Ad-HOC measurement gap for mobility measurement

Abstract

A method performed by a user equipment (UE) is provided. The method includes receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell. The method includes activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE. The method includes performing at least one measurement on the at least one neighbor cell in the ad- hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell. And the method includes accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

Description

AD-HOC MEASUREMENT GAP FOR MOBILITY MEASUREMENTTECHNOLOGICAL FIELD

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

[0002] A telecommunications system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and / or other nodes by providing carriers between the various entities involved in the communications path. A telecommunications system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and / or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

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

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

[0005] The telecommunications system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how operations should be achieved. Communication protocols and / or parameters which shall be used for connection of the various entities are also typically defined. One example of a telecommunications system is the Universal Mobile Telecommunications System (UMTS). Other examples of telecommunications systems are Long-Term Evolution (LTE), LTE Advanced and the so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP).BRIEF SUMMARY

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

[0007] Some example implementations provide an apparatus implemented by a radio access node providing a serving cell, the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a configuration of reference signal resources for at least one neighbor cell; determine an ad-hoc measurement gap for a user equipment served by the serving cell, wherein the ad-hoc measurement gap is determined based on the reference signal resources; and transmit, to the UE, a control message including a configuration of the ad- hoc measurement gap to trigger the UE to perform at least one measurement of the at least one neighbor cell in the ad-hoc measurement gap.

[0008] Some example implementations provide an apparatus implemented by a radio access node providing a serving cell, the apparatus comprising: means for receiving a configuration of reference signal resources for at least one neighbor cell; means for determining an ad-hoc measurement gap for an user equipment served by the serving cell,wherein the ad-hoc measurement gap is determined based on the reference signal resources; and means for transmitting, to the UE, a control message including a configuration of the ad-hoc measurement gap to trigger the UE to perform at least one measurement of the at least one neighbor cell in the ad-hoc measurement gap.

[0009] Some example implementations provide a method performed by a radio access node providing a serving cell, the method comprising: receiving a configuration of reference signal resources for at least one neighbor cell; determining an ad-hoc measurement gap for a user equipment served by the serving cell, wherein the ad-hoc measurement gap is determined based on the reference signal resources; and transmitting, to the UE, a control message including a configuration of the ad-hoc measurement gap to trigger the UE to perform at least one measurement of the at least one neighbor cell in the ad-hoc measurement gap.

[0010] Some example implementations provide an apparatus implemented by a user equipment (UE), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry onfigured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, the control message including a configuration of an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; perform at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and access the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0011] Some example implementations provide an apparatus implemented by an user equipment (UE), the apparatus comprising: means for receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, the control message including a configuration of an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; means for performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the servingcell; and means for accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0012] Some example implementations provide a method performed by a user equipment (UE), the method comprising: receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, the control message including a configuration of an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0013] Some example implementations provide an apparatus implemented by 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 a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; activate an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; perform at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and access the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0014] Some example implementations provide an apparatus implemented by an user equipment (UE), the apparatus comprising: means for receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; means for activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; means for performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and means for accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0015] Some example implementations provide a method performed by a user equipment (UE), the method comprising: receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0016] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. The present disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable unless the context of the disclosure clearly dictates otherwise.

[0017] 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)

[0018] 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:

[0019] 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;

[0020] FIG. 2 illustrates a 5G deployment of a PLMN, according to some example implementations;

[0021] FIG. 3 is a signaling chart for a L1 / L2 -triggered mobility, also known as lower-layer triggered mobility (LTM) procedure;

[0022] FIGS. 4A and 4B illustrate a signaling chart for an LTM procedure in a central / centralized unit - distributed unit (CU-DU) split architecture;

[0023] FIG. 5 illustrates a measurement gap pattern configured for a user equipment (UE) for a serving cell, and occasions of a reference signal transmitted by a candidate cell, relative to a control message transmitted by the serving cell for an early timing advance acquisition with the candidate cell;

[0024] FIG. 6 illustrates the measurement gap pattern of FIG. 5, and an additional ad- hoc measurement gap that overlaps a first available occasion of the reference signal transmitted by the candidate cell after the control message transmitted by the serving cell, according to some example implementations;

[0025] FIG. 7 illustrates a format of an information element (IE) for a medium access control (MAC) control element (CE) to configure ad-hoc measurement gap for one or more candidate cells, according to some example implementations;

[0026] FIGS. 8 A and 8B illustrate a signaling chart for an LTM procedure including an ad-hoc measurement gap, according to some example implementations;

[0027] FIGS. 9Aand 9B illustrate a signaling chart for an LTM procedure including an ad-hoc measurement gap, according to other example implementations;

[0028] FIG. 10 is a flowchart illustrating various steps in a method performed by a radio access node providing a serving cell, according to various example implementations;

[0029] FIG. 11 is a flowchart illustrating various steps in a method performed by a user equipment (UE), according to various example implementations;

[0030] FIG. 12 is a flowchart illustrating various steps in a method performed by a UE, according to various example implementations; and

[0031] FIG. 13 illustrates an apparatus according to some example implementations.DETAILED DESCRIPTION

[0032] 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.

[0033] 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.

[0034] 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 orindirectly by various means including via one or more switches, routers, gateways, access points or the like.

[0035] 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.

[0036] 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.

[0037] The above definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0038] 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 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 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.

[0039] 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 3 GPP, 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.

[0040] In operation, these UEs 110 may be configured to connect to one or more of the RANs 108 according to their particular radio access technologies to thereby access a particular CN 106 of a PLMN 102, or to access one or more of the external data networks 104 (e.g., the Internet). The external data network may be configured to provide Internet access, operator services, 3rd party services, etc. For example, the International Telecommunication Union (ITU) has classified 5G mobile network services into three categories: enhanced mobile broadband (eMBB), ultra- reliable and low-latency communications (URLLC), and massive machine type communications (mMTC) or massive internet of things (MIoT).

[0041] 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 asIEEE 802.11 (Wi-Fi), IEEE 802.15 (including 802.15.1 (WPAN / Bluetooth), 802.15.4 (Zigbee) and 802.15.6 (WBAN)), Bluetooth, Bluetooth Low Energy (BLE), ultra wideband (UWB), and the like. Generally, a radio access technology may refer to any 2G, 3G, 4G, 5G, 6G or higher generation mobile communication technology and their different versions, as well as to any other wireless radio access technology that may be arranged to interwork with such a mobile communication technology to provide access to the CN 106 of a mobile network operator (MNO).

[0042] In various examples, a RAN 108 may be configured as one or more macrocells, microcells, picocells, femtocells or the like. The RAN may generally include one or more radio access nodes that are configured to interact with UEs 110. In various examples, a radio access node may be referred to as a base station (BS), access point (AP), base transceiver station (BTS), Node B (NB), evolved NB (eNB), macro BS, NB (MNB) or eNB (MeNB), home BS, NB (HNB) or eNB (HeNB), next generation NB (gNB), enhanced gNB (en-gNB), next generation eNB (ng-eNB), or the like. The RAN may include some type of network controlling / governing entity responsible for control of the radio access nodes. The network controlling / governing entity and radio access node may be separate or integrated into a single apparatus. The network controlling / governing entity may include processing circuity configured to carry out various management functions, etc. The processing circuity may be associated with a memory, computer- readable storage medium or database for maintaining information required in the management functions.

[0043] A RAN 108 may be centralized or distributed. In various examples, components of a RAN may be interconnected by Ethernet, Gigabit Ethernet, Asynchronous Transfer Mode (ATM), optical fiber, dark fiber, passive wavelength division multiplexing (WDM), WDM passive optical network (WDM-PON), optical transport network (OTN), time sensitive networking (TSN) and / or any other data link layer network, possibly including radio links. The RAN may be connected to a CN 106 through one or more gateways, network functions or the like.

[0044] As will be appreciated, a PLMN 102 may be deployed in a number of different manners. In a 4GLTE deployment, the EPC is the CN 106, and the evolved UMTS terrestrial radio access network (E-UTRAN) is the RAN 108; and the E-UTRANincludes one or more eNBs (radio access nodes) configured to connect UEs 110 to the E- UTRAN to thereby access the EPC. As shown in FIG. 2, in a 5G deployment 200, the 5GC 202 is the CN, and the next generation (NG) radio access network (NG-RAN) 204 is the RAN; and the NG-RAN includes one or more gNBs 206 (radio access nodes) configured to connect UEs 110 to the NG-RAN to thereby access the 5GC (at times referred to as the NGC). The term ‘gNB’ in 5G may correspond to the eNB in 4G LTE.

[0045] Some deployments of 4G LTE and 5G in particular are considered standalone (SA) deployments. Other deployments combine 4G LTE and 5G technologies, and are referred to as non-standalone (NSA) deployments. In some deployments, the E-UTRAN includes one or more ng-eNBs that are configured to communicate with the 5GC, and that may also be configured to communicate with one or more gNBs. Similarly, in another deployment, the NG-RAN may include one or more en-gNBs that are configured to communicate with the EPC, and that may also be configured to communicate with one or more eNBs. In various instances, a single UE 110, a dual-mode or multimode UE, may support multiple (two or more) RANs — thereby being configured to connect to multiple RANs, such as 4G LTE and 5G.

[0046] In some deployments, operations of a gNB 206 or other radio access node may be distributed or functionally split into components including one or more remote radio head (RRHs) or radio units (RUs) 208, and a baseband unit (BBU); and in some architectures, the BBU may be split into a distributed unit (DU) 210 and a central / centralized unit (CU) 212, such as a server, host or node. In some architectures, the RRH / RU and DU may be co-located. It is also possible that node operations may be distributed among a plurality of servers, hosts or nodes. It should also be understood that the distribution of work between CN operations and radio access node operations may vary depending on implementation.

[0047] As shown and described, for example, some 5G deployments may be based on a so-called CU-DU split including one or more DUs 210 and a CU 212. One gNB-CU (central node) may control one or more gNB-DUs. The gNB-CU may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some example implementations, however, the gNB-DUs (also called DU) may include, for example, a radio link control (RLC), medium access control (MAC) layer and aphysical (PHY) layer, whereas the gNB-CU (also called a CU) may include the layers above the RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC), and an internet protocol (IP) layer. Other functional splits are also possible. It is considered that a skilled person is familiar with the open systems interconnection (OSI) model and the functionalities within each layer.

[0048] In some example implementations, the server or CU 212 may generate a virtual network through which the server communicates with the radio node. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Such virtual network may provide flexible distribution of operations between the server and the radio head / node. In practice, any digital signal processing task may be performed in either the CU or the DU 210, and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

[0049] Currently in 3 GPP, mainstream mobility has been conducted using higher layer (L3 or RRC controlled) mobility. In this regard, L3 handover based mobility is a well-known and proven method for ensuring a robust way of handing over the UE 110 from one serving cell (source cell) of a radio access node 202 to a new serving cell (target cell) of the same or another radio access node. The method has been used at least since GSM and is still in use in 5GNR. It is expected that L3 mobility (legacy handover) will also be commonly used in the future.

[0050] L1 / L2 -triggered mobility, or lower-layer triggered mobility (LTM) moves the execution of the ‘handover’ from one cell to another from higher layers (L3), such as RRC, to lower layers. These lower layers may be either PHY (or LI) or MAC (or L2). LTM may reduce latency, overhead and interruption time when compared to L3 handover based mobility. In a CU-DU split architecture, LTM may support one or more of intra- DU mobility, intra-CU inter-DU mobility, or inter-CU inter-DU mobility.

[0051] FIG. 3 illustrates a signaling chart 300 for an LTM procedure of a UE 110 in a RRC connected state with a gNB 206, which has been proposed. During LTM preparation, as shown at step 301, the UE sends a L3 measurement report to the gNB, which decides to use LTM and initiate LTM candidate preparation. The gNB at step 302transmits a RRC reconfiguration message to the UE, including the configuration of one or more candidate cells. The RRC reconfiguration message may also include a configuration of LI measurement reporting for LTM execution. The UE stores the configurations, and the UE at step 303 transmits a RRC reconfiguration complete message to the gNB.

[0052] An early synchronization of the UE 110 with the candidate cell(s) follows LTM preparation. As shown at step 304, the UE 110 performs downlink (DL) and may perform uplink (UL) synchronization with the candidate cell(s). For DL synchronization, the gNB 206 may perform an early activation of configured transmission configuration indicator (TCI) states for the candidate cell(s), such as via a MAC control element (MAC CE). The UE may receive this TCI state activation MAC CE, and begin monitoring configured DL reference signal (RS) resources associated with the activate TCI states to synchronize with the candidate cell(s).

[0053] During early UL synchronization, the UE 110 may acquire a timing advance (TA) of respective one or more of the candidate cell(s). In this regard, the gNB 206 may request that the UE to perform early TA acquisition for example via contention free random access (CFRA) triggered by a physical downlink control channel (PDCCH) order (using downlink control information (DCI) format 1 0) or other TA acquisition command, following which the UE 110 sends a random access channel (RACH) preamble on the physical random access channel (PRACH) towards an indicated candidate cell. In 3 GPP, the random access (RA) or RACH preamble is sent as a first message (msgl) as part of a RA or RACH procedure; and accordingly, the RA or RACH preamble may at times be referred to as msgl. In order to minimize the data interruption of the gNB due to CFRA towards the candidate cell(s), the UE may not receive a random access response (RAR) from the network (from the candidate cell) for the purpose of TA value acquisition, and the TA value to be used when accessing the candidate cell may be indicated in a subsequent cell switch command.

[0054] This early synchronization may reduce interruption during LTM execution, as compared to L3 handover based mobility. In this regard, the TA may be used to control the timing of uplink transmissions of a UE toward the candidate cell(s). The UE may likewise have an acquired TA of the cell of the gNB to control the timing of uplink transmissions toward the gNB.

[0055] During LTM execution, the UE 110 performs LI measurements on the configured candidate cell(s), and the UE at step 305 transmits LI measurement reports to the gNB 206. The gNB decides to execute a cell switch, and selects one of the candidate cell(s) as a target cell for the cell switch. The gNB then at step 306 transmits a cell switch command, such as a MAC CE, to trigger cell switch. The UE switches to the configuration of the target cell; and if the TA of the target cell (from step 304) is no longer available (or otherwise not acquired), the UE at step 307 initiates a RACH procedure with the target cell to acquire the TA of the target cell. In some cases, the cell switch command may include CFRA RACH related parameters for the UE to perform the RACH procedure. The UE then at step 308 indicates successful completion of the cell switch.

[0056] FIGS. 4A and 4B illustrate a signaling chart 400 for an LTM procedure in a CU-DU split architecture, including a CU 212, a source DU (S-DU) 210Afor a serving cell, and a target DU (T-DU) 210B for a target cell. During preparation for LTM, as shown at step 401, the UE 110 sends a L3 measurement report to the CU via the S-DU, and the CU at step 402 decides prepare one or more candidate cells (DUs) for LTM. As shown at steps 403, 404, 405 and 406, the CU proceeds with the UE context setup / modification procedures. At step 407, the CU generates RRC reconfiguration(s) for the configured candidate cell(s); and at step 408, the CU provides the configurations to the UE 110 via the S-DU.

[0057] At step 409, the UE 110 sends a RRC reconfiguration complete to the CU 212 via the S-DU 210A.

[0058] During execution, at step 410, the UE 110 performs DL synchronization with the candidate cell(s). For DL synchronization, the S-DU 212A / cell may send a MAC CE to the UE for an early activation of configured TCI states for the candidate cell(s). The UE may receive the MAC CE (TCI state activation MAC CE), and begin monitoring configured DL resources associated with the activate TCI states to synchronize with the candidate cell(s).

[0059] At step 411 onwards, the UE 110 performs LI measurements on the configured candidate cell(s), and transmits LI measurement reports to the S-DU 210A. The S-DU at step 412 decides to trigger the TA acquisition of the candidate cell(s)(including the cell of T-DU 210B), and the S-DU at step 413 transmits a a PDCCH order or other TA acquisition command to the UE. The UE at step 414 transmits a RACH preamble (a random access preamble) to the candidate cell(s) (T-DU 210B / cell) to signal the candidate cell(s) to estimate the TA between the UE and the candidate cell(s). And at step 415, the S-DU 210A / cell receives a RAR from respective ones of the candidate cell(s) indirectly via the CU 212.

[0060] The UE 110 at step 416 transmits LI measurements of the candidate cell(s) to the S-DU 210A. The S-DU at steps 417 and 418 decides to initiate a cell change to the T- DU 210B / cell, and transmits a cell switch command (e.g., MAC-CE) to trigger the cell switch. In examples in which the RAR is received at the S-DU at step 415, the S-DU provides the TA of the T-DU / cell to the UE. If the TA of the T-DU / cell is still valid, the UE skips the RACH procedure at step 419 when executing the cell switch. The UE may otherwise perform the UE-based TA acquisition (if configured in RRC Reconfiguration) or RACH procedure using CFRA RACH related parameters provided in the cell switch command. Otherwise, if no TA is given in the cell switch command, UE-based TA acquisition is not configured, and CFRA RACH configuration is not provided in the cell switch command, then UE perform CBRA RACH procedure to access the target cell. And at steps 420, 421, 422 and 423, the UE, S-DU, T-DU and CU proceed with completion of the LTM procedure.

[0061] In 3 GPP, a UE 110 may perform inter- frequency or inter-RAT DL measurements in specific time intervals called measurement gaps (MGs), during which the UE is not required to conduct reception / transmission from / to the serving cell (e.g., S- DU 210A / cell). These measurement gaps are configured opportunities given to the UE to perform measurements of DL signals for example on the configured carriers needing measurement gaps. Most UEs are unable to perform inter-frequency or inter-RAT measurements without measurement gaps, hence while also transmitting or receiving on serving cell. And for some conditions of intra-frequency measurements in 5G, some UEs may require measurement gaps if those measurements are to be performed for example outside the UE’s currently active bandwidth part (BWP).

[0062] Measurement gaps are periodic according to a measurement gap pattern, and the network may configure the UE 110 with measurement gaps via RRC signaling.Measurement gaps may be regarded as semi-statically configured. In general, a UE may support one measurement gap pattern at a time (if not supporting Per-FR measurement gaps). In some examples, however, a UE may be first configured (by the network) with one measurement pattern and the network may later reconfigure the UE with another measurement gap pattern if needed for neighbor cell measurements, such as for handover purposes. Some UEs may, depending on their capability, support configuration of multiple concurrent measurement gaps.

[0063] Measurements performed by the UE are reported to the network either at LI or RRC (L3), but the RRC configures the measurements, and if there is a need, the measurement gap pattern. If a change in the measurement or measurement gap pattern is needed, such as to change the measured carrier(s), gap periodicity or the starting point of the measurement gap, the network may reconfigure the UE, such as using a RRC reconfiguration.

[0064] As currently, LTM shares the same measurement gap configuration for LI measurements, as configured for L3 measurements. That is, there is no additional measurement gap configuration for LTM.

[0065] In short, a measurement gap configuration may include a number of elements, such as a measurement gap repetition period (MGRP), a gap offset, a measurement gap length (MGL), a measurement gap timing advance (MGTA), and a reference serving cell indicator. The MGRP specifies the gap period, and the MGRP may take values such as 20, 40, 80, 160 milliseconds (ms). For a MGRP set to 40 ms, for example, the measurement gap repeats every 40 ms. The gap offset specifies the starting subframe when the measurement gap starts; and as relative to period, the gap offset may be in the range is 0 to (mgrp - 1).

[0066] The MGL specifies the duration of the measurement gap in milliseconds. The MGL may take values such as 1.5, 3, 3.5, 4, 5.5, and 6 ms. For positioning measurements, 10 and 20 ms are applicable values.

[0067] The MGTA indicates when UE 110 starts measurements in advance of the subframe when the gap starts. The MGTA may take values such as 0, 0.25 or 0.5ms. For frequency range 2 (FR2), 0 and 0.25ms are applicable values.

[0068] The reference serving cell indicator is applicable for dual connectivity scenarios such as NR-E-UTRA dual connectivity (NE-DC) and NR-NR dual connectivity (NR-DC). The reference serving cell indicator indicates which cell’s system frame number (SFN) and subframe numbering to use for gap calculation.

[0069] In some cases, as part of a reporting configuration, the network may ask the UE 110 to report cell global identity (CGI). Although not exactly a measurement, this report may involve the UE 110 acquiring system information from neighbor cells. The relevant messages to decode may include a master information block (MIB) or system information block 1 (SIB1). For this report, the UE may be configured by an appropriate information element (IE) to use autonomous gaps (useAutonomousGaps). In this regard, autonomous gaps may be measurement gaps that are not configured by the network for the UE, and the UE instead selects suitable gaps to receive system information of neighbor cells.

[0070] Recent discussions have focused on when shall be the first reference signal, such as the first synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) or a channel state information reference signal (CSI-RS), for candidate cells early TA acquisition measurement. Shall the UE 110 perform a measurement of the first reference signal immediately without measurement gap, or shall the UE perform the measurement on the first reference signal that overlaps a measurement gap. As shown in FIG. 5, according to current agreement, after the PDCCH order that triggers the early TA acquisition measurement, the first SSB that is overlapped with an already configured measurement gap shall be measured for the PDCCH order. It is understood that having the reference signal aligned with a measurement gap, the UE may avoid missing any data transmission due to the measurement of the candidate cell’s reference signal which could be inter-frequency.

[0071] The current agreement, however, may come with an added delay while the UE 110 waits for the measurement gap. This added delay and the process of performing the early TA acquisition may impact the handover. By the time the measurement gap is available, UE may have missed the best time for measurement or handover. But if the UE performs an inter-frequency measurement outside of a measurement gap, the UE may miss data transmission in the serving cell.

[0072] In view of the foregoing, example implementations of the present disclosure provide a network-triggered, ad-hoc measurement gap, which may in some cases be a one-time measurement gap. The ad-hoc measurement gap may be separate from any measurement gap pattern configured for the UE 110 (in addition to when the UE is configured with a measurement gap pattern). The ad-hoc measurement gap may therefore complement a configured measurement gap (e.g., a configured L3 measurement gap). The ad-hoc measurement gap may help avoid an interruption in data transmission in various scenarios of measurements performed by the UE in the connected mode.

[0073] According to some example implementations, the ad-hoc measurement gap may be triggered by a control message that triggers measurement of at least one neighbor cell. In some example implementations, the control message is a PDCCH order for an early timing advance acquisition. In some other example implementations, the control message is a MAC CE for a TCI state activation, such as for DL synchronization or beam refinement.

[0074] In some examples, the gNB 206 providing the serving cell (e.g., S-DU 210A / cell) may configure the ad-hoc measurement gap. In some of these examples, the ad-hoc measurement gap may be configured using RRC or MAC CE or DCI, such as in the PDCCH order when the serving cell decides to trigger a PDCCH order towards a candidate cell (that is on a different carrier frequency). In some other examples, the PDCCH order may explicitly or implicitly trigger the ad-hoc measurement gap.

[0075] The UE 110 may apply the ad-hoc measurement gap when indicated by the network, such as in the DCI that carries the PDCCH order. One example of a suitable DCI is provided below. In other examples, the ad-hoc measurement gap may be implicitly triggered if configured by the network and UE receives a particular control message (e.g., a PDCCH order). The implicitly triggered ad-hoc measurement gap means that parameters concerning the ad-hoc measurement gap may be configured in an RRC field, and the parameters may be applied around the reference signal that is indicated in the PDCCH order.

[0076] As the ad-hoc measurement gap may be configured and the occasion of the ad-hoc measurement gap may be synchronized in time between the serving cell (e.g., S- DU 210A / cell) and the UE 110, the UE may not be required to conductreception / transmission from / to the serving cell during the ad-hoc measurement gap. As shown in FIG. 6, the UE may instead perform measurements of intra- or inter-frequency DL signals from neighbor cell(s), which may be candidate cell(s) for a handover. Example implementations of the present disclosure may therefore avoid data loss, while also performing PDCCH order early TA acquisition at the earliest possible occasion.

[0077] According to some example implementations, then, a PDCCH-order or other control message may be a trigger for the use of an ad-hoc measurement gap. In other examples, other control messages may trigger the use of an ad-hoc measurement gap. Regarding usage of the ad-hoc measurement gap, if the immediate reference signal that follows the trigger is within a given time limit, for example X number of OFDM symbol away, the UE 110 may automatically apply the ac-hoc measurement gap to the next burst or occasion of the reference signal; otherwise, the UE may apply the ad-hoc measurement gap to the immediate burst of the reference signal.

[0078] Some example implementations also provide a PDCCH / MAC CE format to trigger an ad-hoc measurement gap. In this regard, FIG. 7 illustrates a format of an IE for a MAC CE to configure an ad-hoc measurement gap for one or more candidate cells, according to some example implementations. As shown, the IE may include an ad-hoc measurement gap configuration for each of the candidate cells, and the ad-hoc measurement gap configuration may include a gap offset, MGL, and a reference candidate cell indicator.

[0079] The MAC CE illustrated in FIG. 7 is one example of how the ad-hoc measurement gap configuration may be sent to the UE 110. In some examples, the information for the ad-hoc measurement gap may stand alone in one MAC CE. In other examples, the information may be combined with the MAC CE that triggers a semi- persistent or aperiodic CSI-RS from a candidate cell. If the measured reference signal resource from the candidate cell is a periodic signal, such as SSB or periodic CSI-RS, the triggering of the ad-hoc measurement gap may occupy a standalone MAC CE, as shown.

[0080] The possible elements of the ad-hoc measurement gap configuration as indicated (gap offset, MGL, reference candidate cell identifier) may also be provided in a PDCCH order, such as when the ad-hoc measurement gap is used for PDCCH order earlyTA acquisition. As shown below, the DCI format that triggers the PDCCH order may have additional fields that include this information, as shown below.< DCI format 1 0 with CRC scrambled by C-RNU for PDCCH Order >

[0081] In some examples, the control message (e.g., PDCCH order) that triggers the ad-hoc measurement gap may be the implicit start of an ad-hoc measurement gap. In some of these examples, the ending point of the ad-hoc measurement gap may be defined by specification, such as by a maximum time period or a minimum time period.

[0082] FIGS. 8 A and 8B illustrate a signaling chart 800 for an LTM procedure including an ad-hoc measurement gap, according to some example implementations. The illustrated procedure is for an LTM procedure in intra-CU inter-DU mobility, although it should be understood that example implementations of the present disclosure are also equally applicable to inter-CU inter-DU mobility.

[0083] During preparation for LTM, as shown at step 801, the UE 110 sends a L3 measurement report to the CU via the S-DU, and the CU at step 802 decides prepare one or more candidate cells (DUs) for LTM.. The measurement report may include cell quality measurements of serving cell (e.g., S-DU 210A / cell) and neighbor cells (e.g., T- DU 210B / cell). The UE may be configured by the serving cell to send the measurementreport early when the UE still has a good connection to the serving cell. The CU may use the reported measurements to identify a potential set of candidate cells which the UE can be handed over to which may belong to the same DU or different DUs - as shown in the current example.

[0084] As shown at steps 803, 804, 805 and 806, the CU 212 proceeds with the UE context setup / modification procedures to prepare the candidate cell(s), such as T-DU 210B / cell, for handover. In this regard, the CU may at step 803 send a UE context setup request message to request the preparation of the candidate target cell(s). The T-DU / cell may at step 804 provide the configuration of the UE in a UE context setup response message containing a container from DU to CU. The T-DU may here include reference signal(s) which is intended for its own UE in the configuration. The reference signal(s) may include, for example, periodic / semi-persistent / aperiodic CSI-RS, SSB or the like. The CU may then at steps 805 and 806 request and receive UE context modification from the S-DU 210A / cell.

[0085] At step 807, the CU 212 may generate RRC reconfiguration(s) for the configured candidate cell(s); and at step 808, the CU provides the configurations to the UE 110 via the S-DU 210A / cell. The RRC reconfiguration may include, for example, a measurement reporting configuration for LTM, and a configuration of the prepared candidate cell(s) for the UE to execute when the UE receives a MAC CE command to change the serving cell (perform handover). At step 809, the UE 110 sends a RRC reconfiguration complete to the CU 212 via the S-DU 210A.

[0086] The CU 212 may at step 810 forward the reference signal resource configurations for the candidate cell(s), such as T-DU 210B / cell, to the S-DU 210A / cell, as well as it may include a measured relative time difference (RTD) between the serving cell and the candidate cell(s). As explained below, the S-DU may use at least some of this information to determine an ad-hoc measurement gap during which the UE 110 may perform measurement(s) of reference signal(s) transmitted by the candidate cell(s).

[0087] During execution, at step 811, the UE 110 performs DL synchronization with the candidate cell(s) from the lower-layer configurations received by the UE. For DL synchronization, the S-DU 212A / cell may send a MAC CE to the UE for an earlyactivation of configured TCI states for the candidate cell(s). In some examples, the MAC CE (TCI state activation MAC CE) may include an ad-hoc measurement gap towards selected reference signal resource(s) of the candidate cell(s). In some of these examples, the UE may receive the MAC CE (TCI state activation MAC CE), and perform measurement(s) of the first available occasion(s) of the reference signal(s) transmitted by the candidate cell(s) that is overlapped by the ad-hoc measurement gap. The UE may then use the measurement(s) for DL synchronization with the candidate cell(s).

[0088] At step 812 onwards, the UE 110 performs LI measurements on the configured candidate cell(s), and transmits LI measurement reports to the S-DU 210A. Based on the measurements, the S-DU determines the candidate cell(s) that the S-DU wants to better prepare better. As shown at step 813, for example, the S-DU decides to trigger the TA acquisition of the candidate cell(s) (including the cell of T-DU 210B) In another example, the S-DU determines candidate cell(s) for TCI state activation. If not determined earlier (e.g., before DL synchronization), the S-DU at step 814 determines an ad-hoc measurement gap for the candidate cell(s) based on the reference signal resources received by the S-DU at step 810. In some examples, the S-DU may determine the ad-hoc measurement gap also based on the RTD received by the S-DU.

[0089] The S-DU 212A / cell may at step 815 transmit a PDCCH order or other TA acquisition command to the UE 110, and may include the ad-hoc measurement gap towards selected reference signal resources of the candidate cell(s). In another example, the PDCCH order may include an indication allowing the UE to use an ad-hoc measurement gap. Alternatively, the PDCCH order may implicitly indicate the start of an ad-hoc measurement gap to the UE. The This latter part could be configurable behavior.

[0090] The UE may at step 816 perform a measurement of the first available occasion of the reference signal transmitted by each of the candidate cell(s) that is overlapped by the ad-hoc measurement gap. The UE may then at step 817 transmit a RACH preamble (a random access preamble) in a RACH occasion associated with the first available occasion of the reference signal transmitted by the candidate cell(s). The RACH preamble signals the candidate cell(s) to estimate the TA between the UE and the candidate cell(s). And at step 818, the S-DU 210A / cell may receive a RAR including the TA value from respective ones of the candidate cell(s) indirectly via the CU 212.

[0091] The UE 110 may at step 819 transmit LI beam measurements of the candidate cell(s) to the S-DU 210A. The S-DU may at step 820 decide to initiate a cell change (handover) to the T-DU 210B / cell as a target cell for the cell change. The S-DU may optionally at step 821 send a MAC CE for TCI state activation for the target cell, and include an ad-hoc measurement gap towards a selected reference signal resource of the target cell. The UE may in turn at step 822 perform a measurement of the first available occasion of the reference signal transmitted by the target cell that is overlapped by the ad- hoc measurement gap. In some examples, the measurement may be performed in a beam refinement procedure to select a refined beam associated with an activated TCI state of the target cell based on the measurement. The UE may then use the refined beam for access to the target cell.

[0092] The S-DU 212A may at step 823 transmit a cell switch command (e.g., MAC- CE) to trigger the cell switch. In examples in which the RAR is received at the S-DU at step 818, the S-DU may provide the TA of the T-DU 212B / cell to the UE. If the TA of the T-DU / cell is still valid, the UE skips the RACH procedure at step 824 when executing the cell switch. The UE may otherwise perform the UE-based TA acquisition (if configured in RRC Reconfiguration) or RACH procedure using CFRA RACH related parameters provided in the cell switch command. Otherwise, if no TA is given in the cell switch command, UE-based TA acquisition is not configured, and CFRA RACH configuration is not provided in the cell switch command, then UE may perform CBRA RACH procedure to access the target cell. And at steps 825, 826, 827 and 828, the UE, S- DU, T-DU and CU proceed with completion of the LTM procedure.

[0093] FIGS. 9A and 9B illustrate a signaling chart 900 for an LTM procedure including an ad-hoc measurement gap, according to other example implementations. Like the procedure shown in FIGS. 8 A and 8B, the illustrated procedure in FIGS. 9 A and 9B is for an LTM procedure in intra-CU inter-DU mobility, although it should be understood that example implementations of the present disclosure are also equally applicable to inter-CU inter-DU mobility.

[0094] As shown at step 901, the UE 110 may (optionally) notify the CU 212 of a UE capability to implement an ad-hoc measurement gap, such as during an initial access to the serving cell. During preparation for LTM, the UE at step 902 sends a L3 measurementreport to the CU via the S-DU, and the CU at step 903 decides prepare one or more candidate cells (DUs) for LTM. The measurement report may include cell quality measurements of serving cell (e.g., S-DU 210A / cell) and neighbor cells (e.g., T-DU 210B / cell). The UE may be configured by the serving cell to send the measurement report early when the UE still has a good connection to the serving cell. The CU may use the reported measurements to identify a potential set of candidate cells which the UE can be handed over to which may belong to the same DU or different DUs - as shown in the current example.

[0095] As shown at steps 904, 905, 906 and 907, the CU 212 proceeds with the UE context setup / modification procedures to prepare the candidate cell(s), such as T-DU 210B / cell, for handover. In this regard, the CU may at step 904 send a UE context setup request message to request the preparation of the candidate target cell(s). The T-DU / cell may at step 905 provide the configuration of the UE in a UE context setup response message containing a container from DU to CU. The T-DU may here include reference signal(s) which is intended for its own UE in the configuration. The reference signal(s) may include, for example, periodic / semi-persistent / aperiodic CSI-RS, SSB or the like. The CU may then at steps 906 and 907 request and receive UE context modification from the S-DU 210A / cell.

[0096] At step 908, the CU 212 may generate RRC reconfiguration(s) for the configured candidate cell(s); and at step 909, the CU provides the configurations to the UE 110 via the S-DU 210A / cell. The RRC reconfiguration may include, for example, a measurement reporting configuration for LTM, and a configuration of the prepared candidate cell(s) for the UE to execute when the UE receives a MAC CE command to change the serving cell (perform handover). At step 910, the UE 110 sends a RRC reconfiguration complete to the CU 212 via the S-DU 210A.

[0097] During execution, at step 911, the UE 110 performs DL synchronization with the candidate cell(s) from the lower-layer configurations received by the UE. For DL synchronization, the S-DU 212A / cell may send a MAC CE to the UE for an early activation of configured TCI states for the candidate cell(s). In some examples, the UE may receive the MAC CE (TCI state activation MAC CE), activate an ad-hoc measurement gap at the UE, and perform measurement(s) of the first availableoccasion(s) of the reference signal(s) transmitted by the candidate cell(s) that is overlapped by the ad-hoc measurement gap. The UE may then use the measurement(s) for DL synchronization with the candidate cell(s).

[0098] In situations in which the UE 110 activates an ad-hoc measurement gap to perform measurement(s), the S-DU 212A / cell may know the UE has activated the ad- hoc measurement gap based on the UE notification to the S-DU / cell at step 901. Alternatively, the S-DU / cell may know the UE has activated the ad-hoc measurement gap if there is no data interruption to the S-DU / cell transmission according to UE capability.

[0099] At step 912 onwards, the UE 110 performs LI measurements on the configured candidate cell(s), and transmits LI measurement reports to the S-DU 210A. Based on the measurements, the S-DU determines the candidate cell(s) that the S-DU wants to better prepare better. As shown at step 913, for example, the S-DU decides to trigger the TA acquisition of the candidate cell(s) (including the cell of T-DU 210B) In another example, the S-DU determines candidate cell(s) for TCI state activation.

[0100] The S-DU 212A / cell may at step 914 transmit a PDCCH order or other TA acquisition command to the UE 110.

[0101] The UE may at steps 915 and 916 activate an ad-hoc measurement gap at the UE, and perform a measurement of the first available occasion of the reference signal transmitted by each of the candidate cell(s) that is overlapped by the ad-hoc measurement gap. In some examples, the network may know UE has activated the ad hoc measurement gap if there is no data interruption to the serving cell (e.g., S-DU 212A / cell) transmission according to UE capability.

[0102] The UE may then at step 917 transmit a RACH preamble (a random access preamble) in a RACH occasion associated with the first available occasion of the reference signal transmitted by the candidate cell(s). The RACH preamble signals the candidate cell(s) to estimate the TA between the UE and the candidate cell(s). And at step 918, the S-DU 210A / cell may receive a RAR including the TA value from respective ones of the candidate cell(s) indirectly via the CU 212.

[0103] The UE 110 may at step 919 transmit LI beam measurements of the candidate cell(s) to the S-DU 210A. The S-DU may at step 920 decide to initiate a cell change(handover) to the T-DU 210B / cell as a target cell for the cell change. The S-DU may optionally at step 921 send a MAC CE for TCI state activation for the target cell, and include an ad-hoc measurement gap towards a selected reference signal resource of the target cell. The UE may in turn at steps 922 and 923 activate an ad-hoc measurement gap at the UE, and perform a measurement of the first available occasion of the reference signal transmitted by the target cell that is overlapped by the ad-hoc measurement gap. In some examples, the measurement may be performed in a beam refinement procedure to select a refined beam associated with an activated TCI state of the target cell based on the measurement. The UE may then use the refined beam for access to the target cell.

[0104] The S-DU 212A may at step 924 transmit a cell switch command (e.g., MAC- CE) to trigger the cell switch. In examples in which the RAR is received at the S-DU at step 919, the S-DU may provide the TA of the T-DU 212B / cell to the UE. If the TA of the T-DU / cell is still valid, the UE skips the RACH procedure at step 925 when executing the cell switch. The UE may otherwise perform the UE-based TA acquisition (if configured in RRC Reconfiguration) or RACH procedure using CFRA RACH related parameters provided in the cell switch command. Otherwise, if no TA is given in the cell switch command, UE-based TA acquisition is not configured, and CFRA RACH configuration is not provided in the cell switch command, then UE may perform CBRA RACH procedure to access the target cell. And at steps 926, 927, 928 and 929, the UE, S- DU, T-DU and CU proceed with completion of the LTM procedure.

[0105] FIG. 10 is a flowchart illustrating various steps in a method 1000 performed by a radio access node providing a serving cell, according to various example implementations. The method includes receiving a configuration of reference signal resources for at least one neighbor cell, as shown at block 1002. The method includes determining an ad-hoc measurement gap for a user equipment served by the serving cell, In some of these examples, the ad-hoc measurement gap is determined based on the reference signal resources, as shown at block 1004. And the method includes transmitting, to the UE, a control message including a configuration of the ad-hoc measurement gap to trigger the UE to perform at least one measurement of the at least one neighbor cell in the ad-hoc measurement gap, as shown at block 1006.

[0106] In some examples, the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure.

[0107] In some examples, the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0108] In some examples, the TCI state activation is an early TCI state activation for downlink synchronization of the UE with the at least one neighbor cell.

[0109] In some examples, the TCI state activation is for a beam refinement procedure for the UE to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cel l.

[0110] FIG. 11 is a flowchart illustrating various steps in a method 1100 performed by a user equipment (UE), according to various example implementations. The method includes receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, the control message including a configuration of an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE, as shown at block 1102. The method includes performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell, as shown at block 1104. And the method includes accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell, as shown at block 1106.

[0111] In some examples, the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure. In some of these examples, the at least one candidate cell is accessed at block 1106 based on the at least one measurement performed on the at least one candidate cell.

[0112] In some examples, the ad-hoc measurement gap overlaps a first available occasion of a reference signal transmitted by the at least one candidate cell after thePDCCH order transmitted by the serving cell. In some of these examples, the at least one measurement performed on the at least one candidate cell at block 1104 includes a measurement of the first available occasion of the reference signal transmitted by each of the at least one candidate cell.

[0113] In some examples, the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0114] In some examples, the TCI state activation is an early TCI state activation, and the at least one measurement is performed at block 1104 on at least one reference signal transmitted by the at least one candidate cell for a downlink synchronization of the UE with the at least one neighbor cell.

[0115] In some examples, the at least one measurement is performed at block 1104 in a beam refinement procedure to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell using the at least one measurement. In some of these examples, the neighbor cell is accessed at block 1106 using the refined beam.

[0116] In some examples, the neighbor cell is a target cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and the method 1100 further includes receiving a handover command to trigger handover of the UE to the target cell during which the target cell is accessed using the refined beam associated with the activated TCI state.

[0117] FIG. 12 is a flowchart illustrating various steps in a method 1200 performed by a user equipment (UE), according to various example implementations. The method includes receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, as shown at block 1202. The method includes activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE, as shown at block 1204. The method includes performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell, as shown at block 1206. And the method includes accessing the at least one neighborcell using the at least one measurement performed on the at least one neighbor cell, as shown at block 1208.

[0118] In some examples, the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure. In some of these examples, the at least one candidate cell is accessed at block 1208 based on the at least one measurement performed on the at least one candidate cell.

[0119] In some examples, the ad-hoc measurement gap overlaps a first available occasion of a reference signal transmitted by the at least one candidate cell after the PDCCH order transmitted by the serving cell. In some of these examples, the at least one measurement performed on the at least one candidate cell at block 1206 includes a measurement of the first available occasion of the reference signal transmitted by each of the at least one candidate cell.

[0120] In some examples, the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0121] In some examples, the TCI state activation is an early TCI state activation, and the at least one measurement is performed at block 1206 on at least one reference signal transmitted by the at least one candidate cell for a downlink synchronization of the UE with the at least one neighbor cell.

[0122] In some examples, the at least one measurement is performed at block 1206 in a beam refinement procedure to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell using the at least one measurement. In some of these examples, the neighbor cell is accessed at block 1208 using the refined beam.

[0123] In some examples, the neighbor cell is a target cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and the method 1200 further includes receiving a handover command to trigger handover of the UE to the target cell during which the target cell is accessed using the refined beam associated with the activated TCI state.

[0124] According to example implementations of the present disclosure, a telecommunications system 100 or PLMN 102, and its components such as a UE 110, gNB 206, CU 208, DU 210, S-DU 210A and / or T-DU 210B, may be implemented by various means. Means for implementing the system and its components may include hardware, firmware, software, or combinations thereof. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its components shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

[0125] According to some example implementations, at least some of the method 1000 described with respect to FIG. 10 may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Similarly, at least some of the method 1100 described with respect to FIG. 11 may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. And at least some of the method 1200 described with respect to FIG. 12 may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may include a 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.

[0126] FIG. 13 illustrates an apparatus 1300 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 1302 connected to computer-readable storage medium or other memory 1304.

[0127] The processing circuitry 1302 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 1304 (of the same or another apparatus).

[0128] The processing circuitry 1302 may be a number of processors, a multi-core processor or some other type of processor, depending on the particular implementation. Further, the processing circuitry may be implemented using a number of heterogeneous processor systems in which a main processor is present with one or more secondary processors on a single chip. As another illustrative example, the processing circuitry may be a symmetric multi-processor system containing multiple processors of the same type. In yet another example, the processing circuitry may be embodied as or otherwise include one or more ASICs, FPGAs or the like. Thus, although the processing circuitry may be capable of executing a computer program to perform one or more functions, the processing circuitry of various examples may be capable of performing one or more functions without the aid of a computer program. In either instance, the processing circuitry may be appropriately programmed to perform functions or operations according to example implementations of the present disclosure.

[0129] The memory 1304 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 1306 (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 nonvolatile 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.

[0130] The memory 1304 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.

[0131] In addition to the memory 1304 (e.g., computer-readable storage medium), the processing circuitry 1302 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communications interface 1308 and / or one or more user interfaces. The communications interface may be configured to transmit and / or receive information, such as to and / or from other apparatus(es), network(s) or the like. The communications interface may be configured to transmit and / or receive information by physical (wired) and / or wireless communications links. Examples of suitable communication interfaces include a network interface controller (NIC), wireless NIC (WNIC) or the like.

[0132] The user interfaces may include a display 1310 and / or one or more user input interfaces 1312. 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 userinterfaces may further include one or more interfaces for communicating with peripherals such as printers, scanners or the like.

[0133] Execution of the instructions 1306 by the processing circuitry 1302, or storage of the instructions in the memory 1304, supports combinations of operations for implementing example implementations of the present disclosure. In this manner, an apparatus 1300 may comprise at least one processing circuitry and at least one memory coupled to the at least one processing circuitry, where the at least one processing circuitry is configured to execute instructions stored in the at least one memory. It will also be understood that one or more functions, and combinations of functions, may be implemented by special purpose hardware-based computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions.

[0134] Some example implementations of the present disclosure may also be carried out in the form of a computer process defined by one or more computer programs or portions thereof. Example implementations of the present disclosure may be carried out by executing at least one portion of a computer program comprising instructions. The computer program may be in source code form, object code form, or in some intermediate form. The computer program may be stored in a computer-readable medium that is readable by a computer, processing circuitry or other suitable apparatus. As indicated above, for example, the computer program may be stored in a memory, such as a computer-readable storage medium. Additionally or alternatively, for example, the computer program may be stored in a computer-readable transmission medium. The coding of software for carrying out example implementations of the present disclosure is well within the scope of a person of ordinary skill in the art.

[0135] 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 therebygenerate 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.

[0136] Retrieval, loading and execution of instructions comprising program code instructions may be performed sequentially such that one instruction is retrieved, loaded and executed at a time. In some example implementations, retrieval, loading and / or execution may be performed in parallel such that multiple instructions are retrieved, loaded, and / or executed together. Execution of the program code instructions may produce a computer-implemented process such that the instructions executed by the computer, processing circuitry or other programmable apparatus provide operations for implementing functions described herein.

[0137] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0138] Clause 1. A method performed by a radio access node providing a serving cell, the method comprising: receiving a configuration of reference signal resources for at least one neighbor cell; determining an ad-hoc measurement gap for a user equipment served by the serving cell, wherein the ad-hoc measurement gap is determined based on the reference signal resources; and transmitting, to the UE, a control message including a configuration of the ad-hoc measurement gap to trigger the UE to perform at least one measurement of the at least one neighbor cell in the ad-hoc measurement gap.

[0139] Clause 2. The method of clause 1 , wherein the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure.

[0140] Clause 3. The method of clause 1 or clause 2, wherein the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0141] Clause 4. The method of clause 3, wherein the TCI state activation is an early TCI state activation for downlink synchronization of the UE with the at least one neighbor cell

[0142] Clause 5. The method of clause 3 or clause 4, wherein the TCI state activation is for a beam refinement procedure for the UE to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell

[0143] Clause 6. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to perform the method of any of clauses 1 to 5.

[0144] Clause 7. An apparatus comprising means for performing the method of any of clauses 1 to 5.

[0145] Clause 8. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 5.

[0146] Clause 9. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 5.

[0147] Clause 10. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 1 to 5.

[0148] Clause 11. A method performed by a user equipment (UE), the method comprising: receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell, the control message including a configuration of an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and accessing the at least oneneighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0149] Clause 12. The method of clause 11, wherein the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and wherein the at least one candidate cell is accessed based on the at least one measurement performed on the at least one candidate cell.

[0150] Clause 13. The method of clause 12, wherein the ad-hoc measurement gap overlaps a first available occasion of a reference signal transmitted by the at least one candidate cell after the PDCCH order transmitted by the serving cell, and the at least one measurement performed on the at least one candidate cell includes a measurement of the first available occasion of the reference signal transmitted by each of the at least one candidate cell.

[0151] Clause 14. The method of any of clauses 11 to 13, wherein the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0152] Clause 15. The method of clause 14, wherein the TCI state activation is an early TCI state activation, and the at least one measurement is performed on at least one reference signal transmitted by the at least one candidate cell for a downlink synchronization of the UE with the at least one neighbor cell.

[0153] Clause 16. The method of clause 14 or clause 15, wherein the at least one measurement is performed in a beam refinement procedure to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell using the at least one measurement, and the neighbor cell is accessed using the refined beam.

[0154] Clause 17. The method of clause 16, wherein the neighbor cell is a target cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and the method further comprises receiving a handover command to trigger handover of the UE to the target cell during which the target cell is accessed using the refined beam associated with the activated TCI state.

[0155] Clause 18. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to perform the method of any of clauses 11 to 17.

[0156] Clause 19. An apparatus comprising means for performing the method of any of clauses 11 to 17.

[0157] Clause 20. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 11 to 17.

[0158] Clause 21. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 11 to 17.

[0159] Clause 22. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 11 to 17.

[0160] Clause 23. A method performed by a user equipment (UE), the method comprising: receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

[0161] Clause 24. The method of clause 23, wherein the method further comprises notifying the serving cell of a UE capability to implement the ad-hoc measurement gap.

[0162] Clause 25. The method of clause 23 or clause 24, wherein the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower- layer triggered mobility (LTM) cell switch or a handover procedure, and wherein the at least one candidate cell is accessed based on the at least one measurement performed on the at least one candidate cell.

[0163] Clause 26. The method of clause 25, wherein the ad-hoc measurement gap overlaps a first available occasion of a reference signal transmitted by the at least one candidate cell after the PDCCH order transmitted by the serving cell, and the at least one measurement performed on the at least one candidate cell includes a measurement of the first available occasion of the reference signal transmitted by each of the at least one candidate cell.

[0164] Clause 27. The method of any of clauses 23 to 26, wherein the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

[0165] Clause 28. The method of clause 27, wherein the TCI state activation is an early TCI state activation, and the at least one measurement is performed on at least one reference signal transmitted by the at least one candidate cell for a downlink synchronization of the UE with the at least one neighbor cell.

[0166] Clause 29. The method of clause 27 or clause 28, wherein the at least one measurement is performed in a beam refinement procedure to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell using the at least one measurement, and the neighbor cell is accessed using the refined beam.

[0167] Clause 30. The method of clause 29, wherein the neighbor cell is a target cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and the method further comprises receiving a handover command to trigger handover of the UE to the target cell during which the target cell is accessed using the refined beam associated with the activated TCI state.

[0168] Clause 31. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to perform the method of any of clauses 23 to 30.

[0169] Clause 32. An apparatus comprising means for performing the method of any of clauses 23 to 30.

[0170] Clause 33. 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 23 to 30.

[0171] Clause 34. 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 23 to 30.

[0172] Clause 35. A computer program comprising instructions which, when executed by an apparatus, causes the apparatus to perform the method of any of clauses 23 to 30.

[0173] 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. An apparatus implemented by an user equipment (UE), the apparatus comprising: means for receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; means for activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; means for performing at least one measurement on the at least one neighbor cell in the ad-hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and means for accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

2. The apparatus of claim 1, wherein the apparatus further comprises means for notifying the serving cell of a UE capability to implement the ad-hoc measurement gap.

3. The apparatus of claim 1 or claim 2, wherein the control message is a physical downlink control channel (PDCCH) order for an early timing advance acquisition with the at least one neighbor cell as at least one candidate cell for a lower- layer triggered mobility (LTM) cell switch or a handover procedure, and wherein the at least one candidate cell is accessed using the at least one measurement performed on the at least one candidate cell.

4. The apparatus of claim 3, wherein the ad-hoc measurement gap overlaps a first available occasion of a reference signal transmitted by the at least one candidate cell after the PDCCH order transmitted by the serving cell, and the at least one measurement performed on the at least one candidate cell includes a measurement of the first available occasion of the reference signal transmitted by each of the at least one candidate cell.

5. The apparatus of any of claims 1 to 4, wherein the control message is a medium access control (MAC) control element (CE) for a transmission configuration indicator (TCI) state activation for the at least one neighbor cell.

6. The apparatus of claim 5, wherein the TCI state activation is an early TCI state activation, and the at least one measurement is performed on at least one reference signal transmitted by the at least one candidate cell for a downlink synchronization of the UE with the at least one neighbor cell.

7. The apparatus of claim 5 or claim 6, wherein the at least one measurement is performed in a beam refinement procedure to select a refined beam associated with an activated TCI state of a neighbor cell of the at least one neighbor cell using the at least one measurement, and the neighbor cell is accessed using the refined beam.

8. The apparatus of claim 7, wherein the neighbor cell is a target cell for a lower-layer triggered mobility (LTM) cell switch or a handover procedure, and the apparatus further comprises means for receiving a handover command to trigger handover of the UE to the target cell during which the target cell is accessed using the refined beam associated with the activated TCI state.

9. A method performed by a user equipment (UE), the method comprising: receiving a control message transmitted by a serving cell to trigger measurement of at least one neighbor cell; activating an ad-hoc measurement gap that is separate from any measurement gap pattern configured for the UE; performing at least one measurement on the at least one neighbor cell in the ad- hoc measurement gap during which the UE is not required to conduct reception or transmission from or to the serving cell; and accessing the at least one neighbor cell using the at least one measurement performed on the at least one neighbor cell.

10. A computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform the method claims 9.

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