Lower-layer triggered mobility fast switch

Abstract

A method performed by a source access node serving a user equipment (UE) is provided. The method includes receiving baseline configurations including default configuration information for layer 3 (L3) mobility and lower-layer triggered mobility (LTM). The method includes retrieving UE-specific layer 1 (L1) measurement configuration information for LTM candidate target cell(s) based on L3 measurements performed by the UE. A message is sent to the UE that includes the default configuration information and the UE- specific L1 measurement configuration information for the LTM candidate target cell(s). A determination is made to execute a handover to a target cell. A handover command is sent to the UE to trigger the handover; and in connection with the handover, handover information associated with the UE is sent to the target cell for providing the UE with UE-specific configuration information for the target cell based on the handover information.

Description

LOWER-LAYER TRIGGERED MOBILITY FAST SWITCHTECHNOLOGICAL FIELD

[0001] The present disclosure relates generally to telecommunications and, in particular, to lower-layered triggered mobility of a user equipment 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 include, 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. Nonlimiting examples of services provided include 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 systems include 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 system are permitted to do and how that should be achieved. Communication protocols and / or parameters which shall be used for the connection 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-layered triggered mobility of a user equipment in a telecommunications system. The present disclosure includes, without limitation, the following example implementations.

[0007] Some example implementations provide an apparatus implemented by a source access node providing a source cell serving a user equipment, UE, the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieve UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; send a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE- specific LI measurement configuration information for the one or more LTM candidate target cells; determine to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; send a handover command to the UE to trigger the handover; and in connectionwith the handover, send handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[0008] Some example implementations provide an apparatus implemented by a source access node providing a source cell serving an user equipment, UE, the apparatus comprising: means for receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower- layer triggered mobility, LTM; means for retrieving UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; means for sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; means for determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; means for sending a handover command to the UE to trigger the handover; and in connection with the handover, means for sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE- specific configuration information for the target cell based on the handover information.

[0009] Some example implementations provide a method performed by a source access node providing a source cell serving a user equipment, UE, the method comprising: receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieving UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE- specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells;determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; sending a handover command to the UE to trigger the handover; and in connection with the handover, sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[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 a source access node providing a source cell serving a user equipment, UE, to at least: receive baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieve UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; send a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; determine to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; send a handover command to the UE to trigger the handover; and in connection with the handover, send handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[0011] Some example implementations provide an apparatus implemented by a target 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 apparatus to at least: send one or more baseline configurations of one or more cells provided by the target access node to a source access node providing asource cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receive a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determine the UE- specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; send the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receive handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determine UE-specific configuration information for the target cell based on the handover information associated with the UE; and send the UE-specific configuration information for the target cell to the UE.

[0012] Some example implementations provide an apparatus implemented by a target access node, the apparatus comprising: means for sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving an user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; means for receiving a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; means for determining the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; means for sending the UE- specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; means for receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; means for determining UE- specific configuration information for the target cell based on the handover information associated with the UE; and means for sending the UE-specific configuration information for the target cell to the UE.

[0013] Some example implementations provide a method performed by a target access node, the method comprising: sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receiving a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determining the UE- specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; sending the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determining UE-specific configuration information for the target cell based on the handover information associated with the UE; and sending the UE-specific configuration information for the target cell to the UE.

[0014] 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 a target access node to at least: send one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower- lay er triggered mobility, LTM; receive a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determine the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; send the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receive handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cellof the one or more LTM candidate cells; determine UE-specific configuration information for the target cell based on the handover information associated with the UE; and send the UE- specific configuration information for the target cell to the UE.

[0015] Some example implementations provide an apparatus implemented by a user equipment, UE, served by a source cell provided by a source 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 apparatus to at least: receive, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; report LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receive a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carry out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0016] Some example implementations provide an apparatus implemented by an user equipment, UE, served by a source cell provided by a source access node, the apparatus comprising: means for receiving, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; means for reporting LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; means for receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and means for carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0017] Some example implementations provide a method performed by a user equipment, UE, served by a source cell provided by a source access node, the method comprising:receiving, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; reporting LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[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 a user equipment, UE, served by a source cell provided by a source access node to at least: receive, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; report LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receive a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carry out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0019] 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. This 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.

[0020] 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)

[0021] 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:

[0022] 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;

[0023] FIG. 2 illustrates a deployment of a PLMN, according to some example implementations;

[0024] FIG. 3 is a signaling chart of a conventional handover procedure;

[0025] FIG. 4 is a signaling chart of a conditional handover procedure;

[0026] FIG. 5 a signaling chart of a lower-layer triggered mobility (LTM) procedure;

[0027] FIGS. 6A and 6B illustrate a signaling chart of an LTM fast switch (LFS) procedure with random access channel (RACH)-less access using a dynamic grant, according to some example implementations;

[0028] FIGS. 7Aand 7B illustrate a signaling chart of an LFS procedure with RACH-less access using a configured grant, according to some example implementations;

[0029] FIGS. 8Aand 8B illustrate a signaling chart of an LFS procedure with RACH- based access, according to some example implementations;

[0030] FIG. 9 is a flowchart illustrating various steps in a method performed by a source access node providing a source cell serving a user equipment (UE), according to various example implementations;

[0031] FIGS. 10A, 10B, 10C, 10D, 10E and 10F are flowcharts illustrating various steps in a method performed by a target access node, according to various example implementations;

[0032] FIGS. 11 A, 11B, 11C and 1 ID are flowcharts illustrating various steps in a method performed by a UE served by a source cell provided by a source access node, according to various example implementations; and

[0033] FIG. 12 illustrates an apparatus according to some example implementations.DETAILED DESCRIPTION

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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) accompanyingsoftware 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.

[0040] 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.

[0041] 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 (IIoT 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.

[0042] 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, operatorservices, 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).

[0043] 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 (e.g., 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).

[0044] 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 (at times more simply referred to as “access nodes” or “nodes”) that are configured to provide cells 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.

[0045] ARAN 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), WDMpassive 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.

[0046] As will be appreciated, a PLMN 102 may be deployed in a number of different manners. FIG. 2 illustrates a deployment 200 of a PLMN, such as a 4G LTE, 5G or 6G deployment, according to some example implementations. As shown, the deployment includes a CN 106, and RAN 108 with one or more radio access nodes 202 configured to interact with UEs 110. In a 4G LTE deployment, the EPC is the CN, and the evolved UMTS terrestrial radio access network (E-UTRAN) is the RAN; and the E-UTRAN includes one or more eNBs (radio access nodes) configured to connect UEs to the E-UTRAN to thereby access the EPC. Similarly, in a 5G deployment, the 5GC is the CN 106, and the next generation (NG) radio access network (NG-RAN) is the RAN 108; and the NG-RAN includes one or more gNBs (radio access nodes) configured to connect UEs 110 to the NG-RAN to thereby access the 5GC. The term ‘gNB’ in 5G may correspond to the eNB in 4G LTE.

[0047] Some deployments of 4G LTE and 5G in particular are considered standalone (SA) deployments. Other deployments combine 4G LTE and 5 G 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.

[0048] In some deployments, operations of a radio access node 202 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 distributed unit (DU) and a central / centralized unit (CU), such as a server, host or node. Insome 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.

[0049] It should also be understood that the distribution of work between CN 106 operations and radio access node 202 operations may vary depending on implementation. Thus, a 5G network architecture may be based on a so-called CU-DU split. 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 skilled person is familiar with the OSI model and the functionalities within each layer.

[0050] In some example implementations, the server or CU 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, and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

[0051] Although only one radio access node 202 is shown in FIG. 2, the deployment may include multiple radio access nodes, and at least some of the radio access nodes may be connected to one another by a network interface, such as an Xn interface. Similarly, the radio access nodes may be connected to the CN 106 by a network interface. In 5GNR, the network interface between a radio access node and the CN is referred to as the NG interface, which is a network interface between the radio access node and an access and mobility management function (AMF) of the 5GC. These and other network interfaces may support the exchange of signaling messages between network entities. The signaling messages may be formattedaccording to an application layer protocol, such as the NG application protocol (NGAP) for the NG interface between the radio access node and the CN.

[0052] For a UE 110 in an RRC connected state, it is generally desirable to keep the UE’s traffic uninterrupted when the UE moves within a cell (at times referred to as a radio cell) or across different cells of one or more radio access nodes 202. To continuously monitor the UE’s radio link condition toward a serving cell provided by a serving radio access node, the UE may be configured to measure received signal level and quality from the serving cell as well as a list of configured neighboring cells, and report the results to the radio access node periodically and / or whenever a configured reporting event is met. These measurements may then be evaluated at the radio access node, and may result in preparation of one target cell (conventional handover) or multiple candidate target cells (conditional handover), and a conventional / conditional handover of the UE from the serving cell provided by the serving radio access node (a “source access node” or more simply a “source node”) to a new cell provided by a target radio access node (a “target access node” or more simply a “target node”).

[0053] FIG. 3 is a signaling chart 300 of a conventional (inter-node) handover (HO) procedure involving a UE 110, a source access node 202A that is currently serving (connected to) the UE, and one or more candidate target access nodes 202B. As shown, the UE at step 301 may be configured, such as by an RRC reconfiguration, to report measurements of one or more neighboring cells, such as on an event basis. Once the event condition holds, the UE may at step 302 send (transmit) a measurement report indicating relevant measurements for one or more cells provided by the candidate target access node(s). Depending on various configurations and requirements, the measurement may be performed on any of a number of suitable objects. Based on measurements performed and reported by the UE and other UEs served by the source access node, the source access node may be configured to derive information, such as a number of actively connected UEs, number of RRC connections, number of physical resource blocks (PRBs) in use, the transport network load (TNL) capacity, or the like.

[0054] The source access node 202A may at step 303 decide to initiate the handover procedure, and initiate a handover preparation in which the source access node at step 304 sends (transmits) a handover request message with a current configuration of the UE 110towards the candidate target access node 202B that provides a target cell. In some cases, the handover request message may be sent over an Xn interface between the source access node and the candidate target access node, such as according to a procedure referred to as Xn handover. In some possible cases where there is no Xn interface between these two nodes, the candidate target access node may be accessed over AMF, such as according to a procedure referred to as NGAP handover.

[0055] The candidate target access node 202B may at step 305 perform admission control, such as to accept or reject the handover request, and at step 306 provide a handover request acknowledgement (ACK) message including a configuration of initial access resources for the UE 110 in case of acceptance. This configuration may include, for example, a cell radio network temporary identifier (C-RNU), a contention-free random access (CFRA) preamble, a data radio bearer (DRB) configuration, quality of service (QoS) flow to DRB mapping, UE capability related features enabled by the candidate target access node, or the like. The source access node 202A may then at step 307 send (transmit) a handover command message that includes the configuration for the target cell towards the UE.

[0056] Upon receipt of the handover command from the source access node 202A, the UE 110 may at steps 308, 309, 310 obtain downlink (DL) and uplink (UL) synchronization with the candidate target access node 202B, and thereafter complete the handover procedure. As shown, in some examples, the handover command may be provided at step 307 by an RRC reconfiguration; and in some of these examples, the handover procedure may include a random access procedure for handover, including DL and UL synchronization and random access channel (RACH) access to the candidate target access node, and random access response (RAR) message from the candidate target access node. The UE may then send (transmit) an RRC reconfiguration complete message to the candidate target access node to complete the handover procedure.

[0057] In the case of conditional handover (CHO), a UE 110 may be configured with a CHO command containing the candidate target cell configuration and one or more CHO conditions for carrying out the handover to one or more candidate target cells. The condition may be based on radio measurements. For example, a condition may be that a measured reference signal received power (RSRP) from the serving cell falls below a threshold RSRP.Each of the candidate target cell(s) / candidate target access node(s) 202B may have prepared a necessary configuration, such as contention free random access (CFRA) resources for the UE. Such configuration may then be communicated to the UE in the CHO command. When UE evaluates the CHO condition and determines that the condition holds for a specific candidate target cell, UE may be configured to apply the CHO command and use the reserved CFRA resources to initiate the random access procedure to the candidate target cell. In some examples, the UE may be configured with multiple conditions for multiple candidate target cells.

[0058] The CHO procedure may be seen to be so designed that the UE 110 may perform / execute the handover without the need of the serving cell / source access node 202A to trigger the HO execution (as shown at step 307 of FIG. 3 for a conventional HO) after the measurement report (as shown at steps 302 of FIG. 3).

[0059] FIG. 4 is a signaling chart 400 of a CHO procedure involving a UE 110, a source access node 202A that is currently serving (connected to) the UE, and one or more candidate target access nodes 202B (two candidate target access nodes shown). Similar to the conventional HO procedure, the UE at step 401 may be configured to report measurements of one or more neighboring cells, and at step 402 send (transmit) a measurement report indicating relevant measurements for one or more candidate target cells provided by the candidate target access node(s).

[0060] The source access node 202A may at step 403 decide to initiate the handover procedure as a conditional handover procedure; and similar to the conventional HO procedure, initiate a handover preparation in which the source access node at step 404 sends (transmits) a handover request message with a current configuration of the UE 110 towards each of the candidate target access node(s) 202B.

[0061] Each candidate target access node 202B may at step 405 perform admission control, such as to accept or reject the handover request, and at step 406 provide a handover request ACK message including a configuration of initial access resources for the UE 110. This configuration may be the same as or similar to the conventional HO procedure, including for example, a C-RNTI, a CFRA preamble, a DRB configuration, QoS flow to DRB mapping, UE capability related features enabled by the candidate target access node, or the like.

[0062] The source access node 202A may then at step 407 send (transmit) a CHO command message that includes the configuration for the candidate target cell towards the UE. The CHO command message may be sent similar to the HO command message, such as by an RRC reconfiguration. The CHO command message also includes one or more CHO conditions for one or more candidate target cells of the candidate target access node(s) 202B.

[0063] Upon receipt of the handover command from the source access node 202A, when the CHO command message is sent by an RRC reconfiguration, the UE 110 may at step 408 send (transmit) an RRC reconfiguration complete message to the source access node. The UE maintains its connection with the source access node, and at step 409 starts evaluating the CHO condition(s) for the candidate target cell(s). If at least one candidate target cell satisfies a corresponding CHO condition, the UE may at steps 410, 411, 412 obtain DL and UL synchronization and RACH access with the candidate target access node 202B that provides the candidate target cell, and thereafter complete the handover procedure, such as in a manner similar to steps 308, 309, 310 described above for the conventional HO procedure. After successful HO to a candidate target cell, handover to other prepared candidate target cell(s) may be cancelled.

[0064] As the wireless generations evolve, so does the need for new and different solutions enabling more flexible, more efficient and sometimes faster procedures making the system seem more agile. One such enhancement includes moving 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 layer 1, LI) or MAC (or layer 2, L2). This feature is currently referred to as Ll / L2-triggered mobility, or lower-layer triggered mobility (LTM), which may reduce latency, overhead and interruption time when compared to L3 handover based mobility. In a CU-DU split architecture, LTM may support one or more of intra-DU mobility, intra-CU inter-DU mobility, or inter-CU inter-DU mobility.

[0065] FIG. 5 illustrates a signaling chart 500 for an LTM procedure of a UE 110 in an RRC connected state with a radio access node 202. During LTM preparation, as shown at step 501, the UE sends a L3 measurement report to the radio access node, which decides to use LTM and initiate LTM candidate preparation. The radio access node at step 502 transmits an RRC reconfiguration message to the UE, including the RRC configuration of one or moreLTM candidate target cells. The RRC configuration of an LTM candidate target cell may be provided by an LTM candidate configuration information element (IE) within an LTM candidate IE. 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 503 transmits an RRC reconfiguration complete message to the radio access node.

[0066] An early synchronization of the UE 110 with the LTM candidate target cell(s) follows LTM preparation. As shown at steps 504A, 504B the UE performs early DL / UL synchronization with the LTM candidate target cell(s). During early UL synchronization, the UE may perform early timing advance (TA) acquisition with the LTM candidate target cell(s) as requested by the radio access node 202 before receiving a cell switch command. 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 UL transmissions of a UE toward the LTM candidate target cell(s). The UE may likewise have an acquired TA of the cell of the radio access node to control the timing of UL transmissions toward the radio access node.

[0067] During early UL synchronization at step 504B, the radio access node 202 may trigger the UE to perform early TA acquisition via contention free random access (CFRA) by a physical downlink control channel (PDCCH) order (using downlink control information (DCI) format 1 0), following which the UE 110 sends a random access (RA) preamble on the physical RACH (PRACH) towards an indicated LTM candidate target cell. In 3GPP, the RA preamble is sent as a first message (msgl) as part of a RA procedure; and accordingly, the RA preamble may at times be referred to as msgl. In order to minimize the data interruption of the radio access node due to CFRA towards the LTM candidate target cell(s), the UE may not receive a random access response (RAR) from the network for the purpose of TA value acquisition, and the TA value of the LTM candidate target cell may be indicated in a subsequent cell switch command.

[0068] During LTM execution, the UE 110 performs LI measurements on the configured LTM candidate target cell(s), and the UE at step 505 transmits LI measurement reports to the radio access node 202. In some examples, the LI measurements include LI reference signalreceived power (RSRP) measurements. In some of these examples, the LI measurement reports may be referred to as LI RSRP measurement reports.

[0069] The radio access node 202 decides to execute a cell switch, and selects one of the LTM candidate target cell(s) as a target cell for the cell switch. The radio access node then at step 506 transmits a cell switch command (e.g., MAC control element (CE)), to trigger cell switch. The UE 110 switches to the configuration of the target cell; and if the TA of the target cell (from step 504B) is no longer available, the UE at step 507 initiates a RACH procedure with the target cell to acquire the TA of the target cell. The UE then at step 508 indicates successful completion of the cell switch. In this regard, the UE may transmit an RRC reconfiguration complete message to indicate completion of the cell switch. If the UE performed a RACH procedure at step 507, the UE may consider the cell switch execution successfully completed when the RACH procedure is successfully completed. For a RACH- less cell switch, the UE may consider the cell switch execution successfully completed when the UE determines that the RAN 108 has successfully received its first UL data.

[0070] The early DL / UL synchronization at steps 504a, 504b may be performed toward each configured candidate target cell for subsequent LTM cell switch using the LTM candidate configuration(s) provided during LTM preparation at step 502.

[0071] Relative to L3 -based mobility, LTM introduces improvement in handover latency and interruption time. Although the configuration is at the RRC level in LTM, the measurement reporting from the UE 110, switching decision and triggering by the radio access node 202 are done at the MAC level without RRC involvement. The UE also performs early synchronization and T A acquisition which enables faster access. Despite its improvements, however, LTM requires allocated resources at preparation time, which is waste of network resources at more than one LTM candidate target cell.

[0072] In view of the foregoing, example implementations of the present disclosure provide a solution, referred to at times as LTM fast switch (LFS), whereby an LTM candidate target cell configuration may be divided into different parts that are provided to the UE 110 at different stages of LTM. At high level, a baseline configuration may be provided that includes default configuration information for L3 mobility along with default configuration information for LTM, from radio access nodes 202 supporting the feature to their neighboring nodes at1 early stage. Later, when the source access node 202A decides to configure a UE for LI measurements - based on L3 measurement reports - the source access node may request a LI measurement configuration tailored for the given UE’s beam-based radio link in its current source cell. The baseline configuration and LI measurement configuration may enable the UE to perform and report LI measurements, and access a selected target cell using a resource efficient approach for the first UL (for RACH-less access) or RACH access. The UE may then receive a UE-specific configuration for measurement and resources needed when the UE arrives at the target cell.

[0073] According to some example implementations of the present disclosure, during LTM preparation, one or more candidate target access nodes 202B that may generate send baseline configuration(s) of cell(s) provided by the candidate target access node(s) to a source access node 202A providing a source cell serving a UE 110. The cell(s) provided by the candidate target access node(s) may be neighboring cell(s) of the source cell, and the source access node may receive receive baseline configuration(s) of the neighboring cell(s) provided by the candidate target access node(s). In some examples, baseline configuration(s) may be generally considered specific to a cell pair (or in other words, source access node and target cell-specific).

[0074] The baseline configuration(s) include default configuration information for L3 mobility and LTM to the neighboring cell(s). Depending on various implementations and / or requirements, the default configuration information for L3 mobility may include default low layer configuration information, that is, configuration information for lower layer(s), such as LI (e.g., PHY layer), L2 (e.g., MAC layer, RLC layer, or PDCP layer), or the like. The default configuration information for L3 mobility may also include default high layer configuration information, that is, a configuration for higher layer(s), such as L3 or even above (e.g., RRC layer, non-access stratum (NAS) layer). The default high layer configuration information may also include measurement-related configurations for higher layers (in contrast to LI measurement configurations).

[0075] In some examples, the default high layer configuration information may include some or all of the L2 sub-layers, such as the service data adaptation protocol (SDAP) layer (e.g., for signaling radio bearers - SRBs), instead of low lower configuration information. Insome examples, the default low layer configuration information and default high layer configuration information may be collectively referred to as default configuration information for L3 mobility for a target cell of candidate target access node 202B.

[0076] The default configuration information for LTM may include cell-specific LI (LFS) configuration information, which may include static / semi-static LI configuration information and / or dynamic LI configuration information. In some examples, the static / semi-static LI configuration information may include synchronization signal block (SSB) configuration(s) of the neighboring cell(s), and the dynamic LI configuration information may include channel state information (CSI) reference signal (RS) (CS RS) resource(s) active in the neighboring cell(s). In some examples of dynamic LI configuration information, the candidate target access node(s) 202B may determine updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of its cell(s), and send the updated dynamic LI configuration information to the source access node 202A.

[0077] In addition to the default configuration information for L3 mobility and LTM, the baseline configuration may include a pool (list) of one or more RA preambles (e.g., CFRA preambles) that can be used for L3 mobility, or for early TA acquisition in connection with LTM. The pool of RA preambles may be predetermined, preconfigured or (pre-)reserved at the candidate target access node(s) 202B. Any one of the preambles selected (by the source access node 202A) from this pool and assigned to the UE 110 may be later recognizable by the candidate target access node during a subsequent synchronization / random access process.

[0078] The UE 110 may perform L3 measurements on the source cell and the neighboring cell(s), and report the L3 measurements to the source access node 202A. The source access node may decide to configure the UE for LI measurements and select one or more LTM candidate target cells from the neighboring cell(s), based on the L3 measurments. The source access node may retrieve UE-specific LI measurement configuration information for the LTM candidate target cell(s) from the candidate target acces node(s) 202B based on the L3 measurements performed by the UE. The candidate target access node(s) may receive a request from the source access node for UE-specific LI measurement configuration information for the LTM candidate target cell(s), where the request may be based on the L3 measurements. In some examples, the request may include the L3 measurements. In otherexamples, the request may include information drawn from the L3 measurements by the source access node. In some of these other examples, the request may include LI information extracted from the L3 measurments by the source access node.

[0079] The candidate target access node(s) 202B may determine the UE-specific LI measurement configuration information for the LTM candidate target cell(s) based on the L3 measurements, and send the UE-specific LI measurement configuration information to the source access node 202A. In some examples, the UE-specific LI measurement configuration information may include measurement resource(s) for the UE 110 to perform LI measurements on the LTM candidate target cell(s), but exclude reporting resources for the UE to report LI measurements to the LTM candidate target cell(s).

[0080] The source access node 202A may send a message to the UE 110 that includes the default configuration information and the UE-specific LI measurement configuration information for the LTM candidate target cell(s) provided by the candidate target access node(s) 202B. In some examples, the message may further include one or more RA preambles (e.g., CFRA preambles) usable by the UE for early TA acquisition towards the LTM candidate target cell(s). In some of these examples, the source access node may tretrieve the RA preamble(s) from the LTM candidate target cell(s). In this regard, the candidate target access node(s) may receive a request from the source access node for the RA preamble(s), and send the RA preamble(s) to the source access node. In other examples in which the baseline configuration(s) include pool(s) of RA preambles for the neighboring cell(s), and the source access node may select the RA preamble(s) from the pool(s) of RA preambles for the LTM candidate target cell(s).

[0081] During early UL synchronization of the UE 110 with the LTM candidate target cell(s), the UE may send the RA preamble(s) to the candidate target access node(s) 202B providing the LTM candidate target cell(s). The candidate target access node(s) may receive RA preamble(s) from the UE, determine TA value(s) based on the RA preamble(s), and send the TA value(s) towards the UE. In some examples, the UE may receive the TA value(s) from the candidate target access node(s), and synchronize the UE to the LTM candidate target cell(s) based on the TA value(s).

[0082] During LTM execution, the UE 110 may perform and report LI measurements on the the LTM candidate target cell(s) based on the UE-specific LI measurement configuration information. The source access node 202A may determine to execute a handover (e.g., cell switch) of the UE to a target cell of the LTM candidate target cell(s) based on the LI measurements, and send a handover command (e.g., cell switch command) to the UE to trigger the handover.

[0083] The UE 110 may receive the handover command from the source access node 202A, and carry out the handover to the target cell provided by one of the candidate target access node(s) 202B. In connection with the handover, the source access node 202A may send handover information associated with the UE to the target cell. The candidate target access node that provides the target cell may receive the handover information, and determine UE- specific configuration information for the target cell based on the handover information. The candidate target access node may then send the UE-specific configuration information for the target cell to the UE.

[0084] In various examples, the handover may be a RACH-less handover or a RACH- based handover. In some examples of a RACH-less handover, the candidate target access node(s) 202B may determine search space(s) associated with its cell(s) for dynamic UL grants usable by the UE for RACH-less access to the cell(s), and send indication(s) of the search space(s) to the source access node 202A. The source access node may send the indication(s) of the search space(s) associated with the LTM candidate target cell(s) to the UE 110, such as in the message that includes the default configuration information and the UE-specific LI measurement configuration information for the LTM candidate target cell(s). When handover to a selected target access node is triggered by the source access node, the UE may then monitor the search space (e.g., PDCCH) associated with the target cell for a dynamic UL grant, and perform a RACH-less access to the target cell using the dynamic UL grant.

[0085] In other examples of a RACH-less handover, the source access node 202A may retrieve indication(s) of configured UL grant(s) associated with the LTM candidate target cell(s) usable by the UE 110. In this regard, the candidate target access node(s) 202B may prepare configured UL grant(s) associated with the LTM candidate target cell(s), and send indication(s) of the configured UL grant(s) to the source access node 202A. The source accessnode may send the indication(s) of the configured UL grant(s) associated with the LTM candidate target cell(s) to the UE 110, such as in the message that includes the default configuration information and the UE-specific LI measurement configuration information for the LTM candidate target cell(s). During the handover, the UE may then perform a RACH-less access to the target cell using the configured UL grant associated with the target cell.

[0086] To further illustrate some example implementations of the present disclosure, FIGS. 6Aand 6B illustrate a signaling chart 600 of an LFS procedure with RACH-less access using a dynamic UL grant, according to some example implementations. As shown in FIG. 6 A, during LTM preparation - early configuration, a UE 110 is in an RRC connected state with a source access node 202A that supports LTM, and there are one or more candidate target access nodes 202B that provide one or more (N) candidate target cells. At least one candidate target access node may at step 601 generate and share a baseline configuration with the source access node, without a previous handover request or cell switch from the source access node.

[0087] The baseline configuration may include a cell-specific baseline (L3) configuration (default configuration information for L3 mobility), which may include a pool of RA preambles. The baseline configuration may also include a cell-specific, static / semi-static LI (LFS) configuration, a cell-specific, dynamic LI (LFS) configuration, and perhaps also a corresponding timer indicating an expected validity time of the dynamic LI configuration (default configuration information for LTM). As indicated above, for example, the static / semi- static LI configuration information may include SSB configuration(s) of the neighboring cell(s), and the dynamic LI configuration information may include CSLRS resource(s) active in the neighboring cell(s). The candidate target access node(s) may also provide a search space to monitor for a dynamic UL grant.

[0088] The candidate target access node(s) 202B may send (transmit) the baseline configuration(s) and search space for dynamic UL grants to the source access node 202A in a RAN node configuration update message, or any other suitable (existing or new) message. The source access node may at step 602 send (transmit) a corresponding acknowledgment message (e.g., RAN node configuration update ACK) back to the candidate target access node.

[0089] The source access node 202A may have at step 603 configured the UE 110 (one or more UEs) served by the source access node with an L3 radio resource management (RRM)measurement and reporting configuration, and receive L3 measurement reports based on the configuration. The configuration may be received / updated at any time after UE is in the RRC connected state, and the source access node may receive the L3 measurement reports periodically or based on one or more reporting events.

[0090] Each candidate target access node 202B may continuously evaluate whether any (part of) the baseline configuration has changed. In some examples, then, the candidate target access node 202B may at step 604-1 determine a change in the baseline configuration. In particular, for example, the pool of RA preambles may be updated, such as after some of the RA preambles have been used / occupied, reconfigured, freed, or the like. In another example, the candidate target access node may determine a change in the dynamic LI configuration information. In these examples, the candidate target access node may determine updated default configuration information, and at step 504-2 share the updated default configuration information with the source access node 202A.

[0091] Based on received L3 measurement report(s) from the UE 110, the source access node 202A may at step 605 decide to configure the UE with LI measurements on cell(s) in one or more candidate target access nodes 202B, and at step 606 determine LTM candidate target cell(s) from which to retrieve further configuration information to enable the UE to perform the LI measurements.

[0092] The source access node 202A may at step 607 provide the L3 measurement report to the candidate target access node(s) 202B that provide the LTM candidate target cell(s) to enable the candidate target access node(s) to prepare UE-specific LI measurement configuration information, such as an LTM CSI-RS configuration for each of the LTM candidate target cell(s). In some examples, the source access node may send L3 measurements of the LTM candidate target cell(s) / beam(s), which may be extracted from the L3 measurement report. In examples in which the baseline configuration(s) (received at step 601) do not include pool(s) of RA preambles (e.g., CFRA preambles) from which RA preamble(s) may be selected for early TA acquisition, the source access node may also request RA preambles from the candidate target access node(s). In other examples in which the baseline configuration(s) (received at step 601) do not include pool(s) of RA preambles, the source access node may request the pool(s) of RA preambles.

[0093] Based on a preference of candidate cells / beams for LTM mobility, each candidate target access node 202B may at step 608-1 prepare UE-specific LI measurement configuration information for its LTM candidate target cell(s). The UE-specific LI measurement configuration information may include measurement resource(s) for the UE 110 to perform LI measurements on the LTM candidate target cell(s), but exclude reporting resources (e.g., physical uplink control channel (PUCCH) / physical uplink shared channel (PUSCH) resources) for the UE to report LI measurements to the LTM candidate target cell(s). These reporting resources may be excluded in order to minimize resource reservation at the LTM candidate target cell(s), such as until the UE is switched to one of the LTM candidate target cell(s).

[0094] In some more specific examples, the candidate target access node 202B may prepare an LTM CSI-RS configuration for its LTM candidate target cell(s), such as based on SSB and CSI-RS. In the case of CSI-RS-based reporting, there may be coordination across the nodes to obtain the active CSI-RS resources that form the basis for preparing the LTM CSI-RS configuration and LTM report configuration. In this regard, the LTM CSI-RS configuration may be mapped to the prepared (active) CSI-RS resources.

[0095] The candidate target access node may at step 608-2 send the UE-specific LI measurement configuration information, as well as RA preamble(s) / pool(s) of RA preambles (if requested), to the source access node 202A.

[0096] The source access node 202A may at step 609 configure the UE 110 with LFS including the common SSB / CSI-specific LI measurement and reporting, the RA preamble(s) (e.g., CFRA preamble(s)) for early TA acquisition, and search space(s) to monitor for dynamic UL grant(s) usable for RACH-less access. The RA preamble(s) may be selected by the source access node from pool(s) of RA preambles, which may be provided as part of the baseline configuration at step 601 retrieved at steps 608-1, 608-2. In other examples, the RA preambles themselves may be retrieved by the source access node at steps 608-1, 608-2. The source access node may send a message (e.g., RRC reconfiguration) to the UE that includes the baseline configuration (with default configuration information for L3 mobility and LTM), UE- specific LI measurement configuration information, RA preamble(s), and search space(s) to monitor for dynamic UL grant(s).

[0097] As shown in FIG. 6B, an early synchronization of the UE 110 with the LTM candidate target cell(s) follows LTM preparation - early configuration. As shown at steps 610- 1, 610-2 the UE performs early DL / UL synchronization with the LTM candidate target cell(s). During early UL synchronization, for each LTM candidate target cell, the source access node 202A may request that the UE perform early TA acquisition via CFRA triggered by a PDCCH order, following which the UE 110 may send one of the received RA preamble(s) on the PRACH towards the LTM candidate target cell. In some examples, in order to minimize the data interruption of the source access node due to CFRA towards the LTM candidate target cell, in some examples, the UE may not receive a RAR from the network for the purpose of TA value acquisition, and the TA value of the LTM candidate target cell may be indicated in a subsequent handover command.

[0098] An LTM execution - late configuration may follow early synchronization. During LTM execution - late configuration, the UE 110 may perform LI measurements on the LTM candidate target cell(s) based on the UE-specific LI measurement configuration information, and the UE may at step 611 send LI measurement report(s) to the source access node 202A. The source access node 202A may at step 612 decide to execute a LI handover (e.g, cell switch), and selects one of the LTM candidate target cell(s) as a target cell for the handover. The source access node may at step 613-1 send an LI handover command (e.g., MAC CE) to the UE to trigger the handover.

[0099] Before, after or as the handover command is sent to the UE 110, the source access node 202A may at step 613-2 also send handover information associated with the UE to the target cell, or more specifically the target access node 202B that provides the target cell. The handover information may include UE context information. In examples in which the source access node selected the RA preamble for early TA acquisition to the target cell from a pool of RA preambles provided by the target access node, the source access node may also notify the target access node of the RA preamble selected from the pool (and thereby used). The handover information and used RA preamble may be sent to the target cell in a suitable (existing or newly introduced) message.

[0100] Upon receipt of the handover command, the UE 110 may monitor the search space(e.g., PDCCH) associated with the target cell for a dynamic UL grant, and perform a RACH-less access to the target cell using the dynamic UL grant. In this regard, the UE may at step 614 send its first UL data to the target cell using the dynamic UL grant. Notably, as the handover command and handover information towards the UE 110 and the target access node 202B (target cell) as shown at respectively steps 613-1 and 613-2 may be sent in any sequence or in parallel, it is possible that, in some cases, step 614 may take place before step 613-2.

[0101] The target access node 202B (target cell) may determine UE-specific configuration information for the target cell based on the handover information (e.g., UE context) associated with the UE 110. In some examples, the UE-specific configuration information may include a measurement and reporting configuration, and corresponding resources. In this regard, PUCCH / PUSCH resources for LI reporting to the target access node may be configured as part of the UE-specific configuration information at the time of the handover.

[0102] The target access node 202B (target cell) may at step 615 send the UE-specific configuration information for the target cell to the UE, such as in a message (e.g., RRC reconfiguration) sent directly to the UE via the physical downlink shared channel (PDSCH). The UE may then at step 616 send a message (RRC reconfiguration complete) to the target access node to acknowledge receipt of the UE-specific configuration and complete the handover.

[0103] FIGS. 7 A and 7B illustrate a signaling chart 700 of an LFS procedure with RACH- less access using a configured grant, according to some example implementations. This LFS procedure is similar to the LFS procedure shown in the signaling chart 600 in FIGS. 6A and 6B, except that a configured UL grant is provided to the UE 110 for RACH-less access to the target access node 202B (target cell).

[0104] As shown in FIG. 7A, during LTM preparation - early configuration, the UE 110 is in an RRC connected state with a source access node 202A that supports LTM, and there are one or more candidate target access nodes 202B that provide one or more (N) candidate target cells. Similar to step 601, the candidate target access node(s) may at step 701 generate and share a baseline configuration with the source access node, such as in a RAN node configuration update message, or any other suitable (existing or new) message. In contrast to step 601, however, the candidate target access node(s) do not at step 701 provide search space(s) to monitor for dynamic UL grant(s). The source access node may at step 702 send(transmit) a corresponding acknowledgment message (e.g., RAN node configuration update ACK) back to the candidate target access node.

[0105] The source access node 202A, HE 110 and candidate target access node(s) may perform steps 703, 704-1, 704-2, 705 and 706 the same as or similar to respective ones of steps 603, 604-1, 604-2, 605 and 606 described above.

[0106] The source access node 202A may at step 707 provide the L3 measurement report to the candidate target access node(s) 202B that provide the LTM candidate target cell(s) to enable the candidate target access node(s) to prepare UE-specific LI measurement configuration information, such as an LTM CSLRS configuration for each of the LTM candidate target cell(s), such as described above for step 607. Also similar to before, the source access node may also request RA preamble(s) / pool(s) of RA preambles for early TA acquisition.

[0107] Each candidate target access node 202B may at step 708-1 prepare UE-specific LI measurement configuration information for its LTM candidate target cell(s), similar to before. In addition, the target access node may prepare configured UL grant(s) associated with its LTM candidate target cell(s). The configured UL grant(s) may be prepared based on a request from the source access node 202A at step 707, or autonomously based on one or more load / resource conditions at the LTM candidate target cell(s).

[0108] The candidate target access node may then at step 708-2 send the UE-specific LI measurement configuration information and the configured UL grant(s), as well as RA preamble(s) / pool(s) of RA preambles (if requested), to the source access node 202A.

[0109] The source access node 202A may at step 709 configure the UE 110 with LFS including the common SSB / CSI-specific LI measurement and reporting, the RA preamble(s) for early TA acquisition, and the configured UL grant(s) usable for RACH-less access. Similar to before, the source access node may send a message (e.g., RRC reconfiguration) to the UE that includes the baseline configuration (with default configuration information for L3 mobility and LTM), UE-specific LI measurement configuration information, RA preamble(s) (e.g., CFRA preamble(s), and the configured UL grant(s). In other examples, the configured UL grant(s) may be provided to the UE 110 during early synchronization.

[0110] As shown in FIG. 7B, an early synchronization of the UE 110 with the LTM candidate target cell(s) follows LTM preparation ~~ early configuration. As shown at steps 710- 1, 710-2 the UE performs early DL / UL synchronization with the LTM candidate target cell(s). The early DL / UL synchronization may be performed in the same manner described above for steps 610-1, 610-2. In some examples, the configured UL grant(s) may be provided to the UE with the TA value(s) of the LTM candidate target cell(s) during early UL synchronization.

[0111] The remaining steps 714, 715 and 716 may be similar to steps 614, 615 and 616 described above, except that the UE need not monitor the search space (e.g., PDCCH) associated with the target cell for a dynamic UL grant.

[0112] FIGS. 8A and 8B illustrate a signaling chart 800 of an LFS procedure with RACH- based access, according to some example implementations. The LFS procedure with RACH- based access may be similar to a LFS procedure for RACH-less access, such as that shown in either signaling chart 600 or signaling chart 700, with RACH-based access as a fallback in case the RACH-less access is unsuccessful. In other examples, the LFS procedure with RACH-based access may be setup without either search space(s) to monitor for dynamic UL grant(s), or configured UL grant(s), associated with the LTM candidate cell(s).

[0113] As before and shown in FIG. 8A, during LTM preparation - early configuration, the UE 110 is in an RRC connected state with a source access node 202A that supports LTM, and there are one or more candidate target access nodes 202B that provide one or more (N) candidate target cells. The LTM preparation - early configuration may include steps 801, 802, 803, 804-1, 804-2, 805, 806, 807, 808-1, 808-2 and 809, which may correspond to respective ones of the similarly numbered steps in signaling chart 600 or signaling chart 700. In the LFS procedure in signaling chart 800, however, there may not be either search space(s) to monitor for dynamic UL grant(s), or configured UL grant(s), sent to the UE at step 809.

[0114] As shown in FIG. 8B, early synchronization of the UE 110 with the LTM candidate target cell(s) follows LTM preparation - early configuration. Early synchronization includes 810-1, 810-2, which may be performed in the same manner described above for steps 610-1, 610-2. Likewise, LTM execution - late configuration may include steps 811, 812, 813-1 and 813-2, which may be performed in the same manner described above for steps 611, 612, 613-1 and 613-2.

[0115] Upon receipt of the handover command at step 813-1, the UE 110 may at step 814 initiate RACH access to the target access node 202B (target cell). The UE may apply the default configuration information for the target cell received at step 801, and the RA preamble for the target cell received at step 809. In some examples, the RA preamble used for the RACH access to the target access node may instead be provided in the handover command (the RA preamble also selected by the source access node 202A from a pool of RA preambles for the target cell).

[0116] During the RACH access, the UE 110 may obtain DL and UL synchronization and perform random access to be successfully connected to the target cell provided by the target access node 202B. The target access node 202B (target radio cell) may generate any remaining UE-specific configuration information based on the handover information received at step 813-2. The target access node may at step 815 provide this remaining UE-specific configuration information in a RAR message to the UE 110. The UE may then at step 615 send an indication (e.g., LI handover complete) message to the target access node to complete the handover. In another example, the remaining UE-specific configuration information may not be provided in the RAR, and instead sent to the UE in a new RRC message at step 815-1.

[0117] FIG. 9 is a flowchart illustrating various steps in a method 900 performed by a source access node providing a source cell serving a user equipment (UE), according to various example implementations. The method includes receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3 (L3) mobility and lower-layer triggered mobility (LTM), as shown at block 902. The method includes retrieving UE-specific layer 1 (LI) measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE, as shown at block 904.

[0118] The method 900 includes sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells, as shown at block 906. The method includes determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on theone or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information, as shown at block 908. The method includes sending a handover command to the UE to trigger the handover, as shown at block 910. And the method includes, in connection with the handover, sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information, as shown at block 912.

[0119] In some examples, the default configuration information includes static LI configuration information and dynamic LI configuration information. In some of these examples, the method 900 further includes receiving an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

[0120] In some examples, the message sent to the UE at block 906 further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0121] In some examples, the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells. In some of these examples, the method 900 further includes selecting the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

[0122] In some examples, the method 900 further includes retrieving the one or more random access preambles from the one or more LTM candidate target cells.

[0123] In some examples, the method 900 further includes receiving one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for random access channel (RACH)-less access to the one or more neighboring cells. In some of these examples, the message sent to the UE at block 906 further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

[0124] In some examples, the method 900 further includes retrieving one or more indications of one or more configured uplink grants associated with the one or more LTMcandidate target cells usable by the UE for random access channel (RACH)-less access to the one or more LTM candidate target cells. In some of these examples, the message sent to the UE at block 906 further includes the one or more indications of the one or more uplink grants.

[0125] FIGS. 10A - 10F are flowcharts illustrating various steps in a method 1000 performed by a target access node, according to various example implementations. The method includes sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment (UE), the one or more baseline configurations including default configuration information for layer 3 (L3) mobility and lower-layer triggered mobility (LTM), as shown at block 1002 of FIG. 10 A. The method includes receiving a request from the source access node for UE- specific layer 1 (LI) measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE, as shown at block 1004. The method includes determining the UE- specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements, as shown at block 1006.

[0126] The method 1000 includes sending the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node, as shown at block 1008. The method includes receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells, as shown at block 1010. The method includes determining UE-specific configuration information for the target cell based on the handover information associated with the UE, as shown at block 1012. And the method includes sending the UE-specific configuration information for the target cell to the UE, as shown at block 1014.

[0127] In some examples, the UE-specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

[0128] In some examples, the default configuration information includes static LI configuration information and dynamic LI configuration information. In some of these examples, the method 1000 further includes determining updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells, as shown at block 1016 of FIG. 10B. And the method includes sending the updated dynamic LI configuration information to the source access node, as shown at block 1018.

[0129] In some examples, the method 1000 further includes receiving one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells, as shown at block 1020 of FIG. 10C. In some of these examples, the method also includes determining one or more timing advance values based on the one or more random access preambles, and sending the one or more timing advance values towards the UE, as shown at blocks 1022 and 1024.

[0130] In some examples, the one or more baseline configurations sent to the source access node at block 1002 include one or more pools of random access preambles from which the random access preambles are selected by the source access node and sent to the UE.

[0131] In some examples, the method 1000 further includes receiving a request from the source access node for the one or more random access preambles, as shown at block 1026 of FIG. 10D. In some of these examples, the method also includes sending the one or more random access preambles to the source access node from which the one or more random access preambles are sent to the UE, as shown at block 1028.

[0132] In some examples, the method 1000 further includes determining one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel (RACH)-less access to the one or more cells, as shown at block 1030 of FIG. 10E. In some of these examples, the method also includes sending one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE, as shown at block 1032.

[0133] In some examples, the method 1000 further includes preparing one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel (RACH)-less access to the one or more LTM candidatetarget cells, as shown at block 1034 of FIG. 10F. And in some of these examples, the method also includes sending one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE, as shown at block 1036.

[0134] FIGS. 11 A - 1 ID are flowcharts illustrating various steps in a method 1100 performed by a user equipment (UE) served by a source cell provided by a source access node, according to various example implementations. The method includes receiving, from the source access node, a message that includes default configuration information for layer 3 (L3) mobility and lower-layer triggered mobility (LTM) to one or more LTM candidate target cells, and UE-specific layer 1 (LI) measurement configuration information for the one or more LTM candidate target cells, as shown at block 1102 of FIG. 11A. The method includes reporting LI measurements on the one or more LTM candidate target cells based on the UE- specific LI measurement configuration information, as shown at block 1104. The method includes receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells, as shown at block 1106. And the method includes carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell, as shown at block 1108.

[0135] In some examples, the message received from the source access node at block 1102 further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0136] In some examples, the method 1100 further includes sending the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells, as shown at block 1110 of FIG. 1 IB. In some of these examples, the method also includes receiving one or more timing advance values from the one or more target access nodes based on the one or more random access preambles, as shown at block 1112. And in some of these examples, the method includes synchronizing the UE to the one or more LTM candidate target cells based on the one or more timing advance values, as shown at block 1114

[0137] In some examples, the method 1100 further includes receiving, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell. In some of these examples, carrying out the handover at block 1108 includes monitoring the search space associated with the target cell for a dynamic uplink grant, as shown at block 1116 of FIG. 11C. Also in some of these examples, carrying out the handover includes performing a random access channel (RACH)- less access to the target cell using the dynamic uplink grant, as shown at block 1118.

[0138] In some examples, the method 1100 further includes receiving, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the target cell. In some of these examples, carrying out the handover at block 1108 includes performing a random access channel (RACH)-less access to the target cell using the configured uplink grant associated with the target cell, as shown at block 1120 of FIG. 11D.

[0139] 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, radio access node 202, source access node 202A and / or candidate target access node 202B, 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.

[0140] According to some example implementati ons, at least some of the method 900 described with respect to FIG. 9 may be carried out by an apparatus including means for performing functions corresponding steps of the method. Similarly, at least some of the method 1000 described with respect to FIGS. 10A-10F may be carried out by an apparatus including means for performing functions corresponding steps of the method. And at leastsome of the method 1100 described with respect to FIGS. 11 A-l ID may be carried out by an apparatus including means for performing functions corresponding steps of the method. 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. Other examples of a suitable apparatus may include a user equipment, user device, user terminal or the like.

[0141] 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.

[0142] 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).

[0143] 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 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 symmetricmulti-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.

[0144] 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.

[0145] 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.

[0146] 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 beconfigured 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.

[0147] 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.

[0148] Execution of the instructions 1206 by the processing circuitry 1202, or storage of the instructions in 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 hardwarebased computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions.

[0149] 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 including 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, processingcircuitry 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.

[0150] 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.

[0151] Retrieval, loading and execution of instructions including 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.

[0152] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0153] Clause 1. An apparatus implemented by a source access node providing a source cell serving a user equipment, UE, the apparatus comprising: at least one memory configuredto 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 baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieve UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; send a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; determine to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; send a handover command to the UE to trigger the handover; and in connection with the handover, send handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE- specific configuration information for the target cell based on the handover information.

[0154] Clause 2. The apparatus of clause 1, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

[0155] Clause 3. The apparatus of clause 1 or clause 2, wherein the message sent to the UE further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0156] Clause 4. The apparatus of clause 3, wherein the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells, and the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further select the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

[0157] Clause 5. The apparatus of clause 3 or clause 4, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further retrieve the one or more random access preambles from the one or more LTM candidate target cells.

[0158] Clause 6. The apparatus of any of clauses 1 to 5, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more neighboring cells, and wherein the message sent to the UE further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

[0159] Clause 7. The apparatus of any of clauses 1 to 6, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further retrieve one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,- less access to the one or more LTM candidate target cells, and the message sent to the UE further includes the one or more indications of the one or more uplink grants.

[0160] Clause 8. An apparatus implemented by a source access node providing a source cell serving an user equipment, UE, the apparatus comprising: means for receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; means for retrieving UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE- specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; means for sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; means for determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; means for sending a handover command to the UE to trigger the handover; and inconnection with the handover, means for sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[0161] Clause 9. The apparatus of clause 8, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the apparatus further comprises means for receiving an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

[0162] Clause 10. The apparatus of clause 8 or clause 9, wherein the message sent to the UE further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0163] Clause 11. The apparatus of clause 10, wherein the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells, and the apparatus further comprises means for selecting the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

[0164] Clause 12. The apparatus of clause 10 or clause 11, wherein the apparatus further comprises means for retrieving the one or more random access preambles from the one or more LTM candidate target cells.

[0165] Clause 13. The apparatus of any of clauses 8 to 12, wherein the apparatus further comprises means for receiving one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for random access channel, RACE!, -less access to the one or more neighboring cells, and wherein the message sent to the UE further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

[0166] Clause 14. The apparatus of any of clauses 8 to 13, wherein the apparatus further comprises means for retrieving one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells, andthe message sent to the UE further includes the one or more indications of the one or more uplink grants.

[0167] Clause 15. A method performed by a source access node providing a source cell serving a user equipment, UE, the method comprising: receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieving UE- specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; sending a handover command to the UE to trigger the handover; and in connection with the handover, sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[0168] Clause 16. The method of clause 15, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the method further comprises receiving an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

[0169] Clause 17. The method of clause 15 or clause 16, wherein the message sent to the UE further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0170] Clause 18. The method of clause 17, wherein the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells, and the method further comprises selecting the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

[0171] Clause 19. The method of clause 17 or clause 18, wherein the method further comprises retrieving the one or more random access preambles from the one or more LTM candidate target cells.

[0172] Clause 20. The method of any of clauses 15 to 19, wherein the method further comprises receiving one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more neighboring cells, and wherein the message sent to the UE further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

[0173] Clause 21. The method of any of clauses 15 to 20, wherein the method further comprises retrieving one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells, and the message sent to the UE further includes the one or more indications of the one or more uplink grants.

[0174] Clause 22. 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 a source access node providing a source cell serving a user equipment, UE, to at least: receive baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; retrieve UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE-specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; send a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; determine to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information;send a handover command to the UE to trigger the handover; and in connection with the handover, send handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

[0175] Clause 23. The computer-readable storage medium of clause 22, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the source access node to further receive an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

[0176] Clause 24. The computer-readable storage medium of clause 22 or clause 23, wherein the message sent to the UE further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0177] Clause 25. The computer-readable storage medium of clause 24, wherein the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells, and the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the source access node to further select the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

[0178] Clause 26. The computer-readable storage medium of clause 24 or clause 25, 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 source access node to further retrieve the one or more random access preambles from the one or more LTM candidate target cells.

[0179] Clause 27. The computer-readable storage medium of any of clauses 22 to 26, 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 source access node to further receive one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for randomaccess channel, RACH,-less access to the one or more neighboring cells, and wherein the message sent to the UE further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

[0180] Clause 28. The computer-readable storage medium of any of clauses 22 to 27, 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 source access node to further retrieve one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells, and the message sent to the UE further includes the one or more indications of the one or more uplink grants.

[0181] Clause 29. An apparatus comprising means for performing the method of any of clauses 15 to 21.

[0182] Clause 30. 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 15 to 21.

[0183] Clause 31. 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 15 to 21.

[0184] Clause 32. 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 15 to 21.

[0185] Clause 33. An apparatus implemented by a target 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 apparatus to at least: send one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receive a request from the source access node for UE-specific layer 1, LI, measurement configurationinformation for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determine the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; send the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receive handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determine UE-specific configuration information for the target cell based on the handover information associated with the UE; and send the UE-specific configuration information for the target cell to the UE.

[0186] Clause 34. The apparatus of clause 33, wherein the UE-specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

[0187] Clause 35. The apparatus of clause 33 or clause 34, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: determine updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells; and send the updated dynamic LI configuration information to the source access node.

[0188] Clause 36. The apparatus of any of clauses 33 to 35, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: receive one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells; determine one or more timing advance values based on the one or more random access preambles; and send the one or more timing advance values towards the UE.

[0189] Clause 37. The apparatus of clause 36, wherein the one or more baseline configurations sent to the source access node include one or more pools of random accesspreambles from which the random access preambles are selected by the source access node and sent to the UE.

[0190] Clause 38. The apparatus of clause 36 or clause 37, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: receive a request from the source access node for the one or more random access preambles; and send the one or more random access preambles to the source access node from which the one or more random access preambles are sent to the UE.

[0191] Clause 39. The apparatus of any of clauses 33 to 38, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: determine one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more cells; and send one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE.

[0192] Clause 40. The apparatus of any of clauses 33 to 39, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: prepare one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells; and send one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE.

[0193] Clause 41. An apparatus implemented by a target access node, the apparatus comprising: means for sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving an user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; means for receiving a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; means for determining the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; means for sending the UE-specificLI measurement configuration information for the one or more LTM candidate target cells to the source access node; means for receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; means for determining UE- specific configuration information for the target cell based on the handover information associated with the UE; and means for sending the UE-specific configuration information for the target cell to the UE.

[0194] Clause 42. The apparatus of clause 41, wherein the UE-specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

[0195] Clause 43. The apparatus of clause 41 or clause 42, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the apparatus further comprises: means for determining updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells; and means for sending the updated dynamic LI configuration information to the source access node.

[0196] Clause 44. The apparatus of any of clauses 41 to 43, wherein the apparatus further comprises: means for receiving one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells; means for determining one or more timing advance values based on the one or more random access preambles; and means for sending the one or more timing advance values towards the UE.

[0197] Clause 45. The apparatus of clause 44, wherein the one or more baseline configurations sent to the source access node include one or more pools of random access preambles from which the random access preambles are selected by the source access node and sent to the UE.

[0198] Clause 46. The apparatus of clause 44 or clause 45, wherein the apparatus further comprises: means for receiving a request from the source access node for the one or more random access preambles; and means for sending the one or more random access preambles tothe source access node from which the one or more random access preambles are sent to theUE.

[0199] Clause 47. The apparatus of any of clauses 41 to 46, wherein the apparatus further comprises: means for determining one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more cells; and means for sending one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE.

[0200] Clause 48. The apparatus of any of clauses 41 to 47, wherein the apparatus further comprises: means for preparing one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells; and means for sending one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE.

[0201] Clause 49. A method performed by a target access node, the method comprising: sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receiving a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determining the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; sending the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determining UE-specific configuration information for the target cell based on the handover information associated with the UE; and sending the UE-specific configuration information for the target cell to the UE.

[0202] Clause 50. The method of clause 49, wherein the UE-specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

[0203] Clause 51. The method of clause 49 or clause 50, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the method further comprises: determining updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells; and sending the updated dynamic LI configuration information to the source access node.

[0204] Clause 52. The method of any of clauses 49 to 51, wherein the method further comprises: receiving one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells; determining one or more timing advance values based on the one or more random access preambles; and sending the one or more timing advance values towards the UE.

[0205] Clause 53. The method of clause 52, wherein the one or more baseline configurations sent to the source access node include one or more pools of random access preambles from which the random access preambles are selected by the source access node and sent to the UE.

[0206] Clause 54. The method of clause 52 or clause 53, wherein the method further comprises: receiving a request from the source access node for the one or more random access preambles; and sending the one or more random access preambles to the source access node from which the one or more random access preambles are sent to the UE.

[0207] Clause 55. The method of any of clauses 49 to 54, wherein the method further comprises: determining one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel, RACE!, -less access to the one or more cells; and sending one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE.

[0208] Clause 56. The method of any of clauses 49 to 55, wherein the method further comprises: preparing one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells; and sending one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE.

[0209] Clause 57. 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 a target access node to at least: send one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receive a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determine the UE- specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; send the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receive handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determine UE-specific configuration information for the target cell based on the handover information associated with the UE; and send the UE-specific configuration information for the target cell to the UE.

[0210] Clause 58. The computer-readable storage medium of clause 57, wherein the UE- specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

[0211] Clause 59. The computer-readable storage medium of clause 57 or clause 58, wherein the default configuration information includes static LI configuration information anddynamic LI configuration information, and the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the target access node to further at least: determine updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells; and send the updated dynamic LI configuration information to the source access node.

[0212] Clause 60. The computer-readable storage medium of any of clauses 57 to 59, 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 target access node to further at least: receive one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells; determine one or more timing advance values based on the one or more random access preambles; and send the one or more timing advance values towards the UE.

[0213] Clause 61. The computer-readable storage medium of clause 60, wherein the one or more baseline configurations sent to the source access node include one or more pools of random access preambles from which the random access preambles are selected by the source access node and sent to the UE.

[0214] Clause 62. The computer-readable storage medium of clause 60 or clause 61, 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 target access node to further at least: receive a request from the source access node for the one or more random access preambles; and send the one or more random access preambles to the source access node from which the one or more random access preambles are sent to the UE.

[0215] Clause 63. The computer-readable storage medium of any of clauses 57 to 62, 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 target access node to further at least: determine one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel, RACE!, -less access to the one or more cells; and send one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE.

[0216] Clause 64. The computer-readable storage medium of any of clauses 57 to 63, 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 target access node to further at least: prepare one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells; and send one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE.

[0217] Clause 65. An apparatus comprising means for performing the method of any of clauses 49 to 56.

[0218] Clause 66. 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 49 to 56.

[0219] Clause 67. 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 49 to 56.

[0220] Clause 68. 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 49 to 56.

[0221] Clause 69. An apparatus implemented by a user equipment, UE, served by a source cell provided by a source 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 apparatus to at least: receive, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; report LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receive a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carry out the handover in whichUE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0222] Clause 70. The apparatus of clause 69, wherein the message received from the source access node further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0223] Clause 71. The apparatus of clause 70, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further at least: send the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells; receive one or more timing advance values from the one or more target access nodes based on the one or more random access preambles; and synchronize the UE to the one or more LTM candidate target cells based on the one or more timing advance values.

[0224] Clause 72. The apparatus of any of clauses 69 to 71, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell, and wherein the apparatus caused to carry out the handover includes the apparatus caused to: monitor the search space associated with the target cell for a dynamic uplink grant; and perform a random access channel, RACH,-less access to the target cell using the dynamic uplink grant.

[0225] Clause 73. The apparatus of any of clauses 69 to 72, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the target cell, and wherein the apparatus caused to carry out the handover includes the apparatus caused to perform a random access channel, RACH,-less access to the target cell using the configured uplink grant associated with the target cell.

[0226] Clause 74. An apparatus implemented by an user equipment, UE, served by a source cell provided by a source access node, the apparatus comprising: means for receiving,from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; means for reporting LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; means for receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and means for carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0227] Clause 75. The apparatus of clause 74, wherein the message received from the source access node further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0228] Clause 76. The apparatus of clause 75, wherein the apparatus further comprises: means for sending the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells; means for receiving one or more timing advance values from the one or more target access nodes based on the one or more random access preambles; and means for synchronizing the UE to the one or more LTM candidate target cells based on the one or more timing advance values.

[0229] Clause 77. The apparatus of any of clauses 74 to 76, wherein the apparatus further comprises means for receiving, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell, and wherein the means for carrying out the handover includes: means for monitoring the search space associated with the target cell for a dynamic uplink grant; and means for performing a random access channel, RACH,-less access to the target cell using the dynamic uplink grant.

[0230] Clause 78. The apparatus of any of clauses 74 to 77, wherein the apparatus further comprises means for receiving, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the targetcell, and wherein the means for carrying out the handover includes means for performing a random access channel, RACH,-less access to the target cell using the configured uplink grant associated with the target cell.

[0231] Clause 79. A method performed by a user equipment, UE, served by a source cell provided by a source access node, the method comprising: receiving, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE- specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; reporting LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0232] Clause 80. The method of clause 79, wherein the message received from the source access node further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0233] Clause 81. The method of clause 80, wherein the method further comprises: sending the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells; receiving one or more timing advance values from the one or more target access nodes based on the one or more random access preambles; and synchronizing the UE to the one or more LTM candidate target cells based on the one or more timing advance values.

[0234] Clause 82. The method of any of clauses 79 to 81, wherein the method further comprises receiving, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell, and wherein carrying out the handover includes: monitoring the search space associated with the target cell for a dynamic uplink grant; and performing a random access channel, RACH,-less access to the target cell using the dynamic uplink grant.

[0235] Clause 83. The method of any of clauses 79 to 82, wherein the method further comprises receiving, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the target cell, and wherein carrying out the handover includes performing a random access channel, RACH,- less access to the target cell using the configured uplink grant associated with the target cell.

[0236] Clause 84. 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 a user equipment, UE, served by a source cell provided by a source access node to at least: receive, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; report LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receive a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carry out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

[0237] Clause 85. The computer-readable storage medium of clause 84, wherein the message received from the source access node further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

[0238] Clause 86. The computer-readable storage medium of clause 85, 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 UE to further at least: send the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells; receive one or more timing advance values from the one or more target access nodes based on the one or more random access preambles; and synchronize the UE to the one or more LTM candidate target cells based on the one or more timing advance values.

[0239] Clause 87. The computer-readable storage medium of any of clauses 84 to 86, 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 UE to further receive, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell, and wherein the UE caused to carry out the handover includes the UE caused to: monitor the search space associated with the target cell for a dynamic uplink grant; and perform a random access channel, RACH,-less access to the target cell using the dynamic uplink grant.

[0240] Clause 88. The computer-readable storage medium of any of clauses 84 to 87, 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 UE to further receive, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the target cell, and wherein the UE caused to carry out the handover includes the UE caused to perform a random access channel, RACH,-less access to the target cell using the configured uplink grant associated with the target cell.

[0241] Clause 89. An apparatus comprising means for performing the method of any of clauses 79 to 83.

[0242] Clause 90. 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 79 to 83.

[0243] Clause 91. 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 79 to 83.

[0244] Clause 92. 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 79 to 83.

[0245] 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

WHAT IS CLAIMED IS:

1. A method performed by a source access node providing a source cell serving a user equipment, UE, the method comprising: receiving baseline configurations of one or more neighboring cells, the baseline configurations including default configuration information for layer 3, L3, mobility and lower- layer triggered mobility, LTM; retrieving UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more neighboring cells, the UE- specific LI measurement configuration information retrieved based on L3 measurements performed by the UE; sending a message to the UE that includes the default configuration information for the one or more LTM candidate target cells, and the UE-specific LI measurement configuration information for the one or more LTM candidate target cells; determining to execute a handover of the UE to a target cell of the one or more LTM candidate target cells based on LI measurements on the one or more LTM candidate target cells performed by the UE based on the UE-specific LI measurement configuration information; sending a handover command to the UE to trigger the handover; and in connection with the handover, sending handover information associated with the UE to the target cell to enable the target cell to provide the UE with UE-specific configuration information for the target cell based on the handover information.

2. The method of claim 1, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the method further comprises receiving an update of the dynamic LI configuration information for at least one of the one or more neighboring cells.

3. The method of claim 1 or claim 2, wherein the message sent to the UE further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

4. The method of claim 3, wherein the baseline configurations include one or more pools of random access preambles for the one or more neighboring cells, and the method further comprises selecting the one or more random access preambles from the one or more pools of random access preambles for the one or more LTM candidate target cells.

5. The method of claim 3 or claim 4, wherein the method further comprises retrieving the one or more random access preambles from the one or more LTM candidate target cells.

6. The method of any of claims 1 to 5, wherein the method further comprises receiving one or more indications of one or more search spaces associated with the one or more neighboring cells for one or more dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more neighboring cells, and wherein the message sent to the UE further includes one or more of the one or more indications of one or more of the one or more search spaces associated with the one or more LTM candidate target cells.

7. The method of any of claims 1 to 6, wherein the method further comprises retrieving one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,- less access to the one or more LTM candidate target cells, and the message sent to the UE further includes the one or more indications of the one or more uplink grants.

8. An apparatus comprising means for performing the method of any of claims 1 to 7.

9. A method performed by a target access node, the method comprising: sending one or more baseline configurations of one or more cells provided by the target access node to a source access node providing a source cell serving a user equipment, UE, the one or more baseline configurations including default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM; receiving a request from the source access node for UE-specific layer 1, LI, measurement configuration information for one or more LTM candidate target cells selected from the one or more cells, the request based on L3 measurements performed by the UE; determining the UE-specific LI measurement configuration information for the one or more LTM candidate target cells based on the L3 measurements; sending the UE-specific LI measurement configuration information for the one or more LTM candidate target cells to the source access node; receiving handover information associated with the UE from the source access node in connection with a determination to execute a handover of the UE to a target cell of the one or more LTM candidate cells; determining UE-specific configuration information for the target cell based on the handover information associated with the UE; and sending the UE-specific configuration information for the target cell to the UE.

10. The method of claim 9, wherein the UE-specific LI measurement configuration information that is determined includes one or more measurement resources for the UE to perform LI measurements on the one or more LTM candidate target cells, and excludes reporting resources for the UE to report LI measurements to the one or more LTM candidate target cells.

11. The method of claim 9 or claim 10, wherein the default configuration information includes static LI configuration information and dynamic LI configuration information, and the method further comprises: determining updated dynamic LI configuration information based on a change in the dynamic LI configuration information for at least one of the one or more cells; andsending the updated dynamic LI configuration information to the source access node.

12. The method of any of claims 9 to 11, wherein the method further comprises: receiving one or more random access preambles from the UE for early timing advance acquisition towards the one or more LTM candidate target cells; determining one or more timing advance values based on the one or more random access preambles; and sending the one or more timing advance values towards the UE.

13. The method of claim 12, wherein the one or more baseline configurations sent to the source access node include one or more pools of random access preambles from which the random access preambles are selected by the source access node and sent to the UE.

14. The method of claim 12 or claim 13, wherein the method further comprises: receiving a request from the source access node for the one or more random access preambles; and sending the one or more random access preambles to the source access node from which the one or more random access preambles are sent to the UE.

15. The method of any of claims 9 to 14, wherein the method further comprises: determining one or more search spaces associated with the one or more cells for dynamic uplink grants usable by the UE for random access channel, RACH,-less access to the one or more cells; and sending one or more indications of the one or more search spaces to the source access node from which the one or more indications are sent to the UE.

16. The method of any of claims 9 to 15, wherein the method further comprises: preparing one or more configured uplink grants associated with the one or more LTM candidate target cells usable by the UE for random access channel, RACH,-less access to the one or more LTM candidate target cells; andsending one or more indications of the one or more configured uplink grants to the source access node from which the one or more indications are sent to the UE.

17. An apparatus comprising means for performing the method of any of claims 9 to 16.

18. A method performed by a user equipment, UE, served by a source cell provided by a source access node, the method comprising: receiving, from the source access node, a message that includes default configuration information for layer 3, L3, mobility and lower-layer triggered mobility, LTM, to one or more LTM candidate target cells, and UE-specific layer 1, LI, measurement configuration information for the one or more LTM candidate target cells; reporting LI measurements on the one or more LTM candidate target cells based on the UE-specific LI measurement configuration information; receiving a handover command from the source access node to trigger a handover of the UE to a target cell of the one or more LTM candidate target cells; and carrying out the handover in which UE-specific configuration information for the target cell is received from a target access node providing the target cell.

19. The method of claim 18, wherein the message received from the source access node further includes one or more random access preambles usable by the UE for early timing advance acquisition towards the one or more LTM candidate target cells.

20. The method of claim 19, wherein the method further comprises: sending the one or more random access preambles to one or more target access nodes providing the one or more LTM candidate target cells; receiving one or more timing advance values from the one or more target access nodes based on the one or more random access preambles; and synchronizing the UE to the one or more LTM candidate target cells based on the one or more timing advance values.

21. The method of any of claims 18 to 20, wherein the method further comprises receiving, from the source access node, one or more indications of one or more search spaces associated with the one or more LTM candidate target cells for dynamic uplink grants, and the one or more search spaces include a search space associated with the target cell, and wherein carrying out the handover includes: monitoring the search space associated with the target cell for a dynamic uplink grant; and performing a random access channel, RACH,-less access to the target cell using the dynamic uplink grant.

22. The method of any of claims 18 to 21, wherein the method further comprises receiving, from the source access node, one or more indications of one or more configured uplink grants associated with the one or more LTM candidate target cells, and the one or more configured uplink grants include an uplink grant associated with the target cell, and wherein carrying out the handover includes performing a random access channel, RACH,-less access to the target cell using the configured uplink grant associated with the target cell.

23. An apparatus comprising means for performing the method of any of claims 18 to 22.

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