Method for transmitting and receiving prach and apparatus therefor

Abstract

A method according to an embodiment of the present specification comprises the steps of: receiving a configuration for a PRACH for each of candidate cells; receiving DCI; and transmitting the PRACH. The DCI includes a cell indicator field. A candidate cell for the PRACH from among the candidate cells is indicated on the basis of the cell indicator field. On the basis that the candidate cell is a neighbor cell or a secondary cell (SCell), the candidate cell is used as a reference cell for determining a transmit timing of the PRACH.

Description

Method and device for transmitting and receiving PRACH This specification relates to a method and device for transmitting and receiving PRACH. Mobile communication systems were developed to provide voice services while ensuring user activity. However, they have expanded beyond voice to include data services. Currently, explosive growth in traffic is leading to resource shortages and users are demanding faster services, necessitating a more advanced mobile communication system. Next-generation mobile communication systems must support explosive data traffic growth, dramatically increasing data rates per user, a vastly increased number of connected devices, ultra-low end-to-end latency, and high energy efficiency. To achieve these goals, various technologies are being studied, including dual connectivity, massive multiple input multiple output (MIMO), in-band full duplex, non-orthogonal multiple access (NOMA), super wideband support, and device networking. In NR operations prior to Rel-17 / 18, RRM L3 measurements were utilized for handover, and handover operations were performed by higher layers. To reduce handover latency, Rel-17 standardized the operation of performing L1 beam reports by setting the SSB of a neighboring cell to the terminal for L1 measurement of the neighboring cell. In Rel-18, a standardization process for performing TA acquisition of a candidate cell for operations (e.g., cell switching) based on L1 / L2-Triggered Mobility procedures has been implemented. Meanwhile, uplink transmission timing is determined based on the reception of the first detected path of a downlink frame from a reference cell to a reference cell. For serving cells, reference cells for determining uplink transmission timing are defined for each TAG (e.g., primary TAG (pTAG), secondary TAG (sTAG)). For candidate cells, there is no specific definition of uplink transmission timing. Therefore, determining the uplink transmission timing associated with a candidate cell can be ambiguous. Furthermore, if criteria defined for the serving cell are utilized to determine the uplink transmission timing associated with a candidate cell, the acquired TA may be inaccurate. The purpose of this specification is to propose a method for solving the above-described problems. Specifically, the purpose of this specification is to propose a method for determining / defining the transmission timing of a PRACH associated with a candidate cell. The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which this specification pertains from the description below. A method according to one embodiment of the present disclosure comprises the steps of receiving a configuration for a Physical Random Access Channel (PRACH) for each of candidate cells, receiving Downlink Control Information (DCI), and transmitting the PRACH. The DCI includes a cell indicator field. Based on the cell indicator field, a candidate cell for the PRACH among the candidate cells is indicated. Based on whether the candidate cell is a neighbor cell or a secondary cell (SCell), the candidate cell is characterized in that it is used as a reference cell for determining the transmit timing of the PRACH. The above transmit timing may be determined based on reception of a first detected path of a downlink frame from the reference cell. The reception of the first detected path of the downlink frame may be based on reception of a specific DL RS among downlink reference signals (DL RSs) associated with the candidate cell. The above specific DL RS may be based on an SSB index related to the candidate cell among synchronization signal block indices (Synchronization Signal Block, SSB, indexes) within a resource set based on an LTM CSI report configuration (L1 / L2 Triggered Mobility CSI report config). The above specific DL RS may be based on a Transmission Configuration Indication (TCI) state associated with the candidate cell. The above specific DL RS may be based on an SSB index indicated based on the DCI. The above PRACH may be related to TA acquisition (Timing Advance acquisition) prior to reception of a Cell Switch Command Medium Access Control Control Element (MAC CE). The above configuration for the above PRACH may be based on the upper layer parameter EarlyULSyncConfig related to the early uplink synchronization procedure. The above candidate cell can be indicated by a bit field index based on the number of bits of the cell indicator field among the candidate cells for which the upper layer parameter EarlyULSyncConfig is set. The above bit count is And, is a ceiling function, and C may be the number of candidate cells for which the upper layer parameter EarlyULSyncConfig is set. Among the bit field indices based on the above bit number, bit field index 0 can be mapped to the serving cell. The remaining bit field indices among the bit field indices can be mapped to the candidate cells in ascending order of candidate identity, starting from bit field index 1. The above neighboring cells may be related to L1 (Layer 1)-RSRP (Reference Signal Received Power) measurements. The above secondary cell may be a secondary cell without uplink carrier. The above DCI may be based on DCI format 1_0 for a random access procedure initiated by a Physical Downlink Control Channel (PDCCH) order. A terminal according to another embodiment of the present disclosure includes one or more transceivers, one or more processors, and one or more memories connected to the one or more processors and storing instructions. The above instructions are characterized in that they cause the terminal to perform all steps of any one of the above methods based on being executed by the one or more processors. According to another embodiment of the present disclosure, a device comprises one or more memories and one or more processors functionally connected to the one or more memories. The one or more memories are characterized in that they store instructions that cause the device to perform all steps of any one of the above methods based on execution by the one or more processors. In another embodiment of the present disclosure, one or more non-transitory computer-readable media store instructions, the instructions being executable by one or more processors, characterized in that they cause a terminal to perform all steps of any one of the above methods. A method according to another embodiment of the present disclosure includes the steps of transmitting a configuration for a Physical Random Access Channel (PRACH) for each of candidate cells, transmitting Downlink Control Information (DCI), and receiving the PRACH. The DCI includes a cell indicator field. Based on the cell indicator field, a candidate cell for the PRACH among the candidate cells is indicated. Based on whether the candidate cell is a neighbor cell or a secondary cell (SCell), the candidate cell is characterized in that it is used as a reference cell for determining the transmit timing of the PRACH. A base station according to another embodiment of the present disclosure includes one or more transceivers, one or more processors, and one or more memories coupled to the one or more processors and storing instructions. The above instructions are characterized in that they cause the base station to perform all steps of the method based on being executed by the one or more processors. According to embodiments of the present disclosure, ambiguity in determining the transmission timing of a PRACH for early TA acquisition in an LTM cell switch procedure can be resolved. Furthermore, compared to using a reference cell defined for a serving cell when determining the PRACH transmission timing, the accuracy of TA acquired via the PRACH can be improved. The effects that can be obtained from this specification are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the technical field to which this specification belongs from the description below. Figure 1 illustrates a MAC RAR according to an embodiment of the present specification. FIG. 2 illustrates a Timing Advance Command MAC CE according to an embodiment of the present specification. Figure 3 illustrates a procedure related to LTM to which a method according to an embodiment of the present specification can be applied. FIG. 4 is a flowchart illustrating a method according to one embodiment of the present specification. FIG. 5 is a flowchart illustrating a method according to another embodiment of the present specification. FIG. 6 is a drawing showing the configuration of a first device and a second device according to an embodiment of the present specification. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description set forth below, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some cases, to avoid obscuring the concept of the present invention, well-known structures and devices may be omitted or illustrated in block diagram form focusing on the core functions of each structure and device. Hereinafter, downlink (DL) refers to communication from a base station to a terminal, and uplink (UL) refers to communication from a terminal to a base station. In downlink, a transmitter may be part of a base station, and a receiver may be part of a terminal. In uplink, a transmitter may be part of a terminal, and a receiver may be part of a base station. A base station may be expressed as a first communication device, and a terminal may be expressed as a second communication device. A base station (BS) may be replaced by terms such as a fixed station, Node B, eNB (evolved-NodeB), gNB (Next Generation NodeB), BTS (base transceiver system), access point (AP: Access Point), network (5G network), AI system, RSU (road side unit), vehicle, robot, drone (Unmanned Aerial Vehicle, UAV), AR (Augmented Reality) device, VR (Virtual Reality) device, etc. In addition, the terminal may be fixed or mobile, and may be replaced with terms such as UE (User Equipment), MS (Mobile Station), UT (user terminal), MSS (Mobile Subscriber Station), SS (Subscriber Station), AMS (Advanced Mobile Station), WT (Wireless terminal), MTC (Machine-Type Communication) device, M2M (Machine-to-Machine) device, D2D (Device-to-Device) device, vehicle, robot, AI module, drone (Unmanned Aerial Vehicle, UAV), AR (Augmented Reality) device, VR (Virtual Reality) device, etc. <TRP 구분 관련 확장 설명> For convenience of explanation, the proposed method assumes cooperative transmission / reception between two TRPs. However, it can be expanded to multiple TRP environments with three or more TRPs, as well as multi-panel environments. Different TRPs can be recognized by the UE as having different TCI states (associated with different CORESET pool indices). For example, if the UE receives data / DCI using the first TCI state associated with the first CORESET pool index, it means that the data / DCI has been received from TRP1. For example, if the UE transmits data / UCI using the first TCI state associated with the first CORESET pool index, it means that the data / UCI has been transmitted to TRP 1. For example, if the UE receives data / DCI using the second TCI state associated with the second CORESET pool index, it means that the data / DCI was received from TRP2. For example, if the UE transmits data / UCI using the second TCI state associated with the second CORESET pool index, it means that the data / UCI was transmitted to TRP 2. TA (Timing advance) related procedure Transmission of uplink frame number i from a terminal (User Equipment, UE) is earlier than the start of the corresponding downlink frame from that terminal. You have to start earlier. The uplink timing (e.g., uplink frame) associated with can be defined as follows: Uplink timing Uplink frame number for transmission from UE for transmission from the UE) before the start of the corresponding downlink frame from the UE. It should start from . - and silver =0 is provided by clause 4.2 of [5, TS 38.213], except for msgA transmission over PUSCH where it must be used. - given by clause 4.2 of [5, TS 38.213] is derived from the upper layer parameters TACommon, TACommonDrift, and TACommonDriftVariation (if these parameters are set). Otherwise =0; - given by clause 4.2 of [5, TS 38.213] is calculated by the UE based on the UE position and serving-satellite-ephemeris-related higher-layers parameters (if these parameters are set). Otherwise, =0. Above is N TA and N TA,offset can be calculated / determined based on N TA and N TA,offset can be set / applied as follows: N TA : 1) Set via RAR (Random access response), 2) Set via Timing advance command (MAC-CE) N TA,offset: 1) Set specific values ​​for each serving cell, 2) Apply predefined values ​​to each serving cell according to Duplex mode / FR Below is the N described above TA,offset and N TA It specifically explains how to set / apply. N TA,offset Case 1) How to set specific values ​​for each serving cell For example, the terminal is N TA,offset Configuration information (e.g., ServingCellConfigCommon Information) including information about can be received from the base station. The configuration information can be received based on RRC signaling. Table 1 below exemplifies the configuration information. Case 2) How to apply predefined values ​​to serving cells according to duplex mode / FR For example, the terminal is predefined N according to Duplex mode (TDD / FDD) / FR. TA,offset The value of can be applied to the serving cell. Table 2 below shows N TA,offset exemplifies the value of . N TA Case 1) How to set up using RAR (Random access response) For example, in a random access procedure (e.g., a 2-step RACH procedure or a 4-step RACH procedure), the terminal may receive an RAR from the base station. Based on the RAR, N TAcan be determined / set. Specifically, the RAR may include a timing advance command. The timing advance command indicates an index value (e.g., index value TA) related to timing adjustment. Based on the index value, N TA can be determined. The above RAR can be based on MAC RAR. This is described below with reference to FIG. 1. Figure 1 illustrates a MAC RAR according to an embodiment of the present specification. Referring to Figure 1, the MAC RAR may include an R (Reserved bit), a Timing Advance Command, a UL Grant, and a Temporary C-RNTI. The MAC payload of the MAC RAR will be examined in detail below. 6.2.3 MAC Payload for Random Access Response MAC RAR has a fixed size as shown in Figure 6.2.3-1 and consists of the following fields: - R: Reserved bit, set to 0; - TI: If two TAGs are configured for the Serving Cell where the Random Access procedure is performed, this field indicates which of the two TAGs the Timing Advance Command applies to. A field set to 0 indicates the first TAG ID, and a field set to 1 indicates the second TAG ID. If two TAGs are not configured for the Serving Cell where the Random Access procedure is performed, the R bit is present instead; - Timing Advance Command: The Timing Advance Command field indicates the index value TA used to control the amount of timing adjustment that the MAC entity should apply in TS 38.213 [6]. The size of the Timing Advance Command field is 12 bits; - UL Grant: The Uplink Grant field indicates the resources used for the uplink in TS 38.213[6]. The size of the UL Grant field is 27 bits; - Temporary C-RNTI: The Temporary C-RNTI field indicates a temporary identifier used by the MAC entity during random access. The size of the Temporary C-RNTI field is 16 bits. The MAC RAR is octet aligned. Below, we examine transmission timing adjustments based on the Timing advance command. 4.2 Adjusting transmission timing The UE is informed of the timing advance offset for the serving cell by n-TimingAdvanceOffset for the serving cell. The values ​​can be provided. If the UE provides two coresetPoolIndex values ​​0 and 1 for the first and second CORESET for the serving cell, or does not provide a coresetPoolIndex value for the first CORESET and provides a coresetPoolIndex value 1 for the second CORESET, the UE can provide the first and second coresetPoolIndex values. You can get the values: first and second The values ​​are provided by n-TimingAdvanceOffset and n-TimingAdvanceOffset2 for transmissions of the TCI state associated with the first and second CORESET, respectively. The UE selects the first CORESET for transmissions based on the spatial domain filters corresponding to the TCI state associated with the physCellId of the serving cell. In addition to the value, a second one is provided for transmissions based on spatial domain filters corresponding to the physCellId for the serving cell and the TCI states associated with other physCellIds. You can get the values. First and second The values ​​correspond to the first and second joint TCI states provided by the dl-OrJointTCI-StateList or the first and second UL TCI states provided by the ul-TCI-State-List and the first and second TAGs [11, TS 38.321] having an association indicated by the tag-Id-ptr. If the UE is not provided with n-TimingAdvanceOffset for the serving cell, the UE defaults to the timing advance offset for the serving cell as described in [10, TS 38.133]. Decide. When two UL carriers are configured for a serving cell in a UE, the same timing advance offset value is applied to both carriers for transmission in the serving cell associated with the same TAG. This applies. The UE has two I don't expect the values ​​to apply. When a terminal receives a timing advance command for a TAG, the terminal expects the same for all serving cells within the TAG. Based on the value and the received timing advance command, the terminal adjusts the uplink timing for PUSCH / SRS / PUCCH transmission for all serving cells in the TAG. Here, the uplink timing for PUSCH / SRS / PUCCH transmission is the same for all serving cells in the TAG. For bands with synchronous contiguous intra-band EN-DC in a band combination having a maximum transmission timing difference requirement that is not applicable as described in Note 1 of Table 7.5.3-1 of [10, TS 38.133], if the UE indicates ul-TimingAlignmentEUTRA-NR as 'mandatory' and the uplink transmission timing based on the timing adjustment indications for the TAG from the MCG and the TAG from the SCG are determined by the UE to be different, the UE adjusts the transmission timing for PUSCH / SRS / PUCCH transmissions for all serving cell portions of the band with synchronous contiguous intra-band EN-DC based on the timing adjustment indications for the TAG from the serving cell of the MCG in the band. The UE is not expected to transmit PUSCH / SRS / PUCCH in one CG if it overlaps in time, even partially, with a random access preamble transmitted in another CG. For SCS, the timing advance command for TAG is Indicates a change in uplink timing relative to the current uplink timing for the TAG by a multiple of . The starting timing of the random access preamble is described in [4, TS 38.211]. For random access response or for cell transition command T_A for absolute timing advance command MAC CE or TAG, the timing advance command [11, TS 38.321] = with index values ​​of 0, 1,2, ..., 3846 The values ​​represent the time alignment amount of TAG where SCS is 2^μ15kHz. am. is defined in [4, TS 38.211] and relates to the SCS of the first uplink transmission from the UE after receiving a random access response or an absolute timing advance command MAC CE or a cell switching command. In other cases, the timing advance command for TAG [11, TS 38.321], Is The index values ​​of = 0, 1, 2,.. 0, 1, 2,..., 63 are currently value, to new value Indicates that it is adjusted to . Here, for SCS of 2^μ15kHz, am. If a UE has multiple active UL BWPs in the same TAG, including UL BWPs on two UL carriers of the serving cell, the timing advance command value is associated with the largest SCS among the multiple active UL BWPs, as described in Section 12. The SCS applicable to the UL BWP with the lowest SCS is The value may be rounded to match the timing advance granularity for the UL BWP with the lowest SCS while meeting the timing advance accuracy requirements of [10, TS 38.133]. Adjusting the value by a positive or negative amount means advancing or delaying the uplink transmission time for the TAG by the corresponding amount, respectively. For transmissions other than PUSCH scheduled by a timing advance command received in uplink slot n and a RAR UL grant or fallbackRAR UL grant as described in Section 8.2A or 8.3, or PUCCH with HARQ-ACK information in response to a SuccessRAR as described in Section 8.2A, the timing of the corresponding uplink transmission is adjusted by the uplink slot It applies from the beginning. Here is the PDSCH processing time for UE processing capability 1 when additional PDSCH DM-RS is configured. is the duration of the symbols (msec), corresponds to the PUSCH preparation time for UE processing capability 1. The time in msec of the symbols is [6, TS 38.214], is the maximum timing advance value (in msec) that can be provided by the 12-bit TA command field, is the number of slots per subframe, is a subframe period of 1 msec, and Here is provided by cellSpecificKoffset is provided by the Differential Koffset MAC CE command [11, TS 38.321]. Otherwise, if not provided, =0 or =0. For the minimum SCS among the SCSs of all UL BWPs configured for all uplink carriers in the TAG and the SCSs of all DL BWPs configured for the corresponding downlink carriers. class is determined. If μ=0, the UE is [6, TS 38.214]. For slot n and the minimum SCS among the SCSs of all UL BWPs configured for all uplink carriers in the TAG, This is decided. is determined with respect to the minimum SCS among the SCSs of all UL BWPs configured for all uplink carriers in the TAG and the SCSs of all configured initial UL BWPs provided by initialUplinkBWP. Uplink slot n is =0, the last slot among the uplink slot(s) overlapping with the PDSCH reception slot(s), where the PDSCH provides a timing advance command. is defined in [4, TS 38.211]. If the UE changes the active UL BWP between the time it receives the timing advance command and the time it applies the adjustment to the corresponding uplink transmission timing, the UE determines the timing advance command value based on the SCS of the new active UL BWP. If the UE changes the active UL BWP after applying the uplink transmission timing adjustment, the UE assumes the same absolute timing advance command value before and after the active UL BWP change. If the received downlink timing changes and is not compensated or only partially compensated by uplink timing adjustment without timing advance command as described in [10, TS 38.133], the UE changes N_TA accordingly. If the UE operates based on two TAGs in the active UL BWP of the serving cell, the UE expects that the difference between the first downlink timing associated with the first TAG and the second downlink timing associated with the second TAG will not be larger than the CP length for the active UL BWP, unless the UE indicates larger-thanCP-capability. If the UE indicates XYZ_capability, is provided with SRS-autonomousTAupdate [10, TS 38.133], and transmits SRS according to the configuration by SRS-PosResourceSet in SRS-PosRRC-InactiveConfig-ValidityArea in RRC_INACTIVE state, the UE shall change N_TA accordingly during cell reselection. can autonomously update; otherwise, if the UE is not provided with SRS-autonomousTAupdate, the UE shall update the last serving cell before releasing the dedicated RRC connection. maintains [11, TS 38.321]. For the operation of a single TAG in a serving cell, if two adjacent slots overlap due to a TA command, the duration of the later slot is reduced compared to the earlier slot. The UE may transmit PUSCH or PUCCH during the actual transmission time window. [6, TS 38.214]. If a UE is not provided with the activated STx2PofMDCI and operates based on two TAGs in the serving cell, the UE shall not expect transmissions associated with different TAGs to overlap unless the UE indicates XYZ. If the UE indicates XYZ, the UE shall reduce the duration of later transmissions using the first TAG to avoid overlapping with earlier transmissions using the second TAG. Case 2) How to set using Timing advance command (MAC-CE) For example, N TA can be set / determined based on MAC-CE. Specifically, N TA can be determined based on the Timing Advance Command MAC CE. The Timing Advance Command MAC CE may include a timing advance command. N based on the timing advance command TA Since the decision is the same as that described in Case 1, duplicate explanation is omitted (see Table 5). The Timing Advance Command MAC CE is described below with reference to FIG. 2. FIG. 2 illustrates a Timing Advance Command MAC CE according to an embodiment of the present specification. Referring to FIG. 2, the Timing Advance Command MAC CE may include a TAG ID and a Timing Advance Command. The payload of the Timing Advance Command MAC CE will be examined in detail below. 6.1.3.4 Timing Advance Command MAC CE Timing Advanced Commands MAC CE is identified by a MAC subheader with an LCID as specified in Table 6.2.1-1. It has a fixed size and consists of a single octet defined as follows (Figure 6.1.3.4-1): - TAG Identity (TAG ID): This field indicates the TAG ID of the addressed TAG. A TAG containing an SpCell has TAG ID 0. The field length is 2 bits; - Timing Advance Command: This field indicates an index value TA (0, 1, 2...63) used to control the amount of timing adjustment that the MAC entity should apply (as specified in TS 38.213 [6]). The field is 6 bits long. 6.1.3.4a Absolute Timing Advance Command MAC CE An Absolute Timing Advance Command MAC CE is identified by a MAC subheader with an eLCID as specified in Table 6.2.1-1b. It has a fixed size and consists of two octets defined as follows (Figure 6.1.3.4a-1): - Timing Advance Command: This field indicates the index value TA used to control the amount of timing adjustment that the MAC entity should apply in TS 38.213 [6]. The field size is 12 bits; - TI: If two TAGs are configured for the SpCell, this field indicates which of the two TAGs the Timing Advance Command applies to. A field set to 0 indicates the first TAG ID, and a field set to 1 indicates the second TAG ID. If two TAGs are not configured for the SpCell, the R bit is present instead; - R: Reserved bit, set to 0. TAG (Timing advance group) A Timing Advance Group (TAG) is a group of serving cells that use the same Timing Advance value. Table 3 below illustrates the definition of a TAG and the associated configuration information. The above-mentioned content can be applied in combination with the methods proposed in this specification, which will be described later, or can be supplemented to clarify the technical characteristics of the methods proposed in this specification. The methods described below are distinguished for convenience of explanation, and it is understood that certain components of one method may be substituted for or combined with other methods. According to 3GPP standards up to NR Rel-17, handover based on terminal mobility is performed as follows. The terminal reports (L3-based) RSRP measurements to a candidate serving cell, which is a non-serving cell. The base station determines the handover based on the report and triggers the handover to the terminal. At this time, the terminal detaches from the serving cell and performs the RACH procedure for synchronization with the new cell. The terminal can obtain TA information for the cell to which it is newly attaching by receiving an RAR from the cell. In Rel-18 mobility enhancement, discussions are underway on the operation of the base station / terminal to reduce delay (by omitting the RACH procedure) when performing handover by having the base station / terminal acquire TA information about such candidate serving cells before the handover command (see Table 4 below). In addition, while existing handovers are performed via L3 signaling, L1 / L2-based handovers are being considered, utilizing cell switch command MAC CEs to transmit beam / TA information to the UE for use in the candidate serving cell. RACH-based and RACH-less approaches are being considered as TA acquisition methods for the candidate (serving) cell. Meanwhile, the following agreements were reached in Rel-18 mobility - TA management. Agreement Supports acquisition of TA of candidate cell(s) before cell switch command is received in L1 / L2 based mobility. FFS: Whether this can be applied to a candidate cell when that candidate cell is a disabled SCell (if defined in RAN2). Agreement The following solutions can be further studied for the mechanism of acquiring the TA of a candidate cell. RACH-based solutions (e.g., PDCCH ordered RACH, UE-triggered RACH, higher layer triggered RACH from NW other than L3 HO cmd) Solutions without RACH (e.g. SRS based TA acquisition, Rx timing difference based, RACH-less mechanism as in LTE, UE based TA measurement (including UE based TA measurement with one TAC from serving cell) Agreement Supports at least PDCCH ordered RACH for the mechanism to acquire TA of candidate cells in Rel-18 LTM. PDCCH order is triggered only by the source cell. FFS: Details including DCI content, RACH resource configuration, RAR transmission mechanism, etc. Note: Other RACH-based solutions are discussed separately. Agreement For PDCCH ordered RACH in LTM, at least the following enhancements are supported: Introduction of candidate cell and / or RO indication of candidate cell in DCI Providing RACH resource configuration for candidate cells prior to PDCCH order FFS: Whether / How to Transmit RAR Agreement TA update (i.e. TA reacquisition) for a candidate cell can be triggered by the NW. The same triggering mechanism reuses the initial TA acquisition, i.e., the PDCCH order triggered RACH in the candidate cell. Agreement For Rel-18 LTM, a RACH status indication with an SSB index associated with a random access preamble index is configured for each candidate cell. Note: Detailed signaling is left to RAN2. Agreement The PDCCH order of the source cell includes an indication of candidate cell. The reserved bit(s) of DCI format 1_0 for PDCCH order can be used for indication of cell identity. Agreement For PDCCH order based RACH for TA measurement of candidate cells, legacy CBRA is not supported. Agreement When RAR reception is not configured / instructed, the UE selects one of the following alternatives regarding whether to retransmit PRACH. Alt 1: UE autonomous retransmission of PRACH is not allowed (e.g., the number of allowed PRACH transmissions is set to the minimum value of PreambleTransMax = 1) Alt 2: UE autonomous retransmission of PRACH is allowed, The number of PRACH transmissions is defined (e.g., the number of RACH transmissions is set to the minimum value of PreambleTransMax). Agreement Verify the following working assumptions and send LS to RAN4 to clarify the possibility of supporting this mechanism. Working Assumption From a RAN 1 perspective, UE-based TA measurement is supported (UE derives TA based on the Rx timing difference between the current serving cell and candidate cells and the TA value of the current serving cell). This UE feature is introduced to support UE-based TA measurements. UE-based TA measurement configuration is supported if the UE reports that it supports this feature. FFS: Other Impacts on the RAN1 Specification Agreement From a RAN 1 perspective, a RACH-less mechanism can be supported without performing PDCCH-ordered RACH for the candidate cell by indicating the TA value of the target cell as TA=0 or keeping it the same value as the source cell in the cell switch command. NOTE 1: This does not mean that a non-zero TA value and RAR are excluded from the cell switch command for PDCCH-ordered RACHs that have the same value as the source cell, if they are not configured for PDCCH order. Note 2: Feasibility and signaling may be further concluded in RAN2. Agreement For PRACH based on PDCCH order for candidate cells, the candidate cell SSB indicated in the PDCCH order serves as a path loss RS for determining PRACH Tx power. Agreement When RAR reception is not configured, the [1-bit] field of the PDCCH order explicitly indicates an initial transmission or retransmission of the PRACH when determining the PRACH transmission power. Agreement When RAR reception is not configured, the 1-bit field of PDCCH order explicitly indicates the initial transmission or retransmission of the PRACH when determining the PRACH transmission power, FFS. If marked as retransmission, the UE increases power by the value of the power ramping configuration, unless the maximum allowed power is reached. Whether / how to reset the counter Agreement For power control of PDCCH-ordered CFRA in LTM, the UE can maintain only one power ramping counter. Agreement For power control of PDCCH-ordered CFRA in LTM, the power ramping counter is reset at least when the UE receives a PDCCH order indicating the initial transmission of a PRACH. Agreement For power control of PDCCH-ordered CFRA in LTM When the UE receives a PDCCH command indicating a retransmission of a PRACH using the same associated SSB and the same candidate cell as the previous PRACH, the counter is incremented by 1. In addition to Case 1, the power ramping counter is reset in the following cases: Case 2: The candidate cell indicated in the PDCCH order indicates a retransmission and is different from the candidate cell indicated in the last PDCCH order. Note: The initial counter is 0 before receiving the PDCCH order. Agreement When the PDCCH order is transmitted for a candidate cell, The bit size N of DCI format 1_0 for cell indicator is determined by the number of configured candidate cells (e.g., C) with RACH configuration provided for Early TA acquisition, and the following alternatives are supported. Alt 2: N= The number of cells used to calculate the bit width is the number of candidate cells with RACH configuration provided for Early TA acquisition + 1 (serving cell). Agreement In the PDCCH order, the bit field code point '0' of the cell indicator field indicates the PRACH for the current serving cell, and the remaining bit field code points are mapped to candidate cells configured with EarlyUlSyncConfig-r18. That is, the bit field code points from 1 to C are mapped one-to-one with the candidate cell ID in ascending order. The above contents can be summarized as follows. For TA acquisition for a candidate cell, a PDCCH ordered CFRA procedure can be utilized in a RACH-based approach. Whether or not an RAR for the RACH transmission is configured via RRC was discussed in RAN1. Since RAN2 concluded that an RAR is not necessary, the UE does not receive an RAR for the RACH transmission. For RACH transmission for a candidate cell, a PRACH configuration for the candidate cell can be preset for the UE. The ordering DCI (i.e., the DCI that triggers the PRACH transmission, PDCCH order) can indicate the ID of the candidate cell or indicate RACH resources for the candidate cell. The indication can trigger RACH transmission for the candidate cell. In this case, the RACH transmission timing for the candidate cell is ambiguous. This will be described in detail below. Unlike when RACH is transmitted based on the DL reference timing of the reference cell in the serving cell (as shown in Table 5 below), the DL reference timing is ambiguous when transmitting (PDCCH ordered) RACH to a candidate cell. In other words, there is ambiguity (Problem 1) regarding when the UE should perform RACH transmission to the candidate cell. Meanwhile, the contents of the standardization meeting related to L1 measurement enhancement for transmitting beam information to terminals in cell switch command MAC CE are summarized in Table 6 below. The Rel-18 LTM related procedures can be performed as follows: L1 / L2-Triggered Mobility procedures A UE can be instructed with LTM-Config to select a candidate cell and SS / PBCH blocks per candidate cell, so that the UE can obtain synchronization and measure the corresponding L1-RSRP [10, TS 38.133]. The MAC CE command can activate the TCI state provided in LTM-Candidate-TCI-State-r18 or / and LTM-Candidate-TCI-UL-State-r18 to associate it with the SS / PBCH block or TRS of the corresponding candidate cell. The UE is provided with configurations in LTM-CSI-ReportConfigToAddModList for reporting L1-RSRP measurements [6, TS 38.214] that include a number of candidate cells and a number of SS / PBCH blocks per candidate cell from the number of candidate cells. (A UE can be indicated, by LTM-Config, candidate cells and SS / PBCH blocks per candidate cell for the UE to obtain synchronization and measure corresponding L1-RSRPs [10, TS 38.133]. A MAC CE command can activate TCI states, provided by LTM-Candidate-TCI-State-r18 or / and LTM-Candidate-TCI-UL-State-r18, associated with SS / PBCH blocks or TRS of corresponding candidate cells. The UE is provided with configurations by LTM-CSI-ReportConfigToAddModList for reporting L1-RSRP measurements [6, TS 38.214] that include a number of candidate cells and a number of SS / PBCH blocks per candidate cell. candidate cell from the number of candidate cells.)When ueMeasuredTA is provided to the UE, the UE estimates the timing advance to be applied from the first transmission in the candidate cell after receiving the cell switch command for the candidate cell, depending on the UE implementation [11, TS 38.321]. The UE can be provided with configuration for PRACH transmission parameters for each candidate cell by EarlyUlSyncConfig. The UE can trigger PRACH transmission in the candidate cell by the PDCCH order received from the serving cell and containing the indication of the candidate cell for PRACH transmission [4, TS 38.212]. If a UE is provided ueMeasuredTA, the UE estimates based on the UE implementation a timing advance to apply from a first transmission on a candidate cell that is after the reception of a cell switch command for the candidate cell [11, TS 38.321]. A UE can be provided configurations, by EarlyUlSyncConfig, for PRACH transmission parameters for each of the candidate cells.The UE can be triggered a PRACH transmission on a candidate cell by a PDCCH order that the UE receives on a serving cell and includes an indication of the candidate cell for the PRACH transmission [4, TS 38.212]. If the serving cell and the candidate cell operate in a same frequency range and the UE would have transmissions that overlap in time, or when a gap between a first or last symbol of a PRACH transmission to the candidate cell is less than symbols from a last or first symbol, respectively, of an UL transmission to the serving cell, where N is defined in Clause TBD, the UE perform following operations). - When the UE does not support transmissions that overlap in time or are separated by less than the gap on the serving cell and the candidate cell, the UE drops the transmissions on the serving cell. - The UE supports transmissions that are temporally overlapping or separated by less than an interval and the total UE transmit power in the frequency range is When the UE supports transmissions that overlap in time or are separated by less than the gap, and a total UE transmit power in the frequency range would exceed 7.5, the UE prioritizes power allocation to the PRACH transmission on the candidate cell. ). The UE transmits the PRACH on the candidate cell as described in Clause 8.1 with a power determined as described in Clause 7.4. The UE may indicate the number of candidate cells in the TCI-State and / or TCI-UL-State of the LTM-dl-OrJointTCI-StateToAddModList and / or LTM-ul-TCI-ToAddModList indicating the integrated TCI states for applicable reception or transmission of the candidate cells [6, TS 38.214], which may be provided by the MAC CE upon PDSCH reception of the serving cell [11, TS 38.321]. A UE can be provided by a MAC CE in a PDSCH reception on the serving cell [11, TS 38.321] a TCI-State and / or TCI-UL-State in LTM-dl-OrJointTCI-StateToAddModList and / or LTM-ul-TCI-ToAddModList indicating a unified TCI state [6, TS 38.214] for applicable receptions or transmissions on a candidate cell from the number of candidate cells. The UE applies the TCI-State and / or TCI-UL-State, if indicated by the MAC CE, from a first slot that is TBD after the last symbol of a PUCCH or PUSCH with HARQ-ACK information for a PDSCH providing the MAC CE, where μ is an SCS configuration for the TBD. information for the PDSCH providing the MAC CE, and μ is the SCS configuration for the TBD). L1 / L2-Triggered Mobility (LTM) LTM is described below with reference to Fig. 3. Figure 3 illustrates a procedure related to LTM to which a method according to an embodiment of the present specification can be applied. LTM is a procedure in which the gNB receives an L1 measurement report from the UE and, based on this, switches the UE's serving cell using a cell switch command signaled via MAC CE. The cell switch command represents an LTM candidate configuration previously prepared by the gNB and provided to the UE via RRC signaling. The UE then switches to the target configuration based on the cell switch command. The LTM procedure can be used to reduce mobility latency, as described in Appendix G. If configured by the network, the TCI status of one or more cells other than the current serving cell can be activated. For example, the TCI status of an LTM candidate cell can be activated in advance of that cell becoming the serving cell. This allows the UE to perform DL synchronization with that cell, allowing for faster cell switching to one of those cells when the cell switch is triggered. The network may initiate an UL TA acquisition (called early TA) procedure for one or more cells other than the current serving cell, if configured by the network. If the cells have the same NTA as the current serving cell or if NTA=0, the early TA acquisition procedure is not required. The network may request the UE to perform early TA acquisition for a candidate cell before a cell switch. The early TA acquisition procedure is triggered by the PDCCH sequence specified in clause 9.2.6 or by UE-based TA measurement configured in RRC. In the former case, the gNB to which the candidate cell belongs calculates the TA value and transmits it to the gNB to which the serving cell belongs. The serving cell transmits the TA value in the LTM cell switch command MAC CE when triggering the LTM cell switch. In the latter case, the UE performs TA measurements for the candidate cells after RRC configuration, but the exact time when the UE performs the TA measurements depends on the UE implementation. The UE applies its own measured TA value and performs LTM without RACH upon receiving the cell switch command. The network may also transmit the TA value in the LTM cell switch command MAC CE without early TA acquisition. Depending on the availability of a valid TA value, the UE performs a RACH-less LTM or RACH-based LTM cell switch. If a TA value is provided in the cell switch command, the UE applies the TA value as instructed by the network. If UE-based TA measurement is configured but a TA value is not provided in the cell switch command, the UE directly applies the TA value if available. Meanwhile, the UE performs a RACH-less LTM cell switch when it receives a cell switch command. If a valid TA value is not available, the UE performs a RACH-based LTM cell switch. The UE follows the PDCCH sequence, including requesting a random access procedure for a candidate cell, regardless of whether the UE is configured for UE-based TA measurements for that candidate cell. This also applies to candidate cells for which the UE can derive its own TA values. Furthermore, regardless of whether the UE has already performed a random access procedure for that candidate cell, the UE continues to follow the UE-based measurement configuration if configured by the network. For LTM without RACH, the UE accesses the target cell using a configured grant or a dynamic grant. The configured grant is provided in the LTM candidate configuration, and the UE selects a configured grant occasion associated with the beam indicated in the cell switch command. When the LTM cell switch to the target cell is initiated, the UE begins monitoring the PDCCH of the target cell for dynamic scheduling. If there are no valid PUCCH resources for the triggered SR before the RACH-less LTM procedure is completed, the UE does not trigger the random access procedure. The following principles apply to LTM: - Security keys are maintained during LTM cell switches. - Follow-up LTM is supported. LTM supports both intra-gNB-DU mobility and inter-gNB-DU mobility within a gNB-CU. LTM supports both intra- and inter-frequency mobility, including mobility to inter-frequency cells other than the currently serving cell. LTM is supported only in licensed spectrum. The following scenarios are supported: - PCell changes in non-CA and non-DC scenarios; - Change PCell and SCell in CA scenario; - Dual connectivity scenarios, PCell and MCG SCell changes, and PSCell and SCG SCell changes within the SN without MN involvement. LTM for simultaneous PCell and PSCell changes is not supported. While the UE has stored the LTM candidate configuration, the UE can also execute any L3 handover commands sent by the network. The cell switch command is carried in the MAC CE, which contains the information required to perform an LTM cell switch. The overall procedure for LTM is illustrated in Figure 3. Subsequently, LTM is performed by repeating the steps of early synchronization, LTM cell switch execution, and LTM cell switch completion after each LTM cell switch completion, without releasing other LTM candidate configurations. The general procedure for SCG LTM over the air interface applies. For more information on SCG LTM, see TS 37.340.

[0021] You can check it out at . Referring to Figure 3, the procedure for LTM is as follows. 1. The UE sends a MeasurementReport message to the gNB. The gNB decides to configure LTM and begins preparing LTM. 2. The gNB sends an RRCReconfiguration message containing the LTM candidate configuration to the UE. 3. The UE stores the LTM candidate configuration and sends an RRCReconfigurationComplete message to the gNB. 4a. The UE performs DL synchronization with the candidate cell before receiving the cell switch command. 4b. If UE-based TA measurement is configured, the UE acquires the TA value of the candidate cell through measurement. The UE performs early TA acquisition with the candidate cell as requested by the network before receiving the cell switch command as specified in Section 9.2.6. This is performed via a CFRA triggered by the PDCCH order of the source cell, after which the UE transmits a preamble to the designated candidate cell. To minimize data interruption to the source cell due to the CFRA for the candidate cell, the UE does not receive a random access response from the network for TA value acquisition, and the TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain a TA timer for the candidate cell and relies on the network implementation to ensure TA validity. 5. The UE performs L1 measurements on the configured candidate cells and sends an L1 measurement report to the gNB. L1 measurements must be performed as long as RRC reconfiguration (step 2) is applied. 6. The gNB decides to initiate a cell switch to the target cell and sends a MAC CE that triggers the cell switch, including the candidate configuration index of the target cell. The UE switches to the target cell and applies the configuration indicated by the candidate configuration index. 7. The UE performs a random access procedure for the target cell if there is no valid TA of the target cell as specified in clause 6.1.3.xy of TS 38.321[6]. 8. The UE completes the LTM cell switching procedure by sending an RRCReconfigurationComplete message to the target cell. If the UE performed the RA procedure in step 7, the UE considers the LTM cell switching procedure to be completed successfully when the random access procedure is successfully completed. For LTM without RACH, the UE considers the LTM cell switching procedure to be completed successfully when the network determines that the first UL data has been successfully received. Steps 4-8 can be repeated multiple times for subsequent LTMs using the LTM candidate configuration provided in step 2. Against this backdrop, this specification describes a method for a UE to transmit a RACH directed to a candidate serving cell in Rel-18 LTM (L1 / L2-triggered mobility) for mobility enhancement, and proposes related UE operations. In particular, it proposes a method for defining / configuring reference timing, which determines the reference timing for which a UE should transmit a RACH to a candidate cell. Below, reference timing can refer to the standard by which a UE should apply TA when transmitting a specific uplink. Reference timing can be used interchangeably with expressions such as DL frame boundary, DL reference timing, and reference point. When a UE transmits a RACH based on reference timing, the signal arrives at the base station later than the NW DL / UL frame boundary due to propagation delay, etc. The base station can calculate the required timing advance value and set / instruct the UE. A non-serving cell that can be the target of a UE handover (i.e., cell switch) can be used interchangeably with terms such as candidate serving cell, candidate cell, target cell, and target candidate cell. Additionally, the base station may configure one or more candidate cell information items prior to a handover command for Rel-18 LTM. The configuration of the candidate cell information may include PCI, RACH configuration (e.g., RACH preamble, RACH occasion, RACH resource, or / and SSB index associated with each candidate cell), etc. for each candidate cell, which is a non-serving cell that may become a potential serving cell. In this specification, ' / ' can be interpreted as 'and', 'or', or 'and / or' depending on the context. Below, we will specifically examine an embodiment for solving the above-described problem 1. Proposal 1 Below, we examine how to define / set DL reference timing for a candidate cell for RACH-based TA acquisition of a terminal for a candidate cell in Rel-18 LTM. Proposal 1-1 When transmitting RACH (PDCCH ordered CFRA) for a specific candidate cell, the terminal can perform RACH transmission based on the DL reference timing (of the reference cell) defined / set for the serving cell (that received the PDCCH order). Proposal 1-2 When transmitting RACH (PDCCH ordered CFRA) for a specific candidate cell, the terminal can measure the DL reference timing of the candidate cell based on a specific SSB (e.g., by LTM-Config) set for the candidate cell (for L1 measurement). The terminal can perform RACH transmission based on the DL reference timing. For example, the specific SSB may be the SSB with the lowest / first ID or the SSB with the highest / last ID among the SSBs set in the candidate cell. For example, the specific SSB may be based on the lowest / first and / or highest / last SSB index among the SSBs set in the CSI resource set for terminal beam measurement / report for the candidate cell. The CSI resource set may be set based on LTM-CSI-ReportConfigToAddModList. For example, the specific SSB may be the first configured SSB and / or the last configured SSB among the SSBs configured in the CSI resource set for terminal beam measurement / report for the candidate cell. That is, the specific SSB may be determined based on the order configured / defined in the CSI resource set. The CSI resource set may be configured based on LTM-CSI-ReportConfigToAddModList. More specifically, the specific SSB of Proposal 1-2 may be one of the SSBs that the terminal is measuring / tracking. For example, the specific SSB may be the SSB with the lowest / highest ID among the SSBs for which the terminal recently performed L3 measurement / report (for RRM) for a specific candidate cell. For example, the specific SSB may be an SSB with the lowest / highest ID among SSBs whose RSRP / RSRQ / RSSI based on L3 measurement is above a certain threshold. Proposals 1-3 When transmitting RACH (PDCCH ordered CFRA) for a specific candidate cell, the UE can measure the DL reference timing of the candidate cell based on the DL RS associated with a specific TCI state associated with the candidate cell. The UE can perform RACH transmission based on the DL reference timing. For example, the DL RS may be the QCL reference RS of the TCI state or / and the SSB that is the top QCL source of the reference RS. For example, the specific TCI state may be a TCI state having the lowest and / or highest ID among the TCI states in which the SSB associated with the specific candidate cell is set to the QCL reference RS. For example, the specific TCI state may be a TCI state activated for Rel-18 LTM operation among the TCI states in which the SSB associated with the specific candidate cell is set to the QCL reference RS. As a further example, the specific TCI state may be a TCI state having the lowest / highest ID among the TCI states activated for the Rel-18 LTM operation. More restrictively, if the time domain behavior characteristic of the DL RS associated with the specific TCI state is semi-persistent or aperiodic, the TCI state may be excluded from DL reference timing measurement. This is because static / periodic RS reception by the terminal is required for continuous reference timing measurement. In addition, similar to Proposal 1-2, the DL RS associated with the specific TCI state may be one of the DL RSs that the UE is measuring / tracking. For example, the specific TCI state may be a TCI state in which a DL RS (e.g., SSB) on which the UE recently performed L3 measurement / report (for RRM) for a specific candidate cell is set as a reference RS. For example, the specific TCI state may be a TCI state in which a DL RS (e.g., SSB) whose RSRP / RSRQ / RSSI based on the L3 measurement is above a certain threshold is set as a reference RS. In the DL RS related to the above specific TCI state, it can be assumed that two QCL reference RSs are set for the TCI state (e.g., QCL type A reference RS + QCL type D reference RS). In this case, it can be defined / set (by the base station) as to which of the two RSs is used as a reference for measuring the DL reference timing. For example, among the two RSs, the RS for the QCL type A reference can be utilized for measuring the DL reference timing. The embodiments of the above proposals 1-3 can be expressed as follows. For PRACH transmissions for candidate cells, the uplink transmission timing is to receive the first detected path (in time) of the corresponding downlink frame of the reference signal associated with the configured / activated UL / DL / joint TCI state for the candidate cell. (For PRACH transmission toward candidate cell, the uplink transmission timing takes place before the reception of the first detected path (in time) of the corresponding downlink frame of the reference signal associated with UL / DL / joint TCI state configured / activated for the candidate cell). In the above proposal 1-3, it may be assumed that there is no activated TCI state(s) for a specific candidate cell when transmitting a RACH (PDCCH ordered CFRA) for that candidate cell. In this case, another embodiment of proposal 1-3 or another embodiment of proposal 1 may be applied. Proposals 1-4 When a UE transmits a RACH (PDCCH ordered CFRA) for a specific candidate cell, the UE can measure the DL reference timing of the candidate cell based on the SSB index (related to the candidate cell) indicated in the PDCCH order that triggers the RACH for the candidate cell. The UE can perform RACH transmission based on the DL reference timing. The SSB index indicated in the PDCCH order (DCI) may be one of the SSBs being measured by the UE (e.g., maintained RS, periodically measured / reported RS, or known conditions for pathloss reference signal). The UE can expect the SSB index to be only among the above-described SSBs. This is because the UE requires static / periodic RS reception for constant reference timing measurement. In the above proposal 1, measuring the DL reference timing of a candidate cell based on a specific DL RS means that the uplink is transmitted by applying TA based on the reception time of the corresponding DL RS during uplink transmission. In other words, the uplink transmission based on a specific DL RS in proposal 1 is "uplink transmission timing takes place". It may mean "before the reception of the first detected path (in time) of the corresponding downlink frame of the DL RS". Meanwhile, in Rel-18 LTM, it was agreed that UE-based TA measurement would be supported as a RACH-less approach for TA acquisition of candidate cells. Below, we propose a new TA acquisition method for candidate cells, both for RACH-based and RACH-less approaches. Proposal 2 below can be utilized in addition to TA acquisition for a candidate cell in Rel-18 LTM, when multiple TAs are supported within a serving cell (e.g., Rel-18 MIMO two TA feature), or in TA acquisition for a specific TAG in a terminal CA situation. In the following, target TRP can mean i) a candidate cell in Rel-18 LTM, ii) a specific TRP / CORESET pool index / TAG in Rel-18 MIMO two TA, iii) a specific TAG (and its associated serving cell) in a terminal CA situation. In the following, source TRP can mean i) a serving cell in Rel-18 LTM, ii) a serving cell that is a reference for measuring TA of the target TRP, or iii) a reference cell. Proposal 2 Below, we examine a method for TA acquisition for a specific target TRP of a base station. Proposal 2-1 A method may be considered in which a terminal transmits a response based on the DL reference timing of a specific target TRP, and a base station calculates the TA of the target TRP based on the response. The terminal can transmit some kind of response message for the DL RS of the target TRP, which is the reference, based on the DL reference timing defined / set for the target TRP. The response message can be set / defined by the base station (RRC) and can be at least one of PRACH / PUCCH / SRS. The base station can measure the Tx-Rx timing difference, which is the difference between the Tx timing for transmitting the DL RS of the target TRP and the Rx timing for receiving the response message. Considering / based on the timing difference being twice the propagation delay between the target TRP and the terminal, the base station can measure / calculate the TA value for the target TRP of the terminal. For example, the Tx-Rx timing difference / 2 can be the TA value for the target TRP of the terminal. The TA value for this target TRP can be transmitted to the terminal by the base station based on RRC / MAC CE signaling, such as TA command MAC CE. Proposal 2-2 A method in which the terminal reports the Rx timing difference between the source TRP and the target TRP may be considered. The UE measures the DL reference timing of different DL RSs and reports the Rx timing difference. Specifically, the UE measures the DL RS of the source TRP configured (by the base station) and the DL RS of the target TRP. Based on this, the UE can report the Rx timing difference to the base station. Additionally, the UE can report Doppler domain statistics (related to the source / target TRP) to the base station (for more accurate timing difference calculation from the base station's perspective). The above report can be set / defined by the base station and transmitted via PUSCH / PUCCH, etc. The base station can calculate / determine TA based on the Rx timing difference as follows. The base station knows the slot boundary difference between the source TRP and the target TRP (in the asynchronous scenario). In addition, the TA for the serving cell (source TRP) is already known. In the case of the DL RS reception timing of the target TRP, the base station (NW) knows the slot boundary of the source TRP and the target TRP. This timing can be replaced by the source TRP to terminal propagation delay (the TA value for the source TRP of the terminal). The base station can measure the target TRP to terminal propagation delay only with the Rx timing difference between the DL RS of the source TRP and the DL RS of the target TRP. Considering / based on the time interval from the DL slot boundary of the target TRP to the DL RS reception timing of the target TRP of the terminal, which is the propagation delay between the target TRP and the terminal, the base station can calculate the TA value for the target TRP. For example, the time interval from the DL slot boundary of the target TRP to the DL RS reception timing of the target TRP of the terminal can be the TA value for the target TRP of the terminal. This TA value for the target TRP can be transmitted to the terminal by the base station based on RRC / MAC CE signaling, such as TA command MAC CE. The embodiments of the above proposals 1 and 2 can be applied to terminal / base station operation in combination of one or more embodiments. Below, we examine the signaling procedures related to the above-described embodiments. An example of a terminal (or base station) operation based on at least one of the embodiments described above (e.g., at least one of Proposals 1 and 2) is as follows. 1) The terminal (base station) receives (transmits) configuration information for the candidate cell. The configuration information for the above candidate cell may include information based on at least one of proposals 1 and 2. 2) The terminal (base station) receives (transmits) a message that sets up / instructs RACH transmission for the candidate cell. The above message may be a PDCCH (DCI) that triggers / orders a CFRA-based RACH. 3) The terminal (base station) transmits (receives) RACH based on the above message. The DL reference timing associated with the candidate cell for the above RACH transmission may be based on at least one of Proposals 1 and 2. 4) The terminal (base station) receives (transmits) the cell switch command MAC CE. Based on the cell switch command MAC CE, a switch operation can be performed to a specific candidate cell. The above terminal / base station operations are only an example, and each operation (or step) is not necessarily required, and depending on the terminal / base station implementation method, operations related to RACH transmission for the candidate cell of the terminal according to the above-described embodiments may be omitted or added. In terms of implementation, the operations of the base station / terminal according to the embodiments described above (e.g., operations based on at least one of Proposals 1 and 2) can be processed by the device of FIG. 6 described below (e.g., processor (110, 210) of FIG. 6). In addition, the operations of the base station / terminal according to the above-described embodiment (e.g., operations based on at least one of proposals 1 and 2) may be stored in a memory (e.g., 140, 240 of FIG. 6) in the form of commands / programs (e.g., instructions, executable codes) for driving at least one processor (e.g., 110, 210 of FIG. 6). The embodiments described below are specifically described with reference to FIGS. 4 and 5 in terms of the operation of the terminal and base station. The methods described below are distinguished for convenience of explanation, and it is understood that some components of one method may be substituted for or combined with some components of another method. FIG. 4 is a flowchart illustrating a method according to one embodiment of the present specification. Referring to FIG. 4, a method according to one embodiment of the present disclosure includes a step of receiving a configuration for a PRACH (S410), a step of receiving a DCI (DCI) (S420), a step of transmitting a PRACH (S430), and a step of receiving a Cell Switch Command MAC CE (S440). Some steps in the method may be omitted. For example, step S440 may be omitted in the method. In S410, the terminal receives a configuration for a Physical Random Access Channel (PRACH) for each of the candidate cells from the base station. For example, the configuration for the PRACH may be based on an LTM configuration (LTM-config). As a specific example, the terminal may receive the LTM configuration from the base station. The LTM configuration may include a configuration for each of the candidate cells (e.g., LTM-Candidate). The configuration for each of the candidate cells (e.g., LTM-Candidate) may include a configuration for the PRACH (e.g., EarlyUL-SyncConfig). That is, the PRACH configuration may not exist in all candidate cells based on the LTM configuration. The candidate cells referred to in this step and below may mean candidate cells that have a configuration including the PRACH configuration among all candidate cells (i.e., candidate cells for which the upper layer parameter EarlyUL-SyncConfig is set). In S420, the terminal receives downlink control information (DCI) from the base station. The DCI (e.g., DCI format 1_0) includes a cell indicator field. The cell indicator field may indicate a cell (e.g., a serving cell, a candidate cell) for PRACH transmission. For example, a candidate cell for the PRACH among the candidate cells may be indicated based on the cell indicator field. For example, the DCI may be based on DCI format 1_0 for a random access procedure initiated by a physical downlink control channel (PDCCH) order. In other words, the DCI may be interpreted / replaced with a PDCCH order. The random access procedure initiated / triggered by the PDCCH order may be a contention-free based random access (CFRA) procedure. The CFRA procedure may be for early TA acquisition. In other words, the CFRA procedure may be for TA acquisition (Timing Advance acquisition) before receiving the Cell Switch Command Medium Access Control Control Element (MAC CE). In S430, the terminal transmits the PRACH to the base station. For example, the PRACH may be associated with the candidate cell (i.e., the candidate cell indicated by the cell indicator field). In S440, the terminal receives a cell switch command MAC CE (Cell Switch Command Medium Access Control Control Element) from the base station. For example, a cell switch can be performed based on the procedure for L1 / L2 Triggered Mobility (LTM) described above. In the procedure for LTM, a base station can mean a gNB (e.g., a gNB CU (Central Unit) + one or more gNB-DU (Distributed Unit)). A cell switch based on the procedure for LTM can include i) switching from a source cell to a target cell within a gNB-DU (Intra-gNB-DU LTM), and ii) switching from a source cell (gNB-DU) to a target cell (another gNB-DU) within a gNB-CU (Iner-gNB-DU LTM). According to the existing method, the criteria for determining uplink transmission timing are defined only for the serving cell, leaving it unclear how the PRACH transmission timing associated with a candidate cell should be determined. To address this issue, at least one of the above-described embodiments can be applied. This will be described in detail below. In one embodiment, based on whether the candidate cell is a neighbor cell or a secondary cell (SCell), the candidate cell may be used as a reference cell for determining the transmit timing of the PRACH. This embodiment may be based on at least one of Proposal 1-2, Proposal 1-3, and / or Proposal 1-4. For example, the neighbor cell may be related to L1 (Layer 1)-RSRP (Reference Signal Received Power) measurement. For example, the secondary cell may be a secondary cell without an uplink carrier. For example, not all candidate cells configured in the terminal may be related to L1-RSRP measurement. Specifically, the terminal may perform L1-RSRP measurement on cells that should report based on CSI resource configuration and CSI reporting configuration (e.g., 1 to 4 cells among all candidate cells). Additionally, not all candidate cells configured in a terminal may consist solely of secondary cells. Considering this, Proposals 1-2, 1-3, and / or 1-4 may be applied to some of the aforementioned candidate cells (e.g., neighbor cells or secondary cells), while Proposal 1-1 may be applied to the remaining candidate cells (e.g., candidate cells that are neither neighbor cells nor secondary cells). In one embodiment, the transmit timing may be determined based on reception of a first detected path of a downlink frame from the reference cell. In other words, the transmission of the PRACH may be determined based on reception of a first detected path of a downlink frame from the reference cell. It can occur before. In other words, the reference point related to the transmission timing is the downlink timing of the reference cell - The above downlink timing can be defined as the time at which the first path of the downlink frame used by the terminal to determine the downlink timing from the reference cell is received at the UE antenna. For example, N TA can be set / determined via RAR (Random access response) or Timing advance command (MAC-CE). N TA,offset can be set per serving cell or predefined. T C is the basic time unit. For example, N for PRACH TA can be defined as 0. In one embodiment, the reception of the first detected path of the downlink frame may be based on reception of a specific DL RS among downlink reference signals (DL RSs) associated with the candidate cell. The specific DL RS may be a synchronization signal resource block (SSB) or a channel state information reference signal (CSI-RS). For example, the specific DL RS may be based on an SSB index associated with the candidate cell among synchronization signal block indices (SSB, indexes) in a resource set (e.g., LTM-CSI-SSB-ResourceSet) based on an LTM CSI report configuration (L1 / L2 Triggered Mobility CSI report config). The present embodiment may be based on Proposal 1-2. As a specific example, the resource set (e.g., LTM-CSI-SSB-ResourceSet) may include a candidate cell list (e.g., ltm-CandidateIdList) and an SSB index list (e.g., ltm-CSI-SSB-ResourceList). A candidate cell which is the n (n=1, 2, ...)-th entry of the candidate cell list may be associated with an SSB index which is the n (n=1, 2, ...)-th entry of the SSB index list. For example, the specific DL RS may be based on the Transmission Configuration Indication (TCI) state associated with the candidate cell. This embodiment may be based on Proposal 1-3. For example, the specific DL RS may be based on an SSB index indicated based on the DCI. This embodiment may be based on Proposal 1-4. In one embodiment, the PRACH may be related to Timing Advance acquisition (TA acquisition) prior to reception of a Cell Switch Command Medium Access Control Control Element (MAC CE). In one embodiment, the configuration for the PRACH may be based on a higher layer parameter EarlyULSyncConfig related to an early uplink synchronization procedure. For example, the candidate cell may be indicated by a bit field index based on the number of bits of the cell indicator field among the candidate cells for which the upper layer parameter EarlyULSyncConfig is set. For example, the above number of bits is It could be. is a ceiling function. C may be the number of candidate cells for which the upper layer parameter EarlyULSyncConfig is set. For example, among the bit field indices based on the number of bits, bit field index 0 may be mapped to a serving cell. The remaining bit field indices among the bit field indices may be mapped to the candidate cells in ascending order of candidate identity, starting from bit field index 1. The candidate identity may be based on ltm-CandidateId. ltm-CandidateId is used to identify an LTM candidate configuration, and the LTM candidate configuration may mean a configuration (e.g., LTM-Candidate) for each candidate cell in the above-described LTM configuration. That is, a candidate cell may be identified by ltm-CandidateId. The operations based on S410 to S440 described above can be implemented by the device of FIG. 6. For example, the terminal (200) can control one or more transceivers (230) and / or one or more memories (240) to perform the operations based on S410 to S440. The embodiments described below are specifically described in terms of base station operation. S510 to S540 described below correspond to S410 to S440 described in FIG. 4. Considering the above correspondence, redundant descriptions are omitted. That is, the specific description of the base station operation described below may be replaced with the description / example of FIG. 4 corresponding to the corresponding operation. For example, the description / example of S410 to S440 of FIG. 4 can be additionally applied to the base station operation of S510 to S540 described below. FIG. 5 is a flowchart illustrating a method according to another embodiment of the present specification. Referring to FIG. 5, a method according to another embodiment of the present disclosure includes a configuration transmission step for PRACH (S510), a DCI transmission step (S520), a PRACH reception step (S530), and a Cell Switch Command MAC CE transmission step (S540). Some steps in the method may be omitted. For example, S540 may be omitted in the method. In S510, the base station transmits to the terminal a configuration for a Physical Random Access Channel (PRACH) for each of the candidate cells. In S520, the base station transmits downlink control information (DCI) to the terminal. The DCI includes a cell indicator field. The cell indicator field can indicate a cell (e.g., a serving cell, a candidate cell) for PRACH transmission. For example, a candidate cell for the PRACH can be indicated among the candidate cells based on the cell indicator field. In S530, the base station receives the PRACH from the terminal. For example, the PRACH may be associated with the candidate cell (i.e., the candidate cell indicated by the cell indicator field). In S540, the base station transmits a Cell Switch Command Medium Access Control Control Element (MAC CE) to the terminal. In one embodiment, based on whether the candidate cell is a neighbor cell or a secondary cell (SCell), the candidate cell can be used as a reference cell for determining the transmit timing of the PRACH. The operations based on S510 to S540 described above can be implemented by the device of FIG. 6. For example, the base station (100) can control one or more transceivers (130) and / or one or more memories (140) to perform the operations based on S510 to S540. Hereinafter, a device to which an embodiment of the present specification can be applied (a device that implements a method / operation according to an embodiment of the present specification) is described with reference to FIG. 6. FIG. 6 is a drawing showing the configuration of a first device and a second device according to an embodiment of the present specification. The first device (100) may include a processor (110), an antenna unit (120), a transceiver (130), and a memory (140). The processor (110) performs baseband-related signal processing and may include a higher layer processing unit (111) and a physical layer processing unit (115). The higher layer processing unit (111) may process operations of a MAC layer, an RRC layer, or higher layers. The physical layer processing unit (115) may process operations of a PHY layer. For example, when the first device (100) is a base station device in base station-terminal communication, the physical layer processing unit (115) may perform uplink reception signal processing, downlink transmission signal processing, etc. For example, when the first device (100) is a first terminal device in terminal-to-terminal communication, the physical layer processing unit (115) may perform downlink reception signal processing, uplink transmission signal processing, sidelink transmission signal processing, etc. In addition to performing baseband-related signal processing, the processor (110) may also control the overall operation of the first device (100). The antenna unit (120) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO transmission and reception. The transceiver (130) may include an RF (Radio Frequency) transmitter and an RF receiver. The memory (140) may store information processed by the processor (110), and software, an operating system, applications, etc. related to the operation of the first device (100), and may also include components such as a buffer. The processor (110) of the first device (100) may be configured to implement the operation of the base station in the base station-to-terminal communication (or the operation of the first terminal device in the terminal-to-terminal communication) in the embodiments described in the present disclosure. The second device (200) may include a processor (210), an antenna unit (220), a transceiver (230), and a memory (240). The processor (210) performs baseband-related signal processing and may include a higher layer processing unit (211) and a physical layer processing unit (215). The higher layer processing unit (211) may process operations of a MAC layer, an RRC layer, or higher layers. The physical layer processing unit (215) may process operations of a PHY layer. For example, when the second device (200) is a terminal device in base station-terminal communication, the physical layer processing unit (215) may perform downlink reception signal processing, uplink transmission signal processing, etc. For example, when the second device (200) is a second terminal device in terminal-to-terminal communication, the physical layer processing unit (215) may perform downlink reception signal processing, uplink transmission signal processing, sidelink reception signal processing, etc. In addition to performing baseband-related signal processing, the processor (210) may also control the overall operation of the second device (210). The antenna unit (220) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO transmission and reception. The transceiver (230) may include an RF transmitter and an RF receiver. The memory (240) may store information processed by the processor (210), software, an operating system, applications, etc. related to the operation of the second device (200), and may also include components such as a buffer. The processor (210) of the second device (200) may be configured to implement operations of the terminal in base station-to-terminal communication (or operations of the second terminal device in terminal-to-terminal communication) in the embodiments described in the present disclosure. In the operation of the first device (100) and the second device (200), the same explanations given for the base station and the terminal (or the first terminal and the second terminal in the terminal-to-terminal communication) in the examples of the present disclosure may be applied, and redundant explanations are omitted. Here, the wireless communication technology implemented in the device (100, 200) of the present disclosure may include not only LTE, NR, and 6G, but also Narrowband Internet of Things (NB-IoT) for low-power communication. For example, NB-IoT technology may be an example of LPWAN (Low Power Wide Area Network) technology, and may be implemented in standards such as LTE Cat NB1 and / or LTE Cat NB2, and is not limited to the above-described names. Additionally or alternatively, the wireless communication technology implemented in the device (100, 200) of the present disclosure may perform communication based on LTE-M technology. For example, LTE-M technology may be an example of LPWAN technology and may be called by various names such as eMTC (enhanced Machine Type Communication). For example, LTE-M technology may be implemented by at least one of various standards such as 1) LTE CAT 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-BL (non-Bandwidth Limited), 5) LTE-MTC, 6) LTE Machine Type Communication, and / or 7) LTE M, and is not limited to the above-described names. Additionally or alternatively, the wireless communication technology implemented in the device (100, 200) of the present disclosure may include at least one of ZigBee, Bluetooth, and Low Power Wide Area Network (LPWAN) that take low-power communication into account, and is not limited to the above-described names. For example, ZigBee technology can create personal area networks (PANs) related to small / low-power digital communication based on various standards such as IEEE 802.15.4, and may be called by various names.

Claims

1. In the method, A step of receiving a configuration for a physical random access channel (PRACH) for each of the candidate cells; A step of receiving downlink control information (DCI), wherein the DCI includes a cell indicator field, and a candidate cell for the PRACH among the candidate cells is indicated based on the cell indicator field; and A step of transmitting the above PRACH; including, A method characterized in that the candidate cell is used as a reference cell for determining the transmit timing of the PRACH based on whether the candidate cell is a neighbor cell or a secondary cell (SCell).

2. In paragraph 1, A method characterized in that the above transmit timing is determined based on reception of a first detected path of a downlink frame from the reference cell.

3. In paragraph 2, A method characterized in that the reception of the first detected path of the downlink frame is based on reception of a specific DL RS among downlink reference signals (DL RSs) associated with the candidate cell.

4. In paragraph 3, A method characterized in that the above specific DL RS is based on an SSB index related to the candidate cell among synchronization signal block indices (Synchronization Signal Block, SSB, indexes) within a resource set based on an LTM CSI report configuration (L1 / L2 Triggered Mobility CSI report config).

5. In paragraph 3, A method characterized in that the specific DL RS is based on a Transmission Configuration Indication (TCI) state associated with the candidate cell.

6. In paragraph 3, A method characterized in that the specific DL RS is based on an SSB index indicated based on the DCI.

7. In paragraph 1, A method characterized in that the above PRACH is related to TA acquisition (Timing Advance acquisition) before receiving a Cell Switch Command MAC CE (Cell Switch Command Medium Access Control Control Element).

8. In paragraph 1, A method characterized in that the above configuration for the PRACH is based on an upper layer parameter EarlyULSyncConfig related to an early uplink synchronization procedure.

9. In paragraph 8, A method characterized in that the candidate cell is indicated by a bit field index based on the number of bits of the cell indicator field among the candidate cells for which the upper layer parameter EarlyULSyncConfig is set.

10. In paragraph 9, The above bit count is And, A method characterized in that is a ceiling function, and C is the number of candidate cells for which the upper layer parameter EarlyULSyncConfig is set.

11. In paragraph 10, Among the bit field indices based on the above bit number, bit field index 0 is mapped to the serving cell, A method characterized in that the remaining bit field indices among the above bit field indices are mapped to the candidate cells starting from bit field index 1 in ascending order of candidate identity.

12. In paragraph 1, A method characterized in that the above neighboring cell is related to L1 (Layer 1)-RSRP (Reference Signal Received Power) measurement.

13. In paragraph 1, A method characterized in that the secondary cell is a secondary cell without an uplink carrier.

14. In paragraph 1, A method characterized in that the above DCI is based on DCI format 1_0 for a random access procedure initiated by a Physical Downlink Control Channel (PDCCH) order.

15. At the terminal, One or more transmitters and receivers; one or more processors; and One or more memories connected to said one or more processors and storing instructions, A terminal characterized in that the instructions, based on being executed by the one or more processors, cause the terminal to perform all steps of the method according to any one of claims 1 to 14.

16. In a device comprising one or more memories and one or more processors functionally connected to the one or more memories, A device characterized in that said one or more memories store instructions that cause said device to perform all steps of a method according to any one of claims 1 to 14, based on being executed by said one or more processors.

17. In one or more non-transitory computer-readable media storing instructions, One or more non-transitory computer-readable media characterized in that the instructions executable by one or more processors cause a terminal to perform all steps of a method according to any one of claims 1 to 14.

18. In the method, A step of transmitting a configuration for a Physical Random Access Channel (PRACH) for each of the candidate cells; A step of transmitting downlink control information (DCI), wherein the DCI includes a cell indicator field, and a candidate cell for the PRACH is indicated among the candidate cells based on the cell indicator field; and A step of receiving the above PRACH; including, A method characterized in that the candidate cell is used as a reference cell for determining the transmit timing of the PRACH based on whether the candidate cell is a neighbor cell or a secondary cell (SCell).

19. At the base station, One or more transmitters and receivers; one or more processors; and One or more memories connected to said one or more processors and storing instructions, A base station characterized in that the instructions, based on being executed by the one or more processors, cause the base station to perform all steps of the method according to claim 18.

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