Channel state information reference signal (CSI-RS) based random access procedure for cell switch

Abstract

A method is provided that includes receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells. The method includes receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure. The control message includes information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells. And the method includes carrying out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

Description

CHANNEL STATE INFORMATION REFERENCE SIGNAL (CSLRS) BASED RANDOM ACCESS PROCEDURE FOR CELL SWITCHTECHNOLOGICAL FIELD

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

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

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

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

[0005] The telecommunications system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how operations should be achieved. Communication protocols and / or parameters which shall be used for connection of the various entities are also typically defined. 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 (3 GPP).BRIEF SUMMARY

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

[0007] Some example implementations provide an apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receive a control message from a source cell to trigger a channel state information reference signal (CSLRS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSLRS associated with a LTM candidate cell of the one or more LTM candidate cells; and carry out the CSLRS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSLRS.

[0008] Some example implementations provide an apparatus comprising: means for receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; means for receiving a control message from a source cell to trigger a channel state information reference signal (CSLRS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSLRS associated with a LTM candidate cell of the one or more LTM candidate cells; and means for carrying out the CSLRS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSLRS.

[0009] Some example implementations provide a method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and carrying out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0010] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receive a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0011] Some example implementations provide an apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; send the RACH configuration to a user equipment (UE); and trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0012] Some example implementations provide an apparatus comprising: means for receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; means for sending the RACH configuration to an user equipment (UE); and means for triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message tothe UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0013] Some example implementations provide a method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; sending the RACH configuration to a user equipment (UE); and triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0014] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; send the RACH configuration to a user equipment (UE); and trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0015] 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.

[0016] 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)

[0017] 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:

[0018] 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;

[0019] FIG. 2 illustrates a 5G deployment of a PLMN, according to some example implementations;

[0020] FIG. 3 is a signaling chart for a Ll / L2-triggered mobility, also known as lower- layer triggered mobility (LTM) procedure;

[0021] FIGS. 4 A and 4B illustrate a signaling chart for an LTM procedure in a central / centralized unit - distributed unit (CU-DU) split architecture;

[0022] FIG. 5 illustrates beams on which a number of synchronization signal (SS) / physical broadcast channel (PBCH) blocks (SSBs) and channel state information reference signals (CSLRSs) may be transmitted;

[0023] FIGS. 6 A and 6B illustrate a signaling chart for an LTM procedure in a CU-DU split architecture, including CSI-RS based random access channel (RACH) preamble transmission, according to some example implementations;

[0024] FIGS. 7A, 7B, 7C, 7D, 7E and 7F are flowcharts illustrating various steps in a method, according to various example implementations;

[0025] FIGS. 8A, 8B and 8C is a flowchart illustrating various steps in a method, according to various example implementations; and

[0026] FIG. 9 illustrates an apparatus according to some example implementations.DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form. Furthermore, it should be understood that unless otherwise specified, the terms “data,” “content,” “digital content,” “information,” and similar terms may be at times used interchangeably. The term “network” may refer to a group of interconnected computers including clients and servers; and within a network, these computers may be interconnected directly or indirectly by various means including via one or more switches, routers, gateways, access points or the like.

[0030] 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 maybe equally applicable to non-3GPP technologies such as IEEE 802, Bluetooth and BluetoothLow Energy.

[0031] 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.

[0032] 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.

[0033] FIG. 1 illustrates a telecommunications system 100 according to various example implementations of the present disclosure. The telecommunications system generally includes one or more telecommunications networks. As shown, for example, the system includes one or more public land mobile networks (PLMNs) 102 coupled to one or more other external data networks 104 - notably including a wide area network (WAN) such as the Internet. Each of the PLMNs includes a core network (CN) 106 backbone such as the Evolved Packet Core (EPC) of LTE, the 5G core network (5GC) or the like; and each of the core networks and the Internet are coupled to one or more radio access networks (RANs) 108, air interfaces or the like that implement one or more radio access technologies (RATs). As used herein, a “network device” refers to any suitable device at a network side of a telecommunications network.Examples of suitable network devices are described in greater detail below.

[0034] 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 afurther 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.

[0035] 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).

[0036] Examples of radio access technologies include 3 GPP radio access technologies such as GSM, UMTS, LTE, LTE Advanced, 5GNR, 5G Advanced, and 6G. Other examples of radio access technologies include IEEE 802 technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.15 (including 802.15.1 (WPAN / Bluetooth), 802.15.4 (Zigbee) and 802.15.6 (WBAN)), Bluetooth, Bluetooth Low Energy (BLE), ultra wideband (UWB), and the like. Generally, a radio access technology may refer to any 2G, 3G, 4G, 5G, 6G or higher generation mobile communication technology and their different versions, as well as to any other wireless radio access technology that may be arranged to interwork with such a mobile communication technology to provide access to the CN 106 of a mobile network operator (MNO).

[0037] 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 networkcontrolling / goveming entity responsible for control of the radio access nodes. The network controlling / goveming entity and radio access node may be separate or integrated into a single apparatus. The network controlling / goveming 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.

[0038] ARAN 108 may be centralized or distributed. In various examples, components of a RAN may be interconnected by Ethernet, Gigabit Ethernet, Asynchronous Transfer Mode (ATM), optical fiber, dark fiber, passive wavelength division multiplexing (WDM), 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.

[0039] As will be appreciated, a PLMN 102 may be deployed in a number of different manners. In a 4G LTE deployment, the EPC is the CN 106, and the evolved UMTS terrestrial radio access network (E-UTRAN) is the RAN 108; and the E-UTRAN includes one or more eNBs (radio access nodes) configured to connect UEs 110 to the E-UTRAN to thereby access the EPC. As shown in FIG. 2, in a 5G deployment 200, the 5GC 202 is the CN, and the next generation (NG) radio access network (NG-RAN) 204 is the RAN; and the NG-RAN includes one or more gNBs 206 (radio access nodes) configured to connect UEs 110 to the NG-RAN to thereby access the 5GC (at times referred to as the NGC). The term ‘gNB’ in 5G may correspond to the eNB in 4G LTE.

[0040] 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.

[0041] 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.

[0042] As shown and described, for example, some 5G deployments may be based on a so-called CU-DU split including one or more DUs 210 and a CU 212. One gNB-CU (central node) may control one or more gNB-DUs. The gNB-CU may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some example implementations, however, the gNB-DUs (also called DU) may include, for example, a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU (also called a CU) may include the layers above the RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC), and an internet protocol (IP) layer. Other functional splits are also possible. It is considered that a skilled person is familiar with the open systems interconnection (OSI) model and the functionalities within each layer.

[0043] 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.

[0044] 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 5G NR. It is expected that L3 mobility (legacy handover) will also be commonly used in the future.

[0045] Ll / L2-triggered mobility, or lower-layer triggered mobility (LTM) moves the execution of the ‘handover’ from one cell to another from higher layers (L3), such as RRC, tolower 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.

[0046] FIG. 3 illustrates a signaling chart 300 for an LTM procedure of a UE 110 in a RRC connected state with a gNB 206, which has been proposed. During LTM preparation, as shown at step 301, the UE sends a L3 measurement report to the gNB, which decides to use LTM and initiate LTM candidate preparation. The gNB at step 302 transmits a RRC reconfiguration message to the UE, including the configuration of one or more candidate cells. 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.

[0047] 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) / uplink (UL) synchronization with the candidate cell(s).

[0048] During early UL synchronization, the UE 110 may acquire a timing advance (TA) of respective ones of the candidate cell(s). In this regard, the gNB 206 may request that the UE perform early TA acquisition 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. Note that PDCCH order message which is used to trigger RACH preamble is referred by TA acquisition command. In 3GPP, 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 for the purpose of TA value acquisition, and the TA value of the candidate cell may be indicated in a subsequent cell switch command.

[0049] 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.

[0050] During LTM execution, the UE 110 performs LI measurements on the configured candidate cell(s), and the UE at step 305 transmits LI measurement reports to the gNB 206. The gNB decides to execute a cell switch, and selects one of the candidate cell(s) as a target cell for the cell switch. The gNB then at step 306 transmits a cell switch command, such as a MAC control element (MAC-CE), to trigger cell switch. The UE switches to the configuration of the target cell; and if the TA of the target cell (from step 304) is no longer available (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.

[0051] FIGS. 4 A 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) 210A for 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.

[0052] At steps 407 and 408, the CU 212 also configures the UE 110 with LI measurement reporting for LTM execution. The CU provides the S-DU 210A with TA acquisition configuration(s), as well as cell switch configuration(s). The configuration(s) may include triggering criteria for TA acquisition and cell switch may be similar to measurement event report triggering conditions, e.g., A3, A4 or A5 event conditions or validity of acquired TA. The triggering conditions may include, for example, a filter configuration (for LI measurements), trigger offsets, cell individual offsets, or the like.

[0053] At step 409, the UE 110 sends a RRC reconfiguration complete to the CU 212 via the S-DU 210A.

[0054] During execution, at step 410 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 411 decides to trigger the TA acquisition of the candidate cell(s) (including the cell of T-DU 210B), and the S-DU at step 412 transmits a TA acquisition command (e.g., PDCCH order) to the UE. The UE at step 413 transmits a RACH preamble (a random access preamble) to the candidate cell(s) (T-DU 210B / cell) to signal the candidate cell(s) toestimate the TA between the UE and the candidate cell(s). And at step 414, the S-DU 210A / cell receives a RAR from respective ones of the candidate cell(s) indirectly via the CU 212.

[0055] The UE 110 at step 415 transmits LI beam measurements of the candidate cell(s) to the S-DU 210A. The S-DU at steps 416 and 417 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 414 (instead of the UE), 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 may skip the RACH procedure at step 418 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 CBRARACH procedure to access the target cell. And at steps 419, 420, 421 and 422, the UE, S-DU, T-DU and CU proceed with completion of the LTM procedure.

[0056] In 3 GPP, the configuration of a candidate cell (LTM-Candidate) includes a number of information elements (IES), such as a configuration (Jtm-EarlyUL-SyncConfig) used to perform the early UL synchronization procedure. The configuration to perform the early UL synchronization procedure includes an IE (EarlyUL-SyncConfig) used to configure random access resources for the early UL synchronization procedure (referred to at times as a RACH configuration). The EarlyUL-SyncConfig IE in turn includes RACH parameters for performing a random access procedure on a candidate cell (rach-ConfigGeneric and a number of synchronization signal (SS) / physical broadcast channel (PBCH) blocks (SSBs) (ssb-PerRACH-Occasion) per RACH occasion. The rach-ConfigGeneric IE includes, for example, a RACH (a PRACH) configuration index (prach-Configurationlndex).

[0057] Similar to the configuration of a candidate cell for early UL synchronization, the cell switch command (MAC-CE) may include CFRA RACH related parameters for the UE 110 to perform a RACH procedure with the T-DU 210B / cell. These parameters may include, for example, a random access preamble (RACH) index of CFRA resources, a SSB index that indicates the SSB used to determine the RACH occasion for the RACH preamble, and PRACH mask index that indicates RACH occasion(s) associated with the SSB indicated by the SSB index for the RACH preamble.

[0058] LTM was introduced in 3 GPP Release 18 and offers improvements in handover latency and interruption time compared to L3 mobility. But LTM as introduced also has anumber of limitations relative to L3 mobility. A number of enhancements of LTM are currently under discussion to address these limitations. One of the objectives is to enable channel state information reference signal (CSI-RS) measurements for LTM procedures. In particular, enhancements are under discussion to support CSI-RS measurements for LTM procedures and enable CSI-RS beam based management.

[0059] For a CSI-RS resource, there may be an SSB index that serves as a source reference signal (RS) for quasi co-location (QCL) information that may be configured by the NG-RAN 204. The QCL information may be given by an IE qcl-InfoPeriodicCSI-RS) that points to a transmission configuration index (TCI) state, which further points to its QCL source RS. This connection may be made by a direct QCL reference or an indirect QCL chain reference. In case of direct QCL reference, a SSB may be configured as the QCL source of the CSI-RS. In case of indirect QCL reference, for example, a CSI-RS may have another CSI-RS as the QCL reference, where the reference CSI-RS has a SSB as its QCL reference.

[0060] FIG. 5 illustrates beams 500 on which a number of SSBs and CSLRSs may be transmitted. Given that an SSB is typically transmitted using a wider beam compared with a CSI-RS, multiple CSI-RS indices may be associated with the same source SSB index. As shown in FIG. 5, for example, SSB1 serves as a source RS for QCL information of four CSI- RS indices, namely, CSI-RS1, CSI-RS2, CSLRS3 and CSLRS4. Likewise, SSB2 serves as a source RS for another four CSI-RS indices, namely, CSI-RS5, CSLRS6, CSI-RS7 and CSI- RS8.

[0061] As currently specified, a TCI State includes QCL information for receiving on the PDCCH / physical downlink shared channel (PDSCH) from a candidate (target) cell (DL reception), and / or for transmitting on the physical uplink control channel (PUCCH) / physical uplink shared channel (PUSCH) to a candidate (target) cell (UL transmission). The QCL information, in turn, includes the RS, QCL type, and the bandwidth part (bwp) where the RS is located. The QCL type may indicate a typeA (Doppler shift, Doppler spread, average delay, delay spread), typeB (Doppler shift, Doppler spread), typeC (Doppler shift, average delay), or typeD (spatial RX parameter).

[0062] For a RACH (or preamble) transmission by a UE 110 triggered by a TA acquisition command (e.g., PDCCH order) or an LTM cell switch command MAC CE, the PRACH mask index field, if the value of the random access (RACH) preamble index field is not zero, indicates the RACH occasion for the RACH preamble transmission (at times more simply referred to as a RACH transmission). The RACH occasions are associated with the SS / PBCH block index indicated by the SS / PBCH block index field of the PDCCH order or the LTM cellswitch command MAC CE and, if any, a cell indicator field in the PDCCH order or a target configuration identity (ID) field in the LTM cell switch command MAC CE indicates a cell for the RACH preamble transmission.

[0063] Furthermore, typically, the UE 110 derives the spatial transmit filter (e.g., UL beam) corresponding to the downlink spatial Rx filter (e.g., DL Rx beam) used to receive the SSB given in the PDCCH order or cell switch command.

[0064] When CSI-RS measurements of candidate target cells are available at the S-DU 210A / cell, it is possible to configure narrow beam transmission (by the UE 110) and reception (at the corresponding candidate cell) for preamble transmission / reception. The current LTM candidate cell configuration for early UL synchronization (PDCCH order) and cell switch command, however do not support CSI-RS-based CFRARACH procedures.

[0065] In view of the foregoing, example implementations of the present disclosure provide a solution to enable CSI-RS-based RACH preamble transmission for acquiring uplink synchronization (TA acquisition) with a candidate T-DU 210B / cell in an LTM procedure. Some example implementations provide signaling enhancements to the PDCCH order to enable CSI-RS-based early CFRARACH preamble transmission for the early TA acquisition procedure for a candidate T-DU / cell. The signaling enhancements may also be applicable to CFRARACH procedure triggered via a cell switch command. Additionally or alternatively, some example implementations provide configuration enhancements to the RACH configuration for early UL synchronization to enable CSI-RS-based CFRARACH procedure. Example implementations may be primarily described in the context of intra-CU cell switch (handover), although it should be understood that example implementations are equally applicable to inter-CU cell switch (handover).

[0066] The aforementioned signaling enhancements of some example implementations are provided below for a PDCCH order. It should be understood, however, that the same enhancements may also apply to a cell switch command.

[0067] According to some example implementations, a PDCCH order (or cell switch command) triggering a RACH preamble transmission may include information that indicates to the UE 110 whether the RACH preamble transmission is associated with a CSLRS associated with the candidate T-DU 210B / cell. In some examples, the PDCCH order may include a common or the same field used to indicate an SSB index or a CSLRS index.

[0068] In some examples in which the PDCCH order includes a common field, or in other similar examples, the PDCCH order may include a field (e.g., in a reserved bit) to indicate whether the RACH preamble transmission is associated with an SSB or a CSI-RS. When thevalue of the field is set to first value (e.g., ‘0’), the UE 110 may expect that the RACH preamble transmission is associated with an SSB; and when the value of the field is set to a second value (e.g., ‘ 1’), the UE may expect that the RACH preamble transmission is associated with a CSI-RS.

[0069] In other examples, the PDCCH order may include separate fields used to indicate an SSB index and a CSI-RS index. In this other example, the PDCCH order may include an additional field used to indicate a CSI-RS index (in addition to the current field indicating a SSB index). The PDCCH order may in this example include two fields, one for SSB index and one for CSI-RS index. In some examples, when the RACH preamble transmission is associated with a CSI-RS, the field used to indicate the SSB index may be reserved; and when the RACH preamble transmission is associated with an SSB, the field used to indicate the CSI-RS index may be reserved. In some examples, one or more of the reserved bits in the existing PDDCH order may be used to indicate the CSI-RS index.

[0070] In some examples in which the PDCCH order includes separate fields, if both CSI- RS and SSB field are available, the UE 110 may be expected to choose one of the fields and initiate RACH based on one or more of a number of metrics. In this regard, the UE may choose the field for the index (SSB or CS-RS) with the highest measurement such as measured RS received power (RSRP) or RS received quality (RSRRQ) or signal to interference ratio (SINR) (or lowest path loss or better link condition). The UE may choose the field for the index with the earliest RACH occasion. Or the UE may select the index that is above a certain threshold.

[0071] Regardless of the manner by which a CSI-RS index is indicated, when the PDCCH order indicates a CSI-RS index, the PRACH mask index field may indicate the RACH occasion associated with the CSI-RS indicated by the CSI-RS index for the RACH preamble transmission.

[0072] In some examples, instead of a CSI-RS index, the PDCCH order may include information that indicates a TCI state index (a joint candidate TCI state index or an candidate UL TCI state index when separate TCI states are configured for DL and UL). In some similar examples, the PDCCH order may include information that indicates one of a number of activated TCI states. This may reduce the size of the field as only activated TCI states need to be considered. For example, for a candidate T-DU 210B / cell, there may be up to total 128 joint TCI states (or 64 UL TCI states when separate TCI states) that are configured, but then then the number of activated joint TCI states may be up to 16 (or up to 8 UL TCI states).

[0073] In yet other examples, the UE 110 may derive the CSI-RS index from the RS given in the QCL information of the TCI state. In case of two QCL information (QCL-type 1 and QCL-type 2) are available for the TCI state, the UE may use the QCL information associated with a specific QCL type, for example the QCL type = typeD (spatial domain information).

[0074] Some example implementations of the present disclosure provide configuration enhancements to enable CSLRS based RACH preamble transmission. In some examples, dedicated (separate) RACH occasions may be provided for SSB and CSLRS. In some of these examples, the RACH configuration (EarlyUL-SyncConfig) for a candidate T-DU 210B / cell provided to the UE 110 may include a CFRA configuration for one or more CSI-RS associated with the candidate T-DU 210B / cell. The RACH configuration for CSI-RS may include, for example, a CSI-RS index and associated RACH occasion or occasions (when a CSI-RS has more than one RACH occasions). In some examples, the RACH configuration for CSI-RS may include preamble(s) or preamble indices associated with one or more CSI-RS indices. In some examples, only RACH occasions associated with one or more CSI-RS are provided and if there are any dedicated preamble indices provided those may be common for both SSB or CSI-RS based RACH procedures. When there is more than one RACH occasion associated with a CSI-RS, the PRACH mask index in PDCCH order (or in the cell switch command) may indicate which particular occasion to be used.

[0075] In some examples, the UE 110 may indicate its capability to support CSI-RS based RACH procedure for a candidate T-DU 210B / cell. The CU 212 during LTM preparation may share this indication with the candidate T-DU (or candidate CU in inter-CU LTM), such as in a UE context setup message (e.g., at step 403). The T-DU may then decide to provide a RACH configuration for CSI-RS based on the indication. In some examples, the UE capability may be further split into a) a capability for CSI-RS based early UL synchronization, b) a capability for CSI-RS based RACH (for RACH-based LTM), and / or c) a capability for CSI-RS based LTM cell switch.

[0076] In some examples, the RACH configuration for CSI-RS may also be provided to the S-DU 210A / cell, such as in the EarlyUL-SyncConfig IE provided in a UE context modification request message sent by the CU 212 to the S-DU (e.g., at step 405). This may enable the S-DU to select a particular RACH occasion and indicate that particular RACH occasion in the PDCCH order (or the cell switch command). In some examples, when specific preamble indices are also configured for one or more CSLRSs, this may enable the S-DU to select a particular preamble index and indicate that particular preamble index in the PDCCHorder (or the cell switch command). In case of inter-CU LTM, the RACH configuration for CSI-RS may also be indicated from the candidate (target) gNB 206 to the source gNB.

[0077] In some examples in which the PDCCH order (or in the cell switch command) includes a TCI state index instead of a CSI-RS index, the RACH configuration may include TCI state indices and associated RACH occasion (or occasions) or / and preamble indices.

[0078] In other examples, no RACH occasions and preamble indices may be provided associated with a CSI-RS indicated in the PDCCH order (or the cell switch command). In some of these other examples, the S-DU 210A / cell may receive an indication whether a candidate T-DU 210B / cell supports CSI-RS based RACH preamble transmission. The S-DU / cell may also receive a set of CSI-RS indices for which CSI-RS based RACH preamble transmission may be supported.

[0079] When the S-DU 210A / cell includes a CSI-RS index in the PDCCH order, the UE 110 may consider the RACH occasions associated with the SSB QCL’ed with the indicated CSI-RS index. The PRACH mask index may then be derived with respect to the RACH occasions associated with the SSB QCL’ed with indicated CSI-RS. In case of a TCI state index is provided instead of a CSI-RS index, the UE may instead consider the RACH occasions associated with the SSB QCL’ed with the indicated TCI index.

[0080] Before transmitting the PDCCH order (or cell switch command) to the UE 110, the S-DU 210A / cell may send to the candidate T-DU 210B / cell information that indicates there will be a CSI-RS based RACH procedure including a CSI-RS based RACH preamble transmission. The information may include, for example, the CSI-RS index (or TCI index). The information may also include the PRACH mask index selected by the S-DU 210A / cell. Additionally, the information may include the preamble index selected by the S-DU / cell.

[0081] In some examples, the UE 110 may derive other information / parameters (e.g., preamble index, P0 parameter related to transmit power, N gap) used for the RACH preamble transmission, such as based on the parameters / information given for the SSB QCL’ed with indicated CSI-RS.

[0082] At the UE side, if a PDCCH order (or the cell switch command) includes information that indicates a CSI-RS index (or a TCI state index) associated with a candidate T-DU 210B / cell, the UE 110 may transmit a RACH preamble on the PRACH channel using the RACH configuration for CSI-RS (EarlyUL-SyncConfig) for the candidate T-DU 210B / cell, and information provided in the PDCCH order (or the cell switch command). The RACH occasion may be determined based on the RACH occasions associated with the indicated CSI- RS (or TCI state) index, if any. Otherwise, if there are no dedicated RACH occasions for theindicated CSI-RS index given in the configuration, the UE may use the RACH occasions associated with the SSB QCL’ed with the CSI-RS.

[0083] In some examples, the transmit power for RACH preamble transmission may be determined, such as based on the CSI-RS transmit power information (may be given as a part of the candidate cell configuration (LTM-Candidate) and / or path loss derived using the measurements on that CSI-RS. There may be other parameters, e.g., N gap, given as a part of the candidate cell configuration or the RACH configuration for CSI-RS (EarlyUL- SyncConfig), which the UE 110 may use to prepare the RACH preamble transmission. And in some examples, a spatial Tx filter may be determined (e.g., UL beam) corresponding to the downlink spatial Rx filter (e.g., DL Rx beam) used to receive the CSI-RS.

[0084] FIGS. 6 A and 6B illustrate a signaling chart 600 for an LTM procedure in a CU-DU split architecture, including CSI-RS based RACH preamble transmission, according to some example implementations. During preparation for LTM, as shown in FIG. 6A at step 602, the UE 110 indicates the capability to support CSI-RS based early TA acquisition. The UE at step 602 sends a L3 measurement report to the CU 212 via the S-DU 210A / cell, and the CU at step 603 decides prepare one or more candidate cells (DUs) for LTM.

[0085] As shown at steps 604 and 605, the CU 212 proceeds with the UE context setup procedure. The CU indicates the UE capability or requests CSI-RS based early TA configuration, and the T-DU 210B / cell sends a configuration of random access resources for the early UL synchronization procedure (EarlyUL-SyncConfig) to the CU. Then as shown at steps 606 and 607, the CU carries out UE context the UE context modification procedure. The CU indicates the early TA configuration to the S-DU 210A / cell. The TA configuration may include CSI-RS specific RACH configuration (e.g., RACH occasion or / and preamble indices associated with one or more CSLRSs) At step 608, the CU generates RRC reconfiguration(s) for the configured candidate cell(s), including measurement configuration for LI measurements, TA acquisition configuration(s), and other cell switching configuration(s) for one or more prepared candidate cells. The TA acquisition configuration(s) include CSI-RS specific RACH configuration (e.g., RACH occasion or / and preamble indices associated with one or more CSI-RSs). The CU at step 609 provides the configurations to the UE 110 via the S-DU; and the UE at step 610 sends a RRC reconfiguration complete to the CU via the S-DU.

[0086] During execution, as shown in FIG. 6B at step 611 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 612 decides to trigger the TA acquisition of the candidate cell(s) (including the cell of T-DU 210B), and determines to trigger early TA using aCSI-RS mapping RACH occasion and preamble. The S-DU at step 613 transmits a PDCCH order (TA acquisition command) based on a CSI-RS reported by the UE.

[0087] The UE 110 at step 614 calculates the RACH occasion related to a CSI-RS mapping in the CSI-RS resource configuration received from the CU 212 and using the indicated PRACH mask index in the PDCCH order. The UE at step 615 transmits a RACH preamble (indicated in the PDCCH order) in the selected RACH occasion 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).In some examples in which there is no dedicated RACH configuration (RACH occaisons or / and preamble) for the CSI-RS for which the PDCCH order was provided, a CSI-RS index or associated TCI state information may be shared by the S-DU 210A / cell to the T-DU / cell after step 613. The S-DU 210A / cell at step 616 receives a RAR from respective ones of the candidate cell(s) indirectly via the CU 212.

[0088] The UE 110 at step 617 transmits LI beam measurements of the candidate cell(s) to the S-DU 210A. The S-DU at steps 618 and 619 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 616 (instead of the UE), 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 may skip the RACH procedure at step 620 when executing the cell switch. The UE may otherwise perform the RACH procedure using CFRARACH related parameters provided in the cell switch command. And at steps 621, 622, 623 and 624, the UE, S-DU, T- DU and CU proceed with completion of the LTM procedure.

[0089] FIGS. 7A- 7F are flowcharts illustrating various steps in a method 700 according to various example implementations. The method includes receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells, as shown at block 702 of FIG. 7A. The method includes receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, as shown at block 704. And the method includes carrying out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS, as shown at block 706.

[0090] In some examples, the method 700 further includes sending information to the source cell that indicates a capability to support the CSI-RS based RACH procedure for agiven number of candidate cells for LTM, as shown at block 708 of FIG. 7B. In some of these examples, the RACH configuration and the control message are received from the source cell at respectively steps 702 and 704 based on the capability to support the CSI-RS based RACH procedure.

[0091] In some examples, the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0092] In some examples, the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions. In some of these examples, the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0093] In some examples, the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

[0094] In some examples, no RACH occasions are configured for the CSI-RS. The method 700 further includes determining the RACH occasion based on one or more RACH occasions associated with a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi co-location (QCL) source of the CSI-RS, as shown of at block 710 of FIG. 7C.

[0095] In some examples, the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0096] In some examples, the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

[0097] In some examples, the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0098] In some examples, the information that indicates the CSI-RS is provided by a CSI- RS index in a field in the control message that is a dedicated field for the CSI-RS index,separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0099] In some examples, the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state. In some of these examples, the method 700 further includes deriving a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state, as shown at block 712 of FIG. 7D.

[0100] In some examples, the method 700 further includes deriving an uplink spatial transmit filter for transmission of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS, as shown at block 714 of FIG. 7E.

[0101] In some examples, the method 700 further comprises determining a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candidate cell, and a path loss derived using measurements on the CSI-RS, as shown at block 716 of FIG. 7F.

[0102] FIGS. 8 A - 8C are flowcharts illustrating various steps in a method 800 according to various example implementations. The method includes receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells, as shown at block 802 of FIG. 8 A. The method includes sending the RACH configuration to a user equipment (UE), as shown at block 804. And the method includes triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS, as shown at block 806.

[0103] In some examples, the method 800 further includes receiving information from the UE that indicates a capability of the UE to support the CSI-RS based RACH procedure, as shown at block 808 of FIG. 8B. In some of these examples, the RACH configuration and the control message are sent to the UE at respectively blocks 804 and 806 based on the capability of the UE to support the CSI-RS based RACH procedure.

[0104] In some examples, the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0105] In some examples, the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions. In some of these examples, the information thatindicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0106] In some examples, the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

[0107] In some examples, the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0108] In some examples, the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

[0109] In some examples, the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0110] In some examples, the information that indicates the CSI-RS is provided by a CSI- RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.[OHl] In some examples, the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0112] In some examples, the method 800 further comprises sending information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index, as shown at block 810 of FIG. 8C.

[0113] 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 respectiveapparatuses 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.

[0114] According to some example implementations, at least some of the method 700 described with respect to FIGS. 7A-7F may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Simil arly, at least some of the method 800 described with respect to FIGS. 8A-8C may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may a user equipment, user device, user terminal or the like. Other examples of a suitable apparatus may include a gNB (e.g., gNB-DU, gNB-CU), ng-eNB or any suitable apparatus, such as a server, host or node.

[0115] FIG. 9 illustrates an apparatus 900 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 implementati ons 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 902 connected to computer-readable storage medium or other memory 904.

[0116] The processing circuitry 902 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 904 (of the same or another apparatus).

[0117] The processing circuitry 902 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 secondaryprocessors 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.

[0118] The memory 904 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 906 (e.g., computer-readable program code) and / or other suitable information either on a temporary basis and / or a permanent basis. The memory may include volatile and / or non-volatile memory, and may be fixed or removable. Examples of suitable memory include recording media, random access memory (RAM), read-only memory (ROM), a hard drive, a flash memory, a thumb drive, a removable computer diskette, an optical disk or some combination thereof.

[0119] The memory 904 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.

[0120] In addition to the memory 904 (e.g., computer-readable storage medium), the processing circuitry 902 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communications interface 908 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 / orreceive 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.

[0121] The user interfaces may include a display 910 and / or one or more user input interfaces 912. 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 keypadjoystick, touch-sensitive surface (separate from or integrated into a touchscreen), biometric sensor or the like. The user interfaces may further include one or more interfaces for communicating with peripherals such as printers, scanners or the like.

[0122] Execution of the instructions 906 by the processing circuitry 902, or storage of the instructions in the memory 904, supports combinations of operations for implementing example implementations of the present di sclosure. In this manner, an apparatus 900 may comprise at least one processing circuitry and at least one memory coupled to the at least one processing circuitry, where the at least one processing circuitry is configured to execute instructions stored in the at least one memory. It will also be understood that one or more functions, and combinations of functions, may be implemented by special purpose hardwarebased computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions.

[0123] 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.

[0124] As will be appreciated, any suitable instructions may be loaded onto a computer, a processing circuitry or other programmable apparatus from a memory or a computer-readable medium (e.g., computer-readable storage medium, computer-readable transmission medium) to produce a particular machine, such that the particular machine becomes a means for implementing the functions specified herein. The instructions may also be stored in a computer-readable medium that can direct a computer, a processing circuitry or other programmable apparatus to function in a particular manner to thereby generate a particular machine or particular article of manufacture. In some examples, the instructions stored in the computer-readable medium may produce an article of manufacture, where the article of manufacture becomes a means for implementing functions described herein. The instructions may be retrieved from a computer-readable medium and loaded into a computer, processing circuitry or other programmable apparatus to configure the computer, processing circuitry or other programmable apparatus to execute operations to be performed on or by the computer, processing circuitry or other programmable apparatus.

[0125] 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.

[0126] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0127] Clause 1. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receive a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candi date cell of the one or more LTM candidate cells; and carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0128] Clause 2. The apparatus of clause 1, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further send information to the source cell that indicates a capability to support the CSI-RS based RACH procedure for a given number of candidate cells for LTM, and the RACH configuration and the control message are received from the source cell based on the capability to support the CSI-RS based RACH procedure.

[0129] Clause 3. The apparatus of clause 1 or clause 2, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0130] Clause 4. The apparatus of any of clauses 1 to 3, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0131] Clause 5. The apparatus of any of clauses 1 to 4, wherein the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

[0132] Clause 6. The apparatus of any of clauses 1 to 5, wherein no RACH occasions are configured for the CSI-RS, and the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further determine the RACH occasion based on one or more RACH occasions associated with a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi co-location (QCL) source of the CSI-RS.

[0133] Clause 7. The apparatus of any of clauses 1 to 6, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0134] Clause 8. The apparatus of any of clauses 1 to 7, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

[0135] Clause 9. The apparatus of clause 8, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0136] Clause 10. The apparatus of any of clauses 1 to 9, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0137] Clause 11. The apparatus of any of clauses 1 to 10, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state, and the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0138] Clause 12. The apparatus of any of clauses 1 to 11, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further derive an uplink spatial transmit filter for transmission of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS.

[0139] Clause 13. The apparatus of any of clauses 1 to 12, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further determine a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candi date cell, and a path loss derived using measurements on the CSI-RS.

[0140] Clause 14. An apparatus comprising: means for receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; means for receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and means for carrying out the CSI- RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0141] Clause 15. The apparatus of clause 14, wherein the apparatus further comprises means for sending information to the source cell that indicates a capability to support the CSI- RS based RACH procedure for a given number of candidate cells for LTM, and the RACH configuration and the control message are received from the source cell based on the capability to support the CSI-RS based RACH procedure.

[0142] Clause 16. The apparatus of clause 14 or clause 15, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0143] Clause 17. The apparatus of any of clauses 14 to 16, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI- RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0144] Clause 18. The apparatus of any of clauses 14 to 17, wherein the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

[0145] Clause 19. The apparatus of any of clauses 14 to 18, wherein no RACH occasions are configured for the CSI-RS, and the apparatus further comprises means for determining the RACH occasion based on one or more RACH occasions associated with a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi colocation (QCL) source of the CSI-RS.

[0146] Clause 20. The apparatus of any of clauses 14 to 19, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0147] Clause 21. The apparatus of any of clauses 14 to 20, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

[0148] Clause 22. The apparatus of clause 21, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0149] Clause 23. The apparatus of any of clauses 14 to 22, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0150] Clause 24. The apparatus of any of clauses 14 to 23, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state, and the apparatus further comprises means for deriving a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0151] Clause 25. The apparatus of any of clauses 14 to 24, wherein the apparatus further comprises means for deriving an uplink spatial transmit filter for transmi ssi on of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS.

[0152] Clause 26. The apparatus of any of clauses 14 to 25, wherein the apparatus further comprises means for determining a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candidate cell, and a path loss derived using measurements on the CSI-RS.

[0153] Clause 27. A method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including informati on that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and carrying out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0154] Clause 28. The method of clause 27, wherein the method further comprises sending information to the source cell that indicates a capability to support the CSI-RS based RACH procedure for a given number of candidate cells for LTM, and the RACH configuration and the control message are received from the source cell based on the capability to support the CSI-RS based RACH procedure.

[0155] Clause 29. The method of clause 27 or clause 28, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0156] Clause 30. The method of any of clauses 27 to 29, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI- RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0157] Clause 31. The method of any of clauses 27 to 30, wherein the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

[0158] Clause 32. The method of any of clauses 27 to 31, wherein no RACH occasions are configured for the CSI-RS, and the method further comprises determining the RACH occasion based on one or more RACH occasions associated with a synchronization signal(SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi co-location (QCL) source of the CSI-RS.

[0159] Clause 33. The method of any of clauses 27 to 32, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0160] Clause 34. The method of any of clauses 27 to 33, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

[0161] Clause 35. The method of clause 34, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0162] Clause 36. The method of any of clauses 27 to 35, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0163] Clause 37. The method of any of clauses 27 to 36, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state, and the method further comprises deriving a CSI-RS index from a reference signal given in quasi colocation (QCL) information of the TCI state.

[0164] Clause 38. The method of any of clauses 27 to 37, wherein the method further comprises deriving an uplink spatial transmit filter for transmission of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS.

[0165] Clause 39. The method of any of clauses 27 to 38, wherein the method further comprises determining a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candidate cell, and a path loss derived using measurements on the CSI-RS.

[0166] Clause 40. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receive a control message from a source cell to trigger a channel state information reference signal (CSI-RS) basedrandom access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0167] Clause 41. The computer-readable storage medium of clause 40, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further send information to the source cell that indicates a capability to support the CSI-RS based RACH procedure for a given number of candidate cells for LTM, and the RACH configuration and the control message are received from the source cell based on the capability to support the CSI-RS based RACH procedure.

[0168] Clause 42. The computer-readable storage medium of clause 40 or clause 41, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0169] Clause 43. The computer-readable storage medium of any of clauses 40 to 42, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0170] Clause 44. The computer-readable storage medium of any of clauses 40 to 43, wherein the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

[0171] Clause 45. The computer-readable storage medium of any of clauses 40 to 44, wherein no RACH occasions are configured for the CSI-RS, and the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further determine the RACH occasion based on one or more RACH occasions associated with a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi co-location (QCL) source of the CSI-RS.

[0172] Clause 46. The computer-readable storage medium of any of clauses 40 to 45, wherein the control message is a timing advance (TA) acquisition command to request anearly timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0173] Clause 47. The computer-readable storage medium of any of clauses 40 to 46, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

[0174] Clause 48. The computer-readable storage medium of clause 47, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0175] Clause 49. The computer-readable storage medium of any of clauses 40 to 48, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0176] Clause 50. The computer-readable storage medium of any of clauses 40 to 49, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state, and the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0177] Clause 51. The computer-readable storage medium of any of clauses 40 to 50, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further derive an uplink spatial transmit filter for transmission of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS.

[0178] Clause 52. The computer-readable storage medium of any of clauses 40 to 51, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further determine a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candidate cell, and a path loss derived using measurements on the CSI-RS.

[0179] Clause 53. An apparatus comprising means for performing the method of any of clauses 27 to 39.

[0180] Clause 54. 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 27 to 39.

[0181] Clause 55. 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 27 to 39.

[0182] Clause 56. 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 27 to 39.

[0183] Clause 57. An apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; send the RACH configuration to a user equipment (UE); and trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0184] Clause 58. The apparatus of clause 57, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further receive information from the UE that indicates a capability of the UE to support the CSI-RS based RACH procedure, and the RACH configuration and the control message are sent to the UE based on the capability of the UE to support the CSI-RS based RACH procedure.

[0185] Clause 59. The apparatus of clause 57 or clause 58, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0186] Clause 60. The apparatus of any of clauses 57 to 59, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI- RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0187] Clause 61. The apparatus of clause 60, wherein the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

[0188] Clause 62. The apparatus of any of clauses 57 to 61, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0189] Clause 63. The apparatus of any of clauses 57 to 62, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

[0190] Clause 64. The apparatus of clause 63, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0191] Clause 65. The apparatus of any of clauses 57 to 64, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0192] Clause 66. The apparatus of any of clauses 57 to 65, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0193] Clause 67. The apparatus of any of clauses 57 to 66, wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further send information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index.

[0194] Clause 68. An apparatus comprising: means for receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; means for sending the RACH configuration to an user equipment (UE); and means for triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or moreLTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0195] Clause 69. The apparatus of clause 68, wherein the apparatus further comprises means for receiving informati on from the UE that indi cates a capability of the UE to support the CSI-RS based RACH procedure, and the RACH configuration and the control message are sent to the UE based on the capability of the UE to support the CSI-RS based R ACH procedure.

[0196] Clause 70. The apparatus of clause 68 or clause 69, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0197] Clause 71. The apparatus of any of clauses 68 to 70, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI- RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0198] Clause 72. The apparatus of clause 71, wherein the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

[0199] Clause 73. The apparatus of any of clauses 68 to 72, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0200] Clause 74. The apparatus of any of clauses 68 to 73, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

[0201] Clause 75. The apparatus of clause 74, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0202] Clause 76. The apparatus of any of clauses 68 to 75, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is adedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0203] Clause 77. The apparatus of any of clauses 68 to 76, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0204] Clause 78. The apparatus of any of clauses 68 to 77, wherein the apparatus further comprises means for sending information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index.

[0205] Clause 79. A method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; sending the RACH configuration to a user equipment (UE); and triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0206] Clause 80. The method of clause 79, wherein the method further comprises receiving information from the UE that indicates a capability of the UE to support the CSI-RS based RACH procedure, and the RACH configuration and the control message are sent to the UE based on the capability of the UE to support the CSI-RS based RACH procedure.

[0207] Clause 81. The method of clause 79 or clause 80, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0208] Clause 82. The method of any of clauses 79 to 81, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI- RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0209] Clause 83. The method of clause 82, wherein the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

[0210] Clause 84. The method of any of clauses 79 to 83, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0211] Clause 85. The method of any of clauses 79 to 84, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

[0212] Clause 86. The method of clause 85, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0213] Clause 87. The method of any of clauses 79 to 86, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0214] Clause 88. The method of any of clauses 79 to 87, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0215] Clause 89. The method of any of clauses 79 to 88, wherein the method further comprises sending information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index.

[0216] Clause 90. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an apparatus to at least: receive a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; send the RACH configuration to a user equipment (UE); and trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RSassoci ated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

[0217] Clause 91. The computer-readable storage medium of clause 90, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further receive information from the UE that indicates a capability of the UE to support the CSI-RS based RACH procedure, and the RACH configuration and the control message are sent to the UE based on the capability of the UE to support the CSI-RS based RACH procedure.

[0218] Clause 92. The computer-readable storage medium of clause 90 or clause 91, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

[0219] Clause 93. The computer-readable storage medium of any of clauses 90 to 92, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

[0220] Clause 94. The computer-readable storage medium of clause 93, wherein the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

[0221] Clause 95. The computer-readable storage medium of any of clauses 90 to 94, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

[0222] Clause 96. The computer-readable storage medium of any of clauses 90 to 95, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

[0223] Clause 97. The computer-readable storage medium of clause 96, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in thecontrol message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0224] Clause 98. The computer-readable storage medium of any of clauses 90 to 97, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

[0225] Clause 99. The computer-readable storage medium of any of clauses 90 to 98, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

[0226] Clause 100. The computer-readable storage medium of any of clauses 90 to 99, wherein the computer-readable storage medium has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further send information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index.

[0227] Clause 101. An apparatus comprising means for performing the method of any of clauses 79 to 89.

[0228] Clause 102. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 79 to 89.

[0229] Clause 103. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 79 to 89.

[0230] Clause 104. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 79 to 89.

[0231] 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 claim s. Moreover, although the foregoing description and theassociated 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 contempl ated 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

43WHAT IS CLAIMED IS:

1. A method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; receiving a control message from a source cell to trigger a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure, the control message including information that at least indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells; and carrying out the CSI-RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

2. The method of any of claims 1 to 1, wherein the method further comprises sending information to the source cell that indicates a capability to support the CSI-RS based RACH procedure for a given number of candidate cells for LTM, and the RACH configuration and the control message are received from the source cell based on the capability to support the CSI-RS based RACH procedure.

3. The method of any of claims 1 to 2, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

4. The method of any of claims 1 to 3, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

5. The method of any of claims 1 to 4, wherein the control message also includes a physical random access channel (PRACH) mask index that indicates the RACH occasion associated with the CSI-RS among one or more RACH occasions.

6. The method of any of claims 1 to 5, wherein no RACH occasions are configured for the CSI-RS, and the method further comprises determining the RACH occasion based on one or more RACH occasions associated with a synchronization signal(SS) / physical broadcast channel (PBCH) block (SSB) configured as a quasi co-location (QCL) source of the CSI-RS.

7. The method of any of claims 1 to 6, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

8. The method of any of claims 1 to 7, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH transmission is associated with a CSI-RS.

9. The method of claim 8, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

10. The method of any of claims 1 to 9, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

11. The method of claim 1 or claim 10, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state, and the method further comprises deriving a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

12. The method of claim 1 or claim 11, wherein the method further comprises deriving an uplink spatial transmit filter for transmission of the RACH preamble based on a downlink spatial receive filter used to receive the CSI-RS, or determining a transmit power for transmission of the RACH preamble based on CSI-RS transmit power information provided by a configuration of the candidate cell, and a path loss derived using measurements on the CSI-RS.

13. An apparatus comprising means for performing the method of any of claims 1 to 12.

14. A method comprising: receiving a random access channel (RACH) configuration for one or more lower-layer triggered mobility (LTM) candidate cells; sending the RACH configuration to a user equipment (UE); and triggering a channel state information reference signal (CSI-RS) based random access channel (RACH) procedure by sending a control message to the UE, the control message including information that indicates a CSI-RS associated with a LTM candidate cell of the one or more LTM candidate cells, the control message triggering the UE to carry out the CSI- RS based RACH procedure in which a RACH preamble is transmitted to the LTM candidate cell in a RACH occasion associated with the CSI-RS.

15. The method of claim 14, wherein the method further comprises receiving information from the UE that indicates a capability of the UE to support the CSI-RS based RACH procedure, and the RACH configuration and the control message are sent to the UE based on the capability of the UE to support the CSI-RS based RACH procedure.

16. The method of claim 14 or claim 15, wherein the RACH configuration includes a configuration for one or more CSI-RS associated with the candidate cell, and the CSI-RS indicated in the control message is one of the one or more CSI-RS.

17. The method of any of claims 14 to 16, wherein the RACH configuration includes one or more CSI-RS indices and one or more associated RACH occasions, and wherein the information that indicates the CSI-RS is also provided by a CSI-RS index of the one or more CSI-RS indices, and the RACH occasion in which the RACH preamble is transmitted is one of the one or more associated RACH occasions.

18. The method of claim 17, wherein the control message also includes a RACH mask that indicates the RACH occasion associated with the CSI-RS among the one or more RACH occasions.

19. The method of any of claims 14 to 18, wherein the control message is a timing advance (TA) acquisition command to request an early timing advance acquisition with the LTM candidate cell using the CSI-RS based RACH procedure, or a cell switch command to trigger a cell switch to the LTM candidate cell in which the CSI-RS based RACH procedure is used to access the LTM candidate cell.

20. The method of any of claims 14 to 19, wherein the information that indicates the CSI-RS is at least partly provided by an indication in the control message that the RACH preamble is associated with a CSI-RS.

21. The method of claim 20, wherein the information that indicates the CSI-RS is also provided by a CSI-RS index in a field in the control message that is a common field for the CSI-RS index or a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

22. The method of any of claims 14 to 21, wherein the information that indicates the CSI-RS is provided by a CSI-RS index in a field in the control message that is a dedicated field for the CSI-RS index, separate from another field in the control message for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) index.

23. The method of any of claims 14 to 22, wherein the information that indicates the CSI-RS is provided by a transmission configuration index (TCI) state to enable the UE to derive a CSI-RS index from a reference signal given in quasi co-location (QCL) information of the TCI state.

24. The method of any of claims 14 to 23, wherein the method further comprises sending information to the candidate cell that indicates there will be a CSI-RS based RACH procedure, the information including at least one of a CSI-RS index or a TCI state index, a physical random access channel (PRACH) mask index, or a preamble index.

25. An apparatus comprising means for performing the method of any of claims 14

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