WO2025144095A1

WO2025144095A1 - Reporting user equipment beam failure detection and recovery after l1/l2-triggered mobility (ltm)

Info

Publication number: WO2025144095A1
Application number: PCT/SE2024/051081
Authority: WO
Inventors: Icaro Leonardo DA SILVA; Marco BELLESCHI; Antonino ORSINO; Ali PARICHEHREHTEROUJENI; Pradeepa Ramachandra
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-12-29
Filing date: 2024-12-13
Publication date: 2025-07-03
Anticipated expiration: 2026-06-29

Abstract

Embodiments include methods for a user equipment (UE) configured for layer-1/layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN). Such methods include performing an LTM cell switch from a first cell served by a first RAN node to a second cell served by a second RAN node and, based on monitoring beam(s) of the second cell after the LTM cell switch, identifying a beam failure detected (BFD) in at least a first beam of the second cell. Such methods include, based on the BFD in at least the first beam, selecting a second beam in the second cell and performing beam failure recovery (BFR) in the second beam. Such methods include selectively logging information associated with the BFD and/or the BFR, and sending the logged information to the first RAN node or to the second RAN node. Other embodiments include complementary methods for first and second RAN nodes.

Description

REPORTING USER EQUIPMENT BEAM FAILURE DETECTION AND RECOVERY AFTER L1/L2-TRIGGERED MOBILITY (LTM)

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 layer- 1 or layer-2 triggered inter-cell mobility (LTM) operations followed by beam failure detection and recovery.

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).

Although not shown, in some deployments the 5GC may be replaced by an Evolved Packet Core (EPC), which conventionally has been used together with a fourth-generation Long-Term Evolution (LTE) Evolved UMTS RAN (E-UTRAN). In such deployments, gNBs (e.g., 100, 150) may connect to one or more Mobility Management Entities (MMEs) in the EPC via respective Sl-C interfaces and to one or more Serving Gateways (SGWs) in EPC via respective NG-U interfaces.

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 may also use various directional beams to provide coverage in the respective cells. In general, a 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.

Self-Organizing Networks (SON) is an automation technology used to improve the planning, configuration, management, optimization, and healing of mobile RANs. SON features can broadly be categorized as either self-optimization or self-configuration, and are described in 3GPP TS 38.300 (v!7.6.0) for NR networks and in 3GPP TS 36.300 (vl7.5.0) for LTE networks.

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 from a serving cell to a neighbor cell. 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 to declare radio link failure (RLF) or handover failure (HOF). This can occur before the UE sends a measurement report in a source cell, before the UE receives a handover command to a target cell, shortly after the UE executes a successful handover to the target cell, or upon a HOF to the target cell.

An RLF reporting procedure was introduced as part of the mobility robustness optimization (MRO) in LTE Rel-9. In this procedure, a UE logs relevant information at the time of RLF and later reports such information to the network via a target cell to which the UE ultimately connects (e.g., after reestablishment). The reported information can include RRM measurements of various neighbor cells prior to the mobility operation (e.g., handover). Based on the UE’s RLF report and knowledge about the cell in which cell the UE reestablished its connection, the RAN node serving the source cell in which the RLF occurred can determine whether it was caused due to a coverage hole or due to configuration of handover-related parameters.

As specified in 3GPP document RP-213565, NR Rel-18 includes a Work Item on NR mobility enhancements, including in the technical area of L1/L2 based inter-cell mobility, also referred to as L1/L2 triggered mobility (LTM). 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 layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and PSCell (e.g., when dual connectivity is configured), as well as release/add SCells (e.g., when CA is configured).

Currently, all inter-cell mobility involves complete layer 2 (L2, e.g., MAC) and layer 1 (LI, i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. A goal of the Rel-18 mobility enhancements is to facilitate serving cell changes via L1/L2 signaling to address these problems or difficulties.

SUMMARY

To initiate or trigger LTM by a UE, the serving RAN node sends the UE an LTM cell switch command including an indication of an LTM candidate cell and an indication of a beam based on which the UE should access the indicated LTM candidate cell. In 5G/NR, the beam indication is given as a transmission configuration indicator (TCI) state identifier (ID) associated with the LTM candidate cell, which may be indicated by an LTM candidate configuration ID. In response, the UE performs the LTM cell switch, accesses the indicated cell/beam, and transmits a message indicating that the LTM operation is complete.

Shortly after transmitting the complete message indicating a successful LTM cell switch, the UE may declare beam failure detection (BFD) for the indicated beam (e.g., TCI state ID=X) used to access the LTM candidate cell (also referred to as “target cell” once the UE performs the LTM cell switch). The UE then initiates a beam failure recovery (BFR) procedure by which it selects another beam (e.g. TCI state ID=Y) in the target cell and continues communication without declaring an RLF. However, the network remains unaware of this condition, which can cause various problems, issues, and/or difficulties.

An object of embodiments of the present disclosure is to improve reporting of BFD/BFR by UEs in conjunction with LTM, such as by providing, enabling, and/or facilitating solutions to exemplary problems summarized above and described in more detail below.

Embodiments include methods (e.g., procedures) for a UE configured for LTM in a RAN (e g., E-UTRAN, NG-RAN). These exemplary methods include performing an LTM cell switch from a first cell served by a first RAN node to a second cell served by a second RAN node. These exemplary methods also include, based on monitoring one or more beams of the second cell after the LTM cell switch, identifying a beam failure detected (BFD) in at least a first beam of the second cell. These exemplary methods also include, based on the BFD in at least the first beam, selecting a second beam in the second cell and performing beam failure recovery (BFR) in the second beam. These exemplary methods also include selectively logging information associated with at least one of the BFD and the BFR. These exemplary methods also include sending the logged information to the first RAN node or to the second RAN node.

In some embodiments, performing the LTM cell switch includes the following operations:

• receiving, from the first RAN node, one or more configurations associated with respective one or more LTM candidate cells, including the second cell;

• performing layer- 1 measurements on the LTM candidate cells and reporting the LI measurements to the first RAN node; and

• in response to the reported layer- 1 measurements, receiving from the first RAN node an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell,

• performing the LTM cell switch in response to the LTM cell switch command.

In some of these embodiments, the LTM candidate cell configuration identifies the one or more beams in the second cell to be monitored for BFD, including the first beam. Also, BFR is performed in the second beam based on identifying BFD in all of the one or more beams.

In other of these embodiments, the LTM candidate cell configuration does not identify any beams in the second cell to be monitored for BFD, the first beam is monitored in the second cell based on the indication of the first beam included with the LTM cell switch command, and BFR is performed in the second beam based on identifying BFD in the first beam.

In some of these embodiments, the information associated with at least one of the BFD and the BFR is logged selectively by the UE based on one or more of the following:

• a logging configuration received from the first RAN node;

• a configurable UE timer;

• whether the first beam indicated by the LTM cell switch command is also a beam configured for BFD monitoring in the second cell;

• whether any beam switches occurred between completion of the LTM cell switch and identification of the BFD in at least the first beam; and

• whether the second cell is a primary cell or a secondary cell. Other embodiments include exemplary methods (e.g., procedures) for a second RAN node configured to facilitate LTM by UEs in a RAN. In general, these exemplary methods can be complementary to the exemplary methods for a UE summarized above.

These exemplary methods include, after an LTM cell switch by a UE from a first cell served by a first RAN node to a second cell served by the second RAN node, performing BFR for the UE in a second beam of the second cell. The BFR is responsive to a BFD by the UE in at least a first beam of the second cell. These exemplary methods also include at least one of the following operations:

• selectively logging first information associated with at least one of the BFD and the BFR, and

• receiving from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE.

These exemplary methods also include sending to the first RAN node at least one of the first information and the second information.

In some embodiments, the first information is logged selectively by the second RAN node based on one or more of the following:

• a reporting request received from the first RAN node;

• a relation between the following: a logging threshold, and a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam;

• whether any beam switches for the UE occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and

• whether the second cell is a primary cell or a secondary cell for the UE.

In some of these embodiments, the reporting request is one of the following:

• a UE-specific reporting request, received together with an indication of the LTM cell switch of the UE from the first cell to the second cell; or

• a non-UE-specific reporting request.

Other embodiments include exemplary methods (e.g., procedures) for a first RAN node configured to facilitate LTM by UEs in a RAN. In general, these exemplary methods can be complementary to the exemplary methods for a UE and a second RAN node summarized above.

These exemplary methods include initiating an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by a second RAN node. These exemplary methods also include, after completion of the LTM cell switch, receiving one or more of the following from the second RAN node:

• first information logged by the second RAN node and associated with at least one of the following: a BFD by the UE in at least a first beam of the second cell, and a subsequent BFR by the UE in a second beam of the second cell; and

• second information logged by the UE and associated with at least one of the BFD and the BFR.

In some embodiments, initiating the LTM cell switch includes the following operations:

• sending to the UE one or more configurations associated with respective one or more LTM candidate cells, including the second cell;

• receiving from the UE a report of layer- 1 measurements performed on the LTM candidate cells; and

• in response to the reported layer- 1 measurements, sending to the UE an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell.

In some embodiments, these exemplary methods also include performing one of the following operations based on the received one or more of the first information and the second information:

• selecting the second beam, instead of the first beam, as a target beam for a subsequent LTM cell switch of a UE from the first cell to the second cell; or

• selecting a third cell, instead of the second cell, as a target cell for a subsequent LTM cell switch of a UE from the first cell.

Various examples of first information selectively logged by the second RAN node and provided to the first RAN node are described herein. Also, various examples of the (second) information selectively logged by the UE and provided to the first RAN node, via the second RAN node, are described herein.

Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g, base stations, eNBs, gNBs, ng-eNBs, etc.) 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 and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

These and other embodiments described herein may provide various advantages, benefits, and/or solutions to problems. For example, the RAN node (i.e., serving the source cell) that selected the target cell beam indicated in the LTM cell switch command may become aware of the UE’s BFD and BFR (e.g., to a non-indicated beam) that occurred shortly after the UE’s successful LTM cell switch. Based on this information, the RAN node may select different target cell beam(s) to be indicated in subsequent commands for LTM cell switch from the source cell to the target cell, or even select a different target cell. At a high level, embodiments may improve UE mobility in RANs.

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 5G/NR user plane (UP) and control plane (CP) protocol stacks.

Figure 3 shows a logical architecture for an NG-RAN node.

Figure 4 shows various self-organizing network (SON) functionality.

Figure 5 shows a signaling diagram for an exemplary LTM cell switch procedure.

Figures 6-8 show signaling diagrams for procedures involving BFD and BFR shortly after a successful LTM cell switch by a UE, according to various embodiments of the present disclosure.

Figure 9 shows a flow diagram of an exemplary method for a UE (e.g, wireless device), according to various embodiments of the present disclosure.

Figure 10 shows a flow diagram of an exemplary method for a second RAN node (e.g., base station, eNB, gNB, ng-eNB, etc.), according to various embodiments of the present disclosure.

Figure 11 shows a flow diagram of an exemplary method for a first RAN node (e.g., base station, eNB, gNB, ng-eNB, etc.), according to various embodiments of the present disclosure.

Figure 12 shows a communication system according to various embodiments of the present disclosure.

Figure 13 shows a UE according to various embodiments of the present disclosure.

Figure 14 shows a network node according to various embodiments of the present disclosure.

Figure 15 shows a block diagram of a virtualization environment in which various embodiments of the present disclosure may be virtualized.

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, various terms are used throughout the description, including the examples given below.

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.

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.

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

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.

As used herein, a “node” (without prefix) can be any type of node that can operate in or with a wireless network (including RAN and/or core network), including a radio access node (or equivalent term), a core network node, or a 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 3GPP 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 exemplary 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 handles 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 RRC IDLE 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 an NG-RAN node (e.g., gNB or ng-eNB) arranged in the split CU/DU architecture, such as gNB 100 in Figure 1. This logical architecture separates the CU into CP and UP functionality, called CU-C (or CU-CP) and CU-U (or CU-UP) 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). Moreover, the CU-U and CU-C can communicate via an El interface. Each DU may be connected to only one CU-C, and each CU-U may be connected to only one CU-C. However, a single DU may be connected to multiple CU-Us under the control of the same CU-C, or a single CU-U may be connected to multiple DUs under the control of the same CU-C. Note that the terms “Central Entity” and “Distributed Entity” in Figure 3 refer to physical network nodes.

3GPP Rel-10 introduced support for channel bandwidths larger than 20 MHz in LTE networks. To remain compatible with UEs from earlier releases (e.g., LTE Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the same structure as an LTE Rel-8 carrier. A Rel-10 UE can receive the multiple CCs based on Carrier Aggregation (CA). The CCs can also be considered “cells,” such that a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells) that are referred to collectively as a “cell group.” LTE Rel-12 introduced dual connectivity (DC) whereby a UE is connected simultaneously to a master node (MN) that provides a master cell group (MCG) and a secondary node (SN) that provides a secondary cell group (SCG).

Each cell group includes one MAC entity, a set of logical channels with associated RLC entities, a primary cell (PCell or PSCell), and optionally one or more secondary cells (SCells). The term “Special Cell” (or “SpCell” for short) refers to the PCell of the MCG or the PSCell of the SCG depending on whether the UE’s MAC entity is associated with the MCG or the SCG. In non-DC operation (e.g., carrier aggregation), SpCell refers to the PCell. An SpCell is always activated and supports physical UL control channel (PUCCH) transmission and contention-based random access by UEs.

NR includes support for CA and DC in Rel-15 and thereafter. 3GPP TR 38.804 (vl4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply NR, LTE, or both.

Self-Organizing Networks (SON) is an automation technology used to improve the planning, configuration, management, optimization, and healing of mobile RANs. SON functionality can broadly be categorized as either self-optimization or self-configuration. Selfoptimization employs UE and network measurements to auto-tune the RAN. This occurs when RAN nodes are in an operational state, after the node’s RF transmitter interface is switched on. Self-configuration operations include optimization and adaptation, which are typically performed before the RAN nodes are in operational state.

Self-configuration is a pre-operational process in which newly deployed RAN nodes (e.g., eNBs or gNBs) in a pre-operational state are configured by automatic installation procedures to get the necessary basic configuration for system operation. Pre-operational state generally refers to the time when the node is powered up and has backbone connectivity until the node’s RF transmitter is switched on. Self-configuration operations in pre-operational state include (A) basic setup and (B) initial radio configuration, which include the following sub-operations shown in Figure 4:

• (a-1) Configuration of IP address and detection of operations administration and maintenance (0AM);

• (a-2) Authentication of RAN node;

• (a-3) Associate to access gateway (aGW); • (a-4) Downloading of RAN node software (SW) and operational parameters;

• (b-1) Neighbor list configuration; and

• (b-2) Coverage/capacity-related parameter configuration.

Self-optimization is a process in which UE and network measurements are used to autotune the network. This occurs when the nodes are in operational state, which generally refers to when a node’s RF transmitter interface is switched on. Self-configuration operations include optimization and adaptation, which includes the following sub-operations shown in Figure 4:

• (c-1) Neighbor list optimization; and

• (c-2) Coverage/capacity control.

Self-configuration and self-optimization features for NR networks are described in 3GPP TS 38.300 (vl7.6.0) and for LTE networks in 3GPP TS 36.300 (vl7.5.0). These features include dynamic configuration, automatic neighbor relations (ANR), mobility load balancing (MLB), mobility robustness optimization (MRO), random access channel (RACH) optimization, capacity and coverage optimization (CCO), and mobility settings change.

Seamless mobility is a key feature of 3GPP radio access technologies (RATs). 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. 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 RRCReconflguration message with a reconflgurationWithSync 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 is based on 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 mobility 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).

A UE typically triggers an internal RLF procedure when something unexpected happens in any of these mobility-related procedures. The RLF procedure involves interactions between RRC and lower layer protocols such as PHY (or LI), MAC, RLC, etc. including radio link monitoring (RLM) on LI.

The principle of RLM is similar in LTE and NR. In general, the UE monitors link quality of the UE’s serving cell and uses that information to decide whether the UE is in-sync (IS) or out- of-sync (OOS) with respect to that serving cell. If RLM (i.e., by Ll/PHY) indicates number of consecutive OOS conditions to the RRC layer, then RRC starts an RLF procedure and declares RLF after expiry of a timer (e.g., T310). The LI RLM procedure is carried out by comparing the estimated measurements to some targets Qout and Qin, which correspond to block error rates (BLERs) of hypothetical transmissions from the serving cell. Exemplary values of Qout and Qin are 10% and 2%, respectively. In NR, the network can define RS type (e.g., CSI-RS and/or SSB), exact resources to be monitored, and the BLER target for IS and OOS indications.

In case of HOF and RLF, the UE may take autonomous actions such as selecting a cell and initiating reestablishment to remain reachable by the network. In general, a UE declares RLF only when the UE realizes that there is no reliable radio link available between itself and the network, which can result in poor user experience. Also, reestablishing the connection requires signaling with a newly selected cell (e.g., random access procedure, exchanging various RRC messages, etc.), which introduces latency until the UE can again reliably transmit and/or receive user data with the network. Potential causes for RLF include:

1) Radio link problem indicated by PHY (e.g., expiry of RLM -related timer T310);

2) Random access problem indicated by MAC entity;

3) Expiry of a measurement reporting timer (e.g., T312), due to not receiving a HO command from the network while the timer is running despite sending a measurement report;

4) Reaching a maximum number of RLC retransmissions;

5) Consistent UL LBT failures while operating in unlicensed spectrum; and

6) Failing a beam failure recovery (BFR) procedure. On the other hand, HOF is caused by expiry of T304 timer while performing the handover to the target cell.

Since RLF leads to reestablishment in a new cell and degradation of UE/network performance and end-user experience, it is in the interest of the network to understand the reasons for UE RLF and to optimize mobility-related parameters (e.g., trigger conditions of measurement reports) to reduce, minimize, and/or avoid subsequent RLFs. Before Rel-9 mobility robustness optimizations (MRO), only the UE was aware of radio quality at the time of RLF, the actual reason for declaring RLF, etc.

An RLF reporting procedure was introduced as part of mobility robustness optimization (MRO) in LTE Rel-9. In this procedure, a UE logs relevant information at the time of RLF and later reports such information to the network via a target cell to which the UE ultimately connects (e.g., after reestablishment). The reported information can include RRM measurements of various neighbor cells prior to the mobility operation (e.g., handover). A corresponding RLF reporting procedure was introduced as part of MRO for NR Rel-16. The UE can store the RLF report in a UE variable call varRLF-Report and retains it in memory for up to 48 hours, after which it may discard the information.

When sending certain RRC messages such as RRCReconfigurationComplete, RRCReestablishmentComplete , RRCSetup-Complete, and RRCResumeComplete, the UE can indicate it has a stored RLF report by setting a rlf-InfoAvailable field to “true.” If the gNB serving the target cell wants to receive the RLF report, it sends the UE an UEInformationRequest message with a flag “rlf-ReportReq-r!6”. In response, the UE sends the gNB an UEInformationRespon.se message that includes the RLF report, which can include any of the following information:

• Measurement quantities (RSRP, RSRQ) of the last serving cell (PCell).

• Measurement quantities of the neighbor cells in different frequencies of different RATs (e.g., EUTRA, UTRA, GERAN, CDMA2000).

• Measurement quantity (RS SI) associated with WLAN APs.

• Measurement quantity (RS SI) associated with Bluetooth beacons.

• Location information, if available (including location coordinates and velocity)

• Globally unique identity of the last serving cell, if available, otherwise the PCI and the carrier frequency of the last serving cell.

• Tracking area code of the PCell.

• Time elapsed since the last reception of the ‘Handover command’ message.

• C-RNTI used in the previous serving cell.

• Whether or not the UE was configured with a DRB having QCI = 1. Based on a UE RLF report and knowledge of the cell in which the UE reestablished its connection, the RAN node serving the UE’s original source cell can deduce whether the RLF was due to a coverage hole or handover-related parameter configurations. If the latter case, the RAN node serving the UE’s original source cell can also classify the handover-related failure as too- early, too-late, or wrong-cell.

NR Rel-15 introduced beam failure detection (BFD) and beam failure recovery (BFR). The serving RAN node configures a UE with BFD reference signals (e.g., SSB or CSI-RS) to be monitored, and the UE declares beam failure (or BFD) when a quantity of beam failure indications from LI reaches a configured threshold before a configured timer expires. After BFD, the UE initiates a RA procedure in the serving cell and selects a suitable beam to perform BFR. In a multibeam serving cell, RLF occurs when the UE is unable to find any suitable beam within the serving cell to recover the UE’s failed connection. In contrast, RLF is prevented by the UE’s successful BFR to another beam in the same cell.

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 dual connectivity is configured), as well as release/add SCells (e.g., when CA is configured). As specified in 3GPP document RP-213565, NR Rel-18 includes a Work Item on NR mobility enhancements, including in the technical area of L1/L2 based inter-cell mobility, also referred to as 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, a goal of Rel-18 L1/L2 mobility enhancements is to facilitate serving cell changes via L1/L2 signaling to address these issues. These Rel-18 L1/L2 mobility enhancements also must consider the split CU/DU architecture shown in Figures 1 and 3, 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).

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 RRCReconflguration message or a portion thereof, such as one or more lEs/fields/parameters (e.g., CellGroupConflg 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.

Figure 5 shows a signaling diagram for an exemplary LTM cell switch procedure. Although the operations are shown with numerical labels, this is done to facilitate explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

In operation 1, the UE sends a MeasurementReport message to the gNB. Based on this message, the gNB decides to configure LTM for the UE and initiates preparation of one or more LTM candidate cells. In operation 2, the gNB sends an RRCReconflguration message to the UE including LTM candidate cell configurations of one or more candidate cells. In operation 3, the UE stores the received LTM candidate cell configurations and transmits an RRCReconflgurationComplete message to the gNB.

Since a goal of LTM is to reduce interruption time for UE data transmissions, the UE needs to be ready to communicate with an LTM candidate cell upon (or shortly after) receiving the L1/L2 signaling for mobility execution from the source cell. For example, the UE must be able to transmit UL data or a scheduling request (SR) to the LTM candidate cell and/or monitor a DL control channel (e.g., PDCCH) from the LTM candidate cell. In other words, UE needs to know the cell that it is moving to so it can apply the corresponding configuration, including the correct timing alignment and/or TCI state for the cell. Likewise, in the case of inter-DU LTM, when the source DU transmits the L1/L2 signaling for mobility execution, the target DU needs to be prepared for scheduling UL and DL transmissions for the UE in the target cell, and for receiving SR from the UE.

Accordingly, the UE performs operations 4a-b before receiving any LTM cell switch command. In operation 4a, the UE performs early DL synchronization with the configured LTM candidate cells. In operation 4b, when UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. Otherwise, in operation 4b, the UE performs early TA acquisition with the candidate cell(s) as requested by the network. This is done via contention-free random access (CFRA) triggered by a physical DL control channel (PDCCH) order from the source cell, following which the UE sends a RA preamble towards the indicated LTM candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the LTM candidate cell(s), the UE doesn’t receive RA response (with TA) from the LTM candidate cell; instead, TA for the LTM candidate cell is indicated in a subsequent LTM cell switch command. Similarly, the UE doesn’t maintain a TA timer for the LTM candidate cell but relies on the RAN to guarantee the TA validity. In operation 5, the UE performs LI measurements on the configured LTM candidate cells and transmits LI measurement reports to the gNB. The UE performs such LI measurement as long as the LTM candidate cell configurations received in operation 2 remain applicable.

In operation 6, the gNB decides to trigger an LTM cell switch for the UE to one of the configured LTM candidate cells ( “target cell”) and transmits an LTM cell switch command, which is a MAC CE that includes an identifier (e.g., index) of the corresponding LTM candidate cell configurations provided to the UE in operation 2. The MAC CE may also include an identifier of a beam (e.g., a TCI State ID) by which the UE should access the target cell.

The gNB selects the identified beam based on the LI measurements reported by the UE. These are typically per-beam measurements, such as LI reference signal received power (RSRP) for synchronization signal/PBCH blocks (SSBs). These measurements may not be layer 3 (L3) filtered, so they may change relatively frequently as UE radio conditions change. As such, it may be challenging for the gNB to determine the optimal beam to indicate to the UE in the LTM cell switch command.

Upon receiving the LTM cell switch command, the UE monitors PDCCH on the indicated beam of the target cell. In other words, the UE considers the TCI state for the indicated beam/TCI state ID to be “activated” when performing the LTM cell switch. The UE also applies the configuration identified in the MAC CE.

In operation 7, if UE does not have valid TA of the target cell, the UE performs a RA procedure towards the target cell. The UE performs CFRA if the LTM cell switch command contains the necessary information, as specified in clause 6.1.3 of 3GPP TS 38.321 (v!7.7.0). In operation 8, the UE completes the LTM cell switch procedure by sending RRCReconflgurationComplete message to the gNB via the target cell. If the UE has performed a RA procedure in operation 7, the UE considers that LTM cell switch execution is successfully completed when the RA procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the gNB has successfully received its first UL data. The UE determines successful reception of its first UL data by receiving a PDCCH addressing the UE’s C-RNTI in the target cell, which schedules a new transmission following the first UL data. The PDCCH carries either a DL assignment or an UL grant addressing the same HARQ process as the first UL data.

To trigger LTM by a UE, the network sends the UE an LTM Cell Switch command an indication of an LTM candidate cell and an indication of a beam based on which the UE should access the indicated LTM candidate cell. In 5G/NR, the beam indication is given as a transmission configuration indicator (TCI) state identifier (ID) associated with the LTM candidate cell, which may be indicated by an LTM candidate configuration ID. In response, the UE performs the LTM cell switch, accesses the indicated cell/beam, and transmits a complete message.

In some scenarios, shortly after transmitting the RRCReconflgurationComplete message indicating a successful LTM cell switch, the UE may declare beam failure detection (BFD) for the indicated beam (e.g., TCI state ID=X) used to access the LTM candidate cell/target cell. The UE then initiates a BFR procedure by which it selects another beam (e.g. TCI state ID=Y) in the target cell and continues communication without declaring an RLF. However, the network remains unaware of this condition. Although 3GPP has indicated some interest in specifying SON/MRO- related enhancements for LTM, no specific solutions have been identified.

Accordingly, embodiments of the present disclosure address these problems and/or issues by flexible and efficient techniques in which a UE logs and reports various information related to BFD/BFR that occurred shortly after an LTM cell switch, when the UE has not declared RLF in relation to the BFD. The UE reports this information to the RAN node that provides the target cell for the LTM cell switch, or to the RAN node that provides the source cell for the LTM cell switch, according to various embodiments described below. Alternately or in addition, the RAN node that provides the target cell can log information about the UE’s BFD/BFR that occurred shortly after the UE’s LTM cell switch. In case the RAN node logs such information and/or receives it from the UE, that RAN node can forward the collected information to the RAN node that provides the source cell.

Embodiments of the present disclosure may provide various advantages and/or benefits. For example, the RAN node (i.e., serving the source cell) that selected the target cell beam indicated in the LTM cell switch command may become aware of the UE’s BFD and BFR (e.g., to a non-indicated beam) that occurred shortly after the UE’s successful LTM cell switch. Based on this information, the RAN node may select different target cell beam(s) to be indicated in subsequent commands for LTM cell switch from the source cell to the target cell, or even select a different target cell. At a high level, embodiments may improve UE mobility in RANs.

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 RRCReconflguration 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 RRCReconflguration 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 DL pre-sync, e.g., for early TCI state activation;

• a configuration for UL pre-sync, 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 phrase “shortly after a successful LTM cell switch” (or similar) is used throughout the present disclosure. In this context, whether an event is (or isn’t) “shortly after a successful LTM cell switch” can be determined based on one or more time durations or time thresholds that may be predetermined (e.g., by specification), pre-configured (e.g., in a manner unrelated to the LTM cell switch), or configured in association with the LTM cell switch. For example, certain embodiments discussed below involve a configurable timer that runs after a successful LTM cell switch, such that expiration of the timer ends the period “shortly after a successful LTM cell switch”.

Figures 6-8 show signaling diagrams for procedures involving BFD and BFR shortly after a successful LTM cell switch by a UE (610) from a first cell served by a first RAN node (620) to a second cell served by a second RAN node (630), according to various embodiments of the present disclosure.

The following description applies to the initial operations shown in all three figures. Initially, the UE receives from the first RAN node an LTM candidate cell configuration for the second cell served by the second RAN node. Subsequently, the UE performs lower layer (e.g., LI) measurements on its configured LTM candidate cells, including the second cell. The UE reports the lower layer measurements to the first RAN node via the first cell.

Based on the UE’s lower layer measurement report(s), the first RAN node determines to initiate an LTM cell switch by the UE. The first RAN node sends the UE an LTM cell switch command that includes an indication of the second cell as the target cell (e.g., based on an identifier of the configuration previously provided) and an indication of a first beam by which the UE should access the second cell.

Note that the first beam may correspond to a spatial direction in which a reference signal (RS) or a synchronization signal (SS, e.g., SSB) is transmitted by the second RAN node in the second cell. In addition, the first beam may also correspond to a TCI state configuration and the indication of the first beam in the LTM cell switch command may correspond to a first TCI state ID that points to the TCI state configuration, which comprises the RS or the SS configured as the QCL source for the TCI state identified in the LTM cell switch command.

Based on these indications, the UE performs a successful LTM cell switch to the second cell and begins to monitor the first beam, e.g., for PDCCH DL control information (DCI) intended for the UE. At some point shortly after the successful LTM cell switch, the UE declares BFD of the first beam based on the monitoring. This triggers a BFR by the UE, which selects a second beam associated with the second cell during the BFR procedure. Since the UE was able to identify the suitable second beam to continue communication with the second RAN node via the second cell, the UE does not declare RLF.

In some embodiments, the UE monitors the first beam (e.g. an SSB associated with an SSB index and/or a CSI-RS associated with a CSI-RS resource identifier) for BFD after the successful LTM cell switch because it is explicitly indicated in the LTM candidate cell configuration as a beam to be monitored for BFD in the second (target) cell. In other words, the LTM candidate cell configuration for the second cell identifies RS to be monitored for BFD in the second cell, including but not necessarily limited to RS associated with the first beam. In case the UE is configured with RS associated with other beams to be monitored in the second cell, a BFD is declared upon “failure” in the all of the configured beams.

In other embodiments, the UE monitors that first beam (e.g. an SSB associated with an SSB index and/or a CSI-RS associated with a CSI-RS resource identifier) because it is associated with the TCI state ID to be activated in the second cell, as indicated in the LTM cell switch command. This may occur when the LTM candidate cell configuration for the second cell does not identify RS to be monitored for BFD in the second cell. In such case, the UE monitors the RS configured as Quasi-Co-Location (QCL) source for the TCI state to be activated in the second cell, which is the RS of the first beam indicated in the LTM cell switch command. In that case, a BFD means a “failure” in the first beam.

In some embodiments, the UE triggers a BFR to a primary cell (e.g. PCell, PScell, SpCell), causing the UE to initiate a RA procedure. As part of the RA procedure, the UE selects the second beam (e.g., SSB and/or CSI-RS) based on its measurements being above a configured threshold (e.g., RSRP). In some embodiments, the second beam is selected from one or more BFR candidate beams configured for the UE in the second cell (e.g., as part of the LTM candidate cell configuration for the second cell). After selecting the second beam, the UE determines a RA resource (e.g. time/frequency domain resource) associated with the second beam and transmits a RA preamble in the selected RA resource, based on which the UE receives a RA response (RAR) from the second RAN node..

According to the embodiments illustrated by Figure 6, the UE logs information associated with the BFD and the BFR that occurred in the second cell shortly after the successful LTM cell switch. The UE can log various information in accordance with different embodiments, as described in more detail below. Note that the logging of the BFD information and the BFR information is not restricted to occur in any particular order. For example, information associated with both BFD and BFR can be logged at the end of the BFR procedure. The UE subsequently sends a report with the logged information associated with the BFD/BFR to the second RAN node via the second cell. For example, the logged information may be included in a successful LTM cell switch report, a successful handover report (SHR) associated with LTM cell switch, and/or a random access (RA) report after successful BFR. Based on determining that the reported BFD/BFR information occurred shortly after the UE’s LTM cell switch from the first cell, the second RAN node sends the reported information to the first RAN node that serves the first cell.

According to embodiments illustrated by Figure 7, the UE logs information associated with the BFD and the BFR that occurred in the second cell shortly after the successful LTM cell switch. The UE continues performing and reporting lower layer (e.g., LI) measurements on various LTM candidate cells, including the first cell. Based on the UE’s lower layer measurement report(s), the second RAN node determines to initiate an LTM cell switch by the UE. The second RAN node sends the UE an LTM cell switch command that includes an indication of the first cell as the target cell. As mentioned above, the LTM cell switch command may include an indication of a beam by which the UE should access the first cell.

After the UE performs a successful LTM cell switch from the second cell back to the first cell, the UE identifies that it has logged information associated with BFD/BFR that occurred in the second cell shortly after the UE’s successful LTM cell switch from the first cell. The UE sends a report with the logged information associated with the BFD/BFR to the first RAN node via the first cell.

According to embodiments illustrated by Figure 8, the second RAN node logs information associated with the UE’s BFD and BFR that occurred in the second cell shortly after the UE’s successful LTM cell switch from the first cell. Various examples of such information logged by the second RAN node are discussed below. Based on determining that the BFD/BFR occurred shortly after the UE’s LTM cell switch from the first cell, the second RAN node sends the logged BFD/BFR information to the first RAN node that serves the first cell.

Other embodiments may involve a combination of certain aspects of Figure 6 and certain aspects of Figure 8. For example, both the UE and the second RAN node may log information associated with the UE’s BFD/BFR that occurred in the second cell shortly after the UE’s earlier successful LTM cell switch from the first cell. The UE reports its logged information to the second RAN node, which combines and/or correlates the reported information with its own logged information about the same events. The second RAN node sends the combined and/or correlated information to the first RAN node.

In some embodiments, the logged information associated with the BFD includes identifying information and/or one or more measurements (e.g. RSRP, RSRQ, and/or SINR for an SSB or a CSI-RS) for each of one or more beams being monitored for BFD in the second cell, based on which the BFD was triggered. In various embodiments, the one or more beams being monitored (leading to BFD) include the first beam and possibly other beams, as discussed above. The reported information may be used by the first RAN node for selection of beams to indicate in subsequent LTM cell switch commands to the second cell (e.g., in similar radio conditions).

The identifying information may include beam IDs or indices, TCI state IDs, RS IDs, synchronization signal IDs, SSB indices), CSI-RS resource IDs, etc. One benefit of logging and reporting this identifying information and is that it enables the first RAN node to understand which beams have failed in the second cell shortly after the UE’s LTM cell switch, suggesting that these failed beams were not good candidate beams for the LTM cell switch.

For example, the logged measurements may include RSRP, RSRQ, and/or SINR for an SSB or a CSI-RS. The logged measurements may be unfiltered (e.g., “raw”) or filtered based on averaging some number of raw samples over a time period. One benefit of logging and reporting measurements is that it enables the first RAN node to understand radio conditions of the one or more beams that failed in the second cell shortly after the LTM cell switch, such that they were not good candidate beams for the LTM cell switch. Moreover, the first RAN node can compare the reported measurements after LTM cell switch to the measurements received from the UE that led to the LTM cell switch. This comparison may indicate the degree to which radio conditions in the monitored beams changed after the LTM cell switch.

In some embodiments, the logged information associated with the BFD includes BFD state information when BFD was declared, such as the number of beam failure instances (BFI) and/or a value of a BFD-related timer. This state information may be based on parameters that were included the LTM candidate cell configuration. One benefit of logging this information is that it enables the first RAN node to distinguish poor radio conditions in the first beam from a sub- optimal BFD configuration for the UE in the second cell. For example, if the timer value and/or the BFI instances are relatively large, it indicates that the first beam after the LTM cell switch was persistently in bad radio conditions, which led to the BFD. On the other hand, if the timer value and/or the BFI instances were relatively small, it suggests a sub-optimal BFD configuration in the second cell (i.e., the BFD was declared too soon).

In some embodiments, the logged information associated with the BFD includes the duration between initiating the successful LTM cell switch to the second cell and occurrence of BFD in the second cell. One benefit of logging this information is that it enables the first RAN node to understand how long it took for the BFD in the first beam. When that reported duration is relatively short, it suggests that the first beam was not a proper choice for LTM cell switch. This may be supported by the logged information about BFR in the second beam, especially when the second beam could have been selected by the first RAN node to be indicated in the LTM cell switch command. On the other hand, when the reported duration is relatively long (or not short), it suggests that condition of the first beam may have changed over the duration due to UE mobility after the LTM cell switch (or other reasons) and that the first beam may have been a proper choice to indicate in the LTM cell switch command.

In some embodiments, the logged information associated with the BFD includes a location at which BFD occurred. One benefit of logging this information is that it enables the first RAN node to understand how far away UE moved from the location at which the LTM cell switch occurred, which is assumed to be logged by the UE in a similar manner as for conventional L3 handover. When the reported location is relatively close to the location at which the LTM cell switch occurred, it suggests that the first beam was not a proper choice for LTM cell switch. This may be supported by the logged information about BFR in the second beam, especially when the second beam could have been selected by the first RAN node to be indicated in the LTM cell switch command. On the other hand, when the reported location is relatively distant to the location at which the LTM cell switch occurred, it suggests that condition of the first beam may have changed due to UE mobility after the LTM cell switch and that the first beam may have been a proper choice to indicate in the LTM cell switch command.

In some embodiments, the logged information associated with the BFD includes a UE mobility state when BFD occurred or upon initiating the successful LTM cell switch to the second cell. One benefit of logging this information is that it enables the first RAN node to understand how fast the UE moved from the location at which the UE performed LTM cell switch. When that reported mobility state is “low mobility” or “low speed”, it indicates that the first beam was not a proper choice for LTM cell switch. This may be supported by the logged information about BFR in the second beam, especially when the second beam could have been selected by the first RAN node to be indicated in the LTM cell switch command. When the reported mobility state is “high mobility” or “high speed”, it suggests that condition of the first beam may have changed due to UE mobility after the LTM cell switch and that the first beam may have been a proper choice to indicate in the LTM cell switch command.

In some embodiments, when the UE sends the logged information associated with the BFD in a RA report upon successful completion of BFR, the RA report includes an indication of whether the BFD occurred in the first beam indicated in the LTM cell switch command, and/or whether any beam switch occurred between completion of the LTM cell switch and the BFD. This information can be useful for the second (target) RAN node to determine whether the first beam in which BFD occurred was selected by the first (source) RAN node or by the second (target) RAN node. For example, if no beam switch occurred, the second RAN node can determine that the beam was wrongly selected by the first RAN node. In contrast, if a beam switch has occurred, the second RAN node can determine that it should have selected earlier another beam for the UE.

In some embodiments, the logged information associated with the BFR includes identifying information and/or one or more measurements (e.g. RSRP, RSRQ, and/or SINR for an SSB or a CSI-RS) for each of one or more beams configured for BFR in the second cell. In various embodiments, the one or more beams configured for BFR include the second beam and possibly other beams, as discussed above. The reported information may be used by the first RAN node for selection of beams to indicate in subsequent LTM cell switch commands to the second cell (e.g., in similar radio conditions).

The identifying information may include beam IDs or indices, TCI state IDs, RS IDs, synchronization signal IDs, SSB indices), CSI-RS resource IDs, etc. One benefit of logging and reporting this identifying information and is that it enables the first RAN node to understand that the second beam (and possibly other BFR candidate beams) would have been a better candidate to be indicated in the LTM cell switch command, i.e., instead of the first beam.

For example, the logged measurements may include RSRP, RSRQ, and/or SINR for an SSB or a CSI-RS. The logged measurements may be unfiltered (e.g., “raw”) or filtered based on averaging some number of raw samples over a time period. One benefit of logging and reporting measurements for the second beam is that it enables the first RAN node to understand radio conditions in the second beam shortly after the LTM cell switch, e.g., that it was a good candidate beam for the LTM cell switch. Logging and reporting measurements for other BFR candidate beams (i.e., in addition to the second beam) may be beneficial since when the LTM cell switch is triggered, the first RAN node may not have LI measurements available for the second beam but may have LI measurements available for other BFR candidate beams. Moreover, the first RAN node can compare the reported measurements after LTM cell switch to the measurements received from the UE that led to the LTM cell switch. This comparison may indicate the degree to which radio conditions in the BFR candidate beams changed after the LTM cell switch.

In some embodiments, the logged information associated with the BFR includes BFR RA information for each of one or more beams configured for BFR in the second cell, such as number of RA attempts, whether BFR succeeded or failed, preamble and/or RA resources used, and/or whether power ramping was used. In more general terms, the logged BFR RA information can correspond to information logged in a RA report for BFR. One benefit of logging this information is that the first RAN node can understand conditions in the second cell that led to a successful (or failed) BFR. The first RAN node can apply this understanding when selecting beams to indicate in subsequent LTM cell switch commands to the second cell. In some embodiments, the logged information associated with the BFR includes the duration between initiating the successful LTM cell switch to the second cell and either i) selecting the second beam that resulted in successful BFR, or ii) completing successful BFR in the second cell. One benefit of logging this information is that it enables the first RAN node to understand how long it took for BFR to be completed, e.g., from the time the UE received the LTM cell switch command. When the reported duration is relatively short, it suggests that the second beam would have been a better choice to be included in the LTM cell switch command, instead of the first beam. On the other hand, when the reported duration is relatively long (or not short), it suggests some coverage instability in the second cell, such that the second beam may not have been a better choice than the first beam at the time of the LTM cell switch. Also, a relatively long duration to complete BFR and recover the UE’s connection in the second cell may cause the first RAN node to select a different target cell for subsequent LTM cell switches involving the first (source) cell.

In some embodiments, the logged information associated with the BFR includes a location at which BFR is performed. One benefit of logging this information is that it enables the first RAN node to understand how far away UE moved from the location at which the LTM cell switch occurred, which is assumed to be logged by the UE in a similar manner as for conventional L3 handover. When the reported location is relatively close to the location at which the LTM cell switch occurred, it suggests that the first beam was not a proper choice for LTM cell switch. This may be supported by the logged information associated with BFD in the first beam, as mentioned above in relation to other embodiments. On the other hand, when the reported location is relatively distant to the location at which the LTM cell switch occurred, it suggests that condition of the first beam may have changed due to UE mobility after the LTM cell switch and that the first beam may have been a proper choice to indicate in the LTM cell switch command.

In some embodiments, the logged information associated with the BFR which the UE logs comprise a UE mobility state (e.g., indicating low speed or high speed mobility) upon completing BFR or upon initiating the successful LTM cell switch to the second cell. One benefit of logging this information is that it enables the first RAN node to understand how fast the UE moved from the location at which the UE performed LTM cell switch. When that reported mobility state is “low mobility” or “low speed”, it indicates that the first beam was not a proper choice for LTM cell switch. This may be supported by the logged information associated with BFD in the first beam, as mentioned above in relation to other embodiments. When the reported mobility state is “high mobility” or “high speed”, it suggests that condition of the first beam may have changed due to UE mobility after the LTM cell switch and that the first beam may have been a proper choice to indicate in the LTM cell switch command. Note that the UE can log and report (e.g., in a single report) any combination of the information associated with the BFD (i.e., in the first beam) and the information associated with the BFR (i.e., in the second beam) discussed above. Combining logged information associated with the BFD and logged information associated with the BFR may enable the first RAN node to make informed decisions about subsequently LTM cell switches from the first (source) cell to the second (target) cell.

In some embodiments, the UE logs information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch based on one or more configurations the UE receives before the LTM cell switch. For example, the UE may receive an RRCReconflguration message that indicates one or more of the following:

• whether the UE should log information about BFD and/or BFR occurring shortly after an LTM cell switch;

• one or more thresholds or conditions for logging information about BFD and/or BFR occurring shortly after an LTM cell switch, such as a timer duration as discussed in more detail below; and

• one or more specific types of information the UE should log about BFD and/or BFR occurring shortly after an LTM cell switch, such as any of the information discussed above in relation to other embodiments.

In this manner, the first RAN node can configure the UE to perform logging only when the first RAN node sees a need to adjust its settings and/or decisions for beam indication in an LTM cell switch command to the second cell.

In some embodiments, the UE logs information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch based on a configurable timer. The UE initiates the timer when the UE determines a successful LTM cell switch and when the BFD and/or the BFR occurs while the timer is running (i.e., has not reached a terminal value), the UE logs the relevant information associated with the BFD and/or the BFR. On the other hand, when the timer expires before a BFD and/or BFR, the UE does not log the BFD and BFR information. Optionally, when the UE logs information about the LTM cell switch while the timer was running but the timer expires before all of the relevant information has been logged, the UE discards the logged information upon timer expiration.

The duration for the timer (e.g., a non-zero terminal value if the timer counts from upward from zero, an initial value if the timer counts downward to zero) may be configured by an RRCReconflguration message received from the first RAN node. One benefit of relying on such a timer is that it enables the RAN to configure a threshold (i.e., the timer duration) between what is considered “shortly” after successful LTM cell switch and what is not. In some embodiments, the UE logs information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch when the first beam, indicated in the LTM cell switch command, is also a beam configured for BFD monitoring in the second cell. When the RS for BFD in the second cell (e.g., defined in LTM candidate cell configuration) do not include the first beam indicated in the LTM cell switch command, information associated with the BFD in the second cell does not inform the first RAN node about whether the indicated first beam was a proper choice for LTM cell switch. On the other hand, when the UE is not configured with an explicitly list of RS for BFD in the target cell, the UE performs BFD monitoring based on the QCL source RS of the activated TCI state, which corresponds to the first beam indicated in the LTM cell switch command. In such case, it is beneficial to the first RAN node that the UE logs information about the BFD in the first beam.

In some embodiments, the UE logs information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch when beam switch does not occur between the successful LTM cell switch and the BFD. When a beam switch occurs (e.g. activation of a TCI state not associated with the first beam indicated in the LTM cell switch command) between the LTM cell switch and the BFD, the beam subject to BFD has been selected by the second RAN node rather than the first RAN node. In such case, the information associated with BFD is unhelpful to the first RAN node and does not need to be logged by the UE.

In some variants, the decision on whether to log information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch can be based on a combination of a configurable timer (discussed above) and whether a beam switch occurred between the successful LTM cell switch and the BFD. When the BFD and/or the BFR occurs while the timer is running (i.e., has not reached a terminal value) and no beam switch has occurred, the UE logs the information associated with the BFD and/or the BFR. If either the timer expires or a beam switch occurs before a BFD, the UE does not log the BFD and BFR information.

In some embodiments, the decision on whether to log information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch can be based on the type of cell in which the BFD occurred. For example, the UE logs BFR and/or BFD information when the BFD occurred in a primary cell that was the LTM candidate cell in the LTM cell switch. On the other hand, the UE does not log BFR and/or BFD information when the BFD occurred in a secondary cell.

In some embodiments, the decision on whether to log information associated with a BFD and/or a BFR that occurred shortly after a successful LTM cell switch can be based on the cell group (e.g., MCG, SCG) in which the BFD occurred. For example, the UE logs BFR and/or BFD information when the BFD occurred in the cell group for which the LTM cell switch was performed, but does not log BFR and/or BFD information when the BFD occurred in another cell group than the cell group in which the LTM cell switch was performed.

In some embodiments, the indication of the LTM candidate cell may correspond to a target configuration ID (e.g., Itm-Candidateld), which is an index of a candidate target configuration to apply for LTM cell switch. In some embodiments, the indication of the first (target) beam in the LTM cell switch command may correspond to one or more of the following:

• RS ID or index (e g., SSB index, SSB ID, CSI-RS resource ID);

• index associated with a RS identifier, e.g., pointing to a position in a list of SSB indices, CSI-RS resource IDs, etc.;

• TCI state ID of a TCI state in which the RS ID is a QCL source; and

• a beam identifier.

As discussed above in relation to Figure 8, in some embodiments the second RAN node logs information associated with the BFD and/or BFR by the UE shortly after a successful LTM cell switch to the second (target) cell, and sends the logged information to the first RAN node. For example, the first RAN node can be a first (source) DU that serves the first (source) cell and the second RAN node can be a second (target) DU that serves the second (target) cell, with both DUs associated with the same CU. The information logged and sent to the first RAN node can include one or more of the following:

• an indication that the UE changed beams shortly after a successful LTM cell switch;

• an indication of the UE’s BFD in the first beam indicated in the LTM cell switch command;

• an indication of the second beam in which the UE performed the successful BFR;

• the duration between the UE initiating the successful LTM cell switch to the second cell and the UE’s successful completion of BFR in the second beam;

• time elapsed since changing the UE’s serving beam in the second cell;

• an indication of BFD RS (e.g., SSB or CSI-RS) configured for the UE in the second cell;

• list of suggested beams for subsequent LTM cell switches to the second cell;

• information associated with the BFD and/or the BFR, discussed above, that was logged by the UE and sent to the second RAN node.

In some embodiments, the information sent to the first RAN node is partially derived at the second RAN node and partially received from the UE. For example, the second RAN node may determine the first beam which failed and the second beam in which the UE successfully performed BFR, and also receive an LTM success report from the UE. In such case, the second RAN node correlates the determined BFR/BFD information with the UE-reported information, prior to sending the information to the first RAN node.

In some embodiments, the second RAN node sends the first RAN node the information that it logged or received from the UE, only when the duration between completion of the UE’s successful LTM cell switch to the second cell and completion of BFR in the second beam is larger than a threshold.

In some embodiments, the second RAN node sends the above-described information in response to a request from the first RAN node for such information. In some variants, the request from the first RAN node may indicate a time period for which the second RAN node should inform the first RAN node about any BFR performed by the UE. In some variants, the request from the first RAN node may be included in a message that indicates an LTM cell switch is being triggered, such that the requested information is associated with that LTM cell switch. For example, the first RAN node (as source DU) can send a DU-CU Cell Switch Notification message to the CU, which in turn sends a CU-DU Cell Switch Notification message to the second RAN node (as target DU).

In some embodiments, the request by the first RAN node for logging and reporting by the second RAN node can be non-UE specific, e.g., for any LTM cell switch from the first cell to the second cell, or from any cell served by the first RAN node to any cell served by the second RAN node. In some variants, the first RAN node can include with the request one or more configuration parameters that limit the scope of the request, such as one or more of the following:

• a duration threshold for the logging and reporting, e.g., logging and reporting shall take place only when a duration between a UE initiating a successful LTM cell switch and the UE’s successful completion of BFR is greater (less) than the threshold. By such a threshold, the first RAN node can ensure that it receives reports for LTM cell switches that are problematic and potentially addressable.

• information associated with UE BFD/BFR to be logged and reported by the second RAN node (e.g., when time threshold is met).

• information associated with BFD/BFR logged and reported by UEs to the second RAN node, to be forwarded to the first RAN node (e.g., when time threshold is met).

One advantage of a non-UE specific request is the amount of inter-node communication is reduced, relative to requesting and configuring reporting on a UE-specific basis and/or for each LTM cell switch.

In some embodiments, when the first RAN node sends a non-UE-specific request for the second RAN node to log and report information associated with BFDs/BFRs that occur shortly after LTM cell switches to the second cell, the first RAN node can include a flag in UE-specific inter-node communication that indicates whether the current UE’s LTM cell switch is subjected to the previously requested non-UE-specific logging and reporting.

Various features of the embodiments described above correspond to various operations illustrated in Figures 9-11, which show exemplary methods (e.g., procedures) for a UE, a second RAN node, and a first RAN node, respectively. In other words, various features of the operations described below correspond to various embodiments described above. Furthermore, the exemplary methods shown in Figures 9-11 can be used cooperatively to provide various benefits, advantages, and/or solutions to problems described herein. Although Figures 9-11 show specific blocks in particular orders, the operations of the exemplary methods 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.

In particular, Figure 9 shows an exemplary method (e.g., procedure) for a UE configured for LTM in a radio access network (RAN), according to various embodiments of the present disclosure. The exemplary method can be performed by a UE (e.g., wireless device) such as described elsewhere herein.

The exemplary method includes the operations of block 910, where the UE performs an LTM cell switch from a first cell served by a first RAN node to a second cell served by a second RAN node. The exemplary method also includes the operations of block 920, where based on monitoring one or more beams of the second cell after the LTM cell switch, the UE identifies a beam failure detected (BFD) in at least a first beam of the second cell. The exemplary method also includes the operations of block 930, where based on the BFD in at least the first beam, the UE selects a second beam in the second cell and performing beam failure recovery (BFR) in the second beam. The exemplary method also includes the operations of block 940, where the UE selectively logs information associated with at least one of the BFD and the BFR (e.g., as in Figures 6-7). The exemplary method also includes the operations of block 970, where the UE sends the logged information to the first RAN node or to the second RAN node.

In some embodiments, performing the LTM cell switch in block 910 includes the following operations, labelled with corresponding sub-block numbers:

• (911) receiving, from the first RAN node, one or more configurations associated with respective one or more LTM candidate cells, including the second cell;

• (912) performing layer- 1 measurements on the LTM candidate cells and reporting the LI measurements to the first RAN node; and

• (913) in response to the reported layer- 1 measurements, receiving from the first RAN node an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell, • (914) performing the LTM cell switch in response to the LTM cell switch command.

In some of these embodiments, the information associated with at least one of the BFD and the BFR is logged selectively in block 940 based on one or more of the following:

• a logging configuration received from the first RAN node;

• a configurable UE timer;

• whether the second cell is a primary cell or a secondary cell.

In some variants of these embodiments, selectively logging information in block 940 includes the following operations, labelled with corresponding sub-block numbers:

• (941) initiating the configurable timer upon completion of the LTM cell switch;

• (942) logging the information when at least one of the BFD and the BFR occurs while the timer is running; and

• (943) refraining from logging the information when at least one of the BFD and the BFR occurs after the timer expires or reaches a terminal value.

In some variants of these embodiments, the logging configuration indicates one or more of the following:

• whether the UE should log information associated with at least one of a BFD and a BFR that occur after an LTM cell switch;

• one or more thresholds or conditions for logging information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; and

• one or more types of information that the UE should log in association with at least one of a BFD and a BFR that occur after an LTM cell switch.

In some embodiments, the logged information associated with the BFD includes one or more of the following: • identifying information for each of the one or more beams being monitored;

• one or more measurements for each of the one or more beams being monitored;

• BFD state information at the time when BFD was identified;

• a duration between initiating the LTM cell switch to the second cell and identifying BFD in at least the first beam;

• a location at which the BFD was identified;

• a UE speed or mobility state upon initiating the LTM cell switch to the second cell or when the BFD was identified; and

• an indication of whether any beam switches occurred between completion of the LTM cell switch and identification of the BFD in at least the first beam.

In some of these embodiments, the BFD state information includes one or more of the following: a number of beam failure instances in the first beam, and/or a value of a BFD-related timer.

In some embodiments, the logged information associated with the BFR includes one or more of the following:

• identifying information for each of one or more beams configured for BFR in the second cell;

• one or more measurements for each of one or more beams configured for BFR in the second cell;

• random access (RA) information for each of one or more beams configured for BFR in the second cell;

• a duration between initiating the LTM cell switch to the second cell and one of the following: selecting the second beam, or completing BFR in the second beam;

• a location at which the BFD was performed;

• a UE speed or mobility state upon initiating the LTM cell switch to the second cell or upon completing BFR in the second beam.

In some of these embodiments, for each beam, the RA information includes one or more of the following: number of RA attempts, an indication of whether BFR succeeded or failed, preamble and/or RA resources used, and whether power ramping was used.

In some embodiments, the logged information is sent to the second RAN node after the BFR in one of the following: an LTM success report, or a random access (RA) report. In other embodiments, the exemplary method also includes the operations of block 950, where the UE performs a further LTM cell switch from the second cell served by the second RAN node to the first cell served by the first RAN node. In such case, the logged information is sent to the first RAN node in block 970 based on the operations of block 960, where the UE determines after the further LTM cell switch that the logged information pertains to the first cell.

In addition, Figure 10 shows an exemplary method (e.g., procedure) for a second RAN node configured to facilitate LTM by UEs in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g, base station, eNB, gNB, ng-eNB, etc.) such as described elsewhere herein.

The exemplary method includes the operations of block 1010, where after an LTM cell switch by a UE from a first cell served by a first RAN node to a second cell served by the second RAN node, the second RAN node performs BFR for the UE in a second beam of the second cell. The BFR is responsive to a BFD by the UE in at least a first beam of the second cell. The exemplary method also includes the operations of blocks 1020 and/or 1030 (i.e., at least one of these blocks), where the second RAN node selectively logs first information associated with at least one of the BFD and the BFR (e.g., as in Figure 8) and receives from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE (e.g., as in Figures 6-7). The exemplary method also includes the operations of block 1040, where the second RAN node sends to the first RAN node at least one of the first information and the second information.

In some embodiments, the second information associated with at least one of the BFD and the BFR is logged selectively by the UE based on one or more of the following:

• a logging configuration received by the UE from the first RAN node;

• a configurable UE timer;

• whether the first beam is a beam configured for BFD monitoring in the second cell;

• whether any beam switches occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and

• whether the second cell is a primary cell or a secondary cell.

In some of these embodiments, the logging configuration can indicate any of the same information as the logging configuration described above in relation to UE embodiments.

In some embodiments, the received second information associated with the BFD includes one or more of the following:

• identifying information for each of one or more beams that were monitored by the UE for BFD;

• one or more measurements for each of the one or more beams that were monitored by the UE for BFD;

• BFD state information at time of the BFD by the UE in at least the first beam;

• a duration between the UE initiating the LTM cell switch to the second cell and the BFD by the UE in at least the first beam; • a location of the BFD by the UE in at least the first beam;

• a UE speed or mobility state when the UE initiated the LTM cell switch to the second cell or at the BFD by the UE in at least the first beam; and

• an indication of whether any beam switches occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam.

In some embodiments, the received second information associated with the BFR includes one or more of the following:

• a duration between the UE initiating the LTM cell switch to the second cell and one of the following: the UE selecting the second beam, or the UE completing BFR in the second beam;

• a location at which the UE performed BFR; and

• a UE speed or mobility state when the UE initiated the LTM cell switch to the second cell or when the UE completed BFR in the second beam.

In some embodiments, the second information is received from the UE after the BFR in one of the following: an LTM success report, or a random access (RA) report.

In some embodiments, the logged first information includes one or more of the following:

• an indication that the UE changed beams shortly after the LTM cell switch;

• an indication of the BFD detected by the UE in at least the first beam;

• an indication of the second beam in which the BFR was performed;

• a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam;

• time elapsed since changing the UE’s serving beam in the second cell;

• an indication of reference signals configured in the second cell for BFD by the UE; and • list of suggested beams for subsequent LTM cell switches to the second cell.

In some embodiments, the first information is logged selectively based on one or more of the following:

• a reporting request received from the first RAN node;

• whether the second cell is a primary cell or a secondary cell for the UE.

In some of these embodiments, the reporting request is one of the following:

• a non-UE-specific reporting request.

In some variants of these embodiments, the UE-specific reporting request indicates a time period during which the second RAN node should log and report to the first RAN node information about BFRs performed by the UE. In other variants of these embodiments, the non- UE-specific reporting request applies to one of the following:

• any LTM cell switch from the first cell to the second cell, which is followed by BFD and BFR in the second cell;

• any LTM cell switch from a source cell served by the first RAN node to a target cell served by the second RAN node, which is followed by BFD and BFR in the target cell;

• any LTM cell switch that meets one or more conditions included with the non-UE-specific reporting request.

In addition, Figure 11 shows an exemplary method (e.g., procedure) for a first RAN node configured to serve UEs via a first cell, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng-eNB, etc.) such as described elsewhere herein.

The exemplary method includes the operations of block 1110, where the first RAN node initiates an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by a second RAN node. The exemplary method also includes the operations of block 1120, where after completion of the LTM cell switch, the first RAN node receives one or more of the following from the second RAN node:

• first information that was logged by the second RAN node and is associated with at least one of the following: a BFD by the UE in at least a first beam of the second cell, and a subsequent BFR by the UE in a second beam of the second cell (e.g., as in Figure 8); and

• second information that was logged by the UE and is associated with at least one of the BFD and the BFR (e.g., as in Figures 6-7).

In some embodiments, initiating the LTM cell switch in block 1110 includes the following operations, labelled with corresponding sub-block numbers:

• (1111) sending to the UE one or more configurations associated with respective one or more LTM candidate cells, including the second cell;

• (1112) receiving from the UE a report of layer- 1 measurements performed on the LTM candidate cells; and

• (1113) in response to the reported layer-1 measurements, sending to the UE an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell.

In some of these embodiments, the LTM candidate cell configuration identifies the one or more beams in the second cell to be monitored for BFD, including the first beam. In such case, BFR is performed by the UE in the second beam based on BFD by the UE in all of the one or more beams.

In other of these embodiments, the LTM candidate cell configuration does not identify any beams in the second cell to be monitored for BFD, the first beam is monitored by the UE based on the indication of the first beam included with the LTM cell switch command, and BFR is performed by the UE in the second beam based on BFD by the UE in the first beam.

In some of these embodiments, the second information associated with at least one of the BFD and the BFR is logged selectively by the UE based on any of the same conditions or criteria discussed above in relation to UE embodiments. For example, the logging configuration sent to the UE by the first RAN node can indicate any of the same information discussed above in relation to UE embodiments.

In some embodiments, the received second information associated with the BFD can include any of the same information as the second information associated with the BFD that was discussed above in relation to second RAN node embodiments. In some embodiments, the received second information associated with the BFR can include any of the same information as the second information associated with the BFR that was discussed above in relation to second RAN node embodiments.

In some embodiments, the received first information can include any of the same information as the first information logged and sent by the second RAN node, as discussed above. In some embodiments, the first information can be logged selectively by the second RAN node based on any of the criteria or conditions discussed above in relation to second RAN node embodiments. For example, when the second RAN node logging is based on a reporting request sent to the second RAN node by the first RAN node, the reporting request can be one of the following:

• a UE-specific reporting request, sent together with an indication of the LTM cell switch of the UE from the first cell to the second cell; or

• a non-UE-specific reporting request.

Each of these types of reporting requests can have any of the same characteristics and/or content as discussed above in relation to second RAN node embodiments.

In some embodiments, the exemplary method can also include the operations of block 1130, where the first RAN node performs one of the following operations (labelled with corresponding sub-block numbers) based on the received one or more of the first information and the second information:

• (1131) selecting the second beam, instead of the first beam, as a target beam for a subsequent LTM cell switch of a UE from the first cell to the second cell; or

• (1132) selecting a third cell, instead of the second cell, as a target cell for a subsequent LTM cell switch of a UE from the first cell.

Some specific examples of these operations based on BFD/BFR information were discussed above.

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 12 shows an example of a communication system 1200 in accordance with some embodiments. In this example, communication system 1200 includes a telecommunication network 1202 that includes an access network 1204 (e.g., RAN) and a core network 1206, which includes one or more core network nodes 1208. Access network 1204 includes one or more access network nodes, such as network nodes 1210a-b (one or more of which may be generally referred to as network nodes 1210), or any other similar 3GPP access nodes or non-3GPP access points.

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 1202 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1202 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 1202, including one or more network nodes 1210 and/or core network nodes 1208.

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. , r App), or any combination thereof (the adj ective “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 0-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 1210 facilitate direct or indirect connection of UEs, such as by connecting UEs 1212a-d (one or more of which may be generally referred to as UEs 1212) to core network 1206 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 1200 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 1200 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

UEs 1212 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with network nodes 1210 and other communication devices. Similarly, network nodes 1210 are arranged, capable, configured, and/or operable to communicate directly or indirectly with UEs 1212 and/or with other network nodes or equipment in telecommunication network 1202 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in telecommunication network 1202.

In the depicted example, core network 1206 connects network nodes 1210 to one or more hosts, such as host 1216. 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 1206 includes one or more core network nodes (e.g., 1208) 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 the descriptions thereof are generally applicable to the corresponding components of core network node 1208. 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 1216 may be under the ownership or control of a service provider other than an operator or provider of access network 1204 and/or telecommunication network 1202, and may be operated by the service provider or on behalf of the service provider. Host 1216 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 1200 of Figure 12 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 1202 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1202 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1202. For example, telecommunication network 1202 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 1212 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 1204 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1204. 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 1214 communicates with access network 1204 to facilitate indirect communication between one or more UEs (e.g., 1212c and/or 1212d) and network nodes (e.g., 1210b). In some examples, hub 1214 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1214 may be a broadband router enabling access to core network 1206 for the UEs. As another example, hub 1214 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 1210, or by executable code, script, process, or other instructions in hub 1214. As another example, hub 1214 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 1214 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1214 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1214 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, hub 1214 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 1214 may have a constant/persistent or intermittent connection to network node 1210b. Hub 1214 may also allow for a different communication scheme and/or schedule between hub 1214 and UEs (e.g., UE 1212c and/or 1212d), and between hub 1214 and core network 1206. In other examples, hub 1214 is connected to core network 1206 and/or one or more UEs via a wired connection. Moreover, hub 1214 may be configured to connect to an M2M service provider over access network 1204 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1210 while still connected via hub 1214 via a wired or wireless connection. In some embodiments, hub 1214 may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to network node 1210b. In other embodiments, hub 1214 may be anon-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1210b, but which is additionally capable of operating as a communication start and/or end point for certain data channels.

In some embodiments, network node 1210 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 10-11. In some embodiments, UE 1212 may be configured to perform operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 9.

Figure 13 shows a UE 1300 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless 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.

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

UE 1300 includes processing circuitry 1302 that is operatively coupled via a bus 1304 to an input/output interface 1306, a power source 1308, a memory 1310, a communication interface 1312, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 13. 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 1302 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 1310. Processing circuitry 1302 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 1302 may include multiple central processing units (CPUs).

In the example, input/output interface 1306 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 1300. 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 1308 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 1308 may further include power circuitry for delivering power from power source 1308 itself, and/or an external power source, to the various parts of UE 1300 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1308. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1308 to make the power suitable for the respective components of UE 1300 to which power is supplied.

Memory 1310 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 1310 includes one or more application programs 1314, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1316. Memory 1310 may store, for use by UE 1300, any of a variety of various operating systems or combinations of operating systems.

Memory 1310 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 1310 may allow UE 1300 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 1310, which may be or comprise a device-readable storage medium.

Processing circuitry 1302 may be configured to communicate with an access network or other network using communication interface 1312. Communication interface 1312 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1322. Communication interface 1312 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 1318 and/or a receiver 1320 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1318 and receiver 1320 may be coupled to one or more antennas (e.g., antenna 1322) and may share circuit components, software, or firmware, or alternatively be implemented separately.

In the illustrated embodiment, communication functions of communication interface 1312 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, a UE may provide an output of data captured by its sensors, through its communication interface 1312, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

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

A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are 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 1300 shown in Figure 13.

As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another UE and/or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-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 1300 may be configured to perform operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 9.

Figure 14 shows a network node 1400 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

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

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

Network node 1400 includes processing circuitry 1402, memory 1404, communication interface 1406, and power source 1408. Network node 1400 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 1400 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 1400 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1404 for different RATs) and some components may be reused (e.g., a same antenna 1410 may be shared by different RATs). Network node 1400 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1400, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1400.

Processing circuitry 1402 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in conjunction with other network node 1400 components, such as memory 1404, to provide network node 1400 functionality.

In some embodiments, processing circuitry 1402 includes a system on a chip (SOC). In some embodiments, processing circuitry 1402 includes one or more of radio frequency (RF) transceiver circuitry 1412 and baseband processing circuitry 1414. In some embodiments, RF transceiver circuitry 1412 and baseband processing circuitry 1414 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1412 and baseband processing circuitry 1414 may be on the same chip or set of chips, boards, or units. Memory 1404 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device-readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by processing circuitry 1402. Memory 1404 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions (collectively denoted computer program 1404a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1402 and utilized by network node 1400. Memory 1404 may be used to store any calculations made by processing circuitry 1402 and/or any data received via communication interface 1406. In some embodiments, processing circuitry 1402 and memory 1404 is integrated.

Communication interface 1406 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, communication interface 1406 comprises port(s)/terminal(s) 1416 to send and receive data, for example to and from a network over a wired connection. Communication interface 1406 also includes radio frontend circuitry 1418 that may be coupled to, or in certain embodiments a part of, antenna 1410. Radio front-end circuitry 1418 comprises filters 1420 and amplifiers 1422. Radio front-end circuitry 1418 may be connected to an antenna 1410 and processing circuitry 1402. The radio front-end circuitry may be configured to condition signals communicated between antenna 1410 and processing circuitry 1402. Radio front-end circuitry 1418 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1418 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1420 and/or amplifiers 1422. The radio signal may then be transmitted via antenna 1410. Similarly, when receiving data, antenna 1410 may collect radio signals which are then converted into digital data by radio front-end circuitry 1418. The digital data may be passed to processing circuitry 1402. In other embodiments, the communication interface may comprise different components and/or different combinations of components.

In certain alternative embodiments, network node 1400 does not include separate radio front-end circuitry 1418, instead, processing circuitry 1402 includes radio front-end circuitry and is connected to antenna 1410. Similarly, in some embodiments, all or some of RF transceiver circuitry 1412 is part of communication interface 1406. In still other embodiments, communication interface 1406 includes one or more ports or terminals 1416, radio front-end circuitry 1418, and RF transceiver circuitry 1412, as part of a radio unit (not shown), and communication interface 1406 communicates with baseband processing circuitry 1414, which is part of a digital unit (not shown).

Antenna 1410 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. Antenna 1410 may be coupled to radio front-end circuitry 1418 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, antenna 1410 is separate from network node 1400 and connectable to network node 1400 through an interface or port.

Antenna 1410, communication interface 1406, and/or processing circuitry 1402 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node. Any information, data and/or signals may be received from a UE, another network node and/or any other network equipment. Similarly, antenna 1410, communication interface 1406, and/or processing circuitry 1402 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and/or signals may be transmitted to a UE, another network node and/or any other network equipment.

Power source 1408 provides power to the various components of network node 1400 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1408 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1400 with power for performing the functionality described herein. For example, network node 1400 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 1408. As a further example, power source 1408 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

Embodiments of network node 1400 may include additional components beyond those shown in Figure 14 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, network node 1400 may include user interface equipment to allow input of information into network node 1400 and to allow output of information from network node 1400. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1400. In some embodiments, network node 1400 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 10-11.

Figure 15 is a block diagram illustrating a virtualization environment 1500 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1500 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1500 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface.

Applications 1502 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1500 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein. For example, one or more virtual nodes 1502 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 10-11.

Hardware 1504 includes processing circuitry, memory that stores software and/or instructions (collectively denoted computer program 1504a, which may be in the form of a computer program product) executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1506 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1508a and 1508b (one or more of which may be generally referred to as VMs 1508), and/or perform any of the functions, features and/or benefits described in relation with some embodiments described herein. Virtualization layer 1506 may present a virtual operating platform that appears like networking hardware to the VMs 1508.

VMs 1508 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1506. Different embodiments of the instance of a virtual appliance 1502 may be implemented on one or more of VMs 1508, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

In the context of NFV, each VM 1508 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each VM 1508, and that part of hardware 1504 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1508 on top of the hardware 1504 and corresponds to the application 1502.

Hardware 1504 may be implemented in a standalone network node with generic or specific components. Hardware 1504 may implement some functions via virtualization. Alternatively, hardware 1504 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration function 1510, which, among others, oversees lifecycle management of applications 1502. In some embodiments, hardware 1504 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1512 which may alternatively be used for communication between hardware nodes and radio units.

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, and so on, as 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 carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit 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. These and similar principles are considered 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, may be used synonymously in certain instances (e.g, “data” and “information”). Although such terms may be used synonymously herein, there may be instances 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 layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: performing an LTM cell switch from a first cell served by a first RAN node to a second cell served by a second RAN node; based on monitoring one or more beams of the second cell after the LTM cell switch, identifying a beam failure detected (BFD) in at least a first beam of the second cell; based on the BFD in at least the first beam, selecting a second beam in the second cell and performing beam failure recovery (BFR) in the second beam; selectively logging information associated with at least one of the BFD and the BFR; and sending the logged information to the first RAN node or to the second RAN node.

A2. The method of embodiment Al, wherein performing the LTM cell switch comprises: receiving, from the first RAN node, one or more configurations associated with respective one or more LTM candidate cells, including the second cell; performing LI measurements on the LTM candidate cells and reporting the LI measurements to the first RAN node; and in response to the reported LI measurements, receiving from the first RAN node an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell, performing the LTM cell switch in response to the LTM cell switch command.

A2a. The method of embodiment A2, wherein: the LTM candidate cell configuration identifies the one or more beams in the second cell to be monitored for BFD, including the first beam; and

BFR is performed in the second beam based on identifying BFD in all of the one or more beams. A2b. The method of embodiment A2, wherein: the LTM candidate cell configuration does not identify any beams in the second cell to be monitored for BFD; the first beam is monitored in the second cell based on the indication of the first beam included with the LTM cell switch command; and

BFR is performed in the second beam based on identifying BFD in the first beam.

A3. The method of any of embodiments A2-A2b, wherein the information associated with at least one of the BFD and the BFR is logged selectively based on one or more of the following: a logging configuration received from the first RAN node; a configurable UE timer; whether the first beam indicated by the LTM cell switch command is also a beam configured for BFD monitoring in the second cell; whether any beam switches occurred between completion of the LTM cell switch and identification of the BFD in at least the first beam; and whether the second cell is a primary cell or a secondary cell.

A3a. The method of embodiment A3, wherein selectively logging information comprises: initiating the configurable timer upon completion of the LTM cell switch; logging the information when at least one of the BFD and the BFR occurs while the timer is running; and refraining from logging the information when at least one of the BFD and the BFR occurs after the timer expires or reaches a terminal value.

A3b. The method of embodiment A3, wherein the logging configuration indicates one or more of the following: whether the UE should log information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; one or more thresholds or conditions for logging information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; and one or more types of information that the UE should log in association with at least one of a BFD and a BFR that occur after an LTM cell switch.

A4. The method of any of embodiments Al-A3b, wherein the logged information associated with the BFD includes one or more of the following: identifying information for each of the one or more beams being monitored; one or more measurements for each of the one or more beams being monitored;

BFD state information at the time when BFD was identified; a duration between initiating the LTM cell switch to the second cell and identifying BFD in at least the first beam; a location at which the BFD was identified; a UE speed or mobility state upon initiating the LTM cell switch to the second cell or when the BFD was identified; and an indication of whether any beam switches occurred between completion of the LTM cell switch and identification of the BFD in at least the first beam.

A4a. The method of embodiment A4, wherein the BFD state information includes one or more of the following: a number of beam failure instances in the first beam, and/or a value of a BFD- related timer.

A5. The method of any of embodiments Al-A4a, wherein the logged information associated with the BFR includes one or more of the following: identifying information for each of one or more beams configured for BFR in the second cell; one or more measurements for each of one or more beams configured for BFR in the second cell; random access (RA) information for each of one or more beams configured for BFR in the second cell; a duration between initiating the LTM cell switch to the second cell and one of the following: selecting the second beam, or completing BFR in the second beam; a location at which the BFR was performed; and a UE speed or mobility state upon initiating the LTM cell switch to the second cell or upon completing BFR in the second beam.

A5a. The method of embodiment A5, wherein for each beam, the RA information includes one or more of the following: number of RA attempts, an indication of whether BFR succeeded or failed, preamble and/or RA resources used, and whether power ramping was used.

A6. The method of any of embodiments Al-A5a, wherein the logged information is sent to the second RAN node after the BFR in one of the following: an LTM success report, or a random access (RA) report.

A7. The method of any of embodiments Al-A5a, further comprising performing a further LTM cell switch from the second cell served by the second RAN node to the first cell served by the first RAN node, wherein the logged information is sent to the first RAN node after the further LTM cell switch based on determining that the logged information pertains to the first cell.

BL A method for a second radio access network (RAN) node configured to facilitate layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: after an LTM cell switch by a UE from a first cell served by a first RAN node to a second cell served by the second RAN node, performing beam failure recovery (BFR) for the UE in a second beam of the second cell, wherein the BFR is responsive to a beam failure detected (BFD) by the UE in at least a first beam of the second cell; performing one or more of the following operations: selectively logging first information associated with at least one of the BFD and the BFR, and receiving from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE; and sending to the first RAN node at least one of the first information and the second information.

B2. The method of embodiment Bl, wherein the second information associated with at least one of the BFD and the BFR is logged selectively by the UE based on one or more of the following: a logging configuration received by the UE from the first RAN node; a configurable UE timer; whether the first beam is a beam configured for BFD monitoring in the second cell; whether any beam switches occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and whether the second cell is a primary cell or a secondary cell. B2a. The method of embodiment B2, wherein the logging configuration indicates one or more of the following: whether the UE should log information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; one or more thresholds or conditions for logging information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; and one or more types of information that the UE should log in association with at least one of a BFD and a BFR that occur after an LTM cell switch.

B3. The method of any of embodiments Bl-B2a, wherein the received second information associated with the BFD includes one or more of the following: identifying information for each of one or more beams that were monitored by the UE for BFD; one or more measurements for each of the one or more beams that were monitored by the UE for BFD;

BFD state information at time of the BFD by the UE in at least the first beam; a duration between the UE initiating the LTM cell switch to the second cell and the BFD by the UE in at least the first beam; a location of the BFD by the UE in at least the first beam; a UE speed or mobility state when the UE initiated the LTM cell switch to the second cell or at the BFD by the UE in at least the first beam; and an indication of whether any beam switches occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam.

B3a. The method of embodiment B3, wherein the BFD state information includes one or more of the following: a number of beam failure instances in the first beam, and/or a value of a BFD- related timer.

B4. The method of any of embodiments Bl-B3a, wherein the received second information associated with the BFR includes one or more of the following: identifying information for each of one or more beams configured for BFR in the second cell; one or more measurements for each of one or more beams configured for BFR in the second cell; random access (RA) information for each of one or more beams configured for BFR in the second cell; a duration between the UE initiating the LTM cell switch to the second cell and one of the following: the UE selecting the second beam, or the UE completing BFR in the second beam; a location at which the UE performed BFR; and a UE speed or mobility state when the UE initiated the LTM cell switch to the second cell or when the UE completed BFR in the second beam.

B4a. The method of embodiment B4, wherein for each beam, the RA information includes one or more of the following: number of RA attempts, an indication of whether BFR succeeded or failed, preamble and/or RA resources used, and whether power ramping was used.

B5. The method of any of embodiments Bl-B4a, wherein the second information is received from the UE after the BFR in one of the following: an LTM success report, or a random access (RA) report.

B6. The method of any of embodiments B1-B5, wherein the logged first information includes one or more of the following: an indication that the UE changed beams shortly after the LTM cell switch; an indication of the BFD detected by the UE in at least the first beam; an indication of the second beam in which the BFR was performed; a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; time elapsed since changing the UE’s serving beam in the second cell; an indication of reference signals configured in the second cell for BFD by the UE; and list of suggested beams for subsequent LTM cell switches to the second cell.

B7. The method of any of embodiments B1-B6, wherein the first information is logged selectively based on one or more of the following: a reporting request received from the first RAN node; a relation between the following: a logging threshold, and a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; whether any beam switches for the UE occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and whether the second cell is a primary cell or a secondary cell for the UE.

B7a. The method of embodiment B7, wherein the reporting request is one of the following: a UE-specific reporting request, received together with an indication of the LTM cell switch of the UE from the first cell to the second cell; or a non-UE-specific reporting request.

B7b. The method of embodiment B7a, wherein the UE-specific reporting request indicates a time period during which the second RAN node should log and report to the first RAN node information about BFRs performed by the UE.

B7c. The method of embodiment B7a, wherein the non-UE-specific reporting request applies to one of the following: any LTM cell switch from the first cell to the second cell, which is followed by BFD and BFR in the second cell; any LTM cell switch from a source cell served by the first RAN node to a target cell served by the second RAN node, which is followed by BFD and BFR in the target cell; any LTM cell switch that meets one or more conditions included with the non-UE- specific reporting request.

CL A method for a first radio access network (RAN) node configured to facilitate layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: initiating an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by a second RAN node; after completion of the LTM cell switch, receiving one or more of the following from the second RAN node: first information logged by the second RAN node and associated with at least one of the following: a beam failure detected (BFD) by the UE in at least a first beam of the second cell, and a subsequent beam failure recovery (BFR) by the UE in a second beam of the second cell; and second information logged by the UE and associated with at least one of the BFD and the BFR. C2. The method of embodiment Cl, wherein initiating the LTM cell switch comprises: sending to the UE one or more configurations associated with respective one or more LTM candidate cells, including the second cell; receiving from the UE a report of LI measurements performed on the LTM candidate cells; and in response to the reported LI measurements, sending to the UE an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell.

C2a. The method of embodiment C2, wherein: the LTM candidate cell configuration identifies the one or more beams in the second cell to be monitored for BFD, including the first beam; and

BFR is performed by the UE in the second beam based on BFD by the UE in all of the one or more beams.

C2b. The method of embodiment C2, wherein: the LTM candidate cell configuration does not identify any beams in the second cell to be monitored for BFD; the first beam is monitored by the UE based on the indication of the first beam included with the LTM cell switch command; and

BFR is performed by the UE in the second beam based on BFD by the UE in the first beam.

C3. The method of any of embodiments C2-C2b, wherein the second information associated with at least one of the BFD and the BFR is logged selectively by the UE based on one or more of the following: a logging configuration sent to the UE by the first RAN node; a configurable UE timer; whether the first beam indicated by the LTM cell switch command is also a beam configured for BFD monitoring in the second cell; whether any beam switches occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and whether the second cell is a primary cell or a secondary cell for the UE. C3a. The method of embodiment C3, wherein the logging configuration indicates one or more of the following: whether the UE should log information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; one or more thresholds or conditions for logging information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; and one or more types of information that the UE should log in association with at least one of a BFD and a BFR that occur after an LTM cell switch.

C4. The method of any of embodiments Cl-C3a, wherein the received second information associated with the BFD includes one or more of the following: identifying information for each of one or more beams that were monitored by the UE for BFD; one or more measurements for each of the one or more beams that were monitored by the UE for BFD;

C4a. The method of embodiment C4, wherein the BFD state information includes one or more of the following: a number of beam failure instances in the first beam, and/or a value of a BFD- related timer.

C5. The method of any of embodiments Cl-C4a, wherein the received second information associated with the BFR includes one or more of the following: identifying information for each of one or more beams configured for BFR in the second cell; one or more measurements for each of one or more beams configured for BFR in the second cell; random access (RA) information for each of one or more beams configured for BFR in the second cell; a duration between the UE initiating the LTM cell switch to the second cell and one of the following: the UE selecting the second beam, or the UE completing BFR in the second beam; a location at which the UE performed BFR; a UE speed or mobility state when the UE initiated the LTM cell switch to the second cell or when the UE completed BFR in the second beam.

C5a. The method of embodiment C5, wherein for each beam, the RA information includes one or more of the following: number of RA attempts, an indication of whether BFR succeeded or failed, preamble and/or RA resources used, and whether power ramping was used.

C6. The method of any of embodiments Cl-C5a, wherein the received first information includes one or more of the following: an indication that the UE changed beams shortly after the LTM cell switch; an indication of the BFD detected by the UE in at least the first beam; an indication of the second beam in which the BFR was performed; a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; time elapsed since changing the UE’s serving beam in the second cell; an indication of reference signals configured in the second cell for BFD by the UE; and list of suggested beams for subsequent LTM cell switches to the second cell.

C7. The method of any of embodiments C1-C6, wherein the first information is logged selectively by the second RAN node based on one or more of the following: a reporting request sent to the second RAN node by the first RAN node; a relation between the following: a logging threshold, and a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; whether any beam switches for the UE occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and whether the second cell is a primary cell or a secondary cell for the UE.

C7a. The method of embodiment C7, wherein the reporting request is one of the following: a UE-specific reporting request, sent together with an indication of the LTM cell switch of the UE from the first cell to the second cell; or a non-UE-specific reporting request.

C7b. The method of embodiment C7a, wherein the UE-specific reporting request indicates a time period during which the second RAN node should log and report to the first RAN node information about BFRs performed by the UE.

C7c. The method of embodiment C7a, wherein the non-UE-specific reporting request applies to one of the following: any LTM cell switch from the first cell to the second cell, which is followed by BFD and BFR in the second cell; any LTM cell switch from a source cell served by the first RAN node to a target cell served by the second RAN node, which is followed by BFD and BFR in the target cell; any LTM cell switch that meets one or more conditions included with the non-UE- specific reporting request.

C8. The method of any of embodiments Cl-C7c, further comprising performing one of the following operations based on the received one or more of the first information and the second information: selecting the second beam, instead of the first beam, as a target beam for a subsequent LTM cell switch of a UE from the first cell to the second cell; or selecting a third cell, instead of the second cell, as a target cell for a subsequent LTM cell switch of a UE from the first cell.

DI. A user equipment (UE) configured for layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with first and second RAN nodes; 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 A1-A7.

D2. A user equipment (UE) configured for layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments A1-A7.

D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured for layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A7.

D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A7.

EL A second radio access network (RAN) node configured to facilitate layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the second RAN node comprising: communication interface circuitry configured to communicate with UEs via at least a second cell and with at least a first RAN node; 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 Bl-B7c.

E2. A second radio access network (RAN) node configured to facilitate layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the second RAN node being further configured to perform operations corresponding to the methods of any of embodiments Bl-B7c.

E3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to facilitate layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the second RAN node to perform operations corresponding to the methods of any of embodiments Bl-B7c. E4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to facilitate layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the second RAN node to perform operations corresponding to the methods of any of embodiments Bl-B7c.

Fl. A first radio access network (RAN) node configured to facilitate layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the second RAN node comprising: communication interface circuitry configured to communicate with UEs via at least a first cell and with at least a second RAN node; 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 C1-C8.

F2. A first radio access network (RAN) node configured to facilitate layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the first RAN node being further configured to perform operations corresponding to the methods of any of embodiments C1-C8.

F3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to facilitate layer-1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the first RAN node to perform operations corresponding to the methods of any of embodiments C1-C8.

F4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to facilitate layer- 1 (L2)/layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the first RAN node to perform operations corresponding to the methods of any of embodiments C1-C8.

Claims

1. A method for a user equipment, UE, configured for layer-l/layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: performing (910) an LTM cell switch from a first cell served by a first RAN node to a second cell served by a second RAN node; based on monitoring one or more beams of the second cell after the LTM cell switch, identifying (920) a beam failure detected, BFD, in at least a first beam of the second cell; based on the BFD in at least the first beam, selecting (930) a second beam in the second cell and performing beam failure recovery, BFR, in the second beam; selectively logging (940) information associated with at least one of the BFD and the BFR; and sending (970) the logged information to the first RAN node or to the second RAN node.

2 The method of claim 1, wherein performing (910) the LTM cell switch comprises: receiving (911), from the first RAN node, one or more configurations associated with respective one or more LTM candidate cells, including the second cell; performing (912) layer-1 measurements on the LTM candidate cells and reporting the lay er- 1 measurements to the first RAN node; and in response to the reported layer- 1 measurements, receiving (913) from the first RAN node an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell, performing (914) the LTM cell switch in response to the LTM cell switch command.

3. The method of claim 2, wherein: the LTM candidate cell configuration identifies the one or more beams in the second cell to be monitored for BFD, including the first beam; and

BFR is performed in the second beam based on identifying BFD in all of the one or more beams.

4. The method of claim 2, wherein: the LTM candidate cell configuration does not identify any beams in the second cell to be monitored for BFD; the first beam is monitored in the second cell based on the indication of the first beam included with the LTM cell switch command; and

BFR is performed in the second beam based on identifying BFD in the first beam.

5 The method of any of claims 2-4, wherein the information associated with at least one of the BFD and the BFR is logged selectively by the UE based on one or more of the following: a logging configuration received from the first RAN node; a configurable UE timer; whether the first beam indicated by the LTM cell switch command is also a beam configured for BFD monitoring in the second cell; whether any beam switches occurred between completion of the LTM cell switch and identification of the BFD in at least the first beam; and whether the second cell is a primary cell or a secondary cell.

6 The method of claim 5, wherein selectively logging (940) the information associated with at least one of the BFD and the BFR comprises: initiating (941) the configurable timer upon completion of the LTM cell switch; logging (942) the information when at least one of the BFD and the BFR occurs while the timer is running; and refraining (943) from logging the information when at least one of the BFD and the BFR occurs after the timer expires or reaches a terminal value.

7. The method of claim 5, wherein the logging configuration indicates one or more of the following: whether the UE should log information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; one or more thresholds or conditions for logging information associated with at least one of a BFD and a BFR that occur after an LTM cell switch; and one or more types of information that the UE should log in association with at least one of a BFD and a BFR that occur after an LTM cell switch.

8. The method of any of claims 1-7, wherein the logged information associated with the BFD includes one or more of the following: identifying information for each of the one or more beams being monitored; one or more measurements for each of the one or more beams being monitored;

9. The method of claim 8, wherein the BFD state information includes one or more of the following: a number of beam failure instances in the first beam, and/or a value of a BFD-related timer.

10. The method of any of claims 1-9, wherein the logged information associated with the BFR includes one or more of the following: identifying information for each of one or more beams configured for BFR in the second cell; one or more measurements for each of one or more beams configured for BFR in the second cell; random access information for each of one or more beams configured for BFR in the second cell; a duration between initiating the LTM cell switch to the second cell and one of the following: selecting the second beam, or completing BFR in the second beam; a location at which the BFR was performed; and a UE speed or mobility state upon initiating the LTM cell switch to the second cell or upon completing BFR in the second beam.

11. The method of any of claims 1-10, wherein the logged information is sent to the second RAN node in an LTM success report or in a random access report.

12. The method of any of claims 1-10, further comprising performing (950) a further LTM cell switch from the second cell served by the second RAN node to the first cell served by the first RAN node, wherein the logged information is sent to the first RAN node after the further LTM cell switch based on determining (960) that the logged information pertains to the first cell.

13. A method for a second radio access network, RAN, node configured to facilitate layer- l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: after an LTM cell switch by a UE from a first cell served by a first RAN node to a second cell served by the second RAN node, performing (1010) beam failure recovery, BFR, for the UE in a second beam of the second cell, wherein the BFR is responsive to a beam failure detected, BFD, by the UE in at least a first beam of the second cell; performing one or more of the following operations: selectively logging (1020) first information associated with at least one of the BFD and the BFR, and receiving (1030) from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE; and sending (1040) to the first RAN node at least one of the first information and the second information.

14. The method of claim 13, wherein the first information includes one or more of the following: an indication that the UE changed beams shortly after the LTM cell switch; an indication of the BFD detected by the UE in at least the first beam; an indication of the second beam in which the BFR was performed; a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; time elapsed since changing the UE’s serving beam in the second cell; an indication of reference signals configured in the second cell for BFD by the UE; and list of suggested beams for subsequent LTM cell switches to the second cell.

15. The method of any of claims 13-14, wherein the first information is logged selectively by the second RAN node based on one or more of the following: a reporting request received from the first RAN node; a relation between the following: a logging threshold, and a duration between the UE initiating the LTM cell switch to the second cell and completion of BFR in the second beam; whether any beam switches for the UE occurred between completion of the LTM cell switch and the BFD by the UE in at least the first beam; and whether the second cell is a primary cell or a secondary cell for the UE.

16. A method for a first radio access network, RAN, node configured to facilitate layer- l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: initiating (1110) an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by a second RAN node; and after completion of the LTM cell switch, receiving (1120) one or more of the following from the second RAN node: first information that was logged by the second RAN node and is associated with at least one of the following: a beam failure detected, BFD, by the UE in at least a first beam of the second cell, and a subsequent beam failure recovery, BFR, by the UE in a second beam of the second cell; and second information that was logged by the UE and is associated with at least one of the BFD and the BFR.

17. The method of claim 16, wherein initiating (1110) the LTM cell switch comprises: sending (1111) to the UE one or more configurations associated with respective one or more LTM candidate cells, including the second cell; receiving (1112) from the UE a report of layer-1 measurements performed on the LTM candidate cells; and in response to the reported layer-1 measurements, sending (1113) to the UE an LTM cell switch command that includes indications of the following: the second cell as a target cell, and the first beam by which the UE should access the second cell.

18. The method of any of claims 16-17, further comprising performing (1130) one of the following operations based on the received one or more of the first information and the second information: selecting (1131) the second beam, instead of the first beam, as a target beam for a subsequent LTM cell switch of a UE from the first cell to the second cell; or selecting (1132) a third cell, instead of the second cell, as a target cell for a subsequent LTM cell switch of a UE from the first cell.

19. User equipment, UE (210, 610, 1212, 1300) configured for layer-l/layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), the UE comprising: communication interface circuitry (1312) configured to communicate with first and second RAN nodes (100, 150, 220, 620, 630, 1210, 1400, 1502); and processing circuitry (1302) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: perform an LTM cell switch from a first cell served by the first RAN node to a second cell served by the second RAN node; based on monitoring one or more beams of the second cell after the LTM cell switch, identify a beam failure detected, BFD, in at least a first beam of the second cell; based on the BFD in at least the first beam, select a second beam in the second cell and perform beam failure recovery, BFR, in the second beam; selectively log information associated with at least one of the BFD and the BFR; and sending the logged information to the first RAN node or to the second RAN node.

20. The UE of claim 19, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-12.

21. User equipment, UE (210, 610, 1212, 1300) configured for layer-l/layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), the UE being further configured to: perform an LTM cell switch from a first cell served by a first RAN node (100, 150, 220, 620, 1210, 1400, 1502) to a second cell served by a second RAN node (100, 150, 220, 630, 1210, 1400, 1502); based on monitoring one or more beams of the second cell after the LTM cell switch, identify a beam failure detected, BFD, in at least a first beam of the second cell; based on the BFD in at least the first beam, select a second beam in the second cell and perform beam failure recovery, BFR, in the second beam; selectively log information associated with at least one of the BFD and the BFR; and sending the logged information to the first RAN node or to the second RAN node.

22. The UE of claim 21, being further configured to perform operations corresponding to the methods of any of claims 2-12.

23. Non-transitory, computer-readable medium (1310) storing computer-executable instructions that, when executed by processing circuitry (1302) of user equipment, UE (210, 610, 1212, 1300) configured for layer-l/layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), configure the UE to perform operations corresponding to the methods of any of claims 1-12.

24. Computer program product (1314) comprising computer-executable instructions that, when executed by processing circuitry (1302) of user equipment, UE (210, 610, 1212, 1300) configured for layer-l/layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1204), configure the UE to perform operations corresponding to the methods of any of claims 1-12.

25. Second radio access network, RAN, node (100, 150, 220, 630, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), the second RAN node comprising: communication interface circuitry (1406, 1504) configured to communicate with UEs via at least a second cell and with at least a first RAN node (100, 150, 220, 620, 1210, 1400, 1502); and processing circuitry (1402, 1504) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: after an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by the second RAN node, perform beam failure recovery, BFR, for the UE in a second beam of the second cell, wherein the BFR is responsive to a beam failure detected, BFD, by the UE in at least a first beam of the second cell; perform one or more of the following operations: selectively log first information associated with at least one of the BFD and the BFR, and receive from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE; and send to the first RAN node at least one of the first information and the second information.

26. The second RAN node of claim 25, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 14-15.

27. Second radio access network, RAN, node (100, 150, 220, 630, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), the second RAN node being further configured to: after an LTM cell switch by a UE from a first cell served by a first RAN node (100, 150, 220, 620, 1210, 1400, 1502) to a second cell served by the second RAN node, perform beam failure recovery, BFR, for the UE in a second beam of the second cell, wherein the BFR is responsive to a beam failure detected, BFD, by the UE in at least a first beam of the second cell; perform one or more of the following operations: selectively log first information associated with at least one of the BFD and the BFR, and receive from the UE second information associated with at least one of the BFD and the BFR, the second information being selectively logged by the UE; and send to the first RAN node at least one of the first information and the second information.

28. The second RAN node of claim 27, being further configured to perform operations corresponding to the methods of any of claims 14-15.

29. Non-transitory, computer-readable medium (1404, 1504) storing computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a second radio access network, RAN, node (100, 150, 220, 630, 1210, 1400, 1502) configured to facilitate layer- l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), configure the second RAN node to perform operations corresponding to the methods of any of claims 13-15.

30. Computer program product (1404a, 1504a) comprising computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a second radio access network, RAN, node (100, 150, 220, 630, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), configure the second RAN node to perform operations corresponding to the methods of any of claims ISIS.

31. First radio access network, RAN, node (100, 150, 220, 620, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), the first RAN node comprising: communication interface circuitry (1406, 1504) configured to communicate with UEs via at least a first cell and with at least a second RAN node (100, 150, 220, 630, 1210, 1400, 1502); and processing circuitry (1402, 1504) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: initiate an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by the second RAN node; and after completion of the LTM cell switch, receive one or more of the following from the second RAN node: first information that was logged by the second RAN node and is associated with at least one of the following: a beam failure detected, BFD, by the UE in at least a first beam of the second cell, and a subsequent beam failure recovery, BFR, by the UE in a second beam of the second cell; and second information that was logged by the UE and is associated with at least one of the BFD and the BFR.

32. The first RAN node of claim 31, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 17-18.

33. First radio access network, RAN, node (100, 150, 220, 620, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), the first RAN node being further configured to: initiate an LTM cell switch by a UE from a first cell served by the first RAN node to a second cell served by a second RAN node (100, 150, 220, 630, 1210, 1400, 1502); and after completion of the LTM cell switch, receive one or more of the following from the second RAN node: first information that was logged by the second RAN node and is associated with at least one of the following: a beam failure detected, BFD, by the UE in at least a first beam of the second cell, and a subsequent beam failure recovery, BFR, by the UE in a second beam of the second cell; and second information that was logged by the UE and is associated with at least one of the BFD and the BFR.

34. The first RAN node of claim 33, being further configured to perform operations corresponding to the methods of any of claims 17-18.

35. Non-transitory, computer-readable medium (1404, 1504) storing computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a first radio access network, RAN, node (100, 150, 220, 620, 1210, 1400, 1502) configured to facilitate layer- l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), configure the first RAN node to perform operations corresponding to the methods of any of claims 16-18.

36. Computer program product (1404a, 1504a) comprising computer-executable instructions that, when executed by processing circuitry (1402, 1504) of a first radio access network, RAN, node (100, 150, 220, 620, 1210, 1400, 1502) configured to facilitate layer-l/layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1212, 1300), configure the first RAN node to perform operations corresponding to the methods of any of claims 16-18.