WO2025198513A1

WO2025198513A1 - Selecting candidate cells and configurations for recovery from radio-related failure

Info

Publication number: WO2025198513A1
Application number: PCT/SE2025/050251
Authority: WO
Inventors: Antonino ORSINO; Icaro Leonardo DA SILVA
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2024-03-20
Filing date: 2025-03-20
Publication date: 2025-09-25
Anticipated expiration: 2026-09-20

Abstract

Embodiments include methods for a user equipment (UE) configured for operation in a radio access network (RAN) Such methods include receiving from the RAN a plurality of candidate configurations for mobility candidate cells, including conditional layer-3 (L3) candidate configuration(s) for respective conditional L3 mobility candidate cell(s) and layer-1/layer-2 triggered inter-cell mobility (LTM) candidate configurations for respective LTM candidate cell(s). These include one or more common mobility candidate cells. Such methods include detecting a radio-related failure and selecting a cell of the RAN for recovery from the radio- related failure based on fulfillment of one or more conditions, including selecting a common mobility candidate cell when one or more first conditions are fulfilled. Such methods include selectively performing reestablishment or fast failure recovery to the selected cell, including selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells.

Description

SELECTING CANDIDATE CELLS AND CONFIGURATIONS FOR RECOVERY FROM RADIO-RELATED FAILURE

TECHNICAL FIELD

The present disclosure relates generally to wireless networks, and more specifically to techniques for improving mobility of user equipment (UEs) across multiple cells in a radio access network (RAN), specifically in relation to UE selection of candidate cells and configurations to use for recovery from a radio-related failure detected by the UE.

BACKGROUND

Currently the fifth generation (5G) of cellular systems is being standardized within the Third-Generation Partnership Project (3GPP). 5G is developed for maximum flexibility to support many different use cases including enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device- to-device (D2D), and several other use cases.

Figure 1 illustrates a high-level view of an exemplary 5G network architecture, consisting of a Next Generation Radio Access Network (NG-RAN, 199) and a 5G Core (5GC, 198). The NG-RAN can include one or more gNodeB’s (gNBs) connected to the 5GC via one or more NG interfaces, such as gNBs (100, 150) connected via respective interfaces (102, 152). More specifically, the gNBs can be connected to one or more Access and Mobility Management Functions (AMFs) in the 5GC via respective NG-C interfaces and to one or more User Plane Functions (UPFs) in 5GC via respective NG-U interfaces. The 5GC can include various other network functions (NFs), such as Session Management Function(s) (SMF).

In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a downlink (DL) “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

NG RAN logical nodes (e.g., gNB 100) include a Central Unit (CU or gNB-CU, e.g., 110) and one or more Distributed Units (DU or gNB-DU, e.g., 120, 130). CUs are logical nodes that host higher-layer protocols and perform various gNB functions such controlling the operation of DUs. DUs are decentralized logical nodes that host lower layer protocols and can include, depending on the functional split option, various subsets of the gNB functions. Each CU and DU can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., transceivers), and power supply circuitry.

A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1). However, each gNB-DU can be connected to only one gNB-CU. The gNB-CU and its connected gNB-DU(s) are only visible to other gNBs and the 5GC as a gNB. In other words, the Fl interface is not visible beyond gNB-CU.

3 GPP Release 12 (Rel-12) introduced Long-Term Evolution (LTE) dual connectivity (DC), whereby a UE can be connected to two network nodes simultaneously, thereby improving connection robustness and/or capacity. In particular, a master node (MN) provides a master cell group (MCG) for the UE and a secondary node (SN) provides a secondary cell group (SCG). Each cell group includes a primary cell (PCell) and may include one or more secondary cells (SCells).5G/NR also supports DC, including NR-DC that is similar to LTE -DC except that both the MN and SN use the NR interface to communicate with the UE. In addition, 5G/NR supports various multi-RAT DC (MR-DC) scenarios in one of the MN and SN uses the NR radio interface and the other uses the LTE radio interface to communicate with the UE.

Seamless mobility is a key feature of 3GPP radio access technologies (RATs). In general, a RAN (e.g., NG-RAN) configures a UE to perform and report radio resource management (RRM) measurements to assist network-controlled mobility decisions, such as for handover (HO) from a serving (or source) cell to a target cell. HOs ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission.

Even so, HO and other mobility procedures can have various robustness problems. For example, a HO command is normally sent when UE’s connection is degraded, such as at or near cell borders. As such, the HO command may need to be segmented (e.g., to allow for redundancy to protect against errors) and/or retransmitted one or more times before it reaches the UE. The HO command may not reach the UE in time (or at all) before the degraded connection is dropped. Failure of handover to a target cell may lead to the UE declaring radio link failure (RLF) in the serving cell and reestablishing its connection in another cell.

3GPP Rel-16 and Rel-17 support conditional HO (CHO) and other conditional mobility procedures. A main principle is that transmission and execution of a mobility (e.g., HO) command are separated. This allows the mobility command to be sent to UE when the radio conditions are still good, thus increasing the likelihood of successful reception. The UE executes the mobility command later based on an associated execution condition. These conditional mobility procedures are facilitated by a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). 3GPP Rel-16 also supports fast failure recovery for CHO. When a UE configured with one or more CHO candidate cells detects a failure (e.g. RLF, HO failure, CHO execution failure) and performs cell selection for re-establishment, if the selected cell is a configured CHO candidate cell, the UE performs a CHO execution instead of continuing with re-establishment.

As specified in 3GPP document RP-223520, NR Rel-18 includes a Work Item on further NR mobility enhancements, including in the technical area of L1/L2 based inter-cell mobility, also referred to as L1/L2 triggered mobility (LTM). Conventionally, serving cell change was triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and PSCell (e.g., when DC is configured) and to release/add SCells.

Conventionally, all L3 conditional and non-conditional inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI, i.e., PHY) resets, leading to greater latency, signaling overhead, and interruptions relative to intra-cell beam switching. Thus, a goal of Rel-18 L1/L2 mobility enhancements is to facilitate serving cell changes via L1/L2 signaling to address these problems and/or difficulties. These Rel-18 L1/L2 mobility enhancements also support the split CU/DU architecture shown in Figure 1, including intra-DU and inter-DU/intra-CU cell changes.

In LTM, a UE is pre-configured by its serving RAN node with one radio resource control (RRC) configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger the LTM cell switch procedure by sending the UE an LTM cell switch command.

SUMMARY

3GPP Rel-18 also supports fast failure recovery for LTM. In this procedure, when a UE configured with one or more LTM candidate cells detects a failure (e.g. RLF, HO failure, LTM cell switch failure) and selects a cell for connection re-establishment, if the selected cell is a configured LTM candidate cell, the UE performs an LTM cell switch instead of continuing with re-establishment.

3GPP has also agreed that the UE can perform this type of fast failure recovery when the UE is configured with both CHO and LTM. In other words, the RAN can configure both CHO and LTM candidate cells for a UE and enable the UE’s fast failure recovery using these configured CHO and LTM candidate cells. However, there are currently no mechanisms and/or rules for the UE to select between CHO and LTM candidate cells when performing fast recovery. This can cause unpredictable UE behavior. An object of embodiments of the present disclosure is to improve fast failure recovery for UEs operating in a RAN, such as by providing, enabling, and/or facilitating solutions to overcome exemplary problems summarized above and described in more detail below.

Embodiments include methods (e.g., procedures) for a UE configured for LTM in a radio access network (RAN, e.g., E-UTRAN, NG-RAN).

These exemplary methods include receiving from the RAN a plurality of candidate configurations for mobility candidate cells, including one or more conditional L3 candidate configurations for respective conditional L3 mobility candidate cells and one or more LTM candidate configurations for respective LTM candidate cells. For example, the one or more conditional L3 candidate configurations are CHO candidate configurations for respective CHO candidate cells. The conditional L3 mobility candidate cells and the LTM candidate cells include one or more common mobility candidate cells, i.e., cells for which the UE received candidate configurations for both conditional L3 mobility and LTM.

These exemplary methods also include detecting a radio-related failure and selecting a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting one of the common mobility candidate cells when one or more first conditions are fulfilled. These exemplary methods also include selectively performing reestablishment or fast failure recovery to the selected cell, including selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells.

In some embodiments, the first conditions include one or more of the following:

• the one or more conditional L3 mobility candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE; and

• the detected radio-related failure is related to an LTM cell switch to a common mobility candidate cell, which is the common mobility candidate cell selected for fast failure recovery.

In some embodiments, the first conditions include one or more of the following:

• the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE; and

• the detected radio-related failure is related to conditional L3 mobility to a common mobility candidate cell, which is the common mobility candidate cell selected for fast failure recovery.

In some embodiments, selecting a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions also includes the following operations, labelled with corresponding sub-block numbers: • selecting one of the LTM candidate cells that is not among the common mobility candidate cells, when one or more second conditions are fulfilled;

• selecting one of the conditional L3 mobility candidate cells that is not among the common mobility candidate cells, when one or more third conditions are fulfilled; and

• selecting a cell that is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells, when one or more fourth conditions are fulfilled.

In some embodiments, selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells may be based on various rules or criteria. Various first conditions, second conditions, third conditions, fourth conditions, rules, and criteria are disclosed herein.

In some embodiments, selectively performing reestablishment or fast failure recovery to the selected cell also includes the following operations, labelled with corresponding sub-block numbers:

• performing fast failure recovery based on LTM when the selected cell is among the LTM candidate cells but not among the common mobility candidate cells;

• performing fast failure recovery based on conditional L3 mobility when the selected cell is among the conditional L3 mobility candidate cells but not among the common mobility candidate cells; and

• performing reestablishment when the selected cell is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells.

Other embodiments include UEs (e.g., wireless devices) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program instructions that, when executed by processing circuitry, configure such UEs to perform operations corresponding to any of the exemplary methods described herein.

These and other embodiments described herein may provide various advantages and/or benefits. In general, embodiments may reduce and/or prevent further UE mobility operations (e.g., LTM cell switch, HO, CHO) that occur shortly after a UE’s fast failure recovery, which indicates that the selected cell and candidate configuration used in fast recovery was not optimal (even if suitable). As such, by facilitating an improved selection of cell and candidate configuration for fast failure recovery, embodiments may reduce risk of failure during or shortly after the procedure used for fast recovery. Moreover, by facilitating improved selection of cell and candidate configuration for fast failure recovery, embodiments may avoid excess UE energy consumption, longer connection interruptions, and excess signaling caused by further failures after fast failure recovery. At a high level, embodiments may improve mobility of UEs between cells of a RAN. These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a high-level view of an exemplary 5G/NR network architecture.

Figure 2 shows exemplary NR user plane (UP) and control plane (CP) protocol stacks.

Figures 3-4 show logical architectures for a gNB arranged in the split CU/DU architecture illustrated by Figure 1.

Figure 5 shows a signaling diagram for an exemplary CHO procedure.

Figure 6 shows a signaling diagram for an exemplary LTM cell switch procedure.

Figure 7 shows a flow diagram of an exemplary method for a UE (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

Figure 8 shows a communication system according to various embodiments of the present disclosure.

Figure 9 shows a UE according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and/or implied from the context of use. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and/or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and/or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

Furthermore, the following terms are used throughout the description given below: • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3GPP 5G/NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

• Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

• Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other wireless devices. Communicating wirelessly can involve transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

• Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

• Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g., a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and/or operable to communicate directly or indirectly with a wireless device and/or with other network nodes or equipment in the cellular communications network, to enable and/or provide wireless access to the wireless device, and/or to perform other functions (e.g., administration) in the cellular communications network. • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and/or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and/or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and/or descriptions conflict with the above definitions, the above definitions should control.

Note that the description given herein focuses on a 3 GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system and can be applied to any communication system that may benefit from them.

Figure 2 shows an exemplary configuration of NR user plane (UP) and control plane (CP) protocol stacks between a UE (210), a gNB (220), and an AMF (230). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between UE and gNB are common to UP and CP. PDCP provides ciphering/deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data.

On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection/correction, concatenation, segmentation/reassembly, sequence numbering, reordering of data transferred to/from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and manages transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

On the CP side, the non-access stratum (NAS) layer between UE and AMF handles UE/gNB authentication, mobility management, and security control. RRC sits below NAS in the UE but terminates in the gNB rather than the AMF. RRC controls communications between UE and gNB at the radio interface as well as the mobility of a UE between cells in the NG-RAN. RRC also broadcasts system information (SI) and performs establishment, configuration, maintenance, and release of DRBs and Signaling Radio Bearers (SRBs) and used by UEs. Additionally, RRC controls addition, modification, and release of carrier aggregation (CA) and dual-connectivity (DC) configurations for UEs, and performs various security functions such as key management.

After a UE is powered ON it will be in the RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state (e.g, where data transfer can occur). The UE returns to RRCJODLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception ( DRX ) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. An NR UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, NR RRC includes an RRC_INACTIVE state in which a UE is known (e.g., via UE context) by the serving gNB. RRC INACTIVE has some properties similar to a “suspended” condition used in LTE.

Figure 3 shows a logical architecture for a gNB arranged in the split CU/DU architecture, such as the gNB (100) in Figure 1. This logical architecture separates the CU into CP and UP functionality, called CU-C and CU-U respectively. Furthermore, each of the NG, Xn, and Fl interfaces is split into a CP interface (e.g., NG-C) and a UP interface (e.g., NG-U). Note that the terms “Central Entity” and “Distributed Entity” in Figure 3 refer to physical network nodes.

Figure 4 shows another exemplary gNB logical architecture that includes two gNB-DUs, a gNB-CU-CP, and multiple gNB-CU-UPs. The gNB-CU-CP may be connected to the gNB-DU through the Fl-C interface, and the gNB-CU-UP may be connected to the gNB-DU through the Fl-U interface and to the gNB-CU-CP through the El interface. Each gNB-DU may be connected to only one gNB-CU-CP, and each gNB-CU-UP may be connected to only one gNB-CU-CP. One gNB-DU may be connected to multiple gNB-CU-UPs under the control of the same gNB-CU-CP. Also, one gNB-CU-UP may be connected to multiple DUs under the control of the same gNB- CU-CP. When referring herein to an operation performed by a “CU”, it should be understood that this operation can be performed by any entities within the CU (e.g., CU-CP, gNB-CU-CP) unless stated otherwise.

Seamless mobility is a key feature of 3GPP radio access technologies (RATs). When the UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, serving cell change is triggered by L3 (e.g., RSRP) measurements and involves RRC signaling to change PCell and PSCell (e.g., when DC is configured), as well as release/add SCells (e.g., when carrier aggregation is configured). In general, a RAN (e.g., NG-RAN) configures a UE in RRC_CONNECTED state to perform and report radio resource management (RRM) measurements to assist network- controlled mobility decisions, such as for handover from a serving cell to a target cell (e.g., PCell change). Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by layer 3 (L3, i.e., RRC) and the messages exchanged are part of L3.

These reconfigurations are prepared in advance by a target RAN node serving the target cell, upon a request from the UE’s serving RAN node. This request is transmitted over the Xn interface in case the serving and target RAN nodes are part of the NG-RAN. The reconfiguration in the handover command considers the UE’s existing RRC configuration in its current serving cell (also referred to as “source cell”), which are provided in the inter-node request. In some cases, the reconfiguration can be provided as a “delta” to the UE’s existing configuration in the source cell, which reduces the size of the handover command.

The reconfiguration provided by the target RAN node contains all information the UE needs to access the target cell, e.g., random access configuration, a new cell radio network temporary identifier (C-RNTI) assigned to the UE in the target cell, and parameters enabling the UE to calculate security keys that it can use when communicating with the target cell (including sending a handover complete message).

In general, UE nobility in RRC CONNECTED state is network-based since the network has the most information about conditions such as cell loading (UEs and/or traffic), available node resources (e.g., processing), available frequencies, etc. Seamless handovers ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission. However, there will be scenarios when the network fails to handover the UE to the “correct” neighbor cell in time, which can cause the UE will declare radio link failure (RLF) or handover failure (HOF).

As briefly mentioned above, conditional handover (CHO) was introduced in 3GPP Rel- 16 to improve robustness of UE handover. The key idea in CHO is separation of transmission and execution of the handover command. This allows the handover command to be sent to a UE earlier when the radio conditions are still good, thus increasing the likelihood that the message is successfully transferred. The execution of the handover command is done later in time based on an associated execution condition. The execution condition is typically based on a threshold. For example, a signal strength of candidate target cell becomes X dB better than the serving cell (so called “A3 event”). A preceding measurement reporting event could use a threshold Y that is selected to be lower than X used as the handover execution condition. This allows the serving cell to prepare the handover upon reception of an early measurement report and to provide the RRCConnectionReconfiguration with mobilityControlInfo (for LTE), or a RRCReconfiguration with either a reconfigurationWithSync or a CellGroupConfig (for NR) at a time when the radio link between the source cell and the UE is still relatively stable.

As used herein, a cell for which conditional handover (or other conditional mobility procedure) is configured is called a “candidate target cell” or “potential target cell.” Similarly, a RAN node controlling a candidate/potential target cell is called “candidate target node” or “potential target node.” Once the conditional mobility execution condition has been fulfilled for a candidate/potential target cell and mobility execution towards this cell has been triggered, this cell is no longer “potential” or a “candidate” in the normal sense of these words, since it is now certain that the mobility operation will be executed towards it. Rather, the candidate/potential target cell may then be referred to as the “target cell.”

Figure 5 shows a signaling diagram for an exemplary CHO procedure. The signaling shown in Figure 5 is between a UE (510), a source RAN node (520), and a target RAN node (530). For example, the source and target nodes can be gNBs and/or components of gNBs, such as CUs and/or DUs.

This procedure involves two different measurement thresholds: a low threshold and a high threshold. The two thresholds can be expressed as different levels of a particular metric, e.g., signal strength, signal quality, etc. For example, the high threshold could be that the quality of the mobility reference signal (MRS) of the target cell or beam becomes X dB stronger than the MRS of the UE’s serving cell (e.g., provided by the source RAN node), with the low threshold being less than the high threshold (i.e., target exceeds source by lower amount). As used in this context, MRS denotes a reference signal used for any mobility-related purpose. For example, in NR, MRS can be either SSB (SS/PBCH block) or CSI-RS. As a further example, for NR operating in unlicensed spectrum (referred to as NR-U), MRS can be a discovery reference signal (DRS) in addition to any of the signals mentioned above.

The UE can be provided with a measurement configuration including the low threshold (not shown in the figure). Upon performing measurements that meet the low threshold, the UE can send a measurement report to the serving node (operation 1). While performing the measurements and evaluating the low threshold, the UE continues operating in its current RRC configuration. In operation 2, based on this report, the source RAN node can decide to request an early handover of the UE to the target RAN node (e.g., to a cell indicated in the measurement report). For example, this early handover request can include a HandoverPreparationlnformation IE such as described above.

The target RAN node performs admission control for the UE and responds with a CHO request acknowledgement (operation 5) that includes RRC configuration, similar to conventional handover. In operation 6, the source RAN node then sends the UE a RRCReconfiguration message that includes a “CHO Configuration”, which can include the high threshold. After responding with an RRCReconfigurationComplete message (operation 7), the UE continues to perform measurements and whenever the high threshold condition is met for a target cell, it can detach from the source cell and, after performing a RA procedure and synchronizing with the target cell, send the target RAN node an RRCReconfigurationComplete message (e.g., operations 8-9). Even so, the UE can remain in the source cell for an extended amount of time in case the high threshold condition is not fulfilled.

In operation 10, the target RAN node sends a HANDOVER SUCCESS message to the source gNB indicating the UE has successfully established the target connection. Upon reception of the handover success indication, the source RAN node stops scheduling any further DL or UL data to the UE and sends an SN STATUS TRANSFER message to the target RAN node indicating the latest PDCP SN transmitter and receiver status (operation 11). The source RAN node now also starts to forward User Data to the target RAN node (operation 12). Upon receiving the handover complete message (operation 9), the target RAN node can start exchanging user data with the UE. The target RAN node also requests the AMF to switch the DL data path from the UPF from the source RAN node to the target RAN node (not shown). Once the path switch is completed the target RAN node sends the UE CONTEXT RELEASE to the source RAN node (operation 13).

When a UE successfully connects (e.g., completes RA) to a target cell during a CHO or a conventional handover, it releases all the conditional reconfigurations that it has stored. The RAN node serving the target cell may then provide the UE with new conditional reconfigurations if desired.

The CHO procedure discussed above can be generalized into a generic conditional reconfiguration framework, wherein a UE may be configured in advance with other types of reconfigurations that can be executed by an RRCReconfiguration message (in NR) or an RRCConnectionReconfiguration message (in LTE) when associated execution condition(s) is(are) triggered. Each such message is prepared by a candidate target RAN node, associated with a candidate target cell, and includes execution conditions that can be represented by one or more identifiers of measurement configuration(s). This conditional reconfiguration framework can be applied to the following mobility operations: • CHO (e.g., target candidate RRCReconfiguration message contains a reconfiguration with sync for the MCG);

• Conditional PSCell Addition (CPA e.g., target candidate RRCReconfiguration message contains an SCG configuration which contains a reconfiguration with sync for a cell to be the PSCell of the SCG);

• Conditional PSCell Change (CPC, e.g., target candidate RRCReconfiguration message includes an SCG configuration that contains a reconfiguration with sync for a new target candidate cell to be the PSCell of the SCG);

• Conditional PSCell Release (e.g., source RRCReconfiguration message to be conditionally applied contains an SCG release indication); or

• Conditional PSCell Suspend (e.g., source RRCReconfiguration message to be conditionally applied contains an SCG suspend indication).

An SN-initiated intra-SN CPC procedure was specified in 3GPP Rel-16. In this procedure, a UE operating in MR-DC receives a conditional reconfiguration that includes an RRCReconfiguration message containing an SCG configuration (e.g., a secondaryCellGroup field of a CellGroupConfig information element) with an associated execution condition (e.g., an A3/A5 event configuration). When the UE detects that the execution condition is fulfilled (i.e., finds a neighbor cell better than current PSCell by a configured amount), the UE performs PSCell change. The intra-SN solution for Rel-16 is only for scenarios where the (candidate) target PSCells are provided by the UE’s current SN. Similar to CHO, when a UE successfully connects (e.g., completes RA) to a target cell during intra-SN CPC, it releases all the conditional reconfigurations that it has stored.

3GPP Rel-16 also supports fast failure recovery for CHO. When a UE configured with one or more CHO candidate cells detects a failure (e.g. RLF, HO failure, CHO execution failure) and performs cell selection for re-establishment, if the selected cell is a configured CHO candidate cell, the UE performs a CHO execution instead of continuing with re-establishment. The RAN enables fast failure recovery for CHO based on including an attemptCondReconfig field in the ConditionalReconfiguration IE used to provide one or more each CHO candidate configurations for respective CHO candidate cells (e.g., Figure 5 operation 6).

3GPP Rel-17 introduces support for Conditional PSCell Addition (CPA) and inter-SN CPC. The CPA procedure is used to add a PSCell/SCG to a UE currently configured with only an MCG, when associated execution conditions are fulfilled. CPA is initiated after the MN requests and receives an SCG configuration from a candidate target SN (T-SN), which the MN then provides to the UE as part of a conditional reconfiguration together with the associated execution condition(s). An inter-SN CPC procedure can be initiated by the MN or by the source SN (S-SN), with the MN handling signaling toward the T-SN and the UE in either case.

3 GPP Rel-18 includes an NR mobility enhancement referred to as L1/L2 based inter-cell mobility or L1/L2 triggered mobility (LTM). Current L3 -based inter-cell mobility procedures involve LI and L2 resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, Rel-18 LTM is intended to facilitate serving cell changes via L1/L2 signaling that reduce latency, signaling overhead, and interruptions.

In LTM, a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration”. This configuration may be an RRCReconfiguration message or a portion thereof, such as one or more lEs/fields/parameters (e.g., CellGroupConfig IE). The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN, which triggers the execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., DCI or MAC CE). Based on this command, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this cell.

The split CU/DU architecture shown in Figure 1 also supports LTM, including for intra- DU and inter-DU/intra-CU cell changes. In the inter-DU/intra-CU scenario, the candidate cell for LTM is a cell served by a neighbor DU to the (serving or source) DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell for LTM is a cell served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC).

Figure 6 shows a signaling diagram for an exemplary inter-DU/intra-CU LTM cell switch procedure. The signaling in Figure 6 is between a UE (610), a source DU (620), a candidate DU (630), and a CU (640) associated with both the source and candidate DUs. This arrangement is similar to the arrangement shown in Figure 1, where gNB-CU (110) is associated with gNB-DU (120) and gNB-DU (130). Although the operations are shown with numerical labels, this is done to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

In operation 1, the UE sends the source DU a MeasurementReport message containing measurements of neighboring cells to the UE’ s serving cell provided by the source DU. The source DU sends an UL RRC MESSAGE TRANSFER message conveying the received MeasurementReport message to the CU. In operation 2, the CU determines to initiate LTM configuration of the UE based on the received MeasurementReport message. In operation 3, the CU sends a UE CONTEXT SETUP REQUEST message to the candidate DU, containing one LTM candidate cell ID. If the candidate DU accepts the request of LTM configuration for the identified cell, it responds to the CU in operation 4 with a UE CONTEXT SETUP RESPONSE message including the generated lower layer RRC configuration for the accepted LTM candidate cell.

In operation 5, the CU sends a DL RRC MESSAGE TRANSFER message to the source DU, which includes the generated RRCReconfiguration message with the LTM configuration. Other messages also may be used to convey this information to the source DU. In operation 6, the source DU forwards the received RRCReconfiguration message to the UE.

In operation 7, the UE responds to the source DU with an RRCReconfigurationComplete message. In operation 8, the source gNB-DU forwards the RRCReconfigurationComplete message to the CU using an UL RRC MESSAGE TRANSFER message, or any other appropriate message.

In operation 9, the UE sends the source DU results of lower layer measurements performed by the UE on the configured LTM candidate cell. In operation 10, based on these measurement results, the source DU decides to trigger UE execution LTM to the LTM candidate cell. In operation 11, the source DU sends an LTM command to the UE. In operation 12, the source DU sends the CU an LTM CELL CHANGE NOTIFICATION message to indicate that LTM execution to the LTM candidate cell provided by the candidate DU has been initiated by the source DU.

In operation 13, the UE performs random access to the LTM candidate cell. Upon completion of the random access in operation 14 the candidate DU sends the CU an ACCESS SUCCESS message that includes a target cell ID, which corresponds to the identifier of the LTM candidate cell. In operation 15, the CU sends the source DU a UE CONTEXT RELEASE COMMAND message that indicates to release the UE’s resources in the serving cell. In operation 16, the source DU responds with a UE CONTEXT RELEASE COMPLETE message. Subsequently, user data may be transferred between the UE, the candidate (target) DU, and the CU.

3GPP Rel-18 also supports fast failure recovery for LTM. When a UE configured with one or more LTM candidate cells detects a radio-related failure (e.g. RLF, HO failure, LTM cell switch failure) and performs cell selection for re-establishment, if the selected cell is a configured LTM candidate cell, the UE performs an LTM cell switch instead of continuing with re-establishment. The RAN enables fast failure recovery for LTM based on including an attemptLTM-Switch field in the LTM-Config IE used to convey the LTM candidate configurations for one or more LTM candidate cells (e.g., Figure 6 operation 6). 3 GPP has also agreed that the UE can perform the so called fast failure recovery when the UE is configured with both CHO and LTM. In other words, the RAN can configure both CHO and LTM candidate cells for a UE and enable the UE’s fast failure recovery using these configured CHO and LTM candidate cells. However, there are currently no mechanisms and/or rules for the UE to select between CHO and LTM candidate cells when performing fast recovery from a detected failure (e.g., RLF, HO failure, CHO failure, LTM cell switch failure). This can cause various problems, issues, and/or difficulties.

Consider a first scenario in which a UE is configured with multiple candidate cells, with each candidate cell being configured for CHO or LTM, but not for both. When a failure is detected, the UE initiates a timer (e.g., supervision timer T304 or RLF timer T310). If the timer expires, the UE initiates re-establishment and performs cell selection. The selected cell may one of three types: an LTM candidate cell, a CHO candidate cell, neither a CHO candidate nor an LTM candidate.

Consider a second scenario in which a UE is configured with multiple candidate cells, with each candidate cell being configured for CHO, LTM, or both. When a failure is detected, the UE initiates a timer (e.g., supervision timer T304 or RLF timer T310). If the timer expires, the UE initiates re-establishment and performs cell selection. The selected cell may be one of four types: an LTM candidate, a CHO candidate, a candidate for CHO and LTM, and neither a CHO candidate nor an LTM candidate.

While the UE is allowed to select suitable LTM or CHO candidates, there are currently no rules that the UE uses to make such a selection in these two scenarios. In other words, the UE’s selection is implementation-specific, which can lead to inconsistent and/or undesirable UE behavior.

At a minimum, the UE’s selection of a suitable cell may be based on measurement results that meet one or more criteria, including sufficient Reference Signal Received Power (RSRP) and/or Reference Signal Received Quality (RSRQ). Even so, this may lead to the problems, issues, and/or difficulties, as explained below.

For example, the UE selects a suitable LTM candidate cell or CHO candidate cell and, after applying the associated LTM or CHO configuration and accessing that candidate cell, the UE transmits a measurement report and receives a HO command for another target cell. This other target cell may have been one of the suitable LTM or CHO candidate cells that the UE could have selected originally. Thus, performing two mobility operations to reach the other target cell results in wasted UE energy consumption, longer connection interruptions, and excessive signaling.

As another example, the UE selects a suitable target cell that is not an LTM or CHO candidate cell, and initiates reestablishment rather than fast failure recovery. The UE transmits measurement reports in the target cell and receives a handover command to another target cell. This other target cell may have been one of the suitable LTM or CHO candidate cells that the UE could have selected originally. As in the other example, performing two mobility operations to reach the other target cell results in wasted UE energy consumption, longer connection interruptions, and excessive signaling.

As another example, the UE selects a suitable cell that is both an LTM candidate and a CHO candidate. After applying the associated LTM or CHO configuration and accessing that candidate cell, the UE transmits a measurement report and receives a HO command for another target cell, which was neither an LTM candidate nor a CHO candidate for the UE but could have been selected for reestablishment rather than fast failure recovery. As in the other examples, performing two mobility operations to reach the other target cell results in wasted UE energy consumption, longer connection interruptions, and excessive signaling.

As another example, the UE selects a suitable cell that is an LTM candidate, but is also a CHO candidate. After applying the associated LTM configuration and performing an LTM cell switch, the UE transmits a measurement report and receives a HO command for another target cell, which is one of the UE’s configured CHO candidates. In this case, it would have been beneficial for the UE to select this CHO candidate initially rather than the LTM candidate that was selected. As in the other examples, performing two mobility operations to reach the other target cell results in wasted UE energy consumption, longer connection interruptions, and excessive signaling.

As another example, the UE selects a suitable cell that is a CHO candidate. After applying the associated CHO configuration and performing a CHO, the UE transmits a measurement report and receives an LTM cell switch command for another target cell, which is one of the UE’s configured LTM candidates. In this case, it would have been beneficial for the UE to select this LTM candidate initially rather than the CHO candidate that was selected. As in the other examples, performing two mobility operations to reach the other target cell results in wasted UE energy consumption, longer connection interruptions, and excessive signaling.

Accordingly, embodiments of the present disclosure address these and related problems and/or issues by flexible and efficient techniques for a UE, in response to detecting a radiorelated failure in a serving cell, to select a suitable cell for fast failure recovery from configured LTM candidate cells and configured CHO (or more generally, conditional L3 mobility) candidate cells, including cells that are configured as both LTM candidates and CHO candidates. For example, the UE may select a cell that is both a CHO candidate and an LTM candidate (i.e., a “common mobility candidate cell”) based on determining that one or more first conditions are fulfilled. Moreover, the UE may select between performing an LTM cell switch or a CHO to the selected cell - according to the respective configurations - based on one or more rules or criteria, which may include any of the following:

• numbers of configured LTM candidate cells and configured CHO candidate cells;

• availability of UL synchronization for the selected cell (e.g., time alignment and/or timing advance);

• availability of a DL synchronization for the selected cell;

• whether the failure that triggered fast recovery occurred during LTM cell switch or CHO execution;

• whether the cell in which the failure occurred was an LTM candidate cell or a CHO candidate cell;

• order in which the LTM configuration and the CHO configuration for the selected cell were provided to the UE;

• whether carrier aggregation (CA) is configured for the selected cell;

• number of SCells configured for the selected cell;

• whether SCells for the selected cell are activated or deactivated;

• whether DC is configured for the selected cell;

• whether an L2 (e.g., MAC) reset needs to be performed for the selected cell;

• whether an early ASN.1 decoding and validity check is performed;

• whether contention-free random access (CFRA) resources are available in the selected cell;

• whether the UE’ s SCG is activated or deactivated;

• whether a particular feature is configured in the LTM candidate configuration, the CHO candidate configuration, both, or neither for the selected cell;

• a random selection, e.g., based on two generated random numbers;

• a prioritization of LTM or CHO, when both LTM and CHO candidate configurations are available for the selected cell.

In some embodiments, the UE may apply further conditions to select cells that are not configured as both LTM candidates and CHO candidates, including:

• selecting a cell that is only an LTM candidate based on determining that one or more second conditions are fulfilled;

• selecting a cell that is only a CHO candidate based on determining that one or more third conditions are fulfilled; and

• selecting a cell that is neither an LTM candidate nor a CHO candidate based on determining that one or more fourth conditions are fulfilled Depending on the type of candidate configuration selected, the UE performs an LTM cell switch or a CHO (or other L3 mobility procedure) to the selected cell as part of a fast recovery procedure. In various embodiments, the fast recovery procedure can be in response to the UE detecting any of the following radio-related failures:

• Radio link failure (RLF), e.g., expiry of timers T310 or T316;

• HO failure or reconfiguration with sync failure (e.g., expiry of timer T304);

• LTM cell switch failure (e.g., expiry of LTM supervision timer);

• CHO execution failure;

• Beam failure detected (BFD), e.g., due to maximum count of Beam Failure Indications (BFIs) from received by UE MAC layer from UE PHY layer;

• RLC unrecoverable error (e.g., maximum number of retransmissions by UE RLC layer). Embodiments of the present disclosure may provide various advantages and/or benefits.

In general, embodiments may reduce and/or prevent further UE mobility operations (e.g., LTM cell switch, HO, CHO) that occur shortly after a UE’s fast failure recovery, which indicate that the selected cell and candidate configuration used in fast recovery was not optimal, even if suitable. As such, by facilitating an improved selection of cell and candidate configuration for fast failure recovery, embodiments may reduce the risk of failure during or shortly after the procedure used for fast recovery. Moreover, facilitating an improved selection of cell and candidate configuration for fast failure recovery, embodiments may avoid wasted UE energy consumption, longer connection interruptions, and excessive signaling caused by further failures shortly after fast failure recovery. At a high level, embodiments may improve mobility of UEs between cells of a RAN.

In the present disclosure, the following terms may be used interchangeably: “L1/L2 based inter-cell mobility”, “L1/L2 mobility,” “LI -mobility,” “LI based mobility,” “Ll/L2-centric inter-cell mobility,” “L1/L2 inter-cell mobility,” “inter-cell beam management,” “inter-DU L1/L2 based inter-cell mobility”, and “L1/L2 triggered mobility” (or LTM). These terms refer to a scenario in which a UE receives lower layer (i.e., below RRC, such as MAC or PHY) signaling from a network indicating for the UE to change of its serving cell (e.g., PCell) from a source cell to a target cell.

The content of the lower layer signaling may be referred to as “LTM cell switch command”. Exemplary lower layer signaling includes LI DL control information (DCI) and L2 MAC control element (CE). Compared to conventional RRC signaling, lower layer signaling reduces processing time and interruption time during mobility and may also increase mobility robustness since the network can respond more quickly to changes in the UE’s channel conditions. The term “LTM candidate cell” refers to a cell for which the UE is configured for LTM, specifically a cell the UE can move to in a LTM cell switch procedure in response to receiving an LTM cell switch command. An LTM candidate cell may also be referred to herein as “candidate cell”, “(LTM) candidate, “mobility candidate”, “non-serving cell”, “additional cell”, “(LTM) target candidate cell”, “(LTM) target candidate”, and comparable terms. A UE may perform and report measurements (e.g., CSI measurements) on an LTM candidate cell, based on which the UE’s serving RAN node may make an informed decision about which beam (or TCI state) and/or cell to switch the UE. 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). In the case of LTM fast recovery, when a failure is detected and the UE selects an LTM candidate cell, the UE performs an LTM cell switch towards the selected LTM candidate cell (e.g., by applying the associated LTM candidate cell configuration) rather than performing RRC re-establishment.

The change of serving cell (e.g., PCell) may also lead to a change in SCell(s) of the same cell group, e.g., in case an LTM cell switch command triggers the UE to change to another cell group configuration of the same type (e.g., another MCG configuration). For example, an LTM cell switch may include a change in SpCell (e.g., PCell for MCG, PSCell for SCG) and a change (e.g., addition, modification and/or release) in SCells of the same cell group. This may happen when the command triggers the UE to change to another cell group configuration of the same type (e.g., another SCG 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” via an RRCReconfiguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and/or an embedded RRCReconfiguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and/or structure of the IE and/or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”. A UE may receive an LTM candidate cell configuration in complete form or as a delta (or difference) relative to a reference configuration (which may be signaled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

The lower layer signaling from the RAN may include an identifier (or index) associated with an LTM candidate cell configuration. The identifier may be sent together with an LTM cell switch command, indicating for the UE to perform an LTM cell switch to the associated LTM candidate cell.

The term “LTM configuration” refers to a data structure that is used for or related to UE LTM operations, and may include one or more of the following elements (non-exclusive):

• an LTM candidate configuration, i.e., for an LTM candidate cell;

• a measurement configuration, e.g., LI measurement and reporting configuration for the LTM candidate cell;

• a configuration for early DL synchronization, e.g., for early TCI state activation;

• a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

• a configuration for execution of an LTM cell switch procedure according to a given LTM candidate cell configuration (e.g., whether to perform RA, RLC reestablishment, MAC reset, PDCP recovery, etc.).

The term “part of an LTM configuration” may refer to a subset of the elements in the above list, and/or a subset of items comprising any of the elements present (e.g., subset of configurations for DL pre-sync).

The phrase “LTM cell switch procedure” refers to the process of a UE switching (or changing) from a source cell to a target cell (i.e., an LTM candidate cell) using LTM. An LTM cell switch procedure may also be referred to 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”. Similarly, the phrase “switching to an LTM candidate cell configuration” means that the UE applies an LTM candidate cell configuration such that the associated LTM candidate cell becomes its new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, an LTM candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell.

Furthermore, an LTM cell switch may involve a UE switching (or changing) from a source cell group to a target cell group using LTM. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and/or release of one or more SCells), and/or a swap between SpCell and SCell roles for two cells in the same cell group.

The terms “CHO,” “CHO execution,” and “CHO execution procedure” refer to the process of a UE evaluating certain conditions configured by the RAN and, upon the fulfilling of such criteria, switching (or changing) from a source cell to a CHO candidate cell (which becomes a target cell) without further involvement of the source cell (e.g., signaling). In switching to the CHO candidate cell, the UE applies an CHO candidate configuration such that the CHO candidate cell becomes the UE’s new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, a CHO candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell. Further, when the CHO candidate cell is the PSCell, CHO may also be referred to as CPA, CPC, CP AC, or subsequent CP AC.

Furthermore, CHO execution witch may involve a UE switching (or changing) from a source cell group to a target cell group using CHO. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and/or release of one or more SCells), and/or a swap between SpCell and SCell roles for two cells in the same cell group.

Some embodiments include methods or procedures performed by a UE configured for operation in a RAN. While operating in a serving cell, the UE is configured with a plurality of candidate configurations for mobility candidate cells, including one or more LTM candidate configurations for respective LTM candidate cells and one or more CHO (or conditional L3 mobility) candidate configurations for respective CHO candidate cells. At least one of the mobility candidate cells is both an LTM candidate cell with an associated LTM candidate configuration and a CHO candidate cell with an associated CHO candidate configuration. As such, these particular mobility candidate cells may be referred to as “common mobility candidate cells.” The UE then detects a radio-related failure, such as one of the following:

• Radio link failure (RLF), e.g., expiry of timers T310 or T316;

• LTM cell switch failure (e.g., expiry of LTM supervision timer);

• CHO execution failure;

• RLC unrecoverable error (e.g., maximum number of retransmissions by UE RLC layer).

Based on detecting the radio-related failure, the UE selects a suitable cell for reestablishment or fast failure recovery from among the configured mobility candidate cells and possibly other cells not configured as mobility candidates. For a cell to be “suitable”, the UE must be able to camp on the cell (e.g., receive the cell broadcast) and the cell must fulfill certain cell selection criteria. 3GPP TS 38.304 (vl8.0.0) section 4.5 specifies various additional criteria for a “suitable cell.” The UE may select a suitable cell among multiple cells that are considered suitable.

During cell selection to find a suitable cell, the UE may use previously prior knowledge and/or stored information, such as knowledge of frequencies and/or measurement information previously obtained. This is referred to as cell selection leveraging stored information. When no such information is available or cell selection using such information resulted in that no suitable cell was found, the UE falls back to use what is referred to as initial cell selection which may include a scan of RF channels in relevant bands and searching for cells with highest signal strength. The UE may identify multiple cells that are classified as suitable cells, and may select from among these cells based on various conditions, including conditions associated with various embodiments described below.

In some embodiments, the UE may select a suitable cell that is both a CHO candidate cell and an LTM candidate cell (i.e., a common mobility candidate cell) based on determining that one or more first conditions are fulfilled. For example, when the detected radio-related failure was an LTM cell switch failure (e.g. expiry of LTM supervision timer) and the LTM candidate cell for which the failure occurred is also configured as an CHO candidate cell, the UE selects that same cell and executes a CHO to the selected cell (i.e., if the RAN has enabled the UE to perform CHO fast failure recovery). The benefit is that the UE switches to in the same cell as selected for LTM, but with a better chance of success due to the CHO candidate configuration being different than the LTM candidate configuration forthat mobility candidate cell. For example, the CHO candidate configuration may have security keys refreshes while LTM candidate configuration does not. Furthermore, if the failed LTM cell switch was performed without random access to the LTM candidate cell, performing CHO to the same cell causes the UE to perform random access, thereby increasing chances of success.

In some embodiments, the UE may select a suitable mobility candidate cell that is only an LTM candidate cell based on determining that one or more second conditions are fulfilled. For example, a second condition can be that the RAN has configured the UE to perform LTM fast failure recovery (e.g., attemptLTM-Switch field in the LTM-Config IE). This second condition can be combined with one or more other second conditions, such as:

• The RAN has not configured the UE to perform CHO fast failure recovery (e.g., no attemptCondReconfig field in ConditionalReconfiguration IE). One benefit is that the UE selects a cell for which fast recovery is possible. • The detected radio-related failure was an LTM cell switch failure (e.g., expiry of LTM supervision timer). One benefit is that the UE executes the type of mobility procedure that the RAN intended the UE to execute based on the original LTM cell switch command.

• The detected radio-related failure was a CHO execution failure (e.g., expiry of T304) to a CHO candidate cell but there are no other configured CHO candidate cells. One benefit is that the UE is able to execute fast recovery rather than re-establishment, which reduces interruptions.

• The UE has UL synchronization or is otherwise able to forego random access in the selected LTM candidate cell, due to valid/running time alignment timer (TAT) and/or available TA value. One benefit is that the fast recovery by LTM requires less time than re-establishment or CHO, both of which would random access towards the target cell.

In some embodiments, the UE may select a mobility candidate cell that is only a CHO candidate cell based on determining that one or more third conditions are fulfilled. For example, a third condition can be that the RAN has configured the UE to perform CHO fast failure recovery (e.g., no attemptCondReconfig field in ConditionalReconfiguration IE). This third condition can be combined with one or more other third conditions, such as:

• The RAN has not configured the UE to perform LTM fast failure recovery (e.g., no attemptLTM-Switch field in the LTM-Config IE). One benefit is that the UE selects a cell for which fast recovery is possible.

• The detected radio-related failure was a CHO execution failure (e.g. expiry of T304). One benefit is that the UE executes the type of mobility procedure that the RAN intended the UE to execute based on the original CHO command.

• The selected mobility candidate cell is a second CHO candidate cell that also fulfilled its associated execution conditions, along with a first CHO candidate cell that resulted in a CHO execution failure. One benefit is that the UE executes the type of mobility procedure that the RAN intended the UE to execute based on the original CHO command and fulfillment of the associated conditions.

• The detected radio-related failure was an LTM cell switch failure (e.g., expiry of LTM supervision timer) but there are no other configured CHO candidate cells. One benefit is that the UE is able to execute fast recovery rather than re-establishment, which reduces interruptions.

After selecting a mobility candidate cell that is an LTM candidate or a CHO candidate, the UE performs fast failure recovery in the selected cell, including applying an LTM candidate configuration or a CHO candidate configuration associated with the selected cell. In some embodiments, the UE may select a cell that is neither an LTM candidate nor a CHO candidate based on determining that one or more fourth conditions are fulfilled. An example fourth condition is that the RAN has not configured the UE to perform LTM fast failure recovery (e.g., no attemptLTM-Switch field in the LTM-Config IE) nor to perform CHO fast failure recovery (e.g., no attemptCondReconfig field in ConditionalReconfiguration IE). This example fourth condition may be combined with one or more other fourth conditions, such as:

• a default selection when none of the first, second, and third conditions are fulfilled;

• best radio conditions (e.g., highest RSRP) among suitable cells;

• same frequency as the mobility (e.g., LTM or CHO) candidate cell associated with the detected radio-related failure.

• When the detected radio-related failure is CHO execution failure, another CHO candidate cell whose execution conditions were also fulfilled prior to the radio-related failure. One benefit that it is unlikely a new HO will be triggered by the RAN after UE re-establishment in the selected cell.

After selecting a cell that is neither an LTM candidate nor a CHO candidate based on determining that one or more of the fourth conditions are fulfilled, the UE performs a re-establishment procedure to the selected cell rather than fast recovery.

In some embodiments, when the UE select a mobility candidate cell that is both a CHO candidate cell and an LTM candidate cell (i.e., a common mobility candidate cell) based on determining that one or more first conditions are fulfilled, the UE also selects between performing an LTM cell switch or a CHO to the selected mobility candidate cell - according to the respective configurations - based on one or more rules or criteria. Some examples are given below.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on number of configured LTM candidate cells and/or number of configured CHO candidate cells. In some variants, the UE can select the procedure for which the total number of configured candidate cells is greater. The rationale for this selection is a RAN preference inferred from the greater number of configured candidate cells. In other variants, the UE can select the procedure for which the UE has a greater number of candidate configurations for the selected common mobility candidate cell (e.g., two for the cell as an LTM candidate cell, one for the cell as a CHO candidate cell). The UE can select between multiple candidate configurations for the procedure and the selected cell based on other embodiments described herein.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on availability of UL synchronization in the selected cell, such as time alignment, timing advance (TA), and/or the ability to otherwise forego random access in the selected cell. For example, a valid TA may have been provided to the UE to facilitate early UL synchronization for LTM, so the UE selects LTM and applies the LTM candidate configuration instead of the CHO candidate configuration for the selected cell. As another example, when the UE can access the selected cell without random access via LTM but not via CHO, the UE selects LTM and applies the LTM candidate configuration instead of the CHO candidate configuration for the selected cell. One benefit of avoiding random access is reduced latency for connecting to the selected cell.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on availability of DL synchronization for the selected cell. For example, when the UE has already performed DL synchronization to the selected cell (e.g. pre-activation of one or more beams and/or TCI states), the UE performs an LTM cell switch rather than a CHO. One benefit is avoiding the extra delay needed to establish the DL synchronization. The UE may have performed DL synchronization to the selected mobility candidate cell in response to a command (e.g. MAC CE) received before the radio-related failure was detected.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether the failure that triggered fast recovery occurred during LTM cell switch or CHO execution. For example, if the failure was related to an LTM cell switch, the UE selectively applies the LTM candidate configuration for the selected cell. Otherwise, if the failure was related to CHO execution, the UE selectively applies the CHO candidate configuration for the selected cell. One benefit is that if the UE detected a failure during an LTM cell switch, the UE may be already pre-synchronized to other cells than the one related to the failure, thereby reducing latency of connecting to the selected cell. Another benefit is that the UE performs the same mobility procedure for fast recovery as it was executing when the failure occurred.

As an alternative, if the failure was related to an LTM cell switch, the UE selectively applies the CHO candidate configuration for the selected common mobility candidate cell. Otherwise, if the failure was related to CHO execution, the UE selectively applies the LTM candidate configuration for the selected common mobility candidate cell. One benefit of selecting CHO when the failure was LTM-related is that LTM cell switch may be performed without random access while CHO is performed using random access, which increases the likelihood of success.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether the cell in which the failure occurred was an LTM candidate cell or a CHO candidate cell. In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on the order in which the LTM and CHO candidate configurations for the selected cell were provided to the UE. For example, if the UE received the two candidate configurations in different RRC messages, the UE selects the candidate configuration received in the earlier RRC message. As another example, if the UE received the two candidate configurations in the same RRC message, the UE selects the candidate configuration appearing earlier in the RRC message (e.g., order of ASN.l IES in the message).

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on one or more of the following in the LTM and CHO candidate configurations for the selected cell:

• whether CA is configured;

• number of SCells configured;

• whether SCells are activated or deactivated; and

• whether DC is configured.

Some benefits from selecting a candidate configuration for which CA and/or DC is configured, and/or with a greatest number of activated SCells, is increased data capacity and reduced latency.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether an L2 (e.g., MAC) reset needs to be performed for the selected cell. For example, the UE selects LTM cell switch and applies the LTM candidate configuration when L2 reset is not required (or enabled) for the selected cell. This reduces execution latency, interruption time, and data loss relative to CHO, which always requires L2 reset.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether an early ASN.1 decoding and validity check has been performed on the respective candidate configurations. For example, if the UE has already performed ASN.l decoding and validity check on a received configuration (e.g., prior to storing), this may result in shorter interruption or less data loss compared to having to perform ASN.1 decoding and validity check when the UE applies the configuration.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether CFRA resources are available in the selected cell. For example, the UE selects CHO when CFRA resources are included in the CHO candidate configuration but not in the LTM candidate configuration (but which requires random access). On the other hand, the UE selects LTM when CFRA resources are not included in the CHO candidate configuration but are included in the LTM candidate configuration (which requires random access). In either case, since both procedures require random access to the selected cell, the UE selects the procedure to apply with CFRA resources configured. One benefit is that using dedicated CFRA resources reduces interruption and data loss compared to contentionbased RA resources.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether the UE’s SCG is activated or deactivated in the respective configurations. For example, by selecting a configuration for which the UE’s SCG is activated, the UE will be able to operate in DC using the activated SCG soon after completing the fast failure recovery. If the SCG is deactivated the UE cannot really benefit from DC until the RAN node serving the selected cell activates the UE’s SCG after the fast failure recovery.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on whether a particular feature is configured in the LTM candidate configuration, the CHO candidate configuration, both, or neither for the selected mobility candidate cell. For example, the UE may select the configuration with a larger number of multi-input/multi-output (MIMO) layers for transmission, which increases data capacity for the UE in the selected cell. Alternately, the UE may select the configuration for which DC (i.e., SCG) is activated but with a lower number of MIMO layers due to better reliability for data transmission.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on a random selection, e.g., based on comparison of two generated random numbers.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on a prioritization of LTM over CHO or vice versa. One benefit to prioritizing LTM is that an LTM cell switch may be performed without a random access procedure, which reduces execution time for the fast failure recovery. Another benefit of prioritizing LTM is that the UE retains LTM candidate configurations after LTM execution, so that a subsequent LTM cell switch may be performed. In contrast, the UE does not retain CHO candidate configurations after CHO execution. One benefit of prioritizing CHO is that CHO execution requires random access, which increases the likelihood of success for the fast failure recovery.

In some embodiments, the UE selects between performing an LTM cell switch or a CHO to the selected common mobility candidate cell based on various combinations of the rules and/or criteria discussed above, including but not limited to specific combination examples mentioned above.

Various features of the embodiments described above correspond to various operations illustrated in Figure 7, which shows an exemplary method e.g., procedures) for a UE ) configured for operation in a RAN, according to various embodiments of the present disclosure. In other words, various features of the operations described below correspond to various embodiments described above. The exemplary method shown in Figure 7 can be performed by a UE (e.g., wireless device) such as described elsewhere herein. Although Figure 7 shows specific blocks in a particular order, the operations of the exemplary method can be performed in different orders than shown and can be combined and/or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

The exemplary method includes the operations of block 710, where the UE receives from the RAN a plurality of candidate configurations for mobility candidate cells. These include one or more conditional L3 candidate configurations for respective conditional L3 mobility candidate cells and one or more LTM candidate configurations for respective LTM candidate cells. For example, the one or more conditional L3 candidate configurations are CHO candidate configurations for respective CHO candidate cells. The conditional L3 mobility candidate cells and the LTM candidate cells include one or more common mobility candidate cells, i.e., cells for which the UE received candidate configurations for both conditional L3 mobility and LTM.

The exemplary method also includes the operations of blocks 720-730, where the UE detects a radio-related failure and selects a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting in sub-block 731 one of the common mobility candidate cells when one or more first conditions are fulfilled. The exemplary method also includes the operations of block 740, where the UE selectively performs reestablishment or fast failure recovery to the selected cell, including sub-block 741 where the UE selectively performs fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells.

In some embodiments, the first conditions include one or more of the following:

• the one or more conditional L3 mobility candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE (e.g., attemptCondReconfig field in ConditionalReconfiguration IE); and

In some embodiments, the first conditions include one or more of the following:

• the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE (e.g., attemptLTM-Switch field in the LTM- Config IE); and • the detected radio-related failure is related to conditional L3 mobility to a common mobility candidate cell, which is the common mobility candidate cell selected for fast failure recovery.

In some embodiments, selecting a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions in block 730 also includes the following operations, labelled with corresponding sub-block numbers:

• (732) selecting one of the LTM candidate cells that is not among the common mobility candidate cells, when one or more second conditions are fulfilled;

• (733) selecting one of the conditional L3 mobility candidate cells that is not among the common mobility candidate cells, when one or more third conditions are fulfilled; and

• (734) selecting a cell that is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells, when one or more fourth conditions are fulfilled. In some of these embodiments, the one or more second conditions applied in block 732 include one or more of the following:

• the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE (e.g., attemptLTM-Switch field in the LTM- Config IE);

• the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE (e.g., no attemptCondReconfig field in ConditionalReconfiguration IE);

• the detected radio-related failure is related to an LTM cell switch;

• a single conditional L3 mobility candidate configuration is received and the detected radiorelated failure is related to conditional L3 mobility based on the single conditional L3 mobility candidate configuration; and

• availability of UL synchronization with the selected LTM candidate cell.

In some of these embodiments, the one or more third conditions applied in sub-block 733 include one or more of the following:

• the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE (e.g., no attemptLTM-Switch field in the LTM- Config IE);

• the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE (e.g., attemptCondReconfig field in ConditionalReconfiguration IE);

• the detected radio-related failure is related to conditional L3 mobility; • the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure; and

• a single LTM candidate configuration is received and the detected radio-related failure is related to an LTM cell switch based on the single LTM candidate configuration.

In some of these embodiments, the one or more fourth conditions applied in sub-block 734 include one or more of the following:

• none of the first, second, and third conditions are fulfilled;

• the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE;

• the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE;

• the selected cell has best radio conditions among cells suitable for reestablishment;

• the selected cell has the same frequency as a cell associated with the detected radio-related failure; and

• the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure.

In some embodiments, selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is one of the common mobility candidate cells, in sub-block 741, is based on one or more of the following rules or criteria:

• number of configured LTM candidate cells and number of configured conditional L3 mobility candidate cells;

• availability of UL synchronization with the selected cell;

• availability of downlink (DL) synchronization with the selected cell;

• whether the detected radio-related failure is related to an LTM cell switch or a conditional L3 mobility procedure;

• whether the cell in which the detected radio-related failure occurred was an LTM candidate cell or a conditional L3 mobility candidate cell;

• order in which the LTM candidate configuration and the conditional L3 mobility candidate configuration for the selected cell were received by the UE;

• whether an L2 reset needs to be performed for the selected cell; • a random selection; and

• a prioritization of LTM or conditional L3 mobility.

In some of these embodiments, selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells, in sub-block 741, comprises performing fast failure recovery based on LTM in response to one or more of the following conditions related to the rules or criteria:

• number of configured LTM candidate cells is greater than number of configured conditional L3 mobility candidate cells;

• when UL synchronization with the selected cell is available (i.e., the UE is UL synchronized with the selected cell);

• when DL synchronization with the selected cell is available (i.e., the UE is DL synchronized with the selected cell);

• the detected radio-related failure is related to an LTM cell switch;

• when the LTM candidate configuration for the selected cell was received before the conditional L3 mobility candidate configuration for the selected cell;

• when an L2 reset does not need to be performed for the selected cell; and

• when LTM is prioritized over conditional L3 mobility.

In some of these embodiments, selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells, in sub-block 741, comprises performing fast failure recovery based on conditional L3 mobility in response to one or more of the following conditions related to the rules or criteria:

• number of configured conditional L3 mobility candidate cells is greater than number of configured LTM candidate cells;

• when UL synchronization with the selected cell is not available (i.e., the UE is not UL synchronized with the selected cell);

• when DL synchronization with the selected cell is not available (i.e., the UE is not DL synchronized with the selected cell);

• the detected radio-related failure is related to conditional L3 mobility;

• when the conditional L3 mobility candidate configuration for the selected cell was received before the LTM candidate configuration for the selected cell;

• when an L2 reset needs to be performed for the selected cell; and

• when conditional L3 mobility is prioritized over LTM.

In some embodiments, selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is one of the common mobility candidate cells, in sub-block 741 , is based on one or more of the following for the respective LTM and conditional L3 mobility configurations for the selected cell:

• whether fast failure recovery is enabled;

• settings for carrier aggregation (CA) and/or dual -connectivity (DC);

• whether decoding and validity checking have been performed;

• availability of contention-free random access (CFRA) resources; and

• number of MIMO layers for data transmission or reception.

In some of these embodiments, the settings for CA and/or DC include one or more of the following: whether CA is configured, number of secondary cells (SCells) configured for CA, whether the configured SCells are activated or deactivated, whether DC is configured, and whether the UE’s SCG is activated or deactivated.

In some embodiments, selectively performing a reestablishment or a fast failure recovery to the selected cell in block 740 also includes the following operations, labelled with corresponding sub-block numbers:

• (742) performing fast failure recovery based on LTM when the selected cell is among the LTM candidate cells but not among the common mobility candidate cells;

• (743) performing fast failure recovery based on conditional L3 mobility when the selected cell is among the conditional L3 mobility candidate cells but not among the common mobility candidate cells; and

• (744) performing reestablishment when the selected cell is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells.

In some embodiments, the radio-related failure is one of the following:

• radio link failure (RLF);

• L3 handover failure;

• L3 reconfiguration with sync failure;

• LTM cell switch failure;

• conditional L3 mobility execution failure;

• beam failure detected (BFD); and

• radio link control (RLC) unrecoverable error.

Although various embodiments are described above in terms of methods, techniques, and/or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and/or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc. Figure 8 shows an example of a communication system 800 in accordance with some embodiments. In this example, communication system 800 includes a telecommunication network 802 that includes an access network 804 (e.g., RAN) and a core network 806, which includes one or more core network nodes 808. Access network 804 includes one or more access network nodes, such as network nodes 810a-b (one or more of which may be referred to as network nodes 810), or any other similar 3GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a 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, telecommunication network 802 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 802 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 telecommunication network 802, including one or more network nodes 810 and/or core network nodes 808.

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 (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 Al, Fl, Wl, El, 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 O-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 810 facilitate direct or indirect connection of UEs, such as by connecting UEs 812a-d (one or more of which may be referred to as UEs 812) to core network 806 over one or more wireless connections.

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, communication system 800 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. Communication system 800 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

UEs 812 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with network nodes 810 and other communication devices. Similarly, network nodes 810 are arranged, capable, configured, and/or operable to communicate directly or indirectly with UEs 812 and/or with other network nodes or equipment in telecommunication network 802 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in telecommunication network 802.

In the depicted example, core network 806 connects network nodes 810 to one or more hosts, such as host 816. 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. Core network 806 includes one or more core network nodes (e.g., 808) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and/or hosts, such that these descriptions are also applicable to the corresponding components of core network node 808. 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).

Host 816 may be under the ownership or control of a service provider other than an operator or provider of access network 804 and/or telecommunication network 802, and may be operated by the service provider or on behalf of the service provider. Host 816 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio/video content, data collection services such as 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. As a whole, communication system 800 of Figure 8 enables connectivity between the 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 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 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.

In some examples, telecommunication network 802 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 802 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 802. For example, telecommunication network 802 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 loT services to yet further UEs.

In some examples, UEs 812 are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 804 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 804. Additionally, a UE may be configured for operating in single- or multi-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-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

In the example, hub 814 communicates with access network 804 to facilitate indirect communication between one or more UEs (e.g., 812c and/or 812d) and network nodes (e.g., 810b). In some examples, hub 814 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 814 may be a broadband router enabling access to core network 806 for the UEs. As another example, hub 814 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 810, or by executable code, script, process, or other instructions in hub 814. As another example, hub 814 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, hub 814 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 814 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 814 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, hub 814 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

Hub 814 may have a constant/persistent or intermittent connection to network node 810b. Hub 814 may also allow for a different communication scheme and/or schedule between hub 814 and UEs (e.g., 812c and/or 812d), and between hub 814 and core network 806. In other examples, hub 814 is connected to core network 806 and/or one or more UEs via a wired connection. Moreover, hub 814 may be configured to connect to an M2M service provider over access network 804 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 810 while still connected via hub 814 via a wired or wireless connection. In some embodiments, hub 814 may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to network node 810b. In other embodiments, hub 814 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 810b, but which is additionally capable of operating as a communication start and/or end point for certain data channels.

Figure 9 shows a UE 900 in accordance with some embodiments. Examples of UE 900 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 cameras, 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 3GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE.

UE 900 may support device-to-device (D2D) communication, for example by implementing a 3 GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), orvehicle-to- everything (V2X). In other examples, UE 900 may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, UE 900 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, UE 900 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).

UE 900 includes processing circuitry 902 that is operatively coupled via a bus 904 to an input/output interface 906, a power source 908, a memory 910, a communication interface 912, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 9. 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.

Processing circuitry 902 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 memory 910. Processing circuitry 902 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, processing circuitry 902 may include multiple central processing units (CPUs).

In the example, input/output interface 906 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 UE 900. 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.

In some embodiments, power source 908 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. Power source 908 may further include power circuitry for delivering power from power source 908 itself, and/or an external power source, to the various parts of UE 900 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 908. Power circuitry may perform any formatting, converting, or other modification to the power from power source 908 to make the power suitable for the respective components of UE 900 to which power is supplied.

Memory 910 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, memory 910 includes one or more application programs 914, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 916. Memory 910 may store, for use by UE 900, any of a variety of various operating systems or combinations of operating systems.

Memory 910 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 USIM and/or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 910 may allow UE 900 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 910, which may be or comprise a device-readable storage medium.

Processing circuitry 902 may be configured to communicate with an access network or other network using communication interface 912. Communication interface 912 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 922. Communication interface 912 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 918 and/or a receiver 920 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 918 and receiver 920 may be coupled to one or more antennas (e.g., antenna 922) and may share circuit components, software, or firmware, or alternatively be implemented separately.

In the illustrated embodiment, communication functions of communication interface 912 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) 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, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol/intemet protocol (TCP/IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

Regardless of the type of sensor, UE 900 may provide an output of data captured by its sensors, through its communication interface 912, 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 reporting load from several sensors), in response to a triggering event (e.g., alert is sent when moisture is detected), in response to a request (e.g., user initiated request), or a continuous stream (e.g., live video feed of a patient).

As another example, UE 900 may include 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 to a robotic arm performing a medical procedure according to the received input.

When in the form of an Internet of Things (loT) device, UE 900 may be used in one or more application domains such as wearable technology, extended industrial application, and healthcare. Non-limiting examples of such an loT device are a device which is or which is 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 Virtual Reality (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 of the intended application of the loT device in addition to other components as described in relation to UE 900 shown in Figure 9.

As yet another specific example, in an loT scenario, UE 900 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-IoT 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.

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.

In some embodiments, UE 900 may be configured to perform operations attributed to a UE in various methods or procedures described above, including the exemplary method shown in Figure 7

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 spirit and scope of the disclosure. Various 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.

The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and/or electronic devices and can include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, etc., such as those that are described herein.

Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for performing one or more of the techniques described herein. In some implementations, the processing circuitry may cause the functional units to perform corresponding functions according to one or more embodiments of the present disclosure.

As described herein, device and/or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and/or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood that although such terms are often used synonymously herein, there may be instances herein when such terms are not intended to be used synonymously.

Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

Al . A method for a user equipment (UE) configured for operation in a radio access network (RAN), the method comprising: receiving from the RAN a plurality of candidate configurations for mobility candidate cells, including: one or more conditional L3 candidate configurations for respective conditional L3 mobility candidate cells, and one or more layer-1 (L12)/layer-2 (L2) triggered inter-cell mobility (LTM) candidate configurations for respective LTM candidate cells, wherein the conditional L3 mobility candidate cells and the LTM candidate cells include one or more common candidate cells; detecting a radio-related failure; selecting a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting one of the common candidate cells when one or more first conditions are fulfilled; and selectively performing reestablishment or fast failure recovery to the selected cell, including selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is one of the common candidate cells.

A2. The method of embodiment Al, wherein the first conditions include one or more of the following: the one or more conditional L3 mobility candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE; and the detected radio-related failure is related to an LTM cell switch to a common candidate cell, which is the common candidate cell selected for fast failure recovery.

A3. The method of any of embodiments A1-A2, wherein the first conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE; and the detected radio-related failure is related to conditional L3 mobility to a common candidate cell, which is the common candidate cell selected for fast failure recovery.

A4. The method of any of embodiments Al -A3, wherein selecting a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions further comprises: selecting one of the LTM candidate cells that is not a conditional L3 mobility candidate cell, when one or more second conditions are fulfilled; selecting one of the conditional L3 mobility candidate cells that is not an LTM candidate cell, when one or more third conditions are fulfilled; and selecting a cell that is neither an LTM candidate cell and nor a conditional L3 mobility candidate cell, when one or more fourth conditions are fulfilled.

A5. The method of embodiment A4, wherein the second conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE; the detected radio-related failure is related to an LTM cell switch; a single conditional L3 mobility candidate configuration is received and the detected radio-related failure is related to conditional L3 mobility based on the single conditional L3 mobility candidate configuration; and availability of UL synchronization with the selected LTM candidate cell.

A6. The method of any of embodiments A4-A5, wherein the third conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE; the detected radio-related failure is related to conditional L3 mobility; the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure; and a single LTM candidate configuration is received and the detected radio-related failure is related to an LTM cell switch based on the single LTM candidate configuration.

A7. The method of any of embodiments A4-A6, wherein the fourth conditions include one or more of the following: none of the first, second, and third conditions are fulfilled; the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE; the selected cell has best radio conditions among cells suitable for reestablishment; the selected cell has the same frequency as a cell associated with the detected radio-related failure; and the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure.

A8. The method of any of embodiments A1-A7, wherein selectively performing fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common candidate cells, is based on one or more of the following rules or criteria: numbers of configured LTM candidate cells and configured conditional L3 mobility candidate cells; availability of uplink (UL) synchronization with the selected cell; availability of downlink (DL) synchronization with the selected cell; whether the detected radio-related failure is related to an LTM cell switch or a conditional L3 mobility procedure; whether the cell in which the detected radio-related failure occurred was an LTM candidate cell or a conditional L3 mobility candidate cell; order in which the LTM candidate configuration and the conditional L3 mobility candidate configuration for the selected cell were received by the UE; whether an L2 reset needs to be performed for the selected cell; a random selection; and a prioritization of LTM or conditional L3 mobility.

A8a. The method of embodiment A8, wherein selectively performing fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common candidate cells, comprises performing fast failure recovery based on LTM in response to one or more of the following conditions related to the rules or criteria: number of configured LTM candidate cells is greater than number of configured conditional L3 mobility candidate cells; when UL synchronization with the selected cell is available; when DL synchronization with the selected cell is available; the detected radio-related failure is related to an LTM cell switch; when the LTM candidate configuration for the selected cell was received before the conditional L3 mobility candidate configuration for the selected cell; when an L2 reset does not need to be performed for the selected cell; and when LTM is prioritized over conditional L3 mobility.

A8b. The method of embodiment A8, wherein selectively performing fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common candidate cells, comprises performing fast failure recovery based on conditional L3 mobility in response to one or more of the following conditions related to the rules or criteria: number of configured conditional L3 mobility candidate cells is greater than number of configured LTM candidate cells; when UL synchronization with the selected cell is not available; when UDL synchronization with the selected cell is not available; the detected radio-related failure is related to conditional L3 mobility; when the conditional L3 mobility candidate configuration for the selected cell was received before the LTM candidate configuration for the selected cell; when an L2 reset needs to be performed for the selected cell; and when conditional L3 mobility is prioritized over LTM.

A9. The method of any of embodiments Al-A8b, wherein selectively performing fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common candidate cells, is based on one or more of the following for the respective LTM and conditional L3 mobility configurations for the selected cell: whether fast failure recovery is enabled; carrier aggregation (CA) and/or dual -connectivity (DC) settings; whether decoding and validity checking have been performed; availability of contention-free random access (CFRA) resources; and number of MIMO layers for data transmission or reception.

A10. The method of embodiment A9, wherein the CA and/or DC settings include one or more of the following: whether carrier aggregation (CA) is configured, number of secondary cells (SCells) configured for CA, whether configured SCells are activated or deactivated, whether DC is configured, and whether the UE’s SCG is activated or deactivated.

Al l. The method of any of embodiments A1-A10, wherein the one or more conditional L3 candidate configurations are conditional handover (CHO) candidate configurations for respective CHO candidate cells.

Al 2. The method of any of embodiments Al -Al 1, wherein selectively performing a reestablishment or a fast failure recovery to the selected cell further comprises: performing fast failure recovery based on LTM when the selected cell is one of the LTM candidate cells; performing fast failure recovery based on conditional L3 mobility when the selected cell is one of the conditional L3 mobility candidate cells; and performing reestablishment when the selected cell is neither an LTM candidate cell nor a conditional L3 mobility candidate cell.

Al 3. The method of any of embodiments Al -Al 2, wherein the radio-related failure is one of the following: radio link failure (RLF);

L3 handover failure;

L3 reconfiguration with sync failure;

LTM cell switch failure;

Conditional L3 mobility execution failure; beam failure detected (BFD); and radio link control (RLC) unrecoverable error.

B 1. User equipment (UE) configured for operation in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with cells of the RAN; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments Al -Al 3.

B2. User equipment (UE) configured for operation in a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments Al -Al 3.

B3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for operation in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments Al -Al 3.

B4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for operation in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments Al -Al 3.

Claims

1. A method for a user equipment, UE, configured for operation in a radio access network, RAN, the method comprising: receiving (710) from the RAN a plurality of candidate configurations for mobility candidate cells, including: one or more conditional layer-3, L3, candidate configurations for respective conditional L3 mobility candidate cells, and one or more layer- l/layer-2 triggered inter-cell mobility, LTM, candidate configurations for respective LTM candidate cells, wherein the conditional L3 mobility candidate cells and the LTM candidate cells include one or more common mobility candidate cells; detecting (720) a radio-related failure; selecting (730) a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting (731) one of the common mobility candidate cells when one or more first conditions are fulfilled; and selectively performing (740) reestablishment or fast failure recovery to the selected cell, including selectively performing (741) fast failure recovery based on LTM or conditional L3 mobility when the selected cell is among the common mobility candidate cells.

2. The method of claim 1, wherein the first conditions include one or more of the following: the one or more conditional L3 mobility candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE; and the detected radio-related failure is related to an LTM cell switch to a common mobility candidate cell, which is the common mobility candidate cell selected for fast failure recovery.

3. The method of any of claims 1-2, wherein the first conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE; and the detected radio-related failure is related to conditional L3 mobility to a common mobility candidate cell, which is the common mobility candidate cell selected for fast failure recovery.

4. The method of any of claims 1-3, wherein selecting (730) a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions further comprises: selecting (732) one of the LTM candidate cells that is not among the common mobility candidate cells, when one or more second conditions are fulfilled; selecting (733) one of the conditional L3 mobility candidate cells that is not among the common mobility candidate cells, when one or more third conditions are fulfilled; and selecting (734) a cell that is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells, when one or more fourth conditions are fulfilled.

5. The method of claim 4, wherein the second conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is enabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE; the detected radio-related failure is related to an LTM cell switch; a single conditional L3 mobility candidate configuration is received and the detected radio-related failure is related to conditional L3 mobility based on the single conditional L3 mobility candidate configuration; and availability of uplink, UL, synchronization with the selected LTM candidate cell.

6. The method of any of claims 4-5, wherein the third conditions include one or more of the following: the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is enabled for the UE; the detected radio-related failure is related to conditional L3 mobility; the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure; and a single LTM candidate configuration is received and the detected radio-related failure is related to an LTM cell switch based on the single LTM candidate configuration.

7. The method of any of claims 4-6, wherein the fourth conditions include one or more of the following: none of the first, second, and third conditions are fulfilled; the one or more LTM candidate configurations are received with an indication that LTM fast failure recovery is disabled for the UE; the one or more conditional L3 candidate configurations are received with an indication that conditional L3 fast failure recovery is disabled for the UE; the selected cell has best radio conditions among cells suitable for reestablishment; the selected cell has a same frequency as a cell associated with the detected radio-related failure; and the detected radio-related failure is related to a first one of the conditional L3 mobility candidate cells and the selected cell is a second one of conditional L3 mobility candidate cells for which UE measurements fulfilled associated execution conditions prior to the detected radio-related failure.

8. The method of any of claims 1-7, wherein selectively performing (741) fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common mobility candidate cells, is based on one or more of the following rules or criteria: number of configured LTM candidate cells and number of configured conditional L3 mobility candidate cells; availability of uplink, UL, synchronization with the selected cell; availability of downlink, DL, synchronization with the selected cell; whether the detected radio-related failure is related to an LTM cell switch or a conditional L3 mobility procedure; whether the cell in which the detected radio-related failure occurred is one of the LTM candidate cells or one of the conditional L3 mobility candidate cells; order in which the LTM candidate configuration and the conditional L3 mobility candidate configuration for the selected cell were received by the UE; whether an L2 reset needs to be performed for the selected cell; a random selection; and a prioritization of LTM or conditional L3 mobility.

9. The method of claim 8, wherein selectively performing (741) fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is among the common mobility candidate cells, comprises performing fast failure recovery based on LTM in response to one or more of the following conditions related to the rules or criteria: number of configured LTM candidate cells is greater than number of configured conditional L3 mobility candidate cells; when UL synchronization with the selected cell is available; when DL synchronization with the selected cell is available; the detected radio-related failure is related to an LTM cell switch; when the LTM candidate configuration for the selected cell was received before the conditional L3 mobility candidate configuration for the selected cell; when an L2 reset does not need to be performed for the selected cell; and when LTM is prioritized over conditional L3 mobility.

10. The method of claim 8, wherein selectively performing (741) fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is among the common mobility candidate cells, comprises performing fast failure recovery based on conditional L3 mobility in response to one or more of the following conditions related to the rules or criteria: number of configured conditional L3 mobility candidate cells is greater than number of configured LTM candidate cells; when UL synchronization with the selected cell is not available; when UDL synchronization with the selected cell is not available; the detected radio-related failure is related to conditional L3 mobility; when the conditional L3 mobility candidate configuration for the selected cell was received before the LTM candidate configuration for the selected cell; when an L2 reset needs to be performed for the selected cell; and when conditional L3 mobility is prioritized over LTM.

11. The method of any of claims 1-10, wherein selectively performing (741) fast failure recovery based on LTM or conditional L3 mobility, when the selected cell is one of the common mobility candidate cells, is based on one or more of the following for the respective LTM and conditional L3 mobility configurations for the selected cell: whether fast failure recovery is enabled; settings for carrier aggregation, CA, and/or dual -connectivity, DC; whether decoding and validity checking have been performed; availability of contention-free random access, CFRA, resources; and number of MIMO layers for data transmission or reception.

12. The method of claim 11, wherein the settings for CA and/or DC include one or more of the following: whether CA is configured; number of secondary cells, SCells, configured for CA; whether configured SCells are activated or deactivated; whether DC is configured; and whether the UE’s secondary cell group, SCG, is activated or deactivated.

13. The method of any of claims 1-12, wherein the one or more conditional L3 candidate configurations are conditional handover, CHO, candidate configurations for respective CHO candidate cells.

14. The method of any of claims 1-13, wherein selectively performing (740) reestablishment or fast failure recovery to the selected cell further comprises: performing (742) fast failure recovery based on LTM when the selected cell is among the LTM candidate cells but not among the common mobility candidate cells; performing (743) fast failure recovery based on conditional L3 mobility when the selected cell is among the conditional L3 mobility candidate cells but not among the common mobility candidate cells; and performing (744) reestablishment when the selected cell is neither among the LTM candidate cells nor among the conditional L3 mobility candidate cells.

15. The method of any of claims 1-14, wherein the radio-related failure is one of the following: radio link failure, RLF;

L3 handover failure;

L3 reconfiguration with sync failure;

LTM cell switch failure; conditional L3 mobility execution failure; beam failure detected, BFD; and radio link control, RLC, unrecoverable error.

16. User equipment, UE (210, 510, 610, 812, 900) configured for operation in a radio access network, RAN (199, 804), the UE comprising: communication interface circuitry (912) configured to communicate with cells of the RAN; and processing circuitry (902) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive from the RAN a plurality of candidate configurations for mobility candidate cells, including: one or more conditional layer-3, L3, candidate configurations for respective conditional L3 mobility candidate cells, and one or more layer- l/layer-2 triggered inter-cell mobility, LTM, candidate configurations for respective LTM candidate cells, wherein the conditional L3 mobility candidate cells and the LTM candidate cells include one or more common mobility candidate cells; detect a radio-related failure; select a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting one of the common mobility candidate cells when one or more first conditions are fulfilled; and selectively perform reestablishment or fast failure recovery to the selected cell, including selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is one of the common mobility candidate cells.

17. The UE of claim 16, wherein the processing circuitry and the communication interface circuitry are further configured perform operations corresponding to the methods of any of claims 2-15.

18. User equipment, UE (210, 510, 610, 812, 900) configured for operation in a radio access network, RAN (199, 804), the UE being further configured to: receive from the RAN a plurality of candidate configurations for mobility candidate cells, including: one or more conditional layer-3, L3, candidate configurations for respective conditional L3 mobility candidate cells, and one or more layer- l/layer-2 triggered inter-cell mobility, LTM, candidate configurations for respective LTM candidate cells, wherein the conditional L3 mobility candidate cells and the LTM candidate cells include one or more common mobility candidate cells; detect a radio-related failure; select a cell of the RAN for recovery from the radio-related failure based on fulfillment of one or more conditions, including selecting one of the common mobility candidate cells when one or more first conditions are fulfilled; and selectively perform reestablishment or fast failure recovery to the selected cell, including selectively performing fast failure recovery based on LTM or conditional L3 mobility when the selected cell is one of the common mobility candidate cells.

19. The UE of claim 18, being further configured to perform operations corresponding to the methods of any of claims 2-15.

20. Non-transitory, computer-readable medium (910) storing computer-executable instructions that, when executed by processing circuitry (902) of user equipment, UE (210, 510, 610, 812, 900) configured for operation in a radio access network, RAN (199, 804), configure the UE to perform operations corresponding to the methods of any of claims 1-15.

21. Computer program product (914) comprising computer-executable instructions that, when executed by processing circuitry (902) of user equipment, UE (210, 510, 610, 812, 900) configured for operation in a radio access network, RAN (199, 804), configure the UE to perform operations corresponding to the methods of any of claims 1-15.