell configuration comprises the UE considering that an LTM candidate cell becomes its new special cell (SpCell), e.g. PCell in case of LTM being configured for a Master Cell Group (MCG) and / or PSCell in case of LTM being configured for a Secondary Cell Group (SCG); or, changing its SpCell from the current PCell to an LTM candidate cell.

[0093] Even if the term “change of cell” is used, that may comprise a change of a whole cell group configuration, which includes a change in the SpCell (e.g. change of PCell, or change of PSCell) and a change in SCells of the cell group (e.g. addition, modification and / or release of one or more SCells).

[0094] An LTM cell switch procedure may be triggered in the UE by reception of a LTM cell switch command, or alternatively, triggered by some other event, such as a condition, e.g. a triggering condition used for conditional configuration, such as conditional handover, being fulfilled, as a result of recovery from radio link failure or handover failure.

[0095] This disclosure refers to a LTM candidate cell, which is a cell the UE is configured with when configured with L1 / L2-triggered mobility. That is a cell the UE can move to in a LTM cell switch procedure, upon reception of a LTM cell switch command. These cells may also be called candidate cell(s), candidates, mobility candidates, non-serving cells, additional cells, target candidate cell, target candidate, etc. A LTM candidate cell is a cell the UE performs measurements on (e.g. Channel State Information (CSI) measurements) so that the UE reports these measurements and the network may take an informed decision on which beam (e.g. Transmission Configuration Indication (TCI) state) and / or cell the UE is to be switched to. An LTM candidate cell may be a candidate to be a target PCell or PSCell, or an SCell of a cell group (e.g. MCG SCell).

[0096] This disclosure refers to “at least one LTM candidate cell configuration” and that the UE has received at least one LTM candidate cell configuration. This is also sometimes referred to as a configuration of a LTM candidate cell, which may be an RRC configuration, such as that encapsulated in an RRC Reconfiguration message, that the UE receives when being configured with L1 / L2-Triggered Mobility. A LTM candidate cell configuration comprises the configuration that the UE needs to start to operate accordingly when it performs an LTM cell switch procedure to that LTM candidate cell, e.g. upon reception of the LTM cell switch command indicating the UE to perform a LTM cell switch procedure to that LTM candidate cell, which becomes the target cell and the current (new) SpCell, or an SCell in a serving frequency. The LTM candidate cell configuration comprises parameters of a serving cell (or multiple serving cells, such as a cell group), comprising one or more of the groups of parameters, such as an RRCReconfiguration message, an IE CellGroupConfig or an IE SpCellConfig (or the IE SCellConfig, in the case of a Secondary Cell). A LTM candidate cell configuration may, in one example, comprise one or more of: (i) the PCell configuration and one or more SCell configuration(s) of a Master Cell Group (MCG); and (ii) the PSCell configuration and one or more SCell configuration(s) of a secondary Cell Group (SCG). The terms (LTM) candidate configuration, LTM configuration, (LTM) candidate target cell configuration, (LTM) target candidate (cell) configuration may be used interchangeably when referring to LTM candidate cell configuration. An LTM candidate cell configuration is associated with an identifier which is used in the signalling when referring to a certain LTM candidate cell configuration, such as when the UE receives the LTM candidate cell configuration, and when the UE receives an LTM cell switch command indicating the UE to perform a LTM cell switch procedure to that LTM candidate cell. This identifier is sometimes known as the LTM candidate cell configuration identity or LTM candidate configuration index (or similar).

[0097] This disclosure refers to a “LTM related failure”. A LTM related failure may be triggered for the Master Cell Group (MCG) or the Secondary Cell Group (SCG) and may be one of:

[0098] • a failure to execute a LTM cell switch procedure, e.g. expiry of the LTM supervision timer;

[0099] • a validity / compliance check failure for an LTM candidate cell configuration;

[0100] • a beam failure detection (BFD), e.g. as defined in 3GPP TS 38.321 v17.4.0;

[0101] • a handover failure (HOF), e.g. expiry of timer T304 (as defined in 3GPP TS 38.331 V17.4.0);

[0102] • A radio link failure (RLF), e.g. expiry of timer T310 or T316 (as defined in 3GPP TS 38.331 V17.4.0);

[0103] • A failure to (re)transmit a maximum number N of RLC Protocol Data Unit (PDU);

[0104] • A failure to (re)transmit a maximum number of N of MAC PDU. This maximum number N can be N of MAC PDU for which a Negative Acknowledgement (NACK) has been received or N of MAC PDU for which neither NACK nor an Acknowledgement (ACK) has been received.

[0105] This disclosure refers to “LTM related failure information”, which is information relating to a failure of a LTM procedure.

[0106] Fig. 7 illustrates a system structure including the entities involved in the techniques described herein. The User Equipment (UE) 701 is a wireless terminal, such as a cellular smartphone, which may be configured for multi-radio dual connectivity (MR-DC), such as NR-DC, EN-DC or NE-DC. The UE may also, at the same time be configured for L1 / L2-triggered mobility (LTM).

[0107] The UE 701 is connected via a first cell group 702 to a first network node 706 over a radio interface 704. The UE 701 is also connected via a second cell group 703 to a second network node 707 over a radio interface 705.

[0108] The first network node 706 controls the first cell group 702. The second network node 707 controls the second cell group 703. The first network node 706 is connected with the second network node 707 over an interface 708, which may for example be an Xn type of interface (i.e. an interface between base stations / RAN nodes.

[0109] Both the first cell group 702 and the second cell group 703 may be configured with a main cell, such as a Special Cell, SpCell, sometimes known as Primary Cell (PCell), or Primary Secondary Cell (PSCell), and optionally multiple additional cells, such as secondary cells (SCells), in a carrier aggregation (CA) configuration.

[0110] First set of methods

[0111] In a first set of methods, the first network node 706 is a Master Node (MN) and the first cell group 702 is the Master Cell Group (MCG). In these methods, the second network node 707 is a Secondary Node (SN) and the second cell group 703 is the Secondary Cell Group (SCG).

[0112] In this set of methods, the UE is configured with multi-radio dual connectivity (MR-DC) with a Master Cell Group and a Secondary Cell Group, and is also configured with LTM in at least the Secondary Cell Group, which may, for example, imply it has at least one LTM candidate cell configuration including a secondary cell group and L1 measurements are configured for LTM candidate cells. This means that the UE may perform L1 measurements according to the LTM configuration on candidate cells and transmit L1 measurement reports in the SCG to the SN. The SN may in turn trigger an LTM cell switch procedure to one of the LTM candidate cells by transmitting an LTM cell switch command to the UE in the SCG, resulting in the UE applying an LTM candidate cell configuration which may result in a reconfiguration of the SCG.

[0113] The UE detects a LTM related failure in the Secondary Cell Group (SCG). In one example the LTM related failure in the SCG is that the UE fails to execute an LTM cell switch procedure for the SCG, as determined by expiry of the LTM supervision timer that is started by the UE upon LTM cell switch procedure execution. In another example, the LTM related failure in the SCG is that the UE performs a validity / compliance check for an LTM candidate cell configuration including a secondary cell group and this check fails.

[0114] In another example, upon receiving, from the SN in the SCG, an LTM cell switch command, which is a MAC CE, the UE sends a positive acknowledgment for this MAC CE in the SCG, to the SN, only if the LTM cell switch procedure is successful. In such a case, the positive acknowledgment by the UE can be sending a “Hybrid Automatic Repeat Request (HARQ) ACK” in the SCG, or not sending anything at all. In case instead the LTM cell switch procedure has failed, the UE may send a “HARQ NACK” in the SCG. In this latter case, the SN may understand that the LTM cell switch command has not been correctly received by the UE and it may try to resend it. However, the UE will continue to reply with a “HARQ NACK” until a maximum number of MAC PDU retransmissions is reached that the SN may consider the triggering of the LTM cell switch procedure as not successful. In such a case, the UE after sending a number N of “HARQ NACK” in the SCG, this is determined by the UE to having detected an LTM related failure.

[0115] Sometimes the UE may release the SCG as triggered by the LTM related failure in the SCG. This may be when the UE cannot recover from the LTM related failure as determined by other failure handling during an LTM cell switch procedure.

[0116] Triggered by the detection of a LTM related failure in the SCG, the UE can transmit, to the Master Node (MN) in the MCG, a notification message, such as an SCGFailurelnformation message encapsulated into an ULInformationTransferMRDC message, including LTM related failure information. The notification message may include one or more of the following:

[0117] • the LTM candidate configuration ID of the cell toward which the LTM cell switch has previously failed;

[0118] • L1 measurements;

[0119] • an indication that the UE has released the SCG triggered by the LTM related failure;

[0120] • a new failure cause;

[0121] • an indication whether the failure was relating to the MCG or the SCG.

[0122] If the LTM related failure relates to the SCG, the MN will then transmit a message to the SN including LTM related failure information. In one option, the MN can forward the received SCGFailurelnformation message to the SN. In one option, the MN can determine whether the LTM related failure related to the SCG based on the content of the LTM related failure information. In one alternative, the MN determines that the LTM related failure was related to the MCG and does not send a message to the SN.

[0123] An alternative solution that may be performed by the UE upon the detection of a LTM related failure in the SCG, such as when the UE fails to execute an LTM cell switch procedure for the SCG, is that the notification message is an RRC message or an Uplink (UL) MAC CE, which is sent by the UE in the cell group in which the LTM cell switch command that initiated the failed LTM cell switch procedure was received. In such a case, the notification message, e.g. an RRC message or an UL MAC CE, may include one or more of the following:

[0124] • a failure cause;

[0125] • an indication on whether the LTM candidate cell indicated within the LTM cell switch command has been released.

[0126] The network may configure whether the UE shall transmit the notification message when an LTM related failure in the Secondary Cell Group (SCG) is detected by the UE.

[0127] In some embodiments, the UE is configured with EN-DC, where the MCG uses LTE and SCG uses NR. In this case, if the UE is configured with LTM for the SCG, and detects an LTM related failure in the SCG, it may transmit a notification message in the MCG to the first network node, which will send a notification to the second network node controlling the SCG. In this case, the notification message sent to the first network node may be an SCGFailurelnformationNR message encapsulated into an ULInformationTransferMRDC message, including LTM related failure information. Second set of methods

[0128] In a second set of methods, the first network node 706 is a Secondary Node (SN) and the first cell group 703 is the Secondary Cell Group (SCG). In these methods, the second network node 707 is a Master Node (MN), and the second cell group 703 is the Master Cell Group (MCG).

[0129] In this set of methods, the UE is configured with multi-radio dual connectivity (MR-DC) with a Master Cell Group and a Secondary Cell Group and is also configured with LTM in at least the Master Cell Group, which may for example imply it has at least one LTM candidate cell configuration including a master cell group and L1 measurements are configured for LTM candidate cells. This means that the UE may perform L1 measurements according to the LTM configuration on candidate cells and transmit L1 measurement reports in the MCG to the MN. The MN may in turn trigger an LTM cell switch procedure to one of the LTM candidate cells by transmitting an LTM cell switch command to the UE in the MCG resulting in the UE applying an LTM candidate cell configuration which may result in a reconfiguration of the MCG.

[0130] The UE detects a LTM related failure in the Master Cell Group (MCG). In one example the LTM related failure in the MCG is that the UE fails to execute an LTM cell switch procedure for the MCG, as determined by expiry of the LTM supervision timer that is started by the UE upon LTM cell switch procedure execution. In another example, the LTM related failure in the MCG is that the UE performs a validity / compliance check for an LTM candidate cell configuration including a master cell group and this check fails.

[0131] In another example, upon receiving, from the MN in the MCG, an LTM cell switch command, which is a MAC CE, the UE sends a positive acknowledgment for this MAC CE in the MCG only if the LTM cell switch procedure is successful. In such a case, the positive acknowledgment by the UE can be sending a “HARQ ACK” in the MCG or not sending anything at all. In case the LTM cell switch procedure has failed, the UE may send a “HARQ NACK” in the MCG. In this latter case, the MN may understand that the LTM cell switch command has not been correctly received by the UE and it may try to resend it. However, the UE will continue to reply with a “HARQ NACK” until a maximum number of MAC PDU retransmissions is reached so that the MN considers the triggering of the LTM cell switch procedure to be unsuccessful. In such a case, the UE, after sending a number N of “HARQ NACK” in the MCG, determines that there is an LTM related failure.

[0132] Triggered by the detection of a LTM related failure in the MCG, the UE transmits, to the Secondary Node (SN) in the SCG, a notification message, such as an MCGFailurelnformation message encapsulated into an ULInformationTransferMRDC message, including LTM related failure information. The notification message may include one or more of the following: • the LTM candidate configuration ID of the cell toward which the LTM cell switch has previously failed;

[0133] • L1 measurements;

[0134] • a new failure cause (i.e. an indication of the cause of the failure);

[0135] • an indication whether the failure related to the MCG or the SCG.

[0136] If the LTM related failure related to the MCG, the SN will then transmit a message to the MN including LTM related failure information. In one option, the SN will forward the received MCGFailurelnformation message to the MN. In one option, the SN determines whether the LTM related failure related to the MCG based on the content of the LTM related failure information. In one alternative, the SN can determine that the LTM related failure was related to the SCG, and it does not send a message to the MN.

[0137] An alternative solution that may be performed by the UE upon the detection of a LTM related failure in the MCG, such as when the UE fails to execute an LTM cell switch procedure for the MCG, is that the notification message is an RRC message or an UL MAC CE, which is sent by the UE in the cell group in which the LTM cell switch command that initiated the failed LTM cell switch procedure was received. In such a case, the notification message, e.g. an RRC message or an UL MAC CE, may include one or more of the following:

[0138] • a failure cause;

[0139] • an indication on whether the LTM candidate cell indicated within the LTM cell switch command has been released.

[0140] The network may configure whether the UE shall transmit the notification message when an LTM related failure in the Master Cell Group (MCG) is detected by the UE.

[0141] Whether the UE is able to transmit the notification message to the SN may sometimes depend on whether there is a signalling radio bearer (RB), sometimes known as signalling radio bearer 3, SRB3. When SRB3 is configured, the UE may transmit the notification message, such as an MCGFailurelnformation message encapsulated into an ULInformationTransferMRDC message to the SN on SRB3.

[0142] In an alternative embodiment, the UE can be configured with a split signalling radio bearer 1 (SRB1), for communication between the UE and the MN. By configuring the split SRB1 with PDCP duplication, PDCP PDUs carrying RRC signalling will be duplicated, where one copy is transmitted via the MCG and the other copy is transmitted via the SCG. In this way, even if MCG transmission is not possible, packets can be transmitted via the SCG and still reach the MN.

[0143] In an alternative embodiment, regardless of whether an SRB3 is configured, the UE transmits the notification message for the SN embedded in a message for the MN via the SRB1. In such a case, the MN will in turn forward this message to the SN. In one embodiment, instead of transmitting a notification message to the SN, the UE may perform alternative actions, for example if the detected LTM related failure is that the UE after having received an LTM cell switch command from the MCG and it has transmitted a number N of “HARQ NACK” to the MCG:

[0144] • transmit a notification message to the MN, or

[0145] • initiate a RRC Re-establishment procedure.

[0146] In one set of embodiments the UE can be configured with NE-DC, where the MCG uses NR and the SCG uses LTE. In this case, if the UE is configured with LTM for the MCG, and detects an LTM related failure in the MCG, it may use the split SRB1 to transmit the MCGFailurelnformation message to the MN via the SCG.

[0147] Fig. 8 is a signalling diagram illustrating one example of the techniques described herein. In this example, the UE is configured with multi-radio dual connectivity (MR-DC), with a Master Node (MN) controlling a Master Cell Group (MCG), and a Secondary Node (SN) controlling a Secondary Cell group (SCG).

[0148] In step 801 of Fig. 8, the UE is configured with LTM for at least the SCG. In this illustrated example, the configuration (e.g. RRC Configuration) is sent by the MN, but in another example it may be sent by the SN. In step 802 the UE confirms the LTM configuration by sending a reconfiguration complete (e.g. RRC Reconfiguration Complete) to the MN.

[0149] In step 803, the UE detects an LTM related failure relating to the SCG, for example that the UE failed to execute an LTM cell switch procedure for the SCG.

[0150] In step 804, the UE transmits a notification message to the MN in the MCG, including LTM related failure information. In this example, the notification message is an SCGFailurelnformation message encapsulated into an ULInformationTransferMRDC message.

[0151] In step 805, the MN sends a notification message to the SN including the LTM related failure information. In this example, the notification message is an RRC TRANSFER message including the received SCGFailurelnformation message.

[0152] Fig. 9 is a signalling diagram illustrating another example of the techniques described herein. In this example, the UE is configured with multi-radio dual connectivity (MR-DC), with a Master Node (MN) controlling a Master Cell Group (MCG), and a Secondary Node (SN) controlling a Secondary Cell group (SCG).

[0153] In step 901 of Fig. 9, the UE is configured with LTM for at least the MCG. In this illustrated example, the configuration (e.g. RRC Configuration) is sent by the MN, but in another example it may be sent by the SN. In step 902 the UE confirms the LTM configuration by sending a reconfiguration complete (e.g. RRC Reconfiguration Complete) to the MN.

[0154] In step 903, the UE detects an LTM related failure relating to the MCG, for example that the UE failed to execute an LTM cell switch procedure for the MCG.

[0155] In step 904, the UE transmits a notification message to the SN in the SCG, including LTM related failure information. In this example, the notification message is sent on SRB3 as an MCGFailurelnformation message encapsulated into an ULInformationTransferMRDC message.

[0156] In step 905, the SN sends a notification message to the MN including the LTM related failure information. In this example, the notification message is an RRC TRANSFER message including the received MCGFailurelnformation message.

[0157] The flow chart in Fig. 10 illustrates exemplary steps performed by a UE in one example of the techniques described herein. In this example, the UE is configured with multi-radio dual connectivity (MR-DC), with a first cell group controlled by a first network node and a second cell group controlled by a second network node. In one implementation (corresponding to Fig. 8), the first cell group is the MCG, the first network node is the MN, the second cell group is the SCG and the second network node is the SN. In another implementation (corresponding to Fig. 9), the first cell group is the SCG, the first network node is the SN, the second cell group is the MCG and the second network node is the MN.

[0158] The UE may perform the method in Fig. 10 in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0159] In step 1001 of Fig. 10 (which can be optional), the UE receives at least one LTM candidate cell configuration. This can be received from the first network node or the second network node.

[0160] In step 1002, the UE detects a LTM related failure relating to the second cell group (i.e. the SCG in the example of Fig. 8, and the MCG in the example of Fig. 9).

[0161] In step 1003, the UE transmits, or sends, to a first network node in the first cell group (i.e. the MN in the MCG in the example of Fig. 8, and the SN in the SCG in the example of Fig. 9), a notification message including LTM related failure information.

[0162] The flow chart in Fig. 11 illustrates another exemplary method performed by a UE according to the techniques described herein. In this example, the UE is configured / operating with MR-DC, with a first cell group and a second cell group. The UE may perform the method in Fig. 11 in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0163] In step 1101 of Fig. 11 , the UE detects a failure of a LTM procedure.

[0164] In step 1103, the UE sends a notification message including information relating to the failure to a first network node associated with the first cell group. The notification message may be a RRC message, or an UL MAC CE.

[0165] Prior to step 1101, the method may further comprise the UE receiving a configuration for a candidate cell for the LTM procedure.

[0166] The information relating to the failure may comprise any one or more of: an identity of a cell that the failed LTM procedure relates to; L1 measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a MCG or a SCG.

[0167] The failure of the LTM procedure may be one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of MAC PDUs.

[0168] The failure of the LTM procedure may relate to the second cell group. That is, the notification message is sent to a network node associated with a different cell group to the cell group that the LTM failure relates to. The failure of the LTM procedure may relate to a failure to change cell in the second cell group.

[0169] The first cell group may be a MCG and the second cell group may be a SCG. In this case, the LTM procedure can relate to a change of cell in the SCG. In these embodiments, the first network node may be a MN in the MCG. In these embodiments, the notification message can be a SCGFailurelnformation message, which can be encapsulated into an U LI nformationT ransferM RDC message.

[0170] Alternatively, the first cell group may be a SCG and the second cell group may be a MCG. In this case, the LTM procedure can relate to a change of cell in the MCG. In these embodiments, the first network node can be a SN in the SCG. In these embodiments, the notification message may be an MCGFailurelnformation message, which can be encapsulated into an ULInformationTransferMRDC message.

[0171] In some embodiments, the first cell group can be a MCG, the first network node can be a MN in the MCG, the second cell group can be a SCG, and the LTM procedure can relate to a change of cell in the MCG.

[0172] The flow chart in Fig. 12 illustrates another exemplary method performed by a UE according to the techniques described herein. In this example, the UE is configured / operating with MR-DC, with a MCG and a SCG. The UE may perform the method in Fig. 12 in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0173] In step 1201 of Fig. 12, the UE detects a failure of a LTM procedure relating to a change of cell in the MCG.

[0174] In step 1203, the UE initiates a RRC Re-establishment procedure.

[0175] The flow chart in Fig. 13 illustrates exemplary steps performed by a first network node in one example of the techniques described herein. In this example, the first network node is associated with / is controlling a first cell group for a UE that is operating with MR-DC. In one implementation (corresponding to Fig. 8), the first cell group is the MCG, and the first network node is the MN. In another implementation (corresponding to Fig. 9), the first cell group is the SCG, and the first network node is the SN.

[0176] The first network node may perform the method in Fig. 13 in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0177] In step 1301 , the first network node receives a notification message that comprises information relating to a failure of a LTM procedure. The notification message is received from the UE. The notification message may be a RRC message or an UL MAC CE.

[0178] The information relating to the failure may comprise any one or more of: an identity of a cell that the failed LTM procedure relates to; L1 measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a MCG or a SCG.

[0179] The failure of the LTM procedure may be one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of MAC PDUs.

[0180] Prior to step 1301 , the method may further comprise sending a configuration for a candidate cell for the LTM procedure to the UE.

[0181] The method may further comprise the first network node sending a message comprising information relating to the failure of the LTM procedure to a second network node associated with the second cell group.

[0182] The failure of the LTM procedure may relate to a second cell group for the UE. The failure of the LTM procedure may relate to a failure to change cell in the second cell group.

[0183] As noted above, in some implementations the first network node is a MN, and the first cell group is a MCG. In this case, the second cell group can be a SCG. In these embodiments, the LTM procedure can relate to a change of cell in the SCG. The notification message may be an SCGFailurelnformation message, which can be encapsulated into an ULInformationTransferMRDC message.

[0184] Also as noted above, in other implementations the first network node is a SN and the first cell group is a SCG. In this case, the first cell group can be a MCG. In these embodiments, the LTM procedure can relate to a change of cell in the MCG. The notification message may be an MCGFailurelnformation message, which can be encapsulated into an ULInformationTransferMRDC message.

[0185] Alternatively, the first cell group may be a MCG, the first network node may be a MN in the MCG, the second cell group may be a SCG, and the LTM procedure may relate to a change of cell in the MCG.

[0186] The flow chart in Fig. 14 illustrates exemplary steps performed by a second network node in one example of the techniques described herein. In this example, the second network node is associated with / is controlling a second cell group for a UE that is operating with MR-DC. In one implementation (corresponding to Fig. 8), the second cell group is the SCG, and the second network node is the SN. In another implementation (corresponding to Fig. 9), the second cell group is the MCG, and the second network node is the MN.

[0187] The second network node may perform the method in Fig. 14 in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0188] In step 1401 , the second network node receives a notification message that comprises information relating to a failure of a LTM procedure. The notification message is received from a first network node. In the implementation corresponding to Fig. 8, the first network node is the MN in the MCG. In the implementation corresponding to Fig. 9, the first network node is the SN in the SCG. The notification message may be a RRC message.

[0189] The information relating to the failure may comprise any one or more of: an identity of a cell that the failed LTM procedure relates to; L1 measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a MCG or a SCG.

[0190] The failure of the LTM procedure may be one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of MAC PDUs.

[0191] The failure of the LTM procedure may relate to a second cell group for the UE. The failure of the LTM procedure may relate to a failure to change cell in the second cell group.

[0192] Prior to step 1401 , the method may further comprise the second network node sending a configuration for a candidate cell for the LTM procedure to the UE.

[0193] The first network node may be associated with a first cell group for the UE.

[0194] As noted above, in some implementations the first network node is a MN of a MCG. In this case, the second network node can be a SN, and the second cell group can be a SCG. In these embodiments, the LTM procedure can relate to a change of cell in the SCG. The notification message may be an SCGFailurelnformation message, which can be encapsulated into an ULInformationTransferMRDC message.

[0195] Also as noted above, in other implementations the first network node is a SN of a SCG. In this case, the second network node is a MN, and the second cell group can be a MCG. In these embodiments, the LTM procedure can relate to a change of cell in the MCG. The notification message may be an MCGFailurelnformation message, which can be encapsulated into an ULInformationTransferMRDC message.

[0196] The following provides an implementation of one of the examples of the techniques described herein into 3GPP RRC specification TS 38.331 v17.4.0.

[0197] In this example, LTM related failure information is added to the SCGFailurelnformation message.

[0198] SCGFailurelnformation the SCGFailurelnformation message is used to provide information regarding NR SCG failures detected by the UE.

[0199] Signalling radio bearer: SRB1

[0200] RLC-SAP: AM

[0201] Logical channel: DCCH

[0202] Direction: UE to Network

[0203] SCGFailurelnformation message

[0204] i measResultSCG-Failure i The field contains the MeasResultSCG-Failure IE which includes available results of measurements on NR

[0205] I frequencies the UE is configured to measure by the NR SCG RRCReconfiguration message.

[0206] I previousPSCellld i This field indicates the physical cell id and carrier frequency of the cell that is the source PSCell of the last

[0207] I PSCell change. failedPSCellld

[0208] I This field indicates the physical cell id and carrier frequency of the cell in which SCG failure is detected or the

[0209] I target PSCell of the failed ^SCell change orfailed PSCe I aooition

[0210] I timeSCGFailure

[0211] I This field is used to indicate the time elapsed since the last execution of RRCReconfiguration with

[0212] ; reconfigurationWithSync for the SCG until the SCG failure. Actual value = field value * 100ms. The maximum

[0213] I value 1023 means 102.3s or longer. i ItmFailurelnformation

[0214] : This field is used to indicate an LTM

[0215] Fig. 15 shows an example of a communication system 1500 in accordance with some embodiments. In the example, the communication system 1500 includes a telecommunication network 1502 that includes an access network 1504, such as a radio access network (RAN), and a core network 1506, which includes one or more core network nodes 1508. The access network 1504 includes one or more access network nodes, such as access network nodes 1510a and 1510b (which are interchangeably referred to as RAN network nodes 1510 herein), or any other similar 3rdGeneration Partnership Project (3GPP) access node or non-3GPP access point (AP). Moreover, as will be appreciated by those of skill in the art, a RAN network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, the telecommunication network 1502 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 1502 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in the telecommunication network 1502, including one or more network nodes 1510 and / or core network nodes 1508.

[0216] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU-CP) or an O- CU user plane (O-CU-UP), a RAN intelligent controller (RIC) (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an A1 , F1 , W1 , E1 , E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the O-RAN Alliance or comparable technologies.

[0217] The access network nodes 1510 facilitate direct or indirect connection of wireless devices (also referred to interchangeably herein as user equipment (UE)), such as by connecting UEs 1512a, 1512b, 1512c, and 1512d (one or more of which may be generally referred to as UEs 1512) to the core network 1506 over one or more wireless connections. The access network nodes 1510 may be, for example, access points (APs) (e.g. radio access points), base stations (BSs) (e.g. radio base stations, Node Bs, evolved Node Bs (eNBs) and New Radio (NR) NodeBs (gNBs)).

[0218] Unless otherwise indicated, the general term ‘network node’ as used herein refers to access network nodes 1510 and core network nodes 1508.

[0219] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication system 1500 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. The communication system 1500 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0220] The wireless devices / UEs 1512 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with the network nodes 1510 and other communication devices. Similarly, the access network nodes 1510 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 1512 and / or with other network nodes or equipment in the telecommunication network 1502 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in the telecommunication network 1502.

[0221] In the depicted example, the core network 1506 connects the access network nodes 1510 to one or more hosts, such as host 1516. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 1506 includes one more core network nodes (e.g. core network node 1508) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the wireless devices / UEs, access network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 1508. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0222] The host 1516 may be under the ownership or control of a service provider other than an operator or provider of the access network 1504 and / or the telecommunication network 1502, and may be operated by the service provider or on behalf of the service provider. The host 1516 may host a variety of applications to provide one or more services. Examples of such applications include the provision of live and / or pre-recorded audio / video content, data collection services, for example, retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0223] As a whole, the communication system 1500 of Fig. 15 enables connectivity between the wireless devices / UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2ndGeneration (2G), 3rdGeneration (3G), 4thGeneration (4G), 5thGeneration (5G) standards, or any applicable future generation standard (e.g. 6thGeneration (6G)); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0224] In some examples, the telecommunication network 1502 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 1502 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 1502. For example, the telecommunications network 1502 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive Internet of Things (loT) services to yet further UEs.

[0225] In some examples, the UEs 1512 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 1504 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 1504. Additionally, a UE may be configured for operating in single- or multi-radio access technology (RAT) or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved- UTRA (UMTS Terrestrial Radio Access) Network) New Radio - Dual Connectivity (EN-DC).

[0226] In the example illustrated in Fig. 15, the hub 1514 communicates with the access network 1504 to facilitate indirect communication between one or more UEs (e.g. UE 1512c and / or 1512d) and access network nodes (e g. access network node 1510b). In some examples, the hub 1514 may be a controller, router, a content source and analytics node, or any of the other communication devices described herein regarding UEs. For example, the hub 1514 may be a broadband router enabling access to the core network 1506 for the UEs. As another example, the hub 1514 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1510, or by executable code, script, process, or other instructions in the hub 1514. As another example, the hub 1514 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 1514 may be a content source. For example, for a UE that is a Virtual Reality VR headset, display, loudspeaker or other media delivery device, the hub 1514 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 1514 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 1514 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy Internet of Things (loT) devices.

[0227] The hub 1514 may have a constant / persistent or intermittent connection to the network node 1510b. The hub 1514 may also allow for a different communication scheme and / or schedule between the hub 1514 and UEs (e.g. UE 1512c and / or 1512d), and between the hub 1514 and the core network 1506. In other examples, the hub 1514 is connected to the core network 1506 and / or one or more UEs via a wired connection. Moreover, the hub 1514 may be configured to connect to a Machine-to-Machine (M2M) service provider over the access network 1504 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 1510 while still connected via the hub 1514 via a wired or wireless connection. In some embodiments, the hub 1514 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to the network node 1510b. In other embodiments, the hub 1514 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1510b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0228] Fig. 16 shows a wireless device or UE 1600 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a wireless device / UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless camera, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-loT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0229] A wireless device / UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to- everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human userwho owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g. a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g. a smart power meter).

[0230] The UE 1600 includes processing circuitry 1602 that is operatively coupled via a bus 1604 to an input / output interface 1606, a power source 1608, a memory 1610, a communication interface 1612, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Fig. 16. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0231] The processing circuitry 1602 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 1610. The processing circuitry 1602 may be implemented as one or more hardware-implemented state machines (e.g. in discrete logic, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1602 may include multiple central processing units (CPUs). The processing circuitry 1602 may be operable to provide, either alone or in conjunction with other UE 1600 components, such as the memory 1610, to provide UE 1600 functionality. For example, the processing circuitry 1602 may be configured to cause the UE 1602 to perform the methods as described with reference to Fig. 10.

[0232] In the example, the input / output interface 1606 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 1600. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g. a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0233] In some embodiments, the power source 1608 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g. an electricity outlet), photovoltaic device, or power cell, may be used. The power source 1608 may further include power circuitry for delivering power from the power source 1608 itself, and / or an external power source, to the various parts of the UE 1600 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1608. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1608 to make the power suitable for the respective components of the UE 1600 to which power is supplied.

[0234] The memory 1610 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 1610 includes one or more application programs 1614, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1616. The memory 1610 may store, for use by the UE 1600, any of a variety of various operating systems or combinations of operating systems.

[0235] The memory 1610 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a Universal Subscriber Identity Module (USIM) and / or integrated SIM (ISIM), other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUlCC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 1610 may allow the UE 1600 to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to offload data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 1610, which may be or comprise a device- readable storage medium.

[0236] The processing circuitry 1602 may be configured to communicate with an access network or other network using the communication interface 1612. The communication interface 1612 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1622. The communication interface 1612 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g. another UE or a network node in an access network). Each transceiver may include a transmitter 1618 and / or a receiver 1620 appropriate to provide network communications (e.g. optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1618 and receiver 1620 may be coupled to one or more antennas (e.g. antenna 1622) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0237] In some embodiments, communication functions of the communication interface 1612 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) or other Global Navigation Satellite System (GNSS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, NR, UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0238] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1612, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g. once every 15 minutes if it reports the sensed temperature), random (e.g. to even out the load from reporting from several sensors), in response to a triggering event (e.g. when moisture is detected an alert is sent), in response to a request (e.g. a user initiated request), ora continuous stream (e.g. a live video feed of a patient).

[0239] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or controls a robotic arm performing a medical procedure according to the received input.

[0240] A UE, when in the form of an loT device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are devices which are or which are embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or VR, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence on the intended application of the loT device in addition to other components as described in relation to the UE 1600 shown in Fig. 16.

[0241] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-loT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0242] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0243] Fig. 17 shows an access network node 1700 or RAN network node 1700 in accordance with some embodiments. As used herein, access network node or RAN network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other RAN network nodes or equipment or core network nodes, in a telecommunication network. Examples of access network nodes include, but are not limited to, access network nodes such as APs (e.g. radio access points), base stations (BSs) (e.g. radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), Open RAN (O-RAN) nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0244] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A RAN network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node), and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0245] Other examples of access network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g. Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0246] The RAN network node 1700 includes processing circuitry 1702, a memory 1704, a communication interface 1706, and a power source 1708, and / or any other component, or any combination thereof. The RAN network node 1700 may be composed of multiple physically separate components (e.g. a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the RAN network node 1700 comprises multiple separate components (e.g. BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the RAN network node 1700 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g. separate memory 1704 for different RATs) and some components may be reused (e.g. a same antenna 1710 may be shared by different RATs). The RAN network node 1700 may also include multiple sets of the various illustrated components for different wireless technologies integrated into RAN network node 1700, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within RAN network node 1700.

[0247] The processing circuitry 1702 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other RAN network node 1700 components, such as the memory 1704, to provide network node 1700 functionality. For example, the processing circuitry 1702 may be configured to cause the RAN network node to perform the methods as described with reference to Figs. 11 and / or 12.

[0248] In some embodiments, the processing circuitry 1702 includes a system on a chip (SOC). In some embodiments, the processing circuitry 1702 includes one or more of radio frequency (RF) transceiver circuitry 1712 and baseband processing circuitry 1714. In some embodiments, the radio frequency (RF) transceiver circuitry 1712 and the baseband processing circuitry 1714 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1712 and baseband processing circuitry 1714 may be on the same chip or set of chips, boards, or units.

[0249] The memory 1704 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1702. The memory 1704 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 1702 and utilized by the RAN network node 1700. The memory 1704 may be used to store any calculations made by the processing circuitry 1702 and / or any data received via the communication interface 1706. In some embodiments, the processing circuitry 1702 and memory 1704 is integrated.

[0250] The communication interface 1706 is used in wired or wireless communication of signalling and / or data between network nodes, the access network, the core network, and / or a UE. As illustrated, the communication interface 1706 comprises port(s) / terminal(s) 1716 to send and receive data, for example to and from a network over a wired connection.

[0251] The communication interface 1706 also includes radio front-end circuitry 1718 that may be coupled to, or in certain embodiments a part of, the antenna 1710. Radio front-end circuitry 1718 comprises filters 1720 and amplifiers 1722. The radio front-end circuitry 1718 may be connected to an antenna 1710 and processing circuitry 1702. The radio front-end circuitry may be configured to condition signals communicated between antenna 1710 and processing circuitry 1702. The radio front-end circuitry 1718 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 1718 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1720 and / or amplifiers 1722. The radio signal may then be transmitted via the antenna 1710. Similarly, when receiving data, the antenna 1710 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1718. The digital data may be passed to the processing circuitry 1702. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0252] In certain alternative embodiments, the access network node 1700 does not include separate radio front-end circuitry 1718, instead, the processing circuitry 1702 includes radio frontend circuitry and is connected to the antenna 1710. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1712 is part of the communication interface 1706. In still other embodiments, the communication interface 1706 includes one or more ports or terminals 1716, the radio front-end circuitry 1718, and the RF transceiver circuitry 1712, as part of a radio unit (not shown), and the communication interface 1706 communicates with the baseband processing circuitry 1714, which is part of a digital unit (not shown).

[0253] The antenna 1710 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 1710 may be coupled to the radio front-end circuitry 1718 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 1710 is separate from the network node 1700 and connectable to the RAN network node 1700 through an interface or port.

[0254] The antenna 1710, communication interface 1706, and / or the processing circuitry 1702 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, the antenna 1710, the communication interface 1706, and / or the processing circuitry 1702 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0255] The power source 1708 provides power to the various components of RAN network node 1700 in a form suitable for the respective components (e.g. at a voltage and current level needed for each respective component). The power source 1708 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1700 with power for performing the functionality described herein. For example, the RAN network node 1700 may be connectable to an external power source (e.g. the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1708. As a further example, the power source 1708 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0256] Embodiments of the RAN network node 1700 may include additional components beyond those shown in Fig. 17 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the RAN network node 1700 may include user interface equipment to allow input of information into the RAN network node 1700 and to allow output of information from the RAN network node 1700. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the RAN network node 1700.

[0257] Fig. 18 is a block diagram illustrating a virtualization environment 1800 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1800 hosted by one or more of hardware nodes, such as a hardware computing device that operates as an access network node, a wireless device / UE, a core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g. a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1800 includes components defined by the Open-RAN (O-RAN) Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface.

[0258] Applications 1802 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1800 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0259] Hardware 1804 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1806 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1808a and 1808b (one or more of which may be generally referred to as VMs 1808), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. The virtualization layer 1806 may present a virtual operating platform that appears like networking hardware to the VMs 1808.

[0260] The VMs 1808 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1806. Different embodiments of the instance of a virtual appliance 1802 may be implemented on one or more of VMs 1808, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0261] In the context of NFV, a VM 1808 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1808, and that part of hardware 1804 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1808 on top of the hardware 1804 and corresponds to the application 1802.

[0262] Hardware 1804 may be implemented in a standalone network node with generic or specific components. Hardware 1804 may implement some functions via virtualization. Alternatively, hardware 1804 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1810, which, among others, oversees lifecycle management of applications 1802. In some embodiments, hardware 1804 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signalling can be provided with the use of a control system 1812 which may alternatively be used for communication between hardware nodes and radio units.

[0263] Although the computing devices described herein (e.g. UEs, RAN network nodes, core network node, hosts) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[0264] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device- readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

[0265] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the scope of the disclosure. Various exemplary embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art. EMBODIMENTS

[0266] Group A Embodiments

[0267] A1. A method for a User Equipment (UE), being configured with multi-radio dual connectivity (MR-DC), with a first cell group controlled by a first network node and a second cell group controlled by a second network node, to perform recovery from a LTM related failure, comprising the UE:

[0268] • receiving at least one LTM candidate cell configuration;

[0269] • detecting a LTM related failure;

[0270] • transmitting, to a first network node, a notification message including LTM related failure information.

[0271] A1a. The method in A1 , wherein the detected LTM related failure relates to the second cell group.

[0272] A1b. The method in A1 , wherein the detected LTM related failure relates to the first cell group.

[0273] A1c. The method in A1 , wherein the notification message is a Radio Resource Control, RRC, message.

[0274] Aid. The method in A1, wherein the notification message is an uplink Medium Access Control, MAC, Control Element, CE (UL MAC CE).

[0275] A2. The method in A1 , wherein the first cell group is a Master Cell Group, MCG, and the second cell group is a Secondary Cell Group, SCG.

[0276] A2a. The method in A2, wherein the first network node is a Master Node, MN, and the second network node is a Secondary Node, SN.

[0277] A2b. The method in A1c and A2, wherein the notification message is an SCGFailurelnformation message.

[0278] A2c. The method in A2b, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0279] A3. The method in A1, wherein the first cell group is a Secondary Cell Group, SCG, and the second cell group is a Master Cell Group, MCG.

[0280] A3a. The method in A3, wherein the first network node is a Secondary Node, SN, and the second network node is a Master Node, MN.

[0281] A3b. The method in A1c and A3, wherein the notification message is an MCGFailurelnformation message.

[0282] A3c. The method in A3b, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0283] A4. The method in A1 , A2 or A3, wherein the LTM related failure information is one of the following:

[0284] • the LTM candidate configuration ID of the cell toward which the LTM cell switch has previously failed;

[0285] • L1 measurements;

[0286] • an indication that the UE has released the second cell group triggered by the LTM related failure;

[0287] • new failure cause;

[0288] • an indication whether the failure was relating to the first cell group or the second cell group.

[0289] A4a. The method in A1 and A2, wherein the LTM related failure information is an indication that the UE has released the SCG triggered by the LTM related failure.

[0290] A5. The method in A1 , wherein the LTM related failure is one of the following:

[0291] • a failure to execute a LTM cell switch procedure for the second cell group, e.g. expiry of the LTM supervision timer;

[0292] • a validity / compliance check failure for an LTM candidate cell configuration including a second cell group;

[0293] • a failure to (re)transmit a maximum number of N of MAC PDU (this maximum number N can be N of MAC PDU for which a NACK has been received, or N of MAC PDU for which neither NACK nor ACK has been received).

[0294] Group B Embodiments B1 . A method for a first network node, to handle a LTM related failure for a UE configured with multi-radio dual connectivity (MR-DC), with a first cell group controlled by the first network node and a second cell group controlled by a second network node, comprising:

[0295] • receiving, from the UE, a notification message including LTM related failure information.

[0296] B1a. The method in B1 , wherein the first network node transmits, to a second network node, a message including LTM related failure information.

[0297] B2. The method in B1, wherein the first network node is a Master Node, MN, controlling a Master Cell Group, MCG.

[0298] B2a. The method in B2, wherein the second network node is a Secondary Node, SN, controlling a Secondary Cell Group, SCG.

[0299] B2b. The method in B2, wherein the notification message is an SCGFailurelnformation message.

[0300] B2c. The method in B2b, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0301] B3. The method in B1 , wherein the first network node is a Secondary Node, SN, controlling a Secondary Cell Group, MCG.

[0302] B3a. The method in B3, wherein the second network node is a Master Node, MN, controlling a Master Cell Group, MCG.

[0303] B3b. The method in B3, wherein the notification message is an MCGFailurelnformation message.

[0304] B3c. The method in B3b, wherein the MCGFailurelnformation message. is encapsulated into an ULInformationTransferMRDC message.

[0305] Group C Embodiments

[0306] C1 . A method for a second network node, to handle a LTM related failure for a UE configured with multi-radio dual connectivity (MR-DC), with a first cell group controlled by a first network node and a second cell group controlled by the second network node, comprising: • receiving, from the first network node, a notification message including LTM related failure information.

[0307] C2. The method in C1, wherein the second network node is a Secondary Node, SN, controlling a Secondary Cell Group, SCG.

[0308] C2a. The method in C2, wherein the first network node is a Master Node, MN, controlling a Master Cell Group, MCG.

[0309] C2b. The method in C2, wherein the notification message is an SCGFailurelnformation message.

[0310] C2c. The method in C2b, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0311] C3. The method in C1, wherein the second network node is a Master Node, MN, controlling a Master Cell Group, MCG.

[0312] C3a. The method in C3, wherein the first network node is a Secondary Node, SN, controlling a Secondary Cell Group, MCG.

[0313] C3b. The method in C3, wherein the notification message is an MCGFailurelnformation message.

[0314] C3c. The method in C3b, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0315] Group D Embodiments

[0316] 1. A method performed by a user equipment, UE, wherein the UE is operating with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, the method comprising: detecting a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure; and sending, to a first network node associated with the first cell group, a notification message that comprises information relating to the failure.

[0317] 2. The method of embodiment 1 , wherein the failure of the LTM procedure relates to the second cell group. 3. The method of embodiment 1 or 2, wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

[0318] 4. The method of any of embodiments 1-3, wherein the notification message is a Radio Resource Control, RRC, message.

[0319] 5. The method of any of embodiments 1-3, wherein the notification message is an uplink Medium Access Control Control Element, UL MAC CE.

[0320] 6. The method of any of embodiments 1-5, wherein the method further comprises: receiving a configuration for a candidate cell for the LTM procedure.

[0321] 7. The method of any of embodiments 1-6, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;

[0322] Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

[0323] 8. The method of any of embodiments 1-7, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

[0324] 9. The method of any of embodiments 1-8, wherein the first cell group is a Master Cell Group, MCG, and the second cell group is a Secondary Cell Group, SCG.

[0325] 10. The method of embodiment 9, wherein the LTM procedure relates to a change of cell in the SCG. 11. The method of embodiment 9 or 10, wherein the first network node is a Master Node, MN, in the MCG.

[0326] 12. The method of any of embodiments 9-11, wherein the notification message is an SCGFailurelnformation message.

[0327] 13. The method of embodiment 12, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0328] 14. The method of any of embodiments 1-8, wherein the first cell group is a Secondary Cell Group, SCG, and the second cell group is a Master Cell Group, MCG.

[0329] 15. The method of embodiment 14, wherein the LTM procedure relates to a change of cell in the MCG.

[0330] 16. The method of embodiment 14 or 15, wherein the first network node is a Secondary Node, SN, in the SCG.

[0331] 17. The method of any of embodiments 14-16, wherein the notification message is an MCGFailurelnformation message.

[0332] 18. The method of embodiment 17, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0333] 19. The method of any of embodiments 1 or 4-8, wherein the first cell group is a Master Cell Group, MCG, the first network node is a Master Node, MN, in the MCG, the second cell group is a Secondary Cell Group, SCG, and the LTM procedure relates to a change of cell in the MCG.

[0334] 20. A method performed by a user equipment, UE, wherein the UE is operating with multi-radio dual connectivity, MR-DC, with a Master Cell Group, MCG, and a Secondary Cell Group, SCG, the method comprising: detecting a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure relating to a change of cell in the MCG; and initiating a Radio Resource Control, RRC, Re-establishment procedure. Group E Embodiments

[0335] 21. A method performed by a first network node, wherein the first network node is associated with a first cell group for a user equipment, UE, that is operating with multi-radio dual connectivity, MR-DC, the method comprising: receiving, from the UE, a notification message that comprises information relating to a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure.

[0336] 22. The method of embodiment 21 , wherein the failure of the LTM procedure relates to a second cell group for the UE.

[0337] 23. The method of embodiment 21 or 22, wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

[0338] 24. The method of any of embodiments 21-23, wherein the notification message is a Radio Resource Control, RRC, message.

[0339] 25. The method of any of embodiments 21-23, wherein the notification message is an uplink Medium Access Control Control Element, UL MAC CE.

[0340] 26. The method of any of embodiments 21-25, wherein the method further comprises: sending, to the UE, a configuration for a candidate cell for the LTM procedure.

[0341] 27. The method of any of embodiments 21-26, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;

[0342] Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the LTM related failure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

[0343] 28. The method of any of embodiments 21-27, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

[0344] 29. The method of any of embodiments 21-28, wherein the method further comprises: sending, to a second network node associated with the second cell group, a message comprising information relating to the failure of the LTM procedure.

[0345] 30. The method of any of embodiments 21-29, wherein the first network node is a Master Node, MN, the first cell group is a Master Cell Group, MCG, and the second cell group is a Secondary Cell Group, SCG.

[0346] 31. The method of embodiment 30, wherein the LTM procedure relates to a change of cell in the SCG.

[0347] 32. The method of embodiment 30 or 31, wherein the notification message is an SCGFailurelnformation message.

[0348] 33. The method of embodiment 32, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0349] 34. The method of any of embodiments 21-29, wherein the first network node is a Secondary Node, SN, the first cell group is a Secondary Cell Group, SCG, and the second cell group is a Master Cell Group, MCG.

[0350] 35. The method of embodiment 34, wherein the LTM procedure relates to a change of cell in the MCG.

[0351] 36. The method of embodiment 34 or 35, wherein the notification message is an MCGFailurelnformation message.

[0352] 37. The method of embodiment 36, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message. 38. The method of any of embodiments 21 or 24-28, wherein the first cell group is a Master Cell Group, MCG, the first network node is a Master Node, MN, in the MCG, the second cell group is a Secondary Cell Group, SCG, and the LTM procedure relates to a change of cell in the MCG.

[0353] Group F Embodiments

[0354] 39. A method performed by a second network node, wherein the second network node is associated with a second cell group for a user equipment, UE, that is operating with multi-radio dual connectivity, MR-DC, the method comprising: receiving, from a first network node, a notification message that comprises information relating to a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure.

[0355] 40. The method of embodiment 39, wherein the failure of the LTM procedure relates to the second cell group for the UE.

[0356] 41. The method of embodiment 39 or 40, wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

[0357] 42. The method of any of embodiments 39-41 , wherein the first network node is associated with a first cell group for the UE.

[0358] 43. The method of any of embodiments 39-42, wherein the notification message is a Radio Resource Control, RRC, message.

[0359] 44. The method of any of embodiments 39-43, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;

[0360] Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

[0361] 45. The method of any of embodiments 39-44, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

[0362] 46. The method of any of embodiments 39-45, wherein the first network node is a Master Node, of a Master Cell Group, MCG, the second network node is a Secondary Node, SN, and the second cell group is a Secondary Cell Group, SCG.

[0363] 47. The method of embodiment 46, wherein the LTM procedure relates to a change of cell in the SCG.

[0364] 48. The method of embodiment 46 or 47, wherein the notification message is an SCGFailurelnformation message.

[0365] 49. The method of embodiment 48, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0366] 50. The method of any of embodiments 39-45, wherein the first network node is a Secondary Node, SN, of a Secondary Cell Group, SCG, the second network node is a Master Node, MN, and the second cell group is a Master Cell Group, MCG.

[0367] 51. The method of embodiment 50, wherein the LTM procedure relates to a change of cell in the MCG.

[0368] 52. The method of embodiment 50 or 51, wherein the notification message is an MCGFailurelnformation message.

[0369] 53. The method of embodiment 52, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

[0370] 54. The method of any of embodiments 50-53, wherein the method further comprises: sending, to the UE, a configuration for a candidate cell for the LTM procedure.

[0371] Group G Embodiments 55. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of the Group A embodiments, the Group B embodiments, the Group C embodiments, the Group D embodiments, the Group E embodiments or the Group F embodiments.

[0372] 56. A user equipment, UE, that is configurable for operation with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, wherein the UE is configured to perform the method of any of the Group A embodiments or the Group D embodiments.

[0373] 57. A user equipment, UE, that is configurable for operation with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, the UE comprising a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative to perform the method of any of the Group A embodiments or the Group D embodiments.

[0374] 58. A network node, configured to perform the method of any of the Group B embodiments, the Group C embodiments, the Group E embodiments or the Group F embodiments.

[0375] 59. A network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to perform the method of any of the Group B embodiments, the Group C embodiments, the Group E embodiments or the Group F embodiments.

[0376] 60. A user equipment, comprising: processing circuitry configured to cause the user equipment to perform any of the steps of any of the Group A embodiments or the Group D embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0377] 61. A network node, the network node comprising: processing circuitry configured to cause the network node to perform any of the steps of any of the Group B embodiments, the Group C embodiments, the Group E embodiments or the Group F embodiments; power supply circuitry configured to supply power to the processing circuitry. 62. A user equipment (UE), the UE comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments or the Group D embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

Claims

Claims1. A method performed by a user equipment, UE, wherein the U is operating with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, the method comprising: detecting (1101) a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure; and sending (1103), to a first network node associated with the first cell group, a notification message that comprises information relating to the failure.

2. The method of claim 1 , wherein the failure of the LTM procedure relates to the second cell group.

3. The method of claim 1 or 2, wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

4. The method of any of claims 1-3, wherein the notification message is a Radio Resource Control, RRC, message.

5. The method of any of claims 1-3, wherein the notification message is an uplink Medium Access Control Control Element, UL MAC CE.

6. The method of any of claims 1-5, wherein the method further comprises: receiving a configuration for a candidate cell for the LTM procedure.

7. The method of any of claims 1-6, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

8. The method of any of claims 1-7, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group;a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

9. The method of any of claims 1-8, wherein the first cell group is a Master Cell Group, MCG, and the second cell group is a Secondary Cell Group, SCG.

10. The method of claim 9, wherein the LTM procedure relates to a change of cell in the SCG.

11. The method of claim 9 or 10, wherein the first network node is a Master Node, MN, in the MCG.

12. The method of any of claims 9-11 , wherein the notification message is an SCGFailurelnformation message.

13. The method of claim 12, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

14. The method of any of claims 1-8, wherein the first cell group is a Secondary Cell Group, SCG, and the second cell group is a Master Cell Group, MCG.

15. The method of claim 14, wherein the LTM procedure relates to a change of cell in the MCG.

16. The method of claim 14 or 15, wherein the first network node is a Secondary Node, SN, in the SCG.

17. The method of any of claims 14-16, wherein the notification message is an MCGFailurelnformation message.

18. The method of claim 17, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

19. The method of any of claims 1 or 4-8, wherein the first cell group is a Master Cell Group, MCG, the first network node is a Master Node, MN, in the MCG, the second cell group is a Secondary Cell Group, SCG, and the LTM procedure relates to a change of cell in the MCG.

20. A method performed by a first network node, wherein the first network node is associated with a first cell group for a user equipment, UE, that is operating with multi-radio dual connectivity, MR-DC, the method comprising: receiving (1301), from the UE, a notification message that comprises information relating to a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure.

21. The method of claim 20, wherein the failure of the LTM procedure relates to a second cell group for the UE.

22. The method of claim 20 or 21 , wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

23. The method of any of claim 20-22, wherein the notification message is a Radio Resource Control, RRC, message.

24. The method of any of claims 20-22, wherein the notification message is an uplink Medium Access Control Control Element, UL MAC CE.

25. The method of any of claims 20-24, wherein the method further comprises: sending, to the UE, a configuration for a candidate cell for the LTM procedure.

26. The method of any of claims 20-25, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the LTM related failure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

27. The method of any of claims 20-26, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration;a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

28. The method of any of claims 20-27, wherein the method further comprises: sending, to a second network node associated with the second cell group, a message comprising information relating to the failure of the LTM procedure.

29. The method of any of claims 20-28, wherein the first network node is a Master Node, MN, the first cell group is a Master Cell Group, MCG, and the second cell group is a Secondary Cell Group, SCG.

30. The method of claim 29, wherein the LTM procedure relates to a change of cell in the SCG.

31. The method of claims 29 or 30, wherein the notification message is an SCGFailurelnformation message.

32. The method of claim 31 , wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

33. The method of any of claims 20-28, wherein the first network node is a Secondary Node, SN, the first cell group is a Secondary Cell Group, SCG, and the second cell group is a Master Cell Group, MCG.

34. The method of claim 33, wherein the LTM procedure relates to a change of cell in the MCG.

35. The method of claim 33 or 34, wherein the notification message is an MCGFailurelnformation message.

36. The method of claim 35, wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

37. The method of any of claims 20 or 23-27, wherein the first cell group is a Master Cell Group, MCG, the first network node is a Master Node, MN, in the MCG, the second cell group is a Secondary Cell Group, SCG, and the LTM procedure relates to a change of cell in the MCG.

38. A method performed by a second network node, wherein the second network node is associated with a second cell group for a user equipment, UE, that is operating with multi-radio dual connectivity, MR-DC, the method comprising: receiving (1401), from a first network node, a notification message that comprises information relating to a failure of a Layer 1 / Layer 2 Triggered Mobility, LTM, procedure.

39. The method of claim 38, wherein the failure of the LTM procedure relates to the second cell group for the UE.

40. The method of claim 38 or 39, wherein the failure of the LTM procedure relates to a failure to change cell in the second cell group.

41. The method of any of claims 38-40, wherein the first network node is associated with a first cell group for the UE.

42. The method of any of claims 38-41 , wherein the notification message is a Radio Resource Control, RRC, message.

43. The method of any of claims 38-42, wherein the information relating to the failure comprises any one or more of: an identity of a cell that the failed LTM procedure relates to;Layer 1, L1 , measurements; an indication that the UE has released the second cell group triggered by the failure of the LTM procedure; a failure cause; and an indication of whether the second cell group is a Master Cell Group, MCG, or a Secondary Cell Group, SCG.

44. The method of any of claims 38-43, wherein the failure of the LTM procedure is one of: a failure to execute a LTM cell switch procedure for the second cell group; a failure of a validity / compliance check for an LTM candidate cell configuration; a failure to transmit or retransmit a number, N, of Medium Access Control, MAC, Protocol Data Units, PDUs.

45. The method of any of claims 38-44, wherein the first network node is a Master Node, of a Master Cell Group, MCG, the second network node is a Secondary Node, SN, and the second cell group is a Secondary Cell Group, SCG.

46. The method of claim 45, wherein the LTM procedure relates to a change of cell in the SCG.

47. The method of claim 45 or 46, wherein the notification message is an SCGFailurelnformation message.

48. The method of claim 47, wherein the SCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

49. The method of any of claims 38-44, wherein the first network node is a Secondary Node, SN, of a Secondary Cell Group, SCG, the second network node is a Master Node, MN, and the second cell group is a Master Cell Group, MCG.

50. The method of claim 49, wherein the LTM procedure relates to a change of cell in the MCG.

51. The method of claim 49 or 50, wherein the notification message is an MCGFailurelnformation message.

52. The method of claim 51 , wherein the MCGFailurelnformation message is encapsulated into an ULInformationTransferMRDC message.

53. The method of any of claims 49-52, wherein the method further comprises: sending, to the UE, a configuration for a candidate cell for the LTM procedure.

54. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 1-53.

55. A user equipment, UE, that is configurable for operation with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, wherein the UE is configured to perform the method of any of claims 1-19.

56. A user equipment, UE, that is configurable for operation with multi-radio dual connectivity, MR-DC, with a first cell group and a second cell group, the UE comprising a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative to perform the method of any of claims 1-19.

57. A network node, configured to perform the method of any of claims 20-53.

58. A network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to perform the method of claims 20-53.

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