Cell control method and apparatus therefor

Abstract

The present disclosure relates to a mobility control technique for a mobile communication terminal. Provided are: a method by which a distributed unit (DU) for configuring a base station performs an L1 / L2 triggered mobility (LTM) operation; and an apparatus, the method comprising the steps of: transmitting, to a terminal, an RRC reconfiguration message including LTM candidate cell configuration information; determining LTM execution of the terminal; sending an MAC control element used for LTM cell switching to the terminal; and transmitting, to a central unit (CU) for configuring the base station, information indicating initiation of LTM cell handover or information indicating success of cell handover.

Description

Technical Field

[0001] The present invention relates to a mobility control technology for a mobile communication terminal. Background Art

[0002] The popularity of small wireless communication devices such as smartphones is leading to an increasing number of users. In particular, not only smartphones but also various vehicles such as cars and airplanes are equipped with wireless communication devices, allowing people to communicate while moving.

[0003] When a wireless communication device moves, it switches from one cell coverage area to another. The development of high-speed vehicles further increases the demand for cell switching.

[0004] This cell switching is called handover. Usually, a terminal in an RRC connected state performs handover through RRC signaling. Therefore, when handover is performed based on L3 signaling, the handover process between the base station, the core network entity and the terminal is complicated and takes a long time.

[0005] Meanwhile, according to the beamforming technology introduced in NR, beam-level mobility based on synchronization signal block (SSB) is based on the SSB associated with the initial downlink bandwidth part (BWP). However, beam-level mobility has limitations because it only supports mobility within the same cell.

[0006] Therefore, a technology is needed that can more simply perform cell switching in a shorter time when a terminal frequently moves between cells. Summary of the invention

[0007] Technical issues

[0008] The present disclosure provides a method and apparatus for quickly performing a mobility control operation of a terminal in a lower layer.

[0009] Technical Solutions

[0010] In one aspect, a method for performing L1 / L2 triggered mobility (LTM) operation by a distributed unit (DU) constituting a base station may be provided. The method may include sending an RRC reconfiguration message including LTM candidate cell configuration information to a terminal, determining LTM execution of the terminal, sending a MAC control element for LTM cell switching to the terminal, and sending information indicating the initiation of LTM cell switching or information indicating successful cell switching to a central unit (CU) constituting the base station.

[0011] In another aspect, a method for performing L1 / L2 triggered mobility (LTM) operation by a terminal may be provided, comprising receiving an RRC reconfiguration message including LTM candidate cell configuration information from a distributed unit (DU) constituting a base station, receiving a MAC control element for LTM cell switching from the distributed unit, and if the MAC control element is received, controlling to notify that the LTM cell switching has been triggered from the MAC layer to the RRC layer, and sending data indicating successful completion of the LTM cell switching to the distributed unit based on a result of performing the LTM cell switching operation.

[0012] In another aspect, a distributed unit (DU) constituting a base station may be provided for performing L1 / L2 triggered mobility (LTM) operations. The DU may include a transmitter that sends an RRC reconfiguration message including LTM candidate cell configuration information to a terminal; and a controller that determines LTM execution of the terminal, wherein the transmitter sends a MAC control element for LTM cell switching to the terminal, and sends information indicating initiation of LTM cell switching or information indicating success of cell switching to a central unit (CU) constituting the base station.

[0013] In another aspect, a terminal may be provided to perform an L1 / L2 triggered mobility (LTM) operation. The terminal may include a receiver that receives an RRC reconfiguration message including LTM candidate cell configuration information from a distributed unit (DU) constituting a base station and receives a MAC control element for LTM cell switching from the distributed unit; a controller that controls to notify that an LTM cell switching has been triggered from the MAC layer to the RRC layer if the MAC control element is received; and a transmitter that sends data indicating successful completion of the LTM cell switching to the distributed unit according to a result of performing the LTM cell switching operation.

[0014] Beneficial Effects

[0015] According to this embodiment, the terminal can quickly perform a mobility control operation at a lower layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a view schematically showing the structure of an NR wireless communication system.

[0017] Figure 2 is a view showing the frame structure in the NR system.

[0018] Figure 3 is a diagram showing a resource grid supported by a radio access technology.

[0019] Figure 4 is a diagram showing bandwidth portions supported by radio access technologies.

[0020] Figure 5 is a view exemplarily showing a synchronization signal block in a radio access technology.

[0021] Figure 6 is a view showing a random access procedure in radio access technology.

[0022] Figure 7 is a view showing CORESET.

[0023] Figure 8 is a flow chart illustrating the operation of a distributed unit according to an embodiment.

[0024] Fig. 9 is a flowchart illustrating the operation of a terminal according to an embodiment.

[0025] Fig.10 is a block diagram showing a configuration of a distributed unit according to another embodiment.

[0026] Fig.11is a block diagram showing a configuration of a terminal according to another embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. When assigning reference numerals to the components of each of the accompanying drawings, the same reference numerals may be assigned to the components even when the same components are displayed on different accompanying drawings. When determining that the subject matter of the present disclosure will make it unclear, the detailed description of known technologies or functions may be skipped. The terms "include" and / or "include", "have" and / or "have" or "include" and / or "include" used in this specification are intended to specify the presence of the features, regions, integers, steps, operations, elements, components and / or their groups, but do not exclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components and / or their groups. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "the" used herein are also intended to include plural forms.

[0028] When describing the components of the present invention, terms such as "first", "second", "A", "B", "(a)", and "(b)" may be used. These terms are provided only to distinguish one component from another, and the nature, order or number of the components are not limited by these terms.

[0029] When describing the positional relationship between components, when two or more components are described as being “connected,” “coupled,” or “linked,” the two or more components may be directly “connected,” “coupled,” or “linked,” or there may be intermediate components. In this case, the intermediate components may be included in one or more of the two or more components that are “connected,” “coupled,” or “linked” to each other.

[0030] When such terms as "after", "next", "before" and similar expressions are used to describe time-flow relationships related to components, methods of operation and methods of manufacture, they may include non-continuous relationships unless the terms "immediately" or "directly" are used.

[0031] When a component is specified by a value or its corresponding information (eg, a level), the value or the corresponding information may be interpreted as including tolerances caused by various factors (eg, process factors, internal or external influences, or noise).

[0032] In the present disclosure, a 'wireless communication system' refers to a system that provides various communication services such as voice and data packets using radio resources, and may include a terminal, a base station, or a core network.

[0033] The present embodiment disclosed below can be applied to wireless communication systems using various radio access technologies. For example, the present embodiment can be applied to various radio access technologies, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA) or non-orthogonal multiple access (NOMA). In addition, radio access technology can refer not only to a specific access technology, but also to each generation of communication technology established by various communication organizations, such as 3GPP (third generation partnership project), 3GPP2, Wi-Fi, Bluetooth, IEEE (Institute of Electrical and Electronics Engineers) and ITU (International Telecommunication Union). For example, CDMA can be implemented as a radio technology, such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA can be implemented as GSM (Global System for Mobile Communications) / GPRS (General Packet Radio Service) / EDGE (Enhanced Data Rates for GSM Evolution). OFDMA can be implemented with wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA UTRA), etc. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of UMTS (Universal Mobile Telecommunications System). 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) is part of E-UMTS (Evolved UMTS) using Evolved-UMTS Terrestrial Radio Access (E-UTRA, evolved-UMTS terrestrial radio access), and adopts OFDMA for downlink and SC-FDMA for uplink. Therefore, this embodiment can be applied to currently disclosed or commercialized radio access technologies, and can also be applied to radio access technologies that are currently being developed or to be developed in the future.

[0034] Meanwhile, in the present disclosure, "terminal" is a comprehensive concept, which refers to a device including a wireless communication module that communicates with a base station in a wireless communication system, and should be interpreted as including not only user equipment (UE, user equipment) in, for example, WCDMA, LTE, NR, HSPA, and IMT-2020 (5G or new radio), but also mobile stations (MS, mobile station), user terminals (UT, user terminals), subscriber stations (SS, subscriber station) or wireless devices in GSM. In addition, depending on the type of use, the terminal may be a user portable device (such as a smartphone), and in a V2X communication system, the terminal may refer to a vehicle or a device including a wireless communication module in a vehicle. In addition, in the case of a machine type communication system, the terminal may refer to a machine type communication (MTC, machine type communication) terminal, a machine-to-machine (M2M, machine-to-machine) terminal, or an ultra reliable low latency communication (URLLC, ultra reliable low latency communication) terminal equipped with a communication module to perform machine type communication.

[0035] In the present disclosure, "base station" or "cell" refers to a terminal that communicates with a terminal according to a network, and conceptually includes various coverage areas, such as node B, evolved node B (eNB, evolved node-B), gNode-B (gNB, gNode-B), low power node (LPN, low power node), sector, site, various types of antennas, base transceiver system (BTS, base transceiver system), access point, point (such as a transmission point, a reception point or a transmission / reception point), relay node, giant cell, macro cell, micro cell, pico cell, femto cell, remote radio head (RRH, remote radio head), radio unit (RU, radio unit) or small cell. In addition, "cell" may refer to a cell including a bandwidth part (BWP, bandwidth part) in the frequency domain. For example, "serving cell" may refer to an activated BWP of a terminal.

[0036] Since there is a base station that controls one or more of the various cells listed above, the base station can be interpreted in two meanings. The base station can be 1) a device itself that provides a giant cell, a macro cell, a micro cell, a pico cell, a femto cell or a small cell associated with a radio area, or 2) the radio area itself. In 1), all devices that provide a predetermined radio area and are controlled by the same entity or interact via collaboration to configure the radio area are represented as base stations. An embodiment of a base station is a sending / receiving point, a sending point or a receiving point depending on the scheme for configuring the radio area. In 2), the radio area itself that receives or sends a signal from the perspective of a terminal or a neighboring base station can be a base station.

[0037] In the present disclosure, a "cell" may refer to the coverage of a signal transmitted from a transmission / reception point, a component carrier having coverage of a signal transmitted from a transmission / reception point (transmission point or transmission / reception point), or the transmission / reception point itself.

[0038] An uplink (UL) refers to a scheme for sending data from a terminal to a base station or for receiving data from a base station at a terminal, and a downlink (DL) refers to a scheme for sending data from a base station to a terminal at a base station. A downlink may refer to a communication or communication path from a plurality of transmission / transmission points to a terminal, and an uplink may refer to a communication or communication path from a terminal to a plurality of transmission / reception points. In this case, in the downlink, a transmitter may be part of a plurality of transmission / reception points, and a receiver may be part of a terminal. In addition, in the uplink, a transmitter may be part of a terminal, and a receiver may be part of a plurality of transmission / reception points.

[0039] The uplink and downlink configure control channels (such as physical downlink control channel (PDCCH) or physical uplink control channel (PUCCH)) and send and receive control information through the control channels. The uplink and downlink configure data channels (such as physical downlink shared channel (PDSCH) or physical uplink shared channel (PUSCH)) to send and receive data. In the following, the context of sending or receiving signals through channels (such as PUCCH, PUSCH, PDCCH and PDSCH) is expressed as "sending or receiving PUCCH, PUSCH, PDCCH and PDSCH".

[0040] Although, for clarity of description, the technical spirit is mainly described with respect to 3GPP LTE / LTE-A / New Radio (NR) communication systems, the technical features are not limited to such communication systems.

[0041] After studying fourth-generation (4G) communication technologies, 3GPP developed fifth-generation (5G) communication technologies to meet the requirements of ITU-R for next-generation radio access technologies. Specifically, 3GPP developed new NR communication technologies separate from LTE-A Pro and 4G communication technologies as 5G communication technologies, which have enhanced LTE Advanced technologies to meet the requirements of ITU-R. LTE-A Pro and NR both refer to 5G communication technologies. Hereinafter, unless specified as a specific communication technology, 5G communication technologies will be described focusing on NR.

[0042] The operation scenarios in NR define various operation scenarios by adding considerations for satellites, automobiles, and new vertical domains to existing 4G LTE scenarios. From the perspective of services, NR supports i) the enhanced mobile broadband (eMBB) scenario, ii) the massive machine communication (mMTC) scenario characterized by high terminal density, wide deployment, low data rate, and asynchronous access, and iii) the ultra-reliability and low latency (URLLC) scenario, which requires high reliability and also supports high-speed mobility.

[0043] To meet these scenarios, NR introduces a wireless communication system that adopts new waveform and frame structure technologies, low-latency technologies, millimeter-wave (mmWave) support technologies, and forward compatibility provision technologies. In particular, the NR system proposes various technical changes in terms of flexibility to provide forward compatibility. The main technical features of NR will be described below with reference to the accompanying drawings.

[0044] <Overview of the NR System>

[0045] Figure 1 is a view schematically showing the structure of the NR system.

[0046] Refer to Figure 1, the NR system is divided into a 5G core network (5GC) and an NR-RAN part. The next-generation radio access network (NG-RAN) includes gNBs and ng-eNBs, which provide user plane (SDAP / PDCP / RLC / MAC / PHY) and user equipment (UE) control plane (RRC) protocol terminations. gNBs or gNBs and ng-eNBs are interconnected via the Xn interface. gNBs and ng-eNBs are connected to the 5G core network (5GC) via the NG interface. The 5GC may include i) an access and mobility management function (AMF) responsible for the control plane, including terminal access and mobility control functions, and ii) a user plane function (UPF) that processes user data control functions. NR supports frequency bands below 6 GHz (Frequency Range 1 (FR1)) and above 6 GHz (Frequency Range 2 (FR2)).

[0047] A gNB refers to a base station that provides NR user plane and control plane protocol terminations for terminals, and an ng-eNB refers to a base station that provides E-UTRA user plane and control plane protocol terminations for terminals. In the present disclosure, a base station should be understood to include gNBs and ng-eNBs and may be used to separately represent a gNB or an ng-eNB when necessary.

[0048] <NR Waveform, Numerology, and Frame Structure>

[0049] NR uses the CP-OFDM waveform with a cyclic prefix for downlink transmission and uses CP-OFDM or DFT-s-OFDM for uplink transmission. OFDM technology is easy to integrate with multiple input multiple output (MIMO) and offers advantages such as high spectral efficiency and the ability to use low-complexity receivers.

[0050] At the same time, since the above three scenarios in NR have different requirements for data rate, latency, and coverage, it is necessary to effectively meet the requirements of each scenario through the frequency bands that make up any NR system. To achieve this, techniques based on multiple different numerologies have been proposed for the efficient reuse of radio resources.

[0051] Specifically, the NR transmission parameter set is determined based on the subcarrier spacing and the cyclic prefix (CP). As shown in Table 1 below, it changes exponentially, where the exponent value 2 is used as μ relative to 15kHz.

[0052] [Table 1]

[0053]

[0054]

[0055] As shown in Table 1 above, NR parameter sets can be divided into five types according to the subcarrier spacing. This is different from the fixed subcarrier spacing of 15kHz in LTE of 4G communication technology. Specifically, in NR, the subcarrier spacing for data transmission is 15, 30, 60 and 120kHz, and the subcarrier spacing for synchronization signal transmission is 15, 30, 120 and 240kHz. In addition, the extended CP is only applied to 60kHz subcarrier spacing. At the same time, as part of the frame structure in NR, a frame of length 10ms is defined, which consists of 10 subframes of equal length (each 1ms). Each frame can be divided into two half frames of 5ms, each half frame can include 5 subframes. For 15kHz subcarrier spacing, a subframe consists of a time slot, and each time slot consists of 14 OFDM symbols. Figure 2 is a view showing the frame structure in the NR system.

[0056] Reference Figure 2 , in the case of normal CP, the time slot is fixedly composed of 14 OFDM symbols, but the length of the time slot in the time domain can vary according to the subcarrier spacing. For example, for a parameter set with a 15kHz subcarrier spacing, the length of the time slot is the same as the length of the subframe, which is 1ms. In contrast, for a parameter set with a 30kHz subcarrier spacing, the time slot consists of 14 OFDM symbols, but one subframe may include two time slots with a length of 0.5ms. In other words, subframes and frames are defined to have a fixed length, and the time slot is defined by the number of symbols, and the time length can vary according to the subcarrier spacing.

[0057] At the same time, NR defines the time slot as the basic unit of scheduling, and in order to reduce the transmission delay of the radio section, mini time slots (or also called sub-time slots or non-time slot based scheduling) are adopted. When a wide subcarrier spacing is used, the length of a time slot is inversely proportional to the subcarrier spacing, thereby allowing the transmission delay in the radio section to be reduced. Mini time slots are used to effectively support URLLC scenarios and enable scheduling in units of 2, 4 or 7 symbols.

[0058] In addition, different from LTE, NR defines uplink and downlink resource allocation at the symbol level within a time slot. To reduce HARQ latency, a time slot structure is introduced to enable the direct transmission of HARQ ACK / NACK within the transmission time slot. In the description, this time slot structure is referred to as a self - contained structure.

[0059] NR is designed to support a total of 256 time slots, of which 62 time slot formats are used in 3GPP Rel - 15. In addition, a common frame structure for FDD or TDD frames is supported through various combinations of time slots. For example, NR supports i) a time slot structure in which all symbols in the time slot are configured as downlink, ii) a time slot structure in which all symbols are configured as uplink, and iii) a time slot structure in which downlink symbols and uplink symbols are combined. In addition, NR supports distributed data transmission at both ends of one or more time slots. Therefore, the base station can use the slot format indicator (SFI) to notify the terminal whether a given time slot is a downlink time slot, an uplink time slot, or a flexible time slot. The base station can indicate the time slot format by indicating (e.g., providing) the index of a table configured by UE - specific RRC signaling via the SFI, and can indicate it dynamically through downlink control information (DCI) or statically or semi - statically through RRC.

[0060] <NR Physical Resources>

[0061] Regarding the physical resources in NR, factors such as antenna ports, resource grids, resource elements, resource blocks, and bandwidth parts are considered.

[0062] Antenna ports are defined such that the channel carried by a symbol on an antenna port can be inferred from the channel carried by another symbol on the same antenna port. When the large - scale characteristics of the channel carrying a symbol on one antenna port can be inferred from the channel carrying a symbol on a different antenna port, the two antenna ports can be considered to have a QC / QCL (Quasi - Co - Located) relationship. Here, the large - scale characteristics include one or more of delay spread, Doppler spread, frequency shift, average received power, and reception timing.

[0063] Figure 3 is a view showing the resource grid supported by a radio access technology.

[0064] Refer to Figure 3 Since NR supports multiple parameter sets on the same carrier, the resource grid can be defined for each parameter set. In addition, the resource grid can also vary according to antenna ports, sub - carrier spacing, or transmission direction.

[0065] A resource block consists of 12 subcarriers and is defined only in the frequency domain. In addition, a resource element consists of one OFDM symbol and one subcarrier. Therefore, as Figure 3 shown, the size of a resource block can vary according to the subcarrier spacing. In addition, in NR, "Point A" which serves as a common reference point for the resource block grid, common resource blocks, and virtual resource blocks is defined.

[0066] Figure 4 is a view showing the bandwidth part supported by a radio access technology.

[0067] In NR, different from LTE where the carrier bandwidth is fixed at 20Mhz, the maximum carrier bandwidth ranges from 50Mhz to 400Mhz, depending on the subcarrier spacing. Therefore, it is not assumed that all terminals utilize all of these carrier bandwidths. Thus, in NR, as Figure 4 shown, a bandwidth part (BWP) can be specified within the carrier bandwidth and allocated for use by a terminal. In addition, the bandwidth part is associated with a parameter set, consists of a subset of consecutive common resource blocks, and can be dynamically activated as time progresses. Up to four bandwidth parts (BWPs) can be configured for each of the uplink and downlink in a terminal. Data is sent / received using the bandwidth part (BWP) activated at a given time.

[0068] For paired spectra, the uplink and downlink bandwidth parts are configured independently, while for unpaired spectra, the uplink and downlink bandwidth parts are paired to share the center frequency, thus preventing unnecessary frequency retuning between downlink and uplink operations.

[0069] <NR Initial Access>

[0070] In NR, a terminal performs a cell search and a random access procedure to connect to a base station and perform communication.

[0071] Cell search is a process in which a terminal synchronizes with a cell of a base station using a synchronization signal block (SSB) sent by the base station, retrieves the physical layer cell ID, and obtains system information.

[0072] Figure 5 is a view exemplarily showing the synchronization signal block in a radio access technology.

[0073] Refer to Figure 5The SSB consists of a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) (each occupying 1 symbol and 127 subcarriers respectively) and a PBCH spanning 3 OFDM symbols and 240 subcarriers.

[0074] The terminal monitors the SSB in the time domain and the frequency domain and receives the SSB.

[0075] SSB can be transmitted up to 64 times within 5ms. Multiple SSBs are transmitted using different transmission beams within 5ms, and it is assumed that SSB is transmitted once every 20ms period based on the specific beam used for transmission, and the terminal performs detection. As the frequency band increases, the number of beams available for SSB transmission within 5ms can increase. For example, up to 4 SSB beams can be transmitted at 3GHz, up to 8 different beams can be used to transmit SSB in the 3-6GHz frequency band, and up to 64 different beams can be used to transmit SSB in the 6GHz or higher frequency band.

[0076] Two SSBs are included in one slot, and the starting symbol position and the number of repetitions within the slot are determined based on the subcarrier spacing, as described below.

[0077] At the same time, unlike the SS of typical LTE, SSB is not sent at the center frequency of the carrier bandwidth. Instead, SSB can be sent at a location other than the center of the system band, and multiple SSBs can be sent in the frequency domain when broadband operation is supported. Therefore, the terminal monitors SSB using a synchronization grid, which represents the candidate frequency position for monitoring SSB. The carrier raster and synchronization raster are newly defined in NR, which provide center frequency position information for initial access. In addition, the synchronization raster is characterized by a wider frequency interval than the carrier raster, enabling the terminal to perform faster SSB searches.

[0078] The terminal can obtain the master information block (MIB) through the PBCH of the SSB. The master information block (MIB) includes the minimum information required for the terminal to receive the remaining system information (remaining minimum system information (RMSI)) broadcast by the network. In addition, the PBCH may include information about the position of the first DM-RS symbol in the time domain, information required for the terminal to monitor SIB1 (for example, SIB1 parameter set information, information related to SIB1 CORESET, search space information, PDCCH-related parameter information, etc.), offset information between common resource blocks and SSBs (the absolute position of SSBs within the carrier is sent through SIB1), and similar information. Here, the SIB1 parameter set information is also applied to some messages used in the random access process that enables the terminal to access the base station after completing the cell search process. For example, parameter set information about SIB1 can be applied to at least one of messages 1 to 4 of the random access process.

[0079] The above-mentioned RMSI may refer to system information block 1 (SIB1, systeminformation block 1). SIB1 is broadcast periodically (for example, every 160ms) in the cell. SIB1 includes information required for the terminal to perform the initial random access process and is periodically sent through the PDSCH. In order to receive SIB1, the terminal must first obtain the parameter set information associated with the SIB1 transmission and the control resource set (CORESET) information for SIB1 scheduling through the PBCH. The terminal uses the SI-RNTI in the CORESET to identify the scheduling information of SIB1 and obtains SIB1 from the PDSCH according to the scheduling information. In addition to SIB1, the remaining SIBs may be sent periodically or upon request of the terminal.

[0080] Figure 6 is a view showing a random access procedure in radio access technology.

[0081] Reference Figure 6 , if the cell search is successfully completed, the terminal sends a random access preamble to the base station to initiate random access. The random access preamble is sent through PRACH. Specifically, the random access preamble is sent to the base station through PRACH consisting of continuous radio resources in a specific time slot that is repeated periodically. Generally, when the terminal initially accesses a cell, a contention-based random access procedure is performed, and when performing random access for beam failure recovery (BFR, beam failure recovery), a non-contention-based random access procedure is performed.

[0082] The terminal receives a random access response to the random access preamble sent. The random access response may include a random access preamble identifier (ID, identifier), uplink radio resources (UL authorization), a temporary cell-radio network temporary identifier (C-RNTI, cell-radio network temporary identifier) ​​and a time alignment command (TAC, time alignment command). Since a random access response may include random access response information of multiple terminals, a random access preamble identifier may be included to indicate which terminal the included UL authorization, temporary C-RNTI and TAC apply to. The random access preamble identifier may be an identifier of a random access preamble received by a base station. TAC may be included as information for the terminal to adjust uplink synchronization. The random access response may be indicated by a random access identifier (specifically, a random access-radio network temporary identifier (RA-RNTI, random access-radio network temporary identifier)) on a PDCCH.

[0083] After receiving a valid random access response, the terminal processes the information included in the random access response and performs scheduled transmission to the base station. For example, the terminal applies the TAC and stores the temporary C-RNTI. In addition, the terminal uses the UL grant to send the data stored in its buffer or the newly generated data to the base station. In this case, information that can identify the terminal should be included.

[0084] Finally, the terminal receives a downlink message for contention resolution.

[0085] <NR CORESET>

[0086] In NR, the downlink control channel is sent in a control resource set (CORESET) of length 1 to 3 symbols and carries uplink / downlink scheduling information, slot format index (SFI), transmit power control (TPC) information and other related information.

[0087] Therefore, NR introduces the concept of CORESET to ensure the flexibility of the system. The control resource set (CORESET) refers to the time-frequency resources used for downlink control signals. The terminal can use one or more search spaces in the CORESET time-frequency resources to decode the control channel candidates. A quasi co-location (QCL) assumption for each CORESET has been defined, which is used to indicate not only the characteristics of the simulated beam direction, but also the delay spread, Doppler spread, Doppler shift and average delay, all of which are assumed by typical QCL.

[0088] Figure 7 is a view showing CORESET.

[0089] Reference Figure 7 , a CORESET can exist in various forms within the carrier bandwidth and within a time slot. In the time domain, a CORESET can consist of up to 3 OFDM symbols. In addition, a CORESET is defined as a multiple of up to 6 resource blocks of the carrier bandwidth in the frequency domain.

[0090] The first CORESET is indicated as part of the initial bandwidth portion configuration through the MIB to enable the terminal to receive additional configuration and system information from the network. After establishing a connection with the base station, the terminal can receive and configure one or more CORESET information through RRC signaling.

[0091] As used herein, terms such as frequency, frame, subframe, resource, resource block, area, band, subband, control channel, data channel, synchronization signal, various reference signals, various signals, and various messages related to new radio (NR) may be interpreted with various meanings that are currently used or may be defined in the future.

[0092] The mobility control described in the present disclosure refers to a series of control procedures for changing the connection state of a terminal when a cell change is required due to various situations such as movement of the terminal.

[0093] NR Mobility

[0094] In typical NR technology, mobility control of cell change of the terminal in RRC connected state involves handover through explicit RRC signaling. The cell change can be triggered by L3 measurement, and the handover can be performed through RRC message signaling, which includes the information required for accessing the target cell (with Sync reconfiguration, target cell ID, new C-RNTI, target gNB security algorithm identifier of the selected security algorithm, a set of dedicated RACH resources, association between RACH resources and one or more SSBs, association between RACH resources and one or more UE-specific CSI-RS configurations, common RACH resources, and one or more pieces of information in the system information of the target cell). When the cell change is performed, the MAC entity of the corresponding cell group is reset. The received new C-RNTI value is used as the C-RNTI of the cell group. The terminal configures the PHY / MAC / RLC / PDCP / SDAP layer according to the configuration information.

[0095] Compared with beam changes within the same cell (beam-level mobility), this will cause more delays, overhead and interruption time. Beam-level mobility does not require explicit RRC signaling to be triggered during the beam change process. The base station (network) can provide measurement configuration to the terminal through RRC signaling, where the measurement configuration includes SSB / CSI resources and resource sets, the trigger state of the trigger channel, and the interference measurement and reporting configuration. Beam-level mobility can be provided by control signaling (e.g., DCI or MAC CE) of the lower layer physical layer / MAC layer. SSB-based beam-level mobility is based on the SSB associated with the initial downlink BWP. It can be configured only for the initial one or more downlink BWPs, which include the SSB associated with the initial downlink BWP. Beam-level mobility of other DL BWPs can be performed only based on CSI-RS. However, in the related art, beam switching only supports intra-cell mobility.

[0096] As a solution to these problems, the present disclosure proposes a technology for supporting cell change / handover through L1 / L2 signaling.

[0097] Therefore, in typical NR technology, cell-level mobility (cell change) is performed based on L3 signaling, resulting in greater latency, overhead, and interruption time compared to beam-level mobility. In addition, beam-level mobility is limited to movement within the same cell.

[0098] In order to solve these problems, the present disclosure proposes a method and apparatus for controlling PCell / PSCell / SCell in a cell change / handover process based on L1 / L2 signaling.

[0099] In the following, a method for providing cell-level mobility based on 5G NR radio access technology is described. However, this is provided for ease of description, and the present embodiment can be applied to cell changes / switching based on any radio access technology (e.g., 6G). The embodiments described in the present disclosure include information elements, processes, and operation contents specified in any NR standard (e.g., TS 38.321 as the NR MAC standard and TS 38.331 as the NR RRC standard). Although the present disclosure does not include the definition of corresponding information elements, related processes, and related terminal operations, the contents set forth in the standards of known technologies can be incorporated into the present embodiments. The embodiments provided below can be practiced alone or in combination.

[0100] For ease of description, a scenario related to this embodiment is first described. However, this is only for description purposes, and this embodiment can be applied to any other network deployment scenario other than that described below.

[0101] L1 / L2 (signaling)-based cell change / switching can be performed for service cell change scenarios, including i) PCell change or SCell change within a cell group in an NR independent structure, or ii) SpCell (PCell / PSCell) change or SCell change within a cell group (e.g., MCG or SCG) in a dual-connection structure. For example, in a cell other than the current service cell of an RRC-connected terminal, the target PCell and / or target SCell can be indicated by a cell change / switching based on L1 / L2 signaling, thereby allowing the corresponding PCell / SCell to be configured / modified / added / activated as a service cell. As another example, in the current service cell of an RRC-connected terminal, the target PCell and / or target SCell can be indicated by a cell change / switching based on L1 / L2 signaling, thereby allowing the corresponding target PCell / SCell to be configured / modified / changed / switched / added / activated as a service cell.

[0102] L1 / L2-based cell changes within DU within a CU can be performed between different cells associated with a corresponding DU within a DU connected to a corresponding CU within the CU (intra-CU). For example, the corresponding cells may have different PCIs and be synchronized between cells. For different DUs connected to a corresponding CU within a CU, L1 / L2-based cell changes between DUs within a CU can be performed accordingly between cells associated with different DUs. For example, the corresponding cells may have different PCIs and there may be no inter-cell synchronization. For another example, the corresponding cells may have different PCIs and inter-cell synchronization may be performed. Any operations according to the embodiments described below may be performed individually / independently, or may be performed in any combination thereof, and it is obvious that they are also included in the scope of the present disclosure.

[0103] For ease of description, a transmission point / receive point / TRP / one or more beams / beam groups (BG) (via the corresponding TRP) of a service cell / PCell / SCell configured / activated in the terminal is represented as a first transmission point / receive point (TRP). This term is used for descriptive purposes and can be replaced by any other name (e.g., primary / main / basic / SpCell-associated / service cell-associated TRP / beam / BG). Similarly, a transmission point / receiving point / TRP / one or more beams / beam groups (beam group, BG) (via the corresponding TRP) that provides a physical cell ID (physical cell Id, PCI) different from the corresponding service cell / PCell / SCell, or a transmission point / receiving point / TRP / one or more beams / beam groups (beam group, BG) (via the corresponding TRP) associated with a physical cell ID (physical cell Id, PCI) different from the corresponding service cell / PCell / SCell is represented as a second transmission point / receiving point (transmit / receive point, TRP). This term is also used for convenience of description and can be replaced by any other name (for example, TRP / beam / BG associated with auxiliary / additional / auxiliary / non-service cell). The cell associated with the second TRP or the second TRP can be configured / released in the terminal. In addition, the cell associated with the second TRP or the second TRP can be activated / deactivated for the terminal. A first TRP and one or more second TRPs can provide / support / configuration / release / activate / deactivate for a terminal.

[0104] For ease of description, cell change / switching by L1 / L2 signaling is referred to as L1 / L2 triggered mobility. This term is used for convenience of description and can be replaced by any other name (e.g., fast HO, low latency HO, HO based on L1 / L2 signaling, HO based on low layer signaling, or LTM). Here, L1 / L2 may represent at least one of the following: i) L1 / L2 signaling (e.g., MAC-CE / DCI), ii) L1 / L2 execution instruction information, iii) quasi co-location (QCL) / transmission configuration indication (TCI) state activation / update / instruction, iv) L1 / L2 execution condition (based on L1 measurement), v) L1 / L2 event (based on L1 measurement), vi) L1 / L2 process, and vii) terminal operation in L1 / L2 layer.

[0105] Any function described below is defined as a single terminal capability (UE radio capability or UE core network capability), and can be sent by the terminal to the base station / core network entity (e.g., AMF / SMF) through corresponding signaling. Alternatively, any combination of functions can be combined / merged to be defined as a corresponding terminal capability, which can then be sent by the terminal to the base station / core network entity through corresponding signaling.

[0106] The base station may send / indicate information on the corresponding function / function combination of any function or any function combination described below to the terminal through an RRC message. For example, the information may be indicated / provided to the terminal before, after, or simultaneously with the configuration / application of the corresponding function / function combination. The RRC message may be broadcast through system information. Alternatively, it may be indicated / sent to the terminal through a dedicated RRC message.

[0107] At the same time, the distributed unit DU described in the present disclosure can form a base station together with the central unit CU. For example, the next generation radio network can be composed of a group of base stations connected to the 5G core network (5G core network, 5GC) through the NG interface. The base stations are connected to each other through the Xn interface. A base station can be composed of a CU and one or more DUs. The CU and DU are connected to each other through the F1 interface. A DU can be connected to only one CU. The NG interface and the Xn-C interface of a base station composed of a CU and a DU are terminated at the CU. The DU connected to the CU is shown as only one base station to other base stations and 5GC. The CU is a logical node for the RRC, SDAP and PDCP protocols of the hosting base station. The DU is a logical node for the RLC, MAC and PHY layers of the hosting base station. One DU supports one or more cells. A cell is supported by only one DU. The node hosting the user plane part of the NR PDCP should perform user inactivity monitoring and notify the node with the control plane connection that it is inactive or (re)activated. The node hosting the NR RLC can perform user inactivity monitoring and notify the control plane hosting node that it is inactive or (re)activated.

[0108] Therefore, according to the user plane protocol structure in the 5G / NR radio network using the base station separation structure, the CU and the DU are connected through the F1 interface between the PDCP and the RLC.

[0109] Figure 8 is a flow chart illustrating the operation of a distributed unit according to an embodiment.

[0110] Reference Figure 8 , a distributed unit (DU) constituting a base station may execute a step (S810) of sending an RRC reconfiguration message including LTM candidate cell configuration information to a terminal when performing an L1 / L2 triggered mobility (L1 / L2 triggered mobility, LTM) operation.

[0111] According to an embodiment, the distributed unit may send LTM candidate cell configuration information for configuring LTM in the terminal to the terminal. The LTM candidate cell configuration information may be sent, included in the information field of the RRC reconfiguration message. For example, the RRC reconfiguration information may include at least one of the reference configuration information stored in the terminal and the candidate cell configuration information including the difference of the reference configuration. As another example, the LTM candidate cell configuration information may include at least one of the complete overall configuration information about the corresponding candidate cell and the incremental configuration information including the difference of the reference configuration.

[0112] The reference configuration stored in the terminal can be pre-configured in the terminal via an RRC message. Alternatively, the reference configuration can be transmitted to the terminal via a message (such as system information) transmitted from the base station to the terminal. Adding / modifying candidate cell configuration information can be combined with the reference configuration pre-configured in the terminal. According to an embodiment, adding / modifying candidate cell configuration information can be applied to the reference configuration configured in the terminal to perform an add or modify operation on a specific candidate cell. Here, the reference configuration is a configuration typically used for LTM candidate configuration, and can be applied to the incremental configuration to be described below.

[0113] The distributed unit may perform the step of determining the LTM execution of the terminal (S820).

[0114] According to an embodiment, the distributed unit may determine whether to perform LTM for the terminal. For example, the distributed unit may determine whether to perform LTM based on the L1 / L2 measurement result of the terminal. As another example, the distributed unit may use any information received from the terminal to determine whether to perform LTM for the terminal based on whether a preset condition is met.

[0115] The distributed unit may perform a step of sending a MAC control element (MAC control element, MAC CE) for LTM cell switching to the terminal (S830).

[0116] According to an embodiment, if it is determined to perform LTM on the terminal, the distributed unit may send control information for the LTM cell switching operation of the terminal. The control information may be included in the MAC CE and indicated to the terminal. After receiving the MAC CE, the MAC entity of the terminal may transmit the LTE cell switching trigger to the RRC layer in the terminal.

[0117] When the LTM candidate cell configuration information included in the RRC reconfiguration message includes information indicating the activation state of the secondary cell configured in the terminal, the terminal can control the activation or deactivation operation of the secondary cell accordingly when receiving the MAC CE. For example, if the terminal receives a MAC CE instructing LTM execution, the terminal can identify the activation state information about the secondary cell based on the LTM candidate cell configuration information and activate or deactivate the secondary cell.

[0118] Therefore, the distributed unit may indicate the initiation of LTM execution to the terminal via MAC CE.

[0119] The distributed unit may perform the step of sending i) information indicating initiation of LTM cell switching or ii) information indicating success of cell switching to a central unit (CU) constituting the base station (S840).

[0120] According to an embodiment, the distributed unit may transmit information indicating that the cell handover of the terminal is successful to the connected central unit. Alternatively, the distributed unit may send information indicating that the terminal has initiated an LTM cell handover operation to the connected central unit.

[0121] According to an embodiment, upon receiving data indicating successful completion of LTM cell handover from the terminal, information indicating successful cell handover may be sent to the central unit via an F1 application protocol (F1AP) message including target cell identification information.

[0122] According to another embodiment, information indicating the initiation of LTM cell handover may be sent to the central unit via an F1 application protocol (F1AP) message, which includes target cell identification information to indicate the initiation of the LTM cell handover procedure of the terminal.

[0123] Through the above operations, the distributed unit can trigger the cell switching of the terminal at the lower layer L1 / L2, thereby realizing a fast and efficient cell change of the terminal. In addition, when the cell change operation of the terminal is initiated or successfully completed, the information can be transmitted to the central unit, allowing the central unit to identify the terminal cell change.

[0124] Fig. 9 is a flowchart illustrating the operation of a terminal according to an embodiment.

[0125] Reference Fig. 9 When performing L1 / L2 triggered mobility (L1 / L2 triggered mobility, LTM) operation, the terminal can perform the step of receiving an RRC reconfiguration message including LTM candidate cell configuration information from a distributed unit (DU) constituting a base station (S910).

[0126] According to an embodiment, the terminal may receive LTM candidate cell configuration information for configuring LTM in the terminal from a distributed unit. The LTM candidate cell configuration information may be received and included in an information field of an RRC reconfiguration message. For example, the RRC reconfiguration information may include at least one of the following: i) reference configuration information stored in the terminal and ii) candidate cell configuration information including a difference from the reference configuration. As another example, the LTM candidate cell configuration information may include at least one of the following: i) complete overall configuration information about the corresponding candidate cell and ii) incremental configuration information including a difference from the reference configuration.

[0127] The reference configuration stored in the terminal may be preconfigured via an RRC message. Alternatively, the reference configuration may be transmitted to the terminal via a message (such as system information) transmitted from the base station to the terminal. Adding / modifying candidate cell configuration information may be combined with the reference configuration preconfigured in the terminal. For example, adding / modifying candidate cell configuration information may be applied to the reference configuration configured in the terminal to perform an add or modify operation on a specific candidate cell. Here, the reference configuration is a configuration typically used for LTM candidate configurations, and may be applied to the incremental configuration to be described below.

[0128] The terminal may perform the step of receiving a MAC control element for LTM cell switching from a distributed unit (S920).

[0129] The distributed unit may determine the execution of LTM cell switching based on any information or L1 / L2 measurement results received from the terminal when a preset condition is met. If the execution of LTM cell switching is determined by the distributed unit, the terminal may receive the LTM cell switching instruction from the distributed unit via MAC CE.

[0130] The terminal may perform a control step upon receiving the MAC control element to notify the RRC layer that the LTM cell switching has been triggered by the MAC layer (S930).

[0131] According to an embodiment, if a MAC CE is received, the terminal may perform an LTM cell switching operation. For example, if a MAC CE is received, the MAC entity of the terminal may transmit a trigger for an LTM cell switching to the RRC layer in the terminal. When the LTM candidate cell configuration information included in the RRC reconfiguration message includes information indicating the activation status of a secondary cell configured in the terminal, after receiving the MAC CE, the terminal may control the activation or deactivation operation of the secondary cell accordingly. For example, upon receiving a MAC CE directing LTM execution, the terminal may identify the activation status information of the secondary cell based on the LTM candidate cell configuration information, and activate or deactivate the secondary cell accordingly.

[0132] The terminal may perform a step of sending data to the distributed unit to indicate that the LTM cell switching is successfully completed ( S940 ) based on the result of performing the LTM cell switching operation.

[0133] According to an embodiment, the terminal may perform an LTM cell switching operation and send data to the distributed unit based on the result of the operation to indicate that the LTM execution has been successfully completed. For example, the terminal may indicate the successful completion of the LTE cell change to the distributed unit through at least one of the following: HARQ ACK, UCI, UL MAC CE, MSG1, MSG A, and PUSCH. As another example, if the terminal fails to complete the LTM cell switching for any reason, the fault information may be sent to the distributed unit. For example, the terminal may indicate the fault through at least one of HARQ ACK, UCI, UL MAC CE, MSG1, MSG A, and PUSCH. In this case, the cause information about the cause of the fault may be included.

[0134] At the same time, the distributed unit may transmit information indicating that the cell handover of the terminal is successful to the connected central unit. Alternatively, the distributed unit may send information indicating that the terminal has initiated an LTM cell handover operation to the connected central unit.

[0135] For example, upon receiving data indicating successful completion of LTM cell handover from the terminal, the distributed unit may send information indicating successful cell handover to the central unit via an F1 application protocol (F1AP) message including target cell identification information.

[0136] As another example, information indicating initiation of LTM cell handover may be sent to the central unit via an F1 application protocol (F1AP) message including target cell identification information to indicate initiation of the LTM cell handover procedure of the terminal.

[0137] According to the above embodiment, the distributed unit can trigger the cell switching of the terminal in the lower layer L1 / L2 to indicate the fast and effective cell change of the terminal. In addition, when the cell change operation of the terminal is initiated or successfully completed, the information can be transmitted to the central unit, allowing the central unit to identify the terminal cell change.

[0138] Hereinafter, more various embodiments related to the above-mentioned operations of the distributed unit, the terminal, and the central unit are described below for each step. Each of the embodiments described below can be performed according to any combination. In addition, these embodiments can be performed in any of the above-mentioned steps, or individual steps can be added or modified. Each of the above-mentioned steps can also be combined or separated, and the order can be changed as needed. The term "base station" used below can refer to the above-mentioned distributed unit, and the division of operations between the central unit and the distributed unit can be adjusted according to the functional separation between them.

[0139] Candidate target configuration for L1 / L2 triggered mobility procedure

[0140] The L1 / L2 triggered mobility procedure may include a dynamic handover triggering step, which performs a cell change / handover for the terminal through L1 / L2 signaling and provides a candidate target configuration to the terminal through an RRC message.

[0141] The base station may indicate the candidate target configuration to the terminal through an RRC message.

[0142] For example, a single RRC reconfiguration message can be used to indicate a candidate target configuration. Alternatively, a candidate target configuration can be included in an RRC message and indicated by a single RRC reconfiguration information element (RRC reconfiguration IE) / container. The candidate target configuration may include one or more of the following as specified in the RRC reconfiguration message or the RRC reconfiguration information element: i) radio bearer configuration, ii) primary cell group configuration, and iii) secondary cell group configuration. Therefore, the base station can configure / activate / deactivate / deactivate the PCell / one or more PSCels indicated by the target configuration of the terminal as a serving cell by the following L1 / L2 signaling. The base station can indicate one or more candidate target configurations to the terminal by one or more RRC reconfiguration information elements (RRC reconfiguration IE) / containers. The corresponding candidate configuration can be distinguished by an index / ID identifying the corresponding candidate configuration. In addition, the corresponding candidate configuration can be indexed and classified based on the order in which the corresponding candidate configuration is provided.

[0143] As another example, a candidate target configuration may be mapped to a cell group configuration information element (CellGroupConfig IE) and indicated. The configuration of another information element (e.g., radio bearer configuration) on the RRC reconfiguration message including the corresponding candidate target configuration may be applied to / maintained to the terminal by another corresponding information element. In this way, the base station may configure / activate one or more PCell / PSCell / SCells of the current / source service of the terminal by changing / switching it to one or more PCell / PSCells indicated by the target configuration through the following L1 / L2 signaling. The base station may indicate one or more candidate target configurations to the terminal through one or more cell group configuration information elements. The corresponding candidate configurations may be distinguished by indexes. For each candidate target configuration, other information elements (e.g., all / part of the radio bearer configuration) in addition to the cell group configuration information element may be defined and applied as common configuration information. Information elements requiring different configurations for each candidate target configuration may be included as separate dedicated information elements in each candidate target configuration, or may be included as associated separate dedicated information elements.

[0144] As another example, after receiving L1 / L2 signaling, the terminal may maintain a configuration specified by an information element not indicated by the candidate target configuration, or a configuration specified by an information element other than the cell group configuration included in the candidate target configuration (e.g., all / part of the radio bearer configuration). For example, the terminal may maintain any MAC terminal variables (e.g., Bj maintained for each logical channel j, BFI_COUNTER (each serving cell or each BFD-RS serving cell set configured with two BFD-RS sets): a counter indicating a beam failure instance, LBT_COUNTER (each serving cell): a counter indicating an LBT failure (if not initiated)) without performing a MAC reset. As another example, any L2 buffer (e.g., MSG3 buffer, MSGA buffer, RLC buffer, PDCP buffer) may be maintained without being refreshed. As another example, the terminal may not perform RLC reconstruction, PDCP reconstruction, or PDCP recovery. As another example, the terminal may maintain i) any RLC terminal variables / timers (TX_Next_Ack-acknowledgement state variable, TX_Next-transmission state variable, POLL_SN-polling transmission state variable, RX_Next-reception state variable, RX_Next_Status_Trigger, RX_Highest_Status, RX_Next_Highest, TX_Next-UM transmission state variable, RX_Next_Reasassembly, RX_timer_Trigger-UMt-Reassembly state variable, RX_Next_Highest-UM reception state variable, t-PollRetransmit, t-Reassembly, t-StatusProhibit), and ii) any PDCP terminal variables / timers (TX_NEXT: this state variable indicates the COUNT value of the next PDCP SDU to be sent, RX_NEXT: this state variable indicates the COUNT value of the next PDCP SDU expected to be received, RX_DELIV: this state variable indicates the first PDCP SDU that has not been delivered to the upper layer but is still waiting COUNT value of SDU, RX_REORD: This state variable indicates the COUNT value after the COUNT value associated with the PDCP data PDU that triggered t-Reordering, discardTimer, t-Reordering timer) (do not set it to the initial value and / or do not stop / reset the running timer). The terminal can also maintain terminal variables / timers for SRBs and UM DRBs.

[0145] In the above embodiment, a candidate target configuration may include a special cell (SpCell) configuration and / or one or more SCell configurations through a primary cell group configuration / a secondary cell group configuration / a cell group configuration.

[0146] When the base station indicates to the terminal an RRC message including a candidate target configuration, the candidate target configuration may be configured as a candidate target configuration with an incremental configuration (e.g., indicating information different from the reference) of the previous candidate target configuration as the candidate target configuration. Therefore, compared with the method of indicating a complete / complete configuration as the candidate target configuration, the signaling overhead can be reduced. When the previous candidate target configuration is not indicated / stored / configured / applied / executed / kept as reference configuration information, or when the previous candidate target configuration with the corresponding candidate target configuration index is not indicated / stored / configured / applied / executed / kept, the base station may be configured as a candidate target configuration for the corresponding candidate target configuration with an incremental (for difference) configuration of the current / source configuration of the terminal as the reference configuration. Alternatively, the base station may use the incremental configuration of the current (applied) serving cell configuration / primary cell group configuration / radio configuration / RRC reconfiguration with the reference configuration as the candidate target configuration, and indicate it to the terminal. Otherwise, the incremental configuration of the previous / stored candidate target configuration (with the corresponding candidate target configuration index) as the reference configuration of the candidate target configuration may be indicated as the candidate target configuration.

[0147] As another example, when a previous candidate target configuration is indicated / stored / configured / applied / executed / maintained as reference configuration information of a terminal, the base station may use an incremental configuration of a previous candidate target configuration with a corresponding candidate target configuration index as a reference configuration candidate target configuration as a candidate target configuration and indicate it to the terminal. For example, when the base station instructs the terminal to configure an LTM candidate target, it may indicate a complete / complete LTM candidate cell configuration. For example, when the base station indicates an LTM candidate target configuration to the terminal, the base station may indicate a complete / complete LTM candidate cell configuration. The terminal may store the received candidate target configuration and information indicating that the candidate target configuration is a complete LTM candidate cell configuration as terminal variables. As another example, when the base station indicates an LTM candidate target configuration, the base station may use a source cell / gNB-DU configuration as a reference configuration to indicate an incremental configuration of the corresponding reference configuration as an LTM candidate cell configuration. The corresponding reference configuration may be indicated to the terminal together with the corresponding candidate target configuration. The terminal may store the received candidate target configuration and the corresponding reference configuration. As another example, when the base station indicates an LTM candidate target configuration, the base station may use the target cell / gNB-DU configuration as a reference configuration to indicate an incremental configuration of the corresponding reference configuration as the LTM candidate cell configuration. The corresponding reference configuration may be indicated to the terminal together with the corresponding candidate target configuration. The terminal may store the received candidate target configuration and the corresponding reference configuration. As another example, a complete LTM configuration may be generated by applying the candidate target configuration to the reference configuration.

[0148] If the base station indicates the candidate target configuration to the terminal through an RRC message, the terminal adds it as a new candidate target configuration entry under the index used to identify the candidate target configuration in the corresponding terminal variable. If the index used to identify the corresponding candidate target configuration already exists, the corresponding candidate target configuration entry is replaced / modified in the corresponding terminal variable. The terminal variable storing the candidate target configuration can be defined and used as an RRC terminal variable. Alternatively, the terminal variable can be defined and used as a (RRC) lower layer terminal variable (e.g., PHY / MAC / RLC / PDCP). In addition, according to the detailed information element included in the corresponding candidate target configuration, the terminal variable storing the candidate target configuration can be defined and used as a terminal variable of the corresponding sublayer.

[0149] L1 / L2 Mobility Trigger Command for L1 / L2 Triggered Mobility Procedure

[0150] In order to indicate dynamic switching through L1 / L2 signaling, MAC CE (or DCI or any L1 / L2 signaling) can be defined. For ease of description, an embodiment using MAC CE is described below; however, it should be understood that DCI or any L1 / L2 signaling is also included in the scope of the embodiment.

[0151] The MAC CE may include information indicating the application / execution of the candidate target configuration received through the RRC message. For example, it may include index information for identifying the corresponding candidate configuration.

[0152] If the candidate target configuration includes a special cell (SpCell) configuration and / or one or more SCell configurations, the terminal receiving the MAC CE may apply / perform a cell change / switching to the special cell / PCell of the candidate target configuration. The terminal may configure one or more SCells of the corresponding candidate target configuration.

[0153] For example, when a MAC CE indicating dynamic switching is received, if the MAC CE indicates that one or more SCells are configured as an activated state in the LTM candidate target configuration (for example, information indicating that the SCell state is activated is set or included as activated), the terminal can configure / apply / execute one or more target SCells. The MAC of the terminal can request the RRC to apply the corresponding SCell configuration. The MAC of the terminal can indicate to the RRC that the LTM cell switching process has been triggered. In addition, the MAC of the terminal can indicate to the RRC that the LTM cell switching MAC CE has been received. The MAC of the terminal can indicate index information to the RRC to identify the corresponding target candidate configuration included in the corresponding MAC CE. The RRC of the terminal can apply the stored LTM candidate cell configuration. The RRC of the terminal can also apply the corresponding SCell configuration and configure the SCell to be in an active state. Alternatively, the MAC of the terminal can apply the corresponding SCell configuration stored (in the MAC layer) and activate the corresponding SCell.

[0154] As another example, upon receiving a MAC CE indicating dynamic switching, if the terminal is directed to configure one or more SCells with corresponding SCellindex as an activated state in the candidate target configuration (for example, information indicating that the SCell state is activated is set or included as activated), the terminal can configure / apply / execute one or more target SCells. Then, the MAC of the terminal can activate the corresponding SCell. The corresponding service SCell and the corresponding SCell of the candidate target configuration can be the same cell. If the corresponding service SCell is already in an active state, after receiving the corresponding MACCE, the terminal can maintain the active state of the corresponding SCell to continue sending and receiving data. Otherwise, the terminal can activate the corresponding SCell.

[0155] If a cell configured by SCell in the current configuration is used as SCell in the candidate target configuration, the SCellindex of the corresponding SCell may be shared and used (eg, reused). The current SCellindex value of the cell configured as SCell may remain the same as the SCellindex included in the candidate target configuration.

[0156] As another example, upon receiving a MAC CE indicating dynamic switching, if the terminal is directed to configure one of one or more service SCells with a corresponding SCellindex as a PCell in a candidate target configuration, the terminal may configure / apply / execute the cell as a target PCell. The corresponding service SCell and the corresponding PCell of the candidate target configuration may be the same cell.

[0157] If a cell configured as an SCell in the current configuration is used / indicated as a PCell in a candidate target configuration, the SCellindex value assigned to the SCell in the current configuration may not (e.g., need not) be assigned as an SCellindex value to any other SCell of the candidate target configuration. As another example, in order to allow unrestricted use of the SCellindex (if a cell configured by the SCell in the current configuration is used / indicated as a PCell in a candidate target configuration), the corresponding SCellindex value may be assigned to any SCell in the current configuration, regardless of the SCellindex value assigned to the corresponding SCell. The SCellindex may be independently allocated between the current configuration and the candidate target configuration. Alternatively, the SCellindex may not be shared between the current configuration and the candidate target configuration.

[0158] As another example, information indicating an index for distinguishing SCells for candidate target configurations may be defined and indicated (e.g., provided) as information different from a typical SCellindex. Thus, SCellindex may be independently allocated between the current configuration and the candidate target configurations. Alternatively, SCellindex may not be shared between the current configuration and the candidate target configurations.

[0159] As another example, upon receiving a MAC CE indicating dynamic switching, if the terminal is directed to configure the terminal's service PCell as an SCell in a candidate target configuration, the terminal may configure / apply / execute the cell as the target SCell. The corresponding service PCell and the corresponding SCell of the candidate target configuration may be the same cell.

[0160] If the cell configured by PCell in the current configuration is used / indicated as the SCell in the candidate target configuration, the service cell index (Servcellindex) value assigned to PCell in the current configuration may be zero. In the candidate target configuration, the SCellindex of the corresponding cell may be allocated from the SCellindex value not allocated in the current configuration. As another example, in order to allow unrestricted use of SCellindex (if the cell configured by PCell in the current configuration is used / indicated as the SCell in the candidate target configuration), the corresponding SCellindex value may be assigned to any SCell in the current configuration, regardless of the SCellidex value assigned to the corresponding SCell. Alternatively, SCellindex may be defined and indicated as information different from the typical SCellindex.

[0161] As another example, when receiving a MAC CE indicating dynamic switching, the terminal may configure / apply / execute one or more corresponding target SCells (in an inactive state) for one or more service SCells with corresponding SCellindex. The terminal may configure the corresponding SCell to be in an inactive state. Alternatively, the MAC of the terminal may deactivate the corresponding SCell.

[0162] As another example, after receiving a MAC CE indicating dynamic switching, the terminal can configure / apply / execute one or more target SCells in an active / inactive state for one or more service SCells with corresponding SCellindex. For example, if a corresponding MAC CE is received for an SCell that is in an inactive state in the current configuration, the terminal's MAC can configure the corresponding SCell to remain in an inactive state in the candidate target configuration. If a corresponding MAC CE is received for a PCell / SCell that is operating in an active state in the current state, the terminal's MAC can configure the corresponding SCell to be active in the candidate target configuration.

[0163] As another example, a MAC CE indicating dynamic switching may include information for indicating the state of an SCell included in a candidate target configuration. If the base station indicates the candidate target configuration to the terminal via an RRC message, the terminal adds the configuration as a new candidate target configuration entry, where the index is used to identify the candidate target configuration in the corresponding terminal variable. If the index for identifying the corresponding candidate target configuration already exists, the corresponding candidate target configuration entry is replaced / modified in the corresponding terminal variable. Before the base station adds / modifies the candidate target configuration to the terminal and actually determines the dynamic switching, the base station load or radio environment may change. When indicating dynamic switching, it may be desirable to activate / deactivate the SCell while considering the state of one or more candidate target SCells to facilitate data transmission and reception. For example, a MAC CE for indicating dynamic switching may be defined separately as: i) a MAC CE including information indicating whether to activate one or more SCells; and ii) a MAC CE that does not include the information. For example, each MAC CE may be defined by assigning different LCIDs. Therefore, when it is not necessary to indicate whether to activate one or more SCells, the overhead for indicating activation or deactivation may be reduced to perform signaling.

[0164] As another example, the maximum number of SCells (including information about whether to activate one or more SCells) that can be indicated in a MAC CE for indicating dynamic switching can be limited to a specific number (e.g., 4, 8). For example, the limitation can be based on the number of one or more SCells included in the candidate target configuration. In the related art, the SCell activation / deactivation MAC CE can indicate whether to activate / deactivate up to 31 SCells through four octets, which may result in excessive overhead. To address this issue, based on the number of one or more SCells included in the target configuration, a bitmap can be configured to indicate the active / inactive state of the SCell, which is configured to indicate the index / ID / identification information of the SCell.

[0165] As another example, a one-bit indicator indicating whether to activate one or more SCells may be included in a MAC CE for indicating dynamic switching. For example, based on the corresponding information, the corresponding one or more SCells may be activated / deactivated for all one or more SCells included in the candidate target configuration. As another example, a one-bit indicator instructing to maintain the state of one or more SCells may be included in a MAC CE for indicating dynamic switching. For example, based on this information, the terminal may maintain the active or inactive state of the corresponding SCell for the corresponding SCell included in the candidate target configuration according to the current serving PCell / SCell state.

[0166] As another example, the MAC CE for indicating dynamic switching may include information indicating whether the activation / deactivation bitmap information is successfully included for the SCell included in the candidate target configuration according to the corresponding SCellindex. If the corresponding information is included, the MAC CE including the SCell activation / deactivation bitmap may be sent. Otherwise, the MAC CE not including the corresponding SCell activation / deactivation bitmap may be sent.

[0167] As another example, when the base station sends a MAC CE indicating dynamic switching to the terminal, the terminal may simultaneously send an SCell activation / deactivation MAC CE indicating activation / deactivation of the SCell included in the candidate target configuration according to the SCellindex. The two MAC CEs may be multiplexed and included in one MAC PDU. The two MAC CEs may be included in the MAC PDU and indicated in the following order: (1) MAC CE indicating dynamic switching, followed by (2) MAC CE indicating SCell activation / deactivation.

[0168] As another example, upon receiving a MAC CE indicating dynamic switching, the terminal may configure the current service SCell as the target service SCell and keep it active. To this end, the candidate target configuration may include adding / modifying information (e.g., sCellToAddModList) for the corresponding SCell. The corresponding candidate target configuration may be configured by sharing the same value with the index of the corresponding SCell (e.g., the SCellindex included in the candidate target configuration) and the index of the current service SCell. The SCellindex included in the candidate target configuration then becomes part of the current UE configuration. The terminal may modify the corresponding SCell configuration according to the dedicated SCell configuration information (e.g., SCellConfigDedicated) included in the candidate target configuration. The candidate target configuration may include information indicating the corresponding SCell state. If this information is included, the terminal may configure the corresponding SCell to be in an active state. Then, the MAC of the terminal may activate the corresponding SCell. The information indicating the SCell state may be provided as Boolean information indicating the activation or deactivation of the SCell. Alternatively, the information may be indicated as an optional field when the corresponding SCell is activated. If the corresponding information is omitted, the terminal may configure the corresponding SCell to be in an inactive state.

[0169] As another example, after receiving a MAC CE indicating dynamic switching, the terminal may apply / execute the corresponding candidate target configuration (or the corresponding candidate target configuration stored in the corresponding terminal variable). If the current reference configuration and the candidate target configuration share the index of one or more SCells and / or the corresponding one or more SCells in the current reference configuration, and the candidate target configuration continues to be configured as one or more SCells of the current reference configuration, the candidate target configuration may be indicated to the terminal using the incremental configuration of the corresponding SCell. If the current reference configuration and the candidate target configuration share the index of one or more SCells, but one or more SCells included in the current reference configuration are no longer configured as one or more SCells in the candidate target configuration (for example, the SCell in the current reference configuration is reconfigured as the PCell in the candidate target configuration, and the SCell in the current reference configuration is not included in the candidate reference configuration), the terminal (or base station) may release the SCell included in the current configuration. In addition, the terminal may stop the deactivation timer (sCellDeactivationTimer) associated with the SCell. Therefore, when the corresponding SCell is changed to a PCell, the configuration of the corresponding SCell may be explicitly removed from the terminal to remove ambiguity. Alternatively, the base station may reuse the corresponding SCell index.

[0170] Provide intra-DU MAC CE and inter-DU MAC CE respectively

[0171] When dynamic cell change / switching is performed based on L1 / L2 triggered mobility, there may be significant differences in terminal operations between intra-DU cell change / switching and inter-DU cell change / switching. When inter-DU cell change / switching occurs, the PHY / MAC / RLC sublayers included in the DU are changed, requiring the terminal to perform synchronization / MAC reset / RLC reset on the corresponding PHY / MAC / RLC sublayers.

[0172] On the other hand, intra-DU cell change / switching may not require one or more operations related to synchronization / MAC reset / RLC reset on the PHY / MAC / RLC sublayers. For example, the corresponding DU may include any timing advance information in the corresponding MAC CE (for example, the timing advance command field indicates the index value TA of the timing adjustment amount that must be applied in TS 38.213 for controlling the MAC entity, and the length of the corresponding information field (TA index value) may be set to one of 12 bits and 6 bits). The DU may send this information in the corresponding MAC CE, thereby performing dynamic cell switching / changing without a random access operation. In addition, the corresponding DU may maintain the RLC entity, thereby avoiding RLC reset.

[0173] Therefore, the MAC CE for indicating dynamic switching can be defined separately as a MAC CE (including information) for inter-DU cell change / switching and a MAC CE (including information) for intra-DU cell change / switching. For example, each MAC CE can be defined by assigning a different LCID. Therefore, unnecessary overhead can be reduced to perform signaling. When a MAC CE for intra-DU cell change / switching (or including the information) is received, the terminal can perform dynamic cell switching / changing without one or more operations (such as MAC reset, random access, and RLC reset).

[0174] As another example, in order to reduce the interruption time of L1 / L2 triggered mobility by simplifying the above-mentioned synchronization operation, a MAC CE for indicating timing advance information about a candidate target cell may be indicated (e.g., sent). The MAC CE may include one or more of the following: i) information for identifying a candidate target configuration, ii) a serving cell ID of a PCell in the candidate target configuration, iii) a cell index (e.g., PCI) of a PCell in the candidate target configuration, and iv) timing advance information. This information may be defined with an LCID of a timing advance MAC CE different from that of a typical technology. If the terminal receives the corresponding MAC CE, the terminal may apply a timing advance command to the corresponding candidate target PCell. The terminal may start / restart a specific timer (e.g., a timing alignment timer) for the corresponding candidate target PCell. If a MAC CE for indicating dynamic switching is received while the timer is working, if the MAC CE corresponds to the candidate target configuration (if it is a cell change / switching of the candidate target PCell), the terminal may perform a cell change / switching without performing random access.

[0175] CU / DU signaling for L1 / L2 triggered mobility procedures

[0176] NR provides a separation structure that separates the base station (gNB) into a central unit (hereinafter referred to as CU / gNB-CU for ease of description) and a distributed unit (hereinafter referred to as DU / gNB-DU for ease of description) to support efficient network construction. The radio network consists of a group of base stations connected to the 5G core network (5GC) through an NG interface. The base stations are connected to each other through the Xn interface. One base station can be composed of one gNB-CU and one or more gNB-DUs. The gNB-CU and the gNB-DU are connected to each other through the F1 interface. One gNB-DU can be connected to only one gNB-CU. The NG interface and the Xn-C interface of one base station composed of the gNB-CU and the gNB-DU are terminated at the gNB-CU. The gNB-DU connected to the gNB-CU is shown as only one base station connected to other base stations and the 5GC. The gNB-CU is a logical node for the RRC, SDAP, and PDCP protocols of the hosting base station. The gNB-DU is a logical node for the RLC, MAC, and PHY layers of the hosting base station. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU.

[0177] First described is a cell change scenario based on L1 / L2 within a DU within a CU between different cells associated with a corresponding DU within a DU, which is connected to a corresponding CU within a CU (within a CU). Dynamic cell change / switching determination of L1 / L2 triggered mobility can be performed by a DU. For example, a DU that receives a report on an L1 measurement result of a terminal can determine a dynamic cell change / switching to provide L1 / L2 triggered mobility. The DU can indicate (e.g., send / provide) a MAC CE for dynamic cell change / switching to the terminal. As described above, the corresponding MAC CE may include index information for identifying a candidate target configuration. The base station / CU may change / modify the radio configuration of the corresponding terminal based on a base station load, an L3 measurement report, or similar parameters. In this case, the base station needs to be aligned with the current wireless configuration configured in the corresponding terminal. Therefore, if the dynamic cell change / switching is performed by the DU, the CU needs to receive and identify information indicating that the dynamic cell change / switching is performed by the corresponding candidate target configuration.

[0178] For example, the DU may instruct (e.g., notify) the CU to instruct it to perform dynamic cell change / switching to provide L1 / L2 triggered mobility to the CU. The corresponding information may send information to the CU, which is used to instruct the sending of the corresponding cell change command when any uplink data / confirmation information (e.g., HARQ ACK, UCI, UL MAC CE, MSG1, or MSGA) of the MAC CE indicating the dynamic cell change / switching is received from the terminal. For example, information for indicating that the LTM cell change MACCE transmission has been initiated to the terminal may be sent to the CU. As another example, the DU may send an access success to the CU when receiving any uplink data / confirmation information (e.g., HARQ ACK, UCI, UL MAC CE, MSG1, MSGA, or RRC reconfiguration completion message) to indicate that the dynamic cell change / switching has been successfully completed for the MAC CE indicating the dynamic cell change / switching. For example, if the terminal performs a random access process during the LTM cell switching process, when the random access process is successfully completed, the terminal may consider that the LTM execution is successfully completed. If the random access procedure is not performed, the LTM execution can be considered to be successfully completed when the distributed unit determines that the first uplink data of the terminal has been successfully received. The terminal can send MSG1 including a random access preamble to the DU. The terminal can send a scheduling request (scheduling req terminal, SR) to the DU for uplink data transmission. The terminal can send a buffer status report (buffer status report, BSR) MAC CE for uplink data transmission to the DU. The terminal can send an RRC reconfiguration completion message to the DU when the LTM execution is successfully completed. If the DU receives the above-mentioned uplink data / confirmation information, the DU can consider that the terminal has successfully completed the LTM cell switching and send an access success to the CU.

[0179] The corresponding information may be sent to the CU via an F1AP message. The corresponding message may include index information to identify the corresponding candidate target configuration. The message may include any information contained in the present disclosure (e.g., information indicating the SCell state, information identifying the candidate target configuration, the service cell ID of the PCell of the candidate target configuration, the cell index of the PCell of the candidate target configuration (e.g., NR CGI or PCI), timing advance information, SSB, etc.). When the CU receives the corresponding message, the RRC / PDCP of the CU may perform one or more operations according to an embodiment of the present disclosure. For example, the CU may use the received candidate target configuration as a reference configuration to indicate an incremental configuration to the terminal.

[0180] Next described is the L1 / L2-based cell change scenario between different DUs connected to the corresponding CU within the CU. The dynamic cell change / switching determination of L1 / L2 triggered mobility can be performed by the source DU. For example, the source DU can receive a report on the L1 measurement results of the terminal and determine the dynamic cell change / switching to provide L1 / L2 triggered mobility. The source DU can indicate the MAC CE for dynamic cell change / switching to the terminal. As described above, the corresponding MAC CE may include index information for identifying the candidate target configuration. The base station / CU may change / modify the radio configuration of the corresponding terminal based on the base station load, L3 measurement report, or similar information. In this case, the base station needs to be aligned with the existing wireless configuration configured in the corresponding terminal. Therefore, if the dynamic cell change / switching is performed by the source DU so that the cell change to the target DU is performed, the CU needs to receive and identify information indicating that the dynamic cell change / switching has been performed by the corresponding candidate target configuration. For example, the source DU may indicate the CU for guiding the execution of dynamic cell change / switching to provide L1 / L2 triggered mobility to the CU. The corresponding information may send information to the CU, which is used to guide the sending of the corresponding cell change command when any uplink data / confirmation information (e.g., HARQ ACK, UCI, or UL MAC CE) of the MACCE indicating the dynamic cell change / switching is received from the terminal. For example, information indicating that the LTM cell change MAC CE transmission has been initiated to the terminal may be sent to the CU. As another example, the target DU may send an access success to the CU when receiving any uplink data / confirmation information (e.g., MSG1, MSGA, UCI, ULMAC CE, or RRC reconfiguration completion message) to indicate that the dynamic cell change / switching has been successfully completed for the MAC CE indicating the dynamic cell change / switching. For example, if the terminal performs a random access process during the LTM cell switching process, when the random access process is successfully completed, the terminal may consider the LTM execution to be successfully completed. If the random access process is not performed, the LTM execution may be considered to be successfully completed when the distributed unit determines that the first uplink data of the terminal has been successfully received. The terminal may send MSG1 including a random access preamble to the target DU. Alternatively, the terminal may send a scheduling request (scheduling request, SR) to the target DU for uplink data transmission. The terminal may send a buffer status report (buffer status report, BSR) MAC CE for uplink data transmission to the target DU. The terminal may send an RRC reconfiguration completion message to the DU when the LTM execution is successfully completed. If the DU receives the above-mentioned uplink data / confirmation information, the target DU may consider that the terminal has successfully completed the LTM cell handover and send an access success to the CU.

[0181] The corresponding information may be sent to the CU via an F1AP message. The corresponding message may include index information for identifying the corresponding candidate target configuration. The message may include various types of information included in the present disclosure (e.g., information indicating the SCell state, information for identifying the candidate target configuration, a service cell ID for the PCell of the candidate target configuration, a cell index for the PCell of the candidate target configuration (e.g., NR CGI or PCI), timing advance information, SSB, etc.). When the CU receives the corresponding message, according to an embodiment of the present disclosure, the RRC / PDCP of the CU may perform one or more operations. For example, the CU may use the received candidate target configuration as a reference configuration to indicate an incremental configuration to the terminal.

[0182] According to the above-described embodiments, a specific configuration and signaling information for controlling mobility based on L1 / L2 can be provided. Therefore, cell change to reduce delay can be performed efficiently.

[0183] Hereinafter, the hardware and software configurations of the distributed units and terminals capable of executing all or part of the above-mentioned embodiments will be described in conjunction with the accompanying drawings.

[0184] Fig.10 is a block diagram illustrating a distributed unit according to another embodiment.

[0185] Reference Fig.10 , the distributed unit 1000 can constitute a base station with a central unit (CU) and perform L1 / L2 triggered mobility (LTM) operation. Such a distributed unit 1000 may include a transmitter 1020, which sends an RRC reconfiguration message including LTM candidate cell configuration information to a terminal; and a controller 1010, which determines the LTM execution of the terminal. The transmitter 1020 can send a MAC control element for LTM cell switching to the terminal. The transmitter 1020 can send information indicating the initiation of LTM cell switching or information indicating the success of cell switching to a central unit (CU) constituting a base station with the distributed unit 1000.

[0186] According to an embodiment, the LTM candidate cell configuration information may be transmitted and included in the information field of the RRC reconfiguration message. For example, the RRC reconfiguration information may include at least one of the reference configuration information stored in the terminal and the candidate cell configuration information including the difference of the reference configuration. As another example, the LTM candidate cell configuration information may include at least one of the complete overall configuration information about the corresponding candidate cell or the incremental configuration information including the difference with the reference configuration.

[0187] The reference configuration stored in the terminal may be preconfigured via an RRC message. Alternatively, the reference configuration may be transmitted to the terminal via a message (such as system information) transmitted from the base station to the terminal. Adding / modifying candidate cell configuration information may be combined with the reference configuration preconfigured in the terminal. For example, adding / modifying candidate cell configuration information may be applied to the reference configuration configured in the terminal to perform an add or modify operation on a specific candidate cell. Here, the reference configuration may refer to the above-mentioned incremental configuration.

[0188] In addition, the controller 1010 may determine whether to perform LTM for the terminal. For example, the controller 1010 may determine whether to perform LTM based on the L1 / L2 measurement result of the terminal. As another example, the controller 1010 may determine whether to perform LTM of the terminal based on whether a preset condition is met and any information received from the terminal.

[0189] In addition, if the LTM execution of the terminal is determined, the transmitter 1020 may send control information for the LTM cell switching operation of the terminal. The control information may be included in the MAC CE and indicated to the terminal. If the MAC CE is received, the MAC entity of the terminal may transmit the trigger of the LTM cell switching to the RRC layer in the terminal.

[0190] When the LTM candidate cell configuration information included in the RRC reconfiguration message includes information indicating the activation state of the secondary cell configured in the terminal, upon receiving the MAC CE, the terminal can control the activation or deactivation operation of the secondary cell accordingly. For example, if a MAC CE directing LTM execution is received, the terminal can identify the activation state information about the secondary cell according to the LTM candidate cell configuration information, and activate or deactivate the secondary cell indicated by the MAC CE. Therefore, the transmitter 1020 can indicate (e.g., direct) the initiation of LTM execution to the terminal through the MAC CE.

[0191] The transmitter 1020 may transmit information indicating that the cell switching of the terminal is successful to the connected central unit. Alternatively, the transmitter 1020 may transmit information indicating that the terminal has initiated an LTM cell switching operation to the connected central unit.

[0192] For example, upon receiving data indicating successful completion of the LTM cell handover from the terminal, information indicating successful cell handover may be sent to the central unit via an F1 application protocol (F1AP) message including target cell identification information.

[0193] As another example, information indicating the initiation of the LTM cell handover may be sent to the central unit via an F1 application protocol (F1AP) message including target cell identification information to indicate the initiation of the LTM cell handover procedure of the terminal.

[0194] Furthermore, the controller 1010 controls the overall operation of the distributed unit 1000 according to performing L1 / L2 signaling based cell change / switching operations required for performing the above-described embodiments.

[0195] The transmitter 1020 and the receiver 1030 are used to transmit or receive signals, messages or data required for executing the above embodiments together with the terminal or the central unit.

[0196] Fig.11 is a block diagram showing a terminal according to another embodiment.

[0197] refer to Fig.11 The terminal 1100 that performs L1 / L2 triggered mobility (LTM) operation may include a receiver 1130 that receives an RRC reconfiguration message including LTM candidate cell configuration information from a distributed unit (DU) constituting a base station and receives a MAC control element for LTM cell switching from the distributed unit; a controller that, upon receiving the MAC control element, controls to notify that the LTM cell switching from the MAC layer to the RRC layer has been triggered; and a transmitter 1120 that sends data indicating that the LTM cell switching is successfully completed to the distributed unit according to the result of performing the LTM cell switching operation.

[0198] According to an embodiment, the receiver 1130 may receive LTM candidate cell configuration information for configuring LTM in the terminal from the distributed unit. The LTM candidate cell configuration information may be received and included in the information field of the RRC reconfiguration message. For example, the RRC reconfiguration information may include at least one of the reference configuration information stored in the terminal and the candidate cell configuration information including the difference from the reference configuration. As another example, the LTM candidate cell configuration information may include at least one of the complete overall configuration information about the corresponding candidate cell and the incremental configuration information including the difference from the reference configuration.

[0199] The reference configuration stored in the terminal may be preconfigured via an RRC message. Alternatively, the reference configuration may be transmitted to the terminal via a message (such as system information) transmitted from the base station to the terminal. Adding / modifying candidate cell configuration information may be combined with the reference configuration preconfigured in the terminal. For example, adding / modifying candidate cell configuration information may be applied to the reference configuration configured in the terminal to perform an add or modify operation on a specific candidate cell.

[0200] Meanwhile, the distributed unit may determine the initiation of LTM cell switching based on any information received from the terminal or L1 / L2 measurement results when a preset condition is met. If the distributed unit determines the initiation of LTM cell switching, the receiver 1130 may receive an LTM cell switching instruction from the distributed unit via a MAC CE.

[0201] In addition, upon receiving the MAC CE, the controller 1110 may perform an LTM cell switching operation. For example, if the MAC CE is received, the MAC entity of the terminal may transmit a trigger for the LTM cell switching to the RRC layer in the terminal. When the LTM candidate cell configuration information included in the RRC reconfiguration message includes information indicating the activation status of a secondary cell configured in the terminal, upon receiving the MAC CE, the controller 1110 may control the activation or deactivation operation of the secondary cell accordingly. For example, after receiving a MAC CE directing LTM execution, the controller 1110 may identify activation status information about the secondary cell according to the LTM candidate cell configuration information, and activate or deactivate the secondary cell indicated by the MAC CE.

[0202] The transmitter 1120 may perform an LTM cell switching operation and send a success indication message of the LTM cell switching to the distributed unit according to the execution result. For example, the transmitter 1120 performs a cell change operation according to the LTM cell switching trigger, and when the cell change is successfully performed, sends information indicating that the cell switching has been successful to the distributed unit. For example, the transmitter 1120 may indicate to the distributed unit that the cell change according to the LTM cell switching operation is successful through at least one of HARQ, UCI, UL MAC CE, MSG1, and MSG A in response to MAC CE. As another example, when the terminal fails in the LTM cell switching for any reason, the transmitter 1120 may send information indicating the same to the distributed unit. For example, the transmitter 1120 may indicate the failure through at least one of HARQ ACK, UCI, UL MAC CE, MSG1, MSG A, and RRC reconfiguration completion message. In this case, cause information about the cause of the failure may be included.

[0203] At the same time, the distributed unit may transmit information indicating that the cell switching of the terminal is successful to the connected central unit. Alternatively, the distributed unit may send information indicating that the terminal has initiated an LTM cell switching operation to the connected central unit. For example, if uplink data indicating that the LTM cell switching is successfully completed is received from the terminal, the information indicating that the cell switching is successful may be sent to the central unit via an F1 application protocol (F1 application protocol, F1AP) message including target cell identification information. As another example, the information indicating the initiation of the LTM cell switching may be sent to the central unit via an F1 application protocol (F1 application protocol, F1AP) message including target cell identification information to indicate the initiation of the LTM cell switching process of the terminal.

[0204] In addition, the controller 1110 controls the overall operation of the terminal 1100 according to performing the L1 / L2 signaling-based cell change / switching operation required for performing the above-mentioned embodiments.

[0205] The transmitter 1120 and the receiver 1130 are used to send or receive signals, messages or data required to execute the above embodiments together with the distributed units and the central unit.

[0206] The above-mentioned embodiments may be supported by standard documents disclosed in IEEE 802, 3GPP, and 3GPP2 as radio access systems. In other words, the above-mentioned standard documents may support steps, components, and parts that are not described in the embodiments to clarify the technical spirit. In addition, all terms disclosed in the present disclosure may be described by the above-mentioned disclosed standard documents.

[0207] The above-mentioned embodiment can be implemented in various ways. For example, the embodiment can be implemented in various ways (for example, hardware, firmware, software or a combination thereof).

[0208] When implemented in hardware, the method according to the present embodiment can be implemented by, for example, one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers or microprocessors.

[0209] When implemented in firmware or hardware, the method according to the present embodiment can be implemented in the form of a device, program or function that performs the above-mentioned functions or operations. The software code can be stored in a memory unit and driven by a processor. The memory unit can be located inside or outside the processor to exchange data with the processor through various known means.

[0210] The above terms (such as "system", "processor", "controller", "component", "module", "interface", "model" or "unit") generally refer to computer-related physical hardware, a combination of hardware and software, software, or software being executed. For example, the above components can be but are not limited to processes driven by one or more processors, controllers, control processors, entities, execution threads, programs and / or computers. For example, both an application executed by a controller or processor and the controller or processor can be a component. One or more components can reside within a process and / or execution thread, and these components can be located in one device (e.g., a system, a computing device, etc.) or distributed among two or more devices.

[0211] The above embodiments are merely examples, and those of ordinary skill in the art will appreciate that various changes may be made thereto without departing from the scope of the invention. Therefore, the embodiments described herein are provided for illustrative purposes, but do not limit the scope of the invention, and it should be understood that the scope of the invention is not limited by the embodiments. The scope of the present disclosure shall be interpreted by the following claims, and all technical spirits within their equivalents shall be interpreted as belonging to the scope of the present disclosure.

[0212] CROSS-REFERENCE TO RELATED APPLICATIONS

[0213] This patent application claims priority under 35 U.S.C. § 119(a) to Korean Patent Application Nos. 10-2022-0137390 and 10-2023-0140086 filed in the Korean Intellectual Property Office on October 24, 2022 and October 19, 2023, respectively, the disclosures of which are incorporated herein by reference in their entireties. This patent application claims priority to other applications filed in other countries, the disclosures of which are also incorporated herein by reference in their entireties.

Claims

1. A method for performing L1 / L2 triggered mobility (LTM) operation by a distributed unit (DU) constituting a base station, the method include: Sending an RRC reconfiguration message including LTM candidate cell configuration information to the terminal; determining LTM execution of the terminal; Sending a MAC control element for LTM cell switching to the terminal; as well as Information indicating the initiation of the LTM cell handover or information indicating the success of the cell handover is sent to a central unit (CU) constituting the base station.

2. The method according to claim 1, in, The RRC reconfiguration message includes at least one of reference configuration information stored in the terminal and candidate cell configuration information including a difference from the reference configuration.

3. The method according to claim 1, in, If the MAC control element is received, the MAC entity of the terminal indicates to the RRC layer that the LTM cell switching is triggered.

4. The method according to claim 1, in, When the LTM candidate cell configuration information includes information indicating an activation state of a secondary cell, the terminal controls activation or deactivation of the secondary cell in the LTM execution.

5. The method according to claim 1, in, If data indicating that the LTM cell handover is successfully completed is received from the terminal, information indicating that the cell handover is successful is sent through an F1 Application Protocol (F1AP) message including target cell indication information.

6. The method according to claim 1, in, The information indicating the initiation of the LTM cell handover is sent via an F1 Application Protocol (F1AP) message, and the F1 Application Protocol (F1AP) message includes target cell indication information for indicating the initiation of the LTM cell handover process of the terminal.

7. A method for performing L1 / L2 triggered mobility (LTM) operation by a terminal, the method include: receiving an RRC reconfiguration message including LTM candidate cell configuration information from a distributed unit (DU) constituting a base station; receiving a MAC control element for LTM cell handover from the distributed unit; If the MAC control element is received, controlling to notify that the LTM cell switching has been triggered from the MAC layer to the RRC layer; as well as According to the result of executing the LTM cell switching operation, data indicating that the LTM cell switching is successfully completed is sent to the distributed unit.

8. The method according to claim 7, in, The RRC reconfiguration message includes at least one of reference configuration information stored in the terminal and candidate cell configuration information including a difference from the reference configuration.

9. The method according to claim 7, in, When the LTM candidate cell configuration information includes information indicating an activation state of a secondary cell, the LTM cell switching operation includes controlling activation or deactivation of a secondary cell in the LTM execution.

10. The method according to claim 7, in, If data indicating successful completion of the LTM cell handover is received from the terminal, the distributed unit sends an F1 Application Protocol (F1AP) message including target cell indication information to a Central Unit (CU) constituting the base station.

11. A distributed unit (DU) constituting a base station and performing L1 / L2 triggered mobility (LTM) operations, the distributed unit include: A transmitter, wherein the transmitter sends an RRC reconfiguration message including LTM candidate cell configuration information to the terminal; as well as a controller, the controller determining LTM execution of the terminal, The transmitter sends a MAC control element for LTM cell switching to the terminal, and sends information indicating the initiation of the LTM cell switching or information indicating the success of the cell switching to a central unit (CU) constituting the base station.

12. The distributed unit according to claim 11, in, The RRC reconfiguration message includes at least one of reference configuration information stored in the terminal and candidate cell configuration information including a difference from the reference configuration.

13. The distributed unit according to claim 11, in, If the MAC control element is received, the MAC entity of the terminal indicates to the RRC layer that the LTM cell switching is triggered.

14. The distributed unit according to claim 11, in, When the LTM candidate cell configuration information includes information indicating an activation state of a secondary cell, the terminal controls activation or deactivation of the secondary cell in the LTM execution.

15. The distributed unit according to claim 11, in, If data indicating that the LTM cell handover is successfully completed is received from the terminal, information indicating that the cell handover is successful is sent through an F1 Application Protocol (F1AP) message including target cell indication information.

16. The distributed unit according to claim 11, in, The information indicating the initiation of the LTM cell handover is sent via an F1 Application Protocol (F1AP) message, and the F1 Application Protocol (F1AP) message includes target cell indication information for indicating the initiation of the LTM cell handover process of the terminal.

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