Timing advance value provision and validation for subsequent lower-layer triggered mobility

Abstract

A method performed by a user equipment (UE) is provided. The method includes performing first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined. The method includes carrying out a cell switch to a first cell among the candidate cells. The method includes receiving information from a radio access node of the first cell, where the information indicates a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for the candidate cells. And the method includes determining that the TA value for the second cell is valid based on the performed a first measurement for the second cell, and performing a random access channel (RACH)-less cell switch to the second cell based on the TA value.

Description

TIMING ADVANCE VALUE PROVISION AND VALIDATION FOR SUBSEQUENT LOWER-LAYER TRIGGERED MOBILITYTECHNOLOGICAL FIELD

[0001] The present disclosure relates generally to telecommunications and, in particular, to lower-layer triggered mobility (LTM) 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. Oneexample 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 generally to telecommunications and, in particular, to target asset (TA) value provision and validation for subsequent lower-layer triggered mobility (LTM). The present disclosure thus includes, without limitation, the following example implementations.

[0007] Some example implementations provide an apparatus to implement a user equipment (UE), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: perform first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined; carry out a cell switch to a first cell among the candidate cells; receive information from a radio access node of the first cell, the information indicating a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for the candidate cells; determine that the TA value for the second cell is valid based on the performed a first measurement for the second cell; and perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

[0008] Some example implementations provide a method performed by a user equipment (UE), the method comprising: performing first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined; carrying out a cell switch to a first cell among the candidate cells; receiving information from a radio access node of the first cell, the information indicating a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for the candidate cells; determining that the TA value for the second cell is valid based on the performed a first measurement for the second cell; and performing a random access channel (RACH)-less cell switch to the second cell based on the TA value.

[0009] Some example implementations provide an apparatus to implement a radio access node, 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 apparatusto at least: receive timing advance (TA) values for candidate cells and associated first measurements performed on the candidate cells; determine that a TA value for a second cell of the radio access node is available among the TA values for the candidate cells; determine that the TA value is valid based on the associated first measurement for the second cell; and send information to a user equipment (UE), the information indicating the TA value for the UE to perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

[0010] Some example implementations provide a method performed by a radio access node, the method comprising: receiving timing advance (TA) values for candidate cells and associated first measurements performed on the candidate cells; determining that a TA value for a second cell of the radio access node is available among the TA values for the candidate cells; determining that the TA value is valid based on the associated first measurement for the second cell; and sending information to a user equipment (UE), the information indicating the TA value for the UE to perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

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

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

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

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

[0015] FIG. 2 illustrates a 5G NR deployment of a PLMN, according to some example implementations;

[0016] FIG. 3 illustrates a signaling chart for a lower-layer triggered mobility (LTM) procedure;

[0017] FIGS. 4A, 4B and 4C illustrate a signaling chart for an inter-gNB LTM procedure;

[0018] FIGS. 5A, 5B, 5C and 5D illustrate a signaling chart for an inter-gNB LTM procedure, according to other example implementations;

[0019] FIGS. 6A, 6B, 6C and 6D illustrate a signaling chart for an inter-gNB LTM procedure, according to other example implementations;

[0020] FIGS. 7A, 7B, 7C and 7D illustrate a signaling chart for an inter-gNB LTM procedure, according to yet other example implementations;

[0021] FIG. 8 is a flowchart illustrating various steps in a method performed by a user equipment, according to some example implementations;

[0022] FIGS. 9A and 9B are flowcharts illustrating various steps in a method that may be implemented by a target gNB, according to some example implementations; and

[0023] FIG. 10 illustrates an apparatus according to some example implementations.DETAILED DESCRIPTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The present disclosure discusses systems and architectures that, while specific terms may be used, are broadly applicable across various technologies. For instance, while the present disclosure may reference technologies from 3GPP such as Global System for Mobile Communications (GSM), UMTS, LTE, LTE Advanced, 5G NR, 5G Advanced, and 6G, the present disclosure is equally relevant to non-3GPP technologies like IEEE 802, Bluetooth, and Bluetooth Low Energy. Example implementations of the present disclosure described herein also mention public land mobile networks (PLMNs) and mobile network operators (MNOs), but example implementations are similarly applicable to standalone non-public networks (SNPNs) and the private entities operating these networks. Furthermore, although some examples and figures focus on radio access networks (RANs) and 3GPP access, example implementations are applicable to any type of network access. This includes not only 5G or 6G 3GPP access but also non-3GPP access, such as wireline access, untrusted non-3GPP access, and trusted non-3GPP access using wireless access gateway function (W-AGF), non-3GPP interworking function (N3IWF), or trusted non-3GPP gateway function (TNGF) to connect to a 5G or 6G core network.

[0028] 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.

[0029] 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.

[0030] 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 morePLMNs 102 coupled to one or more other external data networks 104 - notably including a wide area network (WAN) such as the Internet. As will be appreciated, a PLMN may be deployed in a number of different manners. Some deployments of 4G LTE and 5G NR in particular are considered standalone (SA) deployments. Other deployments combine 4G LTE and 5G technologies, and are referred to as non-standalone (NSA) deployments.

[0031] Each of the PLMNs 102 includes a core network (CN) 106 backbone, such as the Evolved Packet Core (EPC) of 4G LTE, and the 5G core network (5GC) (at times referred to as the NGC) of 5G NR; and each of the core networks and the Internet are coupled to one or more RANs 108, air interfaces or the like that implement one or more radio access technologies (RATs). Examples of these RANs include the evolved UMTS terrestrial radio access network (E-UTRAN) of 4G LTE, and the next generation (NG) radio access network (NG-RAN) of 5G NR. As used herein, a “network device” refers to any suitable device at anetwork side of a telecommunications network. Examples of suitable network devices are described in greater detail below.

[0032] Examples of RATs include 3GPP radio access technologies such as GSM, CDMA2000 1xEV-DO (HRPD), CDMA2000 1x (1xRTT), UTRA, E-UTRA, 5G NR, 5G Advanced, and 6G. Other examples of RATs include IEEE 802 technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.15 (including 802.15.1 (WPAN / Bluetooth), 802.15.4 (Zigbee) and 802.15.6 (WBAN)), Bluetooth, Bluetooth Low Energy (BLE), ultra wideband (UWB), and the like. Generally, a RAT may refer to any 2G, 3G, 4G, 5G, 6G or higher generation RAT and their different versions, as well as to any other RAT that may be arranged to interwork with such a mobile communication technology to provide access to the CN 106 of a MNO.

[0033] The telecommunications system 100 also 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 (lloT 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-loT) device, an enhanced machine-type communication (eMTC) device, a reduced capability (RedCap) device, an ambient loT device, or the like.

[0034] In operation, these UEs 110 may connect to one or more of the RANs 108 according to their particular RATs to thereby access a particular CN 106 of a PLMN 102, or to access one or more of the external data networks 104 (e.g., the Internet). The external data network may 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).

[0035] 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 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 term ‘gNB’ in 5G NR may correspond to the eNB in 4G LTE. Also, a NG-RAN node may refer to a gNB or a ng-eNB.

[0036] The RAN 108 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.

[0037] FIG. 2 illustrates a 5G NR deployment 200, referred to at times as the 5G system (5GS). As shown, the NG-RAN 202 includes one or more gNBs 204 configured to connect one or more UEs 110 to the NG-RAN to thereby access the 5GC 206. In some deployments, operations of a gNB or other a radio access node may be distributed or functionally split into components including one or more remote radio head (RRHs) or radio units (RUs), and a baseband unit (BBU); and in some architectures, the BBU may be split into a central / centralized unit (CU) 208 (central node) and a distributed unit (DU) 210 (distributed node). The CU may be, for example, a server, host or node. In some architectures, the RRH / RU and DU may be collocated. It is also possible that node operations may be distributed among a plurality of servers, hosts or nodes.

[0038] It should also be understood that the distribution of work between core network operations and radio access node operations may vary depending on implementation. A 5G network architecture may be based on a so-called CU-DU split. One gNB-CU (a CU 208) may control one or more gNB-DUs (DUs 210). The gNB-CU may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some example implementations, however, the gNB-DUs may include, for example, a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU may include the layers above the RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC), and an internet protocol (IP) layer. Other functional splits are also possible. It is considered that skilled person is familiar with the OSI model and the functionalities within each layer.

[0039] In some example implementations, the server or CU 208 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 taskmay 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.

[0040] Currently in 3GPP, mainstream mobility has been conducted using higher layer mobility, such as layer 3 (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 gNB 204 to a new serving cell (target cell) of the same or another gNB. 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.

[0041] L1 / L2-triggered mobility, or lower-layer triggered mobility (LTM) moves the execution of the ‘handover1from one cell to another from higher layers (L3), such as RRC, to lower layers. These lower layers may be either PHY (or layer 1 - (L1)) or MAC (or layer 2 (L2)). In LTM, the network (NG-RAN 202) configures the UE 110 with up to eight candidate cells, and eventually sends a cell switch command to the UE to perform a cell switch to a target cell among the candidate cells. The cell switch decision may be based on L1 or L3 measurements reported by the UE. In a CU-DU split architecture, LTM may support one or more of intra-DU mobility, intra-CU inter-DU mobility, or inter-CU inter-DU mobility.

[0042] LTM may reduce latency, overhead and interruption time when compared to L3 handover based mobility. The reduced latency in LTM is achieved at least in part through different early procedures, including early downlink (DL) synchronization through early transmission configuration indicator (TCI) state activation, early uplink (UL) synchronization through physical downlink control channel (PDCCH)-ordered random access channel (RACH) or UE-based timing advance (TA) estimation, and early abstract syntax notation one (ASN.1) decoding and validity check.

[0043] LTM supports early DL synchronization through early TCI state activation for one or more candidate cells before the cell switch command. The network may sends candidate cell specific MAC control element (CE) to activate one or more TCI states for a candidate cell. If the network wants to activate TCI states for more than one candidate cell, the network may send a separate MAC CE for each of those cells. At the time of receiving the TCI state activation MAC CE, the UE 110 may performs DL synchronization with one or more synchronization signal blocks (SSBs) or tracking reference signals (TRSs) associated to the target TCI state(s).

[0044] When TCI state is considered active and the UE 110 has DL synchronization of the target TCI state, cell switch delay does not include time for DL synchronization. When TCI state is not on the activeTCI state list or when the UE does not have DL synchronization of the target TCI state, the UE may be allowed time to perform DL synchronization during the cell switch.

[0045] LTM supports early UL synchronization / TA acquisition in a number of different manners. As indicated above, LTM supports early UL synchronization / TA acquisition through PDCCH-ordered RACH transmission. In this regard, the network may send a PDCCH order to the UE 110 for candidate cell(s), and UE may perform RACH transmission on those cell(s) before the cell switch. The candidate cell(s) may send the TA value(s) to the source cell, which may then give the TA value for a target cell among the candidate cell(s) to the UE in a cell switch command. The UE may then apply the TA value for the first UL transmission on the target cell, and hence perform a RACH-less cell switch to the target cell.

[0046] LTM may also support early UL synchronization / TA acquisition through UE autonomous TA estimation. The network may configure the UE 110 to autonomously estimate the TA for one or more candidate cells. And when the UE receives a cell switch command for a target cell among the candidate cell(s) without a TA value for the target cell, the UE may apply the UE-estimated TA for the first UL transmission and hence perform RACH-less cell switch. In another manner of supporting early UL synchronization / TA acquisition, the network may also use the serving cell TA or give TA= 0 value in the cell switch command, which may also lead to a RACH-less cell switch. And if UL synchronization / TA acquisition is not performed, the UE may perform RACH-based cell switch, i.e., perform RACH procedure after receiving the cell switch command.

[0047] LTM was introduced in 3GPP Release 18 and offers improvements in handover latency and interruption time compared to L3 mobility. But LTM as introduced also has a number of limitations relative to L3 mobility. A number of enhancements of LTM are currently under discussion to address these limitations. One of the enhancements under discussion is support for conditional LTM (CLTM or C-LTM). The details of CLTM are currently under discussion, but it has been agreed that at least the baseline of conditional handover CHO will be reused. In this regard, the UE 110 may be configured with one or more (L1 or L3 based) conditions for one or more candidate cells or RSs associate with one or more candidate cells. The conditions can be provided in the common LTM configuration or can be candidate cell / reference signal (RS) specific. At the event of such condition becoming met, the UE may execute a CLTM cell switch to a candidate cell for which the condition was met.

[0048] An updated work item description includes the objective to specify support for conditional intra-CU LTM. This includes, specification of UE-evaluated conditions for triggering LTM, an aim to supportCLTM including subsequent LTM, and limit specifying the CLTM to the scenario in which the UE is in nondual connectivity. Network-triggered LTM will also be supported for inter-CU LTM.

[0049] FIG. 3 illustrates a signaling chart for an LTM procedure of a UE 110 in a RRC connected state with a gNB 204, 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 target cells. The RRC reconfiguration message may also include a configuration of L1 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.

[0050] An early synchronization of the UE 110 with the candidate target cell(s) follows LTM preparation. As shown at step 304, the UE 110 performs downlink (DL) / uplink (UL) synchronization with the candidate target cell(s). During this procedure, the TA values of the candidate target cell(s) may be acquired by the source cell and / or the UE. 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 target 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.

[0051] During LTM execution, the UE 110 performs L1 / L3 measurements on the configured candidate target cell(s), and the UE at step 305 transmits L1 / L3 measurement reports to the gNB 204. The gNB decides to execute a cell switch, and selects one of the candidate target 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 a RACH 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.

[0052] FIGS. 4A-4C illustrate a signaling chart 400 for an inter-g N B LTM procedure involving a UE 110, a source gNB 204A, a target gNB 204B, additional candidate gNB(s) 204C, as well as an access and mobility management function (AMF) and user plane function (UPF) of a core network. As shown, the UE 110 and source gNB 204A initially exchange user data. In step 401, the UE performs measurement control procedures and sends a measurement report with L3 measurement results for neighboring cells to the source gNB 204A. The source gNB decides to configure inter-g N B LTM and, at step 403, requests LTM configuration for candidate cells associated with one or more candidate gNB(s). Admission control isperformed by the candidate gNB(s) at step 404, followed by LTM configuration preparation and response back to the source gNB 204A in step 405. The source gNB may then send configuration updates to candidate gNB(s) at steps 406 and 407.

[0053] As shown in FIG. 4B, during RRC reconfiguration at step 408, the source gNB 204A sends an RRC reconfiguration message to the UE 110, which stores the candidate configurations and completes the reconfiguration at step 409. Optionally, early data forwarding from the source gNB to candidate gNB(s) may occur, as shown in step 409a. At step 410, the UE 110 can perform early synchronization with the candidate gNB(s). If synchronization is successful, the candidate gNB(s) provide TA value(s) for the candidate gNB(s) back to the source gNB at step 411. L1 / L3 measurements are performed by the UE on candidate cells, and L1 / L3 measurement reports are sent to the source gNB 204A in step 412.

[0054] If conditions are met, the source gNB 204A initiates an inter-g N B LTM cell switch. The source gNB 204A, after reviewing the L1 / L3 measurement reports provided by the UE 110 on the candidate target cells, determines that a cell switch should be initiated to improve connectivity or performance at step 413. Based on the reported measurements, the source gNB 204A identifies the optimal target cell among the candidate cells. This determination is based on factors such as signal quality, timing alignment, and readiness of the candidate cells. Once the target cell is selected, the source gNB 204A prepares to execute the inter-gNB LTM process. The decision to proceed with the cell switch in this step lays the groundwork for the subsequent cell switch command sent to the UE in step 414, where the specific configuration for the target cell will be communicated to the UE.

[0055] In FIG. 4C, at step 415, the source gNB 204A sends a cell switch notification to the target gNB 204B, indicating the upcoming cell switch for UE 110. The cell switch notification may include a list of the TA values for the candidate gNB(s) which the target gNB may provide later on to the UE. Upon detecting UE access to the target cell at step 416, the target gNB confirms the switch. If needed, the UE performs a RACH procedure to obtain the TA value for the target cell. A handover success message is sent from the target to source gNB at step 417, followed by serving node (SN) status transfer at step 418. The UE completes the reconfiguration at step 419, and the target gNB releases context-related resources at step 420.

[0056] In 3GPP, proposals have been made to include a time alignment timer (TAT) or time-stamp together with the TA list to the target gNB. The disadvantage this approach, however, is that the TAT value is set “blindly” or based on previous experience, but does not take into account the current channel conditions. In RACH-less uplink short data transfer (UL-SDT), the UE 110 may store the TA value obtainedwhile in RRC_CONNECTED mode and an associated reference signal received power (RSRP) value. The UE may also be configured with a threshold for the difference between the RSRP measurement before the UL-SDT transmission and the RSRP measurement associated with the TA value. If the difference of the two measurements is below the configured threshold, the TA value may be considered to be valid and the UE uses the TA value for RACH-less SDT

[0057] Example implementations of the present disclosure provide solutions to problems in a scenario in which a UE 110 is served by a first cell controlled by a first CU 208. The UE is configured with LTM candidates comprising a second cell controlled by a second CU, a third cell controlled by a third CU, and CLTM is configured for cell switches between the second cell and the third cell. The UE may perform RACH-based early TA acquisition to the second cell and the third cell. Since the second cell and the third cell are inter-CU candidates, the TA values may be delivered to the source DU 210 (S-DU), but may not be provided to the UE. The network sends a cell switch command to the UE for an inter-CU LTM cell switch from the first cell to the second cell.

[0058] In 3GPP Release 18, the S-DU may send a list of TA values to the a target DU (T-DU) via the CU in the cell switch notification messages (DU-CU and CU-DU) over an F1 interface. Likewise, in Release 19, a list of TA values may be provided to the target CU (T-CU) over the Xn interface, and from the T-CU to the T-DU. This list of TA values may be provided to the T-DU to be used in subsequent LTM cell switches.

[0059] A first problem in the above scenario is that when receiving the list of TA values, the T-DU does not have sufficient information about the validity of the TAs. There have been proposals to use a timer, such as a TAT or a timestamp, but as indicated above, this approach does not capture the actual channel conditions and whether they have changed.

[0060] A second problem is that the TA value for the third cell is available at the T-DU (the new serving DU) and can be used for a network-triggered cell switch to the third cell (e.g., included in a cell switch command), but the TA value is not available at the UE 110. The UE therefore may not use the TA value in case a conditional cell switch to the third cell is triggered. Furthermore, the UE is not configured to maintain that TA value. An unnecessary RACH procedure will therefore be needed either before or during the cell switch to acquire a new TA value.

[0061] Some example implementations provide solutions to the aforementioned first problem and second problem. As a solution to the first problem, RSRP measurements (also called first measurements), which may be obtained when the TA values were computed, may be stored and provided to the new serving DU along with the corresponding TA values upon cell switch in a cell switch notification. Storing ortransferring (sending or receiving) measurements comprises e.g. storing of transferring results of the measurements or any information that indicates results of such measurements. This may allow the new serving DU to evaluate the validity of the shared TAs. This is a similar concept as in UL-SDT on the UE side, where the UE checks whether a current (second) measurement differs less than a configured threshold value from the first measurement when the TA was obtained; and if so, the UE uses the TA value for its UL transmission. The UE otherwise performs RACH-based SDT

[0062] In some examples, the aforementioned solution to the first problem may also be used in a solution to the second problem. That is, the T-DU (as the new serving DU) may send the RSRP measurements (of the time the UE has performed RA, i.e., first measurements) including beam information (i.e., SSB index) to the T-DU along with the TA values. In simple form, the RSRP measurement belongs to the cell and SSB (mapped to random access occasion) for which the RAhas been triggered. In some more advanced cases, supplementary RSRP measurements of the target cells or other cells (including the serving cell) may be provided to facilitate a more-accurate TA validity evaluation. In some other examples, a path-loss estimation may be sent instead of RSRP. And in some examples, one or more additional measurement variation thresholds under which the TA is expected to remain unchanged (valid) may be provided.

[0063] The T-DU (new serving DU) may provide the TA values to the UE 110; and in some examples, the T-DU may also provide a TAT value or timestamp (depending on what was provided by the S-DU). In some examples, the RSRP value associated with the TA value may also be provided to the UE, such as when the candidate cell associated with the TA value is configured as a CLTM candidate cell. This message may be triggered in a number of different manners, such as after receiving a L1 / L3 measurement report from the UE, similar to the triggering of a PDCCH order.

[0064] In some other examples, as a solution to the second problem, the UE 110 may store the RSRP values (results of the first measurements) associated with the (latest) TA acquisition for a candidate cell and maintains the RSRP value after a cell switch. In some of these examples, the UE may be configured to store the RSRP values when the candidate cell associated with the TA is configured as a CLTM candidate cell for the target cell. In other words, the UE may be configured to store the RSRP values when the candidate cell associated with the TA is configured as a subsequent CLTM candidate cell.

[0065] The T-DU (new serving DU) may provide the TA values to the UE 110; and similar to before, the T-DU may also provide a TAT value or timestamp (depending on what was provided by the S-DU). This message may be triggered in a number of different manners, such as after receiving a L1 / L3 measurementreport from the UE, similar to the triggering of a PDCCH order. And in some examples, the solution to the first problem may also be used. In this regard, the S-DU may send the RSRP measurements (first measurements) to the T-DU along with the TA values, which may allow the T-DU to decide whether the T-DU should provide the TA values to the UE.

[0066] To further illustrate the solution to the first problem, FIGS. 5A-5D illustrate a signaling chart 500 for an inter-gNB LTM procedure, according to some example implementations. As shown in FIGS. 5A and 5B, the procedure may include steps 401-409A, as described above. At step 510A, the UE 110 sends L1 / L3 measurement results (first measurements) to the source gNB 204A. These measurements include the configured candidate cells, and the UE transmits updated measurement reports to assist in early uplink synchronization. At step 510B, the source gNB 204A may issue a PDCCH order for the UE to initiate early TA acquisition. Following this, at step 510C, the UE synchronizes with the candidate gNB(s), such as target gNB 204B or other candidate gNB(s) 204C. The source gNB 204A stores RSRP values (first measurements) associated with TA obtained through the PDCCH-triggered procedure at step 510D. These stored first measurement values may be the ones obtained in step 510A, for example.

[0067] At steps 511 and 512 in FIG. 5B, the candidate gNB(s) may provide TA information to the source gNB 204A upon completion of early TA acquisition. The UE continues its L1 / L3 measurements for candidate cells at step 513, while the source gNB initiates LTM at step 514. The source gNB 204A issues a cell switch command with target configuration details at step 515, guiding the UE 110 to switch to the target cell while applying the indicated configuration.

[0068] In FIG. 5C, the cell switch notification is sent from the source gNB to the target gNB 204B at step 516, including TA values and their associated RSRP measurements (first measurements). In some examples, this message may include additional path loss estimation for enhanced TA validation. Following successful detection of UE access at step 517, the target gNB sends the handover success message to the source gNB at step 518, completing the cell switch procedure, with SN status transfer and subsequent reconfiguration messages concluding the handover at steps 519 and 520, respectively. The target gNB 204B sends a UE context release message to the source gNB 204A at step 521, directing it to release radio and control-plane resources that were previously allocated to the UE 110 in the source gNB.

[0069] The UE 110 performs L1 / L3 measurements on the configured LTM candidate cells under the target gNB 204B and transmits L1 / L3 measurement reports (second, current measurements from the target gNB’s perspective) to the target gNB 204B at step 522. At step 523, the T-DU of the gNB assesses whether early uplink synchronization to an intra-CU or inter-CU CLTM to candidate cell is necessary. If earlysynchronization is to be performed, the T-DU evaluates the validity of an existing TA for the CLTM candidate cell. If the current RSRP measurement (second measurement) closely matches the RSRP measurement (first measurement) associated with the stored TA (within a set threshold), the TA is deemed valid, alleviating the need for the UE to perform a random access procedure during which a TA is acquired. In some examples, this threshold is configured by the CU and communicated to the DU. As shown in FIG.5D, the target gNB 204B sends a cell switch command including the TA provided in the cell switch notification to the UE at step 524. The UE then performs a RACH-less LTM cell switch procedure, as seen in step 525. It can be seen that in FIG. 5D, the UE need not make TA validity evaluation, because the T-DU of the gNB 204B has done such validity evaluation in step 523, and provided the TA value to UE in step 524.

[0070] FIGS. 6A-6D illustrate a signaling chart 600 for an inter-gNB LTM procedure, including a solution to the second problem, according to some example implementations. As shown in FIGS. 6A, 6B and 6C, the procedure may include steps 401-409A, steps 510A-523, as described above. As shown in FIG. 6D, the target gNB 204B may send a TA information message, which includes the TA, provided in the previous cell switch notification, and the associated RSRP measurement, to the UE 110 at step 624. The UE evaluates the validity of the TA based on the associated RSRP measurements (first measurements) and current measurements (second measurements) at step 625. A RACH-less cell switch to the target cell is then performed if the TA value is valid, as seen in step 626.

[0071] FIGS. 7A-7D illustrate a signaling chart 700 for an inter-gNB LTM procedure, including another solution to the second problem, according to some example implementations. As shown in FIGS. 7A and 7B, the procedure may include steps 401-409A, and steps 510A-510C, as described above. In FIG. 7B, step 710D, the source gNB 204A may optionally store RSRP values (results of the first measurements) reported by the UE following a PDCCH order for early TA acquisition, associating them with the corresponding TA values. At step 711, the UE stores RSRP values (results of the first measurements) with the TA values for candidate cells, specifically for cells configured as CLTM candidates. In step 712, the candidate gNB(s) may send TA information transfer messages to the source gNB if early TA acquisition has been completed.

[0072] At step 713, the UE performs L1 / L3 measurements and transmits measurement reports to the source gNB. The source gNB 204A initiates an LTM procedure at step 714 and issues a cell switch command at step 715 with the target configuration ID and TA command for the target cell. The UE applies the configuration indicated by the target configuration ID.

[0073] As shown in FIG. 7C, the cell switch notification from the source gNB to the target gNB 204B at step 716 includes TA values and optionally the associated RSRP measurements (first measurements). Upon UE access detection at step 717, if a TA is unavailable, the UE initiates RACH toward the target cell per the specifications. The handover success message is sent to the source gNB 204A at step 718, followed by SN status transfer and reconfiguration messages at steps 719 and 720, respectively. The target gNB 204B sends a UE context release message to the source gNB 204A at step 721.

[0074] The UE 110 performs L1 / L3 measurements on the configured LTM candidate cells associated with the target gNB 204B and transmits L1 / L3 measurement reports to the target gNB at step 722. The T-DU within the target gNB evaluates whether early uplink synchronization to an intra-CU CLTM candidate cell should be performed. At step 723, the T-DU checks if a TA value is available for a CLTM candidate cell and optionally determines its validity by comparing the current RSRP measurement (second measurement received, e.g., in step 722) with the RSRP measurement (first measurement) associated with the stored TA value. If the difference between these measurements is within a predefined threshold, the TA is considered valid. This threshold can be configured by the CU and communicated to the DU.

[0075] As shown in FIG. 7D, the target gNB 204B sends a TA information message to the UE 110 at step 724. This message includes the TA value previously provided in the cell switch notification. At step 725, the UE 110 determines the validity of the TA value for the CLTM candidate cell by comparing the TA-associated RSRP measurement (first measurement) with its current RSRP measurement (second measurement from the UE’s perspective) for that cell. If the difference between these two measurements is within a threshold value, the UE considers the TA value valid. With a valid TA value confirmed, the UE 110 performs a RACH-less CLTM cell switch to the CLTM candidate cell using the provided TA, as shown in step 726. In this embodiment of Figure 7A-7D, it can be seen that the UE stores the RSRP values in step 711 and the T-gNB 204B need not provide those to the UE in step 724 (whereas in Figure 6D the RSRP were provided to the UE in step 624).

[0076] FIG. 8 is a flowchart illustrating various steps in a method 800 performed by a user equipment (UE), according to various example implementations. The method includes performing at block 802 first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined. The method includes carrying out a cell switch to a first cell among the candidate cells, as shown at block 804 of FIG. 8A. The method includes receiving information from a radio access node of the first cell, the information indicating a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for thecandidate cells, as shown at block 806. The method includes determining that the TA value for the second cell is valid based on the performed a first measurement for the second cell, as shown at block 808. And the method includes performing at block 810 a random access channel (RACH)-less cell switch to the second cell based on the TA value.

[0077] In some examples, the first measurements on the candidate cells associated with the early uplink synchronization comprise at least one of the following: last reported measurements on the candidate cells before receiving a physial downlink control channel (PDCCH) order triggering the early uplink synchronization; first measurements on the candidate cells after receiving the PDCCH order; measurements on the candidate cells which are temporally closest to transmission of a random access preamble for the early uplink synchronization; or first measurements on the candidate cells after transmission of the random access preamble for the early uplink synchronization.

[0078] In some examples, the method 800 further includes sending a measurement report to the radio access node. In some of these examples, receiving the information from the radio access node at block 806 is based on a decision by the radio access node to trigger early uplink synchronization of the UE to the second cell based on the measurement report.

[0079] In some examples, the method 800 further includes performing a second measurement on the second cell, the second measurement being performed after the first measurement. In some of these examples, the TA value is determined to be valid based on a comparison of the second measurement performed on the second cell and the first measurement for the second cell.

[0080] In some examples, the TA value is determined to be valid when the second measurement is within a threshold value from the first measurement.

[0081] In some examples, receiving the information that indicates the TA value for the second cell at block 806 includes receiving a cell switch command from the radio access node that includes the information. In some of these examples, the cell switch command is sent by the radio access node to trigger the UE to perform the RACH-less cell switch to the second cell using the TA value.

[0082] In some examples, the TA values and the first measurements for the candidate cells are sent to the radio access node upon the cell switch to the first cell of the radio access node. In some of these examples, the information that indicates the TA value is received from the radio access node with the first measurement for the second cell.

[0083] In some examples, the method 800 further includes storing the first measurements on the candidate cells.

[0084] FIGS. 10A and 10B are flowcharts illustrating various steps in a method 900 performed by a radio access node, according to various example implementations. The method includes receiving timing advance (TA) values for candidate cells and associated first measurements performed on the candidate cells, as shown at block 902 of FIG. 10A. The method includes determining that a TA value for a second cell of the radio access node is available among the TA values for the candidate cells, as shown at block 904. The method includes determining that the TA value is valid based on the associated first measurement for the second cell, as shown at block 906. And the method includes sending at block 908 information to a user equipment (UE), the information indicating the TA value for the UE to perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

[0085] In some examples, the method 900 further includes receiving a measurement report from the UE that includes measurements performed on one or more of the candidate cells, as shown at block 910 of FIG. 10B. In some of these examples, the method also includes making a decision to trigger a cell switch or an early uplink synchronization of the UE to the second cell based on the measurements, as shown at block 912. Also in some of these examples, determining that the TA value for the second cell is available and valid at block 906, and the sending the information to the UE at block 908, are triggered by the decision.

[0086] In some examples, the method 900 further includes receiving a measurement report from the UE that includes a second measurement performed on the second cell. In some of these examples, the TA value is determined to be valid at block 906 based on a comparison of the second measurement on the second cell, and the associated first measurement for the second cell.

[0087] In some examples, the TA value is determined to be valid at block 906 when the second measurement is within a threshold value from the associated measurement.

[0088] In some examples, sending the information that indicates the TA value at block 908 includes sending a cell switch command to the UE that includes the information. In some of these examples, the cell switch command is sent to trigger the UE to perform the RACH-less cell switch to the second cell using the TA value.

[0089] In some examples, the information that indicates the TA value is sent at block 908 to the UE with the associated first measurement for the second cell for the UE to determine whether the TA value is valid based on the associated first measurement.

[0090] According to example implementations of the present disclosure, a telecommunications system 100 or PLMN 102, and its components such as a UE 110, CN 106, RAN 108, NG-RAN 202, gNB 204,204A, 204B, 204C, 5GC 206, CU 208 and / or DU 210, may be implemented by various means. Means for implementing the system and its components may include hardware, firmware, software, or combinations thereof. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its components shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

[0091] According to some example implementations, at least some of the method 800 described with respect to FIG. 8 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 and 9B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may include a user equipment, user device, user terminal or the like. 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.

[0092] FIG. 10 illustrates an apparatus 1000 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 1002 connected to computer-readable storage medium or other memory 1004.

[0093] The processing circuitry 1002 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 1004 (of the same or another apparatus).

[0094] The processing circuitry 1002 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 in which a main processor is present with one or more secondary processors on a single chip. As another illustrative example, the processing circuitry may be a symmetric multi-processor system containing multiple processors of the same type. In yet another example, the processing circuitry may be embodied as or otherwise include one or more 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.

[0095] The memory 1004 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 1006 (e.g., computer-readable program code) and / or other suitable information either on a temporary basis and / or a permanent basis. The memory may include volatile and / or non-volatile memory, and may be fixed or removable. Examples of suitable memory include recording media, random access memory (RAM), read-only memory (ROM), a hard drive, a flash memory, a thumb drive, a removable computer diskette, an optical disk or some combination thereof.

[0096] The memory 1004 is a non-transitory device capable of storing information. One example of a suitable memory is a computer-readable storage medium, which is distinguishable from a computer-readable transmission medium capable of carrying information from one location to another. Examples of suitable computer-readable transmission media comprise electronic carrier signals, telecommunications signals, or some combination thereof. As used herein, the term “non-transitory” is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM versus ROM). A computer-readable medium as described herein generally refers to a computer-readable storage medium or computer-readable transmission medium. A computer-readable medium is any entity or device capable in which information, such as one or more computer programs or portions thereof, may be stored and carried.

[0097] In addition to the memory 1004 (e.g., computer-readable storage medium), the processing circuitry 1002 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communications interface 1008 and / or one or more userinterfaces. The communications interface may be configured to transmit and / or receive information, such as to and / or from other apparatus(es), network(s) or the like. The communications interface may be configured to transmit and / or receive information by physical (wired) and / or wireless communications links. Examples of suitable communication interfaces include a network interface controller (NIC), wireless NIC (WNIC) or the like.

[0098] The user interfaces may include a display 1010 and / or one or more user input interfaces 1012. The display may be configured to present or otherwise display information to a user, suitable examples of which include a liquid crystal display (LCD), light-emitting diode (LED) display, organic LED (OLED) display, active-matrix OLED (AMOLED) or the like. The user input interfaces may be wired or wireless, and may be configured to receive information from a user into the apparatus, such as for processing, storage and / or display. Suitable examples of user input interfaces include a microphone, image or video capture device, keyboard or keypad, joystick, touch-sensitive surface (separate from or integrated into a touchscreen), biometric sensor or the like. The user interfaces may further include one or more interfaces for communicating with peripherals such as printers, scanners or the like.

[0099] Execution of the instructions 1006 by the processing circuitry 1002, or storage of the instructions in the memory 1004, supports combinations of operations for implementing example implementations of the present disclosure. In this manner, an apparatus 1000 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.

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

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

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

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

[0104] 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 withoutdeparting 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

WHAT IS CLAIMED IS:

1. An apparatus, the apparatus comprising:at least one memory configured to store instructions; andat least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least:perform first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined;carry out a cell switch to a first cell among the candidate cells;receive information from a radio access node of the first cell, the information indicating a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for the candidate cells;determine that the TA value for the second cell is valid based on the performed first measurement for the second cell; andperform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

2. The apparatus of claim 1, wherein the first measurements on the candidate cells associated with the early uplink synchronization comprise at least one of the following:last reported measurements on the candidate cells before receiving a physical downlink control channel (PDCCH) order triggering the early uplink synchronization;first measurements on the candidate cells after receiving the PDCCH order; measurements on the candidate cells which are temporally closest to transmission of a random access preamble for the early uplink synchronization; orfirst measurements on the candidate cells after transmission of the random access preamble for the early uplink synchronization.

3. The apparatus of claim 1 or claim 2, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further send a measurement report to the radio access node, andwherein the apparatus caused to receive the information from the radio access node is based on a decision by the radio access node to trigger early uplink synchronization of the apparatus to the second cell based on the measurement report.

4. The apparatus of any of claims 1 to 3, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further perform a second measurement on the second cell, the second measurement being performed after the first measurement, andwherein the TA value is determined to be valid based on a comparison of the second measurement performed on the second cell and the first measurement for the second cell.

5. The apparatus of claim 4, wherein the TA value is determined to be valid when the second measurement is within a threshold value from the first measurement.

6. The apparatus of any of claims 1 to 5, wherein the apparatus caused to receive the information that indicates the TA value for the second cell includes the apparatus caused to receive a cell switch command from the radio access node that includes the information, and the cell switch command is received from the radio access node to trigger the apparatus to perform the RACH-less cell switch to the second cell using the TA value.

7. The apparatus of any of claims 1 to 6, wherein the TA values and the first measurements for the candidate cells are sent to the radio access node upon the cell switch to the first cell of the radio access node, andwherein the information that indicates the TA value is received from the radio access node with the first measurement for the second cell.

8. The apparatus of any of claims 1 to 7, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further store the first measurements on the candidate cells.

9. A method performed by a user equipment (UE), the method comprising:performing first measurements on candidate cells associated with an early uplink synchronization in which timing advance (TA) values for the candidate cells are determined;carrying out a cell switch to a first cell among the candidate cells;receiving information from a radio access node of the first cell, the information indicating a TA value for a second cell of the radio access node, the TA value for the second cell being available among the TA values for the candidate cells;determining that the TA value for the second cell is valid based on the performed a first measurement for the second cell; andperforming a random access channel (RACH)-less cell switch to the second cell based on the TA value.

10. An apparatus comprising means for performing the method of claim 9.

11. 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 claim 9.

12. 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 claim 9.

13. An apparatus, the apparatus comprising:at least one memory configured to store instructions; andat least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least:receive timing advance (TA) values for candidate cells and associated first measurements performed on the candidate cells;determine that a TA value for a second cell of the radio access node is available among the TA values for the candidate cells;determine that the TA value is valid based on the associated first measurement for the second cell; andsend information to a user equipment (UE), the information indicating the TA value for the UE to perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

14. The apparatus of claim 13, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least:receive a measurement report from the UE that includes measurements performed on one or more of the candidate cells; andmake a decision to trigger a cell switch or an early uplink synchronization of the UE to the second cell based on the measurements, andwherein determination that the TA value for the second cell is available and valid, and the transmission of the information to the UE are triggered by the decision.

15. The apparatus of claim 13 or claim 14, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive a measurement report from the UE that includes a second measurement performed on the second cell, andwherein the TA value is determined to be valid based on a comparison of the second measurement on the second cell and the associated first measurement for the second cell.

16. The apparatus of claim 13, wherein the TA value is determined to be valid when the second measurement is within a threshold value from the associated measurement.

17. The apparatus of any of claims 13 to 16, wherein the information that indicates the TA value includes a cell switch command to the UE that includes the information, and the cell switch command is sent to trigger the UE to perform the RACH-less cell switch to the second cell using the TA value.

18. The apparatus of any of claims 13 to 17, wherein the information that indicates the TA value is sent to the UE with the associated first measurement for the second cell for the UE to determine whether the TA value is valid based on the associated first measurement.

19. A method performed by a radio access node, the method comprising:receiving timing advance (TA) values for candidate cells and associated first measurements performed on the candidate cells;determining that a TA value for a second cell of the radio access node is available among the TA values for the candidate cells;determining that the TA value is valid based on the associated first measurement for the second cell; andsending information to a user equipment (UE), the information indicating the TA value for the UE to perform a random access channel (RACH)-less cell switch to the second cell based on the TA value.

20. An apparatus comprising means for performing the method of claim 19.

21. 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 claim 19.

22. 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 claim 19.

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