System and method for cfra resource configuration based on mobility of lower layer signal

Abstract

A method performed by a user equipment (UE) in a wireless communication system is provided. The method comprises: receiving a radio resource control (RRC) reconfiguration message from a base station of a serving cell, the RRC reconfiguration message comprising a configuration of one or more candidate target cells associated with Layer 1 (L1) or Layer 2 (L2) triggered mobility (LTM); sending an RRC reconfiguration completion message to the base station; sending, to the base station, a report for L1 measurements associated with the one or more candidate target cells; and receiving a cell handover command message associated with the LTM from the base station via media access control-control element (MAC-CE) signaling, the cell handover command message including random access information about a target cell.

Description

Technical Field

[0001] The present disclosure relates to a wireless communication system. More specifically, the present disclosure relates to an apparatus, method, and system for configuration associated with mobility based on lower layer signals. Background Art

[0002] The 5th generation (5G) mobile communication technology defines a wide frequency band, enabling high transmission rates and new services, and can be implemented not only in the "below 6 gigahertz (GHz)" band (such as 3.5 GHz), but also in the "above 6 GHz" band called millimeter wave (mmWave) including 28 GHz and 39 GHz. In addition, in order to achieve a transmission rate fifty times faster than the 5G mobile communication technology and an ultra-low latency one-tenth of the 5G mobile communication technology, the 6th generation (6G) mobile communication technology (referred to as the Beyond 5G system) has been considered to be implemented in the terahertz band (e.g., 95 GHz to 3 THz band).

[0003] At the beginning of the development of 5G mobile communication technology, in order to support services and meet the performance requirements related to enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine type communication (mMTC), standardization has been ongoing regarding: beamforming and massive multiple-input multiple-output (MIMO) for reducing radio wave path loss and increasing radio wave transmission distance in millimeter waves, numerology (e.g., operating multiple subcarrier spacings) to support dynamic operations for efficiently utilizing millimeter wave resources and time slot formats, initial access technology to support multi-beam transmission and broadband, the definition and operation of bandwidth part (BWP), new channel coding methods such as low-density parity-check (LDPC) codes for large data transmission and polar codes for highly reliable transmission of control information, L2 preprocessing, and network slicing for providing a dedicated network dedicated to a specific service.

[0004] Currently, considering the services to be supported by 5G mobile communication technology, discussions are ongoing regarding the improvement and performance enhancement of the initial 5G mobile communication technology, and physical layer standardization already exists for technologies such as vehicle-to-everything (V2X) for assisting the driving determination of autonomous vehicles based on information about the position and status of the vehicle sent by the autonomous vehicle and for enhancing user convenience, new radio unlicensed (NR-U) for system operation aiming to comply with various regulatory requirements in the unlicensed band, NR user equipment (UE) power saving, and non-terrestrial network (NTN) as UE-satellite direct communication for providing coverage in areas where communication with the terrestrial network is unavailable.

[0005] In addition, there is ongoing standardization in the air interface architecture / protocol for technologies such as Industrial Internet of Things (IIoT) to support new services through interoperability and convergence with other industries, integrated access and backhaul (IAB) for providing nodes for network service area expansion by supporting wireless backhaul links and access links in an integrated manner, mobility enhancements including conditional handover and dual active protocol stack (DAPS) handover, and two-step random access (2-step RACH for NR) to simplify the random access process. There is also ongoing standardization in the system architecture / services for 5G baseline architectures that combine network function virtualization (NFV) and software-defined networking (SDN) technologies (e.g., service-based architecture or service-based interfaces), and mobile edge computing (MEC) for receiving services based on UE location.

[0006] As 5G mobile communication systems are commercialized, the exponentially growing connected devices will be connected to the communication network, and thus it will be necessary to enhance the functions and performance of 5G mobile communication systems and integrate the operation of connected devices. For this purpose, new research is planned in combination with the following: extended reality (XR) to effectively support augmented reality (AR), virtual reality (VR), mixed reality (MR), etc., improving 5G performance and reducing complexity by leveraging artificial intelligence (AI) and machine learning (ML), AI service support, metaverse service support, and drone communication.

[0007] In addition, the development of 5G mobile communication systems will not only serve as the basis for the development of new waveforms for coverage in the terahertz band for 6G mobile communication technologies, multi-antenna transmission technologies such as full-dimensional MIMO (FD-MIMO), array antennas, and massive antennas, metasurface-based lenses and antennas for improving the coverage of terahertz band signals, high-dimensional space multiplexing technologies using orbital angular momentum (OAM) and reconfigurable intelligent surfaces (RIS); but also serve as the basis for full-duplex technologies for increasing the frequency efficiency of 6G mobile communication technologies and improving the system network, AI-based communication technologies for implementing system optimization by leveraging satellites and AI from the design phase and internalizing end-to-end AI support functions, and next-generation distributed computing technologies for implementing services at a complexity level exceeding the limitations of UE operating capabilities by leveraging ultra-high-performance communication and computing resources.

[0008] The above information is presented only as background information to assist in understanding the present disclosure. No determination has been made, nor is any assertion made, as to whether any of the above is applicable as prior art with respect to the present disclosure. Summary of the Invention

[0009] Technical Problem

[0010] Aspects of the present disclosure are directed to solving at least the above problems and / or disadvantages, and providing at least the following advantages. Accordingly, one aspect of the present disclosure is to provide a method for supporting layer 1 (L1) or layer 2 triggered mobility (LTM) based on L1 measurements.

[0011] Another aspect of the present disclosure is to provide a method for a configuration associated with a random access procedure when a UE performs a random access procedure triggered by LTM.

[0012] Additional aspects will be set forth in part in the following description, and will be in part apparent from the description, or may be learned by practice of the presented embodiments.

[0013] Technical Solutions

[0014] According to one aspect of the present disclosure, there is provided a method performed by a user equipment (UE) in a wireless communication system. The method includes: receiving, from a base station of a serving cell, a radio resource control (RRC) reconfiguration message, the RRC reconfiguration message including a configuration of one or more candidate target cells associated with layer 1 (L1) or layer 2 triggered mobility (LTM); sending an RRC reconfiguration complete message to the base station; sending a report of L1 measurements associated with the one or more candidate target cells to the base station; and receiving, via media access control - control element (MAC-CE) signaling, a cell handover command message associated with the LTM from the base station, wherein the cell handover command message includes random access information about a target cell.

[0015] According to another aspect of the present disclosure, there is provided a method performed by a base station of a source cell in a wireless communication system. The method includes: sending an RRC reconfiguration message to a UE, the RRC reconfiguration message including a configuration of one or more candidate target cells associated with LTM; receiving an RRC reconfiguration complete message from the UE; receiving a report of L1 measurements associated with the one or more candidate target cells from the UE; and sending, via MAC-CE signaling, a cell handover command message associated with the LTM to the UE, wherein the cell handover command message includes random access information about a target cell.

[0016] According to another aspect of the present disclosure, there is provided a UE in a wireless communication system. The UE includes: a transceiver; and a processor, coupled to the transceiver and configured to: receive an RRC reconfiguration message from a base station of a serving cell, the RRC reconfiguration message including configurations of one or more candidate target cells associated with LTM; send an RRC reconfiguration complete message to the base station; send a report on L1 measurements associated with the one or more candidate target cells to the base station; and receive, via MAC-CE signaling, a cell handover command message associated with the LTM from the base station, wherein the cell handover command message includes random access information about a target cell.

[0017] According to another aspect of the present disclosure, there is provided a base station in a wireless communication system. The base station includes: a transceiver; and a processor, coupled to the transceiver and configured to: send an RRC reconfiguration message to a UE, the RRC reconfiguration message including configurations of one or more candidate target cells associated with LTM; receive an RRC reconfiguration complete message from the UE; receive a report on L1 measurements associated with the one or more candidate target cells from the UE; and send, via MAC-CE signaling, a cell handover command message associated with the LTM to the UE, wherein the cell handover command message includes random access information about a target cell.

[0018] Other aspects, advantages, and main features of the present disclosure will become apparent to those skilled in the art from the following detailed description, which discloses various embodiments of the present disclosure in conjunction with the accompanying drawings.

[0019] Beneficial effects

[0020] According to embodiments of the present disclosure, the number of radio link failures can be reduced by performing cell change based on LTM.

[0021] In addition, according to embodiments of the present disclosure, the time for configuring a target cell can be reduced.

[0022] In addition, according to embodiments of the present disclosure, when a UE performs a random access procedure triggered by LTM, configurations associated with the random access procedure can be determined.

[0023] The effects that can be obtained in the present disclosure are not limited to the above effects, and those of ordinary skill in the art to which the present disclosure pertains will be able to clearly understand other unmentioned effects. Brief description of the drawings

[0024] From the following description in conjunction with the accompanying drawings, the above and other aspects, features, and advantages of certain embodiments of the present disclosure will become more apparent, in which:

[0025] Figure 1Illustrates the handover process between gNBs in a wireless communication system according to an embodiment of the present disclosure;

[0026] Figure 2 Illustrates a lower layer-based mobility process according to an embodiment of the present disclosure;

[0027] Figure 3 Illustrates a block diagram of a UE according to an embodiment of the present disclosure; and

[0028] Figure 4 Illustrates a block diagram of a base station according to an embodiment of the present disclosure.

[0029] In all the drawings, it should be noted that the same reference numerals are used to describe the same or similar elements, features, and structures. Detailed Description

[0030] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure defined by the claims and their equivalents. It includes various specific details to assist in the understanding, but these details should be considered merely exemplary. Thus, those skilled in the art will recognize that various changes and modifications can be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and structures may be omitted for clarity and conciseness.

[0031] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventors to enable a clear and consistent understanding of the present disclosure. Thus, those skilled in the art should understand that the following description of the various embodiments of the present disclosure is provided for illustrative purposes only and not for the purpose of limiting the present disclosure defined by the appended claims and their equivalents.

[0032] It should be understood that the singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more such surfaces.

[0033] The following discussion Figures 1 to 4 and the various embodiments for describing the principles of the disclosure in this patent document are merely exemplary and should not be construed in any way as limiting the scope of the present disclosure. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any appropriately arranged system or device.

[0034] Embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0035] Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used in this patent document: The terms "comprising" and "including" and their derivatives mean including but not limited to; the term "or" is inclusive and means and / or; the phrases "associated with" and "associated therewith" and their derivatives may mean including, being included within, interconnected with, containing, being contained within, connected to or coupled with, communicating with, cooperating with, interlacing, juxtaposing, adjacent to, bound to or coupled to, having, having the attribute of, etc.; and the term "controller" means any device, system or part thereof that controls at least one operation, and such device may be implemented in hardware, firmware or software, or in some combination of at least two of hardware, firmware or software. It should be noted that the functions associated with any particular controller may be centralized or distributed, whether local or remote.

[0036] In addition, the various functions described below may be implemented or supported by one or more computer programs, each of which is formed of computer-readable program code and is implemented in a computer-readable medium. The terms "application" and "program" refer to one or more computer programs, software components, instruction sets, procedures, functions, objects, classes, instances, related data, or portions thereof suitable for implementation in a suitable computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer-readable medium" includes any type of medium that can be accessed by a computer, such as read-only memory (ROM), random access memory (RAM), hard disk drive, compact disc (CD), digital video disc (DVD), or any other type of memory. A "non-transitory" computer-readable medium does not include wired, wireless, optical, or other communication links that transmit transitory electrical or other signals. Non-transitory computer-readable media include media in which data can be permanently stored and media in which data can be stored and later rewritten, such as rewritable optical discs or erasable memory devices.

[0037] Throughout this patent document, definitions of certain words and phrases are provided, and those of ordinary skill in the art should understand that in many instances, if not most instances, such definitions apply to both the prior and future use of such defined words and phrases.

[0038] In the following description, the BS is an entity that allocates resources to a terminal and may be at least one of a gNodeB, eNodeB, Node B, BS, radio access unit, BS controller, and a node on the network. The terminal may include a UE, mobile station (MS), cellular phone, smart phone, computer, or a multimedia system capable of performing communication functions.

[0039] In recent years, several broadband wireless technologies have been developed to meet the increasing number of broadband users and provide more and better applications and services. The second-generation wireless communication systems have been developed to provide voice services while ensuring user mobility. The third-generation wireless communication systems support not only voice services but also data services. In recent years, the fourth-generation wireless communication systems have been developed to provide high-speed data services. However, currently, the fourth-generation wireless communication systems lack resources to meet the growing demand for high-speed data services. Therefore, the fifth-generation wireless communication systems (also known as next-generation radio or NR) are being developed to meet the growing demand for high-speed data services, support for ultra-reliability and low-latency applications.

[0040] The fifth-generation wireless communication systems support not only lower frequency bands but also higher frequency (millimeter-wave) bands, for example, the 10 GHz to 100 GHz bands, in order to achieve higher data rates. To reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive MIMO, FD-MIMO, array antennas, analog beamforming, massive antenna technologies are being considered in the design of the fifth-generation wireless communication systems. In addition, it is expected that the fifth-generation wireless communication systems will address different usage scenarios with quite different requirements in terms of data rate, latency, reliability, mobility, etc. However, it is expected that the design of the air interface of the fifth-generation wireless communication systems will be flexible enough to serve UEs with quite different capabilities, depending on the usage scenario and the market segment in which the UE serves the end user.

[0041] A few example usage scenarios that the fifth-generation wireless communication systems are expected to address are eMBB, mMTC, URLLC, etc. The eMBB requirements such as data rates of dozens of Gbps, low latency, high mobility, etc. address the market segment representing traditional wireless broadband users who require ubiquitous, always-on, anytime, anywhere Internet connectivity. The mMTC requirements such as very high connection density, infrequent data transmission, very long battery life, low mobility, etc. address the market segment representing the Internet of Things (IoT) / Internet of Everything (IoE) that envisions the connectivity of billions of devices. The URLLC requirements such as very low latency, very high reliability, and variable mobility, etc. address the market segment representing industrial automation applications, vehicle-to-vehicle / vehicle-to-infrastructure communication that is foreseen as one of the enablers for autonomous vehicles.

[0042] In a fifth-generation wireless communication system, operating in a higher frequency (e.g., millimeter wave) band, a User Equipment (UE) and a next-generation Node B (gNB) communicate with each other using beamforming. Beamforming techniques are used to mitigate propagation path loss and increase the propagation distance for communication in the higher frequency band. Beamforming uses high-gain antennas to enhance transmit (TX) and receive (RX) performance. Beamforming can be classified into TX beamforming performed at the transmit end and RX beamforming performed at the receive end. Generally, TX beamforming allows the area where the propagation arrives to be densely located in a specific direction by using multiple antennas to increase directivity. In this case, the aggregation of multiple antennas can be referred to as an antenna array, and each antenna included in the array can be referred to as an array element. The antenna array can be configured in various forms, such as a linear array, a planar array, etc. The use of TX beamforming results in an increase in the directivity of the signal, thus increasing the propagation distance. In addition, since the signal is hardly transmitted in directions other than the directional direction, the signal interference acting on another receiving end is significantly reduced. The receiving end can perform beamforming on the RX signal by using an RX antenna array. RX beamforming increases the RX signal strength transmitted in a specific direction by allowing the propagation to be concentrated in a specific direction and excludes the signals transmitted in directions other than the specific direction, thus providing an effect of blocking interference signals. By using beamforming techniques, a transmitter can generate multiple transmit beam patterns in different directions. Each of these transmit beam patterns can also be referred to as a transmit (TX) beam. A wireless communication system operating at high frequencies uses multiple narrow TX beams to transmit signals in a cell because each narrow TX beam provides coverage to a part of the cell. The narrower the TX beam, the higher the antenna gain, and thus the greater the propagation distance of the signal transmitted using beamforming. A receiver can also direct multiple receive (RX) beam patterns in different directions. Each of these receive patterns can also be referred to as an RX beam.

[0043] The fifth-generation wireless communication system supports stand-alone operation mode and dual connectivity (DC). In DC, multiple Rx / Tx UEs can be configured to utilize resources provided by two different nodes (or NBs) connected via a non-ideal backhaul. One node acts as the master node (MN), while the other node acts as the secondary node (SN). The MN and SN are connected via a network interface, and at least the MN is connected to the core network. NR also supports multi-RAT dual connectivity (MR-DC) operation, whereby a UE in RRC_CONNECTED is configured to utilize radio resources provided by two different schedulers located in two different nodes connected via a non-ideal backhaul and providing E-UTRA (i.e., if the node is an ng-eNB) or NR access (i.e., if the node is a gNB). In NR, for a UE in RRC_CONNECTED that is not configured with CA / DC, there is only one serving cell, which includes the primary cell. For a UE in RRC_CONNECTED that is configured with CA / DC, the term'serving cell' is used to denote the set of cells that includes (multiple) special cells ((multiple) SpCell) and all secondary cells. In NR, the term master cell group (MCG) refers to the group of serving cells associated with the MN, which includes the primary cell (PCell), and optionally includes one or more secondary cells (SCell). In NR, the term secondary cell group (SCG) refers to the group of serving cells associated with the SN, which includes the primary SCG cell (PSCell), and optionally includes one or more SCell. In NR, the PCell refers to the serving cell in the MCG operating on the primary frequency, where the UE performs the initial connection establishment process or initiates the connection reconstruction process. In NR, for a UE configured with CA, the SCell is a cell that provides additional radio resources on top of the SpCell. The PSCell refers to the serving cell in the SCG where the UE performs random access when a Reconfiguration with Sync process is executed. For dual connectivity operation, the term SpCell (i.e., special cell) refers to the PCell of the MCG or the PSCell of the SCG; otherwise, the term SpCell refers to the PCell.

[0044] Physical Downlink Control Channel (PDCCH) in the fifth-generation wireless communication system

[0045] In the fifth-generation wireless communication system, the PDCCH is used to schedule downlink (DL) transmissions on the physical downlink shared channel (PDSCH) and uplink (UL) transmissions on the physical uplink shared channel (PUSCH), where the downlink control information (DCI) on the PDCCH includes: downlink allocation, including at least modulation and coding format, resource allocation, and hybrid automatic repeat request (HARQ) information related to the downlink shared channel (DL-SCH); UL scheduling grant, including at least modulation and coding format, resource allocation, and HARQ information related to the uplink shared channel (UL-SCH). In addition to scheduling, the PDCCH can also be used for: activating and deactivating configured PUSCH transmissions using configured grants; activating and deactivating semi-persistent PDSCH transmissions; notifying one or more UEs of the slot format; notifying one or more UEs of (multiple) physical resource blocks (PRBs) and (multiple) OFDM symbols, where in the (multiple) PRBs and (multiple) OFDM symbols, the UE can assume that no transmission is intended for the UE; transmitting transmission power control (TPC) commands for the physical uplink control channel (PUCCH) and PUSCH; transmitting one or more TPC commands for one or more UEs to transmit sounding reference signals (SRS); switching the active bandwidth part of the UE; initiating a random access process.

[0046] The UE listens for a set of PDCCH candidates in the configured monitoring occasions in one or more configured control resource sets (CORESETs) according to the corresponding search space configuration. A CORESET consists of a set of PRBs with a duration of 1 to 3 OFDM symbols. Resource element groups (REGs) and control channel elements (CCEs) are defined within the CORESET, where each CCE includes a set of REGs. Control channels are formed by aggregating CCEs. Different coding rates of the control channel are achieved by aggregating different numbers of CCEs. Interleaved and non-interleaved CCE-to-REG mappings are supported in the CORESET. Polar coding is used for the PDCCH. Each resource element group carrying the PDCCH carries its own demodulation reference signal (DMRS). Quadrature phase shift keying (QPSK) modulation is used for the PDCCH.

[0047] In the fifth-generation wireless communication system, the gNB signals a list of search space configurations for each configured BWP, where each search space configuration is uniquely identified by an identifier. The identifier of the search space configuration to be used for a specific purpose (such as paging reception, system information (SI) reception, random access response reception) is explicitly signaled by the gNB. In NR, the search space configuration includes the following parameters: Monitoring-periodicity-PDCCH-slot, Monitoring-offset-PDCCH-slot, Monitoring-symbols-PDCCH-within-slot, and duration. The UE uses the PDCCH monitoring period (Monitoring-periodicity-PDCCH-slot), PDCCH monitoring offset (Monitoring-offset-PDCCH-slot), and PDCCH monitoring pattern (Monitoring-symbols-PDCCH-within-slot) parameters to determine the (multiple) PDCCH monitoring opportunities within a time slot. The PDCCH monitoring opportunities in time slots 'x' to x + duration (where the time slot with number 'x' is in a radio frame with number 'y') satisfy the following equation:

[0048] (y * (number of time slots in a radio frame) + x - Monitoring-offset-PDCCH-slot) mod (Monitoring-periodicity-PDCCH-slot) = 0;... Equation 1

[0049] The starting symbol of the PDCCH monitoring opportunity in each time slot with a PDCCH monitoring opportunity is given by Monitoring-symbols-PDCCH-within-slot. The length (in symbols) of the PDCCH monitoring opportunity is given in the corset associated with the search space. The search space configuration includes the identifier of the coreset configuration associated with it. For each configured BWP, the gNB signals a list of coreset configurations, where each coreset configuration is uniquely identified by an identifier. Note that each radio frame has a duration of 10 ms. The radio frame is identified by a radio frame number or a system frame number. Each radio frame includes a number of time slots, where the number of time slots in a radio frame and the duration of a time slot depend on the subcarrier spacing. The number of time slots in a radio frame and the time slot duration for each supported subcarrier spacing (SCS) are predefined in NR.

[0050] Each coreset configuration is associated with a list of transmission configuration indicator (TCI) states. A DL reference signal (RS) identity (e.g., a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS)) is configured per TCI state. The list of TCI states corresponding to the coreset configuration is signaled by the gNB via radio resource control (RRC) signaling. One of the TCI states in the list of TCI states is activated and indicated to the UE by the gNB via media access control - control element (MAC-CE). The TCI state indication is used by the gNB for the DL TX beam for transmitting the PDCCH in the PDCCH monitoring occasion of the search space (the DL TX beam is quasi co-located (QCL) with the SSB / CSI-RS of the TCI state). For the PDSCH, the TCI state of the scheduling PDCCH can be used for the scheduled PDSCH. Alternatively, the TCI state of the PDCCH for the lowest coreset ID in the slot is used for the PDSCH. Alternatively, a combination of RRC + MAC CE + DCI is used to indicate the TCI state of the PDSCH. The RRC configures the list of TCI states, the MAC CE indicates a subset of these TCI states, and the DCI indicates one of the TCI states from the list of TCI states indicated in the MAC CE.

[0051] Bandwidth adaptation (BA) in the fifth generation wireless communication system

[0052] In the fifth generation wireless communication system, BA is supported. With BA, the receive and transmit bandwidths of the UE do not need to be as large as the bandwidth of the cell and can be adjusted: the width can be commanded to change (e.g., shrink during low activity periods to save power); the position can be moved in the frequency domain (e.g., to increase scheduling flexibility); and the subcarrier spacing can be commanded to change (e.g., to allow for different services). A subset of the total cell bandwidth of the cell is called a BWP. BA is achieved by configuring the RRC-connected UE with (one or more) BWPs and telling the UE which of the configured BWPs is currently active. When BA is configured, the UE only needs to monitor the PDCCH on one active BWP, i.e., it does not need to monitor the PDCCH on the entire DL frequency of the serving cell. In the RRC connected state, the UE is configured with one or more DL and UL BWPs for each configured serving cell (i.e., the PCell or SCell). For an active serving cell, there is always one active UL and DL BWP at any point in time.

[0053] The BWP switch for the serving cell is used to activate an inactive BWP and deactivate an active BWP at a time. The BWP switch is controlled by a PDCCH indicating a downlink allocation or a UL grant, by the bwp-InactivityTimer, by RRC signaling, or by the media access control (MAC) entity itself when initiating a random access procedure. When adding an SpCell or activating an SCell, without receiving a PDCCH indicating a downlink allocation or a UL grant, the DL BWP and UL BWP indicated by the firstActiveDownlinkBWP-Id and firstActiveUplinkBWP-Id respectively are active. The active BWP of the serving cell is indicated by RRC or PDCCH. For unpaired spectrum, the DL BWP is paired with the UL BWP, and the BWP switch is common for both UL and DL. When the BWP inactivity timer expires, the UE switches the active DL BWP to the default DL BWP or the initial DL BWP (if the default DL BWP is not configured).

[0054] Random Access (RA) in the Fifth Generation Wireless Communication System

[0055] In the 5G wireless communication system, RA is supported. RA is used to achieve UL time synchronization. RA is used by an asynchronous UE in the RRC connected (RRCCONNECTED) state during initial access, handover, RRC connection reestablishment procedure, scheduling request (SR) transmission, SCG addition / modification, beam failure recovery (BFR), and data or control information transmission in UL. Several types of random access procedures are supported.

[0056] Contention-based Random Access (CBRA):

[0057] This is also known as 4-step CBRA. In this type of random access, the UE first sends a random access preamble (also known as Message 1 (Msg1)), and then waits for a random access response (RAR) in the RAR window. The RAR is also known as Message 2 (Msg2). The gNB sends the RAR on the PDSCH. The PDCCH scheduling the PDSCH carrying the RAR is addressed to the RA-Radio Network Temporary Identifier (RA-RNTI). The RA-RNTI identifies the time-frequency resource where the gNB detected the RA preamble (also known as the Physical RA Channel (PRACH) occasion or PRACH transmission occasion or RA Channel (RACH) occasion). The RA-RNTI is calculated as follows: RA-RNTI = 1 + s_id + 14 * t_id + 14 * 80 * f_id + 14 * 80 * 8 * ul_carrier_id, where s_id is the index of the first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the PRACH occasion where the UE has sent Msg1 (i.e., the RA preamble); 0 ≤ s_id < 14; t_id is the index of the first slot of the PRACH occasion (0 ≤ t_id < 80); f_id is the index of the PRACH occasion in the frequency domain within the slot (0 ≤ f_id < 8), and ul_carrier_id is the UL carrier used for Msg1 transmission (0 for normal UL (NUL) carrier and 1 for supplementary UL (SUL) carrier). A number of RARs detected by the gNB for various random access preambles can be multiplexed by the gNB in the same RAR MAC protocol data unit (PDU). If the RAR includes the RA preamble identifier (RAPID) of the RA preamble sent by the UE, then the RAR in the MAC PDU corresponds to the UE's RA preamble transmission. If no RAR corresponding to its RA preamble transmission is received during the RAR window, and the UE has not sent the RA preamble a configurable (configured by the gNB in the RACH configuration) number of times, the UE returns to the first step, i.e., selects a random access resource (preamble / RACH occasion (RO)), and sends the RA preamble. A backoff can be applied before returning to the first step.

[0058] If the UE receives a RAR corresponding to its RA preamble transmission, it transmits Message 3 (Msg3) in the UL grant received in the RAR. Msg3 includes messages such as RRC connection request, RRC connection reestablishment request, RRC handover confirmation, SR, SI request, etc. It may include the UE identity (i.e., Cell Radio Network Temporary Identifier (C-RNTI) or System Architecture Evolution (SAE)-Temporary Mobile Subscriber Identity (S-TMSI) or random number). After transmitting Msg3, the UE starts a contention resolution timer. When the contention resolution timer is running, if the UE receives a PDCCH addressed to the C-RNTI included in Msg3, the contention resolution is considered successful, the contention resolution timer is stopped and the RA procedure is completed. When the contention resolution timer is running, if the UE receives a contention resolution MAC CE including the UE's contention resolution identity (the first X bits of the common control channel (CCCH) service data unit (SDU) transmitted in Msg3), the contention resolution is considered successful, the contention resolution timer is stopped and the RA procedure is completed. If the contention resolution timer expires and the UE has not transmitted the RA preamble a configurable number of times, the UE returns to the first step, i.e., selects a random access resource (preamble / RACH occasion) and transmits the RA preamble. A backoff may be applied before returning to the first step.

[0059] Contention-free random access (CFRA):

[0060] This is also known as legacy CFRA or 4-step CFRA. The CFRA procedure is used in scenarios such as handovers that require low latency, timing advance establishment for SCell, etc. The evolved Node B (eNB) allocates a dedicated random access preamble to the UE. The UE transmits the dedicated RA preamble. The eNB transmits the RAR on the PDSCH addressed to the RA-RNTI. The RAR conveys the RA preamble identifier and timing alignment information. The RAR may also include a UL grant. Similar to the CBRA procedure, the RAR is transmitted within the RAR window. After receiving the RAR including the RA preamble identifier (RAPID) of the RA preamble transmitted by the UE, the CFRA is considered successfully completed. In the case of initiating RA for BFR, if a PDCCH addressed to the C-RNTI is received in the search space for BFR, the CFRA is considered successfully completed. If the RAR window expires and the RA is not successfully completed, and the UE has not transmitted the RA preamble a configurable (configured by the gNB in the RACH configuration) number of times, the UE retransmits the RA preamble.

[0061] For certain events such as handover and BFR, if dedicated preambles are allocated to the UE, during the first step of random access, i.e., during the random access resource selection for Msg1 transmission, the UE determines whether to send a dedicated preamble or a non-dedicated preamble. Dedicated preambles are typically provided for a subset of SSB / CSI RS. If there is no SSB / CSI RS with a DL reference signal received power (RSRP) higher than a threshold in the SSB / CSI RS for which the gNB provides contention-free random access resources (i.e., dedicated preamble / RO), the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Thus, during the RA procedure, one random access attempt can be CFRA while other random access attempts can be CBRA.

[0062] Two-step contention-based random access (2-step CBRA):

[0063] In the first step, the UE sends a random access preamble on the PRACH and a payload (i.e., MAC PDU) on the PUSCH. The random access preamble and payload transmission are also referred to as Message A (MsgA). In the second step, after MsgA transmission, the UE listens for a response from the network (i.e., gNB) within the configured window. This response is also referred to as Message B (MsgB). The gNB sends MsgB on the PDSCH. The PDCCH scheduling the PDSCH carrying MsgB is addressed to the MsgB-radio network temporary identifier (MSGB-RNTI). The MSGB-RNTI identifies the time-frequency resource (also referred to as the PRACH occasion or PRACH TX occasion or RACH occasion) in which the gNB detected the RA preamble. The MSGB-RNTI is calculated as follows: RA-RNTI = 1 + s_id + 14*t_id + 14*80*f_id + 14*80*8*ul_carrier_id + 14X80X8X2, where s_id is the index of the first orthogonal frequency division multiplexing (OFDM) symbol of the PRACH occasion in which the UE has sent Msg1 (i.e., RA preamble); 0 ≤ s_id < 14; t_id is the index of the first time slot of the PRACH occasion (0 ≤ t_id < 80); f_id is the index of the PRACH occasion in the frequency domain within the time slot (0 ≤ f_id < 8), and ul_carrier_id is the UL carrier used for Msg1 transmission (0 for normal UL (NUL) carrier and 1 for supplementary UL (SUL) carrier).

[0064] If the CCCH SDU is sent in the MsgA payload, the UE uses the contention resolution information in MsgB to perform contention resolution. If the contention resolution identity received in MsgB matches the first 48 bits of the CCCH SDU sent in MsgA, the contention resolution is successful. If a C-RNTI is sent in the MsgA payload, the contention resolution is successful if the UE receives a PDCCH addressed to the C-RNTI. If the contention resolution is successful, the random access procedure is considered to be successfully completed. Instead of the contention resolution information corresponding to the sent MsgA, MsgB may include fallback information corresponding to the random access preamble sent in MsgA. If the fallback information is received, the UE sends Msg3 and performs contention resolution using Msg4 as in the CBRA procedure. If the contention resolution is successful, the random access procedure is considered to be successfully completed. If the contention resolution fails during fallback (i.e., when sending Msg3), the UE re-sends MsgA. If the configured window for the UE to listen for a network response expires after sending MsgA and the UE does not receive MsgB including the contention resolution information or fallback information as described above, the UE re-sends MsgA. If the random access procedure is not successfully completed even after sending MsgA a configurable number of times, the UE falls back to the 4-step RACH procedure, i.e., the UE only sends a PRACH preamble.

[0065] The MsgA payload may include one or more of a CCCH SDU, a dedicated control channel (DCCH) SDU, a dedicated traffic channel (DTCH) SDU, a buffer status report (BSR) MAC CE, a power headroom report (PHR) MAC CE, SSB information, a C-RNTI MAC CE, or padding.

[0066] MsgA may include a UE ID (e.g., a random ID, S-TMSI, C-RNTI, recovery ID, etc.) and the preamble in the first step. The UE ID may be included in the MAC PDU of MsgA. A UE ID such as C-RNTI may be carried in a MAC CE, where the MAC CE is included in the MAC PDU. Other UE IDs (such as random ID, S-TMSI, C-RNTI, recovery ID, etc.) may be carried in the CCCH SDU. The UE ID may be one of a random ID, S-TMSI, C-RNTI, recovery ID, IMSI, idle mode ID, inactive mode ID, etc. The UE ID may be different in different scenarios where the UE performs the RA process. When the UE performs RA after power-on (before it attaches to the network), the UE ID is a random ID. When the UE performs RA in the idle state after it attaches to the network, the UE ID is S-TMSI. If the UE has an assigned C-RNTI (e.g., in the connected state), the UE ID is C-RNTI. In the case where the UE is in the inactive state, the UE ID is the recovery ID.

[0067] In addition to the UE ID, some additional control information may be sent in MsgA. The control information may be included in the MAC PDU of MsgA. The control information may include one or more of a connection request indication, a connection recovery request indication, an SI request indication, a buffer status indication, beam information (e.g., one or more DL TX beam IDs or SSB IDs), a BFR indication / information, a data indicator, a cell / BS / TRP handover indication, a connection reestablishment indication, a reconfiguration complete or handover complete message, etc.

[0068] Two-step contention-free random access (2-step CFRA):

[0069] In this case, the gNB allocates (multiple) dedicated random access preambles and (multiple) PUSCH resources for MsgA transmission to the UE. (Multiple) ROs for preamble transmission may also be indicated. In the first step, the UE uses contention-free random access resources (i.e., dedicated preambles / PUSCH resources / ROs) to send a random access preamble on the PRACH and send a payload on the PUSCH. In the second step, after MsgA transmission, the UE listens for a response from the network (i.e., the gNB) within a configured window. This response is also referred to as MsgB.

[0070] The gNB sends MsgB on the PDSCH. The PDCCH scheduling the PDSCH carrying MsgB is addressed to the MSGB-RNTI. The MSGB-RNTI identifies the time-frequency resource (also referred to as the PRACH occasion or PRACH TX occasion or RACH occasion) in which the gNB detected the RA preamble. The MSGB-RNTI is calculated as follows: RA-RNTI = 1 + s_id + 14*t_id + 14*80*f_id + 14*80*8*ul_carrier_id + 14X80X8X2, where s_id is the index of the first Orthogonal Frequency Division Multiplexing (OFDM) symbol of the PRACH occasion in which the UE has sent Msg1 (i.e., the RA preamble); 0 ≤ s_id < 14; t_id is the index of the first time slot of the PRACH occasion (0 ≤ t_id < 80); f_id is the index of the PRACH occasion in the frequency domain within the time slot (0 ≤ f_id < 8), and ul_carrier_id is the UL carrier used for Msg1 transmission (0 for normal UL (NUL) carriers and 1 for supplementary UL (SUL) carriers).

[0071] If the UE receives a PDCCH addressed to the C-RNTI, the random access procedure is considered to be successfully completed. If the UE receives fallback information corresponding to the preamble it has sent, the random access procedure is considered to be successfully completed.

[0072] For certain events such as handover and BFR, if dedicated preambles and PUSCH resources are allocated to the UE, during the first step of random access, i.e., during the random access resource selection for MsgA transmission, the UE determines whether to send a dedicated preamble or a non-dedicated preamble. Dedicated preambles are usually provided as a subset of SSB / CSI RS. If there is no SSB / CSI RS with a DL RSRP higher than the threshold among the SSB / CSI RSs for which the gNB provides contention-free random access resources (i.e., dedicated preambles / RO / PUSCH resources) to the UE, the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Thus, during the RA procedure, one random access attempt can be a two-step CFRA, while other random access attempts can be two-step CBRA.

[0073] When starting the random access procedure, the UE first selects a carrier (SUL or NUL). If the carrier to be used for the random access procedure is explicitly signaled by the gNB, the UE selects the signaled carrier to perform the random access procedure. If the carrier for the random access procedure is not explicitly signaled by the gNB; and if the serving cell for the random access procedure is configured with SUL and if the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL: the UE selects the SUL carrier to perform the random access procedure. Otherwise, the UE selects the NUL carrier to perform the random access procedure. Once the UL carrier is selected, the UE determines the UL and DL BWPs for the random access procedure as specified in Section 5.15 of TS 38.321. Then, the UE determines whether to perform a two-step or four-step RACH for this random access procedure.

[0074] - If this random access procedure is initiated by a PDCCH command and if the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000, the UE selects a four-step RACH.

[0075] - Otherwise, if two-step contention-free random access resources are signaled by the gNB for this random access procedure, the UE selects a two-step RACH.

[0076] - Otherwise, if four-step contention-free random access resources are signaled by the gNB for this random access procedure, the UE selects a four-step RACH.

[0077] - Otherwise, if the UL BWP selected for this random access procedure is configured with only two-step RACH resources, the UE selects a two-step RACH.

[0078] - Otherwise, if the UL BWP selected for this random access procedure is configured with only four-step RACH resources, the UE selects a four-step RACH.

[0079] - Otherwise, if the UL BWP selected for this random access procedure is configured with both two-step RACH resources and four-step RACH resources,

[0080] - If the RSRP of the downlink path loss reference is below the configured threshold, the UE selects a four-step RACH. Otherwise, the UE selects a two-step RACH.

[0081] Mobility in the fifth-generation wireless communication system:

[0082] There are two types of mobility, cell-level mobility and beam-level mobility.

[0083] Cell-level mobility requires triggering explicit RRC signaling, i.e., handover. For handover between gNBs, the signaling procedure at least includes the following basic components as shown in Figure 1 below.

[0084] Figure 1 Fig. shows the handover procedure between gNBs in a wireless communication system according to an embodiment of the present disclosure.

[0085] Referring to Figure 1 , in operation 101, the source gNB initiates a handover and sends a handover request (HANDOVER REQUEST) via the Xn interface. The source gNB sends a handover request message to the target gNB.

[0086] In operation 102, the target gNB performs admission control and provides a new RRC configuration as part of the handover request acknowledgement (HANDOVER REQUEST ACKNOWLEDGE). The target gNB sends a handover request acknowledgement message to the source gNB.

[0087] In operation 103, the source gNB provides the RRC configuration to the UE by forwarding the RRC Reconfiguration (RRC reconfiguration) message received in the handover request acknowledgement. The RRC Reconfiguration message at least includes the cell ID and all the information required to access the target cell, so that the UE can access the target cell without reading the system information. For some cases, the information required for contention-based and contention-free random access can be included in the RRC Reconfiguration message. The access information to the target cell can include beam-specific information (if any).

[0088] In operation 104, the UE moves the RRC connection to the target gNB and responds with RRC Reconfiguration Complete (RRC reconfiguration complete).

[0089] Several types of handovers are supported, e.g., normal handover, conditional handover, and DAPS handover.

[0090] Beam-level mobility does not require explicit RRC signaling to trigger. The gNB provides a measurement configuration for the serving cell to the UE via RRC signaling, which contains the configuration of SSB / CSI resources and resource sets, reporting, and trigger states for triggering channel and interference measurement and reporting. Then, beam-level mobility is handled at the lower layer by physical layer and MAC layer control signaling, and RRC does not need to know which beam is being used at a given time point. Based on the physical layer and MAC layer control signaling, the UE can switch from one beam to another in the serving cell.

[0091] Lower layer mobility:

[0092] A new type of lower layer mobility, also known as layer 1 (L1) / layer 2 (L2)-triggered mobility (LTM), is being studied. Lower layer mobility is based on L1 measurements provided by the UE to the serving cell. Based on these measurements, handovers are triggered by sending L1 (e.g., DCI) or L2 (e.g., MAC CE) commands. In lower layer mobility, the serving cell change is triggered based on L1 beam measurements instead of the L3 cell power and quality measurements configured in the Rel.15 NR baseline handover. The L3 cell quality measurements are reported only after the expiration of a certain trigger time (Time-to-Trigger, TTT) of the measurement event. Before reporting, the L3 measurements are also filtered based on the L3 configuration over multiple measurements. The advantage of L1 measurements is that the network can react faster to radio link degradation in the serving link because the network can save the delay introduced by L3 filtering and the TTT for handover decision. This will result in a reduction in the number of radio link failures compared to the baseline handover.

[0093] In traditional handovers, the RRC process delay includes RRC signal processing related to the decoding of the handover command and L2 / 3 reconfiguration of the protocol layers. For lower layer mobility, the RRC process delay can be reduced assuming that the UE can receive and decode the configuration of the target cell before the cell change occurs. In addition, since lower layer mobility is restricted to the intra-central unit (CU) scenario with the same packet data convergence protocol (PDCP) and RRC, the L2 / 3 reconfiguration can be minimized by maintaining the same configuration for PDCP and RRC and possibly other layers (e.g., radio link control (RLC) and MAC) in the intra-distributed unit (DU) scenario (i.e., in the inter-DU scenario, the new target cell can have different configurations for RLC and MAC). In the best case for intra-DU, the target cell can reconfigure only the new C-RNTI, which can save the entire L2 / 3 reconfiguration of the UE.

[0094] In traditional handovers, there are delays caused by RF / baseband retuning, derivation of the target gNB security key, and configuration of the security algorithm to be used in the target cell. These problems can also be avoided in lower layer mobility. Assuming that the PDCP entity in the CU is the same for the source cell and the target cell, the same security key and algorithm can be applied, which reduces the interruption time.

[0095] In traditional handovers, there are interruptions due to the uncertainty of obtaining the first available PRACH opportunity in the new cell. Additionally, there are interruptions in transmitting the PRACH preamble and receiving the RACH response (RAR). These RACH-related interruption components can be reduced in lower layer mobility by introducing RACH-less handovers, where in a RACH-less handover, the UE skips the entire random access procedure for the target cell. For cases where RACH-less cannot be applied, the UE can obtain the timing advance of the prepared target cell before the actual handover occurs.

[0096] For L1 / L2-based mobility, CFRA can be supported. The problem is how to configure CFRA resources for L1 / L2-based mobility.

[0097] Method 1

[0098] Figure 2 Illustrates a lower layer-based mobility procedure according to an embodiment of the present disclosure. The order of operations can be changed. Figure 2 Furthermore, some steps in Figure 2 can be omitted, or two or more steps can be combined for execution.

[0099] Referring to Figure 2 , in operation 201, the UE can send (a) measurement report(s) containing the measurement results of the serving cell and the (multiple) target cells. The measurement report(s) can be sent to the serving cell (e.g., the source DU of the serving cell). In operation 202, the source DU of the serving cell can then forward the measurement report to the CU. The measurement report can be based on L3 measurements or L1 measurements.

[0100] In operation 203, based on the reported measurement results, the CU can identify a potential set of candidate target cells to which the UE can be handed over. In this example, the CU can identify candidate target cells served by the source DU or another DU (i.e., the target DU), where the source DU or another DU is controlled by the same CU.

[0101] In operation 204, the CU can request the preparation of candidate target cells controlled by the target DU by sending a UE Context SetupRequest message to the target DU.

[0102] In operation 205, the target DU can provide the configuration of the UE in a UE Context SetupResponse message respectively, which contains a container from the DU to the CU. The configuration can include a UE-specific part and a non-UE-specific part.

[0103] Note that if no candidate target cell of other DUs is identified in operation 203, operations 204 and 205 may not be performed.

[0104] This configuration may include a 4-step RA configuration (rach-ConfigCommon) and / or a 2-step RA configuration (msgA-ConfigCommon). These RA configurations of the candidate target cell are BWP-specific and may be included in the corresponding BWP configuration of the candidate target cell. This configuration may be included in the UE context establishment response message.

[0105] rach-ConfigCommon indicates the prach-ConfigurationIndex used to identify the PRACH occasion in the time domain. rach-ConfigCommon indicates msg1-FDM (the number of PRACH transmission occasions FDM in one time instance) and msg1-FrequencyStart (the offset of the lowest PRACH transmission occasion in the frequency domain relative to PRB 0) to identify the PRACH occasion in the frequency domain. rach-ConfigCommon also indicates other parameters, such as preambleReceivedTargetPower, preambleTransMax, powerRampingStep, ra-ResponseWindow, ra-ContentionResolutionTimer, rsrp-ThresholdSSB, rsrp-ThresholdSSBSUL, preamble group B configuration, msg1-SubcarrierSpacing, and ssb-perRACH-OccasionAndCB-PreamblesPerSSB. rach-ConfigCommon may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI), which are to be applied to the 4-step RA initiated towards the cell upon an L1L2 cell change / handover command.

[0106] msgA-ConfigCommon includes the configuration of cell-specific MsgA PUSCH parameters, such as the MsgA PUSCH resources (msgA-PUSCH-ResourceGroupA) that the UE will use when performing MsgA transmission using preamble group A, and the PUSCH resources (msgA-PUSCH-ResourceGroupB) that the UE will use when performing MsgA transmission using preamble group B. msgA-ConfigCommon indicates the msgA-PRACH-ConfigurationIndex that is used to identify the PRACH occasion in the time domain. msgA-ConfigCommon indicates msgA-RO-FDM (the number of PRACH transmission occasions FDM in one time instance) and msgA-RO-FrequencyStart (the offset of the lowest PRACH transmission occasion in the frequency domain relative to PRB 0) to identify the PRACH occasion in the frequency domain. msgA-ConfigCommon also indicates other parameters, such as msgA-PreambleReceivedTargetPower, preambleTransMax, msgA-TransMax, msgA-PreamblePowerRampingStep, msgB-ResponseWindow, ra-ContentionResolutionTimer, msgA-RSRP-ThresholdSSB, preamble group B configuration, msgA-SubcarrierSpacing, and msgA-SSB-PerRACH-OccasionAndCB-PreamblesPerSSB. msgA-ConfigCommon may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) that are to be applied to the 4-step RA towards the cell when there is an L1L2 cell change / handover command.

[0107] The candidate target cell configuration for SpCell (which may be included in the UE context establishment response message) may include a dedicated RA configuration for SUL (rach-ConfigDedicated for CFRA) and / or a dedicated RA configuration for NUL (rach-ConfigDedicated) to be applied to the RA initiated towards the cell when indicating an L1L2 cell change / handoff command to switch to the cell. The rach-ConfigDedicated may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) to be applied to a 4-step RA. The rach-ConfigDedicated may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) to be applied to a 2-step RA.

[0108] The rach-ConfigDedicated may include 4-step RA parameters (such as prach-ConfigurationIndex, msg1-FDM, msg1-FrequencyStart) to identify the PRACH occasion, and other parameters (such as preambleReceivedTargetPower, preambleTransMax, powerRampingStep, ra-ResponseWindow). For a 4-step RA, the rach-ConfigDedicated may include a list of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB} and / or a list of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and list of RACH occasions for the CSI RS}. For a 4-step RA, the rach-ConfigDedicated may include ra-ssb-OccasionMaskIndex, which indicates a subset of the RACH occasions of each SSB that can be used among the RACH occasions of the 4-step RA.

[0109] rach-ConfigDedicated may include two-step RA parameters (such as msgA-PRACH-ConfigurationIndex, msgA-RO-FDM, msgA-RO-FrequencyStart) to identify the PRACH occasion, and other parameters (such as msgA-PreambleReceivedTargetPower, preambleTransMax, powerRampingStep, msgB-ResponseWindow). For two-step RA, rach-ConfigDedicated may include the MsgA PUSCH resource (msgA-CFRA-PUSCH) that the UE should use when performing MsgA transmission for CFRA. For two-step RA, rach-ConfigDedicated may include a list of one or more {SSB index, RA preamble index used in the RA occasion associated with the SSB, PUSCH resource index (msgA-PUSCH-Resource-Index) of the PUSCH resource to be used for the SSB} and / or a list of one or more {CSI RS index, RA preamble index, and PUSCH resource index (msgA-PUSCH-Resource-Index) of the PUSCH resource to be used for the SSB}. The PUSCH resource index indicates the valid PUSCH occasion and the associated DMRS resource corresponding to the PRACH time slot. The PUSCH resource index is sequentially numbered and mapped to the valid PUSCH occasion corresponding to the PRACH time slot, in the following order: first, in ascending order of the frequency resource index of the PUSCH occasion with frequency multiplexing; second, in ascending order of the DMRS resource index within the PUSCH occasion, where the DMRS resource index DMRS id is determined first in ascending order of the DMRS port index and then in ascending order of the DMRS sequence index; third, in ascending order of the time resource index of the PUSCH occasion with time multiplexing within the PUSCH time slot; and fourth, in ascending order of the index of the PUSCH time slot. For the case of the non-competitive two-step random access type, if this field does not exist, the UE will use the value 0. For two-step RA, rach-ConfigDedicated may include ra-ssb-OccasionMaskIndex, which indicates the subset of the RACH occasions of each SSB that can be used among the RACH occasions of the two-step RA. rach-ConfigDedicated may include the (multiple) PUSCH resource configurations for msgA CFRA, msgA-TransMax (the maximum number of MsgA preamble transmissions performed before switching to the four-step type random access).

[0110] In operation 206, the CU may request to prepare a candidate target cell controlled by the source DU by sending a UE Context Modification Request message to the source DU.

[0111] In operation 207, the source DU may provide the configuration of the UE in a UE Context Modification Response message containing a container from the DU to the CU. The configuration may include a UE-specific part and a non-UE-specific part.

[0112] Note that if no candidate target cell of the source DU is identified in operation 203, operations 206 and 207 may not be performed.

[0113] The configuration may include a 4-step RA configuration (rach-ConfigCommon) and / or a 2-step RA configuration (msgA-ConfigCommon). These RA configurations of the candidate target cell are BWP-specific and may be included in the corresponding BWP configuration of the candidate target cell. The configuration may be included in the UE Context Modification Response message.

[0114] The rach-ConfigCommon indicates the prach-ConfigurationIndex that is used to identify the PRACH occasion in the time domain. The rach-ConfigCommon indicates msg1-FDM (the number of PRACH transmission occasions FDM'd in one time instance) and msg1-FrequencyStart (the offset of the lowest PRACH transmission occasion in the frequency domain relative to PRB 0) to identify the PRACH occasion in the frequency domain. The rach-ConfigCommon also indicates other parameters such as preambleReceivedTargetPower, preambleTransMax, powerRampingStep, ra-ResponseWindow, ra-ContentionResolutionTimer, rsrp-ThresholdSSB, rsrp-ThresholdSSBSUL, preamble group B configuration, msg1-SubcarrierSpacing, and ssb-perRACH-OccasionAndCB-PreamblesPerSSB. The rach-ConfigCommon may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) that are to be applied to the 4-step RA towards the cell upon an L1L2 cell change / handover command.

[0115] msgA-ConfigCommon includes the configuration of cell-specific MsgA PUSCH parameters, such as the MsgA PUSCH resources (msgA-PUSCH-ResourceGroupA) that the UE will use when performing MsgA transmission using preamble group A, and the PUSCH resources (msgA-PUSCH-ResourceGroupB) that the UE will use when performing MsgA transmission using preamble group B. msgA-ConfigCommon indicates the msgA-PRACH-ConfigurationIndex that is used to identify the PRACH occasion in the time domain. msgA-ConfigCommon indicates msgA-RO-FDM (the number of PRACH transmission occasions FDM in one time instance) and msgA-RO-FrequencyStart (the offset of the lowest PRACH transmission occasion in the frequency domain relative to PRB 0) to identify the PRACH occasion in the frequency domain. msgA-ConfigCommon also indicates other parameters, such as msgA-PreambleReceivedTargetPower, preambleTransMax, msgA-TransMax, msgA-PreamblePowerRampingStep, msgB-ResponseWindow,, ra-ContentionResolutionTimer, msgA-RSRP-ThresholdSSB, preamble group B configuration, msgA-SubcarrierSpacing, and msgA-SSB-PerRACH-OccasionAndCB-PreamblesPerSSB. msgA-ConfigCommon may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) that are to be applied to the 4-step RA towards the cell when an L1L2 cell change / handover command is received.

[0116] The candidate target cell configuration of SpCell (which may be included in the UE context modification response message) may include a dedicated RA configuration for SUL (rach-ConfigDedicated for CFRA) and / or a dedicated RA configuration for NUL (rach-ConfigDedicated) to be applied to the RA initiated towards the cell when indicating an L1L2 cell change / handover command to switch to the cell. The rach-ConfigDedicated may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) to be applied to the 4-step RA. The rach-ConfigDedicated may include RA prioritization parameters (powerRampingStepHighPriority and scalingFactorBI) to be applied to the 2-step RA.

[0117] The rach-ConfigDedicated may include 4-step RA parameters (such as prach-ConfigurationIndex, msg1-FDM, msg1-FrequencyStart) to identify the PRACH occasion, and other parameters (such as preambleReceivedTargetPower, preambleTransMax, powerRampingStep, ra-ResponseWindow). For the 4-step RA, the rach-ConfigDedicated may include a list of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB} and / or a list of one or more {CSI-RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and list of RACH occasions for the CSI RS}. For the 4-step RA, the rach-ConfigDedicated may include ra-ssb-OccasionMaskIndex, which indicates a subset of the RACH occasions of each SSB that can be used among the RACH occasions of the 4-step RA.

[0118] rach-ConfigDedicated may include two-step RA parameters (such as msgA-PRACH-ConfigurationIndex, msgA-RO-FDM, msgA-RO-FrequencyStart) to identify the PRACH occasion, and other parameters (such as msgA-PreambleReceivedTargetPower, preambleTransMax, powerRampingStep, msgB-ResponseWindow). For two-step RA, rach-ConfigDedicated may include the MsgA PUSCH resource (msgA-CFRA-PUSCH) that the UE shall use when performing MsgA transmission for CFRA. For two-step RA, rach-ConfigDedicated may include a list of one or more {SSB index, RA preamble index used in the RA occasion associated with the SSB, PUSCH resource index (msgA-PUSCH-Resource-Index) of the PUSCH resource to be used for the SSB} and / or a list of one or more {CSI RS index, RA preamble index and PUSCH resource index (msgA-PUSCH-Resource-Index) of the PUSCH resource to be used for the SSB}. The PUSCH resource index indicates the valid PUSCH occasion and the associated DMRS resource corresponding to the PRACH time slot. The PUSCH resource index is numbered sequentially and mapped to the valid PUSCH occasion corresponding to the PRACH time slot, in the following order: first, in ascending order of the frequency resource index of the PUSCH occasion according to frequency reuse; second, in ascending order of the DMRS resource index within the PUSCH occasion, where the DMRS resource index DMRS id is determined first in ascending order of the DMRS port index and then in ascending order of the DMRS sequence index; third, in ascending order of the time resource index of the time-multiplexed PUSCH occasion within the PUSCH time slot; and fourth, in ascending order of the index of the PUSCH time slot. For the case of the non-competitive two-step random access type, if this field does not exist, the UE shall use the value 0. For two-step RA, rach-ConfigDedicated may include ra-ssb-OccasionMaskIndex, which indicates the subset of the RACH occasions of each SSB that can be used among the RACH occasions of the two-step RA. rach-ConfigDedicated may include the (multiple) PUSCH resource configurations for msgA CFRA, msgA-TransMax (the maximum number of MsgA preamble transmissions performed before switching to the four-step type random access).

[0119] After receiving the UE configuration for the candidate target cell(s), in operation 208, the CU may generate an RRC reconfiguration. The RRC reconfiguration may include the configuration of the candidate target cell(s) sent to the UE in operations 209 / 210. The RRC reconfiguration may include a separate RRC reconfiguration IE for each candidate target cell in the candidate target cell(s) or a CellGroupConfig IE for each candidate target cell in the candidate target cell(s).

[0120] In operation 209, the CU may send the configuration to the source DU. Then, in operation 210, the source DU may send it to the UE via RRCReconfiguration (RRC reconfiguration). In addition to other information, the RRC reconfiguration message may include: a measurement report configuration for L1 / L2 mobility, i.e., a configuration on how to report the L1 beam measurements of the serving cell and the target cell; the configuration of the candidate cell(s) for which the UE needs to perform the (multiple) preparations when receiving an L1 / L2 command to change the serving cell, such as the random access configuration, radio bearer configuration, indication of whether to perform PDCP reconstruction (per DRB or common for all DRBs), indication of whether to perform PDCP-level data recovery (per DRB or common for all DRBs), indication of whether to perform RLC reconstruction (per DRB or RLC channel or common for all DRBs or RLC channels), indication of whether to perform MAC reset or partial MAC reset, etc. The RRC reconfiguration may also include the firstActiveUplinkBWP and firstActiveDownlinkBWP for each prepared candidate cell, and a list of DL and UL BWP configurations for each prepared candidate cell. The RRC reconfiguration may also include the InitialUplinkBWP and InitialDownlinkBWP for each prepared candidate cell, and a list of DL and UL BWP configurations for each prepared candidate cell.

[0121] In operations 211 and 212, the UE may confirm the RRC reconfiguration to the network. In operation 211, the UE may send an RRC reconfiguration complete message to the source DU. In operation 212, the source DU may pass the RRC reconfiguration complete message to the CU.

[0122] After confirming the RRC reconfiguration to the network, in operation 213, the UE may start reporting the L1 beam measurements of the serving cell and the candidate target cells.

[0123] Based on the measurement, the serving cell (e.g., the source DU of the serving cell) may decide to trigger a cell change command in operation 214. In an example, when it is determined that there is a target candidate cell with better radio link / beam measurement than the serving cell, e.g., when the L1-RSRP of the target beam measurement > the L1-RSRP of the serving beam measurement + the offset for the time period (i.e., the triggering time (TTT) period), in operation 215, the serving cell may send an L1 or L2 cell change / handover command to trigger a cell change to the target candidate cell. The target cell is indicated in the L1 or L2 cell change / handover command. It should be noted that the RRCReconfiguration may also be sent based on the measurement received in operation 213, and later when the conditions for cell change are met, the serving cell may send an L1 or L2 cell change / handover command. The L1 or L2 cell change / handover command may be sent using DCI or MAC CE.

[0124] Upon receiving an L1 or L2 cell change / handover command (MAC CE or DCI) for the target cell (e.g., SpCell), the UE may perform the following operations:

[0125] (Condition 1) In an embodiment, if the UE maintains a timing advance (TA) for the target cell (e.g., SpCell) before receiving the L1 / L2 cell handover change / command, and the time alignment timer (TAT) for the timing advance group (TAG) for the target cell is not running;

[0126] Or

[0127] (Condition 2) In an embodiment, if the RRCReconfiguration message received in operation 210 or the L1 / L2 cell handover / change command received in operation 215 includes an indication to perform RA towards the target cell;

[0128] Or

[0129] (Condition 3): In an embodiment, if the L1 / L2 cell handover / change command received in operation 215 does not include the TA of the target cell, and the UE does not have a valid TA for the target cell (e.g., the TA received from the network before the L1 / L2 cell handover / change command or estimated by the UE), then:

[0130] The UE may initiate an RA procedure towards the target cell. The indication to perform RA upon receiving the L1 / L2 cell handover / change command towards the target cell may be the presence of the ReconfigurationwithSync IE or a new indication in the SpCellConfig received in operation 210.

[0131] Specifically, for the RA procedure initiated upon receiving an L1 / L2 cell handover / change command, the UE may perform the operations described below (e.g., UL carrier selection, BWP selection, RA type selection, msgA-TransMax processing, RA prioritization processing, SSB and preamble selection, PRACH occasion selection, PUSCH occasion selection, etc.).

[0132] ■ UL Carrier Selection , for the RA procedure initiated upon receiving an L1 / L2 cell handover / change command

[0133] UL transmissions such as RACH preambles, MsgA, Msg3, etc. during the RA procedure are sent to the target cell on the selected UL carrier.

[0134] ● If SUL is not configured for the target cell, the UE selects NUL.

[0135] ● If SUL is configured for the target cell:

[0136] ● In the case where rach-ConfigDedicated is received / included in the configuration of the target cell (received in operation 210),

[0137] ● If rach-ConfigDedicated is received / included in the configuration of the target cell for SUL, the UE selects the SUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for NUL, the UE selects the NUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for both SUL and NUL, the UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL, otherwise NUL.

[0138] ● In the case where rach-ConfigDedicated is not received / included in the configuration of the target cell,

[0139] ● The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL, otherwise NUL.

[0140] ● (Or) If SUL is configured for the target cell:

[0141] ● In the case where the L1 / L2 cell handover / change command (DCI or MAC CE) indicates the UL carrier to be used:

[0142] ● If SUL is indicated in the L1 / L2 cell handover / change command, the UE selects the SUL carrier.

[0143] ● If NUL is indicated in the L1 / L2 cell handover / change command, the UE selects the NUL carrier.

[0144] ● In the case where the L1 / L2 cell handover / change command (DCI or MAC CE) does not indicate the UL carrier to be used:

[0145] ● (Option 1) The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0146] ● (Option 2) In the case where rach-ConfigDedicated is received / included in the configuration of the target cell,

[0147] ● If rach-ConfigDedicated is received / included in the configuration of the target cell for SUL, the UE selects the SUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for NUL, the UE selects the NUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for both SUL and NUL, the UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0148] ● In the case where rach-ConfigDedicated is not received / included in the configuration of the target cell,

[0149] ● The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0150] ■ BWP Selection , for the RA procedure initiated by the L1 / L2 cell handover / change command

[0151] - Option 1:

[0152] ● The UE uses the BWP corresponding to the BWP ID indicated by the fields firstActiveUplinkBWP and firstActiveDownlinkBWP included in the configuration of the target cell received in operation 210. The BWP configuration of the BWP indicated by the fields firstActiveUplinkBWP and firstActiveDownlinkBWP is also provided in the configuration of the target cell received in operation 210.

[0153] ● If firstActiveUplinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialUplinkBWP configured / included in the configuration of the target cell received in operation 210.

[0154] ● If firstActiveDownlinklinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialDownlinkBWP configured / included in the configuration of the target cell received in operation 210.

[0155] ● If RACH is to be performed on the target cell and firstActiveUplinkBWP is not configured for the RACH opportunity, the UE uses the UL BWP indicated by the initialUplinkBWP for UL and uses the DL BWP indicated by the initialDownlinkBWP (if firstActiveDownlinkBWP is different from the initialDownlinkBWP), where the fields initialUplinkBWP and initialDownlinkBWP are included in the configuration of the target cell received in operation 210.

[0156] - Option 2:

[0157] ● The DL / UL BWP (BWP ID) to be used is indicated in the L1 / L2 cell change / handover command. The UE uses the indicated BWP in the target cell. The BWP configuration of the BWP indicated by the L1 / L2 cell change / handover command is provided in the configuration of the target cell received in operation 210.

[0158] - Option 3:

[0159] ● The DL / UL BWP (BWP ID) to be used is optionally indicated in the L1 / L2 cell change / handover command. The BWP configuration of the BWP indicated by the L1 / L2 cell change / handover command is provided in the configuration of the target cell received in operation 210.

[0160] ● If there is no uplink BWP ID in the L1 / L2 cell change / handover command:

[0161] ● The UE uses the BWP indicated by the field firstActiveUplinkBWP in the configuration of the target cell received in operation 210;

[0162] ● If firstActiveUplinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialUplinkBWP configured / included in the configuration of the target cell received in operation 210.

[0163] ● Otherwise,

[0164] ● The UE uses the UL BWP indicated in the L1 / L2 cell change / handover command.

[0165] ● If there is no downlink BWP ID in the L1 / L2 cell change / handover command:

[0166] ● The UE uses the BWP indicated by the field firstActiveDownlinkBWP in the configuration of the target cell received in operation 210;

[0167] ● If firstActiveDownlinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialDownlinkBWP configured / included in the configuration of the target cell received in operation 210.

[0168] ● Otherwise,

[0169] ● The UE uses the UL BWP indicated in the L1 / L2 cell change / handover command.

[0170] ■ RA Type Selection , for the RA procedure initiated by the L1 / L2 cell handover / change command

[0171] - Option 1:

[0172] ● If contention - free random access resources for 4 - step RA type have been explicitly provided in rach - ConfigDedicated (rach - ConfigDedicated is received in the configuration of the target cell in operation 210 / rach - ConfigDedicated is included in the configuration of the target cell in operation 210) for the BWP selected for the random access procedure: The UE performs / initiates a 4 - step RA procedure.

[0173] ● Otherwise, if contention - free random access resources for 2 - step RA type have been explicitly provided in rach - ConfigDedicated for the BWP selected for the random access procedure: The UE performs / initiates a 2 - step RA procedure.

[0174] ● Otherwise, if the BWP selected for the random access procedure is configured with both 2 - step and 4 - step RA type random access resources and the RSRP of the downlink path - loss reference is higher than msgA - RSRP - Threshold: The UE performs / initiates a 2 - step RA procedure.

[0175] ● Otherwise,

[0176] ● The UE performs / initiates a 4 - step RA procedure.

[0177] - Option 2:

[0178] ● If contention - free random access resources for only 4 - step RA type have been explicitly provided in rach - ConfigDedicated (rach - ConfigDedicated is received in the configuration of the target cell in operation 210 / rach - ConfigDedicated is included in the configuration of the target cell in operation 210) for the BWP selected for the random access procedure: The UE performs / initiates a 4 - step RA procedure.

[0179] ● Otherwise, if contention - free random access resources for only 2 - step RA type have been explicitly provided in rach - ConfigDedicated (rach - ConfigDedicated is received in the configuration of the target cell in operation 210 / rach - ConfigDedicated is included in the configuration of the target cell in operation 210) for the BWP selected for the random access procedure: The UE performs / initiates a 2 - step RA procedure.

[0180] ● Otherwise, if the BWP selected for the random access procedure is configured with both 2 - step and 4 - step RA type random access resources and the RSRP of the downlink path - loss reference is higher than msgA - RSRP - Threshold: The UE performs / initiates a 2 - step RA procedure.

[0181] ● Otherwise,

[0182] ● The UE performs / initiates a 4-step RA procedure.

[0183] ■ msgA-TransMax Processing:

[0184] If the above selects 2-step RA, then

[0185] 1> If the random access procedure is initiated for synchronization reconfiguration, or for SCG activation, or for cell change triggered by an L1L2 cell change / handover command (MAC CE or DCI); and

[0186] 1> If cfra-TwoStep is configured for the selected carrier (note that the cfra-TwoStep IE is optionally included in rach-ConfigDedicated):

[0187] 2> If msgA-TransMax is configured in cfra-TwoStep:

[0188] 3> Apply msgA-TransMax configured in cfra-TwoStep.

[0189] 1> Otherwise, if msgA-TransMax is included in RACH-ConfigCommonTwoStepRA (msgA-ConfigCommon includes RACH-ConfigCommonTwoStepRA):

[0190] 2> Apply msgA-TransMax included in RACH-ConfigCommonTwoStepRA.

[0191] ■ RA Prioritization Processing for 2-step RA :

[0192] If the above selects 2-step RA, then

[0193] 1> If the random access procedure is initiated for synchronization reconfiguration, or for SCG activation, or for cell change triggered by an L1L2 cell change / handover command (MAC CE or DCI); and

[0194] 1> If rach-ConfigDedicated is configured for the selected carrier; and

[0195] 1> If ra-PrioritizationTwoStep is configured in rach-ConfigDedicated:

[0196] 2> Set PREAMBLE_POWER_RAMPING_STEP to the powerRampingStepHighPriority included in ra-PrioritizationTwoStep in rach-ConfigDedicated;

[0197] 2> If scalingFactorBI is configured in ra-PrioritizationTwoStep in rach-ConfigDedicated:

[0198] 3> Set SCALING_FACTOR_BI to scalingFactorBI.

[0199] ■ RA Prioritization Processing for 4-step RA:

[0200] If the above selects 4-step RA,

[0201] 1> If the random access procedure is initiated for synchronous reconfiguration or for SCG activation; and

[0202] 1> If rach-ConfigDedicated is configured for the selected carrier; and

[0203] 1> If ra-Prioritization is configured in rach-ConfigDedicated:

[0204] 2> Set PREAMBLE_POWER_RAMPING_STEP to the powerRampingStepHighPriority included in ra-Prioritization in rach-ConfigDedicated;

[0205] 2> If scalingFactorBI is configured in ra-Prioritization in rach-ConfigDedicated:

[0206] 3> Set SCALING_FACTOR_BI to scalingFactorBI.

[0207] If the selected RA_TYPE is set to 4-step RA (4-step RA), the MAC entity will:

[0208] ■ SSB and Preamble Selection

[0209] 1> If contention-free random access resources associated with an SSB have been explicitly provided in rach-ConfigDedicated (in operation 210), and at least one SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the associated SSBs is available:

[0210] 2> Select an SSB among the associated SSBs with an SS-RSRP higher than rsrp-ThresholdSSB;

[0211] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0212] 1> Otherwise, if contention-free random access resources associated with CSI-RS have been explicitly provided in rach-ConfigDedicated (in operation 210), and at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the associated CSI-RSs is available, then:

[0213] 2> Select a CSI-RS among the associated CSI-RSs with a CSI-RSRP higher than rsrp-ThresholdCSI-RS;

[0214] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0215] 1> Otherwise (i.e., for contention-based random access preamble selection): Perform the operation in the traditional manner

[0216] ■ PRACH Timing Selection

[0217] 1> If an SSB was selected above:

[0218] 2> Determine the next available PRACH occasion from the PRACH occasions corresponding to the selected SSB permitted by the restrictions given by ra-ssb-OccasionMaskIndex (if configured) or ssb-SharedRO-MaskIndex (if configured).

[0219] 1> Otherwise, if a CSI-RS was selected above:

[0220] 2> Determine the next available PRACH occasion from the PRACH occasions in the ra-OccasionList corresponding to the selected CSI-RS

[0221] Note: Use the prach-ConfigurationIndex included in rach-ConfigDedicated (in operation 210) to determine the PRACH occasion. If the prach-ConfigurationIndex is not included in rach-ConfigDedicated, use the prach-ConfigurationIndex in RACH-ConfigurationCommon (in operation 210) of the BWP selected for the RA procedure to determine the PRACH occasion. rach-ConfigDedicated is a rach-ConfigDedicated corresponding to the selected UL carrier.

[0222] 1> Execute the random access preamble transmission procedure.

[0223] If the selected RA_TYPE is set to 2-stepRA (two-step RA), the MAC entity shall:

[0224] ■ SSB and Preamble Selection

[0225] 1> If non-competitive two-step RA type resources associated with the SSB have been explicitly provided in rach-ConfigDedicated (in operation 210) and at least one SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs is available:

[0226] 2> Select the SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs;

[0227] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0228] 1> Otherwise (i.e., for contention-based random access preamble selection): Perform the operation in the traditional manner

[0229] ■ PRACH Timing Selection

[0230] 1> Determine the next available PRACH occasion from the PRACH occasions corresponding to the selected SSB permitted by the restrictions given by msgA-SSB-SharedRO-MaskIndex (if configured), or ra-ssb-OccasionMaskIndex (if configured), or ssb-SharedRO-MaskIndex (if configured).

[0231] ■ PUSCH Timing Selection

[0232] 1> If the MAC entity does not select a random access preamble among the (multiple) contention-based random access preambles:

[0233] 2> Select a PUSCH occasion from the PUSCH occasions configured in msgA-CFRA-PUSCH (in operation 210) corresponding to the PRACH slot of the selected PRACH occasion according to the msgA-PUSCH-Resource-Index corresponding to the selected SSB;

[0234] 2> Determine the UL grant for the MSGA payload and the associated HARQ information for the selected PUSCH occasion;

[0235] 2> Deliver the UL grant and the associated HARQ information to the HARQ entity.

[0236] 1> Otherwise:

[0237] 2> Select a PUSCH occasion corresponding to the selected preamble and PRACH occasion;

[0238] 2> Determine the UL grant for the MSGA payload according to the PUSCH configuration associated with the selected random access preamble group, and determine the associated HARQ information;

[0239] 2> If the selected preamble and PRACH occasion are mapped to a valid PUSCH occasion:

[0240] 3> Deliver the UL grant and the associated HARQ information to the HARQ entity.

[0241] 1> Execute the MSGA transmission procedure.

[0242] In an embodiment, the L1 / L2-triggered mobility / cell change can be accomplished by sending an L2 message similar to a C-RNTI MAC CE, or by sending an L3 message similar to an RRC reconfiguration complete in response to a received L1 / L2 cell change command.

[0243] Method 2

[0244] Figure 2 Operations 201 to 215 can be applied to Method 2. Therefore, reference can be made to the Figure 2 description described above, and redundant descriptions will be omitted for convenience.

[0245] In an alternative embodiment of the process described above,

[0246] - The L1L2 cell change / handover command (MAC CE or DCI) may include a CFRA configuration / resource for 4-step RA, which includes at least a list of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB} and / or a list of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and a list of RACH occasions for the CSI RS}. The size of the list may be one. During the RA process, the UE may select the SSB and RA preamble index indicated in the L1L2 cell change / handover command. The ra-ssb-OccasionMaskIndex and / or ssb-SharedRO-MaskIndex and / or ra-OccasionList may also be included in the L1L2 cell change / handover command. If not included in the L1L2 cell change / handover command, the UE may apply the ra-ssb-OccasionMaskIndex and / or ssb-SharedRO-MaskIndex and / or ra-OccasionList configured in rach-ConfigDedicated in Operation 210.

[0247] o In an alternative embodiment, rach-ConfigDedicated in Operation 210 may include a list X of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB} and / or a list Y of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and a list of RACH occasions for the CSI RS}. One or more row indices of list X and / or list Y, or the row indices of the combined list X and list Y, may be signaled in the L1 / L2 cell handover change / command. Based on the (multiple) row indices, the UE may identify a list of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB} and / or a list of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and a list of RACH occasions for the CSI RS} in the signaled L1L2 cell change / handover command.

[0248] - The L1 / L2 cell change / handover command (MAC CE or DCI) may include the CFRA configuration / resources for two-step RA, which at least includes a list of one or more {SSB index, RA preamble index used in the RA occasion associated with the SSB, PUSCH resource index of the PUSCH resource to be used for the SSB (msgA-PUSCH-Resource-Index)} and / or a list of one or more {CSI RS index, RA preamble index, and PUSCH resource index of the PUSCH resource to be used for the SSB (msgA-PUSCH-Resource-Index)}. The size of the list may be one.

[0249] o In an alternative embodiment, the rach-ConfigDedicated in operation 210 may include a list X of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB, PUSCH resource index of the PUSCH resource to be used for the SSB (msgA-PUSCH-Resource-Index)} and / or a list Y of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and list of RACH occasions of the PUSCH resource for the CSI-RS, PUSCH resource index of the PUSCH resource to be used for the CSI-RS (msgA-PUSCH-Resource-Index)}. One or more row indexes of list X and / or list Y, or the row indexes of the combined list X and list Y, may be signaled in the L1 / L2 cell handover change / command. Based on the (multiple) row indexes, the UE may identify in the signaled L1 / L2 cell change / handover command a list of one or more {SSB index and RA preamble index used in the RA occasion associated with the SSB, PUSCH resource index of the PUSCH resource to be used for the SSB (msgA-PUSCH-Resource-Index)} and / or a list of one or more {CSI RS index, RA preamble index used in the RA occasion associated with the CSI-RS, and list of RACH occasions of the PUSCH resource for the CSI-RS, PUSCH resource index of the PUSCH resource to be used for the CSI-RS (msgA-PUSCH-Resource-Index)}.

[0250] When receiving an L1 or L2 cell change / handover command (MAC CE or DCI) for a target cell (e.g., SpCell), the UE may perform the following operations:

[0251] (Condition 1) In an embodiment, if the UE maintains a TA for the target cell (e.g., SpCell) before receiving an L1 / L2 cell handover change / command, and the TAT of the TAG of the target cell is not running;

[0252] Or

[0253] (Condition 2) In an embodiment, if the RRCReconfiguration message received in operation 210 or the L1 / L2 cell handover / change command received in operation 215 includes an indication to perform RA towards the target cell;

[0254] Or

[0255] (Condition 3): In an embodiment, if the L1 / L2 cell handover / change command received in operation 215 does not include the TA of the target cell, and the UE does not have a valid TA for the target cell (e.g., a TA received from the network before the L1 / L2 cell handover / change command or estimated by the UE):

[0256] The UE may initiate an RA procedure towards the target cell. In an embodiment, the indication to perform RA upon receiving an L1 / L2 cell handover / change command towards the target cell may be the presence of the ReconfigurationwithSync IE or a new indication in the SpCellConfig received in operation 210.

[0257] Specifically, for an RA procedure initiated by an L1 / L2 cell handover / change command, the UE may perform the operations described below (e.g., UL carrier selection, BWP selection, RA type selection, msgA-TransMax processing, RA prioritization processing, SSB and preamble selection, PRACH timing selection, PUSCH timing selection, etc.).

[0258] ■ UL Carrier Selection , for an RA procedure initiated by an L1 / L2 cell handover / change command.

[0259] UL transmissions such as RACH preambles, MsgA, Msg3, etc. during the RA procedure are sent to the target cell on the selected UL carrier.

[0260] ● If SUL is not configured for the target cell, the UE selects NUL.

[0261] ● If SUL is configured for the target cell:

[0262] ● In the case where rach-ConfigDedicated is received / included in the configuration of the target cell (received in operation 210),

[0263] ● If rach-ConfigDedicated is received / included in the configuration of the target cell for SUL (received in operation 210), the UE selects the SUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for NUL (received in operation 210), the UE selects the NUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for both SUL and NUL (received in operation 210), the UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0264] ● In the case where rach-ConfigDedicated is not received / included in the configuration of the target cell (received in operation 210),

[0265] ● The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0266] ● (Or) If SUL is configured for the target cell:

[0267] ● In the case where the L1 / L2 cell handover / change command (DCI or MAC CE) indicates the UL carrier to be used:

[0268] ● If SUL is indicated in the L1 / L2 cell handover / change command, the UE selects the SUL carrier.

[0269] ● If NUL is indicated in the L1 / L2 cell handover / change command, the UE selects the NUL carrier.

[0270] ● In the case where the L1 / L2 cell handover / change command (DCI or MAC CE) does not indicate the UL carrier to be used:

[0271] ● (Option 1) The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0272] ●(Option 2) In the case where rach-ConfigDedicated is received / included in the configuration of the target cell (received in operation 210),

[0273] ● If rach-ConfigDedicated is received / included in the configuration of the target cell for SUL (received in operation 210), the UE selects the SUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for NUL (received in operation 210), the UE selects the NUL carrier. If rach-ConfigDedicated is received / included in the configuration of the target cell for both SUL and NUL (received in operation 210), the UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0274] ● In the case where rach-ConfigDedicated is not received / included in the configuration of the target cell (received in operation 210),

[0275] ● The UE selects the UL carrier based on the RSRP threshold rsrp-ThresholdSSB-SUL. If the RSRP of the downlink path loss reference is less than rsrp-ThresholdSSB-SUL, the UE selects SUL; otherwise, it selects NUL.

[0276] ■ BWP Selection for the RA procedure initiated by the L1 / L2 cell handover / change command

[0277] - Option 1:

[0278] ● The UE uses the BWP corresponding to the BWP ID indicated by the fields firstActiveUplinkBWP and firstActiveDownlinkBWP included in the configuration of the target cell received in operation 210. The BWP configuration of the BWP indicated by the fields firstActiveUplinkBWP and firstActiveDownlinkBWP is also provided in the configuration of the target cell received in operation 210.

[0279] ● If the firstActiveUplinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialUplinkBWP configured / included in the configuration of the target cell received in operation 210.

[0280] ● If the firstActiveDownlinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialDownlinkBWP configured / included in the configuration of the target cell received in operation 210.

[0281] ● If RACH is to be performed on the target cell and the firstActiveUplinkBWP is not configured for the RACH occasion, the UE uses the UL BWP indicated by the initialUplinkBWP for UL and uses the DL BWP indicated by the initialDownlinkBWP (if the firstActiveDownlinkBWP is different from the initialDownlinkBWP), where the fields initialUplinkBWP and initialDownlinkBWP are included in the configuration of the target cell received in operation 210.

[0282] - Option 2:

[0283] ● The DL / UL BWP (BWP ID) to be used is indicated in the L1 / L2 cell change / handover command. The UE uses the indicated BWP in the target cell. The BWP configuration of the BWP indicated by the L1 / L2 cell change / handover command is provided in the configuration of the target cell received in operation 210.

[0284] - Option 3:

[0285] ● The DL / UL BWP (BWP ID) to be used is optionally indicated in the L1 / L2 cell change / handover command. The BWP configuration of the BWP indicated by the L1 / L2 cell change / handover command is provided in the configuration of the target cell received in operation 210.

[0286] ● If there is no uplink BWP ID in the L1 / L2 cell change / handover command:

[0287] ● The UE uses the BWP indicated by the field firstActiveUplinkBWP in the configuration of the target cell received in operation 210;

[0288] ● If the firstActiveUplinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialUplinkBWP configured / included in the configuration of the target cell received in operation 210.

[0289] ● Otherwise,

[0290] ● The UE uses the UL BWP indicated in the L1 / L2 cell change / handover command.

[0291] ● If there is no downlink BWP ID in the L1 / L2 cell change / handover command:

[0292] ● The UE uses the BWP indicated by the field firstActiveDownlinkBWP in the configuration of the target cell received in operation 210;

[0293] ● If the firstActiveDownlinkBWP is not configured / included in the configuration of the target cell received in operation 210, the UE uses the initialDownlinkBWP configured / included in the configuration of the target cell received in operation 210.

[0294] ● Otherwise,

[0295] ● The UE uses the UL BWP indicated in the L1 / L2 cell change / handover command.

[0296] ■ RA Type Selection , for the RA procedure initiated by the L1 / L2 cell handover / change command

[0297] - Option 1:

[0298] ● If contention-free random access resources for the 4-step RA type have been explicitly provided in the rach-ConfigDedicated of the BWP selected for the random access procedure or in the L1 / L2 cell handover / change command: The UE performs / initiates the 4-step RA procedure.

[0299] ● Otherwise, if contention-free random access resources for the 2-step RA type have been explicitly provided in the rach-ConfigDedicated of the BWP selected for the random access procedure or in the L1 / L2 cell handover / change command: The UE performs / initiates the 2-step RA procedure.

[0300] ● Otherwise, if the BWP selected for the random access procedure or the L1 / L2 cell handover / change command is configured with / includes both two-step and four-step RA type random access resources and the RSRP of the downlink path loss reference is higher than msgA-RSRP-Threshold: the UE performs / initiates a two-step RA procedure.

[0301] ● Otherwise,

[0302] ● The UE performs / initiates a four-step RA procedure.

[0303] - Option 2:

[0304] ● If contention-free random access resources only for the four-step RA type have been explicitly provided in rach-ConfigDedicated of the BWP selected for the random access procedure or in the L1 / L2 cell handover / change command: the UE performs / initiates a four-step RA procedure.

[0305] ● Otherwise, if contention-free random access resources only for the two-step RA type have been explicitly provided in rach-ConfigDedicated of the BWP selected for the random access procedure or in the L1 / L2 cell handover / change command: the UE performs / initiates a two-step RA procedure.

[0306] ● Otherwise, if the BWP selected for the random access procedure or the L1 / L2 cell handover / change command is configured with / includes both two-step and four-step RA type random access resources and the RSRP of the downlink path loss reference is higher than msgA-RSRP-Threshold: the UE performs / initiates a two-step RA procedure.

[0307] ● Otherwise,

[0308] ● The UE performs / initiates a four-step RA procedure.

[0309] ■ msgA-TransMax Processing

[0310] If two-step RA is selected above, then

[0311] 1> If the random access procedure is initiated for synchronization reconfiguration, or for SCG activation, or for cell change triggered by an L1L2 cell change / handover command (MAC CE or DCI); and

[0312] 1> If cfra-TwoStep is configured for the selected carrier (note that the cfra-TwoStep IE is optionally included in rach-ConfigDedicated):

[0313] 2> If msgA-TransMax is configured in cfra-TwoStep:

[0314] 3> Apply msgA-TransMax configured in cfra-TwoStep.

[0315] 1> Otherwise, if msgA-TransMax is included in RACH-ConfigCommonTwoStepRA (msgA-ConfigCommon includes RACH-ConfigCommonTwoStepRA):

[0316] 2> Apply msgA-TransMax included in RACH-ConfigCommonTwoStepRA.

[0317] ■ RA Prioritization Processing

[0318] If the above selects 2-step RA, then

[0319] 1> If a random access procedure is initiated for synchronous reconfiguration, or for SCG activation, or for cell change triggered by an L1L2 cell change / handover command (MAC CE or DCI); and

[0320] 1> If rach-ConfigDedicated is configured for the selected carrier; and

[0321] 1> If ra-PrioritizationTwoStep is configured in rach-ConfigDedicated:

[0322] 2> Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStepHighPriority included in ra-PrioritizationTwoStep in rach-ConfigDedicated;

[0323] 2> If scalingFactorBI is configured in ra-PrioritizationTwoStep in rach-ConfigDedicated:

[0324] 3> Set SCALING_FACTOR_BI to scalingFactorBI.

[0325] If the above selects 4-step RA,

[0326] 1> If the random access procedure is initiated for synchronization reconfiguration or for SCG activation; and

[0327] 1> If rach-ConfigDedicated is configured for the selected carrier; and

[0328] 1> If ra-prioritization is configured in rach-ConfigDedicated:

[0329] 2> Set PREAMBLE_POWER_RAMPING_STEP to the powerRampingStepHighPriority included in ra-prioritization in rach-ConfigDedicated;

[0330] 2> If scalingFactorBI is configured in ra-prioritization in rach-ConfigDedicated:

[0331] 3> Set SCALING_FACTOR_BI to scalingFactorBI.

[0332] If the selected RA_TYPE is set to 4-step RA (4-step random access), the MAC entity shall:

[0333] ■ SSB & Preamble Selection

[0334] 1> If contention-free random access resources associated with the SSB have been explicitly provided in the L1L2 cell change / handover command (MAC CE or DCI) (in operation 215), and at least one SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the associated SSBs is available:

[0335] 2> Select, among the associated SSBs (i.e., the SSBs in the L1L2 cell change / handover command), the SSB with an SS-RSRP higher than rsrp-ThresholdSSB; in an embodiment, in the case where there is only one SSB in the L1L2 cell change / handover command, the UE may select this SSB.

[0336] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB. In an embodiment, in the case where there is only one ra-PreambleIndex in the L1L2 cell change / handover command, the UE may select this ra-PreambleIndex.

[0337] 1> Otherwise, if contention-free random access resources associated with CSI-RS have been explicitly provided in the L1L2 cell change / handover command (MAC CE or DCI) in operation 215, and at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS is available among the associated CSI-RS, then:

[0338] 2> Select a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS from among the associated CSI-RS (i.e., the CSI-RS in the L1L2 cell change / handover command);

[0339] 2> Set PREAMBLE_INDEX to ra-PreambleIndex corresponding to the selected CSI-RS.

[0340] 1> Otherwise, if contention-free random access resources associated with SSB have been explicitly provided in rach-ConfigDedicated (in operation 210), and at least one SSB with an SS-RSRP higher than rsrp-ThresholdSSB is available among the associated SSB:

[0341] 2> Select an SSB with an SS-RSRP higher than rsrp-ThresholdSSB from among the associated SSB (i.e., the SSB in rach-ConfigDedicated);

[0342] 2> Set PREAMBLE_INDEX to ra-PreambleIndex corresponding to the selected SSB.

[0343] 1> Otherwise, if contention-free random access resources associated with CSI-RS have been explicitly provided in rach-ConfigDedicated (in operation 210), and at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS is available among the associated CSI-RS, then:

[0344] 2> Select a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS from among the associated CSI-RS (i.e., the CSI-RS in rach-ConfigDedicated);

[0345] 2> Set the PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0346] 1> Otherwise (i.e., for contention-based random access preamble selection): Perform the operation in the traditional manner.

[0347] Alternatively (here it is assumed that the rach-ConfigDedicated does not provide contention-free random access resources associated with the SSB or CSI-RS for 4-step RA):

[0348] 1> If contention-free random access resources associated with the SSB have been explicitly provided in the L1L2 cell change / handover command (MAC CE or DCI) in operation 215 (and at least one SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the associated SSBs is available):

[0349] 2> Select an SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the associated SSBs (i.e., the SSB in the L1L2 cell change / handover command); in an embodiment, when there is only one SSB in the L1L2 cell change / handover command, the UE can select this SSB.

[0350] 2> Set the PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB. In an embodiment, when there is only one ra-PreambleIndex in the L1L2 cell change / handover command, the UE can select this ra-PreambleIndex. 1> Otherwise, if contention-free random access resources associated with the CSI-RS have been explicitly provided in the L1L2 cell change / handover command (MAC CE or DCI) in operation 215 (and at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the associated CSI-RSs is available), then:

[0351] 2> Select a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS from among the associated CSI-RSs (i.e., the CSI-RS in the L1L2 cell change / handover command);

[0352] 2> Set the PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0353] 1> Otherwise (i.e., for contention-based random access preamble selection): Perform operations in a traditional manner.

[0354] ■ PRACH Timing Selection

[0355] 1> If SSB is selected above:

[0356] 2> Determine the next available PRACH occasion from the PRACH occasions corresponding to the selected SSB permitted by the restrictions given by ra-ssb-OccasionMaskIndex (if configured) or ssb-SharedRO-MaskIndex (if configured).

[0357] 1> Otherwise, if CSI-RS is selected above:

[0358] 2> Determine the next available PRACH occasion from the PRACH occasions in the ra-OccasionList corresponding to the selected CSI-RS.

[0359] Note: Use the prach-ConfigurationIndex included in rach-ConfigDedicated in operation 210 to determine the PRACH occasion. If the prach-ConfigurationIndex is not included in rach-ConfigDedicated, use the prach-ConfigurationIndex in RACH-ConfigurationCommon in operation 210 of the BWP selected for the RA procedure to determine the PRACH occasion. rach-ConfigDedicated is a rach-ConfigDedicated corresponding to the selected UL carrier.

[0360] 1> Perform the random access preamble transmission procedure.

[0361] If the selected RA_TYPE is set to 2-stepRA (two-step RA), the MAC entity shall:

[0362] ■ SSB & Preamble Selection

[0363] 1> If the contention-free two-step RA type random access resources associated with the SSB have been explicitly provided in the L1L2 cell change / handover command (MAC CE or DCI) in operation 215 (and at least one SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs is available):

[0364] 2> Select an SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs (i.e., the SSB in the L1L2 cell change / handover command); in an embodiment, when there is only one SSB in the L1L2 cell change / handover command, the UE may select this SSB.

[0365] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB. In an embodiment, when there is only one ra-PreambleIndex in the L1L2 cell change / handover command, the UE may select this ra-PreambleIndex.

[0366] 2> The msgA-PUSCH-Resource-Index in the L1L2 cell change / handover command corresponding to the selected SSB is used to select the PUSCH timing. In an embodiment, if there is only one msgA-PUSCH-Resource-Index in the L1L2 cell change / handover command, the UE may select this msgA-PUSCH-Resource-Index.

[0367] 1> If the contention-free two-step RA type random access resources associated with the SSB have been explicitly provided in rach-ConfigDedicated in operation 210 (and at least one SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs is available):

[0368] 2> Select an SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs (i.e., the SSB in rach-ConfigDedicated);

[0369] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0370] 2> The msgA-PUSCH-Resource-Index in the L1L2 cell change / handover command corresponding to the selected SSB is used to select the PUSCH timing

[0371] 1> Otherwise (i.e., for contention-based random access preamble selection): Perform the operation in a traditional manner.

[0372] Alternatively (assuming here that rach-ConfigDedicated does not provide contention-free random access resources associated with the SSB or CSI-RS for 2-step RA):

[0373] 1> If contention-free 2-step RA type random access resources associated with the SSB have been explicitly provided in the L1L2 cell change / handoff command (MAC CE or DCI) in operation 215, and at least one SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs is available:

[0374] 2> Select an SSB with an SS-RSRP higher than msgA-RSRP-ThresholdSSB among the associated SSBs (i.e., the SSB in the L1L2 cell change / handoff command);

[0375] 2> Set PREAMBLE_INDEX to ra-PreambleIndex corresponding to the selected SSB.

[0376] 2> The msgA-PUSCH-Resource-Index in the L1L2 cell change / handoff command corresponding to the selected SSB is used to select the PUSCH timing

[0377] 1> Otherwise, (i.e., for contention-based random access preamble selection): Perform the operation in the traditional manner.

[0378] ■ PRACH Timing Selection

[0379] 1> Determine the next available PRACH timing from the PRACH timings corresponding to the selected SSB permitted by the restrictions given by msgA-SSB-SharedRO-MaskIndex (if configured), or ra-ssb-OccasionMaskIndex (if configured), or ssb-SharedRO-MaskIndex (if configured).

[0380] Note: Use the msgA-PRACH-ConfigurationIndex in rach-ConfigDedicated included in operation 210 to determine the PRACH occasion. If the msgA-PRACH-ConfigurationIndex is not included in rach-ConfigDedicated, use the msgA-PRACH-ConfigurationIndex in RACH-ConfigCommonTwoStepRA in operation 210 of the BWP selected for the RA procedure to determine the PRACH occasion. rach-ConfigDedicated is a rach-ConfigDedicated corresponding to the selected UL carrier.

[0381] ■ PUSCH Timing Selection

[0382] 1> If the MAC entity does not select a random access preamble among the (multiple) contention-based random access preambles:

[0383] 2> Select a PUSCH occasion from the PUSCH occasions configured in msgA-CFRA-PUSCH in operation 210 corresponding to the PRACH time slot of the selected PRACH occasion according to the msgA-PUSCH-Resource-Index corresponding to the selected SSB;

[0384] 2> Determine the UL grant for the MSGA payload in the selected PUSCH occasion and the associated HARQ information;

[0385] 2> Deliver the UL grant and the associated HARQ information to the HARQ entity.

[0386] 1> Otherwise:

[0387] 2> Select a PUSCH occasion corresponding to the selected preamble and PRACH occasion;

[0388] 2> Determine the UL grant for the MSGA payload according to the PUSCH configuration associated with the selected random access preamble group, and determine the associated HARQ information;

[0389] 2> If the selected preamble and PRACH occasion are mapped to a valid PUSCH occasion:

[0390] 3> Deliver the UL grant and the associated HARQ information to the HARQ entity.

[0391] 1> Execute the MSGA transmission procedure.

[0392] MAC Reset for SPCell Change within DU

[0393] In the case of traditional handover, when a handover command is executed, the MAC is reset. In the case of PCell change within DU triggered by LTM, some operations performed by the MAC entity during MAC reset are not required. If a partial MAC reset indication (via MAC CE or DCI or RRC) is received, the UE can perform the following operations when receiving a cell change / handover command.

[0394] 1. Time Alignment Timer

[0395] If the target SpCell is one of the current serving cells of a cell group (CG):

[0396] - There is no need for the MAC entity to stop the running timeAlignmentTimer associated with the TAG of this cell.

[0397] - If the target SpCell and the current SpCell belong to different TAGs, since the current SpCell is unavailable during cell change, the timeAlignmentTimer associated with the TAG of the current SpCell is stopped by the MAC entity.

[0398] If the target SpCell is not one of the current serving cells of the CG:

[0399] - If a random access is initiated to the target SpCell, the MAC entity stops the timeAlignmentTimer associated with the PTAG. In this case, it may not be necessary to stop the timeAlignmentTimer associated with the STAG. However, stopping the timeAlignmentTimer associated with the STAG can be considered.

[0400] 2. RACH

[0401] The RA configuration is cell-specific. Therefore, the ongoing RACH process in the MAC entity can be stopped, and the MsgA / Msg3 buffers can be flushed. When a SpCell change is triggered, CFRA resources can be configured for SpCellBFR. These can be discarded.

[0402] 3. Scheduling Request (SR) Procedure

[0403] The SR process triggered in the MAC entity for the current SpCell can be stopped (e.g., triggered by LBT failure, or triggered for BFR, or triggered due to unconfigured PUCCH resources, etc.). There is no benefit in continuing the ongoing SR process when the SpCell changes.

[0404] 4. Buffer Status Report Procedure

[0405] The triggered buffer status report procedure (at least the regular BSR) in the MAC entity can be continued to reduce the delay in reporting BSR when the SpCell changes.

[0406] 5. Persistent LBT Failure

[0407] Since LBT failure is specific to the physical resources of a cell, the triggered persistent LBT failure can be cancelled. The LBT_COUNTER of the SpCell can also be reset.

[0408] 6. Beam Failure Recovery (BFR)

[0409] Since BFR is specific to a cell, the triggered BFR can be cancelled, and the BFI_COUNTER can be reset.

[0410] 7. UL HARQ

[0411] The HARQ retransmission of the ongoing HARQ process on the new SpCell can be considered to avoid packet loss and RLC retransmission. To achieve this, it is not necessary to set the new data indicator (NDI) of all uplink HARQ processes for the SpCell to the value 0.

[0412] 8. DL HARQ

[0413] The HARQ retransmission of the ongoing HARQ process on the new SpCell can be considered to avoid packet loss and RLC retransmission. To achieve this, the soft buffers of all DL HARQ processes for the SpCell are not flushed.

[0414] Figure 3 A block diagram of a UE according to an embodiment of the present disclosure is shown.

[0415] Referring to Figure 3, the UE includes a receiver 300, a transmitter 304, and a processor 302. The receiver 300 and the transmitter 304 can generally be referred to as a transceiver. The transceiver can send signals to the BS and receive signals from the BS. The signals can include control information and data. To this end, the transceiver can include: an RF transmitter that up-converts and amplifies the frequency of the transmitted signal; an RF receiver that low-noise amplifies the received signal and down-converts the frequency, etc. In addition, the transceiver can receive signals through a wireless channel, output the signals to the processor 302, and send the signals output from the processor 302 through the wireless channel.

[0416] The processor 302 can control a series of processes so that the UE operates according to the embodiments of the present disclosure. For example, according to the above embodiments of the present disclosure, the processor 302 controls the operation of the UE. The processor 302 is configured to: receive an RRC reconfiguration message from the base station of the serving cell, the RRC reconfiguration message including the configuration of one or more candidate target cells associated with the LTM; send an RRC reconfiguration complete message to the base station; send a report on L1 measurements associated with the one or more candidate target cells to the base station; and receive a cell handover command message associated with the LTM from the base station via MAC-CE signaling, where the cell handover command message includes random access information about the target cell.

[0417] Figure 4 A block diagram of a base station according to an embodiment of the present disclosure is shown.

[0418] Refer to Figure 4 , the base station includes a receiver 401, a transmitter 405, and a processor 403. The receiver 401 and the transmitter 405 can generally be referred to as a transceiver. The transceiver can send signals to the UE and receive signals from the UE. The signals can include control information and data. To this end, the transceiver can include an RF transmitter that up-converts and amplifies the frequency of the transmitted signal, an RF receiver that low-noises amplifies the received signal and down-converts the frequency, etc. In addition, the transceiver can receive signals through a wireless channel, output the signals to the processor 403, and send the signals output from the processor 403 through the wireless channel.

[0419] The processor 403 may control a series of processes such that the base station operates according to embodiments of the present disclosure. For example, the processor 403 controls the operation of the base station according to the above embodiments of the present disclosure. The processor 403 is configured to: send an RRC reconfiguration message to the UE, the RRC reconfiguration message including the configuration of one or more candidate target cells associated with the LTM; receive an RRC reconfiguration complete message from the UE; receive a report of L1 measurements for the one or more candidate target cells from the UE; and send a cell handover command message associated with the LTM to the UE via MAC-CE signaling, wherein the cell handover command message includes random access information about the target cell.

[0420] The methods according to various embodiments described in the claims or the specification of the present disclosure may be implemented by hardware, software, or a combination of hardware and software.

[0421] When these methods are implemented by software, a computer-readable storage medium for storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium may be configured to be executed by one or more processors within the electronic device. The at least one program may include instructions that cause the electronic device to execute the methods according to various embodiments of the present disclosure defined by the appended claims and / or disclosed herein.

[0422] The program (software module or software) may be stored in non-volatile memory, including RAM and flash memory, ROM, electrically erasable programmable read-only memory (EEPROM), magnetic disk storage devices, CD-ROM, DVD, other types of optical storage devices, or cassette tapes. Alternatively, any combination of some or all of the memory devices may form the memory in which the program is stored. In addition, multiple such memories may be included in the electronic device.

[0423] In addition, the program may be stored in an attachable storage device, and the attachable storage device may access the electronic device through a communication network such as the Internet, intranet, local area network (LAN), wide area network (WLAN), and storage area network (SAN), or a combination thereof. Such a storage device may access the electronic device via an external port. In addition, a separate storage device on the communication network may access the portable electronic device.

[0424] The embodiments of the present disclosure described and illustrated in the specification and the drawings have been presented to easily explain the technical content of the present disclosure and help understand the present disclosure, and are not intended to limit the scope of the present disclosure. In other words, it will be apparent to those skilled in the art that other modifications and changes can be made based on the technical idea of the present disclosure. In addition, the various embodiments described above can be used in combination as needed. For example, one embodiment of the present disclosure is partially combined with other embodiments to operate the BS and the UE. As an example, the embodiments of the present disclosure described herein can be combined with each other to operate the BS and the UE.

[0425] In the drawings describing the method of the present disclosure, the described order does not always correspond to the order in which each method step is performed, and the order or relationship between steps can be changed or the steps can be performed in parallel.

[0426] Alternatively, in the drawings describing the method of the present disclosure, some elements can be omitted and only some elements can be included therein without departing from the basic spirit and scope of the present disclosure.

[0427] In addition, in the method of the present disclosure, some or all of the content of each embodiment can be combined without departing from the scope of the present disclosure.

[0428] Although the present disclosure has been shown and described with reference to its various embodiments, those skilled in the art will understand that various changes in form and detail can be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

Claims

1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising: Receiving a Radio Resource Control (RRC) reconfiguration message from the base station of the serving cell, the RRC reconfiguration message including configurations of one or more candidate target cells associated with Layer 1 (L1) or Layer 2 (L2) Triggered Mobility (LTM); Sending an RRC reconfiguration complete message to the base station; Sending a report on L1 measurements associated with the one or more candidate target cells to the base station; And Receiving, via Media Access Control - Control Element (MAC-CE) signaling, a cell handover command message associated with the LTM from the base station, wherein the cell handover command message includes random access information about the target cell.

2. The method according to claim 1, further comprising: Triggering a change from the serving cell to the target cell based on the cell handover command message and initiating a random access procedure to the target cell.

3. The method according to claim 2, wherein, The random access procedure is initiated when timing advance is maintained for the target cell and a time alignment timer associated with the target cell is not running.

4. The method according to claim 2, wherein, The cell handover command message further indicates Synchronization Signal Block (SSB) information, a preamble index, and a random access occasion mask index for the random access procedure.

5. The method according to claim 4, wherein, Initiating the random access procedure includes: Selecting an uplink (UL) carrier for the random access procedure; Selecting a Synchronization Signal Block (SSB) based on the SSB information and a preamble corresponding to the preamble index; Selecting a Random Access Opportunity (RO) corresponding to the SSB from the random access channels opportunities (ROs) configured by the RRC reconfiguration message; and Sending a preamble in the selected RO to the target cell.

6. The method according to claim 5, wherein, The cell handover command message further includes information indicating the UL carrier, wherein, in the case where the information indicating the UL carrier indicates a Supplementary UL (SUL) carrier, the SUL carrier is selected as the UL carrier, and wherein, in the case where the information indicating the UL carrier indicates a Normal UL (NUL) carrier, the NUL carrier is selected as the UL carrier.

7. A method performed by a base station of a source cell in a wireless communication system, the method comprising: Sending a Radio Resource Control (RRC) reconfiguration message to a User Equipment (UE), the RRC reconfiguration message including configurations of one or more candidate target cells associated with Layer 1 (L1) or Layer 2 (L2) Triggered Mobility (LTM); Receiving an RRC reconfiguration complete message from the UE; Receiving a report on L1 measurements associated with the one or more candidate target cells from the UE; And Sending, via Media Access Control - Control Element (MAC-CE) signaling, a cell handover command message associated with the LTM to the UE, wherein the cell handover command message includes random access information about the target cell.

8. The method according to claim 7, wherein, The random access procedure to the target cell is initiated by triggering a change from the serving cell to the target cell based on the cell handover command message.

9. The method according to claim 8, wherein, The random access procedure is initiated when timing advance is maintained for the target cell and a time alignment timer associated with the target cell is not running.

10. The method according to claim 8, wherein, The cell handover command message further includes: Information indicating an uplink (UL) carrier for the random access procedure Synchronization signal block (SSB) information Preamble index, and Random access occasion mask index for the random access procedure 11. A user equipment (UE) in a wireless communication system, the UE comprising: Transceiver; And A processor, coupled to the transceiver and configured to: Receive a radio resource control (RRC) reconfiguration message from a base station of a serving cell, the RRC reconfiguration message including configurations of one or more candidate target cells associated with layer 1 (L1) or layer 2 (L2) triggered mobility (LTM); Send an RRC reconfiguration complete message to the base station; Send a report on L1 measurements associated with the one or more candidate target cells to the base station; And Receive, via media access control - control element (MAC - CE) signaling, a cell handover command message associated with the LTM from the base station, Wherein the cell handover command message includes random access information about a target cell.

12. The UE according to claim 11, wherein, The processor is further configured to: Trigger a change from the serving cell to the target cell based on the cell handover command message and initiate a random access procedure to the target cell.

13. The method according to claim 12, wherein, The cell handover command message further includes: Information indicating an uplink (UL) carrier for the random access procedure Synchronization signal block (SSB) information Preamble index, and Random access occasion mask index for the random access procedure 14. A base station of a source cell in a wireless communication system, the base station comprising: Transceiver; And A processor, coupled to the transceiver and configured to: Send a radio resource control (RRC) reconfiguration message to a user equipment (UE), the RRC reconfiguration message including configurations of one or more candidate target cells associated with layer 1 (L1) or layer 2 (L2) triggered mobility (LTM); Receive an RRC reconfiguration complete message from the UE; Receive a report on L1 measurements associated with the one or more candidate target cells from the UE; And Send, via media access control - control element (MAC - CE) signaling, a cell handover command message associated with the LTM to the UE, Wherein the cell handover command message includes random access information about a target cell.

15. The base station according to claim 14, wherein, The random access procedure to the target cell is initiated by triggering a change from the serving cell to the target cell based on the cell handover command message, and Wherein the cell handover command message further includes: Information indicating an uplink (UL) carrier for the random access procedure Synchronization signal block (SSB) information Preamble index, and Random access occasion mask index for the random access procedure

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