WO2025171958A1

WO2025171958A1 - Methods and apparatuses for rach resource selection for ltm recovery

Info

Publication number: WO2025171958A1
Application number: PCT/EP2025/050477
Authority: WO
Inventors: Prasna Kumar SAHU; Shehzad Ali ASHRAF; Endrit DOSTI; Tero Henttonen; Panagiotis SPAPIS
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2024-02-16
Filing date: 2025-01-09
Publication date: 2025-08-21
Anticipated expiration: 2026-08-16

Abstract

A method for initiating a L1/L2 triggered mobility (LTM) recovery procedure, the method to be performed by a user equipment (UE), wherein the UE is configured to determine at least one random access (RA) resource usable for LTM recovery, wherein the random access resources comprise at least one of contention-based random access (CBRA) resources and contention- free random access (CFRA) resources; the method comprising: receiving an LTM configuration including selection information (SI) for determining at least one RA resource useable for LTM recovery; and in case of determining a condition for LTM recovery applies, identifying a cell for LTM recovery and determine at least one RA resource useable for LTM recovery for the identified cell, and initiating a random access procedure towards the identified cell using at least one of the determined RA resources useable for LTM recovery

Description

METHODS AND APPARATUSES FOR RACH RESOURCE SELECTION FOR LTM RECOVERY

TECHNICAL FIELD

[0001] Various example embodiments generally relate to a wireless communication technique. More specifically, measures/mechanisms (including methods, apparatuses, and computer program products) are described for RACH resource prioritization for LTM recovery.

BACKGROUND

[0002] Various example embodiments relate to considerations in a (e.g., mobile/wireless) communication system or network, such as a 5G/NR system and a next-generation system beyond 5G. For example, various example embodiments are applicable in a 3 GPP-standardized mobile/wireless communication system or network of Release 18 onwards.

[0003] State of the art is described in 3GPP TS 38.300, 3GPP TS 38.321, 3GPP TS 38.331, 3GPP TS 38.401, 3GPP TS 38.423 and 3GPP TS 38.473.

[0004] In 3GPP Rel.18, a new type of inter-cell mobility is introduced, called L1/L2 based inter-cell mobility (L1/L2 triggered mobility, LTM). However, there is a need for a mechanism to determine which resources are used by a user equipment (UE) for random access during the LTM recovery procedure.

LIST OF ACRONYMS AND ABBREVIATIONS

[0005] The following acronyms and abbreviations are used throughout the subject disclosure:

3GPP 3rd Generation Partnership Program

BHO Baseline Handover

CBRA Contention-based Random Access

CE Connection Element

CFRA Contention Free Random Access

CHO Conditional Handover

CSC Cell Switch Command

CU Centralized Unit

DU Distributed Unit

HO Handover

IE Information Element

LI Layer 1

L2 Layer 2

LTM L1/L2 Triggered Mobility MAC Medium Access Control

MCG Master Cell Group

MN Master Node

NR New Radio

NW Network

QoS Quality of Service

RACH Random Access Channel

RLF Radio Link Failure

RRC Radio Resource Control

SCG Secondary Cell Group

SN Secondary Node

TA Timing Advance

UE User Equipment

SUMMARY

[0006] The invention is defined by the independent claims. The dependent claims describe optional example embodiments.

[0007] This summary is intended to provide a brief overview of some of the aspects and features according to the subject disclosure. Accordingly, it will be appreciated that the abovedescribed features are merely examples and should not be construed to narrow the scope of the subject disclosure in any way. Other features, aspects, and advantages of the subject disclosure will become apparent from the following detailed description, drawings, and claims.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A better understanding of the subj ect disclosure can be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0010] FIG. 1 shows a schematic diagram of an example (mobile/wireless) communication system or network;

[0011] FIG. 2 shows a schematic diagram of an example wireless device or entity;

[0012] FIG. 3 shows a schematic diagram of an example network node or entity;

[0013] FIG. 4 illustrates an exemplary message sequence chart for LTM recovery;

[0014] FIG. 5 illustrates an exemplary message sequence chart for LTM recovery;

[0015] FIG. 6 illustrates an exemplary message sequence chart for LTM recovery;

[0016] FIG. 7 illustrates an exemplary message sequence chart for LTM recovery;

[0017] FIG. 8 illustrates schematically a user equipment (UE);

[0018] FIG. 9 illustrates schematically a network (NW); [0019] FIGS. 10A and 10B illustrate schematic block diagrams showing structures of apparatuses according to embodiments of the subject disclosure.

[0020]

DETAILED DESCRIPTION

[0021] For example, random access preambles may be separated into distinct sets of values, one for LTM recovery and one for LTM HO, but may still allow to have CBRA resource for LTM HO or LTM recovery and/or CFRA resource for LTM HO or LTM recovery. The same CFRA resource may be used for LTM HO and LTM recovery and, for example, shared with several UEs. For example, distinct resource for LTM recovery (either CRFA or CBRA) can be made available. The present disclosure allows for a Network 900 (exemplarily illustrated in Fig. 9), e.g. for one or more servers 910 of the Network 900, and a UE 800 (exemplarily illustrated in Fig. 8) to prioritize and/or select resource for LTM recovery to a candidate cell in LTM configuration which provides faster completion of random access procedure after LTM handover failure.

[0022] The examples and embodiments set forth below represent information to enable those skilled in the art to practice the subject disclosure. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the description.

[0023] In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art, with the included description, will be able to implement appropriate functionality without undue experimentation.

[0024] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0025] It is to be noted that the detailed description, at times, refers to one or more specifications being used as non-limiting and illustrative examples for certain architectures, network configurations and system deployments. More specifically, the detailed description refers to 3 GPP standards, being used as non-limiting and illustrative examples. As such, the example embodiments provided herein can specifically employ terminology which is directly related thereto. Such terminology is only used in the context of the non-limiting and illustrative examples and is not intended to limit the example embodiments in any way. Rather, any other system configuration or deployment may be utilized while complying with what is described herein and/or example embodiments are applicable to it.

[0026] For example, various example embodiments are applicable in any (e.g., mobile/wireless) communication system, such as a 5G/NR system and a next-generation system beyond 5G. For example, various example embodiments are applicable in a 3 GPP-standardized mobile/wireless communication system of Release 18 onwards.

[0027] Hereinafter, various example embodiments are described using several variants and/or alternatives. It is generally to be noted that, according to certain implementations or constraints, all the described variants and/or alternatives may be provided alone or in any conceivable combination (e.g., also including combinations of individual features of these various variants and/or alternatives).

[0028] As used herein, the words "comprising" and "including" should be understood as not limiting the example embodiments to consist of only those features that have been mentioned, and example embodiments may also contain, among other things, e.g., features, structures, units, modules, or the like, that have not been specifically mentioned.

[0029] As used herein, "at least one of the following: <a list of two or more elements>" and "at least one of <a list of two or more elements>" and similar wording, like "one or more of, where the list of two or more elements are joined by "and" or "or", mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0030] As used herein, according to various example embodiments, any operations of sending or receiving may comprise actual transmission or communication operations, i.e., transmitting or communicating associated messages or signals, but may additionally or alternatively comprise related processing operations, i.e., preparing/generating/issuing associated messages or signals before sending and/or obtaining/handling/processing of associated messages or signals after receiving. For example, sending a message at/by an entity may comprise generating/issuing and/or transmitting/communicating thereof or a corresponding signal in/at/by the entity, and receiving a message at/by an entity may comprise obtaining/handling and/or processing thereof or a corresponding signal in/at/by the entity. As used herein, a message may refer to and/or encompass any kind of corresponding information, signal, or the like.

[0031] In the drawings, it is to be noted that lines/arrows interconnecting individual blocks or entities are generally meant to illustrate an operational coupling there-b etween, which may be a physical and/or logical coupling, which on the one hand is implementation-independent (e.g., wired, or wireless) and on the other hand may also comprise an arbitrary number of intermediary functional blocks or entities not shown. In flowcharts or sequence diagrams, the illustrated order of operations or actions is generally non-limiting and illustrative, and any other order of respective operations or actions is conceivable, if feasible.

[0032] As the UE changes its location in the NW, its radio link to a serving cell can experience significant fluctuations. To ensure radio connectivity, the NW may trigger cell change. The cell switch may either triggered by the NW based on the reported measurements from the UE (e.g., in L3 HO), or it may triggered by the UE when a certain set of conditions (evaluated locally) provided by the NW is meet (e.g., in CHO). In either case, the HO decision is made based on L3 measurements.

[0033] In LTM the gNB-DU may receive LI measurement reports from UEs, and on this basis the gNB-DU may change UEs’ serving cell(s) by a cell switch command through a MAC CE, which indicates an LTM candidate cell configuration that the gNB previously prepared and provided to the UE through RRC signaling. An LTM candidate cell configuration may be added, modified, and released by network via RRC signaling. The LTM procedure can be used to reduce the mobility latency. LTM supports inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell.

[0034] Now focusing on preamble allocation mechanisms for LTM HO Failure recovery. Fig. 4 shows an exemplary message sequence chart for LTM recovery procedure when selected cell is a LTM configured candidate cell and network configured to perform LTM as part of recovery according to the state of the art.

Step 1-12: UE sends L3 measurement report to CU and the serving CU decides the potential targets based on the L3 measurement reports, prepares the target cells and shares the target cell configurations to UE including CFRA/CBRA configured resources.

Step 13-19: UE performs DL synchronization and upon PDCCH order from serving DU, UE shares the TA to target candidate cells.

Step 20-21 : UE sends LI Measurement Report and serving DU decides the target cell where UE needs to switch.

Step 22: Optionally serving DU sends MAC CE to UE for TCI state activation.

Step 23 : Serving DU sends Cell Switch Command to UE contain target cell information’s like TA.

Step 24: At UE LTM HO fails to target candidate cell.

Step 25: UE performs cell selection procedure and selects a cell to connect.

Step 26-31 : UE does RACH procedure and sends Reconfiguration complete (if selected cell is an LTM configured cell) and target DU sends access notification to CU.

Steps 32-34: UE context releases at serving DU followed by a path switch procedure.

[0035] For example, upon an LTM cell switch failure (e.g., supervision timer expiry) or REF, LTM recovery may be similar to CHO: a) UE may perform cell selection; and/or b) if selected cell is an LTM candidate cell, UE may perform RACH-based LTM cell switch on the selected cell (network-controlled); and or c) if selected cell is not an LTM candidate cell, UE may transmit RRC reestablishment request.

[0036] For example, in LTM, CFRA resources may be shared by UEs belonging to the same gNB-DU. gNB-DU may select one CFRA resource out of the pool of CFRA resources configured to the UE and indicates the CFRA resource to the UE. Once the CFRA resource is free, gNB-DU can allocate the same CFRA resource to another UE as well.

[0037] For example, in inter-DU LTM, the gNB-CU may provide the CFRA resource received from the candidate gNB-DU to the source gNB-DU via UE Context Modification procedure. CFRA resources could be shared only among the UEs in a single gNB-DU to avoid the RACH access conflict between UEs from different DU. The source gNB-DU ID may be indicated when request the CFRA resources to the candidate DU.

[0038] After an LTM handover failure, a UE may perform cell selection and if the selected cell is one of prepared candidate LTM cells, the UE may perform RACH transmission towards the selected cell instead of doing RRC reestablishment.

[0039] An exemplary UE is configured to determine at least one random access (RA) resource usable for LTM recovery. For example, the random access resources comprise at least one of contention-based random access (CBRA) resources and contention-free random access (CFRA) resources.

[0040] For initiating a L1/L2 triggered mobility (LTM) recovery procedure, the UE may perform (one or more of): receiving an LTM configuration including selection information (SI) for determining at least one RA resource useable for LTM recovery; and, in case of determining a condition for LTM recovery applies, identifying a cell for LTM recovery and determine at least one RA resource useable for LTM recovery for the identified cell; and initiating a random access procedure towards the identified cell using at least one of the determined RA resources useable for LTM recovery.

[0041] For example, if CFRA and CBRA resources are configured for LTM recovery, the UE may prioritize CFRA resources for LTM recovery if the SI indicates that CFRA resources are not shared. Additionally or alternatively, if CFRA and CBRA resources are configured for LTM recovery, the UE may prioritize CBRA resources for LTM recovery if the SI indicates that CFRA resources are shared. Additionally or alternatively, if only CFRA resources are configured for LTM recovery then the UE may use dedicated CFRA resources for LTM recovery if the SI indicates dedicated CFRA resources else using any CFRA resources configured by the NW. Additionally or alternatively, if only CBRA resources are configured for LTM recovery then the UE may use dedicated CBRA resources for LTM recovery if the SI indicates dedicated CBRA resources else using any CBRA resources configured by the NW. Various examples therefore differ in that one or more or even all of these optional criteria are implemented. [0042] The SI may be configured to indicate whether CFRA resources are shared or not shared. The SI may be configured to indicate dedicated CFRA resources. The SI may be configured to indicate dedicated CBRA resources. For example, the SI may be comprised by a radio resource control (RRC) reconfiguration message.

[0043] In some examples, the UE may (also) use the same resources which are configured for LTM handover. In some of these examples, there is no need to configure dedicated resources for LTM recovery.

[0044] The LTM configuration may further include an indication of at least one target candidate cell for potential LTM handover and corresponding at least one resource useable for LTM handover. For example, the resource useable for LTM handover and the resource useable for LTM recovery at least partly overlap. For example, for each target candidate cell a separate resource useable for LTM handover may be allocated and the resource useable for LTM recovery at least partly may overlap with a corresponding allocated resource for LTM recovery. For example, in case of receiving a trigger to handover to a particular target candidate cell, and in case handover to the target candidate cell fails, the UE may identify a cell for LTM recovery, wherein the cell for LTM recovery is chosen from the at least one target candidate cell prepared for potential LTM handover and the respective resource allocated for handover is re-used for LTM recovery.

[0045] For example, a network (NW), e.g. one or more servers in a network, perform a method for L1/L2 triggered mobility (LTM) recovery, the method comprises: configuring one or more random access (RA) resources for LTM recovery; and sending selection information (SI) to a user equipment (UE), the SI configured to enable the UE to select a random access (RA) resource for LTM recovery. For example, the SI is configured to indicate whether CFRA resources are shared or not shared. For example, the SI is configured to indicate dedicated CFRA resources. For example, the SI is configured to indicate dedicated CBRA resources. The method may further comprise sending a radio resource control (RRC) reconfiguration message to the UE, the RRC reconfiguration message comprising the SI. The method may further comprise indicating, by a distributed unit (DU) of the NW, to a centralized unit (CU) of the NW whether CFRA resources are shared or not. The method may further comprise indicating by a UE context setup request of the CU to the DU to include dedicated CFRA resource configuration for LTM recovery; and including, by the DU, dedicated CFRA resource configuration in a UE context setup response. The method may further comprise indicating by a UE context setup request of the CU to the DU to include dedicated CBRA resources for LTM recovery; and including, by the DU, dedicated CBRA configurations in the UE context setup response.

[0046] In some scenarios/examples without specific resource allocated to UE for LTM recovery: In some examples, a UE context setup response message may be received by a CU from target DU comprising CFRA and CBRA resources for LTM configuration and new IE indicating that the CFRA resource is shared or not (CFRA resource sharing indicator). In some examples, a RRC reconfiguration message may be prepared and sent to the UE from CU comprising a candidate LTM configuration received from candidate DU, a new IE CFRA resource sharing indicator indicates whether the CFRA resource of candidate LTM configuration is shared or not. In some examples, LTM HO (TCI state activation, cell switch command) is sent to UE from source DU but LTM HO fails for UE. Since LTM HO to candidate cell failed for UE, in some examples, cell selection at UE may be performed and selecting a cell which has been prepared as candidate cell for LTM (benefit: cell already has the UE context available). In some examples, the UE may select a resource/preamble for RACH access from the CBRA and CFRA resources provided in the LTM configuration of a candidate cell depending on the value of the CFRA resource sharing indicator. In some examples, the value of the CFRA resource sharing indicator may be used to prioritize a resource over the other available resources and the prioritized resource is selected for RACH access. In some examples, the UE may perform RACH access with the prioritized / selected resource.

[0047] As to the UE selecting a resource/preamble for RACH access: In some examples or scenarios, if CFRA resource sharing indicator indicates that the CFRA resource is not shared, then the UE may prioritize CFRA resource for RACH access to candidate LTM cell (LTM recovery). In some examples or scenarios, if CFRA resource sharing indicator indicates that the CFRA resource is shared, then the UE may prioritize CBRA resource for RACH access to candidate LTM cell (LTM recovery). In some examples or scenarios,

[0048] The UE may select the same target cell (target cell intended by cell switch command for LTM HO). For example, if the UE selects the same target cell, the UE may prioritize the CFRA resource that has been received in cell switch command (MAC CE) or in LI signalling (PDCCH).

[0049] In some scenarios/examples, specific resource may be allocated to UE for LTM recovery. In some examples, a UE context setup request message may be sent from CU to target DU comprising an indicator indicating whether to allocate a specific LTM recovery resource in addition to the LTM configuration of the UE. For example, the indicator may further specify whether a CBRA or CFRA resource has to be allocated as LTM recovery resource. In some examples, UE context setup response message may be received by a CU from target DU comprising CFRA and CBRA resources for LTM configuration and new IE LTM recovery resource indicating that the resource is to be used in case of LTM recovery (ie., if the LTM HO fails, RACH access to a cell for which LTM configuration has been prepared). For example, specific resource for UE for LTM recovery allows identification of UE already by first message towards target cell/DU. For example, the LTM recovery resource further indicates the type of resource whether it is intended for contention free or contention based random access in the cell. In some examples, a RRC reconfiguration message may be prepared and sent to the UE from CU comprising a candidate LTM configuration received from candidate DU, a new IE LTM recovery resource indicating a resource to use for random access of UE after LTM HO failure. In some examples, LTM HO (TCI state activation, cell switch command) may be sent to UE from source DU but LTM HO fails for UE. Since LTM HO to candidate cell failed for UE, in some examples, cell selection at UE may be performed and selecting a cell which has been prepared as candidate cell for LTM (benefit: cell already has the UE context available). In some examples, at the UE a resource/preamble for RACH access may be selected from the resources provided in the LTM configuration of a candidate cell depending on whether the IE LTM recovery resource is available. For example, the type of the LTM recovery resource can be used to prioritize a resource over the other available resources and the prioritized resource is selected for RACH access. For example, selecting at UE a resource for RACH access may comprise selecting whether to perform CBRA or CFRA depending on the availability of CFRA or CBRA resource. For example, selecting at UE a resource for RACH access comprises selecting whether to perform CBRA or CFRA further depending on the availability of nonshared CFRA resource in LTM configuration. In some examples, the UE RACH access may be performed with the prioritized / selected resource.

[0050] In some scenarios/examples, selecting by UE a resource for LTM recovery from LTM configuration provided to UE may depend on the resource sets defined in LTM configuration. For example, the LTM configuration may comprise a first resource set (CFRA preambles) and a second resource set (CBRA preambles). For example, where the selecting by UE comprises selecting a first resource set if both resource sets are available and selecting a specific resource of first resource set if the resource is not-shared (=specific to the UE), else selecting a resource from the second resource set. For example, where the selecting by UE comprises selecting a second resource set if first resource set is not available in LTM configuration and selecting a resource dedicated to LTM recovery if a resource in second set is dedicated to LTM recovery, else selecting a resource from second resource set.

[0051] Note that the present description and Figs, describe examples with a single CU. Corresponding still further examples (not explicitly described or shown by figures) differ in that there is a source CU connected to source DU and communicating to target CU which is connected to a target DU.

[0052] Before explaining further optional implementation details, certain general principles of a (mobile/wireless) communication system or network are briefly explained with reference to FIGS. 1 to 3 to assist in understanding the underlying technology.

[0053] FIG. 1 illustrates an example of a (mobile/wireless) communication system or network 100 that may be used for wireless communications. Communication system or network 100 includes wireless devices or entities, such as UEs 110 (e.g., 110A-110C), and network nodes or entities, such as radio access nodes 120 (e.g., 120A-120B) (e.g., eNBs, gNBs, etc.), connected to one or more network nodes or entities 130 via an interconnecting network 125. Communication system or network 100 may use any suitable deployment scenarios. UEs 110 within coverage area 115 may each be capable of communicating directly with radio access nodes 120 over a wireless interface. [0054] As an example, UE 110A may communicate with radio access node 120A over a wireless interface. That is, UE 110A may transmit wireless signals to and/or receive wireless signals from radio access node 120A. The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information.

[0055] As used herein, the term "user equipment" (UE) has the full breadth of its ordinary meaning and may refer to any type of wireless device or entity which can communicate with a network node or entity and/or with another UE in a cellular or mobile or wireless/mobile communication system. Examples of UE are target device, D2D UE, machine type UE or UE capable of machine-to-machine (M2M) communication, personal digital assistant, tablet, mobile terminal, smartphone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, ProSe UE, vehicle-to-vehicle (V2V) UE, V2X UE, MTC UE, eMTC UE, FeMTC UE, UE Cat 0, UE Cat Ml, narrow band loT (NB-IoT) UE, UE Cat NB1, etc. Example embodiments of a UE are described in more detail below with respect to FIG. 2.

[0056] In some embodiments, an area of wireless signal coverage 115 associated with a radio access node 120 may be referred to as a cell. However, particularly with respect to the fifth generation (5G)/ New Radio (NR) mobile communication concepts, beams may be used instead of cells and, as such, it is important to note that concepts described herein are equally applicable to both cells and beams.

[0057] With respect to a beam-based mobile communication system, the radio access node 120 (base station) may transmit a beamformed signal to the UE 110 in one or more transmit directions (transmission beam, Tx beam). The UE 110 may receive the beamformed signal from the base station 120 in one or more receive directions (reception beam, Rx beam). The UE 110 may also transmit a beamformed signal to the base station 120 in one or more directions and the base station 120 may receive the beamformed signal from the UE 110 in one or more directions. The base station 120 and the UE 110 may determine the best receive and transmit directions, e.g., best in the sense of these directions leading to the highest link quality or fulfilling other quality conditions in the most suitable manner, for each of the base station/UE pairs.

[0058] The interconnecting network 125 may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, etc., or any combination of the preceding. The interconnecting network 125 may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

[0059] In some embodiments, the network node 130 may be a core network node, managing the establishment of communication sessions and other various other functionalities for UEs 110. Examples of network node 130 may include mobile switching center (MSC), MME, serving gateway (SGW), packet data network gateway (PGW), operation and maintenance (O&M), operations support system (OSS), SON, positioning node (e.g., Enhanced Serving Mobile Location Center, E-SMLC), location server node, MDT node, etc. UEs 110 may exchange certain signals with the network node 130 using the non-access stratum (NAS) layer. In non-access stratum signaling, signals between UEs 110 and the network node 130 may be transparently passed through the radio access network. In some embodiments, radio access nodes 120 may interface with one or more network nodes 130 over an internode interface.

[0060] As used herein, the term "network node or entity" has the full breadth of its ordinary meaning and may correspond to any type of radio access node (or radio network node) or any network node, which can communicate with a UE and/or with another network node in a cellular or mobile or wireless communication system. Examples of network nodes are NodeB, MeNB, SeNB, a network node may belonging to MCG or SCG, base station (BS), multistandard radio (MSR) radio access node such as MSR BS, eNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission point, transmission node, RRU, RRH, node in distributed antenna system (DAS), core network node (e.g., MSC, MME, etc.), O&M, OSS, Self-organizing Network (SON), positioning node (e.g., E-SMLC), MDT, test equipment, etc. Example embodiments of a network node are described in more detail below with respect to FIG. 3.

[0061] In some embodiments, radio access node 120 may be a distributed radio access node. The components of the radio access node 120, and their associated functions, may be separated into two main units (or sub-radio network nodes) which may be referred to as the central unit (CU) and the distributed unit (DU). Different distributed radio network node architectures are possible. For instance, in some architectures, a DU may be connected to a CU via dedicated wired or wireless link (e.g., an optical fiber cable) while in other architectures, a DU may be connected a CU via a transport network. Also, how the various functions of the radio access node 120 are separated between the CU(s) and DU(s) may vary depending on the chosen architecture.

[0062] Exemplary wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology (RAT). The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence/Radio Link Control/Medium Access Control/Physical layer protocol (PDCP/RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other RAT examples comprise those provided by base stations of systems that are based on technologies such as WLAN and/or Worldwide Interoperability for Microwave Access (WiMax). A base station can provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME), Serving Gateway (S-GW) and Packet Gateway (P-GW).

[0063] An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-A. Base stations of NR systems may be known as next generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer Quality of Service (QoS) support, and some on-demand requirements for QoS levels to support Quality of Experience (QoE) of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input-multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0064] Future networks may utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running instructions using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes, or hosts. It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0065] An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN). An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UEs exchanging traffic with the data network (DN). The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The CN may also include an AMF (Access & Mobility Function).

[0066] Generally, all concepts disclosed herein may be applicable to different communication networks, comprising but not limited to LTE, LTE-A, 5G, 5G advanced, 6G, and other future or already implemented networks.

[0067] FIG. 2 is a schematic diagram of an example wireless device, UE 110, according to certain example embodiments. UE 110 may include one or more of at least one transceiver 210, at least one processor 220, at least one memory 230, and at least one network interface 240. In certain example embodiments, the transceiver 210 facilitates transmitting wireless signals to and receiving wireless signals from radio access node 120 (e.g., via transmitter(s) (Tx), receiver(s) (Rx) and antenna(s)). The processor 220 executes instructions to provide some or all of the functionalities described herein as being provided by a wireless device/entity or UE, and the memory 230 stores the instructions executed by the processor 220. In some embodiments, the processor 220 and the memory 230 form processing circuitry.

[0068] The processor 220 may include any suitable combination of hardware to execute instructions and manipulate data to perform some or all the described functions of a wireless device or entity, such as the functions of UE 110 described herein. In some embodiments, the processor 220 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and/or other logic.

[0069] The memory 230 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by a processor 220. Examples of memory 230 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non- transitory computer-readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processor 220 of UE 110. For example, the memory 230 includes instructions causing the processor 220 to perform processing according to any corresponding methods described herein. [0070] The network interface 240 is communicatively coupled to the processor 220 and may refer to any suitable device operable to receive input for UE 110, send output from UE 110, perform suitable processing of the input or output or both, communicate to other devices, or any combination thereof. The network interface 240 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

[0071] Other embodiments of UE 110 may include additional components beyond those shown in FIG. 2 that may be responsible for providing certain aspects of the wireless device’s functionalities, including any of the functionalities described herein and/or any additional functionalities (including any functionality necessary to support the mechanisms according to the subject disclosure). As an example, UE 110 may include input devices and circuits, output devices, and one or more synchronization units or circuits, which may be part of the processor 220. Input devices include mechanisms for entry of data into UE 110. For example, input devices may include input mechanisms, such as a microphone, input elements, a display, etc. Output devices may include mechanisms for outputting data in audio, video and/or hard copy format. For example, output devices may include a speaker, a display, etc. [0072] In certain example embodiments, the wireless device UE 110 may comprise a series of modules configured to implement the functionalities of the wireless device described herein. [0073] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver s) of UE 110 shown in FIG. 2. Certain example embodiments may also include additional modules to support additional and/or optional functionalities.

[0074] FIG. 3 is a schematic diagram of an example radio access node 120 or network node or entity 130 according to certain example embodiments. Radio access node 120 or network node or entity 130 may include one or more of at least one transceiver 310, at least one processor 320, at least one memory 330, and at least one network interface 340. In certain example embodiments, the transceiver 310 facilitates transmitting wireless signals to and receiving wireless signals from wireless devices, such as UE 110 (e.g., via transmitted s) (Tx), received s) (Rx), and antenna(s)). The processor 320 executes instructions to provide some or all the functionalities described herein as being provided by the radio access node 120 or the network node or entity 130, the memory 330 stores the instructions executed by the processor 320. In some embodiments, the processor 320 and the memory 330 form processing circuitry. The network interface 340 can communicate signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes or radio network controllers, etc.

[0075] The processor 320 can include any suitable combination of hardware to execute instructions and manipulate data to perform some or all the described functions of the radio access node 120 or the network node or entity 130, such as those described herein. In some embodiments, the processor 320 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and/or other logic.

[0076] The memory 330 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by a processor 320. Examples of memory 330 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non- transitory computer-readable and/or computer-executable memory devices that store information. For example, the memory 330 includes instructions causing the processor 320 to perform processing according to any corresponding methods described herein.

[0077] In certain example embodiments, the network interface 340 is communicatively coupled to the processor 320 and may refer to any suitable device operable to receive input for the radio access node 120 or the network node or entity 130, send output from the radio access node 120 or the network node or entity 130, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. The network interface 340 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

[0078] Other example embodiments of the radio access node 120 or the network node or entity 130 can include additional components beyond those shown in FIG. 3 that may be responsible for providing certain aspects of the node’s functionalities, including any of the functionalities described herein and/or any additional functionalities (including any functionality necessary to support the solutions described herein). The various different types of radio access nodes or network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

[0079] Processors, interfaces, and memory similar to those described with respect to FIG. 3 may be included in other nodes or entities (such as UE 110, radio access node 120, etc.). Other nodes or entities may optionally include or not include a wireless interface (such as the transceiver described in FIG. 3).

[0080] In certain example embodiments, the radio access node 120 or the network node or entity 130 may comprise a series of modules configured to implement the functionalities of the radio access node 120 or the network node or entity 130 described herein.

[0081] It will be appreciated that the various modules may be implemented as combination of hardware and software, for instance, the processor, memory, and transceiver(s) of the radio access node 120 or the network node or entity 130 shown in FIG. 3. Certain example embodiments may also include additional modules to support additional and/or optional functionalities.

[0082] In some examples, both CFRA resources and CBRA resources are configured for LTM candidate cells. For example, DU may prepare a UE context setup Response that includes CFRA and CBRA configurations for UE and indicates whether CFRA resources are shared or not. For example, CU prepares the RRC reconfiguration that includes an indication whether CFRA resources are shared or not. For example, CU sends the Reconfiguration message to UE. For example, in some cases, CU can determine if CFRA resources (provided by DU) are shared or not and indicates this to UE.

[0083] This allows for the UE with time critical service to be back into service faster/with lower interruption time because the CFRA resource is not shared and target DU immediately knows which UE is accessing via random access. For example, UE selects preamble from LTM configuration during LTM recovery.

[0084] For example, UE prioritizes CFRA resources for LTM recovery if the CFRA resources are not shared (indicated to UE during LTM preparation). If CFRA resources are shared among other UEs, UE prioritizes CBRA resources for LTM recovery. In some cases when UE selects same cell, UE may use the same CFRA resource that is received in MAC CE or LI signaling (i.e., PDCCH).

[0085] Fig. 5 schematically illustrates an example LTM recovery when both CFRA resources and CBRA resources are configured for LTM candidate cells.

Step 1-3 : L3 measurement report for UE received and CU initiates LTM candidate preparation.

Step 4, 6: CU initiates UE context setup procedure with target DUs for LTM candidates.

Step 5, 7: DU prepares UE context setup Response. It includes CFRA and CBRA configurations for UE and indicates whether CFRA resources are shared or not.

Step 8, 9: CU initiates UE Context modification procedure with source DU to update on target LTM configs for UE.

Step 10-12: CU prepares the RRC reconfiguration. It includes the indication whether CFRA resources are shared or not. CU sends the Reconfiguration message to UE. In some cases, CU can determine if CFRA resources (provided by DU) are shared or not and indicates this to UE.

Benefit: UE with time critical service is back into service faster/with lower interruption time because the CFRA resource is not shared and target DU immediately knows which UE is accessing via random access. UE selects preamble from LTM configuration during LTM recovery.

Step 13-14: UE sends RRC reconfiguration Complete to CU.

Step 15-19: UE performs the DL synchronization and TA accusation

Step 20: UE reports LI Measurement Reports

Step 21-23: DU takes decision for LTM HO. Initiates TCI state activation and Cell Switch Command towards UE.

Step 24: LTM Handover fails to the cell that indicated Cell Switch Command.

Step 25: UE performs cell selection an selects an LTM prepared candidate cell. UE prioritizes CFRA resources for LTM recovery if the CFRA resources are not shared (indicated to UE during LTM preparation). If CFRA resources are shared among other UEs, UE prioritizes CBRA resources for LTM recovery. In some cases when UE selects same cell, UE use the same CFRA resource that is received in MAC CE or LI signaling (i.e., PDCCH).

Step 26-29: UE performs RACH procedure depending on CFRA/CBRA resources selected.

Step 30-31 : DU sends UL RRC Transfer congaing RRC Reconfiguration Complete to CU and target DU sends access notification to CU.

Step 32-34: UE context releases at serving DU followed by a path switch procedure. [0086] Fig. 6 schematically illustrates an example LTM recovery when only CFRA resources are configured for LTM candidate cells.

Step 4, 6: CU initiates UE context setup procedure with target DUs for LTM candidates. Optionally includes the indication to include specific CFRA resources for LTM recovery. In one case, such request can be optional.

Step 5, 7: DU prepares UE context setup response. It includes CFRA configurations for

UE. DU includes specific CFRA resources for LTM recovery. In other words, dedicated CFRA resources for LTM recovery are configured.

Step 10-12: CU prepares the RRC reconfiguration. It includes explicit CFRA resources for LTM recovery in the RRC Reconfiguration message to the UE.

Step 13-14: UE sends RRC reconfiguration Complete to CU.

Step 15-19: UE performs the DL synchronization and TA acquisition

Step 20: UE reports LI Measurement Reports

Step 24: LTM Handover fails to the cell that indicated Cell Switch Command.

Step 25: UE performs cell selection and selects an LTM prepared candidate cell. If specific CFRA resources are configured for LTM recovery, then UE uses specific CFRA resources for LTM recovery.

Step 30-31 : DU sends UL RRC Transfer containing RRC Reconfiguration Complete to CU and target DU sends access notification to CU

Step 32-34: UE context releases at serving DU followed by a path switch procedure [0087] Fig. 7 schematically illustrates an example LTM recovery when only CBRA resources are configured for LTM candidate cells.

Step 4, 6: CU initiates UE context setup procedure with target DUs for LTM candidates. It also includes the indication to include specific CBRA resources. In one case, such request can be optional.

Step 5, 7: DU prepares UE context setup Response. DU includes CBRA configurations for UE and includes specific CBRA resources for LTM recovery. In some cases, specific CBRA resources can be configured separately for LTM recovery than CBRA resources for normal LTM HO. Step 8, 9: CU initiates UE Context modification procedure with source DU to update on target LTM configs for UE.

Step 10-12: CU prepares the RRC reconfiguration. CU includes specific CBRA resources for LTM recovery and sends it in the RRC Reconfiguration message to UE.

Step 13-14: UE sends RRC reconfiguration Complete to CU.

Step 15-19: UE performs the DL synchronization and TA acquisition

Step 20: UE reports LI Measurement Reports

Step 24: LTM Handover fails to the cell that indicated Cell Switch Command.

Step 25: UE performs cell selection an selects an LTM prepared candidate cell. UE prioritizes the use of specific CBRA resources, if specific CBRA resources configured for LTM recovery.

Step 30-31 : DU sends UL RRC Transfer comprising RRC Reconfiguration Complete to CU and target DU sends access notification to CU

Step 32-34: UE context releases at serving DU followed by a path switch procedure [0088] Figs. 5-7 show examples for Intra-CU scenarios. In further examples, the doctrine of Figs. 5-7 is applied for Inter-CU scenarios. In this case, the indication of sharing of CFRA resources among multiple UEs or request and provisioning of dedicated CFRA/CBRA resources will also impact Xn signaling (i.e. between two CUs). In both Intra-CU and Inter-CU scenarios interruption time can be reduced due to use of specific CBRA usage and network priorities. In case dedicated CFRA used, failure recovery interruption time can be reduced. [0089] FIGS. 10A and 10B illustrate schematic block diagrams showing structures of apparatuses according to embodiments of the subject disclosure.

[0090] In FIGS. 10A and 10B, the blocks are basically configured to perform respective methods, procedures and/or functions as described above. It is to be noted that the individual blocks are meant to illustrate respective functional blocks implementing a respective function, process, or procedure, respectively. Such functional blocks are implementation-independent, i.e., may be implemented by means of any kind of hardware or software or combination thereof, respectively.

[0091] An apparatus according to at least one embodiment may represent or realize/embody (e.g., a part of) a UE or loT device as an example of a wireless device or entity. Such apparatus may be illustrated or realized as is shown in FIG. 2. The apparatus or the at least one processor 220 (e.g., together with instructions stored in the at least one memory 230) may be configured to transmit, to a non-terrestrial node, a registration request to authenticate to the network. [0092] Further, the apparatus or the at least one processor 220 (e.g., together with instructions stored in the at least one memory 230) may be configured to receive, from the nonterrestrial node, a message comprising binding information associated with the non-terrestrial node to be used by the UE or loT device, the binding information being assigned to the UE or loT device.

[0093] Such apparatus may be illustrated or realized as is shown in FIG. 10A as apparatus 1000. The apparatus 1000 may comprise (at least) one or more unit/means/circuitry, denoted by transmitting section 1010, which represent any implementation for (or configured to) transmitting, to a non-terrestrial node, a registration request to authenticate to the network, and (at least) one or more unit/means/circuitry, denoted by receiving section 1020, which represent any implementation for (or configured to) receiving, from the non-terrestrial node, a message comprising binding information associated with the non-terrestrial node to be used by the UE or loT device, the binding information being assigned to the UE or loT device.

[0094] As indicated by dashed lines, the apparatus 1000 may comprise (at least) one or more unit/means/circuitry, denoted by processing section 1030, which represent any implementation for (or configured to) performing one or more operations described above.

[0095] Further, an apparatus according to at least one embodiment may represent or realize/embody (e.g., a part of) a non-terrestrial network entity (such as any kind of base station, or the like, incorporated in a satellite) as an example of a non-terrestrial network device or entity.

[0096] Such apparatus may be illustrated or realized as is shown in FIG. 3. The apparatus or the at least one processor 320 (e.g., together with instructions stored in the at least one memory 330) may be configured to receive, from a UE or loT device, a registration request to authenticate to the network.

[0097] Further, the apparatus or the at least one processor 320 (e.g., together with instructions stored in the at least one memory 330) may be configured to store the registration request and assign binding information associated with the non-terrestrial network entity to the UE or loT device responsive to a link between the non-terrestrial network entity and a terrestrial network entity (e.g., such as any kind of ground-based base station or the like) of the network to forward the registration request not being available. Also, the apparatus or the at least one processor 320 (e.g., together with instructions stored in the at least one memory 330) may be configured to transmit, to the UE or loT device, a message comprising the binding information to be used by the UE or loT device.

[0098] Such apparatus may be illustrated or realized as is shown in FIG. 10B as apparatus 1100. The apparatus 1100 may comprise (at least) one or more unit/means/circuitry, denoted by receiving section 1110, which represent any implementation for (or configured to) receiving, from a UE or loT device, a registration request to authenticate to the network, (at least) one or more unit/means/circuitry, denoted by storing and assigning (i.e., processing) section 1120, which represent any implementation for (or configured to) storing the registration request and assigning binding information associated with the non-terrestrial network entity to the UE or loT device responsive to a link between the non-terrestrial network entity and a terrestrial network entity of the network to forward the registration request not being available, and (at least) one or more unit/means/circuitry, denoted by transmitting section 1130, which represent any implementation for (or configured to) transmitting, to the UE or loT device, a message comprising the binding information to be used by the UE or loT device.

[0099] The apparatus 1100 may comprise (at least) one or more unit/means/circuitry (not shown in FIG. 10B), which represent any implementation for (or configured to) performing one or more operations described above.

[0100] For further details regarding the operability/functionality of the apparatuses (or units/means thereof) according to some embodiments of the subject disclosure, reference is made to the above description in connection with any one of FIGS. 1 to 10, respectively.

[0101] For further example embodiments and details regarding the operability/functionality of the apparatuses (or units/means thereof) and/or methods according to some embodiments, reference is made to the following, which is to be understood in the context of, e.g. Release 18 and/or Release 19 of, the above-mentioned 3GPP standards.

RACH Resource Prioritization for LTM Recovery

After the LTM handover failure, UE will perform cell selection and if the selected cell is one the prepared candidate LTM cells, it will perform RACH transmission towards the selected cell instead of doing RRC reestablishment. However, it was not agreed on which resources are used by the UE to perform random access during LTM recovery procedure.

Observation X: It is not clear whether CFRA/CBRA resources to be used for LTM recovery are explicitly configured or not.

In our view, there is no need to configure dedicated resources for LTM recovery and the UE can use the same resources which are configured for LTM handover.

Proposal X: CFRA/CBRA resources for LTM recovery are not explicitly configured to the UE in addition to CFRA/CBRA resources for LTM handover.

However, in this case, there is a possibility of following three configurations:

CFRA resource is configured to the UE (and no sharing of CFRA resources among UEs) o This can be used by UE for both LTM and LTM recovery.

CBRA resource is configured to the UE o This can be used by the UE for both LTM and LTM recovery.

- Both CFRA and CBRA resources are configured to the UE o In this case, there are two possibilities:

■ If CFRA resources are shared among multiple UEs There is a possibility of collision since LTM recovery is UE initiated procedure

■ If CFRA resources are not shared among multiple UEs There is no possibility of collision o UE uses CFRA resources for LTM recovery if the configured CFRA resources are not shared among UEs o UE uses CBRA resources for LTM recovery if configured CFRA resources are shared among UEs.

In order to enable above UE behavior, the target gNB-DU may indicate if CFRA resource is shared or not. Such indication may have RAN3 impact.

Proposal: Target DU indicates if configured CFRA resources are shared or not.

[0102] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0103] For example, an apparatus, e.g. a user equipment (UE), for initiating a L1/L2 triggered mobility (LTM) recovery procedure, wherein the apparatus is configured to determine at least one random access (RA) resource usable for LTM recovery, wherein the random access resources comprise at least one of contention-based random access (CBRA) resources and contention-free random access (CFRA) resources; the apparatus comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receiving an LTM configuration including selection information (SI) for determining at least one RA resource useable for LTM recovery; and in case of determining a condition for LTM recovery applies, identifying a cell for LTM recovery and determine at least one RA resource useable for LTM recovery for the identified cell, and initiating a random access procedure towards the identified cell using at least one of the determined RA resources useable for LTM recovery. For example, the instructions are further configured to cause the apparatus at least to: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CFRA resources for LTM recovery if the SI indicates that CFRA resources are not shared. For example, the instructions are further configured to cause the apparatus at least to: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CBRA resources for LTM recovery if the SI indicates that CFRA resources are shared. For example, the instructions are further configured to cause the apparatus at least to: if only CFRA resources are configured for LTM recovery then using dedicated CFRA resources for LTM recovery if the SI indicates dedicated CFRA resources else using any CFRA resources configured by the NW. For example, the instructions are further configured to cause the apparatus at least to: if the SI indicates dedicated CFRA resources, using a specific CFRA resource out of CFRA resources configured by the NW, wherein the specific CFRA resource is indicated in a command from the distributed unit (DU) of the NW. For example, the command from the DU comprises a cell switch command or early TA command. For example, the instructions are further configured to cause the apparatus at least to: if only CBRA resources are configured for LTM recovery then using dedicated CBRA resources for LTM recovery if the SI indicates dedicated CBRA resources else using any CBRA resources configured by the NW. For example, the SI is to indicate whether CFRA resources are shared or not shared. For example, the SI is to indicate dedicated CFRA resources. For example, the SI is to indicate dedicated CBRA resources. For example, the SI is comprised by a radio resource control (RRC) reconfiguration message. For example, the LTM configuration further includes an indication of at least one target candidate cell for potential LTM handover and corresponding at least one resource useable for LTM handover. For example, the resource useable for LTM handover and the resource useable for LTM recovery at least partly overlap. For example, for each target candidate cell a separate resource useable for LTM handover is allocated and the resource useable for LTM recovery at least partly overlaps with a corresponding allocated resource for LTM recovery. For example, the instructions are further configured to cause the apparatus at least to: in case of receiving a trigger to handover to a particular target candidate cell, and in case handover to the target candidate cell fails, identifying a cell for LTM recovery, wherein the cell for LTM recovery is chosen from the at least one target candidate cell prepared for potential LTM handover and the respective resource allocated for handover is re-used for LTM recovery.

[0104] For example, an apparatus, e.g. a network (NW), for L1/L2 triggered mobility (LTM) recovery, the apparatus comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: configuring one or more random access (RA) resources for LTM recovery; and sending selection information (SI) to a user equipment (UE), the SI configured to enable the UE to select a random access (RA) resource for LTM recovery. For example, the SI is provided by a distributed unit (DU) of the NW to a centralized unit (CU) of the NW. For example, the SI is to indicate whether CFRA resources are shared or not shared. For example, the SI is to indicate dedicated CFRA resources. For example, the SI is to indicate dedicated CBRA resources. For example, the instructions are further configured to cause the apparatus at least to: sending a radio resource control (RRC) reconfiguration message to the UE, the RRC reconfiguration message comprising the SI. For example, the instructions are further configured to cause the apparatus at least to: indicating, by the DU to the CU whether CFRA resources are shared or not. For example, the instructions are further configured to cause the apparatus at least to: indicating by a UE context setup request of the CU to the DU to include dedicated CFRA resource configuration for LTM recovery, and including, by the DU, dedicated CFRA resource configuration in a UE context setup response. For example, the instructions are further configured to cause the apparatus at least to: indicating by a UE context setup request of the CU to the DU to include dedicated CBRA resources for LTM recovery, and including, by the DU, dedicated CBRA configurations in the UE context setup response.

[0105] It should be understood that the apparatuses described may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities. [0106] It is noted that whilst embodiments have been described in relation to LTE and 5G NR, similar principles can be applied in relation to other networks and communication systems where enforcing fast connection re-establishment is required. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0107] It is also noted herein that while the above describes exemplary embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the subject disclosure.

[0108] In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic, or any combination thereof. Some aspects of the subject disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor, or other computing device, although the subject disclosure is not limited thereto. While various aspects of the subject disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0109] Example embodiments of the subject disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computerexecutable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0110] Further in this regard it should be noted that any blocks of the logic flow as in the figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks, and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media. [OHl] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), FPGA, gate level circuits and processors based on multicore processor architecture, as non-limiting examples. [0112] Example embodiments of the subject disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate. [0113] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of the subject disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of the subject disclosure as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1. A method for initiating a L1/L2 triggered mobility (LTM) recovery procedure, the method to be performed by a user equipment (UE), wherein the UE is configured to determine at least one random access (RA) resource usable for LTM recovery, wherein the random access resources comprise at least one of contention-based random access (CBRA) resources and contention-free random access (CFRA) resources; the method comprising: receiving an LTM configuration including selection information (SI) for determining at least one RA resource useable for LTM recovery; and in case of determining a condition for LTM recovery applies, identifying a cell for LTM recovery and determine at least one RA resource useable for LTM recovery for the identified cell, and initiating a random access procedure towards the identified cell using at least one of the determined RA resources useable for LTM recovery.

2. The method of claim 1, further comprising: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CFRA resources for LTM recovery if the SI indicates that CFRA resources are not shared.

3. The method of claims 1-2, further comprising: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CBRA resources for LTM recovery if the SI indicates that CFRA resources are shared.

4. The method of claims 1-3, further comprising: if only CFRA resources are configured for LTM recovery then using dedicated CFRA resources for LTM recovery if the SI indicates dedicated CFRA resources else using any CFRA resources configured by the NW.

5. The method of claim 4, wherein, if the SI indicates dedicated CFRA resources, using a specific CFRA resource out of CFRA resources configured by the NW, wherein the specific CFRA resource is indicated in a command from the distributed unit (DU) of the NW.

6. The method of claim 5, wherein the command from the DU comprises a cell switch command or early TA command.

7. The method of claims 1-6, further comprising: if only CBRA resources are configured for LTM recovery then using dedicated CBRA resources for LTM recovery if the SI indicates dedicated CBRA resources else using any CBRA resources configured by the NW.

8. The method of claims 1-7, wherein the SI is to indicate whether CFRA resources are shared or not shared.

9. The method of claims 1-8, wherein the SI is to indicate dedicated CFRA resources.

10. The method of claims 1-9, wherein the SI is to indicate dedicated CBRA resources.

11. The method of claims 1-10, wherein the SI is comprised by a radio resource control (RRC) reconfiguration message.

12. The method of claims 1-11, wherein the LTM configuration further includes an indication of at least one target candidate cell for potential LTM handover and corresponding at least one resource useable for LTM handover.

13. The method of claim 12, wherein the resource useable for LTM handover and the resource useable for LTM recovery at least partly overlap.

14. The method of claims 12-13, wherein for each target candidate cell a separate resource useable for LTM handover is allocated and the resource useable for LTM recovery at least partly overlaps with a corresponding allocated resource for LTM recovery.

15. The method of claims 12-14, wherein in case of receiving a trigger to handover to a particular target candidate cell, and in case handover to the target candidate cell fails, identifying a cell for LTM recovery, wherein the cell for LTM recovery is chosen from the at least one target candidate cell prepared for potential LTM handover and the respective resource allocated for handover is re-used for LTM recovery.

16. A method for L1/L2 triggered mobility (LTM) recovery, the method to be performed by a network (NW), the method comprising: configuring one or more random access (RA) resources for LTM recovery; and sending selection information (SI) to a user equipment (UE), the SI configured to enable the UE to select a random access (RA) resource for LTM recovery.

17. The method of claim 16, wherein the SI is provided by a distributed unit (DU) of the NW to a centralized unit (CU) of the NW.

18. The method of claims 16-17, wherein the SI is to indicate whether CFRA resources are shared or not shared.

19. The method of claims 16-18, wherein the SI is to indicate dedicated CFRA resources.

20. The method of claims 16-19, wherein the SI is to indicate dedicated CBRA resources.

21. The method of claims 16-20, further comprising: sending a radio resource control (RRC) reconfiguration message to the UE, the RRC reconfiguration message comprising the SI.

22. The method of claims 16-21, further comprising: indicating, by the DU to the CU whether CFRA resources are shared or not.

23. The method of claims 16-22, further comprising: indicating by a UE context setup request of the CU to the DU to include dedicated CFRA resource configuration for LTM recovery, and including, by the DU, dedicated CFRA resource configuration in a UE context setup response.

24. The method of claims 16-23, further comprising: indicating by a UE context setup request of the CU to the DU to include dedicated CBRA resources for LTM recovery, and including, by the DU, dedicated CBRA configurations in the UE context setup response.

25. An apparatus, in particular a user equipment (UE), for initiating a L1/L2 triggered mobility (LTM) recovery procedure, wherein the apparatus is configured to determine at least one random access (RA) resource usable for LTM recovery, wherein the random access resources comprise at least one of contention-based random access (CBRA) resources and contention-free random access (CFRA) resources; the apparatus comprising means for: receiving an LTM configuration including selection information (SI) for determining at least one RA resource useable for LTM recovery; and in case of determining a condition for LTM recovery applies, identifying a cell for LTM recovery and determine at least one RA resource useable for LTM recovery for the identified cell, and initiating a random access procedure towards the identified cell using at least one of the determined RA resources useable for LTM recovery.

26. The apparatus of claim 24, further comprising means for: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CFRA resources for LTM recovery if the SI indicates that CFRA resources are not shared.

27. The apparatus of claims 25-26, further comprising means for: if CFRA and CBRA resources are configured for LTM recovery then prioritizing CBRA resources for LTM recovery if the SI indicates that CFRA resources are shared.

28. The apparatus of claims 25-27, further comprising means for: if only CFRA resources are configured for LTM recovery then using dedicated CFRA resources for LTM recovery if the SI indicates dedicated CFRA resources else using any CFRA resources configured by the NW.

29. The apparatus of claim 28, wherein, if the SI indicates dedicated CFRA resources, using a specific CFRA resource out of CFRA resources configured by the NW, wherein the specific CFRA resource is indicated in a command from the distributed unit (DU) of the NW.

30. The apparatus of claim 29, wherein the command from the DU comprises a cell switch command or early TA command.

31. The apparatus of claims 25-30, further comprising means for: if only CBRA resources are configured for LTM recovery then using dedicated CBRA resources for LTM recovery if the SI indicates dedicated CBRA resources else using any CBRA resources configured by the NW.

32. The apparatus of claims 25-31, wherein the SI is to indicate whether CFRA resources are shared or not shared.

33. The apparatus of claims 25-32, wherein the SI is to indicate dedicated CFRA resources.

34. The apparatus of claims 25-33, wherein the SI is to indicate dedicated CBRA resources.

35. The apparatus of claims 25-34, wherein the SI is comprised by a radio resource control (RRC) reconfiguration message.

36. The apparatus of claims 25-35, wherein the LTM configuration further includes an indication of at least one target candidate cell for potential LTM handover and corresponding at least one resource useable for LTM handover.

37. The apparatus of claim 36, wherein the resource useable for LTM handover and the resource useable for LTM recovery at least partly overlap.

38. The apparatus of claims 36-37, wherein for each target candidate cell a separate resource useable for LTM handover is allocated and the resource useable for LTM recovery at least partly overlaps with a corresponding allocated resource for LTM recovery.

39. The apparatus of claims 36-38, wherein in case of receiving a trigger to handover to a particular target candidate cell, and in case handover to the target candidate cell fails, identifying a cell for LTM recovery, wherein the cell for LTM recovery is chosen from the at least one target candidate cell prepared for potential LTM handover and the respective resource allocated for handover is re-used for LTM recovery.

40. An apparatus, in particular a network (NW), for L1/L2 triggered mobility (LTM) recovery, the apparatus comprising means for: configuring one or more random access (RA) resources for LTM recovery; and sending selection information (SI) to a user equipment (UE), the SI configured to enable the UE to select a random access (RA) resource for LTM recovery.

41. The apparatus of claim 40, wherein the SI is provided by a distributed unit (DU) of the NW to a centralized unit (CU) of the NW.

42. The apparatus of claim 40-41, wherein the SI is to indicate whether CFRA resources are shared or not shared.

43. The apparatus of claims 40-42, wherein the SI is to indicate dedicated CFRA resources.

44. The apparatus of claims 40-43, wherein the SI is to indicate dedicated CBRA resources.

45. The apparatus of claims 40-44, further comprising means for: sending a radio resource control (RRC) reconfiguration message to the UE, the RRC reconfiguration message comprising the SI.

46. The apparatus of claims 40-45, further comprising means for: indicating, by the DU to the CU whether CFRA resources are shared or not.

47. The apparatus of claims 40-46, further comprising means for: indicating by a UE context setup request of the CU to the DU to include dedicated CFRA resource configuration for LTM recovery, and including, by the DU, dedicated CFRA resource configuration in a UE context setup response.

48. The apparatus of claims 40-47, further comprising means for: indicating by a UE context setup request of the CU to the DU to include dedicated CBRA resources for LTM recovery, and including, by the DU, dedicated CBRA configurations in the UE context setup response.

49. A computer program product comprising program instructions stored on a computer readable medium to execute a method of any of claims 1 to 24 when said program is executed on a computer.