Method and apparatus for performing random-free access handover in NTN system

Abstract

The present disclosure relates to a method and an apparatus for performing a Random Access Channel (RACH)-less handover in a non-terrestrial network (NTN), the method and the apparatus for a first NTN base station in a wireless communication system, and comprising the steps of: determining a RACH-less handover to a second NTN base station for a terminal; configuration information related to RACH-less switching is obtained from the second NTN base station; and transmitting, to the terminal, a radio resource control (RRC) reconfiguration message including configuration information and timing information applicable to a second NTN base station, in which whether the timing control value of the second NTN base station is the same as the timing control value of the first NTN base station is indicated by the timing information, and performing a physical uplink shared channel (PUSCH) transmission from the terminal to the second NTN base station based on the timing information and the configuration information.

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for performing RACH-less handover in an NTN. Background Technology

[0002] Fifth-generation (5G) mobile communication technology defines wide bandwidths to enable fast transmission speeds and new services, and can be implemented not only in the "sub-6GHz" band ("sub 6GHz") such as 3.5 GHz, but also in ultra-high frequency bands ("Above 6GHz") such as 28 GHz or 39 GHz, known as millimeter waves. Additionally, 6G mobile communication technology, known as "super 5G systems," is being considered for implementation in terahertz (THz) bands (e.g., the 95 GHz to 3 THz band) to achieve transmission speeds up to 50 times faster and ultra-low latency reduced to 1 / 10 compared to 5G mobile communication technology.

[0003] In the early stages of 5G mobile communication technology, to meet the service support and performance requirements of enhanced mobile broadband (eMBB), ultra-reliable and low-latency communication (URLLC), and massive machine-type communication (mMTC), standardization was implemented for the following: beamforming to mitigate path loss of radio waves and increase their propagation distance in the millimeter-wave band; massive MIMO; support for various parameter sets for efficient use of UHF resources (e.g., operating multiple subcarrier spacings); dynamic operation of time slot formats; initial access schemes supporting multi-beam transmission and broadband; definition and operation of bandwidth portions (BWP); new channel coding schemes (such as low-density parity-check (LDPC) codes for high-capacity data transmission and polar codes for reliable transmission of control information); L2 preprocessing; and network slicing for providing dedicated networks for specific services.

[0004] Currently, discussions are underway to improve 5G mobile communication technology and enhance its performance, taking into account the services that 5G mobile communication technology was originally intended to support. Physical layer standardization for technologies such as V2X (Vehicle to Everything), which aims to help autonomous vehicles make driving decisions based on their own location and status information sent by the vehicle and increase user convenience; New Radio Unlicensed (NR-U), which is intended for system operation purposes to meet various regulatory requirements in unlicensed frequency bands; low-power schemes (UE power saving) for NR terminals; non-terrestrial networks (NTN) as direct terminal-satellite communication to protect coverage in areas where communication with terrestrial networks is impossible; and positioning.

[0005] Furthermore, standardization is underway in wireless interface architectures / protocols, such as smart factories (Industrial Internet of Things, IIoT) to support new services through links and convergence with other industries, Integrated Access and Backhaul (IAB) to provide nodes for network service area extension by integrating and supporting wireless backhaul and access links, mobility enhancements including conditional handover and dual active protocol stack (DAPS) handover, and two-step random access (two-step RACH for NR) to simplify the random access process; and standardization is also underway in system architectures / services for 5G baseline architectures (e.g., service-based architectures, service-based interfaces) to integrate Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, as well as mobile edge computing (MEC) for terminals to receive services based on their location.

[0006] When 5G mobile communication systems are commercialized, a surge in the number of connected devices will connect to the communication network; therefore, it is anticipated that there will be a need to enhance the functionality and performance of 5G mobile communication systems, as well as the integrated operation of connected devices. To this end, new research will be conducted on 5G performance improvements and complexity reductions, AI service support, metaverse service support, and drone communications by leveraging extended reality (XR), artificial intelligence (AI), and machine learning (ML) to effectively support augmented reality (AR), virtual reality (VR), and mixed reality (MR).

[0007] Furthermore, this advancement in 5G mobile communication systems will form the basis for the development of technologies such as new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, full-dimensional MIMO (FD-MIMO), multi-antenna transmission (such as array antennas or massive MIMO), metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing using orbital angular momentum (OAM), reconfigurable smart surface (RIS) technology, full-duplex technology to improve the frequency efficiency of 6G mobile communication technology and system networks, satellites, AI-based communication that leverages artificial intelligence (AI) from the design stage and internalizes end-to-end AI support capabilities to achieve system optimization, and next-generation distributed computing that utilizes ultra-high-performance communication and computing resources to enable services whose complexity exceeds the limits of terminal computing capabilities.

[0008] Non-terrestrial networks (NTNs) are technologies that provide data services to terminals on the ground by utilizing satellites or unmanned aerial systems (UAS) located at high altitudes. In NTNs, data transmission and reception are supported by satellites at high altitudes; therefore, when a terminal performs random access, it takes a long time to complete, which may increase the probability of handover failure. Summary of the Invention

[0009] Technical issues Therefore, the purpose of this disclosure is to propose a method for introducing RACH-less switching into NTN.

[0010] Solution to the problem A method for resolving the above-mentioned problem by a first non-terrestrial network (NTN) base station in a wireless communication system, according to an example of the present disclosure, may include: determining a random access channel-less (RACH) handover for a terminal to a second NTN base station; obtaining configuration information associated with the RACH-less handover from the second NTN base station; and sending a radio resource control (RRC) reconfiguration message to the terminal, the RRC reconfiguration message including the configuration information and timing information applied to the second NTN base station, wherein whether a timing adjustment value for the second NTN base station is equal to a timing adjustment value for the first NTN base station can be indicated by the timing information, and wherein a physical uplink shared channel (PUSCH) transmission from the terminal to the second NTN base station can be performed based on the timing information and the configuration information.

[0011] Additionally, a method performed by a terminal in a wireless communication system according to an example of this disclosure may include: receiving a Radio Resource Control (RRC) reconfiguration message from a first non-terrestrial network (NTN) base station, the RRC reconfiguration message including configuration information associated with a random access channel (RACH)-less handover to a second NTN base station and timing information applied to the second NTN base station; and performing a Physical Uplink Shared Channel (PUSCH) transmission to the second NTN base station based on the timing information and the configuration information, wherein whether the timing adjustment value for the second NTN base station is equal to the timing adjustment value for the first NTN base station can be indicated by the timing information.

[0012] Additionally, a first non-terrestrial network (NTN) base station in an example wireless communication system according to this disclosure may include: a transceiver; and a controller configured to: determine a random access channel-less (RACH) handover for a terminal to a second NTN base station; obtain configuration information associated with the RACH-less handover from the second NTN base station; and control the transceiver to send a Radio Resource Control (RRC) reconfiguration message to the terminal, the RRC reconfiguration message including the configuration information and timing information applied to the second NTN base station, wherein whether a timing adjustment value for the second NTN base station is equal to a timing adjustment value for the first NTN base station can be indicated by the timing information, and wherein a Physical Uplink Shared Channel (PUSCH) transmission from the terminal to the second NTN base station can be performed based on the timing information and the configuration information.

[0013] Additionally, a terminal in a wireless communication system according to an example of this disclosure may include: a transceiver; and a controller configured to control the transceiver to receive a Radio Resource Control (RRC) reconfiguration message from a first non-terrestrial network (NTN) base station, the RRC reconfiguration message including configuration information associated with a random access channel (RACH)-less handover to a second NTN base station and timing information applied to the second NTN base station, and to control the transceiver to perform a Physical Uplink Shared Channel (PUSCH) transmission to the second NTN base station based on the timing information and the configuration information, wherein whether the timing adjustment value for the second NTN base station is equal to the timing adjustment value for the first NTN base station can be indicated by the timing information.

[0014] Beneficial effects of the present invention According to embodiments of this disclosure, by applying appropriate factors that take into account the characteristics of NTN, such as the additional delays occurring in the links between ground stations, satellites and terminals, and the coordination required between the source cell and the target cell, it is assumed that existing random access channel-less handover can be effectively supported in NTN. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating the architecture of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0016] Figure 2 This is a diagram used to describe a random access process according to an embodiment of the present disclosure.

[0017] Figure 3This is a diagram used to describe a non-terrestrial network (NTN) according to embodiments of the present disclosure.

[0018] Figure 4 This is a diagram illustrating the format of a timing advance report MAC CE according to an embodiment of the present disclosure.

[0019] Figure 5 This is a sequence diagram of a process for performing RACH-less handover in a mobile communication system according to embodiments of the present disclosure.

[0020] Figure 6 This is a diagram illustrating a scenario for performing RACH-less handover in an NTN according to embodiments of the present disclosure.

[0021] Figure 7 This is a sequence diagram of the first process for performing RACH-less handover of NTN according to an embodiment of the present disclosure.

[0022] Figure 8 This is a sequence diagram of a second process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0023] Figure 9 This is a sequence diagram of a third process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0024] Figure 10 This is a diagram used to describe a scenario supporting CA / DC in NTN according to embodiments of the present disclosure.

[0025] Figure 11 This is a sequence diagram of the fourth process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0026] Figure 12 This is a diagram illustrating the format of a new timing advance report MAC CE according to an embodiment of the present disclosure.

[0027] Figure 13 This is a flowchart of a UE operation for performing RACH-less handover of NTN according to an embodiment of the present disclosure.

[0028] Figure 14 This is a flowchart of base station operations for performing RACH-less handover of NTN according to embodiments of the present disclosure.

[0029] Figure 15 This is a diagram illustrating a scenario where a satellite within an NTN performs a RACH-less handover according to an embodiment of this disclosure.

[0030] Figure 16This is a block diagram illustrating the internal structure of a UE according to an embodiment of the present disclosure.

[0031] Figure 17 This is a block diagram illustrating the structure of a base station according to an embodiment of the present disclosure. Detailed Implementation

[0032] In the following description of this disclosure, detailed descriptions of relevant well-known functions or configurations will be omitted where such descriptions may unnecessarily obscure the subject matter of this disclosure. Embodiments of this disclosure will be described below with reference to the accompanying drawings. The description of this disclosure is based on the LTE system, but it is also applicable to other mobile communication systems, such as NR as a next-generation mobile communication system. For example, in this disclosure, 'eNB' in LTE corresponds to 'gNB' in NR, and 'MME' in LTE corresponds to 'AMF' in NR.

[0033] Figure 1 This is a diagram illustrating the architecture of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0034] refer to Figure 1 As shown in the figure, the radio access network of the next-generation mobile communication system (New Radio, NR) consists of a next-generation base station (New Radio Node B, referred to as gNB) 1a-10 and an AMF (New Radio Core Network) 1a-05. User terminals (New Radio User Equipment, referred to as NR UE or terminal) 1a-15 connect to the external network through gNB 1a-10 and the Access and Mobility Management Function (AMF) 1a-05.

[0035] exist Figure 1 In this context, the gNB corresponds to the Evolved Node B (eNB) of the existing LTE (Long Term Evolution) system. The gNB can connect to NR UEs via radio channels and can provide superior service compared to existing Node Bs (1a-20). It serves all user services through a shared channel in the next-generation mobile communication system. Therefore, an entity is needed to perform scheduling by collecting state information (such as buffer state, available transmission power state, and channel state of each UE), and gNBs 1a-10 are responsible for this scheduling. Typically, one gNB controls multiple cells. To achieve ultra-high-speed data transmission compared to existing LTE, bandwidth exceeding the existing maximum bandwidth can be utilized. Furthermore, beamforming technology can be combined with Orthogonal Frequency Division Multiplexing (OFDM) used as the radio access technology. Additionally, an Adaptive Modulation and Coding (AMC) scheme is applied to determine the modulation scheme and channel coding rate to match the UE's channel state.

[0036] The AMF 1a-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. The AMF 1a-05 is the entity responsible not only for mobility management but also for various control functions of the UE, and it connects to multiple base stations. Furthermore, next-generation mobile communication systems can interoperate with existing LTE systems, and the AMF connects to the Mobility Management Entity (MME) 1a-25 via a network interface. The MME connects to the eNB 1a-30, which serves as an existing base station. UEs supporting LTE-NR dual connectivity can maintain a connection not only to the gNB but also to the eNB to send and receive data (1a-35).

[0037] Figure 2 This is a diagram illustrating a random access procedure according to embodiments of the present disclosure.

[0038] Random access is performed when uplink synchronization is achieved or when data is sent to the network. More specifically, it can be performed when transitioning from idle mode to connected mode, during Radio Resource Control (RRC) re-establishment, during handover, and when uplink or downlink data transmission begins.

[0039] When UE 1b-05 receives a dedicated preamble from base station 1b-10, UE 1b-05 uses this dedicated preamble to perform preamble transmission. Conversely, if no dedicated preamble is provided, the UE selects one of two preamble groups and chooses the preamble belonging to the selected group. These groups are referred to as Group A and Group B. If the channel quality state is better than a certain threshold and the size of msg 3 is greater than a certain threshold, the UE selects the preamble belonging to Group B; otherwise, it selects the preamble belonging to Group A.

[0040] If the aforementioned preamble (1b-15) is transmitted at subframe n, UE 1b-05 begins the Random Access Response (RAR) window from subframe n+3 and monitors whether a RAR (1b-20) is transmitted within the window interval. The RAR scheduling information is indicated by the RA-RNTI (Random Access-Temporary Radio Network Identifier) ​​of the Physical Downlink Control Channel (PDCCH). The RA-RNTI is derived using the time-domain and frequency-domain radio resource locations already used to transmit the aforementioned preamble. The aforementioned RAR includes timing advance, UL grant, and temporary cell (C)-RNTI. The UE uses the timing advance information to determine the timing for transmitting uplink signals.

[0041] If the RAR is successfully received within the RAR window, UE 1b-05 sends msg 3 (1b-25) using the UL authorization information included in the RAR. Msg 3 includes different information depending on the purpose of the random access. Table 1 below shows the information included in msg 3.

[0042] [Table 1] Examples of information included in msg3

[0043] If UE 1b-05 receives RAR in subframe n, it sends Msg3 in subframe n+6. Hybrid Automatic Repeat Request (HARQ) is applied starting with msg3. After sending msg3, UE 1b-05 starts a specific timer and monitors for Contention Resolution (CR) messages until the timer expires (1b-30). Depending on the purpose of the random access, in addition to CR MAC (Media Access Control) CE (Control Element), the CR message may also include an RRC connection establishment or RRC connection re-establishment message.

[0044] In base station 1b-10, signals transmitted from multiple UEs should be received in a time-synchronized manner, allowing each signal to be separated and decoded. Therefore, base station 1b-10 provides timing advance command information to each UE via a random access procedure or using a timing advance command MAC CE to adjust the synchronization of uplink signals. Upon receiving the timing advance command information, UE 1b-05 uses it to adjust the timing for transmitting uplink signals.

[0045] Use the following equation to derive the timing advance time T_TA.

[0046] [Equation 1]

[0047] Here, N_TA is the timing advance command information provided by RAR / MSGB or the timing advance command MAC CE, N_TA,offset is the offset value, and T_c indicates the sampling time. During the initial random access procedure, the N_TA value is set to 0.

[0048] Figure 3 This is a diagram used to describe a non-terrestrial network (NTN) according to embodiments of the present disclosure.

[0049] NTN is a technology that provides data services to UEs on the ground by utilizing artificial satellites or unmanned aerial systems (UAS) located at high altitudes. Satellite 1c-05 acts as an independent gNB or DU, gNB-DU, or RF (radio frequency) repeater in the CU (Central Unit) - DU (Distributed Unit) functional split; and depending on the satellite's role, there are gNB-CUs or gNB 1c-20s connected to the NTN-Gateway (GW) 1c-15 on the ground. The radio portion between satellite 1c-05 and the NTN-GW 1c-15 on the ground is called feeder link 1c-10, and the radio portion between satellite 1c-05 and the UEs 1c-30 or 1c-35 on the ground is called service link 1c-25.

[0050] Because satellites move at high speeds and high altitudes, significant propagation delays and Doppler distortion occur. Therefore, to ensure smooth communication between the satellite and the UE, these distortions must be compensated for in advance. This requires specific information, which satellite 1c-05 provides to UEs 1c-30 and 1c-35 on the ground via System Information SIB19 1c-40. SIB19 includes various information necessary to compensate for propagation delays and Doppler distortion, such as information about the position and velocity of the satellite and neighboring satellites. UEs 1c-30 and 1c-35 compensate for the distortions by utilizing the aforementioned information along with their own position information.

[0051] In communication with the NTN, a very long propagation delay occurs. Therefore, the time synchronization described in Equation 1 is insufficient to compensate for this delay. For example, with existing time synchronization schemes, the delay time in the long-distance feeder link between the satellite and the UE, and the delay time in the service link, exceed the adjustment range. Therefore, the timing advance time T_TA in the NTN uses Equation 2 below.

[0052] [Equation 2]

[0053] Here, N_TA,common is the value for compensating for delay time in the feeder link, and the information required to calculate it (TA-Info IE) is provided by SIB19, and the UE derives this value through specified information and specified equations. TA-Info IE includes ta-Common, ta-CommonDrift, and ta-CommonDriftVariant, and the definitions of these fields are shown in Table 2 below (extracted from TS38.331).

[0054] [Table 2]

[0055] NTA, UE-specific This is the value for compensating for latency in the service link. Satellite location information is provided via SIB19, and the UE uses this information, along with its own location information, to calculate the distance between the satellite and the UE, thus arriving at the aforementioned value.

[0056] In this disclosure, T TA, common and T TA, UE-specific These represent the propagation delay time of the feeder link and the propagation delay time of the service link, respectively. These values ​​are derived by N... TA, common and N TA, UE-specific Multiply by T c To get to the conclusion.

[0057] T TA The value is useful for UE scheduling in NTN cells. Therefore, the UE can report values ​​including T to the NTN cell based on the gNB settings. TA The value is reported in advance via MAC CE (TAR MAC CE). The conditions under which the UE should report TAR MAC CE are as follows.

[0058] - During RRC establishment, RRC recovery, RRC reconstruction (RRE), or switchover - When receiving TAR-Config sent from the base station - When the difference between the TA value stored in the most recently reported TAR MAC CE and the current TA value exceeds a preset threshold. Figure 4 This is a diagram illustrating the format of a timing advance report MAC CE according to an embodiment of the present disclosure.

[0059] The Timing Advance Report (MAC CE) is 2 bytes in size and consists of a 2-bit reserved field 1d-05 and a 14-bit Timing Advance (TA) field 1d-10. The Timing Advance field includes the T of the serving NTN cell. TA value.

[0060] Figure 5 This is a sequence diagram of a process for performing RACH-less handover in a mobile communication system according to embodiments of the present disclosure.

[0061] In LTE systems, random access channel-less (RACH-less) handover is introduced, which performs handover without random access when the timing of the target cell is clearly identified.

[0062] More specifically, in order to perform a RACH-less handover, UE 1e-05 reports its capability information (UE capability information) (1e-20) to the source base station 1e-10. This capability information may include an indicator indicating whether UE 1e-05 supports RACH-less handover. In LTE, this indicator corresponds to rach-Less-r14 extracted from the TS36.331 standard document, as shown in Table 3 below.

[0063] [Table 3]

[0064] When it is determined that a RACH-less handover will be performed on UE 1e-05, the source base station 1e-10 exchanges necessary configuration information with the neighboring target base station 1e-15 through handover coordination (1e-25). At this time, the target base station 1e-15 can provide the source base station 1e-10 with timing advance information (i.e., timing adjustment indication, for example, N). TA The uplink scheduling information (ul-ConfigInfo) and the uplink value are used by the UE when sending signals to the target cell. Here, the uplink scheduling information may not be provided.

[0065] Based on the information provided by the target base station 1e-15, the source base station 1e-10 sends a MobilityControlInfo IE (1e-30) containing specific RACH-less configuration information to the UE 1e-05. The specific RACH-less configuration information corresponds to RACH-Skip-r14 extracted from the TS36.331 standard document, as shown in Table 4 below.

[0066] [Table 4]

[0067] The targetTA information corresponds to a timing adjustment instruction. If ta0 is indicated as the targetTA value, it means N TA =0; mcg-PTAG means N of the PTAG (Primary Timing Advance Group) applied in the MCG (Primary Cell Group). TA ;scg-PTAG means the N of the PTAG applied in the SCG (Secondary Cell Group). TA A mcg-STAG with a STAG-Id means that the N applied to the STAG (auxiliary timing advance group) corresponding to the STAG-Id in the MCG. TA ; an scg-STAG with a STAG-Id means that the N applied to the STAG corresponding to the STAG-Id in the SCG. TA UE 1e-05 uses the set NTA The TA value is derived from the value to be used to send signals to the target cell.

[0068] Therefore, the target cell for RACH-less handover is limited to those where 0 can be used as N. TA The target cell is either a cell with a specified value, or a serving cell in an existing CA (carrier aggregation) / DC (dual connectivity) configuration, or a cell with the same TA. In other words, the target cell is limited to those N cells already known to the UE. TA The neighborhood is worth it.

[0069] The numberOfConfUL-Processes information indicates the number of HARQ processes corresponding to the uplink grant to be applied by UE 1e-05 in the target cell.

[0070] The ul-SchedInterval information indicates the period (1e-50) of uplink scheduling to be applied by UE 1e-05 in the target cell.

[0071] The ul-StartSubframe information indicates that UE 1e-05 can perform uplink transmission in the target cell in a subframe (1e-45). A value of 0 indicates a subframe corresponding to subframe number 0, and a value of 1 indicates a subframe corresponding to subframe number 1.

[0072] ul-Grant information refers to the radio resources (1e-40) that enable UE 1e-05 to perform uplink transmissions in the target cell.

[0073] The target cell 1e-15 allocates radio resources to UE 1e-05 at the scheduling time derived through the RACH-less configuration information.

[0074] UE 1e-05, which has received RACH-less configuration information, sends the Physical Uplink Shared Channel (PUSCH) (1e-35) including the RRCConnectionReconfigurationComplete message to the target cell at the transport timing derived from the above configuration information.

[0075] Figure 6 This is a diagram illustrating a scenario in which RACH-less handover is performed in an NTN according to an embodiment of the present disclosure.

[0076] Because NTNs utilize satellites located at high altitudes for data transmission and reception, the UE requires a considerable amount of time to perform and complete random access. During handover, the UE must perform random access to the target cell, and the long time required for this process can increase the probability of handover failure. Therefore, introducing RACH-less handover into NTNs can solve these problems.

[0077] However, there are several problems with directly applying RACH-less handover to existing LTE.

[0078] First, in NTN, there is a feeder link 1f-30 or 1f-45 between ground station 1f-15 or 1f-25 and satellite 1f-05 or 1f-10, and a service link 1f-35 or 1f-40 between satellite 1f-05 or 1f-10 and UE 1f-20, with additional delays occurring in each link. Therefore, unlike existing terrestrial LTE, additional factors, namely N, must be considered when deriving the timing advance value for performing RACH-less handover in NTN. TA,common N TA,UE-specific .

[0079] Secondly, Rel-17 NTN does not support carrier aggregation (CA) / dual connectivity (DC). Therefore, it can be restricted that RACH-less handover can only be configured if the NTN supports CA / DC and the target cell is one of the serving cells in the CA / DC. If RACH-less handover is configured regardless of the above restrictions, it may require RACH-less configuration information different from that of LTE. To perform RACH-less handover, specific coordination is required to exchange the configuration information needed for RACH-less handover between the source and target cells. In this embodiment, it is assumed that such coordination (1f-50 and 1f-55) is performed via the interface between source ground station 1f-15 and target ground station 1f-25 or the interface between source NTN satellite 1f-05 and target NTN satellite 1f-10.

[0080] Next, in this embodiment, a method for performing RACH-less switching in NTN is proposed.

[0081] Figure 7 This is a sequence diagram of the first process for performing RACH-less handover of NTN according to an embodiment of the present disclosure.

[0082] UE 1g-05 sends its UE capability information (1g-20) to the source NTN base station 1g-10. This capability information includes an indicator that indicates whether UE 1g-05 supports RACH-less handover in an NTN environment.

[0083] Source NTN base station 1g-10 broadcasts specific information (1g-25) about source NTN base station 1g-10 and neighboring NTN cells via System Information SIB19. This specific information includes the positions (ephemeris) of NTN satellites and derived N... TA,commonInformation required for (ta-Common, ta-CommonDrift, ta-CommonDriftVariant).

[0084] The source NTN base station 1g-10 determines to initiate a RACH-less handover for UE 1g-05 (1g-30). The source NTN base station 1g-10 sends PropDelayDiffReportConfig configuration information to UE 1g-05 via an RRCReconfiguration message (1g-35). This means that the UE reports configured TA information about neighboring NTN cells at a preset time. This configuration information includes the threshold threshPropDelayDiff and the ephemeris information of the neighboring NTN cells' neighborCellInfoList. The neighborCellInfoList includes the target NTN cell.

[0085] Upon receiving the above configuration information, UE 1g-05 uses the pre-configured ephemeris information of neighboring NTN cells to derive the serving link propagation delay (T) of the neighboring NTN cells. TA, UE-specific (1g-40); and UE 1g-05 includes a PropagationDelayDifference value (in milliseconds) in UEAssistanceInformation (UAI), which is the difference between the service link propagation delay of the serving cell and the service link propagation delay of the neighboring NTN cells, and sends it to the source NTN base station 1g-10 (1g-45).

[0086] When the above configuration information is received, if the difference between the most recently reported TA value and the current TA value becomes greater than the threshPropDelayDiff value, then UE 1g-05 sends a UAI message including the current PropagationDelayDifference value to the source NTN base station 1g-10.

[0087] In this embodiment, if certain conditions are met, it is recommended that UE 1g-05 report the PropagationDelayDifference value to the base station. These specific conditions may mean periodically reporting the PropagationDelayDifference value or meeting a preset condition from the following categories.

[0088] -CondEvent A3: The offset of the conditional reconfiguration candidate becomes better than PCell / PSCell; -CondEvent A4: The conditional reconfiguration candidate becomes better than the absolute threshold; -CondEvent A5: PCell / PSCell becomes worse than the absolute threshold 1, and the condition reconfiguration candidate becomes Better than another absolute threshold of 2; -CondEvent D1: The distance between the UE and the reference location referenceLocation1 becomes greater than the configured distance. The threshold distanceThreshFromReference1, and the reference position of the UE relative to the conditional reconfiguration candidate. The distance between referenceLocation2 becomes shorter than the configured threshold distanceThreshFromReference2; -CondEvent T1: The time measured at the UE becomes greater than the configured threshold t1-Threshold but less than t1- Threshold + duration; The conditions described above are those introduced during the handover of related technical conditions and can be reused as conditions for reporting PropagationDelayDifference values. A specific description of each condition is provided according to TS38.331. However, these conditions are specifically for reporting PropagationDelayDifference values ​​and are provided to the UE through separate configuration information distinct from that used during the handover of related technical conditions. The base station can configure one or more conditions for the UE; and if at least one or all of the preset conditions are met, the UE reports the most recent PropagationDelayDifference value to the base station. In addition to the conditions described above, new conditions based on signal strength or quality can be introduced to indicate the handover time.

[0089] Upon receiving the PropagationDelayDifference value, the source NTN base station 1g-10 derives the serving link propagation delay in the target NTN cell 1g-15 based on its serving link propagation delay and the received PropagationDelayDifference value from the target NTN cell 1g-15. The source NTN base station 1g-10 then includes the derived value in a HandoverPreparationInformation message and sends it to the target NTN cell 1g-15 (1g-55). This message is used when making a handover request to the target cell and may include an indicator indicating that the handover is for RACH-less handover.

[0090] The target NTN cell 1g-15, which has already received the HandoverPreparationInformation message, can identify the value T of UE 1g-05. TA,UE-specific (i.e., service link propagation delay), and the feeder link propagation delay (T) can be directly derived. TA,common Furthermore, the target NTN cell 1g-15 is based on T... TA,UE-specific and T TA,common Value export UE 1g-05 timing advance (T) TA The value is (1g-60). At this point, the target NTN cell 1g-15 can finally determine whether to perform a RACH-less handover.

[0091] The target NTN cell 1g-15 sends a HandoverCommand message (1g-65) to the source NTN base station 1g-10. This message may include the derived T TA (or N for UE 1g-05 and target NTN cell 1g-15) TA ), T TA,UE-specific (or N) TA,UE-specific ), T TA,common (or N) TA,common ) and scheduling information (UL authorized).

[0092] Upon receiving the aforementioned message, the source NTN base station 1g-10 sends an RRCReconfiguration message (1g-70) to UE 1g-05, including handover configuration information. This handover configuration information may include specific information required to perform a RACH-less handover. This specific information includes the information needed to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell, as well as the scheduling information in the target NTN cell. The information required to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell is as follows.

[0093] - Timing offset value compared to the timing advance value applied to the source NTN cell.

[0094] In other words, the timing advance value applied to the target NTN cell is derived by adding the timing offset value to the timing advance value applied to the source NTN cell.

[0095] -Location information (ephemeris) of the target NTN cell In other words, ephemeris information can be used to derive the service link propagation delay of a target NTN cell.

[0096] -Target NTN cell TA-Info IE information In other words, the above information can be used to derive the feeder link propagation delay for the target NTN cell.

[0097] Upon receiving the above configuration information, UE 1g-05 derives the timing advance value (T) to be applied when sending PUSCH to the target NTN cell 1g-15 based on the received information. TA (1g-75). Alternatively, UE 1g-05 can derive the timing advance value to be applied when sending PUSCH to the target NTN cell 1g-15 by utilizing the PropagationDelayDifference value most recently derived and sent to the source NTN base station 1g-10. Therefore, UE 1g-05 and the target NTN cell 1g-15 derive and have the same timing advance value.

[0098] Based on the derived TA value, target NTN cell 1g-15 periodically allocates radio resources (1g-80) to UE 1g-05 according to preset scheduling information. If the above scheduling information is not provided, UE 1g-05 monitors the physical downlink control channel (PDCCH) of the target cell.

[0099] UE 1g-05 transmits a PUSCH (1g-85) at a specific time and radio resource location based on the derived TA value and scheduling information in the target NTN cell 1g-15. The PUSCH includes an RRCReconfigurationComplete message. Upon successful reception of the PUSCH, the target NTN cell 1g-15 can receive a TARMAC CE or a TAC (Timing Advance Command) MAC CE (1g-90) from UE 1g-05 to set more accurate uplink timing. If UE 1g-05 fails to successfully transmit a PUSCH including an RRCReconfigurationComplete message within a preset time period after receiving configuration information for RACH-less handover, the RACH-less handover is considered to have failed, and UE 1g-05 can either re-perform a reconstruction operation or perform a normal handover involving a random access procedure to the target cell. If a RACH-less handover fails, the UE 1g-05 can store an indicator indicating that the RACH-less handover has failed in the contents of a Radio Link Failure (RLF) report, and can later report an RLF report to the base station in connected mode.

[0100] Figure 8 This is a sequence diagram of a second process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0101] UE sends its UE capability information (1h-20) to the source NTN base station at 1h-10. This capability information includes an indicator that shows whether the UE supports RACH-less handover in the NTN environment.

[0102] From 1 hour to 10 minutes, the source NTN base station broadcasts specific information about itself and neighboring NTN cells via System Information SIB19 (from 1 hour to 25 minutes). This specific information includes the positions (ephemeris) of NTN satellites and derived N... TA,common Information required for (ta-Common, ta-CommonDrift, ta-CommonDriftVariant).

[0103] The source NTN base station determined at 1h-10 to initiate a RACH-less handover for UE at 1h-05 (1h-30).

[0104] The source NTN base station 1h-10 requests the TA information (1h-35) of the target NTN cell 1h-15 from the UE 1h-05 using specific L2 signaling or RRC messages. The L2 signaling or RRC message may include the ID information, absolute radio frequency channel number (ARFCN) information (frequency), location information (ephemeris), or TA-Info of the target NTN cell 1h-15.

[0105] For the purpose of deriving TA information, UE 1h-05 performs random access (1h-40) to the target NTN cell 1h-15. This random access can be contention-based random access (CBRA) or contention-free random access (CFRA). In the case of CFRA, prior coordination may be required to determine radio RACH resources dedicated to RACH-less handover between the source and target base stations, and the source base station 1h-10 provides CFRA configuration information to UE 1h-05 via system information or dedicated signaling.

[0106] UE 1h-05 considers the ephemeris information and TA-Info of the target NTN cell 1h-15, as well as the TAC, MAC, and CE values ​​provided by the target NTN cell 1h-15, to derive the TA value (1h-45) of the target NTN cell 1h-15. Because the N... TA,common (or T) TA,common The NTN can be derived from the target NTN cell 1h-15 itself, therefore UE 1h-05 can only derive the NTN. TA and N TA,UE-specific value.

[0107] UE 1h-05 sends the derived TA value (or N) to the source NTN base station 1h-10 using TAR MAC CE or a specific RRC message. TA and N TA,UE-specific Value (1h-50).

[0108] Upon receiving the above information, the source NTN base station 1h-10 includes it in a HandoverPreparationInformation message and sends it to the target NTN cell 1h-10 (1h-55). This message is used when requesting a handover to the target cell, and the message may include an indicator indicating that the handover is for RACH-less handover.

[0109] The target NTN cell, which has already received the HandoverPreparationInformation message, knows the TA value (1h-60) of UE 1h-05. Feeder link propagation delay (T) TA,commonThe result can be directly derived from the target NTN cell 1h-15. At this point, the target NTN cell 1h-15 can finally determine whether to perform a RACH-less handover.

[0110] The target NTN cell sends a HandoverCommand message to the source NTN base station from 1h-15 to 1h-10 (1h-65). This message may include the derived T TA (or N for UE 1h-05 and target NTN cell 1h-15) TA ), T TA,UE-specific (or N) TA,UE-specific ), T TA,common (or N) TA,common ) and scheduling information (UL authorized).

[0111] Upon receiving the aforementioned message, the source NTN base station 1h-10 sends an RRCReconfiguration message (1h-70) containing handover configuration information to UE 1h-05. This handover configuration information may include specific information required to perform a RACH-less handover. This specific information includes the information needed to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell 1h-15, and the scheduling information in the target NTN cell 1h-15. The information needed to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell 1h-15 is as follows.

[0112] - Timing advance value applied to the target NTN cell, N TA,UE-specific (or T) TA,UE-specific ), N TA,common (or T) TA,common ) - Timing offset value compared to the timing advance value applied to the source NTN cell.

[0113] In other words, the timing advance value applied to the target NTN cell is derived by adding the timing offset value to the timing advance value applied to the source NTN cell.

[0114] -Location information (ephemeris) of the target NTN cell In other words, ephemeris information can be used to derive the service link propagation delay of a target NTN cell.

[0115] -Target NTN cell TA-Info IE information In other words, the above information can be used to derive the feeder link propagation delay for the target NTN cell.

[0116] Upon receiving the above configuration information, UE 1h-05 derives the timing advance value (T) to be applied when sending PUSCH to the target NTN cell 1h-15 based on the received information. TA (1h-75). Therefore, UE 1h-05 and target NTN cell 1h-15 are derived and have the same timing advance value.

[0117] Based on the derived TA value, target NTN cell 1h-15 periodically allocates radio resources to UE 1h-05 (1h-80) according to preset scheduling information. If the aforementioned scheduling information is not provided, UE 1h-05 monitors the target cell's PDCCH. UE 1h-05 transmits PUSCH (1h-85) at a specific time and radio resource location based on the derived TA value and the scheduling information in target NTN cell 1h-15. The PUSCH includes an RRCReconfigurationComplete message.

[0118] Upon successful receipt of PUSCH, in order to set more accurate uplink timing, the target NTN cell 1h-15 can receive TAR MAC CE or TAC (Timing Advance Command) MAC CE (1h-90) from UE 1h-05.

[0119] Figure 9 This is a sequence diagram of a third process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0120] UE 1i-05 sends its UE capability information (1i-20) to the source NTN base station 1i-10. This capability information includes an indicator that shows whether the UE supports RACH-less handover in the NTN environment.

[0121] Source NTN base station 1i-10 broadcasts specific information (1i-25) about itself and neighboring NTN cells via System Information SIB19. This specific information includes the positions (ephemeris) of NTN satellites and derived N... TA,common Information required for (ta-Common, ta-CommonDrift, ta-CommonDriftVariant).

[0122] The source NTN base station 1i-10 determines that it will initiate a RACH-less handover (1i-30) for UE 1i-05.

[0123] The source NTN base station 1i-10 requests the TA information (1i-35) of the target NTN cell 1i-15 from the UE 1i-05 using specific L2 signaling or RRC messages (e.g., RRCReconfiguration). The aforementioned L2 signaling or RRC messages may include the ID information, reporting conditions, ARFCN information (frequency), location information (ephemeris), or TA-Info of the target NTN cell 1i-15.

[0124] In this embodiment, if certain conditions are met, it is recommended that UE 1i-05 report specific TA information of neighboring target cells to the base station. These specific conditions may mean periodically reporting the timing advance value of neighboring target cells or meeting a preset condition from the following categories.

[0125] -CondEvent A3: The offset of the conditional reconfiguration candidate becomes better than PCell / PSCell; -CondEvent A4: The conditional reconfiguration candidate becomes better than the absolute threshold; -CondEvent A5: PCell / PSCell becomes worse than the absolute threshold 1, and the condition reconfiguration candidate becomes Better than another absolute threshold of 2; -CondEvent D1: The distance between the UE and the reference location referenceLocation1 becomes greater than the configured distance. The threshold distanceThreshFromReference1, and the reference position of the UE relative to the conditional reconfiguration candidate. The distance between referenceLocation2 becomes shorter than the configured threshold distanceThreshFromReference2; - CondEvent T1: The time measured at the UE becomes greater than the configured threshold t1-Threshold but less than... t1 - Threshold + duration; The conditions described above are those introduced during the handover of related technical conditions and can be reused as conditions for reporting timing advance values. A specific description of each condition is provided according to TS38.331. However, these conditions are for reporting timing advance values ​​and are provided to the UE through separate configuration information different from that used during the handover of related technical conditions. The base station can configure one or more conditions for the UE; and if at least one or all of the preset conditions are met, the UE reports the most recent timing advance value to the base station using a TAR MAC CE or a specific RRC message (e.g., a MeasurementReport message). Here, the TAR MAC CE can be improved to report the TA values ​​of neighboring target cells in addition to the serving cell. For example, the TAR MAC CE can additionally include the ID information or cell index information of the neighboring target cells. Alternatively, it can be distinguished from the traditional TAR MAC CE by using a new LCID (Logical Channel ID). In addition to the conditions described above, new conditions based on signal strength or quality can be introduced to indicate the handover time.

[0126] UE 1i-05 uses the ephemeris information and TA-Info of the target NTN cell to derive the TA value and N of the target NTN cell 1i-15. TA,UE-specific Value (or T) TA,specific ) or N TA,common (or T) TA,common(1i-45). Due to the N of the target NTN cell 1i-15 TA,common (or T) TA,common It can be directly exported from the target NTN cell, therefore UE 1i-05 can export only the NTN. TA,UE-specific Value (or T) TA,specific UE 1i-05 sends the derived N to the source NTN base station 1i-10 via TAR MAC CE or a specific RRC message. TA,UE-specific Value (or T) TA,specific ) or N TA,common Value (or T) TA,common (1i-50).

[0127] The source NTN base station 1i-10 includes information obtained from UE 1i-05 in its HandoverPreparationInformation message and sends it to the target NTN cell 1i-15 (1i-55). This message is used when making a handover request to the target cell, and the message may include an indicator indicating that the handover is for RACH-less handover.

[0128] The target NTN cell 1i-15, which has already received the HandoverPreparationInformation message, can identify the value T used for UE 1i-05. TA,UE-specific Furthermore, the feeder link propagation delay (T) can be directly derived. TA,common ). Target NTN cell 1i-15 based on T TA,UE-specific and T TA,common Value export for timing advance (T) of UE 1i-05 TA The value is (1i-60). At this point, the target NTN cell 1i-15 can finally determine whether to perform a RACH-less handover.

[0129] The target NTN cell 1i-15 sends a HandoverCommand message (1i-65) to the source NTN base station 1i-10. This message may include the derived T TA (or N for UE 1i-05 and target NTN cell 1i-15) TA ), T TA,UE-specific (or N) TA,UE-specific ), T TA,common (or N) TA,common ) and scheduling information (UL authorized).

[0130] Upon receiving the aforementioned message, the source NTN base station 1i-10 sends an RRCReconfiguration message (1i-70) to UE 1i-05, including handover configuration information. This handover configuration information may include specific information required to perform RACH-less handover. This specific information includes information needed to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell, and scheduling information within the target NTN cell. The information needed to derive the timing advance value to be applied when sending the PUSCH to the target NTN cell is as follows.

[0131] - Timing advance value applied to the target NTN cell, N TA,UE-specific (or T) TA,UE-specific ), N TA,common (or T) TA,common ) - Timing offset value compared to the timing advance value applied to the source NTN cell.

[0132] In other words, the timing advance value applied to the target NTN cell is derived by adding the timing offset value to the timing advance value applied to the source NTN cell.

[0133] -Location information (ephemeris) of the target NTN cell In other words, ephemeris information can be used to derive the service link propagation delay of a target NTN cell.

[0134] -Target NTN cell TA-Info IE information In other words, the above information can be used to derive the feeder link propagation delay for the target NTN cell.

[0135] Upon receiving the above configuration information, UE 1i-05 derives the timing advance value (T) to be applied when sending PUSCH to the target NTN cell 1i-15 based on the received information. TA (1i-75). Alternatively, UE 1i-05 can utilize the TA value (e.g., T) recently exported and sent to the source NTN base station 1i-10. TA T TA,UE-specific or N TA,UE-specific This is used to derive the timing advance value to be applied when sending PUSCH to the target NTN cell 1i-15. Therefore, UE 1i-05 and the target NTN cell 1i-15 derive and have the same timing advance value.

[0136] Based on the derived TA value, target NTN cell 1i-15 periodically allocates radio resources to UE 1i-05 according to preset scheduling information (1i-80). If the aforementioned scheduling information is not provided, UE 1i-05 monitors the target cell's PDCCH. UE 1i-05 transmits PUSCH (1i-85) at a specific time and radio resource location based on the derived TA value and the scheduling information in the target NTN cell. The PUSCH includes an RRCReconfigurationComplete message.

[0137] Upon successful receipt of PUSCH, in order to set more accurate uplink timing, the target NTN cell 1i-15 can receive TAR MAC CE or TAC (Timing Advance Command) MAC CE (1i-90) from UE 1i-05.

[0138] Figure 10 This is a diagram illustrating a scenario supporting CA / DC in NTN, according to embodiments of the present disclosure.

[0139] NTN uses satellites located at high altitudes for data transmission and reception, classifying them according to altitude as high-altitude geostationary satellites (1j-05) and low-Earth orbit (LEO) satellites (1j-10). Geostationary satellites move at the same speed as the Earth's rotation, so they appear fixed at a certain altitude when viewed from the ground. LEO satellites, on the other hand, are greatly affected by Earth's gravity, so they must travel at a much faster speed than geostationary satellites to maintain their altitude relative to the Earth. Therefore, when viewed from the ground, because LEO satellites move much faster than the Earth's rotation, they typically appear to be moving at a certain altitude.

[0140] In Rel-18 NTN, a method for providing data transmission and reception services to the UE by considering both geostationary satellites and low-Earth orbit (LEO) satellites is discussed. For example, geostationary satellites are advantageous in providing a wide service area due to their relatively high altitude; while LEO satellites, compared to geostationary satellites, provide a narrower service area due to their low altitude, but are advantageous in terms of latency and received signal strength compared to geostationary satellites due to their low altitude relative to the ground. Therefore, geostationary satellites can be configured as primary nodes (MNs) to support stable mobility, and LEO satellites can be configured as secondary nodes (SNs) to improve service quality, which can provide dual connectivity to UE 1j-20. If a CA or DC is introduced for the NTN as described above, then when considering RACH-less handover in the NTN, the target cell can be a serving cell in either the CA or DC, and in this case, TA-related configuration information can be provided similarly to the LTE case.

[0141] Figure 11 This is a sequence diagram of the fourth process for performing RACH-less switching of NTN according to an embodiment of the present disclosure.

[0142] UE 1k-05 sends its UE capability information (1k-20) to the source NTN base station 1k-10. This capability information includes an indicator that shows whether the UE supports RACH-less handover in the NTN environment.

[0143] The source NTN base station 1k-10 broadcasts specific information about itself and neighboring NTN cells (1k-25) via System Information SIB19. This specific information includes the positions (ephemeris) of NTN satellites and derived N... TA,common Information required for (ta-Common, ta-CommonDrift, ta-CommonDriftVariant).

[0144] To configure carrier aggregation (CA) or dual connectivity (DC) for UE 1K-05, the source NTN base station 1k-10 exchanges relevant configuration information with a specific neighboring NTN cell 1h-15 (1k-27). The source NTN base station 1k-10 uses the RRCReconfiguration message to configure the neighboring NTN cell 1k-15 as the serving cell for UE 1k-05 (1h-35). At this time, the corresponding TAG IDs can be set together to indicate which TAG (timing advance group) the serving cell belongs to.

[0145] For the purpose of deriving TA information, UE 1k-05 performs random access (1k-35) to the neighboring NTN cell 1k-15.

[0146] UE 1k-05 takes into account the ephemeris information and TA-Info of the target NTN cell 1k-15, as well as the TAC MAC CE value provided by the target NTN cell 1k-15, to derive the TA value (1k-40) of the neighboring NTN cell 1k-15.

[0147] UE 1k-05 sends the derived TA value (1k-45) to the source NTN base station 1k-10 using a TAR MAC CE or a specific RRC message. Here, the TAR MAC CE may include the corresponding TAG ID or specific indicator information (ID field) indicating neighboring NTN cells. The following describes the enhanced TAR MAC CE and propagationDelayDifference report to support CA or DC in the NTN.

[0148] The target NTN cell 1k-15, which has received a TAR MAC CE or a specific RRC message, identifies the TA value (1k-50) of UE 1k-05. Taking the above TA into account, the NTN serving cell performs scheduling for UE 1k-05.

[0149] The source NTN base station 1k-10 determines to hand over UE 1k-05 to the NTN serving cell (1k-53) in CA or DC state. Then, the source NTN base station 1k-10 sends it to the target NTN cell 1k-15 (1k-55) via a HandoverPreparationInformation message. This message is used to make a handover request to the target cell.

[0150] The target NTN cell 1k-15, having received the HandoverPreparationInformation message, determines whether to perform a RACH-less handover and sends a HandoverCommand message (1k-65) to the source NTN base station 1k-10. This message includes TA information and scheduling information (UL authorization), meaning that UE 1k-05 should perform a RACH-less handover.

[0151] Upon receiving the aforementioned message, the source NTN base station 1k-10 sends an RRCReconfiguration message (1k-70) to UE 1k-05, including handover configuration information. This handover configuration information may include specific information required to perform a RACH-less handover. This specific information includes information needed to derive the timing advance value to be applied when sending PUSCH to the target NTN cell, and scheduling information in the target NTN cell. The targetTA information required to derive the timing advance value to be applied when sending PUSCH to the target NTN cell corresponds to a timing adjustment indication, where if ta0 is indicated as the targetTA value, it means T... TA =0; mcg-PTAG means the T of the PTAG applied in the MCG is 0. TA ;scg-PTAG means the T of the PTAG applied in SCG. TA mcg-STAG with STAG-Id means that the T applied to the STAG corresponding to the STAG-Id in the MCG is... TA ; an scg-STAG with a STAG-Id means that the T applied to the STAG corresponding to the STAG-Id in the SCG is... TA In LTE, N TA It is considered a timing adjustment indicator, but in NR, there exists a component that constitutes T. TA Other elements, namely N TA,common and NTA,UE-specific Therefore, T should be considered. TA Instead of N TA .

[0152] Upon receiving the above configuration information, UE 1k-05 identifies the timing advance value (T) to be applied when sending PUSCH to the target NTN cell 1k-15 based on the received information. TA (1k-75). Therefore, UE 1k-05 and target NTN cell 1k-15 are derived and have the same timing advance value.

[0153] Considering the derived TA value mentioned above, target NTN cell 1k-15 periodically allocates radio resources according to preset scheduling information (1k-80). If the aforementioned scheduling information is not provided, UE 1k-05 monitors the target cell's PDCCH. UE 1k-05 transmits PUSCH (1k-85) at a specific time and radio resource location based on the derived TA value and the scheduling information in target NTN cell 1k-15. PUSCH includes an RRCReconfigurationComplete message. Upon successful reception of PUSCH, in order to set more accurate uplink timing, target NTN cell 1k-15 can receive a TAR MAC CE or a TAC (Timing Advance Command) MAC CE (1k-90) from UE 1k-05.

[0154] Figure 12 This is a diagram illustrating the format of a new timing advance report MAC CE according to an embodiment of the present disclosure.

[0155] When CA / DC is supported in NTN, one or more timing advance groups (TAGs) can be configured for each cell group (CG). A TAG is a set of serving cells with the same timing advance. A TAG that includes a PCell (primary cell) or PSCell (primary / secondary cell) is called a PTAG (primary TAG), and a TAG consisting only of SCells (secondary cells) is called a STAG (secondary TAG). Each CG can be configured with up to four TAGs.

[0156] In this embodiment, an improved TAR MAC CE is proposed, enabling the UE to report the timing advance for each TAG. This can be done in a format that stores the timing advance value for one TAG or in a format that stores the timing advance values ​​for multiple TAGs. The UE can report capability information to the base station, including indicators suggesting whether it supports the new TAR MAC CE. Furthermore, the base station can send UE configuration information indicating that the new TAR MAC CE can be used.

[0157] TAR MAC CE (used to report the timing advance value of a TAG) Figure 12Part (a) consists of 2 bits 1l-05 indicating the TAG ID and 14 bits 1l-10 indicating the TA value. Here, TAG ID 0 indicates PCell or PSCell.

[0158] TAR MAC CE (for reporting timing advance values ​​of multiple tags) Figure 1 Part (b) of 'l' can include up to four pairs, each consisting of 2 bits (11-15) indicating the TAG ID and 14 bits (11-20) indicating the TA value. When consisting of multiple pairs, the TA fields of the TAG can be arranged in ascending order of the corresponding TAG IDs. Alternatively, the TA field corresponding to the PTAG can always be at the beginning of the TAR MAC CE described above.

[0159] It's always possible to include TA values ​​corresponding to the four TAGs belonging to a CG; in this case, the TAG ID field is unnecessary. Therefore, as... Figure 1 As shown in part (c) of l, the TAG ID field can be omitted, and the TA fields of the TAG can be arranged in ascending order of the corresponding TAG ID. If no specific TAG belonging to a CG is configured, the UE can set a random value in the TA field corresponding to the above TAG, and the base station receiving the TAR MAC CE can ignore the TA field set to a random value.

[0160] If CA / DC is introduced into the NTN, the UE can report the propagationDelayDifference value for each TAG. The propagationDelayDifference reported by the UE using UAI messages is the difference between the serving link propagation delay of the serving cell and the serving link propagation delay of neighboring cells. Therefore, the propagationDelayDifference value can vary depending on the TAG to which the serving cell belongs. In this embodiment, the PropDelayDiffReportConfig IE can include ID information for the reference serving cell or TAG used to derive the propagationDelayDifference value. ID information can be provided for each entry in the neighborCellInfoList of the PropDelayDiffReportConfig IE. For example, entries in a new IE storing the aforementioned ID information can sequentially correspond to entries in the neighborCellInfoList of the PropDelayDiffReportConfig IE. Here, the UE derives the propagationDelayDifference value using the serving link propagation delay of the reference serving cell indicated above or the serving link propagation delay of a serving cell belonging to the indicated TAG. When reporting the propagationDelayDifference value, the UE can also report the following specific information.

[0161] - The ID of the serving cell used to derive the propagationDelayDifference value, such as CGI, PCI, or serving cell index.

[0162] - ID of the TAG used to export the propagationDelayDifference value To reduce complexity, the reference serving cell can always be fixed to SpCell (i.e., PCell or PSCell).

[0163] Figure 13 This is a flowchart of a UE operation for performing RACH-less handover of NTN according to an embodiment of the present disclosure.

[0164] At step 1m-05, the UE sends its UE capability information to the source NTN base station. This capability information includes an indicator that shows whether the UE supports RACH-less handover in the NTN environment.

[0165] In step 1m-10, the UE receives specific configuration information about the serving NTN cell and neighboring NTN cells through system information SIB19.

[0166] In step 1m-15, the UE receives specific configuration information from the source NTN base station, enabling it to obtain the TA information of neighboring NTN cells. The TA information is T... TA Or constitute T TA T TA,UE-specific (or N) TA,UE-specific ) and T TA,common (or N) TA,common ).

[0167] In steps 1m-20, the UE exports the TA information of the preset neighboring NTN cells using an appropriate method.

[0168] In step 1m-25, the UE reports the exported TA information to the source NTN base station.

[0169] In step 1m-30, the UE receives RACH-less handover configuration information from the source NTN base station. Here, the target cell in the RACH-less handover is the neighboring NTN cell.

[0170] In step 1m-35, the UE sends a PUSCH to the target NTN cell at a specified time using the TA derived from the application.

[0171] Figure 14 This is a flowchart of base station operations for performing RACH-less handover of NTN according to embodiments of the present disclosure.

[0172] At step 1n-05, the base station broadcasts specific configuration information about the serving NTN cell and neighboring NTN cells via system information SIB19.

[0173] At step 1n-10, the base station receives UE capability information from the UE, including an indicator indicating whether RACH-less is supported in the NTN environment.

[0174] In steps 1n-15, the base station sends specific configuration information to the UE to obtain the TA information of the neighboring NTN cells.

[0175] In steps 1n-20, the base station receives TA information from the UE of the neighboring NTN cell.

[0176] In steps 1n-25, the base station sends a HandoverPreparationInformation message containing TA information to the neighboring NTN cell.

[0177] In steps 1n-30, the base station receives a HandoverCommand message from a neighboring NTN cell. The HandoverCommand includes information required to perform a RACH-less handover.

[0178] In steps 1n-35, the base station sends an RRCReconfiguration message including HandoverCommand to the UE.

[0179] Figure 15 This is a diagram illustrating a scenario where a satellite within an NTN performs a RACH-less handover according to an embodiment of this disclosure.

[0180] If the source ground station 1o-15 and the target ground station 1o-25 are connected to UE 1o-20 via the same NTN satellite 1o-05, then the service link propagation delay 1o-35 of the source cell and the target cell will be the same. Therefore, for RACH-less handover, the service link propagation delay of the source cell can be directly used as the service propagation delay of the target cell. Thus, in the NTN-intra-location scenario described above, the process of UE 1o-20 reporting the target cell's TA information to the source base station 1o-15 can be omitted in the above embodiment.

[0181] Figure 16 This is a block diagram illustrating the internal structure of a UE according to an embodiment of the present disclosure.

[0182] refer to Figure 16 The UE may include a radio frequency (RF) processor 1p-10, a baseband processor 1p-20, a storage device 1p-30, and a controller 1p-40.

[0183] RF processor 1p-10 performs functions for transmitting and receiving signals via a wireless channel, such as signal band conversion and amplification. Specifically, RF processor 1p-10 performs up-conversion of the baseband signal provided by baseband processor 1p-20 to an RF band signal and transmits it via an antenna, and performs down-conversion of the RF band signal received via the antenna back to a baseband signal. For example, RF processor 1p-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, digital-to-analog converters (DACs), and analog-to-digital converters (ADCs). Although only one antenna is shown in the figures, multiple antennas may be provided to the UE. Furthermore, RF processor 1p-10 may include multiple RF chains. Additionally, RF processor 1p-10 can perform beamforming. For beamforming, RF processor 1p-10 can adjust the phase and amplitude of individual signals transmitted and received via multiple antennas or antenna elements. Furthermore, the RF processor can perform MIMO and can receive multiple layers during MIMO operation.

[0184] The baseband processor 1p-20 performs the conversion between baseband signals and bitstreams according to the system's physical layer specifications. For example, during data transmission, the baseband processor 1p-20 generates complex symbols by encoding and modulating the transmitted bitstream. Furthermore, during data reception, the baseband processor 1p-20 recovers the received bitstream by demodulating and decoding the baseband signal provided by the RF processor 1p-10. For example, in the case of data transmission using Orthogonal Frequency Division Multiplexing (OFDM), the baseband processor 1p-20 generates complex symbols by encoding and modulating the transmitted bitstream, maps the complex symbols to subcarriers, and assembles OFDM symbols through inverse Fast Fourier Transform (IFFT) operations and cyclic prefix (CP) insertion. Furthermore, for data reception, the baseband processor 1p-20 divides the baseband signal provided by the RF processor 1p-10 into units of OFDM symbols, recovers the signals mapped to subcarriers through Fast Fourier Transform (FFT) operations, and recovers the received bitstream through demodulation and decoding.

[0185] The baseband processor 1p-20 and RF processor 1p-10 transmit and receive signals as described above. Therefore, the baseband processor 1p-20 and RF processor 1p-10 can be referred to as a transmitter, receiver, transceiver, or communication unit. Furthermore, to support different wireless access technologies, at least one of the baseband processor 1p-20 or RF processor 1p-10 may include multiple communication modules. Additionally, to process signals in different frequency bands, at least one of the baseband processor 1p-20 or RF processor 1p-10 may include different communication modules. For example, different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. Furthermore, different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.0 NRHz, NRhz) and millimeter wave (mmWave) bands (e.g., 60 GHz).

[0186] Storage device 1p-30 stores data such as basic programs, application programs, and configuration information for UE operation. Specifically, storage device 1p-30 can store information about a second access node performing wireless communication using a second wireless access technology. Storage device 1p-30 provides the stored data in response to requests from controller 1p-40.

[0187] Controller 1p-40 controls the overall operation of the UE. For example, controller 1p-40 transmits and receives signals via baseband processor 1p-20 and RF processor 1p-10. Furthermore, controller 1p-40 writes data to or reads data from storage device 1p-30. For this purpose, controller 1p-40 may include at least one processor. For example, controller 1p-40 may include a communication processor (CP) for controlling communications and a higher-level application processor (AP) for controlling applications.

[0188] Figure 17 This is a block diagram of a base station in a wireless communication system according to an embodiment of the present disclosure.

[0189] refer to Figure 17 The base station includes an RF processor 1q-10, a baseband processor 1q-20, a backhaul communication unit 1q-30, a storage device 1q-40, and a controller 1q-50.

[0190] RF processor 1q-10 performs functions for transmitting and receiving signals via a wireless channel, such as signal band conversion and amplification. Specifically, RF processor 1q-10 performs up-conversion of the baseband signal provided by baseband processor 1q-20 to an RF band signal and transmits the converted signal through an antenna, and performs down-conversion of the RF band signal received through the antenna to a baseband signal. For example, RF processor 1q-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, DACs, and ADCs. Although only one antenna is shown in the figures, the first access node may have multiple antennas. Additionally, RF processor 1q-10 may include multiple RF chains. Furthermore, RF processor 1q-10 can perform beamforming. For beamforming, RF processor 1q-10 can adjust the phase and amplitude of individual signals transmitted and received through multiple antennas or antenna elements. The RF processor can perform downlink MIMO operation by transmitting one or more layers.

[0191] The baseband processor 1q-20 performs the conversion between baseband signals and bitstreams according to the physical layer specifications of the first radio access technology. For example, for data transmission, the baseband processor 1q-20 generates complex symbols by encoding and modulating the transmission bitstream. Furthermore, for data reception, the baseband processor 1q-20 recovers the received bitstream by demodulating and decoding the baseband signal provided by the RF processor 1q-10. For example, in the case of data transmission using OFDM, the baseband processor 1q-20 generates complex symbols by encoding and modulating the transmission bitstream, maps the complex symbols to subcarriers, and assembles OFDM symbols through IFFT operations and CP insertion. Furthermore, for data reception, the baseband processor 1q-20 divides the baseband signal provided by the RF processor 1q-10 into units of OFDM symbols, recovers the signals mapped to subcarriers through FFT operations, and recovers the received bitstream through demodulation and decoding. The baseband processor 1q-20 and the RF processor 1q-10 transmit and receive signals as described above. Therefore, the baseband processor 1q-20 and the RF processor 1q-10 can be referred to as transmitters, receivers, transceivers, communication units, or wireless communication units.

[0192] The backhaul communication unit 1q-30 provides an interface for communicating with other nodes in the network. That is, the backhaul communication unit 1q-30 converts the bit stream to be sent from the primary base station to another node (e.g., a secondary base station or the core network) into a physical signal, and converts the physical signal received from another node into a bit stream.

[0193] Storage device 1q-40 stores data such as basic programs, application programs, and configuration information for the operation of the main base station. Specifically, storage device 1q-40 can store information about bearers assigned to connected UEs and measurement results reported from connected UEs. Furthermore, storage device 1q-40 can store information used as a criterion for determining whether to provide or suspend multi-connectivity to a UE. Additionally, storage device 1q-40 provides the stored data in response to requests from controller 1q-50.

[0194] The controller 1q-50 controls the overall operation of the main base station. For example, the controller 1q-50 transmits and receives signals via the baseband processor 1q-20 and the RF processor 1q-10 or via the backhaul communication unit 1q-30. Furthermore, the controller 1q-50 writes data to or reads data from the storage device 1q-40. For this purpose, the controller 1q-50 may include at least one processor.

[0195] In the specific embodiments of this disclosure described above, the elements included in this disclosure are represented in a singular or plural form according to the presented embodiments. However, for ease of description, the singular or plural expression is appropriately chosen according to the presented situation, and this disclosure is not limited to a single element or multiple elements. Those elements described in plural form may be configured as a single element, and those elements described in singular form may be configured as multiple elements.

[0196] Furthermore, the embodiments disclosed in the foregoing specification and accompanying drawings are merely specific examples presented to facilitate explanation and understanding of the content of this disclosure, and are not intended to limit the scope of this disclosure. Therefore, the scope of this disclosure should be interpreted as including not only the embodiments disclosed herein, but also all changes or modifications derived from the technical concepts of this disclosure.

Claims

1. A method performed by a first non-terrestrial network (NTN) base station in a wireless communication system, the method comprising: Determine the RACH-less handover from the terminal to the second NTN base station; Obtain configuration information associated with RACH-less handover from the second NTN base station; as well as A Radio Resource Control (RRC) reconfiguration message is sent to the terminal. The RRC reconfiguration message includes the configuration information and timing information applied to the second NTN base station. Whether the timing adjustment value used for the second NTN base station is equal to the timing adjustment value used for the first NTN base station is indicated by the timing information. The Physical Uplink Shared Channel (PUSCH) transmission from the terminal to the second NTN base station is performed based on the timing information and the configuration information.

2. The method according to claim 1, wherein, The timing information indicates either a timing adjustment value of 0 for the second NTN base station or a timing adjustment value for the first NTN base station.

3. The method according to claim 1, further comprising: Receive the advance timing report (TAR) from the Media Access Control (MAC) control element CE on the terminal; as well as The timing information is determined based on the timing advance information for the first NTN base station and the timing advance information for the second NTN base station included in the TAR.

4. The method according to claim 1, wherein the method comprises: System information is sent to the terminal, including information associated with the location of the second NTN base station and information associated with the delay of the feeder link between the second NTN base station and the ground station; as well as Receive timing advance information for the second NTN base station from the terminal. The timing advance information includes at least one of a first timing advance information for the service link between the terminal and the second NTN base station or a second timing advance information for the feeder link.

5. A method performed by a terminal in a wireless communication system, the method comprising: The radio resource control (RRC) reconfiguration message is received from the first non-terrestrial network (NTN) base station. The RRC reconfiguration message includes configuration information associated with the random access channel (RACH-less) handover to the second NTN base station and timing information applied to the second NTN base station. as well as Based on the timing information and the configuration information, physical uplink shared channel (PUSCH) transmission to the second NTN base station is performed. Whether the timing adjustment value used for the second NTN base station is equal to the timing adjustment value used for the first NTN base station is indicated by the timing information.

6. The method according to claim 5, wherein, The timing information indicates either a timing adjustment value of 0 for the second NTN base station or a timing adjustment value for the first NTN base station.

7. The method according to claim 5, further comprising: Obtain timing advance information for the first NTN base station and timing advance information for the second NTN base station; as well as A timing advance report (TAR) on the Media Access Control (MAC) control element (CE) is sent to the first NTN base station. The TAR includes timing advance information for the first NTN base station and timing advance information for the second NTN base station. The timing information is based on the TAR.

8. The method according to claim 5, further comprising: System information is received from the first NTN base station, the system information including information associated with the location of the second NTN base station and information associated with the delay of the feeder link between the second NTN base station and the ground station; as well as Send timing advance information for the second NTN base station to the first NTN base station. The timing advance information includes at least one of a first timing advance information for the service link between the terminal and the second NTN base station or a second timing advance information for the feeder link.

9. A first non-terrestrial network (NTN) base station in a wireless communication system, the first NTN base station comprising: transceiver; as well as The controller is configured to: Determine the RACH-less handover from the terminal to the second NTN base station. Obtain configuration information associated with the RACH-less handover from the second NTN base station, and The transceiver is controlled to send a Radio Resource Control (RRC) reconfiguration message to the terminal. The RRC reconfiguration message includes the configuration information and timing information applied to the second NTN base station. Whether the timing adjustment value used for the second NTN base station is equal to the timing adjustment value used for the first NTN base station is indicated by the timing information. The Physical Uplink Shared Channel (PUSCH) transmission from the terminal to the second NTN base station is performed based on the timing information and the configuration information.

10. The first NTN base station according to claim 9, wherein, The timing information indicates either a timing adjustment value of 0 for the second NTN base station or a timing adjustment value for the first NTN base station.

11. The first NTN base station according to claim 9, wherein, The controller is also configured to control the transceiver to receive a timing advance report (TAR) from the terminal on the Media Access Control (MAC) control element (CE), and to determine the timing information based on the timing advance information for the first NTN base station and the timing advance information for the second NTN base station included in the TAR.

12. The first NTN base station according to claim 9, in, The controller is also configured to control the transceiver to send system information to the terminal, the system information including information associated with the location of the second NTN base station and information associated with the delay of the feeder link between the second NTN base station and the ground station, and to control the transceiver to receive timing advance information for the second NTN base station from the terminal. The timing advance information includes at least one of a first timing advance information for the service link between the terminal and the second NTN base station or a second timing advance information for the feeder link.

13. A terminal in a wireless communication system, the terminal comprising: transceiver; as well as The controller is configured to: The transceiver is controlled to receive a Radio Resource Control (RRC) reconfiguration message from a first non-terrestrial network (NTN) base station. The RRC reconfiguration message includes configuration information associated with a random access channel (RACH-less) handover to a second NTN base station and timing information applied to the second NTN base station. The transceiver is controlled to perform Physical Uplink Shared Channel (PUSCH) transmission to the second NTN base station based on the timing information and the configuration information. Whether the timing adjustment value used for the second NTN base station is equal to the timing adjustment value used for the first NTN base station is indicated by the timing information.

14. The terminal according to claim 13, in, The controller is further configured to obtain timing advance information for the first NTN base station and timing advance information for the second NTN base station, and to control the transceiver to send a Timing Advance Report (TAR) on the Media Access Control (MAC) control element (CE) to the first NTN base station, the TAR including timing advance information for the first NTN base station and timing advance information for the second NTN base station. The timing information is based on the TAR.

15. The terminal according to claim 13, in, The controller is also configured to control the transceiver to receive system information from the first NTN base station, the system information including information associated with the location of the second NTN base station and information associated with the delay of the feeder link between the second NTN base station and the ground station, and to control the transceiver to send timing advance information for the second NTN base station to the first NTN base station. The timing advance information includes at least one of a first timing advance information for the service link between the terminal and the second NTN base station or a second timing advance information for the feeder link.

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