Redundant random access response from target for lower-layer triggered mobility (LTM) cell switch

Abstract

An early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell 212B is carried out, in which a timing advance (TA) value for the candidate cell is estimated and reported to

Description

TECHNOLOGICAL FIELD

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

[0002] A telecommunications system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and / or other nodes by providing carriers between the various entities involved in the communications path. A telecommunications system can be provided for example by means of a communication network and one or more compatible communication devices. 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 wireless telecommunications system, at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless telecommunications systems comprise public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). Some wireless systems can be divided into cells, and are therefore often referred to as cellular systems.

[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. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and / or receive communications on the carrier.

[0005] The telecommunications system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how operations should be achieved. Communication protocols and / or parameters which shall be used for connection of the various entities are also typically defined. One example of a telecommunications system is the Universal Mobile Telecommunications System (UMTS). Other examples of telecommunications systems are Long-Term Evolution (LTE), LTE Advanced and the so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP). 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 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: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; make a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell, the RAR including the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0008] Some example implementations provide an apparatus comprising: means for carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; means for making a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, means for applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; means for skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; means for receiving the RAR from the target cell, the RAR including the TA value; and means for accessing the target cell using the TA value to complete the LTM cell switch.

[0009] Some example implementations provide a method comprising: carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; making a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; receiving the RAR from the target cell, the RAR including the TA value; and accessing the target cell using the TA value to complete the LTM cell switch.

[0010] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; make a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell, the RAR including the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0011] Some example implementations provide an apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, 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 a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE, the RAR including the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0012] Some example implementations provide an apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the apparatus comprising: means for receiving a random access preamble from an user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; means for estimating a timing advance (TA) value for the LTM candidate cell; means for reporting the TA value to a serving cell of the UE; means for sending a random access response (RAR) one or more times to the UE, the RAR including the TA value; and means for carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0013] Some example implementations provide a method performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the method comprising: receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimating a timing advance (TA) value for the LTM candidate cell; reporting the TA value to a serving cell of the UE; sending a random access response (RAR) one or more times to the UE, the RAR including the TA value; and carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0014] Some example implementations provide a computer-readable storage medium implemented at a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the computer-readable storage medium being non-transitory and having instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE, the RAR including the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0015] Some example implementations provide 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 at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; detect a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell that includes the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0016] Some example implementations provide an apparatus comprising: means for carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; means for detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, means for applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; means for skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; means for receiving the RAR from the target cell that includes the TA value; and means for accessing the target cell using the TA value to complete the LTM cell switch.

[0017] Some example implementations provide a method comprising: carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell m which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; receiving the RAR from the target cell that includes the TA value; and accessing the target cell using the TA value to complete the LTM cell switch.

[0018] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; detect a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell that includes the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0019] Some example implementations provide an apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, 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 a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE that includes the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0020] Some example implementations provide an apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the apparatus comprising: means for receiving a random access preamble from an user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; means for estimating a timing advance (TA) value for the LTM candidate cell; means for reporting the TA value to a serving cell of the UE; means for sending a random access response (RAR) one or more times to the UE that includes the TA value; and means for carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0021] Some example implementations provide a method performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the method comprising: receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimating a timing advance (TA) value for the LTM candidate cell; reporting the TA value to a serving cell of the UE; sending a random access response (RAR) one or more times to the UE that includes the TA value; and carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0022] Some example implementations provide a computer-readable storage medium implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the computer-readable storage medium being non-transitory and having instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE that includes the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0023] 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.

[0024] 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)

[0025] 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:

[0026] 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;

[0027] FIG. 2 illustrates a 5G deployment of a PLMN, according to some example implementations;

[0028] FIG. 3 is a signaling chart for a L1 / L2-triggered mobility, also known as lower-layer triggered mobility (LTM) procedure;

[0029] FIGS. 4Aand 4B illustrate a signaling chart for an LTM procedure in a CU-DU split architecture;

[0030] FIGS. 5 A and 5B illustrate a signaling chart for an LTM procedure in which a radio link failure (RLF) is detected by a user equipment (UE) during early synchronization;

[0031] FIGS. 6A and 6B illustrate a signaling chart for an LTM procedure, according to some example implementations;

[0032] FIGS. 7Aand 7B illustrate a signaling chart for an LTM procedure, according to some other example implementations;

[0033] FIGS. 8A and 8B are flowcharts illustrating various steps in a method according to various example implementations;

[0034] FIGS. 9A, 9B, 9C and 9D are flowcharts illustrating various steps in a method 900 performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, according to various example implementations

[0035] FIGS. 10A and 10B are flowcharts illustrating various steps in a method according to various example implementations

[0036] FIGS. 11 A. I IB, 11C and 1 ID are flowcharts illustrating various steps in a method performed by a radio access node providing a LTM candidate cell, according to various example implementations; and

[0037] FIG. 12 illustrates an apparatus according to some example implementations. DETAILED DESCRIPTION

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Reference may be made herein to terms specific to a particular system, architecture or the like, but it should be understood that example implementations of the present disclosure may be equally applicable to any of a number of systems, architectures and the like. For example, reference may be made to 3 GPP technologies such as Global System for Mobile Communications (GSM), UMTS, LTE, LTE Advanced, 5GNR, 5G Advanced and 6G; however, it should be understood that example implementations of the present disclosure may be equally applicable to non-3GPP technologies such as IEEE 802, Bluetooth and Bluetooth Low Energy.

[0042] 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 an apparatus, 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.

[0043] 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.

[0044] FIG. 1 illustrates a telecommunications system 100 according to various example implementations of the present disclosure. The telecommunications system generally includes one or more telecommunications networks. As shown, for example, the system includes one or more public land mobile networks (PLMNs) 102 coupled to one or more other external data networks 104 - notably including a wide area network (WAN) such as the Internet. Each of the PLMNs includes a core network (CN) 106 backbone such as the Evolved Packet Core (EPC) of LTE, the 5G core network (5GC) or the like; and each of the core networks and the Internet are coupled to one or more radio access networks (RANs) 108, air interfaces or the like that implement one or more radio access technologies (RATs). As used herein, a “network device” refers to any suitable device at a network side of a telecommunications network. Examples of suitable network devices are described in greater detail below.

[0045] In addition, the system includes one or more radio units 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 or a further UE in a telecommunications network. 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 (11 oT device), a vehicle equipped with a vehicle-to-everything (V2X) communication technology, or the like. In some examples, as referenced by 3GPP, the UE 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.

[0046] In operation, these UEs 110 may be configured to connect to one or more of the RANs 108 according to their particular radio access technologies 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). The external data network may be configured to provide Internet access, operator services, 3rd party services, etc. For example, the International Telecommunication Union (ITU) has classified 5G mobile network services 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).

[0047] Examples of radio access technologies include 3 GPP radio access technologies such as GSM, UMTS, LTE, LTE Advanced, 5GNR, 5G Advanced, and 6G. Other examples of radio access technologies 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 radio access technology may refer to any 2G, 3G, 4G, 5G, 6G or higher generation mobile communication technology and their different versions, as well as to any other wireless radio access technology that may be arranged to interwork with such a mobile communication technology to provide access to the CN 106 of a mobile network operator (MNO).

[0048] In various examples, a RAN 108 may be configured as one or more macrocells, microcells, picocells, femtocells or the like. The RAN may generally include one or more radio access nodes that are configured to interact with UEs 110. In various examples, a radio access node may be referred to as a base station (BS), access point (AP), base transceiver station (BTS), 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), or the like. The RAN may include some type of network controlling / governing entity responsible for control of the radio access nodes. The network controlling / governing entity and radio access 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, etc. The processing circuity may be associated with a memory, computer-readable storage medium or database for maintaining information required in the management functions.

[0049] A RAN 108 may be centralized or distributed. In various examples, components of a RAN may be interconnected by Ethernet, Gigabit Ethernet, Asynchronous Transfer Mode (ATM), optical fiber, dark fiber, passive wavelength division multiplexing (WDM), WDM passive optical network (WDM-PON), optical transport network (OTN), time sensitive networking (TSN) and / or any other data link layer network, possibly including radio links. The RAN may be connected to a CN 106 through one or more gateways, network functions or the like.

[0050] As will be appreciated, a PLMN 102 may be deployed in a number of different manners. In a 4G LTE deployment, the EPC is the CN 106, and the evolved UMTS terrestrial radio access network (E-UTRAN) is the RAN 108; and the E-UTRAN includes one or more eNBs (radio access nodes) configured to connect UEs 110 to the E-UTRAN to thereby access the EPC. As shown in FIG. 2, in a 5G deployment 200, the 5GC 202 is the CN, and the next generation (NG) radio access network (NG-RAN) 204 is the RAN; and the NG-RAN includes one or more gNBs 206 (radio access nodes) configured to connect UEs 110 to the NG-RAN to thereby access the 5GC (at times referred to as the NGC). The term ‘gNB’ in 5G may correspond to the eNB in 4G LTE.

[0051] Some deployments of 4G LTE and 5G in particular are considered standalone (SA) deployments. Other deployments combine 4G LTE and 5G technologies, and are referred to as non-standalone (NSA) deployments. In some deployments, the E-UTRAN includes one or more ng-eNBs that are configured to communicate with the 5GC, and that may also be configured to communicate with one or more gNBs. Similarly, in another deployment, the NG-RAN may include one or more en-gNBs that are configured to communicate with the EPC, and that may also be configured to communicate with one or more eNBs. In various instances, a single UE 110, a dual-mode or multimode UE, may support multiple (two or more) RANs—thereby being configured to connect to multiple RANs, such as 4G LTE and 5G.

[0052] In some deployments, operations of a gNB 206 or other radio access node may be distributed or functionally split into components including one or more remote radio head (RRHs) or radio units (RUs) 208, and a baseband unit (BBU); and in some architectures, the BBU may be split into a distributed unit (DU) 210 and a central / centralized unit (CU) 212, such as a server, host or node. In some architectures, the RRH / RU and DU may be co-located. It is also possible that node operations may be distributed among a plurality of servers, hosts or nodes. It should also be understood that the distribution of work between CN operations and radio access node operations may vary depending on implementation.

[0053] As shown and described, for example, some 5G deployments may be based on a so-called CU-DU split including one or more DUs 210 and a CU 212. One gNB-CU (central node) may control one or more gNB-DUs. 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 (also called DU) may include, for example, a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU (also called a 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 a skilled person is familiar with the open systems interconnection (OSI) model and the functionalities within each layer.

[0054] In some example implementations, the server or CU 212 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 210, and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

[0055] Currently in 3GPP, 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 radio access 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.

[0056] 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 mtra-DU mobility, intra-CU inter-DU mobility, or inter-CU inter-DU mobility.

[0057] FIG. 3 illustrates a signaling chart 300 for an LTM procedure of a UE 110 in a RRC connected state with a gNB 206, which has been proposed. During LTM preparation, as shown at step 301, the UE sends a L3 measurement report to the gNB, which decides to use LTM and initiate LTM candidate preparation. The gNB at step 302 transmits a RRC reconfiguration message to the UE, including the configuration of one or more candidate cells, which may include an early timing advance (TA) acquisition configuration of the one or more candidate cells. 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 gNB.

[0058] An early synchronization of the UE 110 with the candidate cel 1(s) follows LTM preparation. As shown at step 304, the UE 110 performs downlink (DL) / uplink (UL) synchronization with the candidate cell(s). During this procedure, the UE may acquire a TA of respective ones of the candidate cell(s). This early synchronization may reduce interruption during LTM execution, as compared to L3 handover based mobility. In this regard, the TA may be used to control the timing of uplink transmissions of a UE toward the candidate cell(s). The UE may likewise have an acquired TA of the cell of the gNB to control the timing of uplink transmissions toward the gNB.

[0059] During LTM execution, the UE 110 performs LI measurements on the configured candidate cell(s), and the UE at step 305 transmits LI measurement reports to the gNB 206. The gNB decides to execute a cell switch, and selects one of the candidate cell(s) as a target cell for the cell switch. The gNB then at step 306 transmits a cell switch command, such as a MAC control element (MAC-CE), to trigger cell switch. The UE switches to the configuration of the target cell; and if the TA of the target cell (from step 304) is no longer available, the UE at step 307 initiates if the UL synchronization was not successful a physical random access channel (PRACH) procedure with the target cell to acquire the TA of the target cell. The UE then at step 308 indicates successful completion of the cell switch.

[0060] FIGS. 4A and 4B illustrate a signaling chart 400 for an LTM procedure in a CU-DU split architecture, including a CU 212, a source DU (S-DU) 210Afor a serving cell, and a target DU (T-DU) 210B for a target cell. During preparation for LTM, as shown at steps 401 and 402, the UE 110 sends a L3 measurement report to the CU via the S-DU, and the CU at step 403 decides prepare one or more candidate cells (DUs) for LTM. As shown at steps 404, 405, 406 and 407, the CU proceeds with the UE context setup / modification procedures. At step 408, the CU generates RRC reconfiguration(s) for the configured candidate cell(s); and at steps 409 and 410, the CU provides the configurations to the UE 110 via the S-DU.

[0061] At steps 408, 409 and 410, the CU 212 also configures the UE 110 with LI measurement reporting for LTM execution. The CU provides the S-DU 210A with TA acquisition triggering criteria and configuration(s), as well as cell switch triggering criteria and configuration(s). The triggering criteria for TA acquisition and cell switch may be similar to measurement event report triggering conditions, e.g., A3, A4 or A5 event conditions or validity of acquired TA. The triggering conditions may include, for example, a filter configuration (for LI measurements), trigger offsets, cell individual offsets, or the like.

[0062] At steps 411 and 412, the UE 110 sends a RRC reconfiguration complete to the CU 212 via the S-DU 210A.

[0063] During execution, at step 413 onwards, the UE 110 performs LI measurements on the configured candidate cell(s), and transmits LI measurement reports to the S-DU 210A. The S-DU at step 414 decides to trigger the TA acquisition of the candidate cell(s) (including the cell of T-DU 210B), and the S-DU at step 415 transmits a TA acquisition command to the UE. The UE at steps 416, 417 waits for an appropriate PRACH occasion and transmits a PRACH (random access) preamble to the candidate cell(s) (T-DU 210B / cell) to signal the candidate cell(s) to estimate the TA between the UE and the candidate cell(s). And at step 418, the S-DU 210A / cell receives a random access response (RAR) including the TA from respective ones of the candidate cell(s) indirectly via the CU 212.

[0064] The UE 110 performs LI measurements of the candidate cell(s), and the UE at step 419 transmits the LI measurements to the S-DU 210A. The S-DU at steps 420 and 421 decides to initiate a cell change to the T-DU 210B / cell, and transmits a cell switch command (e.g., MAC-CE) to trigger the cell switch. The S-DU provides the TA of the T-DU / cell to the UE in the cell switch command. If the TA of the T-DU / cell is still valid, the UE may skip a RACH procedure towards the T-DU / cell; and at step 422, the UE and T-DU carry out the cell change to the T-DU.

[0065] In some scenarios, the UE 210 may detect a radio link failure (RLF) with the S-DU 210A during LTM, which may result in an interruption of the cell switch procedure. FIGS. 5A and 5B illustrate a signaling chart 500 for the LTM procedure in which a RLF is detected during early synchronization. As shown in FIG. 5B, after the UE at step 417 transmits the PRACH preamble to the candidate cel 1 (s) (T-DU 210B / cell), the source link degrades. The duration of the interruption for PRACH transmission varies between 1 milliseconds and 15 milliseconds depending on the candidate cell UL bandwidth part (BWP) configuration compared to serving cell (S-DU 212A) active UL BWP configuration. Then after a T310 timer expires, UE at step 519 detects radio link failure.

[0066] The UE 110 at step 520 triggers re-establishment procedure and starts performing cell re-selection measurements (LI measurements). UE selects the best cell based on the cell re-selection measurements. If UE is configured with LTM recovery, UE triggers LTM execution if the best selected cell is also a candidate cell (e.g., T-DU 210B / cell). The UE at steps 521, 522 waits for an appropriate PRACH occasion and transmits a PRACH preamble to T-DU / cell. The T-DU / cell at step 523 sends a RAR including a TA value for the T-DU / cell. And the UE at step 524 sends a RRC reconfiguration complete message to the T-DU / cell using the TA value to complete the cell switch to the T-DU / cell.

[0067] The LTM procedure shown in FIGS. 5A and 5B illustrates a number of issues. During the re-establishment procedure, the UE 110 performs LI measurements of one or more of the same cells reported to the S-DU 212A to trigger (at step 414) the TA acquisition. The UE also resends a PRACH for a cell (T-DU 210B / cell) that the UE has already sent a PRACH (assuming the same candidate cell is selected after the cell re-selection measurements). Repeating the LI measurements and PRACH may cause an increased interruption at the UE from detection of the RLF until the RRC reconfiguration complete message is sent.

[0068] Example implementations of the present disclosure provide a solution in which a UE 110 may resume with an RAR from a target cell (e.g., T-DU 210B / cell) to complete an LTM cell switch procedure when the serving cell (S-DU 212A / cell) link quality degrades. In this regard, the solution provides a RAR sent by the target cell one or more times to the UE to improve UE failure recovery. As described, the RAR sent one or more times to the UE is at times referred to as a redundant RAR.

[0069] In some examples, the UE 110 may be configured with an event that is optionally activated after early TA transmission to monitor a radio link quality of the serving cell (S-DU 212A / cell) versus one or more candidate cell(s). If this condition is fulfilled for one of the candidate cell(s) (e.g., T-DU 210B / cell), the UE may detach from the serving cell to receive a redundant RAR from the one of the candidate cell(s) as a target cell for a cell switch, and complete the cell switch. In some other example implementations, the UE may be configured to skip re-establishment procedure after RLF detection, and trigger a cell switch starting with a redundant RAR from the target cell if early TA has already been triggered.

[0070] Some example implementations of the present disclosure provide a gNB 206 that provides a LTM candidate cell (e.g., T-DU 210B / cell) in a LTM procedure. During LTM preparation, the LTM candidate cell may carry out a LTM candidate preparation with a serving cell (S-DU 212A / cell) of a UE 110 during which the LTM candidate cell is configured by the serving cell for a RAR transmission. The UE may also receive a configuration for the LTM cell switch that includes a configuration of the LTM candidate cell, and an LTM cell switch condition. Additionally or alternatively, in some examples, the configuration may include a configuration for a LTM recovery procedure.

[0071] During early synchronization, the UE that may carry out an early UL synchronization with the LTM candidate cell. In this regard, the LTM candidate cell may receive a random access (PRACH) preamble from the UE, estimate a TA value for the LTM candidate cell, and report the TA value to a serving cell (S-DU 212A / cell) of the UE.

[0072] The UE 110 may make a determination that the LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell (S-DU 212A / cell). In some examples, the LTM cell switch condition may be fulfilled when the radio link quality of the serving cell (S-DU 212A / cell) is below a radio link quality of the LTM candidate cell. Additionally or alternatively, the LTM cell switch condition may be fulfilled when the radio link quality of the serving cell (S-DU 212A / cell) is below a radio link quality threshold, which may be above a radio link quality at which a RLF on the serving cell is detected.

[0073] Based on the determination that the LTM cell switch condition is fulfilled, the UE 110 may apply the configuration of the LTM candidate cell (e.g., T-DU 210B / cell) as a target cell for a LTM cell switch. The UE may skip a random access preamble, and monitor for a RAR from the target cell. More particularly, for example, the UE may monitor a physical donwlink control channel (PDCCH) at the target cell for a RAR to the UE’s previous (at step 417) PRACH preamble. The target cell may send a RAR (including the TA value) one or more times to the UE, which may be based on the configuration for RAR transmission by the serving cell.

[0074] In some examples, the UE 110 and LTM candidate cell (e g., T-DU 210B / cell) may start a (redundant RAR) timer in connection with the early synchronization. The UE may then monitor for the RAR until the timer expires, the LTM candidate cell may send the RAR one or more times to the UE until the timer expires. The UE may start the timer after sending the random access preamble during early UL synchronization, and the LTM candidate cell may start the timer after receiving the random access preamble. In some examples, the LTM candidate cell may start to send the RAR one or more times to the UE based on an indication received from the serving cell (S-DU 212A / cell). The LTM candidate cell may stop sending the RAR when the timer expires. Additionally or alternatively, in some examples, the LTM candidate cell may stop sending the RAR one or more times ot the UE based on an indication received from the serving cell.

[0075] When the determination is made that the LTM cell switch condition is fulfilled before expiration of the timer, UE 110 may receive the RAR from the LTM candidate cell (e.g., T-DU 210B / cell) as the target cell. The UE and target cell may then carry out the LTM cell switch in which the UE may access the target cell using the TA value to complete the LTM cell switch.

[0076] According to some example implementations, the UE 110 may additinally or alternatively detect a RLF on the serving cell (S-DU 212A / cell) that triggers a LTM recovery procedure (e.g., before expiration of the timer). Before triggering the LTM recovery procedure, in some examples, the UE may first determine a radio link quality of the LTM candidate cell is above a threshold radio link quality. According to the LTM recovery procedure, then, the UE may apply the configuration of the LTM candidate cell (e.g., T-DU 210B / cell) as the target cell for a LTM cell switch. The UE may skip a random access (PRACH) preamble, and monitor for the RAR from the target cell, similar to before. The UE may receive the RAR (including the TA value) from the target cell that includes the TA value. The UE and target cell may then carry out the LTM cell switch m which the UE may access the target cell using the TA value to complete the LTM cell switch.

[0077] To further illustrate some example implementations, FIGS. 6A and 6B illustrate a signaling chart 600 for an LTM procedure, according to some examples. As shown at steps 604, 605, during LTM preparation, the CU 212 performs a UE context setup procedure during which T-DU 210B / cell is configured for redundant RAR transmission. This configuration may be requested by the CU or the T-DU / cell. Also during LTM preparation, the serving cell (S-DU 212A / cell) at step 610 configures the UE 110 with a LTM cell switch condition to be monitored by the UE, and a redundant RAR timer. More particularly, for example, the UE may be configured with the LTM cell switch condition to monitor after PRACH preamble transmission for early TA acquisition, after a timer (separate from the redundant RAR timer) expires to delay evaluation of the LTM cell switch condition, or irrespective of either or both the PRACH preamble transmission or timer.

[0078] As shown in FIG. 6B, after the UE 110 (at step 417) transmits the PRACH (random access) preamble to the candidate cell(s) (T-DU 210B / cell), the UE at step 619 starts the redundant RAR timer. The T-DU / cell may also be aware of the redundant RAR timer configured to the UE, and similarly the T-DU / cell may at step 620 start the redundant RAR timer.

[0079] The UE 110 at step 621 monitors for the LTM cell switch condition to switch to RAR over a target cell (e.g., T-DU 212B / cell). The UE at step 622 determines the LTM cell switch condition is fulfilled before expiration of the redundant RAR timer. The UE applies the configuration of the LTM candidate cell as a target cell for a LTM cell switch, skips PRACH transmission, and monitors a PDCCH at the target cell for a RAR to the UE’s previous (at step 417) PRACH preamble. If the redundant RAR timer has expired, UE may instead perform a RACH-based LTM similar to FIGS. 5A and 5B.

[0080] The candidate cell (T-DU 210B / cell) at steps 623 and 624 sends a RAR one or more times to the UE 110. The UE receives the RAR (including the TA value) from the candidate cell as the target cell for the LTM cell switch; and the UE at step 625 sends a RRC reconfiguration complete message to the T-DU / cell using the TA value to complete the cell switch to the T-DU / cell.

[0081] In some examples, the candidate cell (T-DU 210B / cell) may send multiple repetitions of the RAR to the UE 110 before the redundant RAR timer expires, and estimate a delay between repetitions of the RAR. In other examples, the candidate cell may send multiple repetitions of the RAR until the candidate cell receives a PRACH preamble from the same UE. The candidate cell may receive an indication from the S-DU 212A / cell to stop sending the RAR, such as after the CU detects that the UE has connected back to the S-DU / cell, and that the UE is able to receive the TA value for the T-DU / cell from the S-DU / cell. The candidate cell may also stop sending the RAR based on other indication(s) from the S-DU / cell (e.g., LTM cell switch notification notifying about the target cell and target transmission configuration indicator (TCI) states).

[0082] The S-DU 212A / cell may inform the candidate cell (T-DU 210B / cell) to start sending the RAR from the candidate cell (i.e., trigger redundant RAR) upon the S-DU failing to provide the RAR to the UE 110. This may be relevant for conditional LTM where the RAR from S-DU / cell may be a default option. In case delivery of RAR from S-DU fails (e.g., no acknowledgment of the MAC-CE), the S-DU may have an indication that the UE - S-DU link is insufficient / unreliable, and indicate to the candidate cell (as the target cell) to start sending the RAR. This may avoid the candidate cell sending the RAR one or more times to the UE unnecessarily because the UE - S-DU link is sufficient for S-DU to send the TA value to the UE.

[0083] In some examples, if the UE 110 fails to receive a RAR from the candidate cell (T-DU 210B / cell) within a RA-response window configured to the UE, the UE may reinitiate a PRACH procedure as configured in the candidate cell configuration. In some of these examples, the UE may be configured to increase its transmit power for the new PRACH preamble relative to its last PRACH preamble (at step 417). In some other examples, the UE may reset its transmit power for the new PRACH preamble.

[0084] FIGS. 7A and 7B illustrate a signaling chart 700 for an LTM procedure, according to some other example implementations. Relative to the LTM procedure of FIGS. 6 A and 6B, the serving cell (S-DU 212A / cell) at step 710 configures the UE 110 for a LTM recovery procedure, and a redundant RAR timer. The LTM recovery procedure may be indicated to the UE on a candidate cell basis or as part of the LTM procedure. Once triggered, the LTM recovery procedure may indicate that the UE should start monitoring a PDCCH at a target cell (e g., T-DU 210B / cell) to receive a RAR to a previous PRACH preamble (at step 417). This configuration may be indicated in a target cell configuration or in a source configuration of the UE.

[0085] As shown in FIG. 7B, after the UE 110 (at step 417) transmits the PRACH (random access) preamble to the candidate cell(s) (T-DU 210B / cell), the UE at step 619 starts the redundant RAR timer. The T-DU / cell may also be aware of the redundant RAR timer configured to the UE, and similarly the T-DU / cell may at step 620 start the redundant RAR timer.

[0086] The UE 110 at step 721 detects RLF on the serving cell (S-DU 212A / cell). The UE at step 722a determines an ongoing early TA acquisition with a candidate cell (T-DU 210B / cell), and that the redundant RAR timer has not expired. The UE triggers the LTM recovery procedure for the candidate cell. According to the LTM recovery procedure, then, the UE at step 722b applies the configuration of the LTM candidate cell as a target cell for a LTM cell switch, skips PRACH transmission, and monitors a PDCCH at the target cell for a RAR to the UE’s previous (at step 417) PRACH preamble. If the redundant RAR timer has expired, UE may instead perform a RACH-based LTM similar to FIGS. 5A and 5B.

[0087] The candidate cell (T-DU 210B / cell) at steps 623 and 624 sends a RAR one or more times to the UE 110, such as in the manner described above. The UE receives the RAR (including the TA value) from the candidate cell as the target cell for the LTM cell switch; and the UE at step 625 sends a RRC reconfiguration complete message to the T-DU / cell using the TA value to complete the cell switch to the T-DU / cell.

[0088] FIGS. 8Aand 8B are flowcharts illustrating various steps in a method 800 according to various example implementations. The method includes carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE, as shown at block 802 of FIG. 8 A. The method includes making at block 804 a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell or additionally that a preamble is transmitted towards the candidate cell which fulfilled the cell switch condition; and based on the determination applying at block 806 a configuration of the LTM candidate cell as a target cell for a LTM cell switch. The method includes skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell, as shown at block 808. The method includes receiving the RAR from the target cell, the RAR including the TA value, as shown at block 810. And the method includes accessing the target cell using the TA value to complete the LTM cell switch, as shown at block 812.

[0089] In some examples, the method 800 further includes receiving a configuration for the LTM cell switch that includes the LTM cell switch condition and the configuration of the LTM candidate cell.

[0090] In some examples, the method 800 further includes starting a timer in connection with the early uplink synchronization, as shown at block 816 of FIG. 8B. In some of these examples, the determination that the LTM cell switch condition is fulfilled is made at block 804 before expiration of the timer.

[0091] In some examples, the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality of the LTM candidate cell.

[0092] In some examples, the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality threshold.

[0093] FIGS. 9A - 9D are flowcharts illustrating various steps in a method 900 performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, according to various example implementations. The method includes receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell, as shown at block 902 of FIG. 9A. The method includes estimating a timing advance (TA) value for the LTM candidate cell, as shown at block 904. The method includes reporting the TA value to a serving cell of the UE, as shown at block 906. The method includes sending a random access response (RAR) one or more times to the UE, the RAR including the TA value, as shown at block 908. And the method includes carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, as shown at block 910.

[0094] In some examples, the LTM cell switch is carried out at block 910 based on a determination by the UE that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell.

[0095] In some examples, the method 900 further includes carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0096] In some examples, the method 900 further includes starting a timer in connection with the early uplink synchronization, as shown at block 912 of FIG. 9B. In some of these examples, the RAR is sent at block 908 one or more times to the UE before expiration of the timer.

[0097] In some examples, the method 900 further includes receiving an indication from the serving cell to start sending the RAR, as shown at block 914 of FIG. 9C. In some of these examples, sending the RAR one or more times to the UE at block 908 is started based on the indication.

[0098] In some examples, the method 900 further includes receiving an indication from the serving cell to stop sending the RAR, as shown at block 916 of FIG. 9D. In some of these examples, sending the RAR one or more times to the UE at block 908 is stopped based on the indication.

[0099] FIGS. lOAand 10B are flowcharts illustrating various steps in a method 1000 according to various example implementations. The method includes carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell, as shown at block 1002 of FIG. 10A. The method includes detecting at block 1004 a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, applying at block 1006 a configuration of the LTM candidate cell as a target cell for a LTM cell switch. The method includes skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell, as shown at block 1008. The method includes receiving the RAR from the target cell that includes the TA value, as shown at block 1010. And the method includes accessing the target cell using the TA value to complete the LTM cell switch, as shown at block 1012.

[0100] In some examples, the method 1000 further includes receiving a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

[0101] In some examples, the method 1000 further includes starting a timer in connection with the early uplink synchronization, as shown at block 1016 of FIG. 10B. In some of these examples, the radio link failure is detected at block 1004 before expiration of the timer.

[0102] In some examples, the method 1000 further includes determining a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recover}' procedure is triggered toward the LTM candidate cell.

[0103] FIGS. 11A 1 ID are flowcharts illustrating various steps in a method 1100 performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, according to various example implementations. The method includes receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell, as shown at. block 1102 of FIG. 11A. The method includes estimating a timing advance (TA) value for the LTM candidate cell, as shown at block 1104. The method includes reporting the TA value to a serving cell of the UE, as shown at block 1106. The method includes sending a random access response (RAR) one or more times to the UE that includes the TA value, as shown at block 1108. And the method includes carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell swatch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell, as shown at block 1110.

[0104] In some examples, the method 1100 further includes carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0105] In some examples, the method 1100 further includes starting a timer in connection with the early uplink synchronization, as show n at block 1112 of FIG. 1 IB. In some of these examples, the RAR. is sent at block 1108 one or more times to the UE before expiration of the timer.

[0106] In some examples, the method 1.100 further includes receiving an indication from the serving cell to start sending the RAR, as shown at block 1114 of FIG. 1 IC. In some of these examples, sending the RAR one or more times to the UE at block 1108 is started based on the indication,

[0107] In some examples, the method 1100 further includes receiving an indication from the serving cell to stop sending the RAR, as shown at block 1116 of FIG. 11D. In some of these examples, sending the RAR one or more times to the UE at block 1108 is stopped based on the indication.

[0108] According to example implementations of the present disclosure, a telecommunications system 100 or PLMN 102, and its components such as a UE 110, gNB 206, CU 208, DU 210, S-DU 210A and / or T-DU 210B, 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.

[0109] According to some example implementations, at least some of the method 800 described with respect to FIGS. 8A and 8B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Similarly, at least some of the method 900 described with respect to FIGS. 9A-9D may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. At least some of the method 1000 described with respect to FIGS. 10A and 10B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. And at least some of the method 1100 described with respect to FIGS. 11 A-l ID may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may a user equipment, user device, user terminal or the like. Other examples of a suitable apparatus may include a gNB (e.g., gNB-DU, gNB-CU), ng-eNB or any suitable apparatus, such as a server, host or node.

[0110] FIG. 12 illustrates an apparatus 1200 in which means for performing various functions 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. Generally, an apparatus of example implementations of the present disclosure may comprise, include or be embodied in one or more fixed or portable electronic devices. Examples of suitable electronic devices include a wearable computer, mobile phone, portable computer, desktop computer, workstation computer, server (server computer) or the like. The apparatus may include one or more of each of a number of components such as, for example, processing circuitry 1202 connected to computer-readable storage medium or other memory 1204.

[0111] The processing circuitry 1202 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 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 1204 (of the same or another apparatus).

[0112] The processing circuitry 1202 may be a number of processors, a multi-core processor or some other type of processor, depending on the particular implementation. Further, the processing circuitry may be implemented using a number of heterogeneous processor systems m which a mam processor is present with one or more secondary processors on a single chip. As another illustrative example, the processing circmlry 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 ASICs, 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.

[0113] The memory 1204 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 1206 (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.

[0114] The memory 1204 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.

[0115] In addition to the memory 1204 (e.g., computer-readable storage medium), the processing circuitry 1202 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communications interface 1208 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), wareless NIC (WNIC) or the like.

[0116] The user interfaces may include a display 1210 and / or one or more user input interfaces 1212. 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.

[0117] Execution of the instructions 1206 by the processing circuitiy 1202, or storage of the instructions m the memory 1204, supports combinations of operations for implementing example implementations of the present disclosure. In this manner, an apparatus 1200 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 hardware-based computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions. [Oil 8] Some example implementations of the present disclosure may also be earned 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 maybe 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.

[0119] 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.

[0120] 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. [01211 As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0122] Clause 1. 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 at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate ceil in -which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; make a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, apply a configuration of the LTM candidate ceil as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell, the RAR including the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0123] Clause 2. The apparatus of clause 1, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive a configuration for the LTM cell switch that includes the LTM cell switch condition and the configuration of the LTM candidate cell.

[0124] Clause 3, The apparatus of clause 1 or clause 2, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further start a timer in connection with the early uplink synchronization, and the determination that the LTM cell switch condition is fulfilled is made before expiration of the timer.

[0125] Clause 4. The apparatus of any of clauses 1 to 3, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cel! is below a radio link quality of the LTM candidate cell.

[0126] Clause 5. The apparatus of any of clauses 1 to 4, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality threshold.

[0127] Clause 6. An apparatus comprising: means for carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a sewing cell of the UE; means for making a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, means for applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; means for skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; means for receiving the RAR from the target cell, the RAR including the TA value; and means for accessing the target cell using the TA value to complete the LTM cell switch.

[0128] Clause 7. The apparatus of clause 6, wherein the apparatus further comprises means for receiving a configuration for the LTM cell switch that includes the LTM cell switch condition and the configuration of the LTM candidate cell.

[0129] Clause 8. The apparatus of clause 6 or clause 7, wherein the apparatus further comprises means for starting a timer in connection with the early upimk synchronization, and the determination that the LTM cell switch condition is fulfilled is made before expiration of the timer.

[0130] Clause 9. The apparatus of any of clauses 6 to 8, wherein the LTM cell switch condition is fulfilled when the radio link quality' of the serving cell is below a radio link quality of the LTM candidate cell.

[0131] Clause 10. The apparatus of any of clauses 6 to 9, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality threshold.

[0132] Clause 11. A method comprising: carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; making a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell; and based on the determination, applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch, skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell, receiving the RAR from the target cell, the R.AR including the TA value; and accessing the target cell using the TA value to complete the LTM cell swatch.

[0133] Clause 12. The method of clause 11, wherein the method further comprises receiving a configuration for the LTM cell switch that includes the LTM cell switch condition and the configuration of the LTM candidate cell.

[0134] Clause 13. The method of clause 11 or clause 12, wherein the method further comprises starting a timer in connection with the early uplink synchronization, and the determination that the LTM cell swatch condition is fulfilled is made before expiration of the tinier.

[0135] Clause 14. The method of any of clauses 11 to 13, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below' a radio link quality of the LTM candidate cell.

[0136] Clause 15. The method of any of clauses 11 to 14, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality threshold.

[0137] Clause 16, A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry’, causes an apparatus to at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell of the UE; make a determination that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell, and based on the determination, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell, the RAR including the TA value; and access the target cell using the TA value to complete the LTM cell switch,

[0138] Clause 17. The computer-readable storage medium of clause 16, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further receive a configuration for the LTM cell switch that includes the LTM cell switch condition and the configuration of the LTM candidate cell.

[0139] Clause 18. The computer-readable storage medium of clause 16 or clause 17, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further start a timer in connection with the early uplink synchronization, and the determination that the LTM cell switch condition is fulfilled is made before expiration of the timer.

[0140] Clause 19. The computer-readable storage medium of any of clauses 16 to 18, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below7 a radio link quality of the LTM candidate cell.

[0141] Clause 20. The computer-readable storage medium of any of clauses 16 to 19, wherein the LTM cell switch condition is fulfilled when the radio link quality of the serving cell is below a radio link quality threshold.

[0142] Clause 21. An apparatus comprising means for performing the method of any of clauses 11 to 15.

[0143] Clause 22, 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 11 to 15.

[0144] Clause 23. 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 11 to 15.

[0145] Clause 24. 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 11 to 15.

[0146] Clause 25. An apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, 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 a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell ; estimate a timing advance (TA) value for the LTM candidate cell, report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE, the RAR including the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM. cell switch.

[0147] Clause 26. The apparatus of clause 25, wherein the LTM cell switch is carried out based on a determination by the UE that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell.

[0148] Clause 27. The apparatus of clause 25 or clause 26, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further carry out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0149] Clause 28. The apparatus of any of clauses 25 to 27, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further start a timer in connection with the early uplink synchronization, and the RAR. is sent one or more times to the UE before expiration of the timer.

[0150] Clause 29, The apparatus of any of clauses 25 to 28, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive an indication from the serving cell to start sending the RAR, and the apparatus is caused to start sending the RAR one or more times to the UE based on the indication.

[0151] Clause 30. The apparatus of any of clauses 25 to 29, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive an indication from the serving cell to stop sending the RAR, and the apparatus is caused to stop sending the RAR one or more times to the UE based on the indication.

[0152] Clause 31. An apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the apparatus comprising: means for receiving a random access preamble from an user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; means for estimating a timing advance (TA) value for the LTM candidate cell; means for reporting the TA value to a serving cell of the UE; means for sending a random access response (RAR) one or more times to the UE, the RAR including the TA value; and means for carrying out a LTM cell switch of the U E to the LTM candidate ceil as a target cell m which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0153] Clause 32. The apparatus of clause 31, wherein the LTM cell switch is carried out based on a determination by the UE that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell.

[0154] Clause 33. The apparatus of clause 31 or clause 32, wherein the apparatus further comprises means for carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0155] Clause 34. The apparatus of any of clauses 31 to 33, wherein the apparatus further comprises means for starting means for starting a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE. before expiration of the timer.

[0156] Clause 35. The apparatus of any of clauses 31 to 34, wherein the apparatus further comprises means for receiving an indication from the serving cell to start sending the RAR, and the means for sending the RAR starts sending the RAR. one or more times to the UE, based on the indication.

[0157] Clause 36, The apparatus of any of clauses 31 to 35, wherein the apparatus further comprises means for receiving an indication from the serving cell to stop sending the RAR, and the means for sending the RAR stops sending the RAR one or more times to the UE based on the indication.

[0158] Clause 37. A method performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the method comprising: receiving a random access preamble from a user equipment (UE) m connection with an early uplink synchronization of the UE with the LTM candidate cell; estimating a timing advance (TA) value for the LTM candidate cell; reporting the TA value to a serving cell of the UE; sending a random access response (RAR) one or more times to the UE, the RAR including the TA value; and carrying out a LTM cell switch of the UE to the LTM. candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch.

[0159] Clause 38. The method of clause 37, wherein the LTM cell swatch is carried out based on a determination by the UE that a LTM cell switch condition is fulfilled based on an evaluation of at least a. radio link quality of the serving cell. [0160| Clause 39. The method of clause 37 or clause 38, wherein the method further comprises carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0161] Clause 40. The method of any of clauses 37 to 39, wherein the method further comprises starting a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the tinier.

[0162] Clause 41. The method of any of clauses 37 to 40, wherein the method further comprises receiving an indication from the serving cell to start sending the RAR, and sending the RAR one or more times to the UE is started based, on the indication.

[0163] Clause 42. The method of any of clauses 37 to 41, wherein the method further comprises receiving an indication from the serving cell to stop sending the RAR, and sending the RAR one or more times to the UE is stopped based on the indication.

[0164] Clause 43. A computer-readable storage medium implemented at a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the computer-readable storage medium being non-transitory and having instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE, the RAR including the TA value; and cany out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch,

[0165] Clause 44. The computer-readable storage medium of clause 43, wherein the LTM cell switch is carried out based on a determination by the UE that a LTM cell switch condition is fulfilled based on an evaluation of at least a radio link quality of the serving cell.

[0166] Clause 45. The computer-readable storage medium of clause 43 or clause 44, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further carry out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0167] Clause 46. The computer-readable storage medium of any of clauses 43 to 45, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further start a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

[0168] Clause 47. The computer-readable storage medium of any of clauses 43 to 46, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry', causes the apparatus to further receive an indication from the serving cell to start sending the RAR, and the apparatus is caused to start sending the RAR one or more times to the UE based on the indication.

[0169] Clause 48. The computer-readable storage medium of any of clauses 43 to 47, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry', causes the apparatus to further receive an indication from the serving cell to stop sending the RAR, and the apparatus is caused to stop sending the RAR one or more times to the UE based on the indication.

[0170] Clause 49, An apparatus comprising means for performing the method of any of clauses 37 to 42.

[0171] Clause 50. 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 37 to 42.

[0172] Clause 51. 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 37 to 42.

[0173] Clause 52. 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 37 to 42.

[0174] Clause 53. 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 at least: carry out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate ceil is estimated and reported by the LTM candidate cell to a serving cell; detect a radio link failure on the serving cell that triggers a LTM recovery procedure, and according to the LTM recovery procedure, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target cell; receive the RAR from the target cell that includes the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0175] Clause 54. The apparatus of clause 53, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

[0176] Clause 55. The apparatus of clause 53 or clause 54, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further start a tinier in connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

[0177] Clause 56, The apparatus of any of clauses 53 to 55, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further determine a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recovery procedure is triggered toward the LTM candidate cell.

[0178] Clause 57. An apparatus comprising: means for carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; means for detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, means for applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; means for skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell, means for receiving the RAR from the target cell that includes the TA value; and means for accessing the target cell using the TA value to complete the LTM cell switch.

[0179] Clause 58. The apparatus of clause 57, wherein the apparatus further comprises means for receiving a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

[0180] Clause 59. The apparatus of clause 57 or clause 58, wherein the apparatus further comprises means for starting means for starting a timer in connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

[0181] Clause 60. The apparatus of any of clauses 57 to 59, wherein the apparatus further comprises means for determining a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recovery procedure is triggered toward the LTM candidate cell.

[0182] Clause 61. A method comprising: carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate ceil to a serving cell; detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell; receiving the RAR from the target cell that includes the TA value; and accessing the target cell using the TA value to complete the LTM cell switch.

[0183] Clause 62. The method of clause 61, wherein the method further comprises receiving a configuration for the LTM. cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

[0184] Clause 63. The method of clause 61 or clause 62, wherein the method further comprises starting a timer m connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

[0185] Clause 64. The method of any of clauses 61 to 63, wherein the method further comprises determining a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recovery procedure is triggered toward the LTM' candidate cell.

[0186] Clause 65. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: cany out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell; detect a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure, apply a configuration of the LTM candidate cell as a target cell for a LTM cell switch; skip a random access preamble, and monitor for a random access response (RAR) from the target ceil; receive the RAR from the target cell that includes the TA value; and access the target cell using the TA value to complete the LTM cell switch.

[0187] Clause 66. The computer-readable storage medium of clause 65, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing ctrcmiry. causes the apparatus to further receive a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

[0188] Clause 67. The computer-readable storage medium of clause 65 or clause 66, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further start a timer in connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

[0189] Clause 68. The computer-readable storage medium of any of clauses 65 to 67, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further determine a radio link quality of the I .TM candidate cell is above a threshold radio link quality-before the LTM recovery procedure is triggered toward the LTM candidate cell.

[0190] Clause 69. An apparatus comprising means for performing the method of any of clauses 61 to 64.

[0191] Clause 70. 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 61 to 64.

[0192] Clause 71. 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 61 to 64.

[0193] Clause 72. 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 61 to 64.

[0194] Clause 73. An apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, 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 a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell; report the TA value to a serving cell of the UE; send a random access response (RAR.) one or more times to the UE, that includes the TA value; and carry out a LTM cell switch of the UE to the LTM candidate cell as a target ceil in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM ceil switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0195] Clause 74, The apparatus of clause 73, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further carry out a LTM candidate preparation with the serving cell during which the LTM' candidate cell is configured by the serving cell for a RAR transmission.

[0196] Clause 75. The apparatus of clause 73 or clause 74, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further start a tinier in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

[0197] Clause 76. The apparatus of any of clauses 73 to 75, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive an indication from the serving cell to start sending the RAR, and the apparatus is caused to start sending the RAR one or more times to the UE based on the indication.

[0198] Clause 77. The apparatus of any of clauses 73 to 76, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive an indication from the serving cell to stop sending the RAR, and the apparatus is caused to stop sending the RAR one or more times to the UE based on the indication.

[0199] Clause 78. An apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the apparatus comprising: means for receiving a random access preamble from an user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; means for estimating a timing advance (TA) value for the LTM candidate cell; means for reporting the TA value to a serving cell of the UE; means for sending a random access response (RAR) one or more times to the UE that includes the TA value, and means for carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

[0200] Clause 79. The apparatus of clause 78, wherein the apparatus further comprises means for carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0201] Clause 80. The apparatus of clause 78 or clause 79, wherein the apparatus further comprises means for starting means for starting a tinier in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

[0202] Clause 81. The apparatus of any of clauses 78 to 80, wherein the apparatus further comprises means for receiving an indication from the serving cell to start sending the RAR and the means for sending the RAR starts sending the RAR one or more times to the UE based on the indication,

[0203] Clause 82, The apparatus of any of clauses 78 to 81, wherein the apparatus further comprises means for receiving an indication from the serving cell to stop sending the RAR, and the means for sending the RAR stops sending the RAR one or more times to the UE based on the indication.

[0204] CClause 83. A method performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the method comprising: receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimating a timing advance (TA) value for the LTM candidate cell; reporting the TA value to a serving cell of the UE; sending a random access response (RAR) one or more times to the UE that includes the TA value; and carrying out a LTM cell swatch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell swatch carried out based on detection by the UE of a radio link failure on the serving cell.

[0205] Clause 84. The method of clause 83, wherein the method further comprises carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a R / kR transmission.

[0206] Clause 85. The method of clause 83 or clause 84, wherein the method further comprises starting a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

[0207] Clause 86. The method of any of clauses 83 to 85, wherein the method further comprises receiving an indication from the serving cell to start sending the RAR, and sending the RAR one or more times to the UE is started based on the indication.

[0208] Clause 87, The method of any of clauses 83 to 86, wherein the method further comprises receiving an indication from the serving cell to stop sending the RAR, and sending the RAR one or more times to the UE is stopped based on the indication.

[0209] Clause 88. A computer-readable storage medium implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the computer-readable storage medium being non-transitory and having instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell; estimate a timing advance (TA) value for the LTM candidate cell, report the TA value to a serving cell of the UE; send a random access response (RAR) one or more times to the UE that includes the TA value; and cany out a LTM: cell switch of the UE to the LTM candidate cell as a target cell m which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell swatch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell. [0210| Clause 89. The computer-readable storage medium of clause 88, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further cany out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

[0211] Clause 90. The computer-readable storage medium of clause 88 or clause 89, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further start a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

[0212] Clause 91. The computer-readable storage medium of any of clauses 88 to 90, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry', causes the apparatus to further receive an indication from the serving cell to start sending the RAR, and the apparatus is caused to start sending the RAR one or more times to the UE based on the indication.

[0213] Clause 92, The computer-readable storage medium of any of clauses 88 to 91, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further receive an indication from the serving cell to stop sending the RAR, and the apparatus is caused to stop sending the RAR one or more times to the UE based on the indication.

[0214] Clause 93. An apparatus comprising means for performing the method of any of clauses 83 to 87.

[0215] Clause 94. 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 83 to 87.

[0216] Clause 95. 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 83 to 87.

[0217] Clause 96. A computer program comprising instructions that, m response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 83 to 87.

[0218] 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

1. An apparatus comprising:means for carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell;means for detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure,means for applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch;means for skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell;means for receiving the RAR from the target cell that includes the TA value; and means for accessing the target cell using the TA value to complete the LTM cell switch.

2. The apparatus of claim 1, wherein the apparatus further comprises means for receiving a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

3. The apparatus of claim 1 or claim 2, wherein the apparatus further comprises means for starting means for starting a timer in connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

4. The apparatus of any of claims 1 to 3, wherein the apparatus further comprises means for determining a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recovery procedure is triggered toward the LTM candidate cell.

5. A method comprising:carrying out an early uplink synchronization with a lower-layer triggered mobility (LTM) candidate cell in which a timing advance (TA) value for the LTM candidate cell is estimated and reported by the LTM candidate cell to a serving cell;detecting a radio link failure on the serving cell that triggers a LTM recovery procedure; and according to the LTM recovery procedure,applying a configuration of the LTM candidate cell as a target cell for a LTM cell switch;skipping a random access preamble, and monitoring for a random access response (RAR) from the target cell;receiving the RAR from the target cell that includes the TA value; andaccessing the target cell using the TA value to complete the LTM cell switch.

6. The method of claim 5, wherein the method further comprises receiving a configuration for the LTM cell switch that includes the configuration of the LTM candidate cell, and a configuration for the LTM recovery procedure.

7. The method of claim 5 or claim 6, wherein the method further comprisesstarting a timer in connection with the early uplink synchronization, and the radio link failure is detected before expiration of the timer.

8. The method of any of claims 5 to 7, wherein the method further comprises determining a radio link quality of the LTM candidate cell is above a threshold radio link quality before the LTM recovery procedure is triggered toward the LTM candidate cell.

9. 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 5 to 8.

10. An apparatus implemented by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the apparatus comprising:means for receiving a random access preamble from an user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell;means for estimating a timing advance (TA) value for the LTM candidate cell;means for reporting the TA value to a serving cell of the UE;means for sending a random access response (RAR) one or more times to the UE that includes the TA value; andmeans for carrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

11. The apparatus of claim 10, wherein the apparatus further comprises means for carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

12. The apparatus of claim 10 or claim 11, wherein the apparatus further comprises means for starting means for starting a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

13. The apparatus of any of claims 10 to 12, wherein the apparatus further comprises means for receiving an indication from the serving cell to start sending the RAR, and the means for sending the RAR starts sending the RAR one or more times to the UE based on the indication.

14. The apparatus of any of claims 10 to 13, wherein the apparatus further comprises means for receiving an indication from the serving cell to stop sending the RAR, and the means for sending the RAR stops sending the RAR one or more times to the UE based on the indication.

15. A method performed by a radio access node providing a lower-layer triggered mobility (LTM) candidate cell, the method comprising:receiving a random access preamble from a user equipment (UE) in connection with an early uplink synchronization of the UE with the LTM candidate cell;estimating a timing advance (TA) value for the LTM candidate cell;reporting the TA value to a serving cell of the UE;sending a random access response (RAR) one or more times to the UE that includes the TA value; andcarrying out a LTM cell switch of the UE to the LTM candidate cell as a target cell in which the target cell is accessed by the UE using the TA value from the RAR to complete the LTM cell switch, the LTM cell switch carried out based on detection by the UE of a radio link failure on the serving cell.

16. The method of claim 15, wherein the method further comprises carrying out a LTM candidate preparation with the serving cell during which the LTM candidate cell is configured by the serving cell for a RAR transmission.

17. The method of claim 15 or claim 16, wherein the method further comprisesstarting a timer in connection with the early uplink synchronization, and the RAR is sent one or more times to the UE before expiration of the timer.

18. The method of any of claims 15 to 17, wherein the method further comprises receiving an indication from the serving cell to start sending the RAR, and sending the RAR one or more times to the UE is started based on the indication.

19. The method of any of claims 15 to 18, wherein the method further comprises receiving an indication from the serving cell to stop sending the RAR, and sending the RAR one or more times to the UE is stopped based on the indication.

20. A computer-readable medium comprising instructions that, in response toexecution by at least one processing circuitry, causes an apparatus to perform the method of any of claims 15 to 19.51

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