Managing l1 / l2 triggered mobility (LTM) configurations for user equipment (UE) performing reestablishment

Abstract

Embodiments include methods for a user equipment (UE) configured to perform layer-1 or layer- 2 triggered inter-cell mobility (LTM) in a radio access network (RAN). Such methods include receiving from the RAN a reconfiguration message that includes one or more LTM configurations, and initiating a re-establishment procedure towards a second cell in response to and detecting a failure event while connected to the RAN via a first cell. Such methods also include, in response to determining that the UE is not configured to perform LTM fast recovery, discarding one or more of the following information after initiating the re-establishment procedure: at least one of the LTM configurations, or portions thereof; and information derived from the one or more LTM configurations. Such methods also include, after discarding the information, sending a re-establishment request to the RAN via the second cell. Other embodiments include complementary methods for a RAN node.

Description

[0001] MANAGING L1 / L2 TRIGGERED MOBILITY (LTM) CONFIGURATIONS FOR USER EQUIPMENT (UE) PERFORMING REESTABLISHMENT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks and more specifically to improving mobility of user equipment (UEs) across multiple cells in a radio access network (RAN), such as by managing layer- 1 or layer-2 triggered inter-cell mobility (LTM) configurations of a UE that is performing a layer-3 re-establishment procedure with the RAN.

[0004] BACKGROUND

[0005] 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 multiple and substantially different use cases. These include 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.

[0006] 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).

[0007] Although not shown, in some deployments the 5GC can be replaced by an Evolved Packet Core (EPC), which conventionally has been used together with a fourth generation (4G) Long- Term Evolution (LTE) Evolved UMTS RAN (E-UTRAN). In such deployments, gNBs (e.g., 100, 150) can connect to one or more Mobility Management Entities (MMEs) in EPC 198 via respective Sl-C interfaces. Similarly, gNBs can connect to one or more Serving Gateways (SGWs) in EPC via respective NG-U interfaces.

[0008] In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a DL “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

[0009] 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.

[0010] 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, a gNB-DU can be connected to only a single 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.

[0011] LTE Rel-10 introduced channel bandwidths larger than 20 MHz, which continues into NR. To remain compatible with UEs from earlier releases (e.g., Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the structure of a Rel-8 carrier. A Rel- 10 UE can receive multiple CCs based on Carrier Aggregation (CA). The CCs can be considered “cells”, so a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells). These are referred to collectively as a “cell group”. NR also supports CA starting in Rel-15.

[0012] LTE Rel-12 introduced dual connectivity (DC) whereby a UE is connected to two network nodes simultaneously, thereby improving connection robustness and / or capacity. In LTE DC, these two network nodes are referred to as “Master eNB” (MeNB) and “Secondary eNB” (SeNB), or more generally as master node (MN) and secondary node (SN). More specifically, a UE is configured with a Master Cell Group (MCG) provided by the MN and a Secondary Cell Group (SCG) provided by the SN. Each CG includes a primary cell (PCell) and optionally one or more secondary cells (SCells).

[0013] Several DC (or more generally, multi -connectivity) scenarios have been considered for NR. These include NR-DC that is like LTE -DC discussed above, except that both MN and SN (referred to as “gNBs”) use the NR interface to communicate with a UE. In addition, 5G includes various multi-RAT DC (MR-DC) scenarios in which a UE can be configured to utilize resources of two different nodes, one providing E-UTRA / LTE access and the other one providing NR access. One node acts as the MN (e.g., providing MCG) and the other as the SN (e.g., providing SCG), with the MN and SN being connected via a network interface and at least the MN being connected to a core network (e.g., EPC or 5GC). 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). Upon detecting RLF or HOF, the UE initiates a radio resource control (RRC) re-establishment procedure for its connection to the RAN.

[0014] In MR-DC, a UE also monitors the MCG PCell for RLF (called “M-RLF”). Once an M- RLF is detected, the UE either transmits an MCGFailur eInformation message via the SCG or initiates RRC reestablishment for its connection to the RAN. 3GPP Rel-16 introduced a feature call MCG fast recovery, whereby a UE that detects M-RLF suspends only the failed radio link (e.g., to PCell) rather than performing a full RRC reestablishment of its connection.

[0015] As specified in 3GPP document RP-213565, NR Rel-18 includes a Work Item on NR mobility enhancements including layer- 1 / layer-2 (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. Conventionally, 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).

[0016] Currently, all inter-cell mobility involves complete L2 and LI (i.e., PHY) 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 problems and / or difficulties.

[0017] SUMMARY

[0018] Based on some recent 3 GPP agreements on LTM, there can be scenarios in which a UE performs an RRC re-establishment procedure in response to detecting a failure (e.g., RLF), even when the UE was previously provided one or more LTM configurations for LTM candidate cells. When an RRC re-establishment procedure is triggered by a UE configured in this manner, it is unclear which LTM configurations are discarded or retained by the UE. With respect to corresponding LTM configurations stored in the RAN, the target RAN node (e.g., CU) for the UE’s re-establishment is unaware of which LTM configurations for the UE should be discarded and maintained. An object of embodiments of the present disclosure is to address these and related problems, issues, and / or difficulties, thereby facilitating better coexistence between LTM procedures and RRC (or L3) procedures such as re-establishment.

[0019] Some embodiments of the present disclosure include methods (e.g., procedures) for a UE configured to perform LTM in a RAN.

[0020] These exemplary methods include receiving from the RAN a reconfiguration message that includes one or more LTM configurations . These exemplary methods also include initiating a re-establishment procedure towards a second cell in response to detecting a failure event while connected to the RAN via a first cell. These exemplary methods also include, in response to determining that the UE is not configured to perform LTM fast recovery, discarding one or more of the following information after initiating the re-establishment procedure:

[0021] • at least one of the LTM configurations, or portions thereof; and

[0022] • information derived from the one or more LTM configurations;

[0023] These exemplary methods also include, after discarding the information, sending a reestablishment request to the RAN via the second cell.

[0024] In some embodiments, the detected failure event is one of the following: a radio link failure (RLF), a handover failure (HOF), an LTM cell switch failure, a conditional handover (CHO) failure, a reconfiguration failure, a random access failure, a beam failure detection (BFD), or reaching a maximum number failed transmission or retransmission of radio link control (RLC) protocol data units (PDUs).

[0025] In some embodiments, determining that the UE is not configured to perform LTM fast recovery includes detecting absence of an attempt-LTM field in one of the LTM configurations.

[0026] In some embodiments, these exemplary methods can also include performing one or more of the following operations based on determining that the UE is not configured to perform LTM fast recovery for the failure event:

[0027] • resetting the UE’s medium access control (MAC) layer;

[0028] • suspending at least a portion of configured radio bearers, backhaul radio link control (RLC) channels, and sidelink relay RLC channels;

[0029] • releasing one or more configurations previously provided by the RAN; and

[0030] • stopping one or more supervision timers that are running in the UE.

[0031] In some embodiments, each LTM configuration includes one or more of the following:

[0032] • one or more LTM candidate cell configurations;

[0033] • lower layer measurement configurations for respective LTM candidate cells;

[0034] • measurement reporting configurations for respective LTM candidate cells;

[0035] • downlink (DL) pre-synchronization configuration for LTM; • uplink (UL) pre-synchronization configuration for LTM;

[0036] • an indication of whether a layer-2 (L2) reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell;

[0037] • an indication of whether fast LTM recovery should be attempted; and

[0038] • execution configurations for LTM cell switch procedures to respective LTM candidate cells.

[0039] Other embodiments include methods (e.g., procedures) for a RAN node configured to facilitate LTM by UE. In general, these exemplary methods are complementary to the exemplary methods for a UE summarized above and described in more detail herein.

[0040] These exemplary methods include sending to a UE a reconfiguration message that includes one or more LTM configurations and receiving a re-establishment request from the UE via a second cell. The re-establishment request is received responsive to a failure event at the UE while the UE is connected to the RAN node via a first cell but not configured to perform LTM fast recovery. These exemplary methods also include, in response to the re-establishment request, discarding at least one of the LTM configurations or portions thereof.

[0041] In various embodiments, the failure event can be any of the failure events summarized above in relation to UE embodiments. In various embodiments, the one or more LTM configurations can have any of the contents and / or structure of the corresponding LTM configurations summarized above in relation to UE embodiments, thereby facilitating complementary operations by UE and RAN node. For example, absence of an attempt-LTM field in one of the LTM configurations can indicate that the UE should not attempt LTM fast recovery.

[0042] In some embodiments, the RAN node includes a CU and a second DU that serves the second cell. The re-establishment message is an RRCReestablishmentRequest message and is received by the second DU. In such case, these exemplary methods also include the second DU sending the RRCReestablishmentRequest message to the CU in an Uplink RRC Message Transfer message.

[0043] In some of these embodiments, the RAN node also includes a first DU that serves the first cell. The reconfiguration message is an RRCReconfiguration message sent by the first DU via the first cell. In such case, these exemplary methods also include the CU sending the RRCReconfiguration message to the first DU in a Downlink RRC Message Transfer message.

[0044] In some of these embodiments, the RAN node also includes a third DU that serves a third cell and at least one of the LTM configurations includes an LTM candidate cell configuration for the third cell. In such case, discarding at least one of the LTM configurations or portions thereof includes the CU sends to the third DU a command or request to discard at least the LTM candidate cell configuration for the third cell. Other embodiments include UEs and RAN nodes (or CUs / DUs thereof) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments also include non-transitory, computer-readable media storing computerexecutable instructions that, when executed by processing circuitry, configure such UEs and RAN nodes (or CUs / DUs thereof) to perform operations corresponding to any of the exemplary methods described herein.

[0045] These and other embodiments described herein may provide various benefits and / or advantages. For example, embodiments may avoid a mismatch after a UE’s RRC reestablishment procedure between LTM configurations stored by the UE and LTM configurations stored by the RAN. Thus, both UE and RAN may be aware of which LTM configurations the UE may subsequently use for an LTM procedure. Additionally, embodiments may facilitate proper UE operation under various conditions that cause the UE to perform LTM fast recovery or RRC re-establishment. More generally, embodiments may improve mobility of UEs in RANs.

[0046] These and other objects, features, and advantages of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 shows a high-level view of an exemplary 5G network architecture.

[0049] Figure 2 shows an exemplary configuration of NR UP and CP protocol stacks.

[0050] Figure 3 shows a logical architecture for an NG-RAN node arranged in a split CU / DU architecture, such as illustrated in Figure 1.

[0051] Figure 4 shows a high-level illustration of DC in combination with CA.

[0052] Figures 5 and 6A-B show signaling diagrams of various LTM procedures.

[0053] Figures 7-9 show various ASN.1 data structures that can be utilized in some embodiments of the present disclosure.

[0054] Figure 10 shows a signaling diagram for an exemplary procedure in which a UE detects a failure event, triggers an RRC re-establishment procedure, and removes at least one LTM configuration, according to some embodiments of the present disclosure.

[0055] Figures 11-13 show various ASN. l data structures that can be utilized in some embodiments of the present disclosure.

[0056] Figure 14 shows an exemplary method (e.g., procedure) for a UE, according to various embodiments of the present disclosure.

[0057] Figure 15 shows an exemplary method (e.g., procedure) for a RAN node, according to various embodiments of the present disclosure. Figure 16 shows a communication system according to various embodiments of the present disclosure.

[0058] Figure 17 shows a UE according to various embodiments of the present disclosure.

[0059] Figure 18 shows a network node according to various embodiments of the present disclosure.

[0060] Figure 19 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

[0061] DETAILED DESCRIPTION

[0062] Embodiments briefly summarized above will now be described more fully with reference to the accompanying drawings. These descriptions are provided by way of example to explain the subject matter to those skilled in the art and should not be construed as limiting the scope of the subject matter to only the embodiments described herein. More specifically, examples are provided below that illustrate the operation of various embodiments according to the advantages discussed above.

[0063] 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.

[0064] Furthermore, the following terms are used throughout the description given below:

[0065] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3 GPP 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.

[0066] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0067] • Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both terms having a different meaning than the term “network node”.

[0068] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0069] • Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g., a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or equipment in the cellular communications network, to enable and / or provide wireless access to the wireless device, and / or to perform other functions (e.g., administration) in the cellular communications network.

[0070] • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

[0071] 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.

[0072] Note that the description given herein focuses on a 3 GPP cellular communications system and, as such, 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.

[0073] Figure 2 shows an exemplary configuration of NR user plane (UP) and control plane (CP) protocol stacks between a UE (210), a gNB (220), and an AMF (230). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between UE and gNB are common to UP and CP. PDCP provides ciphering / deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data.

[0074] On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection / correction, concatenation, segmentation / reassembly, sequence numbering, reordering of data transferred to / from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and manages transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0075] 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.

[0076] 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.

[0077] An NR LIE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. The UE must perform a random-access (RA) procedure to move from RRC IDLE to RRC CONNECTED state, where the cell serving the UE is known and an RRC context is established for the UE in the serving gNB, such that the UE and gNB can communicate. As part of (or in conjunction with) the RA procedure, the UE also transmits nRRCSetupRequest message to the serving gNB. NR RRC also includes an RRC INACTIVE state in which a UE is known (e.g., via UE context) by the serving gNB.

[0078] 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.

[0079] 5G / NR technology shares many similarities with 4G / LTE. For example, both PHYs utilize similar arrangements of time-domain physical resources into 1-ms subframes that include multiple slots of equal duration, with each slot including multiple OFDM-based symbols. DC is another LTE feature also used in 5G / NR networks. 3GPP TR 38.804 (vl4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply NR RAT, LTE RAT, or both, and can connect to either EPC or 5GC. The following terminology is used to describe these exemplary DC scenarios or configurations:

[0080] • DC: LTE DC (i.e., both MN and SN employ LTE, as discussed above);

[0081] • EN-DC: LTE -NR DC where MN (eNB) employs LTE and SN (gNB) employs NR, and both are connected to EPC.

[0082] • NGEN-DC: LTE -NR dual connectivity where a UE is connected to one ng-eNB that acts as a MN and one gNB that acts as a SN. The ng-eNB is connected to the 5GC and the gNB is connected to the ng-eNB via the Xn interface. • NE-DC: LTE-NR dual connectivity where a UE is connected to one gNB that acts as a MN and one ng-eNB that acts as a SN. The gNB is connected to 5GC and the ng-eNB is connected to the gNB via the Xn interface.

[0083] • NR-DC (or NR-NR DC): both MN and SN employ NR.

[0084] • MR-DC (multi-RAT DC): a generalization of Intra-E-UTRA DC described in 3GPP TS 36.300 (vl6.0.0), where a multiple Rx / Tx UE may be configured to utilize resources provided by two different nodes, one providing E-UTRA access and the other one providing NR access. One node acts as the MN and the other as the SN, with MN and SN connected via a network interface and at least the MN is connected to the core network. EN-DC, NE-DC, and NGEN-DC are examples of MR-DC.

[0085] Figure 4 shows a high-level illustration of a UE (440) arranged in DC and CA in a RAN (460). In this illustration, each of the UE’s MN (410) and the SN (420) can be an eNB or a gNB, in accordance with the various DC scenarios mentioned above. The MN provides the UE’s MCG (411) consisting of a PCell and three SCells arranged in CA, while the SN provides the UE’s SCG (421) consisting of a PSCell and three SCells arranged in CA. Figure 4 also shows a third RAN node (430), which provides a cell (431) that is proximate to the cells of the MCG and / or the cells of the SCG. For example, the UE may communicate with the third RAN node via the cell (431) in case of failure in the MCG (or PCell), failure in the SCG (or PSCell), or in mobility procedures in which the third RAN node is a target node for the UE. In some cases, the cell (431) may be part of a cell group (not shown) that the third RAN node can provide to UEs. The MN, the SN, and the third RAN node can be interconnected via appropriate interfaces, such as described in more detail below.

[0086] When a UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, a serving cell change is triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and / or PSCell (e.g., when DC is configured), as well as release / add SCells (e.g., when CA is configured).

[0087] A UE in RRC CONNECTED state can be configured to perform and report measurements of its serving cell(s) and neighbor cells to its serving RAN node. Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by layer 3 (L3, i.e., RRC) and the messages exchanged are part of L3.

[0088] As specified in 3GPP document RP-213565, NR Rel-18 includes a Work Item on NR mobility enhancements including layer- 1 / layer-2 (L1 / L2) based inter-cell mobility, also referred to as L1 / L2 triggered mobility (LTM). Conventionally, all inter-cell mobility operations are triggered by L3 RSRP measurements and involve complete L2 and LI (i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, a high-level goal of the Rel-18 L1 / L2 mobility enhancements is to facilitate serving cell change via L1 / L2 signaling to address these problems and / or difficulties. Some more specific goals include specifying the following:

[0089] • Configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells;

[0090] • Dynamic switch mechanism among candidate serving cells (including SpCell and SCell) for the potential applicable scenarios based on L1 / L2 signalling;

[0091] • LI enhancements for inter-cell beam management, including LI measurement and reporting, and beam indication;

[0092] • Timing Advance (TA) management; and

[0093] • CU-DU interface signaling to support L1 / L2 mobility, if needed.

[0094] 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).

[0095] In LTM a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration”. This configuration may be an RRCReconfiguration message or a portion thereof, such as one or more IEs / fields / parameters (e.g., CellGroupConfig E). The UE performs measurements on these 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 LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., MAC control element (GE)). Based on this commend, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this LTM candidate cell.

[0096] Figure 5 shows a signaling diagram for an intra-DU LTM procedure for a UE. The signaling shown in Figure 5 is between a UE, a DU, and a CU. Although operations shown in Figure 5 are given numerical labels, this is done to facilitate the following description rather than to require any specific operational order, unless expressly stated otherwise. In operation 1, the UE sends a MeasurementReport message (L3 measurement result) to the DU containing measurements of neighboring cells. The DU sends an UL RRC MESSAGE TRANSFER message conveying the received MeasurementReport message to the CU.

[0097] In operations 2-3, the CU determines to initiate LTM configuration and sends a UE CONTEXT MODIFICATION REQUEST message to the DU containing one target candidate cell ID. In operation 4, if the DU accepts the request for LTM configuration, it responds to the CU with a UE CONTEXT MODIFICATION RESPONSE message including the generated lower layer RRC configurations for the accepted target candidate cell. It is for further study whether single or multiple UE Context Modification procedure(s) should be used in operations 3-4.

[0098] In operation 5, the CU sends a DL RRC MESSAGE TRANSFER message to the DU, which includes the generated RRCReconfiguration message with the LTM configuration. It is for further study whether this is a DL RRC MESSAGE TRANSFER message or UE CONTEXT MODIFICATION REQUEST message. In operation 6, the DU forwards the received RRCReconfiguration message to the UE.

[0099] In operation 7, the UE responds to the DU with an RRCReconfigurationComplete message. In operation 8, the DU forwards the RRCReconfigurationComplete message to the CU via an UL RRC MESSAGE TRANSFER message. It is for further study whether this is an UL RRC MESSAGE TRANSFER message or a UE CONTEXT MODIFICATION RESPONSE message.

[0100] In operation 9, the UE sends the lower layer measurement result to the DU. In operations 10-11, based on the measurement result, the DU decides to execute LTM and sends an LTM command to the UE. In operation 12, the DU sends the LTM CELL CHANGE NOTIFICATION message to the CU to indicate the initiation of the LTM command to the UE including the target cell ID.

[0101] In operation 13, the DU detects the UE access in the target cell. It is for further study how the DU detects the UE access. In operation 14, the DU sends an ACCESS SUCCESS message to the CU with the target Cell ID. In operation 15, which is optional, the CU sends a UE CONTEXT MODIFICATION message to the DU to release the resources of prepared cells. After receiving such a message, the DU responds in operation 16 with a UE CONTEXT MODIFICATION RESPONSE message.

[0102] Figures 6A-B shows a signaling diagram for an inter-DU / intra-CU LTM procedure for a UE. The signaling shown in Figure 5 is between a UE, a source DU, a candidate DU, and a CU. Although operations shown in Figures 6A-B are given numerical labels, this is done to facilitate the following description rather than to require any specific operational order, unless expressly stated otherwise. In operation 1, the UE sends MeasurementReport message (L3 measurement result FFS) to the source DU containing measurements of neighboring cells. The source DU sends the CU an UL RRC MESSAGE TRANSFER message conveying the received Measure me ntReport message.

[0103] In operations 2-3, the CU determines to initiate LTM configuration and sends a UE CONTEXT SETUP REQUEST message to the candidate DU, including one target candidate cell ID. In operation 4, if the candidate DU accepts the request for LTM configuration, it responds to the CU with a UE CONTEXT SETUP RESPONSE message including the generated lower layer RRC configuration for the accepted target candidate cell.

[0104] In operation 5, the CU sends a DL RRC MESSAGE TRANSFER message to the source DU, which includes the generated RRCReconfiguration message with the LTM configuration. It is for further study whether this is a DL RRC MESSAGE TRANSFER message or UE CONTEXT MODIFICATION REQUEST message. In operation 6, the source DU forwards the received RRCReconfiguration message to the UE.

[0105] In operation 7, the UE responds to the source DU with an RRCReconfigurationComplete message. In operation 8, the source DU forwards the RRCReconfigurationComplete message to the CU via an UL RRC MESSAGE TRANSFER message. It is for further study whether this is an UL RRC MESSAGE TRANSFER message or a UE CONTEXT MODIFICATION RESPONSE message.

[0106] In operation 9, the UE sends the lower layer measurement result to the source DU. In operations 10-11, based on the measurement result, the source DU decides to execute LTM to a candidate target cell and sends an LTM command to the UE. In operation 12, the source DU sends an LTM CELL CHANGE NOTIFICATION message to the CU to indicate the initiation of the LTM command to the UE including the target cell ID.

[0107] In operation 13, the candidate (now target) DU detects the UE access in the candidate (now target) cell. It is for further study how the target DU detects the UE access in the target cell. In operation 14, the target DU sends the ACCESS SUCCESS message to the CU with the target cell ID. In operation 15, which is optional, the CU sends a UE CONTEXT MODIFICATION message to the source DU to release the resources of prepared cells. After receiving such a message, the source DU responds in operation 16 with a UE CONTEXT MODIFICATION RESPONSE message.

[0108] The following agreements regarding behavior of an “LTM supervisor timer” were reached at the May 2023 3 GPP RAN2 meeting:

[0109] • The UE starts the LTM supervisor timer, upon reception of the LTM cell switch MAC CE;

[0110] • The UE stops the LTM supervisor timer, upon successful completion of LTM cell switch; • If the LTM supervisor timer for MCG expires, as baseline, the UE considers LTM failure and initiates RRC re-establishment. (SCG switch case FFS)

[0111] Additionally, it was agreed that upon occurrence of RLF or LTM failure (for MCG), a UE should support fast recovery to a candidate cell by LTM execution.

[0112] Based on these agreements, there can be scenarios in which a UE performs an RRC reestablishment procedure in response to a failure, even when the UE was previously provided one or more LTM configurations for LTM candidate cells. When an RRC re-establishment procedure is triggered by a UE configured in this manner, it is unclear which LTM configurations are discarded or retained by the UE. With respect to corresponding LTM configurations stored in the RAN, the target RAN node for the UE’ s re-establishment is unaware of which LTM configurations for the UE should be discarded and maintained.

[0113] Furthermore, the conditions under which a UE should perform LTM fast recovery instead of re-establishment (or vice versa) are unclear, as well as specific UE actions when the UE is not configured with LTM fast recovery and when the UE is configured with LTM fast recovery but the selected cell is not an LTM candidate cell.

[0114] Embodiments of the present disclosure address these and other problems, difficulties, and / or issues by providing flexible and efficient techniques for a UE configured with one or more LTM configurations associated with LTM candidate cells, in which the UE discards (e.g., releases, removes, deletes, or otherwise makes unusable) at least one of the LTM configurations as part of an RRC Re-establishment procedure triggered by a failure event detected at the UE. The LTM configuration(s) discarded by the UE can include any of the following information in various embodiments:

[0115] • lower layer measurement configuration for LTM;

[0116] • time alignment (TA) acquisition configuration (also called UL pre-sync configuration);

[0117] • transmission configuration indicator (TCI) state configuration (also called DL pre-sync configuration);

[0118] • LTM reference configuration and one or more cell-specific (or delta) LTM candidate configurations;

[0119] • complete LTM candidate configurations; and

[0120] • other LTM related indications.

[0121] Other embodiments include complementary methods for a CU of a RAN node. The CU initially provides a UE with one or more LTM configurations associated with LTM candidate cells for the UE. The CU also stores these LTM configurations. Subsequently, in response to determining that the UE performed an RRC Re-establishment procedure, the CU discards at least one of the stored LTM configurations. Embodiments may provide various benefits and / or advantages. For example, embodiments may avoid a mismatch after a UE’s RRC re-establishment procedure between LTM configurations stored by the UE and LTM configurations stored by the RAN. Thus, both LIE and RAN may be aware of which LTM configurations the UE may subsequently use for an LTM procedure. Additionally, embodiments may facilitate proper UE operation under various conditions that cause the UE to perform LTM fast recovery or RRC re-establishment. More generally, embodiments may improve mobility of UEs in RANs.

[0122] 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.

[0123] 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.

[0124] 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 the 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).

[0125] Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more “LTM candidate cell configurations” via an RRCReconfiguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0126] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconfiguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”.

[0127] 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 signalled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0128] 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.

[0129] 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):

[0130] • One or more LTM candidate cell configurations, i.e., for respective LTM candidate cells;

[0131] • Measurement configuration for LTM, e.g., LI measurement and reporting configuration for LTM candidate cells;

[0132] • Configurations for DL pre-sync for LTM, e.g., for early TCI state activation;

[0133] • Configurations for UL pre-sync for LTM, e.g., for reception of PDCCH ordered preamble transmission and reception of TA; • Configurations 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.).

[0134] 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).

[0135] 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.

[0136] Furthermore, an LTM cell switch procedure 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.

[0137] The term “beam” may refer to a spatial direction in which a signal is transmitted (e.g., by a RAN node) or received (e.g., by a UE), or to a spatial filter applied to a signal which is transmitted or received. Thus, transmitting signals in different beams can involve transmitting signals in different spatial directions. A beam may be identified and / or associated with an index or other identifier, such as a Synchronization Signal block (SSB) index, a channel state information reference signal (CSLRS) resource identifier, etc. Thus, selecting a beam may involve selecting an SSB associated with an SSB index or selecting a CSLRS associated with a CSLRS resource identifier.

[0138] In some embodiments, the UE receives a reconfiguration message (e.g., RRCReconfiguration) from a serving RAN node including one or more LTM configurations. The UE then detects a failure event while connected to a serving cell and initiates an RRC reestablishment procedure in response to the failure event. As part of the RRC re-establishment procedure, the UE discards (e.g., deletes or otherwise makes unusable) at least one of the LTM configurations that were previously configured. After the UE discards the at least one LTM configuration that was / were previously configured, the UE transmits a re-establishment request message (e.g., RRCReestablishmentRequesf) to a target RAN node (or a CU thereof).

[0139] In some embodiments, each LTM configuration can include one or more lower layer measurement configurations for LTM. Each lower layer measurement configuration may include a configuration for performing measurements on one or more LTM candidate cells (e.g., on beams, SSBs, and / or CSLRS resources of these cells). The UE can then report these lower layer measurements to the serving RAN node to assist with the RAN node’s LTM cell switch decisions for the UE. These measurement reports may include information such as synchronization signal reference signal received power (SS-RSRP), Ll-RSRP, SS reference signal received quality (SS- RSRQ), Ll-RSRQ, SS signal-to-interference-and-noise ratio (SS-SINR), and / or Ll-SINR.

[0140] In some of these embodiments, a lower layer measurement configuration may include one or more reporting configurations, which may be included in a serving cell configuration, e.g., ServingCellConfig IE. For example, a reporting configuration may be provided in an existing CSI- ReportConfig IE or in a newly defined LTM-CSI-ReportConfig IE (or similar name). Alternately, the reporting configuration can be included in a CSI measurement configuration or an LTM measurement configuration for a serving cell (e.g., PCell or MCG SCell). When the UE discards a lower layer measurement configuration for an LTM candidate cell, the UE also discards any corresponding reporting configuration for that cell.

[0141] In some of these embodiments, each reporting configuration may include one or more of the following:

[0142] • an indication of reporting timing, e.g., periodic, aperiodic, semi-persistently, etc.; and

[0143] • an indication of which LTM candidate cells are to be reported.

[0144] In some variants, each lower layer measurement configuration may include one or more resource configurations indicating resources to be measured by the UE, such as one or more LTM candidate cells and / or one or more RS resources (e.g., SSB, CSLRS) in LTM candidate cells. In other variants, a resource configuration can be included in an LTM candidate cell configuration but outside of a lower layer measurement configuration. For example, the resource configuration can be in an LTM-CSI-ResourceConfig field that is included in an LTM-Config IE. In that case, a resource configuration may include an identity of the associated LTM candidate cell.

[0145] In some of these embodiments, each lower layer measurement configuration may include indications of one or more of the following associated with an LTM candidate cell to be measured:

[0146] • SSB frequency, sub-carrier spacing, and / or periodicity (e.g., number of subframes);

[0147] • time domain positions of SSBs in a half frame;

[0148] • average energy per resource element (EPRE, in dBm) of REs that carry secondary synchronization signals (SSS); • physical cell identity (PCI);

[0149] • an Itm-CSI-ResourceConfigToAddMod list of LTM CSI resource configurations (e.g., LTM-CSI-ResourceConfig^e A'& each indicating CSI resources to be measured by the UE for LTM;

[0150] • an Itm-CSI-ResourceConfigToARelease list of existing LTM CSI resource configurations (or identifiers thereof) to be released by the UE;

[0151] • one or more SSB resource sets (e.g., LTM-CSI-SSB-ResourceSet fields) to be measured by the UE, or identifiers thereof; and

[0152] • PCIs associated with the SSB resource sets.

[0153] In some embodiments, each LTM configuration can include a time alignment (TA) acquisition configuration, which is also referred to as an UL pre-sync configuration. Each TA acquisition configuration includes information necessary for the UE to transmit an UL message to an LTM candidate cell (e.g., random access preamble on a Physical Random Access Channel (PRACH) time / frequency resource). Based on the UL message, the candidate DU calculates a TA value that would align the UE’s UL transmissions with the timing of the LTM candidate cell. The serving DU may provide the TA value for the LTM candidate cell to the UE together with an LTM cell switch command. When applied by the UE, the UE becomes UL synchronized with the LTM candidate cell.

[0154] In some variants, the TA acquisition configuration is provided per LTM candidate cell (e.g., an EarlyUL-SyncConfig IE within an LTM-Candidate IE). In some variants, the TA acquisition configuration includes one or more random access (RA) parameters such as indications of RA preambles to be used (e.g., preamble indices), one or more parameters for power ramping of RA preamble transmissions, etc.

[0155] In some embodiments, each LTM configuration can include one or more transmission configuration indicator (TCI) state configurations, also referred to as DL pre-sync configuration. The DL pre-sync configuration includes necessary information for the UE to obtain DL pre-sync with an LTM candidate cell, such as one or more indications of reference signals e.g., SSB indexes and / or CSLRS resource identifiers and associated configuration(s).

[0156] In some variants, a DL pre-sync configuration is included in each LTM candidate cell configuration, e.g., in an LTM-Candidate IE. In some variants, each DL pre-sync configuration includes one or more TCI state configurations, e.g., an Itm-CandidateTCI-States-ToAddModList- rl8 that is part of or included in a candidateTCI-StatesToAddModList-rl8 IE.

[0157] In some variants, each DL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: • a list of DL TCI states, with each DL TCI State including a quasi -co-locati on (QCL) relationship between one or two DL RS (e.g., SSB or CSLRS) and demodulation RS (DM- RS) associated with a physical downlink shared channel (PDSCH). Two antenna ports (e.g., SSB and DM-RS) are said to be QCL if properties of a channel, over which a signal transmitted from one antenna port is received by a UE, can be inferred from a channel over which a signal transmitted from one antenna port is received by the same UE.

[0158] • a list of UL TCI states, with each UL TCI state including a QCL relationship between one or two UL RS (e.g., SRS) and demodulation RS (DM-RS) associated with a physical uplink shared channel (PUSCH);

[0159] • a unified TCI state type for DL and UL; and

[0160] • a QCL type associated with one or more DL RS.

[0161] In some embodiments, each LTM configuration can include an LTM reference configuration that is common to multiple configured LTM candidate cells. The UE uses the LTM reference configuration to generate a complete LTM candidate cell configuration via combination with a cell-specific LTM candidate cell configuration. In some variants, the reference configuration can be arranged as an RRCReconfiguration message within an LTM-Config IE. Figure 7 shows an ASN. l data structure according to these variants. In this data structure, the LTM-Config IE includes an Itm-ReferenceConfiguration field arranged an octet string that contains an RRCReconfiguration message.

[0162] In some embodiments, each LTM configuration can include one or more complete LTM candidate cell configurations generated when the UE is configured with LTM. Each complete LTM candidate cell configuration includes a complete LTM configuration for an LTM candidate cell, which contains all fields / parameters needed for the UE to perform an LTM cell switch procedure to the LTM candidate cell.

[0163] In different variants, a complete LTM candidate cell configuration may be used on its own or may be generated by applying a received LTM candidate cell configuration to an LTM reference configuration, e.g., as a delta to the LTM reference configuration. The following exemplary text for 3GPP TS 38.331 illustrates how a complete LTM candidate cell configuration may be generated by applying a received LTM candidate cell configuration to an LTM reference configuration.

[0164] *** Begin exemplary 3 GPP specification text ***

[0165] 1> if there is no entry in ue-ltm-ConfigCandidateList within VarLTM-UE-Config with Itm- Candidateld value set to the value of Itm-Candidateld included in the LTM-Candidate'.

[0166] 2> create an entry in ue-ltm-ConfigCandidateList within VarLTM-UE-Config with value

[0167] Itm-Candidateld 2> set to the value of Itm-Candidateld in that entry to the value included in the LTM- Candidate ; > in the entry of ue-ltm-ConfigCandidateList within VarLTM-UE-Config with Itm-Candidateld set to the value of Itm-Candidateld value included in the LTM-Candidate 2> if the LTM-Candidate includes ltm-ConfigComplete

[0168] 3> consider the received Itm-CandidateConfig within Itm-Candidate as a complete LTM candidate cell configuration;

[0169] 3> if z / e-ZTiW-config is present within VarLTM-UE-Config:

[0170] 4> replace ue-LTM-Config vTdh the Itm-CandidateConfig included in the LTM-Config

[0171] 3> else:

[0172] 4> store in ue-LTM-Config the Itm-CandidateConfig included in the LTM-Config

[0173] 2> else:

[0174] 3> generate a complete LTM candidate cell configuration by applying Itm- CandidateConfig on top of Itm-referenceConfiguration, according to clause 5.3.5.x.5.3> z / e-ZTiW-config is present within VarLTM-UE-Config :

[0175] 4> replace ue-LTM-Config with the generated complete LTM candidate cell configuration;

[0176] 3> else:

[0177] 4> store in ue-LTM-Config the generated complete LTM candidate cell configuration;

[0178] *** End exemplary 3 GPP specification text ***

[0179] In some embodiments, each LTM configuration can also include one or more of the following information:

[0180] • an indication of whether a L2 reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell, e.g., ltm-ServingCellNoResetID-rl8 field of LTM- Config-rl8 IE;

[0181] • an indication of whether LTM fast recovery should be attempted, e.g., attempt-LTM-rl8 field of LTM-Config-rl8 IE, which when present with a value of “TRUE” indicates that LTM fast recovery should be attempted by the UE when a failure is detected and a cell is selected while timer T311 is running.

[0182] In some embodiments, the UE initiates an RRC re-establishment procedure in response to detecting any of the following failure events:

[0183] • RLF in an MCG, triggered by the expiry of timer T310. In this case, timer T310 starts when the number of Out of Sync indications received from lower layers exceeds a maximum (defined by the N310 counter) • HOF, triggered by the expiry of timer T304 or a new timer related to LTM. In this case the timer T304 or the new timer starts when the UE starts to execute a handover e.g. reception of a Reconfiguration with Sync IE. And, when the timer expires the UE declares a HOF.

[0184] • LTM cell switch failure triggered by the expiry of an LTM supervisory timer started when the UE receives the LTM cell switch command. In this case the supervision timer starts when the UE receives an LTM cell switch command, to execute LTM. When the timer expires the UE declares an LTM cell switch failure.

[0185] • conditional handover (CHO) failure triggered by the expiry of timer T304, started when a CHO execution condition was fulfilled for a CHO candidate cell. In this case the timer T304 starts when the UE starts to execute CHO, upon fulfilled of CHO execution condition and selection of a triggered cell.

[0186] • reconfiguration failure, e.g., a compliance check failure.

[0187] • random access failure, e.g., reaching a maximum number of preamble transmission attempts.

[0188] • beam failure detection (BFD), e.g., as defined in 3GPP TS 38.321 (vl7.5.0).

[0189] • failure to (re)transmit a maximum number N of RLC protocol data units (PDUs).

[0190] In some embodiments, the UE discards at least one LTM configuration that was previously configured by removing or deleting one or more UE variables (or fields / entries therein) in which the at least one LTM configuration was stored by the UE after receipt from the RAN. For example, the UE can store LTM configuration information in two variables: VarLTM-Config, used to store a reference configuration and LTM candidate cell configurations; and VarLTM-UE-Config, used to store UE configuration information generated or derived based on the received LTM candidate cell configurations. Figures 8-9 show ASN. l data structure for exemplary VarLTM-Config and VarLTM-UE-Config variables, respectively.

[0191] Figure 10 shows a signaling diagram for an exemplary procedure in which a UE detects a failure event, triggers an RRC re-establishment procedure, and removes at least one LTM configuration, according to some embodiments of the present disclosure. The signaling is between a UE (1010), a first DU (1020) that provides a first (serving) cell for the UE at the start of the procedure, a second DU (1030) that provides a second cell in which the UE performs the RRC re-establishment procedure, a third DU (1040) that provides a third cell for which the UE has an LTM configuration, and a CU (1050) that is coupled to the first, second, and third DUs. Note that the first DU may be referred to as an old serving DU, the second DU may be referred to as a new serving DU, and the third DU may be referred to as a candidate DU in accordance with their respective roles. The CU and the three DUs may collectively form a RAN node (1060), such as a gNB shown in Figure 1. Although operations shown in Figure 10 are given numerical labels, this is done to facilitate the following description rather than to require any specific operational order, unless expressly stated otherwise.

[0192] In operation 1, the CU and the three DUs collectively prepare one or more LTM configurations for the UE, including an LTM candidate cell configuration for the third cell provided by the third DU. In operation 2, the first DU configure the UE with the one or more LTM configurations prepared in operation 1.

[0193] In operation 4, the UE detects a failure event, e.g., an RLF or an HOF. In operation 5, the UE initiates an RRC re-establishment procedure, including selecting the second cell provided by the second DU as a target cell. In this example, the UE initiates RRC re-establishment rather than LTM fast recovery because the UE is either not configured for LTM fast recovery or does not select a cell which is an LTM candidate cell.

[0194] In operation 6, the UE removes at least one of the LTM configurations previously configured. In operations 7-8, the UE transmits an RRCReestablishmentRequest message to the CU via the second cell provided by the second DU, which the UE selected as the target cell for re-establishment. In operations 9-10, since the CU has stored a valid context for the UE, it responds to the UE (via the second DU) with an RRCReestablishment message to acknowledge the UE request for RRC re-establishment in the second cell.

[0195] In operations 11-12, the UE confirms completion of RRC re-establishment procedure by sending an RRCReestablishmentComplete message to the CU via the second DU. In operations 13-15, as result of the RRC re-establishment procedure, the CU determines that at least one LTM configuration for the UE should be removed, including the LTM candidate cell configuration for the third cell. The CU requests the third DU to remove at least one LTM configuration for the UE, including the LTM candidate cell configuration for the third cell. Note that operations 13-15 may be performed at any point of time after the CU has received the RRCReestablishmentRequest message in operation 8.

[0196] Some of the techniques and / or procedures described herein can be embodied in 3GPP specifications. The following is some example text that can be added to 3GPP TS 38.331 (RRC protocol specification) V17.3.0 with a change request (CR), in accordance with some embodiments of the present disclosure. Underline indicates added text and ellipses indicate less relevant existing text omitted for brevity.

[0197] *** Begin 3GPP 38.331 text ***

[0198] 5.3.5.x LTM configuration and execution

[0199] 5.3.5.x.6 LTM cell switch execution Upon the indication by lower layers that an LTM cell switch procedure is triggered, or upon performing LTM cell switch execution upon cell selection performed while timer T311 was running, as defined in 5, 3, 7, 3, the UE shall:

[0200] 1> if the LTM cell switch execution is triggered by the indication of lower layers:

[0201] 2> apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received from lower layers according to clause 5.3.5.3;

[0202] 1> else (LTM cell switch execution upon cell selection performed while timer T311 was running):

[0203] 2> apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration of the LTM candidate cell selected while timer T311 was running, according to clause 5, 3, 5, 3;

[0204] 2> remove all entries within the MCG VarLTM-UE-Config, if any;

[0205] 2> remove all entries within the MCG VarLTM-Config, if any;

[0206] 2> remove LTM-Config, if any;

[0207] 2> remove the Itm-CSI-ReportConfigToAddModList instances for all Serving cells;

[0208] 2> perform the random access procedure;

[0209] 5.3.7 RRC connection re-establishment

[0210] 5.3.7.2 Initiation

[0211] Upon initiation of the procedure, the UE shall: l>if UE is not configured with attempt-LTM: or l>if UE is not configured with attemptCondReconfig'.

[0212] 2> reset MAC;

[0213] 2> release spCellConfig, if configured;

[0214] 2> suspend all RBs, and BH RLC channels for IAB-MT, and Uu Relay RLC channels for L2 U2N Relay UE, except SRBO and broadcast MRBs;

[0215] 2> release the MCG SCell(s), if configured;

[0216] 5.3.7.3 Actions following cell selection while T311 is running

[0217] Upon selecting a suitable NR cell, the UE shall: 1> if the cell selection is triggered by detecting radio link failure of the MCG or reconfiguration with sync failure of the MCG or mobility from NR failure, and l>if attemptCondReconfig is configured; and

[0218] 1> if the selected cell is not configured with CondEventTI , or the selected cell is configured with CondEventTl and leaving condition has not been fulfilled; and

[0219] 1> if the selected cell is one of the candidate cells for which the reconfigurationWithSync is included in the masterCellGroup in the MCG VarConditionalReconfig'.

[0220] 2> if the UE supports RLF-Report for conditional handover, set the choCellldm the VarRLF-Report to the global cell identity, if available, otherwise to the physical cell identity and carrier frequency of the selected cell;

[0221] 2> apply the stored condRRCReconfig associated to the selected cell and perform actions as specified in 5.3.5.3;

[0222] 1> if the cell selection is triggered by detecting radio link failure of the MCG or reconfiguration with sync failure of the MCG, or LTM cell switch failure or mobility from NR failure; and

[0223] 1> if attempt-LTM is configured; and

[0224] 1> if the selected cell is one of the LTM candidate cells in ue-LTM-Config within VarLTM- UE-Config

[0225] 2> perform LTM cell switch execution procedure for the selected LTM candidate cell and perform actions as specified in 5,3.5.x, 6; l>else:

[0226] 2>if UE is configured with attempt-LTM,' or

[0227] 2> if UE is configured with attemptCondReconfig'.

[0228] 3> reset MAC;

[0229] 3> release spCellConfig, if configured;

[0230] 3> release the MCG SCell(s), if configured;

[0231] 2> remove all the entries within the MCG VarConditionalReconfig, if any;

[0232] 2> remove all entries within the MCG VarLTM-UE-Config, if any;

[0233] 2> remove all entries within the MCG VarLTM-Config, if any;

[0234] 2> remove LTM-Config, if any;

[0235] 2> remove the Itm-CSI-ReportConfigToAddModList instances for all Serving cells; Editor ’s Note: FFS on whether a sub-clause is created for LTM release e.g., in case that is called by multiple procedures.

[0236] 2> release the PC5 RLC entity for SL-RLCO, if any;

[0237] 2> start timer T301 ;

[0238] 2> apply the default LI parameter values as specified in corresponding physical layer specifications except for the parameters for which values are provided in SIBf

[0239] 2> apply the default MAC Cell Group configuration as specified in 9.2.2;

[0240] 2> apply the CCCH configuration as specified in 9.1.1.2;

[0241] 2> apply the timeAlignmentTimerCommon included in SIBl,'

[0242] 2> initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;

[0243] NOTE 2: This procedure applies also if the UE returns to the source PCell.

[0244] Upon selecting an inter-RAT cell, the UE shall: l>perform the actions upon going to RRC IDLE as specified in 5.3.11, with release cause 'RRC connection failure'.

[0245] *** End 3GPP 38.331 text ***

[0246] As another example, rather than being added to clause 5.3.5.x.6 as above, a function for releasing LTM configurations can be specified in a newly defined clause referenced by clause

[0247] 5.3.5.x.6, as illustrated in the example text below. Underline indicates added text and ellipses indicate less relevant existing text omitted for brevity.

[0248] *** Begin 3 GPP text ***

[0249] 5.3.5.x.y Release LTM configuration

[0250] The UE shall:

[0251] 1> as a result of the release of LTM configurations:

[0252] 2> remove all entries within the MCG VarLTM-UE-Config, if any;

[0253] 2> remove all entries within the MCG VarLTM-Config, if any;

[0254] 2> remove LTM-Conflg, if any;

[0255] 2> remove the Itm-CSI-ReportConfigToAddModList instances for all Serving cells;

[0256] 5.3.5.x LTM configuration and execution

[0257] 5.3.5.x.6 LTM cell switch execution

[0258] Upon the indication by lower layers that an LTM cell switch procedure is triggered, or upon performing LTM cell switch execution upon cell selection performed while timer T311 was running, as defined in 5, 3, 7, 3, the UE shall: 1> if the LTM cell switch execution is triggered by the indication of lower layers:

[0259] 2> apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration identity as received from lower layers according to clause 5.3.5.3;

[0260] 1> else (LTM cell switch execution upon cell selection performed while timer T311 was running):

[0261] 2> apply the LTM configuration in ue-LTM-Config within VarLTM-UE-Config related to the LTM candidate cell configuration of the LTM candidate cell selected while timer T311 was running, according to clause 5, 3, 5, 3;

[0262] 2> perform the release of LTM configuration, as specified in clause 5.3.5.x.y;

[0263] 2> perform the random access procedure;

[0264] 5.3.7 RRC connection re-establishment

[0265] 5.3.7.2 Initiation

[0266] Upon initiation of the procedure, the UE shall: l>if UE is not configured with attempt-LTM or l>if UE is not configured with attemptCondReconfig'.

[0267] 2> reset MAC;

[0268] 2> release spCellConfig, if configured;

[0269] 2> suspend all RBs, and BH RLC channels for IAB-MT, and Uu Relay RLC channels for L2 U2N Relay UE, except SRBO and broadcast MRBs;

[0270] 2> release the MCG SCell(s), if configured;

[0271] 5.3.7.3 Actions following cell selection while T311 is running

[0272] Upon selecting a suitable NR cell, the UE shall:

[0273] 1> if the cell selection is triggered by detecting radio link failure of the MCG or reconfiguration with sync failure of the MCG or mobility from NR failure, and l>if attemptCondReconfig is configured; and

[0274] 1> if the selected cell is not configured with CondEventTI . or the selected cell is configured with CondEventTl and leaving condition has not been fulfilled; and 1> if the selected cell is one of the candidate cells for which the reconfigurationWithSync is included in the masterCellGroup in the MCG VarConditionalReconfig'.

[0275] 2> if the UE supports RLF-Report for conditional handover, set the choCellldm the VarRLF-Report to the global cell identity, if available, otherwise to the physical cell identity and carrier frequency of the selected cell;

[0276] 2> apply the stored condRRCReconfig associated to the selected cell and perform actions as specified in 5.3.5.3;

[0277] 1> if the cell selection is triggered by detecting radio link failure of the MCG or reconfiguration with sync failure of the MCG, or LTM cell switch failure or mobility from NR failure; and

[0278] 2> if attempt-LTM is configured; and

[0279] 2> if the selected cell is one of the LTM candidate cells in ue-LTM-Config within VarLTM- UE-Config:

[0280] 2> perform LTM cell switch execution procedure for the selected LTM candidate cell and perform actions as specified in 5,3.5.x, 6; l>else:

[0281] 2>if UE is configured with attempt-LTM., or

[0282] 2> if UE is configured with attemptCondReconfig'.

[0283] 3> reset MAC;

[0284] 3> release spCellConfig, if configured;

[0285] 3> release the MCG SCell(s), if configured;

[0286] 2> remove all the entries within the MCG VarConditionalReconfig, if any;

[0287] 2> perform the release of LTM configuration, as specified in clause 5.3,5,x,y;

[0288] 2> release the PC5 RLC entity for SL-RLCO, if any;

[0289] 2> start timer T301 ;

[0290] 2> apply the default LI parameter values as specified in corresponding physical layer specifications except for the parameters for which values are provided in SIBf

[0291] 2> apply the default MAC Cell Group configuration as specified in 9.2.2;

[0292] 2> apply the CCCH configuration as specified in 9.1.1.2;

[0293] 2> apply the timeAlignmentTimerCommon included in SIBE,

[0294] 2> initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4; NOTE 2: This procedure applies also if the UE returns to the source PCell.

[0295] Upon selecting an inter-RAT cell, the UE shall: l>perform the actions upon going to RRC IDLE as specified in 5.3.11, with release cause 'RRC connection failure'.

[0296] *** End 3GPP text ***

[0297] Figures 12-13 show some ASN.l data structures for RRC information elements (IES) that can be used with the example 3GPP TS 38.331 specification text listed above. In particular, Figure 12 shows an ASN.1 data structure for an RRCReconfiguration-vl8xy-IEs IE that can be part of an RRCReconfiguration message received by a UE. The IE shown in Figure 12 includes an Itm- Config-rl8 field that is further specified in Figure 13. This field includes the following sub-fields, all of which are optional:

[0298] • Itm-ReferenceConfiguration-r 18, which specifies a reference configuration for LTM;

[0299] • ltm-CandidateToReleaseList-rl8, which specifies a list of current LTM candidates to release;

[0300] • ltm-CandidateToAddModList-rl8, which specifies a list of LTM candidates to add or modify;

[0301] • ltm-CandidateNoResetL2-List-rl8, which specifies a list of existing LTM candidates that should not undergo an L2 reset; and

[0302] • attempt ETM-r 18, whose presence with a value of “TRUE” indicates that the UE should attempt LTM fast recovery and whose absence indicates that the UE is not configured to perform (i.e., should not attempt) LTM fast recovery.

[0303] The embodiments described above can be further illustrated with reference to Figures 14- 15, which depict exemplary methods (e.g., procedures) for a UE and a RAN node, respectively. Put differently, various features of the operations described below correspond to various embodiments described above. Even so, the description of Figures 14-15 may refer to other embodiments not explicitly described above.

[0304] The exemplary methods shown in Figures 14-15 can be used cooperatively to provide benefits, advantages, and / or solutions to problems described herein. Although Figures 14-15 illustrate the exemplary methods by specific blocks in particular orders, the operations corresponding to the blocks can be performed in different orders than shown and can be combined and / or divided into blocks and / or operations having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0305] More specifically, Figure 14 illustrates an exemplary method (e.g., procedure) for a UE configured to perform LTM in a RAN, according to various embodiments of the present disclosure. The exemplary method shown in Figure 13 can be performed by a UE (e.g., wireless device) such as described elsewhere herein.

[0306] The exemplary method includes the operations of block 1410, where the UE receives from the RAN a reconfiguration message that includes one or more LTM configurations. The exemplary method also includes the operations of blocks 1420-1425, where the UE initiates a re-establishment procedure towards a second cell in response to detecting a failure event while connected to the RAN via a first cell. For example, the re-establishment procedure may be a layer- 3 (e.g., RRC) re-establishment procedure.

[0307] The exemplary method also includes the operations of blocks 1430 and 1450, where in response to determining that the UE is not configured to perform LTM fast recovery (i.e., from the failure event), the UE discards one or more of the following information after initiating the reestablishment procedure:

[0308] • at least one of the LTM configurations, or portions thereof; and

[0309] • information derived from the one or more LTM configurations;

[0310] The exemplary method also includes the operations of block 1460, where after discarding the information, the UE sends a re-establishment request to the RAN via the second cell.

[0311] In some embodiments, the detected failure event is one of the following:

[0312] • a radio link failure (RLF);

[0313] • a handover failure (HOF);

[0314] • an LTM cell switch failure;

[0315] • a conditional handover (CHO) failure;

[0316] • a reconfiguration failure;

[0317] • a random access failure;

[0318] • a beam failure detection (BFD); or

[0319] • reaching a maximum number failed transmission or retransmission of radio link control (RLC) protocol data units (PDUs).

[0320] In some embodiments, determining that the UE is not configured to attempt LTM fast recovery in block 1430 includes the operations of sub-block 1431, where the UE detects absence of an attempt-LTM field in one of the LTM configurations. Figure 13 shows an example of these embodiments.

[0321] In some embodiments, the exemplary method can also include the operations of block 1440, where the UE can perform one or more of the following operations (labelled below with corresponding sub-block numbers) based on determining it is not configured to perform LTM fast recovery: • (1441) resetting the UE’s medium access control (MAC) layer;

[0322] • (1442) suspending at least a portion of configured radio bearers, backhaul radio link control (RLC) channels, and sidelink relay RLC channels;

[0323] • (1443) releasing one or more configurations previously provided by the RAN; and

[0324] • (1444) stopping one or more supervision timers that are running in the UE.

[0325] For example, operations for releasing configurations in sub-block 1443 and stopping supervision timers in sub-block 1444 can include any of the following:

[0326] • releasing spCellConfig, if configured;

[0327] • releasing MCG SCell(s), if configured;

[0328] • releasing MR-DC, if configured:

[0329] • releasing delayBudgetReportingConfig, if configured, and stopping timer T342, if running;

[0330] • releasing overheatingAssistanceConfig, if configured, and stopping timer T345, if running;

[0331] • releasing idc-AssistanceConfig, if configured;

[0332] • releasing btNameList, if configured;

[0333] • releasing wlanNameList, if configured;

[0334] • releasing sensorNameList, if configured;

[0335] • releasing drx-PreferenceConfig for the MCG, if configured, and stopping timer T346a associated with the MCG, if running;

[0336] • releasing maxBW-PreferenceConfig for the MCG, if configured, and stopping timer T346b associated with the MCG, if running;

[0337] • releasing maxCC-PreferenceConfig for the MCG, if configured, and stopping timer T346c associated with the MCG, if running;

[0338] • releasing maxMIMO-LayerPreferenceConfig for the MCG, if configured, and stopping timer T346d associated with the MCG, if running;

[0339] • releasing minSchedulingOffsetPreferenceConfig for the MCG, if configured, and stopping timer T346e associated with the MCG, if running;

[0340] • releasing rlm-RelaxationReportingConfig for the MCG, if configured, and stopping timer T346j associated with the MCG, if running;

[0341] • releasing bfd-RelaxationReportingConfig for the MCG, if configured, and stopping timer T346k associated with the MCG, if running;

[0342] • releasing releasingPreferenceConfig, if configured, and stopping timer T346f, if running;

[0343] • releasing onDemandSIB-Request if configured, and stopping timer T350, if running; • releasing referenceTimePreferenceReporting, if configured;

[0344] • releasing sl-AssistanceConfigNR, if configured;

[0345] • releasing obtainCommonLocation, if configured;

[0346] • releasing musim-GapAssistanceConfig, if configured, and stopping timer T346h, if running;

[0347] • releasing musim-LeaveAssistanceConfig, if configured;

[0348] • releasing ul-GapFR2-PreferenceConfig, if configured;

[0349] • releasing scg-DeactivationPreferenceConfig, if configured, and stopping timer T346i, if running;

[0350] • releasing propDelayDiffReportConfig, if configured;

[0351] • releasing rrm-MeasRelaxationReportingConfig, if configured;

[0352] • releasing maxBW-PreferenceConfigFR2-2, if configured;

[0353] • releasing maxMIMO-LayerPreferenceConfigFR2-2, if configured; and

[0354] • releasing minSchedulingOffsetPreferenceConfigExt, if configured.

[0355] In some embodiments, each LTM configuration includes one or more of the following:

[0356] • one or more LTM candidate cell configurations;

[0357] • lower layer measurement configurations for respective LTM candidate cells;

[0358] • measurement reporting configurations for respective LTM candidate cells;

[0359] • downlink (DL) pre-synchronization configuration for LTM;

[0360] • uplink (UL) pre-synchronization configuration for LTM;

[0361] • an indication of whether a layer-2 (L2) reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell;

[0362] • an indication of whether fast LTM recovery should be attempted; and

[0363] • execution configurations for LTM cell switch procedures to respective LTM candidate cells.

[0364] In some of these embodiments, the one or more LTM candidate cell configurations are arranged according to one of the following:

[0365] • respective complete LTM candidate cell configurations; or

[0366] • a reference configuration and respective LTM candidate cell configurations that are deltas relative to the reference configuration.

[0367] In some variants of these embodiments, each LTM candidate cell configuration is arranged as an octet string that contains an RRCReconfiguration message.

[0368] In some of these embodiments, each lower layer measurement configuration includes one or more of the following associated with an LTM candidate cell to be measured: • frequency, sub-carrier spacing, periodicity, and / or time-domain positions of synchronization signal / PBCH blocks (SSBs) to be measured;

[0369] • average energy per resource element (EPRE) of REs that carry secondary synchronization signals (SSS);

[0370] • physical cell identity (PCI);

[0371] • a first list of LTM channel state information (CSI) resource configurations, with each LTM CSI resource configuration indicating CSI resources to be measured by the UE for LTM;

[0372] • a second list of existing LTM CSI resource configurations to be released by the UE;

[0373] • one or more SSB resource sets to be measured by the UE, or identifiers thereof; and

[0374] • PCIs associated with the SSB resource sets.

[0375] In some of these embodiments, one or more of the following is included in each of the LTM candidate cell configurations:

[0376] • the lower layer measurement configurations for the LTM candidate cell;

[0377] • the measurement reporting configurations for the LTM candidate cell;

[0378] • DL pre-synchronization configuration for the LTM candidate cell; and

[0379] • UL pre-synchronization configuration for the LTM candidate cell.

[0380] In some of these embodiments, each DL pre-sync configuration includes one or more of the following associated with an LTM candidate cell:

[0381] • a list of DL transmission configuration indicator (TCI) states;

[0382] • a list of UL TCI states;

[0383] • a unified TCI state type for DL and UL;

[0384] • a quasi-colocation (QCL) source configuration; and

[0385] • a QCL type associated with one or more DL RS.

[0386] In some of these embodiments, each UL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: a random-access preamble configuration, and a time / frequency resource configuration for a Physical Random Access Channel (PRACH).

[0387] In some embodiments, the exemplary method can also include the operations of block 1415, where the UE can store the following information:

[0388] • the received one or more LTM configurations in a first RRC variable; and

[0389] « information derived from the received one or more LTM configurations in a second RRC variable

[0390] In such embodiments, discarding the information in block 1450 after initiating the reestablishment procedure includes the operations of sub-block 1451, where the UE removes or deletes information from one or more entries in the first and second RRC variables. In some of these embodiments, the first RRC variable is Var-LTM-Config and the second RRC variable is VarL TM- UE-Config.

[0391] In some embodiments, the first cell is served by a first DU of the RAN node and the second cell is served by a second DU of the RAN node. The discarded information includes an LTM candidate cell configuration for a third cell served by a third DU of the RAN node. Figure 10 shows an example of these embodiments.

[0392] In some embodiments, the reconfiguration message is an RRCReconfiguration message and is received via the first cell and the re-establishment request is an RRCReestablishmentRequest message.

[0393] In addition, Figure 15 illustrates an exemplary method (e.g., procedure) for a RAN node configured to facilitate LTM by UEs in the RAN, according to various embodiments of the present disclosure. The exemplary method shown in Figure 15 can be performed by a RAN node (e.g., base station, gNB, etc.) or CU / DUs thereof, such as described elsewhere herein.

[0394] The exemplary method includes the operations of block 1510-1520, where the RAN node sends to a UE a reconfiguration message that includes one or more LTM configurations and receives a re-establishment request from the UE via a second cell. The re-establishment request is received responsive to a failure event at the UE while the UE is connected to the RAN node via a first cell but not configured to perform LTM fast recovery (i.e., from the failure event). For example, the re-establishment request may be for initiating a layer-3 (e.g., RRC) re-establishment procedure, such as discussed above in relation to UE embodiments. The exemplary method also includes the operations of block 1530, where in response to the re-establishment request, the RAN node discards at least one of the LTM configurations or portions thereof.

[0395] In various embodiments, the failure event can be any of the failure events discussed above in relation to UE embodiments. In various embodiments, the one or more LTM configurations can have any of the contents and / or structure of the corresponding LTM configurations discussed above in relation to UE embodiments, thereby facilitating complementary operations by UE and RAN node. For example, absence of an attempt-LTM field in one of the LTM configurations can indicate that the UE should not (i.e. is not configured to) attempt LTM fast recovery.

[0396] In some embodiments, the RAN node includes a CU and a second DU that serves the second cell. The re-establishment message is an RRCReestablishmentRequest message and is received by the second DU. In such case, the exemplary method also includes the operations of block 1540, where the second DU sends, to the CU, the RRCReestablishmentRequest message in an Uplink RRC Message Transfer message.

[0397] In some of these embodiments, the RAN node also includes a first DU that serves the first cell. The reconfiguration message is an RRCReconfiguration message sent by the first DU via the first cell. In such case, the exemplary method also includes the operations of block 1525, where the CU sends, to the first DU, the RRCReconfiguration message in a Downlink RRC Message Transfer message.

[0398] In some of these embodiments, the RAN node also includes a third DU that serves a third cell and at least one of the LTM configurations includes an LTM candidate cell configuration for the third cell. In such case, discarding at least one of the LTM configurations or portions thereof in block 1530 includes the operations of sub-block 1531, where the CU sends to the third DU a command or request to discard at least the LTM candidate cell configuration for the third cell. Figure 10 shows an example of these embodiments.

[0399] 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.

[0400] Figure 16 shows an example of a communication system 1600 in accordance with some embodiments. In this example, communication system 1600 includes a telecommunication network 1602 that includes an access network 1604 (e.g., RAN) and a core network 1606, which includes one or more core network nodes 1608. Access network 1604 includes one or more access network nodes, such as network nodes 1610a-b (one or more of which may be generally referred to as network nodes 1610), or any other similar 3 GPP access nodes or non-3GPP access points.

[0401] As will be appreciated by those of skill in the art, network node implementations are not limited to a radio portion and a baseband portion that are supplied and integrated by a single vendor, but may include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1602 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1602 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 1602, including one or more network nodes 1610 and / or core network nodes 1608.

[0402] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the 0-RAN Alliance or comparable technologies. Network nodes 1610 facilitate direct or indirect connection of UEs, such as by connecting UEs 1612a-d (one or more of which may be generally referred to as UEs 1612) to core network 1606 over one or more wireless connections.

[0403] 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 1600 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 1600 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0404] UEs 1612 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1610 and other communication devices. Similarly, network nodes 1610 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1612 and / or with other network nodes or equipment in telecommunication network 1602 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1602.

[0405] In the depicted example, core network 1606 connects network nodes 1610 to one or more hosts, such as host 1616. 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 1606 includes one or more core network nodes (e.g., 1608) 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 1608. 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).

[0406] Host 1616 may be under the ownership or control of a service provider other than an operator or provider of access network 1604 and / or telecommunication network 1602, and may be operated by the service provider or on behalf of the service provider. Host 1616 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.

[0407] As a whole, communication system 1600 of Figure 16 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.

[0408] In some examples, telecommunication network 1602 is a cellular network that implements 3 GPP standardized features. Accordingly, telecommunication network 1602 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1602. For example, telecommunication network 1602 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.

[0409] In some examples, UEs 1612 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 1604 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1604. 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).

[0410] In the example, hub 1614 communicates with access network 1604 to facilitate indirect communication between one or more UEs (e.g., 1612c and / or 1612d) and network nodes (e.g., 1610b). In some examples, hub 1614 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1614 may be a broadband router enabling access to core network 1606 for the UEs. As another example, hub 1614 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 1610, or by executable code, script, process, or other instructions in hub 1614. As another example, hub 1614 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 1614 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1614 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1614 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1614 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0411] Hub 1614 may have a constant / persistent or intermittent connection to network node 1610b. Hub 1614 may also allow for a different communication scheme and / or schedule between hub 1614 and UEs (e.g., 1612c and / or 1612d), and between hub 1614 and core network 1606. In other examples, hub 1614 is connected to core network 1606 and / or one or more UEs via a wired connection. Moreover, hub 1614 may be configured to connect to an M2M service provider over access network 1604 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1610 while still connected via hub 1614 via a wired or wireless connection. In some embodiments, hub 1614 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1610b. In other embodiments, hub 1614 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1610b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0412] Figure 17 shows a UE 1700 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 3 GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0413] 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 the benefit of a user (e.g., a smart power meter).

[0414] UE 1700 includes processing circuitry 1702 that is operatively coupled via bus 1704 to input / output interface 1706, power source 1708, memory 1710, communication interface 1712, and / or optionally one or more other components not explicitly shown. Certain UEs may utilize all or a subset of the components shown in Figure 17. 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.

[0415] Processing circuitry 1702 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 1710. Processing circuitry 1702 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 1702 may include multiple central processing units (CPUs).

[0416] In the example, input / output interface 1706 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 1700. 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.

[0417] In some embodiments, power source 1708 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 1708 may further include power circuitry for delivering power from power source 1708 itself, and / or an external power source, to the various parts of UE 1700 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 1708. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1708 to make the power suitable for the respective components of UE 1700 to which power is supplied.

[0418] Memory 1710 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 1710 includes one or more application programs 1714, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1716. Memory 1710 may store, for use by UE 1700, any of a variety of various operating systems or combinations of operating systems.

[0419] Memory 1710 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 1710 may allow UE 1700 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 1710, which may be or comprise a device-readable storage medium.

[0420] Processing circuitry 1702 may be configured to communicate with an access network or other network using communication interface 1712. Communication interface 1712 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1722. Communication interface 1712 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 1718 and / or a receiver 1720 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1718 and / or receiver 1720 may be coupled to one or more antennas (e.g., 1722) and may share circuitry components, software, and / or firmware, or may alternatively be implemented separately.

[0421] In the illustrated embodiment, communication functions of communication interface 1712 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 / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0422] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1712, 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., an alert is sent when moisture is detected), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0423] 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.

[0424] 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 1700 shown in Figure 17.

[0425] As 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 3 GPP 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.

[0426] 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.

[0427] Figure 18 shows a network node 1800 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and 0-RAN nodes or components of an 0-RAN node (e.g, 0-RU, 0-DU, O-CU).

[0428] 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 0-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).

[0429] 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).

[0430] Network node 1800 includes processing circuitry 1802, memory 1804, communication interface 1806, and power source 1808. Network node 1800 may be composed of multiple physically separate components (e.g, NodeB and RNC components, or BTS and BSC components, etc.), each of which may include their own respective components. In certain scenarios in which network node 1800 comprises multiple separate components (e.g, BTS and BSC), one or more of these 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 1800 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g, separate memory 1804 for different RATs) and some components may be reused (e.g, a same antenna 1810 may be shared by different RATs). Network node 1800 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1800, 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 1800.

[0431] Processing circuitry 1802 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 1800 components, such as memory 1804, to provide network node 1800 functionality.

[0432] In some embodiments, processing circuitry 1802 includes a system on a chip (SOC). In some embodiments, processing circuitry 1802 includes radio frequency (RF) transceiver circuitry 1812 and / or baseband processing circuitry 1814. In some embodiments, RF transceiver circuitry 1812 and / or baseband processing circuitry 1814 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 1812 and / or baseband processing circuitry 1814 may be on the same chip or set of chips, boards, or units.

[0433] Memory 1804 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 1802. Memory 1804 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 1804a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1802 and utilized by network node 1800. Memory 1804 may be used to store any calculations made by processing circuitry 1802 and / or any data received via communication interface 1806. In some embodiments, processing circuitry 1802 and memory 1804 is integrated.

[0434] Communication interface 1806 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 1806 comprises port(s) / terminal(s) 1816 to send and receive data, for example to and from a network over a wired connection. Communication interface 1806 also includes radio front- end circuitry 1818 that may be coupled to, or in certain embodiments a part of, antenna 1810. Radio front-end circuitry 1818 comprises filters 1820 and amplifiers 1822. Radio front-end circuitry 1818 may be connected to an antenna 1810 and processing circuitry 1802. The radio front-end circuitry may be configured to condition signals communicated between antenna 1810 and processing circuitry 1802. Radio front-end circuitry 1818 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1818 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1820 and / or amplifiers 1822. The radio signal may then be transmitted via antenna 1810. Similarly, when receiving data, antenna 1810 may collect radio signals which are then converted into digital data by radio front-end circuitry 1818. The digital data may be passed to processing circuitry 1802. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0435] In certain alternative embodiments, network node 1800 does not include separate radio front-end circuitry 1818, instead, processing circuitry 1802 includes radio front-end circuitry and is connected to antenna 1810. Similarly, in some embodiments, all or some of RF transceiver circuitry 1812 is part of communication interface 1806. In still other embodiments, communication interface 1806 includes one or more ports or terminals 1816, radio front-end circuitry 1818, and RF transceiver circuitry 1812, as part of a radio unit (not shown), and communication interface 1806 communicates with baseband processing circuitry 1814, which is part of a digital unit (not shown).

[0436] Antenna 1810 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1810 may be coupled to radio front-end circuitry 1818 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1810 is separate from network node 1800 and connectable to network node 1800 through an interface or port.

[0437] Antenna 1810, communication interface 1806, and / or processing circuitry 1802 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 1810, communication interface 1806, and / or processing circuitry 1802 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.

[0438] Power source 1808 provides power to the various components of network node 1800 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1808 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1800 with power for performing the functionality described herein. For example, network node 1800 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 1808. As a further example, power source 1808 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.

[0439] Embodiments of network node 1800 may include additional components beyond those shown in Figure 18 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 1800 may include user interface equipment to allow input of information into network node 1800 and to allow output of information from network node 1800. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1800.

[0440] Figure 19 is a block diagram illustrating a virtualization environment 1900 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 1900 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 1900 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.

[0441] Applications 1902 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1900 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0442] Hardware 1904 includes processing circuitry, memory that stores software and / or instructions (collectively denoted computer program 1904a, 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 processing circuitry to instantiate one or more virtualization layers 1906 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1908a- b (one or more of which may be generally referred to as VMs 1908), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1906 may present a virtual operating platform that appears like networking hardware to VMs 1908.

[0443] VMs 1908 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1906. Different embodiments of the instance of a virtual appliance 1902 may be implemented on one or more of VMs 1908, 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.

[0444] In the context of NFV, each VM 1908 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 1908, and that part of hardware 1904 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 1908 on top of hardware 1904 and corresponds to application 1902.

[0445] Hardware 1904 may be implemented in a standalone network node with generic or specific components. Hardware 1904 may implement some functions via virtualization. Alternatively, hardware 1904 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 1910, which, among others, oversees lifecycle management of applications 1902. In some embodiments, hardware 1904 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 1912 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.

[0446] 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.

[0447] 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.

[0448] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0449] Furthermore, functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and / or network nodes. In other words, it is contemplated that the functions of a network node and a wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

[0450] 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.

[0451] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood, that although these terms (and / or other terms that can be synonymous to one another) can be used synonymously herein, there can be instances when such words can be intended to not be used synonymously.

[0452] The techniques and apparatus described herein include, but are not limited to, the following enumerated examples:

[0453] Al . A method for a user equipment (UE) configured to perform layer- 1 or layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: receiving from the RAN a reconfiguration message that includes one or more LTM configurations; detecting a failure event while connected to the RAN via a first cell; initiating a re-establishment procedure towards a second cell in response to detecting the failure event; and discarding one or more of the following information after initiating the reestablishment procedure: at least one of the LTM configurations, or portions thereof; and information derived from the one or more LTM configurations; after discarding the information, sending a re-establishment request to the RAN via the second cell. A2. The method of embodiment Al, wherein the detected failure event is one of the following: a handover failure (HOF); an LTM cell switch failure; a conditional handover (CHO) failure; a reconfiguration failure; a random access failure; a beam failure detection (BFD); and reaching a maximum number failed transmission or retransmission of radio link control (RLC) protocol data units (PDUs).

[0454] A3. The method of any of embodiments A1-A2, wherein initiating the re-establishment procedure towards the second cell is based on determining not to perform an LTM fast recovery procedure in response to detecting the failure event.

[0455] A3a. The method of embodiments A3, wherein determining not to perform an LTM fast recovery procedure in response to detecting the failure event is based on one of the following: selecting the second cell while a timer (T311) is running, wherein the second cell is not an LTM candidate cell configured for the UE; or determining that the UE is not configured to perform LTM fast recovery.

[0456] A3b. The method of embodiment A3a, wherein determining that the UE is not configured to perform LTM fast recovery is based on a value of a field in one of the LTM configurations.

[0457] A3c. The method of any of embodiments A3-A3b, further comprising performing one or more of the following operations based on determining not to perform an LTM fast recovery procedure in response to detecting the failure event: resetting the UE’s medium access control (MAC) layer; suspending at least a portion of configured radio bearers, backhaul radio link control (RLC) channels, and sidelink relay RLC channels; releasing one or more configurations previously provided by the RAN; and stopping one or more supervision timers that are running in the UE.

[0458] A4. The method of any of embodiments Al-A3c, wherein each LTM configuration includes one or more of the following: one or more LTM candidate cell configurations; lower layer measurement configurations for respective LTM candidate cells; measurement reporting configurations for respective LTM candidate cells; downlink (DL) pre-synchronization configuration for LTM; uplink (UL) pre-synchronization configuration for LTM; an indication of whether a layer-2 (L2) reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell; an indication of whether fast LTM recovery should be attempted; and execution configurations for LTM cell switch procedures to respective LTM candidate cells.

[0459] A4a. The method of embodiment A4, wherein the one or more LTM candidate cell configurations are arranged according to one of the following: respective complete LTM candidate cell configurations; or a reference configuration and respective LTM candidate cell configurations that are deltas relative to the reference configuration.

[0460] A4b. The method of embodiment A4a, wherein each LTM candidate cell configuration is arranged as an octet string that contains an RRCReconfiguration message.

[0461] A4c. The method of any of embodiments A4-A4b, wherein each lower layer measurement configuration includes one or more of the following associated with an LTM candidate cell to be measured: frequency, sub-carrier spacing, periodicity, and / or time-domain positions of synchronization signal / PBCH blocks (SSBs) to be measured; average energy per resource element (EPRE) of REs that carry secondary synchronization signals (SSS); physical cell identity (PCI); a first list of LTM channel state information (CSI) resource configurations, with each LTM CSI resource configuration indicating CSI resources to be measured by the UE for LTM; a second list of existing LTM CSI resource configurations to be released by the UE; one or more SSB resource sets to be measured by the UE, or identifiers thereof; and PCIs associated with the SSB resource sets. A4d. The method of any of embodiments A4-A4c, wherein one or more of the following is included in each of the LTM candidate cell configurations: the lower layer measurement configurations for the LTM candidate cell; the measurement reporting configurations for the LTM candidate cell;

[0462] DL pre-synchronization configuration for the LTM candidate cell; and UL pre-synchronization configuration for the LTM candidate cell.

[0463] A4e. The method of any of embodiments A4-A4d, each DL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: a list of DL transmission configuration indicator (TCI) states; a list of UL TCI states; a unified TCI state type for DL and UL; a quasi-colocation (QCL) source configuration; and a QCL type associated with one or more DL RS.

[0464] A4f. The method of any of embodiments A4-A4e, wherein each UL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: a random-access preamble configuration, and a time / frequency resource configuration for a Physical Random Access Channel (PRACH).

[0465] A5. The method of any of embodiments A1-A4, further comprising storing the following information: the received one or more LTM configurations in a first radio resource control (RRC) variable; and information derived from the received one or more LTM configurations in a second RRC variable, wherein discarding the information after initiating the re-establishment procedure comprises removing or deleting information from one or more entries in the first and second RRC variables.

[0466] A5a. The method of embodiment A5, wherein the first RRC variable is Var-LTM-Config and the second RRC variable is VarLTM-UE-Config .

[0467] A6. The method of any of embodiments A1-A5, wherein: the reconfiguration message is an RRCReconfiguration message received from a central unit (CU) of a RAN node; the first cell is served by a first DU of the RAN node; the second cell is served by a second DU of the RAN node; and at least one of the LTM configurations include an LTM candidate cell configuration for a third cell served by a third DU of the RAN node.

[0468] Bl. A method for a radio access network (RAN) node configured to facilitate layer- 1 or layer-2 triggered inter-cell mobility (LTM) by user equipment (UE) in the RAN, the method comprising: sending, to a UE, a reconfiguration message that includes one or more LTM configurations; receiving a re-establishment request from the UE via a second cell, wherein the reestablishment request is received responsive to the UE detecting a failure event while connected to the RAN node via a first cell; in response to the re-establishment request, discarding at least one of the LTM configurations or portions thereof.

[0469] B2. The method of embodiment Bl, wherein the detected failure event is one of the following: a handover failure (HOF); an LTM cell switch failure; a conditional handover (CHO) failure; a reconfiguration failure; a random access failure; a beam failure detection (BFD); and reaching a maximum number failed transmission or retransmission of radio link control (RLC) protocol data units (PDUs).

[0470] B3. The method of any of embodiments B1-B2, wherein: the RAN node comprises a centralized unit (CU) and a second distributed unit (DU) that serves the second cell; the reconfiguration message is an RRCReconfiguration message sent by the CU; the re-establishment message is an RRCReestablishmentRequest message received by the second DU; and the method further comprises forwarding, by the second DU to the CU, the RRCReestablishmentRequest message in an Uplink RRC Message Transfer message.

[0471] B3a. The method of embodiment B3, wherein the RAN node also comprises a first DU that serves the first cell.

[0472] B3b. The method of any of embodiments B3-B3a, wherein the RAN node also comprises a third DU and at least one of the LTM configurations include an LTM candidate cell configuration for a third cell served by the third DU.

[0473] B3c. The method of embodiment B3b, wherein discarding at least one of the LTM configurations or portions thereof comprises sending to the third DU a command or request to discard at least the LTM candidate cell configuration for the third cell.

[0474] B4. The method of any of embodiments Bl-B3c, wherein each LTM configuration includes one or more of the following: one or more LTM candidate cell configurations; lower layer measurement configurations for respective LTM candidate cells; measurement reporting configurations for respective LTM candidate cells; downlink (DL) pre-synchronization configuration for LTM; uplink (UL) pre-synchronization configuration for LTM; an indication of whether a layer-2 (L2) reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell; an indication of whether fast LTM recovery should be attempted; and execution configurations for LTM cell switch procedures to respective LTM candidate cells.

[0475] B4a. The method of embodiment B4, wherein the one or more LTM candidate cell configurations are arranged according to one of the following: respective complete LTM candidate cell configurations; or a reference configuration and respective LTM candidate cell configurations that are deltas relative to the reference configuration. B4b. The method of embodiment B4a, wherein each LTM candidate cell configuration is arranged as an octet string that contains an RRCReconfiguration message.

[0476] B4c. The method of any of embodiments B4-B4b, wherein each lower layer measurement configuration includes one or more of the following associated with an LTM candidate cell to be measured: frequency, sub-carrier spacing, periodicity, and / or time-domain positions of synchronization signal / PBCH blocks (SSBs) to be measured; average energy per resource element (EPRE) of REs that carry secondary synchronization signals (SSS); physical cell identity (PCI); a first list of LTM channel state information (CSI) resource configurations, with each LTM CSI resource configuration indicating CSI resources to be measured by the UE for LTM; a second list of existing LTM CSI resource configurations to be released by the UE; one or more SSB resource sets to be measured by the UE, or identifiers thereof; and PCIs associated with the SSB resource sets.

[0477] B4d. The method of any of embodiments B4-B4c, wherein one or more of the following is included in each of the LTM candidate cell configurations: the lower layer measurement configurations for the LTM candidate cell; the measurement reporting configurations for the LTM candidate cell;

[0478] DL pre-synchronization configuration for the LTM candidate cell; and UL pre-synchronization configuration for the LTM candidate cell.

[0479] B4e. The method of any of embodiments B4-B4d, each DL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: a list of DL transmission configuration indicator (TCI) states; a list of UL TCI states; a unified TCI state type for DL and UL; a quasi-colocation (QCL) source configuration; and a QCL type associated with one or more DL RS.

[0480] B4f. The method of any of embodiments B4-B4e, wherein each UL pre-sync configuration includes one or more of the following associated with an LTM candidate cell: a random-access preamble configuration, and a time / frequency resource configuration for a Physical Random Access Channel (PRACH).

[0481] Cl . A user equipment (UE) configured to perform layer-1 or layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with the RAN via one or more cells; and processing circuitry operably coupled to the communication interface circuitry, wherein the processing circuitry and communication interface circuitry are further configured to perform operations corresponding to any of the methods of embodiments A1-A6.

[0482] C2. A user equipment (UE) configured to perform layer-1 or layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE being further configured to perform operations corresponding to any of the methods of embodiments A1-A6.

[0483] C3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform layer- 1 or layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A6.

[0484] C4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform layer- 1 or layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A6.

[0485] DI. A radio access network (RAN) node configured to facilitate layer-1 or layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs) in the RAN, the RAN node comprising: processing circuitry and communication interface circuitry arranged as a centralized unit (CU) and one or more distributed units (DUs), wherein the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments Bl- B4f. D2. A radio access network (RAN) node configured to facilitate layer- 1 or layer-2 triggered inter-cell mobility (LTM) by user equipment (UE) in the RAN, the RAN node being further configured to perform operations corresponding to any of the methods of embodiments Bl-B4f. D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate layer- 1 or layer-2 triggered inter-cell mobility (LTM) by user equipment (UE) in the RAN, configure the RAN node to perform operations corresponding to any of the methods of embodiments Bl-B4f.

[0486] D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate layer- 1 or layer-2 triggered inter-cell mobility (LTM) by user equipment (UE) in the RAN, configure the RAN node to perform operations corresponding to any of the methods of embodiments Bl -B4f.

Claims

CLAIMS1. A method for a user equipment, UE, configured to perform layer-1 or layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: receiving (1410) from the RAN a reconfiguration message that includes one or more LTM configurations; initiating (1425) a re-establishment procedure towards a second cell in response to detecting (1420) a failure event while connected to the RAN via a first cell; in response to determining (1430) that the UE is not configured to perform LTM fast recovery, discarding (1450) one or more of the following information after initiating the re-establishment procedure: at least one of the LTM configurations, or portions thereof; and information derived from the one or more LTM configurations; and after discarding the information, sending (1460) a re-establishment request to the RAN via the second cell.

2. The method of claim 1, wherein the failure event is one of the following: a radio link failure, RLF; a handover failure, HOF; an LTM cell switch failure; a conditional handover, CHO, failure; a reconfiguration failure; a random access failure; a beam failure detection, BFD; and reaching a maximum number failed transmission or retransmission of radio link control, RLC, protocol data units, PDUs.

3. The method of any of claims 1-2, wherein determining (1430) that the UE is not configured to perform LTM fast recovery comprises detecting (1431) absence of an attempt- LTM field in one of the LTM configurations.

4. The method of any of claims 1-3, further comprising performing (1440) one or more of the following operations based on determining (1430) that the UE is not configured to perform LTM fast recovery: resetting (1441) the UE’s medium access control, MAC, layer;suspending (1442) at least a portion of configured radio bearers, backhaul radio link control, RLC, channels, and sidelink relay RLC channels; releasing (1443) one or more configurations previously provided by the RAN; and stopping (1444) one or more supervision timers that are running in the UE.

5. The method of any of claims 1-4, wherein each of the one or more LTM configurations includes one or more of the following: one or more LTM candidate cell configurations; lower layer measurement configurations for respective LTM candidate cells; measurement reporting configurations for respective LTM candidate cells; downlink, DL, pre-synchronization configuration for LTM; uplink, UL, pre-synchronization configuration for LTM; an indication of whether a layer-2 reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell; an indication of whether fast LTM recovery should be attempted; and execution configurations for LTM cell switch procedures to respective LTM candidate cells.

6. The method of claim 5, wherein the one or more LTM candidate cell configurations are arranged according to one of the following: respective complete LTM candidate cell configurations; or a reference configuration and respective LTM candidate cell configurations that are deltas relative to the reference configuration.

7. The method of claim 6, wherein each of the one or more LTM candidate cell configurations is arranged as an octet string that contains an RRCReconfiguration message.

8. The method of any of claims 5-7, wherein one or more of the following is included in each of the LTM candidate cell configurations: the lower layer measurement configurations for the LTM candidate cell; the measurement reporting configurations for the LTM candidate cell;DL pre-synchronization configuration for the LTM candidate cell; and UL pre-synchronization configuration for the LTM candidate cell.

9. The method of any of claims 1-8, wherein:the first cell is served by a first distributed unit, DU, of a RAN node; the second cell is served by a second DU of the RAN node; and the discarded information includes an LTM candidate cell configuration for a third cell served by a third DU of the RAN node.

10. The method of any of claims 1-9, wherein: the reconfiguration message is an RRCReconfiguration message and is received via the first cell; and the re-establishment request is an RRCReestablishmentRequest message.

11. A method for a radio access network, RAN, node configured to facilitate layer-1 or layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, in the RAN, the method comprising: sending (1510) to a UE a reconfiguration message that includes one or more LTM configurations; receiving (1520) a re-establishment request from the UE via a second cell, wherein the re-establishment request is received responsive to a failure event at the UE while the UE is connected to the RAN node via a first cell but not configured to perform LTM fast recovery; and in response to the re-establishment request, discarding (1530) at least one of the LTM configurations or portions thereof.

12. The method of claim 11, wherein the failure event is one of the following: a radio link failure, RLF; a handover failure, HOF; an LTM cell switch failure; a conditional handover, CHO, failure; a reconfiguration failure; a random access failure; a beam failure detection, BFD; and reaching a maximum number failed transmission or retransmission of radio link control, RLC, protocol data units, PDUs.

13. The method of any of claims 11-12, wherein absence of an attempt-LTM field in one of the LTM configurations indicates that the UE should not attempt LTM fast recovery.

14. The method of any of claims 11-13, wherein: the RAN node includes the following: a centralized unit, CU; and a second distributed unit, DU, that serves the second cell; the re-establishment request is an RRCReestablishmentRequest message and is received by the second DU; and the method further comprises sending (1515), by the second DU to the CU, the received RRCReestablishmentRequest message in an Uplink RRC Message Transfer message.

15. The method of claim 14, wherein: the RAN node also includes a first DU that serves the first cell; and the reconfiguration message is an RRCReconfiguration message sent by the first DU via the first cell; and the method further comprises sending (1540), by the CU to the first DU, the RRCReconfiguration message in a Downlink RRC Message Transfer message.

16. The method of any of claims 14-15, wherein: the RAN node also includes a third DU that serves a third cell; at least one of the LTM configurations includes an LTM candidate cell configuration for the third cell; and discarding (1530) at least one of the LTM configurations or portions thereof comprises sending (1531), by the CU to the third DU, a command or request to discard at least the LTM candidate cell configuration for the third cell.

17. The method of any of claims 11-16, wherein each of the one or more LTM configurations includes one or more of the following: one or more LTM candidate cell configurations; lower layer measurement configurations for respective LTM candidate cells; measurement reporting configurations for respective LTM candidate cells; downlink, DL, pre-synchronization configuration for LTM; uplink, UL, pre-synchronization configuration for LTM; an indication of whether a layer-2 reset should be performed in conjunction with an LTM cell switch to an LTM candidate cell; an indication of whether fast LTM recovery should be attempted; andexecution configurations for LTM cell switch procedures to respective LTM candidate cells.

18. The method of claim 17, wherein the one or more LTM candidate cell configurations are arranged according to one of the following: respective complete LTM candidate cell configurations; or a reference configuration and respective LTM candidate cell configurations that are deltas relative to the reference configuration.

19. The method of any of claims 17-18, wherein one or more of the following is included in each of the LTM candidate cell configurations: the lower layer measurement configurations for the LTM candidate cell; the measurement reporting configurations for the LTM candidate cell;DL pre-synchronization configuration for the LTM candidate cell; and UL pre-synchronization configuration for the LTM candidate cell.

20. User equipment, UE (210, 440, 1010, 1612, 1700, 2106) configured to perform layer-1 or layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 460, 1604), the UE comprising: communication interface circuitry (1712) configured to communicate with the RAN via one or more cells; and processing circuitry (1702) operably coupled to the communication interface circuitry, wherein the processing circuitry and communication interface circuitry are configured to: receive from the RAN a reconfiguration message that includes one or more LTM configurations; initiate a re-establishment procedure towards a second cell in response to detection of a failure event while connected to the RAN via a first cell; in response to a determination that the UE is not configured to perform LTM fast recovery, discard one or more of the following information after initiating the re-establishment procedure: at least one of the LTM configurations, or portions thereof; and information derived from the one or more LTM configurations; and after discarding the information, send a re-establishment request to the RAN via the second cell.

21. The UE of claim 20, wherein the processing circuitry and communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 2-10.

22. User equipment, UE (210, 440, 1010, 1612, 1700, 2106) configured to perform layer-1 or layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 460, 1604), the UE being further configured to: receive from the RAN a reconfiguration message that includes one or more LTM configurations; initiate a re-establishment procedure towards a second cell in response to detection of a failure event while connected to the RAN via a first cell; in response to a determination that the UE is not configured to perform LTM fast recovery, discard one or more of the following information after initiating the re-establishment procedure: at least one of the LTM configurations, or portions thereof; and information derived from the one or more LTM configurations; and after discarding the information, send a re-establishment request to the RAN via the second cell.

23. The UE of claim 22, being further configured to perform operations corresponding to any of the methods of claims 2-10.

24. A non-transitory, computer-readable medium (1710) storing computer-executable instructions that, when executed by processing circuitry (1702) of user equipment, UE (210, 440, 1010, 1612, 1700, 2106) configured to perform layer-1 or layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 460, 1604), configure the UE to perform operations corresponding to any of the methods of claims 1-10.

25. A computer program product (1714) comprising computer-executable instructions that, when executed by processing circuitry (1702) of user equipment, UE (210, 440, 1010, 1612, 1700, 2106) configured to perform layer- 1 or layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 460, 1604), configure the UE to perform operations corresponding to any of the methods of claims 1-10.

26. A radio access network, RAN, node (100, 220, 410, 1060) configured to facilitate layer-1 or layer-2 triggered inter-cell mobility, LTM, by user equipment, UE (210, 440, 1010, 1612, 1700, 2106) in the RAN (199, 460, 1604), the RAN node comprising: communication interface circuitry (1806, 2004) configured to communicate with the UE; and processing circuitry (1802, 2004) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: send to the UE a reconfiguration message that includes one or more LTM configurations; receive a re-establishment request from the UE via a second cell, wherein the re-establishment request is received responsive to a failure event at the UE while the UE is connected to the RAN node via a first cell but not configured to perform LTM fast recovery; and in response to the re-establishment request, discard at least one of the LTM configurations or portions thereof.

27. The RAN node of claim 26, wherein the processing circuitry and the communication interface circuitry are arranged as a centralized unit, CU (100, 1050) and one or more distributed units, DUs (120, 130, 1020, 1030, 1040).

28. The RAN node of any of claims 26-27, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 12-19.

29. A radio access network, RAN, node (100, 220, 410, 1060) configured to facilitate layer-1 or layer-2 triggered inter-cell mobility, LTM, by user equipment, UE (210, 440, 1010, 1612, 1700, 2106) in the RAN (199, 460, 1604), the RAN node being further configured to: send to the UE a reconfiguration message that includes one or more LTM configurations; receive a re-establishment request from the UE via a second cell, wherein the reestablishment request is received responsive to a failure event at the UE while the UE is connected to the RAN node via a first cell but not configured to perform LTM fast recovery; andin response to the re-establishment request, discard at least one of the LTM configurations or portions thereof.

30. The RAN node of claim 38, being further configured to perform operations corresponding to any of the methods of claims 12-19.

31. A non-transitory, computer-readable medium (1804, 2004) storing computer-executable instructions that, when executed by processing circuitry (1802, 2004) of a access network, RAN, node (100, 220, 410, 1060) configured to facilitate layer-1 or layer-2 triggered inter-cell mobility, LTM, by user equipment, UE (210, 440, 1010, 1612, 1700, 2106) in the RAN (199, 460, 1604), configure the RAN node to perform operations corresponding to any of the methods of claims 11-19.

32. A computer program product (1804a, 2004a) comprising computer-executable instructions that, when executed by processing circuitry (1802, 2004) of a access network, RAN, node (100, 220, 410, 1060) configured to facilitate layer- 1 or layer-2 triggered inter-cell mobility, LTM, by user equipment, UE (210, 440, 1010, 1612, 1700, 2106) in the RAN (199, 460, 1604), configure the RAN node to perform operations corresponding to any of the methods of claims 11-19.

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