Method for transmitting and receiving prach and apparatus therefor

Abstract

A method according to an embodiment of the specification includes receiving a configuration for a PRACH for each of candidate cells; receiving a DCI; and transmitting the PRACH. The DCI includes a cell indicator field. A candidate cell for the PRACH among the candidate cells is indicated based on the cell indicator field. The candidate cell is used as a reference cell for determining a transmission timing of the PRACH based on the candidate cell being a neighbor cell or a secondary cell (SCell).

Description

Technical Field

[0001] This disclosure relates to methods and apparatus for transmitting and receiving PRACH. Background Technology

[0002] Mobile communication systems have evolved to the point where they can provide voice services while maintaining user activity. These systems are expanding their services from voice-only to data. The current surge in data traffic is exhausting resources, and user demand for higher data rates necessitates more advanced mobile communication systems.

[0003] Next-generation mobile communication systems need to meet requirements such as handling explosive growth in data traffic, significantly increasing transmission rates for individual users, working with a large number of connected devices, and supporting very low end-to-end latency and high energy efficiency. To this end, various research efforts are underway on a range of technologies, including dual connectivity, massive MIMO, in-band full-duplex, non-orthogonal multiple access (NOMA), ultra-wideband support, and device networking.

[0004] In NR operations prior to Rel-17 / Rel-18, RRM L3 measurements were used for handover, and the handover operation was performed by higher layers. To reduce latency during handover, Rel-17 standardized the operation of configuring the SSB of neighboring cells to the UE and performing L1 beam reporting for L1 measurements of neighboring cells.

[0005] In Rel-18, the method for obtaining the TA (Transmission Timing) of candidate cells for operations (e.g., cell handover) triggered by L1 / L2-based mobility procedures was standardized. The uplink transmission timing is determined based on the reception of the first detection path of downlink frames from the reference cell. Summary of the Invention

[0006] Technical issues

[0007] For the serving cell, a reference cell is defined for determining uplink transmission timing per TAG (e.g., primary TAG (pTAG) and secondary TAG (sTAG)). For candidate cells, there is no specific definition related to uplink transmission timing. Therefore, how to determine the uplink transmission timing associated with a candidate cell may be ambiguous. Furthermore, if the criteria defined for the serving cell are used to determine the uplink transmission timing associated with a candidate cell, the obtained TA may be inaccurate.

[0008] The purpose of this disclosure is to provide a method for solving the above-mentioned problems. Specifically, the purpose of this disclosure is to provide a method for determining / defining the transmission timing of PRACH associated with candidate cells.

[0009] The technical objectives to be achieved by this disclosure are not limited to those described above by way of example only, and other technical objectives not mentioned can be clearly understood by those skilled in the art from the following description.

[0010] Technical solution

[0011] The method according to an embodiment of this disclosure includes the following steps: receiving configuration for a Physical Random Access Channel (PRACH) for each of the candidate cells; receiving downlink control information (DCI); and transmitting the PRACH. The DCI includes a cell indicator field. The candidate cells for the PRACH are indicated based on the cell indicator field.

[0012] Based on whether the candidate cell is a neighboring cell or a secondary cell (SCell), the candidate cell is used as a reference cell for determining the transmission timing of PRACH.

[0013] The transmission timing can be determined based on the reception of the first detection path of the downlink frame from the reference cell.

[0014] The reception of the first detection path of the downlink frame can be based on the reception of a specific DL RS in the downlink reference signal (DL RS) associated with the candidate cell.

[0015] A specific DL RS can be an SSB index related to the candidate cell within the Synchronization Signal Block (SSB) index in the resource set configured according to the L1 / L2 triggered Mobility (LTM) CSI report.

[0016] A specific DL RS can be based on the Transport Configuration Indicator (TCI) status associated with the candidate cell.

[0017] A specific DL RS can be based on an SSB index as indicated by the DCI.

[0018] PRACH can be associated with the timing advance (TA) acquisition prior to the reception of the cell handover command medium access control-control element (MAC CE).

[0019] The configuration for PRACH can be based on the high-level parameter EarlyULSyncConfig, which is associated with the early uplink (UL) synchronization process.

[0020] Among candidate cells configured with the higher-level parameter EarlyULSyncConfig, candidate cells are indicated by a bit field index based on the number of bits in the cell indicator field.

[0021] The number of bits can be ,in, It is the ceiling function, and C This is the number of candidate cells configured with the higher-level parameter EarlyULSyncConfig.

[0022] In the bit field index based on bit count, bit field index 0 can be mapped to the serving cell. The remaining bit field indices in the bit field index can be mapped to candidate cells in ascending order of candidate identifier, starting from bit field index 1.

[0023] Neighboring cells can be correlated with Layer 1 (L1)-Reference Signal Received Power (RSRP) measurements.

[0024] A secondary cell (SCell) can be a secondary cell that does not have an uplink carrier.

[0025] DCI can be based on DCI format 1_0, which is used for random access procedures initiated via physical downlink control channel (PDCCH) commands.

[0026] A user equipment according to another embodiment of the present disclosure includes: one or more transceivers; one or more processors; and one or more memories connected to one or more processors and storing instructions.

[0027] The instructions, based on execution by one or more processors, allow a user device to perform all steps according to any of the methods described.

[0028] An apparatus according to another embodiment of this disclosure includes: one or more memories; and one or more processors connected to the one or more memories. The one or more memories store instructions executed by the one or more processors, and the instructions allow the apparatus to perform all steps according to any of the methods described.

[0029] According to another embodiment of this disclosure, non-transitory computer-readable medium stores instructions. These instructions, executable by one or more processors, allow a user device to perform all steps according to any of the methods described.

[0030] A method according to another embodiment of this disclosure includes the steps of: transmitting a configuration for the Physical Random Access Channel (PRACH) for each of the candidate cells; transmitting downlink control information (DCI); and receiving the PRACH. The DCI includes a cell indicator field. The candidate cells for the PRACH are indicated based on the cell indicator field.

[0031] Based on whether the candidate cell is a neighboring cell or a secondary cell (SCell), the candidate cell is used as a reference cell for determining the transmission timing of PRACH.

[0032] 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 connected to one or more processors and storing instructions.

[0033] The instructions, based on execution by one or more processors, allow a user device to perform all steps according to any of the methods described.

[0034] Beneficial effects

[0035] According to embodiments of this disclosure, the ambiguity in determining the transmission timing of the PRACH for early TA acquisition during LTM cell handover can be resolved. Furthermore, the accuracy of the TA acquired via PRACH can be improved compared to using a reference cell defined for the serving cell when determining the PRACH transmission timing.

[0036] The effects that can be achieved using this disclosure are not limited to those described above by way of example only. Other effects and advantages of this disclosure will become clearer to those skilled in the art from the following description. Attached Figure Description

[0037] Figure 1 An example of a MAC RAR according to an embodiment of the present disclosure is shown.

[0038] Figure 2 An example of a timing advance command MAC CE according to an embodiment of the present disclosure is illustrated.

[0039] Figure 3 The LTM-related processes applicable to the methods according to embodiments of this disclosure are illustrated.

[0040] Figure 4 This is a flowchart illustrating a method according to an embodiment of the present disclosure.

[0041] Figure 5 This is a flowchart illustrating another embodiment of the method according to the present disclosure.

[0042] Figure 6 The configurations of the first and second devices according to embodiments of the present disclosure are illustrated. Detailed Implementation

[0043] In the following, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following detailed description with reference to the accompanying drawings aims to describe embodiments of the present disclosure, but does not represent the only embodiments of the present disclosure. The following detailed description includes specific details to convey a thorough understanding of the present disclosure. However, those of ordinary skill in the art will readily understand that the embodiments of the present disclosure can be practiced even without these details.

[0044] In some cases, to avoid conceptual ambiguity, known structures or devices may be omitted or shown in block diagrams, while focusing on the core features of each structure and device.

[0045] In the following, the downlink (DL) means communication from the base station to the terminal, and the uplink (UL) means communication from the terminal to the base station. In the downlink, the sender may be part of the base station, and the receiver may be part of the terminal. In the uplink, the sender may be part of the terminal, and the receiver may be part of the base station. The base station may be represented as the first communication device, and the terminal may be represented as the second communication device. The base station (BS) may be replaced with terms including a fixed station, Node B, evolved Node B (eNB), next-generation Node B (gNB), base transceiver system (BTS), access point (AP), network (5G network), AI system, roadside unit (RSU), vehicle, robot, unmanned aerial vehicle (UAV), augmented reality (AR) device, virtual reality (VR) device, etc. In addition, the terminal may be fixed or mobile and may be replaced with terms including user equipment (UE), mobile station (MS), user terminal (UT), mobile subscriber station (MSS), subscriber station (SS), advanced mobile station (AMS), wireless terminal (WT), machine-type communication (MTC) device, machine-to-machine (M2M) device, and device-to-device (D2D) device, vehicle, robot, AI module, unmanned aerial vehicle (UAV), augmented reality (AR) device, virtual reality (VR) device, etc.

[0046] <Extended description related to TRP classification>

[0047] For ease of description, the present disclosure is applied to the proposed scheme by assuming cooperative transmission / reception between two TRPs, but it can be widely applied to a multi-TRP environment with three or more TRPs and can also be widely applied to a multi-panel environment. Different TRPs may be perceived by the UE as different TCI states (associated with different CORESET pool indices).

[0048] 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 is received from TRP1. Similarly, if the UE sends data / DCI using the first TCI state associated with the first CORESET pool index, it means that the data / DCI is sent to TRP1.

[0049] 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 sends data / DCI using the second TCI state associated with the second CORESET pool index, it means that the data / DCI was sent to TRP1.

[0050] Timely advance (TA) related processes

[0051] The uplink frame number i used for transmission from the user equipment (UE) should begin before the start of the corresponding downlink frame at that UE. start.

[0052] It can be defined as follows: Related uplink timing (e.g., uplink frames).

[0053] Uplink timing

[0054] Uplink frame number used for transmission from the UE i It should be before the start of the corresponding downlink frame at the UE start.

[0055] - and As given in Clause 4.2 of [5, TS 38.213], except for msgA transmissions on PUSCH, whereby the following shall be used .

[0056] - As given by Clause 4.2 of [5, TS 38.213]. It is obtained based on the high-level parameters TACommon, TACommonDrift, and TACommonDrift (if configured); otherwise, ; - As given by Clause 4.2 of [5, TS 38.213]. It is calculated by the UE based on higher-level parameters related to the UE's location and the serving satellite ephemeris (if configured); otherwise, .

[0057] Based on and To calculate / determine. and It can be configured / applied as follows.

[0058] 1) Configured via Random Access Response (RAR) and 2) Configured via Pre-Time Command (MAC-CE) 1) Configure specific values ​​for the serving cell and 2) Appropriately apply predefined values ​​based on duplex mode / FR to the serving cell. The above configuration / application is described in detail below. and The method.

[0059]

[0060] Case 1) Method of configuring specific values ​​based on serving cell

[0061] For example, the UE can receive information from the base station including details about... Configuration information (e.g., ServingCellConfigCommon information). This configuration information can be received based on RRC signaling. Table 1 below shows the configuration information.

[0062] [Table 1]

[0063] Case 2) Appropriately applying predefined values ​​based on duplex mode / FR to the serving cell

[0064] For example, the UE can use predefined duplex modes (TDD / FDD) / FR. The values ​​are appropriately applied to the serving cell. Table 2 below shows... The value of .

[0065] [Table 2]

[0066] Scenario 1) Configuring via Random Access Response (RAR)

[0067] For example, in a random access procedure (e.g., a 2-step RACH procedure or a 4-step RACH procedure), the UE can receive a RAR from the base station. N can be determined / configured based on the RAR. TASpecifically, a RAR can include a timing advance command. This timing advance command indicates an index value (e.g., index value TA) associated with the timing adjustment. The timing can be determined based on this index value. RAR can be based on MAC RAR. This will be referenced below. Figure 1 Describe it.

[0068] Figure 1 An example of a MAC RAR according to an embodiment of the present disclosure is shown.

[0069] Reference Figure 1 A MAC RAR can include reserved bits R, timing advance commands, UL authorization, and temporary C-RNTI. The MAC payload of a MAC RAR is described in detail below.

[0070] 6.2.3 MAC payload for random access response

[0071] MAC RAR has the following features: Figure 6 It has a fixed size as shown in .2.3-1 and consists of the following fields.

[0072] - R: Reserved bit, set to 0; - TI: If two TAGs are configured for the serving cell performing a random access procedure, this field indicates one of the two TAGs for which the application timing advance command is applied. Setting this field to 0 indicates the first TAG ID, and setting it to 1 indicates the second TAG ID. If no two TAGs are configured for the serving cell performing a random access procedure, an R bit is present instead. - Timing Advance Command: The Timing Advance Command field in TS 38.213[6] indicates the index value TA of the timing adjustment that must be applied to control the MAC entity. The Timing Advance Command field is 12 bits in size; - UL Authorization: The uplink authorization field in TS 38.213[6] indicates the resources to be used on the uplink. The UL authorization field is 27 bits in size; - Temporary C-RNTI: The Temporary C-RNTI field indicates a temporary identifier used by the MAC entity during random access. The Temporary C-RNTI field is 16 bits in size.

[0073] MAC RAR is octet aligned.

[0074] The following describes the timing adjustment of transmission based on the timing advance command.

[0075] 4.2 Sending timed adjustments

[0076] The timing advance offset of the serving cell can be provided to the UE via the n-TimingAdvanceOffset of the serving cell. If, for the serving cell, the UE is provided with two coresetPoolIndex values ​​of 0 and 1 for the first and second CORESETs, or is not provided with a coresetPoolIndex value for the first CORESET but is provided with a coresetPoolIndex value of 1 for the second CORESET, then the UE can be provided with the first coresetPoolIndex value via n-TimingAdvanceOffset and n-TimingAdvanceOffset2. value and second Values ​​are used for transmissions having TCI states associated with the first CORESET and the second CORESET, respectively. This is in addition to the first transmission utilizing a spatial domain filter corresponding to the TCI state associated with the serving cell's physCellId. In addition to the value, the UE can also be provided with a second transmission method that utilizes a spatial domain filter corresponding to a TCI state associated with a physCellId different from that of the serving cell. Value. First value and second The values ​​correspond to the first and second tags [11, TS 38.321], which have an association with the first and second joint TCI states provided by dl-OrJointTCI-StateList or the first and second UL TCI states provided by ul-TCI-StateList, as indicated by tag-Id-ptr. If no n-TimingAdvanceOffset of the serving cell is provided to the UE, the UE determines the default value of the timing advance offset of the serving cell. As described in [10, TS 38.133].

[0077] If the UE is configured with two UL carriers for the serving cell, the same timing advance offset value will be used. Applied to two carriers associated with the same tag for transmission on the serving cell. The UE does not expect the two... The value is applied to transmission on the SUL carrier.

[0078] Upon receiving a timing advance command for the TAG, the UE will base its actions on the value... (The UE expects this value to be the same for all serving cells in this TAG) and adjusts the uplink timing of PUSCH / SRS / PUCCH transmissions for all serving cells in this TAG based on the received timing advance command (where the uplink timing of PUSCH / SRS / PUCCH transmissions is the same for all serving cells in this TAG).

[0079] For a frequency band with synchronous continuous EN-DC in a frequency band combination having an inapplicable maximum transmission timing difference requirement (as described in Note 1 of Table 7.5.3-1 of [10, TS 38.133]), if the UE indicates ul-TimingAlignmentEUTRA-NR as "Required" and the UE determines that the uplink transmission timing based on timing adjustments for TAGs from MCGs and TAGs from SCGs are different, the UE adjusts the transmission timing of PUSCH / SRS / PUCCH transmissions on all serving cell portions of the frequency band with synchronous continuous EN-DC based on the timing adjustment indication for TAGs from serving cells in the MCGs of that frequency band. The UE does not expect to transmit PUSCH / SRS / PUCCH in one CG when PUSCH / SRS / PUCCH overlaps in time with (even partially overlaps) a random access preamble transmitted in another CG.

[0080] against The SCS, for a TAG, indicates a change in the timing advance command relative to the current uplink timing for the TAG. Multiples of. The start timing of the random access preamble is described in [4, TS 38.211].

[0081] In the case of random access response, or in the absolute timing advance command MAC CE, or in the timing advance command in the cell handover command [11, TS 38.321] For TAG passing = 0, 1, 2, ..., 3846 to indicate Values, where for SCS are The time alignment of the tag is . Defined in [4, TS 38.211], and related to the SCS transmitted from the UE for the first time on the uplink after receiving a random access response or absolute timing advance command MAC CE or cell handover command.

[0082] In other cases, the timing advance command for TAG [11, TS 38.321] Indicates by index value =0, 1, 2,..., 63 will be the current value Adjusted to new value Among them, targeting SCS, .

[0083] If a UE has multiple active UL BWPs in the same TAG (as described in Clause 12), including UL BWPs in two UL carriers of the serving cell, the timing advance command value is associated with the largest SCS among the multiple active UL BWPs. For UL BWPs with lower SCS, the applicable... The value can be rounded to maintain consistency with the timing advance granularity of the UL BWP with a lower SCS, while meeting the timing advance accuracy requirements in [10, TS 38.133].

[0084] Adjust by increment or decrement The values ​​indicate the amount by which the uplink transmission timing for the TAG will be advanced or delayed.

[0085] For timing advance commands received on uplink time slot n, and for PUSCHs scheduled by RAR UL authorization or fallbackRAR UL authorization as described in Clauses 8.2A or 8.3, or for transmissions other than PUCCHs responding to successRAR with HARQ-ACK information as described in Clause 8.2A, the corresponding adjustment of uplink transmit timing from the uplink time slot... The application begins here, where , This corresponds to the PDSCH processing time for UE processing capability 1 when additional PDSCH DM-RS is configured. The duration of each symbol (in milliseconds). This corresponds to the PUSCH preparation time for UE processing capability 1. Duration of each symbol (in milliseconds) [6, TS 38.214], It is the maximum timing advance value (in milliseconds) that the 12-bit TA command field can provide. It is the number of time slots in each subframe. It is the duration of a 1-millisecond subframe, and ,in Provided by cellSpecificKoffset, and Provided by the Differential Koffset MAC CE command [11, TS 38.321]; otherwise, if not provided separately, then or . and It is determined by the minimum SCS among all configurations of UL BWP for all uplink carriers in the TAG and all configurations of DL BWP for the corresponding downlink carriers. UE assumption [6, TS 38.214]. Time slot n and It is determined by the minimum SCS among all configured UL BWPs for all uplink carriers in the TAG. It is determined by the minimum SCS among all configured UL BWPs for all uplink carriers in the TAG and all configured initial UL BWPs provided by the initialUplinkBWP. Uplink slot n It is the last uplink time slot that overlaps with the PDSCH reception time slot, assuming Among them, PDSCH provides timing advance commands and Defined in [4, TS 38.211].

[0086] If the UE changes the active UL BWP between the time the timing advance command is received and the time the application sends the corresponding adjustment for uplink 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 the application sends the adjustment for uplink timing, the UE will use the same absolute timing advance command value before and after the active UL BWP change.

[0087] If the received downlink timing changes and is not compensated or is only partially compensated by uplink timing adjustment without a timing advance command (as described in [10, TS 38.133]), then the UE will change accordingly. If the UE operates on an active UL BWP in the serving cell using two tags, the UE expects the difference between the first downlink timing associated with the first tag and the second downlink timing associated with the second tag to be no greater than the CP length for that 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 sends SRS in the RRC_INACTIVE state based on the configuration of SRS-PosResourceSet in SRS-PosRRC-InactiveConfig-ValidityArea, the UE can update autonomously during cell reselection. Otherwise, if the UE is not provided with SRS-autonomousTAupdate, the UE remains in the last serving cell prior to the release of the dedicated RRC connection. [11, TS38.321].

[0088] For operations using a single TAG on the serving cell, if two adjacent time slots overlap due to a TA command, the duration of the later time slot is shortened relative to the duration of the earlier time slot. During the actual transmission time window used for PUSCH or PUCCH transmission, the UE does not change... [6, TS 38.214]. If the UE is not provided with enableSTx2PofMDCI and operates using two TAGs on the serving cell, the UE does not expect transmission overlap associated with different TAGs unless the UE indicates XYZ; if the UE indicates XYZ, the UE shortens the duration of the subsequent transmission using the first TAG to avoid overlap with the preceding transmission using the second TAG.

[0089] Scenario 2) Configuring via Pre-Time Command (MAC-CE)

[0090] For example, MAC-CE can be used to determine / configure Specifically, it can be determined based on the timed advance command MAC CE. The MAC CE can include timed advance commands. This is because the determination is based on the timed advance commands. This is the same as described in Case 1, so repeated descriptions are omitted. See below for details. Figure 2 To describe the scheduled advance command MACCE.

[0091] Figure 2 An example of a timing advance command MAC CE according to an embodiment of the present disclosure is illustrated.

[0092] Reference Figure 2 The timing advance command MAC CE can include a TAG ID and a timing advance command. The payload of the timing advance command MAC CE is described in detail below.

[0093] 6.1.3.4 Pre-timed command MAC CE

[0094] The MAC CE (Pre-Timed Command) is identified by a MAC sub-header with LCID, as specified in Table 6.2.1-1.

[0095] It has a fixed size and consists of a single octet, defined as follows ( Figure 6 .1.3.4-1): - TAG Identifier (TAG ID): This field indicates the TAG identifier of the addressed TAG. TAGs containing SpCells have TAG identifier 0. This field is 2 bits long; - Timing Advance Command: This field indicates the index value TA (0, 1, 2...63) of the timing adjustment amount that must be applied to control the MAC entity (as specified in TS 38.213 [6]). The field is 6 bits long.

[0096] 6.1.3.4a Absolute timing advance command MAC CE

[0097] The absolute timing advance command (MAC CE) is identified by a MAC subheader with eLCID, as specified in Table 6.2.1-1b.

[0098] 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 time adjustment that the MAC entity must apply in TS 38.213 [6]. This field is 12 bits in size; - TI: If two tags are configured for SpCell, this field indicates the tag on which the timing advance command is applied. Setting this field to 0 indicates the first tag ID, and setting it to 1 indicates the second tag ID. If no two tags are configured for SpCell, the R bit is used instead. - R: Reserved bit, set to 0.

[0099] Scheduled advance group (TAG)

[0100] A timing advance group (TAG) refers to a group of serving cells that use the same timing advance value. Table 3 below shows the definition of a TAG and the configuration information associated with it.

[0101] [Table 3]

[0102] The foregoing can be applied in conjunction with the methods presented in this specification, which will be described later, or can be supplemented to clarify the technical characteristics of the methods presented in this specification. The methods described below are categorized for ease of explanation only, and some components of one method can be replaced by some components of another method, or can be combined with each other.

[0103] According to the 3GPP standards up to NR Rel-17, handover operations via UE mobility are performed as follows: The UE reports the (L3-based) RSRP measurement for a candidate serving cell that is not a serving cell. The base station (BS) performs a handover decision based on this report and then triggers a handover to the UE. In this case, the UE performs separation on the serving cell and performs the RACH procedure for synchronization with the new cell. The UE can obtain TA information about the cell from the cell intended for the new attachment via RAR reception.

[0104] In Rel-18 Mobility Enhancement, BS / UE operations that reduce latency when the BS / UE obtains TA information about the candidate serving cell before the handover command is used to perform the handover are discussed (by skipping the RACH procedure). (See Table 4 below)

[0105] Additionally, when performing existing handovers via L3 signaling, L1 / L2-based handovers are being considered, using the Cell Handover Command (MAC CE) to send the beam / TA information to be used in the candidate serving cell to the UE. As methods for obtaining the TA for the candidate (serving) cell, RACH-based and RACH-free methods are being considered.

[0106] [Table 4]

[0107] The following agreement was reached in Rel-18 Mobility-TA Management.

[0108] protocol

[0109] TA acquisition support for candidate cells before receiving cell handover commands in L1 / L2-based mobility.

[0110] FFS: When used as a deactivated SCell (if defined in RAN2), can this be applied to candidate cells?

[0111] protocol

[0112] Regarding the mechanism used to obtain the TA for candidate cells, the following solutions can be further investigated.

[0113] RACH-based solutions (e.g., RACH based on PDCCH commands, UE-triggered RACH, and RACH triggered by higher layers from the NW, excluding L3 HO cmd).

[0114] RACH-free solutions (e.g., SRS-based TA acquisition, Rx timing difference-based, RACH-free mechanisms such as those in LTE, UE-based TA measurement (including UE-based TA measurement with a TAC from the serving cell)).

[0115] protocol

[0116] Regarding the mechanism for obtaining the TA of candidate cells in Rel-18 LTM, at least the RACH of the PDCCH command is supported.

[0117] The PDCCH command is triggered only by the source cell.

[0118] FFS: Includes details about DCI content, RACH resource configuration, RAR transfer mechanism, etc.

[0119] Note: Any other RACH-based solutions are discussed separately.

[0120] protocol

[0121] For RACH of the PDCCH command in LTM, at least the following enhancements are supported.

[0122] Introducing candidate cells in DCI and / or the RO of candidate cells

[0123] Configure the RACH resources for candidate cells before the PDCCH command.

[0124] FFS: Whether / How to send RAR

[0125] protocol

[0126] TA updates (i.e., TA reacquisition) for candidate cells can be triggered by NW.

[0127] The same triggering mechanism is reused for initial TA acquisition, i.e., RACH triggered by the PDCCH command in the candidate cell.

[0128] protocol

[0129] For Rel-18 LTM, a random access preamble index and an indication of RACH timing with an associated SSB index are configured for each candidate cell.

[0130] Note: Detailed signaling is determined by RAN2.

[0131] protocol

[0132] The PDCCH command from the source cell contains indications of candidate cells.

[0133] Reserved bits in DCI format 1_0 for the PDCCH command can be used to indicate the cell identifier.

[0134] protocol

[0135] For RACH based on PDCCH commands used for TA measurements of candidate cells, traditional CBRA is not supported.

[0136] protocol

[0137] Regarding whether the UE should initiate a PRACH retransmission when RAR reception is not configured / indicated, select the next option from the following alternatives.

[0138] Alternative Option 1: Disallow UE-initiated retransmission of PRACH (e.g., by setting the number of allowed PRACH transmissions to a minimum value PreambleTransMax=1).

[0139] Alternative Option 2: Allow UEs to autonomously retransmit PRACH. The number of PRACH transmissions will be defined, for example, the number of RACH transmissions will be set to the minimum value of PreambleTransMax.

[0140] protocol

[0141] The following working assumptions were confirmed, and the LS was sent to RAN4 to demonstrate the feasibility of supporting this mechanism.

[0142] Working assumptions

[0143] From RAN 1's perspective, it supports UE-based TA measurement (the UE derives TA based on the Rx timing difference between the current serving cell and the candidate cell, as well as the TA value for the current serving cell).

[0144] To support UE-based TA measurements, corresponding UE capabilities need to be introduced.

[0145] This capability is supported for UE reporting, and configuration of UE-based TA measurements is also supported.

[0146] FFS: Other Impacts on RAN1 Specifications

[0147] protocol

[0148] From RAN 1's perspective, in the case of RACH without executing PDCCH commands for candidate cells, a mechanism without RACH can be supported by indicating the target cell's TA value as TA=0 or keeping it the same as the source cell in the cell handover command.

[0149] Note 1: This does not mean that when RAR is not configured for PDCCH commands, TA values ​​other than 0 and the same value as the source cell are excluded in the RACH cell handover command for PDCCH commands.

[0150] Note 2: Feasibility and signaling can be further derived through RAN2.

[0151] protocol

[0152] For PRACH based on PDCCH commands regarding candidate cells, the candidate cell SSB indicated in the PDCCH command is used as the path loss RS for PRACH Tx power determination.

[0153] protocol

[0154] Regarding the determination of PRACH transmission power when receiving without RAR configuration, the [1-bit] field in the PDCCH command is supported to explicitly indicate the initial transmission or retransmission of PRACH.

[0155] protocol

[0156] Regarding the determination of PRACH transmission power when receiving without RAR configuration, a 1-bit field in the PDCCH command explicitly indicates the initial transmission or retransmission of PRACH, FFS.

[0157] If instructed to retransmit, the UE will increase its power by the configured power boost value, unless the maximum allowed power is reached.

[0158] Should / How to reset the counter?

[0159] protocol

[0160] For power control of CFRA in the PDCCH command of LTM, the UE can maintain only one power boost counter.

[0161] protocol

[0162] For CFRA power control of PDCCH commands in LTM, the power boost counter is only reset at least when the UE receives a PDCCH command indicating the initial transmission of PRACH.

[0163] protocol

[0164] Power control of CFRA for PDCCH commands in LTM

[0165] When the UE receives a PDCCH command indicating a retransmission of a PRACH with the same associated SSB and the same candidate cell as the previous PRACH, the counter increments by 1.

[0166] In addition to case 1, the power boost counter is reset in the following cases.

[0167] Case 2: The candidate cell indicated in the PDCCH command that indicates retransmission is different from the candidate cell indicated in the last PDCCH command.

[0168] Note: The initial counter is 0 before any PDCCH command is received.

[0169] protocol

[0170] When sending a PDCCH command for a candidate cell The bit size N in the DCI format 1_0 for the cell indicator is determined by the number (e.g., C) of candidate cells with the RACH configuration provided for early TA acquisition, supporting the following alternative schemes.

[0171] Alternative Option 2:

[0172] The number of cells used to calculate the bit width is the number of candidate cells with the RACH configuration provided for early TA acquisition + 1 (serving cell).

[0173] protocol

[0174] In the PDCCH command, the bit field code point "0" in the cell indicator field indicates the PRACH for the currently serving cell, and the remaining bit field code points are mapped to candidate cells configured with EarlyUlSyncConfig-r18. That is, there is a one-to-one mapping between the bit field code points from 1 to C and the candidate cell IDs in ascending order.

[0175] The above content can be summarized as follows.

[0176] In the RACH-based approach, the CFRA procedure of the PDCCH command can be used for TA acquisition for candidate cells. In RAN1, it is discussed whether a RAR exists for the corresponding RACH transmission, allowing configuration via RRC. In RAN2, it is inferred that no RAR is needed, therefore the UE does not receive the RAR for the corresponding RACH transmission. For RACH transmissions to candidate cells, PRACH configuration for candidate cells can be pre-configured to the UE. The command DCI (i.e., the DCI that triggers PRACH transmission, the PDCCH command) can indicate the candidate cell ID or indicate the RACH resources for the candidate cell. This indication can trigger RACH transmissions for candidate cells. In this case, the timing of RACH transmissions for candidate cells is ambiguous. This is described in detail below.

[0177] Unlike when RACH is transmitted from the serving cell based on the DL reference timing of the reference cell (as shown in Table 5 below), the DL reference timing is ambiguous when transmitting RACH for a candidate cell (PDCCH command). That is, there is ambiguity about when the UE should perform RACH transmission for the candidate cell (Question 1).

[0178] [Table 5]

[0179] Table 6 below summarizes the contents of standardization meetings related to L1 measurement enhancements used to send beam information from the cell handover command MAC CE to the UE.

[0180] [Table 6]

[0181] The procedures related to Rel-18 LTM can be executed as follows.

[0182] L1 / L2 triggered mobility process

[0183] LTM-Config can be used to indicate candidate cells and the SS / PBCH blocks of each candidate cell to the UE for synchronization and measurement of the corresponding L1-RSRP [10, TS 38.133]. The MAC CE command can activate the TCI state associated with the TRS or SS / PBCH blocks of the corresponding candidate cell provided by LTM-Candidate-TCI-State-r18 or / and LTM-Candidate-TCI-UL-State-r18. LTM-CSI-ReportConfigToAddModList provides the UE with a configuration for reporting L1-RSRP measurements [6, TS 38.214], which includes the number of candidate cells and the number of SS / PBCH blocks per candidate cell based on the number of candidate cells.

[0184] If the UE is provided with ueMeasuredTA, the UE estimates the timing advance based on the UE implementation to apply a first transmission on the candidate cell after receiving a cell handover command for the candidate cell [11, TS38.321]. Configuration of PRACH transmission parameters for each of the candidate cells can be provided to the UE via EarlyUlSyncConfig. The UE can trigger a PRACH transmission on the candidate cell via a PDCCH command received by the UE on the serving cell that 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 the same frequency range and the UE will have transmissions that overlap in time, or when the gap between the first or last symbol of the PRACH transmission and the candidate cell is less than the gap between the last or first symbol of the UL transmission (correspondingly) and the serving cell. N When N is a symbol (where N is defined in the TBD clause), the UE performs the following operations.

[0185] - When the UE does not support transmissions that overlap or are separated in time by less than the gap between the serving cell and the candidate cell, the UE discards the transmission on the serving cell.

[0186] - When the UE supports transmissions that overlap or separate in time for less than the interval, and the total UE transmit power within the frequency range will exceed In Clause 7.5, the UE prioritizes the power allocation for PRACH transmissions on candidate cells.

[0187] As described in Clause 8.1, the UE transmits PRACH on the candidate cell at the power determined as described in Clause 7.4.

[0188] The UE can be provided with the TCI-State and / or TCI-UL-State in the LTM-dl-OrJointTCI-StateToAddModList and / or LTM-ul-TCI-ToAddModList via MAC CE during PDSCH reception on the serving cell [11, TS 38.321], which indicates the applicable unified TCI state for reception or transmission on candidate cells out of the candidate cell count [6, TS 38.214]. If indicated via MAC CE, the UE applies the TCI-State and / or TCI-UL-State from the first slot of TBD after the last symbol of the PUCCH or PUSCH, which has HARQ-ACK information for the PDSCH providing the MAC CE, and μ is the SCS configuration for TBD.

[0189] L1 / L2 triggered mobility (LTM)

[0190] The following reference Figure 3 Describe LTM.

[0191] Figure 3 The LTM-related processes applicable to the methods according to embodiments of this disclosure are illustrated.

[0192] LTM is the process by which the gNB receives an L1 measurement report from the UE, and based on this report, the gNB changes the UE's serving cell via a cell handover command signaled via the MAC CE. The cell handover command represents an LTM candidate configuration that the gNB has previously prepared and provided to the UE via RRC signaling. The UE then switches to the target configuration according to the cell handover command. The LTM procedure can be used to reduce mobility latency, as described in Appendix G.

[0193] If configured in the network, the TCI state of one or more cells different from the current serving cell can be activated. For example, the TCI state of an LTM candidate cell can be pre-activated before the corresponding cell becomes the serving cell. This allows the UE to perform DL synchronization with the corresponding cell, so that when a cell handover is triggered, the UE can switch to one of the corresponding cells more quickly.

[0194] If configured in the network, an ULTA acquisition (referred to as “early TA”) procedure can be initiated for one or more cells different from the current serving cell. An early TA acquisition procedure is not required if the cell has the same NTA as the current serving cell or if NTA=0. The network can request the UE to perform early TA acquisition for candidate cells before cell handover. The early TA acquisition procedure is triggered by a PDCCH command as specified in Clause 9.2.6, or implemented via UE-based TA measurement configured in the RRC. In the former case, the gNB to which the candidate cell belongs calculates the TA value and sends it to the gNB to which the serving cell belongs. The serving cell sends the TA value in the LTM cell handover command MAC CE when triggering LTM cell handover. In the latter case, the UE performs TA measurement for the candidate cell after configuring it in the RRC, but the exact timing of the TA measurement depends on the UE implementation. The UE applies the TA value measured by itself and performs LTM without RACH when receiving the cell handover command. The network can also send the TA value in the LTM cell handover command MAC CE without early TA acquisition.

[0195] Based on the availability of a valid TA value, the UE performs either LTM without RACH or LTM based on RACH for cell handover. If a TA value is provided in the cell handover command, the UE applies the TA value indicated by the network. If UE-based TA measurement is configured but no TA value is provided in the cell handover command, the UE applies the TA value directly if available. If the UE receives a cell handover command, it performs LTM without RACH for cell handover. If a valid TA value is unavailable, the UE performs LTM based on RACH for cell handover.

[0196] The UE follows PDCCH commands (including requests for random access procedures for candidate cells), regardless of whether the UE is configured for UE-based TA measurements for a specific candidate cell. This also applies to candidate cells where the UE can derive its TA value itself. Additionally, if configured within the network, the UE continues to follow UE-based measurement configurations, regardless of whether the UE has already performed random access procedures for candidate cells.

[0197] For LTM without RACH, the UE uses either configuration grant or dynamic grant to access the target cell. Configuration grant is provided in the LTM candidate configuration, and the UE selects the timing of the configuration grant related to the beam indicated in the cell handover command. When an LTM cell handover to the target cell is indicated, the UE begins monitoring the target cell's PDCCH for dynamic scheduling. If no valid PUCCH resource exists for triggering the SR before the LTM without RACH procedure is completed, the UE does not trigger the random access procedure.

[0198] The following principles apply to LTM.

[0199] - The UE does not update its security key during LTM cell handover.

[0200] - Supports subsequent LTM.

[0201] LTM supports intra-gNB-DU and inter-gNB-DU mobility within and between gNB-CUs. LTM also supports intra-frequency and inter-frequency mobility, including mobility to inter-frequency cells that are not the current serving cell. LTM only supports licensed spectrum. It supports the following scenarios.

[0202] - PCell changes in non-CA and non-DC scenarios; - Changes to PCell and SCell in the CA scenario; - In dual-connection scenarios, PCell and MCG SCell change, and PSCell and SCG SCell within the SN also change, without MN involvement. LTM is not supported for simultaneous changes in PCell and PSCell.

[0203] When the UE saves the LTM candidate configuration, the UE can also execute any L3 handover command sent by the network.

[0204] Send a cell handover command from the MAC CE, including the information necessary to perform an LTM cell handover.

[0205] The entire process of LTM Figure 3 Example. Subsequent LTMs are completed by repeating the early synchronization, LTM cell handover execution, and LTM cell handover completion steps without releasing other LTM candidate configurations after each LTM cell handover completion. The standard procedure via the radio interface is applied to SCG LTM. For more details on SCG LTM, see TS37.340

[21] .

[0206] Reference Figure 3 The process for LTM is as follows.

[0207] 1. The UE sends a message to the gNB. Measurement Report Message. gNB decides to configure LTM and initiates LTM preparation.

[0208] 2. The gNB sends the LTM candidate configuration to the UE. RRCReconfiguration information.

[0209] 3. The UE stores the LTM candidate configuration and sends it to the gNB. RRCReconfigurationComplete information.

[0210] 4a. Before receiving a cell handover command, the UE performs DL synchronization with the candidate cell.

[0211] 4b. When UE-based TA measurement is configured, the UE acquires the TA value of the candidate cell through measurement. As specified in Clause 9.2.6, the UE performs early TA acquisition using the candidate cell requested by the network before receiving the cell handover command. This is performed via CFRA triggered by a PDCCH command from the source cell, after which the UE sends a preamble toward the indicated candidate cell. To minimize data interruption to the source cell due to CFRA toward the candidate cell, the UE does not receive a Random Access Response (RAR) from the network for TA value acquisition and indicates the TA value of the candidate cell in the cell handover command. The UE does not maintain a TA timer for the candidate cell and relies on the network implementation to guarantee TA validity.

[0212] 5. The UE performs L1 measurements for the configured candidate cells and sends an L1 measurement report to the gNB. L1 measurements should be performed whenever RRC reconfiguration is applied (step 2).

[0213] 6. The gNB decides to perform a cell handover to the target cell and sends a MAC CE to trigger the handover by including a candidate configuration index of the target cell. The UE hands over to the target cell and applies the configuration indicated by the candidate configuration index.

[0214] 7. As specified in Clause 6.1.3.xy of TS 38.321[6], if the UE does not have a valid TA for the target cell, the UE performs a random access procedure toward the target cell.

[0215] 8. The UE sends a message to the target cell. RRCReconfigurationComplete The LTM cell handover process is completed using a message. If the UE has already performed the RA procedure in step 7, the UE considers the LTM cell handover to be successfully completed when the random access procedure is successfully completed. For LTM without RACH, the UE considers the LTM cell handover to be successfully completed when it determines that the network has successfully received its first UL data.

[0216] Steps 4 through 8 can be executed multiple times using the LTM candidate configuration provided in step 2 for subsequent LTM cell handover.

[0217] Based on the aforementioned background technology, this disclosure describes a method for a UE to transmit a RACH toward a candidate serving cell for mobility enhancement in Rel-18 LTM (L1 / L2 triggered mobility), and proposes related UE operations. More specifically, this disclosure proposes a method for defining / configuring reference timing to determine which reference timing the UE should use when transmitting a RACH toward a candidate cell.

[0218] Below, reference timing can refer to the criteria used when a UE transmits 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 RACH based on reference timing, the signal arrives at the base station later than the NW DL / UL frame boundary due to propagation delays, etc. The base station can calculate the required timing advance value and configure / indicate it to the UE. Non-serving cells that can be targeted for UE handover (i.e., cell handover) can be referred to as candidate serving cells, candidate cells, target cells, target candidate cells, etc.

[0219] Additionally, for Rel-18 LTM, the base station can configure information for one or more candidate cells before the handover command. This configuration may include PCI, RACH configuration, etc., for each candidate cell (e.g., RACH preamble, RACH timing, RACH resources, and / or SSB index associated with each candidate cell), where each candidate cell is a non-serving cell that can become a potential serving cell.

[0220] In this disclosure, depending on the context, " / " can be interpreted as "and", "or", or "and / or".

[0221] The following describes in detail the implementation method for solving the above-mentioned problem 1.

[0222] Suggestion 1

[0223] The following describes a method for defining / configuring DL reference timing for candidate cells in Rel-18 LTM for UE to obtain TA based on RACH for candidate cells.

[0224] Suggestion 1-1

[0225] When a UE performs a RACH transmission (CFRA of PDCCH command) for a specific candidate cell, the UE can perform the RACH transmission based on the DL reference timing defined / configured for the serving cell (receiving the PDCCH command).

[0226] Suggestions 1-2

[0227] When a UE performs a RACH transmission (CFRA of PDCCH command) for a specific candidate cell, the UE can measure the DL reference timing of the candidate cell (for L1 measurement purposes) based on a specific SSB configured for the candidate cell (e.g., via LTM-Config). The UE can perform the RACH transmission based on the DL reference timing.

[0228] For example, a specific SSB can be the SSB with the lowest / first ID or the SSB with the highest / last ID among the SSBs configured in the candidate cell.

[0229] For example, a specific SSB can be based on the lowest / first and / or highest / last SSB index among the SSBs configured in a CSI resource set for UE beam measurement / reporting purposes for candidate cells. The CSI resource set can be configured based on LTM-CSI-ReportConfigToAddModList.

[0230] For example, a specific SSB can be the first and / or last SSB configured in a CSI resource set for the purpose of UE beam measurement / reporting for candidate cells. In other words, a specific SSB can be determined based on the order in which it is configured / defined within the CSI resource set. The CSI resource set can be configured based on LTM-CSI-ReportConfigToAddModList.

[0231] More specifically, the specific SSB proposed in Proposal 1-2 can be one of the SSBs that the UE is measuring / tracking.

[0232] For example, a specific SSB can be the SSB with the lowest / highest ID among those SSBs that the UE recently performed L3 measurement / reporting (for RRM) for a specific candidate cell.

[0233] For example, a specific SSB can be the SSB with the lowest / highest ID among those SSBs whose RSRP / RSRQ / RSSI is equal to or greater than a certain threshold based on L3 measurements.

[0234] Suggestions 1-3

[0235] When a UE performs a RACH transmission (CFRA of PDCCH command) for a specific candidate cell, the UE can measure the DL reference timing of the candidate cell based on the DL RS associated with the specific TCI state of the candidate cell. The terminal can perform the RACH transmission based on the DL reference timing. For example, the DL RS can be the QCL reference RS of the TCI state or / and the SSB that serves as the top QCL source of the reference RS.

[0236] For example, a specific TCI state can be the TCI state with the lowest and / or highest ID among the TCI states of the QCL reference RS associated with a specific candidate cell and the SSB is configured as such.

[0237] For example, a specific TCI state can be one of the TCI states that is activated for Rel-18 LTM operation among the TCI states of the SSB associated with a specific candidate cell and configured as the QCL reference RS. As an additional example, a specific TCI state can be the TCI state with the lowest / highest ID among the TCI states activated for Rel-18 LTM operation.

[0238] More restrictively, if the temporal behavior of the DL RS associated with a particular TCI state is semi-persistent or aperiodic, the TCI state can be excluded from the DL reference timing measurement. This is because continuous reference timing measurements require static / periodic RS reception by the UE.

[0239] In the same manner as Proposals 1-2, the DL RS associated with a specific TCI state can be one of the DL RSs that the UE is measuring / tracking. For example, a specific TCI state can be the TCI state of a DL RS (e.g., SSB) for which the UE has recently performed L3 measurements / reports (for RRM) on a specific candidate cell, configured as a reference RS. For example, a specific TCI state can be the TCI state of a DL RS (e.g., SSB) based on L3 measurements where RSRP / RSRQ / RSSI is greater than or equal to a certain threshold, configured as a reference RS.

[0240] In a DL RS associated with a specific TCI state, it can be assumed that two QCL reference RSs are configured for the TCI state (e.g., QCL type A reference RS + QCL type D reference RS). In this case, it can be defined / configured (by the base station) which of the two RSs is used to measure DL reference timing. For example, of the two RSs, the RS for QCL type A reference can be used to measure DL reference timing.

[0241] The implementation methods of Proposals 1-3 can be represented as follows.

[0242] For PRACH transmissions toward the candidate cell, the uplink transmission timing occurs before the reception of the first detection path (in time) of the corresponding downlink frame of the reference signal associated with the UL / DL / joint TCI state configured / activated for the candidate cell. .

[0243] In Proposals 1-3, it can be assumed that when the UE performs a (CFRA) RACH transmission for a specific candidate cell, there is no TCI state active for the candidate cell. In this case, other implementations of Proposals 1-3 or other implementations of Proposal 1 can be applied.

[0244] Suggestions 1-4

[0245] When a UE performs a RACH transmission (CFRA of PDCCH command) for a specific candidate cell, the UE can measure the DL reference timing of the candidate cell based on the SSB index (as indicated in the PDCCH command that triggers the RACH for the candidate cell). The UE can perform the RACH transmission based on the DL reference timing. The SSB index indicated in the PDCCH command (DCI) can be one of the SSBs measured by the UE (e.g., a maintained RS, a periodically measured / reported RS, or a known condition for the path loss reference signal). The UE can expect the SSB index to be one of the aforementioned SSBs. This is because continuous reference timing measurement requires static / periodic RS reception by the UE.

[0246] In Proposal 1, the DL reference timing based on a specific DL RS for measuring candidate cells refers to the UE applying TA to transmit uplink based on the reception time of the corresponding DL RS. In other words, uplink transmission based on a specific DL RS in Proposal 1 can mean that "the uplink transmission timing occurs before the reception of the first detection path (in time) of the corresponding downlink frame of the DL RS." ".

[0247] In Rel-18 LTM, it is agreed that UE-based TA measurement is supported as a RACH-free method for TA acquisition of candidate cells. Below, new methods for TA acquisition of candidate cells are proposed, both RACH-based and RACH-free.

[0248] In addition to TA acquisition for candidate cells in Rel-18 LTM, the following proposal 2 can be utilized when multiple TAs are supported within the serving cell (e.g., Rel-18 MIMO dual TA feature), or when TA acquisition for multiple TAs is performed, or when TA acquisition for a specific TAG is performed in the UE CA scenario. Hereinafter, the target TRP can refer to i) a candidate cell in Rel-18 LTM, ii) a specific TRP / CORESET pool index / TAG in Rel-18 MIMO dual TA, or iii) a specific TAG (associated with the serving cell) in the UE CA scenario. Hereinafter, the source TRP can be i) a serving cell in Rel-18 LTM, ii) a serving cell used as the standard for measuring the TA of the target TRP, or iii) a reference cell.

[0249] Suggestion 2

[0250] The following describes a method for obtaining the TA for a specific target TRP of a base station.

[0251] Proposal 2-1

[0252] The following method can be considered: the UE sends a response based on the DL reference timing of a specific target TRP, and the base station calculates the TA of the target TRP based on the response.

[0253] The UE can send a response message to the DL RS of the target TRP, which serves as a reference, based on a DL reference timing defined / configured for the target TRP. The response message can be configured / defined by the base station (via 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 of the DL RS sending the target TRP and the Rx timing of receiving the response message. Considering / based on the timing difference being twice the propagation delay between the target TRP and the UE, the base station can measure / calculate the TA value of the target TRP for the UE. For example, Tx-Rx timing difference / 2 could be the TA value of the target TRP for the UE. The TA value of the target TRP can be sent by the base station to the UE based on RRC / MAC CE signaling (such as TA command MAC CE).

[0254] Suggestion 2-2

[0255] The following method can be considered: UE reports the Rx timing difference between the source TRP and the target TRP.

[0256] The UE measures the DL reference timing of different DL RS to report the Rx timing difference. Specifically, the UE measures the DL RS of the source TRP and the DL RS of the target TRP, configured (by the base station). Based on this, the UE can report the Rx timing difference to the base station. In addition, (to calculate the timing difference more accurately from the base station's perspective) the UE can report Doppler domain statistics (related to the source TRP / target TRP) to the base station.

[0257] Reports can be configured / defined by the base station and can be sent via PUSCH / PUCCH, etc.

[0258] The base station can calculate / determine the timing difference (TA) based on the Rx time difference as follows.

[0259] The base station has identified the time slot boundary difference between the source TRP and the target TRP (in asynchronous scenarios). Furthermore, the TA of the serving cell (source TRP) is already known. For the DL RS reception timing of the target TRP, the base station (NW) knows the time slot boundary between the source TRP and the target TRP. The corresponding timing can be replaced by the propagation delay from the source TRP to the UE (the TA value of the source TRP for the UE). If only the Rx timing difference exists between the DL RS of the source TRP and the DL RS of the target TRP, the base station can measure the propagation delay from the target TRP to the UE.

[0260] Considering / based on the time interval from the DL timeslot boundary of the target TRP to the DL RS reception timing of the target TRP at the UE, which is the propagation delay between the target TRP and the UE, the base station can calculate the TA value of the target TRP. For example, the time interval from the DL timeslot boundary of the target TRP to the DL RS reception timing of the target TRP at the UE can be the TA value of the target TRP at the UE. The TA value of the target TRP can be sent by the base station to the UE based on RRC / MAC CE signaling (such as TA command MAC CE).

[0261] The implementations of Proposal 1 and Proposal 2 can be combined in one or more ways for UE / base station operation.

[0262] The signaling process related to the above implementation method is described below.

[0263] Examples of UE (or base station) operation based on at least one of the above embodiments (e.g., at least one of Proposal 1 to Proposal 2) are as follows.

[0264] 1) The UE (base station) receives (sends) configuration information for candidate cells.

[0265] The configuration information for candidate cells may include information based on at least one of Proposal 1 to Proposal 2.

[0266] 2) The UE (base station) receives (sends) messages configuring / indicating RACH transmissions for candidate cells.

[0267] The message can be a PDCCH (DCI) that triggers / commands a RACH based on CFRA.

[0268] 3) UE (base station) based on message sending (receiving) RACH.

[0269] The DL reference timing associated with the candidate cell used for RACH transmission can be based on at least one of Proposal 1 to Proposal 2.

[0270] 4) The UE (base station) receives (sends) the Cell Handover Command (MAC CE). Based on the Cell Handover Command (MAC CE), a handover operation to a specific candidate cell can be performed.

[0271] The UE / base station operations are merely examples, and each operation (or step) is not necessarily necessary. Based on the UE / base station implementation method, operations related to RACH transmission to the candidate cell of the UE according to the above implementation method can be omitted or added.

[0272] From an implementation perspective, the operation of the UE / base station according to the above embodiments (e.g., operation based on at least one of Proposal 1 to Proposal 2) can be described as follows. Figure 6Devices (e.g., Figure 6 Processors 100 and 200 in the processor are used to process it.

[0273] Furthermore, the operation of the UE / base station according to the above embodiments (e.g., based on the operation of at least one of Proposal 1 to Proposal 2) can be used to run at least one processor (e.g., Figure 6 The commands / programs (e.g., instructions, executable code) of the processors 110 and 210 are stored in memory (e.g., Figure 6 In the memory (140 and 240).

[0274] Below, refer to Figure 4 and Figure 5 The above implementation methods are described in detail from the perspective of UE and base station operation. The methods described below are distinguished only for ease of explanation. Therefore, it is obvious that a portion of the configuration of any method can replace a portion of the configuration of another method or be combined with a portion of the configuration of another method.

[0275] Figure 4 This is a flowchart illustrating a method according to an embodiment of the present disclosure.

[0276] Reference Figure 4 The method according to embodiments of this disclosure includes steps S410 of receiving configuration for PRACH, S420 of receiving DCI, S430 of transmitting PRACH, and S440 of receiving a cell handover command MAC CE. In this method, some steps may be omitted. For example, step S440 may be omitted.

[0277] In step S410, the UE receives from the base station the configuration for the Physical Random Access Channel (PRACH) for each of the candidate cells.

[0278] For example, the PRACH configuration can be based on the LTM-config. Specifically, the UE receives the LTM-config from the base station. The LTM-config can include configurations for each of the candidate cells (e.g., LTM-Candidate). The configurations for each of the candidate cells (e.g., LTM-Candidate) can include PRACH configurations (e.g., EarlyUL-SyncConfig). That is, based on the LTM-config, the PRACH configuration may not exist for all candidate cells. The candidate cells mentioned in this step and below can refer to candidate cells among all candidate cells that have configurations including the PRACH configuration (i.e., candidate cells that have set the higher-layer parameter "EarlyUL-SyncConfig").

[0279] In step S420, the UE 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 can indicate the cell used for PRACH transmission (e.g., serving cell, candidate cell). For example, the cell indicator field can indicate a candidate cell for PRACH among candidate cells. For example, the DCI can be based on DCI format 1_0 for a random access procedure initiated by a Physical Downlink Control Channel (PDCCH) command. In other words, the DCI can be interpreted / replaced using a PDCCH command. The random access procedure initiated / triggered by the PDCCH command can be a contention-free random access (CFRA) procedure. The CFRA procedure can be used for early TA acquisition. In other words, the CFRA procedure can be used for timing advance (TA) acquisition before receiving the cell handover command medium access control-control element (MAC CE).

[0280] In step S430, the UE sends a PRACH to the base station. For example, the PRACH may be associated with a candidate cell (i.e., a candidate cell indicated by the cell indicator field).

[0281] In step S440, the UE receives the cell handover command MAC CE from the base station.

[0282] For example, cell handover can be performed based on the L1 / L2 triggered mobility (LTM) process described above. During the LTM process, the base station can refer to a gNB (e.g., a gNB central unit (CU)) plus one or more gNB distributed units (DUs). Cell handover based on the LTM process can include i) a handover from the source cell to a target cell within a gNB-DU (intra-gNB-DU LTM), and ii) a handover from the source cell (gNB-DU) to a target cell (other gNB-DUs) within a gNB-CU (inter-gNB-DU LTM).

[0283] Under current practices, criteria for determining uplink transmission timing are defined only for the serving cell; therefore, how to determine the PRACH transmission timing associated with candidate cells is unclear. To address this issue, at least one of the above-described embodiments can be applied. This is described in detail below.

[0284] According to the implementation, a candidate cell can be used as a reference cell for determining the transmission timing of PRACH, based on whether it is a neighboring cell or a secondary cell (SCell). This implementation can be based on at least one of Proposal 1-2, Proposal 1-3, and / or Proposal 1-4. For example, a neighboring cell can be associated with Layer 1 (L1)-Reference Received Signal Power (RSRP) measurement. For example, a secondary cell can be a secondary cell without an uplink carrier. For example, all candidate cells configured for the UE can be independent of L1-RSRP measurement. Specifically, the UE can perform L1-RSRP measurement for the cells that should be reported (e.g., 1 to 4 cells out of all candidate cells) based on CSI resource configuration and CSI reporting configuration. In addition, all candidate cells configured for the UE may include more than just secondary cells. With this in mind, Proposal 1-2, Proposal 1-3, and / or Proposal 1-4 can be applied to some of the aforementioned candidate cells (e.g., neighboring cells or secondary cells), and Proposal 1-1 can be applied to the remaining candidate cells (e.g., candidate cells that are not neighboring cells or secondary cells).

[0285] According to the implementation method, the transmission timing can be determined based on the reception of the first detection path of the downlink frame from the reference cell. In other words, PRACH transmission can occur before the first detection path of the downlink frame from the reference cell is received. In other words, the reference point related to transmission timing could be the downlink timing of the reference cell. Downlink timing can be defined as the time of the first detection path when a downlink frame is received, which is used by the UE to determine the downlink timing from the reference cell at the UE antenna. For example, the NTA can be configured / determined via Random Access Response (RAR) or Timing Advance Command (MAC-CE). TA,offset It can be configured or predefined by serving cell. TC is the basic time unit. For example, N for PRACH. TA It can be defined as 0.

[0286] According to the implementation method, the reception of the first detection path of the downlink frame can be based on the reception of a specific DLRS associated with the candidate cell in the downlink reference signal (DLRS). The specific DLRS can be a synchronization signal block (SSB) or a channel state information-reference signal (CSI-RS).

[0287] For example, a specific DL RS can be configured based on the SSB index associated with a candidate cell within the Synchronization Signal Block (SSB) index in a resource set (e.g., LTM-CSI-SSB-ResourceSet) configured based on L1 / L2-triggered Mobility (LTM) CSI reports. This implementation can be based on Proposals 1-2. Specifically, 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). The candidate cell that is the nth entry (n=1, 2, ...) in the candidate cell list can be associated with the SSB index that is the nth entry (n=1, 2, ...) in the SSB index list.

[0288] For example, a specific DL RS can be based on the Transmission Configuration Indication (TCI) status associated with the candidate cell. This implementation can be based on Proposals 1-3.

[0289] For example, a specific DL RS can be based on an SSB index based on a DCI indicator. This implementation can be based on proposals 1-4.

[0290] According to the implementation method, PRACH can be associated with the timing advance (TA) acquisition prior to the reception of the cell handover command medium access control-control element (MAC CE).

[0291] According to the implementation, the configuration for PRACH can be based on the high-level parameter "EarlyULSyncConfig" associated with the early uplink (UL) synchronization process.

[0292] For example, among candidate cells configured with the higher-level parameter "EarlyULSyncConfig", the candidate cell can be indicated by a bit field index based on the number of bits in the cell indicator field.

[0293] For example, the number of bits can be ,in, It is the ceiling function, and C This refers to the number of candidate cells configured with the higher-level parameter "EarlyULSyncConfig".

[0294] For example, in a bit field index based on bit count, bit field index 0 can be mapped to the serving cell. The remaining bit field indices in the bit field index can be mapped to candidate cells in ascending order of candidate identifier, starting from bit field index 1. Candidate identifiers can be based on ltm-CandidateId. ltm-CandidateId can be used to identify LTM candidate configurations, and an LTM candidate configuration can refer to the configuration for each candidate cell within the aforementioned LTM configuration (e.g., LTM-Candidate). In other words, candidate cells can be identified using ltm-CandidateId.

[0295] Based on the operations of steps S410 to S440 above, it is possible to... Figure 6 The device implementation. For example, UE 200 can control one or more transceivers 230 and / or one or more memories 240 to perform operations based on steps S410 to S440.

[0296] The above implementation method will now be described in detail from the perspective of base station operation.

[0297] Steps S510 to S540 described below correspond to reference Figure 4 Steps S410 to S440 are described. Redundant descriptions are omitted considering the above correspondence. That is, the detailed description of the base station operation described below can be replaced with the corresponding base station operation... Figure 4 Description / implementation method.

[0298] For example, Figure 4 The description / implementation of steps S410 to S440 can also be applied to the base station operation of steps S510 to S540 described below.

[0299] Figure 5 This is a flowchart illustrating another embodiment of the method according to the present disclosure.

[0300] Reference Figure 5 Another embodiment of the method according to this disclosure includes steps S510 of sending configuration for PRACH, S520 of sending DCI, S530 of receiving PRACH, and S540 of sending a cell handover command MAC CE. In this method, some steps may be omitted. For example, step S540 may be omitted.

[0301] In step S510, the base station sends the configuration for the Physical Random Access Channel (PRACH) for each of the candidate cells to the UE.

[0302] In step S520, the base station sends downlink control information (DCI) to the UE. The DCI includes a cell indicator field. The cell indicator field can indicate the cell used for PRACH transmission (e.g., serving cell, candidate cell). For example, the cell indicator field can be used to indicate a candidate cell for PRACH among candidate cells.

[0303] In step S530, the base station receives a PRACH from the UE. For example, the PRACH may be associated with a candidate cell (i.e., a candidate cell indicated by the cell indicator field).

[0304] In step S540, the base station sends a cell handover command Media Access Control-Control Element (MAC CE) to the UE.

[0305] According to the implementation method, based on whether the candidate cell is a neighboring cell or a secondary cell (SCell), the candidate cell can be used as a reference cell for determining the transmission timing of PRACH.

[0306] Based on the operations of steps S510 to S540 above, it can be achieved... Figure 6 The device is implemented in this way. For example, base station 100 may control one or more transceivers 130 and / or one or more memories 140 to perform operations based on steps S510 to S540.

[0307] The following reference Figure 6 Describes the apparatus to which embodiments of this disclosure are applicable (apparatus for implementing the methods / operations according to embodiments of this disclosure).

[0308] Figure 6 The configurations of the first and second devices according to embodiments of the present disclosure are illustrated.

[0309] The first device 100 may include a processor 110, an antenna unit 120, a transceiver 130, and a memory 140.

[0310] Processor 110 can perform baseband-related signal processing and includes a higher-layer processing unit 111 and a physical layer processing unit 115. Higher-layer processing unit 111 can handle operations at the MAC layer, RRC layer, or higher layers. Physical layer processing unit 115 can handle PHY layer operations. For example, if the first device 100 is a base station (BS) device in BS-UE communication, physical layer processing unit 115 can perform uplink receive signal processing, downlink transmit signal processing, etc. For example, if the first device 100 is a first UE device in UE-to-UE communication, physical layer processing unit 115 can perform downlink receive signal processing, uplink transmit signal processing, sidelink transmit signal processing, etc. In addition to performing baseband-related signal processing, processor 110 can also control the overall operation of the first device 100.

[0311] Antenna unit 120 may include one or more physical antennas, and if antenna unit 120 includes multiple antennas, MIMO transmission / reception is supported. Transceiver 130 may include a radio frequency (RF) transmitter and an RF receiver. Memory 140 may store information processed by processor 110, as well as software, operating system, and applications related to the operation of first device 100. Memory 140 may also include components such as buffers.

[0312] In the embodiments described in this disclosure, the processor 110 of the first device 100 may be configured to implement the operation of the BS in BS-UE communication (or the operation of the first UE device in UE-UE communication).

[0313] The second device 200 may include a processor 210, an antenna unit 220, a transceiver 230, and a memory 240.

[0314] Processor 210 can perform baseband-related signal processing and includes a higher-layer processing unit 211 and a physical layer processing unit 215. Higher-layer processing unit 211 can handle operations at the MAC layer, RRC layer, or higher layers. Physical layer processing unit 215 can handle PHY layer operations. For example, if the second device 200 is a UE device in BS-UE communication, physical layer processing unit 215 can perform downlink receive signal processing, uplink transmit signal processing, etc. For example, if the second device 200 is a second UE device in inter-UE communication, physical layer processing unit 215 can perform downlink receive signal processing, uplink transmit signal processing, sidelink receive signal processing, etc. In addition to performing baseband-related signal processing, processor 210 can also control the overall operation of the second device 200.

[0315] Antenna unit 220 may include one or more physical antennas, and if antenna unit 220 includes multiple antennas, MIMO transmission / reception is supported. Transceiver 230 may include an RF transmitter and an RF receiver. Memory 240 may store information processed by processor 210, as well as software, operating system, and applications related to the operation of second device 200. Memory 240 may also include components such as buffers.

[0316] In the embodiments described in this disclosure, the processor 210 of the second device 200 may be configured to implement the operation of the UE in BS-UE communication (or the operation of the second UE device in inter-UE communication).

[0317] The descriptions of the BS and UE (or the first UE device and the second UE device in inter-UE communication) in the examples of this disclosure are equivalent to those for the operation of the first device 100 and the second device 200, and redundant descriptions are omitted.

[0318] In addition to LTE, NR, and 6G, the wireless communication technologies implemented in apparatus 100 and apparatus 200 according to this disclosure may also include narrowband Internet of Things (NB-IoT) for low-power communication. For example, NB-IoT technology may be an example of low-power wide-area network (LPWAN) technology and may be implemented in standards such as LTE Cat NB1 and / or LTE Cat NB2. NB-IoT technology is not limited to the names mentioned above.

[0319] Additionally or alternatively, the wireless communication technology implemented in apparatus 100 and apparatus 200 according to this disclosure may be based on LTE-M technology to perform communication. For example, LTE-M technology may be an example of LPWAN technology and may be referred to by various names, such as enhanced machine-type communication (eMTC). For example, LTE-M technology may be implemented using at least one of various standards, such as 1) LTE Cat0, 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. LTE-M technology is not limited to the names mentioned above.

[0320] Additionally or alternatively, considering low-power communication, the wireless communication technologies implemented in apparatus 100 and apparatus 200 according to this disclosure may include at least one of ZigBee, Bluetooth, and Low Power Wide Area Network (LPWAN), and are not limited to the aforementioned names. For example, ZigBee technology can be based on various standards such as IEEE 802.15.4 to create personal area networks (PANs) associated with small / low-power digital communication, and may be referred to by various names.

Claims

1. A method comprising the following steps: Receive the configuration for the Physical Random Access Channel (PRACH) for each of the candidate cells; Receive downlink control information (DCI), wherein the DCI includes a cell indicator field, and the candidate cells for the PRACH among the candidate cells are indicated based on the cell indicator field; and Send the PRACH, Wherein, based on whether the candidate cell is a neighboring cell or a secondary cell SCell, the candidate cell is used as a reference cell for determining the transmission timing of the PRACH.

2. The method according to claim 1, wherein, The transmission timing is determined based on the reception of the first detection path of the downlink frame from the reference cell.

3. The method according to claim 2, wherein, The reception of the first detection path of the downlink frame is based on the reception of a specific DL RS in the downlink reference signal DL RS associated with the candidate cell.

4. The method according to claim 3, wherein, The specific DL RS is based on the SSB index associated with the candidate cell in the synchronization signal block SSB index of the resource set configured according to the mobility LTM CSI report triggered by L1 / L2.

5. The method according to claim 3, wherein, The specific DL RS is based on the Transmission Configuration Indicator (TCI) status associated with the candidate cell.

6. The method according to claim 3, wherein, The specific DL RS is based on the SSB index indicated by the DCI.

7. The method according to claim 1, wherein, The PRACH is related to the timing advance TA acquisition before receiving the cell handover command medium access control - control element MAC CE.

8. The method according to claim 1, wherein, The configuration for the PRACH is based on the high-level parameter EarlyULSyncConfig, which is associated with the early uplink UL synchronization process.

9. The method according to claim 8, wherein, Among the candidate cells configured with the higher-layer parameter EarlyULSyncConfig, the candidate cell is indicated by a bit field index based on the number of bits in the cell indicator field.

10. The method according to claim 9, wherein, The number of bits is ,in, It is the ceiling function, and C It is the number of candidate cells configured with the higher-level parameter EarlyULSyncConfig.

11. The method according to claim 10, wherein, In the bit field index based on the number of bits, bit field index 0 is mapped to the serving cell, and The remaining bit field indices in the bit field index are mapped to the candidate cells starting from bit field index 1 in ascending order of candidate identifiers.

12. The method according to claim 1, wherein, The neighboring cell is related to the Layer 1 L1-reference signal received power (RSRP) measurement.

13. The method according to claim 1, wherein, The secondary cell SCell is a secondary cell that does not have an uplink carrier.

14. The method according to claim 1, wherein, The DCI is based on DCI format 1_0 for random access procedures initiated via physical downlink control channel (PDCCH) commands.

15. A user equipment (UE), the UE comprising: One or more transceivers; One or more processors; as well as One or more memories, said one or more memories being connected to said one or more processors and storing instructions. The instructions are based on the one or more processors executing the UE to perform all the steps of the method according to any one of claims 1 to 14.

16. An apparatus, the apparatus comprising: One or more memory units; and one or more processors, said one or more processors being operatively connected to said one or more memories, The one or more memory storage instructions, which are executed by the one or more processors to cause the device to perform all the steps of the method according to any one of claims 1 to 14.

17. One or more non-transitory computer-readable media, wherein the one or more non-transitory computer-readable media stores instructions. in, The instructions, which can be executed by one or more processors, cause the user equipment (UE) to perform all the steps of the method according to any one of claims 1 to 14.

18. A method comprising the following steps: Send the configuration for the Physical Random Access Channel (PRACH) for each of the candidate cells; Sending downlink control information (DCI), wherein the DCI includes a cell indicator field, and the candidate cells for the PRACH among the candidate cells are indicated based on the cell indicator field; and Receive the PRACH, Wherein, based on whether the candidate cell is a neighboring cell or a secondary cell SCell, the candidate cell is used as a reference cell for determining the transmission timing of the PRACH.

19. A base station, the base station comprising: One or more transceivers; One or more processors; as well as One or more memories, said one or more memories being connected to said one or more processors and storing instructions. The instructions are based on the one or more processors executing the base station to perform all the steps of the method according to claim 18.

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