Master cell group link failure recovery

Abstract

A user equipment comprising: means for receiving a configuration message comprising lower layer conditions for sending failure information relating to master cell group link failure recovery. means for conditionally sending failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure. An access node apparatus comprising: means for sending to a user equipment a configuration message comprising lower layer conditions for user-equipment sending of failure information relating to master cell group link failure recovery. means for receiving conditionally sent failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

Description

[0001] TITLE

[0002] Master cell group link failure recovery

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to master cell group link failure recovery.

[0005] BACKGROUND

[0006] Dual Connectivity (DC) is a feature in wireless communication networks that enables a user equipment (UE) to simultaneously connect to two different network access nodes 120. A network access node can be split into two parts a Central Unit (CU) and a Distributed Unit (DU). The CU performs higher-layer functions, while the DU handles lower-layer functions. A single CU can interface to multiple DUs.

[0007] In Intra-MN (CU) Dual Connectivity a UE is connected to two cells served by the same CU. In Inter-MN (CU) Dual Connectivity a UE is simultaneously connected to cells served by different CUs.

[0008] A Master node (MN) makes a primary connection (via a Primary Cell -PCell) with a UE. The terms Master Cell Group (MCG) is used to refers to the carriers / cells controlled by the MN.

[0009] A Secondary node (MN) makes a secondary connection (via a Secondary Cell - SCell) with a UE. The term Secondary Cell Group (SCG) is used to refer to the carriers / cells controlled by the SN.

[0010] Handover / switching between cells is required for mobility and for link failure recovery.

[0011] BRIEF SUMMARY

[0012] According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

[0013] While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function

[0014] BRIEF DESCRIPTION

[0015] Some examples will now be described with reference to the accompanying drawings in which:

[0016] FIGs. 1 to 10 show examples of the subject matter described herein.

[0017] The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures.

[0018] DETAILED DESCRIPTION

[0019] Fig. 1 illustrates an example of a network 100 comprising a plurality of network entities including terminal apparatus 110, node apparatus 120 and one or more network apparatus 130. The terminal apparatus 110 and node apparatus 120 communicate 124 with each other. The one or more network apparatus 130 communicate 128 with the node apparatus 120.

[0020] In some examples the one or more network apparatus 130 communicate with the terminal apparatus 110. The one or more network apparatus 130 can, in some examples, communicate with each other. The one or more node apparatus 120 can, in some examples, communicate 126 with each other.

[0021] The network 100 can be a cellular network comprising a plurality of cells 122 each served by a node apparatus 120. In this example, the interface between the terminal apparatus 110 and a node apparatus 120 defining a cell 122 is a wireless interface 124.

[0022] The node apparatus 120 comprises one or more cellular radio transceivers. The terminal apparatus 110 comprises one or more cellular radio transceivers. In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal apparatus 110 are user equipment (UE) and the node apparatus 120 can be access nodes such as base stations.

[0023] A user equipment comprises a mobile equipment. Where reference is made to user equipment that reference includes and encompasses, wherever possible, a reference to mobile equipment.

[0024] In some examples, during operation, a user equipment 110 comprises a mobile equipment comprising a smart card for authentication / encryption etc. such as a Subscriber Identity Module (SIM). In some examples, during operation, a user equipment 110 comprises mobile equipment comprising circuitry embedded as part of the user equipment 110 for authentication / encryption such as software SIM.

[0025] The node apparatus 120 can be any suitable access node such as a base station or transmission reception point. The node apparatus 120 can be a network element responsible for radio transmission and reception in one or more cells 122, to or from the UE 110. The node apparatus 120 can be a network element in a Radio Access Network (RAN), an Open-Radio Access Network (O-RAN) or any other suitable type of network.

[0026] The network apparatus 130 can be part of a core network. The network apparatus 130 can be configured to manage functions relating to connectivity for the UEs 110. For example, the network apparatus 130 can be configured to manage functions such as connectivity, mobility, authentication, authorization, and / or other suitable functions. In some examples the network apparatus 130 can comprise an Access and Mobility management Function (AMF) and / or a User Plane Function (UPF) or any other suitable entities.

[0027] In the example of Fig. 1 the network apparatus 130 is shown as a single entity. In some examples the network apparatus 130 could be distributed across a plurality of entities. For example, the network apparatus 130 could be cloud based or distributed in any other suitable manner. The network apparatus 130 can be a core network node.

[0028] The network 100 can be a 4G or 5G network, for example. It can for example be a New Radio (NR) network that uses gNB or eNB as access nodes 120. New Radio is the 3GPP name for 5G technology. In such cases the node apparatus 120 can comprise gNodeBs (gNBs) 120 configured to provide user plane and control plane protocol terminations towards the UE 110 and / or to perform any other suitable functions. The gNBs 120 are interconnected with each other by means of an X2 / Xn interface 126. The gNBs are also connected by means of the N2 interface 128 to the network apparatus 130. The gNBs can be connected to an AMF or any other suitable network apparatus 130. Other types of networks and interfaces could be used in other examples. Other types of network could comprise next generation mobile and communication network, for example, a 6G network.

[0029] FIG 2 illustrates a system comprising multiple radio access nodes 120 and a user equipment 110.

[0030] The user equipment 110 is configured for dual connectivity. The user equipment 110 is capable of maintaining a configured primary radio link with a PCell of a Master Cell Group.

[0031] Node refers to an access node 120. In the FIG MN is a master node. SN is a secondary node. S-xN is serving node e.g. S-MN is serving master node. T-xN is target / candidate node e.g. T-SN is target / candidate secondary node.

[0032] S-MN sends, to a user equipment (UE) 110 a configuration message 309 relating to master cell group link failure recovery.

[0033] The configuration message 309 comprises lower layer conditions 311 for userequipment sending of failure information 321 relating to master cell group link failure recovery.

[0034] In at least some examples, the configuration message 309 additionally comprises a configuration of one or more lower layer measurements to be included in failure information 321 . In at least some examples, configuration of one or more lower layer measurements comprised in the configuration message 309 comprises a configuration of one or more physical layer measurements to be included in the failure information 321.

[0035] The UE receives, directly from S-MN 120 of a master cell group, the configuration message 309 relating to master cell group link failure recovery.

[0036] After a passage of time, there is a MN-UE radio link failure 210 (master cell group link failure). This is detected by the UE and the S-MN

[0037] As a consequence of detection of master cell group link failure 210 by the S-MN, the S-MN tests 220 fulfilment of the lower layer conditions 311 defined bu the received configuration message 309. The lower layer measurements conditions can relate to beam measurements (e.g. channel state information reference signal CSI-RS) and / or cell measurements (e.g. synchronization signal block SSB).

[0038] In some examples, the fulfilment of the lower layer measurements conditions requires one or more of the following to be true: i. The L1 RSRP of the “x” candidate beam is above a specific threshold. ii. The UE has acquired timing advance (TA) for the candidate beam iii. The UE has transmission configuration indicator (TCI) state activated for the candidate beam iv. A given candidate is within the list of cell(s) configured by the network

[0039] If the lower layer conditions 311 received in the configuration message 309 are fulfilled, the UE sends to the SN, failure information 321 relating to master cell group link failure recovery

[0040] The sending of failure information 321 is conditional sending because it is conditional on fulfilment of the lower layer conditions 311 received in the configuration message 309.

[0041] In at least some examples, the failure information 321 comprises a result 323 of one or more lower layer measurements performed at the UE in accordance with the configuration of one or more lower layer measurements sent to the UE in the configuration message 309.

[0042] In at least some examples, the failure information 321 comprises a result 323 of one or more physical layer measurements performed at the UE in accordance with the configuration of one or more lower layer measurements sent to the UE in the configuration message 309.

[0043] The SN receives the failure information 321 relating to master cell group link failure recovery and sends the a message 325 to the S-MN. In at least some examples, the message 325 comprises the failure information 321.

[0044] The S-MN does not send a higher layer e.g. layer 3 message to the UE. The S- MN sends, to the SN, a trigger message 331 to enable early synchronization for RACH-less connection following master cell group link failure 210. The trigger message 331 is a LTM trigger command to SN, not a RRC Reconfig message to the UE.The trigger message 331 comprises TCI. The SN sends , to the UE, a handover switch instruction 333 relating to master cell group link failure recovery. In at least some examples, the handover switch instruction 333 is sent as a secondary cell group (SCG) medium access control(MAC) control element (CE) configured as a proxy trigger for a handover switch instruction 333.

[0045] In at least some examples, the handover switch instruction 333 uses a single bit indicator to indicate master cell group (MCG) lower layer triggered (LTM) mobility switch.

[0046] One value of the bit can indicate master cell group (MCG) lower layer triggered (LTM) mobility switch. Another value of the bit can indicate secondary cell group (SCG) lower layer triggered (LTM) mobility switch.

[0047] The UE receives, directly from the SN, the handover switch instruction 333 relating to master cell group link failure recovery.

[0048] Where the handover switch instruction 333 is received as a secondary cell group medium access control (MAC) control element (CE), the UE determines 260 whether or not it is configured as a proxy trigger for a master cell group handover switch instruction.

[0049] The SN directly triggers LTM at UE.

[0050] The UE performs 270 handover, without random access channel (RACH), in accordance with the handover switch instruction 333. This is so-called RACH-less handover. In this example the handover is MCG LTM handover. This handover can be inter MN MCG LTM handover or intra MN MCG LTM handover.

[0051] Dual Connectivity (DC) is a feature in wireless communication networks that enables a user equipment (UE) to simultaneously connect to two different network access nodes 120

[0052] A network access node can be split into two parts a Central Unit (CU) and a Distributed Unit (DU). The CU performs higher-layer functions, while the DU handles lower-layer functions. A single CU can interface to multiple DUs.

[0053] In Intra-MN (CU) Dual Connectivity a UE is connected to two cells served by the same CU. In Inter-MN (CU) Dual Connectivity a UE is simultaneously connected to cells served by different CUs.

[0054] A Master node (MN) makes a primary connection (via a Primary Cell -PCell) with a UE. The terms Master Cell Group (MCG) is used to refers to the carriers / cells controlled by the MN. A Secondary node (MN) makes a secondary connection (via a Secondary Cell - SCell) with a UE. The term Secondary Cell Group (SCG) is used to refer to the carriers / cells controlled by the SN.

[0055] Lower layer mobility switching refers to switching triggered at lower layers (layers 1 and 2) as opposed to RRC (layer 3) switching.

[0056] The Xn interface is an interface between access nodes 120. The access nodes 120 connect to the core network via a NG interface. In a CU-Dll implementation, the Xn interface is between the CU of one access node 120 and the CU of another access node 120; the NG interface is between the CU and the network core, and the CU has an F1 interface to each of its DUs.

[0057] Network architecture can be considered from a control place (c, CP) perspective or from a user plane (u, UP) perspective.

[0058] FIGs 3A, 3B, 3C illustrate different examples of MCG switching (a change in DU of MN). The solid arrows illustrate a change in connection caused by handover switching.

[0059] FIG 3A illustrates inter MN (CU) MCG switching. For MN / MCG here is a change in CU and there is a change in DU. There is no change in SN / SCG.

[0060] FIG 3B illustrates intra MN (CU) MCG switching. For MN / MCG here is no change in CU and there is a change in DU. There is no change in SN / SCG.

[0061] FIG 3C illustrates intra MN (CU) MCG switching with intra-SN SCG switching.

[0062] For MN / MCG there is no change in CU and there is a change in DU.

[0063] For SN / SCG there is no change in CU and there is a change in DU.

[0064] FIG 4 is similar to FIG2. It illustrates in more detail an example of creation of the configuration message 309 comprising lower layer conditions 311 .

[0065] The S- MN will prepare a candidate PCell(s) that belongs to a different MN.

[0066] S-MN-CU sends HO Request 301 to T-MN-CU.

[0067] T-MN-CU sends SN Addition Request 303 to SN-CU.

[0068] SN-CU sends SN Addition Request ACK 305 to T-MN-CU.

[0069] T-MN-CU sends HO Request ACK 307 with complete configuration of MCG candidate cells (or equivalent) plus CSI-Resource-Config to S-MN-CU over the Xn interface containing either the complete config of the MCG Candidate cell or the delta that can be applied on top of the serving cell MCG Reference Config.

[0070] S-MN-CU sends to UE configuration message 309 (RRC Reconfiguration message plus Fast MCG link recovery configured plus modified measurement reporting configuration for fast recovery).

[0071] FIG 4 also illustrates validation process used before sending the trigger message 331. The S-MN validates that a target handover cell, identified based on lower layer measurements received via the failure information 321 (in message 325), is a prepared candidate for handover.

[0072] In examples where there is network provide timing advance (TA) it also validates that the network configured timing advance is valid

[0073] Once the validity test is passed, the S-MN sends the trigger message 331. If the validation fails, the process falls back 280 to layer 3 (RRC) handover procedures .

[0074] The trigger message 331 comprises the TCI. In examples where there is network provide timing advance (TA) it also comprises the timing advance.

[0075] The communication 240 between DU and CU of the S-MN, in advance of sending the trigger message 331 , is illustrated.

[0076] The communication 250 between DU and CU of the SN in advance of sending the handover switch instruction 333 is illustrated

[0077] FIG 5 illustrates the DU-CU communications 240 in more detail.

[0078] The signals 301 , 303, 305, 307, 325 are sent between respective CUs.

[0079] The message 309 is sent from the CU.

[0080] The message 321 is sent to the CU.

[0081] The trigger message 331 is sent from DU to CU.

[0082] The handover switch instruction 333 is sent from DU to UE.

[0083] FIG 6A and 6B use FIG 5 as a basis to explain early synchronization. FIG 6A illustrates early synchronization in accordance with a network configured / provided timing advance (TA). The trigger message 331 comprises a timing advance if timing advance is network configured. the trigger message comprises a timing advance if timing advance is network configured.

[0084] Optionally early synchronization is configured. This includes downlink synchronization 420 with MN candidate cells.

[0085] The S-MN-DU sends PDCCH order 371 to UE.

[0086] The UE performs 373 random access with T-MN-DU.

[0087] T-MN-DU provides 375 a timing advance for the UE to T-MN-CU

[0088] T-MN-CU provides 377 the timing advance for the UE to S-MN-CU

[0089] The S-MN-CU starts 422 a new timing advance validity timer

[0090] S-MN-CU sends 379 the timing advance for the UE to the UE

[0091] If early synchronization is configured for the UE to obtain network based early timing advance information, S-MN-CU upon receiving the early timing advance information from the candidate cell(s), starts a new TA validity timer. If this timer is running, the timing advance value of the prepared MN candidate cell(s) are assumed to be valid. Optionally, this timer can also be maintained at the S-MN-DU.

[0092] Validation 230 is performed on two main conditions:

[0093] 1) if the candidate cell based on best L1 measurements is a valid prepared candidate PCell

[0094] And

[0095] 2) if the timing advance (TA) is still valid based on the current state of the (newly introduced) timer. The TA is assumed to be valid if the timer is still running.

[0096] If the proposed timer is maintained at the S-MN-DU (Optional scenario), then the second condition about the network provided early TA can be validated upon receiving indication from S-MN-CU. If the timer has lapsed, the network can fall back to layer 3 (RRC) based MCG Link Recovery procedure and starts preparing the RRCReconfigurationWithSync to be sent to the UE.

[0097] FIG 6B illustrates early synchronization in accordance with user equipment 110 controlled timing advance. The UE upon reception of the configuration message 309 (RRC Recofiguration of the candidate PCell) finds 403 that the Itm-UE-MeasuredTA-ID within LTM-Candidate is equal to the value of Itm-ServingCellUE-MeasuredTA-ID within VarLTM- ServingCellUE-MeasuredTA-ID. UE thus inform 405 its lower layers that it is configured with UE based TA estimation. There is no requirement for using a timing advance validity timer (422).

[0098] Validation 230 is performed on one condition:

[0099] 1) if the candidate cell based on best L1 measurements is a valid prepared candidate PCell

[0100] FIG 7 uses FIG 5 as a basis to explain intra-CU SCG LTM.

[0101] It additionally comprises configuring 400 intra-CU SCG LTM. The SN-CU prepares

[0102] 400 the RRC Reconfiguration of the candidate PSCell under SN-T-DU and shares

[0103] 401 the same to the UE through SN-S-DU.

[0104] After MCG LTM handover 270, based on periodic L1 measurements reporting 501 for the SCG by the UE, SN-S-DU decides to trigger 502 MAC CE for SCG LTM cell switch.

[0105] SN-S-DU triggers (SCG) handover switch instruction 333 (Cell Group Reference Specific MAC Switching Command with differentiation indication value assigned as bit ”0”). Which implies that the handover switch instruction 333 (cell switching command) sent by SN is for SCG LTM (SCG MAC CE for SCG LTM) .

[0106] UE receives the handover switch instruction 333 and triggers RACH-less cell switch execution to the candidate cell PCell under T-MN-CU.

[0107] FIG 8A illustrates an example where the UE is configured with Dual Connectivity (DC) and inter-CU Master Cell Group (MCG) lower layer triggered mobility (LTM). The MN is configured with ‘extended’ fast MCG link Recovery .

[0108] Initially, it is assumed that the UE is configured with Dual connectivity and inter-MN MCG LTM.

[0109] During a preparation phase, MN prepares potential candidate PCell(s) that belongs to a different access nodes 120. Once radio link failure (RLF) is detected at the MN (S- MN), the UE triggers a modified MCG failure Information, starts the T316 timer and shares the modified MCG Failure Information to the SN over SRB3 to be relayed to the MN as there is no direct MN to UE connectivity. In this example the is MN configured with Extended fast MCG link Recovery with i) no SCG LTM based PSCell change ii) NW provided Early Timing Advance Information

[0110] The SN is not configured with PSCell change. The example relates to inter- MN(Cll) MCG LTM. This example corresponds to FIG 3A.

[0111] The UE is configured with DC and SRB3. MN is configured with MCG LTM while no PSCell change is configured at the SN.

[0112] The S- MN will prepare a candidate PCell(s) that belongs to a different MN. S-MN-CU sends HO Request 301 to T-MN-CU. T-MN-CU sends SN Addition Request 303 to SN-CU. SN-CU sends SN Addition Request ACK 305 to T-MN-CU. T-MN-CU sends HO Request ACK 307 with complete configuration of MCG candidate cells (or equivalent) plus CSI-Resource-Config to S-MN-CU over the Xn interface containing either the complete config of the MCG Candidate cell or the delta that can be applied on top of the serving cell MCG Reference Config.

[0113] S-MN-CU sends to UE configuration message 309 (RRC Reconfiguration message plus Fast MCG link recovery configured plus modified measurement reporting configuration for fast recovery).

[0114] The configuration message 309 relates to master cell group link failure recovery and comprises lower layer conditions 311 for user-equipment sending of failure information 321 relating to master cell group link failure recovery. In at least some examples, the configuration message 309 additionally comprises a (measurement) configuration of one or more lower layer measurements to be included in failure information 321.

[0115] Thus measurement reporting is based on some (lower layer) conditions whereby UE is, for example, configured to report “X” beams of the “Y” candidate cell(s) if MCG failure is detected.

[0116] When fast MCG Link recovery is configured, the network configures a measurement reporting configuration. The configuration indicates the UE to report L1 measurements of the candidate cell if all or some of the I following conditions are met i. The L1 RSRP of the “x” candidate beam is above a specific threshold. ii. The UE has acquired TA for the candidate beam iii. The UE has TCI state activated for the candidate beam iv. A given candidate is within the list of cell(s) configured by the network The reporting configuration may indicate UE to report “X” beam measurements from “Y” candidate cell(s)

[0117] Optionally early synchronization is configured. This includes downlink synchronization 420 with MN candidate cells.

[0118] The S-MN-DU sends PDCCH order 371 to UE.

[0119] The UE performs 373 random access with T-MN-DU.

[0120] T-MN-DU provides 375 a timing advance for the UE to T-MN-CU

[0121] T-MN-CU provides 377 the timing advance for the UE to S-MN-CU

[0122] The S-MN-CU starts 422 a new timing advance validity timer

[0123] S-MN-CU sends 379 the timing advance for the UE to the UE

[0124] If early synchronization is configured for the UE to obtain network based early timing advance information, S-MN-CU upon receiving the early timing advance information from the candidate cell(s), starts a new TA validity timer. If this timer is running, the timing advance value of the prepared MN candidate cell(s) are assumed to be valid. Optionally, this timer can also be maintained at the S-MN-DU.

[0125] RLF 210 is detected at the UE based on N310 out-of-sync indication from the lower layer and UE declares MCG Failure.

[0126] As a consequence of detection of master cell group link failure 210 by the S-MN, the S-MN tests 220 fulfilment of the lower layer conditions 311 received in the configuration message 309. The lower layer measurements conditions can relate to beam measurements (e.g. channel state information reference signal CSI-RS) and / or cell measurements (e.g. synchronization signal block SSB). In some examples, the fulfilment of the lower layer measurements conditions requires one or more of the following to be true: v. The L1 RSRP of the “x” candidate beam is above a specific threshold. vi. The UE has acquired timing advance (TA) for the candidate beam vii. The UE has transmission configuration indicator (TCI) state activated for the candidate beam viii. A given candidate is within the list of cell(s) configured by the network

[0127] The UE checks 220 on the conditions based on the modified reporting configurations depending on the beam level measurements of the candidate cell. If all or some of the conditions are met 220, the UE decides to include L1 measurement snapshots along with the MCG Failure Information in the failure information 321.

[0128] The UE sends the failure information 321 to the SN-S-CU (via SN-S-DU):

[0129] Thus If the lower layer conditions 311 received in the configuration message 309 are fulfilled, the UE sends to the SN, failure information 321 relating to master cell group link failure recovery. The sending of failure information 321 is conditional sending because it is conditional on fulfilment of the lower layer conditions 311 received in the configuration message 309. In at least some examples, the failure information 321 comprises a result 333 of one or more lower layer measurements performed at the UE in accordance with the configuration of one or more lower layer measurements sent to the UE in the configuration message 309.

[0130] The failure information 321 is the MCG Failure information plus a L1 measurement snapshot of MCG before MCG failure as transparent container as L1 measurement report.

[0131] The UE triggers the extended MCG Failure Information 321 over SRB3 to the SN- CU that includes in addition the latest L1 measurement reports (beam level measurements based on updated measurement reporting configuration as per the configured conditions ) as a transparent container to SN.

[0132] Thus If the configured conditions are met, the latest L1 measurement snapshot which UE have as part of MCG LTM which it had at the time of triggering MCG Failure Recovery containing “X” beam measurements of “Y” candidate cell(s) is sent as a transparent container inside the modified MCG Failure Information as L1 measurement report. This L1 measurement can be helpful at the MCG side for selecting the right beam for recovery thus assisting towards network-controlled beam specific recovery.

[0133] The UE starts the T316 after transmitting the extended MCG Failure Information 321.

[0134] The SN-CU transmits the extended MCG Failure Information 325 containing the latest L1 measurement snapshot which was a transparent to the SN-CU to the S-MN- CU over the Xn interface. The S-MN-CU reads the extended MCG Failure information along with the latest L1 measurement reports. Based on the latest L1 measurements, S-MN-CU checks validation 230 on two main conditions:

[0135] 1) if the candidate cell based on best L1 measurements is a valid prepared candidate PCell

[0136] And

[0137] 2) if the timing advance (TA) is still valid based on the current state of the (newly introduced) timer (422). The TA is assumed to be valid if the timer is still running.

[0138] If the proposed timer is maintained at the S-MN-DU (Optional scenario), then the second condition about the network provided early TA can be validated upon receiving indication from S-MN-CU.

[0139] The second condition may be relevant only for network configured TA obtained at the S-MN-DU during the early synchronization phase and may not be relevant when UE is configured with UE based TA estimation.

[0140] If the timer has lapsed, the network can fall back to layer 3 (RRC) based MCG Link Recovery procedure and starts preparing the RRCReconfigurationWithSync to be sent to the UE.

[0141] In this example, S-MN-CU finds the candidate cell prepared condition (1) valid and TA validity condition (2) valid.

[0142] S-MN CU upon checking and validating both conditions to be true, triggers a RLF detection indication 241 towards source MN DU which prevents any further scheduling of data from source MN DU. In addition, the source MN-CU may also share to the source MN DU, the L1 measurements for DU to identify the best candidate cell for LTM Recovery.

[0143] If the proposed ETA validity timer is maintained at the S-MN-DU, the S-MN-CU will send both RLF detection indication and L1 measurements for DU to identify the best candidate cell for LTM Recovery to the S-MN-DU based on the fulfilment of the first condition. Now, if S-MN-DU based on the timer expiry determines that the early timing advance is not valid, then it may trigger a fallback-indication over F1 interface to the S-MN-CU indicating to fall back to legacy fast MCG Link recovery procedure.

[0144] The S-MN-DU transmits the MCG LTM confirmation indication 242 to the S-MN- CU over the F1 interface which also contains the valid available TA value of the candidate PCell along with its TCI state information. The S-MN-DU upon reception of the RLF detection indication 241 , finds that it also contains L1 measurements for LTM Recovery, it would trigger MCG LTM confirmation indication 242 towards S-MN- CU which is a MAC CE cell switch command towards the best prepared candidate cell based on L1 measurements and is sent over F1 interface. Along with the cell switch command, this MAC CE also includes the Early Timing Advance for the best identified candidate cell along with its TCI state.

[0145] The S-MN-CU upon receiving the MCG LTM confirmation indication 242 from the S-MN-DU, sends a trigger message 331 (LTM Triggering command for MCG switching) over Xn interface to the SN-Cll along with the TA and TCI state of the identified best cell for the MN in a container transparent to SN.

[0146] The S-SN-CU upon receiving the trigger message 331 (LTM Triggering command for MCG switching), triggers SCG MAC CE for MCG LTM triggering indication 250 over F1 interface to the SN-S-DU.

[0147] The SN-S-DU upon receiving the SCG MAC CE for MCG LTM triggering indication 250 from S-MN-CU, triggers a handover switch instruction 333 (Cell Group Reference Specific MAC Switching Command with differentiation indication value assigned as bit ”1”). Which implies that the cell switching command sent by SN is a proxy for cell switch command for MCG LTM (SCG MAC CE for MCG LTM). The Cell Group Reference Specific MAC Switching Command which contains a single bit differentiation indication (0 / 1).

[0148] In case where SCG LTM is not configured, the differentiation indication can be assigned value bit “1” which would imply that the MAC switching command is SCG MAC CE for MCG LTM.

[0149] Else, if SCG LTM is configured at the SN and the specific MAC CE cell switching command is intended for SCG LTM, the single bit differentiation indication within the Cell Group Reference Specific MAC Switching Command can be assigned value with bit “0” which would imply that the MAC switching command is SCG MAC CE or SCG LTM.

[0150] The UE interprets 260 the SCG MAC CE 333 as a cell switch command for MCG and triggers RACH-less MCG LTM 270 towards the candidate PCell.

[0151] In terms of UE behavior, UE in DC, if it receives Cell Group Reference Specific MAC Switching Command with differentiation indication bit assigned value as bit “1”, it should interpret that SCG MAC CE as a proxy cell switch command for MCG LTM i.e. SCG MAC CE for MCG LTM.

[0152] If both MCG and SCG LTM is configured simultaneously, then this differentiation indication can have two possible binary values assigned. If this value is bit “1”, UE must interpret the SCG MAC CE is to trigger MCG LTM and if the assigned value is bit “0”, the UE interpretation is this SCG MAC CE is to trigger SCG LTM.

[0153] As an alternate, when no SCG LTM is configured, any MAC CE triggered by SN-S- DU can be interpreted by the UE as SCG MAC CE for MCG LTM and act accordingly.

[0154] The UE performs 270 handover, without random access channel (RACH), in accordance with the handover switch instruction 333. This is so-called RACH-less handover. In this example the handover is MCG LTM handover. This handover can be inter MN MCG LTM handover or intra MN MCG LTM handover. Thus the UE triggers RACH-less cell switch execution 270 to the candidate cell.

[0155] In the preceding description, the MAC CE cell switch command generated by the S- MN-DU is sent via MCG LTM confirmation indication 242 from S-MN-DU to the S- MN-CU, via trigger message 331 sent from S-MN-CU to SN-CU, via MCG LTM triggering indication 250 from SN-CU to SN-S-DU, and via handover switch instruction 333 from SN-S-DU to UE.

[0156] In some examples, the he MAC CE command generated by the S- MN-DU is sent from S-MN-DU to S-MN-CU via F1-C, S-MN-CU to S-SN-CU via Xn-C between source MN and source SN, S-SN-CU to S-SN-DU via F1-C,S-SN-DU to UE.

[0157] The forwarding of ‘MCG failure information via SCG radio link to source MN-DU’ and the ‘MAC CE cell switch command from source MN-DU to UE via SCG radio link’ uses control plane link . This can be over a stream control transmission protocol (SCTP) / IP stack. This guarantees in-sequence and reliable delivery of packets. However, the user plane protocol (GTP-u / UDP / IP) has low latency transport and is much faster than SCTP / IP. The SCTP / IP is a unicast protocol and is slower than UDP / IP which is a multicast protocol.

[0158] In some examples, GTP-u protocol path is used instead of control plane protocol path for faster message transfer (faster MCG link failure recovery).

[0159] There are two options to transfer a message (MAC CE cell switch command) from S-MN-DU to the UE via SCG radio link:

[0160] 1) via user plane path from source MN DU (S-MN-DU to S-MN-CU via F1-U, S- MN-CU to S-SN-CU via Xn-U between source MN and source SN, S-SN-CU to S-SN- DU via F1-U, S-SN-DU to UE)

[0161] 2) via direct GTP-u tunnel between S-MN-DU and S-SN-DU The purpose of the user plane signaling is to enable faster message transfer with low latency. GTP is the GPRS Tunnelling Protocol. GTP-ll is used for carrying user data within the GPRS core network and between the radio access nodes and the core network. GTP-ll is an IP based tunnelling protocol a user equipment can have different tunnels for different end point connections and / or different quality of service requirements.

[0162] Thus in at least some examples, user plane signaling or GTP-u tunnelling protocol is used to minimize inter node signaling latency and make the MCG link recovery faster.

[0163] In some examples, the user plane is used (to reduce inter node signaling latency) prior to transmission of handover switch instruction. Thus use of the user plane can comprise user plane tunneling or multicast messaging.

[0164] In an alternate embodiment, the MAC CE cell switch command generated by the S- MN-Dll is sent as an RRC message from S-MN-CU to S-SN-CU and from S-SN CU to S-SN-DU as a MCG LTM triggering indication 250, transparent to the SN-S-DU, to be forwarded by SN-S-DU to the UE over SRB3 as RRC message 333..

[0165] FIG 8B illustrates an example where the UE is configured with Dual Connectivity (DC) and inter-CU Master Cell Group (MCG) lower layer triggered mobility (LTM). The MN is configured with ‘extended’ fast MCG link Recovery .

[0166] In this example the is MN configured with Extended fast MCG link Recovery with i) SCG LTM based PSCell change ii) NW provided Early Timing Advance Information

[0167] The SN is configured with PSCell change

[0168] FIG 8B differs from FIG 8A in that the MN is configured with SCG LTM based PSCell change (in addition to being configured with ‘extended’ fast MCG link Recovery .

[0169] This example corresponds to FIG 3B.

[0170] FIG 8B, compared to FIG 8A, additionally comprises configuring 400 intra-CU SCG LTM. The SN-CU prepares 400 the RRC Reconfiguration of the candidate PSCell under SN-T-DU and shares 401 the same to the UE through SN-S-DU. After MCG LTM handover 270, based on periodic L1 measurements reporting 501 for the SCG by the UE, SN-S-DU decides to trigger 502 MAC CE for SCG LTM cell switch.

[0171] SN-S-DU triggers (SCG) handover switch instruction 333 (Cell Group Reference Specific MAC Switching Command with differentiation indication value assigned as bit ”0”). Which implies that the handover switch instruction 333 (cell switching command) sent by SN is for SCG LTM (SCG MAC CE for SCG LTM) .

[0172] UE receives the handover switch instruction 333 and triggers RACH-less cell switch execution to the candidate cell PCell under T-MN-CU.

[0173] FIG 8C illustrates an example where the UE is configured with Dual Connectivity (DC) and inter-CU Master Cell Group (MCG) lower layer triggered mobility (LTM). The MN is configured with ‘extended’ fast MCG link Recovery .

[0174] In this example the is MN configured with Extended fast MCG link Recovery with i) no SCG LTM based PSCell change ii) UE based TA estimation

[0175] The SN is not configured with PSCell change

[0176] The example relates to inter-MN(CU) MCG LTM switch with intra-SN(CU) SCG LTM switch.

[0177] FIG 8C differs from FIG 8A in that there UE based TA estimation instead of network provided early Timing Advance (TA) estimation.

[0178] Comparing FIG 8C with FIG 8A, synchronization 420 (311, 313, 315, 317, 422, 319) is replaced with 403, 405.

[0179] This example relates to intra-MN(CU) MCG LTM. This example corresponds to FIG 3B.

[0180] The UE upon reception of the RRC Recofiguration of the candidate PCell finds 403 that the Itm-UE-MeasuredTA-ID within LTM-Candidate is equal to the value of Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID. UE thus inform 405 its lower layers that it is configured with UE based TA estimation.

[0181] There is no requirement for using a timing advance validity timer (422)

[0182] When S-MN-CU checks validation 230, it checks only condition 1), it does not check condition 2).

[0183] The S-MN-CU checks validation 230, it checks if the candidate cell based on best L1 measurements is a valid prepared candidate PCell The S-MN-DU transmits the MCG LTM confirmation indication 242 to the S-MN- Cll over the F1 interface which also contains TCI state information. It does not contain a TA value of the candidate PCell .

[0184] FIG 8D illustrates an example where the UE is configured with Dual Connectivity (DC) and intra-CU Master Cell Group (MCG) lower layer triggered mobility (LTM). The MN is configured with ‘extended’ fast MCG link Recovery .

[0185] This example relates to intra-MN(CU) MCG LTM. This example corresponds to FIG 3B.

[0186] In this example the is MN configured with Extended fast MCG link Recovery with i) no SCG LTM based PSCell change ii) NW provided Early Timing Advance Information

[0187] The SN is not configured with PSCell change

[0188] The example relates to intra-MN(CU) MCG LTM. This example corresponds to FIG 3B.

[0189] The UE sends 601 L3 measurements to the MN-S-DU.

[0190] The MN-S-DU sends 603 the L3 measurements to the MN-s-CU.

[0191] The MN-S-CU decides 604 to prepare LTM candidate PCell(s).

[0192] The MN-S-CU sends 605 a UE Connect Set up Request to the MN-T-DU.

[0193] The MN-T-DU sends 607 a UE Connect Set up Response to the MN-S-CU.

[0194] The MN-S-CU sends 609 a UE Context Modification Request to MN-S-DU.

[0195] The MN-SDU sends 611 a UE Context Modification Response to MN-S-CU.

[0196] In some examples there is provided a user equipment 110 comprising: means for receiving a configuration message 309 comprising lower layer conditions 311 for sending failure information 321 relating to master cell group link failure recovery. means for conditionally sending failure information 321 relating to master cell group link failure recovery, in dependence upon master cell group link failure 210.

[0197] In some but not necessarily all examples, the configuration message 309 comprises a configuration of one or more lower layer measurements to be included in the failure information 321.

[0198] In some but not necessarily all examples, the failure information 321 comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements received in the configuration message 309.

[0199] In some but not necessarily all examples, the configuration comprises a configuration of one or more physical layer measurements to be included in the failure information 321.

[0200] In some but not necessarily all examples, the failure information 321 comprises a result of one or more physical layer measurements performed in accordance with the configuration of one or more lower layer measurements received in the configuration message 309.

[0201] In some but not necessarily all examples, the user equipment comprises means for detecting master cell group link failure 210, and for testing 220 fulfilment of the lower layer conditions 311 received in the configuration message 309.

[0202] In some but not necessarily all examples, the configuration message 309 is received from a first access node (S-MN) 120 and the failure information 321 is conditionally sent to a second access node (SN) 120.

[0203] In some but not necessarily all examples, the configuration message 309 is received directly from a first access node (S-MN) 120, and the user equipment comprises means for receiving a handover switch instruction 333 directly from a different access node, the second access node (SN) 120.

[0204] In some but not necessarily all examples, the first access node (S-MN) 120 is a master cell group access node and the different access node is a secondary cell group access node.

[0205] In some but not necessarily all examples, the handover switch instruction 333 is received as a secondary cell group medium access control (MAC) control element (CE) configured as a proxy trigger for a master cell group handover switch instruction.

[0206] In some but not necessarily all examples, the handover switch instruction 333 uses a single bit indicator 335 to indicate either a secondary cell group (SCG) lower layer triggered mobility (LTM) switch or master cell group (MCG) lower layer triggered (LTM) mobility switch

[0207] In some but not necessarily all examples, the user equipment comprises means for performing 270 handover, without random access channel (RACH), in accordance with the handover switch instruction 333. In some examples there is provided an access node apparatus 120 comprising: means for sending to a user equipment 110 a configuration message 309 comprising lower layer conditions 311 for user-equipment sending of failure information 321 relating to master cell group link failure recovery. means for receiving conditionally sent failure information 321 relating to master cell group link failure recovery, in dependence upon master cell group link failure 210.

[0208] In some but not necessarily all examples, the configuration message 309 comprises a configuration of one or more lower layer measurements to be included in the failure information 321 and the failure information 321 comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements sent in the configuration message 309.

[0209] In some but not necessarily all examples, the configuration comprises a configuration of one or more physical layer measurements to be included in the failure information 321, and the failure information 321 comprises a result of one or more physical layer measurements performed in accordance with the configuration of one or more lower layer measurements sent in the configuration message 309.

[0210] In some but not necessarily all examples, the access node is an access node of a master cell group and the failure information 321 is received from an access node of a secondary cell group.

[0211] In some but not necessarily all examples, the access node apparats comprises means for validating that a target handover cell, identified based on lower layer measurements received via the failure information 321 , is a prepared candidate for handover.

[0212] In some but not necessarily all examples, the network access node apparatus comprises means for validating that network configured timing advance if valid.

[0213] In some but not necessarily all examples, the access node apparatus 120 comprises means, responsive to the means for validating, for causing sending to another access node a trigger message to enable early synchronization for RACH- less connection.

[0214] In some but not necessarily all examples, the trigger message comprises TCI.

[0215] In some but not necessarily all examples, the trigger message comprises a timing advance if timing advance is network configured. In some but not necessarily all examples, the access node apparatus comprises means, responsive to the means for validating, for falling back to radio resource control handover.

[0216] In some examples there is provided a user equipment 110 comprising means for: means for receiving, directly from a first access node (S-MN) 120 of a master cell group, a configuration message 309 relating to master cell group link failure recovery. means for receiving, directly from a second access node (SN) 120 of a secondary cell group, a handover switch instruction 333 relating to master cell group link failure recovery.

[0217] In some but not necessarily all examples, the handover switch instruction 333 is received as a secondary cell group medium access control control element configured as a proxy trigger for a handover switch instruction 333.

[0218] In some but not necessarily all example, the handover switch instruction 333 uses a single bit indicator to indicate either a secondary cell group (SCG) lower layer triggered mobility (LTM) switch or master cell group (MCG) lower layer triggered (LTM) mobility switch

[0219] In some but not necessarily all examples, the user equipment 110 comprises means for performing handover, without random access channel (RACH), in accordance with the handover switch instruction 333.

[0220] In some but not necessarily all examples, the user equipment 110 comprises means for enabling early synchronization in accordance network configured timing advance (371 , 373) or user equipment 110 controlled timing advance (410)

[0221] In some but not necessarily all examples, the configuration message 309 comprises a configuration of one or more lower layer measurements to be included in the failure information 321

[0222] In some but not necessarily all examples, the received configuration message 309 comprises lower layer conditions 311 for sending failure information 321 relating to master cell group link failure recovery and the user equipment 110 comprises: means for conditionally sending failure information 321 relating to master cell group link failure recovery, in dependence upon master cell group link failure 210,.

[0223] In some but not necessarily all examples, the failure information 321 comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements received in the configuration message 309.

[0224] In some but not necessarily all examples, the user equipment 110 comprises means for detecting master cell group link failure 210, and for testing fulfilment of the lower layer conditions 311 received in the configuration message 309.

[0225] In some but not necessarily all examples, the configuration message 309 is received from a first access node (S-MN) 120 and the failure information 321 is conditionally sent to the second access node (SN) 120.

[0226] In some examples there is provided an access node apparatus 120 (SN) comprising: means for receiving from a first access node (S-MN) 120 means a trigger message to enable early synchronization for RACH-less connection following master cell group link failure 210; means for sending or causing sending to a user equipment 110 of a handover switch instruction 333 relating to master cell group link failure recovery.

[0227] In some but not necessarily all examples, the handover switch instruction 333 is sent as a secondary cell group medium access control control element configured as a proxy trigger for a handover switch instruction 333.

[0228] In some but not necessarily all examples, the handover switch instruction 333 uses a single bit indicator to indicate either a secondary cell group (SCG) lower layer triggered mobility (LTM) switch or master cell group (MCG) lower layer triggered (LTM) mobility switch.

[0229] In some but not necessarily all examples, the trigger message comprises TCI.

[0230] In some but not necessarily all examples, the trigger message comprises a timing advance if timing advance is network configured.

[0231] In some but not necessarily all examples, the access node apparatus comprises means for enabling early synchronization in accordance network configured timing advance.

[0232] In some but not necessarily all examples, the user equipment 110 comprises means for receiving, from the user equipment 110, failure information 321 comprising a result of one or more lower layer measurements performed at the user equipment 110 after master cell group link failure 210 and means for sending the failure information 321 to the first access node (S-MN) 120

[0233] In some but not necessarily all examples, the user equipment 110 comprises means for performing user equipment 110 handover, without random access channel (RACH), in accordance with the handover switch instruction 333.

[0234] In some examples there is provided an access node comprising means for: means for sending to a user equipment 110 a configuration message 309 relating to master cell group link failure recovery; means for sending, to a second access node (SN) 120 of a secondary cell group, a trigger message to enable early synchronization for RACH-less connection following master cell group link failure 210.

[0235] In some but not necessarily all examples, the trigger message comprises TCI.

[0236] In some but not necessarily all examples, the trigger message comprises a timing advance if timing advance is network configured.

[0237] In some but not necessarily all examples, the user equipment 110 comprises means, responsive to the means for validating, for falling back to radio resource control handover.

[0238] In some but not necessarily all examples, the user equipment 110 comprises means for receiving failure information 321 relating to master cell group link failure recovery, in dependence upon master cell group link failure 210.

[0239] In some but not necessarily all examples, the configuration message 309 comprises a configuration of one or more lower layer measurements to be included in the failure information 321 and the failure information 321 comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements sent in the configuration message 309.

[0240] In some but not necessarily all examples, the access node is an access node of a master cell group and the failure information 321 is received from the second access node (SN) 120

[0241] In some but not necessarily all examples, the user equipment 110 comprises means for validating that a target handover cell, identified based on lower layer measurements received via the failure information 321 , is a prepared candidate for handover.

[0242] In some but not necessarily all examples, the user equipment 110 comprises means for validating that network configured timing advance is valid. Fig 9 illustrates an example of a controller 800 suitable for use in an apparatus 110, 120. Implementation of a controller 800 may be as controller circuitry. The controller 800 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

[0243] As illustrated in Fig 9 the controller 800 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions 806 in a general-purpose or special-purpose processor 802 that may be stored on a machine readable storage medium (disk, memory etc.) to be executed by such a processor 802.

[0244] The processor 802 is configured to read from and write to the memory 804. The processor 802 may also comprise an output interface via which data and / or commands are output by the processor 802 and an input interface via which data and / or commands are input to the processor 802.

[0245] The memory 804 stores instructions, program, or code 806 that controls the operation of the apparatus 110, 120 when loaded into the processor 802. The computer program instructions, program or code am 806, provide the logic and routines that enables the apparatus 110, 120 to perform the methods illustrated in the accompanying FIGs. The processor 802 by reading the memory 804 is configured to load and execute the instructions, program, or code 806.

[0246] In some examples, the apparatus 110 comprises: at least one processor 802; and at least one memory 804 storing instructions that, when executed by the at least one processor 802, cause the apparatus at least to perform: receiving a configuration message comprising lower layer conditions for sending failure information relating to master cell group link failure recovery; conditionally sending failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

[0247] In some examples, the apparatus 20 comprises: at least one processor 802; and at least one memory 804 storing instructions that, when executed by the at least one processor 802, cause the apparatus (CN) at least to perfform: sending to a user equipment a configuration message comprising lower layer conditions for user-equipment sending of failure information relating to master cell group link failure recovery; receiving conditionally sent failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

[0248] In some examples, the apparatus 110 comprises: at least one processor 802; and at least one memory 804 storing instructions that, when executed by the at least one processor 802, cause the apparatus (UE) at least to perform: receiving, directly from a first access node of a master cell group, a configuration message relating to master cell group link failure recovery; and receiving, directly from a second access node of a secondary cell group, a handover switch instruction relating to master cell group link failure recovery.

[0249] In some examples, the apparatus 120 comprises: at least one processor 802; and at least one memory 804 storing instructions that, when executed by the at least one processor 802, cause the apparatus (SN) at least to perform: receiving from a first access node means a trigger message to enable early synchronization for RACH-less connection following master cell group link failure; sending or causing sending to a user equipment of a handover switch instruction relating to master cell group link failure recovery.

[0250] In some examples, the apparatus 120 comprises: at least one processor 802; and at least one memory 804 storing instructions that, when executed by the at least one processor 802, cause the apparatus (MN) at least to perform: sending to a user equipment a configuration message relating to master cell group link failure recovery; sending, to a second access node of a secondary cell group, a trigger message to enable early synchronization for RACH-less connection following master cell group link failure. As illustrated in Fig 10, the instructions, program, or code 806 may arrive at the apparatus 110, 120 via any suitable delivery mechanism 808. The delivery mechanism 808 may be, for example, a machine readable medium, a computer- readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read- Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 806. The delivery mechanism may be a signal configured to reliably transfer the computer program 806. The apparatus 110, 120 may propagate or transmit the computer program 806 as a computer data signal.

[0251] The term “non-transitory” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal ) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0252] Computer program instructions for causing an apparatus 110 to perform at least the following or for performing at least the following: receiving a configuration message comprising lower layer conditions for sending failure information relating to master cell group link failure recovery; conditionally sending failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

[0253] Computer program instructions for causing an apparatus 120 to perform at least the following or for performing at least the following: sending to a user equipment a configuration message comprising lower layer conditions for user-equipment sending of failure information relating to master cell group link failure recovery; receiving conditionally sent failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

[0254] Computer program instructions for causing an apparatus 110 to perform at least the following or for performing at least the following: receiving, directly from a first access node of a master cell group, a configuration message relating to master cell group link failure recovery; and receiving, directly from a second access node of a secondary cell group, a handover switch instruction relating to master cell group link failure recovery.

[0255] Computer program instructions for causing an apparatus 120 to perform at least the following or for performing at least the following: receiving from a first access node means a trigger message to enable early synchronization for RACH-less connection following master cell group link failure; sending or causing sending to a user equipment of a handover switch instruction relating to master cell group link failure recovery.

[0256] Computer program instructions for causing an apparatus 120 to perform at least the following or for performing at least the following: sending to a user equipment a configuration message relating to master cell group link failure recovery; sending, to a second access node of a secondary cell group, a trigger message to enable early synchronization for RACH-less connection following master cell group link failure.

[0257] The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

[0258] Although the memory 804 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0259] Although the processor 802 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 802 may be a single core or multi-core processor. References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

[0260] As used in this application, the term ‘circuitry’ may refer to one or more or all the following:

[0261] (a) hardware-only circuitry implementations (such as implementations in only analog and / or digital circuitry) and

[0262] (b) combinations of hardware circuits and software, such as (as applicable): i. a combination of analog and / or digital hardware circuit(s) with software / firmware and ii. any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory or memories that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

[0263] (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

[0264] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0265] The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the computer program 806. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

[0266] As used here ‘module’ refers to a unit or apparatus that excludes certain parts / components that would be added by an end manufacturer or a user. The apparatus 110, 120 can, for example be a module. A controller 800 of the apparatus 110, 120 can, for example be a module.

[0267] Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

[0268] The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

[0269] The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility.

[0270] The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’

[0271] In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e. , to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components.

[0272] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database, or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0273] In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

[0274] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or” mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0275] Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

[0276] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0277] The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus.

[0278] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0279] The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

[0280] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0281] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description.

[0282] Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0283] Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

34CLAIMS1. A user equipment comprising: means for receiving a configuration message comprising lower layer conditions for sending failure information relating to master cell group link failure recovery; and means for conditionally sending failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

2. A user equipment as claimed in claim 1 , comprising means for detecting master cell group link failure, and for testing fulfilment of the lower layer conditions defined by the configuration message to conditionally send failure information relating to master cell group link failure recovery.

3. A user equipment as claimed in claim 2, wherein the lower layer conditions comprise one of more of: the L1 RSRP of an identified candidate beam is above a specific threshold; the user equipment has acquired timing advance for the candidate beam; the user equipment has TCI state activated for the candidate beam; an identified candidate cell is within a list of cell(s) configured by the network.

4. A user equipment as claimed in claim 1 , 2 or 3, wherein the configuration message comprises a configuration of one or more lower layer measurements to be included in the failure information.

5. A user equipment as claimed in claim 4, wherein the failure information comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements received in the configuration message.

6. A user equipment as claimed in claim 1 , 2 or 3, wherein the configuration message is received from a first access node and the failure information is conditionally sent to a second, different access node.

357. A user equipment as claimed in claim 6, wherein the first access node is a master cell group access node and the second, different access node is a secondary cell group access node.

8. A user equipment as claimed in any of claims 1 to 7, wherein the configuration message is received directly from a first access node, and the user equipment comprises means for receiving a handover switch instruction directly from a different access node.

9. A user equipment as claimed in claim 8, wherein the handover switch instruction is received as a secondary cell group medium access control control element configured as a proxy trigger for a master cell group handover switch instruction.

10. A user equipment as claimed in claim 8 or 9, wherein the handover switch instruction uses a single bit indicator to indicate either a secondary cell group (SCG) lower layer triggered mobility (LTM) switch or master cell group (MCG) lower layer triggered (LTM) mobility switch.

11. A user equipment as claimed in any of claims 1 to 10 , comprising means for performing handover, without random access channel (RACH), in accordance with the handover switch instruction.

12. A user equipment as claimed in any of claims 1 to 10 , comprising means for enabling early synchronization in accordance network configured timing advance or user equipment controlled timing.

13. An access node apparatus comprising: means for sending to a user equipment a configuration message comprising lower layer conditions for user-equipment sending of failure information relating to master cell group link failure recovery; and means for receiving conditionally sent failure information relating to master cell group link failure recovery, in dependence upon master cell group link failure.

14. An access node apparatus as claimed in claim 13, wherein the configuration message comprises a configuration of one or more lower layer measurements to be included in the failure information and the failure information comprises a result of one or more lower layer measurements performed in accordance with the configuration of one or more lower layer measurements sent in the configuration message.

15. An access node apparatus 14, wherein the lower layer conditions comprise one of more the L1 RSRP of an identified candidate beam is above a specific threshold; the user equipment has acquired timing advance for the candidate beam; the user equipment has TCI state activated for the candidate beam; an identified candidate cell is within a list of cell(s) configured by the network.

16. An access node apparatus as claimed in any of claims 13 to 15, wherein the configuration comprises a configuration of one or more physical layer measurements to be included in the failure information, and the failure information comprises a result of one or more physical layer measurements performed in accordance with the configuration of one or more lower layer measurements sent in the configuration message.

17. An access node apparatus as claimed in any of claims 13 to 16, wherein the access node is an access node of a master cell group and the failure information is received from an access node of a secondary cell group.

18. An access node apparatus as claimed in any of claims 13 to 17, comprising means for validating that a target handover cell, identified based on lower layer measurements received via the failure information, is a prepared candidate for handover.

19. An access node apparatus as claimed in claim 18, comprising means, responsive to the means for validating, for causing sending to another access node a trigger message to enable early synchronization for RACH-less connection.

20. An access node apparatus as claimed in any of claims 18 or 19, comprising means, responsive to the means for validating, for falling back to radio resource control handover.

21. An access node apparatus as claimed in any of claims 13 to 17, wherein user plane signaling or GTP-u tunnelling protocol is used to reduce inter node signaling latency.

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