Lower-layer triggered mobility (LTM) with user equipment (UE)-based timing advance estimation

Abstract

A method performed by a user equipment (UE) is provided. The method includes receiving lower-layer triggered mobility (LTM) candidate configuration(s) for LTM candidate cell(s) for a LTM procedure, the LTM candidate configuration(s) indicating the UE is configured with UE-based timing advance (TA) measurements for the candidate cell(s). The method includes detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure. According to the LTM recovery procedure, the method includes selecting an LTM candidate cell of the LTM candidate cell(s) as a target cell for an LTM cell switch procedure. And the method includes performing a UE-based TA measurement for the target cell, and performing the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of a UE-based TA measurement for the target cell.

Description

LOWER-LAYER TRIGGERED MOBILITY (LTM) WITH USER EQUIPMENT (UE)-BASED TIMING ADVANCE ESTIMATION TECHNOLOGICAL FIELD

[0001] The present disclosure relates generally to telecommunications and, in particular, to lower-layer triggered mobility in a telecommunications system.BACKGROUND

[0002] Telecommunications systems can be seen as facilities that enable communications between two or more entities such as between two user equipment, between a user equipment and a base station, between two base stations, a user equipment and a network function of a communication network and / or a base station and other nodes. A telecommunications system can include a communication network and one or more user equipment. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and / or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

[0003] In a telecommunications system that includes a wireless communication network, at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless communication networks comprise public land mobile networks (PLMN), satellite based communication networks and different wireless local networks, for example wireless local area networks (WLAN). Some wireless communication networks can be divided into cells, and are therefore often referred to as cellular networks.

[0004] A user can access the telecommunications system by means of an appropriate communication device or terminal. A communication device of a user may be referred to as user equipment (UE) or user device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. Thecommunication device may access a carrier provided by, for example, a base station of a cell, and transmit and / or receive communications on the carrier.

[0005] Telecommunications systems have evolved through multiple generations, each bringing advancements in speed, capacity, and functionality. The Evolved Packet System (EPS) represents the 4G architecture, which includes Long-Term Evolution (LTE) and LTE-Advanced (LTE- A) as its radio access technologies. The 5G System (5GS) builds upon EPS, introducing 5G New Radio (5G NR) for enhanced mobile broadband, massive machine-type communications, and ultra-reliable low-latency communications. The future 6G System (6GS) is expected to further revolutionize telecommunications with even more advanced capabilities. These systems are interconnected, with 5GS designed to interwork with EPS for seamless service continuity. The 3rd Generation Partnership Project (3GPP) plays a crucial role in developing and maintaining standards for these telecommunications systems, ensuring global interoperability and evolution from Universal Mobile Telecommunications System (UMTS) (3G) through to the ongoing development of 6G technologies.BRIEF SUMMARY

[0006] Example implementations of the present disclosure are directed to telecommunications and, in particular, to lower-layer triggered mobility in a telecommunications system. The present disclosure includes, without limitation, the following example implementations.

[0007] Some example implementations provide an apparatus to implement a user equipment (UE), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detect a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, select an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure; skip UE-based TAmeasurements for the target cell; and perform the LTM cell switch procedure for the target cell.

[0008] Some example implementations provide a method performed by a user equipment (UE), the method comprising: receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure; skipping UE-based TA measurements for the target cell; and performing the LTM cell switch procedure for the target cell.

[0009] Some example implementations provide an apparatus to implement a user equipment (UE), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detect a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, select an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure; perform a UE-based TA measurement for the target cell; and perform the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

[0010] Some example implementations provide a method performed by a user equipment (UE), the method comprising: receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting an LTM candidate cell of the at least one LTM candidate cell asa target cell for an LTM cell switch procedure; performing a UE-based TA measurement for the target cell; and performing the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

[0011] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. The present disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable unless the context of the disclosure clearly dictates otherwise.

[0012] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.BRIEF DESCRIPTION OF THE FIGURE(S)

[0013] Having thus described example implementations of the disclosure in general terms, reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein:

[0014] FIG. 1 illustrates a telecommunications system that includes one or more public land mobile networks (PLMNs) coupled to one or more external data networks, according to some example implementations of the present disclosure;

[0015] FIG. 2 illustrates a PLMN, according to some example implementations;

[0016] FIG. 3 is a diagram of a procedure for a Ll / L2-triggered mobility, also known as lower-layer triggered mobility (LTM) procedure;

[0017] FIGS. 4A and 4B illustrate a diagram of a procedure for LTM in a CU-DU split architecture, according to some example implementations;

[0018] FIGS. 5A, 5B and 5C illustrate a diagram of a procedure for LTM in a CU-DU split architecture, according to some other example implementations;

[0019] FIGS. 6Aand 6B are flowcharts illustrating various steps in a method performed by a user equipment (UE), according to various example implementations;

[0020] FIGS. 7Aand 7B are flowcharts illustrating various steps in a method performed by a UE, according to various example implementations; and

[0021] FIG. 8 illustrates an apparatus according to some example implementations.DETAILED DESCRIPTION

[0022] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

[0023] Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0024] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus,for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form. Furthermore, it should be understood that unless otherwise specified, the terms “data,” “content,” “digital content,” “information,” and similar terms may be at times used interchangeably. The term “network” may refer to a group of interconnected computers including clients and servers; and within a network, these computers may be interconnected directly or indirectly by various means including via one or more switches, routers, gateways, access points or the like.

[0025] The present disclosure discusses telecommunication systems and mobile or cellular networks and user equipment thereof, and while specific terms may be used, are broadly applicable across various technologies. For instance, while the present disclosure may reference radio access technologies such as 5GNR and 5G Advanced, the present disclosure is equally relevant to next generation radio access technologies, such as 6G. Example implementations of the present disclosure described herein also mention public land mobile networks (PLMNs) and mobile network operators (MNOs), but example implementations are similarly applicable to standalone non-public networks (SNPNs) . Furthermore, although some examples and figures focus on radio access networks (RANs) and in particular radio access networks that operate in accordance with the 3GPP standard for 5G NR (generally referred to as 3GPP access or 3GPP access networks), example implementations are applicable to any type of access networks. This includes not only 3GPP access networks but also non-3GPP access networks, such as wireline access, untrusted non-3GPP access network, and trusted non-3GPP access network using wireless access gateway function (W-AGF), non-3GPP interworking function (N3IWF), or trusted non-3GPP gateway function (TNGF) to connect to a core network (e.g., a 5G core network (5GC) or a 6G core network (6GC)) of a mobile or cellular network.

[0026] Further, as used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry); (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause anapparatus, such as a mobile phone or server, to perform various functions); or (c) hardware circuit(s) and / or processor(s), such as a microprocessor(s) or a portion of a microprocessor s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0027] The above definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0028] FIG. 1 illustrates a telecommunications system 100 according to various example implementations of the present disclosure. Examples of suitable telecommunications systems include UMTS, EPS and 5GS, as well as the future 6GS. The telecommunications system 100 (otherwise referred to as system 100) generally includes one or more mobile or cellular networks, and these mobile or cellular networks may interwork between telecommunications systems. As shown, for example, the system 100 includes one or more PLMNs 102 coupled to one or more other external data networks 104 - notably including a wide area network (WAN) such as the Internet. As will be appreciated, a PLMN may be a standalone PLMN that includes a 5GC, or may be a non-standalone PLMN that includes both an Evolved Packet Core (EPC) and a 5GC connected to a RAN.

[0029] Each of the PLMNs 102 includes a core network (CN) 106, such as the EPC, the 5GC, or a 6GC; and each CN is coupled to one or more RANs 108 that implement one or more radio access technologies (RATs). Examples of these RANs include the evolved UMTS terrestrial radio access network (E-UTRAN) of 4G LTE, the next generation (NG) radio access network (NG-RAN) of 5G NR, and the 6G RAN. As used herein, a “network device” refers to any suitable device of a RAN or a core network of a telecommunications system. Examples of suitable network devices are described in greater detail below.

[0030] Examples of RATs include 3 GPP radio access technologies such as GSM, CDMA2000 IxEV-DO (HRPD), CDMA2000 lx (IxRTT), UTRA, E-UTRA, 5GNR, 5GAdvanced, and 6G. Other examples of RATs include IEEE 802 technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.15 (including 802.15.1 (WPAN / Bluetooth), 802.15.4 (Zigbee) and 802.15.6 (WBAN)), Bluetooth, Bluetooth Low Energy (BLE), ultra wideband (UWB), and the like. Generally, a RAT may refer to any 2G, 3G, 4G, 5G, 6G or higher generation RAT and their different versions, as well as to any other RAT that may be arranged to interwork with such a RAT to provide access to the CN 106 of a MNO.

[0031] The telecommunications system 100 also includes one or more communication devices that may be varyingly known as user equipment (UE) 110, terminal device, terminal equipment, mobile station or the like. The UE is generally a device configured to communicate with a network device (e.g., an access node such as a RAN node of RAN 108) or a or a further UE in the telecommunications system. The UE may be a portable computer (e.g., laptop, notebook, tablet computer), mobile phone (e.g., cell phone, smartphone), wearable computer (e.g., smartwatch), or the like. In other examples, the UE may be an Internet of things (loT) device, an industrial loT (IIoT device), a vehicle equipped with a vehicle-to-everything (V2X) communication technology, or the like. In some examples, as referenced by 3 GPP, the UE 110 may be a narrowband loT (NB-IoT) device, an enhanced machine- type communication (eMTC) device, a reduced capability (RedCap) device, an ambient loT device, or the like.

[0032] In operation, these UEs 110 may connect to one or more RAN nodes of the RANs 108 according to their particular RATs to thereby access a particular CN 106 of a PLMN 102, or to access one or more of the external data networks 104 (e.g., the Internet) or services provided by the PLMN. The external data network may provide Internet access, or 3rd party services. For example, the International Telecommunication Union (ITU) has classified 5G mobile network services (e.g., services provided by a 5G mobile network) into three categories: enhanced mobile broadband (eMBB), ultra-reliable and low- latency communications (URLLC), and massive machine type communications (mMTC) or massive internet of things (MIoT).

[0033] In various examples, a RAN 108 may be configured to provide one or more macrocells, microcells, picocells, femtocells or the like. The RAN 108 may generally include one or more RAN nodes that interact with UEs 110. In various examples, a RAN node may be referred to as a base station (BS), access point (AP), base transceiver station (BTS). Examplesof RAN nodes includes a Node B (NB), evolved NB (eNB), macro BS, NB (MNB) or eNB (MeNB), home BS, NB (HNB) or eNB (HeNB), next generation NB (gNB), enhanced gNB (en-gNB), next generation eNB (ng-eNB), 6G NB (6gNB), or the like. The term ‘gNB’ in 5G NR may correspond to the eNB in 4G LTE. Also, a NG-RAN node may refer to a gNB or a ng-eNB. And unless otherwise specified, a gNB in 5G NR or a 6gNB in 6G may at times be more generally referred to as a (6)gNB or more simply a gNB.

[0034] The RAN 108 may include some type of network controlling / governing entity responsible for control of the RAN nodes. The network controlling / governing entity and RAN node may be separate or integrated into a single apparatus. The network controlling / governing entity may include processing circuity configured to carry out various management functions for controlling RAN nodes of the RAN 108. The processing circuity may be associated with a memory, computer-readable storage medium or a data storage device comprising a database for maintaining information required in the various management functions.

[0035] FIG. 2 illustrates an example of a PLMN 102, such as 4G LTE, 5G NR or 6G PLMN that communicates with a UE 110 and an external data network 104 of the telecommunications system 100. As shown, the RAN 108 (e.g., E-UTRAN, NG-RAN, 6G RAN) includes one or more RAN nodes 202 configured to connect one or more UEs to the RAN to thereby access the CN 106 (e g., EPC, 5GC, 6GC). In 4G LTE, the UE, E-UTRAN and EPC compose EPS. Similarly, in 5GNR, the UE, NG-RAN and 5GC compose the 5GS. And in 6G, the UE, 6G RAN and 6GC compose the 6GS.

[0036] In some implementations, operations of a gNB or other a RAN node may be distributed or functionally split into components including one or more remote radio head (RRHs) or radio units (RUs), and a baseband unit (BBU); and in some implementations, the BBU may be split into a central / centralized unit (CU) (central node) and a distributed unit (DU) (distributed node). The CU may be, for example, a server, host or node. In some implementations, the RRH / RU and DU may be collocated at a network device. It is also possible that operations of a gNB or RAN node may be distributed among a plurality of servers, hosts or nodes.

[0037] It should also be understood that the distribution of work between core network operations and RAN node operations may vary depending on implementation. A 5G or 6G network architecture, for example, may be based on a so-called CU-DU split. One gNB-CU (aCU 204) may control one or more gNB-DUs (DUs 206). The gNB-CU may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some example implementations, however, the gNB-DUs may include, for example, a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU may include the layers above the RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC), and an internet protocol (IP) layer. Other functional splits are also possible. It is considered that skilled person is familiar with the open systems interconnection (OSI) model and the functionalities within each layer.

[0038] In some example implementations, the server or CU 204 may generate a virtual network through which the server communicates with the radio node. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Such virtual network may provide flexible distribution of operations between the server and the radio head / node. In practice, any digital signal processing task may be performed in either the CU or the DU 206, and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

[0039] Currently in 3 GPP, mainstream mobility has been conducted using higher layer (L3 or RRC controlled) mobility. In this regard, L3 handover based mobility is a well-known and proven method for ensuring a robust way of handing over the UE 110 from one serving cell (source cell) of a RAN node 202 to a new serving cell (target cell) of the same or another radio access node. The method has been used at least since GSM and is still in use in 5G NR. It is expected that L3 mobility (legacy handover) will also be commonly used in the future.

[0040] Ll / L2-triggered mobility, or lower-layer triggered mobility (LTM) moves the execution of the ‘handover’ from one cell to another from higher layers (L3), such as RRC, to lower layers. These lower layers may be either PHY (or LI) or MAC (or L2). LTM may reduce latency, overhead and interruption time when compared to L3 handover based mobility. In a CU-DU split architecture, LTM may support one or more of intra-DU mobility, intra-CU inter-DU mobility, or inter-CU inter-DU mobility. LTM may also support both intra-frequency and inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell.

[0041] FIG. 3 illustrates a signaling chart 300 for an LTM procedure of a UE 110 in a RRC connected state with a RAN node 202, which has been proposed. The UE may receive a configuration of L3 measurement reporting. During LTM preparation, as shown at step 301, the UE sends a L3 measurement report to the RAN node based on the configuration for L3 measurement reporting, which decides to use LTM and initiate LTM candidate preparation. The RAN node at step 302 transmits a RRC reconfiguration message to the UE. The RRC reconfiguration message may include a LTM configuration (Itm-Config), which may include LTM candidate configurations (LTM-Candidate) for one or more LTM candidate cells, in some examples, the RRC reconfiguration message may also include a configuration of L3 measurement reporting for LTM execution. In some other examples, the RRC reconfiguration message may also include a configuration of LI measurement reporting for LTM execution. The UE stores the configurations, and the UE at step 303 transmits a RRC reconfiguration complete message to the RAN node.

[0042] An early synchronization of the UE 110 with the LTM candidate cell(s) follows LTM preparation. As shown at step 304, the UE performs downlink (DL) / uplink (UL) synchronization with the LTM candidate cell(s). In this regard, when configured by the network, it is possible to initiate UL timing advance (TA) acquisition (called early TA) procedure of one or more LTM candidate cells that are different from the current serving cell. If the cell has the same NTA as the current serving cell or NTA=0, early TA acquisition procedure is not required. The RAN node may request the UE to perform early TA acquisition of a LTM candidate cell before an LTM cell switch. The early TA acquisition procedure may be triggered by a physical downlink control channel (PDCCH) order or realized through UE-based TA measurement as configured by RRC. In the former case, the RAN node to which the LTM candidate cell belongs may calculate the TA value and send the TA value to the RAN node to which the serving cell belongs.

[0043] During LTM execution, the UE 110 performs measurements on the configured LTM candidate cell(s), and the UE at step 305 transmits a measurement reports to the RAN node 202. In some examples in which the UE receives only a configuration for L3 measurement reporting, the UE may perform L3 measurements and transmit L3 measurement reports, according to the configuration for L3 measurement reporting. In other examples in which the UE may also receive a configuration for LI measurement reporting, the UE mayperform LI measurements and transmit LI measurement reports, according to the configuration for LI measurement reporting. The RAN node decides to execute an LTM cell switch based on the measurements on the configured LTM candidate cell(s), and the RAN node selects one of the LTM candidate cell(s) as a target cell for the LTM cell switch. The RAN node then at step 306 transmits a cell switch command, such as a MAC control element (MAC CE), to trigger LTM cell switch. The UE switches to the configuration of the target cell.

[0044] When early TA acquisition procedure is triggered by PDCCH order, the RAN node 202 may send the TA value for the target cell in the cell switch command MAC CE when triggering the LTM cell switch. When the early TA acquisition procedure is realized through UE-based TA measurement, the UE performs TA measurement for the LTM candidate cell(s) (including the target cell) after being configured by RRC, but the exact time the UE performs TA measurement is up to UE implementation. The UE applies the TA value measured by itself and performs random access channel (RACH)-less LTM upon receiving the cell switch command. The network may also send a TA value in the cell switch command MAC CE without early TA acquisition.

[0045] As shown at steps 307, 308, depending on the availability of a valid TA value, the UE 110 performs either a RACH-based LTM cell switch or a RACH-less LTM cell switch. If the TA value is provided in the cell switch command, the UE applies the TA value as instructed by the RAN node 202. In the case where UE-based TA measurement is configured, but no TA value is provided in the cell switch command, the UE applies the TA value by itself if available. Meanwhile, the UE performs RACH-less LTM cell switch upon receiving the cell switch command. If no valid TA value is available, the UE performs RACH-based LTM cell switch.

[0046] Regardless of whether the UE 110 is configured for UE-based TA measurement for a certain candidate cell, the UE will still follow the PDCCH order or early TA acquisition, which includes requesting a RACH procedure towards the LTM candidate cell(s). This also applies to the LTM candidate cell(s) for which the UE is capable of deriving TA values by itself. Additionally, regardless of whether the UE has already performed a RACH procedure towards the LTM candidate cell(s), the UE may still follow the UE-based measurement configuration if configured by the RAN node 202.

[0047] For RACH-less LTM, the UE 110 may access the target cell using either a configured grant or a dynamic grant. The configured grant may be provided in the LTM candidate configuration for the target cell, and the UE may select the configured grant occasion associated with the beam indicated in the cell switch command. Upon initiation of LTM cell switch to the target cell, the UE may start to monitor PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the UE may not trigger RACH procedure if the UE does not have a valid PUCCH resource for triggered scheduling requests (SRs).

[0048] When an initial LTM execution attempt fails or handover fails, the UE 110 may perform cell selection and if the selected cell is an LTM candidate cell and if RAN node 202 configured the UE to try LTM after LTM execution failure, then the UE attempts LTM execution once, otherwise re-establishment is performed. In some examples, failure associated with the LTM procedure may be detected by a radio link failure (RLF) on the serving cell. In other examples, failure associated with the LTM procedure may be detected by a failure in the execution of the LTM cell switch following a cell switch command from the RAN node. In either case, detection of the failure may trigger the UE perform an LTM recovery procedure in which the UE may select a new cell, and if that is configured as a LTM candidate cell, the UE may perform an LTM cell switch procedure for the selected cell. As currently specified, the LTM recovery procedure is performed as a contention based random access (CBRA)-based recovery in which the LTM cell switch is performed as a random access channel (RACH)-based LTM cell switch.

[0049] It has also been agreed to support UE-based TA measurements for RACH-less intra-CU LTM. According to a procedure applicable to LTM and LTM recovery, upon selection of an LTM candidate cell as a target cell for an LTM cell switch, the UE 110 may check the LTM candidate configuration for a TA measurement identifier (ID) (Itm-UE-MeasuredTA-II)). When the value of the TA measurement ID is not equal to the value of a TA measurement ID for the (former) serving cell (Itm-ServingCellUE-MeasuredTA-ID) within a corresponding variable (VarLTM-ServingCellUE-MeasuredTA-ID)' in UE context information for the UE, the UE may replace the value in the corresponding variable with the value of the TA measurement ID for the target cell (as the new serving cell).

[0050] To enable subsequent LTM cell switches, for each LTM candidate configuration for each LTM candidate cell in the LTM configuration, the UE 110 may also check if the value of the TA measurement IDwithin the LTM candidate configuration (LTM-Candidate) is equal to the value of the TA measurement ID for the new serving cell (Itm-ServingCellUE-MeasuredTA-ID) within the corresponding variable VarLTM-ServingCellUE-MeasuredTA-ID). If equal, the UE (e.g., RRC layer) may inform lower layers (e.g., MAC layer) that the UE is configured with UE-based TA measurements for the LTM candidate cell; otherwise, the UE may inform the lower layers that the UE is not configured with UE-based TA measurements for the LTM candidate cell.

[0051] As currently specified in 3 GPP, LTM recovery procedure is performed as a CBRA-based recovery in which the LTM cell switch is performed as a RACH-based LTM cell switch. But as also specified, if a selected cell (a LTM candidate cell) contains a TA measurement ID, and the value is equal to the value of the TA measurement ID for the serving cell within the corresponding variable in the UE context information, the UE may inform lower layers that the UE is configured with UE-based TA measurements for the selected cell. These two behaviors may result in a situation in which the RRC layer informs the MAC layer that UE is configured with UE-based TA measurements for the LTM candidate cell, which causes the MAC layer to perform the UE-based TA measurements. But when UE is about to execute an LTM cell switch due to LTM recovery, the MAC layer ignores the UE-based TA value and performs CBRA.

[0052] In view of the foregoing, example implementations of the present disclosure provide solution(s) to the aforementioned unexpected and inconsistent UE behavior, such as in an RRC configuration. According to example implementations, at least one LTM candidate configuration may indicate the UE is configured with UE-based TA measurements for the candidate cell. In some examples, each of at least one LTM candidate configuration in the LTM configuration may include a TA measurement ID (Itm-UE-MeasuredTA-ID) for an LTM candidate cell. When the value of the TA measurement ID for the LTM candidate cell is equal to a value of a TA measurement ID of a serving cell (Itm-ServingCellUE-MeasuredTA-ID) within a corresponding variable (VarLTM-ServingCellUE-MeasuredTA-ID)' in UE context information, the value of the TA measurement ID for the LTM candidate cell indicates the UE is configured with UE-based TA measurements for the LTM candidate cell.

[0053] According to a first option, the UE 110 may skip UE-based TA measurements for the target cell during LTM recovery. The UE may not inform the MAC layer that the UE is configured with UE-based TA measurements for the target cell. In some more particular examples, the UE may inform the MAC layer that the UE is not configured with UE-based TA measurements for the target cell. The UE may, then, perform the LTM cell switch procedure for the target cell as a RACH-based LTM cell switch. In particular, for example, the UE may send a random access (RA) preamble to the target cell, and receive a random access response (RAR) from the target cell. The RAR may include a TA value for the target cell, and the UE may access the target cell using the TA value to complete the RACH-based LTM cell switch.

[0054] According to a second option, the UE 110 may perform a UE-based measurement for the target cell during LTM recovery. UE may then perform an LTM cell switch procedure for the target cell as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement. In some examples, the measure of accuracy may be a TA estimation error, which the UE may determine in a number of different manners. For example, the UE may have previously stored at least one prior TA value for the target cell, which the UE may have acquired from the target cell, such as from prior access to the target cell. The UE may then determine the TA estimation error as a difference between the UE-based TA measurement and the prior TA value(s).

[0055] In some examples, the UE 110 may itself determine whether the UE-based TA measurement is sufficiently accurate for RACH-less LTM cell switch. For example, the UE may generate multiple values of the UE-based TA measurement, and if the values are consistent (e.g., within an error range), the UE may determine that the UE-based TA measurement is sufficiently accurate, and the UE may perform the LTM cell switch procedure as a RACH-less LTM cell switch. Otherwise, if the values are inconsistent and / or deviate beyond an acceptable error range (or accuracy level), the UE may conclude that UE-based TA measurement is insufficiently accurate, and the UE may perform the LTM cell switch procedure as a RACH-based LTM cell switch.

[0056] The UE 110 may determine a value of the measure of accuracy, and perform a comparison of the value of the measure of accuracy and a threshold. Depending on the measure of accuracy, examples of a suitable threshold include an accuracy, precision, recall, or Fl -score threshold. The threshold may in some examples be expressed as a bound, such as aconfigured error bound. For example, the UE may compare the value of a TA estimation error and a configured error bound. The LTM cell switch procedure may be performed as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison. More particularly, for example, the LTM cell switch procedure may be performed as a RACH-less LTM cell switch when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch when the value of the measure of accuracy is outside the threshold.

[0057] In some examples, the UE 110 may indicate the LTM candidate cell(s) for which value of the measure of accuracy of the UE-based TA value is within the threshold. Before executing LTM recovery, the UE may check if the value of the measure of accuracy for the UE-based TA value for the target cell is within the threshold. If so, the UE may perform the LTM cell switch procedure as a RACH-less LTM cell switch using the UE-based TA value; otherwise, the UE may perform the LTM cell switch procedure as a RACH-based LTM cell switch without using the UE-based TA value.

[0058] In some examples, in a CU-DU split architecture, a source CU 204 may collect information from DU(s) 206 that provide the LTM candidate cell(s). This information may include, for example, a report configuration for reporting the UE-based TA value(s) and / or the value(s) of the measure of accuracy for the LTM candidate cell(s). Additionally or alternatively, for example, the information may include an indication whether the UE 110 is allowed to use its UE-based TA value(s) during LTM recovery. As another example, the information may include an acceptable value of the measure of accuracy, which may indicate the threshold to which the value is compared. And in yet another example, the information may indicate whether the UE is to implement the first option or the second option for LTM recovery.

[0059] To further illustrate the first option, FIGS. 4Aand 4B illustrate a diagram of a procedure for intra-CU LTM in a CU-DU split architecture, including a CU 204, a source DU (S-DU) 206A for a serving cell, and a target DU (T-DU) 206B for a target cell. During preparation for LTM, as shown in FIG. 4A, a UE 110 may at step 401 send information to the CU 204 (via the S-DU 206A) that indicates a capability of the UE for performing UE-based TA acquisition. The UE may at steps 402, 403 send a L3 measurement report (according to a received configuration for L3 measurement reporting) to the CU via the S-DU, and the CUmay at at step 404 decide to prepare one or more LTM candidate cells for LTM. As shown at steps 405, 406, the CU may proceed with UE context setup / modification procedures. At step 407, the CU generates RRC reconfiguration(s) for the configured LTM candidate cell(s); and at steps 408, 409, the CU sends a RRC reconfiguration message to provide the configurations to the UE 110 via the S-DU. At steps 410, 411, the UE sends a RRC reconfiguration complete to the CU via the S-DU.

[0060] During execution, as shown in FIG. 4B, at step 412 onwards, the UE 110 performs LI (or L3) measurements on the configured LTM candidate cell(s) (according to a received configuration for LI measurement reporting, or the configuration for L3 measurement reporting), and transmits LI (or L3) measurement reports to the S-DU 206A. The S-DU at steps 413, 414 decides to initiate an LTM cell switch to the LTM candidate cell (target cell) provided by the T-DU 206B, and transmits a cell switch command (e.g., MAC CE) to trigger the LTM cell switch procedure.

[0061] As shown at step 415, in some scenarios, the UE 110 may detect a RLF with the S-DU 210A, which may result in the UE not receiving the cell switch command (CSC). When LTM recovery is configured, the UE may perform cell selection, and if the selected cell is an LTM candidate cell, the UE may perform a LTM cell switch procedure for the selected LTM candidate cell as a target cell. Even when the UE is configured with UE-based TA measurements for the target cell, the UE may skip the UE-based TA measurements for the target cell. The UE may not inform the MAC layer that the UE is configured with UE-based TA measurements for the target cell. More specifically, for example, the RRC layer in the UE may not inform the MAC layer that the UE is configured with UE-based TA measurements for the target cell. In some more particular examples, the UE (e.g., RRC layer) may inform the MAC layer that the UE is not configured with UE-based TA measurements for the target cell.

[0062] In some examples in which the UE 110 is otherwise configured with UE-based TA measurements for selected LTM candidate cell (the target cell), the UE may not perform the UE-based TA measurements, and also not update Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID. In some other examples, the UE may update the Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID, but not perform the UE-based TA measurements. Again, as an example, the RRC layer may notinform the MAC layer to perform UE-based TA measurement for the selected LTM candidate cell.

[0063] The UE may perform the LTM cell switch procedure for the target cell as a RACH-based LTM cell switch. For example, the UE may send a RA preamble to the target cell (T-DU 206B), and receive a RAR from the target cell. The RAR may include a TA value for the target cell. The UE may apply the LTM candidate configuration for the target cell, and the UE may access the target cell using the TA value. The UE may then at steps 416, 417 send a RRC reconfiguration complete message to the CU 204 (via the T-DU) to complete the RACH-based LTM cell switch. The S-DU 206A and CU may then at steps 418, 419, 420 perform a UE context release procedure and a path switch procedure.

[0064] To further illustrate the second option, FIGS. 5A, 5B and 5C illustrate a diagram of a procedure for intra-CU LTM in a CU-DU split architecture. During preparation for LTM, as shown in FIG. 5A, a UE 110 may at step 501 send information to the CU 204 (via the S-DU 206A) that indicates a capability of the UE for performing UE-based TA acquisition. The UE may at steps 502, 503 send a L3 measurement report (according to a received configuration for L3 measurement reporting) to the CU via the S-DU, and the CU may at at step 504 decide to prepare one or more LTM candidate cells for LTM.

[0065] As shown at steps 505, 506, the CU 204 may proceed with UE context setup / modification procedures. The CU, S-DU 206A and T-DU 206B may exchange a report configuration for the UE to report information regarding UE-based TA measurements for the LTM candidate cell(s). In some examples, this information may be or include the UE-based TA value(s) and / or the value(s) of the measure of accuracy for the LTM candidate cell(s) (e.g., TA estimation error). In some examples, the T-DU (or any other candidate DU) may also provide an indication on whether the UE 110 is allowed to use UE-based TA acquisition for the LTM candidate cell. Additionally or alternatively, in some examples, the T-DU may provide a threshold associated with the measure of accuracy (e.g., configured error bound).

[0066] At step 507, the CU 204 generates RRC reconfiguration(s) for the configured LTM candidate cell(s); and as shown in FIG. 5B, at steps 508, 509, the CU sends a RRC reconfiguration message to provide the configurations to the UE 110 via the S-DU. At steps 510, 511, the UE sends a RRC reconfiguration complete to the CU via the S-DU.

[0067] The RRC reconfiguration message may include an indication for the UE to report the information regarding UE-based TA measurements for the LTM candidate cell(s). In some examples, the indication may be provided by a flag either inside or outside an LTM candidate configuration for an LTM candidate cell. In other examples, the indication may be implicit. In this regard, the CU 204 may provide the indication in a configuration for LI measurement reporting that may indicate for the UE to report the information regarding UE-based TA measurements. In some examples, RRC reconfiguration may also include an indication on whether the UE 110 is allowed to use UE-based TA acquisition for the LTM candidate cell(s), which may have been provided by the T-DU 206B for its LTM candidate cell. Additionally or alternatively, in some examples, the RRC reconfiguration message may include a threshold associated with the measure of accuracy (e.g., configured error bound), which may have also been provided by the T-DU for its LTM candidate cell.

[0068] During execution, at step 512 onwards, the UE 110 performs LI (or L3) measurements on the configured LTM candidate cell(s) (according to a received configuration for LI measurement reporting, or the configuration for L3 measurement reporting), and transmits LI (or L3) measurement reports to the S-DU 206A. As shown, in some examples, the measurement reports may include information regarding UE-based TA measurements for the LTM candidate cell(s), such as an indication of any of the LTM candidate cell(s) for which the measure of accuracy (e.g., TA estimation error) for the UE-based TA value is within the threshold (e.g., configured error bound).

[0069] The S-DU at steps 513, 514 decides to initiate an LTM cell switch to the LTM candidate cell (target cell) provided by the T-DU 206B, and transmits a cell switch command (e.g., MAC CE) to trigger the LTM cell switch procedure.

[0070] As shown at step 515, in some scenarios, the UE 110 may detect a RLF with the S-DU 210A, which may result in the UE not receiving the cell switch command (CSC). When LTM recovery is configured, the UE may perform cell selection, and if the selected cell is an LTM candidate cell, the UE may perform a LTM cell switch procedure for the selected LTM candidate cell as a target cell. Assuming the UE is configured for UE-based TA measurements for the target cell, the UE may measure and report information regarding the UE-based TA value (even though the UE is instructed to perform RACH-based LTM recovery). In some examples, the UE may report the UE-based TA value and / or a value of the measure ofaccuracy. For example, the UE may report a TA estimation error as a difference between the UE-based TA measurement and prior TA value(s) for the target cell (e.g., received from the network).

[0071] The UE 110 may compare the value of the measure of accuracy (e.g., TA estimation error) and the threshold (e.g., configured error bound). The UE may perform the LTM cell switch procedure as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison. More particularly, for example, the LTM cell switch procedure may be performed as a RACH-less LTM cell switch (using the UE-based TA value) when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch (without the UE-based TA value) when the value of the measure of accuracy is outside the threshold. As shown in FIG. 5C, the UE may then at steps 516A, 517A send a RRC reconfiguration complete message to the CU 204 (via the T-DU) to complete the RACH-based LTM cell switch.

[0072] In some examples, upon successful completion of the LTM cell switch procedure for LTM recovery, the UE 110 may at steps 516B, 517B report (i.e., send a report) information regarding the UE-based TA measurement for the target cell to the CU 204. This information may include, for example, the UE-based TA value, the value of the measure of accuracy for the UE-based TA value, and / or an indication whether the UE was able to obtain a UE-based TA value. In some examples, the information may be reported via RRC signaling (e.g., dedicated RRC message or as part of RLF information reporting). In some other examples, the information may be reported via a MAC CE, such as a dedicated MAC CE. In some examples in which the information is reported by MAC CE, the T-DU 206B (new serving DU) may forward the information to the CU through the Fl interface.

[0073] As shown at steps 520, 521, 522, the S-DU 206A and CU may perform a UE context release procedure and a path switch procedure.

[0074] Although the procedures are shown and described in the context of LTM recovery for intra-CU LTM, some example implementations may be equally applicable to LTM recovery for inter-CU LTM. In some of these example implementations, candidate CUs 204 may share information pertaining to their LTM candidate cells (provided by respective DUs 206). This information may include, for example, an indication on whether the UE 110 is allowed to use UE-based TA acquisition when performing LTM recovery. Additionally oralternatively, in some examples, the T-DU may provide a threshold associated with the measure of accuracy (e.g., configured error bound). As before, during LTM recovery, the UE may perform an LTM cell switch procedure to a selected LTM candidate cell (target cell). The LTM cell switch procedure may be performed as a RACH-less LTM cell switch (using the UE-based TA value) when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch (without the UE-based TA value) when the value of the measure of accuracy is outside the threshold.

[0075] FIGS. 6A and 6B are flowcharts illustrating various steps in a method 600 performed by a user equipment (UE), according to various example implementations. The method includes receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell, as shown at block 602 of FIG. 6A. The method includes detecting at block 604 a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting at block 606 an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure. The method includes skipping UE-based TA measurements for the target cell, as shown at block 608. And the method includes performing the LTM cell switch procedure for the target cell, as shown at block 610.

[0076] In some examples, detecting the failure at block 604 comprises detecting a radio link failure on a serving cell of the UE.

[0077] In some examples, the method 600 further includes receiving a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell. In some of these examples, detecting the failure at block 604 comprises detecting a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

[0078] In some examples, the LTM procedure includes not informing a medium access control (MAC) layer that the UE is configured with UE-based TA measurements for the target cell.

[0079] In some examples, the method 600 further includes informing the MAC layer that the UE is not configured with UE-based TA measurements for the target cell.1

[0080] In some examples, each of the at least one LTM candidate configuration in the LTM configuration includes a TA measurement identifier (ID) for an LTM candidate cell of the at least one LTM candidate cell. In some of these examples, the value of the TA measurement ID of the LTM candidate cell is equal to a value of a TA measurement ID of the serving cell, and the value of the TA measurement ID of the LTM candidate cell thereby indicates the UE is configured with UE-based TA measurements for the LTM candidate cell.

[0081] In some examples, the LTM cell switch procedure is a random access channel (RACH)-based LTM cell switch, and performing the RACH-based LTM cell switch includes sending a random access preamble to the target cell, as shown at block 612 of FIG. 6B. In some of these examples, the RACH-based LTM cell switch also includes receiving a random access response from the target cell, the random access response including a TA value for the target cell, as shown at block 614. And the RACH-based LTM cell switch includes accessing the target cell using the TA value to complete the RACH-based LTM cell switch, as shown at block 616.

[0082] FIGS. 7A and 7B are flowcharts illustrating various steps in a method 700 performed by a user equipment (UE), according to various example implementations. The method includes receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell, as shown at block 702 of FIG. 7A. The method includes detecting at block 704 a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting at block 706 an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure. The method includes performing a UE-based TA measurement for the target cell, as shown at block 708. And the method includes performing at block 710 the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

[0083] In some examples, detecting the failure at block 704 comprises detecting a radio link failure on a serving cell of the UE.

[0084] In some examples, the method 700 further includes receiving a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell. In some of these examples, detecting the failure at block 704 comprises detecting a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

[0085] In some examples, the method 700 further includes reporting, to a serving cell of the UE, information regarding the UE-based TA measurement for the at least one LTM candidate cell. In some of these examples, the information regarding the UE-based TA measurement includes at least one of information that indicates a value of the UE-based TA measurement for the at least one LTM candidate cell, or information that indicates a value of the measure of accuracy of the UE-based TA measurement for the at least one LTM candidate cell.

[0086] In some examples, the method 700 further includes determining a value of the measure of accuracy of the UE-based TA measurement for the target cell, as shown at block 712 of FIG. 7B. In some of these examples, the method also includes performing a comparison of the value of the measure of accuracy and a threshold, as shown at block 714. Also in some of these examples, the LTM cell switch procedure is performed at block 710 as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison.

[0087] In some examples, the LTM cell switch procedure is performed at block 710 as a RACH-less LTM cell switch when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch when the value of the measure of accuracy is outside the threshold.

[0088] In some examples, the method 700 further includes reporting, to the target cell, information regarding the UE-based TA measurement for the target cell.

[0089] In some examples, the information regarding the UE-based TA measurement for the target cell is reported via radio resource control (RRC) signaling or medium access control (MAC) control element (CE).

[0090] According to example implementations of the present disclosure, a telecommunications system 100 or PLMN 102, and its components such as a UE 110, CN 106, RAN 108, RAN node 202, CU 204 and / or DU 206, may be implemented by various means. Means for implementing the system and its components may include hardware, firmware,software, or combinations thereof. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its components shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

[0091] According to some example implementations, at least some of the method 600 described with respect to FIGS. 6Aand 6B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Similarly, at least some of the method 700 described with respect to FIGS. 7A and 7B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may include a user equipment, user device, user terminal or the like.

[0092] FIG. 8 illustrates an apparatus 800 in which means for performing various operations includes hardware, alone or under direction of one or more computer programs from a computer-readable storage medium or other memory, such as computer memory, according to some example implementations of the present disclosure. The apparatus may include one or more of each of a number of components such as, for example, processing circuitry 802 connected to computer-readable storage medium or other memory 804.

[0093] The processing circuitry 802 may be composed of one or more processors alone or in combination with one or more computer-readable storage media. The processing circuitry is generally any piece of computer hardware that is capable of processing information such as, for example, data, computer programs, computer code and / or other suitable electronic information. The processing circuitry is composed of a collection of electronic circuits some of which may be packaged as an integrated circuit or multiple interconnected integrated circuits (an integrated circuit at times more commonly referred to as a “chip”). The processing circuitry may be configured to execute computer programs, which may be stored onboard the processing circuitry or otherwise stored in the memory 804 (of the same or another apparatus).

[0094] The processing circuitry 802 may comprise a number of processors, a multi-core processor or some other type of processor, such as a central processing unit, a graphics processing unit, a tensor processing, unit, or an accelerator, depending on the particular implementation. Further, the processing circuitry may be implemented using a number of heterogeneous processor systems in which a main processor is present with one or moresecondary processors on a single chip. As another illustrative example, the processing circuitry may be a symmetric multi-processor system containing multiple processors of the same type. In yet another example, the processing circuitry may be embodied as or otherwise include one or more application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or the like. Thus, although the processing circuitry may be capable of executing a computer program to perform one or more functions, the processing circuitry of various examples may be capable of performing one or more functions without the aid of a computer program. In either instance, the processing circuitry may be appropriately programmed to perform functions or operations according to example implementations of the present disclosure.

[0095] The memory 804 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 806 (e.g., computer-readable program code) and / or other suitable information either on a temporary basis and / or a permanent basis. The memory may include volatile and / or non-volatile memory, and may be fixed or removable. Examples of suitable memory include recording media, random access memory (RAM), read-only memory (ROM), a hard drive, a flash memory, a thumb drive, a removable computer diskette, an optical disk or some combination thereof.

[0096] The memory 804 is a non-transitory device capable of storing information. One example of a suitable memory is a computer-readable storage medium, which is distinguishable from a computer-readable transmission medium capable of carrying information from one location to another. Examples of suitable computer-readable transmission media comprise electronic carrier signals, telecommunications signals, or some combination thereof. As used herein, the term “non-transitory” is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM versus ROM). A computer-readable medium as described herein generally refers to a computer-readable storage medium or computer-readable transmission medium. A computer-readable medium is any entity or device capable in which information, such as one or more computer programs or portions thereof, may be stored and carried.

[0097] In addition to the memory 804 (e.g., computer-readable storage medium), the processing circuitry 802 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communicationsinterface 808 and / or one or more user interfaces. The communications interface may be configured to transmit and / or receive information, such as to and / or from other apparatus(es), network(s) or the like. The communications interface may be configured to transmit and / or receive information by physical (wired) and / or wireless communications links. Examples of suitable communication interfaces include a network interface controller (NIC), wireless NIC (WNIC) or the like.

[0098] The user interfaces may include a display 810 and / or one or more user input interfaces 812. The display may be configured to present or otherwise display information to a user, suitable examples of which include a liquid crystal display (LCD), light-emitting diode (LED) display, organic LED (OLED) display, active-matrix OLED (AMOLED) or the like. The user input interfaces may be wired or wireless, and may be configured to receive information from a user into the apparatus, such as for processing, storage and / or display. Suitable examples of user input interfaces include a microphone, image or video capture device, keyboard or keypad, joystick, touch-sensitive surface (separate from or integrated into a touchscreen), biometric sensor or the like. The user interfaces may further include one or more interfaces for communicating with peripherals such as printers, scanners or the like.

[0099] Execution of the instructions 806 by the processing circuitry 802, or storage of the instructions in the memory 804, supports combinations of operations for implementing example implementations of the present disclosure. In this manner, an apparatus 800 may comprise at least one processing circuitry and at least one memory coupled to the at least one processing circuitry, where the at least one processing circuitry is configured to execute instructions stored in the at least one memory. It will also be understood that one or more functions, and combinations of functions, may be implemented by special purpose hardwarebased computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions.

[0100] Some example implementations of the present disclosure may also be carried out in the form of a computer process defined by one or more computer programs or portions thereof. Example implementations of the present disclosure may be carried out by executing at least one portion of a computer program comprising instructions. The computer program may be in source code form, object code form, or in some intermediate form. The computer program may be stored in a computer-readable medium that is readable by a computer,processing circuitry or other suitable apparatus. As indicated above, for example, the computer program may be stored in a memory, such as a computer-readable storage medium.Additionally or alternatively, for example, the computer program may be stored in a computer-readable transmission medium. The coding of software for carrying out example implementations of the present disclosure is well within the scope of a person of ordinary skill in the art.

[0101] As will be appreciated, any suitable instructions may be loaded onto a computer, a processing circuitry or other programmable apparatus from a memory or a computer-readable medium (e.g., computer-readable storage medium, computer-readable transmission medium) to produce a particular machine, such that the particular machine becomes a means for implementing the functions specified herein. The instructions may also be stored in a computer-readable medium that can direct a computer, a processing circuitry or other programmable apparatus to function in a particular manner to thereby generate a particular machine or particular article of manufacture. In some examples, the instructions stored in the computer-readable medium may produce an article of manufacture, where the article of manufacture becomes a means for implementing functions described herein. The instructions may be retrieved from a computer-readable medium and loaded into a computer, processing circuitry or other programmable apparatus to configure the computer, processing circuitry or other programmable apparatus to execute operations to be performed on or by the computer, processing circuitry or other programmable apparatus.

[0102] Retrieval, loading and execution of instructions comprising program code instructions may be performed sequentially such that one instruction is retrieved, loaded and executed at a time. In some example implementations, retrieval, loading and / or execution may be performed in parallel such that multiple instructions are retrieved, loaded, and / or executed together. Execution of the program code instructions may produce a computer-implemented process such that the instructions executed by the computer, processing circuitry or other programmable apparatus provide operations for implementing functions described herein.

[0103] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0104] Clause 1. A method performed by a user equipment (UE), the method comprising: receiving at least one lower-layer triggered mobility (LTM) candidate configuration for atleast one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure; skipping UE-based TA measurements for the target cell; and performing the LTM cell switch procedure for the target cell.

[0105] Clause 2. The method of clause 1, wherein detecting the failure comprises detecting a radio link failure on a serving cell of the UE.

[0106] Clause 3. The method of clause 1 or clause 2, wherein the method further comprises receiving a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell, and wherein detecting the failure comprises detecting a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

[0107] Clause 4. The method of any of clauses 1 to 3, wherein the LTM procedure includes not informing a medium access control (MAC) layer that the UE is configured with UE-based TA measurements for the target cell.

[0108] Clause 5. The method of clause 4, wherein the method further comprises informing the MAC layer that the UE is not configured with UE-based TA measurements for the target cell.

[0109] Clause 6. The method of any of clauses 1 to 5, wherein each of the at least one LTM candidate configuration in the LTM configuration includes a TA measurement identifier (ID) for an LTM candidate cell of the at least one LTM candidate cell, and wherein the value of the TA measurement ID of the LTM candidate cell is equal to a value of a TA measurement ID of the serving cell, and the value of the TA measurement ID of the LTM candidate cell thereby indicates the UE is configured with UE-based TA measurements for the LTM candidate cell.

[0110] Clause 7. The method of any of clauses 1 to 6, wherein the LTM cell switch procedure is a random access channel (RACH)-based LTM cell switch, and performing the RACH-based LTM cell switch comprises: sending a random access preamble to the target cell; receiving a random access response from the target cell, the random access responseincluding a TA value for the target cell; and accessing the target cell using the TA value to complete the RACH-based LTM cell switch.

[0111] Clause 8. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to perform the method of any of clauses 1 to 7.

[0112] Clause 9. An apparatus comprising means for performing the method of any of clauses 1 to 7.

[0113] Clause 10. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 7.

[0114] Clause 11. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 7.

[0115] Clause 12. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 7.

[0116] Clause 13. A method performed by a user equipment (UE), the method comprising: receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell; detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure, selecting an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure; performing a UE-based TA measurement for the target cell; and performing the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

[0117] Clause 14. The method of clause 13, wherein detecting the failure comprises detecting a radio link failure on a serving cell of the UE.

[0118] Clause 15. The method of clause 13 or clause 14, wherein the method further comprises receiving a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell, and wherein detecting the failure comprises detecting a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

[0119] Clause 16. The method of any of clauses 13 to 15, wherein the method further comprises reporting, to a serving cell of the UE, information regarding the UE-based TA measurement for the at least one LTM candidate cell, and wherein the information regarding the UE-based TA measurement includes at least one of information that indicates a value of the UE-based TA measurement for the at least one LTM candidate cell, or information that indicates a value of the measure of accuracy of the UE-based TA measurement for the at least one LTM candidate cell.

[0120] Clause 17. The method of any of clauses 13 to 16, wherein the method further comprises: determining a value of the measure of accuracy of the UE-based TA measurement for the target cell; and performing a comparison of the value of the measure of accuracy and a threshold, and wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison.

[0121] Clause 18. The method of clause 17, wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch when the value of the measure of accuracy is outside the threshold.

[0122] Clause 19. The method of any of clauses 13 to 18, wherein the method further comprises reporting, to the target cell, information regarding the UE-based TA measurement for the target cell.

[0123] Clause 20. The method of clause 19, wherein the information regarding the UE-based TA measurement for the target cell is reported via radio resource control (RRC) signaling or medium access control (MAC) control element (CE).

[0124] Clause 21. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to perform the method of any of clauses 13 to 20.

[0125] Clause 22. An apparatus comprising means for performing the method of any of clauses 13 to 20.

[0126] Clause 23. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 13 to 20.

[0127] Clause 24. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 13 to 20.

[0128] Clause 25. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 13 to 20.

[0129] Many modifications and other implementations of the disclosure set forth herein will come to mind to one skilled in the art to which the disclosure pertains having the benefit of the teachings presented in the foregoing description and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated figures describe example implementations in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions may be provided by alternative implementations without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and / or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

32CLAIMS1. An apparatus to implement a user equipment (UE), the apparatus comprising: at least one memory configured to store instructions; andat least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least:receive at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell;detect a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure,select an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure;perform a UE-based TA measurement for the target cell; andperform the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

2. The apparatus of claim 1, wherein the apparatus caused to detect the failure includes the apparatus caused to detect a radio link failure on a serving cell of the UE.

3. The apparatus of claim 1 or claim 2, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell, andwherein the apparatus caused to detect the failure includes the apparatus caused to detect a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

334. The apparatus of any of claims 1 to 3, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further report, to a serving cell of the UE, information regarding the UE-based TA measurement for the at least one LTM candidate cell, andwherein the information regarding the UE-based TA measurement includes at least one of information that indicates a value of the UE-based TA measurement for the at least one LTM candidate cell, or information that indicates a value of the measure of accuracy of the UE-based TA measurement for the at least one LTM candidate cell.

5. The apparatus of any of claims 1 to 4, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: determine a value of the measure of accuracy of the UE-based TA measurement for the target cell; andperform a comparison of the value of the measure of accuracy and a threshold, and wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison.

6. The apparatus of claim 5, wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch when the value of the measure of accuracy is outside the threshold.

7. The apparatus of any of claims 1 to 6, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further report, to the target cell, information regarding the UE-based TA measurement for the target cell.

8. The apparatus of claim 7, wherein the information regarding the UE-based TA measurement for the target cell is reported via radio resource control (RRC) signaling or medium access control (MAC) control element (CE).

9. A method performed by a user equipment (UE), the method comprising: receiving at least one lower-layer triggered mobility (LTM) candidate configuration for at least one LTM candidate cell for a LTM procedure, the at least one LTM candidate configuration indicating the UE is configured with UE-based timing advance (TA) measurements for the at least one candidate cell;detecting a failure associated with the LTM procedure that triggers an LTM recovery procedure; and according to the LTM recovery procedure,selecting an LTM candidate cell of the at least one LTM candidate cell as a target cell for an LTM cell switch procedure;performing a UE-based TA measurement for the target cell; andperforming the LTM cell switch procedure for the target cell as a random access channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch based on a measure of accuracy of the UE-based TA measurement for the target cell.

10. The method of claim 9, wherein detecting the failure comprises detecting a radio link failure on a serving cell of the UE.

11. The method of claim 9 or claim 10, wherein the method further comprises receiving a cell switch command from a serving cell to initiate execution of an LTM cell switch procedure for another LTM candidate cell of the at least one LTM candidate cell, and wherein detecting the failure comprises detecting a failure in the execution of the LTM cell switch procedure for the other LTM candidate cell.

12. The method of any of claims 9 to 11, wherein the method further comprises reporting, to a serving cell of the UE, information regarding the UE-based TA measurement for the at least one LTM candidate cell, andwherein the information regarding the UE-based TA measurement includes at least one of information that indicates a value of the UE-based TA measurement for the at least one LTM candidate cell, or information that indicates a value of the measure of accuracy of the UE-based TA measurement for the at least one LTM candidate cell.

13. The method of any of claims 9 to 12, wherein the method further comprises: determining a value of the measure of accuracy of the UE-based TA measurement for the target cell; andperforming a comparison of the value of the measure of accuracy and a threshold, and wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch or a RACH-based LTM cell switch based on the comparison.

14. The method of claim 13, wherein the LTM cell switch procedure is performed as a RACH-less LTM cell switch when the value of the measure of accuracy is within the threshold, and as a RACH-based LTM cell switch when the value of the measure of accuracy is outside the threshold.

15. The method of any of claims 9 to 14, wherein the method further comprises reporting, to the target cell, information regarding the UE-based TA measurement for the target cell.

16. The method of claim 15, wherein the information regarding the UE-based TA measurement for the target cell is reported via radio resource control (RRC) signaling or medium access control (MAC) control element (CE).

17. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of claims 1 to 16.

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